Design theory analysis of automobile gear hob

The gear hob used in the automobile industry is usually the tool for Machining Involute Cylindrical Gear by generating method on the gear hobbing machine. During gear hobbing, the hob is installed on the main shaft of the gear hobbing machine. It makes rotary cutting movement on one side and feed movement along the axis of the gear blank on the other side. At the same time, the gear blank also makes corresponding rotation with the rotation of the hob (tooth splitting motion when cutting spur gear and tooth splitting motion and additional motion when cutting helical gear), so as to process the whole gear. Because the gear hob processes the gear by generating method, its cutting process is equivalent to the meshing process of a pair of staggered helical gears.

Worm is essentially a helical gear with large helical angle and few teeth or equal to 1). Therefore, a gear hob with module can process various cylindrical gears with the same module and tooth shape angle but different tooth number, displacement coefficient and helical angle.

The design principle of hob is based on the gear meshing principle. In theory and practical use, the gear can transfer the rotary motion form between two parallel shafts, intersecting shafts and staggered shafts, such as spur cylindrical gear, non cylindrical gear, helical gear and helical gear, worm gear (common design form of automobile gear hob), bevel gear and quasi double-sided gear, etc. In recent years, new gear meshing forms have emerged in the world, such as double circular arc gear and plane double enveloping cambered worm gear pair, many of which have been used in the machinery industry and achieved good results.

However, the theoretical research of automobile can only correspond to the correct gear transmission form, and study this kind of gear according to the special situation of a transmission form or tooth shape. For example, the involute gear can only be studied according to the involute form, and the conclusions obtained are not fully applicable to other gears. In this way, it will cause a great workload for the engineers who use the tool. It is necessary to study each form of gear pair separately in order to use the tool correctly. So, is there a theory that can be used as a general theory for all types of gear meshing? This theory can make tool users guide them in the application field more correctly and reasonably. So that they do not need to study the essential theory and research methods of gear meshing, but start from the actual production and use conditions and focus more deeply and effectively on the productive work such as product quality improvement and efficiency improvement.

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