Braking method for vehicle, vehicle, and storage medium

Abstract

The present application provides a braking method for a vehicle, a vehicle, and a storage medium. The vehicle comprises two drive shafts, a main hydraulic unit, and a backup hydraulic unit, and each drive shaft is provided with a motor. The braking method comprises: when the main hydraulic unit fails and a braking request is detected, determining a target braking torque of each drive shaft; comparing a regenerative braking torque available from each motor with a corresponding target braking torque; when the available regenerative braking torque is greater than or equal to the target braking torque, controlling the motor to provide the target braking torque to the corresponding drive shaft; and when the available regenerative braking torque is less than the target braking torque, controlling the motor and the backup hydraulic unit to together provide the target braking torque to the corresponding drive shaft.

Description

Braking method for vehicle, vehicle and storage medium

[0001] Priority claim

[0002] This application claims priority to the following Chinese invention patent application: Chinese invention patent application No. 202311605448.1, filed on November 24, 2023. The contents of that application are incorporated herein by reference in their entirety. Technical Field

[0003] The present application relates to the field of vehicles, and specifically provides a braking method for a vehicle, a vehicle, and a storage medium. Background Art

[0004] Cars use braking systems to slow down and stop. The braking system refers to a series of specialized devices that forcibly reduce the speed of a car. Its main functions are to slow down or even stop a moving car, maintain a stable speed when driving downhill, and keep a stopped car stationary. The braking system typically includes a controller and a hydraulic brake unit, and the controller can issue instructions to the hydraulic brake unit. The vacuum booster pump in the hydraulic brake unit applies pressure to the brake oil in the cylinder. This pressure is transmitted to the pistons of the front and / or rear wheel brake calipers through hydraulic lines. The pistons drive the brake calipers to clamp the brake friction discs, thereby applying braking force to the front and / or rear wheels, automatically correcting the instability of the vehicle body and helping to prevent accidents.

[0005] Autonomous driving at levels L3 and above allows the driver to completely take their hands off the wheel, leaving the system in control until the vehicle requests takeover. This places high demands on vehicle control safety, particularly for the braking system. To meet the safety requirements of autonomous driving at levels L3 and above, the current approach to improving braking system safety is through increased redundancy. Redundancy involves adding more than one set of functional channels, working elements, or components that perform the same function in areas where a system or device plays a critical role in completing a task. This ensures that even if that part fails, the system or device can still function normally, reducing the probability of failure and improving system reliability.

[0006] The main redundancy implementation method in the prior art is to add a backup hydraulic unit, that is, the hydraulic brake unit in the braking system is configured to include a main hydraulic unit and a backup hydraulic unit. When the main hydraulic unit fails, the backup hydraulic unit can still play the role of braking and deceleration. Most of the backup hydraulic units in the prior art are configured to only provide the braking torque of the entire vehicle (that is, the torque applied to each wheel is the same), and single-axis control cannot be achieved. When a single-axis wheel slips, such as the wheel on the rear axle, it means that the rear axle braking torque is too large, causing the rear axle wheel to lock. The longitudinal stability control function of the vehicle can only reduce the braking torque of the four wheels at the same time to restore the rotation of the rear axle wheel to prevent the vehicle from skidding. However, the above configuration in the prior art causes a large loss of braking deceleration of the entire vehicle and a long braking distance, which has an adverse effect on the safety of the vehicle.

[0007] Therefore, this field needs a new technical solution to solve the above problems.

[0008] Summary of the Invention

[0009] In order to solve or improve to a certain extent the problem of poor braking effect of redundant design of braking system in the prior art, the present application provides a braking method for a vehicle. The vehicle includes two drive shafts, a main hydraulic unit and a backup hydraulic unit, and a motor is provided on each drive shaft. The braking method includes: when the main hydraulic unit fails and a braking request is detected, determining the target braking torque of each drive shaft; comparing the recovery braking torque that can be provided by each motor with the corresponding target braking torque; when the recovery braking torque that can be provided is greater than or equal to the target braking torque, controlling the motor to provide the target braking torque to the corresponding drive shaft; and when the recovery braking torque that can be provided is less than the target braking torque, controlling the motor and the backup hydraulic unit together to provide the target braking torque to the corresponding drive shaft; wherein the backup hydraulic unit provides the braking torque of the entire vehicle, and the braking torque of the entire vehicle is determined based on the difference between the target braking torque and the recovery braking torque.

