Dynamic Behaviour of Spur Gears

Abstract

In an earlier paper by one of the authors (9) a theoretical analysis suggested that, at certain speeds, large vibrations can occur in a pair of spur gears, without any manufacturing errors and without any external excitation, provided the damping is less than about 0·07 of critical. In this paper a summary is given of an extension to this theoretical analysis, but the main part is concerned with experimental observations on a back-to-back gear test rig. From these observations the maximum dynamic loads on the teeth have been deduced. It has been found that for all applied loads between zero and 1 1/4 times design load, the maximum dynamic load never exceeds twice the design load (the design load is the load which gives a constant transmission error at low speed). It should be noted that if the design load (for which the profile modification is specified) is appreciably greater than the applied load, the dynamic increment may be very large. Excessive profile modification should therefore be avoided. As the damping in the rig is only about 0·02 of critical, these figures are likely to be an upper limit for isolated, precision spur gears.