Oil seal, clutch piston mechanism, and method for manufacturing oil seal

Abstract

To provide an oil seal which can elongate a life of a mold for use in molding.SOLUTION: An annular oil seal attached to an external peripheral side or an internal peripheral side of a metal plate comprises: a first joining part joined to a first face of the metal plate; a second joining part joined to a second face of the metal plate; a connection part for connecting the joining parts, and covering an end edge of the metal plate; and a seal lip obliquely protruding from the first joining part and the connection part. The first joining part has a first parallel portion parallel with the first face, and a first tapered portion extending so that its thickness becomes smaller gradually from the first parallel portion, and the first tapered portion has a first end edge whose thickness is zero. The second joining part has a second parallel portion parallel with the second face, and a second tapered portion extending so that its thickness becomes smaller gradually from the second parallel portion, and the second tapered portion has a second end edge whose thickness is zero. A diameter of the first end edge of the first tapered portion is equal to a diameter of the second end edge of the second tapered portion.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an oil seal, a clutch piston mechanism, and a method for manufacturing an oil seal. [Background technology]

[0002] A clutch piston mechanism for actuating a multi-plate clutch in a transmission used in an automobile or the like, such as an automatic transmission (AT) or a continuously variable transmission (CVT), is known (Patent Document 1). The clutch piston mechanism has a piston that reciprocates in a piston chamber into which oil flows, and the piston actuates the multi-plate clutch. An oil seal that seals the oil in the piston chamber is attached to the piston.

[0003] The clutch piston mechanism described in Patent Document 1 has a canceller that faces the piston and defines an oil chamber between the piston and the canceller. An oil seal that contacts the piston and seals the oil in the oil chamber is attached to the canceller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-203524 A Summary of the Invention [Problem to be solved by the invention]

[0005] The oil seal attached to the canceller or piston is generally formed by press molding or injection molding. At this time, high pressure is applied to the oil seal material. It is preferable that the mold used for press molding or injection molding has as long a life as possible.

[0006] The present invention provides an oil seal capable of extending the life of a mold used for molding and a method for manufacturing the oil seal, and further provides a clutch piston mechanism having this oil seal. [Means for solving the problem]

[0007] An oil seal according to one embodiment of the present invention is an annular oil seal made of an elastomer material attached to the outer or inner peripheral edge of a metal plate having a first surface and a second surface, the oil seal comprising a first joint portion joined to the first surface of the metal plate, a second joint portion joined to the second surface of the metal plate, a connecting portion connecting the first joint portion and the second joint portion and covering the edge of the metal plate, and a seal lip projecting obliquely from the first joint portion and the connecting portion. The first joint portion has a first parallel portion parallel to the first surface and a first tapered portion extending from the first parallel portion so as to gradually decrease in thickness, the first tapered portion having a first edge having a thickness of zero. The second joint portion has a second parallel portion parallel to the second surface and a second tapered portion extending from the second parallel portion so as to gradually decrease in thickness, the second tapered portion having a second edge having a thickness of zero. A diameter of a first edge of the first tapered section is equal to a diameter of a second edge of the second tapered section.

[0008] In this embodiment, the first joint and the second joint joined to both sides of the metal plate each have a tapered portion, so that when pressure is applied to the elastomer material in the mold to mold the oil seal, stress is unlikely to concentrate on the portion of the mold forming the first joint and the portion of the mold forming the second joint. Also, since the diameter of the first edge of the first tapered portion of the first joint is equal to the diameter of the second edge of the second tapered portion of the second joint, when pressure is applied to the elastomer material in the mold to mold the oil seal, the load applied to the portion of the mold forming the first tapered portion and the load applied to the portion of the mold forming the second tapered portion are similar, and the moment applied to the mold is small. Therefore, it is possible to extend the life of the mold used to mold the oil seal.

