I was very fortunate to be assigned to the radial truck development team within the Truck Development Group in 1982 at EMD. I had spent the previous 9 years of my career there working on noise control projects culminating the introduction of exhaust silencers and quiet fans in response to the EPA noise regs that became effective the first of 1980. Mechanical/structural design was my expertise and I fit well into the team taking the design lead.
Radial steering trucks got a lot of attention in the rail industry globally in the 1970's, particularly for freight cars. Scheffel in South Africa and List in the US were prominent designs with use in fleets with the Barber-Scheffel and Dresser DR-1 (subsequently AR-1 after ASF bought out Dresser) trucks, respectively. EMD recognized that radial steering trucks on locomotives could be very beneficial with advantages of:
- Reduced wheel flange and rail gauge face wear (locomotive trucks were projected to cause perhaps 20% of the rail wear based on numbers of wheels consumed),
- Improved adhesion in curves (conventional 3 axle trucks were known to lose about 10% of their adhesion in 10 degree curves),
-Reduce wheel squeal in curves.
In the late 1970's EMD started seriously studying radial trucks beginning with literature study and the creation of math models to evaluate truck curving and adhesion performance. EMD had hired a brilliant mathmetical mind in Dr. Mostafa Rassaian and he and Karl Smith, who went on to become Direct of Engineering at EMD, worked on these math models on a part time basis until there was confidence that the models reasonably predicted truck curving performance based on EMD's extensive test data from instrumented wheelsets. Karl moved on to lead other truck projects and in 1982 I joined with Mostafa to start developing truck concepts that had the freedom of axle movement to allow radial steering that were evaluated using the math models. We had about 10 design concepts schematically built that we judged based on the model results and manufacturing feasibility ultimately selecting the "steering beam" concept where a cross beam parallel to the axle that was pivoted at its center and linked thru traction rods to the bearing housings. This allowed the axle to yaw (rotate about a vertical centerline thru its center) taking tractive and braking forces without moving longitudinally within the truck frame. Each axle had a steering beam, in a 2-axle truck with motors facing each other, the steering beams were placed between the traction motors and then cross-connected so they would yaw in equal and opposite amounts. With rubber bushings at each end of the traction rods, the axles had lateral freedom of movement that was limited by stops between the bearing housing and truck frame similar to the limits in a pedestal truck.
This arrangement as designed into our pre-prototype truck, is best shown in patent 4,628,824 which can be seen here: http://www.freepatentsonline.com/4628824.pdf
Using a spare HT-B truck frame we had in inventory from the GP40X project, I designed a modification where we cut off the lower portion of the cast sideframe that connected to the inclined rubber springs and welded on bottom plates to restore the structure. A heavy plate was welded into the opening between the transoms that GP compression rubber secondary springs rested on and wearplates were added on the transom faces to transmit tractive forces from a small fabricated bolster that sat on the rubber springs and had the centerbearing receiver to mate with a standard GP loco with swinghanger trucks. A center plate was welded between the transoms underneath that held the pivots for the steering beams. The patent drawings have some good cross-section views that show the actual tested truck arrangement. Included in the mods were a change from the standard nose pack that supports the traction motor on the transom to a rubber bushed link.
We had a 1/4 scale model of the HT-B truck built during the development of that truck; since the HT-B was a dead design at that point, we modified the model to match our full size design. This album contains the pictures I took during the test and includes a picture of Mostafa and me with the model:
https://flic.kr/s/aHsmMphH8d
After completing the kit-bash to make the truck and installing the instrumented wheelsets, we got agreement from the Santa Fe to use one of their GP50's to test the truck. We installed it in place of the rear truck on the 3810 at EMD, then shipped it with the ET-840 test car to the Transportation Test Center in Pueblo. Looking back on it, they really trusted us since this truck had never run before.
It was an eventful trip, not due to any problem with the truck, but our Engineering test department failed to put oil in the support bearings on one motor before we shipped. We left Corwith at 8 pm, at about 2 am, we set off a hotbox detector - I ended up crawling under the loco and checking the support bearings which I found dry. The only oil we had on the test car was crankcase oil for the gensets so I filled it with that after lubing the wick and we didn't have a further problem. However, when we got to Avondale, the Santa Fe crew unlocked the gate and pushed us into the Pueblo Army Depot, where at 4 am soldiers with rifles drawn escort our test engineer and me into a vehicle where they took us the headquarters building where we were rescued by TTC people about 8 am.
Once at TTC, we connected the instrument wheelsets and other tranducers to measure how the truck steered to the test car and did some running up to 75 mph to see if we experienced any truck hunting. The truck proved to be stable at that speed - from there we moved to Trinidad to test on the Colorado side of Raton Pass where there are plentiful 10 deg curves not available at the time at TTC.
We learned the truck curved very well with almost 0 angle of attack, which is the goal of any radial truck design. It curved well coasting and nearly as well under maximum tractive effort. We did, however, learn a major shortfall of this design was that after curving with tractive effort, coming out of the curve, the truck did not straighten itself out, instead it generated a large angle of attack on the leading wheelset and high lateral rail force, much higher that a rigid truck curves with. Further experimenting showed if we were coasting on tangent track, we could apply up to about 700 amps tm current with no problem, but above that, the lead axle would yaw and attack one rail. The direction it turned was random, sometimes right, sometimes left, but it happened consistently.
