Method for identifying errors in sensor signals during operation of a fuel injector

Abstract

The invention relates to a method for recognizing an error in a sensor signal (S) during the operation of a fuel injector of an internal combustion engine, wherein a switching valve of the fuel injector is actuated by means of a control signal, and wherein the sensor signal is detected as a signal (S) of a sensor which is provided for detecting a characteristic operating point of the fuel injector, wherein in a respective predetermined time window (Δt U , Δt O ) of the sensor signal (S) which comprises the time point of the characteristic operating point of the fuel injector, at least one property of the sensor signal is determined which comprises a signal level (P) and / or a rise time (Δt A ), and wherein it is determined by means of the at least one property of the sensor signal whether an error is present.

Description

Technical Field

[0001] The present invention relates to a method for identifying errors in sensor signals during the operation of a fuel injector in an internal combustion engine, wherein the sensor signal is detected as a signal of a sensor configured to detect a characteristic operating point of the fuel injector, and to a computing unit and a computer program for performing the method. Background Technology

[0002] Modern internal combustion engines are equipped with fuel injectors, which allow fuel to be injected into the combustion chamber in a targeted manner. In order to precisely control the internal combustion engine, it is necessary to detect characteristic operating points as accurately as possible, such as the timing of the injection process, especially the opening and closing of the fuel injector's injection valve.

[0003] For fuel injectors that are opened and closed directly by solenoid valves, piezoelectric actuators, or similar devices, electrical control variables can typically be used to detect these characteristic time points.

[0004] However, for fuel injectors that primarily control switching or servo valves, there is no direct correlation between the electrical control variables of the fuel injector and the opening or closing timing of the injection valve. Therefore, additional sensors can be used in such fuel injectors, and the signals of these additional sensors are influenced, for example, by the fuel pressure in the fuel injector's control chamber or high-pressure line. Summary of the Invention

[0005] According to the present invention, a method for identifying errors in sensor signals during fuel injector operation is provided, along with a computational unit and computer program for executing the method. Advantageous designs are the subject matter described below.

[0006] This invention is based on the use of a sensor configured to detect or determine characteristic operating points of a fuel injector, such as the time when the fuel injector switching valve opens, the time when the fuel injector nozzle needle closes, or the time when the nozzle needle reverses direction. This type of sensor is also known as a needle valve closure sensor (NCS).

[0007] For the pressure balance switching valve (solenoid valve) of a fuel injector, the central anchor bolt is sensitive to changes in characteristics such as nozzle needle closure. For example, integrating a piezoelectric sensor directly above this anchor bolt can achieve robust feature recognition with relatively low design complexity. Thus, the sensor signal is typically proportional to the valve chamber pressure curve located below the central anchor bolt. However, it is also possible to use such a sensor to detect deformation of the stationary structure near the high-pressure orifice of the fuel injector.

[0008] The signal of this sensor (sensor signal) can be detected and evaluated in terms of the characteristic features in the curve in order to infer the specific time point of the fuel injector's operating point.

[0009] However, various errors can now occur that distort sensor signals, potentially leading to incorrect identification of the aforementioned time points. Since these time points are also used, in particular, to determine or adjust the amount of fuel to be injected, inaccurate injection can result, especially increased emissions. Therefore, such errors should be identified whenever possible so that they can be rectified or, if necessary, the fuel injector replaced. This can be done, for example, within the scope of on-board diagnostics (OBD). For this purpose, sensor signals can be evaluated using appropriate methods.

[0010] Typical errors include short circuits in the sensor signal or to sensor ground, short circuits to the battery (positive terminal), and electrical interruptions to the sensor signal (e.g., cable breakage or sensor malfunction). To identify these errors, one can, for example, examine whether the signal amplitude (sensor signal amplitude) within a predetermined time window (measurement window) of the sensor signal is too small, particularly unreasonably small, where the sensor signal includes the time point of nozzle needle reversal (needle valve reversal point) as a characteristic operating point of the fuel injector. If so, the average value of the sensor signal within the measurement window can be calculated, for example. The error can then be categorized into one of the three error types or categories mentioned above using the average value.

[0011] If the sensor signal is interrupted (due to a broken cable or sensor failure), the quiescent level of the sensor signal will be detected or measured in the readout unit (e.g., controller, measurement circuit), for example, approximately 3V. During a ground short circuit, the sensor signal level will be significantly lower than this quiescent level (approximately 3V), and during a battery short circuit, the sensor signal level will be significantly higher than this quiescent level (approximately 3V).

[0012] To classify errors, for example, two identification thresholds (thresholds) can be used. If the average value is below, for example, a lower identification threshold of 1.3V, a ground short circuit is identified and reported if necessary. If the average value is above, for example, an upper identification threshold of 7V, a battery short circuit is identified and reported if necessary. Preferably, the upper identification threshold is defined based on the battery voltage. As the battery voltage increases, the upper identification threshold should increase.

[0013] However, it turns out that there are other errors that cannot be identified in this way. In particular, there are grounding bypasses or battery voltage bypasses (short circuits with non-negligible resistance) and increased transition resistance between the sensor and the reading unit.

