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.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method for injecting fresh air into the exhaust of an internal-combustion engine, notably for a motor vehicle.[0002]It more particularly relates to such a method applied to an engine running on a cycle during which the expansion phase is longer than the compression phase, as for a Miller cycle.BACKGROUND OF THE INVENTION[0003]As it is generally known, the pollutants emitted during cold start of internal-combustion engines, notably spark-ignition engines, are a problem for car manufacturers.[0004]In fact, during this cold start, the exhaust gas depollution means these engines are usually equipped with, such as a catalyst, do not have a sufficiently high operating temperature, referred to as light-off temperature, to be able to treat these pollutants efficiently.[0005]A large part of the pollutants contained in this exhaust gas, such as unburnt hydrocarbons (HC) and / or carbon oxides (CO), is therefore discharged to the atm...

AI Technical Summary

Problems solved by technology

As it is generally known, the pollutants emitted during cold start of internal-combustion engines, notably spark-ignition engines, are a problem for car manufacturers.

In fact, during this cold start, the exhaust gas depollution means these engines are usually equipped with, such as a catalyst, do not have a sufficiently high operating temperature, referred to as light-off temperature, to be able to treat these pollutants efficiently.

A large part of the pollutants contained in this exhaust gas, such as unburnt hydrocarbons (HC) and / or carbon oxides (CO), is therefore discharged to the atmosphere without being treated beforehand, which represents a quite significant nuisance.

However, since the air supplied is cold in relation to the burnt gas that is very hot, the mixing rate is a determining factor for this post-combustion.

On the other hand, if this amount of air is insufficient, the heat release due to the reaction of the mixture is not sufficient to start the combustion of this mixture.

This therefore requires very precise adjustment of the amounts of fresh air and of exhaust gas present at the exhaust in order to obtain the appropriate mixture, failing which it is not possible to achieve post-combustion of the fresh air / exhaust gas mixture.

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