METHOD OF MANUFACTURING METAL ELEMENT FOR CONTINUOUSLY VARIABLE TRANSMISSION

Abstract

An inclined surface corresponding portion (30) of a metal element raw material (23) and inclined surface forming portions (47b, 47c) of dies (47, 49) are parallel to each other and are in contact with each other without gap. Therefore, a press load required while forming a metal element (23) is suppressed to a minimum and durability of the dies (47, 49) is enhanced. In addition, recess portions (24a, 26a) are formed on both rear surfaces of an ear portion (26) and a body portion (24) of the metal element (23) through pressing by using the dies (47, 49). Therefore, the sizes of both the recess portions (24a, 26a) are adjusted to change radially inward/outward distributions of the press loads on the dies (47, 49), so that it is possible to prevent the dies from tilting and to reduce a difference in radially inward/outward plate thickness of the metal element (23).

Claims

1. A method of manufacturing a metal element for a continuously variable transmission comprising: pressing and punching a belt plate-shaped metal element raw material (23) having a constant cross section by using dies (47, 49) to manufacture a metal element (23), wherein the metal element (23) has a pair of ring slots (27) that allow a pair of metal rings (22) to be fitted, a neck portion (25) that is positioned between the pair of ring slots (27), an ear portion (26) that extends radially outward from the neck portion (25), and a body portion (24) that extends radially inward from the neck portion (25) and has saddle surfaces (28) being formed to respectively support inner circumferential surfaces of the metal rings (22); and wherein a locking edge (29) overlapping front edges of the saddle surfaces (28) and extending in a transverse direction, and an inclined surface (30) extending radially inward and rearward from the locking edge (29) are formed on a front surface of the body portion (24), wherein an inclined surface corresponding portion (30) of the metal element raw material (23) and inclined surface forming portions (47b, 47c) of the dies (47, 49) are parallel to each other and are in contact with each other with no gap, and recess portions (24a, 24b, 26a) are formed on rear surfaces of both the ear portion (26) and the body portion (24) of the metal element (23) through the pressing by using the dies (47, 49).

2. The method of manufacturing a metal element for a continuously variable transmission according to claim 1, wherein a raw material recess portion (34) is formed in advance on a front surface or a rear surface of a neck portion corresponding portion (25) of the metal element raw material (23) to be subjected to the pressing by using the dies (47, 49).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a view illustrating the overall configuration of a belt-type continuously variable transmission (first embodiment).

[0015] FIG. 2 is a perspective view of a metal belt and a metal element (first embodiment).

[0016] FIGS. 3A to 3C are drawings of a single article of the metal element (first embodiment).

[0017] FIG. 4 is an enlarged view of FIG. 3B (first embodiment).

[0018] FIG. 5 is a perspective view of a metal element raw material (first embodiment).

[0019] FIG. 6 is a cross-sectional view of a punching apparatus and the metal element raw material (first embodiment).

[0020] FIG. 7 is a view describing an operation corresponding to FIG. 6 (first embodiment).

[0021] FIG. 8 is a view describing an operation corresponding to FIG. 6 (first embodiment).

[0022] FIGS. 9A to 9D are views describing an operation at the time when the metal elements are positionally misaligned (first embodiment).

[0023] FIG. 10 is a view describing an operation at the time of performing pressing of the metal element (second embodiment).

[0024] FIGS. 11A to 11C are views corresponding to FIGS. 3A to 3C (third embodiment).

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

[0025] Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 to 9D.

