Low-speed braking control method, system, and vehicle

Abstract

The application relates to a low-speed braking control method, system and vehicle, wherein the method comprises the following steps: acquiring actual output torque of a motor in the vehicle and actual output torque of a hydraulic braking system; in the case that it is detected that the vehicle is in a regenerative braking exit stage, determining a virtual compensation torque for representing a total vehicle braking force gap according to target output torque and actual output torque of the motor and the hydraulic braking system respectively; controlling the motor to keep a preset field weakening output torque, and controlling the hydraulic braking system to increase corresponding actual output torque according to a preset torque increasing gradient until the actual output torque of the hydraulic braking system reaches a sum of the target output torque and the virtual compensation torque of the hydraulic braking system. By using the application, the braking safety and braking smoothness of the vehicle during the regenerative braking exit stage are improved.

Description

Technical Field

[0001] This invention relates to the field of vehicle control technology, and in particular to a low-speed braking control method, system, and vehicle. Background Technology

[0002] Regenerative braking technology is one of the core technologies for electric vehicles to extend their driving range by converting the vehicle's kinetic energy into electrical energy and storing it in the battery through regenerative braking of the drive motor. During vehicle braking, the regenerative braking torque and the hydraulic braking torque need to work together to meet the driver's braking needs. When the vehicle speed decreases to near a stop, the regenerative braking function gradually disengages due to the limited low-speed operating characteristics of the motor, and the braking task is completely taken over by the hydraulic braking system.

[0003] Currently, during the transition process of regenerative braking disengagement, existing control methods typically employ a direct switching mode. This involves instructing the hydraulic braking system to output braking torque simultaneously with the reduction of the electric motor's torque to zero. However, due to the inherent response delay of the hydraulic braking system, the total braking force experiences a momentary drop. Some existing technologies mitigate this problem by adding a constant hydraulic torque compensation. However, in these methods, the time mismatch between the sudden drop in electric motor torque and the lag in hydraulic braking response leads to a momentary drop in total braking force, reducing braking safety. Furthermore, the constant compensation cannot adapt to the real-time changes in braking force, resulting in low compensation accuracy and impacting braking smoothness and ride comfort.

[0004] Therefore, how to eliminate the instantaneous drop in braking force during the regenerative braking exit process, achieve a smooth connection between electric motor power and hydraulic braking force, and at the same time enable the compensation amount to adapt to the changes in braking force gap in real time is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, it is necessary to provide a low-speed braking control method, system and vehicle to solve the technical problems of insufficient braking safety and low braking smoothness of vehicles when regenerative braking is disengaged in the prior art.

[0006] To address the aforementioned problems, in a first aspect, the present invention provides a low-speed braking control method, comprising: Obtain the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system; When the vehicle is detected to be in the regenerative braking disengagement phase, a virtual compensation torque is determined to characterize the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system, respectively. The motor is controlled to maintain a preset field weakening output torque, and the hydraulic braking system is controlled to increase the corresponding actual output torque according to a preset torque increase gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

[0007] In one possible implementation, the steps for determining the target output torque of the motor and the hydraulic braking system respectively include: The vehicle speed, battery state of charge, and brake pedal pressure are obtained. The total braking torque of the vehicle is determined based on the brake pedal pressure. When the vehicle speed is in the low-speed range, the corresponding working condition type is determined according to the vehicle speed. A first correction factor is determined based on the battery state of charge. The second correction factor is determined based on the brake pedal travel. The target output torque of the motor is calculated based on the target value of the total braking torque of the vehicle, the operating condition type, the first correction coefficient, and the second correction coefficient. The target output torque of the hydraulic braking system is determined based on the difference between the total braking torque of the vehicle and the target output torque of the motor.

[0008] In one possible implementation, the operating condition type includes a first type of low-speed creep operating condition and a second type of braking critical operating condition; determining the corresponding operating condition type based on the vehicle speed includes: When the vehicle speed exceeds a preset threshold, it is determined to be the first type; When the vehicle speed is less than or equal to the preset threshold, it is determined to be the second type.

[0009] In one possible implementation, determining the second correction factor based on the brake pedal travel includes: When the brake pedal travel is less than or equal to a preset travel threshold, the second correction coefficient is determined to be the first preset value; When the brake pedal travel exceeds the preset travel threshold, the second correction coefficient K s The following formula is used for calculation: K s = (S max - s) / (S max - S0); Where s is the percentage value of the brake pedal travel, S0 is the preset travel threshold, and S max This represents the maximum travel distance.

