Power Rack and Pinion

Except for differences in valve machining, the design of the VES power rack and pinion assembly is the same as a non-VES system. As with non-VES steering, the steering wheel movement is transferred to the pinion; the pinion moves the rack left or right through meshing pinion and rack teeth; the force is then transmitted through the tie rod ends and steering knuckles to steer the wheels.
The power rack and pinion steering system has a rotary control valve which directs hydraulic fluid (from the power steering pump) to one side or the other side of the rack piston. The piston is attached to the rack, and uses hydraulic pressure in order to assist the rack movement left or right. The rotary control valve regulates the degree of assist by responding to the driver's torque input.
If hydraulic assist is not available, manual control is maintained. However, under this condition, more driver steering effort is required.