system, the driver is able to steer the vehicle manually although with increased effort. Fig shows atypical power steering system installed on a car. The power steering systems are operated by fluid under pressure. The fluids usually used are oils of viscosity rating SAE 5 W or SAE 10 W or higher depending upon atmospheric conditions. The systems operate under fairly high pressures which maybe as much as 7 MPa. The principle of working of all the power steering systems is same. The slight movement of the steering wheel actuates a valve so that the fluid under pressure from the reservoir enters on the appropriate side of a cylinder, thereby applying pressure on the side of a piston to
operate the steering linkage, which steers the wheel in the appropriate direction. When the driver applies a force on the steering wheel to steer,
the far end of the torsion bar, being connected to the spool of the rotary valve and the worm offers resistance. When the force at the wheel exceeds a predetermined value, the spool
turns through a small angle, when the return line is closed and the fluid under pressure goes to one side of the rack piston and moves it to effect steering in the desired direction. The torsion bar is meant to give a feel of the steering to the driver. The rotation of the steering wheel in the opposite direction connects the other side of the steering gear to the pressure line. In the neutral steer position both sides of the piston (nut) are shutoff to the pressure line and so they are at the same pressure but the return line is open due to which the fluid goes on circulating through the valve without causing any steering effect.
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