Fault-tolerant control system and method for improving driving safety of heavy multi-axle steered vehicles

Abstract

The application relates to a fault-tolerant control system and method for improving the driving safety of a heavy multi-axle steering vehicle, which comprises a fault diagnosis module for receiving wheel angle information of the vehicle output and judging whether the steering wheel is stuck; an upper control module for calculating additional lateral force and additional yaw moment required for maintaining the stability of the vehicle by using an adaptive sliding mode control algorithm when the steering wheel is stuck; a lower control module for optimizing the distribution of tire lateral force of non-fault wheels according to the additional force and moment obtained by the upper control module; and a fault-tolerant control module for solving a fault-tolerant feasible region of tire force after the fault occurs, judging whether the optimized tire lateral force is within the range of the fault-tolerant feasible region, and selecting the optimal fault-tolerant controller for different failure modes to perform fault-tolerant control on the fault vehicle according to the judgment result. The system and method are favorable for improving the trajectory tracking accuracy and yaw stability of the heavy multi-axle vehicle when the steering wheel is stuck.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multi-axle vehicle control, and in particular to a fault-tolerant control system and method for improving the driving safety of heavy multi-axle steering vehicles. BACKGROUND

[0002] Heavy multi-axle vehicles are widely used in the fields of large equipment transportation and infrastructure construction. Heavy multi-axle vehicles use multi-axle steering technology. The more axles a vehicle has, the more difficult it is to steer and pass through complex curves. During steering, heavy multi-axle vehicles are prone to wheel steering mechanism failure, which can cause the wheels to be stuck, resulting in a deviation of the vehicle's driving trajectory, even instability, and serious safety problems. Therefore, it is necessary to perform fault-tolerant control on the wheel steering of heavy multi-axle vehicles to improve the steering stability and trajectory tracking accuracy of heavy multi-axle vehicles. Existing vehicle steering fault-tolerant control systems, such as the fault-tolerant control system of the autonomous steering system of the unmanned vehicle disclosed in patent CN114043995A, use differential steering to compensate for the front wheel angle, achieving fault-tolerant control of the steering system. The system and method for improving the safety of heavy multi-axle vehicles when the wheels are stuck disclosed in patent CN114560011A controls the lateral force of the tires to improve the driving safety of heavy multi-axle vehicles when a single axle's wheels are stuck. These control methods can improve the trajectory tracking accuracy of the vehicle when the steering system fails, but still have some deficiencies and limitations, mainly as follows:

[0003] 1. Existing research on vehicle steering system failure mostly uses differential steering to urgently replace the original autonomous steering system, uses different wheel torques to make the ground generate different longitudinal forces on the tires to generate yaw moments and achieve compensation control under steering system failure. Although the longitudinal force control method can maintain the yaw stability of the vehicle to some extent, it does not fully utilize the redundant steering system actuators, so the lateral dynamics control performance is greatly weakened.

[0004] 2. Existing research on heavy multi-axle vehicle steering system failure only considers single-tire failure, but in actual conditions, multi-axle vehicle steering system failure modes are not limited to single-axle sticking, and multiple axles may also be stuck. According to the redundancy characteristics of multi-axle vehicles, the compensation capability provided by the remaining non-fault actuators is different under different working conditions. When multiple axles are stuck, the traditional control method does not consider the friction circle constraint and the lateral-longitudinal coupling characteristics of tire forces, which limits the application of the control method. SUMMARY

[0005] The application aims to provide a fault-tolerant control system and method for improving the driving safety of heavy multi-axle steering vehicles, which is beneficial to improving the trajectory tracking accuracy and lateral stability of the heavy multi-axle steering vehicles when the steering wheels are stuck.

[0006] To achieve the above-mentioned purpose, the application adopts the technical scheme of a fault-tolerant control system for improving the driving safety of heavy multi-axle steering vehicles, comprising:

[0007] a fault diagnosis module for judging whether the steering wheels are stuck; the fault diagnosis module receives the wheel angle information output by the vehicle and judges whether the wheels are stuck;

[0008] an upper control module for calculating the additional lateral force ΔF y and the additional yaw moment ΔM Z needed for maintaining the stability of the vehicle by using an adaptive sliding mode control algorithm when the fault diagnosis module determines that the steering wheels are stuck;

[0009] a lower control module for optimizing the distribution of the tire lateral force of the non-faulty wheels according to the ΔF y and the ΔM Z obtained by the upper control module;

[0010] a fault-tolerant control module for solving the fault-tolerant feasible region of the tire force after the fault occurs, judging whether the optimized tire lateral force is within the range of the fault-tolerant feasible region, and selecting the optimal fault-tolerant controller for different failure modes to perform fault-tolerant control on the faulty vehicle according to the judgment result.

[0011] Further, considering different failure modes of the steering systems, the steering wheel sticking is generally divided into single-axle steering wheel sticking, two-axle steering wheel sticking and three-axle steering wheel sticking.

