GF46.30-P-3300-04A | Tandem pump, function | MODEL 215 MODEL 220, 230 with CODE (487a) Active body control (ABC) | |
P46.20-0251-72
A To steering gear
B From supply reservoir
c Unpressurized
f Pressurized
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 ring. 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 ring 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.
P46.30-2096-79
Figure 1: Pressure and flow control valve (30) open, pressure limiting valve (30c) open
30c Pressure limiting valve
31 Pressure oil connection from vane-type pump
32 To intake side of vane-type pump
2 Vane-type pump
3 Input shaft
30 Pressure and flow control valve
30a Piston
30b Calibrated borehole
P46.30-2095-79
Figure 2: Pressure and flow control valve (30) closed, pressure limiting valve (30c) closed
30c Pressure limiting valve
31 Pressure oil connection from vane-type pump
32 To intake side of vane-type pump
2 Vane-type pump
3 Input shaft
30 Pressure and flow control valve
30a Piston
30b Calibrated borehole
Oil volume regulation
The vane-type 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 intake side of the vane-type pump via the infinitely variable opening of the pressure and flow control valve (30t).
The pressure and flow control valve (30) 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 end face of the piston (30a) in the pressure and flow control valve (30) is subjected to the pressure oil generated by the vane-type pump. The opposite side of the piston (30a) is acted on by the spring pressure and also by a reduced oil pressure via the calibrated borehole (30b).
In total, the pressure on the end face of the piston (30a) is greater than that on the opposite side.
The pressure and flow control valve (30) opens and the surplus pressure oil flows back to the intake side of the vane-type pump (2) (Figure 1).
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Engine ON, idle speed, steering wheel turned:
As the pressure on the end face of the piston (30a) falls, the pressure on the opposite side remains approximately the same, causing the pressure and flow control valve (30) to close. The oil pumped by the vane-type pump is directed in its entirety to the steering gear (Figure 2).
High engine speed:
As the engine speed rises, the pressure on the end face of the piston (30a) increases. This decreases the difference between the pressures acting on the end face and opposite side of the piston. The pressure and flow control valve (30) opens smoothly against the force of the spring. The surplus oil can flow to the intake side of the vane-type pump (Figure 1).
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Pressure limiting
A pressure limiting valve (30c) is installed in the pressure and flow control valve (30) to protect the steering system against overloading and to reduce pressure spikes in the system. It opens at approx.120 bar pressure (Figure 1). This occurs e.g. at full steering lock, and is audible as a high-pitched whirring whistle.
Note
Some tandem pumps are equipped with a stub pipe. The purpose of this stub pipe is to allow for additional compensation of any pressure surges that may occur.