Wear interface evolution method of high-speed train brake pad friction block on long and steep slopes

Abstract

The present invention belongs to the field of rail transit technology and discloses a method for the evolution of the wear interface of the brake pad friction block of a high-speed train on a long and steep slope. First, an initial finite element model is constructed and meshed; the connection relationship and constraint conditions of each component are defined; a first braking pressure is applied to the end of the push rod, and based on static analysis, the initial finite element model is simulated and analyzed to obtain a cloud diagram of the wear distribution of the friction block over time; a second braking pressure is applied to the end of the push rod, and based on static analysis, the simulated finite element model is further simulated and analyzed to obtain a cloud diagram of the wear distribution of the friction block over time. Through finite element simulation, the present invention can realize the evolution process of the wear interface of the brake pad friction block of a high-speed train on a long and steep slope, analyze the friction behavior between the brake pad friction block and the brake disc, and provide the necessary theoretical basis and application guidance for the optimal design of the brake pad friction block of a high-speed train.

Description

Technical Field

[0001] The present invention belongs to the field of rail transportation technology, and relates to a study on the wear of a high-speed train brake pad friction block, and in particular to a method for evolving the wear interface of a high-speed train brake pad friction block on a long slope. Background Art

[0002] Disc brakes, a crucial component for ensuring the safe operation of high-speed trains, utilize frictional contact between brake pads and discs to achieve train braking, precise stopping, and stable speed regulation. In recent years, the increasing speed of trains and the increasingly complex and changing operating environment, particularly the steep and undulating slopes of high-speed rail lines, have posed greater challenges to train safety. When trains are constantly braking on steep slopes, brake pad wear is more severe than on normal lines, placing higher demands on the brake pads' tribological properties.

[0003] At present, relevant scholars mainly focus on the research of brake tribological behavior under normal lines. Fan Zhiyong used microscopic testing methods to obtain the main damage characteristics and causes of brake pad friction blocks [see Fan Zhiyong, Xiang Zaiyu, Tan Deqiang, et al. Analysis of friction damage of brake pads of CRH380A high-speed train [J]. Journal of Tribology, 2020, 40(02): 185-194. DOI: 10.16078 / j.tribology.2019156]. AbuBakar et al. designed a braking test and found that as wear progresses, the contact area between the brake pad and the brake disc increases and the brake pad exhibits eccentric wear [see AbuBakar AR, Ouyang H. Wear prediction of friction material and brake squeal using the finite element method [J]. Wear, 2008, 264(11-12): 1069-1076]. Tang Bin et al. conducted drag braking tests on triangular friction blocks in four different installation directions. The results showed that when one corner of the triangular friction block first entered the friction area, the stress concentration at the friction entry end was the most obvious, resulting in the highest intensity vibration noise [see Tang Bin, Fan Zhiyong, Xiang Zaiyu, et al. Influence of the Cutting-End Characteristics of High-Speed Train Braking Friction Blocks on the Braking Interface Characteristics [J]. China Mechanical Engineering, 2021, 32(04): 412-419]. The above studies have preliminarily explored the tribological behavior of brake pad friction blocks under the influence of different factors, but because the braking friction behavior is easily affected by the line state, it cannot fully explain the actual evolution of braking wear under long and steep slope lines. In particular, the tribological behavior of the braking interface is very complex, and research on the influence of long and steep slopes on key parameters of the tribological behavior of the braking interface (such as contact inclination angle, contact stress, wear characteristics, friction self-excited vibration, etc.) is still relatively scarce. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for the evolution of the wear interface of the brake pad friction block of a high-speed train on a steep slope, and to analyze the friction behavior between the brake pad friction block and the brake disc through a finite element simulation method.

[0005] The long and steep slope targeted in the present invention refers to a road section with a large slope and a long slope length. For example, the slope of some lines may reach 20‰-30‰, and the slope length may exceed 10 kilometers.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solutions to achieve them.

[0007] The present invention provides a method for evolving the wear interface of a high-speed train brake pad friction block on a long and steep slope, comprising the following steps:

[0008] S1 constructs an initial finite element model and performs meshing on the initial finite element model; the initial finite element model includes a brake disc pattern, a friction pad pattern, a fixture pattern, a vibration acceleration sensor pattern, a bearing pattern, and a push rod pattern;

[0009] S2 defines the connection relationship and constraints of each component;

[0010] In step S3, a first braking pressure is applied to the end of the push rod. Based on static analysis, the initial finite element model is simulated and analyzed to obtain a wear distribution cloud diagram of the friction block over time. This is performed until the contact stress on the friction block is evenly distributed, and then the process proceeds to step S4. The first braking pressure is the parking brake pressure of the train.

