tire pressure AUDI S4 1998 B5 / 1.G Engine Manual

16
Engine
The component parts of the oil circuit
is integrated in the primary flow. By increasing
the capacity and optimising the flow
resistance, the entire oil flow can be routed
through the oil cooler. Unlike the V6 naturally
aspirated engine, a bypass is not required.
The oil cooler ......
contains an oil retention valve, the filter
element, a bypass filter and the filter bypass
valve. The latter has the task of maintaining
engine lubrication via the bypass filter if the
filter element becomes clogged up or if the oil
has a high viscosity.
The oil filter ......
opens up the oil flow to the piston spray jets if
the oil pressure is greater than 1.8 bar.
Reason: at low oil viscosity and low engine
speeds, the oil pressure would otherwise drop
below the minimum permissible level. That
aside, piston cooling is not necessary at low
engine speeds.
The spray jets valve ......
SSP 198/57

Oil pressure control valve
Oil pressure limiting valve
Chain guard

is an internal gear pump. It is attached to the
crankcase as a separate component.
The oil pump is designed in such a way that it
projects deep down into the oil sump and is
immersed completely in the engine oil when
the oil level is correct. This prevents the oil
pump running dry.
The oil pump, in combination with the
extremely short intake path, enables oil
pressure to build up more quickly and safely,
particularly during cold starts.
The oil pump is driven by the crankshaft by
means of a single chain.
A spring-loaded flat plate produces the
necessary tension.
A new feature of the oil pump is the chain
guard made from sheet steel. It encapsulates
both the chain wheel and the chain over a large
area.
This reliably prevents oil frothing and the
problems associated with this.
The oil pump ......

27
The solenoid valve for charge pressure control
N75 changes the opening time to atmospheric
pressure according to the signals it receives
from the engine control unit (duty cycle).
Thus, a control pressure is produced by
modulating the charge pressure and
atmospheric pressure. This pressure acts on
the pressure unit for the wastegate.
The wastegate is kept closed in a
depressurised state by a spring inside the
pressure unit . The entire exhaust gas flow is
routed via the turbine, and a charge pressure is
built up.
The control pressure counteracts this spring
force and opens the wastegate. Part of the
exhaust gas flow is fed from the wastegate
past the turbine, and the charge pressure stops
rising.
If there is no flow, N75 is closed and the charge
pressure acts directly on the pressure unit. The
waste gate opens even if the charge pressure
is low.
If the charge pressure control fails, the charge
pressure is thus limited to a “basic charge
pressure“ in order to prevent the maximum
permissible charge pressure being exceeded.
This results in a loss of performance.
The “basic charge pressure“ is the charge
pressure (approx. 300 - 400 mbar) which is
achieved without regulation (mechanical
charge pressure).

SSP 198/66

Turbine wheel
to catalytic converter
Impeller
Exhaust gas from
combustion chamber
Wastegate flap
(open)
Control pressure from solenoid
valve for charge pressure control
pressure unit N75charge pressure to solenoid valve
for charge pressure control N75
Intake air
to
combustion
chamber

SSP 198/67

Atmospheric
pressure from
distributor piece
Solenoid valve for
charge pressure
limitation N75
Charge pressure from compressor housing
RestrictorPassage in no
flow state
Control
pressure to
pressure unit

67
Problem:
As the clutch plate wears, the position of the
main diaphragm spring changes, as do the
characteristics for contact pressure and
releasing load.
The main diaphragm spring has a digressive
characteristic. To prevent the contact pressure
of the pressure plate dropping too low over a
wear range of approx. 1.5 - 2 mm, the
characteristic of the main diaphragm spring is
such that the forces initially increase as a
factor of distance travelled.
This has the knock-on effect of producing
uncomfortably high pedal forces.
The clutch in the biturbo engine is required to
transmit high levels of torque.
Higher contact pressures have to be applied to
compensate for the limitations on the surface
area of the clutch lining for design reasons.
This in turn results in higher releasing loads
(particularly as wear progresses).

Solution to problem:
If the position of the main diaphragm spring
remains constant over the entire wear range,
the associated forces will also remain
unchanged.
This effect is achieved using the new SAC
clutch pressure plate.
SSP 198/41

Housing cover
SSP 198/72
0 -1 -2 1 2 3 4

Pressure plate travel in mm
Contact pressure
Fitting location
Wear reserve

Contact pressure characteristic
(conventional clutch )
Sensor plate spring
Main diaphragm spring
Adjusting ring
Auxiliary spring
Disengaging stop