Development of a Flexible-Wiring Junction Blockby Kengo Kimura *, Masakazu Murakami *, Shin Hasegawa *,and Tatsuo Satori *2, Keiji Edamura *3

To improve the productivity of the automobiles’ wire harness systems that arebecoming ever more diversified, a production method called “complete subassembly system” constitutes the mainstream presently. In response to this circumstance, theauthors have developed a flexible-wiring junction block, which accommodates the jointing sections of wire harnesses thereby eliminating a number of joint connectors conventionally used.
The product has been adopted in the minor model change program of Toyota’s Land Cruiser, andbegan to appear in the marketplace since August 2002.

ABSTRACT

1.

Upper case

INTRODUCTION

1.0 III insulation-displacement
terminal

As the electric components installed in vehicles improve infunction, wire harnesses grow in size accompanying theincrease of joint connectors (hereafter called J/C). We
have developed, therefore, a flexible-wiring junction block(hereafter called J/B) that allows flexible configuration ofcircuit wiring thus accommodating many J/Cs. The structure is shown in Figure 1.
The employment of this new J/B has resulted in significant reductions in mounted components including 20 J/Cs
and 30 circuits together with a cost reduction of 350 yen.

2.

Terminal holder plate
Center plate

Electric wire (TEX-JB)
Joint connector

DEVELOPMENT OF EACH COMPONENT

2.1 Center Plate
The center plate shown in Photo 1 is an important component that constitutes a base, on which electrical wires arewound and terminals are connected by insulation displacement.
The product developed here has a terminal interval of
2.5 mm, since use of 1.0 III connector was assumed atfirst. Taking into consideration the necessities of winding
electrical wires at these regular intervals and of assuring astructure capable of holding the connected terminals, it
was decided to divide the terminal section into two rows
up and down, each of which taking a staggered configuration. In this case, the maximum wire diameter will be 1.0mm, since the width of the intervening rib has to be about
1.5 mm so as not to influence the formability of the center

Lower case

Figure 1

Structure of flexible-wiring junction block.

Photo 1

Center plate.

*Electric Components Engineering Dept., AutomotiveProducts Div.
*2 Third Planning Dept., Plants and Facilities Div.
*3 Electric Components Production Dept., Automotive ProductsDiv.

plate.
Moreover, since the number of winding turns of electrical wires changes depending on the number of circuits

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2003

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Development of a Flexible-Wiring Junction Blockrequired, the center plate was provided with connectableprojections and press fit sections, making the structure
capable of arbitrary numbers of connection.
2.2 Insulation-Displacement Terminal
The insulation-displacement terminal shown in Photo 2
has a slit section that is required to penetrate the insulation of electrical wires by a single action to come into
direct contact with the conductor. Besides, the connected
portion must pass reliability tests including thermal shock
test and the like.
We therefore carried out a stress analysis (shown inFigure 2) and reliability evaluation tests (shown in Figure3) using prototype terminals, and were successful inobtaining a suitable slit width.
Moreover, it was requested to supply the products in theform of tape carrier mounting in order to shorten the cycle
time of assembly, so that the center carrier was set to an
appropriate position that would not interfere with the slit on
the insulation-displacement section.
Because, as mentioned in Section 2.1, the terminal section of the center plate is designed to have a staggeredconfiguration, it became necessary to prepare two typesof terminals. Despite this, they share the mold to reducethe costs.
2.3 Electrical Wire
As mentioned in Section 2.1, electrical wire to be used
had to be not more than 1.0 mm in outer diameter, whereas its conductor had to be about 0.8 mm in the outer
diameter corresponding to 0.5 sq. in cross sectional area,
and we were unable to find any appropriate wire among
conventional insulated wires.
We therefore directed our attention to the triple-insulated wire developed by the Winding Wire Division of thecompany, and, after partially modifying its insulation adhesion to make it applicable to wiring J/Bs, adopted the wirein the J/B developed here under the name of TEX-JB.
TEX-JB has sufficient insulation performance and flexibility despite its small insulation thickness of 0.1 mm. Interms of insulation-displacement connection using the terminal, satisfactory results were obtained with cross-section photographs and reliability tests.

Wire-holding force (N)Slit height: 0.7 mm

Photo 2

Figure 2

Insulation-displacement terminal.

Example of stress analysis of insulation-displacement terminal.

2.4 Cases
Basically cases were to be installed manually, so that theirstructure was required to be able to prevent wrong connection and avoid interference with the insulation-displacement terminals. Accordingly, the projections provided
for jointing with the center plate were used to prevent
installations in the reverse direction, and the grooves forelectrical wire winding were reinforced with guide ribs on
the case to help smooth insertion. See Photo 3.

Slit height: 1.2 mm

Slit height: 2.2 mm

40.0
35.0
30.0
25.0
20.0
15.0

Slit width (mm): 0.55 0.55
Before (B) or after (A) test: B
AFigure 3

0.60 0.60
BA

0.65 0.65
BA

0.55 0.55
BA

0.60 0.60
BA

0.65 0.65
BA

0.55 0.55
BA

0.60 0.60
BA

0.65 0.65
BA

Comparison of wire-holding force of insulation-displacement terminals before andafter thermal shock test. Speed of insulation displacement is 10 m/s.