[0026] FIG. 1 illustrates a schematic structure of a belt-type continuously variable transmission T mounted in an automobile. The belt-type continuously variable transmission T includes a drive shaft 11 which is connected to an engine and a driven shaft 12 which is connected to driving wheels. An endless metal belt 15 is wound around a drive pulley 13 which is provided in the drive shaft 11 and a driven pulley 14 which is provided in the driven shaft 12. The drive pulley 13 includes a fixed side pulley half 16 which is fixed to the drive shaft 11 and a movable side pulley half 17 which can come into contact with and be separated from the fixed side pulley half 16. The movable side pulley half 17 is biased toward the fixed side pulley half 16 due to oil pressure acting on an oil chamber 18. The driven pulley 14 includes a fixed side pulley half 19 which is fixed to the driven shaft 12 and a movable side pulley half 20 which can come into contact with and be separated from the fixed side pulley half 19. The movable side pulley half 20 is biased toward the fixed side pulley half 19 due to oil pressure acting on an oil chamber 21.

[0027] As illustrated in FIGS. 2 to 4, the metal belt 15 has a configuration in which a pair of right and left metal rings 22 are each supported by a number of metal elements 23. In this specification, a direction in which the metal belt 15 travels is defined as the forward direction in the forward-rearward direction. The outer circumferential sides of the drive pulley 13 and the driven pulley 14 in a state in which the metal belt 15 is wound around the drive pulley 13 and the driven pulley 14 are defined as the outsides in the radial direction. A direction orthogonal to the forward-rearward direction and the radial direction is defined as the transverse direction. In addition, in regard to a metal element raw material 23 (refer to FIG. 5) which serves as a raw material for the metal element 23 and a punching apparatus 41 (refer to FIG. 6) which punches the metal element raw material 23 and forms the metal element 23, directions corresponding to the forward-rearward direction, the radial direction, and the transverse direction of the metal element 23 are respectively defined as the forward-rearward direction, the radial direction, and the transverse direction thereof.

[0028] The metal element 23 manufactured from the metal element raw material 23 includes a body portion 24 which extends in the transverse direction, a neck portion 25 which extends radially outward from the center of the body portion 24 in the transverse direction, and a substantially triangular ear portion 26 which is connected to an outer end of the neck portion 25 in the radial direction. A pair of ring slots 27, which are open outward in the transverse direction and in each of which the metal ring 22 is fitted, are each formed between the body portion 24, the neck portion 25, and the ear portion 26. Saddle surfaces 28, on each of which the inner circumferential surface of the metal ring 22 is seated, are formed at the outer ends of the body portion 24 in the radial direction facing the ring slots 27. A locking edge 29 extending in the transverse direction is formed at the outer end in the radial direction on a front surface of the body portion 24. An inclined surface 30 which inclines radially inward and rearward from the locking edge 29 is formed on the front surface of the body portion 24. The locking edge 29 overlaps front edges of the saddle surfaces 28. Therefore, the locking edge 29 is positioned at the outer end in the radial direction on the front surface of the body portion 24.

[0029] Pulley contact surfaces 31 in contact with V-surfaces of the drive pulley 13 and the driven pulley 14 are formed at both the right and left ends of the body portion 24 of the metal element 23. In addition, a truncated cone-shaped nose 32, which can be fitted into a truncated cone-shaped hole 33 formed on the rear surface of the ear portion 26, is formed on the front surface of the ear portion 26 of the metal element 23.

[0030] The inclined surface 30 of the metal element 23 is constituted by a first inclined surface 30a which inclines radially inward and rearward from the locking edge 29 at a first inclination angle 1 and a second inclined surface 30b which inclines radially inward and rearward from an inner end in the radial direction of the first inclined surface 30a at a second inclination angle 2. The plate thickness of the body portion 24 in the forward-rearward direction becomes gradually thinner radially inward within the range of the inclined surface 30.

[0031] In addition, a flat first recess portion 25a is formed on the rear surface of the neck portion 25 of the metal element 23, and a flat second recess portion 26a is formed in a central portion in the transverse direction on the rear surface of the ear portion 26 of the metal element 23. The first recess portion 25a and the second recess portion 26a have the same depth and are connected to each other. The inner end in the radial direction of the first recess portion 25a and rear edges of the ring slots 27 are aligned in the radial direction. Moreover, a rectangular third recess portion 24a is formed in the central portion in the transverse direction at the inner end in the radial direction on the rear surface of the body portion 24 of the metal element 23.

