FR3069282A1 - METHOD FOR CONTROLLING A SUPERIOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The invention relates to a method for controlling a turbocharged supercharged engine (1), in which variable engine timing means (40) are activated to control a partial lift of an exhaust valve (SE). a cylinder of the engine during a main lift of an intake valve (SA) to reintroduce exhaust gases into the cylinder during an air intake phase, said method comprising the following steps: - generating a a motor air flow setpoint value taking into account the engine speed and load, said air flow setpoint being able to set a target value of reintroduced exhaust rates; - regulating the intake air flow rate (Qair) in the engine by acting on the turbocharger with respect to said air flow setpoint value, so as to reduce the intake air flow rate to reach said value of air flow instruction.

Description

Method for controlling a supercharged internal combustion engine

The present invention relates to a method for controlling an internal combustion engine supercharged by at least one turbocharger, said engine comprising at least one cylinder, at least one inlet valve in said cylinder and at least one gas exhaust valve burned of said cylinder, said engine being equipped with at least one exhaust gas recirculation circuit and variable distribution means making it possible to vary the lift law of said exhaust valve, in particular at the instant d opening and closing of said exhaust valve.

In internal combustion engines, more particularly in diesel engines, the reintroduction of exhaust gases to the intake is useful for reducing the polluting emissions of the engine and, in particular, makes it possible to reduce, in a non negligible manner, the quantity nitrogen oxides (NOx) which are released to the atmosphere.

Generally, this recirculation is carried out thanks to a circuit, called EGR-HP circuit (Exhaust Gas Recirculation - High Pressure) comprising a line connecting the engine exhaust manifold to its intake distributor and a valve, called EGR-HP valve. , placed in this line. This circuit therefore takes part of the gases circulating in the exhaust circuit, called recirculation gas or EGR gas, directly downstream of the exhaust manifold, to reinject it into the engine cylinders. This circuit can be completed by a low pressure exhaust gas recirculation circuit, called EGR-LP (Exhaust Gas Recirculation - Low Pressure) circuit. This EGR-LP circuit begins in the exhaust circuit, at the outlet of the exhaust gas aftertreatment system, and opens into the engine intake circuit, upstream of the turbocharger. It includes a valve called an EGRLP valve to regulate the flow of EGR gas opening into the intake circuit 2

In certain engine operating phases, in particular the cold operating phases, the EGR-HP and EGR-LP circuits are not available for reliability reasons, in particular because their use would cause significant fouling of the EGR valves due to the presence of condensate forming at low temperature.

Also, under these conditions, it is known to use, to improve the efficiency of the post-treatment system, an internal EGR, usually called IGR for Internai Gas Recirculation, which makes it possible to reintroduce exhaust gases at the intake of the engine, without using a specific external exhaust gas recirculation circuit, such as the EGR-HP circuit or the EGR-LP circuit.

For this, there is provision for a re-admission of the exhaust gases into the combustion chamber of the engine cylinders by reopening the corresponding exhaust valves during the intake phase. Variable valve actuation means WA (Variable Valve Actuation), known per se, making it possible to vary the lifting laws of the valves and in particular of the exhaust valves, in particular at their opening and closing times, so independently of one another or jointly, can advantageously be used. For example, these variable distribution means can comprise a WA type camshaft controlling the exhaust valves and carrying a plurality of cams with different profiles making it possible to control each exhaust valve according to different lifting laws, under the impulse of control means, and in particular according to a lifting law allowing at least partial lifting of the exhaust valve during the intake phase, that is to say during a main lifting of the valve d 'admission. It should be noted that the term lifted corresponds to the graphic representation (along two axes) of the movement of a valve from the start of its opening to the end of its closure passing through its fully open position or at least partial.

Combustion is then favored since the initially low temperature of the gases admitted into the combustion chamber can be notably increased due to the presence of hot exhaust gases.

Patent document JP2008157155 discloses a method of controlling an internal combustion engine in which a partial lifting of the exhaust valve during a lifting is controlled, as a function of at least one pair of engine operating parameters. main valve.

However, in this context, the main difficulty lies in how to control the setting of the supercharged engine when the variable distribution means WA are activated. In particular, there is a need for a strategy for controlling the operation of the engine when the variable exhaust distribution means are activated, which make it possible to effectively control a desired rate of reintroduced exhaust gases.

The present invention aims to meet this need.

