Topology optimization of nonlinear elastomer engine mounts considering the transfer behavior

Increasing global competition among electric vehicle manufacturers has elevated the Noise, Vibration, and Harshness (NVH) properties of drivetrains to a key quality feature. Unfavorable NVH properties occur when the drivetrain’s dynamic excitation forces excite modes of the sound-transmitting components at the respective eigenfrequencies. An established strategy to avoid this unwanted NVH behavior is topology optimization (TO), as it can shift unwanted modes of the drivetrain out of the excitation frequency range through geometrical adaptations using finite-element (FE) simulation. Another way to significantly influence unwanted NVH behavior in electric vehicle drivetrains are elastomer engine mounts which are employed to isolate the engine’s vibrations from the surrounding system and to dissipate vibrational energy. However, the effectiveness of these functionalities is limited in frequency ranges of local elastomer modes. Despite TO being well-established, challenges are given in shifting elastomer modes due to the complex material behavior. Firstly, the material’s softness results in an uncontrollably high density of local mount modes for TO, which presents a challenge in developing engine mounts without modes in the drivetrain’s excitation range, especially for electrified engines. Secondly, the elastomer’s nonlinear material impedes calculating the component’s modes with a linearized material approach. The goal of this contribution therefore is to develop a method that considers the complex material behavior of engine mounts in a TO process. To achieve this goal, the ideal transfer behavior of the engine mount, and consequently the positioning of mount modes within the frequency range, is determined based on the sound-transmitting structure and used as an objective for the optimization process. To consider the elastomer’s nonlinear transfer behavior during optimization, material parameters for each considered frequency are applied. The application of the new method results in a mount design that ensures both, sufficient quasi-static stiffness, and high-frequency compliance to decouple the transfer behavior at critical frequencies. Verification is achieved by comparing the transfer behavior of an electric drive unit with the optimized mount geometry and with a non-optimized geometry.