FEMALE AUTOMOTIVE FUSE

Abstract: A female fuse (10) has a one-piece fuse link (20) and thermal blocks (24) molded around fuse clips (30). The fuse link (20), thermal blocks (24), and fuse clips (30) are enclosed in an insulating housing (40). The fuse link (20) and thermal blocks (24) may be made by various processes but are preferably injection-molded as a one piece unit. The resulting fuse is smaller in size and operate at a cooler temperature than prior art fuses.

Description: FEMA E AUTOMOTIVE FUSE BACKGROUND OF THE INVENTION This invention relates to fuses in general, and in particular to a female fuse with a fuse clip insert molded into a one piece fuse link and thermal block, and still more particularly to methods of producing the one piece fuse link. State of the art fuses in the automotive industry, are, for the most part, male, blade type fuses. A bus bar includes blade type connectors for connecting to male bladed type fuses. To connect the bus bar blade to the blades on the fuses, a double female clip is required which connects to the blade on the bus bar at one end and the blade from the blade type fuse at the other end. The fuses plug into fuse blocks which have metal, spring clips. Further, the prior art fuses are physically large. One prior art fuse is 29 millimeters long and approximately nine millimeters wide. Further, prior art fuses typically have an overall height of approximately 34 millimeters. This causes the fuses of the prior art to have substantial size. The double female spring clip between the bus bar and the fuse blades is an additional component that adds cost, increases the size of the product, and requires additional labor to assemble. Further, the double female spring clip must be manually installed which adds more expense. The double female spring clips are the weakest part of the assembly and are relatively expensive compared to their size and function since their only purpose is to connect the two male blades together. The fuse link of prior art fuses is typically made of a continuous strip of zinc which is stamped and then bent into shape. Zinc has a melting temperature of approximately 440°C. When either the fuse or the bus bar overheats, the double female clip and the metal spring clips on the end of the incoming wires anneal causing them to lose their flexibility and requiring that they be replaced. When this occurs, not only must the fuse be replaced, but the fuse block must be disassembled to replace the double female spring clips. This is expensive and labor intensive. Furthermore, if the spring clip on the wire anneals, the wire must be replaced, thereby adding an additional expense. Prior art patents have met with limited success in seeking a solution to these problems. Yazaki , et al , U.S. Patent No. 5,294,906, shows a male fuse and a mechanism for trapping the link in the body. The purpose is to prevent the housing from being deformed and discolored due to generation of heat. Jung et al , U.S. Patent No. 2,055,866, shows a moveable heat accumulator to vary the overload characteristics of the link. Matsunaga, U.S. Patent No. 4,646,052, uses high melt temperatures and avoid the "M" effect. In the Jung et al and Matsunaga et al patents, the accumulators are separate pieces added to the link and raise the cost of manufacturing. The present invention overcomes the deficiencies of the prior art. SUMMARY OF THE INVENTION The present invention incorporates a fuse clip which is insert molded into a thermal block. The thermal block and fuse link are injection molded in a one piece unit. A female fuse incorporating this invention is smaller in size, operates cooler, and does not require soldering or welding of the parts. One objective of the present invention is to eliminate the need for a double female spring clip which extends between the bus bar and the fuse blades. Another objective of the present invention is to significantly reduce the installed cost of the fuse. The female fuse of the present invention has a length approximately one-half that of prior art fuses with very little increase in width. Further, the fuse of the present invention has a reduced height as compared to prior art fuses and thus has a substantial reduction in volume. This permits the use of a smaller PDB (power distribution block) and eliminates the double female clip along with the labor to install it. The female fuse of the present invention utilizes a fuse link and thermal blocks which have low melting temperatures thus minimizing the generation of heat which will damage the surrounding insulating housing which is made of plastic. High melting temperature metals of the prior art raise the temperature of the surrounding physical environment of the fuse link thereby causing the plastic housing to deform or melt. By using low melting temperature metals in the present invention, the housing may be made of lower temperature plastics which have a lower cost . Other objects and advantages of the present invention will appear from the following description. BRIEF DESCRIPTION OF THE DRAWINGS For a detailed description of the preferred embodiments of the present invention, reference will now be made to