Disc brakes

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. The present application claims priority based on Japanese Patent Application No. 2018-102315 filed in Japan on May 29, 2018, the content of which is incorporated herein by reference.

Background Art

[0002] 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, the piston is advanced, and a brake pad is pressed against a disc rotor (see, for example, Patent Documents 1 to 3).

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problem to be Solved by the Invention

[0004] In a disc brake, so-called dragging, in which the brake pad keeps in contact with the disc even after braking is released, may occur. Suppression of such dragging is desired.

[0005] The present invention provides a disc brake capable of suppressing dragging.

Means for Solving the Problem

[0006] According to one aspect of the present invention, a disc brake comprises 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 the inner circumferential surface, and a seal member having a rectangular cross-section that fits into the seal groove and seals the space between the piston and the cylinder bore, wherein the seal groove has a bottom surface portion inclined in a direction that expands in diameter toward the opening side of the cylinder bore, a side surface portion extending from the larger diameter side of the bottom surface portion toward the opening side of the seal groove, and a rounded portion that curves in a rounded shape from the side surface portion closer to the opening side of the cylinder bore toward the opening side of the cylinder bore, and the rounded portion has different radii of curvature Two types of First radius of curvature and the second radius of curvature It has, The second radius of curvature portion extends inward in the bore diameter direction from the smaller diameter end edge of the first radius of curvature portion, and is located on the bottom surface side of the first radius of curvature portion. Displaced on the inner circumferential surface side of the cylinder bore The second of the above Radius of curvature of the radius of curvature section small The seal groove has a stepped portion on the opening side of the cylinder bore and on the opening side of the seal groove. The stepped portion has an axially extending surface portion that extends axially from the small-diameter end edge of the second radius of curvature portion toward the opening side of the cylinder bore, and in a cross-section of the plane including the central axis of the cylinder bore, the center of the radius of curvature portion of the first radius of curvature portion is located radially inward of the cylinder bore from the bisector of the angle between the side portion and the axially extending surface portion. This was the structure. [Effects of the Invention]

[0007] The disc brakes described above make it possible to suppress drag. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view showing a disc brake according to the first embodiment of the present invention. [Figure 2] This is a side cross-sectional view showing a disc brake according to the first embodiment of the present invention. [Figure 3A] This is a partial cross-sectional view showing a sealing member of a disc brake according to a first embodiment of the present invention. [Figure 3B] This is a partial cross-sectional view showing the state of the seal groove of the disc brake according to the first embodiment of the present invention before assembly. [Figure 4A] This is a partial cross-sectional view showing the seal groove of Comparative Example 1 of a disc brake. [Figure 4B] This is a partial cross-sectional view showing the seal groove of Comparative Example 2 of a disc brake. [Figure 5] This is a characteristic diagram showing the piston return amount with respect to brake fluid pressure for the first and second embodiments of the present invention and comparative examples 1 and 2. [Figure 6] This is a partial cross-sectional view showing a seal groove of a disc brake according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0009] "First Embodiment" The first embodiment will be described below with reference to Figures 1 to 5.

[0010] Figures 1 and 2 show a disc brake 10 of the first embodiment. This disc brake 10 provides braking force to vehicles such as automobiles. Specifically, the disc brake 10 is for braking four-wheeled vehicles. 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 will be referred to as the disc axial direction, the radial direction of the disc rotor 11 will be referred to as the disc radial direction, and the circumferential direction (rotational direction) of the disc will be referred to as the disc circumferential direction.

[0011] The disc brake 10 comprises a carrier 12, a pair of brake pads 13 and 14 as shown in Figure 2, a caliper 15, and a pair of boots 16 as shown in Figure 1. The carrier 12 is positioned across the outer circumference of the disc rotor 11 and fixed to the non-rotating part of the vehicle. The pair of brake pads 13 and 14 are positioned on either side of the disc rotor 11 and 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 grips the pair of brake pads 13 and 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. 1.

