Electric linear motion actuator and electric disk brake system

An electric linear motion actuator comprising:

• a cylindrical housing;
• an outer ring member mounted in the housing;
• a rotary shaft extending along a center axis of the outer ring member and configured to be rotated by an electric motor;
• planetary rollers mounted between a radially outer surface of the rotary shaft and a radially inner surface of the outer ring member;
• and
• a carrier supported by the rotary shaft so as to be rotatable about the rotary shaft and rotatably supporting the planetary rollers, the carrier including an inner disk;
• wherein a helical groove or circumferential grooves are formed in a radially outer surface of each of the planetary rollers, and a helical rib is formed on the radially inner surface of the outer ring member, the helical rib being in engagement with the helical grooves or the circumferential grooves of the respective planetary rollers, wherein the rotary shaft is kept in frictional contact with the respective planetary rollers, whereby when the rotary shaft rotates, the planetary rollers are configured to rotate about respective axes of the planetary rollers while revolving around the rotary shaft, thereby moving the outer ring member in one axial direction;
• wherein thrust bearings are mounted between the respective planetary rollers and the inner disk of the carrier and configured to receive an axial force applied to the respective planetary rollers from the outer ring member when the outer ring member is moved in the one axial direction;
• wherein a plurality of pairs of aligning seats are provided such that each of the pairs of the aligning seats is provided between each of the planetary rollers and a corresponding one of the thrust bearings or between each of the thrust bearings and the inner disk of the carrier;
• wherein each of the pairs of the aligning seats comprises a convex spherical surface and a concave surface which contacts and guides the convex spherical surface;
• and
• wherein at least one of the convex spherical surface and the concave surface is formed with at least one groove for retaining lubricant, or a large number of independent minute recesses arranged in a random manner for retaining lubricant.