Patent Application
20170009610
Example aspects described herein relate to switchable rocker arms that facilitate multiple discrete engine valve lift events for an internal combustion (IC) engine.
More stringent fuel economy regulations in the transportation industry have prompted the need for improved efficiency of the IC engine. Light-weighting, friction reduction, thermal management, variable valve timing and a diverse array of variable valve lift (VVL) technologies are all part of the technology toolbox for IC engine designers.
VVL systems typically employ a technology in a valve train of an IC engine that allows different engine valve lifts to occur. The valve train consists of the components that are required to actuate an engine valve, including a camshaft, the valve, and all components that lie in between. VVL systems are typically divided into two categories: continuous variable and discrete variable. Continuous variable valve lift systems are capable of varying a valve lift from a design lift minimum to a design lift maximum to achieve any of several lift heights. Discrete variable valve lift systems are capable of switching between two or three distinct valve lifts. Components that enable these different valve lift modes are often called switchable valve train components. Typical two-step discrete valve lift systems switch between a full valve lift mode and a partial valve lift mode, often termed cam profile switching, or between a full valve lift mode and a no valve lift mode that facilitates deactivation of the valve. Valve deactivation can be applied in different ways. In the case of a four-valve-per-cylinder configuration (two intake+two exhaust), one of two intake valves can be deactivated. Deactivating only one of the two intake valves can provide for an increased swirl condition that enhances combustion of the air-fuel mixture. In another scenario, all of the intake and exhaust valves are deactivated for a selected cylinder which facilitates cylinder deactivation. On most engines, cylinder deactivation is applied to a fixed set of cylinders, when lightly loaded at steady-state speeds, to achieve the fuel economy of a smaller displacement engine. A lightly loaded engine running with a reduced amount of active cylinders requires a higher intake manifold pressure, and, thus, greater throttle plate opening, than an engine running with all of its cylinders in the active state. Given the lower intake restriction, throttling losses are reduced in the cylinder deactivation mode and the engine runs with greater efficiency. For those engines that deactivate half of the cylinders, it is typical in the engine industry to deactivate every other cylinder in the firing order to ensure smoothness of engine operation while in this mode. Deactivation also includes shutting off the fuel to the dormant cylinders. Reactivation of dormant cylinders occurs when the driver demands more power for acceleration. The smooth transition between normal and partial engine operation is achieved by controlling ignition timing, cam timing and throttle position, as managed by the engine control unit (ECU). Examples of switchable valve train components that serve as cylinder deactivation facilitators include roller lifters, pivot elements, rocker arms, roller finger followers, and camshafts; each of these components is able to switch from a full valve lift mode to a no valve lift mode. The switching of lifts occurs on the base circle or non-lift portion of the camshaft; therefore the time to switch from one mode to another is limited by the time that the camshaft is rotating through its base circle portion; more time for switching is available at lower engine speeds and less time is available at higher engine speeds. Maximum switching engine speeds are defined by whether there is enough time available on the base circle portion to fully actuate a locking mechanism to achieve the desired lift mode.
In today's IC engines, many of the switchable valve train components that enable valve deactivation for cylinder deactivation contain a coupling assembly that is actuated by an electro-hydraulic system. The electro-hydraulic system typically contains at least one solenoid valve within an array of oil galleries that manages engine oil pressure to either lock or unlock the coupling assembly within the switchable valve train component to enable a valve lift switching event. These types of electro-hydraulic systems require time within the combustion cycle to actuate the switchable valve train component.
In most IC engine applications, switchable valve train components for cylinder deactivation in an electro-hydraulic system are classified as “pressureless-locked”, which equates to:
a). In a no or low oil pressure condition, the spring-biased coupling assembly will be in a locked position, facilitating the function of a standard valve train component that translates rotary camshaft motion to linear valve motion; and,
b). In a condition in which engine oil pressure is delivered to the coupling assembly that exceeds the force of the coupling assembly bias spring, the coupling assembly will be displaced a given stroke to an unlocked position, facilitating valve deactivation where the rotary camshaft motion is not translated to the valve.
“Pressureless-unlocked” electro-hydraulic systems can be found in some cam profile switching systems that switch between a full valve lift and a partial valve lift, which equates to:
a). In a no or low oil pressure condition, the spring-biased coupling assembly will be in an unlocked position, facilitating a partial valve lift event; and,
b). In a condition in which engine oil pressure is delivered to the coupling assembly that exceeds the force of the coupling assembly bias spring, the coupling assembly will be displaced a given stroke to a locked position, facilitating a full valve lift event.
