MULTIPLE AXLE TAPPET LIFTER ASSEMBLY

Abstract

The invention allows for a larger bronze axle outer diameter for increased contact area to carry system loads in tappet body assemblies of engine valve trains; thereby, improving wear and improving the life of the tappet. Relatively small diameter steel pins are used to secure the bronze axle and because the pins are within the bronze axle they do not need to be specifically processed for stress contact or retention. The bronze axle requires the cam roller follower inside diameter to increase as well to reduce the cross section of the cam roller follower. This thinner cross section improves the rotational inertia reducing the risk of skidding at the cam-to-roller interface. Skidding at this interface significantly reduces the life of the cam roller follower and/or the cam lobe. The smaller pin diameter provides addition clearance when packaged next to an adjacent cam lobe.

Description

BACKGROUND OF THE INVENTION

Tappet/Lifter assemblies are used to transfer rotational motion from a cam into linear motion at the valve. The tappet assembly contacts the cam via the roller at one end and the push rod at the opposite end. In between is typically a hydraulic lash compensation device which keeps the roller in contact with the cam through the complete cam rotation. The push rod contacts the rocker arm at one end and the valve at the opposite end to provide valve motion. The valves regulate the air in and out of the engine for proper operation. The rolling contact between the cam and the tappet is a very difficult interface to develop long life products. Tile bearing life is even more taxing in diesel applications. The reason for this is the higher engine combustion levels and particulate matter generated in the oil from these movements.

Current tappet assemblies use a fixed single axle for retaining the bearing components that are in direct contact with a rolling element. A large number of heavy duty diesel applications utilize a bronze axle for the cam roller follower to ride against. The reason for the bronze axle is that the softness of the material allows for the hard diesel particulate material to imbed itself within the relatively softer bronze thereby increasing bearing life. The invention accordingly results from the discovery that the long bearing life of the bronze material can be more effectively utilized by a reconfiguration of the bearing. Bronze, because of its relative softness requires that the axles be larger in diameter, to function properly in supporting tile cam loads. Typical diameter range for a bronze axle is 10 mm to 30 mm. In small diesel applications the tappet does not have enough space to secure a large bronze axle to the body. As a consequence means comprising the use of two small steel pins was developed to secure the larger bronze axle. By using the two small steel pins, the diameter of the bronze axle can be increased without jeopardizing packaging requirements.

SUMMARY OF THE INVENTION

The invention accordingly comprises a system that permits the accommodation of a larger bronze axle outer diameter for contact area and wear in engine cam roller components. The steel pins used to secure the bronze axle do not need to be specifically processed for stress contact or retention because the pins arc within the bronze axle. Lower inertia helps prevents cam to roller interface skidding. Smaller axle diameter provides addition clearance from the outside cam roller follower to the lower edge of the body strut when packaged next to an adjacent cam lobe. The use of commercially available computer aided engineering analysis tools demonstrate that the concept is sound. Looking at loads obtained from the customer indicated that the bending of the steel pins and the bronze axle stress were well within material life limits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical cam in block valve train with a center pivot rocker arm, valve, pushrod and hydraulic lifter.

FIG. 2 is an elevational view of a prior art tappet assembly.

FIG. 3 is a cross sectional view taken along line 3-3 of FIG. 2 and shows the relationship between the body, bronze axle and cam roller follower.

FIG. 4 is an elevational view of the invention tappet assembly.

FIG. 5 is a cross sectional view taken along line 5-5 of FIG. 4.

FIG. 6 is an exploded perspective view showing a prior art assembly.

FIG. 7 is an exploded perspective view of the assembly of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 a center pivot cam-in-block valve train 10 is illustrated. A rocker arm 14 is mounted on a fulcrum (not shown) center ball 15. The rocker arm 14 has an end portion to receive a pushrod 13 and an opposite end to contact a valve 17. The valve 17 extends upwards from the cylinder head (not shown) through a coiled compression spring 16 conventionally seated against the cylinder head and mounted to the valve 17. A pushrod 13 is located between the rocker arm 14 and tappet assembly or tappet body 12, also referenced at 21 in FIG. 2 and at 31 in FIG. 4. The rotating motion of the cam lobe 11 provides lift to the rocker arm 14 through the tappet assembly 12 and pushrod 13. The rocker arm 14 pivots on the center ball 15 and moves the valve 17 in a linear motion.

As shown in FIG. 2 and FIG. 3 the prior art tappet assembly 20 is comprised of a body 21, a bronze axle 22 and a cam roller follower 23. FIG. 4 shows the bronze axle 22 extending into the body 21 via the struts 24. The bronze axle 22 is fixed to the struts 24 so as not to rotate. The cam roller follower 23 is free to rotate about the bronze axle 22. The diameter of the bronze axle 22 is constrained by the allowable material thickness of the cross section of strut 24 that is needed to support the bronze axle 22. The dimension of the bronze axle 22 also limits the clearance available at the bottom of the strut 24 and the outer surface of the cam roller follower 23.

As shown in FIG. 5 and FIG. 6 the improved tappet assembly 30 is comprised of a body 31, steel pins 32, a bronze axle 33 and a cam roller follower 34. FIG. 7 shows the steel pin's 32 extending into the body 31 via the struts 35. The steel pins 32 are fixed to the struts 35 so as not to rotate and are pressed through the bronze axle 33. The bronze axle 33 is contained between the struts 35 and is prevented from rotating by the steel pins 32 that are offset to each other. The cam roller follower 34 is free to rotate about the bronze axle 33.

It is thus seen that the invention allows for a larger bronze axle outer diameter for increased area to carry system loads in tappet assemblies in engine valve trains thereby, improving wear and improving the life of the tappet. The relatively small steel pins used to secure the bronze axle are within the bronze axle and they do not need to be specifically processed for stress contact or retention. The bronze axle increases the cam roller follower inside diameter as well as reducing the cross section of the cam roller follower. The thinner cross section improves the rotational inertia reducing the risk of skidding at the cam-to-roller interface. Skidding at this interface significantly reduces the like of the cam roller follower and/or the cam lobe. The smaller pin diameter provides additional clearance when packaged next to an adjacent cam lobe.

The principle aspects of the invention and the best mode in which it is contemplated to apply that principle have been described. It is to be understood that details provided in the foregoing are illustrative only and that other means and techniques can be employed without departing from the true scope of the invention as described in the following claims.

Claims

1. A cam roller follower assembly for tappet bodies comprising:

a. a tappet body;

b. a bronze axle;

c. a plurality of pins spaced within said bronze axle securing said axle to said tappet body; and

d. a cam roller follower rotatably secured on said bronze axle.

2. The assembly of claim 1 with two pins.

3. The assembly of claim 1 wherein the pins are spaced relatively about 180°.

4. The assembly of claim 1 wherein the pins extend through said bronze axle and into struts of said tappet body.

5. The assembly of claim 1 wherein said bronze axle is secure between struts formed on said tappet body.

6. A method of securing a bronze axle on a tappet body comprising positioning a bronze axle between struts formed on said tappet body by at least two spaced steel pins contained within said bronze axle and securing said pins to said struts.