WO2017060076A1 - Method for detecting a useful signal - Google Patents

Abstract

A method for detecting a useful signal corresponding to a sought event is described. In the method, after the useful signal has been identified, a variation in one or more parameters is determined. The parameter variation is carried out using test pulses or by means of concomitant measurement. The mean value of all individual measurements is formed and the useful signal is obtained from the mean value formed. The method makes it possible to achieve a particularly high detection accuracy.

Description

description

Method for detecting a wanted signal The present invention relates to a method for detecting a wanted signal which corresponds to a searched event.

The scope of the present invention will be explained, for example, with reference to an injection system of a motor vehicle. An increasingly stringent emissions legislation related to emissions requires fuel injections to reali ^¬ Sieren into the combustion chamber of an internal combustion engine with ever greater accuracy in terms of time and quantity. However, manufacturing tolerances and aging / wear on the fuel injectors result in deviations between the requested times / quantities of the injections and those actually performed. In this context, the accuracy can be increased if the closing ^¬ time of the injection valve can be determined as accurately as possible in order to correct it to a desired value.

For example, to determine the closing time of an injector needle in a servo-hydraulic injector with piezo actuator, the piezo element can be used in addition to its function as an actuator as a sensor. This can be used for

Example, pressure changes generated by the needle closing in a control volume can be measured under the servo valve. In the measured piezo voltage is then searched for this purpose, a specific useful signal of known form, which is caused by the needle shooting. Depending on the design of the injector, depending on the operating point and depending on the type of useful signal for the detection, however, there is the problem that the useful signal is superimposed by interfering signals from various sources. For example, the piezoelectric element is excited by the control as an actuator (electrical charging and discharging processes) to oscillate, which can be found in its tension due to the electromechanical nature of the piezo. In addition, too From the outside mechanical vibrations are transmitted to the piezo, for example in the form of structure-borne noise.

Although it is possible to filter out interfering signals whose frequencies are far from the determining frequencies of the useful signal efficiently by using high / low / bandpass filters. However, interfering signals with a frequency comparable to the useful signal are only more difficult and can be removed with greater effort. Since the main task of the piezoelectric element is to control the injector as an actuator, possible measurement windows, where it can be used as a sensor, are severely limited and can not be extended arbitrarily. Since a hardware or software-side filtering of these interfering signals using

High / low / bandpass filtering always results in a reduction of the range where detection is possible, these filters can be used only limited use of the piezoelectric element as an actuator and sensor.

Regardless of the above-described case, the present invention relates generally to a method for signal detection, the detection accuracy corresponding ge to be ^¬ increases in relation to a wanted signal despite the existence of interfering signals. In principle, the useful signal to be detected can have any desired (but known) form and can be found in any desired measurement signal. One application of this is, for example ector with piezo drive, it comes here to close from the measured piezo voltage on the exact time of the needle made a closing force ^¬ material servo Inj.

The present invention has for its object to provide a method of the type mentioned above, with a particularly high detection accuracy with respect to a useful signal despite the presence of interfering signals can be achieved.

This object is achieved according to the invention by a method for detecting a useful signal which corresponds to a searched event, comprising the following steps: Identifying the payload;

Determining a variation of one parameter or several parameters for which one knows the temporal behavior of the useful signal via the variation or can determine it by simple means, wherein only the temporal position of the event / useful signal is changed, the parameter variation is carried out by means of test points or by measuring , a range of variation is spanned that is large enough to adequately attenuate corresponding signal disturbances,

Forming the mean value from all individual measurements; and

Obtaining the useful signal from the mean value formed.

The method according to the invention is based on the use of a parameter variation, which exploits the fact that useful and interference signals have a different phase position, depending on the selected parameters. The method can generally be used in a variety of areas for signal detection. A particular application is the above-described determination of the time of needle closing of an injector. Especially with small injection quantities, the timing of Na ^¬ delschließens is here very close to the earliest possible use of the

Piezo element as sensor (directly after unloading). For this reason, filtering with high / low / band pass filters ^¬ according to the prior art is not possible to the same extent as would be needed to bring the signal-to-noise ratio to a necessary for a robust detection level.

In the concrete example of a piezo servo Inj ector is made possible by the inventive process, the Sig ^¬ nal-to-noise ratio for the detection of the closing of needle "

to increase significantly without having to use traditional high / low / bandpass filters, which allows robust detection of needle closure even with smaller injection volumes. However, robust and accurate detection of the needle closure and correction of the appropriate time to a setpoint will increase the accuracy of the fuel injection in terms of quantity and timing.

In the following, the necessary steps which are necessary for the application of the method according to the invention will be described concretely. First, a useful signal is identified, which corresponds to the searched event. It is then determined a variation of one or more parameters for which one knows the temporal behavior of the useful signal on the variation or can determine by simple means. This parameter variation must meet a number of criteria. It may only change the temporal position of the event / useful signal and must leave its form largely unchanged. You must be able to be carried out in practice, for example in the field of internal combustion engines, in particular by requesting test pulses or by a "Mitmessen" in the transient engine operation. In addition, they must have a variation ^¬ area span which is large enough to the known disturbances sufficiently The required width of the variation range depends on the relative phase shift between useful and interference signals, which can be achieved by the parameter variation.

