Citroën Debuts Oddly Brilliant Hybrid Air Powertrain, Production Version Coming [2013 Geneva Auto Show]

Gasoline-electric hybrids have floundered near-dead in the waters of Europe, not least because of their added expense or fuel-economy that fails to better that of the small, diesel-powered cars that populate the Continent. But Citroën might have a something on its hands that could change Europeans' perception of hybrids, and it's—drum roll, please—a hybrid. It's not just any hybrid, though—instead of combining an internal combustion engine with an electric motor, Citroën's Hybrid Air powertrain utilizes a hydraulic motor and a gas engine. The French automaker is showing the system in a chopped-up C3 hatchback at the 2013 Geneva auto show. Although it sounds massively complicated and exceedingly strange, Hybrid Air, in fact, isn't very complex. Here's how it works: A planetary gearbox is sandwiched between the gasoline engine and a hydraulic motor. The hydraulic motor is powered by—you guessed it—a hydraulic pump that's also located under the C3′s small hood. As for what powers the hydraulic pump, well, this is where the "Air" part of Hybrid Air comes in. The prototype C3 features a pair of tanks, one mounted longitudinally down the middle of the car and another "low-pressure" unit sitting transversely behind the rear axle. The rear tank stores compressed air, which can be piped into the central tank or, more appropriately, chamber, which is initially filled with hydraulic fluid. During acceleration, the air (which likely inflates a bladder within the main tank) is released, forcing the fluid through the hydraulic pump and into the motor, driving the wheels. Although Citroën doesn't specify, there most likely is a reservoir tank where the hydraulic fluid is stored after it cycles through the motor.  Like most other hybrids, the Citroën has a regenerative braking system to capture energy that would normally be lost during deceleration. Unlike gas-electric hybrids, which recharge their batteries via an electric motor/generator, the C3′s hydraulic motor, when turned by the drive wheels, draws hydraulic fluid out of the reservoir tank and pumps it back into the main tank. (Hydraulic motors are essentially pumps; simply switch its output to its input—in this case, the drive wheels—and it turns into a pump.) As hydraulic fluid is forced into the chamber—the fluid is not compressible—the displaced air in the system is compressed into the rear tank where it is stored until needed again. A prototype hydraulic-hybrid delivery truck cooked up by UPS, the EPA, and several truck makers here in the U.S. operates similarly; during acceleration an engine powers a hydraulic pump that turns two motors mounted in series, but on deceleration the motors turn the pump, forcing fluid against a nitrogen-filled bladder and pressurizing it; later, the pressurized fluid is released back into the system to drive the motors during acceleration.  Besides the unique method by which the Citroën's gas-engine-augmenting hydraulic motor receives its energy, the relationship between the motor and the engine is like that in any gas-electric hybrid. This means that at higher speeds, the gas engine does most of the motivation. At lower speeds (less than 43 mph) or taking off from a stop, the system punts accelerative duties to the hydraulic motor, unless there isn't a sufficient amount of compressed air, at which point the gas engine either takes over or aids the motor. The engine and hydraulic motor can each power the front wheels individually, or combine forces to move the C3, depending on what the car's computer deems necessary. Instrumented Test: 2012 Toyota Prius C Comparison Test: 2012 Chevrolet Volt vs. 2012 Fisker Karma EcoSport Instrumented Test: 2013 Tesla Model S Citroën claims total output from the Hybrid Air powertrain stands at 120 horsepower, and that the setup improves fuel economy by up to 45 percent in city driving. Factoring in a mix of highway driving, the automaker maintains Hybrid Air is still good for a 35-percent bump in efficiency. The improvements are impressive, but not outrageous compared to, say, a Prius. What is impressive is that Hybrid Air doesn't require a plug or several hundred pounds of batteries; the air tanks and hydraulic gear certainly add weight, but likely not hundreds of pounds. Plus, air tanks' capacity doesn't degrade over time like batteries' energy storage, and likely won't fluctuate with temperature extremes, either. Perhaps more intriguing than Hybrid Air's inner workings is that Citroën plans to introduce the technology in a production B-segment car by 2016. According to the automaker, the system can even be scaled to power larger C-segment vehicles, as well. Without question we look forward to testing this new frontier in hybridization. from Car and Driver Blog http://blog.caranddriver.com

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