GB2525604A

GB2525604A - Method of operating a fuel injector of a three-cylinder internal combustion engine

Info

Publication number: GB2525604A
Application number: GB1407429.8A
Authority: GB
Inventors: Stefano Cassani; Davide Mercuri; Simone Barbero; Giorgio Nati; Isadora Ricci
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2014-04-28
Filing date: 2014-04-28
Publication date: 2015-11-04
Also published as: GB201407429D0

Abstract

Disclosed is a method of operating a fuel injector of a three-cylinder internal combustion engine. The engine comprises an electronic engine control unit, ECU, having two driver circuits for driving three fuel injectors where one torque forming injection of a first injector is not executed if it angularly coincides with an injection of the other two injectors. Also disclosed is a three-cylinder internal combustion engine having an ECU with exactly two injector driver circuitries.

Description

METHOD OF OPERATING A FUEL INJECTOR

OF A THREE-CYLINDER INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of operating a fuel injector of a three-cylinder internal combustion engine, in particular a fuel iniector of a common rail system (CRS) utilized for Diesel engines.

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 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 of the fuel injector. and it is determined by the ECU as a function of a desired quantity of fuel to be injected.

Currently, the engine control units (ECU) for four-cylinder engines are typically equipped with two hardware drivers (so called, banks) for driving fuel injectors, wherein each injector bank has the possibility to command one injector for once. This limitation is fulfilled by selling up the proper sequence of cylinder firing in order to avoid cylinders injection overlapping for a given bank. Present requirements about fuel pulses range allow grouping the injectors in two banks ensuring a fuel pulses range of 3600 for each injector.

Fig. 3 shows a standard driving sequence for injectors of a four-cylinder engine. Sank 1 drives the injectors of the cylinders 1 and 4. For cylinder I the fuel pulse ranges from 900 before top dead center of cylinder 1 (TDC#1) to 2700 after TDCC#1 (positive angular values before TDC, negative angular values after TDC) and for cylinder 4 the fuel pulse ranges from 90° before top dead center of cylinder 4 (TDCC#4) to 270° after TDCE#4.

The two ranges are equal to 360° each covering without overlap the whole 720° engine cycle. In the same way, bank 2 drives the injectors of the cylinders 2 and 3. For cylinder 2 the fuel pulse range.s from 90° before top dead center of cylinder 2 (TDCC#2) to 270° after r) TDCC#2 and for cylinder 3 the fuel pulse ranges from 90° before top dead center of cylinder 3 (TDCC#3) to 2700 after TDC3#3. The two ranges are equal to 3600 each covering without overlap the whole 720° engine cycle.

Moving to three-cylinder engines, no cylinder sequence set-up can be put in place to avoid overlap among cylinders. In fact, the three cylinders are angularly phased 240° one afier the other. Using two banks as for a four-cylinder engine, no couple of cylinders (1-2, 1-3 or 2-3) can be driven by the same bank without overlapping.

To guarantee a full injection pulse range, in other words a full angular window for the injection pattern, an additional ECU driver (a third bank) would be needed to fit three-cylinder engine needs, resulting in additional cost for engine controllers. Full angular windows are needed in case of aftertreatment regeneration modes (e.g., particulate filter regeneration) where late injections, both after injection (single pulse or multi-pulses) and post injection (single pulse or multi-pulses), are mandatory.

Therefore, a need exists for a method of operating a fuel injector, which does not suffer of the above inconvenience.

An object of an embodiment of the invention is to provide a method of operating a fuel injector of a three-cylinder internal combustion engine, which can be optimized according to the several engine operating conditions.

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 operating a fuel injector of a three-cylinder internal combustion engine, the engine comprising an electronic control unit having two drivers for driving three fuel injectors, each fuel injector executing a fuel injection sequence within a predetermined angular window of an engine crankshaft rotation, wherein at least one not torque forming injections of a first injector is not executed, if it angularly coincides with an injection of the other two injectors.

Consequently, an apparatus is disclosed for performing the method of operating a fuel injector of a three-cylinder internal combustion engine, the apparatus comprising means for not executing at least one not torque forming injections of a first injector, if it angularly coincides with an injection of the other two injectors.

Driving three injectors with the current ECU architecture (two injector driver circuitries) is not possible without overlapping the full injection pattern of at least two injectors.

Therefore, an advantage of this embodiment is that the method, by cutting some post injections (i.e. not torque forming injections) on one injector, allows not to have overlapping between injection sequence of two different cylinders. This avoids the cost increase of an ECU upgrade to three drivers instead of two.

