Method and control unit for operating an injection system

Abstract

Method for operating an injection arrangement (10) for injecting fuel into an internal combustion engine (12), wherein the injection arrangement (10) has a piezo actuator (30) and a nozzle needle (28) that can be actuated by means of the piezo actuator (30), comprising the steps: - time-dependent determination (S4) of a signal that is indicative of a closing of the nozzle needle (28) during an injection process of the injection arrangement (10), - depending on the time-dependent determined signal, determining (S8) whether a load drop occurring at the piezo actuator (30) during the injection process is present, and - reducing (S10) an injection pressure in the injection arrangement (10) below an opening pressure of the nozzle needle (28) when the load drop (32) is present.

Description

[0001] The invention relates to a method and a control unit for operating an injection arrangement for injecting fuel into an internal combustion engine, as well as a computer program and a machine-readable storage medium. State of the art

[0002] It is known from practical experience that piezo injectors, which are components of an injection system, have a piezo actuator and a nozzle needle that can be actuated by the piezo actuator. In a so-called direct-acting piezo injector, the nozzle needle can be actuated directly by the piezo actuator, while in a so-called servo piezo injector, it can be actuated by means of a hydraulic coupler. During operation of the piezo injector, the piezo actuator can be subjected to a voltage during a charging process, causing it to expand and, optionally mediated by the hydraulic coupler, deflecting the nozzle needle so that it moves from its closed position to its open position. The closed position is characterized by the nozzle needle being in fluid-tight engagement with a nozzle seat.In the open position, a gap is formed between the nozzle needle and the nozzle seat, through which fuel can be introduced into the internal combustion engine. To terminate an injection process, it is necessary for the piezoelectric actuator to be actively discharged in order to cause the nozzle needle to move into its closed position. Self-discharge of the piezoelectric actuator is too slow for the discharge required to close the needle.

[0003] Continuous fuel injection into the internal combustion engine occurs when the injector needle cannot be moved to its closed position after an injection cycle. Such continuous injection can lead to damage to the internal combustion engine, defects in the exhaust aftertreatment system, and / or damage to the engine's turbocharger.

[0004] It is also known that a load drop at the piezo actuator, which occurs during the injection process, can lead to an undesired continuous injection, since it may then no longer be possible to actively discharge the piezo actuator in order to cause the nozzle needle to move into its closed position.

[0005] From DE 10 2008 001 971 A1, a method for diagnosing a load drop at a piezoelectric actuator in an injection system is known, in which the load drop occurs during a charging phase of the piezoelectric actuator. The load drop can be detected by measuring a voltage during the charging process of the piezoelectric actuator or directly after the charging process. Disclosure of the invention

[0006] The invention relates to a method for operating an injection arrangement, in particular a common-rail injection arrangement, for injecting fuel into an internal combustion engine, wherein the injection arrangement has a piezo actuator and a nozzle needle that can be actuated by means of the piezo actuator, comprising the steps of determining a signal that is indicative of the closing of the nozzle needle during an injection process of the injection arrangement as a function of the time-dependent signal, determining whether a load drop occurring during the injection process is present at the piezo actuator, and reducing an injection pressure in the injection arrangement below an opening pressure of the nozzle needle when the load drop is present.

[0007] Using the method according to the invention, it is therefore possible to determine simply and accurately whether continuous fuel injection into the internal combustion engine is occurring by monitoring the closing of the nozzle needle to its closed position, at least during the injection process, by observing a signal that indicates the nozzle needle moving into its closed position. If it can be determined that a load drop has occurred at the piezoelectric actuator during the injection process, the injection pressure in the injection assembly can be reduced below the opening pressure of the nozzle needle, thus forcing a hydraulic closure of the nozzle needle and allowing the injection assembly and the internal combustion engine to continue operating, for example in emergency driving mode or engine emergency mode, despite the piezoelectric actuator no longer being actively discharged.The injection pressure can be a pressure prevailing in the piezo injector, which may include the piezo actuator and the nozzle needle. This injection pressure can essentially correspond to, and / or depend on, a high-pressure accumulator pressure in a high-pressure accumulator of the injection system that is in fluidic communication with the piezo injector. The opening pressure can correspond to a minimum pressure at which the nozzle needle can be moved from its closed position to its open position under given operating parameters.