[0012] The application also provides a fault-tolerant control method for improving the driving safety of heavy multi-axle steering vehicles based on the above-mentioned system, comprising the following steps:

[0013] Step S1: establishing an ideal vehicle dynamics model of the multi-axle steering vehicle, detecting the actual wheel angle of the vehicle through a wheel angle sensor, comparing the actual wheel angle with the ideal wheel angle calculated through a zero mass center side slip strategy, and judging whether the wheels are stuck by the fault diagnosis module;

[0014] Step S2: when the fault diagnosis module determines that the wheels are stuck, inputting the deviation between the actual mass center side slip angle and the yaw angular velocity of the faulty vehicle and the ideal mass center side slip angle and the yaw angular velocity into the upper control module, and solving the additional force and moment for making the faulty vehicle reach the expected state through the upper control module;

[0015] Step S3: according to the additional force and torque obtained by the upper control module, the tire lateral force of the remaining non-fault wheel is optimized and distributed with the goal of minimizing the tire load rate;

[0016] Step S4: solving the fault-tolerant feasible region of the tire force after the fault occurs, judging whether the tire lateral force after the optimized distribution is within the range of the fault-tolerant feasible region, so as to select the best fault-tolerant controller to perform fault-tolerant control on the faulty vehicle; when the fault occurs, if the tire lateral force after the optimized distribution is within the range of the fault-tolerant feasible region, the fault-tolerant controller I is selected to perform fault-tolerant control on the faulty vehicle, and the fault-tolerant controller I takes the yaw stability and trajectory tracking as the control target; if the tire lateral force after the optimized distribution is not within the range of the fault-tolerant feasible region, the fault-tolerant controller II is selected to make the faulty vehicle maintain the original driving trajectory as much as possible, and the fault-tolerant controller II takes the yaw stability as the main control target.

[0017] Further, the specific method for establishing the ideal dynamics model of the multi-axle steering vehicle is:

[0018] Ignoring the influence of the suspension, i.e. ignoring the vertical movement of the vehicle, the front and rear pitching of the vehicle body, and the left and right roll of the vehicle, only the movement in the horizontal plane; ignoring the air resistance and the disturbance of the lateral wind during driving; assuming that the vertical load and the side stiffness of each tire are equal;

[0019] The ideal dynamics model of the vehicle is represented as:

[0020]

[0021]

[0022] Assuming that the tire working state is in the linear region, the expression of the tire lateral force of the vehicle is obtained:

[0023] F yi =C i α i

[0024]

[0025] F y is the resultant force of the vehicle along the Y-axis direction; M Z is the yaw moment of the vehicle around the Z-axis direction; I Z is the moment of inertia of the vehicle around the Z-axis; γ is the yaw angular velocity of the vehicle; is the yaw angular acceleration of the vehicle; m is the mass of the vehicle; F yi is the lateral force of the i-th axle; v x is the component of the center of mass velocity v on the X-axis; v y is the component of the center of mass velocity v on the Y-axis; δ i is the wheel rotation angle of the i-th axle; Li represents the distance from the vehicle center of mass to the ith axle, positive before the center of mass and negative after the center of mass; C i is the cornering stiffness of the tire.

[0026] Further, the ideal steering angle of the multi-axle steering vehicle is calculated, and the ideal steering angle information and the actual steering angle information are sent to the fault diagnosis module. If the actual steering angle is consistent with the ideal steering angle, the vehicle is in normal operation. If the actual steering angle is not consistent with the ideal steering angle, it is determined that the vehicle wheel is stuck.

[0027] Further, the method for calculating the ideal steering angle of each axle of the multi-axle steering vehicle through the zero center of mass cornering strategy is as follows:

[0028] The first axle steering angle δ1 is input, and the relationship between the steering angle of each axle and the first axle steering angle δ1 is as follows:

[0029]

[0030]

[0031] In the formula, D0 is the projection distance of the line connecting the center of mass to the instantaneous rotation center of the vehicle in the direction of the vehicle length.

[0032] Further, a joint controller for the center of mass cornering angle and the yaw rate is designed based on the adaptive sliding mode control algorithm, so as to calculate the additional lateral force ΔF y and the additional yaw moment ΔM Z needed to maintain the stability of the vehicle according to the deviation of the actual center of mass cornering angle and the yaw rate of the fault vehicle from the ideal center of mass cornering angle and the yaw rate.

[0033] The deviation of the center of mass cornering angle is used to set the sliding surface:

[0034] e β = β d - β

[0035] wherein e β is the deviation of the center of mass cornering angle, β is the actual center of mass cornering angle of the vehicle, and β d is the ideal center of mass cornering angle of the vehicle.

[0036] The control rate is designed as:

[0037]

[0038] wherein γ d is the ideal yaw rate of the vehicle, k1 is a sliding mode control parameter, is the estimated value of F y ;

[0039] The adaptive rate is taken as:

[0040]

[0041] input ΔF y satisfies:

[0042]

[0043] wherein, is the ideal vehicle mass center side slip angle rate;

[0044] The sliding mode surface is set by the yaw rate deviation:

[0045] e γ = γ d - γ

[0046] wherein, e γ is the yaw rate deviation, γ is the actual vehicle mass center side slip angle, γ d is the ideal vehicle mass center side slip angle;

[0047] The control rate is designed as:

[0048]

[0049] wherein, k2 is a sliding mode control parameter, is the estimated value of M Z ;

[0050] The adaptive rate is taken as:

[0051]

[0052] input ΔM Z satisfies:

[0053]

[0054] Further, when optimizing the distribution of tire lateral force of the remaining non-faulty wheels, in order to effectively and uniformly use all the tires as much as possible and avoid that a specific tire reaches a severe load condition during driving, the tire load rate J is minimized as the target to optimize the distribution of tire lateral force, and the objective function is:

[0055]

[0056] wherein, ξ i is the weight corresponding to each wheel, F zi is the vertical force received by each wheel.

