Abstract:
A method for producing a magnetic field sensor for use in drive train of a motor vehicle includes encapsulating an electrical assembly and an end of a connecting cable via injection molding and integrally extruding a fastening tab. After a first injection step in which the electrical assembly and the connecting cable are encapsulated in a core-type first molded part, a second injection molding step in implemented in which a fastening tab is integrally formed via injection molding on the core-type insertion part in a specifiable longitudinal and/or angular position. The core-like insertion part is held in the injection mold in a longitudinally displaceable and/or rotatable manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2008 005 315.5 filed on Jan. 21, 2008. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a method and a device for producing a magnetic field sensor according to the preamble of the independent claims. A magnetic field sensor that is produced using the proposed method and/or using the claimed device is likewise the subject matter of the present invention. 
     DE 101 29 222 A1 made known a magnetic field sensor and a method for its manufacture by encapsulating, via injection molding, a carrier that contains a sensor element. The sensor element is situated on a carrier element which is composed of metal, and it is fixed in a defined position relative to a rotating sensor element by encapsulating it in plastic via injection molding. The position of the sensor element is established by a stop that defines the distance between the sensor and the encoder; neither this distance nor the angular position of the sensor relative to the encoder are changeable. 
     Furthermore, DE patent application 10 2006 050 177.2 has already proposed a magnetic field sensor that is designed as a rotational speed sensor and/or a direction of rotation sensor for a motor vehicle, in which a sensor element that is sensitive to a magnetic field, and its carrier, are encapsulated in plastic via injection molding. The plastic injection-molded coating also encapsulates the end of a connecting cable, and is designed such that the injection-molded part forms a connecting tab having a fastening socket in which a sensor is installed. As a result, it is possible to adjust the angular position of the sensor, within narrow limits, relative to a sensor ring by rotating it about the central axis of the fastening socket, without changing the axial positioning of the sensor. 
     SUMMARY OF THE INVENTION 
     In contrast, a sensor which is manufactured according to the proposed method and/or using the device according to the present invention has the advantage that, in accordance with the particular installation conditions of the sensor, the longitudinal position and the angular position of the fastening tab, and therefore, the position of the sensor relative to a transmitter element are changeable, thereby making it possible to manufacture sensors for different installation situations without changing tool inserts or even the entire injection mold. 
     It is particularly advantageous if a core-type insertion part, which has been produced in a first injection step, is held, in a second injection step, in a tool insert which is longitudinally displaceable and/or rotatable in the injection mold. In this manner, the insertion part may be positioned exactly and easily before the second injection step, and the fastening tab may be integrally formed thereon, via injection molding, in the specified longitudinal and angular position. Advantageously, the core-type insertion part is substantially cylindrical in shape, and is positioned in a bore, thereby further simplifying the insertion and orientation of the insertion part that includes the electrical assembly. 
     In terms of the design of the device, according to the present invention, for manufacturing a magnetic field sensor that includes a fastening tab that determines the installation position of the sensor, it is particularly advantageous when, in order to integrally extrude the fastening tab, a tool insert is situated in an injection mold such that it is longitudinally displaceable and/or rotatable, in order to accommodate a core-type insertion part which was manufactured in a previous working step and contains the electrical assembly. It is thereby possible to manufacture sensors, which are based on the same basic design, for use in different installation conditions having different longitudinal and angular positions relative to a transmitter element without the need to make expensive changes to the injection mold. 
     Advantageously, the tool insert is continually displaceable in the injection mold, and it may be locked in different longitudinal and/or angular positions. The tool insert and the core-type insertion part which includes the electrical assembly are preferably designed cylindrical or hollow-cylindrical in shape, thereby simplifying installation and positioning. 
     Further details and advantageous embodiments of the present invention result from the dependent claims and the description of an embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of a magnetic field sensor which was produced according to the present invention, and a device for its manufacture, are presented in the drawings and are described in greater detail in the description that follows. 
         FIG. 1  shows a schematic depiction of a magnetic field sensor according to the present invention, 
         FIG. 2  shows a perspective view of a core-type insertion part that accommodates the electronic assembly, including a connecting cable, as a preassembled component of the magnetic field sensor, 
         FIG. 3  shows a perspective view of a finished magnetic field sensor, 
         FIG. 4  shows a perspective view of the bottom part of an injection mold, into which the tool insert has been inserted and is used to receive the insertion part shown in  FIG. 1 , 
         FIG. 5  shows a cross section through the injection mold, including an illustration of a finished magnetic field sensor, and 
         FIG. 6  shows a cross sectional along line VI-VI in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows electrical assembly  10  of a magnetic field sensor  13 , which is to be encapsulated in thermoplastic according to the proposed method, magnetic field sensor  13  being designed as a rotational speed sensor for use to detect the wheel speed of a motor vehicle. It contains an IC component  11  which includes a sensor element and an integrated circuit for preparing the measurement signals and the measured value output. The magnetic field which is used to generate the measured signals is provided by a cylindrical permanent magnet  12  which is located directly adjacent to IC component  11 . Two conductor tracks  14  and  16  of integrated circuit  11  are bridged by a capacitor  18  in order to reduce signal spikes, and are connected via crimp connections  20  and  22  to connecting lines  24  and  26  of a cable  28 , the front end of which is encapsulated in plastic together with lines  24  and  26 , capacitor  18 , permanent magnet  12 , and integrated circuit  11  to create the finished magnetic field sensor, the design and mode of operation of which is known. The individual parts that are encapsulated in plastic are indicated in  FIG. 1  using dashed lines, and they are described in greater detail in the figures that follow. 
