Internal combustion engine combustion state determining device

摘要

The device has a coil (4) which generates a high voltage for ignition. A spark plug (8) ignites an air/fuel mixture in a cylinder of the engine by discharging the high voltage. An ion current detector detects an ion current signal corresponding to the number of ions that are generated in the cylinder directly after the combustion of the air/fuel mixture. A pulse-generating circuit (20) executes wave-shaping of the ion current signal into an ion pulse signal. A crankshaft angle sensor generates a signal indicating a first and second reference crankshaft angles (75 and 5 deg before top dead centre). An electronic control unit generates an ignition signal to excite or de-excite the coil according to the crankshaft angle and which determines the combustion state in the plugs according to the ion pulse signal. The electronic control unit has a flank detector for the end flank of an ion pulse which is contained in the pulse signal in the detection zone extending from the second to the first reference angle. A level detector detects the level of the pulse signal at the first reference angle. It also has a device to determine the combustion state of the engine according to the outputs received from the previous two devices.