Mitsubishi Electric ADVANCE vol87

VOL.87/SEP.1999

Environmental Technology Edition

MITSUBISHIELECTRIC

●Vol. 87/Sep. 1999 Mitsubishi Electric ADVANCE

A Quarterly Survey of New Products, Systems, and Technology

Environmental Technology Edition

CONTENTS

Our cover illustration shows the symbol markof the Mitsubishi Electric Group’s environmen-tal activities. First devised in 1993, it ex-presses our commitment to being an indus-trial group whose continued existence isjustified by its contributions to a sustainablesociety — that is, one founded on recyclingvaluable resources.

Shin Suzuki

Haruki NakamuraToshimasa UjiMasakazu OkuyamaYasuo KobayashiMasao HatayaHideki NakajimaMichio OtsuboMasashi HonjoTakashi NagamineHiroaki KawachiHiroshi KayashimaKouji IshikawaTsuneo TsuganeToshikazu SaitaAkira Inokuma

Masao Sakai

Masakazu OkuyamaCorporate Total Productivity Management& Environmental ProgramsMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-2465

Yasuhiko KaseGlobal Strategic Planning Dept.Corporate Marketing GroupMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-3455

Orders:Four issues: ¥6,000(postage and tax not included)Ohm-sha Co., Ltd.1 Kanda Nishiki-cho 3-chomeChiyoda-ku, Tokyo 101-0054, Japan

Editor-in-Chief

Editorial Inquiries

Mitsubishi Electric Advance is publishedquarterly (in March, June, September, andDecember) by Mitsubishi Electric Corporation.Copyright © 1999 by Mitsubishi ElectricCorporation; all rights reserved.Printed in Japan.

Editorial Advisors

Vol. 87 Feature Articles Editor

Product Inquiries

TECHNICAL REPORTS

OVERVIEW

Time for a personal commitment to sustainabledevelopment ....................................................................................... 1by Ryoichi Yamamoto

Ecofriendly Ozone-Based Wet Processes forElectron Device Fabrication ............................................................... 2by Hirozoh Kanegae

A Recycling Plant for Home Electric Appliances .............................. 7by Eiichi Hirasawa

An Ecological Design Support Tool for Recyclability ...................... 12by Takao Bamba and Niall Murtagh

Ecomaterials ..................................................................................... 17by Fumiaki Baba

An Electrically Operated EGR Valvethat Reduces Automotive Emissions .............................................. 20by Toshihiko Miyake and Hidetoshi Okada

"Advance" to Become Online MagazineReaders are advised that this edition of Advancewill be the last one to be printed as a traditionalmagazine. From December, Advance willcontinue to be available, as it is now, at theMitsubishi Electric global homepage website(URL http://www.mitsubishielectric.com/ghp_japan/corporate_profile/advance/advance_index.html). It is hoped that the move toonline format will speed publication and enablereaders to print out only those articles of specialinterest to them.

MITSUBISHI ELECTRIC OVERSEAS NETWORK

TECHNICAL REPORTS

If Ernst Von Weizsächer is a realist, does that make Schmidt-Bleek an idealist? Weizsächer, Amory B.Lovins and his wife L. Hunter Lovins are co-authors of the book “Factor 4,” while Schmidt-Bleek wrote“Factor 10,” both of which have become best sellers around the world. Weizsächer stresses that to prevent theworldwide gap between poverty and affluence from opening up still further, we need to multiply theproductivity of our energy resources immediately by a factor of four, while Schmidt-Bleek emphasizes that afundamental solution to the world’s environmental problems will require the absolute volume of theworldwide flow of materials to be halved and, if the quality of life in the OECD nations is to be maintained,the productivity of energy will have to be increased at least ten-fold by the year 2050.

However, there are those who say that with the population of the world in 2050 estimated at nine billion,it will take an improvement of a factor of 20 in energy productivity to provide for everyone. To achieve a factorof ten improvement certainly implies a factor of four improvement, so it is not really a matter of whichestimate is right and which wrong. The real issue is that any foreseeable solution of environmental problemswill require major revolutions in technology, and in social and financial systems.

I have only known the two authors for three years, but I am grateful to count them among my friends.Weizsächer is 60 years old, and Schmidt-Bleek is approaching 70, but I am overwhelmed by the enthusiasm,intellectual rigor, and intensity of their activities in the search for far-reaching and comprehensive solutionsto the world’s environmental problems, and by the wide circle of their supporters. Weizsächer, for instance,is never without a Lüfthansa flight schedule in his briefcase. Both of them take personally the problems ofenergy, the environment and poverty confronting mankind, and are utterly committed to comprehensiveglobal solutions. “It needs to be done now and I need to do it” expresses a commitment that seems to derivefrom a sense of responsibility for modern culture, which owes so much to European influences. In discussionswith members of the “Factor 10” club at Schmidt-Bleek’s villa in Provence, in the South of France, I wonderedwhy so few concepts or theories of how to save the world had originated in Japan. Sustainable development,eco-efficiency, environmental management, Factor 10, post-materialism, eco-design, life-cycle assessment...all of them are European proposals.

However, I certainly do not accept that the Japanese are lacking in creativity. For instance, the sophisti-cated culture of Japan’s Edo era was by no means one of affluence, and I think we could properly stress theappeal of its non-materialistic nature to the world. Certainly, in the 21st century, one of the problems will becreating a rich post-materialistic culture.

At my first meeting with Weizsächer this year, he was saying how the productivity of energy resources inJapan was double that in Europe and America, and that this was one of the reasons he was urging ecologicaltax reform there. Isn’t it time that the Japanese were more self-confident, and took up the challenge ofsustainable development? ❑

Note: Weizsächer is the son of a famous astrophysicist and the grandson of a President of Federal Germany. He currently heads the Wuppertal Institute for Climate, Environment and Energy.

Schmidt-Bleek is an authority on environmental toxicity. After working on the OECD’s regulationsfor toxic substances, he retired last year as deputy director of the Wuppertal Institute, and now, asthe director of the Factor 10 Research Institute, he is active in eco-design consulting.

*Dr. Ryoichi Yamamoto is a Professor at the Institute of Industrial Science & Technology, Tokyo University.

OverviewTime for a personal commitment to sustainable development

by Ryoichi Yamamoto*

September 1999 · 1

TECHNICAL REPORTS

*Hirozoh Kanegae is with the Advanced Technology R&D Center.

Ecofriendly Ozone-Based Wet Processesfor Electron Device Fabrication

2 · Mitsubishi Electric ADVANCE

Mitsubishi Electric has developed ozone-basedwet processes for fabrication of LCDs and othersemiconductor devices. These low-cost and low-environmental-impact processes use tinyamounts of chemical reactants and can be con-ducted at room temperature. This report intro-duces technology for contamination-freeproduction of high-density ozone and ozonatedwater, and discusses use of ozonated water as asubstitute for a standard RCA cleaning processand for the removal of photoresist.

Public concern is driving manufacturers toreduce the environmental impact of their manu-facturing processes. The imperative to manu-facture good products at a low price is intransition to a new model of sustainable devel-opment in which consumers and manufactur-ers jointly participate.

Reducing the environmental impact associ-ated with manufacturing processes is now tak-ing importance alongside the more conventionalobjectives of making electronic equipmentsmaller, lighter and more power efficient. Novelmanufacturing processes will consume smaller

by Hirozoh Kanegae*

energy, chemical and gas supplies, reducing bothcost and manufacturing wastes with small foot-print installations.

This article introduces cost-effective and en-vironmentally-friendly wet cleaning processesfor semiconductor-device and LCD fabricationusing ozonated water. Ozone is a strong oxidiz-ing agent suitable for wafer cleaning and its onlybreakdown product is oxygen.

Ozone Gas and Ozonated WaterOzone consists of three oxygen atoms joinedby covalent bonds with a strength somewherebetween single and double bonds. Its applica-tions include disinfecting and deodorizingdrinking water supplies, bleaching and removalof organics in wastewater, and surface treatmentand oxidation of organic materials in industrialprocesses. All of these applications rely onozone’s powerful oxidation capabilities andharmless decomposition to oxygen.

Like other gases, ozone’s solubility in waterobeys Henry’s Law. The amount of ozone thatdissolves in water increases as the partial pres-sure of ozone rises and as the water temperature

Fig. 1 General design of an ozonizer producing high-concentration contamination-free ozonated oxygen.

