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Technical Paper

Mechanical Retractor Noise Evaluation on Electrodynamic Shaker: Test Procedure

Modern vehicles are driven with various speeds over specific rough road tracks to detect the presence of annoying buzz, squeak and rattle sounds. As known in the occupant safety industry the mechanical locking systems of seat belt retractors can be significant noise sources, when excited by road vibrations. A reliable bench test procedure is necessary to quantify the acoustic performance of retractors, verify production quality, and derive realistic acoustic product targets. With this goal, a vibration noise test procedure has been developed condensing the work over three years by the K2 Comet automotive research project X2T1, various OEM retractor noise specifications closed to public and own research. The load case in this specification has been defined as horizontal 60 Hz bandlimited broadband excitation, while the N10 instationary loudness metric has been selected to characterize the retractor acoustic performance.
Technical Paper

Seat Belt Retractor Noise Test Correlation to 2DOF Shaker Test and Real Vehicle Comfort

Seatbelt retractors as important part of modern safety systems are mounted in any automotive vehicle. Their internal locking mechanism is based on mechanically sensing elements. When the vehicle is run over rough road tracks, the retractor oscillates by spatial mode shapes and its interior components are subjected to vibrations in all 6 degrees of freedoms (DOF). Functional backlash of sensing elements cause impacts with neighbouring parts and leads to weak, but persistent rattle sound, being often rated acoustically annoying in the vehicle. Current acoustic retractor bench tests use exclusively uni-directional excitations. Therefore, a silent 2 DOF test bench is developed to investigate the effect of multi-dimensional excitation on retractor acoustics, combining two slip-tables, each driven independently by a shaker. Tests on this prototype test bench show, that cross coupling between the two perpendicular directions is less than 1%, allowing to control both directions independently.