Almost everyone knows that the train wheels are pressed against the rails, but many people may not carefully look at the position relationship between the train wheels and the rails.

The picture shows the relationship between train wheelsets and rails.

It can be seen that the wheels of the train are really pressed against the rails to transmit the gravity of the train. However, there is still a place to pay attention to. The red part of the picture shows that there is a circle of disks with a larger radius inside the train wheel. This thing is called "wheel rim" (knocking with a hammer will make a clear sound like a gong ...). This thin layer makes the wheel not only press on the track, but also "get stuck" in the track. This structure can ensure that the wheels always run on the track without derailment, which is used to control the running direction of the train.

2. Switch principle

The rim is used to control the running direction of the train, so realizing "track change" is actually to control the position of the rim.

So people invented such a thing as "turnout", and realized track change by controlling the position of the rim.

Figure 2. Schematic diagram of turnout

The schematic diagram of the first turnout has a moving part. When there is a small slit in this part, the rim can pass through the small slit and travel in the direction guided by the external rail. When the two tracks are closely attached, the rim is guided in the direction of the inner track.

When the red point rail on the picture is close to the right, open the A-B direction ... If you insist on the left, open the A-C direction.

Therefore, the running direction of the train depends on the opening direction of the turnout.

Having said that, we can know that the running direction of the train at the turnout is not controlled by the driver at all, but by the ground to control the opening direction of the turnout. ...

Therefore, drivers don't have to worry about the running direction of the train, and they don't have to change tracks or anything, just drive the train forward honestly.

However, before the general train enters the station, or when shunting in the station, the driver still needs to know the line situation, what turnout to pass, which track to enter, and which direction to turn off. First, in order to confirm whether the turnout is in the correct position, it is necessary to control the speed. Generally speaking, the lateral speed is slower than the forward speed because of the curve.

3. How to ensure that the turnout is opened without mistakes?

Theoretically, as long as the position of the switch is right, there is no problem for the train to enter the right track or pass the station. But manual operation really can't guarantee that it will be adjusted every time, and even mechanical methods can't guarantee that it won't break.

Once the turnout is not pulled down, it is easy for the train to derail when passing through the turnout.

The wrong direction of the switch means that the train may enter the wrong track. On the wrong track, other trains may stop, oncoming trains may be picked up at the same time, and there may also be construction workers (suddenly remembering the example of choosing to hit 1 or n people in Harvard open class, the insider said that the driver was innocent ...), so we must do everything possible to ensure that the train cannot enter the wrong track. So the railway people invented the "interlocking" thing.

"Interlocking" is a mechanism to ensure the mutual restriction between the route, turnout position and signal.

For example, if a train wants to enter from the downward direction and stop at the station 1 lane, the signalman will give an instruction in the interlocking system to enter 1 lane, and then the switches related to this instruction will start to switch, and all related switches will switch to the direction leading to 1 lane, and the system will automatically detect whether all switches are in place. If all the switches are in place, the system will be open. At the same time, shield other routes that conflict with this route.

In a word, under the constraint of interlocking rules, it can ensure that trains pass through different routes in the station and conflict at different times, so as to avoid train collision.

Not long ago, 6502 relay interlocking was widely used in various stations, and relays were used to realize the constraint relationship. Now, after technical transformation, microcomputer interlocking system is adopted in each station one after another, and the constraint relationship of interlocking is realized by computer. Even so, each station has its own way and can control its own route. In the next step, the railway dispatching system will develop to CTC centralized dispatching, and the routes, turnouts and signals of all stations will be directly controlled by the dispatching command center and automatically arranged.

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I saw some comments that CTC is not suitable for big stations, because the operation of big stations is complicated and the route control is complicated, so CTC is not acclimatized, so I think it is necessary to add one point.

The development of railway equipment and railway transportation in China has not been driven by technological innovation, but by demand. In other words, I will ship you as many things as you have. Only when I can't deliver them, will I try to expand production capacity, and then I remember to update my technology.

The appearance of high-speed rail has reversed this thinking to some extent, and started to pursue better speed, better equipment, more advanced transportation organization concept and marketing organization model.