US2460651A

US2460651A - Self-adjusting tappet

Info

Publication number: US2460651A
Application number: US591577A
Authority: US
Inventors: Paquin Joseph Norman
Original assignee: Weatherhead Co
Current assignee: Weatherhead Co
Priority date: 1945-05-02
Filing date: 1945-05-02
Publication date: 1949-02-01
Anticipated expiration: 1966-02-01

Description

Patented Feb. 1, 1949v SELF-ADJUSTING 'TAPPET Joseph Norman Paquin, Euclid, Ohio, assignor to The Weather-head Company, Cleveland, Ohio,

a corporation of Ohio Application May 2, 1945, Serial No. 591,577

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. p

The principal object of the invention is to compensate 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.

3 Claims. (Cl. 123-90).

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.

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

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

Still another 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 pre-determined means for metering the flow.

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

Still another object of my invention is to provide improved sealing arrangements for movable pistons and plungers.

Still another object is to provide improved methods and apparatus for producing an orifice or opening of accurately determined, very minute, cross-section in a thick wall, sheet, plate or the like. It is, also, anobject to provide an improved arrangement for reducing the size of orifices.

Other and further objects, features, and advantages of my 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 hollow cylinder, and the other a hollow piston adapted to slide in the cylinder with a hydraulic fluidsuch as oil contained in the cylinder and in a reservoir formed in the piston. Means are provided for' causing the hydraulic fluid to be transferred from the reservoir to thecylinder, tending to push the piston out from the cylinder and to extend the tappet for taking up any clearance occurring between the valve stemand the cam.

The piston has an inner transverse wall or base with an opening therein for enabling the fluid to be transferred between the reservoir in the piston and the cylinder. Preferably a relatively minute opening or orifice is utilized which is formed by drilling a hole in the base of the piston and inserting a plug which has been flattened on one side to leave an orifice. The orifice is preferably near a side wall of the piston for the purpose of introducing turbulence and coolin effects in the hydraulic fiuid or oil.

Suitable means such as liners or sac-like membranes of rubber. or other suitable flexible material are provided for the piston reservoir and the cylinder to overcome any tendency for leakage of the hydraulic fluid, or a seal may be provided between the cylinder and the piston.

A better understanding of the invention will be afiorded 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 an embodiment of my invention;

Fig. 2 is a fragmentary sectional view of a portion of the base of the piston of the tappet shown in Fig. 1;

Fig. 3 is a fragmentary sectional view representing a portion of the apparatus as cut by a plane 3-3 indicated in Fig. 2; and

Fig. 4 is a sectional view of a tappet employing flexible sacs in the cylinder and the piston reservoir.

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

Referring to Fig.- 1, the arrangement shown therein by way of illustration comprises a portion of a casing I I for an internal combustion engine, such as a gasoline engine, for example, having a conventional poppet valve l2 controlled by valve stem I 3 or controlled by valve rod represented by the rod i3 slidable in a suitable guide or bushing I4. A valve spring I5 is provided for normally closing the valve i3 by moving the stem l3 in a downward direction. A tappet I6 is provided for transferring the action of a valve-operating cam H to the valve rod i3. As in conventional constructions, the tappet l6 has a hardened lower surface I3 adapted to ride on the cam I! and a hardened upper surface I9 adapted to contact the lower end 2! of the rod N. The tappet I 6 comprises two

parts

22 and 23 which are relatively movable longitudinally although the extent of movement required is relatively limited. One of these parts, for example, the part 22, takes the form of a hydraulic cylinder, and the other which is the part 23 takes the form of a hollow piston. A suitable relatively incompressible hydraulic fluid such as oil, for example, is provided for filling the cylinder 22, and a reservoir 25 formed in the piston 23 for supplying oil to the cylinder 22 to extend the tappet length.

The piston 23 and the cylinder 22 areeach closed at the outer end, and the piston 23 is pro- 4 between the com I? and the valve rod l3, the spring 36 forces the piston 35 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 I1,

' the cam follower I8 is lifted, and the oil pressure vided with an inner transverse wall 26, which 4 may be at the base of the piston 23. There are means permitting the restricted passage of the hydraulic fluid or oil between the reservoir and the cylinder 22. For this purpose a minute passageway 21 is formed in the transverse wall 26, permitting metered or accurately controlled transfer of oil to the reservoir 25 from the cylinder 22.

Suitable sealing means are provided for preventing leakage of oil from the cylinder 22 ex cept through the orifice 21 and for, likewise, preventing escape of oil from the reservoir 25 except through the orifice 21 into the cylinder 22. For example, as illustrated in Fig. 4,

liners

26 and 23 may be provided in the cylinder 22 and the reservoir 25 respectively for sealing the oil in the respective chambers. The liners 28 and 29 are preferably composed of a suitable flexible rubberlike material such as rubber or composition sheeting. The liner 28 is formed as a continuous sac with an opening or mouth having a bead adapted to snap into an annular groove 32 around the lower edge of the piston 23 for sealing the sac 28 to the lower surface of the piston 23. The liner 29 comprises a sac having an opening or mouth 33 with a lip 34 around the orifice 2'! sealed to the upper surface of the transverse piston wall 26 preferably by cementing and bonding by vulcanization.

Suitable means are provided for tending to cause transfer of oil from the reservoir 25 to the cylinder 22. Such means may take the form of an arrangement for resiliently expelling oil from the reservoir 25. For example. a pressure plate or plunger 35 maybe provided above the upper end of the reservoir liner or sac 29 with a biasing spring 36 serving to press the plunger 35 downward for expelling oil from the reservoir 25. Preferably, a cap 31 is provided for closing the upper end of the hollow piston 23 and facilitating the assembling of the apparatus with the spring 36 in the space between the cap 31 and the plunger.

