In-wheel motor vehicles are gaining attention as a new type of electric vehicle due to their efficient power units located inside each wheel hub. However, they are more susceptible to wheel resonance due to the increase in unsprung mass caused by the motor's weight. This can result in decreased both the ride comfort and driving stability. To resolve this issue, this study aims to apply an optimal switching controller with a semi-active n actuator; magnetorheological (MR) damper. For the implementation of the optimal switching controller, a road type classification is also carried out. An acceleration sensor is used for road type classification, and control logics include a ride comfort controller; the linear quadratic regulator (LQR _Paved Road) and a wheel motion controller (LQR_Off Road) for improved driving stability. For paved roads, the LQR_Paved Road control input is applied to the MR damper. However, if a road type prone to wheel resonance is detected, the control logic switches to the LQR_Off Road. During the transition, a weighted average of both LQR_ Paved Road and LQR_Off Road control input is applied to the actuator. Computer simulations are undertaken to evaluate vibration control performance, including the ride comfort and driving stability at various road profiles.

Magnetorheological (MR) fluid is recognized as one of intelligent materials that is widely used for various kinds of controllable devices since its rheological characteristics can be controlled by an external magnetic field (or input current). However, the density mismatch of the compositions between iron particles and carrier oil leads to inevitable sedimentation. Therefore, many works on the sedimentation problem of MR fluids have been carried out to improve the sedimentation stability using appropriate additives, surfactants, nanoparticles, particle coating as well as using several carrier oils with different densities. However, a study on the effect of the current magnitudes and profiles on the sedimentation is considerably rare. This study experimentally investigates the sedimentation behaviors due to the different current magnitudes and different profiles such as square and sine wave. It is shown that average sedimentation rate is 98.61% by applying 1 A of the square wave, while it is 97.83% under the sine type of the current. It is also identified that the higher intensity of the applied current results in stronger electromagnetic which can slow down the sedimentation rate. The results presented in this work are very helpful in designing a controller which provides the input current in terms of the magnitude and profile configuration.