[0009] In addition, because the first tapered portion and the second tapered portion are bonded to both sides of the metal plate, the bonding area between the oil seal and the metal plate is large, making it difficult for the oil seal to peel off from the metal plate. Also, because the first joint portion and the second joint portion each have a tapered portion, stress is less likely to concentrate on the first joint portion and the second joint portion of the oil seal itself when the oil seal is molded. This makes it possible to extend the life of the oil seal itself.

[0010] A clutch piston mechanism according to one aspect of the present invention includes a piston that reciprocates in a piston chamber into which oil flows, a canceller that is the metal plate that faces the piston and defines an oil chamber between the piston and the canceller, and the oil seal described above that is attached to the canceller and seals the oil in the oil chamber. When the piston reciprocates, the seal lip of this oil seal slides against an inner wall surface of the piston that forms the oil chamber.

[0011] A clutch piston mechanism according to another aspect of the present invention includes a piston that is the metal plate and that reciprocates within a piston chamber into which oil flows, and the oil seal that is attached to the piston and seals the oil within the piston chamber. When the piston reciprocates, the seal lip of this oil seal slides against the wall surface of the piston chamber.

[0012] The above-mentioned oil seal can be manufactured by a manufacturing method for an oil seal, which includes fixing the metal plate to a mold so that the outer peripheral end or inner peripheral end of the metal plate is positioned in a cavity of the mold for molding the oil seal, and introducing an elastomer material into the cavity to mold the oil seal. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view showing a clutch piston mechanism according to the embodiment of the present invention. [Diagram 2]FIG. 4 is an enlarged cross-sectional view showing an oil seal according to an embodiment attached to a canceller of a clutch piston mechanism. [Diagram 3] 3A to 3C are diagrams illustrating a process for forming the oil seal of FIG. 2. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing an oil seal according to a comparative example. [Diagram 5] 5A to 5C are diagrams illustrating a process for forming the oil seal of FIG. 4. [Figure 6] FIG. 4 is an enlarged cross-sectional view showing an oil seal according to another comparative example. [Figure 7] 7A to 7C are diagrams illustrating a process for forming the oil seal of FIG. 6. [Figure 8] FIG. 11 is an enlarged cross-sectional view showing an oil seal according to another embodiment attached to a piston of a clutch piston mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Various embodiments of the present invention will now be described with reference to the accompanying drawings, in which the drawings are not necessarily drawn to scale and some features may be exaggerated or omitted.

[0015] As shown in Fig. 1, a clutch piston mechanism 1 according to the embodiment is used to operate a multi-plate clutch 6 arranged in a clutch chamber 4 of a clutch housing 2 of an automobile. The multi-plate clutch 6 is provided in, for example, an automatic transmission (AT) or a continuously variable transmission (CVT). A part of the clutch chamber 4 is used as a piston chamber 8 in which the clutch piston mechanism 1 is arranged. An oil supply passage 9 formed in the clutch housing 2 is connected to the piston chamber 8, and the pressure in the piston chamber 8 can be changed by oil supplied from this oil supply passage 9.

[0016] The clutch piston mechanism 1 according to the embodiment includes a piston (piston seal) 10, a canceller (canceller seal) 12, and a return spring .

[0017] The piston 10 is formed by bending a metal plate by, for example, press working. The piston 10 reciprocates within the piston chamber 8 in response to a change in pressure of oil supplied from an oil supply passage 9 within the piston chamber 8.

[0018] The canceller 12 is also formed by bending a metal plate by, for example, press working. The canceller 12 faces the piston 10, and an oil chamber 14 is defined between the canceller 12 and the piston 10. An oil supply passage 15 formed in the clutch housing 2 is connected to the oil chamber 14, and oil is supplied from the oil supply passage 15.

[0019] The canceller 12 is supported by a seal washer (snap ring) 16 fixed to the clutch housing 2, and the seal washer 16 restricts the movement of the canceller 12 downward in FIG.

