Electrically driven braking system

Abstract

an electrically driven braking device (1) comprising: a transmission mechanism (114, 115) configured to transmit a rotational force from an electric motor (31); a ball screw mechanism (116) configured to convert the rotational force of the transmission mechanism (114, 115) into a thrust force; a pressure element (53) driven by the ball screw mechanism (116); and a brake caliper (4) configured to movably support the pressure element (53); wherein the ball screw mechanism (116) comprises: a nut element (191) mounted non-rotatably relative to the brake caliper (4); and a shaft element (190) configured to receive the rotational force from the transmission mechanism (114, 115);wherein the shaft element (190) is movable relative to the mother element (191) in an axial direction of the shaft element (190), and wherein the shaft element (190) is movably arranged in a housing (70) which accommodates a control board (74) for controlling the drive of the electric motor (31); and the control board (74) is formed with a cut-out section (104) or a hole to prevent interference with the shaft element (190), wherein the brake caliper (4) has a thrust force sensing part (117) for sensing a reaction force to the thrust force of the pressure element (280); and the thrust force sensing part (117) abuts against the mother element (191) to detect a magnitude of the reaction force transmitted by the mother element (191).

Description

TECHNICAL FIELDThe present invention relates to an electric motor-driven brake device used for braking vehicles.PRIOR ARTJP 2006-105 170 A discloses an electric motor driven brake device including, among other things, a piston capable of abutting against the rear of a brake pad in a vehicle; a motor; a ball ramp mechanism that transmits the rotation of the motor to the piston after the rotation is converted into a rectilinear motion; a speed reduction mechanism that transmits the rotation of the motor to the ball ramp mechanism after the speed of the rotation is reduced; a thrust force detection sensor that detects a reaction force to the thrust force applied from the piston to the brake pad; a brake pad wear following mechanism that advances the piston according to the wear of the brake pad; a brake release mechanism that releases the brake by automatically returning the piston to a home position when the motor fails during braking.DE 602 06 417 T2, DE 11 2018 004 232 D4 and DE 11 2017 000 459 B4 show similar brake devices.SUMMARY OF THE INVENTIONTECHNICAL PROBLEMIn the above-described electromotively driven brake device according to JP 2006-105 170 A, the ball ramp mechanism that operates during normal braking and the brake pad wear following mechanism that operates when the pad is worn, and the thrust force detection sensor that detects a reaction force on the thrust force applied to the brake pad are arranged along the axial direction; therefore, the electromotively driven brake device is likely to become larger in the axial direction, which is disadvantageous in terms of vehicle assemblability. Accordingly, the electric motor-driven brake device must be improved in its assembly capability.SOLUTION OF PROBLEMThe object of the invention is to provide an electric motor-driven brake device configured to suppress an increase in size and improve assemblability on vehicles.An electric motor-driven brake device according to the present invention has the features of claim 1. Advantageous refinements are described in the further claims.The electric motor-driven brake device according to an embodiment of the present invention is capable of suppressing an increase in size and improving vehicle assemblability.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view of an electric motor-driven brake device according to the embodiment. FIG. 2 is a perspective view of the electric motor-driven brake device with a cover part removed. FIG. 3 is a sectional view of the electric motor-driven brake device. FIG. 4 is an enlarged sectional view of a motor gear unit and its periphery in the electric motor driven brake device. FIG. 5 is an enlarged sectional view through the inside of a cylinder in the electric motor-driven brake device. FIG. 6 is a plan view of the electromotively driven brake device with the cover part and the carrier plate removed.DESCRIPTION OF THE EMBODIMENTSAs shown in FIGS. 1, 2 to 3, an electric motor-driven brake device 1 according to the embodiment is provided with a pair of brake pads, i.e., an inner brake pad 2 and an outer brake pad 3 respectively disposed on axially opposite sides opposite to a disc rotor D mounted on a rotating part of a vehicle, and a brake caliper 4. The electric motor-driven brake device 1 is designed as a floating-caliper brake device. Note that the pair of inner and outer brake pads 2 and 3 and the caliper 4 are supported by a bracket 5 fixed to a non-rotating part, e.g., a joint, of the vehicle such that the brake pads 2 and 3 and the caliper 4 are movable in the axial direction of the disc rotor D.As shown in FIGS. 1 and 2, the bracket 5 includes a pair of bolt fixing portions 12 into which sliding bolts 10 are inserted, respectively, and inner and outer support portions 14 and 15 integrally connected to the pair of bolt fixing portions 12 and support the inner and outer brake pads 2 and 3, respectively, independently of each other. The pair of bolt fastening portions 12 are spaced apart from each other in the rotational direction of the disc rotor D and extend along the axial direction of the disc rotor D. Each bolt fastening portion 12 is in the shape of a circular bottomed cylinder. A slide bolt 10 is inserted into each bolt fixing portion 12. The opening side of each bolt fixing portion 12 is directed toward the inside and the bottom side toward the outside. Each bolt fastening portion 12 has a circular cylindrical bolt bore protrusion 16 formed at an inner end. In the bolt fastening portions 12, the outer support portion 15 is integrally connected to the outside. In the bolt fixing portions 12, the inner support portion 14 is connected thereto such that the inner support portion 14 is spaced apart from the outer support portion 15 in the axial direction direction of the disc rotor D.The inner support portion 14 includes a pair of inner arm portions 20 extending from the bolt fixing portions 12 substantially perpendicularly thereto, respectively, and an inner support portion 21 connecting the ends of the pair of inner arm portions 20 to each other. The inner brake pad 2 is movably supported within the pair of inner arm portions 20 along the axial direction of the disc rotor D. The inner support portion 21 has through-holes 23 formed at opposite ends thereof in the rotational direction of the disc rotor D, the through-holes 23 extending through the inner support portion 21 along the axial direction of the disc rotor D. The bracket 5 is fixed to a non-rotating part of the vehicle through the through holes 23 in the inner support member 14 (inner support portion 21). The outer support portion 15 includes a pair of outer arm portions 25 respectively extending from the bolt fixing portions 12 substantially perpendicularly thereto, and an outer support portion 26 connecting the ends of the pair of outer arm portions 25 to each other. The outer brake pad 3 is movably supported within the outer arm portions 25 along the axial direction of the disc rotor D.As illustrated in FIGS. 1, 2 to 3, the caliper 4 includes a caliper body 30 that is a main component of the caliper 4, and an electric motor 31 disposed adjacent to the caliper body 30. The caliper body 30 has a circular cylindrical cylinder portion 34 disposed with its proximal end side facing the inner brake pad 2 on the inside of the vehicle such that the cylinder portion 34 is open toward the inner brake pad 2. The caliper body 30 also has claw portions 35 that extend from the cylinder portion 34 toward the outside via the disc rotor D and are disposed on a distal end side of the caliper body 30 that faces the outer brake pad 3 on the outside of the vehicle. In addition, the caliper body 30 has a pair of caliper arm portions 36 extending