Vehicle braking control methods, devices, equipment and storage media

Abstract

This application discloses a vehicle braking control method, device, and related equipment applied in the field of vehicle control technology. In this method, based on the acquired braking fault signal of a target wheel, it is determined that the actuator of the target wheel has malfunctioned, and the longitudinal force of the target wheel is set to 0. Using overall constraint conditions and speed change conditions, the target rear wheel steering angle and the longitudinal force of each controllable wheel are determined. Through the rear wheel steering system, the angle of the rear wheels is adjusted based on the target rear wheel steering angle to reduce the lateral deviation of the vehicle's posture and ensure the vehicle's lateral stability. Based on the longitudinal force of the controllable wheels, braking control is applied to the other three wheels whose actuators are not malfunctioning to compensate for the reduced braking effect caused by the target wheel malfunction, thereby achieving longitudinal speed control of the vehicle. This enables effective braking control in both the lateral and longitudinal directions, meeting driving requirements.

Description

Technical Field

[0001] This application relates to the field of vehicle control technology, specifically to a vehicle braking control method, device, equipment, and storage medium. Background Technology

[0002] Electro-Mechanical Braking (EMB) is a relatively advanced vehicle braking system. The EMB system mainly consists of an electronic brake pedal, a higher-level controller, and four actuators located at the wheel ends. During driving, when the driver presses the electronic brake pedal, a pedal travel sensor collects the pedal travel and sends it to the higher-level controller. The pedal travel indicates the driver's braking intention. Based on the pedal travel, the higher-level controller generates a vehicle braking force request and distributes this request to the clamping force requests of the four wheel-end actuators. Finally, the motors inside the actuators generate the corresponding clamping force, mechanically clamping the brake calipers and thus causing vehicle deceleration. The EMB system no longer uses a hydraulic system for braking force transmission; instead, it uses four independently controllable actuators to generate braking force, enabling faster braking torque response and a safer redundancy mechanism.

[0003] However, in actual use of the EMB system, an actuator malfunction may occur. A malfunctioning actuator cannot generate the clamping force corresponding to the clamping force request, thus failing to brake the wheels. This results in insufficient braking force for the entire vehicle, causing the overall deceleration to fall short of the driver's expectations and potentially leading to vehicle yaw.

[0004] Currently, there is a lack of methods to effectively control vehicle braking in the event of an actuator failure in the EMB system. Summary of the Invention

[0005] In view of this, this application provides a vehicle braking control method, device, and related equipment that can effectively control vehicle braking in the event of an actuator failure in the EMB system.

[0006] The technical solution provided in this application is as follows:

[0007] In a first aspect, this application provides a vehicle braking control method, the method being applied to a vehicle equipped with an electromechanical braking system and a rear-wheel steering system, the electromechanical braking system including an upper controller connected to the rear-wheel steering system, the method comprising:

[0008] In response to acquiring a braking fault signal of the target wheel, the upper controller sets the value of the longitudinal force of the target wheel to 0;

[0009] The upper-level controller obtains the total constraints, which include vehicle lateral stability constraints and vehicle longitudinal deceleration constraints.

[0010] The upper-level controller determines the target rear wheel angle and the longitudinal force of each controllable wheel that satisfy the overall constraint condition and the speed change condition. The speed change condition is that the difference between the vehicle's longitudinal speed change rate and the normal vehicle longitudinal speed change rate is minimized. The controllable wheels are the three wheels of the vehicle other than the target wheel.

[0011] The upper controller controls the controllable wheel according to the longitudinal force of the controllable wheel, and sends the target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle.

[0012] In one possible implementation, the total constraint condition further includes a wheel adhesion limit constraint condition, which is that the sum of the square of the longitudinal force of the wheel and the square of the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel.

[0013] In one possible implementation, sending a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle includes:

[0014] A target rear wheel angle and a fault signal are sent to the rear wheel steering system so that the rear wheel steering system, in response to receiving the fault signal, controls the rear wheel angle of the vehicle according to the target rear wheel angle.

[0015] In one possible implementation, the vehicle lateral stability constraint and the vehicle longitudinal deceleration constraint are obtained in the following manner:

[0016] The vehicle parameters, state variables, handling variables, and lateral forces of the four wheels are obtained. The vehicle parameters include the front half wheelbase, rear half wheelbase, wheelbase, track width, vehicle mass, and yaw moment of inertia. The state variables include the vehicle yaw rate, vehicle center of gravity sideslip angle, and vehicle longitudinal velocity. The handling variables include the longitudinal forces of the four wheels, front wheel steering angle, and rear wheel steering angle.

[0017] A first lateral and longitudinal dynamic model of the vehicle is constructed using the vehicle parameters, the state variables, the manipulation variables, and the lateral forces of the four wheels. The first lateral and longitudinal dynamic model includes an expression describing the yaw moment, an expression describing the rate of change of the vehicle's center of gravity sideslip angle, and an expression describing the longitudinal dynamics of the vehicle.

[0018] Based on the correspondence between the lateral forces of the four wheels, the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables, the lateral forces of the four wheels in the first lateral and longitudinal dynamic model are replaced by the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables to obtain the second lateral and longitudinal dynamic model.

[0019] The rate of change of the vehicle's yaw rate and the rate of change of the vehicle's center of gravity sideslip angle are set to 0. The lateral stability constraints of the vehicle are constructed using the expressions describing the yaw moment and the rate of change of the vehicle's center of gravity sideslip angle included in the second lateral and longitudinal dynamic model.

[0020] The expression describing the longitudinal dynamics of the vehicle, included in the second lateral and longitudinal dynamics model, is used as the longitudinal deceleration constraint condition for the vehicle.

