Cable lug

The invention relates to a cable lug for connecting a cable end to a screw type terminal. The cable lug comprises a flat, u-shaped contact fork which is open toward the front and which merges into a fork shaft toward the rear. The fork shaft is provided with connection means for a cable end. At least one base plate configured as a signal conductor, at least one damping disk made of elastic material, and at least one cover plate are assembled in a stacked, sandwich-like manner in the area of the contact fork. In order to improve functional characteristics and durability, and more particularly to obtain an improved vibration-damping action, the invention provides that the cover plate extends over the sides of the damping disk.

CROSS-REFERENCE TO RELATED APPLICATIONS:
 Applicants claim priority under 35 U.S.C. .sctn.119 of German Application
 No. 198 13 370.7 filed Mar. 26, 1998. Applicants also claim priority under
 35 U.S.C. .sctn.120 of PCT/EP99/02090 filed Mar. 26, 1999. The
 international application under PCT article 21(2) was not published in
 English.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a cable lug for connecting the end of a cable to a
 screw-type terminal, with a flat U-shaped contact fork that is open toward
 the front and merges into a fork shaft toward the rear, said fork shaft
 being provided with connecting means for the connection to a cable end,
 whereby at least one base plate configured as a signal conductor, and at
 least one damping disk made of elastic material with at least one cover
 plate, are assembled in a stacked, sandwich-like manner within the area of
 the contact fork.
 2. The Prior Art
 Such cable lugs are preferably employed as connection elements for
 electrical high-current connections for connecting the ends of cables to
 screw bolt-type connectors, the latter being referred to as screw or
 connection terminals. Such terminals are substantially formed by a
 threaded bolt that projects vertically from a contact surface, whereby a
 nut or another type of terminal element with a female thread can be
 screwed to the free end of said threaded bolt. For connecting the cable
 lug to such a terminal, the contact fork is first pushed into an axial gap
 between the contact surface and the nut and then radially onto the screw
 bolt, and the nut is subsequently tightened, so that the contact fork is
 axially solidly clamped between the nut and the contact surface of the
 terminal.
 Due to the relatively large contact surfaces in the U-shaped zone of the
 contact fork, the transition resistance to the corresponding contact
 surfaces on the terminal is accordingly low. Such cable lugs are therefore
 frequently used for connecting loudspeaker cables with large conductor
 cross sections with high-load capacity, to the output terminals of
 amplifier output stages.
 However, it has already been found that forming the contact fork from a
 simple sheet metal tab or plate is inadequate for such applications. Even
 if such a contact fork is solidly tightened by hand, it is possible that
 the contact fork is excited to mechanical vibrations by the sound
 frequency signals, which are transmitted with high current intensities, by
 magnetostriction, and also by body and air sound. Such vibrations lead to
 relative movements of the contact surfaces stacked one on top of the
 other, which is directly reflected by signal interferences. Such
 interferences are, of course, absolutely undesirable especially when
 connecting high-quality sound transformers to amplifier output stages.
 In order to deal with the problems mentioned above, is has already been
 proposed in the prior art disclosed by U.S. Pat. No. 5,108,320, to realize
 the contact fork within the zone of the contact surfaces in the form of a
 sandwich-like construction comprising a base plate, an elastomer disk, as
 well as a cover plate. The base plate and the cover plate are realized in
 this connection as metal sheet forks congruently disposed on top of the
 other, with an also U-shaped rubber disk being clamped or glued in between
 said sheet metal forks within the zone of the U-shaped contact surfaces.
 The contact surfaces clamped together in the connection terminal are
 elastically pressed against each other by the inherently elastic rubber or
 elastomer disk. The elastic initial clamping assures that the contact
 surfaces are pressed against each other in an elastic manner, which
 enhances the electrical transfer.
 However, a basic problem in connection with the known cable lug lies in
 fixing the elastomer disk between the base plate and the cover plate in
 such a way that its optimal function is assured under all operating
 conditions, because it is necessary for such fixation that both shifting
 of the elastomer disk as a whole and any lateral squeezing out of the
 latter is effectively avoided when it is pressed axially. Gluing the disk
 to the cover or base plate would be considerably stressed by elastic
 deformations. Furthermore, the rubber would continue to swell out from
 between the cover and the base plates sideways, and the rubber material
 may be damaged by the wedge effect caused on the edges.
 Furthermore, in connection with the known cable lugs, the elastomer disk is
 subjected to the risk that it may be crushed by the forces of pressure
 occurring in the terminal during clamping when the clamping nuts are
 tightened.
