Electric vehicles – the sound of silence?

For passengers in electric cars, interior noises from actuation of the powertrain and auxiliary systems should be as non-disruptive as possible. By contrast, electric cars do need to make noise outside so others around them can hear them. Customized new development methods are allowing acoustics experts at IAV to resolve this conflict of goals.

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Compensating for unwanted noises

This is where IAV’s experts on noise, vibration, and harshness (NVH) come in. With their wide range of acoustics expertise and the experience they have gained through numerous series projects, they make sure an electric vehicle has just the right sound. Take the powertrain, for instance: They minimize bothersome noises right at the source, in the area of the air gap in the electric motor and the tooth contacts in the gear box, thereby noticeably reducing the noise by around three to five decibels. “To do this, we use FEA and MBS simulations early on in the development phase, working closely with the other areas involved,” says Mario Schwalbe, team manager of NVH Simulation at IAV. “This approach means we need fewer prototypes, save on costs, and significantly reduce development time.”

The quiet electric drive is a boon to passengers – but it also lets overly noisy ancillary systems take center stage. The electric compressor used in the air conditioning system can be a particular issue. The acoustic experts study it and other troublemakers on a special test bench where they can measure individual components separately from the rest of the system.

«Together with the manufacturers, we optimize the components by doing things like changing the mounting or putting ribs on the enclosure. We also adjust insulation and damping components, such as the front wall damping, to the higher frequency range.»

Oliver Olbrich — Team manager of NVH Testing at IAV

Sound design for electric vehicles

The experts at IAV also tackle bothersome interior noises. In most cases, these are dominated by lower frequencies of up to 600 Hz and can be suppressed using active noise control (ANC). To do this, a reference microphone records the annoying noise, and a controller generates a customized counter-signal and sends it out via the in-car entertainment system, so the two noises cancel each other out in the specified quiet zone. “We’ve developed our own algorithms to do this. They can suppress both static and dynamic noises,” explains Dr. Samira Mohamady, technical consultant in the Communication & Audio Functions department at IAV.

The article appeared in automotion 03/2021, IAV’s automotive engineering trade magazine. Here you can order the automotion free of charge.

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