WO2019214821A1

WO2019214821A1 - An egr flow determination method, an egr rate error determination method, a control method for an internal combustion engine, and an internal combustion engine

Info

Publication number: WO2019214821A1
Application number: PCT/EP2018/062100
Authority: WO
Inventors: Matthieu STUCKY; Christos MANETAS-VIOLETAS; Rohan RAVINDRAN; Benjamin REPOUX; Julien CLARET TOURNIER; Clement DELPECH
Original assignee: Toyota Motor Europe
Priority date: 2018-05-09
Filing date: 2018-05-09
Publication date: 2019-11-14

Abstract

A method for determining an EGR flow (I) in an EGR passage (80) of a gas circuit (3) of an internal combustion engine (1), the gas circuit (3) comprising:. an exhaust after-treatment device (52) for storing a component (Xn) present in the exhaust gas;. an intake path (4) and an exhaust path (5), connected by an EGR passage (80) comprising an EGR valve (82);. an upstream and a downstream sensors (55u,55d) for measuring concentrations of the component (Xn) upstream and downstream the exhaust after-treatment device (52); the method comprising the steps of: S40) determining at least a first value Cmax_closed of a component storage capacity Cmax of the exhaust after-treatment device (52) when the EGR valve (82) is fully closed; S60) determining at least a first value Cmax_open of Cmax when the EGR valve (82) is fully or partially open; and S110) determining the actual EGR flow (II) using formula (III) wherein (IV) is an average mass flow of EGR gas expected in the EGR passage (80), and (V) is an average mass flow of exhaust gas expected in the exhaust after treatment device (52).

Description

An EGR flow determination method, an EGR rate error determination method, a control method for an internal combustion engine,

and an internal combustion engine

TECHNICAL FIELD

The present disclosure is directed to an EGR flow determination method, an EGR rate error determination method, a control method for an internal combustion engine, and an internal combustion engine.

BACKGROUND ART

Exhaust Gas Recirculation (EGR) of exhaust gases rejected by an internal combustion engine is a well-known technique implemented in various types of engines. This technique has certain benefits, like reduced fuel consumption, better emissions control, and/or improved protection of the engine components, according to the specific application. The amount of gas recirculation is controlled by a regulating or control valve usually called the EGR valve. This valve is controlled by an engine control unit, so that the actual EGR rate of the engine attains a target EGR Rate.

The targeted EGR rate is usually defined by an EGR rate target map. Such a map provides the value of the EGR rate in principle for any operating condition of the engine. Accordingly, the map values have to be defined for all engine operating conditions.

The term 'map' as used herein encompasses broadly not only a static table providing values of output variables based on the values of input variables, but also any means to realize this function. For instance, a map can essentially be a program run on a computer, which program is based on a mathematical model describing the functioning of the engine, and which provides values of the output variables as a function of the input variables.

In addition, the EGR flow (hereinafter noted rhegr, and expressed for instance in g/s) is defined here as the mass flow of gases flowing through an EGR passage of an internal combustion engine. The EGR rate (l†legr%) is defined as the ratio between the EGR mass flow (rhegr) and the total mass flow of gases entering in the engine. This latter amount is the sum of the mass flow of intake air (l†lair) and the mass flow of gases recirculated through the EGR passage(s) (ITIegr).

Usually, as well known in the art, the EGR rate target map is defined beforehand. In this purpose for instance, the actual EGR flow is measured for various operating conditions of the engine. For each operating point, the optimum EGR rate, that is, the EGR rate which is the best compromise between fuel consumption, emission control, reliability, etc., is selected.

This defines an EGR rate target map which is optimised with respect to fuel consumption, emission control, engine reliability (misfire, exhaust clogging,...), etc.

However, when the engine is in operation, it is not possible to determine the error between the estimated value of the EGR rate, based on the EGR rate target map values, and the actual value of the EGR rate.

Since this error cannot always be estimated accurately, for reliability reasons (that is, to be sure not to damage the engine), the engine has to be controlled assuming that there is a rather large difference between the actual EGR rate and the estimated EGR rate. Consequently, the engine cannot be controlled optimally. This leads to an increased fuel consumption and/or worse emission control of the engine, as compared with the optimal operating point.

Document EP2198141 discloses an EGR rate estimation method in which the gas flow through each EGR passage and a catalytic device is estimated, using differential pressure sensors. Estimations of the actual gas flow are calculated by an electronic control unit using an open loop control method.

EP0837237 proposes to use additional devices (aperture or pressure or air flow sensors) to perform diagnostics of the EGR proper operation.

However, these additional devices introduce some complexity in the engine, and therefore increase the costs.

SUMMARY OF THE DISCLOSURE

The disclosure has been constructed in view of the above problems of the prior art.

A first purpose of the present disclosure is to propose a method for determining an actual value of an EGR flow in an EGR passage, for a predetermined target value of the EGR flow. The actual EGR flow determined with this method can be used to determine the EGR rate error between the actual EGR rate and predetermined target value of the EGR rate (which is usually calculated based on the EGR rate target map). This error value can thereafter be used to adjust the position of the EGR valve, so that the actual EGR flow will match the targeted EGR flow, thus reducing the actual EGR rate error. Consequently, this allows to control the EGR rate, and therefore the engine, more accurately. In this purpose and according to the present disclosure, it is therefore proposed a method for determining an EGR flow in an EGR passage of a gas circuit of an internal combustion engine, the gas circuit comprising:

. an intake path and an exhaust path, configured respectively to supply intake gas to the internal combustion engine and to remove exhaust gas from the internal combustion engine;

. an exhaust after-treatment device provided on the exhaust path, and capable of storing a component (Xn) present in the exhaust gas;

. an EGR passage connecting the intake path and the exhaust path, the branching point on the exhaust path being located downstream the exhaust after-treatment device;

. an EGR valve, configured to adjust the flow of gas in the EGR passage;

. an upstream sensor configured to measure a concentration of the component in the gas entering the exhaust after-treatment device;

. a downstream sensor configured to measure the concentration of the component in the gas exiting the exhaust after-treatment device;

wherein a CMax parameter is a parameter representative of a capacity of the exhaust after-treatment device to store the component;

the method comprising the steps of:

S40) determining at least a first value Cmax_closed_l of Cmax when the EGR valve is fully closed;

S60) determining at least a first value Cmax_open_l of Cmax when the EGR valve is in a fully or partially open position; and

SI 10) determining the actual EGR flow l†legr_actual using formula:

+ l†l egr_target;

wherein GP egr_target is an average mass flow of EGR gas expected to flow in the EGR passage while Cmax is being determined;

Cmax_closed is an average value of Cmax based on said at least a first value Cmax_closed_l of Cmax determined with the EGR valve fully closed; and

Cmax_open is an average value of Cmax based on said at least a first value Cmax_open_l of Cmax determined with the EGR valve in said fully or partially open position.

The above method lies on the following principle.

