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

Abstract

Method for determining the wear condition of at least one fuel injector (21 - 26) for an internal combustion engine connected to a high-pressure fuel storage tank (27), comprising the steps: - Determining a pressure gradient (300) in the high-pressure fuel storage tank (27) due to an injection by the at least one fuel injector (21 - 26), if the determined pressure gradient (300) falls below a predetermined threshold value (350), - Incrementing a sub-counter (400) of at least fuel injector (21 - 26); - Determining a time (500) during which the pressure gradient (300) due to the injection of the at least one fuel injector (21 - 26) remains below the predetermined threshold (350); and - Determining the wear condition of at least one fuel injector (21 - 26) based on a value of its undershoot counter (400) and a value of its undershoot time (500).

Description

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

[0002] Aging effects, such as carbon buildup, on fuel injectors in an internal combustion engine's injection system can lead to extended injection times of the affected injector, which can result in increased exhaust emissions from the engine. Therefore, it is desirable to detect such aging effects early and replace the affected fuel injector.

[0003] In this context, DE 10 2018 219 232 A1 discloses a method for detecting a delayed 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 the fuel injector has been activated.

[0004] German patent application DE 10 2012 222 851 B4 discloses a method for controlling piezo injectors in internal combustion engines. A quality parameter is determined by analyzing the voltage signal at the piezo actuator before and after needle closing. This parameter enables the assessment of injector quality and the reliability of needle closing detection, which is essential for precise fuel regulation.

[0005] German patent DE 10 2020 214 001 A1 discloses a method for the operation and evaluation of the wear condition of injectors in internal combustion engines. By recording and classifying wear values ​​for various operating events, an overall wear value is calculated. Based on this value, the injector condition can be assessed and the remaining service life estimated, thereby avoiding unnecessary maintenance intervals.

[0006] German patent DE 10 2021 122 846 A1 discloses systems and methods for detecting fuel injector malfunctions. By comparing the measured fuel consumption rate with an expected value, a potential blocked injector state is identified. Further analysis eliminates other sources of error and, if necessary, initiates a corrective action.

[0007] German patent DE 10 2021 211 924 A1 discloses a method for identifying drifting injectors in fuel injection systems. By monitoring engine speed fluctuations and analyzing deviations in the injected fuel quantity, the defective injector can be located within a group. This enables targeted maintenance and avoids unnecessary compensation work on functioning injectors.

[0008] German patent DE 10 2022 209 989 A1 discloses a method for detecting the failure of individual injectors in vehicles. By comparing the actual current supply duration with a target current supply duration under specific operating conditions, an injector failure is detected as soon as the difference exceeds a predefined threshold. A warning informs the user of the failure.

[0009] In order to determine the severity of aging / wear on a fuel injector and to be able to determine a replacement time for the injector based on this, the pressure gradient in the high-pressure fuel accumulator must be specifically determined and analyzed. Disclosure of the invention

[0010] According to the invention, a method for determining the wear state of at least one fuel injector for an internal combustion engine connected to a high-pressure fuel storage tank, as well as a computing unit and a computer program for carrying out this method, are proposed, comprising the features of the independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0011] The present invention makes it possible to determine the severity of wear of individual fuel injectors in an injection system and, based on this, to predictively determine their replacement time. In this way, the failure of one or more fuel injectors during operation of the internal combustion engine can be avoided.

[0012] In embodiments of the invention, the internal combustion engine can be a diesel engine or a gasoline engine. In embodiments of the invention, the fuel injector can be part of a high-pressure injection system that also includes a high-pressure fuel accumulator and a high-pressure pump (so-called common-rail system). In particular, a pressure sensor for measuring fuel pressure can be installed in the high-pressure fuel accumulator. In particular, the high-pressure injection system can include a plurality of fuel injectors.

