disc brake

Abstract

Disc brake (1), comprising: a pair of blocks (2,3) arranged on both sides of a rotor (D) in an axial direction of the rotor (D); a piston (18) designed to push one of the pair of blocks (2,3) against the rotor (D); a brake caliper body (6) with a cylinder (15) in which the piston (18) is movably arranged; an electric motor (40) which is installed on the brake caliper main body (6); and a rotation-translation conversion mechanism (43) installed on the brake caliper main body (6) designed to push the piston (18) so as to hold the piston (18) in a braking position, wherein: the rotation-translation-conversion mechanism (43) exhibits: a rotational transmission element (75) to which a rotation of the electric motor (40) is transmitted; a shaft element (102) which is threaded and joined to the rotation transmission element (75) so that rotation and translation of the shaft element (102) are possible; and a ball-and-ramp mechanism (127) which is threaded and joined to the shaft element (102) which is designed to apply a thrust in the axial direction to the piston (18) by the rotation of the shaft element (102); wherein the shaft element has a first thread (103) which is threaded into the rotation transmission element (75) formed on one end face of the shaft element (102), and a second thread (104) which is threaded into the ball-and-ramp mechanism (127) formed on another end face of the shaft element (102); and a rotational friction torque of the first thread (103) is greater than a rotational friction torque of the second thread (104).

Description

TECHNICAL AREA

[0001] The present invention relates to a disc brake which is used to provide a brake for a vehicle. BACKGROUND TECHNOLOGY

[0002] Some disc brakes of comparable technology include a mechanism to prevent rotation (detent mechanism) to maintain a braking force during the application of a parking brake and the like in a planetary gear speed reduction mechanism (see JP 2010-169248 A, JP 2014-92165 A and DE 103 53 695 A1).

[0003] However, in the disc brake disclosed in JP 2010-169248 A, a mechanism for maintaining braking force is complex, leading to concerns that the manufacturing efficiency of the disc brake will decrease. PRESENTATION OF THE INVENTION

[0004] It is an object of the present invention to provide a disc brake with a simplified mechanism for maintaining a braking force during the application of a parking brake and the like, in order to increase manufacturing efficiency.

[0005] As a means of solving the aforementioned problem, according to one embodiment of the present invention, a disc brake is provided, comprising: a pair of pads arranged on both sides of a rotor in an axial direction of the rotor; a piston configured to press one of the pair of pads against the rotor; a caliper body with a cylinder in which the piston is movably arranged; an electric motor installed on the caliper body; and a rotation-translation conversion mechanism installed on the caliper body, configured to push the piston so as to hold the piston in a braking position, wherein the rotation-translation conversion mechanism comprises: a rotation transmission element onto which a rotation of the electric motor is transmitted;a shaft element joined in threaded engagement to the rotational transmission element, such that rotation and translation of the shaft element are possible; and a ball-and-ramp mechanism joined in threaded engagement to the shaft element, configured to apply thrust in the axial direction to the piston through the rotation of the shaft element; wherein the shaft element has a first thread joined in threaded engagement to the rotational transmission element, which is formed on one end face of the shaft element, and a second thread joined in threaded engagement to the ball-and-ramp mechanism, which is formed on another end face of the shaft element; and a rotational friction torque of the first thread is greater than a rotational friction torque of the second thread.

[0006] According to one embodiment of the present invention, it is possible to provide the disc brake with the simplified mechanism of maintaining the braking force during the application of the parking brake and the like, thereby increasing manufacturing efficiency. SHORT FIGURE DESCRIPTION Fig. Figure 1 is a cross-sectional view to illustrate a disc brake according to a first embodiment. Fig. Figure 2 is an enlarged cross-sectional view of a rotation-translation conversion mechanism used in the disc brake according to this embodiment. Fig. Figure 3 is a cross-sectional view taken along line AA of the rotation-translation-conversion mechanism located in Fig. 2 is illustrated. Fig. Figure 4 is a cross-sectional view taken along line BB of the rotation-translation-conversion mechanism located in Fig. 2 is illustrated. Fig. Figure 5 is a perspective exploded view of the rotation-translation conversion mechanism that is in Fig. 2 is illustrated. Fig. Figure 6 is a cross-sectional view to illustrate step-by-step an action when a parking brake is applied. Fig. Figure 7 is a cross-sectional view to illustrate the action step by step when the parking brake is applied. Fig. Figure 8 is a cross-sectional view to illustrate the action step by step when the parking brake is applied. Fig. Figure 9 is a cross-sectional view to illustrate the action step by step when the parking brake is applied. Fig. Figure 10 is a cross-sectional view to illustrate step-by-step an action when the parking brake is released. Fig. Figure 11 is a cross-sectional view to illustrate step-by-step an action when the parking brake is released. Fig. Figure 12 is a cross-sectional view to illustrate step-by-step an action when the parking brake is released. Fig. Figure 13 is a cross-sectional view to illustrate a disc brake according to a second embodiment. Fig. Figure 14 is a perspective exploded view inside a disc brake housing, which is located in Fig. 13 is illustrated. Fig. Figure 15 is a perspective exploded view of the disc brake housing, which is located in Fig. 13 is illustrated. Fig. Figure 16 is an enlarged cross-sectional view of the rotation-translation conversion mechanism of the disc brake, which is located in Fig. 13 is illustrated. Fig. Figure 17 is a perspective exploded view of the rotation-translation-conversion mechanism that is in Fig. 16 is illustrated. Fig. Figure 18 is a perspective view of the rotation-translation conversion mechanism of the disc brake, which is shown in Fig. 13 is illustrated. Fig. Figure 19 is a side view of the rotation-translation conversion mechanism of the disc brake, which is located in Fig. 18 is illustrated. DESCRIPTION OF EXECUTION FORMS

[0007] A first embodiment of the present invention will now be described in detail with reference to Fig. 1 to Fig. 12 described.

[0008] As in Fig. As illustrated in Figure 1, a disc brake 1 according to this embodiment comprises a pair of an inner brake pad 2 and an outer brake pad 3, arranged on both sides in an axial direction of a disc rotor D mounted on a rotating unit of a vehicle, and also includes a brake caliper 4. The disc brake 1 of this embodiment is a disc brake with a floating caliper. It should be noted that the pair of inner brake pads 2 and outer brake pads 3 and the brake caliper 4 are held by a bracket 5, which is attached to a stationary unit such as a steering knuckle of the vehicle, so that they are movable in the axial direction of the disc rotor D. A suitable description is given below, assuming that a right side in Fig. 1. One end page is a left page. Fig. 1 is the other end.

[0009] A brake caliper main body 6, which is a main body of the brake caliper 4, comprises a cylinder section 7 arranged at a proximal end part (the part opposite the inner brake pad 2 on an inboard side of the vehicle) of the brake caliper main body 6, and a gripper section 8 arranged at a distal end part (the part opposite the outer brake pad 3 on an outboard side of the vehicle) of the brake caliper main body 6. The cylinder section 7 includes a cylinder 15 with a larger-diameter opening part 9A opening towards the side of the inner brake pad 2, and a base closed by a base wall 11, which has an opening part 10 arranged on one side opposite this base wall.An opening section 9B with a smaller diameter, which is formed continuously with the opening section 9A with a larger diameter and has a smaller diameter than the opening section 9A with a larger diameter, is formed in a section adjacent to the bottom wall 11 in the cylinder 15. A piston seal 16 is arranged on an inner circumferential surface of the opening section 9A with a larger diameter.

[0010] As in Fig. 1 and Fig. As illustrated in Figure 2, a piston 18 is designed as a cup shape, with a base section 19 and a cylindrical section 20. The piston 18 is received in the cylinder 15 such that the base section 19 faces the inner brake pad 2. The piston 18 is installed internally in the larger-diameter opening section 9A of the cylinder 15 to allow axial movement in a state where the piston 18 is in contact with the piston seal 16. A hydraulic chamber 21 is defined by the fact that it is sealed by the piston seal 16 between the piston 18 and the bottom wall 11 of the cylinder 15. Hydraulic pressure is supplied to this hydraulic chamber 21 through a port (not shown) formed in the cylinder section 7 from a hydraulic pressure source (not shown), such as a master cylinder or a hydraulic control unit.Several longitudinal grooves 22 for limiting rotation are formed along a circumferential direction on a circumferential surface of the piston 18. According to this embodiment, the longitudinal grooves for limiting rotation 22 are formed at twelve locations along the circumferential direction (see ). Fig. 3).

[0011] A recess 25 is formed on the base 19 of the piston 18 on an outer circumferential side of the opposite end surface from the inner brake pad 2. A projection 26, formed on a rear surface of the inner brake pad 2, engages this recess 25, and this engagement prevents the piston 18 from rotating relative to the cylinder 15 and thus to the caliper body 6. Furthermore, a dust boot 21 is inserted between the outer circumferential surface of the base 19 of the piston 18 and the inner circumferential surface of the larger-diameter opening 9A of the cylinder 15 to prevent foreign matter from entering the cylinder 15.On an end surface of the bottom part 19 of the cylinder 18 opposite the rotation-translation conversion mechanism 43, a circular flat surface part 30 is formed on a radial central part thereof, and a circularly curved surface part 31, which extends continuously from the circular flat surface part 30 towards the inner circumferential surface of the piston 18 in order to increase in diameter towards one end side, is formed.

[0012] As in Fig. As illustrated in Figure 1, a housing 35 is mounted airtight to the side of the bottom wall 11 of the cylinder 15. A cover 36 is mounted airtight to an end opening of the housing 35. It should be noted that the airtightness is maintained by a sealing element 37 between the housing 35 and the cylinder section 7. Furthermore, the airtightness is maintained by a sealing element 38 between the housing 35 and the cover 36. An electric motor 40 is mounted close to the housing 35 via a sealing element 41, positioned next to the brake caliper body 6. It should be noted that while the motor 40 is located outside the housing 35 according to this embodiment, the housing 35 can be designed to cover the motor 40, thus accommodating the motor 40 within the housing 35. In this case, the sealing element 41 is no longer required, and assembly work can be reduced.Furthermore, the housing 35 and the cover 36 can be joined together by welding. In this case, the sealing element 38 is no longer required and assembly work can be reduced.

[0013] The brake caliper main body 6 contains the rotation-translation conversion mechanism 43 to push the piston 18 and hold it in a braking position, and a multi-stage spur gear speed reduction mechanism 44 and a planetary gear speed reduction mechanism 45 to increase the force of the rotation of the motor 40. The multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45 are housed in the casing 35.

[0014] The rotation-translation conversion mechanism 43 converts a rotational motion from the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45, namely the rotation of the motor 40, into a motion in one direction along a straight line (hereinafter referred to as a translation), applies a thrust to the piston 18, and holds the piston 18 in the braking position. The rotation-translation conversion mechanism 43 is accommodated between the bottom wall 11 of the cylinder 15 and the bottom part 19 of the piston 18 and comprises a base nut 75, a pushrod 102, and a ball-and-ramp mechanism 127.The base nut 75 is designed as a rotary transmission element onto which the rotation of the motor 40 is transmitted. It is rotatably held by the cylinder 15 and receives the transmission of the rotary motion of the motor 40 through the interposition of the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45. The pushrod 102 comprises a first male thread 103, which engages with a female thread 97 of the base nut 75 formed at one end, and a second male thread 104 formed at the other end. The pushrod 102 is designed as a shaft element to engage with the rotary transmission element in threaded engagement and is held in such a way that rotation and translation are possible.The ball-and-ramp mechanism 127 is threaded into the second male thread 104 of the pushrod 102 and applies thrust in the axial direction of the piston 18 by the rotation of the pushrod 102. In the rotation-translation conversion mechanism 43 according to this embodiment, a first threaded joining element 105 is constructed between the female thread 97 of the base nut 75 and the male thread 103 of the pushrod 102. In the rotation-translation conversion mechanism 43 according to this embodiment, a second threaded joining element 106 is constructed between a female thread 162 of a rotation-translation ramp 151 of the ball-and-ramp mechanism 127 and the second male thread 104 of the pushrod 102.

[0015] The multi-stage spur gear speed reduction mechanism 44 comprises a gear 46, a first speed reduction gear 47, and a second speed reduction gear 48. The gear 46 is cylindrical and includes an opening portion 50, which is press-fitted onto and attached to a rotating shaft 40A of the motor 40, and a gear 51 formed on an outer circumferential surface of the opening portion 50. The first speed reduction gear 47 integrally comprises a larger gear 53, which has a larger diameter and meshes with the teeth 51 of the gear 46, and a smaller gear 54, which has a smaller diameter and is designed to extend axially from the larger gear 53. The first speed reduction gear 47 is rotatably held on a shaft 55, which is held at one end by the housing 35 and at the other end by the cover 36.The second speed reduction gear 48 integrally includes a larger gear 56, which has a larger diameter and meshes with the smaller gear 54 of the first speed reduction gear 47, and a sun gear 57, which has a smaller diameter and is designed to extend axially from the larger gear 56. The sun gear 57 is designed as part of the planetary gear speed reduction mechanism 45. The second speed reduction gear 48 is rotatably mounted on a shaft 58, which is held by the cover 36.

