Design optimization of Engine Mount bracket to reduce various gear noises in the passenger car cabin

With the advancement of regulatory norms in the automobile industry, there is challenging to meet performance efficiency targets, especially with a lightweight platform, while providing a superior driving experience to customers. The shift towards weight optimization makes the vehicle structure more susceptible to transfer a diverse range of noise and vibrations through the body. Although most undesirable noises perceived inside the cabin can be reduced by superior technology engine mounts and NVH packaging, all such solutions lead to cost addition. Intelligent considerations in part design can be used to supplement predictable transfer paths to quell unwanted vibrations. One such case is of the gear whine noise in certain rpm bands caused by inherent gear meshing frequency coinciding with the natural frequency of an engine mounting bracket. This paper demonstrates two methodologies to counter such a phenomenon, either through engine mount bracket natural frequency optimization or addition of a dynamic damper. However, the focus is on frequency and mobility optimization approaches. Another case is gear “JAA” noise originating from the rattling of remaining freely engaged gears. This kind of gear-induced vibration tends to transfer along dynamically lesser rigid structural parts and become audible inside the cabin. This is countered by reducing the mobility of the transfer path viz. engine mounting brackets. Both approaches allow several iterations of bracket shape, which can be verified using analytical CAE tools and physical tests on the part level as well as vehicle level, with minimal cost implications.