[0057] Further, the specific method for solving the fault-tolerant feasible region is:

[0058] First, the effective range of tire force is solved based on the tire friction circle principle, and the fault-tolerant feasible region of tire lateral force is obtained by adding the influence of the steering system stuck fault, and then the fault-tolerant feasible region of the resultant force of the vehicle is derived based on the fault-tolerant feasible region of the tire lateral force;

[0059] According to the friction circle principle, the lateral tire force limit value of the wheel is calculated, which is represented as:

[0060] -μ i ·F zi sinθ i ≤F yi ≤μ i ·F zi sinθ i ,(i=1,...,k)

[0061] Wherein, μ is the adhesion coefficient of the road surface of the vehicle, θ i is the angle between the longitudinal force of the tire of the vehicle and the lateral force of the tire, the change value q i of the tire lateral force caused by the steering system stuck, q k is the change value of the kth axle of the vehicle, and the fault-tolerant feasible region of the tire lateral force is obtained as:

[0062]

[0063] Further, the fault-tolerant controller I is used to control the fault-tolerant vehicle in the fault-tolerant feasible region of the optimized and distributed tire lateral force, and the fault-tolerant controller I focuses on the yaw stability control and trajectory tracking control of the fault-tolerant vehicle:

[0064] The fault-tolerant controller I converts the tire lateral force into executable steering angle through the tire model; the tire lateral force formula is simplified as:

[0065]

[0066] Wherein, Δδ i is the additional steering angle of the wheel;

[0067] Therefore, the additional steering angle Δδ i of the wheel is:

[0068]

[0069] When the steering system stuck of the vehicle has a greater influence on the system, the optimized and distributed lateral forces of each wheel exceed the range of the fault-tolerant feasible region, that is, the tire lateral force after the optimized distribution is saturated, the fault-tolerant controller II is used to control the fault-tolerant vehicle, and the fault-tolerant controller II focuses on the yaw stability control:

[0070] The fault-tolerant controller II uses the method of weakening the control input to perform fault-tolerant control on the vehicle, and the dynamic balance equation of the vehicle is as follows:

[0071] ∑F yt =∑F yf +f y (v x ,δ t )

[0072] Wherein, ∑F yt is the control quantity obtained after fault-tolerant control, which satisfies the fault-tolerant feasible region; ∑F yt is the control quantity which does not satisfy the fault-tolerant feasible region; f y is the coefficient of adjusting the control input, that is, the influence caused by the steering system stuck fault is repaired by adjusting the driving speed and the front wheel angle; the independent variable v x1 =m·v x , δ t =n·δ1; v x and δ1 are the input quantities of the vehicle system, driving speed and front wheel angle, m and n are the weakening coefficients of the speed and the front wheel angle, the value range is (0, 1], v x1 and δ t are the weakened control inputs, that is, the driving speed and the front wheel angle of the vehicle after fault-tolerant control.

[0073] Compared with the prior art, the present application has the following beneficial effects:

[0074] 1) The present application is aimed at various stuck fault types of heavy multi-axle vehicles, and different fault-tolerant controllers are formulated according to whether the optimized distribution of tire lateral force is within the fault-tolerant feasible region to perform fault-tolerant control on the faulty vehicle. When the distributed tire lateral force is within the fault-tolerant feasible region, the fault-tolerant controller takes the yaw stability and trajectory tracking performance as the control target, fully utilizes the redundancy characteristics of the multi-axle vehicle, adjusts the turning angle of the remaining non-faulty vehicle wheels to perform fault-tolerant control on the faulty vehicle. When the distributed tire lateral force exceeds the fault-tolerant feasible region, the fault-tolerant controller takes the yaw stability as the control target, adjusts the driving speed and the first axle angle, and then redistributes the tire lateral force through the fault-tolerant controller, so that the optimized lateral force falls within the fault-tolerant feasible region to make the faulty vehicle drive as stably as possible.

[0075] 2) The fault-tolerant feasible region is constructed, various fault types of different positions and different numbers of steering system actuators are considered, the fault-tolerant controller considering the lateral and longitudinal force coupling of the tire is designed, the traditional fault-tolerant control scheme is effectively solved, which is only applicable to the fault-tolerant controller of single steering actuator fault, and the reliability and fault-tolerance of the system are improved. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1A flow chart for implementing the method of the embodiment of the present application is shown in the figure;

[0077] Figure 2 A whole vehicle fault-tolerant control framework for the heavy multi-axle vehicle in the embodiment of the present application is shown in the figure;

[0078] Figure 3 A schematic diagram of normal operation of the steering system of the heavy multi-axle vehicle in the embodiment of the present application is shown in the figure;

[0079] Figure 4 A schematic diagram of the steering system of the heavy multi-axle vehicle in the embodiment of the present application stuck failure is shown in the figure;

[0080] Figure 5 A control effect diagram of the fault-tolerant controller in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0081] The present application is further described below in conjunction with the accompanying drawings and embodiments.

[0082] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0083] It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of a feature, step, operation, device, component and / or combination thereof.

[0084] The embodiment provides a fault-tolerant control system for improving the driving safety of a heavy multi-axle steering vehicle, comprising a fault diagnosis module, an upper control module, a lower control module and a fault-tolerant control module. The working process is as shown in the figure. Figure 1

[0085] The fault diagnosis module is used to determine whether the steering wheel is stuck. The fault diagnosis module receives the wheel angle information output by the vehicle and determines whether the wheel is stuck. Considering different failure modes of each steering system, the steering wheel stuck is generally divided into single-axle steering wheel stuck, two-axle steering wheel stuck and three-axle steering wheel stuck.

