BACKGROUND OF THE INVENTION

Field of the Invention

The invention concerns systems for controlling an internal combustion engine, and more particularly when the internal combustion engines are provided with an exhaust gas post-treatment system of the selective catalysis type.

Description of the Related Art

At present, the best compromise between polluting emissions of the type of unburned hydrocarbons HC, carbon monoxide CO, carbon dioxide CO2, nitrogen oxides NOxand particulates is obtained during normal combustion mode by adjusting the combustion parameters such as the injection pattern, the exhaust gas recirculation rate EGR and the engine charge, expressed as flow or pressure. This compromise is obtained during stabilized tests.

The nitrogen oxide NOxemissions result from a given engine setting, and it is not possible to obtain a setpoint for the nitrogen oxide NOxemissions. Injection and air loop setpoints are determined which allow a given level of nitrogen oxide NOxemissions that is fixed for each operating point.

Legislation imposes a reduction in the emissions of nitrogen oxide NOx. However, the reduction in such emissions is achieved at the cost of an increase in the emissions of carbon dioxide CO2and particulates.

The efficacy of the nitrogen oxide NOxpost-treatment system of the selective catalysis SCR type depends on the temperature of the catalytic element, which must be higher than a threshold temperature, generally 280° C. Adapting the combustion to these efficacy criteria is fairly approximate and is characterized at stable points.

There is therefore a problem concerning the lack of optimization of the combustion settings, defined during stabilized tests, under transient conditions and it is not possible to control the engine with a setpoint of nitrogen oxide NOxemissions.

In the prior art, document JP2002371893 discloses controlling an internal combustion engine by controlling the nitrogen oxides NOxproduced at the outlet from the engine.

However, the model used is particularly complex and hence costly in terms of calculation time, and does not take into account the efficacy of post-treatment of nitrogen oxides NOx.

Document EP2617972 also describes a method for controlling the rate of exhaust gas recirculation EGR as a function of measurements from sensors for nitrogen oxides NOxin an open-loop control of the EGR.

SUMMARY OF THE INVENTION

The object of the invention is a system for controlling an internal combustion engine provided with an exhaust gas post-treatment system of the selective catalysis type, characterized in that it comprises a closed-loop control of nitrogen oxides upstream of the exhaust gas post-treatment system of the selective catalysis type, according to the following steps:a means for determining a nitrogen oxide emission setpoint upstream of the exhaust gas post-treatment system as a function at least of the rotational speed and the torque setpoint of the internal combustion engine,a means for determining a value for the quantity of nitrogen oxides upstream of the exhaust gas post-treatment system, anda cascade control means which is able to determine an introduced oxygen setpoint and a charging pressure correction destined for the air loop control means of the internal combustion engine, and a fuel injection pressure correction and a start of injection correction destined for the injection control means of the internal combustion engine, as a function of a difference in nitrogen oxide emissions between a nitrogen oxide emission setpoint or corrected nitrogen oxide emission setpoint upstream of the exhaust gas post-treatment system, and a determined value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system.

The means for determining a nitrogen oxide setpoint upstream of the exhaust gas post-treatment system may comprise a three-dimensional map linking the torque setpoint, the setpoint for the nitrogen oxide emissions which can be treated by the post-treatment, and the rotational speed of the internal combustion engine.

The system may comprise a summing integrator able to determine a corrected setpoint for nitrogen oxide emissions upstream of the exhaust gas post-treatment system by adding the nitrogen oxide emission setpoint received from the map to a first correction produced by a map as a function of the temperature of the air introduced into the internal combustion engine, and/or to a second correction produced by a map as a function of the temperature of the cooling liquid of the internal combustion engine.

The means for determining a value for the nitrogen oxide quantity upstream of the exhaust gas post-treatment system may comprise at least a model of the quantity of nitrogen oxides at the level of the exhaust manifold of the engine as a function of at least one operating parameter of the engine and as a function of an introduced oxygen quantity value and of a charging pressure value provided by the air loop control means, and of a fuel injection pressure value and a start of injection value provided by the injection control means.

The means for determining a value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system may comprise at least a first map of the nitrogen oxide concentration as a function of at least one cylinder pressure measurement supplied by a cylinder pressure sensor.

The means for determining a value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system may comprise at least a second map of the nitrogen oxide concentration as a function of at least the total quantity of fuel injected into the cylinders, which is determined as a function of the values supplied by the engine electronic control unit.