[0016] The planetary gear speed reduction mechanism 45 comprises the sun gear 57, several (for example, three) planet gears 60, an inner gear 61, and a carrier 62. Each of the planet gears 60 includes a gear 63 that meshes with the sun gear 57 of the second speed reduction gear 48, and an opening 64 for inserting a pin 65, which is provided upright on the carrier 62. The three planet gears 60 are arranged at equal angular intervals on a circumference of the carrier 62.

[0017] The carrier 62 is shaped like a disc, and a polygonal opening 68, into which a polygonal support 81 of the base nut 75 is inserted, is formed at its radial center. The rotational torque can be transmitted between the carrier 62 and the base nut 75 by inserting the polygonal support 81, which extends continuously from a distal end of a column-shaped part 76 of the base nut 75, into the polygonal opening 68. Several pin openings 69 are formed on an outer circumferential side of the carrier 62. A pin 65 for rotatingly holding each planetary gear 60 is press-fitted to and attached to each pin opening 69.The carrier 62 and each planetary gear 60 are restricted in axial movement by a wall surface 35B projecting from one end side of a circumference of an opening portion 35A of the housing 35, and an annular wall portion 72 integrally formed on the side of the second speed reduction gear 48 of the inner gear 61. According to this embodiment, relative rotation with respect to the base nut 75 is restricted by the polygonal opening 68 formed in the carrier 62, but a mechanical element suitable for transmitting the rotational torque, such as a splined shaft or a fitting, can be used.

[0018] The inner gear 61 contains internal teeth 71 that mesh with the gears 63 of the respective gear sets 60, and the annular wall section 72, which is integrally formed with and extends through the inner teeth 71 on the side of the second speed reduction gear 48 and is designed to limit the axial movement of each planet gear 60. The inner gear 61 is press-fitted to and attached to the housing 35.

[0019] It should be noted that according to this embodiment, the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45 are provided as a speed reduction mechanism to increase the force of rotation of the motor 40 in order to obtain the rotational force to push the piston 18, but as long as this rotational force can be output, one or both speed reduction mechanisms can be omitted.

[0020] As in Fig. 2 and Fig. As illustrated in Figure 5, the base nut 75 comprises a column-shaped part 76 and a nut part 77, which is integrally formed at the other end of the column-shaped part 76. A washer 80 is arranged such that it rests against the bottom wall 11 of the cylinder 15. The column-shaped part 76 of the base nut 75 is inserted through an insertion opening 80A of the washer 80 and the opening part 10 formed by the bottom wall 11 of the cylinder 15. A distal end face of the column part 76 is the polygonal support part 88, which is formed by chamfering to a polygon. The polygonal support part 81 is inserted through the opening part 35A of the housing 35 and fitted into the polygonal opening 68 of the support 62. According to this embodiment, as shown in Figure 5, the base nut 75 is formed by the insertion of the washer 80 into the base nut 75. Fig. As illustrated in Figure 5, the polygonal support part 81 is shaped as a hexagon, and the polygonal opening 68 is formed by a hexagonal opening. It should be noted that the polygonal support part 81 can be shaped as a polygon such as a triangle, a quadrilateral, a pentagon, a heptagon, an octagon, and the like, in addition to the hexagon, or it can have a shape with two chamfered surfaces. The nut part 77 of the base nut 75 is formed in a cylindrical shape with a base. The nut part 77 is formed on a proximal end face of the column part 76 and is designed to have a circular wall part 82 with one end surface facing the base wall 11 of the cylinder 15 and a cylindrical part 83 projecting integrally from the other end surface of the circular wall part 82.An outer circumferential surface of the circular wall section 82 is located close to the inner wall surface of the opening section 9B, which has a smaller diameter cylinder 15. A circular wall section 84, also with a smaller diameter, projects from a radial central portion of an end surface of the circular wall section 82. The column section 76 projects from an end surface of the circular wall section 84, which has a smaller diameter. The outer diameter of the column section 76 is such that it is smaller than the outer diameter of the cylindrical portion 83 of the mother section 77.

[0021] A thrust bearing 87 is arranged between the base nut 75 and the washer 80. The thrust bearing 87 abuts the circular wall section 82 around the circular wall section 84 with the smaller diameter of the nut section 77 of the base nut 75. The base nut 75 is then rotatably held by the thrust bearing 87 against the side of the bottom wall 11 of the cylinder 15. A sealing element 88 and a sleeve 89 are arranged between the outer circumferential surface of the columnar section 76 of the base nut 75 and the opening section 10 of the bottom wall 11 of the cylinder 15. The sealing element 88 and the sleeve 89 are arranged to maintain the fluid tightness of the hydraulic chamber 21. An annular groove 81A is formed between the columnar section 76 of the base nut 75 and the polygonal support section 81. A snap ring 90 is installed in the annular groove 81A.The snap ring 90 restricts movement of the base nut 75 in the axial direction of the cylinder 15.

[0022] The cylindrical part 83 of the nut part 77 of the base nut 75 comprises a large-diameter cylindrical part 91 located at one end and a small-diameter cylindrical part 92 located at the other end. An inner circumferential surface 91A of the large-diameter cylindrical part 91 and an inner circumferential surface 92A of the small-diameter cylindrical part 92 are formed by an opening 83A that opens at the other end of the cylindrical part 83. One end of the large-diameter cylindrical part 91 is integrally connected to the circular wall part 82. An annular step surface 93 opposite the bottom part 19 of the piston 18 is formed between the outer circumferential surface of the large-diameter cylindrical part 91 and the outer circumferential surface of the small-diameter cylindrical part 92.The annular step surface 93 includes several recesses and projections 94 that project in the axial direction of the base nut 75 and is formed in a wave shape that is continuous along the circumferential direction. Several through-holes 95, extending in the radial direction of and passing through the large-diameter cylindrical part 91, are formed in the large-diameter cylindrical part 91. The several through-holes 95 are formed at intervals in the circumferential direction. A female thread 97 is formed on the inner circumferential surface 92A of the small-diameter cylindrical part 92 of the nut part 77. Several locking grooves 98 (for example, at four locations) are formed at intervals in the circumferential direction on the other end surface of the circumferential wall portion of the small-diameter cylindrical part 92 (see ). Fig. 4 and Fig. 5).

[0023] As in Fig. 2, Fig. 4 and Fig. As illustrated in Figure 5, a distal end part 100A of a first spring coupling 100 is joined to one of the corresponding locking grooves 98. The first spring coupling 100 comprises the distal end part 100A, which is directed radially outwards, and a coil part 100B, which is wound once, starting at the distal end part 100A. The distal end part 100A is then joined to one of the respective locking grooves 98, and the coil part 100B is wound around an outer circumference at the other end of the first male thread 103 of the pushrod 102.The first spring coupling 100 is designed to apply a rotational resistance torque against one direction of rotation when the pushrod 102 moves towards the bottom wall 11 of the cylinder 15 with respect to the base nut 75, namely a release rotation direction for releasing the parking brake, and allows rotation in one direction of rotation when the pushrod 102 moves towards the bottom part 19 of the piston 18 with respect to the base nut 75, namely an actuation rotation direction for actuating the parking brake. In other words, the first spring coupling 100 is designed as a one-way coupling to apply rotational resistance against rotation in one direction.

[0024] One end of the pushrod 102 is positioned in the opening 83A of the nut portion 77 of the base nut 75. The first male thread 103, which is to engage with the female thread 97 of the small-diameter cylindrical portion 92 of the base nut 75 to form the first threaded section 105, is formed on one end of the pushrod 102. The first threaded section 105 is designed such that the base nut 75 is not rotated by an axial load transmitted from the piston 18 to the pushrod 102 and is therefore 0 or less in reverse efficiency, i.e., designed as a threaded section with high irreversibility.

[0025] On the other side, at the opposite end of the pushrod 102, the second male thread 104 is formed, which engages with the female thread 162 formed on the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 to construct the second threaded joining element 106. The second threaded joining element 106 is designed such that the pushrod 102 is not rotated by an axial load transmitted from the piston 18 to the rotation-translation ramp 151, and is therefore 0 or less in reverse efficiency, i.e., designed as a threaded joining element that is large in irreversibility.

[0026] The pushrod 102 includes a tapered shaft 108 between the first male thread 103 and the second male thread 104. The outer diameter of the first male thread 103 is configured to be larger than the outer diameter of the second male thread 104. The outer diameter of the first male thread 103 is configured to be larger than the outer diameter of the tapered shaft 108. The other end surface of the pushrod 102 faces the circular flat surface portion 30 of the bottom portion 19 of the piston 18.

[0027] A receptacle 110 is axially movably held between the outer circumferential surface of the small-diameter cylindrical part 92 of the base nut 75 and the inner circumferential surface of the cylindrical part 20 of the piston 18. The receptacle 110 comprises an annular wall section 111 at one end opposite the annular step surface 93 of the base nut 75 and is generally formed in an approximately cylindrical shape. Several projections 112 are formed at intervals along the circumferential direction on one end surface of the annular wall section 111. A recessed surface 113 is formed on one end of the outer circumferential surface of the receptacle 110. Several circular through-openings 114 are formed in an outer circumferential wall with the recessed surface 113 of the receptacle 110.According to this embodiment, three circular through-openings 114 are formed at intervals in the circumferential direction within a region of the recessed surface 113, and three circular through-openings 114 are formed at intervals in the circumferential direction through the outer circumferential wall on the other end side than the recessed surface (see . Fig. 3 and Fig. 5) Within the area of ​​the recessed surface 113 on the outer circumferential side of the receptacle 110, several rectangular through-openings 115 are formed. According to this embodiment, three rectangular through-openings 115 are formed at intervals in the circumferential direction (see Fig. 4).

[0028] In the receptacle 110, the following components are arranged in sequence from one end side: a washer 120, a coil spring 121, a washer 122, a retaining plate 123, a second spring coupling 124, a rotating element 125, a thrust bearing 126, the ball-and-ramp mechanism 127, a thrust bearing 128, and an annular pressure plate 129. The washer 120 is positioned such that it rests against the other end surface of the annular wall section 111 of the receptacle 110.

[0029] The coil spring 121 is inserted between the washer of one end 120 and the washer of the other end 122. The coil spring 121 presses the washer of one end 120 and the washer of the other end 122 in one direction to separate them. On the other end surface of the circumferential wall portion of the receptacle 110, several (for example, three) locking grooves 132 of a predetermined depth are formed at intervals in the circumferential direction. The locking groove 132 comprises a narrow locking groove 133, which is arranged at one end of the receptacle 110, and a wide locking groove 134, which is arranged at the other end. The wide locking groove 134 is designed to have a greater depth than the narrow locking groove 133.On the other end part of the receptacle 110 opposite the base part 19 of the piston 18, several pawl parts 136 (for example, at six locations) are formed, extending radially inwards. After components such as the washer of one end 120, the coil spring 121, the washer of the other end 122, the retaining plate 123, the second spring coupling 124, the rotating element 125, the thrust bearing 126, the ball-and-ramp mechanism 127, the thrust bearing 128, and the annular pressure plate 129 are received in predetermined positions in the receptacle 110, the respective pawl parts 136 are bent towards receiving recesses 171 of the annular pressure plate 129 of the receptacle 110 in order to integrally arrange the aforementioned components in the receptacle 110. It should be noted that the washer on one end side 120 and the washer on the other end side 122 can be omitted.

[0030] The annular retaining plate 123 is arranged such that it abuts the other end surface of the washer at the other end 122. Several projecting pieces 137 (for example, at three locations) are formed at intervals along the circumferential direction on an outer circumferential surface of the retaining plate 123. Each of the projecting pieces 137 is engaged with the narrow locking groove 133 of the receptacle 110. As a result, the retaining plate 123 is held such that it is not rotatable relative to the receptacle 110, but is movable in the axial direction with respect to the receptacle 110. It should be noted that the projecting piece 137 can be enlarged in width to engage with the rotation-limiting longitudinal groove 22 formed on the inner circumferential surface of the piston 18.

