6 patents filed on the same day in Japan indicate Mazda is working on something big.
CarBuzz has discovered that Mazda has filed six fresh patents with the Japanese Patent Office, all published at the beginning of June 2023, detailing new designs for a two-rotor Wankel rotary engine. The number of rotors is important here, as two rotors imply a proper engine driving the wheels rather than the single-rotor design of the 8C range extender, as found in the unusual MX-30 e-Skyactiv R-EV plug-in hybrid.
This indicates Mazda hasn't given up on one day producing a successor to the RX-7 and RX-8 rotary sports cars, backing up previous statements that the rotary is integral to the brand's heritage and that Mazda would love to keep it alive.
CarBuzz JPO JPO
Three of the six patents (which can be read here, here, and here) relate specifically to the design of the rotors themselves – the spinning Dorito-shaped element of a rotary engine.
The goal of these patents is to “improve the fuel efficiency of a rotary engine,” according to the patent literature – rectifying one of the rotary engine's big problems, necessary to make it viable for production once more. To that end, each outer face of the rotor in the new designs is to have a recessed cutout (each patent showcases a different cutout design), with varying length, width, and depth to their concavity.
These cutouts alter the size and shape of the combustion chamber, which is created when the rotor swings past the air intake and fuel injection ports and to the point where the spark plug initiates ignition.
JPO JPO
In turn, the geometry of the combustion chamber affects ignition timing, as the shape will promote the growth of the flame, which according to Mazda, makes it possible to “possible to shorten the advance ignition and the ignition delay period, and improve the thermal efficiency by advancing the combustion center of gravity.”
The shapes of these recesses in the rotor would not just accelerate the flame growth but also control the flame growth and ensure complete combustion before the rotor swings to its exhaust phase, preventing additional heat and noise from being generated along with incomplete combustion. The secret to this is that the recess in the curved face mitigates an inherent design flaw of the Wankel rotary engine – that the curved face effectively narrows the combustion chamber when it reaches top dead center (TDC) of the ignition stroke.
By increasing this, the air-fuel mixture maintains fluidity and burns cleaner, reducing gas leakage – which was another issue preventing the rotary from being used in a new sports car.
JPO JPO
But there's more.
Instead of just having a rectangular recess, Mazda proposes a wider, deeper recess at the center of the rotor, while the leading and trailing edges have a narrower, shallower recess. These would enable a depressurization and re-pressurization of the air-fuel mixture, decreasing and increasing the ignitability of the fuel, respectively, in the same way that high compression makes fuel more prone to ignition.
By adjusting the pressurization of the air-fuel mixture during the combustion phase, the combustion process can be smoothed out, resulting in a single combustion event rather than two-stage combustion, which generates excess heat, gas, and wasted fuel.
With varying shapes and depths of these recesses, Mazda can actively change ignition timing without impeding the combustion process, all because of the angles at which the rotor will be facing the spark plug and outer housing of the combustion chamber.
The second trio of patents focuses less on the rotors and more on the air intake structure of the rotary engine.
JPO JPO JPO JPO
Unlike the three patents detailing variations of the same invention discussed above, however, each of these intake-related patents addresses something different: EGR, or exhaust gas recirculation, and how the EGR system can help suppress vibrations – which would be of use in a range-extender application.
The three specifically mention a single-rotor engine, but they can likely be applied to dual-rotor applications, too, and the patents mentioned above all refer to EGR being possible with the new rotor design.
The first patent details an intake structure capable of mixing intake air with these exhaust fumes. The intake structure comprises an intake manifold, a butterfly valve throttle body, and an EGR inlet valve, the design of which is meant to effectively mix intake and EGR gases prior to their introduction into the combustion chamber.
The second and third patents on this topic relate to this invention and the larger structure, detailing how it attaches to the engine, and specifically the construction of the EGR tube being more rigid in a bid to suppress vibration of the intake manifold, smoothing airflow and reducing NVH.
JPO JPO JPO JPO
While the intake-related patents aren't all that interesting, the first three are for a number of reasons. It seems Mazda is avidly trying to find fixes for all of the rotary engine's known afflictions, especially in the way of their high emissions and thirst for fuel.
Mazda has, over the last few years, filed dozens of patents for various aspects of a rotary-powered car, from chassis diagrams detailing three-rotor sports cars to various enhancements for the rotary engine itself. Company representatives had also confirmed they were trying to make a new rotary engine emissions-compliant.
If Mazda can bring the efficiency of a rotary engine to the point that it can meet global emissions targets while enhancing power delivery and fuel economy, then the dream of a rotary-powered Mazda sports car is still alive.
JPO JPO
Keyword: Mazda Working On New Wankel Rotary Engine For RX-7 Successor