GB2526322A - Method of diagnosing clogged fuel injectors - Google Patents

Abstract

A method of diagnosing a fault of fuel injectors 160 (see Figure 1) of an internal combustion engine 110 (see Figure 1), wherein the method comprises the following steps: a) operating the engine at idle speed, with a maximum injection pressure (prail_max); b) de-rating all but one fuel injector to a predetermined value of a fuel injection quantity (Qderat); c) increasing a fuel injection request (fuelreq), by means of a control strategy for operating the engine at idle speed; d) repeating steps b) and c) for each group of all but one fuel injector; e) diagnosing a fault of an injector if an instantaneous increase of the engine speed (Δrpmlocal), during a crank angle window corresponding to the actuation of said injector, is smaller than an engine speed threshold (Δrpmlocal_thr). Diagnosing a fault in all the injectors if the fuel injection request is larger than a fuel injection request threshold.

Description

METHOD OF DIAGNOSING CLOGGED FUEL INJECTORS

TECHNICAL FIELD

The present disclosure relates to a method of diagnosing a fault of fuel injectors of an internal combustion engine, in particular a fuel injector of a common rail system (CR8) utilized for Diesel engines, whenever its flow-rate is reduced due to clogging of the injector nozzle.

BACKGROUND

It is known that modern engines are provided with a fuel injection system for directly injecting the fuel into the cylinders of the engine. The fuel injection system generally comprises a fuel common rail and a plurality of electrically controlled fuel injectors, which are individually located in a respective cylinder of the engine and which are fluid and hydraulically connected to the fuel rail through dedicated injection pipes.

Each fuel injector, particularly injectors of a Common rail system, generally comprises an injector housing, a nozzle and a movable needle which repeatedly opens and closes this nozzle; the fuel, coming from the rail and passing through the injection pipe and, inside the injector housing, a delivery channel, reaches the nozzle and can thus be injected into the cylinder giving rise to single or multi-injection patterns at each engine cycle.

The needle is moved with the aid of a dedicated actuator, typically a solenoid actuator, which is controlled by an electronic control unit (ECU). The ECU operates each fuel injection by generating an electric opening command, causing the actuator to open the fuel injector nozzle for a predetermined amount of time, and a subsequent electric closing command, causing the actuator to close the fuel injector nozzle.

The time between the electric opening command and the electric closing command is generally referred as energizing time (ET) of the fuel injector, and it is determined by the ECU as a function of a desired quantity of fuel to be injected.

Typically, fuel injectors become clogged or restricted by a buildup of fuel varnish deposits.

This reduces the amount of fuel that the injector sprays, which in turn may cause the engine to run lean and misfire, hesitate or stall. Problems can occur even with a slight buildup of deposits. For good combustion, the injectors must produce a fine cone-shaped mist of fuel vapor. Wear or deposits in the nozzle can create "streamers" of liquid fuel that vaporize and burn poorly. This, in turn, can cause hesitation, emissions and performance problems. Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and can't deliver their normal dose of fuel, then performance, fuel economy and emissions are all going to suffer. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it cannot correct the underlying condition that is causing the problem.

Current control strategies are not able to identify a clogged injector in a reliable way. For example, the injector flow test (lfl) and the cylinder balancing (CB) diagnosis. Based on current judgment criteria, IFT can only detect the worst of four injectors within the set. If more than one injector is faulty, no detection is possible. As far as CB is concerned, which performs cylinder-by-cylinder torque equalization, the reason for not being reliable is that the cylinder balancing diagnosis is working during idle speed conditions, and the influence of the clogging rate itself, running in an area of smaller energizing time and injection pressure, is very small in comparison to larger ET and injection pressure areas.

Therefore a need exists for a method of diagnosing a fault of fuel injectors which does not suffer of the above inconvenience.

An object of an embodiment of the invention is to provide a method of diagnosing a fault of fuel injectors of an internal combustion engine, that allows to identify one or more clogged injectors, without disassembling them, and therefore can be advantageously used for service operations.

Another object is to provide an apparatus which allows to perform the above method.

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

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

SUMMARY

An embodiment of the disclosure provides a method of diagnosing a fault of fuel injectors of an internal combustion engine, wherein the method comprises the following steps: a) operating the engine at idle speed, with a maximum injection pressure, b) de-rating all but one fuel injectors to a predetermined value of a fuel injection quantity, c) increasing a fuel injection request, by means of a control strategy for operating the engine at idle speed, d) repeating steps b) and c) for each group of all but one fuel injectors, e) diagnosing a fault of an injector if an instantaneous increase of the engine speed, during a crank angle window corresponding to the actuation of said injector, is smaller than an engine speed threshold.

