Abstract:
A method for producing a sensor which is equipped to detect a physical field as a function of a dimension to be measured using a measuring sensor and to emit an electrical output signal based on the detected physical field via a data cable, including:—placing the measuring sensor and the data cable on a mould defining the position of the measuring sensor and the data cable,—Coating the measuring sensor and the data cable positioned in the mould with a first material,—Removing the measuring sensor and data cable coated with the first material from the mould, and—Coating the measuring sensor and data cable removed from the mould and coated with the first material with a second material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2014/071588, filed Oct. 8, 2014, which claims priority to German Patent Application No. 10 2013 224 464.9, filed Nov. 28, 2013 and German Patent Application No. 10 2014 208 425.3, filed May 6, 2014, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for producing a sensor and to the sensor produced by the method. 
       BACKGROUND OF THE INVENTION 
       [0003]    WO 2010/037 810 A1, which is incorporated by reference discloses a sensor for outputting an electrical signal which is dependent on a physical variable which is detected by means of a physical field on the basis of a measuring sensor. 
       SUMMARY OF THE INVENTION 
       [0004]    An aspect of the invention aims to improve the known sensor. 
         [0005]    According to one aspect of the invention, a method for producing a sensor which is configured to detect a physical field, dependent on a variable to be measured, by means of a measuring sensor, and to output an electrical output signal on the basis of the detected physical field via a data cable, comprises the steps:
       placing the measuring sensor and the data cable in a mold which defines the position of the measuring sensor and of the data cable,   encapsulating the measuring sensor and data cable positioned in the mold with a first material,   removing the measuring sensor and data cable encapsulated with the first material from the mold, and   encapsulating the measuring sensor and data cable encapsulated with the first material and removed from the mold with a second material.       
 
         [0010]    The specified method is based on the idea that the measuring sensor and the data cable have to be enclosed completely by at least one of the two materials for both elements to be protected from moisture and other influences which bring about weathering. In order to enclose the two elements, they can be placed in a mold, which is then, for example, filled with the first material by injection molding. However, the problem basically arises here that part of the elements always rest on the edge of the mold, and therefore no complete seal is possible with the material at these locations because the elements cannot be encapsulated with the material at these locations. 
         [0011]    Although, for example, by using a securing mechanism the measuring sensor can be secured in such a way that all the elements can be encapsulated completely with the material, the measuring sensor must be positioned in this securing mechanism, which, in particular owing to the rigidity of the cable, is only possible to a limited degree within sufficient tolerances. In addition, the use of the measuring sensor in the securing mechanism requires additional fabrication steps, and also the securing mechanism cannot be completely encapsulated, as a result of which gaps remain through which the abovementioned moisture can penetrate and reach the measuring sensor and/or the data cable. 
         [0012]    Within the scope of the specified method, a different approach is therefore adopted. Here, the measuring sensor with the data cable is encapsulated with the first material in a first step. In the process, no consideration is given to whether the measuring sensor and/or the data cable are partially exposed and have locations which are not encapsulated by the first material. Instead, the measuring sensor and the data cable can be positioned highly precisely when they are encapsulated with the first material by injection molding. Only subsequently, during the encapsulation with the second material by injection molding, are the measuring sensor and the data cable encapsulated in such a way that no exposed locations which are subjected to moisture or other influences which produce weathering remain on these elements. In this way, a sensor can be produced with a highly precisely positioned measuring sensor which is resistant to the influences of the weather such as moisture. 
         [0013]    In one development of the specified method, the mold comprises a positioning element in which the measuring sensor is positioned. This positioning element can be made available in any desired way like, for example, the abovementioned securing mechanism. The highly precise position of the measuring sensor can be implemented with a simple means by virtue of the positioning element. 
         [0014]    In an additional development of the specified method, the mold comprises a shaping element on which the measuring sensor is shaped before or during the encapsulation with the first material. With the shaping element, the data cable and the measuring sensor can be placed in the mold which they require for the final application, during the encapsulation of the first material. In this way, the clocking times while the specified method is carried out can be reduced. 
         [0015]    In a particular development of the specified method, the shaping element is a bending element. With such a bending element, the measuring sensor can be bent into a position in which it can detect the abovementioned physical field particularly favorably. 
