RegistrulAutoRomân

Societatea pentruIngineria Automobilului

din România

IngineriaAutomobilului

S U P L I M E N T T R I M E S T R I A L G R A T U I T E D I T A T D E R E G I S T R U L A U T O R O M Â N

N R . 3 / M A I 2 0 0 7

SIAR ESTE AFILIATÃ LA

EUROPEANAUTOMOBILEENGINEERSCOOPERATION

INTERNATIONALFEDERATION OFAUTOMOTIVEENGINEERING SOCIETIES

Pila de combustibil

Viitorul automobilului

Anghelache, G., Moisescu, R. ºi Ciubotaru, O. - „Încercarea Autovehiculelor - sisteme de mãsurare clasice ºi asistate de calculator", 180 pagini,Editura BREN, ISBN 978-973-648-630-2, Bucureºti, 2007.Cartea face referire la douã categorii de sisteme de mãsurare, o primã grupã cuprinzând sisteme ana-logice pentru mãsurarea, prelucrarea, afiºarea ºi/sau înregistrarea datelor. A doua categorie se referãla sisteme de mãsurare pe cale numericã, asistate de calculator, întâlnite de obicei sub titulatura desisteme de achiziþie de date. în prezent se utilizeazã la încercarea autovehiculelor ambele tipuri de sis-teme de mãsurare, dar se constatã, în ultimii ani, o creºtere substanþialã a ponderii celor numerice.Sistemele clasice de mãsurare sunt prezentate în scopul familiarizãrii potenþialilor experimentatoricu structura ºi modul de lucru al sistemelor respective, cu obþinerea, prelucrarea ºi interpretarearezultatelor, cu formularea observaþiilor ºi a concluziilor, precum ºi cu erorile ºi cu aprecierea can-titativã a acestora. Au fost realizate mai multe grupe de sisteme analogice de mãsurare. O primãcategorie are drept obiectiv prezentarea aparatelor pentru vizualizarea, afiºarea ºi înregistrareasemnalelor. Urmãtoarele douã conþin sisteme de mãsurare bazate pe traductoare tensometricerezistive, respectiv pe traductoare de vibraþii. Un alt domeniu este reprezentat de sistemele opticepentru mãsurarea turaþiilor.Introducerea în domeniul sistemelor de mãsurare asistate de calculator se face prin prezentareaconceptelor de bazã privind achiziþia de date. Aplicaþii ale unor astfel de sisteme sunt realizatepentru mãsurarea parametrilor dinamici ai unui impact, pentru analiza transmisibilitãþii vibraþi-ilor ºi pentru analiza în frecvenþã a vibraþiilor mecanice. De asemenea, sunt prezentate sis-temele de mãsurare a zgomotului produs de autovehicul, a parametrilor de demarare ºi acelor de frânare.Toate aplicaþiile software au fost concepute pentru a fi utilizate în cadrul activitãþilor de cer-cetare experimentalã a autovehiculelor. Direct sau cu mici modificãri, aceste sisteme com-plexe de mãsurare pot fi utilizate ºi în alte domenii ale cercetãrii inginereºti. Fiecare pachetsoftware conþine aplicaþii pentru achiziþia ºi pentru prelucrarea datelor experimentale.În cuprinsul lucrãrii se regãsesc ºi informaþii asupra prevederilor unor norme ºi regula-mente referitoare la modul de organizare, condiþiile, pregãtirea autovehiculelor pentru efectu-area încercãrilor specifice.Lucrarea se adreseazã specialiºtilor implicaþi în activitatea de cercetare experimentalã a autovehiculelor, cât ºi celor aflaþi înproces de pregãtire în acest domeniu. în particular, volumul oferã informaþii utile studenþilor din domeniul „Ingineria autovehiculelor".

AUTOMOTIVE HANDBOOK BOSCHGhidul Automotive Handbook, publicat de firma Robert Bosch GmbH în septembrie 2003,prezintã în limbile englezã, francezã ºi germanã, pe CD ROM, principalele realizãri dindomeniul tehnicii automobilului, cu accent pe cele mai recente ºi de perspectivã soluþiiavansate din acest domeniu.Principalele avantaje ale ghidului sunt:- instalare foarte simplã cu demarare automatã;- comandã prin meniu;- tablã de materii ºi un index de cuvinte cheie care permit peste 3000 de intrãri- funcþiuni de cãutare cuprinzãtoare;- mãrirea electronicã a imaginii pentru mai mult de 600 de figuri;- funcþii de calcul pentru 700 de formule.El cuprinde, în partea introductivã, noþiuni de bazã din domeniul fizicii, matematicii,materialelor utilizate la construcþia automobilului, elementelor de maºini, tehnologii defabricaþie, cerinþele cãtre automobile (inclusiv dinamica automobilelor) .în continuare sunt prezentate - ultimele evoluþii în domeniul motoarelor cu combustie internã, inclusiv motoarelorhibride, Stirling, Wankel ºi turbinelor cu gaz, elementele ºi componentelemotoarelor;- evoluþia ºi ultimele realizãri în domeniul protecþiei mediului ºi reducerea consumu-lui de carburant ºi soluþiile tehnice aplicate, soluþii alternative de propulsie;

- caroseria autovehiculelor;- sisteme de siguranþã rutierã controlul stabilitãþii;

- aparatura eletricã-electronicã ºi alte sisteme ale automobilului- tehnologii moderne de fabricaþie a vehiculelor;- echipamente pentru atelierele auto, aparaturã hidraulicã ºi pneumaticã.

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The decision no.1.175/2006 of theRomanian govern-

ment defined the "Automo-tive engineering" as a do-main of university and doc-toral studies. Several spe-cialties are available withinthis framework: Automo-bile architectures, Engi-neering of automotive pro-pulsion systems, Road vehi-

cles, Automotive operation and control equipments andsystems, Armored vehicles, automobiles and tractors.The well known synergic characteristic of automotiveengineering led to the foundation of the "IntegratedAutomotive Engineering Platform", a new research anddevelopment entity at POLITEHNICA University ofBucharest, which gathers academic staff, engineers,researchers, students and technicians from 10 of the 13university's faculties. Its main goals are the improve-ment of the university laboratories infrastructure andthe enhancement of education and research activities inthe benefit of the Romanian automotive industry, aswell as the cooperation with foreign universities andcompanies in the field of automotive engineering.The Automotive Engineering Department of thePOLITEHNICA University has already developedcooperation with important automotive manufacturers,such as FORD and BOSCH, that organized two mod-ern laboratories where technical training activities arecarried out with students of the Transport Faculty andwith technicians from allover the country involved inautomotive maintenance activities.At present, a new project, based on structural fundsfrom EU, is under construction: the organization of apole of excellence in automotive engineering that willgather the human and technical capacities ofPOLITEHNICA University, several research institutesand automobiles and spare parts manufacturers.

Prof. Dr. Eng. Cristian Andreescu,Head of Automotive Engineering Department

Politehnica University of Bucharest

Activitatea de Con-trol Tehnic înTrafic a început

sã fie desfãºuratã de Re-gistrul Auto Român îm-preunã cu organe ale poli-þiei rutiere începând încãdin anul 1998, pe baza în-cheierii unui protocol decolaborare între cele douãinstituþii. Prin Controlul Tehnic înTrafic se realizeazã supravegherea parcului rutier cir-culant. Totodatã, acesta reprezintã un feed-back alactivitãþii staþiilor de inspecþii tehnice periodice ºi opârghie a activitãþii de monitorizare a acestora, avândîn vedere cã în þara noastrã, inspecþiile tehnice peri-odice se efectueazã de Registrul Auto Român, orga-nism tehnic specializat al Ministerului Transportu-rilor, prin reprezentanþele sale judeþene sau de agenþieconomici autorizaþi ºi monitorizaþi de Registrul AutoRomân. Dacã un vehicul înmatriculat în alt stat membru UEeste depistat cu defecþiuni tehnice în urma unui con-trol tehnic în trafic în România, datele de identificareale acestuia ºi defecþiunile constatate sunt comunicateoficialitãþilor responsabile din statul membru UE încare este înmatriculat vehiculul. Numãrul autolaboratoarelor implicate în aceastãactivitate a crescut de la an la an, ajungând ca înprezent, fiecare Reprezentanþã Judeþeanã a Regis-trului Auto Român sã fie dotatã cu un autolaborator,pentru Municipiul Bucureºti ºi judeþul Ilfov fiind alo-cate patru astfel de autolaboratoare. Trebuie precizat faptul cã selectarea vehiculelor învederea efectuãrii controlului tehnic nu se realizeazãdupã un algoritm prestabilit în scop pur statistic, cisunt selectate acele vehicule care vizual sunt suscepti-bile a prezenta defecþiuni cu implicaþii în securitateadesfãºurãrii traficului rutier.