This objective is achieved by a method of controlling an internal combustion engine supercharged by at least one turbocharger, said engine comprising at least one cylinder, at least one inlet valve into said cylinder and at least one exhaust valve from the burnt gases from said cylinder, said engine being equipped with at least one exhaust gas recirculation circuit and variable distribution means making it possible to vary the lift law of said exhaust valve, in particular at the instant d opening and closing of said exhaust valve, in which the activation of said variable distribution means is controlled as a function of engine operating parameters so as to control an at least partial lifting of said exhaust valve during a lifting main of said intake valve for reintroducing exhaust gases into the combustion chamber of the cylinder during an air intake phase, said method being characterized in that it comprises the following steps in the event of activation of said variable distribution means:

- generate an engine air flow setpoint taking into account the engine speed and load, said air flow setpoint being able to set a target value for the rate of exhaust gas reintroduced;

- regulate the air flow admitted into the engine by acting on the turbocharger until reaching the air flow setpoint value making it possible to obtain said target value of the rate of exhaust gas reintroduced.

Thus, thanks to the invention which is based on the observation that the rate of reintroduced exhaust gases and the air flow are linked, it is possible to control the rate of reintroduced exhaust gases by regulating the flow of air.

In other words, the turbocharger is controlled on an air flow setpoint value, making it possible to set the rate of exhaust gas that one wishes to reintroduce, according to the engine operating conditions defined by the engine torque and engine load.

Advantageously, said air flow setpoint value is generated from a map previously constructed in which engine airflow setpoint values are stored as a function of the engine speed and load, each value of mapped air flow setpoint corresponding to a target value of reintroduced exhaust gas rate.

According to one embodiment, the turbocharger being of the type comprising a variable geometry turbine, geometry change elements of the variable geometry turbine are controlled so as to regulate the air flow admitted into the engine.

Advantageously, the elements for changing the geometry of the variable geometry turbine comprising movable fins with variable orientation at the inlet of the turbine making it possible to modify a cross section for the passage of exhaust gases towards the turbine, said fins are closed until closed. reaching said generated air flow setpoint.

According to another embodiment, the turbocharger being of the type comprising a turbine with fixed geometry, a discharge valve of the turbocharger is controlled so as to regulate the flow of air admitted into the engine.

Advantageously, the activation of the variable distribution means is controlled as a function of at least the following parameters: the temperature of the outside air, the temperature of the liquid in the engine cooling circuit, the engine speed, the engine load and a parameter relating to the efficiency of the engine after-treatment system.

The invention also relates to a device for controlling an internal combustion engine supercharged by at least one turbocharger, said engine comprising at least one cylinder, at least one inlet valve in said cylinder and at least one exhaust valve for burnt gases from said cylinder, said engine being equipped with at least one exhaust gas recirculation circuit and variable distribution means making it possible to vary the lift law of said exhaust valve, in particular at the instant opening and closing of said exhaust valve, said device comprising an electronic engine control unit adapted to control the activation of said variable distribution means as a function of engine operating parameters so as to control at least one lift partial of said exhaust valve during a main lift of said inlet valve for reintro reduce exhaust gases in the combustion chamber of the cylinder during an air intake phase, characterized in that said control unit is suitable for implementing the method as described above.

Advantageously, said control unit is associated with data storage means, said data storage means comprising a map in which engine air flow setpoint values are stored as a function of the engine speed and load. , each mapped air flow setpoint value corresponding to a target value of reintroduced exhaust gas rate.

The invention also relates to a motor vehicle characterized in that it comprises a control device 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 is a diagram showing an example of an internal combustion engine on which the method according to the invention can be implemented, in the case where the variable distribution means WA at the exhaust are activated;

- Figure 2 is a diagram illustrating the law of lifting of the exhaust and intake valves of an internal combustion engine as a function of an angle a of the engine crankshaft;

- Figure 3 is a flowchart describing the engine control strategy according to the invention.

FIG. 1 illustrates a supercharged internal combustion engine 1, of the type with four combustion cylinders 10, 12, 14, 16 in line in the example illustrated, each opening into a combustion chamber. Each cylinder receives a piston, not shown, mounted in translation in the cylinder and secured to a crankshaft. The engine here is equipped with an SA intake valve per cylinder and an SE exhaust valve per cylinder. Means for actuating the intake valves and the intake valves respectively are provided, which make it possible to respectively control a lift, called the main lift, of an intake valve SA and of an exhaust valve SE. In addition, the means for actuating the exhaust valves SE comprise means 40 of variable distribution of WA type, making it possible to control, when activated, a partial lifting of an exhaust valve SE during the main lifting an SA inlet valve.

