Evaluation method and system for braking heat fade of whole heavy truck

Abstract

The invention discloses an evaluation method and system for braking heat fade of a whole heavy truck, and relates to the technical field of active safety of automobiles. The evaluation method comprises the steps that on the basis of the temperature of a brake, a characteristic curve obtained through a drum brake bench test and boundary conditions determined through analog simulation are used for evaluating the braking heat fade of the whole heavy truck; determining the heat fade rate of a single drum brake and the average braking deceleration of the whole truck, and constructing a grading evaluation index system of the braking efficiency heat fade of the heavy truck; the method comprises the following steps of: setting a plurality of threshold intervals based on a grading evaluation index system of the braking efficiency heat fade of the heavy truck, dividing the heat fade degree into a mild grade, a moderate grade and a heavy grade, and establishing a heat fade grading evaluation model; and based on the driving data of the heavy truck under the typical actual road condition, verifying the effectiveness and applicability of the heat fade grading evaluation model. According to the invention, quantitative evaluation of performance evolution from a single brake to a whole vehicle system is realized, and design optimization and safety performance of a heavy truck braking system are improved.

Description

Technical Field

[0001] This invention relates to the field of active safety technology for automobiles, specifically to an evaluation method and system for brake fade in heavy-duty trucks. Background Technology

[0002] During the operation of heavy-duty trucks, the reliability of the braking system is crucial, and heat fade is one of the key factors affecting braking performance. Heat fade leads to a decrease in braking efficiency, seriously threatening driving safety.

[0003] According to relevant statistics, traffic accidents caused by brake fade due to long downhill slopes account for more than 40% of traffic accidents on mountain roads. Heavy-duty trucks are characterized by their large mass, high inertia, and high braking energy. Combined with their driving conditions, which are mostly long downhill sections in mountainous areas, heavy-duty trucks pose a higher driving safety risk than other types of vehicles. Heavy-duty trucks account for approximately 60% to 80% of accident vehicles. my country is a mountainous country, and the working conditions of heavy-duty trucks are even more severe than those of vehicles in Europe and America. Furthermore, with the increasing emphasis on driving safety in modern society, heavy-duty trucks are required to complete braking in a shorter time and distance. This inevitably increases the probability of brake fade and the risk of brake system failure. Therefore, research on the evolution mechanism of brake fade in heavy-duty trucks is of significant theoretical and practical value for improving the thermal stability of truck braking systems, enhancing the driving safety of heavy-duty trucks, and reducing traffic accidents caused by brake fade.

[0004] In response to the frequent accidents caused by brake fade in heavy-duty trucks, this paper proposes an evaluation method and system for brake fade of heavy-duty trucks. Based on the evolution mechanism of brake fade of drum brakes and the evolution mechanism of brake fade of heavy-duty trucks, evaluation indicators for brake fade are determined. Based on the safety threshold of braking performance of drum brakes and the whole vehicle, a graded evaluation method for brake fade of braking performance of heavy-duty trucks is proposed. Summary of the Invention

[0005] To address the aforementioned technical problems, a method and system for evaluating the braking performance of heavy-duty trucks in the event of thermal fade are provided. This technical solution solves the problem of frequent accidents caused by thermal fade in heavy-duty trucks.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for evaluating the braking performance thermal fade of heavy-duty trucks includes: S1. Based on the brake temperature, using the characteristic curves obtained from the drum brake bench test and the boundary conditions determined by simulation, the thermal fade rate of a single drum brake and the average braking deceleration of the whole vehicle are determined, and a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks is constructed. S2. Based on the graded evaluation index system for the braking performance heat fade of heavy-duty trucks, multiple threshold ranges are set to divide the degree of heat fade into three levels: mild, moderate and severe, and a graded evaluation model for heat fade is established. S3. Based on driving data of heavy-duty trucks under typical real-world road conditions, the effectiveness and applicability of the thermal degradation grading evaluation model are verified.

[0007] Preferably, step S1 specifically includes: Based on brake temperature, the thermal fade rate of a single drum brake for heavy-duty trucks is determined using the characteristic curves obtained from drum brake bench tests and the boundary conditions determined by simulation.

