WO2008084169A2

WO2008084169A2 - Method for estimating the exhaust gas pressure upstream from the turbine of a turbocharger

Info

Publication number: WO2008084169A2
Application number: PCT/FR2007/052557
Authority: WO
Inventors: Thomas Turpin; Jean Christophe Schmitt
Original assignee: Renault S.A.S.
Priority date: 2006-12-19
Filing date: 2007-12-19
Publication date: 2008-07-17
Also published as: WO2008084169A3; FR2910059A1

Abstract

The invention relates to a method for estimating the exhaust gas pressure (P31) upstream from the turbine of a supercharger in a vehicle internal combustion engine. The method comprises estimating the turbine upstream pressure (P<SUB>31</SUB>) using the following relation Formula P <SUB>31</SUB>

Description

Method for estimating the exhaust gas pressure upstream of a turbocharger turbine

The invention relates to the field of control of a vehicle engine, comprising a turbocharger.

The invention relates more specifically to a method for estimating the pressure upstream of the turbine of the turbocharger.

The invention applies in particular to a turbocharged supercharger diesel engine. The pressure upstream of the turbine can be used for engine control for different purposes.

For example, it is interesting to know this one to protect the turbine of possible overpressures or for the calculation of the losses by pumping of the engine, or insofar as it serves as an input parameter in the thermodynamic models to determine the performance of the engine.

To know the pressure upstream of the turbine of the turbocharger, a pressure sensor is often used. But a pressure sensor has several disadvantages such as the disturbance of the measurement signal, the drifts and dispersions thereof, especially in a severe thermal environment, or the difficulties of implantation.

To avoid these drawbacks, it is therefore necessary to use methods and means for providing an estimate of the pressure upstream of the turbine.

Document DE 103293 discloses, for example, a method for estimating this pressure, which is based on a power budget on the turbocharger shaft and on the knowledge of the characteristics of the turbine. A disadvantage of this method is that it requires heavy mathematical operations, difficult to implement in the calculators usually used. Another disadvantage is related to manufacturing dispersions, which cause inaccuracy on the knowledge of the characteristics of the turbine. The document FR 2 853 693 presents, for example, a method for estimating this pressure, which is based on a measurement of the mass of gases in the exhaust manifold.

An object of the invention is to provide a new method for estimating the pressure of the exhaust gas am am turbocompressor turbine.

Another object of the invention is to propose a com m eted motor, for which this new process is implemented.

To achieve this objective, a method for estimating the exhaust gas pressure in a turbocharger turbine of an internal combustion vehicle engine is provided within the scope of the invention, characterized in that the turbine upstream pressure is estimated by the following formula:

where P ₄ i is the exhaust gas pressure downstream of the turbine, P ₁ the air intake pressure in am have compressor, P ₂₁ the air pressure downstream of the compressor , the functions f! and f ₃ corrective functions of constant value or dependent on one of the following parameters: admission air flow rate, fuel flow rate, engine exhaust gas flow rate, gas flow rate recirculation, variation of the air flow at the intake, variation of the fuel flow, variation of the exhaust gas flow at the engine output, variation of the recirculation gas flow rate, engine speed, torque demand m operator, variation of the engine torque demand, com m iter of the position of the fins or bypass, variation of the turbocompressor control, temperature and pressure upstream of the particulate filter in the case of a diesel engine, coolant temperature; and the functions f ₂ a dependent corrective function at the pressures P ₂₁ and P ₁ .

The method according to the invention may also have at least one of the following characteristics: the pressure upstream of the turbine is estimated by the relation (2), considering the corrective functions fi = 1, f ₂ = P21-P1, and f ₃ = constant; the pressure upstream of the turbine is estimated by relation (2), considering the corrective functions fi = A (Q _gas , P21-P1), f ₂ =