outward from the cylinder portion 34. The cylinder portion 34, the claw portions 35, and the caliper arm portions 36 are formed as an integrated structure. The pair of caliper arm portions 36 have slide bolts 10 respectively fixed thereto by lock nuts 38. Between the caliper arm portions 36 of the caliper body 30 and the bolt fixing portions 12 of the bracket 5, rubber bolt collars 40 are provided. The pin collars 40 have expandable bellows portions each covering the slide pins 10.For completeness, note that the following explanation is made on the assumption that a side closer to a lid part 100 is the one end side and the side of the disc rotor D is the other end side.As illustrated in FIGS. 3, 4 to 5, the cylinder portion 34 is formed with a lower cylinder bore 50 having a large-diameter opening portion 43 that is open at an end closer to the inner brake pad 2. The cylinder bore 50 is closed at an end opposite to the end closer to the inner pad 2 by a bottom wall 46 having an insertion bore 47. The cylinder bore 50 has a small-diameter opening portion 44 formed on a side closer to the bottom wall 46. The small-diameter opening portion 44 is provided adjacent to the large-diameter opening portion 43 and smaller in diameter than the large-diameter opening portion 43.A piston 53 is configured to press the inner brake pad 2, and is formed in a bottom cup shape including a bottom portion 54 and a circular cylindrical portion 55. The piston 53 corresponds to the pressing member. The circular cylindrical portion 55 has a plurality of circumferentially spaced anti-rotation recesses 58 formed in an inner circumferential surface nearer to the one end thereof. The circular cylindrical portion 55 has an annularly extending annular groove 59 formed in its inner circumferential surface nearer to the other end thereof within an axial range in which the rotation inhibiting recesses 58 are formed. An annular plate 245 is inserted into the annular groove 59. The bottom portion 54 of the piston 53 has a receiving portion 60 formed on its inner surface so as to protrude toward the one end side. One end surface of the receiving portion 60 is formed into a concave spherical surface 61 against which abuts a convex spherical surface 284 provided on the other end surface of a slide member 280 (described later).The piston 53 is disposed in the cylinder bore 50 such that the lower portion 54 faces the inner brake pad 2. The piston 53 has a recess 64 provided in the outer circumferential side of the other end surface of the bottom portion 54 and facing the inner brake pad 2. The recess 64 is engaged with a protrusion (not shown) formed on the rear side of the inner brake pad 2. The engagement prevents the piston 53 from rotating relative to the cylinder bore 50 and thus the caliper body 30. The cylinder bore 50 has a sealing member 67 disposed on the inner circumferential surface on the other end side of the large-diameter opening portion 43. The piston 53 is axially movably fitted into the large-diameter opening portion 43 of the cylinder bore 50 in a state of being in contact with the seal member 67. A dust boot 68 is disposed between an outer circumferential surface of the piston 53 on a side closer to the bottom portion 54 and the other end-side inner circumferential surface of the large-diameter opening portion 43 of the cylinder bore 50. The seal member 67 and the dust boot 68 prevent the entry of foreign matter into the cylinder bore 50.A gear housing 70 is disposed on the bottom wall 46 of the cylinder portion 34 of the caliper body 30. The transmission housing 70 receives a motor transmission assembly 73 and a control board 74. The transmission case 70 includes a bottom wall portion 76 disposed on the other end side, i.e., on the side closer to the cylinder bore 50, and a side wall portion 77 integrally extending from the outer peripheral portion of the bottom wall portion 76 toward the one end side. The bottom wall portion 76 of the transmission case 70 has a support recess 78 that supports the bottom wall 46 of the cylinder portion 34 (cylinder bore 50). The bottom wall 46 of the cylinder portion 34 (cylinder bore 50) is air-tightly supported by the support recess 78 via a sealing member 79. The support recess 78 has a bottom wall portion having a first opening portion 81 through which a circular cylindrical small diameter portion 153 of a bracket 145 including a push rod 190 (described later) is inserted. The lower wall portion 76 of the gear case 70 is provided with a second opening portion 82 into which the case part of the electric motor 31 is inserted and fixed.The bottom wall portion 76 of the gear case 70 is provided with a circular cylindrical restricting portion 84 protruding toward an end side from substantially the same position as the support recess 78. The circular cylindrical delimiting section 84 has discontinuous regions along its circumferential direction. The gear housing 70 has connectors 91 supported by the side wall portion 77 in the vicinity of the electric motor 31, the connectors 91 being electrically connected to the control board 74. The transmission case 70 has a support plate 94 disposed therein to divide the inside of the transmission case 70 into a space for accommodating the motor transmission assembly 73 and a space for accommodating the control board 74. The support plate 94 also supports the control board 74, and the support plate 94 is fixed to the gear case 70.The motor gear assembly 73 is disposed in the gear housing 70 at a position closer to the other end side than the support plate 94. the control board 74 is fixed to the one end side of the support plate 94. The support plate 94 has an opening portion 96 formed in a region facing a rotating shaft 32 of the electric motor 31. The opening portion 96 receives an annular magnetic member 184 of a rotation angle detection part 119 (described later). The support plate 94 is provided with a circular cylindrical support portion 97 protruding toward the other end side, i.e., toward the motor gear assembly 73, to receive one end of the later-described push rod 190. The support plate 94 is provided with a substantially rectangular parallelepiped protruding portion 98 protruding toward the one end side from an outer peripheral portion near the circular cylindrical support portion 97. The gear case 70 has a cover part 100 that is airtightly fixed to an end opening thereof through a sealing member 101 so as to cover the control board 74.The control board 74 has a cut-out portion 104 (see also FIG. 2 ) formed in an end portion near the circular cylindrical support portion 97 of the support plate 94 to prevent interference with the push rod 190. The cut-out portion 104 is cut out in an arc shape. The cut-out portion 104 makes it possible to expand the range of movement of the push rod 190 described later from a range in which the control board 74 is disposed, i.e., from the support plate 94, toward one end side. Note that, although the interference prevention cut portion 104 with the push rod 190 is formed in the end portion of the control board 74 in this embodiment, a hole or the like may be formed instead of the cut portion 104. The cover member 100 has a first through hole 106 at a position opposite to an end of the push rod 190. The first through hole 106 is air-tightly closed with a cap 109 by a sealing member 110. The lid part 100 has a substantially rectangular second through hole 107 formed at a location close to the first through hole 106. In the second through hole 107, the protruding part 98 of the support plate 94 is airtightly inserted through a sealing member 111.The caliper body 30 includes an electric motor 31, a combination of a spur gear multi-stage reduction mechanism 114 and a planetary gear reduction mechanism 115, a ball screw mechanism 116, a thrust force sensor 117, a return mechanism 118, a rotation angle detection part 119, and a thrust force holding part 120. The spur gear multi-stage reduction mechanism 114 and the planetary gear reduction mechanism 115 serve as a motor gear assembly 73 which is a transmission mechanism that increases the torque from the electric motor 31. The ball screw