[0008] Among them, at a specific temperature The formula for calculating the heat fade rate of a single drum brake is as follows:

[0009] in, Brake temperature, in °C. The maximum brake efficiency number achieved by the brake at 120°C, as determined by bench test results. For this temperature The thermal fade rate of a single drum brake. To set the brake at this temperature The braking efficiency factor under the specified conditions.

[0010] Preferably, step S1 further includes: The temperature of the brakes of each axle of a heavy-duty truck is obtained, and the average braking deceleration of the whole vehicle is calculated through Bayesian regression equation. The average braking deceleration index can effectively capture the system-level thermal fade behavior of the whole vehicle during long-term, high-frequency braking, and provide basic data support for safety evaluation and control strategies. Based on the thermal fade rate of a single drum brake and the average braking deceleration of the entire vehicle, a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks is constructed.

[0011] The expression for the average braking deceleration of the entire vehicle is as follows:

[0012] in, This represents the average braking deceleration, in units of... , , , and These represent the temperatures of the second, third, fourth, and sixth axis brakes, respectively.

[0013] Preferably, step S2 specifically includes: Based on the graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks, the degree of thermal fade of drum brakes is divided into three levels according to the safety threshold of the thermal fade rate of drum brakes and the safety threshold of the brake drum material performance: mild thermal fade, moderate thermal fade, and severe thermal fade. A graded evaluation model for thermal fade is established. When the brake temperature is between 120℃ and 211℃, the drum brake is in a state of slight thermal decay. According to the calculation formula of the thermal decay rate of a single drum brake, the thermal decay rate is between 0% and 10%, indicating that although the brake performance has decreased, the decrease is small and the overall braking performance can still be maintained at a certain level. When the brake temperature is between 211℃ and 282℃, the drum brake is in a state of moderate thermal decay. According to the calculation formula of the thermal decay rate of a single drum brake, the thermal decay rate is between 10% and 30%, indicating that the performance of the drum brake has decreased significantly. When the brake temperature exceeds 282℃, the drum brake is in a state of severe thermal degradation. According to the calculation formula for the thermal degradation rate of a single drum brake, the thermal degradation rate exceeds 30%, indicating that the performance of the drum brake begins to decline sharply.

[0014] Preferably, step S3 specifically includes: The effectiveness and applicability of the thermal degradation grading evaluation model are verified based on driving data of heavy-duty trucks under typical real-world road conditions. Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 4.15 m / s². ~5m / At this stage, the vehicle is in a state of mild heat fade. Under this level, the vehicle's braking performance is slightly reduced, but it can still basically meet the normal braking needs. Under normal road conditions, the vehicle can still maintain relatively stable braking performance. During emergency braking, the braking distance will increase slightly, but it is still within an acceptable range and has little impact on driving safety. Preferably, step S3 further includes: For a single brake, when the brake temperature is between 211℃ and 282℃, the drum brake is in a state of moderate thermal decay, with a thermal decay rate between 10% and 30%, indicating that the performance of the drum brake has decreased significantly. The maximum thermal stress on the friction surface of the brake drum is 95.5~120MPa, which gradually approaches the upper limit of the tensile-compressive fatigue strength of the brake drum material. When the brake drum is used for braking at this temperature for a long time, the brake drum structure begins to become unstable, and the friction surface of the brake drum may be at risk of thermal fatigue cracks. When the thermal stress reaches 120MPa, the crack propagation rate increases.

[0015] Preferably, step S3 further includes: Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 3.3 m / s. ~4.15m / When the vehicle is in a state of moderate heat fade, its braking performance is significantly reduced and its braking distance is significantly increased. The vehicle should take measures as soon as possible to reduce the brake temperature, such as using auxiliary braking devices, exhaust braking, or choosing a safe place to park and dissipate heat, in order to avoid further aggravation of the heat fade and ensure driving safety.

[0016] Preferably, step S3 further includes: For a single brake, when the brake temperature is above 282℃, the drum brake is in a state of severe thermal decay, with a thermal decay rate exceeding 30%, indicating that the performance of the drum brake begins to decline sharply. The maximum thermal stress on the brake drum friction surface exceeds 120MPa, which exceeds the upper limit of the tensile-compressive fatigue strength of the brake drum material. The structural stability of the brake drum declines sharply. When the brake drum is used for braking at this temperature for a long time, it will exacerbate the propagation of thermal fatigue cracks. If the stress concentration is severe, it may induce local material spalling of the brake drum, which will greatly affect the braking performance of the drum brake. Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is less than 3.3 m / s. When a vehicle is in a state of severe heat fade, it poses a great threat to driving safety, significantly increases the risk of loss of vehicle control, and is very likely to cause serious traffic accidents. Once signs of severe heat fade appear, emergency measures must be taken immediately.