[0010] The braking method of the present application first determines whether the primary hydraulic unit has failed. If the primary hydraulic unit fails and a braking request is detected, additional braking torque is required to stop the vehicle. By determining the target braking torque for each drive axle of the vehicle, the vehicle controller controls the corresponding braking components (e.g., motors, hydraulic brake units, etc.) to provide the corresponding braking torque, enabling the vehicle to stop in the shortest possible distance while maintaining driving stability. The regenerative braking torque provided by each motor is compared with the corresponding target braking torque. When the regenerative braking torque provided by the motor is greater than or equal to the target braking torque, the regenerative braking torque generated by the motor alone during power regeneration can smoothly decelerate the vehicle. Thus, the motors can be controlled to provide the target braking torque to the corresponding drive axles, fully utilizing the advantages of regenerative braking using motors, such as fast response (after receiving a braking command, the braking force of the hydraulic unit must be transmitted through the hydraulic lines before it can be applied to the wheels, resulting in a slow response speed; in particular, backup hydraulic units typically use weaker motors, which have a slower pumping speed to build pressure), precise target control, and low braking noise. When the recovery braking torque that the motor can provide is less than the target braking torque, it means that the motor alone is not enough to stop the vehicle in the shortest possible distance, and other braking components are needed to supplement the braking torque. Therefore, the control motor and the backup hydraulic unit together provide the target braking torque to the corresponding drive shaft. The backup hydraulic unit provides the braking torque of the entire vehicle, and the braking torque of the entire vehicle is determined based on the difference between the target braking torque and the recovery braking torque. Through the above configuration, the braking method of the present application enables the braking torque required by the vehicle to be met preferentially by the recovery braking torque of the motor, with precise distribution and fast response speed, which can ensure that the vehicle is stopped in the shortest possible distance.

[0011] In the preferred technical solution of the vehicle braking method described above, the braking method further includes: obtaining the axle slip ratio of each drive axle after providing a target braking torque to each drive axle; when the axle slip ratio exceeds a predetermined slip ratio, reducing the regenerative braking torque applied to the drive axle while maintaining the overall vehicle braking torque; re-obtaining the axle slip ratio of each drive axle; and stopping reducing the regenerative braking torque when the re-obtained axle slip ratio is less than or equal to the predetermined slip ratio. With the above configuration, after providing the target braking torque to each drive axle, the braking torque is adjusted, i.e., the braking torque is adjusted based on the slip ratio between the vehicle and the ground to maintain vehicle driving stability. Obtaining the axle slip ratio of each drive axle indicates that a wheel lock on that drive axle is severe, making the wheel prone to slipping on the road surface and resulting in poor braking performance. Therefore, reducing the regenerative braking torque applied to the drive axle while maintaining the overall vehicle braking torque is effective, fully utilizing the fast response speed and precise target control characteristics of regenerative braking torque. The axle slip ratio of each drive axle is then re-acquired. If the re-acquired axle slip ratio is less than or equal to the predetermined slip ratio, the vehicle's slip ratio is suitable for maintaining the current braking torque. Therefore, the reduction of regenerative braking torque is stopped, minimizing the braking distance. This technical solution further solves the problem of braking torque loss caused by the difficulty of adjusting the braking torque to a single axle using only the backup hydraulic unit.

[0012] In the preferred technical solution of the above-mentioned vehicle braking method, the braking method further includes: when the reacquired axle slip ratio is greater than a predetermined slip ratio, determining whether the corresponding regenerative braking torque is zero; when the regenerative braking torque is zero, reducing the vehicle braking torque; after reducing the vehicle braking torque, acquiring the axle slip ratio of each drive axle for a third time; and when the axle slip ratio acquired for the third time is less than or equal to the predetermined slip ratio, stopping the reduction of the vehicle braking torque. With the above configuration, when the reacquired axle slip ratio is greater than the predetermined slip ratio, it indicates that the sum of the braking torques currently applied by the motor on the drive axle and the backup hydraulic unit on the wheel is large, causing severe wheel slippage on the road surface, and braking torque reduction should be continued. Therefore, determining whether the corresponding regenerative braking torque is zero indicates that the motor's regenerative braking torque has been fully reduced, and the vehicle braking torque provided by the backup hydraulic unit can be reduced. Through the above configuration, in the process of adjusting the braking torque to maintain vehicle stability, the recovery braking torque with a faster response speed is first reduced, and independent adjustment of a single drive shaft is achieved, so that the vehicle braking torque provided by the backup hydraulic unit is efficiently utilized.

[0013] In the preferred technical solution for the vehicle braking method described above, when the regenerative braking torque is non-zero, the step of "reducing the regenerative braking torque applied to the drive shaft while maintaining the overall vehicle braking torque" is repeated. With this configuration, when the regenerative braking torque is non-zero, indicating that there is room for reduction in the motor's regenerative braking torque, the regenerative braking torque is further reduced to fully utilize the overall vehicle braking torque applied by the backup hydraulic unit.

[0014] In the preferred technical solution of the above-mentioned braking method for a vehicle, the vehicle further includes a deceleration sensor, the braking request includes a desired deceleration, and the step of "determining the target braking torque of each drive axle" includes: determining the desired braking torque based on the desired deceleration; obtaining the real-time deceleration of the vehicle using the deceleration sensor; calculating the distribution ratio of the desired braking torque based on the real-time deceleration; and determining the target braking torque of each drive axle based on the distribution ratio and the desired braking torque. Through the above-mentioned configuration, the vehicle can obtain the current load transfer state of the vehicle in real time, so as to determine the maximum braking torque that can be applied to each drive axle based on the load transfer state (for example, when the vehicle decelerates on a horizontal road, that is, when the deceleration is greater than zero, the load of the vehicle is offset to the front drive axle, so the maximum braking torque that can be applied to the front drive axle is greater than the maximum braking torque that can be applied to the rear drive axle), thereby distributing the target braking torque on the two drive axles to achieve a better braking effect.

