The kinetic energy of the Sapsan at maximum speed is over 1500 megajoules. For a complete stop, all of it must be dispersed on the braking devices.
It was a deal right here, on Habré. There are quite a lot of review articles on railway topics published here, but this topic has not yet been covered in detail. I think it would be quite interesting to write an article about this, and perhaps more than one. Therefore, I ask under the cat for those who are interested in how the brake systems of railway transport are arranged, and for what reasons they are arranged that way.
1. The history of the air brake
The task of managing any transport includes regulating the speed of its movement. Rail transport is no exception; moreover, its design features introduce significant nuances into this process. The train consists of a large number of coupled carriages, and the resulting system has a significant length and mass at a very decent speed.
By definition, brakes - a set of devices designed to create artificial, adjustable resistance forces used to control the speed reduction of the vehicle.
The most obvious, lying on the surface, way to create a braking force is the use of friction. From the very beginning to the present day, a friction shoe brake has been used. Special devices - brake pads made of a material with a high coefficient of friction are mechanically pressed against the wheel tread (or against special disks mounted on the wheelset axle). Between the pads and the wheel there is a friction force that creates a braking torque.
The braking force is regulated by changing the force of pressing the pads to the wheel - brake pressure. The only question is what drive is used to press the pads, and, in part, the history of the brakes is the history of the development of this drive.
The first railway brakes were mechanical and were operated manually, separately on each car by special people - brakemen or conductors. The conductors were located on the so-called brake pads, which each car was equipped with, and actuated the brakes at the signal of the locomotive driver. The exchange of signals between the driver and the conductors was carried out using a special signal rope stretched along the entire train, which actuated a special whistle.
An old two-axle freight car with a brake platform. Visible handbrake knob
By itself, the brake with a mechanical drive has little power. The amount of brake pressure depended on the strength and skill of the conductor. In addition, the human factor interfered with the work of such a braking system - the conductors did not always perform their duties correctly. There was no need to talk about the high efficiency of such brakes, as well as the increase in the speed of trains equipped with them.
Further development of the brakes required, firstly, an increase in brake pressure, and secondly, the possibility of remote control of it on all cars from the driver's workplace.
The hydraulic drive used in automobile brakes is widely used due to the fact that it provides high pressure with compact actuators. However, when using such a system in a train, its main drawback will appear: the need for a special working fluid - brake fluid, the leakage of which is unacceptable. The large length of the brake hydraulic lines in the train, together with the high requirements for their tightness, make it impossible and irrational to create a hydraulic railway brake.
Another thing is the pneumatic drive. The use of high-pressure air makes it possible to obtain high brake pressures with acceptable dimensions of actuators - brake cylinders. There is no shortage of a working fluid - the air is around us, and even if there is a leak of the working fluid from the brake system (and it will certainly occur), it can be relatively easily replenished.
The simplest brake system using compressed air energy is direct acting non-automatic brake
Scheme of a direct-acting non-automatic brake: 1 - compressor; 2 - main tank; 3 - nutrient line; 4 — train crane driver; 5 - brake line; 6 - brake cylinder; 7 - release spring; 8, 9 - mechanical brake gear; 10 - brake pad.
To operate such a brake, a supply of compressed air is required, stored on the locomotive in a special reservoir called main reservoir (2). Injection of air into the main tank and maintaining a constant pressure in it is carried out compressor (1) driven by the power plant of the locomotive. The supply of compressed air to the brake control devices is carried out through a special pipeline called nutrient (PM) or pressure highway (3).
The control of the brakes of the cars and the supply of compressed air to them is carried out through a long pipeline that runs through the entire train and is called brake line (TM) (5). When compressed air is supplied through the TM, it fills brake cylinders (TC) (6) connected directly to the TM. Compressed air presses on the piston, pressing the brake pads 10 to the wheels, both on the locomotive and on the wagons. Braking occurs.
To stop braking, that is vacations brakes, it is necessary to release air from the brake line into the atmosphere, which will lead to the return of the brake mechanisms to their original position due to the force of the release springs installed in the shopping center.
For braking, it is necessary to connect the brake line (TM) with the supply line (PM). For vacation - connect the brake line to the atmosphere. These functions are performed by a special device - train crane driver (4) - when braking, it connects the PM and TM, when released, it disconnects these pipelines, simultaneously releasing air from the TM into the atmosphere.
In such a system, there is a third, intermediate position of the driver's crane - overlapping when the PM and TM are separated, but the release of air from the TM into the atmosphere does not occur - the driver's crane completely isolates it. The pressure accumulated in the TM and TC is maintained and the time it takes to maintain it at the set level is determined by the amount of air leakage through various leaks, as well as the thermal stability of the brake pads that heat up when rubbing against the wheel tires. Setting in the overlap both during braking and during vacation allows you to adjust the braking force in steps. Such a brake provides both stepped braking and stepped release.
