Abstract:
A clamp for a cable duct having, at its open side ( 23 ), in regions of the free ends ( 24 ) of the side walls, inward projecting, strip-shaped edges, with the clamp including connection portions ( 3 ) provided at opposite longitudinal ends ( 5 ) of the bridge section ( 2 ) of the clamp, which bridges the open side ( 23 ) of the cable duct ( 20 ) being formed as inwardly bent, facing each other hooks lockingly engageable in undercuts ( 29 ) provided in respective anchoring grooves ( 28 ) extending in a longitudinal direction of the cable duct ( 20 ) and limited by respective bent-out portions ( 27 ) of respective side wall edges ( 26 ) and respective side walls ( 22 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a clamp for a cable duct that has, at its open side, in regions of free ends of its side walls, inward projecting strip-shaped edges with the clamp including a bridge section for bridging the open side of the cable duct, and connection portions provided at opposite longitudinal ends of the bridge section for engaging the strip-shaped edges. 
     2. Description of the Prior Art 
     Cable ducts mentioned above serve generally for receiving electrical cables and conductors. They can be mounted in indentations formed in walls, ceilings, or floors. Often, they are mounted on outer surfaces of walls. Often used cable ducts have a substantially U-shaped cross-section and have a bottom wall from which two side walls extend primarily at an approximately right angle. A side of the cable duct opposite the bottom wall remains open to provide for insertion of cables. Also known are so-called angular ducts which are formed for mounting in a corner formed by two butt-joined walls. The angular ducts have essentially a triangular cross-section which is formed of a bottom wall and two side walls projecting from the bottom wall and forming an obtuse angle or is formed of two side walls connected with each other along their longitudinal sides. 
     Conventional cable ducts are closed with covers after cables have been placed into the ducts. The covers lockingly engage in undercuts formed in outer sides of the side walls at their free ends. The inserted cable loads the side walls pushing them outwardly. This can cause difficulties during mounting and securing of the cover. To provide for a greater stability of the side walls, which are loaded by inserted cables, there are provided clamps which bridge the open side of the cable duct and are secured on strip-shaped edges which project inward from inner surfaces of the side walls in the regions of the free ends of the side walls and which extend in a longitudinal direction of the cable duct. German Utility Model DE-U-79 31 274 discloses a clamp for a cable duct which is secured in elongate slots formed in the strip-shaped edges of the side walls. To this end, the clamp has, at its opposite longitudinal ends, respectively, two locking fingers with hooks, which are separated by a slot. The locking fingers are pressed together by a force acting transverse to the longitudinal extent of the clamp. Thereby, the width of the clamp, in the region of the hooks, is reduced, and the locking fingers can be inserted in the slot. A locking member inserted into the slot between the locking fingers, which can be removed, if necessary, prevents an accidental disengagement of the clamp from the edges of the side walls. 
     The clamp described above can only be secured in slots provided in respective edges and which are spaced by a predetermined distance. Mounting of the clamp in any arbitrary location of the cable duct, e.g., in the region of a duct or cover junction, is not possible. The release of the mounted clamp, e.g., for insertion of another cable, is very cumbersome. In order to press the locking finger toward each other, first, the locking member need be removed from the slot between the two fingers. To effect this, the use of both hands is necessary and, sometimes, the use of an auxiliary tool, e.g., a screwdriver or the like is required for removing the locking member. 
     German Utility Model DE-U-295 15 365 discloses a clamp having, at its longitudinal ends, somewhat U-shaped clamping sections. The strip-shaped edges, which project inward from the free ends of the side walls, are provided with longitudinal flutes at least on their upper surfaces. Together with correspondingly formed inner surfaces of the clamping sections of the clamp, they form a fluted locking connection. The advantage of this clamp consists in that it can be longitudinally displaced, if necessary, and can be mounted at any arbitrary location on the wall edges of the cable duct. The mounting of the clamp is rather easy. However, the clamp dismounting, e.g., in order to insert a new cable, requires the use of both hands for releasing the fluted connection. 
