Towards active engine mounting systems for commercial vehicles: modeling and analysis

Licentiate thesis, 2009

The vehicle engine mounting system, which consists of several mounts connecting the engine to the vehicle structure, not only supports the weight of the engine but also isolates the noise, vibration and the transmitted forces to the vehicle structure. At present conventional elastomeric mounts are widely used in engine mounting systems for commercial vehicles. However, these mounts cannot fulfill the conflicting characteristic requirements for the best isolation concerning both road and engine induced vibrations. Therefore, to improve the noise and vibration isolation of commercial vehicles it is necessary to go beyond traditional passive isolators and use semi-active or active vibration control systems due to their capabilities of addressing the conflicting requirements in different road and engine conditions. The aim of the research presented in this thesis is to first develop mathematical and computational models of elastomeric engine mounts for heavy trucks and investigate the nonlinear behavior of dynamic stiffness and damping of the mounts, and finally use the developed models to design and analyze an adaptronic engine mounting system. Adaptronic engine mounting system is referred to a mounting system where actuators, sensors and controller are optimally incorporated in the conventional elastomeric mounting system. The developed computational model of the engine mounts is implemented in Matlab/ Simulink and used in a 3D engine model with which vibration dynamics analysis under different engine and realistic road inputs is conducted. Moreover, the possibility and advantages of using active engine mounts have been studied by incorporating actuators into the above mentioned 3D engine model with conventional mounting system for heavy trucks. Simulations of the engine vibration dynamics under similar engine and road excitations have been done for the adaptronic mounting system and compared to the results from the conventional engine mounting system. The results of simulations of engine vibration dynamics and transmitted forces to the vehicle structure have shown good potential for vibration isolation improvement in heavy trucks by using adaptronic engine mounting systems.