The invention relates to a device for measuring the level of a liquid in a tank of a vehicle. The invention is in particular applicable to a tank for storing fuel or for storing a liquid for cleaning up exhaust gases, such as for example a urea-based solutions such as AdBlue® (registered trademark). The invention also relates to a vehicular or tank comprising such a device.
Vehicular tanks, in particular fuel tanks, generally incorporate a plurality of measuring devices, including a device for measuring the level of a liquid.
One known device for measuring the level of a liquid is based on the use of a segmented capacitive probe. Such a probe comprises a plurality of capacitive segments that are placed above one another at regular intervals. Each segment is formed by interdigitated electrodes. Such a device is for example described in patent document EP 2 657 663. This device has a number of drawbacks, such as for example the fact that the dielectric constant of the liquid has an impact on the measured level. Generally, the dielectric constant of the liquid varies during its use. A second drawback is that the sensitivity and resolution of the sensor depend on the geometry and dimensions of the segments, on the distance between the electrodes and on the area of the electrodes. Thus, with this type of known sensor, it is difficult to obtain a precise measurement of level.
One of the aims of the invention is therefore to provide a device for measuring the level of a liquid that decreases the impact of the dielectric constant of the liquid on the measured level, and that has a higher sensitivity and a better resolution.
Thus, in one particular embodiment of the invention, a device is provided for measuring the level of a liquid in a tank of a vehicle, said device comprising at least one capacitive probe, said capacitive probe comprising a supporting structure supporting at least a plurality of capacitive elements arranged so as to form at least two rows of capacitive elements extending along a longitudinal axis, said at least two rows of capacitive elements being spaced apart from one another along an axis that is transverse to said longitudinal axis. The capacitive elements are such that they are offset along the longitudinal axis with respect to one another from one row to the next.
Thus, a pattern of distribution of the plurality of capacitive elements is proposed, whereby the capacitive elements are offset with respect to one another, from one row to the next, along the longitudinal axis, and whereby each capacitive element is able to generate a capacitance value depending on the level of liquid on the capacitive element. With this pattern of distribution, additional zones for measuring the level of a liquid are created in the space defined between two elements of a given row. The device according to the invention therefore has a high resolution. It will be noted that the resolution of the device for measuring the level of a liquid according to the invention depends on the number of rows of capacitive elements. The higher the number of rows of capacitive elements the better the resolution. For example, in the case where a first row of capacitive elements alone allows a resolution of 4 mm to be achieved, the use of a second row of capacitive elements (in which the capacitive elements are offset along the longitudinal axis with respect to the capacitive elements of the first row) allows a resolution of 2 mm to be obtained; the use of third and fourth rows of capacitive elements allows a resolution of 1 mm to be obtained; etc.
In one particular embodiment, said plurality of capacitive elements may be associated with another plurality of capacitive elements that is arranged in a different pattern of distribution on the supporting structure, such as for example a prior-art pattern of distribution (without offset of the capacitive elements along the longitudinal axis with respect to one another from one row to the next).
A capacitive element comprises at least one excitation electrode and at least one measurement electrode that are separated from each other by an insulating medium, air for example. In one particular embodiment, the capacitive elements may be any geometric shape and may for example be square or round. In another particular embodiment, the capacitive elements may be interdigitated capacitive electrodes.
In one advantageous embodiment, the capacitive probe comprises a supporting structure comprising a first face supporting at least one of said rows of capacitive elements and at least one second face supporting at least one other of said rows of capacitive elements. The rows of capacitive elements are thus advantageously arranged on these at least two faces, but still spaced apart from each other along the longitudinal axis, with the aim of considerably decreasing the width of the supporting structure.
In one particular embodiment, the supporting structure may be a dielectric material, such as for example a glass-fiber-reinforced epoxy resin composite, on which the plurality of capacitive elements, which may be made of copper or any other conductive material, is arranged. These capacitive elements may be fastened to the supporting structure using a printed circuit board (PCB) manufacturing process, which has the advantage of being a manufacturing process that is known and that allows high production at relatively low cost.
In one particular embodiment, the supporting structure may have any geometric shape having two or more faces, such as for example a cubic or pyramidal shape.
