EP2529098A1

EP2529098A1 - Process and device for testing a fuel injector

Info

Publication number: EP2529098A1
Application number: EP11700512A
Authority: EP
Inventors: Jochen Friedmann; Christian Boie; Joerg Staib; Edgar Holl; Bertram Rensch; Gunter Freitag; Daniel Strack; Dirk Freundt; Wolfgang Henner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-01-29
Filing date: 2011-01-03
Publication date: 2012-12-05
Also published as: CN102713222B; CN102713222A; BR112012018381B1; BR112012018381A2; DE102010001387A1; US8646322B2; US20130025354A1; WO2011092042A1

Abstract

The invention relates to a process for selecting a method for determining the injection time of individual injection processes of a fuel injector (2), which can be supplied with pressurized fuel via a feed line (4), comprising the following steps: actuating the fuel injector (2) using various known actuation durations around a predefined operating point of the fuel injector (2); detecting (100) the pressure course over time in the feed line (4) for a number of injection processes; evaluating (200) the detected pressure courses over time using at least two different methods (211, 212, 213) for determining the injection time from the associated pressure course; determining the correlation (221, 222, 223) between the determined injection times and the associated actuation duration; selecting (230) the method with the highest correlation.

Description

Description Title Method and apparatus for testing a fuel injector

State of the art

For the fuel supply of internal combustion engines, storage injection systems are increasingly being used in which very high injection pressures are used. In these accumulator injection systems, fuel is conveyed by means of a high-pressure pump into a high-pressure accumulator, from which the fuel is injected via injectors into the combustion chambers of the internal combustion engine. In particular for diesel engines injectors are used which have an injection valve which is hydraulically opened and closed by a servo valve in order to determine the time course of the injection process into the combustion chamber. The servo valve is actuated by a magnetic or piezoelectric actuator. Ever stricter emissions legislation worldwide and the steady increase in the efficiency of the engines in these common-rail systems result in a larger number of

Part injections per injection process or per duty cycle of the internal combustion engine required, the fuel quantity of the individual injection smaller and smaller and the variance of the injection quantity between several injection operations or duty cycles is tolerated more closely. This also places new demands on methods and devices for injector testing.

Disclosure of the invention

An object of the invention is to provide an inexpensive and robust solution for injector testing with increased accuracy.

This object is achieved by methods of the invention and a device according to the invention. The invention is based on the basic idea that the opening and closing of the injector generates pressure waves in the feed line of the injector and that the injection time (ie the time duration that the injector is open) can be determined by measuring and evaluating the pressure profile in the feed line. There are different methods for this, based on the evaluation of different features in the pressure curve. Since the pressure variation changes due to various influencing factors for each injector type and operating point (temperature, pressure, injection time, etc.) of the injector, there is so far no universally applicable method that provides the best possible result for each type of injector at each operating point. The invention therefore comprises a method for selecting the most suitable method for the specific application from a number of different methods.

An inventive method for selecting a method for determining the injection time of individual injections of a fuel! Njektors, which can be supplied via a supply line with pressurized fuel, comprises the steps of driving the fuel injector with various known driving times in the vicinity of a predetermined operating point of the fuel! njektors; detecting the time pressure curve in the supply line for a number of injection events for each actuation period; evaluating the detected temporal pressure profiles with at least two different methods for determining the injection time for each injection event; determining the correlation between the determined injection times and the respective associated drive time; and selecting the method with the highest correlation.

The correlation between the injection times and the drive durations can be determined, for example, by calculating the Pearson correlation coefficient. On the match of the absolute values of the injection times and the drive times it does not matter.

The method selected in this way shows the best linear relationship, but there may still be zero and / or slope errors. In order to exactly determine the relationship between the injection times and the activation periods, a compensation function is calculated from the value pairs of the activation periods and the determined injection times, eg with the "least squares method". put on. In the case of a compensation straight line, the injection time from the pressure curve can be determined from the gradient and the axis section. Such a linearization is particularly well possible if only a relatively small area around the respective operating point of the injector is considered.

