Retarding braking system of pure electric bus and control method of retarding braking system

Abstract

The invention relates to the technical field of speed control, in particular to a pure electric bus retarding braking system and a control method thereof.The system comprises a state sensing module, a road slope and dynamic parameter calculating module, a safe vehicle speed adjusting module according to the slope, a permissible electric quantity calculating module according to the temperature, a torque and amplification determining module according to a multi-dimensional table and a signal triggering module; the vehicle speed and electric quantity are compared to generate a trigger signal, a torque decision module and a judgment signal, if activated, a torque coefficient is calculated according to the vehicle speed difference value and PI control, and the retarding braking torque is obtained by combining the amplification and the basic torque. According to the method, dynamic matching is achieved by calculating the road slope, considering the motor and battery temperature, inquiring data, determining dynamic torque and amplification, calculating the allowable electric quantity according to the battery temperature and calculating the retarding torque according to the difference value between the current vehicle speed and the dynamic safe vehicle speed during triggering, the battery high temperature or high electric quantity charging risk is avoided, and the motor thermal load is guaranteed; and the braking safety and reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of speed control technology, and in particular to a slow braking system and control method for a pure electric bus. Background Technology

[0002] Speed ​​control technology relates to the propulsion management of electric drive vehicles, with its core focus on adjusting the operating state of the drive motor to change the vehicle's speed. This technology typically includes the regulation of acceleration and deceleration, receiving driver commands via specific circuits or devices to control the torque output or speed changes of the drive motor. A traditional pure electric bus's retarded braking system refers to a device used to provide auxiliary braking when the vehicle is descending a long slope or needs to decelerate. The technical challenge of this system is to provide continuous braking torque to control vehicle speed and prevent the main brake from overheating. Traditional pure electric buses typically achieve retarded braking using regenerative braking of the drive motor, i.e., controlling the motor to operate as a generator, converting the vehicle's kinetic energy into electrical energy and storing it in the power battery.

[0003] Traditional pure electric buses employ a regenerative braking system that uses electric motor energy. This system has a relatively fixed braking strategy and does not fully consider the real-time operating conditions and environmental changes of the vehicle. In actual long downhill driving, the system cannot accurately sense the road gradient, resulting in the slow braking torque output failing to match the actual needs and unstable braking performance. Furthermore, the system is not responsive enough to the instantaneous temperature, charge percentage, and motor temperature of the power battery. If regenerative braking is continued when the battery is at high temperature or high charge, it can easily lead to safety hazards. It also cannot adjust the braking force in real time according to the motor's thermal state, affecting the reliability of the system operation. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a slow braking system and control method for pure electric buses.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a retarding braking system for a pure electric bus, comprising: The status perception module collects battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude. It calculates the altitude change between the current altitude and the altitude of the previous control cycle, calculates the driving distance based on the current vehicle speed and the duration of the control cycle, and calculates the road gradient ratio based on the altitude change and the driving distance. The dynamic parameter module adjusts the basic safe vehicle speed based on the road gradient ratio value to generate a dynamic safe downhill vehicle speed. It calculates the dynamic allowable charging percentage based on the comparison results of the battery temperature with high temperature and ultra-high temperature thresholds. It queries a multi-dimensional lookup table based on the road gradient ratio value, the motor temperature, and the battery temperature to determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase. The trigger signal module compares the current vehicle speed with the dynamic safe downhill vehicle speed, and compares the battery charge percentage with the dynamic allowable charging charge percentage, and generates a slow braking trigger signal based on the comparison results; The torque decision module determines the state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, the deceleration braking torque is set to 0. If the deceleration braking trigger signal is active, the module calculates the speed difference between the current vehicle speed and the dynamic safe downhill vehicle speed. Based on the speed difference and a preset proportional-integral control strategy, the module calculates the torque coefficient and limits the torque coefficient. The module then calculates the torque increase using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. Finally, the module adds the torque increase to the dynamic deceleration base torque to obtain the deceleration braking torque.

[0006] As a further aspect of the present invention, the specific function of the state sensing module is as follows: The status acquisition submodule acquires sensor data through the vehicle controller local area network bus, and acquires the battery temperature, the battery charge percentage, the motor temperature and the vehicle's current speed. At the same time, it uses the global positioning system module to acquire the vehicle's current altitude and packages the current altitude and the current speed to generate a real-time status data packet. The mileage calculation submodule extracts the current vehicle speed from the real-time status data packet and retrieves the control cycle duration. It calculates the distance traveled by the vehicle within the current control cycle by multiplying the current vehicle speed by the control cycle duration, and updates the real-time status data packet to include the travel distance. The slope calculation submodule retrieves the current altitude and the driving distance from the real-time status data packet, reads the historical altitude stored within the control cycle from the storage unit, calculates the difference between the current altitude and the historical altitude to obtain the altitude change, and finally calculates the road slope ratio value by the ratio of the altitude change to the driving distance.

[0007] As a further aspect of the present invention, when calculating the road slope ratio value, the slope calculation submodule also performs filtering processing on the road slope ratio value. The specific process of the filtering processing is as follows: The road slope ratio value is obtained as the original slope value for the current cycle, and the preset filtering coefficient and the filtered slope value of the previous cycle are retrieved from the storage unit. A first-order lag filtering algorithm is used to multiply the original slope value of the current period by the filtering coefficient to obtain the current weighted slope, and then the filtered slope value of the previous period is multiplied by... Multiplying them together yields the historical weighted slope; The current weighted slope is added to the historical weighted slope to obtain the current periodically filtered slope value. The current periodically filtered slope value is updated and stored in the storage unit. At the same time, the current periodically filtered slope value is output as the final road slope ratio value.

[0008] As a further aspect of the present invention, the specific function of the dynamic parameter module is as follows: The safe vehicle speed submodule acquires the road gradient ratio value and reads the preset basic safe vehicle speed reference value. It dynamically corrects the basic safe vehicle speed reference value based on the road gradient ratio value. When the road gradient ratio value is positive, the basic safe vehicle speed reference value is lowered; when the road gradient ratio value is negative, the basic safe vehicle speed reference value is raised, thereby generating the dynamic safe downhill vehicle speed. The power calculation submodule acquires the battery temperature and reads the high temperature and ultra-high temperature thresholds, as well as the preset basic charging power percentage. When the battery temperature is higher than the ultra-high temperature threshold, the basic charging power percentage is reduced to a first preset low value. When the battery temperature is between the high temperature threshold and the ultra-high temperature threshold, the basic charging power percentage is reduced to a second preset low value. The dynamic allowable charging power percentage is calculated. The torque lookup table submodule uses the road slope ratio, motor temperature, and battery temperature as a composite lookup index to perform interpolation lookup in the multidimensional lookup table to determine the dynamic retarding base torque and the dynamic permissible retarding braking torque increase corresponding to the current operating condition.

