Western Railroad Discussion > Radial Trucks

I'd like to think that there's still a lot of you out there wondering exactly how these things work.

Try as I might I cannot figure out how the EMD radial trucks are actually capable of "steering" the end axles into a curve as is claimed in all their descriptions. Here are my onservations and questions:

1. I can see that the front and rear axles are connected by visible linkage and inside torque arms going from one side of the truck to the other, but the outside axles have a shock absorber mounted vertically to the truck frame. This would seem to greatly limit horizontal motion of the axles (as in "steering through a curve?")

2. How do the traction motor supports on the truck frame (supposedly rigid) accomodtae any axle and motor displacement which occurs since the other end of the motor is hung on to the axle and geared to it ?

3. I know that these are "bolsterless" trucks and connected to the locomotive frame by four "drivepins." Are they rigidly attached to the locomotive frame, or do the drivepins allow a certain amount of truck swivel (just like kingpins) in a curve
in addition to the axle dispalcement ?

4. Just how much can the axles be displaced ? What happens when they exceed these limit ? I notice there are some loops of chain under each axle attaching them to the truck frame. Does this chain limit the maximum motion or is it just thyere to keep the axle from falling out if the frame is lifted (for maintenance) ?

Would really appreciate some answers from those of you who work on these things.


Regards,

Auburnrail

The EMD HTCR radial (and also the non-radial HTSR) trucks as well as the GE High-Adhesion trucks are "connected" to the locomotive platforms at five points:

A large cast steel "traction pin", welded to the bottom of the platform, extends down about 18-24 inches below the platform. Each truck has a "pin box" in the casting into which the traction pin "sits". The pin and the traction box are actually separated by a round sleeve bearing, I believe material like Kevlar for strength and wear resistance. The traction pin-and-traction box arrangement replaces the historic center plate-and-center bearing arrangement used on older locomotives.

The traction pin only transmits traction-and-braking loads to the platform. That is, only the force produced by the motors in the truck pulling a train and only the braking forces coming from the wheels in that truck due to dynamic braking or independent air brakes. The traction pins do not transmit any "lateral" or side loads such as those from going around a curve.

The four large steel-rubber sandwich "springs" (2 on each side above each "side frame area") actually support the weight of the locomotive body, and also transmit any side or lateral forces between the truck frame and the platform and carbody. Those "springs" are very stiff, the purpose being to minimize the amount of "truck frame tipping" due to high traction or braking forces at the rail.

The purpose for preventing truck frame tipping is to minimize weight transfer at the end axles. When an automobile, for example, accelerates fast, the front end tends to "lift up" and the rear end tends to "drop down". With powered axles in a locomotive truck frame, that would result in the frontmost axle losing some weight, making it more likely to get wheelslip. So all of these high adhesion locomotives (all ACs plus the EMD SD70-series and GE Dash-9s) use truck designs which minimize weight transfer between the axles.

By the way, EMD service people usually refer to those large steel-rubber springs as "elephant feet". Here's a photo of one of those "springs".

---

Go to Electro-Motive Diesel's web site for an explanation of the radial truck:
http://emdiesels.com/en/locomotive/innovations/radial_bogie/index.htm

They have a good color photograph of an HTCR truck from above.

The "elephant feet" pads are the round black objects on top the side frame areas.

They painted the steering linkage reddish-brown to highlight the links.

EMD and GE both have radial self-steering trucks. The general concepts are the same (use of steering linkages, etc.), but I believe each has slightly different specific features as both designs are patented.

As for lateral movement, I believe the center axle in both the EMD and GE radila trucks can have fairly large lateral movement. In fact, have heard that FRA inspectors sometimes erroneously took exception for "excessive lateral movement" because the regulations don't match capabilities of the radial truck designs.

You can see from the EMD web page how the two end axles "swivel" slightly as the truck goes around a curve (they swivel in opposite manner depending on going around a right-hand or left-hand curve) so that the wheels and wheel flanges are more-aligned with the curving rail.

