Test device for a gas injector

Abstract

Test device (1) for an injector (4), comprising a measuring chamber (2) which can be pressurized with a test gas (3), wherein the wall (2a) of the measuring chamber (2) has a receptacle (2b) for the injector (4) so ​​that it can inject a gas (5) into the measuring chamber (2), further comprising means (6) for directly or indirectly measuring the pressure p in the measuring chamber (2) and means (7) for directly or indirectly measuring the temperature T in the measuring chamber (2), characterized in that it additionally includes an optical measuring device (8, 9, 10) for determining the two- or three-dimensional spatially dependent distribution (n(x,y) or n(x,y,z)) of the refractive index n, and / or a gradient (Vn(x,y) or Vn(x,y,z)) of this distribution (n(x,y) or n(x,y,z)), in at least one two- or three-dimensional subregion. (2c) the measuring chamber (2) is provided, and the optical measuring device (8, 9,10) comprises a light source (8) and a spatially resolved detector (9) and at least one beam path (11) is provided from the light source (8) through the measuring chamber (2) to the spatially resolved detector (9), wherein the spatially resolved detector (9) records an image in the manner of schlieren photography.

Description

[0001] The invention relates to a testing device with which the injection behavior of a gas injector can be studied for the purpose of optimization and functional testing of the same. State of the art

[0002] In vehicle fuel injectors, it is important that a precisely defined quantity of fuel is delivered to a cylinder chamber at a precisely defined time. Therefore, there is a need to accurately record both the actual time of delivery and the quantity of fuel delivered. For testing injectors that inject fuel in liquid form, such a test apparatus is known, for example, from US Pat. No. 8,205,491 B2. The injected fuel causes a pressure increase in a measuring chamber, which is measured with a pressure sensor. The time at which fuel enters the measuring chamber from the injector is recorded with an optical sensor. Further test devices for such injectors are known from US Pat. No. 6,234,002 B1 and WO 2014 / 195326 A1.

[0003] For functional testing of injectors that inject fuel in gaseous form, flow meters based on the Coriolis principle have proven effective. Such devices are known, for example, from EP 2 625 492 B1. The injected gas volume, which can be distributed across various injections per working cycle, is fed into an oscillating measuring tube. This causes the oscillation of the measuring tube to be phase-shifted compared to the state in which no flow is passing through the measuring tube. This phase shift is proportional to the mass flow through the measuring tube.

[0004] Furthermore, DE 103 35 739 A1 discloses a method for determining the quality of an injection nozzle, in which a spray pattern of a medium emerging from the injection nozzle is recorded. US 2011 / 0 239 751 A1 discloses another method and a test system for fuel injectors. Disclosure of the invention

[0005] Within the scope of the invention, a test device for an injector was developed. This test device has a measuring chamber that can be pressurized with a test gas. The pressure of the test gas can be freely selected. This pressure can, for example, correspond to the ambient pressure outside the measuring chamber, but can also be higher. However, it can also be advantageous, for example, to select a test gas pressure that is lower than the ambient pressure. The test gas pressure can, in particular, be up to 0.5 bar lower than the ambient pressure.

[0006] The wall of the measuring chamber has a receptacle for the injector, allowing it to inject a gas into the measuring chamber. This gas can, in particular, be a vehicle fuel. Furthermore, means for directly or indirectly measuring the pressure p in the measuring chamber, as well as means for directly or indirectly measuring the temperature T in the measuring chamber, are provided.

[0007] In particular, the temperature in the measuring chamber can be measured indirectly, for example, using an ultrasonic sensor. Such measurements are often faster than direct measurements, which first require a temperature equilibrium to be established between the gas in the measuring chamber and the sensor. If the pressure p and temperature T in the measuring chamber are known, the injected fuel quantity can be calculated using the ideal gas equation.

[0008] According to the invention, an optical measuring device is additionally provided for determining the two- or three-dimensional location-dependent distribution n(x, y) or n(x, y, z) of the refractive index n, and / or a gradient Vn(x, y) or Vn(x, y, z) of this distribution n(x, y) or n(x, y, z), in at least one two- or three-dimensional sub-region of the measuring chamber.

