EP2102473A1

EP2102473A1 - Fuel injection system and method for determining a needle stroke stop in a fuel injection valve

Info

Publication number: EP2102473A1
Application number: EP07847292A
Authority: EP
Inventors: Andreas Rau; Oliver Becker; Erik Tonner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-12-14
Filing date: 2007-11-23
Publication date: 2009-09-23
Also published as: JP2010513768A; US20100059021A1; DE102006059070A1; CN101595291A; WO2008071531A1

Abstract

The invention relates to a fuel injection system comprising at least one fuel injection valve (10) and a control unit (20) for actuating the injection valve (10). Each injection valve (10) comprises a piezoelectric actuator (12), a nozzle element having at least one nozzle opening (15) and at least one movable nozzle needle (13) for selectively closing and opening the at least one nozzle opening (15), a hydraulic coupling element which is connected between the piezoelectric actuator (12) and the nozzle needle (13), and at least one stroke stop (14, 21), against which the nozzle needle (13) bears in its completely open and/or its completely closed position. In order for it to be possible to determine the reaching of the stroke stop (14; 21) in an improved manner in fuel injection valves (10) of this type, it is proposed that the needle stroke stop (14, 21) is determined during a current application pause of the piezoelectric actuator (12) by evaluation of a voltage signal (U) which prevails at the piezoelectric actuator (12). Oscillations of the voltage signal (U) during the current application pause are preferably evaluated. To this end, it is proposed that regression straight lines (30; 31) are laid through the voltage profile (U), a correlation coefficient of the regression straight lines (30; 31) to the voltage profile (U) is determined and a needle stroke stop is detected using the correlation coefficient.

Description

description

title

A fuel injection system and method for determining a needle lift stop in a fuel injector

State of the art

The present invention relates to a fuel injection system according to the preamble of claim 1 and a method for determining a Nadelhubanschlags in a fuel injection valve according to the preamble of claim 13th

From the prior art, fuel injection valves for injecting diesel or gasoline into the intake manifold or directly into the combustion chamber of an internal combustion engine are known. The injectors can be actuated by piezo actuators to meet high dynamic requirements. As a temperature compensation and translation, a hydraulic coupler is interposed between the piezoelectric actuator and a nozzle needle of the injection valve. In the known injection valves of the type CRI-PDN (Common Rail Injector - Piezo Direct Neadle) from Robert Bosch GmbH, the nozzle needle is set in motion almost directly by the piezoelectric actuator, that is, the movement of the nozzle needle follows, in a first approximation, the actuator stroke. The Aktorhub is again proportional to the drive voltage at a constant actuator force in the first approximation.

Due to manufacturing tolerances and wear over the life of a fuel injector and due to fluctuating operating temperatures, the mechanical and electrical parameters and relationships in the injector may change. For example, with increasing life, the actuator stroke may subside, causing the nozzle needle to open later and close sooner, resulting in less fuel being injected than desired. Disclosure of the invention

The present invention is based on the object, in fuel injection valves, which are actuated by means of piezoelectric actuators, to detect the achievement of a stroke stop and in particular to determine the time of reaching the stroke stop.

To achieve this object, the present invention proposes according to claim 1, a fuel injection system in which the achievement of a stroke stop or the time of reaching the Hubanschlags in a particularly simple manner, that is particularly time and resource-saving, but still can be determined with high accuracy. As a further solution to this problem, the invention proposes a method with the features of claim 11, which also has a particularly simple, that is particularly time and resource saving, but still highly accurate detection of reaching a Hubanschlags or determination of the time of reaching the Hubanschlags allowed.

According to the invention, it is proposed to determine the achievement of the stroke stop by evaluating the voltage curve of the voltage applied to the piezoelectric actuator during an energization break. In particular, oscillations in the voltage curve should be evaluated and evaluated, which arise when the nozzle needle is not applied to a stroke stop. The results of the determination (stroke stop is not reached, stroke stop is reached later than estimated, stroke stop is not reached) can be taken into account when controlling the amount of fuel to be injected. As a result, the combustion of the fuel in the combustion chamber of the internal combustion engine can be positively influenced, and the combustion takes place particularly low consumption and low emissions and low.

Using the example of a direct-coupled injection valve, in which the piezoelectric actuator is charged when the nozzle needle is closed (so-called inversely controlled injector), this principle will be explained in more detail. At the beginning, an initial voltage greater than zero is applied to the piezoelectric actuator, and the needle stroke is 0 μm (valve closed). In order to initiate an injection, the piezoactuator is discharged, that is to say charged with a discharging current, whereby the applied voltage decreases (beginning of the Discharging). Delayed at the beginning of the discharge process, the nozzle needle lifts from the valve seat and releases the at least one nozzle opening at least partially. Shortly before reaching the stroke stop, the energization of the actuator ends and the actuator is disconnected (end of discharge process). At this time, the voltage has reached its lowest value. Since the nozzle needle has not reached the stroke stop at this time, it moves due to the inertia further in the previous direction, so that the pressure in the coupling space of the hydraulic coupler increases again. This causes due to the piezoelectric effect for an increase in Aktorklemmspannung (so-called. As soon as the nozzle needle reaches the stroke stop, the pressure in the coupling space no longer changes, so that the tension remains almost constant (so-called plateau area). The voltage buckling between the rise area and the plateau area or the voltage maxima after reaching the lowest value at the end of the discharge process are therefore correlated in time with the achievement of the needle stroke stop.