Gas outlet

Conductive layer

High-voltage ceramic-covered electrode

Pressure vessel

Ceramic spacer

Ceramic-covered ground electrode

Power supply

Gas flow

Gas inlet

TECHNICAL REPORTS

September 1999 · 3

drops. The following rule for calculating dis-solved ozone concentration is based on experi-mental measurements.

Cw = 0.604(1+t/273)/(1+0.063t)\Cg .......... Eq. 1

where Cw is the dissolved ozone concentrationin mg/l, Cg is the atmospheric ozone concen-tration in mg/l, and t is the water temperaturein degrees Centigrade.

Ozone has three main mechanisms of chemi-cal activity. First, it attacks the unsaturatedbonds in double bonded and aromatic hydro-carbon chains by the well known Criegeemechanism yielding ketones, carboxylic acidand carbon dioxide. Second, it reacts with wa-ter to form the hydroperoxy radical (HO2.) andhydrogen peroxide (H2O2) which attack satu-rated hydrocarbon chains. Third, it reacts withinorganic materials based on the difference inoxidation-reduction potential and oxidizes allmetals except gold and platinum.

Controlling ContaminantsTo replace the highly evolved manufacturingprocesses currently used for semiconductor pro-duction, ozone based processes will have toachieve comparable tact (or process “step”)times and control contaminants that would ad-versely affect yields. High concentrations arerequired, and ozone and ozonated water gen-erators must achieve the cleanliness requiredby today’s high scales of integration.

Fig. 1 shows the basics of a system that pro-duces clean, high-concentration ozone. A nar-row discharge gap is formed by a conductivelayer on the bottom surface of disc-shaped ce-ramic substrate and a ceramic-coated groundelectrode separated by a ceramic spacer. Theelectrodes are housed in a pressure vessel. Oxy-gen gas supplied to the vessel passes throughthe discharge gap and exits through a port inthe center of the ground electrode as ozonatedoxygen[1],[2]. The discharge gap is extremely nar-row to prevent temperature rise of gas in thegap and to control the number of low-energyelectrons that could cause the ozone to breakdown. These features enables the system to

achieve ozone concentrations over 230g/Nm3

at a gas flow rate of 2l/min (Fig. 2).In addition to high concentration, ozone pro-

duced for semiconductor manufacturing mustbe free of metallic contaminants. This isachieved by ensuring that the gas contacts onlyceramic surfaces. Metallic contamination of theozonated water was measured at below the partsper trillion detection levels of microwave in-duced plasma mass spectroscopy and flamelessatomic absorption spectroscopy (Table 1).

Wafers immersed in ozonated water were thentested for metallic contamination by total re-flection X-ray fluorescence spectroscopy andtypical contaminants including Ca, Cr, Mn, Fe,Ni and Cu were below the detection thresholdof 1 × 1010 atoms/cm2.

A particle counter at the ozone generator’soutlet detected no particles over 0.27µm in di-ameter[3].

Fig. 2 Effect of gas flow rate on ozoneconcentration.

Pressure: 2.5kgf/cm2G Discharge power: 1,000W Temperature: 20˚C

8010100 15 20

100

120

140

160

180

200

220

240

Ozo

ne c

once

ntra

tion

(g/N

m3 )

Ozonated gas flow rate (Nl/min)

Table 1 Metallic Contaminants in Ozonated WaterElement Na, K, Ca, Fe, Zn, Al Mg, Ni, Cu Cr, Mn

Concentration<50ppt <20ppt <10ppt

(DI water)

Conc. (ozonated<50ppt <20ppt <10ppt

DI water)

Detection 50ppt 20ppt 10pptthreshold

TECHNICAL REPORTS

Ozonated Water Cleaning TechnologyControl of particles and other contaminants isessential to maintain high yields in productionof high-density memory devices. At present, thisis accomplished using a series of chemical bathsknown as the RCA washing method[4]. Initially,a sulfuric acid and hydrogen peroxide bath (SPM)at 120~150°C removes organics and somemetallics. Second, a bath of dilute hydrofluoricacid (DHF) at room temperature removes theoxide layer and incorporated metallic contami-nants. Third, an ammonium hydroxide and hy-drogen peroxide bath (APM) at 80~90°C removesparticles. Fourth, an 80~90°C bath of hydrochlo-ric acid and hydrogen peroxide (HPM) removesmetals. Finally, dilute hydrofluoric acid is usedto remove metallics from the oxide layer formedin the preceding step. Seven rinsings in deion-ized water follow for a total of 12 process steps(Table 2). LCD manufacture employs a similarprocess with fewer steps, but the large substratesize means larger baths that consume morechemical supplies.

Replacing these complicated cleaning proce-dures with ozonated water cleaning dramati-cally reduces use of chemical supplies, savingthe cost of the chemicals and waste processing.Ozone processing also eliminates processing atelevated temperatures, avoiding the associatedventing of vapors to the atmosphere. Reducedrinsing saves dionized water.

Ozone can oxidize organic residues from photo-resist processes. Spin washing the wafers withultrasonically activated ozonated water achievescleaning performance equivalent to a sulfuricacid and hydrogen peroxide bath[5].

Fig. 3 Copper contamination on wafers beforeand after cleaning. The ozoneconcentration is 12ppm.

Not detectable

Con

tam

inat

ion

leve

l (at

oms/

cm2 )

1010

1011

1012

1013

1014

Bef

ore

clea

ning

Afte

r cl

eani

ng b

y oz

onat

ed w

ater

+0.

1wt%

HF

Afte

r re

peat

ed

clea

ning

s by

oz

onat

ed w

ater

+0.

1wt%

HF

Afte

r cl

eani

ng b

y oz

onat

ed w

ater

+0.

025w

t% H

F

Afte

r re

peat

ed

clea

ning

s by

oz

onat

ed w

ater

+0.

025w

t% H

F

Table 2 A Comparison of RCA and Ozonated Cleaning Systems Target Organic photoresist Particles Metals Native oxides

Method residue

Cleaning agent SPM APM HPM DHF

RCA cleaningMechanism

OxidativeElectrical repulsion Dissolution Etching

decomposition

Cleaning agent Ozonated water

Ozonated waterMechanism

OxidativeDissolutioncleaning decomposition

Acceleration method Ultrasonic power pH control and ultrasonic power Add a little HF

Ozonated water alone does not remove metal-lic contaminants incorporated into the oxidelayer, but is effective when supplemented by a0.1% hydrofluoric acid solution, a combinationthat has been thoroughly investigated[6],[7]. Fig. 3shows that ozonated water bath with hydrofluo-ric acid reduces copper contamination withperformance comparable to a conventional hy-drochloric acid and hydrogen peroxide bath. Theacid exposes metallic contaminants embeddedin the oxide layer, so that an oxidation reactioncan proceed. This forms metal ions that aredrawn into solution. This constitutes a dramaticreduction in chemical usage.


TECHNICAL REPORTS

Use of ozonated water for particle removalhas been investigated[7],[8]. The ammonium hy-droxide and hydrogen peroxide bath normallyused has a high pH so that particles receive anegative charge repelling them away from thenegatively charged wafer. Since ozone water so-lutions are either neutral or mildly acidic,ozonated water processes will require activa-tion by pH modifiers or ultrasonic energy. Re-placing the ammonium-hydroxide based processeliminates a major source of ammonia contami-nation, increasing yields and reducing clean airconsumption.

Ozonated Water for Photoresist RemovalPhotoresists can be removed by oxygen plasmaashing (a dry process), by organic solvents, or ina sulfuric acid and hydrogen peroxide bath. Forprocessing LCD panels, a mixture of dimethylsulfoxide (DMSO) and monoethanol amine(MEA) is generally used.

Both the solvent and sulfuric acid process are

performed at elevated temperature and ventfumes. In the widely used sulfuric acid perox-ide process, Caro’s acid (H2SO5) strips the re-sist, which oxidizes as soon as it is free. Froman environmental impact perspective, trappingthe fumes requires special equipment and thebath must be periodically replaced followingdepletion of the hydrogen peroxide.

An ozone-and-water method would not re-quire the high temperatures or fume traps ofthe sulfuric acid method, reducing air costs andsaving on dionized water—a much smaller en-vironmental impact.

