Patent Grant
11181013
All of the above applications are hereby incorporated by reference in their entirety.
This application is related to novel variable valve actuation systems for internal combustion engines, and more specifically to novel variable valve actuation systems with compatible engine cylinder head arrangements.
Global environmental and economic concerns regarding increasing fuel consumption and greenhouse gas emission, the rising cost of energy worldwide, and demands for lower operating cost, are driving changes to legislative regulations and consumer demand. As these regulations and requirements become more stringent, advanced engine technologies must be developed and implemented to realize desired benefits.
In Type III (23), the first end of the rocker arm 28 rides on and is positioned above a cam lobe 30 while the second end of the rocker arm 28 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31. An HLA 812 can be implemented between the valve 29 tip and the rocker arm 28.
In Type V (24), the cam lobe 30 indirectly drives the first end of the rocker arm 26 with a push rod 27. An HLA 812 is shown implemented between the cam lobe 30 and the push rod 27. The second end of the rocker arm 26 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31.
As
Technologies focused on Type II (22) valve trains, that improve the overall efficiency of the gasoline engine by reducing friction, pumping, and thermal losses are being introduced to make the best use of the fuel within the engine. Some of these variable valve actuation (VVA) technologies have been introduced and documented.
A VVA device may be a variable valve lift (VVL) system, a cylinder deactivation (CDA) system such as that described U.S. patent application Ser. No. 13/532,777, filed Jun. 25, 2012 “Single Lobe Deactivating Rocker Arm” hereby incorporated by reference in its entirety, or other valve actuation system. As noted, these mechanisms are developed to improve performance, fuel economy, and/or reduce emissions of the engine. Several types of the VVA rocker arm assemblies include an inner rocker arm within an outer rocker arm that are biased together with torsion springs. A latch, when in the latched position causes both the inner and outer rocker arms to move as a single unit. When unlatched, the rocker arms are allowed to move independent of each other.
Switching rocker arms allow for control of valve actuation by alternating between latched and unlatched states, usually involving the inner arm and outer arm, as described above. In some circumstances, these arms engage different cam lobes, such as low-lift lobes, high-lift lobes, and no-lift lobes. Mechanisms are required for switching rocker arm modes in a manner suited for operation of internal combustion engines.
Rocker arms that are driven by a camshaft to actuate the cylinder intake and exhaust valves are typically mounted on the cylinder head.
There are structures extending from the cylinder head such as cam towers to secure and support the camshafts in an overhead cam design. There are also spark plug tubes that extend upward from the top of each cylinder through the head to receive spark plugs. There may be other structures that extend from the cylinder head that support elements of the valve train.
As described above, some embodiments of VVA switching rocker arm assemblies include a rocker arm within a rocker arm that are biased together with a spring on either side. Since the inner/outer arm design often employs a roller in the center to engage a cam lobe, it is advantageous to keep the roller the same width of the cam lobe. Therefore, the structures on either side of the roller add width to the rocker assembly causing it to be wider than original non-VVA rocker arms and too wide to fit certain cylinder head designs.
For example, some Type II engine heads employ cam towers that have a hydraulic lifter adjuster (HLA) near the centerline of the head and spark plug tubes that obstruct one side of a wide VVA switching rocker arm assembly.
Many engine parts are designed by manufacturers to work with a specific cylinder head, making the cylinder head very difficult to modify because changes may impact many interrelated components, possibly increasing cost and causing assembly clearance issues. In some cases, VVA switching systems do not fit in the space defined by the existing head design.
One example of VVA technology used to alter operation and improve fuel economy in Type II gasoline engines is discrete variable valve lift (DVVL), also sometimes referred to as a DVVL switching rocker arm. DVVL works by limiting engine cylinder intake air flow with an engine valve that uses discrete valve lift states versus standard “part throttling”. A second example is cylinder deactivation (CDA). Fuel economy can be improved by using CDA at partial load conditions in order to operate select combustion cylinders at higher loads while turning off other cylinders.
The United States Environmental Protection Agency (EPA) showed a 4% improvement in fuel economy when using DVVL applied to various passenger car engines. An earlier report, sponsored by the United States Department of Energy lists the benefit of DVVL at 4.5% fuel economy improvement. Since automobiles spend most of their life at “part throttle” during normal cruising operation, a substantial fuel economy improvement can be realized when these throttling losses are minimized. For CDA, studies show a fuel economy gain, after considering the minor loss due to the deactivated cylinders, ranging between 2 and 14%. Currently, there is a need for VVA rocker arms for increased performance, economy and/or reduced emissions that fit specific engine head designs.
Switching rocker arms have been used to alter the operation and performance of the engines. For example, specialized rocker arms may be used that provide variable valve actuation (VVA), such as variable valve lift (VVL), and cylinder deactivation (CDA). U.S. Provisional Patent Application No. 61/636,277 (EATN-0205-P01, pending) describes in detail the structure and function of a VVL switching rocker arm, and the reader is referred to this document for a full description. These have been developed that improve performance, fuel economy, and/or reduce emissions of the engine. Several types of the VVA rocker arm assemblies include an inner rocker arm within an outer rocker arm that are biased together with torsion springs. A latch, when in the latched position causes both the inner and outer rocker arms to move as a single unit. When unlatched, the rocker arms are allowed to move independent of each other. The latch of the inner arm rests on a latch seat of the outer arm. (Alternatively, the latch may be on the outer arm.)
In the past is was thought that in order to utilize a round rocker arm latch you would need the mating surface of the other rocker arm in the assembly to have a ground in curved mating surface. This mating surface can be referred to as a latch seat.
This latch seat would need to have a radius that very closely matches the latch radius. A seat that is slightly too small causes sticking, and a delayed release. It also causes the latch to impact the corners of the latch seat during engagement of the latch. A larger seat or smaller seat could cause undesirable wear.
Due to the tolerances, it would need to be processed by way of grinding. This would require more exact and expensive manufacturing processes. Also, the latch should not be restricting from properly extending and retracting.
Another latch design included creating a number of latches, measuring each and sorting them by latch width. The proper latch was selected having a specific shelf height from an assortment of latches with varying shelf heights to result in a proper lash. This was time-consuming and required an array of parts.
As indicated above, at least some VVA rocker arm assemblies are wider than conventional rocker arms. The increased width tends to interfere with the spark plug tubes, cam towers and other structures of the head. Without modifications, the VVA rocker arm assemblies may not fit existing head designs, and cannot be used. Changes may be required to be made to the head design to accommodate the VVA rocker arm assemblies. However, large changes to the head design may affect parts manufactured by other manufacturers that interface with the head. Therefore, it would be beneficial to provide a head that has small modifications that would allow use of the VVA rocker arm assemblies.
Currently, there is a need for a head arrangement that can accommodate a VVA system while still being compatible with other equipment that interfaces with the head.
Advanced VVA systems for piston-type internal combustion engines combine valve lift control devices, such as CDA or DVVL switching rocker arms, valve lift actuation methods, such as hydraulic actuation using pressurized engine oil, software and hardware control systems, and enabling technologies. Enabling technologies may include sensing and instrumentation, OCV design, DFHLA design, torsion springs, specialized coatings, algorithms, physical arrangements, etc. Innovative modifications are made to the cylinder head assemblies to meet space requirements of VVA systems.
In an embodiment, a switching rocker arm assembly is disclosed having a plurality of rocker arms and additional structures connected together having manufacturing tolerances that introduce mechanical lash, a latch with a latch pin and a latch seat, the latch seat adapted to receive and secure the latch pin. The latch seat comprises an indentation having a shape that is complementary to that of the latch pin; the indentation has a depth chosen to compensate for at least a portion of the mechanical lash to result in a predefined lash.
In embodiments, an economical switching rocker arm assembly is disclosed that exhibits a predetermined lash even though this is constructed with parts having tolerances greater than prior art designs. The rocker arm assembly a first rocker arm manufactured with greater tolerances than prior art designs having with a first end and second end. It also has a second rocker arm manufactured with greater tolerances that prior art designs having a first end pivotally connected to the first end of the first rocker arm, and a roller bearing on the first rocker arm adapted to ride upon a cam and actuate the first rocker arm. The rocker arm assembly has a latch having a latch pin on the second end of one of the first and second arms and a latch seat on the second end of the other rocker arm, the latch operating to cause the arms to be fixed relative to each other when latched and allowed to pivot independently of each other when not latched. The latch seat has an indentation shaped to receive the latch pin and sized to compensate for at least a portion of the increase lash caused by increased manufacturing tolerances, and result in a predefined lash.
In an embodiment, a modified rocker assembly is disclosed having an obstructed side and a non-obstructed side, having an outer structure having a first end, an inner rocker structure fitting within the outer structure, the inner structure also having a first end. The modified rocker assembly has an axle pivotally connecting the first ends of inner structure to the outer structure, such that the inner structure may rotate within the outer structure around the axle. At least one torsion spring on one side of axle, rotationally biases the inner structure relative to the outer structure. The outer structure, on the obstructed side as it extends from the second end toward the first end is offset toward the non-obstructed side creating a first offset portion to provide additional clearance on the obstructed side. This design allows the modified rocker arm to fit into an engine head having an obstruction on its obstruction side.
In an embodiment, a modified rocker assembly is disclosed having an obstructed side and a non-obstructed side, with an outer structure having a first end, an inner rocker structure fitting within the outer structure, the inner structure also having a first end. An axle pivotally connects the first ends of inner structure to the outer structure, such that the inner structure may rotate within the outer structure around the axle. At least one torsion spring is mounted on the non-obstructed side of the axle that rotationally biases the inner structure relative to the outer structure. As the outer structure on the obstructed side extends from the second end toward the first end, the outer structure is offset toward the non-obstructed side creating a first offset portion. The first offset portion provides additional clearance on the obstructed side.
In an embodiment, a modified rocker assembly is disclosed having an obstructed side and a non-obstructed side. The modified rocker assembly has an outer structure having a first end with an offset portion, an inner rocker structure fitting within the outer structure. The inner structure also has a first end. An axle pivotally connects the first ends of inner structure to the outer structure, such that the inner structure may rotate within the outer structure around the axle. The modified rocker assembly has at least one torsion spring on one side of the axle, rotationally biasing the inner structure relative to the outer structure. As the outer structure on the obstructed side extends from the second end toward the first end, the outer structure smoothly curves toward the non-obstructed side. This creates a first offset portion that provides additional clearance on the obstructed side. This allows this embodiment to fit in an engine head that has an obstruction on the obstructed side.
In one embodiment, an advanced discrete variable valve lift (DVVL) system is described. The advanced discrete variable valve lift (DVVL) system was designed to provide two discrete valve lift states in a single rocker arm. Embodiments of the approach presented relate to the Type II valve train described above and shown in
Mode switching (i.e., from low to high lift or vice versa) is accomplished within one cam revolution, resulting in transparency to the driver. The SRFF prevents significant changes to the overhead required for installing in existing engine designs. Load carrying surfaces at the cam interface may comprise a roller bearing for low lift operation, and a diamond like carbon coated slider pad for high lift operation. Among other aspects, the teachings of the present application is able to reduce mass and moment of inertia while increasing stiffness to achieve desired dynamic performance in low and high lift modes.
A diamond-like carbon coating (DLC coating) allows higher slider interface stresses in a compact package. Testing results show that this technology is robust and meets all lifetime requirements with some aspects extending to six times the useful life requirements. Alternative materials and surface preparation methods were screened, and results showed DLC coating to be the most viable alternative. This application addresses the technology developed to utilize a Diamond-like carbon (DLC) coating on the slider pads of the DVVL switching rocker arm.
System validation test results reveal that the system meets dynamic and durability requirements. Among other aspects, this patent application also addresses the durability of the SRFF design for meeting passenger car durability requirements. Extensive durability tests were conducted for high speed, low speed, switching, and cold start operation. High engine speed test results show stable valve train dynamics above 7000 engine rpm. System wear requirements met end-of-life criteria for the switching, sliding, rolling and torsion spring interfaces. One important metric for evaluating wear is to monitor the change in valve lash. The lifetime requirements for wear showed that lash changes are within the acceptable window. The mechanical aspects exhibited robust behavior over all tests including the slider interfaces that contain a diamond like carbon (DLC) coating.
With flexible and compact packaging, this DVVL system can be implemented in a multi-cylinder engine. The DVVL arrangement can be applied to any combination of intake or exhaust valves on a piston-driven internal combustion engine. Enabling technologies include OCV, DFHLA, DLC coating. In some cases, innovative cylinder head assemblies and arrangements, combined with DVVL switching rocker arms, are required to meet space and cost requirements. For example, cam towers and camshaft support bearings may be eliminated, moved, or added for certain cylinder head arrangements with limited space, particularly in in-line 4 cylinder and 8 cylinder engines.
In a second embodiment, an advanced single-lobe cylinder deactivation (CDA) system is described. The advanced cylinder deactivation CDA system was designed to deactivate one or more cylinders. Embodiments of the approach presented relate to the Type II valve train described above and shown in
Mode switching for the CDA system is accomplished within one cam revolution, resulting in transparency to the driver. The SRFF prevents significant changes to the overhead required for installing in existing engine designs. Among other aspects, the teachings of the present application is able to reduce mass and moment of inertia while increasing stiffness to achieve desired dynamic performance in either lift or no-lift modes.
CDA system validation test results reveal that the system meets dynamic and durability requirements. Among other aspects, this patent application also addresses the durability of the SRFF design necessary to meet passenger car durability requirements. Extensive durability tests were conducted for high speed, low speed, switching, and cold start operation. High engine speed test results show stable valve train dynamics above 7000 engine rpm. System wear requirements met end-of-life criteria for the switching, rolling and torsion spring interfaces. One important metric for evaluating wear is to monitor the change in valve lash. The lifetime requirements for wear showed that lash changes are within the acceptable window. The mechanical aspects exhibited robust behavior over all tests.
With flexible and compact packaging, the CDA system can be implemented in a multi-cylinder engine. Enabling technologies include OCV, DFHLA, and specialized torsion spring design. In some cases, innovative cylinder head assemblies and arrangements, combined with CDA switching rocker arms, are required to meet space and cost requirements. For example, cam towers and camshaft support bearings may be eliminated, moved, or added for certain cylinder head arrangements with limited space, particularly in in-line 4 cylinder and 8 cylinder engines.
A rocker arm is described for engaging a cam having one lift lobe per valve. The rocker arm includes an outer arm, an inner arm, a pivot axle, a lift lobe contacting bearing, a bearing axle, and at least one bearing axle spring. The outer arm has a first and a second outer side arms and outer pivot axle apertures configured for mounting the pivot axle. The inner arm is disposed between the first and second outer side arms, and has a first inner side arm and a second inner side arm. The first and second inner side arms have an inner pivot axle apertures that receive and hold the pivot axle, and inner bearing axle apertures for mounting the bearing axle.
The pivot axle fits into the inner pivot axle apertures and the outer pivot axle apertures.
The bearing axle is mounted in the bearing axle apertures of the inner arm.
The bearing axle spring is secured to the outer arm and is in biasing contact with the bearing axle. The lift lobe contacting bearing is mounted to the bearing axle between the first and the second inner side arms.
