DE202006002674U1 - Fluid e.g. fuel, level sensor for e.g. passenger car, has thermocouples heating hot contact point and cooling cold contact points, depending on electric current, by Peltier effect and producing thermovoltage based on temperature difference - Google Patents

Abstract

The sensor has multiple thermocouples (6) arranged one after another in a row. Each thermocouple has hot and cold contact points (7, 8) on its opposite sides. The thermocouples heat the hot contact point and cool the cold contact points depending up on the electric current by the Peltier effect. The thermocouples produce a thermovoltage based on a temperature difference between the hot and cold contact points. An independent claim is also included for a level measurement device with a fluid level sensor.

Description

The The invention relates to a level sensor for Measurement of a level a liquid, in particular for detecting the level a fuel in a fuel tank of a motor vehicle.

From Various manufacturers are level sensors thermocouple known, which are used for example can, around the level of the fuel in a fuel tank of a motor vehicle measure up. These known level sensors Thermocouple based have a variety of thermocouples which are electrically connected in series and an elongated, strip thermopile form, the hot ones Contact points in a row on top of each other one side of the thermopile are arranged while the cold contact points of the thermocouples also in one Row on the opposite Side of the thermopile are arranged. The individual thermocouples are here on a substrate applied, which is for example a plastic film (e.g., Kapton). About that In addition, the known fill level sensors Thermocouple on a heat conductor on, next to the Series of hot contact points the thermocouples extends and electrical heating of the be called Contact points allows. When energizing the heating element, the thermocouples heat up below and above the liquid level differently.

So leads the Heating by the heating element at the immersed in the liquid thermocouples only to a rela tively low temperature difference between the hot and cold contact points, since the heat generated by the heating conductor there over the good thermal conductivity liquid largely dissipated becomes.

at the thermocouples, which are located above the liquid level, On the other hand, only a small part of the heat generated by the heat conductor is dissipated, which to a correspondingly larger temperature difference between the hot ones and cold contact points leads.

The known level sensors Thermocouple based thus produce in the fully immersed state; i.e. with a full tank, a minimum thermoelectric voltage, whereas the generated thermoelectric voltage is the maximum when the tank is empty. From the of the level sensor generated electrical voltage can therefore be in a simple Way the level to calculate.

Especially advantageous to these level sensors thermocouple-based is the automatic compensation of fluctuations the ambient temperature, since the individual thermocouples respectively only the difference temperature between cold and warm contact point measure, making a change the ambient temperature in the same way on the hot and cold contact points and therefore has no influence metrologically Has.

adversely at these level sensors On the other hand, the thermoelement-based complex structure and thus associated comparatively high price.

Of the The invention is therefore based on the object described above known level sensors thermocouple based accordingly.

These Task is by a level sensor according to the main claim solved.

The Invention includes the general technical teaching, the individual Do not heat thermocouples by a separate heating, but by a self-heating by means of the thermocouples themselves, so that on a separate heater as in the known described above level sensors can be dispensed thermocouple-based. The private heating Thus, in the case of the fill level sensor according to the invention, it consists of the thermocouples and works according to the well-known Peltier effect.

The However, the invention also claims protection for known level sensors Thermocouple-based with a separate heater, provided the heater remains unused and warming the thermocouples in the manner according to the invention takes place.

For the warming of Thermocouples is exploited in the invention of the Peltier effect, when a current flows through a thermocouple in dependence of direction and altitude the current flow in the contact points generates or destroys heat, resulting in a corresponding temperature difference between the hot and the cold contact points and thus to a corresponding thermal voltage leads. After switching off the power you can then during the Current flow constructed according to the Peltier effect temperature difference between the hot ones and cold contact points of the thermocouples as Seebeck voltage measure at the output.

Again, the built-up during the current flow temperature difference and thus the subsequently measurable voltage depends on whether the respective thermocouple was immersed in the liquid or not, since the liquid in the immersed thermocouples the Temperaturdif due to the good heat conduction degrades relatively quickly. In the case of the fill level sensor according to the invention, the fill level can therefore also be calculated in a simple manner from the electrical voltage generated by the fill level sensor.

at the level sensor according to the invention Thus, preferably, the structure of a temperature gradient takes place alternately according to the Peltier effect and a measurement of the temperature gradient according to the Seebeck effect.