When an ozone concentration of 150~250g/Nm3 and ozonated water flow of 4.0 l/min isused in the ejector-type resist stripping appara-tus of Fig. 4, Fig. 5 shows the stripping perfor-mance for positive resist. The stripping rate isproportional to the water’s ozone concentrationand increases with temperature.

Fig. 6 shows the normalized resist removalrate as a function of temperature. R is inversely

Ozonated water

Ejector Ozone generator

Ozonated oxygen

Temperature controller

Pb

Pg

Pf

PReactor

To decomposition tower

Ozone monitor

Fig. 4 Resist removal apparatus with ozone ejector

KeyPf, Pb and Pg: Pressure gaugesP: Pump

September 1999 · 5

TECHNICAL REPORTS

References1. Details are available, in Japanese only, in Mitsubishi Denki Giho,

Vol.73 No.5 (May 1999).2. J. Kitayama, M. Kuzumoto: Theoretical and Experimental Study on

Ozone Generation Characteristics of an Oxygen-fed OzoneGenerator in Silent Discharge, J.Phys.D, 30, 2453-2461 (1997)

3. Details are available, in Japanese only, in Mitsubishi Denki Giho,Vol.73 No.5 (May 1999).

4. W. Kern, D. Puotinen: Cleaning Solution based on HydrogenPeroxide for use in Silicon Semiconductor Technology, RCAReview, 31, 187 (1970).

5. S. Ojima, K. Kubo, M. Toda, T. Ohmi, Megasonic Excited OzonizedWater for the Cleaning of Silicon Surfaces, J. Electrochem. Soc.,144, 1482 (1997).


7. T. Osaka, A. Okamoto, K. Saga, H. Kuniyasu, T. Hattori,Environment Friendly Single Water Spin Cleaning with AlternateUse of Ozonated Water and Dilute HF, 7th Intl. Symp. onSemiconductor Manufacturing, pp.113 (1998).

8. M. Alessandri, E. Bellandi, B. Crirelli, F. Pipia, K. Wolke, M.Schenkl: Particle Removal Efficiency and Silicon Roughness in HF-DIW/O3/Megasonics Cleaning, USPSS '98, pp.13 (1998).


proportional to T, expressed according toArrehenius’ equation:

R = Roexp(-E/kT) ........................................ Eq.2

where Ro is the frequency factor, k is Boltzman’sConstant, T is the water temperature (K) and Eis the activation energy.

The activation energy calculated from Fig. 6and Eq. 2 is 0.29eV, substantially smaller thanthe 4~5eV activation energy needed for carbon-to-carbon single and double bonds or carbon-to-oxygen single bonds, suggesting that one or moreintermediate steps are involved[9].

The rate of reaction increases with tempera-ture, but the dissolved ozone capacity reduceswith temperature according to Eq. 1. For maxi-mum resist removal speed, the processing tem-perature should be set to a level that matchesthe activation energy requirements of the resist.The type of resist, degree of baking, and the pres-ence of ion implantation all affect activationenergy. A key issue in ozone-based resist removalsystems is achieving satisfactory removal speed.

Chemical-free, energy-saving room-temperatureozone-based processes promise to reduce the costand environmental impact of semiconductor and

Fig. 5 Effect of ozone concentration on resistremoval rate.

Res

ist r

emov

al r

ate

(µm

/min

)

0.01

00 20 40 60 80 100

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

Concentration of ozone in water (ppm)

40˚C 23˚C 15˚C

7˚C

Fig. 6 Effect of water temperature on normalizedresist removal rate.

R x

100

0 (µ

m/m

in/p

pm)

0.1

1

10

1,000/T (1/K) 3.1 3.2 3.3 3.4 3.5 3.6

LCD manufacture. Development of an efficientsilent discharge ozone generator capable of sup-plying a high concentration of clean ozonatedoxygen and a clean ozonated water generatorpromises to revolutionize semiconductor wa-fer and LCD cleaning and resist removal. ❑


TECHNICAL REPORTS

*Eiichi Hirasawa is with the Home Appliances Recycling Business Development Office.

A Recycling Plant forHome Electric Appliances

by Eiichi Hirasawa*

September 1999 · 7

Basic Plant DesignThe purpose of this project was to develop safeand efficient methods to recycle post-use homeelectric appliances, achieving a high rate of re-covery of materials that can be reused as wellas those that could have significant environ-mental impact. A key feature of this system isuse of a primary disassembly process to removemajor components prior to a chip-and-sort pro-cess for handling the remainder. Automationand mechanization have been introduced to en-sure safe handling of large and heavy products.The disassembly line has the following key fea-ture: Product model numbers are used to refer-ence a database of disassembly information. Thefirst time a particular product is disassembled,data is acquired at teaching stations and thedatabase makes this information immediatelyavailable to processing stations throughout theplant. Details are recorded when disassemblyproblems arise, and the next time the same prod-uct model is received, it is routed to a teachingstation and the database is updated with moreaccurate information. Table 1 lists the basicspecifications of the recycling plant and Fig. 1illustrates the concepts used to guide the de-sign of the primary disassembly process.

UnloadingTable 2 lists specifications of a conveyer sys-tem that transports work from the truck bed tothe sorting platform inside the plant building.Table 3 describes a second conveyer that usesceiling-mounted rails for sorting and trans-

Table 1 Specifications of the Recycling PlantAppliance External dimensions Weight Processing time Components removed in primary disassembly

TVs 350 x 300 x 360mm min., 70kg max. 35 units/h (1.7 min/unit) CRT (including band and electron gun),900 x 700 x 610mm max. housing, deflection yoke, PCBs

Refrigerators 400 x 480 x 450mm min., 100kg max. 25 units/h (2.4 min/unit) Compressor, housing, CFC12, R502950 x 1,950 x 600mm. max.

Washing machines 520 x 394 x 780mm min., 60kg 27 units/h (2.2 min/unit) Motor, plastic housing860 x 660 x 1,030mm max.

Air conditionersOutdoor units 540 x 200 x 420mm min., 72kg 17 units/h (3.5 min/unit) Motor, CFCs

870 x 470 x 785mm max.Indoor units 698 x 109 x 235mm min., 32kg 17 units/h (3.5 min/unit) Motor, fan, heat exchanger

1,200 x 294 x 450mm max.

Table 2 Time and Capacity Specifications of theUnloading Unit

Hoist capacity 100kg

Max. turning radius 2,928mm

Hoist travel 2,756mm

Equipment height 3,331mm

Hoist speeds2m/min,9m/min

Operation times

Arm movement 20s

Tool attachment 10s

Transport into plant 25s

Tool removal 5s

Total operation time 60s

porting work. A hoist and clamp fittingshold the work were specially developed forthe application.

Preprocessing LineThe preprocessing line prepares the appliancesfor transport by removing or modifying partsthat could interfere with the conveyor. All ACcords, hoses, etc. are removed. Refrigeratordoors, hinges, glass shelves, water collectors andmetal handles are removed. Refrigerant gas isrecovered from air-conditioner indoor units,while the connection pipes of the outdoor unitsare bent close to the body. The glass covers areremoved from TVs. Washing-machine motorcapacitors are removed.

TECHNICAL REPORTS


Sorting LineFig. 2 shows the configuration of the sortingline. Four unloading stations allow work to bereceived from up to four trucks at a time. Theproduct is identified and also whether or notthe line can handle it is evaluated on the roundconveyor. This allows processing tasks to beperformed at a single location. The round con-veyor sorts and distributes products to the ap-propriate processing lines, and has the additionalability to serve as a buffer in the case that oneof the lines is delayed and work has backed up.A return conveyor allows lines to return pal-lets awaiting service to the round conveyor.

Product Recognition SystemInstalled on the round conveyor, this labor-sav-ing system identifies the model number bymeasuring appliance size and shape and usingimage recognition technology to read the printedmodel number.

* Products automatically cleaned prior to disassembly

* Visual display of specialized disassembly procedures

Implementation in prototype recycling plant Goal

* AI and image processing technology to measure product dimensions and read model number * Use of categorized robot disassembly patterns * Robot control program with parametric processing * Vision sensor for screw pattern and position measurements * Screw loosening unit with multiple tool heads

* Teaching data is entered in database when particular model first arrives in the line. This data is retrieved to facilitate automatic processing of subsequent products of the same type. * The database can be updated with supplemental teaching data in cases where the disassembly procedure needs correction, so the database improves over time.

