US2442566A - Self-adjusting tappet - Google Patents

Description

June H, 3948. 5, H, HUFFERD 2,4256

SELF-ADJUSTING 'rAPBET Filed April 19, 1945 INVENTOR. 650E675 H- HUFFEIED A TT'OENEYS Patented June 1, 1948 sELF-anms'rmo 'rarra'r George H. Hniierd, Shaker Heights, Ohio, assignor to The Weather-head Company, Cleveland. Ohio, a corporation of Ohio Application April 19, 1945, Serial bio. 589,235

1 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 com- 1 Claim. (01. 123-90) I pensate for variations in length of valve stems,

valve rods or other operating rods for communicating reciprocating motion.

It is an object of the invention to overcome lost motion in internal combustion engines and to avoid variation of period and timing of valve opening as well as to avoid noise and wear of loose parts.

Another object is to compensate for the eil'ect of variations in temperature on length of the valve rod and to avoid undue loss of efllciency of an internal combustion engine when the engine is still cool.

Morespeciflcally, an object is to provide for close adjustment of tappets while the engine is cool as well as when heating up.

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

Stillanother object is to provide reliable selfcontained hydraulic compensation for tappets in which paths for uncontrolled leakage of hydraulic fluid are eliminated.

A further object is to provide hydraulic compensation for a tappet in which passage of hydraulic fluid from one part to another of the tappet is limited to predetermined means for metering the flow.

An object of my invention is to provide a selfadjusting tappet which will take up clearance between the valve stem and cam regardless of the operating temperature of the engine.

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

' vided for causing the hydraulic fluid to be transferred from the reservoir to the cylinder tending to push the sleeve out from the cylinder and to extend the tappet to take up any clearance occurring between the valve stem and the cam.

A better understanding of the invention will be aiiorded 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 appended hereto,

, In the drawing:

Fig. 1 is a longitudinal sectional view of an embodiment of my invention;

Fig. 2 is an enlarged detailed fragmentary view of a portion of th apparatus shown in Fig. 1; and I Fig. 3 is a view of the cross section represented as cut by a plane in Fig. 1.

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

Referring to Fig. 1 the arrangement shown therein by way of illustration comprises a portion of a casing II for an internal combustion engine such as a gasoline engine for example, having a conventional poppet valve [2 controlled by a valve stem l3 or controlled by a valve rod represented by the rod l3 slidable in a suitable guide or bushing I 4. A valve spring I5 is provided for normally closing the valve l2 by moving the stem la in the downward direction. A tappet I6 is provided for transferring the action of a valve operating cam IT to the valve rod l3. As in conventional constructions the tappet I 6 has a'hardened portion l8 adapted-to ride on the cam l1 and a hardened surface [9 adapted to contact the lower end 2| of the rod [3.

The tappet l6 comprises two parts 22 and 23 i which are relatively movable longitudinally, although, as will be explained hereinafter, the extent of movement required is relatively limited.

One of these parts, for example, the part 22, takes the form of an hydraulic cylinder and the other which is the part 23 takes the form of a sleeve. A suitable relatively incompressible hydraulic fluid 24 such as oil, for example, is provided for filling the cylinder 22, and a reservoir 25 is formed in the sleeve 23. for supplying oil to the cylinder 22 to extend the tappet length.

The sleeve 23 has a substantially cylindrical outer surface adapted to fit the inner surface of the cylinder 22 and is provided with an inner transverse wall 26 having a very small aperture, orifice. or constricted opening 21 therein for permltting transfer of hydraulic fluid between the cylinder 22 and the reservoir 25. The opening 21 is so minute that the passage of oil or other fluid is metered or accurately controlled.

For closing the upper end of the sleeve 23 above the reservoir 25 a piston 28 is provided and to facilitate manufacturing and assembling operation a screw cap 29 having the hardened top surface is may be provided at the upper end or the sleeve 23 to form the top of the tappet I 8, The cylinder 22 is closed at the lower end. Suitable means are provided for sealing the piston 23 in the sleeve 23 such as an O-ring 3| composed of resilient material such as rubber or synthetic composition fitted in an-annular groove 32 around the piston 23 of greater cross section than the sealing ring 3|. In unflexed or uncompressed condition the resilient ring 3| has a diameter greater than the depth of the groove 32.