[0032] The plate thickness of the body portion 24 in the forward-rearward direction reaches a maximum plate thickness t1 at the position of the locking edge 29. The maximum plate thickness t1 coincides with a plate thickness t2 in the forward-rearward direction of each flat portion 26b which is a portion other than the second recess portion 26a of the ear portion 26. In addition, the plate thickness of the portion in the first recess portion 25a of the neck portion 25 and the plate thickness of the portion in the second recess portion 26a of the ear portion 26 are t3 which is smaller than the maximum plate thicknesses t1 and t2 by the depths of the first recess portion 25a and the second recess portion 26a.

[0033] Therefore, in a chord portion of the metal belt 15 extending linearly from the drive pulley 13 toward the driven pulley 14, the front surface of the ear portion 26 of the metal element 23 on the rear side comes into contact with the flat portions 26b of the ear portion 26 of the metal element 23 on the front side, and the locking edge 29 of the metal element 23 on the rear side comes into contact with the upper end (the rear edges of the saddle surfaces 28) of the body portion 24 of the metal element 23 on the front side. In addition, with respect to the rear surface of the metal element 23 on the front side, the metal element 23 on the rear side can oscillate with the locking edge 29 as a fulcrum. Accordingly, the metal belt 15 can be wound around the drive pulley 13 and the driven pulley 14.

[0034] As illustrated in FIG. 5, the metal element raw material 23 which serves as a raw material when the metal element 23 is manufactured is made of a belt-shaped metal plate which is subjected to rolling such that the metal plate has a constant cross section in the longitudinal direction. The metal element raw material 23 includes an ear portion corresponding portion 26, a neck portion corresponding portion 25, and a body portion corresponding portion 24 respectively corresponding to the ear portion 26, the neck portion 25, and the body portion 24 of the metal element 23. A raw material recess portion 34 extending in a groove shape along the metal element raw material 23 in the longitudinal direction is formed on the front surface of the neck portion corresponding portion 25 of the metal element raw material 23. The raw material recess portion 34 is positioned in the front of the first recess portion 25a of the neck portion 25 of the metal element 23.

[0035] The ear portion corresponding portion 26 has substantially the same constant plate thickness as the plate thickness t2 of each flat portion 26b of the ear portion 26. The neck portion corresponding portion 25 has substantially the same constant plate thickness as the plate thickness t3 of the neck portion 25, the plate thickness t3 is smaller than the plate thickness t2 by the depth of the raw material recess portion 34. The body portion corresponding portion 24 has substantially the same plate thickness as the maximum plate thickness t1 of the body portion 24 at a position corresponding to the locking edge 29, and the plate thickness decreases radially inward from that position. That is, an inclined surface corresponding portion 30 of the body portion corresponding portion 24 of the metal element raw material 23 is constituted by a first inclined surface corresponding portion 30a which inclines radially inward and rearward from a locking edge corresponding portion 29 at the first inclination angle 1 and a second inclined surface corresponding portion 30b which inclines radially inward and rearward from the inner end of the first inclined surface corresponding portion 30a in the radial direction at the second inclination angle 2.

[0036] As described above, the cross-sectional shape of the metal element raw material 23 is different from the cross-sectional shape of the metal element 23 in that the metal element raw material 23 does not have a portion corresponding to the nose 32 and the hole 33 of the ear portion 26, a portion corresponding to the first recess portion 25a of the neck portion 25, and a portion corresponding to the second recess portion 26a of the ear portion 26, but has the raw material recess portion 34.

