Hydraulic hybrid technology is already used in commercial trucks that travel at lower speeds and experience lots of starts and stops. Now, the PSA Peugeot Citroën Group plans to offer hydraulic hybrid cars in 2016, a first. It calls it technology ‘Hybrid Air’ because it uses compressed air for energy storage rather than the nitrogen gas usually used in hydraulic hybrid trucks. Hybrid Air was developed by PSA Peugeot Citroën in collaboration with Bosch.
The Hybrid Air’s powertrain adjusts automatically to one of three modes – Hybrid Air, Gasoline, or Combined – depending on driving conditions. The system uses a gasoline engine, hydraulic motor/pump, and an energy storage system consisting of two hydraulic units and their pressure accumulators. Power from the engine and motor/pump is transmitted to the wheels via an automatic transmission. A smart control system adapts the operating mode to the driver’s commands and optimizes energy efficiency in the three different modes.
The hydraulic pump/motor unit recovers energy generated by the gasoline engine and from braking and deceleration. Energy is stored by pumping hydraulic fluid into the high pressure storage tank and by compressing air in the tank. When power is required in the Hybrid Air or Combined Hybrid Air modes, the high pressure hydraulic fluid powers the motor/pump driving the wheels. Afterward, the now-low pressure hydraulic fluid is stored in a low pressure reservoir.
For continuous highway driving, the engine alone powers the car. At speeds of less than 43 mph (70 km/h), the vehicle switches to the motor/pump for zero-emission operation. When more power is required at lower speeds or when the compressed air energy storage needs topping off, the system will run in Combined Hybrid Air mode.
Initially, PSA plans to use the system in its B segment super-mini models like the Peugeot 208 and Citroen C3, and C segment compacts like the Peugeot 308 and Citroen C4. It will also be used in the group’s light commercial vehicles. Its advantages over hybrid electric vehicles include being more cost-effective, robust, and service-friendly.
A distinct advantage is that this Hybrid Air system is expected to provide fuel savings of 45 percent in city driving and increase a vehicle’s range by 90 percent compared to conventional engines, while offering the same horsepower. In urban driving, Hybrid Air-powered vehicles can run on air power alone for 60 to 80 percent of the time. When used in standard body styles such as the Citroen C3 and Peugeot 208, the system achieves combined fuel consumption of 81 mpg.