DE102017201877A1 - Measuring arrangement and method for determining the time-related mass flow profile during an injection carried out by a fuel injector into a measuring space - Google Patents

Abstract

Measuring arrangement and method for determining the temporal mass flow profile during an injection of a liquid test medium carried out by a fuel injector (5) into a measuring chamber (2) of a hydraulic pressure rise analyzer (HDA), which has a pressure sensor (6) connected to the measuring chamber (2) for measuring the current pressure Pressure in the measuring chamber (2), a temperature sensor (12) for measuring the mean temperature herein and an ultrasonic sensor (7) also connected to the measuring space (2) for measuring the speed of sound in the measuring chamber (2), and a downstream electronic evaluation unit (4) for calculating the mass (m) of the test medium injected as a result of the injection into the measuring space (2) taking into account at least one correction factor compensating for the measurement error, the evaluation unit (4) determining a temperature-dependent volume change of the measuring space (2) as a first correction factor (K) as a second correction factor (K) involves a temperature-dependent pressure change in the measuring chamber (2), whereby the injected mass (m) of test medium calculated on the basis of the measuring signals of the pressure sensor (6) and the ultrasonic sensor (7) is error-corrected. Furthermore, the invention also relates to a computer program product and a storage medium.

Description

The present invention relates to a measuring arrangement and a method for determining the time course of mass flow during a fuel injector performed injection of a liquid test medium in a measuring chamber of a hydraulic pressure rise analyzer (HDA), the pressure sensor connected to a measuring space for measuring the current pressure in the measuring chamber and also a The ultrasonic sensor connected to the measuring space for measuring the speed of sound along the measuring space, and a downstream electronic evaluation unit for calculating the mass of test medium injected into the measuring space as a result of the injection in consideration of at least one correction error compensating error. Furthermore, the invention also relates to a computer program product according to claim 9 and a computer-readable medium according to claim 10.

The field of application of the invention extends primarily to the measurement technology for functional testing of fuel injectors, preferably common rail injectors in motor vehicle technology. The measuring apparatus used here is the hydraulic pressure increase analyzer of interest (HDA), with which a high-precision injection rate measurement of single or multiple injections is possible.

State of the art

From the DE 10 2008 040 628 A1 the hydraulic pressure increase process used in the HDA is apparent. The injected mass of a liquid test medium, so-called test oil, is injected into a measuring space also filled with test medium. During the injection, the time pressure drop of the liquid pressure prevailing in the measuring space is measured. The injected mass is determined from the speed of sound of the test oil in the measuring space and from the time pressure drop measured in the measuring space during the injection.

With the help of the well-known container equation of thermodynamics can be calculated from the temporal pressure curve in the measuring chamber, the injection curve, the so-called injection rate, or physically correct, the mass flow curve, the injected test medium. This results in the injected mass of test medium as the measured value for the fuel injector.

The injected mass of test medium is distributed in practice to up to ten partial injections per injection cycle.

From the "Manual Diesel Engines" (Author: Prof. Dr.-Ing. Klaus Mollenhauer et. al., VDI book, edition 2007, ISBN: 978-3-540-72164-2 ), pages 192 to 196 show the well-known measuring technology for injection systems. With regard to the HDA measuring principle, it is stated that the course of the injection dm / dt is calculated with the aid of the measuring space volume V of the speed of sound c and the change in the absolute pressure in the chamber dp / dt. The pressure measurement in the measuring room is carried out with a high-precision piezo pressure sensor, which is characterized by a very short response time. The speed of sound is calculated by means of an ultrasonic transducer from the duration of a sound pulse in the measuring volume. The described hydraulic pressure increase method is used in injector development for simultaneous injection history and mass measurement.

The injection mass of single or multiple injections determined in this way by testing should strike the actual injected mass in the internal combustion engine as exactly as possible. To check this, the test medium is emptied onto a weighing device after injection into the HDA. It has been found that in practice, depending on the injection pressure and the temperature in the measuring chamber, differences of up to +/- 5 mg result between the test-technically determined values of the HDA on the one hand and the balance values on the other hand.