[0014] The bypass aspect should be considered first. The diagnostic methods described above can only be used to identify ground short circuits or short circuits to battery voltage when the short-circuit resistance is so low that the amplitude of the sensor signal changes significantly. A typical identification threshold is, for example, that the signal amplitude must be less than approximately 5%-10% of the nominal value. This results in the limitation that the (short-circuit) resistance in typical applications must be less than approximately 400 ohms, but at least (usually) below a certain value. Larger resistances, such as greater than approximately 400 ohms, between the sensor signal and ground or battery voltage cannot usually be identified using typical methods.

[0015] In the following text, the terms short circuit and bypass should be used in particular to define errors. These should be understood as follows: An electrical short circuit exists when the resistance is less than 400 ohms, or if it can be identified using the (conventional) methods described above. An electrical bypass exists when the resistance is greater than 400 ohms, or if it cannot be identified using the methods described above. However, a bypass is also a short circuit in principle.

[0016] In practice, ground bypass is generally much more likely to occur than battery bypass because the entire body of the fuel injector is typically permanently connected to the signal ground. Conversely, the battery voltage is temporarily applied only to the high-side connection of the coil during electrical control with periodic interruptions (for solenoid injectors). Therefore, the effect on the sensor signal will be illustrated exemplarily below for ground bypass; however, this also applies to battery bypass.

[0017] Grounding bypass will cause the resting level of the sensor signal to be lower than normal before the first control. In addition, the time constant of sensor charge outflow is also smaller than normal.

[0018] A ground bypass with a resistance of, for example, 1 megohm or 100 kilohms, will essentially cause the signal level to shift downwards. However, the shape of the sensor signal will not change significantly. Conversely, a ground bypass with a resistance of 10 kilohms will cause a significant change in the signal shape. In this case, the typical algorithms used (in the controller) to determine the valve opening time, needle valve reversal time, and needle valve closing time may provide significantly erroneous measurements in some situations.

[0019] However, the error identification (diagnosis) methods described above will not identify or report errors because the signal amplitude may even be slightly larger than in the error-free state. Even with a ground bypass with a resistance of, for example, 1 kΩ, the diagnosis will not respond, even though the sensor signals of the initial shape no longer share many commonalities. Strong changes in signal shape often result in the inability to find valid measurements of valve opening, needle valve reversal, or needle valve closing times in the controller because the plausibility check criteria included in the signal evaluation algorithm are not met. Examples of the above with different resistances and the resulting signal changes are shown in the attached figures.

[0020] Therefore, bypassing a sensor signal to ground (or to a battery) can lead to erroneous or completely lost measurements. However, typical diagnostic methods cannot identify electrical bypasses.

[0021] Ground short circuits are generally considered a possible and foreseeable risk, such as due to cable clamping. However, bypasses with resistances of several thousand ohms are currently considered unlikely. Nevertheless, it has been shown that such bypasses can occur, particularly in two situations. Firstly, this can occur in engine test benches or test vehicles when measuring instruments are connected to record sensor signals. The input impedance of the measuring instruments creates a ground bypass. This problem can be addressed, for example, by using an isolation amplifier.

[0022] On the other hand, it has been found that during assembly, metal parts or metal fragments may become encased in the plastic injection-molded package of the sensor connector within the fuel injector. This very thin wire, wrapped in this way, can cause an electrical bypass between the sensor signal and the fuel injector body (ground). The resistance of the wire encased within the fuel injector can vary drastically, depending, for example, on the geometry of the wire and its contact with the body. Here, the resistance value is largely dependent on the temperature of the fuel injector. Some bypasses occur, for example, at room temperature, while others only occur at the high temperatures of the engine. Due to this temperature dependence, it is difficult to reliably identify such defective fuel injectors during factory inspection. Other causes, such as sensor contamination during production, can also lead to bypasses.

[0023] In this context, as an aspect of the invention, a method is proposed that identifies errors, particularly by means of a sensor signal as at least one characteristic of the sensor signal, including, for example, grounding or short circuits to the battery (positive) voltage, particularly the bypass. For this purpose, within a predetermined time window (measuring window) of the sensor signal, specifically including the time point when the switching valve opens (valve opening time point) as the operating point, the signal level of the sensor signal is determined as at least one characteristic of the sensor signal. Then, the presence of an error is determined by means of the signal level. For example, the start of the predetermined time window can be determined based on the start of actuator control, and if necessary, its end. The duration can also be appropriately selected. Here, the signal level can be understood in particular as the average value of the sensor signal or its amplitude before the sensor signal is changed due to the control of the fuel injector or by its actuator. Therefore, the signal level relates to a static level.

[0024] It is preferable to determine the signal level in the "valve open" measurement window during the first controlled injection sequence, because the sensor signal curve is typically substantially constant. Hydraulic vibrations triggered by previous injections are usually fully or mostly attenuated at this point.

[0025] In particular, the signal level can be compared with one or more level thresholds, and the presence of an error can be determined based on the comparison. Here, the level thresholds can be, in particular, thresholds or identification thresholds that have been used for routine error identification.

[0026] In this regard, it is worth mentioning that, in addition to the conventional error identification methods mentioned above, error identification can also be performed based on signal levels.

[0027] Furthermore, to improve the robustness of error detection, i.e., diagnostic methods, it is also possible to verify whether there is a sufficiently large injection interval (e.g., 2 ms) before the "valve opening" measurement window. This ensures that the signal level is sufficiently stable and reliable and will not be distorted by hydraulic vibrations from the previous intense injection.