[0017] An evaluation system for brake fade in heavy-duty trucks includes a preprocessing module, a fade grading module, and an evaluation module. The preprocessing module obtains the thermal fade rate of a single drum brake and the average braking deceleration of the whole vehicle through experiments, and constructs a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks. The heat fade grading module, based on the grading evaluation index system for the braking performance heat fade of heavy-duty trucks, sets multiple threshold ranges and divides the degree of heat fade into three levels: mild, moderate and severe, and establishes a heat fade grading evaluation model. The evaluation module verifies the effectiveness and applicability of the thermal degradation grading evaluation model based on driving data of heavy-duty trucks under typical real-world road conditions.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes an evaluation scheme for brake fade in heavy-duty trucks, enabling quantitative assessment of performance evolution from individual brakes to the entire vehicle system. This method has good applicability and engineering guidance value, providing a scientific basis and effective support for the design optimization and safety performance improvement of heavy-duty truck braking systems. Attached Figure Description

[0019] Figure 1 A flowchart of a method for evaluating the braking performance thermal fade of heavy-duty trucks; Figure 2 The curves show the brake's performance factor versus temperature characteristics. Figure 3 The temperature curves of the brake drum friction surface and the temperature difference-time curves at different locations of the brake drum are shown. Figure 4 The maximum stress-friction surface temperature curve of the brake drum; Figure 5 It refers to the thermal fade rate of drum brakes and the temperature characteristics of the brakes. Figure 6 It is the calculation of the vehicle's average braking deceleration. Detailed Implementation

[0020] The following description is provided to enable those skilled in the art to implement the invention. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0021] Reference Figure 1 As shown, a method for evaluating the braking performance heat fade of heavy-duty trucks includes: S1. Based on brake temperature, using the characteristic curves obtained from drum brake bench tests and the boundary conditions determined by simulation, determine the thermal fade rate of a single drum brake and the average braking deceleration of the whole vehicle, and construct a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks; the graded evaluation index includes: brake temperature, thermal fade rate of a single drum brake and average braking deceleration of the whole vehicle. S2. Based on the graded evaluation index system for the braking performance heat fade of heavy-duty trucks, multiple threshold ranges are set to divide the degree of heat fade into three levels: mild, moderate and severe, and a graded evaluation model for heat fade is established. S3. Based on driving data of heavy-duty trucks under typical real-world road conditions, the effectiveness and applicability of the thermal degradation grading evaluation model are verified.

[0022] The data collected included brake temperature, individual drum brake thermal fade rate, and average vehicle braking deceleration. Brake temperature is measured by collecting temperature changes at various points on the inner surface of the brake. Figure 2 It can be seen that as the brake temperature rises, the brake efficiency factor exhibits different trends at different temperature stages. Figure 3 Figure 4 This indicates that during the operation of the brake, as the brake temperature rises, the temperature difference between different locations of the brake drum continuously increases, which leads to a continuous increase in stress in the friction area of ​​the brake drum and a significant decrease in the stability of its material properties. As the temperature continues to rise, the stress of the brake may exceed the material yield limit, thereby causing brake damage. The thermal fade rate of a single drum brake uses 120℃ as the critical point for thermal fade. It measures the degree of thermal fade by comparing the brake efficiency factor at a certain temperature during operation with the maximum brake efficiency before 120℃. The braking efficiency factor is as follows: The formula for calculating the thermal fade rate of a single drum brake at this temperature is as follows:

[0023] in, Brake temperature, in °C. The maximum brake efficiency number achieved by the brake at 120°C, as determined by bench test results. For temperature The thermal fade rate of a single drum brake, according to Figure 5 It allows for clear observation of the degree to which the performance of a single brake decreases with increasing temperature, and intuitively reflects the degree of thermal fading of the brake at different temperatures. Under the same braking conditions, the degree of thermal fading of brakes on different axles varies. According to the mechanism of thermal fading evolution of the whole vehicle, the temperature of the rear axle brake of a heavy-duty truck rises faster. Therefore, the thermal fading rate of the rear axle brake of a heavy-duty truck is generally higher than that of the front axle.

