Mazda files patent for a capacitor-based, in-wheel motor hybrid AWD, possibly rotary

More news that Mazda’s signature rotary engine is making a return. Previously, it was speculated that Mazda’s upcoming SkyActiv-R rotary engine will return only as a small capacity range extender engine, used to charge a series hybrid’s or an electric vehicle’s battery.

The idea of a rotary engine being the primary source of motion in a car today is pretty much out of the question because the inherent nature of rotary engine means that it will not pass today’s exhaust emissions regulation.

Or so we thought. Reports have emerged that Mazda have filed a patent for a capacitor-based, all-wheel drive hybrid vehicle with in-wheel electric motors.

The general idea behind the powertrain is that a front-mounted combustion engine will send power to the rear wheels, while a combination of lightweight, small capacity lithium-ion battery and capacitors will drive a pair of electric motors mounted on each individual front wheels.

What’s drawing attention is that the patent says the combustion engine can be of various configurations, from piston-type Vs to in-lines, as well as a rotary engine.

To keep emissions low, obviously the rotary engine can no longer work in the same way as an RX-7 and RX-8. Electrification is necessary.

The concept of in-wheel electric motors is not new. Mitsubishi Motors and Nissan have produced various concepts using such solutions. The benefits are obvious – significantly sharper handling thanks to precise control of torque vectoring. However none of such concepts have made it production because it was just too complex, too expensive, and too heavy.

Mazda’s solution is to offset the weight penalty by using a lighter, smaller capacity lithium-ion battery, supplemented by capacitors, which are a lot smaller and lighter than batteries.

Recall that Mazda already have a lot of experience with energy storing capacitors in the Mazda 6’ i-ELOOP.

Another method of reducing weight outlined in the patent is to run the electric motor at a higher voltage, and if you recall your basic physics lessons, power (P) equals Voltage (V) x Current (I). In other words, for the same power output, a setup with a higher voltage requires less current, and with lower current, cable thickness can be reduced, thus reducing overall weight of the high voltage power cables required.

This is easier said than done as it requires multiple inverters to convert between the battery and capacitors’ DC output into AC input for the motors. Mazda’s patent listed three inverters. How does this not negate any weight saving benefits is something only Mazda engineers can answer.

The new powertrain will most likely be introduced in a production version of the Mazda RX-Vision Concept.