[0015] In the preferred technical solution for the vehicle braking method described above, the vehicle also includes an autonomous driving domain controller, and the desired deceleration is generated by the autonomous driving domain controller based on data acquired by the autonomous driving hardware. With this configuration, the vehicle includes a highly integrated autonomous driving domain controller capable of generating the desired deceleration required for braking at an appropriate distance based on real-time data acquired by components such as lidar or cameras.

[0016] In the preferred technical solution of the above-mentioned braking method for a vehicle, the two drive shafts are the front drive shaft and the rear drive shaft; and the braking method further includes: determining a first difference between the target braking torque of the front drive shaft and the recovery braking torque that can be provided by the motor on the front drive shaft; determining a second difference between the target braking torque of the rear drive shaft and the recovery braking torque that can be provided by the motor on the rear drive shaft; when the first difference is greater than zero and the second difference is less than or equal to zero, determining that the braking torque of the entire vehicle is equal to the first difference; when the first difference is less than or equal to zero and the second difference is greater than zero, determining that the braking torque of the entire vehicle is equal to the second difference; and when both the first difference and the second difference are greater than zero, determining that the braking torque of the entire vehicle is equal to the sum of the first difference and the second difference. Through the above-mentioned configuration, the vehicle controller first ensures that the target braking torque is met when controlling the motor and the backup hydraulic unit to apply the braking torque. On this basis, the backup hydraulic unit supplements the portion of the target braking torque that exceeds the braking capacity of the motor.

[0017] In the preferred technical solution for the vehicle braking method described above, the step of "obtaining the axle slip ratio of each drive axle" includes obtaining the average wheel speed of all wheels on each drive axle and the vehicle speed, and calculating the axle slip ratio of each drive axle based on the average wheel speed and the vehicle speed. Through this configuration, the wheel slip ratio is converted into the axle slip ratio of the drive axle, allowing the vehicle controller to control the motor to apply regenerative braking torque based on the axle slip ratio.

[0018] In order to solve or to some extent improve the problem of poor braking effect caused by redundant design of the braking system in the prior art, the present application also provides a vehicle. The vehicle includes: a front drive shaft and a rear drive shaft; a motor, the motor being arranged on each of the front drive shaft and the rear drive shaft; a main hydraulic unit; a backup hydraulic unit; and a controller, the controller being configured to control the motor to provide a recovery braking torque to the corresponding front drive shaft or rear drive shaft according to the braking method for the vehicle in the above-mentioned preferred technical solution, and to control the backup hydraulic unit to provide a whole-vehicle braking torque to the front drive shaft and the rear drive shaft. Through the configuration of the above-mentioned braking method, the vehicle of the present application uses the motor and the backup hydraulic brake unit to achieve redundant braking in the event of failure of the main hydraulic unit, which can effectively solve the problems caused by braking with the backup hydraulic unit alone, thereby improving the braking effect of redundant braking.

[0019] To address or, to a certain extent, improve the problem of poor braking effectiveness caused by redundant designs in existing braking systems, this application also provides a storage medium suitable for storing multiple program codes, which are suitable for being loaded and executed by a processor to execute the vehicle braking method described in the preferred technical solution. Through the configuration of the above-described braking method, the storage medium of this application can be used on a vehicle to resolve the problems associated with solely using a backup hydraulic unit for braking, thereby improving the braking effectiveness of redundant braking. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The preferred embodiments of the present application are described below with reference to the accompanying drawings, in which:

[0021] FIG1 is a partial structural diagram of an embodiment of a vehicle of the present application;

[0022] FIG2 is a schematic flow chart of a braking method for a vehicle according to the present application;

[0023] FIG3 is a first part of a flow chart of an embodiment of a braking method for a vehicle according to the present application;

[0024] FIG4 is a force analysis diagram of an embodiment of a vehicle of the present application;

[0025] FIG5 is a second part of a flow chart of an embodiment of a braking method for a vehicle according to the present application;

[0026] FIG6 is a third part of a flowchart of an embodiment of a braking method for a vehicle according to the present application;

[0027] FIG7 is a fourth part of a flowchart of an embodiment of a braking method for a vehicle according to the present application.

[0028] Reference numerals list: 100, vehicle; 10, drive shaft; 10a, front drive shaft; 10b, rear drive shaft; 11, wheel; 20, motor; 30, backup hydraulic unit. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the scope of protection of the present application.

[0030] It should be noted that, in the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0031] Furthermore, it should be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed" and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0032] To address or, to a certain extent, improve the problem of poor braking performance caused by redundant designs in existing braking systems, the present application provides a braking method for a vehicle. A vehicle 100 includes two drive shafts 10, a primary hydraulic unit, and a backup hydraulic unit 30, with a motor 20 provided on each drive shaft 10. The braking method includes: determining a target braking torque for each drive shaft 10 when the primary hydraulic unit fails and a braking request is detected; comparing the regenerative braking torque that can be provided by each motor 20 with the corresponding target braking torque; controlling the motor 20 to provide the target braking torque to the corresponding drive shaft 10 when the available regenerative braking torque is greater than or equal to the target braking torque; and controlling the motor 20 and the backup hydraulic unit 30 to jointly provide the target braking torque to the corresponding drive shaft 10 when the available regenerative braking torque is less than the target braking torque. The backup hydraulic unit 30 provides the entire vehicle braking torque, and the entire vehicle braking torque is determined based on the difference between the target braking torque and the regenerative braking torque.

