Abstract:
The present invention relates to a contactless detector unit for a load suspension device, which may be used, for example, for recognizing passengers in a motor vehicle, and to a corresponding load suspension device. In order to provide a detector unit for a load suspension device that, on the one hand, may be optimally calibrated and thus provides improved precision and, on the other hand, may be produced particularly cost-effectively, the overall structure being particularly stable and robust, the detector unit comprises a sensor for producing a sensor signal in response to a geometrical position of an indicator with respect to the sensor. The sensor is assembled in an assembly unit, and the position of the indicator may be changed by an actuating unit in response to a load. According to the invention, the indicator is arranged on the assembly unit, and the assembly unit comprises a flexible region, which may be moved for changing the geometrical position of the indicator with respect to the sensor.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a contactless detector unit for a load suspension device and to a corresponding load suspension device. The present invention relates, in particular, to load suspension devices of the type that may be used for recognizing passengers in a motor vehicle.  
       BACKGROUND  
       [0002]     In relation to airbag systems in motor vehicles, passenger recognition devices that recognize a passenger occupying a seat on the basis of his weight are frequently used to control the airbag. As a function of the recognized weight, an airbag control system may, for example, inactivate the triggering of the airbag, or it may be check whether a passenger is wearing his seat belt in accordance with the legal requirements.  
         [0003]     Passenger recognition devices of this type require load suspension devices, which deliver corresponding electrical output signals as a function of the weight acting on the seat. Both strain gauges and various pressure sensors may be used for this purpose.  
         [0004]     A contactless detector unit for a load suspension device of this type generally comprises a sensor for producing a sensor signal in response to a geometrical position of an indicator with respect to the sensor, the sensor signal being produced without mechanical contact between the sensor and indicator. Sensors such as Hall effect sensors and also inductive or capacitive proximity switches may be used for detection.  
         [0005]     Load suspension devices of this type for a safety-relevant feature, such as the airbag control have problems in that known detector units for a these devices are either insufficiently accurate or else are too expensive to produce.  
       SUMMARY  
       [0006]     An object of the present invention is therefore to provide a detector unit for a load suspension device that, on the one hand, may be optimally calibrated and thus provides improved precision and, on the other hand, may be produced particularly cost-effectively. Furthermore, the overall structure should be particularly stable and robust under the harsh environmental conditions during operation of a motor vehicle.  
         [0007]     The present invention is based on the idea that, in the case of a contactless detector unit for a load suspension device, which unit comprises a sensor for producing a sensor signal in response to a position of an indicator with respect to the sensor, the sensor and the indicator are arranged on a single assembly unit, and the assembly unit comprises a flexible region, which is movable or deformable for changing the position of the indicator with respect to the sensor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The invention will be described below in greater detail with reference to the configurations illustrated in the accompanying drawings. Similar or corresponding details are provided in the figures with identical reference numerals. In the drawings:  
         [0009]      FIG. 1  is a perspective, exploded view of a load suspension device according to a first embodiment;  
         [0010]      FIG. 2  is a cross-sectional view taken through the load suspension device of  FIG. 1 ;  
         [0011]      FIG. 3  is a perspective view of a detector unit according to the first embodiment in the final assembled state;  
         [0012]      FIG. 4  is a perspective view of the detector unit from  FIG. 3  during the pre-assembly process;  
         [0013]      FIG. 5  is a perspective view of a load suspension device according to a second embodiment during the installation of the electrical connections;  
         [0014]      FIG. 6  is a perspective view of the arrangement from  FIG. 4  in the assembled state;  
         [0015]      FIG. 7  is a perspective view of a detector unit according to a third embodiment;  
         [0016]      FIG. 8  is a rotated perspective view of the detector unit from  FIG. 7 ;  
         [0017]      FIG. 9  is a cross-sectional view through the detector unit of  FIG. 8  taken along the sectional line A-A from  FIG. 11 ;  
         [0018]      FIG. 10  is a side view of the detector unit from  FIG. 8 ; and  
         [0019]      FIG. 11  is a plan view of the detector unit of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0020]      FIG. 1  is a perspective, exploded illustration of a first embodiment of a load suspension device  100  according to the present invention. The load suspension device  100  operates on the principle that a force is exerted onto the actuating unit  102  by a load in direction  104 . The actuating unit  102  is thus deformed, as may be seen in conjunction with  FIG. 2 , and an indicator  106  is displaced, with respect to a sensor  108 , in direction  1   10 . In the illustrated embodiment, the indicator  106  is a permanent magnet, the magnetic field of which is detected by the sensor  108  which in this case is a Hall effect sensor.  
