Chapter 2 Power Train

CHAPTER 2 POWER TRAIN The heart of the power train is the internal combustion engine that provides the power required to move a vehicle. However, this task is made much more efficient with the aid of the transmission and the other drive-line components that make up the power train (fig. 2-1). This chapter covers the basic principles of manual and automatic transmissions, propeller shaft assemblies, and final drives. TRANSMISSIONS Power from the engine provides the torque required for the transmission to overcome inertia. Inertia is a property of matter by which it remains at rest or in uniform motion in a straight line unless acted upon by some external force. In this case, the inertia of the vehicle at rest is overcome by an external force—the engine power in the form of torque. Once the vehicle is moving, acceleration begins and increases and very little torque is then required. The bigger the load on the engine, the bigger and more efficient the transmission must be. Once a vehicle gains the desired speed, it moves along with very little effort until something is encountered, such as a grade in the road, that increases the resistance to its movement. Now torque is required again and the operator has to select a lower gear. The transmission (fig. 2-2) provides the mechanical advantage that enables the engine to move the vehicle. It allows the operator to control the power and speed of the vehicle and allows disengaging and reversing the flow of power from the engine to the wheels by means of a clutch. CLUTCH The clutch engages and disengages the engine crankshaft to or from the transmission and the rest of the power train. Engine power to the load must be applied slowly to allow a smooth engagement and to lessen shock on the driving and driven parts. After engagement, the clutch must transmit the engine power to the transmission without slipping. Additionally, the engine must be disconnected from the power train in order to shift gears. Figure 2-1.-Typical power train. 2-1