The storage capacity CMAX of the exhaust after-treatment device is normally constant, because it is a physical property of the exhaust after-treatment device. Moreover, in the proposed method, the engine is preferably operated in steady state and only for a short period, which gives an additional reason to consider that the storage capacity CMAX of the exhaust after-treatment device is constant during the period in which the EGR flow measurements are made pursuant to the above- defined method.

Therefore in principle, when measuring CMAX successively with and without flow of gas in the EGR passage, the same values of CMAX should be obtained.

Accordingly, if there is a difference between the two values of CMAX

respectively determined in these two cases, this difference indicates an error in the estimated value of the EGR flow, because this error is the only cause of a difference between the two CMAX measurements.

Based on this principle, according to the proposed method, the storage capacity Cmax of the after-treatment device is measured at least once with the EGR passage closed, and at least once with the EGR passage fully or partially open. In each case, the storage capacity Cmax is calculated by integrating variations of the amount of the component contained in the exhaust after-treatment device between the full state and the empty state of the exhaust after-treatment device (that is, either while the exhaust after-treatment device passes from empty state to full state, or vice-versa).

Based on the so calculated values of CMAX, the actual EGR flow can then advantageously be determined very simply using equation (1) above. It is possible thereafter to determine the EGR rate, and consequently, to determine the EGR rate error which is made when the EGR valve is controlled on the basis of the EGR rate determined with the EGR rate target map.

Several methods can be used to calculate the storage capacity Cmax.

In an embodiment, Cmax is determined by integrating the difference between :

- the mass flow (l†l_Xn_u) of the component (Xn) entering the exhaust after- treatment device (52), and

- the mass flow (l†l_Xn_d) of the component (Xn) exiting the exhaust after- treatment device (52)

between two states of component (Xn) storage of the exhaust after-treatment (52) which can be either:

- from an empty state when the exhaust after-treatment device (52) has released all the component (Xn) until a full state when the exhaust after-treatment device (52) has stored as much as component (Xn) as it can; or - from a full state when the exhaust after-treatment device (52) has stored as much as component (Xn) as it can until an empty state when the exhaust after-treatment device (52) has released all the component (Xn).

In particular, in a variant of the above embodiment, the mass flows (l†l_Xn_u) and (f†l_Xn_d) of the component (Xn) entering and exiting (respectively) the after-treatment device (52) are calculated based on equations:

wherein

Cx_n_u is the concentration of component (Xn) in the exhaust gas upstream the exhaust after-treatment device (52) measured by sensor (55u);

Cxn _d the concentration of component (Xn) in the exhaust gas downstream the exhaust after-treatment device (52) measured by sensor (55d);

M_ex_hgas_u is the average molar mass of the exhaust gas upstream the exhaust after- treatment device (52);

M_eXhgas_d is the average molar mass of the exhaust gas downstream the exhaust after-treatment device (52);

M_xn is the molar mass of component (Xn)

rh e _h_gas is the mass flow of exhaust gases through the exhaust after-treatment device (52) calculated based on below formula:

(5) rilexh_gas = ITlair + ITIf + ITIegr_Target wherein

ftlair is the mass flow of air entering in the intake path;

l†lf is the mass flow of fuel injected in the internal combustion engine;

rilegr_target is the expected mass flow of EGR gases through the EGR passage.

The proposed method can be applied to determine the EGR flow in the EGR for different components: It only requires that an exhaust after-treatment device be provided on the exhaust path, and capable of storing the component present in the exhaust gas; and that the branching point of the EGR passage be located on the exhaust path downstream the exhaust after-treatment device. In an embodiment, the component is ammonia (NH3). In this case, the upstream and downstream sensors are sensors capable of measuring a

concentration of ammonia in a gas. In addition, the exhaust after-treatment device can be for instance a Selective Catalytic Reduction device.

In another embodiment, the component is nitrogen oxides (NOx). In this case, the upstream and downstream sensors are sensors capable of measuring a concentration of nitrogen oxides in a gas. In addition, the exhaust after-treatment device (52) can then be NOx trap catalyst.

In another embodiment, the component is oxygen (O2); the upstream sensor and the downstream sensor are sensors capable of measuring oxygen concentration in a gas. For instance, at least one of the upstream and downstream sensor can be a Universal Exhaust Gas Oxygen sensor (UEGO sensor), in particular with wide band or narrow band.

Furthermore, when the component is oxygen, the exhaust after-treatment device can be a three Way Catalyst, a NOx trap Catalyst, or an Oxidation Catalyst.

When the component is oxygen, the Cmax parameter can be determined by integrating variations of the oxygen content of the exhaust after-treatment device between two states of oxygen storage of the exhaust after-treatment which can be either:

- from an empty state when the exhaust after-treatment device has released all the oxygen until a full state when the exhaust after-treatment device has stored as much as oxygen as it can; or

- from a full state when the exhaust after-treatment device has stored as much as oxygen as it can until an empty state when the exhaust after-treatment device (52) has released all the oxygen.

The variations dOSAegr of the oxygen content of the exhaust after-treatment device per time period being calculated based on formula below:

(2) dOSAegr = 0.23 * (ftlair + ITIf + l†)egr_target) * (AFu - AFstoich) / (1+ AFu) wherein:

ftlair is the mass flow of air entering in the intake path;

rhf is the mass flow of fuel injected in the internal combustion engine;

AFstoich is an Air/Fuel ratio of the exhaust gas, when air and fuel are supplied to the engine in stoichiometric proportions;

AFu is an Air/fuel ratio detected by the upstream sensor; and megr_target is an average mass flow of EGR gas expected to flow in the EGR passage while Cmax is being determined.

The above-defined method provides an accurate value of the EGR flow. Advantageously, this method does not require additional sensors on the gas circuit, and mainly use a Cmax determination procedure which is readily available in many internal combustion engines, which in many cases only uses the sensors already available in the gas circuit.

In order to obtain the best results, the above-defined method must be used in a stabilized operating mode of the engine; or at least, the operating state of the engine during the Cmax_closed determination step and the Cmax_open determination step should be substantially the same - except the opening of the EGR passage.

For this reason, the above-defined method is preferably implemented in an internal combustion engine of a hybrid vehicle. As known per se, the powertrain of such a hybrid vehicle comprises a motor (for instance an electric motor) in addition to the internal combustion engine.

For instance, in a hybrid vehicle, the vehicle can be operated so as to be driven solely by said motor of the vehicle, while the proposed method is performed for the internal combustion engine.

In particular in this latter case, but not only, the internal combustion engine can for instance remain idling while the proposed method is performed.

More generally, the proposed method can be carried out during any stationary operation of the engine. For example, when the internal combustion engine is mounted on a hybrid vehicle, the method can be carried out when the engine delivers a non-zero torque, with the energy delivered being stored in the energy storage component of the motor of the powertrain (in the battery of the vehicle, if the motor is an electric motor).

