Design guidelines to avoid hygroscopic effects on outer handles 2018-36-0257
Generally, exterior handles are one of the first parts that the user has physical interaction in the vehicle. A robust handle concept gives the user the idea of trust and good quality vehicle as first impression. Exterior handles, in which the concept is a handle body operated by applying a horizontal pull force, always pivoted in the front end and sliding against a reinforcement rail at rear end, are called strap handles. The kinetics seems to be simple, nevertheless special attention must be given regarding the interaction materials used in this system. Various plastic materials used in this system are subjected to water absorption at molecular level, changing their internal structure, resulting in swell and consequently a volume increase. This phenomenon that modifies the dimensions is known as hygroscopic expansion. In one hand, handles must present reduced wobble and free play. Although, it must be remembered that hygroscopic phenomenon may be associated with cases of handle jamming, where the handle presents higher resistance to be operated or simply do not return to home position, configuring a safety issue if not addressed. For an assertive conclusion, the project for exterior handle systems must execute a sequence of techniques, not only the Dimension Variation Analysis considering the tolerances by project, but also take into account the expansion undergone for those materials. To complete the design validation, a specific abusive weather conditioning test must be applied to reflect the worst condition that exterior handles might be exposed during its lifetime.