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

Abstract

This 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 to establish a group train dynamic system model, group operation control sensors, wheel-rail adhesion controller, braking system model, and 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 begins braking, the braking torque, distance difference, communication delay, wheelset creep rate, and wheelset angular acceleration are input in real time. The safe braking distance of the group train is calculated using the three-level judgment rule. After the braking process is completed, the safe tracking distance of the group train under braking conditions is output. This method can accurately calculate the safe tracking distance of the group train under braking conditions by using the three-level judgment rule consisting of adhesion judgment, tracking judgment, and braking judgment under complex operating conditions and train conditions of different types.

Description

Technical Field

[0001] The present invention relates to the field of rail transit technology, and in particular to a method for calculating the 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, highly reliable 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, enables rapid marshaling and disassembling, efficient train reception and dispatching at stations, and improves railway transportation efficiency.

[0003] Despite continuous advancements in group operation control technology, safe train operation remains the most critical control objective, and controlling the safe braking distance of group trains is crucial for safe train operation. Therefore, dynamic modeling can be used to effectively estimate the safe distance between trains. However, due to the complexity of the track surface and adverse weather conditions, wheel-rail adhesion directly impacts locomotive traction power, train stability, and braking, posing a threat to wheel-rail interaction and the control of safe train distance. Therefore, wheel-rail adhesion must be considered when calculating safe train distance.

[0004] In group operation, most rail vehicles still use adhesion braking, whose braking performance is limited by wheel-rail adhesion. When trains travel on rail surfaces contaminated by third media such as rain, frost, oil, and leaves, the available wheel-rail adhesion is limited, making slippage very likely. In severe cases, the train may even lock. This leads to insufficient adhesion, extending the train's braking distance, preventing it from stopping within the specified distance, and even causing major accidents such as derailment, seriously impacting train safety, economy, comfort, and punctuality. The safe tracking interval of group trains is closely related to wheel-rail adhesion conditions. To improve transportation efficiency, the traditional fixed block mode has been eliminated and a smaller train tracking interval has been adopted. Especially under braking conditions, when extreme slippage occurs, the tracking interval can be longer than the normal braking distance. Therefore, based on the wheel-rail adhesion issue, a coordinated controller for locomotive wheel-rail adhesion and locomotive braking is designed during train group operation. Calculating the safe braking distance of trains under complex horizontal and vertical section track conditions is particularly critical. 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 of trains based on adhesion braking. The method can take heavy-loaded group trains as the research object, with the calculation of the safe tracking distance of trains in braking mode as the main goal. Through the coordinated control of group train adhesion braking, the method provides a key basis for accurately quantifying the minimum safe tracking distance of trains, so as to simulate the dynamic tracking of multi-unit trains more realistically and accurately, ensure the normal operation and scheduling of trains, and improve the efficiency of organized transportation.

[0006] The present invention solves the technical problem and adopts the following technical solution:

[0007] A method for calculating the safe tracking distance of a group train based on adhesion braking comprises the following steps:

[0008] Establish a group train dynamic system model;

[0009] Based on the group train dynamics system model, a group operation control sensor based on time, position and speed is established between the two trains, and the communication delay and output distance difference are set;

[0010] A wheel-rail adhesion controller is established, and the vehicle speed and the rotational speed of each bogie wheel set are input from the group train dynamics system model. The wheel set angular acceleration and wheel set creep rate are calculated.

[0011] 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;

[0012] 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.

[0013] For further optimization, a group train dynamics system model is established using SIMPACK, UM, SIMULINK, or ADAMS simulation platforms, and the basic parameters, structural parameters, and suspension parameters of the heavy-load locomotive, freight car, and train retarder are obtained, as well as the track structure parameters.

[0014] When establishing the group train dynamics system model, it is assumed that the rear train will brake only when the front train is in a stopped state.

[0015] As a further optimization, the group train dynamics system model is used to establish a group operation control sensor based on time, position and speed between the two trains, and to set the communication delay and output distance difference, which means:

[0016] A simplified model of the group communication system was established to simulate data transmission between the front and rear trains through sensors;

[0017] Based on the group train dynamics system model, the locomotive body center of mass 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.

