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Audi e-trons in Munich (Audi)
Audi e-trons in Munich (Audi)

How it works

What do you get when you cross an EV with a rotary? Add to ...

Audi is toying with a seemingly perfect blend of electric drive and a rotary engine.

Its A1 e-Tron extended-range concept car, being tested in various areas of the world, utilizes an electric motor for propulsion and a tiny rotary gasoline engine as a range extender. Just like the Chevrolet Volt, the internal combustion engine is used to maintain a charged battery. Except in this case, a rotary is used instead of a conventional engine. The advantages are the rotary’s small size, light weight and incredible smoothness.

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The A1 e-Tron’s front wheels are driven by a transverse synchronous electric motor positioned low in the front of the vehicle powered by a 12 kilowatt-hour lithium-ion battery pack under the A1’s floor. The result is 61 horsepower and, for short bursts, up to a very impressive 177 lb-ft of torque. This allows the A1 to scoot from rest to 100 km/h in slightly more than 10 seconds, not exactly stunning, but faster than most current hybrid and electric vehicles, and achieve a top speed of 130 km/h, enough to get by on the highway.

So far, so good, but what happens when the juice runs out, when that battery loses its charge? Plugged into a 110-volt outlet, the discharged battery takes about six hours to recharge. But with this arrangement, as the battery pack nears depletion, the quarter-litre (254-cc) single rotor engine mounted in the rear kicks into action, driving a 15-kilowatt generator to maintain a charged battery. The engine has no links to the drive wheels. It is used purely to drive the generator. With a little 15-litre fuel tank, this “range extender” arrangement stretches the range to 250 kilometres.

Audi says the A1 e-Tron is a “compact electric car in the premium class” and plans to run a pilot project in Europe later this year or in early 2013, perhaps labeled as the A2. The first test fleet of 20 vehicles has been deployed in the Munich area. Audi says the compact 1 e-Tron with four full-sized-seats is an ideal urban commuter.

If so, the rotary engine will have come full circle. NSU, a German car company, employed Felix Wankel in the 1950s. Between 1958 and 1973, 25 motorcycle, marine, car and industrial engine makers signed Wankel rotary engine licence agreements. NSU was the first to put one under the hood of a production car – a single rotor unit developing 50 horsepower for the two-seat NSU Spider in 1964. NSU was absorbed by Audi becoming part of the Volkswagen group of companies.

But it was Mazda that pursued development of the Wankel engine, putting it into production under the hood of the Familia Rotary Coupe in 1968, also called the Cosmo Sport 110S. By 1990, three-rotor Cosmos were on the road in Japan. A Mazda race car with a four-rotor Wankel won the 24 Hours of Le Mans in 1991 and the engine was immediately banned from endurance racing.

Mazda introduced a new and lighter generation of the rotary engine in 2007, featuring direct injection and a significant hike in power. But the rotary’s development was slowed by difficulties meeting ever-more strict emission regulations. When Ford sold off its controlling interest in Mazda to raise some of the capital needed to avoid bankruptcy, the Japanese company lost access to Ford’s massive development funds.

Mazda’s limited resources have thus been tied up in development of its SkyActiv systems. But there are rumors it has a back-door agreement with Audi to develop the rotary for use in extended-range vehicles.

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