EP1954938B1 - Method and device for measuring the injection quantity and the injection rate of an injection valve for liquids - Google Patents

Abstract

Method involves injection of liquid by the injection valve (3) in the measuring volume (1). The method also involves measurement of the pressure in the measuring volume by means of the pressure sensor (20) during the injection and recording these measuring values. The speed of sound is determined in the measuring volume before and after the injection. The method involves determination of the injected test liquid quantity from the pressure measuring values and the speed of sound dependent on pressure. An independent claim is included for measuring the injection quantity and the injection rate of an injection valve for liquids.

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 test methods are described for volume measurement. For example, from the DE 100 64 511 A1 The measuring piston principle is known in which the injection valve injects fuel into a measuring medium 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, such as in W. Zeuch: "New methods for measuring the injection law and the injection uniformity of diesel injection pumps", Motortechnische Zeitschrift (MTZ) 22 (1961), pp 344-349 , 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. From the time course of the pressure increase In principle, the course of the injection rate and the injected quantity can be calculated.

In practice, however, this is made difficult by a number of factors: In the measuring volume V, the injected fuel causes pressure oscillations in the corresponding natural frequencies of the measuring volume, these natural frequencies depending on the geometric dimensions of the measuring 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.

wobei K der Kompressionsmodul ist, ρ die Dichte der Flüssigkeit und V das Volumen des Messvolumens. Da sowohl der Kompressionsmodul K als auch die Dichte ρ vom Druck abhängen, ist eine präzise Bestimmung der eingespritzten Menge und insbesondere des zeitlichen Verlaufs der Einspritzrate nur mit eingeschränkter Genauigkeit möglich.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. It applies here $$\mathrm{Dm}\mathrm{=}\mathrm{\rho }\mathrm{\cdot }\mathrm{.DELTA.V}\mathrm{=}\mathrm{V}\mathrm{\cdot }\mathrm{\rho }\mathrm{/}\mathrm{K}\mathrm{\cdot }\mathrm{Ap}$$

where K is the modulus of compression, ρ the density of the liquid and V the volume of the measurement volume. Since both the compression modulus K and the density ρ depend on the pressure, a precise determination of the injected quantity and in particular the time profile of the injection rate is only possible with limited accuracy.

In the DE 102 49 754 A1 It is proposed to calculate the speed of sound from pressure oscillations induced by the injection in the measuring volume and to determine therefrom the compression modulus. This allows the injection rate to be calculated directly from the change in pressure.

However, this method does not take into account the change in the speed of sound due to the pressure increase. Especially with injection processes, which consist of up to five partial injections, such a measurement is not always possible with the necessary precision, which is necessary for the testing of modern injectors. Also, the calculation of the speed of sound from the induced pressure oscillations by the superimposed vibrations of different modes is not always possible with the required accuracy.

Disclosure of the invention

In contrast, the method according to the invention with the features of claim 1 has the advantage that it is possible to determine very precisely both the injection quantity and the course of the injection, that is to say the injection rate, from the pressure curve. For this purpose, the time course of the pressure in the measuring volume is recorded during the injection and, moreover, the speed of sound is measured at least before and after the injection. From these quantities can be calculated with high accuracy the mentioned sizes.

By means of the method according to the invention, the speed of sound is determined by emitting a sound pulse from a sound transducer into the measuring volume, which is reflected at the opposite, parallel base and in turn is received as an echo by the sound transducer. From the length of the measurement volume and the duration of the sound signal can be calculated directly the speed of sound. Because of the long running distance and thus large time, the measured variables are subject to a relatively small error.

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.

The device according to the invention has the advantage over the prior art that a sound transducer provided in the measuring volume simultaneously serves as a sound generator and as a sound receiver. Since this eliminates a separate sound receiver, this arrangement is cheaper and it also eliminates the implementation of a signal cable, would otherwise be routed to the measurements of the sound receiver to the electronic computer.

drawing

Figur 1

die Messvorrichtung mit den schematisch dargestellten Komponenten und

Figur 2

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 and

FIG. 2

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

Description of the embodiment

In the FIG. 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 a cylindrical 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 projects with its tip into 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 may be more than 200 MPa depending on the injection valve used.

