A dual-flank asymmetric microgeometry modification method for coaxial gear reducers

The noise problem of coaxial gear reducers in new energy vehicles (NEVs) is worsening due to increased rotational speeds and distinct load characteristics under driving and regenerative braking conditions. This paper proposes a dual-flank asymmetric microgeometry modification (MGM) methodology for coaxial gear reducers under bidirectional torque conditions. The proposed method is developed based on a system-level rigid-flexible coupling multi-body dynamic model, in which reverse-torque-induced planet-carrier deformation, loaded meshing misalignment, and tooth-surface load redistribution are used as the physical basis for flank-specific MGM optimization. Condition-specific objectives and independent parameter sets are assigned to the drive and coast flanks, thereby integrating NVH-oriented drive-flank optimization and contact-reliability-oriented coast-flank compensation within a unified asymmetric modification framework. For the drive flank, peak-to-peak transmission error is prioritized to suppress gear whine at the excitation source. For the coast flank, load distribution and contact stress are prioritized by minimizing the face load factor and balancing the edge load ratio, thereby compensating for system deflection. A genetic algorithm is then used to optimize the modification parameters. Simulations show that under driving conditions, the peak-to-peak transmission error and system vibration response are significantly reduced after optimization. Under regenerative braking, the asymmetric modification compensates for meshing misalignment, eliminates unilateral load concentration and edge contact risks, and improves the contact stress distribution. This strategy provides a novel foundation for enhancing full-condition NVH performance and reliability of EV transmission systems.