WO2013117447A1

WO2013117447A1 - Method and system for performing diagnostics on the intake air admitted to a motor vehicle internal combustion engine

Info

Publication number: WO2013117447A1
Application number: PCT/EP2013/051533
Authority: WO
Inventors: Remy BRUNEL; Laurent Fontvieille; Ludovic Martin; Olivier Grondin
Original assignee: Renault S.A.S.
Priority date: 2012-02-06
Filing date: 2013-01-28
Publication date: 2013-08-15
Also published as: FR2986565A1; FR2986565B1; CN104105859B; CN104105859A; KR20140125371A; EP2812550A1; JP2015524888A; RU2611056C2; RU2014136398A

Abstract

Method for performing diagnostics on the intake air admitted to a motor vehicle internal combustion engine, the engine being equipped with a turbo compressor and with a low-pressure partial exhaust gas recirculation circuit (3) and/or a high-pressure partial exhaust gas recirculation circuit (4). The method involves the following steps: parameters characterizing the operation of the engine are determined, the richness in the exhaust is estimated, the richness in the exhaust is measured using a richness probe (31) placed in an exhaust pipe (7) of the internal combustion engine, a diagnostics criterion is determined by calculating the ratio between the measured richness in the exhaust and the estimated richness in the exhaust, the diagnostics criterion is compared against at least one diagnostics threshold that incorporates system spread, and a diagnostics signal dependent on the result of the comparison is emitted.

Description

Method and system for diagnosing the air intake in an internal combustion engine of a motor vehicle.

The technical field of the invention is the control of the admission of gases into an engine, and more particularly the diagnosis of leaks of air admitted.

The amount of nitrogen oxides produced by a diesel engine is strongly related to the quantities of air, fuel and inert gases included in the reaction mixture admitted to the engine cylinders. The amount of inert gases may be varied by controlling the opening of a partial exhaust gas recirculation (EGR) valve included in a circuit of the same name. The partial exhaust gas recirculation circuit connects the exhaust circuit and the intake circuit via a passage section whose size is regulated by the EGR valve.

When an engine is equipped with a turbocharger, two different configurations of EGR circuits can be defined.

A first configuration, called a high pressure EGR circuit, consists of communicating the intake circuit downstream of the compressor with the exhaust circuit upstream of the turbine. This configuration is called high pressure because it is located in a high pressure zone due to the supercharging.

A second configuration, called a low pressure EGR circuit, involves communicating the intake circuit upstream of the compressor with the exhaust system downstream of the turbine. This configuration is called low pressure because it is located in an area of the engine in which the pressure is lower than the supercharging pressure.

A motor can be equipped with either one or both configurations, or both configurations simultaneously.

In order to control the stoichiometry of the gas and fuel mixture admitted to the engine, it is necessary to have reliable information as to the amount of air admitted. The amount of air admitted is generally determined by a flowmeter, it is also advantageous to diagnose the reliability.

For this purpose, a diagnosis of plausibility of the flowmeter is currently being made to determine whether there is a presence of leakage on admission. The principle is based on a criterion defined by the ratio between the estimation of the air entering the engine and the measurement coming from the flow meter (rh _air ). The criterion is determined by the following equation:

This criterion makes it possible to define three cases according to its value and a diagnostic threshold which integrates the dispersions of the system. It is thus possible to determine a nominal operation of the flowmeter, an inlet leak downstream of the compressor or a flowmeter fault, an intake leak upstream of the compressor or a flowmeter fault.

However, the criterion ε _Γ does not take into account the flow rates of the exhaust gases recirculated by the low pressure EGR circuit and the high pressure EGR circuit. However, with the extension of the EGR area to meet the future regulations, this diagnosis has its coverage area reduced sharply. The detection of leaks on admission will become more and more difficult if not impossible if the EGR is still active.

An object of the invention is to reliably detect leaks on admission.

Another object of the invention is to detect leaks at the inlet when the partial recirculation of the exhaust gas is active.

A method for diagnosing the air intake in an internal combustion engine of a motor vehicle is provided, the internal combustion engine being provided with a turbocharger and at least one of a partial recirculation circuit of the combustion gases. low pressure exhaust and partial gas recirculation circuit high pressure exhaust. The method comprises the following steps:

determining a set of quantities characterizing the operation of the internal combustion engine,

we estimate the wealth in the exhaust,

the exhaust richness is measured by means of a richness probe disposed in an exhaust pipe of the internal combustion engine,

a diagnostic criterion is determined by realizing the relationship between the measurement of the exhaust richness and the estimate of the exhaust richness,

comparing the diagnostic criterion with at least one diagnostic threshold integrating the dispersions of the system, and

a diagnostic signal is issued depending on the result of the comparison.

