Functional description, see BMW Service Technology:
TIS -> Document -> SI Technology -> Enter SBT Number
SBT number:
The DME activates the ignition coils via the ionic current control units. There is an ionic current control unit for each cylinder bank.
The ionic current control units make it possible to monitor each individual combustion and misfire and to detect combustion knock. Here, a distinction can be made by the DME as to whether misfires were caused by a lack of ignition sparks or poor combustion.
Ignition activation:
via the signals S_IGZ1-10, the DME activates the final stages for the ignition in the ionic current control units.
Ionic current measurement:
immediately after the end of the ignition sparks, the ionic current control units apply a constant measured voltage to the electrodes of the spark plugs. Here, the ionic current control units receive and amplify the currents that arise (ionic currents).
Via the signals A_ION1 and A_ION2, the ionic current that arises with each combustion is then sent from each ionic current control unit to the DME. The ionic current is 0 - 20 mA and is evaluated in the DME. This evaluation enables the DME to detect misfires and combustion knocks.
The measured voltage is created in that the spark current that flows during the duration of spark combustion flows into a capacitor in the ionic current control unit. The energy that is stored in the process is applied after the ignition spark as measured voltage to the spark plug electrodes. The ionic current flows in the opposite direction to that of the spark current.
Signal amplification:
the DME assesses the quality of the incoming ionic current signals and indicates to the ionic current control units via the signals S_IONV1 and S_IONV2 the extent to which the ionic current signals have to be amplified. The amplification factor ranges from 1 - 5.
Measurement voltage selection:
the DME decides depending on the operating range whether 80 V or 160 V is to be applied as measured voltage at the spark plugs. Via the signals S_IONS1 and S_IONS2, the DME sends the measurement voltage selection to each ionic current control unit.
If misfires are detected, faults are stored in the fault code memory. The type of fault indicates whether ignition or combustion misfires were detected.