[0008] In particular, detecting whether a load drop has occurred can be done very quickly, as it is not necessary, as with conventional diagnostics, to monitor the charging process of the piezo actuator following the injection process. It is also possible to differentiate between a load drop that occurs during the injection process, i.e., with a charged piezo actuator, and a load drop with an uncharged piezo actuator, which prevents injection, by monitoring the signal that indicates the nozzle needle is closing.

[0009] Despite the load drop at the piezo actuator, closing the nozzle needle can occur particularly quickly compared to known methods. One such known method for closing the nozzle needle is, for example, a slow discharge of the piezo injector, which can be connected in parallel to a high-resistance resistor. Another method is a so-called "draining" of the hydraulic coupler in a servo-piezo injector, where a fuel-containing coupling volume between the piezo actuator and the hydraulic coupler can slowly empty during operation, thus causing the nozzle needle to close.Another known measure is based on observing a violation of the fuel quantity balance in the injection system and a consequent reduction in the high-pressure accumulator pressure in the high-pressure fuel chamber of the injection system below a minimum injection pressure, which, for example, can be 100 bar for a CRI3-20 type piezo injector from Robert Bosch GmbH. The resulting closing of the nozzle needle and the automatic shutdown of the internal combustion engine then terminates the continuous injection. In contrast to, for example, the piezo injector running dry, the closing of the nozzle needle using the method according to the invention can also be carried out independently of the operating behavior of the piezo injector.The method according to the invention can also be used if a piezo injector, such as a DNC TD2 type piezo injector from Robert Bosch GmbH, does not support the coupler running dry as a measure to terminate continuous injection.

[0010] Furthermore, the method according to the invention can be applied to a directly controlled piezo injector, which may be free of a hydraulic coupler, and to a servo piezo injector, which may have a hydraulic coupler.

[0011] Overall, the operation of the internal combustion engine can be improved, as automatic shutdown of the internal combustion engine due to continuous injection is avoided and the internal combustion engine can continue to operate in emergency driving mode despite a drop in load.

[0012] In one embodiment of the method, the detection can be performed at least towards the end of the injection process, when the nozzle needle is expected to close. This allows the method to be carried out in a particularly resource-efficient manner. The detection can also be performed during the entire injection process or continuously, i.e., during the charging process of the piezoelectric actuator, the injection process, and the discharge process of the piezoelectric actuator. The discharge process and the injection process can overlap in time, since the nozzle needle can close from the beginning of the discharge process, and the closed position of the nozzle needle can mark the end of the injection process.

[0013] The presence of load drop can be inferred if the signal is substantially lower than it would be if load drop were absent. In particular, the signal may be essentially zero. In other words, the presence of load drop during injection can be inferred from the at least partial absence of the signal indicative of nozzle needle closing. This allows for a simple and accurate determination of whether load drop is present.

[0014] The signal can be a voltage applied to the piezoelectric actuator, a current applied to the piezoelectric actuator, a capacitance drop across the piezoelectric actuator, and / or a force applied to the nozzle needle by the piezoelectric actuator. The voltage and / or current can represent electrical signals that can be determined by measurement or detection using a suitable sensing circuit. The capacitance and / or force can be calculated, i.e., determined, based on the voltage and / or current. The force can represent an actual force acting on the nozzle needle or a virtually defined quantity. This allows for a particularly simple determination, directly from the electrical behavior of the piezoelectric actuator, of whether a load drop occurs across the piezoelectric actuator during the injection process.

[0015] The method can further include the time-dependent acquisition of an additional signal during the injection process. This additional signal can be a high-pressure storage pressure in a high-pressure fuel accumulator of the injection system, a current applied to a pressure regulating valve of the high-pressure fuel accumulator (particularly for its control), a current applied to a metering unit of a high-pressure pump for supplying fuel to the high-pressure fuel accumulator (particularly for its control), and / or a cylinder pressure in a cylinder of the internal combustion engine that is pressurized with fuel by means of the nozzle needle. The determination can also be performed depending on the additional signal, in particular by comparison with a nominal or standard curve of the additional signal expected when the load drop is absent.In a common-rail injection system, the high-pressure accumulator pressure can correspond to a so-called common-rail pressure. The metering unit can be designed as an inverse metering unit or an electric suction valve, or incorporate the corresponding component. This measure increases the accuracy with which it is determined whether a load drop occurs at the piezoelectric actuator during the injection process and avoids the unnecessary continuous closing of the nozzle needle. The aforementioned configurations of the further signal represent parameters of the injection system or the internal combustion engine that change characteristically due to continuous fuel injection into the engine.For example, the high-pressure accumulator pressure, the current applied to the pressure regulating valve, and the current applied to the metering unit can influence operating parameters of the injection system, allowing for particularly rapid detection of load drops when these parameters change suddenly. Comparing the resulting signal with its expected normal curve can then be performed very easily.

