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A Breath of Fresh Air for the Hybrid Vehicle

David Alexander — January 31, 2013

Source: PSA Peugeot CitroënWhile hybrid technology has recently taken a back seat to plug-in and all-electric vehicles, it is nice to see the spirit of innovation is still alive in the automotive industry.  On January 22, 2013, PSA Peugeot Citroën held an Innovation Day at its Automotive Design Network R&D center in Vélizy, France.  Among a number of other announcements, PSA unveiled its Hybrid Air technology, the result of a 2-year secret project with strategic partners Bosch and Faurecia that has resulted in the filing of more than 80 patents.

The system works in a way that is very similar to most parallel hybrid cars on the market today, such as the Toyota Prius.  Instead of an electric motor/generator there is a hydraulic motor/pump, and the battery storing electrical energy is replaced by a tank that stores the energy as compressed air.  The system can capture kinetic energy via regenerative braking and reuse it to supplement the conventional engine, thus maintaining vehicle performance while allowing the engine to run in its most efficient mode.  The system should be capable of moving the vehicle from a standing start, but the energy capacity of about 150 kilojoules (kJ) will not allow prolonged driving on air storage alone.  PSA estimates that the vehicle can be driven 60% to 80% of the time in zero-emissions mode, on average, in city traffic.

Hydraulic hybrids (using liquid rather than air) have also been under development for many years, though so far only heavy truck applications have been put into service in small numbers, mainly in refuse collection trucks.  A demonstration SUV was shown at the 2004 SAE World Congress.  The size of the pump and storage tank has always been a challenge for installation in smaller vehicles, with the efficiency of the motor typically lower than its electric competition.  PSA has clearly managed to overcome these issues, and announced that Hybrid Air technology will be fitted on B-segment models (potentially the Citroën C3 or Peugeot 208?) starting in 2016.  Undoubtedly the historic expertise of Citroën engineers with hydropneumatic systems was invaluable.

The big challenge for hybrid and electric vehicles is currently the cost of battery energy storage, and the air hybrid offers a low-cost alternative.  However, this approach will only work in a hybrid; the required size of an air tank to store enough energy for significant zero-emission driving will be prohibitive, making a pure air-powered vehicle impractical.  In that sense, the pressurized air cylinder is really more of an alternative to an ultracapacitor than a battery.  In addition to being lower in cost, the system should be much more robust than a battery and not suffer from any performance degradation over time.

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