Mazda's Complex Plug

Aug 30, 2023

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Earlier this month, news broke about a very interesting hybrid concept Mazda put into some patent applications. Instead of building an EV or even a regular plug-in hybrid, the company is looking into building a much more complex electrified machine. But, it wasn’t long before EV fans started bagging on it.

EVs: simplification ✅🙏

meanwhile, Mazda:

k let’s wildly mix drivetrains, three different electric motors and a rotary engine, and add a swappable hybrid battery to the mix!

because…why not, I guess 🤷‍♂️https://t.co/r7b7WJaZG6

— stekkerauto 🚗⚡️ (@stekkerauto) August 7, 2023

In this article, I want to explain what Mazda’s doing, why it is doing it, and why it’s a better solution (but only for a couple of niche applications). EV fans are both right and wrong about this because it’s an apples-to-oranges comparison.

At first glance, the idea looks a lot like a typical plug-in hybrid. In this case, three electric motors work in tandem with a rotary engine to produce power and run the car. But, this is where Mazda takes a turn into left field.

Instead of having one permanently-mounted battery pack that provides the juice for local driving, the patent calls for multiple removable battery packs, which look a lot like batteries you’d find in a Gogoro electric scooter. The system then combines the power from the packs and either boosts or lowers the voltage depending on driving needs at any given time.

The end result is a plug-in hybrid with somewhere around 3.7 kWh of battery capacity, but which can be swapped out in just a couple of minutes at a station or at home. That might not sound like much, but let’s keep in mind that Mazda’s drawings depict it being installed in something small like a Miata, so the range could be enough for 3oish miles of local driving.

But, given that we’re looking at something like a Miata, the real point could be to have enough juice for a few runs at the track, followed by a quick battery swap for more fun. And, really, that’s what this kind of a system could excel at.

At this point in the EV adoption effort, you’d think the sensible move would be to just make a small BEV and be done with it, but the biggest problem is one of power density.

A 33.7 kWh battery pack theoretically can hold the same amount of energy as a gallon of gasoline, but trying to compare batteries to gallons of combustion fuel isn’t fair to the EV. A gas-powered car wastes around 3/4 of the energy making waste heat instead of mechanical energy to move the vehicle down the road, while the EV uses up to 90% of the energy. But, a 33.7 kWh battery pack is a LOT bigger and heavier than a gallon of regular unleaded.

So, despite the efficiency, an EV still needs somewhere between 500 and 3000 pounds of battery pack to give enough range for the driver’s transportation needs. It could be even more for medium and heavy duty trucks.

There are ways that EVs can make up for this. Electric motors are relatively small and light, so there’s no big and heavy ICE engine in a BEV. A single-speed gear reducer also cuts back on extra weight compared to a multi-speed transmission. Other innovations, like structural battery packs, can help compensate for the extra weight of the battery pack. The end result is that some EVs are pretty close in weight to comparable ICE cars.

Sadly, though, this can’t happen in every vehicle category. Relatively heavy luxury ICE sedans and SUVs are within striking distance of an optimized EV’s weight, but when you go to the smallest and lightest vehicles, like a two-seat roadster vehicle, you’re facing a completely different challenge.

Mazda could probably build a small vehicle the size of a Miata with a couple hundred miles of range, but it would be a whole lot heavier than a Miata. Would it be a fun car? Sure. It might even be a performer on the drag strip. But, on a track with turns, the disadvantages would immediately become obvious.

Human laws can be violated, perhaps with some man-made consequences if you get caught doing it, but the laws of physics are a little more hard-nosed. More weight means more inertia, and when the vehicle’s tires try to force all that extra weight to change directions, the big battery pack is going to try to drag the vehicle off the side of the pavement.

The all-electric version of the Miata will be a blast in the straight sections, but the gas Miata will eat it for lunch in the curves.

While a lightweight track gas car like the Miata can be a lot of fun in the curves, there’s no denying that a little four-pot gas engine can be severely lacking in torque compared not only to big V8s, but especially compared to a modern electric vehicle. There’s got to be a way to have your cake and eat it too, right?

A hybrid is one way to do this (use liquid fuel to store energy, and electric motors to deliver it), but Mazda is trying to wring out even more of the advantages from both sides here.

For weight, a small battery pack is just the beginning. They’re also pulling more power out of the small pack by boosting voltages using innovative electronics, which means more torque delivery than is usually possible with so few battery cells. Then, on top of that, they’re avoiding a heavy and complicated piston engine and accompanying transmission, instead using a compact and lightweight rotary engine.

But, at the same time, they’re also trying to get as many advantages of EVs as they reasonably can given the weight requirement. Hot-swappable battery packs can make limited range much less of a problem and possibly even allow apartment dwellers to lug the batteries indoors for home charging overnight. Road trips would probably still happen on gas power, but if they offered vehicles with more modules, road trips using swapping could also be a possibility.

But, the biggest advantage is getting low-end torque, some higher-end horsepower, light weight in the turns, and thus great overall track or canyon performance.

Does this still sound like far too much complexity? You’re right. This patent concept probably isn’t the right drivetrain tech for 90% of people. The average commuter doesn’t want to deal with swapping little battery packs, maintaining a rotary engine, or any of that nonsense. Most people who even want a fun car probably don’t need this kind of specialized performance. Being able to nail the run from 0-40 at a traffic light from time to time is enough for most of us.

But, if you’re one of the few people looking for something only a small and light canyon-carving car like the Miata could provide, this is a great solution.

Featured image provided by Mazda.

Jennifer Sensiba is a long time efficient vehicle enthusiast, writer, and photographer. She grew up around a transmission shop, and has been experimenting with vehicle efficiency since she was 16 and drove a Pontiac Fiero.She likes to get off the beaten path in her "Bolt EAV" and any other EVs she can get behind the wheel or handlebars of with her wife and kids.You can find her on Twitter here,Facebook here, andYouTube here.

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