Method for purifying the exhaust gases of an internal combustion engine having a catalytic converter

Abstract

The present invention relates to a method for purifying the exhaust gases of an internal combustion engine having a catalytic converter which comprises oxygen storage components. The invention is concerned particularly with the restoration of the optimum filling degree of the oxygen storage components for regulated stoichiometric operation after the engine has been operated under lean conditions for a relatively short or relatively long period of time.

1 . A method for purifying the exhaust gases of an internal combustion engine having a catalytic converter which comprises an oxygen storage composed of oxygen storage components, with the engine being equipped with an electronic engine controller and being operated with a regulated, stoichiometric air/fuel mixture over the greater part of the operating duration thereof, with temporary lean operating phases also occurring as a function of the driving situations,
 wherein, after a temporary lean operating phase of the engine, which is associated with a substantial filling of the oxygen store, and before the resumption of regulated engine operation, the filling degree of the oxygen storage is returned to an optimum level for stoichiometric operation by virtue of the engine being supplied with a rich pulse followed by a lean pulse, with the quantity of oxidative components supplied to the catalytic converter by means of the lean pulse being lower than would be required for fully compensating the quantity of rich exhaust-gas components supplied by means of the rich pulse.   
     
     
         2 . The method as claimed in  claim 1 ,
 wherein the quantity of rich exhaust-gas components supplied by means of the rich pulse is greater than that required for setting the optimum filling degree for stoichiometric operation but is smaller than the quantity of rich exhaust-gas components which would be required for completely emptying the storage capacity of the oxygen store.   
     
     
         3 . The method as claimed in  claim 2 ,
 wherein, after the first rich pulse and lean pulse, the engine is supplied with further rich and lean pulses, with the quantity of rich components supplied by means of the respective rich pulse being greater than could be compensated by means of the oxidative components of the subsequent lean pulse.   
     
     
         4 . The method as claimed in  claim 1 ,
 wherein the rich pulse and lean pulse have an amplitude and a duration and the amplitude and/or duration are adapted as a function of the temperature and spatial velocity of the exhaust gas and/or an aging state of the catalytic converter.   
     
     
         5 . The method as claimed in  claim 4 ,
 wherein the amplitudes of the rich pulse and lean pulse are reduced by a factor corresponding to the aging state of the catalytic converter.   
     
     
         6 . The method as claimed in  claim 1 ,
 wherein the temporary lean operating phase is an overrun fuel cutoff.   
     
     
         7 . The method as claimed in  claim 1 ,
 wherein the temporary lean operating phase is a lean operating phase of an internal combustion engine operated both stoichiometrically and also lean as a function of the driving situation.   
     
     
         8 . The method as claimed in  claim 1 ,
 wherein the temporary lean operating phase is caused by regulation fluctuations of the stoichiometric operation.   
     
     
         9 . The method as claimed in  claim 8 ,
 wherein the temporary lean operating phase is detected in that an oxygen probe arranged downstream of the catalytic converter indicates lean exhaust gas when the signal voltage of said oxygen probe falls below a threshold value.   
     
     
         10 . The method as claimed in  claim 9 ,
 wherein the threshold value is selected as a function of the temperature and the spatial velocity of the exhaust gas, as a function of the exhaust-gas stoichiometry and as a function of the aging state of the catalytic converter.   
     
     
         11 . The method as claimed in  claim 1 ,
 wherein an oxygen probe is arranged in the exhaust section downstream of the catalytic converter and the signal voltage which said oxygen probe actually reaches after the step from the temporary lean operating phase into regulated stoichiometric operation is used to determine therefrom a remaining oxygen storage capacity of the oxygen storage.   
     
     
         12 . The method as claimed in  claim 11 ,
 wherein a signal is activated if the remaining oxygen storage capacity has fallen below a predefined value.   
     
     
         13 . The method as claimed in  claim 12 ,
 wherein the quantity of rich and lean components supplied to the catalytic converter by means of the rich and lean pulses is adapted to the remaining oxygen storage capacity.   
     
     
         14 . The method as claimed in  claim 2 ,
 wherein the rich pulse and lean pulse have an amplitude and a duration and the amplitude and/or duration are adapted as a function of the temperature and spatial velocity of the exhaust gas and/or an aging state of the catalytic converter.   
     
     
         15 . The method as claimed in  claim 14 ,
 wherein the amplitudes of the rich pulse and lean pulse are reduced by a factor corresponding to the aging state of the catalytic converter.