Power steering is a system to aid the steering of an automobile by use of a hydraulic device (driven from the engine) that amplifies the turning moment, or torque, applied to the steering wheel by the driver.It is relatively difficult to turn the steering wheel when the vehicle is to be stopped. Turning the wheel requires a certain amount of upper body strength. To reduce the torque required from the driver as cars became heavier and tires softer, gears were introduced between the steering wheel shaft and the linkage that turns the wheels.
There are two types of conventional power steering systems. The first type uses a hydraulic cylinder attached to the drag link and the chassis. A control valve is attached to the end of the drag link replacing the tie rod end and the valve actuator is connected by a tapered shaft to the pitman arm.
The second type uses a hydraulic cylinder that is an integral part of the steering gear and is connected to the recirculating ball nut located on the steering shaft. The rotary control valve is connected to a torsion bar that is part of the steering shaft. The rack and pinion steering gear hydraulic cylinder is part of the rack gear and the control valve is connected by a torsion bar to the steering shaft. In all these types of power steering, the pump delivers fluid to the control valve. The control valve opens a pressurized flow to and from the hydraulic cylinder.
Most modern power-steering systems consist of hydraulic boosts applied to either the steering linkage or the steering gear. Rotation of the steering wheel activates a valve that directs oil, pressurized by a pump driven by the engine, to act on a piston. The hydraulic boost acts only while the steering wheel is moving.
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