Rail Car Adhesion and

Wheel Slide Protection SystemsDelivered by: Gil OlveraOriginating from: Downtown Baltimore Office

REMOTE PARTICIPANTS

Please mute your phone by dialing *6*. To un-mute, dial *6* again.

Please do NOT put your phone on HOLD.

If your screen freezes, please log out and then log in again before

contacting the STV Help Desk.

• STV is a Registered Provider with The American Institute of

Architects Continuing Education Systems (AIA/CES). Credit(s)

earned on completion of this program will be reported to AIA/CES

for AIA members. Certificates of Completion for both AIA members

and non-AIA members are available upon request.

This program is registered with AIA/CES for continuing professional

education. As such, it does not include content that may be deemed

or construed to be an approval or endorsement by the AIA of any

material of construction or any method or manner of handling, using,

distributing, or dealing in any material or product.

• Questions related to specific materials, methods, and services will

be addressed at the conclusion of this presentation.

2

Learning Objectives

At the end of this program, participants will be able to:

1.Discuss the difference between wheel slide,

wheel slip, and wheel creep in rail vehicles.

2.Determine why wheel slide happens.

3.Calculate the “adhesion demand” by knowing

only the train deceleration rate and grade.

4.Advise others on why wheel flats should be

avoided.

5.Describe how a wheel slide protection system

works.3

4

What is Wheel Slide, Slip, Creep?

Wheel slide is the condition where one or more axles on

a rail car or locomotive lock or stop spinning and slide

along the rail.

Wheel slip occurs when axles spin faster than theoretical

speed during acceleration due to low “Adhesion.”

Wheel creep occurs when adhesion is low and axles

spin slower than theoretical speed but do not lock.

All three are caused by traction or braking forces and

insufficient adhesion between running rail and wheels.

Focus of this presentation is Wheel Slide, which is very

detrimental to rail equipment and impedes system

operation.

5

Why Slip – Slide Happens

Most trains run with steel wheels on steel rails.

Lack of adhesion will cause the wheel to lose

rolling action, thus causing a slip or complete

slide under load from traction or braking effort.

Adhesion Demand is the minimum level of

friction required to keep a wheel rolling on rails.

Adhesion demand is often stated as a %, (i.e.

0.20 = 20%).

When actual adhesion is below the demand, the

wheels will start slipping or sliding.

6

Why Slip – Slide Happens

A locked wheel delivers less retarding force than

a rotating wheel with brakes applied and

extends the braking distance.

Locked wheels will cause flat spots, which are

highly undesirable.

Brake systems most prone to wheel slide have

disc brakes only.

Tread brakes allow some amount of wheel

cleaning or scrubbing to increase adhesion.

7

Wheel Flats

Wheel flat damage is the result of sustained sliding.

With increasing speeds, flats create a loud, buzzing noise that disrupts passenger comfort.

Flats cause high impact loading and vibrations that damage rails and truck-mounted equipment.

Heat generated from sliding can alter wheel steel micro-structure (embrittlement), causing spalls and voids.

Repairs are costly; cars are out of service for wheel turning or wheel replacement.

8

Flat Spots

9

Flat Spots

10

Flat Spots

11

Wheel Flat Avoidance

Modern rail vehicles are equipped with a wheel

slide protection (WSP) system.

WSP is typically part of the brake system scope.

Sanding system is often included with WSP

Train operators can minimize wheel slide by

braking earlier with a lower brake rate and

“drive” the train into the station.

– Wheel slide system has a good chance of preventing

flats under very low adhesion.

12

What is Adhesion Demand Adhesion demand is the minimum level of

friction required to keep a wheel rotating on

running rails.

The adhesion demand can be calculated and

depends on the acceleration or braking rate.

Does not depend on weight, passenger load,

or speed.

Equation: The instantaneous deceleration or

acceleration rate in (f/s/s) divided by gravity

rate (32.17 f/s/s).

Grade is factored in as needed.

What is Adhesion Demand?

