Linear actuator with anti-reverse-rotation mechanism

A linear actuator comprising:

• a housing member;
• a pair of axially opposed bearings with built-in one-way clutch, each of said bearings including
• an outer race and an inner race concentric with said outer race,
• a plurality of rolling elements capable of bearing both a radial and a thrust load and assembled between said outer race and said inner race, and
• a plurality of clutch elements assembled between said outer race and said inner race in juxtaposed relation to said rolling elements in the axial direction of said bearing, said clutch elements being cooperative to permit relative rotation between said outer race and said inner race in one direction only,
• wherein said bearings are assembled in said housing member with the respective outer races firmly connected to said housing member such that a direction in which rotation of the inner race of one of said bearings is locked is opposite to a direction in which rotation of the inner race of the other bearing is locked;
• a ball screw shaft extending through the respective inner races of said bearings and relatively and rotatably supported on said inner races with a bearing bushing disposed therebetween, said ball screw shaft having a ball screw portion formed thereon and being driven to rotate in both forward and reverse directions by means of a rotary drive source;
• a ball nut threaded with said ball screw portion of said ball screw shaft with a plurality of balls disposed therebetweern;
• an actuating member supported by said housing member in such a manner that said actuating member is reciprocally movable in unison with said ball nut in the axial direction of said ball screw shaft for projection and contraction relative to said housing member while it is prevented from rotating about the axis of said ball screw shaft;
• a first friction collar and a second friction collar rotatably mounted on said ball screw shaft;
• at least one load transmitting collar fixedly mounted on said ball screw shaft, said load transmitting collar having a first end face facing an end face of said inner race of one of said bearings with said first friction collar disposed therebetween, and a second end face facing an end face of said inner race of the other bearing with said second friction collar disposed therebetween, said inner race of said one bearing being locked against rotation when said ball screw shaft is subjected to a first thrust load tending to retract said ball screw shaft, said inner race of said other bearing being locked against rotation when said ball screw shaft is subjected to a second thrust load tending to extend said ball screw shaft, wherein when said ball screw shaft is subjected to said first thrust load, said load transmitting collar transmits the first thrust load through said first friction collar to said inner race of said one bearing, and when said ball screw shaft is subjected to said second thrust load, said load transmitting collar transmits the second thrust load through said second friction collar to said inner race of said other bearing.