     Accordingly, an object of the present invention is a clamp for a cable duct which can be easily mounted at any arbitrary location along the cable duct. Another object of the present invention is a clamp for a cable duct which, after being mounted, can be easily displaced to a desired position, if needed. A further object of the invention is a clamp for a cable duct which will prevent a cable inserted into the duct from falling out. A still further object of the present invention is a clamp for a cable duct which will insure that it could not be accidentally released, in particular, with the closed cover. A yet further object of the present invention is a clamp for a cable duct which can be released with one hand, at least at one of its side, for insertion of another cable. Also, an object of the present invention is a clamp for a cable duct which will insure an adequate stiffness of the side walls so that the cover can be mounted with an adequate clamping force. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a clamp for a cable duct having, at its open side, in regions of free ends of its side walls, inward projecting, strip-shaped edges. The clamp includes a bridge section for bridging the open side of the cable duct, the opposite longitudinal ends of which are provided with connection portions for engaging the strip-shaped edges. The connection portions are formed as inwardly bent, facing each other hooks lockingly engageable in undercuts provided in respective anchoring grooves formed at the free ends of the side wall, extending in a longitudinal direction of the cable duct and limited by respective bent-out portions of respective edges of the side walls and respective side walls. 
     The clamp according to the present invention can be mounted at any arbitrary location along the wall edges and can be pushed, if necessary along the edges. The hook-shaped connection portion can be easily inserted into anchoring grooves provided with undercuts and can be hooked in the undercuts which extend in the longitudinal direction of the cable duct. Upon being loaded, e.g. by weight of the cable upon mounting of the cover, the locking engagement is further enhanced. This increases the holding force of the clamp and prevents an accidental disengagement of the clamp from the cable duct. 
     The locking connection, which is formed by engagement of the hook-shaped connection portions of the clamp in the undercuts of the anchoring grooves, on the other hand, is easily released, if needed, by grasping the clamp at one end and pulling it out of a respective anchoring groove. When the clamp is lifted in this manner for insertion of another cable in the cable duct, the respective hook-shaped connection portion can be easily reintroduced into the undercut of the respective anchoring groove. The longitudinal ends of the clamp are supported against the inner surfaces of the side walls of the cable duct. The hooked connection becomes latched in the undercut of the opposite groove and forms a type of a hinge which permits the clamp to be pulled upward at one end while the opposite ends remains connected with the associated edge. The mounted clamp provides for stiffening of the side walls and insures a correct spacing of the side walls from each other. This insures mounting of the cover on the cable duct with a necessary clamping force. 
     It is advantageous for the holding force of the clamp when a distance of a hook stop of the hook-shaped connection portion from an associated longitudinal end of the clamp measured transverse to the longitudinal extent of the cable duct is larger than a width of the respective anchoring groove at its mouth. The selected geometrical relationship insures that the longitudinal edges of the clamp are pressed against sections of the side walls, which extend above the wall edges forming the cable duct opening. As a result of the preload, which results from the pressing of the clamp edges against the side wall sections, the hook-shaped connection portions further penetrate into the undercuts of the anchoring grooves formed in the bent-out edge portions of the side wall edges. 
     For increasing the holding force of a clamp mounted on the side wall edges, the clamp-forming bridge section has at least one, manually actuable locking element. The locking element includes a latch, which can be bent outwardly transverse to the longitudinal extend of the cable duct and which includes a locking hook that, in the locking position, of the clamp, lockingly engages a locking nose formed on the inwardly facing side of the bent-out portion of the respective edge of the side wall. Because an additional securing means is provided for the clamp, the clamping force, with which the connection portions of the bridge section are retained on the side wall edges, can be reduced. The connection of the connection portions with the side wall edges serves for pre-mounting of the clamp on the cable duct. The clamp is mounted from above, with the hook-shaped connection portions engaging in the anchoring grooves. The pre-mounted clamp, if needed, can be easily pushed along the strip-shaped edges with a relatively small force. However, the holding force of the locking mechanism is sufficiently large to prevent the disengagement of the clamp from the side wall edges under the weight of the cable, which is inserted in the duct, at the overhead mounting. In spite of this, the clamp can be easily released at one of its side, if necessary, to provide for insertion of another cable into the cable duct. The locking elements insure fixing of the clamp on the side wall edges. The use of the locking elements increases the holding force of the clamp, preventing an accidental displacement of the clamp along the side wall edges. 