The non-steerable trucks under some of the recent SD70ACe's (I believe the CSX SD70ACe's have non-radial trucks) are similar to the radial truck but simpler, obviously they don't have the necessary steering linkages, arms, etc.

The small "chains" between the EMD truck frame and the journal adapters are simply to keep the entire wheel-and-motor from dropping out of position if the locomotive is picked-up as in rerailing.

Thanks for some of the the explanations. I have seen the diagram on the EMD website, however it still does not answer some of my questions:

> How the traction motors can pivot on their supports on the truck frame ?
> Just how far can the axles pivot ? Remember there are both coil springs and
a vertical shock absorber constraining them.
> Does the drive pin arrangement allow for the truck to swivel slightly, or is all the swiveling (around curves) done by displacement of the axles ?

Thanks in advance

Auburnrail

When curving, the truck frame actually rotates around the traction pin, and the end axles swivel quite a bit.

The axles can "rotate" relative to the truck frame itself because they are not constrained inside "journal pedestals" like on an HTC truck under an SD40-2 or SD60. There is a fair amount of "play" or "freedom to move" rotationally at the journal bearing area at the end of each axle.

What keeps the axles from going way of out alighnment is the various linkages which keep the axles aligned properly on straight track and allowing swiveling of the proper amount on curved track.

When an end axle swivels or rotates slightly, the traction motor of course also has to rotate slightly, as you note. Each motor is supported at two points: (1) on the axle itself (there are two large roller bearings riding on the axle between the wheels) and (2) at the traction motor support arm at the opposite end of the motor, where the motor is hung from the truck frame itself. Those links are called "dogbones" 'cause they look just like a dogbone only forged out of high-strength steel. The top and bottom ends of the dogbone links are equipped with spherical bearings (like a roller bearing only with additional "degrees of freedom") which allow the motor-and-link to swivel slightly relative to the truck frame. Go back to the color photo on the EMD web site .. you can se the bottom of the dogbone link closest to the camera, at the bottom of the truck below the crosswise casting part called the transom.

Very informative--thanks!

What looks like the center pin isn't weight bearing, like the centerplate of a standard truck, but rather servers as a refrence point to adjust the angularity of the axles as the truck swivels. The weight of the locomotive is carried by those rubber pads on the side frames.

On the EMD page, if you look at the bottom of the first traction motor, there is a vertical dog-bone like affair connecting it to the truck frame. This is what has replaced the traction motor nose pack, and contrary to what EMD asserts, it will need inspecting because it will wear out (it does have a lot fewer wearing parts). What the page doesn't explain is how the buff forces are transmitted between the wheels and the locomotive carbody.

The J. G. Brill Co developed radial trucks over 100 years ago along similar principles, but they were for streetcars. The radial locomotive trucks are bolsterless. The US transit industry gave up on bolsterless trucks over 100 years ago, and the Boeing Co proved the point with their bolsterless center trucks on their LRVs of the 1970s. How are these things going to track when they are worn out?

greendot Wrote:
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> The four large steel-rubber sandwich "springs" (2
> on each side above each "side frame area")
> actually support the weight of the locomotive
> body, and also transmit any side or lateral forces
> between the truck frame and the platform and
> carbody. Those "springs" are very stiff, the
> purpose being to minimize the amount of "truck
> frame tipping" due to high traction or braking
> forces at the rail.

The are relatively stiff in the vertical direction but relatively compliant or soft in the horizontal direction. This is what allows the truck to rotate.

Where on the EMD webpage photo is the "pin box"?

In the video "995 Days", about the electrification and construction of the Tumbler Ridge line in British Columbia, it's mentioned in passing that the new coal gons were equipped with Dressler (sp?) radial self-steering trucks, made under license by CN. Does anybody know more about these? It would seem to be a good idea on unit trains. Also, it's interesting how CN, among a few other roads, order their GEs with radial trucks, but most (like BNSF) do not.