So we learned the basic concept worked as intended; we could steer in curves under power, but we had a tangent tracking problem we need to figure out before we could claim success. So back to drawing board.
I'll continue this in another post.
Dave Goding
An informative post!
I also liked the Lego Shay.
One question in regards to loss of adhesion in curves: Is this due to the tractive forces from the end axles being at a significant angle from the rail?
Erik, When you examine how a truck goes thru curves, the trailing axle within each truck generally assumes close to a radial orientation to the curve and the axle(s) ahead of it have an angle of attack wherein the outer wheel is grinding against the flange. On a 3-axle truck due to the long wheelbase, the leading axle is at an angle of about 1.2 deg relative to radial line. So there is lateral slippage at the contact patch with the rail that takes away force that could be tangential to the rail where it is does the tractive work. Of course, that's a simplification but the lead outer wheel always has the greatest "angle of attack" to the rail is trying to climb it.
Dave,
Makes sense and thanks for the detailed explanation. I'd also imagine the angle of attack would also contribute to rail wear.
Model Railroader had an article on grades in issue from 1968, and the effect of curves on train resistance has intrigued me since. Specifically how much was due to the wheels slipping against each other and how much was drag from the forces pulling the wheels towards the center of the curve. Most of the texts on calculating train from years ago tend to punt on the "true cause". Figure this is sort of the flip side of adhesion versus curvature.
I am watching this with considerable interest, and hope it turns into thread of the year...
Erik_Magthe effect of curves on train resistance has intrigued me since. Specifically how much was due to the wheels slipping against each other and how much was drag from the forces pulling the wheels towards the center of the curve.
Keep in mind that the dynamics are very different for powered wheels vs. trailing wheels being steered indirectly from carbody 'guidance' (including "Talgo-style" truck arrangements or Jacobs articulation).
I believe Mr. Goding has already discussed this in some respects; as I recall it was brought up in Wickens from 'the opposite perspective' regarding wheelset stability in unpowered trailing vehicles. I look forward to seeing a full discussion.
I would expect that there are differences between powered and unpowered steered axles, with tractive forces being the opposite sign from drag forces as well as being MUCH larger magnitude when not braking.
There are also effects on the coned-tread-wheel and railhead interaction, and on the way the axles try to 'steer' the truck frame.
This is in part inherent in Mr. Goding's description of how the trailing axle of a powered C truck is the only one that experiences 'radial' centering. You can easily model some of the force couples that the leading and center tread, fillet, and flange face experience when this is true on a pin-guided truck with three motors independently pulling (at what can inherently be three slightly different resultant speeds for a given common admitted voltage, but will not be different for an early EMD single-inverter-per-truck AC drive).
The role of the geometry involved is also important, both for the pivoted and semi-attached 'centerless' styles of truck rotation accommodation. As a comparison, look at the American Arch 'articulated' truck frame as seen on the early Woodard Super-Power engines. Here the rear wheelset (especially when fitted with a booster) was supposed to take up a radial position relative to the track -- but the front articulation pivot location and the need for proper weight distribution make the subsequent location of the leading wheelset geometrically improper for proper Bissel steering of a two-axle truck that is providing active guiding for the chassis. The 'solution' circa 1927 was to float that axle with minimal lateral 'friction' restoring force between it and the truck frame, but still with full springborne weight transfer to the equalization -- this was done with a pair of hardened steel rollers acting on hardened bearing surfaces. Now, since this was an idler axle, there was no particular need to steer it radially, but it would 'theoretically' be possible to use Cartazzi-style curvature of the guide plates in the pedestals so the axle would 'float' in radial alignment with the effective forward pivot point of the articulated truck; you would then at least in theory be able to use the kind of cam or toothed-rocker/sector-gear centering that made the two-axle Delta truck so successful at chassis guiding, and this would greatly ameliorate some of the problems encountered with the American Arch truck design when trying to back a load in buff...
Overmod This is in part inherent in Mr. Goding's description of how the trailing axle of a powered C truck is the only one that experiences 'radial' centering. You can easily model some of the force couples that the leading and center tread, fillet, and flange face experience when this is true on a pin-guided truck with three motors independently pulling (at what can inherently be three slightly different resultant speeds for a given common admitted voltage, but will not be different for an early EMD single-inverter-per-truck AC drive).
Bear in mind that the single inverter per truck guarantees the traction motors will have the same synchronous rpm's, but the the torque produced from each motor will be proportional to the difference between synchronous speed and actual speed. This is why you need to keep wheel diameters close to equal on such locomotives, but it isn't as critical as on a K-M hydraulic.
Another truck/bogie related question is the effect of articulated trucks found on a lot of pre-WW2 electrics and Centipedes.
Do you know how much EMD were involved (if at all) in the radial trucks built by EMD's Australian associate Clyde Engineering (later EDI and later still Downer and now Progress Rail)?
There were two designs:
The first, applied to standard gauge GT46C units and 1067mm gauge JT42C units from 1998, used swing arm supported axleboxes not seen on USA designs of radial truck.
