WO2014091273A1

WO2014091273A1 - Method for controlling an injection system of an internal combustion engine having a common rail, injection system and automotive vehicle

Info

Publication number: WO2014091273A1
Application number: PCT/IB2012/003059
Authority: WO
Inventors: Damien Brunel
Original assignee: Renault Trucks
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2014-06-19
Also published as: EP2932075A1

Abstract

This method for controlling an injection system in an internal combustion engine having a common rail includes: - a first step 2000) before a given injection phase of a given cylinder, in which the requested fuel quantities (Q_B, Q_M and Q_A) and the requested injection start times (t_B, t_M and t_A) are computed for each individual injection of the given injection phase, - a second step 3000) in which an adaptive model (K, W) of the variations of the pressure in the common rail is used to compute calculated values (P_Bi, P_Mi, P_Ai. Ρ_Bf, P_Mf, P_Af) of the pressure in the common rail for each individual injection of the given injection phase, in accordance with the requested fuel quantities (Q_B, Q_M, Q_A) and the requested injection times (t_B, t_M, t_A) set during step 2000), - 4000) the values (P'_Bi, P'_Mi, P'_Ai, P'_Bf, P'_Mf, Ρ'_Af) of the pressure (P) in the common rail are recorded during each individual injection of the given injection phase, - 5000) the adaptive model (K, W) is adjusted depending on the difference between the computed pressure values (P_Bi, Ρ_Μi, P_Ai, P_Bf, P_Mf, P_Af) of step 3000) and the recorded pressure values (P'_Bi, P'_Mi, P'_Ai, P'_Bf, P'_Mf, P'_Af) of step 5000).

Description

Method for controlling an injection system of an internal combustion engine having a common rail, injection system and automotive vehicle

TECHNICAL FIELD OF THE INVENTION

The present invention concerns, on the one hand, a method for controlling an injection system of an internal combustion engine having a common rail, and on the other hand an injection system and an automotive vehicle.

BACKGROUND OF THE INVENTION

In the field of internal combustion engines having a common rail, it is known to use an engine electronic control unit (EECU) to compute the start time and the duration, on which depend the injected fuel quantity, of each fuel injection into one of the cylinders of the engine. The fuel quantities and the start times are computed based on the required engine torque and in accordance with requirements relative to the emissions of pollutant gases and temperature, depending on injection conditions such as fuel temperature, common rail pressure and injectors wear.

In modern injection systems, a plurality of separate fuel injections may be fed into each cylinder during a given cylinder cycle, in order to reduce the combustion noise and noxious emissions.

In operation, pressure fluctuations occur inside of the common rail during and between fuel injections. As the pressure fluctuations change the duration of the injections, they must be taken into account when computing the required fuel quantities.

US-B-7 152 575 discloses a method for controlling the fuel injections in an internal combustion engine. A characteristic map is used to determine a mapping value for the injection durations, in dependence on the fuel pressure and the fuel quantity to be injected. This estimated mapping value does not take into account the pressure fluctuations in the common rail and is corrected with a formula which takes into account the pressure fluctuations caused by the preceding injections of the cylinder cycle. This method is long and complicated and consequently, it requires expensive hardware and the injected fuel quantities are not precise.

SUMMARY OF THE INVENTION

The aim of this invention is to provide an improved method for controlling the fuel injections in an internal combustion engine of an automotive vehicle.

To this end, the invention concerns a method for controlling an injection system in an internal combustion engine having a common rail, for injecting fuel to cylinders, each injection phase comprising several individual injections occurring during a cylinder cycle, the method including:

- a first step before a given injection phase of a given cylinder, in which the requested fuel quantities and the requested injection start times are computed for each individual injection of the given injection phase,

- a second step in which an adaptive model of the variations of the pressure in the common rail is used to compute calculated values of the pressure in the common rail for each individual injection of the given injection phase, in accordance with the requested fuel quantities and the requested injection times set during the first step, - a third step in which the values of the pressure in the common rail are measured and recorded during each individual injection of the given injection phase,

- a fourth step in which the adaptive model is adjusted depending on the difference between the computed pressure values of the second step and the recorded pressure values of the third step,

Thanks to the invention, the adaptive model is adjusted between cylinder cycles, depending on the difference between the computed and the recorded pressure values. In this way, the computed pressure values are more accurate, which allows improving the precision of the injected fuel quantities.

