The latest manufacturer to develop a Wankel engine, Mazda is reintroducing it as a range extender for the MX-30 R-EV plug-in hybrid.
By Yves Maroselli
LMazda engineers never stop believing in it. After being resolved to see their beloved rotary piston engine disappear with the RX-8 coupe in 2011, they finally found an opportunity to update it, this time in the form of an extended autonomy for the MX-30 R- EV. In fact, if the concept of this engine developed by the German Felix Wankel met its prosperity in the 1960s – with the models NSU (RO80), Mazda (Cosmo then RX), and even Citroën with the GS Birotor -, since then it has been gradually abandoned due to high oil consumption leading to high polluting emissions, but also to lower thermodynamic efficiency than a conventional reciprocating piston engine.
A compact and lightweight motor
Two points where Japanese engine manufacturers announced that they have made significant progress, thanks to wider gaskets that ensure better sealing of the combustion chamber on the one hand, and on the other hand to the adoption of direct injection, which makes it possible to claim a specific consumption (per kWh produced) is reduced by 25% compared to the RX-8 block! The traditional characteristics of the rotary engine are very desirable for a range extender that rarely works: absence of vibration, compactness and lightness. So Mazda estimates that the MX-30 R-EV block, a single rotor of 830 cm3 capable of developing a maximum power of 74 hp (55 kW) at 4,700 rpm and weighing only 71 kg, is 18% more compact than a 3-cylinder engine of equivalent power. Oddly, this motor can be installed under the front bonnet of the car and in the same casing as the 170 hp electric propulsion motor (25 more than the MX-30 BEV), it cannot mechanically drive the latter and therefore will drive wheels as in the recent Honda hybrid system. It is for Mazda to retain the sensations of an electric traction chain. As a result, the rotating machine is content to turn into a generator and play the role of a simple generator.
85 km of electric range
Compared to the 100% electric version of the MX-30, the lithium-ion battery saw its capacity reduced from 35.5 to 17.8 kWh to make room for the 50-liter tank that powers the rotary engine. Therefore, Mazda presents the MX-30 R-EV as a rechargeable hybrid capable of a 100% electric range of 85 km, but also of a total autonomy of more than 600 km. The official release of CO2 according to the WLTP cycle is 21 g/km. These figures assume a relatively high consumption of the rotary engine when the battery is discharged (about 9 l/100 km, resulting from the lower efficiency of the rotary engine and its electric transmission), but again, this is a case of relatively rare use , which only occurs when the autonomy allowed by the battery capacity is exceeded. Then it is enough, depending on the circumstances, to find a service station, or an electrical outlet. Recharging can be done in 2h45 with single-phase alternating current at 7.4 kW, in 1h45 with three-phase at 11 kW, or in half an hour with direct current of 36 kW. Finally, a socket in the boot can be used to supply electrical consumers (V2L function for Vehicle Load), up to 1.5 kW. The MX-30 e-Skyactiv R-EV (that’s its full name) should go on sale in mid-2023 at a price starting at 38,250 euros, like the BEV version, but, unlike the latter, without qualifying at least some bonuses.
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