Disc brake

Abstract

To provide a disc brake capable of suppressing the dragging.SOLUTION: The disc brake includes a cylinder bore (35) into which a piston is fitted, a seal groove (55) provided as an annular groove in the cylinder bore (35), and a sectionally rectangular seal member fitted into the seal groove (55) for sealing a space between the piston and the cylinder bore (35), the seal groove (55) having a bottom face part (103), a side face part (104), and a chamfered part (105), the chamfered part (105) being formed so as to enlarge an opening (108) of the seal groove (55)in the axial direction of the cylinder bore (35).SELECTED DRAWING: Figure 3B

Description

[Technical field]

[0001] The present invention relates to a disc brake. This application claims priority based on Japanese Patent Application No. 2018-102315, filed on May 29, 2018, the contents of which are incorporated herein by reference. [Background technology]

[0002] 2. Description of the Related Art There is a disc brake in which brake fluid pressure is introduced between a cylinder bore and a piston slidably fitted in the cylinder bore, causing the piston to move forward and press a brake pad against a disc rotor (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-175041 A [Patent Document 2] JP 2011-214623 A [Patent Document 3] U.S. Patent No. 6,244,393 Summary of the Invention [Problem to be solved by the invention]

[0004] In disc brakes, a phenomenon known as dragging may occur, in which the brake pads continue to contact the disc even after braking is released. It is desirable to suppress such dragging.

[0005] The present invention provides a disc brake capable of suppressing drag. [Means for solving the problem]

[0006] According to one aspect of the present invention, a disc brake includes brake pads arranged on both sides of a disc rotor, a piston for pressing at least one of the brake pads against the disc rotor, a cylinder bore into which the piston is slidably fitted, a seal groove provided in the cylinder bore as an annular groove recessed from an inner circumferential surface thereof, and a seal member having a square cross section that is fitted into the seal groove to seal between the piston and the cylinder bore, the seal groove having a bottom surface portion that inclines in a direction expanding in diameter toward an opening side of the cylinder bore, a side surface portion that extends from the large diameter side of the bottom surface portion toward the opening side of the seal groove, and a rounded portion that is curved round from the side surface portion closest to the opening side of the cylinder bore toward the opening side of the cylinder bore, the rounded portion having a plurality of radius of curvature portions with different radii of curvature, and the radius of curvature of the radius of curvature portion arranged closest to the inner circumferential surface of the cylinder bore is the smallest. Effect of the Invention

[0007] The above-described disc brake makes it possible to suppress drag. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing a disk brake according to a first embodiment of the present invention. [Diagram 2] 1 is a side cross-sectional view showing a disk brake according to a first embodiment of the present invention. [Figure 3A] FIG. 2 is a partial cross-sectional view showing a seal member of the disk brake according to the first embodiment of the present invention. [Figure 3B] FIG. 2 is a partial cross-sectional view showing a state before assembly of a seal groove of the disc brake according to the first embodiment of the present invention. [Figure 4A] FIG. 2 is a partial cross-sectional view showing a seal groove of a disc brake according to Comparative Example 1. [Figure 4B] FIG. 11 is a partial cross-sectional view showing a seal groove of a disc brake according to Comparative Example 2. [Diagram 5] 4 is a characteristic diagram showing piston return amount versus brake fluid pressure in the first and second embodiments of the present invention and comparative examples 1 and 2. FIG. [Figure 6] FIG. 6 is a partial cross-sectional view showing a seal groove of a disc brake according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] "First embodiment" The first embodiment will be described below with reference to FIGS.

[0010] 1 and 2 show a disc brake 10 according to a first embodiment. This disc brake 10 applies a braking force to a vehicle such as an automobile. Specifically, the disc brake 10 is used for braking a four-wheeled vehicle. The disc brake 10 brakes the vehicle by stopping the rotation of a disc rotor 11 that rotates together with a wheel (not shown). Hereinafter, the direction of the central axis of the disc rotor 11 is referred to as the disc axial direction, the radial direction of the disc rotor 11 as the disc radial direction, and the circumferential direction (rotational direction) of the disc as the disc circumferential direction.

[0011] The disc brake 10 includes a carrier 12, a pair of brake pads 13, 14 shown in FIG. 2, a caliper 15, and a pair of boots 16 shown in FIG. 1. The carrier 12 is disposed across the outer periphery of the disc rotor 11 and is fixed to a non-rotating portion of the vehicle. The pair of brake pads 13, 14 are disposed on both sides of the disc rotor 11 and are supported by the carrier 12 so as to be movable in the disc axial direction. The caliper 15 is supported by the carrier 12 so as to be movable in the disc axial direction. The caliper 15 holds the pair of brake pads 13, 14 and presses them against both sides of the disc rotor 11.

[0012] The caliper 15 includes a caliper body 20, a piston 21, a seal member 22, a boot member 23, and a pair of slide pins 24 shown in FIG.

