Exhaust gas deNOx apparatus for engine

Claim 1

An exhaust gas deNOx apparatus for an engine comprising an NOx adsorber catalyst in an exhaust pipe line of an engine, for adsorbing NOx when an air fuel ratio of an exhaust gas flowing therein is in a lean state and releasing NOx when the air fuel ratio of the exhaust gas flowing therein is in a rich state, and an exhaust gas recirculating circuit for mixing the exhaust gas into intake air, the exhaust gas deNOx apparatus comprising: exhaust gas recirculating amount control means for recirculating a predetermined amount of exhaust gas for reducing NOx when an adsorbed NOx accumulation amount is not more than a predetermined value, and recirculating said predetermined amount or more of exhaust gas to bring the air fuel ratio into a rich state when the adsorbed NOx accumulation amount exceeds the predetermined value and the NOx is to be released; wherein said exhaust gas recirculating circuit comprises a first exhaust gas recirculating circuit and at least one second exhaust gas recirculating circuit provided in parallel with said first exhaust gas recirculating circuit, wherein said exhaust gas recirculating amount control means comprises a second recirculating circuit adjusting valve free to be opened and closed, which is provided in said second exhaust gas recirculating circuit, NOx amount detection means for detecting an NOx amount, and a controller for calculating an NOx accumulation amount in said NOx adsorber catalyst based on the NOx amount outputted from said NOx amount detection means and determining whether said calculated NOx accumulation amount is a predetermined value or less, or not, and wherein when said calculated NOx accumulation amount exceeds the predetermined value, said controller outputs a control signal to open said second recirculating circuit adjusting valve to make the air fuel ratio of the exhaust gas of said engine rich.