Abstract:
An extrusion-coating method for a sensor device, including the following steps:
       providing a sensor module, which is completely enclosed by a first medium,   supporting by a support bar on the first medium of the sensor module,   extrusion-coating the sensor module using a second medium, so that a sealing connection is formed between the first medium and the second medium and   extracting the support bar. Also, a sensor device.

Description:
BACKGROUND INFORMATION 
       [0001]    It is known that sensors may be extrusion-coated with an elastomer to form an elastomer sheathing around the sensor. To contact the extrusion-coated sensor electrically, an electrical plug contact of the sensor is not completely extrusion-coated in the known methods. This means that this plug contact remains partially exposed and protrudes from the elastomer sheathing. In a second extrusion-coating step, the elastomer sheathing is extrusion-coated with a thermoplastic to form a thermoplastic housing. To ensure trouble-free operation of the sensor, the sensor must be situated in a precisely defined position in the thermoplastic housing. This is achieved in particular by a support bar, which supports the elastomer sheathing on the protruding plug contact. The support bar is pulled during the thermoplastic extrusion-coating. The point in time of pulling of the support bar thus determines both the positional accuracy of the sensor and the imperviousness of the thermoplastic sheathing, which determines the robustness of the sensor over its lifetime. Such a method is described in German Patent No. DE 10 2007 057 441. 
       SUMMARY OF THE INVENTION 
       [0002]    An object of the present invention is to provide an extrusion-coating method for a sensor device, which ensures improved imperviousness of the sensor device while ensuring improved positional accuracy. 
         [0003]    In addition, an object of the present invention is to provide a sensor device which has reliable imperviousness with respect to external influences. 
         [0004]    These objects are achieved by an extrusion-coating method and by a sensor device according to the present invention. 
         [0005]    The present invention includes the idea of providing an extrusion-coating method for a sensor device such that a sensor module, which is completely enclosed by a first medium, is provided in a first step. It is possible in particular for the sensor module to be completely extrusion-coated by the first medium. Thus, in contrast to the related art, no plug contacts of the sensor module protrude from the sheathing formed by the first medium, for example. 
         [0006]    In a second step, a support bar supports the first medium of the sensor module. For example, the support bar may act on support areas of the sheathing. In particular, the support areas may be designed in such a way that they correspond to a negative impression with respect to the shape of the support bar. Thus, the support bar may support the first medium in a particularly reliable manner. In another exemplary specific embodiment, the first medium may also be supported in additional areas, for example, by additional support bars. 
         [0007]    In the next step, the sensor module is extrusion-coated using a second medium, the support bar continuously supporting the first medium during this extrusion-coating step, so that high positional accuracy of the sensor module in the second medium is achieved. The first and the second medium form a sealing connection which ensures permanent imperviousness of the sensor module with respect to external environmental influences. 
         [0008]    After the sheathing of the sensor module has been extrusion-coated using the second medium, the support bar is extracted. 
         [0009]    The present invention also includes the idea of providing a sensor device having a sensor module, the sensor module being completely enclosed by a first medium. Furthermore, a second medium which partially surrounds the first medium is provided so that a support area for a support bar remains exposed. The sensor device may be manufactured using the extrusion-coating method in particular. 
         [0010]    According to a preferred embodiment of the present invention, a first medium having hollow spheres with a hydrocarbon fluid is used. Fluid here includes both a gas and a liquid. The hydrocarbon preferably includes pentane or octane. The hollow spheres have in particular a diameter of 10 μm to 40 μm. According to a particularly preferred embodiment, the hollow spheres are formed from an outer sheathing, in particular a thermoplastic sheathing. The hollow spheres are preferably homogeneous. This means, for example, that they have the same features and same properties. Alternatively, the hollow spheres are not homogeneous. 
         [0011]    According to another exemplary specific embodiment of the present invention, a plug unit is electrically connected to the sensor module before and/or during the extrusion-coating of the sheathing of the sensor module using the second medium. The sensor module preferably includes an insert part and a sensor situated on the insert part, the first medium completely enclosing both the insert part and the sensor in particular. The insert part is also formed in particular so that electrical contacting of the sensor module is made possible in this way. For example, the insert part includes a circuit board. An electrical connection between the plug unit and the sensor may then be accomplished via the insert part. 
