Mazda Design Breakthrough May Give Rotary New Life
Improvements in sealing and other changes have Mazda looking at the rotary again, including for potential extended-range hybrids, a top engineer tells WardsAuto.
February 29, 2012
HIROSHIMA, Japan – The rotary is dead. Long live the rotary.
Despite plans to stop production of the RX-8 sports coupe in June and no commitment from management to replace it with another Wankel-powered car, Mazda may be on the verge of a major rotary breakthrough.
Mitsuo Hitomi, general manager-powertrain development, says the auto maker soon will complete development of an all-new rotary engine that meets future fuel-economy and emissions standards.
While Hitomi won’t confirm a completion date, his disclosure is evidence the rotary is alive and well at Mazda and that a new car powered by the engine could be on the way.
“We think we’ve found a way to improve the rotary’s fuel economy to be truly equal to that of conventional piston engines and, if so, we believe we can reintroduce the rotary to the market,” he tells WardsAuto in an interview.
Hitomi declines to pinpoint when that might happen, but suggests the timeframe roughly would be equivalent to any other engine plugged into one of Mazda’s vehicle programs. Best guess is two years, once the application has been determined.
Fuel economy and emissions were improved in the developmental engine “first, by changing the shape of the troichoid housing,” the Mazda executive says.
“The rotary has many seals, and ‘sealability,’ particularly at the apex, or tip, of the rotor has been a longstanding problem” dating back to the mid-1960s and the Cosmo Sport, Mazda’s first rotary car.
“Even with our current 1.3L Renesisrotary, gaps can develop between the apex seal and troichoid housing in light-load operation when imbalances in centrifugal force and gas pressure occur,” he says.
Specifically, centrifugal force pushes the seal onto the housing surface. In low engine-rpm ranges, or under low-load conditions, gas pressure in the combustion chamber can cause the seal to lift off the surface, resulting in combustion gas leaking into the next chamber.
By changing the shape of the troichoid housing, the seals remain flush to the housing, Hitomi says. “In addition to reducing emissions, better sealing improves fuel economy and overall performance.”
A second engineering enhancement focuses on ignition.