It is also possible to set a threshold value for the correlation value such that injection times are only determined when the threshold value is exceeded, so that the method has a sufficiently high linear relationship between the injection time and the activation duration. Alternatively, the injection times can be determined even when falling below the threshold and output with a corresponding warning.

The invention also relates to a method for determining the injection quantity of individual injection processes of a fuel! njektors, which can be supplied via a supply line with pressurized fuel, with the steps: selecting the most suitable for the respective operating point method for determining the injection time by the method described above; Activation of the fuel! njektors at least one predetermined operating point and simultaneously measuring the occurring during a supply line pressure curve; Determining the injection time of each injection event from the measured pressure profile using the selected method; and determining the injection amount of each injection from the predetermined injection time.

By the method according to the invention, the injection time of a single injection process of a fuel injector can be reliably determined with high accuracy even for short injection times.

The method is applicable to every type of injector and the entire operating range of the respective injector and covers the entire range of different injectors (car, truck, piezoelectric actuator, solenoid valve). The measuring technique itself limits the pressure range only by the pressure sensor. If necessary, adjust or replace it.

By using a frequently existing pressure sensor in the supply line, the acquisition and maintenance costs are reduced. The procedure is insensitive to the installation position of the injector and easy to use, since neither a complex mechanism nor the construction of a back pressure are required. The process allows for easy retrofitting of existing systems with continuous flow measurement and is workshop-ready, as it is robust and dirt-resistant.

The invention also relates to a method for testing a fuel injector comprising the steps of determining the respective injection quantity of a number of individual injection events of a fuel injector at at least one operating point with the method described above and statistically evaluating the injection quantities thus determined. Such a test method allows a particularly accurate and effective testing of modern high-performance injectors, which are operated with high injection pressures of several thousand bar and short injection times.

In one embodiment, the method for testing a fuel injector also includes evaluating a scattering amount, such as the standard deviation or the variance of the determined injection quantities. This can further improve the quality of the test.

In one embodiment, each injection event includes multiple partial injection events. The method is so flexible that it can also evaluate injection events that include multiple partial injection events.

In one embodiment, the method for evaluating the temporal pressure curve includes the transformation of the detected pressure profile into the frequency domain. By the transformation of the pressure curve in the frequency space, the evaluation of the pressure curve can be improved; In particular, disturbing frequency components can be filtered out before the further evaluation. In a further embodiment, the method for evaluation also includes the inverse transformation of the pressure profile from the frequency into the local time or period.

In one embodiment, the method for evaluating the temporal pressure curve concludes the determination of maxima, minima and / or turning points of the pressure curve. This makes it particularly effective, reliable and easy to determine the beginning and end of the injection process.

In one embodiment, the method includes driving the fuel injector with drive durations above and below the operating point. In particular, the method includes successively activating the fuel injector with a series of stepping or stepping ascending or descending activation periods. With such a stepped control, the correlation between the actuation duration and the injection time determined from the pressure curve can be determined particularly well, and the most suitable method for evaluating the pressure profile for the respective injector at the considered operating point can be selected particularly effectively.

The invention also relates to a device for testing a fuel! njektors. Such a device has at least one receiving device for receiving at least one fuel injector; at least one supply line configured to supply pressurized fluid to the fuel injector; at least one sensor, which is designed to measure the temporal pressure curve; a volume measuring unit configured to detect the flow through the injector; at least one drive device, which is designed to drive the fuel injector; and at least one evaluation unit operatively connected to the volume measurement unit, the sensor, and the driver. The evaluation unit is designed to carry out at least one of the methods according to the invention.

The sensor for measuring the temporal pressure curve in the supply line can be a pressure sensor arranged in the supply line or a structure-borne sound sensor which is attached to the supply line and measures the sound which is generated by the pressure fluctuations propagating in the supply line. Such a structure-borne sound sensor may be formed, for example, as a piezoelectric element. Embodiments of the invention are explained in more detail below with reference to the attached figures:

FIG. 1 shows schematically a device according to the invention for testing an injector.

FIG. 2 shows a schematic flow diagram of a test method according to the invention.

