US2577852A - Self-adjusting tappet - Google Patents

Description

ec. H, MSE

SELF' ADJUSTING TAPPET Filed April 19, 1945 INVENTOR. GEORGE H- HUFFEED Patented Dec. 11, 1951 vUNITED STATES PATENT GFFICE 'SELF=ADJUSTING i TAPPET George lI--IuiferlL Shaker, Heights,v Ohio, .as-

signor to' The .Weatherhead 'Coiipan'm Cleveland, Ohio,"a corporationof Ohio l'Application April19, 1945; `Serial No.f589,234

(Cl: 12a-,90)

2.Claims. l Myi-nvention relates to tappets l and concerns particularly valve tappetsfor gas engines. Y--One of the obdectscof my invention is lto :provide self-adjusting valve tappet.

Theprincipal Vobject of vthe invention is to compensate for variations in length of valve stems,valve rods or other operating rods for communicating reciprocating. motion.

:Itfisan. object of the invention to overcome lost motion in internal combustion engines and toiavoidrvariation ofv period and timing of valve opening .as :well as to avoid noisea-nd `wear of loose parts.

Another objectV is to. compensateL for the effect of variations intemperature on length of the valve'rodfandto avoid-.undue loss of efficiency :of an internal combustion. engine where the engine is still cool.

More specifically, an Objectis .togprovide for closeadjustment of tappets while the engine is cool as well as when heating up. A

A further object is'to provide self-elongation .and contraction of .atappet'without rexternal connections orcontrols. y

VStill-another object is tov provide: reliable selfcontained hydraulic compensationgfor tappets in 'whichl paths for uncontrolledy leakage of -hydraulic uidare eliminated. Y

A further object is to provide hydraulic compensation for: a tappet in .whichpassage ofwhydraulic uid from one part to another of 4the .tappet isv limited topredetermined meansfor metering the flow. v y

`Other and further objects, featuresandiad- 'vantagesof the invention will become .apparent as the description proceeds. Y

In carrying out my inventionfaccordanee with apreferred form thereon-I provide-a valve tappet .comprising two relatively.- movable parts in the form of a cylinder-and a piston,the.cylinder being filled with a hydraulic fluid-such as oi1,and .the piston having `a reservoir therein. A metering orice and a check valve are provided .between the reservoir andthe cylinder. The arrangement is such as totend to cause--uid to be transferred fromtheppiston reservoir to the cylinder through the check valve forr the `purpose of lengthening the tappet and'to returnfthrough 4the .metering orice ,for the Y purpose :of lz contracting the tappet. when necessary.

A. better understanding: of: the rinventiong-will 4beaiorded'by the following detailed description considered in conjunction wthzthetaccompanying drawing yand the scope ofLlthe.. invention .twillz'fbe set. forth .1in the claims.

. Irn the-drawings: K

.Eig ylis a-longitudinal sectional view of..a poppet .valveand stem fwith a self-adjusting tappet therefor forming` an embodiment of my invention; l

Fig. :lisa longitudinal sectional view of va modication Vin the tappet illustrated in Fig. 1; .and

\ lig. 3 is a cross-sectional view of the-apparatus of Fig. 2 represented as -cut by a plane3--3 indicated inFi'g. 2V. n I

Like're'ference characters are utilized 4throughout the drawings to designate like parts.

.Referring toFig. l the arrangementshown Atherein by wayv f illustration comprises a portion vof a casing II for anv internal combustion engine such as afgasoline engine for example, having aconventional puppet valve I2 controlled Aby a valve stern I3 or controlled by a valverod represented bythe rod I3 slidable in a suitable guide or bushing IG. A valvespring I5 is provided for normally closing the valve I2 by moving the stem I3 in the downward direction. A

tappet I5 is provided for transferring the action of .a valve operating cam Il to the valve rod I3. As inconventional constructions the tappet I6 has a hardened portion I8 adapted to .ride on thecarn I'I anda hardened surface I9 adapted tocontact thelowerend 2| ofthe rod I3. K

.The tappetl comprises-two parts 22Vand 23 which .are Lvrelatively movable longitudinally, although, -as will be explained hereinafter, the extent of movement required is relatively limited. One Yof these parts, for example, the Vpart V2i, takes the Vform of a hydraulic cylinder and the other'whichisthef part 23 takes the formro'ffa piston. Asuitable 'relatively' incompressible hydraulic luidl2d such as oil, for example, isprovided' fonllingthe cylinder 22,"and a reservoir 25 is formed vin Athe'piston 23 for'supplying oil tofthecylinder 22 *to-extend the tappet length. Phe-pistonZS-andthe cylinder 22 areeach -closedat theouterend and the piston 23 is pro- The piston 23 is arranged to be slidable within the cylinder 22 at the open or upper end thereof. In the specific arrangement illustrated, the piston 23 is provided with an expanded or flaring lower end 29 serving as a guide slidably fitting within the cylinder 22. In the arrangement of Fig. 1 suitable means are provided for resiliently expelling or tending to expell hydraulic fluid from the reservoir 25 into the cylinder 22. Such means may take the form of a closed air or gas nlled ball or inflated bulb 3I composed of rubber or synthetic plastic or other suitable flexible impervious material.

