Firelock76 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.
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.
.
carnej1 tomikawaTT 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 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..
tomikawaTT 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
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
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.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
BaltACD 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.
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.
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.
BigJim oltmannd 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.
oltmannd 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....
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.
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 real "gear" work is done by the excitation system.
Never too old to have a happy childhood!
Mr. Railman Random question popped into my mind while listening to the Movin' on Theme, but do locomotives shift gears, like automatic transmission cars?
Random question popped into my mind while listening to the Movin' on Theme, but do locomotives shift gears, like automatic transmission cars?
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.
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...
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.
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.
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.
Johnny
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