Abstract

Whole body vibration in operational vehicles can cause serious musculo-skeletal disorders among the exposed workers. Consequently, considerable efforts have been made to protect vehicle operators from potentially harmful vibration. This thesis was aimed at the development of a semi-active suspension seat equipped with a magneto-rheological (MR) fluid damper. A damper controller was synthesized to minimize the vibration transmitted to the seated body and the frequency of end-stop impacts, which is known to induce high intensity vibration or shock motions to the seated occupant. A suspension seat was modeled by considering the kinematic non-linearity due to the cross-linkages and the damper link, while the cushion characteristics were linearized about the operating preload. The force-velocity properties of the MR damper were modeled by piecewise polynomial functions of applied current on the basis of the laboratory-measured data. The kineto-dynamic model of the suspension seat was thoroughly validated using the laboratory-measured responses under harmonic excitations in the 0.5 to 10Hz range. The performance characteristics of the passive suspension seat model were evaluated under different vehicular excitations in terms of frequency-weighted rms acceleration, vibration dose value (VDV), seat effective amplitude transmissibility (SEAT) and VDV ratio. These performance characteristics are also evaluated under amplified vehicular excitations in order to investigate the frequency as well as the potential suppression of end-stop impacts. The controller synthesis was realized in two stages: (1) attenuation of continuous vibration; and (2) suppression of end-stop impacts. Two different algorithms were explored in the first stage synthesis, which included a sky-hook control algorithm and a relative states feedback control algorithm. Each algorithm was further utilized in two different control current modulations. The performance potentials of each control synthesis were investigated using the 2 MATLAB Simulink platform under harmonic, transient, and random vehicular excitations in terms of SEAT and VDV ratio. One controller design (overall best suited for implementations) was subsequently implemented in a hardware-in-the-loop (HIL) test platform coupled with a MR-fluid damper mounted on an electro-hydraulic actuator that was linked to the HIL simulation platform. The semi-active suspension seat performance characteristics were further evaluated under different excitations using the selected control scheme. The results showed that the selected control scheme yielded SEAT and VDV ratio reductions in the 5 to 30% range depending upon the nature of excitations. The implementation of the second-stage controller, which was tested only by simulations, entirely eliminated the occurrence of end-stop impacts at nominal vibration level and attenuated the end-stop impact severity of three times amplified excitations by up to 10% . The results further suggested that the use of MR-fluid damper in suspension seat was most beneficial to city buses and class I earth moving vehicles amongst the selected inputs.