US2442575A - Self-adjusting tappet - Google Patents

Description

June 1, 1948. VANDERVOORT 2,442,575.

SELF-ADJUSTING TAPPET Filed May :5, 1945 IN NTO. ZOE/ NN vA/vp v0 7 A TTOENEYS Patented time i, 1948 SEW-ADJUSTING TAPPET Lorain Vandervoort, Cleveland, Ohio, assignor to The eatherhead Company, Cleveland, Ohio, a corporation of Ohio Application y 3, 1945, Serial No. 591,681

'7 Clas. (Cl. 123-90) My invention relates to tappets and concerns particularly valve tappets for gas engines.

One of the objects of my invention is to provide a self-adjusting valve tappet.

The principal object of the invention is to compensate for variations in length of valve stems or valve rods, or other operating rods for com-muni eating reciprocating motion.

It is an object of the invention to overcome lost motion in internal combustion engines, and to avoid variation of period and timin of valve opening, as well as to avoid noisy parts.

Another object is to compensate for the effect of variations in temperature on length of the valve rod, and to avoid undue loss of efiiciency of an internal combustion engine when the engine is still cool. a

More specifically, an object is to provide equally close adjustment of tappets at all engine tem peratures.

A further object is to provide self-elongation and contraction of a tappet without external connections or controls.

Still another object of the invention is to provide a tappet capable of withstanding high cam loads or pressures and having an extremely fine adjustment for taking up even the most minute clearances. l

Other and further objects, features, and advantages of the invention will become apparent as the description proceeds.

In carrying out the invention in accordance with a preferred embodiment thereof, a tappet is formed in two relatively movable parts one comprising a hollowcylinder and the other a plunger, adapted to slide in the cylinder, with a hydraulic fluid such as oil contained in chambers in the cylinder, and in the plunger. A differential piston is provided having piston heads fittin within the hollow plunger and within the hollow cylinder, and means are provided for tending to cause the hydraulic fluid to be transferred to the plunger chamber from the cylinder chamber and tending to move the difierential piston so as to push the plunger out from the cylinder and extend the tappet to take up any clearance occurring between the valve stem and the cam. A metering orifice is provided in the difierential piston for limiting the transfer of hydraulic fluid from the plunger chamber to the cylinder chamher,

If desired, a check valve may be provided in the orifice, in which case the arrangement is such as to tend to cause fiuid to be transferred from the piston to the plunger chamber through 2 the check valve for the purpose of lengthening the tappet and to return the fluid through the metering orifice for the purpose of contracting the tappet when necessary.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing, and the scope of the invention will be set forth in the claims.

In the drawing:

Fig. 1 is a longitudinal sectional view of a pop pet valve and stem with a self-adjusting tappet therefor, forming an embodiment of my invention;

Fig. 2 is an enlarged fragmentary sectional view of the portion of the apparatus of Fig. 1, showing an orifice and ball-check valve in the differential piston of the tappet;

Fig. 3 is a cross-sectional view representing a portion of the apparatus of Fig. l as out by a plane 3-3; and

Fig. 4 is a fragmentary sectional view representing a modification in a portion of the apparatus of Fig. 1.

Like reference characters are utilized throughout the drawing to designate like parts.

Referring to Fig. 1, the arrangement shown therein by way of example, comprises a portion of the casing H of an internal combustion engine such as a gasoline engine, for example, having ,a conventional poppet valve l2 controlled by a valve stem l3, or controlled by a valve rod represented by the rod l3, slidable in a suitable guide or bushing it. A valve spring i5 is provided for normally closing the valve l2 by moving the stem it in a downward direction, A tappet I6 is provided for transferring the action of a valve-operating cam H to the valve rod l3. As in conventional constructions the tappet It has a, hardened portion l8 adapted to form a cam follower ridin on the cam l1 and a; hardened upper end surface 19 adapted to contact the lower end 2! of the rod l3.

The tappet l6 comprises two parts 22 and 23 which are relatively movable longitudinally, although as will be explained hereinafter, the extent of movement is relatively limited. One of these parts, for example the part 22, takes the form of a hydraulic hollow cylinder and the other, which is the part 23, takes the form of a hollow plunger. A suitable relatively incompressible hydraulic fluid such as oil, for example, is provided for filling a chamber 24 in the cylinder 22 and a chamber 25 in the plunger 23.