An attempt has already been made to multiply the injected mass of test medium determined and calculated by means of the HDA with a correction factor in order to achieve a better agreement with the actual balance values. This correction factor compensating the measurement error is a device-specific calibration factor determined by comparison with the balance values.

It is the object of the present invention to further improve a measuring arrangement and a method for determining the temporal mass flow profile during an injection of a liquid test medium carried out by a fuel injector into a measuring chamber of a hydraulic pressure rise analyzer in such a way that the most accurate possible measurement correction is achieved with simple technical means.

Disclosure of the invention

The object is achieved on the basis of a measuring arrangement according to the preamble of claim 1 in conjunction with its characterizing features. Technically, the object is achieved by claim 7. The respective dependent dependent claims give advantageous Further developments of the invention. With regard to a computer program product, reference is also made to claim 11, and claim 12 indicates a computer-readable medium in this regard.

The invention includes the technical teaching that the evaluation unit of an HDA error-corrects the injected mass of test medium calculated on the basis of the measurement signals of the pressure sensor and of the ultrasound sensor with a first correction factor K ₁ and a second correction factor K ₂ which uses the measurement signal of a temperature sensor in the measurement space wherein the first correction factor K _1, a temperature-dependent volume change of the measuring space of the HDA, the second correction factor K _2, a temperature-dependent pressure change in the measuring chamber error corrected to bring about a pressure and temperature-dependent mass correction.

The advantage of the solution according to the invention lies, in particular, in the fact that a calibration of an HDA for determining a device-specific correction factor via a comparison with balance values is replaced by an error correction, which can be derived purely analytically. It is taken into account that the measuring room of the HDA is not a closed adiabatic system under real measuring conditions, but that both heat inputs and heat discharges are present. Thus, a temperature increase in the test medium within the measuring space leads to an increase in volume of the measuring space. Conversely, an increase in temperature, which acts on sensor elements arranged within the measuring space or the like, leads to a reduction in volume of the measuring space. This is taken into account by the correction factor K ₁ . By the other correction factor K ₂ is taken into account that the injected test medium has an elevated temperature T _inj compared to the temperature of the test medium in the measuring chamber T _HDA and therefore occupies a larger volume than an injected test medium with the same temperature compared to the test medium in the measuring chamber, which in real non-adiabatic system an excessively high pressure rise would be measured.

In order to provide a temperature-constant measuring system which is as temperature-constant as possible, it is proposed that the measuring space of the HDA, which is preferably formed by a cylinder or a sphere, be advantageously equipped with a cooling device. This cooling device can be realized, for example, by cooling channels embedded in the wall through which a cooling medium flows, in order to create temperature conditions as constant as possible. The cooling device can also extend over the region of the end-side measuring chamber cover in order to develop the best possible effect on the internal measuring space.

Preferably, the ultrasonic sensor is arranged on the end face of the measuring chamber opposite the injector or on its lateral surface in order to measure the speed of sound along the axial extent of the measuring space. At this end face of the preferably placement of the ultrasonic sensor, an electronics housing can be connected directly to the cylinder, so that the pressure rise analyzer with integrated evaluation electronics can be realized compactly in one device. The electronics housing preferably houses the signal processing of the measuring signals of the pressure sensor, temperature sensor and the ultrasonic sensor, for which electrical measuring lines run between the said sensors and the evaluation unit.

The evaluation electronics are preferably designed in the form of a software-controlled computer with at least one microprocessor, memory and associated peripherals. This forms the basis for the fact that the method according to the invention for determining the temporal mass flow profile can be implemented as a computer program product which is stored on a computer-readable medium in order to carry out the signal-processing-technical method steps according to the invention.

