Abstract: A control valve controls hydraulic pressure of oil supplied to a hydraulic actuator for generating steering assist power, based on elastic relative rotation between input and output shafts. A restricting device restricts relative rotation between input and output shafts based on a driving condition of the vehicle, and adjusts the hydraulic pressure for pressing the input shaft via a plunger inserted into a guide bore formed in the output shaft, based on the driving condition of the vehicle by the hydraulic pressure adjustment mechanism. The plunger is guided by the inner circumference of the guide bore along the direction that the plunger approaches to and goes away from the output shaft when the input and output shafts relatively rotate. A friction reducing element is interposed between the inner circumference of the guide bore and the outer circumference of the plunger.

Abstract: The control valve of the hydraulic power steering apparatus controls hydraulic pressure of the oil supplied to the hydraulic actuator for generating steering assist power, in accordance with the amount of elastic relative rotation between the input and output shafts. The restricting device restricting the relative rotation between the input and output shafts in accordance with a driving condition of the vehicle adjusts the hydraulic pressure for pressing one of the input and output shaft via the plunger inserted into the guide bore formed in the other of the input and output shaft, in accordance with the driving condition of the vehicle by means of the hydraulic pressure adjustment mechanism. The plunger is guided by the inner circumference of the guide bore to the direction in which the plunger approaches to and goes away from the other of the input and output shaft when the input and output shafts relatively rotate.