The Beaverton, Fanno Creek & Bull Mountain Railroad
"Ruby Line Service"
they are designed so that bigger 6 axle power can go where 4 axle power could only go befor due to tight curves...
csx engineer
In the world of physics, a train operates most effieciently on a straight piece of track and when the axles are perpendicular to the rails (wheels would be parallel). When a locomotive traverses a curve with non-steerable wheels, the wheels and axles are no longer perpendicular to the rails, which results in a loss of effiencey. The steerable trucks alters the truck such that the the axles will be perpendicular to the rails (and center point of the curve) in a curve.
Things often get named inappropriately. In this case 'self-aligning' might have been better than 'steerable'.
artschlosser wrote:Things often get named inappropriately. In this case 'self-aligning' might have been better than 'steerable'.
Depends upon whether or not the self-steering is passive or forced. The EMD HTCR and HTCR II are passive, and self-aligning would be an accurate description. But the "B" truck used under the ABB-SLM "Lok 2000" locomotives is a forced steer design. The axles assume a radial position because the truck is rotated from being aligned straight with the locomotive body. Examples of the "Lok 2000" are the Swiss SBB Re 460 locomotives, and the Finnish Vr2 locomotives.
Thanks to Chris / CopCarSS for my avatar.
Good point, beaulieu. Perhaps 'auto' instead of 'self' might be more accurate. But IMHO 'steerable' implies human interaction which is definitely missing in both designs.
Art
Murphy Siding wrote: Is the "self aligning" part similar to the front truck on a 4-4-2 steam locomotive, in that the whole truck pivots on a center pin?
No, it is not. When the locomotive on your 4-4-2 goes around a curve the truck rotates around the center pin, but the distance between the center of the front axle on the truck, and the rear axle of the truck is the same on both sides. If the front truck of the same locomotive was a radial steer truck then they would be different. Let's say the locomotive was going around a curve to the left. The axles within the truck would shift to a radial position and point to the center of the curve. If you would measure the distance from the center of the front axle to the rear axle, the distance would be less on the left side of the truck, than it would be on the right side of the truck. Further more the distance of the left side would be less than the distance measured when the locomotive is on straight track and the right side would be greater than the measured distance on straight track.
KBCpresident wrote:Question, Do they have a steering wheel in the cab to steer the trucks, or do they steer themselves?
No, the "steering" is the result of forces applied to the locomotive wheels by the track. They steer themselves, it is a function of the taper of the wheels. The wheels are smaller diameter on the outside and larger diameter near the flange. In a curve the locomotive wants to go straight because of Inertia, this pushes the outside wheel up the taper near the flange and lowers the inside wheel to near the outside smaller diameter. Since both wheels are locked together the outside wheel goes further for each revolution of the axle turning the locomotive into the direction of the curve and bringing things back into equilibrium. Ideally in a curve the axles will assume a radial position. In a normal truck they cannot so, so some wear results on both the wheel and rail because the wheel is not turning in exactly the direction its moving, there is a little slippage involved. The sharper the curve, and the longer the truck axle spacing the greater the force and wear. The "C" truck has a longer distance between the front and rear axles so it creates greater wear than a "B" truck. This is why in the US the only self-steering trucks are "C" trucks. The savings from wear on a "C" truck can offset the greater cost and complexity of the self-steering truck.
"B" truck is a two axle truck with both axles powered
"C" truck is a three axle truck with all three axles powered
An E unit rode on two A1A trucks.
Yes, the wheelbase is slightly shorter on the left side during a left curve. It isn't much, but it doesn't take much.
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
Murphy Siding wrote: Am I reading this correctly? In a turn to the left, for example, the *wheelbase* of the two left wheels becomes less than the *wheelbase* of the two right wheels?
Yes.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
oltmannd wrote: Murphy Siding wrote: Am I reading this correctly? In a turn to the left, for example, the *wheelbase* of the two left wheels becomes less than the *wheelbase* of the two right wheels? Yes.