[0013] The caliper body 20 is formed by machining a metal material integrally formed by casting. The caliper body 20 has a cylinder 26 arranged on one side of the disk rotor 11 in the disk axial direction, a bridge portion 27 extending from the outer side of the cylinder 26 in the disk radial direction so as to straddle the outer periphery of the disk rotor 11, a claw portion 28 extending inward in the disk radial direction from the bridge portion 27 opposite the cylinder 26 and arranged on the other side of the disk rotor 11 in the disk axial direction, and a pair of arms 29 shown in FIG. 1 extending from the cylinder 26 to both sides in the disk circumferential direction. The caliper body 20 is movably supported by the carrier 12 by slide pins 24 attached to the pair of arms 29. A pair of boots 16 cover the slide pins 24.

[0014] As shown in FIG. 2, the cylinder 26 is formed with a cylinder bore 35 having one end open toward the claw portion 28 and recessed toward the opposite side of the disk rotor 11 in the disk axial direction. By forming the cylinder bore 35 opening toward the claw portion 28, the cylinder 26 has a cylinder bottom 39 including an inner bottom 38 of the cylinder bore 35 on the opposite side of the claw portion 28, and a cylinder body 42 extending from the cylinder bottom 39 toward the claw portion 28 and including an inner wall 41 of the cylinder bore 35. The cylinder bore 35 has an opening 43 on the opposite side of the cylinder body 42 from the cylinder bottom 39. The cylinder bottom 39 side of the cylinder bore 35 is referred to as the bore bottom side, and the opening 43 side of the cylinder bore 35 is referred to as the bore opening side.

[0015] The piston 21 is fitted in the cylinder bore 35 so as to be slidable in the disk axial direction. The inner wall portion 41 of the cylinder bore 35 has a guide inner circumferential surface 51 (inner peripheral surface) which is a cylindrical surface of a constant inner diameter over its entire length and guides the movement of the piston 21. The central axis of this guide inner circumferential surface 51 is the central axis of the cylinder bore 35. This central axis is referred to as the bore axis. The direction perpendicular to this central axis is referred to as the bore radial direction, and the circumferential direction about this central axis is referred to as the bore circumferential direction.

[0016] The inner wall portion 41 of the cylinder bore 35 has an annular large diameter groove 52 that is recessed radially outward from the guide inner peripheral surface 51 toward the bore bottom side relative to the guide inner peripheral surface 51. The large diameter groove 52 is annular about the bore axis, and the groove bottom diameter is larger than the guide inner peripheral surface 51.

[0017] The inner wall 41 of the cylinder bore 35 has an annular seal groove 55 recessed radially outward from the guide inner circumferential surface 51 at an intermediate position on the bore opening side of the guide inner circumferential surface 51. The seal groove 55 is an annular groove recessed from the guide inner circumferential surface 51 on the inner wall 41 of the cylinder bore 35 and centered on the bore axis. The groove bottom diameter of the seal groove 55 is larger than that of the guide inner circumferential surface 51.

[0018] A circular boot fitting groove 58 is formed in the inner wall 41 of the cylinder bore 35, closer to the bore opening than the seal groove 55 and recessed radially outwardly of the bore than the guide inner circumferential surface 51. The boot fitting groove 58 is circular about the bore axis, and the diameter of the groove bottom is larger than the diameter of the guide inner circumferential surface 51.

[0019] A boot arrangement hole 59 is formed in the inner wall 41 of the cylinder bore 35 on the bore opening side of the boot fitting groove 58. The boot arrangement hole 59 has a tapered shape centered on the bore axis and has a larger diameter as it moves away from the boot fitting groove 58. The end of the boot arrangement hole 59 opposite the cylinder bottom 39 forms the opening 43 of the cylinder bore 35. The large diameter groove 52 and the inner bottom 38 connected to it are cast when the material for the caliper body 20 is cast. The guide inner peripheral surface 51, the seal groove 55, the boot fitting groove 58 and the boot arrangement hole 59 are formed by cutting the material for the caliper body 20.

[0020] A piping hole 68 is formed in the cylinder bottom 39, penetrating along the bore axial direction so as to open into the cylinder bore 35. The piping hole 68 is formed by cutting the material of the caliper body 20. A brake piping (not shown) is connected to the piping hole 68.

[0021] The piston 21 includes a disk-shaped piston bottom 71 and a cylindrical piston body 72. The piston 21 is formed in a bottomed tubular shape with the end of the piston body 72 opposite to the piston bottom 71 being open. The piston body 72 is formed with an annular fitting groove 75 recessed radially inward from an outer diameter surface 74 consisting of a cylindrical surface, on the axial opposite side of the piston bottom 71. The piston 21 is accommodated in the cylinder bore 35 such that the piston bottom 71 is located on the bore bottom side within the cylinder bore 35, and in this state, the tip on the claw portion 28 side protrudes further from the cylinder bore 35 toward the claw portion 28. The piston 21 is formed with the fitting groove 75 on the tip side protruding further from the cylinder bore 35 in this way.

