EP1561029B1 - Method and device for measuring the injection rate of an injection valve for liquids - Google Patents

Abstract

A method for measuring the injection rate of an injection valve for liquids, preferably for liquid fuel, in which the injection valve injects the liquid into a liquid-filled measurement volume, the measurement volume being closed off on all sides and a pressure sensor being located in the measurement volume. From the measured pressure values or by a separate measurement, the speed of sound is determined and thus the injection quantity or the course over time of the injection rate is calculated. The apparatus includes a measurement volume, an injection valve, which protrudes with at least one injection opening into the measurement volume, and a pressure sensor, which is located in the pressure node of the first natural pressure oscillation of the measurement volume.

Description

State of the art

In manufacturing and functional testing of fuel injection components, such as injectors, common rail injectors, and other high pressure injectors, various prior art test devices and methods are described for volume measurement. For example, from DE 100 64 511 A1 the measuring piston principle is known, in which the injection valve injects fuel into a measuring volume filled with a test medium. The pressure in the measuring volume is kept constant by displacing a volumetric flask by the injection quantity. From the displacement of the volumetric flask, the injection quantity can then be calculated directly. This method is dynamically limited because of the mechanical piston movement and thus can not meet the increasing demands for high-temporal measurement of the injection rate in modern high-pressure injection systems for internal combustion engines, which often comprise multiple partial injections per injection cycle.

An alternative and accurate method, as described for example in W. Zeuch: "New methods for measuring the injection law and the injection regularity of diesel injection pumps", Motortechnische Zeitschrift (MTZ) 22 (1961), pp 344-349 described , is the hydraulic Pressure increase method (HDV). Here, the injection valve also injects into a liquid-filled measuring volume, but here the measuring volume is kept constant. This leads to a pressure increase in the measuring volume, which is measured with a suitable pressure sensor. Modern piezo-based pressure sensors are characterized by a very short response time, which makes temporally high-resolution measurements possible. In principle, the course of the injection rate and the injected quantity can be calculated from the time course of the pressure rise.

In practice, however, this is made difficult by a number of factors: In the measurement volume V, the injected fuel causes pressure oscillations in the corresponding natural frequencies of the measurement volume, these natural frequencies depending on the geometric dimensions of the measurement volume. In addition to the fundamental vibration also many harmonics are usually excited, with several vibration modes are usually possible. This makes it difficult to filter the pressure sensor measuring signal, since the frequencies of the natural oscillations are partly in the range of the frequencies of the measuring signal.

Furthermore, an accurate measurement of the absolute value of the injection quantity Δm is made more difficult by the fact that the measured variable of the pressure must first be converted to the amount of liquid injected. The conversion factors include the compression modulus and the density. These quantities depend on the test conditions and history and therefore are not available with the necessary accuracy from previous measurements. In order to determine these quantities, a separate, complex calibration process is necessary for each measurement, which makes the measurement cumbersome and difficult to carry out in practice. To this end, is introduced via a separate calibrating a defined calibration volume .DELTA.V _k in the measurement volume V and the Pressure change Δp _k measured. The compression modulus K then results from the relationship $$\mathrm{K}=\mathrm{\Delta }{\mathrm{p}}_{\mathrm{k}}/\mathrm{\Delta }{\mathrm{V}}_{\mathrm{k}}\cdot \mathrm{V}$$

This now allows to calculate the injected volume ΔV: $$\mathrm{\Delta }\mathrm{V}=\mathrm{V}/\mathrm{K}\cdot \mathrm{\Delta }\mathrm{p}$$

In order to finally calculate the injection quantity, a conversion to the mass is necessary, which makes the knowledge of the density ρ necessary: $$\mathrm{\Delta }\mathrm{m}=\mathrm{\rho }\cdot \mathrm{\Delta }\mathrm{V}=\mathrm{V}\cdot \mathrm{\rho }/\mathrm{K}\cdot \mathrm{\Delta }\mathrm{p}$$

The density depends on the temperature of the test medium. To take this into account, the temperature is measured by means of a temperature sensor in the measuring volume and the density is corrected accordingly. The temperature measurement is selective and does not take into account a possibly unequal temperature in the entire measuring volume. Such a method is described in WO 02/064970 A.