[0028] As mentioned above, the two monitoring and error identification methods, namely "signal amplitude at the 'needle valve reversal point' measurement window" and "signal level at the 'valve open' measurement window," can be performed in parallel and independently. Error information from both methods can be collected in the sense of a logical "OR" relationship.

[0029] It can also distinguish between electrical short circuits (e.g., resistance less than 400 ohms) and electrical bypasses (e.g., resistance greater than 400 ohms). However, to simplify on-board diagnostics, it is recommended to use a common error path for both error types, as the troubleshooting strategy in the workshop is the same in both cases.

[0030] Compared to the previous diagnostic approach, error debouncing remains unchanged. Only the meaning of error path has been expanded: ground short circuit or bypass, and battery short circuit or bypass.

[0031] Furthermore, it can be specified that bypass resistance can be calculated using signal levels. That is, it is advantageous, for example, for workshop diagnostics or market fleet observation, to have additional information about electrical faults known besides the faulty path. For this purpose, specific physical quantities can be calculated from the digital values ​​of the signal levels typically present in the software. For example, the voltage value of the signal level. This can be converted using a characteristic curve stored in the controller. This voltage value roughly corresponds to a multimeter measurement at the controller connector or one of the fuel injectors. Additionally, the resistance value for grounding or electrical bypass to the battery can be determined. For grounding bypass, a characteristic curve stored in the controller can be used for conversion. For battery bypass, a characteristic field is required for conversion because the value additionally depends on the battery voltage.

[0032] The aforementioned additional information can, for example, be stored as freeze frame data in the error memory. These values ​​can also be displayed on a diagnostic instrument during troubleshooting in the workshop.

[0033] The following section considers the issue of increased transition resistance. An increase in transition resistance can only be identified using the diagnostic scheme described above when the attenuation of the RC element, composed of the transition resistance and the input capacitance, significantly reduces the signal amplitude; that is, the transition resistance between the sensor and the reading unit is higher than the target value (or normal or reference value). This corresponds to a transition resistance of approximately 400 kΩ at idle and 800 kΩ at full load (of an internal combustion engine).

[0034] However, the increased transition resistance between the sensor (NCS) and the controller has consequences. This transition resistance forms an RC low-pass filter with the input capacitance of the NCS measurement circuit (readout unit) in the controller. This additional filtering has two main effects. On the one hand, the sensor signal is attenuated by the low-pass filter, and the amplitude of the sensor signal decreases. On the other hand, the time constant for the sensor charge to flow into the measurement circuit increases. Therefore, the characteristics in the sensor signal are delayed in time.

[0035] It has been shown that, at a transition resistance of, for example, 50 kΩ, the sensor signal is much smoother than in the error-free state. Algorithms used to determine time points—valve opening, needle valve switching, and needle valve closing—may already provide significantly erroneous measurements at this transition resistance. As the transition resistance increases, the cutoff frequency of the low-pass filter decreases, so the shape of the sensor signal, for example, at 500 kΩ, no longer shares much similarity with its initial shape. This drastic change in signal shape often results in the inability to find valid measurements for valve opening, needle valve switching, or needle valve closing times in the controller, because the plausibility checks included in the signal evaluation algorithm are not met. Examples of the above with different resistances and the resulting signal variations are shown in the accompanying figures.

[0036] The diagnostic methods described above will not report errors even when the transition resistance is 400 kΩ, for example, because the signal amplitude is still above the diagnostic threshold for amplitude. Therefore, an increased transition resistance at the sensor (NCS) could lead to erroneous or missing measurements. However, typical diagnostic methods fail to detect an increase in transition resistance.

[0037] Even though the probability of increased transition resistance at the NCS is low, possible causes include, for example, vibrational loads from the fuel injector, which can lead to wear of the silver coating on the connector pins. Additionally, moisture may enter the connector, corroding the underlying copper.

[0038] In this context, as another aspect of the invention, a method is proposed here, which in particular uses rise time as at least one characteristic of the sensor signal to identify errors, including transition resistance between the sensor and the readout unit that is higher than the target value.

[0039] Therefore, within a predetermined time window (measurement window) that serves as the operating point for the sensor signal, particularly the time point of the reversal of the fuel injector nozzle needle (needle valve reversal time point), the rise time of the sensor signal is determined as at least one characteristic of the sensor signal. Then, the presence of an error is determined by means of the rise time. For example, the start of the predetermined time window can be determined based on the start of actuator control, and if necessary, the end of control. The duration can also be appropriately selected. Here, the rise time can be understood in particular as the time interval required until the amplitude or average value of the sensor signal rises from a low level (the start of the measurement window) to a high level (the end of the measurement window).

[0040] In the measurement window "needle valve reversal point", the rise time of the sensor signal is preferably determined based on the gradient curve, i.e., the time derivative curve of the sensor signal. For this purpose, a threshold is calculated, for example, using the maximum gradient in the measurement window "needle valve reversal point" via a threshold factor, and further, the time points before and after the maximum gradient time point that intersect with this threshold are determined. The rise time can then be calculated as the difference between the two time points intersecting the threshold. Alternatively, the rise time can be determined at the sensor signal (original signal) using amplitude.

