In this era of engine downsizing, the powertrains with higher power densities are configured on next generation vehicles. The bare four cylinder engine without balancer shaft has higher surface velocities, sound pressure & power levels and nearly 10 to 15% higher base level vibration/forces over older generations. Adapting such engines on a new vehicle platform with stringent NVH targets is challenging. Powertrain mount modal analysis, 6DOF or 16DOF is a primary tool followed for initial mount positioning and stiffness definition. From our earlier experiences we have the knowledge that most of the 6DOF iterations lead to the mount positions which are less feasible as per vehicle architecture and packaging point of view, and further optimization is needed to arrive at suitable mount position through 6DOF analysis.
In a drive to have first time right solution with minimal modifications, the study was conducted to understand the role of mount position & isolation on different vehicles. Generally to meet durability & NVH targets, four point mounting is preferred and same was observed. Front mounts are generally mounted on engine cross member whereas the rear mounts are usually in the plane of flywheel housing.
The difference is created when the rear mounts are shifted on transmission housing, leading to controlled pitch mode frequency below 12Hz and roll mode frequency below 14Hz. The yaw mode goes much below 7.4Hz and clearly separated from roll mode. Results show more than 90% decoupling of all modes and close to 1Hz spacing between all modes including vehicle modes.