Abstract:
The invention relates to a measuring apparatus ( 10 ) for measuring a filling level of a container, which measuring apparatus has a measuring arm ( 12 ) with a float element ( 18 ) which is designed to change its angular position about a rotation axis ( 38 ) depending on the filling level. A magnet element ( 24 ) is connected to one end of the measuring arm ( 12 ) in a rotationally fixed manner. A magnet-sensitive element ( 26 ) is designed to output a measurement signal ( 27 ) depending on the angular position of the magnet element ( 24 ). The measuring apparatus ( 10 ) is characterized in that the measuring arm ( 12 ) is mounted in a first bearing ( 22 ) and additionally in a second bearing ( 36 ), wherein the magnet element ( 24 ) is arranged in an intermediate space ( 34 ) between the first bearing ( 22 ) and the second bearing ( 36 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention concerns the measurement of a filling level in a container. In particular, the invention concerns a measuring apparatus for measurement of a filling level based on a magnetic measurement principle. 
         [0002]    Level measuring devices are used in many different technological areas. In particular, in vehicle technology measurement apparatuses can be used that measure different liquid levels, such as of fuel, cooling liquid, brake fluid or similar for example. Accurate measurement of filling levels with small measurement tolerances can be necessary for the safe operation and reliability of a vehicle. For the technical implementation, a number of different requirements can be placed on such measurement apparatuses at the same time. For example, besides robustness and durability, as well as a resistance to different chemical compounds, high accuracy of the measurement results may be required. 
         [0003]    Thus for example, measurement sensors are known from the prior art, with which a change of a filling level causes rotation of a magnetic element. Said change of the angular position of a magnet element causes a change of an electrical output signal at a magnetically coupled static sensor element. An apparatus for the measurement of a filling level, in which the sensor element and the magnet element are disposed in a common chamber of a sensor housing, is presented in DE 10 2005 062775 A1. In this the magnet element is mechanically coupled to a floating arm that is mounted so as to be rotatable about a rotation axis. The design and the operation of said measurement apparatuses can often make a compromise necessary regarding the diverse requirements. 
       SUMMARY OF THE INVENTION 
       [0004]    Ideas of the invention can be viewed as being based on the ideas and knowledge described below among other things. 
         [0005]    A measurement arm connected for example to a float element is often implemented in the form of a metallic shaft or of a metallic pin that is fed by means of a bearing into an internal region of a housing and that extends across the entire width of a sensor housing to an opposite housing wall for example. Here the magnet element is often disposed directly on the measurement arm or on the shaft, wherein the magnet element rotates together with the measurement arm or the shaft in the event of a change of the filling level. During this the spatial change of position of the magnet element produces a change of the magnetic field produced by the magnet element. Said change is detected by a magnetically sensitive element and the corresponding electrical measurement signals are generated. For this the magnetically sensitive element is often disposed away from the rotation axis of the measurement arm, for example radially separated from the magnetic element. Said non-axial arrangement of the magnet element and the magnetically sensitive element can result in a compromise regarding the accuracy and linearity of the measurement results depending on a filling level. 
         [0006]    In order to take said aspect into account, there are solutions in the prior art with which the magnet element and the magnetically sensitive sensor are disposed on the rotation axis of the measurement arm. Here the magnet element can be disposed on one end of the measurement arm or on one end of the shaft for example. Said arrangement is often referred to as an end of shaft arrangement. However, it is necessary for this that the magnet element can perform a rotary movement together with the measurement arm depending on the filling level, wherein the magnetically sensitive sensor is fixedly joined to a sensor housing for example as a reference. For this the measurement arm is supported in a single bearing in the sensor housing with such solutions. Feeding the measurement arm through to an opposite side of the housing is not possible with such end of shaft magnet elements. By using only one bearing, a play or tolerance of a measurement arm bearing can be undesirably increased with time owing to the friction and forces that occur. In particular, with bearings made of plastic an increase of the bearing area can result in displacement limitations and frictional forces between the bearing and the measurement arm. Furthermore, leverage forces can occur owing to the comparatively small supporting surfaces on the housing, and said leverage forces can result in expansion of the bearing and resulting additional room to move for the measurement arm and hence measurement inaccuracies. 