[0041] The rise time of the sensor signal in the measurement window "needle valve reversal point" is particularly dependent on the control time, fuel rail pressure (the pressure of the high-pressure reservoir supplying fuel to the fuel injectors), fuel injector temperature, and fuel, and exhibits high dynamism during operation. Since similar levels of dynamic change occur at the operating points of all cylinders (internal combustion engines), an increase in the transition resistance at a fuel injector can be detected by comparing it with fuel injectors at other cylinders. The fuel injector at the affected cylinder has a longer rise time compared to other cylinders.

[0042] Therefore, it is preferable to compare the rise time with a reference rise time and determine whether an error exists based on the comparison. For example, if the rise time is higher than the reference rise time by a predetermined time threshold, an error is determined to exist. Thus, the reference rise time is particularly considered in relation to the rise time of one other fuel injector of the internal combustion engine or the average rise time of multiple other fuel injectors of the internal combustion engine.

[0043] Preferably, the cylinders with the second shortest rise time are selected in each injection cycle, and the difference between them is calculated for each cylinder. To further improve robustness, the difference between each cylinder can be filtered using a PT1 filter. If the output of the PT1 filter exceeds the identification threshold, an increase in transition resistance is identified or reported if necessary.

[0044] In order to compare the rise time with a similar control duration in each injection cycle, it is preferable to calculate the difference with the second minor rise time specifically for the injection type or only for one injection type, such as the main injection.

[0045] In this regard, it is worth mentioning that, in addition to the conventional error identification methods described above, error identification can also be performed using signal levels, especially when these other error identification methods would not lead to an error. Besides bypass identification, an increase in transition resistance can also be identified.

[0046] Since monitoring rise time in the event of an electrical interruption in the sensor (NCS) or a short circuit to battery voltage or ground in the NCS will not provide meaningful results, it is preferable to monitor the signal amplitude at the needle valve commutation point in the measurement window before monitoring the rise time at the needle valve commutation point in the measurement window to detect electrical interruptions. It is also feasible to distinguish between an electrical interruption and an increase in transition resistance. However, to simplify on-board diagnostics, it is recommended to use a common error path for both error types, as the troubleshooting strategy in the workshop is the same in both cases. Error debouncing remains unchanged compared to previous diagnostic approaches.

[0047] In summary, each of the proposed aspects offers the following advantages: Improved reliability and product safety across the entire fuel injection system; reduced risk of unintended functional failures and / or customer complaints in the market; improved workshop diagnostics; and savings for customers in troubleshooting. Furthermore, regulatory OBD requirements can be met better or more easily. The workload for new model certification will be reduced.

[0048] The computing unit according to the invention, such as the controller of a motor vehicle, is configured, in particular, by programming techniques, to execute the method according to the invention.

[0049] Furthermore, it is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product having program code for performing all method steps, as this particularly contributes to a very low cost, especially when the execution control unit is already available for other tasks. Finally, a machine-readable storage medium is provided, having the computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memory, EEPROM, DVDs, etc. The program can also be downloaded via a computer network (Internet, Intranet, etc.). Here, such downloading can be performed via wired or wireless means (e.g., via Wi-Fi networks, 3G, 4G, 5G, or 6G connections, etc.).

[0050] Other advantages and design solutions of the present invention are apparent from the specification and drawings. Attached Figure Description

[0051] The invention is schematically illustrated in the accompanying drawings with reference to embodiments, and will now be described with reference to the drawings.

[0052] Figure 1 An internal combustion engine with a common rail system is schematically shown, which is suitable for performing the method according to the invention.

[0053] Figure 2 The switching valve of a fuel injector is schematically shown, in which the method according to the invention can be performed.

[0054] Figure 3 A circuit arrangement for explaining the method according to the invention in a preferred embodiment is shown.

[0055] Figures 4 to 11 Signal curves are shown to explain the method according to the invention in a preferred embodiment.

[0056] Figure 12 The flow chart of the method according to the invention in a preferred embodiment is shown.

[0057] Figure 13 A circuit arrangement for explaining the method according to the invention in another preferred embodiment is shown.

[0058] Figures 14 to 19 Signal curves are shown to explain the method according to the invention in another preferred embodiment.

[0059] Figure 20 The flow of the method according to the invention in another preferred embodiment is shown. Detailed Implementation

[0060] exist Figure 1 The diagram schematically illustrates an internal combustion engine 160 adapted to perform the method according to the invention. For example, the internal combustion engine 160 includes three combustion chambers or corresponding cylinders 165. Each combustion chamber 165 is assigned a fuel injector 170 with a switching valve 100, which is in turn connected to a high-pressure fuel reservoir 175, the so-called fuel rail, through which fuel is supplied. It should be understood that the method according to the invention is also applicable to internal combustion engines having any other number of cylinders, such as one, two, four, five, six, eight, ten, or twelve cylinders.

[0061] The high-pressure fuel reservoir 175 is supplied with fuel from the fuel tank 195 by the high-pressure pump 161. The high-pressure pump 161 is connected to the internal combustion engine 160, i.e., the high-pressure pump is driven by the internal combustion engine, for example.