In an embodiment, the method further comprises the steps of:

S80) determining a second value Cmax_closed_2 of Cmax when the EGR valve is in the closed position;

S100) calculating an average value Cmax_closed_average as the mean of Cmax_closed_l and Cmax_dosed_2; and

at step S110, the Cmax_closed value used in formula (1) is Cmax_closed_average; and

the Cmax_open determination step S60 is carried out between the Cmax_closed_l determination step S40 and the Cmax_closed_2 determination step In an embodiment of the method, step 60 further comprises an additional step of determining a second value Cmax_open_2 of Cmax when the EGR valve is in said fully or partially open position; the method comprises at step S100, calculating an average value Cmax_open_average as the mean of Cmax_open_l and Cmax_open_2; and

at step S110, the Cmax_open value used in formula (1) is Cmax_open_average.

According to the present disclosure, it is further proposed a method for determining an EGR rate error. The EGR rate error is the difference between the actual EGR rate, and the value of a theoretical EGR rate, determined by means of an EGR rate target map or the like, as a function of various state variables of the engine. The actual EGR rate is the EGR rate that can be actually observed when the EGR valve is controlled based on the theoretical EGR rate.

This latter method comprises determining the EGR flow rhegr_actual with the above-described EGR flow determination method, and then carrying out the following steps:

S120) calculating an EGR rate rilegr% as a percentage of the total mass flow of gases flowing into the engine, using formula below:

(6) l†legr%_actual = lilegr_actual / (Phegr_actual + rilair);

S130) calculating an EGR rate error l†legr%_error using formula below:

(7) l†legr%_error = l†legr%_actual - l†legr%_target.

According to the present disclosure, it is further proposed a control method for controlling an internal combustion engine mounted with a gas circuit to supply intake gas to the internal combustion engine and to remove exhaust gas from the internal combustion engine;

the method comprising the steps of:

A) calculating an EGR rate error by an afore described method;

E) calculating an adjusted position (a_adjusted) of the EGR valve which is an opening value of the EGR valve adjusted based on the EGR rate error so that an actual EGR rate be equal to a target EGR rate; and

F) controlling the position of the EGR valve so as to attain the adjusted opening position.

Advantageously in the above control method, the opening position of the EGR valve is adjusted based on EGR rate errors. Therefore, the position of the EGR valve can be determined accurately, so that the EGR rate in the EGR passage be equal to the targeted EGR rate. This method therefore makes it possible to compensate a deterioration of the EGR valve, causing the actual EGR flow to be different from its theoretical (or target) value.

According to the present disclosure, it is further proposed an EGR system failure On-Board Diagnostic (OBD) detection method for an internal combustion engine mounted with a gas circuit to supply intake gas to the internal combustion engine and to remove exhaust gas from the internal combustion engine;

the method comprising the steps of:

A) calculating an EGR rate error (l†legr%_error) by an afore described method;

H) issuing a warning signal in case EGR rate error (ITIegr%_error) is above a predetermined threshold (the OBD threshold')·

The value of the OBD threshold is preferably sufficiently high to avoid sending unnecessary warnings to the driver and/or to the passenger(s) of the vehicle.

The warning signal can be any type of signal. It can be a signal sent to the driver, for instance a visible, audible, and/or haptic signal, but it can be as well an electronic signal (a 'flag' or a CAN message), issued by an electronic control unit to trigger any additional possible procedure(s).

Advantageously in the above EGR system failure OBD detection method, the EGR system OBD is performed at the same time as the EGR rate error measurement procedure, thus eliminating the need to have a specific control method for EGR system OBD. As well, because actual EGR rate error is determined rather precisely using afore described methods, accuracy of EGR system failure detection is improved compared to traditional methods.

A second purpose of the present disclosure is to propose an internal combustion engine in which the actual EGR flow can be determined aboard a vehicle. Subsequent purposes, as for the above-defined methods, are to propose an internal combustion engine in which the EGR rate error between the actual EGR rate and the targeted EGR rate (provided by the EGR rate target map) can be determined, and an internal combustion engine, whose EGR valve position can be adjusted based on EGR rate error, so as actual EGR rate to be equal to targeted EGR rate (on-board) and which, consequently, can be controlled more accurately, leading to a reduced fuel consumption and a better emission control.

According to the first aspect of the present disclosure, it is proposed an internal combustion engine mounted with a gas circuit, the internal combustion engine comprising an electronic control unit configured to calculate an EGR rate (rilegrjarget) based on a EGR model including a plurality of parameters, the gas circuit comprising: . an intake path and an exhaust path, configured respectively to supply intake gas to the internal combustion engine and to remove exhaust gas from the internal combustion engine;

. an exhaust after-treatment device provided on the exhaust path, and capable of storing a component present in the exhaust gas;

. an EGR valve, configured to adjust the flow of gas in the EGR passage;

wherein, with a CMax parameter being a parameter representative of a capacity of the exhaust after-treatment device to store the component, the electronic control unit is configured to:

S40) determine at least a first value Cmax_closed_l of Cmax when the EGR valve is fully closed;

S60) determine at least one value Cmax_open_l of Cmax when the EGR valve is in a fully or partially open position; and

SI 10) determine the actual EGR flow rhegr_actual using formula:

(1) fTlegr_actual = (Cmax_closed/Cmax_open - 1) * (l†l exh_gas) + rilegr_target;

wherein l†l egr_target is an average mass flow of EGR gas expected to flow in the EGR passage (80) while Cmax is being determined;

Cmax_closed is an average value of Cmax based on said at least a first value Cmax_closed_l of Cmax determined with the EGR passage fully closed; and

The electronic control unit of this engine can be adapted to determine the EGR mass flow in the EGR passage by executing one of the above-presented methods, if the engine has the right configuration: that is, if an exhaust after- treatment device is provided on the exhaust path, capable of storing the component present in the exhaust gas, and if the branching point of the EGR passage is located on the exhaust path downstream the exhaust after-treatment device. As the case may be, the component can be for instance ammonia, nitrogen oxides, or oxygen, as mentioned previously.

In addition, the electronic unit can be configured to calculate the Cmax parameter as in any one of the above-presented methods.

In particular, if the component is oxygen, in an embodiment the control unit is configured to determine Cmax by integrating variations of the oxygen content of the exhaust after-treatment device between two states of oxygen storage of the exhaust after-treatment which can be either:

- from a full state when the exhaust after-treatment device has stored as much as oxygen as it can until an empty state when the exhaust after-treatment device has released all the oxygen.

The variations dOSAegr of the oxygen content of the exhaust after-treatment device per time period are then calculated based on formula below:

(2) dOSAegr = 0.23 * (itlair + itlf + ftlegr.target) * (AFu - AFstoich) / (1+ AFu) wherein:

ITlair is the mass flow of air entering In the intake path;

itlf is the mass flow of fuel injected in the internal combustion engine;

AFu is an Air/fuel ratio detected by the upstream sensor (which is therefore an Air/fuel ratio sensor); and

rilegrjarget is an average mass flow of EGR gas expected to flow in the EGR passage while Cmax is being determined.

