Abstract:
The object of the invention is a contact element, in particular of ignition voltage parts in internal combustion engines, with an outer sleeve in whose inside an axially acting compression spring is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to German Patent Application Serial No. DE20 2004 015917.1, filed on Oct. 13, 2004. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a contact element, particularly for ignition voltage parts in internal combustion engines, with an outer sleeve inside which is provided an axially acting compression spring. 
   When internal combustion engines are operated the ignition of the gas content in the cylinders is brought about by means of ignition sparks which are generated by spark plugs. The ignition voltage required for ignition is generated by an ignition device, an ignition coil, via a rigid connection or an ignition cable. 
   Contact elements which consist of a sleeve incorporating an axially acting compression spring are used for contacting the spark plug and each voltage feed cable. When placed on the spark plug the compression spring is pressed against the spring pressure into the sleeve. This provides good transient contact between the voltage feeds and the spark plug. 
   The conventional compression spring of the contact element of prior art is founds from spring strip steel and is displaced out of the sleeve with the end directed toward the spark plug. The compression spring consists of spring bronze or copper. 
   During operation of the internal combustion engine corona phenomena, which result in corrosion, occur due to the high voltages to be transmitted. Because the compression spring escapes from the sleeve and the inlet port to the inside of the sleeve is therefore open, considerable corrosion occurs on the compression spring. The sleeve, with its compression spring, must be regularly replaced. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide a contacting sleeve on which less corrosion takes place. 
   This object is achieved according to the invention by the use of a contacting sleeve according to claim  1 . Preferred embodiments constitute the object of the sub-claims or are described below. 
   The significant feature of this design is that one of the spring ends rests inside the outer sleeve on a first stop, and the other spring end inside the outer sleeve engages in a cup with which this other spring end is displaceable under the action of the spring as far as a second stop still located inside the outer sleeve. 
   Therefore the spring does not escape from the outer sleeve because the cup seals the outer sleeve on the outside. For this reason the corona effects cannot affect the parts inside the contact element so easily and cannot cause corrosion so easily, particularly on the spring. The displaceable cups allow an equalisation of tolerances. 
   According to a further embodiment of the invention provision is made for the second stop for the cup to be provided with another spring end on a bush which is inserted in the outer sleeve. The second stop can therefore be assembled after the spring and cup. 
   According to a further embodiment of the invention provision is made for the bush and outer sleeve to be connected together by means of a screw connection, particularly on the outside diameter of the sleeve and the inside diameter of the outer sleeve. 
   According to a further embodiment of the invention provision is made for the bush inside the outer sleeve to be extended so that it guides the compression spring in the outer sleeve. The spring windings preferably rest against the inner walls of the bush. 
   According to a further embodiment of the invention provision is made for a feed section to connect to the end of the outer sleeve with the first stop, which section exhibits an axial hole about which extends a collar which is enclosed by a spring which, with contact pieces, contacts an ignition voltage feed line in the axial hole through wall openings in the collar. The voltage feed line is well contacted. 
   According to a further embodiment of the invention provision is made for the parts of the contact element consist of any current conducting material, particularly metal. Here all parts of the contact element preferably consist of material insensitive to corrosion. 
   All parts of the contact element preferably consist of an alloy steel which is marketed under the commercial name of V2A. This material is insensitive to corrosion. Regular replacement because of possible corrosion phenomena is therefore unnecessary. 
   According to a further embodiment of the invention provision is made for the outer sleeve to be placed on the end of a spark plug serving for contacting with the end in which the cup is displaceable, and for the other end of the outer sleeve to be connected to an ignition voltage feed line. 
   For this purpose the outer sleeve can preferably be placed on a spark plug with the end in which the cup is displaceable, so that the contact end of the spar plug penetrates the contact element against the mechanical resistance of the spring, when the cup is displaced, and independently of this for the contact end of the spark plug to be designed at least partially tapered so that the surface areas of the outer conical surfaces of the contact end of the spark plug rest on the correspondingly designed inner cup walls at the bottom of the cup. 
   Furthermore, the ignition voltage is fed directly via an ignition voltage contact of an ignition coil. The entire area of the ignition voltage supply with the ignition voltage contact and the contact element is preferably surrounded by insulating material, apart from at least the cup contact surface which serves for contacting with the spark plug contact. 
   According to a further embodiment of the invention provision is made for the ignition voltage to be supplied via a resistance element which is located, for example, in a ceramic cover which is in turn enclosed by a cover of a PTFE-based material, for example, wherein one end of the resistance element is connected to the contact element and the other end of the resistance element is connected to a connecting piece to an ignition cable, which is in turn connected to the ignition coil. 
   According to a further embodiment of the invention provision is made for the connecting piece to be sealed with the ignition cable and the resistance element by means of an insulating material. Similarly, the contact element can also be sealed at least partially with the resistance element by means of an insulating material. 
   The sealing compound consists in all cases preferably of a two-component epoxy resin. 

   
     BREIF DESCRIPTION OF THE DRAWINGS 
     The invention is explained further with reference to the drawing, in which: 
       FIG. 1  shows a contacting sleeve according to the invention, in section. 
       FIG. 2  shows the contacting sleeve according to  FIG. 1 , in elevation. 