Another embodiment can be described as a rocker arm for engaging a cam having a single lift lobe per engine valve. The rocker arm includes an outer arm, an inner arm, a cam contacting member configured to be capable of transferring motion from the single lift lobe of the cam to the rocker arm, and at least one biasing spring.
The rocker arm also includes a first outer side arm and a second outer side arm.
The inner arm is disposed between the first and the second outer side arms, and has a first inner side arm and a second inner side arm.
The inner arm is secured to the outer arm by a pivot axle configured to permit rotating movement of the inner arm relative to the outer arm about the pivot axle.
The cam contacting member is disposed between the first and second inner side arm.
At least one biasing spring is secured to the outer arm and is in biasing contact with the cam contacting member.
Another embodiment may be described as a deactivating rocker arm for engaging a cam having a single lift lobe having a first end and a second end, an outer arm, an inner arm, a pivot axle, a lift lobe contacting member configured to be capable of transferring motion from the cam lift lobe to the rocker arm, a latch configured to be capable of selectively deactivating the rocker arm, and at least one biasing spring.
The outer arm has a first outer side arm and a second outer side arm, outer pivot axle apertures configured for mounting the pivot axle, and axle slots configured to accept the lift lobe contacting member, permitting lost motion movement of the lift lobe contacting member.
The inner arm is disposed between the first and second outer side arms, and has a first inner side arm and a second inner side arm. The first inner side arm and the second inner side arm have inner pivot axle apertures configured for mounting the pivot axle, and inner lift lobe contacting member apertures configured for mounting the lift lobe contacting member.
The pivot axle is mounted adjacent the first end of the rocker arm and disposed in the inner pivot axle apertures and the outer pivot axle apertures.
The latch is disposed adjacent the second end of the rocker arm.
The lift lobe contacting member mounted in the lift lobe contacting member apertures of the inner arm and the axle slots of the outer arm and between the pivot axle and latch.
The biasing spring is secured to the outer arm and in biasing contact with the lift lobe contacting member.
It will be appreciated that the illustrated boundaries of elements in the drawings represent only one example of the boundaries. One of ordinary skill in the art will appreciate that a single element may be designed as multiple elements or that multiple elements may be designed as a single element. An element shown as an internal feature may be implemented as an external feature and vice versa.
Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and description with the same reference numerals, respectively. The figures may not be drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.
The terms used herein have their common and ordinary meanings unless redefined in this specification, in which case the new definitions will supersede the common meanings.
It is also to be appreciated that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including”, “comprising”, “having”, “containing”, “involving” and variations thereof are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to “front and back”, “left and right”, “top and bottom”, and “upper and lower” are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. Also the terms “coining”, “impression”, and “indenting” are synonymous. Reference is also made to the “carbide pin” or “carbide rod” which are also synonymous.
As illustrated in the various figures, some sizes of structures or portions are exaggerated relative to other structures or portions for illustrative purposes and, thus, are provided to illustrate the general structures of the present subject matter. Furthermore, various aspects of the present subject matter are described with reference to a structure or a portion being formed on other structures, portions, or both. As will be appreciated by those of skill in the art, references to a structure being formed “on” or “above” another structure or portion contemplates that additional structure, portion, or both may intervene. References to a structure or a portion being formed “on” another structure or portion without an intervening structure or portion are described herein as being formed “directly on” the structure or portion. Similarly, it will be understood that when an element is referred to as being “connected”, “attached”, or “coupled” to another element, it can be directly connected, attached, or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected”, “directly attached”, or “directly coupled” to another element, no intervening elements are present.
Furthermore, relative terms such as “on”, “above”, “upper”, “top”, “lower”, or “bottom” are used herein to describe one structure's or portion's relationship to another structure or portion as illustrated in the figures. It will be understood that relative terms such as “on”, “above”, “upper”, “top”, “lower” or “bottom” are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, structure or portion described as “above” other structures or portions would now be oriented “below” the other structures or portions. Likewise, if devices in the figures are rotated along an axis, structure or portion described as “above”, other structures or portions would now be oriented “next to” or “left of” the other structures or portions. Like numbers refer to like elements throughout.
VVA SYSTEM EMBODIMENTS—VVA system embodiments represent a unique combination of a switching device, actuation method, analysis and control system, and enabling technology that together produce a VVA system. VVA system embodiments may incorporate one or more enabling technologies.
I. Discrete Variable Valve Lift (DVVL) System Embodiment Description
1. DVVL System Overview
A cam-driven, discrete variable valve lift (DVVL), switching rocker arm device that is hydraulically actuated using a combination of dual-feed hydraulic lash adjusters (DFHLA), and oil control valves (OCV) is described in following sections as it would be installed on an intake valve in a Type II valve train. In alternate embodiments, this arrangement can be applied to any combination of intake or exhaust valves on a piston-driven internal combustion engine.
As illustrated in
Referring to
The intake valve train elements illustrated in
The system used to control DVVL switching uses hydraulic actuation. A schematic depiction of a hydraulic control and actuation system 800 that is used with embodiments of the teachings of the present application is shown in
Several enabling technologies previously mentioned and used in the DVVL system described herein may be used in combination with other DVVL system components described herein thus rending unique combinations, some of which will be described herein:
2. DVVL System Enabling Technologies
Several technologies used in this system have multiple uses in varied applications; they are described herein as components of the DVVL system disclosed herein. These include:
2.1. Oil Control Valve (OCV) and Oil Control Valve Assemblies
Now, referring to
2.2. Dual Feed Hydraulic Lash Adjuster (DFHLA):
Many hydraulic lash adjusting devices exist for maintaining lash in engines. For DVVL switching of rocker arm 100 (
As illustrated in
Selected materials for the ball plunger end 601 may also have higher allowable kinetic stress loads, for example, chrome vanadium alloy.
Hydraulic flow pathways in the DFHLA 110 are designed for high flow and low pressure drop to ensure consistent hydraulic switching and reduced pumping losses. The DFHLA is installed in the engine in a cylindrical receiving socket sized to seal against exterior surface 511, illustrated in
As shown in
2.3. Diamond-Like Carbon Coating (DLC)
A diamond-like carbon coating (DLC) coating is described that can reduce friction between treated parts, and at the same provide necessary wear and loading characteristics. Similar coating materials and processes exist, none are sufficient to meet many of the requirements encountered when used with VVA systems. For example, 1) be of sufficient hardness, 2) have suitable loadbearing capacity, 3) be chemically stable in the operating environment, 4) be applied in a process where temperatures do not exceed part annealing temperatures, 5) meet engine lifetime requirements, and 6) offer reduced friction as compared to a steel on steel interface.
A unique DLC coating process is described that meets the requirements set forth above. The DLC coating that was selected is derived from a hydrogenated amorphous carbon or similar material. The DLC coating is comprised of several layers described in
The combined thickness of layers 701-704 is between two and six micrometers. The DLC coating cannot be applied directly to the metal receiving surface 700. To meet durability requirements and for proper adhesion of the first chrome adhesion layer 701 with the base receiving surface 700, a very specific surface finish mechanically applied to the base layer receiving surface 700.
2.4 Sensing and Measurement
Information gathered using sensors may be used to verify switching modes, identify error conditions, or provide information analyzed and used for switching logic and timing. Several sensing devices that may be used are described below.
2.4.1 Dual Feed Hydraulic Lash Adjuster (DFHLA) Movement
Variable valve actuation (VVA) technologies are designed to change valve lift profiles during engine operation using switching devices, for example a DVVL switching rocker arm or cylinder deactivation (CDA) rocker arm. When employing these devices, the status of valve lift is important information that confirms a successful switching operation, or detects an error condition/malfunction.
A DFHLA is used to both manage lash and supply hydraulic fluid for switching in VVA systems that employ switching rocker arm assemblies such as CDA or DVVL. As shown in the section view of
2.4.2 Valve Stem Movement
Variable valve actuation (VVA) technologies are designed to change valve lift profiles during engine operation using switching devices, for example a DVVL switching rocker arm. The status of valve lift is important information that confirms a successful switching operation, or detects an error condition/malfunction. Valve stem position and relative movement sensors can be used to for this function.
One embodiment to monitor the state of VVA switching, and to determine if there is a switching malfunction is illustrated in
Now, as to
The core 873 is free to move axially inside the primary winding 899, and secondary windings 897, 898, and it is mechanically coupled to the valve 872, whose position is being measured. There is no physical contact between the core 873, and valve guide 871 inside bore.
In operation, the LVDT's primary winding, 899, is energized by applying an alternating current of appropriate amplitude and frequency, known as the primary excitation. The magnetic flux thus developed is coupled by the core 873 to the adjacent secondary windings, 897 and 898.
As shown in 14A, if the core 873 is located midway between the secondary windings 897, 898, an equal magnetic flux is then coupled to each secondary winding, making the respective voltages induced in windings 897 and 898 equal. At this reference midway core 873 position, known as the null point, the differential voltage output is essentially zero.
The core 873 is arranged so that it extends past both ends of winding 899. As shown in
In a second embodiment, illustrated in
It will be appreciated in light of the disclosure that the LVDT sensor components in one example can be located near the top of the valve guide 871 to allow for temperature dissipation below that point. While such a location can be above typical weld points used in valve stem fabrication, the weld could be moved or as noted. The location of the core 873 relative to the secondary winding 897 is proportional to how much voltage is induced.
The use of an LVDT sensor as described above in an operating engine has several advantages, including 1) Frictionless operation—in normal use, there is no mechanical contact between the LVDT's core 873 and coil assembly. No friction also results in long mechanical life. 2) Nearly infinite resolution—since an LVDT operates on electromagnetic coupling principles in a friction-free structure, it can measure infinitesimally small changes in core position, limited only by the noise in an LVDT signal conditioner and the output display's resolution. This characteristic also leads to outstanding repeatability, 3) Environmental robustness—materials and construction techniques used in assembling an LVDT result in a rugged, durable sensor that is robust to a variety of environmental conditions. Bonding of the windings 897, 898, 899 may be followed by epoxy encapsulation into the valve guide body 871, resulting in superior moisture and humidity resistance, as well as the capability to take substantial shock loads and high vibration levels. Additionally, the coil assembly can be hermetically sealed to resist oil and corrosive environments. 4) Null point repeatability—the location of an LVDT's null point, described previously, is very stable and repeatable, even over its very wide operating temperature range. 5) Fast dynamic response—the absence of friction during ordinary operation permits an LVDT to respond very quickly to changes in core position. The dynamic response of an LVDT sensor is limited only by small inertial effects due to the core assembly mass. In most cases, the response of an LVDT sensing system is determined by characteristics of the signal conditioner. 6) Absolute output—an LVDT is an absolute output device, as opposed to an incremental output device. This means that in the event of loss of power, the position data being sent from the LVDT will not be lost. When the measuring system is restarted, the LVDT's output value will be the same as it was before the power failure occurred.
The valve stem position sensor described above employs a LVDT type transducer to determine the location of the valve stem during operation of the engine. The sensor may be any known sensor technology including Hall-effect sensor, electronic, optical and mechanical sensors that can track the position of the valve stem and report the monitored position back to the ECU.
2.4.3 Part Position/Movement
Variable valve actuation (VVA) technologies are designed to change valve lift profiles during engine operation using switching devices, for example a DVVL switching rocker arm. Changes in switching state may also change the position of component parts in VVA assemblies, either in absolute terms or relative to one another in the assembly. Position change measurements can be designed and implemented to monitor the state of VVA switching, and possibly determine if there is a switching malfunction.
Now, with reference to
In one embodiment, movement sensor 828 is located near the first end 101 (
It can be seen that position sensor 828 may be positioned to measure movement of other parts in the rocker arm assembly 100. In a second embodiment, sensor 828 may be positioned at second end 103 of the DVVL rocker arm assembly 100 (
A third embodiment can position sensor 828 to directly evaluate the latch 200 position in the DVVL rocker arm assembly 100. The latch 200 and sensor 828 are engaged and fixed relative to each other when they are in the latched state (high lift mode), and move apart for unlatched (low-lift) operation.
Movement may also be detected using and inductive sensor. Sensor 877 may be a Hall-effect sensor, mounted in a way that allows measurement of the movement or lack of movement, for example the valve stem 112.
2.4.4 Pressure Characterization
Variable valve actuation (VVA) technologies are designed to change valve lift profiles during engine operation using switching devices, for example a DVVL switching rocker arm. Because latch status is an important input to the ECU that may enable it to perform various functions, such as regulating fuel/air mixture to increase gas mileage, reduce pollution, or to regulate idle and knocking, measuring devices or systems that confirm a successful switching operation, or detect an error condition or malfunction are necessary for proper control. In some cases switching status reporting and error notification is necessary for regulatory compliance.
In embodiments comprising a hydraulically actuated DVVL system 800, as illustrated in
Now, with reference to
Using a similar method, but using data measured and analyzed on the microsecond level during a switching event, provides enough detailed control pressure information (
The test system included four switching rocker arm assemblies 100 as shown in (
As noted previously, and in following sections, the fixed geometric configuration of the hydraulic channels, holes, clearances, and chambers, and the stiffness of the latch spring, are variables that relate to hydraulic response and mechanical switching speed for changes in regulated hydraulic fluid pressure. The pressure curves 880, in
The test data in these examples were measured with oil pressure of 50 psi and oil temperature of 70 degrees C. A series of tests in different operating conditions can provide a database of characteristic curves to be used by the ECU for switching diagnosis.
An additional embodiment that utilizes pressure measurement to diagnose switching state is described. A DFHLA 110 as shown in
Compensating force for the ball plunger load 615 is provided by hydraulic fluid pressure in the lower control gallery 805 as it is communicated from the lower port 512 to chamber 905 (
In embodiments, a pressure transducer is placed in the hydraulic gallery 805 that feeds the lash adjuster part of the DFHLA 110. The pressure transducer can be used to monitor the transient pressure change in the hydraulic gallery 805 that feeds the lash adjuster when transitioning from the high-lift state to the low-lift state or from the low-lift state to the high-lift state. By monitoring the pressure signature when switching from one mode to another, the system may be able to detect when the variable valve actuation system is malfunctioning at any one location. A pressure signature curve, in embodiments plotted as pressure versus time in milliseconds, provides a characteristic shape that can include amplitude, slope, and/or other parameters.
For example,
During steady state operation, pressure signature curves 1005, 1006 exhibit cyclical behavior, with distinct spikes 1007, 1008 caused as the DFHLA compensates for alternating ball plunger loads 615 that are imparted as the cam pushes down the rocker arm assembly to compress the valve spring (
As noted previously, and in following sections, the fixed geometric configuration of DFHLA hydraulic channels, holes, clearances, and chambers, are variables that relate to hydraulic response and pressure transients for a given hydraulic fluid pressure and temperature. The pressure signature curves 1005, 1006, in
A series of tests in different operating conditions can provide a database of characteristic curves to be used by the ECU for switching diagnosis. One or several values of pressure can be used based on the system configuration and vehicle demands. The monitored pressure trace can be compared to a standard trace to determine when the system malfunctions.