A seal is provided between the cylinder 22 and the piston 23 and the arrangement is such that no hydraulic fluid can leak back from the cylinder 22 to the reservoir 25 without passing through the metering orifice 21. In this manner exact control of the fluid passage is obtained. In the' specific arrangement illustrated in Fig. 1 the parts 22 and 23 are sealed to each other by means of a gasket or ring of flexible material, such as rubber or the like 32. The piston 23 is formed with a reduced-diameter upper portion or neck 33 to provide space for the sealing ring 32 between the neck 33 and the inner surface of the upper end of the cylinder 22. Preferably surfaces of the sealing ring 32 are cemented to the surfaces of the piston neck 33 and the cylinder 22 and then bonded by vulcanization.

When the engine starts up cold with any looseness of the tappet I6 between the cam I1 and the valve rod I3, the pressure bulb 3I expells oil from the reservoir 25 through the check valve 28 into the cylinder 22 in order to extend the tappet and pick up the looseness. The design is such that the pressure on the fluid produced by the bulb 3| is insufficient to counteract the strength of the spring I 5, so that no compression of the spring I is produced by the tendency of the hydraulic fluid or oil to pass from the reservoir 25 to the cylinder 22.

When the cam I1 rises the body of oil 24 is subjected to pressure by a force of the cam against the surface I8 and the tappet 32 is driven upward against the lower end 2| of the valve rod I3 so as to open the poppet valve I2. A minute amount of oil is pushed under pressure from the cylinder 22 back through the orifice 21 into the reservoir 25. However, the orifice is of suiliciently small diameter so that the small leakage of oil taking place will not prevent requisite opening of the poppet valve I2. The oil returned to the reservoir 25, however, tends to produce momentarily a slight shortening of the tappet and consequently would tend to introduce a slight clearance. Nevertheless, owing to the fact that the dwell of the cam I1 is longer in the downward position of the follower I8 than during the 90 degrees of cam rotation during which the follower I8 is caused to rise, oil is permitted to travel back through the orifice 21 and the check valve 28 to re-extend the tappet before the next upward stroke. Consequently. no clearance occurs between the tappet end I9 and the lower end of the push rod 2|, during the power stroke of the cam I1. Thus the tappet constantly hunts for its correct length without ever being out of llimits of clearance.

It will be observed that the orifice 21 is somewhat oiT-center so that there is a tendency for the oil in passing back and forth between the reservoir 25 and the cylinder 22 to introduce turbulence in a body of oil 24, thereby tendingto 4 ,g cause some flow of oil along the surfaces of the cylinder 22 to cool the cylinder.

Since the oil 24 cannot return to the reservoir 25 on the upward stroke of the stem I1 except through the orifice 21, the return flow of oil is precisely metered and constancy and regularity of operation of the poppet valve I2 in response to the operation of the cam I1 is obtained.

Preferably the arrangement is such that the hydraulic fluid 24 cannot leak around the lower edges of the open end of the piston 23 back into the reservoir 25 in order that the only flow of hydraulic fluid from the cylinder 22 to the reservoir 25 would be the metered flow through the orifice 21. This is accomplished in the arrangement of Fig. 1. However, my invention is not limited to the specc arrangement illustrated in Fig. 1. For example, as illustrated in Fig. 2 a piston 23 substantially uniform in diameter fits against the internal surface of the cylinder 22. The upper end of the piston 23' extends beyond the open upper end of the cylinder 22. In this case, however, the sealing between the cylinder 22 and the piston 23' is accomplished by means of an O-ring 34 which comprises a suitable resilient material such as rubber or synthetic compound fitted loosely in an annular channel 35 of greater normal cross-section than the O-ring 34, but of less depth than the uncompressed diameter of the ring 34.

A metering orifice 21 is provided in the inner transverse wall l26 of the piston 23' the orifice 21' being very close to the outer side wall of the piston 23'. A vent 36 is preferably provided at the upper end of the otherwise closed piston 23' for relieving air pressure above the transverse inner wall 26 and permitting oil 24 to flow freely into the reservoir 25 and flow freely therefrom through the orifice 21'.