         [0012]    According to another preferred specific embodiment, the plug unit includes another insert part. The additional insert part is preferably connected to the insert part of the sensor module and held by an insert part holder. The insert part holder here holds the insert part and the additional insert part. For example, the insert part holder as an injection-molded component, in particular as a preliminary extrusion-coated part, may be injected around the insert part and the additional insert part. For example, the insert part of the sensor module may be brought into electrical contact with the additional insert part of the plug unit before the sensor module is enclosed by the first medium, in particular by extrusion-coating. The insert part holder is then molded around the insert part and the additional insert part. Next the sensor module, i.e., the sensor and the insert part, are completely enclosed by the first medium, in particular by extrusion-coating, the insert part holder being at least partially surrounded by the first medium, in particular by extrusion-coating. This means that the insert part holder is situated or embedded at least partially in the sheathing formed by the first medium. The insert part holder is preferably embedded completely in the sheathing. During the extrusion-coating step of the sensor module with the second medium, the insert part holder, the additional insert part and the plug unit are also extrusion-coated. However, an area of the plug unit is left exposed here, so that access to the additional insert part from the outside is made possible via the plug unit. The insert part and the additional insert part may also be referred to as electrical plug contacts. 
         [0013]    According to another preferred specific embodiment, a bushing is formed in the second medium during the extrusion-coating of the sensor module. For example, the housing formed by the second medium may be secured by the bushing, for example, in a motor vehicle. 
         [0014]    In another exemplary embodiment, the first medium and/or the second medium is/are formed from a material selected from the following group of materials: elastomer, thermoplastic, thermoplastic elastomer, polymer having an elastomer backing, polyurethane, silicone, liquid silicone or a combination thereof. In particular a silicone may be used with an adhesion promoter and/or an adhesion-modified thermoplastic elastomer. Furthermore, the materials may preferably include a primer. The aforementioned materials are preferably formed as foam, for example, as an elastomer foam, a silicone foam or a thermoplastic foam. In general, such materials, which enter into a physical and/or chemical bond with one another, are preferred for use here. Because of this bond, a tight connection is formed between the first and the second medium, so that good imperviousness of the sensor module is ensured in particular. 
         [0015]    According to a particularly preferred specific embodiment, a particularly hard material is used for the first medium. It is possible in this way to influence in a targeted manner the extent to which the sheathing formed by the first medium may yield to the support bar during extrusion-coating using the second medium. 
         [0016]    According to another exemplary embodiment, the sensor device may be used in an airbag sensor system of a motor vehicle. The sensor preferably includes an acceleration sensor, for example, a PAS (“peripheral acceleration sensor”) airbag sensor and/or a pressure sensor. However, the sensor device may preferably also be used in airbag sensor systems for personal safety clothing, for example, a cycling suit having one or more integrated airbags. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a sensor device according to the related art. 
           [0018]      FIG. 2  shows a sensor device according to the present invention during extrusion-coating. 
           [0019]      FIG. 3  shows the sensor device from  FIG. 2  after extrusion-coating. 
           [0020]      FIG. 4  shows a detailed view of the sensor device from  FIG. 3 . 
           [0021]      FIG. 5  shows a flow chart of a specific embodiment of the extrusion-coating method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows a sensor device  101  according to the related art during an extrusion-coating step according to a known extrusion-coating method. Sensor device  101  includes a sensor module  103 . Sensor module  103  has an insert part  105  and a sensor  107  situated on insert part  105 . Insert part  105  is preferably formed in such a way that electrical contacting of sensor  107  via insert part  105  is made possible. For example, insert part  105  may be formed as a circuit board. Another insert part  109  is situated on insert part  105 , contacting insert part  105 , so that an electrical connection is formed between insert part  105  and additional insert part  109 . Insert part  109  is part of a plug unit  111  and transitions into a pin  113 , which is situated in a plug housing  114 . Plug housing  114  has an opening  114   a , through which pin  113  is accessible from the outside. Insert part  105  and additional insert part  109  are held by an insert part holder  115 . Insert part  105  and additional insert part  109  form electrical plug contacts. 
         [0023]    Sensor module  103  is partially enclosed by a first medium  117 . In other words, insert part  105  of sensor module  103  protrudes from first medium  117 . The area of insert part  105 , which protrudes from first medium  117 , is labeled with reference numeral  119 . First medium  117  also partially surrounds insert part holder  115 , so that insert part holder  115  protrudes from first medium  117 . 
         [0024]    A support bar  121  engages with protruding area  119  of insert part  105  and thereby supports insert part  105  as well as sensor module  103 . A second medium  123  is injected around sensor module  103  and plug unit  111 , thereby forming a housing  125  around sensor module  103  and plug housing  114 , with pin  113  of plug unit  111  remaining accessible from the outside of housing  125  through opening  114   a  of plug housing  114  for the purpose of electrical contacting. During the extrusion-coating, support bar  121  is pulled away from protruding area  119  of insert part  105 . A resulting clearance is filled with second medium  123 . 
