A method for calculating safe tracking distance of group trains based on adhesion braking

Abstract

The present invention belongs to the field of rail transit technology, and proposes a method for calculating the safe tracking distance of a group train based on adhesion braking. The main scheme is: respectively establish a group train dynamic system model, a group operation control sensor, a wheel-rail adhesion controller, a braking system model and a group train adhesion braking coordinated control system model, and set a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment. When the train starts braking, the braking torque, distance difference, communication delay, wheelset creep rate and wheelset angular acceleration are input in real time, and the group train safe braking distance is calculated through the three-level judgment rule. After the braking process is completed, the group train safe tracking distance under the braking condition is output. The present invention can accurately calculate the group train safe tracking distance when the train brakes by using the three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment under complex working conditions and train conditions of different models.

Description

Technical Field

[0001] The present invention relates to the field of rail transit technology, and in particular to a method for calculating a safe tracking distance of a group of trains based on adhesion braking. Background Art

[0002] Traditional train control systems have reached bottlenecks in tracking intervals and transport capacity. At present, the train group operation control system has broken the traditional block system. It performs two-dimensional control of target-distance and target-speed based on the real-time speed and real-time position of the preceding vehicle, and uses dynamic collaborative technology between trains in the group for tracking. It adopts advanced technologies such as low-latency, high-reliability wireless communication, precise positioning, speed measurement, dynamic collaborative tracking, marshaling and disassembling, and fine control management, which shortens the tracking distance between trains in the group, realizes rapid marshaling and disassembling, and efficient reception and dispatch of trains at stations, thereby improving railway transportation efficiency.

[0003] Although group operation control technology continues to develop and break through, the safe operation of trains is always the most critical control target, and the control of the safe braking distance of group trains is the key guarantee for the safe operation of trains. Therefore, the safe distance of trains can be effectively estimated based on dynamic modeling calculations, but due to the complexity of the track surface and severe weather changes, the wheel-rail adhesion problem has a direct impact on the performance of locomotive traction power, train operation stability, train braking and many other aspects, thus posing a threat to the wheel-rail interaction characteristics and the control of the safe distance of trains. When calculating the safe distance of trains, the influencing factor of wheel-rail adhesion must be considered.

[0004] In the group operation mode, most rail vehicles still use adhesion braking, and the braking performance is limited by the adhesion between the wheel and the rail. When the train runs on the rail surface contaminated by third media such as rain, frost, oil, and leaves, the adhesion between the wheel and the rail is limited, and it is very easy to slip. In severe cases, it may even lock, resulting in insufficient adhesion, extending the braking distance of the train, and failing to stop within the specified distance. It may even cause major accidents such as derailment, which seriously affects the safety, economy, comfort and punctuality of train operation. The size of the safe tracking interval of the group train is closely related to the wheel-rail adhesion condition. In order to improve transportation efficiency, the traditional fixed block mode is lifted and a smaller train tracking interval is adopted. Especially under braking conditions, when extreme slip conditions occur, the tracking interval will be larger than the normal braking distance. Therefore, based on the wheel-rail adhesion problem, a locomotive wheel-rail adhesion and locomotive braking coordinated controller is designed during the operation of the train group. It is particularly critical to calculate the safe braking distance of the train under complex horizontal and vertical section line conditions. Summary of the invention

[0005] The purpose of the present invention is to provide a method for calculating the safe tracking distance of a group train based on adhesion braking. The method can take a heavy-load group train as the research object, and take calculating the safe tracking distance of the train under the braking mode as the main goal. Through the coordinated control of the adhesion braking of the group train, a key basis is provided for accurately quantifying the minimum safe tracking distance of the train, so as to simulate the dynamic tracking of multi-train groups more realistically and accurately, ensure the normal operation and scheduling of the train, and improve the efficiency of organized transportation.