[0037] As illustrated in FIG. 6, the punching apparatus 41 which punches the metal element 23 out of the metal element raw material 23 includes a lower die 43 which is fixed to a lower portion of a frame body 42; an upper die 45 which is supported by an upper portion of the frame body 42 such that the upper die 45 can be lifted and lowered, and is driven by a die driving cylinder 44 such that the upper die 45 is lifted and lowered; a counter punch 47 which is fitted into a recess portion 43a open on the upper surface formed in the lower die 43 and is driven by a counter punch driving cylinder 46 such that the counter punch 47 is lifted and lowered; and a main punch 49 which is fitted into a recess portion 45a open on the lower surface formed in the upper die 45 and is driven by a main punch driving cylinder 48 such that the main punch 49 is lifted and lowered.

[0038] The contour shapes of the counter punch 47 and the main punch 49 are the same as the contour shape of the metal element 23. A nose forming portion 47a for forming the nose 32 of the metal element 23, a first inclined surface forming portion 47b for forming the first inclined surface 30a of the metal element 23, and a second inclined surface forming portion 47c for forming the second inclined surface 30b of the metal element 23 are formed in the counter punch 47. A hole forming portion 49a for forming the hole 33 of the metal element 23, a first recess portion forming portion 49b for forming the first recess portion 25a of the neck portion 25 of the metal element 23, a second recess portion forming portion 49c for forming the second recess portion 26a of the ear portion 26 of the metal element 23, and a third recess portion forming portion 49d for forming the third recess portion 24a of the body portion 24 of the metal element 23 are formed in the main punch 49. The first recess portion 25a and the second recess portion 26a of the metal element 23 are formed such that they are connected to each other, so that the first recess portion forming portion 49b and the second recess portion forming portion 49c of the main punch 49 are also formed such that they are connected to each other.

[0039] The first inclined surface forming portion 47b and the second inclined surface forming portion 47c of the counter punch 47 are respectively parallel to the first inclined surface corresponding portion 30a and the second inclined surface corresponding portion 30b of the metal element raw material 23. Both the first inclined surface forming portion 47b and the first inclined surface corresponding portion 30a incline at the first inclination angle 1, and both the second inclined surface forming portion 47c and the second inclined surface corresponding portion 30h incline at the second inclination angle 2. Thus, when the metal element 23 is press-formed, the first inclined surface forming portion 47b and the second inclined surface forming portion 47c of the counter punch 47 are respectively in contact with the first inclined surface corresponding portion 30a and the second inclined surface corresponding portion 30b of the metal element raw material 23 with no gap.

[0040] Next, an operation effect achieved due to the shape of the metal element 23 having the above-described configuration will be described.

[0041] The metal belt 15 wound around the drive pulley 13 and the driven pulley 14 transmits a driving force through a pushing force of the chord portion extending linearly from the drive pulley 13 toward the driven pulley 14. The metal elements 23 are arranged parallel to each other in the chord portion. In contrast, in a winding portion in which the metal belt 15 is wound around the pulleys 13 and 14, the metal element 23 changes its posture radially about the axial line of the pulleys 13 and 14. Therefore, a space between the outer ends of adjacent metal elements 23 in the radial direction is widened, and a space between the inner ends of the metal elements 23 in the radial direction is narrowed such that the metal elements 23 oscillate relatively to each other. In this case, the locking edge 29 of the metal element 23 on the rear side coming into contact with the rear surface of the metal element 23 on the front side becomes a fulcrum, and the metal elements 23 in the front and the rear are caused to relatively pitch (oscillate in the forward-rearward direction) within a range of the gap between the nose 32 and the hole 33, so that the posture is allowed to be changed.

[0042] In addition, in the metal element 23 of the present embodiment, the locking edge 29 thereof is formed at the front ends of the saddle surfaces 28, and the height of the locking edge 29 in the radial direction and the heights of the saddle surfaces 28 in the radial direction coincide with each other. Accordingly, when the metal element 23 pitches in the winding portion, the saddle surfaces 28 of adjacent metal elements 23 are prevented from being separated from each other in the forward-rearward direction, and deterioration of the efficiency of transmitting power due to sliding occurring between the saddle surfaces 28 and the inner circumferential surfaces of the metal rings 22 is avoided. If the locking edge 29 is provided radially inward from the saddle surfaces 28, when the metal element 23 pitches in the winding portion, the saddle surfaces 28 of adjacent metal elements 23 are separated from each other in the forward-rearward direction. Therefore, in addition to the occurrence of sliding between the saddle surfaces 28 and the inner circumferential surfaces of the metal rings 22, the metal rings 22 are stretched, thereby resulting in deterioration of the efficiency of transmitting power.

