Mar 18, 2017, 1:33pm ET

Mazda files two new rotary engine patents

The pistonless wonder is poised for a comeback, but in a different role

Could Mazda's rotary engine see a revival? On again, off again rumors have cycled through the media for the last decade, but two filings that surfaced Thursday on the US Patent and Trade Office website appear to confirm that the Hiroshima-based automaker is planning for the pistonless motor's return.

As reported by Autoblog, the patents hint that the rotary in this case would be used as a range extender. This is in contrast with its traditional role in Mazdas as the sole powerplant for a sports car or luxury vehicle.

Unlike the dual- or triple-rotor rotary engines Mazda has employed since 1967, the first patent details a rear-mounted single-rotor engine powering a generator. The system would be used in conjunction with a lithium-ion battery to store energy and an electric motor driving the front wheels.

The other patent introduces a new technology not seen on the rotary engine before, a start-stop function. Like similar functions common on regular reciprocating piston engines, the system would shut off the rotary engine when not needed to save fuel. The pistonless, valveless design of the rotary presents some unique challenges, though. The patent shows that rotor itself has to be clocked at a certain resting orientation to make sure exhaust gases don't escape into the intake port, while an additional sparkplug burns off excess gasoline emissions.

About a year ago, a Mazda patent for what appeared to be a rotary engine for a front-engine, rear-wheel-drive application also appeared on the USPTO website. We know that engineers in Hiroshima are working on it. Now the question is when it will come to market.