GB2512930A

GB2512930A - Method of operating a fuel injection system

Info

Publication number: GB2512930A
Application number: GB1306680.8A
Authority: GB
Inventors: Massimiliano Melis; Angelo Cancellieri
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-04-12
Filing date: 2013-04-12
Publication date: 2014-10-15
Also published as: GB201306680D0

Abstract

Disclosed is a method of operating a fuel injection system (165), said fuel injection system comprising at least one injector (160) and a common rail (170), the common rail not having a pressure regulator valve. The method comprises the steps of supplying at least an energizing electrical current to an injector solenoid (161) which causes the opening of an injector control volume (CV) and discharges fuel from the control volume towards an injector leakage line (164) leading to a pressure reduction in the injector control volume (CV). The supply of the energizing electrical current is stopped after a predetermined time threshold (tthr), when the pressure in the injector control volume (CV) approximates a value which an injector needle (163) would start to raise up and fuel injection start. An internal combustion engine using the method, a computer program to implement the method, a program product carrying the program and a control apparatus loaded with the program are also disclosed.

Description

METHOD OF OPERATING A FUEL INJECTION SYSTEM

TECHNICAL FIELD

The present disclosure relates to a method of operating a fuel injection system.

Particularly, the method is related to fuel injection systems for internal combustion engines. More particularly, the method describes how to decrease the injection pressure in a Common Rail System (CR8), wherein a pressure regulator valve is not used.

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 pump, 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, with one or more injection holes, and a movable needle, which repeatedly covers (when it is in its closing position) and uncovers (when it is in its opening position, i.e. raised up) the injection holes of the nozzle. The fuel, coming from the rail, flows passing through the injection pipe and a delivery channel, inside the injector housing; then the fuel reaches the nozzle and, whenever the needle uncovers the injection holes, can thus be injected into the cylinder giving rise to single or multi-injection patterns at each engine cycle.

S The needle movement is caused by the forces acting from above and from below the needle itself. The first one is the needle closing force, the other is the needle opening force. Both are the product between a pressure and a sealing surface. When no injection is required, the needle closing force is higher than the needle opening force, thus ensuring that the injection holes are covered. On first approximation and for a predetermined injection pressure, the needle opening force can be considered as a constant. Therefore, to cause the raising up of the needle, it will be sufficient to decrease the closing force, for example, by decreasing the pressure, which acts on top of the needle. Such pressure is due to the fuel, which fills a so called injector control volume (CV). The control volume is a small volume inside the injector housing and is delimited by injector housing walls, a first calibrated hole (known as A" hole), a second calibrated hole (known as "1' hole) and the top surface of the injector needle. The hole Z always joins the common rail through the injection pipe to the injector control volume. The A hole is normally closed, when no fuel injection is required, otherwise it joins the injector control volume with an injector leakage line at low pressure (as a first approximation, atmospheric pressure), when the injection is performed. The control volume is fed through the hole 7 and can be emptied through the hole A. When no injection is required, being the A hole closed, the pressure in the control volume is equal to the injection pressure. When the injection is required, being the hole A larger than the Z hole, it is possible to discharge the fuel from the control volume, thus reducing the pressure in the control volume itself.

The injection is operated thanks to aid of a dedicated injector solenoid and injector actuator. The injector solenoid is controlled by an electronic control unit (ECU). The ECU operates each fuel injection, by energizing the solenoid for a predetermined period of time, causing, in turn, the injector actuator to open the A hole, the fuel discharge from the control volume to the injector leakage line, the pressure decrease in the control volume, the needle to raise up and uncover the injection holes. When the energizing time is ended, the injector actuator will close the A hole and the pressure in the control volume will increase up to the injection pressure value, causing the needle to go down and cover the injection holes. 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.

Another important parameter to control the injection quality is the injection pressure.

