Configuration design and kinematic analysis of compound power-split mechanisms for in-wheel motor-driven electrical vehicles

• A synthesis method generated multi-mode compound planetary gear configurations for EV powertrains. • Kinematic modeling and velocity sequencing defined gear ratio limits and mode-switching feasibility. • Motor assignment and OWC integration enabled efficient torque control and mode transitions. • An input-coupled compound gear architecture was validated against patented transmission designs. • MATLAB analysis confirmed valid speed ratios and identified high-performance configuration spaces. • The designs support compact, high-torque, and energy-efficient in-wheel EV drivetrains. This study proposes a systematic synthesis and evaluation framework for compound power-split mechanisms (CPSMs) tailored for in-wheel motor electric vehicles. Unlike previous CPSM designs that focus solely on geometric feasibility, this work incorporates electric motor characteristics (specifically their high-speed, low-torque output) into the configuration analysis. The hypothesis is that valid CPSM configurations must not only meet kinematic constraints but also satisfy torque amplification and dual-input balance requirements to support compact, high-performance drivetrains. The framework evaluates a wide set of two-input planetary gear arrangements, classifies operating modes with and without a reaction link, and filters configurations based on three design criteria: (1) torque amplification, (2) feasible dual-input power contribution, and (3) practical gear ratios constrained by manufacturable tooth counts. From 32 candidate arrangements, 36 feasible speed ratio regions were identified, mapping to 22 unique CPSM configurations. Among them, 18 were verified to meet all constraints and support six major operating modes, including motor drive, charging, regenerative braking, and continuously variable transmission. Several configurations rediscover known architectures in the literature, while others represent previously undocumented but mechanically viable designs. The study thus provides both a theoretical and practical basis for advancing in-wheel CPSM technology. Future expansions include dynamic modeling, real-time control strategies, and experimental prototyping.