Basic structure of vehicle

Although there are many kinds of vehicles, their structures are similar. This should be said to be the credit of standardization and the need of large-scale production line. With the development of society, the progress of science and technology and the change of demand, the appearance of railway vehicles has also begun to change, especially the passenger cars are no longer the same old faces. However, their basic structure has not changed obviously, but the specific parts have more scientific and advanced structural design.

Generally speaking, the basic structure of a vehicle consists of five parts: body, underframe, running gear, coupler buffer device and braking device. The car body is the part of the vehicle carrying goods or passengers, and it is also the basis for installing and connecting other parts of the vehicle. The bodies of early vehicles were mostly wooden structures, supplemented by steel plates and bow bars. Modern automobile body is mainly steel structure or light metal structure.

Truck body:

The main components include side walls (walls), end walls (walls), roofs, etc. The steel structure of the car body consists of many longitudinal beams and beams (columns), and the underframe of the car body is supported on the bogie through the center plate or side bearing. The steel structure of the car body bears the dead weight, load, kerb quality and vertical dynamic load caused by wheel-rail impact and sprung vibration; Longitudinal loads such as traction and compression impact generated between vehicles when the train starts, changes speed and goes up and down the ramp; And lateral loads, including wind, centrifugal force, the pressure of goods on the side wall, etc.

Bus body:

It is an all-metal welded structure, which consists of chassis, side walls, roof and end walls. A metal floor is welded outside the steel skeleton. Side wall panels, roof panels and end wall panels form a closed shell with an arc at the top and a rectangle at the bottom, commonly known as a thin-walled cylinder. The inner surface of the shell is reinforced by longitudinal bars, beams and columns, and some of the steel bars are replaced by wallboard steel bars to enhance the strength and rigidity of the structure and form an integral load-bearing embedded structure. Bus body must have good thermal insulation performance. In order to facilitate passengers to get on and off the bus, there are traffic platforms at both ends of the bus, and folding sheds and crossing boards are set at the outer ends of the traffic platforms to prevent the invasion of wind, rain and cold currents. In addition to doors and windows, seats and sleepers, the car body should also be equipped with sanitary equipment, ventilation equipment, water supply equipment, vehicle electrical equipment, heating equipment, broadcasting equipment and air conditioning equipment. The underframe is a rectangular frame composed of various longitudinal and transverse steel beams. It supports the car body and is the foundation of the car body. The underframe bears all the weight and load of the upper car body, and transmits the weight to the running gear through the upper and lower center plates. When the train is running, it also bears the traction of the locomotive, various impact forces caused by the train running and other external forces. Therefore, it must have sufficient strength and rigidity to be durable.

The underframe of freight car is generally composed of center beam, side beam, pillow beam, cross beam, end beam and floor cross beam. The center beam is located in the center of the underframe, which is the foundation and main stress component of the whole underframe. The end of the intermediate beam is where the coupler buffer device is installed, which directly bears the longitudinal force. The bolster is where the underframe and bogie are connected. The lower part of the bolster is provided with an upper bearing and an upper center plate, which are respectively opposite to the lower bearing and the lower center plate on the bogie bolster. It bears great force, bears the weight of the whole vehicle, and transmits the weight to the walking mechanism through the center plate. The underframe structure of tank car is different from other trucks. Because the tank itself has great rigidity, the weight of the liquid in the tank is mainly borne by the tank, and then transferred to the bogie through the bracket and bolster, so the underframe of the tank car mainly bears the horizontal and longitudinal traction impact. The center beam of the tank car is made of two channel steels, with an upper cover plate in the middle, and the lower saddle plate of the tank body is welded on the cover plate; The bolster has a box section, on which a storage tank bracket is mounted, and is welded to the bolster through a web to support the storage tank.