the accompanying drawings wherein: Figure 1 is a plan view of a fuse element sub-assembly according to the present invention. Figure 2 is a plan view from the right side of the f se element sub-assembly shown in Figure 1. Figure 3 is a sectional view, partially in phantom, of a female fuse according to the present invention. Figure 4 is a perspective view, partially exploded, of a fuse according to the present invention. Figure 5 is a sectional view of an alternative embodiment of the female fuse of the present invention. Figure 6 is a section view at plane 6-6 shown in Figure 5. DETAILED DESCRIPTION OF THE INVENTION Referring now to Figures 1-4, the female fuse is referred to in general by reference numeral 10. The major components of female fuse 10 are element assembly 28 and housing 40, best shown in Figures 3 and 4. Referring particularly now to Figures 1 and 2, the element assembly 28 is comprised of a pair of female fuse clips 30, 31, thermal blocks 24, 25, and fuse link 20. The fuse clips 30, 31 are made from a copper alloy such as tin-bronze, red brass, or ceramic bearing copper alloys. In the preferred embodiment, fuse clips 30, 31 are stamped out of sheet material and formed to shape. Fuse link 20 and thermal blocks 24, 25 are injection molded as a one piece unit. Fuse link 20 includes a hole or weak spot 36 which determines, in part, the fuse rating for the fuse 10. Fuse clips 30, 31 are encapsulated into each thermal block 24, 25, respectively, during the casting and molding process, hereinafter described in further detail. The base 33 of the clips 30, 31 includes aperture (s) 34 for receiving the molten metal forming thermal blocks 24, 25 thereby locking the clips 30, 31 to blocks 24, 25, respectively. As the metal used for thermal blocks 24, 25 and fuse link 20 cools, it contracts and locks the fuse clips 30, 31 into place. This construction eliminates the need for soldering or welding parts together, and hence reduces the cost of fuse 10. The size of the thermal blocks 24, 25 is determined by the size of the fuse clips 30, 31 since the fuse clips 30, 31 must be embedded in blocks 24, 25. Thus the thermal blocks 24, 25 are substantially the same size for fuses of all ratings. The rating of fuse 10 is determined by the configuration of the fuse link 20. The fuse link 20 is a generally flat strip of metal having a U-shaped cross section extending between clips 30, 31. The rating of the fuse 10 is determined by the over all length, width, and thickness of fuse link 20 together with the particular metal being used for fuse link 20. The weak spot 36 and the material are used to adjust the rating for a particular f se. Element assembly 28 is enclosed in an insulating housing 40 made of material such as plastic. In the preferred embodiment, the plastic is polypropylene which includes a talc fill. Housing 40 serves as a heat absorber. The plastic housing 40 may be injection molded and then assembled around the assembly 28 or constructed by other methods known in the art. Ears 32 on female clips 30, 31 hold fuse assembly 28 into housing 40 by fitting grooves 42 found in the housing 40. In the preferred embodiment, grooves 42 are molded into the housing 40. The metal used for injection molding fuse link 20 and thermal block 24 is a low melting temperature metal such as tin-silver, lead-antimony, tin-antimony, or other alloys and pure metals with melt or transition temperatures lower than 300 degrees C. The various alloys of the female fuse of the present invention have a melting temperature of less than 300°C and preferably the present invention utilizes alloys that have a melting temperature in the range of 220-250°C. The alloys used are eutectic. For example, a tin/lead (60/40) alloy has a range of approximately 15°C where the metal is both solid and liquid. The eutectic alloys of the present invention do not have a transition range such that the material of the fuse link 20 does not have a state of liquid and solid where it has no mechanical strength. Using a metal for fuse link 20 and thermal blocks 24, 25 having low melting temperatures provides certain advantages. Using low melting temperature alloys and metals lowers the amount of heat generated so as not to damage the surrounding insulating housing 40 made of plastic. Higher melting temperature metals raise the temperature of the surrounding physical environment of the fuse link thereby causing the plastic housing to deform or melt. Copper, for example, melts at approximately 1,083°C requiring that expensive plastics be used for prior art housing so as to have a high heat deflection to withstand such a high temperature. All fuse parts that are in contact with the prior art fuse link and terminal assembly will get very hot causing deterioration. By using low melting temperature metals as in the present invention, the insulating housing 40 may be made of lower temperature plastics having a lower cost . The lower temperature plastics are the result of being able to use low melting temperature metals for fuse link 20 and thermal blocks 24, 25. The material for the fuse link 20 and thermal blocks 24, 25 is important in determining the fuse rating. Thermal