Automobile single wheel failure fault-tolerant control method and system for distributed brake-by-wire

Abstract

The application relates to a distributed brake-by-wire automobile single-wheel failure fault-tolerant control method and system, which comprises the following steps: obtaining state signals of an automobile brake-by-wire system, obtaining fault factors respectively representing fault types and fault degrees, and thus obtaining corresponding fault codes; according to the fault codes, corresponding fault control strategies are adopted, brake force reconstruction is carried out on each wheel of the vehicle based on brake force balance; according to the vehicle speed and the steering angle, a linear two-degree-of-freedom automobile model is loaded, an ideal yaw angular velocity is obtained, then yaw moment control is carried out through a sliding film controller, additional yaw moment is obtained, differential brake control is realized; if the target brake force of the wheel is greater than the maximum brake force, active steering control is carried out, and a weight factor for coordinating the differential brake control and the active steering control is set, the additional yaw moment is adjusted, and overall control with auxiliary steering is realized. Compared with the prior art, the application has the advantages of high system safety, fault-tolerant capability and stability.

Description

Technical Field

[0001] This invention relates to the field of automotive braking control technology, and in particular to a fault-tolerant control method and system for single-wheel failure of automobiles oriented towards distributed brake-by-wire. Background Technology

[0002] With the electrification and intelligentization trends in the automotive industry, drive-by-wire technology has become a key technology for realizing vehicle intelligence, and its application in vehicle control is becoming a new trend. Initially used in the aerospace field, drive-by-wire technology has, with its development, replaced almost all the mechanical mechanisms of traditional automobiles with electric actuators, enabling electronic control of vehicles. Currently, drive-by-wire chassis integration control and drive-by-wire vehicles are the main trends in future vehicle research.

[0003] In drive-by-wire technology, brake-by-wire systems utilize electronic control technology to replace the original complex and heavy hydraulic lines and related mechanical structures. They offer fast response and high precision, making them a hot research topic in the field of intelligent vehicles. Brake-by-wire converts braking intent into an electrical signal, which is then transmitted to the brake controller, and the brake motor is used to achieve vehicle braking. Compared to traditional braking systems, this significantly improves braking response speed and accuracy. However, brake-by-wire systems can have extremely serious consequences when malfunctions occur. Failure of some electronic control units in the system can directly lead to brake system failure or abnormality. When single-wheel or unbalanced braking force fails, not only will the total braking force of the vehicle decrease, but more seriously, it can lead to vehicle instability and rollover. Therefore, to ensure braking safety, fault diagnosis measures and fault-tolerant control to ensure vehicle safety in the event of brake failure are key technologies for future development.

[0004] The invention disclosed in application number CN201910930418.5 is a fault-tolerant control system and control method for automotive brake-by-wire failure, which can be applied to brake-by-wire hydraulic braking systems. When a brake-by-wire system malfunctions, the control unit stops the brake-by-wire system from working and controls a two-position three-way solenoid valve to connect the master cylinder and wheel cylinders of the hydraulic braking system, thereby achieving vehicle braking using the hydraulic braking system.

[0005] The invention with application number CN202110346836.7 discloses a brake-by-wire system based on digital twin and its dynamic optimization control method. It proposes a control method that combines a physical brake-by-wire system, a vehicle control system, and a digital twin braking system. The physical brake-by-wire system and the vehicle control system are connected through an on-board CAN bus. The vehicle control system and the digital twin braking system are connected through a high-speed communication link. The vehicle control system is connected to the vehicle control system through the high-speed communication link, realizing indirect communication and data interaction with the physical brake-by-wire system.

[0006] The invention with application number CN202121121661.1 discloses a vehicle brake-by-wire system based on a six-phase fault-tolerant motor. It proposes a vehicle brake-by-wire system including a brake detection device, a brake actuation device, an electronic control device, and a warning device. The system employs a six-phase fault-tolerant brake actuation motor, which can be controlled as two sets of three-phase motors. The six-phase fault-tolerant brake actuation motor has a through-type output shaft at both ends. The output shafts at both ends of the motor are respectively connected to cams and pistons on both sides, forming two sets of ABS pumps. The outputs of the two sets of three-phase motors are redundant. Under normal operating conditions of the brake-by-wire system, both sets of three-phase motors work together. If one motor fails, a warning is given and basic ABS functions are implemented.

[0007] The invention disclosed in application number CN202211157787.3 is a redundant safety control system based on brake-by-wire. It proposes an electric power-assisted braking mechanism and an electronic stability control system connected via at least two CAN buses, with the information transmitted through the two CAN buses serving as backups for each other. The electric power-assisted braking mechanism and the electronic stability control system are also connected to the vehicle controller, motor controller, and electronic parking system via one of the CAN buses. This enables fault risk identification and corresponding redundant safety control of the brake-by-wire system.

[0008] The invention disclosed in application number CN202211231810.9 is a dual-redundant electronic brake assist system and control method, consisting of a pedal module U1 and an assist module U2. The former includes a linkage pedal, a first simulated master cylinder, and a second simulated master cylinder. When the driver applies pedal force to the linkage pedal, the linkage pedal pushes the two simulated master cylinders to simultaneously establish hydraulic pressure. The first and second pedal sensing sensors send the pedal travel signal to the ECU controller. The assist module U2 is connected to U1 through a pipeline and is externally connected to the ESC. The ESC is connected to the brake, enabling mutual redundancy and providing multi-level backup capability.

[0009] The aforementioned prior art has the following drawbacks:

[0010] 1. Currently, most vehicle brake-by-wire systems are EHB systems, which do not completely eliminate the hydraulic structure. Therefore, hydraulic systems are often used for redundancy backup, and they are not completely brake-by-wire systems.

[0011] 2. Currently, most solutions to improve the safety of line-controlled braking involve adding redundant devices. While this approach can improve system reliability, it significantly increases system manufacturing costs.

