Fuel supply control system for an internal combustion engine of an automotive vehicle

A method for controlling the air/fuel ratio in an internal combustion engine under both open loop control and .lambda.-control modes of operation, said method comprising the steps of:

• determining the air flow rate flowing through an air intake passage and generating a first signal indicating said determined air flow rate;
• determining the engine speed and generating a second signal indicating said determined engine speed;
• determining oxygen concentration in the exhaust gas of said engine and generating a third signal indicative of the oxygen concentration of the exhaust gas;
• determining a basic fuel injection amount based on said first and second signals respectively indicating determined air flow rate and engine speed;
• determining an engine temperature and generating a fourth signal corresponding thereto;
• correcting said determined fuel injection amount based on said fourth signal;
• determining a correction coefficient based on said temperature corrected fuel injection amount and the second signal;
• comparing said correction coefficient with a first and a second given value to discriminate whether .lambda.-control or open loop control is to be carried out said first value being higher than said second value;
• clamping said .lambda.-control when the correction coefficient exceeds said first given value and producing open loop control by modifying said temperature corrected fuel injection amount based on said correction coefficient;
• and
• clamping open loop control when the correction coefficient is less than said second given value, and producing .lambda.-control by sensing said third signal and controlling the air/fuel ratio at a stoichiometric value.

A fuel supply control system for an internal combustion engine comprising:

• first sensor means for detecting an air flow rate flowing through an air intake passage and producing a first sensor signal having a value proportional to the detected air flow rate;
• second sensor means for detecting engine speed and producing a second sensor signal having a value proportional to the detected engine speed;
• third sensor for detecting oxygen concentration in an exhaust gas and producing a third signal having a value proportional to the detected oxygen concentration;
• fourth sensor means for detecting engine temperature and producing a fourth sensor signal having a value proportional to the detected engine temperature;
• fifth means for determining a basic fuel injection amount based on said first and second sensor signal values and correcting the basic fuel injection value based on the fourth sensor signal value;
• sixth means for determining a correction coefficient for further correcting the fuel injection amount, said correction coefficient determined by said sixth means based on said temperature corrected basic fuel injection amount and said second sensor signal value;
• seventh means for effecting .lambda.-control based on said third sensor signal value;
• eighth means for effecting open loop control, said eighth means calculating a final fuel injection value by correcting the fuel injection amount determined by said fifth means by the correction coefficient determined by said sixth means;
• and
• ninth means for selectively operating said seventh and eighth means, said ninth means comparing said correction coefficient with first and second reference values respectively defining first and second threshold values, said ninth means clamping operation of said seventh means, when the correction coefficient exceeds said first reference value to switch from .lambda.-control to open loop control and clamping operation of said eighth means when the correction coefficient is lower than said loop control to switch control mode from open loop control to -control.