Steerable truck variants

[Allen Hazen]

A reasonable number of AC-motored GE six-axle locomotives (for, among others, CSX, KCS, CP) have been equipped with "steerable" trucks -- GE's answer to EMD's HTCR radial truck. Questions.
(1) Recent ES44AC for Canadian Pacific, and CSX's first ET44, have had the non-radial, "roller blades," truck. Is this a trend? Have the railroads decided that the added cost of the steerable truck isn't worth it?
(2) There are (at least!) two distinguishable variants of the design. By far the more common has a pair of diagonal -- cranks? levers? struts? -- outside the truck frame near the centre axle. These are attached (hinged, maybe in a socket?) to the outer face of the truck frame outboard of the centre axle on either side, and then angle upwards to meet (meeting at a vertically oriented hinge) above the centre axle. The other version
(2A) I'm sure I have seen a photo of a unit with this style, but which railroad did it belong to? I think it may have been a Mexican railroad.
The other version, I say, has a triangular frame on each side of the centre axle. One leg of the triangle is about in the location of the … bars? … in the first version, and the two triangular frames meet at their apexes on a hinge joint at about the same position as the hinge the … arms? … of the first version meet at. A second leg is horizontal: running from the apex hinge outboard to a point vertically above the start of the diagonal leg. The base of the triangle is (or contains) a vertical hinge.
(2B) Somebody please correct me if in what follows I have misinterpreted the design!
(i) I suspect the basic design is quite similar, and that the function of the triangular frames in the second version is the same as that of the diagonal … for? … in the first.
(ii) The first version looks like an awkward arrangement. I would guess that the hinge at the lower, outboard, end is vertical, that whatever forces it has to withstand come on an element that is NOT perpendicular to the axis of the hinge but angled from it, and that similarly the vertically mounted hinge at the top centre has to cope with forces at an angle. The second design seems to address this by using a longer hinge at the outboard end, one extending up to the level of the centre hinge, and supplementing the diagonally mounted element with a horizontal one from the centre hinge out to the top of this longer hinge.
(ii.a) This makes me think that the second design is more robust… but that GE found that, in normal service, the first design -- probably lighter in weight -- is good enough, and so in general doesn't use the second version.
(ii.b) I don't know how the truck works. (Anybody have a link to drawings that show what happens INSIDE, hidden from casual observers by the truck side frame?) At a guess, the lower, outboard, end of the whatever is connected to something inside the truck frame that is part of the linkage "steering" the axles. Ideally the hinged connections would be mounted horizontally and would meet… right in front of the hub of the centre axle. The angled arrangement we see, then, is dictated by the need for access to the wheel hub.

(3) EMD came out with its radial truck first, and patented it. (I think EMD's truck may have been used as early as the SD60MAC prototypes. GE's was not available until a year or so into AC44 production.) I have read --- somewhere! --- that it is not as neat a design, but that its Rube-Goldberg-ish features were dictated by the need for a truck that duplicated the FUNCTIONS of the HTCR but didn't infringe on EMD's patent. Is there truth to this rumour?

[Allen Hazen]

Sorry about the long-winded descriptions! Here's a photo of what I call the "second variant" of GE's steerable truck (on an AC60CW belonging to one of the Western Australian iron ore railroads).
http://www.railpictures.net/viewphoto.php?id=126306" onclick="window.open(this.href);return false;

[Fan Railer]

GE Radial Truck patent (lots of images) - http://www.google.com/patents/US5613444" onclick="window.open(this.href);return false;

[NorthWest]

1. The general trend is that railroads have considered the extra maintenance of steerable trucks more expensive than the extra wheel and rail wear and so have stopped purchasing them.
2. I think that the BHP AC6000CWs were the only ones to receive their style of steerable truck. I wonder if this was an option or a modification for some reason (extra ventilation?) that only BHP wanted.

[Allen Hazen]

Fan Railer--
Thank you for that link: it's exactly what I was hoping someone could give me! It will take time to study, so no immediate comments. (Well, one: the drawings show what I called the "first variant," the one used on the majority of AC44/ES44AC units with steerable trucks. This SUGGESTS that this version came first, and that the second version was a later idea. Since the only user of the second version I have documentation for was an iron-ore railroad using AC60CW in heavy haul service, PERHAPS the motivation was to provide robusticity to handle forces higher than in other applications. But that's complete guesswork.)

Northwest--
(1) is what I suspected. Not sure what I ***FEEL*** about it: I like railroads and hope they will continue to have an important role in the future, and I'm a bit sad to see railroad management retreating from new technology, returning to the old familiar. But, I guess, not all NEW technological ideas are GOOD ones, so maybe I should be glad that an experiment (to the tune of several hundred locomotives!) has been done and that railroad operators are responding in an "evidence based" way.

(2) I ***thought*** I had seen a photo of an AC44 with the second variant built for a North American railroad, but then again, I've had other lessons in the fallibility of my memory!

[es80ac]

Allen, I have been told GE steerable truck is very complex by necessity due to the EMD patents preventing the adoption of a simpler design. That was not a rumor. I have always been fascinated by the steerable II trucks (the one used on the BHP units), it just looks brutish and cool. There was a pretty detailed article in Diesel Era years back on the prototype CSX AC6000CW 600-602, one of them was equipped with steerable II truck and the other one was equipped with steerable I truck when they were undergoing testing on CSX. There was a discussion on the merits of each design. Unfortunately I don't have that copy of the Diesel Era available.

