Catalyst monitoring system and monitoring method

Abstract

A catalyst monitoring system diagnoses deterioration of an NOx catalyst (18) which is arranged in an exhaust passage (12) of an internal combustion engine (10). An NOx sensor (25) is arranged downstream of the NOx catalyst (18). An output integrated value of the NOx sensor (25) is calculated by integrating an output from the NOx sensor (25) is calclated by integrating an outputfrom the NOx sensor (25) during at least a period near the end of rich spike control. Deterioration of the NOx catalyst (18) is diagnosed based on the output integrated value of the NOx sensor (25), as there is a correlation between the amount of ammonia NH3 which flows downstream of the NOx catalyst and the NOx sensor output integrated value near the line when the rich spike control ends.

Description

technical field [0001] The invention relates to a catalyst monitoring system and a monitoring method. Background technique [0002] Emission regulations to control the amount of harmful substances discharged from vehicles are currently being enforced from the viewpoint of environmental protection. In addition, so-called "on-board diagnostics (OBD) regulations" are being enforced, which require vehicles to be equipped with an OBD system that automatically diagnoses exhaust purification devices to check for malfunctions or deterioration of exhaust purification devices. [0003] The three-way catalyst cannot sufficiently purify NOx when the air-fuel ratio of the exhaust gas flowing in is leaner than the stoichiometric air-fuel ratio. Therefore, for example, a lean-burn engine capable of operating at a leaner air-fuel ratio than the stoichiometric air-fuel ratio is equipped with a NOx catalyst in the exhaust passage. The NOx catalyst can store NOx when the air-fuel ratio of th...

AI Technical Summary

Problems solved by technology

[0003] The three-way catalyst cannot sufficiently purify NOx when the air-fuel ratio of the incoming exhaust gas is leaner than the theoretical air-fuel ratio

Therefore, for the US SULEV emission standard, even if the NOx sensor detects the amount of NOx flowing through the NOx catalyst during lean operation, it is difficult to judge the deterioration of the NOx catalyst

On the other hand, there is a large difference between the amount of NOx emitted from the NOx catalyst corresponding to the emission regulation value during the rich peak control and the NOx amount emitted from the NOx catalyst corresponding to the OBD regulation value during the rich peak control

However, as described above, when the air-fuel ratio of the exhaust gas is rich, it is difficult to accurately detect only the concentration of NOx with the NOx sensor because the NOx sensor also detects NH in the exhaust gas. 3 responding to

Therefore, it is also difficult to judge the deterioration of the NOx catalyst using the difference in the amount of NOx discharged from the NOx catalyst during the rich peak control.

[0012] In this way, the increasingly stringent OBD regulations make it difficult to determine the deterioration of the NOx catalyst by using the NOx sensor to detect the NOx concentration in the exhaust gas

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