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A partnership with Toyota on the e-Palette autonomous vehicle offers a chance to look back at the auto maker's unique motor

A twin-turbo Mazda RX-7 Sprint R sits on the shoulder of a road near Irvine, Calif.

Not in a racing machine, not with a sports car, not tucked away behind sharp-edged sheet metal; Mazda's rotary engine looks set to return, not as a warrior, but propelling another end to human driving.

Revealed at the 2018 Consumer Electronics show in Las Vegas, the Toyota e-Palette autonomous delivery and ride-sharing vehicle may get a small Mazda rotary engine packaged as part of a range-extender for its electrified powertrain.

From a technological viewpoint, the idea is very sensible. Mazda and Toyota have already formed a partnership, and will together be opening a US$1.6-billion assembly plant in Alabama. Mazda has already spent several years experimenting with the use of rotary engines as range-extenders and generators, and has shrunk them down to about the size of a wastebasket.

With a flat layout, the very compact single-rotary range extender takes up very little space.

However, if you're familiar with the history of the rotary engine, relegating the rotary to a second-string backup function seems a bit sad. And if you're not familiar, you might wonder why Mazda and Toyota are bothering at all. If it's compact internal-combustion engines we're looking for, then you need only look at the BMW i3 and its three-cylinder range-extender to see that the world of motorcycles has done pretty much all the shrink-ray groundwork already.

To better understand Mazda's obsession with the rotary, and why that obsession might provide one final chance for the technology, we must hop in our time machine. Better bring your ear plugs. This is going to get loud.

We begin with Felix Wankel, the engineer who would give the Wankel rotary engine its proper name. Born in Germany in 1902, Wankel would receive a patent for his idea by the age of 28, and go on to produce a running prototype by the 1950s. His invention would influence the German automotive industry, but perhaps not in the way he expected.

In a normal, piston-powered combustion engine, a combustion event drives a piston downward, which turns a crankshaft the same way your legs turn the pedal assembly on a bicycle. The rotation is then converted into forward motion through a transmission, driveshaft, axles and wheels.

A rotary engine doesn't bother with pistons, replacing that up-and-down motion with a three-sided rotor that spins around a central crankshaft instead. Set inside a peanut-shaped housing, the rotor's rotation draws in air and fuel, compresses them, ignites the mixture and expels exhaust – all the usual four-stroke combustion operations. It just does so in a manner that allows for tight packaging, smooth high-rpm engine speeds and efficient use of engine volume.

There is just one huge problem. At each of the three points it contacts the housing, the triangular rotor has a weak point. It's like a Grecian hero with three Achilles heels; called the apex seals, these contact points can blow out or start chattering and wearing on the housing.

A rotor from a Mazda RX-8, right, pictured next to a compact rotor as used in range-extenders and generators.

In the case of the NSU Ro80, the first mainstream sedan powered by a rotary engine, the weak point was fatal. Engine failures and warranty claims sunk not just the car but the company. NSU was so financially wounded by the Ro80's woes that it was snapped up by Volkswagen, who merged it with Auto Union to form Audi. Mercedes would experiment with a rotary engine in their C-111 concept car, but Germany was finished trying to figure out the rotary as a production offering.

Enter Japan. In many instances, the Japanese automotive industry's greatest successes have been in taking an existing idea and making it reliable. One only need look at the Miata, a testament to all the traditions of the Great British Sports Car, except for the bits where the oil leaks out and the doors occasionally fall off.

For Mazda, the rotary engine wasn't just a novel concept, it was a lifeline. The nascent Japanese car industry had been given directive to replace diversity with strength. Small manufacturers were to be swallowed up by larger ones, and tiny, Hiroshima-based Mazda looked vulnerable.

The defence would come down to the Shi-ju-shichi-shi, the 47 ronin. Taking their name from a famous Japanese tale of feudal samurai, 47 engineers laboured within Mazda's research and development department, trying to find a solution where the world's best had thrown in the towel. Under the direction of the late Kenichi Yamamoto, they tried everything – until they reached a breakthrough.

The otherwordly Cosmo Sport was the first production rotary-powered Mazda. Delicate-looking and rare, they are highly sought-after by collectors today

Using a shaped seal eliminated the harmonics that were causing the chatter and premature wear, and the rotary engine suddenly became viable for the mass-production market. Mazda would go on to first produce a rotary-powered sports car, the Cosmo Sport, and then sedans, pickups and even a rotary-powered bus.

For its greatest victory, however, we need to jump forward several decades, and stand on the sidelines at the 1991 running of the 24 Hours of Le Mans. Remember those earplugs I said to bring? Now's the time.

With an unholy scream, the 700-horsepower, four-rotor Mazda 787B comes howling past the stands. Revving to 10,500 rpm, the quad-rotor powerplant emits an eardrum-perforating shriek like no engine before or since. It sounds like a dentist's drill designed by the god of war.

It was also good enough for victory. At time of writing, Mazda is the only Japanese manufacturer to win Le Mans outright, although Toyota has come close in recent years. Adding to that single victory are the countless trophies won by the RX-7, Mazda's most popular rotary sports car.

The best of the RX-7s was, perhaps, the third-generation car, a twin-turbocharged machine that was far lighter and edgier than rivals such as the Toyota Supra Turbo or the Mitsubishi 3000GT. Not long ago, I had the chance to pilot a one-off, left-hand-drive 2002 RX-7 Spirit R through the California canyons above Mazda's R&D centre in Irvine.

Classically pretty from any angle, Mazda’s RX-7s have genuine racing pedigree.

Specially built for a racing-obsessed executive at Mazda's North American operations, the Spirit R dive-bombed the hills, attacked the corners and shredded the straights with turbine-like thrust. It was magical to drive and, it has to be said, stank of unburnt hydrocarbons.

This last part is the issue that keeps the next generation of Mazda engineers up at night. The rotary engine, so important to Mazda's identity, is not very emissions-friendly. Part of the problem is that Mazda is the only manufacturer to stick with the rotary, so it doesn't benefit from any shared improvements in the industry. The last Mazda rotary-powered machine, the RX-8, went out of production in 2012. Concepts have been shown, but there's no rotary-powered machine on the horizon.

Except, that is, for Toyota's futuristic box and its potential rotary-powered range-extender. One of the rotary engine's strengths, besides its compact size, is a turbine-like ability to run efficiently at higher constant engine speeds. Low-end torque isn't great, but the light demands of a generator are a great fit.

Toyota's interest is enough to keep Mazda funnelling development money into their rotary, and perhaps enough to find a path to a reborn rotary-powered sports car. All it takes is one breakthrough, and in the case of the Mazda rotary engine, you should never say die.

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