Development of Idealistic Hydromount Characteristics to Minimize Engine Induced Vibrations Using Unconstrained Minimization

The paper presents the results of the development work on engine mounts. The objective of the present study is to develop idealistic hydromount stiffness and damping characteristics, to minimize the engine induced vibrations over a wide frequency range. A total system level non-linear unconstrained optimizer is used to develop the optimum frequency dependent stiffness and damping characteristics, locations and orientations. Typical engine inertial values and packaging constraints representing a traditional three mount rear wheel drive power plant system, is used in the present study. The front two mounts are hydromounts and the rear mount is an elastomeric mount The study is performed using unit harmonic excitations with a broad frequency range, since the typical engine inertial values are modeled and not an actual engine. A wide range of values for stiffness (minimum and maximum), are subjected to frequency constraints, manufacturing (compression to shear stiffness ratio) constraints and other standard criterion such as roll decoupling, etc. The main goal of this study is to minimize the force transmitted from the engine into the body structure or other subsystems in order to reduce the tactile and acoustic responses. A forced frequency response optimization technique is used to develop various sets of frequency dependent mount stiffness and damping characteristics, orientations and locations which satisfy all constraints and result in minimum transmissibility corresponding to each excitation frequency. A proprietary intelligent scheme is then used to sort all of these results and select one set which will produce minimum transmissibility over a wide frequency range of interest. The mathematical formulation coded in EGS/ISOLATOR, rigorous enough to develop mount characteristics in total system level, is used for this study.

For the considered problem, two governing designs are identified. Front governing design leads to lower transmissibility in the front mounts and the rear governing leads to lower transmissibility in the rear mount. Rear governing design is recommended for this case, as it leads to lower transmissibility into the body structure and hence a reduction in the overall acoustic response.