Method for monitoring the injection behavior of a fuel injector of a fuel metering system

Abstract

Method for monitoring the injection behavior of a fuel injector (109) of a fuel metering system (100) of an internal combustion engine (116), wherein - fuel is repeatedly injected from a high-pressure storage tank (108) under a storage pressure (pRail) into a cylinder (124) by means of the fuel injector (109), causing a pressure drop (Δp) of the storage pressure (pRail), the internal combustion engine (116) is operated at a characteristic operating point (450), a measured value (201) characterizing the pressure drop (Δp) is recorded (460) and stored (470), and - a temporal development of the injection behavior of the fuel injector (109) is determined from the stored measured values ​​(201).

Description

[0001] The present invention relates to a method for monitoring the injection behavior of a fuel injector of a fuel metering system. State of the art

[0002] Fuel injectors used to inject fuel into the cylinders of internal combustion engines must typically cover a wide quantity range. This range usually extends from idle, which defines a minimum quantity, to full load at high engine speeds, which defines a maximum quantity. Ideally, the injected fuel quantity correlates linearly with the injection duration (injector activation time). However, a very large linear range means a comparatively high manufacturing cost for the injector. Consequently, not all cylinders of the internal combustion engine produce the same torque for the same injection duration. This can be due, for example, to differences in cylinder compression, cylinder friction, or the hydraulic injection components.The consequence of these torque differences is rough engine running and increased emissions from the internal combustion engine. In practice, so-called quantity balancing controls are therefore used to equalize the injected fuel quantities. One method for quantity balancing control is known, for example, from DE 33 36 028 A1.

[0003] Due to aging, the differences in injection behavior between individual fuel injectors or between an individual fuel injector and a new part can increase, so that quantity compensation controls may no longer be able to counteract sufficiently and the combustion behavior is negatively affected.

[0004] German patent DE 10 2005 018 576 A1 discloses a supply pump for the forced delivery of high-pressure fuel to a common rail system. This maintains a high pressure within the common rail. Furthermore, it proposes a fuel injection system for detecting the delivery quantity in an injector and correcting the injection quantity from the injector in accordance with the delivery quantity, so that the actual injection quantity corresponds to the target injection quantity. German patent DE 10 2011 005 981 A1 discloses a common rail system consisting of a high-pressure fuel accumulator and injectors. It proposes a method for determining the control quantity of the injectors. The control quantity is the portion of the return flow resulting from the actuation of the injector. An excessive change in the control quantity indicates a defective injector.For this purpose, a pressure drop is determined during several fuel injections of an injector into the combustion chamber of a cylinder, and the change in the control quantity is deduced from the comparison of the pressure drops.

[0005] It is desirable to be able to monitor the injection behavior of a fuel injector in the simplest possible way in order to detect excessive changes in a timely manner and to be able to counteract them. Disclosure of the invention

[0006] According to the invention, a method for monitoring the injection behavior of a fuel injector of a fuel metering system is proposed, comprising the features of claim 1. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] The invention utilizes the pressure drop in a fuel accumulator caused by each injection for the (long-term) monitoring of the injection behavior. These pressure drops are hereinafter referred to as cylinder-specific pressure drops.

[0008] In internal combustion engines with a fuel metering system with a high-pressure accumulator, such as a common-rail system, fuel is pumped from a fuel tank into the high-pressure accumulator. A specific pressure, known as the accumulator pressure or rail pressure, prevails in the high-pressure accumulator. When a quantity of fuel is injected into a cylinder of the internal combustion engine via a fuel injector, for example, a solenoid or piezo injector, this leads to a decrease in the accumulator pressure, which can be measured and analyzed. Reference is made, for example, to DE 10 2010 042 736 A1. Advantages of the invention

[0009] The invention is suitable for all types and uses of internal combustion engines. In particular, the method according to the invention is suitable for on-highway use of the internal combustion engine, especially for motor vehicles and commercial vehicles. Furthermore, the invention is also particularly suitable for off-highway use of the internal combustion engine.

