POWER STEERING Description PRINCIPLES OF POWER STEERING Power steering is one type of hydraulic device for utilizing engine power to reduce steering effort. Consequently, the engine is used to drive a pump to develop fluid pressure. This pressure is used to a piston within the power cylinder so that the piston will move by rack effort. The amount of this as- sistance depends on the extent of pressure acting on the piston. Therefore, if more steering force is required, the pressure must be raised. The varia- tion in the fluid pressure is accomplished by a con- trol valve which is linked to the intermediate shaft and the steering main shaft. Reservoir Tank Vane Pump Rack Main Shaft Intermediate Shaft Gear Housing SR31/6 NEUTRAL (STRAIGHT-AHEAD) POSITION Fluid from the pump is sent to the control valve. If the control valve is in the neutral position, all the fluid will flow through the control valve into the reservoir tank back to the pump. At this time, hardly any pressure is created and because the pressure on the cylinder piston is equal on both sides, the piston will not move in either direction. PUMP Control Valve Relief Port Power Cylinder Cylinder Piston SR7390 WHEN TURNING When the steering main shaft is turned in either direction, the control valve also moves, closing one of the fluid passages. The other passage then opens wider, causing a change in fluid flow volume and, at the same time, pressure on the cylinder. Actual- ly, a pressure difference occurs between both sides of the cylinder, and the piston moves in the direction of the lower pressure so that the fluid in the cylinder is forced back to the pump through the control valve. PUMP SR7391