Method for determining wear state of at least one fuel injector, computing unit and computer program

Abstract

The invention relates to a method for determining a wear state for at least one fuel injector (21-26) of an internal combustion engine, and a computing unit (30) and a computer program for carrying out the method. In the method, a pressure gradient (300) in the high-pressure fuel reservoir (27) is determined as a function of the injection of the at least one fuel injector (21-26), and if the determined pressure gradient (300) is below a predetermined threshold value (350), a deficit counter (400) of the at least one fuel injector (21-26) is incremented, a deficit time (500) is determined, the pressure gradient (300) is kept below a predetermined threshold value (350) due to the injection of the at least one fuel injector (21-26) during the insufficient time; and determining a wear state of the at least one fuel injector (21-26) on the basis of a value of an insufficiency counter (400) of the at least one fuel injector and a value of an insufficiency time (500) of the at least one fuel injector.

Description

Technical Field

[0001] The invention relates to a method for determining the wear state of at least one fuel injector of an internal combustion engine, as well as to a computing unit and a computer program for carrying out the method. Background Art

[0002] Aging effects, such as coking, at the fuel injectors of the injection system of an internal combustion engine can lead to a prolonged injection time of the relevant fuel injector, which can lead to increased exhaust emissions of the internal combustion engine. It is therefore desirable to detect such aging effects early and replace the relevant fuel injectors.

[0003] Against this background, DE 10 2018 219 232 A1 shows a method for identifying a late-closing fuel injector in a fuel injection system of an internal combustion engine based on a pressure gradient in a high-pressure fuel accumulator after actuation of the fuel injector.

[0004] In order to be able to determine the severity of aging / wear at the fuel injectors and, based thereon, to be able to determine the time for replacing the injectors, the pressure gradient in the high-pressure fuel accumulator must be determined and analyzed in a targeted manner. Summary of the invention

[0005] According to the invention, a method for determining a wear state of at least one fuel injector for an internal combustion engine, a computing unit and a computer program for carrying out the method are provided. Advantageous embodiments are the subject of the following description.

[0006] The invention makes it possible to determine the severity of wear of individual fuel injectors of an injection system and, based thereon, predictively determine the time of their replacement. In this way, failure of one or more fuel injectors can be avoided during operation of an internal combustion engine.

[0007] In one embodiment of the invention, the internal combustion engine can be a diesel engine or a gasoline engine. According to the embodiment of the invention, the fuel injector can be part of a high-pressure injection system, which also has a high-pressure fuel reservoir and a high-pressure pump (so-called common rail system). In particular, a pressure sensor for measuring the fuel pressure can be attached in the high-pressure fuel reservoir. In particular, the high-pressure injection system can have a plurality of fuel injectors.

[0008] In the method according to the invention, a pressure gradient in a high-pressure fuel accumulator is determined based on the injection of at least one fuel injector, i.e., the pressure gradient in the high-pressure fuel accumulator that occurs due to the injection through at least one fuel injector. For example, the pressure gradient can be determined by the numerical difference in the direction of the fuel pressure measured in the high-pressure fuel accumulator. Depending on the spacing and spacing units of the values ​​of the pressure (n) and the pressure (n+1) used for this purpose, the gradient (dp) can also be a pressure drop (Δp), i.e., the numerical difference between the pressure before the injection and the pressure after the injection. The pressure drop is obtained as a non-temporal but unitless gradient, wherein the pressure measurement values ​​are stored sequentially without a time reference. Similarly, a time reference or an angle reference is also feasible, such as KW or NW.

[0009] If there are multiple fuel injectors in the high-pressure injection system, the fuel injectors can be actuated according to a predetermined injection sequence. In this case, the pressure gradient determined in the high-pressure fuel accumulator can be associated with the last actuated fuel injector.

