Method of abnormality detection of oxygen concentration sensor

A method for controlling an air/fuel ratio of the intake air/fuel mixture of an internal combustion engine provided with an oxygen concentration sensor at the exhaust system thereof, said sensor including a sensor unit having oxygen pump and sensor cell elements forming a gas diffusion control region therebetween into which the exhaust gas is supplied, voltage supply means for supplying a pump voltage determined in accordance with deviation of a sensor voltage appearing across said sensor cell element from a reference voltage so as to maintain said sensor voltage at said reference voltage and signal generating means for generating an oxygen concentration signal varying with a pump current flowing through said oxygen pump element, said method comprising:

• setting a target air/fuel ratio in accordance with the load of said engine;
• determining an air/fuel ratio control value in accordance with the engine operating conditions of said engine while comparing the oxygen concentration signal with said target air/fuel ratio;
• controlling the intake air/fuel ratio in accordance with said air/fuel ratio control value;
• detecting an appearance of a sensor value normally indicative of a rich condition in which the sensed intake air/fuel ratio is within a rich region;
• comparing said pump current with a critical high level;
• and determining an abnormality of said oxygen concentration sensor according to when said pump current is larger than said critical high level upon detection of the rich condition in said step of detecting.

A method for controlling an air/fuel ratio of the intake air-fuel mixture of an internal combustion engine provided with an oxygen concentration sensor at the exhaust system thereof, said sensor including a sensor unit having oxygen pump and sensor cell elements forming a gas diffusion control region therebetween into which the exhaust gas is supplied, voltage supply means for supplying a pump voltage determined in accordance with deviation of a sensor voltage appearing across said sensor cell element from a reference voltage so as to maintain said sensor voltage at said reference voltage, and signal generating means for generating an oxygen concentration signal varying with a pump current flowing through said oxygen pump element, said method comprising:

• determining a basic air/fuel ratio control value in accordance with the engine operating conditions o said engine;
• setting a target air/fuel ratio in accordance with the load of said engine;
• deriving a compensation value which increases as long as an air/fuel ratio represented by the oxygen concentration signal is leaner than said target air/fuel ratio;
• correcting said basic air/fuel ratio control value by said compensation value;
• controlling the intake air/fuel ratio in accordance with the corrected basic air/fuel ratio control value;
• comparing said sensor volatge with said reference voltage and said compensation value with a predetermined value;
• and
• determining an abnormality of said oxygen concentration sensor according to when said sensor voltage is lower than said reference voltage and said compensation value is larger than said predetermined value.

A method for controlling an air/fuel ratio of an intake air-fuel mixture of an internal combustion engine progided with an oxygen concentration sensor at the exhaust system thereof, said sensor including a sensor unit having oxygen pump and sensor cell elements forming a gas diffusion control region therebetween into which the exhaust gas is supplied, and a reference gas region sandwiching said sensor cell element together with said gas diffusion control region, voltage supply means for supplying a pump voltage determined in accordance with deviation of a sensor voltage appearing across said sensor cell element from a reference voltage so as to maintain said sensor voltage at said reference voltage, and signal generating means for generating an oxygen concentration signal varying with a pump current flowing through said oxygen pump element, said method comprising:

• setting a target air/fuel ratio in accordance with the load of said engine;
• determining an air/fuel ratio control value in accordance with the engine operating conditions of said engine while comparing the oxygen concentration signal with said target air/fuel ratio;
• controlling the intake air/fuel ratio in accordance with said air/fuel ratio control value;
• comparing said pump current with a critical high level and said sensor voltage with said reference voltage;
• and
• determining an abnormality of said oxygen concentration sensor according to when said pump current is larger than said critical high level and said sensor voltage is lower than said reference voltage.