FIG. 3 a shows, by way of example, the activation of an injector during the injection quantity correlation.

FIG. 3b shows the injection quantity as a function of the activation duration.

FIGS. 4a and 4b show the determined corresponding injection times for different activation periods, wherein two different methods have been used to determine the injection times.

FIGS. 5a and 5b show the optimum correlation values determined for different operating points as a function of the activation duration.

FIGS. 6a and 6b show, by way of example, the activation of an injector at the operating point and the resulting pressure curve in the supply line.

FIGS. 7a to 7d show the measured pressure curve in the time period (FIGS. 7a and 7d) and in the frequency space (FIGS. 7b and 7c).

Fig. 8 shows an enlarged section of a processed pressure curve in the period.

Fig. 9 shows a number of injections and the associated injection quantities. 1 shows schematically a device according to the invention for testing an injector 2. The injector 2 to be tested is arranged in an injector holder 1 and via a (high-pressure) supply line 4 to a (high) pressure accumulator 6, the fluid to be injected, such as ( Diesel) fuel or a test oil, contains, connected. The injector 2 is electrically actuated by a triggering device 8, for example an engine control unit or a test device, which simulates an engine control unit. A pressure sensor 10 is arranged in the supply line 4 and measures the time pressure curve in the supply line 4. A trigger sensor 12, which may be formed as a current sensor, detects the start time of the electrical drive signal as a trigger. Alternatively, the starting time can also be output directly from the triggering device 8. A measurement data acquisition 14 records the measurement data, in particular the pressure profile and the trigger signal. A volume measuring unit 16 makes it possible to detect the continuous flow or the sum of the injection quantities of several injections. As shown in FIG. 1, the volume measuring unit 16 may be located on the low-pressure side, ie in the outlet of the injector 2 or in the supply line 4 on the high-pressure side. It can also be connected directly to the measurement data acquisition 14. FIG. 2 shows, by way of example, the course of a method according to the invention in a schematic flowchart.

In a first step 100, a number of injection processes are carried out with different activation periods in the vicinity of an operating point to be measured (test point) and the pressure profiles occurring in the supply line 4 are measured and possibly stored. In the following evaluation (step 200), the pressure curves are evaluated. In this case, either previously stored pressure profiles can be used, or the measured pressure profiles can be evaluated immediately without intermediate storage. In particular, from the pressure curves with different

Methods determines the respectively associated injection times (steps 21 1, 212, 213) and the correlation of the thus determined injection times with the associated drive times is calculated (steps 221, 222, 223). The thus determined correlation values are compared with each other, and the method with the best correlation, ie, the highest correlation value, is selected for the evaluation of the following measurement (step 230). For the method thus selected, a relationship between the injection time and the injection amount is established (step 240). For this purpose, a sum of injection quantities measured with the volume measuring unit 16 can be used for a number of injection events in order to determine the relationship between

Injection time and injection quantity to determine. In order that a proportional relationship between injection quantities and injection time can be calculated, the mean drive times must be different from the corresponding injection quantities.

If the injection quantities are determined from a continuous flow, which lasts, for example, over 2 to 3 minutes, an average injection quantity is obtained. This eliminates errors due to measured value spreads. Alternatively, the injection time can be considered. It is determined in two points around the operating point of the relationship between injection quantity and injection time and a compensation function by these two points. To calculate the injection quantity from the injection time, interpolation takes place between these points. A linearization is particularly well possible if only a small area around the respective operating point is considered.

In step 300, the measurement data, i. the temporal pressure fluctuations in the supply line in the control of the injector at the operating point, measured and possibly stored. This can be done before or after the selection of the most suitable method (injection quantity correlation) in steps 100 and 200. This may be done before or after step 100, as well as, after, or during the selection of the most appropriate method (injection amount correlation) in step 200. The data measured at the operating point are evaluated (step 400), in particular the injection times of the individual injection processes are determined from the recorded pressure curves with the method determined during the injection quantity correlation (step 410) and the individual injection quantities are determined from the injection times (step 420). It can be used either on previously stored pressure curves, or the measured

Pressure curves can be evaluated directly without intermediate storage. The individual injection quantities are statistically evaluated (step 500) to determine the quality of the injector 2.

