A method for coordinated control of vehicle anti-lock braking and active front wheel steering

Abstract

This invention discloses a coordinated control method for vehicle anti-lock braking and active front wheel steering. The method includes: S1: Under vehicle braking and steering conditions, using the maximum yaw rate as a first threshold value; and using the maximum adjustment angle of the active front wheel steering as a second threshold value; S2: Constructing a coordinated control strategy for vehicle ABS and AFS based on the first and second threshold values; S3: Realizing coordinated control of vehicle anti-lock braking and active front wheel steering based on the constructed coordinated control strategy. This invention addresses the problem that current research on ABS or AFS control strategies mostly focuses on single braking or steering conditions. However, under special conditions, such as vehicle steering braking which is prone to instability, existing coordinated control methods for vehicle ABS and AFS are insufficient, leading to the inability to meet vehicle driving stability and handling performance during braking.

Description

Technical Field

[0001] This invention relates to the field of automotive electrical control technology, and in particular to a coordinated control method for vehicle anti-lock braking and active front wheel steering. Background Technology

[0002] ABS (Anti-lock Braking System) uses wheel speed sensors to collect dynamic wheel parameters in real time as system feedback. By dynamically adjusting the brake line pressure, it precisely controls the frictional braking torque of the brakes, effectively preventing skidding and fishtailing during braking. It also significantly reduces braking distance and time, providing a solid guarantee for the safety of the driver and their property. AFS (Active Front Steering) adds an active steering motor to the traditional vehicle steering structure. Based on the driver's steering wheel input, the active steering motor applies an additional steering angle independent of the driver's control, improving steering ease and reducing steering sensitivity, thereby enhancing vehicle stability at high speeds.

[0003] Current research on control strategies for ABS or AFS mostly focuses on single braking or steering conditions. However, in special conditions, such as vehicle steering and braking, which are prone to instability, vehicle ABS and AFS must be coordinated to ensure vehicle stability. Summary of the Invention

[0004] This invention provides a coordinated control method for vehicle anti-lock braking and active front wheel steering to overcome the above-mentioned technical problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for coordinated control of anti-lock braking and active front wheel steering in a vehicle includes the following steps:

[0007] S1: Under the condition of vehicle braking and steering, the maximum yaw rate is taken as the first threshold value;

[0008] The maximum adjustment angle of the active front wheel steering angle is used as the second threshold value;

[0009] S2: Based on the first threshold value and the second threshold value, construct a coordinated control strategy for vehicle ABS and AFS; and the coordinated control strategy for vehicle ABS and AFS specifically includes:

[0010] Obtain the vehicle's actual yaw rate and the actual adjustment angle of the front wheels, and determine the relationship between the actual yaw rate and the actual adjustment angle and the first threshold value and the second threshold value, respectively.

[0011] If the actual yaw rate exceeds the first threshold and the actual adjustment angle does not exceed the second threshold, then front wheel control is achieved by constructing a fuzzy PID controller based on the ABS system; and the rear wheels of the vehicle are controlled with fixed braking force, and the AFS system operates at the maximum adjustment angle.

[0012] If the actual yaw rate exceeds the first threshold and the actual steering angle exceeds the second threshold, the front wheels are controlled by a fuzzy PID controller built based on the ABS system; and the rear wheels of the vehicle are controlled by fixed braking force, while the AFS system uses a built AFS sliding mode controller to maintain vehicle operation.

[0013] If the actual yaw rate does not exceed the first threshold and the actual steering angle does not exceed the second threshold, then the independent control of the four wheels of the vehicle is achieved by constructing a fuzzy PID controller based on the ABS system; the AFS system operates at the maximum steering angle.

[0014] If the actual yaw rate does not exceed the first threshold and the actual adjusted steering angle exceeds the second threshold, then the independent control of the four wheels of the vehicle is achieved by constructing a fuzzy PID controller based on the ABS system; the AFS system uses the constructed AFS sliding mode controller to maintain vehicle operation.

[0015] S3: Based on the constructed vehicle ABS and AFS coordinated control strategy, the coordinated control of vehicle anti-lock braking and active front wheel steering is realized.

[0016] Furthermore, the method for constructing a fuzzy PID controller based on the ABS system described in S2 includes:

[0017] S100: Obtain the actual wheel slip ratio of the vehicle, define and obtain the slip ratio error between the preset expected wheel slip ratio and the actual wheel slip ratio;

[0018] And the formula for obtaining the slip ratio error is:

[0019] ,

[0020] In the formula: e This represents the error between the expected slip ratio and the actual slip ratio of the wheel. S 0 represents the expected slip ratio of the wheel; S This indicates the actual slip ratio of the wheel;

[0021] S101: Obtain the rate of change of slip ratio error e Its expression is

[0022] ,

[0023] And based on the slip ratio error e and the rate of change Construct a fuzzy controller with two inputs and three outputs;

[0024] Furthermore, the inputs to the fuzzy controller include the slip rate error e and the rate of change. The output of the fuzzy controller includes the adjustment increments Δ of the proportional, integral, and derivative coefficients in the PID control system. K P , △ K I and △ K D ;

[0025] The fuzzy set is set according to the input and output of the fuzzy controller, and the membership degree is obtained according to the fuzzy set based on the preset triangular membership function;

[0026] Fuzzy rules are constructed by combining membership degrees with fuzzy sets to obtain a set of fuzzy rules.

