Patent Application
20090044775
1. Technical Field
The present disclosure relates to a hydraulic lash adjuster with a damping device for use in an internal combustion engine valvetrain.
2. Background Art
Modern valvetrain systems use hydraulic lash adjusting elements to compensate for valve train wear, thermal expansion during engine warm-up, and any other phenomena that change clearances within the valve train mechanical linkage. Hydraulic lash adjusters use hydraulic fluid within a variable volume pressure chamber behind a plunger to transmit the valve actuating force from a camshaft to the rocker arm. The volume of fluid within the chamber changes to move the plunger and remove the clearance or lash within the mechanical linkage of the valvetrain. Under some operating conditions or in particularly compliant valvetrains, the lash adjuster may “pump-up” or over compensate by allowing too much hydraulic fluid into the pressure chamber during events where rapid unloading of the mechanical linkage occurs. If the duration of the unloading event is longer than the time required for the lash adjuster to respond and increase the hydraulic fluid volume within the high pressure chamber, the lash adjuster may prevent the valve from closing properly, which could result in undesirable operation or engine damage. Conventional lash adjuster design does not allow for explicit control of the damping characteristics of the adjustment system. Instead, the system response is dictated by the geometry and design of the passage between the high and low pressure chambers within the lash adjuster. While this approach may be suitable for many applications, it may be difficult to tune or adapt the response to a particular valve train system.
A system and method for adjusting lash in the valvetrain of an internal combustion engine using a hydraulic lash adjuster include a damping device to limit the rate of movement of a lash adjuster plunger relative to the lash adjuster body. Embodiments include a hydraulic lash adjuster having a body with a closed end and an open end for receiving a plunger with the plunger moving in response to a varying quantity of hydraulic fluid within a variable volume high-pressure chamber disposed between the plunger and the body. A damping device associated with at least one of the plunger and the body limits the rate of movement of the plunger relative to the body. A damping element disposed within the high-pressure chamber, or alternatively within a damping chamber, limits flow rate of hydraulic fluid past or through the damping element.
The present disclosure includes embodiments having various advantages. For example, the system and method of the present disclosure incorporate a hydraulic damper into the design of the lash adjuster with either a normally closed, normally open, or free-ball lash adjuster suitable for overhead cam or pushrod engines. Controlling flow passage geometry and/or damper chamber volume facilitates tuning of the lash adjuster response for particular valvetrain designs and/or operating conditions. Response time tuning of the lash adjuster using the damping device may facilitate better control over valve opening and closing events, valve duration, and valve lift. In addition, a tunable response may be used to better match the characteristics of a particular valvetrain design to reduce noise, vibration, and harshness (NVH). The tunable damping feature of the present disclosure may be used to compensate for valve growth during aggressive cold start strategies while providing a more robust control system that is less sensitive to variations in oil temperature and viscosity.
The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.
As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. The representative embodiments used in the illustrations relate generally to a hydraulic lash adjuster for the valvetrain of a four-stroke, multi-cylinder, internal combustion engine. Those of ordinary skill in the art may recognize similar applications or implementations with other engine/vehicle technologies.
Multiple cylinder internal combustion engine 10 includes a camshaft 12 disposed within an engine block 14, and may be referred to as a cam-in-block engine. Each cylinder 16 (only one of which is shown) includes a reciprocating piston 18 coupled by a connecting rod 20 to a crankshaft (not shown). Cylinder head 22 is secured to engine block 14 and provides conventional intake and exhaust passages 15 (
Engine 10 includes a valvetrain 50 to control intake of air and/or fuel (for port injected engines) into cylinder 16 and exhaust of combustion gases. Valvetrain 50 includes valves 28, valve springs 52, rocker arms 54, pushrods 56, and lifters 58, sometimes referred to as tappets or cam followers, that include hydraulic lash adjusters with damping features as illustrated in
In operation, lifter 58 contacts a corresponding lobe 70 of camshaft 12 as camshaft 12 rotates, which raises lifter 58 and an associated lash adjuster to transfer the force to an associated pushrod 56. The pushrod 56 exerts a corresponding force on an associated rocker arm 54, which pivots about an integral ball/socket pivot point 120 with the ball supported by an associated fulcrum 126 secured to cylinder head 22. Rocker arms 54 translate the generally upward motion from pushrods 56 to a generally downward motion to move intake valves 30, 32 against associated springs 52 to open the intake ports. As camshaft 12 continues rotating, lifter 58 follows the profile of lobe 70 and begins a generally downward motion so that the associated springs 52 close intake valves 30, 32. Actuation of exhaust valves 36, 38 proceeds in a similar manner.
