Questions about traction

[Paul_D_North_Jr]

See also the explanation by beaulieu in the "Wheel Slip Control on NS SD60I's - Question" thread at - http://cs.trains.com/trccs/forums/t/164145.aspx 

I've alao run across some other explanations - I'll see if I can retreive/ find the links to those and post them here, too.

Here's a good one, for starters: http://www.republiclocomotive.com/ac_traction_vs_dc_traction.html 

- Paul North.

[CSSHEGEWISCH]

I have heard of a controlled wheel-slip technique used at low speeds to improve traction.  I remember comments about it while watching a video of the York Canyon coal train at Raton Pass.

[petitnj]

Traction is the weight of the locomotive times the coefficient of static friction of the metal to metal surface. In general you cannot increase traction by adding wheels or changing the shape of the wheel. The coefficient of static friction for steel on steel is anywhere from 0.2 to 0.8 depending on the cleanliness and oxide on the surface. The typical rail coefficient is about 0.35. For practicality, I use 0.25 for our training because often the rail has a layer rust and is a little wet on our first trip. Thus to determine the pulling capability of the locomotive take 1/4th of its weight on the drivers. The trick with modern locomotives is to give just enough power to each of the wheels so they approach the highest adhesion they can experience before they slip. Each wheel has a different coefficient because other wheels and sand may have already covered that rail. The problem is that once a wheel on a steam engine slips, they all slip (since they are coupled together by driving rods). Once the slip occurs, the dynamic coefficient of friction is lower (it has to be otherwise wheels would never slip) and the wheel continues to slip until power is unloaded off that wheel. Since each diesel axle is separately powered and experiences different static friction, by adjusting power to each wheel we can maximize traction.

[aegrotatio]

 This is very interesting information.  The talk about the oddly-cut wheels seemed to be related to avoiding contamination by lubrication.  What I'm asking about is if there are trains that have special high-friction wheels for acceleration that may or may not be removed for cruising (if there is such a concept in railroading).  I refer to the clever application of the extra axle for accleration in some newer locomotives (using hydraulics to raise/lower the axles for better adhesion).

 

 

[pajrr]

A lot of modern steam locomotives had railwashers installed after the rear drivers to clean sand off the rails. The locomotive would put down sand under the drivers for increased traction then wash the sand off the rails so that the rest of the train would not have to run over the sand and increase the friction. It seemed to work pretty well.

[JamesP]

Check out Marty Banes' steam pages, in particular:

http://www.martynbane.co.uk/modernsteam/ldp/wheelprofile/profilefcaf.htm

This is a high adhesion wheel profile for steam locomotives.  Lots of other modern steam development information, too.

 - James

[GP40-2]

The biggest advances lately have been in new software to enhance the traction on AC motored locomotives. GE and CSX have been the leaders on this.

[BaltACD]

Friction modification in the rail environment can be a double edged sword.  Modifiers that can increase the traction of engines can also increase the resistance to the cars movement.  Modifiers that can ease the movement of cars, may also decrease the traction available to the engine.

[oltmannd]

Sort of . There were some experiments with "traction sticks" that rubbed on the wheel treads to increase adhesion in the late 80s and early 90s I think.

[chad thomas]

 Gear & racks (cog railways)

Hi-ad radial trucks

Maxitrax, and other electric / electronic traction controll systems for better adheasion

AC traction motors

 

[aegrotatio]

I am curious if any experiments were done to increase locomotive traction in ways other than weighing down the engine for adhesion and spreading the effort over multiple engines and using sand.

Have other ways been explored, such as wheels with friction treads?