最早的齿轮是怎样发明出来的？它源于何方？用于何处？——这是近百年来人们在探索的一个谜。 两千年前，在中国、印度、希腊、罗马、埃及出土和出水的铸铁齿轮与青铜齿轮似乎解开了这个谜。其实不然， 它们只是第2代齿轮。第1代齿轮是木制齿轮。它源于四千年前，各文明古国发明水力机械中伴生。这是由于 这些文明古国聚居大河与海湾，与水有“缘分”所致。第2代齿轮的辉煌点表现在公元前200年中国的发明 ——指南车上。它在世界上第一次发明了差动机构，第一次实现半自动控制机构，第一次出现有走向功能的机 器人。1800年工业革命带来了第3代齿轮，其特征是用直刃刀具成批生产渐开线的钢制齿轮形成了现代齿轮的 技术平台。进人21世纪，以高强度复合材料代替资源匮乏的钢材，标志着新一代（第4代）齿轮的到来，它将 与知识经济共存。未来50年齿轮创新的趋势，是追求小化、净化、静化，高可靠性、高强度、高转速和低材 耗、低能耗、低重量。

“How were the earliest gears invented? Where were the sources and uses of the earliest gears? It is the mystery for men to unravel in a century.

This mystery seems soluble by unearthed gears or by “un-seaed” gears which were discovered from China, India. Greece, Rome and Egypt in 2 000 years ago.

But these gears made of bronze or cast-iron are mere 2nd-generation gears. The lst-generation gears madeof wooden. The invention of 1st generation gears would be accompanied with water machine water mill forgrinding grain. In ancient-civilization countries people lived together along rivers or sea-side 4 000 years ago. They came into contact with water. The “South-Pointing Chariot” is a unique Chinese invention before 200 B. C. It is the 1st set of differential mechanism in the world, the 1st self-control machine and the 1st robot machine in the world. It is the essence of 2nd-generation gears. The 3rd-generation gear is made of steel. This modern gears began at industry-revolutiion in 1800. The characteristics are using cutter with straight-edge to generat involute profile gears by mass production.

The 4th-generation gear will be coexisting with knowledge-economics. Creating the new high-strength composite materials and plastics to substitude for steel, of which the resources is getting shorten, will mark the beginning of the 4th-generation gears.

The trend of innovation of gears in the coming 50 years will be seeking miniaturization, puification and quietness, developing high-reliability, high-capacity, high-velocity and low-consumption of material, energy and weight.