Study on the coupling vibration mechanism and amplitude-frequency modulation characteristics of electromechanical composite transmission system used in HEV

With the automotive industry transitioning toward electrification, electromechanical composite transmission (EMT) system have emerged as a new-generation powertrain solution for heavy-duty vehicles. The incorporation of permanent magnet synchronous motor (PMSM) in EMT system not only significantly enhances off-road mobility, fuel efficiency, and dynamic response performance but also introduces novel electro-mechanical-magnetic coupling characteristics. And the electro-mechanical-magnetic coupling characteristics may induce coupled vibrations, thereby affecting the overall operational performance of the EMT system. Therefore, it is crucial to elucidate this coupling mechanism in EMT system. This study develops an EMT dynamic model based on Lagrange-Maxwell equations that incorporates multiple nonlinear factors including current harmonics, time-varying mesh stiffness, gear backlash, and transmission errors. Furthermore, a characterization method for the machine-electricity-magnet coupling interface is innovatively proposed. Subsequently analytical expressions for coupled vibration signals are derived by integrating coupling interface model and Amplitude-Frequency Modulation (AFM) analysis, thereby elucidating the underlying electro-mechanical-magnetic coupling mechanisms among multiple physical fields. Ultimately, the AFM laws are validated by numerical simulations and experimental tests based on the developed model and derived expressions. The results demonstrate that coupled vibration signals from the mechanical subsystem and electrical subsystem exhibit asymmetric sidebands around their respective carrier frequencies—gear meshing frequency and electrical frequency—modulated by component rotational frequencies. The revealed AFM mechanism provides a theoretical foundation for excitation source decoupling, vibration suppression strategy formulation, and EMT system optimization.