FR3059719B1 - METHOD FOR CONTROLLING A SUPERIOR THERMAL MOTOR COMPRISING AN EXHAUST GAS RECIRCULATION CIRCUIT - Google Patents

Abstract

The invention relates to a method for controlling a supercharged engine, comprising a turbocharger compressor (21) and an additional compressor (25) in an intake circuit and a turbocharger turbine (31) with variable geometry in a circuit exhaust system comprising an exhaust flap (38) downstream of the turbine, the engine comprising an exhaust gas recirculation circuit (33) upstream of the turbine to the intake manifold. In case of activation (EO) of the exhaust gas recirculation circuit, if the additional compressor (25) is in operation, the exhaust flap (38) is controlled (E2) so as to increase the pressure (PAVT ) to the exhaust upstream of the variable geometry turbine, so as to restore a positive pressure difference between the exhaust pressure upstream of the variable geometry turbine and a supercharging pressure at the intake manifold .

Description

A method of controlling a supercharged engine comprising an exhaust gas recirculation circuit

The present invention generally relates to the field of recirculation of exhaust gases from the exhaust to the intake of an internal combustion engine.

It relates more particularly to a method of controlling a supercharged engine, the engine comprising: - combustion cylinders, - an intake gas intake circuit comprising a turbocharger compressor and an additional compressor to increase the amount of fuel. intake gas supplied to an intake manifold of the intake circuit connected to the cylinders, - an exhaust system comprising an exhaust manifold connected to the cylinders, a turbocharger turbine of variable geometry at the outlet of the exhaust manifold , coupled in rotation to the turbocharger compressor, and an exhaust outlet, downstream of the turbine, provided with an exhaust flap, the engine further comprising an exhaust gas recirculation circuit from the exhaust circuit. exhaust, between the exhaust manifold and the variable geometry turbocharger turbine, to the intake manifold we.

In the case of a supercharged engine as described above, the additional compressor, whether it is an electric compressor driven in rotation by means of an electric motor or a mechanical compressor, can not not be used to increase the amount of air supplied to the intake during certain phases of engine operation and, in particular, during operating phases where the recirculation of the exhaust gas is activated.

Indeed, when the additional compressor works in addition to the turbocharger compressor, the pressure at the intake manifold, said intake pressure, becomes greater than the exhaust pressure. Also, in this configuration, it is no longer possible to drive the flow of gases in the exhaust gas recirculation circuit from the exhaust circuit to the intake manifold. Therefore it is not possible to use the additional compressor in the phases where the recirculation of the exhaust gas to the inlet is activated, nor to activate this recirculation when the additional compressor is running.

The present invention aims to overcome this limitation.

This objective is achieved by a control method, moreover in accordance with the generic definition given in the preamble above, in which, in case of activation of the exhaust gas recirculation circuit, if the additional compressor is in operation, the exhaust flap is controlled so as to increase the exhaust pressure upstream of the variable geometry turbine, so as to restore a positive pressure difference between the exhaust pressure upstream of the turbine variable geometry and supercharging pressure at the intake manifold.

In this way, it is possible to ensure that the exhaust gas recirculation circuit is used simultaneously with the operation of the additional compressor.

Advantageously, the exhaust flap is controlled from the determination of the pressure upstream of the turbine, for example by means of a pressure sensor disposed in the exhaust circuit upstream of the turbine.

Advantageously, the control of the exhaust flap consists in controlling a position of greater closure of the exhaust flap with respect to a normally used closed position.

Preferably, the rate of exhaust gases present in the intake gases entering the intake manifold is regulated by means of the geometry change elements of the variable geometry turbine and the exhaust flap, with respect to a difference set point between the pressures in the exhaust circuit upstream of the variable geometry turbocharger turbine and at the intake manifold.

Alternatively, the rate of exhaust gas present in the -I is regulated; I ΖΧΙΛ ΖΜ + + + + + + + + + '' 'ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ί ΙΠ. ! Zt Ζ1! Ζ-ν t t t ίΛ ίΛ ίΛ ίΛ ίΛ ίΛ---I I I I. ΖΊ. Ι · ~ 1 Εζΐ geometry change of the variable geometry turbine and exhaust flap (38), with respect to a rate setpoint.