In an embodiment, the electronic control unit is further configured to:

S80) determine a second value Cmax_closed_2 of Cmax when the EGR valve (82) is in the closed position;

S100) calculate an average value Cmax_closed_average as the mean of Cmax_closed_l and Cmax_closed_2; and wherein

when the electronic control unit determines the actual EGR flow ITIegr_actual, the Cmax_closed value used in formula (1) is Cmax_closed_average; and

the electronic control unit determines Cmax_open after having determined Cmax_closed_l and before determining Cmax_closed_2. In an embodiment, the electronic control unit is further configured to:

S120) calculate an EGR rate rhegr% as a percentage of the total mass flow of gases flowing into the engine, using formula below:

(6) rilegr%_actual = l†legr_actual / (l†legr_actual + ftlair);

S130) calculate an EGR rate error l†legr%_error using formula below:

(7) l†legr%_error = l†legr%_actual - l†legr%_target.

In a first advantageous variant, in the internal combustion engine according to the above embodiment, the electronic control unit is further configured:

. to calculate an adjusted position of the EGR valve which is an opening value of the EGR valve adjusted based on the EGR rate error (l†legr%_error) so that an actual EGR rate be equal to a target EGR rate;

. to control the position of the EGR valve so as to attain the adjusted opening position.

In a second advantageous variant (which can possibly be combined with the first variant) of an the internal combustion engine according to the above embodiment, the electronic control unit is further configured to issue a warning signal in case the EGR rate error (rhegr%_error) is above a predetermined threshold (the afore-mentioned OBD threshold).

As mentioned before, to improve the accuracy of the methods according to the present disclosure, it is preferable to keep the internal combustion engine at a constant operating point during the whole EGR flow determination procedure. Consequently, these methods can be implemented particularly easily in an internal combustion engine which is configured to be mounted on a hybrid vehicle.

In addition, these methods can be implemented in a spark ignition engine, a compression ignition engine, etc.

The gas circuit of the internal combustion engine can comprise various catalyst units provided to store oxygen, with various catalysts.

As optional components, an internal combustion engine in accordance with the present disclosure can include a turbo charger, an intake/exhaust variable valve timing system, a direct injection system and/or port injection system, an EGR cooler, as well as any other additional component such an engine might be equipped with.

Advantageously, the methods according to the present disclosure provide actual values of the EGR rate error, thus making it possible to control the functioning of the engine on the basis of a more accurate value of the EGR rate. Consequently, the operating point of the engine can be set more accurately, fuel consumption can be reduced, and emission control can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood and its numerous other objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings wherein like reference numerals refer to like elements in the several figures and in which :

FIG. 1 is a schematic drawing representing an internal combustion engine according to an embodiment of the present disclosure;

FIG. 2 is a flow chart showing the steps of a method for determining an EGR rate error, according to the present disclosure;

FIG. 3 is a flow chart showing the steps of a method for controlling an internal combustion engine, according to the present disclosure; and

FIG. 4 is a diagram showing variations of Air/Fuel ratios during determination of the Cmax value.

DESCRIPTION OF THE PREFERRED EMBODIMENT

First, an internal combustion engine in accordance with the present disclosure will be described with reference to Fig. 1.

The internal combustion engine 1 shown in FIG. 1 is a four-stroke cycle internal combustion engine, in this case, a spark ignition internal combustion engine such as a gasoline engine. Alternatively, the internal combustion engine 1 may be a compression ignition internal combustion engine such as diesel engine.

The internal combustion engine 1 includes a plurality of cylinders 2.

Moreover, while the internal combustion engine 1 is shown in FIG. 1 to have four cylinders 2, the number of cylinders 2 may be 3 or less or 5 or more.

In addition, a gas circuit 3 is mounted on the internal combustion engine 1. The gas circuit 3 comprises an intake pipe or path 4 and an exhaust pipe or path 5, configured respectively to supply intake gas to the internal combustion engine 1 and to remove exhaust gas from the internal combustion engine 1.

The internal combustion engine 1 is connected to the intake pipe 4. The intake pipe 4 is a pipe for guiding fresh air (air) taken in from the atmosphere to the internal combustion engine 1. A throttle valve 40 is arranged in an upstream portion of the intake pipe 4. The throttle valve 40 adjusts an amount of air flowing through the intake pipe 4 by changing a passage sectional area inside the intake pipe 4. An air flow meter 42 is arranged in the intake pipe 4 on an upstream side of the throttle valve 40. The air flow meter 42 is for measuring an amount (mass flow) of air flowing through the intake pipe 4.

In the intake pipe 4, a compressor 60 of a turbocharger 6 separates the intake pipe 4 into an upstream portion and a downstream portion. The compressor 60 is a centrifugal compressor that compresses intake air when being driven by the turbine 61 of turbocharger 6.

An intercooler 41 for cooling intake air which has been compressed by the compressor 60 is arranged in the downstream portion of the intake pipe 4. The intercooler 41 is, for example, an air-cooled or water-cooled heat exchanger that exchanges heat between outside air or respectively cooling water and intake air.

In addition, the internal combustion engine 1 is connected to the exhaust pipe 5. The exhaust pipe 5 is a pipe for circulating gas (burned gas) that has been burned in the cylinders 2 of the internal combustion engine 1.

An exhaust gas control apparatus 50 is arranged along the exhaust pipe 5. The exhaust gas control apparatus 50 comprises three catalyst units 52, 54 and 56 interposed successively on the exhaust pipe 5. Each catalyst unit comprises a catalyst inside a casing. Catalyst unit 52 is a three-way catalyst unit (as an exemple of 'exhaust after-treatment device') containing a three-way catalyst. Each of catalyst units 54 and 56 includes at least one of, for example, an oxidation catalyst, a storage reduction catalyst, and a selective reduction catalyst.

In the exhaust pipe 5, the turbine 61 of the turbocharger 6 described earlier is arranged on the exhaust pipe 5 on the upstream side of the exhaust gas control apparatus 50. The turbine 61 is a motor which converts energy of exhaust gas of the internal combustion engine 1 into rotational energy and which rotates and drives the compressor 60 (compressor wheel) using the converted rotational energy.

The gas circuit 3 also includes a low pressure EGR apparatus 8. The low pressure EGR apparatus 8 is an apparatus which includes an EGR passage 80, an EGR valve 82, and an EGR cooler 84 and which recirculates a part of exhaust gas flowing through the exhaust pipe 5 into the intake pipe 4. The EGR passage 80 communicates the exhaust pipe 5 on a downstream side of the turbine 61 with the intake pipe 4 on an upstream side of the compressor 60. More precisely, the EGR passage 80 branches at a point P on the exhaust path 5 downstream the catalyst unit 52 and upstream the catalyst unit 54.

The EGR valve 82 is provided midway along the EGR passage 80 and adjusts an amount of EGR gas by changing a passage sectional area of the EGR passage 80. The EGR cooler 84 is a heat exchanger which is provided midway along the EGR passage 80 and which exchanges heat between outside air or cooling water and EGR gas.