[0022] The seal member 22 is made of an elastic material, specifically rubber. The seal member 22 is fitted into the seal groove 55 of the cylinder bore 35 with an interference. The piston 21 is fitted into the inner peripheral side of the seal member 22 with an interference. The seal member 22 elastically deforms in the radial direction to come into close contact with the piston 21 and the seal groove 55, thereby sealing between the cylinder bore 35 of the cylinder 26 and the piston 21. The seal member 22 supports the outer diameter surface 74 of the piston 21 together with the guide inner peripheral surface 51 of the cylinder bore 35 so that the outer diameter surface 74 can move in the bore axial direction. The seal member 22, together with the cylinder bore 35 and the piston 21, form a hydraulic chamber 69. Brake fluid is supplied to and discharged from the hydraulic chamber 69 via a brake pipe connected to a pipe hole 68.

[0023] The boot member 23 is an expandable and contractable bellows-like cylindrical body. One end of the boot member 23 fits into the boot fitting groove 58 of the cylinder 26, and the other end fits into the fitting groove 75 of the piston 21. The boot member 23 covers a portion of the outer diameter surface 74 of the piston 21 that is exposed from the cylinder bore 35 and is closer to the piston bottom 71 than the fitting groove 75. The boot member 23 expands and contracts as the piston 21 moves relative to the cylinder bore 35.

[0024] When the brake pedal (not shown) of the disc brake 10 is operated, brake fluid is introduced into the hydraulic chamber 69 through a brake pipe (not shown) connected to the pipe hole 68. Then, brake fluid pressure acts on the piston bottom 71 of the piston 21 in a direction away from the cylinder bottom 39. As a result, the piston 21 advances toward the disc rotor 11 relative to the cylinder bore 35, and presses the brake pad 13 disposed between the piston 21 and the disc rotor 11 toward the disc rotor 11. This causes the brake pad 13 to move and come into contact with the disc rotor 11. When the piston 21 advances toward the disc rotor 11 relative to the cylinder bore 35 in this way, the piston 21 elastically deforms the inner peripheral side of the seal member 22 housed in the seal groove 55 so that the contact portion of the seal member 22 moves integrally with the seal member 22 by friction.

[0025] Also, due to the reaction force pressing the brake pad 13 against the disc rotor 11, the caliper body 20 slides against the carrier 12 on the pair of slide pins 24, and the claws 28 press the brake pad 14 arranged between the claws 28 and the disc rotor 11 toward the disc rotor 11. As a result, the brake pad 14 comes into contact with the disc rotor 11. In this way, the caliper 15, by the operation of the piston 21, sandwiches the pair of brake pads 13, 14 from both sides between the piston 21 and the claws 28 and presses them against both sides of the disc rotor 11. As a result, the caliper 15 applies friction resistance to the disc rotor 11 to generate a braking force. The piston 21 presses the brake pads 13, 14 on both sides against the disc rotor 11 by the brake fluid pressure.

[0026] When the brake pedal (not shown) is released from this state, the hydraulic pressure in the hydraulic chamber 69 drops, and the force that the piston 21 applied to the seal member 22, which had been elastically deformed as described above, is reduced. Then, the seal member 22 returns from its deformed state due to its own elasticity. At that time, the piston 21 is moved back toward the bottom of the bore by friction, that is, a so-called rollback occurs, forming a gap between the piston 21 and the brake pad 13. Then, the disc rotor 11 swings out, and the brake pads 13, 14 and the claws 28 move in a direction away from the disc rotor 11 in the disc axial direction.

[0027] 3A, when the seal member 22 made of an elastic material is adjusted to a circular shape in its natural state before being fitted into the seal groove 55, it has an outer peripheral surface 91 formed of a cylindrical surface, an inner peripheral surface 92 formed of a cylindrical surface having a smaller diameter than the outer peripheral surface 91, a flat end surface 93 perpendicular to the outer peripheral surface 91 and the inner peripheral surface 92 and connecting one end edges of these surfaces in the axial direction, and a flat end surface 94 perpendicular to the outer peripheral surface 91 and the inner peripheral surface 92 and connecting the other end edges of these surfaces in the axial direction. In other words, when the seal member 22 is adjusted to a circular shape in its natural state before being fitted into the seal groove 55, its cross-sectional shape when cross-sectioned along a plane including the central axis is a rectangle having long sides parallel to the central axis.

[0028] The seal groove 55 has an annular shape centered on the bore axis and has, in the bore axial direction from the bore bottom side (BBS shown in FIG. 3B), a bore bottom chamfered portion 101, a bore bottom side portion 102, a groove bottom surface portion 103 (bottom surface portion), a bore opening side side portion 104 (side portion), a bore opening side chamfered portion 105 (chamfered portion), an axially extending surface portion 106, and a radially extending surface portion 107. The small diameter side of the seal groove 55 forms a groove opening 108 that opens toward the bore axis.