The variation over the parameters x, y .. consists of a finite number of individual steps. For each of these steps, the corresponding signal is measured, in a time-fixed range [t _eve nt ^~ t_; t _eve nt + t ₊ ] around the event expected for a nominal injector at t _eve nt · This requires knowledge of the instant t _eve nt (X _/ y ··) for each individual step of the parameter variation, so that the time t ^x (x) = t - tevent (x) can be determined. Then the desired event is always to be expected at t ^λ = 0, regardless of the choice of the parameters x, y. At the end of the parameter variation, t ^λ = [-t_; t ₊ ] for each constant t ^x the average of all N individual measurements:

^N

V _Sl signal (t ^X ) = 1 / N Σ ^ signal (t ^X ),

t = l wherein here V _s i _gna i refers to a measured voltage signal when detecting the needle closing time at an In ^¬ jektor.

The useful signal can be found with the original amplitude from the above-mentioned mean value from all measurements, while interference signals were strongly attenuated by the averaging, resulting in a considerable improvement in the detectability of the useful signal.

Further developments of the invention will become apparent from the dependent claims.

In one embodiment of the method according to the invention, the piezoelectric voltage in the region around the expected needle closing is measured by the ECU for detecting the needle closing in an injector and is available for further processing and evaluation. In the present case, a direct detection of the needle closing from the measured voltage is not possible without further processing of the measured signal. Namely, the piezoelectric element is excited by the charging and discharging in each case to oscillations, which are reflected in its voltage due to the electromechanical nature of the piezoelectric element. Furthermore, it is also possible to transmit mechanical vibrations to the piezo element from outside. These spurious signals superimpose the useful signal of the needle closing and thus make it more difficult to detect them clearly. The voltage increase, .

6 caused by the needle closing, can be read as the maximum in the time derivative of the (filtered) signal. However, if there is no high signal-to-noise ratio, the absolute maximum in the derivative of the filtered voltage does not necessarily correspond to the needle ^closing time. It is precisely for this case that it is necessary to increase the signal-to-noise ratio by further processing of the signal, which is achieved with the method according to the invention.

The invention will now be described below with reference to a displayed exporting ^¬ approximately embodiment in conjunction with a corresponding diagrams figure in detail. In this case, an injection quantity variation at 800 bar injection pressure with increasing amounts between 2 mg and 8 mg is used, whereby this is realized with 36 specially requested test pulses (see illustration). In this case, the behavior of the closing of the needle t _max (x) and thus the rescaled time t ^{x were} determined in advance for the quantity variation (parameter x) carried out (eg by rate measurements). The signal used for the evaluation is the piezo voltage measured at the injector after the end of the discharge of the piezoelectric element. After a few first hardware and software low-pass filters, the time derivative of the signal plotted as V _tot (t ^x ) as a function of time t ^x and the requested amount MF has been calculated. V _tot (Τ ^λ ) is present as a time-discrete signal with a resolution of 5 \ is present. The needle closure to be expected for a nominal injector was set to the time t ^x = 0.

In the lower half of the figure, the mean value V _tot (t ^x ) is plotted over all 36 test pulses with respect to time t ^x . It can be seen very well that those in V _tot (t ^x ) in the upper picture visual interfering signals were largely filtered away and only the useful signal with the maximum at about t ^y = 12 με remains.

This maximum thus corresponds to the determined needle closing time offset of the examined injector compared to a nominal injector. This systematic offset can now be corrected for all injections on this injector by means of an intervention in the actuation time of the injector in order to increase the accuracy of the injection quantity.

Claims

claims A method of detecting a payload corresponding to a searched event, comprising the steps of: Identifying the payload; Determining a variation of one parameter or several parameters for which one knows the temporal behavior of the useful signal via the variation or can determine it by simple means, wherein only the temporal position of the event ^¬ ses / Nutzsignales is changed, the parameter variation based on test pulses or by Mitmessen is carried out, a range of variation is spanned, which is large enough to adequately attenuate corresponding signal interference, Forming the mean value from all individual measurements; and Obtaining the useful signal from the mean value formed. 2. The method according to claim 1, characterized in that it is used for detecting the needle closing time of an injector of an injection system of a motor vehicle. 3. The method according to claim 2, characterized in that is used for detecting the needle closing time of a servo-hydraulic injector with piezo actuator. 4. The method according to claim 2 or 3, characterized in that the voltage signal is detected as a useful signal after the end of the discharge of the piezo actuator of a sensor acting as a piezo actuator. 5. The method according to any one of claims 2 to 4, characterized in that an injection quantity variation is performed as a parameter variation. 6. The method of claim 4 or 5, characterized in that the derivative of the voltage signal is determined and the maximum value of its average value is regarded as a needle closing ^¬ time offset relative to a Nominalinjektor. 7. The method according to claim 6, characterized in that the offset is corrected by means of an intervention in the drive time of the injector to the nominal value.