[0011] S4 sets the push rod end to apply a second brake pressure. Based on static analysis, the finite element model simulated in step S3 is further simulated and analyzed to obtain a wear distribution cloud diagram of the friction block over time; until the contact stress on the friction block is evenly distributed; the second brake pressure is less than the first brake pressure; the second brake pressure is the speed limit brake pressure for trains on long and steep slopes;

[0012] The wear evolution law of the brake pad friction block of the high-speed train on a long slope is obtained through the above steps S3 and S4;

[0013] In steps S3 and S4, a wear distribution cloud diagram of the friction block over time is obtained by following the steps below:

[0014] (1) According to the first braking pressure or the second braking pressure applied at the end of the push rod, the contact stress p and relative slip distance of the grid node are extracted through the UMESHMOTION subroutine.

[0015] (2) According to Archard's wear theory, the calculation formula for determining the wear thickness increment dh of a grid node on the contact surface of the friction block in an incremental step is as follows:

[0016]

[0017] Where k′ is the wear amplification factor; ω is the angular velocity, and dt is a time increment;

[0018] (3) The wear thickness increment is converted into the displacement of the contact surface mesh through the UMESHMOTION subroutine, and the wear thickness increment is represented by the displacement of the contact surface mesh;

[0019] (4) The wear distribution cloud diagram of the corresponding friction block surface is obtained by spreading the wear distribution cloud diagram over the friction block surface;

[0020] As time changes, the above steps (1)-(4) are repeated to obtain a wear distribution cloud diagram of the friction block pattern as it changes with time.

[0021] In the above step S2, the connection relationship and constraints of the components include:

[0022] (1) The brake disc pattern and the friction pad pattern, as well as the push rod pattern and the bearing pattern are in surface-to-surface contact. The main surface is the contact surface between the brake disc pattern friction surface and the push rod pattern, and the secondary surface is the corresponding contact surface.

[0023] (2) The contact behavior between the brake disc pattern and the friction pad pattern is set to tangential friction and normal hard contact;

[0024] (3) Constrain the translational freedom of the inner ring coupling point of the brake disc pattern in all directions and the rotational freedom of the X and Y axes, and retain the rotational freedom of the brake disc pattern in the Z axis;

[0025] (4) Tie constraints are set between the friction block pattern and the fixture pattern, the vibration acceleration sensor pattern and the fixture pattern, and the fixture pattern and the push rod pattern.

[0026] In the above step S2, the density, Young's modulus and Poisson's ratio of the brake disc pattern, friction pad pattern, fixture pattern, vibration acceleration sensor pattern, bearing pattern and push rod pattern are also defined.

[0027] In the above step S4, the second braking pressure is 20%-50% of the first braking pressure.

[0028] In step S3 or step S4, based on the wear distribution cloud of the friction block pattern over time, several grid nodes are selected along the diagonal line of the friction block, and the wear thickness increments obtained at each node over time are extracted. The diagonal line can be from the lower left corner to the upper right corner, or from the upper left corner to the lower right corner. Furthermore, the ratio of the wear thickness increment difference between the two most distant grid nodes to the length of the diagonal line is defined as the eccentric wear, and a temporal trend graph of the eccentric wear is generated.

[0029] In the above step S3 or step S4, before simulating with the finite element model, several grid nodes on the same normal line of the contact surface between the friction pad pattern and the brake disc pattern are selected, and the displacement values of the corresponding grid nodes are simultaneously extracted during the simulation process. The angle between the straight line obtained by fitting the several grid nodes and the normal direction of the brake disc pattern is defined as the contact tilt angle of the friction pad; and then the trend of the contact tilt angle of the friction pad changing with time is obtained.

[0030] The above-mentioned method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope further includes:

[0031] S5 sets the push rod end to apply a first braking pressure, performs simulation analysis on the initial finite element model based on implicit dynamics analysis, and obtains time domain signals of normal and / or tangential vibration acceleration of the friction block;

[0032] S6 sets a first braking pressure to be applied at the end of the push rod, and performs simulation analysis on the finite element model simulated in step S3 based on implicit dynamics analysis to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block;

[0033] S7 sets the push rod end to apply a second brake pressure, and based on implicit dynamics analysis, performs simulation analysis on the finite element model simulated in step S3 to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block;

[0034] Through the above steps S5-S7, the vibration response evolution law of the brake pad friction block of the high-speed train on the long slope is obtained.

