WO2011044891A1

WO2011044891A1 - Device and method for measuring the filling level in containers having any shape, in particular inside motor vehicle tanks

Info

Publication number: WO2011044891A1
Application number: PCT/DE2010/001229
Authority: WO
Inventors: Sascha Berger; Lutz Berger
Original assignee: Digades Gmbh - Digitales Und Analoges Schaltungsdesign
Priority date: 2009-10-12
Filing date: 2010-10-12
Publication date: 2011-04-21
Also published as: DE102009049676A1; EP2488836A1

Abstract

The present invention relates to a device for determining the filling level of a liquid in a container, comprising the container (1) that can be filled with the liquid, a first pressure sensor (2), by means of a which a first measured variable p_sens can be detected, which characterizes the total pressure resulting from the hydrostatic pressure of an amount of liquid inside the container and bearing on the first pressure sensor and an ambient pressure bearing on said amount of liquid, a second pressure sensor (3), by means of which a second measured variable p_umg characterizing said ambient pressure can be detected, and an evaluating unit (4), to which the first and the second measured variables can be transmitted, by means of which evaluating unit a third measured variable p_diff characterizing said hydrostatic pressure alone can be determined from the first and the second measured variables and by means of which evaluating unit a filling level parameter F associated with the determined third measured variable p_diff can be determined from the determined third measured variable p_diff on the basis of a functional relationship F(p_diff) between the third measured variable p_diff and the filling level parameter F characterizing the filling level of the liquid in the container, said functional relationship being pre-determined and preferably stored in the evaluating unit.

Description

Device and method for level measurement in arbitrarily shaped containers, in particular within motor vehicle tanks

The present invention relates to a device for determining the level of liquids in a container (in particular in a motor vehicle tank), to a corresponding determination method for the filling level and to motor vehicles having a corresponding device.

Devices for determining the level of the

Fuel in motor vehicle tanks are already known from the prior art. Usually, such devices are based on the principle that

Float depending on the level in the fuel tank via a lever arm an electric potentiometer controls. Depending on the fill level, the electrical properties of the potentiometer (for example, the ohmic resistance between two Potentiometer connections) changed. The change of the potentiometer thus allows a statement about the

Fill level in the tank.

Due to the design-related often complex geometric shape of the tank or the tank interior, the accuracy of the level indicator of the float-based systems is often limited. In particular, there is the problem in this regard that, when using alternative, for example float-based sensor systems, only part of the tank volume can be measured due to the design.

In addition, during the life of the motor vehicle or the tank, the electrical properties of the potentiometer often change in an unpredictable manner. This may cause the tank level to no longer be displayed correctly.

Based on the prior art, it is therefore an object of the present invention to provide a device for level determination in containers, especially in mobile containers such as motor vehicle tanks, with the simplest, most cost-effective and reliable way the most accurate determination of the current Level of the container is possible. The object of the invention is moreover to provide a corresponding determination method and motor vehicles comprising a corresponding device.

This object is achieved by a device according to claim 1, by a motor vehicle according to claim 11 and by a method according to claim 12. Advantageous design variant Each can be found in the dependent claims. In addition to the use in motor vehicles, the present invention, however, in principle, even in immobile containers such. B. fuel oil tanks are used in buildings or in containers of chemical and / or biological reactors.

Hereinafter, the present invention will be described first in general, then by means of an embodiment. In the context of the present invention, the combination of individual features shown in the concrete embodiment need not be realized exactly in the manner shown in the exemplary embodiment; The individual features according to the invention can therefore also be combined with one another in the context of the scope of protection specified by the claims in a different manner. In particular, individual features of the embodiment shown can also be omitted or combined with each other in other ways.

The present invention provides a device for determining the level of a liquid in a container (hereinafter alternatively referred to as a measuring arrangement) and a corresponding determination method (hereinafter also referred to as measuring method) with which an exact determination of the liquid content of an arbitrarily shaped Container or tanks is possible. The container or the tank can be designed so that in it the ambient air pressure prevails; However, the invention can also be realized in containers, within which (due to a gas-tight seal against the environment) the pressure above a liquid in the container is determined by the vapor pressure or gas pressure within this closed system. In both cases described above, the additional pressure acting in addition to the hydrostatic pressure of a liquid column (ie either the air pressure or the vapor pressure or gas pressure) is referred to as ambient pressure in the context of the present invention.

