Developing Robust Vibration Excitation and Control Methods for Evaluating Rattle Noise in Automotive Components 1999-01-1725
The authors participated in a task force that was required to develop a repeatable, dependable, and reliable test procedure to compare, rate, and evaluate the severity of rattles. The assemblies involved in the study are designed and manufactured by different companies and are tested by different people on test equipment and instrumentation from different suppliers. The challenges therefore, were considerable and involved both the vibration inputs and responses as well as the acoustic responses. At the beginning of this activity, it was observed that different test labs using the same Ford vibration specs were obtaining different sounds from the same test item! Clearly, this was unacceptable and the test methods had to be improved and standardized.
This paper focuses on vibration related to rattle testing. The particular assemblies used in this study were seat belt retractors. However, the lessons learned can be applied to vibration testing of any automotive component that rattles (e.g., HVAC modules, instrument panels, ashtrays, radios, etc).
Challenges in producing appropriate vibration conditions in a test lab included:
minimizing the sound levels generated by the shaker itself (without test item) while creating the vibration
selecting the type of vibration to use: sine tones vs. random vibration vs. time histories
out-of-band energy caused by rattles in the test item which “shake” the shaker
minimizing or eliminating the resonances of the excitation system
undesirable, off-axis motion of the exciter that results from offset payloads
Firm specs were established on all these parameters, and qualification tests for the test system(s) were developed. The end result was a specification that contained enough detail and guidance to ensure that good tests could be run by different test labs. This produces more consistent results that will be directly comparable across different models from different seat belt retractor suppliers.