DE10057939A1 - Measurement of fuel level in a motor vehicle fuel tank using a dual sensor arrangement that allows compensations to be made for variations in fuel tank capacity due to manufacturing tolerances and tank expansion - Google Patents

Abstract

Method for measuring the level of fluid in a container, especially a motor vehicle fuel tank, in which a first sensor (3) is mounted on the bottom of the tank and measures the distance between the tank bottom and the fuel level, while a second sensor (4) is mounted at the tank top and measures the distance between the top and the fuel level. When the fuel level lies on both sensors the fuel level can be determined and in addition tolerance adjustments or expansion compensations made. An Independent claim is made for a vehicle fuel level measurement device that enables adjustments to be made for varying tolerances in fuel tank manufacture and for expansion of the fuel tank during its lifetime.

Description

The present invention relates to a method for measuring the level of a Liquid in a container according to the preamble of claim 1 and a corresponding device according to the preamble of claim 6. In particular The present invention relates to a method and an apparatus for measuring the Tank level in a motor vehicle.

Nowadays, sensors are usually used to measure the tank level, which work on the so-called leverage principle.

In FIG. 4 is an example of such a lever-type sensor which is arranged in a fuel tank 1, is shown. The lever transmitter comprises a float 9 , a lever arm 10 and an angle detection device 11 . The float 9 floats on the fuel surface and is connected via the lever arm 10 to the angle detection device 11 , which detects the deflection angle ϕ of the lever arm 10 and thus generates a statement about the swimming height of the float 9 or about the fill level of the fuel tank 1 . The lever transmitter 9-11 is generally combined with the fuel pump 2, which is likewise located in the fuel tank 1 and serves to convey the fuel, to form a component or a unit. This lever sensor fuel pump unit is usually supported on the bottom of the fuel tank 1 .

From today's perspective, the use of a lever encoder has a number of disadvantages. For example, the lever transmitter in the reserve and full area of the fuel tank 1 is too imprecise, requires a relatively large installation space and is only suitable to a limited extent for multi-chamber tanks.

Another problem associated with leverage is the fact that Measurement accuracy as with all simple level measurement systems depends on  Tank tolerances is. The fuel tank that is customary today and manufactured by inflation shows Comparatively large manufacturing tolerances in the range of several when new Liters (e.g. approx. ± 2 liters) and expands over the course of the vehicle's life additionally by up to several liters (for example up to 2 liters). However, this is problematic in that the one with the lever encoder or in general with the Level sensor detected fuel level using a predetermined Height-volume characteristic curve in the fuel volume in the fuel tank is converted. Changes with increasing lifespan of the motor vehicle the volume of the fuel tank, leads to the procedure described above comparatively large mistakes.

In FIG. 5, the curve of the fuel gauge depending on the filling level of a fuel tank (curve (b)) and the course is shown of the fuel gauge in an example, 15% extended in the height in relation to the original state fuel tank (curve (a)) by way of example. The resulting fuel gauge error (characteristic (c)) is also shown. As can be seen from FIG. 5, when the display is full, there is a maximum error of approximately 17.7%, which corresponds to an error of 10.2 l in the original state for a fuel tank with a volume of 67.7 l.

Due to the aforementioned disadvantages, alternative methods and Devices for measuring the tank level sought. For example, in the DE 198 16 455 A1 a level sensor with a larger number of on one Printed circuit board or a flexible conductor track arranged side by side Sensor elements described, each of these sensor elements having a capacitive Level switch forms so that by evaluating the number of in the fuel immersing capacitive level switch with the help of an electronic evaluation logic the level of the corresponding fuel tank can be determined if the individual sensor elements are distributed vertically over the height of the fuel tank.

With this new type of measurement system, however, the problem arises that an im Expansion of the fuel tank to a measuring or display error.  

The present invention is therefore based on the object of a method and a corresponding device for measuring the level of a liquid in a To propose containers, especially in a fuel tank, which on the one hand extremely precise level measurement is possible and on the other hand errors due to a Volume change of the container or fuel tank can be avoided.

This object is achieved by a method with the features of Claim 1 and a device with the features of claim 6 solved. The Sub-claims each define preferred and advantageous embodiments of the present invention.

According to the invention, at least two sensors are used to measure the fill level used, wherein the first sensor is designed and arranged such that it Distance between the bottom of the container or fuel tank and the Can detect liquid surface or fuel surface. The second sensor is designed and arranged such that it covers the distance between the top of the Container or fuel tanks and the liquid surface or fuel surface can record, by evaluating the output signals of the two sensors. respectively. the distances recorded by the two sensors provide information about the fill level the liquid or fuel in the container or fuel tank is derived.