The means for determining a value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system may be connected to a nitrogen oxide sensor situated in the exhaust line.

The means for determining a value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system may comprise at least one means for correcting the nitrogen oxide quantity value determined by one of the first map or the second map.

The cascade control means may comprise a means for determining an introduced oxygen setpoint, an injection correction means, a charging pressure correction means, a proportional-integral-derivative corrector able to determine a first control value as a function of the difference in nitrogen oxide emissions, and a first saturation means able to determine a control value saturated as a function of the oxygen, a function of the first control value and maximum and minimum limits, a function of the introduced oxygen quantity, and to emit a first control signal when the first control value is saturated,the means for determining an introduced oxygen setpoint may comprise a means for determining a target introduced oxygen setpoint, a first multiplier able to determine a correction of the introduced oxygen setpoint as a function of the control value saturated as a function of the oxygen, and a factor linked to the introduced oxygen setpoint stored in a first memory, and a summing integrator able to determine an introduced oxygen setpoint by adding a target introduced oxygen setpoint and the correction to the introduced oxygen setpoint.

The injection correction means may comprise an activation means able to activate the injection correction means when the first control signal is received,a calculation means able to determine a second control value as a function of the first control value and the control value saturated as a function of the oxygen,a second saturation means able to determine a second control value saturated as a function of the second control value and maximum and minimum limits, and able to emit a second control signal when the second control value is saturated,a second multiplier able to determine a correction of the fuel pressure in the injector supply rail as a function of the second saturated control value and a factor linked to the fuel pressure,a third multiplier able to determine a correction of the start of injection as a function of the second control value and a factor linked to the start of injection,the charging pressure correction means comprises a means for activating the charging pressure correction means when a second control signal is received,a calculation means able to determine a third control value as a function of the second control value and the second saturated control value, anda fourth multiplier able to determine a charging pressure correction as a function of the third control value and a factor linked to the charging pressure.

The injection correction means may comprise an activation means able to activate the injection correction means when the first control signal is received,a calculation means able to determine a second control value as a function of the first control value and the control value saturated as a function of the oxygen,a third saturation means able to determine a second control value saturated as a function of the fuel pressure in the injector supply rail, as a function of the second control value and a maximum limit value and a minimum limit value linked to the fuel pressure in the injector supply rail, and able to emit a third control signal when the second control value is saturated,a second multiplier able to determine a correction of the fuel pressure in the injector supply rail as a function of the second control value saturated as a function of the fuel pressure in the injector supply rail and a factor linked to the fuel pressure,a fourth saturation means able to determine a second control value saturated as a function of the start of injection, as a function of the second control value and a maximum limit value and a minimum limit value linked to the start of injection, and able to emit a fourth control signal when the second control value is saturated,a third multiplier able to determine a correction of the start of injection as a function of the second control value saturated as a function of the start of injection and a factor linked to the start of injection,an OR logic operator able to emit a second control signal when the third control signal or the one fourth control signal is received,the charging pressure correction means comprises a means for activating the charging pressure correction means when a second control signal is received,a calculation means able to determine a third control value as a function of the second control value, of the second control value saturated as a function of the fuel pressure in the injector supply rail, and of the second control value saturated as a function of the start of injection,a fourth multiplier able to determine a charging pressure correction as a function of the third control value and a factor linked to the charging pressure.

The cascade control means may comprise a means for determining an introduced oxygen setpoint, an injection correction means, a charging pressure correction means,a proportional-integral-derivative corrector able to determine a first control value as a function of the difference in nitrogen oxide emissions, andthe means for determining an introduced oxygen setpoint comprises a means for determining a target introduced oxygen setpoint, a first multiplier able to determine a correction to the introduced oxygen setpoint as a function of the first control value and a factor linked to the introduced oxygen setpoint stored in a first memory, a first saturation means able to determine an introduced oxygen setpoint correction value that is saturated as a function of the introduced oxygen setpoint correction and maximum and minimum limits and as a function of the introduced oxygen setpoint, and to emit a first control signal when the introduced oxygen setpoint correction is saturated,and a summing integrator able to determine an introduced oxygen setpoint by adding a target introduced oxygen setpoint to the saturated value of the introduced oxygen setpoint correction.

