Abstract: A ball screw nut of a ball screw device is fastened to a motor shaft by engaging a male thread portion thereof with a female thread portion of the motor shaft. In a case where, in a movement pathway for balls, an area where the balls roll under load from a rack shaft and the ball screw nut is set as a load area, an area that does not receive the load is set as a no-load area, and areas for transition from the load area to the no-load area are set as transition areas, the male thread portion is formed such that the transition area on the nut-side joint portion-side closest to a seating surface does not overlap phase ranges of cut portions in a state where the ball screw nut is fastened to the motor shaft.

Abstract: A knurled press-fitting portion and an annular groove, which receives foreign matter and is formed to extend in a circumferential direction in front of the press-fitting portion of a cylindrical protruding portion, are provided at an outer peripheral surface of the protruding portion of an output shaft. A fitting portion, which is fitted to a coupling tube by press-fitting, is formed at an outer periphery of an opening end of the protruding portion. An outer peripheral surface of the cylindrical fitting portion and an inner peripheral surface of the cylindrical coupling tube coupled to a Z4 gear are fitted and coupled to each other. The annular groove is closed by the fitting portion in a state where the protruding portion and the coupling tube are coupled to each other. The annular groove is configured so as to prevent foreign matter from being discharged toward a bearing gear.

Abstract: A preload adjusting plug is inserted through a communication hole extending through center portions of a Z1 gear, a Z4 gear, and an inner ring of a nutation gear. A male thread portion is formed at an outer periphery of one end of the preload adjusting plug, and is screwed to a female thread portion formed at an inner periphery of the Z1 gear. A disc-shaped flange portion extending radially outward is formed at the other end of the preload adjusting plug, and axially presses a back face of the Z4 gear through a bearing. The preload adjusting plug applies predetermined preloads to meshing portions in the nutation gear mechanism.

Abstract: A second shaft is configured by a shaft portion extending outside a housing in which a nutation gear mechanism is housed, a housing portion, and a cylindrical portion. A communicating hole, through which an outside and an inside of the housing portion communicate with each other, is formed in the shaft portion. A preload applying mechanism includes a preload adjusting plug that is screwed to the housing portion and is able to be operated from outside through the communicating hole, a wave washer compressed in accordance with a position of the preload adjusting plug, and a lock nut that is screwed to the housing portion of the second shaft so as to press the preload adjusting plug toward the nutation gear mechanism.

Abstract: A preload adjusting plug is inserted through a communication hole extending through center portions of a Z1 gear, a Z4 gear, and an inner ring of a nutation gear. A male thread portion is formed at an outer periphery of one end of the preload adjusting plug, and is screwed to a female thread portion formed at an inner periphery of the Z1 gear. A disc-shaped flange portion extending radially outward is formed at the other end of the preload adjusting plug, and axially presses a back face of the Z4 gear through a bearing. The preload adjusting plug applies predetermined preloads to meshing portions in the nutation gear mechanism.

Abstract: A knurled press-fitting portion and an annular groove, which receives foreign matter and is formed to extend in a circumferential direction in front of the press-fitting portion of a cylindrical protruding portion, are provided at an outer peripheral surface of the protruding portion of an output shaft. A fitting portion, which is fitted to a coupling tube by press-fitting, is formed at an outer periphery of an opening end of the protruding portion. An outer peripheral surface of the cylindrical fitting portion and an inner peripheral surface of the cylindrical coupling tube coupled to a Z4 gear are fitted and coupled to each other. The annular groove is closed by the fitting portion in a state where the protruding portion and the coupling tube are coupled to each other. The annular groove is configured so as to prevent foreign matter from being discharged toward a bearing gear.

Abstract: A ball screw nut of a ball screw device is fastened to a motor shaft by engaging a male thread portion thereof with a female thread portion of the motor shaft. In a case where, in a movement pathway for balls, an area where the balls roll under load from a rack shaft and the ball screw nut is set as a load area, an area that does not receive the load is set as a no-load area, and areas for transition from the load area to the no-load area are set as transition areas, the male thread portion is formed such that the transition area on the nut-side joint portion-side closest to a seating surface does not overlap phase ranges of cut portions in a state where the ball screw nut is fastened to the motor shaft.

Abstract: A variable transmission ratio mechanism is provided on an intermediate portion of a steering shaft, and is able to change a transmission ratio between a shaft on the steering wheel side and a shaft on the steered wheel side by transmitting the sum of rotation of the first shaft and rotation of a rotary shaft of a motor to the second shaft. The variable transmission ratio mechanism is provided with a lock mechanism that restricts the operation of the variable transmission ratio mechanism. When the fact that a rate of change in torque that acts on the steering shaft exceeds a predetermined rate is detected, a period of time until the torque that acts on the steering shaft reaches a torque determination value is estimated. On the condition that the estimated time is shorter than or equal to a predetermined period of time, the lock mechanism is activated.

Abstract: A second shaft is configured by a shaft portion extending outside a housing in which a nutation gear mechanism is housed, a housing portion, and a cylindrical portion. A communicating hole, through which an outside and an inside of the housing portion communicate with each other, is formed in the shaft portion. A preload applying mechanism includes a preload adjusting plug that is screwed to the housing portion and is able to be operated from outside through the communicating hole, a wave washer compressed in accordance with a position of the preload adjusting plug, and a lock nut that is screwed to the housing portion of the second shaft so as to press the preload adjusting plug toward the nutation gear mechanism.

Abstract: A first gear set includes an input member that serves as a first gear and an inner ring that serves as a second gear. A first end of the inner ring is inclined with respect to the input member and is in mesh with the input member. The input member has a plurality of retention grooves that are formed in an input member body and a plurality of pins that are retained in the respective retention grooves and that respectively constitute teeth of the input member. The first end has a plurality of tooth grooves that are engageable with the pins. A resultant force of forces applied to each pin from the retention groove and the tooth groove urges the pin toward the retention groove.

Abstract: A first gear set includes an input member that serves as a first gear and an inner ring that serves as a second gear. A first end of the inner ring is inclined with respect to the input member and is in mesh with the input member. The input member has a plurality of retention grooves that are formed in an input member body and a plurality of pins that are retained in the respective retention grooves and that respectively constitute teeth of the input member. The first end has a plurality of tooth grooves that are engageable with the pins. A resultant force of forces applied to each pin from the retention groove and the tooth groove urges the pin toward the retention groove.