estimation of wheel-rail friction at vehicle certification
TRANSCRIPT
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Estimation of wheel-rail friction at
vehicle certification measurementsNordic Seminar on Railway Technology, 2016Márton Pálinkó, Mats Berg, Lars Andersson
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Contents
1. Introduction
2. Background
3. Methodology
4. Results
5. Conclusions
6. Further work
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Introduction
• Increased rail traffic, increased requirements on vehicles
• Wheel-rail friction is an important question at vehicle
certification tests
• The friction should be high according to EN 14363
• The measurement at operation is not possible
• Gives an insight to other phenomena
• Algorithm for estimation (Petrov et al.) applied to test data
• Cooperation between KTH and SNC Lavalin
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Background - Forces in operation
Steel-on-steel force transmission
Contact area - slip, called creep in rail operation
Creep forces/moment
• Longitudinal (𝑋 = 𝑇𝑥) – Traction/braking, curves
• Lateral (𝑇𝑦) - Curves
• Spin - Curves
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Background – Coefficient of friction (CoF)
The estimated friction (used):
Friction attributes:
• Limit to the transmittable forces
• Smaller than for road traffic
• Condition – dependent
Creep and spin monitored for correlation
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Background – Creep equations
The longitudinal creep:
The lateral creep:
The spin:
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Background - Certification tests
• Dynamic tests according to EN14363
• Different track attributes
• IWT4 technology by SNC Lavalin (Interfleet)
• A total of 3 runs in an S – curve of 150 meter radius
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Background - Certification tests
Quantities of interest
• Forces (Q, X, Y)
• Lateral contact point position (Lcpp)
• Angle of attack (AoA)
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Methodology
• Matlab environment
• Low pass filters of 20/10 Hz for forces/AoA and 5/2 Hz Lcpp
• Instantaneous values of coefficient of friction,
total creep and spin
• Statistical analysis for better estimation
• Possibility to put errors into the system – Sensitivity analysis
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Results – Test 1
• Smoothest behavior - Peaks are observable
• Both parts of the S-curve show normal behavior
Time [s]
Coefficient of friction Total creep Spin
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Results – Test 1A
Statistical tool:
• Moving average with 5 meter window and 1 meter for deviation
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Results – Test1A
Coefficient of friction against the total creep
Instantaneous Moving averaged (5m)
Total creep Total creep
Coeffic
ient
of F
riction
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Results – All tests – Inner wheel
• The overall mean of the moving average for different filters
• CoF – Force and Lcpp dependent
• Constant total creep – mostly dependent on angle of attack
• 20/5 Hz fiter combination is adequate
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Results – All tests – Inner and outer wheel
• Outer wheel gives lower estimate
• Total creep stays fairly constant
• Increasing coefficient of friction with the tests
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Results – Sensitivity analysis – Inner wheel
• Angle of attack effects the creep
• Only calculating with the curve gives a big difference
• CoF does not vary significantly – straight cone of the
wheel most of the time instances
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Results – Sensitivity analysis – Outer wheel
• Significant variation in CoF value – Lcpp error approx. +/- 6 mm
• Effects can be decoupled:
• AoA - linear, Lcpp - proportional to the wheel profile curve -
fairly linear on the tread, nonlinear reaching the flange part
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Conclusions
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Conclusions
• In tight curves the friction cannot be estimated on the outer
wheel – minimum
• T/N at small contact angle has to be high
Tight curves
Traction/braking
Irregularities – only for small time interval
• Above a certain spin, the algorithm overestimates the friction
• Around zero spin and around this limit, good estimation
• High creep – not a quality factor in this case
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Further work
Other available test to be included to prove the conclusions -
With different attributes like:
• Varying curves with radii down to 400 meter
• High speed for higher dynamic effects
• Various tracks with real-life irregularities
Challenge: good estimation of bogie rotation as the angle of
attack is not available
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Thank you for the attention!
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