         [0007]    Using the present invention, among other things higher accuracy of a filling level measurement in a container should be achieved. 
         [0008]    Therefore, a measuring apparatus for the measurement of a filling level of a container is proposed that comprises a measurement arm that is designed to change its angular position about a rotation axis depending on the filling level. The measurement arm comprises a float element on its first end and a magnet element on a second end, wherein the magnet element is rotationally fixedly joined to the measurement arm. Further, a magnetically sensitive element is provided, which is implemented to output a measurement signal depending on the angular position of the magnet element. Furthermore, the measuring apparatus comprises a first bearing, in which the measurement arm is rotatably supported. The measuring apparatus is characterized in that a second bearing is provided, in which the measurement arm is rotatably supported, wherein the magnet element of the measurement arm is disposed in an intermediate space between the first bearing and the second bearing. 
         [0009]    One advantage can be seen in that an end of shaft arrangement of the magnet element can be achieved with improved stability owing to less play in the bearings as well as improved accuracy. Owing to the mutually separate bearing points, a more favorable measurement arm force distribution can be achieved. As a result, for example leverage forces transverse to the rotation axis of the measurement arm can be reduced, which can result in a reduction of friction and wear and hence more accurate measurement results. 
         [0010]    A measurement arm for this can be a rigid shaft or a rigid wire for example. The measurement arm can comprise a plurality of subregions that are in an angled arrangement relative to each other. For example, the part of the measurement arm that extends from the surface of the liquid to the housing can be disposed at an angle relative to a subregion of the measurement arm that protrudes into the housing. In one example, the measurement arm is made of a preferably rigid metal wire. 
         [0011]    In one embodiment of the invention, the first bearing and the second bearing are provided on a housing. 
         [0012]    A housing can mean for example a supporting body consisting of plastic. For example, in this case the housing can be made rigid in order to achieve mechanical stability against ambient influences and mechanical loads. 
         [0013]    The bearing that is provided in a side of the housing for example can be a bore with a cross-section approximately equal to or slightly larger than a cross-section of the measurement arm in one example. In a further example, the bearing can also comprise a bearing sleeve or other suitable additional guide elements. Said additional elements as well as the bearing itself can comprise different materials and as a result different properties. The first end of the measurement arm can be located at the height of a liquid level of the container for example. For example, a float element that is made of plastic and filled with air can be mounted there, enabling the necessary buoyancy and hence the necessary coupling between the filling level and the corresponding angular position of the magnet element. 
         [0014]    A rotationally fixed connection of the magnet element to the measurement arm can be implemented in a different way. For example, the magnet element can be attached at the level of its central axis directly and rotationally fixedly to the end of the measurement arm opposite from the float element. In one example, the magnet element is connected to the measurement arm by means of a third material, in order for example to minimize unwanted magnetic effects that could arise from the magnetic properties of the magnet element in combination with the magnetic properties of a measurement arm, for example a metallic measurement arm. 
         [0015]    A magnetically sensitive element can mean a sensor that is implemented to detect changes of a magnetic field and to convert the same into corresponding electrical signals. The electrical signals that are produced can then be further processed by an analysis unit for example. The connection of the magnetically sensitive element to the housing can be used to provide a positionally fixed reference position relative to the rotatably supported magnet element in order thereby to effectively detect position changes of the magnet element. 
         [0016]    In this case a measurement signal can mean for example an electrical voltage and/or an electrical current that is dependent on the angular position of the magnet element. Signals that signal the magnitude of the change are also possible. 
