H i g h l i g h t s a n d R & D A c t i v i t i e s a t F E VT e c h n o l o g y -

Issue 12 / Aug. 1999

A5

6

FEV has proven the feasibility of the electromechanical valve train (EMVT) conceptby demonstrating the conversion of a conventional, camshaft-driven vehicle tothis technology. Significant advantages regarding in-vehicle fuel consumptionand emissions have been demonstrated. The EMVT-Vehicle achieved a fuelconsumption improvement of greater than 15% in the NEDC in comparison tothe baseline (camshaft) vehicle and meets EURO IV emission limits.

Reduction ofFuel Consumptionand Emissions –ElectromechanicalValve Train inVehicle Operation

fully variable valve train offersmany more advantages than sim-

ply avoiding pumping losses at partload. At each operating point, this tech-nology enables much more parametervariation and allows a point-wise opti-mization in the engine map. Therefore,many effective solutions are possibleto achieve optimal fuel economy andemissions.

A number of different mechanisms havebeen suggested to achieve this, inclu-ding hydraulic, mechanical (MVVT) andelectromechanical valve trains (EMVT).Both MVVT and EMVT are currentlybeing developed toward productionfeasibility. For the EMVT concept, newmagnet-controlled valves offer the

SprayPropagationand MixtureFormation inthe FEV DISIEngine

Large BoreDiesel andGas EngineBusiness Area

possibility for individual control of theopening and closing times of theintake and exhaust valves. Hence,they provide the best utilizationof the potential for reduced fuelconsumption and emissions.

In realizing this concept, the ac-tuators as well as specialized elec-tronics have been developed by FEV.These actuators must be able to openthe valves within 3 ms over a lift of8 mm. In addition to meeting durabilityrequirements under all foreseeableenvironmental conditions, the acousticbehavior of an EMVT engine must beequivalent to a modern gasoline enginewith a conventional camshaft. ➧

Please visit our Web-site now athttp://www.fev.com

Pre-announcement:8th Aachener

ColloquiumOct. 4.- 6. 1999

Eurogress Aachen

2

PrefaceBy providing a current to the coil of thelower magnet, the losses during themovement are compensated and thevalve is held in the open position. Toclose the valve, the current is interrup-ted in the lower magnet and the currentis re-applied to the coil of the uppermagnet.

The valve seating velocity and thevelocity of the armature upon contactwith the magnet have a significant effecton wear and acoustics. These velocitiesare determined by the shape of thecurrent curve during armature move-ment. FEV has developed a Closed-Loop-Control system that allows valve-to-seat velocities below 0.05 m/s. ➧

➧ The actuators are designed on thebasis of the electromechanical theory.A moveable armature is guided betweenan upper and a lower magnet. When nomagnetic force exists, the armature isheld by an upper and a lower spring inthe middle position between the twomagnets. This condition, correspondingto the valve half open position, occurswhen the engine is shut off. Duringengine operation, a current in the coilof the upper magnet is used to hold thearmature against the upper magnet sothat the valve is in the closed position.To open the valve, the current is inter-rupted and the armature is moved bythe spring-forces to the lower magnet.

Principle of theElectromechanicalActuator

Dear Reader,

downsizing with supercharging,direct injection and fully variablevalves are new technologieswhich will improve future SI-engines.

This issue of Spectrum containsthe description of an electrome-chanical valve actuator system.This unique device allows theindividual timing control of eachvalve at any engine operationalcondition, resulting in variousimprovements of the engineproperties: Maximum torquecan be reached already at lowerrpm, fuel economy at part-loadimproves considerably, roughemissions are reduced and the3 way cat technology can beused.

At FEV we are convinced thatafter long years of intensivedevelopment work EMV now istechnically sufficiently advancedto be introduced in mass produc-tion engines.

