Rotary actuator

A rotary actuator as a drive device of a shift-by-wire system for a vehicle, comprising:

• an electric motor;
• a case that receives the electric motor;
• a shaft that is configured to transmit an output of the electric motor to an outside of the case;
• a seal that seals between the shaft and the case;
• and
• a labyrinth forming portion that forms a labyrinth space in a path that extends from an outside space of the case to a sealing point of the shaft, wherein:
• the sealing point is a point where the shaft is sealed by the seal;
• the labyrinth forming portion includes a tubular portion that is formed separately from the seal and is placed on a radially outer side of the shaft and also on a radially outer side of the sealing point where the outside space is placed;
• the tubular portion includes a drain passage, wherein the drain passage is a space in an inside of the tubular portion and communicates a space, wherein the space is located between the sealing point and the labyrinth space, to the outside space;
• the drain passage is a passage in a form of a labyrinth;
• the tubular portion entirely circumferentially surrounds the seal and has an inner peripheral surface and an outer peripheral surface that are opposed to each other in a radial direction and are placed on a radially outer side of the seal;
• an outer opening of the drain passage opens at the outer peripheral surface of the tubular portion, and an inner opening of the drain passage opens at the inner peripheral surface of the tubular portion at a location placed on one axial side of the seal that is axially opposite from the electric motor;
• and
• the seal radially contacts both the shaft and the inner peripheral surface of the tubular portion all around the shaft.