Hi all, I have a question about the different types of road power that exist today. I am familiar with the concept of A-units and B-units, and the fact that cabless booster units or “B-units” are not as common in todays fleets. I also know the basic concept behind road “slugs”; that they are basically a form of multiplying the number of powered axles a single engine controls. Anyway back to my question what types of “other” road power are out there? Also on the NS road “slugs” what is the raised section at one end for?
Well, you have the multiple powered head end units, MU’ed together, the distributed power units, (DPU) ususally mid-train, or/and at the end, pushers, that are at the end for certain grade situations through the mountains, where the train needs a “push” to get over the hill, and for passenger car situations, you have head end power (HEP) units to supply the “hotel power” to a train.
On the NS, some road slugs maintained their dynamic brakes, and the raised area is for the heat distribution coils, grills and fans that are part of the dynamic braking system, just as it is with a loco equiped with dynamic braking. You can recognize the system with the “blister” hood. I’m far from an expert, but dynamic braking is like the “jake brake” , a term used by truckers for down shifting to slow the truck down. Many small towns you enter have a sign “No engine breaking aloud” right by the “Welcome” sign. In dynamic breaking, the power from the generator to the traction motors is reversed, so the traction motors act like “down shifting” (reversing the power) The heat created from this is disapated through coils, and the fan, which require the extra bulge, or “blister” in the hood design.
I’m sure others in here no more than I do.
Mike.
Thanks! How often are slugs and b-units used as road power nowadays?
Well that, Steven, I’m not sure of, maybe search around and look. The NS and maybe CSX, maybe a few, because of the mountains they deal with. As far as B units, on todays freights, anything behind the lead loco could be considered a B unit, as they are there for more traction power.
On many Amtrak trains with two locos MU’d on the head end, the second loco is also for more constant “hotel power” along with traction power, when needed.
Mike.
A B unit is a unit that is physically incapable of being a leader. It doesn’t have the controls or seats to be a leader.
Trailing units are not B units because in most cases they are leader capable.
There are very few B units left and slugs were very rare to begin with. For example the UP has the largest locomotive fleet in the US and only has a handful of slugs for yard service and one set of road slugs. The last itme they had B units of any amount was after some of the mergers they had a lot of units that did not have all the equipment (cab signals, dynamic brakes, etc) so “converted” them to B units by adding a “B” to the number and removing seats and radios from the cab. DPU units are mostly just regular units that have DP equipment and are placed in a trailing position.
The vast majority of slugs are not road units, they are used exclusively in yards.
Mike,
Thank you for your explanation on how dynamic brakes work. It really helped me to have a better understanding of how they operate. It was very well done.
Ralph
To quote myself, Ralph, “I’m not an expert”, after reading a lot about it, that is the way I interpreted the information. The flow of power to the traction motors is reversed, which causes a great deal of heat.
Maybe one of the real experts on this will chime in. Another great source for prototype operations of equipment could be found by asking members on the Trains.com forum, which if you are signed up in here, you are also able to join the conversations in there, too, along with all the forums that Trains.com hosts. There are a lot of people in here that also join in over there.
At the very top of the page, in the upper right hand corner, in the small print, you’ll see “Trains.com Sites”.
Mike.
I’ll add CSX uses a GP38-2 or GP40-2 with either a GP30 or a GP35 slug on locals…These slugs has a cab and control stand,horns and bell and can be used as the lead locomotive. The GP30 slugs retained their cowl.
NS has RP-E4C road slugs( 724-731) made from GP38-2 AC ( 4158,4136,4155,4124,4122,4132,4142 and 4131) NS uses these on locals in a mother/slug set. These slugs has control stand,horns snd bell…These slugs kept their GP38-2 Spartan cab.
Are there any additional types of road power? Or a unit that would be located in a lashup of diesels? Like a C-unit?
A unit and B units are a hold over reference from the covered wagons (for example: EMD F series). Almost all diesel locomotives now have cabs. There are no “C units”. There where several different railroads that purchased B unit (cabless) versions of EMD and GE road switchers. The problem with B units is that I there is some sort of failure on the Cab equipped unit that prevents it from being a leader (broken window, headlight fails…those might be the only two), you cant use a B unit as a lead unit. Its actually cheaper in the long run to have all cab equipped units due to the operational flexibility.