         [0017]    For example, the measurement arm can be indirectly rotatably supported in the second bearing, for example by means of a connecting piece. In other words, the geometry of the measuring apparatus can comprise a spatial interruption of the measurement arm at the level of the rotation axis. This enables the support of the measurement arm on the second bearing by means of a mechanical/static local circumvention of the intermediate space. This means that a coupling or connection of the first bearing to the second bearing is made away from the rotation axis. As a result, the intermediate space is provided at the level of the rotation axis, enabling an end of shaft arrangement of the magnet element without a linearly continuous measurement arm. In this way, the magnetically sensitive element can for example be directly disposed at the level of the rotation axis of the magnet element, in order thereby to achieve high accuracy of the measurement arrangement. The rotation axes of the first bearing and of the second bearing are identical in this case. In other words, the measuring apparatus comprises a local circumvention of the region that is formed by the magnet element and the magnetically sensitive element. 
         [0018]    According to one embodiment of the invention, the magnetically sensitive element is provided on the second bearing. 
         [0019]    According to one embodiment of the invention, a connecting piece is provided on the measurement arm that protrudes into the intermediate space with a first segment and that is supported on the second bearing with a second segment. 
         [0020]    A direct connection to the measurement arm can enable an advantageous transmission of force from the measurement arm to the connecting piece. In one example, the measurement arm is rotationally fixedly connected to the connecting piece. In this case a rotationally fixed connection describes a direct mechanical coupling between the connecting piece and the measurement arm during rotation of the measurement arm. 
         [0021]    In one example, the connecting piece is mounted at the level of the rotation axis of the measurement arm. In a further example, the connecting piece is implemented in a curved form. A second end of the connecting piece can for example be supported on the second bearing so as to be rotatable about the rotation axis, so that the measurement arm together with the connecting piece is supported in the first bearing and in the second bearing. 
         [0022]    In one example, the connecting piece is implemented in a curved form. One advantage can be seen to be that, owing to a curvature of the connecting piece, spatial circumvention of the intermediate space can be achieved instead of a direct connection. In this case the connecting piece can adopt different geometric shapes. 
         [0023]    In this case the connecting piece can provide the intermediate space in the region of the rotation axis that can accommodate the magnet element and the magnetically sensitive element, and in doing so can at the same time enable strong support of the measurement arm again at the level of the rotation axis. In other words, the connecting piece bridges a distance between the magnet element and the magnetically sensitive element in order to use a bearing that is disposed in said region for additional support of the measurement arm. In one example, the connecting piece comprises U-shaped form in a cross-section parallel to the rotation axis. The U-shaped design of the connecting piece can be considered to be a special embodiment of the curved form of the connecting piece. For example, the connecting piece can be made symmetrically U-shaped. 
         [0024]    In one embodiment of the invention, the connecting piece comprises a recess into which the first bearing extends for supporting the measurement arm. In a further embodiment of the invention, the measurement arm extends through the recess of the connecting piece in the first segment. 
         [0025]    In one example, the measurement arm comprises a first region and a second region, wherein the first region encloses an angle with the second region. A stabilizing element is connected at one end to the connecting piece and/or to the first region of the measurement arm, and at the other end to the second region of the measurement arm, such that torsion and/or bending of the shaft during a change in the angular position of the measurement arm is reduced. An advantage can be seen in that a filling level-related change of angle in the form of a mainly vertical displacement, for example of the float element, can be converted into a horizontal rotary movement of the measurement arm. 
         [0026]    Torsions and bending effects can sometimes occur here caused by the torques and bending forces that occur, which can possibly cause errors in the measurement results. The stabilizing element has a supporting function here, which can minimize such mechanical effects. For example, leverage forces, which could possibly cause torsion of the first region of the measurement arm, can be supportively absorbed by the stabilizing element. According to one example, the stabilizing element can be implemented as part of the connecting piece or can be implemented in one piece or integrally with the connecting piece. According to one embodiment of the invention, the housing comprises a plastic. One advantage of the use of plastics for housing can be seen in reduced weight with advantageous stability of the housing. Furthermore, plastics can be used advantageously in some cases in or on containers in which other container materials cannot be considered owing to chemical reactions with the container contents. 
