Patent Publication Number: US-11396918-B2

Title: Disc brake

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2019-074930, which was filed on Apr. 10, 2019, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND 
     The following disclosure relates to a disc brake mounted on a wheel of a vehicle. 
     Patent Document 1 (Japanese Patent Application Publication No. 2017-020644) discloses a floating-type disc brake including: an inner pad and an outer pad respectively located on opposite sides of a rotor rotatable with a wheel; a pressing device configured to press the inner pad and the outer pad against the rotor; and a housing mounted on a non-rotating member and holding the pressing device. The pressing device includes: a first pressing member held by the housing and movable toward the rotor; a second pressing member held by the housing and movable away from the rotor; and a caliper held on the housing so as to be movable in a direction parallel with a rotation axis of the rotor and configured to move in response to movement of the second pressing member to press the outer pad against the rotor. Torque acting on the outer pad is received by the caliper. 
     SUMMARY 
     Accordingly, an aspect of the disclosure relates to improvement of a disc brake including a first pressing member and a second pressing member, for example, reduction in movement and rubbing of a driving member that is moved by movement of the second pressing member to press an outer pad against a rotor. 
     In the present disc brake, torque acting on the outer pad is received by a housing. This configuration reduces movement and rubbing of a driving member due to the reception of the torque acting on the outer pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of the embodiments, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a disc brake according to a first embodiment; 
         FIG. 2  is a cross-sectional view of the disc brake, taken along line II-II in  FIG. 5 ; 
         FIG. 3  is a plan view of the disc brake; 
         FIG. 4  is a cross-sectional view of the disc brake, taken along line IV-IV in  FIG. 5 ; 
         FIG. 5  is a front elevational view of the disc brake; 
         FIG. 6  is a view of the disc brake, illustrating components around an inner pad; 
         FIG. 7  is a view of the disc brake, illustrating components around an outer pad; 
         FIG. 8  is a side view of a frame of the disc brake; 
         FIG. 9  is a side view of a housing of the disc brake; 
         FIG. 10  is a side view of a mounting bracket of a conventional disc brake; 
         FIG. 11  is a view of the disc brake, illustrating components around another inner pad; 
         FIG. 12  is a view of the disc brake, illustrating components around another outer pad in an operating state of the disc brake; 
         FIG. 13  is a view of springs mounted on the frame of the disc brake; 
         FIG. 14  is a plan view of a disc brake according to a second embodiment; 
         FIG. 15  is a cross-sectional view of the disc brake, taken along a direction orthogonal to an axial direction; 
         FIG. 16  is a front elevational view of the disc brake; 
         FIG. 17  is a cross-sectional view of the disc brake, taken along a direction parallel with the axial direction; and 
         FIG. 18  is a view of the disc brake, illustrating components around an outer pad. 
     
    
    
     EMBODIMENTS 
     Hereinafter, there will be described embodiments by reference to the drawings. 
     First Embodiment 
     A disc brake according to the present embodiment is a floating disc brake which is provided on a wheel of a vehicle and operable by a hydraulic pressure. As illustrated in  FIGS. 1-5 , the disc brake includes: a rotor  3  that is rotated together with the wheel; an inner pad  4  and an outer pad  6  located on opposite sides of the rotor  3 ; a pressing device  8 ; and a housing  10  holding the pressing device  8 . The pressing device  8  includes a wheel cylinder  14  and a frame  16  as one example of a driving member. As illustrated in  FIG. 2 , the rotation axis L of the rotor  3  and the central axis C of the pressing device  8  are parallel with each other. In the following description, each of the direction parallel with the rotation axis L of the rotor  3  and the direction parallel with the central axis C of the pressing device  8  may be referred to simply as “axial direction”. A side on which the outer pad  6  is located in the axial direction is an outer side in the vehicle, and a side on which the inner pad  4  is located in the axial direction is an inner side in the vehicle. The outer side in the vehicle and the inner side in the vehicle may be hereinafter referred to simply as “outer side” and “inner side”, respectively. 
