Global Efficiency of Power-Split Hybrid Electric Powertrain

The development of a proper energy management strategy in hybrid electric vehicles is crucial to pursue the best balance between emissions reduction and performance. In this respect, this paper addresses a straightforward method to investigate the behaviour of the hybrid powertrain in steady-state operation in terms of speeds and torques both of the thermal engine and the electric machines. The procedure takes into account the conversion power losses in the internal combustion engine and the electric unit and the mechanical power losses occurring in the power-split transmission. This enables the calculation of a set of maps describing the global efficiency of the hybrid powertrain and the power supplied or gathered by the batteries, which can be exploited in the implementation of a proper control strategy. The proposed approach is based on a unified parametric model that enables a comprehensive analysis of any power-split transmission.