“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.