* Automatic or semiautomatic product introduction to line * Automatic transport of products between disassembly processes * Automatic transport of heavy disassembled components

* Automatic chip-and-sort process for electron guns * Automatic CRT transport * Automated housing removal

Automatic disassembly of numerous product variants

Efficiency improvement over time

Improving plant staff working conditions

Mechanization and automation of transport operations

Automation of dangerous operations

Clean working environment

Disassembly operations support

Table 3 Time and Capacity Specifications of theSorting Conveyor

Hoist capacity 160kg

Hoist travel 8.9m

Hoist speeds 3.5m/min, 14m/min

Conveyer travel 40.2m

Operation times

Initial movement 20s

Tool attachment 10s

Transport to round conveyer 24s

Tool removal 5s

Total operation time 59s

Appliance dimensions are measured by threecameras, two facing the front and one facingthe top. Images are processed by a personal com-puter. Measurements were correct 90% of thetime in tests of a wide variety of appliances.

The model number label is read by a separate

Fig. 1 Primary disassembly concepts.

TECHNICAL REPORTS

system consisting of a personal computer andfive cameras: two facing the appliance front,two facing the rear and one facing the right side.

Primary Disassembly Line for TVsFig. 3 illustrates a primary disassembly line forTVs. The TV is clamped at four corners. Thepallet has number flags identifying the palletand the appliance it is carrying, and flags formanaging the pallet’s flow through the variousprocessing stations.

Points on the TV’s rear housing need to beidentified to guide the subsequent cutting pro-cess. The teaching process used to locate thesepoints only needs to be conducted once for eachproduct model. The longer the line runs, the

smaller the proportion of TVs requiring teach-ing. Fig. 4 shows the change over time in thenumber of teaching operations conducted dur-ing line testing.

The teaching data provides work coordinatesand cutting-pattern data that guide operation of asix-axis robot with a saw head. The saw cuts therear panel free, allowing its removal.

Personnel at manual work stations removecomponents not amenable to automated han-dling. Control screens allow easy control of cutheight, depth and other cutting parameters.

Teaching is used to identify the location ofthe electron gun for crushing and removal, andto determine the location and type of the screwsthat attach the CRT to the chassis. Each TV

Fig. 2 A view of the sorting line.

September 1999 · 9

TECHNICAL REPORTS

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000No. of appliances processed

Teac

hing

rate

Key Actual teaching rate for TVs Actual teaching rate for refrigerators

Fig. 4 Cumulative effects of teaching.

must be measured individually to accommo-date variations in screw position among prod-ucts with identical model numbers.

The electron gun is removed by crushing itand vacuuming up the fragments. The crusheris inserted into the gun, and delivers shocks tothe gun, bending and breaking it. The crushingand vacuum work together to capture fragments

Electron gun

CRT (to CRT processing plant)

Plastic parts (Rear cover, front panel, etc., sent to secondary chipping plant)

Automated CRT and front panel removal

Wooden front panel

Automated electron gun and CRT mounting screw removal

Automated CRT mounting screw identification

Manual disassembly

Automated cleaning

Automated cutting away of rear cover

Manual cutting line identification

Load handling process

Delivery (automatic) and line insertion (manual)

Automated rear cover removal

Wooden rear cover

PCBs

Yoke assemblyCable harnesses

Recoverable materials (PCBs, capacitors)

of the gun and surrounding glass. The CRTmounting screws are loosened, the CRT is heldand lifted out of the chassis by a suction head,then is sent to a secondary processing plant.The remainder of the front panel is removedand sorted based on panel materials.

Primary Disassembly Line for RefrigeratorsAn incoming refrigerator and its pallet are turnedonto their side and the refrigerator alone is car-ried into the line by a special conveyor with atilt mechanism. The pallets are sent back to thesorting line. The location of the individual re-frigerators on the line is electronically tracked.

Coordinates needed to guide a saw for cuttingthe compressor mounting plate are performed ata teaching station that takes measurements inthree dimensions.

CFC refrigerant gas and lubricating oil areextracted together from the refrigerator’s com-pressor. Each model requires a slightly differ-ent procedure. Three extraction stations makeit possible for this relatively lengthy process to

Fig. 3 The TV primary disassembly line.


TECHNICAL REPORTS

keep pace with the line. The extraction unit issemiautomatic. The operator places the headof the extraction unit at the lowest point of thecylindrical part of the compressor and drills ahole from which all contents in the refrigerantcircuit are extracted. Heating and agitation arethen used to separate the CFCs from the oil.

At the compressor removal station an auto-matically controlled cutting robot uses coordi-nates from the database to cut the compressorfree from the chassis and then uses a hand topush the compressor down and out.Additional Information TechnologiesThe disassembly support system automaticallyissues disassembly instructions for TVs, refrig-erators, washing machines, and air conditionerindoor and outdoor units. Fig. 5 summarizes itsfunctions.

The transport support system provides a videomonitor to assist workers loading appliancesonto the sorting line.

CRT mount-ing screw coordinates

Loading station

Manual operation

Flow of disassembly data

Disassembly support system

Disassembly database

Data registration

Data referencing

CRT removal station, claw

positioning data

Text and visual instructions for manual

disassembly

Housing removal station, claw positioning data

Cutting robot, cutting data

Cutting robot, cutting data

Pallet clamping

data

To CRT processing plant

From sorting conveyor

CRT removalstation

Screw removal station

CRT screw coordinate teaching station

Manual disassembly stations

Initial TV disassembly line

Cleaning station

Rear housing removal station

Rear housing cutting station

Cutting coordinates

teaching station

CRT mount-ing screw coordinates

The materials-balance management systemcomputes the relative weights of the post-useappliances going in versus the separated materi-als coming out of the chipper during the testoperating period. Statistics are collected on prod-uct disassembly for various weight classifica-tions. The weight classifications correlate withchanging proportions of the product's constitu-ent materials, and allow weight of the materialsto be calculated from the weight of the product.The weight of materials recovered from second-ary disassembly processes is also factored in.

The author would like to express his thanks tothe Association for Electric Home Appliances,the Project for the Development of an IntegratedTreatment and Recycling System for Post-UseElectric Home Appliances, and the companiesthat participated in the project. ❑

Fig. 5 Functions of the disassembly support system.

September 1999 · 11

TECHNICAL REPORTS

*Takao Bamba and Niall Murtagh are with the Industrial Electronics & Systems Laboratory.

An Ecological Design Support Toolfor Recyclability

by Takao Bamba and Niall Murtagh*


The manufacturing industry must embrace glo-bal environmental issues if it is to remain vital.One avenue towards addressing these issues isdesign for environment (DFE), a design philoso-phy that considers the energy consumed in theproduction and use of manufactured goods andfacilitates recycling of products at the end oftheir useful lives. This article reports on a prod-uct design support tool newly developed toevaluate product recyclability.

Design for Environment Support ToolsIn addition to meeting conventional design cri-teria, products designed for minimal environ-mental impact should use recyclable materials,avoid harmful materials and minimize energyrequirements during manufacture and use. Prod-uct design under this philosophy considers thecost of product recycling and disposal alongsidemanufacturing cost. The technology is capableof lowering the product’s environmental impactas well as the cost over the entire product life cycle.Fig. 1 illustrates the basic concept of DFE.

DFE tools provide software support for devel-oping products satisfying these criteria. Thesetools evaluate the environmental impact of aproduct’s constituent materials and operationand the product’s recyclability. Life cycle assess-ment (LCA) tools have been developed for evalu-ating the environmental effects of the phases ofmaterials production, processing and productuse, but do not cater for detailed evaluation ofproduct disposal. The design support system de-scribed here relates product construction torecyclability. A complete DFE system will sub-sequently be achieved by integrating the sys-tem with conventional LCA tools.