In the side wall 303 of the cylindrical wall 2 opens a connected to a control valve 15 line 16, can be derived by the test liquid from the measuring volume 1 in a not shown in the drawing leakage volume. By the time-variable control of the control valve, the maintenance of a certain pressure in the measuring volume 1 and the always complete filling with liquid is ensured.

A holder 22 projects through 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 is led out of the measuring volume 1 in the holder 22 with an electronic computer 28, wherein the passage of the holder 22 through the wall 2 liquid-tight is closed. The pressure sensor 20 is arranged in the median plane between the two base surfaces 102, 202 and thus has the same distance to both base surfaces 102, 202. Via the electronic computer 28, the signal representing the pressure supplied by the pressure sensor 20 can be read out and stored electronically. In order to enable a rapid measurement of the pressure curve, the pressure sensor 20 is constructed on a piezo-based basis, for example, so that even rapid changes in pressure can be measured without significant delay.

At the base 202 of the wall 2, a transducer 30 is arranged, which can both send sound signals and receive the associated echo. The transmitted sound signal is reflected at the base surface 202 opposite the sound transducer 30 and thus passes twice the length of the measurement volume 1 before it is detected by the sound transducer 30 as an echo. Alternatively, it can also be provided that a separate sound receiver 31 is arranged on the base 202 with respect to the sound transducer 30. This allows two measurements of the speed of sound in a very short time interval: The speed of sound is determined on the one hand from the duration of the sound signal from the sound transducer 30 to the sound receiver 31. On the other hand, from the transit time of the sound signal reflected from the base 202 to the sound transducer 30, a second measurement can be taken which immediately follows the first time. This makes it possible to measure the speed of sound in a very short time interval and with a correspondingly small measuring volume because of multiple reflections at the base areas 102, 202 even during the duration of an injection.

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

The wall 2 of the measuring volume 2 can be regarded as inelastic in a good approximation and thus V can be regarded as constant. 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 $$\mathrm{\Delta \rho }\mathrm{=}\mathrm{Ap}\mathrm{\cdot }\mathrm{1}\mathrm{/}\mathrm{<figure-callout\; id="2"\; label="c\; \; p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">c\; </figure-callout>}{\left(\mathrm{p}\right)}^{}{\left(\mathrm{}\right)}^{\mathrm{2}}$$

wobei p_v der Druck vor und p_n der Druck nach der Einspritzung ist. Es gibt also einen Zusammenhang zwischen dem Druckanstieg Δp und der Mengenänderung m bzw. Δm.The speed of sound c depends on the pressure p in the measuring volume 1. The injected quantity m then results from integration with the aid of the above-mentioned relationships $$\mathrm{m}\mathrm{=}\mathrm{V}\mathrm{\cdot }\underset{{\mathrm{p}}_{\mathrm{v}}}{\overset{{\mathrm{p}}_{\mathrm{n}}}{\mathrm{\int }}}\frac{\mathrm{1}}{{\left[\mathrm{<figure-callout\; id="2"\; label="c\; p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">c\; </figure-callout>}\left(\mathrm{p}\right)\left(\mathrm{}\right)\right]}^{\mathrm{2}}}\mathrm{dp}$$

where p _{v is} the pressure before and p _{n is} the pressure after injection. Thus, there is a relationship between the pressure increase Δp and the quantity change m or Δm.

With the pressure sensor 20, the time course of the pressure p (t) 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 equation II, the following equation results for the injection rate r (t), ie the time derivative of the injected quantity dm (t) / dt: $$\mathrm{r}\left(\mathrm{t}\right)\mathrm{=}\frac{\mathrm{dm}\left(\mathrm{t}\right)}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{d}}{\mathrm{dt}}\mathrm{V}\mathrm{\cdot }\underset{{\mathrm{p}}_{\mathrm{v}}}{\overset{{\mathrm{p}}_{\mathrm{n}}}{\mathrm{\int }}}\frac{\mathrm{1}}{{\left[\mathrm{<figure-callout\; id="2"\; label="c\; p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">c\; </figure-callout>}\left(\mathrm{p}\right)\left(\mathrm{}\right)\right]}^{\mathrm{2}}}\mathrm{dp}$$

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. It should be noted that the speed of sound depends on the pressure p and this in turn on the time t. Since the injection process is very short and usually completed in a period of 1 to 2 ms, the speed of sound during the injection can not be measured. Instead, c is measured before and after the injection and a linear relationship between the speed of sound c and the pressure p is assumed, which is a good approximation here. This can be used to solve the integral and determine the absolute quantity according to equation II.

