LASH ADJUSTER
In accordance with the present invention, a lash adjuster is provided for minimizing stress on a valve train system in the event of its failure. Specifically, the present invention lash adjuster is for use in a valve train system having a cam for actuating the opening and closing of a valve, where the cam has a select size and shape for determining the velocity or acceleration of the valve's opening and closing. The present invention lash adjuster generally comprises a housing having a base and a plunger positioned within the housing at a select axial clearance from the base. This clearance is generally sized and shaped such that, in the event of lash adjuster failure, a select maximum velocity or acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system.
This application is a Non-provisional patent application, which claims benefit to U.S. Provisional Application Ser. No. 61/255,601, entitled “Lash Adjuster,” filed Oct. 28, 2009, the complete disclosure thereof being incorporated herein by reference.
BACKGROUND OF THE INVENTIONThe present invention generally relates to a lash adjuster for use in a valve train system. Specifically, the present invention is directed to a lash adjuster that provides a fail-safe condition to avoid damage to a valve exhaust system upon failure of a hydraulic lash adjuster.
As illustrated in
Generally, valve systems are subject to various types of deflection. For example, valve systems may be subject to thermal expansion as the engine heats up and mechanical deflection due to operational loads. If the valve sterns 120a, 120b thermally and mechanically expand and elongate, the valves 106a, 1066 are unable to fully close. Because the components of the valve system are exposed to a range of temperatures throughout the cycle, a lash adjuster is used to provide a means of self-adjusting the length of the valve stems 120a, 120b to facilitate closure thereof. Lash adjusters provide adjustability so that there is zero clearance at all times between the valve bridge 114 and the valve sterns 120a, 120b, thereby allowing the exhaust valves 106a, b to operate effectively, even when thermal expansion occurs. Valve systems may incorporate two hydraulic lash adjusters 102a, 102b, received in sockets 122a, 122b located at opposite distal ends of the cross-arm portion of the valve bridge 114, to engage and directly act upon the ends of the valve stems 120a, 120b.
The cavity 232 of the lash adjuster 202 includes an internal axial clearance 260 between the plunger 242 and the base 240 of the housing 236. In the prior art lash adjuster 202 of
Moreover, when the lash adjuster fails, because there is no internal pressure within the lash adjuster due to the oil escaping through supply channels—no force is exerted upon the valve to open or close it until the plunger makes contact with the base of the housing 236. Therefore, the valve does not begin to open or close until the valve train lifts to about 0.1 inches. As shown in
The timing of valve actuation, in part, depends on what point the cam (i.e. cam angle) is engaging the roller at a given point in time. Because of the select shape of the cam, the steepness of the cam corresponds to the velocity of valve opening and closing. When a lash adjuster is working properly, the opening and closing velocities of the valve gradually increase or decrease, respectively, as the cam rotates. For instance, as illustrated in
However, when the prior art lash adjuster fails or momentarily malfunctions, the opening and closing velocities of the valve are no longer slow and gradual. In the prior art arrangement of
For instance, as shown in
Additionally, when the prior art lash adjuster of
Similarly, when a prior art lash adjuster is working properly, as the cam rotates from about 150 degrees to about 180 degrees, the closing acceleration of the valve should correspondingly decrease gradually from about 30,000 inches/sec2 (shown at 412) to 0 inches/sec2 (shown at 411). However, when the lash adjuster fails, the closing acceleration of the valve spikes to 380,900 inches/sec2 (shown at 414) and decreases abruptly to 0 inches/sec2 (shown at 418). In this failed condition, as the cam rotates from about 150 degrees to about 180 degrees, the acceleration of the valve remains at about 0 inches/sec2 (shown at 416). When the valves open and close at high acceleration rates, the valves, and other system components, are subjected to high impact loads, which frequently results in valve system failure. Thus, it is a further object of the present invention to provide a lash adjuster with a select axial clearance, that is generally sized and shaped such that, in the event of lash adjuster failure, a select maximum acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system in the event of such failure.
SUMMARY OF INVENTIONIn accordance with the present invention, a lash adjuster is provided for minimizing stress on a valve train system in the event of its failure. Specifically, the present invention lash adjuster is for use in a valve train system having a cam for actuating the opening and closing of a valve, where the cam has a select size and shape for determining the velocity or acceleration of the valve's opening and closing. The present invention lash adjuster generally comprises a housing having a base and a plunger positioned within the housing at a select axial clearance from the base. This axial clearance is generally sized and shaped such that, in the event of lash adjuster failure, a select maximum velocity and/or maximum acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system.
The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.
In accordance with the present invention, a fail-safe lash adjuster is provided for minimizing stress on a valve train system in the event of its failure. The valve train system includes a cam for actuating the opening and closing of at least one valve, where the cam has a select size and shape for determining the velocity or acceleration of valve opening and closing. The valve train also includes a member having a lash adjuster to maintain zero clearance between at least one valve tip and a member. This member may be in the form of a rocker arm, a valve bridge, or a cam follower. The lash adjuster comprises a housing and a plunger situated within the housing and positioned at a select axial clearance from the base of the housing. This axial clearance is sized and shaped such that in the event of lash adjuster failure, a select maximum velocity and/or acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system.