Ing. Catalin GhimpusanSef Departament

ITP SPNV

CONTROLULTEHNIC ÎN TRAFICCONTINUÃ

AUTOMOTIVE ENGINEERING AT POLITEHNICA UNIVERSITY OF BUCHAREST

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Prof. Dennis Assanis, University of Michigan

United States of America.

Prof. Bert BreuerTechnical University of Darmstadt,

Germany

Prof. Nicolae BurneteTechnical University of Cluj-Napoca Romania

Dr. Felice E. CorcioneEngines Institute, Naples, Italy

Prof. Cedomir DubokaUniversity of Belgrade,

Belgrade, Serbia

Prof. Pedro EstebanInstitute for Applied Automotive

Research, Tarragona, Spain

Prof. Radu GaiginschiTechnical University „Gh. Asachi“ of

Iaºi, Romania

Dr. Uwe GeigerVizepresident

Development EngineSistems INA-Schaeffler KG,

Herzogenaurach, Germany

Eng. Eduard Golovatai-SchmidtINA-Schaeffler KG, Herzogenaurach,

Germany

Prof. Berthold GrunwaldTechnical University of Darmstadt,

Germany

Prof. Alexandre HerleaUniversite de Technologie de Belfort-Montbeliard, France

Prof. Peter KucharUniversity for Applied Sciences,Konstanz, Germany

Prof. Nicolae V. OrlandeaAssociate Editor at Journal of Multi-body Dynamics, London,United Kingdom

Prof. Andreas SeeligerInstitute of Mining and MetallurgicalMachine, Engineering, Aachen Germany

Prof. Cornel StanWest Saxon University of Zwickau, Germany

Prof. Ulrich SpicherKalrsuhe University, Karlsruhe,Germany

Prof. Ion TabacuUniversity of Piteºti, Romania

Prof. Dinu TarazaWayne State University, United Statesof America

SCIENTIFIC BOARD - LISTA PERSONALITÃÞILOR

Serie nouã a Revistei Inginerilor de Automobile din România (RIA), 1992-2000Cod ISSN 1842 - 4074

Director generalDaniel PATENTAªU

Director tehnicClaudiu MIJA

Editor CoordonatorLorena STROE

RedactoriRadu BUHÃNIÞÃ

Emilia VELCU

Contact:Calea Griviþei 391 A,

sector 1, cod poºtal 010719, Bucureºti, România

Tel/Fax: 021/202.70.17E-mail: autotest@rarom.ro

Contact:Facultatea de Transporturi,Universitatea Politehnica

Bucureºti, Splaiul Independenþei 313,

sala JC 005, Cod Poºtal 060032, Sector 6

Bucureºti, România Telefon/Fax: 021/316.96.08

E-mail: siar@siar.ro

Tipar

Reproducerea integralã sauparþialã a textelor ºi imaginilor se

poate face numai cu acordulRevistei Auto Test, a Registrului

Auto Român ºi a Societãþii pentruIngineria Automobilului din

România

Chairman: Prof. Eugen Miahai NEGRUª - President of SIAR, Romania

Vice-chairman: Prof. Cristian ANDREESCU „Politehnica“ University of Bucharest

Vice-chairman: Prof. Anghel CHIRU „Transilvania“ University of Braºov, Romania

Scientific Secretary: Dr. Cornel VLADU Secretary General of SIAR, Romania

Registrul AutoRomân

Auto Test

SIAR

G. CANALE & C. SRL

REZUMATLucrarea prezintã cele mai recente rezultate

ale cercetãrilor firmei HONDA în domeniulautomobilelor cu pile de combustie (fuel cell). Seprezintã arhitectura noului model al ansambluluide pile de combustie care utilizeazã o soluþie origi-nalã (Aromatic Electrolyte Membrane) pentruPEM cu o structurã molecularã diferitã de ceaconvenþionalã. Membrana electroliticã aromaticãpoate funcþiona pânã la temperatura de 95 °C (cu15 °C mai mult) ºi are o durabilitate de patru orimai mare decât membrana electroliticã conven-þionalã.

Automobilul HONDA-FCX, model 2003, afost primul automobil fuel cell omologat ºi admispe piaþa statului California, SUA.

În anul 2005 HONDA a livrat primul auto-mobil fuel cell pentru un client persoanã particu-larã.

Fuel Cell Development for AutomotiveApplication

1. INTRODUCTIONHonda has been conducting research on the

clean power plants for low emission vehicle(LEV), natural gas vehicle (NGV), electric vehi-cle (EV) and fuel cell vehicle (FCV). As a longterm solution, the hydrogen fuel cell vehicle hasthe great potential to address future environmen-tal and energy issues. In the course of thisresearch, Honda achieved new electronic drivefor EVs, high pressure gas storage technology forNGVs and precise energy management technolo-gy for HEVs. These new developments have allbeen applied to research on fuel cell vehicleswhich incorporate high power electric motors,compressed hydrogen fuel tanks and electric stor-age systems.

In September 1999, Honda announced itsfirst FVC prototypes. An early FC stack manufac-tured by Honda was used in the FCX-V2 proto-type (fig.1) and an improved fuel cell stack in theFCX-V3. In July 2002, the 2003 model FCX (fig.2) became the first FCV to be certified by the

EPA and CARB. The Ballard fuel cell stack wasused in this vehicle. Fig.3 shows the place of themajor components in the FCX. On December 22002, FCX vehicles were delivered to the City ofLos Angeles in California and to the JapaneseCabinet Office.

Following this a new generation Honda stackwas introduced in October 2003 after real-worlddrive-tests in Japan and the United States.

A new Honda FCX fitted with this stack wasdelivered to the government of New York Stateand to the first private customer in June 2005 inCalifornia. The Honda FC stack for the 2005model FCX combines compactness and high out-put with the ability to operate at low and high tem-peratures

2. DEVELOPMENT OF NEW STACK FOR THE 2005 MODELThe Proton Exchange Membrane (PEM)

fuel cell system has been the most commonly usedfuel cell in automobiles because it can be used atcomparatively low temperatures around 80o andbecause of its high power density. Although fuelcell technology is progressing rapidly, issues forautomobile use such as the ability of starting atbelow freezing temperatures, effective utilizationof space and energy efficiency still need to beaddressed. For the 2005 model, the two maingoals for the development of a next generationfuel cell were;

(1) Making it compact but with high output(2) Providing environmental adaptability

(performance at high and low temperatures)The PEM fuel cell uses a proton exchange

membrane for electrochemical reactions, utilizinga polymer electrolyte membrane. It directlycoverts chemical energy to electrical energy. Thepolymer electrolyte membrane that conducts theprotons is sandwiched between the electrode lay-ers and the gas diffusion layers from the MEA, orMembrane and Electrode Assembly (Fig. 4). TheMEA is held between separators on both sides toforma single cell. Since theoretically only 1.23 V

can be obtained from one cell, the cells arestacked to obtain the necessary system voltage.Voltage and current requirements are as follows: Voltage - determined by the number of the cellsCurrent - determined by the area of electrode lay-ers

Therefore to increase power output it is nec-essary to either increase voltage or current. Asthere is a natural limit to how much the surfacearea can be expanded it was important to recon-

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FUEL CELL DEVELOPMENTFOR AUTOMOTIVE APPLICATIONYuji KawaguchiHonda R&D Co. Ltd.4630 Shimotakanezawa, Haga-machi, Haga-gun, Tochigi, 321 - 3393 Japan

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cile the seemingly incompatible ideas of increas-ing the number of cells and reducing the stacklength.

Carbon separators were applied to the stackof the V2 and V3 and disk springs and a thickbackup plate were installed to make it very air-tight. This meant that it was difficult to reduce thetotal stack length. Fuel cells must meet differentrequirements including very as load conditionssuch as idling, highway cruising, climbing and therange of temperatures from high to low.Conventionally fluorine electrolyte membraneswere used for the stack. But as this type of mem-branes softens at high temperatures and displayspoor proton conductivity at low temperatures, itsuse has been restricted to a range of temperaturesbetween 0 degrees Celsius and 80 degrees.

The new fuel cell stack uses an aromatic elec-trolyte membrane that offers outstanding protonconductivity and has stamped metal separatorsformed with unitized seal for superb electrical andthermal conductivity enabling high power outputand a wide operating range of temperature from -20 degrees to 95 degrees. In addition, a simplestack structure is obtained using the springiness ofthe stamped metal separators. As a result, thisarrangement achieved an approximately two-foldincrease and compactness and high output com-pared to the conventional stack.

3. HONDA FUEL CELL STACK3.1. Aromatic Electrolyte MembraneFor the new stack an electrolyte membrane

with a new molecular structure was developed bycombining an ion exchange substrate with themain chains of an aromatic structure having high

thermal stability. The ion exchange substrate con-centration governing ion conductivity wasincreased above that of comparable conventionalfluorine electrolyte membranes. The result wasthat the membrane resistance was halved asshown in fig. 7, and high proton conductivity wasachieved, even at below freezing temperatures.

