GB2090081A

GB2090081A - Plug-in and in-line electrical fuses

Info

Publication number: GB2090081A
Application number: GB8137004A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-12-08
Filing date: 1981-12-08
Publication date: 1982-06-30
Also published as: GB2090081B

Abstract

Fuse 10 comprises two flat parallel coplanar terminals 12, 14, each having a forward portion 38 intended for reception in a pressure clip terminal in a mounting panel, and a rear portion 28 secured in an insulating housing 24. Rear portions 28 are connected by fusible element 18 of a material different from that of terminals 12, 14. The fuse 10 may be used as an in-line fuse with conventional connectors if forward portions 38 are splayed or with right- angled slip-on terminals if forward portions 38 are unsplayed. <IMAGE>

Description

SPECIFICATION Plug-in and in-line electrical fuses This invention relates to plug-in electrical fuses of the type having two blade-like prongs for insertion into a pressure clip terminal in a mounting panel and to in-line fuses; such fuses find particular, but not exclusive, application in the electrical systems of automobiles.

In U.K. Patent Specification No. 1 500183 there is described and claimed a plug-in electrical current overload fuse comprising a fuse element in the form of a one-piece planar plate-like body of fuse-metal, said body comprising a pair of laterally spaced, generally parallel terminals, each terminal comprising a blade portion adapted to be received, in use, by a pressure clip terminal in a mounting panel, and a current carrying extension forward of said blade portion, and a fusible link portion which interconnects the two currentcarrying extensions, said fusible link portion being of much smaller cross-sectional area than the blade portions of said terminals. The current carrying extensions are preferably fitted into a housing comprising a gripping body which extends between and is immovably affixed to the current carrying extensions.

While the unitary nature of the planar plate-like body of fuse metal lends itself to automated production of the fuse element it does have several drawbacks; the whole element must be made of expensive fusible metal and there is little latitude in the choice of fusible material; moreover, no advantage can be taken of the socalled M-effect (this is an increase in resistance, causing accelerated heating and earlier failure of the fuse, the effect being obtained by alloying certain different metals at a certain temperature with the metal of which the fusible link is formed; for example a tin-lead mixture produces an Meffect which alloyed with silver, as does cadmium when alloyed to copper).

According to the present invention there is provided a plug-in electrical fuse comprising two flat elongate terminals, each having a forward portion intended, in use, for reception in a pressure clip terminal in a mounting panel and a rear portion which is secured in an insulating housing to maintain the terminals in laterally spaced, generally parallel and co-planar relationship, the rear portions being conductibly interconnected by a fusible element of a material different from that of said terminals.

The fusible element is preferably formed of ordinary fuse wire which is of circular crosssection in order to give the finest possible fusing characteristics or specification.

At the centre of the element a small amount of M-effect producing metal may be alloyed with that of the element and the length and shape of the element is adjusted to raise the temperature sufficiently under overload conditions to enable the M-effect to be achieved. The best shape for the element is that of a hairpin or horseshoe configuration: more latitude on the length of the element, and therefore better temperature control, is gained by these looped configurations especially if the ends of the element are secured each to an ear projecting laterally inwards from each terminal. Additional temperature control can be achieved by forming one or more holes through each terminal near the end of the fusible element, the holes tending to reduce heat loss by conduction.Each end of the element may be secured to the body of the terminal or projecting ear by soldering or spot welding; in the latter case a very short length of the element is allowed to project beyond the weld.

In an alternative construction the terminals are formed of folded sheet metal with a longitudinal medial join line, a transverse strip of material being folded back to form a tube lying along the inner laterial edge of the rear portion of each terminal. The end of the fusible element is then secured in each tube by crimping and/or soldering.

In a further alternative construction the terminals are again of folded construction but are formed with a hole through the fold line; the end of the fusible element may then be introduced into the hole so as to lie between two layers of metal and there be secured by soldering and/or crushing.

It will be appreciated that in the above constructions according to the present invention the material of the fusible elements may be chosen for optimum fusing properties, while the material of the terminals may be chosen for its physical characteristics and cheapness and be for example copper or brass (the use of a known form of fusible element such as fuse wire enables the potential performance of the fuse to be judged more easily in advance).

The housing is preferably a one-piece moulding of plastics material and each terminal has a rearwardly extending finger at its outer lateral edge which co-operates with a corresponding formation on the housing inset from the forward edge thereof. The finger limits the insertion of the terminals into the housing at the correct distance and also anchors the terminals against laterally inward movement. If a lateral indentation or notch is formed in the rear end of each terminal which co-operates with a corresponding internal projection on the housing, or a series of such notches and corresponding projections is formed, these will keep the terminals securely in the housing. If desired adhesive may be used for this purpose either along or in conjunction with the previously-mentioned notch or notches.Again the housing may be locally fused to cause the material thereof to flow into recesses in the rear portions of the terminals.

