Development of a Seat Module for Automobiles
by Hirotomo Shiozaki *, Akihito Yahara *2, Toshikazu Doi *3, Shigeki Motomura *2,
Atsushi Sasaki *2, Toshihiro Kawazoe *2, Takayuki Matsuoka *4, Shoji Hara *,Shigeki Itabashi *2, Eiji Ichii * and Satoshi Kawai *5

A seat module has been developed for a minor modification program of Toyota’sLand Cruiser, which was put into quantity production in August 2002.
The core of a seat module is an electronic control unit with a memory function to memorize andretrieve the driver’s seat position, and a number of peripheral components are integrated therein.
The developed product integrates the electronic control unit, wire harness, unit casing, and fixing bracket, thereby aiming at cost reduction, upgrading of ease of assembly, and weight reduction.
One of the features of the development is that it implements an infrared ray communication
system for the control of the body system of vehicle --for the first time in the world. This paper
reports on the development of the module, focusing on the development of the infrared ray communication system.

ABSTRACT1.

INTRODUCTION

Module-based production method has been introduced bymany European and American car manufacturers sincethe 1980s as an effective method for cost reduction. In
this method, the constituting modules such as doors,
roofs, and instrument panels are respectively assembled
from their parts, and subsequently they are assembled on
the main line for vehicle assembly to complete a car.
Recently, a number of domestic car manufactures haveintroduced this production method 1).
On the other hand, the number of the equipment andsubsystems mounted on vehicles is continuing to increase
due to the technological trend of IT and electronics 2). With
this trend, the wire harness (hereafter denoted as W/H)
that supplies electric power and signals to each equipment grows in volume, resulting in the increase of vehicle
weight 2). Because equipment to be installed in the limited
space in vehicles increase in number and W/Hs are distributed threading between these equipment, designingequipment installation is becoming more difficult. On thevehicle assembly lines also, the swollen W/Hs cause big
problems such that they are heavy, stiff, difficult to handle
and hard to install. Thus, there is an increasing need forthinning W/Hs.

*

Harness and Electric Components Engineering Dept.,
Electric Components Plant, Automotive Products Div.
*2 Development Promotion Dept., Automotive Products Div.
*3 Toyota Engineering Dept., Automotive Products Div.
*4 Third Planning Dept., Plants and Facilities Div.
*5 Production Engineering Dept., Electric Components Plant,
Automotive Products Div.

Against this background, we have promoted the development of a seat module aimed at a minor modification
program of Toyota’s Land Cruiser. Various means for W/Hthinning have been implemented such as accommodationof joint circuits into the circuit board of electronic control
unit, reduction of wire-to-wire connectors through the useof board connector, and elimination of wire through theemployment of an infrared ray communication system.
This is the first time in the world that a wireless communication system using infrared ray has been adopted as acommunication means for the body system control of amass production car.

2.

OUTLINE OF SEAT MODULE

2.1 Problems with Present Technologies
A seat adjuster of powered seat systems, in which a seatposition is adjusted by electrical motors, has a number ofcomponents such as motors and links accommodated in alimited space. In the case of memory seat, an electronic
control unit called “seat ECU” is additionally required tomemorize and retrieve drivers’ seat positions.
Conventionally, much manpower was needed to assemble
such systems comprised of W/Hs, seat ECU, and brackets because these were all independent components.
Among others, the installation of W/Hs that were stiffened
by increased circuits was known as one of the difficult
works, so that earnest desires for workability improvement
has been created. In particular, the part called “seatadjuster transfer” involves careful considerations from thestandpoint of product quality in terms of circuitry size andpath design. This is where the W/H path transfers from the

