Rotary Engine Finally Could Find Home in Future Hybrids

Developer AVL says auto makers are interested in its serial hybrid concept, and it is discussing with potential suppliers licensing its rotary engine for production.

David E. Zoia

July 16, 2010

4 Min Read
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ANN ARBOR, MI – The rotary engine may have a future after all.

Once thought to be the next big thing in automotive powertrains, the rotary, or Wankel, engine largely was shelved by developers in the late 1970s, a victim of toughening emissions standards and rising fuel-economy demands.

Nearly every major auto maker seemed to have a rotary in the works during the decade, but Mazda Motor Corp. was alone in putting one into volume production during that era and is the sole producer of a Wankel-powered car at present, the RX-8.

But the rotary may have new life, ironically as a result of the industry’s push into vehicle electrification.

Gary Hunter, chief technologist-diesel engines for AVL Powertrain Engineering Inc., says the rotary may find a home in future extended-range electric vehicles, similar to General Motors Co.’s upcoming Chevrolet Volt.

EREVs run on electricity, but use a small internal-combustion engine as an electrical generator once stored battery power begins to run low.

Speaking to a University of Michigan Transportation Research Institute conference here on future powertrain technology, Hunter says the rotary offers a packaging advantage over a conventional piston engine in such applications.

AVL’s rotary hybrid powertrain.<link rel=

Enlarge Photo


“The nice thing about piston engines is everybody has them, but piston engines are too large,” Hunter says.

A 0.57L 2-cyl. piston engine producing the same amount of power as a 0.25L rotary not only would be bulkier but weigh 24 lbs. (11 kg) more, he says.

To prove its point, AVL has cobbled together an EREV based on BMW AG’s Mini Cooper, using a rotary engine to keep the battery charged.

AVL’s powertrain group built the rotary, Hunter tells Ward’s, though it is seeking to license production, not actually manufacture the engine itself.

“We built it only for demonstration purposes,” he says. “Now we’ve been successful in that, so the next step in the development phase will be to find someone to manufacture it.”

Component production is “not AVL’s business model,” he adds. “We design and develop; we don’t manufacture.”

The AVL single-piston rotary engine displaces 0.254L and weighs 64 lbs. (29 kg), including the starter/generator. Combined with the power electronics, cooling circuit for the electronics and core unit to connect to the vehicle’s cooling system, the setup weighs 143 lbs. (65 kg) and measures 19.2 ins. (49.0 cm) long, 38.6 ins. (98.0 cm) wide and 15.7 ins. (40.0 cm) high.

The unit generates 15 kW of electric power at 5,000 rpm, but can be scaled up to 25 kW at 7,000 rpm. A slightly bigger version of the rotary engine, displacing 0.357L, can produce 36 kW at 7,000 rpm, while a double-rotor engine could deliver 50 kW.

The Mini test vehicle uses a 10 kWh lithium-ion battery and can travel 19 miles (30 km) on a single charge. With its 2.6-gallon (10L) fuel tank and 15-kW rotary, range is extended to at least 124 miles (200 km), AVL says in a technical paper. It gets to 62 mph (100 km/h) from a dead stop in 12 seconds.

Hunter says auto makers are intrigued by the hybrid concept, and some component manufacturers have expressed interest in building the rotary engine under license, though he declines to be specific.

J. Gary Smyth, executive director-North American Science Labs for GM, says the near-term future of vehicle electrification is going to come down to “battery-electric vehicles vs. extended-range electric vehicles,” such as the Volt and AVL concept.

While favoring EREVs like the Volt overall, he admits it will take time to determine whether they meet consumer needs better than BEVs.

“The Volt’s early volume is not an issue,” he says when asked how many GM expects to sell. “The real issue is how range-extended vehicles will play out (longer term).”

Michael Omotoso, senior manager-global powertrain forecasting at J.D. Power and Associates, says sales of all hybrids in the U.S. should total 315,000 units this year, accounting for 2.7% of the light-vehicle market. Penetration should grow to 9% in 2015, he predicts.

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