Fuel gauge and gauging system in an aircraft tank

Abstract

One aspect of the invention relates to an aircraft fuel gauge (20) intended to be located inside an aircraft fuel tank (10), the fuel gauge (20) being configured to form at least one capacitor (C1) with fuel in the fuel tank (10), the fuel acting as the dielectric of the capacitor (C1), the fuel gauge (20) comprising at least one memory (212) and a microprocessor (211), the microprocessor (211) being configured to: Convert (51) a measured analog value of the capacitor's capacitance into a digital capacitance value, Calculate (52) a fuel level in the fuel tank (10), from the digital capacitance value and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20), Store (53) the calculated fuel level in the memory of the fuel gauge (20), Transmit (54) the calculated fuel level in a digital signal,The calculated fuel height, to a computer. Figure to be published with the abbreviation: Figure 2,

Description

Title of the invention: Fuel gauge and gauging system in an aircraft tank TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of aeronautics.

[0002] The present invention relates to an analog-to-digital conversion device for sensor data in a fluid tank of a vehicle and in particular, without limitation, for fuel gauging data in an aircraft tank. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Monitoring the fuel content in an aircraft's tank is of great importance during flight. It is therefore necessary to be able to track the quantity and density of the fuel in the tank in real time during flight with a high degree of accuracy.

[0004] For this purpose, it is known to install suitable sensors, such as gauges, densimeters and / or thermometers, in fuel tanks. Such sensors are connected to measuring electronics, located outside the tank, via a harness extending through a wall of the tank.

[0005] However, such a fuel tank constitutes a particularly difficult environment, forming in particular an explosive atmosphere due to fuel vapors, which leads to significant constraints in the choice of the type of sensors as well as their functionalities and their control.

[0006] Usually, these sensors are of the analog and passive type, excited at low powers, so as not to risk having a component that could overheat or, in case of fault, generate a spark.

[0007] However, they require the use of a harness very well protected by electrostatic shielding, with a highly sophisticated design and complex routing to minimize capacitances interfering with the main measurement acquisition. This is the main known drawback of this type of gauging. It also requires a fairly large number of wires with point-to-point excitation of the sensors, as well as a common shielded link for measurement from the computer.

[0008] For these reasons, known sensors incorporate capacitance-to-digital converters (also called CDCs), mounted directly on the gauge body. These CDCs obtain the capacitance of the capacitor formed by the gauge and the fuel, convert it into a digital signal, and transmit it in digital format to the computer located outside the tank.

[0009] Digital gauging has the advantage of directly converting capacitance values ​​in situ, which makes it possible to eliminate parasitic capacitances (related, among other things, to the wiring between the gauge and the computer) or other disturbances to obtain increased accuracy.

[0010] However, it does not solve the problems of increased dispersion of fuel characteristics of importance for gauging, severe environmental constraints in the tank, and insufficient maintenance data.

[0011] First, the arrival of sustainable aviation fuel (SAF) is disrupting historical gauging strategies, whereas fuel properties were previously stable and based on the use of the most common fuel, Jet Al kerosene. Indeed, the gradual introduction of SAF as a replacement for or supplement to fossil kerosene of the JET Al grade leads to a modification of the fuel's important characteristics with regard to the accuracy of fuel quantity measurement, namely the dielectric constant and the fuel's density as a function of its temperature.

[0012] The disparity of possible fuels within an aircraft leads to errors due to the approximation resulting from the extrapolation of a fuel height based on a capacity measurement and the use of the typical dielectric constant of the single JET Al for the entire aircraft.

[0013] It has been proposed to correct each measurement using processing algorithms in the gauging calculator, but this leads to complicating the method of determining the quantity and therefore the demonstrations of gauging accuracy, with risks of implementation errors, in non-nominal cases for example.

[0014] Furthermore, the fuel gauges are subjected to a harsh environment, consisting of aircraft structural tanks: • The beach and temperature variations are significant there, • The permanent presence of humidity due to the condensation of water vapor entering through the vents during descent, • Potential fungal and bacterial contamination at the air-fuel interface in the event of improper drainage.

[0015] Capacitive gauges are sensitive to parasitic capacitances at the connection terminals and harnesses. These parasitic capacitances can be generated by the above conditions, for example through corrosion at the connections. The resulting capacitance faults can be permanent but are often transient, for example when temperature or vibration plays a role in the occurrence of the fault.