According to further aspects of the invention which are advantageous but not compulsory, such a method may incorporate one or several of the following features:

- The process comprises a fifth step, in which the first, second, third and fourth steps are repeated for the following injection phases.

- The adaptive model includes a first adaptive map giving a pressure drop inside the common rail caused by a preceding individual fuel injection.

- The pressure drop given by the first adaptive map depends on the injected fuel quantity during the preceding individual fuel injection and on the pressure inside the common rail before that injection.

- The adaptive model includes a second adaptive map giving the pressure variance inside the common rail between a first and a second injection, especially between two consecutive individual injections, more especially between a given individual injection and an immediately preceding individual injection.

- The pressure variance given by the second adaptive map depends on the pressure at the end of the first injection and on the start time of the second injection.

- During the third step, the pressure in the common rail is measured before and after each individual injection.

- The adaptive model is specific to each cylinder. - The adaptive model includes at least one three dimensional matrix.

- The method includes an initialization step occurring during a subsequent use of the engine, wherein the steps are repeated once with the values of the adaptive model established during the prior use of the engine.

The invention also concerns an injection system for an internal combustion engine having a common rail for supplying fuel to cylinders and means for measuring the pressure in the common rail, and further including a control unit implementing such a method.

Finally, the invention concerns an automotive vehicle, including such an injection system.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be explained in correspondence with the following figures, as an illustrative example and without restricting its object. In the annexed figures:

- figure 1 is a schematic representation of an injection system of an automotive vehicle according to the invention ;

- figure 2 is a graph showing the position of a cylinder of the engine depending on the angular position of the crankshaft of the engine ;

- figure 3 is a graph showing the pressure variations in a common rail of the automotive vehicle depending on the time ; and

- figure 4 is a bloc diagram of a method according to the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Some parts of an automotive vehicle V, for example a truck, are schematically represented on figure 1 and are part of a fuel injection system S of an internal combustion engine E. The injection system S comprises a common rail R where high pressure fuel is accumulated.

The fuel injection system S may include a low pressure fuel pump P1 which moves the fuel contained in a fuel tank T into an entry duct D1 connected to the input of a high pressure fuel pump P2 feeding the common rail R. A first valve V1 may be located on the entry duct, between pumps P1 and P2. A second valve V2 may be located on a return duct D2 which brings back the fuel contained in the common rail R into the fuel tank T.

The common rail R feeds fuel to a number of injectors, for example six injectors 11 , 12, 13, 14, 15 and 16, each injecting fuel into a cylinder C1 , C2, C3, C4, C5 or C6 of the engine E. Each cylinder C1 to C6 includes a combustion chamber 4 closed by a piston 5 attached to a connecting rod 6 linked to a crankshaft 7. The injectors may inject the fuel directly in the corresponding combustion chamber. In operation, an engine electronic control unit 1 receives a signal S_P carrying information relative to the pressure P in the common rail R, measured by a pressure sensor 2. The control unit 1 delivers signals S_Vi and S_V2 for the opening and the closure of the valves V1 and V2, depending on the amount of fuel needed inside of the common rail R. The control unit 1 also delivers a signal S_r to each injector 11 to 16 for driving the opening and the closure of the injectors 11 to 16.

Figure 2 shows the position of the piston 5 of the first cylinder C1 during one cylinder cycle, depending on the angular position ω of the crankshaft 7. A sensor 8 measures and transmits the angular position ω to the control unit 1, via a signal S_u.

At ω = -360°, the piston 5 of the cylinder C1 is in a high position H and air is admitted into the chamber 4 while the piston 5 moves to a low position L reached at u> = - 180°. Then, the air is compressed inside of the chamber 4 by the piston 5 which goes up to the high position H, at an angular engine top dead centre co_TDc located at ω = 0°.

Around the angular top dead center OOTDC, there is an injection phase during which injector 11 injects fuel into the chamber 4 of the cylinder C1. The gas inside the chamber 4 explodes and pushes the piston 5 to the low position L, at ω = 180°. Then, the piston 5 goes back to the high position H at ω = 360° as the gas inside the chamber 4 is evacuated through an exhaust port.

