Tech Papers

[02] Comparison of Objective Functions for Engine Mounts Optimization

Passenger’s comfort is of prime importance in nowadays vehicle design. In order to improve this comfort, engine suspension design has to be based on comfort criteria describing passenger’s perceptions. Acoustic pressure in vehicle cabin and vibration of components in contact with passengers are (seats, driving wheel, floor) typical examples. Using such an approach differs greatly from classical optimization techniques which only consider force injected into a rigid base structure. Considering only force functions limits the power of optimization techniques. In fact, passengers may not even feel the changes in perceptions between different configurations. Furthermore, considering base structure as being rigid suppose that the mobility of the base is significantly different from that of engine mounts. However, in certain circumstances, mounts stiffness and structure impedance may coincide and significantly alter engine’s response to a determined excitation. In fact, at frame natural frequencies and for local mode, the mounts stiffness can even be higher than the attachment point frame stiffness. On the other hand, transfer functions between force injected to the frame at engine mount locations and cabin vibration response or acoustic pressure often show high level peaks at specific frequencies. Cabin comfort can be compromise if there is energy transmitted at these frequencies from the powerplant. For all of these reasons, it is appropriate to adopt a design method which takes into account both structure flexibility and transfer path between engine attachment points and passenger’s zone. The substructuring approach is well suited for these requirements. Finally, classical optimization techniques usually minimize a cost function for only one driving condition, typically idling. This can lead to undesired increase in noise and vibration levels at other driving conditions. This paper presents an optimization method which consider every steady state operating conditions of the engine.

2000 – Annual Meeting of the Canadian Acoustical Society, Sherbrooke, Canada
Denis Blanchet (Vasci, USA)

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