US2847982A - Automatic tappet - Google Patents

Description

Aug'. 19, C, H ALLEN ET AL 2,847,982

AUTOMATIC TAPPET Filed Jan. '7, 1955 ya ITIS- (bf/ww H am/ AUTMATC TAPPET Application January 7, 1955, Serial No. 480,566 Claims. (Cl. 123-90) The present invention is directed to improvements in automatic clearance regulators and particularly to tappet mechanisms which are actuated by a self-contained hydraulic system.

Automatic tappets or regulators are designed to respond to irregularities in the mechanism in which they are operating to take up any looseness or play in that mechanism. The tappets should be equally operable to respond to any irregularities whether they are caused by` mechanical means, or by thermal expansion and contraction. At the same time, the degree of control exercised by the tappets should not be over-compensating in that they should not over-control the linkage and produce an undesired tightness therein. The production of such tightness in the case of poppet valve operating rappels for internal combustion engines would prevent loll seating of the poppet valve.

One of the main problems in the design of the selfcontained hydraulic type `automatic tappet is the provision of a valve element in the tappet capable of operating quickly through a predetermined range of movement, but also, operating characteristics of the hydraulic valve element have 'been more or less la compromise, with some speed of tappet recovery being sacrificed for increase in tappet operating range, and vice versa. As a result, the operation of the automatic self-contained iydraulically operated tappets was not always satisfactory over extended ranges of operating conditions.

Accordingly, an object of the present invention is to provide an improved automatic tappet assembly having the ability to recover rapidly, and operating over an acceptably wide operating range.

A further object of the invention is to provide a tappet mechanism which is etlicient in operation, but economical to manufacture and to assemble.

Other objects and features of the present invention will be apparent to those skilled in the art from the following description of the attached sheet of drawings which illustrates several preferred embodiments thereof.

On the drawings:

Figure l is a fragmentary view in elevation of the tappet mechanism of the present invention in conjunction with the engine valve whose movement it controls:

Figure 2 is a cross-sectional view of one type of tappet assembly embodying the principles of the present invention; and

Figure 3 is a cross-sectional view of another modified form of the invention.

As shown on the drawings:

ln Figure l, the tappet assembly of the present invention is indicated generally by reference numeral and includes a cylindrical hollow `barrel 11 having a closed base portion 11a (Figure 2) arranged to ride on the surface of a cam 12 connected to a cam shaft 13 of an internal combustion engine.

The movement of the tappet mechanism 10 is arranged to open and close a valve member 14 arranged to be seated within a suitable valve seat provided in an nited States Patent ,P engine block 15. The valve 14 includes an elongated valve stem 14a to which a collar 16 is secured. A valve spring 17 has one end bottomed against the collar 16 and another end against a stationary part of the engine block so as to provide a spring retum mechanism for seating the valve.

In the form of the invention illustrated in Figure 2, the barrel 11 is formed with a relatively wide bore 11b throughout the major portion of the length of the barrel 11, and a somewhat reduced diameter bore 11e near the base of the barrel 11, leaving an annular shoulder 11d between the bore 11b and the reduced diameter bore 11e.

A relatively light coiled spring 19 is seated at the base of the bore 11e against the closed bottom 11a, and extends partially into the enlarged diameter bore 11b. Seated on the spring 19 is a choke ring 21 whose outer periphery is smaller than the inner periphery of the 'bore 11b so as to leave a small annular clearance between the choke ring 21 and the inner wall of the barrel 11. The choke ring 21 includes a central -aperture 21a which provides a seating surface for a seating face 22a formed in a cylindrical valve element 22. The valve member 22 includes a cylindrical shank portion 22b and an enlarged head portion 22e which has formed therein a semi-spherical recess 22d for receiving an enlarged head portion on the push rod or valve stem 14a.

Immediately above the choke ring 21 there is a resilient seal ring 23 composed of rubber or similar material. A lower plunger member 24 rides freely on the seal ring 23, the lower plunger member 24 being of sufficiently small diameter so that it does not touch the sides of the inner wall of the barrel 11.

The valve member 22 is provided with an annular groove 22e which receives a lock ring 25. The latter is arranged to abut an upper plunger member 26 which s loosely received within the bore 11b of the barrel 11. The valve member 22 is restrained from rising out of the barrel by the provision of the lock ring 25 abutting against the member 26 which in turn abuts against a second lock ring 38 as illustrated in Figure 2.

