Abstract:
A cable clamp ( 10 ) for clamping cable ( 11 ) in a tubular cable feed-through part ( 12 ) that has a pressure piece ( 33 ) comprised of two pressure rings ( 13, 14 ) with a clamping spring ring ( 15 ) positioned between the two pressure rings ( 13, 14 ) to encircle the cable ( 11 ). The pressure rings ( 13, 14 ) are interconnected so that they are movable with respect to each other in an axial direction over a distance permitting the clamping spring ring ( 15 ) to have an inner diameter equal or somewhat greater than the outside diameter of the cable ( 11 ) or compressed so as to have an inner diameter that is less than the outside diameter of cable ( 11 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cable clamp. More particularly, the present invention relates to a cable clamp having a clamp lock washer that is positioned between two thrust collars that are movably interconnected so that the lock washer can be pressed against a cable. 
     2. Description of the Related Technology 
     A prior art cable clamp is already known from cable glands, for example so-called PG cable glands, such as for example the “UNI-Dicht [UNI-Tight] system from Pflitsch that is shown in FIG.  4 . 
     Here the two pressure disks l, the clamp lock washer  2  and the gasket  3  are separate parts which must be placed in the cable penetration part  4  with a sleeve  5  for installation of the cable clamp in an complex and expensive manner. Moreover the warehousing and mainly the keeping of these separate parts are expensive on site and not always reliably ensured especially for cable connections. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to develop a cable clamp of the initially mentioned type, that is as simple and economical as possible, such that simple and prompt installation and economical storage of parts are enabled and the probability is minimized that parts of the cable clamp would be lost or lacking at the installation site. 
     This object is achieved by providing a movably interconnected pair of thrust collars having an enclosed clamp lock washer to form a thrust piece. The thrust piece which consists of two thrust collars and the clamp lock washer and which is assembled beforehand at the manufacturer to simplify both storage and installation and to make cable connection very fast. To do this simply the thrust piece can be inserted into the cable penetration part which is generally made as a socket piece of a housing, the cable can be guided through the sleeve and the relieved thrust piece and finally the sleeve can be attached to the cable penetration part, all in succession. 
     In the latter installation step moreover the two thrust collars with their permissible axial travel can be pressed against one another, by which the clamp lock washer on the oblique inner end faces of the thrust collars is pressed along the entire periphery towards the axis and thus against the cable so strongly that it is fixed by the desired degree. 
     According to one feature of the invention, the thrust collars are made by having one of the thrust collars have an annular flange with an inside diameter comparable to the outside diameter of the clamp lock washer in an uncompressed state. By this feature, without additional costs the clamp lock washer is retained and it cannot be laterally deflected, but is held centrally between the two thrust collars and thus also uniformly adjoins the cable periphery and can be pressed against it with a pressure which is the same over the entire contact surface. This is not only advantageous when the clamp lock washer is pressed into the plastic jacket of the cable by not doing damage to the jacket, but also, when making electrical contact under pressure it adjoins the shield of the stripped shielded cable because then the maximum contact surface is ensured. 
     Another object of the invention has a thrust piece which can be produced easily and economically, in which the two thrust collars which are provided for example by an injection molding process without additional cost so that one thrust collar has a groove and the other a series of catch arms. Then after insertion of the clamp lock washer between the thrust collars, they be pushed together. Here the width of the groove is such that after subtracting the thickness of the catch arms the desired size of the axial stoke necessary to compress and relieve the clamp lock washer results. 
     The aforementioned insertion-withdrawal process is greatly facilitated by the catch projections extending from one thrust collar being made to elastically fit into a groove included about the other thrust collar. The one thrust collar then need only be clipped with its catch projections by a minimum expenditure of force into the groove of the other thrust collar. This installation process if necessary can be carried out without tools by hand. For mechanical production, very simple tools can be used for this purpose. 
     One advantageous embodiment of the groove wall behind which the catch projections fit is to have a conically tapered projection. With this construction an especially small diameter for the thrust piece projection is enabled. In addition, over its entire length it has a constant diameter and thus optimum guidance in the cable penetration part. 
     For the case of a cable gland which is common in practice for shielded cables the cable shield can be conductively connected to the ground potential, for example by a metal housing. In the cable clamp of the present invention this is done in an advantageously simple manner by at least one of the two thrust collars consisting of electrically conductive material. If the housing-side inner thrust collar is made of metal, conductive connection of the cable shield takes place via the clamp lock washer and this inner thrust collar lies on the stop collar of the metal cable penetration part. The alternative possibility of making the outer thrust collar of metal for conductive connection of the cable shield to the housing presupposes that the sleeve likewise consists of metal and is conductively connected to the outer thrust collar. 