[0033] FIG1 is a partial structural diagram of an embodiment of a vehicle of the present application. The present application also provides a vehicle 100. As shown in FIG1 , in one or more embodiments, the vehicle 100 includes two drive shafts 10. Each drive shaft 10 is provided with a motor 20 and two wheels 11, that is, the vehicle 100 is a four-wheeled electric vehicle with dual motors 20. Alternatively, only one wheel 11 may be provided on the drive shaft 10. Accordingly, the vehicle 100 is a two-wheeled motorcycle or a three-wheeled vehicle. The vehicle 100 of the present application also includes a main hydraulic unit and a backup hydraulic unit 30. The main hydraulic unit is capable of adjusting the braking torque for each wheel 11 individually, while the backup hydraulic unit 30 is capable of applying the same braking torque to each wheel 11 of the vehicle 100. When the main hydraulic unit fails, the backup hydraulic unit 30 is activated, and this redundant design ensures the driving safety of the vehicle. In one or more embodiments, the vehicle 100 of the present application is equipped with an autonomous driving function of level L3 or above and has an autonomous driving domain controller. The autonomous driving domain controller controls actuators such as cameras, millimeter-wave radars, and lidars, enabling the vehicle to perform multi-sensor fusion, positioning, path planning, and decision-making control. Functions performed include image recognition and data processing. Alternatively, vehicle 100 may be equipped with other levels of autonomous driving functionality or have the autonomous driving feature disabled.

[0034] FIG2 is a flow chart of the braking method for a vehicle of the present application. As shown in FIG2 , in one or more embodiments, after the braking method of the present application is started, step S1 is executed, that is, when the main hydraulic unit fails and a braking request is detected, the target braking torque of each drive shaft 10 is determined. By determining the target braking torque of each drive shaft 10, the controller on the vehicle 100 (e.g., a chassis domain controller) can control the corresponding braking components (e.g., motor 20, hydraulic unit, etc.) to accurately provide the corresponding braking torque. Step S2 is then executed, that is, the recovery braking torque that each motor 20 can provide is compared with the corresponding target braking torque. When the recovery braking torque that the motor 20 can provide is greater than or equal to the target braking torque (step S3), it is explained that the recovery braking torque generated by the motor 20 alone during power recovery can cause the vehicle 100 to decelerate smoothly. Therefore, the motor 20 can be controlled to provide the target braking torque to the corresponding drive shaft 10. If the regenerative braking torque provided by motor 20 is less than the target braking torque (step S4), motor 20 alone is insufficient to stop vehicle 100 within the shortest possible distance, and additional braking components are required to provide additional braking torque. Therefore, motor 20 and backup hydraulic unit 30 are controlled to jointly provide the target braking torque to the corresponding drive shaft 10.

[0035] FIG3 is the first portion of a flowchart of an embodiment of a vehicle braking method according to the present application. As shown in FIG3 , in one or more embodiments, after the braking method of the present application begins, step S11 is first executed, which determines whether the main hydraulic unit has failed. If the determination result is negative, the main hydraulic unit is functioning normally and no redundant braking system or braking method is required to provide braking torque. Therefore, the braking method of the present application terminates. If the determination result is positive, the main hydraulic unit has failed and cannot apply braking torque to wheel 11, requiring the redundant braking system or braking method to provide braking torque. Therefore, the braking method proceeds to step S12, which determines whether a braking request exists. In one or more embodiments, a braking request is a signal generated by the autonomous driving domain controller of vehicle 100 and sent to the chassis domain controller of vehicle 100. In other words, the chassis domain controller performs the step of "determining whether a braking request exists." Alternatively, the braking request may be a signal generated by another component of vehicle 100, such as a controller converting the driver's braking action into a braking request. Alternatively, the controller performing the step of "determining whether a braking request exists" may be configured as another suitable controller on vehicle 100. If the determination result is negative, the vehicle does not require braking at this time, and the braking method terminates. If the determination result is positive, the vehicle requires braking to protect the occupants. Therefore, step S13 is executed, which determines the target braking torque required for each drive shaft 10. In alternative embodiments, steps S11 and S12 may be executed in the reverse order.

[0036] Figure 4 is a force analysis diagram of an embodiment of the vehicle of the present application; Figure 5 is the second part of the flow chart of an embodiment of the braking method for a vehicle of the present application. The process of "Step S13: Determine the target braking torque of each drive shaft" is specifically described below in conjunction with Figures 4 and 5. In one or more embodiments, when the judgment result of step S12 is yes, step S131 is entered, that is, the expected braking torque is determined based on the expected deceleration. In one or more embodiments, the expected deceleration is generated by the autonomous driving domain controller based on data obtained by the autonomous driving hardware (such as lidar, camera, etc.). Furthermore, the method of converting the expected deceleration into the expected braking torque includes two parts: (1) an open-loop control part, according to the formula: T a =m*a e *r (where m is the mass of the vehicle, a e is the desired deceleration, r is the rolling radius of the wheel), and the basic value T of the desired braking torque is calculated. a (2) closed-loop control part, according to the actual deceleration and the expected deceleration a measured by the deceleration sensor on the vehicle 100 e The difference between the two values ​​is used to calculate the correction value T of the desired braking torque using the PID algorithm. b . a With T b Add together to get the final desired braking torque T 总 Alternatively, the desired deceleration can also be obtained by other suitable means, such as determining the desired deceleration based on the stroke of the brake pedal. Alternatively, the desired braking torque of the vehicle can also be calculated by other suitable means. Then, step S132 is executed, i.e., the real-time deceleration a of the vehicle is obtained using the deceleration sensor. x In one or more embodiments, the deceleration sensor is an inertial sensor. Alternatively, the deceleration sensor may also be configured as other suitable devices.

