Edit post

Edit your reply below.

Post Body
Enter your post below.
[quote]QUOTE: Originally posted by Overmod There's nothing about the inherent design of the American 'three-piece freight truck' that prevents high speed... it needs different and better damping. Look at the trucks on the MHCs, for example. Much of the "multiple suspension" requirement on passenger cars has to do with improving ride quality as perceived by the passengers, or implementing better carbody tilt or roll control; these are of far less importance on freight equipment. The equalization characteristics of three-piece trucks are inherently excellent; if I recall correctly, some of the early UP streamliners used Taylor-style trucks (which are essentially a glorified three-piece design). There are ways to implement longitudinal damping (e.g. viscous coupling) between the bolster and carbody pivots, which will interrupt the kinds of resonance causing the yaw component of hunting (and which are not difficult to retrofit to existing designs of rolling stock). Torque struts and rods can be used from bolster to sideframes if desired, or across the ends of the truck between sideframes (with rubber bushings at each end) if more force attenuation is desired in any plane of truck action. In the past, it's been desirable to use a longer truck wheelbase for stability, but this inherently causes greater wheel (and track) wear on curves. There have been designs for steerable freight bogies, but the cost and maintenance limitations on these (and the fact that most types don't 'fail safe' if their linkages fail or are bent) will clearly restrict their use in interchange service until a 'critical mass' of parts, service locations, know-how and general awareness has built up. Braking becomes a much more critical factor than dynamic stability at speeds much above 60mph -- remember that kinetic energy roughly doubles between 60 and 80mph. Imho single-acting tread brakes don't cut it... and the logical alternative, cheek-plate disc braking, is expensive and somewhat difficult to apply to these trucks and, perhaps more importantly, traditional American chilled wheel profiles. (For example, applying the disc to the wheel both requires location points, which are stress raisers, and hides the wheel face behind the disc, which makes inspection for cracks and defects originating from those raisers difficult to detect) My opinion is that some form of multiple center-of-axle disc brake, similar in principle to that applied to passenger cars, may be the answer (with the caliper floating vertically, on a bracket close to the truck bolster, which helps absorb torque displacement of the sideframes on braking, and allows use of conventional carbody-mounted brake cylinders and reach rods) -- I've checked with the wheel shop adjacent to the Arkansas Railroad Museum and they see little objective difficulty in sourcing and servicing brake discs at the time wheelsets are renewed. I might add (plug) that I've developed in principle a system to implement semi-ECP braking on standard interchange freight consists, using devices similar to FREDs that connect into the train line at intervals and use buff-and-draft sensors that fit between couplers. This was originally intended to make fast-acting PTC workable on long freight consists, but is perfectly suited for the high-speed service that PTC and PTS would make legal... It might be desirable to put some additional castings or fittings on the trucks, for example to keep the sideframes from separating from the bolsters and wheel bearing casings after impacts or derailments. I believe that tension straps of modern materials could accompli***his easily (and be relatively easy safety retrofits to existing trucks, too, which expands the market and brings down effective marginal cost). But none of this stuff (while it *is* at least in part derived from rocket science) is particularly difficult, or requires expensive capitalization that only applies to boutique high-speed service. In my opinion, air resistance constitutes a logical economic upper bound to most freight service speed well below the critical speed of three-piece truck designs with proper detailing... [/quote] Overmod, I think you were the one who told be this some time back, but is it true that the single axle trucks naturally resist hunting? If I remember correctly, the problems with cars like the TTOX and TTFX Four Runner were with inflexibility through tight yard trackage, rail wear due to the 36' wheelbase ( I understand the TTOX's had some curving flexibility but not a true radial steering mechanism), and of course too light tare weight which could cause pull over on curves. That being said, was it your conclusion that such single axle designs were actually better for high speed service? With larger wheels and journals to bear greater load weight (and adding a little more to the tare), an extended platform to handle 53' trailers, and radial steering, these cars could be apt for high speed intermodal.
Tags (Optional)
Tags are keywords that get attached to your post. They are used to categorize your submission and make it easier to search for. To add tags to your post type a tag into the box below and click the "Add Tag" button.
Add Tag