         [0021]     According to the invention, the sensor  108  and the indicator  106  are assembled on an assembly unit  112 . This assembly unit  112  comprises a flexible region  114 , which may be formed as a film hinge and which allows the sensor  108  and the indicator  106  to be constructed on an integral part, the indicator  106  nevertheless being movable with respect to the sensor  108 . In the illustrated embodiment, the indicator  106  is attached, for example using a flexible film hinge, to a cantilever beam, which is clamped on one side.  
         [0022]     As may also be seen from  FIG. 2 , a set screw  116 , which is provided on the actuating unit  102  as an adjusting screw, is used to calibrate the position of the indicator  106  with respect to the sensor  108  in the unloaded state of the arrangement. If a drop of adhesive  118  is added to the thread of the set screw  116 , the calibrated position may reliably be maintained once the adhesive has cured.  
         [0023]     In addition to the assembly unit  112 , the detector unit  120  also comprises a flexible circuit  122  for electrically contacting the sensor  108 .  
         [0024]     In the illustrated embodiment, the actuating unit  102  forms, together with a mount  124 , a substantially closed housing for the load suspension device  100 . The electrical connections of the flexible circuit  122  are connected to a corresponding connection collar, in the form of a plug connector  126 , and guided outward through the mount  124  in a sealed manner via openings  128 . The plug connector  126  may be adapted to the respective requirements for the electrical connection of the sensor  108 .  
         [0025]     As is also clear with reference to the subsequent figures, the set screw  116  is screwed into the actuating unit  102  in such a way that it enters into direct mechanical contact with an actuating surface  130  on the assembly unit  112 . The set screw  116  thus forms the contact surface  132  and may be used to adjust the position of the indicator  106  into the zero position in the unloaded state.  
         [0026]      FIG. 2  is a cross-section through the load suspension device shown in  FIG. 1 . The assembly unit  112  is inserted into the mount  124  in direction  110 . The mount  124 , which is made, for example, from metal, and the actuating element  102 , which may also be made from metal, forms a robust and protective housing for the load suspension device  100 . A deformable region  134  of reduced thickness, which, when force is exerted in direction  104 , allows the contact surface  132  of the set screw  116  to engage the actuating surface  130  of the assembly unit  112 , is attached along the perimeter of the actuating unit  102 .  
         [0027]     The sensor  108  and the indicator  106  are both held in the assembly unit  112 , the flexible region  114  allowing deflection of the indicator  106  with respect to the sensor  108  when force is exerted onto the load suspension device  100  in direction  104 . For compensation of assembly air and tolerances, the zero position of the indicator  106  with respect to the sensor  108  may, according to the invention, be calibrated via the adjusting screw  116 . This takes place, once the sensor  108  has been connected to the plug connector  126  using the flexible circuit  122 , so the output signal of the sensor  108 , in this case a Hall effect sensor, may be evaluated for the calibration process.  
         [0028]      FIG. 3  is a perspective illustration of the assembly unit  112  according to a further advantageous embodiment. According to the invention, the sensor  108  and the indicator  106  are both located on the assembly unit  112 . The indicator  106  is mounted such that it may move, by means of the flexible region  114 , with respect to the sensor  108 . When compressive force is exerted onto the actuating surface  130  in direction  104 , the indicator  106  also moves in direction  104 , and a corresponding sensor signal is produced by the sensor  108 . If the compressive force in direction  104  then decreases again, the resilience of the flexible region  114  causes the indicator  116  to return to the zero position with respect to the sensor  108 . Locking latches  136  are provided on the assembly unit  112  for guiding the indicator  106 . A coded cavity  138  ensures correct positioning of the assembly unit  112  in the mount  124  during the assembly process. The recess  140  allows installation of the plug connector  126  (not shown).  
