Catalyst degradation determination device for internal combustion engine

Abstract

The invention discloses a catalyst degradation determination device for determining degradation of an exhaust purification catalyst placed in an exhaust path of an internal combustion engine. The determination device forcibly changes the air-fuel ratio of a mixture gas, calculates the amount of oxygen occlusion by the catalyst based on the concentration of oxygen that is present in exhaust gas downstream of the catalyst and changes after the air-fuel ratio is forcibly changed, and determines degradation of the catalyst based on the calculated amount of oxygen occlusion. The engine has a function of incrementally correcting the amount of fuel injection so as to make the air-fuel ratio of the mixture gas richer than a theoretical air-fuel ratio. The determination device has a prohibition section that, when calculating the amount of oxygen occlusion after an incremental correction of the amount of a fuel injection is completed, sets a prohibition period in which calculation of the amount of oxygen occlusion immediately after the completion of the incremental correction is prohibited. The prohibition section variably sets the prohibition period so that the more the amount of fuel increment during an incremental correction of the amount of a fuel injection, the longer the prohibition period.

Description

Technical field [0001] The present invention relates to a device for judging the deterioration of a catalyst provided on an internal combustion engine. Background technique [0002] In an internal combustion engine, exhaust gas components are purified by a catalyst for exhaust gas purification provided on the exhaust gas path. The purification of exhaust components by the catalyst is performed efficiently when the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine is within a predetermined range. In order to adjust the above-mentioned air-fuel ratio within a predetermined range, an air-fuel ratio feedback control that corrects the increase or decrease of the fuel injection amount supplied to the internal combustion engine is generally performed. That is, an oxygen sensor for detecting the oxygen concentration in the exhaust gas is provided on the upstream side of the catalyst in the exhaust gas path. In the air-fuel ratio feedback control, the air-f...