 Finally, an added problem is that in the prior art, the elastomer disk is
 exclusively loaded spring-elastically in the axial direction, which means
 that it is possible that mechanical resonances may occur as a result of
 the undamped spring effect of the rubber material. This causes the contact
 surfaces of the contact fork and of the screw-type terminal to vibrate
 against each other without practically any damping.
 SUMMARY OF THE INVENTION
 In view of said problems the present invention is based on the problem of
 further developing a cable lug based on the prior art specified above in
 such a way that the functional properties as well as the durability are
 improved. In particular, the aim is to achieve enhanced damping of
 vibrations as well as protection of the elastomer disk against damage as
 it is being clamped tight.
 For solving said problem the invention proposes on the basis of the prior
 art specified above that the cover plate extends over the sides of the
 damping disk.
 The design of the cover plate as defined by the invention provides that
 said cover plate has bends, bridges or reinforcements projecting in the
 direction of the base plate and continuously or by sections extending
 along the outer edge in the front zone of the U-shaped contact. The
 elastomer disk is framed in this way along its side edges.
 The embodiment as defined by the invention ensues the basic advantage that
 any lateral movement of the damping disk beyond the edge of the cover
 plate is prevented without requiring any gluing or the like. Due to the
 embodiment as defined by the invention, the damping disk is enclosed by
 the cover plate in the way of a frame, so that it cannot migrate sideways
 beyond the edge of the cover plate. Furthermore, it is protected also
 against being squeezed out sideways in any uncontrolled manner as it is
 being clamped in the connection terminal.
 In view of the vibration-damping properties it is particularly advantageous
 that the damping disk is now additionally supported laterally. When the
 contact fork is pressed together, not only an initial spring tension acts
 on the elastically deformable material of the damping disk in the pressing
 direction, but a hydraulic load is additionally acting in the areas
 enclosed laterally and at the top by the cover plate as well, whereby both
 the inner friction of the hydraulically stressed elastic materials and
 particularly also the interface friction between the damping disk and the
 lateral areas of the cover plate provide for a substantially increased
 damping effect with respect to relative movements between the cover plate
 and the base plate. The tendency to vibration is reduced accordingly,
 which, of course, is to the benefit particularly of any application in
 areas that are sensitive in that regard, for example to a connection of
 high-performance loudspeakers to output stages.
 According to a particularly advantageous further development of the
 invention, provision is made that the cover plate has a side wall
 projecting downwards and extending all around its outer contour at least
 in the zone of the contact fork, said side wall laterally extending over
 the damping disk up to the base plate in the way of a box. The cover plate
 deeply drawn downwards on the sides practically forms a box or case that
 is closed on the sides and on top, and against which the damping disk is
 resting. The space enclosed in the box or base can be covered from the
 bottom by the base plate, i.e. it can be locked. In order to achieve this,
 the side wall, in its unstressed resting condition, may reach down up to
 the top edge of the base plate except for a small gap. Said gap is closed
 when the base plate and the cover plate are pressed together during
 clamping, whereby the box or case is closed at the same time.
 According to another particularly advantageous further development of the
 invention, provision is made that the base plate can be immersed like a
 piston in the space that is defined laterally and at the top by the cover
 plate. In the present embodiment, the box or case formed by the cover
 plate may extend over the top edge of the base plate as well. Thus the
 base plate is forming a piston- or punch-like element which, when the
 contact fork is pressed together, acts upon the damping disk that is now
 enclosed on all sides in the box. The principle of a hydraulic shock
 absorber is practically realized in this way, whereby the enclosed damping
 disk assumes the function of the hydraulic damping medium. As it is known,
 for example from shock absorbers for motor vehicles or the like, a
 particularly high damping effect is achieved with respect to mechanical
 vibrations by means of hydraulic, hydro-mechanical or hydro-pneumatic
 friction effects. Undesirable contact vibrations, regardless of whether
 they are caused by sound or magneto- or electrostriction, are practically
 completely suppressed, which, of course, is a benefit especially to signal
 transmission in high-end equipment of entertainment electronics.
 The piston-like embodiment of the base plate can be advantageously realized
 by providing it in the zone of the contact fork with a step at the top
 edge, providing it thereby with a T-shaped cross section lying upside
 down. Said cross section can immerse in the box or case formed by the
 cover plate to such an extent until the edge of the side wall abuts the
 horizontal surface of the step. A defined end stop is formed in this way,
 and crushing is prevented.