[0035] Compared with the prior art, the method for the evolution of the wear interface of the brake pad friction block of a high-speed train on a long and steep slope provided by the present invention has the following beneficial effects:

[0036] (1) The present invention uses a finite element simulation method to realize the evolution process of the wear interface of the brake pad friction block of a high-speed train on a long slope, and analyze the friction behavior between the brake pad friction block and the brake disc, thereby providing the necessary theoretical basis and application guidance for the optimization design of the brake pad friction block of a high-speed train;

[0037] (2) The present invention obtains the time-varying trend of the wear cloud map by analyzing the wear interface evolution process of the friction block of the brake pad of a high-speed train on a long slope, thereby reflecting the influence of the braking pressure on the contact inclination angle between the friction block and the brake disc, and then obtaining the wear law of the friction block;

[0038] (3) The present invention studies the evolution of the wear interface of the brake pad friction block of a high-speed train on a long slope, and realizes the evolution law of the wear interface caused by the alternation of parking braking conditions and speed-limited braking conditions on a long slope; it also studies the vibration response characteristics during the alternation process, which can provide more theoretical data support. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of brake disc-friction pad braking force analysis;

[0040] Figure 2 A schematic flow chart of a method for evolving the wear interface of a high-speed train brake pad and friction block on a long slope provided by an embodiment of the present invention;

[0041] Figure 3 Finite element model (a) and boundary condition settings (b);

[0042] Figure 4 The contact angle measurement results on the friction block; (a) corresponds to the node selection on the friction block, and (b) corresponds to the contact angle measurement results;

[0043] Figure 5 The contact stress cloud map and wear distribution cloud map of the friction pad under parking brake pressure;

[0044] Figure 6 The simulation results of the brake disc; (a) corresponds to the node selection on the brake disc, (b) corresponds to the time domain signal of the deformation of each node on the brake disc, and (c) corresponds to the deformation cloud map of the brake disc;

[0045] Figure 7 The simulation results of friction block wear thickness are shown below. (a) corresponds to the selected nodes on the friction block, (b) corresponds to the wear thickness of each node at different times, and (c) corresponds to the trend of eccentric wear over time.

[0046] Figure 8 Schematic diagram of friction block wear mechanism;

[0047] Figure 9 The contact stress nephogram and wear distribution nephogram of the friction pad after the friction pad is worn under parking brake pressure and then under speed limit brake pressure;

[0048] Figure 10 The wear mechanism of the friction pad when alternating between different braking pressure conditions;

[0049] Figure 11 The simulation results of the vibration acceleration signal of the friction pad when alternating between different braking pressure conditions. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the technical solutions of various embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0051] Example 1

[0052] During train operation, wear-free electric braking is prioritized, with air braking only stepping in when the electric braking force is insufficient. When a train is operating on a normal line, electric braking can meet all braking needs except parking. However, when a train is traveling on a long downhill slope, the train's gravitational potential energy is converted into kinetic energy, and the electric braking force is insufficient to meet the requirements for safe and stable operation. The brake pads must be applied for a long period of time to prevent the train from overspeeding. Therefore, when a train is operating normally on a line with long slopes, the brake pads operate in two modes: parking braking and speed-limiting braking on long slopes. The speed-limiting braking has low braking pressure and high initial braking velocity.

[0053] When a train runs on a line with a long slope, the demand for speed-limited braking increases, and the braking time and speed increase accordingly. There are multiple friction blocks regularly distributed on the train brake pads. The end of the friction block that first slides over the brake disc during operation is called the cut-in end. Figure 1 As shown. The friction force F exerted by the brake disc on the friction pad f And the support force F of the friction block from the fixture N2 The couple M formed f , which results in stress concentration at the friction pad's cutting edge. Furthermore, the contact stress value at each location on the contact interface is affected by the wear depth and wear state of the contact surface. Changes in stress value further affect contact surface wear. This further complicates the tribological behavior of the brake interface.

[0054] Based on the above analysis, this embodiment provides a method for the evolution of the wear interface of the brake pad friction block of a high-speed train on a long slope. Figure 2 As shown, the following steps are included:

[0055] S1 builds an initial finite element model and performs mesh division on the initial finite element model.

[0056] Aiming at the braking problem of high-speed trains on long and steep slopes, an initial finite element model was established based on Abaqus2021 to simulate the mechanical characteristics of the brake pads during braking.

[0057] like Figure 3 As shown, the initial finite element model provided in this embodiment includes six components: a brake disc pattern 1 , a friction pad pattern 2 , a fixture pattern 3 , a vibration acceleration sensor pattern 4 , a bearing pattern 5 and a push rod pattern 6 .

[0058] The meshing of the initial finite element model is achieved by conventional means. The initial finite element model constructed in this embodiment includes 22057 units and 63829 nodes.

[0059] S2 defines the connection relationship and constraints of each component.

[0060] The connection relationship and constraint conditions between components are set as follows Figure 3 As shown, including:

[0061] (1) The brake disc pattern and the friction pad pattern, as well as the push rod pattern and the bearing pattern are in surface-to-surface contact. The main surface is the contact surface between the brake disc pattern friction surface and the push rod pattern, and the secondary surface is the corresponding contact surface.