A conventional fluorine electrolyte mem-brane softens and deforms abruptly when thetemperature rises above 80 degrees Celsius, andbecomes unusable, making it useless at high tem-peratures. The newly developed aromatic elec-trolyte membrane dose not softens or deforms athigh temperatures as its aromatic main chains arehighly durable and have high thermal resistance.As shown in fig. 8, the new membrane enableduse at the high temperature of 95 degrees Celsius,in addition to exhibiting high durability.

In general the traditional hydrocarbon mem-brane has a tendency to increase water-uptake inaccordance with its high ion exchange rate causedby its hydrophilic characteristics. The new aromat-ic membrane has stable water-uptake characteris-tics, and its unique structure allows for stablemembrane shape and proton conductivity even ifit is soaked in the hot water.

However, fractures occurred between theelectrode layer and the electrolyte membraneduring manufacturing, as shown in fig. 9, eventhough the aromatic main chain displays goodanti-deformity characteristics at high tempera-tures. An original manufacturing method wasdeveloped to address these issues, and superioradhesion was realized between the electrolytemembrane and electrode layer.

3.2. Stamped Metal SeparatorIn the fuel cell the separator forms a pathway

for the electrons, so it needs to have high electri-cal conductivity. At the same time, it should havegood thermal conductivity (temperature riseproperty) so that the water derived does notfreeze when power is generated below freezing.Therefore the stainless steel which has high elec-tric and thermal conductivity was examined.

Using stainless steel, which is stronger thancarbon, allowed Honda to design of a separatoronly half as thick as a carbon separator. As aresult, the thermal conductivity was increasedfive-fold (fig. 10), so that the entire stack can bewarmed quickly, significantly reducing the timerequired from the start of power generation towarm-up of the unit

Because of their superior electrical and ther-mal conductivity, metallic materials were consid-ered for separator material. However, oxidationand corrosion, due to the passage of the current,

are issues with these materials. If passive treat-ment is used to prevent oxidation and corrosion,the resistance of the metallic surface increases,resulting in inadequate performance. Carbon sep-arators were used in the past, but as shown in fig.11, conductive particles (electrically conductivemetallic inclusions) through which electricity canpass easily were dispersed in a stainless steel base,and passive treatment was performed on the sur-face to achieve a good balance between high con-ductivity, and durability and thermal conductivity.This measure reduced the contact resistance toone-fourth the resistance of conventional carbonseparators at -20 degrees Celsius (fig. 12).

3.3. Stack ConstructionIn the previous stack structure, carbon sepa-

rators and separate seals were used, and a diskspring and backup plate were installed and con-nected, using large bolts to make the structure air-tight, as shown in fig. 13. In contrast, the newlydeveloped fuel cell stack shown in fig. 14 uses

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high-strength metallic separators, reducing thethickness by 50% compared to carbon separators.Moreover, the use of unitized seals made it possi-ble to reduce the cell unit thickness and the num-ber of parts. The springiness of stamped metallicseparators was used to maintain the air tightnessusing simplified construction, in which the stackedcells are merely encased by panels, thereby reduc-ing the number of parts of the entire stack to near-ly half. This modification has resulted in morecompact and lighter fuel cell stacks, and the out-put density has been increased to more than twicethat of the conventional stack.

4. 2005 MODEL FCXThe 2005 model FCX delivers much more

power. The improved efficiency of power genera-tion by the stack, the air supply system to the stack,and the hydrogen circulation system results in a22% increase over the previous model in torqueenergy efficiency. A significant improvement infuel efficiency extends the vehicle's driving rangefrom 355 km to 430 km (in-house data). And withthe newly developed Traction Control System(TCS) the stability of the new FCX is evident evenon snowy roads.

By improvement the ion and thermal conduc-tivity, Honda expanded the temperature range inwhich 2005 model FCX runs into sub-freezingtemperatures.

In December 2004, Honda leased two FCXvehicles to the government office of New YorkState (fig. 15). Those vehicles were the first fuelcell vehicle supplied to a customer in the

Northeastern United States. In Japan the FCXwas leased to the Hokkaido PrefectureGovernment (fig. 16). It was the first fuel cell vehi-cle leased in Japan in a region that experiencessub-freezing temperatures.

In June 2005, an FCX was leased for the firsttime to provide customer in California for a peri-od of two years. The FCX is put to everyday use,including commuting to work, taking the childrento school, shopping and household errands. Thelessees are the first private citizens to useCalifornia's Hydrogen Highway refueling stations(fig. 17).

5. FCX CONCEPTIn October 2005 the next generation concept

was announced at the 2005 Tokyo Motor Show.The FCX concept provides a glimpse at the nextstage of the fuel cell vehicle's evolution. This visionof the future boasts a fuel cell system that deliversmore power and uses less space, in a unique, low-floor fuel cell platform. It is a next-generationsedan with a low center of gravity and a full-sizedcabin, offering the kind of driving pleasure androomy interior previously unimaginable in a fuelcell vehicle.

The FCX Concept also features Honda'sadvanced intelligent technologies which reducedriver burden, and the spacious interior allows forextra-large seats to maximize comfort. This pre-mium sedan offers the ultimate in clean-runningperformance.

Compact enough to fit neatly into the centertunnel, but robust enough to output 100 kW ofpower, the fuel cell stack offers both space effi-ciency and high energy output. The key to fuel cellperformance is water management. With verticalgas flow in that oxygen and hydrogen flow down-ward through, the fuel cell stack takes advantageof gravity to efficiency discharge water formedduring electricity generation. This improves sys-

tem performance in sub-zero temperatures,achieving a new level of system reliability. (fig. 19)

6. HOME ENERGY STATIONThe Home Energy Station (HES) is a com-

prehensive system designed to meet residentialenergy needs by supplying electricity and heat inaddition to hydrogen from natural gas suppliedfor residential use, the HES system also offersconsumers the convenience of refueling the fuelcell vehicles at home. The system is equipped withfuel cell vehicles at home. The system is equippedwith fuel cells that generate and supply electricityto the home, and is configured to recover the heatproduced during power generation for domesticwater heating. The third generation of the experi-mental unit was installed to Honda R&DAmericas in Torrance, California (fig. 20).

7. SUMMARYDevelopment of the aromatic electrolyte

membrane allows start-ups at temperatures belowfreezing, through increased proton ion conductiv-ity, while also enhancing durability at high tem-peratures. In addition a stamped metal separator,formed with a unitized seal, significantly reduceswarm-up time following the start of power gener-ation to be significantly reduced, because ofincreased electrical and thermal conductivity. Inaddition, the stack size is significantly smaller.

The combination of the aromatic electrolytemembrane, stamped metal separator formed withits unitized seal, and compact stack structureachieves both compactness and high power output.

Informaþii suplimentare puteþi obþine scriind laurmãtoarea adresã:

[1] Takayuki Ogawa, Kenichiro Kimura, Kenji

Uchibori, Kiyoshi Shimizu, Sachito Fujimoto,

Development of New Power Train for Fuel Cell

Vehicle, HONDA R&D Technical Review, vol. 15,

no. 1, p. 11

[2] Masajiro Inoue, Nobuhiro Saito, Kenji Uchibori:

Next Generation fuel cell stack for HONDA FCX,

HONDA R&D Technical Review, vol. 17, no. 2, p. 8

[3] Honda website

http://www.honda.co.jp/FCX/

http://world.honda.com/FuelCell/

References

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Recenta dezvoltare a injectorului pen-tru sistemul Common Rail pre-supune înlocuirea elementului de

comandã electromagnetic cu un sistem decomandã piezoelectric, la care acul injectoru-lui este comandat direct hidraulic, fãrã nici olegãturã mecanicã ºi care este mult mai rapid.

Injectorul piezoelectric are o serie deavantaje faþã de injectorul cu ventil electro-magnetic dintre care pot fi menþionate urmã-toarele:- spaþiul ocupat este mult mai mic ºi compact;- greutatea sistemului este practic înjumãtãþitã;- se pot realiza mai mute injecþii pentru unciclu de injecþie, ca de pildã douã preinjecþii,o injecþie principalã ºi douã injecþii finale;- cantitatea de carburant pentru o preinjecþiepoate fi redusã în mod sensibil;- poate fi stabilit un interval între douã injecþiimai mic.De aici decurg o serie de avantaje pentru uti-lizator, cum sunt:- zgomotul la injecþii multiple se reduce cu 3%;- consum extrem de mic pentru cantitatea decarburant la preinjecþie, redus cu 3%;- moment de injecþie flexibil ºi reducerea emi-siilor poluante cu pânã la 20%;- creºterea puterii motorului cu pânã la 7% saureducerea corespunzãtoare a consumului decarburant.- datoritã cantitãþilor mici de carburant injec-tat, se poate utiliza o pompã de injecþie deînaltã presiune mult mai micã.

