I see that , the public liked the historical part of my story, and therefore it is not a sin to continue.
High-speed trains like the TGV no longer need air brakes.
Today we will talk about the present, namely, what approaches to the creation of rolling stock brake systems are used in the XNUMXst century, which is literally in a month exchanging its third decade.
1. Classification of rolling stock brakes
Based on the physical principle of creating a braking force, all railway brakes can be divided into two main types: frictional, using the force of friction, and dynamic, using a traction drive to create a braking torque.
Friction brakes include shoe brakes of all designs, including disc brakes, as well as magnetic rail brake, which is used in high-speed trunk transport, mainly in Western Europe. On track 1520, this type of brake was used exclusively on the ER200 electric train. As for the same Sapsan, Russian Railways refused to use a magnetic rail brake on it, although the prototype of this electric train, the German ICE3, is equipped with such a brake.
ICE3 train bogie with magnetic rail brake
Carriage of the Sapsan train
To dynamic, or rather electrodynamic brakes includes all brakes, the action of which is based on the transfer of traction motors to the generator mode (regenerative ΠΈ rheostatic brake), as well as braking opposition
With a regenerative and rheostat brake, everything is relatively clear - the engines are transferred to the generator mode in one way or another, and in the case of recuperation they give energy to the contact network, and in the case of a rheostat, the generated energy is burned on special resistors. Both brakes are used both on trains with locomotive traction and on multi-unit rolling stock, where the electrodynamic brake is the main service brake, due to the large number of traction motors distributed throughout the train. The only drawback of electrodynamic braking (EDB) is the impossibility of braking to a complete stop. With a decrease in the efficiency of the EDT, it is automatically replaced by a pneumatic friction brake.
With regard to braking by reverse, it provides braking to a complete stop, since it consists in reversing the traction motor on the go. However, this mode, in most cases, is emergency - its regular use is fraught with damage to the traction drive. If we take, for example, a collector motor, then when the polarity of the voltage applied to it changes, the back-EMF that occurs in a rotating motor is not subtracted from the supply voltage, but is added to it - the wheels both rotate and rotate in the same direction as in traction mode! This leads to an avalanche-like increase in current, and the best thing that can happen is that the electrical protection devices will work.
For this reason, all measures are taken on locomotives and electric trains to prevent engine reversal on the move. The reversible handle is blocked mechanically when the driver's controller is in the running positions. And on the same "Peregrine Falcons" and "Swallows", turning the reversing switch at a speed above 5 km / h will lead to immediate emergency braking.
However, some domestic locomotives, such as the VL65 electric locomotive, use reverse braking as a standard mode at low speeds.
Reverse braking is a standard braking mode provided by the control system on the VL65 electric locomotive
I must say that despite the high efficiency of electrodynamic braking, any train, always, I emphasize, is always equipped with an automatic pneumatic brake, that is, triggered by the release of air from the brake line. Both in Russia and all over the world, the good old shoe friction brakes stand guard over traffic safety.
According to their functional purpose, friction type brakes are divided into
- Parking, manual or automatic
- Train - pneumatic (PT) or electro-pneumatic (EPT) brakes installed on each unit of the rolling stock in the train and controlled centrally from the driver's cab
- Locomotive - pneumatic direct-acting brakes designed to brake the locomotive, without braking the train. They are operated separately from the train ones.
2. Parking brake
The hand brake with a mechanical drive has not gone away from the rolling stock, it is installed both on locomotives and on wagons - it just changed its specialty, namely it turned into a parking brake, which makes it possible to exclude spontaneous movement of the rolling stock in the event of air escaping from its pneumatic system. The red wheel, similar to a ship's steering wheel, is a hand brake drive, one of its options.
The steering wheel of the manual parking brake in the cabin of the electric locomotive VL60pk
Handbrake in the vestibule of a passenger car
Hand brake on a modern freight car
The handbrake mechanically applies the same pads to the wheels that are used for normal braking.
On modern rolling stock, in particular on the EVS1 / EVS2 Sapsan, ES1 Lastochka electric trains, as well as on the EP20 electric locomotive, the parking brake is automatic and the pads are pressed against the brake disc there spring power accumulators. Some of the tong mechanisms that press the pads to the brake discs are equipped with powerful springs, and so powerful that the release is performed by a pneumatic drive with a pressure of 0,5 MPa. The pneumatic actuator, in this case, counteracts the springs pressing the pads. Such a parking brake is controlled by buttons on the driver's console.
