 Porsche Cayenne Hybrid prototype. Click image to enlarge |
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Porsche Cayenne Hybrid prototype
Beverly Hills, California – Ten years ago, it’s unlikely you would have seen the words “Porsche” and “hybrid” in the same sentence – but as luxury/performance hybrids like the Lexus RX450h, GS450h, LS600hL, and the upcoming Mercedes-Benz ML 450h, S 400 Hybrid and BMW ActiveHybrid X6 and ActiveHybrid 7 have demonstrated, hybrid gas-electric powertrains are capable of delivering the kind of performance that luxury buyers want along with significant fuel savings and a reduction in greenhouse gas emissions.
For Porsche, there’s also the matter of technological parity: Porsche, and other vehicle manufacturers, view hybrids as an interim step towards electric cars, “extended range” electric vehicles, and even fuel cell vehicles. Porsche doesn’t want to be left behind in the technology race, even if the current demand for hybrids is only a fraction of the overall vehicle market.
  Porsche Cayenne Hybrid prototype. Click image to enlarge |
Porsche’s first hybrid, the 2011 Cayenne S Hybrid, will be introduced in North America sometime in 2010 with an all-new bodystyle that’s already been the subject of numerous blogs and spy photos. In the meantime, Porsche has been testing its new hybrid powertrain in the current Cayenne, and last week they brought one of their hybrid prototypes to Los Angeles for Canadian and American journalists to preview. This same hybrid powertrain will also underpin a hybrid version of the new Panamera sedan which is scheduled to arrive in the next few years.
Like the Lexus RX450h, Mercedes ML 450h and BMW ActiveHybrid X6, the Cayenne S Hybrid is a “parallel full” hybrid, meaning that it will run in electric-only mode, engine-only mode, or a combination of both depending on power requirements and battery charge level. It also shuts off the gas engine while stopped, and recharges its battery while braking.
The big difference between Porsche’s hybrid system and other “full” systems is that Porsche’s system allows the Cayenne to coast in electric-only mode at speeds up to 138 km/h, about twice as fast as other full hybrids, according to Porsche. As well, the Cayenne S Hybrid can accelerate up to 50 km/h in electric-mode and travel for about two kilometres on battery power alone.
  Porsche Cayenne Hybrid prototype; bottom photo by Axel Koester. Click image to enlarge |
According to Porsche’s hybrid system designer, Dr. Michael Leiters, the Cayenne S Hybrid prototype averages about 9.0 litres per 100 km (31 mpg Imperial), uses 33 per cent less fuel than a Cayenne S (V8), and emits CO2 emissions of less than 210 g/km, “some 20 per cent less than on a conventional vehicle… with the same kind of power,” all the while offering comparable performance to the V8-equipped Cayenne S.
The Cayenne S Hybrid prototype and the redesigned 2011 model are equipped with a supercharged direct-injection 3.0-litre V6 engine (sourced from the new Audi S4), a 38-kW electric motor/alternator and a disengagement clutch sandwiched between the engine and an eight-speed automatic transmission, a 288-volt nickel metal hybride battery (sourced from Sanyo) under the trunk floor, and an electronic controller to manage the whole process. The hybrid powertrain makes a combined 374 horsepower between 5,500 and 7,000 r.p.m. and combined torque of 405 lb-ft. at just 1,500 r.p.m. – and powers the Cayenne S Hybrid from zero to 60 mph in 6.5 seconds, just a tenth of a second slower than the Cayenne S V8. For that reason, the hybrid is called the Cayenne “S” Hybrid. Leiters says the Cayenne S Hybrid will be faster than the new Mercedes-Benz ML 450h (7.8 seconds) and the Lexus RX450h (7.4 seconds) (Porsche supplied figures). The Lexus RX450h will, however, get better fuel economy, he admitted.
   Porsche Cayenne Hybrid prototype; top photo by Axel Koester. Click image to enlarge |
One of the reasons Porsche chose Audi’s supercharged 3.0-litre V6 is that it offers strong torque over a wide range of speeds (the engine itself develops 324 lb-ft from 2,900 r.p.m. to 5,300 r.p.m.) and is quite fuel efficient at low engine speeds. The eight-speed automatic transmission was chosen instead of a continuously variable transmission because it offers a more sporting driving sensation than the “rubber band” feel of a typical CVT, said Leiters. Top speed can be reached in sixth gear while the seventh and eighth are there to reduce engine speed and enhance fuel economy. In eighth gear, the Cayenne S Hybrid can “sail” or coast on a flat or downhill surface with the gas engine turned off at speeds up to 138 km/h.
The NiMh battery, located in the spare tire well under the cargo floor, weighs almost 70 kg and is made up of 240 cells delivering 288 volts. Canadians will be glad to know that the battery will operate at temperatures down to minus 30 degrees Celsius.
I had the opportunity to drive the Cayenne S Hybrid prototype for about an hour, enough to get some initial impressions of its performance and driveability. Acceleration from a standing start is immediate and aggressive due to the significant low-end torque of the electric motor and supercharged 3.0-litre V6 gas engine. I suspect the Cayenne S Hybrid is quicker off the line than the Cayenne S – the combined torque of the electric motor and gas engine is 405 lb-ft at 1,500 r.p.m., compared to 369 lb-ft at 3500 r.p.m. in the Cayenne S V8.
With standard all-wheel drive and traction control, there is virtually no wheel slip, but there is an electric whine from the electric motor under acceleration and deceleration, though not as loud as some hybrids. I did experience a pulsating vibration from the drivetrain when decelerating suddenly from 50 km/h, which hybrid designer Michael Leiters explained is an issue that Porsche is currently working on. On the freeway, the Cayenne Hybrid does sail along in electric mode without the gas engine running, but applying any pressure to the throttle will result in the engine cutting in. But as Porsche claims, the transition is almost seamless – only a screen graphic in the centre instrument panel and another in the gauge cluster provides an indication as to which mode the hybrid powertrain is in.
  Porsche Cayenne Hybrid prototype. Top photo by Axel Koester; bottom courtesy Porsche. Click image to enlarge |
I did find the hybrid’s suspension a bit firmer than the standard Cayenne, the regenerative brakes a little grabbier, and the electro-hydraulic steering less communicative, but the overall driving experience remained sporty – the eight speed automatic transmission feels much better than a CVT – sportier, more responsive and less noisy – and the modified independent suspension keeps the bulky Cayenne steadfastly upright in the corners and easily controllable over bumpy surfaces.
Interestingly, Porsche conducted studies of hybrids in typical city and highway driving to find out how much driving time is spent in electric-only mode and how much in the combined engine/electric mode. Surprisingly, the study found that the combustion engine was being used only 44 per cent of the time. Electric-only use was 26 per cent, idle stop was 18 per cent, and recuperative braking 12 per cent. Since the latter three don’t use the combustion engine, the total amount of emissions-free driving time totalled 46 per cent, more than the time spent with the gas engine running.
Porsche must be commended for developing a hybrid system that maximizes fuel-saving benefits while retaining a sporty driving experience. People don’t buy a Porsche to save gas, but if it’s more fuel efficient and environmentally-friendly without losing any of the sporting characteristics that Porsches are known for, buyers have little to lose.
The 2011 Cayenne S Hybrid has yet to be unveiled, but Autos will get behind the wheel as soon as it’s available.
