Abstract

From the point of view of suspension damper, semi-active dampers with only minimal power requirement could be applied to achieve variable damping to enhance suspension performance under complex vibration and shock environments. Magneto-rheological (MR) fluid based dampers offer significant potential for realizing semi-actively controlled variable damping with only minimal power. The MR-fluid dampers invariably exhibit considerable hysteresis, while the damping force varies with the intensity of applied electro-magnetic field and the nature of vibration in a highly nonlinear manner. A simulation model based on symmetric and asymmetric sigmoid functions is developed to fully characterize the properties of a MR-damper as function of excitation and control current. A comprehensive laboratory test program is undertaken to characterize the damping properties of a MR damper under wide ranges of excitations and control current. The essential fundamental features are identified for the modeling task, while the model parameters are identified using multi-parameter error minimization techniques. The validity of the proposed generic model is thoroughly examined by comparing the model response with the measured data under a wide range of excitations, particularly the force saturation and the hysteresis behaviour. An independent current function is further derived that could be integrated to reported regression-based hysteresis models to enhance their prediction abilities. From the results of the study, it is concluded that the refined Bouc-Wen and the proposed generalized sigmoid function model can fully characterized the nonlinear MR damping behaviour as function of applied current and excitation. A nonlinear analytical model of a pneumatic suspension seat including the motion limiting stops is developed for synthesis and analyses of the MR-damping control algorithms. The validity of the passive suspension seat model is thoroughly examined under various deterministic and random vibration excitations of varying intensities. The results suggest that attenuation of shock as well as vibration imposes difficulties design compromise of the passive damper. Owing to the strongly nonlinear properties of the suspension-seat and the MR-damper, such as hysteresis, saturation and end-stop impacts, a 'hi-lo' semi-active control algorithm is synthesized to realized modulation of the control current and thus the damping force following the skyhook control law. A continuous modulation function is further synthesized and integrated to ensure smooth transition between the 'hi' and 'lo' states. A relative position control is further introduced to limit the frequency and severity of shock motions caused by end-stop impacts. A set of performance measures is proposed to assess the characteristics of the semi-active and the resulting integrated controller under a wide range of excitations, including deterministic excitations of continuous and transient nature and random excitations of different vehicles. The potential performance benefits of the controller design are further investigated through a hardware-in-the-loop test and simulation program. The results are used to demonstrate the validity of the MR-damper and suspension seat models, and effectiveness of the control algorithm