WO2008147319A1

WO2008147319A1 - Method for identifying a malfunctioning fuel injector of a multi cylinder combustion engine

Info

Publication number: WO2008147319A1
Application number: PCT/SE2008/050620
Authority: WO
Inventors: Tommy Sahi
Original assignee: Scania Cv Ab (Publ)
Priority date: 2007-06-01
Filing date: 2008-05-26
Publication date: 2008-12-04
Also published as: GB0710551D0; GB2449706A; DE112008001486T5; DE112008001486B4

Abstract

The present invention relates to a method for identifying a malfunctioning fuel injector (1-6) associated with an individual cylinder of a multicylinder combustion engine (50), comprising an accumulator tank (120). The method comprises the steps of: determining a first pressure value (P1ij) of the accumulator tank, prior to supplying fuel to one individual cylinder; supplying fuel to the one individual cylinder during a predetermined on-time; determining a second pressure value (P2ij) of the accumulator tank after the fuel supply; processing the first and second pressure values so as to establish a test value (Qi); and identifying, when applicable, a malfunctioning fuel injector based upon said established test value (Qi). The invention also relates to computer program for identifying a malfunctioning fuel injector, a computer program product comprising computer program code for implementing a method according to the invention, a computer, and a platform having a computer.

Description

METHOD FOR IDENTIFYING A MALFUNCTIONING FUEL INJECTOR OF A MULTI CYLINDER COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a method for identifying a malfunctioning fuel in- jector associated with a cylinder of a multi-cylinder combustion engine. The inven- tion also relates to computer program for identifying a malfunctioning fuel injector associated with a cylinder of a multi-cylinder combustion engine. The invention fur- ther relates to a computer program product comprising computer program code for implementing a method according to the invention. The invention also relates to a computer. The invention further relates to a platform having a computer.

BACKGROUND

When a multi-cylinder combustion engine fails to deliver its rated power, this may be due to the malfunctioning of any of the cylinders of the engine. In the case of a diesel engine, the malfunctioning of a cylinder may be due to the underfuelling or overfuelling caused by a faulty fuel injector. The malfunctioning may also be due to worn piston rings and valves which cause toss of compression. The malfunctioning of a cylinder may for instance result in rough engine operation, poor cylinder com- pression and/or reduced engine torque.

Today there exist a number of methods known to a person skilled in the art of iden- tifying a weak or defective cylinder. In these tests a malfunctioning cylinder may be identified. DE 19540826 Al₃ for example, discloses a method for identifying a mal- functioning cylinder, where firstly a specified operation condition is set and the en- gine speed is determined, then the fuel supply to the tested cylinder is interrupted and the engine speed is determined anew. If the difference between the engine speed before and after the fuel supply interruption is smaller than a predetermined value, the tested cylinder is considered to be malfunctioning. Further, EP 1520 163 B 1 dis- closes another method for identifying a malfunctioning cylinder, where the engine is accelerated to a given first engine speed, whereupon the fuel supply is interrupted to all the cylinders of the engine except an individual tested cylinder, which is supplied with a predetermined amount of fuel. The engine speed is then allowed to decrease from the first engine speed to a given second engine speed and the time it takes for the engine to decrease to this second engine speed is counted. This recorded decel- eration time may then for instance be compared with a reference value in order to establish whether or not the tested cylinder is malfunctioning. A disadvantage with the above mentioned methods is that it is not determined if the malfunction is asso- ciated with the cylinder itself, or is due to a faulty fuel injector.

It would be advantageous to provide a new manner for identifying a malfunctioning fuel injector associated with an individual cylinder of a multi-cylinder combustion engine. It would also be advantageous to provide a method for diagnosing a multi- cylinder combustion engine.

SUMMARY OF THE INVENTION

The present invention provides a method for identifying a malfunctioning fuel injec- tor associated with an individual cylinder of a multicylinder combustion engine, said engine comprising an accumulator tank from which pressurised fuel is intended to be distributed to the cylinders by means of the fuel injectors, comprising the first steps of:

- determining a first pressure value of the accumulator tank prior to supplying fuel to one individual cylinder; supplying fuel to the one individual cylinder during a predetermined on-time;

- determining a second pressure value of the accumulator tank after the fuel sup- ply; - processing the first and second pressure values so as to establish a test value; and - identifying, when applicable, a malfunctioning fuel injector based upon said es- tablished test value.

An advantage with this method is that it facilitates determining if the fueJ supply to a certain cylinder is ok, or if it is too high or too low- ϊn combination with a general cylinder malfunctioning test according to prior art, it is thus also possible to deter- mine whether a malfunctioning cylinder is caused by too high or too low fuel injec- tion by means of a faulty fuel injector or if it is due to a malfunction in the cylinder itself and not the fuel injector.

In one embodiment the method comprises the step of repeating the first steps sepa- rately for at least one additional individual cylinder of said engine, preferably for all additional cylinders of said engine, where the steps are carried out under substan- tially the same test conditions. Hereby mutually comparable test values for other fuel injectors of the engine are received such that individual fuel injectors of the en- gine may be compared in order to determine if a fuel injector is malfunctioning.