[0010] If the pressure gradient falls below a predetermined threshold, a shortage counter of at least one fuel injector is incremented. In particular, the shortage counter can be incremented each time the pressure gradient falls below the predetermined threshold. In this way, the value of the shortage counter can be increased with each determined pressure gradient falling below the predetermined threshold. In other words, it can be monitored whether the amount of injected fuel is too large.

[0011] According to one embodiment, the predetermined threshold value of the pressure gradient can be determined based on the operating point of the internal combustion engine and / or the embodiment of at least one fuel injector. For example, the target pressure drop in the high-pressure reservoir can be determined for each operating point of the internal combustion engine based on the target injection quantity of at least one fuel injector, and the predetermined threshold value can be determined by means of an offset from the target pressure drop. When determining the offset, for example, the fuel pressure in the high-pressure reservoir and the rotational speed of the internal combustion engine can be taken into account. Alternatively or additionally, the embodiment of at least one fuel injector can be incorporated into the determination of the predetermined threshold value, for example by taking into account the flow rate characteristics of its nozzle. In other words, it can be determined how steep or strong the pressure drop must usually be when opening or injecting in a specific application.

[0012] Subsequently, a deficiency time is determined, during which the pressure gradient remains below a predetermined threshold value due to the injection of at least one fuel injector. For example, the deficiency time can be determined when the pressure gradient exceeds the predetermined threshold value again. In other words, after the deficiency counter is incremented, the determined duration for which the pressure gradient remains below the predetermined threshold value can be determined as the deficiency time of the relevant injection. In other words, how long the injection was excessive can be determined thereby.

[0013] If the shortage counter is incremented again at the subsequent injection, a further shortage time is determined. According to one embodiment, the shortage time can be added to the previous shortage time and in this way the value of the shortage time of at least one fuel injector can be determined. In other words, the value of the shortage time can be formed by adding the shortage times in different injections.

[0014] Then, the wear state of the at least one fuel injector is determined based on the value of the shortage counter and the value of the shortage time. Thus, the wear state of the at least one fuel injector can be inferred from the frequency or duration of the increase in the pressure drop in the high-pressure fuel accumulator caused by the injection of the at least one fuel injector. In particular, high frequency and long duration are indicative of wear.

[0015] According to one embodiment, at least one correlation between the value of the undercount counter and / or the value of the undercount time and the wear state of at least one fuel injector can be determined and stored in advance. The determined correlation can be stored in a computing unit, which can in particular be a control device of the internal combustion engine.

[0016] In order to determine at least one correlation, for example, the value of the shortage counter and / or the value of the shortage time of one or more reference fuel injectors can be determined continuously, for example within the scope of continuous operation on a test bench. For example, an injector whose injection characteristics in the new state are within a predetermined tolerance range can be selected as a reference fuel injector.

[0017] Likewise, fuel injectors with injection characteristic curves in different tolerance ranges can be used and a correlation can be determined for each tolerance range. Different correlations between the value of the undercount counter and / or the value of the undercount time and the wear state of the reference fuel injector can also be determined during continuous operation by different boundary conditions (fuel pressure and fuel temperature, injection curve, injection frequency, multiple injections, etc.).

[0018] In this way, for fuel injectors with different injection behaviors in the new state and for different operating conditions of the injectors, a correlation between the value of the shortage counter / the value of the shortage time and the wear state can be determined in each case.

[0019] Here, one or more reference fuel injectors can be found when a specific value of the shortage counter and / or the shortage time is reached in each case, in order to determine their wear state. In this way, the wear state of one / multiple reference fuel injectors can be associated with each specific value of the shortage counter and / or the shortage time. For example, when using a plurality of fuel injectors, an average or maximum wear state of all found injectors can be determined.

[0020] In this context, a wear state may be understood to mean, for example, a coke buildup on the nozzle needle of a fuel injector. Another wear state may be, for example, cavitation on the nozzle needle and in the nozzle bore of a fuel injector. Such a wear state may be detected and quantified by visual inspection or also by measurement (e.g., thickness of the coke layer, thickness of material removed by cavitation).