[0031] In the mounting 110, the rotating element 125 is rotatably held at the other end of the retaining plate 123. The rotating element 125 comprises an annular portion 141 of large diameter with a conical opening 140 and a cylindrical portion 142 of small diameter, which projects integrally from one end surface of the annular portion 141. One end of the cylindrical portion 142 abuts the other end surface of the retaining plate 123. An annular groove 143 is formed on an outer circumferential surface of the cylindrical portion 142. The pushrod 102 is arranged in the rotating element 125. The conical opening 140 of the annular portion 141 of the rotating element 125 is coupled by the cone of the conical shaft 108 of the pushrod 102.As a consequence, the rotating element 125 and the pushrod 102 can mutually transmit a rotational torque to each other and can slide axially relative to one another. It should be noted that the cone is used to terminate the rotation, but other known mechanical mechanisms for stopping rotation, such as a fit and a D-slot, can be used. Furthermore, a fastening mechanism such as press fitting can be used instead of axial sliding.

[0032] The second spring coupling 124 is wound in the annular groove 143 formed on the small-diameter cylindrical portion 142 of the rotating element 125. Like the first spring coupling 100, the second spring coupling 124 comprises a distal end section 124A, which is directed outwards in the radial direction, and a coil section 124B, which is wound once starting at the distal end section 124A. The distal end section 124A is engaged with the narrow locking groove 133 of the receptacle 110, and the coil section 124B is wound in the annular groove 143 formed on the outer circumferential surface of the small-diameter cylindrical portion 142 of the rotating element 125.The second spring coupling 124 is designed to apply a rotational resistance torque against one direction of rotation (rotation direction during actuation) when the rotating element 125 (pushrod 102) moves towards the side of the bottom part 19 of the piston 18 with respect to the receptacle 110, and to allow rotation in one direction of rotation (the rotation direction during release) when the rotating element 125 moves towards the side of the bottom wall 11 of the cylinder 15. In other words, the second spring coupling 124 is designed as a second one-way coupling for applying rotational resistance against rotation in one direction.

[0033] The rotational resistance torque when using the second spring coupling 124 is greater than the rotational resistance torque of the first threaded joining element 105, which is defined between the first male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75. The ball-and-ramp mechanism 127 is arranged at the other end of the rotating element 125 by interposing the thrust bearing 126. The rotating element 125 is rotatably held with respect to the ball-and-ramp mechanism 127 by interposing the thrust bearing 126.

[0034] As in Fig. 2, Fig. 3 and Fig. As illustrated in Figure 5, the ball-and-ramp mechanism 127 comprises a fixed ramp 150, a rotation-translation ramp 151, and respective balls 152 inserted between the fixed ramp 150 and the rotation-translation ramp 151. The fixed ramp 150 is arranged at the other end of the rotating element 125 via the thrust bearing 126. The fixed ramp 150 comprises a fixed plate 154 in the shape of a disk and several projections 155 that extend (for example, at three locations) at intervals along the circumferential direction from an outer circumferential surface of the fixed plate 154. An insertion opening 156, through which the pushrod 102 is inserted, is formed in a radial central portion of the fixed plate 154.The corresponding projections 155 of the fixed ramp 150 are joined to the wide locking grooves 134 of the respective locking grooves 132 of the receptacle 110 and are joined to the several rotation-limiting longitudinal grooves 22 formed on the inner circumferential surface of the piston 18 in order to hold the fixed ramp 150 so as to be non-rotatable with respect to the piston 18, but axially movable with respect to the piston 18.

[0035] It should be noted that, as the structure which holds the fixed ramp 150 non-rotatable with respect to the piston 18 but axially movable with respect to it, such a structure can be provided that several flat surface parts are formed at intervals in the circumferential direction on the outer circumferential surface of the fixed ramp 150, several flat surface parts corresponding to the respective flat surface parts of the fixed ramp 150 are also formed on the inner circumferential surface of the piston 18, and these flat surface parts are brought into engagement with each other in order to limit the rotation of the fixed ramp 150 with respect to the piston 18.On the other end surface of the solid plate 154, several spherical grooves 157 (for example at three or four locations) are formed, each extending in an arc shape at a predetermined angle of inclination along the circumferential direction and having a cross-section in an arc shape in the radial direction.

[0036] The rotation-translation ramp 151 comprises an annular rotation-translation plate 160 and a cylindrical portion 161 that projects integrally from the radially central portion of the other end surface of the rotation-translation plate 160. The female thread 162, to which the second male thread 104 of the pushrod 102 is engaged, is formed on an inner circumferential surface extending from the rotation-translation plate 160 to the cylindrical portion 161. On a surface of the rotation-translation plate 160 opposite the fixed plate 154 of the fixed ramp 150, several spherical grooves 163 (for example, at three or four locations) are formed, each extending in an arc shape at a predetermined angle of inclination along the circumferential direction and having an arc-shaped cross-section in the radial direction.It should be noted that each of the spherical grooves 157 of the fixed ramp 150 and each of the spherical grooves 163 of the rotation-translation ramp 151 can be designed such that a bulge is formed in the course of the ramp along the circumferential direction, or the ramp can be changed in its course.

[0037] The balls 152 are each inserted between the ball grooves 163 of the rotation-translation ramp 151 (rotation-translation plate 160) and the ball grooves 157 of the fixed ramp 150 (fixed plate 154). In the ball-and-ramp mechanism 127, when a rotational torque is applied to the rotation-translation ramp 151, the balls 152 roll between the ball grooves 163 of the rotation-translation plate 160 and the ball grooves 157 of the fixed plate 154, thus generating a rotational difference between the rotation-translation plate 160 and the fixed plate 154, thereby variably changing the relative axial distance between the rotation-translation plate and the fixed plate 154.

[0038] Furthermore, an annular ball groove 164 is formed around the cylindrical part 161 on the other end surface of the rotary-translation plate 160. The annular pressure plate 129 is arranged on the other end side of the rotary-translation plate 160 by interposing the thrust bearing 128. An annular ball groove 166 is also formed on one end surface of the annular pressure plate 129. The thrust bearing 128, in which several balls are rotatably held in the circumferential direction, is then arranged between the annular ball groove 164 of the rotary-translation plate 160 and the annular ball groove 166 of the annular pressure plate 129. The cylindrical part 161 of the rotary-translation plate 160 is inserted through the annular pressure plate 129. Several projecting protrusions 168 are formed at intervals along the circumferential direction on the outer circumferential surface of the ring-shaped printing plate 129.The respective projections 168 are joined to the wide locking grooves 134 of the respective locking grooves 132 of the receptacle 110 and are joined to the several longitudinal grooves for rotation limitation 22 which are formed on the inner circumferential surface of the piston 18 in order to hold the annular pressure plate 129 so that it is non-rotatable with respect to the piston 18, but axially movable with respect to it.

[0039] The rotation-translation ramp 151 of the ball-and-ramp mechanism 127 is rotatably held by the annular pressure plate 129 by the insertion of the thrust bearing 128. The other end surface of the annular pressure plate 129 faces the annular curved surface portion 31 of the base portion 19 of the piston 18. A curved pressure portion 170 is formed on the other end surface of the annular pressure plate 129, curved from the radial center to an outer circumferential end portion in the direction of one end side. This annular pressure plate 129 is designed to bear against the annular curved surface portion 31 formed on the base portion 19 of the piston 18 in order to press against the piston 18.On the other end surface of the ring-shaped pressure plate 129, the receiving recesses 171 for receiving the latch parts 136, which are bent inwards from the receiving 110, are formed on outer circumferential parts between the respective projections 168.

[0040] As in Fig. 2 and Fig. As illustrated in Figure 5, a receiving ring 172 is integrally attached to the distal end of the second male thread 104 of the pushrod 102. The receiving ring 172 is arranged within the cylindrical portion 161 of the rotation-translation ramp 151 to suppress a relative rotation angle of a certain angle or less between the pushrod 102 and the rotation-translation ramp 151. A projection 173 is formed on a portion of the receiving ring 172, and the projection 173 engages a wide recess in the cylindrical portion 161. In a non-braking state, the projection 173 is pushed to one side within the recess, and in a braking state, the projection 173 is pushed to the other side. Consequently, in each of these cases, the projection 173 and the recess are in circumferential contact. It follows that the relative rotation angle between the receiving ring 172 and the pushrod 102 is limited.Therefore, in the actuated state, the receiving ring 172 is prevented from falling out of the pushrod 102 by a thrust of the rotation-translation ramp 151. It should be noted that the rotational resistance torque of the second threaded joining element 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 is set such that it is less than a rotational resistance that is the sum of the rotational resistance torque against the loosening direction of the pushrod 102 with respect to the base nut 75, caused by the first spring coupling 100, and the rotational resistance torque of the first threaded joining element 105 between the first male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75.

[0041] As in Fig. As illustrated in Figure 1, an ECU 175, designed as an electronic control device that serves as a control means for controlling the drive of the motor 40, is connected to the motor 40. A parking switch 176, which is actuated to issue instructions for applying and releasing the parking brake, is connected to the ECU 175. Furthermore, the ECU 175 can be actuated independently of the actuation of the parking switch 176 based on a signal from the vehicle side (not shown).

[0042] Next, the operation of the disc brake 1 according to this embodiment will be described. First, the process steps during the braking of the disc brake 1, which serves as a general hydraulic brake, by actuating a brake pedal (not shown) will be described.

[0043] When a driver depresses the brake pedal, hydraulic pressure, corresponding to the pedal force, is supplied from the master cylinder (not shown) through a hydraulic circuit (not shown) to the hydraulic chamber 21 within the brake caliper 4. This moves the piston 18 forward from its initial position in a non-braking state (moving counterclockwise). Fig. 1) while the piston seal 16 is elastically deformed to press the inner brake pad 2 against the disc rotor D. Then, due to a counterforce against the pressure force of the piston 18, the brake caliper body 6 moves in the clockwise direction. Fig. 1 relative to the holder 5, in order to press the outer brake pad 3, which is mounted on the clamp section 8, against the disc rotor D. As a result, the disc rotor D is clamped between the pair of inner and outer brake pads 2 and 3 in such a way that a frictional force is generated, and thus a braking force is produced for the vehicle.

[0044] When the driver releases the brake pedal, the hydraulic pressure supply from the master cylinder is interrupted, causing the hydraulic pressure within the hydraulic chamber 21 to decrease. This causes the piston 18 to return to its original position due to a restoring force generated by the elastic deformation of the piston seal 16. As a consequence, the brake force is released. Furthermore, slippage occurs between the piston 18 and the piston seal 16 if the movement of the piston 18 increases and exceeds a limit of elastic deformation of the piston seal 16, due to wear of the inner and outer brake pads 2 and 3. Even when the brake pads 2 and 3 are worn, the piston 18's original position relative to the caliper body 6 changes as a result of this slippage, and the brake pad clearances are adjusted to a constant value.

[0045] Now, with appropriate reference to Fig. 6 to Fig. 12 and on Fig. 1. A description of an operation as a parking brake to maintain the stopped state of the vehicle was given. It should be noted that Fig. 6-9 illustrate step-by-step operation when the parking brake is applied, and Fig. 10-12 illustrate step-by-step operation when the parking brake is released.

[0046] First, when the parking switch 176 is actuated in the released position to apply the parking brake, the ECU 175 drives the motor 40 to rotate the sun gear 75 of the planetary gear speed reduction mechanism 45 by engaging the multi-stage spur gear speed reduction mechanism 44. The rotation of the sun gear 57 then rotates the carrier 62 by engaging the planetary gears 60. The rotational torque, i.e., the rotation of the motor 40, is then transmitted from the carrier 62 to the base nut 75.

[0047] Due to the rotation of the base nut 75 in the direction of actuation, the first threaded joining element 105 rotates from a starting position that is in Fig. Figure 6 illustrates (a condition in which a predetermined gap exists between the annular pressure plate 129 and the bottom part 19 of the piston 18), between the female thread 97 of the base nut 75 and the first male thread 103 of the pushrod 102 relative to the female thread 97 of the base nut 75 and the first male thread 103 of the pushrod 102, as shown in Figure 6. Fig. As illustrated in Figure 7, in other words only the base nut 75 rotates in the direction of actuation and as a consequence the pushrod 102 moves forward along the axial direction towards the side of the bottom part 19 of the piston 18. On this occasion, the pushrod 102 does not rotate together with the base nut 75 because the rotational resistance torque against the actuation direction of the rotational element 125 (pushrod 102) with respect to the receptacle 110, which is caused by the second spring coupling 124, is greater than the rotational resistance torque caused by the first threaded joining part 105 between the male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75, and rotation in the actuation direction of the cylinder 15 of the pushrod 102 with respect to the base nut 105, which is caused by the first spring coupling 100, is enabled.

[0048] As a consequence, as in Fig. As illustrated in Figure 7, the receptacle 110 and the respective components in the receptacle 110, such as the washer of one end 120, the coil spring 121, the washer of the other end 122, the retaining plate 123, the second spring coupling 124, the rotating element 125, the thrust bearing 126, the ball and ramp mechanism 127, the thrust bearing 128 and the annular pressure plate 129, move integrally forward in the axial direction to the side of the bottom part 19 of the piston 18, together with the pushrod 102, and the curved pressure part 170 of the annular pressure plate 129 rests against the annular curved surface part 31 of the bottom part 19 of the piston 18. As a consequence of this action, the piston 18 moves forward and one end surface of the bottom part 19 of the piston 18 rests against the inner brake pad 2.

