Abstract:
A tool for the primary shaping of a housing for a sensor which is designed to capture, via a sensing element, a physical area that is dependent on a variable to be measured, and to emit an electrical output signal on the basis of the captured physical area, including:—a mould cavity for receiving a material that moulds the housing, and the sensing element, and—a box having a wall that bounds the mould cavity, wherein at least a part of the wall that bounds the mould cavity is mounted in a displaceable manner.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2014/071589, filed Oct. 8, 2014, which claims priority to German Patent Application No. 10 2013 224 466.5, filed Nov. 28, 2013, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a tool for the primary shaping of a housing for a sensor, a method for using the tool and a sensor having a housing that is produced by means of the mentioned method. 
       BACKGROUND OF THE INVENTION 
       [0003]    WO 2010/037 810 A1, which is incorporated by reference discloses housing a measuring element of a sensor in a housing by means of an injection molding method, said measuring element being configured so as to ascertain by way of the measuring element a physical field that is dependent upon a variable that is to be measured, and to output an electrical output signal based upon the physical field that is ascertained. 
       SUMMARY OF THE INVENTION 
       [0004]    An aspect of the invention aims to improve the housing arrangement of the known sensor. In accordance with one aspect of the invention, a tool for the primary shaping of a housing for a sensor that is configured so as to ascertain by way of a measuring element a physical field that is dependent upon a variable that is to be measured, and said sensor is configured so as to output an electrical output signal based upon the physical field that is ascertained comprises a molding cavity for receiving a material, which forms the housing, and the measuring element, and a box having a wall that delimits the molding cavity, wherein at least one part of the wall that delimits the molding cavity is mounted in such a manner that it can be displaced. It is particularly preferred that the primary shaping method is a casting or injection molding method. 
         [0005]    The underlying consideration of the tool that is disclosed is that it is necessary for the measuring element of the sensor to lie somewhere on the wall that delimits the molding cavity when being placed into the molding cavity since the measuring element cannot float in the molding cavity. However, at the position at which the measuring element lies on the wall that delimits the molding cavity, it is not possible however to injection mold or to cast the measuring element with the material that forms the housing, as a result of which the measuring element of the sensor remains uncovered at this site and is exposed to penetrating moisture. This reduces the serviceable life of the sensor. 
         [0006]    In order to avoid the penetration of moisture, it is proposed within the scope of the present invention to embody at least one part of the wall that delimits the molding cavity in such a manner that said part can move. It is possible to place the measuring element on this movable wall in the molding cavity. If the measuring element is then injection molded with the material that forms the housing, it is possible to move the wall away from the measuring element, wherein the material that is to be injected or cast in the molding cavity holds the measuring element in place, said material being hardened or even already cured. It is then possible to cast further material in the resulting free space between the measuring element and the wall that has been moved away so that the finished housing does not have any remaining exposed sites, by way of which moisture could penetrate into the sensor. 
         [0007]    In this manner, it is possible using the disclosed tool to significantly increase the serviceable life of the sensor by means of avoiding the penetration of moisture. 
         [0008]    In a further development of the tool that is disclosed, the displaceable part of the wall is embodied as a slider that is mounted in such a manner that it can move with respect to the other part of the box. A slider of this type can be controlled in a simple manner in order to control the wall during the injection molding or casting procedure. It is possible for the control itself to be performed in an active or passive manner. The term “active control” means that an actuator is present and said actuator actively moves the wall away from the measuring element. In contrast, the term “passive control” means that the wall is moved away from the measuring element by means of the material that is injected into the molding cavity. 
         [0009]    Various inlet or injecting ducts can be embodied on the tool and it is possible by way of said ducts to inject or introduce the material that forms the housing into the molding cavity. In this manner, it is possible to introduce the material for forming the housing by way of a first duct if the measuring element is still lying on the wall, wherein the material in the molding cavity hardens or even cures at the site of the further duct so that the movable wall can be moved by means of the material that is penetrating by way of the further duct. 
         [0010]    In a particular further development of the tool that is disclosed, the slider is a sliding block. A sliding block of this type renders possible a technically simple production procedure and a simple installation in the tool that is disclosed. 