     As illustrated in  FIGS. 6 and 7 , the inner pad  4  includes a back board  4   r  and a pad portion  4   p  as one example of a frictionally engageable portion which is held on the back board  4   r , and the outer pad  6  includes the back board  6   r  and a pad portion  6   p  as another example of the frictionally engageable portion which is held on a back board  6   r . The respective pad portions  4   p ,  6   p  of the inner pad  4  and the outer pad  6  face the rotor  3 . Protrusions  4   a ,  4   b  are provided on an outer circumferential portion of the back board  4   r  at positions spaced apart from each other in the circumferential direction. Each of the protrusions  4   a ,  4   b  extends in the outer circumferential direction. Likewise, protrusions  6   a ,  6   b  are provided on an outer circumferential portion of the back board  6   r  at positions spaced apart from each other in the circumferential direction. Each of the protrusions  6   a ,  6   b  extends in the outer circumferential direction. Through holes  4   h   1 ,  4   h   2 ,  6   h   1 ,  6   h   2  extend through the respective protrusions  4   a ,  4   b ,  6   a ,  6   b  in the axial direction. Each of the through holes  4   h   1 ,  4   h   2 ,  6   h   1 ,  6   h   2  is shaped so as to be elongated in the circumferential direction. 
     As illustrated in  FIG. 1 , the housing  10  includes: a first housing portion  18  located on an inner side of the rotor  3  in the vehicle; and a second housing portion  19  extending from the first housing portion  18  toward the outside of the vehicle over the rotor  3 . The first housing portion  18  extends substantially in the axial direction. As illustrated in  FIGS. 2 and 4 , a cylinder bore  24  is formed in the first housing portion  18  so as to extend through the first housing portion  18  in the axial direction. A first piston  30  as one example of a first pressing member and a second piston  32  as one example of a second pressing member are fluid-tightly and slidably fitted in the cylinder bore  24  via piston seals. A portion of the cylinder bore  24  between the first piston  30  and the second piston  32  serves as a hydraulic-pressure chamber  36 . The first piston  30  and the second piston  32  are movable relative to each other in the axial direction. 
     In the present embodiment, a portion of the first housing portion  18  in which the cylinder bore  24  is formed serves as a cylinder body. Also, the wheel cylinder  14  is constituted by components including the cylinder body, the first piston  30 , and the second piston  32 . 
     As illustrated in  FIGS. 1 and 5 , a pair of mount portions  42 ,  44  are provided on opposite sides, in the circumferential direction, of a rotor-side end portion of the first housing portion  18  in the axial direction. The housing  10  is secured at each of the mount portions  42 ,  44  to a corresponding one of suspension members (which may be also referred to as “vehicle-body-side component”) such as a knuckle as one example of a non-rotating member. 
     As illustrated in  FIGS. 1 and 3 , the second housing portion  19  includes: a bridge portion  46  having a substantially three-sided rectangular shape in plan view; and pad pins  47 ,  48 , as one example of two support rods, each held at its opposite end portions respectively by the bridge portion  46  and the first housing portion  18 . The bridge portion  46  includes: a pair of rods  50 ,  51  spaced apart from each other in the circumferential direction and each extending in the axial direction; and a coupler  52  coupling the rods  50 ,  51  to each other and extending substantially in the circumferential direction. The coupler  52  has two through holes  53 ,  54  spaced apart from each other in the circumferential direction. Through holes, not illustrated, are respectively formed in portions of the first housing portion  18  which correspond to the respective through holes  53 ,  54 . The pair of pad pins  47 ,  48  are supported by the through holes  53 ,  54  formed in the bridge portion  46  and the through holes formed in the first housing portion  18  in a state in which each of the pad pins  47 ,  48  extends in the axial direction. The pad pin  47  extends through a corresponding one of the through holes formed in the first housing portion  18 , the through hole  4   h   1  formed in the back board  4   r  of the inner pad  4 , the through hole  6   h   1  formed in the back board  6   r  of the outer pad  6 , and the through hole  53  of the coupler  52  in this order. The pad pin  48  extends through a corresponding one of the through holes formed in the first housing portion  18 , the through hole  4   h   2  formed in the back board  4   r  of the inner pad  4 , the through hole  6   h   2  formed in the back board  6   r  of the outer pad  6 , and the through hole  54  of the coupler  52  in this order. Thus, the inner pad  4  and the outer pad  6  are held by the pad pins  47 ,  48  so as to be movable in the axial direction. Each of the inner pad  4  and the outer pad  6  is movable in the circumferential direction relative to the pad pins  47 ,  48  and the through holes  4   h   1 ,  4   h   2 ,  6   h   1 ,  6   h   2  within a region determined by a space between the pad pin  47  and each of the through holes  4   h   1 ,  6   h   1  and a space between the pad pin  48  and each of the through holes  4   h   2 ,  6   h   2 . 
