Method for Forming a Cam-Engaged Rocker Arm

Abstract

Valve guides are formed on a U-shaped sheet metal rocker arm by the horizontal displacement inwardly of surface metal from the outboard portion of the rocker arm. A rocker arm body made by forming a steel flat blank into a U-shape cross-section comprising sidewalls that connect a pad end and an opposite socket end. The pad end is defined by a central section and two outboard surfaces. The valve guide walls are formed by displacing material from the outboard surface portions of the pad end and forcing it centrally. This changes, i.e., diminishes, the thickness of the outboard portions of the pad end of the rocker arm which are not aligned with valve contact central surface. The valve contact area defined by horizontal surface and by the vertical sides of the formed guide extensions is created by a tool having a width to accept a known valve stem diameter. The valve guide extensions are parallel to and offset from the pad end rocker arm sidewalls and are created to have the proper thickness as well as suitable height to survive in the rocker arm application. The surface extremity, i.e., height as well as the thickness of the valve guide wall, is determined by the amount of material displaced from surfaces of the outboard portion of the pad end of the rocker arm. Valve guide extension height and thickness dimensions can be achieved that were not attainable by known prior art methods.

Description

TECHNICAL FIELD

The present invention relates to a method of forming a rocker arm by stamping metal blanks. More particularly, the invention relates to a novel method of forming finished valve guides for the rocker arm by the horizontal displacement inwardly of metal from the outer sides at the bottom of the bent U-shaped rocker arm at the pad end of the rocker arm.

BACKGROUND OF THE INVENTION

In automotive and other applications, an overhead cam engine typically utilizes a plurality of cam engaged rocker arms which function to open valves. These rocker arms pivot at one end, contact the valve at an opposite end, and support a roller between the two ends. The roller engages the cam and the cam rotates to move the roller, thereby causing the rocker arm to pivot at the pivot end, and push the valve open.

Rocker arms can be manufactured by casting metals, blanking and forming, ceramic molding, and other methods. Stamping a metal blank to form a rocker arm including a valve stem guide is common in the art. The valve stem guides of the rocker arms are typically formed using a punch and cavity, folding or coining process. During the coining process, an upper die and a lower die punch an area of the metal blank to plastically deform the metal blank. To form the valve guide, the area of the metal blank being coined has a thickness greater than the remaining metal blank, thereby providing additional material to use in forming the valve guides. This deformation of the metal blank typically displaces material from nearby areas of the blank to create a valve guide. In this forming operation, a deficiency may occur when the thickness of the blank area that lost material (used to create the guide) may be below required minimum thickness. It is important that the minimum thickness for a rocker arm be maintained for purposes of strength and durability notwithstanding that some of the material of the blank is used to form valve guides.

The method for forming similar types of stamped rocker arms is known such as that of Ammon (U.S. Pat. No. 6,615,635) (col. 3, lines 40-59 and FIGS. 1 and 2) and Motohashi (U.S. Pat. No. 6,425,361) (col. 4, lines 13-38 and FIGS. 5A-5D) (col. 5, lines 1-19 and FIG. 6). These references describe in general how the guide walls are formed in the blank by applying vertical forces to the upper and lower surfaces of the blank allowing material to plastically flow into cavities. The sidewalls are then bent to form the U-shape cross-section. Process of this kind have the disadvantage of requiring excessive pressure and frequently yields loss of strength which results in crazing and lowering of strength as a result of the pressure needed to create a plastic flow. Additional work is required to finish the guide walls but no description for such needed finishing operation is provided by these patent disclosures.

