Abstract:
To provide a load cell, having a force transducer for recording tensile and compressive forces that are to be determined, which can be produced more economically and, in particular, can also be handled more easily during the adjustment of the sensor arrangement than hitherto, the force transducer comprising a flectionally elastic element and a force introduction part acting on the flectionally elastic element, having a sensor arrangement for detecting a deformation of the flectionally elastic element and the transformation thereof into an electric weighing signal, and having a housing receiving the force transducer and the sensor arrangement, with a flectionally rigid wall part, on which the flectionally elastic element of the force transducer is held, it is proposed that the sensor arrangement be arranged on a separate carrier, which is held on the flectionally rigid wall part and/or a flectionally rigid base part region of the housing

Description:
[0001]     This application is a continuation of international application number PCT/EP2006/001972 filed on Mar. 3, 2006.  
         [0002]     The present disclosure relates to the subject matter disclosed in international application number PCT/EP2006/001972 of Mar. 3, 2006 and German application number 10 2005 010 982.9 of Mar. 3, 2005, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The invention relates to a load cell comprising a force transducer for recording tensile and compressive forces to be determined, wherein the force transducer has a flectionally elastic element and a force introduction part acting on the flectionally elastic element, comprising a sensor arrangement for detecting a deformation of the flectionally elastic element and the transformation thereof into an electric weighing signal and comprising a housing receiving the force transducer and the sensor arrangement with a flectionally rigid wall part, on which the flectionally elastic element of the force transducer is held.  
         [0004]     A load cell, in which the flexible element is configured as a membrane, is known, for example, from DE 36 27 127 A1. This load cell is configured in the form of a load cell, in which a rigid carrier element holds the membrane in an elastically deformable manner, the deformation of the membrane being detected, for example, by means of a sensor arrangement, which contains a Hall generator.  
         [0005]     A load cell is also known from DE 41 32 108 A1, in which a membrane also forms the flexible element. A capacitive sensor arrangement is used as the sensor arrangement.  
         [0006]     The aforementioned load cells have in common that they are only of limited use in a harsh environment.  
         [0007]     An improvement is provided here by the load cell according to DE 103 25 390 A1, which is, on the one hand, robust and, on the other hand, can also be installed in cramped conditions.  
         [0008]     The relatively expensive construction, in particular for the assembly of the flexible element (also configured here as a membrane), and the adjustment of the elements of the sensor arrangement with respect to one another are disadvantageous in this solution.  
       SUMMARY OF THE INVENTION  
       [0009]     In accordance with the present invention, a load cell of the type described at the outset is proposed, which is produced more economically and, in particular, can also be handled more easily during the adjustment of the sensor arrangement.  
         [0010]     In accordance with an embodiment of the invention, a sensor arrangement is arranged on a separate carrier, which is held on the flectionally rigid wall part and/or a flectionally rigid base part region of the housing.  
         [0011]     The carrier, on which the sensor arrangement is arranged, is preferably held directly on the flectionally rigid wall part and/or a flectionally rigid base part region of the housing.  
         [0012]     It is particularly preferred that the carrier be held and supported exclusively on the flectionally rigid wall part of the housing, i.e. housing parts, which do not form part of the flectionally rigid wall part of the housing, maintain a spacing from the carrier so that even at maximally permissible tensile and compressive forces, in which a certain deformation of these other housing parts may take place, these do not exert any influence on the carrier and its geometry and therefore cannot influence the sensor arrangement on the separate carrier. A maximum protection against faulty measurements is therefore achieved even upon the action of high tensile and compressive forces, in particular also upon the action of forces perpendicular to the measuring direction of the measuring cell.  
         [0013]     Preferred sensor arrangements for the load cell according to the invention comprise a transmitter element and a sensor element that is separate from this, a first of these two elements being held stationarily on the carrier and the second of these elements being held movably on the carrier with respect to the first element.  
         [0014]     In this case, the second element is preferably held on a spring part of the carrier, with it being possible for the spring part to be configured in one piece with the carrier, on the one hand, or else to be manufactured as a separate part and fixed to the carrier, for example welded. The possibility is therefore provided of carrying out the alignment of the transmitter and sensor element, which is important for the accuracy of the load cell, in a prior and separate process, which is substantially simpler than not implementing this until assembly of the load cell. Moreover, the transmitter and sensor element can be arranged with respect to one another to achieve maximum signals, even if the spacings to be maintained here should optionally be small. Even in this case, a high degree of constant product quality is easy to ensure.  