In another embodiment the identifying step, when applicable, involves the step of comparing test values associated with said at least one additional individual cylinder of said engine, preferably all additional cylinders of said engine, with the one indi- vidual cylinder. Hereby a malfunctioning fuel injector may be identified. Particularly, if test values for several fuel injectors, e.g. all fuel injectors, are compared it is possible to identify more than one malfunctioning fuel injector.

In yet another embodiment the method comprises the step of repeating the steps of determining the first pressure value of the accumulator tank prior to supplying fuel to the one individual cylinder; supplying fuel to the one individual cylinder during the predetermined on-time; and determining the second pressure value of the accu- mulator tank after the fuel supply, so as to establish a set of pairs of corresponding first and second pressure values associated with the one individual cylinder. In this way a statistically more accurate test value may be achieved.

In a further embodiment the method comprises the steps of:

- generating a reference value based upon the test values corresponding to the one individual cylinder and the at least one additional individual cylinder; and

- identifying the malfunctioning fuel injector/injectors based upon the deviation of said test values from said reference value.

In an embodiment the reference value is the median value of the test values or the mean value of the test values. The advantage is that it is easy to compare the fuel in- jectors and thus identifying the malfunctioning fuel injector/injectors. The advantage of using the median value is that the ability of identifying a malfunctioning fuel injector is increased since the median value is not affected if more than one fuel in- jector is malfunctioning, which is the case when using the mean value. The median value is thus preferred as reference value.

In an additional embodiment the step of processing the first and second pressure values so as to establish a test value, involves the steps of:

- generating a set of pairs of pressure difference values and mean pressure values based upon the set of pairs of corresponding first and second pressure values;

- generating a pressure difference function based upon the set of pairs of differ- ence pressure values and mean pressure values; and

- integrating said function over a predetermined mean pressure range.

In this way a test value which is easily comparable is provided.

In another embodiment said function is a linear function based upon linear regres- sion of said set of pairs of difference pressure values and mean pressure values. By using linear regression quantification errors caused by AD-conversion may be avoided. Further easier comparison of the determined set of values is facilitated.

In yet another embodiment the first pressure value determined prior to supplying fuel to the one individual cylinder is determined based upon a plurality of samples. In this way a statistically more accurate pressure value is achieved, where oscilla- tions of the pressure in the accumulator tank is compensated for.

In a further embodiment the second pressure value determined after supplying fuel to the one individual cylinder is determined by a plurality of samples. In this way a statistically more accurate pressure value is achieved, where oscillations of the pres- sure in the accumulator tank is compensated for.

In a still further embodiment the method comprises the step of prior to determining a first pressure value, pressurising the fuel in the accumulator tank such that a pre- determined pressure is set in said tank. This has the advantage that repeating tests will start under the same condition, i.e. the same pressure in the accumulator tank.

According to an embodiment the present invention comprises a computer, such as an embedded electronic control unit or a vehicle external computer comprising a storing means and a computer program for identifying a malfunctioning fuel injector associated with an individual cylinder of a multicylinder combustion engine, said engine comprising an accumulator tank from which fuel is intended to be distributed to the cylinders by means of the fuel injectors, comprising computer readable pro- gram code means for causing an electronic control unit to perform the method steps according to the invention.

DESCRIPTION OF THE DRAWINGS A better understanding of the present invention will be had upon the reference to die following detailed description when read in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughout the several views, and in which:

Fig. Ia schematically shows a system for performing a method according to the pre- sent invention;

Fig. Ib schematically shows an embodiment of a fuel injection system for perform- ing the method according to the present invention;

Fig. 2a schematically shows an electronic control unit according to the present in- vention:

Fig. 2b schematically shows an external computer according to the present inven- tion;

Fig. 3a schematically shows a linear regression of pressure difference values plotted against mean pressure values of a test according to the present invention;

Fig, 3b shows a bar diagram showing the deviation of the test value for each of the fuel injectors from the median of the test values for all six fuel injectors; and

Fig. 4 shows a flow diagram illustrating a method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With reference to Figure 1a and 1b, a sub-system of a platform 60 is shown. The platform is preferably a ground vehicle, such as a truck or lorry. It should be noted that the platform alternatively can be a water craft or underwater craft, e.g. a ship or submarine. Alternatively the platform can be a stationary power plant.

In the figures described below the number of cylinders/injectors of the system is six. However, it must be understood that the invention is applicable to any multicylinder combustion engine with any known number of cylinders/injectors.

