[steamer_ctn]

I have published my suggested way of calculating the "apparent" adhesion coefficient for modern locomotives on my webpage at the bottom of the Curtius - Kniffler Formula. I have also added a quick and dirty spreadsheet that may assist in the calculations.

Basically it is as follows:

i) The diesel locomotive has been designed to start with a certain starting tractive force and "apparent" adhesive coefficient. The apparent adhesion coefficient can be calculated by dividing the Maximum (Starting) Tractive Effort by the Weight on the Drive Wheels.

ii) Determine the speed point where the starting tractive force starts to decline. For example, on this tractive effort graph it will be the point where the blue and brown lines intersect, ie approximately 10mph.

iii) Using the point above, (ie Adhesion Coefficient @ speed) adjust the "C" value in the Curtius_Kniffler curve until the curve passes through this point. This spreadsheet can be used to perform this operation. The ORTSCurtius_Kniffler parameter value will be shown in the spreadsheet as the graph is adjusted.

[darwins]

Now looking at this I can get closer to an answer. The date and Wikipedia information for the US diesel locomotives that you are describing tells me that the change is really due to the introduction of solid state control technology.

The manual explains that "The adhesion limit is only considered in the adhesion model of locomotives." So that this is all about traction and does not concern braking.


So default settings should be fine for:

steam locomotives
diesel mechanical power units
diesel hydraulic power units

dc electric trains using dc motors controlled by resistances
single phase ac electric trains using dc motors controlled by tap changer
diesel electric locomotives where dc motors are supplied with current from a dc generator


Presumably the default model is also good for some of the less common "old technology":

dc electric trains using metadyne generator to supply infinitely variable voltage to dc motor
dc electric trains using motor generator booster "buck and boost" to supply infinitely variable voltage to dc motor
three phase ac electric trains using ac motors with fixed speeds


Changes to the adhesion model are then needed for:

diesel electric locomotives that provide power to dc motors via an alternator and solid state rectifier
single phase ac locomotives using dc motors supplied via a solid state rectifier
dc locotives using dc motors supplied via a chopper and solid state rectifier

all trains driven by ac motors with power supplied by a solid state variable voltage variable frequency device


Is there large variation between individual units in this second group or would it be possible to produce a reasonable set of generic values that would do for many different power units?


Finally I am assuming that any trains propelled by linear motors (technology not mentioned by Allenbach) come into this final group.

[darwins]

Thank you Peter, the information you have given and the spreadsheet will be very useful for modern diesel electric and electric locomotives.

There is a problem here though - whilst max tractive effort (the blue line on your graph) is commonly published for locomotives, it seems virtually impossible to obtain that information for multiple unit trains, trams and even some modern high speed trains with distributed traction. Do you have any suggestions for dealing with these?

[Laci1959]

Hello.
Thanks for the table. Very useful. Perhaps it would be a useful addition to an imperial-metric shift formula.

Sincerely, Laci 1959

[steamer_ctn]

darwins, on 25 July 2021 - 10:12 PM, said:

Now looking at this I can get closer to an answer. The date and Wikipedia information for the US diesel locomotives that you are describing tells me that the change is really due to the introduction of solid state control technology.

As a rough rule of thumb, and in my opinion, increased adhesion in regard to the OR default will only be required where a technology has been fitted to the locomotive which controls wheel slip by modulating tractive force.

We could get very sophisticated in OR, and code the software algorithms that control wheel slip in modern locomotives. If we did that then we probably wouldn't need to vary adhesion. So this suggested methodology is determining an "apparent" adhesion to mimic slip performance of modern locomotives (as an easier solution).

At the moment I am not sure that solid state rectifiers would fit into this category. Do they control wheel slip in any way?

darwins, on 25 July 2021 - 10:12 PM, said:

The manual explains that "The adhesion limit is only considered in the adhesion model of locomotives." So that this is all about traction and does not concern braking.

Correct, braking uses the default adhesion values.

darwins, on 25 July 2021 - 10:12 PM, said:

Is there large variation between individual units in this second group or would it be possible to produce a reasonable set of generic values that would do for many different power units?

This would require a literature survey, and calculation of a median adhesion value to develop some generic values.

darwins, on 25 July 2021 - 10:20 PM, said:

There is a problem here though - whilst max tractive effort (the blue line on your graph) is commonly published for locomotives, it seems virtually impossible to obtain that information for multiple unit trains, trams and even some modern high speed trains with distributed traction. Do you have any suggestions for dealing with these?

This is the age old problem, where can we find enough detail for our locomotive definitions?

The only two suggestions I can offer at the moment are:

i) Ask the community to pool relevant information. This might help in developing some common "standards". And provide some information that could be used in the next suggestion.

ii) Try and do a "best guess" estimate.

