Piston manufacturing device, piston manufacturing method, piston and disc brake

A piston manufacturing device includes a first forming device (42) configured to form an annular groove (61) in a piston (11), and a second forming device (52) configured to press an edge (15) of an opening (14) of the piston (11) toward other end side in an axial direction of the piston (11) and to form a thick section (65) extruded from an inner circumferential surface (12b) arranged between the edge (15) and the groove (61) toward an axial center side of the piston (11), wherein a recessed section (53) is formed at a portion of the second forming device (52) that is arranged to abut the edge (15) so that an inner circumferential side of the edge (15) is plastically deformed toward the other end side in an axial direction of the piston (11).

TECHNICAL FIELD

The present invention relates to a piston manufacturing device, a piston manufacturing method, a piston and a disc brake.

This application is the U.S. national phase of International Application No. PCT/JP2015/061071 filed Apr. 9, 2015 which designated the U.S. and claims priority to JP Patent Application No. 2014-156158 filed Jul. 31, 2014, the entire contents of each of which are hereby incorporated by reference.

BACKGROUND ART

A manufacturing device for pressing an end surface of an opening side of a cylindrical material from a side in an axial direction of the material when the opening side of the cylindrical material is pressed from an outer circumferential side thereof to form a groove in the material (for example, see Patent Literature 1) is known.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the above-mentioned manufacturing device, a variation may occur in a shape of a surface of the material in contact with the pad of the end surface of the piston.

The present invention provides a piston manufacturing device, a piston manufacturing method, a piston and a disc brake that are capable of suppressing a variation in a shape of a surface of a material which contacts with a pad at an end surface of a piston.

Solution to Problem

According to a first aspect of the present invention, a piston manufacturing device includes a first forming device configured to press a portion of a piston from an outer circumferential side of the piston to form an annular groove, the portion of the piston being separated from an edge of an opening provided at one end side in an axial direction of the piston; and a second forming device configured to press the edge of the opening of the piston toward other end side in the axial direction of the piston and to form a thick section extruded from an inner circumferential surface of the piston toward an axial center side of the piston, the inner circumferential surface being formed between the edge and the groove, wherein a recessed section is formed at a portion of the second forming device that is arranged to abut the edge so that an inner circumferential side of the edge is plastically deformed toward the other end side in the axial direction of the piston.

According to a second aspect of the present invention, a piston manufacturing method includes a groove forming step of pressing a portion of a piston from an outer circumferential side of the piston and forming an annular groove, the portion of the piston being separated from an edge of an opening provided at one end side in an axial direction of the piston; and a thick section forming step of pressing the edge of the opening of the piston toward other end side in the axial direction of the piston and forming a thick section extruded from an inner circumferential surface of the piston toward an axial center side of the piston, the inner circumferential surface being formed between the edge and the groove, wherein the thick section forming step includes plastically deforming an inner circumferential side of the edge toward the other end side in the axial direction of the piston.

According to a third aspect of the present invention, in a piston, a portion in a central axis direction of an edge of an opening of one end side in the axial direction is a thick section protruding in the central axis direction, and the thick section is folded toward the bottom section. A cross section of the folded area is a curved line.

According to a fourth aspect of the present invention, a disc brake includes the piston; a cylinder in which the piston is movably disposed; and a brake pad arranged to be pressed by the edge of the opening of the piston and come in contact with a disc.

Advantageous Effects of Invention

According to the above-mentioned piston manufacturing device, it is possible to provide a piston manufacturing device, a piston manufacturing method, a piston and a disc brake that are capable of suppressing a variation in a shape of a surface of a material which contacts with a pad at an end surface of a piston.

DESCRIPTION OF EMBODIMENTS

First Embodiment

A first embodiment according to the present invention will be described below with reference toFIGS. 1 to 5.

As shown inFIG. 1, a piston manufacturing device10of the first embodiment machines a piston11in a state of a material having a bottomed cylindrical shape.

Referring toFIG. 1, first, the piston11in a state of the material before machining by the piston manufacturing device10will be described. The piston11in a state of a material has a tubular section12having a cylindrical shape, and a bottom section13having a disc shape. Central axes of the tubular section12and the bottom section13coincide with each other, and this central axe is a central axis of the piston11.

The bottom section13closes one end side of the tubular section12in an extension direction of a central axis of the piston11(hereinafter, referred to as a piston axial direction). In addition, a side of the tubular section12opposite to the bottom section13in the piston axial direction is an opening14that is open without being blocked. An edge15of an end portion of the opening14opposite to the bottom section13in the piston axial direction is a farthest end portion of the piston11opposite to the bottom section13in the piston axial direction. Accordingly, the piston11in the state of the material has a bottomed cylindrical shape.

In the tubular section12, a range of an outer circumferential surface12aexcept for both end portions in the piston axial direction is an outer circumferential cylindrical surface12a1formed by a cylindrical surface having a constant diameter about the central axis of the piston11. In addition, in the tubular section12, a range of an inner circumferential surface12bexcept for both end portions in the piston axial direction is an inner circumferential cylindrical surface12b1constituted by a cylindrical surface having a constant diameter about the central axis of the piston11. The piston11in the state of the material has the outer circumferential cylindrical surface12a1having a maximum diameter. In addition, the opening14of the piston11in the state of the material has the inner circumferential cylindrical surface12b1having a minimum diameter.

In an outer bottom surface13aof the bottom section13provided opposite to the opening14in the piston axial direction, a central range in the radial direction of the piston11has an outer bottom flat surface13a1that is planar and perpendicular to the central axis of the piston11. In addition, in an inner bottom surface13bof the bottom section13formed at the opening14side in the piston axial direction, a central range in the radial direction of the piston11has an inner bottom flat surface13b1that is planar and perpendicular to the central axis of the piston11.

The piston11in the state of the material is a forged article formed of, for example, a steel material or an aluminum alloy material, and after forging, is formed in the above-mentioned shape to adjust a length in the piston axial direction when allowing some error (variation) and cutting the opening14side.

The piston manufacturing device10is a rotating plastic working apparatus (a spinning apparatus) configured to plastically deform the piston11serving as a workpiece while rotating the piston11, and has a rotating device21, a groove forming device22and an edge forming device23.

The rotating device21has a gripping part31and a clamping part32. The gripping part31grips the outer circumferential cylindrical surface12a1of the tubular section12of the piston11in the state of the material from the outside in a radial direction of the piston11(hereinafter, referred to as a piston radial direction). The clamping part32sandwiches the bottom section13of the piston11in the state of the material from both sides in the piston axial direction. The rotating device21rotates the gripping part31and the clamping part32about a rotation central axis O1using a driving force of a motor (not shown). The rotating device21is disposed in a posture in which the rotation central axis O1extends vertically.

The gripping part31can be increased and reduced in diameter about the rotation central axis O1. The gripping part31grips the piston11by reducing the diameter and releases the gripping of the piston11by increasing the diameter. The gripping part31uniformly presses a plurality of places (for example, three places) in a circumferential direction on the outer circumferential cylindrical surface12a1of the piston11(hereinafter, referred to as a piston circumferential direction) in a direction of a central axis of the piston11(hereinafter, referred to as a piston central axis direction) when the piston11is gripped. Accordingly, the gripping part31causes the central axis of the piston11to coincide with the rotation central axis O1upon gripping of the piston11to be integrally rotated with the piston11. For example, a collet chuck may be used as the gripping part31.