         [0025]      FIG. 2  shows a sensor device  201  according to the present invention during an extrusion-coating step of the extrusion-coating method according to the present invention. In contrast to known sensor device  101  in  FIG. 1 , insert part  105  of sensor module  103  is completely enclosed by first medium  117 . In other words, insert part  105  does not protrude from first medium  117 . Therefore, support bar  121  does not support sensor module  103  on insert part  105  but instead supports it directly on first medium  117 . This support is accomplished during the entire extrusion-coating step. Support bar  121  is extracted only after housing  125 , which is formed by second medium  123 , is completed.  FIG. 3  shows sensor device  201  after support bar  121  has been extracted. It is clearly apparent here that insert part  105  is cushioned against external environmental influences because it is completely surrounded by first medium  117 . 
         [0026]    Sensor device  201  also has a bushing  203 , which is formed during the extrusion-coating. Sensor device  201  may be secured by bushing  203 , for example, in a motor vehicle. 
         [0027]      FIG. 4  shows a detailed view of sensor device  201  after support bar  121  has been extracted from sensor module  103 . Because of the suitable choice of material of first medium  117  and of second medium  123 , a sealing connection is formed in the area of a sealing face  205  between first medium  117  and second medium  123 . First medium  117  and second medium  123  here enter into a physical and/or chemical bond, forming a tight connection between the two media  117  and  123 . First medium  117  preferably includes an elastomer and second medium  123  includes a thermoplastic. In particular, an adhesion-modified thermoplastic elastomer or a silicone having a corresponding surface treatment, for example, an adhesion promoter, may also be used for first medium  117 . In an exemplary embodiment, which is not shown here, the first medium has hollow spheres having a carbon fluid. 
         [0028]    The tight connection between first medium  117  and second medium  123  is formed here via a basic material or an adhesion promoter of first medium  117 . 
         [0029]      FIG. 5  shows a flow chart of a preferred specific embodiment of the extrusion-coating method according to the present invention. In a first step S 1 , sensor module  103  having insert part  105  and sensor  107  is provided. In a second step S 2 , plug unit  111  is positioned on sensor module  103 , so that additional insert part  109  is in contact with insert part  105  for the purpose of electrical contacting. Both insert parts  105  and  109  are extrusion-coated in next step S 3 , for example, using a material which may also be used for first medium  117  or second medium  123 . Insert part holder  115  is formed by this extrusion-coating, thereby creating a fixed connection between sensor module  103  and plug unit  111 . 
         [0030]    In the next step S 4 , sensor module  103  is extrusion-coated using first medium  117 , so that sensor module  103  is completely enclosed by first medium  117 . 
         [0031]    Next, in a step S 5 , support bar  121  is moved toward sensor module  103  so that support bar  121  supports sensor module  103  on first medium  117 . According to another exemplary embodiment of the extrusion-coating method, an additional support bar may additionally support sensor module  103  on first medium  117  in step S 5 . 
         [0032]    In a next step S 6 , sensor module  103 , insert part holder  115 , additional insert part  109  and plug housing  114  are extrusion-coated using second medium  123 , so that a sealing connection is formed between the two media  117  and  123 . However, opening  114   a  is left exposed here. During step S 6 , support bar  121  supports sensor module  103  continuously, thereby ensuring an accurate position of sensor module  103  in housing  125  formed by second medium  123 . In contrast, there is the possibility with the known extrusion-coating methods of the related art that sensor module  103  changes its position in housing  125  because support bar  121  has already been extracted during extrusion-coating using second medium  123 . The extrusion-coating method according to the present invention waits until housing  125  is completed, in particular until the second medium has cured, so that sensor module  103  is no longer able to change its position in housing  125 . 
         [0033]    Next in a step S 7 , support bar  121  is extracted from first medium  117 . Since sensor module  103  is already completely enclosed by first medium  117 , no more material needs to be injected around sensor module  103  after the extraction of support bar  121 , which advantageously saves time and material in particular. 
         [0034]    The extrusion-coating method according to the present invention is based on extrusion-coating of a sensor module using two media. Therefore, the extrusion-coating method may also be referred to as a direct two-component extrusion-coating method. The extrusion-coating method according to the present invention may be used not only for the extrusion-coating of sensor modules but also for all micromechanical components which are suitable for such an extrusion-coating method. The extrusion-coating method according to the present invention is preferably performed in a special two-component extrusion-coating die, which ensures a continuous manufacturing process.