         [0016]    In another development, the specified method comprises the step of molding a positively locking element in the first material during the encapsulation of the measuring sensor and data cable, positioned in the mold, with a first material. This positively locking element can be used to connect the measuring sensor and the data cable, which are surrounded by the first material, to further elements. 
         [0017]    In one preferred development, the specified method comprises the step of molding a sealing contour around the positively locking element during the encapsulation of the measuring sensor and data cable, positioned in the mold, with a first material. The previously mentioned further element could form, after the encapsulation with the second material, a gap between the further element and the second material. In this context, there is basically the risk of the abovementioned moisture being able to penetrate via this gap. As a result of the sealing element, this risk of penetration can be reduced, if not entirely avoided. 
         [0018]    In one particularly preferred development, the specified method comprises the step of inserting a securing element into the positively locking element, to which securing element the measuring sensor, encapsulated with the first material, and the data cable can be secured after the encapsulation with the first material. In this way, the first material can be completely surrounded by the second material without exposed locations remaining on the first material, with the result that a high degree of leakproofness can be achieved with the second material. 
         [0019]    In a further development of the specified method, the measuring sensor, encapsulated with the first material and removed from the mold, and the data cable are encapsulated with a second material in a non-cured state of the first material. In this way, the first material and the second material can be connected to one another during the encapsulation with the second material, with the result that gaps between the first material and the second material are closed. 
         [0020]    In yet another development, the specified method comprises the step of forming a sealing contour which, when viewed in the direction of the data cable, runs around the first material and is arranged on the first material on a side of the data cable lying opposite the measuring sensor. This sealing element makes it possible to avoid a situation in which moisture penetrates the produced sensor at a connection point for the data cable. 
         [0021]    According to a further aspect of the invention, a sensor for detecting a physical field, dependent on a variable to be measured, by means of a measuring sensor and for outputting an electrical output signal on the basis of the detected physical field by means of a data cable is produced by means of a specified method. 
         [0022]    According to a further aspect of the invention, a mold for use in one of the specified methods comprises a first mold part, and a second mold part which can be placed on the first mold part, wherein the two mold parts form, in the state in which they are placed one on the other, a casting cavity in which the data cable, the measuring sensor and the first material can be at least partially accommodated, and wherein a bending die is formed on the first mold part, and a recess is formed on the second mold part, for accommodating the bending die, by means of which bending die and recess the measuring sensor can be shaped when the second mold part is placed on the first mold part. 
         [0023]    The specified mold can be extended with the positioning aid specified above as well as the abovementioned sealing mold regions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The properties, features and advantages of this invention which are described above and the way in which they are achieved become clearer and more easily understandable in conjunction with the following description of the exemplary embodiments which are explained in more detail in conjunction with the drawings, wherein: 
           [0025]      FIG. 1  shows a schematic view of a vehicle with a vehicle dynamics control system, 
           [0026]      FIG. 2  shows a schematic view of a rotation speed sensor in the vehicle in  FIG. 1 , 
           [0027]      FIG. 3  shows a schematic view of a method sequence for producing a part of the rotational speed sensor in  FIG. 2 , 
           [0028]      FIG. 4  shows an illustration of a detail of the schematic view in  FIG. 3 , 
           [0029]      FIG. 5  shows an illustration of a detail of the schematic view in  FIG. 4 , and 
           [0030]      FIG. 6  shows a schematic view of an alternative method sequence for producing a part of the rotational speed sensor in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    In the figures, identical technical elements are provided with identical reference symbols and are described only once. 
         [0032]    Reference is made to  FIG. 1  which shows a schematic view of a vehicle  2  with a vehicle dynamics control system which is known per se. Details on this vehicle dynamics control system can be found, for example, in DE  10   2011   080   789  Al, which is incorporated by reference. 
         [0033]    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 means of a brake  8  which is attached in a positionally fixed fashion to the chassis  4 , in order to slow down the movement of the vehicle  2  on a road (not illustrated further). 