The two sensors can in particular be configured such that they each several arranged side by side on a common carrier material Sensor elements, for example capacitive sensor elements, which are vertical are arranged distributed over the container or fuel tank. The first one Sensor supported in particular at the bottom of the container or fuel tank while the second sensor is attached to the top of the tank or fuel. In principle, however, can in principle be any within the scope of the present invention configured level measuring devices can be used as sensors.

With the help of the present invention, a double level measurement is thus possible proposed, with the help, for example, especially when using the Present invention for measuring the level of a fuel tank tank tolerances and / or an expansion of the fuel tank, which, for. B. by aging the Fuel tanks or can be caused by excess pressure in the fuel tank,  can be measured and largely compensated. This means that the Calculation of the fuel volume contained in the fuel tank based on the detected fuel level errors due to tank tolerances largely avoided can be.

The present invention will hereinafter be described in more detail with reference to the accompanying Drawing using a preferred embodiment for measuring the Fuel level in a fuel tank explained. Of course the present one However, the invention is not based on measuring the fuel level in a fuel tank limited, but can generally be used to measure the level of any liquid can be used in containers of any design.

Fig. 1 shows the use of a measuring apparatus according to a preferred embodiment of the present invention in a fuel tank,

Fig. 2 shows, in Fig. 1 illustrated fuel tank and the measuring device according to the invention after expansion of the fuel tank, wherein the height of the fuel tank is greater than in Fig. 1

Fig. 3 is a plan view and a side view of a possible arrangement of the sensors shown in Fig. 1 and Fig. 2 on a common carrier foil,

Fig. 4 shows a fuel tank with a conventional lever transmitter for measuring the level of the fuel tank, and

FIG. 5 shows an illustration for explaining the error in the tank display as a result of a height expansion of the fuel tank according to the prior art.

In Fig. 1, a fuel tank 1 is shown with a fuel pump 2. To measure the fill level of the fuel tank 1 , not only one sensor, but two sensors 3 , 4 are used. One sensor 3 is designed such that it measures the distance h _u between the bottom of the fuel tank 1 and the fuel surface, while the other sensor 4 is arranged such that it measures the distance h _o between the top of the fuel tank 1 and the fuel surface , As shown in FIG. 1, the measurement signals generated by the two sensors 3 and 4 are fed to an evaluation logic or evaluation circuit 8 , which evaluates the measurement signals generated by the two sensors 3 , 4 to the fill level h _F or that in the fuel tank 1 located fuel volume V closes.

In principle, all known types of fill level sensors can be used as sensors 3 , 4 . However, sensors of the type described in the aforementioned DE 198 16 455 A1 are particularly well suited, each of which comprises a plurality of sensor elements, in particular capacitive sensor elements, arranged next to one another on a circuit board or a flexible conductor track, each of which represents a level switch in itself. The individual sensor elements of the two sensors 3 , 4 are arranged adjacent to one another in the height direction of the fuel tank 1 , ie in the vertical direction, as shown in FIG. 1, the capacitance of each capacitive sensor element of the two sensors 3 , 4 changing when it changes immersed in the fuel. In this way, the evaluation logic can deduce the distances h _u and h _o by detecting the sensor elements of the two sensors 3 and 4 immersed in the fuel.

The present invention can thus be compared with no significant additional effort the capacitive level sensors already in development are, so that no significant additional manufacturing costs arise.

In particular, in principle no two separate sensors 3 , 4 are required, since with a suitable arrangement of the individual sensor elements, the two sensors 3 , 4 can also be designed to be integrated on a common carrier film or the like. A corresponding exemplary embodiment is shown in FIG. 3. As can be seen from FIG. 3, the two sensors 3 , 4 are configured on a common flexible carrier film 7 and connected to one another via electrical connections 6 . Corresponding electrical connections 5 are provided at the upper end of the carrier film 7 . In this case, the electronic evaluation of the individual capacitive sensor elements of the two sensors 3 , 4 by the evaluation logic 8 must take place in such a way that a separate determination of the fill level is possible for the upper sensor 4 and the lower sensor 3 . However, this is not a fundamental technical problem, but only a question of the execution of the evaluation logic 8 . Since the evaluation logic 8 is preferably integrated in a single electronic module, in this case there is no additional effort in production for the requirements required here.

In the embodiment shown in FIG. 1, the lower sensor 3 is in particular attached to the lower part of the fuel pump 3 and is supported together with it on the bottom of the fuel tank 1 , while the upper sensor 4 is preferably attached to the flange of the fuel pump 2 and from above protrudes into the fuel.

