Integrated stability control method and system for yaw and roll of heavy vehicle

Abstract

The invention discloses a yaw and roll integrated stability control method and system for a heavy vehicle. The method comprises the following steps: (1) establishing a two-degree-of-freedom vehicle model; (2) deducing ideal state information of yaw motion; (3) establishing yaw-roll stability control logic; (4) establishing a yaw stability control method, a roll stability control method and a stability integrated control method; and (5) the braking torque is distributed to control the vehicle. The system comprises a stability target calculation module, a stability judgment module, an integrated stability control module and a braking torque distribution module. According to the method and the system, the yaw and roll instability risks of the vehicle in the running process are considered at the same time, multi-stability target control can be carried out, the coupling conflict existing between the control target of yaw stability and the control target of roll stability is solved, the comprehensive operation stability of the heavy vehicle is greatly improved, and the driving safety of the heavy vehicle is improved.

Description

Technical Field

[0001] The invention belongs to the field of vehicle stability control, and in particular relates to the field of a heavy vehicle yaw and roll integrated stability control method and system. Background Art

[0002] As vehicle safety becomes increasingly high, vehicle stability has received more and more attention. However, current research focuses mostly on one aspect of stability, or there is no systematic control method for integrated stability control.

[0003] Due to the characteristics of heavy weight, high center of gravity, dynamic load changes, etc., heavy vehicles have the risk of yaw instability and roll instability during operation. Therefore, during the movement of heavy vehicles, it is necessary to consider both yaw stability and roll stability. Stability control has many evaluation indicators. Heavy vehicles will face a variety of working conditions during movement. A single stability target is difficult to fully evaluate the stability state of the vehicle, and multiple stability targets need to be considered; and there is a coupling conflict between the control target of yaw stability and the control target of roll stability, which brings challenges to the stability control of heavy vehicles. When performing multi-stability target control, there is no reasonable control logic, which makes it impossible to effectively perform stability control. How to reasonably design a stability integrated control system and method to make the vehicle have better maneuverability is an important research topic.

[0004] As vehicles develop towards high speed, dense traffic and complex traffic, the control pressure on drivers for different driving conditions is increasing. Especially for heavy vehicles, improper control can cause instability in many aspects. Therefore, it is extremely important to carry out integrated stability control. At present, most of the heavy vehicle stability control considers one kind of stability for control design, which is suitable for stability control under general conditions or specific conditions. However, when considering multi-stability control, there is a lack of reasonable control logic, which makes the integrated stability control of heavy vehicles lack the corresponding control effect.

[0005] In order to solve the existing technical problems, a Chinese patent with application number CN200810232797.2 discloses "a vehicle steering and braking stability control system", which discusses a fuzzy control method for controlling the steering wheel steering controller and each wheel brake controller according to the lateral path deviation signal output by the lane deviation measuring device embedded in the electronic control unit. However, this method does not take the roll stability into consideration, and the fuzzy control makes the range control not precise enough.

[0006] The Chinese patent application number CN201610611508.4 discloses a "vehicle braking stability control method and system" that calculates the difference between the target yaw rate and the actual yaw rate and the absolute value of the difference, and controls the increase of the braking force of one wheel or the decrease of the braking force of the other wheel according to the type of braking instability of the vehicle and the slip rate of the wheel, thereby achieving the purpose of vehicle body stability. However, it does not consider the roll stability, and the roll stability of the vehicle cannot be guaranteed after the yaw stability of the vehicle is guaranteed. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method and system for integrated yaw and roll stability control of heavy vehicles. The method and system are based on the characteristics of heavy vehicles such as high center of mass, large external dimensions, and dynamic load changes. At the same time, the risk of yaw and roll instability of the vehicle during operation is taken into account. It can perform multi-stability target control, solve the coupling conflict between the control target of yaw stability and the control target of roll stability, greatly improve the comprehensive handling stability of heavy vehicles, and improve the driving safety of heavy vehicles.

[0008] In order to solve the above technical problems, the present invention adopts the following technical means:

[0009] A heavy vehicle yaw and roll integrated stability control method comprises the following steps:

[0010] (1) Establish a two-degree-of-freedom vehicle model including yaw motion. The motion model equations are:

[0011] The lateral movement of the vehicle,

[0012] The yaw motion of the vehicle,

[0013] A three-degree-of-freedom vehicle model including yaw and roll motion is established, and the motion model equations are:

[0014] The rolling motion of the vehicle around the X-axis,

[0015] The vehicle moves sideways along the Y axis.

[0016] The vehicle's yaw motion around the Z axis,

[0017] Where, the mass center side slip angle β = v y / v x ,but m, m s are the vehicle mass and sprung mass respectively, h is the vehicle height, v is x 、v yare the longitudinal speed and lateral speed of the vehicle, C f , C r are the front and rear wheel cornering stiffnesses, and the front and rear wheel slip angles are a y is the lateral acceleration, I xx is the rolling inertia of the vehicle mass, I xz is the pitching moment of inertia of the vehicle mass, l f , l r are the distances from the center of mass to the front and rear axles, is the vehicle roll angle, are the roll angular velocity and roll angular acceleration, are the yaw rate and yaw acceleration respectively, K φ , C φ are the roll stiffness and roll damping coefficient respectively.

