An improved cylindrical tappet for transmitting motion between a camshaft and a valve of an internal combustion engine. The tappet construction affords improved performance by permitting higher lift rates than possible with conventional tappet designs. In addition, cam and tappet face wear and cam walk are minimized due to the construction. The tappet consists of a body portion that is slidably supported in a bore of the engine adjacent to the cam lobe. The body portion has a pocket that is adapted to receive one end of a push rod for actuating the valve upon reciprocation of the tappet body portion. A follower portion is pivotally supported by the body portion about an axis that extends normally to the axis of rotation of the associated cam. The follower portion has a curved cylinder surface which engages the cam lobe and which has a substantially larger radius of curvature than the bore in which the tappet is supported. The pivotal support of the follower portion permits the follower face to maintain full face-to-face contact with the cam lobe.

BACKGROUND OF INVENTION 
This invention relates to a valve tappet for an internal combustion engine 
and more particularly to an improved shoe concept that permits greater 
engine performance through more radical cam design and minimizes wear on 
the shoe, cam lobe and associated engine components. 
As is well known in cam design for internal combustion engines, it is 
desirable to provide rapid valve lift which has the effect of maximizing 
the breathing capacity of the engine while permitting shorter duration 
than is possible with engines having slower valve lift rates. It has 
normally been the practice to utilize roller followers to permit cam 
designs which give such rapid lift rates. However, if the diameter of the 
roller which engages the cam surface is too small, serious limitations in 
cam design result. That is, the cam profile for such small radius rollers 
causes concave or reverse flanks which increase the likelihood of jamming 
at both the cam and roller engaging surface and unduly large cocking loads 
on the tappet. If standard acceleration rates are used, the cam lobes for 
such engines must be ground by means of extremely small diameter grinding 
wheels which has the effect of increasing the cost of the camshaft. Roller 
tappets in general also have the disadvantage of "edge riding." This 
results from the extreme difficulty in maintaining complete 
perpendicularity between the cam lobe surface and the roller surface with 
the result that the roller follower has a tendency to contact only the 
edge of the cam lobe resulting in very high wear on the lobe. 
When the tappet is used with an engine having its camshaft in the block, 
the roller follower must be small enough so as to pass through the bore in 
which the tappet is supported. If this is not true, assembly and servicing 
of the engine becomes very difficult and major changes must be made to the 
engine block design to permit other forms of assembly. 
For the foregoing reasons, it has been the common practice to provide 
tappets having substantially flat lower faces which contact the cam lobes. 
Such flat face tappets do lend themselves to rapid valve opening and 
closure but have limitations as to the maximum velocity of valve movement 
which may be accomplished due to tappet diameter and nose radius 
development. Another problem inherent with cam and follower design for the 
valve train of an internal combustion engine is the maintenance of low 
unit pressure loads on the engaging surfaces. With conventional flat face 
tappets, which actually are tappets having a large spherical radius rather 
than being flat (about 60 inches radius), the contact between the cam and 
follower is at best line contact. The high unit loading obviously results 
in considerable wear and dictates low valve spring loads through more 
conservative valve opening and closure rates. 
The difficulty in maintaining perpendicularity on the cam mating surfaces 
also gives rise to a situation known as cam walk. That is, misalignment or 
uneven contact between the cam follower and cam lobe surface exerts axial 
forces on the camshaft. With flat type follower it has been the practice 
to use a small degree of inclination so as to reduce such cam walk and to 
induce an axial force on the camshaft in the desired direction. This 
eliminates or reduces the necessity for providing thrust bearings for the 
camshaft. With flat type followers, this practice further aggravates the 
wear situation since it further minimizes the area of contact between cam 
and follower. It has been next to impossible to provide such inclined cam 
lobe surface with roller followers due to the edge riding problem 
aforedescribed. 
It is therefore a principal object of this invention to provide an improved 
valve tappet for an internal combustion engine that minimizes wear on the 
components associated with the valve train. 
It is another object of this invention to provide an improved valve tappet 
which minimizes the likelihood of binding of the tappet in its supporting 
bore and which also reduces the tendency for cam walk to occur. 
It is still a further object of this invention to provide an improved valve 
tappet which improves contact area and permits more rapid valve opening 
and closing while still being capable of use in an overhead valve engine 
in which the camshaft is journaled in the engine block. 
It is yet another object of the invention to provide an improved valve 
tappet that permits a wider latitude of valve timing and duration with a 
given camshaft and which facilitates changes in timing and duration to be 
made without necessitating replacement of the camshaft. 
BRIEF SUMMARY OF THE INVENTION 
This invention is adapted to be embodied in a valve tappet for transmitting 
motion from a cam to the valve of an internal combustion engine. The 
tappet is adapted to be slidably supported in a bore of the engine formed 
adjacent the cam. The tappet has a cylindrical body portion that is 
adapted to be slidably supporting in the bore. The body portion also 
defines a valve actuating segment that is adapted to transmit motion to an 
associated valve upon reciprocation of the body portion in the associated 
supporting bore. A follower portion or shoe is also provided which has a 
curved surface that is adapted to be engaged with the lobe of the 
associated cam for reciprocating the body portion in the bore upon the 
rotation of the cam about its axis. The radius of the curvature of the 
follower portion surface is substantially greater than the diameter of the 
body portion. Means support the follower portion upon the body portion for 
movement about an axis that extends substantially normally to the face of 
the cam engaged by the follower portion for permitting the follower 
portion to maintain substantially full face width engagement with the lobe 
of the associated cam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a portion of a V-type, overhead valve, camshaft in block 
type of engine. Except for the tappet construction employed with the 
engine, the tappet being identified generally by the reference numeral 11, 
the engine is conventional. For this reason only those components of the 
engine which are necessary to understand the construction and operation of 
the tappet 11 will be described in detail. 