A corresponding effect also occurs in the reverse direction, that is, when the injection valve is brought from the open position to the closed position. In the open position of the valve, the piezoelectric actuator is discharged and there is a relatively low initial voltage. To end an injection, the piezoelectric actuator is reactivated, that is, charged with a charging current, whereby the applied voltage increases (beginning of the charging process). Delayed at the beginning of the charging process, the nozzle needle lowers in the direction of the valve seat, which serves as a stroke stop. Before reaching the valve seat, the energization of the actuator can be stopped and the actuator is disconnected (end of the charging process). At this time, the voltage has reached its highest value. The nozzle needle continues to run due to the inertia after the Bestromungsende, so that the pressure in the coupling space of the hydraulic coupler decreases. This causes due to the piezoelectric effect to a fall in Aktorklemmspannung (negative rise range). As soon as the nozzle needle rests firmly against the stroke stop, the pressure in the coupling space and thus also the actuator voltage remain almost constant (so-called plateau area). The stress kink between the sinking area and the

Plateaubereich or the voltage minima after reaching the highest value at the end of the charging process are therefore correlated in time with the achievement of Nadelhubanschlags (the valve seat). The dependent claims have advantageous embodiments of the invention the subject. In particular, even with measurement noise or with pressure-dependent dynamic effects within the injection valve, which, for example, can lead to a strong rounding of the voltage curve, they permit an exact time determination of the bend or of the maximum stress in the proposed manner.

Brief description of the drawings

Some preferred embodiments of the invention are explained below with reference to the figures. Show it:

Fig. 1 is a schematic view of an inventive

A fuel injection system comprising a fuel injection valve with a piezoelectric actuator and a control device;

Fig. 2 shows a voltage and current profile of a fuel injection valve for

Example of the fuel injection system of Figure 1 illustrating a first embodiment of the method according to the invention.

Fig. 3 shows a voltage and current profile of a fuel injection valve for

Example of the fuel injection system of Figure 1 illustrating the first embodiment of the method according to the invention.

Fig. 4 is a voltage and current waveform of a fuel injection valve, for example, the fuel injection system of Figure 1 for illustrating the first embodiment of the method according to the invention.

Fig. 5 is a voltage and a Nadelhubverlauf a fuel injection valve, for example, the fuel injection system of Figure 1 for illustrating a second embodiment of the method according to the invention.

6 shows a section from the voltage curve and the needle lift profile from FIG. 5 for illustrating the second embodiment of the method according to the invention; 7 shows a voltage and current profile of a fuel injection valve for

Example of the fuel injection system of Figure 1 illustrating the second embodiment of the method according to the invention.

8 shows two voltage and current profiles of different fuel injection valves to illustrate a third embodiment of the method according to the invention, wherein one of the fuels inspritzventi Ie reaches a stroke stop and the other not;

9 shows four different voltage and current profiles for illustrating the third embodiment of the method according to the invention;

10 shows a supplemented controller structure with a sum square of the deviations of a regression line from the course of the actuator voltage as a criterion for the stroke stop detection; and

Fig. 11, the operation of the reaction of the controller structure of FIG. 10 to a stroke stop not reached.

Embodiment (s) of the invention

FIG. 1 shows a fuel injection valve 10 for an internal combustion engine, which is provided with a piezoelectric actuator 12. The fuel injection valve 10 is also referred to as an injector and is used to inject fuel 11, such as gasoline or diesel, into a suction pipe and / or directly into a combustion chamber of

Internal combustion engine. The piezoelectric actuator 12 is driven by a control device 20 as indicated in FIG. 1 by the arrow. Furthermore, the fuel injection valve 10 has a nozzle element with a nozzle needle 13, which can sit on a valve seat 14 in the interior of the housing of the fuel injection valve 10. The valve seat 14 surrounds a nozzle opening 15. Of course, the injection valve 10 may also have more than the nozzle opening 15 shown. In addition, the nozzle openings may also be formed on the side walls of the housing of the valve 10.

If the nozzle needle 13 is lifted from the valve seat 14, fuel 11 can flow through the nozzle opening 15, the fuel injection valve 10 is thus opened and fuel 11 is injected. This state is shown in FIG. Is that sitting

Valve needle 13 on the valve seat 14, the nozzle opening 15 is closed and there is no fuel 11 injected, the fuel injection valve 10 is thus closed. In the closed state of the injection valve 10, the valve seat 14 forms a stroke stop for the nozzle needle 13. A stroke stop for the nozzle needle 13 in the open state is indicated in FIG.

The transition from the closed to the open state is effected by means of the piezoelectric actuator 12. For this purpose, a voltage referred to below as the drive voltage U is applied to the actuator 12, which causes a change in length of a arranged in the actuator 12 piezo stack, which in turn is used to open or close the fuel injection valve 10. In the exemplary embodiment illustrated in FIG. 1, the piezoactuator 12 is electrically charged when the nozzle opening 15 is closed by the nozzle needle 13, that is to say the actuator 12 is stretched when the injector 10 is closed (so-called inversely operated injector 10). By discharging the piezo stack in the actuator 12 reduces its longitudinal extent and the nozzle needle 13 lifts off from the valve seat 14.

The fuel injection valve 10 further includes a hydraulic coupling element. This includes within the fuel injection valve 10, a coupler housing 16 in which two pistons 17, 18 are guided. The piston 17 is connected to the actuator 12 and the piston 18 is connected to the nozzle needle 13. Between the two pistons 17, 18, a volume 19 is included, which accomplishes the transmission of the force exerted by the actuator 12 on the valve needle 13.

The piezoactuator 12 is arranged directly above the nozzle needle 13 and can be completely surrounded by pressurized fuel 11. A coating can protect the actuator 12 from the fuel 11 and electrical insulation to ensure. The coupling element is surrounded by the fuel 11, and the volume 19 is also filled with fuel. Via the guide gaps between the two pistons 17, 18 and the coupler housing 16, the volume 19 can be adapted over a longer period of time to the respectively existing length of the actuator 12. For short-term changes in the length of the actuator 12, however, the volume 19 remains virtually unchanged and the change in the length of the actuator 12 is transmitted directly to the nozzle needle 13 and converted into a corresponding movement. A change in length of the piezoelectric actuator 12 thus acts via the coupling element directly in a movement of the nozzle needle 13.