[0018] (2) Based on the two-degree-of-freedom vehicle model in step (1), the ideal state information of yaw motion is derived as follows:

[0019] The ideal yaw rate is calculated by taking the steady-state yaw rate gain of the vehicle in uniform circular motion:

[0020]

[0021] in,

[0022] Considering that the vehicle's motion state is limited by the road adhesion coefficient, the vehicle's maximum lateral acceleration must meet the adhesion condition:

[0023] a ymax ≤μ max g, μ max Road adhesion coefficient. At the same time, the vehicle lateral acceleration can be approximately expressed as: The maximum yaw rate is:

[0024] Then the ideal yaw rate can be further calculated as:

[0025] In vehicle yaw stability control, the center of mass slip angle is generally small. In actual control, the ideal center of mass slip angle is generally set to zero: β d =0.

[0026] The yaw stability is determined based on the ideal state information of the yaw stability, and then it is determined whether the vehicle has yaw instability.

[0027] Derivation of ideal state information of roll motion according to the three-degree-of-freedom vehicle model of step (1) to determine roll stability to determine whether the vehicle is in a roll instability;

[0028] (3) Based on the yaw stability determination and roll stability determination in step (2), a yaw-roll stability control logic is established; in order to improve the operating efficiency of the stability control system, a logical analysis is performed on the stability of the intelligent vehicle under different operating conditions, and the stability operating conditions that may be encountered in the actual operation of the intelligent vehicle are divided into the following three types:

[0029] (301) Yaw instability condition: When the vehicle's yaw rate or center of mass slip angle reaches the instability judgment threshold, and the real-time roll angle and roll rate are still within the stability threshold range, yaw stability control is adopted;

[0030] (302) Roll instability condition: When the vehicle's yaw rate and center of mass slip angle are within the stability threshold range, but the real-time roll angle and roll rate exceed the stability threshold range, roll stability control is required;

[0031] (303) Yaw-roll instability condition: When the vehicle's center of mass slip angle and yaw angular velocity reach the instability judgment threshold, and the real-time roll angle and roll angular velocity exceed the stability threshold range, it is necessary to comprehensively consider the yaw stability and roll stability, and then perform corresponding stability integrated control; according to the obtained yaw stability judgment target and roll stability judgment threshold, respectively perform corresponding stability control, compare the actual vehicle operation state with the ideal state information in real time, make a real-time judgment on the instability state of the vehicle according to the stability judgment condition, and further perform corresponding stability control until the stability condition is within the stability threshold range; the ideal state is calculated by the two-degree-of-freedom and three-degree-of-freedom vehicle models. When an input is given to the vehicle model, a certain state value will be generated accordingly: yaw angular velocity, roll angular velocity, these quantities are the ideal state information, and when the same input is given to the real vehicle, the response obtained is the actual state information;

[0032] (4) establishing a yaw stability control method, a roll stability control method, and a stability integrated control method respectively according to the yaw-roll stability control logic established in step (3);

[0033] (5) Distribute the braking torque to control the vehicle according to the control method established in step (4).

[0034] A heavy vehicle yaw and roll integrated stability control method, wherein the yaw stability is determined by the yaw angular velocity and the sideslip angle of the center of mass of the vehicle, wherein:

[0035] The yaw rate threshold condition is:

[0036] in, is the current ideal yaw rate of the vehicle, is the actual yaw rate of the vehicle at present, It is the calibration constant after experimental testing.

[0037] The center of mass sideslip angle threshold condition is:

[0038] Among them, C β2 , is the calibration constant, β is the sideslip angle of the center of mass, is the acceleration of the sideslip angle of the center of mass; the threshold value of the sideslip angle of the center of mass is determined if Within the stability region, the vehicle is considered to be in a stable state.

[0039] The yaw stability needs to be determined by comprehensively considering the yaw angular velocity and the sideslip angle of the center of mass, that is, the deviation between the real-time feedback values ​​of the two variables and their respective ideal values ​​is comprehensively considered to detect whether the vehicle is in a yaw instability state; if both deviations are within the threshold range, the vehicle is determined to be in a stable driving condition; otherwise, the vehicle is in an unstable condition; when the vehicle meets the above two threshold conditions at the same time, the vehicle is considered to be stable, otherwise the vehicle is determined to be yaw unstable.

[0040] The heavy-duty vehicle yaw and roll integrated stability control method, the roll stability is determined by the real-time roll angle and roll angular velocity of the vehicle, and the real-time roll factor is calculated according to the feedback values ​​of the real-time roll angle and roll angular velocity:

[0041]

[0042] in, is the vehicle roll angle, is the roll angular velocity; C RI1 , C RI2 is a parameter related to the vehicle, expressed as:

[0043]

[0044] Among them, h u is the height of the center of mass of the unsprung mass, h R is the roll center height, m u is the unsprung mass, m s is the sprung mass, m is the total mass of the vehicle, h is the height of the center of mass of the vehicle, t f is the wheelbase, K φ is the roll stiffness coefficient, C φ is the roll damping coefficient, g is the acceleration of gravity;

[0045] The roll stability is determined by the absolute value of the roll factor RI |RI|.

