Design, Analysis, and Experimental Validation of a Variable-Gap Magnetorheological Damper for Seat Suspension

To address the dual challenges of routine driving vibration and impact loads in vehicle seat suspensions, a novel variable-gap magnetorheological damper (VGMRD) is proposed. By combining a tapered piston with a conformal variable-diameter cylinder, stroke-dependent, dual-mode damping characteristics are achieved without the need for complex control valves. A theoretical model incorporating the stroke-dependent gap flow dynamics is established, and a finite element analysis of the internal magnetic field distribution is conducted. Numerical results indicate that the magnetic flux lines are concentrated by the converging geometry of the buffer zone, increasing the magnetic flux density by 17.4% without additional power input. Experimental validations utilizing a servo-hydraulic testing system are performed, and the experimental results show good agreement with the theoretical predictions. Specifically, the damping force remains stable within the damping zone. As the piston enters the buffer zone, the damping force increases significantly with displacement. Through the passive self-reinforcement mechanism, the peak damping force is effectively elevated from 2240 N in the damping zone to a maximum of 4296 N. These findings demonstrate the reliability of the proposed VGMRD in preventing mechanical “bottoming-out” while maintaining routine ride comfort.