Method for controlling multiple injections, especially in a fuel injection system of an internal combustion engine

Abstract

Method for controlling multiple injections in an injection system, in particular in a common-rail injection system for injecting fuel in an internal combustion engine, wherein the injection of at least two successive partial injections is carried out by means of at least one injector having a nozzle needle, characterized in that the closing time of the at least one nozzle needle is detected (300) and that, depending on the detected closing time of the at least one nozzle needle, the presence of an operating condition in which fuel is pumped through between the at least two partial injections is recognized (310).

Description

[0001] The invention relates to a method for controlling multiple injections of an injection system, in particular a common-rail injection system of an internal combustion engine, according to the preamble of claim 1. Furthermore, the invention relates to a computer program, a machine-readable data carrier for storing the computer program, and an electronic control unit by means of which the method according to the invention can be carried out. State of the art

[0002] In common-rail injection systems for injecting fuel into internal combustion engines, it is known to vary the time intervals between individual injections or the duration of individual injections in order to influence the combustion processes taking place in the combustion chambers of the internal combustion engine. The injection is known to be carried out by injectors, which are actuated by means of nozzle needles.

[0003] If the time intervals between individual injections are too short, fuel is known to "drain," meaning that at least two individual injections merge into one another and act as a single, longer injection. This leads to a significant, almost uncontrollable increase in the injected quantity and, consequently, to a deterioration of the combustion process.

[0004] German patent DE 10 2010 021 169 A1 states that in multiple injections of a common-rail injection system in internal combustion engines, the "passing through" of fuel, i.e., the overlapping of two or more individual injections, impairs the combustion process. This is due to the fact that if the time intervals between injections are too short, the closing point of the nozzle needle is delayed, resulting in an uncontrollable increase in the injected quantity.

[0005] German patent application DE 10 2006 033 932 B4 discloses that the "merging" of successive multiple injections in internal combustion engines must be avoided, as this can lead to deviations from the target injection quantity, negative effects on emissions, noise, and operating behavior, as well as potential system damage. Such merging occurs when a valve element is not fully closed after one injection before the next one begins. To counteract this, DE 10 2006 033 932 B4 discloses a method that dynamically adjusts a minimum interval between two successive injections. This minimum interval depends on current operating parameters of the internal combustion engine that influence the closing of the valve element.

[0006] EP 1 217 197 A2 discloses that "over-injection" in multiple injections in internal combustion engines, where individual injection events overlap, leads to uncontrolled fuel quantities and negative effects on exhaust gases, torque, and noise. This occurs when the valve element is not completely closed or when the injection sequences overlap. The document discloses a method for monitoring the interval between two successive injection events in a combustion cycle of an internal combustion engine. Disclosure of the invention

[0007] The invention is based on the understanding that the flow of fuel also results in a delayed closing time of the nozzle needle of the respective injector. According to the invention, this effect is utilized—essentially by way of a reversal—by indirectly detecting and monitoring the flow of fuel during successive multiple injections, particularly two successive single or partial injections, by measuring the precise closing time of the affected nozzle needle. Such measurement of the closing time of a nozzle needle can be carried out in a manner known per se using needle closing sensors.

[0008] A detected change in the needle closing time and / or a detected time delay of the needle closing process indicates the presence of a flow-through condition, which will regularly be associated with a significant increase in the injection quantity. Such a detected flow-through condition can preferably be effectively counteracted by adjusting or changing the time interval between the at least two partial injections and / or the activation duration of the at least two partial injections, or this inherently undesirable operating condition can be eliminated or terminated.

[0009] Thus, the time interval between at least two partial injections can be increased by a corresponding, empirically determined correction value once a flow-through condition is detected, and / or the activation duration of the at least two partial injections can be reduced by a corresponding, empirically determined correction value. A suitable correction value can be selected for each injector from a correction value table or similar document, which, for example, contains correction values ​​for all injectors of one or more internal combustion engines. This allows the method to be advantageously applied to an entire injection system.

[0010] The detection and evaluation of the aforementioned changes in the needle closing time can be advantageously implemented using threshold monitoring, whereby a suitable initial threshold, particularly for the aforementioned time-delayed needle closing time, is empirically determined beforehand. Only when a certain delay in needle closing is present can it be reliably assumed that fuel has passed through between two injections.

[0011] Furthermore, by precisely detecting and monitoring the needle closing time, the smallest hydraulically possible injection intervals can be achieved, and precise adjustment or readjustment / control of the injection intervals can even be carried out during the operation of the injection system or an underlying internal combustion engine.