Fig. 1 a shows a schematic block diagram of a fuel injection system for performing a method according to the present invention. A platform, e.g. a vehicle such as a truck or a ship, comprises an internal combustion engine in the form of a diesel engine. The combustion engine 50, and thus the fuel injection system is controlled by an electronic control unit 100 embedded in the vehicle. The system comprises an ac- cumulator tank 120 arranged to receive pressurised fuel from a pressurising means 140. The electronic control unit 100 is adapted to receive sensed engine data in the form of e.g. a pressure sensor signal. The pressure sensor signal is received on a first line from a pressure sensor 130 arranged to sense the pressure in the accumulator tank 120. Injection means in the form of fuel injectors 1-6, here six, are arranged, respectively, to inject fuel from the accumulator tank into the combustion space of a corresponding cylinder (not shown). Each fuel injector 1-6 is controlled by the elec- tronic control unit 100. The pressurising means 140 may be any kind of arrangement for pressurising and supplying fuel to the accumulator tank 120, such that fuel of high pressure is accumulated in the accumulator tank 120. In fig. Ib an embodiment of a fuel injection system according to the present invention is depicted, which is described in more detail below.

Fig, Ib shows an embodiment of a fuel injection system for a combustion engine 50 in the form of a schematically represented diesel engine having six cylinders. The fuel injection system and the diesel engine are with advantage fitted to a heavy vehi- cle, such as truck or bus. The fuel injection system is a so-called Common RaH sys- tern and comprises a fuel line 115a for supply of fuel from a fuel tank 115 to the cyl- inders of the dlesel engine. A fuel pump 116 is arranged in the fuel line to convey fiiel from the fuel tank 115 via a valve 117 to a high-pressure pump 118. The valve 117 is arranged in an open state to allow fuel to the high pressure pump 118. and to in a closed state interrupt said supply of fuel. The high pressure pump 118 is adapted to pressurize the fuel so that it enters at high pressure an accumulator tank 120 which takes the form of a so-called Common Rail. The high fuel pressure in the accumulator tank constitutes a power source making it possible for fuel to be in- jected at high pressure into the respective cylinders of the diesel engine. The fuel in the accumulator tank 120 is intended to be distributed to all the cylinders of the combustion engine 50.

To control the injection of fuel an injection means in the form of electronic fuel in- jectors 1-6 is arranged in each of the connections between the accumulator tank 120 and the respective cylinders of the diesel engine. When a fuel injector is in an open state, it injects fuel at high pressure into the cylinder concerned. Thus, fuel from the accumulator tank 120 is injected into the combustion spaces of the respective cylin- der by means of the fuel injectors 1-6, which fuel injectors 1-6 are configured to open and close very quickly in a controlled manner. A control unit in the form of an electronic control unit 100 is adapted to control the operation of the fuel pump 116, the valve 117, the high pressure pump 1 18 and the electronic fuel injectors 1-6. A pressure sensor 130 is arranged in the accumulator tank 120 to detect the prevailing pressure therein and to send to the control unit 100 a signal conveying information about the pressure values detected. During normal operation the electronic control unit 100 controls, on the basis of knowing the pressure in the accumulator tank 120, the on-time or opening times of each individual electronic fuel injector 1-6 so that the calculated amount of fuel is supplied with good accuracy to the combustion spaces of the respective cylinders. In the method according to the present invention the electronic control unit 100 is arranged to control each individual fuel injector by means of shutting of all fuel injectors apart from the fuel injector intended to be tested, and then shutting on and off the tested fuel injector, applying the same on- time for the tested fuel injector for different pressures in the accumulator tank 120. The pressure sensor 130 is arranged to detect the pressure in the accumulator tank, and thus the pressure drop may be determined. In order to measure the pressure of the accumulator tank, i.e. the ftiel pressure, an alternative embodiment to the ar- rangement of having one pressure sensor 130 detecting the pressure in the accumu- lator tank 120, is to arrange a pressure sensor at each fuel injector such that the pres- sure of the accumulator tank, i.e. the fuel pressure is detected.

Here, the inventive method is initiated and controlled by means of an external com- puter I 10, for instance in the form of an external PC. The external computer 110 may be directly connected to the electronic control unit 100, but may also be indi- rectly connected to the electronic control unit 100 in any suitable manner. The communication between the external computer and the electronic control unit 100 may be partly or entirely wireless. The inventive method could also be initiated and controlled by the electronic control unit 100 itself or by another electronic control unit. Preferably a display 11 1 is connected to the external computer 110 and/or the electronic control unit 100, which display 1 l l is arranged to show a suitable user interface.

In this description and the subsequent claims, the term "on-time" refers to the open- ing time of a fuel injector, i.e. the duration of the time period during which the fuel injector is kept open in order to inject fuel into the associated cylinder in connection with a single stroke of the engine. The quantity of fuel injected into a cylinder in connection wim a stroke of the engine depends on the length of the on-time and the pressure of the fuel supplied to the fuel injector.