[0010] In one possible implementation, calculating the target output torque of the motor based on the target value of the total braking torque of the vehicle, the operating condition type, the first correction coefficient, and the second correction coefficient includes: Determine the corresponding baseline percentage based on the aforementioned operating condition type; The target output torque of the motor is calculated based on the benchmark ratio, the target value of the total braking torque of the vehicle, and the product of the first correction coefficient and the second correction coefficient.

[0011] In one possible implementation, under the second type, the target output torque of the motor is further adjusted according to a vehicle speed correction coefficient, which is the ratio of the current vehicle speed to the preset threshold.

[0012] In one possible implementation, determining the virtual compensation torque characterizing the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system respectively includes: Determine the first deviation between the target output torque of the motor and the actual output torque of the motor; Determine the second deviation between the target output torque of the hydraulic braking system and the actual output torque of the hydraulic braking system; The virtual compensation torque is determined based on the sum of the first deviation and the second deviation.

[0013] In one possible implementation, the detection step of the vehicle being in the regenerative braking exit phase includes: When the actual output torque of the motor in the vehicle is less than a first preset threshold and the vehicle speed is less than or equal to a second preset threshold, the vehicle is determined to be in the regenerative braking exit phase.

[0014] Secondly, the present invention also provides a low-speed braking control system, comprising: The acquisition unit is used to acquire the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system; The determining unit is used to determine a virtual compensation torque to characterize the total braking force gap of the vehicle, based on the target output torque and actual output torque of the motor and the hydraulic braking system, when the vehicle is detected to be in the regenerative braking disengagement stage. The control unit is used to control the motor to maintain a preset field weakening output torque and to control the hydraulic braking system to increase the corresponding actual output torque according to a preset torque increment gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

[0015] Thirdly, the present invention also provides a vehicle including the low-speed braking control system as described in the second aspect above.

[0016] The beneficial effects of this invention are: The low-speed braking control method provided by this invention acquires the actual output torque of the motor and the actual output torque of the hydraulic braking system in the vehicle, enabling timely perception of the true torque output state of the motor and the hydraulic braking system at the current moment. This ensures the real-time and accurate data used in determining the braking force gap. When the vehicle is detected to be in the regenerative braking exit phase, a virtual compensation torque is determined based on the target output torque and actual output torque of the motor and the hydraulic braking system, respectively. This allows the virtual compensation amount to comprehensively and accurately reflect the torque deviation state of the two braking subsystems, achieving precise matching of the virtual compensation amount to the actual braking force gap and improving the accuracy of braking force gap compensation. The method controls the motor to maintain a preset weak magnetic output torque and controls the hydraulic braking system to increase the corresponding actual output torque according to a preset torque increment gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque. This achieves continuous and stable total braking force during the regenerative braking exit process, improving the braking safety and braking smoothness of the vehicle during the regenerative braking exit process. Attached Figure Description

[0017] Figure 1 A schematic flowchart of an embodiment of the low-speed braking control method provided by the present invention; Figure 2 A schematic flowchart of another embodiment of the low-speed braking control method provided by the present invention; Figure 3 This is a schematic diagram of the low-speed braking control system provided by the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In the description of the embodiments of the present invention, unless otherwise stated, "a plurality of" means two or more.

[0020] The terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a technical feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] This invention provides a low-speed braking control method, system, and vehicle, which are described below.

[0023] The execution subject of the low-speed braking control method in this application embodiment can be the low-speed braking control system provided in this application embodiment, or it can be a vehicle integrated with the low-speed braking control system, a vehicle control unit, an on-board controller, or a hardware device such as a chip, processor, or electronic control unit (ECU) capable of running corresponding computer programs. This application embodiment does not specifically limit this.

[0024] The low-speed braking control method of this application can be applied to the regenerative braking system of electric vehicles, and is particularly suitable for application scenarios where the vehicle is traveling at low speeds and the regenerative braking function is gradually disengaged. This addresses the technical problems of reduced braking safety and deteriorated braking smoothness caused by the instantaneous drop in braking force during the disengagement of regenerative braking.

[0025] Figure 1 A schematic flowchart of an embodiment of the low-speed braking control method provided by the present invention is shown below. Figure 1 As shown, the low-speed braking control method includes: S101. Obtain the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system.

[0026] The actual output torque refers to the current actual torque value that the motor controller and hydraulic brake controller monitor and report in real time through their respective sensors.

