US2812750A - Hydraulic lash adjuster - Google Patents

Description

Nov. 12, 1957 K. w. LEsHl-:R 2,812,750

HYDRAULIC LASH ADJUSTER Filed 0G13. l, 1956 z Z0 i W UMIL! i IN V EN TOR;

BY M v L United States Patent O f' HYDRAULIC LASH ADJUSTER Kenneth W. Lesher, Grand Rapids, Mich., assigner zo General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October` 1, 1956, `Serial No. 613,132

` s Claims. (C1. 12s-.99)

This invention relates `to hydraulic lash adjusters as, for example, those used in the valve operating linkages of in'- ternal combustion engines to transmit the valve opening movement without lash (lost motion) between the valve and the cam or other valve operating member.

in conventional hydraulic lash adjusters of .this general type the motion of the cam is transmitted to the engine valve through a cylinder and Slidably inter-tted plunger resting on a body of hydraulic fluid contained in the cylinder. The fluid used may be the engine lubricating oil, supplied to thelash adjuster by the engine oil pump. The amount of fluid introduced `into the lash adjuster below the plunger is automatically controlled by suitable valving within the adjuster in accordance with thermal expansion and wear occurrin-g in the various parts of the valve linkage to maintain a zero lash in the system. Difficulty is encountered, however, at high engine operating speeds in preventing a condition called pump-up which occurs when too much oil gets below the plunger and results in extending the operating length of the lash adjuster sui ciently to prevent normal closing of the engine valve. The undesirable effects of this are usually oversheating of the valve, loss of engine power, etc. I have found this difficulty can be eliminated by a unique arrangement of valving the admission and escape of oil from a cylinder chamber below the plunger, whereby excessive fluid pressures which might otherwise occur in this chamber incident to pump-up are prevented. As a result, the lash adjuster in accordance with my invention enables obtaining satisfactory engine operation at speeds considerably above those possible heretofore.

it is therefore the principal object of my invention to provide a hydraulic lash adjuster having improved operating characteristics, particularly in respect to increasing the operating speeds thereof without incurring pump-up.

It is a further object to effect this improvement in a manner which is simple and does not increase the cost of the lash adjuster beyond what is commercially acceptable.

The means by which these and other objects of my invention are accomplished will be readily apparent from the following description of a preferred embodiment thereof selected for purposes of illustration, wherein:

Figure l is a sectional View of a portion of an internal combustion engine having a valve operating linkage including my improved hydraulic lash adjuster.

Figure 2 is an enlarged view similar to Figure l showing details of a lash adjuster with parts broken away and in section.

Referring now in detail to the drawing, the numeral 1 designates a conventional cylinder block and cran-kcase of an internal combustion engine having one or more cylinders 2, in each of which is fitted a reciprocating piston 3. Shown reciprocally mounted in the cylinder head 4 above the piston is a poppet valve 5 which controls the inlet (or exhaust) for the cylinder 2. The valve 5 is normally held in closed position, as shown, by the valve spring 6, and during engine operation it is intermittently 2,812,750 Patented Nov. 12, 1957 rice moved downwardly to its open position against the valve spring by the valve operating cam 7, whose motion is transmitted to the upper end 8 of the valve through my hydraulic lash adjuster, designated generally by the nu meral 9, the push rod 10, and a valve rocker 11. Oil

from the engine lubricating system is pumped by means, not shown, to the lash adjuster 9 through the oil gallery 12 in the crankcase 1 and serves as `the hydraulic fluid for effecting the necessary lineal adjustments within the lash adjuster to carry out its function of taking up lash in the valve train.

As shown in Figure 2, the lash adjuster comprises a cylinder 13 in the form of an upwardly open cup which is laterally supported for sliding reciprocation in a bore 14 formed in the crankcase 1. Slidably received in the bore 15 of the lash adjuster cylinder is a plunger 16, also of cup shape, whose upper end is closed by a push rod seat 17 on which rests the lower end of the push rod 10. The opposite or bottom end of `the plunger cooperates with the bottom end of the lash adjuster cylinder in defining an oil pressure chamber 18 in which is contained a body of oil for transmitting the engine valve opening movements between these parts. Oil for supplying this chamber 1S is contained in the reservoir 19 formed by the interior of the cup-shaped plunger which, in turn, receives its oil supply from the oil gallery 12 (Figure l), through the ports 20, 21, 22 in the crankcase and lash adjuster cylinder and plunger, respectively, whose continuous intercommunication is assured by the grooves 23, 24 and 25 provided on the sliding surfaces of the cylinder and plunger.