[0006] The present invention solves the technical problem and adopts the following technical solution: A method for calculating the safe tracking distance of a group train based on adhesion braking comprises the following steps: Establish a group train dynamic system model; Based on the group train dynamics system model, a group operation control sensor based on time, position and speed between two trains is established, and the communication delay and output distance difference are set; A wheel-rail adhesion controller is established, and the vehicle speed and the rotation speed of each wheel set of the bogie are input from the group train dynamics system model, and the wheel set angular acceleration and wheel set creep rate are calculated; Establish a braking system model, input the initial braking speed and time before the train brakes from the group train dynamics system model, and calculate the braking torque; A coordinated control system for adhesion and braking of group trains is established, and a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment is set. When the train starts braking, the braking torque, distance difference, communication delay, wheelset creep rate and wheelset angular acceleration are input in real time, and the safe braking distance of the group train is calculated through the three-level judgment rule. After the braking process is completed, the safe tracking distance of the group train under the braking condition is output.

[0007] As a further optimization, a group train dynamic system model is established through SIMPACK or UM or SIMULINK or ADAMS simulation platform, and the basic parameters, structural parameters and suspension parameters of heavy-load locomotives, freight cars and train retarder are obtained, as well as the track structure parameters; When establishing the group train dynamic system model, it is assumed that the rear train will brake only when the front train is in a stopped state.

[0008] As a further optimization, the group operation control sensor based on time, position and speed between two trains is established based on the group train dynamics system model, and the communication delay and output distance difference are set, which means: A simplified model of the group communication system is established to simulate the data transmission between the front and rear trains through sensors; Based on the group train dynamics system model, the locomotive body mass center position is taken as the reference point, and time, position and speed sensors are established between the two trains for real-time data exchange between the front and rear trains. The controller is established through the MATLAB or SIMULINK simulation platform, the communication delay time is set to 0~2s, and the distance difference between the front and rear vehicles is output.

[0009] As a further optimization, the wheel angular acceleration is expressed as α i , and its calculation formula is: , In the formula, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by differentiating the wheel speed. t is the train running time, i =1~6, indicating the number and order of wheelsets; The wheelset creep rate is expressed as s i , and its calculation formula is: , In the formula, is the wheelset speed, r is the wheel radius, v ref is the reference speed.

[0010] As a further optimization, when establishing the brake system model, the locomotive electric brake characteristic curve is calculated based on the HXN3 diesel locomotive electric brake characteristic curve diagram, and the freight car air brake curve is calculated based on the brake cylinder pressure curve.

[0011] As a further optimization, after calculating the locomotive electric brake characteristic curve, the locomotive electric brake characteristic curve is converted into a brake torque curve, and the locomotive brake torque is obtained from the brake torque curve, and the locomotive brake torque is applied to the main gear of the locomotive wheelset. The calculation expression of the locomotive brake torque is: , In the formula, T is the locomotive braking torque, F b For braking force, r is the wheel radius, n is the number of locomotive wheel sets, ξ is the gear ratio, which is equal to the ratio of the number of teeth on the driving gear to the number of teeth on the driven gear; After calculating the truck air brake curve, the truck braking force is obtained from the truck air brake curve, and the truck braking force is directly applied to the truck body center of mass position; The truck braking force is calculated by the conversion method. The truck braking force calculated by the conversion method means: when the train brakes, the truck braking force generated by the brake shoe pressure B, the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The converted friction coefficient of this brake shoe The product is calculated as follows: .

[0012] As a further optimization, during the air braking process of the freight cars, when the brake cylinder of the last train reaches the maximum pressure, the braking force of each train reaches the same maximum value, and the air braking delay time is set to 5s, that is, the time for the train pipe decompression to be transmitted from the first freight car to the last freight car is 5s, and the time for starting air braking of each freight car is linearized, that is, within 5s, the train pipe decompression pressure is uniformly transmitted to the last freight car.

[0013] As a further optimization, the locomotive braking torque is applied to the main gear of the locomotive wheelset in the SIMPACK simulation software by means of time excitation and speed excitation, and the truck braking force is directly applied to the center of mass of the truck body. Then, the initial braking speed and time before train braking are input from the group train dynamics system model, and the train running resistance, maximum adhesion and minimum adhesion limits are input to complete the modeling of the locomotive braking system model.