     Two pairs of engageable recessed portions engageable with the frame  16  are provided on the first housing portion  18  so as to be spaced apart from each other in the axial direction.  FIG. 6  illustrates only one of the two pairs of engageable recessed portions and omits illustration of the other. As illustrated in  FIG. 6 , the two pairs of engageable recessed portions include: the one pair of engageable recessed portions  63 ,  64  provided at the rotor-side end portion of the first housing portion  18 ; and the other pair of engageable recessed portions, not illustrated, provided at an end portion of the first housing portion  18  which is far from the rotor  3 . The engageable recessed portions  63 ,  64  are spaced apart from each other in the circumferential direction. 
     As illustrated in  FIGS. 1 and 4 , the frame  16  is a rigid member having a substantially frame shape and held by the first housing portion  18  so as to be movable relative to each other in the axial direction. The frame  16  includes: a first side portion  74  and a second side portion  75  extending in a direction orthogonal to the central axis C and spaced apart from each other in the axial direction; and a third side portion  77  and a fourth side portion  78  extending in a direction intersecting the first side portion  74  and the second side portion  75  and spaced apart from each other in the circumferential direction. The third side portion  77  and the fourth side portion  78  couple the first side portion  74  and the second side portion  75  to each other. The first side portion  74  and the second side portion  75  are located on opposite sides of the rotor  3  in the axial direction. The first side portion  74  is located on an inner side of the rotor  3  and opposed to the second piston  32 . The second side portion  75  is located on an outer side of the rotor  3  and engaged with the outer pad  6 . In the present embodiment, while the outer pad  6  is engaged with the second side portion  75  so as to be movable in the axial direction together with the second side portion  75 , the outer pad  6  and the second side portion  75  are spaced apart from each other in the circumferential direction. 
     Each of the third side portion  77  and the fourth side portion  78  extends toward the outer and inner sides of the rotor  3 . Specifically, as illustrated in  FIGS. 3 and 4 , each of the third side portion  77  and the fourth side portion  78  extends over the rotor  3  without extending over outer circumferential surfaces of the inner pad  4  and the outer pad  6  in the radial direction. 
     As illustrated in  FIGS. 4 and 6 , two pairs of engageable protrusions are provided on inner surfaces of the third side portion  77  and the fourth side portion  78  which face each other at positions located on an inner side of the rotor  3 . One pair of the two pairs of engageable protrusions (a pair of engageable protrusions  80 ,  82 ) are located nearer to the rotor  3  than the other pair of engageable protrusions  83 ,  84 . As illustrated in  FIG. 8 , the frame  16  is designed such that the center of gravity G of the frame  16  in the axial direction is located inside a portion K of the frame  16  between the engageable protrusions  80 ,  82  and the engageable protrusions  83 ,  84 . 
     These engageable protrusions  80 ,  82  of the frame  16  are engaged with the respective engageable recessed portions  63 ,  64  of the first housing portion  18 , whereby the frame  16  is held by the housing  10  so as to be movable relative to the housing  10  in the axial direction. It is noted that leaf springs in the form of springs  88  are respectively provided between the engageable protrusion  80  and the first engageable recessed portion  63  and between the engageable protrusion  82  and the first engageable recessed portion  64 . This configuration reduces positional misalignment of the frame  16  relative to the first housing portion  18  in the radial direction and the circumferential direction, resulting in reduced vibrations and abnormal sounds. In the present embodiment, a holding portion or a sliding portion is constituted by the engageable recessed portions  63 ,  64  and so on and the engageable protrusions  80 ,  82  and so on. 
