Radial Trucks

[Anonymous]

I have been searching the entire internet on how radial trucks work with no success. I understand what happens, but mechanically, i have no real understanding. Does anyone have a drawing of the mechanics behind it?

[Cheviot Hill]

Try this one. I think it might be what your looking for. http://onlinepubs.trb.org/onlinepuds/trnews/rpo/rpo.trn134.pdf

Try this it should work better for you. http://trb.org/publications/trnews/rpo/rpo.trn134.pdf

[nanaimo73]

http://www.gmemd.com/en/locomotive/innovations/radial_bogie/index.htm

[Paul Milenkovic]

Don't have links to particularly good drawings, but the basic idea is that to steer the axles in a "radial direction" (point the axle shafts at the center of the curve you are on). If you are on a leftward curve, you need to allow the front axle to pivot left and have the back axle pivot an equal and opposite amount right. You can search freepatentsonline or ep.espacenet.com (European patent database) for "radial truck" or "steering truck" and come up with a lot of drawings of different designs to do this.

One approach to radial steering is to link opposite journal boxes of neighboring axles with a rod -- the right journal of the front axle is connected to the left journal of the back axle by a rod, connected at each journal through ball joints. If the front axle steers left, the right side of the axle moves forward, dragging the left side of the back axle forward by tugging on the rod, which steers the back axle right.

Another approach is to connect journal boxes on the same side through an "equal and opposite displacement" linkage -- if the left front journal moves back, you want the left rear journal to be tugged forward. A common way to do this is something derived from Watt's link -- an approximate straight-line mechanism invented by the James Watt of steam engine fame. The Watt's link has two rods joined by a central crank that pivots about the middle. If the central crank rotates one way, the two rods will push in towards the central crank; if the central crank rotates the other way, the two rods will push outwards by equal amounts -- this produces the desired equal-and-opposite motion of the same-side journal boxes.

The actual Watt's link is meant to have the ends of the two rods fixed, constraining the pivot point of the central crank to move in nearly a straight line. Watt used this on rocking beam steam engine and Ford uses this on the rear axle suspension for the Crown Victoria Police Interceptor. The adaptation for radial steering has the pivot point fixed and allows the ends of the two rods to move in opposition. The guided-axle Talgo train uses the Watt's link in this way as does a number of patented radial-steering trucks. Some of the patents have the central crank arranged in a vertical plane, others in a horizontal plane, but these trucks work on much the same principle.

Another distinction in radial trucks is between self-steer and forced-steer. The self-steer trucks relies on the natural steering of a solid-axle wheelset with cone-shaped wheel taper, but links a pair of axles to steer together in opposition, suppressing the natural instability of the self-steering wheelset. The forced-steer truck adds another constraint -- as the car or locomotive goes around a curve, the truck and hence the truck bolster will pivot relative to the car body, and this displacement operates a crank to fix or force the amount of opposite displacement of the two axles.

The forced-steer truck adds complexity -- not only do the axles have to pivot in opposition but the amount they pivot has to be controlled by the yaw angle of the truck bolster relative to the car body. The perceived advantage of forced-steer is that it further constrains the axles against the unstable natural-steering tendencies and suppresses hunting and is a better high-speed design. The EMD radial truck is a self-steer as freight locomotives don't go that fast. The SIG truck is a forced-steer as it is intended for high-speed passenger equipment.

By the way, the non-steering truck also allows the axles to negotiate curves in a radial direction -- a non-steering truck requires give in the journal box connections to allow the natural steering of each wheel set to align it radially -- if you don't have that give, you are going to be up on the flanges all the time. The problem is that to suppress hunting at high speeds, the journal to side frame connection has to be quite stiff, and this results in wear because you are resisting the natural steering tendency of the wheelset. What the radial-steering truck is supposed to do is make the truck stiff against hunting but allow the wheels to assume a radial alignment with less resistance, resulting in a high-speed truck with much less wear.

Talgo works on similar principles -- the whole Talgo train set is one big multi-axle radial-steer truck -- and Talgo makes similar claims of reduced war. Talgo also allows the two wheels to rotate independently as do some streetcar designs about their axle, unlike every other train (the guided-axle Turbo Train has a rigid connection between the two wheels). There is some controversy has to how Talgo stays off the flanges as a consequence.

If you Google Talgo and look for pictures of the axle-guiding mechanism, the equal-and-opposite displacement of rods about the central crank will be apparent, and all of the same side connected radial trucks work the same way.

[jwillard44]

QUOTE: Originally posted by Paul Milenkovic

Talgo works on similar principles -- the whole Talgo train set is one big multi-axle radial-steer truck -- and Talgo makes similar claims of reduced war.

* I have always been impressed with the Talgo train, but this is an unexpected bonus - "Reduced war!"[:)]

[Hugh Jampton]

QUOTE: Originally posted by jwillard44

QUOTE: Originally posted by Paul Milenkovic

Talgo works on similar principles -- the whole Talgo train set is one big multi-axle radial-steer truck -- and Talgo makes similar claims of reduced war.

* I have always been impressed with the Talgo train, but this is an unexpected bonus - "Reduced war!"[:)]

Maybe they should sell Talgos to Iraq..

[Anonymous]

Paul, an excellent description of how this equipment works. Thanks.

[Anonymous]

Paul, great explaination. Thanks.
K

[STCALRR]

I am surprised how many of the readers picked up on teh claim for reduced war, as it was far down in the discussion. It tells me that it the post was sufficiently well written to be both interesting and technically informative.
Yet it still may be something we can all agree is good: reduced war!
[:)]