P21-P1, and f ₃ = B (Q _gas , P21-P1), where A and B are mappings based on the influence of the pressure variation (P ₂₁ - P ₁ ) at the terminals of the compressor and the flow rate (Q _gas ) of the engine exhaust gases; the pressure upstream of the turbine is estimated by the relation (2), considering the functions fi = A ₁ (Q ₉₃₂ , P ₂₁ -P ₁ ) ^* A ₂ (RCO, T ₃₁ ), f ₂ = P ₂₁ -P ₁ and f ₃ = B (Q _gas , P ₂₁ -P ₁ ) where A ₁ and B are mappings established as a function of the influence of the pressure variation (P ₂₁ - P ₁ ) at the terminals of the compressor and the flow rate Q _gas of the engine exhaust gas and, where a ₂ is a mapping established according to the influence of the temperature T _31, the exhaust gas upstream of the turbine and RCO power control setpoint either a turbine fin actuator if it is a variable geometry turbine or an exhaust gas bypass actuator if the turbine has a fixed geometry; to determine the corrective functions f _1; f ₂ , f ₃ , a measurement is made of the evolution of the pressure upstream of the turbine as a function of time on a motor, functions f ₁ are proposed _; f ₂ , f ₃ , and comparing the estimated values, with these corrective functions, of the pressure P ₃₁ upstream of the turbine to the measured values of this pressure.

To achieve this objective, there is also provided an internal combustion engine for a vehicle, comprising a turbocharger formed of a compressor and a turbine, characterized in that it comprises means for implementing the method according to the invention . Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings, given as nonlimiting examples and in which: FIG. a diagram of an internal combustion engine for a vehicle, fitted with a turbocharger; FIGS. 2, 3 and 4 respectively illustrate the errors between a measurement of the am am pressure of the turbine as a function of the time on a vehicle engine and, respectively, different models for estimating the pressure upstream of the engine. the turbine.

FIG. 1 shows an internal combustion engine 1, comprising a turbocharger, for the purpose of increasing the quantity of air admitted into the cylinders. The turbocompressor consists of a compressor 20 located on the adm ission line of the motor 1 and m onté on the same axis as a turbine 21 as for it located at the output of the exhaust manifold.

The turbine 21 is driven by the exhaust gas and the power supplied by it can be modulated by installing a relief valve if the turbine is a fixed geometry turbine or variable geometry vanes (TGV).

In the case of a turbocharger with fixed geometry, the discharge circuit is a bypass of the turbine permitting not to use the entire flow of the exhaust gas to drive the turbine. In the case of a turbocompressor with variable geometry, the fins allow to modulate the incidence of the flow of the exhaust gases on the turbine and therefore on the power it provides.

The motor 1 also comprises, in a conventional manner, an admission flap 2, an engine block 10 comprising the cylinders, an EGR circuit 3 comprising a valve 31, a cooler 32 and a bypass 33. Finally, the engine 1 also includes in the exhaust line, a set of gas treatment m aines in the case of a diesel engine, namely a pre-catalyst 41, a particulate filter 42 and a silencer 43, for example.

In this FIG. 1, Ti and Pi are defined as the temperature and the motor inlet pressure (or upstream compressor 20). The temperatures and pressure downstream of the compressor are also respectively defined as T ₂₁ and P ₂₁ respectively. T ₃₁ and P ₃₁ respectively define the temperature and pressure am am of the turbine. Finally, T ₄₁ and P ₄₁ respectively define the temperature and pressure downstream of the turbine.

To estimate the upstream pressure P ₃₁ turbine, it is proposed here to be based on a sim plification (or reduction) of the equation governing the operation of the turbocompressor.

To determine the operation of the turbocharger, a power budget is carried out on the shaft thereof, having previously determined the energy exchanged in the compressor on the one hand and in the turbine on the other hand. In stabilized operation of the turbocompressor, the following relationship is then reached:

" ^~~ )

where Cp g _az and C _Pιaιr are the _heating capacities at constant pressure of exhaust gases and air at admission respectively, γ is the ratio of the specific heat capacity at constant pressure and the specific heat capacity at constant volum e (γ = c _p / c _v ), and η _turbine and η compressor rendem ents of the turbine 21 and com presseur 20 respectively.

The relationship (1) resulting from a power budget is perfectly known to the man of the trade.

