Patent Publication Number: US-7595715-B2

Title: High power case fuse

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates in general to fuses, and in particular to high power case fuses. 
     2. Background of Related Art 
     High power distribution box fuse assemblies used in vehicles commonly include a nonconductive housing encasing a conductive set of female terminals (i.e., fuse body). The set of female terminals are joined by a fuse element disposed therebetween. The female terminals are inserted over a set of male blade terminals extending from the power distribution box for completing an electrical circuit. The female terminals are typically designed with a spring-type feature to maintain a strong electrical contact with the male terminal blades. If the current draw of the electrical circuit increases above a predetermined current threshold, the fuse element will open thereby terminating current flow across the respective set of female terminals. 
     Copper which is has good electrical conductivity properties is preferably used to produce the fuse body; however, copper is susceptible to relaxation as temperature increases. That is, as the current drawn in the electrical circuit increases, so does the temperature. In response to the temperature increase, copper has a tendency to relax. As a result, the clamping portion of the fuse body for maintaining a tight connection with the male terminal blades (e.g., the spring-type future of the female terminals) relaxes thereby decreasing the overall contact area which reduces electrical conductivity (i.e., increases resistance). 
     Since the fuse body is encased within the housing, the thickness of the female terminals (i.e., the springs) is limited to a predetermined size due to packaging constraints. As a result, the footprint of the fuse body is limited such that additional material is prevented from being added to strengthen the spring-like features for maintaining contact with the male terminal blades. As a result, copper alloy having lower conductivity properties is typically substituted for the copper-based material having higher conductivity properties to produce the fuse body. The relaxation properties for copper alloy having low conductivity properties occur at much higher temperatures as compared to copper. Therefore, a desired contact area between the female terminals and the male terminal blades can be maintained at elevated temperatures using the copper alloy in comparison to copper-based material having higher conductivity properties. The disadvantage is that the copper alloy has lower conductivity properties in comparison to copper-based material. As a result, the fuse assembly, given the perspective footprint, are limited to 60 amps or less. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has the advantage of providing a high power fuse assembly that maintains a predetermined normal force on a respective set of female terminals that resists relaxation such that a respective contact area is maintained at elevated temperatures using a separate spring/clamp-like member. The clamp-like member is produced from a material having high mechanical stress properties such as stainless steel. That is, the clamp-like member has greater mechanical stress properties at elevated temperatures in comparison to the material of the female terminals of the fuse. Utilizing a material with good stress relaxation properties at elevated temperatures for the clamp-like member allows for the use of high conductive materials for the female terminals. This assists in maintaining the respective contact area at elevated temperatures and allows more current to be carried through the fuse while maintaining a respective footprint of the fuse assembly within a plastic housing. 
     In one aspect of the present invention, a high power fuse includes a fuse body having a first terminal receptor including a first set of terminal legs and a second terminal receptor in spaced relation to the first terminal receptor. The second terminal receptor includes a second set of terminal legs. A fuse element is disposed between the first terminal receptor and the second terminal receptor. A first clamp-like member is mounted to the fuse body for applying a predetermined compression force against the first set of terminal legs and is configured to secure a first male terminal between the first set of terminal legs. A second clamp-like member is mounted to the fuse body for applying a predetermined compression force against the second set of terminal legs and is configured to secure a second male terminal between the second set of terminal legs. 
     In yet another aspect of the present invention, a high power fuse assembly is provided that includes a plastic housing and a fuse body housed in the plastic housing. The fuse body includes a first terminal receptor having a first set of terminal legs and a second terminal receptor having a second set of terminal legs. A fuse element is integrally formed to the first terminal receptor and the second terminal receptor. A first clamp-like member is disposed within the first terminal receptor. The first clamp-like member applies a compression force against the first set of terminal legs that is configured to secure a first male terminal within the first set of terminal legs. A second clamp-like member is disposed within the second terminal receptor. The second clamp-like member applies a compression force against the second set of terminal legs that is configured to secure a second male terminal within the first set of terminal legs. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fuse according to a first preferred embodiment of the present invention. 
         FIG. 2  is a perspective view of a fuse housing according to a first preferred embodiment of the present invention. 
         FIG. 3  is a perspective view of a fuse assembly according to a first preferred embodiment of the present invention. 
         FIG. 4  is a perspective view of the fuse body according to a first preferred embodiment of the present invention. 
         FIG. 5  is a perspective view of a clamp-like member according to a first preferred embodiment of the present invention. 
         FIG. 6  is a perspective view of a fuse assembly according to a second preferred embodiment of the present invention. 
         FIG. 7  is a perspective view of a fuse housing according to a third preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  a high power fuse shown generally at  10 . The high power fuse  10  includes a housing  12  and a fuse assembly  14  disposed within the housing  12 . The housing  12  includes a first slot  16  for receiving a first terminal blade (not shown) and a second slot  18  for receiving a second terminal blade (not shown). 