According to the invention, the device comprises the container which can be filled with a liquid and also a first and a second pressure sensor for detecting the pressure. The first pressure sensor is arranged so that a first measured variable (hereinafter also referred to as p _S ens) can be detected with it: This first measured variable characterizes a total pressure acting within the container, which results from the hydrostatic pressure of a pressure sensor acting on the first pressure sensor . acting on it Flü ^{'ssigkeitsmenge} (ie an amount of liquid within the container) and an amount of liquid in addition to this load-ambient pressure (ie, the air pressure or gas pressure) is obtained. By "characterize" is meant that the first measurand is in a one-to-one relationship to this total pressure, so that the total pressure can be derived from this measurand. This applies accordingly to the other measured quantities and pressures (see below). Advantageously, the first pressure sensor for this purpose at the bottom of the container, ie within the container, arranged.

The device furthermore has a second pressure sensor with which a second measured variable characterizing a said ambient pressure (ie the gas pressure or the air pressure) can be detected. This second measured variable is subsequently also referred to as umg (or in the case of a container in which the atmospheric pressure or air pressure as ambient pressure prevails, also referred to as Patmo).

Finally, the device according to the invention has an evaluation unit (for example a microcontroller) which is in communication with the two pressure sensors for data transmission. If necessary (e.g., if a configuration of the pressure sensors is necessary), this may be a bidirectional data connection. In any case, however, it is necessary that the two measured variables detected by the pressure sensors can be transmitted to the evaluation unit. By means of the evaluation unit, a third measured variable (which is also referred to below as Pdiff) can be determined or calculated from the two measured variables detected by the pressure sensors. This third measured variable (which is advantageously a differential pressure derived from the measured variables of the two pressure sensors) characterizes the hydrostatic pressure (exerted on the first pressure sensor alone), that is to say without the influence of the ambient pressure.

The essential point of the present invention is that one or more functional relationships are determined beforehand, ie before the acquisition of specific measured values for the first and second measured variables by means of the sensors, to which the evaluation unit determines Such a functional relationship F (p _diff ) is a generally specific, fluid type-specific and temperature-specific relationship between the third measured variable p _diff and a level of the liquid in the receptacle characterizing Level characteristic value F. The level characteristic value F is generally the volume V filled with liquid in the container, but it is also conceivable as the level characteristic value F to be the height h of the container

Liquid level above a defined point at the bottom of the container to use.

After having been determined using the two pressure sensors and the evaluation of the current level in the container characterizing third measurand P _d i _ff , thus taking into account the predetermined functional relationship / relationships F (diff), if necessary after prior selection of the appropriate Context of measured values (for example, the current temperature), the fill level characteristic value F belonging to this instantaneous fill level (thus, for example, the instantaneous fill volume V), and advantageously also by a suitable display (eg in the dashboard of the motor vehicle). are displayed.

Advantageously, according to the invention for several different types of liquids (which may for example have different densities) several liquid-specific functional relationships between the third measurand and the filling level in the container characterizing level characteristic determined in advance and deposited for example in the evaluation unit for the calculation of the current level. Thus, for example, in motor vehicles designed for several different types of fuel (for example, in motor vehicles which are additionally designed for the use of biofuels), a highly accurate level measurement can be carried out for each usable type of fuel. For this purpose, the device according to the invention may comprise a unit for determining the density of a liquid filled in the container. In the simplest case, such a unit can be a plurality of individual density sensors arranged one above the other in the liquid-filled volume of the tank, from whose different measured values (with known vertical distance of the individual sensors) the density of the liquid can be determined. The corresponding principle is known to the person skilled in the art. After determining the density Q of the currently filled liquid in the container, the correct relationship Fg ( _d i _ff ) can thus be used to calculate the current fill level. A capacitive sensor and a pressure sensor (eg the first pressure sensor) can also be used to determine the density. The density can then be measured by means of the pressure sensor if the height of the liquid column above the pressure sensor is assumed to be known. For this purpose, the capacitive sensor is arranged at a defined, known location within the container. With the aid of the capacitance-based filling height measurement principle known to the person skilled in the art, the instantaneous local filling level within the container is determined with this sensor for this known location. If the position of the first pressure sensor within the container, ie the positioning of this pressure sensor relative to the capacitive sensor is known (so that the instantaneous height of the liquid column above the pressure sensor can be derived from the fill level value of the capacitive sensor), its density can be measured with its measured pressure value the filled liquid, eg. B. to distinguish whether gasoline or diesel is in the container can be determined.