The low pressure EGR apparatus further comprises an upstream air/fuel ratio sensor 55u, provided on the exhaust path 5 downstream the turbine 61 but upstream the catalyst unit 52, and a downstream air/fuel ratio sensor 55d, located on the exhaust path 5 downstream the catalyst unit 52 but upstream of the catalyst unit 54 and upstream of the point P on the exhaust path 5 where the low pressure EGR passage 80 branches from the exhaust path 5.

An electronic control unit (ECU) 9 is annexed to the internal combustion engine 1. The electronic control unit 9 is a microcomputer having a CPU 91, a ROM 92 (read-only memory), a RAM 93, a back-up RAM (SRAM) 94 and an interface 95. The ROM 92 is configured to store various routines (programs) which can be executed by the CPU 91, data tables (e.g., look-up tables, maps), and parameters which are stored beforehand. The RAM 93 is used by CPU 91 to temporarily store various data as needed. The back-up RAM (SRAM) 94 is used to store data when the ECU 9 is powered; the stored data may be held even when not powered. The interface 95 includes A/D converters, etc., which are all connected via communication buses. The interface 95 is connected to the various aforementioned sensors, transmits the signals outputted by the sensors to the CPU 91, and outputs drive signals to different actuators, in particular the throttle valve 40 and the EGR valve 82, in accordance with commands issued by CPU 91.

Accordingly, the upstream and downstream air/fuel ratio sensors 55u and 55d, as well as the air flow meter 42 described earlier are all connected to the ECU 9.

EGR rate error determination method

An EGR rate error determination method according to the present disclosure will now be presented.

The method or procedure illustrated by Fig.2 is a procedure to determine the EGR rate error in accordance with the present disclosure.

This procedure normally runs once for each driving cycle (A driving cycle starts when the engine 1 is started and terminates when the engine 1 is stopped). However, this procedure can be executed as often as desired in order to have highly accurate values of the EGR rate error at all times. Each time this procedure is executed, it provides an estimate of the EGR rate error l†legr%_error for a specific value of the EGR rate (which is the value of the EGR rate when the procedure was executed), and only for this specific value.

Therefore, in order to minimize the error in the determination of the EGR rate for the whole operating domain of the engine, it is preferable to execute this method for several values of the EGR rate covering the whole range of possible EGR rates (For instance, from 5 % to 35 %). For instance, the procedure can be executed first with a 5 % opening of the EGR valve, then with a 10% opening, etc ; when the 35 % value has been tested, the procedure is executed next with a 5 % value, etc. (Table T below).

When the procedure is executed to determine the EGR rate error for such a predetermined EGR rate value, the engine 1 is operated at an operating point for which the EGR rate, as provided by the EGR rate target map, has the predetermined value.

This value is therefore a target for the EGR rate, noted l†legr%_target, which is the theoretical EGR rate at which exhaust gas should flow through the EGR passage 80 when the procedure is executed.

Table T

For each target of the EGR rate, the procedure illustrated on Fig.2 is executed. Execution lasts about 60 seconds, and comprises the following steps:

At step S10, the procedure is started, and a Cmax measurement request is issued.

Shortly thereafter at step S20, the operating state of engine 1 is stabilized; that is, the main parameters of the engine are kept as constant as possible. This state is maintained throughout steps S20 to S90. For example, in a hybrid vehicle (for instance an electric/ICE hybrid vehicle comprising an electric motor in addition to the internal combustion engine), during this period, the internal combustion engine is operated with constant parameters, while the vehicle is driven only by the electric motor.

At step S30, the EGR valve 82 is closed, which closes the low pressure EGR passage 80.

At step S40, a first value of the oxygen capacity of catalyst 52 Cmax with the EGR duct 80 being closed is determined. This value is noted Cmax_closed_l. The oxygen capacity of catalyst 52 Cmax_closed_l is calculated by integrating the variations of the oxygen content of the catalyst, noted dOSAegr, between the full state and the empty state of the catalyst 52 (The method for calculating Cmax will be presented in more detail later).

The variations dOSAegr of the oxygen content of the catalyst are calculated based on the formula:

(1) dOSAegr = 0.23 * (itlair + ftlf + r†legr_target) * (AFu - AFstoich) / (1+ AFu)

Wherein itlair is the mass flow of air flowing through the intake path 4; l†lf is the mass flow of fuel injected in the internal combustion engine 1; AFu is the air/fuel ratio detected by the upstream Air/Fuel ratio sensor 55u upstream the catalyst 52; AFstoich is the stoichiometric Air/Fuel ratio.

Of course, at step S40, since the EGR passage 80 is closed, l†legr_target is equal to 0.

At step S50, the EGR valve 82 is open (at least partially), to let part of the exhaust gas flow through the EGR passage 80. The opening degree of low pressure EGR valve 82 is selected so that the percentage of exhaust gas rhegr% which flows through the EGR passage 80, as compared to the total mass flow of gases entering in the engine, is equal to the preset value megr%_target. The total mass flow of gases entering in the engine is the sum of the mass flow of intake air (mair) and the mass flow of gases recirculated through the EGR passage(s) (rfiegr).

For instance, based on table T above, at driving cycle n°3, the opening degree of low pressure EGR valve 82 is selected so that the percentage of exhaust gas rhegr% be equal to 15%.

At step S60, the value Cmax_open of Cmax when the EGR duct 80 is in the open state is determined by integrating dOSAegr. The same formulas as in step S40 are used.

In particular, l†legr_target is the EGR flow which corresponds to the predetermined value rhegr%_target, chosen beforehand.

ITlegr_target is calculated with the formula below:

l†legr_target = itlair * (l†legr%_target / (1 - l†legr%_target))

At step S70, the EGR valve 82 is closed, whereby the low pressure EGR passage 80 is closed.

At step S80, a second value of the oxygen capacity of catalyst 52 Cmax with the EGR duct 80 being closed is determined. This value is noted Cmax_closed_2. At step S90, the measurement procedure is terminated; thereafter, it is not necessary anymore to stabilize the operating point of engine 1.

This procedure provides three values of Cmax: two values of Cmax measured when the EGR passage 80 is closed, Cmax_closed_l and Cmax_closed_2, and one value of Cmax measured when the EGR passage is opened, Cmax_open.

The procedure then proceeds to step S100.

An alternative embodiment is represented on Fig.2. In this embodiment, the procedure comprises a loop L (an optional loop) shown by a dotted arrow on Fig.2.

In the alternative embodiment, the loop L is executed one or more times, and then the procedure proceeds to step S100.

Each execution of loop L implies performing again the above-defined steps S50, S60, S70 and S80. Accordingly, each execution of loop L provides an additional value of Cmax_open and an additional value of Cmax_closed.

Consequently if the loop L is executed one or more times, at least two values of Cmax_open and of Cmax_closed are available for calculating the average values of these variables, as it will be explained below.