[0027] Based on the centroid method and the set of fuzzy rules, the adjustment increment Δ is obtained. K P , △ K I and △ K D This refers to the output of the fuzzy PID controller based on the ABS system.

[0028] Furthermore, the rules for setting fuzzy sets in S101 are as follows:

[0029] Set the input slip ratio error e and the rate of change The domain of discourse is [-m, m].

[0030] And the slip ratio error e and the rate of change The fuzzy sets on the universe of discourse [-m, m] are denoted as {NB, NM, NS, ZO, PS, PM, PB}, where NB represents negative large; NM represents negative medium; NS represents negative small; ZO represents zero; PS represents positive small; PM represents positive medium; and PB represents positive large.

[0031] Set the fuzzy set of the output variables of the fuzzy controller to {Z, S, M, B}; where Z represents zero; S represents small; M represents medium; and B represents large.

[0032] Furthermore, the fuzzy rules constructed in S101 specifically include:

[0033] like e Take NB and Let NB be the case, then △ K P Take B and △ K I Take Z and △ K D Take S;

[0034] like e Take NB and Let NM, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0035] like e Take NB and Let NS be the values, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0036] like e Take NB and Taking ZO, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0037] like e Take NB and Let PS be the value, then △ K P Take Z and △ K I Take Z and △ K D Choose M;

[0038] like e Take NB and Let PM be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0039] like e Take NB and Let PB be the value, then △ K P Take Z and △ K I Take Z and △ K D Take S;

[0040] like e Take NM and Let NB be the case, then △ KP Take B and △ K I Take S and △ K D Choose M;

[0041] like e Take NM and Let NM, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0042] like e Take NM and Let NS be the values, then △ K P Take B and △ K I Take S and △ K D Take Z;

[0043] like e Take NM and Taking ZO, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0044] like e Take NM and Let PS be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0045] If e takes NM and Let PM be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0046] If e takes NM and Let PB be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0047] If e takes NS and Let NB be the case, then △ K P Take M and △ K I Take M and △ K D Take Z;

[0048] If e takes NS and Let NM, then △ K P Take M and △ K I Take B and △ K D Take S;

[0049] If e takes NS and Let NS be the values, then △ K P Take S and △ K I Take M and △ K D Take S;

[0050] If e takes NS and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0051] If e takes NS and Let PS be the value, then △ K P Take S and △ K I Take M and △ K D Take S;

[0052] If e takes NS and Let PM be the value, then △ K P Take S and △ K I Take M and △ K D Take S;

[0053] If e takes NS and Let PB be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0054] If e takes ZO and Let NB be the case, then △ K P Take M and △ K I Take B and △ K D Take Z;

[0055] If e takes ZO and Let NM, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0056] If e takes ZO and Let NS be the values, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0057] If e takes ZO and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take Z;

[0058] If e takes ZO and Let PS be the value, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0059] If e takes ZO and Let PM be the value, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0060] If e takes ZO and Let PB be the value, then △ K P Take M and △ K I Take B and △ K D Take Z;

[0061] If e takes PS and Let NB be the case, then △K P Take S and △ K I Take M and △ K D Take Z;

[0062] If e takes PS and Let NM, then △ K P Take S and △ K I Take B and △ K D Take S;

[0063] If e takes PS and Let NS be the values, then △ K P Take S and △ K I Take M and △ K D Take S;

[0064] If e takes PS and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0065] If e takes PS and Let PS be the value, then △ K P Take M and △ K I Take M and △ K D Take S;

[0066] If e takes PS and Let PM be the value, then △ K P Take M and △ K I Take M and △ K D Take S;

[0067] If e takes PS and Let PB be the value, then △ K P Take M and △ K I Take M and △ K D Take Z;

[0068] If e takes PM and Let NB be the case, then △ KP Take S and △ K I Take S and △ K D Choose M;

[0069] If e takes PM and Let NM, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0070] If e takes PM and Let NS be the values, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0071] If e takes PM and Taking ZO, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0072] If e takes PM and Let PS be the value, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0073] If e takes PM and Let PM be the value, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0074] If e takes PM and Let PB be the value, then △ K P Take B and △ K I Take S and △ K D Choose M;

[0075] If e takes PB and Let NB be the case, then △ K PTake Z and △ K I Take Z and △ K D Take S;

[0076] If e takes PB and Let NM, then △ K P Take Z and △ K I Take Z and △ K D Choose M;

[0077] If e takes PB and Let NS be the values, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0078] If e takes PB and Taking ZO, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0079] If e takes PB and Let PS be the value, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0080] If e takes PB and Let PM be the value, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0081] If e takes PB and Let PB be the value, then △ K P Take B and △ K I Take Z and △ K D Take S.