[0010] By repeatedly acquiring the measured values ​​characterizing the cylinder-specific pressure drop according to the invention and determining the cylinder-specific pressure drops from these measured values, long-term monitoring of the fuel injector's injection behavior is enabled. Thus, not only is a current value of the cylinder-specific pressure drop considered, but the long-term development of the cylinder-specific pressure drop during regular operation of the internal combustion engine is also monitored.

[0011] The repeatedly acquired measured values ​​are stored according to the invention. In particular, the cylinder-specific pressure drops determined from the respective measured values ​​are also stored. The acquired measured values ​​and / or the determined cylinder-specific pressure drops are stored, in particular, in a table or a histogram, for example, in a control unit of the internal combustion engine. Thus, all cylinder-specific pressure drops determined at different times are available for each cylinder of the internal combustion engine. These stored cylinder-specific pressure drops are evaluated, e.g., compared with each other and checked for plausibility. In the course of this evaluation, a temporal profile of the cylinder-specific pressure drop is determined. Thus, in particular, any drift profile, i.e., a change in the cylinder-specific pressure drop over time, is determined.

[0012] A first measurement, determined before all subsequent measurements, or a corresponding first cylinder-specific pressure drop, defines a reference point. The time course of the cylinder-specific pressure drop originates from this reference point. In particular, this reference point can describe the cylinder-specific pressure drop of a new fuel injector. Thus, it is specifically monitored how the cylinder-specific pressure drop, and therefore the fuel injector itself, changes compared to a new fuel injector.

[0013] The measured values ​​characterizing the cylinder-specific pressure drop are recorded each time the internal combustion engine is operated at a characteristic operating point. This characteristic operating point preferably describes typical operating conditions of the internal combustion engine. In particular, the characteristic operating point is one at which the internal combustion engine is most frequently operated during its regular operation. Because the measured values, and thus the cylinder-specific pressure drops, are not determined at arbitrarily different operating points of the internal combustion engine, but always at the same operating point, it is ensured that the individual measured values, or cylinder-specific pressure drops, are reproducible and representative. This allows for a reliable and meaningful comparison of the cylinder-specific pressure drops.

[0014] If the specific time-dependent pressure drop in each cylinder reaches a threshold, a compensatory measure is preferably implemented. This compensates for undesirable effects on the internal combustion engine that occur when the cylinder-specific pressure drop, and thus the injection behavior, changes too drastically. In particular, changes in engine power due to drift in the injection behavior, rough engine running, increased fuel consumption, and unnecessary environmental pollution are thus avoided. The internal combustion engine is therefore operated under optimal conditions.

[0015] By taking into account the temporal profile of the cylinder-specific pressure drop and recording the different measured values ​​at the characteristic operating point of the internal combustion engine, it is ensured that not only short-term changes in the cylinder-specific pressure drop are compensated. Such short-term changes in the cylinder-specific pressure drop can occur, for example, between a cold and a warmed-up internal combustion engine or due to different fuel temperatures caused by different ambient temperatures. According to the invention, only long-term changes in the cylinder-specific pressure drop are compensated, which occur in particular due to wear of the fuel injector.

[0016] In particular, the corresponding measured values ​​characterizing the individual pressure drop for each cylinder of the internal combustion engine are recorded, and these individual pressure drops are determined. These determined individual pressure drops are stored for each cylinder. Thus, a profile of the individual pressure drop is determined for each cylinder of the internal combustion engine, and the injection behavior of all fuel injectors is monitored. Specifically, during the evaluation of these stored individual pressure drops for each cylinder, an average value of the individual pressure drops for all cylinders and a time-dependent profile of this average value are determined.

