Electric linear motion actuator and electric brake system

An electric linear motion actuator comprising:

• a rotary shaft (4) to which the rotation of a rotor shaft (2a) of an electric motor (2) is to be transmitted;
• a housing (1) having a radially inner surface;
• an outer race member (5) fitted in the radially inner surface of the housing and provided around the rotary shaft;
• a carrier (6) comprising a carrier body (6a and 6f) and support pins (6c) supported by the carrier body;
• and
• a plurality of planetary rollers (7) disposed between the outer race member and the rotary shaft and rotatably supported by the respective support pins of the carrier;
• 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 (5b) 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 (5a) 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 in an axial direction, thereby driving an object (33) to be driven coupled to the output member;
• wherein axial movement of the carrier relative to the housing is restricted, and the outer race member is rotationally fixed and is axially slidably fitted in the radially inner surface of the housing, such that, upon rotation of the rotary shaft, the outer race member is axially moved relative to the housing and the carrier is held against axial movement relative to the housing, whereby the outer race member serves as the output member;
• wherein the planetary rollers are disposed axially between the carrier body and the object to be driven;
• and
• wherein the outer race member, the housing, the helical rib and the carrier body are arranged such that while an axial portion of the outer race member where the helical rib is present is entirely fitted in the radially inner surface of the housing, the radially outer surface of the carrier body is surrounded by the helical rib.