[0020] The return spring 18 is held by a spring retainer 11 supported by the piston 10 and a spring retainer 13 supported by the canceller 12. The return spring 18 is a spring (e.g., a coil spring) arranged inside the oil chamber 14, and is supported by the canceller 12 to constantly apply a force to the piston 10 to push the piston 10 back toward the back of the piston chamber 8 (upward in FIG. 1). When the oil pressure in the piston chamber 8 increases due to the adjustment of the oil supply passage 9, the piston 10 moves downward in FIG. 1 against the force of the return spring 18, engaging the multi-plate clutch 6, and enabling the multi-plate clutch 6 to transmit the power of the automobile. When the oil pressure in the piston chamber 8 decreases due to the adjustment of the oil supply passage 9, the piston 10 is pushed back toward the back of the piston chamber 8 by the force of the return spring 18, and thus the multi-plate clutch 6 is released from the engagement, and power is no longer transmitted. In this way, the piston 10 reciprocates relative to the clutch housing 2 and the canceller 12.

[0021] 1 shows a common axis C of the clutch housing 2, the multi-plate clutch 6, the piston 10 and the canceller 12. Although Fig. 1 shows only the left side portions of the clutch housing 2, the multi-plate clutch 6, the piston 10 and the canceller 12, these have a rotationally symmetrical structure. Therefore, the piston 10 and the canceller 12 are annular.

[0022] The clutch housing 2, piston 10 and canceller 12 rotate about a common axis C. As the clutch housing 2 and piston 10 rotate, centrifugal force is applied to the oil in the piston chamber 8. The canceller 12 defines an oil chamber 14 on the opposite side of the piston 10 from the piston chamber 8, and is provided to generate in the oil in the oil chamber 14 a centrifugal force that cancels out the centrifugal force of the oil in the piston chamber 8. The cancellation of the centrifugal force improves the responsiveness of the piston 10 to pressure changes in the oil in the piston chamber 8 (and thus the responsiveness of the multi-plate clutch 6).

[0023] The canceller is also called a balancer. A clutch piston mechanism having such a canceller is called a bonded piston seal or a sealed bonded piston.

[0024] To seal the oil in the piston chamber 8, the clutch piston mechanism 1 further has an outer oil seal 20 and an inner oil seal 22.

[0025] The outer oil seal 20 is made of an elastomer material and has a circular ring shape. The outer oil seal 20 has a joint portion 20a joined to the outer wall of the piston 10, and a seal lip 20b that protrudes obliquely from the joint portion 20a radially outward and toward the back of the piston chamber 8 (upward in FIG. 1). The seal lip 20b comes into slidable contact with the outer wall surface of the piston chamber 8.

[0026] The inner oil seal 22 is made of an elastomer material and has a circular ring shape. The inner oil seal 22 has a joint portion 22a joined to the inner circumferential end of the piston 10, and a seal lip 22b that protrudes obliquely from the joint portion 22a radially inward and toward the back of the piston chamber 8. The seal lip 22b comes into slidable contact with the inner wall surface of the piston chamber 8.

[0027] Moreover, in order to seal the oil in the oil chamber 14, the clutch piston mechanism 1 further has a canceller oil seal 24. The canceller oil seal 24 is made of an elastomer material, has an annular shape, and is attached to the outer circumferential end of the canceller 12. The canceller oil seal 24 has a seal lip 36, which is in slidable contact with the outer wall surface of the oil chamber 14 (i.e., the inner wall surface of the piston 10).

[0028] The gap between the inner peripheral end of the canceller 12 and the clutch housing 2 is sealed with an annular seal washer 16. A stopper 26 is arranged around the seal washer 16 to restrict expansion of the diameter of the seal washer 16 due to centrifugal force. The stopper 26 may be a separate member fixed to the canceller 12, or may be a protrusion formed on the canceller 12. Instead of the annular seal washer 16, a C-shaped seal washer with a discontinuous portion in the circumferential direction may be used to allow a small amount of oil to flow out from within the oil chamber 14 through the discontinuous portion.