[0013] The caliper body 20 is formed by processing an integrally molded metal material through casting. The caliper body 20 includes: a cylinder 26 disposed on one side of the disc rotor 11 in the disc axial direction; a bridge portion 27 extending from an outer side of the cylinder 26 in the disc radial direction so as to straddle the outer circumference of the disc rotor 11; a claw portion 28 extending inward in the disc radial direction from a side of the bridge portion 28 opposite to the cylinder 26 and disposed on the other side of the disc rotor 11 in the disc axial direction; and a pair of arm portions 29 shown in FIG. 1 extending from the cylinder 26 to both sides in the disc circumferential direction. The caliper body 20 is movably supported by the carrier 12 via the slide pins 24 attached to the pair of arm portions 29. The 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 that is open at one end toward the claw portion 28 side and is recessed toward a side opposite to the disc rotor 11 in the disc axial direction. By forming the cylinder bore 35 opening toward the claw portion 28 side, the cylinder 26 has a cylinder bottom portion 39 including an inner bottom 38 of the cylinder bore 35 on a side opposite to the claw portion 28, and has a cylinder body portion 42 including an inner wall portion 41 of the cylinder bore 35, which extends from the cylinder bottom portion 39 toward the claw portion 28 side. The cylinder bore 35 has an opening 43 on a side of the cylinder body portion 42 opposite to the cylinder bottom portion 39. The cylinder bottom portion 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] A piston 21 is fitted into the cylinder bore 35 so as to be slidable in the disc axial direction. An inner wall portion 41 of the cylinder bore 35 has a guide inner circumferential surface 51 (inner circumferential surface) which is a cylindrical surface with a constant inner diameter over the entire length and guides the movement of the piston 21. The center axis of this guide inner circumferential surface 51 is the center axis of the cylinder bore 35. This center axis is referred to as the bore axis. Further, a direction orthogonal to this center axis is referred to as the bore radial direction, and a circumferential direction centered on this center 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 outward in the bore radial direction relative to the guide inner circumferential surface 51 on the bore bottom side relative to the guide inner circumferential surface 51. The large-diameter groove 52 is annular centered on the bore axis, and has a groove bottom diameter larger than that of the guide inner circumferential surface 51.

[0017] The inner wall portion 41 of the cylinder bore 35 has an annular seal groove 55 that is recessed outward in the bore radial direction relative to 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 centered on the bore axis, which is provided recessed from the guide inner circumferential surface 51 in the inner wall portion 41 of the cylinder bore 35. The groove bottom diameter of the seal groove 55 is larger than that of the guide inner circumferential surface 51.

[0018] In the inner wall portion 41 of the cylinder bore 35, an annular boot fitting groove 58 that is recessed outward in the bore radial direction relative to the guide inner circumferential surface 51 is formed on the bore opening side relative to the seal groove 55. The boot fitting groove 58 is annular centered on the bore axis, and has a groove bottom diameter larger than that of the guide inner circumferential surface 51.

[0019] The inner wall portion 41 of the cylinder bore 35 has a boot placement hole 59 formed on the bore opening side of the boot fitting groove 58, which is tapered around the bore axis and increases in diameter as it moves away from the boot fitting groove 58. The end of the boot placement hole 59 opposite to the cylinder bottom portion 39 is the opening 43 of the cylinder bore 35. The large-diameter groove 52 and the inner bottom portion 38 connected to it are cast during the casting of the caliper body 20 material. The inner circumferential surface of the guide 51, the seal groove 55, the boot fitting groove 58, and the boot placement hole 59 are formed by machining the material of the caliper body 20.

[0020] A pipe hole 68 is formed in the cylinder bottom 39, extending through the bore axis direction so as to open into the cylinder bore 35. The pipe hole 68 is formed by machining the material of the caliper body 20. Brake piping (not shown) is connected to the pipe hole 68.

[0021] The piston 21 comprises a disc-shaped piston base 71 and a cylindrical piston body 72. The piston 21 is formed in a bottomed cylindrical shape with the end of the piston body 72 opposite to the piston base 71 being open. The piston body 72 has an annular fitting groove 75 formed on the side opposite to the piston base 71 in the axial direction, which is recessed radially inward from the outer diameter surface 74, which is a cylindrical surface. The piston 21 is housed in the cylinder bore 35 such that the piston base 71 is located on the bottom side of the bore within the cylinder bore 35, and in this state, the tip on the claw portion 28 side protrudes beyond the cylinder bore 35 toward the claw portion 28. The fitting groove 75 is formed on the tip side of the piston 21 that protrudes beyond the cylinder bore 35 in this manner.