The structure of passenger car underframe is similar to that of cargo car underframe. However, because the two ends of the bus must be provided with passing platforms, its small beams extend out of the end beams and pass through the platforms through the end beams and side beams. Before crossing the platform end beam, install the buffer beam. Running gear is the part where the vehicle runs along the road under traction power. The function of the running gear is to ensure that the vehicle runs along the track and passes through the curve flexibly, safely and smoothly; Reliably bear various force acting on that vehicle and transmit them to the track; Relieve the mutual impact between vehicles and rails, reduce vehicle vibration, and ensure sufficient running stability and good running quality; The braking mechanism is reliable and the vehicle braking effect is good.

At the early stage of the development of railway vehicles, the load is small, the volume is not large, and the running gear is very simple. Generally, a two-axle vehicle structure is adopted, and the axle is directly installed under the vehicle body, which is called a bogie-free vehicle. With the increase of vehicle load, bogie structure is generally adopted. Bogie is an integral part composed of two or more wheelsets through special parts.

There are many types and different structures of bogies due to the different purposes, operating conditions, manufacturing and maintenance capabilities of vehicles. General bogies are mainly composed of wheelsets, side frames and bolster, axle box lubrication device, spring damping device and foundation braking device.

The wheelset consists of one axle and two wheels, and there is no relative displacement between the wheels and the axle during the running of the vehicle. Wheelsets bear all the weight of the vehicle, and also bear various other forces from the car body and rails when running at high speed on the track. The quality of wheelsets directly affects the safety of train operation, so there are strict regulations on its manufacture and maintenance. According to the type of bearings used, the shafts on wheelsets can be divided into sliding bearing shafts and rolling bearing shafts. Wheels vary in structure, shape, size and material. According to the purpose, it can be divided into wheels for passenger cars, trucks and locomotives, and according to the structure, it can be divided into integral wheels and tire wheels. Tire wheels can be divided into cast steel spoke hubs, rolled steel spoke hubs and cast steel spoke hubs. Integral wheels can be divided into rolled steel wheels and cast steel wheels according to materials. In order to reduce noise and unsprung weight, new types of wheels are also adopted abroad, such as elastic wheels, silent wheels, and wrinkled web wheels. No matter what kind of wheel, the parts that directly contact with the rail are mainly the rim and tread. Rim is a protruding part on the inner side of the wheel, which is used to guide the running direction of the wheel and prevent the wheel from derailing. Tread is the contact surface between wheel and rail head. The tread has a slope of 1: 20, which can make the center of gravity of the vehicle fall on the center line of the line, thus overcoming and reducing the hunting motion of the vehicle and smoothly passing through the curve.

The side frame and bolster are components of the bogie, and the side frame connects all parts of the bogie to form a whole. Axle box guide frames are arranged at both ends for installing the axle box. There is a spring bearing platform in the middle of the side frame, which is where the spring damping device is installed. The bolster, the lower center plate and the side bearing box are cast into a whole, and both ends of the bolster are supported on springs. The weight and load of the car body are transferred to the pillow springs on both sides through the lower middle plate and the bolster, and the frames on both sides are connected through the bolster.

Axle box lubrication device is an important component to ensure the safe operation of vehicles. Its function is to connect the wheelset with the side frame or frame, so that the rolling of the wheelset along the track is converted into the translation of the vehicle along the line; Bear the weight of the vehicle, transmit all forces, ensure good lubrication performance, and make the axle not heat up when driving at high speed. Axle box device is divided into rolling bearing axle box device and sliding bearing axle box device according to the working characteristics of bearings. Rolling bearing can reduce the motion resistance and is suitable for high-speed operation, which is one of the important measures for the technical modernization of railway vehicles. Because of the large starting resistance, the sliding bearing axle box is not suitable for high-speed operation, and the maintenance cost is high. The axle oil needs to be replaced in winter and summer, and the axle is easy to heat up, so it is gradually replaced by the rolling bearing glaze box.

Spring damping device is a device to reduce harmful impact and damp vehicle vibration. According to their main functions, the spring vibration reduction devices used in vehicles can be roughly divided into three categories: one is the spring device which mainly relieves the impact, such as the spiral round spring in the center and axle box; The second type is damping devices that mainly attenuate vibration, such as vertical and lateral dampers; Three kinds of positioning devices are mainly used for positioning (elastic restraint), such as elastic positioning devices for longitudinal and transverse axle box wheelsets, transverse buffers or longitudinal traction rods of vibration tables.

