BMW is developing an ultra-efficient plug-in hybrid vehicle as a rival to the Volkswagen XL1 diesel plug-in hybrid.

At least, that's what patent images filed by BMW in China purportedly show.

The images show a sleek-looking vehicle that vaguely resembles a hatchback, with some noticeable BMW design cues.

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Originally thought to depict a hydrogen fuel-cell vehicle, they in fact represent a plug-in hybrid "research vehicle" being developed by the German carmaker, reports Autocar.

The images--which were reportedly submitted to a patent office in Shanghai earlier this year--are of BMW's answer to the VW XL1, an anonymous insider said.

Unlike the tiny XL1, though, the BMW is intended to be more practical. It will feature seating for four, and a more usable amount of cargo space.

Patent drawing for BMW plug-in hybrid research vehicle - Image via Car News China, PC Auto

Patent drawing for BMW plug-in hybrid research vehicle - Image via Car News China, PC Auto

Consequently, the BMW will be an estimated 355 kilograms (782 pounds) heavier than the XL1, at 1,150 kg (2,535 pounds).

Yet BMW also apparently expects its vehicle to be more aerodynamic than the VW. It will reportedly have a drag coefficient of 0.18, compared to the VW's 0.19.

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The powertrain will consist of a front-mounted 1.0-liter turbocharged two-cylinder engine, working with a rear-mounted electric motor.

The car will also reportedly feature a battery pack that takes advantage of a "newly-developed chemical process" that allows for greater energy density and faster charging.

Patent drawing for BMW plug-in hybrid research vehicle - Image via Car News China, PC Auto

Patent drawing for BMW plug-in hybrid research vehicle - Image via Car News China, PC Auto

All of its adds up to a claimed 706 mpg combined, albeit on the somewhat optimistic European driving cycle.

A 0 to 62 mph time of under seven seconds and a top speed of 112 mph are claimed as part of the package as well.

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The car's designation as a "research vehicle" implies that it will not be offered for sale, although Volkswagen sold a handful of XL1 production models to customers.

Even if the car doesn't go into production, though, elements of its powertrain or its radical styling could transition to future BMW plug-in cars.

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