Consequently, an apparatus is disclosed for performing the method of diagnosing a fault of fuel injectors of an internal combustion engine, the apparatus comprising: a) means for operating the engine at idle speed, with a maximum injection pressure, b) means for de-rating all but one fuel injectors to a predetermined value of fuel injection quantity, c) means for increasing a fuel injection request, by means of a control strategy for operating the engine at idle speed, d) means for repeating steps b) and c) for each group of all but one fuel injectors, e) means for diagnosing a fault of an injector if an instantaneous increase of the engine speed, during a crank angle window corresponding to the actuation of said injector, is smaller than an engine speed threshold.

An advantage of this embodiment is that the method allows to obtain a remarkable cost reduction for warranty, since it provides a reliable criterion for detecting a fault of an injector 2 5 (e.g., due to clogging) and replacing just the single faulted injector instead of the whole injector set. Consequently, also shorter time at service are expected.

According to a further embodiment, the method comprise the further step of diagnosing a fault of all injectors if the fuel injection request is larger than a threshold of the fuel injection request.

Consequently, the apparatus also comprises eans for diagnosing a fault of all injectors if the fuel injection request is larger than a threshold of the fuel injection request.

An advantage of this embodiment is that the method, other than a first diagnostic criterion, based on the local increase of the engine speed, also provides a second diagnostic criterion, based on the fuel injection request, to detect if all injectors are faulty.

According to another embodiment, the predetemiined fuel injection quantity ranges from 50% to 60% of the nominal fuel injection quantity.

Consequently, said means for de-rating all but one fuel injectors are configured to operate with the predetermined fuel injection quantity ranging from 50% to 60% of the nominal fuel injection quantity.

An advantage of this embodiment is that the percentage of the de-rated fuel injector quantity is big enough to provide a strong reaction of the idle speed control and consequently a remarkable local increase of the engine speed.

According to still another embodiment, the engine speed threshold ranges between 130 and 180 rpm.

Consequently, said means for means for diagnosing a fault of fuel injectors are configured to operate with the engine speed threshold ranging between 130 and 180 rpm.

An advantage of this embodiment is that the range of the engine speed threshold is suitable for a wide engine power range.

According to a still further embodiment, the threshold of the fuel injection request ranges between 5 and 8 mm3lstroke for a single injector.

Consequently, said means for means for diagnosing a fault of fuel injectors are configured to operate with the fuel injection request ranging between 5 and B mm3/stroke for a single injector.

An advantage of this embodiment is that the range of the fuel injection request is suitable for a wide engine power range.

Another embodiment of the disclosure provides an internal combustion engine of an automotive system, the engine being equipped with a fuel injection system and a crank speed sensor, wherein a method of diagnosing a fault of fuel injectors according to any of the previous embodiments is actuated.

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 embedded in 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.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a partial section (upper side) of a fuel injector Figure 4 shows a flowchart of the method according to an embodiment of the present injection.

Figure 5 shows a flowchart of the method according to another embodiment of the present injection.

DETAILED DESCRIPTION OF THE DRAWINGS

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. The fuel injection system with the above disclosed components is known as Common Rail Diesel Injection System (CR System). It is a relative new injection system for passenger cars. The main advantage of this injection system, compared to others, is that due to the high pressure in the system and the electromagnetically controlled injectors it is possible to inject the correct amounts of fuel at exactly the right moment. This implies lower fuel consumption and less emissions.

Each of the cylinders 125 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 port(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 fixed geometry turbine 250 including a waste gate 290. In other embodiments, the turbocharger 230 may be a variable geometry turbine (VGT) with a VGT actuator arranged to move the vanes to alter the flow of the exhaust gases through the turbine.

The exhaust system 270 may include an exhaust pipe 276 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 NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems. 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 of 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 and equipped with a data carrier 40. 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, pressure, temperature sensor 340, 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 speed 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 waste gate 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 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 interlace 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 carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it 15 normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non- transitory in nature. -An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulated technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

Instead of an ECU 450, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

Fig. 3 shows a schematic upper section of a fuel injector 160, which comprises an injector solenoid 161 controlled by the ECU 450, and an injector actuator 162. As known and not shown, the injector also comprises a nozzle, provided with an injector needle 163. As already mentioned, the ECU operates each fuel injection by energizing the injector solenoid. The energizing time (ET) of the fuel injector is determined by the ECU as a function of a desired quantity of fuel to be injected.