Alternatively or in combination herewith it is also advantageously possible for the liquids to be used in the container in each case for a plurality of different temperatures T temperature-specific functional relationships F _T (pdi _f f) between the third measured variable and the level (the respective type of liquid) in the container at the respective temperature characterizing

To determine the level characteristic in advance, and to be stored in the evaluation unit. In this way, e.g. the temperature-dependent expansion of a liquid are taken into account, so that regardless of the temperature a highly accurate

Level determination is possible.

For this purpose, the device according to the invention can have a temperature sensor which is arranged (eg inside the container) so that the temperature of a liquid currently filled in the container can be detected with it. The measured values of the temperature sensor can then be transmitted to the evaluation unit which, on the basis of the detected temperature, selects the temperature-specific functional relationship F _T (p _dü f) for determining the fill level characteristic value of the liquid currently being filled in the tank at this temperature and for the Calculation used.

If both a unit for determining the density and a temperature sensor in the container are used, then it can be ensured that the appropriate context F ( _d i _ff ) is used for the container used, the type of liquid used and the instantaneous temperature. The corresponding relationships are (as will be described in detail below) to be determined in advance on the container that later during the recording the first and second measured variable is used. Despite the generally existing dependence of the relationship between the third measured variable and the level characteristic level indicator (this relationship is hereinafter alternatively referred to as characteristic) of the actual liquid used, the currently prevailing temperature and the actual container geometry used is thus according to the invention regardless of the conditions currently present a highly accurate determination of the current liquid level in the container possible.

In principle, however, it is also possible (and sufficient for many applications) to provide only a predetermined characteristic and / or to dispense with the use of a unit for determining the density and a temperature sensor.

A particularly advantageous variant of the present invention comprises an evaluation unit, which, e.g. with the help of a memory, several different, predetermined and adapted to different conditions functional relationships (characteristics) can process and select from these several characteristics (the curves can be stored in the memory).

From these characteristic curves, if the instantaneous fill level in the container of the device is to be determined, a specific functional relationship suitable for the prevailing conditions can be selected from these multiple, for example, previously stored functional relationships. With the selected connection, then from the two erfass- th pressure readings p _se ns and pUMG (on the first subsequent calculation of the hydrostatic pressure

Pdiffi on which the individual functional usammenhänge or characteristics are based) the currently present level (or level characteristic, this may be in particular to the volume or the filling height at a defined location in the container) are determined.

With this device according to the invention, it is possible by the provision of these multiple, predetermined and stored in the memory of the evaluation unit various functional relationships or characteristics to make a highly accurate determination of the liquid level in the tank.

It is precisely through this selection, through which then e.g. Different types of liquids, different instantaneous temperature conditions and / or different container geometries and / or the exact positions of individual arranged to obtain the pressure measurements pressure sensors can be considered, the present invention has the particular advantage that not only a rough estimate or a simple arithmetic Calculation of the parameters that are important in addition to the geometric conditions on the tank for the filling level calculation takes place (as is the case, for example, in the prior art by a simple density calculation from the recorded pressure measured values), but that almost any environmental parameters can be taken into account very accurately.