[0012] 3. Currently, the general solution for handling faults in brake-by-wire systems is to directly shut down or switch to redundant backup devices, and the same control scheme is used for different types of faults. Summary of the Invention

[0013] The purpose of this invention is to overcome the shortcomings of the existing technology, which is not a complete brake-by-wire system and uses the same control scheme for different types of faults, and to provide a fault-tolerant control method and system for single-wheel failure of automobiles oriented towards distributed brake-by-wire.

[0014] The objective of this invention can be achieved through the following technical solutions:

[0015] A fault-tolerant control method for single-wheel failure in a vehicle oriented towards distributed drive-by-wire braking includes the following steps:

[0016] Obtain the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, obtain fault factors that represent the fault type and fault degree, respectively, and thus obtain the corresponding fault code;

[0017] Based on the fault code, a corresponding fault control strategy is adopted, and the braking force of each wheel of the vehicle is reconstructed based on the braking force balance to perform preliminary braking control for single wheel failure.

[0018] Based on the vehicle speed and steering angle in the state signal, a linear two-degree-of-freedom vehicle model based on lateral force and yaw moment is loaded to obtain the ideal yaw rate; based on the ideal yaw rate and the actual yaw rate, the yaw moment is controlled by a diaphragm controller to obtain an additional yaw moment; based on the faulty wheel and the corresponding fault factor, the additional yaw moment is distributed to the remaining wheels of the vehicle for differential braking control.

[0019] Based on the braking force and additional yaw moment of each wheel, it is determined whether the target braking force of each wheel is greater than the maximum braking force. If so, active steering control is performed. Based on the vehicle geometry and tire lateral slip characteristics, the additional steering angle is calculated based on the additional yaw moment. Weighting factors for coordinating differential braking control and active steering control are set to adjust the additional yaw moment and additional steering angle, thereby achieving overall control with the introduction of assisted steering.

[0020] Furthermore, the fault factor includes fault factor λ. 1_i and failure factor λ 2_i The fault factor λ 1_i The fault factor λ is used to represent the fault type of wheel i. 1_i The assignment expression is:

[0021]

[0022] The fault factor λ 2_i The fault factor λ is used to represent the degree of fault of wheel i. 2_i The assignment expression is:

[0023]

[0024] In the formula, i = FL / FR / RL / RR represent the front axle left wheel, front axle right wheel, rear axle left wheel, and rear axle right wheel, respectively, and F xb_i F is the actual braking force of wheel i. exb_i Let i be the desired braking force for wheel i.

[0025] Furthermore, if the left front axle wheel is the faulty wheel, the expression for redistributing the braking force to each wheel of the vehicle based on braking force balance includes:

[0026]

[0027] In the formula, F dxb_FL The braking force distributed to the left front wheel, F exb_f λ is the desired braking force for the front axle. 1_FL For the fault type of the front axle left wheel, λ 2_FL F represents the severity of the front axle left wheel failure. dxb_FR The braking force distributed to the right wheel of the front axle, F exb_r For the desired braking force of the rear axle, F dxb_RL The braking force distributed to the left rear wheel, F dxb_RR Distribute the braking force to the right wheel of the rear axle.

[0028] Furthermore, the expression for the differential equation of motion of the linear two-degree-of-freedom car model based on lateral force and yaw moment is as follows:

[0029]

[0030] In the formula, For the centroid sideslip angle gain, For the yaw rate gain, C f For the front axle lateral stiffness, C r V is the rear axle lateral stiffness, M is the vehicle mass, and V is the total mass. x L is the longitudinal vehicle speed, β is the sideslip angle, and L is the centroid. a L is the distance from the front axle to the center of gravity. b I is the distance from the rear axle to the center of gravity, ω is the yaw rate, δ is the front wheel steering angle, and I z Let ΔM be the moment of inertia about the z-axis. b To add yaw moment;

[0031] Substituting both the sideslip angle and the yaw rate gain of 0 into the aforementioned differential equation of motion, the expression for calculating the ideal yaw rate is obtained as follows:

[0032]

[0033]

[0034] In the formula, ω exp Where yaw rate is the ideal yaw rate, K is the stability factor, and L is the distance from the front axle to the rear axle.

[0035] Furthermore, the process of controlling the yaw moment through the sliding diaphragm controller specifically includes:

[0036] The difference between the ideal yaw rate and the actual yaw rate is set as the sliding surface of the sliding diaphragm controller. The calculation expression for the additional yaw moment obtained by the sliding diaphragm controller is as follows:

[0037]

[0038] In the formula, Let ω be the ideal yaw rate after differentiation. exp Let ξ be the ideal yaw rate, and ξ be the sliding diaphragm control parameter.

[0039] During the control process of the sliding diaphragm controller, there are constraints on the ideal yaw rate and the ideal centroid sideslip angle, including:

[0040]

[0041] In the formula, ω max β is the maximum value of the ideal yaw rate. max This represents the maximum value of the sideslip angle of the ideal centroid.

[0042] Furthermore, the specific process of distributing the additional yaw moment to the remaining wheels of the vehicle includes:

[0043] If the left wheel on the front axle is the faulty wheel, and λ 1_FL ·λ 2_FL When < 0, the calculation expression for distributing the additional yaw moment to the remaining wheels of the vehicle is:

[0044]

[0045] In the formula, ΔF x_FR ' is the distributed longitudinal force on the right front axle wheel, ΔF x_FR To achieve the longitudinal force of the right front wheel with additional yaw moment, ΔM b To add yaw moment, L b L is the distance from the rear axle to the center of gravity, B is the track width between the left and right wheels, and L is the distance from the rear axle to the center of gravity. a δ is the distance from the front axle to the center of gravity, δ is the front wheel steering angle, and ΔF is the distance from the front axle to the center of gravity. x_RL ' represents the distributed longitudinal force on the left rear axle wheel, ΔF x_RL To achieve the longitudinal force of the rear axle left wheel with additional yaw moment, ΔF x_FL To achieve the longitudinal force of the front axle left wheel with additional yaw moment, ΔF x_RR' represents the distributed longitudinal force on the right rear wheel of the rear axle, ΔF x_RR To achieve the additional yaw moment, the longitudinal force of the right rear wheel of the rear axle is applied;

[0046] If the left wheel on the front axle is the faulty wheel, and 2 > λ 1_FL ·λ 2_FL When the value is greater than 0, the calculation expression for distributing the additional yaw moment to the remaining wheels of the vehicle is as follows:

[0047]

[0048] Furthermore, if the left front axle wheel is the faulty wheel, the calculation expression for the weighting factor of the coordinated differential braking control and active steering control is as follows:

[0049]

[0050] In the formula, σ is the weighting factor, and F xb_obj_i For the target braking force of wheel i, F xb_max_i F is the maximum braking force of wheel i. xb_i FR / RL / RR represent the actual braking force of wheel i, and FR / RL / RR represent the right wheel of the front axle, the left wheel of the rear axle, and the right wheel of the rear axle, respectively.