     Based on the manufacturing considerations and for insuring an easy handling, the bridge section is formed as a frame with two locking elements including each a locking arm, which is elastically and springy connected to the middle portion of the frame and which extends toward a respective longitudinal end of the bridge section. 
     Advantageously, each locking arm is formed as a flexible spring which is connected with the middle portion of the bridge section and which smoothly passes into a locking spring which, thus, is formed with the flexible spring as a one-piece element. The locking spring has a substantially V-shaped longitudinal cross-section and has a spring leg which forms the manually bendable latch. Forming the locking arm as one-piece resilient element provides for a simple and cost-effective manufacturing of the clamp. The locking arm is conveniently arranged in the bridge section and does not extend beyond the width of the bridge section. The flexible spring preloads the locking elements of the clamp and increases its holding force. The substantially V-shaped locking spring is compressible transverse to the longitudinal extent of the cable duct and additionally increases the preload of the locking engagement of the locking hook with the locking nose. 
     Because the spring leg of the locking spring projects above the upper surface of the bridge section and is formed as a handle, it can be easily actuated by hand. The length of the handle is so selected that it, in a pre-assembled condition of the clamp, extends above the free end of the side wall of the cable duct. The handle becomes substantially aligned with the free end of the side wall when the locking hook of the latch lockingly engages the locking nose formed on the side wall edge. 
     By extending the handle above the side wall of the cable duct, it becomes possible to effect final fixing of the clamp simultaneously with closing of the duct with the cover. The handle abuts the bottom surface of the cover and, upon the cover being pressed downward, is moved downwardly until the locking hooks engage the locking noses on the bent-out portions of the side wall edges. This insures that the length of the handles does not extend beyond the side walls and, thus, does not interfere with mounting of the cover. 
     For releasing one side of the clamp, the handle is pushed against the biasing force of the locking spring in a direction toward the middle portion of the bridge section. The respective locking hook becomes disengaged from the locking nose. Because of the preload of the flexible spring, the locking arm pivots upward, and the locking element occupies its initial position. 
     Corresponding bevels of the locking hook and the locking nose facilitate their locking engagement. Pressure applied to the handle either by hand or by the mountable cover provides for sliding of the locking hook bevel along the locking nose bevel downwardly until the locking hook lockingly engages the locking nose. Both the flexible spring and the locking spring become preloaded and, as a result, the locking hook engages the locking nose from beneath. The preload of the flexible and locking spring provides a force component which pushes the locking nose, which is formed on the outer side of the bent-out portion of the side wall edge and extends longitudinally, upward. As a result, the bent-out portion of the edge pivots about an axis extending in the longitudinal direction of the duct, pulling the hook-shaped connection portion engaging into the anchoring groove undercut further in. 
     The resistance of the mounted clamp to an accidental displacement along the edges can be increased by increasing friction between the cooperating surfaces of the locking hook and the locking nose. The increase of friction can be achieved, e.g., by providing the cooperating surfaces with a fluted profile. As an alternative or in addition, the locking nose can be made of a softer material than the locking hook. In this case, in the locking condition, the hard, knife-like formed locking hook is biased, as a result of preloading of the flexible and locking springs, into the soft material of the locking nose, forming a formlocking connection which prevents release of the clamp. E.g., the locking hook(s) can be formed of a hard PVC, and the locking nose can be formed of a soft PVC. 