[0012] Furthermore, by means of the method according to the invention, any chain tolerances or manufacturing tolerances that may occur, in particular corresponding tolerances of the injection nozzles or injection valves concerned, can be effectively compensated with a so-called subsequent control (control loop), also during ongoing operation.

[0013] The method according to the invention can only be carried out after two successive partial injections have been detected, thereby saving system capacity and resources. Furthermore, it can be checked whether the time interval between the two partial injections falls below an empirically determined second threshold. Only when this second threshold is not exceeded can the aforementioned fuel flow occur at all.

[0014] The invention can be used in particular in a common-rail injection system, but also in principle in other injection systems in which multiple injections occur successively, e.g. in injection systems for the injection of urea-water solution (HWL) for the purposes of exhaust aftertreatment or reduction of nitrogen oxides occurring during the combustion of fuel.

[0015] The computer program according to the invention is configured to perform each step of the method, particularly when running on a computer or a control unit. It enables the implementation of the method according to the invention on an electronic control unit without requiring any structural modifications to the unit. For this purpose, a machine-readable data carrier is provided on which the computer program according to the invention is stored. By uploading the computer program according to the invention to an electronic control unit, the electronic control unit according to the invention is obtained, which is configured to control multiple injections in an injection system using the method according to the invention.

[0016] Further advantages and embodiments of the invention will become apparent from the following description and the accompanying drawings.

[0017] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings Fig. Figures 1a-c schematically show devices or sensors known in the prior art for detecting the closing time of a nozzle needle of a common-rail injection valve. Fig. Figures 2a-c show curves of injector current, injection rate and nozzle needle movement measured on a common-rail injection system, in comparison to the prior art and when applying the method according to the invention. Fig. Figure 3 shows an embodiment of the method according to the invention by means of a flowchart. Description of exemplary implementations

[0018] Fig. Figure 1a shows a sensor system known from EP 1 961 952 A1 for detecting the closing of the injector needle in a common-rail injection system of an internal combustion engine. The sensor system comprises a sensor 405 for detecting the opening and / or closing movement of a (not shown here) nozzle needle of a respective injection valve or injector, in particular for detecting the closing and / or opening time of the nozzle needle. In the present embodiment, the sensor 405 is designed as a piezoelectric or micromechanical acceleration sensor and serves to detect mechanical vibrations caused by the nozzle needle movement.

[0019] The in Fig. The device shown in Figure 1a further comprises a sensor module 400 for determining the quantity of fuel to be injected by the respective injector into the respective combustion chamber of an internal combustion engine (not shown). The sensor module 400 includes, in particular, a vibration sensor 405, designed here as a piezoelectric accelerometer, for detecting the closing point of a nozzle needle of the injector. Furthermore, a microprocessor 410 is provided for processing the measurement data. The sensor module 400 also includes a temperature sensor 415 with which the fuel temperature in the injector or in an injector supply line in the immediate vicinity of the injector can be measured. Finally, a data storage device 420 is provided in which injector-specific compensation parameters are stored and can be queried by a control unit of the internal combustion engine.The electronic components 405, 410, 415, 420 of the sensor module 400 are arranged on a circuit carrier 430 which in this embodiment is designed as a ceramic circuit board.

[0020] From WO 2011 / 085 867 A1, an alternative device or sensor for detecting the closing time of a nozzle needle is known, with which the closing times of the nozzle needle and thus the operating phases of the fuel injection can be determined with particular precision. This device is based on the principle that characteristic pressure changes occur when the nozzle needle closes or opens, and these changes can be detected very accurately. In particular, it utilizes the knowledge that the control chamber pressure changes significantly at the beginning and end of the injection phase of a fuel injector, and this control chamber pressure can be detected by means of a pressure measurement.

[0021] Fig. Figure 1b shows a partial axial section of a fuel injector, as shown in WO 2011 / 085 867 A1, which is relevant here. Within an injector body 1, the injector has a high-pressure chamber 2 and a low-pressure chamber 3. These two pressure chambers are separated from each other by a valve piece 4. The high-pressure chamber 2 communicates via an inlet channel 5, for example, with a common rail (not shown). The low-pressure chamber 3 is connected to a fuel tank via a return line 21.

