I am playing a game called Trainmaster and I don’t know what it is for. In order to reduce speed, I just use the throttle and the regular break. Is there a purpose for it? Also, what is the automatic brake for?
…Dynamic braking is a major force used to help control tonnage speed running on the downgrade…It is separate from the standard air brakes on all trains. Dynamic braking is generated by putting the traction motors on the engine into generating mood hence developing resistance and the current developed from that process is fed into massive grids and that generates a vast amount of heat which is dissipated by large cooling fans.
DB is a feature of some diesel-electric locomotives, which essentially uses the traction motors as generators to brake the wheels (the electricity so generated being dissipated as heat via resistance grids). There are others on this list who can give you very precise instructions on how to use it on different classes of locomotive.
The system is particularly valuable on extended downgrades, where otherwise the characteristics of train air brakes would require retainers to be set or other actions taken. Can save lots of wear on brakeshoes, wheel treads, etc., and of course can also simplify train handling over uneven grade profiles.
It should be remembered that the effectiveness of conventional DB tapers off with speed, and often can’t be used below a minimum speed. For example, it’s possible in theory to fiddle with the motor fields to allow dynamic to work down to relatively low speeds, but this adds complexity and possible points of failure to the design.
There are versions of ‘dynamic brake’ that work with transmissions other than electrical; for example, diesel-hydraulics can use methods such as partial ‘reverse’ configuration of torque converters to implement braking – the heat being dissipated via radiators in the transmission-oil circuit.
…And Hydraulic retarders, being used as a braking devise is useful on trucks. Was involved in testing such systems 40 plus years ago.
Would it be similar to the principle used by semi’s when “jake-braking”?
Or similar to aan automobile’s manual trans. being downshifted to slow down?
Or am I way off base? J1
BTW Juntionfan, how do you like the game? I have heard of it but nothing in the way of feedback and was thinking about checking into it.
jamison1…If your question is directed to what I was mentioning of the Hyd. retarder…First I know very little of the details of the Jake Brake but believe it uses the back pressure of the engine for very effective braking ability. Hyd. retarder I mentioned functioned by having an impeller splined to the input shaft of the truck automatic transmission and encased in a cavity…When braking action was requested from it, the cavity was filled with oil pressure and the impeller had minimum clearance within to run and the oil created great resistence for the impeller to continue to rotate hence forcing the input shaft of the transmisson to slow…and the lower the gear ratio one was running in the more effective it was…Of course this caused a great amount of heat in the transmission oil and had to have a high capacity heat exchanger to remove it. Of course the radiator could handle the extra load because it was not loaded heavy from engine cooling on the down grade…
I downloaded the demo and it is cool and addicting. I like the F-40 with the amfleets. I just wi***hat the graphics were a bit better so I could check for approaching crossing and speed restrictions.
Can I use the dynamic braking if I need to go slower at 0% grades?
…I surely would think so but I’ll refer you to a railroader for a more qualified answer.
A Jacobs Brake Retarder system is used on Semi Trucks. Basically it uses Oil pressure to delay the opening of the Exhaust Valve at the cylinder head creating resistance onto the piston.
The burned exhaust would eventually be released creating the famous bla bla bla bla sound we all know and love… unless you are on a bottom of a hill in a house at 3 am trying to sleep.
I am not sure of the exact forces generated by Jakes… but I have 14 years in the driving and can tell you it is almost like throwing most of the engine’s horsepower out put “against” the forward motion of the truck in a controlled manner.
A scenario would be Donner Pass by Reno Nevada… one of the most dangerous in the country particularly in the winter. I would have my rig stabilized with the Jacobs brake near the top of my tachometer in a lower gear that allows me to maintain a steady speed with these citeria:
1- Forward momentum balanced with the Jake Resistance
2- Gearing at a level not too dangerous to the transmission
3- No bucking or excessive shoving by the trailer against the 5th wheel
With a 7% grade I expect a Jake to hold me at about 22 mph in the low range all the way down without having to touch the service brakes.
If a trucker did not have a jake, he or she has to execute what is known as “Heat transfer” literally just enough braking against the rig’s wheels allowing the heat to vent to the atmosphere at a rate fast enough to keep pads from burning up or the drums from glazing. You would see this as the tail lights remain on most of the way down. The other method of braking is to sacrifice the trailer brakes using the trolley to preserve the tractor brakes… or to keep the unit from shoving on the 5th wheel in bad weather.
I have traveled down one rather long 5 mile grade in neutral without any braking whatsoever. at 120+ mph things tend to be real simple… live or die. That was the speed which gravity no longer pulled on the v
Did the KM and ALCo diesel hydraulics used by the SP use a Jake Brake? If so they must have sounded awesome coming down off Donner Pass or the Front Range of the D&RGW[8D]!