In a preferred embodiment of Invention, the thermocouples are electrically in series one behind the other switched and preferably form an elongated thermopile, wherein the thermopile obtusely and preferably at right angles to the liquid level is aligned. The term used in the context of the invention an obtuse-angled orientation of the thermopile relative to the liquid level includes angles of more than 45 °, 55 °, 65 °, 75 ° or 85 ° between the thermopile and the liquid level.

at an insert of the fill level sensor according to the invention as a tank sensor for measuring the level in a fuel tank has to be considered that fuel tanks in passenger cars often a jagged Have inner contour. The thermopile is then preferably curved and follows the inner contour of the fuel tank.

The individual thermocouples, however, are preferably rectangular or at least at an obtuse angle to the longitudinal axis of the thermopile, i.e. parallel or at least acute angle to the liquid level. The term used in the context of the invention an acute-angled Orientation of the thermocouples here includes angles of less as 45 °, 35 °, 25 °, 15 ° or even less than 5 °.

In In a variant of the invention, the level sensor has only a single one elongated thermopile on, which contains a plurality of thermocouples, the electrical one behind the other are connected in series.

In In contrast to another variant of the invention, the filling level sensor has several, preferably two, elongated thermopiles, each having a plurality of thermocouples, wherein the thermopile preferably electrically connected in series and substantially parallel to each other are arranged.

at a parallel arrangement of two elongated thermopiles are preferably the hot ones Contact points of the thermocouples of the two thermopile each other facing, whereby the heating is more effective. The hot contact points the thermocouples are in this arrangement so between the two thermopiles.

It however, it is also possible as an alternative that the cold contact points of the two arranged side by side thermopile facing each other. Located in this alternative arrangement the hot ones Contact points outside, while arranged the cold contact points between the two thermopile are.

As with the known thermoelement-based level sensors described above, the individual thermocouples have two different conductor materials, which are connected to one another at a contact point. The one conductor material may be, for example, a copper-nickel alloy, with CuNi44 being particularly suitable. In the other conductor material may contrast to copper, a copper-manganese-nickel alloy, in particular Manganin ^® or act nickel-chromium alloy. However, the invention is not limited to the above-mentioned conductor materials in terms of the conductor materials of the thermocouples, but in principle also feasible with other conductor materials.

A more common with the known level sensor described above preferably in that the two conductor materials are preferably on a carrier material are applied.

In A variant of the invention are the two different conductor materials the thermocouples here on the same side of a substrate (e.g., a plastic film).

In In another variant of the invention, the two are different Conductor materials of the thermocouples on opposite sides of the carrier material arranged, wherein the different conductor materials by a through the carrier material passing via electrically at a contact point connected to each other.

at the carrier material for the It may be different conductor materials of the thermocouples for example, a foil (e.g., plastic, Kapton), however, a thin wall can also be used Tube as carrier material for the different conductor materials of the thermocouples are used.

Furthermore, it should be mentioned that the invention not only the above-described level sensor according to the invention as a single construction part, but also a complete level measuring device with such a level sensor according to the invention.

The Inventive level measuring device preferably has a power source connected to the level sensor is arranged and the level sensor with a current can drive to in the individual thermocouples according to the above described Peltier effect a temperature difference between the be called and to create cold contact points. The within the scope of the invention used term of a power source is to be understood in this case in general and not on idealized power sources with an infinite internal resistance limited.

For example For example, the power source for energizing the level sensor can be a pulse generator comprising the level sensor with current pulses.

Preferably the energization of the level sensor takes place with a predetermined electrical energy input to a predetermined warming to reach. In a pulse control of the level sensor is preferably a regulation is provided which regulates the electric charge, the flowing at a pulse, which at a constant drive voltage to a predetermined electrical Energy input leads.

It however, it is also possible as an alternative that the power source is the level sensor with a continuous current drives to in the thermocouples according to the Peltier effect to generate a temperature difference.

Farther has the level measuring device according to the invention Preferably, a voltmeter connected to the level sensor is and that of the level sensor in the currentless state measures electrical voltage generated, thus making it the level can be derived.

Furthermore has the level measuring device according to the invention preferably an integrator connected to the voltmeter on, the voltage simply or twice over a integrated period of time, which minimizes the noise and an offset is eliminated.

The Control and evaluation of the level sensor However, in the level measuring device according to the invention also by a conventional Microcontroller done, both the electrical control the thermocouples during heating takes over as well as the measurement the voltage generated by the thermocouples performs.

