history
Unearthed Ancient Greek Gear Device
In the West, in 300 BC, the ancient Greek philosopher Aristotle described the problem of using bronze or cast iron gears to transmit rotational motion in "Mechanical Problems". The famous Greek scholars Aristotle and Archimedes have studied gears. The famous Greek inventor Gutisibios evenly inserted pins on the edge of the circular table to make it mesh with the pin wheel. He applied this mechanism to engraving. This is about 150 BC. In 100 BC, Herron, the Alexandrian inventor, invented the odometer and used gears in the odometer. In the 1st century AD, a gear transmission was also used in the waterwheel mill made by the Roman architect Pidobis. By the 14th century, gears began to be used in clocks.
Iron bronze gears at the end of the Warring States period
In the early years of the Eastern Han Dynasty (1st century AD), there were herringbone gears. The guide car and the Jili drum car that appeared in the Three Kingdoms period have adopted a gear transmission system. The water-rotating continuous mill invented by Du Yu in the Jin Dynasty transmits the power of the water wheel to the stone mill through gears. The earliest record of the gear transmission system in the history books is the description of the armillary sphere made by Xing Yi and Liang Lingzhan in the Tang Dynasty in 725. The water transport instrument elephant table (see ancient Chinese timepieces) made in the Northern Song Dynasty used a complicated gear system. In the Ming Dynasty Mao Yuanyi's "Wu Bei Zhi" (written in 1621) recorded a rack and pinion transmission. An iron ratchet gear was discovered in the ruins of the ancient city of Anwuji, Hebei, excavated in 1956. The diameter of the wheel is about 80 mm. Although it is incomplete, the iron quality is better. After research, it is confirmed that it is the end of the Warring States period (3rd century BC). Products from the Western Han Dynasty (206 BC to 24 AD). Bronze spine gears were unearthed in Changjiaya, Yongji County, Shanxi Province in 1954. With reference to the artifacts unearthed in Tongkeng, it can be concluded that they are the relics of the Qin Dynasty (221-206 BC) or the early Western Han Dynasty. The wheel has 40 teeth and the diameter is about 25 mm. Regarding the purpose of the ratchet gear, no written records have been found so far, and it is speculated that it may be used for braking to prevent the axle from turning backwards. A pair of bronze herringbone gears were unearthed in Hongqing Village, Chang'an County, Shaanxi Province in 1953. Based on the analysis of the tomb structure and the tomb objects, it can be determined that the pair of gears came from the early Eastern Han Dynasty. Both wheels have 24 teeth and a diameter of about 15 mm. The same herringbone gear was also found in Hengyang and other places. [1]
Gear transmission structure diagram in "Wu Bei Zhi"
As early as 1694, the French scholar PHILIPPE DE LA HIRE first proposed that the involute could be used as the tooth profile curve. In 1733, the Frenchman M.CAMUS proposed that the common normal of the contact point of the gear tooth must pass through the node on the central line. When an auxiliary instant center line is purely rolling along the instant center line (pitch circle) of the big wheel and the small wheel, the auxiliary tooth profile fixedly connected with the auxiliary instant center line forms two tooth profiles on the big wheel and the small wheel. The curves are conjugate to each other, which is the CAMUS theorem. It considers the meshing state of the two tooth surfaces; it clearly establishes the modern concept of the trajectory of the contact point. In 1765, Swiss L. EULER puts forward the mathematical basis for the analytical study of involute tooth profile, and clarifies the relationship between the radius of curvature of the tooth profile curve and the center of curvature of a pair of gears that are meshing. Later, SAVARY further completed this method and became the EU-LET-SAVARY equation. The contribution to the application of involute tooth profile is ROTEFT WULLS. He proposed that when the center distance changes, the involute gear has the advantage of constant angular speed ratio. In 1873, German engineer HOPPE proposed the involute tooth profile of gears with different numbers of teeth when the pressure angle changes, thus laying the foundation for the thinking of modern shifting gears.
At the end of the 19th century, the principle of the generative gear cutting method and the emergence of special machine tools and tools that used this principle to cut gears have made gear processing more complete, and the involute tooth profile has shown great advantages. As long as the gear cutting tool is slightly moved from the normal meshing position during gear cutting, the corresponding shifted gear can be cut out on the machine tool with a standard tool. In 1908, the Swiss MAAG researched the displacement method and produced the gear shaping machine. Later, the British BSS, the American AGMA, and the German DIN successively proposed a variety of calculation methods for the gear displacement.
Bronze Herringbone Gear in the Early Han Dynasty
In order to increase the service life of the power transmission gear and reduce its size, in addition to improvements in materials, heat treatment and structure, the arc-toothed gear has been developed. In 1907, the British FRANK HUMPHRIS first published the arc tooth profile. In 1926, ERUEST WILDHABER obtained the patent right for the arc tooth profile helical gear. In 1955, the Soviet Union's M. L. NOVIKOV completed the practical research on arc toothed gears and won the Lenin Medal. In 1970, the engineer of ROLH-ROYCE company R． M. STUDER has obtained a US patent for double circular arc gears. This kind of gear has been paid more and more attention to by people, and it has played a significant role in production.
Gears are toothed mechanical parts that can mesh with each other. They are widely used in mechanical transmission and the entire mechanical field. Modern gear technology has reached: gear modulus 0.004 to 100 mm; gear diameter from 1 mm to 150 meters; transmission power can reach up to 100,000 kilowatts; rotation speed can reach hundreds of thousands of revolutions per minute; the highest peripheral speed can reach 300 meters/ Second.
With the development of production, the smoothness of gear operation has been valued. In 1674, the Danish astronomer Romer first proposed to use an epicycloid as a tooth profile curve to obtain a gear that runs smoothly.
During the industrial revolution in the 18th century, gear technology developed rapidly, and people conducted a lot of research on gears. In 1733, the French mathematician Kami published the basic law of tooth profile meshing; in 1765, the Swiss mathematician Euler suggested the use of involute as the tooth profile curve.
Gear hobbing machines and gear shaping machines appeared in the 19th century to solve the problem of mass production of high-precision gears. In 1900, Profort installed a differential device for the gear hobbing machine, which can process helical gears on the gear hobbing machine. Since then, the gear hobbing machine has become popular, and the generative method has an overwhelming advantage in processing gears. Involute gears have become the most widely used gear. .
In 1899, Rasche first implemented the scheme of shifting gears. The shifted gear can not only avoid undercutting of the gear teeth, but also can match the center distance and improve the load-carrying capacity of the gear. In 1923, the American Wild Haber first proposed a gear with a circular arc tooth profile. In 1955, Sunovykov conducted an in-depth study on the circular arc gear, and the circular arc gear was then used in production. This kind of gear has high load-bearing capacity and efficiency, but it is not as easy to manufacture as involute gears, and it needs further improvement.