     The disc brake configured as described above is operated by a hydraulic pressure in the hydraulic-pressure chamber  36  defined by the wheel cylinder  14 . A force related to the hydraulic pressure in the hydraulic-pressure chamber  36  is applied to the first piston  30  and the second piston  32 . The first piston  30  is moved toward the rotor  3  in the axial direction to press the inner pad  4  against the rotor  3 . The second piston  32  is moved away from the rotor  3  in the axial direction to move the frame  16 . The movement of the frame  16  presses the outer pad  6  against the rotor  3 . The rotor  3  is pressed by the inner pad  4  and the outer pad  6  from opposite sides of the rotor  3 , whereby the rotor  3  and each of the inner pad  4  and the outer pad  6  are brought into frictional engagement with each other. This actuates the disc brake to reduce rotation of the rotor  3 , thereby reducing rotation of the wheel. 
     In the case where the disc brake is actuated in the case where the wheel is rotating in the direction indicated by arrow X in  FIGS. 6 and 7  (hereinafter may be referred to as “rotational direction X”), torque in the rotational direction X acts on the inner pad  4  and the outer pad  6 . This moves the inner pad  4  and the outer pad  6  in the X direction. The inner pad  4 , as illustrated in  FIG. 6 , comes into contact with a torque receiver  18   t  of the first housing portion  18 , and the outer pad  6 , as illustrated in  FIG. 7 , comes into contact with at least one of torque receivers  47   t ,  48   t  of the respective pad pins  47 ,  48  in corresponding at least one of the through holes  6   h   1 ,  6   h   2 . The shape of each of the through holes  6   h   1 ,  6   h   2  of the outer pad  6  and a space between the outer pad  6  and the frame  16  are designed such that the outer pad  6  comes into contact with at least one of the pad pins  47 ,  48  before contact of the outer pad  6  with the frame  16 . The torque acting on the inner pad  4  is received by the torque receiver  18   t  of the first housing portion  18 , and the torque acting on the outer pad  6  is received by at least one of the torque receivers  47   t ,  48   t  of the respective pad pins  47 ,  48  of the second housing portion  19 . 
     For example, the outer pad  6 , the second housing portion  19 , and so on are designed such that the outer pad  6  moved in the rotational direction X comes into contact with the pad pin  47  first, and when the torque has increased, the outer pad  6  comes into contact with the pad pin  48 . 
     Thus, the torque acting on the outer pad  6  is received by the housing  10  and not by the frame  16 . This reduces a force applied to the frame  16  in the circumferential direction, thereby well reducing movement of the frame  16  with its rubbing against the housing  10 . Also, the center of gravity of the frame  16  is located between the engageable protrusions  80 ,  82  and the engageable protrusions  83 ,  84 . In other words, the center of gravity of the frame  16  is located between portions of the frame  16  which are held by the housing  10 . In view of the above, it is possible to stabilize a posture of the frame  16  during operation of the disc brake, making it possible to press the outer pad  6  against the rotor  3  well. Also, it is possible to reduce the length of each of the engageable recessed portions  63 ,  64  and the engageable protrusions  80 ,  82  in the axial direction. 
     As illustrated in  FIG. 7 , a centroid Gout of the pad portion  6   p  of the outer pad  6  is located on an inner circumferential side of the torque receivers  47   t ,  48   t . A force Fg in a tangent direction that is tangent to the rotational direction X is applied to the centroid Gout of the pad portion  6   p  of the outer pad  6 . The protrusion  6   b  of the outer pad  6  receives a reaction force Ft from the torque receiver  47   t . These forces Fg, Ft generate a moment in a direction indicated by arrow M in  FIG. 7  which acts on the outer pad  6 , and a couple Fa due to the moment is received by at least one of the pad pins  47 ,  48 . This stabilizes a position of the outer pad  6  during operation of the disc brake. 