[0013] In the method according to the invention, a pressure gradient in the high-pressure fuel accumulator is determined as a result of an injection by the at least one fuel injector; that is, a pressure gradient occurring in the high-pressure fuel accumulator due to an injection by the at least one fuel injector. The pressure gradient can be determined, for example, by numerically differentiating the measured fuel pressure profile in the high-pressure fuel accumulator. Depending on the distance and unit of the distance between the values ​​used for this purpose, pressure(n) and pressure(n+1), the gradient (dp) can also be the pressure drop (Δp), i.e., the numerical difference between the pressure before injection and the pressure after injection. The pressure drop results as a gradient of a non-temporal, but rather dimensionless, profile in which the pressure measurements are stored sequentially without reference to time. A reference to time or angle is also possible, e.g., °KW or °NW.

[0014] If a large number of fuel injectors are present in the high-pressure injection system, the fuel injectors can be controlled according to a predetermined injection sequence. In this case, the measured pressure gradient in the high-pressure fuel accumulator can be assigned to the last activated fuel injector.

[0015] If the pressure gradient falls below a predetermined threshold, a sub-threshold counter for at least one fuel injector is incremented. Specifically, the sub-threshold counter can be incremented each time the pressure gradient falls below the predetermined threshold. In this way, the sub-threshold counter value increases with each detected pressure gradient below the predetermined threshold. In other words, this allows monitoring to determine whether the injected fuel quantity is excessive.

[0016] According to one embodiment, the predetermined threshold for the pressure gradient can be determined depending on an operating point of the internal combustion engine and / or a design of the at least one fuel injector. For example, based on a target injection quantity of the at least one fuel injector, a target pressure drop in the high-pressure accumulator can be determined for each operating point of the internal combustion engine, and the predetermined threshold can be set by means of an offset to the target pressure drop. When determining the offset, factors such as the fuel pressure in the high-pressure accumulator and the rotational speed of the internal combustion engine can be taken into account. Alternatively or additionally, the design of the at least one fuel injector can be incorporated into the determination of the predetermined threshold, for example, by considering the flow characteristics of its nozzle. In other words, this allows the steepness of the pressure gradient to be determined.how strong the pressure drop would normally be in the specific application case when opening or injecting.

[0017] The following process determines the time during which the pressure gradient remains below the predetermined threshold due to the injection from at least one fuel injector. This time can be determined, for example, when the pressure gradient exceeds the predetermined threshold again. In other words, the duration during which the calculated pressure gradient remains below the predetermined threshold after incrementing the threshold counter can be defined as the time during which the injection in question remains below the threshold. In other words, this allows us to determine how long the excess fuel is injected.

[0018] If the undershoot counter is incremented again during a subsequent injection, another undershoot time is determined. According to one embodiment, this can be added to the previous undershoot time, and in this way a value for the undershoot time of the at least one fuel injector can be determined. In other words, the undershoot time value can be calculated by summing undershoot times from different injections.

[0019] Based on a value from the pressure drop counter and a value for the duration of the pressure drop, the wear condition of at least one fuel injector is determined. Thus, the wear condition of the injector can be inferred from the frequency or duration of an increased pressure drop in the high-pressure fuel accumulator caused by an injection from at least one fuel injector. In particular, both a high frequency and a long duration indicate wear.

[0020] According to one embodiment, at least one relationship between the value of the undershoot counter and / or the undershoot time and the wear condition of the at least one fuel injector can be determined and stored in advance. This determined relationship can be stored in a processing unit, which may in particular be a control unit of the internal combustion engine.

[0021] To determine at least one correlation, for example, the value of the undershoot counter and / or the undershoot time of one or more reference fuel injectors can be continuously determined, e.g., during an endurance run on a test bench. Reference fuel injectors can be selected, for example, those injectors whose injection characteristics, when new, lie within a predetermined tolerance range.

[0022] It is also possible to use fuel injectors with injection characteristics from different tolerance ranges and to determine a correlation for each tolerance range. Different correlations between the value of the undershoot counter and / or the undershoot time value and the wear condition of the reference fuel injectors can also be determined by different boundary conditions (fuel pressure and temperature, injection profile, injection frequency, multiple injections, etc.) during the endurance test.