         [0015]     The second element will preferably be arranged in a neutral point of the flectionally elastic element in the unloaded state of the force transducer, so that, on the one hand, a maximum sensitivity of the sensor arrangement or the load cell itself can be achieved and, on the other hand, a non-sensitivity of the measurement of transverse forces possibly occurring during the measurement results.  
         [0016]     Preferred sensor arrangements work according to the principal of contact-free path measurement, so the transmitter and sensor element are two parts which are physically completely separate from one another, which can be moved relative to one another in a loss-free manner.  
         [0017]     A particularly suitable sensor arrangement, which works according to the principle of contact-free path measurement is a Hall sensor arrangement with a magnet as the transmitter element and a Hall sensor as the sensor element.  
         [0018]     Likewise, a preferred sensor arrangement, which functions according to the principle of contact-free path measurement, is an optical sensor arrangement with a light source as the transmitter element and a photo element as the sensor element.  
         [0019]     Obviously, a plurality of alternatives are available for the arrangement of the transmitter and sensor element of the sensor arrangement on the separate carrier, it being preferred, however, to mechanically hold one or both of these elements on the carrier.  
         [0020]     This means that the respective element is arranged in a part of the carrier, for example by a force fit, or is moved into an end position and this is then mechanically secured. Compared to an adhesive connection, the mechanical holding of the sensor and transmitter elements on the separate carrier has the advantage that no ageing processes are to be feared here, which could lead to a change in the position of the transmitter and sensor element relative to one another.  
         [0021]     This is significant, in particular for application of the present load cell in cars, in particular for determining forces exerted on car seats during loading by a person, as these load cells, under certain circumstances, have to remain for many years in the motor vehicle and have to function reliably, to generate reliable data to control the triggering of the airbag.  
         [0022]     The flectionally elastic element is particular preferably to be configured as a flectionally elastic membrane, which is held one the flectionally rigid wall part of the housing by its wall region. Metallic materials, in particular, are suitable for producing the flectionally elastic membrane.  
         [0023]     The flectionally elastic membrane may be configured in the form of a strip or polygonally or else in a circular manner, which is preferred, in particular with regard to the higher non-sensitivity that can then be achieved against tilting moments, which may occur upon the introduction of force, whether tensile or compressive forces, in the load cell.  
         [0024]     Preferred flectionally elastic membranes have a central recess, for example in the form of a through-opening, the membranes with a circular form then being configured as an annular disc.  
         [0025]     The embodiment of the flectionally elastic membrane has a plurality of advantages, which will be elucidated in detail below.  
         [0026]     The force introduction part and the flectionally elastic element are preferably configured in one piece with one another or else initially produced as two separate parts and then rigidly connected to one another. This may take place, for example by welding or another material connection.  
         [0027]     The force introduction part, in a preferred embodiment, is displaceably arranged coaxially in a through-opening of the housing. In particular, in this embodiment, the force introduction part projects partially through the through-opening of the housing, with advantages for the overall construction, so it is directly available for a force introduction from outside.  
         [0028]     With regard to the simplicity of the adjustment of the load cell after assembly, the force introduction part in a preferred embodiment will have a foot part acting on the flectionally elastic element and a contact element which can be adjusted relative to the foot part and is arranged in mechanical contact with a component of the sensor arrangement movably held on the carrier.  
         [0029]     The use is again recommended of a flectionally elastic membrane as a flectionally elastic element with a central recess, in particular a through-opening, wherein the contact element of the force introduction part can then be arranged centrally with respect to the recess of the flectionally elastic membrane and can produce a contact with the component, which is arranged on the carrier, of the sensor arrangement, in particular in the plane of the flectionally elastic membrane.  
         [0030]     The contact element which is adjustable relative to the foot part of the force introduction part allows an adjustment of the zero point of the load cell to also still be carried out in the assembled state of the load cell so that, in the course of assembly of the load cell, lower demands on the precision of the arrangement of the individual components of the load cell are possible without having to tolerate losses in quality of the finished load cell in return.  