Yours sincerely,

Peter Walzer, Vice President

Actuator Spring

Lower Spring

Closing Magnet

Armature

Opening Magnet

Valve

ElectromechanicalActuator

3

➧ FEV has conducted many test cellinvestigations to demonstrate thepotential of the EMVT engine. Thebenefits are not simply limited to theattainment of unthrottled load control.The most important benefits are sum-marized below:

• Residual gas control• Gas motion and turbulence control and

tuning• Realization of various cylinder

deactivation concepts• Idle speed reduction• Cycle-synchronous control of mixture

quantity, residual gas fraction, ignitiontime and injection event

• Improved cold start and warm-upbehavior through special valve-controlalgorithms

It was an important step to demonstratethese potentials in the vehicles. Moreo-ver, FEV desired to show that combina-tion of the EMVT with turbocharging isnot only possible but presents a usefulconcept. Since load-control in EMVTengines is no longer achieved by thethrottle but, rather, by the valve-opening-time, a completely new vehicleECU using a torque-based structurewas developed for the EMVT-vehicle.FEV used the ETAS ASCET SD systemfor the development of speci f icfunctions for valve train actuation andthe various control-signals. Newfunctions included an air-mass-model,a residual-gas-model, as well as idlecontrol and lambda control.

Initially, the engine control unit waspre-calibrated with the results fromsteady-state test cell investigations.After integration of the EMVT-specificcomponents into the vehicle, calibrationof the functions for vehicle driveabilitywere accomplished in combination withevaluation and optimization of the fuelconsumption and emissions behaviorwithin the New European Driving Cycle(NEDC). The operational modes of theEMVT concept are determined withinan engine map, that specifies, as afunction of engine speed and load, whe-

ther the engine should be driven with2, 3 or 4 valves, and whether individualcylinders should be deactivated. FEV’sevaluations revealed that, within theurban driving cycle, an advantage withregard to vehicle fuel consumption ofabout 23 % is reached. In the completeNEDC, a 16 % improvement was obtai-ned. The transmission and the engine

speeds for gear shift were not changedduring these evalu-ations. Therefore,the turbocharger was not used fordownsizing and the benefit in fuel eco-nomy is purely a consequence of theapplication of the EMVT concept.

The bar chart below shows a break-down of the individual fuel consumptionbenefits due to the application of EMVT.Avoiding the pumping losses and usingthe residual gas control alone providesa fuel consumption benefit of approxi-mately 8.5 % in the NEDC. Improved

combustion stability at low loads canbe used to decrease idle speed. Here,an additional 1.5 % reduction in fuelconsumption can be obtained. The util-ization of valve and cylinder deactiva-tion strategies provides the balance ofthe total 16 % fuel economy improve-ment that was measured with thevehicle. This enormous potential is

primarily due to cylinder deactivation,although cylinder deactivation was onlyapplied under low loads where no NVHdisadvantages were noted.

An additional potential exists with thecompression ratio, which was changedfrom 10 to 9 to reduce the risk ofknocking with the turbocharger. Here,exact control of the residual gas fractionand the effective compression ratio(Miller-cycle) allows an increase inthe compression ratio, even with theturbocharger, back to the original ➧

Map of the Operating Modes forValve and Cylinder Deactivation

Operating Modes:

4 Cylinder, 4 Valves

4 Cylinder, 3 Valves

4 Cylinder, 2 Valves

2 Cylinder, 3 Valves

500 40001000 1500 2000 2500 3000 35000

16

14

12

10

8

6

4

2

0

Engine Speed [rpm]

Engi

ne L

oad

IMEP

[bar

]

Full Load Curve

➧ value of the baseline vehicle. Thiswould provide a further reduction infuel consumption of an additional 4 %.Improving alternator efficiency fromabout 50 % to 80 % would provide anadditional 2 % improvement in fuelconsumption. Adaptation of the trans-mission due to the increased low-end-torque of the engine would allow afurther reduction in fuel consumptionof approximately 4%. By using all pos-sibilities mentioned above, an overallfuel consumption benefit of 25 % canbe reached.

In comparison with conventional valveopening times, the movement andturbulence of the mixture can be inten-

sified by late opening of the intakevalves to optimize cold start and tostabilize combustion with lean mixturesduring the warm-up phase. Conse-quently, on the very first cycle, theair/fuel charge burns with a high peakpressure. No misfiring or delayed com-bustion effects occur in the subsequentcycles. Through a very late opening ofthe exhaust valves, it is possible to

improve post-combustion in-cylinderoxidation and to increase the exhaustgas temperature while achieving lowraw emission levels. This results in aclear decrease of more than 50% incold start HC emissions compared withconventional control-strategies. In con-trast to a throttled engine, the start-upemissions with EMVT engines can beminimized by precisely controlling mix-ture quantity and the consequent reduc-tion in the start-fuel quantity.

