Roller Type hydrocushion mechanical tappet

Abstract

A tappet comprises a foot having a convex cam contact surface and an axially extending hub, a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot, and hydrocushions of oil between the foot, a thrust washer, and the lower portion of the tappet body. The cam contact surface operates in a frictional relationship with a cam lobe and the cam contact surface of the foot induces the foot to rotate about the centerline of the tappet. The hydrocushions of oil on each side of the thrust washer operate to reduce friction as the foot independently rotates axially about a centerline of the tappet body.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Patent Application Ser. No. 60/742,080 filed Dec. 2, 2005, herein incorporated by reference.

FIELD OF INVENTION

This invention relates to engine tappets or lifters, and more specifically, to new forms of mechanical tappets including roller ends that interface with a cam.

BACKGROUND OF INVENTION

The tappet in an internal combustion engine is a well-known device, and is also commonly referred to as a lifter, valve lifter, or tappet. For examples of common forms of tappets, see William H. Crouse and Donald l. Anglin's Automotive Mechanics (McGraw-Hill 10th Edition), ISBN 0-02-800943-6 at pp. 131, and 169-170 and Smokey Yunick's and Larry Schrieb's Power Secrets (S-A Design Books 1989) ISBN 0-931472-06-7 at pp. 76-80, both of which are incorporated herein by reference.

FIG. 1 depicts a typical tappet application for a push rod engine. In general, a lifter or tappet interacts directly with a rotating camshaft in the engine's valve train. That interaction begins the chain of events that converts the rotary motion of the camshaft into the reciprocating motion of the engine's intake and exhaust valves. The amount of horsepower generated by an engine is related to how efficiently the valve train operates. Indeed, it is common knowledge that, of all the adjustments that can be made to an internal combustion engine, adjustments to the valve train have the greatest impact on increasing horsepower.

In general, the more efficiently air enters and combusted gas exits an engine, as controlled by the opening and closing of the intake and exhaust valves, the more horsepower the engine will produce. “Lifting,” or opening the valves as high and as fast as possible, and closing the valves as fast as possible, are necessary to obtain efficient air and gas flow, and to achieve optimum horsepower. “High lift” is generally obtained by designing a camshaft having aggressive cam lobes with steep flank angles. Consequently, in high-performance applications, a tappet must be able to reliably negotiate the contour of an aggressive cam lobe at extremely high rpm's. In addition, the tappet must be durable and capable of withstanding extreme frictional forces and high valve spring pressures.

Pushrod type internal combustion engines typically use one of four types of tappets or lifters: the flat mechanical tappet, the mushroom tappet, the roller tappet, or the hydraulic tappet. Each of these types of tappets or lifters is discussed briefly below.

The single piece flat mechanical tappet is inexpensive, simple to produce, and reliable in stock environments, and has been the industry standard for years. In high performance applications, however, the flat mechanical tappet has several limitations. First, the flat mechanical tappet requires an extensive and detailed break-in procedure. The break-in procedure typically includes: (1) polishing the lifter foot without disturbing the contour of its convex foot; (2) coating the camshaft lobes with a high performance lubricant; (3) preheating the engine oil before starting the engine, (4) installing light weight valve springs; (5) starting and running the engine for about thirty minutes at about 2500 rpm's to ensure that adequate oil circulation is present in the valve train, and that the tappets are broken in slowly; (6) after shutting down the engine, installing the proper valve springs. This tedious process is necessary to obtain optimum performance from both the tappets and camshaft. Second, mechanical tappets do not work well in high performance applications using aggressive camshafts characterized by lobes having steep opening and closing flanks.

The “mushroom tappet” was developed in an effort to address some of the limitations of the standard mechanical tappet, particularly for use with aggressive camshaft designs. The mushroom tappet uses a foot with a larger diameter than the body of the tappet, which allows it to more easily negotiate the steeper flank angles of aggressively designed cam lobes. However, several drawbacks are also associated with mushroom tappets. First, before a mushroom tappet can be used, the engine block must usually be machined to ensure adequate clearance with the enlarged tappet foot. Second, the enlarged mushroom tappet foot requires that the tappet be inserted and removed from the bottom of the engine block, thereby complicating repairs or maintenance on the valve train. Third, even the mushroom tappet is characterized by relatively high friction rates requiring significant lubrication.

