Patent ID: 8579090

Claim:
An electric linear motion actuator comprising: a rotary shaft to which the rotation of a rotor shaft of an electric motor is to be transmitted; a housing having a radially inner surface; an outer race member fitted in the radially inner surface of the housing and provided around the rotary shaft; a carrier having a plurality of support pins; a plurality of planetary rollers disposed between the outer race member and the rotary shaft and rotatably supported by the respective support pins of the carrier; and an elastic member biasing the planetary rollers against a radially outer surface of the rotary shaft; wherein the planetary rollers are configured to revolve around the rotary shaft while rotating about axes of the respective planetary rollers when the rotary shaft rotates; wherein a helical rib is formed on a radially inner surface of the outer race member, and wherein each of the planetary rollers has, on a radially outer surface thereof, a plurality of circumferential grooves which are arranged at the same pitch as the helical rib and in which the helical rib is engaged, or a helical groove in which the helical rib is engaged, said helical groove having a different lead angle from the helical rib and being arranged at the same pitch as the helical rib, thereby axially moving the outer race member and the carrier relative to each other, whereby the rotary motion of the rotary shaft is converted to a linear motion of an output member, thereby driving an object to be driven coupled to the output member; wherein said planetary rollers are not in threaded engagement with said rotary shaft; and wherein the axial movement of the carrier is restricted, and the outer race member is rotationally fixed and is axially slidably fitted in the radially inner surface of the housing, whereby the outer race member serves as the output member.