This may be an old question, but I assume that railroads specify gear ratios on their locomotives, so units from different manufacturers can run together. Correct?
In the classic diesel days gear ratios were chosen for various services since the motors were the same across product lines. EMD gear ratios were pretty easy to remember since the sum of the number of teeth on the pinion and the number of teeth on the wheel gear added up to 77. Here are some samples:
65:12 50 MPH (switchers)
62:15 65 MPH (most common on freight locomotives)
61:16 71 MPH (freight and dual-service)
60:17 77 MPH (dual-service)
59:18 83 MPH (dual-service)
58:19 89 MPH (Passenger or fast dual-service)
56:21 102 MPH (Passenger)
55:22 110 MPH (Passenger)
GEs had similar tables, just not so easy to remember. The 74:18 equivalent to GM's 62:15 was very common for freight locomotives.
Southern Pacific eventually standardised on 62:15 for freight, 60:17 for passenger.
rcdrye In the classic diesel days gear ratios were chosen for various services since the motors were the same across product lines. EMD gear ratios were pretty easy to remember since the sum of the number of teeth on the pinion and the number of teeth on the wheel gear added up to 77. Here are some samples: 65:12 50 MPH (switchers) 62:15 65 MPH (most common on freight locomotives) 61:16 71 MPH (freight and dual-service) 60:17 77 MPH (dual-service) 59:18 83 MPH (dual-service) 58:19 89 MPH (Passenger or fast dual-service) 56:21 102 MPH (Passenger) 55:22 110 MPH (Passenger) GEs had similar tables, just not so easy to remember. The 74:18 equivalent to GM's 62:15 was very common for freight locomotives. Southern Pacific eventually standardised on 62:15 for freight, 60:17 for passenger.
So SP didn't operate their passenger trains at the allowed maximum of 79 MPH?
Never too old to have a happy childhood!
BaltACDSo SP didn't operate their passenger trains at the allowed maximum of 79 MPH?
The 'speed' associated with a gear ratio is not the top speed the locomotive can reach (or even the speed above which it will suffer motor damage); it's the road speed for a nominal standard motor rpm. The difference between 77 and 79 mph is just a few volts.
OK gear ratio is one measure of nominal speeds. But what about wheel diameter? Have all locos had the same wheel size ?
blue streak 1OK gear ratio is one measure of nominal speeds. But what about wheel diameter? Have all locos had the same wheel size ?
No. Moreover, a given locomotive will change its wheel size over time via wear. This is less extreme perhaps than permitted steam-locomotive driver wear (which could be several inches or more!) but still a measurable increase in wheel rpm for a given road speed.
The limit for DC traction motors, in part, is 'swell' of the windings due to "centrifugal force" (we can avoid the physics lectures!). There is better technology now than in the day of the locomotives under discussion to restrain the windings in the armature, but the result of 'too much overspeed' is still birdsnesting, NOT a good thing even if only very slight contact between armature copper and field pieces takes place...
The top "rpm limit" of a motor, and hence top road speed for a given wheel diameter through gearing, is safely set below the point that damage such as this would likely start.
blue streak 1Have all locos had the same wheel size ?
Presumably SP E-units were geared higher than 60:17; the 60:17 geared FP7s were allowed 79 mph until the late 1960s.
SP's E-units had 59:18 gears. On most SP routes the MAS was 70-75 MPH, even where the signal system might have otherwise permitted 79. The Coast Route is a good example of this, though UP authorizes 79 there now.
SP's passenger GP9s were all equipped with 62:15 freight gearing for commuter service. The FP7s had 60:17. Some of the boiler-equipped F7s were delivered with 62:15 gears for mountain service, regeared to 61:16 and then 60:17 to match the FP7s, then back to 62:15 when they came out of the passenger pool.
The SDP45s were all delivered with 62:15 gearing, soon changed to 60:17 to match the FP7s, which gearing they retained through Amtrak lease and into the San Francisco Commute pool. The 1976 GP40-2Ps were delivered with 62:15. All of the boiler-equipped SD7s and SD9s originally had 62:15. Some of the SD7s were regeared lower after losing their boilers and getting reclassed as switchers.
rcdryeSP's E-units had 59:18 gears.
rcdryeOn most SP routes the MAS was 70-75 MPH
Man.....this is interesting. I had thought (not sure why) that wheels were a commonality...a standard within the industry.
But to the comment(s) about wear.......in the days of steam, the driving wheels might lose a few INCHES of diameter.....am I reading that correctly.?
