Chapter 4: The Locomotive

The Locomotive
Steam until
mid 1950’s
Types of Locomotives
Two Factors Determine the Ability of a Locomotive to
Start, Accelerate, and Obtain Top Speed
Tractive Effort
• The Ability to Overcome Resistance
-Starting, Grade, Wind, Curve, Rolling
• Tractive Force = Weight of Drivers x Coefficient of Adhesion
Horse Power (mainly 1,500 to 5,000 hp)
• Rate of Doing Work
• Drawbar Horsepower: horsepower available to haul
Adhesion Control
• Grip Rail without Slipping
• Dependent on weather, rail
• Controlled automatically in
modern locomotive
• Sanding
Tractive Force vs. Tonnage and Grade
Performance Curve of the Locomotive
(with train resistance for 420 tons trailing load of passenger stock)
Different Horsepower
• Not all engine power pulls
• On average, 82% of power
is left to pull train
Power Required vs. Speed and Grade
Diesel–Electric Locomotive
• Diesel Engine – Prime Mover
• Turbocharger / Electronic Fuel Injection
• Alternator / Generator / Fans / Batteries
• AC/DC Traction Motors
Locomotive Principal Components
Radial Trucks
Locomotive Controls
• Minimum Levers, but
Connected to Circuitry
• “Microprocessor” Control
• Display Screens
• Interfaces with Primary
Six Axle,
approx. 390,000 pounds
Four Axle, approx. 260,000 pounds
Multiple Unit Arrangements
Distributive Power / ECP
Mid-Train or Rear End
Slugs and Mates
No Prime Mover
Store Excess Power
Provide Weight for Tractive Effort
Maintenance and Life Span
• Most New Locomotives can Self-Diagnose Problems
• Different Inspections Mandatory at Daily, 92-days,
Annual, and Biennial Periods
• Remote Diagnostics
• Average Locomotive Service is 20-25 Years
• Used to be Returned to Manufacturer, but Now Sold to
Smaller Railroads
Genset and Hybrid Locomotives (Mainly for Switching)
Genset – Multiple engine-generators per vehicle
Hybrid – Operates on batteries that are charged overnight

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