In one embodiment, shown in
Like the prior art lash adjuster of
As shown in
When the valve opens between about 0.01 to about 0.03 inches, and preferably about 0.02 inches, there is less damage to the valve train system in the event of failure than when the valve opens about 0.1 inches (as in the prior art lash adjuster arrangement of
For instance, as shown in
In a valve train system with a properly functioning lash adjuster, the increase in valve opening and closing velocities is gradual. However, unlike the prior art lash adjuster, if the present invention lash adjuster fails, the change in opening velocity (shown at 303) and closing velocity (shown at 315) of the valve remains more gradual. For instance, in a valve train system having a failed present invention lash adjuster, as the cam rotates from about 0 degrees (shown at 300) to about 32.5 degrees (shown at 317), the velocity of the valve remains about 0 inches/sec (shown at 303). When the cam reaches an angle of about 32.5 degrees (shown at 317), the valve opens at a velocity of only about 14.40 inches/sec (shown between 317 and 314). However, this increase in velocity is not significantly different from the gradual increase in velocity when the lash adjuster is working properly. The change in velocity remains relatively gradual. As a result, the valve gear is still on the ramp when the valve opens. Therefore, there is limited stress on the system and damage to the valve train is avoided.
Similarly, in a valve train system having a failed present invention lash adjuster, the valve gradually closes until the cam is rotated to an angle of about 158.5 degrees, when the valve train is lifted about 0.03 inches. When the cam reaches an angle of about 158.5 degrees, the valve closes at a velocity of only about −20 inches/see. As the cam rotates from about 158.5 degrees (328) to about 0 degrees (330), the velocity of the valves remains about 0 inches/sec (shown at 315). However, this increase in velocity is not significantly different from the gradual increase in velocity when the lash adjuster is working properly. The change in velocity remains relatively gradual. As a result, the valve gear is still on the ramp when the valve closes. Therefore, there is limited stress on the system and damage to the valve train is avoided.
Additionally, in a valve train system having a failed present invention lash adjuster, the opening and closing valve accelerations remain similar to the opening and closing valve accelerations when the lash adjuster is working properly. In contrast to the rapid acceleration rate that the prior art lash adjuster's failure causes the valve to open at, the valve opening acceleration rate in a system having a failed present invention lash adjuster is relatively small and gradual. As shown in
Lash adjuster failure may involve the failure or malfunction of one or more parts of the lash adjuster, such as the ball retainer, the ball spring, or the engagement between the ball and seat.
Claims
1. A lash adjuster for use in a valve train system, said valve train system having a cam for actuating the opening and closing of at least one valve, wherein said cam has a select size and shape for determining the velocity of valve opening and closing, a member having a lash adjuster to maintain zero clearance between at least one valve tip and said member, said lash adjuster comprising,
- a housing having a base,
- a plunger situated within said housing and being situated at a select axial clearance from the base of said housing, wherein the select axial clearance is sized and shaped such that in the event of lash adjuster failure, a select maximum velocity of valve opening and closing is maintained, thereby minimizing stress on the valve train system in the event of lash adjuster failure.
2. The lash adjuster of claim 1 wherein said member is a rocker arm.
3. The lash adjuster of claim 1 wherein said member is a valve bridge.
4. The lash adjuster of claim 1 wherein said member is a cam.
5. The lash adjuster of claim 1 further comprising a ball retainer for retaining a ball near the base of said housing.
6. The lash adjuster of claim 5, wherein failure of said ball retainer results in lash adjuster failure.
7. The lash adjuster of claim 5 further comprising a ball spring for holding said ball against a seat in the base of said housing.
8. The lash adjuster of claim 7, wherein failure of said spring results in lash adjuster failure.
9. The lash adjuster of claim 7, wherein malfunction of the engagement between said ball and seat results in lash adjuster failure.
10. The lash adjuster of claim 1, wherein the select axial clearance is sized to have a length of between about 0.01 inches and about 0.03 inches.
11. The lash adjuster of claim 1, wherein the select axial clearance is sized to have a length of about 0.02 inches.
12. The lash adjuster of claim 1, wherein the maximum velocity of valve opening is between about 5 inches per second and about 14.40 inches per second and the maximum velocity of valve closing is between about 15 inches per second and about 20 inches per second.
13. The lash adjuster of claim 1, wherein the change in opening and closing velocities of the valve remain relatively gradual.
14. A lash adjuster for use in a valve train system, said valve train system having a cam for actuating opening and closing of at least one valve, wherein said cam has a select size and shape for determining the acceleration of valve opening and closing, a member having a lash adjuster to maintain zero clearance between at least one valve tip and member, said lash adjuster comprising,
- a housing having a base,
- a plunger situated within said housing and being situated at a select axial clearance from the base of said housing, wherein the select axial clearance is sized and shaped such that in the event of lash adjuster failure, a select maximum acceleration of valve opening and closing is maintained, thereby minimizing stress on the valve train system in the event of lash adjuster failure.
15. The lash adjuster of claim 14 wherein said member is a rocker arm.
16. The lash adjuster of claim 14 wherein said member is a valve bridge.
17. The lash adjuster of claim 14 wherein said member is a cam.
18. The lash adjuster of claim 14 further comprising a ball retainer for retaining a ball near the base of said housing.
19. The lash adjuster of claim 18, wherein failure of said ball retainer results in lash adjuster failure.
20. The lash adjuster of claim 18 further comprising a ball spring for holding said ball against a seat in the base of said housing.
21. The lash adjuster of claim 20, wherein failure of said spring results in lash adjuster failure.
22. The lash adjuster of claim 20, wherein malfunction of the engagement between said ball and seat results in lash adjuster failure.
23. The lash adjuster of claim 14, wherein the axial clearance is sized to have a length of between about 0.01 inches and about 0.03 inches.
24. The lash adjuster of claim 14, wherein the axial clearance is sized to have a length of about 0.025 inches.
25. The lash adjuster of claim 18, wherein the maximum acceleration of valve opening is about 78,000 inches/second2 and the maximum acceleration of valve closing is about 107,700 inches/second2.
Type: Application
Filed: Oct 28, 2010
Publication Date: Apr 28, 2011
Inventors: Robert T. MacVicar (Downers Grove, IL), Raji Rexavier (Clarendon Hills, IL)
Application Number: 12/914,366