GB2503219A

GB2503219A - Method of operating an internal combustion engine

Info

Publication number: GB2503219A
Application number: GB1210805.6A
Authority: GB
Inventors: Alberto Vassallo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-06-18
Filing date: 2012-06-18
Publication date: 2013-12-25
Also published as: GB201210805D0

Abstract

A method of operating an internal combustion engine 110, wherein the method comprises a calibration procedure of an air mass flow sensor 340 located in an air intake duct 205, wherein the calibration procedure comprises the steps of: - estimating a reference value of a parameter indicative of an air mass flow in the air intake duct 205, - measuring, by means of the air mass flow sensor 340, a value of the parameter indicative of an air mass flow in the air intake duct, - repeating the steps of estimating a reference value and of measuring for a predetermined number of times, - using each couple of estimated reference values and measured values for determining a correction function to adjust the measured values. The method may be performed during an engine cut off condition, in a stable condition or where no exhaust gas is recirculated in the engine. The estimation may take account of intake manifold pressure, total displacement of the engine, engine speed, intake manifold pressure and engine volumetric efficiency.

Description

METHOD OF OPERATING AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of operating an internal combustion engine. :10

BACKGROUND

Automotive engine systems comprise an internal combustion engine having an engine block defining at least one cylinder having a piston coupled to rotate a crankshaft.

A cylinder head cooperates with the piston to define a combustion chamber. A fuel and air mixture is disposed, in the combustion chamber and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston. Air is provided through at least one intake port which is connected to an intake manifold. An air intake duct may provide air from the ambient environment to the intake manifold. Fuel can be injected into the cylinder by a fuel injector. Fuel may be provided at high pressure to the fuel injector from a fuel rail in fluid communication with a high pressure fuel pump that increases the pressure of the fuel received from a fuel source.

An exhaust gas recirculation (EGR) system may also be provided, the system being coupled between the exhaust manifold and the intake manifold. The EGR system may include an EGR cooler to reduce the temperature of the exhaust gases in the EGR system. An EGR valve regulates a flow of exhaust gases in the EGR system.

To control the engine, an Electronic Control Unit (ECU) is generally provided, the ECU being connected to various sensors and being configured in such a way to provide calculations of various engine parameters such as fuel quantity to be injected in the cylinder.

In order to calculate the fuel quantity, the airflow into engine must be taken into account.

A known method to do so is speed-density airflow calculation, namely the use of an equation that correlates the manifold absolute pressure (MAP) and the intake air temperature with the known volumetric efficiency of the engine to calculate airflow; using airflow data it is possible to calculate fueling requirements.

In speed-density systems, volumetric efficiency must be known and is generally recorded in a reference table stored in data carrier or memory associated to the ECU, the reference table being generally a calibratable map.

Another method of determining airflow relies on measurement of the actual air flow.

In this case, a mass airflow sensor coupled with a temperature sensor, is generally provided in the air intake duct.

The mass air flow sensor is generally an Hot-Film air Mass flow meter (HFM) that is connected to an Electronic Control Unit of the engine and is. used to provide signals representative to the air mass flow èuitable to be used in controlling the engine performance.

However, due to engine packaging constraints, the HFM is usually installed too close to a blow-by return pipe, which causes the progressive build-up of oil deposits on the sensor itself, with a consequent deterioration in air flow measurements, namely causing an underestimation of air flow measurement.

As a consequence, Exhaust Gas Recirculation (EGR) rate during engine life is progressively reduced, increasing NO emissions.

Furthermore air mass flow underestimation may give rise to lack of performance stability or in other words to jerking, in particular during low-speed acceleration, due to fuel injection reduction used for smoke protection.

An object of an embodiment of the invention is to enhance the stability and accuracy of the Hot air mass flow rneter (HFM) measurements during vehicle life in order to improve the stability of engine emissions and performance, as well as avoiding drivability problems, in particular jerking.

Another object is to provide an improvement in the accuracy of the data representative of the mass air flow without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Another object of the present disclosure is to meet these goals by means of a simple, rational and inexpensive solution.