[0051] The additional yaw moment ΔM b The control method has been adjusted to:

[0052]

[0053] In the formula, ΔM b_b ΔM is the yaw moment generated by differential braking. b_s The additional steering angle is generated by adjusting the front wheel steering angle, and its calculation expression is as follows:

[0054]

[0055] In the formula, L a C is the distance from the rear axle to the center of mass. f This refers to the front axle lateral stiffness.

[0056] Furthermore, when the target braking force of the wheel is greater than the maximum braking force, the calculation and distribution expression for the additional yaw moment is as follows:

[0057]

[0058] In the formula, ΔF xc_FR To assist in steering, the longitudinal force on the right front wheel is ΔF. xc_RL To assist in steering, the longitudinal force on the left rear wheel is ΔF. xc_RR To assist in steering, L bB is the distance from the rear axle to the center of gravity, δ is the track width between the left and right wheels, k is the front wheel steering angle, and δ is the distance from the rear axle to the center of gravity. s The steering ratio between the steering wheel angle and the front wheel angle; δ s This refers to the steering wheel angle.

[0059] This invention also provides a fault-tolerant control system for single-wheel failure in automobiles with distributed brake-by-wire, comprising the following steps:

[0060] The system failure identification module is used to acquire the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, it obtains fault factors that represent the fault type and fault degree, respectively, thereby obtaining the corresponding fault code;

[0061] The basic failure control module is used to adopt corresponding failure control strategies based on the fault code, and to reconstruct the braking force of each wheel of the vehicle based on the braking force balance, so as to perform preliminary braking control for single wheel failure of the vehicle.

[0062] The synovial differential control module is used to load the vehicle speed and steering angle from the state signal into a linear two-degree-of-freedom vehicle model based on lateral force and yaw moment to obtain the ideal yaw rate; based on the ideal yaw rate and the actual yaw rate, the synovial controller controls the yaw moment to obtain an additional yaw moment; based on the faulty wheel and the corresponding fault factor, the additional yaw moment is distributed to the remaining wheels of the vehicle for differential braking control.

[0063] The auxiliary steering control module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel. If so, active steering control is performed. Based on the vehicle geometry and tire lateral slip characteristics, the additional steering angle is calculated based on the additional yaw moment, and weighting factors for coordinating differential braking control and active steering control are set to adjust the additional yaw moment and additional steering angle, thereby realizing the overall control of introducing auxiliary steering.

[0064] Furthermore, the basic failure control module is a basic failure controller, which is used to adopt corresponding failure control strategies according to the fault code, and to reconstruct the braking force of each wheel of the vehicle based on the braking force balance, so as to perform preliminary braking control for single wheel failure of the vehicle.

[0065] The synovial differential control module includes a synovial controller and a differential braking controller.

[0066] The synovial controller is used to control the yaw torque by comparing the ideal yaw rate calculated from the linear two-degree-of-freedom car model with the actual yaw rate, thereby obtaining an additional yaw torque.

[0067] The differential brake controller is used to control the braking force based on the reconstructed braking force of the basic failure control module, and further distribute the additional yaw moment to the remaining wheels of the vehicle, and perform differential brake control based on the weighting factor fed back by the auxiliary steering control module.

[0068] The auxiliary steering control module includes an adhesion limit judgment module and an auxiliary steering controller.

[0069] The adhesion limit judgment module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel.

[0070] The auxiliary steering controller is used to perform active steering control when it is determined that the target braking force is greater than the maximum braking force. Based on the vehicle geometry and tire lateral slip characteristics, it calculates the additional steering angle based on the additional yaw moment, sets the weighting factor for coordinating differential braking control and active steering control, adjusts the additional steering angle, and outputs the steering angle control quantity.

[0071] Compared with the prior art, the present invention has the following advantages:

[0072] (1) The failure control scheme proposed in this invention can cover most EMB system fault types. By setting fault factors and fault codes, different control strategies can be adopted for different faults.

[0073] By reconfiguring braking force using wheels that can brake normally, vehicle stability and braking control are achieved without the need for redundant mechanisms. The subsequent fault-tolerant controller design, which uses the vehicle yaw moment as the control target through a diaphragm controller, further improves vehicle stability.

[0074] When braking force is insufficient, auxiliary steering control is introduced. In most cases, vehicle stability control is achieved through direct yaw control. Steering is added when braking force is insufficient to ensure vehicle stability.

[0075] (2) Currently, most vehicle brake-by-wire systems are EHB systems, which do not completely eliminate the hydraulic structure. Therefore, they often use hydraulic redundancy backup and are not truly brake-by-wire systems. This invention is based on a four-wheel independent EMB brake-by-wire system with fault-tolerant control design. It eliminates all hydraulic lines, uses an electric motor as the power source, and uses electrical signals to replace the mechanical transmission mechanism to transmit braking information. This can effectively reduce the size and installation flexibility of the braking system, while significantly improving the control sensitivity and accuracy of the braking system.

[0076] (3) Currently, most solutions to improve the safety of brake-by-wire systems involve adding redundant devices. While this improves system reliability, it significantly increases system manufacturing costs. This invention, however, coordinates and controls the braking force of all four wheels based on the existing four-wheel braking module's capabilities, maximizing the utilization of the original system's braking capacity.