[0014] As a further optimization, the safe braking distance of the group train is calculated by the three-level determination rule, and the safe tracking distance of the group train under the braking condition is output after the braking process is completed, including: The difference between the creep rate of each wheelset and the first threshold is used as the criterion e s1 and the difference criterion Δ between the angular acceleration of each wheel and the first threshold α 1, to determine whether wheelset slip occurs. e s1 or Δ α When 1 is greater than zero, it is determined that the wheelset is slipping, and the initial braking torque is recorded. T 0, by continuously reducing the motor torque, the motor torque reduction value Δ is calculated in real time T 1. Output motor torque T 1 to the braking system model, and then judged by the difference between the wheelset creep rate and the second threshold value e s2 , wheel angular acceleration and the second threshold difference criterion Δ α 2 Make a secondary judgment, when e s2 or α 2 is greater than zero, the torque returns to the decreasing stage and continues to adjust. e s2 and α 2 is less than zero, the motor torque recovery value Δ is calculated in real time T2. The restored motor torque T 2 is input into the brake system model, and then the judgment e s1 or Δ α When 1 is less than zero, the slippage ends and proceeds to the next step; The difference between the current distance to the rear vehicle and the safety limit Δ x When it is greater than zero, the train will continue to brake and calculate the total braking distance of the train in real time. x Less than zero, immediately reduce the torque, and then continue to pass the speed difference Δ v and locomotive brake torque T To determine whether the braking is completed, when Δ v and T When it is greater than zero, it returns to the braking system model and continues braking. v or T When it is equal to zero, the following vehicle stops, and the calculation of the safe braking distance of the group train stops. The braking process ends, and the safe tracking distance of the group train under the braking condition is finally output.

[0015] As a further optimization, when calculating the total braking distance of the train in real time, the communication delay is input, and the braking distance calculation begins when the data is transmitted to the following car.

[0016] The beneficial effects of the present invention are as follows: through the above-mentioned method for calculating the safe tracking distance of a group train based on adhesion braking, first, a group train dynamic system model is established; secondly, a group operation control sensor based on time, position and speed between two trains is established based on the group train dynamic system model, and communication delay and output distance difference are set; then, a wheel-rail adhesion controller is established, and the vehicle speed and the rotation speed of each wheel pair of the bogie are input from the group train dynamic system model, and the wheel pair angular acceleration and wheel pair creep rate are calculated; then, a braking system model is established, and the initial braking speed and time before the train braking are input from the group train dynamic system model, and the braking torque is calculated; finally, a group train adhesion braking cooperative control system model is established, and a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment is set. When the train starts to brake, the braking torque, distance difference, communication delay, wheel pair creep rate and wheel pair angular acceleration are input in real time, and the group train safe braking distance is calculated through the three-level judgment rule, and the group train safe tracking distance under the braking condition is output after the braking process is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of calculating the safe tracking distance of a group train based on adhesion braking in the first embodiment of the present invention; Figure 2 This is a schematic diagram of the wheel-rail adhesion controller in the braking mode in the first embodiment of the present invention; Figure 3 This is a schematic diagram of a group train adhesion braking cooperative control system in Embodiment 1 of the present invention; Figure 4 is a curve diagram showing the electric braking force, running resistance and adhesion force limit value changing with speed in the second embodiment of the present invention; Figure 5 This is a curve diagram of the braking force variation of a truck considering the air brake delay effect in the second embodiment of the present invention; Figure 6 The comparison results of the motor braking torque under normal and slip control conditions in the second embodiment of the present invention; Figure 7 The comparison results of the safe braking distances of trains under normal and slip control conditions in the second embodiment of the present invention are as follows; Figure 8 The train running speed comparison results under normal and slip control conditions in the second embodiment of the present invention; Fig. 9 The results are the comparison of the wheel-rail adhesion coefficients of the locomotive under normal and slip control conditions in the second embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations. Embodiment 1