3. Switching Control and Logic
3.1. Engine Implementation
The DVVL hydraulic fluid system that delivers engine oil at a controlled pressure to the DVVL switching rocker arm 100, illustrated in
3.2. Hydraulic Fluid Delivery System to the Rocker Arm Assembly
With reference to
Purging accumulated air in the upper galleries 802, 803 is important to maintain hydraulic stiffness and minimize variation in the pressure rise time. Pressure rise time directly affects the latch movement time during switching operations. The passive air bleed ports 832, 833 shown in
3.2.1 Hydraulic Fluid Delivery for Low-Lift Mode:
Now, with reference to
3.2.2 Hydraulic Fluid Delivery for High-Lift Mode
Now, with reference to
Solenoid valves in the OCV assembly 820 are de-energized to enable high lift operation. The latch spring 230 extends the latch 200, locking the inner arm 122 and outer arm 120. The locked arms function like a fixed rocker arm. The symmetric high lift lobes 104, 106 (
In high-lift mode, the dual feed function of the DFHLA is important to ensure proper lash compensation of the valve train at maximum engine speeds. The lower gallery 805 in
The table in
3.3 Operating Parameters
An important factor in operating a DVVL system is the reliable control of switching from high-lift mode to low-lift mode. DVVL valve actuation systems can only be switched between modes during a predetermined window of time. As described above, switching from high lift mode to low lift mode and vice versa is initiated by a signal from the engine control unit (ECU) 825 (
3.3.1 Gathered Data
Real-time sensor information includes input from any number of sensors, as illustrated in the exemplary DVVL system 800 illustrated in
In a hydraulically actuated VVA system, the oil temperature affects the stiffness of the hydraulic system used for switching in systems such as CDA and VVL. If the oil is too cold, its viscosity slows switching time, causing a malfunction. This relationship is illustrated for an exemplary DVVL switching rocker arm system, in
Sensor information is sent to the Engine Control Unit (ECU) 825 as a real-time operating parameter (
3.3.2 Stored Information
3.3.2.1 Switching Window Algorithms
Mechanical Switching Window:
The shape of each lobe of the three-lobed cam illustrated in
As previously described and shown in
The mechanical switching window can be optimized by understanding and improving latch movement. Now, with reference to
High-Lift Latch Restriction:
Low-Lift Latch Restriction:
A worst case analysis was performed to define the switching times in
Several mechanical and hydraulic constraints that must be accommodated to meet the total switching window. First, a critical shift 860, caused by switching that is not complete prior to the beginning of the next intake lift event must be avoided. Second, experimental data shows that the maximum switching time to move the latch at the lowest allowable engine oil temperature of 20° C. is 10 milliseconds. As noted in
The DVVL switching rocker arm system was designed with margin to accomplish switching with a 9 millisecond margin. Further, the 9 millisecond margin may allow mode switching at speeds above 3500 rpm. Cylinders three and four correspond to the same switching times as one and two with different phasing as shown in
Now, as to
3.3.2.2 Stored Operating Parameters
Operating parameters comprise stored information, used by the ECU 825 (
3.3 Control Logic
As noted above, DVVL switching can only occur during a small predetermined window of time under certain operating conditions, and switching the DVVL system outside of the timing window may result in a critical shift event, that could result in damage to the valve train and/or other engine parts. Because engine conditions such as oil pressure, temperature, emissions, and load may vary rapidly, a high-speed processor can be used to analyze real-time conditions, compare them to known operating parameters that characterize a working system, reconcile the results to determine when to switch, and send a switching signal. These operations can be performed hundreds or thousands of times per second. In embodiments, this computing function may be performed by a dedicated processor, or by an existing multi-purpose automotive control system referred to as the engine control unit (ECU). A typical ECU has an input section for analog and digital data, a processing section that includes a microprocessor, programmable memory, and random access memory, and an output section that might include relays, switches, and warning light actuation.
In one embodiment, the engine control unit (ECU) 825 shown in
After input is analyzed, a control signal is output by the ECU 825 to the OCV 820 to initiate switching operation, which may be timed to avoid critical shift events while meeting engine performance goals such as improved fuel economy and lowered emissions. If necessary, the ECU 825 may also alert operators to error conditions.
4. DVVL Switching Rocker Arm Assembly
4.1 Assembly Description
A switching rocker arm, hydraulically actuated by pressurized fluid, for engaging a cam is disclosed. An outer arm and inner arm are configured to transfer motion to a valve of an internal combustion engine. A latching mechanism includes a latch, sleeve and orientation member. The sleeve engages the latch and a bore in the inner arm, and also provides an opening for an orientation member used in providing the correct orientation for the latch with respect to the sleeve and the inner arm. The sleeve, latch and inner arm have reference marks used to determine the optimal orientation for the latch.
An exemplary switching rocker arm 100 may be configured during operation with a three lobed cam 102 as illustrated in the perspective view of
As shown in
The rocker arm 100 illustrated in
First and second over-travel limiters 140, 142 of the outer arm prevent over-coiling of the torsion springs 134, 136 and limit excess stress on the springs 134, 136. The over-travel limiters 140, 142 contact the inner arm 122 on the first and second oil gallery 144, 146 when the outer arm 120 reaches its maximum rotation during low-lift mode. At this point, the interference between the over-travel limiters 140, 142 and the galleries 144, 146 stops any further downward rotation of the outer arm 120.
When the outer arm 120 reaches its maximum rotation during low-lift mode as described above, a latch stop 90, shown in
The switching rocker arm assembly 100 must be compact enough to fit in confined engine spaces without sacrificing performance or durability. Traditional torsion springs coiled from round wire sized to meet the torque requirements of the design, in some embodiments, are too wide to fit in the allowable spring space 121 between the outer arm 120 and the inner arm 122, as illustrated in
4.2 Torsion Spring
A torsion spring 134, 136 design and manufacturing process is described that results in a compact design with a generally rectangular shaped wire made with selected materials of construction.
Now, with reference to
In this configuration, as the coils are wound, elongated side 402 of each coil rests against the elongated side 402 of the previous coil, thereby stabilizing the torsion springs 134, 136. The shape and arrangement holds all of the coils in an upright position, preventing them from passing over each other or angling when under pressure.
When the rocker arm assembly 100 is operating, the generally rectangular or trapezoidal shape of the torsion springs 134, 136, as they bend about axis 400 shown in
To meet durability requirements, a combination of techniques and materials are used together. For example, the torsion springs 134, 136 may be made of a material that includes Chrome Vanadium alloy steel along with this design to improve strength and durability.
The torsion spring 134, 136 may be heated and quickly cooled to temper the springs. This reduces residual part stress.
Impacting the surface of the wire 396, 397 used for creating the torsion springs 134, 136 with projectiles, or ‘shot peening’ is used to put residual compressive stress in the surface of the wire 396, 397. The wire 396, 397 is then wound into the torsion springs 134, 136. Due to their shot peening, the resulting torsion springs 134, 136 can now accept more tensile stress than identical springs made without shot peening.
4.3 Torsion Spring Pocket
The switching rocker arm assembly 100 may be compact enough to fit in confined engine spaces with minimal impact to surrounding structures.
A switching rocker arm 100 provides a torsion spring pocket with retention features formed by adjacent assembly components is described.
Now with reference to
Torsion springs 134, 136 can freely move along the axis of pivot axle 118. When fully assembled, the first and second tabs 405, 406 on inner arm 122 retain inner ends 409, 410 of torsion springs 134, 136, respectively. The first and second over-travel limiters 140, 142 on the outer arm 120 assemble to prevent rotation and retain outer ends 407, 408 of the first and second torsion springs 134, 136, respectively, without undue constraints or additional materials and parts.
4.4 Outer Arm
The design of outer arm 120 is optimized for the specific loading expected during operation, and its resistance to bending and torque applied by other means or from other directions may cause it to deflect out of specification. Examples of non-operational loads may be caused by handling or machining. A clamping feature or surface built into the part, designed to assist in the clamping and holding process while grinding the slider pads, a critical step needed to maintain parallelism between the slider pads as it holds the part stationary without distortion.
4.5 DVVL Assembly Operation
Other configurations other than the roller assembly 129 and pads 130, 132 also permit the transfer of motion from cam 102 to rocker arm 100. For example, a smooth non-rotating surface (not shown) such as pads 130, 132 may be placed on inner arm 122 to engage low-lift lobe 108, and roller assemblies may be mounted to rocker arm 100 to transfer motion from high-lift lobes 104, 106 to outer arm 120 of rocker arm 100.
Now, with reference to
To make the design compact, with dynamic loading as close as possible to non-switching rocker arm designs, slider pads 130, 132 are used as the surfaces that contact the cam lobes 104, 106 during operation in high-lift mode. Slider pads produce more friction during operation than other designs such as roller bearings, and the friction between the first slider pad surface 130 and the first high-lift lobe surface 104, plus the friction between the second slider pad 132 and the second high-lift lobe 106, creates engine efficiency losses.
When the rocker arm assembly 100 is in high-lift mode, the full load of the valve opening event is applied slider pads 130, 132. When the rocker arm assembly 100 is in low-lift mode, the load of the valve opening event applied to slider pads 130, 132 is less, but present. Packaging constraints for the exemplary switching rocker arm 100, require that the width of each slider pad 130, 132 as described by slider pad edge length 710, 711 that come in contact with the cam lobes 104, 106 are narrower than most existing slider interface designs. This results in higher part loading and stresses than most existing slider pad interface designs. The friction results in excessive wear to cam lobes 104, 106, and slider pads 130, 132, and when combined with higher loading, may result in premature part failure. In the exemplary switching rocker arm assembly, a coating such as a diamond like carbon coating is used on the slider pads 130, 132 on the outer arm 120.
A diamond-like carbon coating (DLC) coating enables operation of the exemplary switching rocker arm 100 by reducing friction, and at the same providing necessary wear and loading characteristics for the slider pad surfaces 130, 132. As can be easily seen, benefits of DLC coating can be applied to any part surfaces in this assembly or other assemblies, for example the pivot axle surfaces 160, 162, on the outer arm 120 described in
Although similar coating materials and processes exist, none are sufficient to meet the following DVVL rocker arm assembly requirements: 1) be of sufficient hardness, 2) have suitable loadbearing capacity, 3) be chemically stable in the operating environment, 4) be applied in a process where temperatures do not exceed the annealing temperature for the outer arm 120, 5) meet engine lifetime requirements, and 6) offer reduced friction as compared to a steel on steel interface. The DLC coating process described earlier meets the requirements set forth above, and is applied to slider pad surfaces 130, 132, which are ground to a final finish using a grinding wheel material and speed that is developed for DLC coating applications. The slider pad surfaces 130, 132 are also polished to a specific surface roughness, applied using one of several techniques, for example vapor honing or fine particle sand blasting.
4.5.1 Hydraulic Fluid System
The hydraulic latch for rocker arm assembly 100 must be built to fit into a compact space, meet switching response time requirements, and minimize oil pumping losses. Oil is conducted along fluid pathways at a controlled pressure, and applied to controlled volumes in a way that provides the necessary force and speed to activate latch pin switching. The hydraulic conduits require specific clearances and sizes so that the system has the correct hydraulic stiffness and resulting switching response time. The design of the hydraulic system must be coordinated with other elements that comprise the switching mechanism, for example the biasing spring 230.
In the switching rocker arm 100, oil is transmitted through a series of fluid-connected chambers and passages to the latch pin assembly 201, or any other hydraulically activated latch pin mechanism. As described above, the hydraulic transmission system begins at oil flow port 506 in the DFHLA 110, where oil or another hydraulic fluid at a controlled pressure is introduced. Pressure can be modulated with a switching device, for example, a solenoid valve. After leaving the ball plunger end 601, oil or other pressurized fluid is directed from this single location, through the first oil gallery 144 and the second oil gallery 146 of the inner arm discussed above, which have bores sized to minimize pressure drop as oil flows from the ball socket 502, shown in
The latch pin assembly 201 for latching inner arm 122 to outer arm 120, which in the illustrated embodiment is found near second end 103 of rocker arm 100, is shown in
As illustrated in
The oil is provided to oil opening 280 and the latch pin assembly 201 at a range of pressures, depending on the required mode of operation.
As can be seen in
Some of the oil exits back to the engine through hole 209, drilled into the inner arm 122. The remaining oil is pushed back through the hydraulic pathways as the biasing spring 230 expands when it returns to the latched high-lift state. It can be seen that a similar flow path can be employed for latch mechanisms that are biased for normally unlatched operation.
The latch pin assembly design manages latch pin response time through a combination of clearances, tolerances, hole sizes, chamber sizes, spring designs, and similar metrics that control the flow of oil. For example, the latch pin design may include features such as a dual diameter pin designed with an active hydraulic area to operate within tolerance in a given pressure range, an oil sealing land designed to limit oil pumping losses, or a chamfer oil in-feed.
Now, with reference to
An oil in-feed surface 426 can also reduce the pressure and oil pumping losses required for switching by lowering the requirement for the breakaway force between pressurization surface 422 and the sleeve end 427. These relationships can be shown as incremental improvements to switching response and pumping losses.
As oil flows throughout the previously-described switching rocker arm assembly 100 hydraulic system, the relationship between oil pressure and oil fluid pathway area and length largely defines the reaction time of the hydraulic system, which also directly affects switching response time. For example, if high pressure oil at high velocity enters a large volume, its velocity will suddenly slow, decreasing its hydraulic reaction time, or stiffness. A range of these relationships that are specific to the operation of switching rocker arm assembly 100 can be calculated. One relationship, for example, can be described as follows: oil at a pressure of 2 bar is supplied to chamber 250, where the oil pressure, divided by the pressurizing surface area, transmits a force that overcomes biasing spring 230 force, and initiates switching within 10 milliseconds from latched to unlatched operation.
A range of characteristic relationships that result in acceptable hydraulic stiffness and response time, with minimized oil pumping losses can be calculated from system design variables that can be defined as follows:
Latch response times for the previously described hydraulic arrangement in switching rocker arm 100 can be described for a range of conditions, for example:
Oil temperatures: 10° C. to 120° C.
Oil type: 5w-20 weight
This conditions result in a range of oil viscosities that affect the latch response time.
4.5.2 Latch Pin Mechanism
The latch pin assembly 201 of rocker arm assembly 100 provides a means of mechanically switching from high-lift to low-lift and vice versa. A latch pin mechanism can be configured to be normally in an unlatched or latched state. Several preferred embodiments can be described.
In one embodiment, the latch pin assembly 201 for latching inner arm 122 to outer arm 120, which is found near second end 103 of rocker arm 100, is shown in
Sleeve 210 has a generally cylindrical outer surface 211 that interfaces a first generally cylindrical bore wall 241, and a generally cylindrical inner surface 215. Bore 240 has a first generally cylindrical bore wall 241, and a second generally cylindrical bore wall 242 having a larger diameter than first generally cylindrical bore wall 241. The generally cylindrical outer surface 211 of sleeve 210 and first generally cylindrical surface 205 of latch 200 engage first generally cylindrical bore wall 241 to form tight pressure seals. Further, the generally cylindrical inner surface 215 of sleeve 210 also forms a tight pressure seal with second generally cylindrical surface 206 of latch 200. During operation, these seals allow oil pressure to build in chamber 250, which encircles second generally cylindrical surface 206 of latch 200.
