AGMA 93FTM11-1993 pdf free download.The Relative Noise I evels of Parallel Axis Gear Sets with Various Contact Ratios and Gear Tooth Forms by: R. J. Drago, J. W. Lenski and R. H. Spencer,Boeing Defense and Space Group;M. Valco, Lewis Research Center, U.S. Army;F. Oswald, Lewis research Center, NASA.
Since these gears were tested in the NASA test rig, it was also necessary to maintain compatibility with the testrig. The standard NASA test gears incorporated a loose fit between the gear bore and the sbaft outside diameter. In order to be sure that the noise test results, especially for the helical gears, were not affected by this loose fit, it was changed to a press fit which would be more typical of that used in a helicopter application. While this change caused some difficulty in changing from one configuration to another, it was important from a test validity point of view. Previous’ NASA testing of Boeing Helicopters designed small gears using the high profile contact ratio noninvolute tooth form (HCR NIF) indicated that their surface load capacity was substantially higher than that of conventional involute gears and that their bending load capacity (at torque loads) was at least equal to and actually slightly greater than the standard involute gears. The scoring resistance of the HCRNIF gears, in the NASA tests, appeared to be lower than that of equivalent standard gears. The lower scoring load capacity performance may have been due to inadequate profile modification on the small test gears therefore the HCR-NIF gears for this testing incorporated improved profile modifications.
The test gear configurations were selected to be representative of those which are either actually in use or have near term potential of being used in helicopter transmissions. While lower noise levels are generally associated with helical gears as compared to spurs,there was no definitive data, for accurate, ground tooth gears, which defines the noise advantage which may be obtained. Similarly, anecdotal information indicates that higher contact ratios, both face and profile, also tend to reduce noise levels but, again,hard data was not readily available.
While helical gears provide some noise reduction,their use also generates a thrust load which must be dealt with in the design of the overall system,especially the support bearings, gear blank design, and housing structure. Double helical gears provide some relief from the net thrust problems, however, the thrust loads from each helix must still be cancelled within the gear blank and the overall effect of this on the noise level of the gear bas not been studied at all.New tooth forms of various noninvolute types have been investigated for possible use in helicopter transmissions in recent years but these investigations have centered almost universally on the load capacity aspect of the forms and not tbeir noise behavior. One of these has demonstrated some potential for improved load capacity in previous testing.
Considering all of these factors, the range of gear configurations defined in Table I and shown in Figure 1 was selected to provide some basic answers to their respective noise behaviors. The basic gear tooth data for the test gears is provided in Table II.AGMA 93FTM11 pdf download.