[0019] See also Figure 1 This embodiment provides a method for calculating the safe tracking distance of a group train based on adhesion braking, and the method includes the following steps: S1. Establishing a group train dynamics system model; S2. Establishing a group operation control sensor based on time, position and speed between two trains based on the group train dynamics system model, and setting the communication delay and output distance difference; S3, establish a wheel-rail adhesion controller, input the vehicle speed and the rotation speed of each wheel set of the bogie from the group train dynamics system model, and calculate the two criteria of wheel set angular acceleration and wheel set creep rate; S4, establishing a braking system model, and inputting the initial braking speed and time before the train braking from the group train dynamics system model, and calculating the braking torque; S5. Establish a group train adhesion braking coordinated control system model, and set a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment. When the train starts braking, the braking torque, distance difference, communication delay, wheelset creep rate and wheelset angular acceleration are input in real time, and the safe braking distance of the group train is calculated through the three-level judgment rule. After the braking process is completed, the safe tracking distance of the group train under the braking condition is output.

[0020] It should be pointed out that in the above step S1 of this embodiment, the HXN3 diesel locomotive and C80 freight car are used as research objects, and the basic parameters, structural parameters, suspension parameters and track structural parameters of the locomotive vehicle are obtained. The maximum downhill slope of the track is set to 5~8‰, the minimum friction coefficient is set to 0.10~0.15, and the initial speed of the train before braking is set to 60~80km / h. The locomotive space dynamics model, the freight car simplified model and the three-dimensional space model of the coupler buffer are established through the SIMPACK simulation platform. The locomotive is coupled with 50 freight cars to achieve a traction weight of 5,000 tons, and then a group train dynamics system model of two identical trains is established. For the traditional calculation of the braking distance, when the front and rear vehicles are in motion and the rear vehicle is braking, it is not the safest to calculate the braking distance at this time, because the front and rear vehicles have relative motion. Therefore, in this embodiment, the front vehicle is set to be in a stopped state and the rear vehicle is braking again.

[0021] In the above step S2 of this embodiment, the group operation control sensor based on time, position and speed between the two trains is established based on the group train dynamic system model, and the communication delay and output distance difference are set, which means: firstly, a simplified model of the group communication system is established, and the data transmission of the front and rear trains is simulated by sensors, and the locomotive body center of mass position is taken as a reference point. Time, position, and speed sensors are established between the two trains to realize real-time data interaction between the front and rear trains, and then a controller is established through a simulation platform such as MATLAB or SIMULINK. Considering the influence of communication delay, the communication delay time is set to 0~2s, and the distance difference between the front and rear trains is output, so as to control the dynamic tracking of the heavy-loaded group train.

[0022] It should be pointed out that, in the above step S3 of this embodiment, the locomotive traction system is composed of multiple traction motors. In the axle control mode, each traction motor has an independent inverter drive device, so each wheel pair will output a rotation speed, and the vehicle speed is used as a reference speed. The wheel pair angular acceleration and the wheel pair creep rate calculation module are used to calculate the wheel pair angular acceleration and the wheel pair creep rate. In the axle control mode, each traction motor adopts an independent inverter drive device, and the brake torque adjustment module is used to realize the coordinated control of multiple wheel pairs. The control logic is as follows: Figure 2 As shown in the figure T 1-6 is the braking torque of each wheelset, and the wheelset angular acceleration is expressed asα i , its calculation module expression is: , In the formula, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by differentiating the wheel speed. t is the train running time, i =1~6, indicating the number and order of wheelsets; The wheelset creep rate is expressed as s i , its calculation module expression is: , In the formula, is the wheelset speed, r is the wheel radius, v ref is the reference speed.