mechanism 116 receives the rotation transmitted from the multistage spur gear reduction mechanism 114 and the planetary gear reduction mechanism 115 and exerts a thrust force on the piston 53. The thrust force sensor 117 is a thrust force detection part that detects a reaction force to the thrust force (pressing force) applied from the piston 53 to the inner and outer brake pads 2 and 3. The return mechanism 118, when the push rod 190 drives the piston 53, stores the rotational force for rotating the push rod 190 of the ball screw mechanism 116 to be moved in the direction of retraction. The rotation angle detection part 119 detects a rotation angle of the rotating shaft 32 of the electric motor 31. the thrust force holding part 120 maintains the thrust force applied to the inner and outer brake pads 2 and 3 from the piston 53 during braking.The electric motor 31 is arranged substantially parallel to the cylinder portion 34. The electric motor 31 is inserted and secured with its body part into the second opening portion 82 of the transmission case 70. Referring mainly to FIG. 4, the multistage spur gear reduction mechanism 114 has a pinion 124, a first reduction gear 125 and a second reduction gear 126. The first reduction gear 125 and the second reduction gear 126 are made of metal or a resin, for example, a fiber-reinforced resin. The pinion 124 has a bore 128 shaped in the form of a cylinder into which the rotating shaft 32 of the electric motor 31 is press-fitted. The pinion 124 also has a gear 129 formed on the outer periphery of the pinion. The first reduction gear 125 includes a large-diameter gear 131 meshing with the gear 129 of the pinion gear 124, and a small-diameter pinion gear 132 concentrically and axially extending from the gear 131 toward one end side. The first reduction gear 125 is rotatably supported relative to the gear housing 70.The pinion 132 of the first reduction gear 125 is meshed with the second reduction gear 126. The second reduction gear 126 includes a large diameter gear 134 that meshes with the pinion gear 132 of the first reduction gear 125 and a central pinion gear 135 that extends concentrically and axially from the gear 134 toward the other end side. The center pinion gear 135 is configured as a part of the planetary gear speed reduction mechanism 115 described later. The gear 134 and the center pinion 135 of the second reduction gear 126 are integrally connected to each other at one end side by an annular wall portion 136. The second reduction gear 126 has a bore 138 at its radial center. The bore 138 accommodates a circular cylindrical support section 97 which protrudes from the support plate 94 arranged in the transmission housing 70 toward the other end side. Thus, the second reduction gear 126 is rotatably supported relative to the gear housing 70. The annular wall portion 136 of the second reduction gear 126 is formed with an annular stopper portion 140 protruding toward the planetary gear speed reduction mechanism 115.The planetary gear speed reduction mechanism 115 includes the central pinion gear 135 of the second reduction gear 126, a plurality (four in this embodiment) of planetary gears 143, an internal gear 144, and a carrier 145. Each planet gear 143 has a gear 147 meshing with the central pinion 135 of the second reduction gear 126, and a bore 150 rotatably inserted with a pin 148 projecting from the carrier 145. The planetary gears 143 are arranged on the one end side of the carrier 145 at equal intervals along the circumferential direction.The carrier 145 has a polygonal bore 146 formed to extend axially substantially through the radial center of the carrier. The polygonal bore 146 has an inner circumferential surface formed in a hexagonal shape, for example. The support 145 is composed of a large-diameter annular plate-shaped portion 152 and a small-diameter circular cylindrical portion 153 concentrically protruding from the large-diameter annular plate-shaped portion 152 toward the other end side. The small-diameter circular cylindrical portion 153 of the carrier 145 is inserted into the first opening portion 81 of the gear housing 70. The large-diameter ring-plate-shaped portion 152 of the carrier 145 is formed with an outer diameter smaller than the outer diameter of the orbit of the planetary gears 143. The ring plate-shaped portion 152 of the large diameter carrier 145 has a plurality of circumferentially spaced pin holes 155 formed in an outer circumferential portion thereof in correspondence with the planet gears 143.The pins 148 are press-fitted into the pin holes 155 of the bracket 145, respectively. Each pin 148 is rotatably inserted into the bore 150 of the associated planetary gear 143. In addition, the polygonal bore 146 of the carrier 145 and a polygonal rod portion 193 of the push rod 190 of the ball screw 116 described later are connected to each other, whereby the torque can be transmitted between the carrier 145 and the push rod 190.The internal gear 144 is disposed in the gear 134 of the second reduction gear 126. The internal gear 144 includes an internal gear part 161 that meshes with the gear 147 of each planetary gear 143, an annular wall portion 162 that extends radially and continuously from one end of the internal gear part 161 to limit the axial movement of the planetary gear 143, and a circular cylindrical wall portion 163 that extends from the internal gear part 161 toward the other end side. The circular cylindrical wall portion 163 has an inner circumferential surface abutting on the outer circumferential surface of the circular cylindrical restricting portion 84 provided on the gear housing 70 to restrict the radial movement of the internal gear 144. The internal gear 144 is non-rotatably supported relative to the gear housing 70. With respect to the internal gear 144, the other end of the circular cylindrical wall portion 163 abuts on the inner surface of the gear housing 70, and an end surface of the annular wall portion 162 is pressed by the annular stopper portion 140 provided on the annular wall portion 136 of the second reduction gear 126. Thus, the internal gear 144 is supported by the gear housing 70 so that the axial movement thereof is restricted.An annular plate 168 is disposed between the other end surfaces of the planet gears 143 and one end surface of the carrier 145 (large-diameter annular plate portion 152). The annular plate 168 is held between an end face of the internal gear part 161 and an end face of the circular cylindrical boundary portion 84 of the gear housing 70. This limits the axial movement of the planet gears 143. The annular plate 168 has a plurality of pins 148 passing therethrough. Note that, although the spur-type multi-stage gear reduction mechanism 114 and the planetary gear reduction mechanism 115 are used as the reduction mechanism that increases the driving force of the electric motor 31 in this embodiment, only the planetary gear reduction mechanism 115 may be used as the reduction mechanism. It is also possible to combine the planetary gear reduction mechanism 115 with a reduction gear according to other known techniques, such as a cycloid speed reduction mechanism, a shaft speed reduction gear, etc.The thrust force holding part 120 is disposed on the one end side of the pinion gear 124. The rotating shaft 32 of the electric motor 31 protrudes from the pinion 124 on the one end side. The thrust force holding part 120 includes a ratchet wheel 170 fixed to one end of the rotating shaft 32 of the electric motor 31 by press fitting, and a lever member 171 (see FIG. 6 ) engaged with a gear portion 174 of the ratchet wheel 170. The ratchet wheel 170 is formed in the shape of a circular cylinder. The ratchet wheel 170 includes a gear body portion 175 having a first bore 173 and a gear portion 174 formed on an outer circumferential surface thereof, and a circular cylindrical support portion 178 integrally protruding from the gear body portion 175 toward the one end side and having a second bore 177. One end of the rotating shaft 32 of the electric motor 31 is fixed in the first bore 173 of the gear body portion 175 by press fitting. Referring to FIG. 6, the