[0023] In this way, a relationship between the value of the undershoot counter / undershoot time and the wear state can be determined for both fuel injectors with different injection behavior in new condition and for different operating conditions of the injectors.

[0024] In this process, one or more reference fuel injectors can be inspected when specific values ​​of the countdown counter and / or countdown time are reached, in order to determine their wear condition. In this way, a wear condition of the reference fuel injector(s) can be assigned to each specific countdown counter and / or countdown time. When using multiple fuel injectors, for example, an average or maximum wear condition of all inspected injectors can be determined.

[0025] A wear condition can be understood, for example, as a build-up of carbon deposits on the nozzle needle of a fuel injector. Another wear condition can be, for example, cavitation erosion on the nozzle needle and in the nozzle holes of the fuel injector. Such wear conditions can be detected and quantified by visual inspection or by measurement (e.g., thickness of the carbon deposit layer, thickness of material loss due to cavitation erosion).

[0026] In particular, the endurance test can be conducted in such a way that the reference fuel injectors reach the end of their service life during the test, in order to determine the value of the wear counter and / or the wear time for this final wear state (defect). In this way, a defect in at least one fuel injector can be determined based on the specific wear state using the wear counter value and / or the wear time.

[0027] According to one embodiment, the replacement time of the at least one fuel injector can be determined based on its specific wear condition. This can be done, for example, using the specific relationship between the value of the wear counter and / or the wear time and the wear condition. Since this relationship provides a known progression of the wear condition of the at least one fuel injector as a function of the wear counter value / wear time until it reaches its service life, a period until the end of its service life can be determined based on the currently determined wear condition and the current operating time of the injector.

[0028] According to one embodiment, the cause of wear can be determined by analyzing the wear pattern of the at least one fuel injector. In particular, the different wear patterns described above can result in different injection behavior of the at least one fuel injector, which can be detected by means of the associated pressure gradients in the high-pressure fuel accumulator. For example, increasing coking of the nozzle needle can cause the fuel injector to close more frequently and with greater delay, thereby increasing the frequency of an unacceptably high pressure drop and thus the value of the pressure drop counter. Consequently, in this case, the cause of the wear can be determined by analyzing the pressure drop counter values, which here represent the wear pattern of the at least one fuel injector.

[0029] A computing unit according to the invention, e.g. a control unit of the internal combustion engine, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0030] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0031] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0033] The invention is schematically illustrated with reference to exemplary embodiments in the drawings and is described in detail below with reference to the drawings. Character description Fig. Figure 1 schematically shows an injection system with several fuel injectors, the wear state of which can be determined by means of an embodiment of the method according to the invention. Fig. Figure 2 schematically shows a block diagram, based on which an embodiment of the method according to the invention can be implemented in a computing unit. Fig. Figure 3 schematically shows a measurement of several input and output variables of the in Fig. 2 block diagrams shown. Detailed description of the drawing

[0034] Fig. Figure 1 schematically shows an injection system 20 (common-rail system) with several fuel injectors 21-26, the wear condition of which can be determined using an embodiment of the method according to the invention. The fuel injectors 21-26 are each assigned to a cylinder 11-16 of an internal combustion engine (not shown in detail) and inject fuel directly into it. The internal combustion engine can, in particular, be a diesel engine.

[0035] The injection system 20 further comprises a high-pressure fuel pump 29 and a high-pressure fuel accumulator 27, in which a pressure sensor 28 is installed, as well as a processing unit 30. The high-pressure fuel pump 29 delivers fuel, in particular diesel fuel, into the high-pressure fuel accumulator 27, from which the fuel injectors 21–26 are supplied with fuel. With each injection by an injector 21–26, a pressure drop occurs in the high-pressure fuel accumulator 27, which can be detected by the pressure sensor 28 and correlates with the injected quantity of fuel. A pressure gradient of the fuel pressure in the high-pressure accumulator 27 can be determined, for example, by numerically differentiating the measured pressure value profile over time. Alternatively, the pressure drop due to injection, i.e., the numerical difference between the pressure before injection and the pressure after injection, can be determined as the pressure gradient.This results as a gradient of a non-temporal, but rather unitless, progression, in which the pressure measurements are stored sequentially without any reference to time.