[0029] The bore bottom side chamfer 101 is a tapered surface that extends radially outward from the guide inner peripheral surface 51, which is a cylindrical surface, and is inclined so that the more radially outward it is in the bore opening side (BOS shown in FIG. 3B), with the bore bottom side chamfer 101 being centered on the bore axis. The bore bottom side chamfer 101 is annular in shape, with a constant diameter on the small diameter side and a constant diameter on the large diameter side over the entire circumference of the bore.

[0030] The bore bottom side surface portion 102 is an annular plane centered on the bore axis that spreads outward in the bore radial direction, perpendicular to the bore axis, from the large-diameter end edge of the bore bottom side chamfer portion 101. The bore bottom side surface portion 102 is annular in shape with a constant diameter on the small-diameter side and a constant diameter on the large-diameter side over the entire circumference in the bore circumferential direction.

[0031] The groove bottom surface portion 103 has, in order from the bottom side of the bore, a first tapered surface portion 111, a second tapered surface portion 112, a concave surface portion 113, a third tapered surface portion 114, and a fourth tapered surface portion 115.

[0032] The first tapered surface portion 111 is a tapered surface centered on the bore axis that extends from the large-diameter edge portion of the bore bottom side surface portion 102 toward the bore opening side and is inclined so as to be positioned radially outward in the bore direction as it approaches the bore opening side. The taper of the first tapered surface portion 111 is smaller than that of the bore bottom side chamfer portion 101. The first tapered surface portion 111 is annular in shape, with the small-diameter side having a constant diameter and the large-diameter side also having a constant diameter over the entire circumference in the bore circumferential direction.

[0033] The second tapered surface portion 112 is a tapered surface centered on the bore axis that extends from the edge portion on the bore opening side of the first tapered surface portion 111 toward the bore opening side and is inclined so as to be positioned radially outward of the bore as it approaches the bore opening side. The taper of the second tapered surface portion 112 is smaller than that of the first tapered surface portion 111. The second tapered surface portion 112 is annular in shape, with the small diameter side having a constant diameter and the large diameter side also having a constant diameter over the entire circumference in the bore circumferential direction.

[0034] The concave surface portion 113 is a curved surface that extends from the edge portion of the second tapered surface portion 112 on the bore opening side toward the bore opening, inclines so as to be positioned outward in the bore radial direction toward the bore opening side, and then inclines so as to be positioned inward in the bore radial direction toward the bore opening side. The concave surface portion 113 is annular about the bore axis. The cross section of the concave portion 113 taken along a plane including the bore axis has an arc shape with its center on the radially inner side of the bore. The cross section of the concave portion 113 has a constant shape over the entire circumference in the bore circumferential direction.

[0035] The third tapered surface portion 114 is a tapered surface centered on the bore axis, which extends from the edge of the concave surface portion 113 on the bore opening side toward the bore opening side and is inclined so as to be positioned outward in the bore radial direction toward the bore opening side. The third tapered surface portion 114 has the same taper as the second tapered surface portion 112, and is arranged on the same tapered surface as the second tapered surface portion 112. The third tapered surface portion 114 has a constant diameter on the small diameter side over the entire circumference in the bore circumferential direction, and is annular in shape with a constant diameter on the large diameter side as well. Compared to the second tapered surface portion 112 and the third tapered surface portion 114 arranged on the same tapered surface, the concave surface portion 113 is recessed outward in the bore radial direction, and forms an annular bottom groove 118 formed on the groove bottom surface portion 103 of the seal groove 55.

[0036] The fourth tapered surface portion 115 is a tapered surface centered on the bore axis that extends from the edge portion on the bore opening side of the third tapered surface portion 114 toward the bore opening side and is inclined so as to be positioned radially inward of the bore as it approaches the bore opening side. The fourth tapered surface portion 115 is annular in shape with a constant diameter on the larger diameter side and a constant diameter on the smaller diameter side over the entire circumference in the bore circumferential direction.

[0037] Groove bottom surface portion 103 having first tapered surface portion 111, second tapered surface portion 112, concave surface portion 113, third tapered surface portion 114, and fourth tapered surface portion 115 is generally inclined in a direction expanding in diameter toward the bore opening side. The first tapered surface portion 111 side in the bore axial direction is the small diameter side, and the fourth tapered surface portion 115 side is the large diameter side.

[0038] The bore opening side surface portion 104 is an annular plane centered on the bore axis that spreads inward in the bore radial direction perpendicular to the bore axis from the bore opening side edge portion of the fourth tapered surface portion 115. In other words, the bore opening side side portion 104 extends from the large diameter side of the groove bottom surface portion 103 to the groove opening 108 side of the seal groove 55. The bore opening side side portion 104 is annular in shape with a constant diameter on the large diameter side and a constant diameter on the small diameter side over the entire circumference in the bore circumferential direction.