[0018] A controller is established using 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.

[0019] As a further optimization, the wheel angular acceleration is expressed as α i , and its calculation formula is:

[0020] ,

[0021] Where, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by performing differential processing on the wheel speed. t is the train running time, i =1~6, indicating the number and order of wheelsets;

[0022] The wheelset creep rate is expressed as s i , and its calculation formula is:

[0023] ,

[0024] Where, is the wheelset speed, r is the wheel radius, v ref is the reference speed.

[0025] 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.

[0026] 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. The locomotive brake torque is applied to the main gear of the locomotive wheelset. The calculation expression of the locomotive brake torque is:

[0027] ,

[0028] Where, T is the locomotive braking torque, F b For braking force,r is the wheel radius, n is the number of locomotive wheel pairs, 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;

[0029] 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;

[0030] The truck braking force is calculated using the conversion method. The truck braking force calculated using the conversion method means that when the train brakes, the truck braking force generated by the brake shoe pressure is: B , use the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The conversion friction coefficient of this brake shoe The product is calculated as follows:

[0031] .

[0032] 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 transmitted to the last freight car at a uniform speed.

[0033] As a further optimization, the locomotive braking torque is applied to the main gear of the locomotive wheelset using time excitation and speed excitation in the SIMPACK simulation software, and the freight car braking force is directly applied to the center of mass of the freight car body. 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 limits are input to complete the modeling of the locomotive braking system model.

[0034] 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:

[0035] 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 each wheel angular acceleration and the first threshold α 1, to determine whether wheelset slip occurs, when 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. T0, 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 brake system model, and then judged by the difference between the wheelset creep rate and the second threshold 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, then the system returns to the torque reduction stage and continues to adjust. e s2 and α When 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 e s1 or Δ α When 1 is less than zero, the slippage ends and proceeds to the next step;

[0036] The difference between the current distance to the following 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 it is less than zero, the torque is immediately reduced, and then the speed difference Δ between the front and rear vehicles is continued. v and locomotive 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.

[0037] 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 starts when the data is transmitted to the following train.

[0038] The beneficial effects of the present invention are as follows: through the above-mentioned adhesion braking-based group train safe tracking distance calculation method, first, a group train dynamics system model is established; second, based on the group train dynamics system model, a group operation control sensor based on time, position, and speed is established between the two trains, and a 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 bogie wheel set are input from the group train dynamics 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 dynamics system model, and the braking torque is calculated; finally, a group train adhesion braking coordinated control system model is established, and a three-level determination rule consisting of adhesion determination, tracking determination, and braking determination is set. When the train starts braking, the braking torque, distance difference, communication delay, wheel pair creep rate, and wheel pair angular acceleration are input in real time. The safe braking distance of the group train is calculated using 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of calculating the safe tracking distance of a group train based on adhesion braking in Example 1 of the present invention;

[0040] Figure 2 This is a schematic diagram of the wheel-rail adhesion controller in braking mode according to the first embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of a coordinated control system for adhesion braking of a group of trains in accordance with a first embodiment of the present invention;

[0042] Figure 4 This is a graph showing how the electric braking force, running resistance, and adhesion force limit change with speed in the second embodiment of the present invention;

[0043] Figure 5 This is a graph showing the braking force variation of a truck considering the air brake delay effect in the second embodiment of the present invention;

[0044] Figure 6 The comparison results of the motor braking torque under normal and slip control conditions in the second embodiment of the present invention are as follows;

[0045] Figure 7 The comparison results of the safe braking distance of the train under normal and slip control conditions in the second embodiment of the present invention are as follows;

[0046] Figure 8 The comparison results of train running speeds under normal and slip control conditions in Example 2 of the present invention are as follows;

[0047] Figure 91 is a comparison result of the locomotive wheel-rail adhesion coefficient under normal and slip control conditions in Example 2 of the present invention. DETAILED DESCRIPTION