[0027] Specifically, during vehicle braking, the motor controller calculates the actual output torque of the motor in real time using its internal current and speed sensors, while the hydraulic brake controller monitors the actual output torque of the hydraulic braking system in real time using a brake pressure sensor. These actual output torque signals can be transmitted to the braking control system via the vehicle controller area network (CAN) bus. Based on the real-time acquired actual output torque, the system can promptly perceive the true torque output status of the motor and hydraulic braking system at the current moment, thereby ensuring the real-time and accurate data used in subsequent braking force gap determination.

[0028] S102. When the vehicle is detected to be in the regenerative braking withdrawal stage, a virtual compensation torque is determined to characterize the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system, respectively.

[0029] The regenerative braking withdrawal stage refers to the process in which the motor gradually withdraws from the regenerative braking function when the vehicle decelerates to a lower speed due to the limited low-speed operating characteristics. At this time, the braking task needs to be gradually taken over by the hydraulic braking system.

[0030] Virtual compensation torque refers to the torque value calculated based on the deviation between the target output torque and the actual output torque of the motor and hydraulic braking system, respectively. This torque value represents the gap between the current total braking torque of the vehicle and the target braking torque.

[0031] Specifically, during vehicle braking, the braking control system pre-stores the target output torque of the motor and the target output torque of the hydraulic braking system, calculated based on parameters such as brake pedal pressure. When the vehicle enters the regenerative braking exit phase, the braking control system acquires the torque output deviation of the motor and the hydraulic braking system respectively, and determines the virtual compensation torque based on these two deviations. Since the virtual compensation torque is determined by comprehensively considering the deviations between the actual output torque of the motor and the hydraulic braking system and their target output torques, this compensation amount can comprehensively and accurately reflect the torque deviation states of the two braking subsystems, achieving precise matching of the virtual compensation amount to the actual braking force gap and improving the accuracy of braking force gap compensation.

[0032] S103. Control the motor to maintain the preset field weakening output torque, and control the hydraulic braking system to increase the corresponding actual output torque according to the preset torque increase gradient, until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

[0033] The field weakening output torque refers to the minimum torque value that the motor can stably output when running at low speed. Its magnitude is pre-calibrated based on the motor parameters and controller performance. For example, the preset field weakening output torque can be 2.5 N·m.

[0034] Alternatively, a model can be established to show the relationship between the motor output torque and speed: Te = f(n, I), where n is the motor speed and I is the motor current. Based on this model, the motor output torque can be dynamically adjusted according to the motor speed and current to adapt to the motor's operating characteristics under low-speed conditions and avoid torque fluctuations.

[0035] The torque increment gradient refers to the step size of the torque increase in each control cycle of the hydraulic braking system, which can be calibrated based on the response characteristics of the hydraulic system. For example, the preset torque increment gradient can be 0.8 N·m / 10 ms.

[0036] Specifically, after determining the virtual compensation torque, the braking control system sends a torque holding command to the motor controller, maintaining the motor output torque at a preset field-weakening output torque level. Simultaneously, it sends a gradient increase command to the hydraulic brake controller, causing the hydraulic braking system to gradually increase its output torque according to a preset torque increase gradient. As the actual output torque of the hydraulic braking system gradually increases, its value continuously approaches the sum of the target output torque and the virtual compensation torque. When the two are equal, the total braking force gap of the vehicle is completely filled. Because the motor maintains a preset field-weakening output torque level during regenerative braking disengagement, a sudden drop in motor torque is avoided. At the same time, the hydraulic braking system gradually increases its output torque according to a preset torque increase gradient, allowing the hydraulic braking torque to smoothly fill the braking force gap. Therefore, throughout the entire regenerative braking disengagement process, the total braking force of the vehicle remains continuous and stable, avoiding sudden changes in braking deceleration caused by a momentary drop in braking force, thus improving braking safety. Meanwhile, the virtual compensation amount is dynamically determined in real time based on the actual output torque of the motor and the hydraulic system and the target output torque, which can accurately match the current braking force gap, avoid the over-compensation or under-compensation problems that may be caused by constant compensation amount, realize the smooth braking of the vehicle during low-speed braking, and improve the braking smoothness and driving comfort of the vehicle.

[0037] It is worth noting that after the actual output torque of the hydraulic braking system reaches the sum of its target output torque and virtual compensation torque, the braking control system also coordinates the torque of the motor and the torque of the hydraulic system based on the constraint relationship Te_adj + Th_adj = T_total, where Te_adj is the adjusted motor output torque, Th_adj is the adjusted hydraulic output torque, and T_total is the total braking torque of the vehicle, so that the total braking torque remains stable during the regenerative braking disengagement process.