Such pressure is measured in the common rail by a sensor pressure and controlled by the ECU, normally by means of a dedicated pressure regulator valve, normally located on the rail. The pressure in the system will be determined by a so called quantity balance, The quantity balance means the mass balance between the fuel coming from the injection pump and entering the rail and the fuel exiting the rail and flowing towards the injectors. The fuel amount exiting the rail is the sum of the injected portion (established by the ECU control strategies) and the injector leakages amount. More particularly, the injector leakage is the sum of a static leakage and a functional leakage.

The static leakage is due to the small clearances between the movable needle and the fixed portion of the injector (injector housing and injector nozzle). The functional leakage is due to the A hole opening during the energizing time of the injector solenoid.

The balance to reach a target injection pressure value is provided by the recirculated fuel quantity through a pressure regulator valve, which is a fast valve to manage fast pressure transients. As known, to get remarkable cost savings and simplify the fuel injection system, modern Common Rail System are provided without the pressure regulator valve. With this configuration, the injection pressure control is only determined by a low pressure pump metering valve and, intrinsically, by the injector leakages. This pressure control is becoming more difficult, since current injection systems are moving to low leakage injectors (i.e. injectors with a lower static leakage). Therefore, in cut off and deceleration phases and in the case a pressure regulator valve is not used, the injection pressure decrease is slow and can increase the combustion noise, while moving from the 6ut off phase to a normal driving one.

Therefore a need exists for a new method of operating a fuel injection system, allowing the pressure regulator valve not to be used and at the same time a fast injection pressure decrease in the above driving conditions, like cut-off or decelerations.

An object of an embodiment of the invention is to provide a method of operating a fuel injection system, which acts on the injectors, increasing, in a controlled way and when necessary, their functional leakages, in order to reach a fast injection pressure decrease (thus reducing combustion noise) and, at the same time, without incurring in undesired injection.

These objects are achieved by a method, by an apparatus, by an internal combustion engine and by an automotive system provided with an electronic control unit able to control the fuel injection system, 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 injection system, said fuel injection system comprising at least one injector and a common rail, the common rail not having a pressure regulator valve wherein the method comprises: -supplying at least an energizing electrical current to an injector solenoid, causing the opening of an injector control volume, a fuel discharge from it towards an injector leakage line and a pressure reduction in said injector control volume, -stopping the supply of the energizing electrical current after a predetermined time threshold, when the pressure in the injector control volume approximates a value which would cause an injector needle to raise up and a fuel injection to start.

Consequently1 an apparatus is disclosed for operating a fuel injection system, the apparatus comprising: -means for supplying at least an energizing electrical current to an injector solenoid, causing the opening of an injector control volume, a fuel discharge from it towards an injector leakage line and a pressure reduction in said injector control volume, -means for stopping the supply of the energizing electrical current after a predetermined time threshold, when the pressure in the injector control volume approximates a value which would cause an injector needle to raise up and a fuel injection to start.

An advantage of this embodiment is that the supply of an energizing electrical current to an injector solenoid (in other words, an injector actuation) causes the fuel discharge towards the injector leakage line and, consequently, a fast injection pressure reduction in the injector and in the whole common rail. Moreover, the fact that the energizing electrical current is stopped, avoiding movements of the injedtor needle, prevents the uncovering of the injector holes in the nozzle, thus avoiding undesired fuel injections.

Furthermore, multiple energizing electrical current pulses (i.e. injector actuations), with same or different current profiles, can be actuated. In this way, it is easier to reach a target injection pressure value, without incurring in undesired injections: in fact each energizing electrical current can have a shorter energizing time, thus increasing the safety margin with respect to the limit condition for the injection needle to raise up; at the same time, the amount of the total fuel leakage quantity will be higher than in case of single injector actuation, thus granting a faster injection pressure reduction.

According to another embodiment, said energizing electrical current is supplied over a time interval, during which there is exactly one constant current value.

Consequently, the means for supplying at least an energizing electrical current are configured for supplying said energizing electrical current over a time interval, during which there is exactly one constant current value.

An advantage of this embodiment is that a constant current value (for example, a low current value, but sufficient to keep the injector control volume open) can be maintained for a longer energizing time, without incurring in undesired Injections.

