jrbernier Considering that most F7's weighed about 120-124 tons - that would put about 60,000 lbs of Starting TE at 25% adhesion. One would need very 'favorable' dry rail to get this kinds of TE.
Considering that most F7's weighed about 120-124 tons - that would put about 60,000 lbs of Starting TE at 25% adhesion. One would need very 'favorable' dry rail to get this kinds of TE.
EMD's calculations were based on a unit weight of 115 tons.
JayPotter EMD's ratings for F7 starting TE were as follows: 65:12 85,000 62:15 64,600 61:16 59,600 60:17 55,200 59:18 51,200 58:19 47,800 57:20 44,600 56:21 41,800. However it qualified the five highest ratings by stating that those TE levels would only be attained if rail conditions were "favorable".
EMD's ratings for F7 starting TE were as follows:
65:12 85,000
62:15 64,600
61:16 59,600
60:17 55,200
59:18 51,200
58:19 47,800
57:20 44,600
56:21 41,800.
However it qualified the five highest ratings by stating that those TE levels would only be attained if rail conditions were "favorable".
Considering that most F7's weighed about 120-124 tons - that would put about 60,000 lbs of Starting TE at 25% adhesion. One would need very 'favorable' dry rail to get this kinds of TE. Of course, all bets are off until you reach the minumum continuous speed of the engine so you do not fry the electrical system! I can smell the electrical insulation .....
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
timzerikem I would be surprised of most locomotives with 56:21 gear rations have the maximum short term tractive effort limited by adhesion. You would be surprised if ...(etc)? Sounds like you agree the higher-geared engine will have less starting TE as well as less continuous?
erikem I would be surprised of most locomotives with 56:21 gear rations have the maximum short term tractive effort limited by adhesion.
You would be surprised if ...(etc)? Sounds like you agree the higher-geared engine will have less starting TE as well as less continuous?
Meant to say "I wouldn't be surprised..." - oops.
Chances are that a higher-geared engine will have the same starting tractive effort as a lower geared engine - which would typically be limited by adhesion. You just have to feed more current into the traction motor, but that means that the time that a higher-geared engine can produce adhesion limited tractive effort is substantially less than what a lower geared engine is capable of.
beaulieuA EMD D77B traction motor produces 4850 lbs of torque as it starts to rotate.
erikem timz beaulieu higher speed ratios lower the T.E. Just to clarify-- he means when you compare two engines, identical except one has 56:21 and the other has 65:12, the latter engine will have a higher maximum TE. But at a given speed (above, say, 20 mph) the two engines will pull about the same. Probably more correct to say that the latter (65:12) engine will have a higher continuous tractive effort. I would be surprised of most locomotives with 56:21 gear rations have the maximum short term tractive effort limited by adhesion.
timz beaulieu higher speed ratios lower the T.E. Just to clarify-- he means when you compare two engines, identical except one has 56:21 and the other has 65:12, the latter engine will have a higher maximum TE. But at a given speed (above, say, 20 mph) the two engines will pull about the same.
beaulieu higher speed ratios lower the T.E.
Probably more correct to say that the latter (65:12) engine will have a higher continuous tractive effort. I would be surprised of most locomotives with 56:21 gear rations have the maximum short term tractive effort limited by adhesion.
Agree. They'd be thermally limited.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
A EMD D77B traction motor produces 4850 lbs of torque as it starts to rotate. Assuming 40" wheels the T.E. at the rail would be the following
62:15 20,030 lbs.
61:16 18,478 lbs
60:17 17,121 lbs
59:18 15,908 lbs
58:19 14,792 lbs
57:20 13,822 lbs
56:21 12,949 lbs
timzbeaulieu higher speed ratios lower the T.E. Just to clarify-- he means when you compare two engines, identical except one has 56:21 and the other has 65:12, the latter engine will have a higher maximum TE. But at a given speed (above, say, 20 mph) the two engines will pull about the same.
Gear ratio does affect tractive effort so higher speed ratios lower the T.E. You can mix and match ratios as long as you understand that those locomotives with higher ratios also have higher minimum continuous rated speeds, and those with lower top speeds must not be operated faster than their top speed. In practice a little difference is not a big deal, but using locomotives with a big difference is likely to cause trouble.
Thanks for all the replies & to Beaulieu for the great chart. Do higher gear ratios significantly alter the tractive effort numbers? When assigning locomotives to a train, do all the locomotives have the same gear ratio and wheel diameter?
I could have sworn I read about an F40PH on the NEC once hitting 120mph. Maybe not. I thought it was interesting that the DD40AX was in one of the higher ranges.
Ok here are the EMD gear ratios and top speed for each based on pre D77 traction motors and 40" wheels.
65:12 gearing 55 mph. used on a lot of early switch engines and some early road engines.
62:15 gearing 65 mph by far the most common EMD gear ratio for road locomotives
61:16 gearing 71 mph used by roads wanting a little faster speed and on some dual service engines
60:17 gearing 77 mph. used by BN and others for fast freight
59:18 gearing 85 mph used by UP on the DDA40X and "Fast Forty" SD40-2s used by newer pass.
58:19 gearing 92 mph fairly rare but some use made of this ratio
57:20 gearing 98 mph. fairly common passenger gearing for E-units with 36" wheels giving 91 mph
56:21 gearing 105 mph but most common on E-units giving 100 mph top speed
55:22 gearing 115 mph common E-unit gearing giving 110 mph speed with 36" wheels
When the physically stronger D77 and D87 motors appeared top speeds were bumped up about 5 or 6 mph.
