JPS57206773A - Ignition timing control unit for internal combustion engine - Google Patents

Abstract

PURPOSE: To lower the temperature of the gas containing catalyst and to prevent the catalyst from being overheated in an engine whose exhaust system is provided with a catalystic converter, by compulsively advancing the engine ignition timing, regardless of the engine operating condition, depending on whether the run belongs to high speed operation or whether the catalyst bed temperature is high.

CONSTITUTION: The primary ignition signal 'a' is inputted also into a high speed operation detection circuit 34. And if the engine R.P.M. obtained from the primary ignition signal 'a' is in a high speed range higher than the specified, an instruction is given, regardless of other operating conditions, to an ignition timing control circuit 32 in order to bring compulsively the ignition timing to the lead side. In a circuit 32, the primary ignition signal 'a', which is coming from a distributer 10, is supplied into an igniter 30 without delay, in another word, with lead side timing. Accordingly, in this high speed operation range, the temperature of the gas containing catalyst is lowered, preventing overheat of the catalyst. When the catalyst bed temperature is detected to be high, the ignition timing can be brought compulsively to the lead side, using the output signal from a catalyst bed temperature sensor 36.

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