[0022] The sealing member 22 is made of an elastic material, specifically rubber. The sealing member 22 is fitted into the sealing groove 55 of the cylinder bore 35 with an overlap. The piston 21 is fitted to the inner circumference of the sealing member 22 with an overlap. The sealing member 22 elastically deforms radially to tightly adhere to the piston 21 and the sealing groove 55, sealing the space between the cylinder bore 35 of the cylinder 26 and the piston 21. The sealing member 22, together with the guide inner circumferential surface 51 of the cylinder bore 35, supports the outer diameter surface 74 of the piston 21 so that it can move in the bore axis direction. The sealing member 22, together with the cylinder bore 35 and the piston 21, forms a hydraulic chamber 69. Brake fluid is supplied to and discharged from this hydraulic chamber 69 via brake piping connected to the piping hole 68.

[0023] The boot member 23 is a retractable, bellows-shaped 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 the portion of the outer diameter surface 74 of the piston 21 that is exposed from the cylinder bore 35 on the piston bottom 71 side of 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) is operated, brake fluid is introduced into the hydraulic chamber 69 of the disc brake 10 via brake piping (not shown) connected to the piping hole 68. This causes brake fluid pressure to act 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, pressing the brake pad 13, which is positioned 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. As the piston 21 advances toward the disc rotor 11 relative to the cylinder bore 35 in this manner, the inner circumference of the seal member 22, which is housed in the seal groove 55, is elastically deformed so that the contact portion of the seal member 22 is moved together by friction.

[0025] Furthermore, the reaction force pressing the brake pad 13 against the disc rotor 11 causes the caliper body 20 to slide against the carrier 12 on a pair of slide pins 24, and the claw portion 28 presses the brake pad 14, which is positioned between the claw portion 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, through the operation of the piston 21, clamps the pair of brake pads 13 and 14 from both sides with the piston 21 and the claw portion 28 and presses them toward both sides of the disc rotor 11. As a result, the caliper 15 applies frictional resistance to the disc rotor 11 and generates braking force. The piston 21 presses the brake pads 13 and 14 on both sides toward 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 decreases, and the force that the piston 21 was applying to the seal member 22, which had been elastically deformed as described above, decreases. As a result, the seal member 22 returns to its deformed state due to its own elasticity. At that time, the piston 21 is pushed back toward the bottom of the bore by friction, a so-called rollback, which forms a gap between the piston 21 and the brake pad 13. As a result, the runout of the disc rotor 11 causes the brake pads 13, 14 and the claw portion 28 to move away from the disc rotor 11 in the direction of the disc axis.

[0027] As shown in Figure 3A, when the seal member 22, made of an elastic material, is naturally shaped into a circular form before being fitted into the seal groove 55, it has an outer circumferential surface 91 made of a cylindrical surface, an inner circumferential surface 92 made of a cylindrical surface with a smaller diameter than the outer circumferential surface 91, a flat end surface 93 perpendicular to the outer circumferential surface 91 and the inner circumferential surface 92 and connecting one end edge of these surfaces in the axial direction, and a flat end surface 94 perpendicular to the outer circumferential surface 91 and the inner circumferential surface 92 and connecting the other end edges of these surfaces in the axial direction. In other words, when the seal member 22 is naturally shaped into a circular form before being fitted into the seal groove 55, the cross-sectional shape when the plane containing its central axis is used as a cross-section is a rectangle with a long side parallel to the central axis.

[0028] The seal groove 55 is annular in shape centered on the bore axis, and in the direction of the bore axis, starting from the bore bottom side (BBS shown in Figure 3B), it has, in order: a bore bottom chamfered portion 101, a bore bottom side portion 102, a groove bottom portion 103 (bottom portion), a bore opening 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 smaller diameter side of the seal groove 55 is a groove opening 108 that opens toward the bore axis.

[0029] The bore bottom side chamfer 101 is a tapered surface centered on the bore axis that extends outward in the bore diameter direction from the cylindrical inner circumferential surface of the guide 51 and slopes so that the outer side in the bore diameter direction is located towards the bore opening (BOS shown in Figure 3B). The bore bottom side chamfer 101 is an annular shape with a constant diameter on both the small diameter side and the large diameter side along the entire circumference of the bore.

[0030] The bore bottom side surface portion 102 is an annular plane centered on the bore axis, extending outward in the bore diameter direction perpendicular to the bore axis from the large-diameter end edge of the bore bottom side trim portion 101. The bore bottom side surface portion 102 is an annular shape with a constant diameter on both the small-diameter and large-diameter sides along the entire circumference of the bore.