[0009] As a further aspect of the present invention, the specific process by which the power calculation submodule calculates the dynamically allowed charging power percentage is as follows: The battery temperature, the basic charge percentage, the high temperature threshold and the ultra-high temperature threshold included in the high temperature and ultra-high temperature thresholds, the first preset low value, and the second preset low value are obtained. Determine whether the battery temperature is greater than the ultra-high temperature threshold. If so, set the dynamic allowable charging capacity percentage to the first preset low value. If not, then it is further determined whether the battery temperature is greater than the high temperature threshold. If so, the dynamic allowable charging percentage is calculated by linear interpolation using the battery temperature, the high temperature threshold, the ultra-high temperature threshold, the basic charging capacity percentage, and the second preset low value. If the battery temperature is not greater than the high temperature threshold, then the dynamic allowable charging capacity percentage is set to the basic charging capacity percentage.

[0010] As a further aspect of the present invention, the specific function of the trigger signal module is as follows: The vehicle speed comparison submodule obtains the current vehicle speed and the dynamic safe downhill vehicle speed, compares whether the current vehicle speed is greater than the dynamic safe downhill vehicle speed, and if it is greater, generates a high-level vehicle speed over-limit flag; otherwise, it generates a low-level vehicle speed over-limit flag. The battery comparison submodule obtains the battery percentage and the dynamic allowable charging percentage, compares whether the battery percentage is less than the dynamic allowable charging percentage, and if it is less, generates a high-level battery allowance flag; otherwise, it generates a low-level battery allowance flag. The logic AND gate module receives the vehicle speed over-limit flag and the battery level allowance flag, performs a logic AND operation on the vehicle speed over-limit flag and the battery level allowance flag, and generates the deceleration braking trigger signal in an active state only when both the vehicle speed over-limit flag and the battery level allowance flag are high level, and generates the deceleration braking trigger signal in an inactive state in all other cases.

[0011] As a further aspect of the present invention, the vehicle speed comparison submodule introduces hysteresis comparison logic when comparing the current vehicle speed with the dynamic safe downhill vehicle speed. The specific process of the hysteresis comparison logic is as follows: Read the preset vehicle speed trigger threshold and vehicle speed exit threshold, wherein the vehicle speed trigger threshold is greater than the vehicle speed exit threshold; The current vehicle speed and the dynamic safe downhill vehicle speed are obtained, and the difference between the current vehicle speed and the dynamic safe downhill vehicle speed is calculated to obtain the vehicle speed difference value. Determine the state of the previous cycle of the slow braking trigger signal. If the slow braking trigger signal is inactive, then when the vehicle speed difference is greater than the vehicle speed trigger threshold, set the vehicle speed over-limit flag to a high level. If the slow braking trigger signal is active, the speed over-limit flag will be set to low only when the speed difference is less than the speed exit threshold. Otherwise, the current state of the speed over-limit flag will remain unchanged.

[0012] As a further aspect of the present invention, the specific function of the torque decision module is as follows: The PI control submodule determines the state of the slow braking trigger signal. If it is active, it obtains the current vehicle speed and the dynamic safe downhill vehicle speed, calculates the difference between the two to obtain the vehicle speed difference, and performs proportional-integral control operation on the vehicle speed difference based on the preset proportional coefficient and integral coefficient to generate the original torque coefficient. The coefficient limiting submodule obtains the original torque coefficient and reads the preset upper limit and lower limit values ​​of the torque coefficient. It performs saturation limiting processing on the original torque coefficient to ensure that the original torque coefficient is always between the lower limit and the upper limit values ​​of the torque coefficient, thus obtaining the limited torque coefficient. The torque synthesis submodule obtains the torque coefficient after the limit, the dynamic allowable slow braking torque increase, and the dynamic slow base torque. It calculates the torque increase by multiplying the torque coefficient after the limit by the dynamic allowable slow braking torque increase, and adds the torque increase to the dynamic slow base torque to obtain the final slow braking torque.

[0013] As a further aspect of the present invention, the PI control submodule performs proportional-integral control calculations on the vehicle speed difference, and the specific calculation formula is as follows: ; in, This represents the calculation result of the original torque coefficient in the kth control cycle. The vehicle speed difference value represents the k-th control cycle. It equals the current vehicle speed minus the dynamic safe downhill vehicle speed. This represents the proportionality coefficient. Represents the integral coefficient, This represents the cumulative sum of the vehicle speed differences from the 0th cycle to the kth cycle; The PI control submodule also includes integral anti-saturation processing. When the torque coefficient after the limit reaches the upper limit or the lower limit of the torque coefficient, if the sign of the vehicle speed difference is the same as the sign of the torque coefficient after the limit, the accumulation of the vehicle speed difference is paused.

[0014] A control method for a deceleration braking system of a pure electric bus, the method being executed based on the aforementioned deceleration braking system of a pure electric bus, comprising the following steps: S1: Collect battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude; calculate the altitude change between the current altitude and the altitude of the previous control cycle; calculate the driving distance based on the current vehicle speed and the duration of the control cycle; and calculate the road gradient ratio based on the altitude change and the driving distance. S2: Based on the road slope ratio value, adjust the basic safe vehicle speed to generate a dynamic safe downhill vehicle speed. Calculate the dynamic allowable charging percentage based on the comparison results of the battery temperature with high temperature and ultra-high temperature thresholds. Determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase by querying a multidimensional lookup table based on the road slope ratio value, the motor temperature, and the battery temperature. S3: Compare the current vehicle speed with the dynamic safe downhill vehicle speed, and compare the battery charge percentage with the dynamic allowable charging percentage, and generate a slow braking trigger signal based on the comparison results; S4: Determine the state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, set the deceleration braking torque to 0. If the deceleration braking trigger signal is active, calculate the speed difference between the current vehicle speed and the dynamic safe downhill vehicle speed. Calculate the torque coefficient based on the speed difference and limit the torque coefficient. Calculate the torque increase using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. Add the torque increase to the dynamic deceleration base torque to obtain the deceleration braking torque.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In this invention, the road gradient ratio is calculated in real time, and the instantaneous temperatures of the motor and battery are comprehensively considered. Multidimensional data is queried to determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase. At the same time, the dynamic allowable charging percentage is calculated based on the battery temperature. When braking is triggered, the final deceleration braking torque is precisely calculated and adjusted based on the difference between the current vehicle speed and the dynamic safe downhill speed adjusted based on the gradient. This achieves dynamic matching between braking force and actual working conditions, effectively avoids the charging risks when the battery is at high temperature or high charge, ensures that the motor works under reasonable thermal load, and significantly improves the safety and reliability of deceleration braking. Attached Figure Description

[0016] Figure 1 This is a system flowchart of the present invention; Figure 2 This is a flowchart of the state perception module of the present invention; Figure 3 This is a flowchart of the dynamic parameter module of the present invention; Figure 4 This is a flowchart of the trigger signal module of the present invention; Figure 5 This is a flowchart of the torque decision module of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the software-based technical solution is described in detail below with reference to system architecture diagrams and embodiments. It should be understood that the specific embodiments described herein are only for explaining the technical solutions of this invention and do not constitute a limitation on the scope of protection.

