Have you ever wondered what keeps the train on the track? How does a train follow the track during a circular path? After all, there is no steering nor a differential in a train. As a matter of fact, the wheels on either side are connected through an axle which makes them rotate with the same angular velocity
Many of us would think that the flanges on the wheels would do the job. But that is not the answer.
The flanges are just a safety device. If the flanges rub against the track, it gives a horrible noise and it is a huge waste of energy. Moreover, there will be wear of tracks and wheels.
The flanges are a secondary mechanism just in case the real mechanism fails
There is something fundamentally different in the design of wheels of a train and an automobile.
So, why is it different on a train?
- Unlike a normal locomotive, trains have a huge body
- Trains don’t make sharp turns like an automobile
Hence adding a differential would be a potential waste of resources.
So, how does it go around a corner? The solution is simple and elegant and it lies in the geometry of the wheels and tracks
The wheels are tapered, conical in shape. That means they have a varying diameter at different points of contact.
Suppose the track curves left(as shown in the figure below), the whole wheel-set shifts a bit to the right.
This makes the point of contact of the right wheel is at a larger diameter of the cone. While the diameter at the point of contact on the left wheel is much smaller.
As both the wheels are connected by a solid shaft both the wheels must the same angular velocity, making them rotate at different speeds. This system essential replaces the need for the differential in trains.
This also solves another major problem: Whenever there is a bump on tracks, the wheels suddenly slide even when travelling on a straight track & there is a great danger of being derailed, so the same design helps to stabilize the train & to run smoother
The whole beauty of this system is that the amount of shift of the wheelset happens automatically, makes the train move on turns smoothly and keeps the train on track.
Hence the conical geometry along with the flanges ensures the train stays on the track
Video Credit: TheRussianRailways