[0009] It was recognized that in this way the injection quantity, the injection rate (injection quantity per unit of time) and the spray pattern of the injection can be recorded simultaneously. If the injection quantity, the injection rate or the temporal progression of one of these variables does not meet expectations or deviates from the norm within a series of injectors, the next important step is to determine the cause of this deviation. By recording the spray pattern simultaneously with the quantitative recording of the injection process, it is possible to check whether the quantitative deviation is correlated with an anomaly in the spray pattern that occurs at the same time as, or is temporally related to, this deviation. This significantly simplifies the diagnosis of sporadically occurring interference effects that do not occur at regular intervals and are not necessarily reproducible.

[0010] Correlations between quantitative anomalies and anomalies in the spray pattern are difficult to reliably derive if the injection flow and the spray pattern are recorded sequentially. In particular, a sporadically occurring disturbance may then only be evident in one of the two measurements, while in reality, it changes both the injection flow and the spray pattern. Furthermore, it is very difficult to perform the two measurements consecutively under exactly the same boundary conditions. For example, if the injector is moved to a different test bench after the first measurement and then the second measurement is performed, uncertainty arises due to different, test bench-specific boundary conditions.

[0011] According to the invention, the optical measuring device comprises a light source and a spatially resolved detector. At least one beam path is provided from the light source through the measuring chamber to the spatially resolved detector. The spatially resolved detector allows the qualitative information about the beam pattern to be at least partially quantified and thus objectified.

[0012] This applies in particular to a further particularly advantageous embodiment of the invention. In this embodiment, an evaluation unit is provided which is able to at least approximately determine the location-dependent distribution n(x, y) or n(x, y, z) of the refractive index n from the location dependence I(x, z) of the intensity I and / or from the location dependence φ (x, z) of the phase φ of the light of the beam path registered by the detector. Information about the refractive index n along the entire path that the light striking the detector at this location has traversed within the measuring chamber is superimposed on the location dependence I(x, z) of the intensity I and / or on the location dependence φ (x, z) of the phase φ registered by the detector. Since the physical mechanism for this superposition is known, the distribution of the refractive index n can be calculated back from the location dependence.

[0013] The gas blown from the injector into the measuring chamber creates a contrast in the refractive index n in two different ways: If the injected gas is materially different from the test gas in the measuring chamber, it usually has a different refractive index n than the test gas under otherwise identical physical conditions. In addition, the refractive index n of gases is pressure-dependent, and at least at the moment of injection, the gas blown from the injector has a different pressure p than the test gas in the measuring chamber. This results in a contrast in the refractive index n even if the gas blown from the injector is materially identical to the test gas in the measuring chamber. In the context of the invention, the term refractive index n is not limited to its real part, but also includes its imaginary part, which is responsible for the absorption of light from the light source.

[0014] The optical measuring device can particularly take advantage of the fact that the light path from the light source to the spatially resolved detector is influenced by gradients ∇n of the refractive index n, which can be caused, for example, by local pressure and / or density differences. For example, the spatially resolved detector can capture an image similar to schlieren photography.

[0015] In a further particularly advantageous embodiment of the invention, the light source emits a parallel light beam. The light source can be a laser, for example. However, a parallel light beam can also be achieved, for example, by a point light source, such as a lamp, with a downstream collimator. After passing through the measuring chamber, the light beam is focused by a concentrator onto an aperture arranged between the concentrator and the detector, with the exception of a portion that was deflected by the gas in the measuring chamber. During operation of the test device, the gas in the measuring chamber at the time of measurement is a mixture of the test gas and the gas that was blown into the measuring chamber from the injector.

[0016] Depending on the application, the contrast in the refractive index caused by the injection of gas from the injector can be very low. The accuracy and resolution with which this low contrast is detected can be improved, for example, by adjusting the apparatus before injection so that virtually all of the light from the light source is focused on the aperture and does not reach the detector. The detector then initially registers a signal close to zero. The deflection in its signal from the beginning of the injection process is then almost entirely attributable to the change in the refractive index n caused by the injection process.

[0017] In principle, both the light source and the detector can be integrated into the measuring chamber. However, it is advantageous to locate both the light source and the detector outside the measuring chamber. This simplifies the design and adjustment of the beam path, and the optical surfaces of both the light source and the detector do not come into contact with the test gas or the gas injected from the injector.