[0018] In the description of this invention, the system architecture relationships or data processing flows indicated by terms such as "layer," "module," "interface," "data flow," "client," and "server" are all defined based on the architecture diagram or flowchart corresponding to the embodiments. This way of describing is only used to clearly illustrate the logical relationships between the elements in the technical solution, and not to limit the physical deployment form. The term "multiple" includes two or more technical units, including but not limited to multiple data nodes, processing threads, service instances, or functional components and other scalable elements. The specific number is determined according to the actual business scenario and needs to be specifically specified.

[0019] Please see Figure 1 and Figure 2 The present invention provides a technical solution: a deceleration braking system for a pure electric bus includes: The status perception module collects data such as battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude. It calculates the altitude change between the current altitude and the altitude of the previous control cycle, calculates the driving distance based on the current vehicle speed and control cycle duration, and calculates the road gradient ratio based on the altitude change and driving distance.

[0020] The status acquisition submodule acquires sensor data through the vehicle controller local area network bus, including battery temperature, battery percentage, motor temperature, and vehicle speed. It also uses the global positioning system module to obtain the vehicle's current altitude and packages the current altitude and current speed into a real-time status data packet.

[0021] The mileage calculation submodule extracts the current vehicle speed from the real-time status data packet and retrieves the control cycle duration. It calculates the distance the vehicle has traveled within the current control cycle by multiplying the current vehicle speed by the control cycle duration and updates the real-time status data packet to include the travel distance.

[0022] The slope calculation submodule retrieves the current altitude and driving distance from the real-time status data packet, reads the historical altitude stored within the control cycle from the storage unit, calculates the difference between the current altitude and the historical altitude to obtain the altitude change, and finally calculates the road slope ratio value by the ratio of the altitude change to the driving distance.

[0023] The slope calculation submodule, when calculating the road slope ratio value, also performs filtering processing on the road slope ratio value. The specific filtering process is as follows: The road slope ratio value is obtained as the original slope value for the current period, and preset filtering coefficients and the filtered slope value from the previous period are retrieved from the storage unit. A first-order lag filtering algorithm is used to multiply the original slope value of the current period by the filtering coefficients to obtain the current weighted slope, and then the filtered slope value from the previous period is multiplied by... Multiply the values ​​to obtain the historical weighted slope. Add the current weighted slope to the historical weighted slope to obtain the current periodically filtered slope value. Update and store the current periodically filtered slope value in the storage unit, and output the current periodically filtered slope value as the final road slope ratio value.

[0024] State Awareness Module Implementation Example The state-aware module begins data acquisition and processing after system activation. In the... In each control cycle, the module collects the following data through the vehicle controller local area network bus and the global positioning system module: battery temperature 48℃, battery charge percentage 82%, motor temperature 75℃, current vehicle speed 23km / h, and current altitude 1050m. The module reads the altitude stored in the previous control cycle from the storage unit, which is 1054m. Subsequently, the module calculates the altitude change between the current altitude and the stored altitude from the previous control cycle. The calculation process is as follows: Simultaneously, the module retrieves the preset control cycle duration, which is 1.0s, and calculates the travel distance based on the current vehicle speed and the control cycle duration. First, the current vehicle speed is converted to m / s: The process for calculating the travel distance is as follows: Finally, the module calculates the road gradient ratio based on the elevation change and driving distance. The calculation process is as follows: .

[0025] The status acquisition submodule first accesses the vehicle controller local area network (CAN) bus and listens for preset message IDs. By listening to the message with ID 0x101, it parses bits 0 to 7 of its data field, applies an offset of -40, and obtains the battery temperature value. By listening to the message with ID 0x102 (from BMS), parsing bits 0 to 7 of its data field, and applying a scaling factor of 0.5, the battery percentage is obtained. By listening to the message with ID 0x201 (from the motor controller), parsing bits 8 to 15 of its data field, and applying an offset of -40, the motor temperature is obtained. By listening to the message with ID 0x301 (from the VCU), parsing bits 16 to 23 of its data field, and applying a scaling factor of 0.1, the vehicle's current speed is obtained. Simultaneously, the status acquisition submodule reads the NMEA0183 data stream from the GPS module via the UART interface and parses the GPGGA statement. For example, in the message $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,1050.0,M,4.7,M,,*47, the 9th field value 1050.0 is extracted, yielding the current altitude of 1050m. The status acquisition submodule packages the current altitude (1050m) together with the current vehicle speed (23km / h) and other acquired data (48℃, 82%, 75℃) to generate a memory-structured real-time status data packet, which is stored at a predetermined memory address 0x9000.

[0026] The odometer submodule extracts the current vehicle speed from the real-time status data packet at memory address 0x9000, reading a value of 23 in km / h. The module retrieves the control cycle duration stored in non-volatile memory at address 0xFE01, a fixed parameter of 1.0s. Before performing the product operation, the submodule first converts the current vehicle speed from km / h to m / s. The calculation process is as follows: Subsequently, the distance traveled by the vehicle within the current control cycle is calculated by multiplying the current vehicle speed (m / s) by the control cycle duration. The calculation process is as follows: The submodule updates the calculated result (rounded to 6.39m) to the corresponding field at address 0x9000 in the real-time status data packet, so that the data packet contains the travel distance of 6.39m.

[0027] The slope calculation submodule retrieves the current altitude from the real-time status data packet (address 0x9000), obtaining a value of 1050m; it also retrieves the travel distance, obtaining a value of 6.39m. The submodule reads the altitude of the previous control cycle from the storage unit (RAM address 0x8001), obtaining a value of 1054m. The submodule calculates the difference between the current altitude and the stored altitude of the previous control cycle to obtain the altitude change. The calculation process is as follows: The road gradient ratio is finally calculated by the ratio of altitude change to driving distance. The calculation process is as follows: This value -0.62598 is used as the original slope value for the current cycle. After the calculation is completed, the submodule writes the current altitude of 1050m to the RAM address 0x8001, replacing 1054m, and uses it as the stored altitude of the previous control cycle in the next control cycle.

[0028] The slope calculation submodule retrieves the road slope ratio value of -0.62598 calculated in the previous step and uses it as the original slope value for the current cycle. The submodule retrieves preset filtering coefficients from the storage unit and compares them with the filtered slope value from the previous cycle. The filtering coefficient settings are based on real-vehicle road tests. Test vehicles travel on roads with different slopes, comparing the slope measured by the high-precision IMU with the original slope calculated by GPS to analyze noise characteristics.