 The cover plate itself preferably consists of spring-elastic material and
 is permanently joined with the shaft of the fork behind the U-shaped
 contact surfaces. The elastomer disk is then elastically clamped between
 the cover plate and the base plate.
 The cover plate preferably consists of hardened, heat-treated steel sheet
 material, for example V4A. Owing to its hardness and spring elasticity,
 said material has adequate dimensional stability in order to absorb the
 pressure forces occurring when the elastomer disk is hydraulically
 clamped. Furthermore, the surface is largely insensitive to scratches or
 other damage caused when the connection is made to a terminal. The cover
 plate, furthermore, is preferably manufactured by deep-drawing a one-piece
 sheet cut, which is subsequently hardened.
 Is useful, moreover, if the base plate and the fork shaft joined with the
 latter in the form of one piece consist of highly conductive material.
 Preferably high-purity, low-oxygen electrolyte copper or also silver are
 used for the signal conductor. The base plate and/or the cover plate are
 hard-plated with gold.
 The cover plate usefully has stop elements that are movable against the
 damping disk. Such stop elements are projecting spacers that limit the
 movement of the cover plate against the base plate, so that the damping
 disk cannot be crushed accidentally.
 The damping disk can basically consist of any desired elastomer materials,
 for example such a rubber or suitable plastics. Any desired mechanical
 properties and thus the damping effect can be preset by adjusting the
 Shore hardness accordingly. Preferably selected in this connection is an
 elastic material with high inner damping.
 The damping effect can be influenced in an advantageous way if the cover
 plate and/or the damping disk and/or the base plate have hydraulic
 compensation cavities for the elastic material of the damping disk. For
 example, molded depressions that are open toward the interior of the case,
 or also through-extending openings may be provided in the cover plate or
 the base plate as hydraulic compensation cavities. The material of the
 damping disk can then be hydraulically displaced into such molded
 depressions or openings as it is being pressed compressed. In this way,
 the friction values and thus the damping effect can be optimally adapted
 to the given requirements. It is also possible, furthermore, to make
 provision for chambers or molded depressions in the damping disk that
 serve as compensation cavities. For example, the use of porous rubber
 materials is conceivable, or also the introduction of cavities in
 otherwise incompressible materials, with which the hydraulic or
 hydro-pneumatic damping effect can be preset in a defined manner.
 Also, the elastomer material may be directly applied to the cover plate by
 spray application, if need be.
 According to another particularly further development of the invention,
 provision is made that the damping disk and the cover plate are formed
 from elastic material in the form of one single piece. By selecting the
 material or materials and/or through the selected shape, for example by
 providing for hydraulic compensation cavities, different functional areas
 are formed in the body comprising the damping disk/cover plate. Such
 functional areas relate to the function of the cover plate as defined by
 the invention, on the one hand, and to the damping function on the other.
 If the cover plate is combined with the damping disk in the form of one
 single piece, the functional areas mentioned above can be formed in an
 advantageous way from materials with different properties that are then
 joined with one another in the form of one single piece. It is possible,
 for example, to first produce the cover plate in the form of an
 injection-molded plastic part made of a material with greater hardness or
 rigidity, and to subsequently attach the softer damping disk to said cover
 plate, preferably by injection molding as well, so as to form one single
 part. The yielding property of said damping disk can be adjusted by using
 a softer plastic or also through the shape it is provided with, for
 example through compensation cavities, or foam-like porous areas or the
 like.
 The damping disk is fixed in a particularly safe manner by form-locked
 elements of the cover plate that engage the damping disk, for example
 punched tabs or the like.
 The contact fork is usefully embedded outside of the contact surfaces in
 insulating material, for example in plastic injected around it. This is
 advantageous in view of the easy handling.
 The connecting means on the shaft of the fork may have screw clamps for
 receiving the end of a cable, or, as an alternative, such means may be
 provided with crimp connectors, i.e. clamping elements that can be
 squeezed.
 So as to assure that the cover plate extends in the zone of the contact
 surfaces at a spacing parallel with the base plate, it may be provided
 with a support element resting on the shaft of the fork. The height of
 such a support element, which, for example, may be formed by bends, is
 dimensioned depending on the thickness of the elastomer disk. It is
 assured in this way that the cover plate and the base plate will remain
 positioned largely parallel with each other after they have been clamped
 in.
 It is advantageous for the assembly that the cover plate is fixed in its
 position on the fork shaft on laterally protruding locking prongs of the
 base plate. An association of the cover plate and the base plate is
 obtained in this way that it clearly correct with respect to the positions
 of said plates.