The default position of latch 200, shown in
In the latched state, latch 200 engages a latch surface 214 of outer arm 120 with arm engaging surface 213. As shown in
As previously described, and seen in
An exemplary latch 200 is shown in
An alternative latch pin assembly 201 is shown in
With reference to
The latch pin 200 is then rotated clockwise until orientation feature 212 reaches plug 1000, at which point interference between the orientation feature 212 and plug 1000 prevents further rotation. An angle measurement A1, as shown in
A profile of an alternative embodiment of pin 1000 is shown in
The latch embodiments described above utilize a flat mating surface to engage or disengage during switching operations, thus providing a predictable contact area with relatively low contact stress for the mating parts. As described above, this pin design requires additional parts and features to ensure proper orientation during operation, adding complexity and cost to the rocker arm manufacturing and assembly process.
Another latch embodiment incorporates a round or other non-flat latch pin that eliminates the need to provide pin orientation. In the past is was thought that in order to utilize a round or other non-flat rocker arm latch, the mating surface would require an expensive high-tolerance ‘ground-in’ curved mating surface, or latch seat, with a radius very closely matching the latch pin radius. A seat that is slightly too small may cause sticking, a delayed release, and possibly cause impact with the corners of the latch seat. A latch seat that is too large allows too much lateral motion. As described below, a round or other non-flat latch embodiment that does not require grinding can be produced using a coining process.
In the example shown, for a truly round latch with no flat latch shelf, the need to orient the latch in the rocker arm that it resides in is eliminated. By eliminating the need to orient the latch, assembly parts and risk may be eliminated.
This process will also likely reduce or eliminate the need to categorize latch, inner arm, and outer arm dimensions required to meet lash requirements for a given rocker arm assembly. This is accomplished by being able to adjust the latch lash at the end of the assembly processes.
A method for manufacturing a rocker arm assembly that utilizes a round or non-flat latch embodiment is described later. As noted, this process modifies this mating surface by way of a coining process.
The present disclosure employs a non-flat latch, such as a latch with a round cross section that interfaces with a latch seat that has been modified from a flat section. The present disclosure includes a design that can achieve a curved mating surface that matches what the latch requirements are, and does not require a grinding process. The process modifies this mating surface by way of a coining process. By using a truly round latch with no flat latch shelf we eliminate the need to orient the latch in the rocker arm that it resides in. By eliminating the need to orient the latch you eliminate parts from the assembly and risk from the assembly.
This process will likely reduce or eliminate categories of latches and the need to categorize the inner and outer arm. This is accomplished by being able to adjust the latch lash at the end of the assembly processes.
The description here explains a VVL rocker arm assembly that has a normally unlatched latch position. This process also can be used for a CDA rocker arm assembly, and other switching rocker arm assemblies. The rocker assembly is partially assembled with a roller bearing installed. The latch hasn't been installed at this point.
The second end 103 of the outer arm 120 has been investment cast and the latch seat 214 has been coined flat as shown in
Next, the outer arm will be 3-point located on a fixture so that it is supported under the arm directly below the pivot holes on both sides of the arm. It will then be located with a swivel locator directly in the middle of the latch mating surface, giving a 3-point location. It will then be clamped directly above these points with swivel foot clamps so as not to distort the part.
Now the pivot hole will be machined. Next this outer arm will be heat treated. Now the pivot hole will be honed.
After that, the pivot holes are honed. The part is mounted on a fixture with a pin passing through the pivot holes of the outer arm 120 and the datum hole on the fixture. The outer arm 120 will also rest on a swivel foot post that is directly below the coined latch pad surface, again giving 3 point location and eliminating part distortion. While on this fixture the stop bar will be machined to the proper height and parallel to the pivot hole axis. Now the outer arm will be located on the pivot holes and the stop bar to do the final grind on the slider pads. Both arms will now be assembled. Springs are installed on the inner arm spring posts then the two arms are assembled and pivot pin is installed.
This end 103 of the outer arm 120 also shows the latch stop 90. (
The switching rocker arm assembly 100 is now placed on the fixture shown in
The inner arm will rest on the ball plunger post 315 and be guided from side to side by the valve tip post. The latch rod 199 is sized to have a tight slip fit into the latch bore 240 is then slide into the inner arm 122. The latch rod 199 will extend out of the inner arm 122 (for example, by approximately 10 mm). The latch rod 199 will then rest on a flat carbide support shelf 311 on the manufacturing fixture 310. At this point the rocker arm assembly 100 is being supported by the ball plunger post 315 and the latch rod 199 sitting on the support shelf 311 as shown in
The rocker arm assembly 100 is being controlled from side to side by the ball plunger post 315 and the valve tip post 313. Now a load is applied by a press 317 to the outer arm 120 directly above the latch surface and on top of the outer arm 120. (The press may be a hydraulic, screw, or any other form of controlled power press.) This load will be increased until the correct latch lash is achieved. The latch seat 214 of the outer arm 120 now has a perfectly coined indention in the surface that directly matches the latch pin (200 of
Below is an example of steps to implement the process.
A method of managing three or more lash values, or design clearances, in the DVVL switching rocker arm assembly 100 shown in
DVVL Assembly Lash Description
An exemplary rocker arm assembly 100 shown in
The switching rocker arm assembly 100 shown in
During low-lift mode, camshaft lash 610 also prevents the torsion spring 134, 136 force from being transferred to the DFHLA 110 during base circle 609 operation. This allows the DFHLA 110 to operate like a standard rocker arm assembly with normal hydraulic lash compensation where the lash compensation portion of the DFHLA is supplied directly from an engine oil pressure gallery. As shown in
As illustrated in
Referring to the graph shown in
As noted in
Now, as to
Latch lash 602, and camshaft lash 610 shown in
Lash Management, Testing
As described in following sections, the design and manufacturing methods used to manage lash were tested and verified for a range of expected operating conditions to simulate both normal operation and conditions representing higher stress conditions.
Durability of the DVVL switching rocker arm is assessed by demonstrating continued performance (i.e., valves opening and closing properly) combined with wear measurements. Wear is assessed by quantifying loss of material on the DVVL switching rocker arm, specifically the DLC coating, along with the relative amounts of mechanical lash in the system. As noted above, latch lash 602 (
For example, as shown in
4.7 DVVL Assembly Dynamics
The weight distribution, stiffness, and inertia for traditional rocker arms have been optimized for a specified range of operating speeds and reaction forces that are related to dynamic stability, valve tip loading and valve spring compression during operation. An exemplary switching rocker arm 100, illustrated in
As to
As shown in
4.7.1 DVVL Assembly Dynamics Detailed Description
The major components that comprise total inertia for the rocker arm assembly 100 are illustrated in
Referring to
In low-lift mode, the inner arm assembly 622 transmits the cam load 616 to the valve tip 613, compresses spring 114 (of
Now, as to
Now, as to
Now, referencing
4.7.2 DVVL Assembly Dynamics Analysis
For stress and deflection analysis, a load case is described in terms of load location and magnitude as illustrated in
Design parameters for evaluation can be described:
Now, as referenced by
Now, with reference to
To illustrate, select three functioning DVVL rocker arm assemblies 100, illustrated in
This range of component inertia values in turn produces a unique arrangement of major components (torsion springs, outer arm, and inner arm assembly). For example, in this design, the torsion springs will tend to be very close to the ball end plunger tip 611.
As to
Stiffness and mass distribution for the outer arm 120 along an axis related to its motion and orientation during operation, describe characteristic values, and by extension, characteristic shapes.
5 Design Verification
5.1 Latch Response
Latch response times for the exemplary DVVL system were validated with a latch response test stand 900 illustrated in
The latch response test stand 900 utilized production intent hardware including OCVs, DFHLAs, and DVVL switching rocker arms 100. To simulate engine oil conditions, the oil temperature was controlled by an external heating and cooling system. Oil pressure was supplied by an external pump and controlled with a regulator. Oil temperature was measured in a control gallery between the OCV and DFHLA. The latch movement was measured with a displacement transducer 901.
Latch response times were measured with a variety of production intent SRFFs. Tests were conducted with production intent 5w-20 motor oil. Response times were recorded when switching from low lift mode to high lift and high lift mode to low lift mode.
Results from the switching studies show that the switching time for the latch is primarily a function of the oil temperature due to the change in viscosity of the oil. The slope of the latch response curve resembles viscosity to temperature relationships of motor oil.
The switching response results show that the latch movement is fast enough for mode switching in one camshaft revolution up to 3500 engine rpm. The response time begins to increase significantly as the temperature falls below 20° C. At temperatures of 10° C. and below, switching in one camshaft revolution is not possible without lowering the 3500 rpm switching requirement.
The SRFF was designed to be robust at high engine speeds for both high and low lift modes as shown in Table 1. The high lift mode can operate up to 7300 rpm with a “burst” speed requirement of 7500 rpm. A burst is defined as a short excursion to a higher engine speed. The SRFF is normally latched in high lift mode such that high lift mode is not dependent on oil temperature. The low lift operating mode is focused on fuel economy during part load operation up to 3500 rpm with an over speed requirement of 5000 rpm in addition to a burst speed to 7500 rpm. As tested, the system is able to hydraulically unlatch the SRFF for oil temperatures at 200° C. or above. Testing was conducted down to 10° C. to ensure operation at 20° C. Durability results show that the design is robust across the entire operating range of engine speeds, lift modes and oil temperatures.
The design, development, and validation of a SRFF based DVVL system to achieve early intake valve closing was completed for a Type II valve train. This DVVL system improves fuel economy without jeopardizing performance by operating in two modes. Pumping loop losses are reduced in low lift mode by closing the intake valve early while performance is maintained in high lift mode by utilizing a standard intake valve profile. The system preserves common Type II intake and exhaust valve train geometries for use in an in-line four cylinder gasoline engine. Implementation cost is minimized by using common components and a standard chain drive system. Utilizing a Type II SRFF based system in this manner allows the application of this hardware to multiple engine families.
This DVVL system, installed on the intake of the valve train, met key performance targets for mode switching and dynamic stability in both high-lift and low-lift modes. Switching response times allowed mode switching within one cam revolution at oil temperatures above 20° C. and engine speeds up to 3500 rpm. Optimization of the SRFF stiffness and inertia, combined with an appropriate valve lift profile design allowed the system to be dynamically stable to 3500 rpm in low lift mode and 7300 rpm in high lift mode. The validation testing completed on production intent hardware shows that the DVVL system exceeds durability targets. Accelerated system aging tests were utilized to demonstrate durability beyond the life targets.
5.2 Durability
Passenger cars are required to meet an emissions useful life requirement of 150,000 miles. This study set a more stringent target of 200,000 miles to ensure that the product is robust well beyond the legislated requirement.
The valve train requirements for end of life testing are translated to the 200,000 mile target. This mileage target must be converted to valve actuation events to define the valve train durability requirements. In order to determine the number of valve events, the average vehicle and engine speeds over the vehicle lifetime must be assumed. For this example, an average vehicle speed of 40 miles per hour combined with an average engine speed of 2200 rpm was chosen for the passenger car application. The camshaft speed operates at half the engine speed and the valves are actuated once per camshaft revolution, resulting in a test requirement of 330 million valve events. Testing was conducted on both firing engines and non-firing fixtures. Rather than running a 5000 hour firing engine test, most testing and reported results focus on the use of the non-firing fixture illustrated in
5.2.1 Accelerated Aging
There was a need for conducting an accelerated test to show compliance over multiple engine lives prior to running engine tests. Hence, fixture testing was performed prior to firing tests. A higher speed test was designed to accelerate valve train wear such that it could be completed in less time. A test correlation was established such that doubling the average engine speed relative to the in-use speed yielded results in approximately one-quarter of the time and nearly equivalent valve train wear. As a result, valve train wear followed closely to the following equation:
Where VEAccel are the valve events required during an accelerated aging test, VEin-use are the valve events required during normal in-use testing, RPMavg-test is the average engine speed for the accelerated test and RPMavg-in use is the average engine speed for in-use testing.
A proprietary, high speed, durability test cycle was developed that had an average engine speed of approximately 5000 rpm. Each cycle had high speed durations in high lift mode of approximately 60 minutes followed by lower speed durations in low lift mode for approximately another 10 minutes. This cycle was repeated 430 times to achieve 72 million valve events at an accelerated wear rate that is equivalent to 330 million events at standard load levels. Standard valve train products containing needle and roller bearings have been used successfully in the automotive industry for years. This test cycle focused on the DLC coated slider pads where approximately 97% of the valve lift events were on the slider pads in high lift mode leaving 2 million cycles on the low lift roller bearing as shown in Table 2. These testing conditions consider one valve train life equivalent to 430 accelerated test cycles. Testing showed that the SRFF is durable through six engine useful lives with negligible wear and lash variation.
The accelerated system aging test was key to showing durability while many function-specific tests were also completed to show robustness over various operating states.
Table 2 includes the main durability tests combined with the objective for each test. The accelerated system aging test was described above showing approximately 500 hours or approximately 430 test cycles. A switching test was operated for approximately 500 hours to assess the latch and torsion spring wear. Likewise, a critical shift test was also performed to further age the parts during a harsh and abusive shift from the outer arm being partially latched such that it would slip to the low lift mode during the high lift event. A critical shift test was conducted to show robustness in the case of extreme conditions caused by improper vehicle maintenance. This critical shift testing was difficult to achieve and required precise oil pressure control in the test laboratory to partially latch the outer arm. This operation is not expected in-use as the oil control pressures are controlled outside of that window. Multiple idle tests combined with cold start operation were conducted to accelerate wear due to low oil lubrication. A used oil test was also conducted at high speed. Finally, bearing and torsion spring tests were conducted to ensure component durability. All tests met the engine useful lift requirement of 200,000 miles which is safely above the 150,000 mile passenger car useful life requirement.
All durability tests were conducted having specific levels of oil aeration. Most tests had oil aeration levels ranging between approximately 15% and 20% total gas content (TGC) which is typical for passenger car applications. This content varied with engine speed and the levels were quantified from idle to 7500 rpm engine speed. An excessive oil aeration test was also conducted having aeration levels of 26% TGC. These tests were conducted with SRFF's that met were tested for dynamics and switching performance tests. Details of the dynamics performance test are discussed in the results section. The oil aeration levels and extended levels were conducted to show product robustness.
