FR3059719A1 - 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

Holder (s): RENAULT S.A.S Simplified joint-stock company, NISSAN MOTOR CO. LIMITED.

Extension request (s)

Agent (s): RENAULT SAS.

FR 3 059 719 - A1 t54) METHOD FOR CONTROLLING A SUPERCHARGED THERMAL ENGINE INCLUDING AN EXHAUST GAS RECIRCULATION CIRCUIT.

The invention relates to a method for controlling a supercharged combustion engine, comprising a turbocharger compressor (21) and an additional compressor (25) in an intake circuit and a variable geometry turbocharger turbine (31) in an exhaust circuit comprising an exhaust flap (38) downstream of the turbine, the engine comprising an exhaust gas recirculation circuit (33) upstream of the turbine towards the intake manifold. In the event 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 ) 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 boost pressure at the intake manifold .

Method for controlling a supercharged combustion engine comprising an exhaust gas recirculation circuit

The present invention relates generally 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 for controlling a supercharged combustion engine, the engine comprising:

- combustion cylinders,

- an intake gas intake circuit comprising a turbocharger and an additional compressor to increase the quantity of intake gas supplied to an intake manifold of the intake circuit connected to the cylinders,

an exhaust circuit comprising an exhaust manifold connected to the cylinders, a turbocharger turbine with variable geometry at the outlet of the exhaust manifold, coupled in rotation to the turbocharger compressor, and an exhaust outlet, downstream of the turbine, fitted with an exhaust flap, the engine further comprising an exhaust gas recirculation circuit from the exhaust circuit, between the exhaust manifold and the variable geometry turbocharger turbine, towards the manifold of admission.

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 even a mechanical compressor, cannot not be used to increase the quantity of air sent to the intake during certain engine operating phases and, in particular, during the operating phases where exhaust gas recirculation is activated.

When the additional compressor operates in addition to the turbocharger, the pressure at the intake manifold, called intake pressure, becomes higher than the exhaust pressure. Also, in this configuration, it is no longer possible to have a driving pressure between the exhaust and the intake likely to be able to cause the flow of gases in the exhaust gas recirculation circuit from the exhaust circuit. exhaust to the intake manifold.

This is why it is not possible to use the additional compressor in phases where the recirculation of exhaust gases to the intake is activated, nor to activate this recirculation when the additional compressor is operating.

The present invention aims to overcome this limitation.

This objective is achieved by a control process, moreover in accordance with the generic definition given in the preamble above, in which, in the event 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 with variable geometry and a boost 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 relative to a normally used closing position.

Preferably, the rate of exhaust gas present in the intake gases entering the intake manifold is regulated by means of the geometry changing elements of the variable geometry turbine and of the exhaust flap, relative to a setpoint for the difference between the pressures in the exhaust circuit upstream of the turbocharger turbine with variable geometry and at the intake manifold.

As a variant, the rate of exhaust gas present in the intake gases entering the intake manifold is regulated by means of elements for changing the geometry of the variable geometry turbine and the exhaust flap (38), compared 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 heat engine comprising:

- combustion cylinders,

- an intake gas intake circuit comprising a turbocharger and an additional compressor to increase the quantity of intake gas supplied to an intake manifold of the intake circuit connected to the cylinders,

- an exhaust circuit comprising an exhaust manifold connected to the cylinders, a turbocharger turbine with variable geometry at the outlet of the exhaust manifold, coupled in rotation to the turbocharger compressor, and an exhaust outlet downstream of the turbine , fitted with an exhaust flap, the engine further comprising an exhaust gas recirculation circuit from the exhaust circuit, between the exhaust manifold and the variable geometry turbocharger turbine, towards the manifold d intake, 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 at the exhaust upstream of the turbine to variable geometry, so as to restore a positive pressure difference between the exhaust pressure upstream of the varia geometry turbine ble 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 heat engine as described above.

Other features and advantages of the invention will emerge on reading the description given below, given for information but not limitation, with reference to the accompanying drawings in which:

- Figure 1 schematically illustrates an internal combustion engine architecture supercharged with air by a turbocharger and comprising an additional compressor, according to a first embodiment according to the invention;

- Figure 2 is a flowchart describing the engine control strategy 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 gas flow): an air filter 20, a turbocharger compressor 21, called the main compressor, which sucks in the air. ambient air at atmospheric pressure and sends it under pressure to the engine intake, a supercharged intake air cooler 22 (RAS), an intake flap 23, such as for example a throttle body in the case of '' a petrol engine, and an intake manifold or intake manifold 24.