For evaluation of the measurement, the following procedure is used: In the measuring volume 1, in which the test liquid is located, the injection valve 3 injects by a rapid longitudinal movement of the valve needle 5, through which the injection openings 12 are opened and be closed again, a certain amount of liquid. 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 and thus the injection rate r (t), equation III is used. The measured values p (t) stored in the computer are converted into a sound velocity, so that the integral can be calculated according to equation III. This provides a function of time t, which is then numerically differentiated, giving the injection rate r (t).

die Schallgeschwindigkeit c. Nach der Gleichung (II) ergibt sich durch Integration über den Druck p die eingespritzte Menge m.The speed of sound c is determined in a separate procedure. For this purpose, a sound pulse is emitted by the sound transducer 30, which is reflected at the opposite base surface 202 of the measuring volume 1 and is collected as an echo after a running time t _L again from the transducer. From the distance s of sound transducer 30 and base 202 then calculated after $$\mathrm{c}\mathrm{=}\mathrm{2}\mathrm{s}\mathrm{/}{\mathrm{t}}_{\mathrm{L}}$$

the speed of sound c. By the equation (II), by integration over the pressure p, the injected quantity m is obtained.

FIG. 2 shows the time course of the pressure p (t) and its derivative dp (t) / dt as a function of time t in arbitrary units U. The pressure p (t) increases approximately at time t = 1 ms to a first level and about at time t = 2 ms to a second, significantly higher level. This corresponds to an injection, which is divided into a smaller amount and a larger amount of test liquid, the second partial injection of the first follows at a distance of about 1 ms. When an injector is used as used for direct-injection, auto-ignition internal combustion engines, this corresponds to fuel injection subdivided 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 recorded, the evaluation according to equation III results in the injection rate r (t).

The measurement method together with the described test setup thus makes it possible to measure the pressure curve and the speed of sound c under the current test conditions to determine what the injection quantity and the injection rate can be determined from. The test liquid may be fuel or another liquid whose properties approximate the liquid used in normal use of the injector. The measuring volume 1 does not have to be cylindrically shaped, but instead may also be cuboid or in another suitable shape, for example spherical. The pressure sensor may in principle be mounted at any point in all forms of the measuring volume 1, but direct admission to the injected fuel should be avoided.

Claims (8)

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

   - injecting liquid through the injection valve (3) into the measuring volume (1),

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

   - determining the speed of sound (c) in the measuring volume (1) at least before and after the injection,

   - determining the injected test liquid quantity (m(t); Δm) from the pressure measurement values (p(t)) and the pressure-dependent speed of sound (c(p)), with the speed of sound (c) being determined from the propagation time of a sound signal emitted by a sound transducer (30) which receives the echo of said sound signal.
2. Method according to Claim 1, characterized in that the pressure measurement values (p(t)) during the injection are plotted by an electronic computer (28).
3. Method according to Claim 1, characterized in that the speed of sound (c) is determined by means of the propagation time of a sound signal in the measuring volume (1).
4. Device for measuring the injection rate (r(t)) of an injection valve (3) for liquids, having a measuring volume (1) which is closed on all sides and which is filled with a test liquid, having an opening (10) in the wall (2) of the measuring volume (1), which opening (10) serves to hold an injection valve (3) such that, in the installed position, the injection valve (3) projects with at least one injection opening (12) into the measuring volume (1), and with a pressure sensor (20) which is arranged in the measuring volume (1) characterized in that a sound transducer (30) is arranged in the measuring volume (1), which sound transducer (30) emits a sound signal and receives the echo thereof, and having an electronic computer which determines the speed of sound (c) from the propagation time of a sound signal emitted by the sound transducer (30) which receives the echo of said sound signal.
5. Device according to Claim 4, characterized in that the measuring volume (1) is of cylindrical design.
6. Device according to Claim 5, characterized in that the sound transducer (30) is arranged on one of the base surfaces (102, 202) of the wall (2).
7. Device according to Claim 4, characterized in that an electronic computer (28) records and stores the measurement values of the pressure sensor (20).
8. Device according to Claim 4, characterized in that a separate sound receiver (31) is arranged in the measuring volume (1) in addition to the sound transducer (30).

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