         [0029]      FIG. 4  shows the arrangement of  FIG. 3  during the assembly process of the indicator  106 , in this case a permanent magnet, and the sensor  118 . For the assembly of these two elements, the indicator region  142  of the assembly unit  112 , in which region the magnet  106  is to be fitted, may, according to the illustrated embodiment, be bent back by substantially 20°, so the magnet  106  may be inserted in direction  104  and may, for example, be secured to the assembly unit  112  by adhesion. The flexible region  114  is sufficiently resilient for this purpose if, for example, it is in the form of a flexible film hinge.  
         [0030]     The sensor  108  is inserted from behind through a window  143 . Alternatively, the trailing end of the sensor  108  may be glued to the sensor region  146  of the assembly unit  112 .  
         [0031]     Once the magnet has been fitted, the indicator region  142  of the assembly unit  112  may be folded back into the rest position, shown in  FIG. 3 , and secured in this position via the locking latches  136 .  
         [0032]     The integration and the electrical contacting of the load suspension device  100  according to a further advantageous embodiment will be described below in greater detail with reference to  FIGS. 5 and 6 .  
         [0033]     Firstly, the sensor  108  and the permanent magnet  106  are assembled on the assembly unit  112  as described above. The sensor  108  is electrically contacted using a flexible circuit  122  and the conductor tracks embedded therein. A strain relief  144  prevents the flexible circuit  122  from becoming accidentally detached from the sensor  108 . In the illustrated embodiment, the flexible circuit  122  is guided outward through an opening  128  in the mount  124  and is only contacted with the plug connector  126  outside.  
         [0034]     In all of the foregoing embodiments, the indicator region  142 , to which the indicator  106  is fixed, is mechanically connected to the rest of the assembly unit  112 , via the flexible region  114 , on only one side. In other words, in the event of deflection caused by the exertion of forces, the indicator  106  moves substantially on a circular path, the centre of which is defined by the flexible region  114 . In the event of marked deflections caused by compressive force exerted in direction  104 , non-linearities, which may have an adverse effect on the characteristic of the load suspension device  100 , may thus occur. Moreover, the production of an assembly unit  112  according to the embodiments illustrated in FIGS.  1  to  6  is comparatively expensive.  
         [0035]     The alternative embodiment, described below with reference to FIGS.  7  to  11 , is able to overcome these drawbacks. In this case, the indicator region  142 , in which the indicator  106  is assembled, is connected to the rest of the assembly unit  112  via flexible regions  114 ,  115  formed as resilient webs each being cut free and fixed on two sides. The exertion of force in direction  104  causes the flexible regions  114 ,  115  to stretch, and the indicator  106  is deflected precisely parallel to the direction in which force is exerted. The illustrated construction may also be produced more easily.  
         [0036]     Both the sensor  108  and the indicator  106  are assembled, as may be seen from  FIG. 9 , from behind, through corresponding openings in the indicator region  142  and the corresponding sensor region  146 . Moreover, as may be seen from  FIG. 9 , the sensor region is in direct mechanical contact, via a corresponding projection  148 , with the mount  124  and thus allows maximum stability of the position of the sensor  108 .  
         [0037]     The load suspension device  100  according to the invention thus allows a seat load sensor, for example, which is precisely adjustable and operable in a robust and reliable manner even under mechanical and thermal stresses, to be produced in a simple manner. However, the principles according to the invention may, of course, also be used for a broad range of other applications in which load suspension devices are required.  
         [0038]     The sensor  108  and indicator  106  may thus be assembled in a particularly simple manner, a minimal number of individual parts being provided. The solution according to the invention also has the advantage that the indicator  106  and sensor  108  are held in vibration resistant and secure manner, even under high mechanical and thermal stresses.  
         [0039]     According to an advantageous development of the present invention, the indicator  106  is held in an indicator region of the assembly unit  112  in such a way that its position with respect to the sensor  108  is adjustable in an unloaded state. The required calibration process may thus be carried out in a zero position.  
         [0040]     This calibration process may be carried out in a particularly neat manner in that the position of the indicator  106  may be changed by an actuating unit  102 , and the actuating unit  102  comprises a contact region for moving the indicator  106 , the position of which may be adjusted for adjusting the indicator  106  with respect to the sensor  108  in the unloaded state. The contact region may, for example, be formed by an adjusting screw, for example a set screw  116 , which is screwed in to the extent that, in the unloaded state, the indicator  106  assumes a defined zero position with respect to the sensor. A screw of this type does not require any expensive tools and is an inexpensive standard assembly element. In order to prevent the position of the screw from changing accidentally during operation, it may also be secured using an adhesive  118 .  
