Urban rail transit system refers to the transportation system that uses vehicles to run on fixed guide rails in cities, which is mainly used for urban passenger transport. In China's national standard "Common Terms of Urban Public Transport", urban rail transit is defined as "the general name of fast and large-capacity public transport which is usually powered by electric energy and adopts wheel-rail transport mode". Let's take a look at the paper on urban rail transit system.

This paper introduces the working principle of linear motor and the characteristics of linear motor electric vehicle, as well as the development of Japanese subway and normally guided maglev transportation system.

Keywords: linear motor; Urban rail transit; Subway; Magnetic levitation; motor scooter

Urban traffic is becoming more and more important in the process of urban development, and urban rail transit occupies a prominent position. Due to the development and progress of science and technology in recent years, there are various forms of urban rail transit, including subway, light rail transit, monorail transit, new transportation system and maglev transportation system. When improving urban traffic, cities choose a wider range of traffic systems according to their own specific characteristics. Safe, comfortable, high-density operation, energy saving and environmental protection, reducing costs by introducing new technologies, taking measures from the structure and performance, constantly improving and maintaining the advanced nature are the existing values of urban rail transit. In urban rail transit system, according to the characteristics of vehicles, adopting linear motor as driving motor provides a new choice.

First, the working principle of linear motor

Usually, the motor is of the rotary type. The stator surrounds the cylindrical rotor, and the stator forms a magnetic field, and the current flows in the rotor, so that the rotor generates a rotating torque. In the linear motor, two cylindrical parts are unfolded into flat plates, facing each other, and the stator extends in the length direction corresponding to the movement of the rotor. The rotor is supported and kept stable in a certain way, forming a gap between the rotor and the stator.

The principle of generating propulsion is the same as that of generating torque by motor. In the linear motor subway, the linear motor installed on the bogie produces a moving magnetic field along the forward direction. The secondary current (eddy current) passes through the induction plate (equivalent to the secondary coil) installed on the ground facing the magnetic field, and the force generated by the secondary current cutting the magnetic field is used as the reaction force, so that the linear motor installed on the bogie can obtain the propulsion force.

The basic disadvantage of linear motor is that it is difficult to make the gap between stator and rotor as small as that of rotating motor, which is infinite cycle, while linear motor has ends. Therefore, the magnetic flux leakage is high, and the efficiency of electric-mechanical energy conversion is low. If the same output is to be obtained, the capacity of the inverter needs to be larger than that of the rotary type.

Second, the characteristics of linear motor electric vehicles

In the electric vehicle using rotating motor, the rotating torque is generally converted into the traction of the train through gear deceleration, and it is also limited by wheel-rail adhesion.

In the linear motor electric vehicle, the propulsion force is directly transmitted by the induction plate laid between the rails, so it is not limited by the adhesion force, and may get rid of various problems caused by sliding and idling, which is beneficial to passing through large ramps (the maximum slope can reach 60 ‰ ~ 80 ‰) and small radius curves (the minimum radius is 50m). In addition, the linear motor has no rotating parts, no bearing and lubrication mechanism, simple structure and long service life, which is its greatest feature.

In a rotating motor, the rotating torque is proportional to the square of its diameter, so in order to obtain a large rotating torque, the diameter of the motor will increase. In a linear motor, this is equivalent to extending the corresponding part in the length direction and decreasing in the height direction. In large motors, if the gear of 1 slows down, the wheel diameter must also increase; In linear motor drive, this is unnecessary, so the diameter of the wheel can be reduced, which will reduce the height of the vehicle floor.

The above advantages are the reasons why linear motor electric vehicles are used in small-section subways.

However, the linear motor is inefficient and consumes more power than the same subway. In addition to this shortcoming, the above advantages cannot be fully exerted. Because it is not limited by attachment, the slope of the line can be very large during traction; But when braking, if the electric brake fails, it must rely on mechanical braking, which is controlled by adhesion, so the slope of the line should not be too large. In addition, since the linear motor is a flat device, the height of the floor surface of the vehicle can be reduced, and the diameter of the wheel can also be reduced. But a wheel with a small diameter will wear faster, so it should not be too small. Because the length of the flat linear motor can be extended, it is enough to install one motor on each bogie, which is one of the reasons why the linear motor subway is now grouped into a fully mobile vehicle.

Third, the application and development of linear motor electric vehicles in Japan

3. 1 linear motor subway

In the cost of subway construction, the cost of digging underground tunnels accounts for a large part. The use of linear motor electric vehicles is very beneficial to reduce the excavation cost of underground tunnels, thus reducing the construction cost of the whole subway. Take Japan as an example. The diameter of ordinary subway tunnel is 5.8m, and that of linear motor subway tunnel is 4.0~4.3m, as shown in figure 1. It can be estimated that the excavation volume of the latter tunnel project can be reduced by about 1/3 compared with the former one, which means that the cost of the subway will be greatly reduced. In addition, compared with the rotary motor, the linear motor has a flat shape, so it can reduce the height of the vehicle floor and reduce the size of the whole vehicle, but this does not affect the interior space of the vehicle, that is, it will not bring inconvenience to passengers. The linear motor only produces the driving force of the vehicle, and the vehicle still uses steel wheels and rails as the support and guidance system.

3.2 Normally Conducted Magnetic Levitation Traffic System

Although the linear motor subway has many advantages, such as low cost, strong ability to pass through large ramps, small turning curve radius, less maintenance, stable operation and so on. , has been used in some cities, but the passenger capacity is small, so it can only be used as a supplement to the existing subway at present. Compared with the existing railways, the normal oriented maglev transportation system is a brand-new transportation system, and its advantages will make it occupy a place in the urban rail transit system. With the progress of science and technology, linear motor and its application in subway will have a good development prospect.

References:

1 bureau リニソヮンポィントレッスンンンン/kloc-0

2. The development trend of Nagano Hideo's maglev traffic, HSST, JREA 200 1

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