When performing dynamics simulations related to vibration analysis, ride comfort, and handling stability—not only for automobiles—it is essential to input the center-of-gravity location and inertia properties of the target structure into the simulation model accurately.
However, obtaining accurate inertia properties is difficult for purchased components from suppliers with uncertain design information, and even more difficult for the benchmarking hardware.
Even in-house products that have design data, cables and subcomponents that are not included in the data are often installed on the actual unit, making it difficult to obtain accurate inertia properties.
ESTECH developed a method to estimate inertia properties (mass, center-of-gravity location, and moments of inertia) using the least-squares method from the frequency response functions of the target structure obtained through excitation tests.
The basic approach is to estimate inertia properties from the mass line of rigid-body mode that appears in the FRFs (frequency response functions) under flexibly-support conditions.
This method can make it possible to obtain inertia properties for a powertrain of passenger vehicle connected by flexible engine mounts (common for conventional ICE) without removing powertrain from full vehicle.
If the stiffness of the engine mounts is known, inertia properties can also be estimated from rigid-body resonance characteristics.
Furthermore, if the reaction forces of the engine mounts can be measured, this method can be applied even to structures where the mass line does not appear on FRFs clearly due to the influence of elastic deformation modes (e.g., a passenger-car trimmed body).