These environmental parameters can then, depending on, for example, actually used further sensors (eg for temperature detection or density detection) on very different aspects to be considered Respectively. After determining further, for example, in the memory of the evaluation unit deductible relationships by specifically performing preliminary measurements so almost any conditions can be considered by the inventive selection between different predetermined functional relationships: So, for example, a complex liquid behavior in which heavier liquid components in the lower Depositing the area of the container and depositing lighter liquid components in the upper area of the container can be easily taken into account by carrying out appropriate measurements in advance for the corresponding liquid type and depositing them in a corresponding characteristic curve. For the differentiation of different liquid types, it is not crucial to determine just the density, but only that for the possibly filled in the container liquid type previously determined a functional relationship and stored in the memory of the evaluation, so this context then also be selected can.

Thus, the present invention can provide an evaluation unit with a memory in which a plurality of functional relationships adapted to different conditions between the third measured variable or the hydrostatic pressure on the one hand and the instantaneous fill level F resulting therefrom (depending on the prevailing conditions) V or level h) are stored on the other hand.

According to the invention, the container may be designed such that the ambient air pressure is established within the container (no pressure-tight closure of the container relative to the environment). In this Case, the second pressure sensor is preferably arranged outside the container (for example, attached to the outer shell of the container). Alternatively, however, the container may also be designed to be pressure-tight with respect to the environment, so that a vapor pressure above the filled-in quantity of liquid forms as ambient pressure within the container. In this case, the second pressure sensor is preferably arranged inside the container and in an upper region of the container interior (eg on the inner ceiling side of the container interior).

Advantageously, at least one of the

Pressure sensors, a wireless transmission unit, with the aid of which the measured variables detected by him wirelessly to a corresponding receiving unit, which is in communication with the evaluation unit or as part of the evaluation unit, can be transmitted. Particularly preferably, such a transmission unit is an RFID transponder; the receiving unit is then designed as an RFID reader. The structure and design of RFID transponders and readers are known in the art. At least the data transmission between the first pressure sensor and the evaluation unit is thus preferably wireless.

Alternatively, however, a wired signal transmission is possible.

As will be described in detail below, the fill level characteristic value F characterizing the instantaneous liquid level in the container by means of the relationship F (Pdif _f ) from the instantaneous value of p _diff to be calculated or derived via the sensors is the instantaneous value in the Container interior filled liquid volume. Alternatively, however, it is also conceivable, the context or the relationships based on a

Liquid level to define relative to a defined point of the container.

The first pressure sensor is preferably arranged in a lower region of the container interior (for example at the lowest point of the bottom of the container).

In a further advantageous embodiment, a plurality of first pressure sensors may be provided for detecting first measured quantities p _sens . In the case of the stored relationships or characteristic curves, the respective position of the individual first pressure sensors can then be taken into account (sensor-specific characteristic curves). By providing a plurality of first pressure sensors, the statistics of the measured value determination (see also below) can be improved and thus a more reliable measurement result for the current filling level (eg calculated by averaging the individual with the aid of the plurality of sensors and characteristic curves, in particular for a moving motor vehicle

Level characteristic values F) are determined.

Particularly preferably, the device according to the invention is integrated in a motor vehicle, for example in a motorcycle; the container is then the vehicle tank of the vehicle.

Hereinafter, the present invention will be described in detail with reference to an embodiment. Show it

Figure 1 is a sketch of an exemplary inventive structure.

FIG. 2 shows an example of measured pressure values during a test drive with a motor vehicle (motorcycle) having a device according to the invention.

FIG. 3 shows an example of a predetermined one

Characteristic curve for a given liquid (normal gasoline), for a defined temperature (20 ° C) and for a given tank geometry.

FIG. 4 shows examples of an averaging of the third measured variable P _d i _ff over a multiplicity of individual measured values for the purpose of reducing measured value distortions due to unevenness in the surface during driving of the motor vehicle and of vibrations of the motor vehicle engine.