[0017] Advantageously, the acquisition of the measured values ​​characterizing the cylinder-specific pressure drop and the determination of the cylinder-specific pressure drops are repeated at regular intervals. These intervals are freely and appropriately selectable. The intervals are defined project-specifically, in particular as a number of operating hours and / or as a distance traveled by the vehicle powered by the internal combustion engine. The acquisition of the first measured value and the determination of the corresponding cylinder-specific pressure drop as a reference point are carried out, in particular, after a short engine lifespan, shortly after commissioning the internal combustion engine, or shortly after the start of its use for a specific application, e.g., after a maximum of 50 operating hours or 300 km. The reference point thus represents a new fuel injector.The following measurements are taken at longer, regular intervals, covering a greater number of operating hours or a greater distance traveled. Specifically, these intervals are 500 operating hours of the internal combustion engine or 30,000 km traveled by a vehicle powered by the internal combustion engine.

[0018] Preferably, as a compensatory measure, the control signal of a fuel injector in the respective cylinder is modified. In particular, this can involve changing the control signal from a control unit to the respective fuel injector. Specifically, the activation duration of the respective fuel injector is altered. Alternatively or additionally, the control signal of another component of the internal combustion engine and / or the fuel metering system can be modified. This ensures that the correct amount of fuel is always injected into the respective cylinder of the internal combustion engine and that optimal combustion takes place within the engine.

[0019] Preferably, as a compensatory measure, the fuel injector and / or another component of the fuel metering system and / or the internal combustion engine is replaced. In this case, the time course of the cylinder-specific pressure drop reaches a threshold value that describes a maximum permissible tolerance of the corresponding component to be replaced.

[0020] In particular, when the relevant threshold is reached, a message is sent to the user of the internal combustion engine. This message is, for example, an audible alarm and / or, more specifically, the illumination of a warning light, such as in the dashboard of a car or commercial vehicle powered by the internal combustion engine. After the message is sent, the internal combustion engine is taken to a workshop to replace the affected component. This enables long-term monitoring of individual components of the internal combustion engine and / or the high-pressure accumulator.

[0021] After the fuel injector and / or another component of the fuel metering system and / or the internal combustion engine has been replaced, a new reference point for the cylinder-specific pressure drop is determined, particularly as soon as the internal combustion engine is operating again at the characteristic operating point. Thus, a new reference point for the temporal profile of the cylinder-specific pressure drop is established with the new component as soon as possible after the replacement. Specifically, when the fuel injector is replaced, the stored cylinder-specific pressure drops determined with the old, replaced fuel injector are deleted.

[0022] Preferably, during the evaluation of the stored cylinder-specific pressure drops, an extrapolation of the stored measured values ​​or the cylinder-specific pressure drop, and thus of the injection behavior of the fuel injector, is performed. In particular, any drift profile of the cylinder-specific pressure drop is also extrapolated. This allows for the prediction of how much the cylinder-specific pressure drop will change in the future. Using this extrapolation, a maximum operating time or a maximum driving distance of the internal combustion engine can be determined until the cylinder-specific pressure drop reaches the threshold at which the fuel injector and / or another component of the fuel metering system and / or the internal combustion engine must be replaced. This maximum operating time or maximum driving distance can be stored in the control unit.The maximum driving distance can therefore be determined in particular as a point in time or a kilometer mark at which the internal combustion engine must undergo service or repair and the fuel injector, another component of the fuel metering system and / or the internal combustion engine must be replaced.

[0023] Preferably, the accumulator pressure and / or a cylinder-specific injected fuel quantity and / or the cylinder-specific pressure drop itself are determined as the measured value characterizing the cylinder-specific pressure drop. The accumulator pressure is usually already recorded and can be used for the method according to the invention. From a pressure signal of the accumulator pressure recorded in this way, the cylinder-specific pressure drop can be easily determined, in particular as the difference between a maximum value and a minimum value of the pressure signal.

[0024] In a preferred embodiment of the invention, the characteristic operating point of the internal combustion engine is determined in an operating point determination or an application. During the operating point determination, a characteristic, frequently occurring, application-specific operating point of the internal combustion engine is identified.

[0025] During this operating point determination, data characterizing the operation of the internal combustion engine are collected. This data can include various parameters or operating conditions and / or individual operating points of the engine. This data is then analyzed to determine the characteristic operating point of the engine. The characteristic operating point can be defined as an average, mean, weighted average, or median of all operating points at which the engine is operated, or as the operating point at which the engine is most frequently operated during its regular service life.