[0046] The roll stability determination method comprises the following steps:

[0047] Set the lower limit of the absolute value of the roll factor RI |RI| to | RI |、The upper limit value is | RI |=0.7, upper limit Control is carried out in the following situations:

[0048] (401)If |RI|<| RI |, at this time, the risk of vehicle rollover is considered small and anti-roll control is not required;

[0049] (402) If At this time, the risk of vehicle rollover is relatively high, and anti-roll control is required to prevent the vehicle from rolling over;

[0050] (403) If In this case, one side of the wheel has left the ground and rollover has occurred; in order to ensure the stability of the vehicle, a full braking strategy is adopted.

[0051] Heavy vehicle yaw and roll integrated stability control method, the lower limit value of the said | RI |=0.7, upper limit

[0052] The step (4) of the heavy vehicle yaw-roll integrated stability control method is to establish a yaw stability control method according to the yaw-roll stability control logic, comprising the following steps:

[0053] Step 7.1) Establish yaw stability control logic, and perform active steering and active braking control based on yaw instability; during yaw stability control, the active steering system achieves stability control by superimposing additional steering angles, and the active braking system achieves stability control by adjusting the braking forces of the four tires to form a yaw moment; under extreme working conditions, when the vehicle is working in the nonlinear region, the vehicle's center of mass side slip angle phase plane exceeds a certain threshold Active braking alone cannot completely solve the yaw instability problem. The integrated control of active braking and active steering is adopted to improve the instability of the vehicle through active steering intervention. In the process of active braking and active steering integration, in order to avoid interference between the two systems and obtain better stability control effect, the intervention logic of the active braking system and the active steering system is designed. If the judgment condition of the yaw angular velocity determines the instability state, that is, The vehicle is considered to have reached a yaw instability state; if the judgment condition based on the sideslip angle of the center of mass is within the threshold range, that is, The stability control system mainly takes active braking system control; if the judgment condition based on the sideslip angle of the center of mass exceeds the threshold range, that is, Then the integrated control of active braking and active steering is performed;

[0054] Step 7.2) The sliding mode variable structure control principle is used to design the yaw stability controller, which is divided into an active braking system yaw torque controller and an active braking-active steering integrated stability controller according to the yaw instability state of the vehicle;

[0055] Step 7.2.1) In order to solve the stability control based on yaw rate and sideslip angle at the same time, based on the two-degree-of-freedom vehicle model, the sliding mode variable structure control method is used to design the yaw torque controller of the active braking system;

[0056] First, the front wheel steering angle and yaw moment are used as input, and the yaw rate and center of mass sideslip angle are used as state variables to establish a two-degree-of-freedom vehicle model in the following form:

[0057] Among them, C f , C r are the front and rear wheel cornering stiffness, l f , l r are the distances from the front and rear axles to the center of mass, v x is the longitudinal speed of the vehicle, m is the mass of the vehicle, I zz is the yaw moment of inertia of the vehicle mass, δ f is the front wheel turning angle, ΔM z is the additional yaw moment.

[0058] At the same time, the vehicle yaw dynamics equation can be expressed as:

[0059] Among them, F yfl 、F yrl 、F yfr 、F yrr The lateral forces provided by the left front wheel, left rear wheel, right front wheel and right rear wheel, t f For wheelbase.

[0060] The difference between the actual yaw rate and the ideal yaw rate, as well as the difference between the actual center of mass sideslip angle and the ideal center of mass sideslip angle are used as the basis for judgment, and the sliding surface is defined as follows:

[0061] Taking the derivative of the sliding surface, we get:

[0062] Substituting it into the sliding surface, we get:

[0063]

[0064] make The target additional yaw moment can be obtained as follows:

[0065]

[0066] To ensure ΔM z In the presence of disturbances and parameter uncertainties, the sliding mode conditions can still be met. The exponential reaching law sliding mode control is adopted. The yaw torque controller of the active braking system can be specifically expressed as:

[0067] △M zev =△M z -k1s-k2sgn(s);

[0068] Where k1 and k2 are control gains, and k1, k2>0, sgn(s) is the sign function;

[0069] Step 7.2.2) Design an active braking-active steering integrated stability controller;

[0070] With the front wheel steering angle and yaw moment as input, yaw rate and center of mass sideslip angle as state variables, a two-degree-of-freedom vehicle model is established and rewritten into the state space form as follows:

[0071]

[0072] Among them, A and B are coefficient matrices, x and u are state variables and input variables respectively, and the expressions are:

[0073]

[0074] In order to enable the vehicle to better track the ideal yaw rate and sideslip angle, the tracking error is expressed as:

[0075] Among them, x d , x is the ideal and actual state variables - yaw rate and center of mass sideslip angle, e1 is the center of mass sideslip angle deviation, and e2 is the yaw rate deviation.