[0016] Another signal, namely a pressure drop in the high-pressure fuel accumulator caused by continuous injection, can also be determined from the measured time-dependent high-pressure accumulator pressure and its relationship to the high-pressure accumulator pressure compared with a corresponding standard curve when the load drop is absent. In the standard curve, the pressure drop can correspond to the desired amount of fuel flowing from the high-pressure accumulator into a combustion chamber, particularly a cylinder, of the internal combustion engine, including any control quantities. In the event of a fault, i.e., when continuous injection is present, the pressure drop can correspond to the entire fuel flow through the injector into the combustion chamber. Overall, the pressure drop can therefore be considered indicative of the nozzle needle position.

[0017] The high-pressure storage pressure and consequently the pressure drop can be determined using a high-resolution temporal pressure measurement method, in particular a pressure measurement method “ISP” (injection specific pressure) used by Robert Bosch GmbH, so that both parameters are recorded with high temporal resolution.

[0018] The occurrence of the load drop can also be determined by means of a shift in operating parameters of the metering unit of the high-pressure pump, in particular the inverse metering unit or the electric suction valve.

[0019] The further signal can be detected and / or determined at least towards the end of the injection process, in particular during the entire injection process or even continuously, i.e. during the charging process of the piezo actuator, the injection process, and the discharging process of the piezo actuator.

[0020] Reducing the injection pressure can be achieved by opening the pressure regulating valve, closing the metering unit, and / or switching off the metering unit. The metering unit can be switched off, in particular, by deactivating its control unit. These measures easily reduce the injection pressure in the high-pressure fuel accumulator, so that even without discharging the piezo actuator, the nozzle needle can be hydraulically forced into its closed position.

[0021] The method can further include time-dependent detection of a reduced high-pressure accumulator pressure, determination of a pressure drop in the fuel high-pressure accumulator caused by continuous injection as a function of the detected reduced high-pressure accumulator pressure, and increasing the high-pressure accumulator pressure if the detected pressure drop falls below a threshold value. In this way, it is particularly easy to monitor whether and when the nozzle needle has moved into its closed position. As soon as the pressure drop in the fuel high-pressure accumulator decreases, it can be determined that the continuous injection has ended, and the injection system and the internal combustion engine can be switched to emergency driving mode by increasing the high-pressure accumulator pressure, thus preventing an unwanted automatic shutdown of the internal combustion engine.

[0022] The invention further relates to an electronic control unit for operating, in particular controlling, an injection arrangement for injecting fuel into an internal combustion engine, wherein the injection arrangement has a piezo actuator and a nozzle needle that can be actuated by means of the piezo actuator, wherein the control unit is configured to determine, as a function of time, a signal indicative of the closing of the nozzle needle during an injection process of the injection arrangement, to determine, as a function of the time-dependent signal determined, whether a load drop occurring during the injection process is present at the piezo actuator, and to reduce an injection pressure in the injection arrangement below an opening pressure of the nozzle needle when the load drop is present.

[0023] The control unit can be designed to control and / or regulate the injection arrangement even if there is no load drop at the piezo actuator.

[0024] The control unit can be configured to perform all steps of the procedure described above. Individual steps of the procedure can also be performed by individual components of the injection system. Furthermore, functions of the injection system or functions of individual components of the injection system can be implemented as steps of the procedure.

[0025] The invention further relates to a computer program configured to perform each step of the method described above, particularly when the computer program is executed on a control unit.

[0026] The invention further relates to a machine-readable storage medium on which a computer program as described above is stored.

[0027] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. Brief description of the drawings

[0028] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0029] Fig. Figure 1 shows a schematic representation of an injection arrangement for an internal combustion engine according to an exemplary embodiment.