Switchable valve train systems often contain a lost motion spring or springs that provide a force during the unlocked mode to a component of the switchable valve train component assembly that is actuated by the camshaft, but does not translate rotary camshaft motion to linear valve lift. In many shaft-mounted switchable rocker arm systems, the lost motion spring is housed within a cylinder head or valve cover which can create packaging challenges. The lost motion spring provides a force that maintains contact between the actuated component and camshaft up to a maximum unlocked mode engine speed.
While the cam lever assembly 110 is actuated by a full lift cam lobe 180 of a camshaft 160 during an unlocked mode, the valve lever assembly 120 remains stationary. For proper locking and unlocking of the cam lever assembly 110 to the valve lever assembly 120, rotational alignment of the two lever assemblies 110,120 and respective coupling assembly interfaces must be ensured during the base circle portion of the rotating camshaft. While rotational position and control of the cam lever assembly 110 is managed by the camshaft and lost motion spring 150 during the unlocked mode, proper rotational position of the valve lever assembly 120 is provided by an engine valve (not shown) at one end and a camshaft abutment 140 that interfaces with a zero-lift or base circle lobe 170 of the camshaft 160 on the opposite end. The camshaft abutment 140 can be especially helpful in switchable rocker arm designs, such as the one shown in
The packaging space required for the prior art switchable rocker arm 100 shown in
Given the described packaging and corresponding cost challenges of implementing the prior art shaft-mounted switchable rocker arm within an IC engine, example embodiments will now be described that offer solutions for lost motion spring and arcuate lost motion packaging along with elimination of the camshaft abutment.
A switchable rocker arm for valve deactivation is provided for a valve train of an internal combustion engine. The switchable rocker arm includes a cam lever assembly, a valve lever assembly, and a hydraulically actuated coupling assembly that is radially arranged between the cam lever and valve lever assemblies. The coupling assembly includes a shuttle pin, a locking pin, and a resilient element that acts on the locking pin. In a first, locked position, the rotational motion of a camshaft is translated to linear motion of an engine valve. In a second, unlocked position, the cam lever assembly rotates about the valve lever assembly, facilitating valve deactivation. Lost motion of the cam lever assembly is guided by a first curved surface on the valve lever assembly that rotationally guides a second curved surface on the cam lever assembly. An overswing or first rotational stop is arranged at a first end of the first curved surface on the valve lever assembly. A transport or second rotational stop can be arranged at a first end of a third curved surface configured on the valve lever assembly, such that the cam lever assembly can rotate a pre-determined angle in the second unlocked position.
The cam lever assembly is configured with first and second arms that extend along opposed sides of the cam lever assembly. The first arm has a second rocker shaft bore and the second arm has a third rocker shaft bore. A first rocker shaft bore on a first end of the valve lever assembly is axially aligned with the second and third rocker shaft bores on the cam lever assembly.
Various forms of valve interfaces can be arranged on a second end of the valve lever assembly, including a hydraulic lash adjuster assembly or an adjustment screw assembly. In addition, various forms of camshaft interfaces can be arranged on a cam interface end of the cam lever assembly, including a roller follower or a slider pad.
Several variations of the coupling assembly are possible to accommodate different material selections and manufacturing processes. The locking pin can be disposed within a second radial aperture within the cam lever assembly that serves as a locking pin bore. Alternatively, a locking pin sleeve of suitable material and hardness to accommodate durability requirements can be arranged within the second radial aperture of the cam lever assembly to serve as the locking pin bore. The locking pin can have a round cross-section throughout its length or configured with an optional first radial flat on an outer radial surface of the first end. The presence of the first radial flat requires anti-rotation accommodations for the locking pin. Various forms of anti-rotation elements that guide the first radial flat are possible, including an element that is transverse to the locking pin. A bearing needle or similar can be utilized as an anti-rotation element. A locking interface for the locking pin, provided by a radial shuttle pin bore within the valve lever assembly, can be of various forms. The shuttle pin bore, in fluid communication with the first rocker shaft bore, can be in the form of a first radial aperture within the valve lever assembly. The shuttle pin bore can be round throughout its length or contain a flat to interface with the locking pin. An elongated member, having a convex quadrilateral cross-section, can be transversely disposed within the shuttle pin bore to serve as an interface for the optional first radial flat on the locking pin. Alternatively, a shuttle pin sleeve of suitable material and hardness can be arranged within the first radial aperture of the valve lever assembly to serve as the shuttle pin bore and locking pin interface. The shuttle pin sleeve can be configured with a third radial flat on an inner radial surface to receive the optional first radial flat of the locking pin. The third radial flat can extend throughout the length of the shuttle pin sleeve or to a medial distance within the sleeve.