5.2.2 Durability Test Apparatus
The durability test stand shown in
5.2.3 Durability Test Apparatus Control
A control system for the fixture is configured to command engine speed, oil temperature and valve lift state as well as verify that the intended lift function is met. The performance of the valve train is evaluated by measuring valve displacement using non-intrusive Bently Nevada 3300XL proximity probes 906. The proximity probes measure valve lift up to 2 mm at one-half camshaft degree resolution. This provides the information necessary to confirm the valve lift state and post process the data for closing velocity and bounce analysis. The test setup included a valve displacement trace that was recorded at idle speed to represent the baseline conditions of the SRFF and is used to determine the master profile 908 shown in
5.2.4 Durability Test Plan
A Design Failure Modes and Effects Analysis (DFMEA) was conducted to determine the SRFF failure modes. Likewise, mechanisms were determined at the system and subsystem levels. This information was used to develop and evaluate the durability of the SRFF to different operating conditions. The test types were separated into four categories as shown in
The hierarchy of key tests for durability are shown in
Performance Verification
Fatigue & Stiffness
The SRFF is placed under a cyclic load test to ensure fatigue life exceeds application loads by a significant design margin. Valve train performance is largely dependent on the stiffness of the system components. Rocker arm stiffness is measured to validate the design and ensure acceptable dynamic performance.
Valve Train Dynamics
The Valve train Dynamics test description and performance is discussed in the results section. The test involved strain gaging the SRFF combined with measuring valve closing velocities.
Subsystem Testing
Switching Durability
The switching durability test evaluates the switching mechanism by cycling the SRFF between the latched, unlatched and back to the latched state a total of three million times (
Torsion Spring Durability and Fatigue
The torsion spring is an integral component of the switching roller finger follower. The torsion spring allows the outer arm to operate in lost motion while maintaining contact with the high lift camshaft lobe. The Torsion Spring Durability test is performed to evaluate the durability of the torsion springs at operational loads. The Torsion Spring Durability test is conducted with the torsion springs installed in the SRFF. The Torsion Spring Fatigue test evaluates the torsion spring fatigue life at elevated stress levels. Success is defined as torsion spring load loss of less than 15% at end-of-life.
Idle Speed Durability
The Idle Speed Durability test simulates a limit lubrication condition caused by low oil pressure and high oil temperature. The test is used to evaluate the slider pad and bearing, valve tip to valve pallet and ball socket to ball plunger wear. The lift-state is held constant throughout the test in either high or low lift. The total mechanical lash is measured at periodic inspection intervals and is the primary measure of wear.
Extreme Limit Testing
Overspeed
Switching rocker arm failure modes include loss of lift-state control. The SRFF is designed to operate at a maximum crankshaft speed of 3500 rpm in low lift mode. The SRFF includes design protection to these higher speeds in the case of unexpected malfunction resulting in low lift mode. Low lift fatigue life tests were performed at 5000 rpm. Engine Burst tests were performed to 7500 rpm for both high and low lift states.
Cold Start Durability
The Cold Start durability test evaluates the ability of the DLC to withstand 300 engine starting cycles from an initial temperature of −30° C. Typically, cold weather engine starting at these temperatures would involve an engine block heater. This extreme test was chosen to show robustness and was repeated 300 times on a motorized engine fixture. This test measures the ability of the DLC coating to withstand reduced lubrication as a result of low temperatures.
Critical Shift Durability
The SRFF is designed to switch on the base circle of the camshaft while the latch pin is not in contact with the outer arm. In the event of improper OCV timing or lower than required minimum control gallery oil pressure for full pin travel, the pin may still be moving at the start of the next lift event. The improper location of the latch pin may lead to a partial engagement between the latch pin and outer arm. In the event of a partial engagement between the outer arm and latch pin, the outer arm may slip off the latch pin resulting in an impact between the roller bearing and low lift camshaft lobe. The Critical Shift Durability is an abuse test that creates conditions to quantify robustness and is not expected in the life of the vehicle. The Critical Shift test subjects the SRFF to 5000 critical shift events.
Accelerated Bearing Endurance
The accelerated bearing endurance is a life test used to evaluate life of bearings that completed the critical shift test. The test is used to determine whether the effects of critical shift testing will shorten the life of the roller bearing. The test is operated at increased radial loads to reduce the time to completion. New bearings were tested simultaneously to benchmark the performance and wear of the bearings subjected to critical shift testing. Vibration measurements were taken throughout the test and were analyzed to detect inception of bearing damage.
Used Oil Testing
The Accelerated System Aging test and Idle Speed Durability test profiles were performed with used oil that had a 20/19/16 ISO rating. This oil was taken from engines at the oil change interval.
Accelerated System Aging
The Accelerated System Aging test is intended to evaluate the overall durability of the rocker arm including the sliding interface between the camshaft and SRFF, latching mechanism and the low lift bearing. The mechanical lash was measured at periodic inspection intervals and is the primary measure of wear.
Valvetrain Dynamics
Valve train dynamic behavior determines the performance and durability of an engine. Dynamic performance was determined by evaluating the closing velocity and bounce of the valve as it returns to the valve seat. Strain gaging provides information about the loading of the system over the engine speed envelope with respect to camshaft angle. Strain gages are applied to the inner and outer arms at locations of uniform stress.
A Valve train Dynamics test was conducted to evaluate the performance capabilities of the valve train. The test was performed at nominal and limit total mechanical lash values. The nominal case is presented. A speed sweep from 1000 to 7500 rpm was performed, recording 30 valve events per engine speed. Post processing of the dynamics data allows calculation of valve closing velocity and valve bounce. The attached strain gages on the inner and outer arms of the SRFF indicate sufficient loading of the rocker arm at all engine speeds to prevent separation between valve train components or “pump-up” of the HLA. Pump-up occurs when the HLA compensates for valve bounce or valve train deflection causing the valve to remain open on the camshaft base circle. The minimum, maximum and mean closing velocities are shown to understand the distribution over the engine speed range. The high lift closing velocities are presented in
Critical Shift
The Critical Shift test is performed by holding the latch pin at the critical point of engagement with the outer arm as shown in
The Critical Shift test was performed using a motorized engine similar to that shown in
The latching mechanism and bearing are monitored for wear throughout the test. The typical wear of the outer arm (
Subsystems
The subsystem tests evaluate particular functions and wear interfaces of the SRFF rocker arm. Switching Durability evaluates the latching mechanism for function and wear over the expected life of the SRFF. Similarly, Idle Speed Durability subjects the bearing and slider pad to a worst case condition including both low lubrication and an oil temperature of 130° C. The Torsion Spring Durability Test was accomplished by subjecting the torsion springs to approximately 25 million cycles. Torsion spring loads are measured throughout the test to measure degradation. Further confidence was gained by extending the test to 100 million cycles while not exceeding the maximum design load loss of 15%.
Accelerated System Aging
The Accelerated System Aging test is the comprehensive durability test used as the benchmark of sustained performance. The test represents the cumulative damage of the severe end-user. The test cycle averages approximately 5000 rpm with constant speed and acceleration profiles. The time per cycle is broken up as follows: 28% steady state, 15% low lift and cycling between high and low lift with the remainder under acceleration conditions. The results of testing show that the lash change in one-life of testing accounts for 21% of the available wear specification of the rocker arm. Accelerated System Aging test, consisting of 8 SRFF's, was extended out past the standard life to determine wear out modes of the SRFF. Total mechanical lash measurements were recorded every 100 test cycles once past the standard duration.
The results of the accelerated system aging measurements are presented in
5.2.5 Durability Test Results
Each of the tests discussed in the test plan were performed and a summary of the results are presented. The results of Valve train Dynamics, Critical Shift Durability, Torsion Spring Durability and finally the Accelerated System Aging test are shown.
The SRFF was subjected to accelerated aging tests combined with function-specific tests to demonstrate robustness and is summarized in Table 3.
Durability was assessed in terms of engine lives totaling an equivalent 200,000 miles which provides substantial margin over the mandated 150,000 mile requirement. The goal of the project was to demonstrate that all tests show at least one engine life. The main durability test was the accelerated system aging test that exhibited durability to at least six engine lives or 1.2 million miles. This test was also conducted with used oil showing robustness to one engine life. A key operating mode is switching operation between high and low lift. The switching durability test exhibited at least three engine lives or 600,000 miles. Likewise, the torsion spring was robust to at least four engine lives or 800,000 miles. The remaining tests were shown to at least one engine life for critical shifts, over speed, cold start, bearing robustness and idle conditions. The DLC coating was robust to all conditions showing polishing with minimal wear, as shown in
5.2.6 Durability Test Conclusions
The DVVL system including the SRFF, DFHLA and OCV was shown to be robust to at least 200,000 miles which is a safe margin beyond the 150,000 mile mandated requirement. The durability testing showed accelerated system aging to at least six engine lives or 1.2 million miles. This SRFF was also shown to be robust to used oil as well as aerated oil. The switching function of the SRFF was shown robust to at least three engine lives or 600,000 miles. All sub-system tests show that the SRFF was robust beyond one engine life of 200,000 miles.
Critical shift tests demonstrated robustness to 5000 events or at least one engine life. This condition occurs at oil pressure conditions outside of the normal operating range and causes a harsh event as the outer arm slips off the latch such that the SRFF transitions to the inner arm. Even though the condition is harsh, the SRFF was shown robust to this type of condition. It is unlikely that this event will occur in serial production. Testing results show that the SRFF is robust to this condition in the case that a critical shift occurs.
The SRFF was proven robust for passenger car application having engine speeds up to 7300 rpm and having burst speed conditions to 7500 rpm. The firing engine tests had consistent wear patterns to the non-firing engine tests described in this paper. The DLC coating on the outer arm slider pads was shown to be robust across all operating conditions. As a result, the SRFF design is appropriate for four cylinder passenger car applications for the purpose of improving fuel economy via reduced engine pumping losses at part load engine operation. This technology could be extended to other applications including six cylinder engines. The SRFF was shown to be robust in many cases that far exceeded automotive requirements. Diesel applications could be considered with additional development to address increased engine loads, oil contamination and lifetime requirements.
5.3 Slider Pad/DLC Coating Wear
5.3.1 Wear Test Plan
This section describes the test plan utilized to investigate the wear characteristics and durability of the DLC coating on the outer arm slider pad. The goal was to establish relationships between design specifications and process parameters and how each affected the durability of the sliding pad interface. Three key elements in this sliding interface are: the camshaft lobe, the slider pad, and the valve train loads. Each element has factors which needed to be included in the test plan to determine the effect on the durability of the DLC coating. Detailed descriptions for each component follow:
Camshaft—The width of the high lift camshaft lobes were specified to ensure the slider pad stayed within the camshaft lobe during engine operation. This includes axial positional changes resulting from thermal growth or dimensional variation due to manufacturing. As a result, the full width of the slider pad could be in contact with the camshaft lobe without risk of the camshaft lobe becoming offset to the slider pad. The shape of the lobe (profile) pertaining to the valve lift characteristics had also been established in the development of the camshaft and SRFF. This left two factors which needed to be understood relative to the durability of the DLC coating; the first was lobe material and the second was the surface finish of the camshaft lobe. The test plan included cast iron and steel camshaft lobes tested with different surface conditions on the lobe. The first included the camshafts lobes as prepared by a grinding operation (as-ground). The second was after a polishing operation improved the surface finish condition of the lobes (polished).
Slider Pad—The slider pad profile was designed to specific requirements for valve lift and valve train dynamics.
The
The second factor on the slider pads which required evaluation was the surface finish of the slider pads before DLC coating. The processing steps of the slider pad included a grinding operation which formed the profile of the slider pad and a polishing step to prepare the surface for the DLC coating. Each step influenced the final surface finish of the slider pad before DLC coating was applied. The test plan incorporated the contribution of each step and provided results to establish an in-process specification for grinding and a final specification for surface finish after the polishing step. The test plan incorporated the surface finish as ground and after polish.
Valve train load—The last element was the loading of the slider pad by operation of the valve train. Calculations provided a means to transform the valve train loads into stress levels. The durability of both the camshaft lobe and the DLC coating was based on the levels of stress each could withstand before failure. The camshaft lobe material should be specified in the range of 800-1000 MPa (kinematic contact stress). This range was considered the nominal design stress. In order to accelerate testing, the levels of stress in the test plan were set at 900-1000 MPa and 1125-1250 MPa. These values represent the top half of the nominal design stress and 125% of the design stress respectively.
The test plan incorporated six factors to investigate the durability of the DLC coating on the slider pads: (1) the camshaft lobe material, (2) the form of the camshaft lobe, (3) the surface conditions of the camshaft lobe, (4) the angular alignment of the slider pad to the camshaft lobe, {S} the surface finish of the slider pad and (6) the stress applied to the coated slider pad by opening the valve. A summary of the elements and factors outlined in this section is shown in Table 1.
5.3.2 Component Wear Test Results
The goal of testing was to determine relative contribution each of the factors had on the durability of the slider pad DLC coating. The majority of the test configurations included a minimum of two factors from the test plan. The slider pads 752 were attached to a support rocker 753 on a test coupon 751 shown in
Test Results for Cast Iron Camshafts
The first tests utilized cast iron camshaft lobes and compared slider pad surface finish and two angular alignment configurations. The results are shown in Table 2 below. This table summarizes the combinations of slider pad included angle and surface conditions tested with the cast iron camshafts. Each combination was tested at the max: design and 125% max design load condition. The values listed represent the number of engine lives each combination achieved during testing.
The camshafts from the tests all developed spalling which resulted in the termination of the tests. The majority developed spalling before half an engine life. The spalling was more severe on the higher load parts but also present on the max design load parts. Analysis revealed both loads exceeded the capacity of the camshaft. Cast iron camshaft lobes are commonly utilized in applications with rolling elements containing similar load levels; however, in this sliding interface, the material was not a suitable choice.
The inspection intervals were frequent enough to study the effect the surface finish had on the durability of the coating. The coupons with the as-ground surface finish suffered DLC coating loss very early in the testing. The coupon shown in
Scanning electron microscope (SEM) analysis revealed the fractured nature of the DLC coating. The metal surface below the DLC coating did not offer sufficient support to the coating. The coating is significantly harder than the metal to which it is bonded; thus, if the base metal significantly deforms the DLC may fracture as a result. The coupons that were polished before coating performed well until the camshaft lobes started to spall. The best result for the cast iron camshafts was 0.75 lives with the combination of the flat, polished coupons at the max design load.
Test Results for Steel Camshafts
The next set of tests incorporated the steel lobe camshafts. A summary of the test combinations and results is listed in Table 3. The camshaft lobes were tested with four different configurations: (1) surface finish as ground with flat lobes, (2) surface finish as ground with crowned lobes, (3) polished with minimum crowned lobes and (4) polished with nominal crown on the lobes. The slider pads on the coupons were polished before DLC coating and tested at three angles: (1) flat (less than 0.05 degrees of included angle), (2) 0.2 degrees of included angle and (3) 0.4 degrees of included angle. The loads for all the camshafts were set at max design or 125% of the max design level.
The test samples which incorporated as-ground flat steel camshaft lobes and 0.4 degree included angle coupons at the 125% design load levels did not exceed one life. The samples tested at the maximum design stress lasted one life but exhibited the same effects on the coating. The 0.2 degree and flat samples performed better but did not exceed two lives.
This test was followed with ground, flat, steel camshaft lobes and coupons with 0.2 degree included angle and flat coupons. The time required before observing coating loss on the 0.2 degree samples was 1.6 lives. The flat coupons ran slightly longer achieving 1.8 lives. The pattern of DLC loss on the flat samples was non-uniform with the greatest losses on the outside of the contact patch. The loss of coating on the outside of the contact patches indicated the stress experienced by the slider pad was not uniform across its width. This phenomenon is known as “edge effect”. The solution for reducing the stress at the edges of two aligned elements is to add a crown profile to one of the elements. The application utilizing the SRFF has the crowned profile added to the camshaft.
