Valeo StARS Technology: A CompetitiveSolution for Hybridization

Daniel Richard*, Yannick Dubel** Valeo Electrical Systems, France

Abstract-- Whereas costly hybrid applications are flourishingworldwide mainly thanks to strong hybrid applications at theleading edge of technology, Valeo believes the mass marketrequires realistic, cost effective and reliable technical solutionsapplicable at wide scale to large diffusion vehicles so as toefficiently contribute to CO2 emission reduction. Therefore,developing products with an optimized business caseindependently of tax reduction or incentives is a must for Valeo.This paper presents the development work which has beencarried out since the past years, from the first generation of beltdriven starter alternator to the next generations with integratedelectronics, from pure stop-start technology to strongerfunctionalities such as regenerative braking. Description,performances and applications of such products are detailed inthe next sections.

Index Terms-- Starter-alternator, integrated electronics,hybridization, powertrain.

I. INTRODUCTION

Due to oil price increase, environmental concerns, andmore and more demanding consumers, the automotiveindustry is currently mainly driven by needs for fuelsavings and comfort enhancement while reducingpollution drastically, mainly for Diesel. Hybridization ofthe powertrain is one of the solutions which fulfill allthese requirements. Meanwhile, European countries andJapan are introducing labels to encourage the spreadingof clean and low consumption vehicles. Tax credit, taxdeduction and free access to High Occupancy Vehicleslanes are some examples of legislative and regulatoryactivities promoting low emission vehicles and morespecifically HEVs (Hybrid Electric Vehicles) in some USstates. However, mass market is mainly driven by costeffective solutions independently of incentives or taxreduction and significant levels of CO2 emissionreduction can only be achieved once this economicalequation is solved.

II. STARS ALLOWS MAXIMUM BENEFITS AT LOWCOST

Valeo decided to focus its efforts on affordable hybridsolution, excluding complex hybrid electrical architectureor non standard electrical machines as a first industrialstep. Once this fact admitted, the question about thechosen technology arose for Valeo: by which mean Stop-Start shall be operated?

Three pure Stop-Start technologies co-exist today, if inseries production or prototype state:

* Stop-Start is operated throughout the generator as a

reversible machine which starts the engine instartermode,

* Stop-Start is operated throughout the starter motorwith modified parts to allow re-cranking of theengine, and

* Stop-Start is operated with the help of precision-tuning of the engine management, injection andignition.

Valeo has developed the first generation of "Stop-Start" system based on the first approach: Figure 1presents the Valeo StARS rt-hybrid (Starter AlternatorReversible System), today in serial production withCitroen. Valeo StARS rt-hybrid is a Stop-Start conceptbased on a reversible alternator in a standard 14V board-net: a reversible 2.5kW voltage source inverter is placedbetween a conventional AGM battery and the belt-drivenclaw-pole machine to allow for both, silent and quickstarter and efficient alternator operations. Figure 2 showsthe exploded view of StARS and its subcomponents.StARS performs a comfortable "Stop-Start" function incomplete transparency for the driver: the belt drivenstarter-alternator system shuts down the engine duringidle phases and restarts the engine quickly (down to 350ms depending on the application) and silently on request.This results in no fuel consumption, gas emission,vibration and noise at standstill. The crankingperformances of the Valeo StARS on an ET3 engine at25°C ambient temperature are shown on Figure 3,whereas Figure 4 details the torque performances of theValeo StARS 137 6 magnets (the electrical machinefeatures a 137 mm diameter stator and 6 pole pairs clawpole rotor with 6 interpolar magnets) and the ValeoStARS 144 16 magnets (the electrical machine features a144 mm diameter stator and a 8 pole pairs claw pole rotorwith 16 interpolar magnets). Emphasis has been made ondeveloping a range of StARS products to fit gasolineengines up to 2.OL displacement and Diesel engine up to1.6L displacement. Furthermore, as shown on Figure 5,StARS allows a high efficiency alternator mode featuringsynchronous rectifying and providing a better energybalance of the vehicle and improves consequently fuelsavings by comparison with other Stop-Start technologies.

Fig. 1. Valeo introduced its StARS Ist generation in 2004.

1-4244-0844-X/07/$20.00 ©2007 IEEE. 1601

Fig. 2. Exploded view of StARS.