[0016] Capacity faults generally induce undesirable cockpit effects such as incorrect fuel quantities exceeding nominal accuracy, or even false alarms. To this end, the gauge computers continuously provide gauge capacity information to the avionics.

[0017] This information can be used by the aircraft maintenance systems to confirm a gauge / harness fault before opening the tank and removing the gauge or harness suspected of being faulty.

[0018] The gauge is then sent for maintenance to a repair shop, where a visual inspection followed by a functional test is performed at laboratory temperature, in accordance with the gauge's maintenance manual. This test may consist of measuring the gauge's capacity in air, and then measuring it when fully immersed in a fuel with a known dielectric constant. If the measured capacity values ​​are as expected, the gauge is declared fit for service and returned to the customer. It will be recorded by customer service under the category "No Fault Found".

[0019] In the case of intermittent failures, this process proves insufficient to trap parasitic capacity faults. Even though the aircraft's centralized maintenance computers are generally capable of recording the capacity history seen by this gauge when it was installed in the aircraft, as well as important parameters such as, for example, the fuel temperature history in the tank, this information is not, or rarely, transmitted to the gauge repair shop, making the diagnosis of this type of fault laborious, if not impossible.

[0020] There is therefore a need to propose a digital gauging method that does not present the disadvantages of the state of the art. Summary of the invention

[0021] The invention offers a solution to the problems mentioned above, by allowing digital gauging directly at the gauge level and therefore at the capacity measurement level, and easier maintenance by having the ability to store measurements and data related to these measurements directly at the gauge level.

[0022] Thus, the invention relates to an aircraft fuel gauge intended to be located inside an aircraft fuel tank, the fuel gauge being configured to form at least one capacitor with fuel in the tank, the fuel acting as the dielectric of the capacitor, the fuel gauge comprising at least one memory and one microprocessor, the microprocessor being configured to: • Convert a measured analog value of capacitor capacitance into a digital capacitance value, • Calculate the fuel level in the tank, based on the numerical value of the capacity and a predetermined dielectric constant of the fuel stored in the fuel gauge's memory. • Store the calculated fuel level in the fuel gauge's memory, • Transmit, in a digital signal, the calculated fuel height to a computing computer.

[0023] Thanks to the invention, it is possible to obtain high reliability in fuel measurement by calculating the fuel level directly in the tank and by the gauge, which includes a microprocessor. This allows a reliable measurement to be sent to a computer external to the tank, thus facilitating the management of multiple measuring gauges when the aircraft's gauging system includes several gauges and the computer manages these multiple gauges.

[0024] Furthermore, the invention makes it possible to improve the maintenance of fuel gauges, by giving the maintenance operator access to the data calculated by each gauge, making it possible to identify a possible anomaly of the gauge, without having to test it, eliminating at the same time the problem of the absence of reproduction of the anomaly of the gauge during the test, linked to an intermittency of the anomaly.

[0025] In addition to the characteristics just mentioned in the preceding paragraph, the gauge according to an aspect of the invention may have one or more complementary characteristics from among the following, considered individually or according to all technically possible combinations.

[0026] In one embodiment, the memory is a non-volatile memory.

[0027] In one embodiment, the memory is an erasable read-only memory electrically and programmable "EEPROM".

[0028] Another aspect of the invention relates to an aircraft fuel gauging system comprising: • An aircraft fuel tank, • At least one fuel gauge according to the invention located inside the fuel tank, • A computing computer included in the aircraft and located outside the fuel tank, configured to: • Receive the digital signal including the calculated fuel level, • Calculate, from the fuel height and a predetermined tank geometry, a quantity of fuel in the tank.

[0029] In addition to the characteristics just mentioned in the preceding paragraph, the system according to one aspect of the invention may have one or more complementary characteristics from among the following, considered individually or according to all technically possible combinations.

[0030] In one embodiment, the system further includes a thermometer inside the fuel tank.

[0031] Another aspect of the invention relates to an aircraft comprising the system according to the invention.

[0032] Another aspect of the invention relates to a method for measuring the quantity of fuel implemented by a system according to the invention, the method comprising: • Convert, via the fuel gauge microprocessor, a measured analog value of capacitor capacitance into a digital capacitance value, • Calculate, using the fuel gauge microprocessor, the fuel level in the tank, based on the numerical value of the capacity and a predetermined dielectric constant of the fuel stored in the fuel gauge's memory. • Store the calculated fuel level in the fuel gauge's memory, • Transmit, in a digital signal, the calculated fuel level to a computing computer, • Receive, via the computing computer, the digital signal including the calculated fuel level, • Calculate, using the computer, from the fuel height and a predetermined geometry of the tank, a quantity of fuel in the tank.