Moreover, all mechanical tappets are designed to rotate in their bore. The rotation is induced when the convex surface of the lifter foot is in contact the tapered, rotating, cam lobe. The rotation of the lifter or tappet in its bore is necessary to avoid prematurely wearing the lifter foot and cam lobe. However, several additional disadvantages are associated with tappet rotation. First, as the lifter rotates, considerable friction is generated between the surface area of the inside diameter of the lifter bore and the surface area of the outside diameter of the lifter body. Thus, mechanical tappets have relatively high friction rates that often require extensive modifications to the engine to increase the oil flow to the cam lobes and upper valve train in high-performance applications. Secondly, because mechanical tappets rotate, the use of “Rev Kits” (discussed below) has not been successful. Third, because the entire mechanical lifter rotates, it is not possible to use an offset pushrod cup, which is often needed to gain additional pushrod/cylinder head clearance in some applications. More specifically, offset pushrod cups are typically used in applications where the intake ports of the engine block have been bored to a larger size thus sometimes creating a less than zero clearance between the pushrod and engine block.

To reduce the adverse effects of friction between the tappet foot and cam lobe, it is highly desirable to make mechanical tappets that are both light and strong, thereby reducing friction. However, the tappet must still be strong enough to withstand the extreme pressures exerted from the valve springs and cam lobe, and durable enough to withstand the rotational forces between the cam lobe and cam foot. As a result, many types of light-weight, exotic, and expensive materials have been used to fabricate tappets. The optimum solution is one that would be able to utilize two different metals in the lifter. This would make it possible to use one type of metal for the lifter body, and one type for the lifter foot. However, the typical one-piece design of a mechanical tappet dictates using the same material for the entire lifter body.

The “roller tappet” was developed in large part to overcome the many disadvantages of the mechanical tappet. Roller tappets reduce friction between the cam lobe and lifter foot, thereby reducing lubrication requirements. Thus, roller tappets are desirable in high performance applications, as they can maintain valve train stability at high rpm's and aggressive camshaft designs. However, they likewise have several drawbacks.

First, many race sanctioning bodies do not allow the use of roller tappets. Second, to achieve optimum performance with roller tappets, it is necessary to install an anti-rotational device and Rev Kit, thereby further increasing the number of valve train components, as well as the likelihood of failure. If failure occurs in a roller tappet, typically the results are instantly fatal to the engine.

A fourth common form of lifter is a hydraulic lifter. Hydraulic lifters have several advantages over both mechanical lifters and roller lifters. Hydraulic lifters automatically compensate for any clearance changes caused by temperature variation or wear. Thus, they should never need adjustment. Also because there is no clearance between the lifter foot and the cam lobe, hydraulic lifters are extremely quiet while in operation when compared to either mechanical or solid lifters. Mechanical or roller lifters need to have some clearance or “lash” between the lifter foot and the cam lobe to act as a cushion to allow for any tolerance changes due to thermal expansion or contraction encountered during repeated engine cycles.

However, hydraulic lifters also have some undesirable qualities. Hydraulic lifters are only as reliable as the cleanliness of the engine oil. Thus, if any dirt is present in the oil, the lifter will not compress or decompress properly, and valve and camshaft damage would soon result. Hydraulic lifters also do not work well at high rpm's, because the lifters have a tendency to “pump up” as the rpm's increase. In other words, as engine rpm's increase, more oil is introduced into the oil chamber, preventing the lifter from compressing and decompressing, and adversely impacting the stability of the valve train. The result is a loss of compression and horsepower because the valves are held off their seats.

U.S. Pat. No. 5,860,398, Engine Tappet; and U.S Pat. No. 5,947,069, Roller Type Mechanical Tappet, both issued to the inventor of the invention herein described, and both herein incorporated by reference, are directed to a tappet structure that includes a roller bearing located between an upper and a lower race, the races and roller bearing located between the foot of the tappet and the body of the tappet. The invention presented in these two patents differs from the invention here in that the roller bearing and races are not used in this invention. In this invention one difference, in one embodiment, is that the foot of the tappet is placed proximate the bottom of the tappet and spaced apart from it by a film of oil that creates a hydrocushion between the top of the foot and the bottom of the body of the tappet. In this structure the cost and complication of the roller bearing and races has been eliminated thus providing a less expensive and less complicated tappet with a rotatable foot portion that will interface with a cam of a camshaft. In a second embodiment of the invention the roller bearing is eliminated and a thrust washer is located between the top of the foot and the bottom of the body of the tappet. In this situation a hydrocushion of oil is formed between the top of the thrust washer and the body of the tappet and also between the bottom of the thrust washer and the top of the foot. This embodiment is focused on in the following description of the invention.

Thus, the need exists for a new form of lifter or tappet that combines the many advantages of the different types of lifters or tappets with little or none of their varied disadvantages. Thus, a need exists for a multiple piece; roller-type mechanical tappet for use in high performance applications and that is effective, reliable, and inexpensive to produce.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome many problems typically associated with prior art valve train designs.

It is an object of this invention to provide a tappet device that reduces friction between the tappet foot and the lobe of the camshaft.

It is an object of this invention to provide a multi-piece lifter or tappet having one end that rotates on the face of the cam.

