Porsche AG’s first hybrid-electric vehicle, the Cayenne S Hybrid, will hit the market in 2010 with a supercharged Audi AG V-6 under the hood and what could be a small breakthrough in electric-only cruising capability.

The German sports car maker, which now holds a controlling share of Audi parent Volkswagen Group, says the new hybrid cross/utility vehicle will achieve fuel economy of 26 mpg (9 L/100 km) in the European driving cycle and maintain speeds up to 86 mph (138 km/h) without using its internal-combustion engine. U.S. fuel economy numbers have not been released.

The Cayenne S Hybrid is expected to emit 20% less carbon dioxide than a comparable vehicle with a conventional powertrain offering similar performance specifications, Porsche says.

Those specs include the capability to sprint 0-62 mph (100 km/h) in just 6.8 seconds, providing the Cayenne S Hybrid with V8-like performance and 4-cyl. efficiency, the auto maker says.

The new model will comply with U.S. Ultra Low Emission Vehicle II standards.

The powertrain consists of Audi’s 3.0L supercharged V-6 gasoline engine with direct fuel injection, a 3-phase synchronous electric motor and 8-speed automatic transmission. The V-6 is rated at 333 hp and 324 lb.-ft. (439 Nm) of torque from 2,900-5,300 rpm, and the electric motor adds 52 hp and 221-lb.-ft. (300 Nm) of torque.

Delivering the electrical juice is a 154-lb. (70-kg) 38-kW (51-hp) nickel-metal-hydride battery that packs into the space normally occupied by the Cayenne’s spare tire, leaving the rest of the cargo bay uncompromised. Currently, Cayennes can be ordered with internally or externally mounted spares and come standard with a compressor and tire inflation kit.

The onboard Hybrid Manager keeps track of some 20,000 data parameters to regulate the switch from gasoline engine to electrical motor power or a combination of the two. The Cayenne can run solely on electric power for up to 1.2 miles (1.9 km).

Porsche says top speed comes in sixth gear, with the final two steps on the 8-speed transmission serving as overdrive gears that reduce engine rpm to enhance fuel economy. While cruising at freeway speeds in eighth gear, the Hybrid Manager can shut down the V-6 and use the electric motor to maintain the car’s momentum for short distances, Porsche says.

The hybrid powertrain also will be offered eventually in the new Panamera, a 4-door sedan Porsche will launch in late summer.