Transmission ratio variable device

A transmission ratio variable device comprising:

• an input shaft that is coupled to a steering wheel;
• a housing that supports the input shaft so that the input shaft is rotatable;
• a motor that is provided so that a motor output shaft is rotatable relative to the housing;
• a speed reducer that is coupled to the motor output shaft and outputs a steered angle obtained by reducing a motor rotation angle;
• and
• an output shaft that transmits the steered angle output from the speed reducer to steered wheel,
• wherein the speed reducer includes:
• a first gear that is provided so as to be rotatable together with the input shaft and includes first teeth formed at an end face of the first gear;
• a fourth gear that is provided so as to be rotatable together with the output shaft and includes fourth teeth formed at an end face of the fourth gear, the end face of the fourth gear facing the end face of the first gear;
• an inclination shaft that is provided so as to incline with respect to the input shaft;
• and
• a nutation gear that is supported by the inclination shaft so that the nutation gear is rotatable, the nutation gear including a second gear and a third gear that have second and third teeth, respectively, the second and third teeth being formed at different end faces of the nutation gear so as to mesh with the first and fourth gears, respectively, and the nutation gear rotating according to a difference in the number of teeth between the first or fourth gear and the second and third gears while oscillating in an axial direction of the input shaft, between the first and fourth gears due to rotation of the inclination shaft, and
• wherein the output shaft includes a cylindrical protruding portion press-fitted into an opening end of a cylindrical coupling tube that is coupled to the fourth gear so as to be rotatable together with the fourth gear, and a knurled press-fitting portion and an annular groove are provided at an outer peripheral surface of the protruding portion, the annular groove being formed to extend in a circumferential direction at a position in front of the press-fitting portion in a press-fitting direction.