In the 1980s, EMD experimented with high traction HT-BB trucks, and fitted a pair on former BN SDP45 #6599. In contrast to the rigid DD trucks on the DD35/40s, HT-BB was flexible and articulated. I wonder the advantages this axle had over the DD trucks? Would theses articulated axles enable a loco with a longer frame to navigate tighter trackage? IIRC, the EMD double diesels with DD trucks were limited on what tracks they ran on because of frame length What become of this concept? I guess CC is good enough for 4,000+ freight locos. Such an arrangement might be better than CC on 6,000hp or greater, though I doubt such a diesel loco will be built in the foreseeable future, except for maybe China of course. HT-BB might be practical on narrow gauge too.
Isn't this concept being used on some narrow gauge ore hauler in Brazil?
IIRC, EMD only replaced the rear truck on the 6599 for the tests - nothing more was done, so I suspect there was not a lot gained. Those DD35/DDA40X engines had issues on sub-standard trackage and I am sure they could 'straighten' a sharp curve. Where UP used them should have not been a problem.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
I'd love to see a picture of these trucks if you have one! Was it a matter of simply swapping two BB trucks for one DD -- which would give it a similar truck arrangement to the U50 -- or was it more involved than this? And in terms of appearance, did these trucks look like the HT-B trucks that EMD put on the GP40X? (except, Espee's, which had M-type trucks, if memory serves)
I remember seeing pictures of this, it was awhile back now. With all the new technological improvements and new kinds of trucks I just assume they were forgotten about. Probably one of those things where the parts of it that worked were worked into a newer design.
I answered this question on Trainorders.com about 2 years ago:
"------------------------------------------------------- > Can anyone help me out with some information about > Burlington Northern SDP45 #6599 after it was > rebuilt with a B-B rear radial truck? There seems to be a misconception in the railfan community that the HT-BB four axle articulated truck is a radial truck. It is just two rigid two axle trucks connected by a span bolster for vertical load transfer, a low mounted traction linkage to minimize weight shift, and a patented interlink between the two 2-axle trucks that improves the leading axles angles of attack to the rail. It can't be called a radial truck because all axles can never be geometrically radial to a curve. It was developed ahead of the HTCR series of trucks in 1983-84 at EMD. BN's CMO, Thompson (not sure that was his name) was interested in the project because of the potential for high tractive effort. It actually began when EMD was bidding on South African 11E electric locos in conjunction with ASEA. With 8 axles on 3'-6" gauge track, it was a solution to use EMD design traction motors instead of 6 much larger ASEA motors. In the end, the ASEA motors were used in a GSI zero weight shift truck. Scheffel of SAR, a radial truck designer himself, was not a fan of the HT-BB truck since it was not a true radial truck and dismissed it from consideration. The BN donated the 6599 for the conversion which was done in EMD's high bay in LaGrange, as loco production was way down at the time. The test trucks were made from two SD Flexicoil trucks where the single motor end was cut off, leaving a wheelbase of 81.5" on each sub truck. I don't recall the spacing between axles 5 and 6 but it was quite small, about 54-56" if I had to guess. Transoms were added made from plate and a cross link added. Holes were cut in the side frames between axles for the shafts that the traction linkage bellcranks pivot about. The bellcrank pivot bearing was a standard Class F journal bearing. A solid bolster was cast at Rockwell (Atchison) as a one-off using a simple pine pattern. Regular SD Flexicoil secondary and primary coils were used. The traction linkage was only about 10" above the rail and had spherical bearings at each end to allow movement but the lower the better for weight shift. Side posts were welded into the underframe after the underframe was lengthened about 4 feet, using the end of a trade-in loco. The center bearing stayed in the original location. A smaller fuel tank without water tank was added to make room for the truck extra length. I think that came from a trade-in unit as well but I don't recall the size. The center axle of the leading SD truck had it's traction motor removed for use in the HT-BB truck and cabling was modified to suit. Air duct openings also had to be reworked to match the motor locations. The truck was tested in September, 1984 at Stampede Pass in Washington state over a two week period. EMD's instrumented wheels were applied at the BN Interbay shop the week prior to the testing. EMDs test car, I think it was the ET840, was connected and EMD braking units were used. Stampede Pass was closed to traffic at that time but reopened especially for this test. Downed trees had to be removed from the line to make it passible. The consist tied up each night at a yard in Auburn. Testing showed wheel lateral loads better than the SD and less than expected from a single two axle truck. The unit road well with all that suspension travel of the Flexcoil springs. The truck just never found an application to justify the expense to develop it for production as well as the added cost of motors and wheels, not to mention a new alternator to handle 8 motors in parallel. "
Similar span bolster truck arrangements are popular in Brazil for narrow gauge operation where the traction motors are very limited in power capacity, but none have used the patented interlink. Here is a link to the patent for those interested:
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=4,485,743.PN.&OS=PN/4,485,743&RS=PN/4,485,743
Dave
Here are some pictures I found, one is a close up of the trucks:
http://www.rrpicturearchives.net/showPicture.aspx?id=177846
http://www.northeast.railfan.net/images/bn6599a.jpg
http://www.northeast.railfan.net/images/bn6599.jpg
One tends to forget how long those locomotives were. They are impressive even today.
santafe347 Here are some pictures I found, one is a close up of the trucks: http://www.rrpicturearchives.net/showPicture.aspx?id=177846 http://www.northeast.railfan.net/images/bn6599a.jpg http://www.northeast.railfan.net/images/bn6599.jpg
Nice pics, santafe347...and a very impressive account, bogie_engineer!
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