Prime mover and alternator
The large diesel engine is called the prime mover. It turns an alternator or generator rather than mechanically driving the wheels through a conventional automotive-style transmission.
Traction motors
Electrical power is delivered to traction motors connected to the axles through gearing. Modern control systems carefully manage torque and wheel slip so the locomotive can use as much adhesion as conditions allow.
Dynamic braking
During dynamic braking the traction motors act as generators. On most conventional freight locomotives, electrical energy is sent to resistor grids and released as heat while helping slow the train.
Computer control
Modern locomotives coordinate engine output, traction, wheel-slip control, braking and diagnostics. The result is far more precise use of locomotive power than was possible on early diesels.
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