Extended engine-in-the-loop simulation for development of HEV energy management strategies

Abstract

Development and evaluation of energy management strategies(EMS)for hybrid electric vehicles (HEV) in early development phases is challenging. For precise analysis at this early stage, internal combustion engine (ICE) operation has to be reproduced as close as possible to its future in-vehicle use. This paper describes the development of an Engine-in-the-Loop (EIL) system as a tool for research of advanced HEV EMS. The presented EIL system is capable of executing torque controlled ICE starts as performed in Full and Plug-in HEV. To extend the functionality of the EIL system, access to any control unit is realized and actual engine states can be fed into simulated EMS. By this EMS gets access to any information about ICE such as temperatures or in-cylinder pressure signals. This results in maximum flexibility for HEV EMS development and experimental validation with the real ICE is possible. To demonstrate the capability of the EIL system, the development and evaluation of an EMS considering ICE temperature is presented. While state of the art EMS use engine data measured at warmed up conditions, extended electric driving in HEV can prevent the ICE to reach its optimal operating temperature. To set the ICE torque correctly for the respective temperature, a new temperature dependent EMS, based on the Equivalent Consumption Minimization Strategy (ECMS), was developed. Through the extended EIL approach, the simulated EMS can access the actual ICE temperature in real-time and determine the optimal torque distribution. For scenarios under constant low ICE temperature, EIL validation shows fuel saving potentials of up to 3%. A reduction of around 1% is evident even when the ICE temperature is taken into account during standard ICE heating up.