In operation, the cylinder cycle described above . is repeated on a continuous loop: the piston 5 goes back to the low position L at ω = 540° and fresh air is aspirated inside the chamber 4.

The other cylinders C2 to C6 follow the same cycle, with an angular offset which, in the case of a six cylinder engine, is typically of 120° between each of them so that the cycles of the cylinders C1 to C6 repeat in a loop.

In order to reduce the noises and the gas emissions, each injection phase includes a number of separate individual fuel injections, for example three separate individual fuel injections B, M and A shown on figure 3:

- a main injection M, which starts at a main-injection time t_M, lasts for a main- injection duration d_M and during which a fuel quantity Q_M is injected into one of the cylinders C1 to C6,

- a pre-injection B, which starts before the main injection M at a pre-injection time t_B, lasts for a pre-injection duration d_s, and during which a fuel quantity Q_B is injected into the same cylinder C1 to C6,

- a post-injection A, which starts after the main injection M, at a post-injection time t_A, lasts for a post-injection duration d_A and during which a fuel quantity Q_A is injected into the same cylinder C1 to C6, When an injection phase of a given cylinder C1 to C6 is over, the injection phase is repeated for the cylinder cycles of the following cylinder. Thus, from the view point of the common rail R, there is an injection phase once every 120° and the injection phase of a particular cylinder C1 to C6 is repeated once every 720°.

The fuel quantities Q_B, QM and Q_A injected into the chamber 5 are calculated by the control unit 1 depending on the required engine torque. The fuel quantities Q_B, QM and Q_A physically depend inter alia on the injection durations d_B, divi and d_A and on the pressure P inside the common rail R.

The injection times t_B, t_M and t_A and the injection durations d_B, d_M and d_A are expressed in terms of angular positions ω of the crankshaft 7. The angular top dead centre GO_TDC of the crankshaft 7 corresponds to a top dead centre time tjoc equal to zero.

The injection times t_B, t_M and t_A and the fuel quantities Q_B, Q and Q_A need to be very precise, in order to achieve the noise and noxious emissions reduction.

As can be seen in the injection phase depicted in figure 3, the pressure P inside the common rail R decreases during each injection B, M and A because the fuel quantities Q_B, Q_M and Q_A are removed from the common rail R. The pressure P inside the common rail R fluctuates between the injections B, M and A most notably due to acoustic effects caused by the closure of the injector 11 , 12, 13, 14, 15 or 16.

As the fuel quantities Q_B, Q_M and Q_A depend on the pressure P, the control unit 1 needs to know the value of the pressure P at the beginning of each individual injection B, M and A in order to compute the injection times t_M, t_A and t_B and the injection durations d_M, d_B and d_Aof the next injection cycle.

The control unit 1 cannot physically obtain the pressure P and re-calculate the opening times between each individual injections B, M and A because the duration between the individual injections B, M and A is too short relative to embedded control constraints. However, the control unit 1 knows the angular position ω of the crankshaft 7, which correspond to the injection times t_M, t_A and t_B.

Thus, before each injection phase, the control unit 1 has to compute the initial values P_Bi, P_Mi and P_Ai of the pressure P, immediately prior to each injection B, M, A, and the final values P_Bf, P_Mf and P_Af of the pressure P immediately after each individual injection B, M and A. The subscript "i" stands for "initial", because the pressure P immediately prior to each injection B, M and A is considered equal to the pressure at the beginning of the injection B, M and A. The subscript "f stands for "final" because the pressure P immediately after each injection B, M and A is considered equal to the pressure at the end of the injection B, M and A. This prediction is made with an adaptive model of the pressure P in the common rail R. This adaptive model may include adaptive maps K and W.

The adaptive map K gives first-order variations of the pressure. In the described example, the adaptive map K is specific to each cylinder C1 to C6 but in a variant, there may be a single adaptive map K for all the cylinders C1 to C6.

The adaptive map W gives second-order variations of the pressure and is optional.

In the example described, for the six cylinder engine E, the adaptive model includes six maps K and six maps W.

The pressures P_BI, PMI, PAI. ^pBf, Piw and P_AF are then used by the control unit 1 in order to compute, for the next injection phase, each injection time t_M, t_B and t_A and each injection duration d_M, d_B and d_A, so that the required quantities of fuel Q_B, QM and Q_A are injected at the required injection times t_M, t_A and t_B.