     In most applications the cable clamp in a cable penetration part must moreover ensure the tightness of the cable connection. This is achieved for the present invention in the known manner by the arrangement of a gasket between the outer thrust collar and the sleeve which when the sleeve is attached to the cable penetration part they are squeezed together such that the gasket moreover adjoins the cable and the inner surface of the sleeve under pressure. 
     This known gasket is a separate part which must be purchased in addition and stored at the warehouse. It is often not ready at the installation site nonetheless and requires another installation step. 
     Conversely, in another embodiment of the present invention, especially favorable storage and very simple installation processes for the thrust piece are achieved by the gasket being mechanically retained in the thrust collar which faces it. In this compact initial version of the thrust piece the connection, for example by screwing or locking, can be detachable. But the connection can also be nondetachable and thus made captive, for example by cementing the gasket to the outer thrust collar or by injection molding it thereto. This second alternative has the advantage of stronger connection of the gasket to the thrust piece and more economical production because the thrust collar and the gasket which had been injection molded can be produced in a single step by means of a double injection mold. 
     If the elasticity of the material of this thrust collar which faces the cable insertion area of the sleeve is large enough for sealing purposes, but still small enough to be able to accommodate the required pressure of the clamp lock washer when the sleeve is attached to the cable penetration part, it is especially advantageous to use the thrust collar moreover as a gasket. Thus a special gasket—whether as a separate part or one connected to the external thrust collar—is no longer necessary, so that the cable clamp can be produced and used especially easily and economically. 
     The greatest possible compactness of the cable clamp of the present invention is achieved by the version (see FIG. 1) in which a single premounted part is made available to the user by simply clipping the sleeve onto the gasket, which part can be produced not only with minimum cost, but enables extremely uncomplicated handling in practical use. This is because only the (optionally stripped) cable can be inserted through the gasket and the thrust piece as far as the desired position and then the sleeve can be attached to the contact penetration part. Here moreover the cable is clamped securely and the cable penetration area is sealed by compressing the gasket liquid-tight. 
     One especially feasible attachment of the sleeve to the contact penetration part, for example a socket piece of a housing, consists in providing a screw sleeve which can be screwed onto the cable penetration part which is made as a threaded socket. Not only the desired clamping pressure of the clamp lock washer and thus the necessary tension about the cable is achieved, but also the required sealing action according to the requirements of the individual case is achieved by the intensity of tightening of the screw sleeve in conjunction with the material selected for the gasket and the axial dimensions of the interacting parts of the cable clamp. 
     A simple and economical possibility for electrically insulating the metallic housing together with the socket piece and at the same time protecting it mechanically is to have a peripheral plastic molded sleeve positioned about the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained below using one embodiment in the figures. 
     FIG. 1 shows an axial section through are installed cable clamp of the present invention, which has not yet been completely attached to the cable insertion connecting piece; 
     FIG. 2 shows an exploded axial section through the individual parts of the cable clamp of the present invention; 
     FIG. 3 shows an overhead view of the end faces of the two thrust collars facing one another and the clamp lock washer; and, 
     FIG. 4 shows a halved view of a cable gland known from the prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A cable clamp  10  (see FIG. 2) for clamping a shielded cable  11  in a tubular cable insertion connecting piece  12  of a metal housing which is not shown and which is integral with it for holding an electrical circuit is shown in FIG.  1 . The cable clamp  10  consists of a housing-side inner metal thrust collar  13 , a cable-side outer thrust collar  14  of plastic, a clamp lock washer  15  which is located between them and which is bent from a helical metal spring, a gasket  17  which is injection-molded to the cable-side end face  16  of the outer thrust collar  14 , and a screw sleeve  18  which encompasses the gasket and which can be screwed onto a matched external thread  19  of the cable insertion connecting piece  12 . 
     The insertion connecting piece  12  consists of a metallic inner socket piece  20  which is made in one piece with the metal housing, and a tubular plastic jacket  21  which is produced by extrusion coating and which has an external thread  19  on its free end. The screw sleeve  18  has a knurled grip  22  by which the required torque can also be applied when screwing on by hand. 
     The gasket  17  has a collar  23  with a peripheral recess  24  into which a terminal shoulder  25  of the screw sleeve  18  fits such that it can be turned on the one hand relative to the gasket  17  and on the other hand when screwed onto the external thread  10  compresses the gasket  17 . In doing so the screw sleeve  18  and gasket  17  adjoin one another over a large surface by corresponding shaping of their surfaces facing one another such that high pressure is transferred both in the axial and also in the radial direction. The contours  26 ,  27  of the surfaces of the screw sleeve  18  and the gasket  17  which are pressed against one another for this purposes are arched concavely or correspondingly convexly, by which on the one hand the indicated force transfer is produced as in the interacting conical surfaces and on the other hand the gasket  17  is prevented from sliding through the inlet opening  28  of the screw sleeve  18 . 
