Electric mobility may be economically efficient today. Battery-based electric drives can be applied efficiently in urban buses, for instance. Frequent acceleration and slow-down processes as well as a high utilization rate in short-distance traffic make their use profitable even when considering current battery costs. Karlsruhe Institute of Technology (KIT) has developed an e-city bus demonstrator to illustrate the concept.
The key modules of the demonstrator are a drive train with a high-torque electric motor, a high-voltage network, a battery management system, and a novel modular battery system with lithium-ion cells made in Germany.
The battery system consists of flat modules that can be stacked to reach the dimensions and electric characteristics desired. Various spaces in the different types of vehicles can be used for accommodating the energy storage system. The battery management system and drive control developed for the KIT demonstrator allow for driving operation taking into account the current performance limits of the system and its components.
By means of recuperation, braking energy is converted into electrical energy again. The drive consists of a low-torque engine supplying a high driving torque for the vehicle. The engine is connected directly with the differential gear of the rear axle. It decreases the gear reduction to be implemented and, hence, ensures a high efficiency of torque transmission.