[0023] In the above step S4 of this embodiment, when establishing the brake system model, the locomotive electric brake characteristic curve can be calculated based on the HXN3 diesel locomotive electric brake characteristic curve diagram, and the freight car air brake curve can be calculated based on the common brake cylinder pressure curve. After the locomotive electric brake characteristic curve is calculated, the locomotive electric brake characteristic curve is converted into a brake torque curve, and the locomotive brake torque is obtained from the brake torque curve, and the locomotive brake torque is applied to the main gear of the locomotive wheel set. The calculation expression of the locomotive brake torque is: , In the formula, T is the locomotive braking torque, F b For braking force, r is the wheel radius, n is the number of locomotive wheel sets, ξ is the gear ratio, which is equal to the ratio of the number of teeth on the driving gear to the number of teeth on the driven gear; After calculating the truck air brake curve, the truck braking force is obtained from the truck air brake curve, and the truck braking force is directly applied to the truck body center of mass position; The truck braking force is calculated by the conversion method. The truck braking force calculated by the conversion method means: when the train brakes, the truck braking force generated by the brake shoe pressure B , the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The converted friction coefficient of this brake shoe The product is calculated as follows: .

[0024] It should be pointed out that during the air braking process of the freight cars, when the brake cylinder of the last train reaches the maximum pressure, the braking force of each train reaches the same maximum value. Considering the influence of the delayed propagation of the air brake, when the train brakes, the head vehicle slows down first, and as the brake wave propagates backward, the rear vehicles also start to brake one after another. Therefore, the air brake delay time is set to 5s, that is, the time for the train pipe decompression to be transmitted from the first freight car to the last freight car is 5s, that is, when the brake is applied to 5s, each vehicle in the train has generated a braking force. In addition, in order to improve the calculation efficiency, this embodiment linearizes the time for each freight car to start air braking, that is, in 5s, the train pipe decompression is uniformly transmitted to the last freight car.

[0025] Among them, the locomotive braking torque can be applied to the main gear of the locomotive wheelset in the SIMPACK simulation software by means of time excitation and speed excitation, and the truck braking force can be directly applied to the center of mass of the truck body. Then, the initial braking speed and time before the train braking are input from the group train dynamics system model, and the train running resistance, maximum adhesion and minimum adhesion limit values ​​are input to complete the modeling of the locomotive braking system model.

[0026] For the above step S5 of this embodiment, see Figure 3 The safe braking distance of the group train is calculated by the three-level determination rule, and the safe tracking distance of the group train under the braking condition is output after the braking process is completed, including: The difference between the creep rate of each wheelset and the first threshold is used as the criterion e s1 and the difference criterion Δ between the angular acceleration of each wheel and the first threshold α 1, to determine whether wheelset slip occurs. e s1 or Δ α When 1 is greater than zero, it is determined that the wheelset is slipping, and the initial braking torque is recorded. T 0, by continuously reducing the motor torque, the motor torque reduction value Δ is calculated in real time T 1. Output motor torque T 1 to the braking system model, and then through a more stringent wheelset creep rate and the second threshold difference criterion e s2 , wheel angular acceleration and the second threshold difference criterion Δ α 2 Make a secondary judgment, when e s2 or α 2 is greater than zero, the torque returns to the decreasing stage and continues to adjust. e s2 and α 2 is less than zero, the motor torque recovery value Δ is calculated in real time T2. The restored motor torque T 2 is input into the brake system model, and then the judgment e s1 or Δ α When 1 is less than zero, the slippage ends and proceeds to the next step; The difference between the current distance to the rear vehicle and the safety limit Δ x When it is greater than zero, the train will continue to brake and calculate the total braking distance of the train in real time. x If the speed difference is less than zero, the torque is immediately reduced to prevent the train from colliding, and then the speed difference Δ between the front and rear trains is continued. v and braking torque T To determine whether the braking is completed, when Δ v and T When it is greater than zero, it returns to the braking system model and continues braking. v or T When it is equal to zero, the following vehicle stops, and the calculation of the safe braking distance of the group train stops. The braking process ends, and the safe tracking distance of the group train under the braking condition is finally output.

[0027] In this embodiment, after considering conditions such as wheelset slip, communication delay, air brake delay, etc., a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment is adopted to ensure real-time calculation of the safe braking distance of the train, and finally output the safe tracking distance of the group train under braking.