[0024] The average braking deceleration of the entire vehicle is calculated by measuring the temperature of the four-axle brakes and using the Bayesian ridge regression equation, as shown in the following expression:

[0025] in, This represents the average braking deceleration, in units of... , , , and These represent the temperatures of the second, third, fourth, and sixth axis brakes, respectively.

[0026] Based on the above-obtained evaluation index for the thermal degradation of heavy-duty trucks, the thermal degradation of vehicles is divided into the following three levels: mild thermal degradation, moderate thermal degradation, and severe thermal degradation. For a single brake, when the brake temperature is between 120℃ and 211℃, the drum brake is in a state of slight thermal decay, with a thermal decay rate between 0% and 10%. This indicates that although the brake performance has decreased, the decrease is small, and the overall braking performance can still be maintained at a certain level. The maximum thermal stress on the brake drum friction surface is 69.2~95.5MPa, and the lower limit of the tensile-compressive fatigue strength of the brake drum material is within this range. When the thermal stress is lower than or slightly higher than 85MPa, the brake drum structure is in a stable state with no risk of fatigue damage.

[0027] Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 4.15 m / s². ~5m / When the vehicle is in a state of mild heat fade, the braking performance is slightly reduced, but it can still basically meet the normal braking needs. Under normal road conditions, the vehicle can still maintain relatively stable braking performance. During emergency braking, the braking distance will increase slightly, but it is still within an acceptable range and has little impact on driving safety.

[0028] For a single brake, when the brake temperature is between 211℃ and 282℃, the drum brake is in a state of moderate thermal decay, with a thermal decay rate between 10% and 30%, indicating that the performance of the drum brake has decreased significantly. The maximum thermal stress on the friction surface of the brake drum is 95.5~120MPa, which gradually approaches the upper limit of the tensile-compressive fatigue strength of the brake drum material. When the brake drum is used for braking at this temperature for a long time, the brake drum structure begins to become unstable, and the friction surface of the brake drum may be at risk of thermal fatigue cracks. When the thermal stress reaches 120MPa, the crack propagation rate increases.

[0029] Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 3.3 m / s. ~4.15m / When the vehicle is in a state of moderate heat fade, its braking performance is significantly reduced and its braking distance is significantly increased. Measures should be taken as soon as possible to reduce the brake temperature, such as using auxiliary braking devices, exhaust braking, and parking in a safe location to dissipate heat, in order to prevent the heat fade from worsening and to ensure driving safety.

[0030] For a single brake, when the brake temperature exceeds 282℃, the drum brake is in a state of severe thermal decay, with a thermal decay rate exceeding 30%. This indicates that the performance of the drum brake begins to decline sharply, and the maximum thermal stress on the brake drum friction surface exceeds 120MPa, which exceeds the upper limit of the tensile-compressive fatigue strength of the brake drum material. The structural stability of the brake drum decreases sharply. When the brake drum is used for braking at this temperature for a long time, it will exacerbate the propagation of thermal fatigue cracks. If the stress concentration is severe, it may induce local material spalling of the brake drum, which will greatly affect the braking performance of the drum brake.

[0031] Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is less than 3.3 m / s. When a vehicle is in a state of severe heat fade, it poses a great threat to driving safety, significantly increases the risk of loss of vehicle control, and is very likely to cause serious traffic accidents. Once signs of severe heat fade appear, emergency measures must be taken immediately, such as driving into the emergency lane to stop forcibly or seeking rescue.

[0032] Based on the above evaluation of thermal fade in heavy-duty trucks, the comprehensive evaluation method proposed in this invention, which is based on three key parameters—brake temperature, thermal fade rate of a single drum brake, and average braking deceleration of the whole vehicle—can systematically and accurately assess the degree of thermal fade of the vehicle braking system under different operating conditions. This method constructs a three-level thermal fade evaluation system of mild, moderate, and severe, and determines scientific quantitative grading thresholds based on key indicators.

[0033] The evaluation method described in this invention has been verified through the following embodiments: Case 1: The vehicle road test was conducted on a long downhill section in Sichuan Province. The test section had an elevation difference of 1.9km and included several long downhill sections.