[0033] In another embodiment of the process, the predetermined dielectric constant is calculated by: • Obtaining a temperature reading from the temperature sensor, • Calculation of the predetermined dielectric constant from a dielectric constant of the fuel and the temperature obtained.

[0034] In one embodiment, the method further comprises: • Store, in the fuel gauge memory, a data history including at least one of the following data: capacity, capacity standard deviation over a given period, fuel temperature, predetermined dielectric constant, calculated dielectric constant.

[0035] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0036] The figures are presented for illustrative purposes only and are in no way limiting of the invention. • Figure 1 shows a schematic representation of a system comprising a gauge according to the invention, • Figure 2 shows a schematic representation of a gauge according to the invention, • Figure 3 shows a schematic representation of a system comprising a plurality of gauges according to the invention, • Figure 4 shows a schematic representation of a gauging process fuel according to the invention, • Figure 5 shows a schematic representation of a capacitor of fuel gauge according to the invention, • Figure 6 shows charts for determining a dielectric constant of aircraft fuel depending on fuel temperature. DETAILED DESCRIPTION

[0037] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0038] Figure 1 shows a schematic representation of an SI system comprising a gauge 20 according to the invention. The gauge 20 according to the invention makes it possible to obtain a digital measurement of the fluid height in the fluid reservoir in which it is placed.

[0039] The SI system represented in [Fig.1] comprises a tank 10, a gauge 20 according to the invention, a computing computer 30 and an electrical harness 40, connecting the computing computer 30 to the gauge 20.

[0040] The tank 10 comprises walls defining a substantially closed internal space containing fuel. The density of the fuel is likely to vary depending on altitude, temperature and / or the filling level.

[0041] At least a portion of the gauge 20 forms a capacitor Cl with the fuel acting as a dielectric. For this purpose, the gauge 20 comprises a first electrode and a second electrode, for example, cylindrical, concentric, and arranged vertically. In particular, the first electrode may be an external electrode and the second electrode an internal electrode. The first and second electrodes define an annular space between them in which the fuel rises during refueling and falls during consumption. The fuel level in the annular space thus modifies the capacitance value of the capacitor Cl. In particular, the capacitance of the capacitor Cl varies linearly with the fuel level in the internal space.

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] The capacitor Cl provides an analog capacitance measurement at its terminals, i.e., at its electrodes. The gauge 20 further includes electronics 21 adapted to connect to the terminals of the capacitor Cl, preferably reversibly, i.e., with a removable connection means. For example, the gauge 20 includes two connection means, each adapted to connect to one of the two electrodes of the capacitor Cl. Removable connection means are, for example, screws. The removable connection means are connected to the electronics 21 via connecting means, for example, sheathed electrical cables 22a and 22b shown in [Fig. 2]. The electronics 21 include a microprocessor 211 and a memory 212. Thus, the gauge 20 includes at least the microprocessor 211 and the memory 212, which stores instructions that, when executed by the microprocessor 211, cause the microprocessor 211 to implement the step associated with those instructions. Therefore, when an action is performed by the microprocessor 211 or the gauge 20, the microprocessor 211 of the gauge 20 executes instructions stored in memory 212 or in another memory of the gauge. The microprocessor 211 is configured to perform part of the gauging process according to the invention. Preferably, the memory 212 is a non-volatile memory. Even more preferably, the memory 212 is an electrically erasable and programmable read-only memory of the "EEPROM" type. The gauging method 5 according to the invention is schematically represented in [Fig. 4]. This method 5 comprises at least five steps 51 to 55. A first step 51 is performed by the microprocessor 211 of the gauge 20 and is a step of converting a measured analog value of the capacitance of capacitor Cl into a digital capacitance value. For this, the microprocessor 211, being electrically connected to capacitor 21, receives the measured analog capacitance and then converts it into a digital value. In a preferred embodiment, this first digital capacitance value is stored in memory 212. The process 5 includes a step 52 for calculating the fuel level in the tank, based on the numerical value of the capacity and a predetermined dielectric constant of the fuel stored in the memory 212 of the fuel gauge 20. This step 52 is performed by the microprocessor 211 directly in the tank 10, thus providing a reliable measurement of the fuel level, corrected using the predetermined dielectric constant value. At step 52, the fuel level can be obtained using the following formula: _ * nP~ (KrA) a

