Ball screw device

A ball screw device comprising:

• a screw shaft in which an outer peripheral raceway surface is provided on an outer peripheral surface;
• a nut into which the screw shaft is inserted and in which an inner peripheral raceway surface is provided on an inner peripheral surface;
• a plurality of balls arranged on a raceway between the outer peripheral raceway surface and the inner peripheral raceway surface;
• and
• at least one deflector provided with an S-shaped groove surface that circulates the balls, wherein
• the outer peripheral surface of the screw shaft is provided with a recess portion that is recessed to an inner side in a radial direction and that houses the deflector, and
• an inner peripheral surface of the recess portion and an outer peripheral surface of the deflector are not circular when viewed from an outer side in the radial direction of the screw shaft,
• wherein
• the S-shaped groove surface includes:
• a central groove surface on which the balls sink to the inner side in the radial direction, and
• two entrance/exit groove surfaces which are respectively provided on both sides of the central groove surface and through which the balls enter and exit,
• a groove shape of the entrance/exit groove surfaces is larger than a groove shape of the outer peripheral raceway surface,
• a deflector-side opening of the S-shaped groove surface is provided in the outer peripheral surface of the deflector,
• a screw shaft-side opening of the outer peripheral raceway surface that continues to the deflector-side opening is provided in the inner peripheral surface of the recess portion, and
• at least a part of a boundary line between the deflector-side opening and the screw shaft-side opening viewed from the outer side in the radial direction includes a linear portion extending linearly in an axial direction and disposed at the entrance/exit groove surfaces.