2011 Porsche Cayenne S Hybrid First Drive
Bringing Back the Hybrid for a Brave New World
While mentioning "Porsche" and "hybrid" in the same sentence may cause mountains to crumble, glasses to shatter, and babies to wail in the world of the Porsche Purist, said purist may not be aware of one little fact: Porsche invented the first hybrid powertrain more than a century ago.
Using a 15-horsepower four-cylinder engine to power an 80V dynamo, Ferdinand Porsche's Lohner-Porsche Mixte sent current either to two electric motors in the front wheel hubs or to a buffer battery in what was the world's first standard-production hybrid vehicle. That was circa 1900. The Porsche Cayenne S Hybrid is now.
And how times have changed. In an era of CAFE regulations, eco-chic culture, and soaring fuel prices, Porsche will again launch a production hybrid vehicle, this one based on its highly profitable Cayenne SUV. Just as the Cayenne's platform is shared with the Touareg and Q7, its new hybrid powertrain was developed with Porsche's extended family members, Volkswagen and Audi. The hybrid system was originally slated to serve duty in Audi's Q7, until a change in plan favored hybridizing a different Audi -- the newer, smaller Q5. With Porsche needing to meet the same upcoming fuel-economy standards as its bigger cousins, the hybrid system was treated to a thorough updating from its original two-year-old beginnings, and given new life in the Cayenne. The new Panamera sedan will be the next Porsche to undergo the hybrid transformation next year using essentially the same system.
Two years is a long time and the hybrid powertrain in the Cayenne features plenty of changes since it first appeared in the engine bay of an Audi. To start, the combustion engine is now the 333-horse, 3.0-liter twin-supercharged V-6 from the upcoming Audi S4 and is paired with a 38-kilowatt/52-horse electric motor. A new eight-speed automatic transmission adds two overdrive gears compared with the old six-speed Tiptronic, and Porsche has dropped the weight of the hybrid module's electronics by 30 percent. Power steering is now electrohydraulic (a first for the Cayenne's class, says Porsche), and the air-conditioning system is looped into the 240-cell, 288-volt nickel-metal-hydride battery located under the rear cargo area, rather than being belt-driven off the engine. Even the vacuum pump for the brakes and oil pump for the transmission have been given a second look, relocating the vacuum source in the first instance and switching to electric power for the latter.
Porsche's drivetrain is laid out as a full parallel hybrid, allowing electric-only power, combined gasoline-electric, or gasoline-only power. The electric motor is positioned on the Cayenne's driveshaft, between the combustion engine and the transmission. A single disengagement clutch shifts between the three power modes without requiring additional gears or clutches. The transition between electric and gasoline power occurs in just 300 milliseconds and is virtually undetectable, even at higher speeds - a testament to Porsche engineers' efforts to make the transition seamless. Managing the entire hybrid system operation is Porsche's Hybrid Manager ECU, an incredibly complex unit that processes up to 20,000 data parameters (compared with 6000 for a standard ECU) in a constant effort to achieve maximum performance and fuel economy.
The results are rather impressive for a 5000-pound SUV. In fact, Porsche says the Cayenne S Hybrid is on par with its V-8 Cayenne offerings for total output. With 374 horsepower and 406 pound-feet of torque on tap, Porsche claims a 6.5-second 0-to-60-mph time and a top speed of no less than 149 mph. That's nothing to sneeze at - especially when combined with Porsche's target of a combined 27 mpg, an increase of approximately 50 percent over the standard V-6 Cayenne.
Porsche is still in the prototype stages of the hybrid system's development, and during the test drive the vehicle experienced some minor issues with certain components running hotter than normal. But as it continues to tweak its test mules for improved efficiency, Porsche believes two features of its Cayenne S Hybrid could have dramatic implications on real-word fuel economy. First is the Cayenne's ability to rely purely on electric power for up to 1.2 miles at a top speed of 36 mph before depleting the battery. The other is in the Cayenne S Hybrid's ability to coast (or "sail," as Porsche engineers say) at speeds of up to 86 mph on electric power alone. When the Hybrid Manager detects the vehicle coasting, the combustion engine is shut down and power switches to electric mode, simultaneously shifting the car into its eighth speed for decreased rolling resistance. Regenerative braking and the electric motor's dual-function as an alternator both serve to keep the battery charged while on the go.
On the road, the Cayenne S Hybrid prototype we drove worked well. Hard acceleration from a standstill gave the vehicle a torquey push, nearly on par with that from the conventional Cayenne S V-8 or the European diesel Cayenne we drove before hand with an identical torque figure of 406 pound-feet. Underway, the Cayenne S Hybrid's new electrohydraulic steering felt precise, if just a tad overboosted, and despite the hybrid's extra 350 pounds over the V-8 Cayenne S, it still felt well buttoned-down over the twisty hills of Bel Air, California.
A primary goal of Porsche engineers was to make the Cayenne S Hybrid drive like a "normal vehicle," and that it does to a large extent. Under normal acceleration, the vehicle runs up the rev-range and shifts into the next gear like a standard Cayenne. Be a little more delicate with the throttle, and the Cayenne S Hybrid glides forward silently and smoothly until either being given more throttle or exceeding 36 mph, in which case the combustion engine kicks in with nary a shudder or pause.
While driving, the Hybrid Status display can be triggered on the Cayenne S Hybrid's navigation display, showing whether electricity or gasoline (or both) is providing forward momentum. The display also shows when the battery is being recharged, when it is being drained, and what percentage charge it is at for any given moment. We found that the level of charge jumped around quite a bit. Sustained electric movement would drop the charge level accordingly -- the lowest charge level we witnessed in our spirited 20-mile city/highway drive was around 50 percent -- but we were surprised at the rate at which it would recharge itself during the drive, the charge level jumping 20 percent or so during just a few miles of hilly descending. Never did it seem that the electric reserve would drop to zero.
Perhaps most important is that the Cayenne S Hybrid still largely felt like a Porsche. Granted, the Cayenne isn't the sportiest member of the Porsche range, but it does offer a level of precision, feel, and driver gratification that is lacking in many other luxury SUVs. Porsche doesn't expect the Cayenne Hybrid S to be a huge seller, representing just five to 10 percent of total Cayenne sales when it hits U.S. showrooms next year. But at roughly the same price and performance as a V-8-powered Cayenne S, we expect to see quite a few roaming the streets of eco-hip Los Angeles by 2011.
|2011 Porsche Cayenne S Hybrid|
|Base Price||$60,000 (MT est)|
|Vehicle layout||Front engine hybrid, AWD, 5-pass, 4-door SUV|
|Engine||3.0L/333-hp/406 lb-ft supercharged DOHC 24-valve V6/52-hp electric motor|
|Curb Weight||5300 lbs (MT est)|
|Length x width x height||188.9 x 75.9 x 65.94 in|
|0-60 mph||6.5 sec (mfr est)|
|EPA combined city/hwy||27 mpg (mfr est)|
|On sale in U.S.||2010|