It is an object of this invention to provide a lifter or tappet that is both durable and reliable.

It is an object of this invention to provide a lifter or tappet comprising interchangeable components.

It is an object of this invention to provide a mechanical tappet with interchangeable tappet feet to adapt to a variety of cam shaft materials and designs.

It is an object of this invention to provide a mechanical tappet with interchangeable push rod receiver cups.

It is an object of this invention to provide a mechanical tappet with interchangeable receiver cups of different thicknesses, and that can be changed to change overall push rod lengths.

It is an object of this invention to provide a mechanical tappet having a light-weight body section, and a hardened base section capable of enduring substantial frictional forces.

It is an object of this invention to provide a mechanical tappet that can be used effectively with camshafts having steep opening and closing flank angles.

It is an object of this invention to provide a mechanical tappet that is cost effective to produce.

It is an object of this invention to provide a mechanical tappet that will increase engine horsepower.

It is an object of this invention to provide a mechanical tappet that requires little, or no, break-in time.

It is an object of this invention to provide a mechanical tappet that is easily adapted to a rev kit by linking consecutive pairs of tappets.

It is an object of this invention to provide a mechanical tappet including a lubrication system that supplies increased lubrication to the valves and valve springs.

It is an object of this invention to provide a mechanical tappet including a lubrication system that supplies increased lubrication to the cam lobes of the cam shaft.

It is an object of this invention to decrease operating engine oil temperatures by increasing tappet performance and lubrication, while reducing valve train friction.

It is an object of this invention to provide a mechanical tappet that can be used in all major racing classes.

It is an object of this invention to provide a mechanical tappet that is easy to install, remove and break-in.

It is an object of this invention to be able to provide a mechanical tappet able to endure substantial valve spring pressures.

It is an object of this invention to be able to be adapted for use with a hydraulic tappet.

It is an object of this invention to be able to be adapted for use with an overhead direct acting bucket tappet.

The above and other objects are achieved by a tappet comprising a foot having a convex cam contact surface and an axially extending hub and a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot. The cam contact surface operates in a frictional relationship with a cam lobe of a rotating cam. The frictional relationship between the cam lobe and the cam contact surface of the foot induces the foot to rotate about the centerline of the tappet. A hydrocushion of oil between the flat top surface of the foot and a flat lower surface of the tappet body operates to reduce friction as the foot independently rotates axially about a centerline of the tappet body.

The foot is removable from the lower bore in the tappet body. The cam contact, or bottom surface of the foot can be formed with a profile that matches or compliments a corresponding profile of the cam with which it cooperates to enhance efficiency between the cam and the foot.

The tappet includes a replaceable push rod receiver cup assembly supported by a top portion of the tappet body. The top portion of the tappet body includes an upper axial bore and a support shelf formed within the bore, and the replaceable push rod receiver cup assembly is supported on the support shelf within the bore in the top portion of the tappet body. In a preferred form, the push rod receiver cup comprises a spacer and a mated receiver cup.

The tappet includes an oil delivery system forming an oil path leading from the tappet body to the upper surface of the foot and to the convex cam contact surface of the foot. The oil delivery system also includes an oil path leading from the tappet body to the push rod receiver cup assembly. In one form, the oil delivery system includes an oil access orifice formed in the mid-section of the tappet body at a location selected to mate with a source of oil, wherein the orifice leads to an interior chamber of the tappet body. A first oil orifice is formed in the foot to provide a hydrocushion of oil between the top surface of the foot and the bottom surface of the lifter. An oil supply orifice may also be provided on the foot to assist in lubricating the foot to cam lobe interface. A bore is formed in the center of the axially extending hub of the foot and serves as a passage between the interior chamber of the tappet body and the first oil orifice for providing the hydrocushion of oil between the lower surface of the tappet and the flat upper surface and the second orifice for lubricating the cam lobe surface. An oil channel is also formed in the spacer of the push-rod receiver cup assembly, and an oil orifice is formed in the base of the push rod receiver cup. Oil is received from a source in the motor, and is delivered to the oil orifices in the foot and replaceable push rod cup.

The aspects and applications of the invention presented here are described below in the drawings and detailed specification. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given the plain, ordinary and accustomed meaning to those of ordinary skill in the applicable arts. The inventors are fully aware that they can be their own lexicographers if desired. The inventors expressly elect, as their own lexicographers, to use only the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise and then further, expressly set forth the “special” definition from that term and explain how it differs from the plain and ordinary meaning. Absent such clear statements of intent to apply a “special” definition, it is the inventors' intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims.

The inventors are also aware of the normal precepts of English grammar. Thus, if a noun, term or phrase is intended to be further characterized or specified, or narrowed in some way, then such noun, term or phrase will expressly include additional adjectives, descriptive terms or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms or modifiers, it is the intent that the such nouns, terms or phrases be given their plain and ordinary English meaning to those skilled in the applicable arts as set forth above.

