Experimental study of applying plant-derived materials to sound-absorbing structures for cabin noise reduction of electric vehicles

Abstract

Electric vehicles generate different interior noise than internal combustion engine vehicles at low speeds. To investigate the cause of the interior noise of electric vehicles at low speeds (30 km/h) and to reduce the noise, a Helmholtz resonator made of molded pulp, a material derived from plants, is fabricated, and its noise reduction effect is experimentally evaluated. First, a molded pulp Helmholtz resonator is fabricated and tested with an impedance tube. Then, this Helmholtz resonator is installed inside the tire and can reduce the cavity resonance noise. Then, driving tests are conducted on an electric vehicle with tires equipped with this molded pulp, and it is possible to reduce the sound pressure at the ear position at the frequency of the tire cavity resonance. Finally, driving tests are conducted with standard tires, and this molded pulp in the cabin reduces the noise at the tire cavity resonance frequency. From this, at low speeds (30 km/h), we can demonstrate that tire cavity resonance is the source of noise in an electric vehicle's cabin and that it is possible to reduce tire cavity resonance without directly installing Helmholtz resonator in the tires.