[0086] The upper control module is used to calculate the additional lateral force ΔF y and additional yaw moment ΔM Z needed to maintain the stability of the vehicle by using an adaptive sliding mode control algorithm when the fault diagnosis module determines that the steering wheel is stuck. ​

[0087] The lower control module is used for distributing the tire lateral force according to the AF obtained by the upper control module y and AM Z , and optimizing the distribution of the tire lateral force of the non-faulty wheel.

[0088] The fault-tolerant control module is used for solving a fault-tolerant feasible region of the tire force after the fault occurs, judging whether the optimized tire lateral force is within the fault-tolerant feasible region, and selecting an optimal fault-tolerant controller for different failure modes to perform fault-tolerant control on the faulty vehicle according to the judgment result.

[0089] Figure 2 It is a whole fault-tolerant control framework of the heavy multi-axle vehicle in the embodiment.

[0090] The whole structure of the steering failure fault-tolerant control is established. The hierarchical fault-tolerant controller is designed. The upper layer is a parameter adaptive sliding mode controller for solving the additional force and torque for making the vehicle reach the expected state. The lower layer controller optimizes the distribution of the tire lateral force by using a quadratic programming method with the tire load rate as the performance index. The fault-tolerant control module selects different fault-tolerant controllers for different failure modes to control the faulty vehicle. The fault-tolerant controller I takes the yaw stability demand and the trajectory tracking demand as the control target to make the faulty vehicle meet the yaw stability demand and the trajectory tracking demand. The fault-tolerant controller II takes the yaw stability demand as the control target to make the faulty vehicle as stable as possible.

[0091] In the embodiment, a certain seven-axle heavy vehicle is taken as an example. The whole vehicle parameters are as follows:

[0092]

[0093] The front three axles of the researched heavy seven-axle vehicle are mechanical hydraulic power steering systems, and the rear four axles are linear control electric hydraulic servo power steering systems. Generally, the failure probability of the rear four axles is relatively high. The invention only considers the wheel locking failure of the rear four axles. Figure 3 It is a working state schematic diagram of the heavy multi-axle vehicle in the embodiment when the steering locking does not occur. Figure 4 It is a working state schematic diagram of the heavy multi-axle vehicle in the embodiment when the steering locking occurs.

[0094] According to the different number of wheel locking in different positions, since the faulty vehicle is a seven-axle vehicle, the single axle locking, two axle locking and three axle locking are more common. Here, the typical fault working conditions are listed for fault-tolerant control, as shown in the following table:

[0095]

[0096] When the first six axles of a seven-axle vehicle are steering normally, the seventh axle will jam, with a jamming angle of 0°. A schematic diagram of the jamming process is shown below. Figure 4 As shown in (a), the malfunctioning vehicle's trajectory deviates from the normal path at this time, as shown in the image. Figure 5 As shown in (a); the 6th and 7th axles of the seven-axle vehicle jammed at an angle of 0°. The schematic diagram of the jamming is shown below. Figure 4 As shown in (b), the malfunctioning vehicle's trajectory deviates from the normal path at this time, as shown in the image. Figure 5 As shown in (b); the 5th, 6th, and 7th axles of the seven-axle vehicle jammed at an angle of 0°. A schematic diagram of the jamming process is shown below. Figure 4 As shown in (c), the malfunctioning vehicle's trajectory deviates from the normal path at this time, as shown in the image. Figure 5 As shown in (c).

[0097] Figure 5 This diagram illustrates the control effect of a heavy-duty multi-axle vehicle experiencing steering jamming in this embodiment, after being controlled by a fault-tolerant controller. When the 7th axle of the heavy-duty multi-axle vehicle jams, or when the 6th and 7th axles jam simultaneously, fault-tolerant controller I is used to provide fault tolerance for the faulty vehicle. The path after fault-tolerant control is as follows: Figure 5 (a) Figure 5 As shown in (b); when the 5th, 6th, and 7th axles of a heavy multi-axle vehicle simultaneously jam, fault-tolerant controller II is used to provide fault tolerance for the faulty vehicle. The path after fault-tolerant control is as follows. Figure 5 (c)

[0098] like Figure 1 As shown, this embodiment also provides a fault-tolerant control method for improving the driving safety of heavy-duty multi-axle steering vehicles based on the above system, including the following steps:

[0099] Step S1: Establish the ideal dynamic model of the multi-axle steering vehicle, detect the actual steering angle of the wheel through the wheel steering angle sensor, compare it with the ideal steering angle calculated by the zero center of mass sideslip strategy, and determine whether the wheel is stuck by the fault diagnosis module.

[0100] Step S2: When the fault diagnosis module determines that the wheel is stuck, the deviation between the actual sideslip angle and yaw rate of the faulty vehicle and the ideal sideslip angle and yaw rate is input into the upper control module. The upper control module then calculates the additional force and torque required to bring the faulty vehicle to the desired state.

[0101] Step S3: Based on the additional force and torque obtained from the upper control module, optimize the distribution of the lateral force of the remaining non-faulty wheels with the goal of minimizing the tire load rate.

[0102] Step S4: solving the fault-tolerant feasible region of tire force after the fault occurs, judging whether the tire lateral force after the optimal distribution is within the range of the fault-tolerant feasible region, so as to select the best fault-tolerant controller to perform fault-tolerant control on the faulty vehicle; when the fault occurs, if the tire lateral force after the optimal distribution is within the range of the fault-tolerant feasible region, the fault-tolerant controller I is selected to perform fault-tolerant control on the faulty vehicle, and the fault-tolerant controller I takes the yaw stability and trajectory tracking as the control target; if the tire lateral force after the optimal distribution is not within the range of the fault-tolerant feasible region, the fault-tolerant controller II is selected to make the faulty vehicle maintain the original driving trajectory as much as possible, and the fault-tolerant controller II takes the yaw stability as the main control target.

