Gear train
group or sequence of gears which perform a desired mechanical transfer of power. Selected gear train types are:
| Transmission | Gear train characterized by multiple selectable gear speed ratios and the ability to uncouple the gear train from the power source to permit starting and stopping the gear train without stopping the power source. Used in applications where varying speed/torque/output direction requirements must be satisfied by a single geared system. |
| Differential | Gear train characterized by the connection of two output shafts or axles in the same line, with an epicyclic (one or more parts travel around the circumference of another fixed or moving part) gear arrangement permitting one output shaft to revolve faster than the other. |
| Planetary | Gear train characterized by a predominantly epicyclic arrangement, consisting of a series of planet gears rotating in a carrier between a central sun gear and an outer ring gear (of internal gear type). A planetary gearset may be configured in a variety of ways, depending on which part of the gearset is used for power input, which part is held stationary or braked, which part is used for power output, and the actual number and arrangement of sun and planet gears. Generally, the more planet gears the greater the torque capacity of the system. |
| Speed increaser or reducer | Gear train characterized by high to extremely high ratios of input to output speed, for the purposes of large-scale RPM increases or large-scale torque increases. Usually a single-speed gear ratio; if multispeed, they differ from transmissions in that they are shifted as often or as easily. |