       FIG. 3  shows the individual parts of the contacting sleeve, in an exploded view, 
       FIG. 4  shows a side view of the clamping spring used, 
       FIG. 5  shows an application of the contacting sleeve with a resistance element and an ignition cable, and 
       FIG. 6  shows an application connected to a resistance element and an ignition cable, and 
       FIG. 7  shows the contacting sleeve with immersed spark plug contact. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A contact element  1  shown in  FIGS. 1 and 2  serves, for example, to connect a voltage supply to the spark plug. The contact element can of course also be used for other contacting purposes. Examples of contact elements are shown in  FIGS. 5 and 6  and are described below. 
   A compression spring  4  coiled from spring steel wire is located on the inside  3  of an outer sleeve  2  of contact element  1 . Outer sleeve  2  passes at one sleeve end  5  into a contact section  5   a  serving as a supply part. At sleeve end  5  outer sleeve  2  is closed and therefore forms a first stop  6  for compression spring  4 . Compression spring  4  rests on this first stop  6  with a spring end  7 . 
   The other spring end  8  is located in a cup  9  with a cup wall  10  and a cup bottom  11 . Outer sleeve  2  is open in the region of the other spring end  8  before assembly. Compression spring  4  can therefore be inserted with cup  9  in the inside  3  of outer sleeve  2 . After insertion, a bush  13  is inserted in the open end  12  of outer sleeve  2 . For this purpose bush  13  is provided on its outside  14  with a thread. Correspondingly the inside  15  of outer sleeve  2  is provided with a thread. The threads are not shown because they are not absolutely necessary, for bush  13  is either screwed into outer sleeve  2  by means of the thread or—if no threads are provided—are glued in. 
   On its inside bush  13  has a second stop  16 . This second stop  16  stops bush  13  in outer sleeve  2  from escaping. Bush  13  can be pushed further into outer sleeve  2  against the action of compression spring  4  when a part, e.g. a spark plug contact  17  ( FIG. 5 ), is pressed in in the direction of an arrow  17   a , thus providing good pressure contact. Vibrations and construction tolerances are eliminated. 
   Bush  13  is provided on the inside  3  of outer sleeve  2  with an extension  13   a  which is so long that it is able to guide compression spring  4  completely or almost completely over its entire length. Preferably it strikes against the first stop  6  when fully mounted. 
   Contact section  5   a  of outer sleeve  2  exhibits an axial hole  18  into which an ignition voltage contact  19  ( FIG. 4 ) or an ignition cable  20  ( FIG. 5 ) can be inserted for ignition voltage supply. Contact section  5   a  is provided with a collar  21 , which exhibits wall openings  22 . A connection clamp  23  can be clicked onto collar  21 . Contact pieces  24  of connection clamp  23  engage through wall openings  22 . An ignition cable inserted in hole  18  or an inserted ignition voltage contact  19  is therefore contacted and retained in a corresponding collar. 
     FIG. 3  shows the component parts of contact element  1  such as outer sleeve  2  with contact section  5   a , compression spring  4 , cup  9 , bush  13  with extension  13   a , in an exploded view. All these parts  2 ,  5   a ,  4 ,  13  and  13   a  consist of any electrically conducting material. This electrically conducting material may be copper, for example. A material insensitive to corrosion is preferably considered. Preference is given to an alloy steel which is available commercially under the name V2A or V4A. spring clamp  23  also consists preferably of V2A or V4A steel. 
     FIG. 5  shows one embodiment of contact element  1 . An ignition coil  25  exhibits a bar-shaped insulating element  26  through which ignition voltage contact  19  serving to supply the ignition voltage runs axially. An adapter  27 , which engages in the inside  28  of insulating element  26 , with a support sleeve  27   a , is placed on the lower end  26   a  (in the drawing) of insulating element  26 . Adapter  27  preferably consists of silicon and guides contact element  1 . A support ring  29  serves to guide a spark plug  30 . Spark plug  30 , when fully assembled, pushes cup  9  into the inside  3  of outer sleeve  2 , thereby generating a higher contact pressure. Contact element  1  is sealed with adapter  27  and ignition voltage contact  19  by means of an insulating compound, preferably by means of a two-component epoxy resin, thus preventing corona effects in this region. Effects triggering oxidation do not influence contact element  1  of V2A steel. 
     FIG. 6  shows an application of contact element I in which contact element  1  is connected to one end  31  of a resistance denoted by the number  31  a, e.g. an inductive resistance incorporated in a ceramic cover  32 . Here the contact section is designed differently from pin  5   a . A spark plug  30  is pressed into outer sleeve  2  in the application shown in  FIG. 5 . The other end  33  of the resistance arranged in ceramic cover  32  is contacted with a metal transition piece  34 , to which is connected ignition cable  20  as the ignition voltage supply. The entire arrangement is surrounded by a cover  35  of a PTFE-based material. Ignition cable  20  is sealed with transition piece  34  and ceramic resistance  32  by means of an insulating material. Similarly, contact element  1  is sealed with ceramic resistance  32  by means of an insulating material, apart from the contact face of cup  9 . A two-component epoxy resin is preferably used as sealing compound. 
     FIG. 7  shows how the contact end of a spark plug penetrates the contact element against a mechanical resistance, with displacement of the cup, and how the contact end of the spark plug is designed at least partially tapered so that the surface areas of the conical surfaces of the contact end rest upon the correspondingly shaped inner cup walls at the bottom of the cup.