     In accordance with a preferred embodiment, the clamp is formed entirely of a plastic material by injection-molding or extrusion. When a softer material is used for forming the locking noses, a coextrusion process can be used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and objects of the present invention will become more apparent, and the invention itself will be best understood from the following detailed description of the preferred embodiment when read with reference to the accompanying drawings, wherein: 
     FIG. 1 shows a perspective view of a clamp for a cable duct according to the present invention; 
     FIG. 2 shows a cross-sectional view of the pre-assembled clamp taken transverse to a longitudinal extent of a cable duct; and 
     FIG. 3 shows a view similar to that of FIG. 2 but with the clamp being fixed in its position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A clamp for a cable duct according to the present invention, which is shown in FIG. 1, is generally designated with a reference numeral  1 . The clamp  1  has a frame-shaped bridge section  2  with cavities  8 . At the longitudinal ends  5  of the bridge section  2 , there are provided hook-shaped connection portions  3 . The hook-like shape of the connection portions  3  is achieved by bending the bridge section  2  at its longitudinal ends  5  inward so that the obtained hooks face each other. Two latches  9 , which are formed each of a locking arm  11  provided with a fixing hook  10 , project from opposite sides of a middle portion  6  of the bridge section  2 . The latches  9  can be bent out in the longitudinal direction of the clamp  1 . The latches  9  extend in the respective cavities  8  formed on opposite sides of the middle portion  6  of the bridge section  2 . The locking arms  11  are submergible into the cavities  8 . 
     FIG. 2 shows the clamp  1  in its pre-mounted or pre-assembled position on the cable duct  20 . The cable duct  20  has a bottom wall  21  connected at its opposite longitudinal ends with side walls  22 . The manner in which the side walls  22  are connected with the bottom wall  21  is irrelevant for purposes of the present invention. For completeness sake, it can only be indicated that side walls  22  can be connected with the bottom wall  21  rigidly, foldably and/or releasably. The side walls  21  are somewhat inclined with respect to the bottom wall  22  and extend, e.g., about perpendicular to the bottom wall  21 . The open side  23 , which is located opposite the bottom wall  21 , provides for placing of cables into the cable duct  20 . In the region of free ends  24  of the side walls  22 , strip-shaped edges  26  project from the respective side walls  22  inward. The strip-shaped edges  26  extend parallel to the longitudinal extent of the cable duct  20 . A portion  27  of each strip-shaped edge  26  is bent out in a direction of the open side  23  of the cable duct  20 . The bend-out edge portion  27  and the respective side wall  22  limit an anchoring groove  28  which extends parallel to the strip-shaped edge  26 . In the transitional region between the bent-out edge portion  27  and the strip-shaped edge  26 , the anchoring groove  28  has an undercut  29 . 
     The clamp  1  is placed on the strip-shaped edges  26  from above and is pressed into the anchoring grooves  28 . The hook-shaped connection portion  3  slides into the anchoring grooves  28  and become hooked in respective undercuts  29 . The distance of the inward-facing hook stop  4  from the longitudinal end  5  of the clamp  1 , which defines the hook width b, is larger than the width w of the anchoring groove  28  which is determined by the distance of the bent-out portion  27  of the edge  26  from the side wall  22  at the mouth of the anchoring groove  28 . The distance of a stop  30  of the undercut  29  from the sidewall  22  at the bottom of the anchoring groove  28  corresponds substantially to the hook width b. As a result of the hooking of the hook-shaped connection portions  3  in the undercuts  29  of the anchoring grooves  28 , the clamp  1  is preliminary fixed on the channel duct  20 . Upon tensioning, e.g., by the weight of a cable during the overhead mounting, the hooked connections  3 ,  29  become latched even further, and the holding force of the clamp  1  increases. This prevents an accidental release of the clamp  1  from the edges of the cable duct  20 . 
     On the other hand, the interlocking of the hooked-shaped connection portions  3  in the undercuts  29  of the anchoring grooves  28  can be easily released, if necessary, by grasping the clamp  1  at one of its longitudinal ends and pulling it out of the respective anchoring groove  28 . When the clamp  1  is pulled upward in this manner, e.g., to place another cable into the cable duct  20 , the hook-shaped connection portion  3  at the opposite longitudinal end  5  of the clamp  1  is pushed further into the undercut  29  of the opposite anchoring groove  28 . The longitudinal end  5 , in this case, is supported against the inner surface of the side wall  22  of the cable duct  20 . The hooked connection becomes latched in the undercut  29  of the opposite groove  28  and forms a type of a hinge which permits the clamp  1  to be pulled upward at one end  5  while the opposite end  5  remains connected with the associated edge  26 . The mounted clamp  1  provides for stiffening of the side walls  22  and insures a correct spacing of the side walls  22  from each other. This insures mounting of a cover on the cable duct with a necessary clamping force. 
