In-cylinder method for air/fuel ratio control

Abstract

The invention relates to a Method of purging a lean NO x trap (LNT) coupled downstream of a direct injection internal combustuion engine with post injection for achieving a purge air/fuel (A/F) ratio. At least two separate post injections are applied in the expansion stroke after a main injection train, so that a torque produced is decoupled from the A/F-control.

1 . A method of purging a lean NO x  trap (LNT) coupled downstream of a direct injection internal combustion engine, comprising: 
 applying at least two separate post injections in the expansion stroke after a main injection train such that there is substantially no torque generated due to said two separate post injections.    
   
   
       2 . The method according to  claim 1 , further comprising a pre-conditioning of the state of gas in-cylinder through partial combustion of the current injection in preparation for the next injection.  
   
   
       3 . The method according to  claim 2 , further comprising a stimulation the completion of the in-cylinder combustion of the previous injection through the generation of a strong mixing effect resulting from the increased turbulence level caused by the high kinetic energy of the current injection.  
   
   
       4 . The method according to  claim 3 , wherein a total injection quantity required is proportionally split into several injections.  
   
   
       5 . The method according to  claim 4 , wherein a lower range of the quantity change is determined by the torque neutrality criterion whereby an upper limit is determined by the concentration of reducing agent in the exhaust gas.  
   
   
       6 . The method according to  claim 5 , wherein the injection signal is controlled in an open loop manner.  
   
   
       7 . The method according  claim 6 , wherein a closed loop controller responds to an error between desired and measured target F/A (or A/F) ratio by trimming a transient correction part.