[0103] In step S1, the ideal dynamics model of the whole vehicle is established as follows:

[0104] The influence of the suspension is ignored, that is, the vertical motion, the front and rear pitching of the vehicle body, and the left and right roll of the vehicle are ignored, only the motion in the horizontal plane is considered; the air resistance and the disturbance of the side wind during driving are ignored; it is assumed that the vertical load and the side stiffness of each tire are equal.

[0105] The ideal dynamics model of the vehicle is expressed as:

[0106]

[0107]

[0108] In this embodiment, the multi-axle steering vehicle is a seven-axle heavy vehicle, that is, k = 7, and the ideal dynamics model of the vehicle is specifically:

[0109]

[0110]

[0111] It is assumed that the working state of the tire is in the linear region, and the approximate expression of the tire lateral force of the vehicle is obtained:

[0112] F yi =C i α i

[0113]

[0114] F y is the resultant force of the vehicle along the Y-axis direction; M Z is the yaw moment of the vehicle around the Z-axis direction; I Z is the moment of inertia of the vehicle around the Z-axis; γ is the yaw angular velocity of the whole vehicle; is the yaw angular acceleration of the whole vehicle; m is the mass of the whole vehicle; F yi is the lateral force of the i-th axle; v xis the component of the center of mass velocity v on the X-axis; v y is the component of the center of mass velocity v on the Y-axis; δ i is the wheel angle of the ith axle; L i represents the distance from the center of mass of the vehicle to the ith axle, positive before the center of mass and negative after the center of mass; C i is the cornering stiffness of the tire.

[0115] The ideal turning angle of the multi-axle steering vehicle is calculated, and the ideal turning angle information and the actual turning angle information are sent to the fault diagnosis module. If the actual turning angle is consistent with the ideal turning angle, the vehicle is in normal operation, and if the actual turning angle is inconsistent with the ideal turning angle, it is determined that the vehicle wheel is stuck.

[0116] The method for calculating the ideal turning angle of each axle of the multi-axle steering vehicle through the zero center of mass cornering strategy is as follows:

[0117] The first axle turning angle δ1 is input, and the relationship between each axle turning angle and the first axle turning angle δ1 is as follows:

[0118]

[0119]

[0120] In the formula, D is the projection distance of the center of mass to the center of mass of the vehicle in the direction of the vehicle length.

[0121] The fault diagnosis module judges whether the vehicle is stuck. The actual turning angle of each wheel is measured by the turning angle sensor. If the actual turning angle signal of each wheel is consistent with the ideal turning angle, the vehicle is in normal operation, and if the actual turning angle signal of each wheel is inconsistent with the ideal turning angle signal, it is determined that the vehicle wheel is stuck.

[0122] The front three axles of the heavy seven-axle vehicle researched in the embodiment are mechanical hydraulic power steering systems, and the rear four axles are linear control electric hydraulic servo power steering systems. Generally, the failure probability of the rear four axles is relatively high, and the embodiment only considers the case of wheel sticking failure of the rear four axles.

[0123] In step S2, a joint controller of the center of mass cornering angle and the yaw rate is designed based on the adaptive sliding mode control algorithm, so as to calculate the additional lateral force ΔF y and the additional yaw moment ΔM Z needed to maintain the stability of the vehicle according to the deviation of the actual center of mass cornering angle and the actual yaw rate of the fault vehicle from the ideal center of mass cornering angle and the ideal yaw rate.

[0124] The following deviation of the yaw rate and the center of mass cornering angle is used as the control quantity, and the additional ΔF y , ΔM Z is used as the control input.

[0125] The dynamics model of the vehicle is converted into a state space equation:

[0126]

[0127] The sliding surface is set by the deviation of the center of mass side slip angle:

[0128] e β = β d - β

[0129] where e β is the deviation of the center of mass side slip angle, β is the actual center of mass side slip angle of the vehicle, and β d is the ideal center of mass side slip angle of the vehicle.

[0130] The Lyapunov function is defined as:

[0131]

[0132] In the formula:

[0133]

[0134] Then:

[0135]

[0136] The control rate is designed as:

[0137]

[0138] where γ d is the ideal yaw rate of the vehicle, k1 is the sliding mode control parameter, is the estimated value of F y .

[0139] In the formula, k > 0, then:

[0140]

[0141] The adaptive rate is taken as:

[0142]

[0143] The input ΔF y satisfies:

[0144]

[0145] where β is the ideal center of mass side slip angle rate of the vehicle.

[0146] At this time, the derivative of the Lyapunov function is:

[0147]

[0148] iff e β = 0, iff e = 0 β iff e

[0149] The sliding surface is set by the yaw rate error:

[0150] iff e γ = γ d - γ

[0151] where e γ is the yaw rate error, γ is the actual vehicle yaw rate, and γ d is the ideal vehicle yaw rate.

[0152] The Lyapunov function is defined as:

[0153]

[0154] where:

[0155]

[0156] Then:

[0157]

[0158] The control rate is designed as:

[0159]

[0160] where k2 is the sliding mode control parameter, and M Z is the estimated value of M.

