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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates generally to electrical junction boxes for
motor vehicles, and particularly to junction boxes having a number of
advantages over those presently available, as discussed below.
Junction boxes electrically connect plug-in components, such as fuses,
relays and diodes, to wire harnesses by a series of electrical connectors
and circuits located internally of the box. The internal circuitry
typically comprises stamped and formed metal strips called "frets" that
are placed on flat boards made of insulating materials. The stamped frets
or strips are held in place by being located in corresponding recesses
provided in the board surfaces and held in place by cold staking or heat
staking nibs provided on the board surfaces.
This method of manufacturing the circuits does not allow for locating
electronic components on the boards. And, due to the higher component
content required for modern automotive applications, packaging a junction
box within allotted space is becoming increasingly complex. In addition,
modifying the box design by changing the component content requires new
expensive tooling to make circuit changes to the new boards. Further, as
complexity increases, the frets become longer and more complex, thereby
increasing circuit path lengths and reducing electrical efficiency in
current conduction from the harness to plug-in components and vice versa.
SUMMARY OF THE INVENTION
The present invention, inter alia, separates internal box circuitry into
high and low current circuit locations. The high current circuits, which
are handled via the conventional stamped metal fret technology, using one
or both sides of one or more parallel insulating boards, can be slid into
slots molded into a half housing section of a junction box. Low current
circuitry is contained on a standard FR4 printed circuitboard material
(PCB) separate from the fret boards, and is housed in another half portion
of the box housing. The two housing halves are then brought together in a
common plane and fastened about opposed faces of an upstanding bus panel.
The bus panel is located vertically between the two housing halves when
the two halves are joined together about the panel.
The bus panel is an insulating molded component containing an array of
side-by-side bus strips and female terminals mechanically fastened to the
bus strips. The arrangement of the female terminals on the bus strips of
the panel determines circuit geometry for a given box, i.e., circuit
geometry can be changed by relocating the placement of the terminals on
the bus strips.
The junction box is permanently attached to major wire harnesses by a
plurality of insulation-displacement-crimp (IDC) terminals integrally
provided at least at one end of the bus strips. This method of attachment
reduces by 50% the number of electrical interfaces over that of prior art
boxes using electrical connectors to connect the ends of harness wires to
components and circuitry within the box, i.e., the old way employed bus to
terminal to wire interfaces whereas, in the present disclosure, the
connection is from bus to wire directly. Connector terminals are
eliminated.
In addition, the package size of the junction box of the invention is
reduced by having all connections to and from the circuitboards made in
planes parallel to the planes of the boards and in line with the stamped
frets and printed circuits. By such a parallel, in-line orientation, there
is no need to bend the fret conductors for perpendicular connections. This
(1) reduces manufacturing costs of the frets, (2) minimizes the overall
size of the housing unit, and (3) shortens circuit paths for increased
current handling efficiency, as bent frets are typically longer than
planar frets.
By separating low current circuitboards from high current fret boards,
electronics can be permanently incorporated on the circuitboards and
located within a housing unit. In addition, the separation of high current
circuits from low current circuits minimizes high current noise and
interference with low current signals handled by the low current board.
Further, the low current printed circuitboard can be reprogrammed or
exchanged without interfering with the power fret boards, and circuit
geometry within the housing can be changed without incurring retooling
costs by simply relocating connections on the vertical buses. Similarly,
individual fret boards can be substituted without affecting other fret
boards or the low current circuitboard.
Also, integral insulation displacement bus termination of major harness
connections reduces further the overall size of the box assembly, as it
eliminates a large connector that was employed to interface the junction
box and the major wire harness.
Power frets are typically stamped from a brass or copper alloy. Copper
frets offer superior electrical performance but add substantially to the
cost of each junction box made, while brass frets are generally more cost
effective but require greater size, as brass has reduced electrical
conductance, thereby increasing the weight and size of the junction box.
The objective is to reduce cost, weight and size (all three). Instead of
the brass or copper alloy frets, the frets in the subject invention can be
made from tin-plated aluminum alloy, such as 6061-T6. Tin plating is used
to prevent the formation of electrically insulative oxides on the surface
of the aluminum. Such coated frets provide a substantial weight reduction
over either brass or copper, and compared to copper, aluminum frets
provide a 40% cost reduction and 50% increase in current carrying
capability over that of brass.
THE DRAWINGS
The invention, along with its objectives and advantages, will be better
understood from consideration of the following detailed description and
the accompanying drawings in which:
FIG. 1 is an exploded isometric view of certain components of the junction
box of the invention,
FIG. 1A is a sectional view through a vertical bus panel in FIG. 1, and
FIG. 2 is an isometric view of the junction box of FIG. 1 assembled
together and mounted on a surface of a motor vehicle.
FIG. 3 is an exploded view of the displacement terminal of FIG. 2.
PREFERRED EMBODIMENT
Referring now to the drawings, FIG. 1 thereof shows the junction box 10 of
the invention in separated, exploded form to better view the component
parts thereof and assess their relationship when assembled. More
particularly, junction box 10, as a unit, comprises two housing portions
or halves 12 and 14 disposed on opposite sides of an upstanding vertical
panel member 16 containing a plurality of side-by-side bus conductors 18
(hereinafter "buses") terminating in integral insulation displacement
terminals 20 located along the upper edge of the panel member. The panel
member itself (16) is an electrically insulating molded plastic substrate
on which the buses 18 are disposed and fixed. The buses are located on
both sides of the substrate and suitably fixed thereto.