[0049] With Hp the height of the fuel-covered probe, C the capacitance measured by the capacitor Cl when immersed in the fuel, Cv the capacitance of the capacitor Cl when empty (not immersed in fuel), Kf the dielectric constant of the fuel, and a a constant depending on the shape of the capacitor Cl. For example, for a capacitor Cl such as that shown in [Fig. 5] showing a schematic representation of a cylindrical fuel-gauging capacitor Cl, with a concentric cylindrical inner and outer electrode, the constant a is calculated as follows:

[0050] _ ® — I ( Ro 4

[0051] With Eo the permittivity of free space approximately equal to 8.85, Ro the radius of the external cylindrical electrode and Ri the radius of the internal cylindrical electrode.

[0052] The fuel level in the tank 10 is determined by means of the gauge 20, which is fixed to the bottom of the tank. Thus, when the tank 10 is empty of fuel, the gauge 20 measures a fuel level of zero. When the tank 10 contains fuel, the level measured by the gauge 20 corresponds to its immersion level in the fuel. This immersion level is the fuel level in the The fuel level in tank 10 is measured from zero height, that is, from the bottom of tank 10. Thus, the immersion height of gauge 20 is approximately equal to the fuel level in tank 10, measured from the bottom of tank 10. When the fuel tank does not have a flat bottom, several gauges 20 may be present and measure different fuel levels. This point will be explained later in the description with reference to [Fig. 3].

[0053] The dielectric constant of the fuel can be obtained in several ways. The first, and simplest, method is to store a fixed dielectric constant in the memory 212 of the gauge 20. In this case, it is said to be "predetermined" because it is determined, prior to the height calculation, for example, by an operator. A second method of obtaining a dielectric constant, advantageous because it allows adaptation to the fuel temperature and the fuel in the tank 10, involves calculating this dielectric constant from a temperature measurement and / or a measurement obtained from a compensator. The calculation of this dielectric constant can be performed using publicly available charts (for example, CRC 663 from the "Handbook of Aviation Fuel Properties").These charts give the value of the dielectric constant as a function of temperature for each fuel (for example, for the following fuels: JP-10, JP-8, Jet A, Jet Al...). For example, such charts are shown in [Fig. 6]. In the invention, it is possible to use the line corresponding to the... Jet Al from [Fig. 6] can be used to determine the fuel's dielectric constant from the temperature. Jet Al is a fuel used for most commercial flights. It is also possible to use the line for any other fuel, provided it corresponds to the fuel in tank 10.

[0054] A compensator is a reference gauge contained within the tank 10 and fully immersed in the fuel of the tank 10. It allows the calculation of the fuel's dielectric constant because the immersion depth of the compensator is known, its immersion depth being the height of the compensator itself. Thus, the calculated dielectric constant can be obtained using the formula:

[0055] (C-Cv^a kf~ hp

[0056] The method 5 includes a step 53 for storing the fuel level calculated in step 52 in the memory 212 of the fuel gauge 21. This storage step is initiated by the microprocessor 211. Step 53 allows access to the calculated levels during probe maintenance, thus enabling the determination of the origin of a probe anomaly and its time of occurrence. In a preferred embodiment, at least one other metric or data point is stored in the memory. The stored data is at least one of the following: the measured capacitance of capacitor Cl, the standard deviation of the measured capacitance of capacitor Cl over a given period, the fuel temperature measured by the temperature probe when present, the predetermined dielectric constant, or the calculated dielectric constant.

[0057] The method 5 then includes a step 54 of transmitting, in a digital signal, the fuel level calculated in step 52 and stored in step 53 to the external computing computer 30 located outside the tank 10. This step includes transforming the calculated digital level data into a digital signal by encoding. For example, such encoding includes modulation. The signal is then transmitted to the external computing computer 30 via the electrical harness 40, which connects the gauge 20 to the computer 30.

[0058] The computing unit 30 is external to the tank, that is, it is not contained within the tank's enclosure. The computing unit 30 comprises at least one processor and memory that stores instructions which, when executed by the processor, cause the processor to carry out the step associated with those instructions. Thus, when an action is performed by the computing unit 30 or its processor, the processor of the computing unit 30 executes instructions stored in memory.

[0059] The computing computer is configured to implement steps 55 and 56 of process 5.