In addition to the special measures thatare possible with EMVT, conventionalmeasures to increase the exhaustgas temperature were also used in thevehicle. With this combination, the

exhaust gas temperature could beincreased by more than 200°C and ca-talyst light-off occurred before the endof the first driving pulse. Despite theuse of an exhaust gas turbine, thecumulative emissions, measured withthe test vehicle, were only 50 % of theallowable EU IV emission limits for allpollutant components.

Based upon the results obtained at FEV,the electromechanical valve train repre-sents an extremely interesting conceptfor reducing fuel consumption in con-cert with simultaneous fulfillment ofvery challenging future emission limits.

For additional information, contactDr. Martin Pischinger at FEV Motoren-technik GmbH. ◆

4

Fuel Consumption of the Vehicle withEMVT-Technology in the NEDC

23%

5%

8.5% 10% 16% 20% 22% 26%

NEDCExtra-UrbanUrban0

16

14

12

10

8

6

4

2

Fuel

Con

sum

ptio

n [l/

100

km]

EMV

1.6l

, Tu

rbo

EMV

1.6l

, Tu

rbo

EMV

1.6l

, Tu

rbo

Baseline Vehicle 1.6 l

EMVT Vehicle

ε: 9:1

Strategies of Cylinder Deactivation

Idle Speed: 600 rpm

Potentials EMVT

without Cylinder Deactivation

Idle Speed: 880 rpm

Idle Speed: 600 rpm

Additional Potentials EMVT

ε: 10:1

+ Alternator – Efficiency: 80 %

+ Adapted Transmission

5

One of the most promising approachesto achieve a distinct reduction of fuelconsumption for SI engines is the directfuel injection. At part load operation DirectInjection Spark Ignition (DISI) enginescombine the benefits of lean combustionwith a nearly throttle free operation. Thisis a major step to overcome the principaldisadvantages of SI engines comparedto Diesel engines. At full load operationin-cylinder charge is cooled by the fuelspray evaporation. This increases bothvolumetric efficiency and reduces knocksensitivity, which results in a higher fullload performance.

has developed a charge motion con-trolled DISI combustion system

where the in-cylinder charge motion isused both for mixture preparation andtransport to the spark plug. Charge motionis controlled by a Continuos VariableTumble System (CVTS), which allowscontrolled blocking of the lower half ofthe split intake port. This concept avoidsfuel wall film formation and maintains acompact and central position of the pistonbowl. Both are beneficial for the combu-stion process and the reduction of pol-lutant formation.

The advantages of such direct injectedgasoline engines are offset by an increaseof system complexity. Here, CFD simula-tions are very useful to gain processunderstanding and to investigate effectslike the CVTS switching position and theinjection parameters, i.e. the injector typeand position, injection timing, on theengine behavior.

Spray Propagationand Mixture

Formation in theFEV DISI Engine

StarCD is used to simulate in-cylinderflow and mixture formation in part loadconditions. The transient simulationcovers the complete intake and compres-sion stroke taking into account valveand piston motion. The hexahedral meshconsists of several subgrids, which areconnected by arbitrary sliding interfaces.ProStar events are used to generate thegrid motion and cell layer addition ordeactivation.

To simulate the fuel spray propagationand evaporation, StarCD’s built-inLagrangian droplet phase treatment isused to describe droplet motion and eva-poration as well as droplet break-up andcollision. These capabilities are extendedby user routines for spray atomizationmodeling developed by FEV. This atomi-zation model describes the break-up ofthe liquid sheet formed at the nozzle exitof the high pressure swirl injector anddetermines the size and velocity distribu-tion of the primary droplets.

An exact description of the primary dropletcharacteristics and their subsequentbreak-up is essential for an accuratesimulation of momentum, heat and masstransfer between droplet and gas phasein the combustion chamber. Hence, theCFD modeling and its results have beencarefully compared to experimental data.These have been obtained in a high press-ure – high temperature injection chamberwith an optical access to the spray.

In Fig. 1 StarCD results of spray propa-gation and evaporation are directlycompared to Schlieren spray images atdiscrete time increments after the start ofinjection. Due to the temporal delay of

the swirl flow development during injec-tion, the injection starts with a straightpre-jet and subsequently turns to a hollowcone spray. This effect is clearly seen inthe visualization and accounted for in theFEV atomization user routines linked toStarCD.

