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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to an improved structure of connection between a bus
bar (constituting an internal circuitry of an electric connection box) and
a press-connecting branch terminal in the electric connection box used to
interconnect wire harnesses or the like.
There are known many electric connection boxes, such as a fuse box used in
a vehicle or a branch connection box, which includes branch connections of
a wire harness, and in order to simplify a wiring pattern, a branch
circuit is formed in a concentrated manner.
The formation of a branch circuit is made either by a method in which
upstanding branch tabs are formed directly from a bus bar, constituting an
internal circuit, in continuous relation to the bus bar, or by a method in
which there is used a press-connecting branch terminal having a branch tab
at one side and a press-connecting portion at the other side which has a
U-shaped slot, and an electric wire or a bus bar is press-fitted in the
slot for connection.
FIGS. 10 and 11 show the prior art (Japanese Laid-Open Patent Application
No. 45575/86) relating to the formation of such branch circuit.
As shown in FIG. 10, a press-connecting branch terminal a has one or more
branch tabs b at one side and a press-connecting portion c at the other
side which has a U-shaped slot d.
As shown in FIG. 11, the branch tab b of each press-connecting terminal a
is passed through in an insertion hole h formed in a bottom of a housing g
of an upper case e, and is press-fitted at its proximal portion in this
insertion hole, thus fixing the branch tab. Then, a group of connection
electric wires i taken, for example, form a wire harness are disposed in
parallel relation between the upper case e and a lower case f, and each
connection wire i is press-fitted in a desired U-shaped slot d for
connection, thereby forming a branch circuit in a concentrated manner.
FIG. 12 shows a branch connection between a press-connecting terminal a'
and a bus bar j (Japanese Laid-Open Patent Application No. 131483/87).
The press-connecting terminal a' has a pair of opposed press-connecting
portions c' each having a U-shaped slot d', and the distal end of an
opening O of the slot d' is enlarged by a tapered configuration O' to
provide an insertion guide by which the connection can be effected even
when the center line of the bus bar j is slightly out of registry with
(that is, displaced from) the center line of the opening O.
In the prior art structure shown in FIG. 11, the press-connecting terminal
a is press-fitted in and fixed to the insertion hole h. If the branch tab
b is twisted, for example, when attaching an external connector to the
housing g, there is a risk that this force is applied directly to a point
of contact between the tab and the electric wire i. Further, the
press-connecting terminal a is press-fitted and fixed at its portion
indicated by thickened lines P. If the overall length L of the
press-connecting terminal a is increased, it is necessary to increase the
thickness of a resin layer of the upper case e, and therefore the cover
becomes bulky. Further, the press-connecting terminal a is required to
have a terminal width l commensurate with the value of electric current.
Thus, in addition to the above necessity of increasing the thickness of
the resin layer for press-fitting and fixing, the required width l is
needed for securing electric current, and therefore the upper case e is
still more bulky.
In the branch connection construction shown in FIG. 12, the guide (tapered
portion O') for the bus bar j is provided on the press-connecting terminal
a', and therefore reaction forces, resulting from corrections of the angle
and position displacement of the bus bar j, act directly on the
press-connecting portion, which may result in failure to achieve a proper
press-connection by a resilient nature of the press-connecting portion ,
which may result in failure to achieve a proper press-connection by a
resilient nature of the press-connecting portion c'.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems, and an
object of this invention is to provide a connection construction in which
when making a press-connection between a press-connecting branch terminal
and a bus bar, dimensional tolerances such as position displacement are
absorbed to thereby ensuring a press-contact between the bur bar and a
press-connecting portion, and an external force applied to a tab portion
will not act on the press-connecting portion to thereby achieve a stable
connecting condition, and further the size of the press-connecting
terminal can be reduced.
According to the present invention, there is provided a structure of
connection between a bus bar and a press-connecting branch terminal in an
electric connection box wherein a plurality of bus bars constituting a
circuit are accommodated within a casing having an upper case and a lower
case; a housing having at least one tab insertion hole at its bottom is
formed on at least one of the upper and lower cases; a branch tab formed
on one side portion of a press-connecting branch terminal is extended
through the tab insertion hole into the housing to thereby constitute a
connector insertion portion; and a desired one of the bus bars is
press-fitted in and connected to a U-shaped slot formed in a
press-connecting portion formed on the other side portion of the
press-connecting terminal; the press-connecting branch terminal including
a base plate portion, opposed press-connecting portions projecting from
one side of the base plate portion and each having a U-shaped slot, and at
least one branch tab projecting from the other side of the base plate
portion; the structure comprising a first retaining means for retaining
the press-connecting branch terminal in place when the upper and lower
cases are coupled together, the first retaining means including a seat
formed on a bottom of the housing for receiving the base plate portion and
a press portion formed on an inner surface of the case disposed in opposed
relation to the seat, and a second retaining means for retaining the
press-connecting branch terminal in place when the base plate portion is
press-fit in the seat, whereby the press-connecting branch terminal and
the bus bar which are press-connected together are fixedly held between
the seat and the press portion.
