Porsche Cayenne Hybrid 2007 Review - International

What we liked
>> Imperceptible transition from electric to petrol power
>> Improved acceleration and pulling power compared with V6-engined Cayenne
>> Unchanged Porsche steering feel despite new electrohydraulic system
>> No reduction of luggage space or fuel tank capacity

Spurred on by the consumer kudos and increasing market inroads made by Lexus and Toyota with hybrid vehicles on the critical US market, Europe's largest carmaker is poised to strike back.

Volkswagen, its 100 per cent daughter company Audi and its 31 per cent majority shareholder Porsche, have together been working for the past five years on their own hybrid solution, which is claimed to be simpler, more cost effective yet more efficient than the path taken by its Japanese rivals.

Due to go on sale by the end of the decade, their endeavour is called 'parallel full hybrid' and differs substantially, both in hardware and software, to the 'output branched hybrid' system favoured by Toyota.

With parallel hybrid, the hybrid module containing the electric motor and its own clutch is located immediately behind the vehicle's internal combustion engine and directly ahead of the automatic transmission. This differs from the 'power split branch system' currently used by Toyota and others in which a planetary gear set meters drive by different paths to the driven wheels.

The main benefits of the parallel full hybrid system say Porsche, who previewed the system at a comprehensive hybrid workshop at their Weissach, Germany research and development headquarters, are its greater efficiency in offroad and freeway driving, its retention of conventional driving behaviour, minimum technical requirements and superior cost and packaging.

While taking pains to emphasise that it was an equal partner with its VW and Audi colleagues in the development of the system and not the project leader, Porsche's role as technology spokesman is interesting

As a noted R&D company (and the largest shareholder in VW and hence Audi), Porsche's work carries serious street cred. Although rarely the first to bring new technical features to the market, Porsche invariably releases it in highly developed and tested form.

Equally true is that as a sports car specialist that also produces a conspicuously large SUV, Porsche is much more exposed to market disapproval in increasingly green times.

In some ways, the company -- like other German manufacturers -- can be accused of sitting on its hands in recent years while the alternative engine debate has raged.

Back in 1899, Ferdinand Porsche developed the Lohner-Porsche electric car for a Vienna-based coachbuilder, employing pioneering technology that is closely related to today's hybrid developments. But rather than head off prematurely down the hybrid path Porsche, like most other European makers, has instead sought to meet increasingly stringent regulations covering CO2 emissions through greater engine efficiency.

However, despite developing a brand new generation of engines within the past four years, reducing fuel consumption and CO2 emissions by up to 15 per cent, Porsche admitted in Weissach that it was reaching the limits of physics in the development of large power plants for upmarket vehicles like the Cayenne and the forthcoming four-door Panamera Gran Turismo, due out in 2009.

This is particularly relevant in the light of the European Commission's aim to require carmakers to reduce CO2 emissions to an average of 130 grams per vehicle across their model range by 2012. And Porsche, unlike Audi and VW, does not have an A3 or Golf to spread the load.

They might have been pushed and prodded a little, but there's certainly no need for Porsche to apologise for their hybrid contribution based on what we saw -- and drove -- at Weissach.

The engine chosen for the green makeover is the VW-sourced 3.6-litre V6 FSI, which is already doing duty in a number of VW, Audi and Porsche vehicles. In non-hybrid VW and Audi guise it produces 206kW, while additional work on the induction system by Porsche unleashes 213kW in the Cayenne. However because of space requirements and commonality, all the group's hybrid engines will use the same intake manifolding and will be rated at 206kW.

Another casualty for packaging reasons in the hybrid model only is the Cayenne's low-range gear set, bringing it technically into line with VW's Touareg and Audi's Q7.

In the Cayenne application, the V6 is paired to an electric motor that produces 34kW of power, with the connection between then handled by a clutch that engages and disengages in just 300 milliseconds.

At ambient temperatures below 15 degrees Celsius, the internal combustion engine will always start first, although in warmer conditions and on restarts it is possible to drive away silently on electric power alone at speeds up to 50 km/h.

Travelling at 30km/h, the batteries alone will only propel the Cayenne for up to two kilometres, but then -- or at any time when the driver or the road conditions call for more performance -- the V6 internal combustion engine (ICE) slips seamlessly into action.

Porsche is particularly proud of the real-world performance of its parallel hybrid technology, demonstrating how they have overcome the 'jerky' transition from the ICE to electric power that characterised early systems and led companies like Toyota to go the 'branch' path.