[0034] Case 2: The vehicle road test selected a long downhill section in Shaanxi Province. The starting elevation was 2030m and the ending elevation was 500m, with a height difference of 1530m. There were several long downhill sections between the starting and ending points. The test vehicle was a typical six-axle heavy-duty truck for highways, with a total weight of 49 tons after loading cargo. During the test, the vehicle traveled on the test section fully loaded to simulate the load conditions in actual transportation. Data such as vehicle brake temperature, driving speed, and altitude were obtained during the test.

[0035] In Case 1, the test vehicle maintained a speed of 60 km / h during a long downhill continuous braking test. Based on the temperature and time changes in the test results, it can be seen that the brakes on each axle of the test vehicle started braking at an initial temperature of 10℃. At the end of the test, the temperature of the second axle brake was 100.02℃, with no brake fade; the temperature of the third axle brake was 136.43℃, indicating slight brake fade; the temperature of the fourth axle brake was 174.16℃, also indicating slight brake fade; and the temperature of the sixth axle brake was 155.66℃, indicating slight brake fade. In this case, the dynamic trends of the brake temperature rise evolution of the second, third, fourth, and sixth axles of the test vehicle are consistent with the previous study. Substituting the brake temperatures of the second, third, fourth, and sixth axles at the end of the test into the expression for average braking deceleration, the calculated average braking deceleration at the end of braking is 4.386 m / s². The braking performance of heavy-duty trucks is in a state of slight heat fade.

[0036] The test vehicle was subjected to continuous braking on three long downhill sections at a speed of 20-30 km / h. At the end of the test, the temperature of the fourth axle brake was 119.76℃, and no heat fade occurred. The temperature of the sixth axle brake was 106.71℃, and no heat fade occurred. In this case, the dynamic trend of the brake temperature rise evolution process of the fourth and sixth axles of the test vehicle is basically consistent with the previous study. According to the research results of the brake temperature rise test in Chapter 4, the temperature rise rate of the brakes of the second and third axles of the vehicle is less than that of the brakes of the fourth and sixth axles. Therefore, it can be inferred that the brakes of the second and third axles of the vehicle did not experience thermal fade in this test. According to the Bayesian ridge regression equation, the average braking deceleration that the vehicle can fully exert at this time should be greater than 5m / s. The braking performance of the truck did not exhibit thermal fade.

[0037] The evaluation results, obtained from test data under typical operating conditions, are consistent with the pre-set thermal degradation grading criteria, thus verifying the applicability of the evaluation method and providing a reference for evaluating the degree of thermal degradation of trucks in engineering practice.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for evaluating brake fade in heavy-duty trucks, characterized in that, Includes the following steps: S1. By experimentally obtaining the thermal fade rate of a single drum brake and the average braking deceleration of the whole vehicle, a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks is constructed. S2. Based on the graded evaluation index system for the braking performance heat fade of heavy-duty trucks, multiple threshold ranges are set, and the degree of heat fade is divided into three levels: mild, moderate and severe, and a graded evaluation model for heat fade is established. S3. Based on driving data of heavy-duty trucks under typical real-world road conditions, the effectiveness and applicability of the thermal degradation grading evaluation model are verified.

2. The method for evaluating thermal degradation according to claim 1, characterized in that, Step S1 specifically includes: Based on brake temperature, the thermal fade rate of a single drum brake for heavy-duty trucks is determined using the characteristic curves obtained from drum brake bench tests and the boundary conditions determined by simulation.

3. The method for evaluating thermal degradation according to claim 2, characterized in that, At a specific temperature The formula for calculating the heat fade rate of a single drum brake is as follows: in, Brake temperature, in °C. The maximum brake efficiency number achieved by the brake at 120°C, as determined by bench test results. For this temperature The thermal fade rate of a single drum brake. To set the brake at this temperature The braking efficiency factor under the specified conditions.

4. The method for evaluating thermal degradation according to claim 2, characterized in that, Step S1 also includes: The temperature of the brakes of each axle of a heavy-duty truck is obtained, and the average braking deceleration of the whole vehicle is calculated through Bayesian regression equation. The average braking deceleration index can effectively capture the system-level thermal fade behavior of the whole vehicle during long-term, high-frequency braking, and provide basic data support for safety evaluation and control strategies. Based on the thermal fade rate of a single drum brake and the average braking deceleration of the entire vehicle, a graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks is constructed.

