Design and Real-Time Experimental Evaluation of A Semiactive Suspension System of A Four-Wheeler With Costeffective Magneto-Rheological Damper

Abstract

The purpose of a damper in a vehicle suspension system is to isolate the vehicle body from disturbances arising from road undulations, generally referred to as ride comfort, while maintaining contact with the road at all times, generally referred to as road handling. Achieving good ride comfort and good road handling are the two conflicting criteria to be satisfied by an ideal vehicle suspension system. The viscous passive dampers, currently used in vehicle suspension systems, compromise a part of ride comfort to achieve partly good road handling in an attempt to satisfy these two criteria. A semi-active suspension system with Magneto Rheological (MR) dampers is one of the cost-effective methods to overcome the need for this compromise. The semiactive suspension system provides better control over energy dissipation by introducing a damper capable of achieving variable damping force during its operation. Although semi-active MR dampers are the cheapest option among the types of suspension systems (Passive, Active and Semiactive suspension systems), they are not the most affordable ones available in the automobile market. Hence, they can be found factory fitted only in some premium luxury cars. The work presented in this thesis attempts to develop and experimentally evaluate a cost-effective MR damper for application in a passenger vehicle while collaborating with a shock absorber manufacturer, Rambal Ltd., Chennai, India. In the research work presented in this thesis a commercial MR damper is first characterized in the damper testing machine and fitted with two mathematical models, Equivalent Damping Model (EDM) and Magic Formula Model (MFM). The two mathematical models are compared for their accuracy and computational efficiency based on the simulation response of a Quarter Car Model (QCM) with a semiactive seat suspension system. The MFM was as accurate as the EDM while being computationally efficient. Meanwhile, an MR damper was designed for application in the test vehicle, a passenger van, using a commercial MR fluid. The designed MR damper was fabricated at Rambal Ltd., Chennai. The fabricated MR damper was tested on the damper testing machine and also on the test vehicle. The results from the experiments on the damper iv testing machine revealed that the fabricated damper delivered the desired MR effect. The experiments on the test vehicle revealed improved ride comfort and road handling with the developed MR damper. The cost evaluation of the developed MR damper revealed its cost-effectiveness compared to the commercially available MR dampers. An attempt was made to further reduce the cost of the developed MR damper by designing a cost-effective MR fluid. The designing of MR fluid generally involves optimizing the composition of magnetic particles in the carrier fluid. The same was carried out in this study based on the simulation response of the full car model of the test vehicle subjected to the random road and the cost of synthesizing the MR fluid. The performance of the developed MR fluid was compared with the commercial MR fluid, MRF-132DG, on the rheometer, the damper testing machine and the test vehicle. The developed MR fluid yielded higher shear stress than the commercial MR fluid on the rheometer. Consequently, a higher damping force was achieved by the fabricated MR damper using the optimized MR fluid than the commercial MR fluid. The experiments conducted on the test vehicle with the developed MR fluid revealed its superior performance over the commercial MR fluid, indicated by higher ride comfort and road handling of the test vehicle compared to the ones achieved in previous experiments on the test vehicle. The optimized MR fluid was found to be more affordable than commercial MRF-132DG. An acceleration-based control strategy is also proposed in this work to reduce the computational load and improve the overall reaction time of the semiactive suspension system. The performance and computational efficiency of the proposed control strategy were compared with an existing control strategy based on the experimental response and simulation time, respectively, of a Single Degree of Freedom (SDOF) system with an MR damper. The proposed control strategy was both effective and computationally efficient than the existing control strategy.