Buttons for controlling the parking spring brake (SPT) on the electric train ES1 "Lastochka"
In its design, such a brake is similar to that used on powerful trucks. But as the main brake in trains, such a system completely useless, and why, I will explain in detail after the story about the work of train pneumatic brakes.
3. Pneumatic brakes of cargo type
Each freight car is equipped with the following set of brake equipment
Brake equipment of a freight car: 1 - brake connecting sleeve; 2 - end valve; 3 - stop valve; 5 - dust collector; 6, 7, 9 β air distributor modules conv. No. 483; 8 - uncoupling tap; BP - air distributor; TM - brake line; ZR - spare tank; TC - brake cylinder; AR - cargo auto mode
Brake line (TM) - a pipe with a diameter of 1,25" running along the entire car, at the ends it is equipped with end valves, to disconnect the brake line when uncoupling the car before disconnecting the flexible connecting sleeves. In the brake line in normal mode, the so-called charger pressure of 0,50 - 0,54 MPa, so disconnecting the sleeves without closing the end valves is a dubious task, which in the literal sense of the word can deprive you of your head.
The supply of air directly supplied to the brake cylinders is stored in reserve tank (ZR), the volume of which in most cases is 78 liters. The pressure in the reserve tank is exactly equal to the pressure in the brake line. But no, this is not 0,50 - 0,54 MPa. The fact is that such pressure will be in the brake line on the locomotive. And the farther from the locomotive, the less pressure in the brake line, because it inevitably has leaks leading to air leaks. So the pressure in the brake line of the last car in the train will be somewhat less than the charging one.
Brake cylinder, and on most cars it is alone, when filling it from a spare tank, through a brake linkage, it presses all the pads on the car to the wheels. The volume of the brake cylinder is about 8 liters, therefore, with full braking, a pressure of no more than 0,4 MPa is set in it. The pressure in the reserve tank also decreases to the same value.
The main "actor" in this system is air distributor. This device responds to a change in pressure in the brake line, performing one or another operation, depending on the direction and rate of change in this pressure.
When the pressure in the brake line is reduced, braking occurs. But not with any decrease in pressure - the decrease in pressure must occur at a certain pace, called service braking rate. This pace is provided crane driver in the cab of the locomotive and ranges from 0,01 to 0,04 MPa per second. When the pressure decreases at a lower rate, braking does not occur. This is done so that the brakes do not work with standard leaks from the brake line, and also do not work when the overcharge pressure is eliminated, which we will talk about later.
When the air distributor is activated for braking, it performs an additional discharge of the brake line at a service pace by 0,05 MPa. This is done in order to ensure a steady reduction in pressure along the entire length of the train. If additional discharge is not done, then the last cars of a long train may not slow down in principle. Additional discharge of the brake line is performed all modern air distributors, including passenger ones.
When braking, the air distributor disconnects the reserve tank from the brake line and connects it to the brake cylinder. The brake cylinder is being filled. It occurs exactly as long as the pressure drop in the brake line continues. When the pressure reduction in the TM stops, the filling of the brake cylinder stops. Mode is coming overlap. The pressure built into the brake cylinder depends on two factors:
- the depth of discharge of the brake line, that is, the magnitude of the pressure drop in it relative to the charging
- operating mode of the air distributor
The cargo air distributor has three modes of operation: laden (G), medium (S) and empty (L). These modes differ in the maximum pressure gained in the brake cylinders. Switching between modes is carried out manually by turning a special mode handle.
To summarize, the dependence of the pressure in the brake cylinder on the depth of discharge of the brake line with a 483 air distributor in various modes looks like this
The disadvantage of using a mode switch is that a wagon worker must walk along the entire train, climb under each car and switch the mode switch to the desired position. This is done, according to rumors coming out of operation, far from always. Excessive filling of brake cylinders on an empty car is fraught with skidding, reduced braking efficiency and damage to wheel sets. To get out of this situation on freight cars between the air distributor and the brake cylinder include the so-called auto mode (AP), which, mechanically determining the mass of the car, smoothly regulates the maximum pressure in the brake cylinder. If the car is equipped with an auto mode, then the mode switch on the BP is set to the βladenβ position.
