London – With the issue of interior noise now to the forefront in the development of electric vehicles and a continuing cause of customer complaints and warranty claims, researchers at Hyundai Motor Co. have set about analysing the problem.
A particular focus for the Korean team has been on characterising the ‘squeak noise’ of carbon black-filled natural rubber for automotive applications, such as suspension bushings and engine mounts.
There are many, as yet, unidentified factors that determine noise generated by elastomers in these areas of a vehicle, Hyundai’s Dae-Un Sung set out in a presentation at the IoM3-organised International Rubber Conference (IRC 2019), 3-5 Sept in London.
“One of the most difficult topics is squeak noise of elastomeric rubber components such as bushings and engine mounts,” explained Sung. “It is generated by friction-induced stick-slip behaviour in which two rubber surfaces in a relative motion move and stop repeatedly.
“When rubber parts undergo sliding contact, friction forces can cause elastic deformation that acts a mechanism for storing energy, with a squeak or tick sound produced when the energy is released.”
However, said the IRC presenter, by optimising material properties and surface condition designers can avoid noise by minimising elastic deformation and the release of stored elastic energy.
Sung went on to detail the experimental analysis techniques developed at Hyundai to simulate the effect induced by rubber-to-rubber frictional behaviour.
The investigation included analysing the effects of rubber hardness, surface condition, frictional speed, load and environmental conditions. This team also studied the effects of thermal oxidation aging and worn surface of natural rubber.
The work led to validation of statistical prediction model to estimate the occurrence probability of squeak noise of elastomers, as well as the development of an squeak noise evaluation system able to simulate stick-slip behaviour induced by rubber-to-rubber frictional motion.
Using these new testing capabilities, Hyundai’s researchers were able to measure the extent to which surface lubrication and lubricant additives reduce the occurrence of squeak noise.
The team were also able to study the contribution of rubber hardness, friction speed and normal force to noise-generation, as well as the role of surface oxidation and wear.
And, concluded Sung, Hyundai’s simulation work showed “excellent prediction accuracy and the effect of the factors on the squeak noise occurrence can easily be understood through the model.”