US20110094467A1

US20110094467A1 - Lash adjuster

Info

Publication number: US20110094467A1
Application number: US12/914,366
Authority: US
Inventors: Robert T. MacVicar; Raji Rexavier
Original assignee: Electro Motive Diesel Inc
Current assignee: Progress Rail Locomotive Inc
Priority date: 2009-10-28
Filing date: 2010-10-28
Publication date: 2011-04-28
Also published as: WO2011053702A1

Abstract

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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 INVENTION

The 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 FIG. 1 a, it is known in the art relating to internal combustion engines, such as diesel engines, and namely locomotive diesel engines 101, to actuate two adjacent valves 120 a, 120 b of an engine cylinder 103 by a rotating cam. The cam generally includes a select shape which determines the timing, lift, velocity, and acceleration of the intake and exhaust valve actuation. As shown in FIG. 1 b, in order to open the exhaust valves 106 a, 106 b the cam shaft 108 rotates until a cam lobe 104 engages a roller 110 located on a rocker arm 112. Once the cam lobe 104 engages the rocker arm 112, the rocker arm 112 engages a valve bridge 114, which causes compression in adjacent springs 116 a, 116 b causing the exhaust valves 106 a, 106 b to open.
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 120 a, 120 b thermally and mechanically expand and elongate, the valves 106 a, 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 120 a, 120 b 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 120 a, 120 b, thereby allowing the exhaust valves 106 a, b to operate effectively, even when thermal expansion occurs. Valve systems may incorporate two hydraulic lash adjusters 102 a, 102 b, received in sockets 122 a, 122 b 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 120 a, 120 b.
FIG. 2 shows a prior art hydraulic lash adjuster 202 in a closed position where a ball 230 is held against a ball seat 234 in the lash adjuster 202 body by a light spring 238, thereby closing the aperture 224 in the base 240 of the housing 236 of the lash adjuster 202. However, when the exhaust valves begin to open, a force is applied across the lash adjusters, causing a small amount of oil to escape through the diametrical clearance of the lash adjuster 202, situated between the plunger 242 and the sidewall of the housing 236. This force also maintains the internal pressure therein and, acting with the ball spring 238, situates the ball 230 against the seat 234 preventing oil from flowing out the aperture 224 defined in the base 240 of the housing 236. When the exhaust valve is returned to its seat, the force across the lash adjuster 202 is relaxed and the pressure in the cavity 232 drops. This allows the plunger 242 to move downward under the influence of the plunger spring 244, causing the cavity 232 pressure to drop below the oil supply pressure and allowing oil flow into the cavity 232 through the aperture 224, making up for leakage until the pressure equalizes.
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 FIG. 2, this internal clearance 260 is about 0.1 inches. When the lash adjuster 202 is properly functioning, the force across the lash adjuster 202 acts so that the plunger 242 may only travel axially between about 0.001 inches and about 0.005 inches. However, when the lash adjuster 202 fails, the lash adjuster 202 is no longer able to effectively trap oil and maintain the force and pressure that prevents the plunger 242 from traveling the full length of the internal axial clearance 260. Therefore, when the prior art lash adjuster 202 of FIG. 2 fails, the plunger 242 travels about 0.1 inches until it hits the base 240 of the housing 236.
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 FIG. 3, when the valve train is lifted to about 0.1 inches, the cam has already rotated to about 43 degrees (shown at 302). Similarly, when the valve begins to close, the cam is rotated to an angle of about 150 degrees (shown at 320) and the valve train is lifted to about 0.1 inches.
