In some applications, such as a push lawn mower with a vertical crankshaft engine, the power is used at the location that it is produced. The blade is attached directly to the end of the crankshaft. Most machines require a more complex system for transporting the power from the source to the load. In addition, many machines require that the power produced by the motor or engine be modified and/or transported to another part of the machine. These modifications could include changing the speed of rotation, direction of rotation, and location of the power. The collection of machine components that are used to accomplish this are called the transmission, power train, or drive train. In complex agricultural machines, such as a combine, the power must also be modified several times to meet the needs of the different machine components.
The transportation of power can be accomplished using mechanical, pneumatic, hydraulic, or electrical systems. Mechanical systems are very different so they will be discussed separately. Hydraulic and pneumatic systems have enough similarities that they will be discussed together. Electrical systems will not be discussed in this text. Each of these systems use a different means for completing the modifications and delivery of the power and each has advantages and disadvantages. The remaining sections of this chapter will explain how these power transfer systems work. Note: none of the systems are 100% efficient in the transfer of power, but energy losses will be ignored during the following sections to make it easier to understand how each system functions.
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