Furthermore, the engine 1 also has an exhaust circuit 3 connected to an exhaust outlet of the engine cylinders, comprising from upstream to downstream (relative to the direction of flow of the gases): a manifold exhaust 30, a turbocharger turbine 31, one or more exhaust gas post-treatment systems 32 and an exhaust outlet 37 provided with an exhaust flap 38. For example, the post-treatment system for exhaust gas 32 includes a catalyst 320 and a particulate filter 321 located immediately after the catalyst. It may also include a nitrogen oxide (NOx) trap. The exhaust flap 38 makes it possible in particular to control the flow rate of the exhaust gases leaving the exhaust circuit.

The turbocharger turbine 31 is coupled in rotation to the main compressor 21 via a transmission shaft, and makes it possible to drive the main compressor 21 in rotation to compress the air which enters the intake manifold when the turbine 31 of the turbocharger is rotated by the exhaust gases leaving the exhaust manifold 30.

The turbine 31 is here of variable geometry. It includes movable fins 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 exhaust gases on the turbine 31. An actuator (not shown) ) is used to control the orientation of the fins 310 of the turbine. The control signals for this actuator are supplied by an electronic engine control unit. The fins 310 can be controlled in different closed states so as to modify (decrease or increase) the cross section of the exhaust gases to the turbine 31 and thus modulate the power supplied by the exhaust gases to the turbine 31.

Here, the engine 1 also includes a circuit 33 for recirculating the high-pressure exhaust gases, from the exhaust circuit 3 to the intake circuit 2. This recirculation circuit is also commonly called EGR-HP circuit or line , in accordance with the acronym “Exhaust Gaz Recirculation - High Pressure”. It includes 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 EGR-HP line 33 allows part of the gases circulating in the exhaust circuit 3, called recirculation gases or EGR gases, to be taken directly downstream of the exhaust manifold, to be reinjected into the engine cylinders in order to reduce polluting emissions from the engine, and in particular nitrogen oxide emissions. This EGR-HP line 33 includes 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 the EGR-HP 33 line. On the other hand, when it is necessary to introduce EGR gases into the fresh air intake circuit via the EGR-HP 33 line, the EGR-HP 33 line is activated by commanding opening the valve 34, allowing the passage of a more or less significant flow of exhaust gas to the intake circuit.

In addition, this EGR-HP line 33 is here supplemented by a low pressure exhaust gas recirculation circuit 35, also commonly called EGR-LP circuit or line in accordance with the English acronym for "Exhaust Gas Recirculation - Low Pressure >>. This EGR-LP line starts in the exhaust circuit 3, at the outlet of the post-treatment system 32, and leads into the intake circuit 2, between the air filter 20 and the main compressor 21. This line EGR-LP 35 includes an EGR-LP 36 valve to regulate the flow of EGR gas opening into the intake circuit 2. The exhaust gases, which are not re-circulated via the EGR-LP 35 line, are evacuated in the exhaust outlet pipe 37 in which the exhaust flap 38 is located.

The heat engine also includes an additional compressor îo 25, arranged in the intake circuit 2 in series with the main compressor

21. According to the example of FIG. 1, the additional compressor 25 is arranged downstream of the main compressor 21. As a variant, it could be arranged 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 engine crankshaft. Unlike the turbocharger, the operation of the additional compressor is independent of the exhaust gases and makes it possible to increase the quantity of air at the intake regardless of the engine load level, 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 in FIG. 1, and said outlet 27 opening upstream of the supercharged air cooler 22.

The additional compressor 25 can 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 arranged. 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 benefited from a first compression in the main compressor 21, will benefit from a second compression in the additional compressor 25.

The engine also includes control means (not shown), which admit as input a measurement of the PAVT pressure upstream of the turbine 31 (ie at the input of the EGR-HP line 33), obtained by means of a pressure, or alternatively, a measure of the EGR rate, that is the proportion of the exhaust gases present in the intake gases entering the intake manifold 25 of the engine 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 accept a pressure setpoint as input Supercharging Psural_cible at the intake manifold, developed for example according to the engine speed, and a pressure difference setpoint PAVT-PCOLL_target between the PAVT pressure at the exhaust upstream of the turbine 31 and the PCOLL pressure level of c intake manifold 25 or alternatively an EGR rate setpoint. The control means are adapted to deliver a first control signal making it possible to control the turbocharger and the additional compressor in order to regulate the boost pressure relative to the setpoint. The control means are also suitable for delivering a second control signal making it possible to control the position of the exhaust flap 38 to ensure the regulation of the EGR rate. In particular, the aforementioned control signal makes it possible to control an opening / closing position of the exhaust flap 38.

