Patent ID: 8827051

Claim:
An electric brake assembly including an electric linear motion actuator for converting the rotary motion of an electric motor to a linear motion, thereby linearly driving a brake member, and pressing the brake member against a member to be braked, the electric linear-motion actuator comprising: a rotary shaft having an axis and configured to be rotated by the electric motor; an outer ring member mounted around a radially outer surface of the rotary shaft; a planetary roller carrier rotatable about the axis of the rotary 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 rotary shaft, said planetary rollers being disposed between a radially outer surface of the rotary shaft and a radially inner surface of the outer ring member such that, when the rotary shaft rotates, the planetary rollers rotate about the axis of the rotary shaft while simultaneously rotating about the planetary roller axes, respectively; wherein a helical rib is formed on the radially inner surface of the outer ring member; and 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, so as to cause relative axial movement between said outer ring member and said planetary rollers when said planetary rollers rotate about said rotary shaft while simultaneously rotating about the planetary roller axes; wherein first thrust bearings are respectively disposed between the planetary rollers and the carrier to support the respective planetary rollers for rotation about the planetary roller axes, and a second thrust bearing is provided to support the carrier for rotation about the axis of the rotary shaft; 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.