Module 6: Train-Track Dynamics
Module Objectives
•
Understanding the Rail/Wheel Interface
•
Identifying Force Generators
•
Understanding Force Effects
Train-Track Dynamics Definition •
•
Interaction of forces occurring as train moves over the track structure –
Lateral Forces
–
Vertical Forces
–
Vehicle Dynamics
–
Rail & Wheel Profile
Many factors affect these forces –
Train Speed & Handling
–
Train Consist & Placement of Cars, etc.
L/V Ratio •
L/V Definition
•
Effect on Stability
•
Lateral Forces
•
Vertical Forces
•
Wheel/Rail Profile
Lateral Forces •
Flanging Force
•
Centrifugal Force
•
Frictional Curving Force
•
Coupler Force
•
Buff & Draft Force
•
•
Truck Hunting Track Geometry Force
Frictional Curving Force •
Difference in Distance Outside Vs. Inside Wheel Rolls in Curve
•
Effect of Conical Wheel Tread
•
Generation of Creep Forces –
–
•
Cause Truck to Steer to Curve Outside Magnitude of Forces Vs. Wide Gage, Corrugations & Geometry Problems
Importance of Lubrication
Coupler Forces
•
Position of Coupler Faces in Curves
•
Long Car Coupled to Short Car
•
Longitudinal Force Effect •
•
Angularity of Couplers Torque Applied at Wheel-Rail Interface
Buff & Draft Forces Longitudinal Train Forces Result of Changes in Gradient, Curvature & Speed Buff - Run-in = Train in Compression - Produces Outward Force on Curve, Increases Vertical Load on Outside •
Draft - Run-Out = Train in Tension Produces Inward Force on Curve, Increases Vertical Load on Inside •
Train in Simultaneous Buff & Draft -Torque Produced - Force Applied at Coupler Resisted at the Rail •
Slack 6"/Car 50' Slack/6000' Train
Hunting Caused by: •
•
•
•
•
•
•
•
•
Empty or lightly loaded cars (though heavy cars can also hunt). Train speeds above 45 mph. Dry rail. Three piece freight car truck. Roller side bearings. Tangent track or curvature of 1 degree. Roller bearing wheelsets. Worn wheel treads having a hollow appearance over good quality track. Poor vertical snubbing.
v
s
Track Geometry Forces •
Lateral Force Result of Changes in Alignment & Gage –
–
•
Wide Gage > Truck Hunting at High Speeds Tight Gage > Truck Hunting at Low Speeds
Vertical Force Result of Changes in Cross-level/Superelevation & Profile –
–
Vehicle Rocks About CG Produces Horizontal Component at Rail because of Shift in CG
Vertical Forces •
•
•
•
•
Vehicle Weight Unbalanced Elevation in Curves Car/Locomotive Dynamics Track Geometry Input Coupler Forces
Effects of Centrifugal Force OVERBALANCE
EQUILIBRIUM
Centrifugal Center of Force Gravity
Centrifugal Centrifugal Center of Force Center of Force Gravity Gravity
Resultant Gravity
Resultant Gravity
Superelevation
V max V max E a D
Superelevation =
UNDERBALANCE
E a
+
3
0.0007 D
Resultant Gravity
Superelevation
Amount of Underbalance
= Maximum allowable operating speed (mph). = Average elevation of the outside rail (inches). = Degree of curvature (degrees).
Car & Locomotive Dynamics •
Bounce •
Bounce & Pitch Result of Surface Variations
•
Increase & Decrease Vertical Loading
•
Speeds > 40 MPH
•
Change in Track Modulus
Pitch •
Varying Vertical Load Transfers End to End •
•
Square Joints Wheel Climb & Short Flange Marks
Track Geometry Deviations in Geometry Accentuate Pitch & Bounce –
–
–
–
Deviation in Uniform Profile Mismatched, Bent or Battered Joints Worn Points/Battered Frogs & Crossing Diamonds Poor Cross-level •
–
Rock & Roll
Spirals •
Warp Forces Suspension Diagonally to Limits –
Bind Side Bearings - Trucks Can't Turn
Harmonic Oscillation Rock & Roll •
•
•
•
High Center of Gravity Cars & Low Joints at Truck Spacing Rocking Magnifies Alternate Rocking on Other Rail –
Wheel Lift on Successive Joints
–
Especially Dangerous on Curves
Resonance Occurs at Critical Speed Critical Speeds Occurs at Multiples of Frequency & Wavelength
Center of Gravity & Oscillation
Longitudinal Coupler Forces •
•
•
Loaded car coupled to empty car (difference in compression of springs). Differences in wheel wear, especially with multi-wear wheels. Inequality of track surface, or sharp vertical curvature.
•
Vehicle bounce or pitch.
•
Effects of slack run-in or run-out.
Coupler Forces & Derailments •
Time duration of coupler forces
•
Train consist and makeup
•
Train handling by crew
•
Terrain
•
Geometry of coupled cars
Rail-Wheel Profile
New Wheel & New Rail
Worn Wheel & Worn Rail
New Wheel & Worn Rail
Worn Wheel & New Rail
Critical L/V Ratio •
L/V = 1.29 wheel may climb new rail.
•
L/V = .82 wheel lift impending.
•
L/V = .75 wheel may climb worn rail.
•
L/V = .64 rail overturn force starts (unrestrained rail may overturn: rail rollover).
QUESTIONS? Author: Joseph E. Riley, P.E. Federal Railroad Administration (202) 493-6357
[email protected]
Contributors: Robert Kimicata, P.E. Kimicata Rail Consulting
(847) 394-4105
[email protected]
