Abstract:
An arc suppressor fixable to a fusible element to suppress electrical arcs and prevent the spread of electric arc “burn-back.” The arc suppressor includes first and second inner members comprised of pre-cured silicone rubber, and first and second outer members comprised of an arc suppressing material (e.g., melamine). The inner and outer members form a sandwich around a portion of the fusible element, wherein the first inner member is located adjacent to a first surface of the fusible element and the second inner member is located adjacent to an opposing second surface of the fusible element. The first outer member is located adjacent to the first inner member and the second outer member is located adjacent to the second inner member. Mechanical fasteners tightly engage together the first and second inner members, the fusible element, and the first and second outer members.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of arc suppression, and more particularly to an arc suppressor for use with a fusible element. 
     BACKGROUND OF THE INVENTION 
     It is well known to use fuses in electrical circuits to interrupt the flow of current when there is an overcurrent (i.e., overload current or short circuit) or overload event. Fuses typically include one or more fusible elements (also known as “fusible links”) electrically connected to two end conductors or terminals located at opposite ends of the fuse. 
     Under normal operation, when the fuse is operating at or near its amp rating, it functions as a conductor. However, if a short circuit or overload condition occurs and persists for more than a short interval of time, the temperature of the fusible element eventually reaches a level that causes a high resistance segment of the fusible element to melt. As a result, a gap is formed and an electric arc established. However, as the arc causes the fusible element to “burn back,” the gap becomes progressively larger. Electrical resistance of the arc eventually reaches such a high level that the arc cannot be sustained and is extinguished. The fuse will have then completely cut off all current flow in the circuit. If arc suppression is inadequate, under some fault current conditions, a fuse may not safely clear an overcurrent or overload event, thereby resulting in damage to circuit components. 
     One material with arc suppressing characteristics is silicone rubber. Silicone rubber is an elastomer composed of silicone containing silicon together with carbon, hydrogen, and oxygen. Silicone rubber is generally non-reactive, stable, and resistant to extreme environments and temperatures from −55° C. to +300° C. while still maintaining its useful properties. One common type of silicone rubber for use in arc suppression applications is room temperature vulcanizing (RTV) silicone. 
     Silicone arc suppressors have been formed by applying a free flowing (at room temperature) silicone rubber sealant to a fusible element. This free flowing silicone rubber sealant is then air cured to increase its viscosity such that it hardens into a solid-like state and conforms to the shape of the fusible element. 
     One disadvantage to such silicone rubber arc suppressors is that there can be inconsistency in the silicone rubber sealant. In this regard, due to ambient air conditions (e.g., humidity), the cure time of a free flowing silicone rubber sealant is increased, potentially causing the silicone rubber to not fully cure. As a result, the silicone rubber arc suppressor may not function as intended during operation of the fuse, thereby causing unpredictable results during an overcurrent or overload event. 
     Another disadvantage of existing silicone rubber arc suppressors is that cure time for the silicone rubber slows the speed at which a fuse can be manufactured, thereby increasing production costs. 
     The present invention provides an arc suppressor that overcomes these and other problems associated with existing silicone rubber arc suppressors. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a fuse comprising: (1) a fusible element made of a conductive metal having opposing first and second surfaces, said fusible element including (a) an intermediate portion having at least one region of high resistance, and (b) first and second end portions located at opposite sides of the intermediate portion; and (2) at least one arc suppressor fixed to the fusible element. Each arc suppressor comprises: (i) first and second inner members comprised of pre-cured silicone rubber; (ii) first and second outer members comprised of an arc quenching material, wherein said first inner member is located adjacent to the first surface of the fusible element and the second inner member is located adjacent to the second surface of the fusible element, and said first outer member is located adjacent to the first inner member and the second outer member is located adjacent to the second inner member; and (iii) one or more fasteners for fixing the first and second inner members and the first and second outer members to the fusible element. 
     In accordance with another aspect of the present invention, there is provided an arc suppressor fixable to a fusible element, the arc suppressor comprising: (i) first and second inner members comprised of pre-cured silicone rubber; (ii) first and second outer members comprised of an arc quenching material, wherein said first inner member is located adjacent to a first surface of the fusible element and the second inner member is located adjacent to an opposing second surface of the fusible element, and said first outer member is located adjacent to the first inner member and the second outer member is located adjacent to the second inner member; and (iii) one or more fasteners for fixing the first and second inner members and first and second outer members to the fusible element. 
     An advantage of the present invention is the provision of an arc suppressor that can be manufactured more quickly than existing arc suppressors, thereby increasing production throughput. 
     Another advantage of the present invention is the provision of an arc suppressor that uses mechanical fastening means to fix the arc suppressor to a fusible element. 
     Yet another advantage of the present invention is the provision of an arc suppressor that can be applied to a wide variety of DC and AC applications where excessive electric arc “burn-back” is experienced. 