The piston 23 is arranged to be slidable within the cylinder 22 at the open or upper end thereof. However, the required extent of movement is relatively slight inasmuch as the apparatus is originally designed to occupy very nearly the entire space between the cam if and the lower end of the push rod 2|. The tolerances or variations in clearance to be taken care of represent relatively slight movement of the piston 23 within the cylinder 22, consequently relatively little flexing of the upper portions of the liners or the sacs 28 and 29 is required.

The spring 36 is preferably weaker than the valve spring 15. If there should be any clearance forces the piston 23 up together with the cylinder 22.

The rate of fiow of the hydraulic fluid through the minute orifice 21 is restricted by the size of the orifice, and prevents any appreciable con.- traction of the tappet. Nevertheless, gradual contraction of the tappet is permitted in case it should be necessary in order to enable tight sealing of the valve l2 when changes of 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.

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 H to be made; namely, during the time required for the cam to advance from the point 38 to the point 33 in contacting the cam follower 16. During this time the cam pressure opposes the pressure of the spring 36 and there is a tendency for transfer of 011 back through the orifice 21 from the cylinder 22 into the reservoir 25.

The cam follower I3 is permitted to fall during the time required for the cam l! to rotate through the from the point 39 to the point 40. The cam follower dwells on the base circle during the of rotation from the point 60 to the point 38. Consequently, during three-quarters of the revolution of the cam I! the springpressed piston 35 is free to expel 011 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 6 the amount required to overcome any clearance between the push rod l3 and the cam l1. Thus the tappet l6 constantly hunts for its correct length and any changes in operating conditions, temperatures, or wear of the parts which might cause clearance to increase or decrease in a tappet of fixed length are compensated by the self-compensating or self-adjusting tappet arrangement.

For obtaining the requisite sturdiness and durability of the apparatus, it stands to reason that the inner-transverse wall or base 26 of the piston 23 will be of relatively heavy construction or thick in comparison with the diameter of a round orifice which would be sufliciently small. To drill an orifice of such minute diameter through the thick wall 25 would be relatively difficult. Accordingly, for the sake of increasing the precision with which the orifice cross-section is fixed and the ease with which the orifice may be made, and also making it possible to produce much finer orifice than would otherwise be possible, I have found that I may drill a relatively large opening such as an opening 42 in the wall 26 and insert therein a plug 43 in the shape of a right circular' cylinder of the same external diameter as the internal diameter of the opening l2. However, the plug 43 is flattened on one side 44 by removing a segment thereof by grinding, e. g., so as to leave a minute space having a cross-section corresponding to the shape of a circular segment which forms the actual orifice 21. In order to secure the plug 43 permanently within the opening 42 the edges l5 of the openmg "are preferably peened over after the plug.

42 has been inserted in opening 42. The construction of the plug 48 and the orifice 21 are shown in detail in Figs. 2 and 3. As shown in Fig. 1, the orifice 21 is not only at one side of the opening 21 but is preferably also eccentric with respect to the piston22 and the cylinder 22,.

lower surface 46 of the piston 23 being reduced in diameter sufficiently to provide space for the wall of the sac 28. However, my invention is not limited to the specific construction disclosed in F 8. 4. If desired O-ring seals may be employed. Such a seal comprises a ring 41 composed of compressible material such as rubber or synthetic compound fltting in an annular groove 48, as illustrated in Fig. 1. Preferably the groove 48 has a greater axial length than depth and the cross-section of thering 47 is less than the crosssection of the groove 48, but its uncompressed diameter is greater than the depth of the groove 48, so that a rolling eflect is produced when relative motion takes place between the piston 28 and the cylinder. 22.

While I have described my invention as em-' bodied in concrete form, and as operating in its speciflc 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 them-'- selves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What is claimed is:

1. A tappet comprising in combination a crlln v 6 the closed-end of the piston, flexible sacs carried by 'said piston with mouths sealed on opposite sides of the inner end wall of said piston around a 1 said opening, and fluid within said sacs.

2. A- sealed self adjusting tappet unit comprising a cylinder, a hollow piston in said cylinder having an inner wall, fluid sealing means to prevent flow of fluid from said cylinder past said piston, orifice means in the inner end wall of said piston, a sac in said piston with its mouth sealed against said inner piston wall, fluid in said sac, plunger means in said piston engaging an outer wall of said sac, and resilient means cooperating with said plunger means arranged to cause fluid transfer from said sac to said cylinder through the oriflce. and fluid in said cylinder.

3. A sealed self adjusting tappet unit comprising a cylinder, a hollow piston in said cylinder,

der open at one end, a hollow piston within said cylinder projecting from the open end of the cylinder, said piston having a closed outer end and an inner end wall with a constricted opening therein, a plunger in said piston, means for exertmg force on said plunger in a direction away from fluid sealing means to prevent flow of fluid from said cylinder past said piston, orifice means in the inner end wall of said piston arranged to provide for fluid transfer between said cylinder and piston in either direction, a first sac in said piston with its mouth sealed against said inner piston wall, fluid in said sac, a second sac in said cylinder with its mouth sealed to said piston end wall; plunger means in said piston and engaging said first sac arranged to cause fluid transfer to .the

sac in said cylinder through the orifice, and fluid in said sacs.

JOSEPH NORMAN PAQUIN.

REFERENCES crrnn The following references are of record in the tile of this patent:

- mm'sn s'rA'rEs rams Number Barr Feb. 5, 1948