Method for actuating an injector, and control unit

Abstract

The invention relates to a method for actuating an injector (1), in particular a fuel injector, in which method the stroke movement of a nozzle needle (2) for opening and closing at least one injection opening (3) is controlled by means of the pressure in a control chamber (4), and the pressure in the control chamber (4) is measured by means of a pressure sensor (5) integrated into the injector (1), wherein characteristic information, in particular time and volume flow rate data, is derived from the sensor signals from the pressure sensor (5) for the stroke movement of the nozzle needle (3) and is used to correct an injection rate model that is based on previously measured time and volume flow rate data.

Description

[0001] Description

[0002] Title:

[0003] Method for controlling an injector, control unit

[0004] The invention relates to a method for controlling an injector, in particular a fuel injector for injecting fuel under high pressure into a combustion chamber of an internal combustion engine.

[0005] Furthermore, the invention relates to a control device for carrying out the method.

[0006] State of the art

[0007] Prior art fuel injectors include a nozzle needle arranged so as to be longitudinally displaceable in a pressure chamber for opening and closing at least one injection opening. The movements of the nozzle needle are servo-hydraulically controlled, i.e., via the pressure in a control chamber, which exerts a hydraulic closing force on the nozzle needle. The pressure in the control chamber is controlled via a control valve, which regulates the pressure in the control chamber electromagnetically or with the aid of a piezo actuator. The control valve can be controlled very precisely by a control unit. However, there is a time delay between the control current and the actual movement of the nozzle needle. For precise control, it is therefore important to know the exact moment at which the nozzle needle moves and injection begins, in order to adjust the control current for controlling the control valve if necessary.

[0008] The movement of the nozzle needle can be detected, for example, via the pressure curve in the control chamber. DE 10 2015 207 307 A1 proposes a fuel injector with a servo-hydraulically controlled nozzle needle and a pressure sensor. The pressure sensor can be used to detect pressure changes in the control chamber or in a pressure chamber hydraulically connected to the control chamber. By evaluating the pressure signals from the pressure sensor, the exact time at which the nozzle needle opens and closes can be determined. If necessary, the control signal for activating the control valve can be adjusted.

[0009] The temporal pressure profile in the control chamber of a servo-hydraulic injector provides precise information about the movement of the nozzle needle. Using signal analysis algorithms, characteristic injection times such as the start and end of injection, or the needle opening time can be determined. These algorithms typically employ combinations of digital filtering, thresholding, and numerical derivation.

[0010] During operation of an internal combustion engine, injection rate models are typically used to regulate the injected fuel quantity with greater accuracy and to optimize combustion parameters. Due to their lower computing power, OD models are preferred over 1D models based on flow simulations, for example. These models generally use a highly simplified representation of the injection rate curve, for example, in the form of a trapezoid, as shown in Figure 11. However, the measured actual curve (solid line) deviates from the model (dashed line), so that the model's prediction of the injected fuel quantity is inaccurate.

[0011] To increase accuracy, it has been proposed to use the absolute pressure or pressure differences from the sensor signal of a pressure sensor integrated into the injector to estimate the injection quantity. However, wear processes cause the pressure sensor's signal amplitude to change over the injector's lifetime, so this change influences the accuracy of the estimate. Furthermore, if the maximum injection rate is calculated using a fixed linear correlation to the pressure drop, this correlation changes over time due to drift / wear of the pressure sensor, leading to a systematic error in the injection quantity estimate.

[0012] The present invention is therefore concerned with increasing the accuracy of model-based injection quantity estimation. To achieve this objective, the method having the features of claim 1 is proposed. Advantageous further developments of the invention are set forth in the subclaims. Furthermore, a control unit for implementing the method is specified.

[0013] Disclosure of the invention

[0014] A method is proposed for controlling an injector, in particular a fuel injector, in which the stroke movement of a nozzle needle for opening and closing at least one injection opening is controlled via the pressure in a control chamber, and the pressure in the control chamber is measured using a pressure sensor integrated into the injector. Information characteristic of the stroke movement of the nozzle needle, in particular time and flow data, is derived from the sensor signals of the pressure sensor and used to correct an injection rate model based on previously measured time and flow data.

