Exhaust gas purification system for internal combustion engine

An exhaust gas purification system for an internal combustion engine equipped with an NOx adsorber catalyst which absorbs, for deposition, NOx when exhaust gas lean in its air fuel ratio flows in, and releases deposited NOx when the oxygen concentration of exhaust gas inflow is reduced, comprising:

• a NOx deposition calculating means for calculating the amount of NOx deposited on the NOx adsorber catalyst;
• a first air fuel ratio controlling means which, when the NOx deposition calculated by the NOx deposition calculating means reaches a predetermined reference level, alters an air fuel ratio of exhaust gas discharged from the internal combustion engine to come into contact with the NOx adsorber catalyst to stoichiometric air fuel ratio, so as to cause the NOx adsorber catalyst to release NOx deposited thereupon;
• and
• a reference NOx level setting means which sets a reference NOx level depending on a load with which the internal combustion engine runs, or on a load and engine speed with which the internal combustion engine runs,
• wherein the reference NOx level setting means sets a reference NOx level approximately equal to the maximum attainable NOx deposition on the NOx adsorber catalyst when the internal combustion engine runs in a high load range;
• and sets it below the maximum attainable NOx deposition on the NOx adsorber catalyst when the internal combustion engine runs in a low load range.

An exhaust gas purification system for an internal combustion engine equipped with an NOx adsorber catalyst which absorbs, for deposition, NOx when exhaust gas lean in its air fuel ratio flows in, and releases deposited NOx when the oxygen concentration of exhaust gas inflow is reduced, comprising:

• a NOx deposition calculating means for calculating the amount of NOx deposited on the NOx adsorber catalyst;
• a first air fuel ratio controlling means which, when the NOx deposition calculated by the NOx deposition calculating means reaches a predetermined reference level, alters an air fuel ratio of exhaust gas discharged from the internal combustion engine to come into contact with the NOx adsorber catalyst to stoichiometric air fuel ratio, so as to cause the NOx adsorber catalyst to release NOx deposited thereupon;
• and
• a reference NOx level setting means which sets a reference NOx level depending on a load with which the internal combustion engine runs, or on a load and engine speed with which the internal combustion engine runs,
• wherein the reference NOx level setting means sets a reference NOx level approximately equal to the maximum attainable NOx deposition on the NOx adsorber catalyst when the internal combustion engine runs in a high speed/high load range;
• and sets it below the maximum attainable NOx deposition on the NOx adsorber catalyst when the internal combustion engine runs in a low speed/low load range.

An exhaust gas purification system for an internal combustion engine equipped with an NOx adsorber catalyst which absorbs, for deposition, NOx when exhaust gas lean in its air fuel ratio flows in, and releases deposited NOx when the oxygen concentration of exhaust gas inflow is reduced, comprising:

• a NOx deposition calculating means for calculating the amount of NOx deposited on the NOx adsorber catalyst;
• a first air fuel ratio controlling means which, when the NOx deposition calculated by the NOx deposition calculating means reaches a predetermined reference level, alters an air fuel ratio of exhaust gas discharged from the internal combustion engine to come into contact with the NOx adsorber catalyst to stoichiometric air fuel ratio, so as to cause the NOx adsorber catalyst to release NOx deposited thereupon;
• a reference NOx level setting means which sets a reference NOx level depending on a load with which the internal combustion engine runs, or on a load and engine speed with which the internal combustion engine runs;
• and
• a second air fuel ratio controlling means which, as soon as the run of the internal combustion engine shifts from a high load range to a low load range, or from a high speed/high load range to a low speed/low load range, alters the air fuel ratio of exhaust gas from the internal combustion engine to come into contact with the NOx adsorber catalyst to stoichiometric air fuel ratio, so as to cause the NOx adsorber catalyst to release NOx deposited thereupon.

An exhaust gas purification system for an internal combustion engine equipped with an NOx adsorber catalyst which absorbs, for deposition, NOx when exhaust gas lean in its air fuel ratio flows in, and releases deposited NOx when the oxygen concentration of exhaust gas inflow is reduced, and a super charger equipped with a compressor;

• a NOx deposition calculating means for calculating the amount of NOx deposited on the NOx adsorber catalyst;
• a first air fuel ratio controlling means which, when the NOx deposition calculated by the NOx deposition calculating means reaches a predetermined reference level, alters an air fuel ratio of exhaust gas discharged from the internal combustion engine to come into contact with the NOx adsorber catalyst to stoichiometric air fuel ratio, so as to cause the NOx adsorber catalyst to release NOx deposited thereupon;
• and
• a reference NOx level setting means which sets a reference NOx level depending on a load with which the internal combustion engine runs, or on a load and engine speed with which the internal combustion engine runs,
• wherein an air intake restricting means of the compressor is so configured as to be capable of discharging part of feed air at an outlet of the compressor of the super charger towards the downstream side of the NOx adsorber catalyst.