[0037] Then, step S133 is executed, that is, the distribution ratio of the desired braking torque is calculated based on the real-time deceleration. As shown in FIG4 , the support forces from the road surface at the front drive shaft 10a and the rear drive shaft 10b of the vehicle 100 are F and F, respectively. N1 and F N2 , according to the moment analysis:

[0038] Among them, G is the gravity acting on the vehicle, L is the distance between the two drive shafts of the vehicle, a and b are the distances from the axes of the two drive shafts to the center of mass of the vehicle, h is the height of the center of mass of the vehicle, and g is the acceleration due to gravity. Therefore, F N1 and F N2 , respectively constitute only with the real-time deceleration a x Related variables.

[0039] Those skilled in the art will understand that when the brakes on the vehicle apply braking torque to the wheels 11 or the drive shaft 10, the wheels 11 will generate a forward friction force on the ground, and the road surface will generate a backward reaction force on the wheels 11. This reaction force is the road braking force. The external force that actually provides deceleration for the vehicle 100 is the road braking force. The road braking forces acting on the wheels 11 on the two drive shafts 10 are F and F, respectively. f1 and F f2 , and F f1 ≤μF N1 F f2 ≤μF N2

[0040] Wherein, μ is the road adhesion coefficient. Under ideal conditions, the wheels 11 on the two drive shafts 10 are on the same road condition, that is, the road adhesion coefficient μ is the same. When the front drive shaft 10a is locked, the road braking force F f1 Equal to μF N1 Accordingly, when the rear drive shaft 10b is locked, the road braking force F f2 Equal to μF N2 .

[0041] When the road surface has sufficient adhesion, the magnitude of the road braking force and the braking force applied by the brakes of the vehicle 100 are equal, and the drive shaft 10 can rotate smoothly without locking. Therefore, the road braking force and the braking torque applied by the brakes of the vehicle 100 have the following relationship:

[0042] Wherein, T1 is the braking torque on the front axle, T2 is the braking torque on the rear axle, and r is the rolling radius of the wheel 11. It can be understood that when the road surface adhesion is sufficient, as the braking torque applied by the brake increases, its braking force gradually increases, and the road surface braking force also gradually increases. When , it means that the braking force applied by the brake on the front axle is just enough to cause the front drive shaft 10a to lock. , it indicates that the braking force applied by the brake on the rear axle is just enough to cause the rear drive shaft 10b to lock.

[0043] Therefore, when the front drive shaft 10a and the rear drive shaft 10b are locked at the same time, the desired braking torque T 总 When the distribution ratio θ is , there is the following relationship: T 总 =T1+T2

[0044] In a x When the deceleration sensor can be used to obtain the information in real time, T总 That is, the target braking torques on the two drive shafts 10 can be reasonably distributed to the two drive shafts 10, and the magnitudes of the target braking forces on the two drive shafts 10 are T1 and T2 respectively (step S134). In alternative embodiments, the target braking torques on the two drive shafts 10 can also be distributed in other appropriate ways.

[0045] Continuing with FIG3 , after step S13 is completed, a determination is made as to whether the regenerative braking torque that the motor 20 can provide is greater than or equal to the target braking torque (step S21). If the determination is yes, meaning the regenerative braking torque that the motor 20 can provide is greater than or equal to the target braking torque, step S31 is executed, controlling the motor 20 to provide the target braking torque to the corresponding drive shaft 10. At this point, the target braking torque of the drive shaft 10 is entirely provided by the regenerative braking torque. If the determination is no, meaning the regenerative braking torque that the motor 20 can provide is less than the target braking torque, step S41 is executed, controlling the motor 20 and the backup hydraulic unit 30 to jointly provide the target braking torque to the corresponding drive shaft 10. At this point, the target braking torque of the drive shaft 10 is provided by both the motor 20 and the backup hydraulic unit 30. The backup hydraulic unit 30 provides the entire vehicle braking torque, which is determined based on the difference between the target braking torque and the regenerative braking torque. Accordingly, the entire vehicle braking torque is also applied to the other drive shaft 10.

