A ball screw device including a low-cost retainer that is disposed between a ball screw shaft and a ball nut and has a flange portion, a steering system using the ball screw device, and a method for producing the retainer of the ball screw device are provided. The ball screw device includes the ball screw shaft, the ball nut, rolling balls, and the retainer. Both side surfaces of each of retainer grooves are formed so as to allow radially outward movement of the rolling balls and to restrict radially inward movement thereof, and the retainer has a weld joint at both of the opposite ends of each retainer groove in the axial direction of the retainer.

A ball screw device including a low-cost retainer that is disposed between a ball screw shaft and a ball nut and has a flange portion, a steering system using the ball screw device, and a method for producing the retainer of the ball screw device are provided. The ball screw device includes the ball screw shaft, the ball nut, rolling balls, and the retainer. Both side surfaces of each of retainer grooves are formed so as to allow radially outward movement of the rolling balls and to restrict radially inward movement thereof, and the retainer has a weld joint at both of the opposite ends of each retainer groove in the axial direction of the retainer.

A cylindrical retainer configured to retain balls in a rollable manner is provided inside a ball screw nut. The retainer has retainer grooves each having a shape of an elongated hole that extends in an axial direction of a ball screw shaft so as to be inclined at a predetermined angle. A first end of the ball screw nut and a first end of the retainer, which is one of two ends of the retainer that is closer to the first end of the ball screw nut, are spaced away from each other by a distance. The terminal end of the retainer groove closest to the second end of the retainer and a ball that is closest to the second end of the ball screw nut are spaced away from each other by a distance. The distance is set equal to or larger than the distance.

A cylindrical retainer configured to retain balls in a rollable manner is provided inside a ball screw nut. The retainer has retainer grooves each having a shape of an elongated hole that extends in an axial direction of a ball screw shaft so as to be inclined at a predetermined angle. A first end of the ball screw nut and a first end of the retainer, which is one of two ends of the retainer that is closer to the first end of the ball screw nut, are spaced away from each other by a distance. The terminal end of the retainer groove closest to the second end of the retainer and a ball that is closest to the second end of the ball screw nut are spaced away from each other by a distance. The distance is set equal to or larger than the distance.

A ball screw device is provided, including a retainer that can properly retain balls. The difference between a diameter being the pitch circle diameter of the ball screw device and the outside diameter of the rack shaft is set to be equal to or larger than the difference between the bore diameter of a ball screw nut and the diameter. The thickness center diameter of the retainer is set to be smaller than the diameter. Even when the inclination angle is reduced, the clearance between the inclined surfaces of each retainer groove on the radial inside can be easily set to be smaller than the diameter of the balls because the bore diameter of the retainer is set to be smaller. Thus, even when the inclination angle of the inclined surfaces is set to be smaller, the balls can be properly retained.

A ball screw device is provided, including a retainer that can properly retain balls. The difference between a diameter being the pitch circle diameter of the ball screw device and the outside diameter of the rack shaft is set to be equal to or larger than the difference between the bore diameter of a ball screw nut and the diameter. The thickness center diameter of the retainer is set to be smaller than the diameter. Even when the inclination angle is reduced, the clearance between the inclined surfaces of each retainer groove on the radial inside can be easily set to be smaller than the diameter of the balls because the bore diameter of the retainer is set to be smaller. Thus, even when the inclination angle of the inclined surfaces is set to be smaller, the balls can be properly retained.

A ball screw device and a steering system that include a retainer having more uniform stiffness are provided. Between a rack shaft and a ball screw nut, a cylindrical retainer having a plurality of retainer grooves that retain balls in a rollable manner is provided. Each retainer groove has two short inner surfaces that intersect the extending direction of the retainer groove and two long inner surfaces that intersect these short inner surfaces and extend along the extending direction of the retainer groove. In each of interior-angle portions where the short inner surfaces and the long inner surfaces intersect, a corner round surface is formed. The radius of the corner round surface is set to be smaller than one half of the width of the retainer groove.

A ball screw device and a steering system that include a retainer having more uniform stiffness are provided. Between a rack shaft and a ball screw nut, a cylindrical retainer having a plurality of retainer grooves that retain balls in a rollable manner is provided. Each retainer groove has two short inner surfaces that intersect the extending direction of the retainer groove and two long inner surfaces that intersect these short inner surfaces and extend along the extending direction of the retainer groove. In each of interior-angle portions where the short inner surfaces and the long inner surfaces intersect, a corner round surface is formed. The radius of the corner round surface is set to be smaller than one half of the width of the retainer groove.

An electric power steering apparatus is configured to provide steering assistance as rotary torque of a driving toothed-pulley fixedly fitted to a rotary shaft of an electric motor is transmitted through a toothed belt to a driven toothed-pulley that rotates together with a ball screw nut in an integrated manner. The electric power steering apparatus is configured such that the amount of axial travel of a rack shaft is limited when a rack end and a housing come into contact with each other in the axial direction. The electric power steering apparatus includes a tilt allowing portion configured to cause the ball screw nut to tilt relative to a ball screw shaft such that the distance between the center of rotation of the driven toothed-pulley and that of the driving toothed-pulley increases when the rack end and the housing come into contact with each other in the axial direction.

An electric power steering apparatus is configured to provide steering assistance as rotary torque of a driving toothed-pulley fixedly fitted to a rotary shaft of an electric motor is transmitted through a toothed belt to a driven toothed-pulley that rotates together with a ball screw nut in an integrated manner. The electric power steering apparatus is configured such that the amount of axial travel of a rack shaft is limited when a rack end and a housing come into contact with each other in the axial direction. The electric power steering apparatus includes a tilt allowing portion configured to cause the ball screw nut to tilt relative to a ball screw shaft such that the distance between the center of rotation of the driven toothed-pulley and that of the driving toothed-pulley increases when the rack end and the housing come into contact with each other in the axial direction.