At step S100, the average value of the oxygen content of the catalyst as measured with the EGR passage being closed Cmax_closed_average is calculated:

Cmax_closed_average = (Cmax_closed_l + Cmax_closed_2) / 2 Of course, if loop L has been executed one or more times, the value of

Cmax_closed_average is the average of all the values of Cmax (Cmax_closed_l, Cmax_closed_2, etc.) calculated with the EGR passage being closed.

In addition, the average value of the oxygen content of the catalyst as measured with the EGR passage being open Cmax_open_average is also calculated, and is equal to the value or to the average of all the values of Cmax (Cmax_open_l, Cmax_open_2, etc.) calculated with the EGR passage being open.

At step SI 10, the actual EGR flow flowing through the low pressure EGR passage, rhegr_actual, is calculated. This mass flow is calculated using the formula:

(1) rhegr_actual = (Cmax_closed_ average/Cmax_open - 1) * (rilair + l†lf

+ l†legr_target) + l†legr_target.

At step S120, the EGR rate is calculated as a percentage of the total mass flow of gases flowing into the engine 1, using the formula below:

ITIair)

At step S130, the EGR rate error is calculated, using the formula below: l†legr%_error = ITIegr%_actual - rilegr%_target

By executing the above procedure for several values of the EGR rate (several values of l†legr%_target), it is possible to determine the EGR rate error rilegr%_error for these various values of the EGR rate. Thereafter, the EGR rate error can be estimated for any value of the EGR rate by interpolating the values of the EGR rate error determined using the above procedure.

The values of the EGR rate error obtained thanks to this method can then be used to control the operation of the engine 1 and more particularly, to accurately control the flow of exhaust gas flowing through the EGR passage 80.

Engine control

A control method for controlling the engine 1 according to the present disclosure will now be presented in relation with Fig.3.

The purpose of this method is to control the flow of exhaust gas flowing through the EGR passage 80 accurately.

In this purpose, the method comprises the following steps:

A) The EGR rate error l†legr%_error is calculated, using the method described in relation with Fig.2. As explained above, the EGR rate error can then be estimated for any value of the EGR rate.

B) Then, the targeted EGR flow (ITIegr) which is desired in the EGR passage in view of the operating state of the engine, is calculated.

In this purpose, based on the operating state of the engine, first a targeted EGR rate is determined using the EGR rate target map.

The targeted EGR flow is then calculated based on the targeted EGR rate.

Then, the EGR rate error which can be expected for the targeted EGR rate is estimated.

C) It is then determined whether the EGR rate error is below a predetermined EGR rate correction threshold. The value of the EGR rate correction threshold is chosen as the minimum error value above which a corrected value of the EGR rate has to be taken into account.

D) If it is the case ('YES')_/ it is assumed that the EGR rate error is negligible. It is assumed that it is not necessary to adjust the position of the EGR valve. Therefore, the EGR rate of the engine is controlled by placing the EGR valve in a position directly calculated on the basis of the targeted EGR rate.

E) Conversely, if the EGR rate error is above the EGR rate correction threshold ('NO'), it is assumed that it is necessary to adjust the value of the EGR rate. An adjusted position (X_adjusted of the EGR valve is calculated. This value (X_adjusted takes into account the estimated EGR rate error rhegr%_error so that actual EGR rate be equal to the targeted EGR rate.

F) The electronic control unit 9 then controls the EGR rate of the engine by placing the EGR valve 82 in the adjusted opening position (X_adjusted. Thanks to the adjustment performed at step E, the valve 82 is controlled in such a manner that the EGR flow be substantially equal to the targeted EGR flow.

In this method, the EGR rate target map and the targeted EGR rate r†legr%_target remain unchanged; conversely the opening degree of the EGR valve is adjusted.

Additional control for on-board diagnostics fOBDI

An optional additional procedure is also shown on Fig.3.

In addition to the above-described control, when at step C, it is determined that the EGR rate error is above the predetermined threshold ('NO'), in addition to steps E and F, the electronic control unit further executes the following operations:

G) The electronic control unit determines whether the EGR rate error is below a second predetermined threshold: the OBD threshold'. The OBD threshold is substantially higher than the EGR threshold.

If it is determined that the EGR rate error is below the OBD threshold, it is assumed that the EGR rate error is probably small enough to be corrected, and that it is not necessary to issue a warning to the driver.

H) Conversely, If the EGR rate error is above the OBD threshold ('NO , the electronic control unit 9 issues one or more warning signals. For instance, a first signal can be transmitted to the driver to warn him or her that an excessively high EGR rate error has been detected. A second signal can also be issued to trigger a procedure to mitigate the effects of this situation.

Cmax calculation

The procedure for calculating Cmax (or 'Cmax procedure') will now presented in relation with Fig.4.

Fig.4 shows three curves, which all represent the variations of different air/fuel ratio.

The two curves in the upper half represent the variations respectively of the target air/fuel ratio, and the actual air/fuel ratio as measured upstream the three- way catalyst 52. The curve in the lower half represents the theoretical variations of the air/fuel ratio AFd of the exhaust gas flowing immediately downstream catalyst 52 (as should in principle be measured by air/fuel sensor 55d). For both curves, the variations of the air/fuel ratio AFd are illustrated as a function of time (in abscissa), during a calculation step for calculating the Cmax parameter (for instance, during step S40, S60 or S80 of the procedure of Fig.2).

The Cmax is calculated as follows:

The curves of Fig.4 exhibit three consecutive periods.

During the first period, the engine is controlled so that the exhaust gas flowing in the catalyst unit be lean (that is, have an air/fuel ratio above the stoichiometric value; the stoichiometric value is shown with a dotted line on Fig.4).

Consequently during this period, oxygen accumulates in catalyst 52, and the Air/Fuel ratio AFd detected downstream by sensor 55d remains low.

At some point, the catalyst 52 is saturated in oxygen, and stops accumulating oxygen. Consequently, the downstream Air/Fuel ratio AFd suddenly increases. When this change is detected by the electronic control unit 9, the electronic control unit 9 controls the engine so that the exhaust gas flowing in the catalyst 52 be rich. The second period starts.

During this second period, with the Air/Fuel ratio of the gas entering in the catalyst 52 being rich, the oxygen stored in catalyst 52 is reacting with CO, HC, H2, etc., and therefore it is progressively released from the catalyst surface. Accordingly, the downstream Air/Fuel ratio AFd remains high (lean).

Then, at some point the catalyst 52 has released all the oxygen it had accumulated, and stops releasing oxygen. Consequently, the downstream Air/Fuel ratio AFd suddently decreases. When this change is detected by the electronic control unit 9, the electronic control unit 9 controls the engine so that the exhaust gas flowing in the catalyst 52 be lean again. The third period starts.

During the third period, as in the first period, oxygen accumulates in catalyst 52.

The third period terminates when the downstream Air/Fuel ratio AFd suddenly increases again, which is detected by the electronic control unit 9.