Further, the inventors are fully informed of the standards and application of the special provisions of 35 U.S.C. 112, Paragraph 6. Thus, the use of the words “function,” “means” or “step” in the Detailed Description or Description of the Drawings or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. 112, Paragraph 6, to define the invention. To the contrary, if the provisions of 35 U.S.C. 112, Paragraph 6 are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for,” and will also clearly recite “a function” (i.e., will state “means for performing the function of [insert function]”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for performing the function of . . . ” or “step for performing the function of . . . . , ” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventors not to invoke the provisions of 35 U.S.C. 112, Paragraph 6. Moreover, even if the provisions of 35 U.S.C. 112, Paragraph 6 are invoked to define the claimed inventions, it is intended that the inventions not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the invention, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and benefits of the present invention can be more easily understood from the following descriptions of the preferred embodiments in combination with the accompanying drawings.

FIG. 1 is a perspective side view showing a typical tappet and cam application in a push rod engine in its ignition or compression cycle.

FIG. 2 is a perspective side view showing a typical tappet and cam application in a push rod engine in its intake or exhaust cycle.

FIG. 3 is an expanded apart view of a preferred embodiment of the invention.

FIG. 3A is a sectional side view of an intermediate spacer and interchangeable push rod receiver cup used with the present invention.

FIG. 3B is an alternative embodiment where a thrust washer is not used.

FIG. 4 is a fragmentary elevation view depicting the tappet as it appears in its bore, and showing the relationship between the tappet foot and the cam lobe.

FIG. 5 is an assembly view of another embodiment of the device in which an off-set push rod cup and anti-rotational strap are used.

FIG. 6 is an assembly view of another embodiment of the invention employing a “Rev Kit.”

FIG. 7 is a cut away side view of another embodiment of the device as it appears in use with a hydraulic lifter.

FIG. 8 is a cut away side view of another embodiment of the invention as it appears in use with an overhead direct acting bucket tappet.

DESCRIPTION OF THE INVENTION

The purpose and operation of a tappet or lifter is well known in the art. A tappet is a device designed to work in direct relation with a rotating camshaft for the purpose of opening and closing intake and exhaust valves in an internal combustion engine. There are basically four types of tappets; mechanical, mushroom, hydraulic, and roller tappets. The present invention pertains primarily to a form of mechanical tappet in a uniquely modified form.

FIG. 1 is a partial side view representing a conventional tappet and cam arrangement with valve 8 in the closed position, indicating that the engine cylinder is in either the ignition or compression cycle. A foot 10 of tappet 12 is in direct contact with a foot 14 (sometimes referred to as heel) of a cam 13. The opposite end of the tappet body 12 contains a push rod receiver cup 18 that receives spherical end 20 of a push rod 22. The opposing spherical end 24 of push rod 22 is pivotally received into a receiver cup 26 of a rocker arm 28. The rocker arm 28 is mounted on a rocker arm shaft 30. The valve end 32 of the rocker arm 28 is in direct contact with a valve stem end 34. Located beneath the valve stem end 34 is a spring retainer 36 and a valve spring 38. The valve spring 38 is a compression spring and exerts constant pressure on cylinder head surface 40 and a spring retainer 36 when the valve is closed. A valve face 42 comprises machined chamfered radial edge that forms a positive seal 46 with a valve seat 47 of an intake exhaust port 48. The valve head is a flat surface on the bottom of the valve and forms the top of a compression chamber 50. The valve 8 remains in the closed position as long as the cam foot 10 of tappet 12 is in contact with the cam foot portion 14 of cam 13, causing the valve spring 38 to exert force on the spring retainer 36, causing the entire valve train assembly to shift in the direction of the arrows, thus holding the valve 8 in the closed position.

FIG. 2 depicts valve 8 in an open position, which occurs during the intake or exhaust cycle of the cylinder. Cam 13 rotates until the raised cam lobe 16 is positioned under cam foot 10 of tappet 12. The lobe 16 lifts the tappet 12 upward, forcing the push rod 22 to cause the rocker arm 28 to pivot on rocker arm shaft 30. The valve end 32 of rocker arm 28 presses against valve stem top 34, causing valve spring 38 to compress and the valve 8 to open, as illustrated by the direction of the arrows.

FIGS. 1 and 2 collectively illustrate the basic operation of the valve train of a push rod internal combustion engine, including the manner in which the valves open and close. The opening and closing process perpetuates itself as long as fuel, spark, and air are supplied to the combustion chamber. This process is fundamental to the operation of an internal combustion engine.