13

Adhesion

The adhesion demand is affected by uphill and downhill grade (slope). Uphill grade reduces adhesion demand; downhill increases adhesion demand.

Inst. Brake Rate (f/s/s)

Adhesion Demand = ------------------------ + or (-) Grade32.17 (f/s/s)

Add Grade, if downhill

Subtract Grade, if uphill

Adhesion Demand

14

Adhesion Demand

Here is an example:

Train brakes at 3.0 mphps.

Rate converts to 4.40 f/s/s.

Downhill grade is 2.0%.

Adhesion Demand is:

4.40 +.02 = 0.16 (16%)

32.17

15

Braking adhesion demand in rail and

rubber tire vehicles

Passenger Rail 2.0 – 5.0 f/s/s = 0.05 - 0.16

Tractor-Trailer 15.5 f/s/s = 0.48

City transit bus 17 f/s/s = 0.53

Pick up truck 28 f/s/s = 0.88

Automobile 30 f/s/s = 0.95

Formula 1 race car 70 f/s/s = 2.18

16

Low Adhesion Conditions

Normal adhesion between dry, clean steel rails

and wheels typically is above 0.10 or 10%.

Low adhesion under moist, wet conditions is

under 10% and can be near 5% under icy

conditions.

Worst-case adhesion under slippery leaf film can

be below 5%.

17

Low Adhesion Causes

Moisture from condensation, rain, frost, snow,

ice storms.

Dirty rails from environmental soot, dirt/mud,

debris build-up on surfaces.

Autumn leaves falling on rails and constantly

crushed from train traffic leave a slippery pectin

film which becomes hard and wax-like, hard to

rinse off.

18

Leaf matter gets everywhere

Dried leaf matter found in track brake assembly

19

Wheel Slide Protection System

Definition: A automatic system added to each rail vehicle to detect, control, and prevent wheel slides.

System is closed loop micro-processor controlled with axle speeds as primary inputs and brake effort modulation as the primary output.

Speed sensors measure each axle rotation.

Speed signals connected to the WSP controller are measured and compared to each other or a reference ground speed.

If one or more axles have lower rotation speeds than the reference axle, the system sees that as nearing slide.

Micro-processor alters braking on/off in pulses on one or more trucks to allow a controlled amount of creep and re-gain axle rolling.

20

Wheel Slide Protection System

WSP is “per truck based” and controls the truck braking where the sliding axle is detected.

Per axle control requires a dump valve (apply/release) on every axle. However this increases complexity, lowers reliability, and, in many applications, not entirely advantageous.

Computer can determine the correct reduction of braking with constant adjustment until the slide is under control, also trying not to under-brake and increase braking distance.

Wheel creep can be controlled at higher speeds to improve adhesion.

Resulting braking rates and distances are affected.

21

Wheel Slide Protection System

WSP can work down to very low adhesion levels, e.g., 5% (0.05).

A safety timer is set to around 5 seconds and shuts off WSP if the slide is not controllable.

Automatic sanding system is activated when wheel slide signal indicates WSP is active.

Air and hydraulic brakes work similarly. Hydraulic brakes have faster response times due to fluid being incompressible.

Hydraulic brakes are used in light rail and urban trams.

22

WSP System 2-Truck Car Example

ECU1 ECU2

BCU1 BCU2

DMV DMV

MR

23

WSP Equipment

WSP Electronic Control Unit:

– May be stand alone or integrated into brake

ECU.

– Each car may have one control unit with

separate control boards per truck, or may

have one separate control unit per truck.

– WSP software is specialized, tunable for each

application with various adjustable

parameters.

24

WSP Equipment

Dump Magnet Valve:– Typically a two solenoid valve (apply/release)

assembly for rapidly venting, holding, and recharging brake cylinder pressure (BC), one per truck.

– Valve unit is mounted close to the truck BC piping for rapid response.

– Uses Main Reservoir (MR) supply for recharging or piloting.

– Uses pressure transducer for BC pressure feedback.