In some classification yards (both hump and flat yards) there are remote control diesel locomotives. These are identified by special warning placards and flashing orange lights (the ones ive seen on CSX and NS have a special light bar with 2 or three orange lights on them). These locomotives are controlled by one man on the ground who makes the switching moves and uncouples cars.
As far as wheel arrangement: 6 axle diesels with 6 traction motors are classified as C-C. 4 axle with 4 traction motors are B-B. 6 axle with only four traction motors (such as EMD E passenger units) are classified as A1A-A1A. EMD FL9 is a B-A1A
Hopefully this clears some things up.
Well perhaps “c-unit” was not the right word what I meant was are there other units used a road power other that a-units, b-units, and road slugs? Thanks anyway.
Pretty much only carbody units are referred to as “A” units. Hood units are just units. Units that can’t be leaders are B units. Slugs are units that get theor power from another unit.
That’s pretty much it.
Boston and Maine 100 (I guess its PAN AM 100 now) anyway, is a cabless slug built by the B&M shops. It has a semipermanent pair of mother units GP40-2s number 300 and 301. These units are equipped to provide power to one truck on the slug each, essentially creating the equivalent of a pair of SD40-2s.
I see.
Mike, I have been a Truck Driver for more than 28 years, I can ASSURE you that a Jake Brake, is a Product of the Jacobs Engine Brake Co. and NOT “Just a term used by truckers for down shifting”. A “Jake Brake” is an add on option to the vehicles engine that uses the engines own compression for braking purposes.
Dynamic braking, in my understanding, uses the traction motors as generators, and the resistance in doing that is what causes the braking effect. The dynamic brake resistor grids are there to dis
Thanks Doug, that answers some of my questions. I guess I’ve heard so many trucker friends call down shifting to slow the truck, but keep the rpms up, as “jake break”, or engine breaking, which is what dynamic breaking does on a locomotive. And what you said, the traction motors act as generators, just like what I stated, as the power flow is reversed, is what I have read about, which also keeps the engine speed up.
Mike.
There are also electric locomotives, although not many are used for frieght.
There are also Propane and LNG locomotive but they are diesels just using an alternative fuels.
Hi Mike,
Down shifting, does slow a vehicle, using compression braking, but the “Jake Brake” by changing the timing of the exhaust valves, takes the concept to a whole different level of effectivness.
From the Jacobs Vehicle Systems website:
What is an Engine Brake?
The Jacobs Engine Brake (also known as the “Jake Brake®”) is a diesel engine retarder that uses the engine to aid in slowing and controlling the vehicle. When activated, the engine brake alters the operation of the engine’s exhaust valves so that the engine works as a power-absorbing air compressor. This provides a retarding, or slowing, action to the vehicle’s drive wheels, enabling you to have improved vehicle control without using the service brakes*. This conservation results in reduced service brake maintenance, shorter trip times, and lower total cost of ownership.
Just a side note, in all the Jake Brake systems, I have driven, the effect is variable in the number of cylinder pairs retarded. The typical truck diesel is an in-line 6 cylinder, although Cat, and Detroit have offered “V” style engines. The Jake control typically has 1/2/3 settings which select 2/4/or 6 cylinders to be retarded, allowing the driver to select how much braking effect is developed, it’s not an all or nothing choice, allowing for smoother, safer operating.
a little off topic, it is interesting to note that the Jake Brake was invented by the founder of Cummins Diesel engines, after he had left the company. His prior contractual obligations required him to offer new ideas to Cummins first, who then DECLINED their options, OOOOPPS.
In a related note, the inspiration came from a rail related incident. In August of 1931, Clessie Cummins and two other drivers were attempting to set a new, New York to Los Angeles cross country speed record for a truck, when at night of the fifth day of the trip, they desce
Dynamic brakes is slowing down a train by plugging in a big hair dryer.
It is like a “Jake brake” only that the drive train is involved in stopping the train.
The traction motors are connected to work as generators instead of motors, the electricity is forced through a resistance grid and converted to heat. There are fans around the grids to cool them.