[0018] In one embodiment of the invention, the wall of the measuring chamber has at least a first transparent area for the entry of the beam path and at least a second transparent area for the exit of the beam path. These transparent areas can be designed as windows, for example. Such windows should withstand chamber pressures of up to 150 bar, and the measuring chamber should remain tightly closed to prevent the measurement result for the pressure p in the measuring chamber from being falsified.

[0019] In an alternative embodiment of the invention, the wall of the measuring chamber has at least one transparent region for the entry and exit of the beam path. At the same time, at least one region opposite this transparent region on an inner circumference of the wall of the measuring chamber is specularly reflective for the light of the beam path. Only a single opening is then required to create a transparent region (e.g., a window). At the same time, the beam path traverses the volume of the measuring chamber twice, so that the same change in the refractive index n leads to a stronger change in the signal at the detector. The specularly reflective region can be introduced specifically for this purpose on the inner circumference of the wall of the measuring chamber. However, essentially the same effect can be achieved if the wall of the measuring chamber is manufactured from the outset so that its inner circumference is specularly reflective.

[0020] Optical measurement data acquisition with the detector can be performed at least as quickly as the measurement of temperature T and pressure p in the measuring chamber. This also allows time-resolved recording of the injection quantity or injection rate, simultaneously with a time-resolved recording of the refractive index distribution. Overall, the lead time for injector development can be significantly shortened, and the associated costs for machinery, equipment, and facilities (MAE) can be reduced. The test fixture can also be used for quality assurance during production or for functional testing. Other injector characteristics can also be recorded, such as its injection angle or closing behavior.

[0021] In a further particularly advantageous embodiment of the invention, the detector has an internal memory for a time series of measurement data, which is overwritten with the measurement data of the next similar time series after the end of this time series. This internal memory can be a ring buffer, for example. Since injection processes of injectors for vehicle applications occur very quickly, the detector will typically be designed to record a sufficiently large number of measurement data per second in order to be able to separate the various phases of the injection process from one another. In particular, if the spatial dependence I(x,z) or φ (x,z) of the intensity I or phase φ is recorded simultaneously with very high spatial resolution, very large amounts of data are generated.However, especially when diagnosing sporadic errors and during serial injector testing, often only those measurement data relating to a specific fault detected during the quantitative measurement of the injection flow are relevant for further analysis. In this respect, the continuous overwriting of the internal memory enables efficient compression of the large volume of raw data.

[0022] If a fault is detected in the quantitative injection behavior, the contents of the detector's internal memory can be read and saved elsewhere, such as on a hard drive. This can then be used for further diagnosis of the fault. However, the detector can also be triggered to record measurement data only when a fault occurs.

[0023] Therefore, in a further particularly advantageous embodiment of the invention, the detector has a control input via which the recording of measurement data can be initiated and / or the overwriting of measurement data with newer measurement data can be stopped.

[0024] Advantageously, the evaluation unit also receives as inputs the measured values ​​for the temperature T and the pressure p in the measuring chamber, which are recorded simultaneously with the light of the beam path registered by the detector. A fault can then be detected directly in the evaluation unit and, for example, the recording or saving of optical measurement data can be initiated. For this purpose, in a further particularly advantageous embodiment of the invention, the evaluation unit is designed to identify a deviation of the temperature T and / or the pressure p in the measuring chamber and / or a derivative dp / dt of the pressure p in the measuring chamber after time t, from a respective normal value. This derivative dp / dt of the pressure p after time t can be of first or higher order. Based on this derivative, anomalies with regard to the injection rate in particular can be detected and studied.

[0025] The detector can, in particular, be a camera module that records the spatial dependence of the intensity and / or phase in image form. In particular, a phase contrast can be converted into an intensity contrast using additional optical means. Image acquisition can occur either on specific initiation, for example, by the evaluation unit, or continuously in rapid succession (high-speed camera).

[0026] Depending on the application, optical observation through the beam path can be essentially perpendicular to the direction in which the injector injects the gas into the measuring chamber. However, the direction of the beam path can also be essentially opposite to the direction in which the gas exits the injector, so that the beam path points toward the injector.