In order to obtain information about an operating state of the fuel injection valve 10, the inventive method described below is carried out, which may be stored, for example in the form of a computer program on an electronic memory element (not shown) and provided in the control unit 20, by a computing unit of the controller 20 to be processed. But it is also conceivable that the computer program is simply kept on a server of a computer network, such as the Internet, for downloading. Interested parties can download the computer program and run it on a computing device of the control unit. The computer program is used to execute all steps of the method according to the invention when it is executed on a computing device of the controller.

The fuel injection valve 10 shown in Figure 1 is part of a fuel injection system (common rail system), which may include a plurality of injection valves 10, can be injected via the fuel in the intake manifold or in the combustion chambers of an internal combustion engine. It can either be a control unit 20 for all injectors 10 or a separate control unit 20 for each of

Fuel injection valves 10 may be provided. In addition to the injection valve 10 and the control unit 20, the fuel injection system may include other components, such as a fuel tank, in particular a common for all injectors 10 high pressure storage bar (common rail), which connected via a high-pressure fuel line to a connecting piece 22 of the fuel injection valve 10 is. Figures 2 to 4 show schematically the timing of the drive voltage U, which adjusts the actuator 12 when it is acted upon by a discharge current I and a charging current I, to an opening and a subsequent closing of the fuel injection valve 10 and thus a fuel injection cause. The course of the current I is also shown in FIGS. 2 to 4. The sequence of a fuel injection will be explained in more detail with reference to FIG 2.

It is assumed that a closed injection valve 10, the actuator 12 is charged. At the actuator 12 is thus an initial voltage U _a at the time t _a . To trigger an injection, the piezoelectric actuator 12 is discharged. For this purpose, the actuator 12 is subjected to a negative discharge current I and the applied

Voltage U decreases (start of discharge process). Delayed at the beginning of the unloading process, the nozzle needle 13 lifts from the valve seat 14 and releases the at least one nozzle opening 15 at least partially. Shortly before reaching the stroke stop 21, the energization of the actuator 12 ends, and the actuator 12 is disconnected (end of the discharge process). At this point to to the voltage U has reached its lowest value U ₀ . The actuator voltage U is thus lowered in the time interval t _a to t of the voltage U _a to U ₀ by the voltage .DELTA.U. Since the nozzle needle 13 has not reached the stroke stop 21 at this time, it moves due to the inertia further in the previous direction, so that the pressure in the coupling chamber 19 of the hydraulic coupler increases again. As a result of the piezoelectric effect, this leads to an increase in the actuator clamping voltage U. As soon as the nozzle needle 13 reaches the stroke stop 21, the pressure in the coupling space 19 no longer changes, so that the voltage U remains almost constant at the value Ui. The voltage buckling or the voltage maxima after reaching the lowest value at the end of the discharging process, ie after the time to are correlated in time with the reaching of the Nadelhubanschlags 21 and can be evaluated and evaluated accordingly.

A corresponding effect also occurs in the reverse direction, that is, when the injection valve 10 is brought from the open position to the closed position. In the open position of the valve 10, the piezoelectric actuator 12 is discharged and there is a relatively low initial voltage U ₄ . To end an injection, the piezoelectric actuator 12 is reactivated, that is with a positive Charging current I applied, whereby the applied voltage U increases (beginning of the charging process at the time tι). Delayed at the beginning of the charging process, the nozzle needle 13 lowers in the direction of the valve seat 14, which serves as a stroke stop. Before reaching the valve seat 14, the energization of the actuator 12 can be stopped, and the actuator 12 is disconnected (end of the charging process). To this

Time t ₅ , the voltage U has reached its highest value. The nozzle needle 13 continues to run due to the inertia after the Bestromungsende so that the pressure in the coupling chamber 19 of the hydraulic coupler decreases. This causes due to the piezoelectric effect to a fall in the actuator terminal voltage U. As soon as the nozzle needle 13 rests firmly on the stroke stop 14, the pressure in the coupling chamber 19 and thus also the actuator voltage U remains almost constant. The voltage kink or the voltage minima after reaching the highest value at the end of the charging process are therefore correlated in time with the reaching of the Nadelhubanschlags (the valve seat 14) and can be evaluated and evaluated accordingly.

According to the invention, it has therefore been recognized that the course of the actuator terminal voltage U can provide an indication of the achievement of a stroke stop 14, 21, in particular if the actuator 12 is not energized, that is to say the fuel injection valve 10 is left to itself, as appropriate , For evaluating the voltage applied to the piezoelectric actuator

Voltage signal U are a variety of possibilities conceivable. One possibility is to evaluate the oscillations of the voltage signal U in the energizing pauses and to draw conclusions by suitable evaluation, whether the stroke stop 14, 21 has been reached or not. Another possibility, which serves to determine the time of reaching the stroke stop, is that the point of intersection of two compensation functions, in particular two compensation straight lines, which are set by the course of the voltage signal U, determined and used as a time for reaching the stroke stop. In this case, a simplification can be taken into account, according to which the rising line always has the same slope dU, namely U ₄ -U ₀ and / or UrU ₀ .

According to a first proposed method, the voltage signal U between t unloading to start charging and tι and between end of charge t ₅ and the start of unloading sampled. Through an interval of the sampled values of the voltage signal U, a regression function, preferably a regression line, is set and a correlation value R of the regression function to the sampled values is determined. Based on the size of the correlation value, the reaching of a needle stroke stop is detected (eg, from ti to tι in FIG. 2 or from t ₂ to tι in FIG. The regression line is also called a correlation line.

To calculate the regression line, an optimization problem must be solved in such a way that the position of a straight line (y = a + bx) initially arbitrarily set by the sampled points of the voltage curve U must be optimized, so that the distances of the straight lines to the individual point are as small as possible (Minimizing the summed squares of the residuals). This method is also called a least squares method.

RSS = SS _Kes = Σe ^> = Σ (y, - (a + b - x,))> min!

By partially differentiating and zeroing the first-order derivatives, one obtains a system of normal equations. The sought regression coefficients are the solutions

and

a = y - b - x

with x as the arithmetic mean of the x values and y as the arithmetic mean of the y values.

