Patent Grant
7121847
1. Field of the Invention
The invention is directed in general toward an automotive power distribution box cover and more specifically to a flame retardant cap for mounting within the cover to fit over a high current connection.
2. Discussion of Related Art
An electrical junction block or power distribution box (PDB) is commonly used in automotive vehicles to streamline electrical system wiring by eliminating multi-branch wiring. The PDB consolidates fuses, branch circuits, relays, connectors and other electrical components in a single location. This is typically done by incorporating a bus bar or similar conductor into a housing. The housing often includes a surface having a plurality of receptacles for receiving the electrical connectors, fuses, relays and other circuit components. The bus bar is routed beneath the surface and has a plurality of blade-like projections that project into some or all of the receptacles to make electrical contact with the components. The bus bar is used to supply electrical power to the components for serving the vehicle electrical circuit requirements. The electrical power is usually provided to the bus bar through a power supply line from the vehicle alternator and/or battery.
As illustrated in U.S. Pat. No. 6,322,376, a high current connection between the vehicle battery and the PDB is often made by connecting power cables through a terminal to a plate section of the bus bar. A stud bolt mounted in a holder on the PDB extends through apertures in the terminal and bus bar plate section. A nut fastens the terminal onto the bus bar plate section. In this type of high current connection, if the terminal is improperly or inadequately connected to the bus bar, electrical arcing can ignite the PDB housing. In the above-identified patent, the stud bolt holder is made with flame-retardant material so it melts rather than ignites in the event of such a condition. Therefore, only the holder needs to be replaced, and the PDB housing is not damaged.
However, power distribution boxes are provided with plastic covers that are also in danger of igniting if the high current connection becomes loose. While wiring device covers are sometimes made of flame-retardant material, for example as disclosed in U.S. Pat. No. 4,541,538, covers for vehicle power distribution boxes have become rather large as the boxes have expanded in size to meet the increased electric circuit requirements of today's vehicles. Flame-retardant material is relatively expensive as compared to the traditional electrically non-conductive plastic material used for the covers. For production of large numbers of PDB covers, the augmented cost of making the entire covers from flame-retardant material becomes quite significant.
Accordingly, it is an object of this invention to provide a fireproof or flame-retardant shield or cap for a high current connection in a power distribution box.
Another object of the invention is to form the shield or cap such that it closely surrounds and isolates a fastener securing a high current connection terminal to a conductor in the power distribution box.
A further object of the invention is to enable the shield or cap to be readily attached to a power distribution box cover so the cover does not have to be made from a flame-retardant material.
In carrying out this invention in the illustrative embodiment thereof, an underside of a power distribution box (PDB) cover is provided with an integral cup-shaped extension in a location that would encompass a high current connection to the PDB when the cover is closed. The extension has an open end distal from the underside of the cover and apertures on sides of the extension adjacent the open end.
A separate shield or cap made from a fire-resistant or flame-retardant material has a closed end, an open end and sides extending between the ends and forming an inner chamber. On outward faces of opposite sides of the cap adjacent the open end of the cap are projections sized to fit within the apertures of the extension. On other opposite sides of the cap are ribs tapering from a maximum height adjacent the open end of the cap to a negligible or zero height at the closed end of the cap.
The closed end of the cap is inserted into the open end of the extension and pushed inward until the projections of the cap snap into the apertures of the extension. The ribs ensure a tight stable fit. When the cover is closed on the PDB, the cap surrounds and isolates the fastener electrically securing the high current connection to the PDB. Because the cap is flame-retardant it will not burn in the event the high current connection is loose or becomes loose and begins to arc. The separate cap eliminates the need for manufacturing the entire cover from the more expensive flame-retardant material.
This invention, together with other objects, features, aspects and advantages thereof, will be more clearly understood from the following description, considered in conjunction with the accompanying drawings.
Referring now to
Immediately adjacent the first end 12 of the PDB at an in-set corner 34 is a recessed section 36 of the upper surface 20. The recessed section 36 is designed to receive a stud bolt holder (not shown) through the bottom 18 of the PDB, and a threaded shank 38 of a stud bolt extending from the holder. The recessed section 36 also accommodates a flat plate portion (hidden in the Figure) integral with a bus bar 39 for electrically connecting and conducting power to the electrical components inserted in the receptacles. The flat plate portion has an aperture through which the shank 38 extends. An electrical terminal 40 fits over and electrically contacts the plate portion, and also has an aperture through which the stud bolt shank 38 extends. The stud bolt holder, stud bolt, bus bar and flat plate portion of the bus bar are illustrated in commonly assigned U.S. Pat. No. 6,322,376, and that patent is incorporated herein by reference. However, this type of connection is depicted as an example only. The present invention can be used with other types of electrical connections and power distribution conductors, such as different-shaped terminals, non-threaded fasteners or reversed-in-position threaded fasteners, and routed wires or circuit traces within the PDB.
