Actuator for electric park brake system and self-locking mechanism thereof

An actuator for an electric parking brake system, operable to apply or release the brake, the actuator comprising:

• a motor including a shaft;
• an output member;
• and
• a speed reduction device connected between the motor and the output member, the speed reduction device including:
• a transmission mechanism connected to the shaft;
• and
• a self-locking mechanism connected with the transmission mechanism, the transmission mechanism including an output gear, the self-locking mechanism includes a fixed wheel, a movable wheel rotatable relative to the fixed wheel, and a spring sleeved on a part of the fixed wheel and a part of the movable wheel, the movable wheel being connected between the output gear and the output member for transmitting the torque from the output gear to the output member, an inner diameter of the spring in its neutral state being less than or equal to an outer diameter of the part of the fixed wheel and the part of the movable wheel on which the spring is sleeved,
• wherein the provision of the spring allows the torque to be transmitted from the motor to the output member, thereby operating the brake, and
• wherein when the output member rotates under an external force to generate a tendency to release the brake, the movable wheel rotates relative to the fixed wheel in a winding direction of the spring under the driving of the output member, the frictional force between the spring and the fixed wheel and movable wheel causes the spring to tighten and hold onto the fixed wheel to thereby prevent the movable wheel from rotating further.