French giant PSA Peugeot Citroen has revealed a new hybrid drivetrain concept - a 'Hybrid Air' drivetrain that combines a conventional petrol engine with a compressed air-propelled hydraulic motor.
Shown at the recent PSA Innovation Day at its France Technical Centre, the idea of compressed-air-propulsion is hardly new - Tata has been hard at work in development of its purely air-fuelled Mini CAT city car for India.
Despite several years of development, the Mini CAT is yet to reach the market, and PSA’s Hybrid Air concept has more mainstream ambitions.
According to PSA’s demonstration video, the system uses high and low pressure air-tanks to send compressed air to a front-mounted hydraulic pump, in turn powering a hydraulic motor that harmonises with the petrol engine through an epicyclic transmission.
In practice, the system is designed to behave like a conventional hybrid vehicle, with the petrol engine used mainly for high speed cruising, the hydraulic motor for stop/start driving (up to 69km/h), and the two combining up hills or under heavy acceleration.
Also similar to a conventional hybrid, the air supply can be regenerated by reversing the hydraulic motor under braking or coasting downhill, returning air to the storage tanks.
The Hybrid Air drivetrain was fitted to an existing Citroen C3 light car for demonstration, and PSA suggests that fuel economy of 2l/100km is possible in such a vehicle.
Significantly, the Hybrid Air concept drivetrain adds just 100kg to the vehicle’s kerb weight - considerably less than a conventional motor/battery hybrid system - and promises to be less expensive to boot.
PSA currently equips several Peugeot and Citroen models with its Hybrid4 diesel- electric drivetrain overseas, but suggests a production version of the Hybrid Air concept could be available as soon as 2016.