Development of an air spring engine mount system for a medium duty truck

A collaborative research project between universities, a public laboratory, vehicle engineering and testing companies was formed and a prototype vehicle with a diesel engine mounted on four air springs was designed. Concurrently, Genetic Algorithm (hereafter GA) was also implemented to optimize the parameters related to the engine mounting layout, the calculations of the stiffness matrix and the inverse stiffness matrix to prevent the coupled of lateral and rolling vibrational modes, and to obtain the displacement of each mounting point. Finally, the best engine mounting layout was selected for the installation of four air springs to minimize torque roll. Also, the original engine mount layout with cushion rubbers was completely changed to enable installation of four air springs, two lateral and tension rods, and four shock absorbers for the reduction of large engine movements against transient engine torque at engine start and stop, and gear changes. Two leveling valves were also attached to the frame to maintain engine height against large engine torque. As a result, the engine vertical vibration level at 19.1 Hz dropped below 20% of the level designed with the cushion rubber installed on the current vehicle and the engine displacement with the largest torque was within the limit. Further study such as vehicle durability testing is necessary, but the air spring is very useful as a vibration isolation tool for diesel engine mounting layouts.