WO2003081005A1

WO2003081005A1 - System and method for controlling an engine which is supercharged with air by two turbocompressors

Info

Publication number: WO2003081005A1
Application number: PCT/FR2003/000839
Authority: WO
Inventors: Laurent Fontvieille
Original assignee: Renault S.A.S.
Priority date: 2002-03-21
Filing date: 2003-03-17
Publication date: 2003-10-02
Also published as: FR2837526A1; FR2837526B1

Abstract

The invention relates to a system (50) for controlling an engine (1) which is supercharged with air by means of two turbocompressors (18,28) having a common intake manifold (6), said system also comprising an electronic control unit (52) comprising means (54) for determining the required boost pressure value and means (58) for regulating the boost pressure. According to the invention, the ECU (52) also comprises means (56) for limiting the required boost pressure valve, said limiting means (56) being able to deliver a limited boost pressure value to the regulating means (58), the limited value being determined in such a way that for each turbocompressor (18,28) it produces a functioning point located in the compressor field of the turbocompressor (18,28). The invention also relates to a control method for the implementation of such a system (50).

Description

SYSTEM AND METHOD FOR CONTROLLING AN AIR-SUPPLIED ENGINE BY TWO TURBOCHARGERS

DESCRIPTION

TECHNICAL FIELD The present invention relates to systems and methods for controlling an engine supercharged with air by two turbochargers.

More particularly, the invention relates to systems and methods for controlling an engine supercharged with air by a first turbocharger and a second turbocharger supplying a first bank of cylinders and a second bank of cylinders by means of a manifold d 'common intake, the first and second turbochargers being respectively coupled to a first actuator and a second actuator, each capable of driving the turbocharger in order to change the rotational capacity of the turbine rotor.

STATE OF THE PRIOR ART In this technical field, a system for controlling a diesel engine supercharged with air is known by two identical turbochargers, each belonging to a separate supercharging circuit.

In this system, the turbochargers are composed of a turbine and a compressor for the purpose increase the amount of air admitted to the engine cylinders. Each turbine is placed at the outlet of an exhaust manifold, and is driven by ^the exhaust ^gases coming from a bank of cylinders supplied with air by the compressor. In general, ^the power supplied by the exhaust gases to ^the various turbines can be modulated using relief valves (from the English “waste gâte ^” ) ι ^or even using fins , in the case of a variable geometry turbocharger.

Compressors, mounted on the same axis as their associated turbines, the compress has r from outside the engine and directs ^{nt c} compressed air to both intake manifolds, each associated with a turbocharger. It should also be noted that an exchanger is placed between each compressor and its associated cylinder bank, in order to cool the ^aLr heated during its passage through the compressor.

In addition, actuators are

, i - also designed to control the opening & - closing of the relief valves or the wings of the turbochargers, in order to properly regulate ^the a- power supplied by the exhaust gases to the two turbines, and to respond precisely to the needs ^{3 of the} engine. To do this, the system comprises an electronic control unit capable of delivering a control signal to each of the two actuators.

In the control system according to the prior ^art , designed to control an engine whose two air boost circuits are completely independent, the electroπ-i ^£ 3 ^{eu control unit} determines the value of the boost pressure required in the intake manifolds, this value usually being mapped according to engine speed and fuel flow. Then, this value is modified taking into account the temperature and the air pressure at the inlet of the compressor, while respecting the technical characteristics of the turbocharger, such as its compressor field, in order to avoid their damage ent. This gives a required value of the common boost pressure for the two compressors, taking into account the technical characteristics of the turbochargers as well as the ambient conditions of the engine to be supplied. The required boost pressure value is then compared to a boost pressure value measured in one of the engine's two intake manifolds. A regulator is then used to regulate the boost pressure in the two intake manifolds, by developing a single actuator control signal, aimed at regulating the opening and / or closing of the relief valves or of the blades of the turbines. Finally, to balance the two turbochargers operating independently, an additional regulator is provided to cancel the difference between the air flow rates measured at the inlet of the two compressors. Depending on this difference, the single control signal is then readjusted for each of the two actuators. W 03

However, it turns out that this type of control system is in no way compatible with engines supercharged with air, the two compressors of which are connected to a common intake manifold 5. In fact, in the control system according to the prior art, the required value of boost pressure is determined to satisfy an air requirement of the engine, while respecting the compressor field of the two identical turbochargers.

10 However, the determination of this value does not take into account the possible dispersions between two turbochargers having a common supercharging circuit. This failure to take into account can have the effect of deterioration or even destruction

15 total turbochargers, insofar as it can generate interactions between them, capable of causing one or two turbochargers to leave their associated field-compressor. Therefore, the control system ^' according to art

20 prior is not able to cope with this possibility of dispersions between the two turbochargers, ^' thus prohibiting its transposition on an engine supercharged with air having a common intake manifold.