[0043] Incidentally, in adjacent metal elements 23, the nose 32 of the metal element 23 on the rear side is fitted into the hole 33 of the metal element 23 on the front side, and the positions are regulated by the tensile force of the metal rings 22 pressurizing the saddle surfaces 28 radially inward. However, due to the gap between the nose 32 and the hole 33, positional misalignment of the metal elements 23 in the radial direction cannot be avoided in the chord portion.

[0044] FIGS. 9A to 9D illustrate operations at the time when the metal elements 23 of the present embodiment are positionally misaligned in the radial direction. FIGS. 9A and 9B illustrate a state in which the metal element 23 on the rear side is misaligned radially inward with respect to the metal element 23 on the front side. In this case, although the first and second recess portions 25a and 26a do not function, the locking edge 29 of the metal element 23 on the rear side comes into contact with the rear surface of the body portion 24 of the metal element 23 on the front side throughout the length. Therefore, there is no occurrence of bending of the neck portion 25, and the efficiency of transmitting a driving force does not deteriorate.

[0045] Meanwhile, as illustrated in FIGS. 9C and 9D, when the metal element 23 on the rear side is positionally misaligned radially outward with respect to the metal element 23 on the front side, the central portion in the width direction of the locking edge 29 of the metal element 23 on the rear side enters the first and second recess portions 25a and 26a on the rear surface of the neck portion 25 of the metal element 23 on the front side. Therefore, while the inclined surface 30 at the center in the width direction of the body portion 24 of the metal element 23 on the rear side is in slide contact with the inner edges of the first and second recess portions 25a and 26a in the radial direction, the metal element 23 on the rear side moves radially outward and can move forward such that the metal element 23 on the rear side approaches the metal element 23 on the front side.

[0046] In this manner, due to the metal element 23 on the rear side moving radially outward and moving forward such that the metal element 23 on the rear side approaches the metal element 23 on the front side, the contact between both the end portions in the width direction of the inclined surface 30 of the metal element 23 on the rear side and the rear ends of the saddle surfaces 28 of the metal element 23 on the front side is maintained, so that the inclined surface 30 can transmit a driving force throughout the length in the width direction. Accordingly, a bending load added to a portion in which the neck portion 25 is connected to the body portion 24 is reduced and bending of the neck portion 25 is suppressed, and thus, deterioration of the efficiency of transmitting a driving force is suppressed to a minimum.

[0047] In addition, since the flat portions 26b at both ends in the width direction on the rear surface of the ear portion 26 having the first and second recess portions 25a and 26a interposed therebetween are arranged at the same height as the rear surface of the body portion 24, when the metal element 23 is in the chord portion between the drive pulley 13 and the driven pulley 14, the metal element 23 on the front side and the metal element 23 on the rear side come into contact with each other at the locking edge 29. Furthermore, the metal element 23 on the rear side also comes into contact with the rear surface of the metal element 23 on the front side in the flat portions 26b of the ear portion 26. As a result, the metal element 23 which is on the chord portion and is not positionally misaligned in the radial direction comes into contact with three places of the pair of flat portions 26b of the ear portion 26, and the locking edge 29. Accordingly, metal elements 23 can be arranged parallel to each other without pitching and a stable posture can be maintained.