lever member 171 is reciprocally movable by a solenoid actuator 181 to be engaged with or disengaged from the gear portion 174 of the ratchet wheel 170 (gear body portion 175). The solenoid actuator 181 is electrically connected to the control board 74.The rotation angle detecting part 119, which mainly refers to FIGS. 3 and 4, is disposed on the one end side of the ratchet wheel 170. The rotation angle detection part 119 detects a rotation angle of the rotating shaft 32 of the electric motor 31, and includes a magnetic member 184 and a magnetism detecting IC chip 185. The ratchet wheel 170 has a support rod 187 press-fitted into the second bore 177 of the circular cylindrical support portion 178. The support rod 187 protruding from an end surface of the circular cylindrical support portion 178 toward the one end side supports an annular magnetic member 184 disposed in a cup-shaped support member 188. The magnetic member 184 including the support member 188 is disposed in the opening portion 96 of the support plate 94. The magnetism detecting IC chip 185 is disposed to face the one end side of the magnetic member 184. The magnetism detecting IC chip 185 detects a change in a magnetic field generated by the magnetic element 184. The magnetism detecting IC chip 185 is fixed to the other end face of the control board 74. The change in the magnetic flux from the rotating magnetic member 184 is detected by the magnetism detecting IC chip 185, whereby the rotation angle of the rotating shaft 32 of the electric motor 31 is arithmetically detected by the control board 74.The ball screw mechanism 116, which mainly refers to FIGS. 3 and 5, converts the rotational motion of the multistage spur gear reduction mechanism 114 and the planetary gear reduction mechanism 115, i.e., the rotational motion of the electric motor 31, into a rectilinear motion (hereinafter, simply referred to as "linear motion"), and applies a thrust force to the piston 53. The ball screw mechanism 116 is composed of a push rod 190 as a shaft member to which the rotational motion from the multistage spur gear reduction mechanism 114 and the planetary gear reduction mechanism 115 is transmitted, and a base nut 191 as a nut member threadedly engaged with the outer circumferential surface of the push rod 190.The push rod 190 includes a polygonal rod portion 193 formed in a range from the insertion hole 47 provided in the bottom wall 46 of the cylinder portion 34 to substantially the entire axial range in the circular cylindrical support portion 97 of the support plate 94. The push rod 190 also includes a large-diameter rod portion 194 integrally extending from the other end of the polygonal rod portion 193 toward the other end side, and a medium-diameter rod portion 195 integrally extending from the other end of the large-diameter rod portion 194 toward the other end side. In addition, the push rod 190 includes a small-diameter rod portion 196 integrally extending from the other end of the intermediate-diameter rod portion 195 toward the other end side.The polygonal rod portion 193 is formed to have a smaller diameter than the large-diameter rod portion 194. The polygonal rod portion 193 has an outer circumferential surface formed into a polygonal shape, e.g., a hexagonal shape. The polygonal rod portion 193 is fitted into the polygonal bore 146 of the carrier 145 of the planetary gear reduction mechanism 115. The large-diameter rod portion 194 has a helical groove 199 formed in an outer circumferential surface along the radial center line. The large-diameter rod portion 194 is formed in a range from the bottom wall 46 of the cylinder portion 34 to the other end surface of the later-described base nut 191. The intermediate diameter rod portion 195 has an axially extending spline groove (not shown) formed in an outer circumferential surface thereof. The intermediate diameter rod portion 195 is inserted to extend from an insertion hole 233 of a first coupling member 225 (described later) through a second coupling member 226 to a first insertion hole 251 of a third coupling member 228. The small-diameter rod portion 196 is inserted into a second insertion hole 252 of the third coupling member 228 described later. An annular step surface 198 is formed between the large-diameter rod portion 194 and the intermediate-diameter rod portion 195.The base nut 191 is disposed radially outside the large-diameter rod portion 194 of the push rod 190. The base nut 191 is formed in the shape of a circular cylinder. The base nut 191 has a helical groove 201 formed in its inner circumferential surface along the radial center line. The base nut 191 has an axially extending spline groove (not shown) formed in an outer circumferential surface thereof. A plurality of balls 203 are disposed between the helical groove 199 of the push rod 190 and the helical groove 201 of the base nut 191. A circular cylindrical thrust sensor 117 is disposed between one end surface of the base nut 191 and the bottom wall 46 of the cylinder bore 50 so as to abut against the one end surface of the base nut 191 and the bottom wall 46. The thrust force sensor 117 has a circular cylindrical load cell. The thrust force sensor 117 detects a reaction force to the thrust force applied from the piston 53 to the inner and outer brake pads 2 and 3. The one end side outer circumferential surface of the thrust force sensor 117 abuts on the inner circumferential surface of the small diameter opening portion 44 of the cylinder bore 50.A stopper member 205 is disposed between the base nut 191 and the main part of the thrust force sensor 117 (main part of the thrust force sensor 117 other than the one end portion) on the one hand and the inner wall surface of the large-diameter opening portion 43 of the cylinder bore 50 on the other hand. The stopper element 205 is formed as a whole in the shape of a circular cylinder with a bottom. The stopper member 205 includes: a large-diameter thin-wall portion 208 located on the one end side; a large-diameter thick-wall portion 209 integrally extending from the other end of the large-diameter thin-wall portion 208 toward the other end side; a small-diameter thin-wall portion 210 integrally extending from the other end of the large-diameter thick-wall portion 209 toward the other end side; and a bottom wall portion 211 inwardly protruding from the other end of the small-diameter thin-wall portion 210 and having an insertion hole 212 at the radial center.The thin-walled large-diameter portion 208 abuts at its outer circumferential surface against the inner circumferential surface of the large-diameter opening portion 43 of the cylinder bore 50 and at its inner circumferential surface against the outer circumferential surface of the thrust force sensor 117. The thick-walled large-diameter portion 209 has an axially extending spline groove (not shown) formed in an inner circumferential surface thereof. The thick-walled large-diameter portion 209 abuts at its outer circumferential surface against the inner circumferential surface of the large-diameter opening portion 43 of the cylinder bore 50 and at its inner circumferential surface against the outer circumferential surface of the base nut 191. The thick-walled large-diameter portion 209 has an engaging groove (not shown) formed in the outer circumferential surface of its other end. The small-diameter thin-wall portion 210 abuts on the inner circumferential surface thereof against the outer circumferential surface of the base nut 191 and has the other end side thereof disposed in the piston 53. The stopper member 205 has a first small-diameter coupling portion 239 of the later-described first coupling member 225 inserted into the insertion hole 212 provided in its bottom wall portion 211.The stopper member 205 is non-rotatably supported relative to the cylinder portion 34 and prevented from moving toward the other end side by disposing the distal end of a rotation-restraining shaft (not shown) in the engaging recess (not shown) provided in the thick-walled large-diameter portion 209, the rotation-restraining shaft being inserted through the circumferential wall portion of the cylinder portion 