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

list of figures

• 1 einen schematischen Längsschnitt durch eine Druckanstiegsanalysator (HDA) zur Bestimmung des zeitlichen Massenstromverlaufs während einer von einem Kraftstoffinjektor durchgeführten Einspritzung eines flüssigen Prüfmediums,
• 2 eine schematische graphische Darstellung eines exemplarischen Massenstromverlaufs, und
• 3 einen Ablaufplan einzelner Verfahrensschritte zur Ermittlung einer erfindungsgemäßen messfehlerkorrigierten Masse an eingespritztem Prüfmedium.

It shows:

• 1 a schematic longitudinal section through a pressure rise analyzer (HDA) for determining the time course of mass flow during a fuel injector carried out injection of a liquid test medium,
• 2 a schematic graphical representation of an exemplary mass flow profile, and
• 3 a flowchart of individual process steps for determining a Meßfehlerkorrigierten mass of injected test medium according to the invention.

To 1 The hydraulic pressure increase analyzer (HDA) shown here by way of example consists essentially of one cylinder 1 laying a measuring room on the inside 2 forms. Adjacent to the cylinder 1 For example, the pressure rise analyzer includes an electronics housing part 3 for accommodating an internal electronic evaluation unit 4 ,

In the area of the upper face of the cylinder 1 is a fuel injector to be tested 5 used. It is also to the measuring room 2 a pressure sensor 6 with a measuring range between 0 and 100 bar for measuring the current pressure in the measuring chamber 2 connected.

One at the injector 5 opposite end face of the measuring space 2 arranged ultrasonic sensor 7 is used to measure the speed of sound along the axial extent of the measuring space 2 , During the measurement, the measuring room is 2 filled with a suitable test oil as test medium. Dependent on this is the measured speed of sound.

Furthermore, in the cylinder 1 a temperature sensor 12 used to measure the current temperature of the test oil in the measuring room 2 serves.

After a test cycle, this can be done in the measuring room 2 located test oil via an outlet valve 8th Drain. To achieve a constant temperature as possible, the cylinder 1 a cooling device integrated in the jacket area 9 on. For safety reasons is attached to the measuring room 2 also a pressure relief valve 10 connected, which has an impermissible overpressure in the measuring room 2 dissipates to the environment to a bursting of the cylinder 1 to prevent.

The evaluation electronics 4 is via test leads 11a . 11b . 11c to the pressure sensor 6 , the ultrasonic sensor 7 or the temperature sensor 12 connected and subjected to the input side of the pressure sensor 6 supplied raw signal of the pressure p in the measuring room 2 first a signal amplification and subsequent low-pass filtering. The filtered pressure signal as well as that from the ultrasonic sensor 7 Measured sound velocity c enter as input variables in the following formula I for the calculation of the mass flow curve dm / dt: $$\frac{dm}{dt}=\frac{d}{dt}\left(V\cdot {\displaystyle \underset{p_b}{\overset{p_c\left(t\right)}{\int }}\frac{1}{c^2\left(p.T\right)}dp}\right)$$

The variable V represents the volume of the measuring space 2 , T is the temperature of the test oil in the measuring room 2 , t the time, the term c (p, T) the pressure- and temperature-dependent sound velocity, measured by the ultrasonic sensor 7 , p _{b is} the pressure in the measuring room 2 at the beginning of the injection, p (t) the pressure in the measuring chamber 2 at time t.

It results in a 2 Illustrated exemplary mass flow curve, also called rate curve. The maximum of the mass flow profile is reached at the largest opening cross section of the fuel injector. The area under the rate curve is the metrologically determined injection mass m _raw from the HDA on the basis of the c, p measurement and the formula I above as the basic equation of the HDA assuming an adiabatic system. The following formula II applies: $$m_{rOH}={\displaystyle \underset{t_1}{\overset{t_2}{\int }}\frac{dm}{dt}}$$