[0048] As illustrated in FIGS. 9C and 9D, when the metal element 23 on the rear side is positionally misaligned radially outward with respect to the metal element 23 on the front side, and when the locking edge 29 of the metal element 23 on the rear side moves forward such that the locking edge 29 enters the ring slots 27 of the metal element 23 on the front side and the first and second recess portions 25a and 26a, the ear portion 26 of the metal element 23 on the rear side interferes with the flat portions 26b of the ear portion 26 of the metal element 23 on the front side and cannot move forward. Therefore, the outer end in the radial direction of the metal element 23 on the rear side tends to fall down rearward. However, since the flat portions 26b of the ear portion 26 are likely to be elastically deformable forward in the connection portion with respect to the second recess portion 26a, following a forward movement of the locking edge 29 of the metal element 23 on the rear side, the flat portions 26b of the ear portion 26 of the metal element 23 on the front side are elastically deformed forward, so that adjacent metal elements 23 in the front and the rear can maintain a positional relationship of being parallel to each other.

[0049] Next, an operation effect in a manufacturing step of the metal element 23 will be described.

[0050] As illustrated in FIG. 6, the metal element raw material 23 manufactured in advance is placed on the lower die 43 and the counter punch 47 of the punching apparatus 41. Subsequently, as illustrated in FIG. 7, the upper die 45 is lowered through the die driving cylinder 44, and the metal element raw material 23 is caused to be interposed between the lower die 43 and the upper die 45 and is fixed therein. Thereafter, the main punch 49 is lowered through the main punch driving cylinder 48, and the metal element raw material 23 is interposed between the counter punch 47 and the main punch 49, thereby performing pressing.

[0051] As a result, the nose 32 and the hole 33 of the metal element 23 are formed through the nose forming portion 47a of the counter punch 47 and the hole forming portion 49a of the main punch 49. The first inclined surface 30a and the second inclined surface 30b (that is, the first inclined surface corresponding portion 30a and the second inclined surface corresponding portion 30b of the metal element raw material 23) of the metal element 23 are formed through the first inclined surface forming portion 47b and the second inclined surface forming portion 47c of the counter punch 47. The first recess portion 25a, the second recess portion 26a, and the third recess portion 24a of the metal element 23 are respectively formed through the first recess portion forming portion 49b, the second recess portion forming portion 49c, and the third recess portion forming portion 49d of the main punch 49.

[0052] At this time, the first inclined surface forming portion 47b and the second inclined surface forming portion 47c of the counter punch 47 respectively come into contact with the first inclined surface corresponding portion 30a and the second inclined surface corresponding portion 30b of the metal element raw material 23 with no gap. Therefore, the quantity of a material which is pressed by the counter punch 47 and is moved can be suppressed to a minimum and a press load can be reduced.

[0053] In addition, the material of the neck portion corresponding portion 25 of the metal element raw material 23 pressed by the first recess portion forming portion 49b of the main punch 49 is pushed out to the raw material recess portion 34 which is formed in advance on the front surface of the neck portion corresponding portion 25, and the front surface of the neck portion 25 of the metal element 23 becomes flat after pressing is completed.

[0054] When press-forming of the metal element 23 is completed in this manner, as illustrated in FIG. 8, the counter punch 47 and the main punch 49 are relatively lowered with respect to the lower die 43 and the upper die 45 through the counter punch driving cylinder 46 and the main punch driving cylinder 48, and the metal element 23 is punched out of the metal element raw material 23.

[0055] Incidentally, as illustrated in FIG. 7, when the main punch 49 is lowered through the main punch driving cylinder 48, the metal element raw material 23 is interposed between the counter punch 47 and the main punch 49, and pressing is then performed, there are cases in which the second recess portion forming portion 49c of the main punch 49 positioned radially outward receives reaction from the metal element raw material 23, the counter punch 47 tilts in an arrow A direction, and the maximum plate thickness t1 of the body portion 24 becomes smaller than the plate thickness t2 of each flat portion 26b of the ear portion 26.