The magnitude set characterizing the operation of the internal combustion engine may include estimates of the intake flow rate, the high pressure EGR flow rate, the ratio of upstream and downstream pressures of the high pressure EGR valve and the inlet manifold pressure and low pressure EGR flow.

The pressure ratio upstream and downstream of the high-pressure EGR valve can be estimated as a function of the differential pressure measurements on either side of said valve.

The exhaust richness can be estimated by performing a mass balance of representative volumes of the partial recirculation circuit of the high pressure exhaust gas and the partial recirculation circuit of the low pressure exhaust gas.

The representative volume of the high pressure partial exhaust gas recirculation circuit may include the volume of the intake manifold.

The representative volume of the low pressure partial exhaust gas recirculation circuit may include the volume of the intake manifolds, the low pressure EGR output and the compressor. There is also provided a system for diagnosing the air intake of the internal combustion engine of a motor vehicle, the internal combustion engine being equipped with a turbocharger, and at least one of a partial recirculation circuit of low pressure exhaust gas and a partial recirculation circuit of the high pressure exhaust gas. The system comprises a means for estimating the richness at the exhaust, a means for determining the diagnostic criterion, a comparator and at least one memory, the means for determining the diagnostic criterion being able to determine a diagnostic criterion in function of the signal received from the means for estimating the richness at the exhaust and as a function of the signal received from the richness probe disposed in an exhaust pipe of the internal combustion engine, the comparator being able to compare the signal received from the means for determining the diagnostic criterion for the signal received from at least one memory comprising at least one diagnostic threshold integrating the dispersions of the internal combustion engine, the comparator outputting a signal depending on the result of the comparison.

The method and the system have the advantage of using the exhaust richness probe in addition to an estimator to ensure leak diagnosis and plausibility of the flow meter measurement in the presence of EGR.

Other objects, features and advantages will become apparent upon reading the following description given solely as a non-limitative example and with reference to the accompanying drawings, in which:

FIG. 1 illustrates an internal combustion engine equipped with a low pressure EGR and a high pressure EGR, and

FIG. 2 illustrates the diagnostic method, and

- Figure 3 illustrates the diagnostic system.

FIG. 1 shows an internal combustion engine 1 connected to a turbocharger 2 and provided with a low pressure EGR circuit 3 and a high pressure EGR circuit 4. turbocharger 2 comprises a compressor 2a connected to a turbine 2b. The turbine 2b can be of variable geometry.

A fresh air intake pipe 5 is connected to the inlet of the compressor 2a. The output of the compressor 2a is connected to the intake manifold 1a of the internal combustion engine via a heat exchanger 6. The exhaust manifold 1b of the internal combustion engine is connected to the inlet of the turbine 2b. The outlet of the turbine 2b is connected to the exhaust pipe 7 which is provided with a catalytic oxidation device 8 and a particulate filter 9.

The low-pressure EGR circuit 3 comprises an exhaust flap 10 disposed in the exhaust duct 7 downstream of the catalytic oxidation device 8 and the particulate filter 9 and a low pressure EGR duct 11 firstly upstream of the exhaust flap 10 and secondly upstream of the compressor 2a.

The low-pressure EGR line 11 is provided with a low-pressure heat exchanger 12 arranged upstream of the exhaust flap and a low-pressure EGR valve 13 disposed downstream of the low-temperature heat exchanger. pressure 12, the gases flowing from the exchanger to the low pressure EGR valve. The exhaust gas flow rate of the low-pressure EGR circuit is controlled by the low-pressure EGR valve 13. However, given the low pressure ratio across this valve, the flap of the low-pressure EGR valve 13 is also used. Exhaust 10, which increases the pressure ratio across the valve EGR low pressure when it is fully open and the desired flow is not achieved. The exhaust gas passing through the low pressure EGR circuit 3 is cooled before being reintroduced upstream of the compressor 2a.

The high-pressure EGR circuit 4 comprises a high-pressure EGR line 14 stitched on the one hand between the outlet of the compressor 2a and the intake manifold 1a and on the other hand between the exhaust manifold and the inlet of the turbine 2b. The high-pressure EGR line 14 is provided with a high-pressure EGR valve 15. The exhaust gas flow rate of the EGR circuit at high Pressure is controlled by the high-pressure EGR valve 15. Exhaust gases passing through the high-pressure EGR circuit 4 are not cooled. Their flow is determined by means of a differential pressure sensor at the terminals of the high-pressure EGR valve 15 and the Barré Saint Venant equation.

The response time of the low pressure EGR circuit 3 is lower than that of the high pressure EGR circuit 4 because its length is greater.