A similar seal is formed between the sleeve 23 and the cylinder 22 which may take the form of an O-ring 34 in an annular groove 35 around the portion of the sleeve 23 at which th transverse wall 26 is located.

Suitable means are provided for resiliently expelling or tending to expel hydraulic fluid from the reservoir into the cylinder 22. This may be accomplished by means of the piston 23.

For forcing the piston 23 downward upon the top surface of the body or oil in the reservoir 25 suitable means are provided such as a compression spring 33 between the screw cap 33 and the piston 28. The spring 33 is preferably weaker than the valve spring ii.

If these should be any clearance between the cam l1 and the valve rod 13 the spring 33 forces the piston 28 downward expelling hydraulic fluid from the reservoir 25 through the orifice 21 into the cylinder 22. This action extends the tappet l6 and takes up any clearance. Upon the pressure stroke of the cam 11 the cam follower ll is lifted and the oil pressure forces the sleeve 23 up together with the cylinder 22.

The rate of flow of hydraulic fluid through the minute orifice '21 is restricted by the size of the orifice and therefore prevents any appreciable contraction of the tappet. Nevertheless, gradual contraction of the tappet is permitted in case it should be necessary in order to enable tight seating of the valve l2 when changes in temperature or the engine or operating conditions tend to increase the length of the valve rod or push-rod i3 in relation to other parts of the structure.

It will be observed that the cam I1 is so constructed that the power or pressure stroke existsonly during the time required for a quarter revolution of the cam I'I to be made, namely during the time required for the cam to advance from the point to the point 31, in contacting the cam-follower 13. During this timthe cam pressure opposes ,the pressure of the spring 33 and there is a .tiihdency for transfer of oil back through the orifice 27 from the cylinder 22 into the reservoir 25. H

. The cam follower I3 is permitted to fall during the time required for the cam 11 to rotate through the degrees from the point 31 to the point 38, and the cam follower dwells during the degrees of rotation from point 33 to the point 36; conscquently,- during three-quarters of the revolution of the cam 11 the spring-pressed pistom 29 is free to expel oil from the reservoir 25 into the cylinder 22 for the purpose of taking up any clearance. Thus the cylinder 22 is at all times kept adequately filled to extend the tappet I 5 the amount required to overcome any clearance between the push rod l3 and the cam II.

It is understood by those skilled in the valve vart that due to inertia of the valve and main spring, the valve tends to resist the closing action or the main spring on its down stroke, but the main valve spring is often made strong enough to overcome the inertia of the parts and cause the valve stem to engage the tappet during the 4 closing stroke of the valve. Since, as described above, the tappet will lengthen during threequarters of a. revolution of the cam, i. e., during closing of the valve as well as during the dwell period, it is obvious that the tappet spring 33 should be such that the force tending to lengthen the tappet is greater than any'force that may be exerted by the valve stem On the tappet as the valve closes. -Thus 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 self-compensating or self-adjusting tappet arrangement.

While I have described my invention as embodied in concrete form andas operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claim.

What is claimed is:

In a self-adjusting tappet for interposition bedraulic chamber, a hydraulic fluid reservoir chamher formed in one of said members, a sealed spring pressed plunger slidahl'e in saidreservoir chamber and urged to reduce the reservoir volume, said hydraulic chamber and reservoir chamber having a common wall portion, restricted fluid transfer passageway means in said common wail portion provlding'the sole means-of fiuid communication between said chambers and arranged so that the area of the restriction to fluid transfer between said chambers is the same in either direction, there being a quantity of fluid transferred from said hydraulic chamber to said reservoir chamber by relative motion between said members during the lift stroke to shorten the tappet, said relative motion of the said members being hydraulically restrained during the entire lift stroke, the spring pressed piston in said reservoir transferring a sufiicient quantity of fiuid from said reservoir chamber to said hydraulic chamher during the balance of the cycle to lengthen the tappet and take up the clearance between the tappet and the associated valve and valve lifter.

GEORGE H. HUFFERD.

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

' UNITED STATES PATENTS Number

Images