The injection correction means may comprise an activation means able to activate the injection correction means when the first control signal is received,a calculation means able to determine a second control value as a function of the first control value, the saturated value of the introduced oxygen setpoint correction, and the factor linked to the introduced oxygen setpoint,a second multiplier able to determine a correction of the fuel pressure in the injector supply rail as a function of the second control value and a factor linked to the fuel pressure,a third saturation means able to determine a correction value of the fuel pressure in the injector supply rail that is saturated as a function of the correction of the fuel pressure in the injector supply rail, and a maximum limit value and minimum limit value linked to the fuel pressure in the injector supply rail, and able to emit a third control signal when the correction of the fuel pressure in the injector supply rail is saturated,a third multiplier able to determine a correction of the start of injection as a function of the second control value and a factor linked to the start of injection,a fourth saturation means able to determine a saturated value of the start of injection correction as a function of the start of injection correction and a maximum limit value and a minimum limit value linked to the start of injection, and able to emit a fourth control signal when the start of injection correction is saturated,an OR logic operator able to emit a second control signal when the third control signal or the one fourth control signal is received,the charging pressure correction means comprises a means8afor activating the charging pressure correction means when a second control signal is received,a calculation means able to determine a third control value as a function of the second control value, the saturated correction value of the fuel pressure in the injector supply rail, the factor linked to the fuel pressure, the saturated value of the start of injection correction, and the factor linked to the start of injection,a fourth multiplier able to determine a charging pressure correction as a function of the third control value and a factor linked to the charging pressure.

The means for determining a target introduced oxygen setpoint may comprise a means for determining the presence of a cylinder pressure sensor, a means for determining the cylinder temperature, and a means for calculating the target introduced oxygen setpoint,the means for determining the presence of a cylinder pressure sensor is able to emit a signal destined for the means for determining a target introduced oxygen setpoint, indicating the absence of a cylinder pressure sensor when no signal is received or if a value outside a permitted range is received at the input,the means for determining the presence of a cylinder pressure sensor is able to transmit the value received to the means for determining the cylinder temperature, and to emit a signal destined for the means for determining a target introduced oxygen setpoint indicating the presence of a cylinder pressure sensor when a value within a permitted range is received at the input,the means for determining the cylinder temperature is able to determine the cylinder temperature as a function of a model, the cylinder pressure, the charge and the crankshaft position,the means for calculating the target introduced oxygen setpoint is able to determine the target introduced oxygen setpoint as a function of an inverted model of the nitrogen oxide emissions, the maximum temperature reached in the cylinder and the nitrogen oxide emission setpoint or corrected nitrogen oxide emission setpoint, if a cylinder pressure sensor is present,the means for calculating the target introduced oxygen setpoint is able to determine the target introduced oxygen setpoint as a function of an inverted model of the nitrogen oxide emissions, the total quantity of fuel injected into the cylinders and the nitrogen oxide emission setpoint or corrected nitrogen oxide emission setpoint, if a cylinder pressure sensor is not present.

The invention also concerns a method for controlling an internal combustion engine provided with an exhaust gas post-treatment system of the selective catalysis type, as a function of the setpoint of nitrogen oxide emissions upstream of the exhaust gas post-treatment system, characterized it comprises a closed-loop control of nitrogen oxides upstream of the exhaust gas post-treatment system of the selective catalysis type, according to the following steps during which:a nitrogen oxide emission setpoint is determined upstream of the exhaust gas post-treatment system as a function at least of the rotational speed and the torque setpoint of the internal combustion engine,a value for the nitrogen oxide quantity upstream of the exhaust gas post-treatment system is determined, andan introduced oxygen setpoint is determined together with a charging pressure correction destined for air loop control means of the internal combustion engine, and a fuel injection pressure correction and a start of injection correction destined for the injection control means of the internal combustion engine, by cascade determination as a function of a difference in nitrogen oxide emissions between the nitrogen oxide emission setpoint or corrected nitrogen oxide emission setpoint upstream of the exhaust gas post-treatment system and the determined value of the nitrogen oxide quantity upstream of the exhaust gas post-treatment system.

The method has the advantage of taking into account the efficacy of the post-treatment SCR system, which leads to optimization of the control by setpoints of nitrogen oxides NOxleaving the engine so as to maintain an approximately constant rate of nitrogen oxide NOxemissions.

