Importance

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Abstract

An internal combustion engine (1) is provided with a three-way catalytic converter (16) which purifies exhaust gas, a spark plug (6) which ignites a gaseous mixture and a throttle (11) which regulates an intake air flow rate. When the engine (1) is started, the ignition timing of the spark plug (6) is retarded based on the difference of the rotation speed Ne from a target idle rotation speed Net. If the engine rotation speed Ne is higher than the target idle rotation speed even after the ignition timing has reached a retard limit, the ignition timing is fixed to the retard limit and the intake air flow rate is reduced through the throttle (11), thereby forcing the engine rotation speed Ne to converge rapidly to the target idling rotation speed Net while maintaining the ignition timing at the retard limit to ensure rapid temperature increase in the converter (16).

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First Claim