     The clamp  1 , which is pre-mounted on the cable duct  20  in this manner, is immovably fixed on the wall edges with locking means  9 - 11 . Each locking arm  11  is formed of a flexible spring  12  which is secured to the middle portion  6  of the frame-shaped bridge section  2  and which is connected, preferably integrally, with a locking spring  13 . The locking spring  13  has a V-shaped longitudinal cross-section and has a spring leg which forms, together with the locking hook  10 , the latch  9 . The locking hook  10  is designed for locking with a locking nose  31  that projects from an inward-facing side surface of the edge  26  and that extends along the edge  26 . The free end of the spring leg  9  projects beyond the upper surface  7  of the clamp  1  and is used as a handle  14  by a user. The length of the handle  14  is so selected that in the pre-assembled position of the clamp  1 , the handle  14  extends beyond the free end  24  of the side wall  22  of the cable duct  20  and, upon engagement of the locking hook  10  of the latch  9  with the locking nose  31  at a respective edge  26 , it is arranged at the same level as the free end  24  of the side wall  22 . A bevel  15  on the outer surface of the locking hook  10  and bevel  32  on the locking nose  31  facilitate locking of the locking elements of the clamp  1  with respective locking elements of the cable duct  20 . 
     FIG. 3 shows the inventive clamp in its fixed position. The cable duct  20  is shown together with its cover  33 . The locking elements  34  of the cover  33  engage in locking grooves  25  formed in outer surfaces of the free ends  24  of the side walls  22  of the cable duct  20 . The handles  14 , which in the pre-assembled position of the clamp  1 , project beyond the upper surface  7  of the bridge section  2 , are submerged manually or by the applied cover  33  into the cavities  8  of the frame-shaped bridge section  2 . The locking hooks  10  of the latches  9  engage from beneath the locking noses  31  which project inward from the bent-out portion  27  of the edges  26  of the side walls  22 . The surfaces of the locking hooks  10  and of the locking noses  31  can be formed as knurled surfaces. According to an alternative embodiment of the present invention, the locking noses can be formed of a softer material than locking hooks  10 . E.g., the locking hooks can be formed of a hard PVC and the locking noses can be formed of a soft PVC. In the locking condition, the hard, knife-like formed, locking hooks are biased into the soft material of the locking noses  31  and formlocking connection which further contributes to preventing of an accidental release of the clamp  1 . 
     The handles  14 , after fixing of the clamp  1 , do not project anymore over the side  7  of the clamp  1  and do not prevent mounting of the cover  33 . The biasing actions of the flexible spring  12  and of locking spring  13  insure a preloaded locking engagement of the locking hooks  10  with the locking noses  31 . The preload contributes to obtaining of a force component which pushes the locking noses  31 , which extend in a longitudinal direction of the cable duct  20 , upward. As a result, the end sections of the edges  26  pivot about an axis which extends in the longitudinal direction of the cable duct.  20 , with the hook-shaped connection portions  3  of the clamp  1  being pulled further into the undercuts  29 . 
     For releasing of one side of the clamp  1 , the handle  14  of this side is pushed against the biasing force of the locking spring  13  in a direction toward the middle portion  6  of the bridge section  2 , and the locking hook  10 , at this side, becomes disengaged from the locking nose  31 . As a result of preloading of the flexible spring  12 , the locking arm  11  pivots upward, with the locking elements occupying their initial position. After the release of the locking connection, the clamp  1  can be lifted at one of its sides from the respective anchoring groove for placing another cable. 
     Though the present invention was shown and described with references to the preferred embodiments, various modifications thereof will be apparent to those skilled in the art and, therefore, it is not intended that the invention be limited to the disclosed embodiments or details thereof, and departure can be made therefrom within the spirit and scope of the appended claims.