Evaluating RecyclabilityCurrent facilities for recycling electrical productsuse crushers and shredders to reduce old productsto fragments which are then separated and re-cycled. While this approach minimizes process-ing costs, it is difficult to separate the materialseffectively and offers limited possibilities for fu-ture improvements in the proportion of materialsrecycling. We therefore evaluate recyclabilityassuming a two-step recycling process in which

Economy

Material Toxics

Energy LCA evaluation

Development tool

Recyclingevaluation tool

Low-cost design DFE support tools

Fig. 1 The concept of design for environment.

certain components are removed in the first step,and the remainder of the product is then shreddedand recycled conventionally (Fig. 2). From oursurvey of recycling technologies, we believe thisapproach will be adopted to varying degrees bymanufacturers without substantial qualitativedifferences.

Four key components of recyclability werestudied:

EASE OF COMPONENT REMOVAL. Primary dissas-sembly is the term used to describe the removalof certain components in the initial phase of re-cycling. These components are selected for theirreusability, high recycling ease or value, for toxicmaterials content requiring separate disposal,or for the difficulty involved in crushing andshredding them. Recyclable materials are reusedas materials of the same or lower grade. Reus-able components are kept intact as far as pos-sible. The ease of removal of these componentsis an important factor in recyclability.

RECYCLE RATE. This index describes the propor-tion of valuable materials such as iron, copper oraluminum that can be recovered, whether fromindividually removed assemblies, reused compo-nents, or shredded and separated materials.

RECYCLING COST. This figure includes the la-bor costs for primary dissassembly and the costof processing toxic materials and residues fromthe crushing process offset by the sale value ofthe recovered materials.

TECHNICAL REPORTS


ENVIRONMENTAL IMPACT OF MATERIAL USAGE.This index reflects the overall environmentalimpact taking into account the anticipated pro-cessing method. The recycle rate and the resi-due processing method (landfill or incineration)affect the environmental impact. The designsupport tool reported here evaluates these fac-tors during product design to facilitate productdesign and improvement.

Evaluation items from DFE tool

Recyclablematerials

Reusablecomponents

Hard-to-shredcomponents

Toxic materials

Dust

Removal

Valuable materials

Reclamation

Crushing and separation

Complex containingvaluable materials

Primary disassembly

Products at end of life

Evaluation of environmental impact during manufacture

and use

Ease-of-disassembly evaluation

Recycle costevaluation

Environmental impact at end-of-life evaluation

Fig. 2 Recycling process and DFE evaluation.

System Concepts of Development ToolsFig. 3 shows the configuration of the supporttool. Two alternative input systems are beingdeveloped. In the first, the designer or productevaluator specifies components and defines dis-assembly procedures to be used in the evalua-tion. In the second system, product data filescreated by a 3D CAD system are processed forproduct construction and component informa-

TECHNICAL REPORTS

tion, and disassembly procedures are generatedautomatically.

Component attributes in the system includecomponent name, weight, external dimensions,material, method of disposal, environmentalimpact index (eco-indicator) and cost of disposal.

Manual input requires that the user enter theproduct name, weight, dimensions and mate-rial and specify the method of disposal. Currentoptions include disassembly and removal of alltoxic materials and/or reusable components, anddisassembly to achieve a specified recycle rateby weight. These options help determine thedepth of the primary dissassembly, that is howmany components are removed before the prod-uct is crushed and shredded.

The above information is then used to computethe disassembly time, component environmentalimpact and recycling cost. These compu- tationsutilize various databases: a list of the variousmaterials that will be disposed of by recycling,landfill and incineration; an index of environmen-tal impact for toxic materials, recyclable materi-als and incinerated materials; and a recycling cost

Guidelines for redesign

Combine parts A and B? Change connection C?

Manual input: parts list, disassembly order

3D CAD data files

or

Liaison graph, disassembly order

Database (EOL destination, EOL cost, Eco-indicator)

Eco-indicator data (for complete disassembly, for recovery of X% of weight)

Disassembly time information (time for complete disassembly, time for recovery of X% of weight)

Eco-indicator Cost EOL cost

Eco-load

Fig. 3 System configuration.

database listing the value of reclaimable materi-als and costs of specialized processing.

The disassembly time is estimated on the ba-sis of manual disassembly tests and can bedetermined more accurately if the user supple-ments disassembly procedures with data describ-ing tools required and ease of access.

Environmental impact is evaluated using com-prehensive evaluation indices developed in Eu-rope. These indices describe the impact of eachmaterial on global warming, ozone depletion,smog, acid rain, eutrophication, air and waterpollution as well as carcinogenic effects.

Fig. 4 shows a manual input screen for thesystem. Component name, weight, size, connec-tion details and ease of disassembly can bereadily entered. Manual input of the majority ofthese items can be eliminated using the outputfrom 3D CAD data files.

The recycling cost and environmental impact(eco-indicator) indices can be determined usingmanually entered data and the system’s inter-nal databases. Figs. 5 and 6 show typical evalu-ation results.


TECHNICAL REPORTS

The graphs in Fig. 5 show the relationshipbetween disassembly time, environmental im-pact and recycling cost, which can be used todetermine the effect of disassembly depth onenvironmental impact and recycling cost. Re-cycling cost is defined as labor costs of primarydisassembly and the disposal costs of toxic andunusable materials offset by the value of reus-able components and materials.

Fig. 6 shows totals for environmental impactindex and disassembly time, displayed numeri-cally and as bar graphs. Toxic materials data,disassembly procedure data and estimated re-cycle rate are also listed along with general re-design guidelines.

When carrying out the general design of a prod-

Key Cost Eco-indicator

Eco

-indi

cato

r

50

50

100

100

100

200

300

400

150

150

200

200

250

300

Cos

ts

Disassembly time (s)

Fig. 5 Evaluation output graph.

Fig. 4 Input screen.

uct, a recyclability evaluation can be conductedusing manual data entry. Later, during the de-


TECHNICAL REPORTS

tailed design phase, more refined evaluationscan be conducted based on information in 3DCAD data. We have developed software for ex-tracting component information from 3D CADmodel files and for generating information onthe order of dissassembly. The 3D CAD systemused to generate the model file was a commer-cial software package.

Applications and DiscussionThe design support tool was tested in the de-sign of consumer air conditioners. Fig. 7 showspredicted and measured values for disassemblytimes, a single parameter selected for ease ofquantitative comparison. The vertical axisshows the removal time for various componentslisted along the horizontal axis. The calculatedand actual removal times match closely, affirm-ing the model’s efficacy.

Issues to resolve in further development of thesystem include implementing an indigenousdatabase of environmental impact indices forvarious materials and expanding the interfacewith CAD data. Fine-grained measurement ofenvironment impact will become possible when

Total weight: 20.58 kg

Recovered weight: 19.47kg

Percentage recovered: 94.14

Eco-indicator total: 234.72

Disassembly time: 305s

End-of-Life costs: 243yen

Parts to be removed (in removal order): rc-screw1, rc-screw2, rc-screw3, rc-screw4, rear-cover, cord, av-pcb, signal-pcb, vmcrt-pcb, yoke, rs-screw1, rs-screw2, ls-screw1, ls-screw2, r-speaker, l-speaker, ls-holder, rs-holder, t-screw1, t-screw2, t-screw3, t-screw4, tube

Normalized values

0

1.0

Eco-indicator

End-of-life costs

TV contains the following toxic parts: av-pcb, signal-pcb, tube

Fig. 6 Output information.

the European environmental indices used in themodel are supplemented by a Japanese standarddatabase. The CAD data interface needs furtherdevelopment to handle the complexities of com-ponent shape information. Future work will im-prove the system’s functions and a wider range ofproduct applications will be considered. ❑

This research was partly carried out within the IMS/Gnosis project.

400

350

300

250

200

150

100

50

01 2 3 4 5 6 7 8 9 10 1112 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3637 38 39 40 41 42

Key Measured values Estimated values

Part number

Tim

e (s

)

Fig. 7 Disassembly time, measured and estimatedvalues.


TECHNICAL REPORTS

*Fumiaki Baba is with the Advanced Technology R&D Center.

Ecomaterials

by Fumiaki Baba*


The production, use and disposal of electricalappliances and electronic equipment have sub-stantial environmental impact because of thelarge volumes in which these products are manu-factured. The use of ecomaterials can help tolower the environmental impact of products overall phases of the product life cycle. The designcriteria for ecomaterials include compatibilitywith humans and the environment in additionto the traditional physical, mechanical andchemical considerations.