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Development of a Seat Module for Automobiles

inside of a seat-adjusting rail to its outside on which a seatswitch is located, whereby sometimes causing a problem
such that the W/H is jammed between the seat-adjustercomponents as the seat changes its position in the verticaldirection. Figure 1 shows the appearance of a conventional seat-adjuster assembly.
2.2 Development Goals
The development goals of the seat module are as follows.
1) Improving productivity: Reduction in installation manhour through workability upgrading.
2) Improving product quality: Designing a W/H that eliminates jamming.
3) Weight reduction: Reducing weight through integration of components, use of resin to replace metalcomponents, and circuit number reduction.
2.3 Module Configuration
Figure 2 shows the developed product installed on a seatadjuster assembly. In order to reduce the component
number and installation man-hour as well, the seat ECU,
seat W/H, bracket, and casing have been integrated. The
integration of the W/H with the seat ECU enabled a substantial reduction in the number of circuits.
Moreover, the integration with the W/H allowed an opti-

mized module design embodying general design concepts
such as accommodating circuit joints into a board andplacing connectors near to the auxiliary equipment.
In addition, clamping holes for the W/H and fixing parts
for the connectors were provided on the bottom face ofthe casing to reduce the number of components further.
Countermeasures against jamming of the W/H are
known to be such that a path route is selected as far as tothe back of the seat to avoid passing by the transfer partand that an opening for the W/H is provided on the seatadjuster to prevent jamming. However, problems still
remain with these countermeasures such that the cost
increases due to the additional wiring length for the former, and workability degrades for the latter.
At this time, we have investigated wire-reducing technologies to reduce the circuitry size. We have studied
wireless communication systems based on electromagnetic wave as well as infrared ray communication systems, and decided to employ the latter for its advantageous cost.
As shown in Figure 2, a transmitter (LED) and a receiver (PD) are provided at the seat-control switch and theseat ECU, respectively, to effect unidirectional communication between them. The dotted line in the Figure shows
the direct beam path of the infrared ray communication.
Figure 3 and Figure 4 show in comparison the components of the conventional and the developed W/H module,
respectively. It can be confirmed that the number of components has been reduced together with the W/H size.

W/H

Seat control
switchSeat ECU
BracketFigure 1

Appearance of conventional seat-adjuster assembly.

Figure 3

Components of conventional W/H module.

Transmitter

ReceiverFigure 2

Appearance of seat-adjuster assembly using thedeveloped module.

Figure 4

Components of developed W/H module.

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Development of a Seat Module for Automobiles

The infrared ray communication system has been developed jointly with Tokai Rika Co., Ltd. since the seatadjusting switch belongs to their products. Technologies
for this in-vehicle, infrared ray communication system will
be described in detail below.

Transmitter side
Minimum lightintensity requiredb

3.

DEVELOPMENT OF INFRARED RAY
COMMUNICATION SYSTEM

Conventionally, application of in-vehicle infrared ray communication systems has been practically limited to suchsubsystems as remote control for audio systems andopener for door locking systems, which would give little
influences to the vehicle should a failure occurs by any
chance.
Because the seat-adjuster transfer part developed at
this time for wire reduction belongs to a body control communication system, where the signals are transmitted fromthe seat-control switch to the seat ECU, the issue of
ensuring reliability has been identified to be an important
technological task.
3.1

Specifications for Infrared Ray Communication
SystemIn order to implement an infrared ray communication system of high in-vehicle reliability sufficient for body control
and also to make the system easily applicable, basic
specifications have been set as shown in Table 1.
Illegal-signal processing of disturbing lights and the likehas been incorporated in firmware to enhance communication reliability.
3.2 Infrared Ray Intensity Design
Below will be described the infrared ray intensity design
with respect to the light intensity on the transmitter sideand the light receiving performance on the receiver side.
It is supposed that light transmitting and receiving performance may change from their initial performance due
to various factors besides original differences in thedevice performance, so that the Failure Modes andEffects Analysis (FMEA) was utilized to extract variablefactors in the transmitting and receiving device performance, and the results were reflected in the systemdesign.
Light intensity attenuating factors considered are: a) differences in device performance, b) changes in device perTable 1

Basic specifications for the infrared ray communication system.
Item

Content

Communication method Unidirectional multiplex communication
Communication speed

1 kbpsCoding method

Pulse position modulation

Modulation frequency

38 kHzError check

CRC (8 bit)