blocks 24, 25 serve as a heat sink for fuse link 20 absorbing the heat which is generated by the clips 30, 31 on one side and the fuse link 20 on the other side. The thermal blocks 24, 25 absorb heat from clips 30, 31 and from link 20 on both sides. The function of the thermal blocks 24, 25 is to provide a delay between the initiation of the generation of heat and the melting of fuse link 20 at weak spot 36. As heat is generated, heat is transferred to the thermal blocks 24, 25 which act as heat absorbers. Upon the continued generation of heat, the temperature of the entire assembly is raised until the melting temperature of the material of fuse link 20 is reached at weak spot 36. In other words, the assembly continues to absorb heat until the temperature of fuse link 20 at weak spot 36 is raised to the melting point of link 20 and link 20 opens the circuit by breaking at weak spot 36. Thus, the heat sink characteristics of thermal blocks 24, 25 enable the fuse 10 to operate with a time delay and prevent the fuse link 20 from opening during short duration, overcurrent conditions. Referring now to Figures 5 and 6, there is shown an alternative embodiment of the present invention. The alternative female fuse is referred to in general by reference numeral 50. Female fuse 50 includes an element assembly 60 and a housing 70. The element assembly 60 includes a pair of female fuse clips 62, 64, thermal blocks 66, 68, and fuse link 80. Fuse link 80 and thermal blocks 66, 68 are injection molded as a one piece unit, as hereinafter described in further detail. Fuse clips 62, 64 are encapsulated into each thermal block 66, 68, respectively, during the molding process. Fuse link 80 includes a weak spot 82. As distinguished from the fuse link 20 shown in the embodiment of Figures 1-4, fuse link 80 extends in an axial direction away from fuse clips 62, 64. Although this extends the longitudinal length of housing 70, it also locates fuse link 80 further away from the heat generated by clips 62, 64. By projecting fuse link 80 away from fuse clips 62, 64, the life of fuse link 80 is extended. The housing 70 includes a pair of slots 84, 86 for receiving the blades from a bus bar. The end walls 88, 90 of housing 70 include longitudinal slots 92, 94 for receiving projecting ears 96, 98 on clips 62, 64. The lower end of housing 70 is open at 100. The element assemblies 28, 60 may be produced by various molding processes which make it easy to manufacture fuses with different ratings. The size and shape of the mold can be changed to change the size of the thermal block or fuse link, and the composition of the metal alloy can be changed. Any of these actions will change the rating of the fuse. The fuse 10 of the present invention is preferably produced using an insert injection molding process. Injection molding is well known in the art of injecting plastic. However, in the present invention the injection molding process is used for the injection of metal at low temperatures. The same type of molds used for producing fuse 10 are used for producing plastic product by injection molding. In the present process, the fuse clip is stamped, placed into the mold cavity and the molten metal for the fuse link and thermal blocks are shot into the mold cavity around the clips. The insert injection molding process includes a gating process when the metal is injected into the cavity of the mold. The gate is an aperture in the mold which allows the molten metal to enter the mold cavity. A cylinder is charged with air and the air pressure forces the metal into the mold cavity. The tolerances tend to be tighter for metal injection molding than for plastic injection molding since liquid metals will flow into smaller dimensions than plastics. The clips 30, 31 are fitted into the mold and project through an aperture in the mold. The mold is kept at a temperature approximately 20°C below the transition temperature of the link alloy. The clips fit closely within the aperture of the mold so that the metal forced into the mold cavity cannot flow through the apertures between the clips and mold. The above described injection process can be modified by making the fuse links separately and not molding the fuse links into the fuse clips 30, 31. For the most part, low melting temperature alloys are relatively malleable and could be put into a cavity and formed in a punch press. They also could be fed into a punch press or could be stamped into shape by a coining type operation. It would then be necessary to affix the fuse clips 30, 31 to the thermal blocks 24, 25. This could be done by heating the fuse clip and forcing it into thermal blocks 24, 25 allowing the metal of the thermal blocks to flow around it. The fuse clip must not be kept at an elevated temperature for too long a period since this would cause the clip to anneal. One disadvantage to this modified injection process is that it requires the secondary operation of affixing the fuse clips to the thermal blocks. Another technique for producing fuse 10 is that of compression molding. This technique is also used in the plastic industry. In producing the fuse 10 using a compression molding process, the clips 