[0030] Fig. Figure 2 shows a schematic representation of the steps of a procedure for operating the injection arrangement in Fig. 1.

[0031] Fig. Figure 3 shows a schematic diagram with voltage curves of a piezoelectric actuator of the injection arrangement in Fig. 1 applied voltage.

[0032] Fig. 4– Fig. Figure 8 shows schematic diagrams with signal waveforms of other signals from the injection system or the internal combustion engine. Fig. 1.

[0033] Fig. Figure 9 shows, in schematic form, further steps of the procedure in Fig. 1. Exemplary embodiments of the invention

[0034] One in Fig. 1 injection arrangement shown, designed as a common rail 10 for injecting fuel into an internal combustion engine 12 a high-pressure pump 14 , a high-pressure fuel storage tank 16 , a piezo injector 18 and a control unit 19 to control the injection system 10 up. The high-pressure pump 14 It serves to supply fuel from a (not shown) storage tank to the high-pressure fuel storage tank via an inlet and outlet. 16 The high-pressure pump is used for this purpose. 14 with a in Fig. 1 schematically indicated measuring unit 20 , which provide a fuel flow of fuel from a low-pressure side of the injection arrangement 10 on a high-pressure side of the injection assembly 10 regulates, provides. The high-pressure fuel accumulator. 16 is also connected to the piezo injector 18 coupled by means of a line, so that the fuel from the high-pressure fuel reservoir 16 via the piezo injector 18 a cylinder 22 the internal combustion engine 12 is supplied to a part of a combustion chamber of the internal combustion engine 12 represents. It is understood that the injection arrangement 10 multiple piezo injectors 18 and the internal combustion engine 12 an equal number of cylinders 22 can exhibit.

[0035] A high-pressure fuel accumulator 16 connected pressure regulating valve 23regulates a high-pressure storage pressure in the fuel high-pressure storage tank 16 , which in turn uses a high-pressure storage pressure sensor 24 It is measurable. The high-pressure accumulator pressure corresponds to the pressure on the fuel in the high-pressure fuel accumulator. 16 . By means of an electrical detection circuit 26 , which are electrically connected to the piezo injector 18 coupled, is an electrical signal that is indicative of the closing of a jet needle. 28 of the piezo injector 18 is detectable. The detection circuit 26 can a component of the control unit 19 be. The jet needle 28 is via a piezoelectric actuator 30 of the piezo injector 18 directly operable, so that the jet needle 28 between an open position in which the jet needle 28 from a nozzle seat of the piezo injector 28 , which is attached to the cylinder 22is attached, is lifted, and in a closed position in which the jet needle 28 The nozzle needle is in fluid-tight contact with the nozzle seat and is movable. Opening the nozzle needle 28 is used to move the jet needle 28 necessary opening pressure of the nozzle needle 28 compared to one in a piezo injector 18 prevailing injection pressure of the nozzle needle 28 The injection pressure essentially corresponds to, or depends on, the high-pressure accumulator pressure. Pressure sensors 31 , which are inside the cylinder 22 are arranged to detect cylinder pressure in the cylinder 22 .

[0036] The control unit 19 is with the measuring unit 20 the high-pressure pump 14 , the pressure regulating valve 23 , the high-pressure storage tank pressure sensor 24 , the cylinder pressure sensor 31and via the detection circuit 26 with the piezo injector 18 coupled to evaluate signals captured by the respective components and / or to control and / or regulate the respective components.

[0037] Enter into Fig. 1 with the reference numeral 32 provided load drop at the piezoelectric 30 of the piezo injector 18 during an injection process of the injection arrangement 10 on, can the piezoelectric 30 at least partially discharged. This causes the piezoelectric actuator to... 30 is no longer dischargeable and the nozzle needle 28 can only be actuated inadequately, so that the jet needle 28 It can no longer be moved into its closed position. Such a drop in load 32 This can therefore lead to a continuous injection of fuel into the internal combustion engine. 12 which in turn can cause, among other things, damage to the internal combustion engine12 can cause.