The second truck design a year or so later had the same swing arm layout on the outer axles but the middle axle had the swing arm replaced by a wing type axlebox with helical springs each side. This was only used on the 1067mm gauge GT42CU-AC, but this has been one of the most successful units ever built in Australia with around 250 units in service.
Both these designs had traction forces taken by traction rods at axle level connected to a floating transom between the outer axles that connected to the truck frame and the rods connected to brackets fixed on the frame edge close to the truck centre.
Another question is Why did the EMD built radial trucks on the JT42CWM (Class 66) look so different from the domestic designs on the SD70 or example?
Peter
M636C Dave, Do you know how much EMD were involved (if at all) in the radial trucks built by EMD's Australian associate Clyde Engineering (later EDI and later still Downer and now Progress Rail)? There were two designs: The first, applied to standard gauge GT46C units and 1067mm gauge JT42C units from 1998, used swing arm supported axleboxes not seen on USA designs of radial truck. The second truck design a year or so later had the same swing arm layout on the outer axles but the middle axle had the swing arm replaced by a wing type axlebox with helical springs each side. This was only used on the 1067mm gauge GT42CU-AC, but this has been one of the most successful units ever built in Australia with around 250 units in service. Both these designs had traction forces taken by traction rods at axle level connected to a floating transom between the outer axles that connected to the truck frame and the rods connected to brackets fixed on the frame edge close to the truck centre. Another question is Why did the EMD built radial trucks on the JT42CWM (Class 66) look so different from the domestic designs on the SD70 or example? Peter
Peter, The Clyde/EDI design was based on the EMD HTCR but they chose to implement the concept a bit differently to meet the Australian requirements. We didn't have any direct input on their design from LaGrange.
The Class 66 design was done by a different group of engineers at EMD as I was in the Systems Engineering group at the time doing the mechanical design of the DE/DM30AC we built for Long Island RR (let the flaming begin). The British clearance diagram prevented the use of standard EMD outboard cylinders for the air brake so a new design of the brake rigging was required. Rather than choose to design a conventional cast frame using box sections, enccouraged by the casting supplier, they thought that they could save significant casting cost using an open bottom frame, which eliminated most coring in the casting. By the time they got done with the structural design though, the frame was heavier and more costly to produce than the HTCR design but they were committed to that design and soldiered on. Once that design got approved for use in Britain and Europe, changing it would have required going thru the costly and lengthy approval process again. You might notice I am not a fan of that design.
Dave
bogie_engineer ...I was in the Systems Engineering group at the time doing the mechanical design of the DE/DM30AC we built for Long Island RR (let the flaming begin).
...I was in the Systems Engineering group at the time doing the mechanical design of the DE/DM30AC we built for Long Island RR (let the flaming begin).
Off topic, but what exactly were the problems with those? I've never heard the story from someone 'in the know'.
Greetings from Alberta
-an Articulate Malcontent
I'll continue on with the radial truck development program again.
Using what we learned about truck yawing under high tractive effort, we concluded our problem of the truck design was that we were using a centerbearing for the truck pivot which offered no restoring force that would straighten the truck upon leaving a curve and hold it straight on tangent track. The simple solution was to go bolsterless, as many truck designs such as the AEM-7's we were still building at EMD and the Dofasco Hi-Ad trucks used. So I chose to design a bolsterless truck using coil springs (Flexicoils) for yaw stiffness. To support the carbody weight of about 110,000 lbs. required a triple coil spring of 12.5" dia and 24" height which had a lateral stiffness where it would work. A new frame design was required to pocket these springs at the sideframe-transom junctions. We didn't want to invest the $250K+ we'd have to spend for patterns and coreboxes to make a cast frame so I designed and drafted a fabricated frame that would be suitable for testing without worrying so much about fatigue strength any truck design requires since this would be for test and only had to last 6 months or less.
A major shortcoming of the GP swinghanger truck (Blomberg) has always been its weightshift performance. At a locomotive adhesion level of 25%. the lead axle on the lead truck unloads to 84% of its static weight and the trailing axle of the trailing truck is overloaded to 116% of static. High traction truck designs such as the HT-C had it's lead axle at 93% under the same adhesion level and we wanted to get similar improvement on any new design. In a two axle truck with motors facing the center, it's necessary to allow the truck relative freedom to pitch in response to the opposing vertical forces the two nose links impart to the frame. This requires that the tractive effort transfer between the truck frame and underframe take place as close to rail height as possible. The Dofasco ZWT and EMD HT-B accomplish this by focusing rubber springs at the top of rail. That is difficult to fit into a truck with axle height steering beams so I chose to use a crossbeam under the steering beams pivoting at the center of the truck and connected via traction rods to posts extending down from the sidesills. This connection was at about 12" above top of rail and provided weight shift performance similar to the HT-C truck.
In less than a year we had a totally new design truck ready to go to Pueblo along with an adapter structure that contained the posts connecting the truck and underframe. In December 1985, the test truck and accessories were shipped to the TTC and applied under the same Santa Fe GP50 3810 we had used for the pre-prototype test. The adapter plate added 3" between the truck and underframe so the loco sat a bit high at the cab end where the truck was installed.
