Hitachi, Ltd.

Shigeru Kawamoto

Toshio Ishii

Shinji Nakagawa

Yutaka Takaku

Yoshihisa Fujii

Minoru Oosuga

Minoru Ohsuga

Engine exhaust gas cleaning system

An exhaust gas cleaning system for an engine capable of judging the amount of trapped NO and the oxygen storage capacity of an NO trap agent and which can diagnose the deterioration of the NO trap agent. The NO trap is arranged in an exhaust gas passage and the air-fuel ratio of the exhaust gas is temporally changed from a lean air-fuel ratio to the stoichiometric air-fuel ratio or a rich air-fuel ratio with a predetermined cycle. The NO trapping occurs by absorbing or adsorbing NO in the exhaust gas when an air-fuel ratio of the exhaust gas is a lean air-fuel ratio and by releasing or reducing NO when the air-fuel ratio is a rich air-fuel ratio. The amount of trapped NO is judged from the oxygen concentration and the oxygen concentration in the exhaust gas is detected in the exhaust gas passage in the downstream side of the NO trap and determined by taking the oxygen storage capacity when the air-fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or the rich air-fuel ratio.

Exhaust gas cleaning system for an engine

The invention provides a method of controlling an air-fuel ratio and for diagnosing a deterioration of a catalyst having an NOx trapping agent in an internal combustion engine. An exhaust gas purifying apparatus having an NOx trapping agent arranged within an exhaust gas passage, an air-fuel ratio changing means temporarily changing the air-fuel ratio of the exhaust gas from the lean to the stoichiometric or rich air-fuel ratio at a predetermined cycle, a particular component detecting means detecting a particular component in the exhaust gas downstream the NOx trapping agent, a NOx discharge or reduction completion judging means, and NOx discharge or reduction completion time detecting means detecting a time required for purifying the NOx.

Engine exhaust gas purifying apparatus

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Hitachi, Japan

Shigeru Kawamoto