Bi-exponential model and inverse model of magnetorheological damper for the semi-active suspension of a capsule vehicle

The capsule vehicle is a new transportation system that travels in a sub-vacuum tunnel at a speed of about 1000 km/h, and adopts the electrodynamic suspension type levitation system. Accordingly, although it differs according to the driving speed, the vibration of capsule vehicle is expected to be greater than that of the wheel/rail type high-speed rail vehicles. Therefore, a method of applying a semi-active control technique using an MR damper as a secondary suspension of a capsule vehicle to improve passenger comfort is being studied. When performing semi-active control using an MR damper, the most important thing is to determine the current for the MR damper. However, it is difficult to determine the appropriate current for the MR damper because of the hysteretic characteristics of the MR damper. In this study, a practical model named the Bi-exponential model is presented for the application of semi-active control using MR dampers on a capsule vehicle. This Bi-exponential model well reflects the hysteretic characteristics of the MR damper, which makes it easy to obtain the inverse model for determining the current supplied to the MR damper. The semi-active control performance of the Bi-exponential model was evaluated by simulation and a HILS experiment, taking into account the vertical motion of a 1/4-car capsule vehicle. Also, the Bi-exponential model has been validated against the performance of the most commonly used Bouc-Wen model. As a result, the Bi-exponential model showed better hysteretic characteristics of MR dampers compared to the Bouc-Wen model. Furthermore, despite the simpler model compared to the Bouc-Wen model, the semi-active control performance of the Bi-exponential model was found to be better.