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only 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 herein can be arranged and designed in various different configurations. Example 1

[0049] See also Figure 1 This embodiment provides a method for calculating the safe tracking distance of a group train based on adhesion braking, which includes the following steps:

[0050] S1. Establish a group train dynamics system model;

[0051] S2. Based on the group train dynamics system model, establish a group operation control sensor based on time, position and speed between the two trains, and set the communication delay and output distance difference;

[0052] S3. Build a wheel-rail adhesion controller, input the vehicle speed and the rotational speed of each bogie wheel set from the group train dynamics system model, and calculate the two criteria: wheel set angular acceleration and wheel set creep rate;

[0053] S4. 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;

[0054] 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. The safe braking distance of the group train is calculated using 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.

[0055] It should be noted that in step S1 of this embodiment, an HXN3 diesel locomotive and a C80 freight car were used as the research objects. Basic parameters, structural parameters, suspension parameters, and track structural parameters of the locomotive and rolling stock were obtained. The maximum downhill slope of the track was set to 5-8‰, the minimum friction coefficient was set to 0.10-0.15, and the initial speed of the train before braking was set to 60-80 km / h. A locomotive spatial dynamics model, a simplified freight car model, and a three-dimensional spatial model of the coupler buffer were established using the SIMPACK simulation platform. The locomotive was coupled to 50 freight cars to achieve a hauling weight of 5,000 tons. A dynamics system model of two identical trains was then established. Regarding the traditional calculation of braking distance based on the maneuvering of the leading and trailing cars, when the leading car is moving and the trailing car is braking, calculating the braking distance is not the safest method because the leading and trailing cars are in relative motion. Therefore, this embodiment assumes that the leading car is stopped and the trailing car is braking.

[0056] In the above-mentioned step S2 of this embodiment, the said establishing a group operation control sensor based on time, position and speed between the two trains based on the group train dynamics system model, and setting the communication delay and output distance difference means: first establishing a simplified model of the group communication system, simulating the data transmission of the front and rear trains through sensors, taking the locomotive body center of mass position as the reference point, establishing time, position, and speed sensors between the two trains to realize real-time data interaction between the front and rear trains, and then establishing a controller through a simulation platform such as MATLAB or SIMULINK. Taking into account 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, thereby controlling the dynamic tracking of the heavy-load group train.

[0057] It should be noted 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. Therefore, each wheelset will output a rotational speed, and the vehicle speed is used as a reference speed. The wheelset angular acceleration and wheelset creep rate calculation module are used to calculate the wheelset angular acceleration and wheelset creep rate. In the axle control mode, each traction motor uses an independent inverter drive device, and the braking torque adjustment module is used to achieve multi-wheelset adhesion coordinated control. 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 as α i , its calculation module expression is:

[0058] ,

[0059] Where, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by performing differential processing on the wheel speed. tis the train running time, i =1~6, indicating the number and order of wheelsets;

[0060] The wheelset creep rate is expressed as s i , its calculation module expression is:

[0061] ,

[0062] Where, is the wheelset speed, r is the wheel radius, v ref is the reference speed.

[0063] In 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 a common brake cylinder pressure curve. 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. The locomotive brake torque is then applied to the main gear of the locomotive wheelset. The calculation expression for the locomotive brake torque is:

[0064] ,

[0065] Where, T is the locomotive braking torque, F b For braking force, r is the wheel radius, n is the number of locomotive wheel pairs, 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;

[0066] 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;

[0067] The truck braking force is calculated using the conversion method. The truck braking force calculated using the conversion method means that when the train brakes, the truck braking force generated by the brake shoe pressure is: B , use the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The conversion friction coefficient of this brake shoe The product is calculated as follows:

[0068] .