[0046] FIG6 is the third part of a flowchart of an embodiment of a braking method for a vehicle 100 of the present application. The process of step S41 is described in detail below with reference to FIG6 . As shown in FIG1 and FIG6 , in one or more embodiments, the two drive shafts 10 are the front drive shaft 10a and the rear drive shaft 10b of the vehicle 100 . If the judgment result of step S21 is negative, step S411 is first executed to determine a first difference between the target braking torque of the front drive shaft 10a and the recovery braking torque that can be provided by the motor 20 on the front drive shaft 10a. Then, step S412 is executed to determine a second difference between the target braking torque of the rear drive shaft 10b and the recovery braking torque that can be provided by the motor 20 on the rear drive shaft 10b. Alternatively, the execution order of steps S411 and S412 can be interchanged. Then, step S413 is executed to determine whether the first difference is greater than zero. If the judgment result of step S413 is yes, that is, the first difference is greater than zero, it means that the motor 20 on the front drive shaft 10a cannot meet the target braking torque requirement, and the backup hydraulic unit 30 is needed to supplement the braking force. Then continue to judge whether the second difference is greater than zero (step S4132). If the judgment result of step S4132 is yes, that is, the second difference is greater than zero, it means that the motor 20 on the rear drive shaft 10b cannot meet the target braking torque of the rear drive shaft 10b. Therefore, step S416 is executed, that is, it is determined that the braking torque of the whole vehicle is equal to the sum of the first difference and the second difference. If the judgment result of step S4132 is no, that is, the second difference is less than or equal to zero, it means that the motor 20 on the rear drive shaft 10b can meet the target braking torque requirement. Therefore, step S414 is executed, that is, it is determined that the braking torque of the whole vehicle is equal to the first difference, so as to supplement the target braking torque on the front drive shaft 10a. If the judgment result of step S413 is no, that is, the first difference is less than or equal to zero, it means that the motor 20 on the front drive shaft 10a can meet the target braking torque requirement, and then step S4131 is continued. If the judgment result of step S4131 is yes, that is, the second difference is greater than zero, it means that the motor 20 on the rear drive shaft 10b cannot meet the target braking torque of the rear drive shaft 10b. Therefore, step S415 is executed, that is, the second difference of the braking torque of the whole vehicle is determined in order to supplement the target braking torque on the rear drive shaft 10b. If the judgment result of step S4131 is no, that is, the second difference is less than or equal to zero, it means that the motor 20 on the rear drive shaft 10b can also meet the target braking torque, and then step S32 is executed, that is, the braking torque of the whole vehicle is determined to be zero. Since step S41 is executed when the recovery braking torque that can be provided by at least one motor 20 is less than the target braking torque, the setting of step S32 can be canceled.

[0047] The above steps S11-S31 and S11-S41 are the pre-allocation procedures of the control method of this application, that is, the desired braking torque is first met by the motor 20 or the combination of the motor 20 and the backup hydraulic unit 30, so that the vehicle can also ensure a shorter braking distance when using a redundant braking system.

[0048] FIG7 is the fourth part of the flowchart of the embodiment of the braking method for the vehicle 100 of the present application. As shown in FIG7, after providing the target braking torque, step S51 is executed, i.e., obtaining the shaft slip ratio s of each drive shaft 10. The step of obtaining the shaft slip ratio s of each drive shaft 10 includes: obtaining the average wheel speed of all wheels 11 on each drive shaft 10 and the vehicle speed of the vehicle 100, and calculating the shaft slip ratio s of each drive shaft 10 based on the average wheel speed and the vehicle speed, i.e.

[0049] Among them, v 车 is the vehicle's longitudinal speed, v 轮 is the average wheel speed of all wheels on the drive axle.

[0050] Continuing with FIG. 7 , taking one of the two drive shafts 10 as an example, after obtaining the shaft slip ratio on the drive shaft 10, step S52 is executed to determine whether the shaft slip ratio is greater than a predetermined slip ratio. In one or more embodiments, the predetermined slip ratio is a value between 15% and 20%, such as 15%, 18%, or 20%. Alternatively, the predetermined slip ratio can be set to another suitable value. If the determination result of step S52 is negative, that is, the shaft slip ratio of the current drive shaft 10a is less than or equal to the predetermined slip ratio, it indicates that the sliding component between the wheel 11 on this drive shaft and the road surface is small, and the longitudinal stability is high. Therefore, the control method ends, and the regenerative braking torque on this drive shaft 10 does not need to be adjusted; the vehicle braking torque applied to the wheel 11 on this drive shaft also does not need to be adjusted, unless the other drive shaft 10 needs to reduce the vehicle braking torque.

[0051] Continuing to refer to FIG7 , if the judgment result of step S52 is yes, that is, the axial slip rate of the current drive shaft is greater than the predetermined slip rate, it means that the sliding component between the wheel 11 on the drive shaft 10 and the road surface is large, and the longitudinal stability is low. Therefore, step S61 is executed, that is, the recovery braking torque applied to the drive shaft 10 is reduced, while the braking torque of the entire vehicle remains unchanged. Then the axial slip rate is re-acquired, and it is determined whether the re-acquired axial slip rate is greater than the predetermined slip rate (i.e., step S611). If the judgment result of step S611 is no, that is, the re-acquired axial slip rate is less than or equal to the predetermined slip rate, it means that after adjustment by the motor 20, the axial slip rate of the drive shaft 10 has returned to a range that can ensure the longitudinal stability of the vehicle 100. Therefore, step S612 is executed, that is, the reduction of the recovery braking torque is stopped, and the braking method ends.