The basic braking device consists of the push rod of the brake cylinder piston, even the brake shoe and a series of transmission parts such as lever, pull rod and brake beam between them. Its function is to increase the thrust on the piston of the brake cylinder several times, and then transfer it evenly to each brake shoe, so that it can press the wheel and produce braking effect.

In order to adapt to the increase of load and speed, on the one hand, China Railway has developed CW series bogies by digesting and absorbing imported technology; On the one hand, SW series bogies are formed by upgrading the domestic 206 bogies and learning from foreign welding technology. After many tests and improvements, these two kinds of bogies have begun to mature and become the main bogies of speed-up passenger cars in China.

shock

Coupler buffer device is a vehicle component used to connect vehicles, locomotives or motor cars, transfer traction and braking force, and reduce longitudinal impact. It consists of coupler, bumper, coupler tail frame, slave plate, etc., and is installed in the traction beam at the end of the underframe. In order to ensure the safety and reliability of vehicle couplers and the interchangeability of coupler buffers, the relevant regulations of railway rolling stock in China stipulate that the height between the horizontal center line of coupler tongue and the rail surface after the coupler buffers are loaded is 880mm (+ 10mm) for passenger cars and 880 mm (10 mm) for freight cars. The maximum height difference between the horizontal center lines of the couplers of two adjacent cars shall not be greater than 75 mm First, talk about couplers. Coupler is a vehicle component used to realize the connection between locomotive and vehicle, transmit traction and impact force, and keep a certain distance between vehicles. Couplers are divided into two types according to the opening mode: upper acting type and lower acting type. The lifting mechanism at the upper part of the hook head is called upward moving type (this type is mostly used for general freight cars); Push-down type (used by passenger cars) is opened by the push rod action at the lower part of the hook head. Couplers are divided into spiral couplers, close-fitting automatic couplers, automatic couplers and rotating couplers according to structural types. Spiral couplers were first used, but due to many shortcomings, they have been eliminated. High-speed railway vehicles mostly use close-fitting automatic couplers. In China, all heavy-haul unit trains on Daqin Railway adopt automatic couplers except rotary couplers. The so-called automatic coupler is a coupler that can automatically unhook or hook when lifting the handle of a coupler and then pulling the vehicle away with a locomotive or colliding with the coupler of another vehicle. China Railway Department confirmed to 1956 that 1 and No.2 couplers are standard couplers. However, with the increase of train speed and traction tonnage, 1957 and 1965 were successively designed and manufactured. Passenger cars use 15 coupler, and freight cars gradually use 13 coupler to replace No.2 coupler.

Hook head component

Coupler consists of hook head, hook body and hook tail. The thicker part at the front end of the coupler is called the coupler head. The hook head is internally provided with a hook tongue, a hook tongue pin, a lock pin, a hook tongue push iron and a hook lock iron. The rear of the coupler is called coupler tail, and there is a vertical flat keyhole on the coupler tail to connect with the coupler tail frame. In order to connect or disconnect the vehicle, the coupler has the following three positions, namely, the three states of the coupler: the locking position-the position where the coupler tongue is blocked by the coupler lock iron and cannot rotate outward. When two cars are connected together, the coupler is in this position. Unlocking position-that is, the position where the hook lock iron is lifted and the hook tongue can be turned outwards as long as it is pulled. When decoupling, as long as there is a coupler in the unlocked position, the two cars connected together can be separated. Full open position-that is, the position where the hook tongue has been completely turned outwards. When two cars need to be linked, as long as one coupler is in the full open position, it can be linked after colliding with another coupler. The structure of the rotary coupler is different from that of the ordinary coupler, the coupler tail is provided with a lock hole, and the coupler tail pin is connected with the rotary sleeve of the coupler tail frame. The end surface of the hook is spherical and abuts against the front driven plate with concave spherical surface. When the hook head receives torque, the hook body rotates with the tail pin and the rotating sleeve. The rotary coupler is only installed on the vehicles specially designed for the combined train of coal transport unit of Daqin Railway. One end of this car is equipped with a rotating coupler, and the other end is equipped with a fixed coupler. The two couplers connected in each group on the whole train are matched with each other. When the coal loading vehicle enters the dumper in the coal unloading area, the dumper drives the vehicle to overturn 180 degree coal unloading. Rotating coupler can make the vehicle work continuously when it is overturned and unloaded, thus shortening the unloading operation time. Tight couplers are generally used on vehicles of high-speed railway and underground railway. Small in size and light in weight, the relative motion in all directions after the two couplers are connected is very small, and the real "tight connection" can be realized; At the same time, it is very beneficial to improve the reliability of automatic butt joint between brake hose and electrical connector. Train braking is to stop the movement of the train artificially, including slowing down, not accelerating or stopping running. Relieving or weakening the braking effect of a braked train or locomotive is called "relieving". A set of equipment installed on the train for braking and relieving is called "train braking device". "Brake" and "braking device" are commonly called "brakes". Braking is usually called "brake on" or "brake off", while relieving is called "brake off".

