Fluid Pump And Reservoir Tank: Notes

WARNING: This page is about a different car, the 2004 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

The fluid pump is a vane type driven by the engine via belt.

The reservoir tank is mounted on the vehicle body.

The fluid pump incorporates the flow control valve and relief valve, each performing the following functions:

The flow control valve regulates the flow rate of discharged fluid to a constant level irrespective of the engine speed.
The relief valve protects the system from an excessively high pressure which may occur, for example, when the steering wheel is turned all the way.

Fig 1: Identifying Fluid Pump Components
Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Identifying Fuel Pump Flow
Courtesy of SUBARU OF AMERICA, INC.
The fluid pump is belt-driven by the engine. The fluid flow is controlled according to the engine speed so that an adequate steering resistance is given during high-speed operation.
The fluid pump is a variable capacity type vane pump whose delivery rate per rotation decreases as the engine speed increases. The pump is integral with a pump control valve and relief valve.
The vane pump consists of a rotor, a cam ring, and eleven vanes.
When the rotor rotates, the vane in each slot of the rotor is moved out by centrifugal force in radial directions and pressed against the cam ring. The fluid from the suction port is confined in chambers formed between two adjacent vanes and carried to the discharge port. Since the cam ring is movable in relation to the rotor, the volume of each chamber is variable. This enables the delivery rate per rotation of the pump to be changed.

Fig 3: Identifying Rotor
Courtesy of SUBARU OF AMERICA, INC.
Flow control
The variable capacity pump changes its delivery rate per rotation by changing the degree of eccentricity of the cam ring according to its rotating speed (engine speed).

Fig 4: Identifying Fluid Control Graph
Courtesy of SUBARU OF AMERICA, INC.

NOTE: In the following description, pump speed ranges will be indicated using the speed points A through D shown in the drawing above.