         [0041]     According to an advantageous embodiment of the present invention, the flexible region  114  of the assembly unit  112  is formed by a film hinge, so the indicator  106  is pivotally mounted on a portion, fixed only on one side, of the assembly unit  112 . This arrangement has the advantage that only minor forces oppose deflection by the actuating unit  102 , thus allowing the sensor  108  to respond more easily to an exerted load. Moreover, comparatively large deflections are possible. For the assembly of the indicator  106 , this embodiment has the further advantage that the indicator region, in which the indicator is to be assembled, may be swiveled sufficiently far during the assembly process that optimal accessibility for automated fitting of the indicator  106  is ensured.  
         [0042]     In order, in this case, to secure the region in which the indicator  106  is assembled with respect to the sensor  108 , at least in a three-dimensional direction, a locking means may, according to an advantageous development, be provided.  
         [0043]     Alternatively, the flexible region  114  may be formed by at least one resilient web, which is cut free and fixed on two sides. This embodiment has advantages, firstly, in terms of precision, since if the web is fixed on two sides, the deflection of the indicator  106  takes place precisely parallel to the force exerted by the load. This variation is also easier to implement in terms of the production process and provides improved stability with respect to mechanical stresses during operation of the motor vehicle. The resilient characteristics of the web also ensure that the indicator  106  always returns to its zero position in the unloaded state.  
         [0044]     According to an advantageous embodiment of the present invention, the sensor  108  is a Hall effect sensor, and the indicator  106  comprises a permanent magnet. In addition to the conventional advantages of contactless measuring devices, such as the absence of wear, the use of a Hall effect sensor comprising at least one permanent magnet has the further advantage of high measurement precision and reliable detection, which is substantially independent of corrosion and other disturbing factors, of the position of the indicator. A Hall effect sensor responds with a very high degree of sensitivity to changes in the magnetic flux, so even small movements of the indicator  106  may be detected. The characteristic of a Hall effect sensor, i.e. the dependence of the sensor signal on the position of the indicator  106  and thus on the position of the actuating unit  102 , may easily be adapted, by adapting the electrical wiring of the Hall effect sensor or else by programming the evaluation electronics, to given requests and requirements. The permanent magnet, which moves in conjunction with the actuating unit  102 , is used as an indicator  106 , and a fixedly assembled Hall effect sensor is affected by the change in the magnetic flux in its environment and therefore changes its output signal.  
         [0045]     As an alternative to this arrangement, an inductive proximity sensor (eddy-current sensor), which is affected by a displaceable metallic plate, may, of course, also be used as a sensor  108 . Finally, systems that operate on a capacitive or optical basis are also conceivable.  
         [0046]     If a flexible circuit  122  comprising electrically conductive tracks is used for electrically contacting the sensor  108 , this has the advantage of ensuring reliable and robust electrical contacting, while taking up as little space as possible. It is also possible to transfer parts of the electronics for activating the detector unit  120  to this flexible circuit  122 , in order to relieve the central processor units of sensor-specific tasks.  
         [0047]     If a plug connector  126  is provided for connecting the detector unit  120  to external connections, optimal flexibility and exchangeability of the individual components may be achieved. If repairs have to be undertaken, the load suspension device  100  may be exchanged without having to alter the wiring.  
         [0048]     In an advantageous development of the load suspension device  100  according to the invention, the actuating unit  102  is part of a housing in which the assembly unit  112  is at least partially accommodated. The actuating unit  102  may, for example, be formed by a deformable panel, the center of which is deflected under the effect of a load and transmits this deflection, via a contact region, onto the indicator  106 .  
         [0049]     The advantageous characteristics of the detector unit  120  according to the invention and of the load suspension device  100  are particularly effective if the actuating unit  102  may be connected to a vehicle seat, and the sensor signal is configured in such a way that it activates an airbag system as a function of loading of the vehicle seat. However, other vehicle functions may, of course, also be activated as a function of the occupancy of the seat. Moreover, it will be clear to a person skilled in the art that the detector unit  120  according to the invention and the load suspension device  100  may also be used in other fields, for example weighing technology.