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 FIG. 3, with respect to the properly functioning prior art lash adjuster of FIG. 2, when the cam rotates from an angle of about 0 degrees to about 43 degrees (shown at 301), the opening velocity of the valve gradually reaches about 60 inches/sec, at which point (shown at 304) the valve is opened to about 0.1 inches. Similarly, when the cam rotates to an angle of about 150 degrees (shown at 322), the valve begins to gradually close at a reducing velocity from about −65 inches/sec until the cam is rotated to an angle of about 158.5 degrees (shown at 328) and the valve reaches ramp velocity. The valve continues to gradually close at a constant velocity until the cam is rotated to an angle of about 180 degrees (330), at which point the valve is closed.
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 FIG. 2, when the lash adjuster fails or momentarily malfunctions, the plunger travels about 0.1 inches before it contacts the base of the housing 236. When this happens, the valve gear is well beyond the end of the ramp and up the flank of cam profile before the valve opens (the same is true on the closing side of the event). As a result, the valve opens and closes at very high velocities—as much as ten times ramp velocity.
For instance, as shown in FIG. 3, when the prior art lash adjuster of FIG. 2 fails, instead of having a gradual opening velocity, the velocity of the valve increases instantaneously from about 0 inches/sec (shown at 308) to about 60 inches/sec (shown at 316). In this failed condition, as the cam rotates from about 0 degrees (shown at 300) to about 43 degrees (shown at 306), the velocity of the valve remains at about 0 inches/sec (shown at 308). However, when the cam reaches an angle of about 43 degrees, the valve suddenly opens (shown at 316) at a velocity of about 60 inches/sec (shown at 304). Similarly, when the prior art lash adjuster of FIG. 2 fails, the closing velocity of the valve is abrupt, instead of gradual. As the cam rotates from about 140 degrees (shown at 319) to about 150 degrees (shown at 322), the valve is slowly beginning to close at a gradually increasing negative velocity. However, when the prior art lash adjuster has failed, as the cam reaches an angle of about 150 degrees, the valve makes contact with the cylinder head and the velocity suddenly decreases (shown at 326) to a velocity of 0 inches/sec (shown 324). When the valves open and close at high velocities, the valves, and other system components, are subjected to high impact loads, which frequently result in valve system failure. Thus, it is an object of the present invention to provide a lash adjuster with a select axial clearance, between the plunger and housing, that is generally 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 such failure.
Additionally, when the prior art lash adjuster of FIG. 2 fails, the opening and closing accelerations of the valve become abrupt instead of gradual. As shown in FIG. 4, when a prior art lash adjuster is working properly, as the cam rotates from about 0 degrees to about 43 degrees, the opening acceleration of the valve should correspondingly increase gradually from about 0 inches/secinches/sec²to about 27,100 inches/sec²(shown between 400 and 402). However, when the lash adjuster fails, the opening acceleration of the valve increases abruptly from 0 inches/sec²(shown at 408) to about 329,900 inches/sec²(shown at 404). In this failed condition, as the cam rotates from about 0 degrees to about 43 degrees, the acceleration of the valve remains at about 0 inches/sec²(shown at 406). However, when the cam reaches an angle of about 43 degrees (shown at 408), the valve suddenly accelerates at a rate of about 329,887.1 inches/sec²(shown at 404).
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 INVENTION