Response

Latency time of 100 msec or less to be securedbcaMinimum lightintensity requireddLight intensity of device
with minimum outputacdb) changes in device performanceover timec) adhesion of dirt on to the PD coverd) others

Required lightintensity

Receiver side
Light intensity

Figure 5

Design diagram for infrared ray intensity.

formance over time, c) adhesion of dirt on to the PD
cover, and d) others.
These factors were considered for the light transmitterand receiver respectively, and the light intensity at thetransmitter was designed to meet the required light intensity at the receiver. Figure 5 shows the diagram used in
the light intensity design.
The “a) minimum light intensity required” is a necessary
design value of light intensity that has been specified
based on the device data sheets for proper functioning of
the receiving circuit, so that the intensity was determinedby applying statistical processing on the measured results.
As for the device performance changes over time, thedevice performance data sheets were referred to. The“adhesion of dirt on to the PD cover” means a factor oflight intensity attenuation resulting from adhesion of dirt on
to a cover that is provided to protect the light receiving
device and to prevent entering of foreign matters into the
ECU. All these attenuation factors were taken into accountto determine the light intensity required on the receiverside.
The upper limit of loading current for the light transmitting device, an LED, is determined from its durability taking its vehicle mounting conditions into consideration. The“light intensity of device with minimum output” means aminimum light intensity that is set based on the light intensity measurements at the loading current limit. The “minimum light intensity required” was determined considering,
just like as for the receiver side, all the attenuation factors.
In order to reduce attenuation effects due to device
directivity and also to make the transmitting light intensity
meet the light intensity required at the receiver, both the
LED and PD were installed arranging them face to facewith each other.
Next will be described adhesion of dirt, which is one of
the attenuation factors. Infrared remote controllers for TV
sets and the like are easy to maintain by wiping out thedirt adhered on the light transmitter. In contrast, the present product has to be maintenance-free because it is

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Development of a Seat Module for Automobiles

installed under a seat thus making workability for wiping
out very poor. Furthermore, the product has to be provided with some countermeasures against dirt because theplace under a seat is, despite the fact that it is in a vehicle,
likely to be dirty due to mud brought into by the shoes.
Following investigations were carried out to understandthe adhesion conditions of dirt under the seats.
1) Investigation on Under-Seat Conditions of Aged Cars
The under-seat conditions of a car about 10-years aged
were investigated for its pollution. It was found that dust
deposited on the top surface of a duct for rear heater
made of molded resin, while its side-walls had a relatively
small amount of adhesion; differences in the degree ofpollution arise depending on the resin material; and thatthe seat rail gathered dust regardless of position due tothe grease applied.
Figure 6 shows the example of an RV that was driven
170 thousand kilometers.
2) Componential Analysis of Dust Adhered Under-Seat
Samples from the under-seat dust deposition were analyzed for their components and it was identified that sandand cellulose constituted most of them. Moreover, a test
was conducted in which a sample of PD cover was set atthe light receiving position of seat ECU for half a year. In
this test, while sand was also detected, constituents ofseat such as metal dust or fats and oils such as grease
were not detected probably because of their low contents.
We have therefore decided to develop countermeasuresagainst dirt adhesion assuming such pollutants as sandand cellulose.
3.3 Design of PD Cover
The design level for attenuation due to pollution has been
set to 70 % in view of other attenuation factors consideredin the light intensity design. To begin the PD cover design,transmittance changes over two types of pollution werestudied, i.e., grease adhesion and dust adhesion.
The attenuation is defined by the following formula.
Attenuation (%) =(Figure 6)

Transmittance after pollution test
x 100
Transmittance before pollution test

Under-seat view of an RV.