SUMMARY OF THE INVENTION

The present invention provides a unique method for providing finished valve pad side walls and affords a substantial improvement over the known prior art because the forming of the valve guide walls are shaped after the rocker arm is formed into a U-shaped cross-section and because the quantity of material displaced to form the guide elements is accurately controllable. Material from outside the valve pad area of the U-shaped metal blank is displaced laterally by a tool which moves horizontally to transition the desired quantity of metal to create without further work the finished valve guide. Forming of the valve guide elements is effected by displacing material from the outer surface portion of the bottom of the U-shaped metal sheet and forcing it inwardly. This creates new outer surfaces which are thinner, i.e., not aligned with the central pad surface, the thickness of which remains substantially unchanged. The valve contact area surfaces are created by a tool having a width to accept a known valve stem diameter. The valve guide extensions are parallel and offset to the outer rocker arm sidewalls surfaces and by controlling displacement of the appropriate amount of metal, create guides having the proper thickness to survive in the assigned application. The height of the valve guide elements is essentially determined by the amount of material displaced horizontally inwardly by the laterally converging guide forming tool.

The method of the invention employs less cumbersome equipment and affords better control in metal displacement when forming guide elements on sheet metal rocker arms formed by bending a sheet metal blank into a U-shaped intermediate having a pad end, a mid-portion and a socket end. The steps involved include displacing material laterally from the surfaces of the outboard portions at the bottom of the pad end and forcing controlled portions of the displaced material laterally inwardly to form the valve guides. The metal displacement diminishes the thickness of the outboard portions at the bottom of the U-shaped rocker arm intermediate while essentially retaining the thickness of the central pad section contained within said outboard portion.

The lateral displacement of metal at the bottom of the U-shaped sheet metal is effected such that the guides formed by the lateral displacement of metal extend substantially perpendicularly from the pad end surface and have a width conforming to the desired valve stem diameter.

The displacement of the metal from the outer sections of the pad end is also maintained until valve guides of the desired height are formed. Valve guide height and thickness dimensions and control are achievable which have not been attainable by prior art methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cam engaged roller follower U-shaped rocker arm intermediate formed from sheet metal that has been bent to a U-shape cross-section and prior to the creation thereon of the guide walls.

FIG. 2 is a cross-section taken along line A-A of FIG. 1.

FIG. 3 is a perspective view of a cam engaged roller follower rocker arm in which valve guide extensions have been created by displacing metal from the outboard portion of the bottom of the U-shaped rocker arm of FIG. 1 inwardly in accordance with the method of the invention.

FIG. 4 is a cross-sectional view taken along line B-B of FIG. 3.

FIG. 5 is a cross-sectional illustration of a typical die tool used to horizontally displace metal inwardly at the bottom of the U-shaped rocker arm prior to the formation on the bottom of the rocker arm of the valve guides.

FIG. 6 is a view similar to that of FIG. 5 illustrating the die following formation of the valve guides by the horizontal inward displacement of the metal at the bottom of the pad end U-shape rocker arm intermediate of the kind illustrated by FIG. 1.

FIG. 7 is a perspective view of an alternative rocker arm type, i.e., a flat rocker arm, for which guide walls can be created in accordance with the invention.

FIG. 8 is a perspective view of yet another form of rocker arm, a center pivot rocker arm, for which guide walls can be created in accordance with the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A rocker arm body 10 made by forming a steel flat blank into a U-shape cross-section comprising sidewalls 12 and 13 connected by a pad end 14 and a socket end 15. As illustrated, the pad end 14 is defined by a central section 16 and two outer surfaces 17 and 18 (FIG. 2) FIG. 4 is effected. The formation of the valve guide walls 22 by displacing material from the outer pad end surfaces 17 and 18 and forcing it inwardly or centrally towards surface 16. This creates new surfaces 17a and 18a which are not aligned with valve contact central surface 16. The valve contact area defined by surface 16 and sides 20 of the formed valve guides 22 is created by a tool having a width to accept a known valve stem diameter. The valve guide walls 22 are parallel and offset to the sidewalls 23 and 24 and are defined by outer and inner surfaces 19 and 20, respectively, and are formed so as to have a proper thickness to survive in its application. The top, i.e., height, 21 of the valve guide wall 22, as well as the thickness (measured from 19 to 20), is determined by the amount of material displaced inwardly from surfaces 17 and 18.