[0049] Furthermore, when the rotary drive of the motor 40 is applied in the direction of actuation, the movement of the pushrod 102 causes the piston 18 to begin pressing the disc rotor D by interposing the brake pads 2 and 3. When the generation of this pressing force begins, an axial force corresponding to a counterforce against the pressing force increases the rotational resistance torque in the first threaded joint 105 between the first male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75, resulting in an increase in the rotational torque required to move the pushrod 102 forward. The rotational resistance torque of the first threaded joint 105, which is the required rotational torque, then exceeds the rotational resistance torque of the second spring coupling 124.As a consequence, the pushrod 102 begins to rotate in the actuation direction together with the rotating element 125 when the base nut 75 rotates, as shown in . Fig. Figure 8 illustrates this. In other words, the pushrod 102 rotates together with the base nut 75. The rotational resistance torque in the second threaded insert 106, located between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127, is then also increased by the counterforce against the compressive force applied to the disc rotor D. This increases the rotational torque in the actuation direction of the pushrod 102, which is then transferred to the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 by the insertion of the second threaded insert 106.

[0050] Then, as the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 rotates in the direction of actuation, the rotation-translation ramp 151 and the fixed ramp 150 move away from each other against the compressive force of the helical spring 121 through the balls of the respective balls 152. As a consequence, the curved pressure part 170 of the annular pressure plate 129 further presses the annular curved surface part 31 of the base part 19 of the piston 18, and the compressive forces of the inner and outer brake pads 2 and 3 against the disc rotor D increase. At this point, a force, which is the sum of the thrust force generated in the second threaded joining part 106 and the thrust force generated in the ball-and-ramp mechanism 127, is applied to the base part 19 of the piston 18.

[0051] It should be noted that in this embodiment, at the beginning of the actuation of the first threaded joining element 105, the first threaded joining element 105 rotates relatively between the male thread of the pushrod 102 and the female thread 97 of the base nut 75, causing the pushrod 102 to move forward in order to move the piston 18 forward and generate the pressure force on the disc rotor D. Therefore, even if the position of the piston 18 relative to the cylinder 11 changes due to normal wear of the pair of inner and outer brake pads 2 and 3, the original position of the pushrod 102 relative to the piston 18 can be restored.

[0052] On this occasion, the pitch (the pitch of the rotation-translation ramp 151 when the rotation-translation ramp 151 rotates once) when the ball-and-ramp mechanism 127 and the second thread joining part 106 are operating is determined by the following equation. L=LSCREW×LB&R / (LSCREW+LB&R)

[0053] It should be noted that LSCREW is a pitch of the second threaded joining element 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151. Furthermore, LB&R is a pitch of the respective ball grooves 163 of the rotation-translation ramp 151 and the corresponding ball grooves 157 of the fixed ramp 150. Consequently, a gain ratio (thrust force to rotational torque) can be set to a suitable value, depending on the vehicle on which the disc brake 1 is installed, based on the corresponding values ​​of the pitches.

[0054] The ECO 175 then drives the motor 40 until the pressure force applied to the disc rotor D by the pair of inner and outer brake pads 2 and 3 reaches a predetermined value, for example, until the current of the motor 40 reaches a predetermined value. Afterward, when it is detected that the current of the motor 40 has reached the predetermined value and that the pressure force applied to the disc rotor D has reached the predetermined value, the ECO 175 stops the current flowing to the motor 40. Then, the rotation in the actuation direction of the pushrod 102 and the rotation of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 cease.

[0055] As in Fig. As illustrated in Figure 9, the counterforce then acts against the pressure force from the disc rotor D on the rotation-translation ramp 151. The second threaded joining element 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 is designed as the threaded joining element that does not act in reverse between the pushrod 102 and the rotation-translation ramp 151 as described above. Furthermore, the first threaded joining element 105 between the first male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75 is also designed as the threaded joining element that does not act in reverse between the pushrod 102 and the base nut 75 as described above. Furthermore, the rotational resistance torque against the loosening direction with reference to the base nut 75 is applied to the pushrod by the first spring coupling 100.This prevents the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 from rotating and keeps it in the stopped position, thus holding the piston 18 in the braking position. As a result, the braking force is maintained and the parking brake is deactivated. In this state, the reaction force against the pressure force from the disc rotor D is transmitted to the bottom wall 11 of the cylinder 15 via the ball-and-ramp mechanism 127, the pushrod 102, the base nut 75, and the thrust bearing 87, thereby acting as the holding force for the piston 18. According to this embodiment, only the thrust force generated by the ball-and-ramp mechanism 127 acts on the thrust bearing 126, for which only a relatively small diameter thrust bearing is required, thus increasing the durability of the disc brake 1.As described above, in the disc brake 1 the piston 18 is moved by the linear movement of the pushrod 102 during application, and then the piston 18 is moved by the ball and ramp mechanism 127.

[0056] Then, when the parking brake is to be released, the ECU 175, based on the brake release operation of the parking switch 176, drives and rotates the motor 40 in the release direction to retract the piston 18, in other words, to remove the piston 18 from the disc rotor D. As a consequence, the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45 execute the rotary drive in the release direction to retract the piston 18, and the rotary drive is transmitted to the base nut 75 by means of the carrier 62.

[0057] On this occasion, the counterforce acts against the pressure force from the disc rotor D on the pushrod 102. Therefore, the rotational resistance torque of the second threaded joining element 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127, the rotational resistance torque of the first threaded joining element 105 between the first male thread 103 of the pushrod 102 and the female thread 97 of the base nut 75, and the rotational resistance torque against the loosening direction of the pushrod 102 with respect to the base nut 75, which is caused by the first spring coupling 100, are applied. Therefore, the rotational torque, as in Fig. As illustrated in Figure 10, the force is transferred in the loosening direction from the base nut 75 to the pushrod 102 (including the rotating element 125) and is also transferred to the rotation-translation ramp 151 of the ball-and-ramp mechanism 127. As a consequence, the rotation-translation ramp 151 rotates only in the loosening direction to return to its original position in the direction of rotation. During this process, the rotation-translation ramp 151 does not move in the axial direction, and its position in the axial direction remains unchanged.

[0058] On this occasion, when the rotation-translation ramp 151 returns to its original position in the direction of rotation, the helical spring 121 pushes the fixed ramp 154 ​​together with the washer of the other end 122, the retaining plate 123, the rotating element 125, and the thrust bearing 126. Therefore, the rotating element 125, the thrust bearing 126, and the fixed ramp 154 ​​move forward with respect to the receptacle 10, while the corresponding balls 152 roll between the corresponding ball grooves 157 and 163. As a consequence, the pushrod 102 and the rotating element 125 move through the cone in the axial direction.It should be noted that if the rotating element 125 is attached to the pushrod 102 by press fit or the like, the fixed ramp 154 ​​does not move in the axial direction, the balls 152 separate axially from the ball grooves 157 and 163, but do not fall out of them, and subsequent actuation is the same. Furthermore, a configuration can be provided such that the rotational resistance torque of the second threaded joining element 106 is less than the rotational resistance torque of the thrust bearing 128, and in this case, the rotation-translation ramp 151 returns axially simultaneously with the start of rotation.

[0059] Then, when the rotation-translation ramp 151 returns to its initial position in the direction of rotation, the respective balls 152 are squeezed between the respective ball grooves 163 of the rotation-translation ramp 151 and the respective ball grooves 157 of the fixed plate 154. Therefore, the rotation-translation ramp 151 can no longer rotate with respect to the fixed plate 154, and the rotation-translation ramp 151 ceases its rotation. As a consequence, as shown in Fig. As illustrated in Figure 11, only the second threaded joining part 106 rotates first, and thus the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 moves axially together with the receptacle 110 in the direction of the side of the bottom wall 11 (in the release direction) of the cylinder 15 and returns to the original position in the axial direction.

[0060] Furthermore, when the motor 40 is driven to rotate in the loosening direction and the rotation of the base nut 75 in the loosening direction stops, the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 returns to its original position in both the rotational and axial directions. Simultaneously, the threaded engagement position of the second threaded insert 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127 returns to its original position, and therefore the rotation of the pushrod 102 in the loosening direction stops. If the rotation of the base nut 75 continues in the loosening direction, as described in Fig. As illustrated in Figure 12, the pushrod 102 moves backwards along the axial direction towards the side of the bottom wall 11 (in the release direction) of the cylinder 15 against the rotational resistance torque against the release direction of the pushrod 102 with respect to the base nut 75, which is caused by the first spring coupling 100. As a consequence, together with the pushrod 102, the receptacle 110 and the respective components in the receptacle 110, such as the washer of one end 120, the coil spring 121, the washer of the other end 122, the retaining plate 123, the second spring coupling 124, the rotating element 125, the thrust bearing 126, the ball and ramp mechanism 127, the thrust bearing 128 and the annular pressure plate 129, move integrally back along the axial direction towards the side of the bottom wall 11 (in the release direction) of the cylinder 15.The ECU 175 then provides control such that the motor 40 is stopped when a gap between the annular pressure plate 129 of the rotation-translation ramp 151 and the annular curved surface portion 31 of the base portion 19 of the piston 18 reaches an initial position including a predetermined gap. Finally, the piston 18 moves back to its initial position by a restoring force generated by the elastic deformation of the piston seal 16, and the braking force is completely released. As described above, in this disc brake 1, upon release, the ball-and-ramp mechanism 127 is returned to its initial position, then the ball-and-ramp mechanism 127 is moved back, and then the pushrod 102 is moved back to release the holding force on the piston 19.

[0061] As described above, in the disc brake 1 according to this embodiment, when the piston 18 is pressed so that it is held in the braking position, as in the parking brake, and the compressive forces from the pair of inner and outer brake pads 2 and 3 are applied to the disc rotor D, the first threaded joining element 105 between the first male thread 103 of the pushrod 102 and the female thread of the base nut 75 and the second threaded joining element 106 between the second male thread 104 of the pushrod 102 and the female thread 162 of the rotation-translation ramp 151 of the ball-and-ramp mechanism 127, which are of low mechanical efficiency, and the ball-and-ramp mechanism 127, which is of high mechanical efficiency, can be combined to maintain the compressive forces on the disc rotor D while ensuring a suitable operating efficiency of the rotation-translation conversion mechanism 43.As a result, compared to a ratchet mechanism used in state-of-the-art disc brakes, this design can be simplified, thereby increasing the manufacturing efficiency of this disc brake 1.

[0062] Furthermore, in this embodiment of the disc brake 1, not only the compressive force from the first threaded joining part 105 and the second threaded joining part 106, but also the compressive force from the ball-and-ramp mechanism 127 acts on the piston 18. Therefore, even if the size of the motor 40 is reduced, a desired braking force can be applied. Moreover, reducing the size (torque) of the motor 14 prevents the rotational torques applied by the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45 from becoming too small. This reduces operating noise and increases service life.

[0063] Furthermore, in the case of the disc brake 1 according to this embodiment, the response speed until a gap is ensured when the parking brake is applied can be improved by setting the pitch of the first threaded joining part 105 larger than the pitch L that is generated when the ball-and-ramp mechanism 127 and the second threaded joining part 106 are operating.

[0064] In the disc brake 1 according to this embodiment, when releasing, the ball-and-ramp mechanism 127 is returned to its original position, then the ball-and-ramp mechanism 127 is moved backward, and then the pushrod 102 is moved backward to release the holding force for the piston 19. Therefore, even if the release operation is switched to the actuation operation during the release process by an actuation request, the actuation operation can be started immediately.

[0065] It should be noted that in the disc brake 1 according to this embodiment, the multi-stage spur gear speed reduction mechanism 44 and the planetary gear speed reduction mechanism 45 are used as the speed reduction mechanism, but generally known speed reduction mechanisms such as the cycloidal speed reduction machine and the tension wave gear can be used. Furthermore, the balls 152 are used as rolling elements for the ball-and-ramp mechanism 127, but a ball-and-ramp mechanism using cylindrical elements, which are excellent in their load-bearing capacity, can also be used.

[0066] Furthermore, according to this embodiment, a description of the actuation of the rotation-translation conversion mechanism 43 is given, while the parking brake, which is an example of an effect of maintaining a stopped state of the vehicle, is illustrated by way of example, but for cases other than the case of the parking brake, such as the hill start assist and the hill descent assist for assisting the vehicle to start on an incline and to stop automatically when the accelerator pedal is switched off and the vehicle is stopped, the rotation-translation conversion mechanism 43, which is the parking brake mechanism, can be actuated.

[0067] A description of a second embodiment of the present invention will now be given.

