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

MODEL 204.0/2 up to Model Year 8

Shown on engine 646

Location

The power steering pump is located at the front side of the engine.

Fig 1: Identifying Power Steering Pump - Shown On Engine 646

Courtesy of MERCEDES-BENZ USA

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 drawn up from the supply reservoir (B); as the volume decreases, oil is forced into the pressure chamber (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.

Fig 2: Power Steering Pump Flow Diagram

Courtesy of MERCEDES-BENZ USA

Fig 3: Power Steering Pump Flow Diagram (Quantity Control Valve Open)

Courtesy of MERCEDES-BENZ USA

Picture 1 Quantity control valve (30t) open

Fig 4: Power Steering Pump Flow Diagram (Quantity Control Valve Closed)

Courtesy of MERCEDES-BENZ USA

Fig. 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 is delivered than necessary at high engine speeds, the excess oil is led back into 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 across the entire engine speed range.

Engine running, steering wheel not turned

The pressure oil produced by the vane cells is routed via the calibrated bore (9a) to the steering gear and in addition via the 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 (Fig 3) and the excess pressure 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 (Fig 4) and remains in its basic position.

Increased engine speed:

If the oil quantity increases as the engine speed increases, then a larger pressure difference occurs again due to the calibrated borehole. The quantity control valve is pressed against the spring (30s) and the excess oil quantity delivered can flow back into the reservoir (Fig 3).

Fig 5: Power Steering Pump Flow Diagram (Quantity Control Valve Open)

Courtesy of MERCEDES-BENZ USA

Figure 3 Quantity control valve (30t) open

Pressure limiting

A pressure limiting valve (49d) is installed in the quantity control valve to safeguard the steering system against overloading. It opens at an excess pressure (Fig 5) between 65 and 125 bar depending on the power steering pump model.

This occurs, for example, at full steering lock, and is audible as a high-pitched whirring whistle.