[0038] Furthermore, it's worth noting that the braking control system can also establish a closed-loop control model using vehicle speed and braking torque as feedback parameters. By comparing the target value with the actual value in real time, it dynamically adjusts the torque distribution ratio and virtual compensation torque to ensure that the actual output continuously approaches the target value. Specifically, during vehicle braking, the braking control system continuously performs the following closed-loop operations: It acquires the vehicle speed signal, the actual output torque Te_actual of the motor, and the actual output torque Th_actual of the hydraulic braking system in real time as feedback parameters, comparing them with the current target output torque Te_target of the motor, the target output torque Th_target of the hydraulic braking system, the virtual compensation torque ΔT, and the target vehicle speed. Based on the comparison results, it dynamically adjusts the torque distribution ratio and virtual compensation torque for the next moment, including but not limited to: increasing the adjustment force of the vehicle speed correction coefficient kv when the vehicle speed drops to near the braking threshold; and adjusting the duration of the torque increment gradient or the hydraulic target torque value when an increase in the deviation between the actual hydraulic torque and the target hydraulic torque is detected. This closed-loop control is implemented throughout the entire regenerative braking disengagement process, repeating in each control cycle until the vehicle speed drops to zero.

[0039] Understandably, by introducing vehicle speed and braking torque as feedback parameters into closed-loop control, the system can dynamically adjust the control quantity according to the real-time state deviation, avoiding the cumulative error caused by the inability to perceive the deviation between the actual output and the target under open-loop control. This improves the accuracy of torque distribution and the accuracy of virtual compensation torque, ensuring the controllability and stability of the entire braking process.

[0040] In summary, the low-speed braking control method provided by this invention maintains the motor at a preset level of weakened magnetic output torque during the regenerative braking disengagement process, thus avoiding a sudden drop in motor torque. Simultaneously, it controls the hydraulic braking system to gradually increase output torque according to a preset torque increment gradient, enabling the hydraulic braking torque to smoothly fill the braking force gap. The total braking force of the vehicle remains continuous and stable throughout the entire regenerative braking disengagement process, avoiding sudden changes in braking deceleration caused by a momentary drop in braking force, thereby improving braking safety.

[0041] Furthermore, the virtual compensation torque is determined comprehensively based on the deviation between the actual output torque and the target output torque of each of the motor and hydraulic braking systems. This compensation amount can fully reflect the torque deviation state of each of the two braking subsystems, achieving precise matching of the virtual compensation amount to the actual braking force gap, thus improving the compensation accuracy. Moreover, the compensation amount is dynamically determined in real time based on the actual output torque and the target output torque, accurately matching the current actual braking force gap and avoiding over-compensation or under-compensation problems that may occur with a constant compensation amount. This enables smooth braking during low-speed braking, improves braking safety and smoothness during regenerative braking withdrawal, and enhances user driving comfort.

[0042] In some embodiments of the present invention, such as Figure 2 As shown, the steps for determining the target output torque of the motor and the hydraulic braking system respectively include: S201. Obtain the vehicle speed, battery state of charge, and brake pedal pressure; S202. Determine the total braking torque of the vehicle based on the brake pedal pressure; S203. When the vehicle speed is in the low speed range, determine the corresponding working condition type according to the vehicle speed. S204. Determine the first correction coefficient based on the battery state of charge; S205. Determine the second correction coefficient based on the brake pedal travel; S206. Calculate the target output torque of the motor based on the target value of the total braking torque of the vehicle, the operating condition type, the first correction coefficient, and the second correction coefficient; S207. Determine the target output torque of the hydraulic braking system based on the difference between the total braking torque of the vehicle and the target output torque of the motor.

[0043] Among them, the State of Charge (SOC) of the battery refers to the current remaining percentage of the power battery, and its value ranges from 0% to 100%. The total braking torque of the vehicle refers to the total torque value that the vehicle's braking system needs to output to meet the driver's braking needs.

[0044] Specifically, the system acquires vehicle speed, battery state of charge (SBC), and brake pedal pressure. Vehicle speed can be obtained via wheel speed sensors, battery SBC can be read from the Battery Management System (BMS), and brake pedal pressure can be acquired via a pressure sensor located at the brake pedal pushrod. The total braking torque of the vehicle is determined based on the brake pedal pressure. A preset conversion coefficient is used to convert between brake pedal pressure and total braking torque, with the coefficient ranging from 0.8 to 1.2.

