Porsche Adapts Formula E Tech for Its Fastest Cayenne Yet

With an improbable 850 kilowatts (1,140 horsepower), and a digitized launch from 0 to 100 kilometers per hour in a cerebellum-squeezing 2.5 seconds, the 2017 Porsche Cayenne Coupe Electric defies any traditional notion of an SUV. It’s the most powerful Porsche production car in history, thanks in part to DNA from Porsche’s championship Formula E racers.

Automakers are notorious for using poetic license to draw tenuous connections between their racing cars and street cars. In this case, though, Porsche can draw legitimate links between their racers and their first-ever electric Cayenne. Exhibit “A” is the new Cayenne’s oil cooling of its rear electric motor, a direct transfer from its 99X racers. Another high-tech hand-me-down is its robust, 600-kilowatt braking-regeneration system, inherited from both the Formula E cars and Porsche’s Cayman GT4 ePerformance test car.

“Formula E is our development lab for the electromobility of tomorrow,” said Michael Steiner, Porsche’s management board member for R&D, at the Cayenne’s unveiling last year. “The Cayenne Electric shows how quickly such a technology transfer takes place at Porsche.”

I got to experience these innovations this past May during a scenery-blurring test drive south of Munich. I was especially impressed by the motor’s ability to halt this nearly 2,700-kilogram SUV from speeds as high as its electronically limited 261-km/h maximum (which, by the way, the Cayenne had no trouble reaching during my drive on unrestricted portions of the autobahn).

That kind of power in stopping and energy recuperation traces to the race cars and their efficient thermal management. Push harder on the physical brake pedal, and the Porsche transitions from pure regenerative braking through its electric motor to activate its powerful friction brakes. For most drivers, those friction brakes won’t get much use, though: The Cayenne makes about 97 percent of its stops in typical driving using regenerative brakes alone, Porsche says. Those regenerative stops return up to 98 percent of available kinetic energy to the onboard battery, nearly matching the company’s Formula E racers for efficiency.

How Oil Cooling Unlocks Massive Regenerative Stopping Power

The oil-cooled motor is the key that unlocks such massive stopping power and energy recovery, without any risk of cooking internal components. Timo Henn, drive system manager for Porsche SUVs, pointed out the highlights in a cutaway model of the rear electric motor, developed at Porsche’s fabled Weissach R&D facility and built in Zuffenhausen.

Heat is a big challenge in powerful motors, such as the ones used in high-performance electric vehicles (EVs). Excessive heat reduces efficiency by raising resistance. It also embrittles and degrades coil windings and can reduce the effectiveness of the motor’s lubricants. Improved cooling allows higher levels of current through the motor windings and therefore higher power.

In a conventional EV motor, heat is typically dissipated from the stator by means of a water-glycol blend that flows through a cooling jacket outside the stator. But in this Cayenne machine, a non-electrically-conductive synthetic coolant oil flows directly along and through the motor’s live copper conductors, dissipating heat directly from its source. This oil, developed by Mobil, is called Therm Electric P, and it’s about five times thinner than conventional engine oil. That low viscosity allows it to flow freely through narrow gaps in the stator.

The oil courses through its own cooling circuit, Henn says, and never needs replacement. As in some leading EVs, flat rectangular-cross-section winding conductors with hairpin curves replace round wiring, allowing densely packed copper to fill nearly 70 percent of the stator’s area, about 20 percent more than in traditional motors. Porsche does not cite the output of the rear motor alone, but rather a combined total of 850 kilowatts for the dual-motor configuration in all-wheel-drive mode.

With 800 volts, the Cayenne’s PPE (Premium Platform Electric) architecture also enables exceptionally fast DC charging. Formula E racing is now known for its “Pit Boosts,” where a 30-second pit stop can boost the battery of the Porsche 99X racer by 10 percent in just 30 seconds.

All told, the Porsche can charge its 108 kilowatt-hour battery from 10 to 80 percent in less than 16 minutes. It can add up to 328 kilometers (204 miles) of range in 10 minutes.

Interrupting the test drive for a lunch stop on the Starnberger See, a glittering freshwater lake south of Munich, I sample another form of fast food, the Cayenne’s optional inductive charging system. I drive the Cayenne until it rests atop a magnetic ground pad that owners can wire into their electrical panels. An onboard screen guides me into docking position by aligning a pair of animated circles, one representing the moving Porsche, the other the pad. Within seconds, the Cayenne is slurping up 11 kilowatts of juice from the pad’s 85-kilohertz magnetic field, enough to go from 10 to 80 percent in less than eight hours—no grubby cord or bulky connector to deal with, and no forgetting to plug in.

When IEEE Spectrum first covered the charger, my impression was that the €7,000 system (US $8,000) was quite pricey for consumers. Now I’m not so sure. The Turbo Coupe Cayenne I tested starts at US $170,350 and reaches $233,000 with options. Even a base-model Cayenne Coupe Electric starts at US $116,150. With Porsche buyers already spending those kind of sums, another €7,000 or $8,000 to cut the cord may feel like money well spent.