În continuare se prezintã:- Comparaþia între cele douã tipuri de injec-toare în ceea ce priveºte domeniul de pre-siune, returul de carburant ºi masa proprie;- Construcþia injectorului piezo-electric;- Reprezentarea schematicã a piezo-elemen-tului (domeniul de temperaturã, capacitatea,curentul de încãrcare, tensiunea ºi timpul deîncãrcare);- Construcþia schematicã a amplificatorului

hidraulic;- Funcþionarea servoventilului/ventilului decomandã în poziþiile de start, ventil închis(acul duzei deschis) ºi ventil deschis (aculduzei închis);

Documentaþia este oferitã de reprezen-tanþa în România a companiei ROBERTBOSCH GmbH.

COMMON RAIL PIEZO-INJEKTOREN VON BOSCHDiese Berufsschulinformation beschreibt

den Aufbau und die Funktion des Piezo-Injektors.

Vorteile gegenüber dem Magnetven-til-Injektor und Kundennutzen:- Mehrfacheinspritzungen: Geräusch -3 dB(A)

COMMON RAIL PIEZO-INJEKTORENVON BOSCHPiezo-injectoarele Common Rail de la BoschConstrucþia ºi funcþionarea lor

Gekapselter piezoelektrischer Steller: Piezoelement (schematisch dargestellt)

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Notã: Acest articol a fost pus la dispoziþie de reprezentanþa ROBERT BOSCH S.R.L. din România

Piezoelement (schematisch dargestellt) Funktion hydraulischer Koppler/ Verstärker

Funktion Servoventil/ Steuerventil

- extrem kleine Voreinspritzmenge: Verbrauch -3 %- flexibler Einspritzzeitpunkt und Emission -20 % - extrem kleine Zeit zwischen Motorleistung +7 %

Der hydraulische Koppler/ Verstärker ist von seinerFunktion dem Hydrostößel sehr ähnlich. Um bei unter-schiedlichen Temperaturen einen Spielausgleich zuerreichen, wird dieser Koppler eingesetzt. Somit ist eswichtig, dass im Injektorrücklauf ein bestimmterRücklaufdruck aufgebaut ist. Dieser Druck wird durch dasRückschlagventil erreicht und beträgt ca. 8-14 bar. Durchdie unterschiedlichen Durchmesser der beiden Kolbenentsteht eine Druckverstärkung.

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REZUMATLa autoturismele moderne sunt integrate o

serie de dispozitive electromagnetice decomandã, pentru a acþiona sistemele de controlºi confort. Utilizând aliajele cu memoria formei,aceste sisteme existente pot fi simplificate în celemai multe cazuri, realizând aceleaºi funcþiuni cuajutorul unor noi mecanisme cu dimensiuni,greutate ºi costuri reduse. Principalele avantajeale dispozitivelor cu memorie a formei în apli-caþiile pentru aceste vehicule constau în faptul cãau o miºcare linã ºi directã cu cuplu ºi forþã marefãrã mecanisme adiþionale, silenþioase ºi cu fia-bilitate bunã atunci când miºcarea este determi-natã de proprietãþile fizice ale materialului. (1)

Dar cerinþele industriei de automobile deo-camdatã aratã o utilizare restrânsã a aliajelor cumemoria formei, în timp ce stabilitatea pe timpîndelungat a acestor dispozitive înca trebuie con-firmatã.

În aceastã lucrare este datã o scurtã intro-ducere referitoare la efectul memoriei de formã,este descris un sistem de ridicare a capotei ca oaplicaþie aleasã pentru dispozitive cu memorie aformei cu schimbare rapidã, facilitãþile de testareºi primele rezultate privind studiul stabilitãþii deduratã a acestor „materiale funcþionale“.

ABSTRACTIn modern passenger cars a lot of elec-tro-

magnetically driven actuators are integrated torun comfort and control systems. Using shapememory alloys these existing systems can be sim-plified in most cases, performing the same func-

tion through new mechanisms with reduced size,weight and costs. The main advantages of shapememory actuators in these vehicle applicationsare a smooth direct movement with high torqueor force, no additional mechanism, noiselessoperation, and intrinsic reliability, since themotion is related to the physical properties of the

material [i]. But the requirements of automotiveindustry still exhibit a re-straint for the use ofshape memory alloys in automotive applications,since the long-time stability of the actuator mate-rial still has to be proved.

In this paper a short introduction to theshape memory effect is given, a bonnet lifting

STUDY OF THE LONG-TIME STABILITYOF SHAPE MEMORY COMPONENTSFOR VEHICLE APPLICATIONS

Joachim Strittmatter, Dipl.-Ing.(FH), Scientific associate HTWG Konstanz, University of Applied Sciences, Department of Mechanical Engineering, Material Testing Laboratory, Brauneggerstraße 55, D-78462 Konstanz, Germany, Tel. +49 7531 206-317email: joachim.strittmatter@htwg-konstanz.de

Fig. 1: Martensitic phase change and shape memory [2]

Fig. 2: Potential vehicle application for shape memory components [1]

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system as one chosen application for quickchanging shape memory actuators is describedand the testing facilities and first results concern-ing the study of the long-time stability of these'functional materials' is shown.

INTRODUCTIONShape memory materials show the particular

capacity to revert to their original form whenheating if they are plastically deformed below acritical temperature before [ii]. This exceedingeffect is the result of a solid state phase change ofspecial alloys, the so-called shape memory alloys.Figure 1 shows this mechanism referred to asmarten-sitic phase change. The high-tempera-ture modification of the lattice (austenite) "flipsover" into a twinned martensite structure (fromtop left to bottom). This martensite lattice can bede-twinned up to 8% (for NiTi). As long as thematerial remains below the phase change tem-perature, this deformation is lasting. Heating ofthe deformed martensite above the phasechange temperature causes the reversion intothe original space-lattice structure and thereforeinto the original shape of the material. Thisbehaviour is the basis of the shape memoryeffect.

Generally the shape memory effect involvesa considerable reset force and therefore facili-

tates their application as actuators. So it is possi-ble to create a spontaneous contraction of ametallic element in the range of some percentthrough heating. Such actuator appli-cations canbe found e.g. as adjusting, combining, supportingor contacting elements, as active implants or ashigh damping spring elements. They also findapplications as sensors and actua-tors in passen-ger cars. More informa-tion about the techno-logical back-ground of shape memory alloys andits applications can be found in [2,iii , iv]. Figure2 shows potential vehicle appli-cations for shapememory components.

The use of adaptive working safety systemsfor automotive applications is continuouslyincreasing. In modern automotive engineering,especially quick changing actuators are used inapplications concerning safety regula-tions.Nowadays the actuators are mainly operated bycomplicated me-chanical systems, very often byso-called pyrotechnic ignition devices. By usingintelligent materials, e.g. shape memory alloys,an actuator function can be reached easily.Additionally, in comparison with systems drivenby pyrotechnic ignition devices, with such sys-tems it is possible to carry out the actuator func-tion repeatedly, or also reversibly. But the use ofshape mem-ory materials in such safety systems

is reduced because of the lack of material knowl-edge on this section. A central problem is thedurability of the switching function (long-timestability of the shape memory effect), which stillhas to be proved.

BONNET LIFTING SYSTEMA pedestrian protection system was devel-

oped by the consortium IPPS, IntelligentPedestrian Protection Sys-tems [v]. In this safetyconcept the companies Benteler automobiletech-nology, ETO MAGNETIC, Festo,Peguform and Siemens Restraint co-operatestogether since 2001. The con-cept contains agive-way bumper, fiber-optical sensors and anactive hood, raised by a pneumatic muscle. Thefunctional principle of new fiber-optical contactsensors acts in different stages. In parts the plas-tic sheath of the light wave conductor isremoved. If the fibers are bent, a part of the lightthere reflects from the fiber. This reflection isdepending on the bending intensity and there-fore the light loss registers how strong the fiberwas bent. By lay-ing several preserved fibershorizon-tally about the bumper and removingdifferent segments of the sheath, a distortion pic-ture of the vehicle front arises. Through this thecontrol module should be able to recognize if apedes-trian is going to crash into the bumper.

Fig. 3: System set up [6]

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Then it sends an impulse for lifting the modifiedbonnet to catch the head of the pedestrian softly.

In the first system a pneumatic muscle isactivated for lifting the bonnet in combinationwith a reversing mecha-nism it raises the bonnet.In the proto-type of IPPS the control unit signalsat the latest 15ms after the first contact on therelease and raises the bonnet within further35ms. To operate fast enough, the muscle needspressure air from pressure air cartridges or atype of storage, which is filled by a compres-sor.This system weights less than 1kg for sensor, con-

trol device and pneu-matic actuator, but itsdrawback is the weight of the compressor. Thesystem concept is shown in figure 3 [vi].

In order to profit of this system but avoidingits disadvantages this safety-system was chosenas a potential appli-cation for quick changingshape mem-ory actuators. The replacement ofthe pneumatic muscle through changing shapememory actuators leads to some additionaladvantages, e.g. reversible function, compactconstruction and less-cost-intensive-solution. Inprevious works in cooperation with the ETO

MAGNETIC company it has already beenproved, that shape memory alloys are suitable tofulfil the requested actu-ating times and forcesfor this applica-tion [vii, viii].

