Recycling How Old Car Tires Make Electric Cars Quieter

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Used car tires could contribute to making electric cars quieter in the future: Engineers from the Otto von Guericke University Magdeburg (Germany) have successfully used particles from recycled tire rubber to reduce vibrations and noise in the power electronics of electric vehicles.

Instead of wrapping vibrating components with heavy insulation mats, the research team led by Prof. Dr.-Ing. Hermann Rottengruber from the Institute for Engineering of Products and Systems filled granules made from old tire rubber into existing cavities of power electronics. There, the particles move like sand in a rattle, dampening vibrations and preventing them from turning into unpleasant noises. In laboratory tests, the noise level in the particularly noticeable frequency range was reduced by 6.5 decibels, and the vibrations of a component cover dropped by up to 9.7 decibels. In the future, the method aims to help vehicle manufacturers specifically avoid disturbing noises in the early development phases. In the long term, digital models and AI-supported simulations are intended to accelerate the development of noise-optimized electric vehicles by virtually designing and evaluating suitable damping solutions even before a prototype is built. This could save development time and facilitate the transfer to industrial applications.

"With electromobility, the sound environment in the vehicle is changing," explains Prof. Hermann Rottengruber. "Electric cars don't hum like gasoline or diesel vehicles. They drive more quietly, but not silently. Precisely because the familiar engine noise is missing, other sounds become more noticeable: a high-pitched whistling during charging, a humming from the electronics, a fine whirring from the drivetrain." Such noises are often not particularly loud but are perceived as unpleasant due to their high frequencies. "We tackle the noise directly at its source before it even becomes audible," adds project leader Dr. Braj Bhushan Prasad. "The particles take energy away from the structure before it turns into disruptive sound."

Combine Acoustic Comfort, Lightweight Construction, and Circular Economy

The process requires hardly any additional space and adds very little weight to the vehicle, the scientist further explains. "Classic insulation mats or heavy soundproofing layers increase the vehicle's mass. This is unfavorable for electric cars because every additional kilogram costs range," says Prasad. "In contrast, we use cavities that are already present in the component." Every year, millions of old tires are generated worldwide, some of which are already used for sports field surfaces or other recycling products. "We are now demonstrating another possible application of this material in vehicle technology, combining acoustic comfort, lightweight construction, and circular economy." For their measurements, the engineers placed the component in an anechoic chamber, where sounds can be captured with precision. They simultaneously measured how much the cover vibrates and how much sound is emitted. Testing was conducted under realistic operating conditions: once during a speed ramp-up from 50 to 10,000 revolutions per minute under full load and once during constant full-load operation. Across the examined frequency range of 100 to 10,000 Hertz, the sound pressure level dropped from 57.7 to 53.2 decibels. In the particularly critical range between 800 and 1,100 Hertz, the level even fell from 56.5 to 50.0 decibels. This is precisely where noises from power electronics can be especially noticeable. "That may not sound like much, but it's noticeable," says engineer Rottengruber. "A reduction of 6.5 decibels can make the difference between a conspicuous whirring and a significantly subdued background tone."

Our results show that even small particles of recycled tire rubber can make a noticeable contribution to reducing noise levels in electric vehicles.

Prof. Hermann Rottengruber

The scientific challenge lies in making the seemingly simple effect reliably manageable, says Prasad. "Particles behave very differently depending on their size, material, fill quantity, temperature, component geometry, and excitation. Therefore, it’s not enough to simply fill granulate into a component. We need to calculate and test which particles in what quantity and at which location achieve the best effect." According to the engineers, the new particle damper technology could in the future be used not only in power electronics but also in inverters, control units, or other vibration-prone components of electric drive systems. "Our results show that even small particles made from recycled tire rubber can make a noticeable contribution to quieter electric vehicles," says Rottengruber. "Now we want to turn this into a tool for the development of future electric vehicles, ensuring that they not only drive cleaner but also sound more pleasant."