The design content of the involute spur gear transmission mainly includes selecting the transmission type, determining the main parameters, and calculating the geometric dimension check of the gear transmission. When designing a gear transmission, if the given original data is different, the design steps are also different.

1. The given raw data are z1, z2, m, a, ha* and c*

    1. Select the transmission type. If z1+z2<2zmin, positive transmission needs to be selected; otherwise, other types of transmission can be considered.

    2. Select the displacement coefficients x1 and x2 for the two rounds. The selection of the displacement coefficient should ensure that the two wheels are not undercut, and it is beneficial to improve the transmission quality and bearing capacity.

    3. Calculate the meshing angle: inva′=2(x1+x2)tga/(z1+z2)+inva

    4. Calculate the geometric dimensions of the gear drive

    5. Check the coincidence degree and the top circle tooth thickness of the positive displacement gear.

2. The given raw data are z1, z2, m, a, ha*, c* and a'

    1. Calculate the standard center distance: a=m(z1+z2)/2

    2. Calculate the meshing angle: a′=arccos(a cosa/a′)

    3. Calculate the sum of displacement coefficients: x1+x2={(inva′-inva)(z1+z2)}/ 2tga

    4. Assign the displacement coefficients x1 and x2 for the two rounds.

    5. Calculate the geometric gears of the gear drive.

    6. Check the coincidence degree and the top circle tooth thickness of the positive displacement gear.

3. The given raw data are i12, m, a, a', ha* and c*

     Select the number of teeth on both wheels. From a=m(z1+z2)/2 and i12=z2/z1 can be obtained

               a=mz1(1+i12)/2

Because there are many advantages of positive transmission, it should be preferred to choose positive transmission. If positive drive is selected, then:

               a′>a=mz1(1+i12)/2

It can be obtained that z1<2a′/m(1+i12)

while z2=i12z1 (rounded)