25

Knorr Bremse ASV1-S1 (MGS3 system)

Wabtec Decelostat Controller Type E7 on test bench

Electronic Controller

26

Knorr Bremse ASV1-S1 (MGS3 system)

Knorr wheel slide dump valve on light rail vehicle.

Dump Valves

27

Knorr Bremse ASV1-S1 (MGS3 system)

Wabtec air dump valve unit D1 on test bench.

Dump Valves

28

Knorr Bremse ASV1-S1 (MGS3 system)

Knorr’s new advanced design, more compact, lightweight.

Dump Valves

29

WSP Equipment

Speed Sensors:

– One for each axle monitors RPM.

– Can be mounted on axle end, motor shaft.

– Typically “active” powered magnetic pick-up

type, single or multi-channel.

– Signal characteristics must be compatible

with WSP controller.

– Axle speed distributed to one or more ECU

or WSP controllers.

30

WSP Equipment

Sanding System

– Sanding increases adhesion for short

durations.

– Sand is commanded to apply during WSP

activity.

– Sand is sprayed ahead of the first axle onto

rail head.

– Sanding System also is used in slip conditions

and Emergency Brake application.

31

Knorr Bremse ASV1-S1 (MGS3 system)

Honeywell speed sensor mounted to top of axle gearbox.

Speed Sensor

32

WSP Testing

Wheel slide system performance is optimized to

specific vehicle and train operation.

Testing now follows UIC 541-05 standard.

WSP validation process tests reaction to low

adhesion, stable control of wheel creep, ability to

avoid sliding, and evaluating resulting braking

rates and distances.

Low adhesion is sometimes artificially created to

induce slides and trigger the WSP.

33

WSP Testing

Tracks are wetted ahead of lead axle using

spray system on-board test train.

Wetting agent consists of water and detergent

such as dish soap or windshield washer fluid.

Mixture can be adjusted depending on how

slides are induced.

Sanding system is turned off in order to isolate

WSP performance.

Adhesion is determined by calculation based on

deceleration rate during slide event.

Target is to get 0.06-.08 adhesion.

34

WSP Testing

Testing is conducted at the highest service

speeds and highest service brake rates, both

blended and friction only.

Test conducted at empty weight as higher load

has a tendency to increase available adhesion

(mainly scrubbing tread brake shoes on tires).

35

WSP Testing

Emergency brake WSP testing is not typically

required (WSP may not be available during EB)

Results are reviewed as signals, axle speeds,

reference speed, and BC vs. time graphs.

Resulting brake rates and distances are

compared to base line tests.

Wheels are inspected for flat spots.

36

WSP Testing

Sample WSP Testing Result

37

WSP Suppliers

Wabtec “Decelostat” air system. Current

generation is E-7 (US).

Wabtec Poli S.P.A. “Athena” air system (Italy).

Knorr Brake (Bremse) “MGS2” air and hydraulic

systems. New “MSG3” system. (Germany)

Selectron “800” air system (Czech Rep.)

SIEMENS (Germany)

Faiveley “EPAC” air system (France)

38

Review of Objectives

1.Discuss the difference between wheel slide,

wheel slip, and wheel creep in rail vehicles.

2.Determine why wheel slide happens.

3.Calculate the “adhesion demand” by knowing

only the train deceleration rate and grade.

4.Advise others on why wheel flats should be

avoided.

5.Describe how a wheel slide protection system

works.

Course Evaluations

In order to maintain high-quality learning experiences, please access

the evaluation for this course by logging into CES Discovery and

clicking on the Course Evaluation link on the left side of the page.

39

This concludes The American Institute of Architects

Continuing Education Systems Course

STVUniversity@stvinc.com

40

Thank you for your time!

Questions??

41

Q&A

Thank you!

Please remember to confirm your attendance

today by completing the Attendance Confirmation

Survey in the STV University Learn Center.

You will receive instructions via email from

STV University.

If you do not receive the survey, contact:STVUniversity@stvinc.com