     Due to pressure in the radial direction the gasket  17  is moreover pressed against the inner surface  26  of the screw sleeve  18  and over a large area against the cable surface so that the cable insertion area of the cable insertion connecting piece  12  is reliably sealed. In addition, the gasket  17  is also pressed against the inner wall  29  of the free end part of the plastic sleeve  21 , by which the cable clamp  10  is also secured against penetration of liquid via the threaded gland. 
     The end faces  30 ,  31  of the two thrust collars  13 ,  14  facing one another are tapered conically towards the axis A of the cable clamp  10 . The end face  30  of the inner thrust collar  13  has on the outer edge an axially projecting end flange  32  which prevents lateral divergence of the clamp lock washer  15  which in the relieved state adjoins its inner surface and thus the installation of the thrust piece  33  which consists of the thrust collars  13 ,  14 , and the clamp lock washer  15  is greatly facilitated in a simple manner. 
     The inner thrust collar  13  has a peripheral groove  34  with a first groove wall  35  facing the clamp lock washer  15  and a second groove wall  36 . 
     The outer thrust collar  14  bears six catch arms  37  which are integral therewith, which are distributed uniformly on the periphery and which are provided with catch projections  38  which project towards the axis A, which are located on the free ends, and which each have an insertion bevel  39 . The first groove wall  35  is equipped with an leading bevel  40  which corresponds to the insertion bevel  39 . 
     With the thrust piece  33  installed the catch projections  38  fit behind the first groove wall  35  and can be moved axially by a correspondingly chosen width of the peripheral groove  34  [in it] by a stroke which is sufficient to compress the clamp lock washer  15 . With the screw sleeve  18  strongly screwed on the required clamping force is achieved for applying tension to the cable  11 . 
     The diameter of the first groove wall  35  is less by than the material thickness of the catch arm  37  and less than that of the second groove wall  36  so that the thrust piece  33  over its entire length has a constant outside diameter and thus can be inserted unhindered into the cable insertion connecting piece. 
     In the production of the cable clamp  10 , first of all the thrust piece  33  is produced. To do this only the clamp lock washer  15  need be inserted into the inner thrust collar  13  and the outer thrust collar  14  with the gasket  17  molded on its outer end face  16 . Then the outer thrust collar  14  can be clipped onto the inner thrust collar  13 . This can also be done by hand because the corresponding oblique surfaces  39 ,  40  require a low expenditure of force. Afterwards only the screw sleeve  18  need be guided over the gasket  17 , with its terminal shoulder  25  engaged in the peripheral recess  24  of the gasket  17 . 
     In this state the tension of clamp lock washer  15  is relieved and it adjoins on the outside the end flange  32  of the inner thrust collar  13 . The catch projections  38  adjoin the first groove wall and the inside diameter of the clamp lock washer  15  is slightly larger than the outside diameter of the cable shield  41  which is to be clamped. 
     For the user this preinstalled cable clamp  10  can be easily stored and installed at the installation site, the uncertainty of a missing individual part being eliminated. 
     For installation, the cable clamp  10  can be pushed simply into the cable insertion connecting piece  12  as far as a stop of the housing-side external end face  42  of the inner thrust collar  13  on the face edge  43  of the inner socket piece  20 , then the correspondingly stripped cable  11  can be inserted through the gasket  17  and the clamp lock washer  15  so far that the cable shield  41  is positioned at the height of the clamp lock washer  15  and then the screw sleeve  18  can be screwed securely on the external thread  19  of the plastic sleeve  21  of the cable insertion connecting piece  12 . In this final installation step the gasket  17  is pressed over a large area under pressure against the cable jacket  44 , the inner surface  26  of the screw sleeve  18  and the inner surface of the plastic sleeve  20  and moreover the outer thrust collar  14  is pressed against the inner thrust collar  13 , the clamp lock washer  15  on its conical surfaces  30 ,  31  radially sliding centrally towards the axis A and in doing so being pressed into the cable shield  41  until the catch arm  37  adjoins the second groove wall  36  of the peripheral groove  34  of the inner thrust collar  13 . This stroke is such that a sufficiently high clamping force is achieved and thus the required tension about the cable  11  is ensured and [that] on the other hand there is no undue deformation of the cable shield  41 . 
     The described cable clamp  10  is therefore extremely simple and economical in production and handling, thus ensuring effective tension about the cable  11 , high liquid-tightness and permanently securing contact between the cable shield  41  and the metal housing, which takes place via the clamp lock washer  15 , the metal inner thrust collar  13  and the conductive inner socket piece  20 .