Catalyst diagnosis apparatus for internal combustion engine

Abstract

A catalyst diagnosis apparatus comprises a reaction rate calculation unit for calculating a reaction rate of chemical reaction in a three-way catalyst based on an output of an oxygen sensor, and an OSC indicator calculation unit for calculating an OSC indicator indicating an oxygen storage capacity (OSC) of the three-way catalyst based on outputs of a linear air-fuel ratio sensor and the oxygen sensor, and a catalyst degradation determination unit for determining degradation of the three-way catalyst based on the reaction rate and the OSC indicator. The determination of the catalyst degradation can be performed with high accuracy in a manner adapted for influences of external environments, etc.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a catalyst diagnosis apparatus for internal combustion engine. More particularly, the present invention relates to a catalyst diagnosis apparatus for an internal combustion engine, which diagnoses whether a three-way catalyst disposed in an exhaust passage of the internal combustion engine is degraded, and also relates to an automobile equipped with an internal combustion engine including the catalyst diagnosis apparatus. [0003] 2. Description of the Related Art [0004] A three-way catalyst has hitherto been disposed midway an exhaust passage to purify and clean not-yet-burnt hydro carbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), i.e., harmful components in exhaust gas exhausted from an internal combustion engine. [0005] In such an exhaust cleaning device, if the three-way catalyst is degraded or failed for some reason, the efficiency of cleaning the harmful components i...

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Benefits of technology

[0014] With the view of solving the above-mentioned problems, an object of the present invention is to provide a catalyst diagnosis apparatus for an internal combustion engine, which can perform the determination of the catalyst degradation with high accuracy in a manner adapted for influences of external environments, etc.

[0027] With the catalyst diagnosis apparatus the for internal combustion engine according to the present invention, since the degradation of the three-way catalyst is determined in combination of the reaction rate calculated by the reaction rate calculation unit and the OSC indicator calculated by the OSC indicator calculation unit, the accuracy in the determination of the catalyst degradation is improved and a degradation determination enable region is enlarged depending on characteristic changes of the catalyst caused by influences of external environments, etc. Hence the performance of catalyst diagnosis is enhanced.

Problems solved by technology

When the degradation determination method using the catalyst temperature is actually performed like the catalyst degradation detection device disclosed in Patent Document 1, the following problem may occur.

It is hence difficult to precisely detect the catalyst temperature.

Even in the case of using a temperature sensor, it is also difficult to precisely detect the catalyst temperature because the catalyst temperature is not evenly distributed within the catalyst.

Consequently, the estimated result of the catalyst temperature is varied, whereby the accuracy of the range allowing the determination of the catalyst degradation to be executed is deteriorated and so is the accuracy in the determination of the catalyst degradation.

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