A Study of Engine Mount Optimisation of Three-Cylinder Engine through Multi-Body Dynamic Simulation and Its Verification by Vehicle Measurement

Three-cylinder Engine without balancer shaft is a recent trend towards development of lightweight and fuel-efficient powertrain for passenger car. In addition, customer's expectation of superior NVH inside vehicle cabin is increasing day by day. Engine mounts address majority of the NVH issues related to transfer of vibration from engine to passenger cabin. Idle vibration isolation for a three-cylinder engine is a challenging task due to possibility of overlapping of Powertrain's rigid body modes with engine's firing frequency. This Overlapping of rigid body can be avoided either by modifying mount characteristic or by changing the position of mounts based on multi-body-dynamics (MBD) simulation.

This paper explains about two types of engine mounting system for a front-wheel drive transversely mounted three-cylinder engine. The base vehicle was having three-point mounting system i.e. all three engine mounts were pre-loaded. Then for study, positions of front mounts were changed so as to have zero preload on rear mount. The study shows how rigid body modes change when Right Hand Side (RHS) and Left Hand Side (LHS) mount move closer to Torque-roll axis (TRA) and conventional rear mount is converted to a torque-rod. This layout is also called pendulum mounting system. Modal analysis shows that in pendulum mounting system, roll mode purity is improved compared to three point mounting system. In base Three point mounting configuration, Roll mode Eigen frequency is coming close to 1.5^th order engine excitation and after optimizing engine mount's position and characteristic, it has been moved away from 1.5^th order. Vehicle measurement data shows there is overall improvement in vibration isolation during engine idling, crank-on/off conditions. The measurement results co-relate with simulation estimation quite closely. There is also scope of reducing weight of engine mounting brackets in pendulum mounting layout as there is less preload on rear mount (torque rod).