Values. SS _xy denotes the empirical variance of x ,. This estimate is also called the least squares estimate (KQ) or ordinary least squares estimate (OLS). The correlation value R or correlation coefficient is a dimensionless measure of the degree of linear relationship between two features. It can only take values between -1 and +1. At a value of +1 (or -1) there is a complete positive (or negative) linear relationship between the considered features. If the correlation value is 0, the two features do not depend linearly on each other. However, these may non-linearly depend on each other regardless. In the present exemplary embodiment, the linear relationship between the sampled points of the voltage profile U and the regression function or regression line set by the sampled points is determined by means of the correlation value. If the sampled points of the voltage profile U are denoted by xi, X ₂ ,..., X _n and the discrete points of the regression function by yi, y ₂ ,..., Y _n , then the empirical correlation coefficient is calculated according to the following formula:

There are

* = - Σ *, ^and y = -Σy,

the empirical expectation values X and Y based on the series of points.

In the run-up to the detection of whether the nozzle needle 13 has reached a stroke stop 14, 21, a limit value for the correlation value R is determined as a function of the injection valve type used. The limit value can be determined empirically, ie in experiments, by simulation or mathematically. The limit value is chosen such that with a correlation coefficient greater than or equal to the limit value, the stroke stop 14, 21 has been achieved with high probability, or that with a correlation coefficient below the limit value the stroke stop 14, 21 has most likely not been reached. The correlation value or the value of the correlation value determined for the current voltage profile U is selected. rend the runtime of the method compared with the previously determined in dependence on the injector type used limit value and detects a Nadelhubanschlag if the determined correlation value is greater than or equal to the limit.

If the actuator 12 due to loss of stroke over the term or due to a low drive voltage U performs too low a stroke h to pull the needle 13 to its stroke stop 14, 21, then the needle 13 swings after completion of their flight to their subsequent rest position , This oscillation around the rest position generates a vibration in the drive voltage U with a frequency that is similar over the entire high-pressure range. Because of this fixed frequency, a characteristic oscillation valley always occurs at similar times within a drive. In order to evaluate whether the needle stroke stop 14, 21 has been reached, the sum k of the quadratic deviations of a mean voltage value 40 (see FIG. Thus, this sum gives a large value if the stop 14, 21 has not been reached, because in this case many points show a large deviation from the mean value 40. When the stroke stop 14, 21 is reached, then the oscillation frequency changes and in the Area in which in the case of not reached stroke stop 14, 21 was still a Schwingungstal now several oscillation periods are passed through with small amplitude. In this case, substantially fewer points deviate from the mean value 40 by a smaller value. The sum k then changes its value, wherein the change in the sum k can be used to detect the achievement of a stroke stop 14, 21.

If the samples of the voltage curve U are denoted by U, and the

Mean voltage value 40 is denoted by U, the sum k of the quadratic deviations from a mean voltage 40 results by the following equation:

In Figure 9, this embodiment is shown. In the figure, on the one hand, four different voltage waveforms U are shown, wherein the voltage curve Ui relatively many points deviate relatively far from the mean 4Oi. That's why it can be be concluded that the needle 13 has not reached the stroke stop 14, 21. In the case of the voltage curves U ₂ , U ₃ , U ₄ , on the other hand, relatively few points and / or the points deviate from the average values 40 ₂ , 40 ₃ , 40 ₄ by a relatively small amount. Therefore, it can be concluded that the needle 13 reaches the stroke stop 14, 21.

In FIGS. 3 and 4, a regression line 30 is shown, which has been laid by an interval of a plurality of scanned points of the voltage curve U between the discharge end to and the charge start tι. In the example of FIG. 3, the regression line 30 has been laid by sampled points of the voltage profile U between the times% and tι. The voltage curve U from FIG. 3 belongs to a fuel injection valve 10 which reaches the stroke stop 21, and the voltage curve U from FIG. 4 belongs to a fuel injection valve 10 which does not reach the stroke stop 21. Since the regression line 30 in FIG. 3 covers the measurement much better than the regression line 30 in FIG. 4, the regression line 30 from FIG. 3 results in a larger correlation value R than for the straight line 30 from FIG.

By selecting a suitable limit value and comparing the correlation value R with the limit value, it can be reliably and reliably detected whether the stroke stop 14, 21 has been reached or not.

Before determining the regression line or the correlation value, the voltage profile U can be smoothed or filtered, for example by forming an average value over a specific number of sample values, for example over five sample values.

Only after reaching the stroke stop 14, 21, the fuel injection valve 10 is fully closed or opened. The exact time of reaching the Huban- stroke 14, 21 is therefore for a regulation of the fuel quantity of great importance. If, for example, the stroke stop 14, 21 is reached too late or not at all, control can be intervened so that the predetermined amount of fuel is nevertheless injected within a predetermined period of time. In this way, mass drifts can be compensated for due to an aged or worn or a fuel injection valve 10 subject to manufacturing tolerances. According to a further embodiment, the derivative of the first order of the voltage waveform U is formed. This can be done on the basis of the analog voltage signal U or on the basis of discrete samples of the voltage signal U. The time ti in FIG. 2, at which the derivative assumes the value 0 for the first time, is used to divide the voltage profile U into two regions, a rise region between to and ti and a plateau region between ti and tι. In each of these two areas, a regression function 30, 31, preferably a regression line, is placed through the sampled points of the voltage profile U. The intersection of these two regression functions 30, 31 is used as time fe in FIG. 3 for an intact injector 10 and V in FIG. 4 for a non-intact injector 10), to which the nozzle needle 13 reaches the stroke stop 21. The fact that V is greater than t ₃ means that the needle 13 in FIG. 4 reaches the stroke stop 21 too late.