[0029] Table 1 Experimental Data for Filter Coefficients

[0030] As shown in Table 1, the original slope standard deviation is 0.031. Using 0.1 as the filter coefficient, the filtered slope standard deviation decreases to 0.006, close to the IMU baseline (0.005), and the 7.0s response time is acceptable for slope changes. Therefore, the filter coefficient is set to 0.1. The submodule retrieves the filter coefficient. The submodule retrieves the filtered slope value from the memory location (RAM address 0x8002) of the previous cycle, obtaining a value of -0.2500. The submodule then executes a first-order lag filtering algorithm. First, it multiplies the original slope value of the current cycle by the filtering coefficients to obtain the current weighted slope: Then, the slope value after filtering in the previous cycle is compared with ( The historical weighted slope is obtained by multiplying the filter coefficients together. Add the current weighted slope to the historical weighted slope to obtain the current periodically filtered slope value: The submodule updates and stores the current cycle filtered slope value of -0.2876 in the memory unit (RAM address 0x8002), and outputs it (usually with four decimal places, -0.2876) as the final road slope ratio value.

[0031] Please see Figure 1 and Figure 3 The dynamic parameter module adjusts the basic safe vehicle speed based on the road gradient ratio to generate a dynamic safe downhill vehicle speed. It calculates the dynamic allowable charging percentage based on the comparison results of battery temperature with high temperature and ultra-high temperature thresholds. It queries a multi-dimensional lookup table based on the road gradient ratio, motor temperature, and battery temperature to determine the dynamic retarding base torque and the dynamic allowable retarding braking torque increase.

[0032] The safe speed submodule obtains the road gradient ratio value and reads the preset basic safe speed reference value. It dynamically corrects the basic safe speed reference value based on the road gradient ratio value. When the road gradient ratio value is positive, the basic safe speed reference value is lowered; when the road gradient ratio value is negative, the basic safe speed reference value is raised, thus generating a dynamic safe downhill speed.

[0033] The power calculation submodule obtains the battery temperature and reads the high temperature and ultra-high temperature thresholds, as well as the preset basic charging power percentage. When the battery temperature is higher than the ultra-high temperature threshold, the basic charging power percentage is reduced to the first preset low value. When the battery temperature is between the high temperature threshold and the ultra-high temperature threshold, the basic charging power percentage is reduced to the second preset low value. The dynamic allowable charging power percentage is calculated.

[0034] The torque lookup table submodule uses the road slope ratio, motor temperature, and battery temperature as a composite lookup index to perform interpolation lookup in a multidimensional lookup table to determine the dynamic retarding base torque and the dynamic allowable retarding braking torque increase corresponding to the current operating condition.

[0035] The specific process of the power calculation submodule in calculating the dynamically allowed charging percentage is as follows: It obtains the battery temperature, the base charging percentage, the high temperature threshold, the high temperature threshold and the ultra-high temperature threshold (including the high temperature threshold and ultra-high temperature threshold), the first preset low value, and the second preset low value. It determines whether the battery temperature is greater than the ultra-high temperature threshold. If so, the dynamically allowed charging percentage is set to the first preset low value. If not, it further determines whether the battery temperature is greater than the high temperature threshold. If so, the dynamically allowed charging percentage is calculated using linear interpolation based on the battery temperature, high temperature threshold, ultra-high temperature threshold, base charging percentage, and the second preset low value. If the battery temperature is not greater than the high temperature threshold, the dynamically allowed charging percentage is set to the base charging percentage.

[0036] Dynamic parameter module example The dynamic parameter module obtains the final road gradient ratio value output by the state perception module, which is -0.2876. Simultaneously, the module obtains the battery temperature (48℃), motor temperature (75℃), and battery charge percentage (82%) from the real-time state data packet. Based on the road gradient ratio value (-0.2876), the module adjusts the base safe speed (e.g., 50 km / h) to generate a dynamic safe downhill speed (e.g., calculated to be 15.49 km / h). The module compares the battery temperature (48℃) with the high temperature threshold (50℃) and the ultra-high temperature threshold (60℃). Because 48℃ is lower than 50℃, the dynamic allowable charging percentage is calculated as the base charging percentage (e.g., 90%). The module queries a multidimensional lookup table based on the road gradient ratio value (-0.2876), motor temperature (75℃), and battery temperature (48℃). Through three-dimensional interpolation calculations, the dynamic retarding base torque (e.g., -256.6 Nm) and the dynamic allowable retarding braking torque increase (e.g., -322.6 Nm) are determined.

[0037] The safe speed submodule acquires the road gradient ratio value, which is -0.2876. The submodule reads the preset baseline safe speed value, which is 50 km / h. This baseline value is determined based on the 85th percentile speed of a passenger vehicle traveling on a road section with a gradient between -2% and +2%. The submodule dynamically corrects the baseline safe speed value based on the road gradient ratio value. The correction logic is: Dynamic safe downhill speed = Baseline safe speed value + (Road gradient ratio value × Speed ​​correction coefficient). The speed correction coefficient is set to 120, which is calibrated through real-vehicle testing and is used to balance safety and driving efficiency. If the road gradient ratio value (-0.2876) is negative, the baseline safe speed value is lowered. The calculation process is as follows: If the road gradient ratio is positive, such as +0.05 (5% uphill), then an upward adjustment will be performed. Under the current operating conditions, the submodule generates a dynamic safe downhill speed and sets a lower limit (e.g., 10 km / h), with the final output value being 15.49 km / h.

[0038] The power calculation submodule obtains the battery temperature, which is 48℃. The submodule reads the high temperature and ultra-high temperature thresholds, as well as the preset base charge percentage. High temperature threshold (… The temperature is set to 50℃, and the ultra-high temperature threshold is ( The temperature is set to 60℃. Base charging capacity percentage ( The first preset low value is set to 90%. The second preset low value is set to 20%. The threshold is set to 60%. These thresholds are based on the following criteria: (50℃) and (60℃) is a safety limit in the cell specifications provided by the battery supplier. When the temperature exceeds 50℃, the charging current must be limited, and when the temperature exceeds 60℃, charging must be stopped. (90%) is the value set by the operational strategy. (20%) and (60%) is a safety redundancy design, limiting regenerative braking energy recovery at high temperatures; 20% allows for minimal braking; and 60% provides a larger buffer. The submodule determines whether the battery temperature (48℃) is higher than the ultra-high temperature threshold (60℃); if no. The submodule determines whether the battery temperature (48℃) is between the high temperature threshold (50℃) and the ultra-high temperature threshold (60℃); if no. Since 48℃ is not greater than the high temperature threshold of 50℃, according to the specific calculation logic (detailed in the next paragraph), the dynamically allowed percentage of charging capacity is set to 90% of the base charging capacity percentage.

[0039] The power calculation submodule acquires the battery temperature (48℃), basic charge percentage (90%), high temperature threshold (50℃), ultra-high temperature threshold (60℃), first preset low value (20%), and second preset low value (60%). The submodule executes the following judgment process: 1. Determine if the battery temperature (48℃) is greater than the ultra-high temperature threshold (60℃). No (48℃ not greater than 60℃). 2. If no, further determine if the battery temperature (48℃) is greater than the high temperature threshold (50℃). No (48℃ not greater than 50℃). 3. If the battery temperature is not greater than the high temperature threshold, set the dynamically allowed charge percentage to the basic charge percentage. Dynamically allowed charge percentage = 90%.