In FIG. 2, the fuel tank 1 shown in Fig. 1, according to a heightwise dimension of the fuel tank 1, which may be caused for example by aging of the fuel tank or by excess pressure in the fuel tank is illustrated. As can be seen from FIG. 2, the fuel tank 1 now has a height h _T2 compared to the illustration in FIG. 1, which is greater than the height h _{T1 of} the fuel tank 1 shown in FIG. 1. As a result, the upper sensor 4 attached to the flange of the fuel pump 2 is immersed less deeply in the fuel. While in Fig. 1, the individual distances are provided with the subscript "1", the respective distances shown in FIG. 2 are denoted by the index "2".

The following text more specifically, a suitable method for determining the level or volume of fuel in the fuel tank 1 based on the measurement signals supplied by the two sensors 3, 4 will be explained, wherein in each case detected by the lower sensor 3 Distance between the bottom of the fuel tank 1 and of the fuel surface is denoted by h _u , while the distance between the top of the fuel tank 1 and the fuel surface detected by the upper sensor 4 is denoted by h _{o in} each case. In addition, the effective length of the lower sensor 3 is denoted by l _u and the effective length of the upper sensor 4 by l _o . The level of the fuel in the fuel tank 1 is denoted by h _F and the height of the fuel tank 1 by h _T.

The following relationship applies:

h _T = h _o + h _u (1)

That is, the instantaneous height h _{T of} the fuel tank 1 can be inferred from the measurement signals of the two sensors 3 , 4 . It is necessary that the two sensors 3, 4 have a coverage even with expansion of the fuel tank 1, ie in a sub-region (see Fig. 1 and Fig. 2) 4 project both sensors 3, in the fuel inside. The following must therefore apply:

l _u + l _o <h _T (2)

In the lower fill level range, ie when h _F <l _u , the fill level h _F can be determined using the lower sensor 3 . The following therefore applies:

h _F = h _u for h _F <l _u (3)

In the upper fill level range, ie for h _F ≧ l _u , the fill level h _F can be determined with the upper sensor 4 . In this case:

h _F = h _T - h _o for h _F ≧ l _u (4)

As already mentioned, h _o denotes the distance between the top of the fuel tank 1 and the fuel surface, ie the fuel-free area of the upper sensor 4 .

As has also been mentioned previously, the height h _{T of} the fuel tank 1 in the overlap area can be determined in accordance with equation (1) above. With knowledge of the instantaneous height of the fuel tank, errors due to tank tolerances or tank expansion can be largely eliminated by using the height-volume characteristic curve used to convert the fill level or the fill height h _{F of} the fuel tank 1 into the fuel volume V located in the fuel tank Height h _{T is} normalized linearly. In the simplest case, the following applies to a rectangular fuel tank:

V = Ah _F .h _T / h _TN (5)

A denotes the base area and h _TN the nominal height, ie the height in the unexpanded state, of the fuel tank 1 .

As has already been explained, in order to determine the tank height h _{T, it is} necessary for the instantaneous fill level or the fill height h _F of the fuel in the fuel tank 1 to be in the overlap region of the two sensors 3 , 4 , ie the following must apply:

h _T - l _o ≦ h _F ≦ l _u (6)

The respectively determined by the evaluation logic 8 instantaneous value of the height h _T of the fuel tank 1 can be respectively latched by the evaluation logic unit 8 and is subsequently used as a correction value for determining the respective fuel volume V. If no value for the height h _{T of} the fuel tank 1 has been determined in the initial state, h _{T is} initially initialized with the nominal height of the fuel tank 1 , ie the method described above is started with h _T = h _TN .

LIST OF REFERENCE NUMBERS

1

Fuel tank

2

Fuel pump

3, 4

level sensor

5

electrical connection

6

conductor path

7

support film

8th

evaluation logic

9

swimmer

10

lever arm

11

Angle detection means
h _u

, h _o

measuring signal
h _F

level
h _T

tank height
V fuel volume

Claims (14)