The clamping part32has an outer core bar33and an inner core bar34. The outer core bar33abuts the outer bottom flat surface13a1of the bottom section13of the piston11outside the piston11. The inner core bar34is disposed above the outer core bar33, enters the piston11from the opening14, and abuts the inner bottom flat surface13b1of the bottom section13of the piston11. The outer core bar33and the inner core bar34coincide with the rotation central axis O1at the central axes thereof. The outer core bar33of the lower side always causes positions in the extension direction of the gripping part31and the rotation central axis O1to coincide with each other. The inner core bar34can approach and be separated from the outer core bar33in the extension direction of the rotation central axis O1.

The piston11is disposed at the rotating device21such that the outer bottom flat surface13a1abuts the outer core bar33in a state in which the gripping part31is increased in diameter and the inner core bar34is separated from the outer core bar33. Then, from this state, the rotating device21causes the inner core bar34to approach the outer core bar33to abut the inner bottom flat surface13b1and reduces a diameter of the gripping part31. Accordingly, the inner core bar34and the outer core bar33of the clamping part32sandwich the bottom section13and the gripping part31grips the tubular section12. In this way, the rotating device21integrally rotatably supports the piston11. When the piston11is supported by the rotating device21in this way, the piston11has a portion of the opening14side of the tubular section12protruding upward from the gripping part31.

The rotating device21rotates the gripping part31and the clamping part32about the rotation central axis O1using a driving force of a motor (not shown) in a state in which the piston11is supported. Thus, the piston11is also rotated in a state in which a position in an extension direction of the rotation central axis O1is constant about the rotation central axis O1. As a result, the piston11is rotated in the piston circumferential direction while the position in the piston axial direction is constant about the central axis. That is, the rotating device21rotates the piston11in the piston circumferential direction.

The groove forming device22has a head41and a groove forming roller42(a first forming device). The head41is linearly and horizontally moved to approach or be separated from the rotation central axis O1of the rotating device21, i.e., moved in the radial direction of the piston11using a driving force of the motor (not shown). The groove forming roller42is disposed under the head41, and supported by the head41to be rotated about a rotation central axis O2parallel to the rotation central axis O1. The groove forming roller42approaches and is separated from the rotation central axis O1in a state in which a position in the extension direction of the rotation central axis O2is constant.

The groove forming roller42has a tapered outer circumferential surface42a, a stepped surface42b, a cylindrical outer circumferential surface42c, a stepped surface42d, a tapered outer circumferential surface42e, a cylindrical outer circumferential surface42fand an end surface42gin sequence from the head41side in the extension direction of the rotation central axis O2.

The tapered outer circumferential surface42ais a tapered surface formed about the rotation central axis O2and having a diameter that increases downward.

The stepped surface42bextends from the lower edge portion of the tapered outer circumferential surface42aoutward in the radial direction. The stepped surface42bhas an annular shape about the rotation central axis O2and a flat surface disposed at the same plane as the surface perpendicular to the rotation central axis O2.

The cylindrical outer circumferential surface42cis a cylindrical surface extending downward from the outer circumferential edge portion of the stepped surface42band formed about the rotation central axis O2.

The stepped surface42dextends from the lower edge portion of the cylindrical outer circumferential surface42cinward in the radial direction. The stepped surface42dis a flat surface having an annular shape about the rotation central axis O2and disposed at the same plane as the surface perpendicular to the rotation central axis O2. The stepped surface42dhas a difference between inner and outer diameters larger than that of the stepped surface42b, and a width in the radial direction that increases.

The tapered outer circumferential surface42eis a tapered surface extending downward from the inner circumferential edge portion of the stepped surface42dand formed about the rotation central axis O2. The tapered outer circumferential surface42ehas a diameter that decreases downward.

The cylindrical outer circumferential surface42fis a cylindrical surface extending downward from the lower edge portion of the tapered outer circumferential surface42eand formed about the rotation central axis O2. The cylindrical outer circumferential surface42fhas a diameter smaller than that of the cylindrical outer circumferential surface42c.

The end surface42gextends from the lower edge portion of the cylindrical outer circumferential surface42finward in the radial direction. The end surface42gis a flat surface having a circular shape about the rotation central axis O2and disposed at the same plane as the surface perpendicular to the rotation central axis O2.

The groove forming roller42is disposed above the gripping part31of the rotating device21, and overlaps with the tubular section12protruding upward from the gripping part31of the piston11supported by the rotating device21at positions in the extension direction of the rotation central axes O1and O2. More specifically, in the groove forming roller42, a portion of the stepped surface42bside of the tapered outer circumferential surface42a, the stepped surface42b, the cylindrical outer circumferential surface42c, the stepped surface42d, the tapered outer circumferential surface42e, the cylindrical outer circumferential surface42fand the end surface42goverlap the tubular section12at positions in the extension direction of the rotation central axes O1and O2.

The edge forming device23has a head51and an edge forming roller52(a second forming device). The head51linearly moves, i.e., vertically rises in a direction along the rotation central axis O1of the rotating device21using a driving force of the motor (not shown), i.e., moves in the axial direction of the piston11. The edge forming roller52is disposed at the rotation central axis O1side of the head51and supported by the head51to be rotated about a rotation central axis O3perpendicular to the rotation central axis O1. The edge forming roller52is made to approach and is separated from the rotating device21by raising the edge forming roller52in a state in which a position in the extension direction of the rotation central axis O3is constant.

The edge forming roller52has a cylindrical outer circumferential surface52a, a tapered outer circumferential surface52b, a stepped surface52c, a tapered outer circumferential surface52d, a cylindrical outer circumferential surface52e, a spherical outer circumferential surface52f, a tapered outer circumferential surface52gand an end surface52hin sequence from the head51side in the extension direction of the rotation central axis O3.

The cylindrical outer circumferential surface52ais a cylindrical surface formed about the rotation central axis O3.

The tapered outer circumferential surface52bis a tapered surface extending from an edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52atoward the rotation central axis O1and formed about the rotation central axis O3. The tapered outer circumferential surface52bhas a diameter that decreases toward the rotation central axis O1.

The stepped surface52cextends from the edge portion of the rotation central axis O1side of the tapered outer circumferential surface52binward in the radial direction. The stepped surface52cis a flat surface forming an annular shape about the rotation central axis O3and disposed at the same plane as the surface perpendicular to the rotation central axis O3.

The tapered outer circumferential surface52dis a tapered surface extending from the inner circumferential edge portion of the stepped surface52ctoward the rotation central axis O1and formed about the rotation central axis O3. The tapered outer circumferential surface52dhas a diameter that decreases toward the rotation central axis O1.

The cylindrical outer circumferential surface52eis a cylindrical surface extending from the edge portion of the rotation central axis O1side of the tapered outer circumferential surface52dtoward the rotation central axis O1and formed about the rotation central axis O3. The cylindrical outer circumferential surface52ehas a diameter smaller than that of the stepped surface52c.

The spherical outer circumferential surface52fextends from the edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52etoward the rotation central axis O1, and is a portion of a surface of a sphere having a center at the rotation central axis O3or a spheroid having a rotational center at the rotation central axis O3. The spherical outer circumferential surface52fhas a diameter about the rotation central axis O3that increases toward the rotation central axis O1. The spherical outer circumferential surface52fconstituted by the portion of the surface of the sphere or the spheroid is a curved surface having a curved cross section when cut in the rotation axial direction, in other words, having a predetermined curvature.

