Today vehicle owners perceive squeaks and itches inside a vehicle cabin as a major negative indicator of vehicle build quality and durability. Manufacturers struggle to bear the high costs of squeak and rattle (S&R) related warranty. Although the benefits of structural integrity and tight manufacturing tolerances with respect to the prevention of S&R are known, today's cost, weight, crash requirements, aesthetic demands and environmental/fire hazard rules quite often dictate the design of S&R prone sub-systems. Even sub-systems with the best possible structural design and manufacturing tolerances are not immune to extreme environmental conditions, and mating materials can initiate contact leading to S&R. One method of minimizing the possibility of squeaks is by the judicious selection of mating material pairs.
This paper describes a test process aimed at the quantification of material pair compatibility. Also described is a state of the art, flexure-based (virtually frictionless) test instrument that has been developed for such material pair compatibility studies. A group of 17 material pairs with known historical problems were identified by experienced automotive designers and were put through 374 tests encompassing several realistic temperature and humidity extremes in a complex test matrix. Material pair samples were “rubbed together” in an accurately controlled manner. The types of relative displacement that were used were single excursion pull and realistic road inputs in the form of a shaped random profile. The material pairs included combinations of PVC, ABS, TPO, PP and painted metal from sub-systems such as instrument panels, center consoles, body panels, door trim and weather-strips. Instationary Zwicker loudness was used as a metric for quantifying the squeak in addition to classical friction parameters.
From the test data, a classification of the material pairs was made pertaining to their propensity to generate squeak and itch (S&I). Initial levels of correlation with GM material experts' classifications of the same pairs are promising and are the motivation for further studies.
The Team (Defiance, GM and MB Dynamics) feels strongly about the need for a comprehensive materials database that is the result of a uniform experimental procedure to identify pertinent material characteristics in order to understand, verify and significantly reduce stick-slip in automotive applications. The Team feels that the test equipment, test procedures and analysis methods that were developed during this project and that are described in this paper, greatly contribute towards this cause. The Team wants to extend the invitation to other interested parties (tribology researchers, scientists, automotive or other engineers), to bundle efforts, share best practices and lessons learned, and work towards a standard for material friction pair testing.