Internal Gears: Technical Information
Characteristics∧ topKHK stock internal gears are offered in modules 0.5 to 3 in 50 to 200 teeth. They can be used in many applications including planetary gear drives.
|Module||0.5 ~ 3||2 ~ 3|
|Tooth Surface Finish||Cut||Cut|
|Precision JIS B 1702-1:1998||N8 Note 1||N9|
|Features||A popular type of internal gear; low cost and suitable for many applications.||Ring gear large in size / number of tooth. It can be cut to make segment gears and corner racks.|
Selection Hints∧ topPlease select the most suitable products by carefully considering the characteristics of items and contents of the product tables. It is also important to read all applicable notes before the final selection.
1. Caution in Selecting Mating Gears
KHK stock internal gears can mate with any spur gears of the same module, however, there are cases of involute, trochoid and trimming interference occurrences, depending on the number of teeth of the mating gear. Various types of interference and their symptoms and causes are tabulated below, also shown, the number of teeth of allowable mating pinions.
Interferences and the Symptoms
|Involute interference||The tip of the internal gear digs into the root of the pinion.||Too few teeth on the pinion.|
|Trochoid interference||The exiting pinion tooth contacts the internal gear tooth.||Too little difference in number of teeth of the two gears.|
|Trimming interference||Pinion can slide in or out axially but cannot move radially.||Too little difference in number of teeth of the two gears.|
Allowable Mating Pinions and Number of Teeth
|No. of teeth of
|No. of teeth of Allowable Mating Pinions|
|Lower limit No. of teeth by Involute interference||Upper limit No. of teeth by Trochoid interference||Upper limit No. of teeth by Trimming interference|
2. Caution in Selecting Gears Based on Gear Strength
The gear strength values shown in the product pages were computed by assuming a certain application environment. Therefore, they should be used as reference only. We recommend that each user computes his own values by applying the actual usage conditions. The table below contains the assumptions established for these products in order to compute gear strengths.
|Catalog No. Item||KSI||KSIR|
|Calculation Assumptions for Bending Strength of Gears|
|Formula NOTE 1||Formula of spur and helical gears on bending strength (JGMA401-01)|
|No. of teeth of mating gears||30|
|Impact from motor||Uniform load|
|Impact from load||Uniform load|
|Direction of load||Bidirectional|
|Allowable beam stress at root σFlim (kgf/mm²) NOTE 2||19|
|Safety factor SF||1.2|
|Calculation assumptions for Surface Durability (Except where it is common with bending strength)|
|Formula NOTE 1||Formula of spur and helical gears on surface durability (JGMA402-01)|
|Kinematic viscosity of lubricant||100cSt (50°C)|
|Gear support||Symmetric support by bearings|
|Allowable Hertz stress σHlim (kgf/mm²)||49|
|Safety factor SH||1.15|
Application Hints∧ topIn order to use KHK stock internal gears safely, read the Application Hints carefully before proceeding. Also "1. Caution on Performing Secondary Operations>", "3. Notes on Starting Operations" and "4. Other Points to Consider in Applications" in the Spur Gear KHK Technical Section should be consulted.
1. Point of Caution in Assembling
- a KHK stock internal gears are designed to give the proper backlash when assembled using the center distance given by the formula below. The amount of backlash is given in the product table for each gear.
a = d2 - d1 Where
a : Center Distance
d1 : Pitch Diameter of Pinion
d2 : Pitch diameter of internal gear
- Note that the direction of rotation of the internal gear is different from that of two spur gears in mesh.
- To use as a planetary gear drive, the following conditions must be satisfied.
|No. of teeth of internal gear||No. of planet gears||No. of teeth of sun gear||No. of teeth of planet gears||Reduction ratio of planetary type||Reduction ratio of solar type||Reduction ratio of star type|