Fig. 2a schematically shows the electronic control unit 100, which comprises a first CPU 200 connected to a first port 220 via a first bus 220a in order to receive the pressure signal from the pressure sensor 130. a second port 222 via a second bus 222a for communicating with the fuel injector units 1-6 and a third port 224 via a third bus 224a for COmmunication with the external computer 110 directly or indi- rectly via a vehicle internal network- The first CPU 200 is also connected to at least one storing means 230, snch as a hard disk, a flash memory EEPROM and a ROM (Read Only Memory), via a fifth bus 230a. The electronic control unit 100 suitably also comprises other components commonly used in an ECU (Electronic Control Unit) for vehicles, e.g. a Random-Access Memory; an EPROM, a Bus controller and A/D-converters (not shown) in the case where pressure signals are analogue signals. Installed in the storing means are e.g. an engine pressure sensor interface computer program 232 for interpreting the pressure signal, a fuel control computer program 234 for controlling the supply of fuel to the cylinders and a first communication in- terface computer program 236 for communication with the external computer 110 or the vehicle internal network- These computer programs may be program modules in an engine control computer program. It must also be understood that several func- tions may be implemented as partly software and hardware as known to a person skilled in the ait.

Fig. 2b schematically shows an example of the external computer 110, which com- prises a second CPU 210 connected to a fourth port 240 via a fifth bus 240a for communication with the electronic control unit 100 and a fifth port 242 via a sixth bus 242a for communication with a display which may show a graphical or charac- ter-based user interface. The second CPU 110 is also connected to at least one sec- ond storing means 250, such as a hard disk, a flash memory and a ROM via a seventh bus 250a. The second storing means 250 comprises a cylinder test computer program 251 for identifying a malfunctioning fuel injector 1-6 associated with an individual cylinder of a multicylinder combustion engine 50, The second storing means suitably comprises a second communication interface program module 252 for communication with the electronic control unit 100, a user interface program module 254 and a criteria checking program module 256. The criteria checking pro- gram module 256 is further explained beiow in association with a third step of the method according to the present invention as shown in fig. 4. The cylinder tests computer program 251 may be downloaded to the external computer 110, e.g. di- rectly from a computer program product, such as a floppy disk, an external hard disk, a CD, a DVD and a flash memory, and through a server via a Local Area Net- work or Wide Area Network, As alternative embodiments, it must be understood that the invention also comprises embodiments where at least part of the cylinder test computer program 251 may be installed as separate computer programs in the electronic control unit 100 and/or another ECU in the vehicle in order to e.g. create redundancy or a distributed cylinder test computer program.

A flow diagram illustrating an embodiment of an inventive method for identifying a malfunctioning fuel injector associated with a cylinder of a multicylinder combustion engine is shown in fig. 4. In a first step Sl , an operator starts the cylinder test computer program 251 on the computer, for instance on the external computer 110, which causes the display 11 1 connected to the computer to show a suitable user in- terface. In a second step S2, the operator requests a start of a cylinder test via the user interface. The request is sent to the electronic control unit 100, which, by means of the criteria checking program module 256, in a third step S3 checks whether one or several given conditions for a start of the cylinder test are fulfilled. One condition may be that the gear box associated with the engine to be tested is in the neutral position, as a safety precaution. Also other conditions are conceivable, such as e.g. if the parking brake is activated. If any of the given conditions is not fulfilled, the request to start the cylinder test is denied and step S2 has to be re- peated.

If the given conditions are fulfilled, the method proceeds to a fourth step S4, in which a test cycle involving the following steps is executed under the control of the cylinder test computer program 251. Firstly fuel is supplied to the accumulator tank 120 such that a predetermined pressure is set in said tank 120. This is, according to an embodiment, achieved by means of the Common Rail system. However any other means where the fuel may be pressurised in the accumulator tank 120 to a high pres- sure may be used. For example an electric/hydraulic pump could be used instead of a pump driven by means of a crank shaft. In order to supply the fuel to the accumul lator tank 120 the engine 50 is according to an embodiment accelerated to a given first engine speed by means of all cylinders. All the cylinders could throughout this acceleration be supplied with an equal amount of fuel. At the given engine speed a certain predetermined pressure in the accumulator tank is awaited, i.e. when a predel termined pressure is reached in the accumulator tank the fuel supply to the tank is interrupted. The pressure in the accumulator tank is set to a predetermined pressure value to facilitate that tests of each separate fuel injector can be performed under substantially the same test conditions. The pressure in the accumulator tank 120 is detected by means of the pressure sensor 130, and the electronic control unit 100 rel ceives the pressure signal from the pressure sensor 130. In this embodiment fuel is supplied by means of the fuel pump 116, fuel is pressurised by means of the high pressure pump 118, and fuel to the accumulator tank 120 is interrupted by means of the valve 117. The high pressure pump 118 is in one embodiment directly driven be means of the crank shaft of the engine 50. Alternatively the high pressure pump could be controlled by means of the electronic control unit 100. The high pressure pump 118 provides the pressure in the accumulator tank 120. The fuel supply to the high pressure pump 118 is controlled by means of the valve 117. The electronic con- trol unit 100 further controls the valve 117 such that the valve 117 interrupts the fuel supply by an instruction from the electronic control unit 100.