Ok, thanks. I understand the "what" part now. About the "how" part- Is there some sort of sensor, that somehow tells the wheelbase to shorten upon entering a curve?
Murphy Siding wrote: oltmannd wrote: Murphy Siding wrote: Am I reading this correctly? In a turn to the left, for example, the *wheelbase* of the two left wheels becomes less than the *wheelbase* of the two right wheels? Yes. Ok, thanks. I understand the "what" part now. About the "how" part- Is there some sort of sensor, that somehow tells the wheelbase to shorten upon entering a curve?
No, it is a result of the wheel being moved by the curve of the rail, and a linkage rod diagonally connecting the two axles, so that when the left end of the front axle moves back the right end of the rear axle also moves back.
beaulieu wrote:No, it is a result of the wheel being moved by the curve of the rail, and a linkage rod diagonally connecting the two axles, so that when the left end of the front axle moves back the right end of the rear axle also moves back.
Is the linkage rod mechanism for a passive system, a forced system, or both?
Datafever wrote:Is the linkage rod mechanism for a passive system, a forced system, or both?
For both, but there are additional linkages to the body or frame in a forced steer system.
beaulieu wrote: Datafever wrote: Is the linkage rod mechanism for a passive system, a forced system, or both? For both, but there are additional linkages to the body or frame in a forced steer system.
Datafever wrote: Is the linkage rod mechanism for a passive system, a forced system, or both?
I get the hang how this works now. Can you explain the difference between passive and forced? Thanks
A self-steer truck allows the axles to move on their own, but when they move, they have to move together. The simplest kind of self-steer truck has a pair of crosslinks between opposite journal boxes so that if one axle steers left, the back axle steers right. The crosslinks are a bit more complex on a six-axle truck (like EMD).
The forced-steer truck links the coordinated steering of the axles with rotation of the bolster about the kingpin. Thus for the axles to steer into a curve the bolster has to rotate. The typical way to do this is to link journal boxes on the same side with a bell crank linkage so they turn equal and opposite, and to connect to whole works to a bell crank driven by bolster rotation. There has to be correct lengths of the links so the bolster rotation deflects the pair of axles (equal-and-opposite deflection seen from the same side of the truck) by the correct amount. The forced-steer truck is regarded as a higher-speed design because it allows less degrees of freedom for the axles to steer on their own and get into "nosing" or "hunting" that starts with a bad ride and ends with jumping the track.
Then you have TurboTrain and Talgo that use linkages to steer single axles between pairs of train cars in response to the train cars bending around a curve.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Datafever wrote:Thank you, Paul. I am not sure that I understand it completely, but I do have a fairly good idea in my head now. At least I won't be clueless when the subject is discussed.
A good primer on truck (bogie) design is How Bogies Work by Isao Okamoto (http://www.jrtr.net/jrtr18/f52_technology.html -- there is a PDF link to a PDF version of the article with good illustrations of steering trucks).
If you want to see a lot of different implementations of steering bogies (American truck-truck is English lorry-bogie), search the European patent database at ep.espacenet.com. You may have to try different combinations of search words, and the patents are in PDF's that you can only print a page at a time, and the patents are all written in legalize, but I think a person who is mechanically inclined can get a lot of insight out of the patent drawings, which are required to show the basic operating principle of the device in question. I don't have links to these patents because I don't think I can link into their database, but the search engine is easy enough to use.
I am still trying to dig up some information on the truck on the Genesis locomotive -- I tried patent searches on some European companies and haven't found anything. The EMD self-steer truck, however, shows up in the patent database.
The linkages on these steering trucks are sometimes described as "bell cranks", but a true bell crank is for changing a motion by 90 degrees. "You rang, sir?" In wealthy Victorian (pre-electrical) household, the homeowner summoned servants by pulling on a cord from the ceiling, connected through a "bell crank" to a pull rod to an adjoining room.