25 During tests carried out on this type of engine, interactions between the two compressors were effectively highlighted.

With reference to FIG. 1, we see a graph representing a compressor field of a motor with

30 common intake manifold, using a control system such as that described above. On the graph shown, the abscissa axis corresponds to the air flow rate _c (in kg / h) of the compressor, and the ordinate axis corresponds to the compression rate π _c of the compressor. The curves a, b, c, d, e, f correspond to the iso-speed curves, extending in this example between 90,000 rpm for the curve f, and 190,000 rpm for the curve a, beyond which there is a risk of destruction of the turbocharger. Indeed, the zone Zi situated above the curve a corresponds to an overspeed zone, in which the turbocharger exceeds its maximum authorized speed.

Furthermore, curve g defines the pumping limit of the compressor. This curve g therefore delimits an area Z ₂ in which the pumping of the compressor is excessive, and risks damaging the turbocharger. Thus, the curves a and g define a zone Z ₃ in which the risks of damage to the turbocharger are almost nonexistent, this zone Z ₃ also being called the compressor field of the turbocharger.

In the graph of FIG. 1, the points Pi and P ₂ respectively represent the operating points of a first and of a second turbocharger, during a test of the control system according to the prior art, on an engine with common intake manifold. The point P _x is in the pumping zone Z ₂ , while the point P ₂ is in the zone Z ₃ corresponding to the compressor field. With the help of this test, we can see that the different operations carried out by the W

electronic control, in particular taking account of the compressor field for the assembly consisting of the two turbochargers, are insufficient to ensure that the turbochargers maintain their operating points in the compressor field.

Indeed, when an engine has a single air supercharging circuit, the flow of the compressor of the second turbocharger tends to oppose the flow of the compressor of the first

10 turbocharger, or vice versa. As shown in FIG. 1, in the case where the flow rate of the second turbocharger is opposed to the flow rate of the first turbocharger, the latter risks being damaged due to the presence of its operating point P _x

15 in pumping zone Z ₂ . On the other hand, the second turbocharger is also exposed to the risks of deterioration, insofar as it supplies a large part of the air to the common intake manifold, and can therefore be brought out of the compressor field 0 to enter the Zi overspeed zone.

The control system of the prior art which has just been described is therefore completely incompatible with an air supercharged engine, the supercharging circuit of which is common to the two turbochargers.

STATEMENT OF THE INVENTION

First of all, the object of the invention is to propose a system for controlling a motor supercharged with air by a first turbocharger and a second turbocharger supplying a first bench of cylinders and a second bank of cylinders by means of a common intake manifold, the system at least partially remedying the drawbacks relating to the control system of the prior art described above.

The object of the invention is also to present a control system for an engine supercharged with air, considerably limiting the risks of damage to the turbochargers, connected together by a common supercharging circuit.

The object of the invention is finally to propose a method for controlling an engine supercharged with air, capable of implementing a control system fulfilling the aim mentioned above. To do this, the invention relates to a system for controlling a supercharged engine with air by a first turbocharger and a second turbocharger supplying a first bank of cylinders and a second bank of cylinders via a manifold. common intake, the first and second turbochargers being respectively coupled to a first actuator and a second actuator, the system further comprising an electronic control unit comprising: - means for determining the required value of boost pressure;

- means for regulating the boost pressure capable of delivering a control signal to the actuators, the control signal being a function of a boost pressure measured in the common intake manifold. According to the invention, the electronic control unit also comprises means for limiting the required value of boost pressure, the limitation means being able to deliver a limited value of boost pressure to the regulating means, the limited value being determined so that for each turbocharger, it generates an operating point located in the compressor field of the turbocharger.

Advantageously, the boost pressure value used to carry out the regulation corresponds to a limited value compared to the required pressure value. This limitation is implemented in order to take into account the air requirements of the engine, but also to respect the technical characteristics of each of the two turbochargers. In this way, regardless of the boost pressure required by the engine, the fact of determining a limited value of boost pressure aimed at maintaining the operating points of the turbochargers inside the compressor field, greatly reduces the risks of deterioration. related to interactions. According to a preferred embodiment of the present invention, the means for limiting the required value of boost pressure include primary calculation means capable of determining, for each turbocharger, the maximum value of boost pressure generating an operating point. located in the field compressor of the turbocharger, the limiting means also comprising comparison means capable of assigning to the limited value of boost pressure, the minimum value between the maximum values of boost pressure and the required value of boost pressure.

Advantageously, it can be noted that the boost pressure is a function of the compression ratio of the compressor, and that the flow rate of this compressor can be determined using conventional parameter measurements carried out on the engine. Consequently, the compression rate and the flow rate of the compressor corresponding respectively to the ordinates and to the abscissae of a graph representing a compressor field of a turbocharger, it is therefore possible to know the maximum value of boost pressure generating an operating point inside this compressor field.