The tapered outer circumferential surface52gis a tapered surface extending from the edge portion of the rotation central axis O1side of the spherical outer circumferential surface52ftoward the rotation central axis O1and formed about the rotation central axis O3. The tapered outer circumferential surface52ghas a diameter that decreases toward the rotation central axis O1.

The end surface52hextends from the edge portion of the rotation central axis O1side of the tapered outer circumferential surface52ginward in the radial direction. The end surface52his a flat surface having a circular shape about the rotation central axis O3and perpendicular to the rotation central axis O3.

As the stepped surface52c, the tapered outer circumferential surface52d, the cylindrical outer circumferential surface52eand the spherical outer circumferential surface52fare formed, a recessed section53recessed inward in the radial direction is formed at the edge forming roller52. The recessed section53also has an annular shape about the rotation central axis O3. The recessed section53is curved such that the spherical outer circumferential surface52fconstituting a portion thereof has a predetermined curvature.

The edge forming roller52is disposed above the gripping part31of the rotating device21, and the tubular section12including the opening14of the piston11and the edge forming roller52overlap each other at a position in the extension direction of the rotation central axis O3in the state of the material supported by the rotating device21. More specifically, the tapered outer circumferential surface52dand the cylindrical outer circumferential surface52eof the edge forming roller52overlap the tubular section12including the opening14of the piston11in the state of the material at a position in the extension direction of the rotation central axis O3.

The piston manufacturing device10rotates the gripping part31and the clamping part32of the rotating device21about the rotation central axis O1when the piston11in the state of the material is machined in a state in which the piston11is attached to the rotating device21as described above. Then, the piston11is rotated about the rotation central axis O1, i.e., the central axis of the piston11in the piston circumferential direction. This is a rotation step of a piston manufacturing method of rotating the piston11in the state of the cylindrical material in the piston circumferential direction.

The head51of the edge forming device23approaches the piston11driven and rotated by the rotating device21in this way by a driving force of the motor (not shown) while the head41of the groove forming device22approaches the piston11using the driving force of the motor (not shown).

When the head41approaches the piston11, the groove forming roller42mainly brings the cylindrical outer circumferential surface42cin contact with a portion of the piston11separated from the edge15of the opening14of one end side in the axial direction, and presses the portion from the outer circumferential cylindrical surface12a1side of the piston11. Then, the groove forming roller42forms an annular groove61shown inFIG. 2by plastically deforming the tubular section12at the outer circumferential side of the piston11using a portion of the stepped surface42bside of the tapered outer circumferential surface42a, the stepped surface42b, the cylindrical outer circumferential surface42c, the stepped surface42dand the tapered outer circumferential surface42ewhile being rotated around the rotating piston11. This is a groove forming step of the piston manufacturing method of pressing the portion of the piston11separated from the edge15of the opening14at one end side in the axial direction from the outer circumferential surface12aside of the piston11to form the annular groove61.

Here, according to formation of the groove61, an annular swelling section62that swells to have a diameter smaller than that of the inner circumferential cylindrical surface12b1is formed at a back surface of the groove61in the tubular section12. The groove61has an annular shape formed about the rotation central axis O1, i.e., the central axis of the piston11. The swelling section62also has an annular shape formed about the rotation central axis O1, i.e., the central axis of the piston11. Further, the head41sends the groove forming roller42toward the rotation central axis O1, i.e., the central axis of the piston11until the cylindrical outer circumferential surface42fof the groove forming roller42comes in contact with the outer circumferential cylindrical surface12a1of the piston11.

The head51of the edge forming device23approaches the piston11while the head41of the groove forming device22approaches the piston11as described above. As shown inFIG. 1, the edge forming roller52separated from the piston11causes the tapered outer circumferential surface52dand the cylindrical outer circumferential surface52ethat form the recessed section53to abut the edge15of the opening14at one end side in the axial direction of the piston11. Then, the edge15is pressed against the other end side in the axial direction opposite to the edge15of the piston11by mainly the tapered outer circumferential surface52dand the cylindrical outer circumferential surface52e. Then, the edge forming roller52plastically deforms the opening14of the piston11such that the position of the edge15approaches the bottom section13in the piston axial direction as shown inFIG. 2.

Here, the opening14of the piston11is restricted from being deformed toward an opposite side of the rotation central axis O1by the stepped surface52cformed at an opposite side of the rotation central axis O1of the recessed section53. Accordingly, a portion of an inner circumferential side of the edge15mainly extends inward in the radial direction, and at this time, the opening14is plastically deformed along the spherical outer circumferential surface52ftoward the other end side in the axial direction (the bottom section13side in the piston axial direction). As a result, a portion of mainly the inner circumferential side of the edge15becomes a thick section65extruded from the inner circumferential surface12bbetween the edge15and the groove61toward the rotation central axis O1, which serves as an axial center of the piston11, further than the inner circumferential cylindrical surface12b1, and protrudes toward the rotation central axis O1. This is a thick section forming step of the piston manufacturing method of pressing the edge15of the opening14of the piston11against the other end side in the axial direction of the piston11using the recessed section53, and forming the thick section65extruded toward the axial center side of the piston11from the inner circumferential surface12bbetween the edge15and the groove61. The thick section forming step includes plastically deforming the inner circumferential side of the edge15toward the other end side in the axial direction of the piston11.

The recessed section53is formed at the portion of the edge forming roller52abutting the edge15of the piston11such that the inner circumferential side of the edge15is plastically deformed toward the other end side in the axial direction of the piston11.

Here, in the piston manufacturing device10, when the piston11is machined, the inner core bar34does not come in contact with the opening14including the edge15of the piston11, and the inner core bar34does not press the edge15of the piston11from the inside. That is, the piston manufacturing device10does not include a means configured to press the edge15of the piston11from the inside, except for the recessed section53. In other words, the piston manufacturing device10does not include a means configured to form a minimum diameter portion while coming in contact with the thick section65.

As shown inFIG. 3, the groove61of the piston11formed by the piston manufacturing device10has a tapered surface61a, a groove wall surface61b, a groove bottom surface61c, a groove wall surface61dand a tapered surface61ein sequence from a side close to the edge15.

The tapered surface61ais a portion formed by the tapered outer circumferential surface42aof the groove forming roller42and has a shape to which the tapered outer circumferential surface42ais transferred. That is, the tapered surface61ais a tapered surface formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. As shown inFIG. 3, the tapered surface61aextends from the outer circumferential cylindrical surface12a1of the piston11, and has a diameter that decreases toward an opposite side of the edge15in the piston axial direction.

The groove wall surface61bis a portion formed by the stepped surface42bof the groove forming roller42, and has a shape to which the stepped surface42bis transferred. That is, the groove wall surface61bextends from the inner circumferential edge portion opposite to the edge15in the piston axial direction of the tapered surface61ainward in the piston radial direction. The groove wall surface61bis a flat surface having an annular shape formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11, and disposed at the same plane as the surface perpendicular to the rotation central axis O1.

As shown inFIG. 3, the groove bottom surface61cis a portion formed by the cylindrical outer circumferential surface42cof the groove forming roller42, and has a shape to which the cylindrical outer circumferential surface42cis transferred. That is, the groove bottom surface61cextends from the inner circumferential edge portion of the groove wall surface61bin a direction opposite to the edge15in the piston axial direction. The groove bottom surface61cis a cylindrical surface formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11.

