A clutch is configured, when a driving-side rotor is in a non-driven-rotated state, to prevent rotation of a driven-side rotor by setting a rolling element in a lock state in which the rolling element is held by a control surface and a collar. The clutch is configured so that when the driving-side rotor is driven and rotated in the lock state, the driving-side rotor pushes the rolling element via two circumferential holders in a rotation direction to release the rolling element from the lock state. Each of the two circumferential holders includes a guide portion configured to guide the rolling element toward a radially inner side of the collar when the rolling element is released from the lock state.

An electric-motor-operated parking brake system carries out metered actuation without a force and travel sensor. A control unit initiates a primary tensioning process with observation of the current, and wherein secondary or tertiary tensioning processes with increased brake application force are executed exclusively automatically by the control unit if monitoring of the stationary state during an energization interval detects an undesired vehicle movement.

An electric-motor-operated parking brake system carries out metered actuation without a force and travel sensor. A control unit initiates a primary tensioning process with observation of the current, and wherein secondary or tertiary tensioning processes with increased brake application force are executed exclusively automatically by the control unit if monitoring of the stationary state during an energization interval detects an undesired vehicle movement.

A clutch includes a roller arranged between a clutch housing and a driven side rotating body. The roller is rotated about a rotation axis of a drive side rotating body together with the drive side rotating body when the drive side rotating body is rotationally driven. The roller hinders rotation of the driven side rotating body by being sandwiched between the clutch housing and the driven side rotating body when the drive side rotating body is not rotationally driven. The support member sandwiches the roller between the clutch housing and the driven side rotating body. The support member rotates about the rotation axis of the drive side rotating body together with the drive side rotating body. The grease is arranged between the clutch housing and the roller. The support member restricts rotation of the roller about a central axis of the roller.

A clutch is configured, when a driving-side rotor is in a non-driven-rotated state, to prevent rotation of a driven-side rotor by setting a rolling element in a lock state in which the rolling element is held by a control surface and a collar. The clutch is configured so that when the driving-side rotor is driven and rotated in the lock state, the driving-side rotor pushes the rolling element via two circumferential holders in a rotation direction to release the rolling element from the lock state. Each of the two circumferential holders includes a guide portion configured to guide the rolling element toward a radially inner side of the collar when the rolling element is released from the lock state.

A locking-type reverse input blocking clutch includes an unlocking piece having unlocking portions for unlocking an output-side member. The portion of the unlocking piece other than the unlocking portions (i.e., its longitudinally central portion and intermediate portions) is inserted in a recess formed in an inner ring of the output-side member so as to open to the end surface of the inner ring to which torque is applied, and open to the outer periphery of the inner ring so that the entire unlocking piece is located axially within the output-side member. This clutch is thus small in axial dimension, and compact in entire size.

A brake shoe brakes a drum rotor by being pressed against an inner peripheral surface of the drum rotor. A friction material of the brake shoe includes a first lining material, a second lining material, and a third lining material. The first lining material is one end portion of the friction material in an arc shape opposing the inner peripheral surface of the drum rotor in a rotation direction of the drum rotor. The second lining material is another end portion of the friction material in the rotation direction of the drum rotor. The third lining material is positioned between the one end portion and the another end portion in the rotation direction of the drum rotor, and is produced such that the third lining material wears earlier than the first lining material and the second lining material.

A brake shoe brakes a drum rotor by being pressed against an inner peripheral surface of the drum rotor. A friction material of the brake shoe includes a first lining material, a second lining material, and a third lining material. The first lining material is one end portion of the friction material in an arc shape opposing the inner peripheral surface of the drum rotor in a rotation direction of the drum rotor. The second lining material is another end portion of the friction material in the rotation direction of the drum rotor. The third lining material is positioned between the one end portion and the another end portion in the rotation direction of the drum rotor, and is produced such that the third lining material wears earlier than the first lining material and the second lining material.

A clutch includes a rotatable inputting member, a rotatable outputting member, a stationary member, and a contact member. The outputting member includes an output contact portion. The contact member is positioned between the outputting member and the stationary member and includes an arcuate first contact surface and a second contact surface. When the input torque for rotating the inputting member is inputted, the outputting member and the contact member rotate in contact with the inputting member. When a reverse input torque for rotating the outputting member is inputted, the outputting member is spaced from the inputting member, and the output contact portion of the outputting member urges the first contact surface against the stationary member by urging the second contact surface of the contact member thereby to prevent rotation of the outputting member.

An electric-motor-operated parking brake system carries out metered actuation without a force and travel sensor. A control unit initiates a primary tensioning process with observation of the current, and wherein secondary or tertiary tensioning processes with increased brake application force are executed exclusively automatically by the control unit if monitoring of the stationary state during an energization interval detects an undesired vehicle movement.