[0026] If the internal combustion engine is used, for example, for a long-distance truck, the characteristic operating point represents the operation of the internal combustion engine as the truck driving on a level highway at a maximum permitted speed.

[0027] Operating point determination is particularly suitable for on-highway use of the internal combustion engine. In this scenario, the engine is typically operated continuously at the same operating point for an extended period, which is then determined as the characteristic operating point. Operating point determination is also suitable for off-highway use of the internal combustion engine. In this case, the process may take longer to determine a characteristic operating point with sufficient certainty.

[0028] Preferably, the engine speed, accelerator pedal position, cruise control speed, fuel temperature, engine coolant temperature, and / or a load collective measurement of the engine are considered for determining the characteristic operating point. Such parameters provide reliable information about the operating conditions under which the engine is operated.

[0029] The position of the accelerator pedal, detected primarily by a pedal position sensor, ensures that typical and reproducible boundary conditions exist for the accumulator pressure, the injected quantity of fuel, the injection pattern, and the (relative) start of fuel injection in relation to a fuel pump stroke. Since high-pressure accumulators typically lack a fuel temperature sensor to determine the fuel temperature within the accumulator, a correlation between the coolant temperature and the fuel temperature in a fuel inlet, detected primarily by a fuel filter, can be used.

[0030] To determine the characteristic operating point, parameters are only considered when the coolant temperature exceeds a certain value. Therefore, only parameters determined when the internal combustion engine is already warmed up and not just started are taken into account. Analogous to the description above, the characteristic operating point is determined, in particular, by an average, mean, weighted mean, or median of all these specific parameters under which the internal combustion engine operates, or by the parameters under which the internal combustion engine most frequently operates during its regular operation. Analogous to the example above of a long-haul truck, the characteristic operating point is, for example, determined by the engine speed and the associated accelerator pedal position.A set cruise control speed is given, which is achieved when the truck travels on a level motorway at the maximum permitted speed.

[0031] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0032] Implementing the process in software form is also advantageous, as this incurs particularly low costs, especially if the executing control unit is already used for other tasks and is therefore already present. Suitable data carriers for providing the computer program include floppy disks, hard drives, flash memory, EEPROMs, CD-ROMs, DVDs, etc. Downloading the program via computer networks (Internet, intranet, etc.) is also possible.

[0033] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0034] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0035] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Short description of the drawings Fig. Figure 1 schematically shows a common-rail system, which serves as the basis for describing a preferred embodiment of a method according to the invention. Fig. Figure 2 shows an example of a common rail pressure curve during injection into a cylinder. Fig. Figure 3 schematically shows a preferred embodiment of a method according to the invention as a block diagram. Embodiment(s) of the invention

[0036] In Fig. Figure 1 schematically depicts an internal combustion engine, here designed as a common-rail engine, comprising a common-rail fuel injection system 100 and an internal combustion engine 116, e.g. a diesel engine, as it may form the basis of the present invention.

[0037] In a partially cutaway cylinder 124 of the internal combustion engine 116, cooled by cooling water 114, a piston 126 is movably arranged. A fuel injector 109 for injecting fuel into the cylinder is mounted on the cylinder 124.

[0038] The fuel injection system comprises a fuel tank 101, shown in a nearly full state. A pre-supply pump 103 is located inside the fuel tank 101. This pump draws fuel from the tank 101 through a pre-filter 102 and delivers it at a low pressure of 1 bar to a maximum of 10 bar via a fuel line 105 to a fuel filter 104. From the fuel filter 104, another low-pressure line 105' leads to a high-pressure pump 106, which compresses the supplied fuel to a high pressure, typically between 100 bar and 2,500 bar, depending on the system. The high-pressure pump 106 has a metering unit (MMU) 113 for adjusting the fuel quantity. The high-pressure pump 106 feeds the compressed fuel into a high-pressure line 107 and a rail 108 (high-pressure accumulator) connected to it, the so-called common-rail high-pressure accumulator. From rail 108, another high-pressure line 107' leads to the fuel injector 109.