In a fifth step S5 the fuel supply to all the cylinders including the cylinder associated with the fuel injector to be tested is interrupted. This is done by means of the elec- tronic control unit 100, which instructs the fuel injectors 1 -6 to cease injecting fuel to the cylinders when the predetermined pressure in the accumulator tank is reached, i.e. at a point of time when the pressure signal from the pressure sensor 130 received by the electronic control unit 100 corresponds to the predetermined pressure value. Alternatively the fuel supply to all cylinders except the cylinder associated with the fuel injector to be tested could be interrupted. In a sixth step So the pressure in the accumulator tank 120 is determined by means of the pressure sensor 130. The electronic control unit 100 receives the pressure value detected by the pressure sensor 130. In order to provide an accurate pressure, the pressure is sampled a number of times, e.g. 24 samples, and the average pressure of said samples is calculated by means of the electronic control unit 100. This means that the pressure is detected repeatedly a number of times within a short time span in order to determine an accurate pressure value. The pressure in the accumulator tank oscillates after an injection of fuel, and docs thus not immediately stabilize after a pressure drop. The sample frequency is preferably chosen to suit the natural fre- quency of the accumulator tank and its content Λn increased number of samples in- creases the accuracy. The determination of the pressure in the accumulator tank 120 is preferably performed in connection to a seventh step S7, i.e. immediately before the seventh step S7, which step S7 involves injection of fuel during a predetermined on-time. By determining the pressure in the accumulator tank immediately before fuel injection a more accurate pressure value of the pressure before injection is es- tablished. Thus, a first pressure value PI_j immediately before injection of fuel into the cylinder during said on-time is determined, where index i is the number of the tested fuel injector 1-6, and the index j is the number of the repetition of the deter- mination of the pressure before injection of fuel, which injection is repeated a num- ber of times as explained below.

In the seventh step S7 fuel is supplied to the cylinder to be tested during a predeter- mined on-time, which e.g. maybe about of 0,5 ms, by means of the electronic con- trol unit 100 which instructs the corresponding electronic fuel injector to inject fuel into the cylinder during said on-time. The tested fuel injector receives a pulse from the electronic control unit 100 which corresponds to the on-time. As a consequence of injecting fυel into the test cylinder the pressure in the accumulator tank drops during said on-time. In an eighth step S8 the fuel supply to the test cylinder is interrupted by means of the electronic control unit 100> which instructs the tested fuel injector to cease injecting fuel to the cylinder. Actually the injection of fuel is interrupted when the on-time pulse is terminated.

In a ninth step S9 the pressure in the accumulator tank 120 is determined by means of the pressure sensor 130. In order to provide an accurate pressure, the pressure is sampled a number of times, e.g. 24 samples, and the average pressure of the samples is calculated by means of the electronic control unit. This means that the pressure is detected repeatedly a number of times within a short time span in order to determine an accurate pressure value. The pressure in the accumulator tank oscillates after an injection of fuel, and does thus not immediately stabilise after a pressure drop. The sample frequency is preferably chosen to suit the natural frequency of the accumula- tor tank and its content. An increased number of samples increases the accuracy. The determination of the pressure in the accumulator tank is preferably performed in connection to the sixth step S6, i.e. immediately after the sixth step. By determining the pressure in the accumulator tank immediately after fuel injection a more accurate pressure value of the pressure after injection is established. Thus, a second pressure value P2i_j immediately after injection of fuel into the cylinder during said on-time is determined, where index / is the number of the tested fuel injector 1-6, and the index j is the number of the repetition of the determination of the pressure after injection of fuel, which injection is repeated a number of times as explained below.

In a tenth step SlO, steps S6-S9 are repeated a certain number of times in order to provide a set of test data of pairs of first and second pressure values, Pl_y and P2_g.

For each repetition, i.e. each time fuel is injected by means of the tested fuel injector during said on-time, the pressure in the accumulator tank decreases. The repeat of steps S6-S9 thus involves; determining the pressure in the accumulator tank by a number of samples immediately after said on-time; supplying fiiel to the tested cyl- inder during said on-time, whereas the pressure in the accumulator tank drops fur- Cher; interrupting the fuel supply to the tested cylinder; and determining the pressure in the accumulator tank immedialely after said on-time and so on, until a desired set of pairs of pre and post injection pressure values, i.e. first and second pressure val- ues Pl % and Ply have been collected. By repeating steps S6-S9 a statistically more accurate test value may be established.