As illustrated and described with reference to
In the embodiment of
In the representative embodiments illustrated in
Housing 154 includes one or more supply ports 220 that supply hydraulic fluid/engine oil to the outside of body 160, which in turn includes one or more supply ports 222 to deliver oil to the interior of body 160 and lubrication channel 194. Similarly, plunger 160 includes at least one low-pressure port to deliver hydraulic fluid to low pressure chamber 186 from the interior of body 160.
In operation, lash adjusters essentially eliminate any lash or clearance between the valve train components under varying operating and ambient conditions to provide consistent and reliable valve actuations, including repeatable valve opening and closing times and peak lift values. For hydraulic lash adjusters according to the present disclosure, as the length of the valvetrain components varies due to temperature or wear, hydraulic fluid from a pressurized supply enters lifter 58 through transverse bore 220 in housing 154 and enters low pressure chamber 186. A small amount of hydraulic fluid passes through check valve 176 into variable-volume high-pressure chamber 170 to support the plunger in a position to remove any lash or clearance between corresponding pushrods and rocker arms. As such, the force generated by the cam lobe rotating in contact with roller 150 is transferred through housing 154 to lash adjuster body 160 through the hydraulic fluid trapped within high-pressure chamber 170 by check valve 176 to plunger 166. If the valvetrain components increase in length due to thermal expansion, hydraulic fluid escapes very slowly from high-pressure chamber 170 through a “leak-down” path formed by clearance between plunger 166 and body 160 to reduce the volume contained within high-pressure chamber 170.
Some conventional hydraulic lash adjusters that do not include a damping device as described in the present disclosure may be prone to “pump-up” or over compensate due to rapid unloading of the valvetrain mechanical linkage. If the duration of an unloading event is longer than the response time of the lash adjuster, additional (undesirable) hydraulic fluid enters the high-pressure chamber 170 and does not escape quickly enough through the leak-down path such that the lash adjuster may extend sufficiently to hold the valve off of the valve seat resulting in adverse engine operation that could lead to a misfire of one or more cylinders and/or result in permanent damage to the engine. The response time of conventional hydraulic lash adjusters is a function of inherent damping that is controlled by the geometry and design of the passage between the high and low pressure chambers. However, this passage is subject to additional constraints and can not be readily tuned to adapt to a specific valvetrain system design.
According to the present disclosure, a damping device is provided to reduce or eliminate “pump-up” for normally-open and normally-closed lash adjusters. In the embodiment of
As shown in
As also illustrated in
In operation, during a valvetrain unloading event, hydraulic fluid within damping chamber 250 must be displaced from above flange 196 to below flange 196, and/or must exit chamber 250 through the leak-down path for plunger 166′ to move within body 160′. As such, flange 196 operates as a flow restricting damping element limiting the rate of movement of plunger 166′ within body 160′. Similarly, cap 262 may also operate as a flow restricting element that radially overlaps flange 196 to restrict or limit flow rate of hydraulic fluid so that lash adjuster 130′ does not over compensate or pump-up in response to a valvetrain unloading event. The time constant or response time of lash adjuster 130′ can be tuned for a particular application using the volume of damping chamber 250 in combination with the size of the damping element implemented by flange 196, and/or the overlapping area of two or more damping elements to restrict flow of hydraulic fluid. In addition, holes 210′ and 220′ are appropriately sized to deliver the desired damping response.
Referring now to
As such, the system and method of the present disclosure for adjusting lash in the valvetrain of an internal combustion engine incorporate a hydraulic damper into the design of the lash adjuster to provide a normally open or normally closed lash adjuster. Controlling flow passage geometry and/or damper chamber volume facilitates tuning of the lash adjuster response for particular valvetrain designs and/or operating conditions. Response time tuning of the lash adjuster using the damping device may facilitate better control over valve opening and closing events, valve duration, and valve lift. In addition, a tunable response may be used to better match the characteristics of a particular valvetrain design to manage noise, vibration, and harshness (NVH). The tunable damping feature of the present disclosure may be used to compensate for valve growth during aggressive cold start strategies while providing a more robust control system that is less sensitive to variations in oil temperature and viscosity.
While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. One or more embodiments have been described as providing advantages or being preferred over other embodiments or conventional devices in regard to one or more desired characteristics. However, as one skilled in the art is aware, different characteristics may provide advantages and be preferred in some applications while being considered less desirable or disadvantageous in other applications. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, any embodiment described as being preferred or advantageous with respect to one or more characteristics does not preclude embodiments or implementations that may be less desirable or less advantageous but are also within the scope of the disclosure and claims.