Pictures of the modified locomotive and the test consist are here:
https://flic.kr/s/aHsmMpqVtP
The patent for this truck shows the design as we tested it, unfortunately, I have no pictures of just the assembled truck and the adapter structure - EMD does in their photos archives, however. The patent is here:
http://www.freepatentsonline.com/4841873.pdf
The first testing was on tangent track to see if we had tamed the high traction steering issued observed on the pre-prototype truck. We were ecstatic to see that the truck tracked straight at the max tractive effort we could apply, over 1700 amps tm current. So that problem was solved.
We spent a lot of time doing passes around the balloon track at TTC which is 7.5 degree curves with 4" of superelevation IIRC. One section of the balloon incorporated a section called dynamic curving, which is lateral perturbations on a 39' wavelength. During all of our radial truck testing of 2- and 3-axle trucks we never had a derailment of the test truck, but in the balloon track we did have a wheel on the swinghanger truck drop between the guard rail and the rail in the dynamic curving section when our engineer applied the brakes while we were passing thru the section at the critical speed of about 15 mph. One of the pictures linked above shows a flange resting on top of the rail while the opposite wheel was on the tie. No problem, we simply backed up carefully and the wheel re-railed itself.
The curving results were excellent on the balloon track, near zero angle of attack and low curving force compared to the truck with the steering locked out, which was a provision the test truck included. We tested hunting stability and as designed, the truck was stable to over 90 mph, as fast as we could go with the gearing. With the TTC limited at the time with the tightest curve of 7.5 deg, we then moved to Raton to test on 10 deg curves.
We had great co-operation again from the Sante Fe. IIRC, Glen Powers was the Trainmaster in Raton and the time and gave us all the help we needed as well as a great crew, pictured in the photos linked above. During downtime while testing, we heard some great stories from the crew.
We spent about a month running up and down the Colorado side of the pass testing curving performance at a range of speeds and tractive efforts to document truck performance which was again exceeding our expections for lateral curving load and angle of attack. We tested with onboard flange lube documenting no adverse affect on the truck performance as well.
When we were done on Raton, we went back to the TTC, removed the test truck and restored the locomotive, which was returned along with the braking units we borrowed to Santa Fe.
After returning to EMD, work began immediately to design a 3-axle truck using what we learned.
Dave, thanks for another interesting and imformative post! Glad to hear the two axle truck performed to expectations. The lack of hunting at 90MPH was impressive, though wonder if it would hold up with worn wheels - this is from reading about Nystrom's work with high speed passenger car trucks for the Milwaukee Road.
Erik, You are correct that hunting threshold speed is a function of wheel-rail effective conicity which is a function of wear. A new 1:20 wheel profile might be about 1:10 effective conicity due to the way it meets the rail head so depends on rail profile as well as wheel profile. We tested with a fairly new 1:20 profile on the wheels so the 90+ mph stable speed we observed will come down as the wheels wear. Worn wheels wear to about 1:6-1:4 effective conicity on worn rail; that would have dropped stable speed to about 80 mph still above our design goal of 75 mph. Radial trucks that are self-steering such as the EMD designs intended for 10+ deg curves were not designed for service above 75 mph - higher speed radial trucks would not have nearly as much wheelset yaw travel as the steering beam configuration allows (about +/- 1 deg); as with most things there are always compromises to make. European designs for medium speeds above 90 mph typically allow axle yaw only thru deflection of rubber traction rod bushings or rubber chevron springs in the range of +/- 1/4 deg.
I didn't mention a few things we did with the steering beams in the 2-axle prototype design but they are shown in the patent. We added rubber bumpers on the steering beams that engage mating surfaces on the truck frame after some free travel the amount of which we experimented on during the testing finally settling on 1/8" at each bumper. We also changed the connection between steering beams to be a single stiff rubber bushing. This adds axle yaw stiffness and adds a restoring force to center the axles within the frame. This enhances hunting stability as well.
SD70Dude Off topic, but what exactly were the problems with those? I've never heard the story from someone 'in the know'.
It was a difficult contract with no time to prototype a locomotive, the 400 page RR spec required a completely new design with no commonality to anything we were building then, we had RR consultants overseen by MTA consultants dictating how we designed the locomotive. The RR spec'ed systems for train control, communication, station identification, anti-lock brakes and along with the EM2000, Siemens AC traction computer and air brake computer made 7 computers talking to each other which was a first for us and took a while to get right. There was also fatigue cracking in skids the engine-alternator were mounted (never done on an EMD loco before) and other teething issues that resulted in us sending all units to Altoona where mod work was done. I'll suffice it to say the LIRR workforce took full avantage of any issues that came up. So the locomotives got a lot of NY bad press and derision by riders and railfans there. It was such a bad experience for EMD that our General Manager said we would never build another passenger locomotive and we dropped out of bidding for the Metra locomotives that MPI eventually got.
End of rant.
Thanks for that. Wow, seven computers. What a kludge.
Building modern passenger locomotives sounds about as easy as operating passenger trains, the most effort for the least profit.
