Patent Application
20080314343
The present invention relates to hydraulic lifters for activating valves in response to rotation of a camshaft in an internal combustion engine; more particularly, to such lifters having means for selectively engaging and disengaging such activation; and most particularly, to such a hydraulic valve lifter wherein the pin housing surface facing the roller is reconfigured to prevent damage to the cam-following surface of the roller.
It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, especially the intake valves, under certain engine load conditions. A known approach to providing selective deactivation is to equip the hydraulic lifters for those valves with means whereby the lifters may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated pushrods. Typically, a deactivation lifter includes, in addition to the conventional hydraulic lash adjuster, concentric inner and outer portions (pin housing and lifter body) which are mechanically responsive to the pushrod and to the cam lobe, respectively, and which may be selectively latched and unlatched to each other, typically by the engagement of pressurized engine oil acting upon one or more spring loaded latching pins extendable from the pin housing into recesses in the lifter body. See, for example, U.S. Pat. Nos. 6,497,207 and 6,814,040, the relevant disclosures of which are incorporated herein by reference.
In prior art deactivating hydraulic valve lifters, when the movement of the locking mechanism is incomplete at the start of a valve lift event, the lifter may start to open the engine valve and then allow it to close rapidly as the partially-engaged locking mechanism is forced, or ejected, from its coupled state between the pin housing and the lifter body. When such an ejection occurs, the valve spring propels the valve toward the valve seat while simultaneously propelling the lifter pin housing toward the lifter cam-following roller. In a typical deactivating valve lifter, the roller surface is crowned so that only a central region of the crown makes rolling contact with the mating cam lobe. The margins of the roller outside of the central region do not make contact with the mating cam roller.
In prior art deactivating hydraulic valve lifters such as disclosed in U.S. Pat. Nos. 6,497,207 and 6,814,040, if ejection occurs from a high lift position of the valve, the pin housing may actually strike the central region of the roller's crowned surface. Such contact of the roller by the pin housing can cause wear and damage (e.g., material spalling, pitting, debris brinelling) to the central region of the crown. Since the central region of the roller's crown runs against a mating surface of the engine's camshaft lobe, damage to the roller may be transferred to the mating camshaft lobe as well; and, since the camshaft is difficult to examine except by a complete engine teardown, costly repairs may result. Hence, it is important to prevent such damage to the central region of the roller's crown.
It is a principal object of the present invention to provide an improved valve-deactivation hydraulic lifter wherein the pin housing is incapable of striking the central region of the crowned surface of the lifter roller that makes contact with the associated cam lobe as a result of a latch ejection.
It is a further object of the invention to prevent damage to an engine camshaft lobe as a result of a latch ejection of a deactivation lifter.
Briefly described, a valve-deactivation hydraulic valve lifter in accordance with the invention includes a conventional hydraulic lash adjustment disposed conventionally within a pin housing that is slidably disposed within an axial bore in a lifter body. In one example, a transverse bore in the pin housing contains two opposed locking pins urged outwards of the pin housing by a pin-locking spring disposed in compression therebetween to engage a circumferential groove including a locking surface in the lifter body whereby the lifter body and the pin housing are locked together for mutual actuation by rotary motion of the cam lobe to produce reciprocal motion of an engine pushrod disposed in the hydraulic lash means. The pins may be disengaged from the lifter body to place the lifter in lost-motion mode by application of hydraulic fluid such as engine oil to the outer ends of the pins at a pressure sufficient to over come the force of the pin-locking spring.
The invention is directed to a reconfigured surface, preferably a dished recessed surface, on the bottom end face of the pin housing that faces toward the cam-following lifter roller, such that should collision occur between the pin housing and the roller any resulting damage to the roller occurs at the margin of the roller and is outside of the central region of the crowned surface of the roller that makes contact with the mating cam shaft lobe.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
a is a bottom view of prior art cam-follower roller shown in
a is a bottom view of the cam-follower roller shown in
a is a bottom view of the cam-follower roller shown in
Referring to
Plunger assembly 18 is disposed concentrically within pin housing 20, which, in turn, is disposed concentrically within lifter body 14. Pushrod seat assembly 22 is disposed concentrically within pin housing 20 above plunger assembly 18. Roller 12 is associated with lifter body 14. Roller 12 rides on the cam lobe 13 of an internal combustion engine 31 and is displaced vertically thereby. Roller 12 translates the rotary motion of cam lobe 13 to vertical motion of lifter body 14. Deactivation pin assembly 16 latchably engages lifter body 14, thereby transferring the vertical reciprocation of lifter body 14 to pin housing 20 and, in turn, to plunger assembly 18 and pushrod seat assembly 22. Pin housing 16 includes centrally positioned drain hole 17.
In this engaged position, the vertical reciprocation of DRHVL 10 opens and closes a combustion valve (not shown) of internal combustion engine 31. Deactivation pin assembly 16 may be disengaged by applying hydraulic fluid to the ends of the pins to decouple lifter body 14 from pin housing 20 and, in turn, to decouple plunger assembly 18 and pin housing 20 from the vertical reciprocation of lifter body 14. Thus, when deactivation pin assembly 16 is in the disengaged position, only lifter body 14 undergoes vertical reciprocation in lost motion. Drain hole 17 permits hydraulic fluid leaking past the pins to drain from between the pins.
Roller 12 is of conventional construction, having the shape of a crowned cylindrical member within which bearings 28 are disposed and retained. Roller 12 is disposed within a first end 15 of lifter body 14. Shaft 30 passes through roller 12 such that bearings 28 surround shaft 30 and are disposed intermediate of shaft 30 and the inside surface of roller 12. Shaft 30 is attached by, for example, staking to lifter body 14. Lifter body 14 includes on its outside surface anti-rotation flats (not shown) which are aligned with anti-rotation flats on an interior surface of a conventional anti-rotation guide (not shown) within which lifter body 14 of DRHVL 10 is inserted. This assembly 10 is placed in the lifter bore of push-rod type engine 31. Roller 12 rides on cam lobe 13 of push-rod type engine 31, with central region 32 (
Referring to
Referring now to
Such recessing of surface 136 may take any non-planar form that prevents contact from occurring between surface 136 and central region 32 of the crowned roller. When latch ejections occur, the pin housing encounters the roller closer to the chamfer break 140 outside the of central region 32. Further, any peening or distortion of material of roller 12 is displaced outwards toward or into the chamfer 142, thus leaving central region 32 undamaged.
Another embodiment 210 of a non-planar form of the bottom surface of the pin housing is shown in
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