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

[0032] The first tapered surface portion 111 is a tapered surface centered on the bore axis that extends from the large-diameter end edge of the bore bottom side surface portion 102 toward the bore opening and inclined so that it is located further outward in the bore diameter direction toward the bore opening. The taper of the first tapered surface portion 111 is smaller than that of the bore bottom side surface portion 101. The first tapered surface portion 111 is an annular shape with a constant diameter on both the small-diameter and large-diameter sides along 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 bore opening side edge of the first tapered surface portion 111 toward the bore opening and inclined so that it is located further outward in the bore diameter direction toward the bore opening. 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 an annular shape with a constant diameter on both the small diameter side and the large diameter side along the entire circumference in the bore circumferential direction.

[0034] The concave portion 113 is a curved surface that extends from the bore opening side edge of the second tapered surface portion 112 toward the bore opening, inclined to be located further outward in the bore diameter direction toward the bore opening, and then inclined to be located further inward in the bore diameter direction toward the bore opening. The concave portion 113 is an annular shape centered on the bore axis. The concave portion 113 has a cross-section in the plane containing the bore axis that is arc-shaped with its center located inward in the bore radial direction. The cross-section of the concave portion 113 maintains 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 that extends from the bore opening side edge of the concave surface portion 113 toward the bore opening and inclined so that it is located further outward in the bore diameter direction toward the bore opening. The third tapered surface portion 114 has the same taper as the second tapered surface portion 112 and is located on the same tapered surface as the second tapered surface portion 112. The third tapered surface portion 114 is an annular shape with a constant diameter on the smaller diameter side and a constant diameter on the larger diameter side along its entire circumference in the bore circumferential direction. In contrast to the second tapered surface portion 112 and the third tapered surface portion 114, which are located on the same tapered surface, the concave surface portion 113 is recessed outward in the bore diameter direction and constitutes 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 end edge of the third tapered surface portion 114 on the bore opening side toward the bore opening side and inclined so that it is located further inward in the bore diameter direction toward the bore opening side. The fourth tapered surface portion 115 is an annular shape with a constant diameter on both the large diameter side and the small diameter side along the entire circumference in the bore circumferential direction.

[0037] The groove bottom surface 103, which has a first tapered surface 111, a second tapered surface 112, a concave surface 113, a third tapered surface 114, and a fourth tapered surface 115, is generally inclined in a direction that expands in diameter toward the bore opening side. The side with the first tapered surface 111 in the bore axis direction is the smaller diameter side, and the side with the fourth tapered surface 115 is the larger diameter side.

[0038] The bore opening side surface portion 104 is an annular plane centered on the bore axis, extending inward in the bore diameter direction perpendicular to the bore axis from the bore opening side edge of the fourth tapered surface portion 115. In other words, the bore opening side surface 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 surface portion 104 is an annular shape with a constant diameter on both the large diameter side and the small diameter side along the entire circumference in the bore circumferential direction.

[0039] The bore opening side chamfer 105 is provided between the bore opening side surface 104 and the portion of the guide inner circumferential surface 51 that is 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 diameter direction from the small-diameter end edge of the bore opening side surface 104 and inclined so that it is located closer to the bore opening as it is further inward in the bore diameter direction. The bore opening side chamfer 105 is annular around the bore axis. In other words, the bore opening side chamfer 105 is formed from the small-diameter end edge of the bore opening side surface 104 so as to expand the groove opening 108 of the seal groove 55 toward the bore axis. The bore opening side chamfer 105 is annular with a constant diameter on both the large-diameter and small-diameter sides along its entire circumference in the bore circumferential direction. The width of the bore opening side chamfer 105 in the bore diameter direction is smaller than that of the bore opening side surface 104.

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

[0041] The first radius of curvature portion 121 is a curved surface that extends inward in the bore diameter direction from the small-diameter end edge of the bore opening side surface portion 104, and is inclined so that it is located closer to the bore opening the further inward it is in the bore diameter direction. The first radius of curvature portion 121 forms an annular shape centered on the bore axis. The cross-section of the first radius of curvature portion 121 on the plane including the bore axis is an arc shape with a constant radius of curvature r1, with its center on the real part of the cylinder 26 that forms this first radius of curvature portion 121. In the cross-section of the first radius of curvature portion 121 on the plane including the bore axis, the center of the radius of curvature r1 is located inward in the bore diameter direction from the angle bisector of the angle between the bore opening side surface 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 diameter direction than to the bore axis direction. The first radius of curvature section 121 has a constant cross-sectional shape throughout its entire circumference in the bore direction. The first radius of curvature section 121 is an annular shape with a constant diameter on both the larger and smaller sides along the entire circumference in the bore direction.