[0022] The high-pressure chamber 2 can be connected to the combustion chamber of an internal combustion engine (also not shown) via injection nozzles (not shown). The injection nozzles are controlled in a known manner by means of a nozzle needle, from which in Fig. 1b shows only the end furthest from the nozzle, which is designed as a plunger 6. The plunger 6 is arranged in a displacement-acting manner in a control chamber 7 located in the valve piece 4. This control chamber 7 communicates with the high-pressure chamber 2 via an inlet throttle 8 and with the low-pressure chamber 3 via a preferably throttled outlet channel 9, the outlet channel 9 being controlled by a control valve arrangement 10. When the outlet channel is closed by means of the control valve arrangement 10 and the nozzle needle is in its closed position, the same high pressure is established in the control chamber 7 as in the high-pressure chamber 2, with the result that the plunger 6 in Fig. 1b is pressed downwards and the associated nozzle needle is held in the closed position that shuts off the injectors. If the drain channel 9 is opened by means of the control valve assembly 10, a reduced pressure is established in the control chamber 7 compared to the high pressure in the high pressure chamber 2, and the plunger 6 moves together with the nozzle needle into Fig. 1b in an upward direction, i.e. the nozzle needle is placed in its open position so that fuel is injected into the combustion chamber through the injectors.

[0023] The control valve assembly 10 has a sleeve-shaped closing element 11, which is tensioned against a seat concentric with the outlet opening of the drain channel 9 by a closing spring 12, which is designed as a helical compression spring. The sleeve-shaped closing element 11 is guided axially displaceably on a guide rod 13 which is coaxial with the longitudinal axis 100 of the injector body 1, the annular gap between the inner circumference of the closing element 11 and the outer circumference of the guide rod 13 acting as a leak-free sealing gap.

[0024] If the locking element 11 is in Fig. When the closing position shown in Figure 1b is assumed, the pressure chamber 14 formed within the closing body 11, which communicates with the control chamber 7 via the drain channel 9 and therefore has the same fluid pressure as the control chamber 7, is sealed off from the low-pressure chamber 3. A star-shaped armature 15 of an electromagnet assembly 16 is arranged on the closing body 11. This armature serves as an actuator for actuating the control valve assembly 10. This electromagnet assembly 16 has, in a known manner, a solenoid coil 17, which is arranged within an electromagnet assembly concentric with the guide rod 13, with an annular outer pole 18 and an annular inner pole 19. When the solenoid coil 17 is energized, the armature 15 is magnetically attracted to the poles 18 and 19, so that the closing body 11 is lifted from its seat against the force of the closing spring 12 and the control valve assembly 10 is opened.

[0025] During the closed phase of the nozzle needle connected to the plunger 6, i.e., when the injectors are closed, the control valve assembly 10 is closed, and the fluid pressures in pressure chamber 14 and control chamber 7 are equal. Immediately before the nozzle needle closes, the pressure in control chamber 7 drops below the high pressure in the supply channel 5 due to the low pressure under the nozzle seat of the nozzle needle at that time and the associated closing movement of the plunger 6. Immediately after the nozzle needle closes, the pressure in control chamber 7 rises sharply because the plunger 6 is now stationary, increasing to the pressure in the supply channel 5. Consequently, the pressure in control chamber 7 and the practically identical pressure in pressure chamber 14 exhibit a pronounced minimum at the moment the nozzle needle closes.

[0026] In Fig. 1c is for one in Fig. 1b shows the course of the nozzle needle stroke in the injector (diagram A, in the Fig. 1c below) and the course of the control chamber pressure (Diagram B, in the Fig. (1c above) is shown as an example. Since the pressure of the control chamber 7 is also present in the pressure chamber 14 when the closing element 11 is closed, the guide rod 13 inside the closing element 11 is always subjected to the control chamber pressure at its end face in this valve position. The control chamber pressure is transferred to a pressure in the control chamber by means of the guide rod 13. Fig. The pressure sensor 20, shown schematically in Figure 1b, transmits the data so that an evaluation circuit (not shown), connected to the pressure sensor 20 on its input side, continuously receives information about the pressure in the control chamber 7 and thus, in particular, detects the closing times of the nozzle needle. This evaluation circuit can be integrated into a control unit of the internal combustion engine (not shown).

[0027] A described sensor for detecting the closing time of a nozzle needle provides a voltage or voltage change in the range of approximately 1 V as a measurement signal. Instead of the piezoelectric sensor shown in the preceding figures for detecting the closing time, piezoresistive elements are also possible, which utilize the so-called piezoresistive effect, which consists of the fact that many materials change their specific electrical resistance under the influence of pressure forces.

