AUTOMOBILE DRIVE-LINE VIBRATION AND INTERNAL NOISE

This paper describes an experimental study of the drive-line vibration modes, and internal noise under road excitation of a conventional family car. The drive-line comprised the drive-shaft, axle, semi-elliptic multi-leaf springs and wheels. Drive-line vibration modes were identified experimentally in the laboratory by applying harmonic forces to various locations within the drive-line system. Eleven resonant modes were identified in the range 10-200 hz. Diagrams illustrate each mode shape. Under laboratory excitation a significant internal noise was caused by the vibration mode at 23 hz which arises from displacement within the rubber insulator separating spring and axle casing. Axle vibration and internal noise were simultaneously recorded during road testing at 22 constant speeds covering the range 30-75 mph using fourth gear. Typical power spectra are illustrated. Excitation of the axle bending mode (67 hz) at engine rotational frequency caused a measurable noise increase. Sub-audible noise was found to be a large component at all road speeds. At 30-40 mph, large noise contributions were due to excitation of body bending at engine rotation, and cavity acoustic resonance at twice engine rotation frequency. Engine rotation did not excite the cavity resonance at the highest road speed. Frequencies of most noise components were related to engine or wheel rotational frequencies. Important frequencies, largely independent of road speed, were 7.5, 36-39, and 73-77 hz. /Author/ /TRRL/