In the form of the invention shown in the drawings, the tappet assembly is provided with a pair of coaxial springs 28 and 29, the springs having diiferent loading characteristics which depend ultimately upon the type of response desired in the tappet. The smaller diameter spring, spring 28, is disposed between the locking ring 25 and the upper surface of the lower plunger member 24, While the larger diameter spring 29 is disposed between the upper plunger member 26 land the lower plunger member 24.

In some cases, the response desired in the tappet will be such that only one o'f the two springs would be required. However, to achieve the maximum ybenefits of the invention, b'oth springs 28 and 29 cooperate to provide a fast acting tappet over a wide operating range. The characteristics of the outer spring 29 are such as to provide a tappet with a very rapid recovery from the collapsed position, but having a limited operating range. The use of the inner spring 28 alone would provide a tappet With a greater operating range but one in which the tappet recovery would not be las rapid. By using both springs 28 and 29, one can achieve a cumulative result of both spring actions in which tappet recovery is quite rapid and the tappet operable over a considerable range. Another advantage of the Cumulative eiect of the two springs arises from the fact that the lower end of the valve element need not be machined or otherwise formed to provide an enlarged valve bottom. In previous tappet design, such an enlarged bottom was deemed necessary to provide a stop for preventing the seal ring from Ibeing forced ott the valve stem. With the use ofthe two springs,

however, the springs can be chosen so that their free expanded lengths are insufficient to force the seal ring off the valve element, making this type of poppet easier to assemble and more economical to manufacture.

The characteristics of the inner spring 28 are such that sufliciently rapid recovery for the small amount of leakdown occurring during engine operation is accomplished without imposing a high return force on the valve train. It should be noted that the outer spring 29 is not acting on the valve member at this time. On the other hand, when the tappet is completely collapsed during an engine shutdown period, very rapid recovery is required to prevent excessive clatter on starting. The outer heavier spring 29 is then brought into action during the iirst portion of this recovery to assist the inner spring 28 in starting the shaft toward the open end of the barrel.

To secure the proper operating characteristics, the distance between the lower edge of the enlarged head portion 22e of the valve member 22 and the upper surface of the upper plunger member 26 (a distance designated by the letter X in Figure 2) should be smaller than the distance between the lower surface of the choke ring 21 and the shoulder 11d (a distance designated by the letter Y in the drawings). Thus as the valve member 22 moves downwardly the enlarged head portion 22C will contact the upper plunger member 26, picking up the heavier load of outer spring 29 before the choke ring 21 becomes seated lagainst the shoulder 11d. Then on starting, the combined loads of outer spring 29 and inner spring 28 are available to overcome break-away friction to start the valve member 22 moving upwardly.

The choke ring 21 divides the lower portion of the barrel 11 into a pressure chamber A on one side of the choke ring, and a storage chamber B on the opposite side. The chambers A and B are iilled to the level of the seal ring 23 with a hydraulic fluid such as oil, la silicone polymer, or other material of suitable viscosity characteristics.

In the operation of the device, the cam 12 during a portion of its rotational movement lifts the tappet barrel 11 and in doing so applies the load of the valve spring 17 to the valve member 22 and ultimately to the choke ring 21. Since the choke ring 21 rests on the body of hydraulic fluid in the compartment A, the lifting action from the tappet barrel will be transmitted through the trapped fluid in compartment A through the valve element 22 and finally to the engine valve 14. Due to the clearance between the periphery of the choke ring 21 and the inner wall of the barrel 1.1, some leakdown occurs between the periphery of the choke ring 21 and the wall of the barrel so that uid flows from the pressure compartment A to the storage compartment B. As this occurs, the valve member 22 starts to drop in the barrel, thereby shortening the assembly.

The valve member 22 moves downwardly while compressing the inner spring 28. When the load of the valve spring 17 is again removed due to seating of the engine valve 14, the inner spring 28 forces the valve member 22 to move upwardly until it has taken up the endwise clearance created by the shortening of the assembly while leakdown had occured. This action raises the valve seating face 22a off the seat provided by the choke ring 21. When this occurs, the compartments A and B are in full fluid communication under the combined loads of the inner spring 28 and outer spring 29 applied by the lower plunger 24 and the seal ring 23. The choke spring 19 acts to force the choke ring 21 upwardly toward the valve seating face 22a. Due to this upward displacement of the choke ring 21, fluid is forced to ow through the aperture 21a from compartment B to compartment A until the choke ring 21 has again become seated or close to a seated relationship with valve face 22a and the tappet is in position for the next operating cycle.

