~78996 FUSE HOLDER BLOCK
Technical Field The subject matter of the invention is an improved clip-in holder for electrical fuses.
5 Background of Prior Art Conventional clip-in fuse holders for cylindrical cartridge fuses exhibit certain deficien-cies with respect to high voltage insulation protection.
Such holders typically consist of a pair of spring clips mounted on a base and configured to engage the end terminals of a cylindrical cartridge fuse by pressing insertion. The clips, together with unitary or separate terminal lugs, are normally secured to the base by a metallic rivet passing through a hole in the clip base and through a matching hole passing through the mounting base. Since the rivets are in electrical contact with the clips, a short circuit can occur throuah the fuse terminals if the bottom faces of the rivets are exposed below the mounting base to contact any conducting surface on which the fuse holder may be mounted.
One solution involves provision of a separate insulating spacer inserted between the fuse mount base and the supporting surface. This solution is undesirable, since it requires an extra part, raises ~178996 the overall height of the fuse structure and, thus, wastes space and poses tailoring problems for multiple fuse mount arrays of differing numbers of fuses.
An alternative solution is to provide a 5 relatively thick fuse mounting base and to counterbore the rivet hole at the lower face of the mounting base to place the lower end of the rivet higher in the structure. This solution has the drawback that the surface walls of the counterbore walls serve as sur-10 face flashover paths at high voltages unless the basethickness is appropriately increased, again resulting in increased overall height of the fuse mount. Addition-ally, the rivets are extra parts in the assembly, and thus add materially to the manufacturing inventory. Ac-15 cordingly, it is an object of the invention to provide an inexpensive, easily assembled fuse mount with less parts and without conducting passages through the base so as to achieve a reduced structure height for a given voltage rating.
It is frequently observed that low-priced snap-in cartridge fuses have their end terminals oriented significantly off-axis. Such structures are typically rather fragile, owing to the customary method of end terminal attachment, and as a result the terminals fre-25 quently break off when such fuses are inserted into conventional fuse holders with rigidly coaxially aligned fuse clips. Accordingly, it is an object of this inven-tion to provide for self-aligning clips as a feature of the fuse mount to accommodate off-axis end terminals 30 without such breakage.
The present invention resides in an open frame fuse holder for insertable electrical cartridge fuses having cylindrical coaxial end terminals, the holder including an insulating unitary mounting base having a major inner face and a major outer face, the inner face including a pair of spaced apart clip base support areas disposed thereon proximate to opposite edge portions of the inner face, and a pair of electrically conducting spring clips on the mounting base, each of the clips including a terminal lug means on the clip, a clip base mounted on one of the clip base support areas, and two spaced apart upstanding clip jaws with major jaw surfaces facing one another, portions of each of the clip jaws configured with contours to springingly lockingly engage a cylindrical fuse terminal pressed between the jaws. Insertion pressure actuated engaging means is provided for locking the clips to the cli.p support areas by pressing the bases of the clips against the clip support areas and into snap-in engagement with portions of the mounting base, portions of the clips and the portions of
2~ the base configured for mutual snap-in engagement. The jaws of the pair of clips are configured to place the engagement axis of each clip when mounted on the mounting base substantially coaxial with respect to each other.
Pivot means is provided for allowing rotation of at least one of the clips engaged by the pressure actuated engaging means about an axis of rotation passing through the clip support area associated with the at least one clip, the rotation providing a self-aligning feature of the at least one clip during fuse insertion to reduce mechanical stress on the engaged fuse terminal and to reduce electrical contact resistance therewith.
According to a specific embodiment of the invention, insulating barrier walls partially shroud the terminal clips and the terminals of the engaged fuse from accidental touching contact with external objects. The terminal clips preferably lock to the base by locking engagement with the barrier walls, sb/~C-~' 1~
and thus do not require a conventional metal attaching rivet passing at least partially through the base. By eliminating the conducting rivet and its attendant potential for high voltage flashover to the surface on which the base is mounted, e.g. a fuse box wall, the base may be made thinner, resulting in an overall lower profile and reduced space requirements. Further by reducing the number of components and replacing a riveting operation with a snap-in operation, manufacturing costs are reduced.
According to a specific aspect of the feature invention, the snap-in engagement is secured by unitary tabs on the interior faces of the barrier walls engaging suitably shaped contours of the clip jaws.
According to another specific aspect of the invention, additional clip securing means is achieved by a pair of posts unitary with said mounting base and extending therefrom to engage matching holes in the bases of each clip upon clip insertion. The combination of tab engaging means to press the clip against the mounting base and a capture post to prevent lateral travel on the base provides an inexpensive ! easily-manufactured way of making a reliable fuse holder assembly .
According to still another specific aspect of the invention, additional strength is achieved in the assembly by configuring the posts to pass through and beyond the clip bases. The extended portion of each post may be crowned over by conventional hot-forming techniques after clip insertion, thereby imparting additional pull strength protection during fuse removal.
According to a further specific aspect of the invention, by configuring the clip jaws and locking tabs for loose engagement, the mounted clips are able to pivot on the mounting base to provide the self-aligning feature during fuse insertion. This provides for a maximum interfacial contact between the fuse terminals and the clip, thereby reducing contact resistance.
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il~78996 According to a still further aspect of the invention, the barrier walls are disposed in close proximity to the clips so that the clips are effectively secured against excessive rotation on the base, thereby preserving clip alignment for ease of insertion.
