US2116109A - Tappet - Google Patents

Description

E. J. FISK TAPPET Filed July 18, 1935 INVENTOR.

Patented May 3, 1938 UNITED vSTATES TAPPET Edwin J. Fisk,

Cleveland, Ohio VApplmtiom July 1s, 1935, serial No. 32,049

8 Claims.

The principal object of this invention is to provide a device adapted to serve as an interponent between spaced reciprocating parts, which interponent will automatically change in length to compensate both for shrinkage and elongation of the space in which it is adapted to operate.l

A specific object is to provide an improved automatically adjustable valve tappet, and more specifically one that operates mechanically, as distinguished from hydraulically, pneumatically, etc. Such a device has a present need in that it will, for` example, permit tappets to be placed in an engine without requiring any initial adjustment.

A further object is to provide, in connection with a valve operating mechanism, means for insuring that the valve stem and tappet will remain in contact at all times, although unconnected, and irrespective of the provision of operating clearance, so that the resulting impact noise, as this space is taken up in opening the valve, will be less noticeable by reason of occurring in an enclosed part of the engine ordinarily supplied with suflicient lubricant, as fluid or mist to dampen the noise.

A further object is to reduce valve surge in an internal combustion engine.

Other objects and features of the invention will become apparent from the following description relating to the accompanying drawing, showing preferred embodiments.

In the drawing, Fig. 1 is a sectional View of an internal combustion engine valve mechanism assembly, including an embodiment of my invention in the form of a tappet; Figs. 2 to 4 are sectional views, taken as indicated at 2-2 on Fig. 1, showing one form of tappet in various illustrative operating positions of its parts; Figs. 5 and 6 are transverse sectional views, as indicated at 5-5 and 6-6 respectively on Fig. 1; Fig. 'l is a central longitudinal sectional view of a modified form of tappet; Fig. 8 is a side elevation of an adjusting cam (one of the tappet parts of Figs. 1 and 7), and Fig. 9 is a sectional view corresponding to Fig. 2, showing still another modified form of tappet.

As embodied in a valve tappet or push rod, the illustration (Fig. 1) shows the tappet assembly I adapted to operate in a suitable smooth i bore B in the engine block or a bracket thereon.

The lower end of the assembly l is adapted to engage an operating cam C' or other valve operating means and the upper end is arranged to engage the lower end of the valve stem c in a manner to successively unseat and release the (Cl. 12S- 90) valve `V which latter isclosed or seated by the usual spring S, as the cam rotates in contact with the tappet-,all `as is well known. The spring S in automobile engines, usually exerts from between fty to; eighty poundspressure, applied as against a Washer W, e. g. tending to close the valve.

A predetermined operating clearance of from .006 to .008 is ordinarily provided, and this occurs between the top of the tappet and the bottom end of the valve stem, so as toenable full seating of the valve when the valve stem and tappet are lengthened, as by increased engine heat. This clearance-has to be set with great care, for if the clearance is too small, then full seating will not` obtain under high temperature conditions, and iftoo great, the engine becomes noisy in operation, and the valves do not open to the extent they should. The illustrated embodiments, (see first Figs. 2 to 4) effects the necessary takeup when the spacebetween the valve stem and the cam e. g. contracts-as when the engine is hotand the necessary expansion to compensate for shortening of the stem and tappeton cooling e. g., as will now be shown.

The main tappet body comprises an elongated cylindrical block of suitable metal 5, having an appropriately hard, lower face 6 adapted to ride on the cam. The body slides freely in the cylindrical bore of a sleeve 1, which fits snugly in the bore B forming the tappet guide. the desired friction between the guide and sleeve, the latter may be made to have a push fit in the guide or may, for further example, be appro,- priately split, so that it may expand in the guide. If the sleeve is split for its whole length, this may be done longitudinally (see la) at one side only (as illustrated) or it may be split at various places for partr of its length either longitudinally or diagonally or in any other fashion that may be found effective.

Any otherl known or suitable expedient may be used to` insure that the sleeve 1 will move less readily in its bore than does the body 5 in the bore of the sleeve. I prefer to utilize vthis dfferential in effecting the automatic adjustment, as will be later shown.

Near its upper end the body 5 has a central bore 8 adapted to freely slidably receive a plug l0 of suitable material, preferably operatively identical with that of the valve stem.