[0076] The sliding surface is taken as follows: Among them, c1, c2>0, and both are constants;

[0077] Taking the derivative of the sliding surface, we get: Among them, c is the coefficient matrix, the expression is:

[0078]

[0079] Take the exponential reaching law as: in ε a ,ε b ,k a ,k b >0, the expression of the control rate of the active braking-active steering integrated stability controller is:

[0080]

[0081] The step (4) of the heavy vehicle yaw-roll integrated stability control method is to establish a roll stability control method according to the yaw-roll stability control logic, comprising the following steps:

[0082] The sliding mode variable structure control method is used to design the roll stability controller and calculate the additional yaw moment required to reduce the vehicle roll factor RI. According to the expression of yaw motion in step 1), the additional yaw moment is introduced to obtain:

[0083]

[0084] For the analysis of vehicle roll stability, when the vehicle rolls stably, |RI| should be less than 0.7. When the system detects |RI|≥0.7, it starts anti-roll control to make the vehicle roll factor |RI| lower than or close to the roll threshold value |RI|. The sliding surface function is designed as: s=RI- RI ;

[0085] By taking the derivative of the sliding mode function and combining it with the vehicle three-degree-of-freedom model established in step 1), we can obtain:

[0086]

[0087] in,

[0088]

[0089] Among them, K φ is the roll stiffness, C φ is the roll damping coefficient, l e is the distance from the center of mass of the vehicle's sprung mass to the roll center, I xzs is the pitching moment of inertia of the sprung mass, I xx is the rolling inertia of the vehicle mass.

[0090] In order to eliminate the chattering phenomenon of the sliding mode variable structure control system, the sliding mode approach rate is selected as:

[0091]

[0092] In the formula, k1>0, k2>0, k1 is increased as much as possible, and k2 is reduced as much as possible. By reasonably selecting parameters k1 and k2, the state point can be quickly brought close to the sliding surface, and the vibration frequency of the sliding mode can also be effectively reduced;

[0093] Substituting the sliding mode reaching law expression into the above formula, the additional yaw moment expression of the roll stability controller is obtained as follows:

[0094]

[0095] Step (4) of the heavy vehicle yaw-roll integrated stability control method is to design a yaw-roll integrated stability controller according to the yaw-roll stability integrated control method, including the following steps:

[0096] When the vehicle status detection finds that yaw and roll instability exist at the same time, roll stability control is performed first; during the execution of roll stability control, it is necessary to determine whether understeer exists. If understeer does not occur, roll stability control continues; if understeer occurs, it is necessary to determine whether there is a risk of roll; if there is no risk of roll, the wheel braking pressure will be set to the target pressure value calculated by the roll stability control; conversely, when there is a risk of roll, roll stability control will continue; the specific controlled wheels are mainly determined by the wheel braking distribution calculation by the braking force distribution module; after the roll risk is eliminated, the yaw stability control function is performed; at this time, the wheel braking pressure will be set to the target pressure calculated by the yaw stability control, and the controlled wheels are still determined by the braking force distribution module;.

[0097] The implementation of roll stability control is determined by the current roll stability state of the vehicle; the degree of roll is determined mainly by whether the roll factor value exceeds the danger threshold. The danger threshold is set. RI | r =0.8; the roll stability control is specifically implemented as follows: if the vehicle state is small roll, that is, when the roll factor is 0.7≤|RI|≤0.8, the engine torque reduction is executed; if the vehicle state is large roll, that is, when the roll factor is |RI|>0.8, the engine torque reduction is executed and active braking is coordinated;

[0098] The yaw stability control and roll stability control calculate the additional yaw moment and anti-roll braking moment for their own separate control, and then complete the control through the integrated control logic; if the vehicle is in both yaw instability and roll instability at the same time, the roll stability control should be prioritized, followed by the yaw stability control;

[0099] The contradictory logic of yaw-roll integrated stability control can be specifically described as:

[0100] (1) The goals of yaw stability control and roll stability control are to keep the vehicle in proper understeer, ensuring that the vehicle can make stable and accurate steering responses under various complex road conditions and driving conditions, thereby improving the driving safety of the vehicle;

[0101] (2) Roll stability control may cause the vehicle to understeer more severely. Further roll stability control will increase the vehicle's understeer tendency and increase the risk of yaw instability. On the contrary, if yaw stability control works, reducing the vehicle's understeer tendency will increase the risk of roll. Therefore, these two control objectives are contradictory in this case.

[0102] Excessive lateral acceleration may cause serious vehicle roll. Reducing vehicle speed and yaw rate is a conventional method to limit lateral acceleration. However, excessive reduction of yaw rate may cause understeer, which in turn causes the wheels to lose ground adhesion, resulting in reduced steering performance of the vehicle and possible triggering of yaw stability control. Therefore, reducing vehicle speed can better resolve the conflict between these two problems. In roll stability control, the specific braking torque distribution strategy can be adopted in different ways. In terms of preventing vehicle roll, the roll stability of the vehicle can be improved by reducing the yaw rate. The specific control logic of braking torque distribution in this study is as follows:

[0103] When the vehicle is unstable due to yaw or roll, anti-roll control is given priority; during the vehicle's driving, the controller will continuously detect and judge the vehicle's status;

[0104] If the possibility of the vehicle rolling instability is detected, control is performed in the following situations:

[0105] (1) If only the roll instability occurs, only the roll stability control is performed to control the braking of the wheel on one side;

[0106] (2) If only yaw instability occurs, only yaw stability control is performed to control the braking of the wheel on one side;

[0107] (3) In the event of a roll stability problem, continue to apply unilateral wheel braking to the vehicle. If the vehicle oversteers, continue to apply unilateral braking;

[0108] (4) In the event of a roll stability problem, single-side wheel braking is still performed. However, if the vehicle is understeering and in a yaw instability state, |RI| is detected at this time. When |RI| exceeds the threshold value of 0.8, single-side wheel braking is continued to be applied to the vehicle, otherwise double-side wheel braking is performed. If the degree of understeering decreases, double-side wheel braking is performed. If the degree increases, the braking pressure of the inner front wheel is increased to implement yaw stability control. Then, the inspection continues. If there is a roll tendency, the braking pressure of the inner front wheel is reduced.