Different non-represented sensors make it possible to obtain the following measurements:

Pi: the gas pressure in the intake manifold

Tu: the temperature downstream of the charge air cooler (RAS)

T _am b: the ambient temperature

Patm: the atmospheric pressure

F ₂ : the richness of exhaust gases

AP p: the differential pressure across the high-pressure EGR valve

m _air : the air flow

In addition, the following assumptions are made.

Given the low level of pressure and temperature in the volume upstream of the compressor, it is assumed that the pressure and temperature of the gases located between the junction between the low-pressure EGR line and the inlet duct of the compressor. Fresh air and the inlet of the compressor 2a are equal to the atmospheric pressure p _atm and the atmospheric temperature T _atm .

The temperature in the intake manifold Ti is estimated from the temperature Tu of the gases at the outlet of the heat exchanger

6 and the temperature T _egr , hp at the outlet of the high-pressure EGR valve 16 by applying the following equation:

T, -m + T -m Starting from this description of the internal combustion engine, a diagnostic criterion is defined based on the ratio between the measurement of the exhaust richness F ₂ and an estimate F ₂ , _e st. e¾ = ^ 2, ^ is ^(Eq - ³⁾

This diagnostic criterion is general, which makes it possible to use it both in sequential operation (high pressure or low pressure EGR) and in mixed operation (high pressure and low pressure EGR simultaneously) of the partial recirculation circuits of the exhaust gases. .

The estimate F ₂ , _e st of the richness at the exhaust can be obtained by the following equation:

(PCO + 1) -m _f + m, "-F _t

F _¾est =. ^f . ^{m '} (Eq- 4)

m _f + m _in

With:

PCO: richness with stoichiometry

Fi, est: estimation of the composition of gases at admission rh _f : fuel flow

rh _in : intake flow

Stoichiometry richness is a constant that depends on the fuel used.

The fuel flow is assumed to be equal to the set point in the case of an ideal injector.

The suction flow is estimated by a model described below.

The estimation of the composition of the gases at the intake can be obtained by integrating the differential equation which governs the evolution of the composition of the gases on admission. This amounts to making a mass balance on the equivalent volume of the EGR circuit concerned.

In the case of simultaneous use of high pressure EGR and low pressure EGR, the balance of the two circuits must be taken into account.

The balance of the high-pressure EGR involves a volume corresponding to the intake manifold. In order to carry out the assessment mass, it is posited that the inputs of this volume are the flow of the compressor and the flow of the EGR at high pressure while the output is the flow sucked by the engine.

The low pressure EGR balance implies a volume corresponding to a volume located upstream of the intake manifold. This volume includes that of the intake lines, the output of the low-pressure EGR circuit and the compressor. The inputs of this volume are the air flow and the low pressure EGR flow, while the output is the compressor flow.

By adding an additional volume, an additional state variable corresponding to the composition of the gases in this volume F _{3 is introduced} . The variation of the mass of gases burned in the low pressure volume is given by the following relation:

^^ = F ₂ m ^ _{bp +} 0xm _air -F ₃ m _c (Eq.5)

If one replaces the total mass in this volume by using the perfect law of gases, P ₃ V ₃ = m ₃ RT ₃ , then one can write the differential equation which governs the variation of the composition in the volume at low pressure.

eeggrr ,, bbpp ^F 3, is ^m _a (Eq.6)

This equation is integrated to obtain the estimate of exhaust richness.

Exhaust richness is estimated by applying equations 4 and 6 in combination with the following equation: Fl, est =)] (E - ⁷ )

In addition, the suction flow is estimated by the following equation: ώ _π , (Eq.8)

With

: a mapping of the volume efficiency function of the engine speed and the density of the gases in the intake manifold.

The flow of high pressure EGR is calculated via the Baré Saint Venant equation:

With

P _avt : the pressure upstream of the turbine,

T _avt : the temperature upstream of the turbine,

S (u _egrhp ): Section of the high-pressure EGR valve depending on the position,

π _h : Pressure ratio across the high-pressure EGR valve.

The pressure ratio upstream and downstream of the high-pressure EGR valve is deduced from the differential pressure and the pressure measurements in the intake manifold:

π ^ ⁼ ^ ⁼ Υ ^ Γ < ^{Ε <} ι ^{· 10} >

The pressure upstream of the turbine is not measured. It is obtained by summing the measurement of the inlet pressure and the differential pressure measured at the high-pressure EGR valve.