As shown inFIG. 3, the groove wall surface61dis a portion formed by the stepped surface42dof the groove forming roller42and has a shape to which the stepped surface42dis transferred. That is, the groove wall surface61dextends from the edge portion of the groove bottom surface61copposite to the edge15in the piston axial direction outward in the piston radial direction. The groove wall surface61dis a flat surface having an annular shape formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11and disposed at the same plane as the surface perpendicular to the rotation central axis O1.

As shown inFIG. 3, the tapered surface61eis a portion formed by the tapered outer circumferential surface42eof the groove forming roller42and has a shape to which the tapered outer circumferential surface42eis transferred. That is, the tapered surface61eis a tapered surface formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. As shown inFIG. 3, the tapered surface61eextends from the outer circumferential edge portion of the groove wall surface61dto the outer circumferential cylindrical surface12a1of the piston11and has a diameter that increases toward an opposite side of the edge15in the piston axial direction.

As shown inFIG. 4, the edge15of the opening14of the piston11after machining by the piston manufacturing device10has a tapered surface15aand an end surface15bin sequence from a side close to the outer circumferential cylindrical surface12a1.

The tapered surface15ais a portion formed by the tapered outer circumferential surface52dof the recessed section53of the edge forming roller52and has a shape to which the tapered outer circumferential surface52dis transferred. That is, the tapered surface15ais a tapered surface formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. As shown inFIG. 4, the tapered surface15aextends from the edge portion of the edge15side in the piston axial direction of the outer circumferential cylindrical surface12a1and has a diameter that decreases toward an extension end side.

The end surface15bis a portion formed by the cylindrical outer circumferential surface52eof the recessed section53of the edge forming roller52and has a shape to which the cylindrical outer circumferential surface52eis transferred. That is, the end surface15bis a flat surface having an annular shape formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11and disposed at the same plane as the surface perpendicular to the rotation central axis O1. In the piston11, the end surface15bis disposed at the most opposite side of the bottom section13shown inFIG. 2in the piston axial direction.

As shown inFIG. 4, the thick section65after formation by the piston manufacturing device10has a curved surface65a, a curved surface65b, a tapered surface65c, a radial surface65dand a curved surface65ein sequence from the end surface15bside. The curved surface65ais also a portion of the edge15of the opening14.

The curved surface65ais a portion formed by the spherical outer circumferential surface52fof the recessed section53of the edge forming roller52. The curved surface65ahas an annular shape formed about the rotation central axis O1shown inFIG. 2. i.e., the central axis of the piston11. As shown inFIG. 4, the curved surface65ahas a shape to which the spherical outer circumferential surface52fof the recessed section53of the edge forming roller52is transferred. That is, the curved surface65aextends from the inner circumferential edge portion of the rotation central axis O1side shown inFIG. 2of the end surface15bin the piston central axis direction, and is inclined to be disposed closer to the bottom section13as it goes toward a piston axial center side. Accordingly, the thick section65has a shape folded toward the bottom section13. A cross section of the folded area is a curved shape and has a curved surface having a predetermined curvature. The curved surface65ahas a cross section having an arc shape in a plane including the rotation central axis O1, i.e., the central axis of the piston11. The arc has a center disposed closer to the central axis of the piston11than a central position between both end portions thereof and opposite to the bottom section13in the piston axial direction. In other words, the arc has a shape recessed toward the inside of the piston11.

The curved surface65bshown inFIG. 4extends from the inner circumferential edge portion of the curved surface65a, and has an arc shape having a cross section at a plane including the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. The arc has a center at an opposite side of the central axis of the piston11. The curved surface65bhas an annular shape formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11.

The tapered surface65cshown inFIG. 4is a tapered surface extending from the edge portion of the curved surface65bopposite to the curved surface65aand formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. The tapered surface65cshown inFIG. 4is a tapered surface having a diameter that increases away from the end surface15bin the piston axial direction.

The radial surface65dextends from the outer circumferential edge portion of the tapered surface65coutward in the piston radial direction. The radial surface65dhas an annular shape formed about the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11.

The curved surface65eextends from the outer circumferential edge portion of the radial surface65doutward in the piston radial direction to be connected to the inner circumferential surface12b. The curved surface65ehas an annular shape formed about the rotation central axis O1, i.e., the central axis of the piston11. The curved surface65eis inclined to be disposed at an opposite side of the end surface15bin the piston axial direction as it goes outward in the piston radial direction. The curved surface65ehas an arc shape having a cross-sectional shape at a plane including the rotation central axis O1shown inFIG. 2, i.e., the central axis of the piston11. The arc has a concave shape recessed toward the inside of the piston11.

As shown inFIG. 4, the thick section65has a minimum diameter smaller than the minimum diameter of the swelling section62, and the minimum diameter of the curved surface65ais also smaller than that of the swelling section62. The maximum diameter of the curved surface65a, i.e., the minimum diameter of the end surface15bis larger than the minimum diameter of the swelling section62, and smaller than the inner circumferential cylindrical surface12b1of the tubular section12.

The edge15including the tapered surface15aand the end surface15b, and the thick section65including the curved surface65a, the curved surface65b, the tapered surface65c, the radial surface65dand the curved surface65eare portions of the piston11formed by plastic deformation from the state of the material, and portions present in the piston11also in a final product state (a state in which the portions are incorporated in a brake apparatus, which will be described below). That is, cutting of the groove61and the edge15of the opening14is not performed until the piston11reaches the final product state from the material. Further, the piston11is a cuttingless piston in which cutting of the piston including the cutting of the groove61and the edge15are not performed to the entire piston11until the piston11reaches the final product state from the material.

The piston11formed by the above-mentioned piston manufacturing device10is formed in a bottomed cylindrical shape and includes the bottom section13and the tubular section12, and the tubular section12includes the edge15of the opening14at one end side in the axial direction. Thus, the piston11has the thick section65in which an area of the edge15in the central axis direction of the piston11protrudes in the central axis direction. The thick section65is folded toward the bottom section13, and a cross section of the folded area has a curved surface shape, which is curved, having a predetermined curvature.

The piston11formed by the piston manufacturing device10is disposed in a cylinder of a brake apparatus. Specifically, the piston11is incorporated in a disc brake80shown inFIG. 5. The disc brake80may be for a vehicle such as an automobile, specifically, a four-wheeled automobile. The disc brake80brakes the vehicle by stopping rotation of a disc81rotated with a wheel (not shown).

The disc brake80includes a support member82, a pair of brake pads83and84, and a pressing mechanism85. The support member82is disposed over the outer circumferential side of the disc81to be fixed to a non-rotation section of the vehicle. The pair of brake pads83and84are supported by the support member82to be disposed to oppose both surfaces of the disc81. The pressing mechanism85causes the pair of brake pads83and84to sandwich the disc81to press both surfaces of the disc81.

The pressing mechanism85has a caliper body91, the above-mentioned piston11, a piston seal92, a piston boot93and a pressing plate94. The piston11is slidably installed at an inner side of the caliper body91(inside in the vehicle width direction). The piston seal92seals a gap between the caliper body91and the piston11. The piston boot93is connected to the caliper body91and the piston11to cover a portion of the piston11exposed from the caliper body91.