According to a further embodiment, said energizing electrical current is supplied over a first time interval, during which there is a first constant current value and over a second time interval, during which there is a second constant current value, the first constant current value being larger than the second constant current value.

Consequently, the means for supplying at least an energizing electrical current are configured for supplying said energizing electrical current over a first time interval, during which there is a first constant current value and over a second time interval, during which there is a second constant current value, the first constant current value being larger than the second constant current value.

An advantage of this embodiment is to provide an energizing electrical current profile which is similar to the energizing electrical current profile which is implemented in the Electronic Control Unit to actuate fuel injections.

According to an aspect of this embodiment, the ratio of said first constant current value to a peak current value of an energizing electrical current, used to actuate a fuel injection, is smaller than 1.

Consequently, the means for supplying at least an energizing electrical current are configured so that the ratio of said first constant current value to a peak current value of an energizing electrical current, used to actuate a fuel injection, is smaller than t The fact that the first current value has a scaled value, makes sure that a target injection pressure reduction can be reached, without incurring in undesired injections.

According to another aspect of this embodiment, the ratio of said second constant current value to a hold current value of an energizing electrical current used to actuate a fuel injection, is smaller than 1.

Consequently, the means for supplying at least an energizing electrical current are configured so that the ratio of said second constant current value to a hold current value of an energizing electrical current, used to actuate a fuel injection, is smaller than 1.

The fact that also the second current value has a scaled value, makes sure that a target injection pressure reduction can be reached, without incurring in undesired injections.

According to a still further embodiment, the method further comprises: -detecting a driving condition, to establish if the energizing electrical current to the injector solenoid has to be supplied, -determining a number and a profile of said energizing electrical current, said profile being defined in terms of constant current values and related time intervals, -supplying said energizing electrical current to the injector solenoid, -measuring an injection pressure and comparing said value to a target injection pressure value, -repeating the above steps, until the measured injection pressure has reached the target injection pressure value.

Consequently, the above apparatus further comprises: -means for detecting a driving condition, to establish if the energizing electrical current to the injector solenoid has to be supplied, -means for determining a number and a profile of said energizing electrical current, said profile being defined in terms of constant current values and related time intervals, -means for supplying said energizing electrical current to the injector solenoid, S -means for measuring an injection pressure and comparing said value to a target injection pressure value.

An advantage of this embodiment, is to define a control loop on the target injection pressure, so that the ECU will implement this strategy when really needed.

According to an aspect, said driving conditions, which enable the supply of the energizing electrithl current to the injector sdenoid, are an engine cut-off mode or an engine deceleration phase.

Consequently, the means for detecting a driving condition are configured in a way that said driving conditions, which enable the supply of the energizing electrical current to the injector solenoid, are an engine cut-off mode or an engine deceleration phase.

In this way, the strategy is applied during the most critical engine conditions, when a strong injection pressure reduction is required.

According to a further aspect, said constant current values and related time intervals are determined by means of a map, whose input is an actual rail pressure.

Consequently, the means for determining a number and a profile of the energizing electrical current are configured for determining said constant current values and related time intervals by means of a map, whose input is an actual rail pressure.

In this way, the energizing electrical current can be adequate to the injection pressure which is required by the system. This has effect in determining the max. pressure reduction in the injector control volume, in order to avoid injector needle movement, i.e. undesired injections.

A further embodiment of the disclosure provides an internal combustion engine of an automotive system equipped with a fuel injection system, wherein a method of operating a fuel injection according to one 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.

S

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 is a graph depicting a standard current profile for actuating a fuel injector.

Figure 5 is a schematic view representing the control volume of a fuel injector and the mechanism of its pressure discharge.

Figure 6 is a graph depicting two particular current profiles for actuating a fuel injector, according to the present invention.

Figure 7 is a flowchart of a method of pressure discharge for a fuel injection system, according to the present invention

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 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 165 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 dud 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 parts 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 15. 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, and particulate filters. 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 and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors s 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 is (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 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.