The body 5 also has a transverse slot I2 for receiving the `adjusting cam or cams and this slot may extend to the top` of the body (as shown). The planar side and bottom surfaces of the slot To secure indicated at I3 and I 4 are accurately finished to respectively support and embrace a cam member I5, which moves freely in the slot and has an upper cam surface I5a engaging the lower end surface I a of the plug I0 (or the lower end of the valve stern, as desired), and a lower cam surface Ib adapted to ride on the planar bottom surface I4 of the slot. The cam may be maintained in position in the block 5 for vertical floating movement in the slot I2 by a cross-pin IT formed thereon or disposed in a transverse bore of the cam, the ends of the pin extending laterally from the cam into accurately fitting sliding contact with respective slots I9, positioned transversely of the slot I2 and extending beyond the upper Y and lowermost operative positions of the'cross pin.

The slots I9 (as shown) are open at the top of the body.

To operate the cam by relative movement of the body and sleeve a portion of the cam isformed into an arm I6 which may have a cylindrical head 2D adapted to fit into a lateral guideway 2I in the wall of the sleeve 1. As shown, the wall protrudes inwardly somewhat toradially amplify the guiding surfaces and permit a considerable angular movement of the cam arm' without disengaging the head from its guide. This inwardly protrudingrportion` of the Wa'll of thesleeve 'IV may be formed as a punching operation, thus affording the necessary surface amplification and finish to suitably fit the cylindrical head ofthe cam arm. Appropriate clearance is provided at 22 for the inwardly protruding portion of the` sleeve when the parts arev in the relative position shown in Fig. 4 e. g. c l

The connection between the camr arm and sleeve may, of course, comprise a cross-pin in the sleeve and a yoke formation in the end of the arm, (not illustrated). t Y

It is obvious that aspthe body 5 moves with relation to the sleeve, the effective tappet length is increased or diminished, depending. on which way the cam is rotated. Y

As shown in Figs. 2 to 4, the movement of the body 5, with reference to theV sleeve 'I, in a downward direction, is resistedby a suitable compression spring 25 which,Y is interposed between the upper end of the sleeve 1 and a suitable shoulder,

Y formedas by a split ring 26, seated' in a groove 2I in the top portion of thebody 5.

VAn. illustrative cam shape isV shown inV Fig. 8, wherein it will be noted that the lower curve surface I 5b is formed as an arc generated about a point I5c lying eccentric tov-theaxis of the crosspin I'I on one side and the upper curve surface I 5a is generated as an arc, struck about the point |5c offset from the axis of the pin onV the opposite side from said. axis, projections of the arcs being indicated by broken lines at' I5d and I 5d. Alternatively the cam curve may be generated as an involute suggested by the broken Iinebeginning say where the line vI5cl intercepts the hori- Zontal axis-of the cam. The cam surface may be altered to suit practical conditions, and as shown, is developed to produce as much as lAg variation in the effective length of the tappet, which, in actual practice at the present time, wculdnot be necessary.

The modification illustrated Yin Fig. '7 is only with reference tothe manner in which the spring 25Yis secured at its upper end. Otherwise, the ligure shows the previously described tappet' in longitudinal central section,.the plane of which it as right angles to. that of Fig. 2. Since the plug I0 bears upwardly at all times on the valve stem, this may be provided with a suitable rigid head, as at I Bd, and overhanging flange Ille abutted by the spring. Thus the opposite end of the spring constantly tends to urge the sleeve downwardly and to rotate the cam in a manner to relatively elongate the tappet assembly.

Referring to the modication shown in Fig. 9, it Will be noted that the body member 5', lying within the sleeve l', has a reduced portion or stem 30 extending below the cam-carrying slot, and'that thesleeve has its wall partially in spaced relation to the stem and is provided below said space with an inwardly extending flange 3l, having a central opening in sliding contact with the stem. This provides a space inside the tappet assembly for a spring 25 which is in operative effect identical with the spring 25.

