engine AUDI S4 1998 B5 / 1.G Engine Manual

36
SSP 198/09

Subsystems of the Motronic
Electrically actuated throttle
valve (electronic accelerator)
With the Motronic ME 7.1, Audi is
using an electrically actuated
throttle valve for the first time.
There is no longer any need for a
mechanical accelerator cable
between the accelerator and
throttle valve. This has been
replaced by an electronic control
system (drive-by-wire).
The system comprises the following
components:
• Accelerator position sender
• Engine control unit
• throttle valve control part
Accelerator position sender
Safety module
Throttle valve control
part J338
The accelerator position sender records the
accelerator pedal angle and transfers it to the
engine control unit.
The engine control unit adjusts the throttle
valve by means of an electric motor. A
continuous stream of feedback signals on the
position of the throttle valve is sent to the
engine control unit.
Extensive security measures in hardware and
software format - such as twin senders, safety
module and self-monitoring computer
architecture - are integrated in the electronic
accelerator .
Input signalsOutput signals
Angle sender for
throttle valve drive
G187 and G188Accelerator position
senders G79 and
G185
Engine control unit

CPU
CPU = Control Processing Unit
Throttle valve
drive G186

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

38
Subsystems of the Motronic
SSP 198/12

Accelerator position senders G79
and G185
The accelerator position sender transfers an
analog signal corresponding to the accelerator
position to the Motronic. To ensure that the
electronic accelerator functions reliably, the
accelerator position sender has two
independent potentiometers (G79 and G185).
They have different characteristic curves (see
diagram).
The control unit monitors the two senders G79
and G185 for proper functioning and
plausibility.
If a sender fails, the other sender serves as a
substitute.
The accelerator position sender transfers the
driver’s inputs to the Motronic and provides
kickdown information to the automatic
gearbox.
Lever
Acc. position sender
AcceleratorThere is no separate switch for
kickdown information. Integrated in
the accelerator position sender is a
“mechanical pressure point “ which
conveys an authentic “kickdown feel”
to the driver.
When the driver operates the
kickdown, the full-load voltage of the
accelerator position sender is
exceeded. If a voltage defined in the
engine control unit is attained in the
process, this is interpreted as a
kickdown and transferred to the
automatic gearbox (via CAN-Bus).
The accelerator position senders for
the manual gearboxes and automatic
gearboxes are identical. Kickdown is
enabled or disabled via the
accelerator limit stop (refer to chapter
on “TDI engines”).

SSP 198/25

Resistance in

W

Accelerator travel
G79
G185
LL

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

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

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.

44
Subsystems of the Motronic
120
180
°C 60
90
12
93
6
120
°C 60
12
16
120
100
80
50
30
10140
1234
5
6
7
160
180
200
220
260
Volt8
1/2
1/1
8
0
EPC
EPC
SSP 198/47

Fault lamp for electric throttle
control K132
Faults in the Electronic Accelerator System are
detected by the self-diagnosis and indicated
via the separate EPC fault lamp. At the same
time, an entry is made in the fault memory.
When the ignition is turned on, the fault lamp
comes on and must go out again after 3
seconds if a fault state does not exist.
Fault lamp K132 is activated directly by the
engine control unit via an earth potential.
If a fault occurs in the Electronic Accelerator
System, an appropriate emergency running
program will be activated (refer to Accelerator
position sender and throttle valve control part).
EPC
stands for
E
lectronic
P
ower
C
ontrol.

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

47
SSP/198/13

Exhaust gas temperature sender
G235 and G236
To facilitate exhaust gas temperature control,
the exhaust gas temperature must be recorded
to a high degree of accuracy.
An accuracy of ± 5 °C is achieved in the
measurement range from 950 °C to 1025 °C.
The exhaust gas temperature sender is located
inside the exhaust manifold upstream of the
exhaust gas turbocharger.
It comprises a measuring sensor and
evaluation electronics.
The measuring sensor and the control unit are
permanently connected by means of a
shielded, heat-resistant wire.
The evaluation electronics convert the signal
which the measuring sensor generates into a
pulse-width-modulated signal (PWM signal).
This is a square-wave signal with a fixed
frequency and a variable pulse duty factor.
The pulse duty factor is expressed as a
percentage . The measurement range extends
from
³
10% to
£
90%.
A specific pulse duty factor is assigned to each
temperature (refer to diagram).
Substitute function and self-diagnosis:
A pulse duty factor of <1% or >99% is
recognised as a fault.
A fault is detected as of a certain enrichment
quantity.
If a sender fails, the charge pressure is reduced
to a safe level and an emergency enrichment
characteristic (engine speed-dependent) is
used.
Exhaust gas temperature sender
evaluation electronics
SSP 198/56
90%
70%
50%
30%
10%
945°C
950°C
960°C
970°C
980°C
990°C
1000°C
1010°C
1025°C
1030°C
Exhaust gas temperature
Pulse duty factor
Meas.