Despite the simplicity of such a brake system, it has a fatal flaw - when the train is uncoupled, the brake line breaks, air escapes from it and the train remains without brakes. It is for this reason that such a brake cannot be used in railway transport, the cost of its failure is too high. Even without train rupture, if there is a large air leak, the brake efficiency will be reduced.
Based on the foregoing, a requirement arises that the braking of the train is initiated not by an increase, but by a decrease in pressure in the TM. But how then to fill the brake cylinders? This gives the second requirement - each rolling unit in the train must store a supply of compressed air, which must be promptly replenished after each braking.
Engineering thought of the late 1872th century came to similar conclusions, which was expressed in the creation by George Westinghouse in XNUMX of the first automatic railway brake.
Westinghouse brake device: 1 - compressor; 2 - main tank; 3 - nutrient line; 4 — train crane driver; 5 - brake line; 6 - air distributor (triple valve) of the Westinghouse system; 7 - brake cylinder; 8 - spare tank; 9 - stop valve.
The figure shows the structure of this brake (figure a - brake operation during release; b - brake operation during braking). The main element of the Westighaus brake was brake air distributor or, as it is sometimes called, triple valve. This air distributor (6) has a sensitive element - a piston operating on the difference of two pressures - in the brake line (TM) and the reserve tank (SR). If the pressure in the TM becomes less than in the ZR, then the piston moves to the left, opening the way for air from the ZR to the TC. If the pressure in the TM becomes greater than the pressure in the ZR, the piston moves to the right, communicating the TC with the atmosphere, and simultaneously communicating the TM and ZR, ensuring that the latter is filled with compressed air from the TM.
Thus, if the pressure in the TM is reduced for any reason, whether it be the actions of the driver, excessive air leakage from the TM, or a train rupture, the brakes will work. That is, such brakes have automaticity of action. This property of the brake made it possible to add another possibility for controlling the train brakes, which is still used on passenger trains to this day - an emergency stop of the train by a passenger, by communicating the brake line with the atmosphere through a special valve - emergency brake (9)
For those who are familiar with this feature of the train's braking system, it's funny to watch movies where cowboy thieves famously unhook a wagon with gold from the train. In order for this to be possible, cowboys must, before uncoupling, close the end valves on the brake line, which isolate the brake line from the connecting sleeves between the cars. But they never do. On the other hand, closed end valves have repeatedly caused terrible disasters associated with brake failure, both here (Kamensk in 1987, Yeral-Simskaya in 2011) and abroad.
Due to the fact that the filling of the brake cylinders comes from a secondary source of compressed air (reserve tank), without the possibility of its constant replenishment, such a brake is called indirect. The charging of the SP with compressed air occurs only when the brake is released, which leads to the fact that with frequent braking followed by a release, with insufficient time delay after the release, the SP will not have time to charge to the desired pressure. This can lead to complete exhaustion of the brake and loss of control of the train's brakes.
The pneumatic brake also has another drawback related to the fact that the pressure drop in the brake line, like any disturbance, propagates in the air at a high, but still finite speed - no more than 340 m / s. Why not more? Because the speed of sound is ideal. But in the pneumatic system of the train, there are a number of obstacles that reduce the propagation speed of the pressure reduction jump associated with the resistance to air flow. Therefore, if special measures are not taken, the rate of pressure decrease in the TM will be the lower, the farther from the locomotive the car is. In the case of the Westinghouse brake, the speed of the so-called brake wave does not exceed 180 - 200 m/s.
Nevertheless, the appearance of a pneumatic brake made it possible to increase both the power of the brakes and the efficiency of controlling them directly from the driver’s workplace. This served as a powerful impetus for the development of railway transport, an increase in the speed and weight of trains, and as a result, a tremendous increase in freight turnover on the railway, growth in the length of railway lines around the world.
George Westinghouse was not only an inventor, but also an enterprising businessman. He patented his invention in 1869, which allowed him to launch mass production of brake equipment. Quite quickly, the Westinghouse brake became widespread in the United States, Western Europe and the Russian Empire.
In Russia, the brake of Westinghouse reigned supreme until the October Revolution, and for quite a long time after it. The Westinghouse firm built its own brake plant in St. Petersburg, and also skillfully ousted competitors from the Russian market. However, the Westinghouse brake had a number of fundamental shortcomings.
Firstly, this brake provided only two modes of operation: braking until the brake cylinders are completely filled, and vacation - emptying the brake cylinders. It was impossible to create an intermediate value of brake pressure with its long-term maintenance, that is, there was no mode in the Westinghouse brake overlap. This did not allow precise control of the train speed.
Secondly, the Westinghouse brake did not work well on long trains, and if in passenger traffic this could somehow be put up with, then problems arose in freight traffic. Remember the braking wave? So, the Westinghouse brake did not have the means to increase its speed, and in a long train, the pressure drop in the TM on the last car could start too late, and at a rate significantly lower than in the head of the train, which created a wild uneven response of brake devices in composition.