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 (El) of the fuel injector is determined by the ECU as a function of a desired quantity of fuel to be injected.

Fig. 4 shows a standard energizing electrical current profile 500, which comprises, after a quick current ramp up (called pull-in current until the max. value 503 is reached), a first time interval tl during which the current assumes a remarkably high value, in the order of 10-20 A, the so called peak" current 501. Reason for this high current value is to accelerate as much as possible the injector actuator 162 and, in turn the calibrated hole A opening, the fuel discharge from the injector control volume to the injector leakage line 164, the pressure reduction in the injector control volume, the injector needle up movement (uncovering the injection holes) and the start of the injection. As soon as such conditions are satisfied, the current value to guarantee the injector needle remains lifted is lower, in the order of less than 10 A. Therefore, the second time interval t2 of the standard energizing electrical current profile is characterized by a current hold value 502, smaller than the peak current 501.

To apply the present method, the ECU must energize the injector solenoid as well, by supplying an energizing electrical current, having different and specific energizing current profiles in order to increase injector leakages without performing injections. With reference to Fig. 5, when the injector solenoid 161 is energized, the injector actuator 162 rises up and opens the calibrated hole A, so causing the discharge of the injector control volume CV, which is on the injector needle 163. This volume, when the actuator is not energized, has the same pressure of the rail, since it is fed through the calibrated hole Z. As can be appreciated following the arrows in Fig. 5, the fuel coming from the injection pump 180 (and the rail 170) enters the injector 160 according to two paths: a first path towards the injector nozzle 162 (this is the fuel, which is injected in the engine combustion chamber), a second path flows to the injector control volume CV.

S

When the injector is energized and the control volyme opened, the pressure in the control volume is determined by the flow through the hole Z and by the flow through the hole A towards the leakage line 164. As already said, being the diameter of the hole A larger than the diameter of the hole Z, the pressure in the control volume CV will decrease, since more fuel exits the control volume than enters the control volume. This will increase the injector leakage (what has been called "functional" leakage) and will reduce the injection pressure. The injector energizing current and the consequent pressure decease in the injector control volume will be stopped when the needle 163 is in an incipient condition to be lifted. In fact, the closing force Fcl on the injector needle 163 is determined by the pressure value in the control volume multiplied by the upper sealing area of the injector needle 163, while the opening force Fop, acting on the same needle, is determined by the injection pressure acting on the lower sealing area of the injector needle multiplied by the lower sealing area itself (as said, this product can be considered as a constant value in a first approximation). As a consequence, whenever the pressure in the control volume will reach a value, so that Fcl c Fop, the injector needle 163 will start raising and the injection will begin. Therefore, the ECU stops the supply of the energizing electrical current to the injector solenoid 161 after a predetermined time threshold tthr, when the pressure in the injector control volume approximates a value which would cause an injector needle 163 to raise up and, consequently, a fuel injection to start.

A special energizing electrical current profile is defined, which allows the energizing time of the injector to be maintained as long as possible, until the pressure in the control volume CV reaches a value such that the closing force Fcl is close to the opening force S Fop, but not lower than it, thus preventing any injection. Therefore, by means of a different injector solenoid actuation, changing the current profile actuation mode, the injector leakages can be increased (without injection) to have a faster rail pressure decrease and improving the combustion noise. The current profile has to be customized depending on the injector architecture and will be calibrated during the development, ensuring that no injection event can occur even if border samples of injectors are used.

Advantageously, said injection actuation can be realized by means of more than one current profile. In fact, by using multiple actuations, it will be easier to reach a desired pressure value, without incurring undesired injections.