[0029] When the piston 10 reciprocates, the seal lip 20b of the outer oil seal 20 slides against the outer wall surface of the piston chamber 8, and the seal lip 22b of the inner oil seal 22 slides against the inner wall surface of the piston chamber 8. In addition, when the piston 10 reciprocates, the seal lip 36 of the canceller oil seal 24 slides against the inner wall surface that forms the oil chamber 14 of the piston 10.

[0030] 2 is an enlarged cross-sectional view of the outer circumferential end of the canceller 12 and the canceller oil seal 24. As described above, the canceller 12 is a metal plate and has a first surface 12a, a second surface 12b, and an outer circumferential edge 12c. The first surface 12a faces toward the back of the oil chamber 14 (upward in FIG. 1), and the second surface 12b is substantially parallel to the first surface 12a. The second surface 12b and the outer circumferential edge 12c are perpendicular to each other, while the outer end 12d of the first surface 12a is formed as an arc-shaped curved surface and is continuous with the outer circumferential edge 12c.

[0031] The canceller oil seal 24 has a first joint portion 30, a second joint portion 32, a connecting portion 34, and a seal lip 36.

[0032] The first joint 30 is joined to the first surface 12a of the canceller 12, the second joint 32 is joined to the second surface 12b of the canceller 12, and the connecting portion 34 connects the first joint 30 and the second joint 32 and covers the outer peripheral edge 12c and the arc-shaped outer end 12d of the canceller 12.

[0033] The seal lip 36 protrudes obliquely radially outward from the first joint portion 30 and the connecting portion 34 toward the back of the oil chamber 14. A lip edge 38 that comes into contact with the inner wall surface of the piston 10 is formed at the outermost end of the seal lip 36.

[0034] The first joint portion 30 has a first parallel portion 30a parallel to the first surface 12a and a first tapered portion 30b extending from the first parallel portion 30a. The first tapered portion 30b has a thickness that gradually decreases toward the inside in the radial direction, and the thickness of the inner peripheral edge (first inner peripheral edge 30c) of the first tapered portion 30b is zero.

[0035] Similarly, the second joint portion 32 has a second parallel portion 32a parallel to the second surface 12b and a second tapered portion 32b extending from the second parallel portion 32a. The second tapered portion 32b has a thickness that gradually decreases radially inward, and the thickness of the inner peripheral edge (second inner peripheral edge 32c) of the second tapered portion 32b is zero.

[0036] The diameter D1 of the first inner peripheral edge 30c of the first tapered portion 30b is equal to the diameter D2 of the second inner peripheral edge 32c of the second tapered portion 32b. Preferably, the inclination angle θ1 of the first tapered portion 30b is also equal to the inclination angle θ2 of the second tapered portion 32b.

[0037] The canceller oil seal 24 is formed by press molding or injection molding using a mold 40 shown in Fig. 3. In the figure, the parting surface of the mold is omitted.

[0038] First, the canceller 12, which is a metal plate, is fixed to the mold 40 so that the outer peripheral end of the canceller 12 is disposed in the cavity 42 of the mold 40. After that, an elastomer material is introduced into the cavity 42, and the canceller oil seal 24 is formed by press molding or injection molding.

[0039] The effects of the canceller oil seal 24 according to the embodiment will be described below in comparison with a canceller oil seal of a comparative example.

[0040] 4 is an enlarged cross-sectional view of the outer circumferential end of the canceller 12 and an oil seal 44 according to a comparative example. In the oil seal 44, the first joint 30 joined to the first surface 12a of the canceller 12 has only the first parallel portion 30a, and does not have the first tapered portion 30b. Also, the second joint 32 joined to the second surface 12b of the canceller 12 has only the second parallel portion 32a, and does not have the second tapered portion 32b. Other features are the same as those of the canceller oil seal 24.

