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Air damper promises automotive cost savings
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12/03/2008
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The changing needs of the car industry mean that an alternative to hydraulic mounts could soon be ready for commercialisation. Lou Reade reports
Car suspension mounts based on air damping could soon be seen in production vehicles – around 50 years after the idea was first mooted.
Air mounts have never taken off because their performance did not meet the needs of the car industry. Now that some of those needs are changing – such as acoustic performance -- air dampers may now become viable.
“There's always a balance between acoustics and damping performance,” says Eric Eisel, a product engineer at materials supplier Trelleborg. “With air mounts, you are shifting that compromise away from damping and towards acoustics.”
Trelleborg has developed a series of designs for air dampers, which are being trialled by by manufacturers including BMW, Porsche, Audi and Ford. At the same time, Trelleborg says that the mounts might find use in other applications that need damping – such as test beds that need to be decoupled from ambient vibrations.
Damping mounts – used to attach engines, gearboxes and other large components to the car frame – fall into two distinct types. Those made of solid rubber, which are inexpensive and give basic damping performance; and 'hydromounts', which are highly designed, hollow rubber mounts filled with a liquid such as glycol.
Air dampers are almost identical to hydromounts, other than they are filled with air rather than glycol. This, says Trelleborg, makes them more compressible – so they are likely to deliver better isolation, and be cheaper and easier to make.
Some of the factors that could tip the balance towards air dampers include: an even greater focus on cost by the car industry; the advent of lighter engines; and the Asian market's emphasis on low-cost, robust, high-volume applications.
According to Trelleborg, air damping will achieve a balance between force-deflection characteristics and excellent dynamic performance across a broad 'bandwidth' – the frequencies at which vibrations are damped.
Another positive factor is that they fit into the same design envelope as conventional mounts, so would not need radical re-design.
“Vehicles that never had hydromounts are now improving comfort, and are looking for an in-between solution,” says Eisel.
Trelleborg has developed a simulation tool for designing air dampers. This looks at factors such as chamber volume, diameter, height and specific design shapes. This will help designers to “tune it to the required frequency and give the right performance”.
The company is hopeful that serial production of air mounts will begin within two years.
Pointers
Air dampers, first mooted 50 years ago, could soon be used widely in production cars
Changing needs of car manufacturers, such as an even more relentless focus on cost, could help boost the case for air dampers
They are likely to fit into the same design envelope as the commonly used hydromounts
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Author
Tom Shelley
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