Tuned Mass Dampers [TMDs] may be needed for Electric Vehicles for their Best NVH

In a recent Taiwan Earthquake of a 7.4-magnitude, people inside the island’s tallest skyscraper, Taipei 101, were protected by a TMD! What a lovely application of vibration control theory for the whole community!

A 730 ton steel sphere kept hanging as a Pendulum between 87th & 92nd Floors is tuned at the natural frequency of this Tall building (0.15 Hz). There are viscous dampers to convert kinetic energy of the pendulum sway into heat energy.

NVH Managers have been using TMDs (also called as dynamic or harmonic absorbers) since many decades for ICE powered vehicles to avoid booms inside the car-cabin.

They are not with such big masses but with a small disc with a rubber spring attached to an axle or a power-train mounting bracket or a steering wheel or a brake-calliper or a sub-frame/chassis & tuned to reduce their vibrations at the specific frequency of the resonance.

But for silent and vibration-free EVs, will they be needed ? Below Modal Maps will answer this ..

Yes, TMDs will be needed for EVs even though electromagnetic forces or imbalance of the motors are of much small amplitudes in comparison with those of combustion forces of ICE vehicles.

However, any possible resonance of structural components can create a small boom inside a luxurious EV which is otherwise very quiet thanks to excellent air-borne control thru' body-sealing & acoustic insulation everywhere.

In the low frequency range, mainly the cooling fan &/or scroll compressor rotational speeds, depending on thermal loading, can get into close proximity, of the natural frequency of the steering wheel-system as assembled on the trimmed body of EVs.

Generally, finalization of the cooling strategy happens after a lot of validation testing on road and if, at that time, no changes are allowed on the vehicle-chassis to assure the modal separation of minimum +/-2 Hz, then a TMD on the steering wheel integral with the air-bags will be needed.

In the mid/high frequency range, if excitation frequency of electromagnetic & gear-meshing impact forces and their harmonics come closer to structural natural frequencies of the motor-gear-box casing or their ancillary brackets or the front sub-frame supporting them, then also TMDs will be needed.

They will assure the Best-in-class NVH of such EVs where linearity of the In-cab noise will be maintained with a rise in the wheel-speed on road. Tonality of the motor-train sound from 400 to 1500 Hz need be kept under control for the best sound quality experienced by the EV-users!