Advantageously, at least one section of the supporting structure on which the plurality of capacitive elements is arranged may be protected from chemical attack by the liquid to be measured by virtue of an insulating layer covering said plurality of elements. The insulating layer may be a protective varnish, of a few tens of microns thickness, applied directly to said at least one section of the supporting structure on which the plurality of capacitive elements is arranged. It may also be a plastic of a few hundred microns to several millimeters thickness, overmolded directly on said at least one section of the supporting structure on which the plurality of capacitive elements is arranged. The plastic insulating layer may also be a part that is injection molded separately, into which part the supporting structure may be incorporated. Advantageously, the insulating layer is applied to all the supporting structure on which the capacitive elements are arranged.
Advantageously, the measuring device according to the invention may be surrounded by a protective tube, having at least two apertures in order to let the liquid pass. This tube may be made from (optionally conductive) plastic, for example a plastic from the polyamide category. The protective tube may be a part that is injection molded or extruded separately from the device and into which said device may be incorporated. The protective tube protects the device from mechanical impacts, such as impacts against the walls of the tank for example. It may also be connected to ground, thereby allowing electrostatic and electromagnetic interference to be decreased for the device according to the invention.
In one advantageous embodiment, the device for measuring the level of a liquid in a tank of a vehicle comprises a processing unit configured to:
It is thus proposed to associate a switching threshold with each capacitive element. The switching threshold associated with a capacitive element according to the invention corresponds to a capacitance value that said capacitive element is able to generate. For example, for a capacitive element allowing a capacitance ranging from 0.25 pF to 1.5 pF to be measured, the switching threshold of said capacitive element may be set to a capacitance value of 0.75 pF. If the capacitance value obtained for said capacitive element during a measurement is 0.5 pF, then the processing unit will convert this capacitance value into a binary code value of 0. In contrast, if the obtained capacitance is 1 pF, the processing unit will convert this capacitance value into a binary code value of 1.
In one particular embodiment, each capacitive element is associated with the same switching threshold. In another particular embodiment, each capacitive element is associated with a different switching threshold. In one particularly advantageous embodiment, each capacitive element is associated with a high switching threshold and a low switching threshold. This makes it possible to improve the noise immunity of the device according to the invention. During the use of a vehicle, the capacitive elements are successively dry, covered or wet, this impacting the minimum and maximum capacitance values of these capacitive elements. The use of high and low switching thresholds allows these variations to be overcome.
The at least one switching threshold is defined depending on the type of liquid to be measured and is stored in the memory of the processing unit. The processing unit processes these capacitance measurements using a preset conversion strategy. For example, this strategy (i.e. processing) consists in comparing each of the obtained capacitance values to the preset switching threshold in order to generate a binary code depending on the converted capacitance values. In other words, the processing unit according to the invention is configured to convert the obtained capacitance values into logic states (or binary code values) that define said final binary code. Next, the unit is configured to determine (or compute) a value of the level of the liquid in the tank. For example, this value may be determined by comparing the generated binary code with a pre-recorded comparative code stored in the memory of the processing unit, and which relates a binary code to a given value of the level of the liquid.
Thus, the device according to the invention acts as a discrete-level gauge. In one particular embodiment, the unit may furthermore be configured to generate information relating to the inclination of the vehicle from said (generated) binary code. To this end, this information may be generated by comparing the generated binary code with a pre-recorded comparative code stored in the memory of the processing unit, which relates a binary code to a given vehicle inclination value.
Advantageously, the supporting structure integrates a network of electrical connections that is configured to connect the plurality of capacitive elements to the processing unit. In this way, the electrical connections integrated into the supporting structure are protected from any chemical attack by the liquid to be measured.
A plurality of embodiments of the invention will now be presented, which embodiments are described by way of nonlimiting example in the description of the figures and with reference to the following drawings, in which:
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In this example, the level of the liquid is represented by the dashed line. The capacitive elements that are located below this line have capacitance values higher than the switching threshold associated beforehand with each capacitive element, this leading to a binary code value of 1 for each of these capacitive elements. In contrast, the capacitive elements that are located above this line have capacitance values lower than the switching threshold associated beforehand with each capacitive element, this leading to a binary code value of 0 for each of these capacitive elements. Therefore, the binary code obtained in this example is the following: 1111000000.
Number | Date | Country | Kind |
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1553033 | Apr 2015 | FR | national |
1555806 | Jun 2015 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/057623 | 4/7/2016 | WO | 00 |