Abstract:
Contact-making and attachment structures for a cable bushing through an opening in a shielding wall are arranged on two mutually opposite opening edges, to make contact with and attach a cable to be passed through, on the two opposite opening edges. The opening is thus, to a certain extent, bridged by the installed cable, thus reducing any adverse effect on the shielding effect caused by the opening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based on and hereby claims priority to German Application No. 101 55 434.6 filed on Nov. 12, 2001, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   Electromagnetic shielding of appliances or assemblies is becoming increasingly important for development of electrical appliances with a high layer density and very high operating frequencies, owing to the increase associated with this in electromagnetic interference fields within and outside the electrical appliances. 
   Shielding housings or shielding walls are generally provided for electromagnetic shielding. However, in general, openings for cables to pass through are required in such shielding housings or shielding walls, and these adversely affect the shielding effect. In general, relatively large openings have to be provided so that it is also possible to pass through a cable plug, which is large in comparison to the cable diameter, together with a cable. The larger the opening, the greater the extent to which the shielding effect is also reduced, however. With circular openings, the reduction in the shielding effect is governed essentially by their diameter, while with rectangular openings, it is governed essentially by their diagonals. This thus results in the problem of designing such an opening firstly to be sufficiently large for cable plugs to be passed through with ease while, on the other hand, to be sufficiently small to maintain an adequate shielding effect. 
   In practice, openings which are originally designed to be large are frequently subsequently reduced in size by covers which have to be fitted after a cable has been passed through. However, this involves additional material costs and assembly effort. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to specify a cable bushing which has a good shielding effect and involves only a small amount of assembly effort to pass a cable through. 
   This object is achieved by a cable bushing through an opening in a shielding wall which has structures to contact and attach, on two mutually opposite opening edges, to a cable passed through on the two opposite opening edges. The opening is bridged to a certain extent by the installed cable, as a result of which an opening diagonal or an opening diameter is reduced in size by the cable itself. In this way, any adverse effect on the shielding effect caused by the opening is reduced without any additional material costs and with little assembly effort. This is particularly advantageous for openings whose diameter or diagonals are considerably larger than the cable diameter. 
   According to one advantageous embodiment of the invention, contact-making and attachment means can be arranged such that the installed cable essentially connects the two opposite opening edges along their length. This allows relatively large openings to be bridged by the cable. 
   Furthermore, the contact-making means may be designed such that they make it possible to make contact with a cable shield, which rests on the cable, on the two opposite opening edges. Contact can in this case preferably be made by the contact-making means touching the cable shield, which is exposed in places. 
   According to a further advantageous embodiment the attachment means may themselves be in the form of contact-making means. The attachment means can be designed to be conductive, at least in places, for this purpose. Attachment lugs can preferably be arranged, as the attachment means, on the opposite opening edges. The attachment lugs may be conductive, at least in places, to make contact with the cable and/or with its cable shield. 
   The attachment lugs may be designed to be flexible, for example, to make it easier for one or more cables to be passed through or installed. 
   Furthermore, the attachment lugs may be formed integrally from the shielding wall, for example by stamping out. As an alternative to this, attachment lugs which are attached to the opening edge can be provided retrospectively, being composed, for example, of thinner and more flexible sheet metal than the shielding wall. 
   Furthermore, cable ties are provided as part of the attachment means for tying the cable to the attachment lugs of the two opposite opening edges. The attachment lugs may in this case preferably be provided with projecting tabs or hooks, to make it more difficult for the cable ties to slide off. 
   Furthermore, the contact-making and attachment means on a first of the opposite opening edges are designed for making contact with and attachment of the cable to a front or outer face of the shielding wall, and on a second of the opposite opening edges are designed for making contact with and attachment of the cable to a rear or inner face of the shielding wall. This makes it possible to pass the cable obliquely through the opening. 
   According to one advantageous development of the invention, at least one connecting web, which can be knocked out, can be arranged between the opposite opening edges, to shield a part of the opening which is not used for passing through a cable. The connecting web may preferably be arranged between attachment lugs and, furthermore, may be connected to them via a weak point. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a plan view of an unused cable bushing, 
       FIG. 2  is a plan view of the cable bushing with a cable passed through it, 
       FIG. 3  is a side view of the cable bushing with a cable passed through it, and 
       FIG. 4  is a side view of the cable bushing while a cable is being passed through. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     FIGS. 1 and 2  each shown a plan view of a shielding wall SW, for example a rear wall of a metallic appliance housing with an opening OE for cables to pass through. The opening OE is provided on two opposite opening edges OR 1  and OR 2  with attachment lugs BL 1  and BL 2  which project into the opening OE and are electrically conductive and flexible. In the present exemplary embodiment, four attachment lugs BL 1  are provided on the opening edge OR 1  and four attachment lugs BL 2 , which are opposite the attachment lugs BL 1 , are provided on the opening edge OR 2 . For clarity, only two opposite attachment lugs BL 1  and BL 2  are provided with a reference symbol. The opening OE is designed to be sufficiently large that four cables can be passed through, as well as the associated cable plugs. In particular, the distance between opposite attachment lugs BL 1  and BL 2  is considerably larger than the cable diameter of the cables to be passed through. 
