S 65 AMG (220.179) V12-6.0L Turbo (275.981) (2006)
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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.
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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).
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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).
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.
