Rocker Arm For Driving Poppet Valves Of Internal Combustion Engines

Abstract

A rocker arm and a method for manufacturing the rocker arm, for driving poppet valves of automobile internal combustion engines of overhead cam type, which comprises a rocker arm body made of forged steel. A cast iron piece with a round top is secured to each rocker arm body for forming an arcuate contact surface with a cam driving the rocker arm. The cast iron pieces are mass produced by casting round top rectangular members, finishing the round top of the rectangular members while assembling them in a cylindrical manner, and cutting laterally each rectangular member thus finished.

Description

This invention relates to a rocker arm for driving poppet valves, and more particularly to a rocker arm for driving poppet valves of automobile internal combustion engines of overhead cam type and a method for manufacturing such rocker arm, which rocker arm is free from pitching at the cam surface thereof.

When internal combustion engines of overhead cam type are used for driving automobiles, the engines are required to have rocker arms with a high mechanical strength against considerably large bending movement and a high resistance against abrasion and fatigue, to insure satisfactory performance characteristics, such as the ability for high-speed running. To meet such requirement, known rocker arms have been made by forging steel material, machining the forged material, and chromium plating the cam contact surface portion thereof. Alternately, the known rocker arms are made by casting high class cast iron material followed by machining. Such forged rocker arm has a high mechanical strength but it has a drawback in that the chromium layer plated on the cam contact surface thereof tends to be peeled off to cause accelerated abrasion. On the other hand, the aforesaid cast rocker arm has a high mechanical durability at the cam contact surface portion thereof, but it has a drawback in being comparatively weak against mechanical shock and tending to be cracked, due to the inherent brittleness thereof.

Therefore, an object of the present invention is to obviate the aforesaid difficulties of known rocker arms, by providing a rocker arm including a body made of forged steel and a cam contact surface piece attached to the body, said cam contact surface piece is made of high class cast iron.

Another object of the present invention is to provide a method for manufacturing a rocker arm including a body made by forging steel material and a cam contact surface piece made of high class cast iron and attached to said body.

For a better understanding of the invention, reference is made to the accompanying drawings, in which;

FIG. 1 is a sectional view of an internal combustion engine of overhead cam type, having rocker arms according to the present invention;

FIG. 2 is an enlarged partial elevation of the essential portion of the rocker arm, according to the present invention, shown in conjunction with a driving means thereof;

FIGS. 3 and 4 are diagrammatic illustrations of a known method of machining rocker arms;

FIG. 5 is a side view of a rocker arm, according to the present invention;

FIGS. 6A to 6E are diagrammatic illustrations, showing the process of machining a rocker arm, according to the present invention; and

FIGS. 7A to 7F are schematic views, illustrating steps of machining cast iron cam contact surface pieces, according to the present invention.

Like parts are designated by like numerals and symbols throughout the drawings.

Referring to FIGS. 1 and 2, a rocker arm body 1 includes a cam contact surface made of a cast iron piece 2 so as to be driven by a cam 3 for actuating a poppet valve stem 4. A spring 6 is provided to keep the rocker arm 1 in contact with the cam 3 or the top end of the poppet valve stem 4. The rocker arm body 1 is formed by forging steel and then machining. The cam 3 drives the rocker arm body 1 so as to rock around a pivot head 5' secured to a cylinder head of the engine. Thereby, the poppet valve stem 4 is reciprocated by rocking the rocker arm. A groove 1a is formed by the rocker arm body 1 to receive the cast iron piece 2 to form a cam contact surface. The groove 1a can easily be formed by means of suitable cutting tools, such as a broach. With such groove 1a, the iron piece 2 can be registered in the longitudinal direction thereof, or in the direction perpendicular to the axis of rotation of the cam 3.

The cast iron piece 2 is made by casting high class hardenable cast iron, preferably containing chromium, and then by machining the thus cast product. The cast iron has a contact surface portion 2a engageable with the operative surface of the cam 3, which contact surface portion 2a is so finished as to have a curvature in certain relations with the profile of the cam 3. The cast iron piece 2 is securely fastened to the rocker arm 1 at the groove 1a thereof by a suitable means, such as brazing or the like. In short, the position of the cast iron piece 2 is determined in close relation with the profile of the cam 3.