For the determination of the compression modulus K according to the given equation (I), the introduction of a defined calibration volume into the measurement volume is necessary, which makes a separate volume sensor necessary. In addition, there is the disadvantage that a separate measuring time is necessary for the calibration measurement, which reduces the possible frequency of successive measurements.

Advantages of the invention

The method according to the invention with the features of claim 1 has the advantage that from the pressure curve in a simple manner, the injection quantity determine. For this purpose, the time course of the pressure in the measuring volume is recorded during the injection and from this the time course of the injection quantity is calculated. To determine the factor for calculating the absolute value of the injection quantity, the sound velocity is determined. From the increase in pressure and the speed of sound can then directly the injection quantity or its time course, so calculate the rate of injection rate.

In an advantageous development of the method, the speed of sound is determined by means of a separate measurement process, in which a sound pulse is emitted by a sound generator into the measurement volume and is collected by the pressure sensor. If the sound generator and the pressure sensor are arranged opposite each other, the sound velocity can be calculated directly from the distance and the running time. This is a very fast measuring method, which causes hardly any significant delays in the measurement process.

In a further advantageous embodiment of the method, the measurement data of the pressure profile are stored with the aid of an electronic computer, which also makes direct further processing of the data possible.

In a further advantageous development of the measuring method, the frequency of a natural pressure oscillation of the measuring volume is determined from the pressure measured values. From the natural frequency, the sound velocity then results as an average value over the entire measurement volume, without the need for a separate measurement with corresponding devices. By way of example, it is possible in this case to calculate the frequency analysis with the aid of a Fourier method, although other modern methods are also possible.

The filtering of the pressure readings is performed, for example, with a low-pass filter, so that noises and noise be largely eliminated. From the time differentiation of the pressure signal can then determine the injection rate.

The device according to the invention with the features of claim 9 has the advantage over the prior art that the measurement signal can be better filtered. For this purpose, the pressure sensor is arranged in the pressure node of the first compressive natural vibration, that is, the natural vibration, so that the pressure sensor does not detect a signal of the natural vibration. Therefore, the cut-off frequency of the low-pass filter can be shifted upwards by a factor of two for smoothing the pressure measurement values.

drawing

Figur 1

die Messvorrichtung mit den schematisch dargestellten Komponenten,

Figur 2

eine Darstellung des Messvolumens mit dem Druckverlauf der ersten Druckeigenschwingung und

Figur 3

das Diagramm einer Messung, wobei der Druck und dessen Ableitung über der Zeit abgetragen sind.

In the drawing, an embodiment of the device according to the invention is shown. It shows

FIG. 1

the measuring device with the schematically illustrated components,

FIG. 2

a representation of the measuring volume with the pressure curve of the first natural pressure oscillation and

FIG. 3

the diagram of a measurement, where the pressure and its derivative are plotted over time.

Description of the embodiment

In the figure 1, the measuring device is shown in a partially sectioned view. A cylindrical measuring volume 1 with a wall 2 is completely filled with a test liquid, wherein the measuring volume 1 is completed on all sides. The wall 2 has a first base area 102 and a second base area 202, which are connected by the side wall 303, which has a longitudinal axis 4. Through an opening 10 in the first base 102 of the wall 2, an injection valve 3 protrudes with its tip in the measuring volume 1, wherein the passage of the injection valve 3 is closed by the wall 2 liquid-tight. The injection valve 3 has a valve body 7, in which in a bore 6, a piston-shaped valve needle 5 is arranged longitudinally displaceable. By a longitudinal movement of the valve needle 5, a plurality of injection openings 12, which are formed on the projecting into the measuring volume 1 tip of the injection valve 3, opened or closed. When the injection openings 12 are open, test liquid flows from a pressure space 9 formed between the valve needle 5 and the wall of the bore 6 to the injection openings 12 and is injected from there into the measurement volume 1 until the injection openings 12 are closed again by the valve needle 5. The injection of the test liquid takes place here with a high pressure, which can be up to 200 MPa depending on the injection valve used.

In the side wall 303 of the cylindrical wall 2 opens a connected to a pressure holding valve 17 line 16, can be derived by the test liquid from the measuring volume 1 in a not shown in the drawing leakage volume. In the line 16, a control valve 15 is also arranged, through which the line 16 can be closed if necessary, if a derivation of test liquid from the measuring volume 1 is not desired. By the pressure-maintaining valve 17 ensures that a certain pressure in the measuring volume 1 is maintained and this always remains completely filled with liquid.