[0021] In one possible implementation, the expression describing the longitudinal dynamics of the vehicle includes the sine, cosine, sine, and cosine values ​​of the front wheel steering angle, the rear wheel steering angle, and the rear wheel steering angle, wherein the sine value of the front wheel steering angle is replaced with the front wheel steering angle, the cosine value of the front wheel steering angle is replaced with 1, the sine value of the rear wheel steering angle is replaced with the rear wheel steering angle, and the cosine value of the rear wheel steering angle is replaced with 1.

[0022] Secondly, this application provides a vehicle braking control device, which is applied to a vehicle equipped with an electromechanical braking system and a rear-wheel steering system. The electromechanical braking system includes an upper controller connected to the rear-wheel steering system, and the device is applied to the upper controller. The device includes:

[0023] The setting unit is used to set the value of the longitudinal force of the target wheel to 0 in response to the acquisition of the braking fault signal of the target wheel.

[0024] The acquisition unit is used to acquire the total constraint conditions, which include vehicle lateral stability constraint conditions and vehicle longitudinal deceleration constraint conditions.

[0025] The determining unit is used to determine the target rear wheel steering angle and the longitudinal force of each controllable wheel that satisfy the total constraint condition and the speed change condition. The speed change condition is that the difference between the vehicle's longitudinal speed change rate and the normal vehicle longitudinal speed change rate is minimized. The controllable wheels are the three wheels of the vehicle other than the target wheel.

[0026] The control unit is configured to control the controllable wheel according to the longitudinal force of the controllable wheel, and send a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle.

[0027] In one possible implementation, the vehicle lateral stability constraint and the vehicle longitudinal deceleration constraint are obtained in the following manner:

[0028] The vehicle parameters, state variables, handling variables, and lateral forces of the four wheels are obtained. The vehicle parameters include the front half wheelbase, rear half wheelbase, wheelbase, track width, vehicle mass, and yaw moment of inertia. The state variables include the vehicle yaw rate, vehicle center of gravity sideslip angle, and vehicle longitudinal velocity. The handling variables include the longitudinal forces of the four wheels, front wheel steering angle, and rear wheel steering angle.

[0029] A first lateral and longitudinal dynamic model of the vehicle is constructed using the vehicle parameters, the state variables, the manipulation variables, and the lateral forces of the four wheels. The first lateral and longitudinal dynamic model includes an expression describing the yaw moment, an expression describing the rate of change of the vehicle's center of gravity sideslip angle, and an expression describing the longitudinal dynamics of the vehicle.

[0030] Based on the correspondence between the lateral forces of the four wheels, the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables, the lateral forces of the four wheels in the first lateral and longitudinal dynamic model are replaced by the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables to obtain the second lateral and longitudinal dynamic model.

[0031] The rate of change of the vehicle's yaw rate and the rate of change of the vehicle's center of gravity sideslip angle are set to 0. The lateral stability constraints of the vehicle are constructed using the expressions describing the yaw moment and the rate of change of the vehicle's center of gravity sideslip angle included in the second lateral and longitudinal dynamic model.

[0032] The expression describing the longitudinal dynamics of the vehicle, included in the second lateral and longitudinal dynamics model, is used as the longitudinal deceleration constraint condition for the vehicle.

[0033] In one possible implementation, the expression describing the longitudinal dynamics of the vehicle includes the sine, cosine, sine, and cosine values ​​of the front wheel steering angle, the rear wheel steering angle, and the rear wheel steering angle, wherein the sine value of the front wheel steering angle is replaced with the front wheel steering angle, the cosine value of the front wheel steering angle is replaced with 1, the sine value of the rear wheel steering angle is replaced with the rear wheel steering angle, and the cosine value of the rear wheel steering angle is replaced with 1.

[0034] In one possible implementation, the total constraint condition further includes a wheel adhesion limit constraint condition, which is that the sum of the square of the longitudinal force of the wheel and the square of the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel.

[0035] In one possible implementation, the control unit is configured to send a target rear wheel steering angle to the rear wheel steering system, so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle, including:

[0036] The control unit is configured to send a target rear wheel angle and a fault signal to the rear wheel steering system, so that the rear wheel steering system, in response to acquiring the fault signal, controls the rear wheel angle of the vehicle according to the target rear wheel angle.

[0037] Thirdly, this application provides an apparatus, including: a processor, a memory, and a system bus;

[0038] The processor and the memory are connected via the system bus;

[0039] The memory is used to store one or more programs, the one or more programs including instructions that, when executed by the processor, cause the processor to perform the method described in the first aspect.

[0040] Fourthly, this application provides a computer-readable storage medium storing instructions that, when executed on a terminal device, cause the terminal device to perform the method described in the first aspect.

[0041] Therefore, this application has the following beneficial effects:

[0042] This application provides a vehicle braking control method, device, and related equipment applicable to vehicles equipped with an electromechanical braking system and a rear-wheel steering system. In this method, based on the acquired braking fault signal of a target wheel, it is determined that the actuator of the target wheel has malfunctioned. The longitudinal force of the target wheel is set to 0 to achieve braking control of the vehicle even when the actuator of the target wheel cannot brake the target vehicle. Using overall constraints and speed change conditions, the target rear wheel angle and the longitudinal forces of each controllable wheel are determined. The overall constraints include vehicle lateral stability constraints and vehicle longitudinal deceleration constraints, satisfying the vehicle's lateral stability requirements and longitudinal deceleration requirements, respectively. The speed change conditions are used to ensure a relatively stable vehicle speed change rate, resulting in a smoother braking process even in the event of a fault. Through the rear-wheel steering system, the rear wheel angle is adjusted based on the target rear wheel angle to reduce lateral deviation of the vehicle's posture and ensure lateral stability. Based on the longitudinal forces of the controllable wheels, braking control is applied to the other three wheels whose actuators are not malfunctioning to compensate for the reduced braking effect caused by the target wheel malfunction, achieving longitudinal speed control of the vehicle. This allows for effective braking control in both lateral and longitudinal directions, meeting driving requirements, and can be adapted to vehicles with rear-wheel steering systems. Attached Figure Description

[0043] Figure 1 A schematic diagram of a vehicle braking control method provided in an embodiment of this application;

[0044] Figure 2 A schematic flowchart of a vehicle braking control method provided in an embodiment of this application;

[0045] Figure 3 A schematic diagram of a vehicle's lateral and longitudinal dynamics model provided in an embodiment of this application;

[0046] Figure 4 This is a schematic diagram of the structure of a vehicle braking control device provided in an embodiment of this application. Detailed Implementation

[0047] To facilitate understanding and explanation of the technical solutions provided in the embodiments of this application, the background technology of this application will be described first.