Referring now to FIGS. 5 and 6, an embodiment of a stamping die 40 for forming valve guides 42 (FIG. 6) is illustrated to include a center post tool of a size to accommodate the desired valve size. A pair of metal displacing cams 46 having an edge devised to displace metal inwardly from the outer surfaces of the pad end of the rocker arm. Center post 44 is illustrated to include a valve guide forming surface 48.

As shown in FIG. 6, stamping die 40 has the rocker arm 10 positioned therein after the metal displacement operation has formed valve guides 42. In accordance with the method of the invention, a U-shaped rocker arm intermediate (without valve guides) is shaped from a metal blank. The pad end of the U-shaped intermediate is then subjected to the valve guide creating method of the invention.

In the valve guide formation (FIGS. 5 and 6) projections 42 are formed by displacing the adjacent lower surfaces inwardly from the outboard portion of the pad end of the U-shaped rocker arm intermediate metal blank 10 while minimizing any change to the cross-sectional thickness of the intermediate 16 (FIG. 4) of the pad and that doesn't include projections.

At the completion of this stamping step, the valve guide projections 22 (shown as 42 in FIG. 6) are formed due to the displacement of material from the outboard portion of the rocker arm pad end by the lateral converging arms at end 43 of the rod 40, FIGS. 5 and 6.

According to the invention, as illustrated in FIG. 7, the creation of the valve guides 73 and 74 on the flat rocker arm 70 is performed by displacing material from the lower outboard surface toward the center post 44 (FIG. 5). As the material is displaced it is deformed to create the valve guide projections 73 and 74. The displacement of material at the bottom outboard area at the pad end of the U-shaped rocker arm continues until sufficient quantity of material flows to form the guides 73 and 74 of desired height and thickness. The process creates displaced surfaces 17a and 18a (FIG. 4).

As best seen in FIG. 5, distance X, between projection forming recesses used in working the intermediate article, is greater than the width of center post 44 used to determine the desired valve dimension.

The pad end metal displacement process of the invention results in a minimum of approximately 65% of the sheet metal stock thickness being maintained across the displaced pad end areas 17a and 18a so as not to create a through harden heat treat condition in the displaced areas. The stock thickness is the original thickness of the sheet metal blank as measured from upper surface 16 to lower surface 16a (FIG. 2). It is desired to maintain a minimum thickness of the resulting rocker arm in the displace areas 17a and 18a. The minimum required thickness for the rocker arm in the displaced areas 17a and 18a is determined by the depth of hardening experienced by rocker arm 10 in a post-forming hardening treatment and the desired soft core thickness. A rocker arm with a hardened surface and soft core is typically desired for purposes of durability and wear resistance. In the embodiment shown, the post-forming hardening treatment will harden the rocker arm to a depth of about 0.02 inches measured from all surfaces.

In the rocker arm 70, illustrated in FIG. 7, the method of the invention is adaptable to form valve guides 73 and 74 at the pad end 72 of the rocker arm 70.

Similarly, with reference to FIG. 8, which illustrates a center pivot type of rocker arm 80, the invention is generally applicable in forming valve guides 83 and 84 at the pad end 82 of rocker arm 80.

While the invention has been described with respect to specific examples including preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims. For example, while valve guide walls are illustrated, another form of the guides may also be useful at the pivot end.

Claims

1. A method of forming guide elements on a rocker arm formed by bending a sheet metal blank into a U-shaped intermediate having a pad end, a mid-portion and a socket end comprising the steps: (a) displacing material laterally from the surfaces of the outboard portions at the bottom of the pad end and forcing controlled portions of the displaced material laterally inwardly to form valve guides and thereby diminishing the thickness of said outboard portions while essentially retaining the thickness of the central pad section contained within said outboard portion; (b) maintaining the lateral displacement of material such that guides that extend substantially perpendicularly from the pad end surface and have a width conforming to the desired valve stem diameter are formed; and (c) continuing the displacement of said displaced material from the outer sections of the pad end to create valve guides of the desired height.

2. The method of claim 1 applied to form valve guides for a roller follower rocker arm.

3. The method of claim 1 applied to form valve guides for a flat rocker arm.

4. The method of claim 1 applied to for valve guides for a center pivot rocker arm.