Refining Pickup Cabin NVH Quality via Optimising Exhaust Mountings Using DOE Method

In this research the main focus is on reducing the transmitted engine vibration through exhaust line to the passenger cabin in a light commercial vehicle. The main approach is firstly to locate the mountings of the exhaust system based on the results of the modal analysis. Afterwards, the stiffness of the rubber hangers is optimised to minimize the measured vibration in the driver seat rail position. The optimisation approaches are executed considering the design of experiments method.

To achieve this, the partial BIW model of the reference vehicle and the powertrain system is generated in FE software. The FE model of the exhaust system is validated by experimental results. In order to define the optimum stiffness for the exhaust rubber hangers, design of experiments method is used. The main candidate parameters for DOE analysis are exhaust rubber hangers in the front floor region in addition to the exhaust flexible joint stiffness. Dynamic parameters which have the most effects on reduction of vibration transfer function have been chosen based on the type of the joint and vibration transfer path. The selected parameters are involved in the optimisation loop to optimise the passenger cabin vibrations. Eventually, in order to evaluate the effect of the proposed modifications on the transmissibility function between the exhaust pipe line and body structure, results of the original and modified mountings are simulated and compared in the developed FE model of the body structure and powertrain system by measuring the seat rail vibration in the driver position.