The truck you are referring to is the Dresser DR-1 which was designed and patented by Harold List in the mid 70's. Dresser went out of the truck casting business in the early 80's and the rights to the List patent were purchased by American Steel Foundries (ASF) who renamed the truck the AR-1 and still offers it today. Here's a link: http://www.amstedrail.com/freightcar/ar1.asp Harold List passed away in 1992. The AR-1 steers very well but has not been a commercial success in North America. The negatives are that the truck weighs more due to the addition of the steering arms and has a premium price. Since most cars today are purchased by leasing companies or shippers, the only benefit accruing to the car owner relates to truck maintenance costs and wheel wear savings. The railroads pocket the fuel savings from lower rolling resistance and the rail wear savings in the curves rather than share any savings with the car owner. Unless they were mandated by the AAR, radial trucks won't sell until the economics favor the car buyer. NS has some coal cars equipped and there is the fleet that was in the in the Tumbler Ridge service. ASF has sold more AR-1's to the Egyptian railway than in the US.

greendot has done a good job describing the general workings of the EMD HTCR radial truck. The comments below though need correcting:


InsideObserver Wrote:
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> What looks like the center pin isn't weight
> bearing, like the centerplate of a standard truck,
> but rather servers as a reference point to adjust
> the angularity of the axles as the truck swivels.
> The weight of the locomotive is carried by those
> rubber pads on the side frames.

There is no connection that links truck frame rotation to axle rotation as implied by the above. That type of truck would be referred to as forced steering, which describes neither the EMD radial truck or the GE steerable truck. On both the EMD and GE trucks, the axles are self-steering meaning that they adjust their alignment to the rails based on the forces that develop due to the wheel taper and rail profile at the contact patch. The end axles are rotationally coupled to enhance both the truck stability against hunting as well as to balance the steering forces for best performance. The truck frame swivels independently but based on the forces the axles impart to the truck frame. The traction post transmits only traction and braking forces as InsideObserver and greendot note. On EMD's truck, the truck frame is free to move laterally, within limits, by the four bar linkage connecting the truck frame and traction post. On GE's HiAd and steerable trucks, the post engages a box that is constrained through rubber pads to the truck casting which surrounds it. On both EMD and GE trucks, four rubber springs support the locomotive weight directly and provide a yaw, or rotational, resistance that tries to center the truck and also provide the lateral secondary stiffness. On the EMD truck, there is a combination lateral and rotational stop between the truck frame and the underframe that limits the lateral motion to +/- 1.75" and the rotation to less than +/- 7 degrees. GE uses a somewhat different stop configuration.

>
> On the EMD page, if you look at the bottom of the
> first traction motor, there is a vertical dog-bone
> like affair connecting it to the truck frame.
> This is what has replaced the traction motor nose
> pack, and contrary to what EMD asserts, it will
> need inspecting because it will wear out (it does
> have a lot fewer wearing parts). What the page
> doesn't explain is how the buff forces are
> transmitted between the wheels and the locomotive
> carbody.

The EMD traction motor nose link has a rubber bushing at each end that transmits the torque of the traction motor and dynamic forces as well as allows the motor to move laterally and yaw with respect to the truck frame. There are no friction interfaces as the previous nose pack arrangement included. Of course all parts of any truck require period inspection, but service history has shown that the EMD nose link can go over 1 million miles between bushing changeouts.

On the EMD HTCR truck, the traction and braking forces developed at the wheels are transmitted to the truck frame through traction rods that connect the journal bearing adapters to the steering beams positioned inboard of the end axles. The steering beams, one of which can be seen painted red in the EMD photo, are pivoted in their centers at the connections to the truck frame. So the steering beams let the axles rotate with respect to the truck frame but constrain them longitudinally. The axle does have lateral freedom but there are stops on top of each bearing adapter that engage the truck frame allowing a very small movement laterally at the end axles. On the top end of each steering beam is a crank arm - the crank arms are connected by the link that spans diagonally accross the top of the center traction motor. The orientation of the crank arms forces the end axles to rotate equally in opposite directions. The steering beams have rotational stops to the truck frame so that axle rotational movement is limited to a little more than +/- 1 degree, which is adequate for all but the tightest curves. As greendot notes, the middle axle has a large (+/-5/8") lateral freedom with respect to the truck frame but it has no freedom to rotate, as those traction rods connect directly to the truck frame.