[0038] A in Fig. 2. Method for operating the injection arrangement shown 10 It enables such a load drop occurring during the injection process to be compensated for. 32 to quickly identify and take appropriate measures to mitigate the effects of the load drop 32 To terminate the continuous injection process. After starting the procedure in step S0, a performance diagnosis of the injection system is performed in a first optional procedure step S2. 10 and the internal combustion engine 12 The performance diagnostics can be carried out, for example, in accordance with the function of a CY372 output stage module of an EDC17 generation control unit from Robert Bosch GmbH, which is located in the control unit 19 It can be implemented, carried out. If the performance diagnostics show that there is a load drop 32In a subsequent process step S4, a signal is generated that is indicative of the closing of the nozzle needle. 28 is, during an injection process of the injection arrangement 10 The signal is determined over time. It can be measured either only during the injection process or continuously, i.e., during the charging cycle of the piezoelectric actuator. 30 , during the injection process and during a discharge process of the piezo actuator 30 , can be determined. In a further optional step S6, another signal from the injection system can be determined. 10 or the internal combustion engine 12 or further signals from the injection system 10 or the internal combustion engine 12The signal is recorded over time. In a further step S8, depending on the signal determined over time in step S4 and optionally depending on the further signal(s) recorded over time in step S6, it is determined whether a load drop occurs during the injection process. 32 on the piezo element 30 This applies if it is determined in step S8 that the load drop 32 on the piezo element 30 If this is the case, in a further step S10 the injection pressure in the injection arrangement is set. 10 below an opening pressure of the nozzle needle 28 reduced. Provided that the performance diagnostics in step S2 show that there is no load drop. 32 is present or the determination in step S8 leads to a non-existence of the load drop 32 If this leads to the conclusion of the procedure, it ends as indicated by the corresponding procedural step S12.

[0039] With reference to Fig. Steps S4 and S8 are explained in more detail in section 3. The signal that indicates the closing of the jet needle. 28 In one embodiment, this corresponds to an electrical signal that is detected by the detection circuit. 26 the injection arrangement 10 is measurable, namely one at the piezoelectric actuator 30 applied voltage. An abscissa 33 of the in Fig. The diagram shown in section 3 corresponds to a time and an ordinate. 34 The diagram corresponds to the voltage applied to the piezoelectric actuator or to a voltage applied to the piezoelectric actuator. 30 applied current. A voltage curve. 36 corresponds to the one on the piezoelectric switch 30 ideally, the voltage should be applied at a time-dependent rate when there is no load drop. 32 this occurs during the injection process. An example of this is a current flow. 37the current acting on the piezoelectric actuator, which occurs during the closing process of the nozzle needle 28 occurs. Alternatively, a corresponding voltage signal can be detected. A voltage waveform 38 corresponds to the one on the piezoelectric switch 30 applied voltage when a load drop 32 this occurs during the injection process. The beginning of the voltage curve is correct. 38 until the time the load drop occurs 32 with the standard voltage curve 36 agree. During the charging process of the piezoelectric actuator 30 The voltage increases over time until it reaches a maximum value. During a discharge process of the piezoelectric actuator. 30 The one that falls on the piezo element 30 applied voltage continuously within the normal range 36 The duration of the injection process corresponds to a time interval determined by the opening of the nozzle needle. 28 after charging the piezoelectric actuator 30and the complete closing of the jet needle 28 following the discharge process of the piezoelectric actuator 30 is limited. Does the load drop occur? 32 The voltage increases in accordance with the voltage curve. 38 The time difference is only slight, since the piezoelectric actuator 30 no longer actively controlled by the control unit 19 is dischargeable. Within a time interval 39a The performance diagnostics are carried out in step S2. A time interval 39b corresponds to a theoretically calculated duration of the injection process, which is determined by the expected earliest start of the closing process of the nozzle needle. 28 The actual duration of the injection process is longer and is limited by the disappearance of the signal. 37 marked. At least within that time interval 39c will be the one on the piezo element 30The applied voltage is detected in step S4. Step S8 is performed towards the end of, or directly after, the end of the time interval. 39c carried out.

[0040] In step S8, it is determined whether the electrical signal, namely the one described above and responsible for closing the jet needle, is present. 28 The indicative voltage is measurable. If a characteristic feature of this signal is measurable, there is no load drop. 32 If the characteristic feature of this signal is not measurable, the voltage drop can be inferred. With reference to the current waveform... 37 in Fig. 3. It can be determined whether this is necessary for closing the jet needle. 28 characteristic feature 40 in the course of the current 37 the piezo element 30 The flowing current is measurable. If the characteristic feature 40 If it cannot be detected, there is a load drop. 32during the injection process. If the characteristic feature 40 If the signal is detectable, there is no load drop during the injection process. In both configurations, the characteristic feature can be the signal itself.