In a steering truck (or steered axle), you need to change motion by 180 degrees -- if the journal boxes on one side of the truck scrunch together, the boxes on the opposite side need to spread apart -- what I call "equal and opposite" motion. If you have a link pivoting in the middle, pushing left on the top of the link makes the bottom of the link go right. If you search the Web for Talgo photos (assuming the photographer has a fetish for railroad running gear), you will see this rocker link attached to the journal box with rods connecting the top end of the rocker to one train car, the bottom end to the other train car. Anyway, many of the steering truck patents work on this same principle of using such a rocker link to create equal-and-opposite motion of the axles on a truck.
By the way, if you search ep.espacenet.com for Alan Cripe, you will come up with TurboTrain patents, one of which is the marvelously complex single-axle truck, the drawing of which is something to behold. What is interesting is where the Talgo uses that rocker link and tie rods, the Turbo used "traction springs" (wording from the patent) -- those struts you see connecting the axle to the adjoining train cars that you see in many of the Turbo photos. I had an e-mail exchange with Rapido Trains about their upcoming TurboTrain model (we have a habit of shooing people off this forum when model train issues come up, but a model train in this case gives some insight into the 1:1 scale world) -- the upshot of it was that the springs were found not to work and that the Turbo in service had a Talgo-like linkwork for the axle steering.
I had real issues believing this because nothing in the patent databases had steering links on the Turbo, but you can go to the Rapido Trains website, and they have a photo about their train model that show rocker links. OK, the Turbo model reverts to springs to steer the axles because links are hard to build into an HO model, but the model shows "details" of the journal box that suggest rocker links. Instead of the single rocker link of Talgo, they show a compound rocker link that does the same thing but keeps the two tie rods at the same level above the rails. So in one sense, the Rapido Turbo model is just a toy, but in another sense, the model is a kind of 3-D "photo" of a historical train that was one-of-a-kind.
The "detail" on the Rapido model had to come from somewhere -- having seen the patent literature on steering trucks along with some unrelated mechanisms helped make sense of how the compound rocker worked, and the die maker for that model probably went from some drawing of photo. The good people at Rapido said they would look for a photo of this from a collection of materials destined for a railroad museum in Toronto.
If anyone out there has any insight into the Genesis locomotive truck, there are inquiring minds that need to know such things. If anyone has a photo of the TurboTrain showing the guided axle, a computer scan of such of thing would make me very happy indeed. There are a few photos on the Web showing the Talgo guided axle, but I haven't seen such a thing for the Turbo. There was another thread on this forum showing Train-X photos, which also seem to be guided axle but different from Talgo. If anyone has Train-X photos that show more of the axle mechanism, that would really be a find. Does anyone have photos of European steering-trucks on equipment that has them?
Paul,
Re the Genesis truck, that is not a steering truck. It uses traction rods to locate the axles but there is no intentional steering allowed. The axle traction rods have a single spherical rubber bushing at the axlebox end and two spherical rubber bushings at the truck frame end. These bushings are very stiff radially so allow little motion in the steering direction. This gives a very high axle lateral stiffness which is desired for high speed stability. There is a solid lateral stop on top of the axlebox that limits lateral axle motion to +/- .25" IIRC. The truck was designed by GE's partner at the time, (who also designed the Genesis carbody) Krupp in Essen, Germany who was purchased by Siemens in the mid-90's after this truck was designed. The frames were fabricated at Krupp-MAK in Kiel, Germany, that was also purchased by Siemens, but later sold to Vossloh who operates the factory today. While under Siemens control, they designed and built the trucks for EMD's DE/DM30AC's for Long Island Rail Road. Those trucks are very similar and some parts are interchangeable, such as the axle traction rods.
These trucks use a relative soft coil spring secondary suspension as the primary is fairly stiff. Under each secondary spring is a cylindrical rubber adapter, with its axis pointing to the truck rotation center. That lets the bottom of the spring tilt when the truck rotates to lower the yaw stiffness of the truck for lower curving force.
Dave
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