As a locomotive rounds a curve the wheels on the outside of the curve turn faster than the wheels on the inside of the curve. So do the push rods that power the outside wheels also move faster than the pushrods on the inside of the curve, or is there some mechanism to compensate (similar to a differential in an automobile)?
Ulrich As a locomotive rounds a curve the wheels on the outside of the curve turn faster than the wheels on the inside of the curve. So do the push rods that power the outside wheels also move faster than the pushrods on the inside of the curve, or is there some mechanism to compensate (similar to a differential in an automobile)?
The compensation is in the cone shaped of the wheel treads shifting to a larger diameter on the outside rail and a smaller diameter on the inside rail as the wheelset naturally moves to the outside when rounding a curve. The wheels are pressed onto the axles the same as on rolling stock, so there can be no differing of rotation speed between one wheel and it opposite wheel.
There may, however, be some more fine points to the explanation that others might be able to supply. I recall reading that diesel locomotive wheel treads have either less taper than rail cars, or have no taper. I am not sure about steam locomotives. If this is true, I would like to know why these powered wheels lack taper.
To my eye, the blind drivers on steam locomotives that have them appear to lack taper on the tread.
For any given combination of track gauge - wheel gauge = max. allowable sideways motion, and wheel tread taper, there is only 1 radius of curve that will perfectly accomodate the effective difference in the wheel tread diameters, and which will not require a different speed or distance on one wheel or the other. In either of those other cases - sharper or shallower curve - one wheel or the other will have to slip a little bit. That would be faciltiated by the cyclically varying nature of the pulsating driving force, and the "dynamic augment" of the rising and falling drive rods alternately increasing and decreasing the effective weight for traction on each wheel.
I believe the standard taper for freight cars is 1:20, and 1:40 for passenger cars - but I have no info on that for locomotives generally, or the "blind drivers' specifically (other than I don't know how anyone would be able to recognize or identify a taper without getting up real close with an appropriate gauge). Somewhat surprisingly, I understand that the shallower taper tends to resist "truck hunting' more than the steeper taper. (If I got any of this right, credit goes to oltmannd/ Don here; if not, the blame goes to me.) In accordance with that last, perhaps flat blind drivers makes sense, to minimize lateral motions ?
- Paul North.
The "blind" drivers are without flanges to allow the basically rigid wheel base of steam locomotive drivers to be able to negotiate tight curves. A 2-10-0, for example might have the #3 drivers blind, so their flanges would not bind in a curve.
I am not sure of all the criteria for blind drivers, but I think they were a rather unique design feature that was applied to narrow gage locomotives that had to deal with relatively sharp curves, and smaller standard gage locomotives that might be used on logging or industrial railroads. The blind drivers would have to be confined to the inner drivers of a set, of course.
Bucyrus ... and smaller standard gage locomotives that might be used on logging or industrial railroads. The blind drivers would have to be confined to the inner drivers of a set, of course.
... and smaller standard gage locomotives that might be used on logging or industrial railroads. The blind drivers would have to be confined to the inner drivers of a set, of course.
Right you are. There is a now-retired Mikado in Woss, British Columbia (on the Island) whose center two drivers are blind....leaving only the outer two flanged to guide the locomotive.
Crandell
And also some mainline locomotives. UP's 4-12-2's had blind drivers on their 3rd & 4th axles, per - http://www.steamlocomotive.com/4-12-2/ Maybe some others with similar many axles and/ or long rigid wheelbases.
One item related to this that I haven't seen discussed before is that steam and diesel locomotives apply their maximum forces at different points in the same curve. When we were living at Hatton, SK from '53 to '56 CP was in the process of realigning the curves on the mainline to accommodate the newly arriving diesels. I don't remember or understand all of the details, but it meant small adjustments to the ROW both going into and out of the apex of the curves.
It used to be said that steam engines were brutally hard on curves, but it turned out that diesels were almost as hard on curves, only in different spots.
Bruce
So shovel the coal, let this rattler roll.
"A Train is a Place Going Somewhere" CP Rail Public Timetable
"O. S. Irricana"
. . . __ . ______
Our community is FREE to join. To participate you must either login or register for an account.