The next set of tests incorporated the minimum value of crown combined with 0.4, 0.2 degree and flat polished slider pads. This set of tests demonstrated the positive consequence of adding crown to the camshaft. The improvement in the 125% max load was from 0.75 to 1.3 lives for the 0.4 degree samples. The flat parts exhibited a smaller improvement from 1.8 to 2.2 lives for the same load.
The last set of tests included all three angles of coupons with polished steel camshaft lobes machined with nominal crown values. The most notable difference in these results is the interaction between camshaft crown and the angular alignment of the slider pads to the camshaft lobe. The flat and 0.2 degree samples exceeded three lives at both load levels. The 0.4 degree samples did not exceed two lives.
These results demonstrated the following: (1) the nominal value of camshaft crown was effective in mitigating slider pad angular alignment up to 0.2 degrees to flat; (2) the mitigation was effective at max design loads and 125% max design loads of the intended application and, (3) polishing the camshaft lobes contributes to the durability of the DLC coating when combined with slider pad polish and camshaft lobe crown.
Each test result helped to develop a better understanding of the effect stress had on the durability of the DLC coating. The results are plotted in
The early tests utilizing cast iron camshaft lobes did not exceed half an engine life in a sliding interface at the design loads. The next improvement came in the form of identifying ‘edge effect’. The addition of crown to the polished camshaft lobes combined with a better understanding of allowable angular alignment, improved the coating durability to over three lives. The outcome is a demonstrated design margin between the observed test results and the maximum design stress for the application at each estimated engine life.
The effect surface finish has on DLC durability is most pronounced in the transition from coated samples as-ground to coated coupons as-polished. Slider pads tested as-ground and coated did not exceed one third engine life as shown in
The results from the cast iron and steel camshaft testing provided the following: (1) a specification for angular alignment of the slider pads to the camshaft, (2) clear evidence that the angular alignment specification was compatible with the camshaft lobe crown specification, (3) the DLC coating will remain intact within the design specifications for camshaft lobe crown and slider pad alignment beyond the maximum design load, (4) a polishing operation is required after the grinding of the slider pad, (5) an in-process specification for the grinding operation, (6) a specification for surface finish of the slider pads prior to coating and (7) a polish operation on the steel camshaft lobes contributes to the durability of the DLC coating on the slider pad.
5.4 Slider Pad Manufacturing Development
5.4.1 Slider Pad Manufacturing Development
Description
The outer arm utilizes a machined casting. The prototype parts, machined from billet stock, had established targets for angular variation of the slider pads and the surface finish before coating. The development of the production grinding and polishing processes took place concurrently to the testing, and is illustrated in
This section describes the evolution of the manufacturing process for the slider pad from the coupon to the outer arm of the SRFL SRFF.
The first step to develop the production grinding process was to evaluate different machines. A trial run was conducted on three different grinding machines. Each machine utilized the same vitrified cubic boron nitride (CBN) wheel and dresser. The CBN wheel was chosen as it offers (1) improved part to part consistency, (2) improved accuracy in applications requiring tight tolerances and (3) improved efficiency by producing more pieces between dress cycles compared to aluminum oxide. Each machine ground a population of coupons using the same feed rate and removing the same amount of material in each pass. A fixture was provided allowing the sequential grinding of coupons. The trial was conducted on coupons because the samples were readily polished and tested on the wear rig. This method provided an impartial means to evaluate the grinders by holding parameters like the fixture, grinding wheel and dresser as constants.
Measurements were taken after each set of samples were collected. Angular measurements of the slider pads were obtained using a Leitz PMM 654 coordinate measuring machine (CMM). Surface finish measurements were taken on a Mahr LD 120 profilometer.
The same two grinders (A and B) also failed to meet the target for surface finish. The target for surface finish was established based on the net change of surface finish in the polishing process for a given population of parts. Coupons that started out as outliers from the grinding process remained outliers after the polishing process; therefore, controlling surface finish at the grinding operation was important to be able to produce a slider pad after polish that meets the final surface finish prior to coating.
The measurements were reviewed for each machine. Grinders A and B both had variation in the form of each pad in the angular measurements. The results implied the grinding wheel moved vertically as it ground the slider pads. Vertical wheel movement in this kind of grinder is related to the overall stiffness of the machine. Machine stiffness also can affect surface finish of the part being ground. Grinding the slider pads of the outer arm to the specifications validated by the test fixture required the stiffness identified in Grinder C.
The lessons learned grinding coupons were applied to development of a fixture for grinding the outer arm for the SRFF. However the outer arm offered a significantly different set of challenges. The outer arm is designed to be stiff in the direction it is actuated by the camshaft lobes. The outer arm is not as stiff in the direction of the slider pad width.
The grinding fixture needed to (1) damp each slider pad without bias, (2) support each slider pad rigidly to resist the forces applied by grinding and (3) repeat this procedure reliably in high volume production.
The development of the outer arm fixture started with a manual clamping style block. Each revision of the fixture attempted to remove bias from the damping mechanism and reduce the variation of the ground surface.
The development completed by the test plan set boundaries for key SRFF outer arm slider pad specifications for surface finish parameters and form tolerance in terms of included angle. The influence of grind operation surface finish to resulting final surface finish after polishing was studied and used to establish specifications for the intermediate process standards. These parameters were used to establish equipment and part fixture development that assure the coating performance will be maintained in high volume production.
5.4.2 Slider Pad Manufacturing Development
Conclusions
The DLC coating on the SRFF slider pads that was configured in a DVVL system including DFHLA and OCV components was shown to be robust and durable well beyond the passenger car lifetime requirement. Although DLC coating has been used in multiple industries, it had limited production for the automotive valve train market. The work identified and quantified the effect of the surface finish prior to the DLC application, DLC stress level and the process to manufacture the slider pads. This technology was shown to be appropriate and ready for the serial production of a SRFF slider pad.
The surface finish was critical to maintaining DLC coating on the slider pads throughout lifetime tests. Testing results showed that early failures occurred when the surface finish was too rough. The paper highlighted a regime of surface finish levels that far exceeded lifetime testing requirements for the Ole This recipe maintained the DLC intact on top of the chrome nitride base layer such that the base metal of the SRFF was not exposed to contacting the camshaft lobe material.
The stress level on the DLC slider pad was also identified and proven. The testing highlighted the need for angle control for the edges of the slider pad. It was shown that a crown added to the camshaft lobe adds substantial robustness to edge loading effects due to manufacturing tolerances. Specifications set for the angle control exhibited testing results that exceeded lifetime durability requirements.
The camshaft lobe material was also found to be an important factor in the sliding interface. The package requirements for the SRFF based DVVL system necessitated a robust solution capable of sliding contact stresses up to 1000 MPa. The solution at these stress levels, a high quality steel material, was needed to avoid camshaft lobe spalling that would compromise the life of the sliding interface. The final system with the steel camshaft material, crowned and polished was found to exceed lifetime durability requirements.
The process to produce the slider pad and DLC in a high volume manufacturing process was discussed. Key manufacturing development focused on grinding equipment selection in combination with the grinder abrasive wheel and the fixture that holds the SRFF outer arm for the production slider pad grinding process. The manufacturing processes selected show robustness to meeting the specifications for assuring a durable sliding interface for the lifetime of the engine.
The DLC coating on the slider pads was shown to exceed lifetime requirements which are consistent with the system DVVL results. The DLC coating on the outer arm slider pads was shown to be robust across all operating conditions. As a result, the SRFF design is appropriate for four cylinder passenger car applications for the purpose of improving fuel economy via reduced engine pumping losses at part load engine operation. The DLC coated sliding interface for a DVVL was shown to be durable and enables VVA technologies to be utilized in a variety of engine valve train applications.
II. Single-Lobe Cylinder Deactivation (CDA) System Embodiment Description
1. CDA System Overview
Now, in reference to
As shown in
As illustrated in
The engine layout for one exhaust and one intake valve using the SRFF 1100 is shown in
2. CDA System Enabling Technologies
Several technologies used in this system have multiple uses in varied applications, they are described herein as components of the DVVL system disclosed herein. These include:
2.1. Oil Control Valve (OCV)
As described in earlier sections, and shown in
2.2. Dual Feed Hydraulic Lash Adjustor (DFHLA)
Many hydraulic lash adjusting devices exist for maintaining lash in engines. For DVVL switching of rocker arm 100 (
As illustrated in
Selected materials for the ball plunger end 601 may also have higher allowable kinetic stress loads, for example, chrome vanadium alloy.
Hydraulic flow pathways in the DFHLA 110 are designed for high flow and low pressure drop to ensure consistent hydraulic switching and reduced pumping losses. The DFHLA is installed in the engine in a cylindrical receiving socket sized to seal against exterior surface 511, illustrated in
As shown in
2.3. Sensing and Measurement
Information gathered using sensors may be used to verify switching modes, identify error conditions, or provide information analyzed and used for switching logic and timing. As can be seen, the sensing and measurement embodiments described in earlier sections pertaining to the DVVL system may also be applied to the CDA system. Therefore, the valve position and/or motion sensing and logic used in DVVL, may also be used in the CDA system. Similarly, the sensing and logic used in determining the position/motion of the rocker arms, or the relative position/motion of the rocker arms relative to each other used for the DVVL system may also be used in the CDA system.
2.4. Torsion Spring Design and Implementation
A robust torsion spring 1124 design that provides more torque than conventional existing rocker arm designs, while maintaining high reliability, enables the CDA system to maintain proper operation through all dynamic operating modes. The design and manufacture of the torsion springs 1124 are described in later sections.
3. Switching Control and Logic
3.1. Engine Implementation
CDA embodiments may include any number of cylinders, for example 4 and 6 cylinder in-line and 6 and 8 cylinder V-configurations.
3.2. Hydraulic Fluid Delivery System to the Rocker Arm Assembly
As shown in
Purging accumulated air in the upper gallery 802 is important to maintain hydraulic stiffness and minimize variation in the pressure rise time. Pressure rise time directly affects the latch movement time during switching operations. The passive air bleed port 832, shown in
3.2.1. Hydraulic Fluid Delivery for Normal-Lift Mode
3.2.2. Hydraulic Fluid Delivery for No-Lift Mode
3.3. Operating Parameters
An important factor in operating a CDA system 1400 (
3.3.1. Gathered Data
Real-time sensor information includes input from any number of sensors, as illustrated in the exemplary CDA system 1400 illustrated in
In a hydraulically actuated VVA system, the oil temperature affects the stiffness of the hydraulic system used for switching in systems such as CDA and VVL. If the oil is too cold, its viscosity slows switching time, causing a malfunction. This temperature relationship is illustrated for an exemplary CDA switching rocker arm 1100 system 1400 in
Sensor information is sent to the Engine Control Unit (ECU) 825 as a real-time operating parameter.
3.4. Stored Information
3.4.1. Switching Window Algorithms
The SRFF requires mode switching from the normal-lift to no-lift (deactivated), state and vice-versa. Switching is required to occur in less than one camshaft revolution to ensure proper engine operation. Mode switching can occur only when the SRFF is on the base circle 1322 (
The intended functional parameters of the SRFF based CDA system 1400 is analogous to the Type-V switching roller lifter designs that are in production today. The mode switch between normal-lift and no-lift is set to occur during the base circle 1322 event and be synchronized to the camshaft 1300 rotational position. The SRFF default position is set to normal-lift. The oil flow demand on the SRFF is also similar to the Type-V CDA production systems.
A critical shift is defined as an unintended event that may occur when latch is partially engaged, causing the valve to lift partially and suddenly drop back to the valve seat. This condition is unlikely, when the switching commands are executed during prescribed parameters of oil temperature, engine speeds with the camshaft position synchronized switching. The critical shift event creates an impact load to the DFHLA 110, which may require high strength DFHLA's, described in earlier sections, as enabling system components.
The fundamentals the synchronized switching for the CDA system 1400 are illustrated in
Latch Pre-Load
The CDA rocker arm assembly 1100 switching mechanism is designed such that hydraulic pressure can be applied to the latch 1202 after the latch lash is absorbed, resulting in no change in function. This design parameter allows hydraulic pressure to be initiated by the OCV 822 in the upper oil gallery 802 during the intake valve lift event. Once the intake valve lift profile 1452 returns to the base circle 1322 no-load condition, the latch completes its movement to the specified latched or unlatched mode. This design parameter helps to maximize the available switching window.
Hydraulic Response Time Versus Temperature
Variable Valve Timing
Now, with reference to
The plots of valve lift profile as a function of crankshaft angle are shown in
3.4.2. Stored Operating Parameters
These variables include engine configuration parameters such as variable valve timing and predicted latch response times as a function of operating temperature.
3.5. Control Logic
As noted above, CDA switching can only occur during a small predetermined window of time under certain operating conditions, and switching the CDA system outside of the timing window may result in a critical shift event, that could result in damage to the valve train and/or other engine parts. Because engine conditions such as oil pressure, temperature, emissions, and load may vary rapidly, a high-speed processor can be used to analyze real-time conditions, compare them to known operating parameters that characterize a working system, reconcile the results to determine when to switch, and send a switching signal. These operations can be performed hundreds or thousands of times per second. In embodiments, this computing function may be performed by a dedicated processor, or by an existing multi-purpose automotive control system referred to as the engine control unit (ECU). A typical ECU has an input section for analog and digital data, a processing section that includes a microprocessor, programmable memory, and random access memory, and an output section that might include relays, switches, and warning light actuation.
In one embodiment, the engine control unit (ECU) 825 shown in
After input is analyzed, a control signal is transmitted by the ECU 825 to the OCV 822 to initiate switching operation, which may be timed to avoid critical shift events while meeting engine performance goals such as improved fuel economy and lowered emissions. If necessary, the ECU 825 may also alert operators to error conditions.
4. CDA Rocker Arm Assembly
As shown in
The CDA rocker arm assembly 1100 has a bearing 1190 comprising a roller 1116 that is mounted between the first inner side arm 1110 and second inner side arm 1112 on a bearing axle 1118 that, during normal operation of the rocker arm, serves to transfer energy from a rotating cam (not shown) to the rocker arm 1100. Mounting the roller 1116 on the bearing axle 1118 allows the bearing 1190 to rotate about the axle 1118, which serves to reduce the friction generated by the contact of the rotating cam with the roller 1116. As discussed herein, the roller 1116 is rotatably secured to the inner arm 1108, which in turn may rotate relative to the outer arm 1102 about the pivot axle 1114 under certain conditions. In the illustrated embodiment, the bearing axle 1118 is mounted to the inner arm 1108 in the bearing axle apertures 1260 of the inner arm 1108 and extends through the bearing axle slots 1126 of the outer arm 1102. Other configurations are possible when utilizing a bearing axle 1118, such as having the bearing axle 1118 not extend through bearing axle slots 1126 but still mounted in bearing axle apertures 1260 of the inner arm 1108, for example.