[0052] Continuing with FIG7 , if the determination result of step S611 is yes, i.e., the recovered axial slip ratio is greater than the predetermined slip ratio, indicating that the axial slip ratio of the drive shaft 10 is still relatively large after adjustment by the motor 20. It is then determined whether the recovery braking torque on the corresponding drive shaft 10 is zero (step S62). If the determination result of step S62 is no, i.e., the recovery braking torque on the corresponding drive shaft 10 is not zero, indicating that the recovery braking torque provided by the motor 20 still has room to be reduced, and therefore the process returns to step 61 and repeats to further reduce the recovery braking torque. If the determination result of step S62 is yes, i.e., the recovery braking torque on the corresponding drive shaft 10 is zero, indicating that the motor 20 no longer provides recovery braking torque, and the axial slip ratio of the drive shaft 10 can only be further reduced by reducing the entire vehicle braking torque. Therefore, step S63 is executed, i.e., the entire vehicle braking torque is reduced. After the entire vehicle braking torque is reduced, the axial slip ratio of the drive shaft 10 is obtained for the third time and a determination is made whether the axial slip ratio is greater than the predetermined slip ratio (step S64). If the result of step S64 is yes, i.e., the current axle slip ratio is still greater than the predetermined slip ratio, indicating that the reduced vehicle braking torque is insufficient to maintain vehicle 100 stability, the process returns to step S63 and repeats. If the result of step S64 is no, i.e., the current axle slip ratio is less than or equal to the predetermined slip ratio, indicating that the axle slip ratio of drive shaft 10 is sufficient to ensure vehicle 100 stability, the process proceeds to step S65, i.e., stopping reducing vehicle braking torque, and the braking method ends.

[0053] It should be noted that steps S51-S52, S51-S612, or S51-S65 regulate the braking torque of a single drive shaft 10, while the vehicle braking torque output by the backup hydraulic unit 30 affects both drive shafts 10 simultaneously. In one or more embodiments, when both drive shafts 10 require only a reduction in regenerative braking torque, the two motors 20 can each reduce their respective regenerative braking torques. When the regenerative torque on one of the two drive shafts 10 reaches zero and the vehicle braking torque needs to be reduced by a predetermined amount, the backup hydraulic unit 30 can reduce the braking torque by the corresponding predetermined amount. When both drive shafts 10 require a reduction in vehicle braking torque, and the reductions are by first and second predetermined amounts, the first and second predetermined amounts are compared, and the backup hydraulic unit 30 is controlled to reduce the larger of the two. Through the above configuration, vehicle stability during braking is ensured, enhancing the safety of the redundant braking system. Alternatively, the reduction in vehicle braking torque can be configured to other suitable amounts.

[0054] In addition, steps S51, S611, and S64 each acquire the axle slip ratio. In one or more embodiments, each acquisition of the axle slip ratio requires that the preceding steps have been completed. For example, step S611, i.e., acquiring the axle slip ratio, can be performed only after step S61 has completed. Alternatively, the axle slip ratio can be continuously acquired during the execution of the braking method of the present application.

[0055] In summary, after the pre-allocation process in step S31 or S41 is completed, the motors 20 on the two drive shafts 10 each output a corresponding pre-allocated regenerative braking torque, and the backup hydraulic unit 30 outputs a pre-allocated vehicle braking torque. The pre-allocation is based on satisfying the desired braking torque, i.e., the sum of the two pre-allocated regenerative braking torques and the pre-allocated vehicle braking torque is approximately equal to the desired braking torque. Then, through steps S51-S52, steps S51-S612, or steps S51-S65, the two pre-allocated regenerative braking torques and the pre-allocated vehicle braking torque are adjusted accordingly to two optimized regenerative braking torques and optimized vehicle braking torque, wherein the optimization is based on ensuring the stability of the vehicle 100 during braking (determined by the slip ratio). In one or more embodiments, the entire braking process, from the occurrence of a braking request in the event of a primary hydraulic unit failure, to the output of two pre-allocated regenerative braking torques and a pre-allocated vehicle braking torque, to the final output of two optimized regenerative braking torques and an optimized vehicle braking torque, is configured as a step in the process from the start of braking to parking or active stopping of the vehicle. In other words, the vehicle 100 must cycle through the aforementioned braking method multiple times from the start of braking to parking or active stopping. Accordingly, the aforementioned parameters, such as "desired deceleration," "target braking torque," "pre-allocated regenerative braking torque and pre-allocated vehicle braking torque," and "optimized regenerative braking torque and optimized vehicle braking torque," all change in real time throughout the vehicle braking process. Specifically, each time the aforementioned braking method is executed, the desired deceleration and desired braking torque in the braking request change due to changes in vehicle conditions, and the regenerative braking torque output by the motor 20 and the vehicle braking torque output by the backup hydraulic unit 30 also change accordingly. In one or more embodiments, each execution of the aforementioned braking method consumes the same time as the algorithm's scheduled time, for example, 10 ms. This means that the period during which parameters such as the "desired deceleration" change is 10 ms. The aforementioned braking method is then executed again based on the vehicle's condition, and the cycle continues. Alternatively, the execution time of the braking method can be configured to other suitable times. Alternatively, after completing one braking method, the next execution can be performed at a predetermined interval.

[0056] The vehicle 100 of the present application also includes a controller. In one or more embodiments, the two drive shafts 10 of the vehicle 100 are a front drive shaft 10a and a rear drive shaft 10b. The controller is configured to control the motor 20 to provide a regenerative braking torque to the corresponding front drive shaft 10a or rear drive shaft 10b according to the braking method for the vehicle 100 described above, and to control the backup hydraulic unit 30 to provide the vehicle-wide braking torque to the front drive shaft 10a and the rear drive shaft 10b.