[0082] Furthermore, in S101, the adjustment increment Δ is obtained based on the centroid method and the set of fuzzy rules. K P , △K I and △ K D The formula is

[0083] ,

[0084] In the formula: This represents the adjustment increment of the proportional, integral, and derivative coefficients in a PID control system. ; This represents the element in the universe of discourse corresponding to the slip ratio error e; Represents the rate of change Corresponding universe elements; Indicates the number of elements in the universe of discourse; express The degree of membership.

[0085] Furthermore, the method for constructing the AFS sliding mode controller described in S2 specifically includes:

[0086] S200: Obtain the actual yaw angle of the vehicle, define and obtain the yaw angle error between the preset expected wheel yaw angle and the actual yaw angle of the vehicle.

[0087] And the formula for obtaining the yaw angle error is:

[0088] ,

[0089] In the formula: Indicates the yaw angle error; Indicates the actual yaw angle; Indicates the expected yaw angle of the wheel;

[0090] S201: Yaw angle error As a sliding surface ; and according to the sliding surface Construct a sliding mode convergence rate function, and the sliding mode convergence rate function The expression is

[0091] ,

[0092] In the formula: Represents a saturation function; Represents the convergence coefficient and ;

[0093] S202: Based on sliding mode control theory, an AFS sliding mode controller is constructed according to the sliding mode approach rate function;

[0094] And the construction formula of the AFS sliding mode controller is as follows:

[0095] ,

[0096] In the formula: Indicates the steering angle of the active front wheel; This indicates the distance between the front axle and the vehicle's center of gravity. This indicates the distance between the rear axle and the vehicle's center of gravity. Indicates the lateral stiffness of the vehicle's front wheels; Indicates the lateral stiffness of the vehicle's rear wheels; Indicates the side angle of the vehicle's center of gravity; Indicates the wheel speed; This represents the moment of inertia of the vehicle about the Z-axis. This represents the expected yaw acceleration.

[0097] Beneficial Effects: This invention provides a coordinated control method for vehicle anti-lock braking and active front wheel steering, constructing a coordinated control strategy for vehicle ABS and AFS. By designing an ABS-based fuzzy PID controller, using wheel slip ratio deviation and its rate of change as input, and the output being the adjustment increment of the proportional, integral, and derivative coefficients in the PID control system, the fuzzy PID controller can collect wheel slip ratio data in real time under a single braking condition and dynamically optimize the PID controller parameters based on data changes. This not only precisely controls the vehicle braking process but also improves vehicle braking performance under various conditions, enhances driving safety, and avoids problems such as wheel lock-up and vehicle loss of control during braking. The designed AFS sliding mode controller improves the robustness of the vehicle system to parameter uncertainties under a single steering condition, effectively improving vehicle handling stability and enhancing steering system performance. This invention solves the problem of insufficient coordinated control of ABS and AFS in existing vehicles. By working together with ABS, it is possible to not only achieve precise control of the front wheel steering angle with the help of AFS, but also to distribute the braking force of the wheels through ABS, thereby improving the driving stability of the vehicle and enhancing the handling performance of the vehicle during braking. Attached Figure Description

[0098] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0099] Figure 1 This is a flowchart of the coordinated control method for vehicle anti-lock braking and active front wheel steering according to the present invention.

[0100] Figure 2The fuzzy set membership function graph of the input variable error e provided by this invention;

[0101] Figure 3 The input variable error change rate provided by the present invention Fuzzy set membership function graph;

[0102] Figure 4 The fuzzy set membership function graph of the output variable provided by this invention. Detailed Implementation

[0103] 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0104] This embodiment provides a coordinated control method for vehicle anti-lock braking and active front wheel steering, such as... Figure 1 As shown, it includes the following steps:

[0105] S1: Under the condition of vehicle braking and steering, the maximum yaw rate is taken as the first threshold; the maximum adjustment angle of the active front wheel steering angle is taken as the second threshold.

[0106] S2: Based on the first threshold value and the second threshold value, construct a coordinated control strategy for vehicle ABS and AFS; and the coordinated control strategy for vehicle ABS and AFS specifically includes:

[0107] S21: Obtain the actual yaw rate of the vehicle and the actual adjustment angle of the front wheels, and determine the relationship between the actual yaw rate and the actual adjustment angle and the first threshold value and the second threshold value, respectively.

[0108] S22: If the actual yaw rate exceeds the first threshold and the actual adjustment angle does not exceed the second threshold, the ABS system will use a control strategy that combines independent front wheel control with low-selection rear wheel control to control the vehicle. That is, front wheel control is achieved by building a fuzzy PID controller based on the ABS system; and the rear wheels of the vehicle will be controlled by the fixed braking force determined by the low-selection rear wheel control. The AFS system will continue to operate at the maximum adjustment angle to maintain vehicle stability.

