Paper 8: Excitation of Resonant Vibrations in Spur and Helical Gear Systems

Abstract

A back-to-back gear rig (12 000 ft/min maximum pitch-line velocity) was used to demonstrate various causes of high-speed gear vibrations with either straight spur or helical teeth, the transducers being four strain gauges mounted on the gear shaft. The primary cause of excitation is shown to be transmission errors in the straight spur case, but with helical teeth a variation in contact length is the prominent factor, with lateral movement of the resultant load as possibly the chief cause where the contact length is constant. Noticeable temperature effects were only experienced at the highest speeds; here the thickness of the oil film on the tooth face has a considerable effect on the tip relief, the modification becoming less as the temperature rose. Damping varied considerably (0·004 to 0·042 critical) between modes, and slightly with change in load, and therefore no overall damping factor could be taken for the rig; the average damping factor for the specific mode was used in each amplitude calculation. Calculation of the natural frequencies of the gear system was performed with the use of receptance theory with considerable success; the amplitude predictions were not quite so favourable but were generally of the right order.