General description
AUDI 80 gasoline engines have a fuel injection system through a single throttle valve nozzle, developed by BOSCH and named «Mono-Motronic». The system is a block that consists of a body resembling a carburetor in shape and one nozzle. Fuel injection by the injector is determined by the electronic control unit, which simultaneously regulates the ignition timing.
The electronic fuel injection system control unit is located in the footwell of the passenger seat. Via the multi-pin connector, the control unit receives information from the following injection controls:
- Hall sensor on the ignition distributor provides information about the engine speed,
- the lambda probe on the catalyst informs the control unit about the oxygen content in the exhaust gases,
- the throttle valve angle potentiometer informs about the position of the throttle valve and, accordingly, about the volume of incoming fresh air,
- the intake air temperature sensor at the intake port of the injection system reports the temperature of the intake air,
- The coolant temperature sensor on the outlet pipe on the left side of the cylinder head provides information about the current coolant temperature.
Based on the information received, the electronic control unit calculates the duration of the nozzle opening and, accordingly, the amount of fuel injected. In this case, the control unit uses the parameters stored in its memory, obtained during engine tests and representing all conceivable situations that may occur during engine operation. These parameters contain data on the amount of fuel required by the engine in a given situation. This information is electrical signals. In addition to data regarding fuel volume and operating loads, the mentioned parameters contain information on the ignition timing in relation to the respective situation.
The throttle valve is located at the bottom of the fuel injection system and regulates the amount of air sent to the engine for combustion. The degree of opening of the damper is determined by the driver with an effort on the accelerator pedal. Throttle and accelerator pedal are connected to each other by cable traction (see illustration 1.0).
Most of the functional elements of the fuel injection system are combined in one housing. The air entering to form the air-fuel mixture also passes through the system housing. Here, fuel is injected through the nozzle in the same way as the carburetor did before (see illustration 1.0a).
The nozzle is opened by an electromagnet and, depending on the command of the control unit, fuel can be supplied. For optimal dispersion of fuel, the nozzle has inclined outlets, the fuel from which, at the exit, breaks against a conical wall and simultaneously swirls.
The nozzle can only open and close. It does not meter the injected fuel. For this reason, the amount of injected fuel varies by injection duration. This happens as follows: With each pulse from the Hall sensor, the injector injects fuel. If you need a little fuel, then the nozzle, when a pulse is received from the Hall sensor, opens only for a short time. The duration of the opening of the nozzle is often less than one thousandth of a second. If the engine needs more fuel, for example when starting from a cold state or at full operating load, then the injection lasts longer. This happens with every pulse received from the Hall sensor.
The fuel pump delivers fuel under pressure to the pressure reducing valve (see illustration 1.0b).
This valve is designed to provide a constant fuel pressure at the fuel injector in the range of 0.8-1.2 bar. To this end, it diverts the excess of incoming fuel back to the fuel tank, supplying fuel to the fuel return line. The volume of fuel supplied by the fuel pump is generally kept constant.
The throttle angle adjuster is a small angle gear electric motor that moves the throttle lever relative to the idle speed limiter as needed. This ensures a constant idle speed under different operating loads. In front of the throttle lever there is an idle speed sensor that gives the electronic control unit the corresponding signal when the driver takes his foot off the accelerator pedal. This signal is needed by the control unit to stabilize the idle speed. The throttle angle adjuster can be removed. This is necessary, in particular, in the event of a defect in the throttle lever, on which the idle speed sensor is attached (see illustration 1.0c).
The throttle position potentiometer tells the control unit its current position. Rapid throttle opening is recognized as a signal to accelerate and increase speed. As soon as the driver takes his foot off the accelerator pedal, the signal to close the throttle is also a signal to turn off the force directed to open the damper. The transmission of information is carried out using electrical signals, because the potentiometer is nothing more than a modified resistor. Throttle angle potentiometer is factory adjusted and is not disassembled. If the potentiometer is defective, the injection unit must be replaced as a set. In illustration 1.0d, the potentiometer is specially presented disassembled for clarity.
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