A holder 22 projects through the second base 202 of the wall 2 into the measuring volume 1. At the end of the holder 22, a pressure sensor 20 is arranged, which is connected via a signal line 24, which leads out of the measuring volume 1 in the holder 22 with an electronic computer 28, wherein the passage of the holder 22 is sealed by the wall 2 liquid-tight. The pressure sensor 20 is arranged in the median plane between the two base surfaces 102, 202 of the wall 2 and thus has the same distance to both base surfaces 102, 202. Since the pressure sensor 20 is also located on the longitudinal axis 4, it has to the side surface 303 on all sides the same distance s. About the electronic calculator 28, the signal that the pressure sensor 20 supplies read and stored electronically. In order to enable a rapid measurement of the pressure curve, the pressure sensor 20 is constructed, for example, on a piezo-based basis, so that even rapid changes in pressure can be measured without appreciable delay. On the side surface 303 of the wall 2, a sounder 21 is arranged, which has the distance s from the pressure sensor 20. Alternatively, it can also be provided that a separate sound receiver 30 diametrically opposite the sounder 21 on the side surface 303 in order to obtain the largest possible distance of the sound signal and thus greater accuracy in determining the speed of sound c.

The injection quantity Δm of the test liquid to be measured can be calculated from the pressure increase and the sound velocity. If ρ is the density of the test liquid and V is the volume of the measuring volume, injection of the injector at constant volume V results in a change in the density Δρ, so that $$\mathrm{\Delta }\mathrm{m}=\mathrm{V}\cdot \mathrm{\Delta }\mathrm{\rho }$$

und damit gilt $$\mathrm{\Delta }\mathrm{m}=\mathrm{V}\cdot 1/{\mathrm{c}}^2\cdot \mathrm{\Delta }\mathrm{p}=\mathrm{V}\cdot \mathrm{\rho }/\mathrm{K}\cdot \mathrm{\Delta }\mathrm{p}$$

According to the known acoustic theory, the relationship between the speed of sound c, the density change Δρ and the pressure increase Δp is as follows $$\mathrm{\Delta }\mathrm{\rho }=\mathrm{\Delta }\mathrm{p}\cdot 1/{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0002.png"\; state="\{\{state\}\}">c</figure-callout>}}^2$$

and with that applies $$\mathrm{\Delta }\mathrm{m}=\mathrm{V}\cdot 1/{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0002.png"\; state="\{\{state\}\}">c</figure-callout>}}^2\cdot \mathrm{\Delta }\mathrm{p}=\mathrm{V}\cdot \mathrm{\rho }/\mathrm{K}\cdot \mathrm{\Delta }\mathrm{p}$$

So there is a direct relationship between the pressure increase Δp and the amount change Δm.

With the pressure sensor 20, the time course of the pressure is measured, from which in turn the injection rate r (t) can be determined, ie the amount dm (t) of the test liquid injected per unit time dt. From the above connection, the following equation thus results for the injection rate r (t), ie the time derivative of the injected quantity dm (t) / dt: $$\mathrm{r}\left(\mathrm{t}\right)=\mathrm{d}\mathrm{m}\left(\mathrm{t}\right)/\mathrm{d}\mathrm{t}=\mathrm{V}/{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0002.png"\; state="\{\{state\}\}">c</figure-callout>}}^2\cdot \mathrm{d}\mathrm{p}\left(\mathrm{t}\right)/\mathrm{d}\mathrm{t}$$

This means that with knowledge of the speed of sound c and the volume V from the time course of the pressure p (t), the absolute value of the injection rate r (t) can be calculated.

When injecting the test liquid into the measuring volume 1, which initially has a constant pressure, which corresponds for example to 1 MPa, the pressure in the measuring volume 1 increases. Liquids are virtually incompressible compared to gases, so that even a small increase in volume leads to a well-measurable pressure increase. Due to the impact-like introduction of the test liquid, pressure oscillations are excited in the measuring volume 1. The natural frequencies depend on the geometric dimensions of the measurement volume 1: For the first natural pressure oscillation, the so-called fundamental oscillation, in which a longitudinal wave oscillates along the longitudinal axis 4, the half wavelength λ / 2 is equal to the length L of the measurement volume 1, that is $$\mathrm{\lambda }={\mathrm{\lambda }}_{\mathrm{e}}=2\cdot \mathrm{L},$$