[0041] The oil seal 44 according to the comparative example is formed by press molding or injection molding using a mold 46 shown in Fig. 5. The forming procedure is the same as the forming procedure of the canceller oil seal 24.

[0042] In the oil seal 44 according to the comparative example, the first joint 30 and the second joint 32 joined to both sides of the canceller 12 have only parallel portions 30a and 32a. Therefore, when pressure is applied to the elastomer material in the mold 46 to mold the oil seal 44, stress tends to concentrate on the portion of the mold 46 that forms the first joint 30, particularly the corner 48, and stress tends to concentrate on the portion of the mold 46 that forms the second joint 32, particularly the corner 49. When a large number of oil seals 44 are formed, repeated stress concentration may damage the corners 48 and 49. Therefore, the life of the mold 46 may be shortened.

[0043] In addition, in the oil seal 44, the first joint 30 and the second joint 32 do not have the first tapered portion 30b and the second tapered portion 32b, so the joint area between the oil seal 44 and the canceller 12 is large, and there is a risk that the oil seal 44 will peel off from the canceller 12.

[0044] FIG. 6 is an enlarged cross-sectional view showing the outer circumferential end of the canceller 12 and an oil seal 50 according to another comparative example. In the oil seal 50, the first joint 30 joined to the first surface 12a of the canceller 12 has a first parallel portion 30a and a first tapered portion 30b. Also, the second joint 32 joined to the second surface 12b of the canceller 12 has a second parallel portion 32a and a second tapered portion 32b. However, the diameter D1 of the first inner circumferential edge 30c of the first tapered portion 30b is smaller than the diameter D2 of the second inner circumferential edge 32c of the second tapered portion 32b. Other features are the same as those of the canceller oil seal 24.

[0045] The oil seal 50 according to the comparative example is formed by press molding or injection molding using a mold 52 shown in Fig. 7. The forming procedure is the same as the forming procedure of the canceller oil seal 24.

[0046] In the oil seal 50 according to the comparative example, the diameter D1 of the first inner peripheral edge 30c of the first tapered portion 30b of the first joint 30 is different from the diameter D2 of the second inner peripheral edge 32c of the second tapered portion 32b of the second joint 32. Therefore, when pressure is applied to the elastomer material in the mold 52 to mold the oil seal 50, the load applied to the portion 54 forming the first tapered portion 30b of the mold 52 is significantly different from the load applied to the portion 55 forming the second tapered portion 32b of the mold 52, and the moment applied to the mold 52 is large. Therefore, the life of the mold 50 may be short.

[0047] However, in the canceller oil seal 24 according to the embodiment, the first joint 30 and the second joint 32 joined to both sides of the canceller 12 each have the tapered portions 30b, 32b, so that when pressure is applied to the elastomer material in the mold 40 to mold the canceller oil seal 24, stress is unlikely to concentrate on the portion of the mold 40 forming the first joint 30 and the portion of the mold 40 forming the second joint 32. In addition, since the diameter D1 of the first inner peripheral edge 30c of the first tapered portion 30b of the first joint 30 is equal to the diameter D2 of the second inner peripheral edge 32c of the second tapered portion 32b of the second joint 32, when pressure is applied to the elastomer material in the mold 40 to mold the canceller oil seal 24, the load applied to the portion of the mold 40 forming the first tapered portion 30b and the load applied to the portion of the mold 40 forming the second tapered portion 32b are similar, and the moment applied to the mold 40 is small. Therefore, it is possible to extend the life of the mold 40 used to mold the oil seal.

[0048] In addition, since the first tapered portion 30b and the second tapered portion 32b are respectively joined to both sides of the canceller 12, the joining area between the canceller oil seal 24 and the canceller 12 is large, and the canceller oil seal 24 is less likely to peel off from the canceller 12. In addition, since the first joint portion 30 and the second joint portion 32 each have the tapered portions 30b, 32b, when the canceller oil seal 24 is molded, stress is less likely to concentrate on the first joint portion 30 and the second joint portion 32 of the canceller oil seal 24 itself. Therefore, it is possible to extend the life of the oil seal itself.