Preferably, the maximum value of the boost pressure of each turbocharger is calculated as a function of the air flow rate at the inlet of the turbocharger, the air temperature at the inlet of the compressor, the atmospheric pressure, the boost pressure measured, as well as the turbocharger's compressor field. Advantageously, the sensors used to determine the limited value of boost pressure are limited. In addition, since the measurements taken take into account the atmospheric pressure and the temperature at the inlet of the turbocharger, it is no longer necessary to correct the required value according to these parameters, as was the case in the control system of the prior art. The control system according to ^" this preferred embodiment of the invention is therefore both efficient in terms of cost and speed of response.

It can also be provided that the electronic control unit comprises means for balancing the turbochargers further comprising secondary calculation means capable of determining the speed of rotation of each turbocharger, the balancing means being capable of delivering a signal of control corrected to each of the actuators, each corrected control signal being based on the control signal delivered by the regulation means and corrected as a function of the difference in the values of the determined rotational speeds. This specific characteristic makes it possible to obtain a balancing of the turbochargers in steady state or in low transient state. Furthermore, in the same way as for determining the maximum value of boost pressure, the value of the rotation speed of each turbocharger is calculated as a function of the air flow rate at the inlet of the turbocharger, of the temperature of the air at the compressor inlet, atmospheric pressure, as well as the compressor field of the turbocharger.

The invention also relates to a method for controlling a motor supercharged with air by a first turbocharger and a second turbocharger supplying a first bank of cylinders and a second cylinder bank via a common intake manifold, the first and second turbochargers being respectively coupled to a first actuator and a second actuator, the method further comprising the following steps: determining the value boost pressure requirement;

- Determination of an actuator control signal, the control signal being a function of a boost pressure measured in the common intake manifold.

According to the invention, the control method also comprises a step of limiting the required value of boost pressure, the limited value of boost pressure obtained being used for the determination of the actuator control signal, and determined so that for each turbocharger, it generates one. operating point located in the compressor field of the turbocharger.

Preferably, the operation of determining the maximum value of boost pressure of each turbocharger is carried out as follows: calculation of the inlet pressure of the compressor using the measurement of atmospheric pressure and pressure drops inside an air filter, the pressure losses being mapped as a function of the air flow rate at the inlet of the compressor; - calculation of the compressor air flow using the compressor inlet pressure, the air flow at the compressor inlet, as well as the temperature at the compressor inlet; - determination using the compressor field, of the maximum compression rate mapped as a function of the air flow of the compressor;

- calculation of the maximum outlet pressure of the compressor, using the maximum compression rate and the inlet pressure of the compressor;

- calculation of the maximum value of the turbocharger boost pressure, using the maximum outlet pressure of the compressor and the pressure drops inside a heat exchanger, the pressure drops being mapped according to the flow d total air at the inlet of the common intake manifold.

It can also be provided that the method comprises a step of balancing the turbochargers, this step comprising the following operations: determination, for each turbocharger, of the value of the speed of rotation of the turbocharger; - correction, for each turbocharger, of the control signal as a function of the difference in the values of the determined rotation speeds.

Preferably, the operation of determining the value of the speed of rotation of each turbocharger is carried out as follows: calculation of the inlet pressure of the compressor using the measurement of atmospheric pressure and pressure drops inside an air filter, the pressure drops being mapped according to the air flow at the compressor inlet;

- calculation of the compressor air flow using the compressor inlet pressure, the air flow at the compressor inlet, as well as the temperature at the compressor inlet; calculating the compressor compression ratio using the measured supercharge pressure, ^'pressure drop within the heat exchanger, of the atmospheric pressure as well as pressure drops within a air filter ; determination using the compressor field, of the theoretical rotation speed of the turbocharger, mapped as a function of the air flow of the compressor and the compression rate; - calculation of the value of the speed of rotation of the turbocharger, using the theoretical speed of rotation of the turbocharger and the temperature at the inlet of the compressor.

Other characteristics and advantages of the invention will appear in the detailed, non-limiting description, below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the appended drawings in which: - Figure 1, already described, represents a graph highlighting the operating points two turbochargers with respect to their compressor field, when implementing a control system according to the prior art, on a common intake manifold engine; - Figure 2 shows a schematic partial view of an air supercharged engine, provided with a control system according to a preferred embodiment of the present invention; Figure 3 shows a detailed schematic view of an electronic control unit, used in the control system shown in Figure 2;

- Figure 4 shows a flowchart of the operations performed by the primary calculation means, used in the electronic control unit shown in Figure 3; FIG. 5 represents a graph schematically symbolizing the method for determining the maximum compression ratio of the first turbocharger, during an operation carried out by the primary calculation means;