Now back to your regularly scheduled thread, this stuff about radial trucks is fascinating. I'll put on some more popcorn and leave you guys to it.
Great thread Bogie_Engineer! It's always a pleasure to get this info from those directly involved. I just learned more in your thread about dynamics than all of my high school teachers who taught this very subject!
Thanks for the positive comments.
Continuing the radial truck development story...
When we got back from the successful 2-axle radial truck test, we immediately started to brainstorm how we could do a 3-axle truck. After much discussion, we settled on an arrangement that retained the steering beams for axle location and yaw freedom, along with an inter-connecting link running across the top of the middle traction motor. The rubber bumpers limiting steering beam rotation and thus axle yaw were retained. We looked at using bellcranks, as GE eventually did on their steerable truck to avoid EMD's patents, but rejected them due to the difficulty cross-linking them and the greater number of pivot bearings adding cost.
Although it would have been simpler to use a motor arrangement like the SD Flexicoil truck where the outer motors face inward, we kept the HT-C arrangement for its superior weight shift - at 25% adhesion, the lightest axle on the SD Flexicoil truck is at only 78% of its static load, whereas, on the HT-C and now the HTCR, it's at 93%. We knew we needed to retain the feature of truck yaw stiffness to keep the truck tracking straight on tangent, yet needed the high compression stiffness of the secondary springs to keep the truck from pitching to get the minimum weight shift. That led to the tall rubber springs that shear about 8 inches at full truck rotation, not unlike the Dofasco Hi-Ad truck. Round springs gave us a relatively soft lateral stifffness for good ride and soft rotational stiffness necessary for good curving. With this direct support between truck frame and underframe, no bolster is needed, however, a means for transfering the tractive effort of the truck to the underframe is required. This was accomplished with a four bar link arrangement connecting the first transom thru traction rods to a pivot block that rotates about a post extending down from the underframe and is detailed in the patent referenced below. Elimination of the bolster opened the space for the inter-axle link to run above the middle traction motor.
We replaced the rubber traction motor nose support pack, used since the early days at EMD, in favor of a link with rubber bushed ends. This was done for two reasons; first, to get rid of all the wearing parts that including welded wearplates and pins, and secondly, to have a consistent stiffness of axle rotation unaffected by unpredictable friction in the nose pack.
The primary suspension used long travel single coil springs for good vertical ride and axle load equalization on a new bearing adapter casting. A single rather than double coil was used to avoid coil binding during axle yaw and was made possible by spacing the springs away from the axle centerline allowing for taller springs. Additional primary suspension dampers were added to make up for the loss of friction damping provided by the pedestals in conventional trucks. To react the lateral force of the axle against the truck frame, a steel faced rubber pad mounted on top of the bearing housing reacted against a nylon wearplate mounted inside the truck frame between the coil springs. Integrally cast secondary lateral stops on top of the center axle spring pocket react against a wearplate welded to edge of the bottom plate. Blocks welded to the bottom plate limited truck rotation to 6.5 degrees.
Brake rigging was similar to the HT-C truck but we put a brake cylinder adjacent to each wheel which allows enough piston travel to fully wear out a brake shoe so that no adjustment of the brake rigging is needed between shoe changes, a perceived maintenance advantage.
The patent for the HTCR is here showing the truck arrangement: http://www.freepatentsonline.com/4765250.pdf
In about six months from the finish of the 2-axle test, we had the design far enough along to begin procuring parts to build the first HTCR truck. The major part was a new cast truck frame - working with our long time supplier, the former LFM in Atchison, KS (at the time part of Rockwell International), we designed a solid steel cast frame that had no internal coring. This added significant weight, almost 9,000 lbs. more the HT-C bare frame, but it saved us substantially in pattern cost. They built a simple pine pattern and a few coreboxes for some frame external brackets for $125K, a full hollow frame pattern would have cost at least $300K and since it hadn't been tested, we weren't completely confident this would be the final design. Rockwell did a great job and we had a casting to build the truck in about 8 months, a very short time for this kind of procurement.
New axle bearing housings were cast at Racine Steel Castings and are the only other cast parts in the truck. Lord Corporation in Erie, PA made most of the rubber parts and Hadady Corp., EMD's brake rigging supplier made the steering beams, brake rigging, and numerous other fabricated and machined parts.
In 18 months, we had the test truck assembled and on it's way to Pueblo for testing. The EMD Experimental test shop fabricated an adapter structure that was necessary to mount the truck under SD60 EMD3 that we used for testing. This structure incorporated a traction post welded into a 3" plate that connected the truck to the underframe. The truck assembly and the adapter are shown in the only two photos I have from this phase of the project here: https://flic.kr/s/aHsmMz7Mt3
When we had all the material at TTC in fall of 1987, we placed the adapter on top of the truck assembly, raised the locomotive on jacks, rolled the truck under the unit, and lowered the unit onto the truck. Once positioned where we wanted it, the adapter plate was welded to the bottom plate of EMD3.
