Spreadsheet for Diesel Throttle-Power Container

[rweber95]

I've made a diesel enginespec spreadsheet that will generate a throttle-power container. The inputs are TE (lbs), max speed (mph) and horsepower. The spreadsheet assumes that notch 1 provides an eighth of the maximum power and an eighth of the maximum TE. Each subsequent notch increases the power by an eighth. The resulting throttle-power container values replicate the curve shape in the figure. The link is http://home.comcast.net/~eng95/newenginespec.xls

Schematic diagram of tractive effort vs. speed for a 7000 kW locomotive, max TE=350kN and max. speed=90 m/s.
The TE curve from A to B is limited to the maximum TE (350kN). The breakpoint B is where maximum TE (kN) times V (m/s) equals the maximum engine power (kW), 350 x 20 = 7000. The exponential curve B to C is a constant power curve TE = 7000/V to the maximum V.

Bob Weber

 

[wylie]

Thanks for that. I tried it out on an Electric loco that Im currently putting together. It gave me a good base to get started, though in testing the loco seemed a bit underpowered but I think thats because everything else in Trainz is less accurate. I suspect the wagons I was hauling are a bit heavier than they are supposed to be.

One thing I noticed is that the spreadsheet lists the top speed twice in each notch (and the base power as I recall) and CCP cleans this up by removing the duplicate speed in each notch.

Any chance of one for Dynamic Brake?

It seems to me that by now someone should have written a PHP page on the web that we could go to for this kind of thing. Perhaps I could look into that when I have some time.

 

[RPearson]

wylie, I just took a quick look at Bob's spreadsheet. I'd say the premise is pretty good. The old TEE program is one I used occasionally. It was based on using only about 82% of the rated hp as useable at the railhead. It didn't spell that out up front you had to go thru the numbers to see what it did.

With Bob's you have to make that decision for yourself. If the loco is rated 7000kW, is that the rated power of the diesel engine or usable power applied at the rail? A general rule of thumb is that 20% of the installed rated power is lost in the conversion process thru generator, cables, traction motors and gearing plus running auxilary equipment. It will vary with each specific loco. And of course electrics would have different efficencies based on power from the overhead.

Part of the researching effort of engine spec design is determining what power is available at the rail. Usually you'd apply a factor to the rated hp (kW) if actual curves aren't available.

I'd make one change to the spreadsheet as supplied. There should be an increase in the speed parameter for each entry in the table. The last 2 speed entries in each notch container should not be the same as you found out but should differ by say 0.01m/s.

So the last 2 entries would be something like 29.1 and 29.11 m/s in Bob's table for each notch (but of course you should edit the formula in those cells to add 0.01 to the value in the cell above it - EDIT - you'll also need to change the formating to increase the number of decimals displayed for the modified cells to at least 2 so the copy and paste will pick it up). The exact amount isn't that important it just has to be a small increase. The purpose is to drop the te down to 0 above a specified speed. If you knew the actual power curve for the loco you could handle it in a more realisitic fashion. But this works and prevents the loco from acceleration to very high speeds.

Trainz does a linear interpolation in the tables to calculate the tractive force produced by the loco at a particular speed. It needs at least a small increment in speed between entires to do the interpolation.

Bob Pearson

PS There is and has been for some time a web site like you suggest. I don't have the url handy but do a web search on Al Krug. Very interesting site for other reasons too. I think the calculator he's got - which does resistance and power calcs very much like TEE does but of course with no throttle-power curve input for Trainz - is not too bad.

Try http://www.alkrug.vcn.com/home.html

 

[frogpipe]

So I grabbed the spreadsheet and I have ONE question.

I have the specs for the locomotive I want to make a curve for, but it has both "Starting Tractive Effort @ 25%" and "Continuous Tractive Effort @ 11mph", which one should I use?

(Westie is a cute doggie BTW)

 

[Azervich]

The sheet is for starting or max T.E, The continuous T.E you input yourself if you know the speed and the power, I use this convert units to build my e-specs

http://www.digitaldutch.com/unitconverter/

use force to convert lbs to kn and use speed for mph to m/s,

like if you have 311kn at 12mph you type in 12mph and it gives you 5.36448 m/s, the column on the left is speed, so I use continuous rating in the notch 8 container as that's when the engine and generator is running at max revolutions per minute, I always fill out notch 8 and work my way down to notch by reducing tractive power per notch, however some locomotives are sluggish in lower notches so you'll want to reduce those T.E's a fair bit to give that feeling.