[0062] (2) The contact behavior between the brake disc pattern and the friction pad pattern is set to tangential friction and normal hard contact;

[0063] (3) Constrain the translational freedom of the inner ring coupling point of the brake disc pattern in all directions and the rotational freedom of the X and Y axes, and retain the rotational freedom of the brake disc pattern in the Z axis;

[0064] (4) Tie constraints are set between the friction block pattern and the fixture pattern, the vibration acceleration sensor pattern and the fixture pattern, and the fixture pattern and the push rod pattern.

[0065] This step also defines the density, Young's modulus, and Poisson's ratio of the brake disc pattern, friction pad pattern, fixture pattern, vibration acceleration sensor pattern, bearing pattern, and push rod pattern, as shown in Table 1.

[0066] Table 1 Material parameters of each component in the finite element model

[0067]

[0068] S3 sets the first braking pressure applied to the end of the push rod. Based on static analysis, the initial finite element model is simulated and analyzed to obtain a wear distribution cloud diagram of the friction block over time; until the contact stress on the friction block is evenly distributed, then enters step S4; the first braking pressure is the parking brake pressure of the train.

[0069] In step S4, a second brake pressure is applied to the end of the push rod. Based on static analysis, the finite element model simulated in step S3 is further simulated to obtain a time-varying wear distribution cloud diagram of the friction pad. This is performed until the contact stress on the friction pad is evenly distributed. The second brake pressure is less than the first brake pressure. The second brake pressure is the speed limit brake pressure for trains descending on long slopes. The second brake pressure is 20%-50% of the first brake pressure.

[0070] In this embodiment, the first braking pressure p1 is set to 0.6 MPa, and the second braking pressure p2 is set to 0.3 MPa.

[0071] The above steps S3 and S4 are implemented based on static analysis.

[0072] When the train brakes, the friction generated by the interaction between the friction block and the brake disc is the key to achieving the braking effect. Under the drag of the friction force, the friction block produces a contact tilt angle with the brake disc, making the friction interface present an incomplete contact state. In order to analyze the change of the interface contact tilt angle under different braking pressures, the Abaqus software is used to set different braking pressures for simulation analysis without considering wear, and the brake disc speed ω is set to 30rad / s. Select 4 nodes (N-1, N-2, N-3, N-4) on the normal line of the contact surface between the friction block and the brake disc (that is, the line perpendicular to the contact surface) as shown in the following figure: Figure 4 (a) Extract the displacement values of each node. During the friction process between the brake disc and the friction pad, the displacement of the above nodes will change, which can effectively reflect the change in the contact state between the brake disc and the friction pad.

[0073] The displacement transformation value of each node and the fitted curve are as follows: Figure 4 As shown in (b), under the action of interfacial friction, the brake disc pattern drags the friction block toward the pattern tangentially, and the tangential displacements of nodes N-1 to N-4 tend to increase (i.e., they move more tangentially). Although nodes N-1 to N-4 are initially located on the normal line of the brake disc pattern, the tangential displacements of the nodes differ after the relative rotation between the brake disc pattern and the friction block. This indicates that friction causes the push rod to deform, resulting in a certain tilt angle for the friction block. Furthermore, the displacements of these nodes differ when the brake disc is subjected to braking pressures of 0.3 MPa and 0.6 MPa. The angle between the fitted straight line of each node displacement and the horizontal direction (normal to the brake disc pattern) is defined as the contact tilt angle θ of the friction block. The results show that the friction block pattern exhibits different tilt angles under different braking pressures, and the contact tilt angle increases with greater braking pressure.

[0074] The presence of a contact tilt angle results in incomplete contact between the friction pad and the brake disc, which in turn affects the evolution of the friction pad's wear interface. To analyze the wear mechanism of the friction pad, the contact stress distribution at the brake interface is simulated, and according to Archard's wear theory, the wear amount of the friction pad is calculated for each incremental step. The UMESHMOTION subroutine is used to convert the wear amount into displacement of the contact surface mesh to represent the wear of the friction pad. The ALE adaptive meshing function is also used to avoid mesh distortion caused by wear and calculation errors.

[0075] In order to correctly apply Archard's formula in the subroutine, Archard's wear formula is generalized to the differential form under infinitesimal contact area ΔA and infinitesimal time increment dt:

[0076]

[0077] Where dV is the wear volume increment; ds is the sliding displacement increment. Assuming that the wear thickness increment of ΔA at dt is dh, then dV = ΔAdh. Substituting into the above formula, we get:

[0078]

[0079] Where, F N / ΔA is the contact stress at the contact micro-area ΔA, which is set as p; k / H is the dimensionless wear coefficient, which is set as k'. Substituting it into the above formula, we can get:

[0080]

[0081] Where k′ is the wear amplification factor; ω is the angular velocity, and dt is a time increment;

[0082] In a specific implementation, in steps S3 and S4, a wear distribution cloud diagram of the friction block pattern over time is obtained according to the following steps:

[0083] (1) According to the first braking pressure or the second braking pressure applied at the end of the push rod, the contact stress p and relative slip distance of the grid node are extracted through the UMESHMOTION subroutine.

