Design and Development of a Modular Motor-Gearbox-Unit for an Electric Light Vehicle Research and/or engineering questions / objective Small and cost-effective electric light vehicles of the L6e-B class or similar can make a significant contribution to the traffic transition towards climate friendly mobility. Within the scope of a research project, such a vehicle is being built as an experimental vehicle. For this purpose, a modular motor-gearbox-unit (MGU) is to be developed, which makes it possible to use different electric motors with different torque-speed characteristics in the vehicle. A synchronous reluctance machine without the use of rare earth elements is to serve as the basic motor, which is to be adapted and constructed for the required performance class. Methodology For the development of the MGU, the first step was a situation analysis and problem delimitation. For this purpose, the performance data of other vehicles in this class, such as a Renault Twizy, were analyzed. In addition, a simulation model of the vehicle was built with a focus on the drive system. Subsequently, the required torques and driving power for driving through the WLTC Class 2 driving cycle were determined simulatively. Based on these findings, requirements for the motor and the transmission were defined. In the next step, alternative technical solution concepts were developed for the transmission, which were then compared on the basis of evaluation factors such as availability, costs and required design space. After the evaluation, the synchronous belt transmission proved to be the most favorable concept, which is why it was designed and manufactured. The compliance with the requirements was validated and verified on a test bench. Results It has been shown that a single-wheel drive on the rear axle offers the greatest potential for the vehicle. For this reason, two symmetrical MGUs were created as part of the project. To provide the mechanical power, a synchronous reluctance machine was successfully scaled down from 60 kW to 3 kW power and converted to an air-cooling concept. Subsequently, the motors were fabricated. In addition, programmable power electronics were designed and fabricated. Due to the use of a two-stage synchronous belt gearbox, it is possible to allow a variable gear ratio of the gearbox and thus compatibility with other motors. The gearbox is designed in such a way that 14 different ratios between 5.54 and 7.71 can be set by means of 7 different toothed pulleys. The synchronous belt allows a backlash-free load reversal, which allows a pleasant recuperation of the vehicle. Limitations of this study The focus of the project is on light vehicles. Due to the relatively low performance of these vehicles, it is possible to use a transmission technology such as synchronous belt transmissions that does not play a role in larger vehicle classes. In addition, an air-cooled electric motor is not practical for a series application due to its large dimensions. However, the underlying technology is the same. What does the paper offer that is new in the field in comparison to other works of the author? The conception and development of an MGU with the claim of the greatest possible modularity to various electric motor technologies is new and has not been published by the authors before. Furthermore, the authors are not aware of any lightweight vehicles with synchronous reluctance machines. Conclusion As part of this project, a modular motor-gearbox-unit (MGU) was designed and developed for use in an electric light vehicle. The aim was to develop a transmission that allows a variable gear ratio and can thus be driven by different electric motors. For the development of the MGU, the first step was an analysis of the state of the art for drive systems of such vehicles. Based on this, a simulative design of the motor and gearbox could be performed. Several technologies were evaluated and compared. A synchronous belt gearbox was developed due to the advantages for this application.
Mr. Jonas Freyer, Research Associate, Karlsruhe Institute of Technology (KIT) - Institute of Product Engineering (IPEK)