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Originally posted by Overmod
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It should be remembered that the effectiveness of conventional DB tapers off with speed, and often can’t be used below a minimum speed. For example, it’s possible in theory to fiddle with the motor fields to allow dynamic to work down to relatively low speeds, but this adds complexity and possible points of failure to the design.
quote] In older diesels, the effectiveness ( or lack thereof, in certain situations) of dynamics below a certain speed would be more pronounced, especially in mountainous areas… Conrail’s SD40-2 were fitted with what was called ‘extended range dynamic braking’ which allowed the dynamic braking to be effective at lower speeds than standard dynamics…Norfolk Southern still uses ex-Conrail SD40-2’s in helper service over Horseshoe Curve, and the helpers are also used on the downgrades for dynamic braking…The extended range comes in handy here, especially when trains start descending the east slope out of Gallitzin down track one, otherwise known as ‘the slide’ which has a 10 or 12 mph maximum downgrade speed limit…I don’t know how modern dynamics on SD70’s and GE Dash Nines equate to the older dynamics, are they equal to older extended range dynamics, or are the older extended range more effective, maybe someone could answer that part of it…Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown
The Jacobs Compression Brake (which I believe was actually ‘invented’ by Clessie Cummins) is specifically designed for direct-drive diesel engines – it uses the considerable compression of the engine to resist rotation of the driveline, and anything that allows ‘slip’ in that driveline… for example, a non-locked torque converter… will degrade the available brake performance.
My understanding of the brake was that the hydraulics didn’t hold the exhaust valve closed, but rather opened it late in the compression stroke. At the same time, the fuel injection to the cylinder concerned was effectively cut off. Note that the compression heat keeps the cylinder in question ‘hot’ so the engine will promptly fire when the brake is disengaged and fuel injection is resumed.
There would be little point in putting a compression brake on a railroad locomotive equipped with a Voith transmission, when the transmission itself is tremendously more effective – and much quieter, too – as a method of braking. The comparatively slow engine maximum speeds permitted on locomotive diesels might restrict the effective braking effort too, I’d think.
Theoretically, it would be possible to brake a K-M diesel-hydraulic by engaging the reverse, then throttling up the engine and engaging (by filling, IIRC) one of the converters. The drawback here is the speed (slow) with which the mechanical reverse engagement on each truck was accomplished, and the need to get everything done and locked before applying power (this is also the reason why switching with a K-M was not a particularly desirable task – and you thought slow-loading diesel electrics were a problem!) – not to mention that the reverse engagement might have to be done with the unit stationary… no synchromesh!
The DH643s also had Voith transmissions, and would have been poor contenders for compression brakes. Perhaps someone has distinctive knowledge of ‘dynamic brake’ operation on these locomotives.
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QUOTE: Originally posted by dwil89
The newer engines have extended range dynamic brakes that are much more effective than those of the SD40-2’s. The dynamics on the AC units are effective almost to a stop.
Well, I am really in over my head here - but that never slowed me down before! When you come into a town and see a sign that says something to the affect that you can’t use your Jake Brake (because of the noise, I assume) - is it safe to not use the Jake Brake?
Hi mookie, Of course it’s safe not to use the “jake brake”…as a driver, you’d just better have your truck under control so that you don’t have to use it. Moreover, some truck engines don’t even have a jake brake…it’s an option, or at least was a few years back when I drove a truck…didn’t even have one on my truck…not a good truck to drive in the mountains!!!..
…Jen, trucks operated for years and years without a Jake Brake so a driver simply drives his rig concerning using the regular truck air brakes as he would have back when he didn’t have it. Air brakes…{the normal service brakes on large trucks}, are perfectly capable of slowing and stopping a rig as it is driven in an acceptable manner.
The Jake Brake is simply using an alternative method of scrubbing off speed without using those service brakes and wearing the brake lining and drums, etc…The Jake Brake is so constructed that it uses the engine compression in a designed manner to do that work. But they really do make an annoying noise.
Well, that was pretty simple. Thank you!
I guess the same can be said about dynamics…trains were around long before dynamics, so they had to rely on air alot more than now…Look at any old pics of trains descending a mountain grade in steam or early diesel days…the brakeshoe smoke will be much more pronounced, though I’ve been told that grease leaking out of older style bearings combined with heat of braking enhanced this, now, trains can use dynamics as an aid to controlling speed, as a trucker uses a jake brake… However, I have passed through a few communities in hilly Western Pennsylvania, where communities post signs… No Jake braking… This is usually at the end of the grade where some truckers don’t shut them off, and you would have at one time heard jakes at every stoplight and stopsign in town. Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown
Dynamic braking, while primarily used in mountain railroading, also has found some use for controlling speed in the flatlands. Some operating timetables would allow intermodal trains a speed limit of 70 MPH provided that the train could be controlled to that speed without use of the air brake, meaning by use of the dynamic brake. I’m not sure if this provision is still in use.
In Illinois, I’ve noticed several signs posted at the top of short downgrades stating “Engine Braking Prohibited”. I’ve often wondered if this is creating a safety hazard even though the grade is short.
Hi group my name is Rodney and I am a student engineer with the BNSF we are taught to us dynamic braking as opposed to the use of air for fuel conservation when we are running, for the most part dynamics work quite fine and are able to hold the train, but as stated above they fade when the speed drops below their holding point then we use the trains automatic brake to futher control speed to a stop. As for the use of air we the engineer gets called in front of the road foreman of engines when ever we stretch brake i.e. using air above throttle notch 4.
Rodney Beck
Student engineer BNSF