[0040] As an example, if the obtained battery temperature is 55℃: 1. Determine if the battery temperature (55℃) is greater than the ultra-high temperature threshold (60℃). No. 2. If no, further determine if the battery temperature (55℃) is greater than the high temperature threshold (50℃). Yes (55℃ is greater than 50℃). 3. Then, using the battery temperature (55℃), high temperature threshold (50℃), ultra-high temperature threshold (60℃), basic charge percentage (90%), and second preset low value (60%), calculate using linear interpolation. The interpolation is based on two points: (high temperature threshold, basic charge percentage) i.e., (50, 90) and (ultra-high temperature threshold, second preset low value) i.e., (60, 60). Slope = Dynamically allowed percentage of charge = .

[0041] As another example, if the obtained battery temperature is 62℃: 1. Determine if the battery temperature (62℃) is greater than the ultra-high temperature threshold (60℃). Yes. 2. Then set the dynamic allowable charging percentage to the first preset low value. Dynamic allowable charging percentage = 20%.

[0042] In this embodiment, since the battery temperature is 48°C, the final calculated dynamic allowable charging capacity percentage is 90%.

[0043] The torque lookup table submodule uses the road gradient ratio (-0.2876), motor temperature (75℃), and battery temperature (48℃) as a composite lookup index. The system stores a three-dimensional lookup table in non-volatile memory, which defines the dynamic retarding base torque and the dynamic allowable retarding braking torque increment.

[0044] Table 2 Dynamic Retarding Torque Lookup Table (Partial)

[0045] As shown in Table 2, the input index (-28.76%, 75℃, 48℃) is within the table's domain but not on a grid point. The submodule performs trilinear interpolation. 1. Interpolation is performed at motor temperature = 75℃ (midpoint between 70℃ and 80℃) to obtain a two-dimensional plane of slope-battery temperature. - Point A (slope -20, battery 40): base torque = ;Increase = Point B (Slope -20, Battery 50): Base torque = ;Increase = Point C (Slope -30, Battery 40): Base Torque = ;Increase = -Point D (Slope -30, Battery 50): Base Torque = ;Increase = 2. Interpolation is performed at a battery temperature of 48℃ (between 40℃ and 50℃, weighted at 0.8) to obtain a one-dimensional line with a slope. - Point E (slope -20): Basic torque = ;Increase = -Point F (slope -30): Basic torque = ;Increase = 3. Interpolate at a slope of -28.76% (between -20% and -30%, weighted at 0.876). - Dynamic deceleration base torque = -Dynamically permissible increase in slow braking torque= The submodule determines the dynamic retardation base torque as -256.6 Nm and the dynamic permissible retardation braking torque increase as -322.6 Nm.

[0046] Please see Figure 1 and Figure 4 The trigger signal module compares the current vehicle speed with the dynamic safe downhill speed, and compares the battery charge percentage with the dynamic allowable charging charge percentage, and generates a slow braking trigger signal based on the comparison results.

[0047] The vehicle speed comparison submodule obtains the current vehicle speed and the dynamic safe downhill vehicle speed, and compares whether the current vehicle speed is greater than the dynamic safe downhill vehicle speed. If it is greater, a high-level vehicle speed over-limit flag is generated; otherwise, a low-level vehicle speed over-limit flag is generated.

[0048] The battery comparison submodule obtains the battery percentage and the dynamically allowed charging percentage, and compares whether the battery percentage is less than the dynamically allowed charging percentage. If it is less, a high-level battery allow flag is generated; otherwise, a low-level battery allow flag is generated.

[0049] The logic AND gate module receives the vehicle speed limit flag and the battery level allowance flag, performs a logic AND operation on the vehicle speed limit flag and the battery level allowance flag, and generates an active slow braking trigger signal if and only if both the vehicle speed limit flag and the battery level allowance flag are high. In all other cases, it generates an inactive slow braking trigger signal.

[0050] The vehicle speed comparison submodule incorporates hysteresis comparison logic when comparing the current vehicle speed with the dynamic safe downhill speed. The specific process of this hysteresis comparison logic is as follows: It reads preset vehicle speed trigger thresholds and vehicle speed exit thresholds, ensuring the trigger threshold is greater than the exit threshold. It then obtains the current vehicle speed and the dynamic safe downhill speed, calculating the difference between them. Finally, it checks the previous cycle state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, the speed over-limit flag is set to high when the speed difference exceeds the trigger threshold. If the deceleration braking trigger signal is active, the speed over-limit flag is only set to low when the speed difference is less than the exit threshold; otherwise, the current state of the speed over-limit flag remains unchanged.

[0051] Trigger signal module embodiment The trigger signal module acquires the current vehicle speed (23 km / h) and the dynamic safe downhill speed (15.49 km / h) from the dynamic parameter module. The module acquires the battery percentage (82%) and the dynamic allowable charging percentage (90%) from the dynamic parameter module. The module first compares the current vehicle speed with the dynamic safe downhill speed: 23 km / h is greater than 15.49 km / h, so this comparison result is "true". The module then compares the battery percentage with the dynamic allowable charging percentage: 82% is less than 90%, so this comparison result is "true". Based on the comparison result, the module generates a slow braking trigger signal and performs a logical AND operation: ("true" AND "true") = "true". Therefore, the module generates an active slow braking trigger signal (e.g., outputting a high level 1). If the current vehicle speed is 15 km / h (less than 15.49 km / h), the comparison result is ("false" AND "true") = "false". If the battery percentage is 92% (not less than 90%), the comparison result is (true" AND "false") = "false".

[0052] The specific functions of the trigger signal module are as follows: The vehicle speed comparison submodule obtains the current vehicle speed (23km / h) and the dynamic safe downhill vehicle speed (15.49km / h). The submodule compares whether 23 is greater than 15.49. If yes, the submodule generates a high-level (1) vehicle speed over-limit flag. The battery power comparison submodule obtains the battery power percentage (82%) and the dynamic allowable charging percentage (90%). The submodule compares whether 82 is less than 90. If yes, the submodule generates a high-level (1) battery power allowance flag. The logic AND gate submodule receives the vehicle speed over-limit flag (1) and the battery power allowance flag (1). The submodule performs a logic AND operation on the vehicle speed over-limit flag and the battery power allowance flag: Since both the speed limit exceedance sign and the battery charge allowance sign are high, the submodule generates an active slow braking trigger signal (1). In all other cases ( , , All of these generate a deactivated slow braking trigger signal (0).

[0053] The vehicle speed comparison submodule introduces hysteresis comparison logic during comparison. The submodule reads a preset vehicle speed trigger threshold value ( ) and vehicle speed exit threshold ( The vehicle speed trigger threshold (2.0 km / h) is greater than the vehicle speed exit threshold (0.5 km / h). This setting is based on real-vehicle calibration. The 2.0 km / h trigger threshold avoids frequent braking caused by small fluctuations in vehicle speed near the safe speed (e.g., ±1 km / h), while the 0.5 km / h exit threshold ensures the continuity of braking action until the vehicle speed is clearly under control. In the current cycle: 1. Obtain the current vehicle speed (23 km / h) and the dynamic safe downhill speed (15.49 km / h). 2. Calculate the speed difference: 3. Determine the state of the previous cycle. Assume the previous cycle was inactive (e.g., just entering a downhill section). 4. If inactive, determine if the speed difference (7.51) is greater than the speed trigger threshold (2.0). Yes. 5. Set the speed over-limit flag to high level (1).