Most Amtrak EMD locomotives (SDP40F and F40PH) had 57:20 gearing and were set up for 100 mph maximum. A small pool of F40PH locomotives received 56:21 gearing and a 110 mph max. speed for eastern service.
Common GE gear ratios were 74:18 for freight service, and its "Fine Mesh" replacement 83:20. IIRC a common dual service GE ratio was 65:24 giving an 85 mph top speed. This would have been found on RS3 and RS11 locomotives set up for secondary passenger service.
Lets not forget about 83-20 on ge locomotives.
Rodney
Lost my book on gear ratios but it is out of date anyway. What we need is someone's complete table of GEAR RATIOS; WHEEL SIZE; TOP SPEED FOR BOTH AC AND DC; LOCOS INSTALLED ON; ETC.Anyone out there have that information handy?? Maybe Al Krugg? Would be especially informative info for various passenger locos and motors.
spokyone I have been wondering if new locomotives are equipped with different gear ratios for different RRs. I'm thinking coal trains might have a different gear than double stacks. Can someone explain this?
I have been wondering if new locomotives are equipped with different gear ratios for different RRs. I'm thinking coal trains might have a different gear than double stacks. Can someone explain this?
Yes I think youre right. A train carring coal would, don't quote me on this,not need a huge gar ratio. Insted ,like freight steam loco's wheel's passengers wheels being substanually taller than a freight loco's wheels, just need enough power to move the train along. Too big(tall) and the wheels would slip like mad. A intermodal priority train however would need a bigger ratio. Is this what BNSF has on it's mind when it ordered the A-1-A version of the ES44AC? Of course Amtrak's BEAUTIFUL, not being carcastic, P42-P40 loco's need a bigger ratio to run at faster speeds.
The road to to success is always under construction. _____________________________________________________________________________ When the going gets tough, the tough use duct tape.
One of the highest gear ratios I ever read about were those U28CGs, or whatever they were, used on the Super-C. They made speeds of 80 mph I had read. Probably not too difficult when the train is only 3 cars long.
I believe that when a locomotive is geared for speed, such as a passenger unit, it loses some pulling power, like a car or truck when its shifted. It depends on the type of service.
Steam locos were another thing entirely, it went by the size of the drivers. The passenger engines had huge drivers for speed and freight had smaller, I think it gave more torque or something. Please correct me if I am wrong.
Thanks for the update(it has been years). I do seem to remember something like 25 SD40-2 engines delivered with the 'dual service' gearing as a test - and they may have been changed out quite fast. IIRC, the 6700 were Locotrol 'masters' and the 6900's were 'receivers' at one point. Then BN got so many SD40-2 engines, they were all over the roster.
The GN/CB&Q SD45's were indeed 60:17 gear ratio. The ex NP SD45's were 62:15, and some were upgraded so they could run in high speed pool for trains like #97(West Coaster),#3(Pacific Zip) & #4(4-Lite). The F45's and the ex-GN U33C's also operated in that pool for some time.
Being 'out of the business' some things are now a little 'foggy'. Bear with this 59 year old kid as he ages!
Jim Bernier
jrbernier Gear ratios differences have been around for years. The 'sorta' standard EMD gear ratio has been 62:15 - This gave a speed of about 65 mph with 1st generation engines(like the GP9) and 71 mph on most later production. The actual traction motor is the limiter. The maximum rotational speed of the traction motor determines potential top speed. If the motor is spinning too fast at maximum load, the copper winding will 'soften' and fly out - ground short to the motor case. This is why you hear about 'bird nesting' a traction motor. This has been a limitation with DC traction motors. AC traction motors do not have the same limitations. I remember that BN used 60:17 for most of their merchandise SD40-2 fleet at one time, but had 61:16 for dual service merchandise/coal SD40-2's The faster the top end is, the high the minimum continuous speed is(and this affects the 'short time' rating). I am not sure what the current gear ratio information is for the BNSF fleet. Jim
Gear ratios differences have been around for years. The 'sorta' standard EMD gear ratio has been 62:15 - This gave a speed of about 65 mph with 1st generation engines(like the GP9) and 71 mph on most later production. The actual traction motor is the limiter. The maximum rotational speed of the traction motor determines potential top speed. If the motor is spinning too fast at maximum load, the copper winding will 'soften' and fly out - ground short to the motor case. This is why you hear about 'bird nesting' a traction motor. This has been a limitation with DC traction motors. AC traction motors do not have the same limitations.
I remember that BN used 60:17 for most of their merchandise SD40-2 fleet at one time, but had 61:16 for dual service merchandise/coal SD40-2's The faster the top end is, the high the minimum continuous speed is(and this affects the 'short time' rating). I am not sure what the current gear ratio information is for the BNSF fleet.
The BNSF SD40-2s were regeared to 62:15 gearing many years ago, when the higher speed Intermodal trains like the Pacific Zip (#3) died. I don't remember any BN SD40-2s having 61:16 gearing, the 63xx, 68xx, and 69xx series had the 60:17 gearing, along with many of the SD45s and all of the F45s. Starting with the 67xx series BN went to the 62:15 gearing for better performance in unit coal train service. Rock Island was a big user of the 61:16 gear ratio.
The current equivalent EMD ratio for new locomotives (began with GP50) is 70:17. Note that both gear sets give a reduction of 4.1 to 1. The new gear set is a " Fine Mesh" type which give more gear teeth contact area between the two gears. This is done to reduce the incidence of stripped pinion gears in locomotives equipped with more powerful traction motors. EMD's AC locomotives use 85:16 gearing (5.3 to 1 ratio).
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