The basic parameters that determine the geometry of helical gears include the number of teeth Z and the normal pressure angle α n. Normal modulus Mn, normal backlash coefficient C, helical gear thickness B, normal addendum height coefficient h, and helix angle on indexing circle β 。 In order to realize the parametric modeling of helical gear, the above variables are defined in advance, and the expression adopts the form of “parameter expression variable”. The above basic parameters are given initial values before modeling. The main expressions to be established in modeling are as follows:

In the above formulas,

αt – pressure angle of helical gear end face;

mt – module of helical gear end face;

d – diameter of indexing circle on helical gear end face;

da – diameter of addendum circle on helical gear end face;

db – diameter of base circle on the end face of helical gear;

df – diameter of tooth root circle on the end face of helical gear.