In the first, locked position of the coupling assembly, the radial locking pin bore is axially aligned with the radial shuttle pin bore and the locking pin is arranged partially within each of the bores. In the second, unlocked position of the coupling assembly, the locking pin is disengaged from the shuttle pin bore, permitting relative motion of the cam lever assembly relative to the valve lever assembly. A resilient element is in contact with the locking pin at the first, locked and the second, unlocked positions. In the first, locked position, the resilient element has a first compressed length and in the second, unlocked position, the resilient element has a second compressed length. The first compressed length is greater than the second compressed length.
The above mentioned and other features and advantages of the embodiments described herein, and the manner of attaining them, will become apparent and better understood by reference to the following descriptions of multiple example embodiments in conjunction with the accompanying drawings. A brief description of the drawings now follows.
Identically labeled elements appearing in different figures refer to the same elements but may not be referenced in the description for all figures. The exemplification set out herein illustrates at least one embodiment, in at least one form, and such exemplification is not to be construed as limiting the scope of the claims in any manner. A radially inward direction is from an outer radial surface of the outer raceway, toward the central axis or radial center of the outer raceway. Conversely, a radial outward direction indicates the direction from the central axis or radial center of the outer raceway toward the outer surface. Axially refers to directions along a diametric central axis. The words “left” and “right” designate directions in the drawings to which reference is made.
Referring to
Referring to
Referring to
Referring now to
The rotation of the cam lever assembly 22 relative to the valve lever assembly 24 is limited by features that are formed on ends of the first and second curved surfaces 30,44. A first rotational stop 32 is present at a first end of the first curved surface 30 of the valve lever assembly 24, while a first abutment 33 is present at an abutment end of the second curved surface 44 of the cam lever assembly 22. Contact between the first rotational stop 32 with the first abutment 33 is shown in
Now referring to
The arrangement of the first and second lost motion springs 29A,29B within the first and second lost motion spring landings 25A,25B and the first and second lost motion spring retainer posts 42A,42B induces a rotational torque TLMS on each of the cam lever and valve lever assemblies 22,24, as shown in
The previously described arrangement of the lost motion springs 28A,28B within the switchable rocker arm 12 offers two distinct design advantages: a). Elimination of an external housing within the cylinder head or valve cover for one or more lost motion springs; and, b). Elimination of a camshaft abutment feature to ensure the proper rotational location of the cam lever assembly 22 while in the second, unlocked position.
Now referring to
Instead of implementing the shuttle pin sleeves 50,50′,50″ for the previously described coupling assemblies that are disposed within the first radial aperture 41 of the valve lever assembly 24, the first radial aperture 41 can be configured with the appropriate form to serve as a shuttle pin bore. Such an appropriate form can be achieved by a multitude of processes such as machining, powdered metal, or metal injection molding. Optionally, referring now to
In the foregoing description, example embodiments are described. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense. It will, however, be evident that various modifications and changes may be made thereto, without departing from the broader spirit and scope of the present invention.
In addition, it should be understood that the figures illustrated in the attachments, which highlight the functionality and advantages of the example embodiments, are presented for example purposes only. The architecture or construction of example embodiments described herein is sufficiently flexible and configurable, such that it may be utilized (and navigated) in ways other than that shown in the accompanying figures.
Although example embodiments have been described herein, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present example embodiments should be considered in all respects as illustrative and not restrictive.
The following documents are incorporated herein by reference as if fully set forth: U.S. Provisional Application No. 62/190,422, filed Jul. 9, 2015 and U.S. Provisional Application No. 62/295,341, filed Feb. 15, 2016.
| Number | Date | Country | |
|---|---|---|---|
| 62190422 | Jul 2015 | US | |
| 62295341 | Feb 2016 | US |