         [0031]     The foot part of the force introduction part will preferably have larger dimensions than the through-opening of the housing.  
         [0032]     This avoids an overloading of the elastic element occurring upon excessive tensile forces and the foot part of the force introduction part then being able to be supported on the housing.  
         [0033]     As already mentioned above, one region of the force introduction part will preferably project from the housing through the through-opening, so the force can be directly introduced there.  
         [0034]     The mechanical contact of the contact element of the force introduction part with the movably held component of the sensor arrangement should preferably substantially be a point-wise contact.  
         [0035]     It is particularly preferred in this context if the contact element has a rounded tip, by means of which the mechanical contact with the movably held component of the sensor arrangement is produced. With transverse components, which can act on the force introduction part upon the action of force, this avoids these transverse components leading to a signal falsification, as the rounded tip remains substantially unchanged with respect to its vertical position relative to the membrane, as does the movable component of the sensor arrangement inside the load cell.  
         [0036]     In order to further assist this, it is preferably provided that the rounded tip of the contact element of the force introduction part has a sliding mechanical contact with the movably held component of the sensor arrangement.  
         [0037]     In a further preferred embodiment of the load cell according to the invention, the load cell will comprise stop means, which limit the movement of the force introduction part upon the action of force.  
         [0038]     Stop means of this type are preferably configured in such a way that they limit the movement of the force introduction part during the action of tensile and compressive forces.  
         [0039]     In a further preferred embodiment, the stop means will comprise a first element, which is supported on the outside of the housing. Compressive forces, which act on the load cell are thereby limited with regard to their action on the flectionally elastic element to the permissible force range.  
         [0040]     The first element of the stop means will preferably have a receiver for an elastomer element on its side facing the outside of the housing. The elastomer element may fulfill two types of function, on the one hand, the resilient mounting of the first element of the stop means on the outside of the housing, and on the other hand, a sealing function, in particular when the elastomer element extends all the way round the through-opening of the housing.  
         [0041]     The stop means preferably have a second element, which is supported on the inside of the housing. For example, that which was described above as the foot part of the force introduction part, which has a radially larger dimension than the through-opening of the housing, through which the force introduction part extends, is suitable here. With regard to the intended application of the load cell in a motor vehicle, in a preferred embodiment, the housing will surround the force transducer and sensor arrangement with the separate carrier substantially on all sides.  
         [0042]     The housing of the load cell may be configured differently depending on the purpose of application and area of use. For the applications in the motor vehicle sector, which are of particular interest, it is provided that the housing comprises a cover element, a base element and a flectionally rigid side wall connecting the cover to the base element. For the circular membrane described as preferred above, the housing will obviously preferably have a disc shape or hollow cylindrical shape.  
         [0043]     The housing is preferably multi-part, in particular two-part, the housing then being formed from a cover part and a base part. The side wall may then be a component of the cover and/or base part.  
         [0044]     It is easiest to form the housing of the load cell by welding the cover part and base part to one another. It is sufficient here if the cover part and base part are arranged on top of one another and thus fixed to one another and then the weld seam can be formed. Even if this type of assembly of the housing may entail certain tolerances, there is adequate possibility, owing to the possibilities described above for adjusting the sensor arrangement within the already completed housing of the load cell for implementing the quality demands of the load cell without reducing them, even in this simple type of assembly of the load cell.  
         [0045]     In the housing parts, the cover element will preferably comprise the through-opening of the housing, through which the force introduction part works on the flectionally elastic element of the load cell.  
         [0046]     In addition, the housing may comprise a through-opening for electrical supply and/or signal lines, which are used for the current supply of the sensor arrangement or the evaluation electronics which are connected downstream from the sensor arrangement and may optionally also be accommodated in the load cell housing. The signal lines supply the signals generated by the sensor arrangement, which are optionally processed already by the electronics, accommodated in the force measuring cell, to the outside world and make then accessible for control functions.  
         [0047]     The base element of the housing will preferably have one or more fastening elements, with which the latter may be anchored, for example, in the motor vehicle. For example, lugs may be present on the base element, which can be screwed to other parts of the motor vehicle.  
         [0048]     Alternatively or in addition, a threaded part, with which a screw connection with external parts can be produced, may be configured on the base element.  