     The inner pad  4  has configuration and effects similar to those of the outer pad  6 . Specifically, as illustrated in  FIG. 6 , a centroid Gin of the pad portion  4   p  of the inner pad  4  is located on an inner circumferential side of the torque receiver  18   t  of the first housing portion  18 . Thus, a couple Fa due to a moment indicated by arrow M which acts on the inner pad  4  during operation of the disc brake is received by the pad pins  47 ,  48  and the torque receiver  18   t . This stabilizes the posture of the inner pad  4 . 
     As illustrated in  FIG. 9 , in the present embodiment, the torque receivers  47   t ,  48   t  of the second housing portion  19  are located on an outer circumferential side of a position corresponding to the centroid Gout of the pad portion  6   p  of the outer pad  6 . In contrast, in a mounting bracket B of a conventional disc brake, as illustrated in  FIG. 10 , a torque receiver TA is located on an inner circumferential side of a position corresponding to a centroid of a pad portion of an outer pad of the mounting bracket B (noted that this position is illustrated in  FIG. 10  as a position corresponding to the centroid Gout of the pad portion  6   p  of the outer pad  6  in the present embodiment in the radial direction). Thus, a protrusion on an inner circumferential part of an outer portion of the vehicle is small in the present embodiment when compared with the conventional disc brake, resulting in improved mountability of the disc brake. Also, it is possible to improve the flexibility in design of the shape of the wheel. 
     In the conventional disc brake, as illustrated in  FIG. 10 , the mounting bracket B has a substantially three-sided rectangular shape in side view which includes: an inner portion B 1  in the vehicle; a portion B 2  extending over a rotor; and an outer portion B 3  in the vehicle. The mounting bracket B is supported by, e.g., a suspension member at a mount portion ST of an inner circumferential portion of the portion B 1 , and the torque receiver TA is located at an inner circumferential portion of the portion B 3 . Thus, two joints C 1 , C 2  are located between the mount portion ST and the torque receiver TA. The length between the mount portion ST and the torque receiver TA is equal to the sum of the distances D 1 , D 2 , D 3 . In the mounting bracket B, a force applied to the torque receiver TA in the circumferential direction bends the portion B 3  about the joint C 2 , a force applied to the joint C 2  in the circumferential direction bends the portions B 2 , B 3  about the joint C 1 , and a force applied to the joint C 1  in the circumferential direction bends the portions B 1 , B 2 , B 3  about the mount portion ST. This increases an amount of bending of the mounting bracket B about the mount portion ST. 
     In contrast, in the disc brake according to the present embodiment, as illustrated in  FIG. 9 , the housing  10  has a substantially L-shape in side view. The housing  10  is mounted on the suspension member at the mount portions  42 ,  44  of the first housing portion  18 . The torque receivers  47   t ,  48   t  are located near a vehicle-outer end portion of the second housing portion  19  which protrudes outward in the vehicle. Thus, one joint Cs is located between the mount portions  42 ,  44  and the torque receivers  47   t ,  48   t . The length between the mount portions  42 ,  44  and the torque receivers  47   t ,  48   t  is equal to the sum of the distances Ds 1 , Ds 2  and less than the length (D 1 +D 2 +D 3 ) in the case of the conventional mounting bracket B. 
     In the case where a force is applied to the torque receiver  47   t  ( 48   t ) of the housing  10  in the circumferential direction, the second housing portion  19  is bent about the joint Cs, and the second housing portion  19  and the first housing portion  18  about the mount portions  42 ,  44 . An amount of bending of the housing  10  in the present embodiment is less than an amount of bending of the conventional mounting bracket B. This allows low stiffness of the housing  10  in the present embodiment when compared with the conventional disc brake, resulting in reduced weight and size of the housing  10 . Also, it is possible to improve the flexibility in design of the shape of the housing  10 , for example. 
     Since no torque receiver is provided on the frame  16 , only a force in the axial direction acts on the frame  16 . Thus, by increasing the thickness of each of the first side portion  74  and the second side portion  75  of the frame  16 , it is possible to reduce deformation of the frame  16 . Moreover, since no torque receiver is provided on the frame  16 , it is possible to reduce the thickness of each of the third side portion  77  and the fourth side portion  78  of the frame  16 , resulting in reduced weight and improved workability (including formability). Also, it is possible to improve the flexibilities in design of the shape of the frame  16  and materials design. For example, carbon fiber-reinforced plastic (CFRP) may be employed. 
