The Sound of E-Mobility - The New Sound for New Cars

© Fraunhofer IBP
© Fraunhofer IBP

How soft is the sound of electric cars and what is the sound of these electric cars alike? Is noise control getting obsolete in times to come or must electric cars become louder to be heard by pedestrians at crosswalks? These and many other questions are in the focus of the research of acousticians at the Fraunhofer IBP not only in the context of the project "Fraunhofer System Research for Electro-Mobility" funded by the BMBF, which investigates the various aspects of future car concepts, and drive systems, as well as the storage and distribution of energy. One aspect that must not be underestimated is the acceptance and security of electric cars by users and the environment.

The four-wheel roller test bench of the Fraunhofer IBP, where each wheel is individually controlled, allows the measurement of interior and ambient noise of all kinds of motor vehicles, and to determine and assess the specific differences generated for example by the drive systems. Test methods like the uncoupling and bar tests, and modern methods of noise analysis and sound design allow the determination and analysis of other noise components from vehicle parts. This follows the intension to avoid the occurrence of unwanted rattling and humming in the vehicle, and to give the vehicle the desired sound character in the sense of sound quality by targeted influencing of the noise contributions. Moreover, important research topics of Vehicle Acoustics are the enhancement of the driver’s concentration by lower sound levels in the vehicle, the improvement of speech intelligibility for mobile phones and conversations in the vehicle, voice control and acoustical alarm signals as well as the development and testing of acoustic building components.

First measurements of prototypes of electric cars, however, already showed: Due to the reduction of the powertrain noise ancillary units become louder in the driver’s perception. It is, however, impossible to do without compressors necessary for heating and also battery cooling, or motors for windshield wipers and indicators or blowers for ventilation. But also powertrain is not free of noise showing a new and unfamiliar characteristic. In addition, new sound transmission paths and behavior of vibrations and sound occur due to the new concepts to arrange the ancillary units. As concerns electric vehicles it is urgent to reduce the weight, since the batteries have a relatively high weight. Lightweight building components with high sound insulation and attenuation are required and are a challenge for building material technology. In this context, not only the objectively measureable loudness is significant but also the sound in the vehicle must be comfortable to be accepted and to give the impression of functionality and security, since at present the drivers are still missing the familiar sound criteria of the combustion engine and gearbox.

Not only the drivers but also the environment will respond to this class of new vehicles and must get acquainted to. A considerable reduction of the powertrain noise, however, will only occur at low velocities. The noise of the wind and tires continues to dominate the acoustic events on highways so that a significant reduction of complex noise control measures cannot be expected there. This is why solving the rolling noise problem will gain in importance. E-vehicles are not soundless as concerns the ambient noise, hearing habits, however, are still unknown. Thus, an adequate infrastructure and acoustic modules at the vehicle in urban traffic may become essential.