A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A rotational translation unit includes a rotation portion that rotates relative to a housing upon receiving an input of torque output from a speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion relative to the housing. A clutch is provided between a first transmission portion and a second transmission portion that are rotatable relative to the housing, and the clutch allows transmission of the torque between the first transmission portion and the second transmission portion in an engaged state of the clutch, and interrupts the transmission of the torque between the first transmission portion and the second transmission portion in a disengaged state of the clutch. A return spring is capable of urging the rotational translation unit in a direction away from the clutch relative to the housing.

A prime mover includes a stator fixed to the housing and a rotor rotatable relative to the stator. The prime mover outputs torque by being supplied with electric power. A speed reducer reduces the torque of the prime mover and outputs the reduced torque. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving the torque from the speed reducer, and a translation portion that moves relative to the housing in an axial direction. A clutch allows torque transmission in an engaged state, and interrupts the torque transmission in a disengaged state. A state changing unit changes the state of the clutch by receiving a force along the axial direction from the translation portion. Cogging torque generated between the rotor and the stator is set to such a magnitude that the rotor is stoppable at any rotation position relative to the stator.

An object of the present invention is to provide an electric disc brake suitable for improving responsiveness. The electric disc brake includes: a rotation linear motion conversion mechanism configured to convert rotational motion of the rotary member into linear motion; a return spring configured to store torque for retreating the piston according to rotation of a rotary member; and a clutch configured to make a transition between a state in which the torque is able to be stored in the return spring and a state in which storage of the torque in the return spring is deterred. The clutch includes: a first disc and a third disc configured to rotate together with the rotary member, and a second disc disposed between the first disc and the third disc. The return spring has one end portion coupled to the caliper body and another end portion coupled to the second disc.

A prime mover includes a stator fixed to a housing and a rotor relatively rotatable relative to the stator. The prime mover outputs torque from the rotor by being supplied with electric power. A speed reducer reduces the torque of the prime mover and outputs the reduced torque. One bearing portion rotatably supports the rotor. The speed reducer includes an input portion that is coaxial and integrally rotatable with the rotor and receives the torque from the rotor.

A prime mover includes a stator fixed to a housing, and a rotor rotatable relative to the stator. The prime mover is capable of outputting torque from the rotor by being supplied with electric power. A speed reducer is capable of reducing the torque of the prime mover and outputting the reduced torque. The speed reducer includes a sun gear rotatable integrally with the rotor, and planetary gears capable of revolving in a circumferential direction of the sun gear while rotating in a state of meshing with the sun gear. A gear width of the sun gear is set such that a length in the axial direction by which the sun gear and the planetary gear are overlapped is smaller than a gear width of the planetary gear.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A prime mover includes a stator fixed to a housing, and a rotor rotatable relative to the stator. The prime mover outputs torque from the rotor by being supplied with electric power. A speed reducer reduces the torque of the prime mover and outputs the reduced torque. The speed reducer includes a sun gear to which the torque from the rotor is input, and a planetary gear that revolves in a circumferential direction of the sun gear while rotating in a state of meshing with the sun gear. The rotor and the sun gear are formed separately, and are disposed coaxially so as to be integrally rotatable.

Torque of a prime mover is input into a sun gear. A planetary gear revolves in a circumferential direction of the sun gear while rotating and meshing with the sun gear. A carrier has an annular shape, rotatably supports the planetary gear, and is rotatable relative to the sun gear. A first ring gear is fixed to a housing, and meshes with the planetary gear. A second ring gear meshes with the planetary gear, is different from the first ring gear in number of teeth of a tooth portion, and outputs torque to a rotation portion. At least a part of the sun gear in an axial direction is located radially inward of the carrier. At least a part of the first ring gear and at least a part of the second ring gear in the axial direction are located radially outward of the carrier.