Gear mechanisms are used for transmitting motion and power from one shaft to another by means of the positive contact of successively engaging teeth. In about 2,600B.C., Chinese are known to have used a chariot incorporating a complex series of gears like those illustrated in Fig.2.7. Aristotle, in the fourth century B .C .wrote of gears as if they were commonplace. In the fifteenth century A.D., Leonardo da Vinci designed a multitude of devices incorporating many kinds of gears. In comparison with belt and chain drives ,gear drives are more compact ,can operate at high speeds, and can be used where precise timing is desired. The transmission efficiency of gears is as high as 98 percent. On the other hand, gears are usually more costly and require more attention to lubrication, cleanliness, shaft alignment, etc., and usually operate in a closed case with provision for proper lubrication.
Gear mechanisms can be divided into planar gear mechanisms and spatial gear mechanisms. Planar gear mechanisms are used to transmit motion and spatial gear mechanisms. Planar gear mechanisms are used to transmit motion and power between parallel shafts ,and spatial gear mechanisms between nonparallel shafts.
Types of gears
(1) Spur gears. The spur gear has a cylindrical pitch surface and has straight teeth parallel to its axis as shown in Fig. 2.8. They are used to transmit motion and power between parallel shafts. The tooth surfaces of spur gears contact on a straight line parallel to the axes of gears. This implies that tooth profiles go into and out of contact along the whole facewidth at the same time. This will therefore result in th

齒輪機構(gòu)用來傳遞運動和動力，通過連續(xù)嚙合輪齒的正確接觸，從一根軸傳動到另一根軸。大約公元前2600年，中國人就能夠使用一系列戰(zhàn)車而聞名復(fù)雜的齒輪機構(gòu)而構(gòu)成的。公元前4世紀(jì)，亞里士多德寫的齒輪好象推動的是平凡的。在公元15世紀(jì)，Leonardo da Vinci 設(shè)計了能與許多種類的齒輪樞結(jié)合的大量裝置。與皮帶和鏈傳動相比較，齒輪傳動裝置更加緊湊，能高速運行，也能夠被運用在要求準(zhǔn)確定時的場合。齒輪傳動的傳動效率高達98％。另一方面，齒輪傳動機構(gòu)成本高，而且要求注意潤滑、清潔度、軸的對中等等，經(jīng)常用在提供準(zhǔn)確箱體潤滑的閉式情況下。
齒輪機構(gòu)能被分為平面齒輪機構(gòu)和空間齒輪機構(gòu)。平面齒輪機構(gòu)被用于傳遞運動和動力，而平行軸間的運動和動力空間齒輪機構(gòu)用于傳遞不平行軸間的運動和動力。