Hydraulic power steering incorporates a hydraulic boost into a basic manual-steering system. A basic manual-steering system is an arrangement of gears in a box that multiplies the input torque from the steering wheel to a much greater torque at the steering shaft (Figure 6-22). The steering shaft, through the pitman arm (or steering-shaft arm), transmits this increased torque through the steering linkage to the steering arms that turn the wheels. The basic system of manual-steering gears and steering linkage is a steering wheel, steering gear, and linkage to the steered wheel.
The hydraulic boost, which is a mechanically operated hydraulic servo, may be applied to the steering linkage (Figure 6-23) or within the steering gear. Steering-wheel movement actuates the steering valve, which directs the fluid under pressure to the steering-valve body that follows the valve spool. Hydraulic boost is applied only when the steering wheel is being moved.
An integral power-steering system has the hydraulic-boost subsystem built into the mechanical steering gear. The steering valve is actuated by moving the steering shaft. The valve controls the operation of the power cylinder. Thrust from the power cylinder is transmitted directly to the steering shaft. Road shock transmitted back from the wheels is taken up in the steering gear.
Figure 6-24, shows the semi integral power-steering system, or valve-on gear system. The steering valve is built into the steering gear. The power cylinder is attached to the vehicle’s frame and to the linkage. Road shock and thrust are absorbed in the frame.