[0069] It should be noted that during the air braking process of freight cars, when the brake cylinder of the last train reaches maximum pressure, the braking force of each train reaches the same maximum value. Considering the effect of air brake propagation delay, the leading car decelerates first when the train brakes. As the braking wave propagates backward, the trailing cars also begin braking. Therefore, the air brake delay is set to 5 seconds. That is, the time it takes for the train pipe decompression to be transmitted from the first freight car to the last freight car is 5 seconds. In other words, by the time the brake is applied for 5 seconds, all freight cars in the train have generated braking force. In addition, to improve computational efficiency, this embodiment linearizes the time it takes for each freight car to initiate air braking. That is, the train pipe decompression is uniformly transmitted to the last freight car over a period of 5 seconds.

[0070] Among them, the locomotive braking torque can be applied to the main gear of the locomotive wheelset in the SIMPACK simulation software using time excitation and speed excitation, and the freight car braking force can be directly applied to the center of mass of the freight car body. 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 limits are input to complete the modeling of the locomotive braking system model.

[0071] For the above step S5 of this embodiment, see Figure 3 The method of calculating the safe braking distance of the group train by using 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:

[0072] 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 each wheel angular acceleration and the first threshold α 1, to determine whether wheelset slip occurs, when 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 wheel 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, then the system returns to the torque reduction stage and continues to adjust. e s2 and α When 2 is less than zero, the motor torque recovery value Δ is calculated in real timeT 2. The restored motor torque T 2 is input into the brake system model, and then the e s1 or Δ α When 1 is less than zero, the slippage ends and proceeds to the next step;

[0073] The difference between the current distance to the following 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 train stops, and the calculation of the group train safe braking distance stops. The braking process ends, and the final output is the group train safe tracking distance under the braking condition.

[0074] In this embodiment, after considering conditions such as wheelset slip, communication delay, and air brake delay, 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 ultimately output the safe tracking distance of the group train under braking.

[0075] 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 following train, the braking distance is calculated. At this time, the braking distance will be increased. The distance difference between the front and rear trains 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 trains is less than the safety limit, the adhesion controller is immediately triggered and the torque reduction is directly started without the need to judge 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 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.

[0076] Therefore, this embodiment can set the most complex operating 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. Moreover, the safe braking distance of the group train in this embodiment is only calculated after braking under the slipping condition, 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. Example 2

[0077] This example uses a 5,000-ton heavy-haul train pulled by an HXN3 diesel locomotive as an example. Based on the locomotive and vehicle parameters provided by the vehicle manufacturer, a heavy-haul train dynamics model is established. The locomotive weighs 150 tons, and the freight cars are C80, each weighing 100 tons. A 50-car freight car system is used, achieving a single-unit traction mass of 5,000 tons.

[0078] Track line operating condition settings: straight slope line, track unevenness adopts the US Level 4 spectrum, the initial braking speed is 60km / h, the maximum slope is 5‰, the rail 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 rail 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.

[0079] 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 linearly increases to 380kN; when the locomotive braking speed is within 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. This locomotive braking characteristic overcomes the shortcomings of insufficient braking force at low speeds and non-constant braking force caused by braking expansion in DC transmission diesel locomotives. During the braking process, the vector resultant force of the electric braking force, resistance and train gravity component is used as the final total braking force. The braking-related characteristic curves are as follows: Figure 4 shown.

[0080] Truck braking characteristic curve setting: input the converted friction coefficient, converted brake shoe pressure and other parameters, according to the train braking force in this invention B Calculate the expression and finally output the braking force change 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, and 100% normal air braking is applied to the freight car on a straight slope, and the maximum air pressure of the brake cylinder is 600 kPa.

[0081] Adhesion braking coordinated control settings for group trains: vehicle-to-vehicle communication delay is set to 2s, the safety limit for the distance difference between the front and rear vehicles is 80m, the first threshold for wheelset creep rate is 3.2%, the second threshold for wheelset creep rate is 3.0%, and the first threshold for wheelset angular acceleration is 12rad / s 2 The second threshold of wheel angular acceleration is 10 rad / s 2 .

[0082] Figures 6-9 The following are comparative simulation results of the second embodiment of the present invention under normal working conditions and slipping conditions.

[0083] Figure 6 The results show that during the entire braking process, the braking time under normal 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.