In order to determine from the metrologically determined injection mass m _roh the inventively error-corrected injection mass m _HDA , the following formula III applies: $$m_{HDA}=m_{rOH}\cdot {\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102017201877A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}}_1\cdot {\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017201877A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}}_2$$

In this case, the first correction factor K _{1 represents} a temperature-dependent change in volume of the measuring space 2 and the second correction factor K ₂ represents a temperature-dependent pressure change, that is, both of the temperature of the test oil in the measuring chamber 2 as well as on the temperature of the injected test oil dependent pressure change in the measuring chamber 2 , The correction factor K ₂ is derived analytically, whereas the correction factor K _{1 was} derived from measured data and calculated according to the following formula IV: $${\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102017201877A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\frac{b}{T_{HDA}+d}+f$$

The variable T _HDA sets the mean temperature in the measuring room 2 before the injection process, the parameters b and d are constants for the function of K ₁ (T) from adaptation of a nonlinear function to measured data and amount to b = 0.76136 and d = 8.67752 for the previously considered HDA geometries. The parameter f is calculated with the calibration data of each individual HDA, so it is a device-dependent parameter for the function K ₁ (T). For the exemplary measurement arrangement, there is a device-dependent value for f of 1.02081. The second correction factor K _{2 is} calculated according to the following formula V: $${\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017201877A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=1-M\cdot \left(T_{inj}-T_{HDA}\right)$$

Here, the size M is determined fluid-dependent and is considered here as a fluid-dependent correction factor approximately for a pressure range of 50 to 100 bar and a temperature range of 40 to 140 ° C as constant. In an exemplary test oil, M is assumed to be 0.00073783 1 / K for the considered mean pressure in the measurement space and the mean temperature herein before an injection event. The pressure in the measuring room before injection, it is set at 50 bar. T _HDA is the mean temperature in the measuring chamber before an injection process.

For formula V, the temperature T _{inj of} the injected liquid must be measured or calculated. A possible calculation for the approximate determination of T _inj can be analytically derived from the following formula VI: $$T_{inj}=a\cdot p_{rail}+T_{Zulauf}$$

The parameter a is also a liquid-dependent correction factor and is determined as a function of a feed temperature of here 40 ° C for test oil to 0.0521 ° C / bar. The variable p _rail represents the rail pressure in the common rail system. T _inlet is the inlet temperature in the inlet of the high-pressure pump.

The inventive p-T mass correction achieves a significant improvement of the measured injection mass in approximation to the actual balance values.

With regard to 3 the error-corrected injected mass m _HDA according to the invention is then determined on the test medium in the hydraulic pressure rise analyzer as follows:

During an injection process, the pressure p and the temperature T in the measuring space of the HDA is determined. In addition, the speed of sound c along the measuring space of the HDA is also measured. In the context of the subsequent measurement signal processing, first a low-pass filtering TP of the measured pressure signal takes place. Subsequently, the mass flow curve dm / dt is calculated. Integrating this results in the measured injection mass m _raw assuming an adiabatic system. By multiplication with the first correction factor K ₁ , which error-corrects a temperature-dependent change in volume of the measuring space, and the second correction factor K ₂ , which represents a temperature-dependent pressure change in the measuring chamber taking into account fluid-dependent material parameters, the error-corrected injection mass m _{HDA is} calculated from the metrologically determined injection mass m _raw ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008040628 A1 [0003]

Cited non-patent literature

• Prof. Dr.-Ing. Klaus Mollenhauer et. al., VDI book, edition 2007, ISBN: 978-3-540-72164-2 [0006]

Claims (12)