During each individual injection B, M and A, it can be considered the pressure inside the common rail R decreases roughly linearly due to the quantity of fuel Q_B, Q_M or Q_A injected. The adaptive map K gives the pressure drop ΔΡ_Κ inside the common rail R caused by the injection B, M or A, depending on the quantity of fuel Q_B, Q_M or Q_A injected and on the initial pressure P_BI, P_MI or P_AI inside the common rail R, before the injection B, M or A.

For example, the pressure P_BF at the end of the pre-injection B equals to the pressure P_BI at the beginning of the pre-injection B, minus the pressure drop ΔΡ_Κ given by the adaptive map K, depending on the fuel quantity Q_B of the pre-injection and on the pressure P_BI at the beginning of the pre-injection B:

Ρβί ⁼ ΡΒ_Ι - ΔΡΚ = P_Br K(Q_B, P_Bj).

More generally, within a given injection phase, let the subscript n be a given individual injection, for example the injection B, M, or A.

Within a given injection phase, the pressure P_nt at the end of a given injection n equals to the pressure P„i at the beginning of this injection n, minus the pressure drop ΔΡ_Κ given by the adaptive map K, depending on the fuel quantity Q_n of this injection n and on the pressure P^ at the beginning of this injection n :

P_nf = P_NI- AP_K = Pnr K(Q_n, P_ni).

After each individual injection, the pressure P fluctuates. The adaptive map W gives the pressure variance AP_W, at the injector's 11 to 16 connexion point with the common rail R, between a first and a second individual injections B, M or A, depending on the relative time offset between the first injection and the second individual injection, and depending on the pressure inside the common rail at the end of the first injection. In other words, the pressure variance may be expressed depending on the relative time between two consecutive individual injections, more especially between a given individual injection and an immediately preceding individual injection.

For example, the pressure P_Mi at the beginning of the main injection M equals to the pressure P_Bf at the end of the pre-injection B minus the pressure variance AP_W given by the adaptive map W, depending on the relative timing RT_B→M between the end of the pre- injection B and the main injection M start time t_M, and depending on the pressure P_Bf at the end of the pre-injection B:

P I ⁼ Bf- AP ⁼ Pec W(RT B→M> PB - More generally, within a given injection phase, the pressure P_ni at the beginning of a given individual injection n equals to the pressure P_n-1,f at the end of the immediately preceding individual injection r , minus the pressure drop AP_W given by the adaptive map W, depending both on the relative timing RT_N._1→N between the end of the preceding individual injection r and the start time t_n of the given individual injection n, and on the pressure P„-i_,fat the end of the preceding individual injection r :

P_ni = Pn-1 ΔΡνν = P_n-i W(RT_n._1→n, P_n._1if).

The pressure variance AP_wmay be positive or negative.

For example, adaptive maps K and W are two dimensional matrices, or look-up tables. Of course, the maps could have more dimensions if it were chosen to further refine the evaluation of the pressure drop and of the pressure variance. For example, the pressure drop caused by a preceding individual injection or the pressure variance could take into account a variable affecting the fuel compressibility, the fuel viscosity, etc.. Therefore, the maps could have further dimensions for taking into account variables such as the fuel temperature, fuel composition (in particular fuel blends), etc...

Hereunder is a description of a method according to the invention, depicted in figure 4, which aims to estimate the variations of the rail pressure P before each injection cycle in order to compute accurate fuel quantities Q_B, Q and Q_A.

In this description, the measured pressures bear the reference P'.

The method includes a preliminary step 1000, taking place prior to the use of the vehicle V, during which initial values are programmed in the adaptive maps K and W at stable conditions, at steady speed, by measuring the rail pressures P'_Bi, P'_Mi, P'_Ai, P'_Bf, P'_Mf and P'_Af, the injected fuel quantities Q_B, Q and Q_A and the injection times t_M, t_A and t_B. When specific adaptive maps K and W are used for each cylinder C1 to C6, the measures have to be repeated for each cylinder C1 to C6.