The test program began at TTC for preliminary curving tests up to 7.5 deg curves, the max at the time at TTC, dynamic response on the perturbed tracks, and hunting stability testing. The dynamic tests of Dynamic Curving, Twist and Roll, Yaw and Sway, and Bounce showed no problems. Stability speed, however, did not meet our goal - at about 55 mph we experienced significant truck hunting involving both truck yaw and axle yawing. We experimented with different axle yaw damper characteristics but did not solve this issue during this test program, that would have to be studied more and figured out after this test was completed.
We moved on to Raton Pass for the curving portion of the test. For testing, we built a feature into the truck so we could lock the steering to get a good A-B comparison of rigid versus radial steering. We also moved the instrumented wheelsets to the HT-C truck so we had a direct comparison to that truck. Key test parameters were Net Lateral Load (NLL) at the leading outer wheel in the curve, Angle of Attack (AoA) between the leading outer wheel and the rail, and a flange wear index, calculated by multiplying the lead outer wheel flange force by the AoA. We made repeated runs up the hill from Trinidad to Raton tunnel stopping short of the portal after the big sweeping right hand curve at Wooten Ranch.
The test results exceeded our expectations; after averaging many test runs, the data showed for 10 degree curves that the NNL of the radial truck was reduced about 30% coasting and 20% at 30% adhesion compared to the HT-C truck. Angle of Attack was reduced about 90% coasting but only about 10% at 30% adhesion. The flange wear index remained nearly constant for the HTCR truck over the range of adhesion levels as the AoA increased with adhesion level that is nearly offset by a lowering of flange force as more of the available friction is used for traction and less is available to steer the wheelsets. For the HT-C truck, the AoA remained constant with adhesion level but the flange force declined resulting in a about a 30% reduction of flange wear index at 30% adhesion. The end result was that the flange wear index for the HTCR truck was reduced by about 60% coasting and 30% at 30% adhesion compared to the HT-C. These results were presented in detail in a technical paper published and presented at the 4th International Heavy Haul Conference in Brisbane, Australia in 1989.
So at the conclusion of the test in early 1988, we had a 3-axle radial truck that steered very well but needed work on hunting stability before it was ready for production.
Thanks for the post and particularly the link to the patent and the drawings.
One of the differences from the Australian trucks was the flexible link to the centre pivot which was quite different.
In the Clyde/Downer design, the truck centre pin was located by the external brackets and links to a transverse beam seen in the photo of the narrow gauge version on S 2106 illustrated here. The standard gauge locomotives of classes Q, FQ and V had generally similar arrangement, as did the fairly successful narrow gauge GT42CU-AC of which 250 or so have been built, the most successful cape gauge locomotive ever built in Australia.
All these trucks used the four rubber/metal secondary suspension pads as shown on the EMD patent. I think the MLW/ Dofasco truck was the first to use these pads in 1967, but now both EMD and GE use these pads.
Downer changed to the EMD design of centre pivot link as shown in the patent with the GT46C-ACe which was basically an SD70 ACe squeezed into the Australian clearance gauge.
While not as clear as the S class photo, it can be seen that the external brackets and links are not present on the TT.
Downer indicated that the GT46C-ACe trucks were not strictly steering trucks since there was no steering linkage, but since similar bearing and motor mountings were used, the axles were free to take up radial locations in curves.
I was fortunate to be in Melbourne when the first GT46C-ACe units made their first run in service.
I turned up along with quite a crowd, including engineers from EMD, who I asked about the new trucks. I was quite surprised to be told that no instrumented tests had been performed, but they had run high speed test runs that indicated no hunting or other operational problems. (Among the crowd was the CEO of the operator, Mr Smith of SCT, who seeemed to be having a good time, but he did not ride the train, returning (presumably) to the office by car).
I've found a presentation with an excellent photo of the GT46C-ACe truck...
https://web.archive.org/web/20090913111026/http://www.core2008.org/assets/papers/tuesday/1045/Paul-Hewison/Presentation%20-%20DEDIR%20SCT%20HALCROW%20-%2030-8-08%20v2.pdf
This confirms that the truck does not use a steering mechanism...
Page 18 of the presentation.
M636C I've found a presentation with an excellent photo of the GT46C-ACe truck... https://web.archive.org/web/20090913111026/http://www.core2008.org/assets/papers/tuesday/1045/Paul-Hewison/Presentation%20-%20DEDIR%20SCT%20HALCROW%20-%2030-8-08%20v2.pdf This confirms that the truck does not use a steering mechanism... Page 18 of the presentation. Peter
Thanks for the link, had not seen that presentation.
You are right that this truck does not use a steering linkage but it is considered self-steering none the less. Here they use a swingarm-type design with a special design bushing at the pivot that allows some longitudinal travel for steering. With this arrangement, under high tractive effort, there is longitudinal translation of the end axles on tangent track but the axle will steer itself in curves. What we found during testing, where we instrumented the axle traction rods as force transducers, was that if we constrained the steering beams to not allow axle steering, the forces in the traction rods during coasting conditions were nearly equal and opposite. The taper on the wheels is trying to steer the axle into a radial position with the outer traction rod in the curve being in tension and the inner in compression. As tractive effort increases, the tractive force adds to the steering forces in the traction rods such that the inner rod may see a very low force and the outer one very high force. With a pedestal truck, no motion is allowed so the pedestals have greatly different forces acting on them in curves which is not apparent.