Measuring arrangement for determining the time course of mass flow during an injection of a liquid test medium carried out by a fuel injector (5) into a measuring chamber (2) of a hydraulic pressure rise analyzer (HDA) which has a pressure sensor (6) connected to the measuring space (2) for measuring the actual pressure in Measuring chamber (2), a temperature sensor (12) for measuring the current temperature herein and an also connected to the measuring space (2) ultrasonic sensor (7) for measuring the speed of sound in the measuring chamber (2), and a downstream electronic evaluation unit (4) for calculation the mass (m _HDA ) of the test medium injected as a result of the injection into the measuring chamber (2) taking into account at least one correction factor compensating for a measuring error, characterized in that the evaluation unit (4) as a first correction factor (K ₁ ) a temperature-dependent volume change of the measuring chamber ( 2) as well as a second K correction factor (K ₂ ) includes a temperature-dependent pressure change in the measuring chamber ( ₂ ), whereby the measured based on the measurement signals of the pressure sensor (6) and the ultrasonic sensor (7) injected mass (m _raw ) to test medium is error corrected. Measuring arrangement after Claim 1 , characterized in that the measuring space (2) of the pressure increase analyzer (HDA) cooperates with a cooling device (9). Measuring arrangement after Claim 1 , characterized in that the measuring space (2) is cylindrical or spherical. Measuring arrangement according to one of the preceding claims, characterized in that the ultrasonic sensor (7) on the injector (5) opposite end side of the measuring chamber (2) is arranged to measure the speed of sound along the axial extent (L) of the measuring space (2) , Measuring arrangement according to one of the preceding Claims 1 to 3 , characterized in that the ultrasonic sensor (7) on the lateral surface of the measuring chamber (2) is arranged to measure the speed of sound in the measuring space (2). Measuring arrangement according to one of the preceding claims, characterized in that the evaluation unit (4) is accommodated in an electronics housing part (3) of the pressure rise analyzer (HDA), wherein the electrical connections of the pressure sensor (6), the temperature sensor (12) arranged on the measuring space (2) ) and the ultrasonic sensor (7) via electrical measuring lines (11a, 11b, 11c) with the evaluation unit (4) in the electronic valve housing part (3) are connected. Method for determining the time course of mass flow during an injection of a liquid test medium carried out by a fuel injector (5) into a measuring chamber (2) of a hydraulic pressure rise analyzer (HDA), in which the current pressure in the pressure chamber (2) is connected to the pressure chamber (2) Measuring chamber (2) is measured, via a temperature sensor (12) connected to the measuring chamber (2), the mean temperature in the measuring chamber (2) and via an also on the measuring chamber (2) connected ultrasonic sensor (7) the speed of sound in the measuring chamber (2) is measured , wherein with a downstream electronic evaluation unit (4) in the injection chamber (2) injected mass (m _HDA ) is corrected on the test medium taking into account at least one measurement error compensating correction factor, characterized in that as a first correction factor (K ₁ ) Have a temperature-dependent change in volume of the measuring space (2) d the injection and as a second correction factor (K ₂ ) a temperature-dependent pressure change in the measuring chamber (2) is included, to the injected mass (m _raw ) of test medium measured on the basis of the measuring signals of the pressure sensor (6) and the ultrasonic sensor (7) Correct measurement errors. Method according to Claim 7 , characterized in that the first correction factor (K ₁ ) results in accordance with the following mathematical formula: $$K_1=\frac{b}{T_{HDA}+d}+f$$

Method according to Claim 7 , characterized in that the second correction factor (K ₂ ) results in accordance with the following mathematical formula: $$K_2=1-M\cdot \left(T_{inj}-T_{HDA}\right)$$

Method according to one of the preceding Claims 7 to 9 , characterized in that the measured from the pressure sensor (6) raw signal of the current pressure in the measuring chamber (2) at least via a low-pass filter (TP) is processed as a filtered signal of the evaluation unit (4) for calculating the injected mass (m _HDA ) on Test medium is provided. A computer program product for determining the time course of mass flow during a fuel injector Injection of a liquid test medium into a measuring chamber (2) of a hydraulic pressure rise analyzer (HDA), which is stored on a computer-readable medium and in an evaluation unit (4) according to Claim 1 is operable to the steps of the procedure according to Claim 5 perform. Computer readable medium with a computer program product Claim 11 ,

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