Driving almost noiselessly under full electric power from the test lab to the Weissach test track, the Porsche engineer came to a full stop and then flattened the accelerator of the Cayenne hybrid.

The takeoff was rapid and virtually instantaneous, with the V6 engine springing immediately into action with even less delay than the kickdown that you would experience in a normal Tiptronic automatic transmission. But once up to cruising speed, easing right off on the accelerator at speeds up to 120km/h would allow the petrol engine to disengage completely, with the Cayenne 'sailing' alone without either ICE or electric power until the driver or road conditions called on it to maintain speed.

This 'sailing' ability, as Porsche engineers call it, is a major difference between their technology and Toyotas (which Porsche claim cannot operate in this manner beyond 70km/h) and offers the promise of significantly better performance and fuel economy in real world driving conditions -- particularly on freeways.

Harnessing the 206kW petrol and 34kW electric motor together also produces increased performance over a regular Cayenne, with Porsche claiming 8.0 seconds dead for the sprint from 0-100km/h  -- an improvement of 0.5 seconds.

Considerably enhanced torque is another major benefit of the system. Porsche say the Cayenne hybrid develops a peak of 550Nm at 1500rpm, with 500Nm on tap from 800-3200rpm. This compares with a Cayenne V6's 385Nm and a Cayenne S V8's 500Nm -- both at 3000rpm.

While all this is occurring, the operation of the ICE engine and every brake application sends charging power back to the 288 volt, 70kg battery that lies in the spare wheel well, without intruding on either the vehicle's luggage space or its 100-litre fuel tank capacity.

The energy obtained in this way can then be used to drive entirely on electric power without the combustion engine, or to support the combustion engine for greater power and performance on the road.

To maximise the savings, Porsche and its partners have also developed a new electric air conditioning compressor, an electric hydraulic power booster for the brake system and an electric vacuum pump for the power steering system that allow these vital 'organs' to operate independently of the internal combustion engine.

Managing this transition of power so seamlessly is the responsibility of the newly-developed Hybrid Manager that handles some 20,000 data parameters compared with the average 6000 data parameters for conventional engine management systems.

However it won't work exactly the same way for each of the three technology partners. Just as the Tiptronic software developed by Porsche is programmed to respond differently in an Audi or Mitsubishi, so the Hybrid Manager will reflect the priorities of each maker, be they performance or economy.

That's great news for Porsche enthusiasts, who will be now able to hold their heads high in their Cayenne hybrids, but it's the fuel consumption figures that are really going to get the Cayenne hybrid the green vote.

Porsche has already achieved 9.8lt/100km in the New European Driving Cycle, however they claim to have a few more trump cards up their sleeve that ultimately will enable them to reach their launch target of 8.9lt/100km -- fully 4lt/100km or 25 per cent better than the 12.9lt/100km of a conventional Cayenne.

To confirm the vehicle's economy, we were invited to 'drive' a Cayenne hybrid on a rolling road dynamometer over a section of what Porsche calls its 'Stuttgart cycle'. Representing what they say is more realistic driving for a Porsche owner, the cycle has a higher top speed (125 versus 120), a higher average speed (46/33.6), covers nearly six times the distance and involves an elevation of 460 metres (none in the New Euro Cycle), making it theoretically thirstier for the vehicle.

Starting with 60 per cent of full charge in the Cayenne's battery and finishing with 55.5 per cent, I covered 49 per cent of the test distance in electric mode at an average speed of 44.26km/h for a fuel economy of 8.0lt/100km. That's truly outstanding for a large SUV weighing around 2310kg -- 150kg more than a regular Cayenne.

From its developers' viewpoint, even better news is that their parallel full hybrid system slots comfortably into the existing shared platform of the current Cayenne, VW Touareg and Audi Q7 -- and their common replacement models when they arrive -- making the transition to hybrid far less costly than had they been forced to go the 'branch' path and invest in major new pressings.

Which one of these three makers will be the first to unveil the world's first production parallel full hybrid vehicle is a closely guarded secret, with the indication being that all three will unveil their models in rapid succession.

Porsche is already on record as promising to deliver a Cayenne hybrid "by the end of the decade", which means by the end of 2010, however talk of 2009 did not generate shaking heads from any of the engineers we spoke to.

Engineering development is virtually completed by the team of around 300 engineers from the three companies currently working on the project and 25-30 prototypes are engaged in durability driving on three continents.

While pointing out that no manufacturer has made money out of hybrid drive so far, they hold hopes that not only will their simpler, more efficient system will get the greens off their back, but it will also put 'greenbacks' into Porsche's bank.

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