These objects are achieved by a method, by an engine, by an apparatus, by an automotive system, by a computer program and a computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

S An embodiment of the disclosure provides for a method of operating an intemal combustion engine, wherein the method comprises a calibration procedure of an air mass flow sensor located in an air intake duct, wherein the calibration procedure comprises the steps of: -estimating a reference value of a parameter indicative of an air mass flow in the air intake duct, -measuring, by means of the air mass flow sensor, a value of the parameter indicative of an air mass flow in the air intake duct, -repeating the steps of estimating a reference value and of measuring a value for a predetermined number of times, -using each couple of estimated reference values and measured values for determining a correction function to adjust the measured values.

An advantage of this embodiment is that the performance of the air mass flow sensor is regularly checked under specific engine operating conditions.

The information that are obtained are then used to correct the air mass flow sensor output during entire engine operation, allowing a more precise engine operation due to more precise calculation of fuel injections based on corrected air mass flow values.

This result is obtained by leveraging the present engine hardware in the sense that no additional sensor are required.

In addition, engine drivability quality and low-end torque acceleration consistency is improved over time with respect to the prior art, with benefits in the customer perceived quality.

According to an embodiment of the invention, the wherein the steps of estimating a reference value and of measuring a value of the parameter representative of an air mass flow are performed during an engine cut-off condition.

An advantage of this embodiment is that it allows to create a condition in which the air mass flow is substantially equal to the one measured with the speed-density methodology.

According to another embodiment of the invention, the steps of estimating a reference value and of measuring a value of the parameter representative of an air mass flow are performed when the air flow into the engine is in a stable condition.

An advantage of this embodiment is that the reference value is calculated in conditions in which the volumetric efficiency reference table gives accurate values.

More specifically a stable airflow is defined as an engine working condition in which a constant airflow rate is present in order to make the measurement as accurate as possible. In this way the correction function is calculated in a more precise way with respect to flow rate transients.

According to another embodiment of the invention, the steps of estimating reference value and of measuring a value of the parameter representative of an air mass flow are performed when an engine coolant temperature is greater than a predefined temperature threshold.

According to another embodiment of the invention, the steps of estimating a reference value and of measuring a value of the parameter representative of an air mass flow are performed in an engine operating condition in which no exhaust gas is recirculated in the engine.

An advantage of this embodiment is that, also in this case, the reference value is calculated in conditions in which the volumetric efficiency reference table gives accurate values.

According to still another embodiment of the invention, the steps of calculating a reference value and of measuring a value of the parameter representative of an air mass flow are performed when no leakage is detected in an exhaust gas recirculation system associated to the engine.

An advantage of this embodiment is that it gives a further assurance that the reference value is calculated in conditions in which the volumetric efficiency reference table gives accurate values.

According to another embodiment of the invention, the correction function is defined bytheformula: lvIaIrI-IFM.ccrr -IvuaIrHFMTleas Lr_n + -wherein MairHFM.meas represents a value of the air mass flow parameter [kg/hi which is measured by the air mass flow sensor, MairNFM,wrr [kg/hi represents a corrected value of the air mass flow parameter, CF_A [-] and CF_B [-] are coefficients calculated by means of a linear regression analysis of a plurality of couples of estimated reference values and measured values.

An advantage of this embodiment is that it allows to determine a corrected air mass flow value at any time during the use of the vehicle.

According to another embodiment of the invention, the calculation of the reference value MairHFMSPONS [kg/h] is performed by means of the following equation: MairSPONS = PCR_pAct.100. iV -Epm_nEng 3O 1. V1Eff 287 AFS_tEng+273.16 where PCRjAct [kPa] is an intake manifold pressure, iv [I] is a total displacement of the engine, Epm_nEng [rpm] is an engine speed, AES_tEng [Celsius] is an intake manifold temperature and VolEff [-J is an engine volumetric efficiency.

An advantage of this embodiment is that it gives a formula to calculate the air mass flow according to the speed-density methodology and using data available to the Electronic Control Unit (ECU) of the vehicle.

According to another embodiment of the invention, the measurements made by the air mass flow sensor are corrected using the correction function to determine a quantity of fuel to be injected into the engine.

An advantage of this embodiment is that it allows to operate on the engine, at any time and in any condition o.f the engine, with a corrected air mass flow value.

This allow a more precise operation of the engine, avoiding or greatly reducing jerking problems even in severe city cycle driving and allows an improvement in reducing NO emissions.

