The Supremacy Over Piston Power
The basic working principle of a Rotary engine is the same as its Piston-powered counterparts, i.e internal combustion, but the way they go about burning air and fuel is what separates them. Unlike a Piston engine which uses multiple banks of cylinders, wherein each cylinder is responsible for containing the pressure from the explosion, in a Rotary engine, the pressure is contained in an oval chamber that also acts as the engine housing.
On the inside, a Rotary engine houses a triangular rotor, which is colloquially referred to as a spinning Dorito, attached to an eccentric shaft that replaces the Pistons. This results in a void within the chamber that expands and contracts, based on the position of the rotor, and each of these voids acts as combustion chambers. The rotating motion compresses the air and fuel mixture, which expands the chamber as it ignites, and sends the exhaust gases out of the exhaust port.
But the result of this drastically different approach is very evident. For starters, the refinement levels are unparalleled. Some of the other key advantages include:
- Low Vibrations
- Only two moving parts result in fewer mechanical losses
- 1/3 the size and weight of a comparable piston engine
- Linear and smooth powerband
- Can achieve and sustain higher RPMs than a comparable piston engine
As a result, every automaker wanted a piece of the action and in no time, automakers like Skoda, NSU, Mercedes, Citroen, and Chevrolet all were coming up with their implementations of the rotary engine. In fact, contrary to popular lore, it was Skoda that made the rotary-powered 1000 MB in the early 1960s. It was a single rotor compact sedan but it never managed to make it past the prototype stage.
1974 also witnessed the rotary find its way into mass-production bikes, with the German company Hercules presenting the W 2000. Other than Mazda, NSU is the only automaker that was able to achieve some amount of success with the Rotary engine. NSU was a German car manufacturer, that later became a part of Audi. They made the first Rotary-powered production car which was aptly named the Wankel Spider. Then came the NSU Ro80 which was a family sedan designed to compete with the E-class and was known for its refinement, but these cars were plagued with apex seal-related issues.
While NSU had retired the rotary engine with the end of the Ro 80, their “successor” Audi (back then called the “Audi NSU Auto Union AG”) kept experimenting, fitting 25 Audi 100 C2 with a 132kw twin-rotor rotary engine (based on the Ro 80’s engine) for a 1977 fleet-experiment, but it never even got close to production.
The success of the Mazda Cosmo
Mazda sent a team of engineers to West German’s reputed automaker, NSU. There, the team found that there was a huge technological obstacle to the development in the form of “chatter marks.”
To take on the challenging task of adapting this revolutionary and untested new engine, Mazda sent a team of 47 people, led by Kenichi Yamamoto, and this ragtag team mostly comprised of infantile engineers set to work on what had the potential to be the powertrain of the future. On the face of it, all looked promising, but within Mazda, people thought of this to be nothing more than an expensive experiment that was bound to fail.
Mazda, just like every other manufacturer, was facing a major issue, the aforementioned Apex seals. After considering every material under the sun including horse and cow bones, in 1963, an engineer proposed the idea of changing the apex seal’s frequency characteristics by modifying its shape, and the Mazda team quickly whipped up a cross-hollow seal with a cross-shaped hole near the apex of the seal and after initial testing, the results looked promising and the Mazda engineers knew that this was their ticket to Rotary supremacy.
After the success of this experiment, Mazda started the development of its first production Rotary engine with the support of Nippon Carbon Co., Ltd. The new apex seals were made from aluminum-carbon composites, a very cutting edge material for the time.
The First Rotary powered Mazda was the Cosmo Sport that premiered back in 1967, a car that in controversial opinion was considered the better looking Japanese derivative of the E-Type Jag. And the resemblance is striking at first, and it was no accident as Mazda wanted to take inspiration from the best, and the E-Type was described by Enzo Ferrari himself as “the most beautiful car ever made”. The E-Type’s almost spaceship-like silhouette also captured the essence of the space race like nothing else including the name “Cosmo Sport”.
After nearly two years of intensive testing, the production-spec Mazda Cosmo Sport was ready. The production-spec engine had cast iron rotors and the eccentric shafts were chrome-molybdenum steel. The
carburetor setup was fairly conventional but it was mated to unconventional twin ignition distributors and dual spark plugs in the combustion chamber and this setup came mated to a four-speed synchromesh gearbox.
Despite the futuristic name, Cosmo’s suspension was kind of old school. The front end did get fully-independent A-arms with coil springs, tubular shocks, and an anti-roll bar. The rear end got leaf springs and a De Dion tube. As was the case with most vehicles back in the day, the chassis was stainless steel and the brakes were unassisted. All these factors combined result in the period-correct handling characteristics.
The Rotary engine displaced under a 1000cc and produced 109 horsepower and 96 lb-ft of torque and despite these figures looking weak on paper, the Cosmo was capable of reaching 60 mph from a standstill in just 8.2 seconds. After the introduction of the Series 2 in 1968, the Cosmo was retired in 1972 and Mazda had achieved what they had hoped.
The Demise of Rotary Power
After the Cosmo, Mazda introduced the Cosmo AP/CD in 1975, a more conventional bodied application of the same motor for mass-market consumers. In 1981, the Series HB was introduced, a car powered by multiple engines, including petrol and diesel along with the Rotary engine. Then came the Cosmo Eunos, or the Series JC in 1990, and was the first triple rotor car in the Japanese automaker’s lineup with 300 horsepower on tap. Then came the last of the bread, the RX series, and the RX-3, RX-7, and RX-8 marked the last of the production rotary-engined vehicles.
The RX range especially the RX-7 is what made the Rotary engine a pop culture icon. But Mazda’s RX range, notably the RX-8 was the last of the bread and there are good reasons for it. After the initial interest in Rotary technology, Mazda was the only manufacturer that stuck with the Rotary but the reason for its demise comes down to Emission Compliance. All rotary engines have high fuel consumption, and the use of engine oil to lubricate the pistons meant the engine also burnt a lot of oil. This meant it wasn’t as clean as a piston engine and Mazda just couldn’t meet the required emission standards with this engine.
Here’s a list of common problems that plagued Wankle
- Apex Seals constantly failing
- Less torque than a comparable piston engine
- Multi-rotor engines suffer from heat damage between the chambers
- Not fuel-efficient
- High oil consumption
The Return of the Rotary hybrid
After the demise of the Mazda RX-8 in 2010, the rotary engine was thought to be long gone. But the new hybrid and electrified vehicles might give rotary engines a second chance. Cars like the BMW i3 use a small capacity petrol engine as range extenders however those engines need not be as powerful since the wheels will always be driven by electricity. In such use cases, a lightweight and compact Rotary engine can come in handy and save a lot of space and weight which is of utmost priority in heavy EVs. We expect to see a rotary-powered range extender in the upcoming Mazda MX-30 EV.
The more exciting news however is the possibility of a three-rotor Wankel-powered sportscar from Mazda, a true successor to the RX-7 and RX-8.
The new Rotary-powered sports car is also expected to feature a hybrid powertrain of some sort, but unlike the MX-30, the triple-rotor Wankel will be at the heart of this drivetrain.
From the patent images, the new sports car will feature a transaxle layout, and the platform to feature this drivetrain could be the brand’s upcoming Large Architecture which was being designed for a new range of six-cylinder hybrids which makes it the perfect candidate for the triple-rotor engine.