[0056] However, according to the present embodiment, when the third recess portion forming portion 49d of the main punch 49 positioned radially inward receives reaction from the metal element raw material 23, a reaction moment tending to cause the counter punch 47 to tilt in an arrow B direction is generated, thereby offsetting a moment generated by the second recess portion forming portion 49c and a moment generated by the third recess portion forming portion 49d. Accordingly, the main punch 49 and the counter punch 47 are maintained in a parallel state, and the difference in plate thickness between the maximum plate thickness t1 of the body portion 24 and the plate thickness t2 of each flat portion 26b of the ear portion 26 is reduced.

[0057] Moreover, when the first recess portion 25a of the neck portion 25 of the metal element 23 is subjected to pressing through the first recess portion forming portion 49b of the main punch 49, the material of the neck portion corresponding portion 25 of the metal element raw material 23 is pushed out to the raw material recess portion 34 of the metal element raw material 23. Therefore, a load at the time of pressing is reduced in accordance therewith, and durability of the punching apparatus 41 is improved.

[0058] As described above, according to the present embodiment, the second recess portion 26a is formed radially outward in the ear portion 26 through the second recess portion forming portion 49c having the neck portion 25 of the metal element 23 interposed, and the third recess portion 24a is formed radially inward in the body portion 24 through the third recess portion forming portion 49d. Accordingly, the sizes of the second recess portion 26a and the third recess portion 24a are adjusted and the radially inward/outward distribution of a press load on the main punch 49 is changed, so that it is possible to prevent the main punch 49 from tilting and to reduce a difference in radially inward/outward plate thickness of the metal element 23. In addition, the press load on the first recess portion forming portion 49b is reduced through the raw material recess portion 34 of the metal element raw material 23. Accordingly, a moment can be generated in the main punch 49 in accordance with the reduced amount of the press load, and thus, the difference in radially inward/outward plate thickness of the metal element can be controlled with better accuracy.

Second Embodiment

[0059] Next, a second embodiment of the present invention will be described based on FIG. 10.

[0060] In the first embodiment, the raw material recess portion 34 is formed on the front surface of the neck portion corresponding portion 25 of the metal element raw material 23, so that a press load at the time of pressing the first recess portion 25a on the rear surface of the neck portion 25 is reduced. However, in the second embodiment, the raw material recess portion 34 is formed on the rear surface of the neck portion corresponding portion 25 of the metal element raw material 23, so that the press load is reduced. In this case, the first recess portion 25a is formed by performing air-punching of the raw material recess portion 34 of the metal element raw material 23 through the first recess portion forming portion 49b of the main punch 49. Therefore, the press load can be further reduced compared to that in the first embodiment.

Third Embodiment

[0061] Next, a third embodiment of the present invention will be described based on FIGS. 11A to 11C.

[0062] The third embodiment is different from the first embodiment in the configuration of the recess portion on the rear surface of the body portion 24 of the metal element 23. That is, the second recess portion 26a in the first embodiment is formed such that the second recess portion 26a crosses the central portion in the transverse direction of the ear portion 26 radially inward/outward. However, the second recess portion 26a in the present embodiment is annularly formed such that the second recess portion 26a surrounds the hole 33. Moreover, the third embodiment includes a groove-shaped fourth recess portion 24b extending in the transverse direction, in the vicinity of the outer end of the body portion 24 in the radial direction. A moment generated by the third recess portion 24a and the fourth recess portion 24b positioned radially inward from the neck portion 25 functions to offset a moment generated by the second recess portion 26a positioned radially inward from the neck portion 25 and to prevent the main punch 49 from tilting.

[0063] Hereinabove, the embodiments of the present invention are described. The present invention can be subjected to various design changes within the scope not departing from the gist thereof.

[0064] For example, the positions, the shapes, the numbers, and the like of the first recess portion 25a, the second recess portion 26a, the third recess portion 24a, and the fourth recess portion 24b are not limited to those described in the embodiments, and various design changes can be performed.