FIG. 2 illustrates the engine control strategy according to the invention making it possible to provide pollution control 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 33 line is identified in an EO step, in other words if the introduction of exhaust gas into the intake circuit via the EGR-HP 33 line 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 position for closing the flap, called the position of greatest closure, corresponding to a position for closing the flap greater than that normally used. The position of greater closure of the exhaust flap 38 makes it possible to greatly increase the pressure PA VT at the exhaust upstream of the turbine 31, where the EGR-HP line 33 arises, for the same pressure level PCOLL at level of the intake manifold 25, downstream of which the EGR-HP line 33 opens. As a result, the pressure difference PAVT-PCOLL becomes positive again, generating a difference in driving pressure between the two inlet and outlet ends from the EGR-HP line 33, respectively on the exhaust side and on the intake side, making it possible to circulate the recirculation gases through the EGR-HP line from the exhaust to the intake.

îo 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 EGRHP 33 line, capable of supplying a pressure measured at this location. However, the use of this pressure sensor upstream of the turbine can be avoided if other means are available to measure the EGR rate, i.e. the proportion of exhaust gases present in the intake gases. entering the engine's intake manifold 25 via the EGR-HP line 33, and / or the PAVT-PCOLL pressure difference.

In a step E3, a phase of regulation of the Psural supercharging pressure of the intake gases to the intake manifold is implemented, where the turbocharger and the additional compressor are controlled to constantly reduce the pressure measured at the intake manifold. admission to the Psural_cible setpoint.

At the same time, an EGR rate regulation phase 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 stops the PAVT-PCOLL pressure difference determined for example from the pressure measurements upstream of the turbine on the one hand, and at the intake manifold, on the other hand, at a setpoint of difference between these pressures PAVT-PCOLL_target. As a variant, in this regulation phase, the fins of the turbine 31 and the exhaust flap are controlled by measuring the EGR rate, to constantly reduce this measured rate to the EGR rate setpoint rate d 'Target EGR.

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

Claims (8)

1. Method for controlling a supercharged heat engine, the engine comprising: 5 - combustion cylinders (10, 12, 14, 16), - an intake gas intake circuit (2) comprising a turbocharger compressor (21) and an additional compressor (25) to increase the quantity of intake gas supplied to an intake manifold (25) of the circuit intake connected to the cylinders, îo - an exhaust circuit (3) comprising an exhaust manifold (30) connected to the cylinders, a turbocharger turbine (31) with variable geometry at the outlet of the exhaust manifold (30) , coupled in rotation to the turbocharger compressor (21), and an exhaust outlet (37), downstream of the turbine, provided with an exhaust flap (38), 15 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), to the manifold d admission (25), the method being characterized in that, in the event of activation (E0) of the circuit 20 for exhaust gas recirculation, if the additional compressor (25) is in operation, control (E2) the exhaust flap (38) 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 25 boost pressure at the intake manifold. 2. Method according to claim 1, characterized in that the exhaust flap (38) is controlled from the determination of the pressure (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). 30 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 relative to a normally used closing position. 4. Method according to any one of claims 1 to 3, characterized in that regulates (E3) the rate of exhaust gas present in the intake gases entering the intake manifold (25) by means elements (310) for changing the geometry of the geometry turbine 5 variable (31) and the exhaust flap (38), with respect to a setpoint difference (PAVT-PCOLL_cible) between the pressures in the exhaust circuit upstream of the turbine of variable geometry turbocharger (31) and at the intake manifold. 5. Method according to any one of claims 1 to 3, characterized in that one regulates (E3) the rate of exhaust gas present in the intake gases entering the intake manifold (25) by means of elements (310) for changing the geometry of the variable geometry turbine (31) and the exhaust flap (38), with respect to a rate setpoint (rate_d'EGR_cible). 15 6. Method according to any one of claims 4 or 5, characterized in that the boost pressure is regulated by means of the turbocharger and the additional compressor with respect to a boost pressure setpoint (Psural_cible). 7. Supercharged heat engine including: 20 - combustion cylinders (10, 12, 14, 16), - an intake gas intake circuit (2) comprising a turbocharger compressor (21) and an additional compressor (25) to increase the quantity of intake gas supplied to an intake manifold (25) of the circuit of admission connected to the cylinders, 25 - an exhaust circuit (3) comprising an exhaust manifold (30) connected to the cylinders, a turbocharger turbine (31) with variable geometry at the outlet of the exhaust manifold (30), coupled in rotation to the compressor turbocharger (21), and an exhaust outlet downstream of the turbine, fitted with an exhaust flap, 30 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), to the manifold d intake (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 boost pressure at the intake manifold, when the exhaust gas recirculation is activated and the additional compressor (25) is in operation. 8. Motor vehicle characterized in that it comprises a supercharged heat engine according to claim 7. 1/1