[0077] (4) Currently, the general approach to handling faults in brake-by-wire systems is to directly shut down or switch to redundant backup devices, applying the same control scheme to different types of faults. However, this invention employs different control schemes for different types of faults. A fault diagnosis module confirms the fault type and then selects the corresponding fault-tolerant control scheme. This strategy effectively addresses the impact of different faults on the vehicle braking system, thereby achieving superior control performance. Attached Figure Description

[0078] Figure 1 This is a flowchart illustrating a single-wheel failure-tolerant control method for distributed brake-by-wire vehicles provided in an embodiment of the present invention.

[0079] Figure 2 This is a schematic diagram of a vehicle architecture for an EMB system provided in an embodiment of the present invention;

[0080] Figure 3 This is a schematic diagram of a system failure control process provided in an embodiment of the present invention;

[0081] Figure 4 This is a schematic diagram of a linear two-degree-of-freedom model provided in an embodiment of the present invention;

[0082] Figure 5 This is a schematic diagram illustrating the principle of a single-wheel failure-tolerant control method for distributed brake-by-wire vehicles provided in this embodiment of the invention. Detailed Implementation

[0083] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0084] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0085] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0086] In the description of this invention, the relevant terms are explained as follows:

[0087] EMB: Electronic Mechanical Brake;

[0088] EHB: Electronic Hydraulic Brake;

[0089] HARA: Hazard Analysis and Risk Assessment;

[0090] ASIL: Automotive Safety Integrity Level, for hybrid vehicles;

[0091] PID stands for Proportional-Integral-Derivative.

[0092] Example 1

[0093] This invention addresses the new demands of intelligent driving environments by establishing an active fault-tolerant control method for a distributed brake-by-wire system based on a four-wheel independent electromechanical braking (EMB) system. This control strategy mainly comprises two parts: system failure identification and failure control. By identifying faults and reconstructing the system, it further improves system safety and fault tolerance. The desired braking intensity and desired yaw rate of the vehicle are used as system control targets to reconstruct the vehicle's braking force. When the braking force is insufficient, auxiliary steering control is added to ensure braking performance and stability during vehicle malfunctions.

[0094] Specifically, such as Figure 1 As shown, it includes the following steps:

[0095] System failure identification step S1: Obtain the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, obtain the fault factors that represent the fault type and fault degree respectively, thereby obtaining the corresponding fault code;

[0096] Basic failure control step S2: Based on the fault code, adopt the corresponding fault control strategy, reconstruct the braking force of each wheel of the vehicle based on the braking force balance, and perform preliminary braking control for single wheel failure of the vehicle.

[0097] S3 of the slick membrane differential control: Based on the vehicle speed and steering angle in the state signal, load the linear two-degree-of-freedom vehicle model based on lateral force and yaw moment to obtain the ideal yaw rate; Based on the ideal yaw rate and the actual yaw rate, control the yaw moment through the slick membrane controller to obtain the additional yaw moment; Based on the wheel that has failed and the corresponding fault factor, distribute the additional yaw moment to the remaining wheels of the vehicle to perform differential braking control;

[0098] Assisted steering control step S4: Based on the braking force and additional yaw moment of each wheel, determine whether the target braking force of each wheel is greater than the maximum braking force. If so, perform active steering control. Based on the vehicle geometry and tire yaw characteristics, calculate the additional steering angle based on the additional yaw moment, and set the weighting factor for coordinating differential braking control and active steering control. Adjust the additional yaw moment to achieve overall control by introducing assisted steering.

[0099] In the above steps, the basic failure control steps can meet the basic braking strength and braking balance requirements of the vehicle; the slip differential control steps, which use the vehicle yaw moment as the control target for subsequent fault-tolerant controller design, can further improve vehicle stability; and by introducing auxiliary steering control steps, vehicle braking and stability control can be achieved by using differential braking and steering coordination control when the required braking force exceeds the adhesion limit.

[0100] The following is a detailed description.

[0101] I. Controlled Objects

[0102] The object of this invention is the EMB (Electronic Mechanical Braking) system installed in intelligent vehicles. Compared with traditional braking systems, this EMB system can achieve interaction with driver assistance functions and independent braking of four wheels, which can improve the applicability of the system in intelligent vehicles and the vehicle's braking performance, and improve vehicle stability and controllability. Specifically, it consists of six main parts: an electronic pedal simulator, a sensor group, a system control module, an actuator module, a communication network, and a power supply system. Its basic architecture is as follows: Figure 2 As shown.

[0103] II. Overall Overview

[0104] This invention focuses on identifying fault types through failure identification, deriving system fault factors and fault codes, and implementing corresponding failure control based on these results. This primarily includes vehicle braking force reconfiguration and auxiliary steering control when braking force is insufficient. The invention uses the brake-by-wire system status signal as system input, which is processed by the failure identification module to derive system fault factors and fault codes. This reflects the type and severity of the system fault and determines the corresponding failure control strategy. The failure control module consists of four parts: a braking force symmetry controller, a diaphragm controller, a differential brake controller, and an auxiliary steering controller. Different control strategies are adopted according to the different faults occurring. A detailed control flowchart is shown below. Figure 3 As shown.

[0105] III. Detailed Description of Each Step

[0106] 3.1 System Failure Identification Steps

[0107] 3.1.1 Failure Identification Module

[0108] Since this system uses independent braking for four wheels, it is necessary to analyze the actual braking state of each wheel. This invention introduces a fault factor λ based on the relationship between the actual detected wheel braking force and the target braking force. 1_i and λ 2_i The fault codes characterize the wheel braking status and are used to determine system failure. The design rules for the two fault factors are as follows:

[0109] λ 1_i The fault types are categorized into three types and one normal mode:

[0110]

[0111] λ 2_i The degree of failure is represented by the following formula:

[0112]

[0113] In the formula, i = FL / FR / RL / RR represents different wheels; F xb_i Indicates the actual braking force of the wheel; F exb_i This indicates the desired braking force of the wheel.

[0114] In summary, based on the product of the two fault factors, the fault mode and actual braking torque can be basically determined, and a fault code E can be assigned to different faults. i This facilitates the adoption of corresponding fault control strategies.