[0015] The proposed method uses a measured and thus "real" injection rate curve as a model for a correction function instead of a simplified curve, for example, in the form of a trapezoid. This has the advantage of minimizing model errors. For modeling the injection rate, the measured data of a nominal injector are preferably used. These data are preferably composed of time and flow data with a defined sampling frequency.

[0016] Modeling primarily involves varying or adjusting the time and flow data using information derived from the pressure sensor signal. This information is used to parameterize and correct the injection rate model.

[0017] The correction is made during injector operation, preferably over its entire service life. This allows for injector-specific control that takes the actual injector wear condition into account. Preferably, the following information, particularly time and flow data, is derived from the pressure sensor signal and used to correct the injection rate model:

[0018] Start of nozzle needle opening movement (NOS), end of nozzle needle opening movement (NOE), start of nozzle needle closing movement (NCS), end of nozzle needle closing movement (NCE) and maximum injection rate (Qmax).

[0019] Furthermore, it is preferable to derive only this information from the pressure sensor signal to parameterize and correct the injection rate model. In particular, the sensor signal amplitude is not used, since, as already mentioned above, this changes over time due to aging and wear of the pressure sensor. The independence from the absolute sensor signal amplitude increases the accuracy of the model, especially compared to the state of the art mentioned above.

[0020] The time data NOS, NOE, NCS, and NCE can be derived from the pressure sensor signal using a detection algorithm. The detection algorithm can use derivatives and / or averages of the sensor signal. Furthermore, the sensor signal can be preprocessed, particularly filtered, for example, using a low-pass filter.

[0021] The maximum injection rate Qmax is preferably determined from the time data NOS, NOE, NCS, and NCE. This allows changes in the maximum injection rate Qmax over time due to injector aging / wear to be recorded.

[0022] It was discovered that correlations exist between the time data NOS, NOE, NCS, NCE, the maximum injection rate Qmax, and the nozzle needle lift. These can be identified using conventional methods with linear equations or by using artificial intelligence with neural networks and used to determine Qmax. It was also demonstrated that these correlations are independent of other wear parameters, such as wear of the nozzle needle seat and / or changes in the flow conditions in the area of ​​a throttle plate defining the control chamber. The correlations are preferably determined experimentally in advance and stored, preferably in a control unit.

[0023] The quantity Qmax determined from the time data NOS, NOE, NCS, NCE is then preferably used as an input quantity in the injection rate model.

[0024] Furthermore, a corrected injection rate curve is preferably calculated by mathematically transforming the time and flow data derived from the pressure sensor signal. In particular, a linear transformation can be applied. To further increase accuracy, the transformation can be performed using different mathematical models, for example, polynomial, exponential, or logarithmic, and / or applied only over a specific portion of the opening or closing phase.

[0025] During the mathematical transformation of the time data, only the time data NOS, NOE, NCS, and NCE derived from the pressure sensor signal are preferably used. This means that only these time data are used to avoid errors or inaccuracies.

[0026] The corrected injection rate model is then preferably used to calculate the injection quantity, preferably by integrating the corrected curve of the maximum injection rate Qmax. The calculated injection quantity can then be converted into a change in the electrical control duration. The determined deviation from the actual injection quantity can be applied as a factor to the injection duration.

[0027] Furthermore, a control unit is proposed that is configured to carry out the method according to the invention. For this purpose, an injection rate model based on the measurement data of a nominal injector is preferably stored in the control unit. To correct the injection rate model, the control unit evaluates the sensor signal from the pressure sensor. A detection algorithm can be stored in the control unit for this purpose, with the aid of which the relevant time and flow data can be derived from the sensor signal. If the evaluation reveals drift or wear, the injection rate model can be corrected accordingly with the aid of the control unit.

