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The main purpose of this research is to reduce the transmitted engine vibration to the subframe structure via improving the mobility of engine mountings. In fact, the main focus is on the geometry optimization of the subframe part, implementing the design of experiments method, to increase the dynamic stiffness of the part to reduce the vibration transfer function in the mountings location. In order to perform the optimization process, the front end model of the reference vehicle including the suspension, steering system, engine and deriveline system is generated in FE software. According to the prevalent guidelines, the mobility of engine mountings should be greater than target value which is usually obtained through benchmarking. To do so, some structural parameters that are apt to influence on the mobility function, e.g the section of subframe, thickness of subframe and vehicle body are selected as design variables for doing the design of experiments analysis.

Nowadays, outer surface design of passenger cars is not just a matter of styling and safety but air flow around car body and exterior accessories has significant effect on fuel consumption, performance and dominantly on the wind noise. In recent years, passenger comfort is one of the most challenging and important automotive attributes for car makers. Controlling the turbulence eddies that causes aerodynamic noise can remarkably affect passenger's comfort quality. Identification of aerodynamic sources is considered as the first step in order to control the wind noise. In this research, computational fluid dynamics method is applied to simulate the wind flow around the car and the investigation of aerodynamic noise pattern is performed by numerical method which is the most prevalent way that is used by auto industries.

One of the main safety criteria of a passenger car is the accurate and stable lateral response of suspension system in severe handling manoeuvres. This behaviour can dramatically change as a result of compliances in mountings of suspension system. In other words, alteration in suspension alignment dimensions, as a result of handling forces in a cornering manoeuvre, can change rear axle installation angle and consequently it negatively affects lateral stability and understeering behaviour of car. In this research, this defect is investigated in an available passenger car and behaviour of the system is improved by optimising stiffness and installation angle of bushings of rear axle. It is noteworthy that although stiffening axle bushes can increase lateral stiffness of rear axle it is a matter of trade-off between ride and handling performances of vehicle.