[0109] The step (5) performs braking torque distribution to control the vehicle, selects active steering control and active braking control according to the yaw torque calculated by the stability control module in step (4) and in combination with the current motion state, and further distributes the braking wheels of the active braking control. It can be specifically expressed as:

[0110] (1) Braking torque distribution under pendulum stability control. When performing vehicle stability control, the braking force is applied to the outer front wheel or the inner rear wheel first, using two braking methods: single-side braking and double-side braking.

[0111] Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive.

[0112] When the vehicle turns left, that is, the front wheel angle is greater than or equal to 0, and the yaw velocity direction is counterclockwise, and the yaw velocity is greater than 0, if the actual yaw velocity is less than the ideal value, understeer occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw velocity is less than the ideal value, oversteer occurs, and the right front wheel and right rear wheel are braked at this time.

[0113] When the vehicle turns right, that is, the front wheel angle is less than 0, and the yaw velocity direction is clockwise, and the yaw velocity is less than 0, if the actual yaw velocity is less than the ideal value, oversteering occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw velocity is less than the ideal value, understeering occurs, and the right front wheel and right rear wheel are braked at this time.

[0114] (2) Design a braking torque distribution strategy under roll stability control, and perform unilateral and bilateral wheel braking based on the additional yaw torque calculated by the roll stability controller.

[0115] Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive.

[0116] When the vehicle turns left, the vehicle will tend to tilt to the right. If single-side braking is selected, the right front wheel and right rear wheel will be braked. If double-side braking is selected, the right front wheel, left rear wheel and right rear wheel will be braked. When the vehicle turns right, the vehicle will tend to tilt to the left. If single-side braking is selected, the left front wheel and left rear wheel will be braked. If double-side braking is selected, the left front wheel, left rear wheel and right rear wheel will be braked.

[0117] The invention discloses a heavy-duty vehicle yaw and roll integrated stability control method and system, including: yaw stability control, roll stability control and yaw and roll stability integrated control. According to the stability control target calculated by the stability control target calculation module, the vehicle driving speed v is obtained by combining the speed sensor, the navigation positioning sensor and the inertial navigation sensor. x , vehicle yaw angle ψ and angular velocity Roll angle of the vehicle Roll angular velocity Lateral acceleration a y , respectively perform integrated control of yaw, roll and yaw-roll stability, calculate the appropriate active front wheel steering angle and yaw moment, and distribute the braking torque, ultimately achieving heavy vehicle stability control. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Picture 1 It is a heavy vehicle yaw and roll chassis stability integrated stability control logic diagram of the present invention.

[0119] Picture 2 It is the logic block diagram of the yaw stability control of the present invention.

[0120] Picture 3 It is a schematic diagram of the yaw stability control structure of the present invention.

[0121] Picture 4 It is a logic block diagram of the yaw-roll instability control of the present invention.

[0122] Picture 5 It is a schematic diagram of the yaw moment generated by a single brake wheel of the present invention. DETAILED DESCRIPTION

[0123] The present invention will be further described in detail below with reference to the accompanying drawings.

[0124] A heavy vehicle yaw and roll integrated stability control method Picture 1 For example, the following steps are included:

[0125] Step 1) Establish a two-degree-of-freedom vehicle model including yaw motion, and the motion model equations are:

[0126] The lateral movement of the vehicle,

[0127] The yaw motion of the vehicle,

[0128] The three-degree-of-freedom vehicle model in step 1) specifically considers the movement of the vehicle in the three directions of the X, Y, and Z axes, and the motion model equations are:

[0129] The rolling motion of the vehicle around the X-axis,

[0130] The vehicle moves sideways along the Y axis.

[0131] The vehicle's yaw motion around the Z axis,

[0132] Where, the mass center side slip angle β = vy / v x ,but m, m s are the vehicle mass and sprung mass respectively, h is the vehicle height, v is x 、v y are the longitudinal speed and lateral speed of the vehicle, C f , C r are the front and rear wheel cornering stiffnesses, and the front and rear wheel slip angles are a y is the lateral acceleration, I xx is the rolling inertia of the vehicle mass, I xz is the pitching moment of inertia of the vehicle mass, l f , l r are the distances from the center of mass to the front and rear axles, is the vehicle roll angle, are the roll angular velocity and roll angular acceleration, are the yaw rate and yaw acceleration respectively, K φ , C φ are the roll stiffness and roll damping coefficient respectively.

[0133] Step 2) The method for judging yaw and roll instability is as follows:

[0134] Step 2.1) Yaw instability determination based on the comprehensive yaw rate and center of mass sideslip angle threshold conditions.

