Actuator and assembling method thereof

An actuator comprising:

• an electric motor;
• a gear that transmits a drive torque of the electric motor to a shaft of a drive subject to rotate the shaft of the drive subject;
• a spring that has one end portion, which is installed to the gear, wherein the spring generates an urging torque for urging the shaft in a rotational direction to rotate a rotational position of the shaft to a predetermined position;
• and
• an installation member, to which another end portion of the spring is installed, wherein:
• the gear includes:
• a radially inner guide that is formed around a rotational axis of the gear;
• a radially outer guide that is configured into a tubular form and is placed on a radially outer side of the radially inner guide while a receiving hole, which is configured into an annular form, is interposed between the radially inner guide and the radially outer guide;
• and
• a first slit that is located adjacent to an opening of the receiving hole and is formed by recessing a portion of the radially outer guide, wherein the one end portion of the spring is engaged to or is held by the first slit;
• the spring includes a coil that is spirally wound and is located between the one end portion and the another end portion of the spring, and the coil is resiliently deformably received in an inside of the receiving hole;
• the installation member includes:
• a covering wall that is placed adjacent to an opposite side of the receiving hole, which is opposite from the opening of the receiving hole, wherein the covering wall is located on a radially outer side of the radially outer guide in such a manner that the covering wall partially overlaps with the radially outer guide while a predetermined radial gap is interposed between the radially outer guide and the covering wall;
• and
• a second slit that is formed by recessing a portion of the covering wall, wherein the another end portion of the spring is engaged to or held by the second slit;
• the second slit has an opening, which opens at an axial end surface of the covering wall in an axial direction of the rotational axis, and the second slit includes:
• a second slit hole that extends linearly from the opening of the second slit to a deep side in the axial direction of the rotational axis or extends from the opening of the second slit to the deep side in the axial direction of the rotational axis while the second slit is bent in a middle of the second slit, wherein the another end portion of the spring is insertable into the second slit hole from the opening of the second slit toward the deep side;
• and
• a tilted slit portion, which is formed at an opening side of the second slit hole, wherein the another end portion of the spring is moved along the tilted slit portion to twist the coil to a predetermined set angle at a time of installing the another end portion of the spring to the second slit.