"Train braking device" includes locomotive braking device and vehicle braking device. The difference is that the locomotive not only has the equipment to brake and release itself like a vehicle, but also has the equipment to control the braking function of the whole train.

Before introducing the braking device, let's talk about the train braking mode.

Train braking can be divided into "common braking" and "emergency braking" according to its use. In general, the braking applied to adjust or control the train speed, including stopping at the station, is called "common braking", which is characterized by relatively mild effect and adjustable braking force. In an emergency, the braking to stop the train as soon as possible is called "emergency braking" (also called "extraordinary braking"), which is characterized by rapid action and full use of the braking capacity of the train.

From the moment when braking is applied to the moment when the train speed drops to zero, the distance traveled by the train is called braking distance. This is the main technical index that comprehensively reflects the performance and effect of train braking device. The heavier the train, the higher the running speed, and the less likely it is to stop in a short time and a short distance. So, what is the relationship between the running speed of the train and the braking distance? If the train consisting of 15 cars runs at a speed of 50 kilometers per hour, it can stop within 130 meters after braking; When the speed increases to 70 kilometers, it must travel 250 meters forward to stop; When the train speed reaches 100 km, the braking distance is 570 meters; When the train speed is as high as 120km, the braking distance will exceed 800m. It can be seen that if the train speed is doubled, the braking distance will be more than tripled. However, China's current Railway Technical Management Regulations stipulates that "the emergency braking distance of a train on any railway ramp is 800 m". In other words, in order to improve the train speed, more advanced braking devices must be adopted.

Brake shoe braking is the most commonly used braking method for railway vehicles. The tile brake block made of cast iron or other materials tightly grasps the wheel tread during braking and prevents the wheel from rotating through friction. In this process, the braking device will convert huge kinetic energy into heat energy and dissipate it in the atmosphere. But the braking effect mainly depends on the dissipation capacity of friction heat energy. When this braking method is adopted, the friction area of the brake shoe is small, and most of the heat load is borne by the wheel. The higher the train speed, the greater the heat load of the wheels when braking. If cast iron brake shoes are used, the temperature can melt the brake shoes; Even for advanced synthetic brake shoes, the temperature will be as high as 400~450℃. When the wheel tread temperature rises to a certain extent, the tread will be worn, cracked or peeled off, which will not only affect the service life, but also affect the driving safety. It can be seen that the traditional tread brake shoe braking can no longer meet the needs of high-speed trains. So a new type of braking device-disc brake came into being.

