NewNew Products
Products

Development of a New Wire Junction Block

1.

INTRODUCTION

As in-vehicle electric appliances improve in function, thenumber of circuits accommodated in a junction block(hereafter denoted as J/B), which can be defined as aneffective device for simplifying wire harnesses, tends toincrease. Simultaneously, customers require attaching
greater importance to weight reduction from the standpoint of environment preservation. The requirements ofour customer for the development at this time were: 1) thesame dimensional standard as before the minor modelchange, 2) a 25 % increase in the number of circuits
accommodated, and 3) weight reduction. To addressthese requirements, we have employed a wire J/B andreduced the pin pitch of the connector using a 1.0-size
connector. See Figure 1.

2.

BASIC STRUCTURE OF J/B

2.1 Modification toward Wire J/B
The former J/B before the minor car model change comprised seven stacks of busbar layers. In such a stacked
busbar layer configuration, the number of stacks increases in proportion to the number of circuits resulting in a J/Bof large size. We therefore employed a new J/B configuration in which electric wire was used for small current cir-cuits such as signal circuits while the busbars continued to
be used for large current circuits such as power circuits. In
the new configuration for small current circuits, the conventional conductor 2 mm wide and 0.64 mm thick can bereplaced by a φ 0.8 mm electric conductor, thereby realizing such improvements as: 1) circuit density upgrading
due to reduction in needed cross sectional area, and 2)
weight reduction due to reduction in the volume of conductors used. See Figure 2. It was decided to continuously use two busbar layers out of seven layers of the conventional J/B, while assigning the thickness of other fivelayers to the space of wiring so as to accommodate theincreased circuits.
Two types of J/Bs were developed at this time. They
have symmetrical profiles with each other, and are to beinstalled at the driver and passenger seats, respectively.
Regardless of right-hand or left-hand steering cars, theJ/B for the driver seat accommodates circuit boards while
the J/B for the passenger seat has a space corresponding
to the circuit boards. A flexible joint connector comprisingcoiled electric wires was installed in the space, realizing
further an effective use of space. See Figure 3.
2.2 High-Speed Wiring
Conventional wire J/Bs that Furukawa Electric was producing in volume had been manufactured through aprocess such that electric wires were installed in thegrooves provided on the wiring board. See Figure 4 (theinsert on the upper right). This structure made it difficult,since the wires could not reach the bottom of the grooves,
2 mm

1.5 mm2 mm0.64 mm

2 mm

BusbarInsulating board
φ1.0 mmSheathConductor

Figure 1

Appearance of J/Bs before (left) and after (right)
minor model change.

Figure 2

Comparison of circuit configurations between conventional and wire J/Bs.

Furukawa Review, No. 23

2003

123

Development of a New Wire Junction Block

14-pin mold

90° rotation

Center plate

For driver seatwith circuit boards

Figure 3

For passenger seatwith joint connector

Figure 5Center plate divided into two.

Back view of J/Bs.

3.2 Alignment Connector
Because no changes in its profiles were required, thealignment connector with 84 pins on its lateral face that
had been used before the minor model change wasemployed at this time with some modifications made on
the partial structures.
1.0-size housing

Intermediate housing

Figure 4

Wiring board with 1.0-size housing. Conventional
wire J/B is shown in the insert.

to increase the wiring speed thus posing a problem of
immense manhours needed for production. The designconcept of “wiring in the grooves” was reexamined, therefore, to adopt a structure of “fastening properly only thespots that need fastening”. More specifically, the insulation-displacement connections and the bent portions ofelectrical wires were fastened, leaving other portions free,
as shown in Figure 4.

3.2.1 Center Plate
The center plate was adapted to the connector with lateralpin direction by dividing it into two to have a folding angleof 90Åã. The electric wires are led directly into the divided
center plate, and are provided with surplus lengths at thefolding part of the plate taking folding into consideration.
See Figure 5.
3.2.2 14-pin Mold
The alignment connector comprises six blocks of 14-pin
molds to have 84 pins in total. Each block in the form ofmold is bulk jointed to the center plate by insulation-displacement connection, so that the preciseness of the insulation structures and alignment is maintained.

4.
3.

DETAILS OF J/B STRUCTURE

3.1 Issues Involved with 1.0-Size Connector
It was necessary to use a small sized connector to copewith the input and output terminals that increased in number due to the increased circuits. We applied the 1.0-size
connector to the developed product, which is smaller thanthe 2.3-size connector. Whereas Furukawa has developed
a wire J/B using the 2.3-size connector before, a wire J/B
using the 1.0-size connector is the first product for thecompany. Mechanical interference of insulation-displacement connections was eliminated by a staggered arrangement, and a triple insulated winding wire was employed in
the 1.0-size connector reducing the conventional wire sizeof φ 1.6 mm to φ 1.0 mm, thereby succeeding in using theconnector.

ACHIEVEMENTS

The wire J/B developed at this time has achieved significant improvements over the one before the minor modelchange. The number of circuits has increased by 25 %from 231 circuits to 292 circuits, and the mass has
reduced by 20 % from 2250 grams to 1780 grams.
Moreover, the wiring speed has been improved by a factorof three, enabling suppression of manufacturing cost
increase. See Figure 6.

5.

CONCLUSION

Whereas the wire J/B presented here has improved thecircuit density by accommodating increased number of circuits into the same casing volume, downsizing of the casing is insufficiently achieved. Hereafter, we plan to investigate downsizing of the main body of the J/B further as wellas its circuit density improvement.

Furukawa Review, No. 23

2003

124

Development of a New Wire Junction BlockBusbar, first layer

Busbar, second layer

Triple insulatedwinding wire

ECU coverCenter plate

For more information, please contact:
Electric Components Engineering Dept., Automotive
Products Div.
TEL: +81-5958-5-1956
FAX: +81-5958-5-2431

Fuse cover
Circuit board
Joint connector
Dividedcenter plate
Upper case

Figure 6

Side case

14-pin mold

Lower case

Exploded view of developed wire J/B assembly.

Furukawa Review, No. 23

2003

125