[0161] where k > 0, then:

[0162]

[0163] The adaptive rate is taken as:

[0164]

[0165] The input ΔM Z satisfies:

[0166]

[0167] At this time, the derivative of the Lyapunov function is:

[0168]

[0169] iff eγ = 0, i.e. when e γ ≡ 0.

[0170] The adaptive sliding mode controller is a double-input double-output controller, which uses ΔF y and ΔM Z as control inputs. ΔM Z is controlled to track the ideal state γ d , and ΔF y is controlled to control β.

[0171] In step S3, when optimizing the distribution of tire lateral forces of the remaining non-faulty wheels, in order to effectively and evenly use all the tires as much as possible, avoid certain tires from reaching serious load conditions during driving, and minimize the tire load rate J, the tire lateral forces are optimized by quadratic programming, and the objective function is:

[0172]

[0173] wherein ξ i is the weight corresponding to each wheel, and F zi is the vertical force received by each wheel.

[0174] In addition to the optimization objective, constraint conditions are also considered, including equality constraints and inequality constraints:

[0175] (1) Road adhesion limit:

[0176] -μ i ·F zi ≤ F yi ≤ μ i ·F zi

[0177] (2) Lateral force constraint:

[0178] beq = Aeq · x

[0179] Based on the above equality, inequality and optimization function, a quadratic programming mathematical model is established:

[0180]

[0181]

[0182] The objective function and constraint conditions are converted into a standard format, and then substituted into MATLAB for solving, and the lateral forces of the remaining non-faulty wheels are distributed by linear quadratic optimization.

[0183] In step S4, the specific method for solving the fault-tolerant feasible region is:

[0184] First, the effective range of tire force is solved based on the principle of tire friction circle, and the fault tolerance feasible region of tire lateral force is obtained by adding the influence of steering system stuck fault. Then, the fault tolerance feasible region of the resultant force of vehicle operation is derived based on the fault tolerance feasible region of tire lateral force.

[0185] The influence of environment on tire force is mainly the constraint of friction ellipse between road and tire on tire force. The size of tire adhesion force is directly affected by vehicle vertical load and road friction coefficient. Their relationship can be approximated as a friction circle, which can be described as:

[0186]

[0187] According to the principle of friction circle, the lateral tire force limit value of the wheel is calculated, which is expressed as:

[0188] -μ i ·F zi sinθ i ≤F yi ≤μ i ·F zi sinθ i ,(i=1,...,7)

[0189] Let μF zi sinθ i =ζ i and i=1,2,3,4,5,6,7, where μ is the adhesion coefficient of the road on which the vehicle is running, θ i is the angle between the longitudinal force of the vehicle tire and the lateral force of the tire, and ζ i represents the limit value of the tire lateral force, which is used for subsequent fault tolerance control feasible region calculation. The lateral force of each tire is expressed as:

[0190] -ζ i ≤F yi ≤ζ i ,(i=1,...,7)

[0191] The construction of tire force fault tolerance feasible region, when the vehicle steering system is stuck, the steering angle of the wheel is fixed at a value, and the lateral force of the tire changes to:

[0192] F yim =F yi +q i (i=4,5,6,7)

[0193] The change value q i, q4 is the change value of the fourth axle of the vehicle, q5 is the change value of the fifth axle of the vehicle, q6 is the change value of the sixth axle of the vehicle, and q7 is the change value of the seventh axle of the vehicle. Among them, q4, q5, q6, and q7 can exist simultaneously. Therefore, the fault-tolerant feasible region of the tire lateral force can be obtained:

[0194] -μ i ·F zi sinθ i ≤F yi +q i ≤μ i ·F zi sinθ i ,(i=4,...,7)

[0195] The simplified expression is:

[0196] -ζ i ≤F yi =F yi +q i ≤ζ i ,(i=4,...,7)

[0197] Further simplified as:

[0198] -(ζ i -|q i |)≤F yi ≤ζ i -|q i |,(i=4,...,7)

[0199] Therefore, under the constraint of the friction circle, the fault-tolerant feasible region of the tire lateral force is:

[0200]

[0201] In step 4, when the 7th axle is stuck, the 6th and 7th axles are stuck, and the 5th, 6th, and 7th axles are stuck, the fault-tolerant controller is selected to control the fault vehicle by judging whether the tire lateral force planned and optimized is within the fault-tolerant feasible region.

[0202] After judgment, when the 7th axle is stuck, the 6th and 7th axles are stuck, and the 5th, 6th, and 7th axles are stuck, the fault-tolerant controller is selected to control the fault vehicle by judging whether the tire lateral force planned and optimized is within the fault-tolerant feasible region.

[0203] After judgment, when the 7th axle is stuck, the 6th and 7th axles are stuck, and the 5th, 6th, and 7th axles are stuck, the fault-tolerant controller is selected to control the fault vehicle by judging whether the tire lateral force planned and optimized is within the fault-tolerant feasible region.

[0204] The fault-tolerant controller I is used to control the fault vehicle with the tire lateral force within the fault-tolerant feasible region after optimization, and the fault-tolerant controller I focuses on the yaw stability control and trajectory tracking control of the fault vehicle:

[0205] The fault-tolerant controller I realizes by converting the tire lateral force into executable steering angle through tire model. In order to simplify the design of the fault-tolerant controller I, the tire lateral force formula is simplified as follows:

[0206]

[0207] Where, Δδ i is the additional steering angle of the wheel.