The main lift of an intake or exhaust valve corresponds to a valve operating cycle during which it passes from a closed position to a fully open position, then returns to the initial closed position, on a fixed term. The closed position being understood to be the position in which the valve prevents the passage of gas between the combustion chamber and the pipe associated with the valve.

The fully open position is a position in which the valve is completely open, as opposed to partially open, and allows the passage of gas between the corresponding pipe and the combustion chamber.

The partial lifting of a valve corresponds to an operating cycle during which it passes from a closed position to a partially open position, then returns to the initial closed position. The partial valve lift therefore has a height which is less than that of the lift (called the main lift).

FIG. 2 illustrates this principle of reopening the exhaust valve of a cylinder during the intake phase of the engine thanks to the variable distribution of the WA type associated with the exhaust valves. The WA-type means make it possible to carry out the two laws of lifting the exhaust valves. A first law makes it possible to carry out the main lift L1 of the exhaust valves during the exhaust phase of the engine. The other lift law allows partial lift L2 of the exhaust valves during the main lift of the intake valves during an intake phase of the engine.

For example, the variable distribution means 40 associated with the exhaust valves can be of the exhaust camshaft WA type, which comprises a cam associated with a second cam enabling the partial lifting law to be ensured as well as a device clutch capable of making the second cam non-operational so that only the main lifting of the exhaust valves is possible. Of course, the shape of the second cam determines the height of the partial lifting as well as the duration of the partial lifting of the corresponding valves.

According to the example of FIG. 1, the variable distribution means 40 associated with the exhaust valves are provided for one exhaust valve per cylinder. They can also control two exhaust valves per cylinder, without departing from the scope of the invention.

Alternatively, the WA type camshaft associated with the exhaust valves can be replaced by actuation means dedicated to each valve, such as an actuator with electromagnetic or electropneumatic control or the like, which acts directly or indirectly on the rod. valve.

The SA inlet valves are controlled to open and close by any conventional means, such as a conventional camshaft controlled in rotation by a drive track connected to the engine crankshaft.

Again with reference to FIG. 1, the engine comprises an air intake circuit 2 comprising from upstream to downstream (relative to the direction of flow of the gases): an air filter 20, a compressor 21 of turbocharger, which draws 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 and an intake manifold or manifold d admission 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 gas flow): 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. The exhaust flap 38 makes it possible in particular to control the flow of exhaust gases at the outlet of the exhaust circuit.

The turbocharger turbine 31 is coupled in rotation to the compressor 21 via a transmission shaft, and makes it possible to drive the compressor 21 in rotation to compress the air which enters the intake manifold when the turbine 31 of turbocharger is driven in rotation 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 provided by an electronic engine control unit (ECU). The fins 310 can be controlled in different closed positions 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.

Thus, the regulation of the boost pressure PCOLL in the intake manifold can be carried out by acting on the control of the geometry of the turbine, in particular on the control of the closed position of the fins at the inlet of the turbine.

As a variant, the turbocharger ensuring the supercharging of the engine can also be of the type comprising a turbine with fixed geometry. In this case, the boost pressure is regulated by acting on the control of the relief valve (“Wastegate” according to English terminology), which is the valve fitted between the exhaust gas exhaust valve at the outlet. of the engine and the turbine inlet, and which adjusts the amount of exhaust gas passing through the turbine.

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 begins 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 intake manifold 24.

This EGR-HP circuit 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 circuit 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 circuit. On the other hand, when it is necessary to introduce EGR gases into the fresh air intake circuit via the EGR-HP 33 circuit, the EGR-HP 33 circuit 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 circuit 33 is here supplemented by a circuit 35 for low-pressure exhaust gas recirculation, also commonly known as an EGR-LP circuit or line in accordance with the English acronym for "Exhaust Gas Recirculation - Low Pressure ”. This EGR-LP circuit begins 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 compressor 21. This EGR-LP circuit 35 includes an EGR-LP valve 36 for regulating the flow of EGR gas opening into the intake circuit 2. The exhaust gases, which are not recycled via the EGR-LP circuit 35, are evacuated in the outlet pipe exhaust 37 in which is located the exhaust flap 38.

We will now describe in more detail the control of the engine supercharging system when the WA type means associated with the engine exhaust valves are activated. In particular, when the exhaust valve is reopened during the intake phase, burnt gases from the exhaust are reintroduced into the cylinder. These reintroduced exhaust gases drop the air filling rate of the engine cylinders and therefore directly influence the air flow Qair of the engine.

