2-Speed Transmission for E-Drives without Mechanical Synchronization and Clutch

Authors

C. Kneissl BSc, Univ.-Prof. Dr. P. Fischer, Graz University of Technology; Dr. J. Schmid, Ing. P. Stögmüller, Dr.-Ing. H. Bauhoffer, Oberaigner Powertrain GmbH, Nebelberg: 

Year

2021

Print Info

Production/Publication ÖVK

Summary

Transmissions of electric vehicles and drivetrains mostly have one fixed gear ratio. These low-cost and space-optimized gearboxes take advantage of the wide speed range of the electric motor. However in many cases it is necessary to extend the speed and climbing ability of the vehicle. This can be realized e.g. with additional electric axles which are disconnected at higher speeds or with gear boxes with several gear stages. With multiple gears, off-road vehicles or commercial trucks which need high speeds but also high tractive force or crawling capabilities can be realized. At the same time the efficiency of the complete system can be optimized by operating the electric drive at better operating conditions. This leads to an improvement of mileage for fully electric vehicles or a reduction of battery and motor sizes. On the other hand, additional weight of the transmissions and a higher complexity of the system have to be accepted. Also a control unit for gear switching is needed. This paper discusses advantages and disadvantages of single and two speed gearboxes for electric drives and presents the cost and package optimized two-speed transmission for commercial vehicles developed by Oberaigner Powertrain GmbH. Test results which have been recorded at the functionality test bench at the Institute of Automotive Engineering, TU Graz (FTG) are shown. Instead of a mechanical coupling and synchronizing unit, a claw-type coupling is used for cost, weight and packaging optimization. The gears are synchronized by a highly dynamic control of the electric motor in combination with the gearbox shift actuator. For optimized behaviour the shift logic detects the overlap of the clutch teeth and sets the timing for a shock free and ratched-free shift operation.

Number of pages

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