The caliper body91has a cylinder96, a bridge section97and a claw section98. The bridge section97extends from the cylinder96to cross over an outer circumference of the disc81. The claw section98extends from a side of the bridge section97opposite to the cylinder96to oppose the cylinder96. A bore100opening at the claw section98side is formed in the cylinder96, and the piston11is movably disposed in the bore100.

As the bore100is formed, the cylinder96has a bottom section101opposite to the claw section98, and a tubular section102extending from an outer circumferential edge portion of the bottom section101toward the claw section98to form a cylindrical shape. An annular piston seal groove103is formed at an inner circumferential surface of the bore100, and an annular boot support groove104is formed closer to the claw section98than the piston seal groove103. The piston seal92is fitted into the piston seal groove103. A through-hole105is formed in the bottom section101of the cylinder96. The through-hole105is closed by a cap106attached upon assembly to the vehicle.

Then, the piston11is fitted into the bore100and the piston seal92in a posture in which the bottom section13is disposed at the bottom section101side in the bore100. The piston seal92seals a gap between the cylinder96and the piston11. One end side of the piston boot93is fitted into the boot support groove104of the cylinder96to be connected to the cylinder96, and the other end side is fitted into the groove61of the piston11to be connected to the piston11.

The pressing plate94is attached to the piston11. The pressing plate94covers a side of the tubular section12of the piston11opposite to the bottom section13. The piston11abuts the pressing plate94at the end surface15bof the edge15of the tubular section12opposite to the bottom section13.

The pressing mechanism85applies a brake pressure to the bottom section13of the piston11when a brake liquid is introduced into the bore100of the cylinder96from the through-hole105. Then, the piston11advances toward the disc81and presses the brake pad83at the inner side toward the disc81via the pressing plate94. Here, as the edge15of the opening14of the piston11causes the end surface15bto abut the pressing plate94, the brake pad83is pressed at a portion of the end surface15b. Accordingly, the brake pad83is moved to come in contact with the disc81. That is, the brake pad83is pressed by the end surface15bof the edge15of the opening14of the piston11to come in contact with the disc81.

In addition, the caliper body91is moved by a repulsive force of the pressing, and the brake pad84of the outer side is pressed toward the disc81by the claw section98. Accordingly, the brake pad84comes in contact with the disc81.

As described above, the pressing mechanism85sandwiches the pair of brake pads83and84from both sides by an action of the piston11using the piston11and the claw section98to press against both surfaces of the disc81. As a result, the pressing mechanism85applies a frictional resistance to the disc81to generate a braking force.

In the device and method for manufacturing the piston for a brake disclosed in Patent Literature 1, when an annular end portion of an opening side of the material is pressed from an outer circumferential side by a first roller to form a groove, the annular end portion of the material is pressed from the axial direction by a second roller at different positions in the circumferential direction to form a thick section extruded in the central axis direction from the inner circumferential surface of the annular end portion. For this reason, the end surface of the annular end portion of the piston differs in a radial dimension or an axial dimension depending on a position in the circumferential direction, a shape of the surface in contact with the pad differs, and a portion of the surface in contact with the pad may receive an influence of a variation in dimensions of the material to be widened or narrowed to cause a variation (individual differences). Since the portion of the end surface is a portion that presses the brake pad, when variation occurs, a surface pressure may be unstable and brake noise suppression performance may be unstable depending on the piston. In addition, even when an inner diameter or an outer diameter in contact with the pad differs, this causes brake noise.

On the other hand, in the piston manufacturing device10of the first embodiment, the recessed section53is formed at a portion of the edge forming roller52abutting the edge15of the opening14of the piston11such that an inner circumferential side of the edge15is plastically deformed toward the bottom section13in the piston axial direction. Then, in a thick section forming step of pressing the edge15of the opening14of the piston11toward the bottom section13in the piston axial direction and forming the thick section65extruded from the inner circumferential surface12bbetween the edge15and the groove61toward a piston axial center, the inner circumferential side of the edge15is plastically deformed toward the bottom section13in the piston axial direction by the recessed section53. Accordingly, even when there is a variation in the material, a variation in area of the end surface15bof the edge15of the opening14of the piston11can be suppressed. As a result, in the disc brake80into which the piston11is incorporated, the surface pressure to the brake pad83of the piston11can be stabilized and brake noise performance can be stabilized. Moreover, like the case in which the end surface15bis formed through cutting, a variation in area of the end surface15bcan be suppressed by plastic deformation. For this reason, the variation of a contact shape with the pad can be suppressed and manufacturing costs of the piston11can be suppressed.

In other words, in the piston11of the first embodiment, the portion in the piston central axis direction of the edge15of the opening14is the thick section65protruding in the central axis direction, and the thick section65is folded toward the bottom section13of the piston11. For this reason, when a final shape of the edge15side of the opening14is formed by plastic deformation, variations in area, inner diameter and outer diameter of the end surface15bof the edge15of the opening14of the piston11can be suppressed.

Further, in other words, the disc brake80of the first embodiment can suppress the variation in area of the end surface15bof the edge15of the opening14of the piston11. For this reason, the surface pressure to the brake pad83of the piston11can be stabilized and brake noise suppression performance can be stabilized.

In addition, in the piston manufacturing device10of the first embodiment, the spherical outer circumferential surface52fof the recessed section53of the edge forming roller52has a predetermined curvature. For this reason, a difference in circumferential speed between the piston11and the spherical outer circumferential surface52fcan be decreased, and friction due to the difference in circumferential speed can be reduced. Accordingly, stress applied to the edge forming roller52and the piston11can be reduced. As a result, a lifetime of the edge forming roller52can be lengthened and a load to the piston manufacturing device10can be suppressed. In addition, a decrease in quality such as burning or the like of the piston11can be suppressed. In addition, since a contact area between the edge forming roller52and the piston11can be reduced and the surface pressure upon machining can be increased, formability can be improved.

In other words, the folded area of the piston11of the first embodiment has the curved surface65a. For this reason, when the final shape of the edge15side of the opening14is formed by plastic deformation, the variation in area of the end surface15bof the edge15of the opening14of the piston11can be suppressed. In addition, the folded area of the piston11of the first embodiment has the curved surface65a. For this reason, when the edge15of the opening14of the piston11is formed by plastic deformation, stress applied to the piston11and the piston manufacturing device10can be reduced. In addition, a decrease in quality such as burning or the like of the piston11can be suppressed. In addition, formability can be improved.

In addition, in the piston manufacturing device10of the first embodiment, only the recessed section53is provided as a means configured to press the edge15of the opening14of the piston11from the inside of the piston11. For this reason, the structure can be simplified and manufacturing cost can be reduced.

Second Embodiment

Next, a second embodiment will be described with reference toFIG. 6mainly focusing on differences from the first embodiment. Further, parts the same as in the first embodiment are designated by the same names and the same reference numerals.

In the second embodiment, a piston manufacturing device10A partially different from the piston manufacturing device10of the first embodiment is used. In the piston manufacturing device10A, an edge forming device23A partially different from the edge forming device23of the first embodiment is used. Specifically, an edge forming roller52A partially different from the edge forming roller52of the first embodiment is used.