[0036] If wear, such as coking or cavitation, occurs on one or more fuel injectors 21-26, this can result in an increased injection quantity and thus an increased pressure drop / pressure gradient in the high-pressure fuel accumulator 27, which can be detected by the pressure sensor 28. The fuel injectors 21-26 can be controlled according to a predetermined injection sequence, which corresponds in particular to the firing order of the internal combustion engine, and the measured pressure gradient in the high-pressure fuel accumulator 27 can be assigned to each of the last activated fuel injectors 21-26.

[0037] If the measured pressure gradient falls below a predetermined threshold, a threshold counter for the relevant fuel injector 21-26 is incremented. The predetermined threshold for the pressure gradient (pressure drop) can be defined, for example, based on an operating point of the combustion engine and / or a specific configuration of the at least one fuel injector 21-26.

[0038] The following determines the time during which the pressure gradient remains below the predetermined threshold due to the injection from the relevant fuel injector 21-26. This time can be determined, for example, when the pressure gradient has again exceeded the predetermined threshold. In other words, the duration during which the determined pressure gradient remains below the predetermined threshold after incrementing the threshold counter can be defined as the time during which the respective injection remains below the threshold.

[0039] If the undershoot counter is incremented again during a subsequent injection of the relevant fuel injector 21-26, a further undershoot time is determined. This can, for example, be added to the previous undershoot time to determine the undershoot time value for this fuel injector 21-26.

[0040] Based on a value from the pressure drop counter and / or a value from the pressure drop duration, the wear state of fuel injectors 21-26 is determined. In this way, based on the frequency and / or duration of an increased pressure drop in the high-pressure fuel accumulator 27, which can be assigned to each of the most recently activated fuel injectors 21-26, the wear of that injector can be inferred. The activation of the fuel injectors 21-26 and the determination of their wear states can be performed by the shown computing unit 30, which can, in particular, be a control unit of the internal combustion engine.

[0041] Fig. Figure 2 schematically shows a block diagram, based on which an embodiment of the method of the invention can be illustrated, e.g., in the Fig. The computing unit shown in 1 can be implemented as 30.

[0042] The computing unit 30 includes a first and a second function block 31, 32, each of which receives input variables, performs calculations and outputs output variables.

[0043] The first function block 31 receives a cylinder counter 100, a time 200 and a pressure gradient 300 determined from the measured fuel pressure as input variables and calculates from this a value of the undershoot counter 400 and a value of the undershoot time 500 for a fuel injector 21 - 26, which is indicated by the cylinder counter 100 as the last controlled injector 21 - 26.

[0044] In the first function block, for example, the value of the pressure drop counter 400 for the displayed fuel injector 21-26 is incremented whenever the pressure gradient 300 falls below the predetermined threshold. From this point in time (first point in time), which can be determined using the incoming time 200, a drop time for the current injection of the displayed fuel injector 21-26 is calculated. This calculation can be performed, for example, when the pressure gradient 300 again exceeds the predetermined threshold. This point in time (second point in time) can also be determined using the incoming time 200. The drop time for the current injection of the displayed fuel injector 21-26 can then be calculated, for example, by subtracting the first time from the second time.If the undershoot counter 400 for this fuel injector 21-26 is incremented again, a further undershoot time for the displayed fuel injector 21-26 can be determined and added to the previously determined undershoot time. In this way, a value for the undershoot time 500 for each fuel injector 21-26 can also be continuously determined.

[0045] The second function block 32 receives the value of the undershoot counter 400 and the value of the undershoot time 500 of each fuel injector 21 - 26 from the first function block 31 and uses this information to determine, for example, the wear status of the individual fuel injectors 21 - 26. For this purpose, at least one relationship between the value of the undershoot counter 400 and / or the value of the undershoot time 500 and the wear status can be stored in the second function block 32.