[0039] The bore opening side chamfer 105 is provided between the bore opening side portion 104 and a portion of the guide inner peripheral surface 51 closer to the bore opening than the seal groove 55. The bore opening side chamfer 105 is a curved surface that extends inward in the bore radial direction from the small diameter side edge of the bore opening side side portion 104 and is inclined so as to be located closer to the bore opening side as it moves inward in the bore radial direction. The bore opening side chamfer 105 is annular about the bore axis. In other words, the bore opening side chamfer 105 is formed so as to expand the groove opening 108 of the seal groove 55 to the bore axis from the small diameter side edge of the bore opening side side portion 104. The bore opening side chamfer 105 is annular in shape with a constant diameter on the large diameter side and a constant diameter on the small diameter side over the entire circumference of the bore circumferential direction. The bore opening side chamfer 105 has a smaller width in the bore radial direction than the bore opening side side portion 104.

[0040] The bore opening side chamfer 105 is a curved surface having two types of radii of curvature. That is, the bore opening side chamfer 105 has a first radius of curvature 121 consisting of a curved surface formed on the groove bottom surface 103 side of the seal groove 55, and a second radius of curvature 122 consisting of a curved surface formed on the guide inner circumferential surface 51 side of the cylinder bore 35 relative to the first radius of curvature 121.

[0041] The first radius of curvature portion 121 is a curved surface that extends inward in the bore radial direction from the small diameter side edge of the bore opening side side portion 104 and is inclined so as to be located closer to the bore opening side as it moves inward in the bore radial direction. The first radius of curvature portion 121 is annular about the bore axis. The cross section of the first radius of curvature portion 121 on a plane including the bore axis is an arc shape with a constant radius of curvature r1 having a center on the solid part side forming the first radius of curvature portion 121 of the cylinder 26. In the cross section of the plane including the bore axis, the center of the radius of curvature r1 of the first radius of curvature portion 121 is located inward in the bore radial direction from the bisector of the angle between the bore opening side side portion 104 and the axially extending surface portion 106. In other words, the first radius of curvature portion 121 is inclined at an angle closer to the bore radial direction than the bore axial direction. The cross section of the first radius of curvature portion 121 has a constant shape over the entire circumference in the circumferential direction of the bore. The first radius of curvature portion 121 is annular in shape, with a constant diameter on the larger diameter side and a constant diameter on the smaller diameter side over the entire circumference in the bore circumferential direction.

[0042] The second radius of curvature portion 122 is a curved surface that extends inward in the bore radial direction from the small diameter side edge of the first radius of curvature portion 121 and is inclined so as to be located closer to the bore opening side as it moves inward in the bore radial direction. The second radius of curvature portion 122 is annular about the bore axis. The cross section of the second radius of curvature portion 122 on a plane including the bore axis is an arc shape with a constant curvature radius r2 having a center on the solid part side of the cylinder 26 that forms the second radius of curvature portion 122. The cross section of the second radius of curvature portion 122 has a constant shape over the entire circumference in the bore circumferential direction. The second radius of curvature portion 122 is annular with a constant diameter on the large diameter side and a constant diameter on the small diameter side over the entire circumference in the bore circumferential direction. The curvature radius r2 of the second radius of curvature portion 122 is smaller than the curvature radius r1 of the first radius of curvature portion 121. In other words, the second radius of curvature portion 122 has a smaller radius of curvature than the first radius of curvature portion 121. In addition, the second radius of curvature portion 122 has a smaller width in the bore radial direction than the first radius of curvature portion 121.

[0043] The axially extending surface portion 106 is a cylindrical surface centered on the bore axis, which extends toward the bore opening from the small-diameter edge of the second radius of curvature portion 122 of the bore opening side chamfer 105. The axially extending surface portion 106 has a constant inner diameter over its entire length, and is larger than the inner diameter from the guide inner circumferential surface 51.

[0044] The radially extending surface portion 107 is an annular flat surface centered on the bore axis, which spreads from the edge of the axially extending surface portion 106 on the bore opening side toward the inside in the bore radial direction, perpendicular to the bore axis. The radially extending surface portion 107 is annular in shape with a constant diameter on the small diameter side and a constant diameter on the large diameter side over the entire circumference in the bore circumferential direction. The small diameter side of the radially extending surface portion 107 is connected to a portion of the guide inner circumferential surface 51 closer to the bore opening than the seal groove 55.

[0045] The axially extending surface portion 106 and the radially extending surface portion 107 form a stepped portion 125 recessed radially outwardly of the bore at the end portion on the bore opening side and on the groove opening 108 side of the seal groove 55. In other words, the seal groove 55 has a stepped portion 125 recessed radially outwardly of the bore at the end portion on the bore opening side and on the groove opening 108 side.

[0046] The disc brakes described in the above Patent Documents 1 to 3 introduce brake fluid pressure between a cylinder bore and a piston slidably fitted in the cylinder bore, and the piston is advanced to press the brake pad against the disc rotor. Such disc brakes are provided with a seal member for sealing the gap between the cylinder bore and the piston. This seal member rolls back the piston to the bottom side of the cylinder when the brake fluid pressure is released.

