Gears are toothed mechanical components that can mesh with each other, and their application in mechanical transmission and the entire field of machinery is extremely widespread. After reading today's article, you will have a grasp of the past and present of gears.
As early as 350 BC, the famous ancient Greek philosopher Aristotle recorded gears in his documents. Around 250 BC, the mathematician Archimedes also described the use of a hoisting machine with a turban worm in his literature. Gears from before the common era are still preserved in the ruins of Hatra in present-day Iraq.
The history of gears in China is also long-standing. According to historical records, gears were already in use in ancient China between 400 and 200 BC. The bronze gears unearthed in Shanxi, China, are the oldest gears discovered to date. ,which reflects the scientific and technological achievements of ancient times and is centered around a gear mechanism, is a prime example. In the second half of the 15th century, during the Italian Renaissance, the renowned polymath Leonardo da Vinci left an indelible mark in the history of gear technology, as well as in culture and art. After more than 500 years, today's gears still retain the prototype of his sketches.
It was not until the end of the 17th century that people began to study the shapes 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 with cycloidal gears, then with involute gears, until the early 20th century when involute gears had gained a dominant position in applications. Subsequently, various other types of gears were developed, such as shifted gears, circular arc gears, bevel gears, and helical gears.
Modern gear technology has reached the following milestones: gear modulus from 0.004 to 100 millimeters; gear diameter ranging from 1 millimeter to 150 meters; power transmission capacity up to 100,000 kilowatts; rotational speeds up to 100,000 revolutions per minute; and the highest peripheral speed reaching 300 meters per second.
Internationally, power transmission gear devices are evolving towards miniaturization, high speed, and standardization. The application of special gears, the development of planetary gear devices, and the research and development of low-vibration, low-noise gear devices are some of the characteristics in gear design.
There are many types of gears, and the most common classification method is based on the axis of the gears. They are generally divided into three types: parallel axis, intersecting axis, and交错轴.
Parallel axis gears: Including spur gears, helical gears, internal gears, racks, and helical racks, etc.
Intersecting axis gears: Including straight bevel gears, spiral bevel gears, and zero-degree bevel gears, etc.
Intersecting axis gears: Including hypoid gears, worm gears, and bevel-helical gears, etc.
The meshing of parallel and intersecting axis gear pairs is essentially rolling, with very little relative sliding, so the efficiency is high. Intersecting axis helical gears and worm gears, which produce rotation through relative sliding to achieve power transmission, are greatly affected by friction, and their transmission efficiency is lower compared to other gears. The efficiency of gears refers to the transmission efficiency under normal assembly conditions. If the installation is incorrect, especially if the assembly distance of the bevel gears is incorrect, leading to errors at the cone intersection point, their efficiency will significantly decrease.
01 Parallel Axis Gears
Spur Gears
Cylindrical gears with teeth parallel to the axis. Because they are easy to manufacture, they are the most widely used in power transmission.
Racks
Linear gear teeth that mesh with spur gears. Can be considered a special case where the pitch circle diameter of the spur gear becomes infinitely large.
Internal Gears
Gears with teeth machined on the inner side of a ring, meshing with spur gears. Mainly used in planetary gear transmission mechanisms and gear couplings.
Helical Gears
Cylindrical gears with teeth in the form of a helix. Because they have higher strength and smoother operation than spur gears, they are widely used. Axial thrust is generated during transmission.
Helical Racks Strip-shaped gears that mesh with helical gears. helical gears with an infinitely large pitch diameter.
Herringbone Gears Gears composed of two helical gears with left-hand and right-hand threads combined. They have the advantage of not producing thrust in the axial direction.
Straight Bevel Gears Bevel gears with teeth parallel to the generating line of the pitch cone. Among bevel gears, they are relatively easy to manufacture and thus have a wide range of applications in transmission.
Spiral Bevel Gears Bevel gears with curved teeth and a helix angle. Although more difficult to manufacture than straight bevel gears, they are also widely used as high-strength, low-noise gears.
Zerol Bevel Gears
Curved bevel gears with a helix angle of zero degrees. Because they have characteristics of both straight and curved bevel gears, the force on the tooth surface is the same as that of straight bevel gears.
Cylindrical Worm Gears Cylindrical worm gears refer to the combination of a cylindrical worm and the worm gear that meshes with it. Their main features are smooth operation and the ability to achieve a large transmission ratio with a single pair, but they have the disadvantage of low efficiency.
Intersecting Axis Helical Gears The name for cylindrical worm gears when transmitting between intersecting axes. They can be used in situations with helical gear pairs or helical gears with spur gears. Operation is smooth, but they are only suitable for light loads.
Face Gears Disk-shaped gears that can mesh with spur or helical gears. Used for transmission between perpendicular and intersecting axes.
Drum Worm Gears The combination of a drum-shaped worm and the worm gear that meshes with it. Although manufacturing is more difficult, they can transmit heavy loads compared to cylindrical worm gears.
Hypoid Gears Conical gears for transmission between intersecting axes. Both the large and small gears are processed eccentrically, similar to spiral bevel gears, and the principle of meshing is very complex.