Disc brake is to install a brake disc on the axle or the side of the automobile spoke plate, and use the brake caliper to make two brake pads made of synthetic materials tightly press the side of the brake disc, and generate braking force through friction to stop the train from moving forward. Because the force is not on the wheel tread, the disc brake can greatly reduce the thermal load and mechanical wear of the wheel tread. In addition, the brakes are smooth and there is almost no noise. The friction area of disc brakes is large, and several sets can be installed as needed, and the braking effect is obviously higher than that of cast iron brake shoes, especially suitable for high-speed trains with speed above 120 km/h, which is why disc brakes are widely used in various countries. However, the disadvantage is that the wheel tread is not scratched by the brake shoe, which will worsen the adhesion between the wheel and rail; The brake disc increases unsprung weight and impact vibration, and consumes traction power during operation.

According to the different braking power and control methods, railway locomotive and vehicle brakes can be divided into hand brakes, air brakes, electro-pneumatic brakes, electromagnetic brakes and vacuum brakes.

hand brake

It takes manpower as the driving force of braking, and is controlled by the rotation direction of handwheel and the size of hand force. With simple structure and low cost, it is the oldest and toughest brake in railway history. At the early stage of railway development, there was only this kind of braking on railway vehicles, and each car or several cars were equipped with braking mobilization, which was coordinated according to the driver's whistle. Because of the weak braking force and slow action, it is not convenient for the driver to control directly, and it is quickly replaced by non-human brakes, and the hand brake becomes an auxiliary backup brake.

air brake

The pressure air is used as the driving force of braking, and the pressure of the pressure air is changed to control. Large braking force, sensitive and convenient control. In the past, China Railway referred to pressurized air as "wind" and air brake as "air brake". Air brakes are divided into straight-through type and automatic type, and straight-through air brakes are no longer used.

Automatic type

Characterized in that when the train pipe is exhausted (depressurized), the brake cylinder is inflated (supercharged) and depressurized. The advantages are that when the train is separated and the brake hose is pulled off, the wind pressure of the train pipe drops sharply, and the piston of the three-way valve moves to the braking position automatically and quickly, so that the train can brake automatically and quickly until it stops. This not only improves the safety of train operation, but also has a small time difference between the front and rear parts of the train, that is, the braking and relief are good, which is suitable for trains with long formation; Therefore, it is widely used in railways all over the world.

Electro-pneumatic braking is the abbreviation of electronically controlled air braking, which is formed by adding electrical control elements such as solenoid valves on the basis of air braking. Its characteristic is that the braking action is controlled by "electronic control", but the power of braking action is still compressed air. Moreover, when the electric control of the brake fails for some reason, it can still implement "pneumatic control" (pneumatic control) and temporarily become an air brake. When the train speed is very high or the formation is very long, and air braking is difficult to meet the requirements, electro-pneumatic braking can greatly improve the consistency of braking and relieving functions at the front and rear of the train, significantly reduce the longitudinal impact of the train and shorten the braking distance. Many high-speed trains in the world have adopted electro-pneumatic braking, and quasi-high-speed passenger trains on Guangzhou-Shenzhen line and speed-up passenger cars on some trunk lines in China have also adopted electro-pneumatic braking.

vacuum brake

There is also a vacuum brake, which is characterized by being driven by the atmosphere and controlled by changing the "vacuum degree". When the handle of the brake valve is placed in the release position, the vacuum pump is communicated with the train pipe, the air in the train pipe and the brake cylinder is pumped away, and a high vacuum is maintained up and down the train pipe and the brake cylinder, so that the piston falls due to its own weight and the piston rod extends outward. When the brake valve handle is placed in the braking position, the train pipe is communicated with the atmosphere, and the atmosphere enters from below the train pipe and the brake cylinder piston. Because the spherical check valve is closed when the air pumping is completed, the atmospheric pressure can only hold it down but can't open the valve port, so the atmosphere can't enter above the piston. The pressure difference between the piston and the piston pushes the piston upward, and the piston rod retracts into the cylinder for braking. Vacuum braking is simple in structure, cheap in price and convenient to maintain in non-manual braking. However, due to the limited atmospheric pressure itself, it is difficult to achieve "absolute vacuum", which requires a larger brake cylinder and a thicker train pipe. Therefore, with the increase of traction weight and running speed, some railways with vacuum braking have or are transitioning to air braking.