[0208] Therefore, the additional steering angle Δδ i of the wheel is:

[0209]

[0210] When the vehicle steering system is stuck, the optimized distribution of the wheel lateral force exceeds the range of the fault-tolerant feasible region, i.e. the tire lateral force after the optimized distribution is saturated, the fault-tolerant controller II is used to control the fault-tolerant vehicle, and the fault-tolerant controller II focuses on the yaw stability control:

[0211] The fault-tolerant controller II uses the method of weakening the control input to control the vehicle, and the dynamic balance equation of the vehicle is as follows:

[0212] ∑F yt = ∑F yf + f y (v x , δ t )

[0213] Where, ∑F yt is the control quantity after the fault-tolerant control and meets the fault-tolerant feasible region; ∑F yt is the control quantity which does not meet the fault-tolerant feasible region; f y is the coefficient of adjusting the control input, i.e. the influence caused by the stuck fault of the steering system is repaired by adjusting the driving speed and the front wheel steering angle; the independent variable v x1 = m·v x , δ t = n·δ1; v x and δ1 are the input quantities of the vehicle system, i.e. the driving speed and the front wheel steering angle, m and n are the weakening coefficients of the speed and the front wheel steering angle, the value range is (0, 1], v x1 and δ t are the weakened control inputs, i.e. the driving speed and the front wheel steering angle of the vehicle after the fault-tolerant control.

[0214] The application provides a fault-tolerant control method for improving the driving safety of heavy multi-axle steering vehicles, corresponding fault-tolerant controllers are designed for the stuck fault conditions of the heavy multi-axle vehicles, and the designed fault-tolerant controllers perform fault-tolerant control on the fault vehicles of different stuck types with different control targets.

[0215] Figure 5 Figure 1 is a diagram showing the control effect of the method in this embodiment in the process of steering wheel locking. According to the method, after the steering wheel is locked, the lateral stability of the fault vehicle controlled by the controller is improved, and the fault vehicle can better track the ideal trajectory, as shown in (a), (b) and (c). Figure 5 (a)、 Figure 5 (b)、 Figure 5 (c).

[0216] The above description is only the preferred embodiment of the present application, and is not intended to limit the other forms of the present application. Any skilled person in the art can use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution of the present application and according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A fault-tolerant control method for improving the driving safety of a heavy multi-axle steered vehicle, characterized by, Provided is a fault-tolerant control system, comprising: a fault diagnosis module for determining whether a steering wheel is stuck; the fault diagnosis module receives wheel rotation angle information output by a vehicle and determines whether a wheel is stuck; An upper control module is configured to calculate additional lateral force required to maintain stability of the vehicle by using an adaptive sliding mode control algorithm when the failure diagnosis module determines that the steering wheel is stuck and additional yaw moment ​ The lower control module is configured to perform the following functions: and optimizing the distribution of lateral forces on the tires of the non-faulty wheels. a fault-tolerant control module for solving a fault-tolerant feasible region of tire force after a fault occurs, determining whether tire lateral force after optimization and distribution is within the fault-tolerant feasible region, and selecting an optimal fault-tolerant controller for different failure modes to perform fault-tolerant control on the faulty vehicle according to a result of the determination; different failure modes of different steering systems are considered, and steering wheel sticking is generally classified into single-axle steering wheel sticking, two-axle steering wheel sticking, and three-axle steering wheel sticking; when a heavy multi-axle vehicle is single-axle stuck or two axles are simultaneously stuck, a fault-tolerant controller I is used to perform fault-tolerant control on the faulty vehicle; when a heavy multi-axle vehicle is three-axle stuck, a fault-tolerant controller II is used to perform fault-tolerant control on the faulty vehicle; a fault-tolerant control method for improving the driving safety of a heavy multi-axle steering vehicle based on the fault-tolerant control system, comprising the following steps: Step S1: an ideal dynamics model of the multi-axle steering vehicle is established, actual wheel rotation angles are detected by a wheel rotation angle sensor, and ideal rotation angles are calculated by a zero-center side slip strategy; a fault diagnosis module is used to determine whether a wheel is stuck; Step S2: when the fault diagnosis module determines that a wheel is stuck, the deviation of actual center side slip angle and yaw rate of the faulty vehicle from ideal center side slip angle and yaw rate is input into an upper control module, and additional force and torque for making the faulty vehicle reach an expected state are solved by the upper control module; Step S3: additional force and torque obtained by the upper control module are used to optimize and distribute tire lateral force of the remaining non-faulty wheels with the objective of minimizing tire load rate; Step S4: solving the fault-tolerant feasible region of tire force after the fault occurs, judging whether the tire lateral force after the optimal distribution is within the range of the fault-tolerant feasible region, so as to select the best fault-tolerant controller to perform fault-tolerant control on the faulty vehicle; when the fault occurs, if the tire lateral force after the optimal distribution is within the range of the fault-tolerant feasible region, the fault-tolerant controller is selected performing fault-tolerant control on the faulty vehicle, the fault-tolerant controller taking yaw stability and trajectory tracking as the control target; if the tire lateral force after the optimal distribution is not within the range of the fault-tolerant feasible region, the fault-tolerant controller making the faulty vehicle maintain the original driving trajectory as much as possible, the fault-tolerant controller taking yaw stability as the main control target; a specific method for establishing an ideal dynamics model of the multi-axle steering vehicle is as follows: the influence of suspension is ignored, i.e., vertical movement, body pitching and rolling of the vehicle are ignored, and only horizontal plane movement is considered; air resistance and side wind disturbance during driving are ignored; and it is assumed that vertical load and side slip stiffness of each tire are equal; an ideal dynamics model of the vehicle is expressed as: it is assumed that the working state of the tire is in a linear region, and an expression of tire lateral force of the vehicle is obtained: For vehicles along Resultant force in the axial direction; For vehicles to bypass Yaw moment in the axial direction; For vehicles to bypass Moment of inertia of the shaft; This refers to the yaw rate of the entire vehicle. This refers to the yaw acceleration of the entire vehicle. For the overall vehicle weight; For the first Lateral forces along the axis; velocity of the center of mass exist Components on the axis; For the velocity of the center of mass exist Components on the axis; For the first Wheel rotation angle; Indicates the vehicle's center of gravity to the 1st The distance along the axis is positive in front of the center of mass and negative behind the center of mass; This refers to the lateral stiffness of the tire; In optimizing the distribution of tire lateral forces to the remaining non-failed wheels, in order to use all the tires as effectively and uniformly as possible, avoiding that a particular tire reaches a severe load condition during the trip, the tire load rate is minimized The tire lateral forces are optimized to be distributed to the target function: wherein, is a weight corresponding to each wheel, is a vertical force received by each wheel; a specific method for solving a fault-tolerant feasible region is as follows: first, the effective range of tire force is solved based on the tire friction circle principle, and the fault-tolerant feasible region of tire lateral force is obtained by adding the influence of steering system sticking; then, the fault-tolerant feasible region of the vehicle is derived based on the fault-tolerant feasible region of tire lateral force; the limit value of tire lateral force of the vehicle is calculated according to the friction circle principle and is expressed as: wherein, is the adhesion coefficient of the road surface on which the vehicle is travelling, is the angle between the longitudinal force and the lateral force of the tyre of the vehicle, introducing the variation of the lateral force of the tyre of the wheel due to the locking of the steering system , is the variation of the vehicle's first axle, the fault-tolerant feasible region of the lateral force of the tyre being obtained as: Adopting fault-tolerant controller The fault-tolerant controller is used to control the failure vehicle in the fault-tolerant feasible region after the tire lateral force is optimized distributed Focus on the yaw stability control and trajectory tracking control of the failure vehicle: Fault tolerant controller This is achieved by converting the tire side force into an executable steering angle through a tire model; the tire side force formula is simplified to: wherein is the additional rotation angle of the wheel; Thus, the additional rotation angle of the wheel is: When the vehicle steering system is stuck, the system is greatly affected, the optimized distribution of each wheel lateral force exceeds the range of fault tolerance feasible region, that is, the tire lateral force after optimization and distribution is saturated, a fault tolerance controller is adopted The fault tolerance controller is used for fault tolerance control on the vehicle Focus on yaw stability control: Fault tolerant controller A vehicle is fault-tolerantly controlled by weakening the control input, and a dynamic balance equation of the vehicle is as follows: wherein, is the control quantity obtained after fault-tolerant control, which satisfies the fault-tolerant feasible region; is the control quantity which does not satisfy the fault-tolerant feasible region; is the coefficient of the adjusted control input, i.e. the influence brought by the steering system stuck fault is repaired by adjusting the driving speed and the front wheel steering angle of the vehicle; the independent variable , ; and are the input quantities of the vehicle system, the driving speed and the front wheel steering angle, and are the weakening coefficients of the driving speed and the front wheel steering angle, the value range is , and are the weakened control inputs, i.e. the driving speed and the front wheel steering angle of the vehicle after fault-tolerant control.

