Gear displacement is divided into positive displacement and negative displacement
Classification： Blog
Release time：2024-06-20
The tooth profile of the gear we usually use is generally a standard involute, but there are also some situations that need to be modified, such as adjusting the center distance and preventing the undercut of the pinion.
1) Number and shape of gear teeth
The involute tooth profile curve varies with the number of teeth. The more the number of teeth, the more the tooth curve tends to be straight. As the number of teeth increases, the tooth profile of the tooth root becomes thicker and the tooth strength increases.
As can be seen from the above figure, for a gear with a tooth number of 10, part of the involute tooth profile at the tooth root of the gear tooth is excavated, resulting in undercutting. However, if the gear with the number of teeth z = 10 adopts positive displacement, the diameter of the tooth tip circle is increased, and the tooth thickness of the teeth is increased, the gear strength of the gear with the 200 number of teeth can be obtained.
2) Variable gear
The following figure is a schematic diagram of gear positive displacement cutting with tooth number z = 10. When cutting teeth, the amount of movement xm(mm) of the tool in the radial direction is called the radial displacement amount (abbreviated as displacement amount).
xm = displacement (mm)
x = coefficient of displacement
m = modulus (mm)
Tooth profile change by positive displacement. The tooth thickness of the teeth increases, and the outer diameter (addendum diameter> also becomes larger. The gear can avoid the occurrence of undercut (Undercut) by adopting positive displacement. The gear shift can also achieve other purposes, such as changing the center distance, positive shift can increase the center distance, negative shift can reduce the center distance.
Whether it is positive or negative displacement gear, there is a limit to the amount of displacement.
3) Positive and negative displacement
The displacement has positive displacement and negative displacement. Although the tooth height is the same, the tooth thickness is different. The tooth thickness becomes thicker for the positive displacement gear, and the tooth thickness becomes thinner for the negative displacement gear.
When the center distance of the two gears cannot be changed, make a positive displacement of the small gear (to avoid undercutting) and a negative displacement of the large gear to make the center distance the same. In this case, the absolute values of the displacement amounts are equal.
4) meshing of modified gear
The standard gears are meshed in the tangent state of the indexing circle of each gear. The meshing of the shifted gears, as shown in the figure, is tangentially meshed on the meshing pitch circle. The pressure angle on the meshing pitch circle is called the meshing angle. The engagement angle is different from the pressure angle on the indexing circle (indexing circle pressure angle). The meshing angle is an important factor in the design of the displacement gear.
6) The role of gear displacement
It can prevent the undercut phenomenon caused by the small number of teeth during processing; the desired center distance can be obtained by shifting; when the gear ratio of a pair of gears is large, the pinion gear that is prone to wear is positively shifted, Make the tooth thickness thicker. On the contrary, the large gear is negatively shifted to make the tooth thickness thinner, so that the life of the two gears is close.
keyword： Gear,Shaft