key AUDI S4 1998 B5 / 1.G Engine Manual

2
The 2.7-litre V6 biturbo .......
Turbocharged engines are already something
of a tradition at AUDI. The task now facing
AUDI’s engineers was to develop a worthy
successor to the 5-cylinder turbocharged
engine.
One of the key development goals for the
turbocharged engine was to achieve a good
level of dynamic response, particularly at the
bottom end of the rev band.
........ a further milestone in engine development by Audi!
The goal of AUDI’s engineers was to realise a
high “basic torque level“ and a torque
characteristic that rises in direct proportion to
engine speed to its peak.
The term “basic torque level“
describes the torque which is
immediately available when the
throttle is opened (e.g. at part
throttle or in overrun).
SSP 198/77

41
Functional positions of throttle valve control part (linear
representation)
The engine control unit recognises four key functional positions of the throttle valve control part.
• The lower mechanical limit stop
The throttle valve is closed. This
position is required to adapt the angle
sender.
• The lower electrical limit stop
is defined by the control unit and is
located just below the lower
mechanical limit stop. During
operation, the throttle valve closes no
further than the lower electrical limit
stop. This prevents the throttle valve
working its way into the throttle valve
housing.
• The emergency running position
is the position of the throttle valve in
the deenergised state and ensures that
air flow is sufficient if any of the
relevant electronic accelerator functions
fails. Idling speed is higher - approx.
1000 rpm - and uneven.
Very limited vehicle operation is
possible.
SSP 198/21

SSP 198/22

SSP 198/24

Position of lower electrical limit stop
Emergency running position
Lower mechanical limit stop

46
SSP 198/26

Subsystems of the Motronic
Exhaust gas temperature control
A new feature of Audi automobiles
is a function which monitors
exhaust gas temperature over the
entire engine speed range.
For turbocharged engines, the maximum
permissible exhaust gas temperature is a key
design criterion.
To protect the exhaust gas turbocharger and
the exhaust manifold, the exhaust gas
temperature should not exceed 1000 °C for a
lengthy period of time.
Since many of the components which
influence the exhaust gas temperature have
tolerances, thermodynamic adaptation
previously took place at 950 °C for safety’s
sake.
This was achieved by enriching the air/fuel
mixture.
The exhaust gas temperature is recorded in a
cylinder-bank-specific manner by the two
exhaust gas temperature senders G235 and
G236.
The Motronic controls the exhaust gas
temperature to 980 °C by enriching the air/fuel
mixture .
It is therefore possible to largely dispense with
the prophylactic enrichment process that has
been standard practice until now.
The mixture is only enriched...
... when necessary and
... to the extent necessary.
This means that engine operation with lambda
= 1 is possible up to high load and engine
speed ranges.
Advantage:

• Improved efficiency and reduction of fuel
consumption as well as exhaust emissions.
Exhaust gas temperature sender
Engine control unit
Injectors
G235
G236