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Matt Brogan26 Jun 2019
NEWS

Mazda updates rotary engine patents – with turbo

New patent shows turbocharged rotary engine has applications beyond EV range extension

Two new Japanese patent applications – uncovered by Garage Alpha this month – show Mazda has filed two patent updates for its trademark rotary engine.

The patent applications appear to show a new side-port exhaust arrangement that serves to create a scavenging effect for improved intake efficiency (similar to function of the 4-2-1 exhaust system in Mazda’s SKYACTIV-G and SKYACTIV-X engines), and a new turbocharger design that is bespoke to the rotary powerplant.

The new, overlapping peripheral exhaust port, reciprocating valve system and turbine-style turbocharging suggest the new rotary engine will be used to power a vehicle.

Mazda’s previous conversations around rotary engines suggested the rotary engine would only make its return as an EV range extender.

If our interpretation of the Japanese document is correct, it shows Mazda has finally solved the emissions and intake efficiency problems that have plagued the rotary engine for decades.

It also suggests that Mazda may have finessed the delivery of across a broad rev range and in various load conditions.

Mazda has confirmed it will use a rotary engine as a range extender in its EV models not only because of its compact size, but because in that application the engine would operate at a set rpm and load. In other words, it’s either running at maximum efficiency or not at all.

There’s no suggestion of displacement in the 30-page document, or of any output figures or rev ceiling.

mazda rotary 5

Previous rotary engine designs had a redline of around 9000rpm, after which point the triangular shaped rotor (which is mounted eccentrically to the crankshaft) would bend the crankshaft.

Mazda’s last application of the rotary engine in a production vehicle was the discontinued RX-8 coupe (2003-12). In the RX-8, the rotary engine displaced 1308cc and produced 170kW at 8200rpm and 211Nm at 5500rpm.

Mazda previewed a new 1.6-litre twin-rotor engine in the 16X concept of 2007, and a single-rotor 800cc version of this is likely to feature in one of two all-new EVs Mazda will release by 2020 -- one a pure battery-electric model, the other a range-extender EV fitted with a rotary engine/generator.

mazda rotary 4

Mazda has also announced that by 2030, all of its models will incorporate electric power. So in the meantime, it will roll out mild-hybrid and plug-in hybrid versions of its existing models.

But hopes of a born-again rotary sports car to replace the long-lost RX-7 and RX-7 – based on the sleek 2015 RX-VISION concept (pictured) and widely referred to as the RX-9 – being launched in 2020 (Mazda’s centenary year) were dashed by Mazda R&D chief Kiyoshi Fujiwara in October 2017.

“We cannot provide the RX-VISION to the market by 2020, because we do not have enough money to invest, to commercialise it,” Fujiwara said at the time. “It’s going to be too late to make the RX-Vision for the centennial.”

mazda rotary 3

Mazda’s R&D chief did, however, confirm that a rotary engine will power the wheels of a Mazda sports car in future.

“But we have still been developing rotary engines as a sports car. Technology is going well but if we launch this kind of model later, we will have to add more technology to it, like autonomous driving, electrification…

“[In] 2019 or 2020 we release the EV with range extender rotary engine -- this is completely a range extender unit. Because that is one of the merits of the rotary engine we have to utilise it for range extender. That is one of the rotaries,” Fujiwara said..

mazda rotary 2

“[But] Most of the rotary engine fans are still waiting for a sports car with the rotary engine, therefore we are still developing the rotary engine as a sports car. No range extender, no e-power.

“However some cities will ban combustion, therefore we need some additional portion of electrification because the driver can’t use this rotary sports car.

“Some of the regions we don’t need this small electrification, therefore we can utilise pure rotary engines. We would have two versions -- it will be easy.”

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Written byMatt Brogan
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