Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, analyzing and suppressing the MR-damper hysteresis effects, therefore, impose a great challenge. A quarter-vehicle MR-suspension model is formulated in conjunction with proposed hysteretic and mean MR-damper models, and the passive and semi-actively controlled MR-suspension systems are focused to investigate the influence of MR-damper force hysteresis. The semi-actively controlled MR-suspension employs the “on-off” control law in response to direction of the damper velocity, so as to generate the asymmetric damping force property form the symmetric MR-damper design. The results show that the MR-damping hysteresis yields serious transients and oscillations in responses for the semi-actively controlled MR-suspension than the passive MR-suspension due to the current-switching discontinuity, and would thus deteriorate the suspension performance. The undesired strong transients and oscillations in responses can be effectively suppressed by employing the proposed smooth technique without phase shift for modulating the command current discontinuity.
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