Citroen releases more information on Hybrid Air technology

The new technology was hinted at last month (coverey by our own Nic Zart) and has now been given a name and model number for its conceptual debut at the Geneva Motor Show next month.

The Citroen C3 will showcase the technology as a cut-away mule and display chassis. Peugeot Citroen's aim is to create a hybrid powertrain that improve driveability and economy, lowers costs of production, has a global appeal, and leverages their long-time collaboration and inroads with the Indian car market and Tata Motors. The result is the Hybrid Air powertrain system.

The C3 concept combines a standard small vehicle and gasoline power plant with the compressed air propulsion technology that Tata Motors has been perfecting for years along with the hydraulic systems that Citroen is known for in Europe with its commercial machines. The result is a highly efficient urban runabout that is propelled by the petrol engine, but utilizes the assisted/regenerative braking of air and hydraulic compression to store energy and then release that energy to help move the vehicle forward again, taking weight off the engine and thus conserving fuel.

The basic idea is not new, though the addition of compressed air is an interesting twist. Garbage trucks and similar vehicles that do a lot of stop-and-go driving here in the States have been utilizing a hydraulic hybrid system built by Eaton Fuller for a couple of years now. The trucks use hydraulic motors on their drive shafts to stop, compressing hydraulic fluid into frame-mounted tanks. When the driver presses the accelerator to begin moving again, the pressurized hydraulic fluid turns the motor the opposite direction, helping propel the big truck forward. This saves tremendously on both brake wear and fuel use, often cutting fuel consumption by over 30% and nearly doubling brake shoe life.

Citroen's idea will have a similar effect on a small vehicle, though the payoffs will likely be smaller due to the lower amount of stop-and-go the average car has in comparison to a work truck like a refuse collector or delivery van. Still, Citroen believes that they can reduce gasoline fuel consumption by up to 45% for urban driving and CO2 emissions by the same. Were the car a diesel, consumption would likely be lowered by closer to 25% given the energy density and fuel use difference between the two engine types.

To perfect the system, Citroen Peugeot turned to long-time partner Bosch and old Citroen designs dating from 1955 when experiments on a 2CV hybrid concept came to fruition in 1958 in a air and hydraulic pressure-assist powertrain. Talk about the perfect platform for this tech!

How Citroen's System Works
The Hybrid Air system utilizes a PureTech petrol engine, a compressed air storage cylinder, a hydraulic pump/motor and an automatic transmission with an epicyclic gear train. This is all maintained by an intelligent electronic management system as part of the car's power control module. The PCM switches between systems as efficiency and availability dictates, optimizing output. It monitors the charges in the air and hydraulic systems and releases them as needed.

The prototype car is capable of traveling up to 43 mph on just compressed air (Air Mode) in much the same way a plug-in car travels on pure electricity for short distances. The hydraulic motor and control box turns the drive wheels the same way an electric motor does so in the plug-in. With common city stop-and-go traffic, Citroen estimates that Air Mode will be active 60% or more of the time.

The car is also capable of running only from the gasoline engine, of course, and for long-distance driving, this will be the main option. In Combined Mode, the car can run on a hybrid combination of both, including at high speeds and during strong acceleration. The compressed air can assist by up to 90 kW, which means the tiny engine will seem like a much larger unit much the same way the engine in a car like the Prius c seems too small to be putting out the kind of energy it does.

The primary benefits of the Citroen Peugeot Hybrid Air system is its cost effectiveness. For the markets it's aimed for (International urban buyers), it will offer huge fuel savings without the added hybrid premium. The system is cheap to implement, easily achievable with current technology, and robust. While electric hybrids have a given battery failure rate, the lifetime of the Hybrid Air system is beyond that of the vehicle itself. It's also easily recycled and does not encroach on cabin space.

An interesting and innovative plan from Citroen here. Well worth keeping an eye on. Its debut at Geneva will be on March 5 with a follow up the next day.