[0045] When the vehicle speed is in the low-speed range, the corresponding operating condition type is determined based on the vehicle speed. The low-speed range refers to the driving state with a vehicle speed between 0 and 15 km / h. For example, when determining the operating condition type, the vehicle speed is compared with a preset threshold, which can be 3 km / h. A first correction coefficient is determined based on the battery state of charge (SBC), and the value of the first correction coefficient decreases as the battery SBC increases. For example, when the battery SBC is less than or equal to 80%, the first correction coefficient is 1.0; when the battery SBC is greater than 80% but less than 95%, the first correction coefficient is 0.9; and when the battery SBC is greater than or equal to 95%, the first correction coefficient is 0.5. A second correction coefficient is determined based on the brake pedal travel, which reflects the driver's desired braking intensity. The second correction coefficient is used to correct the torque distribution according to different braking intensities.

[0046] The target output torque of the motor is calculated based on the target value of the total braking torque of the vehicle, the operating condition type, and the first and second correction factors. The target output torque of the motor is obtained by multiplying the target value of the total braking torque of the vehicle by a base percentage corresponding to the operating condition type, and then multiplying by the first and second correction factors. The target output torque of the hydraulic braking system is determined by the difference between the total braking torque of the vehicle and the target output torque of the motor.

[0047] Understandably, this embodiment achieves adaptive adjustment of the regenerative braking torque ratio based on the remaining battery charge through the correction coefficient corresponding to SOC, thus avoiding battery overcharging; and achieves adaptive adjustment of torque distribution based on braking intensity through the correction coefficient corresponding to the brake pedal travel, thereby improving the adaptability of torque distribution to battery status and braking intensity.

[0048] In some embodiments of the present invention, the operating condition type includes a first type of low-speed creep operating condition and a second type of braking critical operating condition; step S203 includes: when the vehicle speed is greater than a preset threshold, it is determined to be the first type; when the vehicle speed is less than or equal to the preset threshold, it is determined to be the second type.

[0049] Low-speed creeping refers to a condition where a vehicle continues to travel at a low speed, such as when a vehicle is slowly following another vehicle in congested city traffic. A braking threshold condition refers to a condition where the vehicle speed further decreases to near a complete stop, such as when a vehicle is about to stop at a red light.

[0050] The preset threshold is the vehicle speed boundary value used to distinguish between the two working conditions mentioned above. Its specific value can be pre-calibrated according to vehicle parameters and braking performance requirements.

[0051] Specifically, during vehicle braking, the braking control system obtains the current vehicle speed in real time through the vehicle speed sensor and compares the vehicle speed with a preset threshold. When the vehicle speed is greater than the preset threshold, it is determined that the current condition is low-speed creep; when the vehicle speed is less than or equal to the preset threshold, it is determined that the current condition is critical for stopping. For example, when the preset threshold is set to 3 km / h, if the current vehicle speed is 8 km / h, it is determined to be a low-speed creep condition; if the current vehicle speed is 2 km / h, it is determined to be a critical for stopping.

[0052] Understandably, by precisely dividing the low-speed range into two operating conditions—low-speed creep and critical braking—using a preset threshold, the subsequent torque distribution can employ appropriate control logic based on the differences in motor operating characteristics and braking demands at different vehicle speed stages. In the low-speed creep condition, a higher proportion of motor torque is used, improving energy recovery; in the critical braking condition, the proportion of motor torque is reduced, and the hydraulic braking system assumes the main braking force, avoiding torque fluctuations that might occur when the motor operates in an inefficient range, ensuring braking stability, and improving ride comfort.

[0053] In some embodiments of the present invention, step S205 includes: when the brake pedal travel is less than or equal to a preset travel threshold, determining the second correction coefficient as a first preset value; when the brake pedal travel is greater than the preset travel threshold, the second correction coefficient K... s Calculate using the following formula: K s = (S max - s) / (S max - S0); where s is the percentage value of the brake pedal travel, S0 is the preset travel threshold, and S max This represents the maximum travel distance.

[0054] Brake pedal travel refers to the distance the pedal moves when the driver presses the brake pedal, and is usually expressed as a percentage of the total pedal travel.

[0055] The preset travel threshold is a dividing value used to distinguish between light braking and medium braking. Its specific value can be determined according to the vehicle model calibration, for example, it can be set to 20%.

[0056] Second correction factor K s Used to correct the target output torque of the motor to adapt to the torque distribution requirements under different braking intensities.