[0084] (2) According to Archard's wear theory, the calculation formula for the wear thickness increment dh of a grid node on the contact surface of the friction block in an incremental step is determined, such as the above formulas (3) and (4);

[0085] (3) The wear thickness increment is converted into the displacement of the contact surface mesh through the UMESHMOTION subroutine, and the wear thickness increment is represented by the displacement of the contact surface mesh;

[0086] (4) The wear distribution cloud diagram of the corresponding friction block surface is obtained by spreading the wear distribution cloud diagram over the friction block surface;

[0087] As time changes, the above steps (1)-(4) are repeated to obtain a wear distribution cloud diagram of the friction block pattern as it changes with time.

[0088] The above steps (1) and (3) are implemented using the UMESHMOTION subroutine disclosed in the art, see Zhang Yujia. Research on brake pad eccentric wear and simulation calculation [D]. Dalian Jiaotong University, 2020. DOI: 10.26990 / d.cnki.gsltc.2020.000059.

[0089] Considering that the material removal rate is slow in the actual friction process, a wear amplification factor k′=10 -6, to accelerate the simulation of interface wear. Considering the simulation is a static analysis, the brake disc speed has a linear effect on friction pad wear, with minimal impact on wear trends. Therefore, to shorten simulation time, the brake disc speed ω was uniformly set to 30 rad / s. The pressure applied by the push rod end was set to 0.6 MPa (p1) and 0.3 MPa (p2), respectively, to simulate friction pad wear during parking braking and speed-limited braking on a long slope.

[0090] In step S3 or step S4, based on the wear distribution cloud of the friction block pattern over time, several grid nodes are selected on the diagonal line of the friction block, and the wear thickness increments obtained at each node over time are extracted. Furthermore, the eccentric wear is defined as the difference in wear thickness increments between the two most distant grid nodes, and a temporal trend graph of the eccentric wear is generated.

[0091] Taking the application of a first braking pressure of 0.6 MPa to the end of the push rod pattern in step S3 as an example, the wear distribution cloud diagram of the friction block obtained by the simulation of the finite element analysis over time is analyzed.

[0092] Figure 5 The contact stress and wear volume contours during the 5-second wear simulation of the friction pad are shown. In the contact stress contours at 0.5 and 1.5 seconds, stress concentration is observed at the entry end (i.e., leading edge) of the friction pad, while a stress-free portion is observed at the exit end (i.e., trailing edge). Observing the corresponding wear volume contours, the wear volume at the entry end of the friction pad is significantly greater than that at the exit end. This indicates that the contact inclination angle causes extremely uneven stress distribution at the friction interface, leading to uneven wear of the friction pad. As wear progresses, the stress concentration improves (after 3 seconds), the maximum contact stress decreases, and the distribution becomes more uniform (it can be assumed that the contact stress distribution on the friction pad is uniform at this point). This indicates that after 3 seconds of wear simulation, the friction pad and brake disc have completed their running-in, forming a relatively stable wear contact interface. Furthermore, the outer area of the friction pad (farther from the center of the brake disc) exhibits significant slip, and according to Archard's theoretical formula, the wear thickness increment should also be greater. However, the wear volume contours in the figure indicate that the wear depth is greater on the inner side of the friction pad surface (closer to the center of the brake disc), which is inconsistent with theoretical calculations. In order to further analyze the cause of this phenomenon, several radial nodes (N1-N6) of the brake disc are selected as follows: Figure 6 (a) and extract the time domain signal of its displacement and the brake disc deformation cloud map.

[0093] from Figure 6 (b) It can be seen that the deformation degree of the radial nodes N1 to N6 of the brake disc shows a trend of increasing in sequence. The brake disc is bent. The deformation cloud diagram of the brake disc in the normal direction is extracted from the adjacent peaks (2.89s) and troughs (3.00s) of the node deformation, as shown in the figure. Figure 6(c) The brake disc sampling node moves to the loading position, experiencing significant deformation. The farther away from the center of the disc, the greater the deformation. The locations with greater disc deformation experience less compression between the disc and the friction pad, resulting in lower contact stress. The change in contact stress between the inner and outer sides of the friction pad is greater than the change in slip, resulting in less wear depth on the outer side of the pad.