The invention proposes to reduce equation (1) to equation (2):

in which the functions f ₁ , f ₂ , f ₃ are corrective functions that may be constants or be expressed as a function of at least one of the following parameters, provided in a nonlimiting manner:

- Admission air flow, fuel flow, exhaust gas flow at engine output, recirculation gas flow (EGR circuit);

- variation of the air flow at the intake, variation of the fuel flow, variation of the exhaust gas flow at the engine output, variation of the recirculation gas flow (EGR circuit);

- motor speed, motor torque demand; variation in motor torque demand; - com m ande of the position of the vanes (turbocharger with variable geometry) or of the bypass (turbocompressor with fixed geometry), variation of the turbocompressor com- mander;

- Temperatures and pressures in am of the particle filter in the case of a diesel engine, coolant temperature.

It will be noted that this reduction leading to equation (2) is based on a priori form of the behavior law, inspired by the physical form of the behavior law. Such a reduction has the advantage of taking into account many parameters, unlike the prior art where one chooses most often not to consider some.

FIGS. 2, 3 and 4 respectively illustrate the errors between a measurement of the pressure upstream of the turbine as a function of the time on a vehicle engine and, respectively, different models for estimating the pressure P ₃₁ in _FIG. am have turbine 21.

These models are based on equation (2) and therefore consist in proposing different corrective functions fi, f ₂ and f ₃ . For that, we performs a test in which the pressure P ₃₁ is measured by a pressure sensor, corrective functions f ₁ are proposed _; f ₂ and f ₃ , the same pressure P ₃₁ is determined by equation (2) and the error between the model and the data obtained from the measurements is calculated (FIGS. 2 to 4).

In a first case, illustrated in FIG. 2, the pressure P ₃₁ upstream of the turbine is estimated by the relation (2), considering the corrective functions U = 1, f ₂ = P21-P1, and f ₃ = constant . The model thus considered is very simple, but it results in a relative error of ± 20%.

In a second case, illustrated in FIG. 3, the pressure P ₃₁ upstream of the turbine is estimated by the relation (2), considering the corrective functions f! = A (Q _gas , P ₂₁ -P ₁ ), f ₂ = P ₂₁ -P ₁ , and f ₃ = B (Q _gas , P ₂₁ -P ₁ ), where A and B are mappings based on influence of the pressure variation (P ₂₁ -P ₁ ) at the compressor terminals 20 and at the _gas flow rate Q of the exhaust gas at the engine outlet (turbine inlet). Most often, these mappings are established by means of automatic calculations, which as a function of the variable parameters chosen in this one, can best be glued to the results of the tests.

This model is more complicated than the first and makes it possible to define a generally less spread error with respect to the data resulting from the measurement. In other words, we find that the average value of the error committed over the duration of the test is less than with the first model. (To make this comparison, keep in mind that an absolute error of 500mbar is roughly equivalent to a relative error of 20%).

In a third case, illustrated in FIG. 4, the pressure P ₃₁ upstream of the turbine is estimated by the relation (2), considering the functions f ₁ = A ₁ (Q ₉₃₂ , P ₂₁ -P ₁ ). ₂ (RCO, T ₃₁ ), f ₂ = P ₂₁ -P ₁ and f ₃ = B (Q _gases ,

In this third case, A ₁ and B are mappings based on the influence of the variation of pressure (P ₂₁ -P ₁ ) across the compressor and the flow (Q _gas ) of the exhaust gas at the output of the engine and, A ₂ is a mapping established according to the influence of the temperature T ₃ 1 of the exhaust gases in am have the turbine and the power control setpoint (RCO) is either an actuator of the blades of the turbine if it is a variable geometry turbine or an actuator of bypass of the exhaust gas if the turbine is geometry fixed.

This third model is a little more complicated than the other two, but can further reduce the error estimation of the pressure. Indeed, it is found that the average value of the error com m on the duration of the test is lower than for the other two models.

In fact, the average error is approximately 10%, which corresponds to the measurement accuracy of a pressure sensor which is used for series vehicles.

Whatever the model chosen, the reduction of the equations makes it possible to im plem ent this model in the electronic control unit (ECU) of the motor with a reasonable calculation time.

Depending on the desired application, however, it will be possible to choose to im plem ent, depending on the relative importance attached to the accuracy of the measurement on the one hand or to the calculation time on the other, one or the other. other of these models.

