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Words: John Simister

Spyders webFaster than a Carrera GT, this 918 concept is proof that Porsche is casting its

plug-in hybrid expertise far and wide, with production being a real possibility

If Ferraris 599 hybridbrought a warm, green glow tosupercar-lovers fearful for theirfuture pleasures (see p6), thenthe eco-super car surprise of theyear so far should have themdancing in the streets. That

surprise is the Porsche 918Spyder Concept, a car that stoleall the green limelight earlierthis year at the Geneva MotorShow with its claim it combines

a 70g/km CO2

capability onthe NEDC drive cycle withthe power and pace to lap theNrburgring Nordschleife ina mere 7min 30sec.

In fact, the concept was sucha secret that nobody outside

Porsche knew of the 918 Spyderuntil it was revealed, and only100 people were in the loopwithin the Porsches racingand production prototypes

departments at the Weissachtechnical center.

The machine looks broadlylike a slightly shortened CarreraGT, the car whose open, mid-engined layout and carbon fiberstructure it shares, but in place

of a V10 engine is a 4.6-literversion of the V8 originallybuilt, in 3.4-liter form, for theRS Spyder customer race cars.That would normally be enough

for any supercar, but there arealso three electric motors here:one for each front wheel,centrally mounted with outputtransmitted by driveshafts, andone for the rear wheels builtinto the seven-speed PDK

transmission system.Between them, these motors

produce up to 218bhp, usingpower supplied by, andreturned to, a liquid-cooled

SUPERCARS GO GREEN

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car like this is an outstandingresult for all.

As one would expect, 918

can cover the urban-cycle partof the NEDC test on electricpower alone. This first of fourdriving modes, E-Drive, isselected by a button on thesteering wheel and can last forup to 16 miles with the satnavshowing where it might runout of charge. Hybrid modeuses the motors and the V8engine as required, and is thenormal setting. Sport Hybridmode favors performance overparsimony, ensuring a torque

bias towards the rear wheelsand using the motors as atorque-vectoring system atthe front to go with Porsches

usual electronically controlled,torque vectoring reardifferential. The rear motor

can also have a traction-control function by applyingregenerative braking to counterexcess torque. Finally, RaceHybrid lets the motors andengine run at their power limit,with an F1-like push-to-passbutton allowing a surge ofelectrical energy, provided thatthe battery pack is sufficientlycharged, which essentially is the7min 30sec Nrburgring mode.It starts the lap with a fullbattery, Durheimer explains,

and finishes with a flat batteryso it cant do such a quick timeon the next lap. But the batteryis not quite flat. There are two

bends after the long straightat the end, so theres somerecharging from the braking.

Intriguingly, Porsche has nodevelopment partners for 918.Its a pure Weissach project,with all parameters set in-house.There was nothing we couldpurchase ready-made that couldsatisfy our demand, statesDurheimer, so we worked withsuppliers to get parts we neededand we got the motor makers tobuild to our specifications. Who,then, might these motor makersbe? Its not decided but, yes,Bosch is very close to Weissach.

But theres more to the 918than showcasing what ispossible. At Geneva, Porschehad available letters of intent for

It might only be a concept, but

the Ferraris 599 Hybrid is a clear

guide to the Prancing Horses

thinking for the future. But theres

a problem, as technical director

Roberto Fedeli points out: All

cars are measured in the same

way, which doesnt account for

the different ways they are used,he stresses. A Ferrari is typically

used more on the highway, so

while a 458 is rated at 305g/km,

the reality is around 230.

The problem is centered on

the fact that the low speeds and

engine loads required in the tests

need a Ferrari to run at

proportionally smaller throttle

openings than a less powerful

car would use, which is an

inefficient way to run an engine.

The answer, then, is to optimize

the cars efficiency throughout

the cycle, which means

increasing the load on the enginewhere possible and recovering

the excess energy for re-use

when appropriate. A hybrid

becomes an ideal solution.

But there are provisos, as

Franco Cimatti, the man

responsible for concept design,

explains: There must be no

detriment to vehicle dynamics.

There should be no more than

minimal influence on weight,

size, and interior space. And the

concept must be feasible on all

Ferraris, whether that be front- or

mid-engined.

The chosen architectureemploys a three-phase, liquid-

cooled, 80kW, 150Nm electric

motor of Ferraris own design,

attached to the aft end of the

double-clutch transaxle and

driving the input shaft that carries

first, third, fifth and seventh

gears. Mounting the motor this

way ensures all its influence is on

the rear wheels and it keeps the

center of gravity low. In fact, this

is lower than in a standard 599,

due to the extra weight of the

motor and the layout of the

batteries, which are two banks of

flat Li-ion cells just 20mm thickattached to the underside of the

floor, where airflow over the large

surface area keeps them cool.