In an eleventh step Sl 1 the set of first and second pressure values Pl_φ P2_ϋ are proc- essed so as to establish a test value Q_h where index i is the number of the tested fuel injector. Each pair of first and second pressure values Pl_iJt P2_ijt determined in con- nection to each injection, of the set of pairs of first and second pressure values Pl^ P2i_j of pressure before and after the fuel supply to the tested cylinder are compared so as to establish the test value which is comparable with a test value established in the same way for another individual fuel injector of the engine 50 such that it can be established whether the tested fuel injector is malfunctioning or not. The test value Q) is established by means of the recorded set of data of the pressure before and af- ter the fuel supply to the test cylinder by integrating a plot of corresponding values of the set of values of the pressure difference ΔP_j and the mean pressure P_j within a specified range of mean pressure values. A set of pairs of pressure difference values AP_Q and mean pressure values P_u based upon the set of pairs of corresponding first and second pressure values PI_if, P2j_j are generated. Then a pressure difference func- tion based upon the set of pairs of pressure difference values and mean pressure values is generated, and said function is integrated over a predetermined mean pres- sure range. For a set of fuel injections to the tested cylinder, i.e. for each fuel supply to the tested cylinder of a number of fuel supplies during a test of one fuel injector, the pressure difference ΔP_y of the pressure before the fuel supply, i.e. the first pres- sure value Pl i_j and the pressure after the fuel supply, i.e. the second pressure value P2jj, i.e. ΔP₂y = Pl i_j - P2y, and the mean pressure of the pressure before Pl and the pressure after P2 the fuel supply, Le. P₉ - (Pl_i} + P2_ij)l2 are calculated. Each pair of pressure difference value and mean pressure value is plotted in a graph of pressure difference versus the mean pressure. Each plot corresponds to one fuel supply to the tested cylinder. The integration is preferably performed over a function based on the plot. Preferably the function is a linear function based on a linear regression of said plot. The linear regression is thus performed based on the set of measured data con- stituted by the plotted pressure difference and mean pressure values of the test of a cylinder. The advantage of performing a linear regression of the set of data is that quantification errors due to AD-conversion are avoided. Further_* this improves the ability to compare measured data. The linear regression results in the following equation:

where AP₁ is the equation for the estimated pressure drop, a_t and & are the regres- sion parameters for the linear equation for the i:th fuel injector, i.e. each fuel injec- tor/cySinder will have an own set of α and p\ index / representing the number of the tested fuel injector 1-6.

Fig. 3a shows a set of pairs of pressure difference values and mean pressure values plotted in a graph of pressure difference versus the mean pressure of a test of a fuel injector of an engine 50. The figure also shows a linear regression of said set of de- termined values.

Jn order to establish the comparison value £>, the equation of the linear regression curve is integrated. The integration of the linear regression curve follows from:

In a twelfth step S 12 the test is repeated under substantially the same conditions for all cylinders of the engine 50. During the test Q_t values for all fuel injectors 1-6 he- ing tested, i.e. the fuel injectors of the engine of the particular test, are established. In order to detect a deviation of a certain fuel injector a comparison of Q_b with the median of the Q- value of all the tested fiiel injectors of the engine. If the character- istics of a fuel injector deviate from the median it will show from this comparison.

Fig. 3b shows a comparison of six fuel injectors respectively associated with a cyl- inder of an engine. In this particular example a deviation of 6 % is demonstrated for fuel injector number six, which indicates that the fuel injector 6 supplies an inex- haustive amount of fuel and is thus malfunctioning. The difference between the mu- tual cylinders/injectors can thus be estimated. This information is then used to diag- nose errors.

In the method according to above the test is performed by decelerating the engine 50 from a high engine speed to a low engine speed, e.g. idling speed. Thus, the engine 50 decelerates during each on-time of the tested fuel injector until a low engine speed is reached, when the test is terminated. Alternatively the test is terminated when the pressure in the accumulator tank 120 has dropped to a desired pressure, e.g. 1000 bar. Decelerating the engine from a high engine speed to a low engine speed is a convenient way of combusting fuel, i.e. emptying the accumulator tank 120 of fuel, since the sound from the engine 50 is relatively low, and the engine runs relatively smoothly. This is however also conceivable by running the engine 50 at an idling speed if a sufficient amount of fuel is provided, but this would cause the en- gine to sound bad and not run smoothly, thus providing not so good working condi- tions for the operator. Theoretically it would also be possible to conceive this step with the engine 50 shut down, but this would then require a separate supply of fuel due to the fact that the fuel pump is driven by means of the engine 50, and further a high amount of fuel would be present in the cylinders after the test, which may af- fect a subsequent test

As mentioned above, the inventive method is here initiated and controlled by means of the external computer 1 10, connected to the electronic control unit 100. The in- ventive method could as stated earlier also be initiated and controlled by the elec- tronic control unit 100 itself or by another electronic control unit.

According to an embodiment of the present invention the external computer 110 is arranged to run a computer program 251 for identifying a malfunctioning fuel injec- tor 1-6 associated with an individual cylinder of a multicylinder combustion engine 50, said engine comprising an accumulator tank 120 from which fuel is intended to be distributed to the cylinders by means of the fuel injectors, comprising computer readable program code means for causing an electronic control unit for controlling the engine 50 to perform the first steps of: determining a first pressure value Pl_j of the accumulator tank prior to supplying fuel to one individual cylinder; initiating the supply of fuel to the one individual cylinder during a predetermined on-time; determining a second pressure value P2_j of the accumulator tank after the foel sup- ply; processing the first and second pressure values so as to establish a test value Q₁ identifying, when applicable, a malfunctioning fuel injector based upon said estab- lished test value Q_h

According to another embodiment the external computer 110 is arranged to run the computer program 251 _> comprising computer readable program code means for causing the electronic control unit to perform the step of repeating said first steps separately for al least one additional individual cylinder of said engine, preferably for all cylinders of said engine, where the steps are carried out under substantially the same test conditions.