[0048] The EMB (Electronic Braking Assist) system uses four independently controllable actuators at each wheel to achieve independent control of the wheel, improving braking response and safety. However, when an actuator malfunctions, the EMB system cannot effectively brake the wheel corresponding to the faulty actuator during braking control. With one actuator malfunctioning, it cannot properly clamp the wheel, resulting in a lack of braking control. When one wheel cannot be effectively braked, the vehicle as a whole cannot achieve the braking control expected by the driver or the autonomous driving system, potentially leading to braking distances exceeding the expected distance and affecting driving safety. Furthermore, even when the other three actuators are properly clamping the wheel, the movement of the wheel that cannot be effectively braked can cause deviations in the vehicle's overall posture, potentially resulting in yaw.

[0049] Currently, there are two control methods for actuator failures in EMB systems. The first method, for vehicles equipped with a distributed drive system, generates a counter-drive force on the wheel where the actuator malfunctions, thereby compensating for insufficient braking force. However, distributed drive systems are expensive and are primarily found in high-end vehicles, making widespread application impossible. The second method, for vehicles equipped with a front-wheel steer-by-wire system, compensates for the vehicle's yaw angle by adding front wheel steering angle, thus controlling the vehicle's attitude. However, this method cannot reduce the vehicle's longitudinal speed and interferes with the driver's intentions, failing to meet braking requirements.

[0050] Based on this, this application provides a vehicle braking control method. In response to acquiring a braking fault signal of a target wheel, it is determined that the actuator of the target wheel has malfunctioned. The longitudinal force of the target wheel is set to 0 to trigger braking control of the vehicle in the event of a target wheel actuator malfunction. Using overall constraints and speed change conditions, the target rear wheel steering angle and the longitudinal forces of each controllable wheel are determined. The overall constraints include vehicle lateral stability constraints and vehicle longitudinal deceleration constraints, satisfying the vehicle's lateral stability requirements and longitudinal deceleration requirements, respectively. The speed change conditions are used to ensure a relatively stable vehicle speed change rate, so that the braking process is relatively smooth in the event of a malfunction. Through the rear wheel steering system, the rear wheel angle is adjusted based on the target rear wheel steering angle to reduce lateral deviation of the vehicle's posture and ensure lateral stability. Based on the longitudinal forces of the controllable wheels, braking control is applied to the other three wheels whose actuators are not malfunctioning to compensate for the reduced braking effect caused by the target wheel malfunction, thereby achieving longitudinal speed control of the vehicle. This allows for compatibility with more common rear-wheel steering systems, enabling effective braking control in both lateral and longitudinal directions in the event of an EMB actuator failure, thus meeting driving requirements.

[0051] First, it should be noted that the vehicle braking control method provided in this application is applied to vehicles equipped with a rear wheel steering (RWS) system. The rear wheel steering system is used to generate the rear wheel steering angle, which can reduce oversteer caused by high-speed cornering and also compensate for understeer, thereby improving the vehicle's driving agility and safety.

[0052] See Figure 1 As shown, this figure is a schematic diagram of a vehicle braking control method according to an embodiment of this application. The vehicle is equipped with an EMB system and an RWS system. The EMB system includes an upper-level controller and four actuators located at the wheel ends. The four wheel-end actuators include actuators for wheel A, wheel B, wheel C, and wheel D. The four wheel-end actuators also include a lower-level controller. The lower-level controller is connected to the upper-level controller. The upper-level controller of the EMB system is also connected to the RWS system.

[0053] The lower-level controllers within the EMB system's actuators perform actuator fault detection. When the lower-level controller of the actuator for a particular wheel, such as wheel A, detects a fault, it generates a braking fault signal. The lower-level controller of wheel A's actuator sends this braking fault signal to the upper-level controller of the EMB system. The upper-level controller of the EMB system receives the braking fault signal from wheel A's actuator and determines that the longitudinal force on wheel A is zero. That is, the actuator on wheel A cannot provide longitudinal force to wheel A. The upper-level controller of the EMB system then obtains the overall constraints. These constraints include vehicle lateral stability constraints and vehicle longitudinal deceleration constraints. The lateral stability constraints ensure the vehicle's lateral stability. The longitudinal deceleration constraints describe the vehicle's longitudinal speed deceleration. The upper-level controller of the EMB system determines the target rear wheel steering angle and the longitudinal force of each controllable wheel, satisfying the overall constraints and speed change conditions. The controllable wheels are wheels B, C, and D. The upper-level controller of the EMB system sends the target rear wheel steering angle to the RWS system. The RWS system adjusts the angle of the vehicle's rear wheels based on the target rear wheel steering angle. The upper-level controller of the EMB system sends the longitudinal force of wheel B to the actuator of wheel B, the longitudinal force of wheel C to the actuator of wheel C, and the longitudinal force of wheel D to the actuator of wheel D. The actuators of wheel B, wheel C, and wheel D control the wheels based on the acquired longitudinal forces.