In a preferred embodiment of Inventive level measuring device is the level sensor arranged in a fuel tank of a motor vehicle and measures the level of the Fuel in the fuel tank.

Of the Inventive level sensor can but also for measuring the level other operating fluids a motor vehicle are used, such as the cooling liquid, the engine oil or the brake fluid. The level sensor is then in accordance with a coolant reservoir, a Engine oil tank or arranged a brake fluid reservoir.

Furthermore the level sensor according to the invention is suitable also generally for measuring the level fluids, which are not necessarily liquids must act. For example, the level sensor according to the invention also the level of granules, powder, shavings, bulk, etc. Accordingly, the level sensor according to the invention in a variety of mobile or stationary containers be arranged, such as in tanks, silos, bunkers, etc. The respective fluid should only have sufficient thermal conductivity have that bigger than that should be air.

The Conductor materials of the thermocouples can in this case by different Method on the substrate applied, such as by sputtering, printing, by galvanic processes or by etching techniques. The Invention is, however, with regard to the application of the various Conductor materials of the thermocouples on the substrate not on the above limited examples, but in principle also feasible with other methods.

Other advantageous developments of the invention are characterized in the subclaims or will be discussed below together with the description of the preferred Embodiments of the Invention with reference to the figures explained. Show it:

1 a schematic representation of a level sensor according to the invention with a single thermopile,

2 an alternative embodiment of a filling level sensor according to the invention with two thermopiles,

3 a schematic representation of a Fuel tank of a motor vehicle with a level sensor arranged therein according to 1 .

4 a schematic representation of a single thermocouple of the level sensor according to the invention according to the 1 to 3 .

5 2 is a schematic cross-sectional view of a fill level sensor according to the invention, in which the various conductor materials of the thermocouples are arranged on the same side of a carrier material,

6 a simplified cross-sectional view of an alternative embodiment of a filling level sensor according to the invention, in which the different conductor materials of the thermocouples are arranged on opposite sides of the carrier material,

7 a schematic representation of a section of a thermopile with successively applied conductive materials,

8th a detail of an alternative embodiment of a thermopile of uniform base material with a second low-resistance, thermoelectrically different layer,

9 a schematic representation of a section of a thermopile, in which the different conductor materials of the thermocouples are applied to opposite sides of a carrier layer,

10 a cross-sectional view through the thermopile 9 along the section line AA,

11 a simplified block diagram of a level measuring device according to the invention,

12 an extremely simplified block diagram of a level measuring device according to the invention with a microcontroller for driving and evaluation of the level sensor and

13A -D different courses of current and voltage at the level sensor according to the invention.

The 1 and 3 show a level sensor according to the invention 1 for example, to measure a level 2 a fuel 3 in a fuel tank 4 a motor vehicle can be used as out 3 is apparent.

The level sensor 1 has a single thermopile 5 on, a variety of electrically connected in series thermocouples 6 contains, where 4 the structure of the individual thermocouples 6 shows. The individual thermocouples 6 each have hot contact points 7 and cold contact points 8th on, with the hot contact points 7 on the one hand and the cold contact points 8th on the other hand are arranged side by side in two parallel rows.

Furthermore, the individual thermocouples 6 two different conductor materials each 9 . 10 on, wherein the one conductor material in this embodiment, a copper-nickel alloy, while the other conductor material is Manganin ^®.

The conductor materials 9 . 10 the individual thermocouples 6 are here applied to a substrate, as will be described in detail later.

The thermopile 1 is over two contact surfaces 11 . 12 electrically contacted, wherein the control of the level sensor 1 for example, by a microcontroller 13 can be done as in 12 is shown schematically.

In a level measurement, the microcontroller controls 13 the level sensor 1 initially with power pulses on, so that the individual thermocouples 6 due to the known Peltier effect, a temperature difference between the hot contact points 7 and the cold contact points 8th produce.

After this energization measures the microcontroller 13 then the electrical voltage at the contact surfaces 11 . 12 , This voltage according to the known Seebeck effect according to the temperature difference between the hot contact points 7 and the cold contact points 8th is produced.

In the case of the fuel 3 below the level 2 immersed thermocouples 6 becomes the temperature difference between the hot pads 7 and the cold contact points 8th by the thermal conductivity of the fuel 3 largely balanced, so that the immersed thermocouples 6 only generate a low voltage.