Using the validated DISI injection model,full simulations of the in-cylinder proces-ses are performed. The aim is to investi-gate the interacting effects of tumblecharge motion and spray propagationon mixture formation. The results of anoptimized engine design in Fig. 2 showthe spray and fuel vapor distribution atan early injection phase, end of injectionand ignition timing.

In conclusion it can be stated, that theuse of StarCD helps to improve theunderstanding of the interaction bet-ween flow field, spray propagation andevaporation. In effect this enables usto guide the optimization of the flowcontrol and to predict optimized injec-tion parameters.

FEV

Fig.1:CFD injection

simulation vs.experimental

Schlieren sprayvisualization

t=0.25 ms after start of injection 0.45 ms

CFD Schlieren

0.85 ms 1.25 ms

Fig.2:DISI spraypropagationand mixtureformationat 2000 rpm/2 barIgnition Timing

End of Injection

Early Injection Phase

FEV Motorentechnik GmbHNeuenhofstraße 18152078 Aachen · GermanyPhone: (+49)-02 41-56 89-0Fax: (+49)-02 41-56 89-119http://www.fev.come-mail: marketing@fev.de

Editor: Dr. SpeckensLayout: Der Design Pool, Aachen

I M P R E S S U M

6

equipped with engines up to 5.000 kW,demonstrate immense tractive forces,combined with high economy and relia-bility. Of increasing importance arelarge gas engines, which are normallyderived from the diesel version and areused in combined heat and powerstations, which require minimumemissions such as in greenhouses andmedical centres.

Future large bore engine developmentwill mainly concentrate on the impro-vement of emissions due to upcomingregulations, which are already well esta-blished within the vehicle engine sector.Mainly engines for river and coastalnavigation, locomotives and powerplants will be affected, that is, mediumand fast running 4-shoke engines. Inorder to maintain an economic advan-tage under the constraint of dramaticallyreduced emission values the thermaland mechanical efficiencies of theseengines which are already high, haveto be improved further. This will requirean optimisation of all components,interacting in the engine. It is not suf-ficient to optimise each componentindividually, which is currently the caseand mainly done by subsuppliers. Par-ticularly in smaller companies, it willnot be possible to solve such complexdevelopment in-house. Due to the longproduction life of these engines, thereare relatively long intervals betweensuccessive development projects. The-

Large bore engines are used for shippropulsion, in locomotives and powerplants. World wide transportation ofgoods is mainly serviced by large boreengines and they are also increasinglyused to generate electricity. Both fieldsof application show the immense eco-nomic importance of these engines.

arge bore engines are categorisedabove heavy truck engines. They

can be divided into three classes:

• Slow speed 2-stroke engines, whichrepresent about 75 % of installationsfor ship propulsion. Normally theyare directly coupled to the propeller.12 cylinder in-line engines, produ-cing more than 68.000 kW at lessthan 100 rpm, with a weight of up to

2.000 tonnes, impressively demon-strate this engine technology.

• Medium speed 4-stroke engines inthe range of 1.000 to 30.000 kW andspeeds between 350 and 1.200 rpm,operating in combination with marinegear boxes, to propel large ships, ordirectly coupled for large generatorsin power plants.

• Fast running, high output engines,500 to 7.500 kW at 1.000 to 2.30rpm for smaller, high speed ships,generators and special vehicles.

A rapidly growing application for large4-stroke engines are diesel locomoti-ves. Using the most modern electronicpropulsion systems these machines,

refore, even if the development is per-fo rmed in-house , the exper t isecannot grow continuously and therewill be long and uneconomic stand-offperiods for the specialists involved.However, FEV has established a newbusiness area for large bore engines,in which all projects will be concen-trated. The large bore engine divisionis an experienced team, which, underthe well-proven approach establishedat FEV, co-ordinates this expertise withour Research, Calculation and TestDepartments to optimise the wholeengine in a single focused project.

Parallel to this a completely new largebore engine testcell was erected, inwhich complete fast running enginesup to 4.000 kW and single cylinder testengines up to a weight of 8 tons canbe installed. The basis for the singlecylinder testing is a FEV developeduniversal test engine, using a heavycasted GGG 50 crank case in whichcustomer specified cranking and cylin-derhead units can be installed thusproviding a “close to serial engine”testing.

Large BoreDiesel andGas Engine

Business Area

FEV development: V12/V16 locomotive enginebore: 255 mm, power: 3.180/4.240 kh,stroke: 310 mm, speed: 1.000 rpm

L