Dynamic Behaviour of Spur Gears

TLDR

Earlier theoretical work predicts that spur gears can exhibit large vibrations at certain speeds when damping is below about 0.07 of critical, and the current rig’s low damping (~0.02) suggests the observed limits are likely upper bounds for precision spur gears. This study extends the earlier theory and presents experimental observations from a back‑to‑back gear test rig. Dynamic loads were measured on a back‑to‑back gear test rig to assess the maximum dynamic loads on the teeth. The experiments show that for loads up to 1.25 times the design load, the maximum dynamic load never exceeds twice the design load, but when the design load is much higher than the applied load, the dynamic increment can be large, indicating that excessive profile modification should be avoided.

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.