Potentials to Reduce the Energy Consumption of Electric Vehicles in Urban Traffic

By means of a parameter study using a detailed backwards facing model of the longitudinal vehicle dynamics, the design of the transmission ratio in battery electric vehicles (BEV) is analyzed for different driving cycles and it is shown that the electric consumption in urban operation can be significantly reduced by up-speeding the electric machine (EM) using a high 1st transmission ratio. But this potential currently remains unused in fixed-speed BEV due to various additional driving requirements of extra-urban driving with higher vehicle speeds. For this reason, multi-speed BEV are further investigated as a solution to the conflicting design objectives. An additional parameter study for multi-speed BEV with two transmission ratios shows further potentials for the reduction of electric consumption both in urban and extra-urban driving scenarios. Furthermore, the more complex "Two-Drive-Transmission" (TDT) concept is investigated as a multi-speed BEV powertrain with two downsized EMs instead of one high-power EM and it is compared with the other BEV variants using a comparative optimization approach. The TDT uses low-cost and energetically efficient shifting devices based on the technology of an automated manual transmission with simple dog clutches without friction surfaces, allowing shifting without interruption of traction force. Dynamic programming is applied as operational strategy for all simulations considering shifting losses to achieve a benchmarking of the potentials of fixed-speed and multi-speed BEV.