[0021] In particular, a continuous operation can be performed so that the reference fuel injector reaches the end of its service life during this period, so that the value of the shortage counter and / or the shortage time can be determined for the final wear state (fault). In this way, a fault of at least one fuel injector can be determined based on the wear state determined by means of the value of the shortage counter and / or the shortage time.

[0022] According to one embodiment, the time point for replacing at least one fuel injector can be determined based on a specific wear state. This can be done, for example, based on a specific correlation between the value of the shortage counter and / or the value of the shortage time and the wear state. Since the course of the wear state of at least one fuel injector until the end of its service life is known based on the value of the shortage counter / shortage time by means of the correlation, the time period until the end of its service life can be determined based on the currently determined wear state of the injector and the current duration of use.

[0023] According to one specific embodiment, the cause of the wear can be determined based on the course of the wear state of at least one fuel injector. In particular, the above-mentioned different wear states can lead to different injection behaviors of the at least one fuel injector, which can be detected by means of the associated pressure gradient in the high-pressure fuel accumulator. For example, due to increased coking of the nozzle needle, the fuel injector can be closed later, thereby increasing the frequency of inadmissibly high pressure drops and thus increasing the value of the undercounter. In this case, the cause of the wear can therefore be inferred based on the course of the value of the undercounter, which here represents the course of the wear state of the at least one fuel injector.

[0024] A computing unit according to the present invention, for example a control unit of an internal combustion engine, is designed, in particular with regard to programming, to carry out the method according to the present invention.

[0025] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with program code for executing all method steps, since this results in particularly low costs, in particular if the executing control device is also used for other tasks and is therefore always available. Suitable data carriers for providing computer programs are in particular magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. Downloading via a computer network (Internet, intranet, etc.) is also possible.

[0026] Further advantages and embodiments of the invention emerge from the description and the accompanying drawings.

[0027] It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination but also in different combinations or alone, without departing from the scope of the present invention.

[0028] The invention is schematically illustrated in the drawings based on exemplary embodiments and is described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 An injection system having a plurality of fuel injectors is schematically shown, the wear state of which can be determined by means of an exemplary embodiment of the method according to the invention.

[0030] Figure 2 A block diagram is schematically shown, according to which an exemplary embodiment of the method according to the present invention can be implemented in a computing unit.

[0031] Figure 3 Schematically shows Figure 2 The block diagram shown in the figure shows the measurement of multiple input and output variables. DETAILED DESCRIPTION

[0032] Figure 1 Schematically, an injection system 20 (common rail system) is shown with a plurality of fuel injectors 21-26, the wear state of which can be determined by means of an embodiment of the method according to the invention. The fuel injectors 21-26 are respectively associated with cylinders 11-16 of an internal combustion engine (not shown) and inject directly into said cylinders. The internal combustion engine can in particular be a diesel engine.

[0033] The injection system 20 also includes a high-pressure fuel pump 29 and a high-pressure fuel accumulator 27 and a computing unit 30, in which a pressure sensor 28 is installed. The high-pressure fuel pump 29 delivers fuel, especially diesel fuel, to the high-pressure fuel accumulator 27, from which the fuel injectors 21-26 are supplied with fuel. Here, at each injection of the injectors 21-26, a pressure drop in the high-pressure fuel accumulator 27 is caused, which can be detected by means of the pressure sensor 28 and is related to the amount of fuel injected. The pressure gradient of the fuel pressure in the high-pressure accumulator 27 can be determined, for example, by the numerical difference of the measured pressure value trend over time. Alternatively, the pressure drop caused by the injection, that is, the numerical difference between the pressure before the injection and the pressure after the injection, can be determined as the pressure gradient. This results in a gradient as a non-time, but unitless trend, in which the pressure measurement values ​​are stored in sequence without a time reference.