[0057] Specifically, the percentage value s of the brake pedal travel is obtained and compared with a preset travel threshold S0. When s is less than or equal to S0, the current condition is determined to be light braking, and the second correction coefficient K is then applied. sThe first preset value is determined. The first preset value can be 1, indicating that no additional correction is made to the motor target torque under light braking conditions, preserving the basic distribution ratio. When s is greater than S0, the current condition is determined to be medium braking, at which point the second correction coefficient K... s Calculate using the following formula: K s =(S max - s) / (S max - S0). Where s is the percentage value of the brake pedal travel, S0 is the preset travel threshold, and S max This represents the maximum travel distance, typically set to 100%. With a preset travel threshold S0 of 20% and the maximum travel distance S... max Taking 100% as an example, when the brake pedal travel s is 50%, Ks = (100% - 50%) / (100% - 20%) = 0.625; when s is 80%, K s =(100%-80%) / (100%-20%)=0.25. Therefore, it can be seen that as the brake pedal travel increases, K... s Gradually decrease.

[0058] Understandably, under light braking conditions (s≤S0), the braking intensity is low, and the energy recovery space is large. Setting the second correction coefficient to 1 can maintain a high baseline proportion of the motor's regenerative braking torque, thus improving energy recovery efficiency. Under medium braking conditions (s>S0), the braking intensity is high, and the driver's demand for braking safety is more prominent. As the brake pedal travel further increases, the second correction coefficient gradually decreases, the proportion of the motor's regenerative braking torque decreases accordingly, and the proportion of the hydraulic braking torque gradually increases. This achieves adaptive adjustment of the motor torque proportion under different braking intensities, prioritizing energy recovery during light braking and ensuring braking safety during medium braking.

[0059] In some embodiments of the present invention, step S206 includes: determining the corresponding reference ratio according to the operating condition type; and calculating the target output torque of the motor according to the reference ratio, the target value of the total braking torque of the vehicle, the product of the first correction coefficient and the second correction coefficient.

[0060] The baseline ratio refers to the basic proportion of the regenerative braking torque of the motor to the total braking torque of the vehicle under different operating conditions.

[0061] First correction factor k SOC It refers to a correction factor determined based on the battery's state of charge, used to reduce the proportion of regenerative braking torque when the battery charge is high to avoid overcharging.

[0062] Second correction factor K s It refers to a correction factor determined based on the brake pedal travel, used to adjust the torque distribution ratio under different braking intensities.

[0063] Vehicle speed correction factor k v It refers to a correction factor determined based on the ratio of the current vehicle speed to a preset threshold, used to gradually reduce the target output torque of the motor as the vehicle speed decreases under the critical braking condition.

[0064] Specifically, when determining the target output torque of the motor, the corresponding baseline percentage is first determined based on the identified operating condition type. Under low-speed creep conditions, the motor operates in a high energy conversion efficiency range, and the baseline percentage k1 can be set to any value between 70% and 80%, such as 75%. Under critical braking conditions, the motor speed has decreased to near the lower limit of its efficient operating range, and the baseline percentage k2 can be set to any value between 30% and 40%, such as 35%.

[0065] After determining the baseline proportion, based on the baseline proportion, the target value of the total braking torque of the vehicle T_total, and the first correction coefficient k SOC Second correction coefficient K s The product of these factors is used to calculate the target output torque Te_target of the motor, i.e., Te_target = k × T_total × k. SOC ×K s Where k takes the value k1 or k2 depending on the operating condition. For example, when the total braking torque T_total of the vehicle is 100 N·m, if it is in a low-speed creeping condition and the baseline proportion k1 is 75%, the first correction coefficient k SOC The second correction factor K is 1. s If the value is 1, then the target output torque of the motor Te_target = 75% × 100 × 1 × 1 = 75 N·m.

[0066] Under critical braking conditions, a speed correction coefficient k is also required. v Further adjustments are made to the target output torque of the motor. Vehicle speed correction coefficient k. v = v / v1, where v is the current vehicle speed and v1 is the preset threshold of 3 km / h. Under the critical braking condition, the target output torque of the motor is Te_target = k2 × T_total × k SOC × Ks × k v For example, when the preset threshold v1 is 3 km / h, if the current vehicle speed v is 2 km / h, then the vehicle speed correction coefficient k v The target output torque of the motor is multiplied by 2 / 3 based on the aforementioned product; if the current vehicle speed v approaches 0, the vehicle speed correction coefficient k is... v As the torque approaches 0, the target output torque Te_target of the motor also approaches 0.

[0067] Understandably, by adopting different baseline proportions according to the type of operating condition, the proportion of regenerative braking torque of the motor under low-speed creep conditions is significantly higher than that under critical braking conditions, thereby improving the energy recovery efficiency under low-speed creep conditions; at the same time, through the vehicle speed correction coefficient k v The introduction of this technology allows the target output torque of the motor to gradually decrease to zero as the vehicle speed approaches zero under the critical braking condition, avoiding the jerking phenomenon caused by the motor continuing to output braking torque at extremely low speeds, thus improving braking comfort.