FIG. 1 shows a tank 1 provided with a tank lid 1a as a container of the device according to the invention. Inside the tank, the first pressure sensor 2 is formed at the lowest point of the bottom of the tank 1. With it, p _sen s is the first measurand resulting in a total pressure within the

Container interior measurable. This total pressure is composed of a hydrostatic pressure on the first pressure sensor 2 and an additionally acting on the first pressure sensor 2 ambient pressure. The hydrostatic pressure is the pressure that is due to be above the first pressure sensor 2 be finding liquid column with the height h corresponding to the current level in the tank interior on the first pressure sensor 2 loads. The tank 1 is designed here as an open tank, that is in the gas space above the liquid level in the tank interior prevails ümgebungsluftdruck. With the first pressure sensor 2, thus, a measured variable p _sen s is detected, which corresponds to the total pressure from the above-described hydrostatic pressure and this ambient air pressure. The hydrostatic pressure alone, ie without the ambient air pressure, here correlates (corresponding to the specified specific tank geometry) uniquely with the liquid volume V currently filled in the tank 1.

Outside the tank, the second pressure sensor 3 is attached to an outer wall thereof, with which the ambient air pressure can be detected.

The second pressure sensor 3 has a cable connection 3a, with which it is connected to the evaluation unit 4 for transmitting the second measured variable detected by the second pressure sensor 3 to the evaluation unit 4. The evaluation unit 4 is arranged outside of the tank interior and fixed to the underside of the tank 1.

The transmission of the first measured variable p _sens from the first pressure sensor 2 to the evaluation unit 4 is based on the known to those skilled RFID technology (from English: radio frequency identification): The first pressure sensor 2 has an RFID transponder 7, which is the first Measured p _sen s corresponding measurement data to the formed as part of the evaluation unit 4 RFID reader 8 transmits. Common RFID readers and RFID transponders in known and approved frequency bands (eg at 125 kHz, 869 MHz, 2.4 GHz). It is only necessary to ensure that the positioning between the sensor and the evaluation unit ensures compliance with the relevant approval standards.

In order to be able to carry out a highly accurate fill level determination, a temperature sensor 6 is arranged on an inner wall of the container 1 in a lower region of the tank interior 1, which is still liquid- or fuel-tight, even if the fuel quantity in the tank 1 is low. With this, the temperature of the filled liquid or the fuel can be determined. The temperature sensor 6 also has an RFID transponder 6a, by means of which the corresponding temperature values can be transmitted to the evaluation unit 4. On the basis of the instantaneous temperature T, the evaluation unit 4 then selects the suitable characteristic curve F _T (p _diff ) stored in advance for determining the fill level characteristic value F for the currently present fill volume V.

As temperature sensors, for example, all common known temperature-dependent resistors can be used.

Furthermore, a unit 5 for determining the density Q of the fuel currently in the tank is arranged at the bottom of the tank interior on a side wall. This unit 5 is also arranged in the lower region of the tank so that density values of the fuel can be determined even with a small tank filling. The unit 5 is provided with an RFID transponder 5 a, with the aid of which the corresponding density values are sent to the evaluation unit 4 or their reader 8 can be transmitted. The unit 5 here consists of two superimposed pressure sensors (not shown), from the measured values at a known distance of these two sensors, the density of the currently filled fuel can be determined. However, units 5 based on other principles can also be used for density determination. On the basis of the transmitted density values, the evaluation unit 4 can thus select the appropriate liquid-specific functional relationship Fe (Pd ff).

By means of the units 5 and 6, it is thus ensured that (assuming a determination of the characteristic curves specific to the tank geometry) the correct characteristic adapted to the instantaneous conditions is selected. As a result, a highly accurate determination of the liquid level in the tank is made possible according to the invention. In principle, it is also possible to provide only one of the two units 5 and 6 or to completely dispense with these units 5, 6.

Suitable pressure sensors are common barometric pressure sensors such as those used for altimeters. In level measurement accuracy can be achieved in the range of a few 10 to 100 milliliters of liquid. To achieve fuel resistance, specially adapted membrane and housing types may be necessary.

