Dynamic load on gear

Machine Design

Gear Drive

Dynamic load on gear

Introduction:

The velocity factor was used to make approximate allowance for the effect of dynamic loading.

Reasons of dynamic load:

The dynamic loads are due to the following reasons :

1. Inaccuracies of tooth spacing,
2. Irregularities in tooth profiles, and
3. Deflections of teeth under load.

A closer approximation to the actual conditions may be made by the use of equations based on extensive series of tests, as follows :

WD = WT WI

where WD = Total dynamic load,
WT = Steady load due to transmitted torque, and
WI = Increment load due to dynamic action.
The increment load (WI) depends upon the pitch line velocity, the face width, material of the gears, the accuracy of cut and the tangential load. For average conditions, the dynamic load is determined by using the following Buckingham equation, i.e.

where
WD = Total dynamic load in newtons,
WT = Steady transmitted load in newtons,
v = Pitch line velocity in m/s,
b = Face width of gears in mm, and
C = A deformation or dynamic factor in N/mm.

A deformation factor (C) depends upon the error in action between teeth, the class of cut of the gears, the tooth form and the material of the gears. The following table shows the values of deformation factor (C) for checking the dynamic load on gears.

The value of C in N/mm may be determined by using the following relation :

where K = A factor depending upon the form of the teeth.
              = 0.107, for 14 1/2 ° full depth involute system.
              = 0.111, for 20° full depth involute system.
              = 0.115 for 20° stub system.
EP = Young's modulus for the material of the pinion in N/mm2.
EG = Young's modulus for the material of gear in N/mm2.
e = Tooth error action in mm.

The maximum allowable tooth error in action (e) depends upon the pitch line velocity (v) and the class of cut of the gears