The edge forming roller52A of the second embodiment has a spherical outer circumferential surface52Afin which an angle with respect to the rotation central axis O3is shallower than that of the spherical outer circumferential surface52fof the first embodiment. That is, a ratio of a variation in diameter with respect to a variation in distance in a direction along the rotation central axis O3of the spherical outer circumferential surface52Afis smaller than that for the spherical outer circumferential surface52fof the first embodiment.

A cylindrical outer circumferential surface52iextending from the edge portion of the rotation central axis O1side of the spherical outer circumferential surface52Aftoward the rotation central axis O1is formed at the edge forming roller52A of the second embodiment. The cylindrical outer circumferential surface52iis a cylindrical surface formed about the rotation central axis O3. As the stepped surface52c, the tapered outer circumferential surface52d, the cylindrical outer circumferential surface52eand the spherical outer circumferential surface52Afare formed at the edge forming roller52A, a recessed section53A recessed inward in the radial direction is formed. The recessed section53A also has an annular shape formed about the rotation central axis O3. The recessed section53A is curved such that the spherical outer circumferential surface52Afconstituting a portion of the recessed section53A has a predetermined curvature.

In the piston manufacturing device10A, an angle of the spherical outer circumferential surface52Afof the edge forming roller52A with respect to the rotation central axis O3is shallower than that of the spherical outer circumferential surface52fof the first embodiment. For this reason, in the piston11machined by the piston manufacturing device10A, an angle of the curved surface65aof the thick section65with respect to the rotation central axis O3is shallower than that in the first embodiment. That is, the piston11machined by the piston manufacturing device10A has a ratio of a variation in distance in the piston axial direction with respect to a variation in distance in the piston radial direction of the curved surface65aof the thick section65, which is smaller than that in the first embodiment.

Here, contrary to the second embodiment, it is possible to make the angle of the spherical outer circumferential surface of the edge forming roller deeper than that of the first embodiment. That is, a ratio of a variation in diameter with respect to a variation in distance in a direction along the rotation central axis O3of the spherical outer circumferential surface may be larger than that of the spherical outer circumferential surface52fof the first embodiment.

Third Embodiment

Next, a third embodiment will be described with reference toFIG. 7mainly focusing on differences from the first embodiment. Further, parts the same as those in the first embodiment are designated by the same names and the same reference numerals.

A piston manufacturing device10B partially different from the piston manufacturing device10of the first embodiment is used in the third embodiment. A rotating device21B partially different from the rotating device21of the first embodiment is used in the piston manufacturing device10B. A clamping part32B partially different from the clamping part32of the first embodiment is used in the rotating device21B. Specifically, an inner core bar34B partially different from the inner core bar34of the first embodiment is used.

In addition, an edge forming device23B partially different from the edge forming device23of the first embodiment is used in the piston manufacturing device10B, and specifically, an edge forming roller52B partially different from the edge forming roller52of the first embodiment is used.

The inner core bar34B of the third embodiment has a major axis section121configured to sandwich the bottom section13of the piston11with the outer core bar33at the same outer diameter as the inner core bar34of the first embodiment, and a large diameter section122having an outer diameter larger than that of the major axis section121. The large diameter section122is formed at a predetermined position in the middle of the major axis section121in the axial direction, and has a cylindrical outer circumferential surface122aconstituted by a cylindrical surface formed about the rotation central axis O1.

The edge forming roller52B of the third embodiment is formed so that a spherical outer circumferential surface52Bfhaving a length in an extension direction of the rotation central axis O3smaller than that of the spherical outer circumferential surface52fof the first embodiment extends from the edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52etoward the rotation central axis O1. The spherical outer circumferential surface52Bfalso has a diameter about the rotation central axis O3that increases toward the rotation central axis O1. The spherical outer circumferential surface52Bfconstituted by a surface of a sphere or a spheroid is, in other words, a curved surface having a predetermined curvature.

A cylindrical outer circumferential surface52Biextending from the edge portion of the rotation central axis O1side of the spherical outer circumferential surface52Bftoward the rotation central axis O1is formed at the edge forming roller52B of the third embodiment. The cylindrical outer circumferential surface52Biis a cylindrical surface formed about the rotation central axis O3.

The end surface52hextends from the edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52Biinward in the radial direction.

As the stepped surface52c, the tapered outer circumferential surface52d, the cylindrical outer circumferential surface52eand the spherical outer circumferential surface52Bfare formed at the edge forming roller52B, a recessed section53B recessed inward in the radial direction is formed. The recessed section53B also has an annular shape formed about the rotation central axis O3. The recessed section53B is curved such that the spherical outer circumferential surface52Bfconstituting a portion of the recessed section53B has a predetermined curvature.

The piston manufacturing device10B forms the thick section65using the edge forming roller52B while forming the annular groove61by using the groove forming roller42with respect to the piston11rotated by the rotating device21B, like the first embodiment. Here, the large diameter section122of the inner core bar34B of the rotating device21B abuts the thick section65of the piston11, which is extruded by the edge forming roller52B inward in the radial direction, at the rotation central axis O1side, i.e., a piston axial center side in order to restrict plastic deformation beyond a predetermined amount toward the piston axial center side. In other words, the large diameter section122presses the thick section65from the piston axial center side (inside the piston11) using a repulsive force when the thick section65is plastically deformed toward the rotation central axis O1, i.e., the piston axial center.

As a result, a cylindrical surface65fextending from the inner circumferential edge portion of the curved surface65aof the thick section65toward the bottom section13and constituted by a cylindrical surface formed about the rotation central axis O1, i.e., the central axis of the piston11is formed at the piston11after machining by the piston manufacturing device10B of the third embodiment.

According to the piston manufacturing device10B of the above-mentioned third embodiment, upon plastic deformation of the thick section65, the large diameter section122presses the thick section65from the inside of the piston11. For this reason, plastic deformation of the thick section65can be more stably performed. Accordingly, precision of the edge15having the tapered surface15a, the end surface15band the curved surface65aof the piston11can be improved.

Fourth Embodiment

Next, a fourth embodiment will be described with reference toFIG. 8mainly focusing on differences from the first embodiment. Further, parts the same as in the first embodiment are designated by the same names and the same reference numerals.

In the fourth embodiment, a piston manufacturing device10C partially different from the piston manufacturing device10of the first embodiment is used. A rotating device21C partially different from the rotating device21of the first embodiment is used in the piston manufacturing device10C. A clamping part32C partially different from the clamping part32of the first embodiment is used in the rotating device21C. Specifically, an inner core bar34C (a second forming device) partially different from the inner core bar34of the first embodiment is used. In addition, an edge forming device23C partially different from the edge forming device23of the first embodiment is used in the piston manufacturing device10C. Specifically, an edge forming roller52C (a second forming device) partially different from the edge forming roller52of the first embodiment is used.

The inner core bar34C of the fourth embodiment has a pressing section131, a tapered section132and a large diameter section133in sequence from a side close to the outer core bar33, i.e., from a lower side. The pressing section131sandwiches the bottom section13of the piston11with the outer core bar33at the same outer diameter as the inner core bar34of the first embodiment.

The tapered section132extends from the end portion of the pressing section131opposite to the outer core bar33while increasing in diameter in a direction opposite to the outer core bar33. The tapered section132has a tapered surface132aformed about the rotation central axis O1. The tapered surface132ahas a diameter that is increased toward an opposite side of the pressing section131, i.e., from an upper side.