         [0049]     The threaded part will preferably be configured in one piece with the base element and this saves steps during assembly of the load cell and, moreover, is beneficial to the accuracy of the arrangement of the threaded part relative to the load cell.  
         [0050]     One of the possibilities for holding the flectionally elastic element on the flectionally rigid wall part of the housing is to hold this element between two housing parts with a force fit.  
         [0051]     As an alternative to this, the elastic element may be connected to the housing by means of a weld point, so the elastic element and the housing part may be handled again as a unit. In particular, it is possible to achieve or else improve the rigidity of the wall part only upon the welding operation. Economies of weight in the housing can be achieved thereby  
         [0052]     Something similar also applies to the separate carrier, which can be held between two housing parts by a force fit.  
         [0053]     It is equally possible to connect the carrier to the housing part with a material connection, in particular by means of an adhesive or weld connection.  
         [0054]     The present invention in turn also allows simple manufacturing here without excessively high demands regarding low tolerances during assembly of the flectionally elastic element and the housing or the carrier and the housing and also the arrangement between the carrier and the flectionally elastic element, as the mechanical contact point can preferably be adjustably held between the movable part of the sensor arrangement and the force introduction part.  
         [0055]     The through-opening of the housing is preferably configured as a type of guide for the force introduction part, this not being intended to mean that the force introduction part is guided approximately with sliding friction in the through-opening of the housing. Rather, a gap will preferably be present between the force introduction part and the through-opening of the housing and prevents transverse forces bringing about an excessive deflection of the force introduction part from the normal with respect to the flectionally elastic element.  
         [0056]     In particular, the through-opening of the housing is dimensioned such that it guides the force introduction part so as to be secured against tilting moments.  
         [0057]     The gap preferably provided between the force introduction part and the through-opening has a width of, in particular 0.1 mm to about 0.5 mm.  
         [0058]     In one embodiment it is provided that the transmitter element and the sensor element are arranged non-centrally on the carrier. A flat construction of the carrier and therefore of the load cell can thereby be implemented, so the latter can be configured with a low axial height.  
         [0059]     To achieve a low axial height, it is advantageous if the first element is arranged below the second element, the second element being movable in a space above the first element.  
         [0060]     It is favourable if the carrier has a cut-out, which may be configured as a through hole or as a blind recess, in which the second element is at least partially arranged. The second element can thus be easily fixed to the carrier.  
         [0061]     It is favourable if the cut-out is formed on a spring part of the carrier. A movable arrangement between the first element and the second element can thus be easily implemented.  
         [0062]     The carrier with the sensor arrangement may be configured with a low axial height if the transmitter element and the sensor element are arranged transversely offset with respect to an axis of a contact element.  
         [0063]     It is favourable if the carrier has a contact region, which is concave. A point contact between a contact element and the carrier can thus be implemented. The contact region is preferably formed on a spring part of the carrier, in this case. The corresponding carrier can be produced easily, for example in one piece, as an injection moulding.  
         [0064]     It is favourable if the contact region is arranged between spaced-apart spring webs. The contact region can thus be arranged centrally to achieve a simple symmetrical alignment with a contact element. In this case, it can simultaneously be configured on a spring part to implement a movement between the spring part and a stationary part on the introduction of force.  
         [0065]     It is particularly advantageous if a spring part has spaced-apart spring webs, which are provided in each case with spaced-apart weakening zones. The spring part can thus be configured in a defined manner with respect to its reaction to force loading.  
         [0066]     It is in particular favourable if corresponding weakening zones of different spring webs are located at the same height. A parallelogram structure can thus be implemented in order to obtain an optimised introduction of force.  
         [0067]     These and further advantages of the invention will be described in more detail below with the aid of the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0068]      FIG. 1  shows a lateral sectional view of an embodiment of a load cell with a first embodiment of a separate carrier; and  
         [0069]      FIG. 2  shows a perspective view of a second embodiment of a separate carrier. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0070]      FIG. 1  shows a cross-section through an embodiment of a load cell  10  according to the invention. This is constructed from a housing  12 , a flectionally elastic element  14  arranged in the housing  12 , which, together with a force introduction part  16 , forms a force transducer  17  of the load cell  10 , as well as the separate carrier  18 , on which a sensor arrangement  20  of the load cell  10  is arranged.  
