In chapter 12 we saw how a combination of simple machines and basic mechanisms was used in constructing the internal combustion engine. In this chapter we will learn how the power developed by the engine is transmitted to perform the work required of it. We will demonstrate the power train system used in automobiles and most trucks in our discussion. As we study the application of power trains, again look for the simple machines that make up each of the machines or mechanisms.

In a vehicle, the mechanism that transmits the power of the engine to the wheels or tracks and accessory equipment is called the power train. In a simple situation, a set of gears or a chain and sprocket could perform this task, but automotive and construction vehicles are not usually designed for such simple operating conditions. They are designed to have great pulling power, to move at high speeds, to travel in reverse as well as forward, and to operate on rough terrain as well as smooth roads. To meet these widely varying demands, vehicles require several additional accessory units.

The power trains of automobiles and light trucks driven by the two rear wheels consist of a clutch, a transmission, a propeller shaft, a differential, and driving axles (fig. 13-1).