[0068] Some prior art disc brakes include a piston holding mechanism as the parking brake braking mechanism for actuation, for example, when the parking brake is applied (see JP 2014-92165 A). However, according to JP 2014-92165 A, a coil portion of a one-way coupling for applying a rotational resistance torque against rotation in one direction of an adjusting nut is wound in an annular groove portion formed on an outer circumferential surface of the adjusting nut, and a space for forming the annular groove portion on the outer circumferential surface of the adjusting nut thus requires fixing, which is not preferred with regard to reducing the size of the structure.

[0069] Therefore, the second embodiment provides a disc brake that is compact in its structure.

[0070] In other words, the disc brake according to this embodiment comprises a pair of pads arranged on both sides of a rotor in an axial direction of the rotor, a piston for pressing one of the pair of pads against the rotor, a caliper body with a cylinder for movably receiving the piston, a motor installed on the caliper body, and a rotation-translation conversion mechanism installed on the caliper body, designed to push the piston so as to hold the piston in a braking position.The rotation-translation conversion mechanism comprises a rotational transmission element, to which the rotation of the motor is transferred; a shaft element, which is threaded to the rotational transmission element so that linear movement of the shaft element is possible through the rotation of the rotational transmission element; and a one-way clutch to apply a rotational resistance torque against rotation of the shaft element in one direction. The one-way clutch comprises a coil section, and the coil section is wound on a threaded groove of a male thread formed on a threaded joining part of the shaft element with respect to the rotational transmission element.

[0071] With reference to Fig. 13 to Fig. Section 19 now provides a detailed description of the second embodiment. It should be noted that in Fig. 13 to Fig. 19 the same components as those of the first embodiment are designated by reference numerals which result from adding 200 to the reference numerals of the first embodiment.

[0072] As in Fig. As illustrated in Figure 13, a disc brake 201 according to this embodiment comprises a pair of an inner brake pad 202 and an outer brake pad 203, arranged on both sides in an axial direction of a disc rotor D' mounted on a rotating unit of the vehicle, and also includes a brake caliper 204. This disc brake 201 is a disc brake with a floating caliper. It should be noted that the pair of inner brake pads 202 and outer brake pads 203 and the brake caliper 204 are held by a bracket 205, which is attached to a stationary unit such as a steering knuckle of the vehicle, in order to be movable in the axial direction of the disc rotor D'. It should be noted that for the following description, it is assumed that the right side of Fig. 13 is an end page and a left side of Fig. 13 is the other side.

[0073] As in Fig. 13 and Fig. Figure 16 illustrates a brake caliper main body 206, which is a main body of the brake caliper 204, a cylinder section 207 arranged at a proximal end opposite the inner brake pad 202 on the inside of the vehicle, and a clamp section 208 arranged at a distal end opposite the outer brake pad 203 on the outside of the vehicle. The cylinder section 207 comprises a cylinder 215 with a large-diameter opening portion 209A opening on the side of the inner brake pad 202, and a bottom closed by a bottom wall 211 having an opening portion 210 on one of the opposite sides. A small-diameter opening portion 209B is formed on the side of the bottom wall 211 of the cylinder 215, extending through the large-diameter opening portion 209A.A piston seal 216 is arranged on an inner circumferential surface of the large diameter opening part 209A of the cylinder 215.

[0074] A piston 218 is formed in a cup-shaped housing with a base 219 and a cylindrical section 220. The piston 218 is received in the cylinder 215 such that the base 219 faces the inner brake pad 202. The piston 218 is integrally installed in the large-diameter opening 209A of the cylinder 215, allowing axial movement when the piston 218 is in contact with the piston seal 216. A hydraulic chamber 221 is defined by the fact that it is sealed by the piston seal 216 between the piston 218 and the bottom wall 211 of the cylinder 215. Hydraulic pressure is supplied to this hydraulic chamber 221 from a hydraulic pressure source (not shown), such as a master cylinder or a hydraulic control unit, through a port (not shown) formed in the cylinder section 207.

[0075] Multiple rotation restriction longitudinal grooves 222 (see Fig. 16) are formed along the circumferential direction of the inner circumferential surface of the piston 218. A recess 225 is formed on the bottom part 219 of the piston 218 on the outer circumferential side at the end surface opposite the inner brake pad 202. A projection 226, formed on a rear surface of the inner brake pad 202, engages with this recess 225. This engagement prevents the piston 218 from rotating relative to the cylinder 215 and consequently the caliper body 206. In addition, a dust boot 227 is inserted between the outer circumferential surface of the side of the bottom part 219 of the piston 218 and the inner circumferential surface of the large-diameter opening part 209A of the cylinder 215 to prevent the ingress of foreign substances into the cylinder 215.

[0076] As in Fig. 13 to Fig. As illustrated in Figure 15, a housing 230 is mounted on the side of the bottom wall 211 of the cylinder 215 of the brake caliper main body 206 to accommodate an engine / transmission assembly 229. An opening 230A is formed at one end of the housing 230. A cover 236 for airtight sealing is mounted on the opening 230A. In other words, the opening 230A of the housing 230 is closed by the cover 236. A sealing element 237 is arranged between the housing 230 and the cylinder section 207. Airtightness is maintained within the housing 230 by this sealing element 237.The housing 230 comprises a first housing part 231 for receiving a multi-stage spur gear speed reduction mechanism 244 and a planetary gear speed reduction mechanism 245, which will be described later, to cover an outer circumference of the bottom wall 211 of the cylinder 215, and a second housing part 232, which projects integrally from the first housing part 231 in a bottomed cylindrical form to receive a motor 400. In this way, the housing 230 is designed to utilize the second housing part 232 in the bottomed cylindrical form to receive the motor 400, which is arranged parallel to the brake caliper main body 206.The first housing part 231 comprises an outer wall part 231F and a bottom surface part 231G to accommodate, together with the cover 236, a receiving chamber 231E for receiving the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245, which will be described later; a mounting opening part 231A, which receives part of the bottom wall 211 of the cylinder 215 and through which a polygonal shaft part 281 of a base nut 275 of a rotation-translation conversion mechanism 243, which will be described later, is inserted; an inner annular wall part 231B, which projects around the mounting opening part 231A; an outer annular wall part 231C, which projects on a radial outside at a distance from the inner annular wall part 231B; and several engagement grooves. 231D, which are formed at intervals in the circumferential direction of the outer annular wall part 231C.

[0077] As in Fig. As illustrated in Figure 13, the brake caliper main body 206 comprises the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245 to increase the driving force through the motor 400, and the rotary-translation conversion mechanism 243 to push the piston 218 and hold the piston 218 in the braking position. The multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245 are accommodated in the receiving chamber 231E in the first housing part 231 of the housing 230.

[0078] As in Fig. 13 to Fig. As illustrated in Figure 15, the multi-stage spur gear speed reduction mechanism 244 comprises a gear 246, a first speed reduction gear 247, a non-speed reduction spur gear 248, and a second speed reduction gear 249. The first speed reduction gear 247, the non-speed reduction spur gear 248, and the second speed reduction gear 249 are made of a metal or plastic, such as a fiber-reinforced plastic.

[0079] The gear 246 is formed in a cylindrical shape and comprises an opening section 250, which is press-fitted onto and attached to a rotating shaft 401 of the motor 400, and a gear 251 formed on an outer circumference of the opening section 250. The first speed reduction gear 247 integrally comprises a larger gear 253, which has a larger diameter and meshes with the gear 251 of the gear 246, and a smaller gear 254, which has a smaller diameter and is configured to extend axially from the larger gear 253. The first speed reduction gear 247 is held by a shaft 252 to be rotatable with respect to a retaining plate 259 and a holder 405, which will be described later. The shaft 252 is held at one end by the retaining plate 259 near the cover 36 and is held at the other end by the holder 405.

[0080] The smaller gear 254 of the first speed reduction gear 247 meshes with the non-speed reduction gear 248. The non-speed reduction spur gear 248 is held by a shaft 255 (see Fig. 14) to be rotatable with respect to the retaining plate 259 and the holder 405. The shaft 255 is held at one end by the retaining plate 259 near the cover 236 and is held at the other end by the holder 405. The second speed reduction gear 249 integrally comprises a larger gear 256, which is larger in diameter and meshes with the non-speed reduction spur gear 248, and a sun gear 257, which is smaller in diameter and is configured to extend axially from the larger gear 256. The sun gear 257 is designed as part of the planetary gear speed reduction mechanism 245, which is described later. An opening 249A is formed in the center of the second speed reduction gear 249, and a shaft 258 is inserted through the opening 249A.One end of the shaft 258 is press-fitted to and attached to the retaining plate 259, which is located near the cover 236. The second speed reduction gear 249 is rotatably held by the shaft 258. Furthermore, an annular stop element 256A, projecting towards the side of the planetary gear speed reduction mechanism 245, is formed on an annular wall portion of the larger gear 256 of the second speed reduction gear 249.

[0081] The planetary gear speed reduction mechanism 245 comprises the sun gear 257 of the second speed reduction gear 249, several (four in this embodiment) planet gears 260, an internal gear 261, and a carrier 262. Each of the planet gears 260 comprises a gear 263 that meshes with the sun gear 257 of the second speed reduction gear 249, and an opening 264 for rotatably inserting a pin 265, which is provided upright by the carrier 262. The respective planet gears 260 are arranged at equal angular intervals around a circumference of the carrier 262. An annular plate 266 is arranged on the opposite end face of each planet gear 260.

[0082] The carrier 262 is shaped like a disc, and a polygonal opening 268 is formed approximately at its radial center. The outer diameter of the carrier 262 is approximately the same as the outer diameter of a rotational trajectory of the corresponding planetary gears 260. Several pin opening sections 269 are formed at intervals around the circumference of the carrier 262. The pin 265 is press-fitted to and attached to each pin opening section 269. The pin 265 is rotatably inserted through the opening section 264 of each planetary gear 260. The polygonal opening 268 of the carrier 262 and the polygonal shaft section 281 of the base nut 275 of the rotation-translation conversion mechanism 243, which will be described later, are then joined together to allow the transmission of torque between the carrier 262 and the base nut 275.

[0083] The internal gear 261 comprises internal teeth 271 that mesh with the gears 263 of the respective planet gears 260, an annular wall section 272 that extends continuously from one end at the side of the cover 236 of the internal teeth 271 in the radial direction to restrict the axial movement of the respective planet gears 260, and a cylindrical wall section 273 that extends from the internal teeth 271 toward the bottom wall 211 of the cylinder 215. The internal gear 261 is attached to the housing 230 by inserting the cylindrical wall section 273 through an annular space between the inner annular wall section 231B and the outer annular wall section 231C of the first housing part 231. The annular plate 266 is arranged within the internal gear 261. The ring-shaped plate 266 is squeezed between the end surfaces of the inner teeth 271 of the internal gear 261 and the inner ring-shaped wall part 231B of the first housing part 231.As a consequence, the respective planet gears 260 are arranged between the annular wall part 272 of the internal gear 261 and the annular plate 266, and axial movement of this is restricted.

[0084] Furthermore, several projections 247, arranged at intervals in the circumferential direction, project from the opposite end face of the outer circumferential surface of the internal gear 261. Each of the projections 274 projects outwards and engages with each engagement groove 231D formed on the first housing part 231. The internal gear 261 is held non-rotatably in the first housing part 231 by the respective projections 274 being inserted into the respective engagement grooves 231D of the first housing part 231 and thus brought into engagement. Furthermore, the annular stop part 256A, which is formed on the larger gear 256 of the second speed reduction gear 249, is arranged on the side of the cover 236 of the annular wall part 272 of the internal gear 261 and therefore the internal gear 261 is held in the first housing part 231 in order to be immovable also in the axial direction.

[0085] The motor 400 is held by the holder 405, which is arranged on a flange part 402 thereof. The holder 405 is constructed by integrally connecting a motor holding part 406 and an annular holding part 407. The motor holding part 406 is arranged between the flange part 402 of the motor 400 and each of the first speed reduction gear 247 and the non-speed reduction gear 248 and is configured to hold the motor 400. The annular holding part 407 is arranged around the internal gear 261 of the planetary gear speed reduction mechanism 245 to surround the internal gear 261. A rotary shaft insertion opening 408, through which the gear 246, which is press-fitted and attached to the rotary shaft 401 of the motor 400, is inserted, is formed in the motor holding part 406.Connection through-holes, into which corresponding motor terminals 403 of the motor 400 are inserted, are formed at two locations around the rotary shaft insertion opening 408. A pair of connection insertion openings are formed on both sides in the radial direction of the rotary shaft insertion opening 408. Cable harnesses 450 and 451 are each connected to the motor terminals 403 of the motor 400.