The following of this paper is focused on thestudy of the long-time stability of the shapememory actuator elements, that is required notonly in the potential application of the bonnetlifting system for pedestrian protection, but thatis of significant importance for the success-fulimplementation of shape memory componentsin vehicle applications.

Fig. 5: Laser testing facility, schematic view

Fig. 4: Oil bath testing facility, schematic view

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MATERIALIn the previous works [7, 8] best results were

achieved using a configuration with 30 NiTiwires plaited to a shape memory muscle. Thisconfiguration was actuated via electrical dis-charge of a capacitor and was able to lift a weightof 20kg (bonnet) over a lifting of 12,5mm withinless than 35ms. One single shape memory wirehas a di-ameter of 0,254mm and AP-temperatureof 95°C (supplier specifi-cation Memory-MetalleGmbH). For having the same starting materialfor the long-time stability tests and to achievereproducible results the wires were trainedunder a loading that cor-responds to 135N/mm2.They were trained 80 times by electrical actua-tion in special devices that allow fixing and train-ing of 90 wires. After the last training cycle theshape memory wires were fixed in the pre-strained condition under the tension of135N/mm2 to simulate exactly the mountingcondi-tion of the quick changing actuator in thecar.

AGEINGThe long-time stability of the shape memory

actuators is a significant point that has to be

assured. Safety systems in general could be acti-vated within the first days of a car's lifetime orafter several years, but the functionality of thewhole system and especially the actuators has tobe reliable at any time. In practice the long-timestability can be proved through a testing methodupon stored specimens. By storing the shapememory specimens an ageing process occurs anda statement con-cerning the functionality of thespeci-mens can be made. The test procedurebases on the well known fact, that the parame-ters time and temperature have a direct interre-lationship. So it is possi-ble to achieve artificialageing when the factor time is replaced throughthe factor temperature in a certain range.According to the requirements for parts in theengine compartment and to as-sure that at everytemperature the pre-strained wires still havemartensitic structure, the ageing temperatureswere chosen between 60 and 140°C. In checkingtests with increased weights it was certificated,that even at 140°C the pre-strained wires werestill martensitic in the fixing device. For each teststep concerning ageing temperature and expo-sure time six specimens were aged. In two spe-

cially developed testing fa-cilities these speci-mens were further examined.

THE TESTING FACILITIESThe first facility is schematically shown in

figure 4. Up to six specimens of the SM wires canbe horizontally fixed and connected to a weightthat causes a specified tension of 135N/mm2 inthe shape memory wire. By heating and coolingthe oil bath the specimens are cycled andthrough inductive distance sensors the length ofeach specimen is plotted in a temperature-lengthdia-gram. With the data of the phase changetemperatures and the contrac-tion value evensmallest behaviour differences in the specimenscan be analysed. By comparing the data of theaged specimens with a reference wire possibleageing effects upon the shape memory effect canbe noticed immedi-ately.

A second testing machine was designed inorder to investigate a possible influ-ence of age-ing upon the shape memory effect of actuatorwires concerning their functionality. Shown infigure 5 a sin-gle shape memory wire specimen isconnected on one side to a fixed mounting andon the other side to a mobile weight over a pul-

Fig. 6: Oil bath results: contraction-temperature diagram of specimens aged 120 °C for 4 days, three tests

ley. When the specimen is electrically activatedthe wire is heated and the phase changing frommartensite to austenite takes place. The herebycaused wire contrac-tion and the activation timeare meas-ured by the laser sensor.

FIRST RESULTS AND DISCUSSIONA typical diagram of the results achieved in

the oil bath tests is shown in figure 6. In this dia-gram NiTi wires with a diameter of 0,254mm andlengths of 244mm, aged at 120°C for 4 days wereexamined. Each specimen was cycled three timesbetween 10 and 170°C and compared with a ref-erence wire. All four graphs show the same con-traction values between 4,2% and 4,4%. The redlines in the diagram indicate the Ap-value ofeach graph. A difference can be observed in theAp-temperatures: Compared to the refer-encewire, the phase change tempera-ture at the firsttest after ageing is slightly higher. In the secondand third test of the same wire the observed in-crease was set back almost to the Ap-tempera-ture of the reference wire. This elevation can beexplained with the 'effect of the first phasechange trans-formation'. This well known effectmeans, that during the first phase change trans-formation the Ap-values are slightly higherbecause of the age-ing. This behaviour is due toa natural ageing of stored shape memory mate-rial and also takes place with the artifi-cial agedshape memory specimens of this investigation.

In the same way such diagrams were pre-pared of all the realized tests till exposure timesof 180 days. For each temperature group 'overall

diagrams' were prepared where the AP-tempera-tures can be seen as trend lines. In figure 7 thedata for the temperature group aged at 140°C isshown.

It can clearly be seen that the AP-tempera-ture of the first test is shifted to higher values. Incomparison to the reference data the shifting isabout 20K within the first days and 26K at 180days. The trend lines of the second and third testhave the same course, but their displacementconcerning the reference line is much smaller.All the trend lines, even the reference line are

slightly rising with longer exposure time. It canbe concluded, that tem-perature has an immedi-ate effect on the shifting of the AP-temperature,while the influence of the exposure time is lessintensive, but also leads to higher AP-values withlonger exposure times. In the other temperaturegroups the same observations were made. It wasobserved that the maximum shifting of the AP-temperature always occurred in the first testafter ageing and that the shifting value of the AP-temperatures is less intensive with lower ageingtem-perature. The shifting of the AP-tempera-tures of the first tests over the ageing tempera-ture is shown in figure 8.

By the results of the oil bath tests it can bestated, that ageing temperature as well as expo-sure time has a measurable effect upon the test-ed shape memory wires. Higher ageing tempera-tures lead to stronger shifting of the AP-temper-atures, while the influence of longer exposuretime is not so strong. The displacements havetheir maxima in the first tests after ageing andcan be classified as relatively small.

In the laser test facility two wires for eachtemperature-time group were single tested andthe average graph was compared to the referencegraph. The NiTi wires were electrical activatedvia discharge of a 47000μF-/100V capaci-tor thatwas loaded to a voltage of 30V. The pulse timewas fixed to 30ms. To avoid a strong overshoot ofthe load the impulse was absorbed through a pro-tector that was placed at a distance of 9mm overthe load. In figure 9 it can be seen, that the pro-

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Fig. 7: Overall diagram of the 140°C temperature group

Fig. 8: Maximum shifting of AP-temperature of the first testsaged at different temperatures for 180 days

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i Butera F.: Shape Memory Actuators for Automotive Applications, in Shape Memory Alloys.Advances in Modelling and Applications, edited by F. Auricchio et al, CIMNE, Barcelona,Spain, 1991, pp. 405-426ii Gläser S., Gümpel P.: Formgedächtnislegierungen und ihr metallkundlicher Hintergrund, pp.1-33 in: Gümpel P. et al: „Formgedächtnislegierungen - Einsatzmöglichkeiten inMaschinenbau, Medizintechnik und Aktuatorik", expert verlag, vol. 655, D-Renningen, 2004,156 pp.iii Strittmatter J.: Formgedächtnislegierungen und ihre Einsatzmöglichkeiten in der Praxis -Allgemeine Anwendungsbeispiele in der Technik und ausgewählte Forschungsprojekte derFH-Konstanz, pp. 93-129 in [2]iv Gläser S., Gümpel P., Kilpert H., Strittmatter J: Quick Changing, Actuators for Safety

Systems in Automobiles, Proceedings of the 10th International Congress on Automotive andFuture Technologies CONAT 2004, Brasov, Romania, 24 pagesv N.N.: IPPS-Konsortium: Fünf für Fußgängerschutz, in Automobil-Entwicklung, Mai 2004,p.34vi Scherf O., Bardini R.: A Fibre Optical Sensor System for Control of Active PedestrianProtection Systems, VDI Berichte Nr. 1794, 2003, p. 199-223vii Franke J.: Schnellschalternder Aktor aus FGL, Diploma thesis, University of AppliedSciences, Konstanz, 2002viii Gläser S., Gümpel P.: Schnellschaltende Aktoren aus Formgedächtnislegierungen, fhkfo-rum 2003/2004, p.65-68, 2003

References

tector could not ab-sorb the whole energy ofimpulse: The weight was rejected, the liftingvalue dropped from 9 to 6mm and then swung toa value between 7 and 7,5mm at 150ms.

In all the test data of the different tem-pera-ture-time groups no significant difference to thereference wires could be observed. Even a closeranalyse of the first 50ms of the graphs did notshow any systematic. It can be stated that the smalldifferences were not caused by different agedmaterial, but by the accuracy of measurement.