[0054] In the subsequent One cycle: 1. Assuming the vehicle speed drops to 15.8 km / h, the dynamic safe downhill speed remains 15.49 km / h. 2. Calculate the speed difference: 3. Determine the status of the previous cycle. The deceleration braking trigger signal is currently active. 4. If active, determine if the speed difference (0.31) is less than the speed exit threshold (0.5). Yes. 5. Set the speed over-limit flag to low (0).

[0055] In another subsequent cycle (e.g., the first) (Each cycle): 1. Assuming the vehicle speed is 17.0 km / h, the dynamic safe downhill speed remains 15.49 km / h. 2. Calculate the speed difference: 3. Determine the status of the previous cycle. The deceleration braking trigger signal is currently active. 4. If active, determine if the speed difference (1.51) is less than the speed exit threshold (0.5). No. 5. Maintain the current status of the speed over-limit sign (still high level 1).

[0056] Please see Figure 1 and Figure 5 The torque decision module determines the state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, the deceleration braking torque is set to 0. If the deceleration braking trigger signal is active, the speed difference between the current vehicle speed and the dynamic safe downhill speed is calculated. Based on the speed difference and the preset proportional-integral control strategy, the torque coefficient is calculated and the torque coefficient is limited. The torque increase is calculated using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. The torque increase is added to the dynamic deceleration base torque to obtain the deceleration braking torque.

[0057] The PI control submodule determines the status of the slow braking trigger signal. If it is active, it obtains the current vehicle speed and the dynamic safe downhill vehicle speed, calculates the difference between the two to obtain the vehicle speed difference, and performs proportional-integral control calculation on the vehicle speed difference based on the preset proportional coefficient and integral coefficient to generate the original torque coefficient.

[0058] The coefficient limiting submodule obtains the original torque coefficient and reads the preset upper and lower limits of the torque coefficient. It then performs saturation limiting on the original torque coefficient to ensure that the original torque coefficient is always between the lower and upper limits, thus obtaining the limited torque coefficient.

[0059] The torque synthesis submodule obtains the torque coefficient after limiting, the dynamic allowable retarded braking torque increase, and the dynamic retarded base torque. It calculates the torque increase by multiplying the torque coefficient after limiting by the dynamic allowable retarded braking torque increase, and adds the torque increase to the dynamic retarded base torque to obtain the final retarded braking torque.

[0060] The PI control submodule performs proportional-integral control calculations on the vehicle speed difference, and the specific calculation formula is as follows:

[0061] in, Represents the original torque coefficient in the th The calculation results for each control cycle, Representing the The vehicle speed difference over each control cycle It equals the current speed minus the dynamic safe downhill speed. Represents the proportionality coefficient. Represents the integral coefficient. Represents from the 0th period to the 1st period. The sum of the speed differences over each cycle.

[0062] The PI control submodule also includes integral anti-saturation processing. When the torque coefficient after limiting reaches the upper or lower limit of the torque coefficient, if the sign of the vehicle speed difference is the same as the sign of the torque coefficient after limiting, the accumulation of the vehicle speed difference is paused.

[0063] Torque Decision Module Implementation Example The torque decision module determines the state of the slow braking trigger signal and obtains the active state (1). If the slow braking trigger signal is inactive (0), the slow braking torque is directly set to 0 Nm. Since the signal is active (1), the module calculates the speed difference between the current vehicle speed (23 km / h) and the dynamic safe downhill speed (15.49 km / h), obtaining 7.51 km / h. Based on the speed difference and the preset proportional-integral control strategy, the module calculates the torque coefficient (for example, the original torque coefficient of 0.3254 is obtained through PI calculation). The module limits the torque coefficient to the range of [0.0, 1.0], obtaining the limited torque coefficient of 0.3254. The module uses the limited torque coefficient (0.3254) and the dynamic allowable slow braking torque increase (-322.6 Nm) to calculate the torque increase. The calculation process is as follows: The module adds the torque increase (-105.0 Nm) to the dynamic retarding base torque (-256.6 Nm). The calculation process is as follows: The module obtained a slow braking torque of -361.6 Nm.

[0064] The specific functions of the torque decision module are as follows: The PI control submodule judges the state of the slow braking trigger signal and obtains the active state (1). The submodule obtains the current vehicle speed (23km / h) and the dynamic safe downhill vehicle speed (15.49km / h), and calculates the difference between the two to obtain the vehicle speed difference value. The submodule is based on a preset proportional coefficient ( ) and integral coefficient ( The proportional-integral control is performed on the vehicle speed difference. Based on subsequent examples, assuming the cumulative error sum of the current cycle is 27.51, the original torque coefficient is calculated. The coefficient limiting submodule obtains the original torque coefficient of 0.3254. The submodule reads the preset upper limit value of the torque coefficient (1.0) and the lower limit value of the torque coefficient (0.0). This range [0.0, 1.0] means that 0.0 represents using only the base torque, and 1.0 represents adding all the torque amplification to the base torque. The submodule performs saturation limiting on 0.3254. Since 0.3254 is between the upper limit value of 1.0 and the lower limit value of 0.0, the original torque coefficient remains unchanged. The resulting torque coefficient after limiting is 0.3254. The torque synthesis submodule obtains the torque coefficient after limiting (0.3254), the dynamic allowable slow braking torque amplification (-322.6 Nm), and the dynamic slow base torque (-256.6 Nm). The submodule calculates the torque amplification by multiplying the torque coefficient after limiting by the dynamic allowable slow braking torque amplification. The submodule adds the torque amplification to the dynamic retarding base torque to obtain the final retarding braking torque: .

[0065] The PI control submodule performs proportional-integral control calculations on the vehicle speed difference, and the calculation formula is as follows: In this formula, Represents the original torque coefficient in the th The calculation results for each control cycle. It is the index of the current control cycle. Representing the The speed difference for each control cycle is calculated as the current speed (23 km / h) minus the dynamic safe downhill speed (15.49 km / h). Represents the proportionality coefficient. Represents the integral coefficient. Represents activation from the system ( ) to the current cycle ( The sum of all speed differences. It is an index of historical cycles. The logic of the formula is based on the proportional term. To respond quickly to the current instantaneous speed deviation, and simultaneously through the integral term It responds to historical cumulative deviations and eliminates steady-state errors.

[0066] Parameter acquisition and setting: (proportionality coefficient) and (Integral coefficients): These two coefficients are obtained by tuning the bus dynamics model in the simulation environment and calibrating it on the actual vehicle. Set to 0.025. Set to 0.005. This set of parameters provides a small overshoot (<5%) while ensuring a fast response. : in the One (current) control cycle, vehicle speed difference . Read from memory The value, and with Add them together.