FIG. 3 a shows by way of example the activation of an injector 2 during the injection quantity correlation. In the diagram shown in FIG. 3a, the drive duration T _Ans t (y axis) is plotted over different times for the drive phase.

The injector 2 is first actuated at the operating point with the control period T _B p (phase A). Then the drive time T _Ans t is reduced to a duration ΤΊ below the operating point T _B p and after a stabilization phase, the pressure curve in the supply line 4 is measured and recorded (phase B). At the same time, a flow rate V-1 is measured for a number of injection processes with the activation duration Ti.

Later, the drive duration T _Ans t is increased stepwise (step-shaped) up to an upper drive time T ₂ above the operating point T _B p of the injector (phase C).

For the upper activation duration T ₂ , which is above the operating point T _B p, the flow rate V ₂ for a number of injections with the activation duration T _{2 is} measured again after a stabilization phase (phase D).

For each actuation time T _Ans t, the time pressure curve in the supply line 4 is measured and recorded for a number of injection events that are statistically sufficient to achieve the required accuracy.

From the flow rates V- ₁ , V ₂ measured for the activation periods ΤΊ and T ₂ , the relationship between the injection time and the injection quantity is determined with the aid of a compensation straight line (linear approximation).

3b shows the measured flow rate Q (y-axis) as a function of the drive time T _A (x-axis) for three different drive times, in particular at the operating point (P2), below and above the operating point (P1, P3). FIG. 3b shows that the flow rate can be very well approximated by a straight line as a function of the injection time in the considered region.

FIGS. 4a and 4b show the corresponding injection times T _E (y-axis) determined from the pressure curves in the supply line for different drive durations T _A (x-axis), wherein a different method for determining the injection time T _{E is} used in each of the two figures has been.

It can be clearly seen from FIGS. 4 a and 4 b that the injection times T _E determined with the first method (FIG. 4 a) have a significantly better correlation with the drive times T _A than those determined with the second method (FIG. 4 b) Injection times T _E. For the evaluation of the measured data at the operating point, therefore, the first method (FIG. 4 a) is to be preferred in this case. FIGS. 5a and 5b show the optimum correlation values K (y-axis) determined for different operating points as a function of the activation duration T _A (x-axis).

The data of Figure 5a were taken at an injection pressure of 1000 bar as e.g. in the partial load operation of the engine, and the data of Figure 5b were at an injection pressure of 400 bar, as it e.g. idle occurs, recorded.

FIGS. 5a and 5b each show only the correlation values K determined with the optimum method for the respective operating point. The various methods are identified by different symbols of the measuring points.

The data presented in Figures 5a and 5b show that the optimal method, i. the method with the best correlation between the actuation time and the injection time, is dependent on both the injection pressure and the actuation time. The optimal method must therefore be redetermined for each injector and for each operating point.

The results further show that, in this example, the correlation is better overall at a lower injection pressure (eg in idle mode) and is subject to smaller fluctuations as the triggering time T _A changes (FIG. 5 b). as at a higher injection pressure, such as occurs in the partial load range (Fig. 5a).

FIGS. 6a and 6b show, by way of example, the activation of an injector at the operating point (FIG. 6a) and the resulting pressure curve p in the supply line 4 (FIG. 6b).

From characteristics of this pressure curve, such as maxima, minima and / or turning points, the injection time T _{E associated} with a given activation period T _A can be calculated. This can be done with different methods, which weight the individual characteristics differently. The method described above is used to select the most appropriate method for each operating point.

A method can also involve transforming the measured pressure profile into the frequency domain and further processing it there.

Fig. 7a shows by way of example such a pressure curve in the time domain and Fig. 7b shows that, e.g. using a fast Fourier transform (FFT), in the frequency domain converted signal. The signal has strong frequency components in the range around 500 Hz, which complicate an evaluation of the much weaker frequency components in the range of higher frequencies.