Because grease is applied on the seat-adjuster rail, it isvery likely that the grease adheres, during the time of seatmodule installation on to the seat-adjuster assembly, to
the PD cover via working gloves. A small amount ofgrease was applied to a sheet sample simulating theassembly process, and its infrared transmittance wasmeasured. It was found that the attenuation was as muchas 46.4 %, whereas the design level had been set to 70%.
We have decided, therefore, to provide a cylinder cover
to prevent working gloves from touching the PD coverplaced in the beam path.
In the evaluation of pollution due to dust adhesion, JIS
D 0207 General Rules of Dust Test for Automobile Parts
was adopted for the sake of dust adhesion with highrepeatability.
In the preliminary evaluation where a cylinder was used
as a PD cover, test particles were seen to deposit on thecylinder’s interior. When dust deposits on the cylinder’sinterior, the reflectance for infrared ray changes decreasing light intensity.
We therefore devised a cylinder with a notch on its
underside to prevent dust deposition, and a comparativeevaluation was made with a cylinder having no notch.
In view of the fact that the transmitter position shifts as
the seat position changes, a cylinder 7 mm in diameter
was used to enable a direct reception of the beam in thefull range of the transmitter position, and it was placed
aslant along the lines of the infrared beam. The material isPMMA. Because of the fact that the PD was molded witha visible-light-cut resin and that the receiver was to beinstalled under the seat eliminating design considerations
to conceal the board --as is the case with home appliances, a transparent and colorless material was selectedgiving preference to infrared transmittance. Figure 7
shows the structure of a PD cover.
Figure 8 shows the measured results of transmittanceafter dust tests using PD cover samples with different
structures. Three types of samples, i.e., plate-type without
cylinder, cylinder-type for beam path protection, and cylinder-type with a notch at the underside, were used. The
cylinders were 7.5 mm in height. The initial value means
the transmittance before the dust tests. The low density
and the high density correspond to the transmittance atthe low-density floating dust test (Section F3) and the

Figure 7

Structure of PD cover.

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140.0Transmittance (%)

120.0
100.0
80.0
60.0

Plate-type

Cylinder-type

Cylinder-type with notch

Initial value

40.0

Low density

Figure 9

Test samples of PD cover.

High density

20.0
0.0
Plate

CylinderNotched cylinder

140.0

Sample120.0Comparison of transmittance between different PD
cover structures.

high-density floating dust test (Section F1) both defined in
JIS D 0207, respectively.
Basically, the seat module is an indoor component, sothat it is required to meet the low-density floating dust test
only. However, to ensure reliability against dust, the highdensity floating dust test with severer test conditions was
carried out, which is applicable to outdoor components.
With respect to the test powder, the class 8 Kanto loamy
layer powder specified in JIS Z 8901 Test Powders andTest Particles was used for the light-density test, and theclass 11 Kanto loamy layer powder with finer particle sizefor the heavy-density test to make the test severer.
The transmittance obtained using no PD cover was
defined to be 100 %, so that it exceeded 100 % due to thereflection at the inner surface of the cover when a PD
cover was used.
Test samples of PD covers are shown in Figure 9. They
are, from the left, plate-type without cylinder, cylinder-type
for beam path protection, and cylinder-type with a notch at
the underside. The beam passes through the cylinder.
Kanto loamy layer powder adhered may be seen.
One of the test samples had a notch at the underside in
anticipation of eliminating dust deposition on the beam
window. However, it was found that such a structure tended to gather much dust on the beam path, and that acylinder without a notch worked much more effectively
against dust. It would appear that the notch caused someadverse changes in the airflow.
Figure 10 shows the results of cylinder height optimization.
The initial transmittance is seen to be higher the larger
the height of the cylinders. This is presumably because ofcollimating effects due to the reflection at the cylinder’sinner surface. Results of dust tests showed that, for thecases of both high-density and low-density dust tests, theoptimal result was obtained with a sample 10 mm inheight. It was supposed that, in the case of low cylinder,
the transmittance for direct beam decreased due to thedust adhered on the beam window, while in the case ofhigh cylinders, the reflection in the cylinder decreased dueto the dust deposited on the cylinder’s interior.
Based on these studies, it was decided to use a cylinder-type PD cover with a height of 10 mm.

Transmittance (%)

Figure 8

100.0
80.0
60.0

Initial value
Low density

40.0High density
20.0
0.0
0

5

7.5

10

12.5

Height (mm)Figure 10 Comparison of transmittance between cylinders ofdifferent height.

