Signal shape and setpoint values
The ignition signal calculation also ensures that the ignition spark is produced in the correct cylinder, with optimum ignition timing and with the necessary energy. To do this, the speed signal from the crankshaft is recorded. From this the engine control unit calculates the crank angle and the current engine speed.
The ignition output stages are then switched on and off for any required crank angle (sensible range for petrol engine: - 70 crankshaft degrees before top dead center up to +30 crankshaft degrees after top dead center. In a 4-stroke engine, ignition is only required after every second revolution which means the camshaft sensor is necessary in order to clearly allocate a cylinder.
| Item | Explanation |
|---|---|
| 1 | Voltage at terminal 1 of ignition coil (from ignition output stage) |
| 2 | Charge current, primary coil |
| 3 | Time |
The basis for multiple spark ignition is repeated switching on and off of the ignition coil. As a result, the actual ignition spark is extended to produce a band of sparks. The individual sparks are cancelled by recharging early with the result that no further energy at the spark plug is transmitted to the fuel-air mixture. Residual energy is left In the ignition coil which also minimizes the recharging time. Multiple spark ignition is only intended to be used in the low engine speed range and also during the warm-up phase (spark plug cleaning).
Observe the following setpoint values for the ignition coil:
| Variable | Value |
|---|---|
| Voltage range | 6 to 16 V |
| Voltage, secondary coil, in normal operating mode | up to 29 kV |
| Maximum current consumption in normal operating mode | 8 to 10.5 A |
| Primary resistance | less than 600 mΩ |
| Ratio, primary coil to secondary coil | 1:80 |
| Temperature range | -40 to 140 deg C |