As a result, there is an interdependence between the engine air flow and the rate of reintroduced exhaust gases (IGR rate).

Thus, with regard to the regulation of the boost pressure PCOLL in the engine intake manifold, when the WA type means associated with the engine exhaust valves are activated, when the turbine blades are closed to control with variable geometry in order to regulate the boost pressure (in the case of a variable geometry turbine), the ensuing back pressure on engine exhaust results in an increase in the rate of IGR and by a decrease in the boost pressure and the air flow of the engine, which is the opposite of the operating mode when the when the WA type means associated with the engine exhaust valves are not activated.

Indeed, when these means are not activated, the boost pressure at the PCOLL inlet is regulated as follows: when the fins are closed (in the case of a variable geometry turbine), the boost pressure PCOLL increases and the engine air flow increases; when opened, the boost pressure decreases, which regulates the amount of air introduced into the engine and engine torque, via this air flow and the amount of fuel.

The control of the operation of the engine cannot therefore be done in a conventional manner when the WA type means associated with the engine exhaust valves are activated.

According to the control method of the invention, the rate of IGR and Qair air flow being linked, it is planned to control the rate of IGR by regulating the air flow. The latter is measured by the engine flow meter.

In other words, to obtain the desired IGR rate, the turbocharger regulation system (“wastegate” in the case of a turbine with fixed geometry; fins at the inlet of the turbine, in the case of a turbine with variable geometry) is controlled so as to obtain the corresponding air flow. To do this, it is necessary to first build a torque map (IGR rate, air flow).

The entire engine control strategy according to the invention will now be described in more detail with reference to Figure 3. It is controlled by the computer dedicated to engine control housed in the electronic engine control unit (ECU ). This strategy is applied according to the example on an engine comprising a turbocharger having a turbine with variable geometry.

A first step E0 consists in triggering the activation of the WA type variable distribution means associated with the engine exhaust valves, as a function of engine operating conditions. To do this, the ECU receives a set of parameters making it possible to determine the presence of engine operating conditions requiring the activation of these WA type means. These parameters include the temperature of the outside air T _air , the water temperature of the cooling circuit T _water , the engine speed N, the engine load, supplied for example by the medium effective pressure indicator PME. Other parameters can also be taken into account by the ECU, such as the efficiency ε of the post-processing system.

If the operating conditions which require the use of the WA type means are not verified, we go to a step E01 in which these means are not activated (WA OFF). In this case, the method applies a step E02, in which the engine control operates normally. In other words, step E02 triggers a step of controlling the position of the fins at the inlet of the turbine of the turbocharger to regulate the boost pressure PCOLL at the intake on a pressure setpoint setpoint_PCOLL. Depending on the N speed and the PME load of the engine, this regulation of the boost pressure will be done either in a closed loop (regulation by PID type actuators), or in an open loop (by means of pre-positioning maps of the fins, for example). of the turbine with variable geometry. Conventionally, in step E03, the closing control of the fins of the variable geometry turbine causes an increase in the supercharging pressure PCOLL and the regulation by the closing control of the fins is maintained. as long as the boost pressure PCOLL has not reached the setpoint setpoint_PCOLL (step E04) When this setpoint is reached or exceeded by the boost pressure PCOLL, we go to a step E05 in which the setting of the fin position is stabilized and the control strategy is stopped.

On the other hand, in step E0, if the operating conditions, which require the use of the WA type means, are verified by the ECU, in step E11, the activation of these means (WA ON) is ordered.

In this case, in accordance with the invention, the method triggers a step E12 of driving the turbine with variable geometry in which the position of the fins at the inlet of the turbine of the turbocharger is controlled on an air flow instruction set_Qair . This air flow setpoint was mapped beforehand during tests making it possible to construct a Qair = f (N, PME) map of air flow setpoint values as a function of engine operating conditions defined by engine speed N and PME load values. This mapping fixes the rate of IGR that we want to reintroduce, which is generally the maximum rate achievable by the system. Also in a step E14, the fins of the variable geometry turbine are controlled so as to obtain the air flow setpoint supplied in step E13 by the pre-established map, as a function of the engine operating conditions determined by the speed N and the PME load of the motor.

The control is here reversed with respect to the case where the WA type means are not activated (WA OFF). In fact, as explained above, the operation of the engine control when the WA type means are activated implies that, in a step E14, when the blades of the turbine of variable geometry are controlled towards their closed position, the pressure PCOLL boost and the air flow Qair of the engine decreases, due to the reintroduction of burnt gases into the cylinder. Depending on the operating conditions (N, PME) of the engine, control can be done either in a closed loop (regulation by PID type actuators on the air flow setpoint) or in an open loop (using maps of pre-positioning of the blades of the variable geometry turbine).

