Exhaust gas purifying device for engine

Abstract

An exhaust gas purifying device for an engine according to the present invention includes a NOx absorbing catalytic converter provided in an exhaust path of the engine, an exhaust light oil adding injector which supplies a reducing agent component into the exhaust path, a control unit which executes the rich spike operation that controls an air-fuel ratio to the rich side per predetermined time, which adds the HC component to the NOx absorbing catalytic converter, and which heats to an S purge temperature or higher so as to eliminate a sulfur component absorbed by the NOx absorbing catalytic converter, and a catalyst temperature measuring sensor which measures the temperature of the NOx absorbing catalytic converter, wherein the control unit controls an operation cycle of the rich spike operation based on the deviation of the S purge temperature with respect to the temperature measured by the catalyst temperature measuring sensor.

1 . An exhaust gas purifying device for an engine, comprising: 
 a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich;    a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path;    a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period;    an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and    a catalyst temperature measuring sensor which measures the temperature of the catalytic converter,    wherein the rich spike control unit controls a operation cycle of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.    
   
   
       2 . The exhaust gas purifying device for an engine according to  claim 1 , wherein the cycle is made shorter as the deviation is increased.  
   
   
       3 . An exhaust gas purifying device for an engine, comprising: 
 a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich;    a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path;    a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period;    an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and    a catalyst temperature measuring sensor which measures the temperature of the catalytic converter,    wherein the rich spike control unit controls an operation period of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.    
   
   
       4 . The exhaust gas purifying device for an engine according to  claim 3 , wherein the period is made longer as of the deviation is increased.