Another embodiment of the invention provides an apparatus for operating an internal combustion engine, comprising means for performing a calibration procedure of an air mass flow sensor located in an air intake duct, wherein the apparatus comprises: -means for estimating a reference value of a parameter indicative of an air mass flow in the air intake duct, -means for measuring, by means of the air mass flow sensor, a value of.the parameter indicative of an air mass flow in the air intake duct, -means for repeating the steps of estimating a reference value and of measuring a value of the parameter representative for a predetermined number of times, -means for using each couple of estimated reference values and measured values to determine a correction function for measurements made by the air mass flow sensor.

Another embodiment of the invention provides an internal combustion engine connected to an air intake duct equipped with an air mass flow sensor, the engine being associated to an electronic control unit configured to: -estimate a reference value of a parameter indicative of an air mass flow in the air intake duct, -measure, by means of the air mass flow sensor, a value of the parameter indicative of an air mass flow in the air intake duct, -repeat the steps of estimating a reference value and of measuring a value of the parameter representative for a predetermined number of times, - -use each couple of estimated reference values and measured values to determine a correction function for measurements made by the air mass flow sensor.

These last two embodiments have substantially the same advantages of the various embodiments of the method of the invention.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1; Figure 3 is a schematic representation of the main components of the automotive system of Figure 1 used in an embodiment of the method; Figure 4 is a flowchart illustrating a data generation procedure according to an embodiment of the method according to the invention; Figure 5 is a flowchart illustrating a data generation procedure according to another embodiment of the method according to the invention; Figure 6 is diagram representing a the calculation of correction factors of the air mass flow measured by the air mass flow sensor; and Figure 7 is a flowchart illustrating an embodiment of the method according to the invention.

DETAILED DESCRIPTION

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. Each of the cylinders has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake pod(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NO traps, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems, and particulate fitters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature 01 the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110.

The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow sensor 340 coupled with a temperature sensor 345, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system, or data carrier 460, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carry out the steps of such methods and control the ICE 110.

More specifically, Figure 3 represents the main components of the automotive system of Figure 1 used in an embodiment of the method.

Airflow enters the air intake duct 205 and subsequently the intake manifold 200 and then the engine 110 itself, while sensors 304,345 respectively measure air flow mass and air flow temperature and send data representative of these measures to the ECU 450. A manifold pressure and temperature sensor 350 is also represented and connected to the ECU 450.

Exhaust gas exits through the exhaust manifold 225 while a portion of exhaust gas may be recirculated through the EGR system 300, equipped with the EGR cooler 310, opening the EGR valve 320 that is commanded by the ECU 450.

In some engine conditions, the ECU 450 may command the EGR valve 320 to be closed, therefore operating the engine in a closed EGR state For example, the EGR valve 320 may be closed in steady state operating conditions of the engine or also in a cut-off condition, namely when the accelerator pedal is not pressed.

Figure 4 is a flowchart illustrating a data generation procedure according to an embodiment of the method according to the invention.

The data generated with this procedure can be used to calibrate the air mass flow sensor 340.

Initially a first operating condition of the engine is evaluated by the ECU 450, namely if the engine is in a cut-off state (block 500).

If an engine cut-off state is detected, namely if the accelerator pedal position sensor 445 sends a signal to the ECU 450 that indicates that the accelerator pedal is not pressed, a derivative of the engine speed with respect to time D(Epm_nEng)IDT [rpmls] is evaluated and is compared to a threshold value thereof THR_1.

This check on the engine speed derivative D(Epm_nEng)/DT Irpm/s] is used to determine if state in which the airflow is stable (block 510) is present and therefore a state in which the volumetric efficiency map stored in a data carrier 460 associated to the ECU 450 can accurately be used.

If the derivative of the engine speed with respect to time D(Epm_nEng)/DT [rpm/s] is lower than the threshold THR_1, an engine coolant temperature Englemp [Celsius] is measured and is compared to a threshold temperature THR_2 (block 520). More in particular, this condition is satisfied if the engine coolant temperature EngTemp [Celsius] exceeds the threshold temperature THR_2, namely if EngTemp > THR_2.

The check on the engine coolant temperature Englemp [Celsius] is used to determine a state in which the engine warm-up is sufficiently accomplished and therefore a state in which volumetric efficiency readings of the map are accurate.

