Abstract: An electric power steering apparatus comprises a steering assisting electric motor having an output shaft and a speed reduction mechanism. The speed reduction mechanism includes conical first and second gears to be engaged with each other. The first and second gears include a plurality of teeth each having a tooth surface. The mutually corresponding tooth surfaces of the first and second gears each include engaging regions to be engaged with each other. A center position in a tooth width direction of the engaging region of each tooth surface of the first gear in an unloaded state is offset by a first offset amount from center position in the tooth width direction of the tooth surface of the first gear to a relatively small end portion of the tooth of the first gear.

Abstract: A first ball circulating hole and a second ball circulating hole for connecting a circulator are bored midway at a screw groove formed on an inner circumference of a ball nut, an intermediate groove path between the first and second ball circulating holes becomes the range of a ball screw track for circulating balls, and other ranges become a first outer track and a second outer track which are not the ball screw track. By making the groove depth of the intermediate groove path deeper than the groove depth of a first groove path of the first outer track and the groove depth of a second groove path of the second outer track, steps are formed between the ball screw track and the two outer tracks. These steps prevent an outflow of the balls from the intermediate groove path to the respective groove paths of the outer tracks.

Abstract: A ball screw (26) includes a screw shaft (29) a nut (25) surrounding the screw shaft (29), and a plurality of balls (30) engageable with the screw shaft (29) and the nut (25). The ball screw (26) includes first and second raceways (S, K). The first raceway (S) is defined between the screw shaft (29) and the nut (25), and has first and second ends (S1, S2). The second raceway (K) has first and second ends (K1, K2) respectively connected to the first and second ends (S1, S2) of the first raceway (S) for circulating the balls (30) into the first raceway (S). The second raceway (K) accommodates an odd number of balls (30) at the maximum at a time.

Abstract: An electric power steering apparatus comprises a speed reduction mechanism for decelerating the rotation of an output shaft in an electric motor for steering assist. The speed reduction mechanism comprises a driving gear connected to the output shaft in the electric motor and a driven gear meshed with the driving gear. One of respective tooth sections in the driving gear and the driven gear includes a tooth section formed of a material having a relatively low hardness, and the other tooth section includes a tooth section formed of a material having a relatively high hardness. The profile of the tooth section formed of the material having a relatively low hardness is shifted in the direction in which the thickness at the root of the teeth of the tooth section is increased. The profile of the tooth section formed of the material having a relatively high hardness is shifted in the direction in which the thickness at the root of the teeth of the tooth section is decreased.

Abstract: An electric power steering apparatus comprises a steering assisting electric motor having an output shaft and a speed reduction mechanism. The speed reduction mechanism includes conical first and second gears to be engaged with each other. The first and second gears include a plurality of teeth each having a tooth surface. The mutually corresponding tooth surfaces of the first and second gears each include engaging regions to be engaged with each other. A center position in a tooth width direction of the engaging region of each tooth surface of the first gear in an unloaded state is offset by a first offset amount from center position in the tooth width direction of the tooth surface of the first gear to a relatively small end portion of the tooth of the first gear.

Abstract: An electric power steering apparatus comprises a speed reduction mechanism for decelerating the rotation of an output shaft in an electric motor for steering assist. The speed reduction mechanism comprises a driving gear connected to the output shaft in the electric motor and a driven gear meshed with the driving gear. One of respective tooth sections in the driving gear and the driven gear includes a tooth section formed of a material having a relatively low hardness, and the other tooth section includes a tooth section formed of a material having a relatively high hardness. The profile of the tooth section formed of the material having a relatively low hardness is shifted in the direction in which the thickness at the root of the teeth of the tooth section is increased. The profile of the tooth section formed of the material having a relatively high hardness is shifted in the direction in which the thickness at the root of the teeth of the tooth section is decreased.

Abstract: A first ball circulating hole and a second ball circulating hole for connecting a circulator are bored midway at a screw groove formed on an inner circumference of a ball nut, an intermediate groove path between the first and second ball circulating holes becomes the range of a ball screw track for circulating balls, and other ranges become a first outer track and a second outer track which are not the ball screw track. By making the groove depth of the intermediate groove path deeper than the groove depth of a first groove path of the first outer track and the groove depth of a second groove path of the second outer track, steps are formed between the ball screw track and the two outer tracks. These steps prevent an outflow of the balls from the intermediate groove path to the respective groove paths of the outer tracks.