- Figure 6 shows a flowchart of the operations performed by the secondary calculation means, used in the electronic control unit shown in Figure 3; FIG. 7 represents a graph schematically symbolizing the method for determining the theoretical speed of rotation of the first turbocharger, during an operation carried out by the secondary calculation means. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figure 2, there is shown an engine 1, of the type diesel engine supercharged with air in V twin-turbo architecture. The engine 1 comprises a first bank of cylinders 2 as well as a second bank of cylinders 4, supplied with air by a common intake manifold 6. An exchanger 8 is connected on the one hand to the common intake manifold 6, and on the other hand to a single pipe 10, establishing the junction between a first and a second compressed air pipes 12,14. The first compressed air line 12 is provided for conveying, in the direction of the exchanger 8, air coming from a first compressor 16 belonging to a first turbocharger 18. In addition, as can be seen in the figure 2, the first compressor 16 draws air at a first air inlet 20, this air passing successively through a first air filter 22 and a first flow meter 24, before entering the compressor 16. From the similarly, the second compressed air line 14 is provided for conveying, in the direction of the exchanger 8, air coming from a second compressor 26 belonging to a second turbocharger 28 identical to the first turbocharger 18. In addition, the second compressor 26 draws air at a second air inlet 30, this air passing successively through a second air filter 32 and a second flow meter 34, before entering the compressor 26. The first bank of cylinders 2 communicates with a first exhaust manifold 36, in which is located a first turbine 17 belonging to the first turbocharger 18, and having the same axis 19 as the first compressor 16. After having passed through and driven the first turbine 17, the exhaust gases are evacuated to a first air outlet 38. Furthermore, the second cylinder bank 4 communicates with a second exhaust manifold 40, in which is located a second turbine 27 belonging to the second turbocharger 28 , and having the same axis 29 as the second compressor 26. After passing through and driving the second turbine 27, the exhaust gases are evacuated to a second air outlet 42. The first and second turbines 17 and 27 are respectively coupled first and second actuators 44 and 46, capable of modulating the power supplied by the exhaust gases to each of the two turbines 17,27. It is specified that the actuators 44, 46 are of the same type as the actuators known from the prior art.

Still with reference to FIG. 2, a control system 50 of the motor 1 is shown, according to a preferred embodiment of the invention. The control system 50 is provided to supply control signals to the two actuators 44 and 46, so that the boost pressure in the common intake manifold 6 meets the specific needs of the engine, and respects the technical characteristics of the turbochargers 18 28. The control system 50 comprises an electronic control unit 52, called UCE in the following description, as well as a plurality of sensors connected to the UCE 52. The UCE 52 includes means 54 for determining the required value boost pressure P _s . _r , connected to means 56 for limiting the required value of boost pressure. The latter are themselves connected to means 58 for regulating "the boost pressure, also belonging to the ECU 52. Finally, the ECU 52 comprises means 60 for balancing the turbochargers 18, 28, connected to the means 58. In addition, the control system 50 includes a sensor 62 of the value of atmospheric pressure P _atm , the sensor 62 being connected to the ECU 52. A boost pressure sensor 64 is also located at the inside the common intake manifold 6, and is capable of delivering a measured boost pressure value P _s . _m to the boost pressure regulation means 58. The control system 50 further comprises the first and second flow meters 24,34, capable of delivering values of temperature Tι _c ι, T _lo2 and of air flow Q _airl , Q _air2 at the inlet of the first and second turbochargers 18,28 Finally, it is specified that the ECU 52 also has its di position of the information concerning the engine speed R _m and the fuel flow rate D _c . Referring to Figure 3, the control system 50 operates as follows.

Using information concerning the engine speed R _m and the fuel flow rate D _c , the means 54 for determining the required value of boost pressure deliver a required value of boost pressure P _s . _r means of limitation 56.

The limitation means 56 comprise primary calculation means 66, capable of determining for each turbocharger 18,28, the maximum value of boost pressure Ps.maxi and Ps.maχ ₂ , generating an operating point located in the compressor field. common to the two turbochargers 18,28. In other words, the various measurements made on the motor 1 are used to calculate the value of the flow rate _c ι and _c2 of each compressor 16,26. Using these values _ci and _c2 and knowledge of the compressor field of turbochargers 18,28, we are first able to deduce the maximum compression ratio π _c ι _max and π _c2max that can compressors 16 , 26, then the maximum boost pressure values Ps. _Max ι and Ps.ma ₂ allowed. By way of example, FIG. 4 illustrates the operations carried out by the primary calculation means 66 to determine the maximum value of boost pressure Ps.maxi of the first turbocharger 18, so that it generates, for the turbocharger concerned, a operating point located inside the compressor field. The flowchart which will be described relates to the first turbocharger 18, but can of course be applied to the second turbocharger 28.