When the tappet is completely collapsed during an engine shutdown period, the action proceeds in the same,

4 manner as outlined in the previous paragraph with the exception that the valve member 22 moves downwardly until the enlarged head portion 22C strikes the upper surface of the upper plunger 26. When this occurs the reaction of the outer spring 29 is transferred from the tappet barrel to the tappet valve member 22. The outer spring 29 then functions in the same manner as the inner spring 28. Leakdown continues with the outer spring being compressed by the valve member 22 until the choke ring 21 seats against the shoulder 11d.

The net result is that when the load of the valve spring 17 is removed a much higher load is transmitted to the valve member during the rst part of the recovery than would be available from inner spring 28 acting by itself. This higher load (spring 2S plus spring 29) is available until the upper plunger 26 has seated against the lock ring 38 and the enlarged head portion 22e of valve member 22 has moved away from upper plunger 26. This higher load during the first portion of the recovery assists in overcoming static or break-away friction upon starting without increasing the normal return force of the tappet during operation while the engine is running.

A somewhat modified form of the invention is illustrated in Figure 3 of the drawings. ln this form of the invention, the tappet assembly 10 may consist of a barrel 31 having a closed bottom portion 31a and a substantially uniform diameter bore 31b extending throughout the major portion of the barrel 31. A relatively light spring 32 has one end bottomed on the closed bottom 31a and at its upper end supports a choke ring 33 of a diameter smaller than the diameter of the bore 31b so that hydraulic fluid may pass -between the pressure chamber A and the storage chamber B, as described in conjunction with the previous embodiment.

A valve member 34 has a tapered seating face 3419 arranged to be received in seated relation within a central aperture 33a of the choke ring 33. Disposed along the valve member 34 in spaced relation to the choke ring 33 is a resilient seal ring member 36 and a lower plunger member 37 freely slidable within the interior of the barrel 31.

This form of invention also utilizes an enlarged head portion 34e on the valve member 34. An enlarged shank diameter 34d provides a shoulder 34e against which inner spring 40 abuts. An enlarged portion 34f of the valve shank provides an interference fit with the end coil 40a of inner spring 40. The said end coil of inner spring 4t) upon being forced over the enlarged diameter 34f snaps into an annular groove 34g located immediately below the shoulder 34e. Thus the inner spring 40 is held securely in place with its end coil 40a doing double duty as an abutting coil against shoulder 34e and as a snap ring in groove 34g. the upward motion of valve member 34 by stopping against the lower surface of upper plunger member 42. The diameter 34d is so selected that the inner half of the thickness of the end coil 40a of inner spring 40 abuts. against shoulder 34e and the outer half of this same coil extends beyond this shoulder providing a stop against upper plunger member 42.

A pair of springs 40 and 41 mounted coaxially on the valve member 34 are provided as before, the smaller diameter spring 40 extending between the shoulder 34e and the lower plunger member 37, while the larger diameter spring 41 extends between the upper plunger member 42 and the lower plunger member 37.

The primary difference between the two embodiments resides in the location of the abutment means which determine the limit of collapse of the tappet assembly. In the form of the invention illustrated in Figure 3, the barrel 31 is provided with an annular groove 31e of slightly larger diameter than the bore 31b, so that a shoulder 31d is provided upon which the upper plunger member 42 is bottomed. Movement of the upper plunger member 42 in the upward direction is limited by means As a snap ring, this end coil limits of a snap ring 44 received in a suitable groove in the barrel 31.

In this case the dimensions corresponding to x and y in Figure 2 lie in the thickness of the upper plunger 42 (dimension x) and the distance from the snap ring 44 to the shoulder 31d of groove 31C (dimension y). To secure the advantage of the high load of outer spring 41 in overcoming break-away friction the distance x should be smaller than the distance y.

This form of the invention operates in substantially thc same manner as that previously described, except that the limit of movement of the valve member 34 is detined by the position in which the enlarged head portion 34C strikes the upper plunger member 42 forcing member 42 to seat against shoulder 31d', The distance between these two points therefore determines the stroke of the valve element 34. Otherwise, the action of the tappet element under the conditions of operation is substantially similar to that previously described.