EcomaterialsThe production of large quantities of electrical andelectronic products has had substantial environ-mental consequences that undermine the benefitsthese products confer on society. A systematicapproach to lowering this environmental impactfocuses on each phase of the product life cycle.

Materials used in manufacturing are first ex-tracted from the environment, manufactured intoproducts, and finally returned to the environmentas wastes. The development of ecomaterials thatcan reduce the environmental impact is impor-tant to protecting the earth’s natural environment.

The word “ecomaterial” is used for “environ-mentally conscious material” or “ecologicallyoriented material,” which implies socially ac-ceptable materials with minimal environmen-tal impact. Conversion to ecomaterials is a vitalmeans of addressing the environmental issuesof resource depletion, materials recycling andreuse, global warming, ozone depletion and di-oxin contamination.

Conventional materials analysis deals prima-rily with performance during product use. Eco-materials must satisfy environmental compatibil-ity and amenity criteria as well (see Fig. 1).

ENVIRONMENTAL COMPATIBILITY. Ecomaterialsare utilized to minimize the environmental im-pact over their life cycle of manufacture, distri-bution, use and disposal. Life-cycle assessment(LCA) facilitates development of ecomaterialsby providing a quantitative measure of the en-vironmental impact of materials and productsover their respective life cycles. Evaluation of

Ecomaterials

Classic requirements

Mechanical, Physical & Chemical properties

Environmentally conscious properties

Amenities

materials, for example, extends from miningthrough manufacturing to disposal—all steps of theproduct life cycle. This holistic approach to evalu-ation allows the development of materials and tech-nologies with minimal environmental impact.

AMENITY CRITERIA. Performance criteria forresin materials used in product housings arecurrently limited to mechanical strength, mol-dability and appearance. Ecomaterials introducean amenity index as an additional performancecriterion. People encounter a variety of materi-als in their daily life. Ecomaterials have a de-gree of psychological and physiological impact,so the amenity index includes aesthetic consid-erations and tactility.

Development of EcomaterialsTable 1 lists key categories of material for ame-liorating environmental impact. Some materi-als are already regulated by law, others may bethe target of future regulations, still others areessential to reduce the environmental impactof manufactured products. In Japan, the recentlyenacted Materials Recycling Law and WasteProcessing Law encourage reclamation of ma-terials and other steps to reduce the environ-mental impact of post-consumer products. Herewe survey the state-of-the-art in ecomaterialsdevelopment.

Fig. 1 The concept of ecomaterials.

TECHNICAL REPORTS


OZONE DEPLETION. Mitsubishi Electric haseliminated the use of regulated chlorofluorocar-bon (CFC) products through the introduction ofalternatives. Hydrochlororfluorocarbon (HCFC)and hydrofluorocarbon (HCF) products are be-

Table 1 Materials Related Environmental IssuesOzone depletion

Acid rain

Global warming

Atmospheric pollution

Ocean pollution

Soil pollution

Desertification

Ecosystem destruction

Dioxin contamination

Endocrine disruption

Depletion of non-renewable resources

ing used in refrigerant and foam-blowing appli-cations. Water-based systems and zero-washingsystems have been substituted for CFC solventsin cleaning systems for PCBs and precision com-ponents.

GLOBAL WARMING. Carbon dioxide is the great-est contributor to global warming. Largeamounts of carbon dioxide are emitted by powergeneration facilities, manufacturing plants, andmotor vehicles, and these join the already sig-nificant quantities of natural emissions. Reduc-tions in product power consumption should beaccompanied by similar consideration of prod-uct constituent materials.

The release of greenhouse gases (i.e., gaseswith high-global-warming potential) to the at-mosphere can be lowered by designing productsfor reduced usage, by using substitute gases, andby adopting energy-saving, heat-conduction andthermal insulation technologies. Sulfur hexa-fluoride gas (SF6) used in arc-extinguishing in-

Amenity·Heat insulation·Heat conduction·Vibration damping·Bacteria resistant plastics·Fungicidal plastics

Plastic materials

StandardizationVariety reduction

Recyclable plastic materialsCrystalline thermoplastics

Replacements for thermoset resinsEngineering plastics, elastomers

Avoidance of harmful materialsPVCs and halide flame retardants

Biodegradable plastics

Assessment·Life-cycle assessment·Risk assessment

Material description (for amounts over 50g)

Design for disassembly·Snap fit, press fit

Design

Material recycling

Evaluation

Material separation

Lightening

·Thinner molded panels·Hybrid molding

Molding processes for recycled plastics

·Multilayer molding, sandwich molding·Material improvement

Molding Product

Energy saving

Parts minimization

Parts standardization

Dispose

Incineration/landfill

·Volume reduction

Thermal recycling

Chemical recycling

Fig. 2 Development roadmap for environmentally conscious plastics.

TECHNICAL REPORTS

September 1999 ·19

sulating systems has a high global warmingpotential. Reclamation, leak prevention anddetection technologies, coupled with studies ofalternative insulation gases, are contributing tothe reduced release of this gas.

REDUCED USE OF TOXIC MATERIALS. Lead ispresent in the solder used to mount electroniccircuit components. Halide-based flame-retar-dant chemicals, which are also toxic, are foundin plastics and glues. Because these materialshave the potential to affect ecosystems and hu-mans over all phases of their life cycle, their usemust be reduced or eliminated. This will followthe implementation of international protocolsand subsequent regulations, as with previousregulations enacted on the use of other harmfulmaterials.

AN ECOMATERIAL APPROACH TO PLASTICS DE-VELOPMENT. Because plastics are heavily usedin household appliances and other electrical andelectronic equipment, the reduction of their en-vironmental impact has become increasinglyimportant. Fig. 2 summarizes the work towardecomaterials at Mitsubishi Electric. Impactevaluations and design reviews cover all aspectsof the product life cycle from raw materials toproduct disposal.

Materials Recycling TechnologiesLife-cycle analyses indicate the value of recy-cling in reducing product environmental impact.Materials and processes should therefore be de-signed to promote recycling. A high percentageof metal and glass is already being recycled,while the percentage for plastics remains low.Developing more efficient systems for plastic

recycling is thus a high priority. Plastics may berecycled by chemical means to recover themonomer, incinerated to produce heat energy,or reused directly. The last approach, materialrecycling, is ideal in that the waste is almostentirely converted to a resource, which makesthis option especially attractive. Plastics recy-cling technologies must address the compara-tive weakness of recycled materials, considerways of handling contaminants and, finally, de-velop the technologies to utilize the recycledmaterial.

The degradation of plastic materials is greatlyinfluenced by their exposure to the environment,particularly to heat and ultraviolet radiation. Table2 lists the results of mechanical tests on samplesformed from both new and recycled plastic mate-rials. Most of the measures of mechanical strengthother than impact resistance show little deterio-ration. Mitsubishi Electric is working to improvematerial quality and develop new processing tech-niques that can increase use of this recycled re-source.

The development of environment friendly mate-rials will help reduce the environmental impactof product manufacture and consumption and pro-mote the emergence of a high-recycling-rate soci-ety. The characteristics and functional behaviorrequired of ecomaterials will almost certainlychange over time. The movement toward prod-ucts made of ecomaterials and the reduction ofthe environmental loads imposed by productionwill continue to control the direction of futuretechnology development. ❑

Table 2 Mechanical Properties of Plastic Recycled from Home Electrical AppliancesPlastic

HistoryTensile strength Flex strength Flex modulus Impact absorption energy

(appliance) (MPa) (MPa) (GPa) (J)

Polystyrene Recycled 32.8 72.7 2.74 0.36(air conditioner) Virgin 30.9 64.8 2.54 0.88

Polypropylene Recycled 27.8 48.3 2.09 0.57(refrigerator) Virgin 27.8 47.1 2.05 1.06

TECHNICAL REPORTS

*Toshihiko Miyake and Hidetoshi Okada are with Sanda Works.

An Electrically Operated EGR Valvethat Reduces Automotive Emissions

by Toshihiko Miyake and Hidetoshi Okada*


Automotive exhaust emission regulations aregrowing stricter in parallel with demands forgreater fuel economy. The exhaust-gas recircula-tion (EGR) valve is one technology used to reducethe emissions of automotive engines. The authorsdeveloped EGR valves in which an electronicallycontrolled stepper motor replaces the conven-tional vacuum-driven mechanism. The steppermotor system offers more accurate control over awider range of engine operating conditions than avacuum system, reducing emissions and improv-ing fuel economy.

