CHAPTER 2POWER TRAINThe heart of the power train is the internalcombustion engine that provides the power required tomove a vehicle. However, this task is made much moreefficient with the aid of the transmission and the otherdrive-line components that make up the power train (fig.2-1). This chapter covers the basic principles of manualand automatic transmissions, propeller shaft assemblies,and final drives.TRANSMISSIONSPower from the engine provides the torquerequired for the transmission to overcome inertia.Inertia is a property of matter by which it remains atrest or in uniform motion in a straight line unless actedupon by some external force. In this case, the inertiaof the vehicle at rest is overcome by an externalforce—the engine power in the form of torque. Oncethe vehicle is moving, acceleration begins andincreases and very little torque is then required. Thebigger the load on the engine, the bigger and moreefficient the transmission must be. Once a vehiclegains the desired speed, it moves along with very littleeffort until something is encountered, such as a grade inthe road, that increases the resistance to its movement.Now torque is required again and the operator has toselect a lower gear.The transmission (fig. 2-2) provides the mechanicaladvantage that enables the engine to move the vehicle.It allows the operator to control the power and speed ofthe vehicle and allows disengaging and reversing theflow of power from the engine to the wheels by meansof a clutch.CLUTCHThe clutch engages and disengages the enginecrankshaft to or from the transmission and the rest of thepower train. Engine power to the load must be appliedslowly to allow a smooth engagement and to lessenshock on the driving and driven parts. Afterengagement, the clutch must transmit the engine powerto the transmission without slipping. Additionally, theengine must be disconnected from the power train inorder to shift gears.Figure 2-1.-Typical power train.2-1
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