Control device of an internal combustion engine

A control device of an internal combustion engine, comprising:

• an intake passage;
• a throttle valve arranged in said intake passage;
• switch means operated in response to the degree of opening of said throttle valve and producing an output signal representing a state wherein the degree of opening of said throttle valve is greater than a predetermined degree;
• a vacuum sensor arranged in said intake passage and producing an output signal representing the absolute pressure therein;
• discriminating means operated in response to the output signals of said switch means and said vacuum sensor for discriminating whether said absolute pressure decreases by a predetermined pressure after the degree of opening of said throttle valve becomes smaller than said predetermined degree to produce an output signal representing a state wherein said absolute pressure decreases by said predetermined pressure after the degree of opening of said throttle valve becomes smaller than said predetermined degree;
• a swirl control valve arranged in said intake passage for creating a swirl motion in a combustion chamber when said swirl control valve is closed;
• valve control means actuating said swirl control valve in response to the output signals of said switch means and said discriminating means for opening said swirl control valve when the degree of opening of said throttle valve exceeds said predetermined degree and for closing said swirl control valve when said absolute pressure decreases by said predetermined pressure after the degree of opening of said throttle valve becomes smaller than said predetermined degree;
• fuel supply means arranged in said intake passage for normally forming a lean air-fuel mixture therein;
• fuel supply control means controlling said fuel supply means in response to the output signals of said switch means and said discriminating means for forming a rich air-fuel mixture in said intake passage when the degree of opening of said throttle valve exceeds said predetermined degree and for forming in said intake passage an air-fuel mixture having an intermediate air-fuel ratio between an air-fuel ratio of said lean air-fuel mixture and an air-fuel ratio of said rich air-fuel mixture until the time said absolute pressure decreases by said predetermined pressure after the degree of opening of said throttle valve becomes smaller than said predetermined degree;
• a spark plug arranged in said combustion chamber and normally producing a spark at a predetermined basic ignition timing;
• and,
• ignition timing control means controlling the ignition timing of said spark plug in response to the output signals of said switch means and said discriminating means for retarding the ignition timing when the degree of opening of said throttle valve exceeds said predetermined degree and for changing the ignition timing to an intermediate ignition timing between said basic ignition timing and said retarded ignition timing until the time said absolute pressure decreases by said predetermined pressure after the degree of opening of said throttle valve becomes smaller than said predetermined degree.