Engine Exhaust Gas Purifier

Abstract

In an engine exhaust gas purifier having a urea-SCR-catalyst and an injector, the urea-SCR-catalyst is regenerated periodically to remove stack up sulfur caused by the diesel fuel, by stopping supply of urea water, and raising exhaust gas temperature to heat the catalyst. The injector locates in the downstream of cooling wind of a variable speed cooling fan which creates variable cooling wind based on the temperature of the cooling component like radiator, oil cooler, after cooler of the engine. At the regeneration of the urea-SCR-catalyst, controller changes preset fan-speed to higher speed to increase cooling wind to inhibit overheating.

1 . An engine exhaust gas purifier comprising a urea SCR catalyst installed in an exhaust gas pipe from an engine to reduce and remove NOx, a urea water injector that supplies urea water serving as a reduction agent to an upstream side of the catalyst, and a controller,
 wherein the urea water injector is installed on a downstream side of air blow from a variable speed cooling fan, the rotation speed of which is increased or reduced in accordance with an increase or a decrease in a temperature of a component of the engine to be cooled,   the controller implements a poisoning recovery mode in which supply of urea water is periodically stopped for a predetermined time and exhaust gas temperature is controlled to increase a temperature of a catalyst, the poisoning recovery mode being intended to recover the urea SCR catalyst from sulfur poisoning, and   during the poisoning recovery mode, the controller changes the rotation speed of the variable speed cooling fan to a higher speed to increase an amount of blown air to reduce an atmospheric temperature of the urea water injector, thus preventing the injector from being overheated.   
     
     
         2 . The engine exhaust as purifier according to  claim 1 , wherein the controller has a “normal map” for a poisoning recovery mode non-implementation state and a “high-speed map” for a poisoning recovery mode implementation state in both of which a relation between the temperature of the component to be cooled and the fan rotation speed is continuously specified, and switches the “normal map” to the “high-speed map” in the poisoning recovery mode.