5. The method for evaluating thermal degradation according to claim 4, characterized in that, The expression for the average braking deceleration of the entire vehicle is as follows: in, This represents the average braking deceleration, in units of... , , , and These represent the temperatures of the second, third, fourth, and sixth axis brakes, respectively.

6. The method for evaluating thermal degradation according to claim 4, characterized in that, Step S2 specifically includes: Based on the graded evaluation index system for the thermal fade of braking performance of heavy-duty trucks, the degree of thermal fade of drum brakes is divided into three levels according to the safety threshold of the thermal fade rate of drum brakes and the safety threshold of the brake drum material performance: mild thermal fade, moderate thermal fade, and severe thermal fade. A graded evaluation model for thermal fade is established. When the brake temperature is between 120℃ and 211℃, the drum brake is in a state of slight thermal decay. According to the calculation formula of the thermal decay rate of a single drum brake, the thermal decay rate is between 0% and 10%, which indicates that although the brake performance has decreased, the decrease is small and the overall braking performance can still be maintained at a certain level. When the brake temperature is between 211℃ and 282℃, the drum brake is in a state of moderate thermal decay. According to the calculation formula of the thermal decay rate of a single drum brake, the thermal decay rate is between 10% and 30%, indicating that the performance of the drum brake has decreased significantly. When the brake temperature exceeds 282℃, the drum brake is in a state of severe thermal degradation. According to the calculation formula for the thermal degradation rate of a single drum brake, the thermal degradation rate exceeds 30%, indicating that the performance of the drum brake begins to decline sharply.

7. The method for evaluating thermal degradation according to claim 6, characterized in that, Step S3 specifically includes: The effectiveness and applicability of the thermal degradation grading evaluation model are verified based on driving data of heavy-duty trucks under typical real-world road conditions. Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 4.15 m / s². ~5m / At this time, the vehicle is in a state of mild heat fade. At this level, the vehicle's braking performance is slightly reduced, but it can still basically meet the normal braking needs.

8. The method for evaluating braking performance heat fade of heavy-duty trucks according to claim 7, characterized in that, Step S3 also includes: For a single brake, when the brake temperature is between 211℃ and 282℃, the drum brake is in a state of moderate thermal decay, with a thermal decay rate between 10% and 30%, indicating that the performance of the drum brake has decreased significantly. The maximum thermal stress on the friction surface of the brake drum is 95.5~120MPa, which gradually approaches the upper limit of the tensile-compressive fatigue strength of the brake drum material. When the brake drum is used for braking at this temperature for a long time, the brake drum structure begins to become unstable, and the friction surface of the brake drum may be at risk of thermal fatigue cracks. When the thermal stress reaches 120MPa, the crack propagation rate increases.

9. The method for evaluating braking performance heat fade of heavy-duty trucks according to claim 8, characterized in that, Step S3 also includes: Regarding overall vehicle braking performance, when vehicle brake fade occurs, the average braking deceleration that a heavy-duty truck can fully generate is 3.3 m / s². ~4.15m / When the vehicle is in a state of moderate heat fade, its braking performance will be significantly reduced and the braking distance will be significantly increased. Measures should be taken as soon as possible to reduce the brake temperature, such as using auxiliary braking devices, exhaust braking, or parking in a safe location to dissipate heat, in order to prevent the heat fade from worsening and ensure driving safety.

10. An evaluation system for brake fade in heavy-duty trucks, characterized in that, It includes a preprocessing module, a thermal degradation grading module, and an evaluation module: The preprocessing module is used to obtain the heat fade rate of a single drum brake and the average braking deceleration of the whole vehicle through experiments, construct a graded evaluation index system for the heat fade of braking performance of heavy-duty trucks, and transmit the obtained graded evaluation index system to the heat fade grading module. The heat fade grading module is based on the grading evaluation index system for the heat fade of braking performance of heavy-duty trucks. It sets multiple threshold ranges, divides the degree of heat fade into three levels: mild, moderate and severe, and establishes a heat fade grading evaluation model. The evaluation module verifies the effectiveness and applicability of the thermal degradation grading evaluation model generated by the thermal degradation grading module based on driving data of heavy-duty trucks under typical real-world road conditions.

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