34 from the radially outer side. An elongated first key member (not shown) is disposed between the key groove (not shown) provided in the inner circumferential surface of the thick-walled large-diameter portion 209 of the stopper member 205 and the key groove (not shown) provided in the outer circumferential surface of the base nut 191. The first wedge member prevents the relative rotation between the stopper member 205 and the base nut 191. Two superposed first washers 220 are disposed between the other end surface of the base nut 191 and the bottom wall portion 211 of the stopper member 205. The first washers 220 drive the base nut 191 toward the one end side (toward the thrust force sensor 117) relative to the stopper member 205.The return mechanism 118, sometimes referred to as a "fail-open mechanism", releases the braking force applied to the disc rotor D from the inner and outer brake pads 2 and 3 when a failure occurs in the electric motor 31, the control board 74, etc. during braking. That is, when the push rod 190 drives the piston 53, the return mechanism 118 stores the rotational force for moving the piston 53 in the direction of retraction. When the reaction force to the pushing force is larger than a set reaction force, the returning mechanism 118 stores the rotational force for rotating the push rod 190 to move it in the retracting direction. The return mechanism 118 includes a first clutch member 225, a second clutch member 226, a return spring 227, a third clutch member 228, and a spring holder 229.The first coupling member 225 is in the form of a circular cylinder having an insertion hole 233 into which the intermediate diameter rod portion 195 is inserted. The first coupling member 225 has an axially extending spline groove (not shown) formed in the inner circumferential surface of the insertion bore 233. An elongated second spline member (not shown) is disposed between the spline (not shown) provided in the outer circumferential surface of the intermediate diameter rod portion 195 and the spline (not shown) provided in the inner circumferential surface of the insertion bore 233 of the first coupling member 225. The second wedge member prevents relative rotation between the first clutch member 225 and the push rod 190. The first coupling member 225 includes a first small-diameter coupling portion 239 disposed on the one end side and a first large-diameter coupling portion 240 integrally formed to extend from the other end of the first small-diameter coupling portion 239 toward the other end side.The annular step surface 198 between the large-diameter rod portion 194 and the intermediate-diameter rod portion 195 of the push rod 190 may abut an end surface of the first small-diameter coupling portion 239 of the first coupling part 225. The first large-diameter clutch portion 240 includes a clutch friction material (lining) provided on an annular surface 243 thereof which is the other end surface of the first large-diameter clutch portion 240. An annular plate 245 is disposed around the first small-diameter coupling portion 239 at a position closer to the other end side than the lower wall portion 211 of the stopper member 205. The outer peripheral portion of the annular plate 245 is fitted into the annular groove 59 in the inner peripheral surface of the piston 53.Note that the outer diameter of the annular plate 245 is reduced when it is fitted into the piston 53, and when the annular plate 245 reaches the annular groove 59, the outer diameter thereof increases and the outer peripheral portion of the annular plate 245 engages with the annular groove 59. The annular plate 245 has an insertion hole 246 through which the first small-diameter coupling portion 239 of the first coupling member 225 is inserted. The insertion hole 246 is larger in diameter than the insertion hole 212 provided in the lower wall portion 211 of the stopper member 205. An annular plate 248 is disposed on the other end side of the annular plate 245 in abutting contact therewith. The annular plate 248 has an insertion hole 249 through which the first small-diameter coupling portion 239 of the first coupling member 225 is inserted. The annular plate 248 has a smaller outer diameter than the annular plate 245 and is disposed inside the piston 53. A second wave washer 250 is disposed on the other end side of the annular plate 248 in abutting contact therewith. The third coupling member 228 is disposed on the other end side of the first coupling member 225 with the second coupling member 226 interposed therebetween. The third clutch element 228 is explained first below.The third coupling member 228 is in the form of a circular cylinder having a first insertion hole 251 receiving the intermediate diameter rod portion 195 and the small diameter rod portion 196 of the push rod 190 and also having a second insertion hole 252 disposed on the other end side of the first insertion hole 251 to receive the small diameter rod portion 196. The first insertion hole 251 of the third coupling member 228 and the insertion hole 233 of the first coupling member 225 have the same inner diameter. The first insertion bore 251 has an axially extending spline groove (not shown) formed in the inner circumferential surface thereof. An elongated second spline member (not shown) is disposed between the spline groove (not shown) provided in the outer circumferential surface of the intermediate diameter rod portion 195 of the push rod 190 and the spline groove (not shown) provided in the inner circumferential surface of the first insertion bore 251 of the third coupling member 228, the second spline member being common to the first and third coupling members 225 and 228. The second wedge element prevents the relative rotation between the first and third clutch elements 225 and 228, on the one hand, and the push rod 190, on the other hand.The third coupling member 228 includes a third small-diameter coupling portion 257 located on the one end side and a third large-diameter coupling portion 258 integrally protruding toward the other end side from the other end of the third small-diameter coupling portion 257. The third small-diameter clutch portion 257 includes a clutch friction material (lining) provided on an annular surface 260 thereof which is an end surface of the third small-diameter clutch portion 257. The third small-diameter coupling portion 257 of the third coupling member 228 and the first large-diameter coupling portion 240 of the first coupling member 225 substantially coincide with each other. The third large-diameter coupling portion 258 has a circular recess 262 formed substantially in the radial center of the other end surface thereof. The other end surface of the third large-diameter coupling portion 258 has an annular groove 264 formed around the circular recess 262, the annular groove 264 having a bottom surface of arc-shaped cross section.The small-diameter rod portion 196 of the push rod 190 has a C-shaped snap ring 266 attached to the distal end thereof after the small-diameter rod portion 196 is inserted through the second insertion hole 252 of the third coupling member 228. The second clutch member 226 is disposed in the range between the first large-diameter clutch portion 240 of the first clutch member 225 and the third small-diameter clutch portion 257 of the third clutch member 228 to the radially outer side of the third clutch member 228.The second coupling member 226 includes a disc-shaped coupling portion 268, a skirt portion 269 integrally extending from the outer periphery of the disc-shaped coupling portion 268 toward the other end side, and a flange portion 270 radially extending outward from the other end of the skirt portion 269. The disc-shaped coupling portion 268, the skirt portion 269 and the flange portion 270 are formed to have the same thin wall thickness. The disc-shaped coupling portion 268 has an insertion hole 272 formed in the radial center thereof for receiving the intermediate diameter rod portion 195 of the push rod 190. The disc-shaped coupling portion 268 is disposed between the first large-diameter coupling portion 240 of the first coupling member 225 and the third