30, 31 are inserted into the compression mold and then the metal is placed into the cavity of the mold. The mold and thus the cavity is then closed forcing any excess metal out of the cavity. One draw back to this process is that the clip does not have an adequate opportunity to bond with the metal as the metal is merely pressed around the clip. Another technique for producing fuse 10 is investment casting. To avoid an extended cooling down period for the mold, which would be a very slow process, one part of the mold is heated and the other part of the mold is cooled. The liquid eutectic metal is then poured into the mold with the clips 30, 31 already in position. The mold is then closed. Heat is then removed from that portion of the mold holding the liquid metal allowing the liquid metal to cool and solidify. One draw back to this process is that the clip in the cooled portion of the mold does not have an adequate opportunity to bond with the metal. One side of the mold is at a temperature above the liquid temperature of the metal and the other side of the mold is at the liquid temperature of the metal. Another process for producing fuse 10 is a transfer insert pressing process. The transfer insert pressing process is similar to that of the injection molding process. The clips 30, 31 are inserted into the mold and the mold is closed. The upper portion of the mold includes an aperture. The liquid metal is placed in the cavity and a ram is pushed into the aperture to force the metal into the mold cavity. This is a typical process used for thermoset type plastics, epoxies and phenols. The transfer insert pressing process is preferred when the metal is relatively thick and viscous. The injection process merely uses a screw which is rotated to force the metal through the gate. In the transfer insert pressing process, a much larger force may be applied to the ram and thus the metal, to force the metal into the mold cavity. The mold of the transfer insert pressing process can also be kept at a temperature below the transition temperature of the metal . One of the draw backs of the transfer pressing process is that upon forcing the molten metal into the mold cavity, the mold is cold causing the metal to tend to set up and solidify before it interacts with the clips 30, 31. Another process for producing the fuse 10 is a sintered powdered metal process. The sintered powdered metal process has the advantage in that the products produced in the mold are very near their final shape. This process includes placing a metal powder into the mold cavity and closing the mold under pressure. Compatible metals are required to be used for the sintered powdered metal process. Wax binders may be added to the metal powder to hold the metal powder together upon closing and pressing the mold. The wax binders can then be burned off by placing the fuse in an oven and heating it to just below the melting temperature of the metal . More pressure may then be applied to the fuse to make it near its final shape. Typically, the fuse would have some flash around its outside edges. However, the contours would be very close to its final shape. A certain surface finish will be required because the surface has imperfections caused by the application of pressure. In the sintered powdered metal process, there is a three piece mold. Two halves of the mold are disposed around the clips 30, 31 and with the mold open at the top. The ends of the clips 30, 31 project up inside the mold cavity. The metal powder for the thermal blocks 24, 25 would be inserted in the mold cavity first and tamped into place. The powered metal is then placed into the mold cavity and a tamping tool is used to cause the powdered metal to fill the lower portion of the mold cavity. The tamping tool is typically a piston on the end of a hydraulic ram which is used to apply pressure to the powdered metal in the mold cavity. Additional powered metal is then added to -li¬ the mold cavity and tamped again until the mold cavity is completely filled. The third piece of the mold is then used to close the mold. The third piece of the mold has a movable part in the middle which can be used to apply pressure to the powdered metal while it is in the oven. In using a mix of metals, one preferred embodiment would include thermal blocks of copper and fuse links of one of the tin-alloys. The heat processing of copper powdered metal and a tin-alloy powdered metal is complex because the tin-alloy tends to melt at a much lower temperature than the copper and thus the tin-alloy tends to diffuse into the copper powder. One of the advantages of the powdered metal process is that different metal powders may be mixed together to form the fuse link 20 and thermal blocks 24, 25. This will allow the fuse link 20 to be made of one metal and the thermal blocks 24, 25 to be made of another metal with the thermal blocks 24, 25 being made of a metal having a very high heat capacity. The metals are joined because of the pressure on the mold. This process, however, would not be inexpensive. While a preferred embodiment of the invention has been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit of the invention.