[0042] The second radius of curvature section 122 is a curved surface that extends inward in the bore diameter direction from the small-diameter end edge of the first radius of curvature section 121, and is inclined so that the further inward it is, the closer it is to the bore opening. The second radius of curvature section 122 forms an annular shape centered on the bore axis. The cross-section of the second radius of curvature section 122, on the plane including the bore axis, is an arc shape with a constant radius of curvature r2, centered on the real part of the cylinder 26 that forms this second radius of curvature section 122. The cross-section of the second radius of curvature section 122 maintains a constant shape over the entire circumference in the bore circumferential direction. The second radius of curvature section 122 is an annular shape with a constant diameter on both the large-diameter and small-diameter sides over the entire circumference in the bore circumferential direction. The radius of curvature r2 of the second radius of curvature section 122 is smaller than the radius of curvature r1 of the first radius of curvature section 121. In other words, the second radius of curvature section 122 has a smaller radius of curvature than the first radius of curvature section 121. Also, the second radius of curvature section 122 has a smaller width in the bore diameter direction than the first radius of curvature section 121.

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

[0044] The radially extending surface portion 107 is an annular plane centered on the bore axis, extending inward in the bore radial direction perpendicular to the bore axis from the bore opening side edge of the axially extending surface portion 106. The radially extending surface portion 107 is an annular shape with a constant diameter on both the smaller and larger sides along the entire circumference of the bore. The smaller diameter side of the radially extending surface portion 107 is connected to the portion of the inner circumferential surface 51 of the guide that is closer to the bore opening than the seal groove 55.

[0045] The axially extending surface portion 106 and the radially extending surface portion 107 constitute a stepped portion 125 that is recessed outward in the radial direction of the bore at the end of the seal groove 55 on the bore opening side and the groove opening 108 side. In other words, the seal groove 55 has a stepped portion 125 that is recessed outward in the radial direction of the bore at its end on the bore opening side and the groove opening 108 side.

[0046] The disc brakes described in Patent Documents 1 to 3 above introduce brake fluid pressure between a cylinder bore and a piston slidably fitted into the cylinder bore, causing the piston to advance and press the brake pads against the disc rotor. Such disc brakes are provided with a sealing member to seal the gap between the cylinder bore and the piston. This sealing member performs a rollback, returning the piston to the bottom of the cylinder when the brake fluid pressure is released.

[0047] Incidentally, in order to improve fuel efficiency, it is desirable to suppress so-called brake drag, where the brake pads continue to contact the disc even after braking is released. In particular, when the brake fluid pressure is high, increasing the amount the piston returns when the fluid pressure is released by the sealing member can suppress drag. However, if the amount the piston returns when the fluid pressure is released by the sealing member is increased, the resistance of the sealing member to the piston movement when the brake fluid pressure is low will increase, reducing the responsiveness of the piston and worsening the pedal feel.

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

[0049] Specifically, the bore opening side section 105 has a first radius of curvature section 121 with a radius of curvature r1 on the groove bottom section 103 side, and a second radius of curvature section 122 formed on the inner circumferential surface 51 side of the first radius of curvature section 121, with a smaller radius of curvature r2 than the first radius of curvature section 121. Therefore, when the piston 21 moves forward, the inner circumferential surface 92 side of the seal member 22, which is the side that contacts the piston 21, moves together with the piston 21. At low brake fluid pressure, the end face 93 on the bore opening side deforms with a large radius of curvature r1 following the first radius of curvature portion 121, and the pivot point of the deformation gradually changes, resulting in a smooth increase with a low spring constant. On the other hand, at high brake fluid pressure, the end face 93 deforms with a small radius of curvature r2 following the second radius of curvature portion 122 after the first radius of curvature portion 121, so the pivot point of the deformation gradually changes, resulting in a smooth increase with a high spring constant.

[0050] This allows for drag suppression without reducing the responsiveness of the piston 21 when the brake fluid pressure is low, and by increasing the amount of return of the piston 21 when the fluid pressure is released by the sealing member 22 when the brake fluid pressure is high. In addition, because the bore opening side section 105 is a curved surface, the load on the sealing member 22 during deformation can be reduced, thereby improving the durability of the sealing member 22.

