A steering system is an essential part of vehicle dynamics. There are series of mechanical component with certain important angles which help to steer the front wheels of the vehicle according to input provided by the passenger through steering wheel. Power steering system is an advanced steering system. The effort required to steer the front wheels of the vehicle side to side is reduced by using intermediate electric or hydraulic devices that increases the force applied by the driver through steering wheel to achieve a smooth and quick directional change of the vehicle.
Today most of the cars on the road are equipped with the power steering system, is become the basic need of automobile these days. A power steering system should help the driver when a force is exerted on the steering wheel like starting a turn and when the driver is not exerting force like when driving in a straight road, the system should not provide any support. The rotary valve senses the force that is exerted on the steering wheel.
Rotary vane pump provides the hydraulic power for steering. The pump is driven by engine in the car which contains a set of retractable vanes that spin inside an oval chamber through a belt and pulley. When the vane spins, it pulls the hydraulic fluid from the return line at low pressure and forces it into the outlet at high pressure. The flow of fluid by the pump depends on the speed of the engine. The pump should be designed in such a way that it provides adequate flow when he engine is idling. As a result, the pump moves more fluid than that is required when the engine is running at a faster speed. The pump also contains a pressure relief valve to ensure the pressure does not get high.
The key element in the rotary valve is the torsion bar which is a thin rod of metal that twists when torque is applied to it. The top of the bar is connected to the steering wheel and bottom is connected to pinion which turns the wheels so that the torque in the torsion bar is equal to that of the torque the driver is using to turn the wheels. When the driver uses more torque to turn the wheel, the bar twists the more. Inner part of a spool valves assembly is the input from the steering shaft. It is connected to the inner part of the torsion bar and bottom of the torsion bar connects to the outer part of the spool valve. The torsion bar turns the output of the steering gear, connecting to pinion gear or the worm gear depending on the type of steering of the car.
As the bar twists, it rotates the inside of the spool valve to the outer side. Since the inner part of the spool valve is connected to the steering shaft and steering wheel in turn, the rotation between the inner part and outer part of the spool valve depends on the torque the driver applies to the steering wheel. When the steering wheel is not turned, both hydraulic lines provide the same pressure to the steering gear. But if the spool valve is turned, ports open up to provide higher pressure fluid to the appropriate line.