         [0027]    In one example, the measurement arm comprises metal or a metal alloy. One advantage can be seen, among other things, in increased stability and durability at comparatively low weight of the measurement arm. For example, the measurement arm can consist of a steel wire or a steel profile. In particular, a round cross-sectional shape of the measurement arm in the region of the bearing can be advantageous. 
         [0028]    According to one embodiment of the invention, the bearing surface of the first and/or second bearing comprises a metal. One advantage thereof can be seen in that a metallic surface in the region of the bearing can reduce frictional forces and hence frictional losses and wear. As a result, owing to more advantageous properties of metals, tolerances or play between the bearing and the measurement arm can be kept low. This can enable increased accuracy of the measurement arrangement. For example, steel, copper or similar metals or metal alloys can be used. 
         [0029]    In one example, the measurement arm is made of a metallic material and the first and second bearings comprise metallic bearing surfaces. In one example, the materials of the first bearing and of the second bearing can be implemented differently. For example, the first bearing is made of a plastic, wherein the second bearing is made of a metal. 
         [0030]    According to one embodiment of the invention, the connecting piece comprises a plastic. One advantage can be seen in that owing to malleability during the manufacture of such a connecting piece, an advantageous adaptation of the structures of the connecting piece to the measurement arm and/or the magnet element is possible. Furthermore, diverse forms of the connecting piece can be implemented in a comparatively simple way depending on the circumstances of the housing, of the magnet element and of the magnetically sensitive element. 
         [0031]    In one example, the magnetically sensitive element is a Hall effect sensor. With such a sensor, the so-called Hall effect is used for the measurement of magnetic fields. According to this principle, an output voltage is produced by the sensor that is for example proportional to the product of the magnetic field strength of the magnet element and a current through the sensor. 
         [0032]    In one embodiment of the invention, the first segment of the connecting piece comprises the magnet element. In one example, the magnet element is disposed in or on the connecting piece. In other words, the measurement arm or the end of the measurement arm can be spatially separate from the magnet element. 
         [0033]    For example, the magnet element can be enclosed by the connecting piece so that a magnetic interaction between the measurement arm and the magnet element is minimized. This can have the advantage that unwanted magnetic effects, which are caused for example by metallic properties of the measurement arm, can be minimized or reduced. For example, the magnet element can be encased in a connecting piece consisting of plastic, and the connecting piece is for its part connected to the measurement arm across a spatial separation. As a result, the measurement arm can be rotationally fixedly connected to the magnet element without direct mechanical contact between the measurement arm and the magnet element. 
         [0034]    Furthermore, according to one aspect of the invention a motor vehicle is proposed that comprises a measuring apparatus as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Exemplary embodiments of the invention are described in detail below with reference to the present figures. Neither the description nor the figures should be construed as limiting the invention. 
           [0036]      FIG. 1A  shows a schematic design of a measuring apparatus according to the invention. 
           [0037]      FIG. 1B  shows schematically an alternative design of a measuring apparatus according to the invention. 
           [0038]      FIG. 2  shows a simplified sectional representation of a measuring apparatus according to the invention for measurement of a filling level of a container. 
       
    
    
       [0039]    The figures are only schematic and are not to scale. In principle, identical or similar parts are provided with the same reference characters. 
       DETAILED DESCRIPTION 
       [0040]      FIG. 1A  shows a measuring apparatus  10  for measurement of a filling level of a liquid surface  20 , for example in a container, in a simplified way. The measuring apparatus  10  comprises a measurement arm  12  with a first region  14  and a second region  16 . The second region  16  of the measurement arm  12  protrudes towards the liquid surface  20  in this case. For this purpose, for example a float element  18  can be mounted on the remote end of the second region  16  of the measurement arm  12 , which produces a coupling between the level of the liquid surface  20  and a deflection movement of the second region  16  of the measurement arm  12 . In the event of a change of the liquid surface  20 , a displacement of the float element  18  is produced that triggers an angular displacement of the second region  16  of the measurement arm  12 . The first region  14  of the measurement arm encloses an angle, for example of 90°, with the second region  16  of the measurement arm  12  in this case. In this way, a rotary movement of the first region  14  of the measurement arm  12  occurs in the event of an angular displacement of the second region  16  of the measurement arm  12 . 
