A torsion–translational vibration isolator with quasi-zero stiffness

In this paper, a torsion–translational quasi-zero-stiffness (TT QZS) isolator with convex ball–roller mechanisms was proposed to attenuate the torsion and translational vibrations along shaft systems simultaneously. The mathematical model of the isolator was established, based on which the static characteristics of the isolator were analyzed and the quasi-zero-stiffness condition that the design parameters should satisfy was derived as well. Subsequently, the isolator was integrated into a shaft system to study its dynamical performances under excitations of two independent external forces. Unique phenomenon of so-called vibration frequency–interference was observed and elaborated theoretically with harmonic balance method. In addition, the amplitude–frequency characteristics of the two degrees-of-freedom (DOFs) system subjected to two independent harmonic excitations were analyzed by employing numerical simulations. Accordingly, the small-oscillation regions of the system were determined through the jump-down frequencies. Meanwhile, the force transmissibility in the small-amplitude-oscillation region was discussed by taking advantage of semi-analytical solutions and compared with that of the corresponding linear system. The results indicated that the TT QZS isolator has extra low-frequency vibration isolation performance in both torsion and translational DOFs.