Method for controlling fresh air injection into the exhaust of an internal-combustion engine, notably of a motor vehicle

Abstract

The present invention relates to a method for controlling air injection into the exhaust of an internal-combustion engine running on a cycle during which the expansion phase (D) thereof has a greater stroke than the compression phase (C) thereof and comprising at least one cylinder ( 10 ) with a combustion chamber ( 18 ), a piston ( 16 ), at least one intake means ( 24 ) with a valve ( 28 ) associated with an intake pipe ( 26 ), at least one exhaust means ( 30 ) with a valve ( 34 ) associated with an exhaust pipe ( 32 ), fresh air injection means ( 48 ) at the exhaust and an exhaust line ( 40 ) comprising at least one exhaust gas depollution means ( 46 ). According to the invention, the method consists, during the cold start phase of this engine and during the expansion phase (D) thereof, in injecting fresh air into the exhaust and in opening exhaust valve ( 34 ) when the pressure in the combustion chamber is lower than the pressure prevailing at the exhaust so as to feed into the exhaust gas present in the combustion chamber the fresh air coming from this exhaust.

1 ) A method for controlling air injection into the exhaust of an internal-combustion engine, notably for a motor vehicle, running on a cycle during which the expansion phase thereof has a greater stroke than the compression phase thereof and comprising at least one cylinder with a combustion chamber, a piston sliding in a reciprocating motion between a top dead center and a bottom dead center, at least one intake means with a valve associated with an intake pipe, at least one exhaust means with a valve associated with an exhaust pipe, fresh air injection means at the exhaust and an exhaust line comprising at least one exhaust gas depollution means, characterized in that it consists, during the cold start phase of this engine and during the expansion phase thereof, in injecting fresh air into the exhaust and in opening exhaust valve when the pressure in the combustion chamber is lower than the pressure prevailing at the exhaust so as to feed into the exhaust gas present in the combustion chamber the fresh air coming from this exhaust. 
     
     
         2 ) A control method as claimed in  claim 1 , characterized in that it consists in opening the exhaust valve at a crank angle for which the pressure in the combustion chamber is lower than the pressure prevailing at the exhaust. 
     
     
         3 ) A control method as claimed in  claim 1 , characterized in that it consists in injecting fresh air into exhaust pipe. 
     
     
         4 ) A control method as claimed in  claim 1 , characterized in that it consists in injecting fresh air into exhaust manifold of exhaust line. 
     
     
         5 ) A control method as claimed in  claim 1 , characterized in that it consists in injecting fresh air into the exhaust before opening of exhaust valve. 
     
     
         6 ) A control method as claimed in  claim 1 , characterized in that it consists in injecting fresh air into the exhaust after opening of exhaust valve. 
     
     
         7 ) A control method as claimed in  claim 1 , characterized in that it consists in carrying out a succession of exhaust valve opening and closing cycles in order to feed into combustion chamber the fresh air coming from the exhaust.