FIG. 2 shows this first compressive natural oscillation schematically, wherein the lines designated by p show the pressure curve, in which pressure bellies are to be found at the edges and in the middle, ie in the radial plane of the cylindrical measuring volume in which the pressure sensor 20 is arranged, a pressure node lies. The frequency ν _{e of} the first natural pressure oscillation is then simply calculated from the speed of sound c according to the relationship λ _e · ν _e = c $${\mathrm{\nu }}_{\mathrm{e}}=\mathrm{c}/{\mathrm{\lambda }}_{\mathrm{e}}=\mathrm{c}/\left(2\cdot \mathrm{L}\right)$$

Accordingly, for the frequency ν _{n of} the nth harmonic, the length of the measurement volume L must be a multiple of λ / 2: $${\mathrm{\nu }}_{\mathrm{n}}=\left(\mathrm{n}\cdot \mathrm{c}\right)/\left(2\cdot \mathrm{L}\right)$$

The pressure sensor 20 does not register the first natural pressure vibration since no pressure changes occur at the pressure node. Nor are the 2nd, 4th and all other even harmonics recorded by the pressure sensor 20.

To evaluate the measurement, the procedure is as follows: Into the measuring volume 1, in which the test liquid is located, the injection valve 3 injects a certain amount of liquid by a rapid longitudinal movement of the valve needle 5, through which the injection openings 12 are opened and closed again. The pressure sensor 20 measures the pressure p (t) which is read out and stored by the computer 28 at a specific rate of, for example, 100 kHz.

In order to determine the time course of the injection quantity dm (t) / dt, ie the injection rate r (t), equation (III) is used. The measured values p (t) stored in the computer are time-differentiated and multiplied by the factor V / c ² , which directly yields the injection rate r (t).

In addition to the determination of the speed of sound by a separate measurement, it is also possible to directly determine these from the measured pressure measurements. The pressure readings recorded in the computer 28 are, on the one hand, noisy and, on the other, compressive oscillations of the measuring volume 1 are superimposed, which leads to further distortions. From a frequency analysis, the frequencies of the first harmonic of the natural pressure oscillations can be determined from the pressure measurements, from which, according to the above-mentioned relationship c = ν · L, the speed of sound c is calculated, which prevails in the test fluid used under the present conditions. Although the approximate size of c is of course known, variations in test fluid composition or altered temperatures will result, which would otherwise result in a reduction in measurement accuracy. By filtering the pressure readings through a low pass, high frequency noise can be suppressed. Because of the arrangement of the pressure sensor 20 in the middle of the measuring volume, the cut-off frequency ν _G for the low-pass filter can be selected to be twice as large as the first fundamental vibration is not registered by the pressure sensor 20. The smoothed pressure readings are then differentiated in time, and after multiplication by the factor V / c ² results in a known volume V, the injection rate r (t).

die Schallgeschwindigkeit c. Nach der oben gezeigten Gleichung (II) ergibt sich dadurch sofort die eingespritzte Menge Δm.The speed of sound c can also be determined in a separate method. For this purpose, a sound pulse is emitted from the sounder 21, which is collected by the serving as a sound receiver pressure sensor 20 or by a separate sound receiver 30 after a running time t _L. From the distance s of sounder 21 and pressure sensor 20 is calculated then $$\mathrm{c}=\mathrm{s}/{\mathrm{t}}_{\mathrm{L}}$$

the speed of sound c. According to equation (II) shown above, the injected quantity Δm is thus obtained immediately.

FIG. 3 shows the time profile of pressure p (t) and its derivative dp (t) / dt as a function of time t in arbitrary units U. The pressure p (t) increases to a first level at about time t = 1 ms and at the time t = 2 ms to a second, significantly higher level. This corresponds to an injection of first a smaller amount of test liquid and a distance of about 1 ms of a larger amount. When an injector is used, as used for direct-injection, auto-ignition internal combustion engines, this corresponds to a fuel injection, which is divided into a pilot or pilot injection and a subsequent main injection. After the pressure signal p (t) measured by the pressure sensor 20 has been smoothed according to the above-described method, the derivative dp (t) / dt gives a value which is proportional to the injection rate r (t). By multiplication by the factor V / c ² , one finally obtains from this the absolute value of the injection rate r (t).