     While the torque acting on the inner pad  4  is received by the first housing portion  18 , and the torque acting on the outer pad  6  is received by at least one of the pad pins  47 ,  48  of the second housing portion  19  in the above-described embodiment, the present disclosure is not limited to this configuration. For example, the torque acting on each of the inner pad  4  and the outer pad  6  may be received by the second housing portion  19 . Specifically, the torque acting on each of the inner pad  4  and the outer pad  6  may be received by at least one of the pad pins  47 ,  48  of the second housing portion  19  and may be received by the bridge portion  46 . 
     There will be next described, with reference to  FIGS. 11 and 12 , a case where the torque acting on the outer pad  6  is received by the bridge portion  46  of the second housing portion  19 . In the present embodiment, torque acting on an outer pad  96  is received by at least one of the rods  50 ,  51  ( 50   t ,  51   t ). The outer pad  96  and each of the rods  50 ,  51  are located closer to each other in the circumferential direction by increasing the circumferential-directional size of each of inner circumferential portions of protrusions  96   a ,  96   b  respectively having through holes  96   h   1 ,  96   h   2  in the outer pad  96 , by reducing the distance between the rods  50 ,  51  in the circumferential direction in the bridge portion  46 , or by increasing the width of each of the rods  50 ,  51  in the circumferential direction, for example. 
     In the case where the disc brake is actuated when the wheel is rotating in the direction indicated by arrow X, the outer pad  96  is moved in the X direction by torque acting on the outer pad  96  in the X direction, so that a back board  96   r  is brought into contact with the rod  51 , and the torque is received by a torque receiver  51   t . The outer pad  96  receives the reaction force Ft, and the force Fg in the tangent direction acts on a centroid Gout of a pad portion  96   p . It is noted that the centroid Gout of the pad portion  96   p  is located on an inner circumferential side of the torque receiver  51   t  in the outer pad  96 . Thus, a moment in the direction indicated by arrow M acts on the outer pad  96 , and its couple Fa is received by the pad pins  47 ,  48  and the torque receiver  51   t . This suppresses the moment on the outer pad  96  well to stabilize the posture of the outer pad  96 . 
     Springs  100  each having a shape illustrated in  FIG. 13  may be provided between the engageable recessed portion  63  formed in the first housing portion  18  and the engageable protrusion  80  provided on the frame  16  and between the engageable recessed portion  64  formed in the first housing portion  18  and the engageable protrusion  82  provided on the frame  16 . For example, each of the springs  100  is provided so as to cover an inner circumferential surface of a corresponding one of the engageable protrusions  80 ,  82 . Thus, each of the engageable recessed portions  63 ,  64  and a corresponding one of the engageable protrusions  80 ,  82  may come into direct contact with each other at their respective surfaces facing each other in the circumferential direction. In the case where each of the frame  16  and the first housing portion  18  is formed of a material containing iron, for example, rust can be scraped by sliding movement of these surfaces relative to each other. It is noted that, since movement of the frame  16  with its rubbing against the housing  10  is reduced, it is possible to reduce the length of each of the engageable recessed portions  63 ,  64  and the corresponding one of the engageable protrusions  80 ,  82  in the axial direction, and accordingly there is no problem in the case where irons are brought into surface contact with each other. 
     The engageable recessed portions  63 ,  64  and the engageable protrusions  80 - 84  are not essential. 
     Second Embodiment 
     The pad pins  47 ,  48  are not essential, and an inner pad  104  and an outer pad  106  may be held by a bridge portion so as to be movable in the axial direction.  FIGS. 14-17  illustrate a disc brake including such a configuration. 
     The present disc brake includes: the inner pad  104  and the outer pad  106  located on opposite sides of a rotor  103 ; a pressing device  108  that presses the inner pad  104  and the outer pad  106  against the rotor  103 ; and a housing  110  holding the pressing device  108 . The pressing device  108  includes a wheel cylinder  114  and a frame  116  as another example of the driving member. 