         [0011]    In a particularly preferred further development of the tool that is disclosed, the molding cavity is configured so as to support the measuring element on the displaceable housing wall prior to introducing the material that forms the housing so that the movable wall can be moved away from said measuring element after introducing the material that forms the housing and said material at least in part hardening. 
         [0012]    In accordance with a further aspect of the invention, a method for using one of the tools that are disclosed for producing the housing comprises the steps of placing the measuring element in the molding cavity, introducing the material into the molding cavity, moving the movable part of the wall and introducing a further material into the molding cavity when moving or after moving the movable part of the wall. 
         [0013]    It is preferred that the material and the further material are identical. In this manner, the material and the further material can mix well with one another when injecting the further material so that no gaps occur between the individual material layers and the penetration of moisture into the housing is avoided in an optimal manner. 
         [0014]    In a particular further development of the method that is disclosed, the material is a thermoplastic. A thermoplastic is a synthetic material that can deform in a specific temperature range. The procedure is reversible and can be repeated by means of cooling and reheating in an arbitrary manner. This uses the further development of the method that is disclosed in that by means of injecting the further material that is embodied as a thermoplastic onto the already cured or hardened first material at least one upper layer of the first material is reheated and liquefied, whereby the mixing of the two materials is further encouraged on its boundary layer. 
         [0015]    In a particularly preferred further development of the method that is disclosed, the further material comprises a thermal energy when being introduced into the molding cavity, and the previously introduced material is at least in part melted using the thermal energy of the further material so that an optimal mixture of the two materials is provided at the boundary layer. 
         [0016]    In accordance with a further aspect of the invention, a sensor for ascertaining by way of a measuring element a physical field that is dependent upon a variable that is to be measured and for outputting an electrical output signal based upon the physical field that is ascertained comprises a housing that is produced by means of one of the disclosed methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above described characteristics, features and advantages of this invention and also the manner in which these are achieved are further explained in a clearer and understandable manner in conjunction with the description hereinunder of the exemplary embodiments that are further explained in conjunction with the drawings, wherein: 
           [0018]      FIG. 1  illustrates a schematic view of a vehicle having a driving dynamics control system, 
           [0019]      FIG. 2  illustrates schematically a rotational speed sensor in the vehicle from  FIG. 1 , 
           [0020]      FIG. 3  illustrates schematically a reading head of the rotational speed sensor from  FIG. 2  in a mid-production state, 
           [0021]      FIG. 4  illustrates schematically an arrangement of the reading head from  FIG. 3  in a tool for forming a housing around the reading head, 
           [0022]      FIG. 5  illustrates schematically the arrangement from  FIG. 4  in a mid-production state of the housing, 
           [0023]      FIG. 6  illustrates schematically the arrangement from  FIG. 4  in a further mid-production state of the housing, 
           [0024]      FIG. 7  illustrates schematically the arrangement from  FIG. 4  in a further mid-production state of the housing and 
           [0025]      FIG. 8  illustrates schematically the reading head from  FIG. 3  in the finished housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    In the figures, identical technical elements are provided with identical reference numerals and are only described once. 
         [0027]    Reference is made to  FIG. 1  that illustrates a schematic view of a vehicle  2  having a known driving dynamics control system. Details of this driving dynamics control system can be found by way of example in DE 10 2011 080 789 A1, which is incorporated by reference. 
         [0028]    The vehicle  2  comprises a chassis  4  and four wheels  6 . Each wheel  6  can be slowed down with respect to the chassis  4  by way of a brake  8  that is immovably fastened to the chassis  4  in order to slow down a movement of the vehicle  2  on a road that is not further illustrated. 
         [0029]    It is possible in a manner that is known to the person skilled in the art for the wheels  6  of the vehicle  2  to lose traction and for the vehicle  2  to be moved from a trajectory, which is predetermined by way of example by way of a steering wheel that is not further illustrated, as a result of understeer or oversteer. This is avoided by means of control circuits known per se, such as ABS (anti-lock brake system) and ESP (electronic stability program). 