According to another embodiment the external computer 1 10 is arranged to run the computer program 251, wherein the identification step, when applicable, involves the step of comparing test values Q, associated with said at least one additional indi- vidual cylinder of said engine, preferably all additional cylinders of said engine, with the one individual cylinder.

According to another embodiment the external computer 110 is arranged to run the computer program 251. comprising computer readable program code means for causing the electronic control unit to perform the step of repeating the steps of de- termining the first pressure value PJ,_j of the accumulator tank prior to supplying fuel to the one individual cylinder; supplying fuel to the one individual cylinder during the predetermined on-time; and determining the second pressure value Pl^ of the accumulator tank after the fuel supply, so as to establish a set of pairs of correspond- ing first and second pressure values PJy, P2_ϋ associated with the one individual cyl- inder.

According to another embodiment the external computer 110 is arranged to run the computer program 251 , comprising computer readable program code means for causing the electronic control unit to perform the steps of: generating a reference value K based upon the test values Q₍ corresponding to the one individual cylinder and the at least one additional individual cylinder; and identifying the malfunctioning fuel injector based upon the deviation of said test values from said reference value K.

According to another embodiment the external computer 110 is arranged to run the computer program 251, wherein tht reference value tc is me median value of the test values Qi or the mean value of the test values Q₁.

According to another embodiment the external computer 1 10 is arranged to run the computer program 251, wherein the step of processing the first and second pressure values PJy, P2_Q SO as to establish a test value Q_h involves the steps of: generating a set of pairs of pressure difference values ΔP_y and mean pressure values Pij based upon the set of pairs of corresponding first and second pressure values

Pl(_/\ P2jβ generating a pressure difference function based upon the set of pairs of difference pressure values and mean pressure values ΔPiμ Pij ; and integrating said function over a predetermined mean pressure range.

According to another embodiment the external computer 1 10 is arranged to run the computer program 251, wherein said function is a linear function based upon linear regression of said set of pairs of difference pressure values and mean pressure val- ues ΔPi_j, Pij ,

According to another embodiment the external computer 110 is arranged to run the computer program 251. , wherein the first pressure value PIg determined prior to supplying fuel to the one individual cylinder is determined based upon a plurality of samples.

According to another embodiment the external computer 1 10 is arranged to run the computer program 251, wherein the second pressure value P2_i} determined after supplying fuel to the one individual cylinder is determined by a plurality of samples.

According to another embodiment the external computer i 10 is arranged to run lhe computer program 251, comprising computer readable program code means for causing the electronic control unit to perform the step of prior to determining a first pressure value Pl^ causing a pressurising of the fuel in the accumulator tank such that a predetermined pressure is set in said tank.

The foregoing description of the preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modi- fications as are suited to the particular use contemplated.

Claims

1. A method for identi fying a malfunctioning fuel injector (1-6) associated with an individual cylinder of a multieylϊnder combustion engine (50), said engine compris- ing an accumulator tank (120) from which pressurised fuel is intended to be distrib- uted to the cylinders by means of the fuel injectors, comprising the steps of:

- determining a first pressure N¹BlUe (P/,,) of the accumulator tank prior to supply- ing fiiel to one individual cylinder;

- supplying fuel to the one individual cylinder during a predetermined on-time;

- determining a second pressure value (P 2_j) of the accumulator tank after the fuel supply;

- processing the first and second pressure values so as to establish a test value (Qi); and

- identifying, when applicable, a malfunctioning fuel injector based upon said es- tablished test value (Qj).

2. A method according to claim 1, characterised by the step of repeating the steps of claim I separately for at least one additional individual cylinder of said engine, preferably for all additional cylinders of said engine, where the steps are carried out under substantially the same test conditions.

3. A method according to claim 2, wherein the identification step, when applicable, involves the step of comparing test values (Qi) associated with said at least one addi- tional individual cylinder of said engine, preferably all additional cylinders of said engine, with the one individual cylinder.

4. A method according to any of claims 1-3, characterised by the step of repeating the steps of determining the first pressure value (P U_j) of the accumulator tank prior to supplying fuel to the one individual cylinder; supplying fuel to the one individual cylinder during the predetermined on-time; and determining the second pressure value (P2i_j) of the accumulator tank after the fuel supply, so as to establish a set of pairs of corresponding first and second pressure values (P I^ P2jj) associated with the one individual cylinder.

5. A method according to any of claims 2-4, characterised by the step of:

- generating a reference value (K) based upon the test values (Qi) corresponding to the one individual cylinder and the at least one additional individual cylinder; and

- identifying the malfunctioning fuel injector based upon the deviation of said test values from said reference value (K).

6. A method according to claim 5, wherein the reference value (K) is the median value of the test values (Qi) or the mean value of the test values (Qi).

7. A method according to claim 4, wherein the step of processing the first and sec- ond pressure values (P I^ P2_tj) so as to establish a test value (Qi), involves the steps of:

~ generating a set of pairs of pressure difference values (ΔP_y) and mean pressure values (P ij ) based upon the set of pairs of corresponding first and second pres- sure values (Pl_ip P2_tj);

- generating a pressure difference function based upon the set of pairs of differ- ence pressure values and mean pressure values (ΔP_j/, Pij ); and

- integrating said function over a predetermined mean pressure range.