[0109] In this embodiment, rear wheel low-selection control refers to the simultaneous application of braking pressure to both wheels on the same axle in an anti-lock braking system (ABS). The magnitude of the braking pressure is determined by the wheel with the lower coefficient of friction. The main advantage of rear wheel low-selection control is that it ensures vehicle stability because the braking forces on the left and right wheels are roughly equal, preventing vehicle yaw. Although it cannot fully utilize the traction of the wheel traveling on the high-friction surface, it can achieve greater lateral cornering force. Based on these advantages, low-selection control is widely applicable to the braking control of rear axle wheels.

[0110] Specifically, the method for constructing a fuzzy PID controller based on an ABS system includes:

[0111] S100: Obtain the actual wheel slip ratio of the vehicle, define and obtain the slip ratio error between the preset expected wheel slip ratio and the actual wheel slip ratio;

[0112] And the formula for obtaining the slip ratio error is:

[0113] ,

[0114] In the formula: e This represents the error between the expected slip ratio and the actual slip ratio of the wheel. S 0 represents the expected slip ratio of the wheel; S This indicates the actual slip ratio of the wheel;

[0115] S101: Obtain the rate of change of slip ratio error e Its expression is

[0116] ,

[0117] And based on the slip ratio error e and the rate of change Construct a fuzzy controller with two inputs and three outputs; and the inputs of the fuzzy controller include the slip rate error e and the rate of change. The output of the fuzzy controller includes the adjustment increments Δ of the proportional, integral, and derivative coefficients in the PID control system. K P , △ K I and △ K D ;

[0118] Since wheel slip ratio directly reflects vehicle braking performance, under single braking control or independent ABS control, this embodiment constructs a fuzzy PID controller based on the ABS system. The input is the wheel slip ratio deviation and its rate of change, and the output is the adjustment increment of the proportional, integral, and derivative coefficients in the PID control system, i.e., Δ. K P , △K I , △ K D Based on this, a two-input, three-output fuzzy controller is constructed, with wheel slip ratio set as the controlled object. Under single-stage vehicle braking control, the fuzzy PID controller collects wheel slip ratio data in real time and dynamically optimizes the PID controller parameters based on data changes. In this way, not only can the vehicle braking process be precisely controlled, but the vehicle braking performance can also be improved under various operating conditions, enhancing driving safety and avoiding problems such as wheel lock-up and vehicle loss of control during braking.

[0119] Specifically, this includes: setting a fuzzy set based on the input and output of the fuzzy controller, and obtaining the membership degree based on the fuzzy set using a preset triangular membership function; in this embodiment, the triangular membership function is widely used in fuzzy control systems, for example in fuzzy PID control, where it can be used to define the membership function of the input error and the error change rate, thereby achieving fuzzy control of the system;

[0120] The rules for defining the fuzzy set are as follows:

[0121] Set the input slip ratio error e and the rate of change The domain of discourse is [-m, m].

[0122] And the slip ratio error e and the rate of change The fuzzy sets on the universe of discourse [-m, m] are denoted as {NB, NM, NS, ZO, PS, PM, PB}, where NB represents negative large; NM represents negative medium; NS represents negative small; ZO represents zero; PS represents positive small; PM represents positive medium; and PB represents positive large; as shown below. Figures 2 to 3 Representing the membership functions of a triangle based on a preset ratio, and according to the slip ratio error e and the rate of change, respectively. The triangular membership image obtained in the fuzzy set of the universe of discourse [-m,m];

[0123] Let the fuzzy set of the output variables of the fuzzy controller be {Z, S, M, B}; where Z represents zero; S represents small; M represents medium; and B represents large; for example... Figure 4 The image shown is a triangular membership image of the fuzzy set of the output variables;

[0124] Fuzzy rules are constructed by combining membership degrees with fuzzy sets to obtain a set of fuzzy rules.

[0125] Specifically, in this embodiment, fuzzy rules are established using the form "if and then", where "if" means "if"; "and" means "and"; and "then" means "then". In this embodiment, the fuzzy controller has a total of 49 fuzzy rules, including:

[0126] like e Take NB and Let NB be the case, then △ K P Take B and △ K I Take Z and △ K D Take S;

[0127] like e Take NB and Let NM, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0128] like e Take NB and Let NS be the values, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0129] like e Take NB and Taking ZO, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0130] like e Take NB and Let PS be the value, then △ K P Take Z and △ K I Take Z and △ K D Choose M;

[0131] like e Take NB and Let PM be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0132] like e Take NB and Let PB be the value, then △ K P Take Z and △K I Take Z and △ K D Take S;

[0133] like e Take NM and Let NB be the case, then △ K P Take B and △ K I Take S and △ K D Choose M;

[0134] like e Take NM and Let NM, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0135] like e Take NM and Let NS be the values, then △ K P Take B and △ K I Take S and △ K D Take Z;

[0136] like e Take NM and Taking ZO, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0137] like e Take NM and Let PS be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0138] If e takes NM and Let PM be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0139] If e takes NM and Let PB be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0140] If e takes NS and Let NB be the case, then △ K P Take M and △ K I Take M and △ K D Take Z;