[0028] The inventive method and its advantages are explained in detail below using an example and the accompanying drawings. The drawings show:

[0029] Fig. 1 is a flow chart illustrating the sequence of a method according to the invention,

[0030] Fig. 2 a) a schematic longitudinal section through an injector which can be controlled according to the method according to the invention, and b) an enlarged section of the injector,

[0031] Fig. 3 various diagrams to show the time course of a) the current flow, b) the nozzle needle stroke, c) the injection rate and d) the sensor signal of the pressure sensor,

[0032] Fig. 4 various diagrams showing the time course of a) the injection rate of a reference injector, b) the injection rate scaled by Qmax and c) the injection rate adjusted using the information from the sensor signal of the pressure sensor, with linear operation of the injector (with stop),

[0033] Fig. 5 various diagrams showing the time course of a) the injection rate of a reference injector, b) the injection rate scaled by Qmax and c) the injection rate adjusted using the information from the sensor signal of the pressure sensor, during ballistic operation of the injector (without stop),

[0034] Fig. 6 graphical representation of the transformation of the time axis in the opening phase of the injector, Fig. 7 diagram illustrating the modeling of the injection rate in the closing phase of the injector during linear operation,

[0035] Fig. 8 graphical representation of the transformation of the time axis in the closing phase of the injector,

[0036] Fig. 9 Diagram showing the modeling of the injection rate in the closing phase of the injector during ballistic operation using the EOI threshold,

[0037] Fig. 10 Diagram showing the modeling of the injection rate in the closing phase of the injector during ballistic operation using ballistic points and

[0038] Fig. 11 Diagram comparing a simplified injection rate model (dashed line) and a measured curve (solid line).

[0039] Detailed description of the drawings

[0040] The method according to the invention serves to control an injector 1 with a servo-hydraulically controlled nozzle needle 2 and a pressure sensor 5 for measuring the control pressure applied to the nozzle needle 2. Such an injector 1 is shown as an example in Figure 2. Figure 2a) shows the complete injector 1, while Figure 2b) shows only the area of ​​the nozzle and the control valve.

[0041] The injector 1 shown in Figure 2 has a nozzle needle 2, which is accommodated in a nozzle body 6 for lifting and closing at least one injection opening 3. The end of the nozzle needle 2 facing away from the injection opening 3 delimits a control chamber 4, which is hydraulically connected to a pressure chamber 8 via a channel 7. The pressure chamber 8 is formed in a throttle plate 9 and is delimited by a diaphragm 10 resting on the throttle plate 9, behind which a pressure sensor 5 is arranged, so that pressure changes occurring in the pressure chamber 8 can be detected with the aid of the pressure sensor 5. The pressure sensor 5 is integrated into a valve plate 11, against which a valve body 12 of a control valve 13 rests. The actuation of the control valve 13 leads to a change in the pressure in the control chamber 4, which exerts a hydraulic force on the nozzle needle 2 acting in the closing direction.The pressure in the control chamber 4 thus controls the stroke movement of the nozzle needle 2. Information that is characteristic of the stroke movement of the nozzle needle 2 can therefore be derived from the sensor signal of the pressure sensor 5.

[0042] Figure 3 shows, by way of example, the relationships between the nozzle needle lift (Figure 3b)) and the sensor signal of the pressure sensor 5 (Figure 3d)). The sensor signal allows both the start of the nozzle needle movement during opening (time NOS) and the end of the nozzle needle movement during opening (time NOE) to be identified. Analogously, the start (NCS) and the end (NCE) of the nozzle needle movement during closing can be derived from the sensor signal. The times NOS, NOE, NCS and NCE result in the injection rate curve shown in Figure 3c) with a maximum injection rate Qmax. In contrast, the current curve shown in Figure 3a) has no direct relationship to the nozzle needle lift because there is a time delay between the control current and the movement of the nozzle needle 2.

[0043] Time and flow data can thus be derived from the sensor signal of pressure sensor 5, which allows for the correction of an injection rate model to the current conditions and the corresponding adjustment of the control current. In this way, aging / wear of injector 1 can also be taken into account during control.

[0044] Figure 1 illustrates the essential steps of such a correction function. In this case, it comprises the four main steps AD, which are executed with the aid of a control unit 14. For this purpose, the sensor signal from the pressure sensor 5 integrated into the injector 1 is made available to the control unit 14 via a signal line 15.