Laci1959, on 26 July 2021 - 03:22 AM, said:

Perhaps it would be a useful addition to an imperial-metric shift formula.

I could add another worksheet TAB with metric units (m/s and N), would that solve the issue?

[Laci1959]

steamer_ctn, on 26 July 2021 - 10:46 PM, said:

I could add another worksheet TAB with metric units (m/s and N), would that solve the issue?

Yes, that is also very good. Thanks in advance.

[ErickC]

darwins, on 25 July 2021 - 10:12 PM, said:

Now looking at this I can get closer to an answer. The date and Wikipedia information for the US diesel locomotives that you are describing tells me that the change is really due to the introduction of solid state control technology.

Sort of. The first major improvements in adhesion came with better truck design in the early 1970s. The HT-C, for example, gains an advantage because it handles weight shifting better than the Flexible (later called "Flexicoil") trucks did. The introduction of solid-state controls simplified the electrical cabinet, but WS10 (solid state) and IDAC (not solid-state) are functionally interchangeable. They detect as fast and they react as fast as each other.

The introduction of microprocessor controls provides faster reaction times and more precise control overall, but it can't deliver the traction control we think of today without the last critical component, which is ground radar. Before ground radar, wheelslip was detected via resistance and this was not capable of the speed and precision required to maintain optimum wheel creep.

EMD's first system of this type was Super Series, installed on the GP50 and SD50. It was somewhat flawed and was replaced by Mod3 on the SD60 and GP60. GE had a similar system around the same time (actually, I heard it came a fair bit earlier). Later on, self-steering radial trucks were able to offer yet another slight bump in adhesion due to the wheels following the rail better. This was introduced with the SD70 and AC4400 locomotives.

The AC-rectified transmission for DC locomotives (e.g. GP38AC, SD40-2, SD60) has no absolutely effect on adhesion and is all about ensuring that higher-horsepower engines don't fry the electrical cabinet. The 35-series had already reached the limit of what pure DC hardware could handle and had so many transition stages to handle the power that they suffered from reliability problems. DC locomotives with AC alternators are full-time parallel machines and transition once (around roughly 20 MPH or so). This only affects traction in the sense that a locomotive undergoing transition isn't pulling. Since OR does not currently handle transition, whether a locomotive has a pure DC transmission or AC transmission with DC motors is moot. If it did, we'd get much more accurate ammeter readings, though...

AC has advantages, but adhesion isn't one of them (that modern control systems showed up shortly before AC traction is a pure coincidence, as the first production locomotives for the North American market with ground radar and microprocessor wheel creep control were DC). The major advantage of AC traction is that the locomotive can safely operate at full power at lower speeds, taking advantage of the greater tractive effort available at those speeds. Another way to say this is that they have higher continuous tractive effort ratings because they can safely operate at power and speed configurations that would damage DC motors. They can also use dynamic braking to a full stop.

[darwins]

Quote

AC has advantages, but adhesion isn't one of them

That is interesting - I had thought that since the speed of ac motors is determined by the frequency of the supply (provided that sufficient power is available) then this would reduce the tendency to slip. It was this property of ac motors that gave the fixed running speeds of the old three-phase locos, and it was this same feature that led to the some of the first modern "cruise control" systems.

Thanks so much for your input. Outside of USA I wonder how many locos have ground radar...

[darwins]

I have had a try at using the spreadsheet to adjust the C value to acheive the desired friction at the dropoff point

https://i.imgur.com/c5UlGqI.png

This made me wonder if there was value in trying to adjust the value of starting friction as well like this
https://i.imgur.com/kjDmmU9.png

Does this have any value? In this case I adjusted both A and C values, but found that to do this for some locos the B value would need to be changed as well.

All of the locos I have in mind as far as I know have anti-slip electronics based on detecting changes in wheel rotation speed or current rather than ground radar.

Is adjusting the Curtius-Kniffler adhesion the right way to model these?

Is this an alternative to the use Antislip ( ) in OpenRails?

Would it be more realistic to get Antislip ( ) working correctly for such locos where you would see the power being reduced (without the throttle moving!) and then increased again until the throttle setting could be achieved?

In terms of the antislip technology based on wheel rotation speeds I was reading yesterday of an example where this was applied to individual axles rather than the whole locomotive.

[Laci1959]

Hello.

https://kephost.net/p/2021/30/97_8d02d571b3da.png

In Hungary, the coefficient of adhesion and the starting traction are given. Is it possible that the coefficient of adhesion and 𝐹𝑎𝑑ℎ𝑀𝐴𝑋 are the same? Before I laugh I am not a mechanical specialist just an insurance equipment signal mechanic.
If so, I shouldn't calculate the ORTSCurtius_Kniffler (A B C D) parameters from this, which Open Rails then counts back to this value. Between 240 N/kN and 270 N/KN are the machines I suddenly looked at.