Traction Control

[Anonymous]

Has Any manufacturer prototyped or produced any type of electronic traction control for wheel slip?

[Modelcar]

....If you are talking about railroad engines, I believe it is in production and has been for some time....

[Modelcar]

....GE AC Traction Control.

[M636C]

The earliest version of traction control was the EMD "IDAC" system (for instantaneous detection and control) which detected wheelslip by the change in resistance due to the increase in speed (the electrical resistance of a series wound traction motor is inversely proportional to its speed -resistance goes down as speed goes up). It then automatically dropped sand and cut power to all axles briefly. Alco had a similar system and on a 25000 ton train on a grade you could feel the power cut on a remote unit before the (wheelslip) bells began to ring! GE had a similar system but used a speedometer drive on each axle as the detection system, at least on U25s and similar early units.

There are a number of other systems relying on microprocessors, the best known being Wabtec's Q-tron which is often retrofitted to EMD Dash-2 locomotives.

With the GP50 and SD50 EMD introduced the best of the DC traction control systems, the "Super Series" system that used a radar doppler system (mounted on the front of the fuel tank, looking forward at the track) to detect forward speed. The axles were then allowed to slip in a controlled manner consistent with the forward speed. This greatly increased the available adhesion, which is maximised with slight slipping. This remains on EMD DC locomotives today. It did require that all axles had to be connected in parallel at all times (odd for a system that had the word "series" in its name), and this meant that the alternators had to have greater capacity. EMD at first used bigger alternators (AR15 in the GP50, AR16 in the SD50) which eliminated transition (a really good thing). Later EMD adopted internal series parallel switching inside the alternator itself in the AR11 alternator (and probably in the AR20 in the SD70). This was also (first) used by GE to allow a similar arrangement of motors in parallel, although they used microprocessor control and did not use radar.

An unexpected problem with "Super Series" occurred in tunnels where track had been laid on slip form concrete (like an interstate highway). The radar couldn't detect any movement until a small amount of ballast had been laid on the concrete to give it something to "see".

With AC motors, it is much less likely that the axles will slip, because their speed is determined by the frequency of the AC current being supplied by the inverter. Thus even if a wheel slips, it can't "run away" like a DC motor and the slip is likely to correct tself more quickly.

GE provide a separate inverter for each axle (ie six inverters) and this allows them to cut power to any axle if a slip is detected (even though it won't run away).

EMD provide only two inverters, each powering three axles, and the power would have to be cut to the three axles to stop a slip.

Both EMD and GE claim their system is superior for different reasons. I have seen wheel slip on a locomotive with the EMD system, (and was amazed) but I have little exposure to either system.

Peter

[Anonymous]

peter,
very interesting comment.
any other references, websites available?
thank you

[M636C]

cbt141,

That was all written without references (at least, not checking any!). The EMD and GE web sites have some information. There have been formal engineering papers to SAE and similar. Maybe I could write an article - all I have to do is convince whoever becomes "Trains" editor!

Peter

[jchnhtfd]

Peter -- excellent commentary on wheel slip detection/control. The doppler based systems do work, and work very well indeed.

An amusing (?) aside -- the Budd RDCs were a little light, but had very powerful brakes; they had a wheel slip detecton system for braking which worked by sensing the rotation of the axles and dropped sand if one axle slowed more than the others. Worked pretty well; the RDCs could stop amazingly short. Only problem with the system is that now and then the sand wouldn't get properly wiped off the wheel treads (the brakes were disk brakes, not tread brakes; there was a special wiper for the treads) and you would be sitting there on the sand, and the signals would indicate clear since you weren't shorting the track. Could be embarassing...

[Anonymous]

m636c
"There have been formal engineering papers to SAE and similar. Maybe I could write an article - all I have to do is convince whoever becomes "Trains" editor!"

well, i'm convinced
cbt141