Engineers and Mechanics Encyclopedia 1839: Railways: Robert Stephenson
The extraordinary friction and resistance between the flanges of the wheels of a locomotive engine, and the edges of the rails, in passing round curves, unless the radii be very considerable, struck forcibly the attention of Robert Stephenson, who succeeded in devising a very ingenious mode of obviating it, which he patented on the 25d of January, 1826.
The following description of it is extracted from the Register of Arts:-
"Instead of two wheels, used as usual to the extremities of one axletree, Mr. Stephenson's plan is to have a separate axletree to each wheel, so that they may revolve independently, and at different velocities, as circumstances may require. The outer wheels of a four-wheeled carriage (or those which are on the longest of two curved parallel lines) will therefore be at liberty to run faster than those on the inner side (or on the shortest line), thereby preventing that sliding motion, and its destructive effects, when passing round curves, which, on extensive lines of road, are generally found unavoidable.
Mr. Stephenson's improvements in axles likewise embrace another object of more momentous importance, that of providing a remedy for the unequal strain to which a carriage is subjected in passing over those parts of a railway that lie hollow, or below the level of the contiguous parts, owing to the sleeper, or other supports having sunk or given way, which causes the carriage and its load sometimes to rest upon three wheels instead of four, producing undue strains or fractures, and at other times causing the carriage to pass off the rails.
To provide against these circumstances, the axletree of each wheel turns, in a fixed bearing, which is bolted to the frame of a carriage: this bearing, instead of having a circular aperture for the axle to turn in, has a long vertical slot, in which the axle can rise tip and down, as may suit the undulations or imperfections of the line of rail. This, however, could not take place, unless the opposite . extremity of the axletree moved upon a universal joint, which Mr. Stephenson has adopted, giving the preference to the ball and socket for that purpose, on account of its strength and simplicity.
Fig. 1 exhibits a plan of a carriage-frame, with its wheels and axletrees; and Fig. 2 a side elevation or section, as seen from the interior of the frame. Similar letters of reference in each figure indicate corresponding parts: a-a shows the frame of the carriage; b-c-b-c the four tapered axletrees, having at the small end of each a globular knob, revolving in a hollow spherical socket, as seen at e-e-e-e.
In Fig. 2 the bearings f-f are shown bolted to the carriage-frame a; at g, the axletree is seen. in the upper part of the bearing; and at h, the axletree is shown to have fallen down the slot, allowing the wheel to accommodate itself to the sunken part of the rail i.
In this last contrivance the wheel alone is supported, and the carriage has still to sustain the unequal pressure, owing to its resting upon three wheels. The chief advantage that results from it, is in keeping the wheel always on the rail; because, if the hollow was so great as to allow the flanch to rise above the surface of the rail, the carriage might in its progress be thrown over, producing very serious consequences. An accident of this kind recently occurred to the new locomotive carriage of Braithwaite and Ericsson (the "William the Fourth"), on the Liverpool and Manchester Railway, by which it was very nearly thrown down a deep precipice; proving the necessity of some contrivance to effect the object aimed at by Mr. Stephenson's arrangement.
We have already described, at page 477, a patented improvement by Robert Stephenson on the axletrees of railway carriages. At the period we are now treating of, another invention, from the same celebrated engineer, presents itself to our notice; it is dated the 11th of March 1831, and is entitled, “Improvement in the axles and parts which form the bearings at the centres of wheels, which are to travel upon edge railways."
In order to produce rotation in the wheels, and consequently progression of locomotive carriages, it is necessary to fix the wheels on the ends of the axles, and when this fixture is effected in the usual manner, the weight of the carriage and its contents is supported by concave bearings resting on the upper surfaces of the cylindrical ends of the axles, and hence arises a difficulty in keeping the rubbing parts constantly lubricated, as the oil supplied to the parts in contact will have a tendency to escape by its gravity to a more open space on the looser sides of the axles; and the consequence of this is, considerable waste of oil, with an imperfect lubrication.
To remedy this, Mr. Stephenson employs for each pair of wheels, a double axle, consisting of a hollow casing, on the extremities of which the wheels are firmly fixed, and a solid axis passing through the hollow casing, and supporting on its ends the weight of the carriage, through the medium of hollow bearings attached to springs of the usual construction, which connects the bearings with the side rails of the carriage, placed necessarily on the outside of the wheels. Thus the supporters or wheels being fixed to the concave parts of the bearings, and the supported weight or carriage being connected with the convex or solid part of the bearings, the oil will have a tendency by its gravity to accumulate on the rubbing parts, and thus combine a perfect lubrication with an economical supply of lubricating material.
The solid axles are made thickest near their extremities, so that the parts which pass through those portions of the hollow axles which are fixed into the naves of the wheels, and at the same time the apertures of the corresponding parts of the hollow axles, are diminished, both being turned perfectly cylindrical, that they may be fitted together with facility, and come into contact only where the bearings are intended to take place.