2. The fault-tolerant control method for improving travel safety of a heavy multi-axle turning vehicle according to claim 1, characterized by, ideal rotation angles of the multi-axle steering vehicle during movement are calculated, and the ideal rotation angle information and actual rotation angle information are sent to the fault diagnosis module; if the actual rotation angle is consistent with the ideal rotation angle, the vehicle is in normal operation; if the actual rotation angle is inconsistent with the ideal rotation angle, it is determined that the vehicle wheel is stuck.

3. The fault-tolerant control method for improving travel safety of a heavy multi-axle turning vehicle according to claim 2, characterized by, a method for calculating ideal rotation angles of each axle of the multi-axle steering vehicle by a zero-center side slip strategy is as follows: input first axis angle the relationship between each axis angle and the first axis angle is In the formula, is the projection of the line connecting the center of mass to the instantaneous center of rotation of the vehicle in the vehicle longitudinal direction.

4. The fault-tolerant control method for improving travel safety of a heavy multi-axle turning vehicle according to claim 1, characterized by A combined controller of the vehicle's center of mass side slip angle and yaw rate is designed based on an adaptive sliding mode control algorithm to calculate additional side force required to maintain the vehicle stable according to the deviation of the actual center of mass side slip angle and yaw rate of the faulty vehicle from the ideal center of mass side slip angle and yaw rate and additional yaw moment ​ a sliding surface is set by using the deviation of the center side slip angle: wherein is a deviation of the center of mass side slip angle, is the actual center of mass side slip angle of the vehicle, is the ideal center of mass side slip angle of the vehicle; the control rate is designed as: wherein, is the vehicle ideal yaw rate, is a sliding mode control parameter, is an estimate of the vehicle lateral acceleration. the adaptive rate is taken as: Input Satisfies: wherein, is the desired rate of change of the vehicle's mass center side slip angle; a sliding surface is set by using the deviation of the yaw rate: wherein is a deviation of the yaw rate, is the actual vehicle mass center side slip angle, is the ideal vehicle mass center side slip angle; the control rate is designed as: wherein is a sliding mode control parameter, is an estimate of the value of Adaptation rate taken as: Input satisfies: 。

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