Improvement of Citybus Fuel Economy Using a Hydraulic Hybrid Propulsion System - A Theoretical and Experimental Study

The paper describes the application of a hydraulic pump/motor and a hydro-pneumatic energy-storage as a supplement to the conventional internal combustion engine in a city bus.

The resultant hybrid-system makes it possible to smooth out the combustion engine power output and to regenerate the braking-energy which in conventional busses dissipate as heat.

Computer-simulation and supplementary experiments with a model-system have shown that, depending on the driving pattern of the bus, this type of hybrid-system would lead to a 10 - 30% fuel saving provided that an appropriate control strategy is used.