3.4

Evaluation Methodology for Infrared Ray
Communication System
We have developed and implemented evaluation methods
to simulate the failure modes described in the FMEA,
because our customer and we were lacking in any specifications or evaluation methods for this unprecedented system.
Evaluation items considered are: 1) influence of pollution, 2) influence of obstacles, 3) influence of otherinfrared ray communication equipment used in-vehicle, 4)influence of disturbing lights, and 5) endurance test using
actual cars. The results of each evaluation are described
below.
3.4.1 Influence of Pollution
Infrared ray attenuation under the influence of pollution on
the PD cover window was evaluated. The criterion forattenuation at the window was set to 70 %.
In addition to the high-density as well as low-density
dust tests mentioned before, a dust test using a type of
textile fiber called cotton linter was also carried out simulating the cellulose found in the dust component analysis.
A cotton linter contained in the class 15 mixed dust specified in JIS Z 8901 was used. The attenuation measurements were: 97.5 % for low-density floating dust, 88.2 %for high-density floating dust, 99.9 % for cotton linter; thusachieving the target of 70 % in all the cases.
3.4.2 Influence of Obstacles
To simulate an interruption of the direct beam by an accidental intrusion of obstacles, selected samples were used
to screen the beam path, and proper operation of the system was checked. It was confirmed that the seat adjuster

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Table 2

Effects of seat module.

Item

To receiver
Transmitter
Beam path

Effect over conventional

Weight

40 % reduction

Installation time

57 % reduction

Number of transfer wires

39 % reduction

Number of total wires

47 % reduction

Figure 11 View of obstacle evaluation.

4.
operated properly even when the direct beam was interrupted, thanks probably to light signals reflected from theseat-adjuster components. Figure 11 shows a scene of
the test, where the direct beam represented by the broken
line is interrupted by a stuffed toy.
3.4.3

Influence of Other Infrared Ray Communication
Equipment
Influence of other infrared ray communication equipment
in-vehicle on seat adjuster operation was evaluated. Morespecifically, another infrared remote controller was operated during the time when communication system was inoperation for seat adjusting so as to confirm if there were
any influences.
An infrared ray whose wavelength is within the wavelength band of the PD and whose modulation frequency is
within the pass-band of band-pass filter in the receiving
circuit had a chance of giving influences. It was found,however, ordinary use posed no problems.
3.4.4 Influence of Disturbing Lights
Influence of disturbing lights illuminating the receiver was
evaluated. Disturbing lights considered include sunshine,
lights from the outside such as road lighting, and in-vehicle lighting.
Because of the fact that a visible-light-cut resin is used
for the PD and that the light-receiving amplifier has an
automatic gain control function in response to the environmental brightness preventing saturation, the influence due
to disturbing lights has been confirmed to be almost negligible.
3.4.5 Endurance Test Using Actual Cars
Prototype products have been installed on actual cars forendurance tests in Australia as well as in Japan, and longterm endurance was evaluated, posing no problems.

EFFECTS OF DEVELOPED PRODUCTTable 2 shows the effects of the developed productexcluding, because the comparison was made with conventional specifications, those on function improvement.
The installation time has been reduced to less than half
the conventional, achieving a significant improvement due
to modularization. The weight as well as the number of circuits have been improved. The use of infrared ray communication not only reduced the number of transfer circuits but also mitigated the problem of W/H jamming.

5.

CONCLUSION

Integrating the ECU, W/H, and bracket for seat-adjuster,which have been separate components conventionally,
into a module has proven to be effective in reducing installation time as well as circuit numbers. Further improvements can be expected if the range of modularization is
expanded to design optimization including arrangement ofseat adjuster and auxiliary equipment, connecting method,
power supply, and communication system.
We intend to extend the knowledge concerning modularization acquired through this development to other modules of various parts of the vehicle. We also plan tomature the infrared ray communication technology in aneffort to make it a differential technology.

REFERENCES
1) Yoshiro Tsuruhara: Nikkei Mechanical, 566(2001), 36 (inJapanese)
2) Yasuo Tanokura: Nikkei Electronics, 741(1999), 107 (in Japanese)

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