FIG. 3 is a perspective view of a preferred embodiment of the improved tappet of the invention. The components identified in Section A of FIG. 3 is referred to below as the foot section of the tappet. The foot section includes an interchangeable foot 10 and a flat thrust washer 65. The foot section further (referring additionally to FIG. 4) comprises a convex hardened surface 54. In operation, the hardened surface 54 remains in contact with the tapered surface 56 at contact surface 58 (indicated by the circular track) of cam lobe 13 on camshaft 17. The contact surface 58 is located off-center in relation to the centerline 60 of interchangeable cam foot 10. This offset relationship causes the interchangeable foot 10 to axially rotate about the centerline 60 of the tappet 62 (as indicated by the arrow E shown in FIG. 4) when cam 13 begins to rotate about its longitudinal axis (as indicated by the arrow D shown in FIG. 4). Because of the multi-piece design, foot 10 rotates separately from lifter body 62, as discussed in further detail below.

The independent axial rotation of the foot 10 relative to the flat thrust washer 65 and lifter body 62 is an important improvement in the invention that helps to reduce the negative effects of friction. To further reduce frictional forces, a small hole 64, as seen in FIG. 4, is drilled or otherwise formed through the center of foot 19 to allow the passage of oil to lubricate cam lobe 13. The foot 10 is interchangeable, thereby allowing custom applications that cover a wide variety of camshaft designs and requirements. Specifically, another feature of the invention is the ability to design matched tappet foot 10 and cam lobe profiles 56 for specific applications. This is facilitated by allowing the replacement of one specific foot 10 with another having either a different diameter such as a mushroom tappet, or made of a different material in order to adapt to a variety of camshaft designs. The foot 10 of the tappet includes a raised hub 66 that extends axially along the centerline 60 from a flat bearing race surface 68. The axial hub 66 is slidably received into the bore 84 of a tappet bushing 76. A lubrication passage 85 may be formed on the interior of the bore 84 to allow lubrication of the interior of the bore and to allow lubricant to flow to the top of the thrust washer 65, the bottom of the thrust washer and the flat upper surface 68 of the tappet foot.

It should be pointed out that the thrust washer 65 has a central aperture that is very slightly larger than the diameter of the raised hub 66. That is the thrust washer central aperture may be only a small increment larger, for instance in the range of a few ten thousands of an inch to several ten thousands of an inch more than that, than the diameter of the raised hub. The aperture is also provided with at least one, and preferable two, very small oil passages, running the thickness of the thrust washer from the top service to the bottom surface of the thrust washer. These very small oil passages allow oil to flow to the top and to the bottom of the thrust washer and thus allow a film of oil, forming a hydrocushion of oil between the top surface of the thrust washer and the bottom of the main body. A hydrocushion of oil will also be formed between the bottom of the thrust washer and the top of the foot 10. Thus two hydrocushions of oil will be formed between the top surface of the foot and the bottom of the main body of the tappet.

Returning to FIG. 3, the end of raised axial hub 66 may contain, in one embodiment and as shown in this figure, a threaded hole 78 that receives retention screw 80. The retention screw 80 extends vertically downward through a retaining washer 82. The retaining washer 82 has a larger outer diameter than inside bore 84 of bushing 76. As will become clear below, retention screw 80 operates to hold the foot Section A to the remainder of the tappet 12 when it is installed and removed from the engine. During operation, retention screw 80 is not needed because the tappet 12 is held in place naturally between rotating cam lobe 10 and push rod 22.

An alternative embodiment of the invention shown in FIG. 3 is shown in FIG. 3B. This embodiment does not include the thrust washer mentioned above. In this alternative embodiment a flat upper surface 68 of the foot 10 is separated from contact with the lower flat surface 88 of the lifter body 62 by a hydrocushion of oil between the surfaces.

In FIG. 4 the two hydrocushions of oil will be formed. These hydrocushions are between surface 88 and the upper surface of the thrust washer 65 and between the bottom of the thrust washer 65 and the surface of the foot 68 in the area generally identified as F.

As shown in FIG. 4, the cam bushing 76 is press fit into the axial bore 90 in the lower portion of the lifter body 62 as it is in the embodiments shown in FIGS. 3-5.

In the various embodiments, when the cam shaft 17 begins to rotate, the foot 10 also begins to axially rotate due to the relationship between the tapered surface 56 of the cam 13 and the convex cam surface 54 discussed above and shown in FIG. 4. The hydrocushions of oil between the surfaces of the thrust washer 65, in the interface between the upper surface of the foot and the lower surface of the lifter body 88 in area F greatly reduces friction as the tappet foot 10 rotates. More specifically, instead of requiring rotation of the entire tappet assembly (including the elongated tappet body 62), the foot 10 rotates independently from the lifter body 62 separated by the hydrocushions of oil or in the case of the embodiment shown in FIG. 3B, the single hydrocushion of oil. Because the foot 10 is smaller and lighter than the entire tappet assembly, including the body 62, and further, rotates axially on the hydrocushions of oil less friction is generated between the camshaft 17 and foot 10, thereby greatly increasing performance. Performance is even further increased as a result of the lubrication system (as discussed in greater detail below) and the interchangeable features of the tappet foot 10.