[0115] (1)λ 1_i ·λ 2_i When = 0, fault code E i =0 indicates no fault;

[0116] (2)λ 1_i ·λ 2_i When <0, fault code E i =1 indicates that a loss of braking force has occurred, including brake failure and partial loss of braking force, i.e., -1≤λ 1_i ·λ 2_i <0;

[0117] (3) 0 < λ 1_i ·λ 2_i When <2, fault code E i =2, meaning the actual braking force is greater than the expected braking force, and That is, F xb_i <3F exb_i When the actual braking torque exceeds the expected braking torque by 3 times or more, due to the large difference between it and the expected braking torque, it may lead to a severe imbalance of braking torque. Therefore, it should be handled as a sudden braking fault.

[0118] (4)2≤λ 1_i ·λ 2_i At that time, fault code E i =3 indicates that unexpected braking has occurred or the actual braking force is not less than three times the expected braking force.

[0119] Fault factors are the quantitative processing of detection results. By judging the product of two fault factors, the corresponding fault code value can be obtained, thereby analyzing the specific fault type and severity of the system. Determining the specific fault in the system is the foundation for selecting the appropriate failure control strategy and is the basis for subsequent fault tolerance mechanism design.

[0120] 3.1.2 Failure Control Module

[0121] Since this invention is based on a four-wheel independent braking architecture, taking a left front wheel braking failure as an example, it utilizes the remaining three wheels to design a vehicle braking force reconstruction algorithm to meet the vehicle's braking and stability requirements. For different types of faults, i.e., fault code E... FL When the value is {1,2,3}, formulate the corresponding system control strategy:

[0122] (1)E FL When the value is 1, it indicates that the braking force of the left front wheel has decreased. At this time, the braking force will decrease and become unbalanced. Depending on the actual working conditions, the braking force of the other three wheels will be reconfigured.

[0123] (2)E FL When the value is 2, the braking force of the other three wheels will be reconfigured to ensure the vehicle's stability requirements;

[0124] (3)E FLWhen the value is 3, it indicates that unexpected braking or a significant increase in braking force has occurred. The strategy at this time is to disconnect the power to the brake actuator of the faulty wheel (left front wheel), causing it to enter a state of loss of braking force, and then execute fault code E. FL Three rounds of reconstruction operations when =1.

[0125] 3.2 Basic Failure Control Steps

[0126] 3.2.1 Basic Braking Force Failure Control Strategy

[0127] When the left front wheel experiences a loss of braking force or an unexpected increase in braking force within a certain range, the difference between the expected total braking force and the actual total braking force is:

[0128]

[0129] To meet both braking strength requirements and vehicle stability, the braking force of the remaining three wheels is initially reconfigured based on braking force balance. The specific allocation rules are as follows:

[0130]

[0131] According to the above allocation rule, the actual total braking force can be the same as the desired braking force, thus meeting the vehicle's desired braking requirements. Furthermore, this strategy can simultaneously ensure that the braking forces of the front and rear axle wheels and the left and right side wheels are equal, satisfying the braking force balance requirement.

[0132]

[0133] In the formula F xb_ls and F xb_rs These represent the actual braking force of the left and right wheels, respectively.

[0134] When |λ 1_FL ·λ 2_FL When the braking force is relatively small, it indicates that the actual braking force is close to the desired braking force. The basic braking force failure control strategy described above can meet the vehicle's basic braking strength and braking balance requirements. However, when the lost or increased braking force is too large, or when the vertical load of the four wheels is transferred, the vehicle will generate a severe yaw moment due to the imbalance of braking force at the moment of failure. At this time, the vehicle is prone to instability and deviation. Therefore, after performing symmetrical braking force basic adjustment, to improve vehicle stability and reduce the vehicle yaw moment, a subsequent fault-tolerant controller is designed with the vehicle yaw moment as the control target.

[0135] 3.3, Slippery Diaphragm Differential Control Steps

[0136] 3.3.1 Calculation of Additional Yaw Moment

[0137] The relevant parameters of vehicle yaw rate include longitudinal vehicle speed, steering wheel input angle and its rate of change, vehicle yaw rate deviation, and vehicle center of gravity sideslip angle deviation. Since the main purpose of this invention is to adjust the vehicle yaw moment for stability control, for ease of research, the additional yaw moment is studied in a linear two-degree-of-freedom model, such as... Figure 4 As shown.

[0138] After introducing the additional yaw moment, the formulas for calculating the lateral force and yaw moment in the two degrees of freedom are as follows:

[0139]

[0140] The sideslip angle in the model is:

[0141]

[0142] Lateral force is the product of the slip angle and the tire's lateral stiffness, that is:

[0143]

[0144] In the formula, the lateral stiffness C f and C r Derived from the Magic Tire Formula, this value is obtained by fitting the lateral stiffness curves calculated under different vertical loads. The lateral stiffness varies with different vertical loads.

[0145] By combining the equations, we can obtain:

[0146]

[0147] By processing the above equation, we can obtain the differential equation of motion for a linear two-degree-of-freedom car:

[0148]

[0149] When the vehicle is in a steady state, the sideslip angle and yaw rate gain are both 0, that is... Substituting into the above equation, we can obtain the ideal yaw rate and the sideslip angle of the center of mass:

[0150]

[0151] In the above formula, K is the stability factor, which characterizes the steady-state response of the vehicle, and is calculated as follows:

[0152]

[0153] The parameters in the above formulas correspond to those shown in Table 1.

[0154] Table 1 Parameters of Vehicle Dynamics Model

[0155] Parameter name symbol unit Front axle lateral force <![CDATA[F f ]]> N Rear axle lateral force <![CDATA[F r ]]> N Front axle slip angle <![CDATA[α f ]]> rad Rear axle slip angle <![CDATA[α r ]]> rad Speed V m / s longitudinal speed <![CDATA[V x ]]> m / s Lateral speed <![CDATA[V y ]]> m / s yaw rate ω rad / s Distance from front axle to center of gravity <![CDATA[L a ]]> m Rear axle to center of gravity distance <![CDATA[L b ]]> m distance from front axle to rear axle L m Front axle lateral stiffness <![CDATA[C f ]]> N / rad Rear axle lateral stiffness <![CDATA[C r ]]> N / rad Moment of inertia about the z-axis <![CDATA[I z ]]> <![CDATA[kg*m 2 ]]> Front wheel steering angle δ rad centroid side slip angle β rad Overall vehicle quality M kg

[0156] Currently, the synovial variable structure control algorithm is widely used in yaw moment control due to its good robustness and accuracy. This paper uses this control algorithm to track the ideal yaw moment.

