Monday, July 16, 2012

Mazda's famed rotary engine sputters and dies

Mazda's famed rotary engine sputters and dies

Dan Carney

The 1967 Mazda Cosmo was the first production car powered by a rotary engine.

By Dan Carney, contributor
The new and improved always prevails over the old and stale, doesn’t it? Surely the ancient contraption called an internal combustion reciprocating piston engine – a design that is approaching its 150th anniversary – must be superseded by something newer and simpler.

Maybe. But that replacement won’t be the rotary engine design invented by Felix Wankel in 1957 and popularized by Mazda since its introduction 10 years later. Mazda has announced that it has ended production of the company’s signature engine in favor of concentrating on its trademarked SkyActiv improvements to the piston engine.

It wasn’t supposed to be this way. The 1950s were the future, and when Wankel finally built a running rotary engine after nearly four decades of development, it seemed the engine would doom piston engines the way internal combustion engines killed external combustion steam engines.

Consider the advantages. The rotary, with its spinning triangular rotor is inherently smoother than the reciprocating engine, whose pistons start, stop and reverse direction twice with every single rotation of the crankshaft. The rotary has many fewer parts than the incredibly complex piston engine, especially in these days of variable valve timing, double overhead camshafts, intercooled turbocharging and direct fuel injection.


The rotary is compact and light, which makes packing it into small cars easier and it leaves room for crush space in cars that must meet pedestrian protection impact standards. Finally, in this age of interest in diversifying fuel supplies, the rotary is able to burn a range of fuels, including diesel, gasoline, alcohol and hydrogen gas without modification. The only Japanese car to ever win the 24 Hours of Le Mans sports car race? The rotary-powered Mazda 787B.

Recognizing the engine’s potential, more than 100 companies rushed to license Wankel’s rotary design, but very few saw the engine to fruition.

Mazda has sold rotary-powered cars since introducing the Cosmo Sport in 1967, while Suzuki briefly sold a rotary-powered motorcycle in the ‘70s and Norton sold some rotary motorcycles in the ‘80s. During its heyday, Mazda even sold rotary-powered pickups.

But most companies found that manufacturing rotary engines that would run for more than a few hours an insurmountable task. The apex seals, the part at each tip of the triangular rotor, are an engineering nightmare. The seals are prone to wearing out and to developing vibrations that cause them to gouge the inside of the engine. They can even break off entirely, wrecking the engine. The oil seals on the rotors have also proved challenging to perfect.

Wankel’s employer, the German company NSU, made a short production run of rotary cars but quickly abandoned the technology. General Motors planned to make the Corvette rotary powered in the ‘70s, but gave up. Ford engineers, even while the company held a controlling stake in Mazda, found they couldn’t build successful rotary prototypes. American Motors Co. planned for the much-maligned Pacer to use a super-compact front-drive rotary arrangement, a design that would have made the bloated-looking Pacer’s styling more acceptable because of the resulting huge cabin.

Mazda got the rotary to work, barely. The engines have never lasted as long as piston engines, and along the way they were prone to consuming too much gas and oil. Burning oil led my own ’87 RX-7 to foul its spark plugs monthly. Sometimes I could clean them successfully, but other times I had to replace all four of them at $10 a pop. While getting 16 mpg in a two-seat sports car.

So that’s what it came down to. The rotary, as lovely a device as it is, proved too thirsty and insufficiently durable for widespread adoption. The struggle to preserve its signature technology has contributed to Mazda’s financial struggles, so the company finally had to retire its powerplant, at least until its finances improve.

Mazda’s advances in piston engine technology with its SkyActiv gasoline and diesel piston engine are impressive, especially considering the company’s small size and its long adherence to the rotary religion. But the company says it hopes the rotary is merely on hiatus, not dead.

“Work does continue on the next-generation rotary,” explained Mazda USA spokesman Jeremy Barnes. “Additionally, work continues on the use of fuels other than gasoline, taking advantage of the rotary’s unique ability to operation on multiple fuels without extensive reengineering. We’ll share more information on the next generation of rotary when we can.”

Fans who have experienced the rotary’s effortless rush to redline are surely keeping their fingers crossed. But it may be that the future has slipped into the past.

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