     FIG. 1  shows an unused cable bushing, in which no cable has been passed through the opening OE. In this case, opposite attachment lugs BL 1  and BL 2  are in each case electrically conductively connected by connecting webs VB which can be knocked out. The conductive connection of the opposite attachment lugs BL 1  and BL 2  reduces the size of the diagonal of the opening OE which is the governing factor for the adverse effect on the shielding effect. 
   Weak points SB are in each case provided between the connecting webs VB and the attachment lugs BL 1  and BL 2  to make it possible to knock out a respective connecting web VB when required, that is to say when a cable is being passed through, in a convenient manner. 
   For clarity reasons, only some of the connecting webs VB and weak points SB are identified by reference symbols in  FIGS. 1 and 2 . 
     FIG. 2  shows the cable bushing after a cable K has been passed through and attached. The cable K is attached to two opposite attachment lugs BL 1  and BL 2 , between which the connecting web VB has previously been knocked out. In the following text, the reference symbols BL 1  and BL 2  are now used only for those attachment lugs BL 1  and BL 2  to which the cable K is attached. A cable shield KA of the cable K is exposed by removal of the cable insulation over a length which corresponds approximately to the distance between one of the opening edges OR 1  and OR 2  and the opposite attachment lugs BL 1  and BL 2 . In the area of the exposed cable shield KA, the cable K is firmly connected by a cable tie KB 1  to the front face of the attachment lug BL 1 , and by a cable tie KB 2  to the rear face of the attachment lug BL 2 . The front face and rear face of the attachment lugs BL 1  and BL 2  in this case relate to the front face and rear face of the shielding wall SW. The exposed cable shield KA is pressed against the respective attachment lugs BL 1  and BL 2  by the firmly tightened cable ties KB 1  and KB 2 . Since the attachment lugs BL 1  and BL 2  are conductive, contact is made with the cable shield KA at contact-making points which are separated from one another, by touching the attachment lugs BL 1  and BL 2 . Apart from the exposure of the cable shield KA, no further action is required on the cable shield KA or on the cable for this purpose. The relevant attachment lugs BL 1  and BL 2  thus act both as attachment means and as contact-making means for the cable K. A respective contact-making point is located on the front face of the attachment lug BL 1  and on the rear face of the attachment lug BL 2 . 
   As illustrated in  FIGS. 2 and 3 , the cable shield KA of the attached cable K connects the opposite attachment lugs BL 1  and BL 2  and the opposite opening edges OR 1  and OR 2  in an electrically conductive manner across a largest opening dimension or length, instead of the connecting web that has been knocked out. This avoids increasing the size of the opening diagonals, which govern the adverse effect of the shielding effect. The shielding function of the knocked-out connecting web is thus carried out by that section of the cable shield KA which bridges the opening OE. 
   On the opening side, the attachment lugs BL 1  and BL 2  are provided with projecting tabs VN to prevent the cable ties KB 1  and KB 2  which secure the cable K from sliding off the attachment lugs BL 1  and BL 2 . 
     FIG. 3  shows a side view of the cable bushing with a cable K passed through it. The reference symbols indicated in  FIG. 3  in each case have the same meanings as in all the other figures.  FIG. 3  shows the oblique cable routing of the cable K through the opening OE. The oblique cable routing is assisted by the flexibility of the attachment lugs BL 1  and BL 2 , which are slightly bent—resting parallel on the cable K. 
   Finally,  FIG. 4  shows a side view of the cable bushing with a cable K being passed through. In order to pass the cable K through the cable bushing, the cable is first of all firmly tied to the front face of the attachment lug BL 1  by the cable tie KB 1 . The processes of passing the cable K through and firmly tying it are in this case made considerably easier by the flexibility of the attachment lug BL 1 ,—as indicated in FIG.  4 . The flexible attachment lugs BL 1  and BL 2  mean that the opening OE can be designed to be smaller overall, thus having an advantageous effect on the shielding effect. Once the cable K has been firmly tied to the attachment lug BL 1 , the cable K is also firmly tied to the attachment lug BL 2  by the cable tie KB 2 , as illustrated in  FIGS. 2 and 3 . 
   The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.