In step E15, the regulation by the command to close the fins is maintained as long as the air flow Qair measured by the engine flow meter is greater than the set value of air flow setpoint_Qair provided by the mapping to the step E13, corresponding to the desired IGR rate. When the measured air flow rate reaches or becomes lower than this air flow rate setpoint, we go to a step E16 in which the adjustment of the position of the fins is stabilized and the control strategy is stopped.

Claims (9)

1. Method for controlling an internal combustion engine (1) supercharged by at least one turbocharger, said engine comprising at least one cylinder (10, 12, 14, 16), at least one inlet valve (SA) in said cylinder and at least one exhaust valve (SE) for the burnt gases from said cylinder, said engine (1) being equipped with at least one circuit (33, 34) for recirculating exhaust gases and variable distribution means (40) making it possible to vary the lifting law of said exhaust valve (SE), in particular at the time of opening and closing of said exhaust valve, in which the control (E0) is activation of said variable distribution means as a function of engine operating parameters so as to command an at least partial lifting of said exhaust valve during a main lift of said intake valve to reintroduce exhaust gases into the combustion of the cylinder during an air intake phase, said method being characterized in that it comprises the following steps in the event of activation (E11) of said variable distribution means: - Generate (E13) an air flow setpoint value (setpoint_Qair) of the engine taking into account the engine speed (N) and the engine load (PME), said air flow setpoint being able to set a target value of reintroduced exhaust gas rate; - regulate (E14) the air flow admitted into the engine by acting on the turbocharger with respect to said generated air flow set value, so as to decrease the air flow (Qair) admitted to reaching said generated air flow setpoint value making it possible to obtain said target value of reintroduced exhaust gas rate. 2. Method according to claim 1, characterized in that said air flow setpoint value is generated from a map (Qair = f (N, PME)) previously constructed in which setpoint values are stored. engine air flow as a function of engine speed (N) and engine load (PME), each mapped air flow setpoint corresponding to a target value of reintroduced exhaust gas rate. 3. Method according to claim 1 or 2, characterized in that the turbocharger being of the type comprising a variable geometry turbine (31), elements (310) for changing the geometry of the variable geometry turbine are controlled so as to regulate the air flow admitted into the engine. 4. Method according to claim 3, characterized in that, the elements for changing the geometry of the variable geometry turbine comprising movable fins with variable orientation at the inlet of the turbine making it possible to modify a section for the passage of exhaust gases towards the turbine, said fins are controlled to close until reaching said generated air flow set value. 5. Method according to claim 1 or 2, characterized in that the turbocharger being of the type comprising a turbine with fixed geometry, a discharge valve of the turbocharger is controlled so as to regulate the air flow admitted into the engine. 6. Method according to any one of the preceding claims, characterized in that the activation of the variable distribution means is controlled as a function of at least the following parameters: the temperature of the outside air (Tair), the temperature of the liquid from the engine cooling circuit (Teau), engine speed (N), engine load (PME) and a parameter (ε) relating to the efficiency of the engine after-treatment system. 7. Control device for an internal combustion engine (1) supercharged by at least one turbocharger, said engine comprising at least one cylinder (10, 12, 14, 16), at least one inlet valve (SA) in said cylinder and at least one exhaust valve (SE) for the burnt gases from said cylinder, said engine (1) being equipped with at least one circuit (33, 34) for recirculating exhaust gases and variable distribution means (40) making it possible to vary the lifting law of said exhaust valve (SE), in particular at the time of opening and closing of said exhaust valve, said device comprising an electronic control unit of the motor adapted to control the activation of said variable distribution means as a function of operating parameters of the motor so as to control an at least partial lifting of said exhaust valve during a main lifting of said intake valve ission for reintroducing exhaust gases into the combustion chamber of the cylinder during an air intake phase, characterized in that said control unit is suitable for implementing the method according to any one of previous claims. 8. Device according to claim 7, characterized in that said control unit is associated with data storage means, said data storage means comprising a map in which are stored engine air flow set values as a function of the engine speed (N) and of the engine load (PME), each mapped air flow setpoint value corresponding to a target value of reintroduced exhaust gas rate. 9. Motor vehicle characterized in that it comprises a control device according to claim 7 or 8.