Asked who the supplier of

these thin, low-mounted,

aerodynamically non-intrusive

batteries might be, Cimatti will

say only that Ferrari is working

with several suppliers. I ts all

part of the process of getting the

graphs of cost and benefit to

coincide at a commercially viable

point, not least because the

whole architecture is a leap into

the unknown. No other OEM hasdone it quite this way before.

The more closely one

examines the system, the more it

becomes apparent just how

SIGN OF THE TIMES

There was nothing

we could purchase

ready-made that couldsatisfy our demand

Project 918 Spyder was so top secret that only 100 people were in-the-loop at Porsches technical center in Weissach

The power of the three-phase, liquid-cooled electric

motor is directed to the front of the 599s wheels

06

Porsche 918 Spyder concept

1. Power electronics

2. Electric drive

3. Lithium-ion battery

4. V8 high-rpm engine

5. PDK transmission

6. Electric motor

7. Power electronics

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potential buyers to sign.Durheimer adds: It will be veryinteresting when we have 1,000

orders. If we do, we will contactcustomers with a price and thetiming. But if we have 300, wecould build them in the racedepartment, in which casethe cars would to be morehand-made and developmentwould be faster. The marketsperception is that Porsche hasmaybe not been so keen onhybrids, but we have beenworking on them for a longtime. So we need to show howyou can have fun in the future

while setting an environmentalbenchmark. On the evidence,the 918 Spyder does the jobrather well. E&H

clever this system is, especially

when needing to fit the needs of

the EC test cycle. Cimatti points

out that the real-world gains are

large, too, but the fact is that the

599 Hybrid will run the entire

urban cycle on electricity alone

and runs out of battery power

exactly when the cycle ends.Then, as it enters the highway

cycle, the engine is working

harder than it would in a normal

599 in order to replenish the

battery and this, crucially, lifts

the engine to a more favorable

point on the efficiency map

because it can run on wider

throttles and reduce pumping

losses. Its gains all the way.

Ferrari is linking the idea of a

hybrid energy-recovering road

car with the KERS used in the F1

cars. In road cars, though, the

focus is more on energyefficiency than bursts of power

and regeneration. And there are

subsidiary benefits, such as a

traction control system that

inhibits torque delivery to the rear

wheels by switching the motor to

regenerative braking mode,

thereby recovering the energy.

We can merge the torque

transfer to both engine and wheels

via the double-clutch system,

says engineer Ferdinando

Cannizzo. This arrangementsmooths irregularities of torque

and removes jerks, making the

throttle response more linear.

What, then, are the hard

figures? A normal 599 is rated

at 415g/km, says Cannizzo,

and the Hybrid does 250g/km.

Thats a 36% reduction. Not

bad for a car with 720bhp.

So the question is not if, but

when, will Ferrari build such a

car? Cannizzo again: If we

produced it now, it would be

double the cost of a normal 599.

That is the reason why we needa lot of time three years or

more to decrease cost. The

end result should be that the

increase in cost is not very high.

Ferrari 599 Hybrid concept

Electric motor: 80kW / 150Nm

V12 output: 620bhp

Acceleration: 0-200km/h in 7.5 seconds

Emissions: 250g/km of CO2

HYBRIDS ARE GO

Theres no doubt that the 918 Spyder

is an interesting concept, and a good

showcase for Porsches possible

adoption of hybrids across the range

in the future. The Cayenne Hybrid is

already a production model, and

Porsche has also shown another

concept, the racetrack-destined 911

GT3 R Hybrid with a flywheel energy

reservoir where the passenger seat

would normally be go to page 68 for

this exclusive Porsche/Williams story.

Left: 918 might only be a concept

but Porsches hybrid program is

gaining momentum with the 911

GT3 R Hybrid and the Cayenne Hybrid

07

July 2010| Electric & Hybrid Vehicle Technology

LEA

e y r syste , ut w t up

to 80kW available, the p for each extra kg.

The result is a power-to-weight ratio slightly better than that of the

standard car up from 417bhp/ton to 435, helping the 0-200km/htime to drop from 7.9 seconds to 7.5. Also, the standard, heavy

12 attery s no onger nee e ecause t e - on pac oes t e

o , powerng t e eectrc motor to start t e 620 p 12 va t e

transmss on s a ts. separate, e ectrc motor n t e eng ne ay

powers ancillary drive.