How power steering works?
Power steering is a steering mechanism in which force required at steering wheel to steer the wheels is reduce by multiplying the force with the help of hydraulic pressure. This way driver gets better degree of control over vehicle and driving becomes more effort free.
Power steering consists of following parts:
Hydraulic pump : Hydraulic pump is heart of power steering and Function of hydraulic pump is to continuously feed the Rotary valve with the high pressure hydraulic oil. Hydraulic pump gets the drive from engine through the belt and pulley, in most of cases this pump is Rotary vane type. Speed of the pump varies with the speed of engine.
Rotary valve assembly: Rotary valve gets high pressure oil from hydraulic cylinder and supplies to hydraulic cylinder assembly in a controlled manner. Rotary valve assembly has a torsion bar, spool valve assembly .
Power steering mechanism is also consist of torsion bar which is a thin rod of ductile material which is able to twist. Upper part of this bar is connected to lower end of the spool valve while its lower end is connected to the pinion gear or worm gear of steering mechanism.
Spool valve assembly consists of inner and outer shells having spools on inner and outer side. Inner part of spool is connected to the steering rod while outer shell is connected to the torsion bar, amount of rotation between the inner and outer parts of the spool valve depends on how much torque the driver applies to the steering wheel.
As steering rod and torsion bar is connected indirectly ,the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels.
Hydraulic cylinder assembly: This is made up of cylinder connected to the spool valve assembly and a piston connected to the rack of tie rod. Feed and return line of spool valve is connected to ends of cylinder. Function of hydraulic cylinder is to move back and forth piston, connected to tie rod with the help of hydraulic pressure.
When engine starts , steering hydraulic pump also starts running and develops high pressure oil and sends to spool valve assembly if oil is not utilized by spool valve it returns to the pump from return line.
How power steering works?
When steering wheel is rotated by the driver, Torsion bar twists and actuates the spool valve. As per deflection of the torsion bar spool valve controls the flow of hydraulic oil. This hydraulic oil is then sent to the cylinder assembly in a direction supplied by spool valve.
When pressurized fluid is fed to any one of the connection of cylinder, the piston gets pushed and moves in the opposite direction, dragging the rack along with it. At the same time, the other connection vents out the fluid (if present) on the other side of the piston.
Thus, effectively, the hydraulic pressure does most of the steering work, while the driver controls the direction of the turn with the help of a very precise valve system.