The operation (100) resides in the calculation of the inlet pressure P _c ι of the compressor 16:

(100): Pi _c i = P _atm - ΔP _C F! with:

- P _atm : the atmospheric pressure measured via the sensor 62;

- ΔP ₀ Fχ: the pressure drops of the first air filter 22, mapped as a function of the air flow Q _a i _r i at the inlet of the compressor 16, the air flow Qai _r i being measured by the first flow meter 24. Operation (101) consists in calculating the value of the air flow W _c ι of the compressor 16:

2 cl + 273.15 (101): _c ι = Cnorm - Qairi V ^Tré f with

Nmot Plcl

- Cnor: the scaling coefficient

= 0.1154;

- Qairi: the air flow rate at the inlet of the compressor 16, measured by the first flow meter 24;

- N _word : the engine speed; - Ti _c i. : the temperature at the inlet of the compressor 16, measured by the first flow meter 24;

- T _rβf : the reference temperature used to identify the compressor field. The operation (102) lies in the determination, using the compressor field of the first turbocharger 18 and the value of the air flow rate W ₀ χ calculated in operation (101), of the maximum compression rate π _clmax of compressor 16.

To do this, a graph is used representing a compressor field of the turbocharger 18, as illustrated in FIG. 5.

On the graph shown, the abscissa axis corresponds to the air flow W _c (in kg / h) of the compressor 16, and the ordinate axis corresponds to the compression rate π _c of the compressor 16.

The curves a, b, c, d, e, f correspond to the iso-speed curves, extending in this example between 90,000 rpm for the curve f, and 190,000 rpm for the curve a, beyond which there is a risk of destruction of the turbocharger 18. In fact, the zone Zi situated above the curve a corresponds to an overspeed zone, in which the turbocharger 18 exceeds its maximum authorized speed.

Furthermore, the curve g defines the pumping limit of the compressor 16. This curve g therefore delimits an area Z ₂ in which the pumping of the compressor 16 is excessive, and risks damaging the turbocharger 18. Thus, the curves a and g define a zone Z ₃ corresponding to the compressor field of the turbocharger 18, in which the risks of damage to the turbocharger 18 are almost nonexistent. Using this graph, using the value of the air flow rate _c ι of the compressor 16 calculated during the operation (101), one is effectively able to determine the value of the maximum compression ratio π _c ι _max of the compressor 16.

To do this, simply take on the x-axis the point corresponding to the air flow _ci of the compressor 16, and place yourself at point K, located vertical to W _c ι on the curve g representing the limit pumping of the compressor 16. Thus, the ordinate of the point K located on the curve g will provide information on the value of the maximum compression ratio π _c ι _max of the compressor 16, so that the operating point K of the turbocharger 18 is located in the compressor field. Of course, the interpolation operation, the principle of which has just been described, is carried out by computer means.

The operation (103) resides in the calculation of the maximum outlet pressure P _2c imax of the first compressor 16:

(103): P _2c ia _x = π _c ι _max. P _lc ι with:

- π _c ι _max : the maximum compression ratio of the compressor 16, determined in step (102);

- P _lcl : the inlet pressure of the compressor 16, determined in step (100).

Finally, operation (104) consists in calculating the maximum value of boost pressure Ps. _M a _x i of the turbocharger 18:

(104): P _s . _max ι = P ₂ cimax - ΔP _C E with: - P ₂ ci _m a _x : the maximum outlet pressure of the first compressor 16, determined in step (103);

ΔP _C E: the pressure drops in the exchanger 8, mapped according to the total air flow in the exchanger 8.

In this way, the primary calculation means 66 can deliver the maximum values of boost pressure Ps.mai and Ps.max2 authorized, generating an operating point, for each of the turbochargers 18,28, located in the compressor field.

Furthermore, with reference to FIG. 3, the means 56 for limiting the boost pressure comprise comparison means 68, capable of delivering a limited value of boost pressure P _s .ii _m , corresponding to the minimum value between the maximum values of boost pressure Ps.maxi and Ps.max2r and the required value of boost pressure P _s . _r . It is then the value P _s .ii _m which is retained to be communicated to the regulation means 58.

By proceeding in this way, when there are interactions between the two turbochargers 18, 28 causing the output of one and / or of the two turbochargers 18, 28 from the compressor field, the instruction given to the regulation means 58 on the value of the boost pressure to adopt, allows the 18,28 turbocharger (s) out of the compressor field to return to it. The regulating means 58 are therefore informed of the measured boost pressure P _s . _m in the common intake manifold 6, and of the pressure P _s. ii _m to be obtained to satisfy the needs of the engine 1, the difference between these two pressure values being to be minimized as quickly as possible. Note that to decrease the response time of the operation aimed at canceling the difference between the pressures P _s . _m and P _s. i _{± m} the regulating means 58 can also be informed about the engine speed R _m and the fuel flow rate D _c , in order to use a map making it possible to provide information on pre-positioning values of the discharge or fins (not shown) from the turbines 17.27. The control means 58 employed are means widely used in the prior art, of the PID (proportional, integral, derivative) type. They participate in the development of a control signal S _has 44.46 actuators, the signal delivered is common for both actuators 44,46.