According to an embodiment of the present invention, the method is suitable for an internal combustion engine 110 being equipped with a fuel injection system 165 and at least a crank position sensor 420. The method is aimed to detect faulty injectors, based on a new injector flow test and using a crank speed sensor 420 to detect engine speeds. The method does not require that the injectors are disassembled from the engine and for this reason is very suitable for service operations.

With reference to the flowchart 500 of Fig. 4, the method performs the following steps: at first, the engine shall be working S510 at idle speed and the injection pressure (or rail pressure) Pratmax shall be raised as much as possible in order to maximize the impact of the clogged injector behavior. The injection pressure shall be the maximum available injection pressure at engine idle speed. Then, all but one fuel injectors have to be de-rated according to a predetermined value of fuel injection quantity QderM. With the term de-rating is intended that the fuel quantity the injector should inject is reduced by a certain amount.

As an example, in a four-cylinder engine, three out of four injectors shall be forced to inject less (hereafter these are de-rated injectors) according to a calibrated value. The fourth injector will inject the nominal quantity (hereafter, this is a not de-rated injector).

The de-rated percentage should be remarkable, to obtain a significant reaction of the engine idle speed control. Preferably, the predetermined fuel injection quantity Qdet ranges from 50% to 60% of the current fuel injection quantity. A typical value can be 55%.

In this way, the percentage of the de-rated fuel injector quantity is high enough to provide a strong reaction of the idle speed control and consequently a remarkable local increase of the engine speed.

Consequently, the idle speed control strategy of the ICE will react by increasing 8530 the fuel injection request fuek to avoid an engine stall. Then, the system will be characterized by a local increase of the engine speed when the not de-rated injector is actuated. In other, words, there will be an instantaneous increase of the engine speed Arpmii, during a crank angle window corresponding to the actuation of said injector. The local engine speed increase Arpmii will be proportional to the clogging level of the not de-rated injector. In other words, a not de-rated and not clogged injector will cause a larger instantaneous increase of the engine speed than a not de-rated slightly clogged injector; in turn, the latter will cause a larger speed increase than a not de-rated heavily clogged injector.

The previous steps, i.e. the de-rating process shall be repeated S540 for each group of all but one fuel injectors. In practice, in the four -cylinder engine, calling the injectors as A, B, C, D, the de-rating process will be performed four times, once for each group of three injectors (ABC BCD CDA ADB). In this way, comparing the obtained local speed increase, one or more than one injectors can be detected as clogged injectors.

In fact, the method can diagnose S560 a fault of the fuel injector if an instantaneous increase of the engine speed Arpmi0i, during a crank angle window corresponding to the actuation of said injector, is smaller S550 than an engine speed threshold MpmIithr.

Referring to the four-cylinder engine, the results of the four de-rating process shall be compared: results characterized by a.local rpm increase lower than a threshold will indicate the presence of one or more clogged injector.

As a first example, let us suppose that only the injector B is clogged. The procedure can be the following: at first injectors A, B and Care de-rated. The control strategy of the engine idle speed will increase the fuel request and there will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector D. Being injector D not clogged, the local speed increase will be larger than the speed threshold and this will mean that injector D is not clogged. Of course nothing can be said about other injectors.

Therefore, the method will continue de-rating another triad of injectors, let us say B, C and D. In this case, there will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector A. Being injector A not clogged, the local speed increase will be larger than the speed threshold and this will mean that injector A is not clogged. Going on, the same procedure will be applied to another triad of injectors (for example, C, D, A). There will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector B. In this case, the local speed increase will be smaller than the speed threshold and this will mean that injector B is clogged. Finally the procedure will be applied to the last triad of injectors (A, D, B). There will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector C. Being injector C not clogged, the local speed increase will be larger than the speed threshold and this will mean that injector C is not clogged. Therefore, by applying the method, it has been discovered that injector B (and only injector B) is clogged.