When not in the fuel 3 immersed thermocouples 6 above the level 2 in the fuel tank 4 becomes the temperature difference between the hot pads 7 and the cold contact points 8th On the other hand hardly degraded, since the surrounding air has only a relatively low thermal conductivity. The non-immersed thermocouples 6 therefore generate a relatively large thermoelectric voltage at the contact surfaces 11 . 12 of the level sensor 1 is measurable. The contact areas 11 . 12 measurable electrical voltage is therefore directly the level 2 of the fuel 3 in the fuel tank 4 again.

2 shows an alternative embodiment of a level sensor according to the invention 1 , which largely corresponds to the embodiment described above, so that to avoid repetition of the above description to 1 is referenced, wherein the same reference numerals are used for corresponding components.

A special feature of this embodiment is that the level sensor 1 two thermopiles 5a . 5b has, which are arranged parallel to each other. The cold contact points 8th are here on the outside of the level sensor 1 whereas the hot contact points are 7 the two thermopiles 5a . 5b facing each other. The spatial orientation of the hot and cold contact points 7 . 8th However, it is also possible the other way around.

5 shows a simplified cross-sectional view through the level sensor 1 according to 1 , It can be seen that the conductor materials 9 . 10 on the same side of a substrate 14 are arranged, wherein the carrier material 14 in this embodiment, a plastic film is.

6 shows a simplified cross-sectional view through an alternative embodiment of the level sensor 1 according to 1 in which the conductor materials 9 . 10 the thermocouples 6 on opposite sides of the substrate 14 are arranged. The electrical connection of the two conductor materials 9 . 10 at the contact point 7 takes place here by a via 15 passing through the substrate 14 goes through it.

7 shows a section through a thermopile 5 a fill level sensor according to the invention 1 , wherein the conductor materials 9 . 10 were applied successively, which can be done for example by sputtering, printing or by a galvanic manufacturing process.

8th shows a simplified representation of an alternative embodiment of a thermopile according to the invention 5 in which the conductor material 10 a uniform base material forms on which the conductor material 9 is applied as a second low-resistance, thermoelectrically different layer. The application of the conductor material 9 This can also be done by sputtering, printing or by a galvanic process.

The 9 and 10 show an embodiment of a thermopile 5 in which the conductor materials 9 . 10 the individual thermocouples 6 on both sides of the substrate 14 are applied, wherein at the hot contact points 7 and the cold contact points 8th Through holes are provided, through the substrate 14 go through and the conductor materials 9 . 10 connect with each other.

11 shows a simplified block diagram of a fill level measuring device according to the invention with the above-described level sensor according to the invention 1 ,

The level sensor 1 This is done by a pulse generator 16 energized with current pulses in 13A are shown by way of example. The of the pulse generator 16 generated current pulses lead to the establishment of a temperature difference between the hot contact points 7 and the cold contact points 8th according to the well-known Peltier effect. This results in the contact surfaces 11 . 12 of the level sensor 1 a thermoelectric voltage coming from a voltmeter 17 is measured, wherein the time course of the measured voltage in the 13B - 13D is shown by way of example. After the end of a current pulse that of the level sensor decreases 1 generated voltage gradually, as the temperature difference between the hot contact points 7 and the cold contact points 8th degraded due to the unavoidable heat conduction. However, the measured voltage is a direct measure of the level 2 the liquid to be measured.

To minimize noise and eliminate offset, the level gauge further includes an integrator 18 which simply measures the measured voltage (cf. 13C ) or twice (cf. 13D ) integrated.

The Invention is not limited to those described above embodiments limited. Rather, a variety of variants and modifications is possible, the also make use of the idea of the invention and therefore in fall within the scope of protection.

