Patent Publication Number: US-2007101976-A1

Title: Method for manufacturing an ignition coil and corresponding ignition coil

Description:
FIELD OF THE INVENTION  
      The present invention relates to a method for manufacturing an ignition coil, in particular a rod-type ignition coil.  
     BACKGROUND INFORMATION  
      European Patent No. 862 807 shows an ignition coil in the form of a rod-type ignition coil has a channel running in the longitudinal axis of its core or parallel with respect to it, which extends into the bottom region of the ignition coil housing below the secondary and primary winding. Via a casting nozzle, the initially liquid insulating resin is introduced into the channel from above, i.e. from the side of the ignition coil housing lying opposite from the bottom region, from where it runs down the channel on account of gravity and subsequently fills in the ignition coil housing starting from the bottom region in the form of a so-called rising cast.  
      The known method requires a specially configured ignition coil, which has a channel for introducing the insulating resin into the bottom region that increases the space requirement of the ignition coil. Furthermore, additional structural measures such as separating chambers or the like are possibly required, which prevent the insulating resin from entering, for example, electrical connection regions of the ignition coil in the upper region of the ignition coil housing. In this respect, the end of the casting process, in which the casting nozzle is removed from the lid area of the ignition coil housing, also represents a critical process step since casting resin should be prevented from dripping off from the casting nozzle.  
     SUMMARY OF THE INVENTION  
      By contrast, the method according to the present invention for manufacturing an ignition coil has the advantage that the ignition coil does not require any channel or the like that would increase the space requirement, in particular the diameter.  
      Advantageous further developments of the method according to the present invention as well as suitable ignition coils for implementing the method are indicated in the dependent claims.  
      It is particularly advantageous to introduce the insulating resin into the bottom region of the ignition coil or the ignition coil housing with the aid of a feed device in the form of a hollow needle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a longitudinal cross section through an ignition coil in which the ignition coil housing is filled with an insulating resin laterally in the bottom region with the aid of a hollow needle.  
       FIGS. 2 and 3  show longitudinal cross sections in the bottom region of an ignition coil housing modified with respect to  FIG. 1  as the ignition coil housing is filled coaxially.  
       FIG. 4  shows another modified ignition coil housing for filling with an insulating resin via a laterally premolded riser.  
       FIG. 5  shows a longitudinal cross section through an ignition coil housing as the ignition coil is filled with the aid of a hollow needle from the top region of the ignition coil. 
    