[0068] In some embodiments of the present invention, under the second type, the target output torque of the motor is further adjusted according to a vehicle speed correction coefficient, which is the ratio of the current vehicle speed to the preset threshold.

[0069] In some embodiments of the present invention, step S102 includes: determining a first deviation between the target output torque of the motor and the actual output torque of the motor; determining a second deviation between the target output torque of the hydraulic braking system and the actual output torque of the hydraulic braking system; and determining the virtual compensation torque based on the sum of the first deviation and the second deviation.

[0070] The first deviation refers to the difference between the target output torque of the motor and its actual output torque.

[0071] The second deviation refers to the difference between the target output torque and the actual output torque of the hydraulic braking system.

[0072] Virtual compensation torque refers to the torque value determined based on the sum of the first deviation and the second deviation. This torque value is used to characterize the gap between the current total braking torque of the vehicle and the target braking torque.

[0073] Specifically, the braking control system pre-stores the target output torque Te_target of the motor and the target output torque Th_target of the hydraulic braking system, calculated based on parameters such as brake pedal pressure. Simultaneously, the actual output torque Te_actual of the motor is obtained in real-time through feedback from the motor controller, and the actual output torque Th_actual of the hydraulic braking system is obtained in real-time through feedback from the hydraulic brake controller. The first deviation between the target output torque Te_target and the actual output torque Te_actual of the motor is calculated, i.e., Te_target - Te_actual; the second deviation between the target output torque Th_target and the actual output torque Th_actual of the hydraulic braking system is calculated, i.e., Th_target - Th_actual. The first and second deviations are summed, i.e., ΔT = (Te_target - Te_actual) + (Th_target - Th_actual), to obtain the virtual compensation torque ΔT.

[0074] Understandably, by using the sum of the first deviation and the second deviation as the virtual compensation torque, this compensation amount simultaneously covers the torque deviations on both the motor side and the hydraulic side. Therefore, it can comprehensively reflect the torque deviation states of the two braking subsystems, achieving precise matching of the compensation amount to the actual braking force gap and improving the accuracy of braking force gap compensation.

[0075] In some embodiments of the present invention, the detection step of the vehicle being in the regenerative braking exit phase includes: determining that the vehicle is in the regenerative braking exit phase when the actual output torque of the motor in the vehicle is less than a first preset threshold and the vehicle speed is less than or equal to a second preset threshold.

[0076] Specifically, the method for detecting whether the vehicle is in the regenerative braking exit phase is as follows: the braking control system acquires the actual output torque Te_actual of the motor and the vehicle speed v in real time. When the actual output torque Te_actual of the motor is less than a first preset threshold and the vehicle speed v is less than or equal to a second preset threshold, the vehicle is determined to be in the regenerative braking exit phase. The first preset threshold can be 5 N·m, and the second preset threshold can be 5 km / h. For example, when the actual output torque Te_actual of the motor is 3 N·m (less than 5 N·m) and the vehicle speed v is 4 km / h (less than or equal to 5 km / h), the braking control system determines that it is currently in the regenerative braking exit phase.

[0077] Understandably, by simultaneously incorporating both the actual output torque of the motor and the vehicle speed into the judgment conditions, the starting moment of regenerative braking disengagement can be accurately identified, avoiding misjudgment of the disengagement timing due to a single judgment condition. This ensures that the coordinated force supplementation strategy is activated at the correct time, thereby improving the timeliness and accuracy of braking force connection.

[0078] To better implement the low-speed braking control method in the embodiments of the present invention, based on the low-speed braking control method, such as... Figure 3 As shown, this embodiment of the invention also provides a low-speed braking control system, the low-speed braking control system 300 including: The acquisition unit 301 is used to acquire the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system; The determining unit 302 is used to determine a virtual compensation torque to characterize the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system, when the vehicle is detected to be in the regenerative braking withdrawal stage. The control unit 303 is used to control the motor to maintain a preset field weakening output torque and to control the hydraulic braking system to increase the corresponding actual output torque according to a preset torque increase gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

[0079] The low-speed braking control system 300 provided in the above embodiments can realize the technical solutions described in the embodiments of the low-speed braking control method. The specific implementation principles of each module or unit can be found in the corresponding content in the embodiments of the low-speed braking control method, and will not be repeated here.

[0080] Accordingly, this application also provides a vehicle including the low-speed braking control system provided in any of the above embodiments. The vehicle may be a gasoline-powered vehicle, a plug-in hybrid electric vehicle, or a new energy vehicle, etc., and this specification does not specifically limit it.