small-diameter coupling portion 257 of the third coupling member 228. The disc-shaped clutch portion 268 has clutch friction materials on both surfaces thereof.The skirt portion 269 includes a small diameter skirt portion 274 extending along the outer circumferential surface of the third small diameter coupling portion 257 of the third coupling member 228, and a large diameter skirt portion 275 extending along the outer circumferential surface of the third large diameter coupling portion 258 of the third coupling member 228. The small diameter skirt portion 274 and the large diameter skirt portion 275 are integrally connected together by an annular wall portion 276. The flange portion 270 of the second clutch member 226 is connected to the other end of the return spring 227. One end of the return spring 227 is bent so as to be folded back, and the bent portion of the return spring 227 engages with an engagement groove (not shown) provided in a flange portion 297 of the spring holder 229 described later. In this manner, the return spring 227 is connected to the spring holder 229.The return spring 227 includes a coil spring. The return spring 227 can store the rotational force for rotating the push rod 190 in the retracting direction. The return spring 227 is disposed radially outward of the skirt portion 269 of the third clutch member 228. Note that the return spring 227 is previously applied with a predetermined target torque in the rotational direction. A pressing member 280 is disposed to oppose the third large-diameter coupling member 258 of the third coupling member 228. The pressure element 280 is designed in the form of a circular cylinder. The pressing member 280 has an axially extending through hole 281 having an outer diameter substantially corresponding to the outer diameter of the circular recess 262 provided in the large-diameter coupling portion 258 of the third coupling member 228. The other end surface of the pressing member 280 is formed into a convex spherical surface 284. An end surface of the pressing member 280 has an annular groove 285 formed around the through hole 281, the annular groove 285 having a bottom surface with an arc-shaped cross section.A thrust bearing 288 is disposed between the annular groove 264 provided in the large-diameter coupling portion 258 of the third coupling member 228 and the annular groove 285 provided in the thrust member 280. The thrust bearing 288 includes a holder 292 having a plurality of support holes spaced in a plate-shaped portion extending in the shape of a ring, and balls 293 rotatably supported in the support holes of the holder 292, respectively. The spring retainer 229 is disposed radially outward of the disc-shaped coupling portion 268 of the second coupling member 226 and the small-diameter skirt portion 274 of the skirt portion 269 of the second coupling member 226.The spring retainer 229 includes a skirt portion 296 formed to surround the periphery of the small diameter skirt portion 274 of the second coupling member 226, and a flange portion 297 extending radially outward from one end of the skirt portion 296. The skirt portion 296 and the flange portion 297 are formed to have the same thin wall thickness. The other end surface of the skirt portion 296 is disposed so as to be able to abut on the annular wall portion 276 of the second coupling member 226. The flange portion 297 is located radially outside the disc-shaped coupling portion 268 of the second coupling member 226. The flange portion 297 has an engagement groove (not shown) formed in its outer circumferential surface, which engagement groove can be engaged with the bent portion at the one end of the return spring 227. The flange portion 297 has a stopper portion (not shown) formed on its outer circumferential surface, the stopper portion protruding toward the one end side from a circumferential part of the flange portion 297. The spring holder 229 is non-rotatably supported relative to the piston 53 by engaging the stopper portion with a rotation inhibiting recess 58 provided in the inner circumferential surface of the piston 53. A second wave washer 250 is disposed between the flange portion 297 of the spring holder 229 and the annular plate 248. The second wave washer 250 presses the annular plate 248 and the annular plate 245 toward the one end side relative to the flange portion 297 of the spring holder 229.The drive of the electric motor 31 is controlled by a command from the control board 74. The control board 74 is fixed to the one end side of the support plate 94 which divides the inside of the gear case 70 into two spaces as explained above. The control board 74 is electrically connected to the magnetism detecting IC chip 185 of the rotation angle detecting part 119. The control board 74 is electrically connected to the thrust force sensor 117. In addition, the control board 74 is electrically connected to various detection sensors, such as sensors that detect the driver's requests, for example, a stroke sensor (not illustrated) attached to a brake pedal, and sensors that detect various situations in which braking is required without the driver's request. The control board 74 is electrically connected to a parking switch (not illustrated) that is operated to instruct the activation or the release of the parking brake, which is an example of the operation for maintaining the holding state of the vehicle. The control board 74 is electrically connected to a solenoid actuator 181 for operating the lever member 171 of the thrust force holding part 120.In braking during normal travel, the control board 74 controls the drive of the electric motor 31 based on detection signals such as detection signals from detection sensors that meet the driver's requirements and from various detection sensors that detect various situations that require braking, a detection signal from the magnetism detecting IC chip 185 of the rotation angle detecting part 119, and a detection signal from the thrust force sensor 117. In addition, the control board 74 controls the drive of the lever member 171 of the thrust force holding part 120 while controlling the drive of the solenoid actuator 181 based on an operation signal from the parking switch.Next, the brake and brake release operations during the normal operation performed by the electric motor-driven brake device 1 according to this embodiment will be explained.In braking in normal operation, the electric motor 31 is driven by a command from the control board 74, and the rotation in the forward direction, i.e., the braking direction, is transmitted to the central pinion 135 of the planetary gear reduction mechanism 115 via the multistage spur gear reduction mechanism 114. The rotation of the center pinion 135 of the planetary gear reduction mechanism 115 causes each planetary gear 143 to rotate about the rotational axis of the center pinion 135 while rotating about its own rotational axis, whereby the carrier 145 can rotate. In other words, the rotation from the electric motor 31 is transmitted to the carrier 145 after the rotational speed is reduced and the rotational force is increased at a predetermined reduction ratio by being passed through the multistage spur gear reduction mechanism 114 and the planetary gear reduction mechanism 115. Then, the rotation is transmitted from the carrier 145 to the push rod 190 of the ball screw mechanism 116.Then, when the push rod 190 starts rotating with the rotation of the carrier 145 because the base nut 191 is non-rotatably supported relative to the piston 53, the balls 203 roll between the slant groove 199 of the push rod 190 and the slant groove 201 of the base nut 191, and the push rod 190 moves forward relative to the base nut 191 during the rotation. At this time, as the push rod 190 rotates, the first clutch member 225 and the third clutch member 228 rotate in synchronization with each other.Next, the annular step surface 198 of the push rod 190 slides the first clutch member 225 as the push rod 190 moves forward upon its relative rotation. Thus, the first, second, and third clutch members 225, 226, and 228 move forward together while the first clutch member 225 and the