Looking back
passenger train
individually and press fitted to the axles. The final process was to put the complete wheelset in a lathe, where both treads were turned to a conical taper (usually 1 in 20). The finished wheelset was lifted from the lathe, placed on some rails and rolled away. They went to examine the newly turned treads and found they each had a shallow groove down the centre. The weight of just the wheelset acting on the point contacts between wheel and rail had deformed the steel surface. A number of wheelsets were given identifying marks and followed as they were put under wagons and into service.
The groove deepened and spread across the tread and, after only some 100 km (60 miles), became a stable and consistent slightly hollow shape. The steel surface had become work-hardened by the rolling process. The tread shape and the wheel diameters were carefully measured as mileage built up. After the initial deformation, no further diameter or shape changes were measurable as the distance travelled built up to 16,000 km (10,000 miles). At this point, in accordance
with standard railway practice, the hollow tread was inspected against a 1 in 20 taper and pronounced ‘worn’. The wheelsets were taken away to be re-turned to their original taper. Clearly the inspection was not measuring real wear but only the results of the original deformation. All trains run on ‘worn’ wheels and the model of coned wheel steering was inappropriate.
The research team designed a tread with a double cone, so that it was slightly convex. Wheels machined to this shape were run under test trains and their treads deformed into a less hollow work-hardened shape, which was carefully measured to use as the basis of new dynamic equations for the analysis of railway suspensions. After several prototypes were tested, a new suspension for 4-wheel wagons, with leaf springs and hydraulic dampers, was developed and given extensive testing. Instrumented wagons were attached to the rear of passenger trains running at speeds up to 145 km/h (90 mph), with no instability. Some test wagons were run without their wheels being re-turned and
reached 260,000 km (165,000 miles) before there was any measurable wear. This work has led to a new, faster fleet of freight vehicles.
Early in the research it was noted that if 4-wheel freight wagons could be made to run faster, then so could 4-wheel bogies under passenger trains and the advanced passenger train was born. Analysis showed that a train, with appropriate suspension characteristics, should be able to run safely at least 50% faster on straight track and 40% faster on curves than current passenger rolling stock for any given speed restriction without any track modification. Since track curves were not banked, or ‘canted’, for these speeds, it would be necessary to tilt the trains for passenger comfort. Existing research papers indicated that the tilt should be enough to completely compensate for this ‘cant deficiency’. With a top speed of 250 kph (155 mph), this would require a maximum tilt of 9°. Since the train had to stay within the restrictive BR loading gauge, the amount of tilt constrained the maximum cross-section of the train. At that time, the Japanese and French TGV solution,
At around 55 mph the 4-wheel suspension began oscillating from side to side with the wheel flanges striking sparks from the rails.
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