The determination of the filling level in the tank 1 will be described below by way of example on the basis of averaging of the measured values. Alternatively, however, other evaluation methods can also be implemented in the evaluation unit 4. The first pressure sensor 2 located at the bottom of the tank 1 constantly records the first measured variable p _sens at regular time intervals of, for example, 0.5 seconds, which characterizes the above-described total pressure. In the following, this parameter is also referred to simply as "pressure _pse ns" for the purpose of abbreviation, although the correct absolute total pressure may only result from this measured variable after a measured value correction. Furthermore, the second pressure sensor 3 outside the tank constantly measures the ambient air pressure at these regular time intervals, thus determining the corresponding measured variable Pum _g , which is referred to below as the patmo due to the prevailing atmospheric pressure. This measured variable is also abbreviated to pressure p _sen s or p _a tmo. The air pressure measurement is necessary because the first pressure sensor 2, the pressure of the pressure above him

Liquid column (corresponding to the third measurand Pdiff) only together with the air pressure p _a tmo measures. For the pressure acting on the liquid column above the first pressure sensor 2, Pdiff thus results

⁼ Psens ^- Patmo ·

In general, the two sensors 1, 2 are not calibrated equal, that is, they measure different values for the ambient air pressure. However, the resulting offset Δ remains constant as long as nothing is changed on the device 1 to 8. This results in p _atmo (air) = p _se ns (air) + Δ.

Patmo (air) is the value that the second pressure sensor 3 measures and p _sens (air) is the value that the first pressure sensor 2 measures when the tank 1 is completely empty (no liquid present): In this case it also measures the first pressure sensor the air pressure. By a one-time measurement of this kind the offset Δ can be determined. With the thus determined Δ = p _atmo (air) - p _sens (air), it finally follows for the third measured variable or the corresponding differential _pressure

Pdiff = Psens - (Patmo (air) - Δ) with p _S ens as the total pressure acting on the first pressure sensor 2 and p _atmo (air) as the ambient air pressure detected by the second pressure sensor.

FIG. 2 shows an example of the measurement of the ambient air pressure by a second pressure sensor 3

(Patmo) and by three in the tank interior of an empty tank arranged pressure sensors (P sensl to P sens3).

In order to conclude from the thus measured differential pressure value or the third measured variable Pdiff (which results from the liquid column currently acting on the first pressure sensor 2 alone) on the instantaneous content of the arbitrarily shaped liquid container 1, at least one (liquid container spec - Characteristic curve F (p _diff ) to create and _store in the evaluation unit 4. The microcontroller of the evaluation unit 4 thus includes a suitable arithmetic unit for performing the calculations and a memory.

The characteristic determination is realized by filling a defined volume V of the liquid into the tank in the above-described measuring arrangement at sufficiently large time intervals (of, for example, 3 minutes). By means of the two sensors 2, 3, the pressure of the liquid column Pdiff is as described above. ben determined. Each level or filling volume V can thus be assigned a value P _d i _ff in a unique manner. A corresponding for a defined tank geometry recorded characteristic F (p _d i _ff ) between the differential pressure Pdi _ff and the current level in the container characteristic

Level characteristic value (here: filling volume V of liquid in the tank) is shown in FIG. 3 (filling volume in liters, differential pressure in hectopascals). Corresponding measuring procedures are repeated, starting with the empty tank (V = 0) up to the maximum filled tank (V = V _max ) to generate the characteristic curve.

In this case, the characteristic can be obtained by means of a predefined mathematical function, for example a polynomial, on the basis of a fitting method from the specific measured value pairs (P _d i _ff , V). Corresponding fitting methods are known to the person skilled in the art.

By means of this functional relationship or this characteristic, it is now possible to assign a filling volume V to absolutely every pressure Pdi _ff , which corresponds to the filling level of the tank within the scope of a very small error. The pressure of the liquid column p _D i _ff results in this case

Psens = F / A = (Q × V × g) / A = ρ × h × g where F is the force, A is the area of the sensor, Q is the density of the fluid, g is the acceleration of gravity, and h is the height of the fluid column at the location of the fluid first pressure sensor 2 is. P _d i _ff is thus dependent on the density of the liquid; a characteristic is therefore valid only for a liquid of the same density p_ (and at a defined temperature T). The measurement of further characteristics with other liquid types or

densities and / or for different temperatures T is thus advantageous. The determination of the further characteristic curves for liquids with a different density can be reduced to the measurement of the different densities, since the above considerations result directly for two different densities gi and Q ₂ :

Pdiff, e2 / Pdiff, ei ⁼ 62 / Qi

According to the invention, depending on the type of fuel or its density, on the current temperature and on the given tank geometry, a wide variety of functional relationships F (p _d i _ff ) can be determined and stored in the memory of the evaluation unit 4.