[0157] The sliding membrane controller needs to be configured with a sliding membrane surface because it needs to track the ideal yaw rate. In this invention, the sliding membrane surface is set to the difference between the ideal yaw rate and the actual yaw rate.

[0158] s=ω-ω exp

[0159] Differentiating the above equation, we get:

[0160]

[0161] The following are listed:

[0162]

[0163] make Substituting into the above formula, the additional lateral sway can be calculated:

[0164]

[0165] In the formula, ξ is the synovial control parameter.

[0166] Because the lateral forces acting on the tires are limited by the road surface adhesion coefficient, the ideal yaw rate and sideslip angle of the vehicle are subject to the following constraints:

[0167]

[0168] That is:

[0169]

[0170] 3.3.2 Differential Braking Control Strategy

[0171] By utilizing the reconfiguration of three-wheel braking force to achieve differential braking, the vehicle's yaw moment can be effectively controlled. The longitudinal force of the tires can generate a yaw moment around the z-axis of the vehicle, thereby achieving additional yaw.

[0172] Based on kinematic relationships, we can obtain:

[0173]

[0174] In the above formula, B is the wheelbase of the left and right wheels, and ΔF x_total To achieve the total longitudinal force of the additional yaw moment, when the additional yaw moment is distributed to the four wheels, we have:

[0175]

[0176] When a left front wheel malfunctions, precise braking control of the left front wheel cannot be achieved, necessitating three-wheel differential braking:

[0177]

[0178] To improve braking efficiency, the additional longitudinal force on the left front wheel is distributed to the other three wheels according to different fault conditions:

[0179] (1) When λ 1_FL ·λ 2_FL <0, meaning when the left front wheel loses braking force:

[0180] After a loss of braking force in the left front wheel, following the aforementioned symmetrical braking force distribution adjustment, the braking force of the right front and left rear wheels increases, while the braking force of the right rear wheel decreases. To improve the utilization of ground grip while ensuring good handling, the compensating braking force from the left front wheel is distributed to the rear wheels:

[0181]

[0182] (2) When 2 > λ 1_FL ·λ 2_FL >0, meaning the braking force on the left front wheel is too high:

[0183] After symmetrical braking force control, the braking force of the right rear wheel increases, while the braking forces of the right front wheel and left rear wheel decrease. At this point, the compensating braking forces of the right front wheel and left rear wheel are adjusted to set the three-wheel braking force as follows:

[0184]

[0185] When performing three-wheel differential braking, the calculated target braking force can achieve the desired additional yaw moment. However, in certain extreme scenarios, such as icy or snowy roads or emergency braking, the target braking force may exceed the road adhesion limit. In such scenarios, the actual braking force deviates from the target braking force, and ideal yaw moment control cannot be achieved. Therefore, it is necessary to assess these scenarios and propose solutions.

[0186] 3.4 Assisted Steering Control Procedure

[0187] 3.4.1 Wheel Adhesion Limit Constraints

[0188] Three-wheel differential braking control relies on the longitudinal force generated by the friction between the tires and the ground. Since the friction force has a limit, the additional yaw provided by differential braking is constrained by the limit of the friction force.

[0189] The road surface adhesion coefficient μ limits the maximum frictional force between the vehicle and the road surface; therefore, the forces acting on the wheels must meet the following constraints:

[0190] Fxb_i 2 +F y_i 2 ≤(μ·F z_i ) 2

[0191] In braking scenarios, the lateral force on the tire is much smaller than the longitudinal force, so the lateral force in the above equation can be ignored, resulting in the simplified wheel longitudinal force constraint equation:

[0192] |F xb_i |≤μ·F z_i =|F xb_max_i |

[0193] In the above formula, F xb_i F represents the limit value of wheel braking force, μ is the coefficient of friction, and F is the ground adhesion coefficient. z_i The vertical load on the wheel has been explained in detail in Chapter 3.

[0194] When the target braking force obtained by differential braking is not greater than the maximum braking force, the target braking force is:

[0195] F xb_obj_i =F xb_i +ΔF x_i ′,|F xb_obj_i |≤|F xb_max_i |

[0196] When |F xb_obj_i |>|F xb_max_i At this time, differential braking alone is no longer sufficient to meet the stability control requirements, and a steering system needs to be introduced to ensure vehicle stability.

[0197] 3.4.2 Design of Auxiliary Steering Controller

[0198] When the system determines that the braking force of the wheels is approaching the limit of ground adhesion, it will actively control the steering to calculate and prevent the vehicle's yaw moment from oscillating violently.

[0199] Based on the controller design described above, some additional lateral torque has been achieved through differential braking. If steering control is added, coordinated control between differential braking and active steering is required. A weighting factor σ is introduced to characterize the control weights of the two control methods. Its value is related to the actual braking force and the target braking force, and its calculation formula is:

[0200]

[0201] Combining the above formula, the overall yaw rate control method is as follows:

[0202]

[0203] In the formula M b_bΔM represents the yaw moment generated by differential braking. b_s This is achieved by adjusting the yaw moment generated by the front wheel steering angle. The relationship between this yaw moment and the additional steering angle can be derived from the vehicle geometry and tire lateral slip characteristics. The additional steering angle is:

[0204]

[0205] In the formula C f The front axle lateral stiffness has been derived from the tire model described earlier.

[0206] In summary, when the target braking force is greater than the maximum braking force that can be provided, the additional yaw moment is achieved as follows:

[0207]

[0208] In the formula, δ is the actual front wheel steering angle; k s The steering ratio between the steering wheel angle and the front wheel angle; δ s This refers to the steering wheel angle.