In order to absorb dimensional tolerances such as position and angle
deviations of the U-shaped slot of the press-connecting portion from the
bus bar, it is preferred that a pair of bus bar guide walls each having a
bus bar guide groove be formed on the seat for the press-connecting branch
terminal.
In order to stably seat the press-connecting terminal on the seat when
press-connecting the press-connecting terminal and the bus bar together,
it is preferred that a free end of the base plate portion of the
press-connecting branch terminal be bend into an L-shape to form a
press-fitting piece, and a press-fitting groove be formed in the seat, and
the press-fitting pieces be press-fitted in the press-fitting groove to
thereby fix the press-connecting branch terminal to the seat.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a construction of connection
between bus bars and press-connecting branch terminals in an electric
connection box, provided in accordance with present invention;
FIG. 2 is a cross-sectional view of an important portion of the
construction of FIG. 1 in its assembled condition;
FIG. 3 is an enlarged perspective view of a terminal holder of the
construction of FIG. 1;
FIGS. 4 to 6 are enlarged views explanatory of dimensional relationship of
a press-connecting piece, bus bar guide walls and a U-shaped slot;
FIG. 7 is an enlarged cross-sectional view showing a press-connection
between the press-connecting piece of the bus bar and the press-connecting
branch terminal;
FIG. 8 is a cross-sectional view taken along the line VIII--VIII of FIG. 7;
FIG. 9 is a plan view of the structure of FIG. 7, with an upper case
omitted;
FIGS. 10(a-c) are views illustrative of conventional press-connecting
branch terminals;
FIG. 11 is a cross-sectional view showing a branch connection of the above
conventional press-connecting branch terminal to wires; and
FIG. 12 is a view illustrative of a conventional construction of connection
between a bus bar and a press-connecting terminal.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
The invention will now be described with reference to the drawings.
An electric connection box A shown in FIGS. 1 and 2 comprises an upper case
1 and a lower case 2 both of which are made of a synthetic resin, and a
plurality of bus bars 3 and 3' constituting a circuitry are mounted within
a case made of the upper and lower cases 1 and 2. A plurality of housings
4 for constituting a fuse connector insertion portion, a wire harness
connector insertion portion, etc., are formed on outer surfaces of the two
cases 1 and 2. A plurality of tab insertion holes 5 are formed in the
bottom of each housing (see FIG. 2).
The width of the bus bar can be determined depending on the current
capacity of the circuitry, but here in this embodiment there are used two
kinds of bus bars 3 and 3' having a smaller width and a larger width,
respectively.
Branch tabs 6, 6' are formed integrally on the bus bar 3, 3' in an
upstanding manner, and these branch tabs extend through the respective tab
insertion holes 5 into the respective housings 4, thereby constituting the
above-mentioned connector insertion portions. Female-female terminals 7,
7' for relay purposes are fitted on the branch tabs 6, 6' according to the
need.
The bus bar 3.sub.1 of a smaller width has bridge-like press-connecting
pieces 8 disposed perpendicularly to the plane of its circuitry. The
press-connecting piece 8 is press-connected to a press-connecting branch
terminal 9 supported on a terminal holder 15 mounted on the inner surface
of the lower case 2.
As shown in FIG. 3, the press-connecting branch terminal 9 comprises a base
plate portion 10 in the form of a U-shaped frame, opposed press-connecting
portions 11 formed on and projecting from one side of the base plate
portion 10 and each having a U-shaped slot 12, and one or more branch tabs
13 formed on and projecting from the other side of the base plate portion
10. In the illustrated example, the branch tabs 13 constitutes a four-pin
type, but may constitute a single-pin type. The opposite free ends of the
base plate portion 10 are bent into an L-shape to form press-fitting
pieces 14.
The terminal holder 15 includes a seat 16 for the base plate portion 10 of
the press-connecting branch terminal 9, and a pair of bus bar guide walls
17, 17 holding outer sides of the opposed press-connecting portions 11,
11.
The seat 16 is so formed as to surround the tab insertion hole 5 at the
reverse side of the bottom of the housing 4, and includes a positioning
projection 16a for fitting in the U- shaped base plate portion 10, and a
surrounding wall 16b. Press-fitting grooves 18 (see FIG. 9) for the
press-fitting pieces 14 are provided at one side portion within the
surrounding wall 16b.
