What is a gear?
Gears are Machine element with teeth that can mesh with each other. It is widely used in mechanical transmission and the entire mechanical field.
2 The History of Gears
As early as 350 BC, the famous Greek philosopher Aristotle recorded gears in literature. Around 250 BC, mathematician Archimedes also explained the winch using worm gear in the literature. There are still gears from BC preserved in the ruins of Ketesfin, Iraq today.
The history of gears in China also has a long history. According to historical records, gears have been used in ancient China as far back as 400~200 BC. The bronze gears unearthed in Shanxi Province of China are the oldest gears found so far. As a reflection of ancient scientific and technological achievements, the South-pointing chariot is a mechanical device with gear mechanism as the core. During the Italian Renaissance in the latter half of the 15th century, the famous all-rounder Leonardo da Vinci not only made indelible contributions in cultural and artistic aspects, but also in the history of gear technology. After more than 500 years, the current gear still retains the prototype of the sketch at that time.
It was not until the late 17th century that people began to study the shape of gear teeth that could correctly transmit motion. In the 18th century, after the European Industrial Revolution, the application of gear transmission became increasingly widespread; First cycloid gear was developed, then Involute gear. Until the beginning of the 20th century, Involute gear had already taken advantage in application. Subsequently, it developed modified gears, circular arc gears, bevel gears, helical gears, and so on.
Modern gear technology has reached: gear module 0.004-100mm; The gear diameter ranges from 1 millimeter to 150 meters; The transmission power can reach 100000 kilowatts; The speed can reach 100000 revolutions per minute; The highest circumferential speed is 300 meters per second.
Internationally, power transmission gear devices are developing towards miniaturization, high-speed, and standardization. The application of special gears, the development of planetary gear devices, and the development of low vibration and low noise gear devices are some characteristics of gear design.
3 Gears are generally divided into three categories
There are many types of gears, and the most common classification method is based on the axial nature of the gears. It is generally divided into three types: parallel axis, intersecting axis, and staggered axis.
1) Parallel shaft gears: including spur gears, helical gears, internal gears, rack and helical gears, etc.

2) Intersecting shaft gears: There are straight bevel gears, spiral bevel gears, zero degree bevel gears, etc.
3) Cross axis gear: there are cross axis helical gear, worm gear, quasi Hyperboloid gear, etc.
3.1 Parallel shaft gears
1) Spur gear
A cylindrical gear with a tooth line parallel to the axis. Due to its ease of processing, it is most widely used in power transmission.
2) Rack and pinion
A straight toothed strip gear that meshes with a spur gear. It can be seen as a special case when the pitch diameter of a spur gear becomes infinite.
3) Internal gear
A gear that meshes with a spur gear and has teeth machined on the inner side of the ring. Mainly used in applications such as planetary gear transmission mechanisms and gear couplings.
4) Helical gear
A cylindrical gear with a helical tooth line. Due to its higher strength and smooth operation compared to spur gears, it is widely used. Axial thrust is generated during transmission.
5) Helical gear rack
A strip gear that meshes with a helical gear. Equivalent to the situation where the pitch diameter of a helical gear becomes infinite.
6) Herringbone gear
The tooth line is a combination of two helical gears that rotate left and right. It has the advantage of not generating thrust in the axial direction.