During the second period (reference A on Fig.4), the catalyst 52 progressively releases an amount of oxygen which corresponds to its maximum oxygen capacity. During the third period (reference B on Fig.4), the catalyst 52 progressively accumulates an amount of oxygen which also corresponds to its maximum oxygen capacity. Accordingly, Cmax can be determined by integrating the variations of the oxygen content of the catalyst, that is, by integrating dOSA, either during the second period, or during the third period.

To improve the accuracy of this calculation, Cmax is calculated as the mean value of these two values.

Although the above-presented embodiment is an engine comprising a low pressure EGR passage, the present invention can also be implemented in an engine comprising, in addition to the low pressure EGR passage, a high-pressure EGR passage.

This case concerns engines which comprise a turbocharger with a compressor interposed on the intake passage and a turbine interposed on the exhaust passage (as in the above-described gas circuit 3 of the engine 1).

In the above-described gas circuit 3, the EGR passage 80 is a low pressure passage, since it connects the intake passage 4 upstream the compressor 60 with the exhaust passage 5 downstream the turbine 61.

In engines equipped with a turbocharger, the gas circuit may comprise, in addition to the low pressure EGR passage, a high-pressure EGR passage. This high- pressure EGR passage then connects the intake passage downstream the compressor with the exhaust passage upstream the turbine.

In this case, the respective EGR rates (the total EGR rate GP eg r%_tota I , the

EGR rate through the low pressure EGR passage r†legr%_LP, the EGR rate through the high-pressure EGR passage rhegr%_HP) can be calculated by the formulas below:

rhegr%_total = (fhegrJHP + ltlegr_LP)/( ITlegrJ-IP + rtlegr%_LP + ITlair) r†legr%_LP = l†legr _LP/( rhegr _HP + ITIegr _LP + ITlair)

l†legr%_HP = ITIegr _HP/( l†legr _HP + ltlegr _LP + itlair)

In order to implement the present invention in an engine whose gas circuit comprises a low pressure and a high-pressure EGR passages, the high-pressure EGR passage should preferably remain closed during the procedure of Fig.2, in order to avoid any disturbance due to the high-pressure EGR. Consequently in such case, all the formulas presented above are applicable, since the gas circuit therefore only comprises then a low pressure EGR passage.

Claims

1. A method for determining an EGR flow (GP egr_actual) in an EGR passage (80) of a gas circuit (3) of an internal combustion engine (1), the gas circuit (3) comprising:

. an intake path (4) and an exhaust path (5), configured respectively to supply intake gas to the internal combustion engine (1) and to remove exhaust gas from the internal combustion engine (1);

. an exhaust after-treatment device (52) provided on the exhaust path (5), and capable of storing a component (Xn) present in the exhaust gas;

. an EGR passage (80) connecting the intake path (4) and the exhaust path (5), the branching point on the exhaust path (5) being located downstream the exhaust after-treatment device (52);

. an EGR valve (82), configured to adjust the flow of gas in the EGR passage (80);

. an upstream sensor (55u) configured to measure a concentration of the component (Xn) in the gas entering the exhaust after-treatment device (52);

. a downstream sensor (55d) configured to measure the concentration of the component (Xn) in the gas exiting the exhaust after-treatment device (52);

wherein a Cmax parameter is a parameter representative of a capacity of the exhaust after-treatment device (52) to store the component (Xn);

the method comprising the steps of:

S40) determining at least a first value Cmax_dosed_l of Cmax when the EGR valve (82) is fully closed;

S60) determining at least a first value Cmax_open_l of Cmax when the EGR valve

(82) is in a fully or partially open position; and

SI 10) determining the actual EGR flow ITlegr_actual using formula:

(1) GGΊ egr_actual = (Cmax_dosed/Cmax_open - 1) * (l†l exh_gas) + IT) egr_target;

wherein GP egr_target is an average mass flow of EGR gas expected to flow in the EGR passage (80) while Cmax is being determined;

Cmax_closed is an average value of Cmax based on said at least a first value Cmax_closed_l of Cmax determined with the EGR valve (82) fully closed; and Cmax_open is an average value of Cmax based on said at least a first value Cmax_open_l of Cmax determined with the EGR valve (82) in said fully or partially open position.

2. The method for determining an EGR flow (rhegr_actual) according to claim 1, further comprising the steps of: S80) determining a second value Cmax_closed_2 of Cmax when the EGR valve (82) is in the closed position;

S100) calculating an average value Cmax_closed_average as the mean of Cmax_closed_l and Cmax_closed_2; and wherein

at step SI 10, the Cmax_closed value used in formula (1) is Cmax_closed_average; and

the Cmax_open determination step S60 is carried out between the Cmax_closed_l determination step S40 and the Cmax_closed_2 determination step S80.

3. The method for determining an EGR flow (r†legr_actual) according to claim 1 or 2, wherein the component (Xn) is oxygen; the upstream sensor and the

downstream sensor (55u,55d) are sensors capable of measuring oxygen

concentration in a gas.

4. The method for determining an EGR flow (rilegr_actual) according to claim 3, wherein Cmax is determined by integrating variations of the oxygen content of the exhaust after-treatment device (52) between two states of oxygen storage of the exhaust after-treatment (52) which can be either:

- from an empty state when the exhaust after-treatment device (52) has released all the oxygen until a full state when the exhaust after-treatment device (52) has stored as much as oxygen as it can; or

- from a full state when the exhaust after-treatment device (52) has stored as much as oxygen as it can until an empty state when the exhaust after-treatment device (52) has released all the oxygen;

(2) dOSAegr = 0.23 * (itlair + ITlf + l†legr_target) * (AFu - AFstoich) / (1+ AFu) wherein:

rhair is the mass flow of air entering in the intake path (4);

rhf is the mass flow of fuel injected in the internal combustion engine (1);

AFstoich is an Air/Fuel ratio of the exhaust gas, when air and fuel are supplied to the engine (1) in stoichiometric proportions;

AFu is an Air/fuel ratio detected by the upstream sensor (55u); and

l†legr_target is an average mass flow of EGR gas expected to flow in the EGR passage (80) while Cmax is being determined.

5. The method for determining an EGR flow (PΊ egr_actual) according to any one of claims 1 to 3, wherein Cmax is determined by integrating the difference between:

- the mass flow (rh_Xn_u) of the component (Xn) entering the exhaust after- treatment device (52), and

- from an empty state when the exhaust after-treatment device (52) has released all the component (Xn) until a full state when the exhaust after-treatment device (52) has stored as much as component (Xn) as it can; or

- from a full state when the exhaust after-treatment device (52) has stored as much as component (Xn) as it can until an empty state when the exhaust after-treatment device (52) has released all the component (Xn).