         [0071]     The housing  12  is composed of a base part  22  and a cover part  24 , which together form a side wall  26  of the housing  12 , which is the flectionally rigid wall part of the housing  12 .  
         [0072]     Provided on the regions, which come into contact with one another, of the base part  22  and cover part  24 , bevelled regions are provided on the outer periphery, which together form a wedge-shaped groove  28 , which receives the weld seam when the base part  22  and cover part  24  are connected by means of welding.  
         [0073]     The carrier  18  is arranged in the interior of the housing  12  in such a way that it is only in contact with the flectionally rigid part of the housing  12 , namely the side wall  26 , to which it is preferably bonded or welded at an edge region  30 . The separate carrier  18  keeps an adequate spacing from all other regions of the housing  12 , so, upon possible twisting of the housing  12 , no mechanical contact occurs between the separate carrier  18  and the housing  12 .  
         [0074]     The carrier  18  is preferably formed from a metal sheet or a plastics material part, which is produced by a forming step for example by an injection method, on the one hand, provided with the edge region  30 , and, on the other hand, with the downwardly returning region  32 , which is broken open in its centre and bent up in order to form the holder for a component of the sensor arrangement  20 . This part of the separate carrier  18  comprises a lug  34 , which is bent vertically upwardly, on which, shown only schematically, a Hall sensor element  36  of the sensor arrangement  20  is mechanically held. The transmitter element associated with the Hall sensor element  36 , a magnet  38 , is aligned relative to the Hall sensor element  36  in the position with maximum sensitivity of the Hall sensor element  36 .  
         [0075]     While the Hall sensor element  36  is held stationarily inside the housing by the lug  34  (with respect to the flectionally rigid side wall  26 ), the transmitter part, i.e. the magnet  38 , is movably arranged and in fact held by a spring part  40 , which is supported on the separate carrier  18  in the region of the return  32 . The spring part  40  is preferably formed as an annular plastics material part or spring steel sheet and is supported annularly by a foot part  42  on the carrier part  18 . If the spring part  40  and carrier part  18  are manufactured from plastics material, the spring part  40  and the carrier part  18  are preferably produced in one piece. Toward the centre, the spring part  40  is bent upwardly to form a shoulder  44 , and continues in the direction toward the centre with a type of bellows  46 , adjoined in turn by a parallel holding face  48  parallel to the main membrane plane. The holding face  48 , on its underneath, holds the magnet  38 , it being possible for the position thereof to vary relative to the stationarily held Hall sensor  36  depending on the loading of the force introduction part  16 . The movement which the magnet  38  on the holding face part  48  carries out is mechanically decoupled by the bellows element  46  from the return  32  of the separate carrier, so a change of location of the magnet  38  does not continue in a deformation of the carrier  18 .  
         [0076]     A further part of the spring element  40  may be shaped in such a way that it mechanically secures the Hall sensor  36  in its position on the lug  34 .  
         [0077]     The mechanical decoupling of the change in location of the magnet  38  on loading the load cell  10  relative to the carrier  18 , in particular of the position of the Hall sensor  36  on the lug  34  also comes about in that the material thickness and the strength of the carrier  18  is selected so as to be correspondingly larger.  
         [0078]     A substantial aspect of the present invention is realised in the configuration of the carrier  18  and the sensor arrangement  20  arranged thereon. Before assembly of the load cell in an assembly process to be carried out separately, the carrier  18  can actually already be prepared and the sensor arrangement  20  preassembled on it, so the carrier  18  together with the sensor arrangement  20  already has a defined allocation of the sensor element and transmitter element before the carrier  18  together with the sensor arrangement  20  is installed in the housing  12  of the load cell  10 . The spring element  40  of the carrier  18  is also important for the movable holding of one of the components of the sensor arrangement  20 .  
         [0079]     This advantage is not only produced when using a Hall sensor arrangement, but equally in other contact-free path measuring systems, for example an optical sensor arrangement. An optimal adjustment of the transmitter element and sensor element may also take place here, in each case, separately and independently of the assembly steps of the load cell, which, on the one hand allows better monitoring in the assembly of the individual parts and, on the other hand, also better adjustment if necessary.  