[0094] In order to further analyze the wear trend of the friction block, the points on the diagonal line of the friction block (from the lower left corner of the leading edge to the upper right corner of the trailing edge) are selected, such as Figure 7 (a) Draw the distance-wear curve for different time periods. The value obtained by dividing the difference in wear thickness increments at both ends of the diagonal line by the length of the diagonal line is defined as the eccentric wear amount (that is, the ratio of the difference in wear thickness increments of the two grid nodes farthest apart to the length of the diagonal line is defined as the eccentric wear amount). The change in the eccentric wear amount of the friction block over time when the brake pressure is 0.6 MPa is calculated. Figure 7 (b) It can be seen that the value on the right side of the curve is greater than that on the left side, and the difference between adjacent curves is getting smaller as time increases. This shows that the wear thickness increment at the cutting end of the friction block is larger, and the wear thickness increment is the largest at the beginning, and then the wear thickness increment gradually decreases. After 3s, the value on the far left of the curve begins to change, and the difference between adjacent curves is similar. This shows that the farthest point of the cutting end of the friction block begins to participate in wear, and the wear thickness increment shows a linear increase trend in the subsequent wear process. This means that the contact inclination angle of the friction block disappears at 3s, and the friction block has good contact with the brake disc. Before forming a stable friction interface, the friction block wears rapidly. After the friction block forms a stable friction interface, the wear rate decreases and wears stably at a smaller wear rate. Figure 7 (c) shows the change of the eccentric wear of the friction pad over time, which shows that it first increases and then tends to be constant. This shows that under the condition of constant braking pressure, the friction pad will eventually continue to wear at a certain eccentric wear angle. Through the above analysis, ignoring the change of the contact tilt angle θ′1 caused by wear or vibration, Figure 8 This can describe the wear mechanism of the friction pad under braking pressure.

[0095] Furthermore, before finite element model simulation, several mesh nodes on the same normal line of the contact surface between the friction pad and brake disc patterns were selected. During the simulation, the displacement values of these mesh nodes were simultaneously extracted. The angle between the straight line obtained by fitting these mesh nodes and the normal line of the brake disc pattern was defined as the contact tilt angle of the friction pad. The trend of the contact tilt angle of the friction pad over time was then determined, allowing for a more intuitive display of the changes in the contact tilt angle.

[0096] To analyze the evolution of the friction interface state when the friction pad is worn in two braking modes, after step S3, the friction pad model is extracted after 3 seconds of wear at a braking pressure of 0.6 MPa (the contact stress distribution on the friction pad is uniform at this time). Then the braking pressure is changed to 0.3 MPa, and the wear simulation is performed again through step S4. That is, the friction pad is simulated under normal parking braking conditions, after a good wear interface has been formed between the friction pad and the brake disc, and then the friction pad enters the speed-limited braking mode on a long slope to obtain the evolution of the friction interface state between the friction pad and the brake disc. The results are as follows: Figure 9 shown.

[0097] from Figure 9 The contact pressure cloud diagram shows that at 0.01s, stress concentration occurs at the cut-out end of the friction block, and there is a part with zero stress at the cut-in end. This is due to the mismatch between the worn friction block and the braking pressure, which changes the force conditions between the friction block and the brake disc, causing the contact inclination angle between the friction block and the brake disc to regenerate. Therefore, contrary to the situation during initial wear, the cut-out end of the friction block wears first. The eccentric wear amount of the friction block at 0.01s and 2s was calculated, and it was found that the eccentric wear amount changed from 0.0006 to 0.0004. This shows that the friction interface is evolving in the direction of matching the braking pressure. When the braking pressure is 0.3MPa, the wear thickness increment and eccentric wear amount of the friction block change over time with the same trend as when the braking pressure was 0.6MPa.

[0098] The evolution mechanism of the wear interface of the friction block on a long slope is as follows: Figure 10 As shown in the figure, during parking braking, the friction pad wears at a contact inclination angle θ′1. The contact inclination angle eventually disappears as wear progresses, forming a stable wear interface. When the friction pad continues to wear at a speed-limited braking on a long slope, the good contact interface that has been formed is destroyed, and the contact inclination angle θ′2 is regenerated, causing the friction pad to wear rapidly and re-forming a wear interface that matches the operating condition. Therefore, when the train has a long downhill slope, the use of different brake pressures during speed-limited braking on the long downhill slope can easily cause the stable friction interface that has been formed to change, resulting in increased wear of the friction pad and a reduction in the service life of the friction pad. When the train operates in this operating condition, more attention should be paid to the wear condition of the brake pad to ensure safe operation of the train.

[0099] Example 2

[0100] This embodiment is a further improvement on the embodiment 1. Based on step S1 and step S2 in the embodiment 1, implicit dynamic analysis is performed by setting different wear contact states of the friction block to obtain its vibration signal transformation.