[0057] The present application also provides a storage medium. All or part of the steps in the above-mentioned braking method for a vehicle can be completed by instructing the relevant hardware through program code. The program code is stored in the storage medium of the present application and includes a number of instructions to enable one or more processors (such as a single-chip microcomputer, a chip, etc.) to execute all or part of the steps of the method of the present application. Storage media include but are not limited to various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk. In one embodiment, a control algorithm program that can be executed by the controller in the vehicle 100 of the present application is stored in the storage medium.

[0058] Thus far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present application.

Claims

1. A braking method for a vehicle, characterized in that: The vehicle comprises two drive shafts, a main hydraulic unit and a backup hydraulic unit, each of the drive shafts is provided with a motor, and the braking method comprises: determining a target braking torque for each of the drive shafts when the main hydraulic unit fails and a braking request is detected; comparing the regenerative braking torque that can be provided by each of the motors with the corresponding target braking torque; When the regenerative braking torque that can be provided is greater than or equal to the target braking torque, controlling the motor to provide the target braking torque to the corresponding drive shaft; and When the regenerative braking torque that can be provided is less than the target braking torque, controlling the motor and the backup hydraulic unit to provide the target braking torque to the corresponding drive shaft; The backup hydraulic unit provides a whole vehicle braking torque, and the whole vehicle braking torque is determined based on a difference between the target braking torque and the recovery braking torque.

2. The braking method for a vehicle according to claim 1, characterized in that: The braking method further comprises: After providing the target braking torque to each of the drive shafts, acquiring the shaft slip ratio of each of the drive shafts; When the shaft slip rate is greater than a predetermined slip rate, reducing the recovery braking torque applied to the drive shaft while keeping the whole vehicle braking torque unchanged; reacquiring the shaft slip ratio of each of the driving shafts; When the recovered shaft slip ratio is less than or equal to the predetermined slip ratio, the reduction of the regeneration braking torque is stopped.

3. The braking method for a vehicle according to claim 2, characterized in that: The braking method further comprises: When the reacquired shaft slip ratio is greater than the predetermined slip ratio, determining whether the corresponding recovery braking torque is zero; When the regenerative braking torque is zero, reducing the whole vehicle braking torque; After reducing the braking torque of the entire vehicle, obtaining the shaft slip ratio of each of the driving shafts for a third time; When the axle slip ratio obtained for the third time is less than or equal to the predetermined slip ratio, the reduction of the vehicle braking torque is stopped.

4. The braking method for a vehicle according to claim 3, characterized in that: When the recovery braking torque is not zero, the step of "reducing the recovery braking torque applied to the drive shaft while keeping the whole vehicle braking torque unchanged" is repeated.

5. The braking method for a vehicle according to claim 1, characterized in that: The vehicle further includes a deceleration sensor, the braking request includes a desired deceleration, and the step of "determining a target braking torque for each of the drive shafts" includes: determining a desired braking torque based on the desired deceleration; Using the deceleration sensor to obtain the real-time deceleration of the vehicle; Calculating a distribution ratio of the desired braking torque based on the real-time deceleration; The target braking torque of each drive axle is determined based on the distribution ratio and the desired braking torque.

6. The braking method for a vehicle according to claim 5, characterized in that: The vehicle also includes an autonomous driving domain controller, and the expected deceleration is generated by the autonomous driving domain controller based on data obtained by autonomous driving hardware.

7. The braking method for a vehicle according to claim 1, characterized in that: The two drive shafts are a front drive shaft and a rear drive shaft; And the braking method further comprises: determining a first difference between the target braking torque of the front drive shaft and the regenerative braking torque that can be provided by the motor on the front drive shaft; determining a second difference between the target braking torque of the rear drive shaft and the regenerative braking torque that can be provided by the electric motor on the rear drive shaft; When the first difference is greater than zero and the second difference is less than or equal to zero, determining that the vehicle braking torque is equal to the first difference; When the first difference is less than or equal to zero and the second difference is greater than zero, the integer The vehicle braking torque is equal to the second difference; and When both the first difference and the second difference are greater than zero, it is determined that the whole vehicle braking torque is equal to the sum of the first difference and the second difference.

8. The braking method for a vehicle according to claim 2, characterized in that: The step of "obtaining the shaft slip ratio of each of the driving shafts" comprises: The average wheel speed of all wheels on each of the driving shafts and the vehicle speed of the vehicle are acquired, and the shaft slip ratio of each of the driving shafts is calculated based on the average wheel speed and the vehicle speed.

9. A vehicle, characterized in that: The vehicle comprises: front and rear drive shafts; a motor disposed on each of the front drive shaft and the rear drive shaft; Main hydraulic unit; backup hydraulic unit; and A controller, wherein the controller is configured to control the motor to provide a recovery braking torque to the corresponding front drive shaft or the rear drive shaft according to the braking method for a vehicle according to any one of claims 1 to 8, and to control the backup hydraulic unit to provide the vehicle braking torque to the front drive shaft and the rear drive shaft.

10. A storage medium, wherein the storage medium is suitable for storing a plurality of program codes, characterized in that: The program code is suitable for being loaded and run by a processor to execute the braking method for a vehicle according to any one of claims 1-8.

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