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When the steering wheel is operated, the steering unit measures
the exact oil quantity proportional to the rotation of the steering
wheel. This oil quantity is directed to the steering cylinders.
The steering unit mainly consists of a rotary spool valve and a
metering pump (gear set). The steering column connects the
steering unit to the steering wheel of the vehicle. When turning the
steering wheel, the rotary spool valve makes sure that oil from the
steering pump is guided through the gear set to the cylinder ports L
or R, depending on the turning direction of the steering wheel. The
gear set measures the oil flow to the steering cylinder proportion-
ally to the turning angle of the steering wheel.
Fig. 96
1
Check valve
2
Shock valve
3
Pressure limiting valve
4
Housing with replenishing valves
5
Inner spool
6
Neutral position spring
7
Pin
8
Outer spool
9
Cardan shaft
10 Distributor plate
11 Gear
12 Ring gear
13 Cover
The steering valve is additionally equipped with a pressure limiting
valve which limits the steering pressure.
Suddenly occurring pressure peaks, which may be caused by e.g.
external influences such as driving against a curb stone, are com-
pensated by two shock valves, which are integrated in the steering
valve. Each of these shock valves is fitted with an additional
replenishing valve. These replenishing valves protect the system
against cavitation which could be caused by the reaction of the
shock valves.
A check valve inside the steering unit makes sure that the
hydraulic oil cannot flow to the steering pump if outside forces are
introduced. In such a case, the steering cylinders would act as
pumps and press the oil back to the pump.
Hydraulic system – Description of hydraulic components
BW 900-50
113
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