Electric & Hybrid Vehicle Technology - July 2021
Sound solutions
Karl Vadaszffy 2021-07-21 03:04:43
What lies beneath
When it comes to electric and hybrid vehicles, marginal gains in performance materials can make all the difference
A manufacturer and innovator of technical textiles, nonwovens, and fibers, Freudenberg Performance Materials (FPM), based in Weinheim, Germany, produces friction inserts, acoustic pads, and underbody shields for the automotive market.
The company’s friction inserts are coated and nonwoven, enabling significantly higher static friction coefficients. Angela Weik, strategic R&D manager automotive at Freudenberg Performance Materials, explains: “The demand for higher performance means that screwed and press fitted connections are exposed to increased forces and torques. This applies especially to engine, as well as powertrain, applications in electric vehicles. With our friction inserts, we can provide a solution for such demands.”
Using FPM’s award-winning technology between two joining components can result in a static friction coefficient of up to μ=0.95, which enables users to not only transmit higher shear forces and torques, but also design lighter and more compact components without any sacrifice in performance.
The technology enables the hard particles to penetrate both surfaces, creating a micro interlock. The particle portfolio ranges from 10 μm to 115 μm to guarantee a sufficient friction increase on coated parts and components, for example e-coating. Desired performance can be achieved through the particle distribution, which is specific to the material combination of the joint. “By using only inert materials to produce our friction inserts, there will be no impact on the corrosion behavior of the friction joint,” Weik comments.
The increase in static friction coefficients results in the transmission of higher torques and shear forces due to the optimized friction joint; a reduction in the number and/or size of the bolts used; and minimized micro vibrations, resulting in noise reduction.
Sound solution
Acoustic solutions for electric and hybrid vehicle manufacturers need to be light, easy to handle, and invisible after installation. Electric drive systems generate much less noise than combustion engines, which means that other ambient noises, such as the rolling of tires, airstream, and creaking sounds are more noticeable. The inverter, which ranges between 4 and 12 kHz, is another source of noise. “In other words, more noise at lower and higher frequencies needs to be absorbed,” says Weik
“Not only that but combining acoustics with thermal insulation is becoming increasingly important. In winter, the air conditioning system in an electric car is used to generate heat, which means it requires some of the battery’s power, which reduces battery range. So thermal insulation for components is attracting a great deal of interest.”
“Combining acoustics with thermal insulation is becoming increasingly important” Angela Weik, strategic R&D manager automotive, Freudenberg Performance Materials
By maximizing the fiber-air distribution, FPM’s absorbers provide thermal insulation, achieving thermal conductivity of just 0.04 W/ mK through the use of aerogels.
Generally speaking, Weik explains, the sound absorption performance of porous absorbers can be finetuned by adjusting the weight, thickness, and proportion of fine fibers. “At FPM, we’ve achieved this by combining two core competences from our apparel padding business and filtration activities. These are our ultra-light, maximum-volume drylaid nonwovens, and microfiber nonwovens that have a defined airflow resistance, and can also convert the kinetic energy of the sound into thermal energy.”
With the drylaid nonwovens, absorption in the lower- to mid-frequency range improves as the thickness increases. “Optimal sound absorption occurs at d=/4,” Weik comments, “because the most efficient point to damp sound is when it’s at its fastest. This equation enables us to determine the optimal distance to the wall at a given frequency and thus the thickness of the absorber – for example, 21mm for 4000 Hz and 17mm for 5000 Hz, etc.”
If airflow resistance layers – that is, nonwovens with a high proportion of ultra-fine fibers, resulting in a high airflow resistance – are applied to the substrate, optimal sound absorption shifts to lower frequencies. “As a result, the weight and thickness of our acoustic pads can be reduced. For example, optimal sound absorption with a thickness of 21mm is already achieved at 2500 Hz, rather than the higher frequency of 4000 Hz,” Weik reveals.
Furthermore, an ultra-light, high-volume absorber, coupled with an airflow resistance layer that is as dense as possible, achieves effects similar to those of a flexible panel absorber, helping to absorb sound, and combining porous absorbers and plate transducers enables coverage of a broader bandwidth. Due to the resonant frequency, there is a steeper increase in the gradient of the sound absorption coefficient at a lower frequency, also improving the efficiency of the porous absorber. Consequently, sound absorption can be shifted to low frequencies.
The right combination
Cutting weight is not useful everywhere on a vehicle. Too little weight in some locations can impact driving performance. The underbody, however, is a prime target for weight reduction. Therefore, FPM offers lightweight underbody systems made of 100% polyester.
“Manufacturers like to achieve two fuel-saving measures in one go,” Weik explains. “Firstly, with good aerodynamics and, secondly, by making the part low in weight.” On average, she says, the underbody systems from FPM are at least 20% lighter than its relevant counterparts. Over an entire production series, this would amount to several tons of CO2.
“This is made possible because of a combination of one needle-punched nonwoven layer and self-developed two spunbond layers,” Weik says. These are arranged according to the patented sandwich layer principle, with the needle-punched layer in the middle.
In addition, the material is easy to shape and does not tear at the mounting points. Moreover, the nonwoven mixture poses no health risks, in contrast to glass fiber-reinforced materials, as there is no risk from fine dust and skin-irritating chips. “And the best part,” Weik explains, “is that the material is completely recyclable and also contains approximately 50% already recycled fibers, which opens up new possibilities for sustainable production, an important consideration for manufacturers today and in the future.”
Indeed, looking ahead, Weik believes the industry will focus on maximizing driving range through the use of high thermal insulation properties of materials, meaning that less energy is required to heat and cool. Sustainability, especially recyclability, which is driven by EU guidelines requiring 95% of a vehicle to be recyclable with low emissions of VOC will be brought to the fore, as well as carsharing and autonomous driving, which she suggests will be part of our daily lives.
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Sound solutions
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