In this preferred embodiment of the invention, the control signal S _a is then directed to the means 60 for balancing the turbochargers 18, 28. The balancing means 60 comprise secondary calculation means 70, capable of determining the speed of rotation N _t ι and N _t2 of each turbocharger 18,28. When these rotational speeds N _t ι and N _t2 are determined ^' ,: ^• the balancing means 60 are able to deliver a corrected control signal S _aeq ι and S _aeq2 , respectively to the first and second actuators 44 and 46. Each signal of corrected control S _ae qi, S _aeq2 is based on the control signal S _a delivered by the regulation means 58, and corrected as a function of the difference of the values of the determined rotation speeds N _t ι and N _t2 . By way of example, FIG. 6 illustrates the operations carried out by the secondary calculation means 70, to determine the value of the speed of rotation N _t ι and N _t2 of each turbocharger 18,28. The flowchart which will be described relates to the first turbocharger 18, but can of course be applied to any one of the two turbochargers 18, 28.

The operation (200) lies in the calculation of the inlet pressure Pι _c ι of the compressor 16:

(200): P _lcl = P _atm - Δ _c Fi with:

- P _atm : the atmospheric pressure measured via the sensor 62;

- ΔP _c Fι: the pressure drops of the first air filter 22, mapped according to the air flow Q _a i _r ι at the inlet of the compressor 16, the air flow Qai _r i being measured by the first flow meter 24.

Operation (201) consists in calculating the value of the air flow rate _c ι of the compressor 16:

Tlcl + 273.15

(201): _cl = Cnorm ΞL.J ^r H _with

Nmot Pïcl

- Cnorm '• the scaling coefficient = 0, 1154; Qairi: the air flow rate at the inlet of the compressor 16, measured by the flow meter 24;

- N _mo t 'the engine speed;

Tioi: the temperature at the inlet of the compressor 16, measured by the first flow meter 24;

- T _rβf : the reference temperature when measuring the compressor field.

Operation (202) resides in the calculation of the compression ratio π _c χ of compressor 16:

- Pi _c : the inlet pressure of the compressor

16, determined in step (200). - P _s . _m : the boost pressure measured in the common intake manifold 6;

ΔP _C E: the pressure drops in

1 exchanger 8, mapped according to the total air flow in the exchanger 8. The operation (203) lies in determining, using a part of the compressor field of the first turbocharger 18, and on the other hand, the values of the air flow rate ₀ χ and of the compression ratio π _c χ of the compressor 16 calculated previously, of the theoretical rotation speed N _t χt of the turbocharger 18.

To do this, as illustrated in FIG. 7, a graph is used representing a compressor field of the turbocharger 18, identical to the graph of FIG. 5. As mentioned above, it is recalled that the curves a, b, c, d, e, f correspond to the isovitesses curves.

Using this graph, using the value of the air flow rate _cl of the compressor 16 calculated during the operation (201), and the value of the compression rate π _cl of the compressor 16 calculated during the operation (202) , we are effectively able to determine the value of the theoretical rotation speed N _t χ _t of the first turbocharger 18.

To do this, it suffices to determine the point K ′ having as value the value of the air flow rate c _l of the compressor 16, and as ordinate the value of the compression ratio π _c χ of the compressor 16. Thus, the determination of the positioning from point K ′ makes it possible to detect the iso-speed curve on which it is located, and consequently provides the theoretical rotation speed N _t ιt of the first turbocharger 18.

Finally, the last operation (204) consists in determining the rotational speed N _t χ of the turbocharger 18, as a function of the ambient conditions and of the theoretical rotational speed N _t calculée _t calculated during the previous operation:

(204): N _t ι = N _t ι _t .

with:

- N _t χt '- the theoretical speed of rotation of the turbocharger 18, determined in step (203);

T _lc χ: the temperature at the inlet of the compressor 16, measured by the first flow meter 24; - T _ref : the reference temperature used to identify the compressor field.