In Fig. 6 two exemplifying energizing electrical current profiles are shown. Fig. Ga is a graph depicting an energizing electrical current profile 510 comprising a time interval with a constant current value 512 for a predetermined time interval dt. In other words due to the fact that no injection is needed, it is possible to energize the injector solenoid only with a constant current value 512 comparable to the hold current value used in normal driving conditions. The energizing of the injector can be maintained for a considerable time interval, about 500 p.s. Another suitable energizing electrical current profile is shown in Fig. Gb. Said current profile corresponds to a normal driving current profile, comprising a first time interval dtl with a first constant current value 521 and a second time interval dt2 with a second constant current value 522. Preferably1 the first current value 521 is scaled with respect to a standard peak current value 501 and the second current value 522 is scaled with respect to a standard hold current value 502. Said scaled factor is smaller than 1 and suitable scale factors can be in the range 0.5-0.75; the related time intervals (energizing time) could also be around 500.ts. Both embodiments provide an actuation of the injector, which reach the target to quickly slow down the injection pressure, without incurring undesired injections.

In Fig. 7 is shown a complete block diagram implementing the method according to the invention. The method starts in detecting 520, 521 a driving made to establish if the present strategy must be actuated: in case of normal driving the strategy will not be actuated, while in case of cut-off or deceleration phase, the injection pressure reduction strategy will be actuated, then, in step 522, the number of injection actuations, that is to say, the number of the energizing electrical current profiles is determined; at the same time, the injector actuation mode, in other words, the energizing electrical current 510, 520 profile, in terms of constant current values and the related energizing time for each actuation, is determined 524. More particularly, the injector actuation mode is determined by means of a map, as shown in step 524, whose input is the actual injection pressure. Further, in step 525, an energizing electrical current is supplied to the injector solenoid and the injection pressure Prail is measured S26 and compared S27 to a target injection pressure value; the methód will cyclically continue, until the measured rail pressure has reached the target pressure value 528: in this case the present strategy is ended and the standard injector actuation, according to the normal driving conditions, is restored.

Some tests to validate the present strategy have been performed and the results are shown in the following table: _______ _______ __________ Table_1 _______________ _______________ Prail Static Total Profile 1 Profile 2 Profile 3 (MPa) leakage leakage El Total El (pa) Total Er (pa) Total (%) (%) (ps) leakage leakage leakage ______ ______ ________ ______ (%) ______ (%) ______ (%) 100 120 150 580 500 140 500 300 100 125 130 450 500 275 500 538 100 100 110 153 500 353 500 533 100 100 110 159 500 400 500 278 Pull in 75% 50% 60% current __________ Peak current 75% 50% 50% Hold current 75% _________ 50% _________ 50% _________ Number or 3 3 3 injection actuations __________ __________ ______________________ __________ In the first column different values of the injection pressure Prail are listed. In the second column as reference point (in percentage), the static leakage (as said, the leakage fraction due to the injector clearances between fixed and movable parts) is shown. Then, the third column represents the total leakages (static plus functional), obtained by applying three fake injections that is to say, three short current profiles: this method does not increase the leakages at all or increase them in an almost negligible amount. In the remaining six columns, details of three energizing electrical current profiles (in particular, current profiles according to the scheme in Fig. 6b) are listed. Their characteristics in terms of time intervals (energizing time, ET) are listed and the performance in term of total leakages (always in percentage with respect to the static leakages) is also shown. Moreover, in the last four rows of table 1, the current values (pull in current 523, peak current or first constant current 521 and hold current or second constant current 522) and the number of injection actuations for each profile are listed.

The current values are expressed in percentage with respect to the current values of a normal driving profile. Therefore, profile 1 is scaled with a ratio of about 0.75 with respect to current profile, which is used during normal driving conditions. Profile 2 is scaled with a ratio of about 0.5 with respect to the current profile, during normal driving conditions.

Profile 3 is similar to profile 2, with a different value of the pull in current. As can be seen from table 1, all current profiles allow to achieve a remarkable increase of the total leakages, under different injection pressure Prail values. Therefore the present method will be able to choose the best current profile, depending on the injection pressure S values.

