page_title: Wankel engine
section_title: Vehicle range extender
hierarchical_section_title: Wankel engine / Applications / Vehicle range extender
caption_attribution_description: 日本語: デミオEV
context_page_description: The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion.
  Compared to the reciprocating piston engine, the Wankel engine has more uniform torque and less vibration and, for a given power, is more compact and weighs less.
  The rotor, which creates the turning motion, is similar in shape to a Reuleaux triangle, except the sides have less curvature. Wankel engines deliver three power pulses per revolution of the rotor using the Otto cycle. However, the output shaft uses toothed gearing to turn three times faster giving one power pulse per revolution. This can be seen in the animation below. In one revolution, the rotor experiences power pulses and exhausts gas simultaneously, while the four stages of the Otto cycle occur at separate times. For comparison, in a two-stroke piston engine there is one power pulse for each crankshaft revolution and, in a four-stroke piston engine, one power pulse for every two revolutions.
context_section_description: Due to the compact size and the high power to weight ratio of a Wankel engine, it has been proposed for electric vehicles as range extenders to provide supplementary power when electric battery levels are low. There have been a number of concept cars incorporating a series hybrid powertrain arrangement. A Wankel engine used only as a generator has packaging, noise, vibration and weight distribution advantages when used in a vehicle, maximizing interior passenger and luggage space. The engine/generator may be at one end of the vehicle with the electric driving motors at the other, connected only by thin cables. Mitsueo Hitomi the global powertrain head of Mazda stated, "a rotary engine is ideal as a range extender because it is compact and powerful, while generating low-vibration".
  In 2010, Audi unveiled a prototype series-hybrid electric car, the A1 e-tron, that incorporated a small 250-cc Wankel engine, running at 5,000 rpm, which recharged the car's batteries as needed, and provided electricity directly to the electric driving motor. In 2010, FEV Inc said that in their prototype electric version of the Fiat 500, a Wankel engine would be used as a range extender. In 2013, Valmet Automotive of Finland revealed a prototype car named the EVA, incorporating a Wankel powered series-hybrid powertrain car, utilizing an engine manufactured by the German company Wankel SuperTec. The UK company, Aixro Radial Engines, offers a range extender based on the 294cc-chamber go-kart engine.
  Mazda of Japan ceased production of direct drive Wankel engines within their model range in 2012, leaving the motor industry worldwide with no production cars using the engine. The company is continuing development of the next generation of their Wankel engines, the SkyActiv-R. Mazda states that the SkyActiv-R solves the three key issues with previous rotary engines: fuel economy, emissions and reliability. Takashi Yamanouchi, the global CEO of Mazda said: "The rotary engine has very good dynamic performance, but it's not so good on economy when you accelerate and decelerate. However, with a range extender you can use a rotary engine at a constant 2,000rpm, at its most efficient. It's compact, too." No Wankel engine in this arrangement has yet been used in production vehicles or planes. However, in November 2013 Mazda announced to the motoring press a series-hybrid prototype car, the Mazda2 EV, using a Wankel engine as a range extender. The generator engine, located under the rear luggage floor, is a tiny, almost inaudible, single-rotor 330-cc unit, generating 30 hp (22 kW) at 4,500 rpm, and maintaining a continuous electric output of 20 kW. In October 2017, Mazda announced that the rotary engine would be utilised in a hybrid car with 2019/20 the targeted introduction dates.
  Mazda has undertaken research on Spark Controlled Compression Ignition (SPCCI) ignition on rotary engines stating that any new rotary engines will incorporate SPCCI. SPCCi incorporates spark and compression ignition combining the advantages of gasoline and diesel engines to achieve environmental, power and fuel consumption goals.
  Mazda confirmed that a rotary equipped range extended car would be launched a year late in 2020. The engine/electric motor architecture will be similar to a Toyota Prius Synergy Drive with full engine traction or full electric motor traction, or any percentage of the two combined in between. There may be a choice of a larger battery bank to give full EV running with battery charging from the grid, with the engine performing the dual functions of a range-extender and battery charger when the battery charge is too low. When running on the engine, the electric motor is used to assist in acceleration and take off from stationary.
caption: Mazda2 EV prototype
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