Patent ID: 8109370

Claim:
An electric linear-motion actuator for linearly driving a member to be driven by converting the rotary motion of an electric motor to a linear motion, the electric linear-motion actuator comprising: a motor rotor shaft having an axis; an outer ring member mounted around the radially outer surface of the rotor shaft; and a planetary roller carrier rotatable about the axis of the rotor shaft; and a plurality of planetary rollers supported by said carrier for rotation individually about planetary roller axes and for rotation together around the axis of the rotor shaft, said planetary rollers being disposed between a radially outer surface of the rotor shaft and a radially inner surface of the outer ring member such that, when the rotor shaft rotates, the planetary rollers rotate about the axis of the rotor shaft while simultaneously rotating about the planetary roller axes, respectively; wherein a helical rib is formed on one of the radially outer surface of the rotor shaft and the radially inner surface of the outer ring member; wherein a helical groove is formed in a radially outer surface of each of the planetary rollers, said helical rib being in engagement with the helical grooves of the respective planetary rollers, said helical grooves being equal in pitch to said helical rib, and different in lead angle from said helical rib, such that, when said planetary rollers rotate about said rotor shaft while simultaneously rotating about the planetary roller axes, said planetary rollers move in an axial direction of the rotor shaft relative to the rotor shaft, thereby converting the rotary motion of the rotor shaft to a linear motion of the planetary rollers; wherein said planetary rollers and said planetary roller carrier are arranged to move together axially while the planetary rollers are rotatable with respect to said planetary roller carrier; wherein rolling thrust bearings are provided between said planetary rollers and said planetary roller carrier to support the planetary roller carrier relative to said planetary rollers; and wherein said helical grooves extend in the same helical direction as said helical rib but at a different lead angle than said helical rib.