Power steering apparatus, method of controlling the same and method of assembling the same

A power steering apparatus includes a steering shaft, a hydraulic power cylinder, a hydraulic pump, a steering shaft actuator, a condition sensor, and a fluid pressure controller. The steering shaft is connected to a steering wheel. The hydraulic power cylinder is mechanically linked to the steering shaft. The hydraulic power cylinder has first and second fluid pressure chambers for producing an assist steering effort. The hydraulic pump supplies a first fluid pressure to the hydraulic power cylinder. The steering shaft actuator receives a second fluid pressure from the hydraulic pump, and applies a torque to the steering shaft by the second fluid pressure. The condition sensor collects information concerning at least one of an associated host vehicle, an associated driver and an associated road. The fluid pressure controller receives the collected information from the condition sensor, and controls the steering shaft actuator based on the collected information.