third clutch member 228 relatively rotate while the second clutch member 226 does not relatively rotate. Thus, the thrust member 280 passes through the thrust bearing 288.More specifically, at this time, the torque of the first clutch member 225 is transmitted to the return spring 227 via the second clutch member 226. However, the rotational torque is still smaller than the predetermined target torque of the return spring 227. Therefore, the second clutch member 226 advances without relative rotation. At this time, although the first clutch member 225 and the third clutch member 228 advance upon relative rotation, the annular plate 245, the annular plate 248, and the spring holder 229 do not relatively move in the rotational direction or the axial direction.As the push rod 190 continuously moves forward while rotating relative to the base nut 191, the first clutch member 225 and the third clutch member 228 together move further while rotating relative to each other, and the convex ball surface 284 of the pressing member 280 presses the concave ball surface 61 of the piston 53. The reaction force to the pressing force applied from the piston 53 to the inner brake pad 2 causes the caliper body 30 to move rightward in FIG. 3 relative to the bracket 5, and thus presses the outer brake pad 3 fixed to the claw portions 35 against the disc rotor D.When the braking force is generated by the sandwiching of the disc rotor D between the pair of inner and outer brake pads 2 and 3, the reaction force to the braking force is applied to the thrust force sensor 117 via the pressing member 280, the third clutch member 228, the second clutch member 226, the first clutch member 225, the push rod 190, and the base nut 191. The thrust force sensor 117 detects a thrust force applied to the disc rotor D from the inner and outer brake pads 2 and 3 by advancing the piston 53.When the rotation of the push rod 190 is continued thereafter, the relative rotation of the push rod 190 causes the second clutch member 226 to relatively rotate through the first clutch member 225. Consequently, the first clutch member 225, the second clutch member 226, and the third clutch member 228 move forward together while rotating relative to each other, and this causes the piston 53 to move forward. In addition, the rotation of the second clutch member 226 allows the rotational force for rotating the push rod 190 in the retracting direction to be stored in the return spring 227. Thereafter, the drive of the electric motor 31 is controlled by detection signals of the rotation angle detection part 119, the thrust force sensor 117, and so on to establish a braking state.On the other hand, when releasing the braking, the rotating shaft 32 of the electric motor 31 rotates in the reverse direction, i.e., in the direction of the brake release, in response to a command from the control board 74, and the rotation in the reverse direction is transmitted to the push rod 190 via the multistage spur gear reduction mechanism 114 and the planetary gear reduction mechanism 115. As a result, the push rod 190 retracts while relatively rotating in the opposite direction, whereby the return spring 227 can return to the initial state. Thereby, the braking force applied to the disc rotor D by the pair of inner and outer brake pads 2 and 3 is released.When the electric motor 31 or the control board 74 fails during braking, the second clutch member 226 is rotated in the reverse direction (retracting direction) and the first clutch member 225 is rotated in the reverse direction by the pressing force stored in the return spring 227 during braking. As a result, the push rod 190 retracts while relatively rotating in the reverse direction to release the braking force applied to the disc rotor D from the pair of inner and outer brake pads 2 and 3.For example, in order to activate the parking brake with the above-described electromotively driven brake device 1 according to this embodiment, upon operation of the parking brake switch, the control board 74 generates commands for generating the braking force applied from the inner and outer brake pads 2 and 3 to the disc rotor D through the piston 53 as explained above, and for activating the solenoid actuator 181 to engage the lever member 171 with the gear portion 174 of the ratchet wheel 170 (gear body portion 175) press-fitted on the rotating shaft 32 of the electric motor 31. Thereby, the rotating shaft 32 of the electric motor 31 can rotate in the forward direction to generate braking force, but is prevented from rotating backward to release the braking force.As a result, the braking force applied from the piston 53 to the disc rotor D is held by the inner and outer brake pads 2 and 3, and the application of the parking brake is completed. On the other hand, in order to release the parking brake, when the parking brake switch is operated, the solenoid actuator 181 is activated by a command from the control board 74, so that the lever member 171 is released from the gear portion 174 of the ratchet wheel 170 (gear body portion 175) press-fitted to the rotating shaft 32 of the electric motor 31. Thereafter, the above-described operation is performed, and the braking force applied to the disc rotor D by the inner and outer brake pads 2 and 3 is released. The parking brake is thereby released.As explained above, the electric motor-driven brake device 1 according to this embodiment includes a piston 53 that presses an inner brake pad 2 of a pair of inner and outer brake pads 2 and 3 against a disk rotor D, and a ball screw mechanism 116 that applies a thrust force to the piston 53 by the rotation of an electric motor 31. The ball screw mechanism 116 includes a base nut 191 and a push rod 190 screwed into the base nut 191. These are movable relative to each other in the axial direction. Consequently, it is possible to reduce the axial length of the cylinder portion 34 of the caliper body 30, and thus achieve downsizing. Accordingly, it is possible to improve the assemblability of the electric motor-driven brake device 1 on vehicles.Further, in the electric motor-driven brake device 1 according to this embodiment, the base nut 191 is supported rotationally fixedly relative to the caliper body 30, and the rotation of the electric motor 31 is transmitted to the push rod 190. Consequently, the push rod 190 moves in the axial direction while rotating relative to the base nut 191 to drive the piston 53. Therefore, a space for the linear movement of the base nut 191 does not need to be secured. Accordingly, it is possible to further reduce the axial length of the cylinder portion 34 of the caliper body 30, and thus achieve downsizing.In addition, in the electric motor-driven brake device 1 according to this embodiment, the carrier 145 of the planetary gear reduction mechanism 115 and the push rod 190 are connected to be rotationally fixed and axially movable relative to each other. Accordingly, the axial movable range of the push rod 190 can be widened toward the inside of the planetary gear reduction mechanism 115, and it is possible to further reduce the axial length of the cylinder portion 34 of the caliper body 30, thereby achieving downsizing.Moreover, in the electric motor-driven brake device 1 according to this embodiment, the thrust force sensor 117 abuts an end face of the base nut 191 to detect a reaction force to the thrust force on the inner and outer brake pads 2 and 3 from the piston 53 transmitted to the base nut 191. Thereby, the space in the cylinder bore 50 can be effectively utilized.Moreover, in the electric motor-driven brake device 1 according to this embodiment, the thrust force sensor 117 is formed in a shape of a circular cylinder and is disposed to abut on a surface of the base nut 191 on a side thereof that is closer to the planetary gear reduction mechanism 115 and radially outside the push rod 190. Therefore, it is possible to further reduce the axial length of the cylinder portion 34 of the caliper body 30, and thus achieve a size reduction.Moreover, the electric motor-driven brake device 1 according to this embodiment has a return mechanism 118 that, when the push rod 190 drives the