[0135] According to the two-degree-of-freedom vehicle model in step 1), the ideal state information of yaw motion is derived as follows:

[0136] The ideal yaw rate is calculated by taking the steady-state yaw rate gain of the vehicle in uniform circular motion:

[0137]

[0138] in,

[0139] Considering that the vehicle's motion state is limited by the road adhesion coefficient, the vehicle's maximum lateral acceleration must meet the adhesion condition:

[0140] a ymax ≤μ max g, μ max Road adhesion coefficient. At the same time, the vehicle lateral acceleration can be approximately expressed as: The maximum yaw rate is:

[0141] Then the ideal yaw rate can be further calculated as:

[0142] In vehicle yaw stability control, the center of mass slip angle is generally small. In actual control, the ideal center of mass slip angle is generally set to zero: β d =0.

[0143] The yaw stability is determined based on the ideal state information of the yaw stability, and then it is determined whether the vehicle has yaw instability.

[0144] Derivation of ideal state information of roll motion according to the three-degree-of-freedom vehicle model in step 1) to determine roll stability to determine whether the vehicle is in a roll instability;

[0145] Step 2.1.1) Design the yaw rate threshold condition formula as follows:

[0146] in, is the current ideal yaw rate of the vehicle, is the actual yaw rate of the current vehicle. After a series of tests, the calibration constant C is determined. ψ When the real-time yaw rate of the vehicle deviates from the ideal value within the above range, the vehicle is not unstable; otherwise, it indicates that the vehicle has lost stability.

[0147] Step 2.1.2) Determine the center of mass sideslip angle threshold The position of in the phase plane, if If the vehicle is in the stable region, then it is considered to be in a stable state. The threshold condition formula for the sideslip angle of the design center of mass is as follows:

[0148]

[0149] Among them, C β2 , is the calibration constant, β is the sideslip angle of the center of mass, is the angular acceleration of the center of mass. The phase plane is the relationship between β and A plane area composed of: a stable area and an unstable area.

[0150] The stability of the vehicle is evaluated by judging the sideslip angle of the center of mass and the yaw angular velocity. When the vehicle meets both conditions at the same time, the vehicle is considered stable, otherwise the vehicle is judged to be yaw unstable.

[0151] Step 2.2) Roll stability determination is mainly achieved by designing a roll factor. The real-time roll factor is calculated by the feedback value of the real-time roll angle and roll angle velocity. The roll factor value is used to determine whether the vehicle is in a roll instability state. The roll stability is determined by the absolute value RI of the roll factor RI. The roll stability determination logic is as follows:

[0152] Set the lower limit of the roll factor | RI |=0.7, upper limit

[0153] If |RI|<| RI |At this time, it is considered that the risk of vehicle rollover is small and anti-roll control is not required.

[0154] like At this time, the risk of vehicle rollover is relatively high, and anti-roll control is required to prevent the vehicle from rolling over.

[0155] like In this case, one wheel has left the ground and rollover has occurred. In order to ensure the stability of the vehicle, a full braking strategy is adopted.

[0156] Among them, the roll factor is composed of the roll angle and the roll angular velocity, and the specific formula is as follows:

[0157]

[0158] in, is the vehicle roll angle, is the roll angular acceleration.

[0159]

[0160]

[0161] Among them, h u is the height of the center of mass of the unsprung mass, h R is the height of the roll center, h is the total height of the vehicle, m u is the unsprung mass, m s is the sprung mass, m is the total mass of the vehicle, t f is the wheelbase, K φ is the roll stiffness coefficient, C φ is the roll damping coefficient, and g is the acceleration due to gravity.

[0162] Step 3) Establish the yaw-roll stability control logic as follows: In order to improve the operating efficiency of the stability control system, the stability of the intelligent vehicle under different working conditions is logically analyzed and the corresponding operating logic is established. The stability working conditions that may be encountered in the actual operation of the intelligent vehicle are divided into the following three types:

[0163] (1) Yaw instability condition: When the vehicle's yaw angular velocity or sideslip angle reaches the instability judgment threshold, and the roll factor RI is still within the stability threshold range, yaw stability control is adopted.

[0164] (2) Roll instability condition: When the vehicle's yaw rate and center of mass sideslip angle are within the stability threshold range, but the roll factor RI exceeds the stability threshold range, roll stability control is required.

[0165] (3) Yaw-roll instability condition: When the vehicle's center of mass slip angle and yaw angular velocity both reach the instability judgment threshold, and the roll factor RI exceeds the stability threshold range, it is necessary to comprehensively consider the yaw stability and roll stability, and perform corresponding stability integrated control.

[0166] According to the obtained yaw stability determination target and roll stability determination threshold, corresponding stability control is performed respectively. The actual running state of the vehicle is compared in real time with the ideal state information obtained by the two-degree-of-freedom and three-degree-of-freedom vehicle models, and the instability state of the vehicle is determined according to the stability determination conditions, and corresponding stability control is performed on it until the stability condition is within the stability threshold range.

[0167] Its operation logic reference Picture 1 shown.

[0168] The yaw stability and roll stability control methods are established in step (4), respectively, as follows:

[0169] Step 4.1) Establish yaw stability control logic, and perform active steering and active braking control based on yaw instability. In the yaw stability control process, it is mainly achieved through active braking system and active steering system. The active steering system achieves stability control by superimposing additional steering angles, and the active braking system achieves stability control by adjusting the braking force rectangles of the four tires to form yaw torque. When the vehicle is working in the nonlinear area under extreme conditions, the vehicle's center of mass side slip angle phase plane exceeds a certain threshold Active braking alone cannot completely solve the problem of yaw instability. Integrated control of active braking and active steering is adopted to improve the vehicle's instability through active steering intervention.

