Diesel-Electric Locomotive

Overview

A diesel-electric locomotive is a self-contained traction unit in which a large diesel engine never drives the wheels directly. Instead the engine spins an alternator, the alternator's output is rectified to DC, and traction inverters feed AC motors hung on the axles. This electric transmission gives full tractive effort from a standstill and avoids the mechanical gearbox that would otherwise be impossible at locomotive power levels. Roughly 180,000 of the parts in a modern road locomotive are the structural Structural Bolt & Rivet bolts, rivets and clips holding the underframe, carbody, engine mounts and bogies together.

The locomotive sits on the Underframe & Draft Gear and is clothed by the Carbody & Hood. The Diesel Prime Mover (V16) turns the Main Alternator, whose power passes through the Power Electronics Cabinet to the Bogie / Truck trucks. Braking comes from the Dynamic Brake Assembly and the Air Brake System, all overseen by the Control Electronics from the Cab Interior, with the Underslung Fuel Tank and Auxiliary Systems completing the machine.

The electric transmission is what makes the diesel-electric arrangement work. A mechanical gearbox able to handle several thousand horsepower across the full speed range would be impractically large, so the engine instead runs a generator and the wheels are turned by electric motors. This decouples engine speed from train speed, lets the engine sit at its most efficient operating point, and gives smooth, stepless control of tractive effort from a dead stand to road speed. Multiple locomotives can also be coupled and run from one cab over a trainline.

Underframe and carbody

The Underframe & Draft Gear is a welded Welded Steel Mainframe that carries buffing and traction loads through the Automatic Coupler at each end, cushioned by the Draft Gear Cushioning Unit and Buffer. The Carbody & Hood adds the Long Hood Structure over the engine room, the Short Hood Structure, the Cab Shell, and the Running Board / Walkway.

Prime mover

The Diesel Prime Mover (V16) is a turbocharged four-stroke V16. Inside the Engine Block (V16 crankcase), the Crankshaft is driven by sixteen Piston Assembly units, each breathing through a Cylinder Head. Two Turbocharger units recover exhaust energy to boost intake air, while the Fuel Injection System, Lube Oil System, and Engine Cooling System keep the engine fed, lubricated, and within temperature.

Electric transmission

The engine drives the Main Alternator, which also carries the Auxiliary Generator for onboard loads. Its three-phase output reaches the Power Electronics Cabinet cabinet, where the Traction Rectifier converts it to a DC link and four Traction Inverter units, one per motor, synthesize variable-frequency AC. Each Bogie / Truck carries Traction Motor (AC) units geared to the Wheelset, supported on Primary Suspension Spring and Secondary Suspension Spring springs.

Braking

The locomotive brakes electrically and pneumatically. The Dynamic Brake Assembly runs the traction motors as generators and dumps their output into resistor Dynamic Brake Resistor Grid banks cooled by a Grid Cooling Blower. The Air Brake System supplies and controls the train brake pipe through the Air Compressor, Main Air Reservoir tanks, the Brake Control Valve, and the Air Dryer, acting on the Brake Rigging in each truck.

Control, cab, and auxiliaries

The Control Electronics center on the Locomotive Control Computer, which sequences engine power, traction, and braking and presents data on the Cab Display. The crew works from the Cab Interior, whose Control Stand holds the Throttle Lever, Reverser Handle, and Brake Handle. Fuel rides in the Underslung Fuel Tank, and the Auxiliary Systems add Sander Unit units, a Headlight at each end, and the Air Horn. The Sander Unit units drop sand ahead of the driving wheels to restore adhesion on wet or greasy rail, which is what limits how much tractive effort the locomotive can actually put to the track. A bank of starting batteries cranks the engine and rides through electrical transients when the engine is shut down.