[0054] This allows for adjustment of the longitudinal force of the actuators that are not malfunctioning, thereby adjusting the longitudinal speed. Furthermore, by utilizing the more common rear-wheel steering system in vehicles, the angle of the rear wheels can be adjusted to ensure the lateral stability of the vehicle, effectively controlling vehicle braking even in the event of an actuator failure in the EMB system.

[0055] To facilitate understanding of the technical solutions provided in the embodiments of this application, the vehicle braking control method provided in the embodiments of this application will be described below with reference to the accompanying drawings.

[0056] See Figure 2 As shown, this figure is a schematic flowchart of a vehicle braking control method provided in an embodiment of this application. Figure 2 As shown, the vehicle braking control method provided in this application includes S201-S204.

[0057] S201: In response to acquiring a braking fault signal of the target wheel, the upper-level controller sets the value of the longitudinal force of the target wheel to 0.

[0058] The brake fault signal of the target wheel is used to indicate that the actuator of the target wheel has malfunctioned. As an example, the brake fault signal of the target wheel includes a fault indicator and a wheel indicator of the target wheel. The fault indicator indicates that the actuator has malfunctioned. The wheel indicator of the target wheel indicates the target wheel. This application embodiment does not limit the position of the target wheel on the vehicle; the target wheel can be the right front wheel, the left front wheel, the right rear wheel, or the left rear wheel. That is, it is possible to detect brake faults and perform corresponding compensation control for any wheel on the vehicle where an actuator malfunction has occurred.

[0059] The braking fault signal for the target wheel is generated by the actuator of the EMB system configured on that wheel. As an example, the actuator includes a lower-level controller. The lower-level controller controls the actuator. The lower-level controller monitors the actuator. When a fault occurs in the actuator, a braking fault signal for the target wheel is generated.

[0060] The longitudinal force on the wheel is the force determined by the upper-level controller of the EMB system for controlling the actuators of the wheel. Based on the longitudinal force issued by the upper-level controller, the actuators apply a longitudinal force to the wheel, which is the clamping force on the wheel, to achieve braking control of the wheel.

[0061] Upon receiving a braking fault signal from the target wheel, the upper-level controller of the EMB system determines that the actuator of the target wheel is unable to apply longitudinal force to the target wheel and stops the normal braking control strategy of the actuator. It then initiates a compensation control strategy for the actuator fault. Specifically, the upper-level controller of the EMB system sets the value of the longitudinal force of the target wheel to 0. It should be noted that after setting the value of the longitudinal force of the target wheel to 0, the value of the longitudinal force of the target wheel remains unchanged at 0 during the subsequent execution of S202 and S203, which determine the target rear wheel steering angle and the longitudinal force of each controllable wheel. This continues until the upper-level controller receives a braking recovery signal from the target wheel or a reset signal triggered after the braking fault has been resolved.

[0062] S202: The upper-level controller obtains the total constraints.

[0063] The overall constraints are those that ensure the vehicle's lateral stability and longitudinal speed control. These constraints include lateral stability constraints and longitudinal deceleration constraints. The overall constraints can be pre-configured in the upper-level controller or configured in other modules connected to the upper-level controller for use by the upper-level controller.

[0064] In some possible implementations, the total constraints can be described using expressions. As an example, the vehicle lateral stability constraints are expressed using formulas (1) and (2):

[0065]

[0066] Where a is the front half wheelbase and b is the rear half wheelbase. β ′ γ represents the vehicle's sideslip angle at the current moment, representing the center of gravity. sp This is the set value for the vehicle's yaw rate. γ sp According to the vehicle's normal front wheel steering angle and rear wheel angle Calculation determined. ′ x Let δ be the longitudinal velocity of the vehicle at the current moment. r The rear wheel steering angle is denoted by _T_, where _T_ is the vehicle's track width. _m_ is the vehicle's mass. _C_ is the vehicle's weight. f C represents the lateral stiffness coefficient of the front wheel. r F represents the lateral stiffness coefficient of the rear wheel. xfl F xfr F xrl F xrr These represent the longitudinal forces on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively. The longitudinal force on the target wheel is 0.

[0067] As an example, the target wheel is the left front wheel, meaning that the actuator of the left front wheel malfunctions, then F xfl =0. The above formula (1) can be simplified to formula (3):

[0068]

[0069] The longitudinal deceleration constraint condition of the vehicle is expressed by formula (4):

[0070]

[0071] in, This represents the rate of change of the vehicle's longitudinal speed.

[0072] The overall constraint conditions of formulas (1), (2), and (4) above can be determined based on the vehicle's lateral and longitudinal dynamics model. This application provides a possible implementation method for determining the overall constraint conditions, as detailed below.

[0073] In addition to the aforementioned vehicle lateral stability constraints and vehicle longitudinal deceleration constraints, the overall constraints also include wheel adhesion limit constraints. Wheel adhesion limit constraints are used to ensure that the wheel does not exceed its adhesion limit and does not lose traction.

[0074] As an example, the limit constraint condition for wheel adhesion is that the sum of the squares of the longitudinal force and the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel. Specifically, the limit constraint condition for wheel adhesion is expressed by formula (5):

[0075]

[0076] Where μ represents the ground adhesion coefficient, F z This represents the dynamic vertical load on the wheel. F zfl ,F zfr ,F zrl ,F zrr These represent the dynamic vertical loads on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively. F xfl F xfr F xrl F xrr F represents the longitudinal force on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively. yfl ,F yfr ,F yrl ,F yrr These represent the lateral forces on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively.

[0077] Taking the target wheel as the left front wheel as an example, that is, if the actuator of the left front wheel malfunctions, then F xfl =0. The above formula (5) can be simplified to formula (6):

[0078]

[0079] S203: Upper-level controller, which determines the target rear wheel angle and longitudinal force of each controllable wheel that satisfy the overall constraints and speed change conditions.

