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Mazda files updated rotary engine patents - with turbo

Two new Japanese patent applications have been filed by Mazda Motors, on their flagship 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 the function of the 4-2-1 exhaust system in Mazda’s SKYACTIV-G and SKYACTIV-X engines), and a new turbocharger design. It also involves a new, overlapping peripheral exhaust port, reciprocating valve system and turbine-style turbocharging and 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’s previous conversations around rotary engines suggested the rotary engine would only make its return as an EV range extender. 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.

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.

Nevertheless, hopes of a revived rotary sports car to replace the long-lost RX-7 and RX-8 – 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’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 will 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. He then added: “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."


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