[0141] If e takes NS and Let NM, then △ K P Take M and △ K I Take B and △ K D Take S;

[0142] If e takes NS and Let NS be the values, then △ K P Take S and △ K I Take M and △ K D Take S;

[0143] If e takes NS and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0144] If e takes NS and Let PS be the value, then △ K P Take S and △ K I Take M and △ K D Take S;

[0145] If e takes NS and Let PM be the value, then △ K P Take S and △ K I Take M and △ K D Take S;

[0146] If e takes NS and Let PB be the value, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0147] If e takes ZO and Let NB be the case, then △ K P Take M and △ K I Take B and △ K D Take Z;

[0148] If e takes ZO and Let NM, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0149] If e takes ZO and Let NS be the values, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0150] If e takes ZO and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take Z;

[0151] If e takes ZO and Let PS be the value, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0152] If e takes ZO and Let PM be the value, then △ K P Take S and △ K I Take B and △ K D Take Z;

[0153] If e takes ZO and Let PB be the value, then △K P Take M and △ K I Take B and △ K D Take Z;

[0154] If e takes PS and Let NB be the case, then △ K P Take S and △ K I Take M and △ K D Take Z;

[0155] If e takes PS and Let NM, then △ K P Take S and △ K I Take B and △ K D Take S;

[0156] If e takes PS and Let NS be the values, then △ K P Take S and △ K I Take M and △ K D Take S;

[0157] If e takes PS and Taking ZO, then △ K P Take Z and △ K I Take B and △ K D Take S;

[0158] If e takes PS and Let PS be the value, then △ K P Take M and △ K I Take M and △ K D Take S;

[0159] If e takes PS and Let PM be the value, then △ K P Take M and △ K I Take M and △ K D Take S;

[0160] If e takes PS and Let PB be the value, then △ KP Take M and △ K I Take M and △ K D Take Z;

[0161] If e takes PM and Let NB be the case, then △ K P Take S and △ K I Take S and △ K D Choose M;

[0162] If e takes PM and Let NM, then △ K P Take Z and △ K I Take S and △ K D Choose M;

[0163] If e takes PM and Let NS be the values, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0164] If e takes PM and Taking ZO, then △ K P Take S and △ K I Take Z and △ K D Choose B;

[0165] If e takes PM and Let PS be the value, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0166] If e takes PM and Let PM be the value, then △ K P Take M and △ K I Take S and △ K D Choose M;

[0167] If e takes PM and Let PB be the value, then △ K PTake B and △ K I Take S and △ K D Choose M;

[0168] If e takes PB and Let NB be the case, then △ K P Take Z and △ K I Take Z and △ K D Take S;

[0169] If e takes PB and Let NM, then △ K P Take Z and △ K I Take Z and △ K D Choose M;

[0170] If e takes PB and Let NS be the values, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0171] If e takes PB and Taking ZO, then △ K P Take B and △ K I Take Z and △ K D Choose B;

[0172] If e takes PB and Let PS be the value, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0173] If e takes PB and Let PM be the value, then △ K P Take B and △ K I Take Z and △ K D Choose M;

[0174] If e takes PB and Let PB be the value, then △ K P Take B and △K I Take Z and △ K D Take S;

[0175] Based on the centroid method and the set of fuzzy rules, the adjustment increment Δ is obtained. K P , △ K I and △ K D This refers to the output of the fuzzy PID controller based on the ABS system. In this embodiment, the defuzzification process in the fuzzy controller maps the fuzzy output to a precise control quantity through a specific mathematical transformation method. In this embodiment, the defuzzification adopts the centroid method, which is commonly used in engineering applications. The centroid method determines the output value by calculating the weighted average of each element in the fuzzy set and its corresponding membership degree. In its mathematical expression, the output value is equal to the sum of the products of each element and its membership degree divided by the total membership degree. This method can comprehensively consider the overall distribution characteristics of the fuzzy set and provide a smoother and more continuous control output. The mathematical expression of the centroid method defuzzification method is the adjustment increment Δ. K P , △ K I and △ K D The formula for obtaining it is

[0176] ,

[0177] In the formula: This represents the adjustment increment of the proportional, integral, and derivative coefficients in a PID control system. ; This represents the element in the universe of discourse corresponding to the slip ratio error e; Represents the rate of change Corresponding universe elements; Indicates the number of elements in the universe of discourse; express Membership degree;

[0178] S23: If the actual yaw rate exceeds the first threshold and the actual adjustment angle exceeds the second threshold, the front wheels are controlled by a fuzzy PID controller built based on the ABS system; and the rear wheels of the vehicle are controlled by fixed braking force. The AFS system uses the built AFS sliding mode controller to maintain the continuous operation of the vehicle and ensure vehicle stability.