By the results of the laser tests it can be stat-

ed, that ageing temperature as well as exposuretime has no measurable effect upon the functionof the tested shape memory wires. First, these re-sults seem to be a contrast to the results of the oilbath results, where a slight shifting of the AP-temperatures towards higher values wasobserved and there-fore constant activationenergy should lead to measurable slowing-downof the contraction time. Considering the re-sultsof both tests it can be concluded, that throughthe high-speed discharge of the capacitor such ahigh energy is applied upon the actuator wires,

that even for a AP-temperatures raise of 26K nomeasurable influence can be de-tected concern-ing the function of the actuator wires.

SUMMARYConcerning the present results it can be con-

cluded, that the use of quick changing shapememory elements as actuators in safety systemsshould be possible not only for the bonnet liftingsystem, but also for other automotive applica-tions. A final conclusion can be made after thestudy of shape memory wires that were aged forlonger time periods.

Fig. 9: Laser test results: stroke-time diagram of SM-wires aged at 140°C for different exposure times

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ABSTRACTA fuel cell is an electrochemical energy con-

verter that produces electrical energy fromchemical free energy of some fuels.

The basic structure of a hydrogen fuel cell isshown in Figure 1. It consists of an anode and acathode which are separate by an electrolyte.The reactants supplied to the cell are molecularhydrogen and atmospheric oxygen. The fuel cellbreaks these hydrogen molecules at the anode,due to the chemical reaction, releasing hydrogenions and electrons. The electrolyte allows the twoprotons (hydrogen ions) to move to the cathode.At the cathode chemical reaction takes place intwo stages: first, the bond between the two oxy-gen atoms in the molecule breaks and then oxy-gen atoms grabs two electrons coming from theanode through the external circuit to becomenegatively charged. The negatively charged oxy-gen atoms are balanced by the positively chargedhydrogen atoms at the cathode, and the combi-nation produces water molecules. The flow ofelectrons from the anode to the cathode throughthe external circuit is what has electrical energy.

Fuel cell voltage current relationship isshown in Figure 2. The linear region where thereduction in cell electric potential is due to theohmic losses is where fuel cell operates.

Fuel cells operate, theoretically, isothermal-ly. The hydrogen fuel in the fuel cell does notburn as in the IC engines and its efficiency is notsubject to the Carnot limitation imposed on heatengines. In Figure 3 are shown the efficiencies ofvarious energy converters in comparison withfuel cells electric efficiency.

The six major types of fuel cells are as fol-lows: alkaline, proton exchange membrane,direct methanol, phosphoric acid, molten car-bonate, and solid oxide. The features of thesecells are summarized in Table 1, and its usableenergy and relative costs are given in Table 2.

The selection of fuel cells as the primaryenergy sources in EVs and HEVs depends offuel cell technology and of the infrastructure tosupport the system. Based on the discussion inthis paper, the alkaline and proton exchange

cells are appropriate for vehicular application.The options for storage of hydrogen play a criti-cal role in the development of infrastructure forfuel cell electric vehicles. These options are dis-cussed in the paper too.

Finally, the structure of a drive train of a fuelcell vehicle is described.

PILA CU COMBUSTIBILO pilã cu combustibil este un convertor elec-

trochimic de energie care produce energie elec-tricã din energia liberã stocatã în legãturile chi-mice ale unor combustibili.

Structura de bazã a unei pile cu combustibileste prezentatã în figura 1. Ea conþine doi elec-trozi, unul negativ numit anod ºi altul pozitivnumit catod, electrozi care sunt separaþi de unmediu conductor de ioni, numit electrolit. Pilaeste alimentatã cu doi reactanþi: hidrogen mole-cular (H2), la anod, ºi oxigen molecular atmos-feric (O2), la catod.

Molecula de hidrogen conþine douã nuclee,cu câte un proton fiecare, înconjurate de doielectroni. în urma unor procese chimice care auloc la anod, molecula de hidrogen este spartã încele patru componente ale ei. Cei doi protoni,care au sarcini electrice pozitive, migreazã prinelectrolit cãtre catod iar cei doi electroni, care ausarcini electrice negative, sunt introduºi în cir-cuitul electric în care pila este conectatã. Apare,astfel, un curent electric ce trasferã o anumitãenergie circuitului exterior pilei. Viteza de sepa-rare a componentelor moleculei de hidrogen sepoate creºte folosind catalizatori. La catod,reacþia chimicã are loc în douã etape: mai întâi sesparge legãtura chimicã dintre cei doi atomi ai

moleculei de oxigen iar apoi se ataºeazã atomilorde oxigen câte un electron primit din circuitulelectric în care pila este conectatã, încãrcându-seastfel atomii de oxigen cu sarcini electrice nega-tive. Atomii de oxigen încãrcaþi negativ se vorcombina cu atomii de hidrogen încãrcaþi pozitiv,care sosesc la catod, ºi în urma acestei combinãrise vor produce molecule de apã (H2O). Aºadar,reacþiile chimic care au loc într-o pilã cu hidro-gen-oxigen sunt urmãtoarele:

La anod: H2 → 2H+ + 2e-

La catod: 2e- + 2H+ + ½O2 → H2OÎn pilã: H2 + ½O2 → H2O

Pilele cu combustibil au fost utilizate laînceput ca surse auxiliare de energie pentruvehicule spaþiale (pentru modulul lunar ºi pentrunavetele spaþiale). În ultimii ani existã un mareinteres pentru folosirea acestora ºi la altevehicule cum sunt vehiculele electrice terestre(automobile, autobuze sau scutere).

CARACTERISTICA EXTERNÃTENSIUNE-CURENTO pilã cu combustibil converteºte energia

liberã a legãturilor chimice, numitã ºi energieGibbs, în energie electricã, sub forma unuicurent de electroni, în condiþii izoterme.Valoarea maximã a energiei electrice a unei pilecu combustibil, care funcþioneazã la temperaturãºi presiune constante, este datã de variaþiaenergiei libere Gibbs:

Wel = -)G = nFE (1)unde n este numãrul de electroni produºi de

reacþia anodicã, F este constanta lui Faraday,care are valoarea de 96412,2 C/mol, iar E estepotenþialul electric reversibil. Pentru reaþiachimicã a pilei:

H2(gaz) + ½O2(gaz) → H2O(lichid)În condiþiile standard, când presiunea este

de o atmosferã iar temperatura este de 25°C,variaþia energiei libere Gibbs are valoarea de -236 kJ/mol sau -118 MJ/kg. Din ecuaþia (1), pen-tru n = 2, rezultã pentru potenþialul electricreversibil, în condiþiile standard, valoarea maxi-mã E0 = 1,23 V. În condiþii de funcþionare

PILELE CU COMBUSTIBILSURSE DE ENERGIE PENTRU VEHICULELE ELECTRICE

Prof. Dr. Ing. Aurelian CrãciunescuUniversitatea Politehnica din BucureºtiFacultatea de Inginerie Electricã

Oxidant, O2

Vapori de apa

CatodAnod Electrolit

Sarcina

Combustibil, H2

Ioni pozitivi

I

Electroni

Hidrogenîn exces

Figura 1: Schema de principiu a unei pile cu combustibil

17

Supliment Auto Test

diferite de cele standard, valoarea maximã apotenþialului electric reversibil, pentru pila cuhidrogen-oxigen, este datã de ecuaþia lui Nernst:

(2)

unde T este temperatura în grade Kelvin, Reste constanta gazelor, iar PH, PO ºi PH2O suntconcentraþiile sau presiunile parþiale ale reac-tanþilor ºi, respectiv, produsului de reacþie.

Caracteristica externã tensiune-curent apilei cu hidrogen-oxigen este prezentatã în figu-ra 2. Valorile mari ale tensiunii, apropiate de 1 Vpe celulã, sunt valori teoretice care nu sunt acce-sibile în cazuri practice. Zona în carefuncþioneazã pilele cu combustibil este zona line-arã uºor cãzãtoare în care, din cauza pierderilorohmice interne, tensiunea celulei scade pemãsurã ce curentul debitat creºte. Valori maimari de tensiune, cerute de alimentareamotoarelor electrice, se obþin prin înserierea maimultor celule.

Randamentul electric al pilelor cu com-bustibil este limitat de pierderile interne deenergie. El este însã superior motoarelor cuardere internã deoarece în pilele cu combustibilnu are loc un proces de ardere care sã trans-forme energia chimicã în energie mecanicã prinintermediul energiei termice, transformaresupusã limitãrilor ciclului Carnot. în figura 3 seprezintã pentru comparare randamentelediverselor convertoare de energie.

TIPURI DE PILE CU COMBUSTIBILSunt ºase tipuri principale de pile cu com-

bustibil: 1) pile alcaline; 2) pile cu membranãschimbãtoare de protoni; 3) pile cu metanol; 4)pile cu acid fosforic; 5) pile cu carbonat topit; 6)pile cu oxid solid. În cele ce urmeazã se va face o

scurtã descriere a caracteristicilor reprezentativeale acestor pile în perspectiva aplicaþiilor lor lavehicule.