[0045] Step A is for feature detection. The sensor signal is first processed using a low-pass filter 17. The time data NOS, NOE, NCS, NCE are then derived from the signal using a detection algorithm 18 stored in the control unit 14. Step B is for drift detection. To detect a change in the injection behavior of injector 1 over the runtime, also known as drift, the time data NOS, NOE, NCS, NCE derived from the sensor signal in step A are stored at different system pressures and / or current application durations in order to calculate the change in the maximum injection rate Qmax. For the calculation, correlations between the time data NOS, NOE, NCS, NCE, the maximum injection rate Qmax, and the nozzle needle lift are used. These correlations are determined experimentally in advance.

[0046] For this purpose, the needle closing time tciosing = NCE-NCS can be investigated at two different system pressures in an operating range in which the nozzle needle opens to an upper stop. The experiment is preferably designed to measure relevant variations in needle lift and nozzle flow. The relationship for the two system pressures can then be determined using equation (1). The further apart the two system pressures are, the more accurately the nozzle needle lift and the maximum injection rate Qmax can be determined. This is due to the fact that the coefficients a and b are also far apart when the system pressures are far apart, and thus the difference in the gradient of the two straight lines according to equation (1) is greater.

[0047] In equation (1) a, b and c are at a system pressure p sy s experimentally determined specific constant. The change in the injector flow AQf"“" ncan be determined according to equation (2). For the determination, time data stored in the control unit at 0 km are preferably used with the currently measured time data according to equation (3).

[0048] O? is” the maximum injection rate of the controlled injector at nominal pressure p nom . is calculated using the 0-km measurement of the controlled injector.

[0049] Using these correlations, AQ^”^™, i.e., the change in the injector's maximum injection rate at nominal pressure, can be determined. The result can then be used as an input value for the injection rate model in step C (see Figure 1).

[0050] As already mentioned, the injection rate model—in contrast to the state of the art—is based on a measured injection rate curve. Preferably, the injection rate curve of a nominal injector is measured at various system pressures and over a long energization period and stored in the control unit as a reference. The rate information consists of time data "t" and the associated flow data "Q."

[0051] In a first calculation step of the injection rate model, the nominal flow data are preferably scaled according to the existing system pressure pist with the coefficient k1 , which is defined by equation (4).

[0052] 0^77^ r ' stthe maximum injection rate of the reference injector at nominal pressure. The other input value, which specifies the maximum injection rate of the controlled injector, is calculated using equation (2). These steps are graphically illustrated in Figures 4a)-c) for linear operation and in Figures 5a)-c) for ballistic operation.

[0053] At operating points where the opening nozzle needle reaches a stop (linear operation), the scaled injection rate curve is adjusted using the time data NOS, NOE, NCS, and NCE (see Figure 4c). At the same time, the time axis of the reference rate curve is adjusted using the actual timing. A difference between the NOS time data of the reference injector and the controlled injector is taken into account by preferably correcting the time axis by this value according to equation (5), where ptst is the current system pressure.

[0054] The opening phase is preferably modeled by transforming the time axis from the nominal opening time (NOE-NOS) to the opening time of the controlled injector. A linear transformation, as shown in Figure 6, can be used. The transformation can use different mathematical models, for example, polynomial, exponential, or logarithmic, and / or can only take place over a specific portion of the opening phase.

[0055] A difference between the time data NOE of the reference injector and the controlled injector is taken into account by preferably correcting the time axis by this value according to equation (6).

[0056] As the needle of the controlled injector begins to close, the injection rate curve is modified and the closing process is modeled. The closing process of the reference measurement is used for this purpose. Thus, all linear points can be calculated using the reference injection rate of a long injection (see Figure 7).

[0057] If the NOE of the controlled injector is greater than the NOE of the reference injector, the injection rate curve in this range can be approximated using linear extrapolation. However, a measurement with the maximum possible energization duration is preferably used as a reference to avoid this additional calculation step.

[0058] Preferably, an additional time point is defined to model the closing process, namely the EOI threshold time point, from which the modeled closing process is equal to that of the reference. Between the NCS and the EOI threshold, a similar time axis transformation is applied as previously used in the opening phase. The EOI threshold is defined according to equation (7) as a fraction of the flow at the NCS time point, where the model parameter k2 = G 0; 1 [.

[0059] The entire modeling of the time axis during closing is shown as an example in Figure 8.

[0060] Furthermore, the scaled injection rate curve of the reference injector is preferably transformed during the closing phase in such a way that the continuity of the modeled rate curve is ensured. This is illustrated by way of example in Figure 9.