In the frequency spectrum shown in FIG. 7c, low-frequency components (<1000 Hz) are filtered out, so that the higher-frequency components (> 1000 Hz) are clearly better recognizable and evaluable.

Fig. 7d shows the processed signal transformed back into the period. For comparison, the electrical drive signal is shown as a dashed line.

Fig. 8 shows an enlarged section of the processed signal in the period, ie the pressure p (y-axis) in the supply line 4 as a function of time t (x-axis). The beginning (BIP) and the end (EIP) of the injection process are determined on the basis of given characteristics, here characteristic inflection points. The injection time TIP is the difference between the time between the end (EIP) and the start (BIP) of the injection process. Fig. 9 shows a number of injections (x-axis) and the associated injection quantities (y-axis), which scatter by a normalized to 1 mean value MW. For evaluation, the mean value MW can be compared with a desired value specified for the respective operating point and it can be evaluated whether individual injection quantities exceed or fall short of a predetermined upper limit OG or lower limit UG. Also, the variance of the scattering injection quantities can be determined and compared with a predetermined setpoint.

Claims

claims

1 . Method (200) for selecting a method for determining the injection time of individual injections of a fuel! Njektors (2), which is supplied by a supply line (4) with pressurized fuel, with the steps:

- Actuation of the fuel injector (2) with different, known Ansteuerdauern to a predetermined operating point of the fuel! injector (2);

- detecting (100) the time pressure curve in the supply line (4) for a number of injection events;

- evaluating (21 1, 212, 213) the detected temporal pressure profiles with at least two different methods for determining the respective injection time;

- determining the correlation (221, 222, 223) between the determined injection times and the respective drive time;

Select (230) the method with the highest correlation.

2. A method for determining the injection quantity of individual injection processes of a fuel injector (2), which is supplied via a supply line (4) with pressurized fuel, with the steps:

- selecting (200) the method most suitable for the particular operating point for determining the injection time by a method according to claim 1;

- Activation (300) of the fuel! Njektors (2) at at least one predetermined operating point and measuring the thereby occurring in a supply line (4) pressure curve;

Determining (410) the injection time of each individual injection event from the measured pressure profile using the selected method; Determining (420) the injection quantity of each individual injection event from the injection time.

3. A method of testing a fuel injector (2) comprising the steps of:

Determining the respective injection quantity of a number of individual injection events of a fuel injector (2) at at least one operating point with the method according to claim 2;

- Statistical evaluation of the thus determined injection quantities.

4. A method for testing a fuel injector (2) according to claim 3, wherein in the step of statistical evaluation includes the evaluation of a scattering measure of the determined injection quantities.

5. The method according to any one of the preceding claims, wherein the driving of the fuel! injector (2) includes the fuel! To control the ejector (2) with drive times above and below the operating point.

6. The method according to any one of the preceding claims, wherein the driving of the fuel! injector (2) includes the fuel! To control the ejector (2) with stepping on or off driving periods.

A method according to any one of the preceding claims, wherein each of the injection events includes a plurality of partial injection events.

8. The method according to any one of the preceding claims, wherein at least one method (21 1, 212, 213) for evaluating the temporal pressure curve includes the transformation of the detected pressure profile into the frequency space.

9. The method according to any one of the preceding claims, wherein in at least one method (21 1, 212, 213) for the evaluation of the temporal pressure curve includes the determination of maxima, minima and / or inflection points of the pressure profile.

10. Device for testing a fuel! njektors (2) with

- At least one receiving device (1) for receiving at least one fuel injector (2);

- At least one supply line (4) which is adapted to supply the fuel injector (2) in operation, a pressurized fluid;

- At least one sensor (10) which is designed to measure the temporal pressure curve in the supply line (4);

- At least one volume measuring unit (16) which is adapted to detect the flow through the injector (2);

- At least one Ansteuereinnchtung (8), which is designed for driving the fuel injector (2);

- At least one evaluation unit (14), which is functionally connected to the volume measuring unit (16), the sensor (10) and the Ansteuereinnchtung (8) and configured to perform during operation of at least one of the methods according to one of the preceding claims.