When measuring the fuel level in the tank of motor vehicles while driving, it may lead to distortions of the measured values due to bumps that occur while driving, and vibrations caused by the engine of the motor vehicle. To a sufficiently accurate signal to get it is therefore advantageous to the calculated on the basis of the measured values of the two pressure sensors 2, 3 third measured quantity P _d if _f and the detected differential pressure value over a plurality of measurements to average (e.g., over the set of measured values, which is obtained over a measuring time of five minutes with a measuring interval between adjacent measured values of 0.5 seconds).

For example, at a time ti, the detected signal may be the average of all measurements from the measuring point t _x - 5 minutes to the measuring point t _x . During the first five minutes of measurement, each newly acquired measurement is added to the averaging until the five minutes have passed. Then the newest reading can always replace the oldest (moving averaging). From this determined value of _d i _ff , the tank capacity can be determined as prescribed via the characteristic function.

4 shows such an averaging of the differential pressure value _d i _ff over different time intervals of three minutes, five minutes and ten minutes and the fluctuation of the individual values of _d i _ff calculated on the basis of individual measured values of the sensors 2, 3. Other averaging methods can also be used according to the invention.

Claims

claims

1. A device for determining the level of a liquid in a container, in particular in a motor vehicle tank, comprising the container (1) which can be filled with the liquid, a first pressure sensor (2), with which a first measured variable p _se ns can be detected, comprising the the hydrostatic pressure one on the first

Pressure sensor (2) characterized amount of liquid within the container (1) and from a pressure on this amount of liquid ambient pressure resulting total pressure, a second pressure sensor (3), with a said ambient pressure characterizing second measured value pumg can be detected, and an evaluation unit (4), to which the first and the second measured variable can be transmitted, by means of which a third hydrodynamic pressure alone characteristic third P _d i _{ff can be} determined from these two measured variables and by means of which of the determined third measured variable P _f f f based on a pre-determined and preferably in the evaluation unit (4) deposited functional relationship F (p _d i _ff ) between the third measured variable P _d i _ff and the level of the liquid in the container (1) characterizing

Level characteristic value F of the third characteristic measured variable _d i _ff corresponding fill level characteristic value F can be determined.

2. Device according to the preceding claim, characterized in that the evaluation unit (4) is formed with an arithmetic unit and a memory and as follows:

• The first and the second measured variable can be transmitted to the evaluation unit (4),

• by means of the evaluation unit (4) is off

these two measured variables a third hydrostatic pressure alone characteristic third _d i _ff determinable,

• in the memory of the evaluation unit (4) are stored several different, predetermined and adapted to different conditions functional relationships F (P _d if _f ) between the third variable Pdiff and a level of the liquid in the container (1) characterizing level characteristic value F,

• by the evaluation unit (4) can be selected from these several stored functional relationships, a functional context, and

• by means of the evaluation unit (4) can be determined from the determined third measured variable, P _d i _f f using the selected by the evaluation unit (4) functional relationship of the third measured variable Pdiff belonging filling level characteristic value F.

3. Device according to the preceding claim characterized by a plurality of stored functional relationships F (Pdiff) with respect to their

Container geometry specificity, its fluid specificity, its temperature specificity, and / or, if several first

Pressure sensors for detecting first measured variables, their sensor specificity differ and / or that the level characteristic f corresponds to the filling volume V in the container or a filling level h in the container.

4. Device according to one of the preceding claims, wherein at a plurality of times in each case with the first pressure sensor (2) a first measured value p _S ens and with the second pressure sensor (3) a second measured variable p ^ g can be detected and wherein by means of the evaluation unit (4) p _se ns ^ pUMG respectively a third measurement variable pdiff can be determined from each of these measured quantity couple thus determined plurality of third measurement variables pdiff are indirectly p _diff and the calculated mean P _diff on the basis of or the connection / connections F (pdiff ) the filling level characteristic value F associated with this mean value can be determined.