During a step 2000, occurring before each injection phase of a given cylinder amongst the cylinders C1 to C6, the control unit 1 computes the required fuel quantity Q_M to inject in this cylinder C1 to C6 during the main injection M, depending on the requested engine torque. The injection time t_M of the main injection M, as well as the fuel quantities Q_B and Q_A and the injection times t_A and t_B of the injections A and B of this injection phase, are also set by the control unit 1 according inter alia to combustion efficiency, emission, noise and heat constraints.

During a step 3000, taking place about 60° before the angular top dead centre CO_TDC of the cylinder cycle, the adaptive maps K and W are used to compute estimated pressures P_BI, P_M\, PAI. ΡΕ*_> IW and P_Af for the coming injection cycle. This step is therefore performed for a given injection phase and is completed before the beginning of said injection phase.

In a first sub-step 3001 , the pressure P_B, at the beginning of the pre-injection B is calculated, depending on a rail pressure P' measured by the sensor 2 about 60° before the angular top dead centre ω_τοο of the cylinder cycle, before the beginning of the injection phase. For example, it can be considered that the influence of a fluctuation of the rail pressure P between 60° before the angular top dead centre CO_TDC and the beginning of the injection phase is negligible, so that the pressure P_B, is then considered to be equal to the measured pressure P'.

As an alternative, the pressure P_BI at the beginning of the pre-injection B may be calculated depending on the maximum pressure P'_MAX inside the common rail R, measured by the sensor 2. For example, the pressure P_BI may be considered equal to the maximum pressure P'_MAX. As an option, the pressure P_BI may be calculated depending on the maximum pressure P'_MAX and on the difference in time At between the time t_Pmax when the pressure P is equal to the maximum pressure P_MAX and the injection time t_B of the pre- injection B of the upcoming injection phase.

In a second sub-step 3002, the pressure P_Bf at the end of the pre-injection B is calculated with the adaptive map K. The pressure P_BF equals to the pressure P_BI minus the pressure drop ΔΡ_Κ given by the adaptive map K, depending on the fuel quantity Q_B of the pre-injection and the pressure P_BI at the beginning of the pre-injection B:

The value of the pressure P_BI at the beginning of the pre-injection B is given by sub- step 3001.

In a third sub-step 3003, the injection duration d_B of the pre-injection B is calculated depending inter alia on the fuel quantity Q_B of the pre-injection B and on the pressure Ρ_Β, at the beginning of the pre-injection B. Then, in the third sub-step 3003, the relative timing RT_B_,M between the end of the pre-injection B and the injection time t_M of the main injection M is calculated depending on the injection duration d_B of the pre-injection B, and on the injection times t_B and t_M of the pre-injection B and of the main injection M, calculated during step 2000:

In a fourth sub-step 3004, the pressure P_Mi at the beginning of the main injection M is calculated with the adaptive map W. The pressure P_Mi equals to the pressure P_Bf minus the pressure variance AP_W given by the adaptive map W, depending on the relative timing RT_B→M between the end of the pre-injection B and the main injection M start time t_M, and depending on the pressure P_Bf at the end of the pre-injection B:

Piw ⁼ Ρβί- ΔΡνν ⁼ P_Bf - W(RT_B→M, P_Bf).

The value of the pressure P_Bf at the end of the pre-injection B is given by sub-step

3002.

In a fifth sub-step 3005, the pressure P_Mf. at the end of the main injection Ivl is calculated with the adaptive map K. The pressure P_Mf equals to the pressure P _i at the beginning of the main injection M minus the pressure drop ΔΡ_Κ given by the adaptive map K, depending on the fuel quantity Q_M of the main injection M and on the pressure P_Mi at the beginning of the main injection M:

P|W ⁼ MI - ΔΡ ⁼ P|Wi - K(QM, ΡΜΙ)·

The value of the pressure P_Mi at the beginning of the main injection M is given by sub-step 3004.

In a sixth sub-step 3006, the injection duration d_M of the main injection M is calculated depending inter alia on the fuel quantity Q_M of the main injection M and on the pressure P_M at the beginning of the main injection M. Then, in the sixth sub-step 3006, the relative timing RT_M→A between the end of the main injection M and the injection time t_A of the post-injection A is calculated depending on the injection duration d_M of the main injection M, and on the injection times t_M and t_A of the main injection M and of the post injection A, calculated during step 2000.

