A Comprehensive Study of Propulsion Torque Distribution for a Parallel Hydraulic Hybrid Heavy Bus

Abstract

The purpose of this paper is to improve the fuel economy of a parallel hydraulic hybrid heavy bus. And an optimal distribution strategy of the propulsion torque was proposed based on engine working points of the conventional bus. The universal characteristics map of the engine was divided into three zones by the optimal operating line and the fuel contour CBF. The results indicated this strategy can not only overcome the low energy density disadvantage of the accumulator but also prohibit frequent switching between the engine and the pump/motor. The HHP can provide most of the required torque and make most working points of the engine around or on the optimal operating line. When the value of the fuel contour CBF is 213g/kw.h, the bus has the minimal fuel consumption in the typical urban bus cycle and the fuel economy of the engine improves 24.8% compared to the conventional bus.