Profile modification of helical gear

Helical gear is the most commonly used type of automotive power transmission gear. Generally, it must work under the condition of high speed and heavy load, and requires less vibration and noise. In order to improve their dynamic performance at high speed and reduce vibration and noise, tooth profile modification has become a necessary design and process means.

There are two ways to modify the helical gear profile:

A is oblique modification, that is, the modified tooth surface is along the direction of the contact line of the tooth surface. This kind of modification has no essential difference from spur gear in calculation method, but it is required that the modified surface and involute surface are tangent along the contact line, which is difficult to ensure in technology.

B is straight modification, that is, the modified surface is parallel to the tooth direction, and the whole tooth surface can be processed into a smooth surface in technology. Most of the modifications actually adopted by countries all over the world are straight modifications. However, because the tooth surface contact line of helical gear is inclined, the direct modification will change the load distribution along the contact line, or even become non full-length contact, and then change the coincidence degree and load distribution between teeth, which makes the traditional gear modification calculation method invalid and greatly increases the difficulty of modification design.

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