Deterioration diagnostic device for an exhaust gas purifier
The invention provides a deterioration diagnostic device for diagnosing a degradation condition of an exhaust gas purifier disposed in an exhaust passage in an engine based on a sensor value of an exhaust gas sensor that is disposed downstream of the purifier. The device includes detecting-signal generating unit for generating a detecting-signal having particular frequency components and multiplying the generated signal to a basic fuel injection amount so as to calculate a fuel injection amount and exhaust gas purifier evaluating for extracting a frequency response corresponding to the detecting-signal from an output of the exhaust gas sensor of the engine, the output being in response to the calculated fuel injection amount, so as to determine a condition of the purifier based on the extracted frequency response.
1. A deterioration diagnostic device for diagnosing a deterioration condition of an exhaust gas purifier disposed in an exhaust passage in an internal-combustion engine based on an output of a first exhaust gas sensor that is disposed downstream of the exhaust gas purifier, comprising:
detecting-signal generating means for generating a detecting-signal having particular frequency components and multiplying the generated detecting-signal by a basic fuel injection amount so as to calculate a fuel injection amount, said detecting-signal being a fixed signal obtained by adding a single trigonometric function wave or a composite wave formed by two or more trigonometric function waves to a predetermined offset value;
exhaust gas purifier evaluating means for extracting a frequency response corresponding to the fixed detecting-signal from an output of the first exhaust gas sensor of the engine, the output being in response to the calculated fuel injection amount, so as to determine a condition of the exhaust gas purifier based on the extracted frequency response;
a second exhaust gas sensor disposed upstream of the exhaust gas purifier in the exhaust gas passage;
air-fuel ratio controlling means for controlling an air-fuel ratio to be supplied to the engine to a predetermined value based on at least an output of the second exhaust gas sensor,
wherein the fuel injection amount is corrected in accordance with a feedback coefficient that is determined based on the output of the second exhaust gas sensor; and
responsiveness evaluating means for performing a bandpass filtering of an output from the first exhaust gas sensor.
2. The deterioration diagnostic device claimed as in claim 1 , wherein the exhaust gas purifier evaluating means determines the condition of the exhaust gas purifier when a predetermined time elapses since the fuel injection amount has been supplied to the engine.
3. The deterioration diagnostic device claimed as in claim 1 , wherein the exhaust gas purifier evaluating means determines the condition of the exhaust gas purifier using the output from the first exhaust gas sensor which has been band-pass filtered.
4. The deterioration diagnostic device claimed as in claim 3 , wherein the exhaust gas purifier evaluating means determines that the exhaust gas purifier is in failure when a value obtained by an integral calculation or a smoothing calculation of absolute values of the band-pass filtered outputs of the exhaust gas sensor exceeds a predetermined value.
5. The deterioration diagnostic device claimed as in claim 1 , wherein the air-fuel ratio controlling means adjusts a predetermined parameter in the air-fuel ratio controlling means so as to suspend the control of the air-fuel ratio or slow down a changing speed of the feedback coefficient when supplying the fuel injection amount to the engine.
6. A method for diagnosing a deterioration condition of an exhaust gas purifier disposed in an exhaust passage in an internal-combustion engine based on a sensor value of an exhaust gas sensor disposed downstream of the exhaust gas purifier, comprising the steps of:
generating a detecting-signal having particular frequency components and multiplying the generated detecting-signal by a basic fuel injection amount so as to calculate a fuel injection amount, said detecting-signal being a fixed signal obtained by adding a single trigonometric function wave or a composite wave formed by two or more trigonometric function waves to a predetermined offset value;
extracting a frequency response corresponding to the fixed detecting-signal from an output of the exhaust gas sensor of the engine, the output being in response to the calculated fuel injection amount, so as to determine a condition of the exhaust gas purifier based on the extracted frequency response;
controlling an air-fuel ratio to be supplied to the engine to a predetermined value based on at least an output of a second exhaust gas sensor disposed upstream of the exhaust gas purifier in the exhaust gas passage; and
performing a bandpass filtering of an output from the first exhaust gas sensor;
wherein the fuel injection amount is corrected in accordance with a feedback coefficient that is determined based on the output of the second exhaust gas sensor.