Other objects, advantages, and features of the invention will become apparent upon making reference to the description to follow, the drawings, and the claims.
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Brief Description of Drawings _ Figs. lA, lB, lC, and lD are a perspective view, a top plan view, a front elevational view, and a side elevational view, respectively, of the preferred version of the improved fuse holder;
Fig. 2 is a perspective view of the holder with a fuse inserted;
Fig. 3 is an exploded perspective view showing one end of the fuse holder with a clip positioned for insertion from above;
Figs. 4A and 4B are cross-sectioned side elevations showing details of the clip insertion and clip locking mechanism;
Fig. 5 is a top plan view in cross section showing rotation limiting engagement of the base of a fuse clip with the walls;
Fig. 6A is a cross-section partial front elevation of one end of a clip assembly wherein the fuse post has been crowned for increased pull strength;
Fig. 6~ is a similar view of a conventional riveted fuse clip structure with the same metal-to-base insulation distance, showiny the reduced height achieved with the improved structure for comparison purposes;
Fig. 7 is in perspective view of an alternative form of snap-in clip fuse mount;
Fig. 7A is a cross-sectional view of the form shown in Fig. 7 as seen from the line 7A-7A;
Fig. 8 is front elevation of an alternative version of the fuse holder shown in Fig. lC, wherein the terminal lugs extend upward and away from a mounting surface.
Figs. 9A and 9B are side and end elevations respectively of an alternative form of clip locking means.
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il78996 Detailed ~escription of Invention The exemplary form of the invention is shown in Figs. lA, lB, lC and lD, and consists of a unitary insulation mounting base l and two conducting fuse hold-5 ing clips 2, the base and the clips being configuredto lockingly engage together under snap-in pressing engagement. A central hole 4 in the base 1 allows passage of a mounting screw (not shown). Two connect-ing lugs 3 unitary with each clip 2 extend away from lO the mounting base 1. The clips 2 are partially shroud-ed by insulating barrier walls 5, which provide a measure of protection against accidental electrical contact of external objects with the clip structure. Fig. 2 shows a fuse holder with a cartridge fuse 6 installed. Fig. 8 15 shows an alternative of the fuse holder assembly shown in Fig. lC, wherein the terminal lugs extend upward and away from a mounting surface.
The barrier walls 5 further serve as part of the clip anchoring assembly. Fig. 3 shows details of a 20 clip 2 positioned for insertion. The clip 2 is mounted on the base by pressing the clip downward between t~o compliant wall-mounted locking tabs 7 (Figs. 4A and 4B), forcing them outward until the clip is fully seated on the base. Locking slots 8 (Figs. 3, 4A, 4B) in the clip 25 are then engaged by inward motion of the locking tabs, securing the clip to the base. A unitary post 9 extend-ing up from the base l engages a hole lO in the base of the clip 2 to secure the clip against lateral motion.
Referring to Fig. lC, it will be noted that 30 the engaging slots 8 are configured longer than the width of the locking tabs 7, thereby permitting the clips to rotate about the mounting posts 9 as shown in Fig. 5. The amount of rotation is restrained by close proximity of the interior surface of each of the walls 5 35 (Fig. 5) to the base of the clip ll, thereby holding 117899~;
the clip in proper alignment for fuse insertion and insuring that no substantial motion of the lug 3 can occur to cause an accidental short circuit to adjacent structures. For additional pull strength during 5 fuse removal the posts may be crowned after assembly by conventional hot-forming methods well known to the art. Fig. 6A shows a cross-sectional view of a fuse clip 2 engaged by such a crowned post 12.
Fig. 6B shows a cross-section view of a 10 similar mounting base wherein a clip 2' is secured to the base by a conventional metal rivet 13. This method of attachment places a conductor contacting a clip in closer proximity tG whatever mounting surface on which the fuse holder is attached, and thus reduces the maximum 15 allowable voltage that may safely be applied to a clip before high voltage flashover occurs. By eliminating the rivet 13, a higher voltage rating fuse mount is achieved for a given base thickness and overall height, and may be seen by comparing Fig. 5B with Fig. 6A, wherein 20 the metal-to-mounting plane distance D of both structures is held to the same standoff distance. The elements of the structure are all suited to well-known mass production techniques at competitive cost with respect to conven-tional fuse holders of similar type. The assembly is 25 easily assembled, uses less parts by eliminating the rivets, and is self-aligning. This accomplishes several of the objects of the invention. An alternate form of fuse holAer is shown in Figs. 7 and 7A . In this ver-sion the clips 2" have tabs 14 on their jaw ends compliantly 30 engaging configured interior shoulders 15 on the walls 16.
A capture post of the type previously described may optionally be employed, however, a high degree of compli-ance is necessary in the tabs 14 if significant rotation about the post is to be allowed. Figs- 9A and 9B are 35 side and end elevations respectively of another " ;
1~7899~
alternative form of cli~-in locking means wherein a clip 17 is secured to a mounting base 1~ by a single central tab 19, and is captured by an engaging ridge 20 on the base engaging an appropriately config~red 5 engaging contour on the clip.
While for the purpose of illustration, various forms of this invention have been disclosed, other forms thereof may become apparent to those skilled in the art upon reference to this disclosure 10 and, therefore, this invention shall be limited only by the scope of the appended claims.