The effects of profile relief on narrow face width parallel axis gears.
The well established practice of applying tip and/or root relief to the teeth of low contact
ratio spur gears is reviewed. Results are presented for the experimental validation of a
systematic design method for profile relief that depends critically on how far the relief
extends along the path of contact. This method has proved to be effective in controlling
gear vibration and noise. A good correlation between static transmission error, dynamic
transmission error and sound pressure level was found. This allows design rules to be
formulated which can be applied to achieve the minimum vibration and noise levels at a
given operating load.
A computer program was also developed that allows the introduction of measured gear
tooth profiles from an involute tester, to predict the static transmission error curves and
thus give an indication of gear quality as regards vibration and noise levels for any given
simulated operating load or load range.
The computer program was extended to take into consideration the more complex
geometry of helical gears using the 'Thin Slice' theory. This allows the prediction of the
effects of lead crowning, misalignment, pitch errors and various profile reliefs including
relief coined "cross relief", where the relief is applied parallel to the base helix angle.
An optimisation routine was included in the computer program that systematically varies
the extent of profile relief and amount of lead crowning to minimise transmission error.
Since the amount of required profile relief is concomitant with extent of relief and
amount of lead crowning (load remaining constant), the program iterates to find the
correct amount of profile relief to avoid undesirable comer/tip contact.
This new approach has facilitated the generalisation of the effects of profile relief on
transmission error for a whole range of typical axial and transverse contact ratios for
narrow face width helical gears, previous analyses concentrating on specific designs.
Results are also presented for the experimental validation of predicted static transmission
error in helical gears. A good correlation between static transmission error, dynamic
transmission error and sound pressure level was found as in the spur gear analysis.