The components shown in Section B of FIG. 3 are referred to as the “lifter body portion,” and comprises the main lifter body 62, the bushing 76, and the push rod cup 18. The lifter body 62 is a separate assembly from foot Section A. It can therefore be made of a lighter-weight material than the foot section to still further reduce the forces of friction. The bottom of the lifter body contains axial bore 90, which receives cam foot bushing 76, typically in a press fit relationship. Approximately mid-way up the body 62 of the lifter is a radial grooved recess 94, which operates as an oil relief or lifter gallery. Depending on the application desired, oil orifice 96 can be drilled within the radial grooved recess 94, or slightly above it. If it is drilled within the radial groove 94 it functions as an inertia valve lifter. If the oil orifice is drilled slightly above the radial groove 94 it functions as an edge orifice lifter.

An inertia valve lifter receives oil from an oil gallery in the engine block through orifice 96. Once the oil is inside the lifter, an inertia activated, flapper-type, one way valve (not shown) forces the oil to travel up through a pushrod orifice 102 and down through the foot orifice 64. In essence, the lifter actually acts as a miniature oil pump and provides more oil pressure and volume to the upper valve train. The oil port 96 on an edge orifice lifter (as discussed above) is located slightly above the radial grooved recess 94. In an edge orifice lifter, the oil from the supply gallery enters the lifter through small orifice 96 in much the same way as in the inertia valve lifter. However, additional oil passes around the lifter and down to subsequent lifters in the lifter bank. Because the orifice is located high on the lifter body, it is not exposed to the high pressure in the lifter gallery, and the amount of oil admitted is restricted by the clearance between the lifter bore and the lifter. Because of that fact, an edge orifice lifter typically delivers approximately 20% less oil to the top end of the engine than an inertia-valve lifter. In both types of lifters, once oil enters the lifter body, it flows upward through the lifter body 62, around intermediate spacer 98, through an oil port 100 formed in the bottom of the push rod receiver cup 18 through bored push rod oil channel 102 formed in the bottom of the push rod 22, and through the push rod oil channel 102 to the top end of the engine. The present invention is compatible and functions equally well with either an inertia-valve lifter or an edge-orifice lifter because interchangeable foot 10 can be used with either type of lifter. Therefore, the invention is not restricted to only one type of mechanical tappet.

If additional lubrication is desired between the tapered cam surface 56 and convex hardened surface 54, the present invention provides a lubrication port 64 located at the center foot 10 (See FIG. 4, but this port may also be included but not shown in the other figures.). Oil can then flow through to oil port 64 via hole 81 drilled through retention screw 80.

The intermediate spacer 98 is slidably received into the top of the lifter body 62, and rests on a radial edge 104 machined or otherwise formed in the inside of the lifter body 62. The spacer 98 contains a laterally grooved channel 106 located on its top surface of the intermediate spacer 98. The diameter of intermediate spacer 98 is slightly smaller than inside diameter 108 of the lifter body, thereby allowing lubricating oil to flow around the spacer 98 into the grooved channel 106, through orifice 100 in the pushrod receiver cup 18, through pushrod orifice 102, and into pushrod 22, eventually reaching the top of the engine valve train.

Also slidably received into the top of lifter body 62 is an interchangeable pushrod receiver cup 18. The bottom surface of pushrod receiver cup 18 is in direct contact with the top surface of intermediate spacer 98, thus creating channel 106 (see FIG. 3A) through which lubrication oil flows. Snap ring 110 is received into a radial groove (not shown) formed on the inside surface of the lifter body 62, thereby holding intermediate spacer 98 and pushrod receiver cup 18 within lifter body 62. Thus, another advantage of the invention is the use of a separate pushrod receiver cup 18, thereby allowing the selection from among cups of different thickness to be installed for the purpose of changing the overall pushrod length if desired.

As discussed above, FIG. 4 depicts a fragmentary elevation side view of the assembled device in operation. Tappet or lifter foot 10 is shown in contact with tapered cam surface 56. As tapered cam lobe surface 56 rotates in direction of arrow

D as driven by a cam chain or gear (not shown), the lifter foot 10 rotates axially about the centerline of the lifter body 62, as shown by the direction of arrow E. The rotation of the foot 10 is completely independent from lifter body 62. This independent rotation is made possible because of the off center orientation between the hardened convex surface 54 and tapered cam surface 56, and the hydrocushions of oil on each side of the thrust washer 65. It should be understood from FIG. 4 that the principles of the invention apply equally to any form of tappet, including a bucket-type, hydraulic, or other form of tappet, as long as the foot is allowed to rotate separately from the tappet body at the interface with the cam lobe. In the application of the invention for a bucket-type tappet, the tappet is inverted on a valve spring so that the rotating foot contacts the lobe of an overhead cam.

