What are the braking methods of urban rail vehicles?

In accordance with the braking of the train kinetic energy transfer mode different city rail vehicle braking can be divided into friction braking and electric braking.

One, friction braking

Through the friction of the friction sub-trains will train motion kinetic energy into heat energy, escaping in the atmosphere, thus generating braking effect. Urban rail vehicles commonly used friction braking methods are mainly brake tile braking, disk braking and track electromagnetic braking.

(1) brake tile braking

Gate tile braking is also known as tread braking, it is the most common type of braking. Braking brake tile pressure wheel, wheel and brake tile friction, the train's kinetic energy through the wheel and brake tile friction into thermal energy, escape in the air.

In the wheel and brake tile this pair of friction vice, because the wheel mainly bear the vehicle walking function, so other materials can not be changed. To improve the performance of brake tile braking, only by changing the method of brake tile material. At present, most of the city railcars use synthetic brake tiles. But the thermal conductivity of the synthetic brake tile is poor, so there is also the use of good thermal conductivity, and has good friction properties of powder metallurgy brake tile.

In the brake tile braking, when the brake power is large, the heat generated too late to escape to the atmosphere, and in the brake tile and the wheel tread accumulation, so that their temperature rises, the friction falls, serious cases will lead to the brake tile melting and hub relaxation, etc., therefore, in the brake tile braking, the brake power has a limit.

(2) disc brake)

Disc brake has axle-disc type and wheel-disc type, axle-disc type is generally used, when the middle of the wheelset due to the traction motors and other equipment to make the installation of the brake disc is difficult, wheel-disc type can be used. When braking, the brake cylinder through the brake clamp brake pads clamping brake disc, brake pads and brake disc friction, the train's kinetic energy into thermal energy, thermal energy through the brake disc and brake pads escape in the atmosphere.

(3) track electromagnetic braking

Track electromagnetic braking is also called magnetic track braking. Is a traditional braking method, this braking method is in the bogie before and after the installation of two wheels between the package lift cylinder, cylinder top with two electromagnets, electromagnets, including electromagnet boots and friction plate, electromagnet suspension installed at the appropriate height from the rail surface, braking electromagnet fall, and connect the excitation power to produce electromagnetic suction, electromagnet adsorption on the rail, the train's kinetic energy through the friction plate and rail The kinetic energy of the train is transformed into heat energy through the friction between the wear plate and the rail, which is dissipated in the atmosphere. Track electromagnetic braking can get a larger braking force, so it is often used as a kind of supplementary braking in emergency braking, this kind of braking is not subject to the limitation of the coefficient of adhesion between the wheels and rails, and it can effectively shorten the braking distance under the condition of ensuring the comfort of passengers. When the friction between the wear plate and the rail produces much heat, the wear and tear on the rail is also very serious. However, because of its short braking distance, and the structure is simple and reliable, so this device in the tram and light rail used more.

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Two, electric braking

From the point of view of energy, the nature of braking is to transfer the kinetic energy of the train into other forms of energy. The ability of the braking system to transfer kinetic energy becomes the braking power. In general, under a certain safe braking distance, the braking power of the train is a function of its speed three times. Modern rail transit vehicle speed are very high, the train mass is also very large, its braking power if only a mechanical way to achieve the transfer is very difficult to achieve.

At present, the most used mechanical friction braking method is brake tile braking. However, it is limited by the braking power, brake tile and wheel tread wear dust and heat generated by the environment will also cause serious pollution, especially in the tunnel ventilation conditions are not good, these dust and heat will have a serious impact on passengers and equipment. In addition, the frequent use of friction braking, will make the brake tile replacement frequently, the wheel tread correction turning increased, not only the maintenance cost is high, the vehicle repair time is also very long, the frequency of use of the vehicle will be reduced.

In order to reduce mechanical friction, should try to use non-polluting braking methods, the best way is to use electric braking. And electric braking according to its braking principle can be divided into power braking and electromagnetic eddy current braking.

(1) power braking

Since the modern urban rail transit vehicles are generally used in electric traction electric locomotives, DC or AC motors as the traction power, so power braking as the main braking method has become the development trend of urban rail transit vehicles. In the electric locomotive group, there are both locomotive and trailer, except for the trailer without motor can only use friction braking, all the locomotive can carry out power braking, and can also bear part of the trailer braking force.

(ii)

Electromagnetic eddy current braking

In order to give full play to the advantages of electromagnetic braking of the track, to avoid its shortcomings, and designed the electromagnetic eddy current braking.

Electromagnetic eddy current braking is the use of electromagnetic eddy current in the magnetic field to produce Lorentz magnetic force, the use of Lorentz magnetic force in the direction of the direction of the movement of objects in the opposite direction of the physical principle of the design of a battery braking, this braking method has no friction, no noise, small braking force has the advantage of large. At present, the use of electromagnetic eddy current braking of rail transit vehicles are mainly disc-shaped eddy current braking and track linear eddy current braking

1, disc-shaped eddy current braking

Disc-shaped eddy current braking installed in the axle of the disc cutting the magnetic lines of force to generate eddy current and Lorentz magnetic force, according to the generation of the magnetic field of the mechanism can be divided into electromagnetic eddy current disc braking and permanent magnet eddy current disc braking.

Japan's Shinkansen high-speed trains use electromagnetic eddy current braking principle

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Permanent magnet eddy current disc brake is the use of permanent magnets to generate electromagnetic field, brake disc in the magnetic field to generate eddy current to prevent the magnetic field increases, generating braking torque, braking effect.

Disc eddy current braking structure is similar to mechanical disc braking, but there is no brake disc and brake pad wear between. For train braking, it is also subject to the limitations of the wheel-rail adhesion coefficient.