         [0080]     The membrane  14 , in the present embodiment, is configured as a circular membrane, but may also be configured in the form of a strip or polygonally if it is ensured that the strip or polygonal shape is adequately stable for the acting forces and in particular if no tilting moments acting transversely to the main direction of the forces to be measured are to be expected during the introduction of force.  
         [0081]     The membrane  14  is configured annularly in the present embodiment with a thickened edge  50 , with which the membrane  14  is held on the flectionally rigid side wall  26 . The edge  50  of the membrane  14  can be welded or bonded together with the carrier  18 , for example to the base part  22 , before the cover part  24  is placed on and the housing  12  is welded as a whole in the region of the groove  8 . An increase in the rigidity is achieved by welding the edge part  50  to the side wall  26 .  
         [0082]     The edge  50  of the membrane  14  takes into account here the common assembly of the carrier  18  and membrane  14 , in that a returning edge region is provided there, into which the edge part  30  of the carrier  18  moves, so the edge part is additionally radially held in its position and to a certain degree braced. The carrier  18  thereby receives a defined shape and the position, in particular of the return  32  of the carrier  18  is further improved by the prestressing, which is made possible for the carrier  18  by the movement of the edge region  30  into the corresponding return on the part of the edge  50  of the membrane  14 . It may be provided during assembly that, firstly, the membrane  14  with the already completely assembled carrier  18  with the sensor arrangement  20  are connected to one another, in particular are already welded to one another before this unit of the membrane  14 , carrier  18  and sensor arrangement  20  is inserted in the base part  22  of the housing  12  and then welded thereto.  
         [0083]     Alternatively, during assembly, the already completely assembled carrier  18  with the sensor arrangement  20  with the base part  22  of the housing  12  can firstly be bonded on the edge part  30 . The membrane  14  is then placed on the assembled carrier part  18  and held between the two housing parts, base part  22  and cover part  24 , with a force fit.  
         [0084]     A through-opening  52 , into which the sensor arrangement projects during assembly, is provided in the central part of the membrane  14 , so the most sensitive point of the Hall sensor  30  and the magnet  38  directed thereto are substantially located in the central plane of the membrane  14 .  
         [0085]     The region right round the through-opening  52  of the membrane  14  is so reinforced and has an annular return  54 , which receives a foot part  56  of the force introduction part  16 . The membrane  14  and the force introduction part  16  can be manufactured in one piece or welded to one another in the region of the return  54 .  
         [0086]     This foot part  56  of the force transducer  17  is provided with a radially outwardly projecting edge region  58 , which will be dealt with further below in conjunction with the description of the overload protection present in the load cell  10 .  
         [0087]     The foot part  56  of the force introduction part  16  moreover centrally has a recess  60 , which creates space for a sensor arrangement  20  positioned inside the through-opening  52  of the membrane  14 .  
         [0088]     The force introduction part  16  is substantially hollow cylindrical and in the interior holds a contact element  62  which extends into the recess  60  and is relatively displaceable with respect to its position relative to the recess  60  and therefore in the direction of the central plane of the membrane  14  and can be adjusted. After adjustment, the contact element  62  is fixed in its position relative to the force introduction part  16 . The contact element  62  may be configured as a threaded pin.  
         [0089]     The contact element  62 , at its free end projecting into the recess  60 , has a contact tip  64 , which is in mechanical contact with the holding face  48  of the spring part  40  and thus determines the relative position of the transmitter element in the form of the magnet  38  of the sensor arrangement  20  relative to the sensor element in the form of the Hall sensor element  36 .  
         [0090]     The contact tip  64  has a rounded area, which, during a tilting movement of the force introduction part  16 , slides over the holding face  48  and therefore does not bring about any change in the relative position of the magnet  38  relative to the Hall sensor element. The load cell and therefore the measurement signal are therefore insensitive to transverse forces and tilting movements connected therewith.  
         [0091]     After complete assembly of the load cell, i.e. after insertion of the carrier element  18  with the sensor arrangement  20  and the membrane  14  and the subsequent sealing by means of welding of the two housing parts  22  and  24 , an adjustment can then still be carried out by means of the position of the contact element  62  or its contact tip  64  with respect to the centre plane of the membrane  14 , so the whole of the force transducer (force introduction part  16  and membrane  14 ) and the associated ensemble of the sensor arrangement  20  have an optimum configuration. The contact element  62  is thus fixed with regard to its position inside the force introduction part  16 .  
