Vibroacoustics of engine mounts for electric motors: experiments, continuum mechanical modeling under consideration of aging and validation

• Applicant: Professor Dr.-Ing. Alexander Lion
• Subject Area: Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545950783

When developing engine mounts for electric vehicles, it is necessary to consider the transfer of structure-borne noise. The transfer path leads from the electric engine via the elastomer mounts to the vehicle structure. Depending on the frequency-dependent properties of the elastomers and the moving elastomer mass, the dynamic behavior of the bearings shows resonances and anti-resonances that lead to increases or decreases in the stiffness. If the speed of a vehicle is between 2m/s and 60m/s, the wheel radius is about 1m and reduction ratios of 1/10 are used, the motor's rotational frequencies are between 10Hz and 300Hz. If the motor is not correctly balanced, excitations will occur in this frequency range. Due to the design of the electric motors, additional excitations are caused by cogging torques and torque ripples with frequencies of a few kilohertz. If higher-frequent excitations are transferred to the vehicle body due to bearing resonances, they disturb the passengers in the vehicle. A related issue results from the waste heat of the engines due to electromagnetic losses. In addition changes in the viscoelastic material properties, higher temperature leads to ageing of the elastomers. Thermally aged elastomers exhibit stiffening or softening under quasi-static loads, depending on their composition. The associated modeling is known. The influence of ageing on the dynamic behavior of elastomers has hardly been investigated to date and has not yet been modelled using continuum mechanics. The published data show that both the storage and loss modulus change with ageing. As a result, the frequency-dependent transfer behavior of the aggregate bearings changes during a vehicle's service life. There is therefore a need for research to investigate and understand the influence of ageing on the frequency-dependent behaviour of elastomers and to model it in terms of continuum mechanics. This project will raise the simulation of aggregate bearings to a level that goes beyond the current state of knowledge. The findings contribute to the development of more durable products with meaningful CAE methods. This leads to the innovative project goal of developing, implementing and validating a material model that can be used to simulate the vibroacoustic behavior of aggregate bearings of electric vehicles, taking aging and internal dynamics into account. Based on experimental investigations of the frequency-dependent behaviour of artificially aged elastomer samples, a material model for large deformations is developed, identified, transformed into the frequency range and implemented into a commercial FEM software. This is followed by an initial validation based on the vibroacoustic behavior of aged, component-like elastomer samples. For the final validation, the structural dynamics of a running electric motor on differently aged elastomer bushings is simulated and investigated experimentally.

• DFG Programme: Research Grants