| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a malfunction diagnosis device for an exhaust emission control system having a simple hardware construction for diagnosing the malfunction of the exhaust emission control system such as the quality of a reducing agent. <P>SOLUTION: The malfunction diagnosis device includes conversion rate calculating means S14, S27 for calculating a NOx conversion rate, and quality diagnosing means S28, S32 (diagnosing means) for diagnosing the quality of urea water (reducing agent) in accordance with a degree of the deviation of an conversion rate ηstart at current start of an internal combustion engine from an conversion rate ηlast calculated by the conversion rate calculating means at previous stop of the internal combustion engine. From the fact that there should be no great change of the conversion rate between before and after an engine stopping period unless the quality of the urea water is changed during the engine stopping period, the quality of the urea water (the malfunction of the exhaust emission control system) can be diagnosed without the need for a sensor to detect the concentration of the urea water, in accordance with a degree of the deviation of the starting conversion rate ηstart from the stopping conversion rate ηlast. <P>COPYRIGHT: (C)2010,JPO&INPIT |