With reference to FIG. 3, the values of the rotational speeds N _t χ and N _t2 of the first and second turbochargers 18, 28 are directed towards means 72 of the regulator type, capable of reflecting the difference in values of the rotational speeds N _t χ and N _t2 , in a correction signal S _c of the control signal

Sa- In this way, so that the two turbochargers 18, 28 are balanced, the signal S _c is summed on the control signal going to the second turbine 27, and subtracted on the control signal going to the first turbine 17 This balancing operation of the turbochargers 18, 28 thus provides a first corrected control signal S _aeq χ for the first actuator 44, as well as a second corrected control signal S _aeq2 for the second actuator 46. The control system. 50 which has just been described therefore makes it possible to produce corrected control signals S _aeq ι and S _aeq2 in the direction of the actuators 44,46, so that the turbochargers 18,28 to which they are coupled are balanced, and have a operating point belonging to the compressor field. In addition, while remaining in the compressor field, the turbochargers 18, 28 progressively manage to authorize a maximum boost pressure P _s. Max equal to the required boost pressure P _s . _r by motor 1. Of course, various modifications can be made by those skilled in the art to the control system 50 which has just been described, only by way of nonlimiting example.

Claims

1. Control system (50) of an engine (1) supercharged with air by a first turbocharger (18) and a second turbocharger (28) supplying a first bank of cylinders (2) and a second bank of cylinders (4) via a common intake manifold (6), the first and second turbochargers (18,28) being respectively coupled to a first actuator (44) and a second actuator (46), said system (50) comprising furthermore an electronic control unit (52) comprising:

- Means (54) for determining the required value of boost pressure (P _s . _r ); means (58) for regulating the boost pressure capable of delivering an actuator control signal (S _a ), said control signal (S _a ) being a function of a measured boost pressure (P _s .m) in the common intake manifold (6); said control system (50) being characterized in that the electronic control unit (52) also comprises means (56) for limiting the required value of boost pressure, said limiting means (56) being capable of delivering a limited value of boost pressure (P _s. iim) to the regulating means (58), said limited value (P _s. um) being determined so that for each turbocharger (18,28), it generates an operating point located in the compressor field of the turbocharger (18,28). W

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2. Control system (50) according to claim 1, characterized in that the means (58) for limiting the required value of boost pressure comprise calculation means

5 primaries (66) capable of determining, for each turbocharger (18,28), the maximum value of boost pressure (P _s .max, P _s .ma2) generating an operating point located in the compressor field of the turbocharger ( 18,28), said limiting means 0 (58) also comprising comparison means (68) capable of assigning to the limited boost pressure value (Ps.iim) _/ - the minimum value between the maximum pressure pressure values boost (P _s . _ιn axχ, P _s . _I nax2) and the required value of 5 boost pressure (P _s . _r ) •

3. Control system (50) according to claim 2, characterized in that the maximum value of boost pressure (Ps.mai • s. _M axi of each turbocharger (18,28) is calculated as 0 depending on the flow of air at the inlet to the turbocharger (Qairi Qair2), the air temperature at the inlet to the compressor (Tχ _c χ, T _lc2 ), the atmospheric pressure (Patm) t the measured boost pressure (P _s . _m ), as well as the compressor field of the turbocharger5 (18,28).

4. Control system (50) according to any one of the preceding claims, characterized in that the electronic control unit (52) comprises means for balancing the turbochargers (60) further comprising secondary calculation means ( 70) capable of determining the speed of rotation (N _tl , N _t ) of each turbocharger (18,28), said balancing means (60) being capable of delivering a corrected control signal (S _aβq ι, S _aeq2 ) to each of said actuators (44,46 ), each corrected control signal (S _ae qi, S _ae q ₂ ) being based on the control signal (S _a ) delivered by said regulation means (58) and corrected as a function of the difference in the values of the rotational speeds ( N _t χ, N _t2 ) determined.

5. Control system (50) according to claim 4, characterized in that the value of the speed of rotation (N _t ι, N _t2 ) of ^' each turbocharger (18,28) is calculated according to the air flow at the inlet of the turbocharger (Qairi / Qair2), the air temperature at the inlet of the compressor (Tχ _.c χ, T _lc2 ), the atmospheric pressure (P _a tm), as well as the compressor field turbocharger (18,28).

6. Method for controlling an engine (1) supercharged with air by a first turbocharger (18) and a second turbocharger (28) supplying a first bank of cylinders (2) and a second bank of cylinders (4) through the through a common intake manifold (6), the first and second turbochargers (18,28) being respectively coupled to a first actuator (44) and a second actuator (46), said method further comprising the following steps:

- determination of the required value of boost pressure (P _s .r);

- determination of an actuator control signal (S _a ), said control signal (S _a ) being function of a boost pressure measured in the common intake manifold (6); said control method being characterized in that it also comprises a step of limiting the required value of boost pressure (P _s . _r ) ^' , the limited value of boost pressure (Ps.ii _m ) obtained being used for determining the actuator control signal (S _a ), and determined so that for each turbocharger (18,28), it generates an operating point located in the compressor field of the turbocharger (18,28).