The large diameter section133extends from the edge portion of the tapered section132opposite to the pressing section131in a direction opposite to the pressing section131. The large diameter section133has a cylindrical outer circumferential surface133aconstituted by a cylindrical surface formed about the rotation central axis O1, and the cylindrical outer circumferential surface133aextends from the edge portion of the tapered surface132aopposite to the pressing section131in a direction opposite to the pressing section131.

The edge forming roller52C of the fourth embodiment has a cylindrical outer circumferential surface52Ca, a stepped surface52Cb, a tapered outer circumferential surface52Cc, a cylindrical outer circumferential surface52Cdand an end surface52Cein sequence from the head51side in the extension direction of the rotation central axis O3.

The cylindrical outer circumferential surface52Cais a cylindrical surface formed about the rotation central axis O3.

The stepped surface52Cbextends from the edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52Cainward in the radial direction. The stepped surface52Cbis a flat surface having an annular shape formed about the rotation central axis O3and disposed at the same plane as the surface perpendicular to the rotation central axis O3.

The tapered outer circumferential surface52Ccis a tapered surface extending from the inner circumferential edge portion of the stepped surface52Cbtoward the rotation central axis O1and formed about the rotation central axis O3. The tapered outer circumferential surface52Cchas a diameter that decreases toward the rotation central axis O1.

The cylindrical outer circumferential surface52Cdis a cylindrical surface extending from the edge portion of the rotation central axis O1side of the tapered outer circumferential surface52Cctoward the rotation central axis O1and formed about the rotation central axis O3. The cylindrical outer circumferential surface52Cdhas a diameter that is smaller than that of the stepped surface52Cb.

The end surface52Ceextends from the edge portion of the rotation central axis O1side of the cylindrical outer circumferential surface52Cdinward in the radial direction. The end surface52Ceis a flat surface having a circular shape about the rotation central axis O3and perpendicular to the rotation central axis O3.

When the edge forming roller52C moves toward the gripping part31along the rotation central axis O1while causing the end surface52Ceto approach the cylindrical outer circumferential surface133aof the inner core bar34C, the lower end position of the cylindrical outer circumferential surface52Cdmatches a boundary position between the cylindrical outer circumferential surface133aand the tapered surface132aof the inner core bar34C. Accordingly, a recessed section53C recessed inward in the radial direction is formed by the stepped surface52Cb, the tapered outer circumferential surface52Ccand the cylindrical outer circumferential surface52Cdof the edge forming roller52C, and the tapered surface132aof the inner core bar34C.

In the piston manufacturing device10C of the fourth embodiment, like the first embodiment, the groove forming roller42forms the annular groove61in the piston11rotated by the rotating device21C. Here, the tapered outer circumferential surface52Ccand the cylindrical outer circumferential surface52Cdof the edge forming roller52C abut the edge15of the opening14of one end side in the axial direction of the piston11, and the edge15is pressed toward the other end side in the axial direction opposite to the edge15of the piston11. As a result, the edge forming roller52C plastically deforms the opening14such that a position of the edge15approaches the bottom section13in the piston axial direction.

Here, deformation to a side of the opening14opposite to the rotation central axis O1is restricted by the stepped surface52Cbof the edge forming roller52C. Accordingly, a portion of mainly the inner circumferential side of the edge15of the opening14of the tubular section12extends inward in the radial direction, and the opening14of the tubular section12is plastically deformed toward the other end side in the axial direction (the bottom section13side in the piston axial direction) to follow the tapered surface132aof the inner core bar34C. Then, the portion is extruded from the inner circumferential surface12b, which is between the edge15and the groove61, toward the rotation central axis O1closer to an axial center of the piston11than the inner circumferential cylindrical surface12b1, and becomes the thick section65protruding toward the rotation central axis O1.

That is, as the edge15of the opening14of the piston11is pressed toward the other end side in the axial direction of the piston11by the recessed section53C constituted by the stepped surface52Cb, the tapered outer circumferential surface52Ccand the cylindrical outer circumferential surface52Cdof the edge forming roller52C and the tapered surface132aof the inner core bar34C, a thick section forming step of the piston manufacturing method for forming the thick section65extruded from the inner circumferential surface12bbetween the edge15and the groove61toward the axial center of the piston11. The thick section forming step includes plastically deforming the inner circumferential side of the edge15toward the other end side in the axial direction of the piston11. The recessed section53C is formed at portions of the edge forming roller52C and the inner core bar34C abutting the edge15of the piston11such that the inner circumferential side of the edge15is plastically deformed toward the other end side in the axial direction of the piston11.

As a result, a tapered surface65ghaving a straight cross section instead of the curved surface65ais formed in the piston11after machining by the piston manufacturing device10C of the fourth embodiment at the inside in the piston radial direction of the end surface15band the bottom section13side in the piston axial direction. The tapered surface65gis a portion formed at the tapered surface132aof the inner core bar34and having a shape to which the tapered surface132ais transferred. The tapered surface65gis constituted by a tapered surface formed about the rotation central axis O1, i.e., the central axis of the piston11. The tapered surface65gextends from the edge portion of the rotation central axis O1side of the end surface15b, i.e., the piston axial center side in the piston central axis direction, and is inclined to be disposed closer to the bottom section13as it goes toward the piston axial center. Accordingly, the thick section65has a shape folded toward the bottom section13. The folded area has a tapered surface shape.

According to the piston manufacturing device10C of the above-mentioned fourth embodiment, the recessed section53C is formed of two parts of the edge forming roller52C and the inner core bar34C. For this reason, it is possible to cope with repair of an edge forming roller and modification of an inner core bar of existing equipment that can form the end surface15b. Accordingly, when the existing equipment is modified, costs incurred for modification can be reduced.

Fifth Embodiment

Next, a fifth embodiment will be described with reference toFIG. 9mainly focusing on differences from the fourth embodiment. Further, parts the same as in the fourth embodiment are designated by the same names and the same reference numerals.

In the fifth embodiment, a piston manufacturing device10D partially different from the piston manufacturing device10C of the fourth embodiment is used. A rotating device21D partially different from the rotating device21C of the third embodiment is used in the piston manufacturing device10D. A clamping part32D partially different from the clamping part32C of the fourth embodiment are used, and specifically an inner core bar34D (a second forming device) partially different from the inner core bar34C of the fourth embodiment are used in the rotating device21D.

The inner core bar34D of the fifth embodiment has a pressing section131D, a tapered section141, an intermediate diameter section142, a tapered section132D and a large diameter section133D in sequence from a side close to the outer core bar33, i.e., from the lower side. The pressing section131D sandwiches the bottom section13of the piston11with the outer core bar33at the same outer diameter as the pressing section131of the fourth embodiment. The tapered section141extends from the end portion of the pressing section131D opposite to the outer core bar33while increasing a diameter in a direction opposite to the outer core bar33. The intermediate diameter section142extends from the edge portion of the tapered section141opposite to the pressing section131D in a direction opposite to the pressing section131D. The intermediate diameter section142has a cylindrical outer circumferential surface142aconstituted by a cylindrical surface formed about the rotation central axis O1.

The tapered section132D extends from the end portion of the intermediate diameter section142opposite to the tapered section141while increasing a diameter in a direction opposite to the tapered section141. The tapered section132D has a tapered surface132Daformed about the rotation central axis O1. The tapered surface132Daextends from the edge portion of the cylindrical outer circumferential surface142aopposite to the tapered section141in a direction opposite to the tapered section141and has a diameter that increases toward a side opposite to the tapered section141, i.e., toward the upper side.