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Development of a Flexible-Wiring Junction Block

Photo 3

Photo 4Upper case.

Terminal holder plate.

2.5 Terminal Holder Plate
The terminal holder plate is placed on the center plate toprevent the insulation-displacement terminals in cranked
figure from deformation and falling off. In spite of its simple structure, the holder plate presented certain problemsof warping and terminal falling, and it was after several
changes that the plate was finally settled to have the current structure. See Photo 4.
During that period, the holder plate underwent various
improvements such as the reexamination of the dimensionof ribs that are connected to the center plate by press fit,
the provision of V-grooves to prevent warping, as well as
the provision of a plane surface for vacuum suction at theassembly instruments, thereby establishing a stabilized
assembly process.

3.

DEVELOPMENT OF ASSEMBLY
INSTRUMENTS

3.1 Wiring Instrument
The wiring instrument shown in Photo 5 was developed on
the assumption that it should operate fully automaticallywithout any manual operations, which was aimed at stabilizing the quality of the product of a new structure.
The form, structure and action of the wire supply section
called wiring head shown in Photo 6 constitute the main
factors of wiring performance. The structure of the wiring

Photo 5Photo 6

Wiring instrument.

Wiring head.

head was so designed that the head would operate incontact with the center plate. This enabled the head toguide electric wires to a suitable groove, thus realizing
high-speed winding while decreasing wrong winding. The
average winding speed was 3.5 sec/turn at the initialstage of the development, but it reached 1.2 sec/turn withthe volume production instrument.
Furthermore, the wiring head was made to be capableof motion in three axes. While the X-axis direction is naturally necessitated for guiding the wire to the groove, twomovements in the up-and-down and back-and-forth directions were added to follow the rotation of the center plate,thus enabling smooth and high-speed winding of wire
without damaging the wire insulation.
3.2 Wire-Cutting Instrument
With this J/B, multiple wires have to be cut out of about 50
wires 1.0 mm in diameter, which are arrayed on the one
side at 2.5-mm intervals. These wires are to be designated arbitrarily and specifically in accordance with the partnumber of J/B. In this wire cutting, it is essential that thespecified lengths of the wires be removed without fail not
to cause electric current leaks. Also it is an essential
requirement from the standpoint of quality assurance tokeep the wire chips from mingling with the product.
To meet these requirements, a new rotating cutter wasdeveloped. The cutting machine enabled, with a small
footprint, cutting of each electric wire, and the wire chips

Furukawa Review, No. 23

2003113Development of a Flexible-Wiring Junction Block

Photo 8Instrument for connection of insulation-displacement
terminals.

are accommodated temporarily in the cutter blade to beejected one by one.
The wire cutting instrument for volume production isprovided with a mechanism which detects ejected wirechips one by one, and discriminates a J/B as a defective
product in case no wire chips are detected, thereby contributing a great deal to upgrading of quality. See Photo 7.
3.3

Instrument for Connection of InsulationDisplacement Terminals
Insulation-displacement connection of multitudes of terminals arrayed at regular pitches in two rows, which constitute one of the proprietary structures of this product, wascarried out aimed at realizing a high production rate of nolonger than one sec per one piece. Mechanism adopted
for the purpose was such that, unlike those methods inwhich separated terminals are supplied to other driving
sections using a parts feeder, as soon as the terminals on
the carrier tape were separated respectively, they are
directly connected by insulation displacement. See Photo
8.
Thus we achieved a high rate of insulation-displacement
connection of 0.8 sec per one piece, contributing significantly to the reduction of production cycle time for theproduct.

Photo 9ID tag and reader.

preventing confusion of part numbers or launch of defective products.

4.

DEVELOPMENT IN THE FUTURE

4.1 Downsizing
Although the J/B developed here uses 1.0 III terminals, aone size smaller product that will use 0.64 terminals isunder development in response to customers’ needs,
which is aimed at entering into volume production in 2003.
4.2 Multifunctional Products
Whereas the product developed here accommodates towire winding of only one kind, there is an increasing needfor products capable of accommodating to wire winding ofmultiple kinds, i.e. so-called hybrid type. We are also
investigating the feasibility of various ideas for new products including those that mount other components such as
fuses.

3.4 Serial Number Control
There are six different part numbers representing car’s
specifications and destinations of each J/B developed
here. Different part number means different wire winding,different wire cutting and different position in insulationdisplacement connection. To manufacture a variety ofproducts on a single line of facilities without making errors
at each production step, we have adopted a manufacture
control system using ID tag. The ID tag and its reader are
shown in Photo 9.
In this system, a tag is attached to the conveyor paletteused between the process steps, on which necessary
information such as part number and serial number ismemorized, enabling recording of information on work orproblems. Using this information at each production step,
products that became defective at intermediate steps are
rejected to omit processing at downstream steps, thus

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