SD70Dude Off topic, but what exactly were the problems with those? I've never heard the story from someone 'in the know'.
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.
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.
Dave
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.
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.
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).
Greetings from Alberta
-an Articulate Malcontent
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
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.
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).
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.
There are also effects on the coned-tread-wheel and railhead interaction, and on the way the axles try to 'steer' the truck frame.
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...
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.
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.
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.
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.
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?
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
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