         [0034]    In this context, it is possible that, in a manner known to a person skilled in the art, the wheels  6  of the vehicle  2  lose their grip and the vehicle  2  is moved away even from a trajectory which is predefined, for example, by means of a steering wheel (not shown further), as a result of understeering or oversteering. This is avoided by closed-loop control circuits which are known per se such as ABS (anti-lock brake system) and ESP (electronic stability program). 
         [0035]    In the present embodiment, the vehicle  2  has for this purpose rotational speed sensors  10  on the wheels  6  which detect the rotational speed  12  of the wheels  6 . In addition, the vehicle  2  has an inertial sensor  14  which detects movement dynamics data  16  of the vehicle  2  from which, for example, a pitch rate, a rolling rate, a yaw rate, a lateral acceleration, a longitudinal acceleration and/or a vertical acceleration can be output in a manner known per se to a person skilled in the art. 
         [0036]    On the basis of the detected rotational speeds  12  and movement dynamics data  16 , a controller  18  can determine, in a manner known to a person skilled in the art, whether the vehicle  2  is slipping on the underlying surface or even deviating from the abovementioned, predefined trajectory, and said controller  18  can correspondingly react thereto with a controller output signal  20  which is known per se. The controller output signal  20  can then be used by an actuating device  22  in order to drive, by means of actuation signals  24 , actuating elements such as the brakes  8  which react to the slipping and the deviation from the predefined trajectory in a manner known per se. 
         [0037]    The present invention will now be explained in more detail on the basis of the rotational speed sensor  10  shown in  FIG. 1 , even if the present invention can be implemented in any desired electronic devices and, in particular, in any desired sensors such as magnetic field sensors, acceleration sensors, rotational speed sensors, solid-borne sound sensors or temperature sensors. 
         [0038]    Reference is made to  FIG. 2  which shows a schematic view of the rotational speed sensor  10  in the vehicle  2  in  FIG. 1 . 
         [0039]    The rotational speed sensor  10  is embodied in the present embodiment as an active rotational speed sensor  10 , within the scope of which an encoder disk  26 , which is connected in a rotationally fixed fashion to one of the wheels  6  and is composed of a multiplicity of magnetic poles  28  outputs a magnetic field  30 . The magnetic field  30  penetrates a measuring sensor  34  which is housed in a housing  32  and is connected via a signal-conditioning circuit  36  to a data cable  38  via which the rotational speed  12  can be transmitted to the controller  18 . In this context, the measuring sensor  34 , the signal-conditioning circuit  36  and the data cable  38  can be connected to one another by means of wiring connections  40 , for example in the form of a leadframe. 
         [0040]    Further background information on active rotational speed sensors can be found, for example, in DE 101 46 949 A1, which is incorporated by reference. 
         [0041]    Reference is made to  FIGS. 3 to 5  which show a schematic view of a method sequence for the production of a part  42  of the rotational speed sensor  10  in  FIG. 2 . 
         [0042]    In this context, the part  42  of the rotational speed sensor  10  is illustrated in various fabrication stages  43  to  48 , which are not illustrated in a progressive sequence in terms of the execution of the production method in  FIGS. 3 to 5 . For the sake of clarity, identical elements within the individual fabrication stages are provided with a reference symbol only once in  FIGS. 3 to 5 . 
         [0043]    The method starts in the first fabrication stage  43  with the measuring sensor  34 , the signal-conditioning circuit  36  and the data cable  38  being connected to one another via the wiring connections  40 . In this context, the wiring connections  40  have positioning openings  49  between the signal-conditioning circuit  36  and the data cable  38 . 
         [0044]    Within the scope of the second fabrication stage  44 , the circuit composed of the measuring sensor  34  connected in this way, the signal-conditioning circuit  36  and the data cable  38  are accommodated in a lower mold part  50  of a first molding. Details on how this circuit is inserted into the lower mold part and how the lower mold part  50  is constructed will be explained below with reference to the exploded illustration within the scope of the third fabrication stage  45 . 
         [0045]    The lower mold part  50  comprises two receptacle openings  51  in which positioning elements in the form of positioning pins  52  can be inserted. The abovementioned positioning openings  49  are fitted onto these positioning pins  52 , as can be seen in the second fabrication stage  44 . 