         [0041]    The first region  14  of the measurement arm  12  is rotatably supported in a first bearing  22 . The measurement arm  12  comprises a magnet element  24  on its end in its first region  14 . The magnet element  24  is rotationally fixedly connected to the end of the first region  14  of the measurement arm  12 , so that a rotary movement of the magnet element  24  occurs during a rotational displacement of the measurement arm  12 . Said rotation of the magnet element  24  is detected by a magnetically sensitive element  26  from change of the magnetic field in the surroundings of the magnet element  24  caused hereby. The magnetically sensitive element  26  produces electrical signals  27  during this, which can be processed by a connected analysis unit (not shown) for example. The magnetically sensitive sensor  26  is fixedly connected to a housing  28  in this case. 
         [0042]    In the example shown here, the housing  28  comprises a first side  30  of the housing  28 , which is opposite a second side  32  of the housing  28 . The housing  28  forms an intermediate space  34  or a chamber with its first side  30  and its second side  32 . The magnet element  24  as well as the magnetically sensitive element  26  are disposed in the intermediate space  34 . The housing  28  comprises a stable, rigid shape in its design and owing to its material. This is used for a supporting function or a holding function, in order to enable a defined spatial arrangement of the significant components of the measuring apparatus  10 . 
         [0043]    The first bearing  22  is disposed on the first side  30  of the housing  28 , so that the first region  14  of the measurement arm  12  is rotatably supported. In this way the end of the first region  14  of the measurement arm  12 , on which the magnet element  24  is mounted, is disposed in the intermediate space  34 . A second end of the first region  14  of the measurement arm  12 , which is connected to the second region  16  of the measurement arm  12 , is located outside of the intermediate space  34 . 
         [0044]    With this design, without the further elements mentioned below the supporting forces that occur would only be absorbed by the first bearing  22 . This would possibly result in disadvantageous friction or wear events in the first bearing  22 . Therefore, a second bearing  36  that is spatially separate from the first bearing  22  is disposed on the second side  32  of the housing  28 . Said second bearing  36  forms a common rotation axis  38  with the first bearing  22 . In order to enable a so-called end of shaft arrangement of the magnet element  24  on the measurement arm  12 , a connecting piece  40  is provided to take up the supporting forces, being rotationally fixedly connected to the first region  14  of the measurement arm  12  at a first end  42  of the connecting piece  40 . The connecting piece  40  is supported at a second end  44  in the second bearing  36 . 
         [0045]    In the example represented here, the connecting piece  40  is designed to be curved or U-shaped in order to spatially circumvent the region of the magnet element  24  and of the magnetically sensitive element  26  and to enable a second bearing point that is spatially separate from the first bearing  22  by means of supporting the second end  44  of the connecting piece  40  in the second bearing  36 . The advantageous force distribution of the supporting forces of the measurement arm  12  on the housing  28  can be enabled hereby. Smaller leverage forces act transversely to the rotation axis  38  owing to the spatial separation of the two bearings  22 ,  36 . This can improve the operating life as well as the play or tolerances of the bearings  22 ,  36 . In the example shown here, the second end  44  of the connecting piece  40  comprises an end region that extends along the rotation axis  38  and is supported in the bearing  36 . 
         [0046]    Owing to said design, a gap  46  between the magnet element  24  and the magnetically sensitive element  26  that is advantageous for accurate measurement can be enabled. This can increase the accuracy of the measurement results. 
