Power steering pump, function - GF46.30-P-2100-01B

Models 203, 209, 211

Models 220, 230 except Code (487a)

Active Body Control (ABC)

Identification of power steering pump manufacturers:

Models 220, 230

LF 30 = LuK Clutch and Transmission Systems

FP 42 = ZF (Zahnradfabrik Friedrichshafen)

Models 203, 209, 211 with diesel engines

LF 37 = LuK Clutch and Transmission Systems

FP 42Q = ZF (Zahnradfabrik Friedrichshafen)

Models 203, 209, 211 with gasoline engines

LF 30 = LuK Clutch and Transmission Systems

FP 42 = ZF (Zahnradfabrik Friedrichshafen)

Fig 1: Power Steering Pump Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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 Function Diagram - Quantity Control Valve Open

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 3: Power Steering Function Diagram - Quantity Control Valve Closed

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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 (30t) thus ensures that the steering gear is supplied with a constant oil stream across the entire engine speed range.

Engine ON , steering wheel not turned:
The pressure oil produced by the rotor cells is fed via the calibrated bore hole (9a) to the steering gear and also via the bore (9b) to the spring chamber downstream of the quantity control valve (30t).

The calibrated bore holes (9a, 9b) throttle the oil stream so that the oil pressure in the spring chamber downstream of the quantity control valve (30t) is lower than on the side of the high-pressure chamber. The quantity control valve (30t) opens (Fig 2) and the surplus pressure oil flows back to the supply reservoir.
Engine ON , steering wheel turned:
Because of the rising pressure downstream of the restrictor orifice (a), the pressure downstream of the quantity control valve also rises. The quantity control valve (30t) closes (Fig 3) 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 (30t) is forced against the spring (30s) and the surplus oil can flow back to the supply reservoir (Fig 2).

Fig 4: Power Steering Function Diagram - Quantity Control Valve (30T) Open

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Quantity control valve (30t) open

Pressure limiting

A pressure limiting valve (49d) is installed in the quantity control valve (30t) to protect the steering system against overloading. 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.