Research on Efficiency Improvement of Automotive Transmission Systems

This review article examines research on efficiency improvement in automotive transmission systems. Current studies in this field categorize transmission energy losses into three main sources: mechanical components (such as gears, bearings, seals, and lubrication- related friction), electromechanical coupling systems (including motors, power electronics, and energy conversion interfaces), and losses arising from control and management strategies at the system level. Among these, the third category remains comparatively underexplored, with significant opportunities for further investigation — particularly in areas such as predictive control, thermal management, and real-time optimization under dynamic driving conditions. Furthermore, a substantial body of literature focuses on torque and rotational speed as key control variables, operating on the premise that system-level efficiency can be enhanced through optimized coordination of these two parameters under varying operating conditions. By synthesizing findings across these areas, this review highlights both established approaches and research gaps, with the goal of guiding future work toward more holistic, integrated efficiency strategies in nextgeneration transmission systems.