On opposite sides of the vertical panel 16 and buses 18 are located two
horizontal circuitboards 22 and 24, respectively. Permanently mounted on
board 22 are low current devices 26 (only one of which is shown), such as
solid state relays, while board 24 contains stamped metal frets 28 for
conducting high currents to fuses 30 and relays 32, sometimes referred to
as ISO (International Standards Organization) relays from a main harness
34 (FIG. 2) connected to insulation displacement terminals 20. Low current
circuitboard 22 has circuits (not shown) printed thereon, which connect
low current devices, such as 26, to vertical buses 18 and to insulated
harness wires 34. Additional, relatively small harnesses 36 and 38 are
shown in FIG. 2 connected to junction box 10 via connectors 42 and 40,
respectively.
Harness 34 is the main instrument panel harness of a vehicle, the insulated
wire ends of which are directly connected to vertical buses 18 when their
insulation is displaced by the insulation displacement terminals 20 of the
buses. As shown in FIG. 2, a cover structure 44 encloses the ends of wires
34 and the insulation displacement terminals 20 after the housing halves
12 and 14 are brought and secured together via integral flanges 43, 45 of
the housing halves and suitable fasteners 47. Harnesses 36 and 38 serve
other electrical loads in the vehicle such as miscellaneous lights.
Fret board 24, as shown in FIG. 1, includes several such boards 24a through
c located one above the other. The frets on each board terminate at the
edges of the boards in integral male blades 48 located in the planes of
the frets and parallel to the planes of the boards. The male blades
connect to fuses 30 and relays 32, via female-to-female terminals (not
visible) located in housing half 14, to harness wires 38 via connector 40,
and to female terminals 49 (only every third one shown in FIG. 1 for
clarity) suitably mounted on and electrically connected to respective
vertical buses 18.
Similarly, the printed circuits on board 22 terminate in male blade
terminals 50, which, in FIG. 1, are located along two opposed edges of the
board. The blades are sized to enter female terminals 51, visible in FIG.
1A only, mounted on and electrically connected to respective vertical
buses 18 on the side of vertical board 16 facing horizontal board 22. The
vertical buses are thus effective in making electrical connections between
the two circuitboards 22 and 24, including boards 24a through c, and
between the boards and main harness 34 via integral terminals 20 of the
vertical buses. As mentioned earlier, housing half 14 can be provided with
slotted sidewalls to accommodate and retain in spaced relation boards 24
and 24a through c. Housing half 12 is provided with a height sufficient to
accommodate electronic components such as 26 mounted on board 22.
Connector 42 is located at the rear of housing half 12 (FIG. 2). The
connector has female terminals (not visible in the figures) attached to
the ends of wires 36 for receiving the blades 50 at the rear of board 22
(FIG. 1). Similarly, on the bottom of housing 14 is connector 40 that
contains female terminals (not visible) secured to the ends of respective
harness wires 38 for receiving the blade terminals 48 on the right side of
board 24b (FIG. 1).
Vertical buses 18, with their integral, insulation displacement terminals
20, eliminate a large connector and provides connection to the fret
circuits and components associated with the printed circuitboards of FIG.
1. In the case of the connections made through female terminals 49 and 51,
these connections use a high normal force design that minimizes
constriction resistance (between one half of the electrical interface to
the other half) and stabilizes changes in resistance caused by
environmental conditions and load cycling.
In addition, the location of terminals 49 and 51 on buses 18 conveniently
determines circuit geometry within box 10, i.e., circuit geometry can be
changed by the changing buses to which terminals 49 and 51 are attached.
Such an arrangement is highly flexible in altering circuit configurations
within a given box 10.
Similarly, one fret board can be changed without affecting the other
boards, and the low current, signal board 22 can be changed without
affecting the fret boards. Also, the separation of the high current boards
24 from the signal board 22 minimizes interference and noise in the
information handle by the signal board.
And, lastly, all connections to fret and signal board terminals 48 and 50
are made parallel to the planes of boards and fret layers such that no
conductors need to be bent for connections perpendicular to the boards.
This reduces manufacturing costs, minimizes the size (thickness) of the
junction box unit and shortens circuit paths for electrical efficiency.
Two brackets 54 and 56 are shown in FIG. 1 for mounting respectively on two
vertical buses 18 and electrically grounding the two buses. The two
brackets are connected to vehicle sheet metal via fasteners (not shown)
extending through holes 58 provided in the brackets.
Preferably, frets 28 with terminals 48 located on boards 24 and 24a to c
are strips of tin-plated aluminum alloy, such as 6061-T6. The aluminum
alloy reduces the weight of the board over that of copper and brass frets
by thirty percent, and a forty percent reduction in cost over copper. In
comparison to brass, the aluminum frets provide a fifty percent increase
in electrical conductivity over brass frets. The tin plate on the aluminum
maintains electrical conductivity between the aluminum and components
connected thereto, as bare aluminum surfaces oxidize to form a hard,
electrically insulative surface.
Weight-wise, junction boxes 10 using the tin-plated aluminum frets 28 were
500 grams lighter than boxes using C11000 copper frets.
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