[0086] On the motor mounting part 406 of the bracket 405, a first projection 411, a second projection 412, and a third projection 413 are formed at intervals around the rotary shaft insertion opening 408 on one side opposite the side of the planetary gear speed reduction mechanism 245. These first projection 411, second projection 412, and third projection 413 are column-shaped and project towards the side of the cover 236. Mounting holes 416 are formed at two locations on the motor mounting part 406. Corresponding mounting bolts 415 are fastened to the mounting holes 416 of the motor mounting part 406 through corresponding through-holes 402A in the flange part 402 of the motor 400. As a consequence of this fastening, the motor 400 is held by the motor mounting part 406 of the holder 405.The ring-shaped retaining part 407 is arranged above the respective projections 274, so that it rests against the outer circumferential surface of the internal gear 261 of the planetary gear speed reduction mechanism 245.

[0087] Cylindrical retaining elements 417 are integrally formed at two locations on the holder 405 between the motor retaining element 406 and the annular retaining element 407. The retaining plate 259 is arranged on the corresponding cylindrical retaining elements 417, and each fastening bolt 418 is attached to each cylindrical retaining element 417 of the holder 405 by inserting the retaining plate 259 between them. As a result, the retaining plate 259 is held at a distance above the holder 405.

[0088] Furthermore, as in Fig. 13 to Fig. As illustrated in Figure 15, a cover-side first cylindrical part 421, a cover-side second projection 422, and a cover-side third projection 423 each project at intervals on an inner surface of the cover 236. These cover-side first cylindrical part 421, cover-side second projection 422, and cover-side third projection 423 are each located opposite the holder-side first projection 411, the holder-side second projection 412, and the holder-side third projection 413, which are formed on the holder 405. Then, between the cover-side first cylindrical part 421, the cover-side second projection 422 and the cover-side third projection 423 on the cover 236 and the holder-side first projection 411, the holder-side second projection 412 and the holder-side third projection 413 on the holder 405, a rubber element 430, which is an elastic element, is inserted.

[0089] The rubber element 430 comprises a first cup part 431, a second cup part 432, a third cup part 433 and a base part 434 in a plate form, which integrally connects the opening-side ends of the first cup part 431, the second cup part 432 and the third cup part 433.

[0090] Then the first cup part 431 of the rubber element 430 is attached to the holder-side first projection 411 of the holder 405, the second cup part 432 of the rubber element 430 is attached to the holder-side second projection 412 of the holder 405, and the third cup part 433 of the rubber element 430 is attached to the holder-side third projection 413 of the holder to join the rubber element 430 with the holder 405. Then the cover 236 is placed over it, so that the cover-side first cylindrical part 421 of the cover 236 is joined to the first cup part 431 of the rubber element 430, the cover-side second projection 422 of the cover 236 rests against the second cup part 432 of the rubber element 430, and the cover-side third projection 423 of the cover 236 rests against the third cup part 433 of the rubber element 430.The cable harnesses 450 and 451, which extend from the corresponding motor terminals 403 of the motor 400, are arranged along a top surface of the base part 434 of the rubber element 430.

[0091] Furthermore, as in Fig. As illustrated in Figure 14, according to this embodiment, several types of rubber elements 481, 482, and 483 are provided in the housing 230 independently of the aforementioned rubber element 430. A retaining part 480 in a horizontal U-shape in cross-section is formed at one end on the side of the motor retaining part 406 of the holder 405, and the rubber element 481 in a horizontal U-shape in cross-section is integrally arranged within the retaining part 480. The rubber elements 482 in a block shape are each arranged between the outer circumferential surface of the annular retaining part 407 of the holder 405 at locations near the respective cylindrical retaining parts 417 and the inner wall surface of the first housing part 231. The cylindrical rubber element 483 is arranged between the end of the motor 400 on the main body side and the bottom wall part of the second housing part 232.

[0092] In this way, the motor / gearbox assembly 229 is constructed by assembling the motor 400, the multi-stage spur gear speed reduction mechanism 244, the planetary gear speed reduction mechanism 245, and the rubber elements 430, 481, 482, and 483 on the holder 405 and the mounting plate 259. The motor / gearbox assembly 229 is mounted on the housing 230 and the cover 236 in a suspended state, i.e., floating, by interposing the rubber elements 430, 481, 482, and 483. In other words, the motor / gearbox assembly 229 is attached to the housing 230 and the cover 236 by inserting the rubber elements 430, 481, 482 and 483 without the holder 405 bearing against the housing 230 and the cover 236.As described above, by attaching the motor / gear assembly 229 to the housing 230 and the cover 236 by inserting the rubber elements 430, 481, 482 and 483, the transmission of vibrations originating from the motor 400, the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245 to the housing 230 or the cover 236 is prevented, and the generation of noise caused by the vibrations can be suppressed.

[0093] It should be noted that, according to this embodiment, in order to obtain the rotational force for pushing the piston 225, the multi-stage spur gear speed reduction mechanism 224 and the planetary gear speed reduction mechanism 245 are used as the speed reduction mechanism for increasing the driving force of the motor 400, but the speed reduction mechanism can be constructed solely by the planetary gear speed reduction mechanism 245. Furthermore, other speed reduction machines of the prior art, such as the cycloidal speed reduction mechanism and the stress wave gear, can be combined with the planetary gear speed reduction mechanism 245.

[0094] With reference to Fig. 13 and Fig. 16 to Fig. Section 19 now gives a specific description of the rotation-translation-conversion mechanism 243. It should be noted that the following description is based on the assumption that the right side of Fig. 13 and Fig. 16 is an end page and a left side of Fig. 13 and Fig. 16 is the other end page.

[0095] The rotation-translation conversion mechanism 243 is designed to convert the rotational motion from the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245, namely the rotation of the motor 400, into a motion in a straight linear direction (hereinafter referred to as linear motion for ease of understanding), to apply a thrust to the piston 218 and to hold the piston 218 in the braking position.The rotation-translation conversion mechanism 243 comprises the base nut 275, which serves as the rotation transmission element onto which the rotational motion from the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245 is transmitted and which is rotatably held; a pushrod 302, which is the shaft element which is threaded into a female thread 297 of the base nut 275 and is held in such a way that rotation and translation are possible by the rotation of the base nut 275; and a ball-and-ramp mechanism 327, which is threaded into the pushrod 302 and applies a thrust in the axial direction to the piston 218 by rotating the pushrod 302. The rotation-translation conversion mechanism 243 is located between the cylinder 215 of the brake caliper main body 206 and the piston 218.

[0096] As in Fig. 4 and Fig. As illustrated in Figure 5, the base nut 275 comprises a column-shaped part 276 and a nut part 277, which are integrally formed at the other end of the column-shaped part 276. A washer 280 is arranged to abut the bottom wall 211 of the cylinder 215. The column-shaped part 276 of the base nut 275 is inserted through an insertion opening 280A of the washer 280 and the opening part 210 formed by the bottom wall 211 of the cylinder 215. The polygonal shaft part 281 is integrally connected to a distal end face of this column-shaped part 276. The polygonal shaft part 281 is inserted through the mounting opening part 231A of the first housing part 231 and is joined to the polygonal opening 268 of the support 262. The nut part 277 of the base nut 275 is designed in a cylindrical shape with a base.The mother part 277 comprises a circular wall section 282 and a cylindrical section 283, which projects integrally from the other end surface of the circular wall section 282. The outer circumferential surface of the circular wall section 282 is close to the inner wall surface of the small-diameter opening section 209B of the cylinder 215. A smaller-diameter circular wall section 284 projects from a radial central portion of an end surface of the circular wall section 282. The columnar section 276 projects from an end surface of the smaller-diameter circular wall section 284 toward one end face. The outer diameter of the columnar section 276 is such that it is smaller than the outer diameter of the cylindrical section 283 of the mother part 277.

[0097] A thrust bearing 287 is arranged between the circular wall section 282, which is formed around the smaller-diameter circular wall section 284 on the nut section 277 of the base nut 275, and the washer 280. The base nut 275 is then rotatably held against the bottom wall 211 of the cylinder 215 by the thrust bearing 287. A sealing element 288 and a sleeve 289 are each arranged between the outer circumferential surface of the columnar section 276 of the base nut 275 and the opening section 210 of the bottom wall 211 of the cylinder 215. As a result, the fluid tightness of the hydraulic chamber 221 is maintained. A snap ring 290 is installed in an annular groove formed between the columnar section 276 of the base nut 275 and the polygonal shaft section 281. The axial movement of the base nut 275 is limited by the snap ring 290.

[0098] The cylindrical part 283 of the nut part 277 of the base nut 275 comprises a cylindrical part with a larger diameter 291, located at one end, and a cylindrical part with a smaller diameter 292, located at the other end. One end of the cylindrical part with the larger diameter 291 is integrally connected to the circular wall part 282. Several through-holes 295, extending in the radial direction, are formed in the circumferential wall part of the cylindrical part with the larger diameter 291. The multiple through-holes 295 are spaced at intervals in the circumferential direction. The female thread 297 is formed on the inner circumferential surface of the cylindrical part with the smaller diameter 292 of the nut part 277.Several locking grooves 298 are formed at intervals in the circumferential direction on the opposite end surface of the circumferential wall portion of the cylindrical part with the smaller diameter 292. According to this embodiment, the locking grooves 298 are formed at four locations.

[0099] A distal end section 300A of a first spring coupling 300, which serves as a one-way coupling for applying rotational resistance to rotation in one direction, is joined to one of the respective locking grooves 298 of the smaller-diameter cylindrical part 292 of the base nut 275. The first spring coupling 300 comprises the distal end section 300A, which is directed radially outward, and a coil section 300B, which is wound once continuously by the distal end section 300A. The distal end section 300A of the first spring coupling 300 is then joined to one of the respective locking grooves 298 of the smaller-diameter cylindrical part 292 of the base nut 275. Also with reference to Fig. 18 and Fig. 19 The coil part 300B of the first spring coupling 300 is wound in a threaded groove 303A at the other end of a male thread 303 of the pushrod 302, which will be detailed later. This first spring coupling 300 is designed to provide rotational resistance against one direction of rotation (a direction of rotation when disengaging) when the pushrod 302 moves towards the side of the bottom wall 211 of the cylinder 215 with respect to the base nut 275, and to allow rotation in one direction of rotation (direction of rotation when actuating) when the pushrod 302 moves towards the side of the bottom part 219 of the piston 218 with respect to the base nut 275.

[0100] One end of the pushrod 302 is inserted into the nut 277 of the base nut 275. The male thread 303, which engages with the female thread 297 of the smaller-diameter cylindrical part 292 of the base nut 275, is formed on one end of the pushrod 302. A first threaded joining element 305 between the male thread 303 of this pushrod 302 and the female thread 297 of the smaller-diameter cylindrical part 292 of the base nut 275 is designed such that the base nut 275 is not rotated by an axial load transmitted from the piston 218 to the pushrod 302, and therefore has zero or less reverse efficiency, i.e., is designed as a threaded joining element with high irreversibility. Furthermore, as shown from Fig. 16 can be identified by the thread groove 303A (see Fig. 18 and Fig. 19) of the male thread 303 wound on the other end side of the first thread joining part 305 of the pushrod 302 in relation to the base nut 275 of the coil part 300A of the first spring coupling 300.

[0101] On the other side, at the opposite end of the pushrod 302, a male thread 304 is formed, which engages with a female thread 362 formed on a rotation-translation ramp 351 of the ball-and-ramp mechanism 327, which will be described later. Again, a second threaded joining element 306 is designed between the male thread 304 of the pushrod 302 and the female thread 362 formed on the rotation-translation ramp 351 such that the pushrod 302 is not rotated by an axial load transmitted from the piston 218 to the rotation-translation ramp 351 and therefore has a reverse efficiency of 0 or less than a threaded joining element designed with high irreversibility.

[0102] The pushrod 302 comprises a tapered shaft 308 between the male thread 303 at one end and the male thread 304 at the other end. The outer diameter of the male thread 303 at one end is larger than the outer diameter of the male thread 304 at the other end. The outer diameter of the male thread 303 at one end is also larger than the outer diameter of the tapered shaft 308. A column-shaped portion 307 with a smaller diameter extends continuously from the male thread 304 of the pushrod 302 at the other end. An outer circumferential surface of the column-shaped portion 307 is knurled. A stop element 372 is integrally press-fitted to the column-shaped portion 307 of the pushrod 302.A relative rotation range with respect to the pushrod 302 of the rotation-translation ramp 351 is defined by the stop element 372. The other end surface of the column-shaped part 307 of the pushrod 302 is opposite the bottom part 219 of the piston 218.

[0103] A receptacle 310 is held between the outer circumferential surface of the smaller-diameter cylindrical part 292, which forms the nut part 277 of the base nut 275, and the inner circumferential surface of the cylindrical part 220 of the piston 218, such that it is axially movable. The receptacle 310 comprises an annular wall section 311 at one end and is generally approximately cylindrical. Several through-openings 314 and 315 are formed in the outer circumferential wall of the receptacle 310.