[0209] IV. Holistic Principle

[0210] The overall principle block diagram of the present invention is as follows: Figure 5 As shown, upon receiving a braking signal, the system first distributes braking torque to all four wheels according to a four-wheel distribution strategy. If a system malfunction occurs, failure control is activated, and basic braking force reconfiguration control is performed based on the failure judgment result. During this period, if the required braking force exceeds the adhesion limit, auxiliary steering control is introduced, utilizing differential braking and steering coordination control to achieve vehicle braking and stability control.

[0211] The above is an introduction to the method embodiments. The following system embodiments will further illustrate the solution of the present invention.

[0212] This embodiment also provides a fault-tolerant control system for single-wheel failure in a vehicle oriented towards distributed brake-by-wire, comprising the following steps:

[0213] The system failure identification module is used to acquire the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, it obtains fault factors that represent the fault type and fault degree, respectively, thereby obtaining the corresponding fault code;

[0214] The basic failure control module is used to adopt corresponding failure control strategies based on fault codes, and to reconstruct the braking force of each wheel of the vehicle based on braking force balance, so as to perform preliminary braking control for single wheel failure of the car.

[0215] The slick membrane differential control module is used to load the vehicle speed and steering angle from the state signal into a linear two-degree-of-freedom vehicle model based on lateral force and yaw moment to obtain the ideal yaw rate; based on the ideal yaw rate and the actual yaw rate, the slick membrane controller controls the yaw moment to obtain the additional yaw moment; based on the wheel that has failed and the corresponding failure factor, the additional yaw moment is distributed to the remaining wheels of the vehicle for differential braking control.

[0216] The auxiliary steering control module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel. If so, active steering control is performed. Based on the vehicle geometry and tire lateral slip characteristics, the additional steering angle is calculated based on the additional yaw moment, and weighting factors for coordinating differential braking control and active steering control are set to adjust the additional yaw moment and additional steering angle, thereby realizing the overall control of introducing auxiliary steering.

[0217] Optionally, the basic failure control module is a basic failure controller, which is used to adopt corresponding failure control strategies based on the fault code, reconstruct the braking force of each wheel of the vehicle based on the braking force balance, and perform preliminary braking control for single wheel failure of the vehicle.

[0218] The slicker differential control module includes a slicker controller and a differential braking controller.

[0219] The slick membrane controller is used to control the yaw moment by comparing the ideal yaw rate calculated from the linear two-degree-of-freedom car model with the actual yaw rate, thereby obtaining an additional yaw moment.

[0220] The differential brake controller is used to control the braking force based on the reconstructed braking force of the basic failure control module, and further distribute the additional yaw moment to the remaining wheels of the vehicle, and perform differential braking control based on the weighting factor fed back by the auxiliary steering control module.

[0221] The assisted steering control module includes an adhesion limit determination module and an assisted steering controller.

[0222] The adhesion limit judgment module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel.

[0223] The auxiliary steering controller is used to perform active steering control when it is determined that the target braking force is greater than the maximum braking force. Based on the vehicle geometry and tire lateral slip characteristics, it calculates the additional steering angle based on the additional yaw moment, sets the weighting factor to coordinate differential braking control and active steering control, adjusts the additional steering angle, and outputs the steering angle control quantity.

[0224] It should be noted that the specific content and beneficial effects of the system in this application can be found in the above method embodiments, and will not be repeated here.

[0225] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A fault-tolerant control method for single-wheel failure in a vehicle oriented towards distributed drive-by-wire braking, characterized in that, Includes the following steps: Obtain the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, obtain fault factors that represent the fault type and fault degree, respectively, and thus obtain the corresponding fault code; Based on the fault code, a corresponding fault control strategy is adopted, and the braking force of each wheel of the vehicle is reconstructed based on the braking force balance to perform preliminary braking control for single wheel failure. Based on the vehicle speed and steering angle in the state signal, a linear two-degree-of-freedom vehicle model based on lateral force and yaw moment is loaded to obtain the ideal yaw rate; based on the ideal yaw rate and the actual yaw rate, the yaw moment is controlled by a diaphragm controller to obtain an additional yaw moment; based on the faulty wheel and the corresponding fault factor, the additional yaw moment is distributed to the remaining wheels of the vehicle for differential braking control. Based on the braking force and additional yaw moment of each wheel, it is determined whether the target braking force of each wheel is greater than the maximum braking force. If so, active steering control is performed. Based on the vehicle geometry and tire lateral slip characteristics, the additional steering angle is calculated based on the additional yaw moment. Weighting factors for coordinating differential braking control and active steering control are set to adjust the additional yaw moment and additional steering angle, thereby achieving overall control with the introduction of assisted steering. The fault factors include fault factors and failure factors The fault factor Used to represent wheels The fault type, the fault factor The assignment expression is: The fault factor Used to represent wheels The degree of failure, the failure factor The assignment expression is: In the formula, These represent the left front axle wheel, the right front axle wheel, the left rear axle wheel, and the right rear axle wheel, respectively. For wheels The actual braking force, For wheels The expected braking force; If the left front axle wheel is the faulty wheel, the expression for redistributing the braking force to each wheel of the vehicle based on braking force balance includes: In the formula, Distribute the braking force to the left front wheel. The desired braking force for the front axle, The fault type is for the left front axle wheel. The severity of the damage to the left front axle wheel. Distribute the braking force to the right front wheel. The desired braking force for the rear axle, Distribute the braking force to the left rear wheel. Distribute the braking force to the right rear wheel; The specific process of distributing the additional yaw moment to the remaining wheels of the vehicle includes: If the left wheel on the front axle is the faulty wheel, and The calculation expression for distributing the additional yaw moment to the remaining wheels of the vehicle is as follows: In the formula, The distributed longitudinal force on the right front axle wheel, To achieve the additional yaw moment on the front axle right wheel longitudinal force, To add yaw moment, This is the distance from the rear axle to the center of gravity. The track width between the left and right wheels. This is the distance from the front axle to the center of gravity. For the front wheel steering angle, For the distributed longitudinal force on the left rear axle wheel, To achieve the longitudinal force of the rear axle left wheel with additional yaw moment, To achieve the additional yaw moment on the longitudinal force of the front axle left wheel, The distributed longitudinal force on the right rear axle wheel, To achieve the additional yaw moment, the longitudinal force of the right rear wheel of the rear axle is applied; If the left wheel on the front axle is the faulty wheel, and The calculation expression for distributing the additional yaw moment to the remaining wheels of the vehicle is as follows: If the left front axle wheel is the faulty wheel, the calculation expression for the weighting factor of the coordinated differential braking control and active steering control is as follows: In the formula, As a weighting factor, For wheels The target braking force, For wheels The maximum braking force, For wheels The actual braking force, These are the right front axle wheel, the left rear axle wheel, and the right rear axle wheel, respectively. The additional yaw moment The control method has been adjusted to: In the formula, The yaw moment is generated by differential braking. The additional steering angle is generated by adjusting the front wheel steering angle, and its calculation expression is as follows: In the formula, This is the distance from the rear axle to the center of gravity. For front axle lateral stiffness; When the target braking force of the wheel is greater than the maximum braking force, the calculation and distribution expression for the additional yaw moment is as follows: In the formula, To assist in steering, the longitudinal force on the right front wheel, To assist in the longitudinal force of the left rear wheel after steering, To assist in the longitudinal force on the right rear wheel after steering, This is the distance from the rear axle to the center of gravity. The track width between the left and right wheels. For the front wheel steering angle, The steering ratio is the ratio between the steering wheel angle and the front wheel angle. This refers to the steering wheel angle.

