Lecture Note :Mechanical Engineering (Gear Drive)

Here is some advanced study material for Mechanical Students.

This will be useful for students of KTU

GEAR DRIVE

Gears are compact, positive-engagement, power transmission elements that determine the speed, torque, and direction of rotation of driven machine elements. Gear types may be grouped into five main categories: Spur, Helical, Bevel, Hypoid, and Worm. Typically, shaft orientation, efficiency, and speed determine which of these types should be used for a particular application. Table 1 compares these factors and relates them to the specific gear selections. This section on gearing and gear drives describes the major gear types; evaluates how the various gear types are combined into gear drives; and considers the principle factors that affect gear drive selection. Spur gears Spur gears have straight teeth cut parallel to the rotational axis. The tooth form is based on the involute curve, Figure 1. Practice has shown that this design accommodates mostly rolling, rather than sliding, contact of the tooth surfaces. The involute curve is generated during gear machining processes using gear cutters with straight sides. Near the root of the tooth, however,pur gears are the least expensive to manufacture and the most commonly used, especially for drives with parallel shafts. The three main classes of spur gears are: external tooth, internal tooth, and rack-and-pinion. External-tooth gears — The most common type of spur gear, Figure 3, has teeth cut on the outside perimeter of mating cylindrical wheels, with the larger wheel called the gear and the smaller wheel the pinion. The simplest arrangement of spur gears is a single pair of gears called a single reduction stage, where output rotation is in a direction opposite that of the input. In other words, one is clockwise while the other is counter-clockwise. Higher net reduction is produced with multiple stages in which the driven gear is rigidly connected to a third gear. This third gear then drives a mating fourth gear that serves as output for the second stage. In this manner, several output speeds on different shafts can be produced from a single input rotation.

Objectives:

Types Of Gear: