1998 AUDI S4 torque

33
SSP/198/15

Subsystems of the Motronic
Making allowance for efficiency and the
emissions standards, the engine control unit
coordinates the external and internal requests
and meets them by adjusting the available
control variables accordingly.
Torque-oriented engine
management
The Motronic ME 7.1 has a torque-
oriented functional structure.
This is made possible by the new
electronic accelerator function.
Internal torque requests
External torque requests

• Starting
• Idling speed control
• Catalytic converter
heating
• Power limiter
• Driving comfort
• Components
protection
• Engine governing
• Driver inputs

Throttle valve
angle
Charge pressure
Ignition angle
Injection cut-out
Injection time

Control variables
influencing torque
• Driving
dynamics
• Driving
comfort
• Cruise control
system

Coordination of
torque and
efficiency requests
in engine control
unit

34
Subsystems of the Motronic
In comparison with previously known
systems, the ME 7.1 is not confined to the
output of torque variables to the networked
control units (ABS, automatic gearbox), it also
uses these physical variables to calculate
control variables.All - internal and external - torque demands
are combined, and a nominal torque is derived
from this.
To translate the nominal torque into actions,
the control variables are co-ordinated with
regard to consumption and emissions so as to
optimise torque control.
SSP 198/75

External and
internal
torque
requests
Calculation of
efficiency and
torque reference
variables
Prioritisation of
charging path
Prioritisation
of crankshaft-
synchronous
path
Conversion of
torque into
charge
Throttle valve
angle
Charge
pressure-
control
Calculation of
crankshaft-
synchronous
intervention
Calculation of
throttle valve
opening
Charge
pressure
(Wastegate)
Ignition angle
Injection cut-
out
Injection time
Nominal charging
moment
Nominal charge
Nominal intake
manifold
pressure
Nominal inner
torque
Actual charge

Torque-oriented
functional structure

35
The control variable calculation is subdivided
into two paths
Path 1
The charging path regulates the control
variables which influence charging:
• Throttle valve angle
• Charge pressure
Path 2
All control actions which influence torque
regardless of charging are combined in the
crankshaft-synchronous path:
• Ignition angle
• Injection cut-out
• Injection time
The air mass necessary to develop a specific
torque is determined by means of a
“calculation model“ and is made available
along path
1
.
Path
2
is used to set the injection quantity or
cylinder cut-out necessary under the given
circumstances and the optimal ignition angle.
Prioritisation of
charging pathPrioritisation
of crankshaft-
synchronous
path
By and large, long-term torque requests are
fulfilled along path
1
.
Path 2
is particularly well suited to meeting
short-term torque requests, which usually
have a torque-reducing effect.

37
The electronic accelerator controls the engine
output electronically and, over and above
intake-air control, offers the advantage that
functions such as idling speed control, cruise
control or engine governing can be executed
easily and comfortably.
.
The throttle valve can be opened regardless of
the accelerator position, and this serves to
reduce throttle losses.
The ideal combination of throttle valve cross-
section and charge pressure produce the
necessary torque.
In this way, the throttle valve can be opened
fully while the accelerator pedal has not been
fully depressed.With electronic accelerator, much improved
emissions and higher fuel economy are
achieved in specific load states.
Over and above this, any accelerator
characteristic can be programmed, e.g.
gradual acceleration when driving at low
speed.
The electronic accelerator is used for reducing
and increasing torque and does not adversely
affect exhaust emissions.

• Traction control system
• Engine governer
• Speed limiter
• Power limiter
• Cruise control system
• Driving dynamics control systems
Torque reduction
Torque increase

• Cruise control
• Engine braking torque control
• Load change damping
(Dash pot function)
• Idling speed control
• Driving dynamics control systems

39
Self-diagnosis/emergency
running
If a fault occurs in the accelerator position
sender or the wiring, two emergency running
programs can be run depending on fault type.
Emergency running program 1
If an accelerator position sender fails:
• Accelerator position limited to a defined value.
• If a full load is predefined, the power output is
increased slowly.
• In the case of implausible signals between G79
and G185, the lower value is used.
Prerequisite:
The idling speed position must be learnt once
by the intact sender.
• The signal supplied by brake light switch for
brake pedal switch F47 indicates the idling
speed.
• Comfort functions (CCS) are prohibited.
• The fault lamp for electric throttle control K132
comes on.
Emergency running program 2
If both accelerator position senders fail, driver
input recognition is not possible:
• The engine only runs at idling speed.
• The fault lamp for electric throttle control K132
comes on.
At idling speed, the accelerator
position senders G79 and G185 are
not diagnosed.
If the plug of the accelerator position
sender drops off, no fault is stored in
the control unit.
The fault lamp for electric throttle
control K132 does not come on.
The engine runs at idling speed and
does not respond to the accelerator
pedal.
Safety function:
For safety reasons, the throttle valve
is closed as far as a defined angular
position when both the accelerator
pedal and the brake pedal are
depressed.
If the brake is pressed first followed
by the accelerator pedal, the driver
input (torque request) is executed.

40
SSP 198/28

Subsystems of the Motronic
The throttle valve control part comprises...
... throttle valve housing with throttle valve
... throttle valve drive G186 with reduction
gear
... angle senders for throttle valve drive
G187 and G188
Activated by the engine control unit, the
throttle valve drive controls the air-flow rate
necessary to develop the required torque.
Feedback on momentary throttle valve
position is provided by two potentiometers
G187 and G188.
For safety reasons, two angle senders
(redundancy) are used. They have opposite
impedance characteristics (see diagram).
If an angle sender fails, the second sender
maintains the electronic accelerator function
via an emergency running program.
Throttle valve housing
with throttle valve
Housing cover with electrical
connections
Throttle valve drive G186
(Electric throttle control)
Angle senders for throttle valve
drive G187 and G188
Resistance in

W

Angle senders G187 and G188 cannot
be replaced separately. The throttle
valve control part may not be opened.
Redundancy means: superfluous,
non-essential.
0 100%
SSP 198/27

G188
G187
Throttle valve opening in %

throttle valve control part J338 with throttle valve drive G186, angle
senders 1 G187 and 2 G188 for throttle valve drive

43
Emergency running program 1
If an angle sender for throttle valve drive fails
or an implausible signal is received:
• Torque-increasing requests on engine, e.g. CCS,
EBC (engine braking control) are suppressed.
• The fault lamp for electrical throttle control K132
comes on.
Prerequisite:
An intact angle sender and plausible
air mass flow. The air mass flow is
indicated by the air mass meter and
the charge pressure sender G31.
Self-diagnosis/emergency running mode
If a fault occurs in the throttle valve control part or in the wiring, three emergency running
programs can be run, depending on fault type.
Emergency running program 2
If the throttle valve drive fails or malfunctions:
• The throttle valve drive is switched off and the
throttle valve goes into the emergency running
position. This results in considerable loss of
power, increased idling speed and possibly also
rough idling .
• Driver inputs are executed as far as possible via
the ignition angle and charge pressure. The
engine shows little response to the throttle.
• The fault lamp for electrical throttle control K132
comes on.
Prerequisite:
Emergency running program 2 is only
run if both angle senders for throttle
valve drive recognise the emergency
running position.
Emergency running program 3
If the throttle valve position is not clearly
recognisable and/or if the throttle valve is not
definitely known to be in the emergency
running position:
• The throttle valve drive is switched off and the
throttle valve goes into the emergency running
position. This results in considerable loss of
power, increased idling speed and possibly also
rough idling.
• The engine speed is limited to approx. 1200 rpm
by restricting the injection.
• The fault lamp for electric throttle control K132
comes on.
Repair work may not be performed on
the throttle valve control part J338! If
G186, G187 or G188 becomes faulty,
unit J338 must be replaced
completely and a
basic setting
performed.

50
SSP 198/16
Sensors
The hot-film air mass meter
operates on the same principle as
before.
In certain engine operating states,
pulsations occur in the intake tract,
reversing the air flow - and this
gives rise to measurement errors.
The hot-film air mass meter is designed in such
a way that it is able to recognise this returning
air flow (pulsation fault).
This more exact method of intake air
measurement in all operating states improves
engine management and reduces exhaust
emissions.
The hot-film air mass meter is a thermal
flowmeter. A partial airflow from the
measuring pipe is fed past the sensor element
through a measuring channel in the air mass
meter housing.
The ascertained temperature values are
evaluated in the evaluation electronics. The
Motronic applies a voltage proportional to the
air mass to the air mass meter. This voltage is
needed to calculate the injection period and of
actual engine torque.
Substitute function and self-diagnosis:
The air mass meter detects air masses above
or below predefined limits. If the air mass
meter fails, the air mass is calculated on the
basis of a characteristic curve (throttle valve
angle and engine speed).
Hot-film air mass meter
Sensor element
Meas.
channel
Evaluation electronics
Hot-film air mass meter G70