5. Device according to one of the preceding claims, wherein for several different types of liquids and / or for a plurality of liquids of different density p, in particular for different types of fuels, each liquid at least one liquid-density and / or liquid-specific functional relationship F _p (p _d i _ff ) between the third measured variable diff and a filling level of the respective liquid in the container (1) characterizing level characteristic value F determined in advance and preferably also in the evaluation unit (4) is deposited.

6. Device according to the preceding claim comprising a unit (5) for determining the type and / or density of a liquid, which is arranged so that with it the density and / or the type of a liquid filled in the container (1) can be detected / are, wherein the evaluation unit (4) is formed so that on the basis of such a detected liquid type and / or density of belonging to this liquid type and / or density liquid density and / or liquid-specific functional relationship F _p (Pdi _f f ) is selectable for determining the filling level characteristic value F.

7. Device according to one of the preceding claims, wherein for at least one type of liquid for a plurality of different temperatures T each a temperature-specific functional relationship F _T (p _d i _f f) between the third measured variable diff and a filling level of this type of liquid in the container (1) at the respective temperature characterizing level characteristic F determined in advance and preferably also deposited in the evaluation unit (4) is.

Device according to the preceding claim comprising a. Temperature sensor (6) which is arranged so that with him the temperature of a liquid in the container (1) can be detected, wherein the evaluation unit (4) is designed so that on the basis of such a detected temperature belonging to the temperature-specific functional Relationship FT (Pdiff) for determining the level characteristic F is selectable.

Device according to one of the preceding claims, wherein either the container (1) is not formed pressure-tight relative to the environment, so that within the container (1) the ambient air pressure prevails as ambient pressure, and the second pressure sensor (3) is preferably arranged outside the container, or the container (1) is pressure-tight with respect to the environment, so that inside the container (1) a gas pressure formed above a filled-in amount of liquid is used as the ambient pressure prevails, and the second pressure sensor (3) preferably within the container (1) and above a predefined maximum level of liquid in the container (1), in particular in the upper region of the container interior and / or arranged on the inner ceiling side of the container (1) is.

10. Device according to one of the preceding claims, wherein at least one of the pressure sensors, preferably the first pressure sensor (2), preferably designed as an RFID transponder transmission unit (7), with the help of which the associated (n) measured variable (s) wirelessly to a receiving unit (8) which is preferably designed as an RFID reader and which is designed as part of the evaluation unit (4) or is in contact with the evaluation unit (4) for data transmission, is / are transferable, and / or wherein the first Pressure sensor (2) in the interior of the container (1), in particular in the lower region of the container interior and / or on the inner bottom side of the container (1) is arranged and / or wherein a plurality of first pressure sensors for detecting first measured values p _sen s are provided.

11. Motor vehicle, especially motorcycle, car, truck, bus or tractor, comprising a device for determining the level of the Fuel in his motor vehicle tank; according to one of the preceding claims.

Method for determining the fill level of a liquid in a container, in particular in a motor vehicle tank, wherein the container (1) is at least partially filled with the liquid or already filled, wherein a first measured value p _{sens is} detected by means of a first pressure sensor (2), which characterizes the total pressure resulting from the hydrostatic pressure of a fluid pressure on the first pressure sensor (2) within the container (1) and an ambient pressure which is subject to this fluid quantity, wherein a second measured variable characterizing said ambient pressure is detected by means of a second pressure sensor (3) and wherein a third measured variable P _d i _ff which identifies said hydrostatic pressure alone is determined from these two measured variables and from this determined third measured variable P _d i _ff by means of a predetermined functional relationship F (p _diff ) between the third measured variable Pdi _f f and a fill level characteristic value F characterizing the fill level of the liquid in the container (1), which characterizes the instantaneous fill level of the liquid in the container (1), belonging to the determined third measured variable P _d i _ff

Level characteristic F is determined.