[0170] In the process of active braking and active steering integration, in order to avoid interference between the two systems and obtain better stability control effect, the intervention logic of the active braking system and the active steering system is designed. The instability state is judged based on the judgment condition of the yaw angular velocity in step (3), that is, If the judgment condition based on the sideslip angle of the center of mass is within the threshold range, that is, The stability control system mainly takes active braking system control; if the judgment condition based on the sideslip angle of the center of mass exceeds the threshold range, that is, Steering and braking integrated control is then performed.

[0171] The system monitors the vehicle's dynamic state in real time - yaw rate and center of mass slip angle. The yaw rate is used as the vehicle state judgment condition. After determining instability, if it is a high-adhesion road surface, the yaw stability control based on the active braking system is directly performed. If it is a low-adhesion road surface, the instability degree of the vehicle at this time is judged based on the phase plane diagram of the center of mass slip angle. If it is less than the threshold This indicates that the vehicle is less unstable at this time, and the yaw stability control of the active braking system is adopted; greater than the threshold This means that the vehicle is seriously unstable at this time, and active braking and active steering are integrated for stability control. Finally, after judging that the yaw instability condition is not met, the yaw stability control is exited. Picture 2 shown.

[0172] Step 4.2) The sliding mode variable structure control principle is used to design the yaw stability controller. According to the yaw instability state of the vehicle, it is divided into two types: active braking system yaw torque controller and active braking-active steering integrated stability controller. The control principle of the yaw stability controller refers to Picture 3 shown.

[0173] Step 4.2.1) In order to simultaneously solve the stability control based on yaw rate and sideslip angle of the center of mass, the sliding mode variable structure control method is used based on the two-degree-of-freedom vehicle model to design and optimize the yaw torque controller of the active braking system.

[0174] First, the front wheel steering angle and yaw moment are used as input, and the yaw rate and center of mass sideslip angle are used as state variables to establish a two-degree-of-freedom vehicle model in the following form:

[0175] Among them, C f , C r are the front and rear wheel cornering stiffness, l f , l r are the distances from the front and rear axles to the center of mass, v x is the speed of the vehicle, m is the mass of the vehicle, I zz is the moment of inertia of the vehicle around the z-axis, δ f is the front wheel turning angle, ΔM z is the additional yaw moment.

[0176] At the same time, the vehicle yaw dynamics equation can be expressed as:

[0177] Among them, F yfl 、F yrl 、F yfr 、F yrr The lateral forces provided by the left front wheel, left rear wheel, right front wheel and right rear wheel, t f For wheelbase.

[0178] The difference between the actual yaw rate and the ideal yaw rate, as well as the difference between the actual center of mass sideslip angle and the expected center of mass sideslip angle are used as the basis for judgment, and the sliding surface is defined as follows:

[0179] Taking the derivative of the sliding surface, we get:

[0180] Substituting it into the sliding surface, we get:

[0181]

[0182] make The target additional yaw moment can be obtained as follows:

[0183]

[0184] To ensure ΔM z In the presence of disturbances and parameter uncertainties, the sliding mode conditions can still be met. The exponential reaching law sliding mode control is adopted. The yaw torque controller of the active braking system can be specifically expressed as:

[0185] △M zev =△M z -k1s-k2sgn(s);

[0186] Among them, k1 and are control gains, and k1, k2>0, sgn(s) is the sign function.

[0187] Step 4.2.2) Design an active braking-active steering integrated stability controller. The design process is as follows:

[0188] With the front wheel steering angle and yaw moment as input, yaw rate and center of mass sideslip angle as state variables, a two-degree-of-freedom vehicle model is established and rewritten into the state space form as follows:

[0189]

[0190] Among them, A and B are coefficient matrices, x and u are state variables and input variables respectively, and the expressions are,

[0191]

[0192] In order to enable the vehicle to better track the ideal yaw rate and sideslip angle, the tracking error is expressed as:

[0193]

[0194] The sliding surface is taken as follows: Among them, c1, c2>0, and both are constants.

[0195] Taking the derivative of the sliding surface, we get: Among them, c is the coefficient matrix, the expression is:

[0196]

[0197] Take the exponential reaching law as: in ε a ,ε b ,k a ,k b >0, the expression of the control rate of the active braking-active steering integrated stability controller is:

[0198]

[0199] Step 4.3) Design the roll stability controller and use the sliding mode control algorithm to calculate the additional yaw moment required to reduce the vehicle roll factor RI. According to the expression of yaw motion in step 1), the additional yaw moment is introduced to obtain:

[0200]

[0201] For the analysis of vehicle roll stability, when the vehicle rolls stably, |RI| should be less than 0.7. When the system detects |RI|≥0.7, it starts anti-roll control, mainly controlling the vehicle roll factor |RI| to be lower than or close to the roll threshold value |RI|. The sliding mode function is designed as: s=RI- RI

[0202] By taking the derivative of the sliding mode function and combining it with the vehicle three-degree-of-freedom model established in step 1), we can obtain:

[0203]

[0204] in,

[0205]

[0206] Among them, K φ is the roll stiffness, C φ is the roll damping coefficient, l e is the distance from the center of mass of the vehicle's sprung mass to the roll center, I xzs is the pitching moment of inertia of the sprung mass, I xx is the rolling inertia of the vehicle mass.

