1997-05-20

Intermittent Modal Vibration and Squeal Sounds Found in Electric Motor-Operated Seat Adjusters 972060

Two years after the start of production, some members in a family of power seat adjusters developed an intermittent loud squeal sound when operated in the vehicle. An exhaustive and comprehensive engineering analysis identified the noise source to be primarily a single component in the seat track which was excited under specific conditions to vibrate in its free - free natural resonant frequency mode. The component was identified as the horizontal lead screw which vibrated under stick-slip principles against mating hardware. The noise was not reproducible in any consistent way; therefore, it was not readily detectable with 100% serial testing. Several solutions were enacted for controlling the problem in the short term while an investigation to the root cause was completed. Three long term solutions which addressed the root cause were pursued in parallel up to the production release of the best solution. By means of designed experiments, frequency analysis and systems engineering principles, a newly designed drive nut, having two added degrees of freedom of motion, provided the robustness needed to eliminate the squeal 100% of the time while serving the customers with a safe and secure solution.

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