FIG. 5 represents alternative embodiment of the preferred device. It is similar to the embodiment shown in FIG. 3, but is modified in order to use high seat, offset pushrod cup 122, or a Rev Kit (not shown). In some engine configurations (especially configurations in which the intake ports have been bored larger) it is desirable, if not necessary; to have an offset pushrod receiver cup 122 to prevent the pushrod from contacting the engine block as it moves up and down. Thus, in this modified form of the invention, pushrod receiver cup 122 must retain the same orientation with; respect to the engine manifold. The lifters must therefore incorporate an anti-rotational device. In order to prevent the lifters from rotating, an anti-twist link bar 116 is attached to consecutive lifter bodies by retainer screws 118 and 120 into respective threaded holes, thereby preventing the pair of lifters from rotating. One anti-rotation strap is necessary for each pair of lifters.

FIG. 6 depicts still another embodiment of the invention that employs a Rev Kit. A Rev Kit functions as a counter spring and maintains a constant downward force on the lifter body to help keep the foot 10 in contact with the tapered cam surface 56 of cam 13. This is particularly beneficial in high-rpm applications. In the embodiment depicted in FIG. 6, radial lip 128 of adapter 126 is slidably received into the top of lifter body 62. Counter spring 130 is likewise received into a radial groove 132 machined into the top of adapter 126. Spring holder 134 is positioned in such a way so as to receive the top of compression spring 130 into a machined radial groove 136. Pushrod 22 is then received through spring holder 134, counter spring 130, adapter 126, and into pushrod receiver cup 18 on top of lifter body 62.

Shown in simplified schematic form in FIG. 7 is a modified form of the invention as employed in a hydraulic tappet. Shown in simplified schematic form in FIG. 8 is yet another modified form of the invention as applied to a bucket tappet for use with an overhead cam. In each of these Figures, like numerals indicate like parts as shown in the earlier Figures. Specifically, in each of these modified embodiments, the foot 10 rotates on a hydraulic cushions of oil about the centerline of the tappet body, as induced by friction between the tapered cam surface 56 of the cam 13.

One embodiment of the invention can be summarized as a tappet with a foot having a convex cam contact surface an axially extending hub, a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot; and a hydrocushion of oil between the foot and the lower portion of the tappet body, the hydrocushion of oil operating to reduce friction as the foot separately rotates axially about a center line of the tappet body. The top of the foot is a flat surface and the bottom of the lower portion of the tappet body is a flat surface separated from the top surface of the foot by the hydrocushion of oil.

In this embodiment the hydrocushion of oil reduces friction between the rotating foot and the tappet body.

The apparatus set forth above is summarized in that it includes a tappet comprising a foot having a convex cam contact surface an axially extending hub, a thrust washer carried on the extending hub of the foot and a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot. A hydrocushion of oil between the foot and the thrust washer and a hydrocushion of oil between the thrust washer and the lower portion of the tappet body provides for free rotation as the hydrocushions of oil reduce friction between the rotating foot, the thrust washer and the tappet body.

The foot, the top of the foot being a flat surface and the thrust washer, having a flat bottom surface are removable from the lower bore in the tappet body. The bottom of the thrust washer is separated from the top of the foot by a hydrocushion of oil while the top surface of the thrust washer is separated from the bottom surface of the lower portion of the tappet body by a hydrocushion of oil.

In further summary one aspect of the invention is a method of making a tappet that comprises forming a foot having a cam contact surface and an axially extending hub. A thrust washer, having a central aperture and oil passage on the central aperture, is located on the axially extending hub. A tappet body is formed and has a lower body portion with a lower axial bore formed therein to accept the axially extending hub of the foot. A first hydrocushion of oil is formed between the foot and the thrust washer and a second hydrocushion of oil if formed between the thrust washer and the tappet body.

Furthermore the method also comprises providing oil under pressure to the site of the first cushion of oil through the lower axial bore of the tappet body and providing oil under pressure to the site of the second cushion of oil through the lower axial bore of the tappet body and through the oil passages of the thrust washer. The method also comprises providing a tappet bushing with a through bore, in the lower axial bore of the lower body portion of the tappet body and forming an oil passage on the through bore extending from one end of the tappet bushing to the other end of the bushing. In this method a top flat surface is formed to support the thrust washer on a hydrocushion of oil, and the lower portion of the tappet body includes a lower flat surface formed to contact a hydrocushion of oil between the thrust washer and the lower portion of the tappet body. Also the act of forming an oil passage from the tappet body to the top surface of the thrust washer and to the bottom surface of the thrust washer is contemplated by the inventor.