If these conditions are all satisfied, a reference air flow mass value MairspONS [kg/h] is calculated (block 530), using the speed-density method, according to the following equation (1): MairSPUNS = PCRpAct.100. Epm_nEng *30 I. 287 AFStEng + 273.16 where PCR.pAct [kPa) is the intake manifold pressure measured by sensor 350, iV [I] is the total displacement of the engine, Epm_nEng [rpm] is the engine speed, AFS_tEng [Celsius] is the intake manifold temperature measured by sensor 350 and VolEff [-] is the engine volumetric efficiency that can be read from the stored map thereof.

At the same time a value MairHFMJaW of air mass flow is measured by the air mass flow sensor (HFM) 340.

Then both the value MairHFM,raw [kg/s] and the speed-density calculated value MairspoNs [kg/h] are stored in a memory (or data carrier) 460 associated to the ECU 450 (block 540).

The above procedure may be repeated a number of times N in order to create a series o data representative of an engine cut-off condition, as represented in the diagram of figure 6.

The number of times that this procedure may be repeated may be calibrated according to the particular automotive system employed.

The above data generation procedure creates a plurality of couples of values MairHFM,SPDNS [kg/h] and MairKFM,rBw (kg/h], wherein each couple of values are determined at the same time.

The couple of values MairHFM,5PDNS [kg/hi and MairHFMraW [kg/h] are then used to determine a corrected air flow value MairHFM,corr (kg/h] that may be used to correct the air mass flow sensor output during entire engine operation, allowing a more precise engine operation due to more precise calculation of fuel injections based on corrected air mass flow values.

The determination of the corrected air flow value MairHFMCOIr [kg/h] based on the data population of couples of values MairHFM.SPDNS (kg/h], MairHFMraw (kg/h], will be better explained hereinafter with reference to Figure 6.

Figure 5 is a flowchart illustrating a data generation procedure according to another embodiment of the method according to the invention. Also the data generated with this procedure can be used to calibrate the air mass flow sensor 340.

Initially a first engine operating condition is evaluated by the ECU 450, namely the derivative of the engine speed with respect to time D(Epm_nEng)/DT (rpm/si is compared to a threshold value thereof THR_1 and, at the same time, the engine coolant temperature Englemp (Celsiusj is measured and is compared to a threshold temperature THR_2 (block 600).

This condition is satisfied if D(Epm_nEng)/DT Irpm/slis lower than the threshold value thereof THR_1, namely if D(Epm_nEng)/DT c THR_1 and if, at the same time, the engine coolant temperature EngTemp [Celsiusj exceeds the threshold temperature THR_2, namely if EngTemp> THR_2.

The condition on engine speed Epm_nEng (rpm] derivative and on engine coolant temperature are used to make sure that the airflow is stable and therefore that the volumetric efficiency map stored in the data carrier 460 of the ECU 450 can be accurately used.

If this first condition is satisfied, a check is made (block 610) in order to verify if the EGR system is used, namely if the EGR valve 320 is closed or, in other words, if EGRVIv = 0.

The condition on EGR valve duty EGRVIv [-] is used to detect conditions in which no EGR is used as per volumetric efficiency mapping.

If also this condition is satisfied, a further check is made (block 620) to make sure that EGR valve is actually sealing perfectly the circuit and no EGR leakage is compromising the volumetric efficiency estimation as per steady-state mapping.

This condition may be expressed as (AFS_tEng -AFS_tAir) c THR_3I where AFS_tEng [Celsius] is an air flow temperature measured by a temperature sensor in the intake manifold 200, AFS_tAir [Celsius] is an air flow temperature measured by a temperature sensor in the air intake duct 205, and THR_3 is a threshold value thereof.

If these conditions are all satisfied, a reference air flow mass value MairSPDNS [kg/h] is calculated (block 630), according to the following equation: MairSPDNS = PCRjACt *100* iS' Epm_nEng *30 1 287 AFS_tEng+273.16 where PCRpAct [kPa] is the intake manifold pressure, iv [I] is the total displacement of the engine, Epm_nEng [rpm] is the engine speed, AFS_tEng [Celsius] is the intake manifold temperature and VolEff [-] is the engine volumetric efficiency.

At the same time a value of MairHFM.raw is measured by the HFM sensor.

Then both the value MairHFM,raW and the speed-density evaluated M3irSPONS value are stored in a memory (or data carrier) 460 associated to the ECU 450 (block 640).

