Power Steering Pressure Control Valve: Description and Operation

EPS SOLENOID
SOLENOID VALVE





A solenoid valve is provided in the gear box to control the flow of power steering oil. The solenoid valve is composed of a releasing spring, a piston and a plunger.
The input current is varying from 0A to 1A according to the vehicle speed and is controlled by EPS control module. When the ignition switch is turned on, current is sent to the solenoid valve to push up the plunger and accordingly the piston contacting the plunger is pushed up while overcoming the spring force. As the vehicle speed increasing the current flow to the solenoid decreased pulling down the piston bottom by the releasing spring force.
When the piston is pushed up, it closes the oil passing hole, therefore the power steering oil pressure is delivered into the cylinder without any interruption. But when the hole is opened as the piston is pulling down, some of the oil coming from the rotary valve is drained into reservoir via the hole inside the rotary valve.

NOTE: When it is necessary to remove the EPS gear box, be sure to disconnect the connector to avoid damage.

EPS GEAR BOX
OPERATION
LEFT TURN (COUNTERCLOCKWISE)
The power steering oil pump generates the oil pressure and the oil enters into the rotary valve. And the torsion bar is twisted by the force between the steering wheel rotation and the resistance of the tire to the ground.
At a high speed of vehicle, the oil passing the rotary valve comes into the solenoid valve through the lower hole and goes out through the upper hole flowing the connecting space of piston. At this time the piston is back away due to the spring force overcoming the solenoid plunger. The oil flows through the space between the piston and side wall.
And then the oil flows again into the rotary valve and finally drained to reservoir through the drain hole between the rotary valve and the torsion bar. Therefore the oil Dump pressure does not affect to the steering effort.





As the vehicle speed decreasing the hole of piston connecting the left chamber and right chamber is gradually closed as the oil pressure produced by oil pump is delivered to the left chamber. Therefore, the steering effort is reduced.

RIGHT TURN (CLOCKWISE)





The operation procedure of right turn is the reverse sequence of left turn.