The bottom end wall of the plunger 16 has an opening defined interiorly of the plunger reservoir by a conical seating surface 27. Normally engaging this surface and thereby closing the outer portion of the plunger opening is an annular check valve seat member 28, whose lower end extends below the plunger and serves to pilot the open end of a cup-shaped cage or retainer 29 for a ball check valve 31). The central passage 31 through this seat member 28 interconnects the reservoir 19 with the pressure chamber 18, and its lower end forms the seat for the ball 34). This ball` has freedom of ymovement between its seat at the lower end of passage 31 and the bottom of the cage 29 so as to act as a check `valve which will accommodate flow of oil into the chamber 18, but prevent reverse flow. Oil flowing past 'the ball 30 when unseated may pass into the main portion of the chamber 18 through suitable apertures 32 provided in the bottom end of the cage 29. AS shown, the upper end of this cage is externally flanged to abut the bottom face of the plunger, and is clamped thereagainst by a plunger return spring 33 resting on the bottom of the chamber 18 and tending to move the plunger outwardly of the lash adjuster cylinder. Carried within the plunger reservoir 19 is a second spring 34 whose lower end abuts the check valve seat member 28, and whose upper end is suitably fixed as by abutment with an annular ring 35. An outwardly expansible split ring 36 engages a groove in the plunger side wall to provide a removable support for the retainer 35. Spring 34 is of suflicient stiffness to normally maintain the check valve seat member 28 seated, as shown, but will yield in respouse to the force of a predetermined pressure in chamber 18 acting against the ball 36 and seat 28 to thereby limit the maximum pressure obtainable therein.4

It is believed apparent from the above description that during engine operation the oil which is trapped within the chamber 1S by the ball check valve 3i) operates in conventional manner as a noncompressible body for transmitting the cam lifted movement of the lash adjuster cylinder to the plunger in effecting opening of the engine poppet valve 5. During each such lift stroke some of the oil in the chamber 18 escapes past the plunger between its outer periphery and the bore of the lash adjuster cylinder and enters the plunger reservoir 19 via its groove and port 22. As the lash adjuster returns to the base circle of the cam 7 following each lift stroke, the plunger spring 33 maintains the plunger against the push rod and the push rod, in turn, in operative abutment with the en gine valve through the rocker 1I. Consequently, there is a certain amount of elongation of the lash adjuster during the period it is riding on the dwell portion of the cam, with attendant drop in pressure of the oil in chamber 1S which permits the ball to uncover the passage 31 in the check valve seat 28 and thereby allow sufficient oil to enrter the chamber 18 to replace that which escaped during the preceding lift stroke. At the start of the next operating cycle the pressure again builds up in the chamber 18, causing the ball to again close the passage 31, preparatory to opening the engine poppet valve 5. At relatively high engine operating speeds there is a tendency for the engine valve return spring 6 to surge and thereby lose its eectiveness in closing the poppet valve promptly after the lash adjuster returns to the base circle of the cam. This has the effect of causing an excessive elongation of the lash adjuster during such cam dwell periods, with the result that the lash adjuster pumps up by accumulating too much oil in the chamber 18 and aggravating and prolonging the condition of improper seating of the enginey poppet valve. However, by reason of the check valve seat being operative as a second plunger valve and to open against its biasing spring 34, pressures which would otherwise develop in the chamber 18 incident to excessive opening of the poppet valve during the cam lift stroke are prevented. The raising of the check valve seat member 28 from its seating Isurface Z7 on the plunger, it will be app reciated, is analogous in effect to increasing the rate of leakdown or leakage of oil between the plunger and the cylinder bore, and excessive opening of the engine poppet valve and its consequent inability to reclose are thereby prevented.

While only a single preferred embodiment of the invention has been disclosed, it is appreciated that numerous minor changes in the construction and arrangement of the parts may be made without departing from the spirit and scope of the invention as hereinafter defined.

I claim:

l. In a hydraulic lash adjuster including a generally cup-shaped cylinder having a bore, a generally cup-shaped plunger slidably fitting the bore in nesting relation with the cylinder to define a uid pressure chamber between the respective bottom ends of the cylinder and plunger,

4 said plunger having an opening in its bottom end defined interiorly of the plunger by an annular seating surface, a check valve seat member having an outer peripheral portion normally `seating on said plunger surface and having a passage for flow of hydraulic fluid into said chamber, a check valve engageable with said seat member to block said passage against reverse flow therethrough and movable to engage said seat member in response to chamber fluid pressures of less than a predetermined maximum, and biasing means supported interiorly of the plunger and acting to normally maintain said seat member engaged with said seating surface but yieldable to relieve chamber fluid pressures in excess of said maximum.

2. In a hydraulic lash adjuster havin-g a cylinder and a plunger defining a chamber for a body of fluid in thrust transmitting relation therebetween, means accommodating enlargement and contraction of said body in the thrust direction including a passage in the plunger terminating with an opening to said chamber, a valve seat normally restricting said opening but movable inwardly of said passage to accommodate flow from said chamber, biasing means opposing said movement of the valve seat but yieldable in response to the force of a predetermined chamber fluid pressure acting on said valve seat, and a valve engageable with said seat to normally block fluid flow from said chamber but movable into said chamber to permit flow in the opposite direction incident to enlargement of said body.

3. The invention defined by claim 2 wherein said plunger is hollow and said biasing means is in the form of a spring mounted interiorly of the plunger.

4. In a lash take-up device for transmitting movement between respective driving and driven means, a pair of members having surfaces opposing each other in the direction of said movement and defining a fluid pressure chamber therebetween, one of said members having an opening for flow of fluid into and out of said chamber, a first valve for closing a portion of said opening and openable in response to a predetermined pressure in said chamber, and a second valve for closing the remainder of said opening and closable in response to a lesser pressure in the chamber.

5. The invention defined by claim 4 wherein said portion and said remainder of said opening are concentric with each other.

6. The invention defined by claim 5 wherein said first valve has an aperture defining said remainder of said opening.

No references cited.

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