Deterioration diagnosis device for catalyst

摘要

A deterioration diagnosis device, which performs a deterioration diagnosis of a catalyst, includes an exhaust-gas sensor provided downstream of the catalyst in a flow direction of exhaust gas such that an output value of the exhaust-gas sensor is used at least in the deterioration diagnosis. The deterioration diagnosis device further includes the constant current supply portion which applies a voltage to a sensor element of the exhaust-gas sensor to change an output characteristic of the exhaust-gas sensor, a response-time detection portion which detects a response time required for the output value of the exhaust-gas sensor to change from a rich threshold to a lean threshold, a response-time correction portion which controls the constant current supply portion to change the output characteristic of the exhaust-gas sensor so as to shorten the response time when the response time is longer than a predetermined reference time.

主权项

1. A deterioration diagnosis device which performs a deterioration diagnosis of a catalyst used for purification of exhaust gas discharged from an internal combustion engine, the deterioration diagnosis device comprising:
a downstream exhaust-gas sensor provided downstream of the catalyst in a flow direction of the exhaust gas to detect and output an air-fuel ratio of the exhaust gas or to detect and output whether the exhaust gas is rich or lean such that an output value of the downstream exhaust-gas sensor is used in at least in the deterioration diagnosis, the downstream exhaust-gas sensor including a sensor element that includes a pair of electrodes and a solid electrolyte body located between the pair of electrodes; a constant current supply portion which applies a constant current and a voltage to the pair of electrodes to change an output characteristic of the downstream exhaust-gas sensor; and a controller configured to;
detect a response time required for the output value of the downstream exhaust-gas sensor to change from a predetermined rich threshold to a predetermined lean threshold during a fuel-cut control in which fuel injection of the engine is stopped; andchange the output characteristic of the downstream exhaust-gas sensor by controlling the constant current supply portion and applying the constant current and the voltage to the pair of electrodes so as to shorten the response time when the response time detected by the controller is longer than a predetermined reference time.