[0179] Specifically, in the case of a single steering operation of a car, the yaw rate of the vehicle is used as the controlled variable in this embodiment. The ideal value of the yaw rate is compared with the actual yaw rate of the vehicle, and the deviation value is used as the input signal of the AFS sliding mode controller. The output of the AFS sliding mode controller is the front wheel steering angle, which can be applied to the steering system through the superposition mechanism, thereby effectively improving the yaw stability of the vehicle.

[0180] The method for constructing the AFS sliding mode controller specifically includes:

[0181] S200: Obtain the actual yaw angle of the vehicle, define and obtain the yaw angle error between the preset expected wheel yaw angle and the actual yaw angle of the vehicle.

[0182] And the formula for obtaining the yaw angle error is:

[0183] ,

[0184] In the formula: Indicates the yaw angle error; Indicates the actual yaw angle; Indicates the expected yaw angle of the wheel;

[0185] S201: Yaw angle error As a sliding surface ; and according to the sliding surface Construct a sliding mode approach function for selecting the constant velocity approach rate, and the sliding mode approach function The expression is

[0186] ,

[0187] In the formula: Represents a saturation function; Represents the convergence coefficient and ;

[0188] S202: Based on sliding mode control theory, an AFS sliding mode controller is constructed according to the sliding mode approach rate function;

[0189] And the construction formula of the AFS sliding mode controller is as follows:

[0190] ,

[0191] In the formula: Indicates the steering angle of the active front wheel; This indicates the distance between the front axle and the vehicle's center of gravity. This indicates the distance between the rear axle and the vehicle's center of gravity. Indicates the lateral stiffness of the vehicle's front wheels; Indicates the lateral stiffness of the vehicle's rear wheels; Indicates the side angle of the vehicle's center of gravity; Indicates the wheel speed; This represents the moment of inertia of the vehicle about the Z-axis. This represents the desired yaw acceleration;

[0192] S24: If the actual yaw rate does not exceed the first threshold and the actual adjustment angle does not exceed the second threshold, then the independent control of the four wheels of the vehicle is achieved by constructing a fuzzy PID controller based on the ABS system; the AFS system continues to operate at the maximum adjustment angle to maintain vehicle stability.

[0193] S25: If the actual yaw rate does not exceed the first threshold and the actual adjusted steering angle exceeds the second threshold, then the independent control of the four wheels of the vehicle is achieved by constructing a fuzzy PID controller based on the ABS system; the AFS system uses the constructed AFS sliding mode controller to maintain vehicle operation and ensure vehicle stability.

[0194] S3: Based on the constructed vehicle ABS and AFS coordinated control strategy, the coordinated control of vehicle anti-lock braking and active front wheel steering is realized.

[0195] The beneficial effects of the method described in this embodiment are as follows: By designing a fuzzy PID controller based on ABS, using wheel slip ratio deviation and its rate of change as input, and the output being the adjustment increment of the proportional, integral, and derivative coefficients in the PID control system, the fuzzy PID controller can collect wheel slip ratio data in real time under a single braking condition and dynamically optimize the PID controller parameters based on data changes. This not only precisely controls the vehicle braking process but also improves vehicle braking performance under various conditions, enhances driving safety, and avoids problems such as wheel lock-up and vehicle loss of control during braking. The designed AFS sliding mode controller improves the robustness of the vehicle system to parameter uncertainties under a single steering condition, effectively improving vehicle handling stability and enhancing steering system performance. This invention solves the shortcomings of existing vehicle ABS and AFS coordinated control. Through the collaborative work of ABS and AFS, not only can the AFS achieve precise control of the front wheel steering angle, but the ABS can also distribute wheel braking force, thereby improving vehicle driving stability and enhancing vehicle handling performance during braking. By constructing a coordinated control strategy for vehicle ABS and AFS, ABS and AFS can work together to fully leverage the advantages of both subsystems, significantly improving vehicle braking performance and steering stability, and reducing the risk of lateral slip and loss of control during steering and braking.