For causing transfer of hydraulic fluid or oil from the reservoir 25 to the cylinder 22, in place of the compression bulb 3|, shown in Fig. 1, a spring 31 is provided which is arranged to push the piston 23 upward in the direction of extension of the tappet I6. The spring 31 is shown as a compression spring mounted within the cylinder 22 between the lower inner surface thereof and the lower surface of the transverse piston wall 26.

The operation of the arrangement of Fig. 2 may be similar to that of the arrangement of Fig. 1. Should any clearance occur between the cam I1 and the lower end of the valve rod 2l, the spring 31 causes the piston 23' to move away from the lower end of the cylinder 22 and to transfer hydraulic fluid from the reservoir 25 to the cylinder 22. Upon the power stroke of the cam I1 a contraction of the tappet I6 is resisted by the limitation in the quantity of oil or hydraulic fluid capable of flowing through the orifice 21'. Any requisite contraction of the tappet is provided by the slow rate of flow of hydraulic fluid through the orifice 21.

Owing to the fact that very little relative motion takes place between the cylinder 22 and the piston 23 or 23 very little flexing of the flexible bushing 32 or very little rolling of the O-ring 34 is required.

Although the foregoing description is necessarily of a detailed character, in order that the invention may be completely set forth, it ls to be understood that the specific terminology is not intended to be restrictive or confining, and that various rearrangements of parts and modifications of detail may be resorted kto'without departing from the scope or spirit of the invention as herein claimed.

I claim:

1. A self-adjusting tappet comprising a cylinder member, a piston member telescoped with said cylinder member, said piston and cylinder members having slidably engaging portions cooperating to form a hydraulic pressure chamber, said piston member having a neck of smaller diameter than said cylinder member and disposed outwardly of said slidable engaging portions, a seal of flexible rubber-like material extending between said cylinder and the neck of said piston member and bonded to each member for preventing escape from the tappet of the fluid leaking from said pressure chamber past said piston member, a hydraulic reservoir chamber formed in one of said members, said pressure chamber and reservoir chamber having a. common wall portion integral with one of said members, liquid transfer port means formed in said common wall portion for fluid transfer between said chambers, hydraulic fluid within said pressure chamber and partially filling said reservoir chamber, resilient means in one of said chambers for causing transfer of liquid through said transfer opening from the reservoir chamber to the pressure chamber to thereby allow relative movement of said members in order to increase the tappet length, the wall portions of said piston and cylinder members that define said hydraulic pressure chamber being imperforate except for said liquid transfer port means between said pressure and reservoir chambers, said fluid sealing means blocking flow of liquid out of said pressure chamber in normal operation and insuring that all uid transfer between 4said chambers occurs through said transfer means, said liquid transfer port means forming the sole fluid passage communicating with said reservoir chamber.

2. A self-adjusting tappet comprising a cylinder member, a piston member telescoped with said cylinder member, said piston and cylinder members cooperating to form a hydraulic pressure chamber, said piston member having a neck of smaller diameter than said cylinder member, a seal of flexible rubber-like material extending between said cylinder and the neck of said piston 6 member and bonded to each member for preventing escape from the tappet of fluid leaking from said pressure chamber past said piston member, a hydraulic reservoir chamber formed in one of said members, said pressure chamber and reservoir chamber having a common wall portion integral with one of said members, liquid transfer port means formed in said common wall portion for fluid transfer between said chambers, hydraulic fluid within said pressure chamber and partially filling said reservoir chamber, an inflated flexible bulb filling the remainder of said reservoir chamber for causing transfer of liquid through said transfer opening from the reservoir chamber to the pressure chamber to thereby allow relative movement of said members in order to increase the tappet length, the wall portions of said piston and cylinder members that dene said hydraulic pressure chamber being imperforate except for said liquid transfer port means between said pressure and reservoir chambers, said fluid sealing means blocking flow of liquid out of said pressure chamber in normal operation and insuring that all fluid transfer between said chambers occurs through said transfer means, said liquid transfer port means forming the sole fluid passage communicating with said reservoir chamber.

GEORGE H. HUFFERD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 21,931 Voorhies et al Oct. 21, 1941 1,623,506 Thomas Apr. 5, 1927 1,792,836 Handwerker Feb. 17, 1931 1,916,191 Burkhardt July 4, 1933 1,977,778 Rice Oct. 23, 1934 2,096,257 Moorhouse Oct. 19, 1937 2,109,815 Best Mar. 1, 1938 2,237,854 Voorhies Apr. 18,1941 2,278,963 Arola Apr. 7, 1942 2,290,479 Mercier July 21, 1942 2,325,932 Banker Aug. 3, 1943 2,404,241 MacMillan July 16, 1946

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