The bus bar guide wall 17 has a bus bar guide groove 17a at its central
portion, and a guide taper 17b is provided at an upper open end of the
groove 17a.
FIGS. 4 to 6 are enlarged views explanatory of dimensional relationship of
the press-connecting piece 8, the bus bar guide wall 17 and the U-shaped
slot 12.
Here, the thickness of the press-connecting portion 8 is represented by t,
and the width of the bus bar guide groove 17a is represented by W1, and
the distance between pressing blades 12a and 12a at the U-shaped slot 12
is represented by W2. The formation is made to satisfy the following
formula:
W1.gtoreq.t>W2
In addition, a lower end P1 of the guide taper 17b is slightly higher than
an inlet end P2 of the pressing blade 12a.
With this arrangement, the press-connecting piece 8 is brought into contact
with either the bus bar guide groove 17a or the guide taper 17b before the
piece 8 is brought into contact with the pressing blades 12a, thereby
absorbing dimensional tolerances of the press-connecting piece 8 and the
U-shaped slot 12.
A press projection 19 is formed on the inner surface of the upper case 1
disposed in opposed relation to the terminal holder 15, and is adapted to
be inserted in between the pair of bus bar guide walls 17 and 17.
FIG. 7 is an enlarged cross-sectional view, showing a press-connection
between the press-connecting piece 8 of the bus bar 3.sub.1 and the
press-connecting branch terminal 9. FIG. 8 is a cross-sectional view taken
along the line VIII--VIII of FIG. 7. FIG. 9 is a plan view of the
structure of FIG. 7, with the upper case 1 omitted.
In these Figures, the branch tab 13 of the press-connecting terminal 9
extends through the tab insertion hole 5 into the housing 4, and the base
plate portion 10 rests on the seat 16 of the terminal holder 15, and the
press-connecting terminal 9 is provisionally fixed by the positioning
projection 16a, and then is stabilized by pressing the press-fitting piece
14 into the press-fitting groove 18.
In this condition, the press-connecting piece 8 of the bus bar 3.sub.1 is
extended between the bus bar guide walls 17 and 17, and is disposed in
registry with the bus bar guide grooves 17a.
Then, the upper case 1 is mated with the lower case 2 and is pressed toward
it, so that the press projection 19 presses the press-connecting piece 8
downward. As a result, the piece 8 intrudes into the U-shaped slot 12, and
is resiliently contacted and connected by the press blades 12a, thus
achieving a branch connection between the press-connecting terminal 9 and
the bus bar 3.sub.1.
In this branch connection condition, the base plate portion 10 and the
press-connecting portions 1 are fixedly clamped between the press
projection 19 of the upper case 1 and the seat 16 of the lower case 2 from
the upper and lower sides. Therefore, even if an external force such as a
twisting force acts on the branch tab 13, such force does not affect the
portion of contact with the bus bar 3 (press-connecting piece 8), thereby
maintaining a stable connection condition.
Further, even if the press-connecting piece 8 is displaced from the center
line of the U-shaped slot 12 when fitting the piece 8, the guide grooves
17a of the bus bar guide wall 17 absorbs the dimensional tolerances as
described above with respect to FIGS. 4 to 6, and therefore a stable
contact pressure can be obtained within a range of the resiliency of the
press blades 12a.
Further, as described above, since the press-connecting terminal 9 is
fixedly held between the upper case 1 and the lower case 2, it is not
always necessary to press-fit the branch tab b as in the prior art of
FIGS. 10 and 11. However, by providing the press-fitting pieces 14 making
use of the ends of the base plate portion 10, a holding force of generally
the same level as in the prior art can be obtained. Further, as shown in
FIG. 3, by making use of the width l' of the press-fitting portion 14 in
order to secure electric current, the overall length L' of the terminal
can be made smaller than the overall length L of the prior art
construction.
In the above embodiment, although the terminal holder 15 is mounted on the
lower case 2, the terminal holder may be mounted on the upper case 1.
As described above, in the present invention, even if an external force
acts on the branch tab of the press-connecting branch terminal, its
portion of contact with the bus bar is not affected. In addition, when
press-connecting the press-connecting terminal to the bus bar, the
dimensional tolerances can be absorbed, thereby providing a stable contact
pressure. Further, by forming the press-fitting portions on the base plate
portion of the press-connecting terminal, the press-connecting terminal
can be stabilized prior to the press-connection to the bus bar, thereby
facilitating an assemblage of the electric connection box.
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