Braking is usually performed in steps. The minimum discharge stage of the brake line for VR483 will be 0,06 - 0,08 MPa. In this case, a pressure of 0,1 MPa is set in the brake cylinders. In this case, the driver puts the valve in the shutdown position, in which the pressure value set after braking is maintained in the brake line. If the braking effect from one stage is not enough, the next stage is performed. At the same time, the air distributor does not care at what rate the discharge occurs - when the pressure decreases at any rate, the brake cylinders are filled in proportion to the magnitude of the pressure decrease.
Full release of the brakes (complete emptying of the brake cylinders on the entire train) is carried out by increasing the pressure in the brake line above the charging one. Moreover, on freight trains, a significant overpressure is carried out in the TM over the charging one, so that the pressure increase wave reaches the very last cars. Full release of the brakes in a freight train is a lengthy process and can take up to a minute.
VR483 has two holiday modes: flat and mountain. In flat mode, with increasing pressure in the brake line, a complete, stepless release occurs. In mountain mode, stepwise release of the brakes is possible, which means that the brake cylinders are not completely emptied. This mode is used when driving along a complex profile with a large slope.
The 483 air distributor is generally a very interesting device. A detailed analysis of its device and operation is a topic for a separate large article. Here we have considered the general principles of operation of the cargo brake.
3. Pneumatic brakes, passenger type
Brake equipment of a passenger car: 1 - connecting sleeve; 2 - end valve; 3, 5 - junction boxes of the electro-pneumatic brake line; 4 - stop valve; 6 - tube with electro-pneumatic brake wiring; 7 - insulated suspension of the connecting sleeve; 8 - dust collector; 9 - outlet to the air distributor; 10 - uncoupling tap; 11 - working chamber of the electric air distributor; TM - brake line; BP - air distributor; EVR - electric air distributor; TC - brake cylinder; ZR - spare tank
A greater amount of equipment immediately catches your eye, starting with the fact that there are already three stop cranes (one in each vestibule, and one in the conductorβs compartment), ending with the fact that domestic passenger cars are equipped with both pneumatic and electro-pneumatic brake (EPT).
An attentive reader will immediately note the main drawback of pneumatic brake control - the final speed of propagation of the brake wave, limited from above by the speed of sound. In practice, this speed is lower and amounts to 280 m/s during service braking, and 300 m/s during emergency braking. In addition, this speed is highly dependent on air temperature and in winter, for example, it is lower. Therefore, the eternal companion of pneumatic brakes is the uneven operation of their composition.
The uneven operation leads to two things - the occurrence of significant longitudinal reactions in the train, as well as an increase in the braking distance. The first is not so typical for passenger trains, although containers with tea and other drinks jumping on a table in a compartment will not please anyone. Increasing the braking distance is a serious problem, especially in passenger traffic.
In addition, the domestic passenger air distributor is like the old conv. No. 292, and the new conv. No. 242 (of which, by the way, there are more and more passenger cars in the fleet), both of these devices are direct heirs of the same Westinghouse triple valve, and they work on the difference between two pressures - in the brake line and in the reserve tank. They are distinguished from a triple valve by the presence of an overlap mode, that is, the possibility of stepped braking; the presence of additional discharge of the brake line during braking; the presence in the design of the accelerator emergency braking. These air distributors do not provide a staged release - they immediately give a full release as soon as the pressure in the brake line exceeds the pressure in the reserve tank, which was established there after braking. And step release is very useful for adjusting brakes for precise stops at the landing platform.
Both problems - the uneven operation of the brakes and the lack of stepped release, on a track of 1520 mm are solved by installing an electrically controlled air distributor on the cars - electric air distributor (EVR), arb. No. 305.
Domestic EPT - electro-pneumatic brake - direct-acting, non-automatic action. On passenger trains with locomotive traction, EPT operates on a two-wire circuit.
Structural diagram of a two-wire EPT: 1 - control controller on the driver's crane; 2 - battery; 3 - static power converter; 4 β the panel of control lamps; 5 - control unit; 6 - terminal block; 7 - connecting heads on the sleeves; 8 - isolated suspension; 9 - semiconductor valve; 10 - release solenoid valve; 11 - brake solenoid valve.