The plunger 23 and the cylinder 22 are each closed at the outer end and the plunger 23 is arranged to fit slidably within the cylinder 22. There are means permitting restricted passage of the hydraulic fiuid or oil between the chambers 24 and 25. For controlling such passage of oil, a differential piston 26 is provided, having piston.

heads 21 and 23 fitting in the plunger 23 and cylinder 22 respectively. and having an inner transverse wall 21 in which a minute passageway or orifice 3| is formed for permitting metered or accurately controlled transfer of 011 above and below the differential piston.

As illustrated in Fig. 4, the orifice 3| may be a simple orifice of minute size cut in the inner the groove 33.

A similar seal is formed between the piston head 28 and the interior surface of the cylinder 22, which may take the form of an O-ring 34 in an annular groove 35 around the lower portion of the piston.

Suitable means have been provided for resiliently causing transfer of hydraulic fluid from the chamber 24 in the cylinder 22 to the chamber 25. This may be accomplished by means of the differential piston 26 with means such as a spring 36, for example, for resiliently urging the diiferential piston 26 downward with respect to hollow plunger 23. The spring 36 is shown as a compression spring mounted between the lower end of the plunger 23 and the lower piston head 28 of the difierential piston 26. Thus the spring 36 occupies the space between the main portion of the differential piston 26 and the inner surface of the cylinder 22. The spring 36 is preferably of 4 mitted. in case enable tight sealing of the valve i2 when changes in temperature of the engine or operating conditions tend to increase the length of the valve rod or push rod l3 in relation to other parts of the structure. The intermediate differential piston construction described has a novel function that facilitates manufacture of the device. It will be noted that due to the diiferential ,area piston when the tappet is being lifted by the cam, pressure in the lower reservoir 24 is smaller than pressure in the upper reservoir 25 in proportion to the ratio of the area of the upper part of the piston to the area of its lower portion. This means that the difference in pressure between highpressure chamber 25 and low-pressure chamber 24 is less than that in the conventional construction wherein the low-pressure chamber is sub- I stantially at atmospheric pressure. In my consuch strength. that taking into consideration the mechanical advantages produced by the differential action of the piston 26. the spring 36 is weaker in effect than the valve spring i5 so that there is no tendency for the spring 36 to extend tlsie tappet i6 against the force of the valve spring Considering first the action when the transverse inner piston wall 23 has ample minute orifice 3i therein, as in Fig. 4. if there should be any clearance between the cam l1 and the valve rod l3, the spring 36 forces the differential piston 26 downward and presses upward on the outer plunger 23. This creates a pressure in the chamber 24 and a vacuum in the chamber 25 causing fiuid to flow upward through the orifice 3i. This action extends the tappet l6 and takes up any clearance.

When the valve i2 is to be lifted, that is upon the pressure stroke of'the cam H. the cam follower l3 is lifted and the weight of the valve and the valve spring on the top of the plunger 23 tends to force the plunger 23 down. This causes fiuid to flow downward through the orifice 3i, forcing the piston 26 upward against the force of the spring 36. The rate of flow of the hydraulic fluid through the minute orifice 3| is restricted by the size of the orifice, and therefore prevents any appreciable contraction of the tappet. Nevertheless, gradual contraction of the tappet is perstruction the pressure differential tending to cause fiuid to pass through the minute orifice 3| on the up stroke of the tappet is materially reduced, whereby the orifice can be made larger than would otherwise be possible. It has always been difilcult to accurately machine such minute orifices and obtain exact calibration thereof. With this structure, however, due to a reduction in pressure differential, much of the difllculty of manufacture is eliminated.

It will be observed that the cam I1 is so constructed that the power or pressure stroke exists only during the time required for a quarter revolution of the cam I! to be made, namely, during the time required for the cam to advance from the point 38 to the point 38 incontacting the cam follower l8. During this time, the cam pressure opposes the pressure of the spring 36, and there is a tendency for transfer of oil back through the orifice 3i from the chamber 25 into the chamber 24. The cam follower i8 is permitted to fall during the time required for the cam H to rotate through from the point 33 to the point 4i, and the cam follower dwells during the of rotation from the point 4i to the point 38. Consequently, during the three-quarters of the revolution of the cam l1, the spring-pressed piston 26 is free to expel oil from the chamber 24 into the chamber 25 for the purpose of extending the tappet and taking up any clearance. Thus the plunger 23 is at all times kept adequately filled to extend the tappet IS the amount required to overcome any clearance between the push rod i3 and the cam l1. Conesquently, the tappet l3 constantly hunts for its correct length and any changes in operating conditions, temperature, or wear of the parts which might cause clearance to be increased or decreased in the case of a tappet of fixed length are compensated by the selfcompensating or self-adjusting tappet arrangement.

