1. What is a gear?
 
Gears are toothed mechanical parts that can mesh with each other. It is used in a wide range of applications in mechanical transmission and in the entire mechanical field.
 
2. History of gears
 
As early as 350 BC, the famous Greek philosopher Aristotle recorded the gears in the literature. Around 250 BC, mathematician Archimedes also described the hoist using a worm gear in the literature. The gears of BC are still preserved in the remains of Kate Sven in Iraq today.
 
The history of gears in our country has also a long history. According to historical records, the gears were used in ancient China from 400 to 200 BC. The bronze gears unearthed in Shanxi, China, are the oldest gears ever discovered. The guide car that reflects the achievements of ancient science and technology is the gear mechanism. As the core mechanical device. In the second half of the 15th century, during the Italian Renaissance, the famous all-rounder Leonardo Da Vinci not only left an indelible achievement in the history of gear technology in the field of culture and art, after more than 500 years, now The gear still retains the prototype of the sketch at the time.
 
It was not until the end of the 17th century that people began to study the shape of the teeth that correctly transmitted motion. In the 18th century, after the European industrial revolution, the application of gear transmission became more and more extensive; first, the cycloidal gear was developed, and then the involute gear was used. Until the beginning of the 20th century, the involute gear had already occupied an advantage in the application. Later, displacement gears, circular gears, bevel gears, helical gears, and the like were developed.
 
Modern gear technology has been achieved: gear module 0.004-100 mm; gear diameter from 1 mm to 150 m; transmission power up to 100,000 kW; speed up to 100,000 rpm; maximum peripheral speed of 300 m / s.
 
Internationally, power transmission gear units are developing alongside miniaturization, high speed, and standardization. The application of special gears, the development of planetary gears, the development of low-vibration, low-noise gears are some of the 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 gear shaft. Generally divided into three types: parallel axis, intersecting axis and staggered axis.
 
1) Parallel shaft gears: including spur gears, helical gears, internal gears, racks and helical racks.
 
2) Intersecting shaft gears: Straight bevel gears, spiral bevel gears, zero-degree bevel gears, etc.
 
3) Interlaced shaft gears: interlaced helical gears, worm gears, hypoid gears, etc.
 
The efficiency listed in the appeal is transmission efficiency and does not include losses such as bearings and agitation lubrication. The meshing of the parallel shaft and the gear pair of the intersecting axis is basically rolling, and the relative sliding is very small, so the efficiency is high. Interlaced shaft gears such as crossed helical gears and worm gears, because they are rotated by relative sliding to achieve power transmission, the friction has a great influence, and the transmission efficiency is lower than other gears. The efficiency of the gear is the transmission efficiency of the gear under normal assembly conditions. If the installation is not correct, especially if the bevel gear assembly distance is incorrect and there is an error with the cone intersection, the efficiency will be significantly reduced.
 
2) Rack
 
A linear rack gear that meshes with a spur gear. It can be seen as a special case when the pitch diameter of the spur gear becomes infinite.
 
3) Internal gear
 
A gear that meshes with the spur gear and is machined on the inner side of the ring. Mainly used in applications such as planetary gears and gear couplings.
 
4) Helical gear
 
A spur gear with a helical line. Because it is stronger than the spur gear and runs smoothly, it is widely used. Axial thrust is generated during transmission.
 
5) Helical rack
 
a bar gear that meshes with a helical gear. This is equivalent to the case where the pitch diameter of the helical gear becomes infinite.
 
6) Herringbone gear

The tooth line is a combination of two helical gears that are left-handed and right-handed. There is an advantage that no thrust is generated in the axial direction.
 
3.2 Intersecting shaft gear
 
1) Straight bevel gear
 
A bevel gear in which the tooth line is aligned with the bus bar of the pitch line. In bevel gears, they are of a type that is relatively easy to manufacture. Therefore, it is widely used as a bevel gear for transmission.
 
2) Spiral bevel gear
 
The tooth line is a curved, bevel gear with a helix angle. Although it is more difficult to manufacture than straight bevel gears, it is also widely used as a high-strength, low-noise gear.
 
3) Zero bevel gear
 
Curved bevel gear with a helix angle of zero. Because of the characteristics of both straight and curved bevel gears, the tooth surface is subjected to the same force as the straight bevel gear.
 
3.3 Interlaced shaft gear
 
1) Cylindrical worm pair
 
The cylindrical worm pair is a general term for a cylindrical worm and a worm gear that meshes with it. Quiet operation and single pair can achieve the biggest feature of the large transmission ratio, but it has the disadvantage of low efficiency.
 
2) Interlaced helical gears
 
The name of the cylindrical worm pair when it is driven between staggered shafts. It can be used in the case of a helical gear pair or a helical gear and a spur gear pair. Although the operation is stable, it is only suitable for use under light load.
 
3.4 Other special gears
 
1) Face gear
 
A disc-shaped gear that can mesh with a spur or helical gear. Drive between the orthogonal axis and the staggered axis.
 
2) Drum worm pair
 
A general term for a drum worm and a worm gear that meshes with it. Although it is difficult to manufacture, it can drive a large load compared to a cylindrical worm pair.
 
3) Hypoid gears
 
Conical gears that are driven between staggered shafts. The large and small gears are eccentrically machined, similar to the spiral gears, and the meshing principle is very complicated.