When the rocker arm 1100 is in a no-lift state, the inner arm 1108 pivots downwardly relative to the outer arm 1102 when the lifting portion of the cam (1324 in
As shown in
Other configurations other than bearing 1190 also permit the transfer of motion from the cam to the rocker arm 1100. For example, a smooth non-rotating surface (not shown) for interfacing with the cam lift lobe (1320 in
With reference to
4.1. Torsion Spring
As described in following sections, a rocker arm 1100 in the no-lift state may be subjected to excessive pump-up of the lash adjuster 110, whether due to excessive oil pressure, the onset of non-steady-state conditions, or other causes. This may result in an increase in the effective length of the lash adjuster 110 as pressurized oil fills its interior. Such a scenario may occur for example during a cold start of the engine, and could take significant time to resolve on its own if left unchecked and could even result in permanent engine damage. Under such circumstances, the latch 1202 may not be able to activate the rocker arm 1100 until the lash adjuster 110 has returned to a normal operating length. In this scenario, the lash adjuster 110 applies upward pressure to the outer arm 1102, bringing the outer arm 1102 closer to the cam 1300.
The lost motion torsion spring 1124 on the SRFF was designed to provide sufficient force to keep the roller bearing 1116 in contact with the camshaft lift lobe 1320 during no-lift operation to ensure controlled acceleration and deceleration of the inner arm subassembly and controlled return of the inner arm 1108 to the latching position while preserving the latch lash. A pump-up scenario requires a stronger torsion spring 1124 to compensate for the additional force from pump-up.
Rectangular wire cross sections for the torsion springs 1124 were used to reduce the package space, keeping the assembly moment of inertia low and providing sufficient cross section height to sustain the operating loads. Stress calculations and FEA, and test validation, described in following sections, were used in developing the torsion spring 1124 components.
A torsion spring 1124 (
Now, with reference to
In this configuration, as the coils are wound, elongated side 402 of each coil rests against the elongated side 402 of the previous coil, thereby stabilizing the torsion springs 1124. The shape and arrangement holds all of the coils in an upright position, preventing them from passing over each other or angling when under pressure.
When the rocker arm assembly 1100 is operating, the generally rectangular or trapezoidal shape of the torsion springs 1124, as they bend about axis 400 shown in
4.2. Torsion Spring Pocket
As illustrated in
4.3. Outer Arm Assembly
4.3.1. Latch Mechanism Description
The mechanism for selectively deactivating the rocker arm 1100, which in the illustrated embodiment is found near the second end 1103 of the rocker arm 1100, is shown in
In the assembled rocker arm 1100, the latch 1202 alternates between normal-lift and no-lift states. The rocker arm 1100 may enter the no-lift state when oil pressure sufficient to counteract the biasing force of latch spring 1204 is applied, for example, through the port 1212 which is configured to permit oil pressure to be applied to the surface of the latch 1202. When the oil pressure is applied, the latch 1202 is pushed toward the second end 1103 of the rocker arm 1100, thereby withdrawing the latch 1202 from engagement with the inner arm 1108 and allowing the inner arm 1108 to rotate about the pivot axle 1114. In both the normal-lift and no-lift states, the linear portion 1250 of orientation clip 1214 engages the latch 1202 at the flat surface 1218. The orientation clip 1250 is mounted in the clip apertures 1216, and thereby maintains a horizontal orientation of the linear portion 1250 relative to the rocker arm 1100. This restricts the orientation of the flat surface 1218 to also be horizontal, thereby orienting the latch 1202 in the appropriate direction for consistent engagement with the inner arm 1108.
4.3.2. Latch Pin Design
As shown in
A re-engagement feature was added to the SRFF to prevent the condition where the inner arm 1108 is blocked and trapped in a position below the latch 1202. An inner arm sloped surface 1474 and a latch sloped surface 1472 were optimized to provide smooth latch 1202 movement to the retracted position when the inner arm 1108 contacts the latch sloped surface 1472. The design avoids damage to latch mechanism that may be caused by pressure changes at the switching pressure port 506 (
As described in previous sections pertaining to DVVL rocker arm assembly and operation, several latch embodiments may be employed to allow reliable operation of the latching mechanism during operating conditions, including latches with round or other non-flat shapes.
4.4. System Packaging
The SRFF-1F design is focused on minimizing valvetrain packaging changes compared to a standard production layout. Important design parameters include relative placement of the camshaft lobes in relation to the SRFF roller bearing, and axial alignment between the steel camshaft and aluminum cylinder head. The steel and aluminum components have different thermal growth coefficients that can shift the camshaft lobes relative to the SRFF-1F.
4.5. CDA Latch Mechanism Hydraulic Operation
As previously mentioned, pump-up is a term used to describe a condition in which the HLA is extended past its intended working dimension; thereby preventing the valve from returning to its seat during the base circle event.
The SRFF 1100 was designed with additional consideration for pump-up when the system is in no-lift mode. Pump-up of the DFHLA 110 when the SRFF 1100 is in no-lift mode can create a condition in which the inner arm 1108 does not return to the position where the latch 1202 can re-engage the inner arm 1108.
The SRFF 1100 reacts similarly to a standard RFF 1496 (
The torsion springs 1124 in the SRFF rocker arm assembly 1100 were designed to provide sufficient force to keep the roller bearing 1116 in contact with the camshaft lift lobe 1320 during no-lift mode to ensure controlled acceleration and deceleration of the inner arm 1108 subassembly and return the inner arm 1108 to the latching position while preserving the latch lash 1205. The torsion spring 1124 design for SRFF 1100 design also accounts for a variation in oil pressure at the lash compensation port 512 when the system is in no-lift mode. Oil pressure regulation can reduce the load requirements for the torsion springs 1124 with direct effect on the spring sizing.
4.6. CDA Assembly Lash Management
Camshaft lash was eliminated by design for the single-lobe SRFF. The elimination of the camshaft lash 1504 allows further optimization of the camshaft lift profile, by creating a lifting ramp reduction 1510, thus allowing for longer lift events. The camshaft opening ramps 1506 for the SRFF are reduced up to 36% from the camshaft opening ramps 1506 required for similar designs using multiple lobes.
In addition, mechanical lash variation on the SRFF is improved 39% over an analogous three-lobe design due to the elimination of the camshaft lash and the features associated with it, for example, manufacturing tolerances for the camshaft no-lift lobes base circle radius, lobe run-out, required slider pad to slider pad and slider pad to roller bearing parallelism.
4.7. CDA Assembly Dynamics
4.7.1. Detailed Description
The SRFF rocker arm 1100 and system 1400 (
4.7.2. Analysis
Several design and Finite Element Analysis (FEA) iterations were performed to maximize the stiffness and reduce MOI over the DFHLA end of the SRFF. The mass intensive components were placed over the DFHLA end of the SRFF to minimize the MOI. The torsion springs 1124, one of the heaviest components in the SRFF assembly were positioned in close proximity to the SRFF rotational axis. The latching mechanism was also located near the DFHLA. The vertical section height of the SRFF was increased to maximize stiffness while minimizing MOI.
The SRFF designs were optimized using load information from kinematic modeling. Key input parameters for the analysis include valvetrain layout, SRFF elements of mass, moment of inertia, stiffness (predicted by the FEA), mechanical lash, valve spring loads and rates, DFHLA geometry and plunger spring, and valve lift profiles. Next, the system was altered to meet the predicted dynamic targets, by optimizing the stiffness versus the effective mass over the valve of the CDA SRFF. The effective mass over the valve represents the ratio between the MOI in respect to the pivot point of the SRFF and the square distance between the valve and the SRFF pivot. The tested dynamic performance is described in later sections.
5. Design Verification and Testing
5.1. Valve Train Dynamic Results
Dynamic behavior of a valvetrain is important in controlling the Noise Vibration and Harshness (NVH) while meeting the durability and performance targets of an engine. Valvetrain dynamics are partially influenced by the stiffness and MOI of the SRFF component. The MOI of the SRFF can be readily calculated and the stiffness is estimated through Computer Aided Engineering (CAE) techniques. Dynamic valve motion is also influenced by a variety of factors, so tests were conducted gain assurance in high speed valve control.
A motorized engine test rig was utilized for valvetrain dynamics. A cylinder head was instrumented prior to the test. Oil was heated to represent actual engine conditions. A speed sweep was performed from idle speed to 7500 rpm, recording data as defined by engine speed. Dynamic performance was determined by evaluating valve closing velocity and valve bounce. The SRFF was strain gaged for the purpose of monitoring load. Valve spring loads were held constant to the fixed system for consistency.
5.2. Torsion Spring Validation
Torsion springs are key components for the SRFF design, especially during high speed operation. Concept validation was conducted on the springs to validate the robustness. Three elements of the spring design were tested for proof of concept. First, load loss was documented under the conditions of high cycling at operating temperature. Spring load loss, or relaxation, represents the reduction of the spring load at end of test from beginning of test. The load loss was also documented by applying highest stress levels and subjecting parts to high temperatures. Second, the durability and the springs were tested at worst case load and cycled to validate fatigue life, as well as the load loss as mentioned. Finally, the function of the lost motion springs were validated by using lowest load springs and verifying that the DFHLA does not pump up during all operating conditions in CDA mode.
The torsion springs were cycled at engine operating temperatures in the engine oil environment on a targeted fixture test. Torsion springs were cycled with the full stroke of the application with the highest preload conditions to represent worst case stress. The cycling target value was set at 25 million and 50 million cycles. Torsion springs were also subjected to a heat-set test in which they were loaded to highest application stress and held at 140° C. for 50 hours and measured for load loss.
The results indicated a maximum load loss of 8% and met the design target. Many of the tests showed minimal load loss near 1%. All tests were safely within the design guidelines for load loss.
5.3. Pump-Up Robustness During Cylinder Deactivation
Torsion springs 1124 (
Validation experiments were performed to prove torsion spring 1124 ability to preserve latch lash 1205 at required conditions. The tests were conducted on motorized engines, with instrumentation for measuring the valve and the CDA SRFF motion, oil pressure and temperature at the lash compensation pressure port 512 (
Low limit lost motion springs were used to simulate worst condition. This test was conducted at 3500 rpm which represents the maximum switching speed. Two operating temperatures were considered of 58° C. and 130° C. Test results show pump-up at pressures 25% higher than the application requirement.
5.4. Validation of Mechanical Lash During Switching Durability
Mechanical lash control is important to valvetrain dynamic stability and must be maintained through the life of the engine. A test with loading of the latch and switching between normal-lift mode and no-lift mode was considered appropriate to validate the wear and the performance of the latch mechanism. Switching durability was tested by switching the latch from the engaged to disengaged position, cycling the SRFF in no-lift mode, engaging the latch with the inner arm and cycling the SRFF in normal-lift mode. One cycle is defined to disengage and then re-engage the latch and exercise the SRFF in the two modes. The durability target for switching is 3,000,000 cycles. 3,000,000 cycles represents the equivalent of one engine life. One engine life is defined as an equivalent of 200,000 miles which is safely above the 150,000 mile standard. Parts were tested at highest switching speed target of 3500 engine rpm to simulate worst case dynamic load during switching.
The valvetrain dynamics, Torsion spring load loss, pump-up validation and mechanical lash over an equivalent engine life all met intended targets for the SRFF. The valvetrain dynamics, in terms of closing velocity, is safely within the limit at maximum engine speed of 7200 rpm and at the limit for a higher speed of 7500 rpm. The LMS load loss showed a maximum loss of 8% which is safely within the design target of 10%. A pump-up test was performed showing that the SRFF design operates properly given a target oil pressure of 5 bar. Finally, the mechanical lash variation over an equivalent engine lift is safely within the design target. The SRFF meets all design requirements for cylinder deactivation on a gasoline passenger car application.
6. Conclusions
Cylinder deactivation is a proven method to improve fuel economy for passenger car gasoline vehicles. The design, development, and validation of a single-lobe SRFF based cylinder deactivation system was completed, providing the ability to improve fuel economy by reducing the pumping losses and operating a portion of the engine cylinders at higher combustion efficiencies. The system preserves the base architecture of a standard Type II valvetrain by maintaining the same centerlines for the engine valves, camshaft and lash adjusters. The engine cylinder head requires the addition of the OCV and oil control ports in the cylinder head to allow for hydraulic switching of the SRFF from normal lift mode to deactivation mode. The system requires one OCV per engine cylinder, and is typically configured with four identical SRFF's for the intake and exhaust, along with one DFHLA per SRFF.
The SRFF design provides a solution that reduces system complexity and cost. The most important enabling technology for the SRFF design is the modification to the lost motion torsion spring. The LMS was designed to maintain continuous contact between a single lobe camshaft and the SRFF during both normal-lift and no-lift modes. Although this torsion spring requires slightly more packaging space, the overall system becomes less complex with the elimination of a three lobe camshaft. The axial stack up of the SRFF is reduced from a three-lobe CDA design since there are no outer camshaft lobes that increase the chance of edge loading on the outer arm sliding pads and interference with the inner arm. Rocker arm stiffness levels for the SRFF are comparable with standard production rocker arms.
The moment of inertia was minimized by placing the heavier components over the end pivot that sits directly on the DFHLA, namely the latching mechanism and the torsion springs. This feature enables better valvetrain dynamics by minimizing the effective mass over the valve. The system was designed and validated to engine speeds of 7200 rpm during standard lift mode and 3500 rpm for cylinder deactivation mode. The components also were validated to at least one engine life that is equivalent to 200,000 engine miles.
While the present disclosure illustrates various aspects of the present teachings, and while these aspects have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the claimed teachings of the present application to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the teachings of the present application, in its broader aspects, are not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's claimed teachings of the present application. Moreover, the foregoing aspects are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.
III. VVA Engine and Cylinder Head Arrangements
1. Switching Rocker Arm Assemblies
1.1. Description—General Engine Structure
A plurality of cam towers 10 extend upward having a cam tower bottom 33 section that extends upward from the cylinder head. The upper side of the cam tower bottom 33 has a semi-circular recess.
A cam tower cap 11 is bolted to the cam tower bottom 13. The cam tower cap 11 has a similar semi-circular recess facing downward such that when the cam tower cap 11 is bolted to the cam tower bottom 13, the recesses create a circular cam recess 321 that receives the camshafts. Cam recesses 321 are sized and constructed to secure but allow the intake and exhaust camshafts to freely rotate.
Spark plug tubes 20 in this aspect of the present teachings are located between the cam towers 10 and parallel to a centerline 19 passing through the center of the cylinder head. The spark plug tubes 20 extend downward through the cylinder head into the top of each engine cylinder and is designed to receive a spark plug.
1.2. VVA Switching Rocker Arm Arrangements
1.2.1. Symmetrical Arrangements
This engine head assembly shown in
The VVL rocker arm assembly 100 will be used for the remainder of the description provided here; however, it is understood that these aspects of the present teachings may be applied to various other rocker arm assemblies installed on heads having small clearances on one side of the rocker assemblies.