As a criterion of whether the needle 13 actually reaches the stop 21, the correlation factor can also be used here. As already explained above, the voltage U in the plateau region shows a flat profile when the needle 13 abuts against the stop 21, and the correlation factor thus has a relatively high value (see FIG. If the needle 13 does not reach the stop 21, the voltage U in the plateau region has a ripple, and the correlation factor has a substantially smaller value (compare FIG.

Also in this embodiment, prior to forming the first-order derivative or before determining the regression line or the correlation value, the voltage profile U can be smoothed or filtered, for example, by averaging over a specific number of sample values, for example over five sample values. is formed.

In FIGS. 5 and 6, a voltage curve U is plotted at the top and the corresponding stroke course h of the nozzle needle 13 is plotted over the time t at the bottom. The voltage curve U shown in FIG. 5 qualitatively corresponds to the profile of the voltage U from FIGS. 2 to 4. FIG. 6 shows a section VI of the voltage and the stroke profile from FIG. 5. The voltage curve U shown in FIGS. so to speak: From t = 100 μs, the actuator 12 is discharged starting from the starting voltage U = 170 V. The actuator 12 contracts and thereby reduces the pressure in the coupler chamber 19, which entails an opening of the nozzle needle 13. When to (see Figure 6 above) ends the energization and the actuator 12 is disconnected, that is left to itself. Since the needle 13 has not yet reached the stroke stop 21, it continues to run (see FIG. 6 below), so that the pressure in the coupler space 19 rises again. This ensures via the piezoelectric effect for an increase in the Aktorklemmspannung U. As soon as the needle 13 reaches the stroke stop 21 (time X ₂ in Figure 6 for a new injector), the pressure in the coupler chamber 19 no longer changes, so that the voltage U almost remains constant.

Reference numeral 32 in FIGS. 5 and 6 denotes the voltage curve U and reference numeral 33 denotes the stroke curve h of a new injector 10. Reference numeral 32 'in FIGS. 5 and 6 denotes the voltage curve U and reference numeral 33' denotes the stroke course h of an aged injector 10 '(stroke stop 21 is reached later, if at all). 5 and 6 designate the voltage curve U and the reference curve 33 "designate the stroke course h of an injector 10" with a worn nozzle element The voltage kink or the voltage extrema (maxima or minima) at t ₂ , t ₂ ', t ₂ "are thus correlated in time with reaching the Nadelhubanschlags 21.

When closing the injector 10, the same physical effect acts: The needle 13 continues to run after Bestromungsende so that the pressure in the coupler chamber 19 increases, resulting in a decreasing Aktorklemmspannung U. As soon as the needle 13 rests on the valve seat 14, the pressure in the coupling space 19 and thus also the actuator voltage U remain substantially constant.

In order to determine whether the stroke stop 21 or 14 has been reached, the estimated maximum voltage at time ti (see FIG. 2) or at time t ₂ , t ₂ ', t ₂ "(see FIG to the minimum voltage after the end of charge at the time t ₅ (see FIGS. 3 and 4), a first voltage value of the voltage signal U, as well as before the start of charging at time t I (see FIG. 6) and determines a further voltage value before the discharge process. If the measured first voltage is significantly greater than the measured shortly before the time tι further voltage, this suggests an unachieved stroke stop 21 out. If the measured first voltage is significantly smaller than the measured before the time tι further tension, this indicates that the nozzle needle 13 was pulled too much to the Nadelhubanschlag 21: a large negative pressure in the coupling chamber 19 ensures that te by Leckspal- Fuel 11 is retightened, the pressure and thus on the piezoelectric effect and the actuator voltage U rise. Again, the respective voltage limits must be determined injector type-specific.

Alternatively, it is also possible to determine the transition of the voltage profile from the rise region into the plateau region via the derivative of the voltage profile U and the zero crossing of the derivative. At the instant to (see FIG. 6) at the end of the discharging process and at the beginning of the energizing pause, a first voltage value and at the instant ti (see FIG. 2) or at the instant t ₂ , t ₂ ', t ₂ "(cf. On the basis of these two voltage values and / or on the basis of the difference dU of the two voltage values, the time at which the stroke stop is reached can also be determined The idea is to use the dU described here to determine the time of reaching the stroke stop.If the difference between the first measured voltage value and the further voltage value is very large, it can be assumed be that the stroke stop was not reached or too late, if the difference is very small, it is assumed that the needle 13 drove too hard against the stroke stop. Corresponding injector-type-specific limit values for the voltage values or the difference can be determined in advance and used during the running time of the method for determining a stroke stop or the time of a stroke stop.

In order to determine the exact time of reaching the stroke stop 14, 21 in a particularly simple manner, a simplification is exploited, namely that the slope m in the rise range of the voltage U over the entire rise range and for different voltage curves U over the life of the Injector 10 is almost constant (see Figure 6 above) and therefore quickly and easily determined once and in all subsequent calculations of the time of Reaching the Hubanschlags can be considered. The desired time of Nadelhubanschlags can then be calculated by the voltage difference dU between cut-off voltage (which is known exactly in time, time to) and the steady end voltage in the open Injektorzustand determined before the time tι and the known difference m the time difference between off time to and Reaching the stroke stop 21 is calculated. This is much easier to carry out than the search for a kink between the rise and the plateau area in the course of the voltage U. The constant relationship between the voltage difference dU and the time of reaching the stroke stop from the end of the energization at time to can be stored in a table, so that during the term of the procedure, the slope no longer needs to be considered.

For this purpose, the following example will be explained. If, for example, a gradient of m = 300,000 V / s and a voltage difference U of an injector 10 results in a voltage difference dU = 2 V, the time at which the stroke stop 14, 21 is reached can be calculated using the following equation:

dU \ s - 2V t = - = 6,667μs m 300,000F

This means that t = 6.677 μs after the time to, at which the current is switched off, the stroke stop 14, 21 is reached. This relationship can be calculated for the type of injector considered for many other voltage differences and stored in a table.

