Subaru 2002 Impreza Service Manual page 362

POWER STEERING SYSTEM
Power Assisted System (Power Steering)
0
VANE PUMP
The vane pump consists of a rotor, a cam ring, and ten vanes.
When the rotor rotates, the vane movably fitted in each slot of the rotor is radially moved out by
centrifugal force and pressed against the inside wall of the cam ring. Since the inside of the cam
ring is oval-shaped, the fluid from the suction port is confined and pressurized in the chamber
formed between two adjacent vanes as the rotor rotates and is delivered through the discharge
port. The pressurized fluid circulates through the hydraulic circuit.
FLOW CONTROL AND ENERGY-SAVING VALVE ASSEMBLY
0
During engine idling
When the engine is idling, the fluid pump speed is
low.
As the delivery rate of the pump is small,
the metering orifice allows whole fluid to flow passing through it. So, there is no difference in the
fluid pressure between the right and left of the metering orifice. This means that pressure PI act-
ing on the left end of the flow control valve is equal to pressure
P2
(pressure of the fluid flowing
through the pressure sensing holes in the valve body) acting on the right end of the valve. As
a result, the flow control valve is held pressed leftward by the force of the control valve spring.
With the flow control valve in this position, the passage to the fluid pump suction port is closed,
so that the whole fluid delivered from the pump flows toward the power steering gear box.
(A) From fluid pump delivery port
(E) To steering gear box
(C) To fluid pump suction port
PS-18
NF0301
(1) Metering orifice
(2) Flow control valve
(3) Flow control valve spring
(4) Pressure sensing hole in valve body