The Train’s wheels are not perfectly cylindrical, but slightly conical. In our opinion, this conical shape is a marvel of engineering that accomplishes two major things. First, it corrects the course of the train towards the center, and second, it helps the train achieve differential action.
Self-Centering Force
To understand the self-centering force, let’s consider a simple experiment with glued paper cups. When rolled on tracks, the cups that are glued in the same direction move perfectly straight. However, when the cups are glued in the opposite way, they fail to stay on the track. Railway wheels use a conical shape to ensure they never leave the track.
But how does this conical arrangement produce a self-centering force? We need to examine the forces acting on the wheels during straight track movement. The reaction forces will always be perpendicular to the surface of the cone. When the wheels are centered, the horizontal components of these forces cancel each other out.
Now, let’s assume the wheels have moved to the right. The entire wheel set tilts in that direction, causing the normal forces to also tilt. This creates a net force towards the left, which automatically brings the wheels back to their center. As the wheels approach the center, the self-centering force disappears. It’s a simple but brilliant technique to self-center the wheels.
Right flanges are fitted on both sides of the wheels as an extra safety feature. If the wheels have the opposite angle, the net force developed during a right displacement is towards the right. This is why this wheel geometry causes the train wheels to get thrown out of the track.
Differential Action
The conical shape of the wheels also allows engineers to achieve differential action. When the train needs to take a turn, the left wheel has to travel a greater distance than the right wheel. With a common shaft connecting the wheels, how can one wheel travel more distance than the other? This is where the conical shape comes into play.
As the wheels turn, they slightly slide towards the left. Since the left wheel has a higher radius than the right wheel at the contact point, it travels a greater distance for the same angle rotation. This achieves the differential action without the need to separate the wheels and turn them at different speeds, as is done in cars.
When the wheels slide towards the left, it automatically produces a force towards the right. This force provides the centripetal force needed for the turn, ensuring the wheels do not slide back to the center during cornering.
At Lesicks, we salute the brilliant engineers who accomplished these two main engineering goals just by giving the wheels a taper. Thank you for reading!