         [0030]    In the present embodiment, the vehicle  2  comprises for this purpose rotational speed sensors  10  on the wheels  6 , said rotational speed sensors ascertaining a rotational speed  12  of the wheels  6 . In addition, the vehicle  2  comprises an inertial sensor  14  that ascertains the driving dynamics data  16  of the vehicle  2  from which by way of example it is possible to output a pitch rate, roll rate, a yaw rate, a lateral acceleration, a longitudinal acceleration and/or a vertical acceleration in a manner that is known to the person skilled in the art. 
         [0031]    Based upon the ascertained rotational speeds  12  and driving dynamics data  16 , it is possible for a regulator  18  to determine in a manner known to the person skilled in the art whether the vehicle  2  is slipping on the roadway or even if said vehicle is deviating from the above mentioned predetermined trajectory and accordingly to react thereto using a regulator output signal  20  known per se. The regulator output signal  20  can then be used by an adjusting device  22  in order to control adjusting members such as the brakes  8  by means of adjusting signals  24 , said brakes reacting to the slipping and the deviation from the predetermined trajectory in a known manner. 
         [0032]    The regulator  18  can be integrated into a motor control known per se of the vehicle  2 . It is also possible for the regulator  18  and the adjusting device  22  to be embodied as a common regulating device and optionally to be integrated into the above mentioned motor control. 
         [0033]    The present invention is to be further clarified with reference to the wheel rotational sensor  10  that is illustrated in  FIG. 1  even if the present invention is feasible in arbitrary electronic apparatus and in particular in arbitrary sensors such as magnetic field sensors, acceleration sensors, rotational speed sensors, structure-borne sound sensors or temperature sensors. 
         [0034]    Reference is made to  FIG. 2  that illustrates a schematic view of the rotational speed sensors  10  in the driving dynamics regulating procedure in  FIG. 1 . 
         [0035]    In the present embodiment, the rotational speed sensor  10  is embodied as an active rotational speed sensor that comprises a sensor element in the form of an encoder disc  26  that is fastened to the wheel  6  in a non-rotatable manner and a sensor circuit that is immovably fastened to the chassis  4 , said sensor circuit being referred to hereinunder as reading head  28  for the sake of clarity. 
         [0036]    In the present embodiment, the encoder disc  26  is embodied from magnetic north poles  30  that are arranged in a row together and magnetic south poles  32  that together excite a physical field in the form of a sensor magnetic field  33 . This sensor magnetic field is indicated in  FIG. 2  for the sake of clarity by two dashed field lines. If the encoder disc  26  that is fastened to the wheel  6  rotates with said wheel in a direction of rotation  34 , the sensor magnetic field thus rotates with said wheel and encoder disc. 
         [0037]    In the present embodiment, the reading head  28  comprises a probe in the form of a magnetostrictive element  35 . The magnetostrictive element  35  changes its electrical resistance in dependence upon the angular position of the sensor magnetic field that is excited by the encoder wheel  26 . A test signal  39  is applied to the magnetostrictive element  35  so as to ascertain the rotational speed  12 , said test signal being altered in dependence upon the angular position of the encoder wheel  26  and thereby the electrical resistance magnetostrictive element  35 . Based upon this alteration of the test signal  39 , a signal evaluating circuit  40  evaluates the rotational speed  12  and outputs said rotational speed in a data signal  42  to the regulator  18 . This signal evaluating circuit  40  can likewise be part of the reading head  28 . 
         [0038]    For this purpose and for further background information regarding active wheel rotational speed sensors, reference is made to the relevant prior art, such as by way of example DE 101 46 949 A1, which is incorporated by reference. 
         [0039]    Reference is made to  FIG. 3  that illustrates schematically the reading head  28  for the rotational speed sensor  10 . 
         [0040]    In the present embodiment, the reading head  28  is connected to a wiring carrier in the form of a lead frame, the term “Leadframe” is also used for this. A lead frame of this type is disclosed by way of example in WO 2010/037 810 A1. The reading head  28  is illustrated in  FIG. 3  in a state that is punched out from the lead frame. Therefore, in  FIG. 3  only a populating island  44 , a first contact connection  46  that is connected in a single part manner to the populating island  44 , and a second contact connection  48  that is separated from the populating island  44  are visible. 