     These and other advantages will become apparent from the following description of illustrated embodiments taken together with the accompanying drawings and the appended claims 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
         FIG. 1  is a top plan view of a fuse including a fusible element and a plurality of arc suppressors according to an embodiment of the present invention; 
         FIG. 2  is a side plan view of the fuse shown in  FIG. 1 ; 
         FIG. 3  is an exploded view of the arc suppressor, according to the present invention, and a portion of the fusible element; and 
         FIG. 4  is a cross-sectional portion of the arc suppressor according to the present invention, as attached to the fusible element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for the purposes of illustrating an embodiment of the invention only and not for the purposes of limiting same,  FIGS. 1 and 2  show a fuse  10  comprised of a fusible element  30  and a pair of arc suppressors  60 , according to an embodiment of the present invention. 
     Fusible element  30  is made of a conductive metal having opposing first and second surfaces  52 ,  54 . The conductive metal may include, but is not limited to, silver, gold, copper, aluminum, and the like. Fusible element  30  is comprised of an intermediate portion  32 , having at least one high resistance region  34 , and lateral first and second end portions  42 ,  44  located at opposite sides of intermediate portion  32 . 
     High resistance regions  34  provide intermediate portion  32  with a higher resistance than first and second end portions  42 ,  44 . Each high resistance region  34  has a reduced cross-sectional area that can be created by use of, for example, notches, perforations, and the like. In the illustrated embodiment, circular openings (i.e., punch holes) form perforations in intermediate portion  32 . As a result of the reduced cross-section area, there is a significant likelihood of fuse  10  “blowing” in intermediate portion  32 . This is desirable, since any arc formed in intermediate portion  32  must then travel the longest possible distance before reaching the distal ends of fusible element  30 . 
     First and second end portions  42 ,  44  may be electrically connected to respective end conductors, terminals or end caps (not shown). It should be appreciated that first and second end portions  42 ,  44  may also include one or more high resistance regions  34 , such as illustrated in  FIG. 3 . Moreover, a conventional housing (not shown) may surround the fusible element  30 . 
     It should be understood that the geometric configuration of fusible element  30  shown in  FIGS. 1-2  is for illustrating an embodiment of the present invention, and not for limiting same. In this regard, it is contemplated that fusible element  30  may have alternative geometries. 
     In one example embodiment of the present invention, fusible element  30  has a width in the range of 0.4-0.7 inches, a length in the range of 2.5-2.9 inches, and a thickness of 0.006 - 0.007 inch. However, it should be appreciated that the dimensions of fusible element  30  may vary significantly from the foregoing dimensions depending upon the application, size of the fuse housing, required ampere rating of the fuse, and the like. 
     In the illustrated embodiment a first arc suppressor  60  is fixed to fusible element  30  at first end portion  42  and a second arc suppressor  60  is fixed to fusible element  30  at second end portion  44 . Accordingly, first and second arc suppressors  60  are provided at opposite sides of high resistance regions  34  of intermediate portion  32  so as to contain any electric arc “burn back.” However, it is contemplated that in alternative embodiments one or more arc suppressors  60  may be fixed anywhere axially on fusible element  30  including a location at, or proximate to, a high resistance region  34  of first and second end portions  42 ,  44  and intermediate portion  32 . 
     As best seen in  FIG. 3 , each arc suppressor  60  includes first and second inner members  62 ,  64  comprised of silicone rubber, and first and second outer members  72 ,  74  comprised of melamine. In accordance with an embodiment of the present invention, first and second inner members  62 ,  64  take the form of a sheet or plate comprised of pre-cured (i.e., hardened) silicone rubber; and first and second outer members  72 ,  74  take the form of a sheet or plate comprised of pre-cured melamine. In the illustrated embodiment, first and second inner members  62 ,  64  and first and second outer members  72 ,  74  are generally planar and rectangular-shaped, with holes h formed therein that are dimensioned to receive a mechanical fastener  80 . 
     One suitable material for first and second inner members  62 ,  64  is a high temperature silicone rubber sheet having a durometer of Shore “A” 70+/−5 (preferred but not limited to Shore “A” 70) and a temperature range of up to  500 ° F. The silicone rubber sheet is pre-fabricated into individual plates, wherein the dimensions of the plates are a function of the width of fusible element  30 . 
     One suitable material for first and second outer members  72 ,  74  is a NEMA grade G9 glass-reinforced melamine plastic laminate sheet. Melamine is a preferred material since it provides rigidity, stability, as well as arc quenching abilities. It is also contemplated that other materials (preferably with arc quenching properties) may be substituted for melamine that provide a similar level of rigidity (e.g., a fiber sheet made of vulcanized fiber and other materials including thermosets, or extruded materials). 
     In the one example embodiment of the present invention, first and second inner members  62 ,  64  and first and second outer members  72 , 74  have a width in the range of 0.8-0.9 inch (preferably 0.84 inch), a length in the range of 0.65-0.75 inch (preferably 0.68 inch) and a thickness in the range of 0.025-0.035 inch (preferably 0.031 inch). However, it should be appreciated that the dimensions of the first and second inner members  62 ,  64  and first and second outer members  72 ,  74  may vary significantly from the foregoing dimensions depending upon the application, since the dimensions of the first and second inner members  62 ,  64  and first and second outer members  72 , 74  are selected to accommodate fusible elements  30  of varying dimensions. 