[0046] To determine the minimum correlation, for example, the value of the undershoot counter and / or the undershoot time of one or more reference fuel injectors can be continuously determined, e.g., during an endurance test on a test bench. The one or more reference fuel injectors can then be inspected upon reaching specific values ​​of the undershoot counter and / or undershoot time to determine their wear condition. The endurance test can be conducted in such a way that the reference fuel injectors reach the end of their service life. This final wear condition can also be correlated with the corresponding undershoot counter value (400) and / or undershoot time value (500).In this way, each specific value of the underrun counter 400 and / or the underrun time 500 can be assigned a wear condition of the reference fuel injector(s). When using multiple fuel injectors, for example, an average or maximum wear condition of all injectors tested can be determined. These determined wear condition values ​​and the incremented counter readings of the underrun counters (including their assignment to the individual injectors) are stored in the processing unit 30.

[0047] Based on this relationship determined in this way, a wear condition can be determined for each of the fuel injectors 21 - 26 shown, and, for example, a replacement time for an injector 21 - 26 can be determined.

[0048] Fig. Figure 3 shows a measurement of several input and output variables of the device in Fig.The block diagram shown in Figure 2 depicts the pressure gradient 300, the value of the threshold counter 400, and the threshold time 500 of a single fuel injector 21-26 over time 200. Additionally, the threshold value 350 for the pressure gradient 300 is shown. When this threshold is undershot, the value of the threshold counter 400 is incremented, and a further threshold time 500 is determined, by which the value of the threshold time 500 is increased.

[0049] It is evident that in the present case, the affected fuel injector 21-26 exhibits increased wear, as numerous pressure drops 300 below the threshold value 350 occur, leading to a rapid increase in both the value of the undershoot counter 400 and the value of the undershoot time 500. The progression of these two values ​​400 and 500 can be compared, for example, with the at least one relationship stored in function block 32, and this comparison can be used to determine, for example, when fuel injector 21-26 should be replaced at the latest to prevent its failure.

Claims

[1] Method for determining the wear state of at least one fuel injector (21 - 26) for an internal combustion engine connected to a high-pressure fuel storage tank (27), comprising the steps: - Determining a pressure gradient (300) in the high-pressure fuel storage tank (27) due to an injection by the at least one fuel injector (21 - 26), if the determined pressure gradient (300) falls below a predetermined threshold value (350), - Incrementing a sub-counter (400) of at least fuel injector (21 - 26); - Determining a time (500) during which the pressure gradient (300) due to the injection of the at least one fuel injector (21 - 26) remains below the predetermined threshold (350); and - Determining the wear condition of at least one fuel injector (21 - 26) based on a value of its undershoot counter (400) and a value of its undershoot time (500). [2] Method according to claim 1, wherein the value of the undershoot time (500) of the at least one fuel injector (21 - 26) is formed by summing undershoot times (500) for different injections. [3] Method according to claim 1 or 2, wherein a replacement time of the at least one fuel injector (21 - 26) is determined depending on the specific wear condition. [4] Method according to one of the preceding claims, wherein a defect of the at least one fuel injector (21 - 26) is determined depending on the specific wear condition. [5] Method according to one of the preceding claims, wherein a cause of the wear is determined based on a progression of the wear state of the at least one fuel injector (21 - 26). [6] Method according to one of the preceding claims, wherein at least one relationship between the value of the underrun counter (400) and / or the value of the underrun time (500) and the wear condition of the at least one fuel injector (21 - 26) is determined and stored in advance. [7] Method according to one of the preceding claims, wherein the predetermined threshold (350) is determined depending on an operating point of the internal combustion engine and / or a design of the at least one fuel injector (21 - 26). [8] Computing unit (30) comprising a processor configured to perform the method according to any of the preceding claims. [9] Computer program comprising instructions which, when the program is executed by a computer, cause it to execute the method according to claims 1 to 7. [10] Computer-readable data carrier on which the computer program according to claim 9 is stored.

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