[0080] The speed change condition is that the difference between the rate of change of the vehicle's longitudinal speed and the rate of change of the vehicle's longitudinal speed under normal conditions is minimized.

[0081] Taking the target wheel as the left front wheel as an example, the speed change condition can be expressed by formula (7):

[0082]

[0083] in, δ represents the rate of change of the vehicle's longitudinal velocity under normal conditions. r To determine the target rear wheel steering angle, F xfr ,F xrl ,F xrr These are the longitudinal forces of the three controllable wheels, namely, the longitudinal forces of the right front wheel, the left rear wheel, and the right rear wheel.

[0084] Speed ​​variation conditions ensure relatively stable longitudinal speed changes in the vehicle, meeting the driver's driving needs. Speed ​​variation conditions are also the goal of braking control.

[0085] The upper-level controller uses the overall constraints and speed variation conditions to determine the target rear wheel angle and the longitudinal force of each controllable wheel. The target rear wheel angle is the angle of the rear wheels adjusted through the rear wheel steering system. The controllable wheels are the three wheels other than the target wheel that can normally achieve braking.

[0086] Taking the left front wheel as the target wheel, under the condition that the total constraints include the vehicle's lateral stability constraints and the vehicle's longitudinal deceleration constraints, the target rear wheel angle and the longitudinal force of each controllable wheel are determined according to formula (1), formula (3), and formula (4), with formula (7) as the target. Under the condition that the total constraints include the vehicle's lateral stability constraints, the vehicle's longitudinal deceleration constraints, and the wheel adhesion limit constraints, the target rear wheel angle and the longitudinal force of each controllable wheel are determined according to formula (1), formula (3), formula (4), and formula (6), with formula (7) as the target.

[0087] S204: The upper controller controls the controllable wheel according to the longitudinal force of the controllable wheel and sends the target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system can control the rear wheel steering of the vehicle according to the target rear wheel steering angle.

[0088] The upper-level controller controls the controllable wheels according to the determined longitudinal force of the controllable wheels. Specifically, the upper-level controller sends the longitudinal force of each controllable wheel to the actuator of that wheel. The actuator then performs braking control on the wheel based on the acquired longitudinal force.

[0089] The upper-level controller sends a target rear wheel angle to the rear-wheel steering system. Based on the acquired target rear wheel angle, the rear-wheel steering system adjusts the angle of the vehicle's rear wheels. As an example, the upper-level controller sends the target rear wheel angle to the rear-wheel steering system, causing the rear-wheel steering system to adjust the current rear wheel angle to the target angle. As another example, the upper-level controller determines the difference between the target rear wheel angle and the current rear wheel angle. The upper-level controller sends the difference to the rear-wheel steering system so that the rear-wheel steering system adjusts the rear wheel angle based on the difference. In one possible implementation, the upper-level controller sends the target rear wheel angle and a fault signal to the rear-wheel steering system. The fault signal indicates a brake malfunction, triggering the rear-wheel steering system to control the rear wheel angle. In response to the fault signal, the rear-wheel steering system adjusts the rear wheel angle according to the target rear wheel angle. By triggering the rear wheel steering system to adjust the rear wheel angle using a fault signal, it is possible to adjust the rear wheel angle even in the event of an actuator failure. This prevents erroneous interference with the normal control of the rear wheel angle by the rear wheel steering system under other circumstances, thereby improving the safety of adjusting the rear wheel angle using the rear wheel steering system.

[0090] Based on the aforementioned content in S201-S204, it is clear that for single-wheel actuator failures in the EMB system, the rear-wheel steering system, which is more commonly equipped in vehicles, is used to compensate for rear-wheel angle adjustments, ensuring lateral stability during vehicle braking and offering higher adaptability. Furthermore, when a single-wheel actuator failure is confirmed, the longitudinal forces of the other three normally functioning actuators are adjusted. This ensures both lateral stability and longitudinal speed control, achieving effective braking control, improving vehicle safety, and realizing a fault-tolerant control mechanism for single-wheel actuator failures in the EMB system, thus fulfilling driving intentions.

[0091] In one possible implementation, this application provides a method for determining the overall constraints based on the vehicle's lateral and longitudinal dynamics model. It should be noted that the method for determining the overall constraints can be executed by the upper-level controller or by other modules; this application does not limit this. The possible implementation for determining the overall constraints includes the following steps:

[0092] A1: Obtain the vehicle's overall parameters, state variables, handling variables, and lateral forces on the four wheels.

[0093] Vehicle parameters include the front half wheelbase, rear half wheelbase, wheelbase, track width, vehicle mass, and yaw moment of inertia. State variables include the vehicle yaw rate, vehicle center of gravity sideslip angle, and vehicle longitudinal velocity. Maneuvering variables include the longitudinal forces on the four wheels, front wheel steering angle, and rear wheel steering angle.

[0094] Vehicle parameters are fixed values ​​and can be pre-configured. State variables and control variables are quantities of change determined based on the vehicle's current state. State variables and control variables can be acquired through sensors, computing modules, and other devices within the vehicle system.

[0095] A2: Construct the first lateral and longitudinal dynamic model of the vehicle using the vehicle parameters, state variables, manipulation variables, and lateral forces of the four wheels.

[0096] The first lateral and longitudinal dynamics model includes expressions describing the yaw moment, the rate of change of the vehicle's center of gravity sideslip angle, and the longitudinal dynamics of the entire vehicle.

