Analysis of Subharmonic Torsional Resonance in Powertrains with Two-Stage Spring Isolators

A vehicle powertrain system with a two-stage spring isolator separating a combustion engine from a transmission can exhibit significant nonlinear dynamics if the input torques cause the spring to continuously alternate between its first-stage and second-stage stiffnesses. In particular, this nonlinearity can result in subharmonic resonance of the system’s natural frequencies at half the frequency of the engine’s primary excitation order. A 1D torsional vibration model was prepared using Siemens’s Simcenter Amesim software to study these nonlinear vibrations. First, a correlated vehicle-level model was developed to replicate a half-order torsional resonance that was measured in a test of a research vehicle. Then, simplified theoretical models were used to study and demonstrate the sensitivity of this kind of subharmonic resonant response to changes in mean input torque level, amplitude of input torque oscillation, first-stage capacity of the spring isolator, and other factors.