Claims: CLAIMS l. A fuse, comprising: a fuse link; first and second thermal blocks supporting opposite ends of said fuse link; and a fuse clip connected to each thermal block. 2. The fuse of claim 1, further comprising a housing covering said fuse link, thermal blocks, and fuse clips. 3. The fuse of claim 2, wherein said fuse clips are female fuse clips. 4. The fuse of claim 1, wherein the fuse link and thermal blocks are made from low temperature melting metals. 5. The fuse of claim 1, wherein the fuse link and thermal blocks are made from a metal selected from the group comprising tin-silver, tin-phosphorus, and tin-antimony. 6. The fuse of claim 5, wherein the fuse clips are made from a copper alloy. 7. The fuse of claim 2, wherein the housing includes internal grooves that retain said fuse clips. 8. A female fuse comprising: a fuse link; a first thermal block and a second thermal block connected to said fuse link; a first female fuse clip and a second female fuse clip connected respectively to said first and second thermal blocks, said fuse clips are insert molded into said thermal blocks, and said fuse link and said thermal blocks are injection molded as a one piece unit, said fuse clips, thermal blocks, and fuse link comprise a fuse assembly; and a housing enclosing said fuse assembly. 9. A fuse as in claim 8, wherein said fuse clip is a multifinger fuse clip. 10. A fuse as in claim 8, wherein said fuse link and said thermal blocks are injection molded from alloys having a temperature transition lower than 300 degrees C. 11. A female fuse comprising: a fuse link; a first thermal block and a second thermal block connected to said fuse link; a first female fuse clip and a second female fuse clip connected respectively to said first and second thermal blocks, wherein said fuse clips are insert molded into said thermal blocks, and wherein said fuse link and said thermal blocks are injection molded as a one piece unit, said fuse clips, thermal blocks, and fuse link comprise a fuse assembly; and a housing, enclosing said fuse assembly. 12. A fuse as in claim 11, wherein said fuse clip is a multifinger fuse clip. 13. A fuse as in claim 11, wherein said fuse link and said thermal blocks are injection molded from alloys having a temperature transition lower than 300 degrees C. 14. A fuse as in claim 11, wherein said fuse assembly is held in said housing by ears formed on said fuse clips during stamping that interlock into grooves formed in said housing. 15. A female fuse comprising: a fuse link; a first thermal block and a second thermal block connected to said fuse link; a first female fuse clip and a second female fuse clip connected respectively to said first and second thermal blocks, wherein said fuse clips are electrically connected to said thermal blocks, and wherein said fuse link and said thermal blocks are injection molded as a one piece unit, said fuse clips, thermal blocks, and fuse link comprise a fuse assembly; and a housing, enclosing said fuse assembly. 16. A fuse for an electrical circuit comprising: a fusible element adapted for connection in the circuit; a conductive member adapted for connection in the circuit; a thermal block electrically disposed between said fusible element and conductive member to serve as a heat sink for said fusible element. 17. The fuse of claim 16, wherein said thermal block has heat sink characteristics which enable the fuse to operate with a time delay. 18. The fuse of claim 16, wherein said thermal block prevents said fusible element from opening during over-current conditions of a short duration in the circuit. 19. The fuse of claim 16, wherein said thermal block is made of a metal with a transition temperature of less than 300 degrees centigrade. 20. The fuse of claim 16, wherein said fusible element, conductive member and thermal block are housed within an insulating housing. 21. A fuse comprising: first and second conductive members; a fuse link having one end electrically connected to a first thermal block and a second end electrically connected to a second thermal block; said first and second conductive members electrically connected to said first and second thermal blocks, respectively; and said first and second thermal blocks serving as a heat absorber. 22. The fuse of claim 21, further including an insulating housing around said conductive members, fuse link and thermal blocks. 23. The fuse of claim 22, wherein said housing includes a chamber for receiving said conductive members, fuse link and thermal blocks. 24. A method of producing a link for a fuse comprising the steps of: providing a mold cavity including the shape of a link with a thermal mass; placing fuse clips into the mold cavity; and injecting molten metal into the mold cavity. 25. The method of claim 24, further including the step of maintaining the mold at a temperature below the transition temperature of the metal. 26. The method of claim 24, further including the step of ramming the molten metal into the mold cavity. 27. A method of producing a link for a fuse comprising the steps of: producing a fuse link; providing a mold cavity including the shape of a thermal mass; injecting molten metal into the mold cavity; and pressing the fuse link into the molten metal in the mold cavity. 28. A method of producing a link for a fuse comprising the steps of : providing a mold cavity having the shape of a link with a thermal mass; " placing a fuse clip into the mold cavity; ' providing molten metal into the mold cavity; and closing the mold to force any excess molten metal from the mold cavity. 29. The method of claim 28, further including the steps of heating one side of the mold having a first fuse clip and cooling another side of the mold having a second fuse clip. 30. A method of producing a link for a fuse comprising the steps of : providing a mold cavity having the shape of a link with a thermal mass; placing a first metal powder with binder into that portion of the mold cavity for the thermal blocks; placing a second metal powder with binder into that portion of the mold cavity for the link; and closing the mold under pressure. 31. The method of claim 30, further including the step of burning off the binders. 32. The method of claim 30, wherein said first and second metals are copper and a lead-alloy, respectively. 33. The method of claim 30, further including the step mping the first and second metals into the mold cavity.

Inventors: EVANS TERENCE JOHN, EVANS, TERENCE, JOHN
Applicants: COOPER IND INC, COOPER INDUSTRIES, INC.
Application year: 1996
Main classification: H01H69
IPC codes: B22D19, B22F7, H01H69, H01H85