The working principle of overrunning spring clutch is analyzed and the movement and dynamics character of variable cross-section spring clutch combining process are revealed.Based on the establishment of overrunning spring clutch finite element model and loadings of boundary conditions

the law of spring expansion and the stress of contact in combining process are analyzed.The distribution characteristics of contact force on spring/shell and the combining time of clutch are obtained

as well as the following-speed characteristics of output and input shells.At the same time Mises stress of the radial point and the stress between spring inner ring and arbor in non-steady state and steady-state process is showed.A basis for the structure parameters design and failure analysis of the clutch are provided in this research.