       FIG. 2  shows, in a perspective view, a core-type insertion part  30  that contains electrical assembly  10 , which is connected to connecting cable  28 , in a cylindrical injection-molded coating  32 . A bore  34  marks the position of IC component  11  of electrical assembly  10  as the sensing element, based on which magnetic field sensor  13  is oriented during assembly.  FIG. 2  also shows a metallic socket  36  in the position in which it is connected to insertion part  30  in the second injection step. 
       FIG. 3  shows, likewise in a perspective view, finished magnetic field sensor  30  after the second injection step, in which a fastening tab  38  was integrally extruded on core-type insertion part  30  in a specifiable longitudinal and angular position. In this second injection step, insertion part  30  is positioned via bore  34  in terms of the longitudinal and angular position in an injection mold, which is explained further below, and in which fastening tab  38  is then integrally extruded in the position that is specified for subsequent installation of sensor  13 . 
     Metallic socket  36 , which is shown in  FIG. 2 , is injected into fastening tab  38  in order to increase the stability of the sensor attachment. In addition, a centering sleeve  40 , which partially overlaps plastic injection-molded coating  32  of insertion part  30 , is integrally extruded onto the fastening tab; centering sleeve  40  includes four ribs  42  which are evenly distributed around the circumference of the centering sleeve, and which are used to center entire sensor  13  during installation. Furthermore, an annular flange  44  is also integrally extruded on fastening tab  38 , opposite to centering sleeve  40 ; annular flange  44  encloses connecting cable  38  and stabilizes the transition from the cable to insertion part  30 . 
       FIG. 4  shows a perspective view of bottom part  46  of an injection mold, including tool insert  48  for receiving insertion part  30 . Tool insert  48  is cylindrical in shape, and includes a cylindrical bore  52  for receiving cylindrical insertion part  30 . The tool insert is situated in the injection mold and in a carrier  50  such that it is continually longitudinally displaceable and rotatable into any position, and may then be locked into the selected position, as will be explained in greater detail below with reference to  FIG. 5  in particular. For adjustment purposes, a handle  53  is integrally formed thereon in this embodiment. 
     After carrier  50  has been positioned in bottom part  46  of the injection mold, insertion part  30 , together with connecting cable  28 , is positioned in injection mold  46  and in tool insert  48  in a functional length and angular position as required for subsequent installation, and the tool insert is locked in position in the injection mold. Socket  36 , which will be injected into fastening tab  38 , is slid via a sliding mechanism  54  and a mandrel  55  into its position, which is shown in  FIGS. 2 and 3 , in the region of fastening tab  38  which will be integrally extruded, and sliding mechanism  54  is subsequently retracted. The plastic mass to be used to integrally extrude fastening tab  38  is supplied via a channel  56 . 
       FIG. 4  shows the injection mold, which has been opened after the injection step. The sensor is located in bottom part  46  of the injection mold. In this illustration, fastening tab  38  has already been integrally extruded onto insertion part  30 , and so finished magnetic field sensor  13  may be ejected. 
       FIG. 5  shows a cross section through the injection mold, including bottom part  46 , sliding mechanism  54 , which is designed as an angled slide, and a top part  58 . Carrier  50 , in which tool insert  48  is held in a manner such that it is longitudinally displaceable as indicated by arrow  60 , and is rotatable about its central axis, is located via a portion of its extension in bottom part  46  and in top part  58 . Tool insert  48  is fastened in carrier  50  using a locking part  62 . Insertion part  30  is slid into bore  52  in tool insert  48  in its specified angular position until it reaches the end of bore  52 . The insertion part is locked in position using a retaining pin  64  which secures the angular position that is defined upon insertion, and which holds the insertion part, including connecting cable  28 , in its position; the retaining pin engages in marking bore  34  in insertion part  30  and secures the position which is defined by the position of IC component  11 . 
     The different possibilities for positioning fastening tab  38  become clear by comparing  FIGS. 3 and 5 . In  FIG. 3 , fastening tab  38  is located on the cable-side end of insertion part  30 , whereas, in the embodiment depicted in  FIG. 5 , it is located further in the middle of insertion part  30  and thereby determines another functional length of the sensor. The positioning is determined by the longitudinal displacement as indicated by arrow  60 , and optionally via rotation of tool insert  48 ; insertion part  30  is inserted completely into bore  52  in both cases. The position of fastening tab  38  in the injection mold is fixedly specified. 
       FIG. 6  shows a cross section through the injection mold in the region of line of intersection VI-VI in  FIG. 5 . This illustration also shows the design of fastening tab  38  for insertion part  30 , as well as the position of fastening socket  36  which is oval in this case, in order to obtain a certain amount of fastening tolerance upon installation of the sensor. For the rest, identical parts are labelled in  FIG. 6  with the same reference numerals that are used in the preceding illustrations.