Automotive exhaust emissions include carbonmonoxide (CO), hydrocarbons (HC), and oxidesof nitrogen (NOx). NOx is produced when nitro-gen and oxygen from the air combine at tempera-

Air cleaner

Direct injection engine Conventionally injected engine

Electrically operated EGR valve

Catalyst

Engine

Throttle valve

Engine control unit

Fig. 1 Electrically operated EGR system.

tures over 2,000°C. Although high combustiontemperatures result in better fuel economy andfewer emissions of hydrocarbons and CO due tothe more complete burning that takes place atthese higher temperatures, they also increase NOxproduction. The curves in Fig. 2 show the con-trasting characters of these two emission-produc-ing mechanisms.

EGR valves reduce NOx emissions by rout-ing exhaust gases into the engine’s intake mani-fold (Fig. 1). The presence of these unreactivegases in the cylinder during combustion servesto lower the combustion temperature. The EGRvalve controls the amount of exhaust gas recir-culation to suit engine operating conditions.

Fig. 3 shows NOx reductions achieved using astepper-motor EGR valve developed at Mitsubishi

TECHNICAL REPORTS


Electric in the GDI engine manufactured byMitsubishi Motors. According to papers publishedby Mitsubishi Motors, 97% of the NOx emissionspresent in the exhaust gases can be eliminatedwhen recirculated exhaust gas comprising up to30% of the intake air is used in conjunction witha lean-burn selective-reduction NOx catalyst.

Con

cent

ratio

n

NOxHCCO

CO

Stoichiometric mixture

Fuel economizing mixture

LeanRich Fuel-air mixture

10 12 14 16 18 20

NOx

HC

Fig. 2 Effect of fuel-air mixture on exhaustemissions.

This emissions control performance is comparableto that of a three-way catalyst.

Fuel Economy ImprovementEGRs can improve fuel economy by reducingpumping losses. The accelerator pedal in a gaso-line engine car controls a throttle valve thatregulates the airflow through the intake mani-fold. Pumping losses occur when the engine isoperating under low load and the throttle valveis nearly closed. Energy is wasted overcomingthe resistance to airflow through this narrowpassage. These losses can be reduced by a lean-burn combustion style in which the throttlevalve is opened relatively wide in combinationwith a large EGR flow. The diluted-burn enginesystem developed by Mazda Motor Corporationuses this exact principle: it combines a largeEGR ratio with a wide throttle opening thatserves to reduce pumping losses (Fig. 4).

Problems with Conventional EGR SystemsThe inadequacies of the vacuum-driven EGRvalve make a strong case for an electrically op-erated valve. Conventional EGR systems oper-ate the EGR valve using a diaphragm driven bythe intake manifold vacuum. The vacuum is

Conventional engine

NOx (g/h)

No catalyst

Selective reduction lean-burn NOx catalyst

Stoichiometric fuel-air mixture

Fuel-air mixture 10 15 20 25 30 35 40

97%reduction

0% EGR

30% EGR

GDI

Fig. 3 Reduction of NOx emissions in GDI engine. Emission levels are for an effective vehicle speed of40km/h.

TECHNICAL REPORTS

taken from the intake manifold downstreamfrom the throttle valve. Because it depends onengine vacuum, this arrangement is useful forsmall throttle angles where a vacuum is presentbut not at wide throttle angles where the vacuumvanishes. It is not suitable under the low mani-fold-vacuum conditions that would reduce pump-ing losses (Fig. 5).

Catalyst

EGR valve

Engine

Vacuum control valve

Intake manifold

Throttle valve

Engine control unit

Input signals from sensors

Air cleaner

Electrically Operated EGR ValveMitsubishi Electric has developed an EGR valvedriven by a stepper motor that will operate un-der all engine vacuum conditions. The steppermotor provides the best fit to the requirementsof the EGR system: The power drain is modest,the valve opening is stable despite exhaust gaspressure pulses, no position sensor is required,

Small pumping loss, correct engine output

Normal engine

Intake air (contains oxygen)

Large pumping loss, correct engine output

Small pumping loss, excessive engine output

Diluted-burn engine

Intake air (contains oxygen)

EGR flow (inert gases)

Fig. 4 The diluted-burn engine.

Fig. 5 A conventional vacuum diaphragm EGR system.

Table 1 Electrical ActuatorsDrive power Valve stability Position sensor Cost Weight

Stepper motor High Good Unnecessary Low Light

Linear solenoid Low Fair Required Fair Heavy

DC servo motor High Fair Required High Heavy


TECHNICAL REPORTS

the system is simpler than its vacuum oper-ated counterparts, the cost is relatively low, andthe system is suited to mass production.

Table 1 compares stepper motors against otherelectrical actuators that could be adapted to thisapplication. A stepper motor offers three to fourtimes the flow capability for the same drivepower as a linear solenoid-operated valve.

Durability is also critical, because performancewill suffer if carbon or oil sludge in the exhaustgases builds up in the valve-shaft bearing.

ConstructionFig. 6 shows the construction and Table 2 liststhe performance of stepper-motor EGR valvesdeveloped for gasoline engines. We selected apush-open downward-opening design over apull-open upward-opening design that does notrequire a special coupling between the rotor shaftand valve. Fig. 6a shows an EGR valve for con-ventionally injected engines, Fig. 6a a valve fordirect-injection engines. We designed the systemto be cost competitive with conventional EGRsystems in order to support general-purpose ap-plications as well as fuel-saving engine designs.

Direct-injection engines typically requirethree to five times the EGR flow of conven-tionally injected engines. Our EGR unit for di-rect-inject engines uses a more powerful steppermotor to provide additional drive capacity for alarger valve. The operating load has also beenreduced by introducing an assist spring that actsagainst the valve closing spring while the valveis open. The assist spring is inactive when thevalve is closed, allowing the valve-closing springto function.

Motor shaft

Rotor

Body Valve

Bearing

Valve closing spring

Heat sink Stay

Water passage

Assist spring

a) Conventional fuel injection b) Direct injection

Fig 6 Construction of electrically operated EGR valves.

Table 2 Performance of Stepper Motor EGR ValvesParameter Conventionally injected Direct injection

Motor type Stepper Stepper

No. of poles 48 48

Motor torque 0.035N.m 0.095N.m

Power consumption 13W 19.2W

Max. stroke 5mm 8.5mm

Max. flow at 6.7kPa 200l/min 800l/min

Resolution 4l/min 9l/min

Accuracy 8% 8%


TECHNICAL REPORTS

A four-phase stepper motor is used for bothtypes of application. A unipolar design reducesthe load on the drive circuit. The external threadon the motor shaft and internal thread on therotor convert the motor’s rotary motion to lin-ear motion. A single motor revolution of 48steps drives the valve full stroke. The motor-driven solution provides rapid response for bothopening and closing operations. Heat-resistantmaterials were used so the motor would toler-ate the high temperatures caused by exhaustgases traveling through the valve body.

In the EGR valve for conventionally injectedengines, the casting between motor and thevalve body is supported by two narrow stays.Air flowing between the stays and over the heatsink below the motor provides sufficient cool-ing. A water-cooled aluminum heat sink in thevalve for direct-injection engines provides ad-ditional cooling capacity to support the largerEGR flow.