     When assembled, first inner member  62  is located adjacent to first surface  52  of fusible element  30  and second inner member  64  is located adjacent to second surface  54  of fusible element  30 . Likewise, when assembled, first outer member  72  is located adjacent to first inner member  62  and second outer member  74  is located adjacent to second inner member  64 . 
     While the illustrated embodiment of the present invention shows the first and second inner members  62 ,  64  and first and second outer members  72 ,  74  as planar and rectangular-shaped, it is contemplated that other geometric configurations may also be used. 
     One or more fasteners  80  fix inner members  62 ,  64  and outer members  72 ,  74  to fusible element  30 . Fasteners  80  are used to “sandwich” a section of first end portion  42  and a section of end portion  44  between first and second inner members  62 ,  64 , with first and second outer members  72 ,  74  respectively located adjacent to first and second inner members  62 ,  64 , as best seen in  FIGS. 2 and 4 . 
     In one embodiment, fasteners  80  take the form of brass/bronze eyelets or rivets. However, alternative types of fasteners are also contemplated, such as staples. 
     In the illustrated embodiment, two fasteners  80  are used to fix inner members  62 ,  64  and outer members  72 ,  74  to fusible element  30 . However, it is contemplated that additional fasteners  80  may be used depending upon the dimensions of the inner members  62 ,  64  and outer members  72 ,  74 . 
     The process for assembling arc suppressors  60  according to the illustrated embodiment will now be described in detail. It is contemplated that a conventional riveter press be used to secure eyelets. The riveter press may include both adjustable plates and “hard” stops to accommodate various widths and thicknesses for fusible element  30 . Locating pins are used for placement of the eyelets. 
     First, eyelets are placed onto locating pins and the first outer member  72  is placed over the eyelets by inserting the eyelets through holes h. Next, first inner member  62  is placed over the eyelets by inserting the eyelets through holes h, thereby locating first inner member  62  adjacent to first outer member  72 . Fusible element  30  is then stacked onto the first inner member  62  by inserting the eyelets through holes  38 , thereby locating fusible element  30  adjacent to first inner member  62 . 
     Thereafter, second inner member  64  is placed over the eyelets by inserting the eyelets through holes h, thereby locating second inner member  64  adjacent to fusible element  30 . Next, second outer member  74  is placed over the eyelets by inserting the eyelets through holes h, thereby locating second outer member  74  adjacent to second inner member  64 . 
     The plate of the riveter press is adjusted to accommodate a fusible element  30  of a desired width, and the riveter press is cycled to form rivets that tightly engage together first and second inner members  62 ,  64 , fusible element  30 , and first and second outer members  72 ,  74 , thereby forming a “sandwich” with minimal gaps between adjacent components (see  FIG. 4 ). A typical cycle time for the riveter press is about 4 seconds. 
     The stacked inner and outer members  62 ,  72  and  64 ,  74  create a solid barrier on fusible element  30  that prevents electric arc “burn-back” from traveling beyond the pair of arc suppressors  60 . This allows fusible element  30  to successfully clear a circuit in the event of an overcurrent (i.e., overload current or short circuit) or overload event. 
     It is contemplated that applications for arc suppressor  60  of the present invention include, but are not limited to, photovoltaic applications, traction fuses, Class J fuses, Class L fuses, and special purpose fuses. 
     It is further contemplated that holes  38  in fusible element  30  and holes h in first and second inner and outer members  62 ,  64  and  72 ,  74  may be omitted where fasteners  80  are attached by puncturing members  62 ,  64 ,  72 ,  74  and fusible element  30 . For example, in an embodiment where fasteners  80  take the form of staples, the staples pierce first and second inner members  62 ,  64  and first and second outer members  72 ,  74 . 
     It should be appreciated that the length dimension of first and second inner members  62 ,  64  and first and second outer members  72 ,  74  may be selected such that fasteners  80  are located at distal ends of members  62 ,  64 ,  72 , and  74  “outside” fusible element  30 . In this alternative embodiment, fasteners  80  do not extend through fusible element  30 . 
     According to an alternative embodiment of the present invention, first and second outer members  72 ,  74  take the form of a laminate. In this regard, an arc quenching material comprising first and second outer members  72 ,  74  (e.g., melamine, vulcanized fiber, thermoset, or extruded material) is laminated onto first and second inner members  62 ,  64  before assembly of arc suppressors  60 . In this embodiment first inner member  62  and first outer member  72  form a single unitary component and second inner member  64  and second outer member  74  form a single unitary component, thereby simplifying assembly of arc suppressors  60 . 
     Other modifications and alterations will occur to others upon their reading and understanding of the specification. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.