[0067] Example: Assume the current is the [number]th [number]. One cycle, and (That is, the second cycle immediately after the system is activated). Cycle (Activation period): - (Speed ​​difference from the previous cycle) - (Assuming an initial cumulative sum) -

[0068] cycle (Current Period): - - - - -

[0069] The result of 0.2504 indicates that the original torque coefficient calculated by the PI controller is 0.2504, and this value will be passed to the coefficient limiting submodule.

[0070] The integral anti-saturation processing logic of the PI control submodule is in the integral accumulation term. This is executed during the update. After the PI calculation, when the coefficient limiting submodule determines that the output torque coefficient has reached its upper limit (e.g., 1.0) or lower limit (e.g., 0.0), the anti-saturation logic is triggered. Specifically, when the limited torque coefficient reaches its upper limit, if the current vehicle speed difference... If the value is positive (indicating that the vehicle speed is still exceeding the speed limit and braking force needs to be increased), then the accumulation of the integral term is paused. This means that the integral sum in the next cycle will maintain the value of the current cycle and will not continue to increase. This prevents excessive accumulation of the integral term, allowing the system to quickly exit saturation when the vehicle speed decreases, avoiding large overshoot and oscillations. Similarly, when the torque coefficient reaches its lower limit, if the vehicle speed difference is negative, the integral accumulation is also paused.

[0071] A control method for a retarded braking system of a pure electric bus, wherein the control method for the retarded braking system of a pure electric bus is executed based on the aforementioned retarded braking system of a pure electric bus, and includes the following steps: S1: Collect battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude; calculate the altitude change between the current altitude and the altitude of the previous control cycle; calculate the driving distance based on the current vehicle speed and control cycle duration; and calculate the road gradient ratio based on the altitude change and driving distance. S2: Based on the road slope ratio value, adjust the basic safe vehicle speed to generate the dynamic safe downhill vehicle speed. Calculate the dynamic allowable charging capacity percentage based on the comparison results of battery temperature with high temperature and ultra-high temperature thresholds. Determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase by querying the multidimensional lookup table based on the road slope ratio value, motor temperature, and battery temperature. S3: Compare the current vehicle speed with the dynamic safe downhill speed, and compare the battery charge percentage with the dynamic allowable charge percentage. Generate a slow braking trigger signal based on the comparison results. S4: Determine the status of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, set the deceleration braking torque to 0. If the deceleration braking trigger signal is active, calculate the speed difference between the current vehicle speed and the dynamic safe downhill vehicle speed. Calculate the torque coefficient based on the speed difference and limit the torque coefficient. Calculate the torque increase using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. Add the torque increase to the dynamic deceleration base torque to obtain the deceleration braking torque.

[0072] The above embodiments illustrate preferred embodiments of the present invention. Any equivalent adjustments to the technical solution based on software engineering methods are within the scope of protection, including but not limited to: implementing algorithm logic using different programming languages, performing service-oriented computing on functional modules, adjusting data interaction protocols, and optimizing resource scheduling strategies. Any implementation scheme derived from reasonable modifications to the data processing flow, service call chain, or system architecture layer without departing from the core technology of the present invention should be considered within the scope of protection defined by the claims of the present invention.

Claims

1. A slow braking system for a pure electric bus, characterized in that, The system includes: The status perception module collects battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude. It calculates the altitude change between the current altitude and the altitude of the previous control cycle, calculates the driving distance based on the current vehicle speed and the duration of the control cycle, and calculates the road gradient ratio based on the altitude change and the driving distance. The dynamic parameter module adjusts the basic safe vehicle speed based on the road gradient ratio value to generate a dynamic safe downhill vehicle speed. It calculates the dynamic allowable charging percentage based on the comparison results of the battery temperature with high temperature and ultra-high temperature thresholds. It queries a multi-dimensional lookup table based on the road gradient ratio value, the motor temperature, and the battery temperature to determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase. The trigger signal module compares the current vehicle speed with the dynamic safe downhill vehicle speed, and compares the battery charge percentage with the dynamic allowable charging charge percentage, and generates a slow braking trigger signal based on the comparison results; The torque decision module determines the state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, the deceleration braking torque is set to 0. If the deceleration braking trigger signal is active, the module calculates the speed difference between the current vehicle speed and the dynamic safe downhill vehicle speed. Based on the speed difference and a preset proportional-integral control strategy, the module calculates the torque coefficient and limits the torque coefficient. The module then calculates the torque increase using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. Finally, the module adds the torque increase to the dynamic deceleration base torque to obtain the deceleration braking torque.

2. The pure electric bus slow-speed braking system according to claim 1, characterized in that, The specific functions of the state awareness module are as follows: The status acquisition submodule acquires sensor data through the vehicle controller local area network bus, and acquires the battery temperature, the battery charge percentage, the motor temperature and the vehicle's current speed. At the same time, it uses the global positioning system module to acquire the vehicle's current altitude and packages the current altitude and the current speed to generate a real-time status data packet. The mileage calculation submodule extracts the current vehicle speed from the real-time status data packet and retrieves the control cycle duration. It calculates the distance traveled by the vehicle within the current control cycle by multiplying the current vehicle speed by the control cycle duration, and updates the real-time status data packet to include the travel distance. The slope calculation submodule retrieves the current altitude and the driving distance from the real-time status data packet, reads the historical altitude stored within the control cycle from the storage unit, calculates the difference between the current altitude and the historical altitude to obtain the altitude change, and finally calculates the road slope ratio value by the ratio of the altitude change to the driving distance.

3. The slow-speed braking system for pure electric buses according to claim 2, characterized in that, When calculating the road slope ratio value, the slope calculation submodule also performs filtering processing on the road slope ratio value. The specific process of the filtering processing is as follows: The road slope ratio value is obtained as the original slope value for the current cycle, and the preset filtering coefficient and the filtered slope value of the previous cycle are retrieved from the storage unit. A first-order lag filtering algorithm is used to multiply the original slope value of the current period by the filtering coefficient to obtain the current weighted slope, and multiply the filtered slope value of the previous period by (1 - the filtering coefficient) to obtain the historical weighted slope. The current weighted slope is added to the historical weighted slope to obtain the current periodically filtered slope value. The current periodically filtered slope value is updated and stored in the storage unit. At the same time, the current periodically filtered slope value is output as the final road slope ratio value.

4. The slow-speed braking system for pure electric buses according to claim 1, characterized in that, The specific function of the dynamic parameter module is as follows: The safe vehicle speed submodule acquires the road gradient ratio value and reads the preset basic safe vehicle speed reference value. It dynamically corrects the basic safe vehicle speed reference value based on the road gradient ratio value. When the road gradient ratio value is positive, the basic safe vehicle speed reference value is lowered; when the road gradient ratio value is negative, the basic safe vehicle speed reference value is raised, thereby generating the dynamic safe downhill vehicle speed. The power calculation submodule acquires the battery temperature and reads the high temperature and ultra-high temperature thresholds, as well as the preset basic charging power percentage. When the battery temperature is higher than the ultra-high temperature threshold, the basic charging power percentage is reduced to a first preset low value. When the battery temperature is between the high temperature threshold and the ultra-high temperature threshold, the basic charging power percentage is reduced to a second preset low value. The dynamic allowable charging power percentage is calculated. The torque lookup table submodule uses the road slope ratio, motor temperature, and battery temperature as a composite lookup index to perform interpolation lookup in the multidimensional lookup table to determine the dynamic retarding base torque and the dynamic permissible retarding braking torque increase corresponding to the current operating condition.