Two wires are stretched along the entire train: #1 and #2 in the figure. On the tail car, these wires are electrically connected to each other and an alternating current with a frequency of 625 Hz is passed through the resulting loop. This is done to control the integrity of the EPT control line. When the wire breaks, the alternating current circuit breaks, the driver receives a signal in the form of an extinguishing in the cab of the control lamp "O" (vacation).
The control is carried out by direct current of different polarity. In this case, the rails are the wire with zero potential. When a positive (relative to the rail) voltage is applied to the EPT wire, both electromagnetic valves installed in the electric air distributor are activated: release (OV) and brake (TV). The first of them isolates the working chamber (RK) of the electric air distributor from the atmosphere, the second fills it from the reserve tank. Further, the pressure switch installed in the EVR, which operates on the pressure difference in the working chamber and the brake cylinder, comes into play. When the pressure in the RC exceeds the pressure in the TC, the latter is filled with air from the reserve tank, up to the pressure that was collected in the working chamber.
When a negative potential is applied to the wire, the brake valve turns off, since the current to it is cut off by the diode. Only the release valve remains active, holding the pressure in the working chamber. This is how the overlapping position is realized.
When the voltage is removed, the release valve loses power, opens the working chamber to the atmosphere. When the pressure in the working chamber decreases, the pressure switch releases air from the brake cylinders. If, after a short vacation, the driverβs crane is again put in the shut-off position, then the pressure drop in the working chamber will stop, and the release of air from the brake cylinder will also stop. In this way, stepwise release of the brake is achieved.
What happens when a wire breaks? That's right - EPT will let go. Therefore, this brake (on domestic rolling stock) is not automatic. In case of failure of the EPT, the driver has the opportunity to switch to pneumatic control of the brakes.
EPT is distinguished by the simultaneous filling of brake cylinders and their emptying throughout the train. The rate of filling and emptying is quite high - 0,1 MPa per second. EPT is an inexhaustible brake, since during its operation a conventional air distributor is in the vacation mode and feeds spare reservoirs from the brake line, which in turn is fed by the driver's crane on the locomotive from the main reservoirs. Therefore, the EPT can be braked at any frequency required for the operational control of the brakes. The possibility of step release allows you to control the speed of the train very accurately and smoothly.
The pneumatic control of the brakes of a passenger train is not much different from a freight brake. There is a difference in control methods, for example, the release of the pneumatic brake is carried out up to the charging pressure, without overestimation. In general, excessive overpressure in the brake line of a passenger train is fraught with trouble, therefore, when the EPT is fully released, the pressure in the TM is increased by a maximum of 0,02 MPa above the value of the set charging pressure.
The minimum depth of discharge of TM during braking on the passenger brake is 0,04 - 0,05 MPa, while a pressure of 0,1 - 0,15 MPa is created in the brake cylinders. The maximum pressure in the brake cylinder of a passenger car is limited by the volume of the reserve tank and usually does not exceed 0,4 MPa.
Conclusion
Now I turn to some commentators who are surprised (and I think even outraged, but I do not presume to claim) the complexity of the train brake. In the comments, it is proposed to apply an automotive circuit with power accumulators. It is, of course, from a sofa, or a computer chair in the office, through a browser window, many problems are more visible and more obvious than their solution, but let me say that most of the technical decisions made in the real world have a clear justification.
As already mentioned, the main problem of the pneumatic brake in the train is the final speed of the pressure drop along the long (up to 1,5 km in a train of 100 cars) pipe of the brake line - the brake wave. To accelerate this braking wave, additional discharge is required by the air distributor. There will be no air distributor, there will be no additional discharge. That is, energy-storage brakes will obviously be noticeably worse in terms of uniformity of operation, returning us to the days of Westinghouse. A freight train is not a truck, there are different scales, and hence different principles of brake control. I am sure that this is not just so, and the direction of the world brake science did not accidentally follow the path that led us to such constructions. Dot.
This article is a kind of review of the brake systems existing on modern rolling stock. Further, in other articles of this series, I will dwell on each of them in more detail. We will learn what devices are used to control the brakes, how air distributors are arranged. Let's take a closer look at the issues of regenerative and rheostatic braking. And of course consider the brakes of high-speed vehicles. See you again and thank you for your attention!
PS: Friends! I want to say special thanks for a lot of personal messages indicating errors and typos in the article. Yes, I am a sinner who is not friendly with the Russian language and gets confused on the keys. Tried to correct your comments.
Source: habr.com