2. The method for fault-tolerant single-wheel failure control of a vehicle oriented towards distributed drive-by-wire braking according to claim 1, characterized in that, The expression for the differential equation of motion of the linear two-degree-of-freedom car model based on lateral force and yaw moment is as follows: In the formula, For the centroid sideslip angle gain, For yaw rate gain, For front axle lateral stiffness, For rear axle lateral stiffness, For the overall vehicle quality, For longitudinal vehicle speed, The sideslip angle is the angle of the centroid. This is the distance from the front axle to the center of gravity. This is the distance from the rear axle to the center of gravity. The yaw rate is angular velocity. For the front wheel steering angle, Let z be the moment of inertia about the z-axis. To add yaw moment; Substituting both the sideslip angle and the yaw rate gain of 0 into the aforementioned differential equation of motion, the expression for calculating the ideal yaw rate is obtained as follows: In the formula, For the ideal yaw rate, As a stability factor, This is the distance from the front axle to the rear axle.

3. The method for fault-tolerant control of single-wheel failure in a vehicle oriented towards distributed drive-by-wire braking according to claim 2, characterized in that, The process of controlling yaw moment using a sliding diaphragm controller specifically includes: The difference between the ideal yaw rate and the actual yaw rate is set as the sliding surface of the sliding diaphragm controller. The calculation expression for the additional yaw moment obtained by the sliding diaphragm controller is as follows: In the formula, The ideal yaw rate after differentiation is given. For the ideal yaw rate, These are the synovial control parameters; During the control process of the sliding diaphragm controller, there are constraints on the ideal yaw rate and the ideal centroid sideslip angle, including: In the formula, The maximum value of the ideal yaw rate. This represents the maximum value of the sideslip angle of the ideal centroid.

4. A fault-tolerant control system for single-wheel failure of a vehicle under distributed brake-by-wire, implementing the fault-tolerant control method for single-wheel failure of a vehicle under distributed brake-by-wire as described in any one of claims 1-3, characterized in that, Includes the following steps: The system failure identification module is used to acquire the status signal of the vehicle's brake-by-wire system; based on the actual braking force and expected braking force of the wheels in the status signal, it obtains fault factors that represent the fault type and fault degree, respectively, thereby obtaining the corresponding fault code; The basic failure control module is used to adopt corresponding failure control strategies based on the fault code, and to reconstruct the braking force of each wheel of the vehicle based on the braking force balance, so as to perform preliminary braking control for single wheel failure of the vehicle. The synovial differential control module is used to load the vehicle speed and steering angle from the state signal into a linear two-degree-of-freedom vehicle model based on lateral force and yaw moment to obtain the ideal yaw rate; based on the ideal yaw rate and the actual yaw rate, the synovial controller controls the yaw moment to obtain an additional yaw moment; based on the faulty wheel and the corresponding fault factor, the additional yaw moment is distributed to the remaining wheels of the vehicle for differential braking control. The auxiliary steering control module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel. If so, active steering control is performed. Based on the vehicle geometry and tire lateral slip characteristics, the additional steering angle is calculated based on the additional yaw moment, and weighting factors for coordinating differential braking control and active steering control are set to adjust the additional yaw moment and additional steering angle, thereby realizing the overall control of introducing auxiliary steering.

5. The system according to claim 4, characterized in that, The basic failure control module is a basic failure controller. The basic failure controller is used to adopt corresponding failure control strategies according to the fault code, and to reconstruct the braking force of each wheel of the vehicle based on the braking force balance, so as to perform preliminary braking control for single wheel failure of the vehicle. The synovial differential control module includes a synovial controller and a differential braking controller. The synovial controller is used to control the yaw torque by comparing the ideal yaw rate calculated from the linear two-degree-of-freedom car model with the actual yaw rate, thereby obtaining an additional yaw torque. The differential brake controller is used to control the braking force based on the reconstructed braking force of the basic failure control module, and further distribute the additional yaw moment to the remaining wheels of the vehicle, and perform differential brake control based on the weighting factor fed back by the auxiliary steering control module. The auxiliary steering control module includes an adhesion limit judgment module and an auxiliary steering controller. The adhesion limit judgment module is used to determine whether the target braking force of each wheel is greater than the maximum braking force based on the braking force and additional yaw moment of each wheel. The auxiliary steering controller is used to perform active steering control when it is determined that the target braking force is greater than the maximum braking force. Based on the vehicle geometry and tire lateral slip characteristics, it calculates the additional steering angle based on the additional yaw moment, sets the weighting factor for coordinating differential braking control and active steering control, adjusts the additional steering angle, and outputs the steering angle control quantity.

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