[0049] Although the canceller oil seal 24 according to the embodiment of the present invention has been described above, the present invention may be applied to the inner oil seal 22 attached to the piston 10. FIG. 8 is an enlarged cross-sectional view of the inner oil seal 22 according to another embodiment of the present invention and the inner peripheral end of the piston 10. As described above, the piston 10 is a metal plate and has a first surface 10a, a second surface 10b, and an inner peripheral edge 10c. The first surface 10a faces toward the back of the piston chamber 8 (upward in FIG. 1), and the second surface 10b is substantially parallel to the first surface 10a. The second surface 10b and the inner peripheral edge 10c are perpendicular to each other, while the inner end 10d of the first surface 10a is formed as a curved surface in a circular arc shape and is continuous with the inner peripheral edge 10c.

[0050] The inner oil seal 22 has a first mating portion 60 , a second mating portion 62 , a connecting portion 64 , and a seal lip 66 .

[0051] The first joint 60 is joined to the first surface 10a of the piston 10, the second joint 62 is joined to the second surface 10b of the piston 10, and the connecting portion 64 connects the first joint 60 and the second joint 62 and covers the inner peripheral edge 10c and the arc-shaped inner end 10d of the piston 10.

[0052] The seal lip 66 protrudes obliquely from the first joint portion 60 and the connecting portion 64 radially inward and toward the back of the piston chamber 8. A lip edge 68 is formed at the innermost end of the seal lip 66, which comes into contact with the inner wall surface of the piston chamber 8 formed in the clutch housing 2.

[0053] The first joint portion 60 has a first parallel portion 60a parallel to the first surface 10a and a first tapered portion 60b extending from the first parallel portion 60a. The first tapered portion 60b has a thickness that gradually decreases toward the outside in the radial direction, and the thickness of the outer peripheral edge (first outer peripheral edge 60c) of the first tapered portion 60b is zero.

[0054] Similarly, the second joint portion 62 has a second parallel portion 62a parallel to the second surface 10b and a second tapered portion 62b extending from the second parallel portion 62a. The second tapered portion 62b has a thickness that gradually decreases radially outward, and the thickness of the outer peripheral edge (second outer peripheral edge 62c) of the second tapered portion 62b is zero.

[0055] The diameter D3 of the first outer peripheral edge 60c of the first tapered portion 60b is equal to the diameter D4 of the second outer peripheral edge 62c of the second tapered portion 62b. Preferably, the inclination angle θ3 of the first tapered portion 60b is also equal to the inclination angle θ4 of the second tapered portion 62b.

[0056] In the embodiment relating to the inner oil seal 22 attached to the piston 10, it is possible to achieve an effect similar to that of the embodiment of the canceller oil seal 24. In this embodiment, the canceller 12 may be omitted.

[0057] Although the present invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the scope of the invention as set forth in the appended claims. Such changes, modifications and alterations are intended to be embraced within the scope of the invention.

[0058] For example, the shapes of the seal lip 36 and the seal lip 66 are not limited to those shown in the drawings. [Explanation of symbols]

[0059] 1 Clutch piston mechanism 8 Piston chamber 10 Piston (piston seal) 10a First Side 10b The second aspect 10c Inner edge 10d inner end 12 Canceller (Canceller seal) 12a First Side 12b Second Side 12c Outer edge 12d outer edge 14 Oil chamber 22 Inner oil seal 24 Canceller oil seal 30 First Joint 30a First parallel section 30b First tapered portion 30c first inner peripheral edge 32 Second Junction 32a Second parallel section 32b Second tapered section 32c Second inner edge 34 Connecting part 36 Seal lip 38 Lip Edge 40-inch 42 Cavity 60 First Joint 60a First parallel section 60b First tapered portion 60c first outer peripheral edge 62 Second Joint 64 Connecting part 66 Seal Lip 62a Second parallel section 62b Second tapered section 62c Second outer edge