Both of the described embodiments have the advantage that through proper selection of the characteristic of the springs, the tappet can be provided with a rapid recovery characteristic, and a wide operating range. Furthermore, the presently described structure is substantially simplified from a manufacturing standpoint, so that the tappets of the present invention can be made as inexpensively or less expensively than other hydraulic tappets.

it will be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

l. A tappet assembly comprising a cylindrical barrel having a closed bottom and an open top, a lirst spring bottomed against said closed bottom, a slidable member including a valve seating face, a choke ring disposed on said tirst spring and arranged to provide a seat for said valve seating face, a seal ring slidable along said valve member, a second spring restraining movement of said valve member in one direction, a third spring coaxial with said second spring, said second spring providing said tappct with a rapid recovery rate and said third spring providing said tappet with an extended operating range and means including an annular shoulder within said barrel cooperating with said valve member to limit axial movement of said valve member within said barrel.

2. A tappet assembly comprising a cylindrical barrel having a closed bottom and an open top. a iirst spring bottomed against said closed bottom, a slidable valve member -including a valve seating face, a choke ring disposed on said iirst spring and arranged to provide a seat for said valve seating face, a collar xedly secured to said valve member, a plunger member slidable along said valve member in spaced relation to said collar, a pair of coaxially mounted springs ott' diiferent characteristics mounted between sa-id collar and said plunger member, one spring of said pair providing said tappet with a rapid recovery rate and the other spring of said pair providing said tappet with an extended operating range and means including an annular shoulder within said barrel cooperating with said valve member to limit axial movement of said valve member within said barrel.

3. A tappet assembly comprising a cylindrical barrel having a closed bottom and an open top, a first spring bottomed aga-inst said bottom, a slidable valve member including a valve seating face, a choke ring disposed on said iirst spring and arranged to provide a seat for said valve seating face, a seal ring slidable along said valve member, a lower annular plunger member disposed above said? seal ring, an upper annular plunger member mounted in sliding relation along said valve member, a collar on said valve member below said upper plunger member, an annular shoulder on said valve member arranged to engage said upper plunger member, a pair of springs of different characteristics mounted coaxially along said valve member, one of said pair of springs extending between said collar and said lower plunger member, and the other of said pair extending between said upper plunger member and said lower plunger member, one spring of said pair providing said tappet with a rapid recovery rate and the other spring of said pair providing said tappet with an extended operating range, and said barrel having an internal shoulder providing a stop for limiting axial movement of said choke ring, the axial distance between said choke ring and said internal shoulder being greater than the distance between said annular shoulder and said upper plunger member, whereby downward movement of said valve member causes engagement of said annular shoulder with said upper plunger member prior to engagement of said choke ring with said internal shoulder.

4. A tappet assembly comprising a cylindrical barrel having a closed bottom and an open top, a tirst spring bottomed on said closed bottom, a choke ring seated on said iirst spring, a slidable valve member including a valve seating face arranged to be seated along said choke ring, a seal ring slidable along said valve member, a lower annular plunger member slidable along said valve member, an upper annular plunger mem'ber receiving said valve member in slidable relation therethrough, an annnlar shoulder on said valve member arranged to abut said upper plunger member and thereby limit axial movement of said valve member, a collar secured to said valve member, and a pair of helical springs coaxially mounted on said valve member, one of said pair of springs extending between said collar and said lower plunger member, and the other of said pair of springs extending between said upper plunger member and said lower plunger member, one spring of said pair providing said tappet with a rapid recovery rate and the other spring of said pair providing said tappet with an extended operating range.

5. A tappet assembly comprising a cylindrical barrel having a closed bottom and an open top, a iirst spring bottomed on said closed bottom, a choke ring bottomed on said rst spring, a slidable valve member including a valve seating face arranged to be seated on said choke ring, a seal ring slidable along said valve member, a lower annular plunger member disposed on said seal ring, an upper plunger member on said valve member in spaced relation to said lower plunger member, and a pair of coaxially disposed springs each having one end bottomed on said lower plunger member, one of said pair of springs having its other end engaging said upper plunger member, and the other of said pair of springs having its other end tightly engaging said valve member, one spring of said pair providing said tappet with a rapid recovery rate and the other spring of said pair providing said tappet with an extended operating range.

References Cited in the le of this patent UNITED STATES PATENTS Re 21,931 Voorhies et al. Oct. 2l, 1941 2,109,816 Best Mar. 1, 1938 2,213,195 Banker Sept. 3, 1940 2,325,932 Banker Aug. 3, 1943 2,570,854 Pierce Oct. 9, 1951 2,689,554 Moser Sept. 21, 1954 2,734,495 Pierce Feb. 14, 1956 2,742,030 Gleeson Apr. 17, 1956 2,742,031 Tauschek Apr. 17, 1956

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