# Calculation of Rolling Point Position of Modified Helical Gear

The key to calculate the impact force of rodent is to accurately locate the rodent point.Based on the position of the rodent point, the relative normal speed and meshing stiffness of the two tooth surfaces at this point can be calculated, and then the impact force of the rodent can be calculated.

When the standard gear engages, due to the deformation of the load on the teeth, the tip point of the large gear tooth contacts the tooth surface of the small gear in advance, and the large and small gear contacts the “tip-tooth surface”.After tooth surface modification, under less load, the large and small wheels are in “tooth surface-tooth surface” contact when the teeth engage because the clearance between the teeth produced by modification is sufficient to compensate for the load deformation of the teeth.Under larger load, the clearance between the teeth due to modification is completely compensated by the load deformation of the teeth. At this time, when the gear engages, the tip point of the large teeth first contacts the tooth surface of the small wheel, and the large and small wheels contact the “tip-tooth surface”.

Based on the above analysis, this paper divides the working conditions to solve the position of the rodent point on the tooth surface into two parts. Working condition 1 is to solve the position of the rodent point when the edge contact occurs, including the standard tooth surface and the modified tooth surface under large load; Working condition 2 is to solve the position of the rodent point when the edge contact does not occur and includes the modified tooth surface under small load.

In Figures 1 and 2, geometric transmission error (TE) and loaded transmission error (LTE) are obtained by tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA).

In the calculation of TCA, the angle of rotation of small and large wheel teeth in the first contact at the root of small wheel teeth is shown in the figure.It can be found from the diagram that whether the LTE at 1A is larger than TE or not is the main basis for judging the occurrence of edge contact.

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