Radial/steerable trucks in general is currently going out of favor not just in the US but other places that have tried them. China railways equipped a reasonable number of 4000hp DF4D a few years back using the EMD styled radial truck (but a fabricated version instead of the cast version). They were used in some hilly lines in the south with lots of curves. They found the design to have several shortcomings in terms of 1. wearing out the wheels 2. higher maintenance of the trucks. I believe it was stated there was some safety concerns as well. Those have been retrofitted with rigid trucks. Seems like too bad, as the radial truck initially was billed as a revolutionary innovation based on simplicity and great potential.

[Allen Hazen]

es80ac--
Thanks for confirmation on the patent issue, and for the heads-up to a possible source of further information!

[Allen Hazen]

Further to es80ac's comments: photos (post 2000) of CSX 602 on George Elwood's "Fallen Flags" site show it as having a non-steerable ("roller blades") truck, and photos of 600 and 601 show them with steerable I. So apparently CSX and/or GE decided to retrofit something else on 602 in place of its steerable II trucks after a test period (I'm sure the CSX shops were happy NOT to have a roster-uniqu unit to deal with!), and went with the simple, non-radial, option rather than retrofitting steerable I.

[bogieman]

Radial/steerable trucks in general is currently going out of favor not just in the US but other places that have tried them. China railways equipped a reasonable number of 4000hp DF4D a few years back using the EMD styled radial truck (but a fabricated version instead of the cast version). They were used in some hilly lines in the south with lots of curves. They found the design to have several shortcomings in terms of 1. wearing out the wheels 2. higher maintenance of the trucks. I believe it was stated there was some safety concerns as well. Those have been retrofitted with rigid trucks. Seems like too bad, as the radial truck initially was billed as a revolutionary innovation based on simplicity and great potential.

You can't look at the experience with the GE steerable truck and conclude that radial trucks are falling out of favor. EMD continues to sell the vast majority of their units with the HTCR type trucks in North America and there were hundreds of JT42's built for Britain and Europe with similar concept radial trucks. The GE steerable truck is a nightmare of links, bearings, bushings and pads in a design rushed into production to counter EMD's lead. EMD has published several technical papers at Heavy Haul conferences documenting the improvement in wheel wear in North America and the HTCR truck has proven itself in extending the mileage to overhaul compared to pedestal trucks.

There were two different versions of radial bogies built in China - Ziyang licensed a design from EMD that was only applied on a few locomotives; Qishyuan made their own design based on EMD's design - do you know which builder's locos were retrofitted? I had not heard of this before.

Dave

[es80ac]

Dave, there were a batch of DF4D in the 7000 series made by Dalian that were initially fitted with the self-steering radial trucks. These were painted in the green scheme. Initial tests were good, they showed significant reduction in the flange wear. But after an extended period of use, almost all the trucks frames developed stress cracks as well as severe wear and tear on the bogie parts. They were ordered back to the factory for overhaul and conventional trucks were swapped in as replacement around 2007. Ziyang never produced any recent locomotives in significant numbers other than the copy of the Df8b and Df4b they licensed from the other builders. I am not aware they produced anything with radial trucks. Qishuyan is working with GE with the licensing of the GEVO for their units, and not EMD.

[bogieman]

I did not mean to imply that Qishyuan was partnered in any way with EMD, they simply based a design on EMD's patents around 2000 or so when EMD did the license deal with Ziyang. I was not aware Dalian built any radial bogies, but again, these were not part of any transfer of technology with EMD. When EMD designed the H-engined Chinese locomotives built by Dalian, radial bogies were not included due to weight constraints. Having seen first hand 15 years ago the welding processes used to make bogie frames at Ziyang, which I suspect were similar at other Chinese manufacturers, it is a wonder any of their bogie frames survived service.

[Fan Railer]

Speaking of the EMD radial, here's that patent as well... note the simplicity of the design compared to the GE variant: http://www.google.com/patents/US4765250" onclick="window.open(this.href);return false;

[es80ac]

Thanks for the information on the patents. Oh yeah, EMD's patent definitely looks much simpler. But I also hear people complain about the ride quality of the EMD radial trucks. I wonder if it is due to the slight pivots or due to the coil springs not being long enough since they sit right on top of the axle journal, where in contrast the GE hi-ad trucks have coil springs on both sides of the axle journal? I also wonder if the GE steerable trucks ride any better.

"I did not mean to imply that Qishyuan was partnered in any way with EMD, they simply based a design on EMD's patents around 2000 or so when EMD did the license deal with Ziyang. I was not aware Dalian built any radial bogies, but again, these were not part of any transfer of technology with EMD. When EMD designed the H-engined Chinese locomotives built by Dalian, radial bogies were not included due to weight constraints. Having seen first hand 15 years ago the welding processes used to make bogie frames at Ziyang, which I suspect were similar at other Chinese manufacturers, it is a wonder any of their bogie frames survived service."

Dave, I can also relate to your point about the Chinese welded trucks, they are definitely more fragile than the cast North American trucks, but then again EMD is even moving to welded trucks on the new SD70 tier 4s which is interesting. I don't believe Qishyan built a single locomotive with the radial trucks, neither am I aware of Ziyang built any. I didn't know Dalian's version is unlicensed either. Btw, I love to chat with you offline on this, I am in the Chicago area as well.

[mp15ac]

One thing to remember is that EMD had to go with a steerable truck because of their one inverter per truck design. Since with one inverter per truck all three traction motors will turn at the same RPM, EMD had to use the steerable truck in order to keep all the wheels as close as possible to the same diameter or the differences in torque would cause problems. Since GE went with one inverter per motor, the need for the steerable truck wasn't as critical for them.

Stuart

[MEC407]

Interesting point. EMD eventually came around and now they have an inverter for each motor; yet they have continued to offer the radial truck as standard equipment.