piston 53, stores the rotational force for rotating the push rod 190 to move it in the direction of retraction. The return mechanism 118 is disposed radially outside the push rod 190. Therefore, it is possible to further reduce the axial length of the cylinder portion 34 of the caliper body 30, thereby achieving downsizing.Moreover, in the electric motor-driven brake device 1 according to this embodiment, the return mechanism 118 includes a return spring 227 that presses the push rod 190 in the rotational direction, and the first to third clutch members 225, 226, and 228 that transmit or shut off the rotational force between the return spring 227 and the push rod 190. Accordingly, it is possible to construct the retractor mechanism 118 with a simple structure, thereby suppressing enlargement.Moreover, in the electric motor-driven brake device 1 according to this embodiment, the control board 74 is formed with a cut-out portion 104 to prevent interference with the push rod 190. Therefore, the axial movement range of the push rod 190 into the space in which the control board 74 is disposed can be widened, and it is possible to further reduce the axial length of the cylinder portion 34 of the caliper body 30, and thus achieve downsizing. Note that although in this embodiment, in an end portion of the control board 74, the cut-out portion 104 is formed to prevent interference with the push rod 190, a hole or the like may be formed instead of the cut-out portion 104.Examples of electric motor-driven brake devices 1 based on the above embodiment include those according to the following aspects.An electric motor-driven brake device according to a first aspect includes: transmission mechanisms 114 and 115 configured to transmit the rotational force of an electric motor 31; a ball screw mechanism 116 configured to convert the rotational force of the transmission mechanisms 114 and 115 into a thrust force; a pressing member 53 driven by the ball screw mechanism 116; and a caliper 4 configured to movably support the pressing member 53. The ball screw mechanism 116 includes a nut member 191 that is non-rotatably supported relative to the caliper 4 and a push rod 190 configured to receive the rotational force of the transmission mechanisms 114 and 115. The push rod 190 is movable relative to the nut member 191 in the axial direction of the push rod 190.According to a second aspect, in the first aspect, the push rod 190 of the ball screw mechanism 116 drives the pressing member 63.According to a third aspect, in the first or second aspect, the transmission mechanisms 114 and 115 are supported by the caliper 4, and the push rod 190 is movable relative to the transmission mechanisms 114 and 115 in the axial direction.According to a fourth aspect, in any one of the first to third aspects, the caliper 4 includes a thrust force sensor 117 for detecting a reaction force to the thrust force of the pressing member 53, the thrust force sensor 117 abutting on the nut member 191 to detect a magnitude of the reaction force transmitted from the nut member 191.According to a fifth aspect, in the fourth aspect, the caliper 4 is formed with a lower cylinder bore 50 in which the ball screw mechanism 116 and the pressing member 53 are disposed, and the thrust force sensor 117 is disposed between the nut member 191 and the bottom wall 46 of the cylinder bore 50 and radially outside the push rod 190.According to a sixth aspect, in any one of the first to fifth aspects, a return mechanism 118 is provided between the push rod 190 and the pressing member 53 to store, when the pressing member 53 is driven, the rotational force for rotating the push rod 190 to be moved in the direction of retraction, the return mechanism 118 being disposed radially outside the push rod 190.According to a seventh aspect, the push rod 190 is movably disposed in a housing 70 accommodating a control board 74 for controlling the drive of the electric motor 31, the control board 74 being provided with a cut-out portion 104 or a hole for preventing interference with the push rod 190.Note that the present invention is not limited to the above embodiments, but includes various modifications. For example, the foregoing embodiments have been described in detail in order to clearly explain the present invention. Therefore, the present invention is not necessarily limited to the embodiments having all the configurations described above. In addition, a part of the configurations of a certain embodiment may be replaced with a configuration of another embodiment, and a configuration of a certain embodiment may be added to a configuration of another embodiment. In addition, a part of the configurations of each embodiment may be removed or replaced with another configuration. It is also possible to add a different configuration to the configuration of each embodiment.The present application claims priority to Japanese Patent Application No. 2017-199492 filed on Oct. 13, 2017. The entire disclosure of Japanese Patent Application No. 2017-199492 filed on Oct. 13, 2017, including the specification, claims, drawings and summary, is incorporated herein by reference in its entirety.LIST OF REFERENCE NUMERALS1: Electromotively driven brake device; 2: inner brake pad; 3: outer brake pad; 4: caliper; 30: caliper body; 31: electric motor; 34: cylinder portion; 50: cylinder bore; 53: piston (pressing member); 70: gear case (housing); 74: control board; 104: cut-out portion; 114: multistage spur gear reduction mechanism (transmission mechanism); 115: planetary gear reduction mechanism (transmission mechanism); 116: ball screw mechanism (screw rod mechanism); 117: thrust force sensor (thrust force detection part); 118: return mechanism; 190: push rod (shaft member); 191: base nut (nut member); 199: helical groove; 201: slant groove; 225: first clutch member; 226: second clutch member; 227: return spring; 228: second clutch member; D: disk rotor.

Claims

An electric motor-driven brake device (1) comprising: a transmission mechanism (114, 115) configured to transmit a rotational force of an electric motor (31); a ball screw mechanism (116) configured to convert the rotational force of the transmission mechanism (114, 115) into a thrust force; a pressing member (53) driven by the ball screw mechanism (116); and a caliper (4) configured to movably support the pressing member (53); wherein the ball screw mechanism (116) comprises: a nut member (191) non-rotatably supported relative to the caliper (4); and a shaft member (190) configured to receive the rotational force from the transmission mechanism (114, 115); wherein the shaft member (190) is movable relative to the nut member (191) in an axial direction of the shaft member (190), and wherein the shaft member (190) is movably disposed in a housing (70) accommodating a control board (74) for controlling the drive of the electric motor (31); and the control board (74) is formed with a cut-out portion (104) or a hole for preventing interference with the shaft member (190), wherein the caliper (4) includes a thrust force detecting part (117) for detecting a reaction force to the thrust force of the pressing member (280); and the thrust force detecting part (117) abuts against the nut member (191) to detect a magnitude of the reaction force transmitted from the nut member (191).The electric motor-driven brake device according to claim 1, wherein in the ball screw mechanism (116), the shaft member (190) drives the pressing member (280).The electric motor-driven brake device according to claim 1 or 2, wherein the transmission mechanism (114, 115) is supported by the caliper (4); and the shaft member (190) is movable relative to the transmission mechanism (114, 115) in the axial direction.The electric motor-driven brake device according to claim 1, wherein the caliper (4) is formed with a lower cylinder bore (50) in which the ball screw mechanism (116) and the pressing member (280) are disposed; and the thrust force detection part (117) is disposed between the nut member (191) and a bottom portion of the cylinder bore (50) and radially outside the shaft member (190).

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