The Chevrolet Volt may be the most famous car in the world, but, since it doesn’t quite exist yet, we still know very little about it.

Sure, it is driven by an electric motor and has a small internal combustion engine on board to generate electricity after the primary battery is drained, but how it goes about its business doing all of that is still a mystery.

A few journalists have been given the opportunity to drive prototypes of the Volt, but only in full electric mode. The general consensus that they’ve come away with is that it drives just like electric cars have been driving for over a century now, and there’s nothing new to report there. What the world really wants to know is what happens after the first 40 miles when the battery runs out of juice. Does the engine operate at a set speed, feeding the electric motor with a constant stream of energy, or does it work more like a car with a continuously variable transmission, where the engine tries to stay at a few set points in its rev range, depending on instantaneous power needs?

It’s going to be a while before General Motors lets anyone find out, and it’s probably tweaking the process as we speak, but FOX Car Report recently had the opportunity to drive a car that is very similar to the Volt in design, and what we learned is very enlightening.

The Mazda Premacy Hydrogen RE Hybrid may be the most advanced minivan in the world. Based on the Japanese market version of the Mazda5, the test vehicle uses a series hybrid powertrain similar to the one in the Volt, except that it’s not meant to run in pure electric mode for long distances. Instead, it carries a much smaller battery, and uses a rotary engine like the one in the Mazda RX-8 that has been modified to run on clean-burning hydrogen, as well as gasoline.

Like most traditional hybrids, at low speeds the Premacy RE can toddle about like an electric car, but give it some gas - either kind - and the rotary quickly kicks in. When it does, it follows throttle inputs similar to a regular car, revving the engine linearly to provide power on demand. Mazda says this method fits with the company’s Zoom Zoom ethos, giving drivers the kind of immediate power delivery they are used to.

Based on the experience, however, it would seem that without a charged, high-capacity battery acting as a buffer, the engine needs to operate at a much higher speed than normal most of the time, which would get tiring over time as it can be very loud. That said, the Mazda is still very much a work in progress.

Running on hydrogen, the Premacy RE is a zero-emissions vehicle, with a range of about 120 miles between fill-ups. The major drawback is that the 150 liter pressurized tank is enormous, taking up most of the space where a third row of seating usually goes, while the battery pack located under the second row bench encroaches on foot room. Also, the size of the hydrogen fueling infrastructure around the world is still limited, at best, which is why Mazda chose to make the Premacy a dual-fuel vehicle. Tri-fuel if you count the electricity. A 25 liter gasoline tank provides the vehicle with an additional 240 mile range, and the ability to refuel at any gasoline station.

Taking everything into consideration, the Premacy RE is a very drivable car, with reasonable performance that’s nearly on par with the conventional Mazda5. A small number of them are being made available for lease in Japan, though there are no plans for series production at this point. Until the hydrogen infrastructure expands, the vehicle will remain one with limited appeal, though it’s not impossible that the series hybrid design could be developed for more mainstream Mazdas, without the hydrogen-burning capability of the internal combustion engine.

Throw in a battery with a larger capacity and Mazda may just have a potential competitor for the Chevy Volt on its hands. But since that car doesn’t quite exist yet...

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