Inner Gear are a common transmission solution in modern mechanical design, offering a more compact, efficient, and high-torque transmission. They can be found in robotic joints, automatic transmissions in cars, and hydraulic pumps. Below, we'll provide a deeper understanding of internal gears by explaining their basic principles, how they work, and their advantages.
What is an Inner Gear?
An internal gear is a type of gear with teeth machined on the inside of a ring. Unlike conventional gears with teeth on the outside, it resembles a hollow gear. (See the image below.)
When an internal gear meshes with one or more external gears (often called planetary gears), they form an internal gear transmission system. One of the most notable features of this system is that the internal gear rotates in the same direction as the meshing external gear, unlike when two external gears mesh, where they rotate in opposite directions.
What are the advantages and characteristics of Inner Gear?
Compact Design Saves Space
Because the external gear can be "enclosed" within the internal gear, the radial and axial dimensions of the entire transmission are significantly reduced. This is particularly useful for applications with limited space.
High Transmission Ratios Achievable
In planetary gear systems, the internal gear acts as the stationary or output component, easily achieving significantly higher transmission ratios than conventional gearing while maintaining a compact design.
High Load Capacity
In a planetary transmission, multiple planetary gears simultaneously mesh with the internal gear, evenly distributing the load across multiple contact points. This allows the internal gearing to withstand torques and shock loads far greater than those of a comparably sized external gearing.
Smooth Operation and Extremely Low Noise
Internal gearing offers improved meshing continuity and minimized slip between tooth profiles, resulting in a very smooth and quiet transmission.
How to Manufacture Precision Inner Gear
There are two main machining methods: traditional machining and power skiving. In the past, when technology was less advanced, gear shaping and gear broaching were the primary methods for machining internal gears. These are now considered traditional methods. While mature, these methods suffer from relatively low efficiency, limited flexibility (broaching requires expensive specialized broaching tools), and difficulty in achieving high precision, impacting productivity. This led to the emergence of a new machining method: power skiving.
Power skiving technology has greatly facilitated the manufacture of high-precision internal gears. It is a highly efficient and precise cutting process that combines the advantages of hobbing and gear shaping. This new process increases machining speed by 3-5 times, significantly reducing production cycle time. Furthermore, precision is further enhanced, allowing the entire process from roughing to finishing to be completed in a single clamping setup. Finally, this process offers greater flexibility, enabling the manufacture of internal gears of various complex structures.
This process is key to ensuring the highest performance of our products. We utilize world-class power skiving machines, such as those from Kashifuji in Japan, and are committed to providing customers with a wide range of high-precision gear products.
How do you choose the right Inner Gear for your project?
The following key technical parameters are listed and explained in detail.
Precision Grade: This determines transmission smoothness and noise levels. ISO grades 5-6 are typically used for precision applications.
Module: This determines the size and strength of the gear teeth.
Material & Heat Treatment: This determines the gear's load capacity, wear resistance, and lifespan. Commonly used materials include 20CrMnTi carburized and quenched or 42CrMo nitrided.
Design details: such as the number of teeth, pressure angle, and displacement coefficient, require precise calculation based on specific transmission requirements.
If you have any related needs, please feel free to contact us.
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