[0034] If wear, such as coking or cavitation, occurs at one or more fuel injectors 21-26, this can lead to an increase in the injection quantity and thus to an increase in the pressure drop / pressure gradient in the high-pressure fuel accumulator 27, which can be detected by means of the pressure sensor 28. The fuel injectors 21-26 can be actuated according to a predetermined injection sequence, which corresponds in particular to the ignition sequence of the internal combustion engine, and the pressure gradient determined in the high-pressure fuel accumulator 27 can be respectively associated with the last actuated fuel injector 21-26.

[0035] If the determined pressure gradient falls below a predetermined threshold, the undercount counter of the associated fuel injector 21-26 is incremented. The predetermined threshold for the pressure gradient (pressure drop) can be determined, for example, as a function of the operating point of the internal combustion engine and / or the embodiment of at least one fuel injector 21-26.

[0036] Subsequently, a deficiency time is determined during which the pressure gradient remains below a predetermined threshold value due to the injection of the associated fuel injector 21-26. For example, the deficiency time may be determined when the pressure gradient exceeds the predetermined threshold value again. In other words, the duration of time that the pressure gradient remains below the predetermined threshold value determined after the deficiency counter is incremented may be determined as the deficiency time of the associated injection.

[0037] If the shortage counter is incremented again at a subsequent injection of the relevant fuel injector 21-26, a further shortage time is determined. For example, the further shortage time can be added to the previous shortage time and in this way the value of the shortage time of the fuel injector 21-26 can be determined.

[0038] The wear state of the fuel injectors 21-26 is then determined based on the value of the shortage counter and / or the value of the shortage time. In this way, wear of the injectors can be inferred based on the frequency and / or duration of the pressure drop increase in the high-pressure fuel accumulator 27, wherein the pressure drop increase can be respectively associated with the last actuated fuel injector 21-26. The actuation of the fuel injectors 21-26 and the determination of their wear state can be carried out by the illustrated calculation unit 30, which can in particular be a control device of the internal combustion engine.

[0039] Figure 2 Schematically shows a block diagram, according to which, for example, Figure 1 An exemplary embodiment of the method according to the invention is implemented in the illustrated computing unit 30 .

[0040] To this end, the calculation unit 30 comprises a first function block 31 and a second function block 32 which receive input variables, perform calculations and output output variables, respectively.

[0041] The first functional block 31 receives as input variables a cylinder counter 100 , a time 200 and a pressure gradient 300 determined from the measured fuel pressure and calculates therefrom the value of an underrun counter 400 and a value of an underrun time 500 of the fuel injector 21 - 26 which is indicated by the cylinder counter 100 as the last actuated injector 21 - 26 .

[0042] Here, in the first functional block, for example, when the pressure gradient 300 drops below a predetermined threshold, the value of the insufficient counter 400 of the displayed fuel injector 21-26 is always incremented. From a time point (first time point) that can be determined according to the input time 200, the insufficient time of the current injection of the displayed fuel injector 21-26 is determined. For example, this determination can be made when the pressure gradient 300 exceeds the predetermined threshold again. The time point (second time point) can also be determined according to the input time 200. Then, the insufficient time of the current injection of the displayed fuel injector 21-26 can be calculated, for example, by subtracting the first time from the second time. If the insufficient counter 400 of the fuel injector 21-26 is incremented again, another insufficient time of the displayed fuel injector 21-26 can be determined and added to the previously determined insufficient time. In this way, the value of the insufficient time 500 can also be continuously determined for each fuel injector 21-26.

[0043] The second functional block 32 receives the value of the shortage counter 400 and the value of the shortage time 500 of each fuel injector 21-26 from the first functional block 31, and determines therefrom, for example, the wear state of each fuel injector 21-26. To this end, for example, at least one association between the value of the shortage counter 400 and / or the value of the shortage time 500 and the wear state can be stored in the second functional block 32.