[0196] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of coordinated control of antilock braking and active front wheel steering of a vehicle, characterized by, The method comprises the following steps: S1: in the automobile braking and steering working condition, taking the maximum yaw rate as a first threshold value; taking the maximum adjustment angle of the active front wheel as a second threshold value; S2: constructing a vehicle ABS and AFS coordinated control strategy according to the first threshold value and the second threshold value; and the vehicle ABS and AFS coordinated control strategy specifically comprises: obtaining the actual yaw rate of the vehicle and the actual adjustment angle of the front wheel, and judging the relationship between the actual yaw rate and the actual adjustment angle and the first threshold value and the second threshold value; if the actual yaw rate exceeds the first threshold value and the actual adjustment angle does not exceed the second threshold value, realizing the front wheel control through a fuzzy PID controller constructed based on the ABS system; and the rear wheel of the vehicle adopts a fixed brake force control, and the AFS system operates at the maximum adjustment angle; if the actual yaw rate exceeds the first threshold value and the actual adjustment angle exceeds the second threshold value, realizing the front wheel control through a fuzzy PID controller constructed based on the ABS system; and the rear wheel of the vehicle adopts a fixed brake force control, and the AFS system adopts an AFS sliding mode controller constructed to maintain the vehicle operation; if the actual yaw rate does not exceed the first threshold value and the actual adjustment angle does not exceed the second threshold value, realizing the independent control of the four wheels of the vehicle through a fuzzy PID controller constructed based on the ABS system; and the AFS system operates at the maximum adjustment angle; if the actual yaw rate does not exceed the first threshold value and the actual adjustment angle exceeds the second threshold value, realizing the independent control of the four wheels of the vehicle through a fuzzy PID controller constructed based on the ABS system; and the AFS system adopts an AFS sliding mode controller constructed to maintain the vehicle operation; the construction method of the AFS sliding mode controller specifically comprises: S200: obtaining the actual yaw of the vehicle, defining and obtaining the yaw error of the preset wheel expected yaw and the actual yaw of the vehicle; and the acquisition formula of the yaw error is In the formulae: represents a yaw angle error; represents an actual yaw angle; represents a wheel desired yaw angle; S201: obtaining a yaw angle error as a sliding mode surface ; and constructing a sliding mode reaching rate function according to the sliding mode surface , and the sliding mode reaching rate function is expressed as In the formulae: denotes a saturation function; denotes an approach rate coefficient and ; S202: based on the sliding mode control theory, constructing an AFS sliding mode controller according to a sliding mode approach rate function; and the construction formula of the AFS sliding mode controller is In the formulae: denotes the steering angle of the front wheels; denotes the distance between the front axle of the vehicle and the center of mass of the vehicle; denotes the distance between the rear axle of the vehicle and the center of mass of the vehicle; denotes the cornering stiffness of the front wheels of the vehicle; denotes the cornering stiffness of the rear wheels of the vehicle; denotes the side slip angle of the center of mass of the vehicle; denotes the wheel speed of a wheel; denotes the moment of inertia of the vehicle about the Z axis; denotes the desired yaw angular acceleration; S3: realizing the coordinated control of the vehicle anti-lock braking and the active front wheel steering according to the constructed vehicle ABS and AFS coordinated control strategy.

2. The method of claim 1, wherein The method of constructing a fuzzy PID controller based on the ABS system in S2 specifically comprises: S100: obtaining the actual slip rate of the vehicle wheel, defining and obtaining the slip rate error of the preset wheel expected slip rate and the actual slip rate of the wheel; and the acquisition formula of the slip rate error is In the formulae: e represents the error of the wheel desired slip rate and the wheel actual slip rate; S 0 represents the wheel desired slip rate; S represents the wheel actual slip rate; S101: Obtain the rate of change of the slip ratio error e whose expression is And according to the slip rate error e and the rate of change Construct a two-input three-output fuzzy controller; and the input of the fuzzy controller includes the slip error e and the change rate ; the output of the fuzzy controller includes the adjustment increment Δ of the proportional, integral and differential coefficients in the PID control system K P , Δ K I and Δ K D ; setting the fuzzy set according to the input and output of the fuzzy controller, and obtaining the membership degree based on the preset triangular membership function according to the fuzzy set; constructing a fuzzy rule according to the membership degree and the fuzzy set to obtain a fuzzy rule set; Based on the barycenter method, the adjustment increment Δ is obtained according to the fuzzy rule set K P , Δ K I and Δ K D , that is, the output of the fuzzy PID controller based on the ABS system.

3. The method of claim 2, wherein the control method is characterized by: the setting rule of the fuzzy set in S101 is: Setting input slip ratio error e and rate of change Domain is [-m, m] and the slip rate error e is compared with the change rate The fuzzy sets on the domain [-m, m] are all set to: {NB, NM, NS, ZO, PS, PM, PB}, where NB represents negative big; NM represents negative medium; NS represents negative small; ZO represents zero; PS represents positive small; PM represents positive medium; and PB represents positive big. the fuzzy set of the fuzzy controller output variable is set as {Z, S, M, B}; wherein Z represents zero; S represents small; M represents medium; and B represents large.