[0097] As an example, this application provides a first transverse and longitudinal dynamic model. The first transverse and longitudinal dynamic model is expressed by formula (8):

[0098]

[0099] Where a is the front half of the wheelbase, b is the rear half of the wheelbase, L is the wheelbase, T is the track width, m is the vehicle weight, and I is the weight of the vehicle. zLet γ be the yaw moment of inertia, β be the vehicle's yaw rate, and v be the sideslip angle of the vehicle's center of gravity. x Let δ be the longitudinal velocity of the vehicle. f For the front wheel steering angle, δ r This refers to the rear wheel steering angle. F xfl F xfr F xrl F xrr These represent the longitudinal forces on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively. F yfl ,F yfr ,F yrl ,F yrr These represent the lateral forces on the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively.

[0100] Figure 3 This is a schematic diagram of a vehicle's lateral and longitudinal dynamics model provided in an embodiment of this application. For the meaning of each parameter and variable, please refer to [link / reference needed]. Figure 3 As shown.

[0101] Furthermore, for the above formula (8), in order to facilitate calculation, the calculation process of the sine and cosine values ​​in formula (8) is simplified. During the vehicle's operation, the turning angles of the front and rear wheels are relatively small. The sine value of the front wheel turning angle is replaced with the front wheel turning angle, and the cosine value of the front wheel turning angle is replaced with 1. The sine value of the rear wheel turning angle is replaced with the rear wheel turning angle, and the cosine value of the rear wheel turning angle is replaced with 1.

[0102] Simplifying the calculation of formula (8), we can make sinδ f =δ f cosδ f =1, sinδ r =δ r cosδ r =1, thus obtaining formula (9).

[0103]

[0104] By taking advantage of the small turning angle of the wheels, the calculation of trigonometric functions can be simplified. This can reduce the calculation cost while ensuring that the calculation results are relatively accurate and effective. It can also help improve the calculation speed of the target rear wheel turning angle and the longitudinal force of each controllable wheel, thus enabling a rapid response in vehicle braking control.

[0105] A3: Based on the correspondence between the lateral forces of the four wheels, the wheel lateral stiffness coefficient, vehicle parameters, state variables, and control variables, the lateral forces of the four wheels in the first lateral and longitudinal dynamic model are replaced by the wheel lateral stiffness coefficient, vehicle parameters, state variables, and control variables to obtain the second lateral and longitudinal dynamic model.

[0106] The lateral forces of the four wheels in the first longitudinal dynamic model can be replaced by other parameters. The correspondence between the lateral forces of the four wheels, the wheel's lateral stiffness coefficient, vehicle parameters, state variables, and handling variables can be determined based on the principles of vehicle kinematic geometry.

[0107] The correspondence between the lateral forces of the four wheels, the wheel's lateral stiffness coefficient, vehicle parameters, state variables, and control variables includes the first relationship between the lateral forces of the front wheels, the wheel's lateral stiffness coefficient, the vehicle's center of gravity sideslip angle, the front half wheelbase, the vehicle's yaw rate, the vehicle's longitudinal velocity, and the front wheel steering angle; and the second relationship between the lateral forces of the rear wheels, the wheel's lateral stiffness coefficient, the vehicle's center of gravity sideslip angle, the rear half wheelbase, the vehicle's yaw rate, the vehicle's longitudinal velocity, and the rear wheel steering angle.

[0108] Based on the first relationship, the lateral force on the front wheels is replaced by the wheel's lateral stiffness coefficient, the vehicle's center of gravity slip angle, the front wheelbase, the vehicle's yaw rate, the vehicle's longitudinal velocity, and the front wheel steering angle. The front wheels include the left and right front wheels.

[0109] Similarly, based on the second relationship, the lateral force of the rear wheels is replaced by the wheel's lateral stiffness coefficient, the vehicle's center of gravity lateral slip angle, the rear wheelbase, the vehicle's yaw rate, the vehicle's longitudinal velocity, and the rear wheel rotation angle. The rear wheels include the left and right rear wheels.

[0110] The first and second relationships are determined based on the definition of the lateral force of the wheel and the relationship between the slip angle and vehicle parameters, state variables, and handling variables.

[0111] When the wheel slip angle is small, the relationship between the lateral force of the wheel and the wheel slip angle can be approximated as a direct proportionality. The direct proportionality between the lateral force of the wheel and the wheel slip angle is shown in formulas (10) and (11).

[0112] F yfl =F yfr =C f α f (10)

[0113] F yrl =F yrr =C r α r (11)

[0114] Among them, C f C is the lateral stiffness coefficient of the front wheel. r α is the lateral stiffness coefficient of the rear wheel. f Let α be the slip angle of the front wheel. r This is the slip angle of the rear wheel.

[0115] In addition, based on vehicle kinematics, the relationship between the wheel slip angle and vehicle parameters, state variables, and control variables is determined. The relationship between the wheel slip angle and vehicle parameters, state variables, and control variables is shown in Equations (12) and (13).

[0116]

[0117] Substitute formula (12) into formula (10) and formula (13) into formula (11) to obtain formula (14) for the first relation and formula (15) for the second relation.

[0118]

[0119] As an example, taking the simplified first transverse and longitudinal dynamic model formula (9) as an example, substitute formula (14) and formula (15) into the above formula (9) to obtain the second transverse and longitudinal dynamic model, which is formula (16).

[0120]

[0121] The second lateral and longitudinal dynamic model does not include the lateral force of the wheel, so there is no need to use the lateral force of the wheel, which is not easy to obtain, to calculate, thus reducing the calculation difficulty and improving the calculation efficiency.

[0122] A4: Set the rate of change of the vehicle's yaw rate and the rate of change of the vehicle's center of gravity sideslip angle to 0, and use the expressions describing the yaw moment and the rate of change of the vehicle's center of gravity sideslip angle included in the second lateral and longitudinal dynamic model to construct the vehicle's lateral stability constraints.

[0123] To maintain lateral stability of the vehicle, the rates of change of the vehicle's yaw rate and the rates of change of the vehicle's sideslip angle are both zero. Setting these rates of change to zero yields the lateral stability constraints for the vehicle.

