Exploration of Optimal Powertrain Design Using Realistic Load Profiles

Abstract

The electrification of bus-based public transportation contributes to the goal of reducing the adverse environmental impacts caused by urban transportation. However, the penetration of electric vehicles has been slow due to their lower vehicle range and total costs in comparison to vehicles driven by internal combustion engines. By improving the powertrain efficiency, the total costs can be reduced for the same vehicle range. Therefore, this paper proposes a holistic design exploration approach to investigate and identify the optimal powertrain concept for electric city buses based on the component costs and energy consumption costs. The load profiles of speed, slope, and passenger occupancy profiles are derived for a selected bus route in Singapore, which is used in a powertrain design exploration for a 30-passenger vehicle. Six different powertrain architectures are analyzed, together with single and multi-speed gearbox configurations, to identify the optimal powertrain architecture and the resulting component sizes. The powertrain configurations are further analyzed in terms of their influence on the vehicle characteristics and total costs. Multi-motor configurations were found to have better vehicle characteristics and lower total costs in comparison to single rear motor configurations. Concepts with motors on the front and a rear axle could shift the load points to a higher efficiency region, resulting in lower energy consumption and energy costs. The optimal powertrain concept was a fixed-speed two-motor configuration, with a booster motor on the front axle and a motor on the rear axle.

Development of a parametric packaging and sizing tool for autonomous electric bus system

“…The tool shows the driving cycle, driving and powertrain losses incurred, battery energy consumption and recuperation, overall efficiency of the powertrain and the efficiency maps of each motor. Based on the results of previous works from the authors 16,20 the tool allows users to choose between different all-wheel drive configurations with multiple motors. The multiple motor architectures distribute the load between the motors and optimise their operation.…”

“…The implementation of the powertrain component sizing within the tool is based on the validated simulation model from the author’s previous work. 16…”

“…Pathak et al 16 conducted a holistic design exploration to identify the optimal powertrain configuration for electric city buses. Figure 6 shows the framework of the powertrain component selection.…”

“…The energy consumption and the powertrain cost are further calculated. The results of Pathak et al 16 and Krapf et al, 20 showed that the overall efficiency of the powertrain is strongly influenced by the load points resulting from the driving resistances, and multiple motor configurations were found to have better vehicle characteristics in addition to lower energy consumption, in comparison to the single rear motor configuration.…”

“…Within the tool, it is possible to choose from four different powertrain variants for each vehicle concept. Based on the results from Pathak et al, 16 there is the possibility to select one or two motors per axle and a total range of 300 km or 400 km for the vehicle, as shown in Figure 7.…”