     As illustrated in  FIGS. 14 and 15 , the housing  110  includes: a first housing portion  118  located on an inner side of the rotor  103  in the vehicle; and a second housing portion  119  extending from the first housing portion  118  over the rotor  103  to the outside of the vehicle. As illustrated in  FIGS. 15 and 17 , a cylinder bore  124  is formed in the first housing portion  118  so as to extend through the first housing portion  118  in the axial direction. A first piston  130  as another example of the first pressing member and a second piston  132  as another example of the second pressing member are fluid-tightly and slidably fitted in the cylinder bore  124  via piston seals. A portion of the cylinder bore  124  between the first piston  130  and the second piston  132  serves as a hydraulic-pressure chamber  136 . 
     In the present embodiment, a portion of the first housing portion  118  in which the cylinder bore  124  is formed serves as a cylinder body. The wheel cylinder  114  is constituted by the cylinder body, the first piston  130 , and the second piston  132 . 
     The inner pad  104  includes a back board  104   r  and a pad portion  104   p  held on the back board  104   r . The inner pad  106  includes a back board  106   r  and a pad portion  106   p  held on the back board  106   r . The respective pad portions  104   p ,  106   p  of the inner pad  104  and the outer pad  106  face the rotor  103 . Each of the back boards  104   r ,  106   r  is provided at its outer circumferential portion with protrusions  140 ,  141 ,  142 ,  143  spaced apart from each other in the circumferential direction and each extending toward an outer circumferential side. Each of the protrusions  140 - 143  may, for example, have a stepped shape in the radial direction and include an inner circumferential portion and an outer circumferential portion that is greater than the inner circumferential portion in width in the circumferential direction. 
     As illustrated in  FIG. 16 , a pair of mount portions  146 ,  147  are provided on opposite sides, in the circumferential direction, of a rotor-side end portion of the first housing portion  118  in the axial direction. The housing  110  is secured at each of the mount portions  146 ,  147  to a corresponding one of suspension members (which may be also referred to as “vehicle-body-side component”) such as a knuckle as another example of the non-rotating member. 
     As illustrated in  FIG. 14 , the second housing portion  119  includes the bridge portion having a substantially three-sided rectangular shape in plan view. The second housing portion  119  includes: a pair of rods  148 ,  149  spaced apart from each other in the circumferential direction and each extending in the axial direction; and a coupler  150  coupling the rods  148 ,  149  to each other and extending substantially in the circumferential direction. As illustrated in  FIG. 18 , inner circumferential portions of the respective rods  148 ,  149  have groove portions  152 ,  153  each extending in the axial direction. Each of the groove portions  152 ,  153  extends to an outer end face of the coupler  150  in the vehicle. Each of the groove portions  152 ,  153  has a shape corresponding to ones of the protrusions  140 - 143  of each of the inner pad  104  and the outer pad  106 . Specifically, an outer circumferential portion of each of the groove portions  152 ,  153  is greater than an inner circumferential portion thereof in width in the circumferential direction. The protrusions  140 ,  142  of each of the inner pad  104  and the outer pad  106  are fitted in the groove portion  152  of the rod  148 , and the protrusions  141 ,  143  of each of the inner pad  104  and the outer pad  106  are fitted in the groove portion  153  of the rod  149 , whereby the inner pad  104  and the outer pad  106  are held by the housing  110  so as to be movable in the axial direction. 
     As illustrated in  FIGS. 14 and 17 , the frame  116  is a rigid member having a substantially frame shape and held by the first housing portion  118  so as to be movable relative to each other in the axial direction. The frame  116  includes: a first side portion  174  and a second side portion  175  extending in the direction orthogonal to the central axis C and spaced apart from each other in the axial direction; and a third side portion  177  and a fourth side portion  178  extending in a direction intersecting the first side portion  174  and the second side portion  175  and spaced apart from each other in the circumferential direction. The third side portion  177  and the fourth side portion  178  couple the first side portion  174  and the second side portion  175  to each other. The first side portion  174  and the second side portion  175  are located on opposite sides of the rotor  103  in the axial direction. The first side portion  174  is located on an inner side of the rotor  103  in the vehicle. The second side portion  175  is located on an outer side of the rotor  103  in the vehicle. 