FIG. 1 shows a perspective view of a cable lug as defined by the invention
 viewed inclined from the top and denoted as a whole by the reference
 numeral 1. Said cable lug has a U-shaped contact fork 2, which is open
 toward the front, and which changes into a fork shaft 3 toward the rear,
 said shaft of the fork being embedded in an insulating and handle body 4
 made of plastic.
 For the connection to the end of a cable, the fork shaft 3 is provided in
 its rear zone with the connecting means 5 which, however, are hidden in
 the present representation by the insulating body 4 except for the heads
 of the clamping screws. Said clamping screws are screw clamps whose
 connection opening for connecting the end of a cable is located at the
 rear end of the insulating body 4.
 It is already shown by said representation that the contact fork 2 is
 formed by a U-shaped base plate 6 forming the signal conductor, and a
 cover plate 7 arranged above said base plate in a stacked, sandwich-like
 assembly, and having the form of an also U-shaped, downwardly open box or
 case, with a damping disk 8 made of elastic material, for example rubber
 being enclosed between said base and cover plates. While the damping disk
 boxed-in in said manner is not visible in FIG. 1, and only indicated for
 said reason by dashed lines, the arrangement is particularly clearly shown
 in FIG. 2. In FIG. 2, the part of the contact fork 2 that is disposed in
 front in said representation, is shown cut open in a slanted way. The same
 reference numerals are used.
 The base plate 6, which is connected via the fork shaft 3 with the
 connecting means 5, forming one single piece jointly with said base plate,
 consists of highly conductive material, for example high-purity copper, or
 also silver. The cover plate 7 is a heat-treated and hardened, deep-drawn
 stain steel component and, like the base plate 6, is preferably
 hard-plated with gold. As an alternative, the cover plate 7 may also
 consist of another, harder material that is resistant in relation to the
 damping disk 8, for example plastic. Within the zone of the fork shaft 3,
 the cover plate 7 is permanently joined with said fork shaft, so that
 within the zone of the contact fork 2 it is practically movable
 vertically, i.e. in the axial direction against the base plate 6.
 The cross section through the contact fork according to FIG. 2 is
 schematically shown again enlarged in FIG. 3. The latter clearly shows how
 the cover plate 7, whose side walls 7a are drawn downwards up to the top
 edge of the base plate 6, is forming a closed box for the damping disk B.
 The base plate 6 may in this connection have a T-shaped stepped cross
 section that can be immersed like a piston in the direction of the arrow
 up to the edge of the step in the box formed by the cover plate 7 up to
 the edge of the step.
 The special feature of the embodiment shown in FIG. 4 consists in that both
 the cover plate 7 and the base plate 8 are provided with the hydraulic
 compensation cavities 9, which are partly realized in the form of molded
 depressions and partly as through-expending openings. The damping disk 8
 is provided with such compensation cavities 9 as well, which are partly
 realized in the form of open molded depressions and partly in the form of
 closed chambers. The elastomer material may be realized in this sense as a
 whole in the form of a porous material as well.
 FIG. 5 shows a similar embodiment, where the base plate 6 has a non-stepped
 cross section.
 With the contact fork 2 according to FIG. 6, the cover plate 7 and the
 damping disk 8 are combined to form a one-piece cover plate/damping disk
 element 7/8. The inner zone with the hydraulic compensation cavity 9 has
 in this connection substantially the damping function, whereas the outer
 zone assumes the cover plate function.
 In the embodiments according to the representations in FIGS. 1 to 5, the
 cover plate 7 may accordingly also consist of a harder plastic material or
 the like, with which the softer material of the damping disk 8 is joined,
 forming one single piece. Such a single piece is manufactured, for example
 by two-component injection molding.
 All embodiments of the cable lug 1 as defined by the invention have in
 common that vibrations of the base plate 6 and the cover plate 7 against
 each other due to the damping effect of the enclosed damping disk 8 are
 effectively suppressed, because when the base plate 6 and the cover plate
 8 are pressed together, the damping disk 8 consisting of elastomer
 material is quasi-hydraulically deformed. The hydraulic, hydro-mechanical
 and hydro-pneumatic friction occurring during such compression entails
 effective damping. Such effective damping can be adjusted within wide
 limits by the arrangement of the hydraulic compensation cavities 9, into
 which the material of the damping disk 8 can flow as it is being
 compressed, as well as by the hardness selected for the elastic material.