4. The method of claim 3, wherein the fuzzy rule constructed in S101 specifically comprises: If e Take NB and Take NB, then Δ K P Take B and Δ K I Take Z and Δ K D Take S; If e Take NB and Take NM, then Δ K P Take B and Δ K I Take Z and Δ K D Take M; If e Take NB and Take NS, then Δ K P Take B and Δ K I Take Z and Δ K D Take B; If e Take NB and Take ZO, then Δ K P Take B and Δ K I Take Z and Δ K D Take B; If e Take NB and Take PS, then Δ K P Take Z and Δ K I Take Z and Δ K D Take M; If e Take NB and Take PM, then Δ K P Take Z and Δ K I Take S and Δ K D Take M; If e Take NB and Take PB, then Δ K P Take Z and Δ K I Take Z and Δ K D Take S; If e Take NM and Take NB, then Δ K P Take B and Δ K I Take S and Δ K D Take M; If e Take NM and Take NM, then Δ K P Take M and Δ K I Take S and Δ K D Take M; If e Take NM and Take NS, then Δ K P Take B and Δ K I Take S and Δ K D Take Z; If e Take NM and Take ZO and K P Take S and K I Take Z and K D Take B; If e Take NM and Take PS, then Δ K P Take Z and Δ K I Take S and Δ K D Take M; If e takes NM and If e takes PM, then Δ K P If e takes Z and Δ K I If e takes S and Δ K D If e takes M; If e is taken as NM and If PB is taken, then Δ K P If Z is taken and Δ K I If S is taken and Δ K D If M is taken; If e takes NS and If e takes NB, then Δ K P If e takes M and Δ K I If e takes M and Δ K D If e takes Z; If e takes NS and If e takes NM and K P If e takes M and K I If e takes B and K D If e takes S; If e takes NS and If e takes NS, then Δ K P If e takes S and Δ K I If e takes M and Δ K D If e takes S; If e takes NS and If e takes ZO and K P If e takes Z and K I If e takes B and K D If e takes S; If e takes NS and If e takes PS, then Δ K P If e takes S and Δ K I If e takes M and Δ K D If e takes S; If e takes NS and If e takes PM, then Δ K P If e takes S and Δ K I If e takes M and Δ K D If e takes S; If e takes NS and If PB, then Δ K P If Z and Δ K I If S and Δ K D If M; If e takes Z0 and If e takes Nband K P If e takes M and K I If e takes B and K D If e takes Z; If e takes ZO and If e takes NM, then Δ K P If e takes S and Δ K I If e takes B and Δ K D If e takes Z; If e takes ZO and If e takes NS, then Δ K P If e takes Z and Δ K I If e takes B and Δ K D If e takes S; If e takes Z0and If e takes Z0, then Δ K P If e takes Z and Δ K I If e takes B and Δ K D If e takes Z; If e takes Z0 and If e takes Z0 and K P If e takes Z0 and K I If e takes Z0 and K D If e takes Z0 and If e takes Z0 and If e takes Z0 and K P If e takes Z0 and K I If e takes Z0 and K D If e takes Z0 and If e takes Z0 and If e takes PB, then Δ K P If e takes M and Δ K I If e takes B and Δ K D If e takes Z; If e takes PS and If e takes NB, then Δ K P If e takes S and Δ K I If e takes M and Δ K D If e takes Z; If e takes PS and If e takes NM, then Δ K P If e takes S and Δ K I If e takes B and Δ K D If e takes S; If e takes PS and If e takes NS, then Δ K P If e takes S and Δ K I If e takes M and Δ K D If e takes S; If e takes PS and If e takes ZO and K P If e takes Z and K I If e takes B and K D If e takes S; If e takes PS and If e takes PS, then Δ K P If e takes M and Δ K I If e takes M and Δ K D If e takes S; If e takes PS and If e takes PM, then Δ K P If e takes M and Δ K I If e takes M and Δ K D If e takes S; If e is taken as PS and If PB is taken, then Δ K P If M is taken and Δ K I If M is taken and Δ K D If Z is taken; If e takes PM and If e takes NB, then Δ K P If e takes S and Δ K I If e takes S and Δ K D If e takes M; If e takes PM and If e takes NM, then Δ K P If e takes Z and Δ K I If e takes S and Δ K D If e takes M; If e takes PM and If e takes NS, then Δ K P If e takes S and Δ K I If e takes Z and Δ K D If e takes B; If e takes PM and If ZO, then Δ K P If S and Δ K I If Z and Δ K D If B; If e takes PM and If e takes PS, then Δ K P If e takes M and Δ K I If e takes S and Δ K D If e takes M; If e takes PM and If e takes PM, then Δ K P If e takes M and Δ K I If e takes S and Δ K D If e takes M; If e takes PM and If e takes PB, then Δ K P If e takes B and Δ K I If e takes S and Δ K D If e takes M; If e takes PB and If e takes NB, then Δ K P If e takes Z and Δ K I If e takes Z and Δ K D If e takes S; If e is taken PB and If NM is taken, then Δ K P If Z is taken and Δ K I If Z is taken and Δ K D If M is taken; If e takes PB and If e takes PB and K P If e takes PB and K I If e takes PB and K D If e takes PB and If e takes PB and If ZO, then Δ K P If B and Δ K I If Z and Δ K D If B; If e is taken PB and If e is taken PB and K P If e is taken PB and K I If e is taken PB and K D If e is taken PB and If e takes PB and If e takes PB and K P If e takes PB and K I If e takes PB and K D If e takes PB and If e takes PB and If e takes PB, then Δ K P If e takes PB and Δ K I If e takes Z and Δ K D If e takes S.

5. The method of claim 4, wherein In S101, the adjustment increment Δ is obtained according to the fuzzy rule set based on the barycentric method K P , Δ K I and Δ K D The formula is wherein: represents the adjustment increment of the proportional, integral, and derivative coefficients in the PID control system and ; represents the argument element in the argument domain corresponding to the slip rate error e; represents the rate of change of the argument element in the argument domain; represents the number of argument elements; represents the membership degree of .

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