Pile alcaline. În pilele cu combustibil alca-line se foloseºte ca electrolit o soluþie apoasã dehidroxid de potasiu (KOH). în comparaþie cupilele cu combustibil care folosesc electroliþiacizi, pilele alcaline au performanþe la fel debune dar au în plus avantajul cã electrozii lorsunt mult mai puþin supuºi la coroziune. Pilele cucombustibil alcaline sunt utilizate de mult timp ºiau un randament electric de pânã la 60%. Elenecesitã hidrogen pur ca combustibil ºifuncþioneazã la temperaturi joase (la 80°C), faptcare recomandã folosirea lor la vehicule.

Pile cu membranã schimbãtoare de protoni.Aceste pile folosesc electroliþi solizi ºifuncþioneazã la temperaturi joase (aproximativ80°C). Randamentul lor electric este mai micdecât al pilelor cu combustibil alcaline (aproxi-mativ 40%), însã construcþia lor simplã ºi robustãface ca ele sã fie recomandabile pentru utilizarela vehicule. în plus, faþã de pilele alcaline carenecesitã hidrogen pur, pilele cu membranãschimbãtoare de protoni au avantajul cã tole-reazã impuritãþi în combustibil.

Pile direct cu metanol. Aceste pile folosescca combustibil metanolul care este transportatde vehicul ºi reformat pentru a furniza hidrogenpilei. Pentru ca reformarea internã a metanolu-lui în hidrogen sã fie posibilã, temperatura defuncþionare a pilei trebuie sã fie între 90 ºi1200C. Randamentul electric al acestor pile esteaproximativ de 30%. în prezent, pilele cumetanol sunt încã în faza de cercetare, cãutãrilefiind îndreptate în direcþia descoperirii unorcatalizatori care sã creascã eficienþa procesuluide reformare ºi de reducere a oxigenului.

Pile cu acid fosforic. Acestea sunt cele mai

vechi pile cu combustibil. Ele folosesc ca elec-trolit acidul fosforic ºi funcþioneazã la tempera-turi de aproximativ 200°C. Randamentul lorelectric este de aproximativ 40% ºi produc ºienergie termicã. Pentru vehicule ele nu suntrecomandabile din cauza gabaritelor mari darsunt indicate pentru aplicaþii staþionare datoritãrandamentului lor ridicat.

Pile cu carbonat topit. Aceste pile au fostdezvoltate iniþial ca sã funcþioneze direct cu cãr-bune. Ele folosesc ca electrolit carbonatul.Alimentarea lor la catod se face cu monoxid saucu bioxid de carbon (CO sau CO2).Randamentul lor este de aproximativ 50% iartemperatura lor de funcþionare este de aproxi-mativ 600°C. Ele nu sunt indicate pentru a fi uti-lizate la vehicule din cauza temperaturii mari defuncþionare, dar sunt recomandabile pentru apli-caþii staþionare.

Pile cu oxid solid. Aceste pile folosesc caelectrolit un conductor ionic solid de tip ceramic,astfel cã problemele de coroziune sunt multreduse faþã de cele existente în pilele cu electrolitlichid sau polimer. Pentru realizarea, însã, a uneiconductivitãþi adecvate, pila trebuie sãfuncþioneze la temperaturi foarte mari, aproapede 1000°C. Randamentul electric al acestor pileeste între 50 ºi 60% iar cãldura produsã poate fiºi ea utilizatã. Pentru vehicule nu este o soluþiedar pentru aplicaþiile staþionare este, în prezent,cea mai bunã opþiune.

Caracteristicile pilelor cu combustibildescrise mai înainte sunt centralizate în tabelul 1.Energia utilizabilã ºi costurile raportate alediferitelor tipuri de combustibili utilizaþi în pilesunt date în tabelul 2.

Pentru vehiculele electrice ºi hibride,alegerea pilelor cu combustibil ca surse deenergie trebuie sã þinã seamã atât de perfor-manþele pilelor cât ºi de cele ale infrastructuriicapabile sã suporte sistemul de transport. Dincele prezentate mai înainte, pentru vehicule potfi alese pilele alcaline ºi pilele cu membranãschimbãtoare de protoni. Dimensiunile, costul,randamentul cât ºi timpul de amorsare la acestepile sunt acceptabile pentru vehiculele electriceºi hibride actuale. Sistemul de comandã, însã, alpilelor de combustie este extrem de complex ºi,deºi a fost verificat în aplicaþiile spaþiale ºi peprototipurile unor vehicule, nu este maturizatsuficient pentru a fi utilizat pe scarã largã.

SISTEME DE STOCAREA HIDROGENULUIPentru realizarea infrastructurii de ali-

mentare cu hidrogen a vehiculelor electrice ºihibride, modul de stocare al hidrogenului are un

2

1/ 2

0 ln H O

H O

P PRTE EnF P

⎡ ⎤⎛ ⎞= + ⎢ ⎥⎜ ⎟⎝ ⎠ ⎢ ⎥⎣ ⎦

100

80

60

40

20

01 10 102 103 104 105 106

Puterea, kW

Randamentul, %

Densitatea de current, A/cm20,2 0,4 0,6 0,8 1,0

Tensiunea, V1,2

1,0

0,8

0,6

0,4

0,2

Pila cu combustibil

MotorDiesel

Turbina

Motor Otto

Figura 2: Caracteristica externa a Figura 3: Randamentele unorunei pile cu combustibil convertoare de energie

18 Ingineria Automobilului Nr.3

Supliment Auto Test

rol esenþial. Hidrogenul sub formã de gaz la pre-siunea atmosfericã are o densitate de energiefoarte micã ºi nu este o formã potrivitã pentrustocare. Hidrogenul poate fi stocat sub formã degaz comprimat sau lichefiat, ori sub o formã maiavansatã folosind hidruri metalice sau nano-tuburi de carbon.

Stocarea gazelor sub formã comprimatã esteo soluþie utilizatã de mult timp. Realizarea eieste necesitã o cantitate mare de energie pentrucomprimarea gazului la un nivel la care stocareasã fie eficientã (de obicei, la o presiune de câte-va sute de atmosfere). Lichefierea hidrogenuluinecesitã comprimãri ºi mai mari, asociate curefrigerãri la temperaturi criogenice ºi nu repre-zintã o soluþie acceptabilã pentru vehicule.

Stocarea hidrogenului cu ajutorul hidrurilormetalice sau a nanotuburilor de carbon se facecomprimând gazul la presiuni cuprinse întrecâteva atmosfere ºi câteva zeci de atmosfere,într-un recipient în care se aflã un material carepoate absorbi sau elibera hidrogen molecular(H2) în funcþiune de presiune, temperaturã ºivolumul de hidrogen stocat. Hidrurilor metalice,când sunt complet saturate cu hidrogen, potconþine de douã ori mai mulþi atomi de hidrogendecât un volum echivalent de hidrogen lichid, iargreutatea rezultatã, deºi este mare, ar putea ficonsideratã acceptabilã pentru vehicul.Folosirea nanotuburilor de carbon ar puteaelimina dezavantajul greutãþii mari a stocãrii cu

hidruri metalice dar performanþele acestei posi-bilitãþi de stocare sunt încã controversate.

Existã prejudecata conform cãreia prezenþape vehicul a hidrogenului sub presiune este unpotenþial pericol pentru pasageri. Experienþa aarãtat însã cã, folosind soluþii inginereºti adec-vate, pericolul prezentat de hidrogenul prezentpe vehicul poate fi mai mic decât pericolulprezenþei propanului sau benzinei.

VEHICULE ELECTRICECU PILE CU COMBUSTIBILSistemul de propulsie al unui vehicule elec-

tric cu pilã cu combustibil conþine urmãtoarelecomponente: un dispozitiv de stocare a com-bustibilului, un reformator de combustibil, pilade combustibil, dispozitivul de comandã a pilei ºilanþul de acþionare electricã format din urmã-toarele componente: un convertor de tensiunecontinuã, un dispozitiv de stocare a energiei elec-trice, un convertor de frecvenþã ºi un motor elec-tric de curent alternativ.

Convertorul de tensiune continuã este nece-sar pentru ridicarea nivelului tensiunii date depila cu combustibil la nivelul cerut de motorulelectric de acþionare. Cu cât tensiunea de ali-mentare a motorului electric, de o anumitã pu-tere, este mai mare, cu atât curentul absorbit deacesta este mai mic, pierderile electrice sunt maimici ºi secþiunea conductoarelor de alimentareeste mai micã.