In a seventh sub-step 3007, the pressure P_Ai at the beginning of the post-injection A is calculated with the adaptive map W. The pressure P_Ai equals to the pressure P_Mf at the end of the main injection M minus the pressure variance AP_W given by the adaptive map W, depending on the relative timing RT_M→A between the end of the main injection M and the post-injection A start time t_A, and depending on the pressure P_Mf at the end of the main injection M:

PAI ⁼ Piw- AP_W - P_Mf - W(RTM→A, PIW)- The value of the pressure P _f at the end of the main injection M is given by sub-step 3005. In an eighth sub-step 3008, the pressure P_A, at the end of the post-injection A is calculated with the adaptive map K. The pressure P_Af equals to the pressure P_Ai at the beginning of the post-injection A minus the pressure drop ΔΡ_Κ given by the adaptive map K, depending on the fuel quantity Q_A of the post-injection M and the pressure P_Ai at the beginning of the post-injection A:

PA, = P_Ai - ΔΡ_Κ = P_Ai - K(QA, P_Ai).

The value of the pressure P_Ai at the beginning of the post injection A is given by sub- step 3007.

In a ninth sub-step 3009, the injection duration d_A of the post-injection A is calculated depending inter alia on the fuel quantity Q_A of the post-injection A and on the pressure P_Ai at the beginning of the post-injection A.

In more generic terms this part of the process includes the sub-steps of, for a given individual injection:

- computing 3004, 3007 an initial value of pressure in the common rail prior to the given individual injection, using the second adaptive map W giving a pressure variance

APW inside the common rail R between a preceding individual injection and the given individual injection (B, M, A).

- computing 3003, 3006, 3009 a duration of the given individual injection

- computing 3005, 3008 a final value of pressure in the common rail at the end of the given individual injection using the first adaptive map K which give a pressure drop

ΔΡΚ inside the common rail R caused by the given individual fuel injection B, M, A.

To be more exact, this generic description applies more specifically to all but the first and last individual injections of an injection phase.

For the first individual injection B, it has been explained above that the initial value of the pressure is calculated not using the second adaptive map W, because there is not an immediately preceding individual injection. For the last individual injection A, it is not compulsory to calculate the final value of the pressure.

In this way, the control unit 1 has predicted the values of all the pressures P_Bi, P I, PAI_> P-t_f. Piw and P_Af for the coming injection cycle. This first prediction is not precise since it does not take into account the pressure fluctuations occurring in operation, because adaptive maps K and W are filled with initial valued.

In a step 4000, the injection system S performs the injections B, M and A. The control unit 1 sends the signal Si to the given injector amongst the injectors 11 to 16, and the sensor 2 records the measured rail pressures P' Bi, P'MII P'AI, P'efi P'wif and P'_Af at the beginning and at the end of each injection B, M and A. When the injection phase is completed, the pumps P1 and/or P2 might be actuated by the control unit 1 in order to feed fuel into the common rail 1. In this case, the pressure P inside the common rail increases. The pumps P1 and P2 are not necessarily actuated between each injection phase.

If the pumps P1 and P2 are not actuated before a given injection phase, the pressure P_Bi at the beginning of the pre-injection of the next injection phase may be considered equal to the pressure P_Af at the end of the post-injection A of the preceding injection phase plus the pressure variance AP_W inside the common rail R after the post- injection A of the preceding injection phase. The pressure variance AP_W may be neglected.

In a step 5000, the values programmed in the adaptive maps K and W, for example during step 1000, are replaced with new values based on the comparison between the calculated pressure values P_Bi, PMI. PAI, P_>f. Piw and P_Af computed during step 2000 and the measured values P' Bi. P'_MII P'_AII P'EHI P Mt and P'_Af recorded during step 4000.

In order to smooth out the variations of the adaptive maps K and W, the new values are preferably incorporated gradually to the adaptive maps K and W. For example, the new values may represent 10% of the preceding values of the adaptive maps K and W:

K(Q_n, P'ni) <- 0,9.K(Q_n, P'_ni) + 0,1.(P'_ni - P_nf),

W(RT_n._1→n, P'_n-i,f) <- 0,9.W(RT_n._1→n, P'_n-i ,,) + 0,1.(P'_n._1>f - P'_nJ,

As indicated by arrow 6000, after the step 5000, the steps 2000 to 5000 may be repeated at the next injection phase for the given cylinder. Of course, the same process is also carried out in parallel for the other cylinders C1 to C6, with an angular offset of 120° between'each of them, with the adaptive maps K and W corresponding to the considered cylinder C1 to C6.

