A new rotary MR damper applicable to a semi-active suspension system featuring a low level between road surface and floor

This study presents a rotary magnetorheological (MR) damper for a suspension system of low floor vehicles (LFVs) where a large stroke cannot be achieved due to the space constraints of damper motion for special purposes. As is well known, MR dampers are highly suitable for the semi-active suspension systems, which show controllable damping force by an external magnetic field. One of the crucial geometrical parameters to achieve high damping force at the same magnetic field is the suspension stroke in conventional linear MR dampers developed or proposed so far. However, LFVs which include purpose-built vehicles (PBVs) and future smart mobilities, do not have enough space for the linear MR damper installation. Due to the confined space in LFVs, the shape of the MR damper and the magnetic circuit design need to be carefully devised to achieve the target damping force. In addition, the time delay of the MR damper which affects suspension performance should be considered in the modeling and control processing. In this work, the time delay caused by increased inductance is resolved using the Smith compensator, which is integrated into the control system to mitigate the time delay, ensuring effective real-time control. The target control range and operating angle were decided through mathematical modeling and simulation, followed by the prototype fabrication and the measurement of the field-dependent damping force characteristics of the rotary MR damper. Subsequently, a quarter-car suspension model with the proposed MR damper is established to evaluate the suspension performance of LVFs. It is shown from the control simulation that the ride comfort (ISO 2631) is enhanced by up to 21%, while the velocity response is reduced by up to 52% under smooth (ISO B-Class) and rough (ISO D-Class) road profiles, respectively. The results presented in this work are useful guidelines for future smart mobilities featuring the space confinement between floor and road for damper installation in the development of the semi-active MR suspension system.