Cheers.

 

[frogpipe]

http://thedieselshop.us/Data EMD SW7.HTML is the data source I'm using.

The spreadsheet has 4 entries:

Model
TE (Lbs)
Vmax (Mph)
Power (HP)

Into which I input

Model: SW7 (obviously)
TE (Lbs): 62000 (taken from "Tractive Effort (starting)" on the page linked above)
Vmax (mph): 65 (taken from "Speed" on the page linked above)
Power (HP): 1200 (taken from "Horsepower" on the page linked above)


You don't sound like your using the same spreadsheet.... The one I downloaded looks like this:

 

[norfolksouthern37]

be cautious about the data you get from that page, sometimes it is incorrect.

 

[frogpipe]

I assume you mean the data source, and thanks for the heads up on that - I can cross check it on other pages, but I can't find a PDF for the SW7 manual, so I can't reference an official source. This has become a recent concern to me, so I have yet to check if there are any books at the library that might help.

Meanwhile, does anyone know WHICH Tractive Effort figure to use in this speadsheet? Starting or Continuous?

 

[Azervich]

You type in starting/max T.E which I mentioned on my post, and no I don't use spread sheets as they are based on generic values.

This page has data http://www.american-rails.com/emd-sw7.html

Cheers.

 

[frogpipe]

Ok, got it now. Thanks!

 

[norfolksouthern37]

no I don't use spread sheets as they are based on generic values.

without having actual data for every locomotive you must be using some form of generic value or taking a crack at a guess. a spreadsheet can do just fine...

 

[Azervich]

What I mean is the sheet give you a smooth curvature of the tractive efforts, I do have some data for specific locomotives, some of the ones I have show a decrease till 50kph then a slight increase of tractive power and begins to lower again when your close to the motors max gearing.

Here's another example of ones I have

Tractive Effort Starting: 38,080lbs
Tractive Continuous: 33,880lbs @ 7.5mph
Tractive Continuous: 28,000lbs @ 9.5mph
Tractive Continuous: 22,120lbs @ 11.5mph

This is for a Model G8B, when you get to 20mph there's a increase of T.E then drops slowly till 100kph with a 63-14 gear ratio, I haven't added it to the trainz e-spec on DLS yet as I still need to re-work the brakes and get them corrected, but I guess it's the result of field shunting that causes the slight increase of T.E. once you hit that speed.

EDIT:

I don't have that office thing installed, was going to try some tests with the sheet

Cheers.

 

[Azervich]

I wonder if it's possible to model Diesel-Hydraulic characteristics into trainz, like if you have a 2 stage make it you have strong slow speed tractive effort and it looses power rapidly as you pick up speed, then at the point where the transmission goes into the next gear you increase it's tractive effort so that your able to accelerate but not too much of an increase and lower the tractive effort again, of cause these will have to be guessed as there's no data on Diesel-Hydraulics besides starting and slow speed continuous.

So if you have a 3 stage or a 4 stage you keep repeating that, but of cause the tractive effort wouldn't be high as you change gears each time it'll be like a car, you loose torque the higher gear you go, but the high gears allows for speeds rather than power.

So for Stage 1 you'll have like 200kn at 7.5mph and drop it till say 20mph and give Stage 2 140kn, then for Stage 3 90kn for 40mph and for stage 4 50kn for 60mph.

Cheers.

 

[Pendolino]

Why not? Nothing prevents you from making an enginespec where TE values at higher speeds increase. Its graphic representation should look like a sawtooth waveform.

Some time ago I played with a diesel-mechanic enginespec for DMU (which are very common on Italian branch lines).
I associated notches 1-5 with the 5 gears of the mechanical transmission:
- notch 1 has TE values up to approx 20 kph, then decreased to 0 kN just after the speed at which the Diesel engine reached max. RPM.
- notch 2 started with a 0.01 kN value at 0 kph, 0.01 kN at 9.9 kph, then 30 kN at 10 kph, then decreased to 0 kN just after the speed at which the Diesel engine reached max. RPM.
- notch 3 started with a 0.01 kN value at 0 kph, 0.01 kN at 19.9 kph, then 20 kN at 20 kph, then decreased to 0 kN just after the speed at which the Diesel engine reached max. RPM.
... and so on.

The enginespec worked quite fine (and I'm using it to simulate traditional, non-electronic electrics), but it lacked the equivalent of a throttle. There is no way, for example, to run at 22 kph in notch 2: since TE at 22 kph is higher than train resistance, the railcar will accelerate anyway.