Characteristics

KHK 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.

Catalog Number SI
Module : 0.5 – 3
Material : S45C
Heat Treatment : –
Tooth Surface Finish : Cut
Precision JIS B 1702-1:1998 : N8 NOTE 1
Secondary Operations : Possible
Features : A popular type of internal gear; low cost and suitable for many applications.

Catalog Number SIR
Module : 2 -3
Material : S45C
Heat Treatment : –
Tooth Surface Finish : Cut
Precision JIS B 1702-1:1998 : N9
Secondary Operations : Possible
Features : Ring gear large in size / number of tooth. It can be cut to make segment gears and corner racks.

[Note 1] The Product accuracy class having a module less than 0.8 corresponds to ‘equivalent’ as shown in the table.

Selection Hints

Please 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 the 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

TYPE / Involute interference
SYMPTOMS / The tip of the internal gear digs into the root of the pinion.
CAUSES / Too few teeth on the pinion.

TYPE / Trochoid interference
SYMPTOMS / The exiting pinion tooth contacts the internal gear tooth.
CAUSES / Too little difference in number of teeth of the two gears.

TYPE / Trimming interference
SYMPTOMS / Pinion can slide in or out axially but cannot move radially.
CAUSES / Too little difference in number of teeth of the two gears.

Allowable Mating Pinions and Number of Teeth

Number of teeth of
Internal Gear
Number of teeth of Allowable Mating Pinions
Lower limit Number of teeth by Involute interference Upper limit Number of teeth by Trochoid interference Upper limit Number of teeth by Trimming interference
50 22 41 33
60 21 51 43
80 20 72 64
100 19 92 84
120 19 112 104
160 19 152 144
200 18 192 184

 

Established equipment and technology. Custom Gears are also available.
Diameter φ700mm maximum, Module 6.5 maximum, Cutting Stroke 170 mm
Gear cutting by CNC Gear Shaper
Gear cutting by CNC Gear Shaper

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.

Calculation assumptions for Bending Strength of Gears

Catalog number SI and SIR
Formula NOTE 1 / Formula of spur and helical gears on bending strength (JGMA401-01)
Number of teeth of mating gears / 30
Rotation / 100rpm
Durability / Over 107cycles
Impact from motor / Uniform load
Impact from load / Uniform load
Direction of load / Bidirectional
Allowable beam stress at root σFlim (kgf/mm 2) 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 deg C)
Gear support / Symmetric support by bearings
Allowable Hertz stress σHlim (kgf/mm2) / 49
Safety factor SH / 1.15

[Note 1] The gear strength formula is based on JGMA (Japanese Gear Manufacturers’ Association) The units for the rotational speed (rpm) and the stress (kgf/mm2) are adjusted to the units needed in the formula.
[Note 2] The allowable bending stress at the root σFlim is calculated from JGMA401-01, and set to 2/3 of the value in the consideration of the use of planetary-, idler-, or other gear systems, loaded in both directions.

Application Hints

In 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 section should be consulted (Page 32).

1. Point of Caution in Assembling

  1. 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 / 2
    Where
    a :Center distance
    d1 :Pitch diameter of Pinion
    d2 :Pitch diameter of Internal Gear
  2. Note that the direction of rotation of the internal gear is different from that of two spur gears in mesh.
    Gear Ratio and Direction of Rotation
    Gear Ratio and Direction of Rotation
  3. To use as a planetary gear drive, the following conditions must be satisfied.
    Condition on number of teeth in planetary mechanism
    Condition 1 … zc = za + 2zb
    Condition 2 … za + zc / N = Integer
    Condition 3 … zb + 2 < (za + zb) sin 180° / N
    za :Number of teeth of Sun Gear
    zb :Number of teeth of Planet Gears
    zc :Number of teeth of Internal Gear
    N :Number of Planet Gears

Example of combinations

Number of teeth of internal gear Number of planet gears Number of teeth of sun gear Number of teeth of planet gears Reduction ratio of planetary type Reduction ratio of solar type Reduction ratio of star type
60 3 18 21 4.333 1.3 -3.333
80 3 16 32 6 1.2 -5
80 3 40 20 3 1.5 -2
100 3 20 40 6 1.2 -5
100 3 50 25 3 1.5 -2

Types of planetary gear reduction mechanism
Types of planetary gear reduction mechanism

Application Examples
The illustration is a design example, not a design for machinery or a device in actual use.

Application Examples
Upper : Planetary Gear Mechanism used in a reduction gear *
Bottom : Mechanical Paradox Gear Mechanism used in a large reduction gear