The aim of this study is to design, implement and investigate the use of a Magneto-Rheological (MR) equipped Hydro-Pneumatic suspension system to solve the ride versus handling compromise of off-road vehicles. This suspension technology makes use of MR fluid viscosity changes which are induced by a varying magnetic fields and this viscosity change serves as the basis for changing the suspension system�s damping as well as the stiffness characteristics. The primary focus of the study is to improve the response time characteristics of an existing prototype system through the use of a more comprehensive design methodology. Once an optimised MR valve has been designed, the system must be manufactured and experimentally tested under known conditions. It was observed experimentally that the new prototype valve does exhibit significantly improved electrical response characteristics while also realising the working principles of the 4S4. Further experimental work showed that this suspension technology�s response characteristics cannot be further improved by improving the magnetic responsiveness of the MR valve as the responses are inherently limited by a MR fluid chain build-up delays. This said the observed response characteristics of the system was proved, through simulation based studies in Chapter 7, to be fast enough to achieve improved vehicle dynamics through semi-active suspension control. Once the newly designed MR valve�s characteristics had been experimentally extracted in Chapter 5, a comprehensive physics based model was developed to predict the output characteristics of the full MR4S4 in Chapter 6, which is defined by the non-linear and complex interrelated elements within the system. This physics based model was validated against a complete set of test data, after which it was implemented on a quarter-car based vehicle dynamics study in Chapter 7 to estimate the achievable vehicle ride comfort and handling contribution of the MR4S4 suspension system under both passive and active control. This study documents the validated approach to design, model and test a MR based MR4S4 system as well as details the research performed to determine whether the MR4S4 can serve as a viable suspension technology.
Dissertation (MEng)--University of Pretoria, 2018.