Recovering the braking energy and reusing it can significantly improve the fuel economy of a vehicle which is subject to frequent braking events such as a city bus. As one way to achieve this goal, pneumatic hybrid technology converts kinetic energy to pneumatic energy by compressing air into tanks during braking, and then reuses the compressed air to power an air starter to realize a regenerative Stop-Start function. Unlike the pure electric or hybrid electric passenger car, the pneumatic hybrid city bus uses the rear axle to achieve regenerative braking function. In this paper we discuss research into the blending of pneumatic regenerative braking and mechanical frictional braking at the rear axle. The aim of the braking function is to recover as much energy as possible and at the same time distribute the total braking effort between the front and rear axles to achieve stable braking performance.
This paper presents an analysis of vehicle behaviour through different bus drive cycles and during braking events and compares two configurations of pneumatic hybrid braking system. The respective configurations, a parallel hybrid brake system and a fully controllable hybrid brake system, are described and the control strategy presented and discussed. Finally the fully controllable hybrid braking system is chosen as the main topic for further research.
A pneumatic hybrid braking optimization simulation model has been built in the MATLAB/Simulink to facilitate an investigation of an optimum air tank pressure for energy recovery. Based on the optimization result, a new control strategy is implemented with a baseline simulation model to explore the benefits of the new control strategy. The results demonstrate that the energy recovery efficiency can be enhanced relative to the baseline vehicle performance and the pneumatic hybrid technology can significantly reduce the fuel consumption of city bus.