A fuse according to the present invention may be manufactured by securing the blade-like portion of each terminal in a jig, attaching each end of the fusible element to a rear portion of a respective one of the terminals and fitting a housing onto the rear portions of the terminals, adhesive previously being applied to the terminals or housing if desired. If a U-shaped configuration of fusible element is being used a pin is preferably provided in the jig to assist in the location of the loop of the element. If holes have been formed in the terminals for the previously-mentioned temperature control purpose these may serve an additional function of locating the terminals by receiving respective pins secured in the jig.It will be appreciated that the laterjl play between the two elements allowed by the hair-pin configuration of the fusible elements considerably simplifies assembly.

The fuse according to the present invention is much cheaper to produce than a conventional glass-bodied fuse and has the additional advantage of conforming to the projected European standards for automobile fuses. A non resonant shape of fusible element may easily be chosen to avoid resonance and consequent mechanical failure through sympathetic vibration.

A known "in-line" fuse-holder comprises an elongate cup portion through the bottom of which projects a spring-loaded terminal which makes contact with the inner end of a conventional cylindrical fuse inserted therein, the other end of the fuse being contacted by a terminal housed within a cap which is securable to the cup by a bayonet fixing.

This is a cumbersome, quite complex device: according to a further aspect of the present invention there is provided a much simpler and cheaper "in-line" fuse which comprises an insulating housing in which are received portions of two terminals, said portions being interconnected by a fusible link, preferably of a metal different from that of said terminals, portions of the terminals projecting from the housing being splayed in opposite directions so as to be capable of receiving shielded or unshielded flat-blade or female connectors. Preferably the projecting portions of the terminals are splayed from the point where they leave the housing.

An important characteristic of the in-line fuse according to the present invention is that it is self supporting. This characteristic makes it very suitable for easy inclusion into an electrical sub assembly, for example of interposition in a lead in an electrical suppression toroid or choke. Perhaps the most important advantage afforded by the in line fuse according to the present invention is its ability to be easily and cheaply introduced into an existing circuit, for example into an automobile wiring loom so as to enable the electrical circuitry of the car to conform to a national or international reguiation or to accommodate extra equipment. A lead may be severed, a connector fitted to each end and the connectors secured to the respective splayed portions of the terminals, all in a very simple and economical operation.

According to a further aspect of the present invention there is provided an in-iine fuse holder comprising a plug-in electrical fuse according to the invention, having terminals with unsplayed forward portions in combination with a pair of shielded or unshielded right-angled female slip-on terminals (sometimes known as flag slip-ons).

Preferably the terminals are housed in a plastics moulding and such a combination may be used with any suitable flat blade fuse whether in accordance with the invention or not.

Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a vertical section through a fuse according to the present invention; Figure 2 is a plan showing a stage in the manufacture of a modification of the fuse of Fig. 1; Figure 3 is an end elevation on the line Ill-Ill in Fig. 2; Figure 4 is a plan similar to that of Fig. 2 showing a further stage in the manufacture of the fuse of Fig. 2; Figures 5 and 6 correspond to Figs 2 and 4 respectively and show stages in the manufacture of another modification of the fuse of Fig. 1; Figure 7 is a perspective view of a further modification of a terminal used in a fuse according to the present invention;; Figure 8 is a perspective view of a modification of the terminal of Fig. 7; Figure 9 is a partial vertical section of a modification of the fuse of Fig. 1 incorporating the terminal of Fig. 8; and Figure 10 is a perspective view of an in-line fuse according to the present invention.

In the following description like reference numerals are used to indicate the same or similar parts.

The fuse 10 shown in Fig. 1 comprises two flat, elongate terminals 1 2, 14, each formed with a respective ear 1 6 projecting laterally inwards to which is soldered an end of a loop-shaped fuse element 1 8 of conventional copper fuse wire. At the centre of the element 18 is a small blob 20 of cadmium which is alloyed to the fuse wire to produce an M-effect. Near the base of each ear 1 6 is punched a hole 22 which reduces the amount of heat transferred away from the element 1 8 to promote earlier fusing.

The terminals 12, 14 are each received in a channel projecting rearwardly into a moulded polystyrene housing 24, the terminals 1 2, 14 being an interfence fit in the channels which open at their laterally inner edges into a wider central cavity in which the fuse element 1 8 is accommodated. A finger 26 projects rearwardly from the outer lateral edge of each terminal 12, 14 and co-operates with a corresponding notch 27 formed in the housing 24 to locate the rear portions 28 of the terminals 12, 14 therewithin and secure them against lateral and rearward movement. The rear portions 28, terminals 12, 14 are also each formed with a lateral notch 30 which receives a corresponding internal projection 32 on the housing 26 to secure the terminals 12, 14 against forward movement. Two openings 34 are moulded into the rear end of the housing 26 which receive integral tabs 26 projecting from the rear portions 28 of the terminals, the ends of the tabs 36 being slightly inset from the rear face of the housing 26. The purpose of having the rear faces of the tabs 36 exposed is to allow probes to be inserted into contact therewith to check the electrical continuity between the terminals 12, 14.