[0062] The fuel injectors 170 are controlled by a processing unit designed as an engine controller 180 to meter or inject fuel into the respective combustion chambers 165. For clarity, only the connection from the engine controller 180 to the fuel injectors 170 is shown; however, it should be understood that each fuel injector 170 is correspondingly connected to the engine controller. Here, each fuel injector 170 can be specifically controlled. Furthermore, the engine controller 180 is configured, for example, to detect the fuel pressure in the high-pressure reservoir 175 via a pressure sensor 190.

[0063] exist Figure 2 The diagram schematically illustrates a (pressure-balanced) switching valve or servo valve of the fuel injector 170, designed as, for example, a solenoid valve, shown only partially herein, in which the method according to the invention can be performed. The switching valve 100 has an electromagnet 110 with a magnetic coil 111 as an actuator, which may, for example, be configured as a ring. A current I flows through the magnetic coil 111 when a voltage is applied, for example, by an actuation unit 180.

[0064] In addition, a magnetic armature 120 is provided, which can be used to close or release the flow and discharge ports 150 of the switching valve 100. Furthermore, a spring 130 is provided, which is applied to the magnetic armature 120 and, when the magnetic coil 111 is not energized and therefore there is no magnetic force, presses the armature 120 into or against the flow port 150 and closes it. The spring 130 can rest against a suitable component (not shown here) of the switching valve 100 on its side opposite to the magnetic armature.

[0065] When the magnetic coil 111 is energized, a magnetic force is generated, and the magnetic armature 120 overcomes the spring force of the spring 130 and is lifted and pulled towards the magnetic coil 111 or the electromagnet 110. This releases the flow port 150. When the magnetic coil is energized accordingly, the magnetic armature 120 can be lifted until it stops at the adjusting ring 115 provided at the electromagnet 110.

[0066] Fuel in the valve chamber 140 of the fuel injector and the connected control chamber 142, due to high pressure, first presses against the nozzle needle 145 and forces it into the valve seat, thus preventing fuel injection. This fuel can then flow into the circuit 155 when released through the flow port 150, and may be delivered, for example, to the fuel tank. Thus, the flow port 150 serves as a discharge port. Under appropriate pressure conditions and with a suitable amount of fuel flowing into the circuit, the nozzle needle 145 can be raised to release the fuel injector opening 147 for fuel, particularly since less fuel is introduced through the inlet 148 than is discharged through the discharge port 150. Thus, the flow port 150 simultaneously forms a discharge throttle valve.

[0067] Pressure changes in valve chamber 140 can be detected by a sensor 141, for example, in the form of a piezoelectric element, also known as an NC sensor. For this purpose, sensor 141 is positioned at the end of bolt 123 passing through magnetic armature 120. Pressure changes act on sensor 141 via bolt 123. Here, sensor 141 is located in the mounting plate 146 of the discharge section or in the housing component.

[0068] exist Figure 3 A circuit arrangement for explaining the method according to the invention in a preferred embodiment is shown. For this purpose, the magnetic coil 111 and sensor 141 (shown here as a capacitor) are shown in particular for the fuel injector 170, as well as the reading unit or measuring circuit 182, which may be part of the arithmetic unit 180. Capacitors C1 and C2, resistors R1, R2, R3 and R4, the AD converter 184, and the power supply voltage V+ are shown in particular here. Furthermore, by means of resistor R... GND The bypass (short circuit) of sensor 141 to ground GND is shown.

[0069] For example, the component values ​​in a measurement circuit might be as follows: C1 = 13.2 nF, C2 = 22 pF, R1 = 100 kΩ, R2 = 215 kΩ, R3 = 82.5 kΩ, R4 = 1 kΩ, V+ = 5V. It should be understood that these values ​​are merely examples of possible measurement circuits, but the explanation of R using these values ​​will be helpful in the following text. GND The influence of various possible values ​​on the sensor signal.

[0070] exist Figure 4 In the figure, the valve stroke h is plotted over time t. V (i.e., the stroke of the magnetic armature of the switching valve), needle stroke h N The curves of the current I applied to the magnetic coil and the sensor signal S of NCS as voltage U during the control process (i.e., the stroke of the nozzle needle of the fuel injector).

[0071] Here, the valve opening time point t is specifically plotted. O,V Needle valve reversal time point t U,N and needle valve closing time t S,N Furthermore, the corresponding time windows or measurement windows, i.e., measurement windows Δt, for these time points are also shown. O "Valve open", measurement window Δt U "Needle valve reversal" and measurement window Δt S "Needle valve closed." Additionally, the control end time point t is also shown. EOE (EOE stands for "Power-on complete").

[0072] exist Figures 5 to 8 The text shows the data based on... Figure 3The sensor signal or its response to different resistance values ​​R GND The curve is used as the actual measured value. These are determined by the resistance R. GND The altered signal curve is labeled S1(R) GND =1 megaohm), S2(R GND =100,000 euros), S3(R GND =10,000 euros) and S4 (R GND =1,000 euros), while with S R This represents a reference curve, applicable to an infinite resistance R. GND =∞, meaning there is no bypass. Here, the reference curve essentially corresponds to... Figure 4 Curve S in the figure. Furthermore, the current I is as shown in the figure. Figure 4 As shown.

[0073] As mentioned earlier, the effects of bypass can be clearly seen here. GND A ground bypass of 1 megohm or 100 kilohm primarily causes the NCS signal level to shift downwards. However, the shape of the NCS signal does not change significantly.

