JP2004132302A - Manufacturing method for rocker arm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a corner part from becoming blunt and to improve a mounting strength of a pivot shaft. <P>SOLUTION: A through hole 22 having a diameter smaller than an outer diameter of the pivot shaft 4 is formed at a mounting part 16 of the shaft 4. This hole is burred to increase its diameter to make the material to flow, thereby forming a boss 18 at a rear surface side of the mounting part in the burring direction. Then, the material of the inner peripheral wall of the hole is made to flow in an opposite direction to the burring direction to form a raised part 28 on the peripheral side of the hole at the surface side of the mounting part. The inner peripheral surface of the hole is threaded for engaging the pivot shaft, and the diameter of the hole is further increased to form a threaded hole 20 for the pivot shaft. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a rocker arm for transmitting a driving force for opening and closing a valve in an engine.
[0002]
[Prior art]
When the cam rotates in conjunction with the crankshaft, the rocker arm swings around the pivot shaft at one end in the longitudinal direction as the swing center, pushes the valve stem at the swing end and moves the valve stem up and down to open the valve. It opens and closes.
[0003]
The rocker arm performing such an operation is formed into a U-shaped cross section having a pair of side walls by bending a thin plate material by press molding. This rocker arm has a support portion for supporting the valve stem at one end, and a mounting portion to which a pivot shaft serving as a swing center is mounted at the other end side.
[0004]
Since such a rocker arm is formed by pressing a thin plate, a boss portion is provided on the mounting portion to secure the strength of the pivot shaft mounting, and a screw for pivot shaft screwing is provided on the boss portion. A mating hole is formed (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-7-150909 (all pages, FIG. 1)
[0006]
[Problems to be solved by the invention]
By the way, the present inventors have intensively studied such formation of the boss portion. An example will be described with reference to FIG. First, as shown in FIG. 4A, a boss portion 44 is formed in the attachment portion 40 by the flow of the peripheral meat portion 42 indicated by a virtual line. Then, a pilot hole 46 is formed in the boss 44 as shown in FIG. Next, as shown in FIG. 4C, a through hole 52 having a diameter larger than that of the pilot hole 46 is formed in the die chip 50 in a state where the outer peripheral surface of the boss portion 44 is fixed by the mold 48. Next, as shown in FIG. 4D, the outer periphery of the boss 44 is pressed by another mold 54 in a state where the die chip 50 is inserted through the through hole 52. Finally, as shown in FIG. 4 (e), a threading process is performed on the through hole 52 to form a screw hole 56. However, according to such a process, a droop 58 occurs on the inner peripheral edge of the surface of the mounting portion 40. Since the pivot shaft cannot be screwed into the droop 58 region, the effective screw hole region is reduced accordingly, and the mounting strength of the pivot shaft is reduced.
[0007]
[Means for Solving the Problems]
The method for manufacturing a rocker arm according to the present invention is characterized in that a burring process is performed on a through hole smaller than the outer diameter of the pivot shaft formed in the pivot shaft mounting portion to flow the wall portion of the inner peripheral wall of the through hole, and the mounting is performed. A first step of forming the boss portion on the back surface side of the portion, and fluidly processing a wall portion of an inner peripheral wall of the through hole in a direction opposite to the burring direction, and surrounding the through hole on the mounting portion surface side. A second step of eliminating the droop in the portion and raising the peripheral portion, and screwing the pivot shaft to the inner peripheral surface of the through hole including the raised peripheral portion so as to increase the inner diameter of the through hole. And a third step of forming the screw hole by performing the thread cutting process.