[0047] In order to improve fuel economy, it is desirable to suppress the so-called drag, which is a phenomenon in which the brake pads continue to contact the disc even after braking is released. In particular, the drag suppression effect can be achieved by increasing the amount of return of the piston caused by the seal member when the hydraulic pressure is released when the brake hydraulic pressure is high. However, if the amount of return of the piston caused by the seal member when the hydraulic pressure is released is increased, the resistance of the seal member to the movement of the piston when the brake hydraulic pressure is low increases, reducing the responsiveness of the piston and deteriorating the pedal feeling.

[0048] In contrast to this, in the disc brake 10 of the first embodiment, the seal groove 55 has a groove bottom portion 103 that is inclined in a direction in which the diameter increases toward the bore opening side, a bore opening side portion 104 that extends from the large diameter side of the groove bottom portion 103 toward the groove opening 108 side of the seal groove 55, and a bore opening side chamfer portion 105 that is provided between the bore opening side side portion 104 and the guide inner peripheral surface 51 of the cylinder bore 35 and is formed so as to expand the groove opening 108 in the bore axial direction. This bore opening side chamfer portion 105 has two types of radii of curvature r1, r2.

[0049] Specifically, the bore opening side chamfer 105 has a first radius of curvature 121 with a radius of curvature r1 on the groove bottom surface 103 side, and a second radius of curvature 122 with a radius of curvature r2 smaller than the first radius of curvature 121, which is formed on the guide inner surface 51 side of the first radius of curvature 121. For this reason, when the piston 21 advances, the seal member 22, whose inner circumferential surface 92 side that is in contact with the piston 21 moves together with the piston 21, has an end face 93 on the bore opening side that deforms with a large radius of curvature r1 following the first radius of curvature portion 121 at low brake fluid pressure, and the fulcrum of deformation changes gradually, resulting in a smooth increase with a low spring constant. On the other hand, when the brake fluid pressure is high, the end face 93 deforms with a small radius of curvature r2 following the first radius of curvature portion 121 and then the second radius of curvature portion 122, resulting in a gradual change of the fulcrum of deformation, resulting in a smooth increase with a high spring constant.

[0050] As a result, when the brake fluid pressure is high, the return amount of the piston 21 by the seal member 22 when the brake fluid pressure is released is increased, thereby obtaining the effect of suppressing drag, without reducing the responsiveness of the piston 21 when the brake fluid pressure is low. In addition, since the bore opening side chamfer 105 is a curved surface, the load on the seal member 22 when it is deformed can be reduced, and the durability of the seal member 22 can be improved.

[0051] Further, a first radius of curvature portion 121 having a radius of curvature r1 larger than the second radius of curvature portion 122 is provided closer to the groove bottom surface portion 103 than the second radius of curvature portion 122 having a radius of curvature r2. In a cross section of a plane including the bore axis, the center of the radius of curvature r1 of the first radius of curvature portion 121 is located radially inward of the bisector of the angle between the bore opening side surface portion 104 and the axially extending surface portion 106. This allows the position of the radially outer portion of the bore opening side chamfer portion 105 to be closer to the bore bottom side. This allows the deflection space of the seal member 22 to be narrowed when the brake fluid pressure is low, and the seal member 22 is compressed by the brake fluid pressure, thereby assisting rollback.

[0052] Furthermore, by optimizing the boundary position between the first radius of curvature portion 121, which serves as the fulcrum for deformation of the seal member 22, and the bore opening side surface portion 104, the stress distribution for the restoration of the seal member 22 can be made uniform.

[0053] Furthermore, since a step portion 125 is provided on the bore opening side of the seal groove 55 and on the groove opening 108 side, when the inner surface 92 side of the seal member 22 deforms so as to move toward the bore opening side together with the piston 21, deformation beyond the second radius of curvature portion 122 and into the gap between the step portion 125 and the piston 21 is permitted, allowing large deformation.

[0054] Here, the return amount of the piston 21 when the hydraulic pressure is released in response to the brake hydraulic pressure (hereinafter referred to as the piston return amount) was experimentally determined for the disc brake 10 of the first embodiment, a disc brake having a similar configuration to the conventional one in which the seal groove 55 has a bore opening side chamfer 105A formed of a single tapered surface as shown in Fig. 4A as a comparative example 1, and a disc brake in which the seal groove 55 has a single bore opening side chamfer 105B with a constant radius of curvature as shown in Fig. 4B. The results are shown in Fig. 5. The graph in Fig. 5 shows the measurement results of the first embodiment and comparative examples 1 and 2 as broken lines, with the brake hydraulic pressure P on the horizontal axis and the piston return amount L on the vertical axis.

[0055] As indicated by the solid line X1 in Fig. 5, the disc brake 10 of the first embodiment can increase the amount of piston return when the brake fluid pressure is high compared to Comparative Example 1 while keeping the amount of piston return low when the brake fluid pressure is low, similar to Comparative Example 1 of the conventional structure indicated by the dashed-dotted line X2 in Fig. 5. In other words, the disc brake 10 of the first embodiment can increase the rate of increase in piston return per unit increase in brake fluid pressure compared to Comparative Example 1 of the conventional structure.