It must be said that all the activities of the Westinghouse company, both in Russia at that time and throughout the world, were thoroughly saturated with the capitalist smell of patent wars and unfair competition. This provided such an imperfect system with such a long life, at least in that historical period.
With all this, it must be admitted that the Westinghouse brake laid the foundations of brake science and the principle of its operation has remained unchanged in modern rolling stock brakes.
2. From the Westinghouse brake to the Matrosov brake - the formation of the domestic brake science.
Almost immediately after the appearance of the Westinghouse brake and the realization of its shortcomings, attempts arose to improve this system, or to create another, fundamentally new one. Our country was no exception. At the beginning of the XNUMXth century, Russia had a developed network of railways, which played a significant role in ensuring the economic development and defense capability of the country. The increase in the efficiency of transport is associated with an increase in the speed of its movement and the mass of the cargo transported at a time, which means that the issues of improving the braking systems were sharply raised.
A significant impetus to the development of brake science in the RSFSR and later the USSR was the decrease in the influence of large Western capital, in particular the Westinghouse company, on the development of the domestic railway industry after October 1917.
F.P. Kazantsev (left) and I.K. Matrosov (right) - the creators of the domestic railway brake
The first sign, the first serious achievement of the young domestic brake science, was the development of engineer Florenty Pimenovich Kazantsev. In 1921 Kazantsev proposed a system direct acting automatic brake. The diagram below describes all the main ideas brought not only by Kazantsev, and its purpose is to explain the basic principles of the improved automatic brake.
Direct-acting automatic brake: 1 - compressor; 2 - main tank; 3 - nutrient line; 4 — train crane driver; 5 - power supply for brake line leaks; 6 - brake line; 7 - connecting brake sleeves; 8 - end valve; 9 - stop valve; 10 - check valve; 11 - spare tank; 12 - air distributor; 13 - brake cylinder; 14 - brake linkage.
So, the first main idea is that the pressure control in the TM is carried out indirectly - through a decrease / increase in pressure in a special reservoir called surge tank (UR). It is shown in the figure to the right of the driver's tap (4) and on top of the HM leak supply device (5). The density of this reservoir is technically much easier to ensure than the density of the brake line - a pipe that reaches kilometers in length and runs through the entire train. The relative stability of the pressure in the HP allows you to maintain the pressure in the TM, using the pressure in the HP as a reference. Indeed, the piston in the device (5), when the pressure in the TM is reduced, goes down, opening the valve that fills the TM from the supply line, thereby maintaining the pressure in the TM equal to the pressure in the HP. This idea still had a long way to go, but now the pressure in TM did not depend on the presence of external leaks from it (up to known limits). Device 5 migrated to the driver's crane and remains in it, in a modified form, to this day.
Another important idea underlying the design of this type of brake is the supply of the SR from the TM through the check valve 10. When the pressure in the TM exceeds the pressure in the SR, this valve opens, filling the SR from the TM. In this way, leaks are continuously replenished from the reserve tank and the inexhaustibility of the brake is ensured.
The third important idea proposed by Kazantsev is the design of an air distributor that operates on a difference of not two pressures, but three - the pressure in the brake line, the pressure in the brake cylinder, and the pressure in a special working chamber (RK), which, when released, is fed by pressure from the brake line , along with a spare tank. In the braking mode, the CV is disconnected from the reserve tank and the brake line, maintaining the value of the initial charging pressure. This property is widely used in rolling stock brakes both to provide stepped release and to control the uniformity of filling the shopping center along the train in freight trains, because the working chamber serves as a standard for the initial charging pressure. Based on its value, it is possible to provide both a stepped release and organize an earlier filling of the shopping center in the tail cars. I will leave a detailed description of these things for other articles on this topic, for now I will only say that Kazantsev’s work served as an incentive for the development of a scientific school in our country, which led to the development of original rolling stock brake systems.
Another Soviet inventor who radically influenced the development of domestic rolling stock brakes was Ivan Konstantinovich Matrosov. His ideas did not fundamentally differ from those of Kazantsev, however, subsequent operational tests of the brake systems of Kazantsev and Matrosov (together with other brake systems) showed a significant superiority of the second system in terms of performance when used primarily on freight trains. Thus, the Matrosov brake with an air distributor conv. No. 320 became the basis for further development and design of brake equipment for 1520 mm gauge railways. A modern automatic brake used in Russia and the CIS countries can rightfully bear the name of the Matrosov brake, as it absorbed, at the initial stage of its development, the ideas and design solutions of Ivan Konstantinovich.
Instead of a conclusion
And what is the conclusion? Working on this article convinced me that the topic is worthy of a series of articles. In this pilot article, we touched on the history of the development of rolling stock brakes. In the following, we will go into juicy details, touching not only on the domestic brake, but also on the developments of colleagues from Western Europe, highlighting the design of brakes of various types and types of rolling stock service. So, I hope the topic will be interesting, and see you on Habré again!
Thank you for your attention!
Source: habr.com