The cost advantages of stepper-motor EGRvalves are driving their introduction in general-purpose automotive applications. We expectdemand for these valves to increase as lean-burnengines are used more widely, as fuel economybecomes more important, and as emission regu-lations are tightened. Although small, this ad-vanced EGR valve can contribute significantlyto preserving the global environment. ❑


Country Address TelephoneU.S.A. Mitsubishi Electric America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500

Mitsubishi Electric America, Inc. Sunnyvale Office 1050 East Arques Avenue, Sunnyvale, California 94086 408-731-3973Mitsubishi Electronics America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500Mitsubishi Consumer Electronics America, Inc. 9351, Jeronimo Road, Irvine, California 92618 949-465-6000Mitsubishi Semiconductor America, Inc. Three Diamond Lane, Durham, North Carolina 27704 919-479-3333Mitsubishi Electric Power Products Inc. 512 Keystone Drive, Warrendale, Pennsylvania 15086 724-772-2555Mitsubishi Electric Automotive America, Inc. 4773 Bethany Road, Mason, Ohio 45040 513-398-2220Astronet Corporation 3805 Crestwood Parkway Suite 400 Duluth, Georgia 30096 770-638-2000Powerex, Inc. Hills Street, Youngwood, Pennsylvania 15697 724-925-7272Mitsubishi Electric Inf ormation Technology Center America , Inc. 201 Broadway, Cambridge, Massachusetts 02139 617-621-7500

Canada Mitsubishi Electric Sales Canada Inc. 4299 14th Avenue, Markham, Ontario L3R 0J2 905-475-7728

Mexico Melco de Mexico S.A. de C.V. Mariano Escobedo No. 69,Tlalnepantla, Edo. de Mexico Apartado 5-565-4925Postal No.417, Tlalnepant la

Brazil Melco do Brazil, Com. e Rep. Ltda. Av. Rio Branco, 123, S/1504-Centro, Rio de Janeiro, RJ CEP 20040-005 21-221-8343Melco-TEC Rep. Com. e Assessoria Tecnica Ltda. Av. Rio Branco, 123, S/1507, Rio de Janeiro, RJ CEP 20040-005 21-221-8343

Argentina Melco Argentina S.A. Florida 890-20-Piso, Buenos Aires 1-311-4801

Colombia Melco de Colombia Ltda. Calle 35 No. 7-25, P.12 A. A. 29653 Santafe de Bogota, D.C. 1-287-9277

U.K. Mitsubishi Electric U.K. Ltd. Livingston Factory Houston Industrial Estate, Livingston, West Lothian, EH54 5DJ, Scotland 1506-437444Apricot Computers Ltd. 3500 Parkside, Birmingham Business Park, Birmingham, B37 7YS, England 121-717-7171Mitsubishi Electric Europe B.V. Corporate Office Centre Point (18th Floor), 103 New Oxford Street, London, WC1A 1EB 171-379-7160

France Mitsubishi Electric France S.A. Bretagne Factory Le Piquet 35370, Etrelles 2-99-75-71-00

The Netherlands Mitsubishi Electric Netherlands B.V. 3rd Floor, Parnassustoren, Locatellikade 1, 1076 AZ, Amsterdam 020-6790094

Belgium Mitsubishi Electric Europe B.V. Brussels Office Avenue Louise 125, Box 6, 1050 Brussels 2-534-3210

Germany Mitsubishi Electric Europe B.V. German Branch Gothaer Strasse 8, 40880 Ratingen 2102-4860Mitsubishi Semiconductor Europe GmbH Konrad-Zuse-Strasse 1, D-52477 Alsdorf 2404-990

Spain Mitsubishi Electric Europe B.V. Spanish Branch Polígono Industrial “Can Ma gí”, Calle Joan Buscallà 2-4, Apartado de Correos 3-565-3131420, 08190 Sant Cugat del Vallês, Barcelona

Italy Mitsubishi Electric Europe B.V. Italian Branch Centro Direzionale Colleoni, Palazzo Persero-Ingresso 2, Via Paracelso 12, 39 -6053120041 Agrate Brianza

China Mitsubishi Electric (China) Co., Ltd. Room No. 1609 Scite Building (Noble Tower), Jianguo Menwai Street, Beijing 10-6512-322 2Mitsubishi Electric (China) Co., Ltd. Shanghai Office 39th Floor, Shanghai Senmao International Building, 101, Yincheng Road (E) , 21-6841-5300

Pudong New Area, ShanghaiMitsubishi Electric (China) Co., Ltd. Guangzhou Office Room No. 1221-4, Garden Tower, Garden Hotel, 368, Huanshi Dong Lu, 20-8385-7797

GuangzhouShanghai Mitsubishi Elevator Co., Ltd. 811 Jiang Chuan Road, Minhang, Shanghai 21-6430-3030

Hong Kong Mitsubishi Electric (H.K.) Ltd. 41st Floor, Manulife Tower, 169 Electric Road, North Point 2510-0555Ryoden (Holdings) Ltd. 10th Floor, Manulife Tower, 169 Electric Road, North Point 2887-8870Ryoden Merchandising Co., Ltd. 32nd Floor, Manulife Tower, 169 Electric Road, North Point 2510-0777

Korea KEFICO Corporation 410, Dangjung-Dong, Kunpo, Kyunggi-Do 343-51-1403

Taiwan Mitsubishi Electric Taiwan Co., Ltd. 11th Floor, 88 Sec. 6, Chung Shan N. Road, Taipei 2-2835-3030Shihlin Electric & Engineering Corp. 75, Sec. 6, Chung Shan N. Road, Taipei 2-2834-2662China Ryoden Co., Ltd. Chung-Ling Bldg., No. 363, Sec. 2, Fu-Hsing S. Road, Taipei 2-2733-3424

Singapore Mitsubishi Electric Singapore Pte. Ltd. 152, Beach Road, #11-06/08, Gateway East, Singapore 189721 295-5055Mitsubishi Electric Sales Singapore Pte. Ltd. 307, Alexandra Road, #05-01/02, Mitsubishi Electric Building, Singapore 159943 473-2308Mitsubishi Electronics Manufacturing Singapore Pte. Ltd. 3000, Marsiling Road, Singapore 739108 269-9711Mitsubishi Electric Asia Co-ordination Centre 307, Alexandra Road, #02-02, Mitsubishi Electric Building, Singapore 159943 479-910 0

Malaysia Mitsubishi Electric (Malaysia) Sdn. Bhd. Plo 32, Kawasan Perindustrian Senai, 81400 Senai, Johor Daruel Takzim 7-5996060Antah Melco Sales & Services Sdn. Bhd. No.6 Jalan 13/6, P.O. Box 1036, 46860 Petaling Jaya, Selangor, Daruel Ehsan 3-755-2088Ryoden (Malaysia) Sdn. Bhd. No. 14 Jalan 19/1, 46300 Petaling Jaya Selongar Daruel Ehsam 3-755-3277

Thailand Kang Yong Watana Co., Ltd. 28 Krungthep Kreetha Road, Huamark, Bangkapi, Bangkok 10240 2-731-6841Kang Yong Electric Public Co., Ltd. 67 Moo 11, Bangna-Trad Road KM. 20, Bangplee, Samutprakarn 10540 2-337-2431Melco Manufacturing (Thailand) Co., Ltd. 86 Moo 4, Bangna-Trad Road KM. 23, Bangsaothong, Samutprakarn 10540 2-312-8350~3Mitsubishi Elevator Asia Co., Ltd. 700/86~92, Amata Nakorn Industrial Estate Park2, Moo 6, Bangna-Trad Road, 38-213-170

Tambon Don Hua Roh, Muang District, ChonburiMitsubishi Electric Asia Coordination Center 17th Floor, Bangna Tower, 2/3 Moo 14, Bangna-Trad Highway 6.5 Km, 2-312-0155~7(Thailand) Bangkawe, Bang Plee, Samutprakarn 10540

Philippines International Elevator & Equipment, Inc. K.m. 23 West Service Road, South Superhighway, Cupang, Muntinlupa, 2-842-3161~5Metro Manila

Australia Mitsubishi Electric Australia Pty. Ltd. 348 Victoria Road, Rydalmere, N.S.W. 2116 2-9684-7777

New Zealand Melco New Zealand Ltd. 1 Parliament St., Lower Hutt, Wellington 4-560-9100

Representatives

Korea Mitsubishi Electric Corp. Seoul Office Daehan Kyoyuk Insurance Bldg., Room No. 2205, #1,1-ka, Chongno-ku, Seoul 2-732-1531~2

India Mitsubishi Electric Corp. New Delhi Liaison Office Dr. Gopal Das Bhawan (8th Floor), 28 Barakhamba Road, New Delhi 110001 11 -335-2343

Viet Nam Mitsubishi Electric Corp. Ho Chi Minh City Office 18th Floor, Sun Wah Tower, 115 Nguyen Hue Street, District 1, 8-821-903 8Ho Chin Minh City

MITSUBISHI ELECTRIC OVERSEAS NETWORK (Abridged)

MITSUBISHI ELECTRIC CORPORATIONHEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310, FAX 03-3218-3455

Date post:	06-Nov-2021
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Mitsubishi Electric ADVANCE vol87

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