         [0092]     The force introduction part  16  projects, with its end opposing the foot part  42 , from the interior of the load cell  10  through a through-opening  66  in the cover part  24  of the housing  12  and is therefore directly available for the introduction of force.  
         [0093]     The force introduction part  16 , on its outer face, preferably has a threaded portion, which is not shown in more detail in the schematic drawing of the figure present here.  
         [0094]     A nut  68  can be screwed onto this external threaded portion of the force introduction part  16  and, on its side facing the housing surface, has an annular groove  70 , in which an elastomer ring  72  is received The groove  70  and the elastomer ring  72  are dimensioned such that the elastomer ring  72  projects slightly over the surface of the nut  68 , so the latter does not come to rest directly on the housing surface of the cover part  24 , but via the elastomer ring  72 .  
         [0095]     The nut  68  is screwed onto the external threaded portion of the force introduction part  16  to such an extent that the nut still maintains a spacing from the surface of the housing part  24 , which corresponds to the maximum permissible movement of the force introduction part  16  into the interior of the housing  12 . A maximum limitation is therefore provided for the force introduction by means of the force introduction part  16  during compressive forces and the stop thus formed by the nut  68  protects the membrane  14  from excessive loading.  
         [0096]     During the action of tensile forces, the radially projecting edge  58  of the foot part  56  also works as a stop as the latter can only be moved to the outside at a maximum until the radially projecting edge  58  comes to rest on the cover part  24  and the return face specially configured here.  
         [0097]     The load cell  10  is therefore protected from overloading during the action of tensile and compressive forces,  
         [0098]     Furthermore, the load cell is protected against excessive tilting movements, i.e. force components which act perpendicularly to the centre axis of the force introduction part  16 , in that the radially projecting foot part engages in a corresponding annular return of the cover upper part  24  and is held there and, on the other hand, by the nut  68  arranged on the housing surface, which is also supported on the outside of the housing from a certain tilting movement of the force introduction part  16  and counteracts further tilting of the force introduction part  16 .  
         [0099]     Because of these measures, the load cell according to the invention is not only easy to manufacture but also withstands excessive loads in a harsh environment. Because of the encapsulation of the force transducer consisting of the membrane  14  and the foot part of the force introduction part  16  inside the housing  12 , which only has a through-opening  66  for the force introduction part  16 , and a through-opening (not shown here) in order to produce an electrical connection to the Hall sensor  36  in the interior of the housing  12 , a substantially tight encapsulation takes place making the load cell reliable to use for many years. Owing to the elastomer ring  72 , which is supported, on the one hand, against the nut  68  and, on the other hand, against the outer surface of the cover part  24 , a sealing of the interior of the load cell  10  or of its housing  12  also takes place in the region of the opening  66 , in which the force introduction part  16  is displaceably held. A gap can thus be allowed between the through-opening  56  and the force introduction part  16 , in the form that in the event of loads, whether tensile or pressure loads, and also in the event of tilting moments which are not excessive, a contact free movement of the force introduction part  16  is made possible inside the through-opening  66 . Nevertheless, the load cell  10  thus formed is reliable to operate in a rough, i.e. even climatically rough environment such as the car.  
         [0100]     The through-opening, not shown, for passing electrical supply and signal lines through to the Hall sensor  36  can be sealed as conventional with sealing materials, as no relative movement of the lines relative to the housing or the housing wall has to be allowed here.  
         [0101]     The force introduction part  16  projecting out of the housing  12  and provided with an external thread portion, on the one hand, facilitates assembly of the load cell at its site of use. A screw bolt  74  is provided centrally on the base part  22  and can also be replaced or supplemented by other fastening elements, such as, for example, radially projecting lugs.  
         [0102]     In a further embodiment, a separate carrier  102  ( FIG. 2 ) is configured in one piece and produced, in particular, from a plastics material. The sensor arrangement  20  of the corresponding load cell is arranged on the carrier  102 . The arrangement is, in particular, as described above, in other words the carrier  102  is arranged in the interior of a housing in such a way that it is only in contact with a flectionally rigid part of the housing, namely a side wall  26  and/or a corresponding region (in particular the outer edge region) of the base part  22 .  