According to a further embodiment, a total fuel amount of the not torque forming injections, which are not executed by the first injector, is split over the other two injectors.

Consequently, said means for not executing at least one not torque forming injections are configured to split a total fuel amount, which are not executed by the first injector, is split over the other two injectors.

An advantage of this embodiment is that, keeping the total amount of post injections allows to preserve temperature levels required by the aftertreatrnent system.

According to a different aspect of this embodiment, the angular window of the fuel injection sequence for the first injector ranges between 900 before top dead center of cylinder 1 and 150° after top dead center of cylinder, for a second injector ranges between 90° before top dead center of cylinder 2 and 270° after top dead center of cylinder 2 and for a third injector ranges between 90° before top dead center of cylinder 3 to 270° after top dead center of cylinderS.

Consequently, the apparatus further comprises means for performing a fuel injection sequence configured in a way that the angular window of the fuel injection sequence for a first injector ranges between 90° before top dead center of cylinder I and 150° after top dead center of cylinder 1, for a second injector ranges between 90° before top dead center of cylinder 2 and 270° after top dead center of cylinder 2 and for a third injector ranges between 90° before top dead center of cylinder 3 to 270° after top dead center of cylinder 3.

An advantage of this embodiment is that for all cylinders, remote pilot injection (up to 90° before top dead center) can be performed, when required by engine operating conditions.

According to another embodiment, the angular window of the fuel injection sequence for the first injector ranges between 600 before top dead center of cylinder 1 and 180° after top dead center of cylinder 1, for the second injector ranges between 60° before top dead center of cylinder 2 and 270° after top dead center of cylinder 2 and for the third injector ranges between 60° before top dead center of cylinder 3 to 270° after top dead center of cylinder 3.

Consequently, the apparatus further comprises means for performing a fuel injection sequence configured in a way that the anguLar window of the fuel injection sequence for the first injector ranges between 60° before top dead center of cylinder 1 and 180° after top dead center of cylinder 1, for the second injector ranges between 60° before top dead center of cylinder 2 and 270° after top dead center of cylinder 2 and for the third injector ranges between 60° before top dead center of cylinder 3 to 270° after top dead center of cylinder 3.

In some engine operating conditions (for example, warm up, full load, low end torque) it is possible to delay the first pilot injection. Therefore, the window for the injectors, performing the post injections, can be reduced, starting closer to the top dead center, and consequently the injection pattern for the injector not performing post injections can be shifted forward, allowing to perform some after injections. This reduces the effect on oil dilution coming from post injection deactivation on 1 over 3 cylinders.

According to a still further embodiment, the angular window of the fuel injection sequence for the first injector ranges up to a given angle after top dead center of cylinder 1, said angle substantially corresponding, for each engine operating point, to the angular position of a start of injection of an earliest pilot injection executed by one of the other two injectors.

Consequently, the apparatus further comprises means for performing a fuel injection sequence configured in a way that the angular window of the first injector ranges up to a given angle after top dead center of cylinder 1, said angle corresponding, for each engine operating point, to a start of injection of an earliest pilot injection executed by one of the other two injectors.

An advantage of this embodiment is that injection windows boundaries can be dynamically adjusted to allow post injection actuation on a first cylinder or at least their partial actuation.

Another embodiment of the disclosure provides a three-cylinder internal combustion engine comprising a fuel injector, wherein the fuel injector is operated by a method according to any of the previous embodiments.

Another embodiment of the disclosure provides an automotive system comprising a three-cylinder internal combustion engine and an electronic control unit, wherein the electronic control unit is provided with exactly two injector driver circuitries.

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 shows the injector driving approach for a four-cylinder internal combustion engine

(prior art).

Figure 4 shows a scheme of a fuel injection sequence Figure 5 shows the injector driving approach for a three-cylinder internal combustion engine, according to an embodiment of the present invention.

S

Figure 6 shows the injector driving approach for a three-cylinder internal combustion engine, according to another embodiment of the present invention.

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 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 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 andlor 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 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 waste gate actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 460 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 interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interlace 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 is 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.

As known, according to the engine operating point, one or more fuel injections can be performed, each other separated in time. Fig. 4 shows a schematic fuel injection sequence, each injection represented by its corresponding energizing current profile. A main fuel injection M is normally performed in a time interval during which the position of the involved engine piston is around the top dead centre. For different engine operating points, for instance in part load, one or more pilot injections M2 can precede main injection. Typically, an injection preceding and being very close to main injection is called boot injection Ml.