Advantageously, the boost pressure is regulated by means of the turbocharger and the additional compressor with respect to a boost pressure setpoint. the invention also relates to a supercharged engine comprising: - combustion cylinders, - an intake gas intake circuit comprising a turbocharger compressor and an additional compressor to increase the amount of intake gas supplied to a collector intake circuit intake system connected to the cylinders; - an exhaust circuit comprising an exhaust manifold connected to the cylinders; a variable geometry turbocharger turbine at the outlet of the exhaust manifold coupled rotatably to the turbocharger compressor; , and an exhaust outlet downstream of the turbine, provided with an exhaust flap, the engine further comprising an exhaust gas recirculation circuit from the exhaust circuit, between the exhaust manifold and the turbocharger turbine with variable geometry, to the intake manifold, the engine being characterized in that it comprises means for controlling a position of the exhaust flap adapted to control the exhaust flap so as to increase the exhaust pressure upstream of the turbine with variable geometry, so as to restore a pressure difference positive between the exhaust pressure upstream of the variable geometry turbine and a boost pressure at the intake manifold, when the exhaust gas recirculation circuit is activated and the additional compressor is in operation. The invention also relates to a motor vehicle characterized in that it comprises a supercharged engine as described above. Other features and advantages of the invention will appear on reading the description given below, given by way of indication but not limitation, in - Figure 1 schematically illustrates an architecture of an internal combustion engine supercharged with air. a turbocharger and having an additional compressor, according to a first embodiment according to the invention; FIG. 2 is a flowchart describing the control strategy of the motor according to the invention.

FIG. 1 illustrates a supercharged heat engine 1 according to a first embodiment of the invention, of the type with four combustion cylinders 10, 12, 14, 16 in line in the example illustrated. The engine comprises an air intake circuit 2 comprising from upstream to downstream (with respect to the direction of flow of the gases): an air filter 20, a turbocharger compressor 21, called a main compressor, which sucks the ambient air at atmospheric pressure and sends under pressure to the intake of the engine, a supercharged air cooler 22 (RAS), an intake flap 23, such as for example a throttle body in the case of a gasoline engine, and an intake manifold or intake manifold 24.

Moreover, the engine 1 also has an exhaust circuit 3 connected to an exhaust outlet of the engine cylinders, comprising from upstream to downstream (with respect to the direction of flow of the gases): a collector of exhaust 30, a turbocharger turbine 31, one or more exhaust aftertreatment systems 32 and an exhaust outlet 37 provided with an exhaust flap 38. For example, the aftertreatment system Exhaust gas 32 comprises a catalyst 320 and a particulate filter 321 located immediately after the catalyst. It may also comprise a trap for nitrogen oxides (NOx). The exhaust flap 38 allows in particular to control the flow of the exhaust gas at the output of the exhaust circuit.

The turbocharger turbine 31 is rotatably coupled to the main compressor 21 via a transmission shaft, and drives the main compressor 21 in rotation to compress air entering the intake manifold when the Turbocharger turbine 31 is rotated by the exhaust gases exiting the exhaust manifold 30.

The turbine 31 is here variable geometry. It comprises movable vanes with variable orientation 310 at the inlet of the turbine, making it possible to modify the geometry of the turbine so as to influence the flow of the exhaust gases on the turbine 31. An actuator (not shown ) is used to control the orientation of the blades 310 of the turbine. The control signals of this actuator are provided by an electronic engine control unit. The fins 310 can be controlled in different closing states so as to modify (decrease or increase) the passage section of the exhaust gases to the turbine 31 and thus modulate the power delivered by the exhaust gases to the turbine 31.

Here, the engine 1 also comprises a high-pressure exhaust gas recirculation circuit 33, from the exhaust circuit 3 to the intake circuit 2. This recirculation circuit is also commonly referred to as an EGR-HP circuit or line. according to the English acronym of "Exhaust Gas Recirculation - High Pressure". It comprises an inlet which originates in the exhaust circuit 3, between the exhaust manifold 30 and the turbine 31, and an outlet which opens into the intake circuit 2, directly upstream of the intake manifold 24, between the intake flap 23 and the manifold 24.

This line EGR-HP 33 can take a portion of the gas flowing in the exhaust circuit 3, called recirculation gas or EGR gas, directly downstream of the exhaust manifold, to reinject it into the engine cylinders to reduce the polluting emissions of the engine, and in particular the emissions of oxides of nitrogen. This line EGR-HP 33 comprises an EGR-HP valve 34 for regulating the flow of EGR gas opening into the intake manifold 24. When the valve 34 is closed, no EGR gas is introduced into the intake circuit via On the other hand, when it is necessary to introduce EGR gas into the fresh air intake circuit via the line EGR-HP 33, the line EGR-HP 33 is activated by controlling opening the valve 34, allowing the passage of a flow of more or less significant exhaust gas to the intake circuit.

In addition, this line EGR-HP 33 is here completed by a circuit 35 for recirculation of exhaust gas at low pressure, also Anglo-Saxon "Exhaust Gas Recirculation - Low Pressure". This EGR-LP line originates in the exhaust circuit 3, at the outlet of the aftertreatment system 32, and opens into the intake circuit 2, between the air filter 20 and the main compressor 21. This line EGR-LP 35 comprises an EGR-LP valve 36 for regulating the flow of EGR gas opening into the intake circuit 2. The exhaust gases, which are not re-circulated via the line EGR-LP 35, are evacuated in the exhaust outlet duct 37 in which the exhaust flap 38 is located.