As described in the foregoing, each rocker arm according to the present invention has a body 1 made of steel and a cast iron piece 2 secured thereto to form a cam contact surface 2a engageable with cam 3. Thereby, the rocker arm is provided with a high mechanical strength inherent to steel, as well as a high antiabrasiveness inherent to cast iron. As a result of it, undesirable pitching at the cam contact surface of the rocker arm can be eliminated successfully.

Such construction of the rocker arm results in considerable simplification of the process of manufacturing it. With a known rocker arm, made of a solid body, it has been necessary to cut and grind a cam contact surface so as to form an arcuate surface, as schematically shown in FIGS. 3 and 4. More particularly, in FIG. 3, the cam contact surface T is formed by grinding a rotary grindstone G while rocking the entire rocker arm 1 around the center of curvature of the arcuate cam contact surface 2a with a radius R in a reciprocative manner, as shown by the arrow of FIG. 3. Such method has a disadvantage in that the locus of the rocking motion of the cam contact surface intersects with a pivotable end portion 5 of the rocker arm, as shown by a dot-dash-line of FIG. 3. With such intersection of the locus of grinding motion and the pivotable end portion 5, there is a danger that the pivotable end portion 5 might be ground by the grindstone G.

FIG. 4 shows another possible method of grinding the contact surface F, in which a disc-shape grindstone G having its peripheral surface recessed in a concave shape with a radius of curvature R is used.

The disc-shape grindstone G rotates around its axis Z, as shown by the arrow in FIG. 4, while the rocker arm reciprocates linearly in a direction perpendicular to a plane passing the axis Z of the grindstone G or to the plane of the FIG. The method of FIG. 4 does not have the disadvantage peculiar to the preceding method described hereinafter, referring to FIG. 3. However, the method of FIG. 4 has a disadvantage in that the peripheral surface of the disc-shape grindstone should be recessed in a concave shape with a radius of curvature R, which makes the grindstone G expensive.

Furthermore, neither of the preceding two methods provides sufficient accuracy in the finished rocker arm, especially in the height A, as measured from the bottom of the pivotable end portion 5 to the tip of the cam contact surface 2a, and the spacing B between the center of the pivotable end portion 5 and the center of the cam contact surface 2a, as shown in FIGS. 3 and 4.

In order to obviate such difficulties of known methods of forming the rocker arm, the present invention provides a new method of manufacturing rocker arms, comprising steps of forging a rocker arm body, forming an iron piece receiving groove on the thus forged body by broaching, forming a separately a cast iron piece having a top surface ground in an arcuate shape, and securing the thus-formed cast iron piece on the rocker arm body at said groove.

FIG. 5 shows a side view of a rocker arm, embodying the present invention, which comprises a body 1 made of forged steel, a cast iron piece 2 secured to the body 1 so as to form a cam contact surface, a groove 1a formed on the surface of the body 1 for receiving the cast iron piece 2, a poppet valve driving surface 1b formed at one end of the body 1 for driving a poppet valve, and a pivotable end portion 5 located at the opposite end of the body 1 for allowing rocking motion of the body 1 thereabout. The pivotable end portion 5 has a top surface 7, a bottom surface 8, an inner spherical surface 9, and an oil hole 10 communicating the top surface 7 and the inner spherical surface 9.

As pointed out hereinbefore, in the rocker arm according to the present invention, the cast iron piece 2 for providing a cam contact surface 2a is made by casting while forming the body portion 1 thereof by forging. Upon completion of forging, the body 1 is subjected to broaching, so as to finish simultaneously the poppet valve driving surface 1b, top and bottom surfaces 7, 8 of the pivot portion 5, and the groove 1a for receiving the cast iron piece 2, all in one stroke of the broaching, as shown by heavy lines in FIG. 6A.

In the next step, the inner spherical surface 9 and the oil hole 10 of the pivotable end portion 5, as well as the side surfaces 11 of the poppet valve driving portion 1b are machined, as shown in heavy lines in FIG. 6B. After the machining the rocker arm 1 is washed.

