What is the purpose of dynamic braking?

[Rodney Beck]

I wi***hat some people would stop compairing apples and oranges the diesel electric locomotive can not be compaired to a over the road truck very, very big differance. Trucks mainly have to control 80,000 lbs while tonnage on trains can be 4,000-22,000 tons and up quite a big differance. a truck can stop with in 300 feet and a train doing the same speed needs a little over a mile to stop. The reason we use dymanic brakes is for fuel conservation. Yes railroads practice fuel conservation we try to squeeze every ton mile out of the diesel fuel that we burn.

Rodney Beck
Student engineer BNSF

[GMS-AU]

Rodney and All

I could make a sweeping statement and say that trains and trucks are like apples and oranges, which is true to a degree, I could also say that train drivers have it easy as opposed to truck drivers. All train drivers have to do is start the train and stop it, where as a truck driver has to steer it, navigate and avoid others on the road, as well as starting it and stopping it. Trains don't float or fly ( despite numerous attempts by wayward engineers, and truck drivers are the same here ), they have wheels just like trucks so as a mode of transport are quite similar. Trains could stop a lot quicker if they had rubber tyres instead of steel tyres, but that is where they gain the advantage of less rolling resistance. Trucks gain where they are able to have a direct drive to the wheels, there by not losing energy that loco's do by producing energy twice so the apples and oranges are starting to look similar. Large mine trucks are in fact diesel electric as large drivelines have not been built to handle the massive torque of that size engine. In Australia we have what are called " Road Trains " whereby an over the road truck can have up to three normal 40 - 45' trailers in open road applications and up to 6 in controlled situations grossing in the range of 450 000lbs. In some situations one of the trailers is powered and controlled from the truck, I suppose you could call that distributed power! It is these sort of applications that a few decades ago might have attracted a light rail system for that type of work, but now road is simply easier to set up. Others have used the comparison of trucks to trains as it helps them understand how each works.

Just on the series 60 question, the number used to refer to the cubic inch displacement eg 353 - 3 cylinders, 53 cubic inches right up to 20645 - 20 cylinders, 645 cubic inches, however the series 60 would work out to 360 cubic inches which works out at about half of the 12.7 litre capacity they are, plus they are four stroke as opposed to two stroke design. GM had decided to go with four stroke designs and eventually drop the two stroke line, at least in truck size engines. EMD is the last bastion of large numbers of two stroke diesels.

G M Simpson

[Anonymous]

QUOTE: Originally posted by Rodney Beck

I wi***hat some people would stop compairing apples and oranges the diesel electric locomotive can not be compaired to a over the road truck very, very big differance. Trucks mainly have to control 80,000 lbs while tonnage on trains can be 4,000-22,000 tons and up quite a big differance. a truck can stop with in 300 feet and a train doing the same speed needs a little over a mile to stop. The reason we use dymanic brakes is for fuel conservation. Yes railroads practice fuel conservation we try to squeeze every ton mile out of the diesel fuel that we burn.

Rodney Beck
Student engineer BNSF

The reason for the talk on the "Jake Braking" is that some people think that trains can use jakes. The signs on the roads against jaking are for truckers.

Yes the weights are about that much, however the horsepower to weight are very close to that of a train. Just have larger values on a train hence more mass to control which needs more time to do the work.

Trucks can stop in 300 fet. That is true if everything is 100% and on dry concrete during the summer time. On Ice in winter with a half asleep driver and a poorly functioning brake system distances needed can be over a mile.

I too recall the "no jake brakes" signs and certain mountain grades although not the one specifically stated on rte 30. I suspect that one is near Bedford where truckers are "Discouraged" from traveling that part.

There is another hill near Altoona called "Babcock ridge" that one is quite steep, no ramps and features a switchback near the bottom where the safe speed is only 10 mph. Try driving that one in winter with just a day cab and a empty flat bed on ice. I did it, but was scared to death because my trainer kept yelling at me DONT TOUCH THAT *&^% JAKE you &^%$!!!!

That was over a decade ago, I can still remember that descent as if I was doing it at this moment typing on this post.

I wanted to ask about what is the worst descent for trains where Dynamic Brakes only work part of the time or worse hardly at all..

[Modelcar]

HighIron2003ar....Re: steep grade on Rt. 30. If it is the one I mentioned with the truck "runaway" ramp, that is on the western sloop decending Laural Hill mountain and leveling off down in Laughlintown, Pa.
Since you mentioned Bedford grades or nearby situations....do you recall driving by the "Ship Hotel" decending Allegheney Mt. grade...it would have been on your right side. Elevation there a bit over 2400 ft. Bedford from that location would be about 17 miles roughly.....

[Modelcar]

...Jake Brake sound can be annoying to say the least...and if it is happening repetitively it is really overbearing....I wonder why proper muffling isn't designed and installed on the Jake Brake equipped vehicles. They can muffle the sound of the diesel under power so it sure should be doable to do the same regarding the compression noise on the brake side.

[BigJim]

The man asks a question about dynamic brakes and you clowns go into a disertation for two pages on "Jake Brakes"!!!

I thought this was the TRAINS Forum, not the AOL boards!

If Junctionfan would like to contact me off line, I will be glad to help out as much as I can.

[GMS-AU]

Jim, M.W.H and All

I wouldn't worry too much about us clowns. Someone asked a question and someone chose to answer it. Not everybody has access to trains where as a cab ride in a truck is much more accessible, so someone has asked if dynamic brakes are the same as engine brakes. Maybe dynamic brakes should be called electromagnetic brakes or reverse polarity brakes and this may explain their function or workings better. I presume dynamic was a term thought up by a sales department rather than a mechanical department. In their early years on electrics I believe they were called regenerative brakes. Maybe others may know the history of the term.

On the Cat mine trucks, M.W.H. you're right, I forgot about the 'ol Cat stuff, as its everywhere it sort of becomes run of the mill.

Mark, on your last statement about the complexities of train operating, I agree that it is not easy, ( a big thank you to Ed King on his many articles on train operating ), however are trains not monitored on every leg of their journey by controllers who decide the route and who else accesses the block. If so, there should be more ways to control the driver and their actions as opposed to a truck which can be steered just about anywhere. A train would not move with out permission from the controller and clear signals and points.

G M Simpson

[Hugh Jampton]

rheostatic brakes is the best description I've seen

regenerative braking is where the power produced by the generating traction motors is fed back into the supply. Obviously this only works for electric trains.