1. A method for measuring the level of a liquid in a container, in particular a fuel tank, wherein a first distance (h _u ) between the bottom of the container ( 1 ) and the liquid surface is detected, characterized in that a second distance (h _o ) between the top of the container ( 1 ) and the liquid surface is detected, and that an evaluation of the level of the liquid in the container ( 1 ) is derived by evaluating the first and second distances (h _u , h _o ) thus detected. 2. The method according to claim 1, characterized in that the detected first distance (h _u ) is used as the fill level (h _F ) of the liquid in the container ( 1 ) if the first distance (h.) Detected by a first sensor ( 3 ) _u ) is smaller than the vertical extent of the first sensor ( 3 ) starting from the bottom of the container ( 1 ). 3. The method according to claim 2, characterized in that the fill level (h _F ) of the liquid in the container ( 1 ) is determined on the basis of the second distance (h _o ) detected by a second sensor ( 4 ), if that of the first Sensor ( 3 ) detected first distance (h _u ) is at least as large as the vertical extent of the first sensor ( 3 ) starting from the bottom of the container ( 1 ). 4. The method according to any one of the preceding claims, characterized in that a statement about the current height (h _T ) of the container ( 1 ) is derived from the detected first distance (h _u ) and the detected second distance (h _o ). 5. The method according to claim 4, characterized in that from the determined fill level (h _T ) of the liquid in the container ( 1 ), a statement about the liquid volume (V) located in the container ( 1 ) is derived using a corresponding characteristic, and that the characteristic curve is standardized according to the instantaneously determined value of the height (h _T ) of the container ( 1 ). 6. Device for measuring the level of a liquid in a container, in particular a fuel tank, with a first sensor ( 3 ) for detecting a first distance (h _u ) between the bottom of the container ( 1 ) and the liquid surface and for generating one of the first Distance (h _u ) corresponding first measurement signal, characterized in that a second sensor ( 4 ) is provided for detecting a second distance (h _o ) between the top of the container ( 1 ) and the liquid surface by a distance of the second distance (h _o ) generate a corresponding second measurement signal, and the evaluation means ( 8 ) are provided for evaluating the first measurement signal of the first sensor ( 3 ) and the second measurement signal of the second sensor ( 4 ), in order to depend on the level (h _F ) of the liquid in the container ( 1 ) to determine. 7. The device according to claim 6, characterized in that the first sensor ( 3 ) and the second sensor ( 4 ) each comprise a plurality of sensor elements arranged adjacent in the longitudinal direction of the respective sensor, and that the first sensor ( 3 ) is arranged such that it extends into the container ( 1 ) from the bottom of the container ( 1 ), while the second sensor ( 4 ) is arranged such that it extends into the container ( 1 ) from the top of the container ( 1 ). 8. The device according to claim 7, characterized in that a liquid delivery device ( 2 ) is arranged in the container ( 1 ), wherein the first sensor ( 3 ) is attached to the lower region of the liquid delivery device ( 2 ) and together with the liquid delivery device ( 2 ) on the bottom of the container ( 1 ), while the second sensor ( 4 ) is attached to the upper region of the liquid delivery device ( 2 ). 9. The device according to claim 7 or 8, characterized in that the first sensor ( 3 ) and the second sensor ( 4 ) are arranged on a common, in particular flexible, carrier material ( 7 ). 10. The device according to one of claims 7-9, characterized in that the evaluation means ( 8 ) are designed such that they as the fill level (h _F ) of the liquid in the container ( 1 ) the first detected by the first sensor ( 3 ) Determine the distance (h _u ) if the level of the liquid in the container ( 1 ) is less than the vertical extent of the first sensor ( 3 ) starting from the bottom of the container ( 1 ). 11. The device according to any one of claims 7-10, characterized in that the evaluation means ( 8 ) are designed such that they the fill level (h _F ) of the liquid in the container ( 1 ) on the basis of the from the second sensor ( 4 ) Determine the detected second distance (h _o ) if the level of the liquid in the container ( 1 ) is at least as large as the vertical extent of the first sensor ( 3 ) starting from the bottom of the container ( 1 ). 12. Device according to one of claims 7-11, characterized in that for the vertical extension l _{u of} the first sensor ( 3 ) starting from the bottom of the container ( 1 ) and the vertical extension 10 of the second sensor ( 4 ) starting from the Top of the container ( 1 ) the following relationship applies:
h _T - l _o ≦ h _F ≦ l _u ,
where h _T denotes the height and h _F the fill level of the container ( 1 ). 13. Device according to one of claims 6-12, characterized in that the evaluation means ( 8 ) are designed such that they by evaluating the first measurement signal generated by the first sensor ( 3 ) and the second generated by the second sensor ( 4 ) Measurement signal determine the current height of the container ( 1 ). 14. The device according to claim 13, characterized in that the evaluation means ( 8 ) are designed such that they use a certain characteristic from the level (h _F ) of the liquid in the container ( 1 ) to make a statement about that in the container ( 1 ) Derive the liquid volume (V) and standardize the characteristic curve according to the instantaneous height (h _T ) of the container ( 1 ) determined in each case.