[0056] Here, in Comparative Example 2 shown by dashed line X3 in FIG. 5, the amount of piston return when the brake fluid pressure is high can be increased compared to Comparative Example 1 of the conventional structure, and the effect of suppressing drag can be obtained. However, the amount of piston return when the brake fluid pressure is low also increases, increasing the resistance of the sealing member to the movement of the piston and reducing the responsiveness of the piston.

[0057] As described above, the disc brake 10 of the first embodiment achieves the effect of suppressing drag by increasing the amount of return of the piston 21 by the sealing member 22 when the brake fluid pressure is high, without reducing the responsiveness of the piston 21 when the brake fluid pressure is low.

[0058] "Second embodiment" Next, the second embodiment will be described with a focus on differences from the first embodiment, mainly with reference to Figures 5 and 6. Note that parts common to the first embodiment will be designated by the same names and reference numerals.

[0059] 6, in the second embodiment, the seal groove 55 has a bore bottom side chamfer 101, a bore bottom side surface 102, a bore opening side surface 104, a bore opening side chamfer 105, an axially extending surface 106, and a radially extending surface 107, similar to those in the first embodiment. Between the bore bottom side surface 102 and the bore opening side surface 104, there is a groove bottom surface 203 (bottom surface portion) which is partially different from the groove bottom surface 103 of the first embodiment.

[0060] The groove bottom portion 203 has a first tapered surface portion 111, a concave surface portion 113, and a fourth tapered surface portion 115, similar to those in the first embodiment, and has a first curved surface portion 212 (first curved surface) between the first tapered surface portion 111 and the concave surface portion 113, which is different from the second tapered surface portion 112 of the first embodiment, and has a second curved surface portion 214 (second curved surface) between the concave surface portion 113 and the fourth tapered surface portion 115, which is different from the third tapered surface portion 114 of the first embodiment.

[0061] The first curved surface portion 212 is a curved surface that extends from the edge of the first tapered surface portion 111 on the bore opening side (BOS shown in FIG. 6) toward the bore opening side and is inclined so as to be positioned radially outward toward the bore opening side, and forms an annular shape centered on the bore axis. The cross section of the first curved surface portion 212 on a plane including the bore axis is an arc shape having a center on the outer side in the bore radial direction. The first curved surface portion 212 is separated farther inward in the bore radial direction toward the bore opening side in the bore axial direction from the tapered surface that connects the edge of the first tapered surface portion 111 on the bore opening side and the edge of the fourth tapered surface portion 115 on the bore bottom side. The first curved surface portion 212 is annular in shape with a constant diameter on the small diameter side and a constant diameter on the large diameter side over the entire circumference in the bore circumferential direction.

[0062] The second curved surface portion 214 is disposed closer to the bore opening side than the first curved surface portion 212. The second curved surface portion 214 is a curved surface that extends from the edge of the concave surface portion 113 on the bore opening side toward the bore opening side and is inclined so as to be positioned radially outward toward the bore opening side, and forms an annular shape centered on the bore axis. The cross section of the second curved surface portion 214 on a plane including the bore axis is an arc shape having a center on the outer side in the bore radial direction. This cross section of the second curved surface portion 214 is disposed on the same arc as the same cross section of the first curved surface portion 212. The second curved surface portion 214 is farther inward in the bore radial direction toward the bore bottom side in the bore axial direction from the tapered surface that connects the edge of the first tapered surface portion 111 on the bore opening side and the edge of the fourth tapered surface portion 115 on the bore bottom side (BBS shown in FIG. 6). The second curved surface portion 214 is annular in shape with a constant diameter on the smaller diameter side and a constant diameter on the larger diameter side over the entire circumference in the bore circumferential direction.

[0063] The first curved surface portion 212 and the second curved surface portion 214 decrease in diameter toward the bottom of the bore in the bore axial direction, and the first curved surface portion 212 decreases in diameter more gradually with a smaller diameter reduction rate than the second curved surface portion 214. In other words, the first curved surface portion 212 and the second curved surface portion 214 increase in diameter toward the bore opening in the bore axial direction. The first curved surface portion 212 increases in diameter more gradually with a smaller diameter expansion rate than the second curved surface portion 214.

[0064] The first curved surface portion 212 and the second curved surface portion 214 are formed with a convex R shape that bulges inward in the radial direction compared to the tapered surface connecting the edge of the first tapered surface portion 111 on the bore opening side and the edge of the fourth tapered surface portion 115 on the bore bottom side. Between the first curved surface portion 212 and the second curved surface portion 214, an annular concave surface portion 113 that is recessed outward in the bore radial direction, i.e., an annular bottom groove 118, is formed. The groove bottom surface portion 203 includes the first curved surface portion 212 that expands in diameter so as to be positioned outward in the bore radial direction toward the bore opening side, and the second curved surface portion 214 that is positioned closer to the bore opening side than the first curved surface portion 212 and expands in diameter so as to be positioned outward in the bore radial direction toward the bore opening side, and has a larger expansion rate than the first curved surface portion 212.