As a second example, let us suppose that two injectors, B and C, are clogged. The procedure will be as follows: at first injectors A, B and C are de-rated. The control strategy of the engine idle speed Will increase the fuel request and there will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector 0.. Being injector 0 not clogged, the local speed increase will be larger than the speed threshold and this will mean that injector D is not clogged. The method will continue de-rating another triad of injectors, let us say B, C and D. In this case, there will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector A. Being injector A not clogged, the local speed increase will be larger than the speed threshold and this will mean that injector A is not clogged. Going on, the same procedure will be applied to another triad of injectors (for example, C, 0, A). There will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector B. In this case, the local speed increase will be smaller than the speed threshold and this will mean that injector B is clogged. Finally the procedure will be applied to the last triad of injectors (A, D, B). There will be an instantaneous speed increase, during the crank angle window corresponding to the actuation of injector C. Being injector C clogged, the local speed increase will be smaller than the speed threshold and this will mean that injector C is also clogged. Therefore, by applying the method, it has been discovered that injector B and C (and only injector B and C) are clogged.

Preferably, the engine speed threshold Arpmbsthr ranges between 130 and 180 rpm. This choice has been done in order to cover a wide engine power range. Of course, a more precise threshold value can be obtained by calibration tests on each specific engine application.

In the worst case, when all four injectors are clogged, first criterion could not be sufficient: in fact, supposing that the clogging level is almost the same for all injectors applying, the described procedure will not highlight any remarkable instaneous speed increase. On the other hand, to avoid engine stall, the control strategy of the engine idle speed will require a larger fuel amount. In other words, the total fuel request will increase above a threshold.

Therefore, with reference to Fig. 5, the method will diagnose 5620 a fault for all injectors if the fuel injection request fuelRq is larger S610 than a threshold of the fuel injection request fuelmttnr.

Preferably, the threshold of the fuel injection request (fuelretthr), for the single injector ranges between 5 and 5 mm3/stroke. Also for this threshold, the choice of suche a range has been done in order to cover a wide engine power range. Of course, a more precise threshold value can be obtained by calibration tests on each specific engine application.

Summarizing the present method allows to obtain a remarkable cost reduction for 2 0 warranty, since it provides a reliable criterion for detecting a faulty (clogged) injector and replacing just the single faulted injector instead of the whole injector set. Consequently, also shorter time at service are expected.

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

data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 161 injector solenoid 162 injector actuator 163 injector needle 164 injector leakage line fuel injection system 166 injector nozzle fuel rail fuel pump fuel source intake manifold 205 air intake duct 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 waste gate valve 295 waste gate actuator or electric pressure valve or boost pressure control valve 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow, pressure, temperature and humidity sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail digital pressure sensor 410 cam position sensor 420 crank speed sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 flowchart 600 flowchart 5510 step S520 step S530 step 5540 step 5550 step 5560 step 8610 step 5620 step Praii injection pressure PraiLmax max. injection pressure Qderat predetermined fuel injection quantity Arpmi01 speed increment due to a not de-rated injector ArpmIoLthr speed increment threshold fueIr fuel request fuelffir fuel request threshold

Claims (9)

1. CLAIMS1. Method of diagnosing a fault of fuel inectors (160) of an internal combustion engine (110), wherein the method comprises the following steps: a) operating the engine at idle speed, with a maximum injection pressure (pmii_max), b) de-rating all but one fuel injector to a predetermined value of a fuel injection quantity (Qderat), c) increasing a fuel injection request (fuel) by means of a control strategy for operating the engine at idle speed, d) repeating steps b) and c) for each group of all but one fuel injectors, e) diagnosing a fault of an injector if an instantaneous increase of the engine speed (Arpmi), during a crank angle window corresponding to the actuation of said injector, is smaller than an engine speed threshold (Arpmioi,,r).
2. 2. Method according to claim 1, wherein the method comprises the further step of diagnosing a fault of all injectors if the fuel injection request (fue6g) is larger than a threshold of the fuel injection request (fuelthr).
3. 3. Method according to claim I or 2, wherein the predetermined fuel injection quantity (Qdorat) ranges from 50% to 60% of the nominal fueF injection quantity.
4. 4. Method according to any of the preceding claims, wherein the engine speed threshold (ArpmIithr) ranges between 130 and 180 rpm.
5. 5. Method according to any of the preceding claims, wherein the threshold of the fuel injection request (fuelrthr) ranges between 5 and 8 mm3/stroke for a single injector.
6. 6. Internal combustion engine (110) of an automotive system (100), the engine being equipped with a fuel injection system (165) and a crank speed sensor (420), wherein a method of diagnosing a fault of fuel injectors according to any of the preceding claims is actuated.
7. 7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
8. 8. Computer program product on which the computer program according to claim 7 is stored.
9. 9. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 7 stored in the data carrier (40).