         [0046]    In addition, the lower mold part  50  comprises a bending die  53 , on which the wiring connection  40  between the measuring sensor  34  and the evaluation circuit  36  is placed. The measuring sensor  34  is bent with respect to the evaluation circuit  36  by means of the bending die  53  within the scope of the production method, as will be explained in more detail later, with the result that the measuring sensor  34  can be bent parallel to the encoder disk  26  for optimum detection of the magnetic field  30 . This bent state is already illustrated within the scope of the second fabrication stage  44 . However, in the unbent state of the measuring sensor  34 , the circuit is inserted into the lower mold part  50 . 
         [0047]    The lower mold part  50  also has a holding mold region  54 , via which a holding mold  55 , to be described later below, can be formed on an intermediate housing  56  which is to be molded with the first mold. More details on this are given at a later location. A sealing mold region  57 , with which a sealing mold  58  can be formed around the holding mold  55 , on the intermediate housing, is formed around this holding mold region  54 . A similar further sealing mold region  57  can be formed on the cable-side end of the lower mold part  50 . 
         [0048]    In the next, third fabrication step  44 , an upper mold part  59 , which is associated with the first mold, is arranged above the lower mold part  50 , said mold part  59  being illustrated in a cut-away form in  FIGS. 3 to 5 . The upper mold part  59  has in a similar way to the lower mold part  50 , a holding mold region  54  and two sealing mold regions  57 , which are, however, not provided with a reference symbol in  FIGS. 3 to 5  for the sake of clarity. In addition, the upper mold part  59  has a recess  60  in which the bending die  53  can be accommodated. 
         [0049]    This upper mold part  59  is then moved, within the scope of the fourth and fifth fabrication stages  46 ,  47  as shown in  FIG. 3 , against the lower mold part  50 , with the result that the casting cavity between the two mold parts  50 ,  59 , which casting cavity comprises, inter alia, the holding mold region  54  and the sealing mold regions  57  as well as a region which molds the intermediate housing  56  and is not provided with further references, is closed. Within the scope of this closing movement, the wiring connections  40  which are placed on the bending die  53  are bent, with the result that the measuring sensor  34  is bent into the position described above, in which it can be oriented parallel to the encoder wheel  26 . 
         [0050]    In the now closed casting cavity, a first encapsulation material, which molds the intermediate housing  56 , is now input by pouring or injection molding. After initial curing of this first encapsulation material, the two mold parts  50 ,  59  are removed within the scope of the sixth fabrication stage  48  and inserted into one of the two holding molds  55  which are formed (above or below the intermediate housing  56 ), or a holding pin  61 , which is embodied as a holding element, is inserted into both holding molds  55 . In this context, the intermediate housing  56  can also be held in a stable way in a rear part  66  of the lower mold part  50 . 
         [0051]    As can be seen within the scope of the sixth fabrication stage  48 , parts of the abovementioned circuit, such as, for example, the cable  39 , are still exposed on the intermediate housing  56 . In order to close these regions, a terminating housing  62  is applied by injection molding to the intermediate housing  56  which has not yet completely cured, said terminating housing  62  completely closing off these exposed regions. As a result of the fact that the terminating housing  62  is applied by injection molding to the intermediate housing  56  in a state of said intermediate housing  56  in which it is not completely cured, the terminating housing and the intermediate housing can be connected to one another better. 
         [0052]    As a result, a rotational speed sensor  10  in which the measuring sensor  34  is enclosed in a sealed fashion and therefore protected against the ingress of moisture is provided. 
         [0053]    Reference is made to  FIG. 6  which shows a schematic view of an alternative method sequence for producing a part of the rotational speed sensor in  FIG. 2 . 
         [0054]    Within the scope of this method sequence, the data cable  38  is not connected directly to the rotational speed sensor  10  but via a plug  63 . In this context, the plug  63  can be cast together with the intermediate housing  56 . 
         [0055]    In this context, the measuring sensor  34  and the signal-conditioning circuit  36  are connected to a leadframe  64  by means of the wiring connection  40 . The leadframe  64  can be embodied here as meterware, wherein an individual leadframe section can be cut out, for example with a punching element  65 , before the molding of the intermediate housing  56 . Otherwise, the production can take place in the same way as in  FIGS. 3 to 5 .