[0074] Conversely, R GND A 10 kΩ ground bypass can cause a significant change in signal shape. In some cases, the algorithms used in the controller to determine the valve opening time, needle valve reversal time, and needle valve closing time may provide noticeably erroneous measurements. However, conventional diagnostic methods typically do not report these errors because, for example... Figure 7 The signal amplitude shown is even slightly larger than the signal amplitude in the error-free state. For example, in Figure 8 The diagram illustrates how to define the signal amplitude A.

[0075] Even in R GND = 1 kΩ grounding bypass ( Figure 8 In this case, even though the sensor or NCS signal no longer shares many similarities with its original shape, the diagnostics have not yet responded. The signal level P of the reference curve and the signal level P' of the curve with a ground bypass are also plotted here.

[0076] Such a sharp change in signal shape often results in the inability to find valid measurements of valve opening time, needle valve reversal time, or needle valve closing time in the controller, because the reasonableness check criteria included in the signal evaluation algorithm are not met.

[0077] In the following, the process of the method according to the invention will be explained in detail by way of example, particularly in the aspect of bypass, a preferred embodiment.

[0078] First, determine or measure the signal level of the sensor signal. The sensor signal has three characteristic features: the valve opening time, the needle valve reversal time, and the needle valve closing time, such as... Figure 4 As shown. To determine the three time points, the sensor signals can be sampled and digitized at defined time intervals in the controller, for example. The time interval, referred to as the measurement window or time window, is as follows: Figure 4 As shown. In principle, the signal level can be determined in each of the three measurement windows. However, it is preferable to determine the signal level in the "valve open" measurement window during the first control injection sequence, because the curve of the sensor signal is generally largely constant at that point.

[0079] This is possible Figure 9 As can be seen, multiple injections are shown sequentially; however, in the first injection, the signal level P is constant before control begins, specifically up to the time point indicated by the arrow. The hydraulic vibrations triggered by the previous injections are generally completely or mostly attenuated here.

[0080] like Figure 10 As shown, the measurement window Δt O The valve opening is preferably at the time point t at the start of electrical control. SOE (SOE stands for "Power On Start") The fixed time interval T1 before the start of the power-on start begins.

[0081] If the width or duration T2 of the measurement window is chosen to be sufficiently large, T2 can have a constant size for all operating points of the internal combustion engine. Alternatively, the spacing T1 and / or the width T2 can also be implemented to vary depending on the operating point.

[0082] like Figure 11 As shown, the signal level P in the measurement window "Valve Open" is preferably calculated as the average value of the sensor signal over a defined time interval prior to the start of the first control of the injection sequence. In this example, the last six sampled values ​​of the sensor signal before the start of control (e.g., ...) are used. Figure 11 The average value of the points (or measurement points shown in the figure) is taken as the signal level P.

[0083] Next, electrical errors are identified and classified. In routine diagnosis, the measurement window Δt at the "needle valve reversal point" is examined first. U Is the signal amplitude unreasonably small? If so, calculate the average value of the sensor signal within the measurement window at the "needle valve reversal point". Based on the average value, classify the error into one of three possible error types. If the sensor signal is interrupted (cable breakage or sensor malfunction), measure the quiescent level of the sensor signal in the controller; it is approximately 3V. In the case of a short circuit to ground, the sensor signal level is significantly lower than 3V. In the case of a short circuit to the battery, the sensor signal level is significantly higher than 3V.

[0084] To categorize errors, it is preferable to use two identification thresholds. If the average value is, for example, less than 1.3V (lower identification threshold), a ground short circuit is reported. If the average value is, for example, greater than 7V (upper identification threshold), a battery short circuit is reported. The upper identification threshold is preferably defined based on the battery voltage. As the battery voltage increases, the upper identification threshold should also increase. The same identification threshold can be used to verify the measured value of the signal level P within the "valve open" measurement window.

[0085] exist Figure 12 The flowchart illustrates an algorithm for identifying and classifying electrical short circuits or bypasses based on the signal level in the "valve open" measurement window. Initialization (step 1200) is performed first, where the signal level value is set to zero, for example. In step 1202, it is checked whether a new measured value of the signal level is available. If yes (Y), then in step 1204, it is checked which cylinder or which fuel injector it applies to.

[0086] With the help of Figures 5 to 9 The four examples readily demonstrate that the change in signal level P caused by electrical bypass is significantly greater than the change in signal amplitude. To improve the robustness of the diagnostic method, in Figure 12 In step 1206, the method checks, for example, whether there is a sufficiently large injection interval (e.g., 2 ms) before the measurement window of the "valve opening". This ensures that the signal level is sufficiently stable and reliable and will not be distorted by hydraulic vibrations from the previous dense injection. If so (Y), the two identification thresholds mentioned above are checked. If the signal level is greater than the upper identification threshold (checked in step 1208), an error is recorded for the relevant cylinder in step 1212, and an error for short-circuiting or bypassing the battery is output in step 1216.

[0087] If the signal level is below the lower limit recognition threshold (check in step 1210), an error is recorded for the relevant cylinder in step 1214, and an error of ground short circuit or bypass is output in step 1218.

[0088] If none of the conditions apply, no error is recorded for any cylinder (step 1220). The output in step 1222 can be: Signal level is normal, therefore the two errors mentioned above do not exist.

