On-Board Powerplant Numerical Optimization of Internal Combustion Engines in Series Hybrid-Powertrains

Abstract

Serial-hybrid-powertrains in extended-range electric vehicles (E-REV) pose different requirements to internal combustion engines (ICE) than conventional vehicles. In E-REVs ICEs are not used for propulsion but for battery charging and cabin heating. This work deals with the design of ICEs in serial-hybrid-powertrains. It considers different operating strategies as well as the dimensioning of the electric components of the powertrain and the thermal management. Therefore, a longitudinal dynamic model was developed using GT-SUITE including the ICE and the thermal management. The engine was operated on a test bench in parallel to create the necessary maps for the numerical investigations. Due to the high amount of parameters that can be optimized when determining the operating strategies and dimensioning the components, by a numerical optimization method that was developed and customized for this problem. The numerical investigations showed that for higher vehicle speeds the direct propulsion of the ICE is more efficient while for lower speeds the operation of the ICE as a generator is the more efficient strategy. Additionally, the influence of the ambient temperature on the efficiency was taken into account. At low ambient temperatures it is necessary to heat up the driver’s cabin electrically. Using a thermal numerical model it was possible to show the dependency on the energy consumption, the component dimensioning and the configuration of the operation strategies. The most favourable powertrain setup and the most efficient operating strategies were achieved by using the described numerical optimization method. The new and comprehensive approach was to consider the entire vehicle including mechanical components, thermal components and operating strategies in the numerical model setup and the holistic optimization of them using self-developed numerical optimization software.