Method for operating an ignition device for an internal combustion engine
An ignition device for an internal combustion engine has an ignition coil disposed as a transformer, a spark plug connected to the secondary winding of the ignition coil, an actuatable switching element connected in series with the primary winding of the ignition coil, and a control unit connected to the primary winding and to the control input of the switching element. After charging the ignition coil, building up an ignition spark through non-conductive switching of the switching element, and after renewed conductive switching of the switching element for operating the ignition coil in transformer operation, the supply voltage of the control unit is detected and if a pre-determined value, representing the presence of a surface gap, is exceeded, the switching element is once more switched non-conductive.
1. A method of operating an ignition device for an internal combustion engine, the ignition device having an ignition coil formed as a transformer with a primary winding and a secondary winding, a spark plug connected to the secondary winding of the ignition coil, a drivable switching element connected in series with the primary winding of the ignition coil, and a control unit connected to the primary winding of the ignition coil and to a control input of the switching element, the method comprising:
providing with the control unit a supply voltage for the ignition coil and a drive signal for the switching element depending on a current through the primary winding and a current through the secondary winding of the ignition coil and on a primary voltage between a node connecting the primary winding of the ignition coil and the switching element and a negative connection of the supply voltage;
alternately switching-on and switching-off the switching element depending on whether threshold values for the primary voltage or a voltage derived therefrom are undershot or exceeded, to thereby transfer energy into an ignition spark of the spark plug through the current through the primary winding of the ignition coil and the current through the secondary winding of the ignition coil; and
once the ignition coil has been charged, an ignition spark has been built up by switching-off the switching element and the switching element has been switched on once more for operating the ignition coil in a transformer operating mode, detecting the supply voltage of the control unit and, if a predetermined value of the supply voltage representing a presence of a surface discharge is exceeded, switching off the switching element.
2. The method according to claim 1 , which comprises, after a wait time for a decay of charges at the ignition coil, once more starting the ignition procedure.
3. The method according to claim 2 , which comprises starting the renewed ignition with reverse polarity of the supply voltage depending on a combustion chamber pressure.
4. The method according to claim 3 , which comprises, in a case of a combustion chamber pressure of less than approximately 15 bar, causing the renewed ignition to take place with reverse polarity.