    
     DETAILED DESCRIPTION  
      An ignition coil  10  for ignition systems, in particular an ignition coil in an internal combustion engine, is provided for direct contact with a spark plug  12 , which is inserted in the conventional manner (not shown) in a shaft in a cylinder head of an internal combustion engine.  
      Ignition coil  10  configured in the form of a so-called rod-type ignition coil  11  is largely rotationally symmetric and contains in a coaxial arrangement with respect to a longitudinal axis  13  a longitudinal cylindrical core  14  made of magnetic material. Concentrically arranged around core  14  is a first winding form  17  as a primary coil form made of plastic, which may be configured as an extrusion coating of core  14  or as a separate mounting form. A primary winding  18  carrying a low voltage is applied on first winding form  17 .  
      At a small radial distance, a second winding form  21  is arranged over a first gap  19  with respect to primary winding  18 , which is provided with a secondary winding  22  carrying a high voltage.  
      Alternatively, secondary winding  22  may also be situated inside and primary winding  18  outside.  
      At a small radial distance over a second gap  23  with respect to secondary winding  22 , this is followed by a housing  24  made of plastic. Outside of housing  24 , alternatively within, a tube-shaped yoke element  26  is situated jacket-like as a sheet metal part for shielding the magnetic field of rod-type ignition coil  11  toward the outside.  
      On one side of housing  24 , this is followed by a high-voltage connector  27  for conducting the ignition energy of rod-type ignition coil  11  to spark plug  12  indicated by a dashed line. A connection section  29  is situated on the other side of housing  24 . An interior space  30  is formed between housing  24 , high-voltage connection  27  and connection section  29 .  
      High-voltage connection  27  comprises in particular a dome  31 , a protective jacket  32 , an electrode  33  and a contact spring  34 . Dome  31  is a plastic part of one piece with housing  24 , alternatively a plastic part separated from housing  24 , in the basic shape of a sleeve and coaxially situated with respect to longitudinal axis  13 , which surrounds contact spring  34  connected to a terminal stud  36  of spark plug  12  in an electrically conductive manner and a terminal pin  37  of stepped cylindrical electrode  33 , which is likewise in electrical contact with contact spring  34 . In an appendage  38  of dome  31  directed towards interior space  30 , electrode  33  is supported in such a way that interior space  30  at this end is tightly sealed. Electrode  33  is connected in an electrically conductive manner via a contact plate  39  running into interior space  30  to one end of secondary winding  22 .  
      Over a partial length of dome  31 , stepped sleeve-shaped protective jacket  32  made of silicone rubber, directed toward spark plug  12 , is attached, which surrounds an insulator  41  of spark plug  12  and seals off the contact region between spark plug  12  and rod-type ignition coil  11 .  
      Connection section  29  comprises a primary connector  42  capable of being contacted by low voltage and, except for a region  43 , in which the plug connector  45  connected to primary winding  18  is situated, is configured as an on its front side essentially sleeve-shaped, one-piece component.  
      Additionally, mention is made of the fact that the housing construction of ignition coil  10  described so far may be modified in multiple ways and is not limited to the specific embodiment described.  
      When installing rod-type ignition coil  11 , among other things, core  14  and the two winding forms  17  and  21  supporting primary winding  18  and secondary winding  22  are inserted into housing  24 . Following the insertion and possibly additional installation steps, interior space  30  is filled up to a level  44  with a cast resin  46 . Cast resin  46 , which is solid once cooled, fills up in particular gap  19  and  23  as well as the possibly existing gap between core  14  and inner winding form  17 . Filling up with cast resin  46  is used to prevent voltage spark-overs between the individual components in the operation of rod-type ignition coil  11 . For this purpose, the present invention provides for cast resin  46  to be preferably introduced into housing  24  in bottom region  47  of housing  24 , i.e. on the side lying opposite of connection section  29 . Subsequently cast resin  46  rises to the top as a so-called rising cast in the direction of connection section  29  in housing  24  such that at least winding forms  17  and  21  are surrounded across their entire length by cast resin  46 .  
      The first specific embodiment of the present invention according to  FIG. 1  provides for cast resin  46  to be introduced with the aid of a feed device  50  from the side, preferably below the two winding forms  17 ,  21 , into bottom region  47  of housing  24 . For this purpose, feed device  50  has a hollow needle  51 , which is capable of being inserted through wall  52  of housing  24  into bottom region  47 . To achieve this, wall  52  of housing  24  is made, at least in the region of the entry point  53  of hollow needle  51  into housing  24 , from a material through which hollow needle  51  is able to penetrate into housing  24 , from an elastomer for example. Entry point  53  is preferably configured in such a way or hollow needle  51  has such a diameter that, after interior space  30  has been filled up and hollow needle  51  subsequently has been pulled out, the material of wall  52  will close by itself or no cast resin  46  will leak out of housing  24  due to the surface tension of cast resin  46 .  
      Filling up interior space  30  from bottom region  47  in the direction of connection section  29  has the advantage of achieving a more homogeneous distribution of material and of preventing inclusions of foreign media or particles. The cast resin front pushes gases present in the interior of housing  24  ahead of itself and thus channels them out of housing  24 , which results in improved venting. Filling occurs at overpressure, i.e. cast resin  46  issues from hollow needle  51  at overpressure. In this regard, the highest possible pressure is to be aimed at in order to make the filling time as short as possible.  
      In the first exemplary embodiment shown in  FIG. 1 , it is advantageous or necessary to fill interior space  30  from the side due to the construction of housing  24  having electrode  33  situated in longitudinal axis  13  near bottom region  47 .  
       FIGS. 2 and 3  show exemplary embodiments in which the construction of housing  54  or  64  allows for it being filled coaxially with respect to longitudinal axis  13  or parallel to it from bottom region  57  or  67 . Analogous to the first exemplary embodiment, in the exemplary embodiment according to  FIG. 2 , wall  55  of housing  54  in the region of at least the entry point  56  of hollow needle  51  is made of a material which allows for hollow needle  51  to penetrate and prevents cast resin from leaking out following the filling process. In the exemplary embodiment according to  FIG. 3 , by contrast, a diaphragm  68  or a pressure-relief valve is situated in bottom region  67 , as it is known in particular from the food sector, e.g. in honey containers. Such a diaphragm  68  or pressure-relief valve has the characteristic of opening at a specific overpressure and thus to create a passage for a medium, in this case the cast resin. As soon as the overpressure has fallen below a structurally determined value, however, diaphragm  68  or the pressure-relief valve recloses the opening such that no medium can emerge from housing  64 . In the embodiment according to  FIG. 3 , hollow needle  51  is situated for this purpose within a bell-like filling stub  70  whose front-side edge  71  can be brought into contact with the bottom side of housing  64  in such a way that diaphragm  68  or the pressure-relief valve is located within edge  71 . To fill housing  64  it is sufficient to guide hollow needle  51  merely up to diaphragm  68  or the pressure-relief valve, that is, to dock it to the latter. It is not necessary for hollow needle  51  to penetrate into diaphragm  68  or the pressure-relief valve, so that this approach promises advantages with respect to operating time of hollow needle  51  and the nonexistent danger of damage to components located within housing  64 .  
      The exemplary embodiment according to  FIG. 4  essentially corresponds to the first exemplary embodiment such that here too housing  74  is filled up from the side. In contrast to the first exemplary embodiment, however, no hollow needle  51 , but rather a so-called riser  75  is used for filling or introducing the cast resin into the bottom region  47 . Riser  75  is integrally formed on housing  74  and is connected via a hole  76  in housing  74  to the interior space  30  of housing  74 . Via riser  75 , the cast resin is introduced, for example by a casting nozzle  78 , at overpressure into interior space  30 . Following the filling and curing of the cast resin, riser  75  is separated at its connecting point to housing  74 .  
      In the exemplary embodiment according to  FIG. 5 , the cast resin is likewise introduced into the bottom region  83  of housing  84  with the aid of a hollow needle  51 . For this purpose, hollow needle  51  is introduced into a gap extending to bottom region  83 , either the gap between core  14  and inner winding form  17  or gap  19  between the two winding forms  17 ,  21  or gap  23  between outer winding form  21  and housing  84 . Which of the gaps is suitable must be decided by considering the size of the gap and a possible danger of damaging the components when hollow needle  51  penetrates into housing  84 . Possibly the (outer) diameter of hollow needle  51  must also be reduced in comparison to the exemplary embodiments described so far. It is advantageous in the last of the exemplary embodiments described that housing  84 , with the exception of the accessibility of hollow needle  51  from the side of connection section  29 , does not require a special configuration or any additional components.