The basics of spiral bevel gears

摘要

The purpose of gears is to transmit motion and torque from one shaft to another. That transmission normally has to occur with a constant ratio, the lowest possible disturbances and the highest possible efficiency. Tooth profile, length and shape are derived from those requirements. With cylindrical gears, it is easier to understand that the involute profile provides a constant ratio and is insensitive to center distance displacement. The generating principle of an involute is derived from a straight rack with straight tooth profile. A particular gear, rolling in the rack with constant center distance to the rack, requires involute flank surfaces. A shaping tool with the shape of a rack can machine a gear with a perfect involute flank form. Figure 1 shows a cylindrical gear rolling in a rack.