       FIG. 2  illustrates a perspective view of the housing  12 . The housing  12  is preferably produced from two sections that include a body portion  20  and a lid portion  22 . The body portion  20  is an elongated chamber that includes an open end  24  and a closed end  26 . The open end  24  is of a sufficient width and length for receiving and housing the fuse assembly  14  (shown in  FIG. 3 ) within the housing  12 . The first slot  16  and the second slot  18  are formed in the closed end  26 . The slots are aligned with respective receiving members for making an electrical connection with a respective terminal blade (shown generally at  28 ). 
     The lid portion  22  attaches to the open end  24  for enclosing the fuse assembly  14  therein. The housing  12  isolates a person or other object from contacting with the fuse assembly  14  within the housing  12  which may otherwise result in an electrical shock to a person contacting the exposed fuse or a short circuit. The body portion  20  includes ventilation slots  29  formed near the closed end  26  of the body portion  20 . As heat is generated by the fuse assembly  14  enclosed within the housing  12 , the ventilation slots  29  formed near the top of the body portion  20  provide ventilation (e.g., a chimney effect) for dissipating the heat generated by the fuse assembly  14 . 
       FIG. 3  illustrates the fuse assembly  14 . The fuse assembly  14  includes a fuse body  30 , a first clamp-like member  32 , and a second claim-like member  34 . The fuse body  30  is preferably made from a single piece of stamped metal such as copper. The fuse body  30  includes a fuse element  35 , a first terminal receptor  36 , for receiving a respective male terminal blade (not shown), and a second terminal receptor  38  for receiving respective male terminal blade (not shown). The fuse element  35  is integrally formed between the first terminal receptor  36  and the second terminal receptor  38 . The fuse element  35  is produced from the same material as the first terminal receptor  36  and the second terminal receptor  38 . In addition, fuse element  35  is plated with a second material, such as tin, that when heated, diffuses into the copper which lowers the melting point of the copper. At a predetermined current draw (i.e., predetermined temperature), the tin begins to diffuse into the copper and the diffused portion of the copper begins to melt thereby creating an open circuit within the fuse element  35  for terminating current flow between the first terminal receptor  36  and the second terminal receptor  38 . 
       FIG. 4  illustrates a fuse body  30  less the respective clamp-like members. The first terminal receptor  36  includes a body portion  41  having a first set of terminal legs  37  extending from the body portion  41 . The body portion  41  is preferably a non-resilient section that conductively couples the fuse element  35  to the first set of terminal legs  37 . The first set of terminal legs  37  includes a first leg  40  and a second leg  42  opposing one another. The first set of terminal legs  37  further includes a third leg  44  and a fourth leg  46  opposing one another and are also positioned adjacent to the first leg  40  and the second leg  42 , respectively. The first leg  42  and the third leg  44  are in spaced relation to one another having a respective space  43  therebetween. The second leg  42  and the fourth leg  46  are in spaced relation to one another having a respective space  45  therebetween. Each of the respective legs are resilient for maintaining a compression force on a respective terminal blade received between the first and second legs  40  and  42  and the second and third legs  44  and  46 . 
     The second terminal receptor  38  includes a body portion  49  having a second set of terminals legs  39  extending from the body portion  49 . The second set of terminal legs  39  includes a first leg  50  and a second leg  52  opposing one another. The second set of terminal legs  38  further includes a third leg  54  and a fourth leg  56  opposing one another and are positioned adjacent to the first leg  50  and the second leg  52 . The first leg  50  and the third leg  54  are in spaced relation to one another having a respective space  53  therebetween. The second leg  52  and the fourth leg  56  are in spaced relation to one another having a respective space  55  therebetween. Each of the respective legs are resilient for maintaining a compression force on a respective terminal blade received between the first and second legs  50  and  52  and the second and third legs  54  and  56 . 
     Referring again to  FIG. 3 , the first clamp-like member  32  is assembled to the fuse body  30  for applying a predetermined compression force against the first set of terminal legs  36 . The first clamp-like member  32  is mounted to the first terminal receptor  36  centrally located between the first set of terminal legs  37  within the respective spaces  43  and  45 . The first clamp-like member  32  is configured to secure a respective terminal blade between the first set of terminal legs  36  for maintaining a respective contact area during elevated temperatures. 
       FIG. 5  illustrates the clamp-like members  32  and  34 . The first clamp-like member  32  is a substantially U-shaped body having a first end portion  60  and a second end portion  62 . The first end portion  60  and the second end portion  62  are arc-shaped. The first end portion  60  and the second end portion  62  extend toward one another as the respective legs of the U-shaped body extend away from the curved end adjoining the respective legs. 