When the parts of the tappet are assembled, the cylinder 22 is first filled with oil, the piston 26 is then forced to the bottom in the cylinder 22 to exclude oil from below the piston. Next the plunger 23 is filled with oil and pushed into the body over the piston 26 and the spring 36. This lifts the piston and excludes air from the plunger 23. The unit may of course also be filled with oil by placing all the parts under oil during the assembly operations to avoid entry of air.

Owing to the fact that the dwell on the cam circle is of longer duration than the pressure stroke of the cam 33. the clearances are substantially taken up at all times because oil isfrge to fiow into the chamber 24 to extend the tappet it should be necessary. in order to I duced in connection with the orifice 3|. Such an arrangement is illustrated in Fig. 1, and Fig. 2 shows the arrangement enlarged.

. When a valve check is to be employed as illustrated, the transverse wall 29 of the piston 28 is formed with a ball-receiving recess 42 therein with a constricted lower opening 3i, having a valve seat 44 at the upper end thereof at which a ball check 45 is adapted to rest. For retaining the ball check 45 in the recess 42, a retainer such as a bent sheet-metal cover 46 is pressed into the recess 42. In order to permit slow bleed-down of fluid from the chamber 25 to the chamber 24 when the tappet is loaded, a nick 41 is provided in the valve seat 44. A relatively large opening 48, preferably off-center, is provided in the top of the cover 46 to permit oil to fiow upward around the valve-check 45 when the tappet is unloaded for the purpose of refilling the chamber 45 and extending the tappet length.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle of operation and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possble, and I aim therefore to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims.

I claim:

1. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed end projecting from the open end of the cylinder, said cylinder and plunger having unequal intemal bores, the cylinder bore being greater, a hollow differential piston in .said plunger having piston heads fitting said bores, and a transverse wall with an orifice therein, fluid in said cylinder, plunger and piston, and a spring exerting separating force between said plunger and said piston for extending said tappet.

2. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed end projecting from the open end of the cyli der, said cylinder and plunger having unequal ternal bores, fluid in said bores, a diflerentialfpiston having piston heads fitting said bores and an orifice providing fluid passage from one bore to the other, and means for causing transfer of fluid from the larger bore to the smaller and causing tappet extension.

3. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed end, projecting from the open end of the cylinder, said cylinder and plunger having unequal internal bores, the cylinder bore being greater, a hollow differential piston in said plunger having piston heads fitting said bores and a transverse wall with an orifice there- 6 in, and fluid in said cylinder, plunger and piston.

4. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed end projecting from the open end of the cylinder, said cylinder and plunger having unequal internal bores, the cylinder bore being greater, a hollow difierential piston.

in said plunger having piston heads fitting in said bores and a transverse wall with an orifice therein, fluid in said cylinder, plunger and piston, said piston heads having annular grooves therein, and O-rings composed of resilientmaterial fitting in said grooves for sealing said piston heads, said O-rings having a smaller cross-section than the said annular grooves, but having a greater normal diameter than the depth of said grooves.

5. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed and projecting from the open end of the cylinder, said cylinder and plunger having unequal internal bores, fluid in said bores, a diiierential piston having piston heads fitting said bores, and an orifice providing fiuid passage from one bore to the other.

6. A tappet comprising in combination a cylinder closed at one end, a hollow plunger in said cylinder having a closed end projecting from the open end of the cylinder, said cylinder and plunger having unequal internal bores, fluid in said bores, a differential piston having piston heads fitting in said bores and a transverse wall with a check valve providing fluid passage from one bore to the other, and means for causing transfer of fiuid from the larger bore to. the smaller for causing tappet extension, said check valve comprising an opening in said tranverse wall, a ball check therein, and a seat for said ball check having a nick at the edge thereof for providing slow rate bleeding from the smaller boreto the larger bore when the tappet is loaded, said opening providing a quick flow away from said seat for permitting rapid clearance takeup by said tappet.

7. A tappet for disposal between a valve stem and an actuator, said tappet comprising telescoping hollow members forming a fluid-tight chamber, a difierential piston engaging the inner wall of each of said members, the valve stem end of the piston having the smaller area, and a bleed orifice in a wall of said piston establishing fluid communication between opposite ends thereof whereby the net pressure tending to transfer fluid from the small end to the large end of the piston is less than the pressure at its small end.

- LORAIN VANDERVOORT.

REFERENCES CITED UNITED s'rA'ra's PATENTS Number Name Date 2,065,081 Lee Dec. 22,1936 2,072,437 Wurtele Mar. 2, 198"! 2,109,815 Best Mar. 1, 1988 55 2,325,932 Banker Aug. 3, 1948 Voorhies Mr. 11. 1944

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