The concept, dubbed Powersplit, incorporates the storage of hydraulic liquid and gas under high pressure. A short-term additional acceleration can be activated through the coaction of a classic internal combustion engine with hydraulic elements and a pressure accumulator with pressures of up to 300 bar. By means of hydraulic liquids, the hydraulic unit compresses the gas (typically nitrogen) in a reservoir. Acting similar to a spring, the compressed gas stores energy. If the pressure accumulator is discharged it releases energy that can be used to provide additional thrust. In comparison with a conventional lithium-ion battery, the pressure accumulator features far lower capacity. However, it can be charged much faster and offers a better energy efficiency.
The concept allows several driving modes: Short distances can be driven utilizing the pressure energy alone. In this case, the combustion engine is off and the vehicle moves along without producing any emissions. On longer travels or for higher speeds the combustion engine is used. In addition, both modes can be combined; the energy stored in the hydraulic system generates a short but strong additional thrust.
Bosch and PSA believe the technology has a strong potential. Compared to a car with standard combustion engine, the hydraulic hybrid can reduce fuel consumption by as much as 30 percent. Used exclusively in urban traffic, the savings potential can even reach 45 percent. The current design aims at compact cars, however, the system can be applied to other passenger car types as well, Bosch said in a press release.