6. The method for determining an EGR flow (GP egr_actual) according to claim 5, wherein the mass flows (l†l_Xn_u) and (ITl_Xn_d) of the component (Xn) entering and exiting respectively the after-treatment device (52) are calculated based on equations:

wherein

Cxn__u is the concentration of component (Xn) in the exhaust gas upstream the exhaust after-treatment device (52) measured by sensor (55u);

Cxn__d the concentration of component (Xn) in the exhaust gas downstream the exhaust after-treatment device (52) measured by sensor (55d);

Mex_hgas._d is the average molar mass of the exhaust gas downstream the exhaust after-treatment device (52);

M_xn is the molar mass of component (Xn) GP e_xh-gas is the mass flow of exhaust gases through the exhaust after-treatment device (52) calculated based on below formula:

(5) r†lexh_gas = ITlair + itlf + l†legr_Target wherein

ITlair is the mass flow of air entering in the intake path (4);

rhf is the mass flow of fuel injected in the internal combustion engine (1);

i†legr_target is the expected mass flow of EGR gases through the EGR passage (80).

7. The method for determining an EGR rate error (l†legr%_error), comprising determining an EGR flow l†legr_actual with the method according to any one of claims 1 to 6, and then by carrying out the following steps:

S120) calculating an EGR rate l†legr% as a percentage of the total mass flow of gases flowing into the engine (1), using formula below:

(6) r†legr%_actual = f†legr_actual / (l†legr_actual + ITlair)

S130) calculating an EGR rate error l†legr%_error using formula below:

(7) rhegr%_error = rhegr%_actual - l†legr%_target

wherein

ITlair is the mass flow of air entering in the intake path (4); and

l†legr_target is the expected mass flow of EGR gases through the EGR passage (80).

8. A control method for controlling an internal combustion engine (1) mounted with a gas circuit (3) to supply intake gas to the internal combustion engine (1) and to remove exhaust gas from the internal combustion engine (1);

the method comprising the steps of:

A) calculating an EGR rate error (l†legr%_error) by the method according to claim 7;

E) calculating an adjusted position (a_adjusted) of the EGR valve (82) which is an opening value of the EGR valve (82) adjusted based on the EGR rate error (l†legr%_error) so that an actual EGR rate be equal to a target EGR rate; and

F) controlling the position of the EGR valve (82) so as to attain the adjusted opening position ((X_adjusted).

9. An EGR system failure On-Board Diagnostic (OBD) detection method for an internal combustion engine (1) mounted with a gas circuit (3) to supply intake gas to the internal combustion engine (1) and to remove exhaust gas from the internal combustion engine (1);

the method comprising the steps of:

A) calculating an EGR rate error (rilegr%_error) by the method according to claim 7;

H) issuing a warning signal in case EGR rate error (l†legr%_error) is above a predetermined threshold.

10. An internal combustion engine (1) mounted with a gas circuit (3), the internal combustion engine (1) comprising an electronic control unit (9) configured to calculate an EGR rate (rilegr arget) based on a EGR model including a plurality of parameters, the gas circuit (3) comprising:

wherein, with a CMax parameter being a parameter representative of a capacity of the exhaust after-treatment device (52) to store the component (Xn), the electronic control unit (9) is configured to:

S40) determine at least a first value Cmax_closed_l of Cmax when the EGR valve (82) is fully closed;

S60) determine at least a first value Cmax_open_l of Cmax when the EGR valve (82) is in a fully or partially open position; and

SI 10) determine the actual EGR flow l†legr_actual using formula: (1) rflegr_actual = (Cmax_closed/Cmax_open - 1) * (GP exh_gas) + l†legr_target;

Cmax_open is an average value of Cmax based on said at least a first value Cmax_open_l of Cmax determined with the EGR valve in said fully or at least partially open position.

11. The internal combustion engine according to claim 10, wherein the electronic control unit (9) is further configured to:

when the electronic control unit (9) determines the actual EGR rate l†legr_actual, the Cmax_closed value used in formula (1) is Cmax_closed_average; and

the electronic control unit (9) is configured to determine Cmax_open after having determined Cmax_closed_l and before determining Cmax_closed_2.

12. The internal combustion engine according to claim 10 or 11, wherein the component (Xn) is ammonia (NH₃), and the upstream and downstream sensors (55u,55d) are sensors capable of measuring a concentration of ammonia in a gas.

13. An internal combustion engine according to claim 10 or 11, wherein the component (Xn) is nitrogen oxides (NOx), and the upstream and downstream sensors (55u,55d) are sensors capable of measuring a concentration of nitrogen oxides in a gas.

14. The internal combustion engine according to claim 10 or 11, wherein the component (Xn) is oxygen (0₂); and the upstream sensor and the downstream sensor (55u,55d) are sensors capable of measuring oxygen concentration in a gas.

15. The internal combustion engine according to claim 14, wherein the control unit is configured to determine Cmax by integrating variations of the oxygen content of the exhaust after-treatment device (52) between two states of oxygen storage of the exhaust after-treatment (52) which can be either:

(2) dOSAegr = 0.23 * (rtlair + l†lf + rhegr_target) * (AFu - AFstoich) / (1+ AFu) wherein:

itlair is the mass flow of air entering in the intake path (4);

Itlf is the mass flow of fuel injected in the internal combustion engine (1);

AFu is an Air/fuel ratio detected by the upstream sensor (55u); and

rilegr_target is an average mass flow of EGR gas expected to flow in the EGR passage (80) while Cmax is being determined.

16. The internal combustion engine according to any one of claims 10 to 15, wherein the control unit is configured to determine Cmax by integrating the difference between :

17. The internal combustion engine according to claim 16, wherein the control unit is configured to calculate the mass flows (l†l_Xn_u) and (ltl_Xn_d) of the component (Xn) entering and exiting (respectively) the after-treatment device (52) based on equations:

wherein

Mexhgas.u is the average molar mass of the exhaust gas upstream the exhaust after- treatment device (52);

M_ex_hgas_d is the average molar mass of the exhaust gas downstream the exhaust after-treatment device (52);

M_xn is the molar mass of component (Xn)

rh exh_gas is the mass flow of exhaust gases through the exhaust after-treatment device (52) calculated based on below formula:

(5) ri1exh_gas = ITlair + ITIf + fTlegr_Target wherein

ITlair is the mass flow of air entering in the intake path (4);

l†lf is the mass flow of fuel injected in the internal combustion engine (1);

18. The internal combustion engine according to any one of claims 10 to 17, wherein the electronic control unit (9) is further configured to:

S120) calculate an EGR rate rhegr% as a percentage of the total mass flow of gases flowing into the engine (1), using formula below:

(6) l†legr%_actual = rhegr_actual / (fhegr_actual + ITlair); S130) calculate an EGR rate error ITIegr%_error using formula below:

(7) l†legr%_error = i†legr%_actual - l†legr%_target.

19. The internal combustion engine according to claim 18, wherein the electronic control unit (9) is further configured:

. to calculate an adjusted position (CX_adjusted) of the EGR valve (82) which is an opening value of the EGR valve (82) adjusted based on the EGR rate error (l†legr%_error) so that an actual EGR rate be equal to a target EGR rate; and . to control the position of the EGR valve (82) so as to attain the adjusted opening position ((X_adjusted).

20. The internal combustion engine according to claim 18, wherein the electronic control unit (9) is further configured to issue a warning signal in case EGR rate error (l†legr%_error) is above a predetermined threshold.