[0051] Furthermore, a first radius of curvature portion 121 with a larger radius of curvature r1 is provided on the groove bottom surface portion 103 side of the second radius of curvature portion 122 having a radius of curvature r2. In the cross-section of the plane including the bore axis, the center of the radius of curvature r1 of this first radius of curvature portion 121 is positioned inward in the bore diameter direction from 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 outer portion of the bore diameter direction of the bore opening side portion 105 to be moved closer to the bore bottom. This narrows the deflection space of the seal member 22 when the brake fluid pressure is low, and the brake fluid pressure compresses the seal member 22, thereby assisting rollback.

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

[0053] Furthermore, because the stepped portion 125 is provided on the bore opening side and groove opening 108 side of the seal groove 55, when the inner circumferential surface 92 side of the seal member 22 deforms to move toward the bore opening side together with the piston 21, deformation beyond the second radius of curvature portion 122 is permitted in the gap between the stepped portion 125 and the piston 21, allowing for significant deformation.

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

[0055] As shown by the solid line X1 in Figure 5, the disc brake 10 of the first embodiment, like Comparative Example 1 of a conventional structure shown by the dashed line X2 in Figure 5, can keep the piston return amount low when the brake fluid pressure is low, while increasing the piston return amount when the brake fluid pressure is high compared to Comparative Example 1. In other words, the disc brake 10 of the first embodiment can increase the rate of increase in piston return amount per unit increase in brake fluid pressure compared to Comparative Example 1 of a conventional structure.

[0056] In Comparative Example 2, shown by the dashed line X3 in Figure 5, the piston return amount can be increased when the brake fluid pressure is high compared to the conventional structure of Comparative Example 1, and the drag suppression effect is obtained. However, the piston return amount is also increased when the brake fluid pressure is low, which increases the resistance force of the sealing member to the movement of the piston and reduces 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, primarily based on Figures 5 and 6, focusing on the differences from the first embodiment. Parts common to both the first and second embodiments will be represented by the same designations and reference numerals.

[0059] As shown in Figure 6, in the second embodiment, the seal groove 55 has the same bore bottom side chamfer 101, bore bottom side surface 102, bore opening side surface 104, bore opening side chamfer 105, axially extending surface 106, and radially extending surface 107 as 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) 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 the first embodiment. Between the first tapered surface portion 111 and the concave surface portion 113, there is a first curved surface portion 212 (first curved surface) which is different from the second tapered surface portion 112 of the first embodiment, and between the concave surface portion 113 and the fourth tapered surface portion 115, there is a second curved surface portion 214 (second curved surface) 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 end edge of the first tapered surface portion 111 on the bore opening side (BOS shown in Figure 6) toward the bore opening side and is inclined so that it is located further outward in the bore diameter direction 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 the plane including the bore axis is an arc shape with its center on the outside in the bore diameter direction. The first curved surface portion 212 is spaced further inward in the bore diameter direction toward the bore opening side toward the bore opening side relative to the tapered surface connecting the end edge of the first tapered surface portion 111 on the bore opening side and the end edge of the fourth tapered surface portion 115 on the bore bottom side. The first curved surface portion 212 is an annular shape with a constant diameter on both the small diameter side and the large diameter side along the entire circumference in the bore circumferential direction.

[0062] The second curved surface portion 214 is positioned closer to the bore opening than the first curved surface portion 212. The second curved surface portion 214 is a curved surface that extends from the bore opening side edge of the concave surface portion 113 toward the bore opening and inclined so that it is located further outward in the bore diameter direction toward the bore opening, forming an annular shape centered on the bore axis. The cross-section of the second curved surface portion 214 on the plane including the bore axis is an arc shape with its center on the outside in the bore diameter direction. This cross-section of the second curved surface portion 214 is positioned in the same arc as the same cross-section of the first curved surface portion 212. The second curved surface portion 214 is spaced further inward in the bore diameter direction toward the bore axial direction toward the bore bottom, relative to the tapered surface connecting the bore opening side edge of the first tapered surface portion 111 and the bore bottom side edge (BBS shown in Figure 6) of the fourth tapered surface portion 115. The second curved surface portion 214 is an annular shape with a constant diameter on both the smaller diameter side and the larger diameter side along the entire circumference in the bore direction.

[0063] The first curved surface portion 212 and the second curved surface portion 214 decrease in diameter towards the bottom of the bore in the bore axis direction, and the first curved surface portion 212 decreases in diameter more gradually 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 towards the bore opening in the bore axis direction. The first curved surface portion 212 increases in diameter more gradually than the second curved surface portion 214.

