Actuator for vehicle-door locking mechanism

An actuator for vehicle-door locking mechanism comprising:

• a driving motor;
• a first deceleration mechanism for decelerating a rotation of the driving motor;
• a lead screw to which the rotation of the driving motor is transmitted through the first deceleration mechanism;
• a nut member fitted on the lead screw and moved in an axial direction of the lead screw in accordance with a rotation of the lead screw;
• an output mechanism for causing a door locking mechanism to perform one of a locking operation and an unlocking operation in association with the movement of the nut member;
• a second deceleration mechanism for decelerating a rotation of the lead screw;
• and
• an automated bidirectional-ring mechanism to which the rotation of the lead screw is transmitted through the second deceleration mechanism, the automatic bidirectonal-returning mechanism automatically returning the nut member to an initial position after the output mechanism performs one of the locking operation and the unlocking operation, and the automatic bidirectional-returning mechanism including:
• a projection having a stopper function, provided on a mounting base and having both sides which are parallel with each other;
• a single home-returning coil spring having engagement end portions on both sides, for bringing the engagement end portions into contact with both sides of the projection at a given pressure;
• and
• a biasing member to which the rotation of the lead screw is transmitted through the second deceleration mechanism, the biasing member biasing one engagement end portion of the home-returning coil spring in a circumferential direction of the coil spring from one side of the projection when the nut member moves in one direction from the initial position, and biasing another engagement end portion of the home returning coil spring in the circumferential direction of the coil spring from other side of the projection when the nut member moves in another direction from the initial position.