Figure 6 is diagram representing the calculation of correction factors of the air mass flow measured by the air mass flow sensor.

In particular, in Figure 6 a first curve 700 is represented in which MairHrM.raw and MairSpDNS values are plotted when the air mass flow sensor is in a new condition. Since these two values coincide by calibration at the start of the life of the HFM sensor, curve 700 is represented as a straight line with a 45° degrees slope in the MairHFM,raw, MairSPONS plane.

A series of values of MairHFM raw MairSPDNS obtained by one of the data collection procedures described before with reference to figures 4 or 5, are also plotted in the MairHFM,raw, MairspoNs plane of Figure 6.

Experimental activity has shown that these values are approximately placed along a line.

The determined values may then be interpolated using known linear interpolation formulas in order to find a straight line 740 that best fits these data. Straight line 740 represents an interpolation curve for a situation in which the air mass flow sensor is not anymore new, for example after 50.000km.

The linear interpolation of the previously acquired and stored MairHFMraW and MairSPDNS values from speed-density and raw measurements, respectively, gives factors CF_A (slope) and CF_B (intercept) for defining the line 740.

Formulas that may be used for respectively calculating CF_A and CF_B may be the following: ((x2D* ((y)) ((x1))*(L@1y)) CF_B = 1=1 i=t N 1=1 N * ( (x2)) -( (x))2 N*((xy1)) -( Ex3)*(&J) CF_A = i=t N N N* ((x2)) ((xfl2 where x represents MairSPDNS [kg/hJ and Yj represents MairPHFM,12W [kg/h].

The storing task frequency for storing couples of data MairHrMr, and MairSPDNS, may be calibrated depending on various criteria, for example in order to get a statistically-representative population a certain number of samples N in a certain amount of sample time (i.e. 100 samples in 1 hour driving) may be taken.

The data plotted are for better clarity subdivided in two sets, a first set 710 is relative to data determined in a cut-off condition, the second set 730 is relative to data determined in a steady state operating conditions in which EGR is not present but the engine is not in a cut-off condition.

For completeness a curve 750 representative of MairFM,raw, MairspONs data taken afterafurther use of the vehicle, for example after 100.000 km, is represented in order to show a further drift of the sensor measurements from the ideal case of curve 700 during time.

Factors CF_A (slope) and CF_B (intercept) so calculated can be used to correct any measured air mass flow value MairHrM,meas [kg/h] to obtain a corrected mass air flow value MairHFM,cc,rr [kg/h] according to the following formula: MairHFM,(r = MairHFM.fleas * CF_A + CF_B Therefore, a corrected air mass flow value MairHFM,CO(r is instantaneously evaluated using the above-reported equation.

The values of MairHFM,00rr thus obtained can be then used also in the EGR relevant area where the speed-density methodology is not applicable or in low-end area where smoke map may be activated based on air mass flow (HFM) corrected readings.

The internal combustion engine 110 may thus be operated using the determined correction value MairHFMCCff.

For example, measurements made by the air mass flow sensor 340 may be corrected using the correction function to determine a quantity of fuel to be injected into the engine 110.

Figure 7 is a flowchart illustrating an embodiment of the method according to the invention.

At the start of the method, a check is made on the EGR system to determine if an engine operating condition in which no exhaust gas is recirculated in the EGR system 300 is verified (block 800).

This may be performed by means of the checks described with reference to blocks 600,610 and 630 of Figure 5.

Altematively, if the engine is in a cut-off condition such as exemplified in block 500 of Figure 4, it may also be assumed that no exhaust gas is recirculated in the EGR system 300.

If this condition is verified, a reference value MairSPDNS of a parameter indicative of an air mass flow in the air intake duct 205 is determined, for example by employing the speed-density methodology.

At the same time, the air mass flow in the air intake duct 205 is measured by means of the air mass flow sensor 340.

Both these values are stored in a data carrier 460 of the ECU 450 (block 820).

The procedure is repeated for a predefined number times to create a population having a sufficient number of data (block 830).

In this way a population of data relative to the values MairSPDNS, MaIrHFM!raW is memorized.

These data are subjected to a linear interpolation, in order to determine factors CF_A and CF_B (block 840).

