Development of Shift Function for a Clutchless Unsynchronized E-Transmission for Commercial Vehicles

There will be a market for electrified medium and heavy commercial vehicles in the future. A multi-speed transmission enhances the output torque and the maximum speed compared to single-speed or direct drive configurations. Alternatively, a smaller motor with less output torque can be used while maintaining the same performance. Additionally, the drivetrain can be operated more close to the sweet spot of highest efficiency.
For commercial transmissions, cost aspects and a short duration of the torque
interruption during the shift process have high priority. Therefore, most of the
conventional heavy good trucks use automatized shifted transmissions.
These demands are followed by the Oberaigner ECV 2-speed transmission for
electric drives. The transmission allows to omit mechanical clutch and
synchronisation unit by a smart shifting process. The smart shift consists of a shifting logic, a spring-decoupled actuation and a shifting mechanism similar to a dog clutch with failsafe architecture. The synchronisation is realized by speed control of the drive motor. To minimize shifting time and wear and to optimize comfort, an observer algorithm for shock-free and direct teeth-on-gaps meshing of the shift sleeve was developed. The predictive algorithm can be further applied e.g. to detect inclines ahead to initiate a necessary downshift earlier to minimize vehicle speed losses. The shifting logic and its parametrization were mainly developed on a function test bench for electric drives a Graz University of Technology.
The presentation shows the principles and challenges of the shift mechanism and
shift logic. The key parameters for short shift duration, maximum comfort and
minimum wear of the mechanism will be discussed.