When each cylinder C1 to C6 has finished a given injection phase, the steps 2000 to 5000 are repeated for a next injection phase of the cylinder C1. During step 2000, the adaptive maps K and W, programmed with modified values set during , step 5000 of the preceding cylinder cycle, are used to compute the fuel quantities Q_B, Q_M and Q_A and the injection times t_B, t_M and t_c of the next cylinder cycle of cylinder C1 , and so on for the other cylinders C2 to C6.

In this way, the adaptive maps K and W are used to estimate precisely the pressure P in the common rail R for the next injection phase, by taking into account the rail pressure P fluctuations. In this way, the injected fuel quantities Q_B, Q_M and Q_A are very close to the computed values.

After the use of the vehicle V, the engine E is turned off. Arrow 7000 on figure 4 shows an initialization step occurring during a subsequent use of the vehicle V, when the engine E starts. The steps 2000 to 5000 are performed once with the values of the adaptive maps K and W established during the prior use of the vehicle. Then, the steps 2000 to 5000 are repeated in a loop as described previously.

Preferably, the values programmed in the adaptive maps K and W are replaced with new values only when the engine E is warm and runs in a steady state. In other words, the step 5000 of the method according to the invention is performed only when the engine E runs in a steady state. Moreover, this step 5000 of updating the adaptive maps is not necessarily performed at each engine cycle. It can be performed from time to time, for example at regular intervals or it can be performed only during adapting periods which occur from time to time, preferably within steady state operating periods of the engine.

According to a variant, the adaptive map W gives the pressure variance AP_W inside the common rail R between a first and a second injection B, M or A, depending on the time offset between the injection start time of the second injection and the top dead centre

For a given injection phase, let RT_B be the relative timing between the injection time t_B of the pre-injection B and the top dead centre time t_TDC. Similarly, for a given injection phase, let RT_M be the relative timing between the injection time t_M of the main injection M and the top dead centre time t_TDc, and let RT_A be the relative timing between the injection time t_A of the post-injection A and the top dead centre time t_TDC.

The relative timings RT_B, RT_M and RT_A are calculated in such a way that they have the same sign. In other words, the relative timings RT_B, RT_M and RT_A are all positive or all negative. For example, the relative timing RT_n of a given individual injection n may be equal to the absolute value of the difference between the injection time t_n of the given injection n and the top dead centre time t_TDC : RT_n = 1 1„ - t_TDc I-

Optionally, the method includes a step occurring after step 3000, in which the control unit 1 computes a delay δ between the times when the fuel is injected and the moment when the signal Si is emitted, based on the measured rail pressure P'_Bi at the beginning of the injection phase.

According to other embodiments of the invention:

- The number of injectors 11 to 16 and cylinders C1 to C6 may vary. In this case, the angular offset between the positions of the cylinders is adapted.

- The engine E may equip another type of automotive vehicle, for example a car.

- The engine E may equip a machine different from a vehicle, or a fixed installation. - The number of individual injections of each injection phase may vary. The technical features of the embodiments and variants mentioned here above can be combined.

Claims

1. - Method for controlling an injection system (S) in an internal combustion engine (E) having a common rail (R), for injecting fuel to cylinders (C1-C6), each injection phase comprising several individual injections (B, M, A) occurring during a cylinder cycle, the method including:

- a first step (2000) before a given injection phase of a given cylinder (C1-C6), in which the requested fuel quantities (Q_B, Q_M, QA) and the requested injection start times (t_B, t_A) are computed for each individual injection (B, M, A) of the given injection phase,

characterized in that the method further includes:

- a second step (3000) in which an adaptive model (K, W) of the variations of the pressure (P) in the common rail (R) is used to compute calculated values (P_Bi, Ρ_Μ,, PAI, PB Pwif. A of the pressure (P) in the common rail (R) for each individual injection (B, M, A) of the given injection phase, in accordance with the requested fuel quantities (Q_B, QM and Q_A) and the requested injection times (t_B, t_M and t_A) set during the first step (2000),