[0027] Further measures improving the invention are presented in more detail below together with the description of the preferred embodiments of the invention with reference to figures. Examples of implementation

[0028] It shows: Fig. 1 Embodiment of the testing device 1 according to the invention with a beam path 11 that passes through the measuring chamber 2 once. Fig. 2 Embodiment of the testing device 1 according to the invention with a beam path 11 that passes through the measuring chamber 2 twice. Fig. 3 Improvement of the sensitivity with a parallel light beam 11a, which is imaged by a concentrator 12 onto an aperture 13.

[0029] After Fig. 1, the wall 2a of the measuring chamber 2 has a receptacle 2b for the injector 4. The injector 4 projects with its injection opening 4a into the measuring chamber 2. The measuring chamber 2 is filled with a test gas 3. The injector 4 is supplied with fuel from a reservoir 100 via a high-pressure pump 101, which it can inject into the measuring chamber 2 as gas 5. The temperature T and the pressure p of the fuel before entering the injector 4 are detected by a temperature sensor 102 and a pressure sensor 103, respectively. The pressure p in the measuring chamber 2 is detected by a pressure sensor 6 and the temperature T by a temperature sensor 7.

[0030] When the injector 4 injects gas 5, which is a gaseous fuel, into the measuring chamber 2, the location-dependent composition of the gas present in the measuring chamber 2 changes. Due to the injection from the injector 4, the test gas 3 is temporarily at least partially displaced by the injected gas 5 in a certain spatial area around the injection opening 4a of the injector 4. This jet pattern is recorded by the optical measuring device 8, 9, 10 provided according to the invention, which comprises a light source 8, a detector 9, and an evaluation unit 10.

[0031] For this purpose, the light source 8 emits light which, along a beam path 11, initially enters the measuring chamber 2 through a first window 2d. The light passes through both areas where the test gas 3 predominates and areas where the gas 5 blown in from the injector 4 predominates. At each location the light passes through, its intensity and / or phase are influenced by the respective prevailing local refractive index n(x, y, z). The light exits the measuring chamber 2 again through a second window 2e and reaches the spatially resolved detector 9. A change in the distribution n(x, y, z) of the refractive index n in the measuring chamber 2 now changes, on the one hand, the intensity I and / or the phase φ with which the light strikes the detector 9. On the other hand, the light may also have been deflected by this change and strike the detector 9 at a different location.The evaluation unit 10, which receives the measurement data of the detector 9 via an output 9b of the detector 9, combines these changes and calculates the location-dependent distribution n(x, y) or n(x, y, z) of the refractive index n at least in a sub-area 2c of the measuring chamber 2.

[0032] Detector 9 is a high-speed camera, thus recording the phase or intensity distribution on its effective surface in very rapid succession as images. These measurement data are stored in an internal memory 9c of detector 9 and read out by evaluation unit 10 only when needed.

[0033] The evaluation unit 10 reports this requirement to the detector 9 via the control input 9a.

[0034] The evaluation unit 10 also receives as inputs the pressure p in the measuring chamber 2 measured by the pressure sensor 6, the temperature T in the measuring chamber 2 measured by the temperature sensor 7, the temperature T of the fuel before entering the injector 4 measured by the temperature sensor 102, and the pressure p of the fuel before entering the injector 4 measured by the pressure sensor 103. The evaluation unit 10 is thus capable of fully characterizing the quantitative injection behavior of the injector 4 (injection quantity, injection profile, injection rate). If a disturbance is detected in the quantitative injection behavior, the saving of optical measurement data for further evaluation is triggered via the control input 9a of the detector 9.

[0035] The Fig. The embodiment shown in Figure 2 differs from that shown in Fig. 1 in that the measuring chamber 2 only has a first window 2d. The beam path 11 emanating from the light source 8 leads through this first window 2d into the measuring chamber 2 and traverses it to a specularly reflecting region 2f on an inner circumference of the wall 2a of the measuring chamber 2, which is opposite the first window 2d. Here, the beam path 11 is reflected back through the interior of the measuring chamber 2, so that it exits again from the first window 2d. The light of the beam path 11 reaches, analogously to the embodiment according to Fig. 1, the detector 9 and is evaluated.

[0036] In the embodiments according to the Fig. 1 and Fig. 2, the beam path 11 runs essentially perpendicular to the direction in which the gas 5 exits the injection opening 4a of the injector 4. The basic measuring principle remains unchanged if the beam path 11 is rotated 90° clockwise so that it enters the underside of the measuring chamber 2 and points towards the injector 4.