Thank You
kenny dorham Man.....this is interesting. I had thought (not sure why) that wheels were a commonality...a standard within the industry. But to the comment(s) about wear.......in the days of steam, the driving wheels might lose a few INCHES of diameter.....am I reading that correctly.? Thank You
Yuh, but it would depend on which direction across the wheel you measured it (locomotive goes down the track lump, lump, lump . . .)
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul Milenkovic kenny dorham Man.....this is interesting. I had thought (not sure why) that wheels were a commonality...a standard within the industry. But to the comment(s) about wear.......in the days of steam, the driving wheels might lose a few INCHES of diameter.....am I reading that correctly.? Yuh, but it would depend on which direction across the wheel you measured it (locomotive goes down the track lump, lump, lump . . .)
kenny dorham Man.....this is interesting. I had thought (not sure why) that wheels were a commonality...a standard within the industry. But to the comment(s) about wear.......in the days of steam, the driving wheels might lose a few INCHES of diameter.....am I reading that correctly.?
It's the need to keep getting rid of that 'lump, lump, lump' as it develops that leads to the diameter changes.
Removing and replacing tires on a steam locomotive is a big and expensive operation. Meanwhile, due in part to the characteristics of torque in a DA two-cylinder reciprocating locomotive, the wheels tend to wear 'out of round' in predictable patterns that have to be turned periodically 'back to round'. So the idea is to provide extra metal in the tires so that a few machinings are possible before reaching a condemning limit on the tire size. The result looks a bit more 'extreme' than it is because the diameter reduction is measured across the wheel but all that 'matters' is the distance from the axle down to the railhead.
The ACE patent describes a more complex issue. There, the drivers themselves are made in one piece, and the intent is to keep them 'circularized' as part of regular maintenance, through the use of underfloor lathes. Up to six inches of diameter reduction was supposed to be allowed before the drivers would need to be replaced -- if I remember the detail discussion correctly -- and there would be adjustments in the suspension, drawbar, etc. to permit the engine ride height to be altered accordingly.
I was under the impression that, on a locomotive with coupled driving axles, be it a steam locomotive or a diesel with torque-converter drive, the diameter of all of the driving wheels had to be the same or within a narrow variation.
Very interesting indeed. Thanks Again
I have seen the old film of guys heating and then fitting new "tires" onto a steam loco wheel. That was another great thing about low tech (relative to today) it was all labor intensive...LOTS of jobs for people to do.
Back to wheel diameter. Weight on each axle causes wheel diameter to increase as weight lncreases. So what is the pesent diameters of the newest heavy locos and electric motors ? That will of course determine gearing ratios.
CSSHEGEWISCHI was under the impression that, on a locomotive with coupled driving axles, be it a steam locomotive or a diesel with torque-converter drive, the diameter of all of the driving wheels had to be the same or within a narrow variation.
It should be, yes, particularly if you have precise longitudinal axle positioning (e.g. with Franklin wedges) and Timken bearings in the rods.
"Regular" steam locomotives can be remarkably tolerant of wheels with different effective diameters ... if there is play in the rods and in the interaxle spacing. I remember a story where one axle -- it might even have been the main -- came completely loose in its pedestal, free to 'work' forward and backward, and the engine not only ran in that state but produced useful work on a train.
The catch, of course, is that some of the wheels will slip relative to others, and this contributes further to differential wear and 'weird' wear patterns on the drivers. This was important enough to the ACE people that they developed special maintenance attention to keep all the drivers 'dressed' to the right roundness and, as you note, common effective diameter on a regular basis.
Porta also developed what he called the HAWP, or high-adhesion wheel profile, which could be cut and then dressed as necessary as part of the regular wheel machinings.
There have been attempts over the years to establish the idea that a 'proper' driver shouldn't be perfectly round, but rather have a kind of four-sided cam shape, adjusting the 'mechanical advantage' of the combined piston thrusts to give even torque at the railhead. Of course this would involve grinding all the drivers to precisely the same shape and diameter initially, and then maintaining all the profiles in common. With computerized modern equipment (either grinding or machining) it should be reasonably possible to achieve this in roughly the same time and at the same cost as true circular machining, with some (fairly trivial but important) setup cost.
WizlishThere have been attempts over the years to establish the idea that a 'proper' driver shouldn't be perfectly round, but rather have a kind of four-sided cam shape, adjusting the 'mechanical advantage' of the combined piston thrusts to give even torque
Back to my original question, how does a railroad ensure that locomotives are exerting equal effort, i.e. how to match an ES-44 to an SD-70, for example. Or do they even bother?
STEVEN L BUTTS Back to my original question, how does a railroad ensure that locomotives are exerting equal effort, i.e. how to match an ES-44 to an SD-70, for example. Or do they even bother?