[0008]
According to the present invention, when the boss portion is formed on the back surface side in the burring direction in the first step, a droop occurs on the front surface side of the mounting portion. Then, in a second step, the wall portion of the inner peripheral wall of the through hole is flow-processed in a direction opposite to the burring direction to raise the periphery of the through hole on the surface side of the mounting portion. As a result, the droop on the surface side of the mounting portion is eliminated, and at the same time, the peripheral portion rises in the direction opposite to the droop direction. As a result, the threaded hole formed in the third step can also be used as a threaded hole effective for attaching the pivot shaft at the periphery thereof, so that the threaded hole area for attaching the pivot shaft is greatly expanded. It will be. Therefore, in the present invention, while the dripping region is eliminated, the dripping region is raised in the opposite direction to the surface of the mounting portion, and the raised portion can be used as an effective screw hole region, so that the mounting strength of the pivot shaft is significantly increased. It will improve.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, details of the present invention will be described based on embodiments shown in the drawings.
[0010]
The rocker arm A to which the manufacturing method of the present invention is applied will be described with reference to FIG. Reference numeral 2 denotes a cam, 4 denotes a pivot shaft (rush adjustment screw), and 6 denotes a valve stem. The rocker arm A includes a rocker arm main body 8 and a roller 10 that contacts the cam 2. The roller 10 is rotatably attached to the middle of the rocker arm main body 8 in the longitudinal direction via a plurality of rollers 11 in the circumferential direction by pins 12. The rocker arm main body 8 is formed by bending a thin plate material by press molding to form a U-shaped cross section in front view (a shape viewed from one direction in FIG. 1) having a pair of side walls 8a and 8b. It should be noted that one of the side walls 8a and 8b is not shown in the figure, but is denoted by a reference numeral. A support portion 14 for supporting the valve stem 6 is mounted between both side walls 8a and 8b on one end side of the rocker arm body 8, and a pivot shaft 4 serving as a swing center is mounted between both side walls 8a and 8b on the other end side. Mounting portions 16 are provided, respectively. The support portion 14 and the mounting portion 16 form a connecting wall integrally provided with the side walls 8a, 8b, but may be provided separately from the side walls 8a, 8b.
[0011]
A boss 18 is provided on the back side of the mounting portion 16 of the rocker arm main body 8 to secure the mounting strength of the pivot shaft 4. The boss 18 has a screw hole 20 for screwing the pivot shaft 4 through the inside and outside including the mounting portion 16.
[0012]
A method for manufacturing the rocker arm A will be described with reference to FIG. First, as shown in FIG. 2A, a through hole 22 having a hole diameter D0 smaller than the outer diameter of the pivot shaft 4 is formed in the mounting portion 16 as a pilot hole for burring. Next, as shown in FIG. 2B, a burring process is performed on the through hole 22 using a die tip 24 having a cylindrical projection 24a having a truncated conical tip and a diameter D1 (> D0). As a result, the diameter of the through hole 22 is increased to a through hole 22 ′ having a larger hole diameter D 1, and the flow of the flesh of the inner peripheral wall of the through hole 22 ′ in the burring direction is caused by the increase in diameter. A boss portion 18 is formed on the back surface side of the mounting portion 16.
[0013]
Then, as shown in FIG. 2 (c), a reverse process using another die tip 26 is performed in the direction opposite to the burring direction, so that the inner peripheral wall of the through hole 22 'flows in the opposite direction and is attached. The raised portion 28 is formed by raising the peripheral portion of the through hole 22 ′ on the surface side of the portion 16. In this case, the die chip 26 has a columnar protrusion 26a having an outer diameter of D2 (> D1) and a protrusion length of L. The outer diameter D2 of the cylindrical projection 26a is larger than the diameter D1 of the through hole 22 ', and is inserted into the through hole 22' as shown by the phantom line 30. The flow amount of the meat portion of the insertion volume indicated by the imaginary line 30 is the sum of the volume required for embedding the droop 32 and the volume of the raised portion 28. The reason why the raised portion 28 is indicated by a virtual line is that before the die chip 26 is inserted into the through hole 22 ′. The formation of the raised portion 28 eliminates the droop 32 around the through hole 22 '.
