High-Efficiency Zone Design for Multi-Row Planetary Gear Transmission of Hybrid Electric Vehicles

To overcome the efficiency degradation caused by independently designing transmission ratios and evaluating mechanical losses in hybrid electric vehicle drivetrains, this study proposes a unified transmission ratio–efficiency coupled modeling and optimization framework for multi-row planetary gear transmissions. An improved kinematic model based on topological analysis is integrated with a refined multi-source loss model that captures meshing, bearing, churning, and windage losses. The resulting nonlinear coupled system is solved using a Newton–Raphson method with adaptive step-size regulation, enabling accurate prediction of speed distribution, torque balance, and efficiency under varying operating conditions. An enhanced Multi-Objective Particle Swarm Optimization (MOPSO) algorithm is further introduced to identify high-efficiency zones and optimize key structural and lubrication parameters. Bench-test verification—including efficiency MAP measurements, thermal endurance tests, and dynamic response evaluations—shows that the proposed model achieves a mean efficiency prediction error of 1.38% and maintains stable thermal and transient performance. The optimized design increases high-efficiency zone coverage from 68.5% to 78.6% and raises comprehensive efficiency from 92.8% to 95.6%. The results demonstrate that the integrated framework offers a computationally efficient and engineering-viable solution for the systematic design and optimization of planetary gear transmissions.