Hydraulic System - Audi TT Roadster Service Training

Hydraulics

Hydraulic system

Convertible top opening cycle
The hydraulic system comprises an electric motor, a
pump housing and the oil tank which are connected
to the hydraulic cylinders by plastic sheathed lines.
The convertible top is opened or closed by reversing
the direction of rotation of the electric motor. When
the convertible top switch is actuated, the hydraulic
pump turns clockwise. The two-way valve closes the
return line on the pressure side and simultaneously
opens the pressureless return line on the opposite
side. A slight excess pressure is applied to the check
valve by increasing the pressure. The hydraulic
pressure flows into the hydraulic cylinder above the
piston rod and pushes it down, opening the
convertible top.
At the same time, pilot pressure is applied to the
pressure-controlled check valve on the pressureless
side through a bypass port from the pressure side.
Spring-loaded valve
is open on reaching
the max. pressure of
approx. 160 bar
Legend:
1 Electric motor with hydraulic pump
2 Two-way valve
3 Spring-loaded pressure relief valve
4 Pressure-controlled check valve
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This causes the pressure relief valve to open and the
hydraulic fluid displaced backwards by the cylinder
flows to the pump or back into the oil pan.
If the dead centre position of the convertible top
kinematics is exceeded, restrictor orifices create a
backpressure which prevents the convertible top
from lowering too quickly.
If the convertible top switch is still being actuated
when the convertible top reaches its end position,
the hydraulic pressure continues rising to a
maximum of approx. 160 bar. A spring loaded valve
opens and the excess hydraulic pressure flows back
into the oil tank.
When the convertible top switch is released, the
check valve closes and a residual pressure in the
cylinder stabilises the convertible top linkage while
driving.
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5 Emergency release
6 Return flow restrictors
7 Hydraulic cylinder
8 Oil filter in the hydraulic pump
Oil pressure side
Oil intake side
Control pressure
Oil return line
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