[0124] As an example, taking the above formula (16) as an example, the first expression and the second expression are... as well as Setting it to 0 yields the vehicle's lateral stability constraints, which are the above formulas (1) and (2).

[0125] A5: The expression describing the longitudinal dynamics of the whole vehicle included in the second longitudinal dynamics model is used as the longitudinal deceleration constraint condition of the vehicle.

[0126] As an example, taking the above formula (16) as an example, the third expression is used as the longitudinal deceleration constraint condition of the vehicle, that is, the above formula (4).

[0127] Furthermore, it should be noted that the aforementioned lateral and longitudinal dynamics model is only one possible mathematical model for describing vehicle dynamics. Those skilled in the art can construct lateral and longitudinal dynamics models in other ways, and this application does not limit such methods.

[0128] Based on the kinematic principles of vehicles, we first construct lateral and longitudinal dynamic models of the vehicle. Then, based on the requirements of vehicle braking control in terms of both lateral stability and longitudinal deceleration, we generate lateral stability constraints and longitudinal deceleration constraints. This allows for relatively accurate and effective lateral and longitudinal control of the vehicle.

[0129] Based on the vehicle braking control method provided in the above embodiments, this application also provides a vehicle braking control device. This vehicle braking control device is applied to a vehicle equipped with an electromechanical braking system and a rear-wheel steering system. The electromechanical braking system includes an upper controller. The upper controller is connected to the rear-wheel steering system, and the vehicle braking control device is applied to the upper controller.

[0130] The vehicle's braking control device will now be described in conjunction with the accompanying drawings.

[0131] See Figure 4 As shown in the figure, this is a structural schematic diagram of a vehicle braking control device provided in an embodiment of this application. Figure 4 As shown, the vehicle braking control device includes:

[0132] Setting unit 401 is used to set the value of the longitudinal force of the target wheel to 0 in response to acquiring the braking fault signal of the target wheel.

[0133] The acquisition unit 402 is used to acquire the total constraint conditions, which include vehicle lateral stability constraint conditions and vehicle longitudinal deceleration constraint conditions.

[0134] The determining unit 403 is used to determine the target rear wheel rotation angle and the longitudinal force of each controllable wheel that satisfy the total constraint condition and the speed change condition. The speed change condition is that the difference between the vehicle's longitudinal speed change rate and the normal vehicle longitudinal speed change rate is the smallest. The controllable wheels are the three wheels of the vehicle other than the target wheel.

[0135] Control unit 404 is used to control the controllable wheel according to the longitudinal force of the controllable wheel, and send a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle.

[0136] In one possible implementation, the vehicle lateral stability constraint and the vehicle longitudinal deceleration constraint are obtained in the following manner:

[0137] The vehicle parameters, state variables, handling variables, and lateral forces of the four wheels are obtained. The vehicle parameters include the front half wheelbase, rear half wheelbase, wheelbase, track width, vehicle mass, and yaw moment of inertia. The state variables include the vehicle yaw rate, vehicle center of gravity sideslip angle, and vehicle longitudinal velocity. The handling variables include the longitudinal forces of the four wheels, front wheel steering angle, and rear wheel steering angle.

[0138] A first lateral and longitudinal dynamic model of the vehicle is constructed using the vehicle parameters, the state variables, the manipulation variables, and the lateral forces of the four wheels. The first lateral and longitudinal dynamic model includes an expression describing the yaw moment, an expression describing the rate of change of the vehicle's center of gravity sideslip angle, and an expression describing the longitudinal dynamics of the vehicle.

[0139] Based on the correspondence between the lateral forces of the four wheels, the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables, the lateral forces of the four wheels in the first lateral and longitudinal dynamic model are replaced by the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables to obtain the second lateral and longitudinal dynamic model.

[0140] The rate of change of the vehicle's yaw rate and the rate of change of the vehicle's center of gravity sideslip angle are set to 0. The lateral stability constraints of the vehicle are constructed using the expressions describing the yaw moment and the rate of change of the vehicle's center of gravity sideslip angle included in the second lateral and longitudinal dynamic model.

[0141] The expression describing the longitudinal dynamics of the vehicle, included in the second lateral and longitudinal dynamics model, is used as the longitudinal deceleration constraint condition for the vehicle.

[0142] In one possible implementation, the expression describing the longitudinal dynamics of the vehicle includes the sine, cosine, sine, and cosine values ​​of the front wheel steering angle, the rear wheel steering angle, and the rear wheel steering angle, wherein the sine value of the front wheel steering angle is replaced with the front wheel steering angle, the cosine value of the front wheel steering angle is replaced with 1, the sine value of the rear wheel steering angle is replaced with the rear wheel steering angle, and the cosine value of the rear wheel steering angle is replaced with 1.

[0143] In one possible implementation, the total constraint condition further includes a wheel adhesion limit constraint condition, which is that the sum of the square of the longitudinal force of the wheel and the square of the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel.

[0144] In one possible implementation, the control unit 404 is configured to send a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle, including:

[0145] The control unit 404 is used to send a target rear wheel angle and a fault signal to the rear wheel steering system, so that the rear wheel steering system responds to receiving the fault signal and controls the rear wheel angle of the vehicle according to the target rear wheel angle.

[0146] Based on the vehicle braking control method provided in the above method embodiments, this application provides a device, including: a processor, a memory, and a system bus;

[0147] The processor and the memory are connected via the system bus;

[0148] The memory is used to store one or more programs, the one or more programs including instructions that, when executed by the processor, cause the processor to perform the vehicle braking control method described in any of the above embodiments.

[0149] Based on the vehicle braking control method provided in the above-described embodiments, this application provides a computer-readable storage medium storing instructions that, when executed on a terminal device, cause the terminal device to perform the vehicle braking control method described in any of the above embodiments.