         [0047]    An example of a measuring apparatus  10  is shown in  FIG. 1B , which shows an alternative design variant of the measuring apparatus  10  according to the invention. The measuring apparatus  10  represented in said example is similar in its implementation to the example represented in  FIG. 1A . In contrast to the exemplary embodiment that is shown in  FIG. 1A , the connecting piece  40  is supported on a casing surface in the bearing  36 . Furthermore, in the example that is shown in  FIG. 1B , the connecting piece  40  is connected at its first end  42  to the first region  14  of the measurement arm  12  outside of the housing  28  and outside of the intermediate space  34 . The axes of the first bearing  22  and of the second bearing  36  lie on the common rotation axis  38  in this case. 
         [0048]      FIG. 2  shows a further exemplary embodiment of a measuring apparatus for the measurement of a filling level of a container. A measurement arm  12  has a shape that is angled by 90° and is disposed in a first bearing  22  on a first side  30  of a housing  28 . A magnet element  24  is enclosed by a connecting piece  40  and is supported thereby. This can be achieved by casting or gluing the magnet element  24  in the connecting piece  40  for example. One end of the first region  14  of the measurement arm  12  is rotationally fixedly connected to the connecting piece  40  in the region of the intermediate space  34  between the first side  30  of the housing and the second side  32  of the housing. Owing to the respective rotationally fixed connection of the measurement arm  12  to the connecting piece  40  as well as the likewise rotationally fixed connection of the connecting piece  40  to the magnet element  24 , an intermediate space is enabled between the end of the first region  14  of the measurement arm  12  and the magnet element  24 . This can have advantageous effects owing to the resulting reduced magnetic interactions between the mainly metallic measurement arm  12  and the magnet element  24 . 
         [0049]    The connecting piece  40  comprises an approximately U-shaped form and is supported at its second end  44  in a second bearing  36  on the outside of the second side  32  of the housing  28 . In this way, a gap  46  is produced between the magnet element  24  and the second side  32  of the housing. A magnetically sensitive element  26  is disposed on or in the second side  32  of the housing  28  in the vicinity of and at the level of the rotation axis  38 . The magnetically sensitive element  26  can be a sensor based on the Hall effect here for example. For example, a centre point of the magnetically sensitive element  26  lies opposite a magnetic centre point of the magnet element  24  on the rotation axis  38 . 
         [0050]    The connecting piece  40  comprises a third segment  50  that is connected to the measurement arm  12  in the example shown here and can for example comprise the stabilizing element  48 . A second segment  54  is used to support the connecting piece  40  on the second bearing  36 . A first segment  52  of the connecting piece  40  protrudes into the intermediate space  34 . The connecting piece  40  comprises a recess  56  in the region of the first bearing  22 . In this case the recess  56  is dimensioned so that it encloses the bearing  22  at a distance. 
         [0051]    In addition, in the example shown here a stabilizing element  48  is provided that rotationally fixedly connects the connecting piece  40  to the first region  14  of the measurement arm  12  and in its further extent additionally connects the first region  14  of the measurement arm  12  to the second region  16  of the measurement arm by means of a separate spatial connection. In this way, bending and/or torsion of the measurement arm  12  caused by the displacement of the measurement arm  12  can be reduced, in particular in the vicinity of the first region  14  of the measurement arm  12 . 
         [0052]    In one example, the housing  28  consists of a plastic. In a further example, the bearing surface of the first bearing  22  and/or of the second bearing  36  comprises a metal. For example, for this purpose metal casings can be mounted in the interior of the bearing in order for example to be able to use different materials for the bearing surfaces and the housing  28 . In one example, the second bearing  36  comprises a metal on its bearing surfaces on the housing side and the connecting piece  40  is made of a plastic, for example in the region of the bearing. In a further example, the connecting piece  40  comprises a different material in the region of the first bearing  22  and/or in the region of the second bearing  36  from the material in the remaining region of the connecting piece  40 . This can be advantageous in order to achieve smaller tolerances and greater durability in the region of the bearing owing to harder materials for example. 
         [0053]    In addition, it is to be noted that “comprising” does not exclude other elements or steps and “a” or “one” does not exclude any number. Further, it is to be noted that features or steps that are described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference characters in the claims are not to be considered as limiting.