The engine includes a cylinder block 12 to which cylinder heads 13 for each 
bank are affixed in a known manner. Only one bank has been illustrated in 
FIG. 1. Cylinder bores 14 are formed in the block and intake and exhaust 
valves are supported in the cylinder head 13 for cooperation with each 
cylinder bore 14. Only one valve 15 has been illustrated in the drawings. 
A camshaft, indicated generally by the reference numeral 16, is rotatably 
supported in the cylinder block 12 in the valley of the V. The camshaft 16 
is formed with cam lobes 17 for operating the valves 15. 
Motion is transmitted from the cam lobes 17 to the tappets 11, which are 
slidably supported in bores 18 of the cylinder block 12 contiguous to the 
camshaft 16. The tappets 11 in turn drive push rods 19 which operate the 
valves 15 through a conventional rocker arm arrangement (not shown). 
Turning now to the construction of tappet 11, they are best shown in FIGS. 
2 through 4 and include a body portion, indicated generally by the 
reference numeral 21, which has a generally hour-glass shape consisting of 
a hollow upper cylindrical portion 22, a lower cylindrical portion 23, and 
an interconnecting tapered portion 24. The body portion 21 may be formed 
from any desired material and may be formed from lower grade or lighter 
materials than normally used with conventional tappets inasmuch as its 
follower surface, as will become apparent, may be made from a different 
material. The cylindrical portion 22 is formed with a longitudinal 
extending groove 25 in one side thereof which receives a pin or spring-pin 
26 which is pressed into the cylinder block 12 for holding the tappet 18 
against rotation. The intermediate tappet body portion 24 is formed with a 
spherical socket 27 which receives the lower end of the push rod 19 for 
operating the push rod 19 upon reciprocation of the tapper 11 in the bore 
18. 
A follower shoe, indicated generally by the reference numeral 28, is 
supported for pivotal movement about an axis that extends normal to the 
axis of rotation of the camshaft 16 by means of a pivot pin or axle 29. 
The axle 29 is received in a pair of aligned bores 31 and 32 formed in the 
body portion 23. The body portion 23 has an internal cavity 33 into which 
an upwardly extending portion 34 of the shoe 28 extends. The shoe portion 
34 is bored, as at 35, so as to pass the pin or axle 29 and pivotally 
support the shoe 28 upon the axle 29 and tappet body portion 21. 
The shoe 28 has a cylindrical sole portion 36 which has a radius of 
curvature that is substantially greater than the diameter of the cylinder 
portions 22 and 23 of the tappet body 21. This has the effect of 
functioning as a roller follower that has such a large diameter. A true 
roller of this diameter could not be employed, however, because of the 
necessity for the roller or follower to pass through the engine block bore 
18 upon assembly or disassembly. 
As seen in FIG. 3, the face 37 of the cam lobe 17 is tapered in a 
predetermined direction so as to create a thrust force in the direction of 
the arrow 38 in FIG. 3. This thrust force is used to properly direct the 
thrust of the camshaft 16. Because of the pivotal support of the shoe 28 
on the tappet body 21, the shoe may pivot about its axis so as to insure 
full face contact with the full lobe surface 37. 
The intermediate portion 23 of the tappet body 21 is formed with an oil 
passage 39 that receives oil pressure from the lubrication system of the 
engine through appropriately located gallery in the block 12. Oil from the 
passage 39 is delivered to a vertically extending passage 41 which 
terminates at its upper end in the socket 27 for delivery to the overhead 
portion of the valve train through the push rod 19 in a known manner. The 
lower end of the passage 41 extends into the cavity 33 and is juxtaposed 
to an oil passage 42 formed in the shoe portion 34 which intersects the 
bore 35 for lubrication of the journaling surface of the shoe 28. 
It should be readily apparent that the construction of the tappet 11 
achieves the aforedescribed advantages. That is, the pivotal mounting of 
the shoe 28 insures high contact area between the shoe 28 and cam lobe 17. 
This high contact area is further maximized due to the substantial radius 
of the shoe sole 36. The large radius of the surface 36 permits high 
opening and closing velocity for valve 15 while maintaining generous cam 
lobe nose radius and eliminating concave or reverse cam lobe flanks. The 
pivotal support of the shoe 28 also minimizes clocking loads on the tappet 
within the bore 18. Because the shoe 28 is formed from a separate piece 
from the body portion 21, it may be formed from a more exotic material 
such as carboloys or high grade steel without significantly adding to the 
overall cost of the tappet 11. The small overall size of the shoe 28 
permits it to be assembled into the bore 18 from above and thus permits 
replacement of conventional tappets in existing engines while achieving 
all of the aforenoted advantages. Also the cam timing with a given 
camshaft may be readily varied by changing the configuration of the shoe 
surface 26. 
It is to be understood that the foregoing description is that of a 
preferred embodiment of the invention and that various changes and 
modifications may be made without departing from the spirit and scope of 
the invention, as defined by the appended claims.