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FUEL INJECTION
Fuel-induction and ignition systems perform individual
assignments:
Jetronic controls the fuel metering function, and electronic
ignition optimises the ignition function. Together they make an essential contribution to
the quality of combustion. Motronic, as an integrated engine control system, combines the
two.
The fuel-injection and ignition systems are controlled by a single computer in accordance
with common optimisation criteria.
Besides ignition and fuel injection, further subsystems are
integrated into Motronic: lambda
closed-loop control with adaptive initial open-loop control, idle-mixture control,over run
fuel cut off with smooth transition,exhaust gas recirculation, torque control in dynamic
processes.
This integrated microprocessor controlled limit makes it possible to use sensors, signal
conditioning, and signal processing jointly.The processing of the same measurement data
and the joint use of calculated values of individual sub systems allows the best possible
compromise to be attained between the sometimes contradictory objectives with regard to
exhaust, consumption and driveability.
Engine adjustment to achieve the lowest possible pollutant emission is possible with out
significant worsening of driveability. The essential system components are:
Sensors for the
acquisition of engine condition data.
Control unit for
digital signal processing.
Actuators for the generation of ignition and injection pulses, idle
auxiliary air and the rate of exhaust-gas recirculation, air, fuel, and high voltage
circulation. |
1. Fuel tank. 2. Electric fuel pump. 3. Fuel
pump. 4. Pressure regulater. 5. Control Unit. 6. Ignition coil. 7. High voltage
distributor. 8. Spark plug. 9. Injection valve. 10. Throttle valve. 11. Throtle valve
switch. 12. Air flow sensor. 13. Air temperature. 14. Lambda sensor. 15. Engine
temperature sensor. 16. Rotary idle actuator. 17. Engine speed and reference mark sensor.
18. Battery. 19. Ignition and starting switch. 20. A/C switch.
ACQUISITION OF OPERATING DATA
Sensors measure condition variables such as engine speed,
air throughflow, exhaust composition, temperature etc.Engine speed and crankshaft position
are determined using an inductive pin sensor (engine-speed and reference-mark sensor)
which senses the teeth of the starting motor ring gear or a special disk.
PROCESSING OF OPERATING DATA
The engine-condition signals as well as further signals from the
engine's periphery (drive train, auxiliary systems, driver) are processed in the control
unit, after suitable interference suppression circuitry, either via an analog digital
converter or directly by the computer in the case of digital signals.
Output variables are calculated in the computer according to programmed criteria.
The data for this are measurement values, counters, buffered partial results and
engine-specific adaptation parameters, such as characteristic maps or curves.
The output signals for duration of injection,dwell time, ignition point, on-off ratio of
the idle actuator and exhaust-gas recirculation are amplified at their output stages and
transmitted to the actuators.
CHARACTERISTIC MAPS
The Motronic contains several characteristic maps as functions of
engine speed and load,or engine speed and battery voltage, for the following operations:
ignition, injection, warmup, acceleration enrichment, lambda closed loop control, dwell
angle.The dwell-angle map Is a function of engine speed and battery voltage and determines
the power data for ignition.
All other characteristic maps are functions of engine speed and load.The engine-specific
parameters in the individual engine speed and load ranges can be individually adjusted
using the maps without undesired influence on other engine-speed and load ranges.
LAMBDA CLOSED-LOOP CONTROL
The control unit receives the lambda-sensor signal and corrects
the air-fuel mixture by changing the injection time.
The parameters (response time) of the controlled system are strongly dependent on engine
speed, load and temperature
Adjustment takes placeover several control-parameter maps which take into account these
dependencies. The adaptation of the injection characteristic map to engine requirements as
a pre-control for lambda closed-loop control is subordinated to several systematic and
random changes:
Manufacturing tolerances of engines and components
Ageing due to deposits and to changes In compression and inner exhaust-gas recirculation
Deviationscaused by air leakage and environmental influences (temperature, altitude)
The adaptive initial open-loop control of lambda closed-loop control detects these
deviations and determines correction factors to compensate for them. The factors
"learned" during operation are stored in a permanent memory and are thus
available when the vehicle is re-started. The adaptation process can be very slow, since
the deviations happen only once or only very slowly.
SELF-DIAGNOSIS
For after-sales service, Motronic has the advantage that the
measurement value acquired for engine operation can also be used for diagnosis during
vehicle inspection.
The computer continuously checks the available measurement data for admissibility or
plausibility with regard to other measurement values, and can thus detect defects.These
defects can be retained in the memory and output in the workshop.