[0039] A system of return lines 110 enables the return flow of excess fuel from the fuel filter 104, the high-pressure pump 106 or metering unit 113, the fuel injector 109 and the rail 108 into the fuel tank 101. A pressure regulating valve (PRV) 112 is connected between the rail 108 and the return line 110, which can regulate the high storage pressure prevailing in the rail 108, the so-called rail pressure or common rail pressure, by changing the amount of fuel flowing from the rail 108 into the return line 110.

[0040] The entire common-rail injection system 100 is controlled by a control unit 111, which is connected via electrical lines 128 to the pre-supply pump 103, the high-pressure pump 106, the metering unit 113, the fuel injector 109, a pressure sensor 134 on the rail 108, the pressure control valve 112 and temperature sensors 130, 132, 122 on the internal combustion engine 116 or on the fuel supply line 105.

[0041] In Fig. Figure 2 in diagram 200 shows an example of a common rail pressure signal that can be detected by pressure sensor 134 on rail 108. In diagram 200, the common rail pressure pRail 201 is plotted as the stored pressure on the ordinate against time t on the abscissa. It can be seen that when fuel is injected into one of the cylinders 124 at approximately time t = 0.020, the common rail pressure pRail drops from approximately 1581 bar to approximately 1535 bar, i.e., by Δp ≈ 46 bar. This pressure drop is different for each of the cylinders 124 and is referred to as the cylinder-specific pressure drop.

[0042] A pressure signal of the common rail pressure 201 according to Fig. 2 is particularly suitable for being determined as a measured value characterizing the cylinder-specific pressure drop of one of the cylinders 124 in a preferred embodiment of a method according to the invention. Such a preferred embodiment of the method according to the invention is described in Fig. Figure 3 is shown as a block diagram. The control unit 111 is specifically designed to carry out the preferred embodiment of the method according to the invention.

[0043] When the common-rail fuel injection system 100 and the internal combustion engine 116 are used in a specific application, an operating point determination 300 is first performed to establish or determine a characteristic operating point of the internal combustion engine 116. In step 300, parameters that characterize the operation of the common-rail fuel injection system 100 and the internal combustion engine 116 are determined during operation. In this specific example, the rotational speed of the internal combustion engine 116 is determined and stored as this parameter.

[0044] Step 300 can last for a predetermined operating time or distance of the internal combustion engine 116. This allows a suitably large amount of data on the rotational speed of the internal combustion engine 116 to be collected as a parameter in order to representatively determine the characteristic operating point of the internal combustion engine 116.

[0045] Based on the characteristic operating point of the internal combustion engine 116, the cylinder-specific pressure drop 400 is monitored, thus monitoring the injection behavior of the fuel injector 109. First, a reference point determination 401 is performed, and an initial cylinder-specific pressure drop is determined as a reference point. In step 410, it is checked whether the internal combustion engine 116 is operating at its characteristic operating point. If so, in step 420, the pressure signal from the pressure sensor 134 is recorded as the measured value characterizing the cylinder-specific pressure drop, and the cylinder-specific pressure drop is determined from this. In step 430, the cylinder-specific pressure drop determined in step 420 is stored in a table in the control unit 111.

[0046] In step 440, the system waits until a specific interval, e.g., an operating time of 500 operating hours, has elapsed. Once this interval has expired, step 450 checks whether the internal combustion engine 116 is operating at its characteristic operating point.

[0047] If this is the case, in step 460, analogous to step 420, the pressure signal from pressure sensor 134 is recorded as a measured value, and the cylinder-specific pressure drop is determined from this. In step 470, analogous to step 430, the cylinder-specific pressure drop determined in step 460 is stored in the table in control unit 111.