If a higher-order control is used to control the difference dU (calculated in a gentle manner) to a desired value, slight changes in the gradient m, for example by changing the actuator capacity, lead only to negligibly small errors in the determined impact time. If the voltage difference dU is too large, the stroke stop will not be reached. If the difference dU is too small, the needle 13 hits too hard against the stroke stop 14, 21. If the difference dU is chosen small enough without being too large and too small, the stroke stop 14, 21 is safely and reliably achieved, but not too strong drive.

Since both the injection duration and the maximum injection rate (apart from nozzle coking) are known in the proposed method, the injected fuel quantity can be set very precisely. By varying the discharge current I, which flows through the actuator 12, the stroke h of the nozzle needle 13 can be increased, so that the stroke stop 14, 21 is achieved as a rule. In the second embodiment, it is therefore not necessary to detect whether the stroke stop 14, 21 is reached on the slope m of the rise range of the drive voltage U of the actuator 12, but only on the voltage difference dU.

If an injection is to take place with an inversely-operated fuel injector 10, the actuator 12 of the closed injector 10 is discharged, the actuator 12 contracts and generates a negative pressure in the coupling space 19 above the needle 13, whereby the needle 13 is set in motion. If the needle 13 has first lifted out of its seat 14, the high-pressure fuel 11 can engage under the seat 14 and accelerate the needle 13 upwards. By this movement upward, the negative pressure in the coupling chamber 19 is first reduced and then generates an overpressure. This overpressure causes a force acting on the actuator 12, in which then due to the piezoelectric effect, a positive voltage U is induced. In the operating state in which the actuator 12 makes sufficient stroke h, the needle movement ends abruptly when the nozzle needle 13 reaches its stroke stop 21. Because then no force acts on the actuator 12, the drive voltage 12 remains substantially constant on a plateau. This relationship is illustrated, for example, in FIG. 8, where the voltage curve U of an intact injector 10 and the voltage curve U 'of an injector 10' are shown, whose nozzle needle 13 'does not reach the valve seat 14. The currents I of these two injectors 10, 10 'are shown.

If the actuator 12 is able to make enough stroke h to pull the needle 13 against its mechanical stop 21, then the time of reaching the stop by the voltage difference dU between the voltage minimum (at time to) and the first then set the local maximum (at the first zero crossing of the derivative of the voltage curve, at time ti or t ₂ ). The underlying simplifying assumption for this is that the slope m, with which the voltage U between these two points increases, is constant (see the above explanations). If the evaluation of one of the criteria described above (correlation value R or sum k) shows that the needle 13 has not reached its stroke stop 14, 21, the compensation method reacts by increasing the discharge time in order to increase the voltage swing (see FIG 11). If now the setpoint of the dU controller kept constant, then the needle 13 would reach its stroke stop 14, 21 too late. For this reason, the extension of the discharge time must be accompanied by a change, preferably a reduction, of the set value of the dU controller. This situation and the mode of action are shown in FIG. 11.

If a safe stroke stop 14, 21 takes place via several activations, then the controller will try to reduce the voltage swing again. This is necessary so that the controller is not allowed to correct only in one direction and thus can no longer correct the errors in case of incorrect measurements. To reduce the voltage swing is done exactly the opposite of the procedure described above. It is thus the discharge time is shortened and enlarged dU.

An exemplary control structure is explained in more detail below with reference to FIG. Here, several control loops are nested in one another in a cascade. The outermost control circuit serves to control the sum k of the quadratic deviations of the voltage signal U from a mean voltage value 40 or the correlation coefficient R from the first example or another variable of another method for detecting the stroke stop. At the injector 10, the voltage U is detected, and after an evaluation in a function _block 50 according to one or more of the methods described above, the actual value k, _st (or R _ιst ) is obtained for the sum k (or the correlation coefficient R ). As desired value k _so n (or R _so n) as small as possible, for example, zero, given. In a subtraction 51, the difference dk (or dR) of desired value k _so n (or R _so n) and the actual value k _ιst (or R _ιst) the sum k of the squared deviations from a mean voltage 40 (or the correlation coefficient is R) formed. The difference dk (or dR) is fed as a control difference to a controller 52, for example a proportional controller with an amplification factor Kp3. The signal magnitude of the regulator 52 of the sum k (or of the correlation coefficient R) is at the same time the reference variable (setpoint dU _so n) of the subordinate control of the calculated difference dU. From the actuator voltage U applied to the injector 10, the actual value dU _lst for the difference dU is also determined in the context of the evaluation 50 according to one or more of the above-described methods. In a subtraction block 53, the difference ddU from setpoint dU is formed _so n and actual value dU, _st . The difference ddU is supplied as a control difference to a controller 54, for example a proportional controller with an amplification factor KpI.

The signal magnitude of the controller 54 of the sum k is at the same time the reference variable (SoII value UbX _so ii) of the subordinate control of the voltage Ubx applied to the actuator 12, the voltage Ubx corresponding to the ΔU described above. The voltage applied to the injector 10 actuator voltage Ubx is detected as the actual value Ubx, _st . In a subtraction block 55, the difference dUbx of setpoint Ubx is formed _so n and actual value Ubx _ιst the voltage Ubx. The difference dUbx of the voltages is supplied as a control difference to a controller 56, for example a proportional controller with an amplification factor Kp2.

The signal magnitude of the regulator 56 is the discharge current I, the course of which is plotted in the various diagrams and which is indicated in FIG. 10 by i _D | _SCh (Discharge) is designated. The injector 10 or its piezoelectric actuator 12 is acted upon by this discharge current. The difference dk of setpoint and actual value n k _as k, k _st to the sum of the quadratic see deviations from a mean voltage 40 is also a controller 57, for example. A proportional controller with a gain K p4, respectively. The signal magnitude of the regulator 57 is the discharge time ti _DlsCh , for which the injector 10 with the discharge current i _D | _{SCh is} applied so that the desired amount of fuel is injected.