Claims

1. A ring-shaped oil seal made of an elastomer material attached to an outer peripheral edge or an inner peripheral edge of a metal plate having a first surface and a second surface, a first bonding portion bonded to a first surface of the metal plate; a second bonding portion bonded to a second surface of the metal plate; a connecting portion that connects the first joint portion and the second joint portion and covers an edge of the metal plate; a seal lip protruding obliquely from the first joint portion and the connecting portion; the first joint portion has a first parallel portion parallel to the first surface and a first tapered portion extending from the first parallel portion so as to gradually reduce in thickness, the first tapered portion having a first edge with a thickness of zero; the second joint portion has a second parallel portion parallel to the second surface and a second tapered portion extending from the second parallel portion so as to gradually reduce in thickness, the second tapered portion having a second edge with a thickness of zero; a diameter of a first edge of the first tapered portion is equal to a diameter of a second edge of the second tapered portion; The inclination angle of the first tapered portion with respect to the axial direction of the oil seal is equal to the inclination angle of the second tapered portion with respect to the axial direction of the oil seal. Oil seal.

2. A piston that reciprocates within a piston chamber into which oil flows; A canceller which is the metal plate and faces the piston and defines an oil chamber between the piston and the canceller; 2. The oil seal according to claim 1, which is attached to the canceller and seals the oil in the oil chamber, and further comprises an oil seal in which the seal lip slides against an inner wall surface that forms the oil chamber of the piston when the piston reciprocates. A clutch piston mechanism comprising:

3. A piston, which is the metal plate, reciprocates within a piston chamber into which oil flows; 2. The oil seal according to claim 1, which is attached to the piston and seals the oil in the piston chamber, the oil seal including: a seal lip that slides against a wall surface of the piston chamber when the piston reciprocates; A clutch piston mechanism comprising:

4. A method for manufacturing an annular oil seal made of an elastomer material and attached to an outer peripheral edge or an inner peripheral edge of a metal plate having a first surface and a second surface, comprising the steps of: The oil seal, a first bonding portion bonded to a first surface of the metal plate; a second bonding portion bonded to a second surface of the metal plate; a connecting portion that connects the first joint portion and the second joint portion and covers an edge of the metal plate; a seal lip protruding obliquely from the first joint portion and the connecting portion; the first joint portion has a first parallel portion parallel to the first surface and a first tapered portion extending from the first parallel portion so as to gradually reduce in thickness, the first tapered portion having a first edge with a thickness of zero; the second joint portion has a second parallel portion parallel to the second surface and a second tapered portion extending from the second parallel portion so as to gradually reduce in thickness, the second tapered portion having a second edge with a thickness of zero; a diameter of a first edge of the first tapered portion is equal to a diameter of a second edge of the second tapered portion; The manufacturing method is preparing a mold having a cavity having a shape for forming the first joint portion, the second joint portion, the connecting portion, and the seal lip of the oil seal, wherein a wall portion forming the first tapered portion of the cavity is a first inclined wall portion having the same inclination as the first tapered portion, and a wall portion forming the second tapered portion of the cavity is a second inclined wall portion having the same inclination as the second tapered portion, the mold having a first flat portion facing and in surface contact with the first surface of the metal plate and a second flat portion facing and in surface contact with the second surface of the metal plate, the first inclined wall portion continuing without a step into the first flat portion, and the second inclined wall portion continuing without a step into the second flat portion; Fixing the metal plate to the mold such that an outer peripheral edge or an inner peripheral edge of the metal plate is disposed in a cavity of the mold; introducing an elastomeric material into the cavity and forming the oil seal. A manufacturing method for oil seals.

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