[0150] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0151] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0152] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0153] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0154] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A vehicle braking control method, characterized in that, The method is applied to a vehicle equipped with an electromechanical braking system and a rear-wheel steering system. The electromechanical braking system includes a supercontroller connected to the rear-wheel steering system. The method includes: In response to acquiring a braking fault signal of the target wheel, the upper controller sets the value of the longitudinal force of the target wheel to 0; The upper-level controller obtains the total constraints, which include vehicle lateral stability constraints and vehicle longitudinal deceleration constraints. The upper-level controller determines the target rear wheel angle and the longitudinal force of each controllable wheel that satisfy the overall constraint condition and the speed change condition. The speed change condition is that the difference between the vehicle's longitudinal speed change rate and the normal vehicle longitudinal speed change rate is minimized. The controllable wheels are the three wheels of the vehicle other than the target wheel. The upper controller controls the controllable wheel according to the longitudinal force of the controllable wheel, and sends the target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle.

2. The method according to claim 1, characterized in that, The overall constraint conditions also include wheel adhesion limit constraint conditions, which are that the sum of the square of the longitudinal force of the wheel and the square of the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel.

3. The method according to claim 1, characterized in that, Sending a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle includes: A target rear wheel angle and a fault signal are sent to the rear wheel steering system so that the rear wheel steering system, in response to receiving the fault signal, controls the rear wheel angle of the vehicle according to the target rear wheel angle.

4. The method according to any one of claims 1-3, characterized in that, The vehicle lateral stability constraint and the vehicle longitudinal deceleration constraint are obtained in the following manner: The vehicle parameters, state variables, handling variables, and lateral forces of the four wheels are obtained. The vehicle parameters include the front half wheelbase, rear half wheelbase, wheelbase, track width, vehicle mass, and yaw moment of inertia. The state variables include the vehicle yaw rate, vehicle center of gravity sideslip angle, and vehicle longitudinal velocity. The handling variables include the longitudinal forces of the four wheels, front wheel steering angle, and rear wheel steering angle. A first lateral and longitudinal dynamic model of the vehicle is constructed using the vehicle parameters, the state variables, the manipulation variables, and the lateral forces of the four wheels. The first lateral and longitudinal dynamic model includes an expression describing the yaw moment, an expression describing the rate of change of the vehicle's center of gravity sideslip angle, and an expression describing the longitudinal dynamics of the vehicle. Based on the correspondence between the lateral forces of the four wheels, the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables, the lateral forces of the four wheels in the first lateral and longitudinal dynamic model are replaced by the wheel lateral stiffness coefficient, the vehicle parameters, the state variables, and the control variables to obtain the second lateral and longitudinal dynamic model. The rate of change of the vehicle's yaw rate and the rate of change of the vehicle's center of gravity sideslip angle are set to 0. The lateral stability constraints of the vehicle are constructed using the expressions describing the yaw moment and the rate of change of the vehicle's center of gravity sideslip angle included in the second lateral and longitudinal dynamic model. The expression describing the longitudinal dynamics of the vehicle, included in the second lateral and longitudinal dynamics model, is used as the longitudinal deceleration constraint condition for the vehicle.

5. The method according to claim 4, characterized in that, The expression describing the longitudinal dynamics of the vehicle includes the sine, cosine, sine, and cosine values ​​of the front wheel steering angle, the rear wheel steering angle, and the rear wheel steering angle. The sine value of the front wheel steering angle is replaced with the front wheel steering angle, the cosine value of the front wheel steering angle is replaced with 1, the sine value of the rear wheel steering angle is replaced with the rear wheel steering angle, and the cosine value of the rear wheel steering angle is replaced with 1.

6. A vehicle braking control device, characterized in that, The device is applied to a vehicle equipped with an electromechanical braking system and a rear-wheel steering system. The electromechanical braking system includes a supercontroller connected to the rear-wheel steering system. The device is applied to the supercontroller and includes: The setting unit is used to set the value of the longitudinal force of the target wheel to 0 in response to the acquisition of the braking fault signal of the target wheel. The acquisition unit is used to acquire the total constraint conditions, which include vehicle lateral stability constraint conditions and vehicle longitudinal deceleration constraint conditions. The determining unit is used to determine the target rear wheel steering angle and the longitudinal force of each controllable wheel that satisfy the total constraint condition and the speed change condition. The speed change condition is that the difference between the vehicle's longitudinal speed change rate and the normal vehicle longitudinal speed change rate is minimized. The controllable wheels are the three wheels of the vehicle other than the target wheel. The control unit is configured to control the controllable wheel according to the longitudinal force of the controllable wheel, and send a target rear wheel steering angle to the rear wheel steering system so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle.

7. The apparatus according to claim 6, characterized in that, The overall constraint conditions also include wheel adhesion limit constraint conditions, which are that the sum of the square of the longitudinal force of the wheel and the square of the lateral force of the wheel is less than the product of the ground adhesion coefficient and the square of the dynamic vertical load of the wheel.

8. The apparatus according to claim 6, characterized in that, The control unit is configured to send a target rear wheel steering angle to the rear wheel steering system, so that the rear wheel steering system controls the rear wheel angle of the vehicle according to the target rear wheel steering angle, including: The control unit is configured to send a target rear wheel angle and a fault signal to the rear wheel steering system, so that the rear wheel steering system, in response to acquiring the fault signal, controls the rear wheel angle of the vehicle according to the target rear wheel angle.

9. A device, characterized in that, include: Processor, memory, system bus; The processor and the memory are connected via the system bus; The memory is used to store one or more programs, the one or more programs including instructions that, when executed by the processor, cause the processor to perform the method according to any one of claims 1-5.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a terminal device, cause the terminal device to perform the method described in any one of claims 1-5.

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