Each locomotive 'does it's thing' and the engineer manipulates the overall result. With the locomotives not being 'geared togther' each is able to perform at it's own maximum level, consistant with throttle position.
Picture a Tug of War - locomotives on one end - the train on the other.
The locomotives (in human terms) are made up of 2 300 pound NFL linemen and two 160 pound world class sprinters - they all grab on to the same rope and pull against the opposition (train) with all the power they possess. Every little bit of power helps - but the bits of power are independent of each other in the power that they actually develop.
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Actually, there was one more EMD gear ratio that was used on some E units. Chicago Burlington & Quincy E-5s and E-7s were built with 52:25 gear ratios good for 117 mph and a minimum continuous speed of 40 mph. Keep in mind that in the early and mid 1950s, the Q held the scheduled speed record start to stop on portions of their route between Chicago and the Twin Cities. At one point at that time, the Q schedule between some stations was 86 mph start to stop. That required frequent speeds in excess of 100 mph.
The Alco-GE TP-500 manual (from 1951) lists 58:25 (with 40" wheels) as the 117 mph ratio for the (by then 2250 hp) PA locomotive.
[quote user="clipperw"]Actually, there was one more EMD gear ratio that was used on some E units. Chicago Burlington & Quincy E-5s and E-7s were built with 52:25 gear ratios good for 117 mph and a minimum continuous speed of 40 mph. Keep in mind that in the early and mid 1950s, the Q held the scheduled speed record start to stop on portions of their route between Chicago and the Twin Cities. At one point at that time, the Q schedule between some stations was 86 mph start to stop. That required frequent speeds in excess of 100 mph.[/quote]
The Q was not the only carrier to have locomotives geared to that speed - as I kid I got a legal cab ride on a B&O train across the flatlands of Indiana - observed 115 MPH on the Barco Speed Recorder.
BaltACD The Q was not the only carrier to have locomotives geared to that speed - as I kid I got a legal cab ride on a B&O train across the flatlands of Indiana - observed 115 MPH on the Barco Speed Recorder.
What year was this, and what form of ATC did B&O have in place at the time?
Reminds me of the very funny story that I saw in a back issue of Trains, about a time that B&O had to detour over NYC and the 'pilot' was a bit arrogant about saying to the B&O crew that they had to hustle on the 'high-speed railroad'. The B&O engineer was a quiet type and just notched it out; the NYC man wasn't used to diesel ride and only noticed the 100+ mph speed a bit late...
I have the impression that in the immediate postwar streamliner period there were quite a few roads that were running diesels at very high speeds -- IC and ACL being a couple that reputedly (I have no 'hard' examples) got to 120-mph range. As I recall some of these practices strongly contributed to the ICC order enforcing 79 mph restriction in the absence of functional ATC. Enforcement of that order plus the dramatic falloff in profitability of very high-speed trains and of many railroad systems that had to accommodate them around other traffic would have led to a falloff in the 'utility' of high gear ratios in many cases.
If you remember the locomotive number (or even the precise type) I can check with the B&O group and find out what gear ratios were used.
Wizlish BaltACD What year was this, and what form of ATC did B&O have in place at the time? Reminds me of the very funny story that I saw in a back issue of Trains, about a time that B&O had to detour over NYC and the 'pilot' was a bit arrogant about saying to the B&O crew that they had to hustle on the 'high-speed railroad'. The B&O engineer was a quiet type and just notched it out; the NYC man wasn't used to diesel ride and only noticed the 100+ mph speed a bit late... I have the impression that in the immediate postwar streamliner period there were quite a few roads that were running diesels at very high speeds -- IC and ACL being a couple that reputedly (I have no 'hard' examples) got to 120-mph range. As I recall some of these practices strongly contributed to the ICC order enforcing 79 mph restriction in the absence of functional ATC. Enforcement of that order plus the dramatic falloff in profitability of very high-speed trains and of many railroad systems that had to accommodate them around other traffic would have led to a falloff in the 'utility' of high gear ratios in many cases. If you remember the locomotive number (or even the precise type) I can check with the B&O group and find out what gear ratios were used.
BaltACD
Don't recall the specific engine numbers - it was on train #9 in 1959 or 1960 out of Garrett, running nearly 1 hour late upon departure from Garrett, as the Capitol Limited could be seen arriving behind #9 On Time. The Division Superintendent's instructions to engineers - Observe all permanent and temporary slow orders, otherwise if you have to 'make up time' - as fast as the train will go. B&O passenger engines were train control equipped, however, that was for operation over the P&LE trackage. The ICC would not have approved.
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