[0037] Fig. Figure 3 illustrates how the contrast in the optical measurement data can be increased. The light source 8 emits a parallel light beam 11a, which is analogous to Fig.1 passes through the measuring chamber 2 via the first window 2d and the second window 2e. The light beam is then focused by a concentrator 12, which is designed here as a lens, onto an aperture 13 arranged between this concentrator 12 and the detector 9. The majority of the light therefore no longer reaches the detector 9. Only that portion 11b of the light that was deflected by a change in the refractive index distribution n(x,z) or n(x,y,z) in the measuring chamber 2 is deflected as beam 11c around the aperture 13 and reaches the detector 9. The optical setup can, for example, be adjusted to a zero signal before injection, so that the full dynamic range of the detector 9 is available for changes in the signal due to the injection process.

Claims

[1] Test device (1) for an injector (4), comprising a measuring chamber (2) which can be supplied with a test gas (3), wherein the wall (2a) of the measuring chamber (2) has a receptacle (2b) for the injector (4) so ​​that it can blow a gas (5) into the measuring chamber (2), further comprising means (6) for directly or indirectly measuring the pressure p in the measuring chamber (2) and means (7) for directly or indirectly measuring the temperature T in the measuring chamber (2), characterized bythat an optical measuring device (8, 9, 10) for determining the two- or three-dimensional location-dependent distribution (n(x,y) or n(x,y,z)) of the refractive index n, and / or a gradient (Vn(x,y) or Vn(x,y,z)) of this distribution (n(x,y) or n(x,y,z)), is additionally provided in at least one two- or three-dimensional sub-region (2c) of the measuring chamber (2), and the optical measuring device (8, 9, 10) has a light source (8) and a spatially resolved detector (9) and at least one beam path (11) is provided from the light source (8) through the measuring chamber (2) to the spatially resolved detector (9), wherein the spatially resolved detector (9) records an image in the manner of schlieren photography. [2] Test device (1) according to claim 1, characterized bythat an evaluation unit (10) is provided which is able to determine at least approximately the location-dependent distribution (n(x,y) or n(x,y,z)) of the refractive index n from the location dependence I(x,z) of the intensity I and / or from the location dependence φ(x,z) of the phase φ of the light of the beam path (11) registered by the detector (9). [3] Test device (1) according to one of claims 1 or 2, characterized by that the light source (8) emits a parallel light beam (11a) and that a concentrator (12) is provided which focuses this light beam (11a) after passing through the measuring chamber (2) onto a diaphragm (13) arranged between the concentrator (12) and the detector (9), with the exception of a portion (11c) which was deflected by the gas (3, 5) in the measuring chamber (2). [4] Test device (1) according to one of claims 1 to 3, characterized by that both the light source (8) and the detector (9) are arranged outside the measuring chamber (2). [5] Test device (1) according to claim 4, characterized by that the wall (2a) of the measuring chamber (2) has at least a first transparent area (2d) for the entry of the beam path (11) and at least a second transparent area (2e) for the exit of the beam path (11). [6] Test device (1) according to claim 4, characterized by that the wall (2a) of the measuring chamber (2) has at least one transparent area (2d) for the entry and exit of the beam path (11) and that at least one area (2f) opposite this transparent area on an inner circumference of the wall (2a) of the measuring chamber (2) is specularly reflective for the light of the beam path (11). [7] Test device (1) according to one of claims 1 to 6, characterized bythat the detector (9) has an internal memory (9c) for a time series of measurement data, which is overwritten with the measurement data of the next similar time series after the end of this time series. [8] Test device (1) according to one of claims 1 to 7, characterized by that the detector (9) has a control input (9a) via which the recording of measurement data can be initiated and / or the overwriting of measurement data with newer measurement data can be stopped. [9] Test device (1) according to one of claims 2 to 8, characterized by that the evaluation unit (10) additionally receives as inputs the measured values ​​for the temperature T and the pressure p in the measuring chamber (2) recorded simultaneously with the light of the beam path (11) registered by the detector (9). [10] Test device (1) according to claim 9, characterized bythat the evaluation unit (10) is designed to identify a deviation of the temperature T, and / or the pressure p in the measuring chamber (2), and / or a derivative dp / dt of the pressure p in the measuring chamber (2) after the time t, from a respective normal value.

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