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

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

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

[0067] In this embodiment, the disc brake 10 is a floating type in which the caliper 15 is movable in the disc axial direction relative to the disc rotor 11. Therefore, the piston 21 located on one side of the disc rotor 11 acts to press both brake pads 13 and 14 against the disc rotor 11. In contrast, in the case of a fixed type caliper in which the caliper is not movable in the disc axial direction relative to the disc rotor, the piston presses only the brake pad on one side that is between it 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] Furthermore, while the explanation described the case where the sealing member 22, when naturally shaped into a circle, has a rectangular cross-section when the plane containing the central axis is used as a cross-section, with the longer side parallel to the central axis, the cross-sectional shape when the plane containing the central axis is used as a cross-section may also be a square with two sides parallel to the central axis. In other words, the sealing member 22 only needs to have a rectangular cross-sectional shape when the plane containing the central axis is used as a cross-section.

[0069] According to the first embodiment of the disc brake described above, the disc brake comprises 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 the inner circumferential surface, and a seal member having a rectangular cross-section that fits into the seal groove and seals the space between the piston and the cylinder bore. The seal groove has a bottom surface portion inclined in a direction that expands in diameter toward the opening side of the cylinder bore, a side surface portion extending from the larger diameter side of the bottom surface portion toward the opening side of the seal groove, and a chamfered portion provided between the side surface portion and the inner circumferential surface of the cylinder bore, 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 different radii of curvature. This makes it possible to suppress drag.

[0070] Furthermore, the second embodiment is characterized in that, in the first embodiment, the chamfered portion comprises 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 circumferential surface side of the cylinder bore, which has a smaller radius of curvature than the first radius of curvature portion.

[0071] Furthermore, the third embodiment is characterized in that, in the first or second embodiment, the bottom surface portion comprises a first curved surface that expands in diameter so as it is located further outward in the radial direction of the cylinder bore towards the opening side of the cylinder bore, and a second curved surface that is located further towards the opening side of the cylinder bore than the first curved surface and has a larger diameter expansion ratio than the first curved surface. [Industrial applicability]

[0072] The disc brakes described above make it possible to suppress drag. [Explanation of Symbols]

[0073] 10 Disc brakes 11 Disc rotors 13,14 Brake pads 21 pistons 22 sealing member 35 Cylinder bore 51 Guide inner surface (inner surface) 55 Seal groove 60 Opening (opening of cylinder bore) 103,203 Groove bottom part (bottom part) 104 Bore opening side section (side section) 105 Bore opening side chamfered section (chamfered section) 108 Groove opening (opening of seal groove) 121 First radius of curvature 122 Second radius of curvature section 212 First curved surface (first curved surface) 214 Second curved surface (second curved surface) r1,r2 radius of curvature

Claims

[Claim 1] Brake pads are positioned 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 is provided in the cylinder bore as an annular groove recessed from the inner circumferential surface, The device comprises a sealing member with a rectangular cross-section that is fitted into the seal groove to seal the space between the piston and the cylinder bore, The aforementioned seal groove is The bottom surface portion is inclined in a direction that expands in diameter toward the opening side of the cylinder bore, A side portion extending from the larger diameter side of the bottom portion to the opening side of the seal groove, The cylinder bore has a rounded portion that curves outwards from the side surface near the opening side of the cylinder bore toward the opening side, The rounded portion has two types of first radius of curvature portions and second radius of curvature portions with different radii of curvature. The second radius of curvature portion extends inward in the bore diameter direction from the smaller diameter end edge of the first radius of curvature portion. The radius of curvature of the second radius of curvature portion, which is located on the inner circumferential surface side of the cylinder bore, is smaller than the radius of curvature of the first radius of curvature portion, which is located on the bottom surface side. The seal groove has a stepped portion on the opening side of the cylinder bore and on the opening side of the seal groove, The aforementioned stepped portion is The second radius of curvature portion has an axially extending surface portion that extends from the smaller diameter end edge toward the opening side of the cylinder bore in the axial direction of the cylinder bore, In the cross-section of the first radius of curvature portion on the plane including the central axis of the cylinder bore, the center of the radius of curvature is located radially inward of the cylinder bore from the angle bisector of the angle between the side surface portion and the axially extending surface portion. Disc brakes.

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