Catalyst degradation detection device and method

Abstract

An object of the present invention is to provide a technique for accurately detecting deterioration of an exhaust purification catalyst used in an internal combustion engine capable of using gaseous fuel and liquid fuel. In the present invention, when only gaseous fuel is used which makes it difficult to release the oxygen stored in the exhaust purification catalyst even if the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is changed to the rich side, the catalyst deterioration determination unit is based on Whether or not the exhaust purification catalyst has deteriorated is determined by one of the following changes: a change in the output of the oxygen concentration detection unit only on the lean side, or a change in the output of the oxygen concentration detection unit on the rich side and the lean side.

Description

technical field [0001] The invention relates to a catalyst degradation detection device and a catalyst degradation detection method. Background technique [0002] In the case of using the oxygen storage capacity (OSC) of the catalyst to detect the deterioration of a catalyst provided in the exhaust passage of an internal combustion engine using natural gas as fuel, there is an O 2 A situation where the sensor gets a false value due to unburned methane reaction. Therefore, a technique for detecting catalyst degradation by changing a determination reference value for catalyst degradation is disclosed (for example, refer to Patent Document 1). Accordingly, in Patent Document 1, it is intended to accurately detect catalyst degradation. [0003] Patent Document 1: Japanese Patent Application Laid-Open No. 11-159375 [0004] When detecting catalyst degradation using the oxygen storage capacity of the catalyst, the air-fuel ratio of the exhaust gas discharged from the internal c...

AI Technical Summary

Problems solved by technology

Here, when natural gas is used as fuel, the stoichiometric point of the catalyst is on the rich side, and since the combustion limit on the rich side is narrow, the air-fuel ratio of the exhaust gas cannot be greatly changed to the rich side.

Also, for natural gas, more than 90% of the fuel is methane, and the ability of methane to release oxygen from the catalyst is low, so the oxygen concentration downstream of the catalyst cannot be increased similarly to the case where the air-fuel ratio of the exhaust gas is changed to the rich side

Therefore, in the case of using natural gas as fuel, it is not possible to accurately detect catalyst degradation

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