Electric brake actuator

An electric brake actuator configured to push a friction member onto a rotary body that rotates together with a wheel, comprising:

• a main body;
• a piston held by the main body so as to be advanceable and retractable, the piston being configured to push the friction member toward the rotary body by advancing;
• an electric motor;
• a motion converting mechanism including an input shaft configured to be rotated by the electric motor, the motion converting mechanism being configured to convert a rotating motion of the electric motor into an advancing and retracting movement of the piston, and
• a torque imparting device including a torsion spring and configured to impart, to the input shaft, a torque in a direction in which the piston retracts, in dependence on an elastic torque generated by the torsion spring,
• wherein the torque imparting device includes:
• a stator fixed to the main body and configured to retain, by one of a plurality of first retaining portions thereof, a first retained portion provided at one end portion of the torsion spring;
• a rotor retaining the other end portion of the torsion spring, the rotor being configured (i) to rotate together with the input shaft relative to the stator so as to twist the torsion spring in a state in which the input shaft receives a reaction force of a force by which the piston pushes the friction member onto the rotary body and (ii) to be allowed to rotate relative to the input shaft in a state in which the input shaft does not receive the reaction force;
• a retained-position-change allowing mechanism configured to allow the first retained portion provided at the one end portion of the torsion spring to be retained by another one of the plurality of first retaining portions of the stator when the elastic torque of the torsion spring exceeds a set upper-limit torque, so as to decrease the elastic torque;
• and
• a lower-limit torque ensuring mechanism configured to permit a second retained portion provided on the rotor to be retained by a second retaining portion provided at the one end portion of the torsion spring, so as to prohibit the elastic torque of the torsion spring from becoming smaller than a set lower-limit torque.