- a third step (4000) in which the values (P'_BI, P'_Mi, P'_Ai, P'_BF, P'_MF, P'A of the pressure (P) in the common rail (R) are measured and recorded during each individual injection (B, M, A) of the given injection phase,

- a fourth step (5000) in which the adaptive model (K, W) is adjusted depending on the difference between the computed pressure values (P_Bi, P_Mi, P_Ai, P_Bf, P_M, P_Af) of the second step (3000) and the recorded pressure values (P'_Bi, P'_Mi, P'_Ai, P'_Bf, P'M P'_Af) of the third step (4000).

2. - Method according to claim 1 , characterized in that a fifth step (6000), in which the first, second, third and fourth steps (2000, 3000, 4000, 5000) are repeated for the following injection phases.

3. - Method according to claim 1 or 2, characterized in that the adaptive model (K, W) includes a first adaptive map (K) giving a pressure drop (ΔΡ_Κ) inside the common rail (R) caused by a preceding individual fuel injection (B, M, A)

4. - Method according to claim 3, characterized in that the pressure drop (ΔΡ_Κ) given by the first adaptive map (K) depends on the injected fuel quantities (Q_B, Q_M, Q_A) and on the pressure (P_Bi, P_Mi, P_A,) inside the common rail (R) before the injection (B, M, A).

5. - Method according to claim 3 or 4, characterized in that the pressure (P_nf) at the end of a given individual injection (n) equals to the pressure (P_ni) at the beginning of the given individual injection (n), minus the pressure drop (ΔΡ_Κ) given by the first adaptive map (K), depending on the fuel quantity (Q_n) of the given injection (n) and on the pressure (P_ni) at the beginning of the given injection (n).

6. - Method according to claims, characterized in that the adaptive model (K, W) includes a second adaptive map (W) giving a pressure variance (AP_W) inside the common rail (R) between a first and a second injections (B, M, A).

7. - Method according to claim 6, characterized in that the pressure variance (AP_W) given by the second adaptive map (W) depends on the pressure at the end of the first injection and on the start time (t_A, t_B, t_c) of the second injection (B, M, A).

8. - Method according to claim 6 or 7, characterized in that the pressure variance (AP_W) given by the second adaptive map (W) for a given individual injection (n) depends both on the relative timing (RT_n-i_→n) between the end of a preceding individual injection (n-1) and the start time (t_n) of the given individual injection (n), and on the pressure (P_n-i _,f ) at the end of the preceding individual injection (n-1).

9. - Method according to any of the preceding claims, characterized in that, during the third step (4000), the pressure (P) in the common rail (R) is measured before and after each individual injection (B, M, A).

10. - Method according to any of the preceding claims, characterized in that the adaptive model (K, W) is specific to each cylinder (C1-C6).

11. - Method according to any of the preceding claims, characterized in that the adaptive model includes at least one two dimensional matrix (K, W).

12. - Method according to claims 1, 6 and 6 in combination, characterized in that the second step (3000) includes the sub-steps of, for a given individual injection:

- computing (3004, 3007) an initial value of pressure in the common rail prior to the given individual injection, using the second adaptive map (W) giving a pressure variance (APw) inside the common rail (R) between a preceding individual injection and the given individual injection (B, M, A).

- computing (3003, 3006, 3009) a duration of the given individual injection, depending on the computed value of the initial pressure,

- computing (3005, 3008) a final value of pressure in the common rail at the end of the given individual injection using the first adaptive map (K) which give a pressure drop (ΔΡ ) inside the common rail (R) caused by the given individual fuel injection (B, M, A).

13. - Method according to any of the preceding claims, characterized in that it includes an initialization step (7000) occurring during a subsequent use of the engine (E), wherein the steps (2000-5000) are repeated once with the values of the adaptive model (K, W) established during the prior use of the engine (E).

14. - An injection system (S) for an internal combustion engine (E), said system having a common rail (R) for supplying fuel to cylinders (C1-C6) and means (2) for measuring the pressure (P) in the common rail (R), characterized in that it further includes a control unit (1) implementing a method according to one of the preceding claims.

15. - An automotive vehicle (T), characterized in that it includes an injection system (S) according to claim 14.