Factors CF_A and CF_ are then used to correct any measured air mass flow value MairhEMmeas value to obtain a corrected mass air flow value Ma1rHFMCOff (block 850) according to the formula: E -KR *flC A uvaIrHrMcorr -IvIaIrHrM.meas #I-_r' + Finally the internal combustion engine 110 is operated (block 860), using the correction value MairHFM.

No additional sensor cost is involved for the performance of the various embodiment of the method disclosed.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

automotive system internal combustion engine (ICE) engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector fuel rail fuel pump iGOfuelsource intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 iritercooler 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow sensor 345 temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carner 500 block 510 block 520 block 530 block 540 block 600 block 610 block 620 block 630 block 640 block 700 curve 710 first set of points 720 points 730 second set of points 740 curve 750 curve 800 block 810 block 820 block 830 block 840 block 850 block 860 block

Claims

CLAIMSl.A method of operating an internal combustion engine (110), wherein the method comprises a calibration procedure of an air mass flow sensor (340) located in an air intake duct (205), wherein the calibration procedure comprises the steps of: -estimating a reference value (MairspONS) of a parameter indicative of an air mass flow in the air intake duct (205), -measuring, by means of the air mass flow sensor (340), a value (MairHEM raw) of the parameter indicative of an air mass flow in the air intake duct (205), -repeating the steps of estimating a reference value (MairSPONS) and of measuring a value (MairHFM,raw) for a predetermined number of times, -using each couple of estimated reference values (MairSpDNS) and measured values (MairHFM,raw) for determining a correction function to adjust the measured values.
2. A method according to claim 1, wherein the steps of estimating a reference value (MairspoNs) and of measuring a value (MairHFM raw) of the parameter representative of an air mass flow are performed during an engine cut-off condition.
3. A method according to claim 1 or 2, wherein the steps of estimating a reference value (MairSPDNS) and of measuring a value (MairHFM raw) of the parameter representative of an air mass flow are performed when the air flow into the engine (110) is in a stable condition.
4. A method according to any of the preceding claims, wherein the steps of estimating reference value (MairSPONS) and of measuring a value (MairHFM.raw) of the parameter representative of an air mass flow are performed when an engine coolant temperature is greater than a predefined temperature threshold (THR_2).
5. A method according to any of the preceding claims, wherein the steps of estimating a reference value (MairSPONS) and of measuring a value (MairHFM.raw) of the parameter representative of an air mass flow are performed in an engine operating condition in which no exhaust gas is recirculated in the engine (110).
6. A method according to any of the preceding claims, wherein the steps of calculating a reference value (MairspONs) and of measuring a value (MairHFMF3W) of the parameter representative of an air mass flow are performed when no leakage is detected in an exhaust gas recirculation system (300) associated to the engine (110).
7. A method according to any of the preceding claims, wherein the correction function is defined by the formula: PtA -PtA * *VIaurHFMfl--IVIaIrHFMmeas -+ -wherein MairHFM rnea, represents a value of the air mass flow parameter measured by the air mass flow sensor (340), MairHFM,CO(r represents a corrected value of the air mass flow parameter, and CF_A and CF_B are coefficients calculated by means of a regression analysis of a plurality of couples of estimated reference values (MairSpONs) and measured values (M8irHFM raw).
8. A method according to any of the preceding claims, wherein the estimation of the reference value (MairspONS [kg/hi) is determined by means of the following equation: MairSPDNS = PCR_pAct 100' iV-Epm_nEng.30* 1 VolEff 287 AFS_tEng+273.16 where PCR_pAct is an intake manifold (225) pressure, iv is a total displacement of the engine, Epm_nEng is an engine speed1 AFS_tEng is an intake manifold (225) temperature and VolEff is an engine volumetric efficiency,
9. A method according to claim 1, wherein the measurements made by the air mass flow sensor (340) are corrected using the correction function to determine a quantity of fuel to be injected.
10. An internal combustion engine (110) connected to an air intake duct (205) equipped with an air mass flow sensor (340), the engine (110) comprising an Electronic Control Unit (450) configured for carrying out the method according to any of the preceding claims.
11. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-9.
12. Computer program product on which the computer program according to claim 11 isstored.
13. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (460) associated to the Electronic Control Unit (450) and a computer program according to claim 11 stored in the data carrier (460).
14. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 11.30. 20