The large diameter section133D extends from the end portion of the tapered section132D opposite to the intermediate diameter section142in a direction opposite to the intermediate diameter section142. The large diameter section133D has a cylindrical outer circumferential surface133Daconstituted by a cylindrical surface formed about the rotation central axis O1. The cylindrical outer circumferential surface133Daextends from the edge portion of the tapered surface132Daopposite to the intermediate diameter section142in a direction opposite to the intermediate diameter section142.

When the edge forming roller52C moves toward the gripping part31along the rotation central axis O1while the end surface52Ceapproaches the cylindrical outer circumferential surface133Daof the inner core bar34D, the lower end position of the cylindrical outer circumferential surface52Cdmatches a boundary position between the cylindrical outer circumferential surface133Daand the tapered surface132Daof the inner core bar34D. Accordingly, the recessed section53D recessed inward in the radial direction is formed by the stepped surface52Cb, the tapered outer circumferential surface52Ccand the cylindrical outer circumferential surface52Cdof the edge forming roller52C and the tapered surface132Daof the inner core bar34D. Since the inner core bar34D is different from the fourth embodiment, the edge forming device23D constituted by the inner core bar34D and the edge forming roller52C is partially different from the fourth embodiment.

In the piston manufacturing device10D, like the fourth embodiment, the edge forming roller52C and the inner core bar34D form the thick section65in the piston11rotated by the rotating device21D while the groove forming roller42forms the annular groove61. Here, the intermediate diameter section142of the inner core bar34D abuts the thick section65of the piston11, which is extruded inward in the radial direction by the edge forming roller52C, at the rotation central axis O1side, i.e., the piston axial center side in order to restrict plastic deformation beyond a predetermined amount to the piston axial center side. In other words, the intermediate diameter section142presses the thick section65from the piston axial center side (the inside of the piston11) using a repulsive force when the thick section65is plastically deformed toward the rotation central axis O1, i.e., the piston axial center.

As a result, in the piston11after machining by the piston manufacturing device10D of the fifth embodiment, a cylindrical surface65hextending from the inner circumferential edge portion of the tapered surface65gof the thick section65toward the bottom section13in the piston axial direction and constituted by the cylindrical surface formed about the rotation central axis O1, i.e., the central axis of the piston11is formed.

According to the piston manufacturing device10D of the above-mentioned fifth embodiment, upon plastic deformation of the thick section65, the intermediate diameter section142presses the thick section65from the inside of the piston11. For this reason, plastic deformation of the thick section65can be more stably performed. Accordingly, precision of the edge15having the tapered surface15a, the end surface15band the tapered surface65gof the piston11can be improved.

In the above-mentioned first to fifth embodiments, the case in which the piston11is rotated in the piston circumferential direction upon machining has been described. However, the groove forming device22and the edge forming devices23,23A to23D may be rotated while the piston11is not rotated. That is, the piston11may be relatively rotated with respect to the groove forming device22and the edge forming devices23,23A to23D. Further, in the above-mentioned embodiment, the case in which the equipment is a vertical type has been described. However, the equipment may be a horizontal type, i.e., a rotation axis of the rotating device21D may be provided in a horizontal direction.

The piston manufacturing device of the above-mentioned embodiment includes a rotating device configured to relatively rotate a tubular piston in a circumferential direction, a first forming device configured to press a portion of the piston from an outer circumferential side of the piston to form an annular groove, the portion of the piston being separated from an edge of an opening provided at one end side in an axial direction of the piston, and a second forming device configured to press the edge of the opening of the piston toward other end side in the axial direction of the piston and to form a thick section extruded from an inner circumferential surface of the piston toward an axial center of the piston, the inner circumferential surface being formed between the edge and the groove. A recessed section is formed at a portion of the second forming device that is arranged to abut the edge so that an inner circumferential side of the edge is plastically deformed toward the other end side in the axial direction of the piston. Accordingly, since the recessed section plastically deforms the inner circumferential side of the edge toward the other side in the piston axial direction, a variation in area of an end surface of the edge of the opening of the piston can be suppressed.

As the recessed section has a predetermined curvature, a difference in circumferential speed between the piston and the second forming device can be reduced, and friction due to the difference in circumferential speed can be reduced. Accordingly, stress applied to the piston and the second forming device can be reduced. As a result, the lifetime of the second forming device can be lengthened and a load to the piston manufacturing device can be suppressed. In addition, a decrease in quality such as burning or the like of the piston can be suppressed. In addition, since a contact area between the second forming device and the piston can be reduced and the surface pressure upon machining can be increased, formability can be improved.

As a configuration in which a means configured to press the edge from the inside of the piston is not provided except the recessed section, the structure can be simplified and equipment costs can be reduced.

The piston manufacturing method of the embodiment includes a rotation step of relatively rotating a tubular piston in a circumferential direction, a groove forming step of pressing a portion of the piston from an outer circumferential side of the piston and forming an annular groove, the portion of the piston being separated from an edge of an opening provided at one end side in an axial direction of the piston, and a thick section forming step of pressing the edge of the opening of the piston toward other end side in the axial direction of the piston and forming a thick section extruded from an inner circumferential surface of the piston toward an axial center side of the piston, the inner circumferential surface being formed between the edge and the groove. The thick section forming step includes plastically deforming the inner circumferential side of the edge toward the other end side in the axial direction of the piston. Accordingly, in the thick section forming step that presses the edge of the opening of the piston toward the other end side in the piston axial direction and that forms the thick section extruded from the inner circumferential surface between the edge and the groove to the piston axial center side, the inner circumferential side of the edge is plastically deformed toward the bottom section in the piston axial direction. For this reason, a variation in area of the end surface of the edge of the opening of the piston can be suppressed.

The piston of the embodiment is formed as a hollow cylinder and includes a bottom section to which a brake pressure is applied, and an edge of an opening of one end side in an axial direction in the hollow cylinder. The portion of the edge in the central axis direction of the piston is a thick section protruding in the central axis direction, the thick section is folded toward the bottom section, and the folded area is a curved surface shape. In this way, since the portion of the edge in the central axis direction of the piston is the thick section protruding in the central axis direction and the thick section is folded toward the bottom section of the piston, when the edge of the opening of the piston is formed by plastic deformation, a variation in area of the end surface of the edge of the opening of the piston can be suppressed. In addition, since the folded area is a curved surface, when the edge of the opening of the piston is formed by plastic deformation, stress applied to the piston and the device can be reduced. In addition, a decrease in quality such as burning or the like of the piston can be suppressed. In addition, formability can be improved.

The disc brake of the embodiment includes the above-mentioned piston, a cylinder in which the piston is movably disposed, and a brake pad arranged to be pressed by the edge of the opening of the piston and come in contact with a disc. Accordingly, since a variation in area of the end surface of the edge of the opening of the piston can be suppressed, a surface pressure to the brake pad of the piston can be stabilized and brake noise performance can be stabilized.

INDUSTRIAL APPLICABILITY

According to the above-mentioned piston manufacturing device, it is possible to provide a piston manufacturing device, a piston manufacturing method, a piston and a disc brake that are capable of suppressing a variation of a shape of a surface of the end surface of the piston on contact with the pad.

REFERENCE SIGNS LIST