Abstract: Structural parameters and mechanical characteristic of rubber bellows are key factors on affecting its mechanical properties of convoluted air spring(CAS). Solving the problems of structural parameters identification and rubber bellows modeling are the key ways to calculate stiffness characteristic of CAS. Taken the arc length of single convolution and effective flange radius of bead plate as the key design parameters, structural parameters models of CAS based on the key design parameters are established. The hysteresis nonlinear mechanical model of rubber bellows is constructed by adopting linear elastic model, Coulomb friction model and Maxwell fractional derivative model in parallel. Based on the above, the unified model of vertical stiffness for CAS is established. Experiments and calculations show that the maximum relative error of the four structural parameters of two samples is 12%, which proves the correctness and generality of structural parameter model of CAS. The relative error of loss energy of hysteresis loop under the excitation amplitude of 5 mm and 8 mm is less than 0.2%, the relative error of static stiffness is less than 4%, and the maximum relative error of dynamic stiffness under different frequencies is less than 1%, which verifies the effectiveness of the unified model of vertical stiffness. Finally, taking sample 1 as an example, it is pointed out that the ratio of rubber bellows stiffness to total stiffness is about 8%-14%, and the influence laws of rubber bellows on the total stiffness of CAS is revealed. The research results lay a foundation for the accurate calculation of mechanical properties of CAS in the design stage, and also provide theoretical support for structure optimization and performance matching of CAS.

Key words: convoluted air spring, unified model of vertical stiffness, structural parameters, rubber bellows