[0081] Accordingly, this application also provides a computer-readable storage medium for storing computer-readable programs or instructions. When the programs or instructions are executed by a processor, they can implement the steps or functions of the low-speed braking control methods provided in the above-described method embodiments.

[0082] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware (such as a processor, controller, etc.), and the computer program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0083] The low-speed braking control method, system, and vehicle provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A low-speed braking control method, characterized in that, include: Obtain the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system; When the vehicle is detected to be in the regenerative braking disengagement phase, a virtual compensation torque is determined to characterize the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system, respectively. The motor is controlled to maintain a preset field weakening output torque, and the hydraulic braking system is controlled to increase the corresponding actual output torque according to a preset torque increase gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

2. The low-speed braking control method according to claim 1, characterized in that, The steps for determining the target output torque of the motor and the hydraulic braking system respectively include: The vehicle speed, battery state of charge, and brake pedal pressure are obtained. The total braking torque of the vehicle is determined based on the brake pedal pressure. When the vehicle speed is in the low-speed range, the corresponding working condition type is determined according to the vehicle speed. A first correction factor is determined based on the battery state of charge. The second correction factor is determined based on the brake pedal travel. The target output torque of the motor is calculated based on the target value of the total braking torque of the vehicle, the operating condition type, the first correction coefficient, and the second correction coefficient. The target output torque of the hydraulic braking system is determined based on the difference between the total braking torque of the vehicle and the target output torque of the motor.

3. The low-speed braking control method according to claim 2, characterized in that, The operating condition types include a first type of low-speed creep operating condition and a second type of braking critical operating condition; determining the corresponding operating condition type based on the vehicle speed includes: When the vehicle speed exceeds a preset threshold, it is determined to be the first type; When the vehicle speed is less than or equal to the preset threshold, it is determined to be the second type.

4. The low-speed braking control method according to claim 2, characterized in that, Determining the second correction factor based on the brake pedal travel includes: When the brake pedal travel is less than or equal to a preset travel threshold, the second correction coefficient is determined to be the first preset value; When the brake pedal travel exceeds the preset travel threshold, the second correction coefficient K s The following formula is used for calculation: K s = (S max - s) / (S max - S0); Where s is the percentage value of the brake pedal travel, S0 is the preset travel threshold, and S max This represents the maximum travel distance.

5. The low-speed braking control method according to claim 2, characterized in that, The step of calculating the target output torque of the motor based on the target value of the total braking torque of the vehicle, the operating condition type, the first correction coefficient, and the second correction coefficient includes: Determine the corresponding baseline percentage based on the aforementioned operating condition type; The target output torque of the motor is calculated based on the benchmark ratio, the target value of the total braking torque of the vehicle, and the product of the first correction coefficient and the second correction coefficient.

6. The low-speed braking control method according to claim 4, characterized in that, In the second type, the target output torque of the motor is also adjusted according to the vehicle speed correction coefficient, which is the ratio of the current vehicle speed to the preset threshold.

7. The low-speed braking control method according to claim 1, characterized in that, The step of determining the virtual compensation torque used to characterize the total braking force gap of the vehicle based on the target output torque and actual output torque of the motor and the hydraulic braking system respectively includes: Determine the first deviation between the target output torque of the motor and the actual output torque of the motor; Determine the second deviation between the target output torque of the hydraulic braking system and the actual output torque of the hydraulic braking system; The virtual compensation torque is determined based on the sum of the first deviation and the second deviation.

8. The low-speed braking control method according to claim 1, characterized in that, The detection steps for the vehicle being in the regenerative braking disengagement phase include: When the actual output torque of the motor in the vehicle is less than a first preset threshold and the vehicle speed is less than or equal to a second preset threshold, the vehicle is determined to be in the regenerative braking exit phase.

9. A low-speed braking control system, characterized in that, The system includes: The acquisition unit is used to acquire the actual output torque of the motor in the vehicle and the actual output torque of the hydraulic braking system; The determining unit is used to determine a virtual compensation torque to characterize the total braking force gap of the vehicle, based on the target output torque and actual output torque of the motor and the hydraulic braking system, when the vehicle is detected to be in the regenerative braking disengagement stage. The control unit is used to control the motor to maintain a preset field weakening output torque and to control the hydraulic braking system to increase the corresponding actual output torque according to a preset torque increment gradient until the actual output torque of the hydraulic braking system reaches the sum of its target output torque and the virtual compensation torque.

10. A vehicle, characterized in that, Includes the low-speed braking control system as described in claim 9.

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