The trasmission of the traction and braking forces from the truck frame to the underframe is through the traction post on the carbody and the linkage it engages which connects to the truck frame, as described above.

>
> The J. G. Brill Co developed radial trucks over
> 100 years ago along similar principles, but they
> were for streetcars. The radial locomotive trucks
> are bolsterless. The US transit industry gave up
> on bolsterless trucks over 100 years ago, and the
> Boeing Co proved the point with their bolsterless
> center trucks on their LRVs of the 1970s. How are
> these things going to track when they are worn
> out?


The Brill trucks coupled truck yaw to force axle yaw so they are forced steering trucks, IIRC. Both EMD and GE have delivered thousands of locomotives over the last 15 years that are bolsterless so it is well proven that they are safe over their life. Conventional pedestal trucks require rebuild after 500,000 - 800,000 miles that involves weld buildup of pedestals and grinding or remachining to restore performance. The EMD trucks require only changeout of rubber bushings and bolt-on wearplates and service is showing they can go well over 1 million miles to overhaul. The hydraulic shock absorbers are the only parts that may need earlier replacement, although the Koni dampers have shown a very long service life compared to earlier designs.

If you are interested to learn more, these patents describe the GE and EMD trucks and have illustrations that match the production trucks quite well.

The patent for the GE steerable truck is here (patent no. 5,613,444):
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,613,444.PN.&OS=PN/5,613,444&RS=PN/5,613,444

The patent for the EMD HTCR radial truck is here (patent no. 4,765,250):
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,765,250.PN.&OS=PN/4,765,250&RS=PN/4,765,250

When you study these two patents you can see how much simpler the EMD truck is compared to the GE truck.


The List patent on the ASF AR-1 radial freight car truck is here (patent no. 4,131,069):
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,131,069.PN.&OS=PN/4,131,069&RS=PN/4,131,069

The List patent covers many variations, some forced steering but Figure 13 shows the AR-1 self-steering configuration.

On all of the patents, there is an Images button at the top of the page that takes you to the patent document with all the drawings. If you don't have a tiff viewer, you will need to install one - this one works well:
http://www.alternatiff.com/

The SD-90's with radial trucks tore the crap out of that railroad.  I was there and saw it.  Lots of very curve worn 90lb stick rail up there...

Earlk Wrote:
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> The SD-90's with radial trucks tore the crap out
> of that railroad.  I was there and saw it.  Lots
> of very curve worn 90lb stick rail up there...

What railroad ?

Earlk Wrote:
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> The SD-90's with radial trucks tore the crap out
> of that railroad.  I was there and saw it.  Lots
> of very curve worn 90lb stick rail up there...

It would be so nice if people would bother to pay attention to what they are responding to, and where...

He is referring to this thread.

Colorado Pacific Rio Grande RR 27 March 2024 of 3-27-24

Earlk Wrote:
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> The SD-90's with radial trucks tore the crap out
> of that railroad.  I was there and saw it.  Lots
> of very curve worn 90lb stick rail up there...

And that surprised you? Why?

The line was perfect for 120 ton F-units, with
short length and four axle trucks. Changing out the
trucks on a SD90 from HTCR to early Flexicoil three
axle trucks would just change the problem from curve
wear to derailments when the locomotives rolled
the outside rail on curves. It just wasn't the right
locomotive for the job. The GT42CU-AC as built for 
Queensland Rail in Australia but on standard gauge
trucks would be perfect for the job. They weigh 130 
tons on six axles, have AC traction, dynamic brakes,
and HTCR trucks.

did those f40 slugs work out down there?