With reference to the figure 11 is explained in more detail how the control of the fuel injection valve 10 must be corrected so that on the one hand the nozzle needle 13 reaches the stroke stop 14, 21 and on the other hand, the nozzle needle 13 reaches the stroke stop 14, 21 even within a desired period of time. In FIG. 11 a), the progression of the drive current I of the actuator 12 in the originally uncorrected state is shown at the top with a solid line. The dashed line shows the course of the drive current I with a corrected discharge time. In Figure 11 a) is below in a corresponding manner with a solid line, the course of the uncorrected voltage applied to the actuator 12 actuator voltage U shown. The dashed line shows the course of the voltage U with a changed discharge time. It can be clearly seen that an extension of the discharge time from a discharge end at t ₇ to a discharge end only at tβ generates an increased voltage swing, but also leads to a later reaching of the Nadelhubanschlags 14, 21. The stop 14, 21 is namely reached only at the time ti ₀ instead of the time t ₉ .

In FIG. 11 b), the course of the discharge current I of the actuator 12 in the original uncorrected state is again shown above by a solid line. The dashed line shows the course of the discharge current I with corrected discharge time and corrected voltage difference dU. In FIG. 11 b), the course of the uncorrected actuator voltage U applied to the actuator 12 is shown below in a corresponding manner with a solid line. The dashed line shows the curve of the voltage U with a changed discharge time and a changed voltage difference dU (dU2 instead of dUl, where dU2 <dUl). It can be clearly seen that prolonging the discharge time from t ₇ to tβ produces an increased voltage swing. The later reaching of the Nadelhubanschlags 14, 21 of Figure 11 a) below is compensated in Figure 11 b), however, characterized in that a smaller value for the voltage difference dU is specified as the desired value. This has the consequence that the stop 14, 21 is already reached at a time ti ₀ , which corresponds exactly to the original time t ₉ . If the voltage swing is to be reduced, of course dU2 <dUl, so that despite a shortened discharge, the stroke stop 14, 21 is not reached too early.

Claims

claims

A fuel injection system comprising at least one fuel injector (10) and a controller (20) for driving the injector (10), each injector (10)

a piezoelectric actuator (12),

a nozzle element having at least one nozzle opening (15) and at least one movable nozzle needle (13) for selectively closing and opening the at least one nozzle opening (15),

a hydraulic coupling element, which is connected between the piezoelectric actuator (12) and the nozzle needle (13), and

at least one stroke stop (14, 21) against which the nozzle needle (13) bears in its fully opened and / or fully closed position, characterized in that the control device (20) comprises detection means for detecting a stop of the nozzle needle (13) on the at least one stroke stop (14, 21), wherein the means are designed such that they

Nadelhubanschlag during a Bestromungspause of the piezoelectric actuator (12) on the basis of the course of a voltage applied to the piezoelectric actuator (12) voltage signal (U) recognize.

2. Fuel injection system according to claim 1, characterized in that the detection means are designed such that they have a vibration amplitude of the

Evaluate the voltage signal (U) between the end of discharge and the start of charge or between the end of charge and the start of discharge.

3. Fuel injection system according to claim 2, characterized in that the detection means are designed such that they see the voltage signal (U) between discharge end and charge start or between end of charge and Entladebeginn sampling, through an interval of the sampled values of the voltage signal (U), a regression function (30), preferably a regression line, and determine a correlation value to the sampled values, recognizing from the magnitude of the correlation value whether or not there is a needle stroke stop.

4. Fuel injection system according to claim 3, characterized in that the

Detection means are designed such that they compare the determined correlation values with a previously determined in dependence on the type of injector used limit and recognize a Nadelhubanschlag if the determined correlation value is greater than or equal to the limit.

5. Fuel injection system according to one of claims 1 to 4, characterized in that the detection means are designed such that they at the beginning of Bestromungspause a first voltage value of the voltage signal (U) and at a later time during the energization break another voltage value of the voltage signal (U ), wherein they determine from the difference (dU) between the first voltage value and the further voltage value, whether a Nadelhubanschlag is present or not.

6. Fuel injection system according to claim 5, characterized in that the time at the beginning of Bestromungspause, at which the first voltage value is determined, at or after the discharge end (to) or at or after the end of the load (t ₅ ).

7. Fuel injection system according to claim 5, characterized in that the time at the beginning of Bestromungspause, at which the first voltage value is determined at a time (tu X ₂ ; h), to which a derivative of the voltage waveform (U) is a first zero crossing having.

8. Fuel injection system according to one of claims 5 to 7, characterized in that the later time at which the further voltage value is determined shortly before the start of charging (tι) or shortly before the start of unloading.

9. Fuel injection system according to claim 6, characterized in that the later time at which the further voltage value is determined at a Time (tu X ₂ , h) is at which a derivative of the voltage waveform (U) has a first zero crossing.

10. Fuel injection system according to claim 7 and 8, characterized in that the detection means are designed such that they compare the determined voltage difference (dU) with a previously determined depending on the type of injector used limit and recognize the failure of a Nadelhubanschlags, if the first voltage value at the beginning (tu X ₂ , Xz) of the energization pause is greater than the further voltage value at the later time (tι) and the magnitude of the determined voltage difference (dU) is greater than or equal to the limit value.

11. Fuel injection system according to claim 7 and 8, characterized in that the detection means are designed such that they compare the determined voltage difference (dU) with a previously determined in dependence on the type of injector used limit and recognize that the nozzle needle (13) was strongly pulled to a stroke stop (14, 21), if the first

Voltage value at the beginning (tu X ₂ ; X _? ) Of Bestromungspause smaller than the other voltage value at a later time (tι) and the amount of the determined voltage difference (dU) is greater than or equal to the limit.

12. A fuel injection system according to claim 2, characterized in that the detection means are designed such that they consider the voltage signal (U) during the energization break, subdivide the course of the voltage signal (U) in the considered area in a rise area and an adjoining plateau area, form a mean voltage (40) by the plateau area and a sum (k) of the square deviations of the voltage signal (U) of the voltage mean value (40) in the plateau area, where they recognize on the basis of the size of the determined sum (k), whether a Nadelhubanschlag is present or not.

