Question dynamic brakes and engine brakes

[CSXrules4eva]

I have a question for my fellow forum members out there. Why don't the locomotive manufacters design engine brakes into their prime movers? I know on-highway diesels like the Cummins ISX 565 has an integrated engine brake, not a seperate jake houseing. Why isn't this design instituted in marine diesels as much? It would seem to me that the engine brake would be ideal, over the dynamic brake (since dynamic brakes require seperate houseings and componets.

This question was inspired by the dynamic brake question thread.
Thankx

[arbfbe]

Trucks have a direct connection between the motor and the drive wheels. Railroad locomotives do not. Marine diesels do not need them account the resistance of the hull in the water and the ability to reverse the propeller while moving.

The railroad interface between the prime mover, the main alternator and the tracktion motors just would not transfer the retarding effect of the engine brake to the wheels.

Alan

[Modelcar]

CSXrules4eva.....First off, I'm not a railroad expert but let me offer my thought....The mechanical operation structure of a prime mover has no mechanical connection to the wheels under a railroad engine, hence an engine brake would not be appropriate.

[Modelcar]

...The prime mover drives the main alternator which in turn supplies power to turn the traction motors hence drive the railroad engine wheels moving it forward or when controls are set into dynamic condition tends to brake the wheels.

[passengerfan]

Engine brakes would only work on diesel hydraulics Not suitable for diesel electrics under any circumstances.

[M636C]

Even Diesel Hydraulic locomotives that do have a direct connection from the engine to the wheels do not use engine braking, but have a "hydrodynamic brake" which uses the fluid coupling and the hydraulic fluid to act as a brake. This heats the fluid which must be cooled in a radiator. This might be because the locomotive and train weight is so large compared to the size of the diesel engine that the amount of engine braking would not be effective! Certainly, the ratio of weight and load to power is much greater for a locomotive and train compared to a truck and trailer.

Peter

[jchnhtfd]

Generally correct. The main engine alternator and controls are not built to be able to drive the main engine; hence the power from the traction motors acting as brakes has to go somewhere else -- the dynamic grids. It happens to be a lot simpler to set up and maintain, too.

I have yet to see any form of brake, other than a shaft brake on some sailing vessel auxiliary engines, on a marine diesel. Slowing/stopping is done (if one is in a hurry to do so) by reversing -- sometimes the engine, sometimes the transmission.

[Rodney Beck]

Hi group my name is Rodney and I am a student engineer with the BNSF as with the other posting it seams that a lot of people are trying to compair apples to oranges i.e. locomotive brakeing with trucks. Dymanic brakeing the engineer is using retardation generated by the traction motors to control the train this is done for fuel conservation. The jake brake is used to dump the compression of the engine not practical for diesel electrical locomotives as it burns more fuel than the dymanic brakes.

Rodney Beck
Student engineer BNSF

[Modelcar]

...Rodney, "this is done for fuel conservation".....But it's primary use is to assist in controling train speed....Not...?

[Anonymous]

Modelcar,

Using dynamic brakes is more fuel efficient than stretch braking using the air is what I think Rodney is trying to say. Leaving the throttle at say N5 and then setting first sevice makes the engines work harder to pull on the train. Dynamic brakes retard the movement of the train at the engines only. This is a really bad explanation, but it is from a very basic understanding. Did I help at all????[%-)]

[Rodney Beck]

Dymanics are the prefered method to control the speed on desinding grade. I can use the trains air brake system to futher control speed as long as I am in throttle notch 4 or less the second I go to throttle notch 5 the big shots are notified and I will have to have a chat with the road foreman of engines because I am stretch brakeing.

Rodney

[Modelcar]

Rodney, I'm not trying to doubt your expertise...I'm only commenting on what I thought the primary use of dynamic braking was designed for...especially in mountain railroading.

[Rodney Beck]

I live in and work in the midwest and we use dynamics more than everyone thinks, with the cost of diesel fuel being what it is. Granted we do not have the 2% grades in the midwest but, we do have some long running 1% grades to contened with and heavy trains like coal and grain the use of dynamics along with the train brakes work great on controling the speed. Some of the 1% grades can run for 8 miles or more.

Rodney

[CSXrules4eva]

WOW! I didn't realize the complecations as to why loco prime movers aren't equiped w/ engine brakes. Now, I see that because of the electrical componets (generator / altenator, traction motors, . . . .etc, there isn't a way to get the retardation of the pistion at TDC to BDC in the cylinder that isn't fireing (engine brake) down to the rail and make use out of it. Interesting.

[Anonymous]

Rodneys qoute above makes me think of an old Rio Grande saying that goes " On this railroad anything under 1% is considered flat and anything less than 8 degrees is considered straight."

[zardoz]

The use of dynamics is great for long grades, but is vastly overrated for use in controlling train speed elsewhere. To use dynamics to slow for speed restrictions is asking for trouble, although you can usually get away with it if you are running a unit train.

In stretch braking you (as the name indicates) keep the slack in the train stretched; if you go to dynamics, you bunch the slack of the entire train, and will have to let the slack out after the desired speed is reached. On a 0% grade, and if you are working less than the 5th notch, dynamics are an option. But if your train is on or entering any type of terrain that undulates (resembles a hogback ~~~~~, which is what that type of track is called), and if you cannot control the speed of the train with the throttle, it's best to do stretch braking. Moreover, in snowy conditions, it is good to apply the brakes occasionally to keep snow and ice from building up too much on the brake rigging. The downside to using air to control train speed is the increased chances of getting 'sticky brakes'. And in real cold weather, and if you have a long train, it takes so long to restore trainline pressure, that to use air for speed control is not the best idea. The good Engineer takes all that into consideration when (s)he decides on how to operate a particulat train.