[0084] Figure 7 The data indicates that due to wheelset slip (six wheelsets), adhesion was reduced, extending the train's braking distance. The normal braking distance is 1505.6m, while the braking distances under slip conditions are 1505.6m and 1588.1m, respectively, an increase of 82.5m. Furthermore, considering communication delays, the train will continue to operate in traction mode for 2 seconds after receiving the braking command, increasing the distance by approximately 33m. Taking into account the established safety limits, the total safe braking distance is 1681.1m, an increase of 175.5m compared to normal, non-slip conditions.

[0085] Figure 8 The results show that before 7 seconds and after 185 seconds of operation, 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 7-185 second period. However, both trains eventually completed safe braking.

[0086] Figure 9The results show 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.

[0087] In summary, during the train braking process, due to the influence of time factors such as communication delay and air brake delay, as well as operating conditions such as changes in track adhesion, the train safety tracking distance under normal operating conditions cannot meet the requirements for safe operation of group trains. Therefore, it is necessary to consider the impact of adhesion braking on group operation control and calculate a minimum train safety tracking distance for heavy-load group trains.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for calculating the safe tracking distance of a group train based on adhesion braking, characterized in that: The steps include: Establish a group train dynamics system model; Based on the group train dynamics system model, a group operation control sensor based on time, position and speed is established between the two trains, and the communication delay and output distance difference are set; A wheel-rail adhesion controller is established, and the vehicle speed and the rotational speed of each bogie wheel set are input from the group train dynamics system model. 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 model for adhesion and braking of group trains was established, and a three-level decision rule consisting of adhesion determination, tracking determination, and braking determination was set. When the train begins braking, the braking torque, distance difference, communication delay, wheelset creep rate, and wheelset angular acceleration are input in real time. The three-level decision rule is used to calculate the safe braking distance of the group trains. After the braking process is completed, the safe tracking distance of the group trains under braking conditions is output. 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 each wheel angular acceleration and the first threshold α 1, to determine whether wheelset slip occurs, when 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 brake system model, and then judged by the difference between the wheelset creep rate and the second threshold 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, then the system returns to the torque reduction stage and continues to adjust. e s2 and α When 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 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 following 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 it is less than zero, the torque is immediately reduced, and then the speed difference Δ between the front and rear vehicles 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 train stops, and the calculation of the group train safe braking distance stops. The braking process ends, and the final output is the group train safe tracking distance under the braking condition.

2. The method for calculating the safe tracking distance of a group train based on adhesion braking according to claim 1, characterized in that: Establish a group train dynamics system model through SIMPACK, UM, SIMULINK, or ADAMS simulation platforms, and obtain the basic parameters, structural parameters, and suspension parameters of the heavy-load locomotive, freight car, and train retarder, as well as the track structure parameters; When establishing the group train dynamics 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 train 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 the communication delay and output distance difference refers to: A simplified model of the group communication system was established to simulate data transmission between the front and rear trains through sensors; Based on the group train dynamics system model, the locomotive body center of mass 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. A controller is established using 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 train 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: ， Where, is the first-order derivative of the wheelset speed, that is, the wheelset angular acceleration is obtained by performing differential processing on 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: ， Where, 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 train 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 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 train 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. The locomotive brake torque is applied to the main gear of the locomotive wheelset. The calculation expression of the locomotive brake torque is: ， Where, T is the locomotive braking torque, F b For braking force, r is the wheel radius, n is the number of locomotive wheel pairs, 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; The truck braking force is calculated using the conversion method. The truck braking force calculated using the conversion method means that when the train brakes, the truck braking force generated by the brake shoe pressure is: B , use the sum of the converted brake shoe pressures of each brake shoe in the truck ∑ K The conversion friction coefficient of this brake shoe The product is calculated as follows: 。 7. The method for calculating the safe tracking distance of a group train 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 train 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 using time and speed excitation, and the freight car braking force is directly applied to the center of mass of the freight car body. The initial braking velocity 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 train 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 starts when the data is transmitted to the following train.

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