Patent Application
20090085712
Not Applicable
Not Applicable
Not Applicable
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.
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.
Referring now to the drawings, there is illustrated in
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.
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
Referring again to
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.
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.