Summarizing, the present strategy allows to reduce the combustion noise after restart from cut-off or engine deceleration driving modes and contemporary is beneficial of about 15 euro in cost reduction, in the markets where pressure regulator valve is not needed, Incidentally it has to be remarked that the present strategy also allow to calibrate lower pilot injection quantities, because of the lower current values during the energizing time and consequently emission improvements.

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. 20.

REFERENCE NUMBERS

S20 block S21 block S22 block S23 block 624 block S25 block S26 block 627 block 628 black S29 block data carrier automotive system internal combustion engine 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector 161 injector solenoid 162 injector actuator 163 injector needle 164 injector leakage line fuel injection system 170 fuel rail fuel pump fuel source intake manifold 205 air intake pipe 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 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature 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 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 500 injector energizing electrical current (fuel injection actuation) 501 peak current (fuel injection actuation) 502 hold current (fuel injection actuation) 503 pull in current (fuel injection actuation) 510 injector energizing electrical current (no fuel injection actuation) 512 constant current value 513 pull in current dt time interval having a constant current value 520 injector energizing electrical current (no fuel injection actuation) 521 first constant current value dtl time interval having a first constant current value 522 second constant current value 523 pull in current dt2 time interval having a second constant current value S CV injector control volume A calibrated hole (control volume outlet) Z calibrated hole (control volume inlet) Prail injection pressure tthr time threshold Fop opening force Fcl closing force

Claims

CLAIMS1. Method of operating a fuel injection system (165), said fuel injection system comprising at least one injector (160) and a common rail (170), the common rail not having a pressure regulator valve, wherein the method comprises: -supplying at least an energizing electrical current (510, 520) to an injector solenoid (161), causing the opening of an injector control volume (CV), a fuel discharge from it towards an injector leakage line (164) and a pressure reduction in said injector control volume (CV), -stopping the supply of the energizing electrical current after a predetermined time threshold (tth,-), when the pressure in the injector control volume (CV) approximates a value which would cause an injector needle (163) to raise up and a fuel injection to start.
2. Method according to claim 1, wherein said energizing electrical current (510) is supplied over a time interval (dt), during which there is exactly one constant current value (512).
3. Method according to claim 1, wherein said energizing electrical current (520) is supplied over a first time interval (dtl), during which there is a first constant current value (521) and over a second time interval (dt2), during which there is a second constant current. value (522), the first constant current value (521) being larger than the second constant current value (522).-
4. Method according to claim 3, wherein the ratio of said first constant current value (521) to a peak current value (501) of an energizing electrical current (500), used to actuate a fuel injection, is smaller than 1.
5. Method according to claim 3 or 4, wherein the ratio of said second constant current value (522) to a hold current value (502) of an energizing electrical current (500), used to actuate a fuel injection, is smaller than 1.
6. Method according to any of the preceding claims, wherein the method further comprises: detecting (S20, S21) a driving condition, to establish if the energizing electrical current (510, 520) to the injector solenoid (160) has to be supplied, -determining (S22) a number and a profile of said energizing electrical current (510, 520), said profile being defined (S24) in terms of constant current values (512, 521, 522) and related time intervals (dt, dtl, dt2), -supplying (S25) said energizing electrical current (510, 520) to the injector solenoid (161), -measuring (S26) an injection pressure (Prail) and comparing (S27) said value to a target injection pressure value, -repeating the above steps, until (S28) the measured injection pressure has reached the target injection pressure value.
7. Method according to claim 6, wherein said driving conditions1 which enable the supply of the energizing electrical current to the injector solenoid (161), are (S21) an engine cut-off mode or an engine deceleration phase.
8. Method according to claim 6 or 7, wherein said constant current values (512, 521, 522) and related time intervals (dt, dtl dt2) are determined by means of a map, whose input is an actual rail pressure.S
9. Internal combustion engine (110) of an automotive system (100) equipped with a fuel injection system (165), wherein a method of operating a fuel injection according to any of the preceding claims is actuated.
10. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-8.
11. Computer program product on which the computer program according to claim 10 is stored.
12. 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 10 stored in the data carrier (40).