7. Control method according to claim 6, characterized in that the step of limiting the required value of boost pressure (Ps.r) comprises the following operations: determination, for each turbocharger (18,28), of the maximum value of boost pressure (Ps.mai / Ps.maxa) generating an operating point located in the compressor field of the turbocharger (18,28); assignment to the limited value of boost pressure (P _s. iim) ι of the minimum value between the maximum values of boost pressure (Ps.mairPs.max∑) and the required value of boost pressure (P _s . _r ) _'

8. Control method according to claim 7, characterized in that the operation of determining the maximum value of boost pressure (P _s . _Maxl , P _s . _M a _x2 ) of each turbocharger (18,28) is carried out using the air flow at the compressor inlet (Q _a ι _r χ, Q _a ι _r2 ), the air temperature at the compressor inlet (T _ic χ, Tχ _σ ) / atmospheric pressure ( P _a tm) of the measured boost pressure (P _s . _M ) _{/ as} well as the turbocharger compressor field (18,28).

9. A control method according to claim 7 or claim 8, characterized in that the operation of determining ^" maximum value of boost pressure (Ps. _M axi, P _s . _M a2) of each turbocharger (18 , 28) is carried out as follows: calculation of the compressor inlet pressure (Pici / P ^' ic2) using the measurement of atmospheric pressure (P _a tm) and pressure losses (ΔP _c F, ΔP _c F ₂ ) inside an air filter (22,32), the pressure losses (ΔP _c Fχ, ΔP _c F) being mapped according to the air flow rate at the inlet of the compressor (16,26); calculation of the compressor air flow (W _cl , _c2 ) using the compressor inlet pressure (Pι _c ijPic ₂ ), the air flow at the inlet of the compressor (Qairi / Qair), as well as the temperature at the compressor inlet (Tχ _c ι, Tχ _c2 ); determination using the compressor field, of the maximum compression ratio (π ₀ χ _max , π _c2max ) Cartograph ie as a function of the compressor air flow ( _c χ, W _c2 );

- calculation of the maximum outlet pressure of the compressor (P _2c ima fl ^> 2c2a), using the maximum compression rate (π _c , _max , π _c2max ) and the inlet pressure of the compressor (Pχ _c ι Pic2); - calculation of the maximum value of the turbocharger boost pressure (Ps.maxi _f P _s . _m aχ ₂ ) _> using the maximum outlet pressure of the compressor (P ₂ cimax / P2c2ma) and pressure losses ( ΔP _C E) inside an exchanger (8), the pressure losses (ΔP _C E) being mapped as a function of the total air flow at the inlet of the common intake manifold (6).

10. Control method according to any one of claims 6 to 9, characterized in that it further comprises a step of balancing the turbochargers (18,28) comprising the following operations: determination, for each turbocharger (18, 28), the value of the speed of rotation (N _t χ, N _t 2) of the turbocharger (18,28);

- correction, for each turbocharger (18,28), of the control signal (S _a ) as a function of the difference in the values of the determined rotational speeds (N _t χ, N _t2 ).

11. Control method according to claim 10, characterized in that the operation of determining the value of the speed of rotation (N _t ι, N _t2 ) of each turbocharger (18,28) is carried out using the air flow at the inlet of the turbocharger (Qairi ιQaîr2), the air temperature at the inlet of the compressor (Tχ _cl , T _lc2 ), atmospheric pressure. (P _a tm), as well as the compressor field of the turbocharger (18,28).

12. Control method according to claim 10 or claim 11, characterized in that the operation of determining the value of the rotation speed (N _t χ, N _t2 ) of each turbocharger (18,28) is carried out as follows: calculation of the inlet pressure of the compressor (Pχ ₀ χ, Pχ _c2 ) using the measurement atmospheric pressure (P _a tm) and pressure drops (ΔP _c Fχ, ΔP _C F ₂ ) inside an air filter (22,32), pressure drops (ΔP _c Fχ, ΔP _c F ₂ ) being mapped. depending on the air flow rate at the compressor inlet (16,26); - calculation of the compressor air flow (W _cl

, _c2 ) using the compressor inlet pressure (Pici / Pic2) / the air flow at the compressor inlet (Qairi / Qair2) as well as the temperature at the compressor inlet (T _lc ι, T _lc2 ); - calculation of the compression ratio of the compressor (π _c χ, π _σ2 ) using the measured boost pressure (P _s .m) of the pressure drops inside an exchanger, atmospheric pressure, as well as pressure drops (ΔP _C E) inside an air filter (22,32); determination using the compressor field, of the theoretical rotation speed (N _t χt _f N _t2 t) of the turbocharger (18,28), mapped according to the air flow of the compressor (W _cl , _c2 ) and the compression ratio (π _cl , π _c2 );

- calculation of the value of the speed of rotation of the turbocharger (N _t χ, N _t2 ), using the theoretical speed of rotation (N _t χ _t , N _t2t ) of the turbocharger (18,28) and the temperature at the compressor inlet (Tχ _c χ, T _lc2 ).