Claims

1. A method for estimating the pressure (P ₃ i) of the exhaust gas upstream of a turbocharger turbine of an internal combustion engine engine, characterized in that it estimates the upstream pressure turbine (P ₃ i) by the following wording:

where P ₄ 1 is the exhaust gas pressure downstream of the turbine, Pi the inlet air pressure upstream of the compressor, P ₂₁ the air pressure downstream of the compressor, the functions U and f ₃ corrective functions of constant value or depending on at least one of the following parameters: intake air flow rate, fuel flow rate, engine exhaust gas flow rate, recirculation gas flow rate, variation of the intake air flow rate, variation of the fuel flow, variation of the exhaust gas flow at the engine output, variation of the recirculation gas flow rate, engine speed, engine torque demand, variation of the engine demand, motor torque, control of the position of the fins or the bypass, variation of the turbocharger control, temperature and pressure upstream of the particulate filter in the case of a diesel engine, coolant temperature; and the functions f ₂ a corrective function depending at least on the pressures P ₂₁ and P ₁ .

2. Method according to claim 1, characterized in that it estimates the pressure (P ₃₁ ) upstream of the turbine by the relation (2), considering the corrective functions f! = 1, f ₂ = P ₂₁ -P ₁ , and f ₃ = constant.

3. Method according to claim 1, characterized in that the pressure (P ₃₁ ) upstream of the turbine is estimated by the relation (2), considering the corrective functions f! = A (Q _gas , P ₂₁ -P ₁ ), f ₂ = P ₂₁ -P ₁ , and f ₃ = B (Q _gas , P ₂₁ -P ₁ ), where A and B are mappings based on the influence of the pressure variation (P21-P1) at the compressor terminals and the flow rate (Q _gas ) of the engine exhaust gases.

4. Method according to claim 1, characterized in that the pressure (P ₃₁ ) upstream of the turbine is estimated by the relation (2), considering the functions:

U = A ₁ (Q ₉₃₁ , P ₂₁ -P ₁ TA ₂ (RCO, T ₃₁ ), f ₂ = P ₂₁ -P ₁ and f ₃ = B (Q _gases , P ₂₁ -P ₁ )

where A ₁ and B are mappings based on the influence of the pressure variation (P ₂₁ -P ₁ ) at the compressor terminals and the flow rate (QgaΣ) of the engine exhaust gases and,

where A ₂ is a map established as a function of the influence of the temperature (T ₃₁ ) of the exhaust gas upstream of the turbine and the power control setpoint (RCO) of an actuator of the fins of the turbine if it is a variable geometry turbine or an exhaust gas bypass actuator if the turbine is fixed geometry.

5. Method according to one of the preceding claims, characterized in that, for determining the corrective functions f _1; f ₂ , f ₃ , a measurement is made of the evolution of the pressure upstream of the turbine as a function of time on a motor, functions f ₁ are proposed _; f ₂ , f ₃ , and comparing the estimated values, with these corrective functions, of the pressure (P ₃₁ ) upstream of the turbine to the measured values of this pressure.

6. Internal combustion engine for a vehicle, comprising a turbocharger formed of a compressor and a turbine, characterized in that it comprises means for estimating the pressure (P ₃₁ ) of the exhaust gas upstream of the turbine according to the following wording:

where (P ₄₁ ) is the exhaust gas pressure downstream of the turbine, P ₁ the air intake pressure upstream of the compressor, P ₂₁ the air pressure downstream of the compressor , the functions ^ and f ₃ corrective functions of constant value or dependent on one of the following parameters: admission air flow, fuel flow, exhaust gas flow output m operator, recirculating gas flow rate, air flow variation at intake, variation in fuel flow, variation in exhaust gas flow at engine output, variation in recirculating gas flow, engine speed, motor torque demand, variation of the motor torque demand, com pletion of the position of the fins or the bypass, variation of the turbocompressor control, temperature and pressure in the particle filter in the case of a diesel engine, coolant temperature; and the function f ₂ a dependent corrective function at the pressures P ₂₁ and P ₁ .