Function of ECU - Ignition

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The uncorrected basic injection time for injection is used as load signal for ignition. A three-dimensional ignition map is superimposed on the load signal and engine speed. So the most favorable ignition timing in respect to exhaust gas emissions and fuel consumption is selected by the control unit at each engine speed/load point.

With the throttle valve closed, the lowest line of the map is selected as the idle/coasting characteristic line. For engine speed below the required idle speed, the ignition timing is advanced in order to obtain idle stabilization. For deceleration operation, the ignition timing is programmed in adaption to exhaust emissions and driveability.

At full load, the uppermost line of the ignition map is selected, where the most favorable ignition value pertaining to the individual injection for full load increase is programmed with the knocking limit being taken into consideration. For starting an ignition timing of 10° BTDC independent from the ignition map is programmed which is retarded down to 5° BTDC at hot engine. Moreover, an ignition timing correction depending on engine temperature is effective in the different operating ranges of the ignition map.

During idle and thrust operation of the cold engine, the ignition timing is advanced up to 5° BTDC beyond the idle/thrust characteristic line to achieve quicker warm-up by increased engine speed.

During partial and full load at cold engine, the ignition timing is advanced up to 8° BTDC in order to match the demands in these operating conditions. With increasing temperature of the intake air and to prevent pinging at partial and full load, the ignition timing is retarded about 8° in comparison to the ignition map.

When the engine is at rest, the electronic control unit prevents the primary circuit of the ignition coil from being closed by means of an open circuit current switch-off.