The exposed, forward portions 38 of the terminals 12, 14 are, in use, received in a pressure clip terminal (not shown) in a mounting panel, insertion and removal of the fuse 10 being facilitated by a peripheral knurled band 40 formed around the rear end of the housing 24.

The terminals 42, 44 shown in Figs. 2 to 4 differ from the terminals 12, 14 in that they are each formed by folding an appropriately shaped stamping along lines corresponding to the laterally inner and outer edges of the terminal which thus has double the thickness of the original stamping; the longitudinal edges of the original stamping; the longitudinal edges of the stamping almost meeting along a line 46. A medial portion of sheet opposite the finger 26 is partially severed and curled back on itself to form a sleeve 48.

To manufacture the fuse using the terminals 42, 44, these are first placed in longitudinal alignment in a jig (not shown) and an end portion of a length of fuse wire 50 inserted in a respective one of the sleeves 48 and secured therein by crimping. The terminals 42, 44 are then folded and placed in a further jig (not shown) to achieve the relative positions shown in Fig. 4 causing the wire 50 to assume an inverted U-shape. The housing 24 is then fitted over the rear portions 28 of the terminals 42,44. In the modification of Figs.

5 and 6 the terminals 52 are formed similarly to the terminals 42, 44 except that a hole 56 is punched through the sheet metal before the folding operation such that it lies along the laterally inner fold line 58 and no sleeve 48 is formed. To manufacture a fuse using the terminals 52, 54 each end portion of a length of fuse wire 60 is inserted into the hole 56 in respective terminal 52, 54 and there secured by locally crushing the adjacent areas of the layers of sheet metal between which lies one of the end portions of wire 60. When the terminals 52, 54 are placed in a jig (not shown) in the relative positions shown in Fig. 6, the wire 60 assumes an inverted U-shape with each arm of the U being spaced from the respective fold line 58.

In Fig. 7 there is shown a further form of terminal 62 which is made from a single thickness of sheet metal. A sleeve 64 is formed by rolling into an almost closed tube a lug projecting from the laterally inner edge of the terminal.

In the modification 62a shown in Fig. 8 of the terminal 62 the square-ended tab 36 is replaced by tab 36a having a notched end and extending from a rear portion 28a which is formed with an additional heat conductive reducing hole 23; the modified rear portion 28a also lacks the notch 30.

In the modified fuse 1 0a incorporating the terminal 62a shown in Fig. 9 the housing 24a has a splayed opening 34a. After the terminal 62a has been inserted into the housing the two limbs of the notched end 36a are laterally swaged so that the end takes the form 36b and firmly anchors the terminal 62a in the housing 24a.

In a variant of the modified terminal 62a the sleeve 64 is replaced by a tubular formation defined by a series of alternately crooked fingers formed by spiitting the lateral marginal portion of the rear portion 28a of the terminal in the region adjacent the sleeve 64. The end of the wire 60 is received in the tube thus defined and secured in place by crimping and/or soldering. In the variant the rear portion 28a extending behind the tube is narrower and has only the width of the tab 36, thus saving material and allowing easier production.

The in-line fuse 66 shown in Fig. 10 has generally the same structure as described with reference to the embodiment of Fig. 1 and essentially comprises a housing 24 from which project the blade portions 70, 72 of the respective terminals 12, 14 which are interconnected within the housing by a fusible link portion 1 8. Instead of being parallel however the blade portions 70, 72 are oppositely splayed and each receives a conventional flat blade push-on connector 74, 76 partly shielded by PVC insulation 78, 80 respectively and attached to the end of a respective lead 82, 84, the connectors being attached by clamping, crimping or soldering. The flat blade connectors 74, 76 may alternatively be of the wholly insulated type and the insulation may be of the pre-insulated type or be applied after the attachment of the lead to the connector by a conventional clamping, crimping or soldering method or of the connector to the splayed blade portions 70, 72 of the terminals by a single sliding action.

The in-line fuse 66 is clearly admirably suited to being introduced into a wire forming part of a wiring loom.

For the fabrication of the in-line fuse 66 any of the previously-described methods may be abapted, the terminals 12, 14 being bent before being interconnected by the fusible link portion 1 8 or insertion of the terminals 1 2, 1 4 into the housing 24.