The electrical terminal 40 is a high current connection and is illustrated as a right-angle, electrically conductive metal terminal with a first section 42 having crimp tabs 44 and 46 for electrical and physical connection with power supply cables (not shown). A second section 48 of the terminal extends at a right angle from the first section and has an aperture for receiving the stud bolt shank 38. The second section 48 of the terminal fits over the plate portion of the bus bar and is tightened down into secured electrical contact with the plate portion by a nut 50 turned onto the threaded stud bolt shank 38.
The power distribution assembly further includes a one-piece cover 52 for the power distribution box. The cover is molded or otherwise formed from a relatively inexpensive and electrically non-conductive plastic material such as conventional polypropylene with ten percent talc. The cover 52 has a first end 54, a second end 56, two sides 58, a top surface 60 and an underside 62. A hinge cradle 64 and outer catches 66 at the second end of the cover engage and cooperate with the hinge axle on the second end 14 of the PDB 10 to enable the cover 52 to be swung or pivoted between open and closed positions over the PDB upper surface. This allows the cover to provide access to and protect the electrical components received in the receptacles 22 of the PDB upper surface 20. A latch arm 68 on the first end 54 of the cover cooperates with the latch tab 28 on the first end 12 of the PDB to lock the cover in a closed position over the PDB upper surface 20. The cover 52 also includes, at the first end 54, an elongated corner guard 70 for fitting around the in-set corner 34, terminal 40, and part of the perimeter of the recessed section 36 of the PDB.
Referring now to
An integral hollow, cup-shaped extension 74 extends from the underside 62 of the cover 52 adjacent the first end 54. The extension is molded as part of the cover and is positioned such that it would be located over the recessed section 36 of the PDB when the cover is closed on the PDB. The extension 74 has four sides 76 forming an inner rectangular cavity 78 with an insertion end 80. In two opposite sides 76 adjacent the insertion end 80 are rectangular shaped apertures 82.
A shield or cap 84, shown in all the Figures but best illustrated in
The cap 84 is made from a fire-resistant or flame-retardant plastic material. An example of a material suitable for the cap is V0PBT, where V0 is the flame-retardant rating as specified by. Underwriter's Laboratory and PBT stands for polybutadiene terephthalte. Other types of flame retardant material could be used, depending on cost and effectiveness. The purpose of the cap is to prevent the cover 52 of the PDB 10 from igniting in the event of electrical arcing at the high current power connection. Another purpose of the cap is to avoid the necessity, and associated expense, of making the entire cover from flame-retardant material.
As demonstrated in
If the high current connection is inadequately tightened or loosens over time and creates an electric arc, the flame-retardant plastic material of the cap will not burn. By making the cap a separate part mountable within the cover, the PDB top cover does not need to be made of flame-retardant material. This provides a cost savings that can be as high as fifty percent when comparing the expense of a cover made entirely of a fireproof or flame-retardant material to a conventional-material cover with an attachable inner flame retardant cap.
It is possible to use, for example, a two-shot molding process to form the cap with the cover, but as a different fireproof material, eliminating the need for extension 74, although having the cap attachable and separate from the cover is less expensive and simplifies the mold and molding process. The attachment feature would also enable the cap to be positioned on the cover according to the location of the high current connection, which may vary with different power distribution boxes. The cover could be provided with multiple extensions 74 to give a choice of cap locations, or different shaped and sized covers with differently located extensions could all receive the same molded cap. The cover and cap concept could also be used in environments other than automotive vehicles, such as in electrical junction boxes for buildings.
The disclosed features provide an inexpensive, efficient and reliable way of firmly securing the cap to the cover but are not meant to limit the main concept of the invention. The cooperating latch means on the cap and extension could be replaced with other types of latch and lock devices. If tolerances could be made tighter the ribs 99 could be eliminated, or the ribs could be replaced with other types of fitting structure. The ribs could also be molded within the extension rather than on the cap to further reduce the use of flame-retardant material, though the cost savings would likely be small.
Since minor changes and modifications varied to fit particular operating requirements and environments will be understood by those skilled in the art, this invention is not considered limited to the specific examples chosen for purposes of illustration. The invention is meant to include all changes and modifications which do not constitute a departure from the true spirit and scope of this invention as claimed in the following claims and as represented by reasonable equivalents to the claimed elements.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4541538 | Swetnam | Sep 1985 | A |
| 4731501 | Clark et al. | Mar 1988 | A |
| 5355274 | Marach et al. | Oct 1994 | A |
| 6178106 | Umemoto et al. | Jan 2001 | B1 |
| 6322376 | Jetton | Nov 2001 | B1 |
