The gear can be classified according to tooth shape, gear shape, tooth line shape, gear tooth surface and manufacturing method.
The tooth profile of gear includes tooth profile curve, pressure angle, tooth height and displacement. The involute gear is relatively easy to manufacture, so the involute gear used in the modern gear is the absolute majority, while the cycloidal gear and the circular arc gear are less applied.
In the angle of pressure angle, the bearing capacity of small pressure angle gear is less; while the large pressure angle gear, although the bearing capacity is high, the load of the bearing increases with the same transmission torque, so it is only used in special case. The gear tooth height has been standardized, generally adopt standard tooth height. The modification gear has many advantages, and it has been widely used in all kinds of machinery and equipment.