The low pressure EGR flow rate is calculated as follows:

me ^ bp = ^m in ^" air ^{" m} ^, hp ( ^E Q · ^{1 1} )

According to the equations detailed above, the diagnostic criterion SF ₂ can be rewritten as follows:

^S ₂ F ₂ ⁼ ½ * 2 '''^vol' ^m air ^'m f ^m egr, hp' ^m egr, bp) (Eq. 12)

It thus appears that the diagnostic criterion depends on eight variables. It can detect an intake leak when the EGR is in operation. Figure 2 illustrates the method of diagnosing the air intake which comprises the following steps:

During a first step 20, a set of quantities involved in the estimation of the exhaust richness is determined. This first step can be decomposed into sub-steps, during which we estimate the flow sucked by applying equation 8, the flow of EGR at high pressure by applying equation 9, the ratio of pressures upstream and downstream of the high pressure EGR valve as a function of the differential pressure measurements at the terminals of said high pressure EGR valve and the pressure in the intake manifold by applying equation 10 and the EGR flow rate at low pressure by applying equation 11.

During a second step 21, the exhaust richness is estimated by applying Equations 4, 6 and 7.

During a third step 22, the exhaust richness is measured by means of a wealth probe.

During a fourth step 23, the diagnostic criterion is determined by applying equation 3.

During a fifth step 24, the diagnostic criterion is compared with at least one diagnostic threshold integrating the dispersions of the system.

During a sixth step 25, a diagnostic signal is issued depending on the result of the comparison made during the fifth step.

Figure 3 illustrates the diagnostic system of the air intake 30 which is connected at the input to a wealth sensor 31 disposed in the exhaust pipe 7 downstream of the turbine.

The air intake diagnostic system 30 comprises an exhaust richness estimation means 32, a diagnostic criterion determining means 33, a comparator 34 and at least one memory 35.

The means for determining the diagnostic criterion 32 is connected at input to the richness probe 31 and to the estimation means of the richness at the exhaust 32, and at the output at an input of the comparator 34.

The means for estimating the exhaust richness 32 applies equation 4. The signal emitted by the exhaust richness estimation means 32 is used by the means for determining the diagnostic criterion 33 applying the equation 3 to determine the diagnostic criterion.

The comparator 34 is able to compare the signal received from the means for determining the diagnostic criterion 33 with the signal received from at least one memory 35 comprising at least one diagnostic threshold integrating the dispersions of the powertrain. The comparator 35 outputs a signal dependent on the comparison.

In conclusion, the method and system for determining a diagnostic criterion makes it possible to detect an intake leakage even when the partial recirculation of the exhaust gas is in operation.

Claims

1. A method of diagnosing the intake of air into an internal combustion engine of a motor vehicle, the internal combustion engine being provided with a turbocharger and at least one of a partial exhaust gas recirculation circuit. at low pressure (3) and a partial recirculation circuit of the high pressure exhaust gas (4), characterized in that it comprises the following steps:

we estimate the wealth at the exhaust,

the richness at the exhaust is measured by means of a richness sensor (3 1) disposed in an exhaust pipe (7) of the internal combustion engine,

a diagnostic signal is emitted from the result of the comparison.

The method of claim 1, wherein the magnitude set characterizing the operation of the internal combustion engine comprises the estimates of the aspirated flow rate, the high pressure EGR flow rate, the ratio of pressures upstream and downstream of the high pressure EGR valve and inlet manifold pressure (2a) and low pressure EGR flow.

3. The method of claim 1, wherein it estimates the ratio of pressures upstream and downstream of the EGR valve at high pressure depending on the differential pressure measurements on either side of said valve.

4. Method according to any one of the preceding claims, in which the exhaust richness is estimated by performing a mass balance of volumes representative of the partial recirculation circuit of the high pressure exhaust gas and the partial recirculation circuit. low pressure exhaust gas.

5. A method as claimed in any one of the preceding claims, wherein the representative volume of the high pressure partial exhaust gas recirculation circuit comprises the volume of the intake manifold (2a).

6. A method as claimed in any one of the preceding claims, wherein the representative volume of the low pressure partial exhaust gas recirculation circuit comprises the volume of the intake manifolds, the outlet of the exhaust gas circuit and the Low pressure EGR and compressor (2a).

Air intake engine diagnostic system for a motor vehicle, the internal combustion engine being equipped with a turbocharger (2) and at least one of a partial recirculation circuit. low - pressure exhaust gas (3) and a high pressure partial exhaust gas recirculation circuit (4), characterized in that it comprises a means for estimating the exhaust richness ( 32), means for determining the diagnostic criterion (33), a comparator (34) and at least one memory (35), the means for determining the diagnostic criterion (33) being able to determine a diagnostic criterion according to of the signal received from the means for estimating the exhaust richness (32) and as a function of the signal received from the richness probe (31) disposed in an exhaust pipe (7) of the internal combustion engine, the comparator (34) being able to compare the received signal from the means for determining the diagnostic criterion (33) to the signal received from at least one memory (35) comprising at least one diagnostic threshold integrating the dispersions of the internal combustion engine, the comparator (35) outputting a dependent signal of the result of the comparison.