A bad Engineer operates the same way all the time, and wonders why (s)he has so many problems.

A good Engineer considers many factors (in various degrees of priority) when operating a train:
The length of the train.
The tonnage of the train.
The distribution of loads / empties in the train.
Grade--what part of the train is going uphill or downhill.
The condition of the rail.
Prior experience on a particular section of track.
Prior experience with that type of train.
Condition of the brakes.
Temperature.
Visibility.
Horsepower / dynamic brake / tonnage ratio.
How many working dynamic brakes.
Speed restrictions.
Work orders.
And probably others factors that I cannot think of right now.

[Rodney Beck]

Hi Zardoz I have been in the ojt portion of engineer training the run ins and outs still happen but not like they did when the ojt part started 3 weeks ago. The other night I was running a grain train and just could not find the right spots to stop all 13,900 tons from running I spent the whole night kicking myself in the butt my trainer asked me how I thought I did I told him terrable he said no you did ok for the amount of time I have spent in the seat was told hang in their and do not let an engineer tell you they never have any run in or run out he said it happens to everybody it is a part of the everyday learning to run trains.

Rodney Beck
Student engineer BNSF

[M636C]

This is a recollection from some years ago, but I was involved in running instrumented trials on BHP Iron Ore and Hamersley Iron, where we measured the forces involved in run -in and run- out of iron ore trains of up to 200 cars carrying more than 100 tons each. The intention was to produce a "mathematical model" that would allow a computer program to simulate the run -in and run- out for each car in the train. Then this would be connected to a locomotive cab simulator, with a video display of car position and force. This was intended to allow trainees to "run" a train, with the correct video of track location in the cab window, but a representation of the gradient diagram and car position on the grades. This was intended to give the trainee drivers a picture of what the cars were doing as a result of the various control actions, different braking and so on. Presumably it didn't actually give the real "thump" that you feel on a hard run-in! Rodney, does BNSF have this sort of equipment for initial trainee engineers? I'm not sure that the Australian equipment was ever got to work properly, but I recall seeing early demonstration.

Peter

[zardoz]

There is no way any simulator could give an accurate representation of what a run-in really feels like. Indeed, there is no way to properly convey in words how a run-in feels.

One instance I remember was when I was approaching St. Francis interlocking on a westbound CNW train. At the time the speed through the interlocking was 10mph. The hill I was descending was only about .6%, and I thought I had the entire train slack bunched. I was in the 5th notch of dynamic braking, with the train (only 8000 tons) feeling under control. However, I misjudged where the end of my train was in relation to where the track begins going downhill. As I drifted along feeling in control, the slack ran in. I was, in one second (literally), bumped from 11mph to 21mph!! If either of us in the cab had been standing, the near-instant acceleration would have slammed us against the back wall with sufficient force to cause injury. Luckily the train was on straight track.

It is rather disconcerting to be in a massive 200 ton locomotive and have this huge mass accelerated so rapidly. The forces involved are quite staggering.

Run-outs are far less dramatic. If the run-out is large enough to be strongly felt in the cab, you will never feel it, because something in the train will break (knuckle or drawbar) before the force makes it to the cab. Usually all you feel is a little tug, just before the air goes. You have just enough time after feeling the tug to say, "Oh, shoot", or words to that effect before POW!

[tree68]

But, somehow, the thought of hearing a brace of {insert your favorite locos} "jake" down a grade has a certain appeal....[:D]

[Anonymous]

Hmmmm, what would jaking a 645 cu in cylinder sound like?

[jkeaton]

Given how bad Jake braking sounds in the tour buses and trucks I hear everyday around here, I wouldn't want to be near something the size of a 645 doing it. Besides, a Jake brake wouldn't work on a two-stroke engine, would it? I would think that without a separate compression stroke, the Jake brake wouldn't work. Big rig engines are all four stroke diesels.

jim

[Modelcar]

...I imagine the noise would really be annoying....and I believe we all agree even if it would work on that engine....it can't work with the powertrain of a locomotive.

[dwil89]

QUOTE: Originally posted by Modelcar

...I imagine the noise would really be annoying....and I believe we all agree even if it would work on that engine....it can't work with the powertrain of a locomotive.

Yes..the best method is through the traction motors, since all the prime mover is there for is to power the alternator to produce electricity to run the traction motors...That is why the correct term is Diesel-Electric Locomotive...there is not the direct connection to a mechanical transmission and axle like a truck where the engine can make a direct impact....I suppose when a locomotive diesel shuts down in service, or shuts off, has catastrophic failure, if that engine is the only one on the train, it would simply coast to a stop,if it was on level, or upgrade track. There is no 'downshifting', or compression braking. If a truck with a standard transmission's engine stalls,and won't restart while in motion, simply leaving it in gear will slow it to a stop by the compression of the engine. The old trick of starting a manual transmission vehicle with a low battery by pushing it with engine off, and then letting out the clutch will start a stalled vehicle too...not so a train... Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown