Air-powered cars are a familiar source of amusement within the green car fraternity, an ideal example of a concept that would be wonderful if it worked, but simply isn't viable in the real-world.

Up until now, the compressed air car has been... well, a load of hot air.

Undeterred, French automaker PSA--owner of both Peugeot and Citroen--is approaching air from a different angle--as a replacement for battery power in hybrid vehicles.

PSA currently makes a small range of through-the-road hybrid vehicles, from the beautiful Citroen DS5 Hybrid to practical Peugeots like the 3008 HYbrid4 and 508 RXH.

These use a diesel engine to power the front wheels, and a battery-fed electric motor to assist via the rear wheels--varying the input of each drivetrain depending on driving conditions.

The new "Hybrid Air" concept is a little different.

The car's main source of power remains an internal combustion engine, albeit powered by gasoline rather than diesel.

But instead of using batteries to supply additional power, or zero-emissions driving when needed, the concept instead uses a compressed air tank mounted in the central transmission tunnel to turn a hydraulic motor.

In regular highway driving, the car uses the internal combustion engine alone. Ask for more power for acceleration or hills, and high-pressure air can be called upon for extra shove--the power of both engine and motor being fed through an epicyclic transmission, not dissimilar to that on a Prius.

In city driving and at speeds of up to 43 mph, where less power is required and emissions-free driving is a priority, the air can work on its own. The air tanks are filled under braking or deceleration, where the motor draws in air and compresses it for future use.

The concept is based around a small, light weight city car. In this format, combined economy of up to 117 mpg is suggested.

The system also makes some sense on smaller cars, where the weight of heavy batteries would normally offset some of the advantage of a regular hybrid drivetrain. It's also cheaper--equally important on small cars.

PSA expects to have the first running prototypes by 2016.


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