Gear module is not the higher the better. If the number of teeth of the gear is certain, the larger the modulus is the larger the radial size of the wheel, and at the same time participate in the meshing of the number of teeth is less, which is not conducive to gear transmission.

Principle of selection of the number of teeth: in order to meet the bending strength conditions, as far as possible to choose more, closed transmission in the number of teeth = 20 ~ 40, open transmission 17 ~ 20, pinion teeth should be avoided to avoid the root of the cut, the number of teeth meshing with each other is best for the prime, and also consider the need to make up with the rounding of the center distance.

Module selection principle: under the conditions of bending strength to meet the smaller module.

Gear modulus is generally obtained through the calculation, comparison, the following are two gear modulus selection method:

(1) hardened gear

To be designed according to the bending fatigue strength, the formula is the calculation of the modulus, just to calculate the value of the standard modulus table with the control, take a value from the calculation of the nearest but larger than the standard modulus value.

(2) soft-toothed gear

To be designed according to the contact fatigue strength, the formula is to calculate the pinion indexing circle diameter, and then determine the number of teeth, pinion teeth are generally taken from 20 to 40 teeth, using the formula m = d/z modulus, and then repeat the process of (1) - take a calculated value from the closest but larger than it! The nearest but larger than the standard modulus value.

Extended information

Gear modulus series standard is based on the design, manufacturing and inspection requirements. For gears with non-straight teeth, modulus has the difference between normal modulus mn, face modulus ms and axial modulus mx, which are all based on the ratio of the respective tooth pitch (normal pitch, face pitch and axial pitch) to the circumference, which are also in millimeters.

For bevel gears, the modulus is divided into large-end modulus me, average modulus mm and small-end modulus m1. For cutting tools, there are corresponding tool modulus, etc.. The standard module is widely used.

In the metric system of gear transmission, worm gear transmission, synchronous toothed belt drive and ratchet, gear coupling, spline and other parts, the standard modulus is one of the most basic parameters. It is on the design of the above parts, manufacturing, maintenance, etc. play the role of the basic parameters (see cylindrical gear transmission, worm gear transmission, etc.).

Baidu Encyclopedia - Gear Modulus