Deterioration diagnosis system for exhaust gas sensor

Abstract

A diagnosis device calculates a lean-direction responsiveness characteristic and a rich-direction responsiveness characteristic of the exhaust gas sensor. The lean-direction responsiveness represents a responsiveness of the sensor in a case that an air-fuel ratio is controlled in such a manner as to be varied in a lean direction. The rich-direction responsiveness represents a responsiveness of the sensor in a case that the air-fuel ratio is controlled in such a manner as to be varied in a rich direction. The diagnosis device determines whether the exhaust gas sensor deteriorates based on at least one of the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic, and on a comparison result between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic view of an engine control system according to an embodiment of the present invention;

FIG. 2 is a time chart for explaining a deterioration diagnosis for an air-fuel ratio sensor;

FIG. 3 is a flowchart showing process of a first diagnosis;

FIG. 4 is a flowchart showing a process of a second diagnosis;

FIG. 5 is a flowchart showing a process of the second diagnosis;

FIG. 6 is a chart showing a dispersion of a deterioration determining parameter in a case that the air-fuel sensor has no deterioration and in a case that the air-fuel ratio sensor deteriorates; and

FIG. 7 is a chart showing a dispersion of a deterioration determining parameter according to a related diagnosis.

Claims

1. A deterioration diagnosis system for an exhaust gas, comprising: an exhaust gas sensor disposed in an exhaust pipe of an internal combustion engine; anda diagnosis means for diagnosing a deterioration of the exhaust gas based on a lean-direction responsiveness characteristic of the exhaust gas sensor and a rich-direction responsiveness characteristic of the exhaust gas sensor, the lean-direction responsiveness representing a responsiveness characteristic of the exhaust gas sensor in a case that an air-fuel ratio detected by the exhaust gas sensor is controlled in such a manner as to be varied in a lean direction, the rich-direction responsiveness representing a responsiveness characteristic of the exhaust gas sensor in a case that the air-fuel ratio detected by the exhaust gas sensor is controlled in such a manner as to be varied in a rich direction, whereinthe diagnosis means determines whether the exhaust gas sensor deteriorates based on at least one of the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic, and on a comparison result between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic.

2. A deterioration diagnosis system according to claim 1, wherein the comparison result is a ratio or a difference between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic.

3. A deterioration diagnosis system according to claim 2, wherein the diagnosis means determines that the exhaust gas senor deteriorates when the lean-direction or the rich-direction responsiveness characteristic exceeds a predetermined deterioration determining value and that the ratio between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic exceeds a predetermined deterioration determining value.

4. A deterioration diagnosis system according to claim 2, wherein the diagnosis means determines that the exhaust gas sensor deteriorates when the lean-direction or the rich-direction responsiveness characteristic exceeds a predetermined deterioration determining value and that the difference between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic exceeds a predetermined deterioration determining value.

5. A deterioration diagnosis system according to claim 1, wherein the diagnosis means is allowed to diagnose the deterioration of the exhaust gas when the internal combustion engine is in idling state.

6. A deterioration diagnosis system for an exhaust gas, comprising: an exhaust gas sensor disposed in an exhaust pipe of an internal combustion engine; anda diagnosis device diagnosing a deterioration of the exhaust gas based on a lean-direction responsiveness characteristic of the exhaust gas sensor and a rich-direction responsiveness characteristic of the exhaust gas sensor, the lean-direction responsiveness representing a responsiveness of the exhaust gas sensor which detects an air-fuel ratio varying lean, the rich-direction responsiveness representing a responsiveness of the exhaust gas senor which detects the air-fuel ratio varying rich, whereinthe diagnosis device determines whether the exhaust gas sensor deteriorates based on at least one of the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic, and on a comparison result between the lean-direction responsiveness characteristic and the rich-direction responsiveness characteristic.