[0048] In step 480, a time-dependent profile of the cylinder-specific pressure drop is determined, starting from the reference point determined in step 420. In step 490, it is checked whether a deviation of the cylinder-specific pressure drop from the reference point exceeds a threshold value. If this is not the case, the internal combustion engine 116 and the common-rail fuel injection system 100 can continue to be operated without modifications. In this case, as indicated by reference numeral 491, the process starts again at step 440 and waits until the determined interval has elapsed again. Alternatively or additionally, a time-dependent profile of the cylinder-specific pressure drop is determined from the stored values, and based on this profile, the future time at which the deviation of the cylinder-specific pressure drop from the reference point will exceed the threshold value is extrapolated.This future point in time can be used for maintenance purposes, for example, to record an error and / or activate a maintenance indicator. If the deviation of the cylinder-specific pressure drop from the reference point already exceeds the threshold value in step 490, a compensation measure is initiated in step 500.

[0049] As a compensatory measure, the control signal from control unit 111 to fuel injector 109 can be modified. Once this modification of the control signal has been made, the process restarts at step 440 (indicated by reference numeral 501) and waits until the specified interval has elapsed again. Furthermore, a fault code can be entered and / or a service indicator can be activated.

[0050] If, however, the deviation of the cylinder-specific pressure drop from the reference point in step 490 exceeds the threshold value to such an extent that a maximum permissible tolerance of the fuel injector 109 is exceeded, the fuel injector 109 is replaced as a compensatory measure. Once the old fuel injector 109 has been replaced with a new one, the process is restarted at step 410, as indicated by reference numeral 502, and the reference point determination 401 is performed again. In this case, a new reference point is determined for the new fuel injector 109.

Claims

[1] Method for monitoring an injection behavior of a fuel injector (109) of a fuel metering system (100) of an internal combustion engine (116), wherein - fuel is repeatedly injected from a high-pressure accumulator (108) under a storage pressure (pRail) into a cylinder (124) by means of the fuel injector (109), whereby a pressure drop (Δp) of the accumulator pressure (pRail) occurs, the internal combustion engine (116) is operated at a characteristic operating point (450), a measured value (201) characterizing the pressure drop (Δp) is recorded (460) and stored (470), and - a temporal development of the injection behavior of the fuel injector (109) is determined from the stored measured values (201). [2] Method according to claim 1, wherein the measured value (201) characterizing the pressure drop (Δp) is recorded (460) and stored (470) as a function of an operating time or driving distance of the internal combustion engine (116). [3] Method according to claim 1 or 2, wherein a compensation measure is carried out (500) when a deviation of the cylinder-individual pressure drop (Δp) from a reference point reaches a threshold value. [4] Method according to claim 3, wherein as a compensation measure, a control of the fuel injector (109) and / or another component of the fuel metering system (100) and / or the internal combustion engine (116) is changed. [5] Method according to claim 3, wherein the fuel injector (109) and / or another component of the fuel metering system (100) and / or the internal combustion engine (116) is replaced as a compensation measure. [6] Method according to one of the preceding claims, wherein an extrapolation of the stored measured values (201) is carried out as the temporal development of the injection behavior of the fuel injector (109). [7] Method according to one of the preceding claims, wherein the accumulator pressure (pRail) and / or a cylinder-specific injected fuel quantity and / or the cylinder-specific pressure drop (Δp) itself is determined as the measured value characterizing the cylinder-specific pressure drop (Δp) (460). [8] Method according to one of the preceding claims, wherein the characteristic operating point of the internal combustion engine is determined in an operating point determination (300), wherein the operating point determination is carried out prior to the determination (401) of a first measured value characterizing the cylinder-individual pressure drop. [9] Method according to one of the preceding claims, wherein a rotational speed of the internal combustion engine (116) and / or a position of an accelerator pedal and / or a cruise control speed and / or a temperature of the fuel and / or a temperature of a cooling water (114) of the internal combustion engine (116) and / or a load spectrum measurement of the internal combustion engine (116) are taken into account for determining the characteristic operating point. [10] Computing unit (111) configured to carry out a method according to any one of the preceding claims. [11] Computer program which causes a computing unit (111) to carry out a method according to one of claims 1 to 9 when it is executed on the computing unit (111), in particular according to claim 10. [12] A machine-readable storage medium having stored thereon a computer program according to claim 11.

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