Application of standard parts and realization of rathersimple power electronics (power bridge full wavecontrol) in a separated box yields a flexible system thatcan be easily integrated to different motor platforms witha short time-to-market. While standards for Stop-Startstrategies are not yet stabilized, StARS rt-hybrid is a costcompetitive solution for medium volumes.

40

0 00 02 0,3 04 0f 06 07 0.0 09Time (s)

Fig. 3. Cranking performances on the ET3 engine at 250C

ambient temperature.e0

Machine speed (rpm)

Fig. 4. Torque performances at 250C ambient temperature (inpink: StARS 137 6 magnets, 12.25V,5m.;in blue StARS 14416 magnets, 12.7V, 6mQ.) -Typical values. Pulley ratio should be

applied to have the resulting torque on crankshaft.

III. INTEGRATED POWER ELECTRONICS TECHNOLOGYWILL CONTRIBUTE TO MAKE HYBRID APPLICATIONS EVEN

MORE AFFORDABLE

Based on this first experience, Valeo is developing thesecond generation of "Stop-Start" system dedicated to bigproduction volumes and to be applied on all vehiclesegments (Gasoline and Diesel).

Tomorrow's hybrid solutions have to be as littleintrusive as possible on standard mass producedpowertrains. This low intrusiveness is imposing a highlevel of integration between the electrical machineassisting the internal combustion engine and itsassociated power and control electronics. This high level

Fig. 5. Iso-efficiency curves of StARS 137 (25°C ambienttemperature, 13.5V).

1602

400E

w 200m

Y- 000

u

Fig. 6. Exploded view of i-StARS.

of integration induces harsh thermo-mechanicalconstraints on the whole system, pushing away standardelectronic assembly technologies as well as robustelectronics developed for railway and industrialapplications which do not correspond to automotiveindustrial requirements in terms of flexibility, yield, costand even reliability.Main objective of i-StARS rt-hybrid (integrated Starter

Alternator Reversible System) development is tointegrate all the power electronics and a part of thecontrol electronics, which is located in a separated box oncurrent generation, at the rear of the electrical machine, asshown on Figure 6.

Therefore, specific electronic components and moduleshave to be developed to achieve this challenge. Strategicpartnerships with companies focused on power electroniccomponents development and packaging and the ASICs(Application Specific Integrated Circuits) design havebeen settled to make the best of IML (Insulated MoldedLeadframe) technology applied in automotive industry.Figure 7 is a picture of the i-StARS power modulefeaturing the so-called IML technology.

Development of next generations of high efficiencyalternators with synchronous rectifying is also at stake.

Fig. 7. Power module with IML technology.

Therefore, micro-hybrid and alternatorsclosely linked with a view to reducealternator performances and makeapplications even more affordable.

roadmaps arecost, improvemicro-hybrid

IV. STARS IS AN EVOLUTIONARY SOLUTION TOWARDSHIGHER HYBRID FUNCTIONALITIES SUCH AS

REGENERATIVE BRAKING AND TORQUE ASSIST

Unlike Stop-Start starters, starter-generators by theirstrategic function of electric energy management allow topursue hybridization with the help of higher voltage thanin the conventional 14V network. The purpose of thisdevelopment based on StARS rt-hybrid, is to provide acost effective architecture for bigger engine capacitieswith extra functions such as Regenerative Braking.As shown on Figure 8, the electrical architecture of the

Valeo StARS +X system consists of the followingcomponents:

* A StARS electrical machine with its control unit,* A bidirectional DC/DC converter, and* An EDLC (Electric Double Layer Capacitor, alsocalled super-capacitor) Pack

Thanks to a smart and cost-effective architecture closeto 14V standards, a number of comfort and safetyfeatures are provided within the vehicle together withsignificant savings in fuel consumption and C02emissions. This arrangement is called the 14+Xarchitecture, X being a value at which the machine canraise its voltage or be driven in both generator and motormodes. A dedicated storage system (the EDLC Pack)allows to optimally store the recovered kinetic energy ofbraking phases for later "free" use. 5 kW generation inregenerative braking mode is available to power electricalloads (fast cabin and seats heating, e-cooling fans, andde-icing systems). When installed on large gasolineengines or Diesel engines, the system eases the crankingby supplying 14+X Volts at the starter-alternatorterminals. The system can supply extra 4kW continuouspower for peak loads. It is also able to provide some light

1603

Fig. 8. StARS+X system architecture.