Back to the EDI design; so with the relatively soft longitudinal bushings, the axle can steer itself within the limits of travel allowed by the bushing design. A truck of this arrangement may not fully radial steer in 10 degree curves as the steering beam arrangement allows, but it will be able to steer radially in up to 6 or 7 degree curves, which is still beneficial.
This same arrangement in a little different form is used on the EMD GFC fabricated frame bogie used on export locomotives such as GT38AC thru GT46AC. That bogie is available with soft and stiffer bushings depending on the service and customer needs.
In the first EDI arrangement with the cross-beam for the carbody connection, an advantage of the that design is that it transmits the tractive effort into the sidesill where that underframe has enough strength, unlike the traditional EMD underframe design where the strength is mostly in the centersills.
You'll note that none of these newer designs have an inter-connection between the end axles linking steering motion. I'll discuss this in the last installment in this thread.
Thanks for the response.
As well as the EMD associate, the GE associate UGL have developed a similar bogie to the last EDI design.
railknowledgebank.com/Presto/content/Detail.aspx?ctID=MTk4MTRjNDUtNWQ0My00OTBmLTllYWUtZWFjM2U2OTE0ZDY3&rID=MjQ3Mg==&sID=NQ==&ph=VHJ1ZQ==&qcf=MTk4MTRjNDUtNWQ0My00OTBmLTllYWUtZWFjM2U2OTE0ZDY3&bckToL=VHJ1ZQ==
This is called the "Flexicurve".
The paper has some diagrams that might help explain to other readers the considerations in the designs being discussed here.
UGL have not applied this design in Australia yet, all the locomotives (including the C44aci, the competitor to the GT46C-ACe) using a familiar GE export design.
UGL have supplied many trucks for GE export locomotives all over the world, and they must be regarded as successful if not reflecting recent ideas.
Interesting paper Peter. The basic design of the UGL bogie is really no different than the latest EDI and EMD GFC bogie where all have adopted axle guidance via fixed traction rods and soft primary, stiff secondary vertical suspensions. The authors dismiss the radial steering bogies using linkages which serves their purpose but the real world improvement in wheel wear and lateral rail force is well documented in technical papers by EMD and AAR. While it is true that the steering of the axles declines with higher tractive effort, the flange force also declines so flange wear is improved. It's worth noting that locomotives don't spend the majority of their operational time at the limits of adhesion where the friction is saturated. As the paper states, it is true that customers that previously bought GE's Steerable Truck on their locos have gone back to the standard "roller blade" trucks, however, EMD's customers continue to purchase HTCR radial trucks even with a cheaper non-steering version available.
Neatly in the middle between the HTCR and UGL trucks was the Adtranz/Bombardier "FLEXX", as mounted on the Blue Tiger locomotive; this as I recall it was a kind of antithesis of soft primary/stiff secondary (with nested harmonic-breaking primary springing, very long secondary springs, and a traction strut as low physically in the locomotive as possible). There was at one time an interesting technical paper (as I recall, for one of the conferences) that went into design detail, including as I recall the line of development from the Henschel Flexi-Float bogie design, and someone astute may still be able to pull this out of the Wayback Machine.
I can still remember when the Fabreeka-style chevron springs were supposed to be the future of controlled primary suspension...
Overmod Neatly in the middle between the HTCR and UGL trucks was the Adtranz/Bombardier "FLEXX", as mounted on the Blue Tiger locomotive; this as I recall it was a kind of antithesis of soft primary/stiff secondary (with nested harmonic-breaking primary springing, very long secondary springs, and a traction strut as low physically in the locomotive as possible). There was at one time an interesting technical paper (as I recall, for one of the conferences) that went into design detail, including as I recall the line of development from the Henschel Flexi-Float bogie design, and someone astute may still be able to pull this out of the Wayback Machine. I can still remember when the Fabreeka-style chevron springs were supposed to be the future of controlled primary suspension...
The Blue Tiger was a bit of a flash in the pan...
I have a nice HO model of the prototype....
But here is a brochure with a good drawing.
https://web.archive.org/web/20081121082622/http://www.bombardier.com/files/en/supporting_docs/BT-Bogies-FLEXX_Power.pdf
The big flexicoils were very popular as secondary suspension for years.
The long travel secondary springs provide a great vertical ride and low bogie yaw stiffness, but in a 3-axle truck, the short travel primary springs would not work in North America where staggered joints are prevalent, they just can't equalize well enough. Our design criteria for any bogie was to negotiate a 39' staggered rail joint profile with a 3" inverted sine profile. After center axle spring pocket cracking on SD Flexicoil trucks, on Rock Island I believe, the criteria was raised to 4" for switcher applications. Stiff primary just won't make it.
We used to refer to our associate Henschel's Flexi-Float bogie as having a wagon tongue. For higher speeds, the rubber chevron springs do a great job of locating the axle and give high axle lateral stiffness necessary for stability. Our only EMD experience was on the AEM-7 and GM10B ASEA designed trucks. They'd never work here in a 3-axle truck due their short travel, about 1.25". We did try to use them on the HT-B truck but they had a lot of set and drift issues there.