     The outer pad  106  is engaged with the second side portion  175  so as to be movable in the axial direction together with the second side portion  175 . The outer pad  106  and the second side portion  175  are spaced apart from each other in the circumferential direction. The second piston  132  is engaged with the first side portion  174  via a spring  180 . This configuration enables the first side portion  74  and the second piston  132  to move together in the axial direction. Thus, in the present embodiment, the frame  116  is engaged with the second piston  132  and held by the second housing portion  119  via the outer pad  106 . Each of the third side portion  177  and the fourth side portion  178  extends to an inner side and an outer side of the rotor  103  in the vehicle. As illustrated in, e.g.,  FIGS. 16 and 17 , each of the third side portion  177  and the fourth side portion  178  extends over the rotor  103  without extending over outer sides of the inner pad  104  and the outer pad  106  in the radial direction. 
     The disc brake configured as described above is operated by a hydraulic pressure in the hydraulic-pressure chamber  136  formed in the wheel cylinder  114 . The hydraulic pressure in the hydraulic-pressure chamber  136  moves the first piston  130  in the axial direction toward the rotor  103  to press the inner pad  104  against the rotor  103 . The second piston  132  is moved in the axial direction away from the rotor  103  to move the frame  116 , thereby pressing the outer pad  106  against the rotor  103 . The inner pad  104  and the outer pad  106  are pressed against the rotor  103  from opposite sides thereof and frictionally engaged with the rotor  103 . As a result, the disc brake is operated to reduce rotation of the rotor  103 , thereby reducing rotation of the wheel. 
     In the case where the disc brake is actuated when the wheel is rotating in the direction indicated by arrow X, as illustrated in  FIG. 18 , torque in the rotational direction acting on the inner pad  104  is received by at least one of wall surfaces of the groove portions  152 ,  153  of the respective rods  148 ,  149 . A portion of the wall surface of the groove portion  152  of the respective rod  148  which contacts the protrusion  140  of the back board  104   r  serves as a torque receiver  148   t . A portion of the wall surface of the groove portion  153  of the respective rod  149  which contacts the protrusion  141  of the back board  104   r  serves as a torque receiver  149   t . A couple Fa of a moment in a direction M in the inner pad  104  due to a force Fg in the tangent direction acting on a centroid Gin of the pad portion  104   p , and a reaction force Ft applied from at least one of the torque receivers  148   t ,  149   t  is received principally by a bottom surface of the trailing-side groove portion  152 . This stabilizes the posture of the inner pad  104 . It is noted that the outer pad  6  has configuration and effects similar to those of the inner pad  4 . 
     Thus, the torque acting on the inner pad  104  and the outer pad  106  is received not by the frame  116  but by the housing  110 . This reduces movement of the frame  116  with its rubbing against the housing  110 . The frame  116  is engaged with the second piston  132  so as to be movable in the axial direction together with the second piston  132  and is held by the second housing portion  119  via the outer pad  106  fitted to the frame  116 . This eliminates the need of the engageable protrusions  80 - 84  and the engageable recessed portions  63 ,  64  provided in the above-described embodiment. That is, a sliding portion between the frame  116  and the first housing portion  118  becomes unnecessary. This accordingly reduces loss of sliding, making it possible to reduce loss of energy. Also, it is possible to facilitate working the frame  116  and the first housing portion  118 , resulting in reduced cost. Moreover, the pad springs for holding the inner pad  104  and the outer pad  106  become unnecessary, resulting in reduced cost. 
     It is preferably to provide a spring, not illustrated, between the outer pad  106  and the frame  116 , for example, so as to allow movement of the outer pad  106  in the circumferential direction in the frame  116  and well allow movement of the frame  116  with movement of the outer pad  106  in the axial direction. 
     A plurality of the first pistons and a plurality of the second pistons may be provided so as to be arranged in the circumferential direction. While the embodiments have been described above, it is to be understood that the disclosure is not limited to the details of the illustrated embodiments, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the disclosure. For example, the disc brake is not limited to the hydraulic brake and may be an electric brake operable by driving of an electric motor.