Design methodology of input and output-split hybrid electric vehicles for searching an optimal configuration

Abstract

In spite of outstanding performance of power-split hybrid electric vehicles (PS-HEV), designing and controlling them are non-trivial. For example, twenty four configurations can be generated from one planetary gear-set (PG) and four components (an engine, two electric machines, and a vehicle wheel), and there exist more than thousand ways of connecting two PG and four components. Furthermore, in order to find an optimal configuration and its PG ratio and final drive (FD) ratio, which satisfies both high fuel economy and fast acceleration time, is a challenge. In this paper, a systematic configuration searching methodology is proposed to find an optimal single PG PS-HEV configuration for multiple requirements

the fuel economy and the acceleration performance. First, twenty four configuration are incorporated into a compound lever design space and thus the configuration design spaces can be modelled in a virtual lever dynamic equation with feasible PG and FD ratios. That is, the discrete design spaces are put into continuous virtual lever design space. Multi-objective optimization problem, which is formed with the two performance metrics, is solved by mapping performance data of each single PG PS-HEV design onto “fuel economy - acceleration time plane”. From the results, many alternative single PG PS-HEV designs which outperform PRIUS design in both performance perspectives are depicted. Among the design candidate pool, the new single PG PS-HEV design, which can potentially be developed into a novel PS-HEV powertrain, is easily sought. (e.g. design which performs higher acceleration performance at the expense of fuel economy: 6.22 sec faster acceleration and 0.14 km/liter decreased fuel economy)