5. The pure electric bus slow-speed braking system according to claim 4, characterized in that, The specific process by which the power calculation submodule calculates the dynamically allowed charging power percentage is as follows: The battery temperature, the basic charge percentage, the high temperature threshold and the ultra-high temperature threshold included in the high temperature and ultra-high temperature thresholds, the first preset low value, and the second preset low value are obtained. Determine whether the battery temperature is greater than the ultra-high temperature threshold. If so, set the dynamic allowable charging capacity percentage to the first preset low value. If not, then it is further determined whether the battery temperature is greater than the high temperature threshold. If so, the dynamic allowable charging percentage is calculated by linear interpolation using the battery temperature, the high temperature threshold, the ultra-high temperature threshold, the basic charging capacity percentage, and the second preset low value. If the battery temperature is not greater than the high temperature threshold, then the dynamic allowable charging capacity percentage is set to the base charging capacity percentage.

6. The slow-speed braking system for pure electric buses according to claim 1, characterized in that, The specific function of the trigger signal module is as follows: The vehicle speed comparison submodule obtains the current vehicle speed and the dynamic safe downhill vehicle speed, compares whether the current vehicle speed is greater than the dynamic safe downhill vehicle speed, and if it is greater, generates a high-level vehicle speed over-limit flag; otherwise, it generates a low-level vehicle speed over-limit flag. The battery comparison submodule obtains the battery percentage and the dynamic allowable charging percentage, compares whether the battery percentage is less than the dynamic allowable charging percentage, and if it is less, generates a high-level battery allowance flag; otherwise, it generates a low-level battery allowance flag. The logic AND gate module receives the vehicle speed over-limit flag and the battery level allowance flag, performs a logic AND operation on the vehicle speed over-limit flag and the battery level allowance flag, and generates the deceleration braking trigger signal in an active state only when both the vehicle speed over-limit flag and the battery level allowance flag are high level, and generates the deceleration braking trigger signal in an inactive state in all other cases.

7. The pure electric bus slow-speed braking system according to claim 6, characterized in that, When comparing the current vehicle speed with the dynamic safe downhill speed, the vehicle speed comparison submodule also introduces hysteresis comparison logic. The specific process of the hysteresis comparison logic is as follows: Read the preset vehicle speed trigger threshold and vehicle speed exit threshold, wherein the vehicle speed trigger threshold is greater than the vehicle speed exit threshold; The current vehicle speed and the dynamic safe downhill vehicle speed are obtained, and the difference between the current vehicle speed and the dynamic safe downhill vehicle speed is calculated to obtain the vehicle speed difference value. Determine the state of the previous cycle of the slow braking trigger signal. If the slow braking trigger signal is inactive, then when the vehicle speed difference is greater than the vehicle speed trigger threshold, set the vehicle speed over-limit flag to a high level. If the slow braking trigger signal is active, the speed over-limit flag will be set to low only when the speed difference is less than the speed exit threshold. Otherwise, the current state of the speed over-limit flag will remain unchanged.

8. The slow braking system for pure electric buses according to claim 1, characterized in that, The specific function of the torque decision module is as follows: The PI control submodule determines the state of the slow braking trigger signal. If it is active, it obtains the current vehicle speed and the dynamic safe downhill vehicle speed, calculates the difference between the two to obtain the vehicle speed difference, and performs proportional-integral control operation on the vehicle speed difference based on the preset proportional coefficient and integral coefficient to generate the original torque coefficient. The coefficient limiting submodule obtains the original torque coefficient and reads the preset upper limit and lower limit values ​​of the torque coefficient. It performs saturation limiting processing on the original torque coefficient to ensure that the original torque coefficient is always between the lower limit and the upper limit values ​​of the torque coefficient, thus obtaining the limited torque coefficient. The torque synthesis submodule obtains the torque coefficient after the limit, the dynamic allowable slow braking torque increase, and the dynamic slow base torque. It calculates the torque increase by multiplying the torque coefficient after the limit by the dynamic allowable slow braking torque increase, and adds the torque increase to the dynamic slow base torque to obtain the final slow braking torque.

9. The slow-speed braking system for pure electric buses according to claim 8, characterized in that, The PI control submodule performs proportional-integral control calculations on the vehicle speed difference, and the specific calculation formula is as follows: ； in, This represents the calculation result of the original torque coefficient in the kth control cycle. The vehicle speed difference value represents the k-th control cycle. It equals the current vehicle speed minus the dynamic safe downhill vehicle speed. This represents the proportionality coefficient. Represents the integral coefficient, This represents the cumulative sum of the vehicle speed differences from the 0th cycle to the kth cycle; The PI control submodule also includes integral anti-saturation processing. When the torque coefficient after the limit reaches the upper limit or the lower limit of the torque coefficient, if the sign of the vehicle speed difference is the same as the sign of the torque coefficient after the limit, the accumulation of the vehicle speed difference is paused.

10. A control method for a slow braking system of a pure electric bus, characterized in that, The method is used to implement the slow braking system for pure electric buses according to any one of claims 1-9. Includes the following steps: S1: Collect battery temperature, battery charge percentage, motor temperature, current vehicle speed, and current altitude; calculate the altitude change between the current altitude and the altitude of the previous control cycle; calculate the driving distance based on the current vehicle speed and the duration of the control cycle; and calculate the road gradient ratio based on the altitude change and the driving distance. S2: Based on the road slope ratio value, adjust the basic safe vehicle speed to generate a dynamic safe downhill vehicle speed. Calculate the dynamic allowable charging percentage based on the comparison results of the battery temperature with high temperature and ultra-high temperature thresholds. Determine the dynamic deceleration base torque and the dynamic allowable deceleration braking torque increase by querying a multidimensional lookup table based on the road slope ratio value, the motor temperature, and the battery temperature. S3: Compare the current vehicle speed with the dynamic safe downhill vehicle speed, and compare the battery charge percentage with the dynamic allowable charging percentage, and generate a slow braking trigger signal based on the comparison results; S4: Determine the state of the deceleration braking trigger signal. If the deceleration braking trigger signal is inactive, set the deceleration braking torque to 0. If the deceleration braking trigger signal is active, calculate the speed difference between the current vehicle speed and the dynamic safe downhill vehicle speed. Calculate the torque coefficient based on the speed difference and limit the torque coefficient. Calculate the torque increase using the limited torque coefficient and the dynamic allowable deceleration braking torque increase. Add the torque increase to the dynamic deceleration base torque to obtain the deceleration braking torque.

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