[0028] In actual application, when calculating the total braking distance of the train in real time, the communication delay is input. When the data is transmitted to the rear car, the braking distance is calculated. At this time, the braking distance will increase. The distance difference between the front and rear cars must be set with a strict safety limit, generally 50~80m, to ensure the safe operation of the train group. When the distance difference between the front and rear cars is less than the safety limit, the adhesion controller is immediately triggered and the torque reduction is started directly without the judgment of the wheelset angular acceleration and wheelset creep rate. In addition, the speed difference Δ v and braking torque T The two indicators are used to determine the braking stop, the main purpose of which is to prevent the misjudgment of no braking when the speed is not zero or the braking is still in progress when the speed is zero.

[0029] Therefore, this embodiment can set the most complex working conditions, and at the same time, trains of different models can be selected to be combined with the braking distance calculation method in this embodiment. Taking into account wheelset slip, communication delay, air brake delay, etc., a three-level judgment procedure is adopted, consisting of adhesion judgment, tracking judgment and braking judgment, so as to ensure real-time calculation of the safe braking distance of the train, and finally output the safe tracking distance of the group train under braking. In addition, the safe braking distance of the group train in this embodiment is only calculated after braking under slipping conditions, while the safe tracking distance of the group train takes into account the communication delay and the safety limit of the distance difference between the front and rear vehicles. Therefore, the safe tracking distance of the group train is calculated based on the safe braking distance. Embodiment 2

[0030] This embodiment takes a 5,000-ton heavy-load train pulled by an HXN3 diesel locomotive as an example, and establishes a heavy-load train dynamic model based on the locomotive vehicle parameters provided by the vehicle manufacturer. The locomotive weight is 150 tons, and the freight car adopts C80, whose single vehicle weight is 100 tons. 50 freight cars are built, which has reached a single-unit traction mass of 5,000 tons.

[0031] Track line working condition settings: straight ramp line, track unevenness adopts the American four-level spectrum, the initial braking speed is 60km / h, the maximum slope is 5‰, the track surface changes from a dry state to an oily state, the maximum friction coefficient is 0.6, the minimum friction coefficient is 0.15, the track surface change length is 140m, the locomotive brakes according to the electric brake characteristic curve, and the freight car brakes according to the air brake curve.

[0032] Setting of the locomotive braking characteristic curve: During the motor starting phase, in order to avoid impact and vibration, when the locomotive braking speed is lower than 1km / h, the braking force changes linearly and increases to 380kN; when the locomotive braking speed is in the range of 1~36km / h, the locomotive enters the constant braking torque control area with a braking force of 380kN; when the locomotive braking speed is greater than 36km / h, the locomotive enters the constant braking power control area with a braking power of 380kW. The maximum braking speed of the train does not exceed 120km / h. The braking characteristics of this locomotive overcome the shortcomings of insufficient braking force of resistance braking of DC-driven diesel locomotives at low speeds and the inconstant braking force caused by braking expansion. During the braking process, the vector resultant force of the electric braking force, resistance and the train gravity component is used as the final total braking force. The braking-related characteristic curves are as follows: Figure 4 shown.

[0033] Truck braking characteristic curve setting: input the converted friction coefficient, converted brake shoe pressure and other parameters, according to the train braking force in the present invention B Calculate the expression and finally output the braking force variation curve of the truck, such as Figure 5As shown, the present invention then linearizes the time for each freight car to start air braking, that is, within 5 seconds, the train pipe decompression pressure is uniformly transmitted to the last freight car, 100% normal air braking is applied to the freight car on the straight ramp, and the maximum air pressure of the brake cylinder is 600 kPa.

[0034] Group train adhesion braking coordinated control settings: vehicle-to-vehicle communication delay is set to 2s, the safety limit of the distance difference between the front and rear vehicles is 80m, the first threshold of the wheelset creep rate is 3.2%, the second threshold of the wheelset creep rate is 3.0%, and the first threshold of the wheelset angular acceleration is 12rad / s 2 The second threshold of wheel angular acceleration is 10 rad / s 2 .

[0035] Figures 6 to 9 The comparative simulation results of the second embodiment of the present invention under normal working conditions and slipping conditions.

[0036] Figure 6 It shows that during the entire braking process, the braking time under normal conditions and slipping conditions is 200s, the initial braking torque of a single motor is 5.93kN•m, and the final braking torque is 3.31kN•m. Since the wheelset slipped during the 6.5-14.5s period, the adhesion control system was triggered, and the torque was adjusted 5 times. The average braking torque was smaller than that under normal conditions, which delayed the time to enter the constant torque zone by 7s. However, the torque gradually returned to the same level at the end of braking.

[0037] Figure 7 It shows that due to the wheelset slippage (6 wheelsets), the adhesion is reduced and the train braking distance is extended. The normal braking distance is 1505.6m, the braking distance under the slipping condition is 1505.6m, and the braking distance is 1588.1m, which is 82.5m longer. At the same time, considering the communication delay, when the braking command is received, it will continue to travel in the traction condition for 2s, and the distance will continue to increase by about 33m. Considering the set safety limit, the total train safety braking distance is 1681.1m, which is 175.5m longer than the normal non-slip condition.

[0038] Figure 8 It shows that before 7s and after 185s of running time, the trains in normal and slipping conditions maintained the same speed. However, due to the reduced braking torque and delayed braking time in the slipping condition, the running speed of the train in the slipping condition was slightly higher than that in the normal condition during the 7~185s period. However, safe braking was finally completed.

[0039] Fig. 9It shows that: in the time period of 6.5~14.5s, the adhesion coefficient of the slipping condition gradually decreases from 0.26 to around 0.1, and then increases to 0.26. The adhesion control effect is very good. Through the reduction, maintenance and recovery of torque, the train safely passes the slipping section, and the adhesion coefficients under subsequent normal conditions and slipping conditions tend to be at the same level.

[0040] In summary, during the train braking process, due to the influence of time factors such as communication delay and air brake delay, and the influence of operating conditions such as changes in track adhesion state, the train safety tracking distance under normal operating conditions cannot meet the safe operation of group trains. Therefore, it is necessary to consider the impact of adhesion braking on group operation control, so as to calculate a minimum train safety tracking distance for heavy-load group trains.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the safe tracking distance of a group of trains based on adhesion braking, characterized in that: The steps include: Establish a group train dynamic system model; Based on the group train dynamics system model, a group operation control sensor based on time, position and speed between two trains is established, and the communication delay and output distance difference are set; A wheel-rail adhesion controller is established, and the vehicle speed and the rotation speed of each wheel set of the bogie are input from the group train dynamics system model, and the wheel set angular acceleration and wheel set creep rate are calculated; Establish a braking system model, input the initial braking speed and time before the train brakes from the group train dynamics system model, and calculate the braking torque; A group train adhesion braking coordinated control system model is established, and a three-level judgment rule consisting of adhesion judgment, tracking judgment and braking judgment is set. When the train starts braking, the braking torque, distance difference, communication delay, wheelset creep rate and wheelset angular acceleration are input in real time, and the safe braking distance of the group train is calculated through the three-level judgment rule. After the braking process is completed, the safe tracking distance of the group train under the braking condition is output.

2. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: Establish a group train dynamic system model through SIMPACK or UM or SIMULINK or ADAMS simulation platform, and obtain the basic parameters, structural parameters and suspension parameters of heavy-load locomotives, freight cars and train retarder, as well as track structural parameters; When establishing the group train dynamic system model, it is assumed that the rear train will brake only when the front train is in a stopped state.

3. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: The method of establishing a group operation control sensor based on time, position and speed between two trains based on the group train dynamics system model, and setting a communication delay and an output distance difference, means: A simplified model of the group communication system is established to simulate the data transmission between the front and rear trains through sensors; Based on the group train dynamics system model, the locomotive body mass center position is taken as the reference point, and time, position and speed sensors are established between the two trains for real-time data exchange between the front and rear trains. The controller is established through the MATLAB or SIMULINK simulation platform, the communication delay time is set to 0~2s, and the distance difference between the front and rear vehicles is output.

4. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: The wheel angular acceleration is expressed as α i , and its calculation formula is: ， In the formula, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by differentiating the wheel speed. t is the train running time, i =1~6, indicating the number and order of wheelsets; The wheelset creep rate is expressed as s i , and its calculation formula is: ， In the formula, is the wheelset speed, r is the wheel radius, v ref is the reference speed.

5. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: When establishing the brake system model, the locomotive electric brake characteristic curve is calculated based on the HXN3 type diesel locomotive electric brake characteristic curve diagram, and the freight car air brake curve is calculated based on the brake cylinder pressure curve.

6. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 5, characterized in that: After calculating the locomotive electric brake characteristic curve, the locomotive electric brake characteristic curve is converted into a brake torque curve, and the locomotive brake torque is obtained from the brake torque curve, and the locomotive brake torque is applied to the main gear of the locomotive wheel set. The calculation expression of the locomotive brake torque is: ， In the formula, T is the locomotive braking torque, F b For braking force, r is the wheel radius, n is the number of locomotive wheel sets, ξ is the gear ratio, which is equal to the ratio of the number of teeth on the driving gear to the number of teeth on the driven gear; After calculating the truck air brake curve, the truck braking force is obtained from the truck air brake curve, and the truck braking force is directly applied to the truck body center of mass position; The truck braking force is calculated by the conversion method. The truck braking force calculated by the conversion method means: when the train brakes, the truck braking force generated by the brake shoe pressure B , the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The converted friction coefficient of this brake shoe The product is calculated as follows: 。 7. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 6, characterized in that: During the air braking process of the freight cars, when the brake cylinder of the last train reaches the maximum pressure, the braking force of each train reaches the same maximum value. The air braking delay time is set to 5s, that is, the time for the train pipe decompression to be transmitted from the first freight car to the last freight car is 5s, and the time for starting air braking of each freight car is linearized, that is, within 5s, the train pipe decompression pressure is uniformly transmitted to the last freight car.

8. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 6, characterized in that: In the SIMPACK simulation software, the locomotive braking torque is applied to the main gear of the locomotive wheelset by time excitation and speed excitation, and the truck braking force is directly applied to the center of mass of the truck body. Then, the initial braking speed and time before train braking are input from the group train dynamics system model, and the train running resistance, maximum adhesion and minimum adhesion limits are input to complete the modeling of the locomotive braking system model.

9. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: The method of calculating the safe braking distance of the group train by the three-level determination rule and outputting the safe tracking distance of the group train under the braking condition after the braking process is completed includes: The difference between the creep rate of each wheelset and the first threshold is used as the criterion e s1 and the difference criterion Δ between the angular acceleration of each wheel and the first threshold α 1, to determine whether wheelset slip occurs. e s1 or Δ α When 1 is greater than zero, it is determined that the wheelset is slipping, and the initial braking torque is recorded. T 0, by continuously reducing the motor torque, the motor torque reduction value Δ is calculated in real time T 1. Output motor torque T 1 to the braking system model, and then judged by the difference between the wheelset creep rate and the second threshold value e s2 , wheel angular acceleration and the second threshold difference criterion Δ α 2 Make a secondary judgment, when e s2 or α 2 is greater than zero, the torque returns to the decreasing stage and continues to adjust. e s2 and α 2 is less than zero, the motor torque recovery value Δ is calculated in real time T 2. The restored motor torque T 2 is input into the brake system model, and then the judgment e s1 or Δ α When 1 is less than zero, the slippage ends and proceeds to the next step; The difference between the current distance to the rear vehicle and the safety limit Δ x When it is greater than zero, the train will continue to brake and calculate the total braking distance of the train in real time. x Less than zero, immediately reduce the torque, and then continue to pass the speed difference Δ v and braking torque T To determine whether the braking is completed, when Δ v and T When it is greater than zero, it returns to the braking system model and continues braking. v or T When it is equal to zero, the following vehicle stops, and the calculation of the safe braking distance of the group train stops. The braking process ends, and the safe tracking distance of the group train under the braking condition is finally output.

10. The method for calculating the safe tracking distance of a group of trains based on adhesion braking according to claim 1, characterized in that: When calculating the total braking distance of the train in real time, the communication delay is input, and the braking distance calculation begins when the data is transmitted to the following train.

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