[0104] In the receptacle 310, the following are arranged in sequence from one end side: a washer 320, a coil spring 321, a washer 322, a retaining plate 323, a second spring coupling 324, a rotating element 325, a thrust bearing 326, the ball-and-ramp mechanism 327, a thrust bearing 328, and an annular pressure plate 329. The washer 320 is positioned such that it rests against the other end surface of the annular wall section 311 of the receptacle 310.

[0105] A coil spring 321 is inserted between the washer of one end 320 and the washer of the other end 322. The coil spring 321 presses the washer of one end 320 and the washer of the other end 322 in the direction necessary to separate them. Several locking grooves 332 of a predetermined depth are formed at intervals in the circumferential direction on the other end surface of the circumferential wall portion of the receptacle 310. Each of the locking grooves 332 comprises a narrow locking groove 333 located at one end and a wide locking groove 334 located at the other end. According to this embodiment, the locking grooves 332 are formed at three locations.At the other end of the receptacle 310, several clamping elements 336 are formed, which are directed towards the bottom part 219 of the piston 218. After the washer of one end 320, the coil spring 321, the washer of the other end 322, the retaining plate 323, the second spring coupling 324, the rotary element 325, the thrust bearing 326, the ball-and-ramp mechanism 327, the thrust bearing 328 and the annular pressure plate 329 are received in the receptacle 310, the respective clamping elements 336 of the receptacle 310 are bent towards receiving recesses 371 of the annular pressure plate 329, as will be described later, in order to integrally arrange and assemble the large number of the aforementioned components in the receptacle 310.

[0106] The annular retaining plate 323 is arranged such that it abuts the other end surface of the washer of the other end 322. Several projecting pieces 337 are formed at intervals along the circumferential direction on an outer circumferential surface of the retaining plate 323. According to this embodiment, the projecting pieces 337 are formed at three locations. Each of the projecting pieces 337 of the retaining plate 323 is joined to each narrow locking groove 333 of the receptacle 310 and each rotation-limiting longitudinal groove 222 formed on the inner circumferential surface of the piston 218. As a result, the receptacle 310, as well as the washer of one end 320, the coil spring 321, the washer of the other end 322, and the retaining plate 323 are held such that they are not rotatable relative to the piston 218, but are axially movable relative to the piston 218.

[0107] In the receptacle 310, the rotating element 325 is rotatably held at the other end of the retaining plate 323. The rotating element 325 comprises an annular part 341 with a larger diameter and a wedge opening 340, and a cylindrical part 342 with a smaller diameter, which project integrally from one end surface of the annular part 341. One end of the cylindrical part 342 rests against the other end surface of the retaining plate 323. The pushrod 302 is inserted into the rotating element 325 such that the conical opening 340 of the annular part 341 of the rotating element 325 is coupled to the conical shaft 308 of the pushrod 302 via the cone. As a result, the rotating element 325 and the pushrod 302 transmit a rotational torque to each other.

[0108] The second spring coupling 324, for applying rotational resistance to rotation in one direction, is wound on the outer circumferential surface of the smaller-diameter cylindrical part 342 of the rotating element 325. Like the first spring coupling 300, the second spring coupling 324 comprises a distal end part 324A, which is directed radially outward, and a coil part 324B, which is wound once continuously from the distal end part 324A. The distal end part 324A of the second spring coupling 324 is then joined to one of the narrow locking grooves 333 of the receptacle 310, and the coil part 324B is wound on the outer circumferential surface of the smaller-diameter cylindrical part 342 of the rotating element 325.The second spring coupling 324 is designed to apply a rotational resistance torque against a direction of rotation (the direction of rotation when actuating) when the rotating element 325 (pushrod 302) moves towards the side of the bottom part 219 of the piston 218 with respect to the receptacle 310, and to allow rotation in a direction of rotation (the direction of rotation when releasing) when the rotating element 325 moves towards the side of the bottom wall 211 of the cylinder 215.

[0109] It should be noted that the rotational resistance torque when actuating the second spring coupling 324 is set to be greater than the rotational resistance torque of the first threaded joining part 305 between the male thread 303 of the pushrod 302 and the female thread 297 of the base nut 275.

[0110] The ball-and-ramp mechanism 327 is arranged at the other end of the rotating element 325 by interposing the thrust bearing 326. The rotating element 325 is rotatably held with respect to the ball-and-ramp mechanism 327 by interposing the thrust bearing 326.

[0111] The ball-and-ramp mechanism 327 comprises a fixed ramp 350, a rotation-translation ramp 351, and corresponding balls 352, which are inserted between the fixed ramp 350 and the rotation-translation ramp 351. The fixed ramp 350 is arranged at the other end of the rotating element 325 by interposing the thrust bearing 326. The fixed ramp 350 comprises a fixed plate 354 in a disk shape and several projections 355, which project at intervals along the circumferential direction from an outer circumferential surface of the fixed plate 354. In this embodiment, the projections 355 are formed at three locations. An insertion opening 356, through which the pushrod 302 is inserted, is formed at a radial center of the fixed plate 354.The corresponding projections 355 of the fixed ramp 350 are attached to the corresponding wide locking grooves 334 of the receptacle 310 and joined to the corresponding rotation-limiting longitudinal grooves 222 formed on the inner circumferential surface of the piston 218, in order to hold the fixed ramp 350 so that it is not rotatable relative to the piston 218 but is axially movable relative to the piston 218. On the other end surface of the fixed plate 354, several (in this embodiment three) spherical grooves 357 are formed, each extending in an arc shape at a predetermined inclined angle along the circumferential direction and having an arc-shaped cross-section in the radial direction.

[0112] The rotation-translation ramp 351 comprises an annular rotation-translation plate 360 ​​and a cylindrical part 361, which projects integrally from a radial central portion of the other end surface of the rotation-translation plate 360. The female thread 362, to which the male thread 304 of the pushrod 302 is threaded, is formed on an inner circumferential surface extending from the rotation-translation plate 360 ​​to the cylindrical part 361. On a surface of the rotation-translation plate 360 ​​that faces the fixed plate 154 of the fixed ramp 350, several (in this embodiment three) spherical grooves 363 are formed, each extending in an arc shape at a predetermined inclined angle along the circumferential direction and having an arc-shaped cross-section in the radial direction.It should be noted that each of the spherical grooves 357 of the fixed ramp 350 and each of the spherical grooves 363 of the rotation-translation ramp 351 can be designed such that an exploitation is formed in the course of the ramp along the circumferential direction or the ramp can be changed in its course.

[0113] As in Fig. As illustrated in Figure 17, the spheres 352 are inserted between the sphere grooves 363 of the rotation-translation ramp 351 (rotation-translation plate 360) and the sphere grooves 357 of the fixed ramp 350 (fixed plate 154). When a rotational torque is applied to the rotation-translation ramp 351, the spheres 352 roll between the sphere grooves 363 of the rotation-translation plate 360 ​​and the sphere grooves 357 of the fixed plate 354, thereby generating a rotational difference between the rotation-translation plate 360 ​​and the fixed plate 354, thus allowing the relative axial distance between the rotation-translation plate 360 ​​and the fixed plate 154 to vary.

[0114] The annular pressure plate 329 is arranged around the cylindrical part 161 of the rotary-translation plate 360 ​​at its opposite end by the insertion of the thrust bearing 328. Several projections 368 protrude at intervals along the circumferential direction on the outer circumferential surface of the annular pressure plate 329. According to this embodiment, the projections 368 are formed at three locations. The respective projections 368 are connected to the corresponding wide locking grooves 334 of the receptacle 310 and are connected to corresponding rotation-limiting longitudinal grooves 222 formed on the inner circumferential surface of the piston 218, thereby supporting the annular pressure plate 329 so that it is not rotatable relative to the piston 218, but axially movable relative to the piston 218.

[0115] The rotation-translation ramp 351 of the ball-and-ramp mechanism 327 is rotatably held by the annular pressure plate 329 by the insertion of the thrust bearing 328. The other end surface of the annular pressure plate 329 rests against the bottom part 219 of the piston 218 to depress the piston 218. On the other end surface of the annular pressure plate 329, the receiving recesses 371 for receiving the clamping parts 336, which are bent inwards from the receiving 310, are formed on outer circumferential parts between the corresponding projections 368.

[0116] Furthermore, as in Fig. As illustrated in Figure 13, an ECU 375, which is constructed from an electronic control device for controlling the drive of the motor 400, is electrically connected to the motor 400. A parking switch 376, which is used to issue instructions for applying and releasing the parking brake, is connected to the ECU 375. Furthermore, the ECU 375 can be operated independently of the parking switch 376 based on a signal from the vehicle side (not shown).

[0117] Next, the operation of the disc brake 201 according to this embodiment will be described.

[0118] First, the actions during braking of the disc brake 201, which serves as a general hydraulic brake by actuating a brake pedal (not shown), will be described.

[0119] When a driver depresses the brake pedal, hydraulic pressure, corresponding to the pedal force, is supplied from the master cylinder (not shown) to the hydraulic chamber 221 within the brake caliper 204 via a hydraulic circuit (not shown). This moves the piston 218 forward from its initial position in a non-braking state (moving in the left direction). Fig. 13), while the piston seal 216 is elastically deformed to press the inner brake pad 202 against the disc rotor D'. Then, due to a restoring force against the pressure force of the piston 218, the brake caliper main body 206 moves in the right direction. Fig.13 relative to the bracket 205, in order to press the outer brake pad 203, which is mounted on the clamp section 208, against the disc rotor D'. As a result, the disc rotor D' is clamped between the pair of inner and outer brake pads 202 and 203, generating a frictional force and thus producing a braking force for the vehicle.

[0120] When the driver releases the brake pedal, the hydraulic pressure supply from the master cylinder is interrupted, causing the hydraulic pressure within the hydraulic chamber 221 to decrease. This causes the piston 218 to return to its initial position due to a restoring force generated by the elastic deformation of the piston seal 216. As a result, the brake force is released. Furthermore, if the movement of the piston 218 increases due to wear of the inner and outer brake pads 202 and 203, and exceeds the limit of elastic deformation of the piston seal 216, slippage occurs between the piston 218 and the piston seal 216. The piston 218 moves to a new position relative to the caliper body 206 as a consequence of this slippage, thereby adjusting the disc clearances to remain constant.

[0121] Now, a description of an operation as a parking brake is given, which is an example of an effect (function) for maintaining the stopped state of the vehicle.

[0122] First, when the parking switch 376 is actuated in the released position to engage (apply) the parking brake, the ECU 375 drives the motor 400 to rotate the sun gear 257 of the planetary gear speed reduction mechanism 245 by interposing the multi-stage spur gear speed reduction mechanism 244. The rotation of the sun gear 257 causes the carrier 262 to rotate by interposing the planetary gears 260. The rotational torque is then transmitted from the carrier 262 to the base nut 275.

[0123] The rotational resistance torque against the actuation direction of the rotating element 325 (pushrod 302) with respect to the receptacle 310 (piston 218), effected by the second spring coupling 324, is then set to be greater than the rotational resistance torque through the first threaded joining element 305 between the pushrod 302 and the base nut 275. As a result, rotation in the actuation direction of the pushrod 302 with respect to the base nut 275, effected by the first spring coupling 300, is enabled. Consequently, while the first threaded joining element 305 is rotated relative to the base nut 275, in other words, only the base nut 275 is rotated in the actuation direction by the rotation of the base nut 275 in the actuation direction, the pushrod moves forward axially towards the side of the bottom part 219 of the piston 218.

[0124] As a consequence, the receptacle 310 and the respective components within the receptacle 310, such as the washer of one end 320, the coil spring 321, the washer of the other end 322, the retaining plate 323, the second spring coupling 324, the rotating element 325, the thrust bearing 326, the ball-and-ramp mechanism 327, the thrust bearing 328, and the annular pressure plate 329, move integrally forward in the axial direction toward the side of the bottom part 219 of the piston 218, together with the pushrod 302. With the forward movement of these components, the annular pressure plate 329 abuts the bottom part 219 of the piston 218. As a result of this abutment, the piston 218 moves forward, and one end surface of the bottom part 219 of the piston 218 abuts the inner brake pad 202.