[0028] The in Fig. Curves 200 and 205 shown in 2a exhibit a relatively small time interval between the initial current injection 210 and a subsequent second injection 215. The curves shown in Fig. The injection rate measurement shown in Figure 2b, performed during the aforementioned current application, reveals two injections 220 that are not sufficiently separated in time. This insufficient temporal separation is primarily caused by the fact that, in the case of current application according to curve 200, the injection rate does not drop to the initial value of approximately 0 mV between the two injections 220, but only to a significantly higher value of approximately 70 mV.

[0029] As shown by the injection rate measurement according to Fig. As can also be seen in 2b, with a larger distance in the current supply between the first injection 210 and the second injection 215 according to curve 205, two clearly separated injections 225 result.

[0030] According to the invention, the lack of or insufficient temporal separation of the two injections 220 also causes a temporal shift or delay in the nozzle needle closing process. The in Fig. The measurement curves of the injector nozzle needle movement 230, 235 shown in Figure 2c, which result from the current application according to curves 200, 205, illustrate this relationship, because the measurement curve 230 resulting from the earlier current application 210 is significantly shifted later in time compared to the measurement curve 235 resulting from the later current application 205, namely by about 0.05 ms later in the present embodiment.

[0031] It should be noted that the respective scaling of the X and Y axes in the Fig. The measurement curves shown in 2a to 2c only represent the results of test examples obtained on a measuring or test stand and therefore the specific measured values ​​shown are in no way to be understood as limiting the invention.

[0032] According to the in Fig. In the embodiment of the method according to the invention shown in Figure 3, a needle closing process or a corresponding electrical voltage value, i.e., the time and / or magnitude of the voltage value, is first detected. Based on the detected voltage value, it is checked whether the time of the needle closing, which is also detected, is delayed by a factor greater than an empirically determined threshold. If this condition is not met, a needle closing process is detected again, since, according to the invention, if this condition is not met, it is assumed that no fuel flow as described above has occurred, with the aforementioned adverse consequences for the combustion process.

[0033] However, if test 305 shows that the aforementioned condition is met, the presence of fuel flow between the respective two injections is assumed or recognized 310 and in the subsequent step 315 an adjustment, in particular an increase in the time interval between the current curves of the two injections, is carried out, thereby counteracting or suppressing or ending the aforementioned fuel flow.

[0034] It should be noted that the in Fig. The routine shown in step 3 is preferably only started when two consecutive injections are detected or present.

[0035] The described method can be implemented in the form of a control program for an electronic control unit for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs).

Claims

[1] Method for controlling multiple injections in an injection system, in particular in a common-rail injection system for injecting fuel into an internal combustion engine, wherein the injection of at least two successive partial injections is carried out by means of at least one injector having a nozzle needle, characterized by , that the closing time of the at least one nozzle needle is detected (300) and that, depending on the detected closing time of the at least one nozzle needle, the presence of an operating condition in which fuel is pumped through between the at least two partial injections is detected (310). [2] Method according to claim 1, characterized by that the detection of the closing time of at least one nozzle needle is carried out by means of a needle closing sensor. [3] Method according to claim 1 or 2, characterized by, that the recorded closing time is compared with a first threshold value (305) and only when the first threshold value is exceeded is it concluded that there is a flow-through state between the at least two partial injections (310). [4] Method according to any one of the preceding claims, characterized by , that when the flow state is detected between the at least two partial injections, the time interval of the control of the at least two partial injections is changed, in particular increased (315), and / or the control duration of the at least two partial injections is changed, in particular decreased. [5] Method according to claim 4, characterized by, that the time interval of the control of the at least two partial injections is increased by a previously empirically determined first correction value and / or that the control duration of the at least two partial injections is reduced by a previously empirically determined second correction value. [6] Method according to claim 5, characterized by , that a correction value table is provided in which injector-specific correction values ​​are stored, whereby a specified correction value is retrieved from the correction value table. [7] Method according to any one of the preceding claims, characterized by that the aforementioned steps according to one or more of the preceding claims are only carried out upon detection of two successive partial injections. [8] Method according to claim 7, characterized by, that the time interval between the two partial injections is compared with a second threshold value and the aforementioned steps are only carried out if the second threshold value is undershot. [9] A computer program configured to cause a computing device to perform each step of a method according to any one of claims 1 to 8 when running on the computing device. [10] Machine-readable data carrier on which a computer program according to claim 9 is stored. [11] Electronic control unit which is configured to control multiple injections in an injection system by means of a method according to any one of claims 1 to 8.

Images