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

MODEL 164 

The power steering pump (30) is mounted on the left front end of the engine. It supplies the steering gear with pressure oil independent of engine speed and works according to the principle of the vane cell pump.

Basic 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 hydraulic oil, which travels from the pressure chamber via bores and grooves and against the internal end faces of the blades. Ten closed pump cells are thus formed between the ten blades of the rotor.

As the volume increases oil is now suctioned out of the reservoir via the intake port (B) and as the volume decreases oil is forced into the pressure chamber via the ducts (A). 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.

Figure 1 Quantity control valve (30t) Open 

Figure 2 Quantity control valve (30t) Closed 

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 than is necessary is pumped at higher engine speeds, the surplus oil is fed back to the supply reservoir via the open quantity control valve (30t). The quantity control valve causes a constant volume of oil to be supplied to the steering gear over the entire speed range.

• Engine ON  , steering wheel not turned:

  The pressure oil produced by the vane cells is lead via the calibrated bore (9a) to the steering gear and in addition via the calibrated borehole (9b) 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 (picture 1) and the excess pressure oil flows back into the reservoir.

• Engine ON  , steering wheel turned:

  The increasing pressure level behind the calibrated borehole (9a) means the pressure behind the quantity control valve also rises. The quantity control valve closes (picture 2) and remains in its basic position.

• High engine speed:

  If the oil quantity increases as the engine speed rises, a greater pressure difference again occurs due to the calibrated bore hole (9a). The quantity control valve is pressed against the spring (30s) and the excess oil quantity delivered can flow back into the reservoir (picture 1).

Pressure limiting 

A pressure limiting valve (49d) (picture 2) 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.