[0041] In addition to or alternatively to the one on the piezoelectric 30 In another embodiment, the applied voltage can be used to control the piezoelectric actuator. 30 applied current via the detection circuit 26 be recorded. The signal determined in step S4 can also be a signal at the piezoelectric actuator. 30 decreasing capacity and / or a change caused by the piezoelectric actuator 30 on the jet needle 28 The applied force can be determined based on the measured voltage and / or current. At least one, several, or all of these quantities can be used in step S8 to control the movement of the jet needle. 28to monitor their closing position and thereby draw a conclusion about the presence of a load drop. 32 to pull during an injection process in step S8.

[0042] With reference to Fig. 4 to Fig. Section 7 explains in more detail the additional signals recorded in step S6 as a time-dependent measure, which can also be used in step S8 to determine whether the load drop 32 during the injection process. A situation relating to Fig. 8. The further signal explained can be derived from the in Fig. The additional signal described in step 4 is determined and also used in step S8. The signals described in the Fig. 4 to Fig. 7 abscissas shown 33 the diagrams of a time and the in Fig. 8 abscissa shown 33 the high-pressure storage pressure. The ones in the Fig. 4 to Fig. 8 shown ordinates 34correspond to the high-pressure storage pressure, one for its control at the pressure regulating valve 23 applied current, one for their control at the metering unit 20 applied current or that measured by the pressure sensor 31 Measured cylinder pressure. An ordinate. 34 of the diagram in Fig. 8 corresponds to a pressure drop in the high-pressure fuel reservoir caused by continuous injection. 16 .

[0043] A pressure curve 40 of the in Fig. The high-pressure storage pressure shown in section 4 corresponds to a pressure in the absence of load drop. 32 expected normal course, while a pressure curve 42 the occurrence of the load drop 32 This corresponds to the high-pressure storage pressure that occurs. A significant pressure drop that occurs over a wide time period is characteristic of the presence of load drop. 32The pressure measurement of the high-pressure storage tank pressure can be carried out using the ISP pressure measurement method of Robert Bosch GmbH.

[0044] A in Fig. 5. Current flow shown 44 of the current that flows through the pressure regulating valve 23 is a situation where the load drop is not present. 32 Expected normal waveform of this signal. A current waveform. 46 This current results when the load drop occurs. 32 and exhibits a characteristic peak-shaped increase that transitions into an approximately constant curve, which increases by an approximately constant amount compared to the current curve. 44 is increased.

[0045] A in Fig. 6. Current flow shown 48 of a current for the metering unit 20 In the expected normal course, if the load drop is not present, it indicates 32 a nearly constant value. A current profile 50this current when the load drop occurs 32 exhibits a characteristic peak-shaped increase that culminates in an almost constant curve, which is greater than the expected normal curve. 48 is.

[0046] The in Fig. 7 depicted normal course 52 of the cylinder pressure when there is no load drop 32 exhibits an approximately constant value. In the event of a load drop... 32 the course 54 The cylinder pressure exhibits a characteristic peak-shaped increase and is subsequently characterized by an approximately constant increase compared to the previous course. 52 characterized by an increased course.

[0047] The in Fig. The pressure reduction shown in section 8 is caused by the continuous injection of fuel into the cylinder. 22 combustion chamber formed during the open position of the nozzle needle 28caused and can be calculated from the measured high-pressure storage pressure in Fig. 4. The pressure drop corresponds to the difference between the high-pressure storage pressure before the injection process and the high-pressure storage pressure at the end of an actuation of the piezo injector. 18 Consequently, the pressure drop is a measure of the amount of fuel drawn from the high-pressure accumulator by the injection system. 16 One or more piezo injectors spray. 18 If fuel is continuously introduced into the combustion chamber, the pressure difference is greater, and this effect is observed in the corresponding pressure measurement on all piezo injectors. 18 A curve is recognizable. 56 in the absence of load drop 32 This corresponds to a straight line passing through the origin of the diagram with a slope of approximately one, while a curve 58 in the event of load drop 32represents a straight line shifted by a constant positive value.

