Screw tightening structure

A screw tightening structure for a switch box wherein an embedded nut is provided for the switch box, there is a bilateral bolt providing screw portions for both sides thereof, one side of screw portions of a bilateral bolt is screwed to the embedded nut, a bus bar and a LA terminal of a connecting electric wire are fixed to the other screw portion of the bilateral bolt by tightening of the nut. Since the damaged bilateral bolt can easily be dismounted, even if the bilateral bolt is damaged, the matter thereof is can be settled by only the replace of the bilateral bolt.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improvements in Screw Tightening structure to 
tighten a bus bar and an end terminal of a connecting electric wire both 
of which constitute an internal circuit of a switch box. 
2. Description of the Prior Art 
Switch boxes such as a relay box or a fuse box have an internal circuit 
which is composed of a plurality of bus bars under normal conditions. End 
terminals of connecting electric wires for either electric supply or 
output are firmly tightened and fixed by screwing the bolts and the nuts 
on main bus bars. 
FIGS. 4 and 5 show a conventional example of a screw tightening structure 
described above as disclosed in the Japanese Utility Model Application 
Laid Open No. 4-29165. Namely, a bolt 23 is fixed on one side of a case 
body 22 of a switch box 21 in such a way that the bolt 23 is integrally 
embedded in the case body 22 by insertion molding. Ends of a plurality of 
bus bars 24 and an end terminal (hereinafter called LA terminal) of the 
connecting electric wire 25 are fixed in such a manner that the ends and 
the LA terminal are securely tightened through a washer 27 by utilization 
of this stud bolt. 
In the above both assembling and electric wiring for the switch box, the 
maker of the switch box has carried out the insertion molding of the bolt 
and distributing wires of the bus bars circuit, and the makers of 
automobiles have carried out the mounting of the LA terminal and 
tightening work of the nut, and as it did so, when the bolt is damaged 
because of excessive tightening of the nut, the only damaged portion can 
not be removed therefrom due to the insertion molding. For this reason, it 
must be substituted every wiring harness. Accordingly, this method 
resulted in the main cause of substantial cost. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide a screw tightening structure for a switch box, in which even if 
the bolt is damaged, it can easily be replaced. Consequently the waste 
that exchanging of the wiring harness must be performed about every 
damages is eliminated. Further, the depression of the manufacturing cost 
can be realized. 
According to one aspect of the present invention, for achieving the 
above-mentioned objective, there is provided a screw tightening structure 
for switch box in which an end terminal of a connecting electric wire for 
either supply or output to a bus bar on an inside of a switch box is 
tightened securely and fixed by means both of a bolt and a nut, an 
embedded nut is provided for the switch box and there is a bilateral bolt 
providing screw portions for both sides of a head thereof, one side of the 
screw portions being screwed into the embedded nut, a bus bar and an end 
terminal of a connecting electric wire be fixed to the other screw portion 
of the bilateral bolt by tightening of the nut. 
As stated above, the screw tightening structure for the switch box 
according to the invention is provided with the bilateral bolt screwed 
into the embedded nut, when the embedded nut is screwed securely on the 
exterior screw portion of the bilateral bolt the interior screw portion of 
which is screwed into the embedded nut with high torque, the interior 
screw portion of the bilateral bolt becomes double tightening, since the 
bus bar, LA terminal and so on are in existence outwardly, outer damage of 
the screw is frequent because stress concentrates the exterior screw 
portion over the interior thereof. In that case, the damaged bilateral 
bolt can easily be dismounted because the head thereof remains in. Even if 
the bilateral bolt is damaged, the matter thereof is can be settled by 
only the replace of the bilateral bolt. 
The above and further objects and novel features of the invention will be 
more fully understood from the following detailed description when the 
same is read in connection with the accompanying drawings. It should be 
expressly understood, however, that the drawings are for purpose of 
illustration only and are not intended as a definition of the limits of 
the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of the present invention will now be described in 
detail referring to the accompanying drawings. 
FIG. 1 is an exploded perspective view showing a switch box according to 
one embodiment of the present invention. FIG. 2 is a plan view showing a 
portion of screw tightening structure of FIG. 1. FIG. 3 is a grossly 
enlarged sectional view showing a cross section taken along the line X--X 
in FIG. 2. 
In these drawings, an example in which a switch box A is formed as a relay 
box or a fuse box is shown. A plurality of cavities 2 for fuses together 
with a cavity 3 for a relay are provided for on one side of a main case 1 
which is made up of synthetic resin insulating material. On the other side 
of the main case 1, a cavity 4 for fusible link (high-amperage current 
capacity fuse) together with a screw tightening portion 5 are formed 
separately in section by section. 
The screw tightening portion 5 comprises a screw room 6 into which the nut 
7 is mounted, and a bus bar engaging room 8 adjacent thereto. There are 
openings at the top and the bottom portions of the screw room 6. The nut 7 
is fixed on a ceiling wall 6a of the upper part of the screw room 6 in 
such a way that the nut 7 is integrally embedded in the ceiling wall 6a by 
insertion molding. It is desirable that an upper end 7a of the nut 7 is 
the same surface of an upper surface of the ceiling wall 6a or that the 
upper end 7a of the nut 7 is slightly protruded from the upper surface of 
the ceiling wall 6a as illustrated in the drawing. A notch 10 is provided 
for a flange wall 1a of the main case 1 to be in the neighborhood of the 
upper end 7a of this nut 7 to set a tool such as a wrench 16 which is said 
later. A flexible arm 9 which has an engaging projection 9a from one side 
of the inside wall of the bus bar engaging room 8 is provided downward. 
