Power Losses Minimization for Optimal Operating Maps in Power-Split HEVs: A Case Study on the Chevrolet Volt

Antonella Castellano,Marco Cammalleri

doi:10.3390/app11177779

Abstract

The power-split architecture is the most promising hybrid electric powertrain. However, a real advantage in energy saving while maintaining high performance can be achieved only by the implementation of a proper energy management strategy. This requires an optimized functional design before and a comprehensive analysis of the powertrain losses after, which could be rather challenging owing to the constructive complexity of the power-split transmission, especially for multi-mode architecture with multiple planetary gearing. This difficulty was overcome by a dimensionless model, already available in the literature, that enables the analysis of any power-split transmission, even in full electric operation. This paper relies on this approach to find the operating points of the internal combustion engine and both electric machines which minimize the total power losses. This optimization is carried out for given vehicle speed and demanded torque, by supposing different scenarios in respect of the battery capability of providing or gathering power. The efficiency of the thermal engine and the electric machines is considered, as well as the transmission mechanical power losses. The aim is to provide a global efficiency map that can be exploited to extract data for the implementation of the most suitable real-time control strategy. As a case study, the procedure is applied to the multi-mode power-split system of the Chevrolet Volt.

Highlights

In the last decades, stricter environmental policies undertaken against increasing global warming have encouraged the spreading uptake of hybrid electric vehicles
The focus of this paper is to provide the global efficiency map of the multi-mode Chevrolet Volt hybrid electric powertrain by assessing all powertrain losses, those occurring in the propulsors and the transmission mechanical power losses
The only reason to let the internal combustion engine (ICE) work at lower speeds is to recharge the battery if possible (SOC = FREE or state of charges (SOCs) = 0)

Summary

Introduction

Stricter environmental policies undertaken against increasing global warming have encouraged the spreading uptake of hybrid electric vehicles. The power-split layout combines the benefits of both series and parallel hybrid, resulting in a highly flexible system where the internal combustion engine (ICE) is kinematically decoupled by the wheels due to the operation of the electric unit. Two electric machines act as an active continuously variable unit (CVU), which can provide additional power for vehicle propulsion or gather the ICE power in surplus for battery recharging. Multi-PG PSU enables the minimization of the electric machines’ power size by deploying a multi-mode power-split continuously variable transmission (PS-CVT), where some clutches operations lead to several constructive arrangements to select under the desired driving conditions [6,7,8,9,10]. The more complex the transmission constructive layout is, the trickiest the identification of the occurring power flows is [11,12,13], as well as their management [14,15,16,17]

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Conclusion