[0014]
Finally, as shown in FIG. 2D, the inner peripheral surface of the through hole 22 is subjected to a threading process for screwing the pivot shaft 4 with a threading tool (not shown) to further expand the diameter of the through hole 22 '. To form a screw hole 20. The screw hole 20 is formed up to the inner peripheral wall of the raised portion 28. In this case, the diameter of the threaded hole 20 at the center between the peaks and the valleys corresponds to the outer diameter D2 of the cylindrical projection 26a of the die chip 26. This is because, when the threaded hole 20 is formed by the threading tool, the flesh flows and rises to form a peak portion along with the formation of the valley portion.
[0015]
Returning to FIG. 2 (c), an effective screwing area in the screwing hole 20 for screwing the pivot shaft 4 is effective. The length of the through hole 22 excluding the dripping region 32 is L0, the length of the dripping region 32 is L1, and the length of the raised portion 28 is L2. The length of the effective screwing region in the case where the dripping region 32 exists is the length L0 obtained by subtracting the length L1 of the dripping region 32 from the total length L0 + L1 of the mounting portion 16 including the boss portion 18. On the other hand, as in the present embodiment, the length of the effective screwing region in the case where there is no droop region 32 and the raised portion 28 exists is longer than the total length L0 + L1 of the mounting portion 16 including the boss portion 18. Further, the length L3 = L0 + L1 + L2 obtained by adding the length L2 of the raised portion 28. That is, in the present embodiment, the effective screw length is increased by L1 + L2, and the mounting strength of the pivot shaft 4 is improved accordingly.
[0016]
As is clear from the above, the screw hole 20 formed in the present embodiment eliminates the drooping 32 around the through hole 22 generated by the burring process in FIG. Since the portion 28 is formed, the screwing area of the screw hole 20 where the pivot shaft 4 is effectively screwed is widened, and the mounting strength of the pivot shaft 4 to the screw hole 20 is greatly improved. Therefore, in the present embodiment, it is possible to manufacture the rocker arm A having excellent mounting strength of the pivot shaft 4.
[0017]
In FIG. 2 (c), as shown in FIG. 3, the tip may be turned back using a die tip 26a having a conical shape. In this case, the inner peripheral wall of the through hole 22 may be formed. The flowing meat portion flows more smoothly along the tip shape of the die tip 26a as shown by 30a.
[0018]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, as a result of the screw hole area effective for a pivot shaft screwing being expanded, the rocker arm excellent in the mounting strength of a pivot shaft can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an entire rocker arm according to an embodiment of the present invention. FIGS. 2A to 2D are used to explain each step of a method of manufacturing a rocker arm according to an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of a pivot shaft mounting portion of the rocker arm body shown in FIG. 1. FIG. 3 corresponds to a step shown in FIG. 2C in a rocker arm manufacturing method according to another embodiment of the present invention. FIGS. 4 (a) to 4 (e) are used to explain each step of the conventional rocker arm manufacturing method, and are all enlarged views of the pivot shaft mounting portion of the rocker arm main body. Cross-sectional view [Explanation of reference numerals]
2 Cam 4 Pivot shaft 6 Valve stem 8 Rocker arm main body 16 Mounting part 18 Boss part 20 Screw hole 22 Through hole 24, 26 Die chip 28 Around the through hole on the surface of the mounting part

Claims (1)

A mounting portion for mounting a pivot shaft is provided, a boss portion for securing the mounting strength of the pivot shaft is formed on the back side of the mounting portion, and the mounting portion including the boss portion is used for screwing a pivot shaft through the inside and outside of the mounting portion. A method for manufacturing a rocker arm provided with a screw hole,
A burring process is performed on a through hole smaller than the outer diameter of the pivot shaft formed on the mounting portion to flow the inner peripheral wall of the through hole, and the boss portion is formed on the back surface side of the mounting portion. A first step of
A second step of flowing the inner wall portion of the through-hole in the direction opposite to the burring direction by flow processing to eliminate droop in the peripheral portion of the through-hole on the surface of the mounting portion and to excite the peripheral portion;
A third step of forming a screw hole by subjecting an inner peripheral surface of the through hole including the raised peripheral portion to an inner diameter of the through hole to a threading for the pivot shaft screwing; When,
A method for manufacturing a rocker arm, comprising:

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