[0101] Based on the different initial states of the friction pad and the applied brake pressure, the following three contact states are classified: (a) the friction pad is not worn and a brake pressure of 0.6 MPa is applied; (b) the friction pad has been worn for 3 seconds under a brake pressure of 0.6 MPa and a brake pressure of 0.6 MPa is continued to be applied; (c) the friction pad has been worn for 3 seconds under a brake pressure of 0.6 MPa and a brake pressure of 0.3 MPa is then applied.

[0102] The method for evolution of the wear interface of the brake pad friction block of a high-speed train on a steep slope provided in this embodiment also includes:

[0103] S5 sets the first braking pressure applied to the end of the push rod, performs simulation analysis on the initial finite element model based on implicit dynamic analysis, and obtains the time domain signal of the normal and / or tangential vibration acceleration of the friction block.

[0104] In this step, the initial finite element model is used as the research object. At this time, the friction block is not worn. The first brake pressure p1 = 0.6 MPa is applied to the end of its push rod. Based on implicit dynamic analysis, the initial finite element model is simulated and analyzed to obtain the time domain signals of the normal and tangential vibration acceleration of the friction block. The simulation results are as follows: Figure 11 As shown in (a).

[0105] S6 sets the push rod end to apply a first braking pressure, and based on implicit dynamics analysis, performs simulation analysis on the finite element model simulated in step S3 to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block.

[0106] In this step, the operation of the previous step S3 is used to obtain a simulation model of the friction block after being worn for 3 seconds under a braking pressure of 0.6 MPa. This model is used as the research object, and the first braking pressure p1 = 0.6 MPa is continued to be applied to the end of the push rod. Based on implicit dynamics analysis, the above finite element model is simulated and analyzed to obtain the time domain signals of the normal and tangential vibration acceleration of the friction block. The simulation results are as follows: Figure 11 (b) shown.

[0107] S7 sets the push rod end to apply a second brake pressure, and based on implicit dynamics analysis, performs simulation analysis on the finite element model simulated in step S3 to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block;

[0108] In this step, the operation of the previous step S3 is used to obtain a simulation model of the friction block after being worn for 3 seconds under a braking pressure of 0.6 MPa. This model is used as the research object, and a second braking pressure p2 = 0.3 MPa is continuously applied to the end of the push rod. Based on implicit dynamics analysis, the above finite element model is simulated and analyzed to obtain the time domain signals of the normal and tangential vibration acceleration of the friction block. The simulation results are as follows: Figure 11 (c) shown.

[0109] Through the above steps S5-S7, the vibration response evolution law of the brake pad friction block of the high-speed train on the long slope is obtained.

[0110] Figure 11 The figure shows the time domain signals of the normal and tangential vibration accelerations of the friction block during the simulation process. It can be seen that the time domain signals of the vibration accelerations of the friction block under different friction block wear contact states have obvious differences in amplitude. In state (a), the vibration intensity between the brake disc and the friction block is the largest, and the vibration is the smallest in state (b). Combined with the analysis given in Example 1, it can be seen that in state (c), there is a contact tilt angle between the friction block and the brake disc, which leads to a large friction vibration. As the wear progresses, the wear state changes from (a) to (b), and the contact tilt angle gradually decreases until it disappears. At this time, the friction block and the brake disc are in a good contact state, and the friction vibration generated is small. In state (c), due to the change in braking pressure, the good contact state between the friction block and the brake disc is changed, and the contact tilt angle is re-generated, so a large friction vibration is induced again. At the same time, it can be seen that the normal acceleration in the three states is greater than the tangential acceleration, indicating that the vibration mainly occurs in the normal direction of the friction interface. The proportion of tangential vibration acceleration in state (c) is significantly higher than that in the other two states, indicating that the mismatch between the wear interface of the friction block and the braking pressure affects the force in the tangential direction of the friction block, further aggravating the friction self-excited vibration.