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 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.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a is a cross-sectional view of a prior art locomotive diesel engine, of which the present invention fail-safe lash adjuster is a part.

FIG. 1 b is a cross-sectional view of a prior art valve train system, of which the present invention fail-safe lash adjuster is a part.

FIG. 2 is a cross-sectional view of a prior art lash adjuster.

FIG. 3 is a chart depicting the relationship between cam angle and valve opening and closing velocity of the present invention fail-safe lash adjuster in comparison to prior art lash-adjusters.

FIG. 4 is a chart depicting the relationship between cam angle and valve acceleration of the present invention fail-safe lash adjuster in comparison to prior art lash-adjusters.

FIG. 5 is a cross-sectional view of the present invention fail-safe lash adjuster.

DETAILED DESCRIPTION OF DRAWINGS

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 FIG. 5 in a closed position, the present invention lash adjuster 502 includes a ball 530 that is held against a ball seat 534 in the lash adjuster body by a light spring 538, thereby closing the aperture 524 in the base 540 of the housing 536 of the lash adjuster 502. In this embodiment, when a valve of the valve train system begins to open, a force is applied across the lash adjuster 502, causing a small amount of oil to escape through the diametrical clearance of the lash adjuster 502, situated between the plunger 542 and the sidewall of the housing 536. Additionally, the force applied across the lash adjuster 502 maintains the internal pressure therein and, acting with the ball spring 538, situates the ball 530 against the seat 534 to prevent oil from flowing out the aperture 524 defined in the base 540 of the housing 536. When the exhaust valve is returned to its seat, the force across the lash adjuster 502 is relaxed and the pressure in the cavity 532 drops. This allows the plunger 542 to move downward under the influence of the plunger spring 544, causing the cavity 532 pressure to drop below the oil supply pressure and allowing oil flow into the cavity 532 through the aperture 524 until the pressure equalizes.
Like the prior art lash adjuster of FIG. 2, when the present invention lash adjuster 502 of FIG. 5 is properly functioning, the force across the lash adjuster 502 acts so that the plunger 542 may only travel axially between about 0.001 inches and about 0.005 inches. Moreover, like the prior art lash adjuster, when the present invention lash adjuster 502 fails, it is no longer able to effectively trap oil and maintain the force and pressure that keeps the plunger 542 from traveling the full length of the internal axial clearance 560. Moreover, when the lash adjuster fails, because there is no internal pressure within the lash adjuster—due to the oil escaping through the 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 536.
As shown in FIG. 5, the internal axial clearance 560 of the present invention lash adjuster 502 is selected at a length of about 0.01 inches to about 0.03 inches, and preferably about 0.02 inches. Therefore, in a failed condition, the valve will begin to open or close when the valve train is lifted between about 0.01 inches and about 0.03 inches, and preferably about 0.02 inches. Moreover, as a result of this decreased internal axial clearance 560, in the event of failure, the present invention lash adjuster 502 may be set at the minimum velocity and travel an axial distance of between about 0.01 inches and about 0.03 inches (preferably about 0.02 inches) within the lash adjuster 502 body. Thus, when the lash adjuster 502 fails or momentarily malfunctions, the plunger 542 only travels between about 0.01 inches to about 0.03 inches, and preferably about 0.02 inches, before it contacts the base 540 of the housing 536, causing the valve to open.
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 FIG. 2). Valve actuation depends on what point the cam is engaging the roller at a given point in time. Thus, the cam angle determines the valve train lift. Additionally, because of the select shape of the cam, the steepness of the cam corresponds to velocity and acceleration of valve opening and closing. Because cam angle also corresponds to valve velocity and acceleration, there is a correlation between valve train lift and valve velocity and acceleration. Thus, the lower the valve train lift when the valve opens or closes, the lower the opening and closing valve velocity will be. The lower the opening and/or closing velocity, the less damage there is to the valve train system.
For instance, as shown in FIG. 3, when the valve train is lifted to about 0.03 inches when the valve opens (when the present invention lash adjuster is functioning properly), the cam rotates from about 0 degrees (shown at 310) to about 32.5 degrees (shown at 312), and the valve opening velocity gradually increases from about 0 inches/sec (shown at 300) to about 14.44 inches/sec (shown at 314). Similarly, when the valve train is lifted to about 0.03 inches when the valve closes (when the present invention lash adjuster is functioning properly), the earn rotates from about 158 degrees (shown at 332) to about 180 degrees (shown at 311), and the valve closing velocity gradually increases from about −20 inches/sec (shown at 328) to 0 inches/sec (shown at 330).
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 FIG. 4, when the present invention lash adjuster is working properly, as the cam rotates from about 0 degrees to about 32.5 degrees, the opening acceleration of the valve correspondingly increases at gradual rate from about 0 inches/sec²(shown at 400) to about 16,00 inches/sec²(shown at 405). In contrast to a failed prior art lash adjuster, which causes the valve opening acceleration to increase abruptly from about 0 inches/sec²to about 329,900 inches/sec²(shown at 404), a failed present invention lash adjuster only causes the valve opening acceleration to increase from about 0 inches/sec²(shown at 400) to about 78,000 inches/sec²(shown at 410). Thus, the opening acceleration rate of a failed present invention lash adjuster is not significantly different from the acceleration rate when the lash adjuster is properly functioning. Similarly, the closing acceleration rate of a failed present invention lash adjuster is not significantly different from that when it is working properly. The valve closing acceleration rate in a system having a failed present invention lash adjuster decreases from about 107,700 inches/sec²(shown at 417) to about 0 inches/sec²(shown at 420), in contrast to decreasing from 19,900 inches/sec²(shown at 419) to about 0 inches/sec²when it is functioning properly. As a result, the present invention lash adjuster minimizes stress on the valve train system in the event of such failure, thereby avoiding damage.
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/second²and the maximum acceleration of valve closing is about 107,700 inches/second².