[0048] In step S8, this can be done in the Fig. 4 to Fig. 7 further signals shown with their respective expected normal curves, which change when the load drop is not present. 32 The expected results can be compared in order to determine, upon detection of the characteristic features described above, whether a load drop occurs during the injection process at the piezo actuator. 30 has occurred. Additionally, the pressure drop can occur in Fig. 8 with its expected normal curve, which is affected if the load drop is not present 32 The expected results will be compared. The evaluation of the further signal(s) will be compared with the evaluation of the one or more signals that are indicative of the closing of the nozzle needle. 28 are combined.

[0049] The in Fig. 9 further steps of the procedure shown Fig. 2 enable monitoring of the closing process of the nozzle needle. 28 into its closed position and operation of the internal combustion engine 12 in an emergency driving mode, in which the jet needle 28 regardless of the charge level of the piezoelectric actuator 30 remains in its closed state and cannot be reopened. The reduction of the injection pressure in step S10 from Fig. 2 can be achieved by lowering the high-pressure accumulator pressure through at least one of the following measures, which are carried out simultaneously or sequentially in corresponding sub-steps S10a, S10b, S10c. In sub-step S10a, the pressure regulating valve can be 23 quickly, i.e., within a short time interval, they are opened so that the high-pressure storage pressure in the fuel high-pressure chamber 16 and thus the injection pressure in the piezo injector 18decreases. The measuring unit 20 can be closed in a substep S10b or the metering unit 21 It can be switched off in a sub-step S10c. In a further step S16, the high-pressure accumulator pressure can be monitored using the high-pressure accumulator pressure sensor. 24 be monitored while the injection pressure is below the opening pressure of the nozzle needle. 28 The pressure decreases. This opening pressure can be approximately 80 bar, for example, in a CRI30-20 type piezo injector. In a further step S18, the nozzle needle closes hydraulically due to the reduced injection pressure. 28 into their closed position, so that the continuous injection of fuel into the internal combustion engine 12 ends. In a further step S20, the time-dependent pressure reduction in the fuel high-pressure accumulator is implemented. 16depending on the detected reduced high-pressure storage pressure, in order to determine the end of continuous injection into the internal combustion engine 12 to detect. This step S20 can be performed simultaneously with at least one of steps S10, S16, and / or S18. In step S20, the determined pressure drop can be continuously compared with a threshold value. The threshold value can be approximately 5 percent (%) higher than the expected standard pressure drop under the same operating conditions without continuous injection. If the determined pressure drop is below the threshold value at a given high-pressure accumulator pressure, the end of continuous injection is detected. In a subsequent step S22, the high-pressure accumulator pressure, and thus the injection pressure, is increased to such an extent that the internal combustion engine 12 It can be operated in emergency driving mode. As shown in step S24, the procedure ends.

[0050] If the inventive method is applied to a piezo injector 18 The CRI3-20 type test from Robert Bosch GmbH can determine a reaction time in which the load drop 32 identified as well as the jet needle 28 The forced closing process is accomplished within approximately 19 milliseconds (ms). The closing of the jet needle 28 is independent of the engine speed 14 and the high-pressure storage pressure. If the inventive method is carried out without step S4 and only with step S6, the reaction time for the aforementioned piezo injector is 18 between approximately 47 ms and approximately 187 ms. The reaction time depends on the rotational speed of the internal combustion engine. 12 dependent on, but independent of, the high-pressure accumulator pressure. A shutdown of the injection system. 10This can only be achieved through secondary measures, not by reducing the injection pressure as carried out in step S10. Such secondary measures include, among other things, closing a throttle valve of the internal combustion engine, which prevents fresh air from entering the cylinder. 22 This occurs so that the fuel cannot burn. During this reaction time, the piezoelectric actuator does not self-discharge. 30 The piezo injector 18 Without using the method according to the invention, the aforementioned type of system results in a reaction time of between approximately 70 ms at a high-pressure storage pressure of approximately 250 bar and approximately 220 ms at a high-pressure storage pressure of approximately 1400 bar. The reaction time depends on the high-pressure storage pressure. The presence of a load drop can also influence this. 32 on the piezo element 30 only by means of performance diagnostics during the period 39a of step S2 during a subsequent charging process of the piezoelectric actuator30 The duration of the load drop detection depends on the rotational speed of the internal combustion engine. 12 This time is dependent and, for example, at a speed of approximately 500 rpm, it is approximately 240 ms; at approximately 1000 rpm, approximately 120 ms; at approximately 1200 rpm, approximately 100 ms; at approximately 1400 rpm, approximately 86 ms; at approximately 1600 rpm, approximately 75 ms; and at approximately 2000 rpm, approximately 60 ms. This is a time period for evaluating whether the jet needle 28 The time it takes to close is approximately 2 ms, and there is a pressure drop when the pressure control valve opens quickly. 23 The response time is less than approximately 15 ms at maximum high-pressure accumulator pressure. The nozzle needle can close via the coupler running dry or a violation of the mass balance, resulting in automatic engine shutdown. QUOTES INCLUDED IN THE DESCRIPTION

