Method of diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter

A method of diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter mounted on an exhaust manifold of an internal combustion engine supplied with an air/fuel mixture, said sensor generating an output signal correlated with an air/fuel composition of said mixture, said method comprising the steps of:

• a) enrichening said mixture, to create a transition of the mixture from a lean to a rich air/fuel composition;
• b) determining a first value assumed by the output signal from said sensor in response to said enrichening;
• c) leaning said mixture, to create a transition of the mixture from a rich to a lean air/fuel composition;
• d) determining a second value assumed by the output signal from said sensor in response to said leaning;
• e) determining an intermediate value lying between said first and second values;
• f) comparing said first value with a first threshold value;
• g) comparing said second value with a second threshold value;
• h) comparing said intermediate value with a third preset threshold value;
• i) comparing said intermediate value with a fourth preset threshold value;
• and
• j) generating a deterioration signal for said sensor if any of the following is true:
• 1) said first value is below said first threshold value;
• 2) said second value is above said second threshold value;
• 3) said intermediate value is less than said third threshold value;
• or
• 4) said intermediate value is greater than said fourth threshold value.

A method of diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter mounted on an exhaust manifold of an internal combustion engine supplied with an air/fuel mixture, said sensor generating an output signal correlated with an air/fuel composition of said mixture, said method comprising the steps of:

• a) enrichening said mixture, to create a transition of the mixture from a lean to a rich air/fuel composition and an enrichening transition of said output signal from said sensor;
• b) acquiring a first value correlated with a first switching time for said output signal from said sensor by determining a first switching delay between said transition of said mixture from a lean to a rich air/fuel composition and said enrichening transition of said output signal, and determining said first value from said first switching delay;
• c) prompting a transition of said mixture from a rich to a lean air/fuel composition and a leaning transition of said output signal from said sensor;
• d) acquiring a second value correlated with a second switching time for said output signal from said sensor by determining a second switching delay between said transition of said mixture from a rich to a lean air/fuel composition and said leaning transition of said output signal, and determining said second value from said second switching delay;
• e) generating a first moving average value correlated with said first value;
• f) generating a second moving average value correlated with said second value;
• g) comparing said first moving average value with a first preset threshold value;
• h) comparing said second moving average value with a second preset threshold value;
• and
• i) generating a deterioration signal for said sensor if said comparisons give different outcomes.

Apparatus for diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter mounted on an exhaust manifold of an internal combustion engine supplied with an air/fuel mixture, said sensor generating an output signal correlated with an air/fuel composition of said mixture, said apparatus comprising:

• a) means for determining a present operating temperature of said engine;
• b) means for determining a present operating condition of said engine;
• and
• c) means for effecting a hot diagnosis of said sensor when the present operating temperature of the engine is greater than a preset reference value, said means for effecting a hot diagnosis comprising means for:
• 1) determining whether said engine is presently in an idle operating condition and said sensor is presently generating an output signal that indicates a lean air/fuel composition of said mixture, and if so:
• i) enrichening said mixture, to create a transition of the air/fuel composition of said mixture from a lean to a rich air/fuel composition;
• and
• ii) determining a first value assumed by the output signal from said sensor in response to said enrichening, said first value being correlated to a rich air/fuel composition of said mixture;
• 2) determining whether said engine is presently in a fuel cut-off condition of a duration greater than a preset threshold, and whether said air/fuel mixture had a rich composition prior to the occurrence of said cut-off condition, and if so:
• i) determining a second value assumed by the output signal from said sensor in response to said cut-off condition, said second value being correlated to a lean air/fuel composition of said mixture;
• 3) comparing said first value with a first threshold value;
• 4) comparing said second value with a second threshold value;
• and
• 5) generating a deterioration signal for said sensor if either said first value is below said first threshold value, or said second value is above said second threshold value.

Apparatus for diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter mounted on an exhaust manifold of an internal combustion engine supplied with an air/fuel mixture, said sensor generating an output signal correlated with an air/fuel composition of said mixture, said apparatus comprising:

• a) means for determining a present operating condition of said engine;
• and
• b) means responsive to a determined condition of said engine for effecting a diagnosis of said sensor comprising means for:
• 1) enrichening said mixture, to create a transition of the mixture from a lean to a rich air/fuel composition;
• 2) determining a first value assumed by the output signal from said sensor in response to said enrichening;
• 3) leaning said mixture, to create a transition of the mixture from a rich to a lean air/fuel composition;
• 4) determining a second value assumed by the output signal from said sensor in response to said leaning;
• 5) determining an intermediate value lying between said first and second values;
• 6) comparing said first value with a first threshold value;
• 7) comparing said second value with a second threshold value;
• 8) comparing said intermediate value with a third preset threshold value;
• 9) comparing said intermediate value with a fourth preset threshold value;
• and
• 10) generating a deterioration signal for said sensor if any of the following is true:
• i) said first value is below said first threshold value;
• ii) said second value is above said second threshold value;
• iii) said intermediate value is less than said third threshold value;
• or
• iv) said intermediate value is greater than said fourth threshold value.

Apparatus for diagnosing the efficiency of an exhaust gas stoichiometric composition sensor placed downstream of a catalytic converter mounted on an exhaust manifold of an internal combustion engine supplied with an air/fuel mixture, said sensor generating an output signal correlated with an air/fuel composition of said mixture, said apparatus comprising:

• a) means for determining a present operating condition of said engine;
• and
• b) means responsive to a determined condition of said engine for effecting a diagnosis of said sensor comprising means for:
• 1) enrichening said mixture, to create a transition of the mixture from a lean to a rich air/fuel composition and an enrichening transition of said output signal from said sensor;
• 2) acquiring a first value correlated with a first switching time for said output signal from said sensor by determining a first switching delay between said transition of said mixture from a lean to a rich air/fuel composition and said enrichening transition of said output signal, and determining said first value from said first switching delay;
• 3) prompting a transition of said mixture from a rich to a lean air/fuel composition and a leaning transition of said output signal from said sensor;
• 4) acquiring a second value correlated with a second switching time for said output signal from said sensor by determining a second switching delay between said transition of said mixture from a rich to a lean air/fuel composition and said leaning transition of said output signal, and determining said second value from said second switching delay;
• 5) generating a first moving average value correlated with said first value;
• 6) generating a second moving average value correlated with said second value;
• 7) comparing said first moving average value with a first preset threshold value;
• 8) comparing said second moving average value with a second preset threshold value;
• and
• 9) generating a deterioration signal for said sensor if said comparisons give different outcomes.