Further, mainly due to the regeneration processes of the exhaust gas aftertreatment system, also one or more after injections A (late injections still contributing to the engine torque) or post injections P (late injections do not contributing to the engine torque formation, since the exhaust port is already open and the related fuel combustion happens in the exhaust system, out of the cylinder) may follow main injection.

On three-cylinder engines, keeping the angular window needed for full injection pattern (360°) as for a four-cylinder engine, means that no injection sequence set-up can be put in place to avoid overlap among different injection sequence, with the present two drivers of the ECU. Since a purpose of the present invention is to avoid the addition of one injector driver circuitry to the diesel engines control unit (in other words, the electronic control unit must have exactly two injector driver circuitries), a different strategy has been defined. By keeping current ECU design (two banks) it is possible to avoid cylinder injection overlap by considering asymmetric angular boundaries of the injection sequence.

In particular, this means that one injector should have a reduced fuel injection sequence, without the possibility to perform late injections, in particular not torque forming injections (post injections) or at least without the possibility to perform some of the not torque forming injections. In other words, the method comprises the step of not executing at least one not torque forming injection of a first injector 160_I if said not torque forming injection angularly coincides with an injection of the other two injectors 1 60_2, I 60_3.

According to a preferred solution, the total fuel amount of the not torque forming injections, which are not executed by the first injector 160_i, is split over the other two injectors 160_2, 160_S. For example, in case the total fuel amount of post injections, due to a particulate filter regeneration, is 9 mm3, this amount would have been shared between the three injectors, 3 mm3 each injector. If no post injections are possible with the first injector, by splitting post injections over only two injectors means to inject 4.5 mm3 each injector.

In practice, if the angular window for one injector is reduced, the loss with respect to symmetrical approach is recovered by properly tuning injection pattern on the other two injectors. This would guarantee to preserve temperature levels, which are required by the aftertreatment system.

One possibility would be to reduce the full injection window for one injector 160_I, for example the injector of the cylinder 1, leaving the window of the other two injectors equal to the ones available for a four-cylinder engine. Taking into account that typical controller specification requires the start of the first possible injection 900 before top dead center, this limit the extension of the range up to 150° after top dead center due to the two banks configuration of the drivers with a range of 2400.

For example, with reference to Fig. 5, the angular window of the fuel injection sequence for the first injector 160_I can range between 90° before top dead center of cylinder I (TDCC#1) and 150° after top dead center of cylinder 1, for the second injector 160_2 can range between 90° before top dead center of cylinder 2 (TDC#2) and 270° after top dead center of cylinder 2 and for a third injector I 60_3 ranges between 90° before top dead center of cylinder 3 (TDCC#3) to 270° after top dead center of cylinder 3. With this solution, limiting late injections for one injector only up to 150° after TDC, all multi-post injection and part of after injection cannot be performed on the first injector. Moreover, the higher is the fuel amount of the late injections, which cannot be executed on one injector, the higher is the fuel amount, which is split over two injectors, the higher is the oil dilution. In fact, oil dilution is a phenomenon of internal combustion engines in which unburned diesel or gasoline accumulates in the crankcase. Excessively rich fuel mixture or incomplete combustion (which is the case of post injections) allows a certain amount of fuel to pass down between the pistons and cylinder walls and dilute the engine oil.

A preferred solution would be the one shown in Fig. 6. In suitable engine operating conditions (for example, warm up, full load, low end torque) it is possible to delay the first injection. Therefore, the window for the injectors, performing the post injections, can be reduced, starting closer to the top dead center. Meanwhile, the window for the first injector can be shifted forward, allowing to perform some after injection more than the previous case. For example, the angular window of the fuel injection sequence for the first injector 160_i can range between 60° before top dead center of cylinder I (TDCC#i) and 1800 after top dead center of cylinder 1, for the second injector I 60_2 ranges between 600 before top dead center of cylinder 2 (TDC#2) and 270° after top dead center of cylinder 2 and for the third injector 160_3 ranges between 60° before top dead center of cylinder 3 (TIJCC#3) to 270° after top dead center of cylinder 3.

Preferably, an additional feature can be added, introducing a dynamic injection range between two cylinders suffering the injection sequence superposition, for example cylinder 1 and cylinder 3. According to this procedure, injection windows boundaries can be dynamically adjusted to allow post injection actuation on cylinder I or at least their partial actuation (maybe not the total number of post injection pulses but just a reduced number).