13. A fuel injection system according to claim 12, characterized in that the detection means are designed such that they determine the determined sum (k) with a pre-determined depending on the type of injector used Compare limit value and recognize a Nadelhubanschlag if the determined sum is less than or equal to the limit.

14. Fuel injection system according to one of claims 1 to 13, characterized in that the detection means are formed such that they form the first derivative via the voltage signal (U) during the energization break, the

Time at which the derivative has a zero crossing for the first time, for subdividing the course of the voltage signal (U) into a rise area and a plateau area, by the voltage signal (U) in the rise area and in the plateau area respectively a regression function (30, 31), preferably a regression line, lay and the intersection of the two

Regression functions (30, 31) than the time fe) at which a Nadelhubanschlag is present.

15. Fuel injection system according to one of claims 1 to 14, characterized in that the detection means are designed such that they only determine the time point fe) of the Nadelhubanschlags, if it was previously determined that even a Nadelhubanschlag is present.

16. A method of determining a needle lift stop in a fuel injector (10) comprising

a piezoelectric actuator (12),

a hydraulic coupling element (16, 17, 18, 19) which is connected between the piezoactuator (12) and the nozzle needle (13), and

- At least one stroke stop (14, 21) on which the nozzle needle (13) rests in its fully open and / or its fully closed position, characterized in that the at least one Nadelhubanschlag (14, 21) during a Bestromungspause of the piezoelectric actuator (12 ) is determined by evaluating the course of a voltage signal (U) applied to the piezoelectric actuator (12).

17. The method according to claim 16, characterized in that an oscillation amplitude of the voltage signal (U) is evaluated between the discharge end and the start of charging or between end of charge and Entladebeginn.

18. The method according to claim 17, characterized in that at least one regression function (30, 31), preferably a regression line, is laid by the voltage signal (U) applied to the piezoactuator (12) during the energization break and the at least one needle stroke stop (14, 21) is determined by evaluating the course of the at least one regression function (30, 31).

19. The method according to claim 18, characterized in that the first derivative of the voltage signal (U) during the Bestromungspause formed, the time at which the derivative has the first zero crossing, for dividing the course of the voltage signal (U) in a rise range and a A regression function (30, 31), preferably a regression line, and the intersection of the two regression functions (30, 31) as the time fe) of the Nadelhubanschlags (14, 21 ) is used.

20. The method according to claim 18, characterized in that by an interval of the voltage signal (U) during the energization break a regression function (30; 31), preferably a regression line, laid and a correlation value to the voltage signal (U) is determined, wherein the Nadelhubanschlag (14, 21) is detected by the magnitude of the correlation value.

21. Method according to claim 19, characterized in that the voltage signal (U) is sampled before the derivation or before the determination of the regression function (30, 31) and the further processing of the voltage signal (U) on the basis of Samples takes place.

22. Method according to claim 20, characterized in that the ascertained correlation values are compared with a limit value previously determined as a function of the injection valve type used and a needle lift is detected, if the determined correlation value is greater than or equal to the limit value.

23. The method according to claim 17, characterized in that the voltage signal (U) considered during the energization break, the course of the voltage signal (U) in the considered area in a rise area and an adjoining plateau area divided in the Plateaubereich a voltage mean value (40), a sum (k) of the amounts of the weighted deviations of the voltage signal (U) from the mean voltage (40) in the plateau region is determined, and a needle lift stop (14, 21) is detected on the basis of the magnitude of the determined sum (k).

24. Method according to claim 23, characterized in that the sum (k) of the quadratic deviations of the voltage signal (U) from the mean voltage value (40) in the plateau region is determined.

25. The method according to claim 23 or 24, characterized in that the determined sum (k) compared with a previously determined in dependence on the injection valve type used limit value and a Nadelhubanschlag (14, 21) is detected if the determined sum ( k) is less than or equal to the limit.

26. The method according to any one of claims 16 to 25, characterized in that at the beginning of Bestromungspause a first voltage value of the voltage signal (U) and at a later time during the Bestromungspause another voltage value of the voltage signal (U) is determined, wherein based on the difference (dU) is detected between the first voltage value and the further voltage value, whether a Nadelhubanschlag is present or not.

27. The method according to claim 26, characterized in that the time at the beginning of Bestromungspause, at which the first voltage value is determined at or after the discharge end (to) or at or after the end of charge (t ₅ ).

28. The method according to claim 26, characterized in that the time at the beginning of the energization break, at which the first voltage value is determined, at a time (tu t ₂ ; t) is at which a derivative of the voltage waveform (U) has a first zero crossing.

29. The method according to any one of claims 26 to 28, characterized in that the later time at which the further voltage value is determined, shortly before the start of charging (tι) or shortly before the start of unloading.

30. The method according to claim 27, characterized in that the later time at which the further voltage value is determined, at a time (tu h; t) is at which a derivative of the voltage waveform (U) has a first zero crossing.

31. The method according to claim 28 and 29, characterized in that the determined voltage difference (dU) compared with a previously determined in dependence on the injector type used limit value and the failure of a Nadelhubanschlags is detected if the first voltage value at the beginning (tu h; t) of the energization break greater than the further voltage value at the later time (tι) and the amount of the determined voltage difference (dU) is greater than or equal to the limit.

32. Method according to claim 28, characterized in that the determined voltage difference (dU) is compared with a limit value previously determined as a function of the valve type used and that the nozzle needle (13) is too strongly connected to a Stroke stop (14, 21) was pulled if the first voltage value at the beginning (tu t ₂ ; h) of the energization break is smaller than the further voltage value at a later time (tθ and the amount of the determined voltage difference (dU) is greater than or equal to the limit ,

33. The method according to any one of claims 16 to 32, characterized in that the method is implemented as a computer program that is executable on a control unit (20) for controlling a fuel injection valve (10) having a piezoelectric actuator (12).