Power steering is an advanced version of the usual mechanical steering mechanism. It helps the driver in maximizing the steering effort put on the steering wheel. With an increased power, power steering mechanisms add extra sensitivity and the driver is able to make very precise turns with little effort. A power steering mechanism can use either hydraulics or electric actuators to do this.
Components of a hydraulic power steering mechanism
Rotary-Vane-Pump
The hydraulic power for the steering is provided by the rotary vane pump. This pump is run by a belt from the engine. It contains a number of vanes arranged around its axis. These vanes draw hydraulic fluid from the reservoir and force it through the outlet tube at high pressure. When the vehicle is traveling at high speeds, steering speed also should be more. To facilitate this, the vane pump is connected to the engine, when the engine spins at higher speeds so that the pump also works fast. To avoid too much pressure in the pump at high speeds, there is also a relieve valve in case too much of fluid is pumped to remove.
Rotary valve
The rotary valve is a device that channels hydraulic fluid into the steering gear. It controls the fluid flow that is directly involved in steering. The rotary valve is designed in such a way that it influences steering only when the driver is steering. Otherwise, the rotary valve performs no function. The input shaft from the steering wheel fits into the upper part of the rotary valve and it leads to the torsion bar.
Spool valve assembly
The spool valve assembly attaches to the driving shaft and it leads to the torsion bar. The spool valve is the component that lets hydraulic fluid to flow in specific levels to turn the steering gear. There are two kinds of valves, the inner valve and the outer valve.
Steering gear:
The steering gear receives the hydraulic fluid and rotates the pinion or the worm gear.
Working:
As the steering shaft is rotated, it turns the torsion bar in the rotary valve in the same direction. Since the rotary pump is already running, there is hydraulic fluid supply to the rotary valve. The inside of the rotary valve, that is, the spool valve assembly rotates in the same direction as that of the torsion bar letting hydraulic fluid pass through them in a single direction. This rotates the outer valve and the outer valve steers the steering gear. When the direction of steering is changed, the torsion bar turns in the opposite direction, making the hydraulic fluid flow in the opposite direction. When there is no steering, the outer valve remains closed, and there is no flow of hydraulic fluid into the spool assembly.