[0089] The two monitoring methods, "signal amplitude at the 'needle valve reversal point' measurement window" and "signal level at the 'valve open' measurement window," can be performed in parallel and independently. Error information from both methods is preferably collected in a logical "OR" relationship.

[0090] In addition, error debouncing can be performed. However, error debouncing remains unchanged compared to existing conventional diagnostic procedures. Only the meaning of error path is expanded (besides are now included in addition to short circuits).

[0091] Figure 13 A circuit arrangement for explaining the method according to the invention in another preferred embodiment is shown. The circuit arrangement corresponds to... Figure 3 As shown, however, what is shown here is not the resistance to ground, but the increased transition resistance R between sensor 141 and measurement circuit 182. NCS .

[0092] The values ​​of the components in the measuring circuit could also be, for example, as follows: C1 = 13.2 nF, C2 = 22 pF, R1 = 100 kΩ, R2 = 215 kΩ, R3 = 82.5 kΩ, R4 = 1 kΩ, V+ = 5V. It should be understood that these values ​​are merely examples of possible measuring circuits, but will be used to explain R in the following text. NCS The influence of various possible values ​​on the sensor signal.

[0093] exist Figures 14 to 17 The text shows the data based on... Figure 13 The sensor signal or its response to different resistance values ​​R NCS The curve is used as the actual measured value. These are determined by the resistance R. NCS The altered signal curve is labeled S5(R) NCS =50,000 euros), S6(R) NCS =100,000 euros), S7 (R NCS =200,000 euros) and S8 (R NCS =500,000 euros), while with S' R This represents a reference curve, which applies to non-existent resistors (R). NCS =0). Here, the reference curve basically corresponds to Figure 4 Curve S in the figure. Furthermore, the current I is as shown in the figure. Figure 4 As shown.

[0094] As mentioned earlier, with a transition resistance of 50 kΩ, the sensor signal is already much smoother than the signal under error-free conditions. Figure 14 The algorithms used in the controller to determine the valve opening time, needle valve reversal time, and needle valve closing time may provide significantly erroneous measurements under this transition resistance. As the transition resistance increases, the cutoff frequency of the low-pass filter decreases. Figure 15 and Figure 16 ), thus reaching 500,000 euros ( Figure 17 In the case of ), the shape of the sensor signal is the same as the original shape S'. R They no longer have much in common.

[0095] Such a sharp change in signal shape often results in the inability to find valid measurements of valve opening time, needle valve reversal time, or needle valve closing time in the controller, because the rationality check criteria included in the signal evaluation algorithm are not met.

[0096] In the following, the process of the method according to the invention will be explained in detail by way of another preferred embodiment, particularly with regard to the increase in transition resistance.

[0097] First, determine the rise time. The sensor signal has three characteristic features: the valve opening time, the needle valve reversal time, and the needle valve closing time, such as... Figure 4 As shown. To determine the three time points, the sensor signals can be sampled and digitized at defined time intervals in the controller, for example. The time interval, referred to as the measurement window or time window, is as follows: Figure 4 As shown. In principle, the rise time can be determined in each of the three measurement windows. Based on the height of the signal rise, the rise time in the measurement window at the "needle valve reversal point" is preferably determined.

[0098] like Figure 18 As shown, the measurement window Δt U The preferred "needle valve reversing point" is at the end of the electrical control (t). EOE See also Figure 4 A fixed time interval T1' begins after this point. If the duration or width T2' of the measurement window is chosen to be sufficiently large, T2' can have a constant size for all operating points of the internal combustion engine. Alternatively, the spacing T1' and / or width T2' can also be implemented to vary depending on the operating point.

[0099] In the measurement window "needle valve reversal point", the rise time of the sensor signal is preferably obtained based on the gradient curve S', such as... Figure 19 As shown. In this example, the sensor signal is displayed as points (measurement points). Here, at each measurement point, the gradient is determined, for example, as the difference between the measurement point and the previous or next measurement point.

[0100] Therefore, for example, by using the maximum gradient or the maximum value of the gradient curve S' in the measurement window "needle valve reversal point" (here t) max (This indicates that the threshold S' is calculated using a threshold factor.) S Furthermore, the time point t is calculated. max The time points before and after the threshold are identified. Then, the rise time Δt can be calculated. A The rise time is calculated as the difference between two time points that intersect with the threshold. Alternatively, the rise time can be determined at the sensor signal by using the amplitude.

[0101] Next, electrical fault identification is performed. In routine diagnostics, the first step is to examine the measurement window Δt at the "needle valve reversal point". U Is the signal amplitude unreasonably small? If so, calculate the average value of the sensor signal within the measurement window at the "needle valve reversal point". Based on the average value, classify the error into one of three possible error types. If the sensor signal is interrupted (cable breakage or sensor malfunction), measure the quiescent level of the sensor signal in the controller; it is approximately 3V. In the case of a short circuit to ground, the sensor signal level is significantly lower than 3V. In the case of a short circuit to the battery, the sensor signal level is significantly higher than 3V.

[0102] To classify errors, it is preferable to use two identification thresholds. If the average value is, for example, below 1.3V (lower identification threshold), a ground short circuit is reported. If the average value is, for example, above 7V (upper identification threshold), a battery short circuit is reported. Preferably, the upper identification threshold is defined based on the battery voltage. As the battery voltage increases, the upper identification threshold should increase.