A bilateral bolt 11 which is screwed into the nut 7 has screw portions 11b 
(when distinguishing inside and outside, these are 11b1 and 11b2) putting 
the head 11a therebetween. The both sides of said bilateral bolt 11 are 
formed with a vertical symmetry. It is desirable that the external shape 
of the head 11a is hexagon shape which is the same as the ordinary bolt, 
and the pointed end portion 11c of the screw portion 11b is square pillar 
with thin diameter. 
In the bus bar 12, as shown in the example of the drawing, the first 
L-shape crooked connecting piece 12a which has a bolt hole 12b on the 
upper portion of one end thereof is continuously formed. The second 
connecting piece 12a' which has a bolt hole 12b' on the lower portion of 
the other end thereof is continuously formed. Further an engaging hole 12c 
is provided for the one end thereof. Besides, in FIG. 1, reference numeral 
17 denotes a fixing leg for fixing the switch box A on the body of the 
car, reference numeral 18 denotes a fixing arm for the same as the fixing 
leg 17, and reference numeral 19 denotes a belt for fixing the electric 
wire. 
Next, fixing of both the bus bar 12 and the LA terminal 13 in accordance 
with the bilateral bolt 11 and the nut 7 will be explained. 
In the first place, the screw portion 11b1 which is the one side screw 
portion of the bilateral bolt 11 is screwed and fixed into the nut 7 in 
the screw tightening portion 5 so as to touch the under surface of the 
head 11a to upper end 7a of the nut 7. 
In the second place, the bus bar 12 is set to the other screw portion 11b2. 
Namely, the bolt hole 12b of the first connecting piece 12a of the bus bar 
12 is passed through the other screw portion 11b2, while retaining the 
condition, the first connecting piece 12a is brought down. This would 
result in that the one end side of the bus bar 12 enters into the bus bar 
engaging room 8. The other end side of the bus bar 12 enters into the 
cavity for the fusible link 4, as it did so, the engaging projection 9a of 
the flexible arm 9 is engaged with the engaging hole 12c of the bus bar 
12, after latching for a time, the second connecting piece 12a' at the 
other end side is fixed by means both of the connecting terminal of the 
fusible link (not illustrated) and the bolt hole 12b' by using bolt. 
Next, both of the LA terminal 13 of the termination of the electric 
connecting wire W and the washer 14 are passed through the screw portion 
11b2 from above the first connecting piece 12a of the bus bar 12, and then 
the nut is fitted thereon, the nut 15 is tightened securely and fixed by 
means of the tool such as the torque wrench which is not illustrated. 
On the occasion of taking the bus bar 12 and LA terminal and so on off by 
loosening the nut 15, the revolution of the bilateral bolt 11 itself is 
prevented in such a way that the head 11a of the bilateral bolt 11 is 
fixed by setting a tool such as the wrench 16 by utilization of the notch 
10 of the main case 1. 
In case where the nut 15 is tightened securely by means of the torque 
wrench, the interior screw portion 11b1 of the bilateral bolt 11 which is 
screwed into the embedded nut 7 becomes double tightening. However, for 
all practical purposes, the bus bar 12, LA terminal 13 together with the 
head 11a are in existence outwardly. Accordingly, outer damage of the 
screw is frequent because stress concentrates the exterior screw portion 
11b2 over the interior thereof. In that case, the damaged bilateral bolt 
11 can easily be dismounted because the head 11a thereof remains in. If 
the exterior screw portion 11b2 or the head 11a might be damaged, the 
remaining screw portion 11b1 can be removed by the way that the tool which 
is inserted from the lower opening end of the screw room 6, operates on 
the square pillar shape pointed end portion 11c. 
For this reason, even if the bilateral bolt 11 is damaged, the matter 
thereof is can be settled by only the replace of the bilateral bolt 11. It 
can be eliminated waste that the switch box as a whole is replaced, in the 
conventional method. 
As described above, according to the present invention there is provided a 
screw tightening structure for switch box in which the end terminal of the 
connecting electric wire for supply or output to the bus bar on the inside 
of the switch box is tightened securely and fixed by means both of the 
bolt and the nut. The embedded nut is provided for the switch box. One 
side screw portion of the bilateral bolt providing the screw portions for 
the both side of the head is screwed into the embedded nut. The bus bar 
and the end terminal of the connecting electric wire are fixed to the 
other screw portion by tightening of the nut. Even if the outside screw 
portion of the bilateral bolt is damaged, the inside screw portion can be 
taken out by the remaining head. The matter thereof caused by the damage 
is can be settled by only the replace of the bilateral bolt. The waste can 
be eliminated by the fact that it is not necessary to replace the switch 
box as a whole in the conventional method.