[0125] Furthermore, as the rotary drive of the motor 400 continues in the actuation direction, the movement of the pushrod 302 causes the piston 218 to begin pressing against the disc rotor D' by interposing the brake pads 202 and 203. When the generation of this pressing force begins, an axial force corresponding to a counterforce against the pressing force subsequently increases the rotational resistance torque in the first threaded joining element 305 between the pushrod 302 and the base nut 275, which becomes greater than the rotational resistance torque of the second spring coupling 224. As a consequence, when the base nut 275 rotates, the pushrod 302 begins to rotate in the actuation direction together with the rotating element 325.Then the rotational resistance torque in the second threaded joining part 306 between the pushrod 302 and the ball-and-ramp mechanism 327 is also increased by the counterforce against the pressure force applied by the disc rotor D', and therefore the rotational torque in the actuation direction of the pushrod 302 is transferred to the rotation-translation ramp 351 of the ball-and-ramp mechanism 327 by interleaving the second threaded joining part 306.

[0126] At this point, the rotational torque in the actuation direction of the pushrod 302 is transmitted to the rotation-translation ramp 351 of the ball-and-ramp mechanism 327, while a relative rotational differential is caused in the second threaded joining part 306 (the rotation-translation ramp 351 rotates slightly after the rotation of the pushrod 302). Then, as the rotation-translation ramp 351 of the ball-and-ramp mechanism 327 rotates in the actuation direction, the corresponding balls 352 roll to separate the rotation-translation ramp 351 and the fixed ramp 350 from each other against the tension force of the helical spring 321. As a consequence, the annular pressure plate 329 further pushes the bottom part 219 of the piston 218. This increases the pressure forces of the inner and outer brake pads 202 and 203 against the disc rotor D'.

[0127] It should be noted that in the disc brake 201 according to this embodiment, the first threaded joining element 305 rotates relative to the pushrod 302 and the base nut 275, and then the pushrod 302 moves forward, causing the piston 218 to move forward, resulting in the pressure force of the disc rotor D'. Consequently, the original position of the pushrod 302 relative to the piston 218, which changes due to normal wear of the inner and outer brake pads 202 and 203, can be adjusted by actuating the first threaded joining element 305.

[0128] The ECU 375 then drives the motor 400 until the pressure force applied by the pair of inner and outer brake pads 202 and 203 to the disc rotor D' reaches a predetermined value, for example, until the motor's current reaches a predetermined value. Afterward, when it is detected that the pressure force applied to the disc rotor D' has reached the predetermined value, based on the detection that the motor 400's current has reached the predetermined value, the ECU 375 stops energizing the motor 400. Then, the linear motion caused by the rotation of the rotation-translation ramp 351 of the ball-and-ramp mechanism 327 is stopped.

[0129] Finally, the reaction force acts against the pressure force from the disc rotor D' on the rotation-translation ramp 351, but the second threaded joining element 306 between the pushrod 302 and the ball-and-ramp mechanism 327 is designed as the threaded joining element that does not operate in reverse, and the first threaded joining element 305 between the pushrod 302 and the base nut 275 is also designed as the threaded joining element that does not operate in reverse. Furthermore, the rotational resistance torque against the loosening direction with respect to the base nut 275 is applied to the pushrod 302 by the first spring clutch 300. This configuration holds the piston 218 in the brake position. Thus, the braking force is maintained and the actuation of the parking brake is completed.

[0130] Next, a case where the parking brake is released is described. When the parking brake is to be released, based on the release actuation of the parking switch 376, the ECU 375 drives and rotates the motor 400 in the release direction to separate the piston 218 from the disc rotor D'. As a consequence, the multi-stage spur gear speed reduction mechanism 244 and the planetary gear speed reduction mechanism 245 perform the rotary drive in the release direction of returning the piston 218, and the rotary drive is transmitted to the base nut 275 by interposing the carrier 262.

[0131] On this occasion, the counterforce acts against the pressure force from the disc rotor D' on the pushrod 302. In other words, the rotational resistance torque of the second threaded joining element 306 between the pushrod 302 and the ball-and-ramp mechanism 327, the rotational resistance torque of the first threaded joining element 305 between the pushrod 302 and the base nut 275, and the rotational resistance torque against the loosening direction of the pushrod 302 with respect to the base nut 275, which is effected by the first spring coupling 300, are applied to the pushrod 302. Therefore, the rotational torque in the loosening direction is transferred from the base nut 275 to the pushrod 302 (including the rotational element 325) and is also transferred to the rotation-translation ramp 351 of the ball-and-ramp mechanism 327.As a consequence, only the rotation-translation ramp 351 rotates in the solution direction to return to the original position in the rotation direction.

[0132] Then the counterforce applied to the pushrod 302 decreases, and the rotational resistance torque of the second threaded joining element 306 between the pushrod 302 and the ball-and-ramp mechanism 327 becomes smaller than the rotational resistance, which is the sum of the rotational resistance torque against the release direction of the pushrod 302 with respect to the base nut 275, caused by the first spring coupling 300, and the rotational resistance torque of the first threaded joining element 305 between the pushrod 302 and the base nut 275. Therefore, the rotation-translation ramp 351 can no longer rotate in the release direction.Thus, only the second threaded joining part 306 rotates relatively, and the rotation-translation ramp 351 of the ball-and-ramp mechanism 327 moves together with the receptacle 310 along the axial direction towards the side of the bottom wall 211 (in the release direction) of the cylinder 215, and returns to the original position in the axial direction.

[0133] Furthermore, when the motor 400 is driven to rotate in the loosening direction, and the rotation of the base nut 275 in the loosening direction stops, the rotation-translation ramp 351 of the ball-and-ramp mechanism 327 returns to its original position in the axial direction, and the second threaded joining element 306 between the pushrod 302 and the ball-and-ramp mechanism 327 returns to its original position in threaded engagement. This terminates the rotation of the pushrod 302 in the loosening direction.

[0134] As the rotation of the base nut 275 continues in the loosening direction, the pushrod 302 moves backwards along the axial direction towards the side of the bottom wall 211 (in the loosening direction) of the cylinder 215 against the rotational resistance torque against the loosening direction of the pushrod 302 with respect to the base nut 275, which is caused by the first spring coupling 300. As a consequence, the receptacle 310 and the corresponding components in the receptacle 310, such as the washer of one end 320, the coil spring 321, the washer of the other end 322, the retaining plate 323, the second spring coupling 324, the rotating element 125, the thrust bearing 328 and the annular pressure plate 329, move integrally along the axial direction towards the side of the bottom wall 211 (in the release direction) of the cylinder 215, together with the pushrod 302.Then, the piston 218 moves back to its original position due to a restoring force through the elastic deformation of the piston seal 216, and the braking force is completely released.

[0135] It should be noted that in a block exchange mode, the pushrod 302 moves further back than in the normal state and assumes a fully released position. In this state, the ECU 375 detects motor current when the end of the pushrod 302 makes contact with the base nut 275 (adjuster) and then stops the motor. Even after the motor current has been interrupted, the motor continues to rotate due to inertia, and the end of the pushrod 302 continues to engage the base nut 275. As a result, the motor must be rotated with high torque upon the next actuation, and consequently, other components may be damaged.

[0136] Then, the surface roughness at the thread stroke position (in the vicinity of a thread start near the tapered shaft 308), which is only used in block replacement mode, is increased. The generated torque is increased by the sliding of the first spring clutch 300 to this part with the increased surface roughness. Furthermore, the motor current increases as a consequence, and therefore, such control can be implemented that the current is interrupted when it increases (before the end of the pushrod 302 engages the base nut 275). This ensures sufficient clearance for block replacement in the fully disengaged state. It should be noted that the magnitude of the generated torque can be adjusted by changing the level of surface roughness.

[0137] As described above, in the disc brake 201 according to this embodiment, the coil part 300B of the first spring coupling 300 is wound onto the threaded groove 303A of the male thread 303 of the pushrod 302. Therefore, a space for winding the coil part 300B does not need to be provided on the pushrod 302, resulting in a compact structure. Furthermore, when the rotational resistance torque is applied to the pushrod 302 during release, the coil part 300B of the first spring coupling 300 comes into contact with both walls of the threaded groove 303A. This increases the contact area and allows the rotational resistance torque to be increased. Consequently, even if the number of windings of the first spring coupling 300 is reduced, the required resistance torque will be maintained.

[0138] Furthermore, the first spring coupling 300 moves along the thread groove 303A, and the positional relationship between the distal end part 300A of the first spring coupling 300 and the locking groove 298 of the base nut remains unchanged. Therefore, the locking groove 298 can be set short, resulting in a space saving.

[0139] Furthermore, the first spring coupling 300 moves along the threaded groove 303A and the sliding part is therefore not concentrated in a single position and can be distributed, which leads to an increase in the durability of the sliding part.

[0140] Furthermore, if the first spring coupling 300 is mounted to the male thread 303, the first spring coupling 300 can be inserted by rotation along the thread groove 303A, which limits the expansion dimension and the deformation dimension of the first spring coupling 300.

[0141] Furthermore, the sliding position is not concentrated on a single location, and thus the generated torque can be adjusted depending on the stroke position by changing the surface roughness and the shape depending on the sliding position of the thread groove 303A.

[0142] Although only some exemplary embodiments of this invention have been described in detail above, the person skilled in the art will already recognize that many modifications to these exemplary embodiments are possible without materially departing from the new teaching and advantages of this invention. Consequently, it is intended that all such modifications are included within the scope of protection of the invention.

Claims

[1] Disc brake (1), comprising: a pair of blocks (2,3) arranged on both sides of a rotor (D) in an axial direction of the rotor (D); a piston (18) designed to push one of the pair of blocks (2,3) against the rotor (D); a brake caliper body (6) with a cylinder (15) in which the piston (18) is movably arranged; an electric motor (40) which is installed on the brake caliper main body (6); and a rotation-translation conversion mechanism (43) installed on the brake caliper main body (6) designed to push the piston (18) so as to hold the piston (18) in a braking position, wherein: the rotation-translation-conversion mechanism (43) exhibits: a rotational transmission element (75) to which a rotation of the electric motor (40) is transmitted; a shaft element (102) which is threaded and joined to the rotation transmission element (75) so that rotation and translation of the shaft element (102) are possible; and a ball-and-ramp mechanism (127) which is threaded and joined to the shaft element (102) which is designed to apply a thrust in the axial direction to the piston (18) by the rotation of the shaft element (102); wherein the shaft element has a first thread (103) which is threaded into the rotation transmission element (75) formed on one end side of the shaft element (102), and a second thread (104) which is threaded into the ball-and-ramp mechanism (127) formed on another end side of the shaft element (102); and a rotational friction torque of the first thread (103) is greater than a rotational friction torque of the second thread (104). [2] Disc brake (1) according to claim 1, wherein a diameter of the first thread (103) is larger than a diameter of the second thread (104). [3] Disc brake (1) according to claim 1, wherein: the rotation-translation conversion mechanism (43) comprises a first one-way coupling (100) configured to apply a rotational resistance torque against rotation in one direction; and the first one-way coupling (100) applies the rotational resistance torque against a rotation of the shaft element (102) with respect to the rotational transmission element (75) in a release direction in which the piston (18) is moved backwards. [4] Disc brake (1) according to claim 1, wherein: the rotation-translation conversion mechanism (43) has a second one-way coupling (124) configured to apply a rotational resistance torque against rotation in one direction; and the second one-way coupling (124) applies the rotational resistance torque against a rotation of the shaft element (102) with respect to the piston (18) in an actuation direction in which the piston (18) is pushed. [5] Disc brake (1) according to claim 3, wherein, when the piston (18) is moved backwards in the release direction, a rotational resistance torque in a threaded joining part (105, 106) between the shaft element (102) and the ball and ramp mechanism (127) is less than a rotational resistance torque obtained by adding a rotational resistance torque in a threaded joining part (105, 106) between the shaft element (102) and the rotational transmission element (75) to the rotational resistance torque exerted by the first one-way coupling (100). [6] Disc brake (1) according to claim 3, wherein, when the piston (18) is moved backwards in the release direction, a rotational resistance torque in a threaded joining part (105, 106) between the shaft element (102) and the ball and ramp mechanism (127) is less than a rotational resistance torque obtained by adding a rotational resistance torque in a threaded joining part (105, 106) between the shaft element (102) and the rotational transmission element (75) to the rotational resistance torque exerted by the first one-way coupling (100). [7] Disc brake (1) according to claim 1, further comprising a one-way coupling (100) configured to apply a rotational resistance torque against a rotation of the shaft element (102) in one direction, wherein the one-way coupling (100) comprises a coil part (100B) and the coil part (300B) is wound around a thread groove (303A) of a male thread (303) formed in a thread joining part (105, 106) of the shaft element (102) with respect to the rotation transmission element (75). [8] Disc brake (1) according to claim 7, wherein: the one-way coupling (100) has a distal end part (100A) that extends outwards in a radial direction of the shaft element (102); and the distal end part (100A) is joined to a locking groove (98) which is formed on the rotation transmission element (75). [9] Disc brake (1) according to claim 7, wherein the one-way clutch (100) applies a rotational resistance torque against rotation of the rotational transmission element (75) when disengaging and allows the rotation of the rotational transmission element (75) when in use.

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