         [0041]    The probe in the form of a magnetostrictive element  35  and the signal evaluating circuit  40  are attached to the populating island  44  and are electrically contacted by way of example by means of solder or adhesive. The magnetostrictive element  35  and the signal evaluating circuit  40  are in addition connected to one another by way of a bond wire  50  so that it is possible to transmit the test signal  39  by way of the populating island  44  and the bond wire  50  between the magnetostrictive element  35  and the signal evaluating circuit  40 . The signal evaluating circuit  40  is connected by way of a further bond wire  50  to the second contact connector  48 . In this manner, the data signal  42  can be output from the signal evaluating circuit  40  by way of the two contact connectors  46 ,  48 . A filter capacitor  52  can be connected between the contact connectors  46 ,  48 . 
         [0042]    A protective layer  54  can be embodied around the populating island  44  which supports the reading head  28 , and a part of the contact connectors  46 ,  48  so as to protect the reading head  28 , said protective layer being visible in  FIG. 4 . For this purpose, for the sake of brevity reference is made to the relevant prior art, such as by way of example WO 2010/037 810 A. 
         [0043]    The reading head  28  is housed in a housing  56  that is illustrated in the  FIGS. 5 to 8  so as to protect the reading head  28  against penetrating moisture or other contaminants. 
         [0044]    For this purpose, the reading head  28  is initially electrically connected to a data cable  58  that transmits the data signal  42  to the regulator. 
         [0045]    The reading head  28  is subsequently bent into a suitable shape for the end application. Since this shape is no longer of significance within the scope of the invention, the reason being that said shape is arbitrary, the shape for the reading head  28  that is illustrated in  FIG. 4  is only to be referred to hereinunder in an exemplary manner. 
         [0046]    The finished bent reading head  28  is finally placed in a tool  59  for the primary shaping of the housing  56 . This tool  59  is constructed within the scope of the present embodiment in a multiple part manner from an immovable tool part, a first movable tool part  60 , a second movable tool part  62  and a third movable tool part  64 . In order to be able to better illustrate the movable tool parts  60  to  64 , the illustration of the immovable tool part is omitted. 
         [0047]    The immovable tool part and the movable tool parts  60  to  64  together form a box having a molding cavity  66  and the reading head  28  and a part of the data cable  58  are received in said molding cavity. Apart from the inlet openings, not further illustrated, that lead through the box, the molding cavity  66  is embodied in a sealed manner for supplying the material  68 ,  70  that is illustrated in  FIGS. 5 to 7  so as to form the housing  56 , wherein the movable tool parts  60  to  64  are arranged in such a manner that they can move with respect to the immovable tool part and thus can form a movable wall for the molding cavity  66  and thereby can alter the dimensions of the molding cavity  66 . 
         [0048]    The movable tool parts  60  to  64  can be embodied in an arbitrary manner. Within the scope of the present embodiment, the movable tool parts  60  to  64  are sliding blocks that can move and are received in a guided manner in the immovable tool part. 
         [0049]    The procedure of embodying the housing  56  by means of introducing a material into the molding cavity  66  within the scope of an injection molding method is to be further explained hereinunder. 
         [0050]    For this purpose, initially as is illustrated in  FIG. 5 , a first material  68  is introduced into the molding cavity  66  by means of injection molding. The first material  68  is introduced, as is previously mentioned, by way of inlet openings into the molding cavity  66  and said inlet openings are not further illustrated. 
         [0051]    After introducing the first material  68  into the molding cavity  66  in the state that is illustrated in  FIGS. 4 and 5  of the movable tool parts  60  to  64 , the movable tool parts  60  to  64  are displaced as is illustrated in  FIG. 6 . This is expediently performed in an at least in part hardened state of the first material  68  and the in part hardened housing can thereby be held by the immovable tool part, not illustrated. The molding cavity  66  is enlarged in the region of the reading head  28  by means of displacing the movable tool parts  60  to  64 . 
         [0052]    The second material  70  is injection molded into this newly produced region of the molding cavity  66 , as is illustrated in  FIG. 7 . In this manner, an absolutely sealed housing  56  is produced in the region of the reading head  28 , wherein however simultaneously the magnetostrictive element  35  is positioned in a highly precise manner within the housing  56 . 
         [0053]    The reading head  28  in the finished housing is finally illustrated in  FIG. 8 .