The heat engine also comprises an additional compressor 25 arranged in the intake circuit 2 in series with the main compressor 21. According to the example of Figure 1, the additional compressor 25 is disposed downstream of the main compressor 21. As a variant it could be disposed upstream of the main compressor 21 in the intake circuit.

The additional compressor 25 is here an electric compressor driven in rotation by means of an electric motor (not shown). It can also be a mechanical compressor, typically coupled to the crankshaft of the engine. Unlike the turbocharger, the operation of the additional compressor is independent of the exhaust gas and increases the amount of air intake regardless of the engine load level and especially at low load and low speed.

This additional compressor has an inlet 26 and an outlet 27, said inlet 26 being connected in the air intake circuit 2 downstream of the main compressor 21, or at the outlet of the latter, according to the example of FIG. and said outlet 27 opening upstream of the supercharged air cooler 22.

The additional compressor 25 may be bypassed (bypassed) by a bypass duct 28 of the intake circuit extending between the inlet 26 and the outlet 27 of the additional compressor 25 and in which a bypass valve 29 is disposed. Thus, when the additional compressor 25 is deactivated, by controlling the opening of the bypass valve 29, the additional compressor 25 is bypassed. On the other hand, when the additional compressor 25 is activated, the bypass valve 29 is closed and the air having received a first compression in the main compressor 21, will benefit from a

The engine also comprises control means (not shown), which admit as input a measurement of the PAVT pressure upstream of the turbine 31 (either at the input of the line EGR-HP 33), obtained by means of a sensor. pressure, or alternatively, a measure of the EGR rate, ie the proportion of the exhaust gases present in the intake gases entering the engine intake manifold 25 via the EGR-HP line 33, and / or an estimate of the PAVT-PCOLL pressure difference between the PAVT pressure at the exhaust upstream of the turbine 31 and the PCOLL pressure at the intake manifold 25. The control means also admit a pressure setpoint input of Psural_cible supercharging at the intake manifold, developed for example according to the engine speed, and a PAVT-PCOLL_poise pressure difference setpoint between the exhaust PAVT pressure upstream of the turbine 31 and the pressure PCOLL at c level intake manifold 25 or alternatively an EGR rate set. The control means are adapted to deliver a first control signal for controlling the turbocharger and the additional compressor to regulate the boost pressure with respect to the setpoint. The control means are also adapted to deliver a second control signal to control the position of the exhaust flap 38 to ensure the regulation of the EGR rate. In particular, the above-mentioned control signal makes it possible to control an open / close position of the exhaust flap 38.

FIG. 2 illustrates the control strategy of the engine according to the invention making it possible to ensure the depollution via the activation of the EGR-HP line 33 and this, simultaneously with the operation of the additional compressor 25.

If a need for activation of the EGR-HP line 33 is identified in a step EO, that is, if the introduction of exhaust gas into the intake circuit via the line EGR-HP 33 is required by the engine strategy it is first determined in a step E1, whether the additional compressor 25 is in operation or must be used.

If this is the case, in a step E2, the exhaust flap 38 is controlled so as to impose a closed position of the flap, said position of greater closure, corresponding to a closed position of the flap plus the flap. exhaust 38 makes it possible to greatly increase the pressure PA VT at the exhaust upstream of the turbine 31, where the line EGR-HP 33 originates, for the same level of pressure PCOLL at the intake manifold 25, downstream of which opens the EGR-HP line 33. As a result, the PAVT-PCOLL pressure difference becomes positive again, generating a difference in driving pressure between the two input and output ends of the EGR-HP line 33, respectively exhaust side and intake side, to circulate the recirculation gas through the EGR-HP line from the exhaust to the inlet.

The control of the exhaust flap is ensured from the determination of the pressure PA VT at the exhaust upstream of the turbine 31, for example by means of a pressure sensor disposed in the exhaust circuit upstream of the turbine at the inlet end of the line EGR-HP 33, able to provide a measured pressure there. Nevertheless, the use of this pressure sensor upstream of the turbine can be avoided if other means are available to measure the level of EGR, ie the proportion of the exhaust gases present in the inlet gases. entering the intake manifold 25 of the engine via the line EGR-HP 33, and / or the pressure difference PAVT-PCOLL.

In a step E3, a step is implemented to regulate the Psural supercharging pressure of the intake gas to the intake manifold, where the turbocharger and the additional compressor are controlled to continuously reduce the measured pressure to the collector. admission to Psural_cible.

