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the vehicle, which may be due to a variety of sources like road surfaces irregularities, aerodynamic forces, vibrations of the engine and transmission. A strong demand for good suspension system exists to mitigate the vibrations that are being transmitted from road surface to the vehicle body. Vehicle suspension system is responsible for isolating the vibrations of the vehicle body to achieve ride comfort and safety. A good ride comfort requires a soft suspension, whereas a hard suspension is required for carrying heavy loads. A good handling of vehicles requires a suspension system which makes better trade-off between two abovestated criteria [1]. To fulfill these conflicting requirements, a fully active or semi-active suspension system is preferred over a conventional passive suspension system. Active suspension system possesses inherent drawbacks as it necessitates large power requirement to drive external energy source. The cost of suspension system will be high and complex and difficulties arise while implementation of control hardware. Semi-active suspension system combines the advantage of the active suspension in terms of improved vehicle performance and the robustness of the passive suspension, without requiring large power source [2]. In semi-active suspension, the amount of damping can be tuned in real time. The variation of damping may be achieved by varying the viscosity of the fluid under the influence of electric or magnetic field. Electrorheological (ER) and MR dampers are semi-active control devices that use ER and MR fluids to produce controllable damping force. MR fluids are similar to ER fluid, but MR fluids are 20-50 times stronger than ER fluid and it can be activated from low-voltage power supply (less than 10 V and 1-2 A). MR fluids are far less sensitive to contamination and extreme temperature (150 °C and higher). Butz and Von [3] presented an overview on properties of MR and ER fluid. Also, the various Abstract This paper presents ride comfort and road holding analysis of passive and semi-active suspension system using quarter car model. Semi-active suspension system with magnetorheological (MR) damper was modeled as non-parametric model-based magnetic flux density in the fluid flow gap. The skyhook control strategy was used to analyze semi-active control performance. The simulation of passive and semi-active suspension system was carried out under random road profile for different velocities. The result shows that semi-active suspension has significant improvement in terms of ride comfort and road holding of vehicle than passive suspension system. Experimental studies have been conducted to characterize MR damper and a good match is observed between results with simulation results obtained using non-parametric model.

A magneto rheological (MR) fluid damper offers cost effective solution for semiactive vibration control in an automobile suspension. The performance of MR damper is significantly depends on the electromagnetic circuit incorporated into it. The force developed by MR fluid damper is highly influenced by the magnetic flux density induced in the fluid flow gap. In the present work, optimization of electromagnetic circuit of an MR damper is discussed in order to maximize the magnetic flux density. The optimization procedure was proposed by genetic algorithm and design of experiments techniques. The result shows that the fluid flow gap size less than 1.12 mm cause significant increase of magnetic flux density.

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This study assesses the dynamic performance of the semi-active quarter car vehicle under random road conditions through a new approach. The monotube MR damper is modelled using non-parametric method based on the dynamic characteristics obtained from the experiments. This model is used as the variable damper in a semi-active suspension. In order to control the vibration caused under random road excitation, an optimal sliding mode controller (SMC) is utilised. Particle swarm optimisation (PSO) is coupled to identify the parameters of the SMC. Three optimal criteria are used for determining the best sliding mode controller parameters which are later used in estimating the ride comfort and road handling of a semi-active suspension system. A comparison between the SMC, Skyhook, Ground hook and PID controller suggests that the optimal parameters with SMC have better controllability than the PID controller. SMC has also provided better controllability than the PID controller at higher road roughness.