ABSTRACT
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit.
Aristotle
Gears are very popular power transmission devices, combining the attributes of high efficiency, long and maintenance-free service life, reasonable manufacturing cost, and relatively large torque capability in a compact size. This chapter introduces gear concepts, including geometry and kinematics, and shows the different gear types. Spur gears, the emphasis of this chapter, are toothed wheels whose geometry does not change through their thickness. These are the easiest gears to manufacture and are very commonly used to transmit torque and power between parallel shafts. Spur gear geometry is discussed, including the importance of the involute profile. The manufacturing processes and materials used for gears are described, as well as their impact on gear performance. Two common failure modes of gears, namely gear tooth bending and surface pitting, are considered. The discussion of bending begins with the mechanics of the Lewis equation, and the standard design approach promulgated by the American Gear Manufacturers Association for bending; the similar approach for contact stress is then described. The chapter ends with a discussion of effective gear lubrication, which is essential for trouble-free performance, as well as a procedure for design synthesis of gears.