In its preferred form, the disclosed tappet device offers many improvements over the prior art. For example, because of its multiple-piece design, friction is greatly reduced between the lifter foot and the cam lobe because only the lifter foot is rotating. Also, the preferred device may be used effectively with camshafts having steep opening and closing flank angles necessary in high performance applications. Also due to the decreased friction, operating engine oil temperatures will be significantly reduced. In addition, because of the multiple piece design, a lighter weight lifter body can be used with a hardened lifter foot. The preferred form of the device also allows for interchangeable push rod receiver cups of different thicknesses so push rods need not be changed to alter their length, only the push rod receiver cup. Further, lubrication to the cam lobes and camshaft will be increased because of the drilled through hole on the lifter foot. Also, the device in its preferred form can be used in all racing classes in addition to any and all stock applications. Still other advantages will be readily apparent to those who use the device. As mentioned above, the invention can be employed on any form of tappet, including mechanical, mushroom, hydraulic and bucket type tappets.

Claims

1. A tappet comprising:

a foot having a convex cam contact surface an axially extending hub;

a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot; and

a hydrocushion of oil between the foot and the lower portion of the tappet body, the hydrocushion of oil operating to reduce friction as the foot separately rotates axially about a center line of the tappet body.

2. The tappet of claim 1 wherein the cam contact surface operates in a frictional relationship with a cam lobe of a rotating cam, and wherein the frictional relationship between the cam lobe and the cam contact surface of the foot induces the foot to rotate about the centerline of the tappet.

3. The tappet of claim 1 wherein the foot is removable from the lower bore in the tappet body.

4. The tappet of claim 1 wherein the hydrocushion of oil reduces friction between the rotating foot and the tappet body.

5. The invention in accordance with claim 1 wherein the top of the foot is a flat surface and the bottom of the lower portion of the tappet body is a flat surface separated from the top surface of the foot by the hydrocushion of oil.

6. A tappet comprising:

a foot having a convex cam contact surface an axially extending hub;

a thrust washer carried on the extending hub of the foot;

a tappet body having a lower body portion with a lower axial bore formed therein to receive the axially extended hub of the foot; and

a hydrocushion of oil between the foot and the thrust washer;

a hydrocushion of oil between the thrust washer and the lower portion of the tappet body.

7. The tappet of claim 6 wherein the cam contact surface operates in a frictional relationship with a cam lobe of a rotating cam, and wherein the frictional relationship between the cam lobe and the cam contact surface of the foot induces the foot to rotate about the centerline of the tappet.

8. The tappet of claim 6 wherein the foot and the thrust washer are removable from the lower bore in the tappet body.

9. The tappet of claim 6 wherein the hydrocushions of oil reduce friction between the rotating foot, the thrust washer and the tappet body.

10. The invention in accordance with claim 6 wherein the top of the foot is a flat surface, the thrust washer has a flat bottom surface, and the bottom of the thrust washer is separated from the top of the foot by a hydrocushion of oil.

11. The invention in accordance with claim 6 wherein the bottom of the lower portion of the tappet body is a flat surface, the thrust washer has a flat top surface, and the top surface of the thrust washer is separated from the bottom surface of the lower portion of the tappet body by a hydrocushion of oil.

12. A method of making a tappet comprising the acts of:

forming a foot having a cam contact surface and an axially extending hub;

locating a thrust washer having a central aperture and oil passage on the central aperture on the axially extending hub;

forming a tappet body having a lower body portion with a lower axial bore formed therein to accept the axially extending hub of the foot;

forming a first hydrocushion of oil between the foot and the thrust washer;

forming a second hydrocushion of oil between the thrust washer and the tappet body.

13. The method of claim 12 further comprising providing oil under pressure to the site of the first cushion of oil through the lower axial bore of the tappet body.

14. The method of claim 12 further comprising providing oil under pressure to the site of the second cushion of oil through the lower axial bore of the tappet body and through the oil passages of the thrust washer.

15. The method of claim 12 further comprising;

providing a tappet bushing, having a through bore, in the lower axial bore of the lower body portion of the tappet body;

forming an oil passage on the through bore extending from one end of the tappet bushing to the other end of the bushing.

16. The invention in accordance with claim 12 further comprising forming a convex surface on the surface of the cam contact surface.

17. The invention in accordance with claim 12 wherein the foot includes a top flat surface formed to support the thrust washer on a hydrocushion of oil, and the lower portion of the tappet body includes a lower flat surface formed to contact a hydrocushion of oil between the thrust washer and the lower portion of the tappet body.

18. The invention in accordance with claim 12 further comprising the act of forming an oil passage from the tappet body to the top surface of the thrust washer and to the bottom surface of the thrust washer.