Junction box with over-current protection

Details Junction box with over-current protection Junction box with over-current protection

1999-05-20

2001-06-19

Ballato, Josie (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

C361S103000, C361S115000

Reexamination Certificate

active

06249412

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates to the field of over-current protection devices, and particularly the field of resettable fuses. More specifically, the invention relates to resettable fuse devices that are fabricated from a conductive polymer material with a positive temperature coefficient (PTC). In a specific embodiment, the present invention relates to a junction box, for a cable harness or the like, that incorporates an array of conductive polymer PTC devices for over-current protection.
The use of conductive polymer PTC devices for over-current protection and for other applications has become well-known in the art. See, for example, U.S. Pat. No. 5,802,709 and the references cited therein. A particular form of conductive polymer PTC device that has achieved widespread use is the type fabricated from a layer of conductive polymer PTC material laminated between a pair of metal foil layers that are formed into electrodes. Devices of this type, and a method of fabricating them, are disclosed in U.S. Pat. No. 5,802,709, the disclosure of which is expressly incorporated herein by reference.
The use of resettable over-current protection devices is desired in certain applications, for example, cable harness junction boxes for motor vehicles. Where over-current protection is provided by standard fuses, the cable harness must be routed so that the junction box is accessible to replace blown fuses. Resettable over-current protection devices, by contrast, do not need to be accessible; hence, the location of the junction box is less important, and the cable harness can be routed more efficiently. Consequently, PTC over-current protection devices, especially devices made of a conductive polymer PTC material, have become more common in cable harness junction boxes.
Heretofore, those cable harness junction boxes that employ PTC conductive polymer devices for over-current protection have used a plurality of discrete devices. While such junction boxes have, for the most part, achieved satisfactory performance objectives, there has been a continuing need to reduce manufacturing costs below the costs associated with discrete devices.
SUMMARY OF THE INVENTION
Broadly, the present invention is an over-current protection device, specifically an over-current protection junction box, comprising a grid or array of conductive polymer PTC components, wherein the array is formed by (1) laminating a layer of conductive polymer PTC material between first and second layers of metal foil, and (2) dividing the laminate into an array of discrete conductive polymer PTC components, all sharing a common ground electrode formed by the lower foil layer. The step of dividing the laminate is preferably performed by masking the first foil layer to expose a grid pattern on the surface of the first foil sheet, and then etching through the first foil layer to form an array of discrete positive electrodes, separated by a grid of exposed polymer material, each of which defines a single conductive polymer PTC device. Optionally, the exposed polymer material can also be removed, by conventional methods, to define a grid of channels separating the discrete positive electrodes to define the individual devices. Each discrete positive electrode is contacted by a conductive spring contact finger. Two or more contact fingers can be arranged to connect two or more devices in parallel, to provide a higher trip current than is provided by a single device. Thus, for example, each single, discrete device may have a trip current of a basic value, so that trip currents in multiples of the basic value can be provided by multiple devices connected in parallel by suitably-arranged spring contact fingers. Thus, the same array of conductive polymer PTC devices can be used with different spring contact arrangements when different mixes of current ratings are desired.
As will be better appreciated from the detailed description that follows, the present invention provides a junction box with over-current protection that can be easily and economically manufactured, and that is conveniently used with cable harnesses and the like. Moreover, each such device in accordance with the present invention can accommodate a wide variety of wiring configurations and mixes of current ratings. These and other advantages of the present invention will be more easily understood from the detailed description that follows.


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