Description of the electronic ignition system, E39
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Description of the electronic ignition system, E39
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Electronic ignition system (EI), function
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The electronic ignition system (EI) produces and regulates a secondary high energy spark. This spark ignites the compressed fuel mixture at exactly the right time, which results in optimum performance, fuel economy and exhaust cleaning. The engine control module (ECM) essentially collects information from the crankshaft and camshaft sensors in order to control the spark sequence, duration and timing.
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Crankshaft position sensor
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The sensor circuit for crankshaft position consists of a 5 V reference circuit which is supplied from the engine control module (ECM), a low reference circuit and an output signal circuit. The crankshaft position sensor is a sensor unit with integrated circuits which with an internal, magnetic prevoltage give a digital output. Sensors sense magnetic changes caused by the teeth and the gaps on a 58-tooth reluctor wheel on the crankshaft. Each tooth on the reluctor wheel is located with a gap corresponding to a 60-tooth wheel, with 2 teeth missing in a reference gap. The crankshaft position sensor generates a TO/FROM direct current at different frequencies with 58 output pulses per crankshaft rotation. The output frequency of the crankshaft position sensor is dependent on the speed of rotation of the crankshaft. The crankshaft position sensor sends a digital signal which represents the crankshaft's solenoid sensor wheel to the ECM while the teeth on the wheel rotate past the crankshaft sensor. The ECM uses each crankshaft position pulse to determine the crankshaft speed and it decodes the reference gap in the crankshaft's reluctor wheel in order to identify the crankshaft position. This information is then used to assess the engine's optimum ignition and injection points. The ECM also uses output data from the crankshaft position sensor to determine the position of the camshaft relative to the crankshaft and to detect incorrect ignitions in the cylinder.
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Crankshaft reluctor wheel
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The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 teeth and one reference gap. The teeth are situated at 6 degree intervals, and with a 12 degree interval as a reference gap. The pulse from the reference gap is also known as a synchronisation pulse. The synchronisation pulse is used to synchronise the ignition coils' ignition sequence with the crankshaft position while the other teeth give the location of the cylinders during a revolution.
The engine has a camshaft sensor for each camshaft. The sensor is activated by a toothed reluctor wheel which is built into the camshaft drive. The camshaft sensor emits four signal pulses per camshaft revolution. Each of the reluctor wheel teeth is of different sizes, which is used to identify the compression stroke of each cylinder and to control the sequential fuel injection. The camshaft sensors are also used to regulate the cam angle. The sensors are connected to the engine control module (ECM) via the following circuits:
The engine has a block mounted knock sensor for each pair of cylinders. The knock sensor system makes it possible for the engine control module (ECM) to control the ignition setting for the best possible performance while at the same time protecting the engine from harmful spikes. The knock sensor generates an AC signal which varies with the level of vibration while the engine is running. The ECM adjusts the ignition pin setting according to the amplitude and frequency of the knock sensor signal. The ECM receives the knock sensor signals via 2 insulated signal circuits. The ECM learns a minimum knock sensor noise level for the entire speed range. The ECM monitors a normal knock sensor signal.
The ECM generates a 20 kHz signal on the output circuit and monitors to ensure that it is returned and registered on the return circuit. The ECM processes the return signal in order to check the internal knock sensor processor.
Every ignition coil/module has the following circuits:
The engine control module (ECM) regulates the individual coils by sending time pulses on the IC circuit for every ignition coil/module in order to activate a spark.
The ignition pins are connected to the relevant coil with a short gaiter. This gaiter contains a spring which transmits the energy of the ignition spark from the coil to the ignition pin. The ignition pin's electrode is coated with platinum for a longer service life and higher efficiency.
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Electronic module, engine (ECM)
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The engine control module, control module, E39, (ECM) controls all ignition system functions and constantly corrects the timing for the spark. The ECM monitors information from various sensor input data which includes the following (where appropriate):
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Throttle valve position sensor (TP)
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Engine coolant temperature sensor (ECT)
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Mass air flow meter (MAF)
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Intake air temperature sensor (IAT)
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Vehicle speed sensor (VSS)
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The engine's knock sensor (KS)
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The intake pipe's pressure sensor (MAP)
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Under normal operation, the engine control module (ECM) controls all ignition functions. If the signal from any of the crankshaft or camshaft sensors is lost, the engine will continue to work because by default the ECM switches to an emergency mode in which the remaining sensor signals are used. Every coil is internally protected against damage from excess voltage. If one or more coils is damaged in this way, this leads to misfires. There are diagnostic trouble codes for carrying out thorough diagnosis of the ignition system using a diagnostic tool.
