Rotary-linear motion converter and shift actuator

A rotary-linear motion converter, including:

• a housing;
• a ball screw mechanism including a screw shaft having a spiral shaft-side ball screw groove on an outer-circumferential surface thereof, a nut having a spiral nut-side ball screw groove on an inner-circumferential surface thereof, and a plurality of balls arranged so as to roll in a load path consisting of the nut-side ball screw groove and the shaft-side ball screw groove;
• and
• an output shaft that is supported so as to move in an axial direction with respect to the housing but not to relatively rotate,
• wherein one of the screw shaft and the nut configures a linear motion member that undergoes a linear motion during use, and the other of the screw shaft and the nut configures a rotary member that undergoes a rotary motion during use, and
• the linear motion member and the output shaft are connected by a connecting structure, the connecting structure, including:
• a first member, which is one of the linear motion member and the output shaft, having a male screw portion on an outer-circumferential surface thereof;
• a second member, which is the other of the linear motion member and the out put shaft, having a female screw portion on an inner-circumferential surface that is screwed with the male screw portion;
• a rotation restraining member placed between the first member and the second member and preventing relative rotation between the first member and the second member;
• and
• an elastic member applying elasticity in an axial direction between the first member and the second member.