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In the design of an automobile, an important consideration is to minimize the amount of “boom” noise that the vehicle occupant could experience. Vehicles equipped with four cylinder engines can experience powertrain boom noise in the 40 to 200 Hz frequency range. Boom noise can also be generated by road input, and it is just as annoying. In this paper, a CAE methodology for predicting boom noise is demonstrated for a vehicle in the early design stage in which only 3-D CAD geometry exists. From the CAD geometry, a detailed finite element (FE) model is constructed. This FE model is then coupled with an acoustic model of the interior cavity. The coupled structural-acoustic model is used to predict acoustic response due to powertrain inputs. As a part of the detailed design process, various design modifications were considered and implemented in the vehicle system model. Many of these modifications proved successful at reducing the boom levels in the vehicle.

A new simulation-based method for design of powerplant mounting systems is presented. Unlike traditional methods, in which the objective is to obtain a set of powerplant rigid body modes found from experience to be favorable, this new method directly seeks minimal response in the vehicle passenger compartment, regardless of what powerplant modes are obtained. Therefore, the simulation objective exactly matches the design objective: minimal response. The new method, which uses optimization based on response sensitivities, has been implemented into software. Results show that the final response levels are significantly reduced from the baseline, and that typically the final mounting configuration is much different, and better, than the mounting system that would have resulted from application of the traditional method. POWERPLANT MOUNTING is one of the fundamental design characteristics of a motor vehicle.