It will be further noted that the wall of the sleeve I is made considerably thicker than the wall of thesleevel, previously described, thus affording adequate radial bearing surfaces for the head 29' of the'cam" I5'. The cam I5' in this instance is shown as comprising two operatively identical parts which may, as above mentioned, be made so that one straddles the other or which may be disposed side by side. The lower end of the valve stem o rests, as shown, directly on the upper cam surfaces. g

If it is desired to amplify the valve-operating cam-contacting surface of the lower endv of the body, any suitable arrangement of the head vfor the stem 30 may beprovided. Preferably' a head member 35 is attached to theV lower end ofthe stem, the head having the desired chilledbottom surface (if cast iron) or being otherwise made suitably hard for engagement with the cam. The head has a socket on its top side for receiving the stem 30, rand preferably the stem 3IJ is made oversizedY and is attached by being packed in frozen carbon dioxide orv other suitable chemical to reduce its diameter to an extent such that it willeasily `slip into the socket of the head. Thereafter, under operating temperatures the jointbetween the stern 30 and headV 35 will be sufhciently tight so that there is no possibility of the Vhead coming loose in service. This feature is obviously applicable toconventional mushroom Ytype tappets. Y Y

V'I'he head35. in the position thereof shown, prevents disassembly of the tappet because the body. may not be moved upwardly far enough with respect to the sleeve to permitdisengagement of the cam heads from their guiding slots in the side walls of the sleeve 'I'.

The manner of assembling the tappet in the form shown in Fig. 2, for example, may be best understood from reference to Fig. 4. Assuming that the spring and its retaining ring 26 has not been lattached to the body, the body is insertedupwardly into the sleeve 1, and then, with the-sleeve and body in the relative position shown inrFig. 2 or 3, the cam or cams may be lowered into position in the slots VI2 and I9 untilthe head or heads 20 are horizontally opposite the guide slot or slots 2I, whereupon the head is, or heads are, swung outwardly into engagement therewith by further lowering of the cam or cams. 'Ihereafter the spring 25 is slippedrover the top of the body and the slit ring 25 expanded and seated in its groove. The tappet remains in assembled condition during shipment without special attention, other than to provide for retaining the separate plug I0 (when used) in place in its bore. At such times the spring holds the body and sleeve relatively extended-about as shown utility in valve tappets irrespective of whether in Fig. 4. y

The operation' is as follows: Assuming that the valve is closed (see Figs. 1 and 2) and that the operating cam C is about to raise the tappet to' openv the valve. It will be seen that during the preceding rest` period the spring 25 will have'acted through the cam I5vto take up all clearance and hold the tappet longitudinally expanded to fill all the space between the valve stem and cam. The spring does this whether its reactions are takenup by the body 5 or by the valve stem (throughthe plug If) e. g. as in Fig. '7). The spring action is merely one of shoving the sleeve down to turn'thecam I5 counter-clockwise, and this accomplishment requires very little spring strength on account of the mechanical advantage afforded by the cam arm and cam.

As the high point of the valve operating cam C now operates to raise the tappet assembly and valve, the cam I5 is definitely locked` against turning, partly by reason of the close proximity of the respective loci of the cam axes to the tappet axis, and partly by reason of the frictional force (braking action) of the surfaces I4 and Illa of the body and plug respectively bearing on the cam with the full force of the valve spring S.

As the high point of the cam C passes the tappet axis the travel of the tappet is reversed, but the valve spring continues to maintain braking pressure on the cam I5, the same as it did during upward travel of the valve, and therefore (except as hereinafter pointed out) the acquired length of the tappet remains the same.

Now, assuming that there has been an alteration in the length of the valve and tappet assembly by which the stem becomes in effect too short (as by expansion of the engine block relative to the valve and tappet assembly and/or by reason of wear between the cam and tappet), the spring will again act after the concentric or low surfaces of the cam C are adjacent (but not in contact with) the lower end of the tappet body, to elongate the tappet and take upv all play and thereafter the acquired length will be positively held as already described.

Now, assuming that wear has occurred between the valve and valve seat or that the valve stem or tappet is expanded by heat and the tappet assembly thereby becomes in effect too long, it will be seen that this must be compensated for or the valve cannot properly seat, and the valve seat surfaces will become unserviceable (burned). The tappet in such case automatically shrinksin length as follows:

Assuming the cam is operating at high speed, as during normal running speed of the engine, the valve is actually kicked, not gradually lifted to open position. This normally either throws the valve stem out of contact with the tappet or the tappet out of contact with the cam and braking pressure on the adjusting cam I5 is momentarily relieved at a time when the valve commences to close` The valve spring, however, acts through the valve stem and parts I and I5 to move the tappet body toward the cam C. At such time the drag of the sleeve 1 in its guide operates to turn the cam I clockwise a slight amount, shortening thetappet. Now, if on full vseating of the valve there is no clearance to take up, the tappet will remain in effect shortened by said action of frictional drag just mentioned.

