Air/fuel ratio control device for an internal combustion engine

A method for controlling the air/fuel ratio in an internal combustion engine having an air/fuel ratio control system and having fuel supply means for controlling the air/fuel ratio, said system including an exhaust gas sensor for determining the concentration of an exhaust gas component and generating an exhaust gas sensor signal corresponding to the sensed exhaust gas component concentration, said system being operable to control the air/fuel ratio by feedback control or by open loop control and having means for switching control operation between feedback control and open loop control corresponding to a condition of said sensor, the method comprising

• supplying an electric current to said exhaust gas sensor;
• changing said current value between predetermined maximum and minimum values;
• generating a sensor signal indicative of the sensed exhaust gas component concentration while applying said electric current to said sensor;
• comparing said sensor signal value with reference values, said reference values defining maximum and minimum values respectively to determine if the sensor is in a condition to carry out feedback control;
• controlling said fuel supply means by feedback control;
• measuring the period of time during which said sensor signal value remains below said minimum value;
• switching control operation from feedback control to open loop control when said measured period of time is longer than a predetermined period;
• and
• resetting the value of said reference values to be compared with said sensor signal value to the minimum value thereof and setting said electric current to be supplied to the exhaust gas sensor to the minimum value thereof when switching control operation from feedback control to open loop control.

A feedback control system for an internal combustion engine, said control system operable as a feedback system or an open loop system comprising:

• fuel supply means for supplying fuel to the engine at a controlled rate, said fuel being supplied as a gas mixture having an air/fuel ratio;
• an exhaust system including an exhaust passage having an oxygen sensor for determining oxygen concentration in the exhaust gas and for producing a sensor signal indicative of the determined oxygen concentration;
• a power circuit for supplying an electric current to said oxygen sensor, said power circuit varying the electric current value to be supplied to the oxygen sensor depending upon the sensor temperature;
• control means for comparing said sensor signal value with a first reference value to discriminate whether the sensor temperature condition satisfies a feedback condition and for feedback controlling said fuel supply means based on a difference between said sensor signal value and a second reference value representative of a desired air/fuel ratio while said feedback condition is satisfied, said control means including means for incrementing said second reference value at a given rate and a given timing and for setting said second reference value at a minimum value when control operation is switched from feedback control to open loop control, said control means varying the current value supplied to the oxygen sensor to a predetermined minimum value during open loop operation.

A feedback control system for an internal combustion engine for controlling air/fuel ratio of a mixture to be supplied thereto, comprising:

• fuel supply means for supplying fuel to the engine at a controlled rate;
• an exhaust system including an exhaust passage having an oxygen sensor for determining an oxygen concentration in the exhaust gas and producing a sensor signal value indicative of said oxygen concentration;
• a power circuit for supplying an electric current to said oxygen sensor, said power circuit varying the current value depending on the oxygen sensor temperature condition within a predetermined range;
• discrimination means for discriminating if said mixture is rich or lean based on said sensor signal value, said discrimination means comprising said sensor signal value with a second reference value representative of a desired air/fuel ratio;
• control means for feedback controlling said fuel supply means based on the difference between said second reference value and said sensor signal value, said control means having means for incrementing said second reference value at a given rate and a given timing during feedback control, said control means further comprising said sensor signal value with a first reference value indicative of the minimum value for feedback control operation and having means for switching control operation from feedback control to open loop control when the sensor signal value is smaller than said first reference value and setting said second reference value to a predetermined minimum value and said current value to be supplied to the sensor by said power circuit to a minimum value in said predetermined range.

A method for controlling air/fuel ratio in a mixture supplied to an internal combustion engine having a fuel supply comprising:

• measuring an oxygen concentration in an exhaust gas and producing a sensor signal indicative of the measured oxygen concentration;
• comparing said sensor signal value with a second reference value representative of a desired air/fuel ratio and obtaining any difference therebetween;
• determining fuel supply to the engine based on said difference between the measured sensor signal value and said second reference value and feedback controlling said fuel supply so that the air/fuel ratio supplied to said engine approaches said desired value;
• supplying electric current to said oxygen sensor,
• varying said electric current to the sensor depending on the sensor temperature condition;
• comparing said sensor signal value with a first reference value representative of the minimum value of the sensor signal for feedback control operation;
• measuring a period of time during which the sensor signal value remains below said first reference value;
• switching operational control of said fuel supply from feedback control to open loop control when the measured period exceeds a predetermined period;
• setting said second reference value to a predetermined minimum value and said electric current to the sensor to a predetermined minimum value during open loop operation;
• and
• returning the operational control from open loop to feedback control when the sensor signal value becomes larger than the minimum first reference value.