Torque Assist to enable the combustion engine workingin optimum operating ranges with adapted load balance.Moreover, standard 14V network quality through ripplefiltering with DC/DC converter and high energydependability namely for any by-wire function areensured within the vehicle through the dual energystorage capability of the 14+X architecture.The combination of Stop-Start and Regenerative

Braking features leads to fuel consumption reduction ofup to 12% in a NEDC cycle with a gasoline engine andmore in city driving cycles. Stop-Start was recognized asone of the important levers of fuel consumption reductionwhereas other functions such as Boost and RegenerativeBraking are really linked to storage system availability.Whereas mild- and full-hybrid applications usually relyon costly automotive battery technologies such as NickelMetal Hydride or Lithium-ion, the StARS +X system isbased on EDLC technology featuring high cycle life andenergy efficiency and allowing maximum poweravailability at low cost. Valeo simulations and resultspresented on Figure 9 prove that the StARS +X systemwill allow 80% of the performance of a current mild-hybrid for 20% of the vehicle on-cost.

Full Hybrid

Mild HybridStARS pi-mild Hybrid

StARS p-hybrid -PomwEI,crFig. 9 Rationale for micro-hybrid applicat.k

Fig. 9. Rationale for micro-hybrid applications.

V. VALEO PROPOSES A COMPLETE OFFER TO EQUIP ALLVEHICLE SEGMENTS

First generation of StARS rt-hybrid already equips theCitroen C3 Stop&Start since November 2004 and theCitroen C2 Stop&Start since January 2006.StARS rt-hybrid solutions apply to most of the gasoline

and Diesel engines through most car segments, withvarious engine displacements and kinds of gearboxes.Whereas cranking torque was the limiting factor for thefirst generation (restricting displacements to 2.OL forgasoline and 1.6L for Diesel), several technical solutionssuch as StARS +X can be applied to larger engines withadded functionalities. Thus, several vehicles withgasoline engines up to 4.2L and Diesel engines up to 3.OL,with manual, automatic or automated manual gearboxeswere demonstrated. Moreover, StARS does not interferewith the performance of the cars, being then applicable toSUVs, sports cars, and heavier applications such as buses.StARS rt-hybrid is a real transversal solution, the first

economically viable step to hybrids and can be applied toany new fuel technology such as flex fuel.

VI. CONCLUSIONSValeo's offer is based on a smooth and continuous

approach towards hybridization of the powertrain, whichconsists in understanding each functionality (Stop-Start,Regenerative Braking, Torque Assist) first step by step,and then developing applications corresponding to clearlyidentified needs. Through a range of strategicpartnerships with universities and internationalcompanies, Valeo has access to expertise incomplementary technologies, which enable to develophigh-performance power electronics, battery managementsystems and create the future electrical architectures.High performance to cost ratio of micro-hybrid

applications will help bring volumes of hybrid vehiclesup and eventually cost of hybrid technology down in theinterest of tier-one suppliers, original equipment

1604

manufacturers and of course end-users. A significantimpact on greenhouse effect reduction could be achievedthanks to these affordable and efficient solutions. Forexample, equipping one tenth of the vehicle's fleet inJapan with such solutions would result in 2 tons of C02saved per minute.

REFERENCES

[1] J.-M. Dubus, P. Masson, C. Plasse, Dr. E. d'Orsay, Dr. E.von Westerholt, "A simple Stop&Go Concept for CityCars - Technical Design and Benefits," AachenerKolloquium Fahrzeug- und Motorentechnik, October 2001.

[2] K. Cogo, J.-M. Dubus, C. Plasse, "The Valeo Belt DrivenStarter Alternator Reversible Systems," Societe desIngenieurs de l'Automobile, July 2004.

[3] J. Pfiffer, B. Rouleau and J.-M. Morelle, "How the needfor cost-effective CO2 emissions reduction throughpowertrain hybridization pushes for innovative, integrated,and robust mechatronics design," Convergence 200606PT-33.

1605

本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页 文献云下载 图书馆入口 外文数据库大全 疑难文献辅助工具

http://www.xuebalib.com/cloud/http://www.xuebalib.com/http://www.xuebalib.com/cloud/http://www.xuebalib.com/http://www.xuebalib.com/vip.htmlhttp://www.xuebalib.com/db.phphttp://www.xuebalib.com/zixun/2014-08-15/44.htmlhttp://www.xuebalib.com/

Valeo StARS Technology: A Competitive Solution for Hybridization学霸图书馆link:学霸图书馆