[0065] According to the second embodiment, since the groove bottom surface portion 203 has a shape that bulges inward in the bore radial direction, the deflection of the seal member 22 is less likely to be hindered by movement of the seal member 22 within the clearance in the bore axial direction. In addition, since the bulging shape of the groove bottom surface portion 203 increases the tightening margin of the seal member 22, the return amount of the piston 21 when the hydraulic pressure is released can be increased.

[0066] According to the second embodiment, as shown by the two-dot chain line X4 in FIG. 5, the piston return amount can be increased from low pressure to high pressure while maintaining the rate of increase in the piston return amount per unit increase in hydraulic pressure substantially the same as in the first embodiment.

[0067] Here, in the disc brake 10 of the embodiment, the caliper 15 is of a floating type that can move in the disc axial direction relative to the disc rotor 11, so that the piston 21 arranged on one side of the disc rotor 11 acts to press the brake pads 13, 14 on both sides against the disc rotor 11. In contrast, in the case of a fixed type caliper that cannot move in the disc axial direction relative to the disc rotor, the piston presses only the brake pad on one side between the caliper and the disc rotor. The shape of the seal groove 55 described above can also be applied to such a fixed type caliper. That is, the shape of the seal groove 55 described above can be applied to a disc brake having a piston for pressing at least one brake pad against the disc rotor.

[0068] In addition, the seal member 22 has been described as having a circular cross-sectional shape in its natural state, which is rectangular when cross-sectionally taken along a plane including the central axis, but the cross-sectional shape may be a square with two sides parallel to the central axis. In other words, the seal member 22 may have a rectangular cross-sectional shape when cross-sectionally taken along a plane including the central axis.

[0069] According to the first aspect of the disk brake of the embodiment described above, the disk brake includes brake pads arranged on both sides of a disk rotor, a piston for pressing at least one of the brake pads against the disk rotor, a cylinder bore in which the piston is slidably fitted, a seal groove provided in the cylinder bore as an annular groove recessed from an inner circumferential surface, and a seal member having a square cross section that is fitted into the seal groove to seal between the piston and the cylinder bore. The seal groove has a bottom surface portion that is inclined in a direction in which the diameter increases toward the opening side of the cylinder bore, a side surface portion that extends from the large diameter side of the bottom surface portion to the opening side of the seal groove, and a chamfered portion that is provided between the side surface portion and the inner circumferential surface of the cylinder bore and is formed to expand the opening of the seal groove in the axial direction of the cylinder bore. The chamfered portion is characterized by having two types of curvature radii. This makes it possible to suppress drag.

[0070] In addition, a second aspect is characterized in that, in the first aspect, the chamfered portion includes a first radius of curvature portion formed on the bottom surface side of the seal groove, and a second radius of curvature portion formed on the inner surface side of the cylinder bore closer to the first radius of curvature portion and having a smaller radius of curvature than the first radius of curvature portion.

[0071] In addition, a third aspect is characterized in that, in the first or second aspect, the bottom surface portion has a first curved surface that expands in diameter so as to be located radially outward of the cylinder bore toward the opening side of the cylinder bore, and a second curved surface that is positioned toward the opening side of the cylinder bore closer to the first curved surface and has a larger expansion rate than the first curved surface. [Industrial Applicability]

[0072] The above-described disc brake makes it possible to suppress drag. [Explanation of symbols]

[0073] 10. Disc brake 11 Disc rotor 13,14 Brake pads 21 Piston 22 Sealing material 35 Cylinder bore 51 Guide inner surface (inner surface) 55 Seal groove 60 Opening (Cylinder bore opening) 103,203 Groove bottom part (bottom part) 104 Bore opening side (side) 105 Bore opening side chamfer (chamfered part) 108 Groove opening (seal groove opening) 121 First curvature radius 122 Second radius of curvature 212 First curved surface portion (first curved surface) 214 Second curved surface portion (second curved surface) r1,r2 radius of curvature

Claims

[Claim 1] Brake pads are arranged on both sides of the disc rotor, a piston for pressing at least one of the brake pads against the disc rotor; a cylinder bore into which the piston is slidably fitted; a seal groove formed as an annular groove recessed from an inner peripheral surface of the cylinder bore; a seal member having a square cross section that is fitted into the seal groove to seal between the piston and the cylinder bore, The seal groove is a bottom surface portion inclined in a direction in which the diameter of the bottom surface portion increases toward an opening side of the cylinder bore; a side surface portion extending from a large diameter side of the bottom surface portion toward an opening side of the seal groove; a rounded portion that is curved from the side portion close to the opening side of the cylinder bore toward the opening side of the cylinder bore, The rounded portion has a plurality of curvature radius portions having different curvature radii, A disc brake in which a radius of curvature of a portion of the cylinder bore that is disposed closest to the inner circumferential surface of the cylinder bore is smallest.

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