A feature of the invention that is of general or not automatic adjusting means is present is the snubbing action of the outer wall surface of the tappet' on theguide bore. This when used in connection with a tappet ci' conventional construction maintains the effective upper end of the tappet in contact with the lower end of the valve stem at all times, so that (in the event of clearance) the noise occurring when the play is taken up as at the beginning of the valve lifting stroke of the valve operating cam, will be dampened because of occurring `in an enclosed and oil bathed partv of the engine,` namely thev cam and cam shaft housing.

Such snubbing is also effective in reducing what is known as valve surge or utter.

Valves in existing engines have a tendency tol valve and tappet guide walls on the respective parts guided thereby. The braking action of the tappet on its guide wall (whether secured by expansion as of a split sleeve or original push fit of the sleeve in the guide bore) reduces this valve utter, rebound or surge to an appreciable extent.

I claim:

1. A clearance take-up device comprising two members and respective means slidably guiding them for movement parallel to each other, means to cause one of the members to slide less freely in its guiding means than does the other in its guiding means, and means operatively connected with both said members and reacting to change the effective length of the device consequent upon lagging of the less freely slidable member relative to the other member.

2. In an internal'combustion engine having a valve and operating means therefor, a tappet comprising a body and a sleeve in which the body slides, said sleeve being slidable in a suitable guide on the engine, frictional means for causing the sleeve to lag behind the body, adjusting.

means actuated by the lagging movement of the sleeve to decrease the effective length of the tappet, during a portion `of its operating cycle, and a spring acting on said adjusting means to increase said effective length during another portion of said cycle.

3. A clearance take-up device comprising two members and means guiding them for substantially synchronous normal movement, means to cause one of the members to move less freely than does the other, and means operatively connected with the less freely movable member', and moved thereby consequent upon lagging in movement of the less freely movable member relative to the other to change the effective length of the device.

4. In a valve mechanism, a tappet guide, a valve tappet comprising a body and a sleeve in which the body slides, said sleeve being also slidable in the tappet guide, fricticnal means between the sleeve .and guide for causing the sleeve to lag behind the body, and means associated with the body and connected With the sleeve and actuated by the lagging movement of the sleeve, said means tending to increase the effective length of the tappet in one direction of movement thereof, and tending to decrease the direction.

5. An adjustable length interponent for spacedV parts, one of which is reciprocated by the other,

comprising two telescoping elements', the outerof said elements being slidably mounted ina guide, the inner element being slidable in the outer element, the outer element having greater Irictional resistance to sliding in its guide than the inner, and means operated by said frictional differential to change the effective length of the interponent at a predetermined portion of the reciprocating movement of the reciprocating part.

6. An adjustable length interponent for spaced parte, one of which is reciprocated by the other, comprising a sleeve having a guide, a body slidable in the sleeve, said body having less resistance to sliding in the sleeve than does the Sleeve in its Y guide, one of said parts operatively engaging the body, a cam carried on the body and having an arm connected with the sleeve so as to be operated by relative movement of the sleeve and body,

the other of said parts operatively engaging the cam formovement,` thereby longitudinally of the interponentwhen the interponent is bodily moved to transmit reciprocating movement to the said reciprocated part. Y

7. An adjustable length interponent for spaced parts, one of which is recprocated by the other, comprising a sleeve having a guide, a body slidable in the sleeve, one of saidv parts operatively engaging the body, a cam carried on the body and having an arm connected with the sleeve, a spring bearing onthe sleeve and acting to turn the cam through said arm, the other of said parts operatively engaging the cam for movement thereby longitudinally of the interponent When the interponent is bodily moved to transmit reciprocating movement tol the reciprocated part.

8. A valve tappet 'comprising axially relatively movable parts'and a cam operatively interposed between them and adapted to be turned to so move said parts for lengthwise adjustment of the tappet, an expansible sleeve forming a guide for one of said parts and adapted to operate in relatively tight frictional engagement with a tappet guide bore of an engine, said sleeve having an operating connection with said cam, said cam being rendered Vactive to move said parts, as stated, consequent upon relative axial movement of the sleeve and the part guided thereby.

' EDWIN J. FISK.

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