Dispozitivul de stocare a energiei electrice

(acumulator sau/ºi ultracondensator), este nece-sar pentru asigurarea alimentãrii motorului laaccelerãri ºi la suprasarcini, deoarece constantade timp a pilei cu combustibil este mult mai micãdecât constantele de timp caracteristice proce-selor dinamice ale vehiculului ºi pila nu poateasigura alimentarea în aceste regimuri. Deasemenea, estenecesarã stocarea energiei recu-perate la frânare. Nivelul de tensiune al baterieide stocare trebuie sã fie ridicat, la nivelul tensiu-nii de alimentare a motorului electric, cerinþãcare se realizeazã prin conectarea în serie a maimultor elemente. în cazul folosirii unei baterii cutensiune joasã, creºterea tensiunii date de ea lanivelul tensiunii motorului electric se face cu unconvertor electronic de tensiune continuã.

Funcþionarea corectã a pilei cu combustibilse asigurã dacã combustibilul este livrat pilei pemãsurã ce el se consumã. Dacã se solicitã pileimai multã putere, fãrã a se modifica admisia dehidrogen, atunci concentraþia acestuia scade, sereduce nivelul tensiunii electrice furnizate depilã ºi se poate distruge membrana ei separa-toare. Dacã gradul de utilizare a hidrogenuluiatinge nivelul de 100%, pila începe sãfuncþioneze în regimul cu curent constant, carac-terizat de pierderi interne mari, situaþie care tre-buie, de asemenea, evitatã. Aºadar, pentru obunã funcþionare a pilei este bine sã fie livrathidrogenul puþin în exces.

Produsele eliminate în urma funcþionãriipilei sunt apa, sub formã de vapori, ºi eventual unexces de hidrogen. Vaporii de apã pot fi utilizaþipentru încãlzirea vehiculului dar hidrogenuleliminat constituie o pierdere pentru sistem.

Tipul pilei Combustibilul Electrolitul Temperaturade funcþionare

Randa-mentul

Aplicaþii

Alacalin H2, Soluþie dehidroxid depotasiu

800C 40-50% Sisteme portabile

Membranãschimbãtoarede protoni

H2, metanol,GNL

Polimer 800C 40-50% VE º i VEH, sistemeindustriale pânã la80 kW

Direct metanol Metanol, etanol Polimer solid 90-1000C 30% VE º i VEH, sistemeportabile mici(1W – 70 kW)

Acid fosforic H2, metanol,GNL

Acid fosforic 2000C 40-50% Staþionare (>250 kW)

Carbonat topit H2, CO, metanol,GNL

Carbonat 600-7000C 50-60% Staþionare (>250 kW)

Oxid solid H2, CO, metanol,GNL

Ceramic 10000C 50-65% Staþionare

Tabelul 1: Tipuri de pile cu combustibil

Combustibilul Energia utilizabilã,MJ / kg

Costul relativ,cost / MJ

Hidrogen:- puritate 95%- puritate 99%

118,3120,0

1,07,4

GNL (propan) 47,4 0,5Benzinã 45,1 0,8Metanol 21,8 3,3Amoniac 20,9 3,6

Tabelul 2: Energia utilizabilã ºi costul relativ

Bibliografie:

Barklay, J. F., Fuell Cells, Engines and Hydrogen. An

Exergy Approach. Willey, 2007

Ehsani, M., Y. Gao, S. E. Gay ºi A. Emadi, Modern

Electric Hybrid Electric, and Fuell Cell Vehicles.

Fundamentals, Theory, and Design. CRC Press, Boca

Raton, 2005.

Hodkinson, R., ºi J. Fenton, Lightweight Electric and

Hybrid Vehicle Design, SAE International, Warrendale,

PA, 2001.

Husain, I., Electric and Hybrid Vehicles. Design

Fundamentals. CRC Press, Boca Raton, 2003.

Karamanolis, S., Brennstoffzellen - Schlüsselelemente

der Wasserstofftechnologie, Vogel, Würzburg, 2003

Kurzweil, P., Brennstoffzellentechnik. Grundlagen,

Komponenten, Systeme, Anwendungen. Vieweg,

Wiesbaden, 2003.

SURSE ALTERNATIVE DE PROPULSIE PENTRU AUTOMOBILEAutorul lucrãrii este profesor al Universitãþilor Paris 6, Pisa, Perugia ºi Zwickau, ºi Director alInstitutului pentru Transfer de Tehnologie al Universitãþii de ºtiinþe Aplicate din Zwickau.Lucrarea prezintã acumulãrile profesionale realizate de autor, atât în calitate de profesor univer-sitar, cât ºi în cea de cercetãtor ºi autor a mai multor vehicule cU surse alternative de propulsie,multe dintre ele aflate deja în producþie de serie. Soluþiile tehnice aplicate pentru optimizareaproceselor de combustie ºi formare a amestecului carburant sunt brevetae de profesorul CornelStan în Germania ºi alte state membre ale Uniunii Europene, precum ºi în SUA.Elaborat pe 312 pagini ºi structurat în ºase capitole, tratatul analizeazã câteva teme majore cumsunt:- Surse energetice clasice ºi alternative pentru motoarele autovehiculelor,- Performanþele ciclurilor maºinilor termice ºi identificarea soluþiilor de ameliorare a acesto-ra;- Potenþialele motoarelor cu combustie internã ºi ale mecanismelor de distribuþie, echipa-mentelor de injecþie ºi traseelor de admisie;- Combustia amestecurilor omogene ºi convergenþa ciclurilor Otto ºi Diesel;- Realizãri tehnice în domeniul motoarelor Wankel ºi Stirling precum ºi al turbinelor cugaze;- Automobile electrice ºi hibride.

EXPERTIZA TEHNICÃ AUTO JUDICIARÃ ªI CRIMINALISTICÃAnalizarea accidentelor de trafic rutier constituie un domeniu în care concurã atât ºtiinþele clasice ºi exacte, cât ºi dezvoltareatehnologiilor care participã la construcþia de automobile ºi cu precãdere a autoturismelor. De la materiale cu compoziþii noi, pânã lasoluþii electronice ºi digitale cu programe ale înaltei tehnologii, toate participã la construcþia ºi dezvoltarea construcþiei autove-hiculelor.Abordarea unei lucrãri de o asemenea amploare care presupune ºi un caracter monografic, reprezintã o sarcinã dificilã deoarece pre-supune cunoaºterea în detaliu a raportului drum, ºofer ºi autovehicul. Numai experienþa poate sã acopere o asemenea iniþiativã ºi nuo rutinã oarecare, ci o experienþã de profesionist în analiza ºi cercetarea accidentelor de trafic rutier. Ca expert cu o experienþãîndelungatã, autorul lucrãrii introduce multe noutãþi în domeniul expertizãrii unui accident soldat cu deces sau cu vãtãmare de per-soane, uzând de cunoºtinþe temeinice de criminalisticã, fãrã de care elaborarea unei lucrãri de o asemenea anvergurã, nu ar fi fostposibilã.Lucrarea de faþã a fost scrisã, chiar pe structura unor obiective formulate de cãtre un organ judiciar, pentru elaborarea unei expertizetehnice auto judiciare sau criminalistice, astfel încât un eventual explorator sã se edifice asupraideii de expertizã la modul propriu. Autorul a urmãrit lãmurirea unor idei noi asupra consumãriiunei pãrþi din energia acumulatã de un autovehicul prin deformarea caroseriei, fapt ce nu estesimplu din punctul de vedere al exprimãrii matematice a fenomenului fizic. Ideea de echivalentenergetic al vitezei, vine ºi clarificã numeroase probleme faþã de calcularea vitezei dupã urmelede frânare la acele autoturisme care nu sunt dotate cu sisteme moderne în echipamentul defrânare, constituind un factor nou abordat într-o lucrare de expertize din domeniul autove-hiculelor ºi circulaþiei rutiere.Autorul lucrãrii a abordat ºi aprofundat în mod ºtiinþific domeniul construcþiei autove-hiculelor împletit cu domeniul comportamentului autovehiculului ºi a conducãtorului auto,pe scurt dinamica autovehiculelor pe roþi. Elaborarea lucrãrii a presupus nu numaicunoºtinþele teoretice ºi practice în domeniu, dar ºi experienþa bogatã în elaborarea exper-tizelor, acoperitã de o activitate îndelungatã, ºi apelarea la noutãþi în domeniul respectiv.Anexele deosebit de valoroase, vin sã serveascã pe cei care consultã lucrarea pentru elab-orarea expertizelor de specialitate.Datoritã structurii sale, lucrarea se adreseazã organelor judiciare, experþilor judiciari dindomeniu, societãþilor de asigurãri, studenþilor, candidaþilor la titlul de expert judiciar ºichiar conducãtorilor auto profesioniºti. Ea este bine închegatã, valorificând ºi utilizândcomunicãri ºtiinþifice din þarã ºi din strãinãtate, demonstrând preocupãri serioase îndomeniul respectiv, precum ºi o activitate de documentare de foarte mulþi ani.Cartea prezintã unele noutãþi într-un domeniu foarte puþin abordat pânã în prezent, constituindo lucrare de referinþã în þara noastrã în domeniul expertizelor tehnice auto judiciare ºi criminalistice.