Has there ever been a study on redesigning the rail car wheel/axle so that each wheel runs on it’s own bearing on a stationary axle instead of the present setup? My thinking is that whenever the wheel/axle has to go around a curve, either the inside or the outside wheel has to slip on the rail causing rail/wheel wear. If the two wheels rolled independently of one another, this wear would not exist. I realize that a wheelset with a traction motor or a single disc brake rotor attached would require the present setup to work properly.
Look at the cross-section of a rail wheel it is not cylindrical but rather conical (cone shaped). As the wheel goes around a curve the wheel and its axle moves slightly to the outside of the curve. This moves the contact portion of the outer wheel closer to the rim and onto a section of the wheel with a larger diameter, at the same time the wheel on the inside rail is moved away from the rim onto a section of the wheel with a smaller diameter. Because the wheels now effectively have different diameters, the wheel on the outside will travel a greater distance for each revolution of the axle than the wheel on the inside.
To expand on what beaulieu said - On a dry day I can get a pretty good feel for wheel slippage on curves on our line. Up to about 2 degrees of curvature, you generally won’t hear anything.
On our 4 and 5.5 degree curves, there’s squealing aplenty - an indication that one or the other wheel is slipping.
Short of sidings, yard tracks, and some branches, you won’t find many curves that sharp on a Class 1 railroad.
There is a great deal of science and study that has been devoted to this question. See publications from TTCI, the Wheel/Rail Interface seminars put on by Advanced Rail Management and suppliers of rail lubrications systems such as Portec among others.
Lubrication is one fo the easiest ways to address this and in higher speed/ higher tonnage areas, this lubrication is moving towards top of rail rather than with gauge face lubrication. As noted above, the squeal is an indication of stress. On the top of rail this is where the wheel is trying to rotate around a vertical axis (torsion) in addition to traversing the horizontal curve of the track. This causes stress in the head of the rail which can lead to small cracks which can then develop into complete fractures.
Grinding of the rail head is another, though more expensive, means to address this issue. This is what is typically done to remove those shallow stress cracks from the torsional load of the wheel. Since it is easier to shape the rail head to an “average” wheel shape than try to re-shape every possible wheel that runs on it, you see a lot of effort directed to determining the optimum contour. This will vary based on type of service. UP’s triple track across Nebraska may need a different profile than Caltrain’s passenger line in California for example.
Close observation of wheels is equally important. UP pays a lot of attention to the wheel sets on the fleets of coal hoppers running and their owners typically have very good wheel maintenance specifications. Equally, systems with relatively captured equipment (Caltrain, Metra, etc) will also pay close attention to their wheels and have prgrams for truing, etc.
This only deals with the system as we have it now and does not answer the original thought about individual wheels without a common axle as a means to address this question. I have no good answer for that other than to note historical precedents where such systems have been used (Europe mostly?) and t
With no good answer to the problem, have any absurd solutions been put forth producing a Rube Goldberg humorous result?
I was going to make a joke about reinventing the wheel, but…
Guess I did.
Most locomotives now carry a Greaer for the Flanges now. It is a Stick of Solid Graphite mixed with a Grease of some sort that wears down and is repalaced at intervals. Keeps the Flanges lubed up and the friction down also.
Isn’t this problem solved by the Talgo, with each wheel turning separately? I believe that the reduced wear, to both wheel and rail, is one of the “selling points” of the unconventional Talgo system.
Talgo wheels do turn separately; but the wheels lose the self-truing effect of a conical tread and connecting axle. This apparently leads to a degree of lateral motion and substantial flange wear that is somewhat mitigated by the lighter wheel load while the u-frame (yoke) connecting the wheels has considerable unsprung mass. Perhaps the inertia of the coach and wheel-rail contact area help keep the wheels on a generally true course. Soft air springs dampen dynamic forces from the wheels to the coach body.
Talgos generally come with the recommended wheel truing and change-out facilities and require more attention than ordinary train wheels.
The Talgo system without an axle allows the car body to be lower without the axle intruding into the passenger space, at a cost of two additional bearings it works well for locomotive hauled passenger trains, not so good for EMUs and DMUs.
The tapered wheel tread solves this problem. When going around a curve the wheels shift on the rails so that the inner wheel runs on a shorter radius than the outer. Not perfect but it has been working a long time. The United Aircraft Turbotrains had free individual wheels as do the Talgos but this was more to accomdate the low floor level rather than for wheel wear. The Turboliners had cylindrical wheel treads. Wheel wear was never a problem although they used “B” hardness wheels. as opposed to the softer"C" wheels used in freight service.