1

level sensor

2

level

3

fuel

4

Fuel tank

5

thermopile

5a, 5b

thermopile

6

thermocouple

7

Hot contact points

8th

Cold contact points

9.10

conductor materials

11.12

contact surfaces

13

microcontroller

14

support material

15

via

16

pulse generator

17

voltmeter

18

integrator

Claims (22)

Level sensor ( 1 ) for measuring a level ( 2 ) of a fluid ( 3 ), in particular for detecting the level ( 2 ) of a fuel ( 3 ) in a fuel tank ( 4 ) of a motor vehicle, with several thermocouples ( 6 ), characterized in that no separate heating is provided to the thermocouples ( 6 ) to heat. Level sensor ( 1 ) according to claim 1 of the preceding claims, characterized in that the thermocouples ( 6 ) are connected in series one behind the other. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the thermocouples ( 6 ) an elongated thermopile ( 5 . 5a . 5b ) form. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the individual thermocouples ( 6 ) in each case substantially at right angles or at an obtuse angle to the longitudinal axis of the thermopile ( 5 . 5a . 5b ) are aligned. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the thermocouples ( 6 ) several elongated thermopiles ( 5a . 5b ), which are connected in series one behind the other and arranged substantially parallel next to each other. Level sensor ( 1 ) according to claim 4 or 5, characterized in that the thermocouples ( 6 ) hot contact points ( 7 ) and cold contact points ( 8th ), where at the hot contact points ( 7 ) on the one hand and the cold contact points ( 8th ) on opposite sides of the thermopile ( 5 . 5a . 5b ) are each arranged in a row. Level sensor ( 1 ) according to claim 5 and claim 6, characterized in that in the adjacent thermopiles ( 5a . 5b ) either the hot contact points ( 7 ) or the cold contact points ( 8th ) face each other. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the individual thermocouples ( 6 ) two conductor materials ( 9 . 10 ) at a contact point ( 7 ) are interconnected. Level sensor ( 1 ) according to claim 8, characterized in that the two conductor materials ( 9 . 10 ) of the individual thermocouples ( 6 ) each on the same side of a substrate ( 14 ) are arranged. Level sensor ( 1 ) according to claim 8, characterized in that the two conductor materials ( 9 . 10 ) of the individual thermocouples ( 6 ) on opposite sides of a carrier material ( 14 ) and by means of a via ( 15 ) are connected together at the contact point. Level sensor ( 1 ) according to one of claims 8 to 10, characterized in that the one conductor material ( 9 ) is a copper-nickel alloy, in particular CuNi44. Level sensor ( 1 ) according to one of claims 8 to 11, characterized in that the other conductor material ( 10 ) Copper, a copper-manganese-nickel alloy, in particular Manganin ^® , or a nickel-chromium alloy. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the thermocouples ( 6 ) when energized as a function of the electric current, the hot contact points ( 7 ) and the cold contact points ( 8th ), whereas the thermocouples ( 6 ) in the currentless state as a function of the temperature difference (ΔT) between the hot contact points ( 7 ) and the cold contact points ( 8th ) a thermoelectric voltage (U) between the hot contact points (U) 7 ) and the cold contact points ( 8th ) produce. Level sensor ( 1 ) according to one of the preceding claims, characterized in that the thermocouples ( 6 ) are arranged on a foil or a thin-walled tube as a carrier material. Level measuring device with a level sensor ( 1 ) according to any one of the preceding claims. Level measuring device according to claim 15, characterized by a) a to the level sensor ( 1 ) connected power source ( 13 . 16 ) for energizing the level sensor ( 1 ) and b) to the level sensor ( 1 ) connected voltage measuring device ( 17 ) for measuring the level of the sensor ( 1 ) in the de-energized state generated electrical voltage (U). Level measuring device according to claim 16, characterized in that the power source ( 16 ) has a pulse generator and the level sensor ( 1 ) with current pulses. Level measuring device according to claim 16 or 17, characterized by a voltage measuring device ( 17 ) connected integrators ( 18 ) for simple or double integration of the measured voltage. Level measuring device according to claim 15, characterized by a to the level sensor ( 1 ) connected microcontroller ( 13 ) for the electrical control of the level sensor ( 1 ) and for measuring the level of the sensor ( 1 ) generated electrical voltage. Level measuring device according to one of claims 15 to 19, characterized in that the level sensor ( 1 ) in a fuel tank ( 4 ) of a motor vehicle and the level ( 2 ) of the fuel ( 3 ) in the fuel tank ( 4 ) measures. Level measuring device according to one of claims 15 to 20, characterized in that the thermopile ( 5 ) or the thermopiles ( 5a . 5b ) at an obtuse angle, in particular substantially at right angles, to the fluid level to be measured. Level measuring device according to one of claims 15 to 21, characterized in that the individual thermocouples ( 6 ) are each aligned substantially parallel or at an acute angle to the fluid level to be measured.