Ball screw device

A ball screw device comprising:

• a housing;
• a nut rotatably supported by the housing and having a first track path on an inner circumferential surface;
• an outer circumferential screw shaft that is a cylindrical component penetrating the nut, has a second track path on an outer circumferential surface, and has a third track path on an inner circumferential surface;
• and
• a plurality of first balls disposed between the first track path and the second track path;
• an inner circumferential screw shaft extending in an axial direction parallel to the outer circumferential screw shaft, one end of the inner circumferential screw shaft pointing in a first direction and the other end of the inner circumferential screw shaft pointing in a second direction, the inner circumferential screw shaft being configured to be inserted into the outer circumferential screw shaft and having a fourth track path on an outer circumferential surface of the inner circumferential screw shaft;
• a plurality of second balls disposed between the third track path and the fourth track path;
• a first stopper fixed to an inner circumferential side of the outer circumferential screw shaft and closer to an end in the first direction;
• a second stopper fixed closer to an end of the inner circumferential screw shaft in the second direction;
• and
• a third stopper fixed closer to an end of the outer circumferential screw shaft in the second direction,
• wherein a track of the first ball and a track of the second ball are helixes running in a same direction,
• the first stopper includes a first protrusion that protrudes in the second direction and rotates together with a rotation of the outer circumferential screw shaft,
• the second stopper includes a second protrusion that protrudes in the first direction, enters a track along which the first protrusion rotates at a movement of the inner circumferential screw shaft in the first direction, and comes in contact with the first protrusion,
• the nut has a restriction protrusion that protrudes in the second direction and rotates together with the rotation of the nut, and
• the third stopper includes a third protrusion that protrudes in the first direction, enters a track along which the restriction protrusion rotates at a movement of the outer circumferential screw shaft in the first direction, and comes in contact with the restriction protrusion.