Origin of gear development
history
Ancient Greek gears unearthed
In the West, in 300 BC, the ancient Greek philosopher Aristotle expounded on the problem of transmitting rotational motion with bronze or cast iron gears in "Mechanical Problems". Famous Greek scholars Aristotle and Archimedes have both studied gears. The famous Greek inventor Gutisibios evenly inserted pins on the edge of the circular plate workbench to make it mesh with the pin wheel, He applied this mechanism to engraving. This is about 150 BC. In 100 BC, the Alexandrian inventor Herron invented the odometer, in which gears were used. In the 1st century AD, a gear transmission was also used in the waterwheel milling machine made by the Roman architect Pidobis. By the 14th century, gears began to be used in clocks.
The late Warring States period iron bronze gear
In the early years of the Eastern Han Dynasty (1st century AD), there were already herringbone gears. The compass car and Jili drum car that appeared in the Three Kingdoms period have adopted gear transmission systems. The water-rotating continuous grinding 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 water-borne armillary sphere made in 725 by a party of Tang Dynasty and Liang Lingzan. The water transport instrument and Xiangtai (see ancient Chinese timepieces) made in the Northern Song Dynasty used a complex gear system. In the Ming Dynasty, Mao Yuanyi's "Wu Bei Zhi" (written in 1621) recorded a rack and pinion transmission. In the ruins of Anwuji ancient city in Hebei Province excavated in 1956, an iron ratchet gear was found. The diameter of the wheel is about 80 mm. Although it is damaged, the iron quality is good. After research, it was confirmed that it was from the end of the Warring States Period (3rd century BC) to Products during the Western Han Dynasty (206 BC to 24 AD). In 1954, a bronze ratchet was unearthed in Tiejiaya, Yongji County, Shanxi Province. Referring to the artifacts unearthed in the same pit, it can be concluded that they are relics of the Qin Dynasty (221 BC-206 BC) or the early Western Han Dynasty. The wheel has 40 teeth and a diameter of about 25 mm. Regarding the use 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 being reversed. In 1953, a pair of bronze herringbone gears were unearthed in Hongqing Village, Chang'an County, Shaanxi Province. According to the analysis of the tomb structure and tomb objects, it can be determined that the pair of gears originated in the early Eastern Han Dynasty. Both wheels are 24 teeth and about 15mm in diameter. Hengyang and other places have also found the same herringbone gear. [1]
Structure diagram of gear transmission in "Wu Bei Zhi"
As early as 1694, the French scholar PHILIPPE DE LA HIRE first proposed that the involute can be used as a tooth curve. In 1733, the Frenchman M.CAMUS proposed that the common normal of the contact point of the gear teeth must pass through the node on the center connection. When an auxiliary instantaneous center line is purely rolling along the instantaneous center line (pitch circle) of the large wheel and the small wheel, the two tooth profiles formed by the auxiliary tooth shape fixedly connected with the auxiliary instantaneous center line on the large wheel and the small wheel Curves are conjugate to each other, this is the CAMUS theorem. It takes into account the meshing state of the two tooth surfaces; it explicitly establishes the modern concept of contact point trajectories. In 1765, the Swiss L. EULER proposes the mathematical basis for the analytical study of the involute tooth profile, and clarifies the relationship between the radius of curvature of the tooth profile curve and the position of the curvature center of a pair of gears meshing. Later, SAVARY further completed this method and became the EU-LET-SAVARY equation. Contributing to the application of the involute tooth profile is ROTEFT WULLS, who proposed that the involute gear has the advantage of a constant angular speed ratio when the center distance changes. In 1873, German engineer HOPPE proposed the involute tooth profile of gears with different numbers of teeth when the pressure angle changed, thus laying the ideological foundation of modern variable gears.
At the end of the 19th century, the principle of the generating gear cutting method and the special machine tools and tools that used this principle to cut teeth appeared one after another. When cutting the teeth, as long as the cutting tool is slightly moved from the normal meshing position, the corresponding displacement gear can be cut out on the machine tool with a standard tool. In 1908, MAAG of Switzerland studied the displacement method and manufactured a gear shaper for gear shaping. Later, British BSS, American AGMA, and German DIN successively proposed various calculation methods for gear displacement.
Early Han bronze herringbone gear
In order to improve the service life of power transmission gears and reduce their size, in addition to improvements in materials, heat treatment and structure, gears with circular arc teeth have been developed. In 1907, the British FRANK HUMPHRIS first published the arc tooth shape. In 1926, ERUEST WILDHABER, a Swiss-born man, obtained the patent right of the helical gear with a circular arc tooth profile. In 1955, the Soviet Union's M. L. NOVIKOV completed the practical research on circular arc toothed gears and received the Order of Lenin. In 1970, British ROLH-ROYCE company engineer R. M. STUDER has obtained a US patent for double arc gears. This kind of gear has been paid more and more attention by people and 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: the gear module is 0.004 to 100 mm; the gear diameter is from 1 mm to 150 meters; the transmission power can reach 100,000 kilowatts; the speed can reach hundreds of thousands of revolutions per minute; second.
With the development of production, the stability of gear operation has been paid attention to. In 1674, the Danish astronomer Romer first proposed to use the epicycloid as the tooth profile curve to obtain a smooth running gear.
During the industrial revolution in the 18th century, gear technology developed rapidly, and a lot of research on gears was carried out. In 1733, the French mathematician Cammy published the basic law of tooth profile meshing; in 1765, the Swiss mathematician Euler suggested the use of involutes as tooth profile curves.
The hobbing and shaping machines that appeared in the 19th century solved the problem of mass production of high-precision gears. In 1900, Profort installed a differential device for the hobbing machine, which could process helical gears on the hobbing machine. Since then, the hobbing gear of the hobbing machine has been popularized, and the gear processed by the generating method has an overwhelming advantage, and the involute gear has become the most widely used gear .
In 1899, Lasher first implemented the scheme of shifting gears. The displacement gear can not only avoid the undercut of the gear teeth, but also match the center distance and improve the bearing capacity of the gear. In 1923, Wilder Haber of the United States first proposed gears with arc tooth profiles. In 1955, Sunovykov conducted in-depth research on arc gears, and arc gears were then used in production. This gear has high load-carrying capacity and efficiency, but is not as easy to manufacture as involute gears and needs further improvement.
