Porsche’s electrifying performance focus

  • 13-Jun-2013 07:53 EDT
Porsche 06-13 918 Spyder.jpg

Porsche's 918 Spyder is a leading indicator of the company's plug-in hybrid program.

“We will be opening a state-of-the-art Electronics Integration Center later this year in which all engineers from various disciplines will work together to develop electrical and electronic systems, on short paths,” said Wolfgang Hatz, Head of Porsche R&D. “This enables highly efficient development processes in the electrical and electronics areas.”

It is a significant development for a company that is investing heavily in plug-in hybrid (PIH) electric powertrain solutions, the most spectacular of which is its latest piece of ultrahigh-performance exotica, the 918 Spyder; it enters production in September. Just 918 will be built, to be sold globally priced from €781,155.

Its 447-kW (559-hp) 4.6-L V8 midmounted dry-sump engine driving the rear wheels is aided by a 115-kW hybrid module mounted on the rear axle and a 95-kW electric motor on the front to provide an all-wheel-drive configuration. Designed entirely around its plug-in hybrid drive, aspects of the 918 Spyder benefit from cutting-edge knowledge gained via Porsche’s racing 911 GT3 R Hybrid, including front axle electric motors and torque vectoring across steering axles, plus the integration of a gasoline engine and electric motors in a high-performance environment.

The new 918 Spyder is a spectacular pointer to Porsche’s priorities; it is referred to within the company as representing a “gene pool” for Porsche’s future sports cars. Many, if not all, of those models are also likely to be hybrids.

“Given the current development status of battery technology, it is still not possible to implement a typical Porsche sports car with an all-electric drive," explained Hatz. "The driving range would be too short, the weight too high. That is why we prefer plug-in technology as shown in the Panamera S E-hybrid and the upcoming 918 Spyder.”

He regards PIH as an “excellent fit” for Porsche because it enhances efficiency and boosts performance. It also avoids performance and range limitations: “For our customers that is a priceless advantage!”

Does all this mean future Porsches will be radically different vehicles? Said Hatz: “A Porsche in 2020 will not differ significantly from today’s models in any of its core attributes.”

But it will be more efficient. “We will be implementing some of the technologies being used today—in individual versions or in top models—over a much broader base of vehicles," he said. "These technologies include lightweight design with a multimaterial mix and new materials, downsizing—and partially electrified powertrains.”

Also very significant will be predictive operating strategies: “These will be for the entire powertrain system based on three-dimensional route data and networking—not only via the Internet but also via the transportation infrastructure.”

The 918 Spyder’s technology has benefited through experience gained from cars entered for the Le Mans 24-hour race. The structural concept of the 918 Spyder includes a rolling chassis (a basic vehicle that can be driven without a body), which the company describes as a Porsche race car tradition, and the car’s IC engine has its origins within the LMP2 RS Spyder race car. Weight balance is 43% front, 57% rear.

CFRP (carbon fiber reinforced polymer) is used for the monocoque and subframe of the production car. In yet more exotic “Weissach” form, unladen mass is 1640 kg (3616 lb). The Weissach specification (€853,155) includes the use of Alcantara instead of leather upholstery, reduced sound insulation, and lightweight magnesium wheels. Total mass saved is 35 kg (77 lb). There are also visual changes including the use of visible CFRP areas.

Electronic chassis subtleties embrace much of what would be expected on such a supercar, but also added is rear-wheel steering with a speed-sensitive electromechanical adjustment system for each wheel turning through 3° in both directions; at low speeds, front and rear turn in opposite directions to enhance agility and tighten the turning circle.

For decades, Porsche road cars have been distinguished by their aerodynamic aids. The 918 Spyder’s include the Porsche Active Aerodynamics (PAA) system, automatically varying within three modes; Race, for instance, is for maximum downforce generated by a retractable and extendable rear wing operating at a steep angle-of-attack. Control is integrated with the hybrid drive system.

Two adjustable underfloor flaps ahead of the front axle channel airflow into diffusers creating required ground effect. The default position, and for E-Power (hybrid) mode, sees aerodynamic aids producing minimum drag up to 130 km/h (81 mph), then increasing downforce.

On a car such as the 918 Spyder, systems integration is crucial and the hybrid technology has five operating modes with driver switchable (via steering wheel buttons) operation: E-Power, Hybrid, Sport Hybrid, Race Hybrid, and Hot Lap. Only with Race Hybrid selected can Hot Lap be activated, taking the traction battery to maximum power, using all available energy for track work.

The naturally aspirated V8 gasoline engine’s rev limit is a heady 9150 rpm. It and its associated components are lightweight. The oil tank (necessary with the use of a dry sump), air-filter box integrated into the subframe, and air induction unit are of CFRP. The crankshaft uses high-strength steel and the engine has titanium con rods, thin-wall casting for the crankcase and cylinder heads, and thin-wall alloy for the exhaust system.

The exhaust system also incorporates a new thermodynamic channeling concept. The hot side is inside the cylinder vee; the intake channels are on the outside. A plus for the system is that it helps keep underhood temperature lower, a significant aspect of ensuring that the liquid-cooled lithium-ion traction battery of about 7.0 kW·h remains within its ideal 20-40°C (68-104°F) range, so cutting energy needs for active cooling. The engine has no external belt drives.

Transmission is a seven-speed double-clutch PDK automated manual mounted upside down from its normal orientation. It has extensive design changes including decoupler clutches for the electric motors, which operate according to ambient driving conditions.

Battery recharging typically takes 4 h via a domestic 230 V ac supply or 25 min using the Porsche Speed Charging dc station, which is an option.

Performance figures for the 918 Spyder include a 0-100 km/h (0-62 mph) time of 2.8 s, top speed in excess of 340 km/h (211 mph)—150 km/h (93 mph) using only electric power—NEDC fuel consumption of 3.3 L/100 km, and CO2 emissions of 79 g/km. In electric-motor-only mode, range is about 30 km (19 mi).

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