8. A method according to claim 7, wherein said function is a linear function based upon linear regression of said set of pairs of difference pressure values and mean pressure values (AP^ Pij ),

9. A method according to any of claims 1-8, wherein the first pressure value (P Ig) determined prior to supplying fuel to the one individual cylinder is determined based upon a plurality of samples.

10. A method according to any of claims 1-9, wherein the second pressure value (P2_jj) determined after supplying fuel to the one individual cylinder is determined by a plurality of samples.

H. A method according to any of claims 1-10, characterised by the step of prior to determining a first pressure value (Ply):

- pressurising the fuel in the accumulator tank such that a predetermined pressure is set in said tank.

12. A computer program for identifying a malfunctioning fuel injector (1-6) associ- ated with an individual cylinder of a multicylinder combuslion engine (50), said en- gine comprising an accumulator tank (120) from which fuel is intended to be dis- tributed to the cylinders by means of the fuel injectors, comprising computer read- able program code means for causing an electronic control unit for controlling the engine (50) to perform the steps of: - determining a first pressure value (Pl jf) of the accumulator tank prior to supply- ing fuel to one individual cylinder;

- initiating the supply of fuel to the one individual cylinder during a predetermined on-time;

- determining a second pressure value (P2_U) of the accumulator tank after the fuel supply;

- processing the first and second pressure values so as to establish a test value (Q₁)

- identifying, when applicable, a malfunctioning fuel injector based upon said es- tablished test value (Qi).

13. A computer program according to claim 12, comprising computer readable pro- gram code means for causing the electronic control unit to perform the step of re- peating the steps of claim 1 separately for at least one additional individual cylinder of said engine, preferably for all cylinders of said engine, where the steps are carried out under substantially the same test conditions.

14. A computer program according to claim 14, wherein the identification step, when applicable, involves the step of comparing test values (Qf) associated with said at least one additional individual cylinder of said engine, preferably all additional cylinders of said engine, with the one individual cylinder.

15. A computer program according to any of claims 12-14, comprising computer readable program code means for causing the electronic control unit to perform the step of repeating the steps of determining the first pressure value (PI_y) of the accu- mulator tank prior to supplying fuel to the one individual cylinder; supplying fuel to the one individual cylinder during the predetermined on-time; and determining the second pressure value (P2ij) of the accumulator tank after the fuel supply, so as to establish a set αf pairs of corresponding first and second pressure values (Ply, P2(f) associated with the one individual cylinder.

16. A computer program according to any of claims 13-15, comprising computer readable program code means for causing the electronic control unit to perform the steps of:

- generating a reference value (K) based upon the test values (QD corresponding to the one individual cylinder and the at least one additional individual cylinder; and

17. A computer program according to claim 16, wherein the reference value (K) is the median value of the test values (Qj) or the mean value of the test values (Qj).

18. A computer program according to claim 15, wherein the step of processing the first and second pressure values (PIq, P2_υ) so as to establish a test value (Qj)₃ in- volves the steps of:

— generating a set of pairs of pressure difference values (ΔP,y) and mean pressure values ( P₉ ) based upon the set of pairs of corresponding first and second pres- sure values (PIg, P2ij), - generating a pressure difference function based upon the set of pairs of differ- ence pressure values and mean pressure values (AP_y-, P_v)'_t and

- integrating said function over a predetermined mean pressure range.

19. A computer program according to claim 18, wherein said function is a linear function based upon linear regression of said set of pairs of difference pressure val- ues and mean pressure values (ΔP_#, i*,).

20. A computer program according to any of claims 32-19, wherein the first pressure value (PI ij) determined prior to supplying fuel to the one individual cylinder is de- terroined based upon a plurality of samples.

21. A computer program according to any of claims 12-20, wherein the second pres- sure value (P2ij) determined after supplying fuel to the one individual cylinder is de- termined by a plurality of samples.

22. A computer program according to any of claims 12-21, comprising computer readable program code means for causing the electronic control unit to perform the step of prior to determining a first pressure value (Pl_y): - causing a pressurising of the fuel in the accumulator tank such thai a predeter- mined pressure is set in said tank.

23. A computer program product comprising a computer program according to any of claims 12-22 and a computer readable medium on which the computer program is stored.

24. A computer comprising:

- storing means; and - a computer program according to any of claims 12-22 stored in the storing means.

25. The computer of claim 24 wherein the computer is an embedded electronic con- trol unit

26. The computer of claim 24 wherein the computer is a vehicle externa) computer.

27. A platform comprising: a computer according to any of claims 24 to 26; and any of a vehicle, a water craft, an under water craft, or a power plant

28. The platform of claim 27 wherein the vehicle is a truck

29. The platform of claim 27 wherein the water craft is a ship

30. The platform of claim 27 wherein the under water craft is a submarine.

31. A computer program which, when executed by a computer, causes the computer to perform the method of any of claims 1 to 11.