Patent ID: 7819217

Claim:
A power steering apparatus comprising: a steering shaft adapted to be connected to a steering wheel, the steering shaft comprising a first shaft and a second shaft; a hydraulic power cylinder mechanically linked to the steering shaft, the hydraulic power cylinder having first and second fluid pressure chambers for producing an assist steering effort; a hydraulic pump for supplying a fluid pressure to the hydraulic power cylinder; a steering shaft actuator for controlling the steering shaft, the steering shaft actuator comprising a first actuator and a second actuator; a condition sensor for collecting information concerning at least one of an associated host vehicle, an associated driver and an associated road; and a fluid pressure controller for receiving the collected information from the condition sensor, and controlling the steering shaft actuator based on the collected information, wherein the first actuator comprises: a first contact surface formed in a radial outer periphery of the first shaft; a first piston provided in the second shaft, and adapted to be in contact with the first contact surface; and a first fluid chamber for receiving the fluid pressure from the hydraulic pump, and pushing the first piston toward the first contact surface so as to apply torque to the first shaft toward an increased relative rotation between the first shaft and the second shaft in a first direction; and the second actuator comprises: a second contact surface formed in a radial outer periphery of the first shaft; a second piston provided in the second shaft, and adapted to be in contact with the second contact surface; and a second fluid chamber for receiving the fluid pressure from the hydraulic pump, and pushing the second piston toward the second contact surface so as to apply torque to the first shaft toward an increased relative rotation between the first shaft and the second shaft in a second direction opposite to the first direction.