At the same time, a phase of regulation of the EGR rate is implemented, so that the regulation is ensured by the fins of the turbine 31 and by the exhaust flap 38, the position of which is controlled to bring back without ceases the pressure difference PAVT-PCOLL determined for example from the pressure measurements upstream of the turbine on the one hand, and the intake manifold, on the other hand, to a set of difference between these pressures VWAP-PCOLL_cible. Alternatively, in this control phase, the fins of the turbine 31 and the exhaust flap are controlled by measuring the rate of EGR, to constantly bring this measured rate to the target zJz-x 4-ZA. .XZ zj'rrn 4-ζ - ,,, χζ zj'rrn

In a step E4, when the line EGR-HP 33 is deactivated, the control strategy is stopped and the regulations of step E3 are interrupted.

Claims (3)

A method of controlling a supercharged engine, the engine comprising: combustion cylinders (10, 12, 14, 16), an intake gas intake circuit (2) comprising a turbocharger compressor. (21) and an additional compressor (25) for increasing the amount of intake gas supplied to an intake manifold (25) of the intake circuit connected to the cylinders, - an exhaust system (3) comprising a manifold exhaust system (30) connected to the cylinders, a variable geometry turbocharger turbine (31) at the outlet of the exhaust manifold (30), rotatably coupled to the turbocharger compressor (21), and an exhaust outlet (37). ), downstream of the turbine, provided with an exhaust flap (38), the engine further comprising an exhaust gas recirculation circuit (33) from the exhaust circuit, between the exhaust manifold (30) and the turbocharger turbine with geometry ie variable (31), to the intake manifold (25), the method being characterized in that, in case of activation (E0) of the exhaust gas recirculation circuit, if the additional compressor (25) is in operation, the exhaust flap (38) is controlled (E2) so as to increase the pressure (PAVT) at the exhaust upstream of the variable geometry turbine, so as to restore a positive pressure difference between the pressure at the exhaust upstream of the variable geometry turbine and a boost pressure at the intake manifold, and in that the rate of exhaust gas present in the incoming intake gases is regulated (E3) in the intake manifold (25) by means of the geometry change elements (310) of the variable geometry turbine (31) and the exhaust flap (38), with respect to a deviation setpoint (PAVT). PCOLL target) between the pressures in the circuit exhaust upstream of the turbocharger turbine with variable geometry (31) and at the intake manifold or with respect to a target rate (target_EGR_rate). 2. Method according to claim 1, characterized in that one controls the exhaust flap (38) from the pressure determination (PAVT) upstream of the turbine (31), for example by means of a pressure sensor disposed in the exhaust circuit (2) upstream of the turbine (31). 3. Method according to claim 1 or 2, characterized in that the control of the exhaust flap (38) consists in controlling a position of greater closure of the exhaust flap with respect to a normally used closed position. 4. Method according to any one of the preceding claims, characterized in that regulates the supercharging pressure by means of the turbocharger and the additional compressor with respect to a supercharging pressure setpoint (Psural_cible). Supercharged engine comprising: combustion cylinders (10, 12, 14, 16), intake gas intake circuit (2) comprising a turbocharger compressor (21) and an additional compressor (25). ) for increasing the amount of intake gas supplied to an intake manifold (25) of the intake circuit connected to the cylinders, - an exhaust system (3) comprising an exhaust manifold (30) connected to the cylinders a variable geometry turbocharger turbine (31) at the outlet of the exhaust manifold (30), rotatably coupled to the turbocharger compressor (21), and an exhaust outlet downstream of the turbine, provided with a flap exhaust system, the engine further comprising an exhaust gas recirculation circuit (33) from the exhaust circuit, between the exhaust manifold (30) and the variable geometry turbocharger turbine (31), the intake manifold (25), the engine being characterized in that it comprises means for controlling a position of the exhaust flap adapted to control the exhaust flap so as to increase the pressure (PAVT) at the exhaust upstream of the variable geometry turbine, so as to restore a positive pressure difference between the exhaust pressure upstream of the variable geometry turbine and a supercharging pressure at the intake manifold, when the recirculation circuit of the exhaust gas is activated and the additional compressor (25) is in operation, said control means being adapted to regulate the rate of exhaust gas present in the intake gas entering the intake manifold (25) by means of the geometry change elements (310) of the variable geometry turbine (31) and the exhaust flap (38), with respect to a deviation set point (PAVT-PCOLLcibl e) between the pressures in the exhaust circuit upstream of the variable geometry turbocharger turbine (31) and at the intake manifold or with respect to a target rate (target_EGR_rate). 6. A motor vehicle characterized in that it comprises a supercharged heat engine according to claim 5.