[0111] Those skilled in the art will appreciate that the embodiments herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art may make various other specific variations and combinations based on the technical teachings disclosed herein without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A method for the evolution of the wear interface of the brake pad friction block of a high-speed train on a long and steep slope, characterized in that: The following steps are involved: S1 constructs an initial finite element model and performs meshing on the initial finite element model; the initial finite element model includes a brake disc pattern, a friction pad pattern, a fixture pattern, a vibration acceleration sensor pattern, a bearing pattern, and a push rod pattern; S2 defines the connection relationship and constraints of each component; In step S3, a first braking pressure is applied to the end of the push rod. Based on static analysis, the initial finite element model is simulated and analyzed to obtain a wear distribution cloud diagram of the friction block over time. This is performed until the contact stress on the friction block is evenly distributed, and then the process proceeds to step S4. The first braking pressure is the parking brake pressure of the train. S4 sets the push rod end to apply a second brake pressure. Based on static analysis, the finite element model simulated in step S3 is further simulated and analyzed to obtain a wear distribution cloud diagram of the friction block over time; until the contact stress on the friction block is evenly distributed; the second brake pressure is less than the first brake pressure; the second brake pressure is the speed limit brake pressure for trains on long and steep slopes; The wear evolution law of the brake pad friction block of the high-speed train on a long slope is obtained through the above steps S3 and S4; In steps S3 and S4, a wear distribution cloud diagram of the friction block over time is obtained by following the steps below: (1) According to the first braking pressure or the second braking pressure applied at the end of the push rod, the contact stress p and relative slip distance of the grid node are extracted through the UMESHMOTION subroutine. (2) According to Archard's wear theory, the calculation formula for determining the wear thickness increment dh of a grid node on the contact surface of the friction block in an incremental step is as follows: Where k′ is the wear amplification factor; ω is the angular velocity, and dt is a time increment; (3) The wear thickness increment is converted into the displacement of the contact surface mesh through the UMESHMOTION subroutine, and the wear thickness increment is represented by the displacement of the contact surface mesh; (4) The wear distribution cloud diagram of the corresponding friction block surface is obtained by spreading the wear distribution cloud diagram over the friction block surface; As time changes, the above steps (1)-(4) are repeated to obtain a wear distribution cloud diagram of the friction block as it changes with time.

2. The wear interface evolution method of the brake pad friction block of a high-speed train on a long and steep slope according to claim 1 is characterized in that: In step S2, the connection relationship and constraints of each component include: (1) The brake disc pattern and the friction pad pattern, as well as the push rod pattern and the bearing pattern are in surface-to-surface contact. The main surface is the contact surface between the brake disc pattern friction surface and the push rod pattern, and the secondary surface is the corresponding contact surface. (2) The contact behavior between the brake disc pattern and the friction pad pattern is set to tangential friction and normal hard contact; (3) Constrain the translational freedom of the inner ring coupling point of the brake disc pattern in all directions and the rotational freedom of the X and Y axes, and retain the rotational freedom of the brake disc pattern in the Z axis; (4) Tie constraints are set between the friction block pattern and the fixture pattern, the vibration acceleration sensor pattern and the fixture pattern, and the fixture pattern and the push rod pattern.

3. The method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope according to claim 2, characterized in that: In step S2 , the density, Young's modulus and Poisson's ratio of the friction pad pattern, brake disc pattern, clamp pattern, vibration acceleration sensor pattern, bearing pattern and push rod pattern are also defined.

4. The wear interface evolution method of the brake pad friction block of a high-speed train on a long and steep slope according to claim 1 is characterized in that: The second braking pressure is 20%-50% of the first braking pressure.

5. The method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope according to any one of claims 1 to 4, characterized in that: In step S3 or step S4, according to the wear distribution cloud diagram of the friction block over time, several grid nodes are selected on the diagonal line of the friction block, and the wear thickness increment of each node over time is extracted.

6. The method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope according to claim 5, characterized in that: The ratio of the wear thickness increment difference between the two grid nodes that are farthest apart to the length of the diagonal line is defined as the eccentric wear amount, and a trend graph of the eccentric wear amount changing with time is obtained.

7. The method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope according to any one of claims 1 to 4, characterized in that: In step S3 or step S4, before simulating with the finite element model, several grid nodes on the same normal line of the contact surface between the friction block and the brake disc are selected, and the displacement values of the corresponding grid nodes are simultaneously extracted during the simulation process. The angle between the straight line obtained by fitting the several grid nodes and the normal direction of the brake disc is defined as the contact inclination angle of the friction block; and then the trend of the contact inclination angle of the friction block changing with time is obtained.

8. The method for evolution of wear interface of brake pad friction block of high-speed train on long and steep slope according to any one of claims 1 to 4, characterized in that: Also includes: S5 sets the push rod end to apply a first braking pressure, performs simulation analysis on the initial finite element model based on implicit dynamics analysis, and obtains time domain signals of normal and / or tangential vibration acceleration of the friction block; S6 sets a first braking pressure to be applied at the end of the push rod, and performs simulation analysis on the finite element model simulated in step S3 based on implicit dynamics analysis to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block; S7 sets the push rod end to apply a second brake pressure, and based on implicit dynamics analysis, performs simulation analysis on the finite element model simulated in step S3 to obtain time domain signals of normal and / or tangential vibration acceleration of the friction block; Through the above steps S5-S7, the vibration response evolution law of the brake pad friction block of the high-speed train on the long slope is obtained.

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