Claims

1. A plug-in electrical fuse comprising two flat elongate terminals, each having a forward portion intended, in use, for reception in a pressure clip terminal in a mounting panel and a rear portion which is secured in an insulating housing to maintain the terminals in laterally-spaced, generally parallel and co-planar relationship, the rear portions being conductibly interconnected by a fusible element of a material different from that of said terminals.

2. A fuse as claimed in Claim 1, in which the fusible element is formed of circular cross-section fuse wire.

3. A fuse as claimed in Claim 1 or 2, in which the fusible element comprises a body of an Meffect producing metal alloyed to the central region of said element.

4. A fuse as claimed in Claim 1,2 or 3, in which the element has a hair-pin or horseshoe configuration.

5. A fuse as claimed in any preceding Claim, in which each terminal has one or more holes formed therethrough near the respective end of the fusible element.

6. A fuse as claimed in any preceding Claim, in which each terminal has a rearwardly extending finger at its outer lateral edge which cooperates with a corresponding formation on the housing inset from the forward edge thereof.

7. A fuse as claimed in any preceding Claim, in which each terminal has a lateral indentation or notch formed near the rear end thereof which cooperates with a corresponding internal projection on the housing.

8. A fuse as claimed in any preceding Claim, in which each terminal is adhesively secured to the housing.

9. A fuse as claimed in any preceding Claim, in which the housing has been locally fused to cause the material thereof to flow into recesses in the rear portion of the terminal.

10. A fuse as claimed in any preceding -Claim, in which the rear end of each terminal is swaged to secure the terminal in the housing.

11. A fuse as claimed in any preceding Claim, in which each terminal is formed of sheet metal having a fold line at each lateral edge.

12. A fuse as claimed in Claim 11, in which each terminal has a hole formed through the fold line for reception of a respective end of the fusible element which is secured between the two constituent layers of the terminal by crushing.

13. A fuse as claimed in any one of Claims 1 to 11, in which each terminal has an ear projecting laterally inwards to which a respective end of the fusible element is secured by soldering or welding.

14. A fuse as claimed in any one of Claims 1 to 11, in which each terminal is formed with an integral sleeve in which a respective end of the fusible element is secured by crimping.

15. A fuse as claimed in Claim 1 and substantially as herein described.

1 6. A plug-in electrical fuse substantially as herein described with reference to Fig. 1, Figs. 2 to 4, Figs. 5 and 6, Fig. 7, or Figs. 8 and 9 of the accompanying drawings.

1 7. A method of producing a fuse as claimed in Claim 1, which comprises securing the forward portion of each terminal in a jig, securing each end of the fusible element to a rear portion of a respective one of the terminals and fitting a housing onto the rear portions of the terminals.

18. A method as claimed in Claim 17, in which adhesive is previously applied to the terminals or the housing.

19. A method as claimed in Claim 17 or 18, in which the housing is locally fused to secure the terminals.

20. A method as claimed in Claim 17, 1 8 or 19.

in which the end of each terminal is swaged to secure the terminals in the housing.

21. A method as claimed in any one of Claims 1 7 to 20, in which the fusible element has a Ushaped configuration and is located by a pin projecting from the jig.

22. A method as claimed in Claim 17 and substantially as herein described.

23. A method of producing a plug-in electrical fuse, substantially as herein described with reference to the accompanying drawings.

24. A plug-in electrical fuse produced by a method as claimed in any one of Claims 1 7 to 23.

25. An in-line electrical fuse comprising an insulating housing, two terminals, the rearward portions of which are received in the housing and interconnected by a fusible link, and the forward portions of which project from the housing and are spiayed in opposite directions so as to be capable of receiving shielded or unshielded flat blade or female connectors.

26. A fuse as claimed in Claim 25, in which the forward portions of the terminals are splayed from the point where they leave the housing.

27. A fuse as claimed in Claim 25 or 26, in which the fuse is a fuse as claimed in any one of Claims 1 to 17 or Claim 24, in which the forward portions of the terminals are oppositely splayed.

28. A fuse as claimed in Claim 25 and substantially as herein described.

29. An in-line electrical fuse substantially as herein described with reference to Figure 10 of the accompanying drawings.

30. An in-line electrical fuse comprising a fuse as claimed in any one of claims 1 to 17 and 24 in combination with a pair of shielded or unshielded right-angled female slip-on terminals.

31. A fuse as claimed in claim 30 and additionally comprising a plastics moulding in which the right-angled terminals are housed and maintained in appropriate spaced relationship for receiving the forward portions of said flat elongate terminals.

32. A moulding housing a pair of right-angled female slip-on terminals and as defined in claim 31.

33. The features as herein disclosed, or their equivalents, in any novei selection.