[0051] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0052] DE 102008001971 A1

[0005]

Claims

[1] Method for operating an injection arrangement ( 10 ) for injecting fuel into an internal combustion engine ( 12 ), wherein the injection arrangement ( 10 ) a piezoelectric actuator ( 30 ) and one using the piezoelectric actuator ( 30 ) actuated jet needle ( 28 ) exhibits, with the following steps: – time-dependent detection (S4) of a signal that is indicative of the closing of the nozzle needle ( 28 ) is, during an injection process of the injection arrangement ( 10 ), – Determine (S8) whether a load drop occurring during the injection process affects the piezo actuator, depending on the time-dependent signal ( 30 ) is present and – Reducing (S10) an injection pressure in the injection arrangement ( 10 ) below an opening pressure of the nozzle needle ( 28 ) in the event of a load drop ( 32 ). [2] Method according to claim 1, wherein the presence of the load drop ( 32 ) is closed when the signal is substantially lower than when the load drop is absent ( 32 ) is. [3] Method according to a preceding claim, wherein the signal is transmitted to a piezoelectric actuator ( 30 ) applied voltage, a voltage at the piezoelectric actuator ( 30 ) applied current, one at the piezoelectric actuator ( 30 ) decreasing capacity and / or a decrease caused by the piezoelectric actuator ( 30 ) onto the jet needle ( 28 ) applied force. [4] Method according to any of the preceding claims, further comprising: – time-dependent acquisition (S6) of a further signal during the injection process, wherein the further signal – a high-pressure storage pressure in a high-pressure fuel storage tank ( 16 ) the injection arrangement ( 10 ), – one connected to a pressure regulating valve ( 32) of the high-pressure fuel storage tank ( 16 ) available electricity, – a current that supplies fuel to the high-pressure fuel storage tank ( 16 ) adjustable metering unit ( 20 ) a high-pressure pump ( 14 ) to supply fuel to the high-pressure fuel storage tank ( 16 ) is pending, and / or – a cylinder pressure in a by means of the nozzle needle ( 28 ) fuel-operated cylinder ( 20 ) the internal combustion engine ( 12 ) is, where the determination (S8) is additionally dependent on the further signal, in particular in a comparison to one in the absence of the load drop ( 32 ) expected normal course of the further signal, occurs. [5] Method according to a preceding claim, wherein the lowering (S10) is carried out by opening (S10a) the pressure regulating valve ( 32 ), closing (S10b) of the metering unit ( 20), and / or switching off (S10c) the metering unit ( 20 ). [6] Method according to any of the preceding claims, further comprising: – time-dependent detection (S16) of a reduced high-pressure storage pressure, – Determining (S20) a pressure drop in the high-pressure fuel accumulator caused by continuous injection ( 16 ) depending on the detected reduced high-pressure storage pressure and – Increase (S20) the high-pressure storage pressure if the determined pressure drop is below a threshold. [7] Computer program configured to perform each step of a method according to any one of claims 1 to 6. [8] Machine-readable storage medium on which a computer program according to claim 9 is stored. [9] Electronic control unit ( 19 ), which is set up to have an injection arrangement ( 10) for injecting fuel into an internal combustion engine ( 12 ), which has a piezoelectric actuator ( 30 ) and one using the piezoelectric actuator ( 30 ) actuated jet needle ( 28 ) exhibits, to be operated by means of a method according to one of claims 1 to 6.

Images