[0044] In order to determine the at least one association, for example, the value of the insufficient counter and / or the value of the insufficient time of one or more reference fuel injectors can be determined continuously, for example, within the scope of continuous operation on a test bench. Here, when a specific value of the insufficient counter and / or the insufficient time is reached, one or more reference fuel injectors can be found in order to determine their wear state. In particular, continuous operation can be performed so that the reference fuel injector reaches the end of its service life during this period. The final wear state can also be related to the value of the insufficient counter 400 and / or the insufficient time 500. In this way, the wear state of one / more reference fuel injectors can be associated with each specific value of the insufficient counter 400 and / or the insufficient time 500. For example, when using multiple fuel injectors, the average or maximum wear state of all injectors found can be determined. The determined value of the wear state and the incremental counter reading of the insufficient counter (including the association with each injector) are stored in the calculation unit 30.

[0045] Based on the correlation determined in this way, the wear state can be determined for each output fuel injector 21 - 26 and, for example, a replacement time of the injector 21 - 26 can be determined.

[0046] Figure 3 Show Figure 2 . In particular, the pressure gradient 300 of a single fuel injector 21-26 and the value of the shortage counter 400 and the value of the shortage time 500 are plotted over time 200. Additionally, a threshold value 350 of the pressure gradient 300 is plotted, below which the value of the shortage counter 400 is incremented, and a further shortage time 500 is determined in order to increase the value of the shortage time 500.

[0047] It is clear that in the present case, the wear of the relevant fuel injector 21-26 increases, since a large number of pressure drops 300 below the threshold value 350 occur, which causes a rapid increase in the value of the shortage counter 400 and the value of the shortage time 500. The course of the two values ​​400, 500 can be compared, for example, with at least one association stored in the functional block 32, and, for example, based on this comparison, it can be determined when the fuel injector 21-26 should be replaced at the latest in order to prevent a failure from occurring.

Claims

1. A method for determining the wear state of at least one fuel injector (21-26) for an internal combustion engine, the at least one fuel injector being connected to a high-pressure fuel reservoir (27), the method comprising the following steps: - determining a pressure gradient (300) in the high-pressure fuel accumulator (27) as a function of the injection of the at least one fuel injector (21-26), If the determined pressure gradient (300) is below a predetermined threshold (350), - a shortage counter (400) of at least one fuel injector (21-26) is incremented; - determining a deficiency time (500) during which the pressure gradient (300) remains below the predetermined threshold (350) due to injection of the at least one fuel injector (21-26); and - determining the wear state of the at least one fuel injector (21-26) based on the value of the shortage counter (400) of the at least one fuel injector (21-26) and the value of the shortage time (500) of the at least one fuel injector (21-26).

2. The method according to claim 1, wherein the value of the shortfall time (500) of the at least one fuel injector (21-26) is formed by summing the shortfall times (500) in different injections.

3. The method according to claim 1 or 2, wherein the replacement time of the at least one fuel injector (21-26) is determined as a function of a specific wear state.

4. The method according to any of the preceding claims, wherein a malfunction of the at least one fuel injector (21-26) is determined as a function of a specific wear state. 5 . The method according to claim 1 , wherein the cause of the wear is determined with the aid of the course of the wear state of the at least one fuel injector ( 21 - 26 ).

6. A method according to any one of the preceding claims, wherein at least one association between the value of the deficiency counter (400) and / or the value of the deficiency time (500) and the wear state of the at least one fuel injector (21-26) is determined and stored in advance.

7. The method according to any of the preceding claims, wherein the predetermined threshold value (350) is determined as a function of an operating point of the internal combustion engine and / or an implementation of the at least one fuel injector (21-26).

8. A computing unit (30) comprising a processor configured such that the processor performs the method according to any one of the preceding claims.

9. A computer program comprising instructions which, when said program is executed by a computer, cause said computer to perform the method according to claims 1 to 7.

10. A computer-readable data carrier on which a computer program according to claim 9 is stored.

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