Power steering pump, component description - GF46.30-P-5136SX

MODEL 216.3, 221.0 /1 up to Model Year 8 

Shown on detached reservoir 

Location 

The power steering pump is attached to the end face on the left of the engine.

Task 

The power steering pump supplies the steering gear with oil independent of the engine speed and operates according to the principle of a vane-type pump.

Function 

The rotation of the drive shaft, and thus of the rotor, produces a centrifugal force which presses the blades on the rotor in the radial direction against the running surface of the non-moving cam insert. This is assisted by the oil which is fed from the pressure chamber to the inner end faces of the vanes via holes and grooves. Ten closed pump cells are thus formed between the ten blades of the rotor.

As the volume increases oil is now drawn out of the reservoir via the intake port and as the volume decreases oil is forced into the pressure chamber via the ports. Because the shape of the cam insert means that two suction and two pressure zones are opposite each other, each of the ten pump cells pumps twice its own volume for each rotation of the drive shaft. Furthermore, this double arrangement of suction and pressure zones causes the radial hydraulic forces acting on the rotor to cancel each other out.

Quantity control valve open 

Oil volume regulation 

The power steering pump is driven by the engine at alternating speeds. Power assistance however requires a constant oil flow.

As more oil is delivered than necessary at high engine speeds, the excess oil is returned to the reservoir via the open quantity control valve. The quantity control valve causes a constant volume of oil to be supplied to the steering gear over the entire speed range.

Engine running, steering wheel not turned 

The oil pressure generated by the vane cells feeds the oil via the calibrated borehole to the steering gear and also via the calibrated borehole to the spring chamber behind the quantity control valve.

The calibrated boreholes throttle the oil flow so that in the spring chamber behind the quantity control valve a lower oil pressure prevails than on the side of the high pressure chamber. The quantity control valve opens and the excess oil flows back into the reservoir.

Engine running, steering wheel turned 

The pressure behind the quantity control valve also increases due to the increasing pressure level behind the calibrated borehole. The quantity control valve closes and remains in its basic position.

Increased engine speed 

If the quantity of oil delivered increases as the engine speed increases, a larger pressure difference occurs again due to the calibrated borehole. The quantity control valve is pressed against the spring and the excess quantity of oil delivered can flow back into the reservoir.

Quantity control valve closed 

Pressure limiting 

A pressure limiting valve is installed in the quantity control valve to protect the steering system against overload.

It opens at a pressure between 65 and 125 bar depending on the model of power steering pump. This occurs, for example, at full steering lock, and is audible as a high-pitched whirring whistle.