In the gear design and manufacturing process, Module (m) is a crucial parameter, which not only affects the size of the gear, but also directly determines the engagement performance of the gear. However, in different types of gears (such as straight gear and inclined gear), the expression of modulus is different, especially the concept of normal modulus (mn) and end surface modulus (mt), often easy to be confused. This paper will deeply analyze the difference between the two, their calculation methods and their application in gear design.

1. Basic concept of gear module number

The us (m) refers to the ratio of the distance between adjacent teeth (pitch p) to π, usually in mm (mm), calculated:

Mode number is the key parameter to measure the size of gear, which directly affects the strength, bearing capacity and manufacturing process of gear. In the standard straight gear, the definition of modulus is relatively simple, but in the inclined gear, due to the influence of the tooth line Angle, modulus needs to be further distinguished into normal modulus (mn) and end face modulus (mt).

• The difference between the normal modulus (mn) and the end surface modulus (mt)

In inclined gear, the spiral angle (β) between the gear line and the gear shaft:

Normal modulus number (mn) the module number of the gear tooth profile on the normal section, that is, the module number perpendicular to the direction of the tooth line.

End face modulus (mt) The modulus of the gear tooth profile on the end surface, which is perpendicular to the direction of the gear shaft.

Their relationship is as follows:

Where β is the spiral angle of the gear, when β = 0, the oblique gear is degenerated to the straight gear, then mn = mt, no need to distinguish.

3. Application scenarios of normal modulus and end face modulus

(1) Straight gear

In the straight gear, the normal section and end face of the gear are identical because the tooth line is parallel to the axis. Therefore, the normal modulus is equal to the end surface modulus, and the design can be directly selected according to the standard modulus, without additional conversion.

(2) Slant gear

In oblique gear design, the actual engagement of the gear is in the normal plane, thus:

The normal modulus mn design can make the inclined gear and straight gear gear tool compatible and easy machining.

Using the end surface modulus mt for calculation, it is more suitable for the applications with strict requirements on the axial dimension, such as aviation gear, rail transit gear box, etc.

4. Standard provisions of normal module and end surface modulus

International Gear Standard (ISO), Chinese National Standard (GB), American Standard (AGMA) and Japanese Standard (JIS) have different definitions and applications of normal module and end surface modulus:

ISO 53 & ISO 21771 defines the standard modulus and its scope of application, and recommends using the normal modulus as the standardized modulus.

GB / T 1357-1987 is applicable to the Chinese domestic inclined gear standard, and the normal analog mn is used as the main calculation basis.

AGMA 2015 The application of end surface module mt in high precision processing, such as aircraft turbine transmission gear.JIS B 1701 The Japanese gear standard, it is recommended to correct the design in machine tools and high-speed transmission devices.

5. Calculate the case analysis

Case 1: straight gear modular calculation

The known pitch of straight gear is 31.42 mm and its module m is calculated.

Since the straight gear has no spiral angle, therefore mn = mt = 10 mm.

Case 2: modular calculation of inclined gear

Known aspect of the diagonal gear modular mt = 10 mm, the gear spiral angle β = 20, find the normal analog mn.

That is, the modulus of the gear in the upward method is 9.39 mm, and the usage modulus should be selected in the design of the tool and processing.

engineering application

Straight gear: the normal and end modulus are equal, without conversion.

Slevel gear: due to the existence of spiral Angle, the normal modulus and the end surface modulus have a conversion relationship, which modulus needs to be used in the design.

Processing and measurement: gear processing generally adopts normal analog, and the end surface analog is usually used for the assembly and calculation of the whole machine.

Standard selection: ISO, GB, AGMA, JIS and other international standards have different usage modes, and appropriate standards should be selected according to the specific industry requirements.

Whether in gear manufacturing, transmission design, or in rail transit, all kinds of transmission equipment, the correct understanding of the concept of normal analog and end surface modulus, is the basis to ensure the reliability and accuracy of gear transmission.