[0103] If none of these errors exist, then the rise time is used to check for an increase in transition resistance. Figure 20 The algorithm for identifying this error is illustrated in the flowchart. First, initialization is performed (step 2000), where, for example, the rise time value is set to zero. In step 2002, it is checked whether new rise time measurements are available, specifically for each cylinder of the previous injection sequence. If yes (Y), then in step 2004, these rise time values ​​are sorted in ascending order of magnitude.

[0104] In the measurement window "needle valve reversal point," the rise time of the sensor signal is particularly dependent on the control duration, fuel rail pressure, injector temperature, and fuel, and exhibits high dynamism during operation. Since similar dynamic changes occur at the operating point in all cylinders, an increase in transition resistance at a particular injector can be detected by comparing it with other cylinders. The affected cylinder has a longer rise time compared to other cylinders. The cylinder with the second shortest rise time is selected; this rise time is used as a reference rise time.

[0105] Then, in step 2006, the difference between the rise time and the reference rise time is calculated for each cylinder. To further improve robustness, in step 2008, the difference for each cylinder is subjected to PT1 filtering. In step 2010, the output of the PT1 filter is compared with an identification threshold (e.g., the maximum permissible deviation of the rise time for an error-free system); if this threshold (Y) is exceeded, an increase in transition resistance is reported in step 2014. If not, no increase in transition resistance is found according to step 2012.

[0106] In order to compare the rise time with similar control durations in each injection cycle, it is preferable to calculate the difference with the second smallest rise time specific to the injection type or only for one injection type, such as the main injection.

[0107] In addition, error debouncing can be performed. However, error debouncing remains unchanged compared to existing conventional diagnostic procedures. Only the meaning of the error path is expanded (in addition to electrical open circuits, there is also increased transition resistance).

Claims

1. A method for identifying errors in sensor signals (S) during operation of a fuel injector (170) of an internal combustion engine (160), wherein a switching valve (100) of the fuel injector (170) is actuated by means of a control signal, and wherein the sensor signal is detected as a signal (S) of a sensor (141) configured to detect a characteristic operating point of the fuel injector (170), The predetermined time window (Δt) of the sensor signal (S) including the characteristic operating point of the fuel injector. U Δt O In the process, at least one characteristic of the sensor signal is determined, the at least one characteristic including signal level (P) and / or rise time (Δt). A ), The presence of an error is determined by using at least one characteristic of the sensor signal. The time point at which the switching valve is opened (t) O,V The characteristic operating point of the fuel injector (170) is defined as the time point (t) of the sensor signal (S) that includes the opening of the switching valve. O,V The scheduled time window (Δt) O In the process, the signal level (P) of the sensor signal is determined to determine whether an error exists, and / or The time point at which the nozzle needle of the fuel injector is reversed (t) U,N ) as the characteristic operating point of the fuel injector (170), and at the time point (t) of the sensor signal (S) including the nozzle needle commutation of the fuel injector. U,N The scheduled time window (Δt) U In the process, the rise time (Δt) of the sensor signal is determined. A This is to determine if an error exists.

2. The method of claim 1, wherein the start of operation of the switching valve (t) SOE ) and / or end (t EOE This determines the start of the predetermined time window.

3. The method according to claim 1 or 2, The errors determined by using the signal level (P) as at least one characteristic of the sensor signal include: The sensor has a short circuit, and / or This is achieved by means of the rise time (Δt) A The error determined as at least one characteristic of the sensor signal includes: the transition resistance (R) between the sensor and the readout unit. NCS () is higher than the target value.

4. The method according to claim 1 or 2, wherein the signal level (P), which is the at least one characteristic of the sensor signal, is compared with one or more level thresholds, and wherein an error is determined based on the comparison.

5. The method of claim 1, wherein the rise time (Δt) is considered as at least one characteristic of the sensor signal. A The rise time is compared with a reference rise time, and an error is determined based on the comparison.

6. The method of claim 5, wherein an error is determined to exist if the rise time of the at least one characteristic of the sensor signal is higher than the reference rise time by a predetermined time threshold.

7. The method according to claim 5 or 6, wherein the rise time of one additional fuel injector of the internal combustion engine or the average rise time of a plurality of additional fuel injectors of the internal combustion engine is used as a reference rise time.

8. The method of claim 1, wherein the presence of other errors is determined by means of the amplitude (A) of the sensor signal (S) within the predetermined time window or another predetermined time window of the characteristic operating point of the fuel injector.

9. The method of claim 8, wherein the signal level (P) is additionally determined.

10. The method according to claim 8 or 9, wherein the rise time (Δt) is included in the predetermined time window only if no other error is identified by means of the amplitude of the sensor signal. A ) determine the at least one characteristic as the sensor signal, or determine the rise time (Δt) A This is used to determine if an error exists.

11. A processing unit (180) configured to perform all method steps of the method according to any one of claims 1 to 10.

12. A computer program product having a computer program, which, when run on a computing unit (180), causes the computing unit (180) to perform all the method steps of the method according to any one of claims 1 to 10.

13. A machine-readable storage medium having a computer program stored on the machine-readable storage medium, which, when the computer program is run on an arithmetic unit (180), causes the arithmetic unit (180) to perform all the method steps of the method according to any one of claims 1 to 10.

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