What is the specific history (and experience) of the use of 'chevron springing' on the GP40X HT-B and then laterally on the "Blomberg-P" trucks?
Also -- what's your opinion of the design approach and details in the Alco Hi-Ad trucks, including what might have been done to address their issues with harmonic rock on that kind of severe cross-level profile?
I'm not familiar with "Blomberg-P" designation but assume that is a railfan name for the GP Inclined Rubber suspension truck. That truck was fitted to some Amtrak F40PH's and some of the GP40X's on the Southern IIRC. This was the first attempt to improve the vertical ride of the GP Single Shoe truck introduced with the Dash 2 series. That truck substituted the long used elliptic springs with a pair of rubber compression pads which were shorter than the elliptics, about 5" versus 9" and those allowed the use of a shorter swinghanger, opening up sufficient clearance under the spring plank to the rail to run a slack adjuster connecting the brake levers on each axles 1 and 2. The original design suspension with leaf springs by Mr. Blomberg had 4" of secondary static deflection and 3.25" of primary static deflection. The rubber spring on the new in 1972 compression rubber suspension had only a little more than 1" of static deflection, bringing the total to about 5.25". This absolutely ruined the good vertical ride of the truck, which RR's started complaining about almost immediately. Effort was made to try to change the damping of the new vertical primary dampers that were added to replace the lost damping in the elliptics to improve the ride but it didn't really help. So a design change to the compression rubber was developed. It used a pair of rubber compression/shear pads placed in a chevron arrangement on each side of an new design spring plank. The deflection in the secondary increased to a bit over 2" so the ride was better but not great. This used the same bolster and the long swinghangers but required a new spring plank (the compression rubber used the original bolster and spring plank with some modifications). There were failures of the steel shims embedded in the rubber springs fixed by some mods to the plates and shimming was required as the rubber took a set. At the time, really throughout Dash 2 production, most of the GP orders were Locomotive Rebuild Orders (LRO) which reused as much of the trade-in loco as possible so EMD was doing a robust business rebuilding swinghanger trucks. Since a new, relatively expensive spring plank and springs were required, it wasn't popular with our Sales Dept. Ultimately, the supplier of the elliptic springs was able to make a lower height elliptic spring with fewer but much thicker leafs that had about 2.5" static deflection. This retained the original spring plank for LRO orders although it used the shorter swinghanger. The Low Profile Elliptic springs as they are known at EMD became the new standard GP single shoe truck suspension around 1984 and it gives a reasonably good ride, but still not as good as the original. EMD has sold a lot of the low profile springs as an upgrade since it is relatively easy to replace the compression rubber springs.
The HT-B experience wasn't a great one either. The design was started around 1974 (before my time in the Truck Group) as a way to improve the weight shift performance on the GP line. The standard GP truck has about 84% of it's static axle load on the leading axle at 25% adhesion which is pretty poor. Dofasco had their Zero Weight Transfer truck which I am sure inspired the EMD engineers. With the ZWT truck and the HT-B truck, within each truck there are nearly equal axle loads at all adhesion levels although the lead truck is at about 96% of it's static load at the 25% rating point we used. In both trucks inclined rubber springs are used to focus at the top of rail, in the ZWT they are inboard, in the HT-B they are spread out wider than the journal centers (79" on EMD trucks) on the arms of a cast bolster that pivots on a center bearing that is extended down from the bottom plate to about 24" above the rail. The rubber springs are in the form of chevrons to give the desired combination of lateral, compression, and shear stiffness. The HT-B was first and last used on 10 GP40X's for UP and SP, Santa Fe got standard GP single shoe trucks and the Southern the inclined rubber. The HT-B worked as intended re weight shift but it had some rubber spring failures and lateral ride complaints that could have eventually been solved I'm sure. What killed it was a bunch of factors:
- With Super Series wheelslip control introduced on the GP40X, even though the HT-B weight shift was far superior to the GP truck, head to head adhesion testing showed it offer no benefit in tractive effort; it was theorized the lighter lead axle slipped more but cleaned the rail more effectively for the trailing axles.
- It cost a lot more to produce - with any new design, the suppliers have the ability to charge for the newness compared to the very mature cost of the design in production for 40 years. The factory didn't like fabricating the underframe with the dropped center bearing. The truck assembly was also heavier by several thousand pounds, not a good thing for 4-axle locomotives.
- The biggest drawback was it killed a major cost saving on an LRO order where the GP truck was sent for scrap instead of being reused.
So even though it showed up in GP50 literature as an available option, no RR wanted it and EMD had no desire to produce it after the GP40X's. There was one spare frame in production inventory in 1984 when I bought it to build the first radial test truck.
Overmod Also -- what's your opinion of the design approach and details in the Alco Hi-Ad trucks, including what might have been done to address their issues with harmonic rock on that kind of severe cross-level profile?
I can't say I know the history on that truck so can't really offer any comment.
Bogie_Engineer It's funny you mentioned the truck used on the AEM-7 and GM10B.. The GM10B has always been a very interesting locomotive. 10,000HP on a Bo-Bo-Bo setup. Anything of interest from the type of truck used on it? Why the choice of a Bo-Bo-Bo layout?
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