[0060] In a step 55, the calculation computer 30 receives the digital signal comprising the fuel level calculated by the gauge 20, possibly corrected by the dielectric constant when calculated. This reception step is possible because the calculation computer 30 includes at least one communication module, for example, an electrical connection or a network module, connected to the gauge. This communication module also allows the calculation computer 30 to control the gauge 20, for example, to request a fuel level. Alternatively, the gauge 20 can be configured to periodically transmit the calculated fuel level.

[0061] In step 56, the computing computer 30 calculates the quantity of fuel in the tank 10. To do this, the computing computer is aware of the geometry of the tank 10 and uses the received fuel level data to obtain the quantity of fuel in the tank 10. The computing computer 30 may, for example, be aware of the tank's geometry because it is predetermined and stored in memory, for example, in the memory of the computing computer 30 or in an accessible database. For example, the geometry of the tank 10 may be obtained by using a lookup table between an identifier of the gauge 20 from which the digital signal received in step 55 originates and a geometry of the tank 10 in which the gauge 20 is located.

[0062] In a preferred embodiment of the system according to the invention, schematically represented in [Fig. 3], the tank 10 comprises a plurality of gauges 20. Each gauge 20 of the plurality of gauges 20 is addressable by the computing computer 30 independently of the others, which allows the computing computer 30 to reconstruct an accurate geometry of the tank 10 and its various fuel levels, even when the bottom of the tank 10 is not flat or when the bottom of the tank 10 has different heights. Furthermore, this allows the computing computer 30 to perform a consistency check between the fuel levels received from the different gauges 20, adding an additional level of security to the invention.

Claims

Demands

1. An aircraft fuel gauge (20) intended to be located inside an aircraft fuel tank (10), the fuel gauge (20) being configured to form at least one capacitor (Cl) with fuel in the fuel tank (10), the fuel acting as the dielectric of the capacitor (Cl), the fuel gauge (20) comprising at least one memory (212) and a microprocessor (211), the microprocessor (211) being configured to: - Convert (51) a measured analog value of the capacitor's capacitance into a digital capacitance value, - Calculate (52) a fuel height in the fuel tank (10), from the digital capacitance value and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20), - Store (53), in the memory of the fuel gauge (20), the calculated fuel height, - Transmit (54), in a digital signal,the calculated fuel level, using a computer.

2. Aircraft fuel gauge (20) according to claim 1 wherein the memory (212) is a non-volatile memory.

3. Aircraft fuel gauging system (IS) comprising: - An aircraft fuel tank (10), - At least one fuel gauge (20) according to any one of the preceding claims located inside the fuel tank (10), - A computing computer (30) included in the aircraft and located outside the fuel tank (10), configured to: • Receive (55) the digital signal including the calculated fuel height, • Calculate (56), from the fuel height and a predetermined geometry of the fuel tank (10), a quantity of fuel in the fuel tank (10).

4. System according to claim 3 further comprising a thermometer inside the fuel tank (10).

5. Aircraft comprising the system (SI) according to one of claims 3 or 4.

6. A method (5) for measuring the quantity of fuel implemented by a system (SI) according to claim 3 or 4, the method comprising: - Converting (51), by the microprocessor (211) of the fuel gauge (20), a measured analog value of the capacitor's capacitance into a digital capacitance value, - Calculating (52), by the microprocessor (211) of the fuel gauge (20), a fuel level in the fuel tank (10), from the digital capacitance value and a predetermined dielectric constant of the fuel stored in the memory (212) of the fuel gauge (20), - Storing (53), in the memory of the fuel gauge (20), the calculated fuel level, - Transmitting (54), in a digital signal, the calculated fuel level to a computing computer (30), - Receiving (55), by the computing computer (30), the digital signal including the calculated fuel level,- Calculate (56), using the calculation computer (30), from the fuel height and a predetermined geometry of the fuel tank (10), a quantity of fuel in the fuel tank (10).

7. Method (5) according to claim 6 implemented by the system (SI) according to claim 4 wherein the predetermined dielectric constant is calculated by: - ​​Obtaining a temperature from the temperature sensor, - Calculating the predetermined dielectric constant from a dielectric constant of the fuel and the temperature obtained.

8. A method (5) according to claim 7 further comprising: - A step of storing, in the memory of the fuel gauge (20), a data history comprising at least one of the following data: capacity, standard deviation of capacity over a given period, temperature of fuel, the predetermined dielectric constant, the calculated dielectric constant.

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