This VVL rocker arm assembly 100 is driven by a camshaft having three lobes per cylinder. It is shown here in
As seen in
As middle cam lobe 324 turns and presses downward onto the VVL rocker arm assembly 100, it causes outboard end 103 of VVL rocker arm assembly 100 to push valve stem 350 downward opening the poppet valve connected to valve stem 350. When an internal latch is operated by providing high-pressure oil to it, the VVL rocker arm assembly 100 causes the valves to lift according to the shape of the outer cam lobes 326. This is further described below in connection with
1.2.2 Non-Symmetrical Arrangements
In
As indicated above, it is very costly to redesign/modify cylinder heads, cam drives and gear trains. Also, many different manufacturers may make equipment based upon the standard design of the cylinder head, making it very difficult to change or modify the cylinder head.
Therefore, the present teachings can be embodied in VVA rocker arm assemblies that are specially designed to fit cylinder heads having little clearance.
In many cylinder head designs, it was determined that there was only a lack of space in one side of the rocker. Typically, the lack of space can occur in the inboard end 101 on the side of the rocker near the spark plug tubes 20. Therefore, it would be viable to package the VVL rocker arm assembly 100 in a redesigned form so that the width on the obstructed side would not be wider than that of a standard rocker arm.
The result was to create modified rocker assemblies for use on cylinder heads that have obstructions on the right-hand side of the rocker assemblies, or left-hand rocker assemblies. In the left-hand rocker assembly most of the functional elements are moved from the right-hand side to the left-hand side. Also, the right-hand side is formed to have reduced width.
Similarly, right-hand rocker assemblies are designed for use when there is an obstruction on the left-hand side. Similarly, structures are moved from the left-hand side to the right-hand side and the left-hand side is formed to create increased clearance on the left side to compensate for the obstruction. Collectively, they will be referred to as modified rocker assemblies.
A novel modified rocker assembly 400 according to one aspect of the present teachings is described in connection with
The modified rocker assembly 400 shown here for illustrative purposes is a variable valve lift (VVL) rocker assembly; however, a cylinder deactivation (CDA) rocker assembly or other rocker assembly employing torsion springs on its first end 408, or otherwise having a widened first (or hinged) end 408 fall within the scope of the present teachings.
This rocker assembly functions in a very similar manner as that shown in
Inner structure 410 can have an axle recess 413 passing through its first end 408. The outer structure 420 also can have an axle recess 433 through its first end 408. When the roller axle recesses 413, 433 are aligned with the inner structure 410 inside of the outer structure 420, the axle 434 can be secured through the axle recesses 413, 433 allowing inner structure 410 to pivot relative to outer structure 420 about axle 434.
The outer structure 420 on the obstructed side 405, as it extends from the second end 409 toward the first end 408, can be offset toward the non-obstructed side 407 creating a first offset portion 428. This offset can be a curved or angled sidearm that can create a smaller width at the first end 408. This first offset portion 428 can provide additional clearance on the obstructed side 405 as compared with standard VVL or CDA rocker arm assemblies. This can now allow the modified rocker assembly 400 to fit into and function with cylinder heads that have narrow obstruction region such as obstruction region 600 of
The outer structure 420 on the non-obstructed side 407, as it extends from the second end 409 toward the first end 408, can be offset outward away from the modified rocker assembly 400 creating a second offset portion 429. This second offset portion 429 can provide additional clearance on the non-obstructed side 407 as compared with standard VVL or CDA rocker arm assemblies, to allow the incorporation of a second torsion spring 437. This now can allow the modified rocker assembly 400 to exert the proper amount of force to bias the inner structure 410 with respect to the outer structure 420. In an alternative aspect of the present teachings, a single larger torsion spring can be used in place of the two or more torsion springs shown here.
The modified rocker assembly 400 employs a latch assembly 500 with a latch pin 501 that can hold the inner structure 410 and outer structure 420 together so they move as a single rocker. The latch assembly 500 can be activated by an oil control valve (not shown) that can provide increased oil pressure through a cup 448 pivoting upon the hydraulic latch adjuster 340. This is further described in connection with
Since there are now two (or more) torsion springs 435, 437 on the non-obstructed side 407 (or here is a single larger torsion spring) with no torsion springs on the obstructed side 405, there will be a twisting force placed upon the inner structure 410 and outer structure 420 of the rocker assemblies. Therefore the amount of play about the axle 434 can be adjusted to make sure that the modified rocker arm 400 functions correctly.
When using two torsion springs 435, 437, torsion spring 435 is considered a right-hand side spring and is wound in the opposite direction of torsion spring 437. These different springs null out some of the torsional forces.
If only a single torsion spring is to be used, the additional torsional forces should be considered when designing the inner and outer structures 410, 420.
For the double torsion spring and single torsion spring designs, the relative strength of the inner and outer structures 410, 420 can be adjusted to reduce flexing, to ensure proper performance. Also the weight distribution of each of the structures along their length can be configured to provide the proper strength and structure while minimizing the inertial force required to pivot the modified rocker assembly 400 at the speed required to operate an engine. The inner and outer structures 410, 420 include many ornamental aspects apart from the functional aspects disclosed herein.
Latch pin seat 485, discussed in connection with
Alternatively, at low oil pressure, the latch pin can normally be in an extended position. When the oil pressure increases above a threshold amount, the latch pin can be retracted. This is a ‘normally latched’ design.
In
In
As with
The camshaft would be secured by and pass through the cam tower 10. Here it can be easily seen that spark plug tube 20 would interfere with a standard CDA or VVL rocker assembly at the obstruction region 600. The first offset portion 428 of the modified rocker assembly 400 is adjacent to the spark plug tube 20 at obstruction region 600. Due to its reduced width, it is now able to fit on this head and function without colliding into the spark plug tube 20.
This shows the same structures as
First offset portion 428 is shown near the obstruction region 600 adjacent to the spark plug tube 20 providing the required clearance.
Second offset portion 429 is also shown providing the additional space for both torsion springs 435, 437.
2. Cylinder Head Arrangements and Assemblies
2.1. Cylinder Head Arrangements, General
As described in previous sections, many engines have designs that incorporate components from multiple manufacturers. Thus, it is desirable to design VVA technologies to work within a predefined cylinder head space, for example, the previously described CDA and VVL switching rocker arms that are modified with an offset design to avoid cylinder head obstructions. In some cases, it is not possible or desirable to change a proven switching rocker arm design so that it can be used in an engine assembly. In such cases, it may be desirable to make limited modifications to specific cylinder head assemblies.
2.2. Cylinder Head Arrangements Modified for Switching Rocker Arms
A cylinder head arrangement is described that positions camshaft supports in locations that provide additional space for wider rocker assemblies, such as switching rocker assemblies without requiring the use of a camshaft carrier. The use of a camshaft carrier typically adds significant cost to the assembly.
It is understood that the teachings of the current application apply to various engines, such as an in-line four cylinder engine having four adjacent in-line cylinders, a three-cylinder head of a 6-cylinder engine, or other engine designs. The current disclosure will also apply to an overhead cam V8 engine having two sets of four in-line cylinders. The current disclosure will also apply to various switching rocker arm assemblies.
Each cylinder of the in-line four cylinder engine is numbered from cylinder 1 on the left through cylinder 4 on the right. Cylinders 1 and 4 are the outboard, or end cylinders, while cylinders 2 and 3 are considered the middle cylinders.
For reference, the top of the
A line through cylinder 1 from front to back of the engine is marked with reference number 21. A cam tower 10 is located on, or near line 21, near the rear of the engine, for securing the intake camshaft 36 that is also shown in phantom below intake rocker arms 51. The cam towers 10 employ cam bearings and a cam tower cap 11 that stabilize the camshafts and allow them to rotate during operation.
Similarly, another cam tower 10 is located on, or near line 21, near the front of the engine, for securing the exhaust cam 40 under the exhaust rocker arms 61.
A line through cylinder 2 from front to back of the engine is marked line 23. A cam tower 10 is located on, or near line 23, near the rear of the engine, for securing the intake cam 30. Similarly, another cam tower 10 is located on, or near line 23, near the front of the engine securing the exhaust cam 40.
There are also other cam towers 10 located near the rear and front of the engine on lines 25 and 27 passing through cylinders 3 and 4, respectively, for securing the intake cam 30, and exhaust cam 40, respectively. There are also end supports 33 and 34 on the left and right sides of the exhaust camshaft, and end support 35 on the left side of the intake camshaft. In this embodiment, the right side of the intake camshaft has no end support.
In this design, the available space between cam towers 10 is generally about 77 mm A VVA switching rocker arm assembly typically has a width of approximately 29 mm Two side-by-side VVA switching rocker arm assemblies, as mounted, will not fit in this space with a cam tower. Therefore, this typical in-line four cylinder engine could not accommodate these VVA switching rocker arm assemblies.
Similarly, a V8 engine having overhead cams should have two heads similar to those shown in
One solution is to move the cam towers 10 between cylinders outward away from the VVA rocker arm assemblies. This solution makes it difficult to reach head bolts since the head bolts are also between cylinders. It is beneficial to allow free access to as many of the head bolts as possible, since the head is typically removed as a single piece with the cams and rocker arms in place.
Another solution is to add a camshaft carrier that encompasses all the camshaft support bearings, and is assembled after the head is bolted to the engine block. But this solution has been shown to be costly and adds extra sealing joints that can be leakage paths over the life of the engine.
According to the teachings of the present application, wider rocker arms are allowed to be used on several cylinders in small engines without using a full camshaft carrier arrangement. In the first embodiment, this is accomplished without any additional camshaft support pieces.
In a second embodiment, the wider rocker arm is accommodated using a simple camshaft support piece that can also serve as an oil control valve (OCV) mounting surface with requisite oil control gallery drillings. The OCV is an ON/OFF hydraulic valve used in conjunction with the VVA rocker arms that enables the VVA function.
It has been determined that the camshaft span between supports may be extended past 77 mm without causing excessive flexing, vibration, or wear.
By revising the placement of the camshaft support towers, a larger unsupported span between tower spacing is produced. The spacing increase is kept to a reasonable amount, typically up to 129 mm without the significant adverse effects indicated above.
The larger spans create additional space for the rocker arm assemblies and can now accommodate the wider VVA rocker arm assemblies.
It is also understood that the embodiments shown and described here are exemplary and not limiting. The present design can employ various other parts near the camshaft that require additional spacing.
The VVA rocker arm assemblies may be VVL SRFF or CDA SRFF rocker assemblies 130, which may be collectively referred to as a variable valve actuation switching roller finger follower (“VVA SRFF”).
Torsion springs 134 and 136 rotationally bias the inner rocker arm 122 relative to the outer rocker arm 124.
Slider pads 131 and 132 each ride on a cam surface. Roller 129 rides on a different cam from that of the slider pads 131, 132. The VVL SRFF is designed to switch a latch pin 200 of a latch 201 to change between a low valve lift and a high valve lift, altering the performance of the engine.
The slider pads 131, 132, pivot axle 118 and springs 134, 136 add additional width to the VVA SRFF 300 and therefore require additional clearance on the head.
A CDA SRFF is described in the “CDA SRFF Application” listed above. It is also wider than conventional rocker arm assemblies and will benefit from the current disclosure.
This embodiment is directed to installing VVA SRFF 300 on outboard, or end cylinders 1 and 4.
The portion of the exhaust camshaft 40 extending over the left end cylinder (cylinder 1) is secured at its left end by end support 13. The portion of the exhaust camshaft 40 extending over the left end cylinder (cylinder 1) is supported on its right side by the cam tower 10 of the left middle cylinder (cylinder 2).
Similarly, the portion of the exhaust camshaft 40 extending over the right end cylinder (cylinder 4) is secured at its left end by the cam tower 10 of the right middle cylinder (cylinder 3). The portion of the exhaust camshaft 40 extending over the right end cylinder (cylinder 4) is supported on its right side by end support 15. The unsupported span of the exhaust camshaft over the right end cylinder (cylinder 4) is approximately 126 mm This is an acceptable unsupported span that would not affect the operation of the engine.
Since there is no end support near cylinder 4 for the intake camshaft 30, an outboard bearing 303 is attached at rear of cylinder head adjacent to the right end cylinder (cylinder 4). In some cases, the intake camshaft 36 should be extended or another piece should be attached to extend the intake camshaft 36 to be supported by the attached outboard bearing.
It is also possible to have the bearing installed inside of the engine casing, if space permits.
This design increases the spacing between cam towers 10 and bearing supports by approximately 64% from 77 mm of unsupported length to approximately 126 mm of unsupported length, assuming an engine with spacing between the center of adjacent cylinders, or cylinder bore spacing, of 90 mm and cam towers of 13 mm width (typical for engine of 1.5-2.0 L displacement). Each VVA SRFF 300 can now be installed as shown in
Here, the VVA SRFFs 130 are shown as they would appear installed and operating in an engine. An end 101 of the VVA SRFFs 130 pivots about a hydraulic lash adjuster 100. Another end 103 actuates the valve stem of either the engine intake valve 70 or the engine exhaust valve 80 against the resistance of valve springs 90.
Cam towers (10 of
A camshaft support piece 307 is mounted between middle cylinders 2 and 3. This camshaft support piece 307 is designed to be removable to allow access to cylinder head bolts during engine assembly. The camshaft support piece 307 may optionally include a mounting structure to secure an oil control valve (OCV) and oil galleries to connect the OCV to the rocker assembly. The OCV and oil galleries function to provide oil pressure to cause switching of the rocker assembly from one mode to a second mode.
This camshaft support piece 307 includes camshaft bearings. The camshaft support piece 307 may be pre-machined, then installed in the cylinder head prior to camshaft bore finishing, then the cylinder head is ready for assembly. At assembly, the camshaft support piece 307 is removed, the cylinder head is fastened to the cylinder block, and the camshaft support piece 307 is reinstalled. Then the VVA SRFF 300 and camshafts 30, 40 are installed.
In the current disclosure, the spacing between cam supports are increased by approximately 58% from 77 mm of unsupported length to approximately 122 mm of unsupported length, assuming an engine having a distance between centers of adjacent cylinders of approximately 90 mm and cam towers of 13 mm width (typical for engine of 1.5-2.0 L displacement). This results in the unsupported length of the camshafts to be 140% of the spacing between the centers of adjacent cylinders commonly referred to as “bore spacing” or “cylinder bore spacing”. Therefore, employing a typical engine with a typical cam shaft having a predetermined stiffness, any unsupported span of up to 140% of the bore spacing would be an appropriate length to use. The effect of flexing of the camshafts begins to increase as the spans get greater than 140% of the bore spacing. Longer unsupported spans may be used, but provide increased cam flexing. Therefore, it is conceivable to offset this span by +/−10 mm with increased cam flexing for the longer spans. This arrangements described above function best in cases where less than all of the cylinder rocker arms are replaced.
HLA recesses 37 are positioned in line with the intake 38 and exhaust valve guide recesses 39. These receive and secure the hydraulic lash adjusters (HLAs).
In
While the present disclosure illustrates various aspects of the present teachings, and while these aspects have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the claimed teachings of the present application to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the teachings of the present application, in its broader aspects, are not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's claimed teachings of the present application. Moreover, the foregoing aspects are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.
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| 20210156284 A9 | May 2021 | US |
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