         [0103]     The carrier  102  comprises a stationary part  104 , which is approximately annular with an inner through-opening  106 . A spring part  108  is arranged on the stationary part  104  and is movable on the introduction of force by means of a contact element  110  in a direction, which is parallel or approximately parallel to an axis  112  of the contact element  110 . The contact element  110  is shown spaced apart from the carrier  102  in  FIG. 2  for illustrative reasons.  
         [0104]     The stationary part  14  rests on the housing  12 ; the spring part  108  is not influenced by the housing.  
         [0105]     The spring part  108  comprises a first spring web  114  and a second spring web  116 . These two spring webs  114  and  116  are connected by a connecting region  118 . Both the first spring web  114  and the second spring web  118 , at their connection to the stationary part  104 , have weakening zones  120   a ,  120   b , for example in the form of constrictions. Furthermore, they have weakening zones  122   a ,  122   b  on their connection to the connecting region  118 . The weakening zones  120   a  and  120   b  rest at the same level relative to the stationary part  104 . The weakening zones  122   a  and  122   b  are furthermore located at the same level relative to the stationary part  104 . The connecting line between the weakening zones  122   a  and  122   b  is parallel to the connecting line between the weakening zones  120   a  and  120   b . A parallelogram structure is thus provided for the spring part  108 .  
         [0106]     Formed centrally between the first spring web  114  and the second spring web  116  is a contact region  124 , on which the contact element  112  acts. The contact region  124  is concave; for example, it is hemispherical. The contact region  124  projects through the through-opening  52  of the flectionally elastic element  14 . The other regions of the carrier  102  (including the spring webs  114 ,  116 ) are located below the flectionally elastic element  14 .  
         [0107]     The contact region  124  is aligned with the axis  112  of the contact element  110 . In particular, a sphere axis of the contact region  124  and the axis  112  are at least approximately coaxial with one another.  
         [0108]     The contact region  124  is also connected to the connecting region  118 .  
         [0109]     In the embodiment shown, the stationary part  104  is flat with a first face  126  and a second face  128 , between which the stationary part  104  extends. In particular, the first face  126  and the second face  128  are parallel to one another.  
         [0110]     In the non-force loaded state of the contact region  124 , the spring part  108  protrudes from the stationary part  104 , so a (flat) surface  130  is spaced apart from the second face  128  of the stationary part  104 . In the region of the surface  130 , the spring part  108  has, in particular, the same thickness as the stationary part  104 .  
         [0111]     In the force-loaded state, the spring part  108  can project into the through-opening  106 . The contact region  124  projects, in this case, beyond the surface  130 .  
         [0112]     The connecting region  118  has a recess  132 , in which an element of the sensor arrangement  20 , such as, for example, the magnet  38  is positioned. The magnet  38  is therefore movable by means of the spring part  108  relative to the stationary part  104 .  
         [0113]     The corresponding element of the sensor arrangement  20 , in the example mentioned then the sensor, such as, for example, a Hall sensor, is arranged below the recess  132  (not shown in  FIG. 2 ). Thus, the magnet  32  can then be moved in a space above the sensor  36  by means of the movement of the spring part  108 . In particular, the magnet  38  and the sensor  36  are then at least approximately aligned with an alignment direction, which is at least approximately parallel to the axis  112 . Because of the introduction of force, the spacing between the magnet  38  and sensor  36  reduces in the alignment direction without a substantial transverse offset. The spacing parallel to the alignment direction between the magnet  38  and sensor  36  is thus precisely detected.  
         [0114]     The recess  132  is transversely offset with respect to the contact region  124 . Accordingly the sensor arrangement with its transmitter element and its sensor element is then arranged offset with respect to the contact region  124 , in fact, in a transverse direction in relation to the axis  112 .  
         [0115]     The contact region  124  is therefore arranged centrally and the sensor arrangement is arranged eccentrically. The carrier  102  with the sensor arrangement can therefore be very flat, so a load cell with a low height can be provided.  
         [0116]     The contact element  110  is thus preferably flat at its end  134 , which contacts the contact region  124 .  
         [0117]     A load cell, which comprises the carrier  102 , otherwise functions as described above.