Patent Publication Number: US-6222435-B1

Title: Stick coil for igntion systems

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a bar-type coil for ignition systems, in particular, a bar type coil for use as an ignition coil in internal combustion engines of motor vehicles according to the definition of the. 
     BACKGROUND INFORMATION 
     German Patent No. 41 32 851 describes a bar-type coil whose basic form is that of a cylindrical housing. Joined to the housing is a primary terminal having contact elements, which are electrically connected to winding ends of a coil assembly of the ignition coil arranged in the housing. 
     Disposed in a central position in the housing and within the coil assembly is a bar-shaped core of an open magnetic circuit. The coil assembly is concentrically surrounded by a longitudinally slotted magnetic return plate for directing the magnetic field. 
     During operation of the ignition coil, an interference energy is produced by an external partial discharging and acts, by way of capacitive re-charging processes, upon the primary terminal. The ignition-coil housing insulates the magnetic return plate from the spark plug shaft. The interference energy is dependent upon the electric field strength between the magnetic return plate and the spark plug shaft. Because of the installation location in the spark plug shaft, the interference energy is greater than in conventional ignition coils having a magnetic circuit that is closed over the core material. 
     The elevated interference energy, which may spread via the primary terminal and the lines connected thereto into the motor vehicle&#39;s electrical system, can cause unwanted degradations in the functions of other electrical components of the motor vehicle, such as a control unit or a radio receiver. 
     SUMMARY OF THE INVENTION 
     An advantage of a bar-type coil according to the present invention for ignition systems is that the deficiencies described above are avoided. This is achieved by configuring the bar-type coil with the magnetic return plate connected to the frame potential and diverting the charge carriers, which form and contribute to a partial discharging, to ground. This decreases the danger of malfunctions in electrical aggregates of the motor vehicle. 
     In certain cases, direct contact of the magnetic return plate with ground, leads to a voltage loss at the secondary side of the ignition coil carrying the high voltage. It is necessary to connect a resistance element having high enough resistance between the magnetic return plate and frame potential to avoid such a voltage loss. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a sectional view of a first embodiment of a bar-type coil for ignition systems according to the present invention. 
     FIG. 2 illustrates a sectional view of a second embodiment of a bar-type coil for ignition systems according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     According to FIGS. 1, and  2 , a bar type coil  11  for ignition systems, in particular, a bar type coil for use as an ignition coil in internal combustion engines of motor vehicles, is provided with a spark plug to enable direct contacting. The spark plug is inserted in a customary manner (not shown) in a shaft of the cylinder head of an internal combustion engine. 
     Disposed in a housing  13  of plastic, co-axially to a longitudinal axis  12 , bar-type coil  11  contains an elongated, cylindrical core  14 , also referred to as an I-core. Core  14  is made of a layered magnetic material and constitutes part of an open magnetic circuit. Arranged concentrically around core  14  is an inner primary winding  16 , which conducts a low voltage, and an outer secondary winding  17 , which conducts a high voltage. To direct the magnetic field, windings  16 ,  17  are surrounded by a magnetic return plate  15 , which is supported on the inside of housing  13 . Magnetic return plate  15  is slotted in parallel to longitudinal axis  12  to prevent any short-circuiting of the magnetic field. 
     As part of a primary terminal  18  of bar-type coil  11 , a plug-connector member is integrally, formed in one piece with housing  13  at one end of bar-type coil  11 . Primary terminal  18  has, in addition to other elements, a first contact element  19 , which is electrically connected to frame potential. This first contact element  19  is part of a line bar  21 , which is formed as a laminated strip and, in the first exemplary embodiment illustrated in FIG. 1, is electrically connected by one unattached end  22  to a resistance element  23 . Resistance element  23 , in turn, is electrically connected to magnetic return plate  15 . 
     If no resistance element  23  is necessary, a laminated strip  24  is then used instead as an electrical bridge, in accordance with the second exemplary embodiment illustrated in FIG.  2 . 
     Resistance element  23 , or laminated strip  24 , has the effect of compensating for the charge carriers, so that no interference energy is produced in this case by an energy-rich partial discharging.