     Referring again to  FIG. 3 , when the first clamp-like member  32  is mounted to the first set of terminal legs  37 , the first end portion  60  contacts an exterior section of the first leg member  40  and third leg member  44 . In addition, the second end portion  62  of the first clamp-like member  32  contacts an exterior section of the second leg member  42  and the fourth leg member  46  thereby holding the first and third leg members  40  and  44  in compression with second and fourth leg members  42  and  46 , respectively. The first leg member  40  and the third leg member  44  have respective end sections for nesting the first end portion  60  of the first clamp-like member  32  for preventing sliding movement between the first and third leg members  40  and  44  and the first end portion  60 . This provides a seating engagement between first and third leg members  40  and  44  and the first end portion  60 . Similarly, the second leg member  42  and the fourth leg member  46  have respective end sections for nesting the second end portion  62  of the second clamp-like member  34  for preventing sliding movement between the second and fourth leg members  42  and  46  and the second end portion. This provides a seating engagement between second and fourth leg members  42  and  46  and the second end portion  62 . 
     The first clamp-like member  32  is made of stainless steel which has low relaxation properties at elevated temperatures. As a result, the first clamp-like member  32  prevents the respective terminal legs from relaxing at elevated temperatures for preventing the reduction of the contact area with an associated blade terminal. As a result, the need for utilizing a copper alloy or similar substitute of material with lesser conductive properties is not necessary since relaxation has been minimized. Therefore a higher conductive material, such as copper (C151), for forming the fuse body  30  may be used in cooperation with the first clamp-like member  32 . 
     Similarly, the second clamp-like member  34  is mounted on the fuse body  30  for applying a predetermined compression force against the second set of terminal legs  38 . The second clamp-like member  34  is configured to secure a respective terminal blade between the first set of terminal legs  38  for maintaining a respective contact area during elevated temperature increases. The second clamp-like member  34  is mounted to the second terminal receptor  38  centrally located between the second set of terminal legs  38  within the respective spaces  43  and  45 . 
     A first end portion of the second clamp-like member  34  contacts an exterior portion of the first leg member  50  and third leg member  54 . In addition, a second end portion of the second clamp-like member  34  contacts an exterior portion of the second leg member  52  and fourth leg member  56  thereby holding the first and third leg member  50  and  54  in compression with second and fourth leg member  52  and  56 , respectively. 
     The first leg member  50  and the third leg member  54  have respective end sections for nesting the first end portion of the second clamp-like member  34  for preventing sliding movement between the first and third leg members  50  and  54  and the first end portion. This provides a seating engagement between first and third leg members  50  and  54  and the first end portion of the second clamp-like member  34 . Similarly, the second leg member  52  and the fourth leg member  56  have respective end sections for nesting the second end portion of the second clamp-like member  34  for preventing sliding movement between the second and fourth leg members  52  and  56  and the second end portion. This provides a seating engagement between second and fourth leg members  52  and  56  and the second end portion of the second clamp-like member  34 . 
     The second clamp-like member  34  is made of stainless steel which has low relaxation properties at elevated temperatures. As a result, the second clamp-like member  34  prevents the respective terminal legs from relaxing which could otherwise reduce the contact area with an associated blade terminal. Alternatively, the first and second clamp-like members  32  and  34  may be made of a material other than stainless steel so long as material has less relaxation at elevated temperatures in comparison to the material forming the fuse body  30 . 
     The contact area of the electrical coupling of the respective leg members and the respective blade terminals is maintained during elevated temperatures as a result of the normal force applied by the first and second clamp-like member. This results in increased resistance between the mating terminals which further results in increased conductivity at the respective electrical coupling. As described earlier, high power fuses are typically limited to 60 amps maximum due conductive properties of the copper alloy which is used to prevent relaxation at elevated temperatures. The use of the clamp-like members as described in the present invention allows the fuse body to be made of a copper-based material having higher conductive properties than copper alloy which provide for increased current rating usage at elevated temperatures. For example, a respective fuse body made from substantially 0.4 mm of copper stock for a respective footprint could handle up to 80 amps. A respective fuse body made from substantially 0.6 mm of copper stock fitting using the same respective footprint could handle up to 100 amps. 
       FIG. 6  illustrates a high power fuse assembly according to a second preferred embodiment. The fuse assembly  70  includes a plurality of heat sinks  72  for dissipating heat within the fuse body  30 . The plurality of heat sinks  72  includes a plurality of fins integrally formed as part of the respective leg members of the fuse body  30 . The plurality of fins is positioned so as to allow air to pass over the plurality of fins thereby dissipating heat from the fuse body  30 . 
       FIG. 7  illustrates a housing  12  according to a third preferred embodiment. The housing  12  may be made of a plastic polymer that is thermally conductive. A plurality of cooling fins  76  may be formed an the exterior surface of the housing  12  such that heat thermally conducted through the plastic material is dissipated by the air as it flows over plurality of cooling fins  76 . 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.