Now, referring to FIGS. 7A and 7F, the process for preparing the cast iron pieces 2 to be secured to the rocker arm body 1 will be described. A round top rectangular member 2' is formed by precision casting, so as to include several, preferably 8 to 10 pieces of the individual cast iron pieces 2, as shown in FIG. 7A. The bottom surface 2a' of the round top rectangular member 2' is at first finished, as shown by heavy lines in FIG. 7B. Thereafter, longitudinal side edges 2b' are ground, and the bottom corner portions 2c' are chamfered, as shown in FIGS. 7C and 7D, respectively.

After a few pieces of such round top rectangular members 2' are thus ground and chamfered, such rectangular members are mounted on a cylindrical jig 12 around the outer periphery thereof, as shown in FIG. 7E. The jig 12 having such round top rectangular members 2' is rotated around its own axis as shown by the arrow H, while feeding the jig slowly in the axial direction thereof, as depicted by the other arrow I thereof. At the same time, a grindstone G operatively engages the round top portion of the members 2' secured on the jig 12, which grindstone G rotates in the direction as shown by the arrow J of FIG. 7E. Thereby, the top surface of the rectangular member 2' is ground with a desired radius of curvature. Then, each of the thus ground rectangular members is served at suitable intervals by thin grindstone (not shown) so that the cast iron pieces 2 of the desired configuration can be produced, as shown in FIG. 7F.

Each cast iron piece 2 thus manufactured is secured to the groove 1a of the rocker arm body 1, as shown in FIGS. 6C and 6D. Such securing is preferably done by using silver solder met meltable at about 600.degree. C. It is also possible to fasten the iron piece 2 to rocker arm body 1 by an organic adhesive endurable against a high temperature above 200.degree. C. The thickness of such solder or adhesive for fastening the cast iron piece to the rocker arm body is usually about five one-hundredths millimeters.

Then, the poppet valve driving portion 1b and the inner spherical surface 9 of the pivotable end portion 5 are quenched, for instance by high frequency quenching.

An example of the chemical composition of the material for the rocker arm 1 and the cast iron piece 2 is as follows.

Rocker arm body 1

i Material: Carbon steel

ii Composition: ##SPC1##

iii Hardness:

Hardness in tempered state before brazing, 22-28 in Rockwell C scale

Hardness after high frequency quenching, more than 50 in Rockwell C scale

Cast iron piece 2

i Material: High class cast iron

ii Composition: ##SPC2##

iii Hardness:

Hardness after chilled, more than 55 in Rockwell C scale

As described in the foregoing, according to the present invention, one stroke of broaching is sufficient for finishing the groove 1a for receiving a cast iron piece 2, the poppet valve driving surface 1b and the upper and lower surface 7, 8 of the pivotable end portion 5. Accordingly, the machining process is materially simplified, and every part of the rocker arm can be accurately finished. Furthermore, a number of cast iron pieces 2 can be made at a time in identical dimension, so that the method of the present invention is suitable for mass production of uniformly sized cast iron pieces.

Claims

I claim:

1. A rocker arm for driving a poppet valve in an automobile internal combustion engines of overhead cam type, comprising a forged rocker arm body, the body having one end pivoted to a stationary portion of the engine and the opposite end engaging the upper end of a poppet, a transverse groove cut on the upper surface of the rocker arm at a point intermediate between the opposing ends, and a cast iron piece integrally secured to the groove, so as to engage a separately driven cam, the cast iron piece having a cam contact surface portion which is so curved as to keep operative engagement with the profile of the cam for driving the poppet in a desired sequence by the movement of the opposite end of the rocker arm.

2. A rocker arm according to claim 1, wherein the forged steel body consists of steel containing 0.38 to 0.43" of carbon, and said cast iron piece consists of high class cast iron containing about 3.45 percent of carbon.

3. A rocker arm according to claim 1, wherein said cast iron piece is substantially rectangular flat piece with the upper edge being so curved as to form the desired contact surface portion.

4. A rocker arm according to claim 1, wherein the cast iron piece is secured to the groove of the rocker arm by means of an organic adhesive capable of withstanding a temperature higher than 200.degree. C.

5. A rocker arm according to claim 2, wherein the vertical lateral section is substantially I-shaped.

6. A rocker arm according to claim 1, wherein the cast iron piece is secured to the groove of the rocker arm by silver solder meltable at about 600.degree. C.