This dynamic range shall be coordinated with the injection calibration to reduce the risk of overlaps between post injection pulses and pilot injection pulses of the following cylinder (for example, cyllnder 3). To exclude superposition, for each engine operating point, the earliest start of injection (SQl) of a pilot injection, that could be requested at the following combustion cycle, has to be calculated and based on this information the maximum possible end of the injection window for post pulses shall be calculated as well. The calculation of earliest pilot injection SQl, that could be requested at the following combustion cycle, can be defined as a static calibration, for example by means of a set of maps whose values are calibrated during the development phase. As an alternative, the calculation of earliest pilot injection SQl can derive from a model, which calculates this value in real time-The model would take into account the maximum torque step that could be actuated in a single combustion cycle, based on instantaneous driver request and operating conditions (such as turbocharger conditions, air/fuel ratio value and drivability constraints). The calculated width of so-called dynamic range, added to the cylinder 1 full injection window, can then be used to actuate one or more post pulses, that shall be calculated and scheduled recalculating how many pulses could be actuated on cylinder 1, based on the range width and the instantaneous rail pressure.

Test campaign demonstrated the feasibility of this approach, without any relevant drawback. Above all, the effects on temperature and on oil dilution coming from post injection deactivation on I over 3 cylinders has been verified. The conclusions about test confirmed that the deactivation of post-injection from some cylinders requires the total quantity to be redistributed among the other available cylinders. The increased oil dilution, expected from the increased fuel quantities coming from each of the injectors performing post injections, can be compensated by increasing the number of post injection splits on the single injector.

Summarizing the present method allows to keep the capability of using the full pattern of late injections (after injections and post injections both with multi-pulse split) avoiding the cost increase of an ECU upgrade to three drivers instead of two.

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 165 fuel injection system 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 position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU

Claims

CLAIMS1. Method of operating a fuel injector (160) of a three-cylinder internal combustion engine (110), the engine comprising an electronic control unit (450) having two drivers (bank 1, bank 2) for driving three fuel injectors (160_i, 160_2, 160_3), each fuel injector executing a fuel injection sequence within a predetermined angular window of an engine crankshaft (145) rotation1 wherein at least one not torque forming injections of a first injector (160_i) is not executed, if it angularly coincides with an injection of the other two injectors (160_2, 160_3).
2. Method according to claim 1, wherein a total fuel amount of the not torque forming injections, which are not executed by the first injector (160_I), is split over the other two injectors (160_2, 160_3).
3. Method according to claim 1 or 2, wherein the angular window of the fuel injection sequence for the first injector (160_i) ranges between 90° before top dead center of cylinder 1 (TDCC#1) and 150° after top dead center of cylinder 1, for a second injector (160_2) ranges between 90° before top dead center of cylinder 2 (TDCO#2) and 270° after top dead center of cylinder 2 and for a third injector (1 60_3) ranges between 90° before top dead center of cylinder 3 (TDCC#3) to 270° after top dead center of cylinder 3.
4. Method according to claim I or 2, wherein the angular window of the fuel injection sequence for the first injector (160_I) ranges between 600 before top dead center of cylinder 1 (TDCC#1) and 180° after top dead center of cylinder 1 for the second injector (160_2) ranges between 60° before top dead center of cylinder 2 (TDCC#2) and 2700 after top dead center of cylinder 2 and for the third injector (160_3) ranges between 60° before top dead center of cylinder 3 (TDCC#3) to 270° after top dead center of cylinder 3.
5. Method according to claim I or 2, wherein the angular window of the fuel injection sequence for the first injector (160_i) ranges up to a given angle (3) after top dead center of cylinder 1, said angle substantially corresponding, for each engine operating point, to the angular position of a start of injection of an earliest pilot injection executed by one of the other two injectors (1 60_2, 1 60_3).
6. Threecylinder internal combustion engine (110) comprising a fuel injector (160), wherein the fuel injector is operated by a method according to any of the preceding claims.
7. Automotive system (100) comprising a three-cylinder internal combustion engine and an electronic control unit (450), wherein the electronic control unit is provided with exactly two injector driver circuitries.
8. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
9. Computer program product on which the computer program according to claim 8 is stored.
10. Control apparatus for an internal combustion engine, comprising an Electronic Control Unfit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 8 stored in the data carrier.