The measurement method together with the described measurement setup thus makes it possible to measure the pressure profile and to determine the speed of sound c under the current test conditions, from which the injection quantity and the injection rate can be determined. If the speed of sound c is calculated from the frequency of the natural vibrations, then all the necessary variables from the pressure curve can be determined, which excludes errors due to additional components. Due to the arrangement of the pressure sensor 20 exactly between the two base areas 102, 202, the cut-off frequency ν _{G of} the low-pass filter can be raised to twice the frequency of the fundamental vibration ν _e , without a qualitative impairment is to be expected by the filtering. costly Calibration methods in which the speed of sound is determined in a separate measuring method can thus be dispensed with.

The test fluid may be fuel or another fluid whose properties are similar to that used in normal use of the fuel injector. The measurement volume 1 need not be cylindrical, but instead of a cylinder, a cuboid measuring volume 1 or another suitable shape may be provided, for example a ball. The pressure sensor 20 is also arranged here in a pressure node of the first natural pressure oscillation of the measuring volume 1 in order to be able to set the cutoff frequency for the filtering as high as possible.

Claims (14)

1. Method for measuring the injection rate of an injection valve for liquids, preferably for liquid fuel, in which the injection valve (3) injects the liquid into a liquid-filled measurement volume (1), the measurement volume (1) being closed off on all sides, and a pressure sensor (20) being arranged in the measurement volume (1), characterized by the following method steps:

   - injection of liquid into the measurement volume (1) by means of the injection valve (3),

   - measurement of the pressure (p(t)) in the measurement volume (1) by means of the pressure sensor (20) during injection, and recording of these measurement values,

   - determination of the sound velocity (c) in the measurement volume (1) by the measurement of the transit time of a sound signal in the measurement volume (1) or directly from the pressure measurement values,

   - determination of the injected test-liquid quantity (m(t); Δm) from the pressure measurement values (p(t)) and from the sound velocity (c).
2. Method according to Claim 1, characterized in that the pressure measurement values (p(t)) are recorded, during injection, by an electronic computer (28).
3. Method according to Claim 1, characterized in that the sound velocity (c) is determined by means of a separate measurement method.
4. Method according to Claim 3, characterized in that the sound velocity is calculated from the transit time of a sound signal running from a sound transmitter (21) to a sound receiver (20; 30).
5. Method according to Claim 1, characterized in that the sound velocity (c) is determined from the characteristic frequencies (v_n) of the measurement volume (1).
6. Method according to Claim 5, characterized in that the characteristic frequencies (v_n) are determined by means of a frequency analysis of the pressure measurement values (p(t)).
7. Method according to Claim 6, characterized in that the pressure measurement values (p(t)) are filtered by means of a low-pass filter.
8. Method according to Claim 7, characterized in that a variable proportional to the injection rate (r(t)) is calculated from the profile of the pressure measurement values (p(t)) by means of time differentiation.
9. Device for measuring the injection rate (r(t)) of an injection valve (3) for liquids, with a measurement volume (1) which is closed off on all sides and is filled with a test liquid, with an orifice (10) in the wall (2) of the measurement volume (1) for receiving an injection valve (3), so that, in the installation position, the injection valve (3) projects with at least one injection orifice (12) into the measurement volume (1), and with a pressure sensor (20) which is arranged in the measurement volume (1), characterized in that the pressure sensor (20) is arranged at the pressure node of the first natural pressure oscillation of the measurement volume (1), and the sound velocity can be determined by the measurement of the transit time of a sound signal in the measurement volume (1) or directly from the pressure measurement values.
10. Device according to Claim 9, characterized in that the measurement volume (1) is of cylindrical design.
11. Device according to Claim 10, characterized in that the pressure sensor (20) is arranged in the radial plane which lies centrally between the two bases (102; 202) of the cylinder.
12. Device according to Claim 9, characterized in that an electronic computer (28) detects and stores the measurement values of the pressure sensor (20).
13. Device according to Claim 12, characterized in that the electronic computer (28) runs a program which calculates the characteristic frequencies of the measurement volume (1) from the recorded pressure measurement values (p(t)).
14. Device according to Claim 9, characterized in that a sound transmitter (21) and a separate sound receiver (30) are arranged in the measurement volume (1).

Images