Random question popped into my mind while listening to the Movin’ on Theme, but do locomotives shift gears, like automatic transmission cars?
Steam locomotives? No. Diesel-electric? A transition from series operation to parallel operation (I think that is the move) is made when a certain speed is reached; I am not sure if this can be termed a shfting of gears.
And, speaking of gears, a certain writer of western novels thinks that steam engines have gear boxes which pop as they cool. He also thinks that they have deadman controls.
I once rode on a Whitcomb 20 ton locomotive that actually did have a gear shifter. The engineer would shift about three times as we went along. There was no clutch in case you are wondering.
Mechanical transmission diesels, Kraus Maffai, have shifting gears. Diesel electrics do not. DC motor diesel electrics have series, series with field shunt, parallel, parallel with field shunt, four electrical connection modes of operation to insure motors and generators operate near maxium efficiency at varouis wheel and motor speeds (listed low to high). AC motor diesel electrics have motor voltage and current and frequency electronically controlled on a continuous basis, with nothing analogous to shifting gears.
Movin’ on? You mean the old 1970’s TV show about truckers?
Diesel Electric locomotives do have gearing between the traction motors and the axles but it doesn’t work like a car or truck transmission…
Transmissions match the speed of the prime mover to the speed of the vehicle so that close to full HP output can be attained at any speed.
Locomotives do this electrically by having the engine drive a generator and motors powering the wheels. The “shifting” is by varying the excitation of the main generator to get the right mix of voltage and current. At low speed - low voltage, high current. At high speed - high voltage, low current.
It doesn’t have discreet steps (gears) like a car transmission. It’s continuous - more like a CVT transmission…
It is called “Transition” and it is done because the DC electric motors produce a counter voltage the faster they go. They get to point where the counter voltage won’t let the motor go any faster.
Now, when you are riding the loco and it changes transition it will feel exactly like a gear change in an automobile. Sometines this change is very hard and sometimes you will barely notice it. The new EMD SD70’s change down transition particularly hard and I know of one engineer who said it caused a broken knuckle in his train. This is the only time I have heard of this happening, but, I can understand why. What I don’t understand is why the SD70’s change transition so hard.
Looking only at the gears, a diesel traction motor has a pinion gear that drives a larger gear on the axle. You will see that stated as a ratio, which actually counts the teeth on each gear.
The only way to change that ratio is to dismantle the truck and physically change the gears to a set having a different ratio of teeth but the same distance between motor shaft and axle centers. It has to be done in a back shop, not in operation.
Chuck
My recollection is that on the first generation of diesel electrics transition was a manual operation. On later generations transition became a automatic function, which it remains today.
And, if you go back to GP30s and GP35s (and SD45s), you have a bunch of stages of traction motor field shunting as well as transition. (what a disaster!)
GP40/50/60 do not have any transition or field shunting.
SD50/60/70 have generator transition which occurs at nearly full load. There are two sets of winding in the generator that can be in series or parallel. Don’t know why a 70 would be worse than a 60, though.
Transition and field shunting are just an accommodation to get a bit more full HP speed range - kind of like having a two speed differential on a truck. The rea
Manual transition remained on switchers for a while longer, sometimes “forward” transition was automatic, but “backward” was not. I suspect the reason was to save a few bucks and give the engineer a bit more control. The Reading SW1000s came with manual transition.
There was an interesting story in Trains some years back about some early E units where the entire consist made transition automatically at nearly the same exact speed, creating quite a jolt as the power came back on and the slack ran back out. It was solved by detuning each end of each locomotive so that each truck would make transition at a slightly different speed.
I know that passenger diesels have different gearing ratios than freight units for higher speeds.In some cases freight railroads have regeared units for specialized high speed service. Good examples were UP’s “Fast Forties” which were SD40-2s geared for high speed (over 80 MPH) service on the Transcontinental mainline…
The analog would be the gear ratio of the differential of a car.
I’ve heard full forward of the Johnson bar in a steam locomotive refered to a “full forward gear”, and full back referred to as “full rearward gear.” Why I don’t know, there’s no gears involved, unless this is modern terminology reflecting everyones familiarity with the automobile.
Probably because it operates what is called Valve Gear.
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And the varying degrees of the Johnson Bar affected the valve timing of the pistons - in a internal combustion engine it would be referred to as ‘variable valve timing’.
A couple of points:
AC motors also have a “counter voltage” (AKA back EMF) that increases with speed, a permanent magnet synchronous motor coupled with a voltmeter will make a respectable tachometer. This is why the AC drives for traction motors are variable voltage as well as variable frequency.
The counter voltage on the DC motor represents the conversion of electrical to mechanical energy (or vice versa when the motor is acting as a generator), where the amount of power converted is “counter voltage” times the current. For a constant power drive, such as the Lemp system, the current is inversely proportional to the voltage.
- Erik
“Valve gear”, OK that makes sense. Thanks!
“Gear” that you bring to enable you to do something…sleeping bag, canteen, rifle to get your deer, camera, tripod, memory card to take photos,… rods, levers cranks, to permit steam input and output from locomotive engine’s cylinders…
“Gear” that consists of machined ridges and gaps that interlock and serve to transmit energy by moving when a rotating gear engages another. Traction-motor or rack-and-pinion?
About gears: DC motor-ed locomotives could have gears allowing 100 mph or 55 mph maximum speed; same motors=same starting tractive effort with similar weight on drivers.
There’s a “critter” here in Central Ca. that has a 1930’s floorshift from an automobile transmission.
The KM hydraulics on SP that I worked used gears to reverse but acceleration used movement of fluid from torque converter to “another stage different range” torque converter; three of them.
Previous revalations about transition open a lot of subjects.
SP’s SDP-45’s were rewired to lock in parallel circuits on starting, 'cause the amount of time for transition to occur somewhere around 23 to 26 mph was too much of the running time between stations…when they succeeded the FM Trainmasters.
GM and Westinghouse DC motors had a variety of gear ratios. For those sets, the total number of teeth added up to 77. Here are some pretty standard ratios:
65:12 Top speed about 50 MPH. Switching, heavy freight.
62:15 Popular freight ratio. Top speed about 65MPH
60:17 Fast freight or mountain passenger (Think SP FP7s on the “City”) Top speed 70-75 MPH
58:19 Dual-service freight/passenger. Top speed 80-85MPH.
56:21 Passenger mid-high speed (Santa Fe F3s/F7s) top speed 102MPH
55:22 High speed pasenger. Mostly found on E-units
The GE motors from the same era have corresponding speed ratios, but not the easy 77-tooth count. The only one I can remember off the top of my head is 74:18 for freight engines (about 65 MPH)
For a time in the 1960s and 70s SP stenciled the ratio on truck frames.
Transition is also part of Electric streetcar, MU and locomotive operation.