[0061] The described transformation processes generate a modeled injection rate, the integration of which can be used to calculate the injection quantity (see Figure 4c). The gradient of the rising and falling edges can also be used as parameters to describe the state of the injector function by selectively averaging the derivative.

[0062] At operating points in which the opening nozzle needle does not reach its stop (ballistic operation), no time NOE exists. The transformation in the opening phase can nevertheless be applied analogously to the transformation in linear operation. Since NOE is not available, this information is taken from actual learned values ​​of linear operation. In principle, the modeled injection rate follows the opening edge calculated above until the closing phase is initiated. In addition, the model parameters At and AQ are introduced and explained using Figure 10. Accordingly, At is defined such that at time NCS At reaches the maximum injection rate Qmax at the scaled reference rate. Thus, Qmax is calculated at point B at time NCS. AQ is defined such that at the time at which the injection rate Qmax AQ reaches point A, the modeled injection rate no longer follows the reference rate.Investigations have shown that At and AQ can be defined using the time constants k3 and k4 given in equations (8) and (9), which lead to good model results.

[0063] In equations (8) and (9)

[0064] ^ope-ninq is the needle opening time of the modeled NCS-NOS curve and to™5 is the needle opening time of the controlled injector for linear operating points or a learning parameter.

[0065] The curve between points A and B is preferably modeled with a parabola.

[0066] Between points B and C, the same transformation as for the linear operating range is then carried out (see right side of the diagram in Figure 10).

[0067] In step D (see Figure 1), the estimated injection quantity can then be converted into a change in the electrical control duration. The determined deviation from the actual injection quantity is preferably applied as a factor to the injection duration. A correspondingly adjusted control current is sent from the control unit 14 to the injector 1 via a control line 16.

Claims

Claims 1. Method for controlling an injector (1), in particular a fuel injector, in which the stroke movement of a nozzle needle (2) for opening and closing at least one injection port (3) is controlled via the pressure in a control chamber (4) and the pressure in the control chamber (4) is measured by means of a pressure sensor (5) integrated into the injector (1), wherein characteristic information, in particular time and flow data, for the stroke movement of the nozzle needle (3) is derived from the sensor signals of the pressure sensor (5) and used to correct an injection rate model based on pre-measured time and flow data.

2. Method according to claim 1, characterized in that the following information, in particular time and flow data, is derived from the sensor signal of the pressure sensor (5) and used to correct the injection rate model: Start of nozzle needle opening movement (NOS), end of nozzle needle opening movement (NOE), start of nozzle needle closing movement (NCS), end of nozzle needle closing movement (NCE) and maximum injection rate (Qmax).

3. Method according to claim 2, characterized in that the time data (NOS, NOE, NCS, NCE) are derived from the sensor signal of the pressure sensor (5) using a detection algorithm that utilizes derivations and / or averaging of the sensor signal.

4. Method according to claim 2 or 3, characterized in that the maximum injection rate (Qmax) is determined from the time data (NOS, NOE, NCS, NCE).

5. Method according to claim 4, characterized in that, in order to determine the maximum injection rate (Qmax), correlations previously determined and stored experimentally are used which exist between the time data (NOS, NOE, NCS, NCE), the maximum injection rate (Qmax) and the stroke of the nozzle needle (2).

6. Method according to one of the preceding claims, characterized in that a corrected profile of the maximum injection rate (Qmax) is calculated by mathematical transformation of the information derived from the sensor signal of the pressure sensor (5), in particular the time and flow data.

7. Method according to claim 6, characterized in that only the time data (NOS, NOE, NCS, NCE) derived from the sensor signal of the pressure sensor (5) are used in the mathematical transformation of the time data.

8. Method according to one of the preceding claims, characterized in that the corrected injection rate model is used to calculate the injection quantity, preferably by integrating the corrected profile of the maximum injection rate (Qmax).

9. Method according to claim 8, characterized in that the calculated injection quantity is converted into a change in the electrical control duration, wherein preferably the determined deviation of the actual injection quantity is applied as a factor to the injection duration.

10. Control unit configured to execute a method according to any of the preceding claims.

Images