[0207] In order to eliminate the chattering phenomenon of the sliding mode variable structure control system, the sliding mode approach rate is selected as:

[0208]

[0209] In the formula, k1>0, k2>0, k1 should be increased as much as possible, and k2 should be reduced as much as possible. By reasonably selecting parameters k1 and k2, the state point can be quickly brought close to the sliding surface, and the vibration frequency of the sliding mode can also be effectively reduced.

[0210] Substituting the sliding mode reaching law expression into the above formula, the additional yaw moment expression of the roll stability controller is obtained as follows:

[0211]

[0212] Step 4.4) Design the yaw-roll integrated stability controller

[0213] The yaw stability control generates additional yaw torque through the braking system to adjust the vehicle's running posture so that the vehicle meets the driver's intention when it is critically unstable. The purpose of implementing roll stability control is to reduce the vehicle's yaw angular velocity (which may cause the vehicle speed to drop) when the vehicle is rolling instability, so as to suppress the vehicle's lateral acceleration and reduce the risk of roll. The control objectives of yaw stability and roll stability are not completely consistent. Therefore, it is necessary to integrate the control of yaw stability and roll stability, and clarify their control logic to resolve possible conflicts.

[0214] When performing chassis stability integrated control, the instability judgment is first made based on the vehicle's state information, namely, yaw instability, roll instability, and yaw and roll instability at the same time. Since the intervention of active steering may cause a secondary accident of the vehicle or make the driver nervous, in the case of mild instability, active braking is first considered for stability control; when the yaw instability is more serious, on the one hand, active braking is used to alleviate the instability, and on the other hand, active steering is introduced to further alleviate the instability. The coordinated control logic is designed in step 4.2.2), namely, the active braking-active steering integrated stability controller design.

[0215] The yaw stability control can be judged by the current yaw stability state of the vehicle. Based on the stability state, when there is understeering or oversteering, the system reduces the vehicle speed through the drive system torque reduction and differential braking to prevent further instability. Specifically: when the left turn is insufficient or the right turn is excessive, the differential braking controls the left double wheels; when the right turn is insufficient or the left turn is excessive, the differential braking controls the right double wheels.

[0216] When the vehicle status detection finds that yaw and roll instability exist at the same time, roll stability control is performed first. During the execution of roll stability control, it is necessary to determine whether there is understeer. If understeer does not occur, roll stability control will continue. If understeer occurs, it is necessary to determine whether there is a risk of roll. If there is no risk of roll, the brake pressure of the wheel will be set to the target pressure value calculated by the roll stability control. Conversely, when there is a risk of roll, roll stability control will continue. The specific controlled wheels are mainly determined by the wheel braking distribution of the braking force distribution module. After the roll risk is eliminated, the yaw stability control function is executed. At this time, the wheel braking pressure will be set to the target pressure calculated by the yaw stability control, and the controlled wheels are still the wheels determined by the braking distribution by the braking force distribution module. Its control logic is as follows Picture 4 shown.

[0217] The implementation of roll stability control is determined by the current roll stability state of the vehicle. The degree of roll is mainly determined by whether the roll factor value exceeds the danger threshold. The danger threshold is set. RI | r =0.8. The specific implementation of the roll stability control is: if the vehicle state is small roll, that is, when the roll factor is 0.7≤|RI|≤0.8, the engine torque reduction is executed; if the vehicle state is large roll, that is, when the roll factor is |RI|>0.8, the engine torque reduction is executed and active braking is coordinated.

[0218] The yaw stability control and roll stability control calculate the additional yaw moment and anti-roll braking moment for their own separate control, and then complete the control through the integrated control logic. If the vehicle is in both yaw instability and roll instability at the same time, the roll stability control should be prioritized, followed by the yaw stability control.

[0219] The contradictory logic of yaw-roll integrated stability control can be specifically described as:

[0220] (1) The goals of yaw stability control and roll stability control are to keep the vehicle in proper understeer, ensuring that the vehicle can make stable and accurate steering responses under various complex road conditions and driving conditions, thereby improving the driving safety of the vehicle;

[0221] (2) Roll stability control may cause the vehicle to understeer more severely. Further roll stability control will increase the vehicle's understeer tendency and increase the risk of yaw instability. On the contrary, if yaw stability control works, reducing the vehicle's understeer tendency will increase the risk of roll. Therefore, these two control objectives are contradictory in this case.

[0222] Excessive lateral acceleration may cause severe roll of the vehicle. Reducing the vehicle speed and yaw rate is a conventional method to limit lateral acceleration. However, if the yaw rate is reduced excessively, understeer may occur, which will cause the wheels to lose ground adhesion, reduce the steering performance of the vehicle, and may trigger yaw stability control. Therefore, reducing the vehicle speed can better resolve the conflict between these two problems. In roll stability control, the specific braking torque distribution strategy can be adopted in different ways. In terms of preventing vehicle roll, the roll stability of the vehicle is improved by reducing the yaw rate. The specific control logic of the braking torque distribution in this study is as follows:

[0223] When the vehicle is unstable due to yaw and roll, anti-roll control is given priority. During the vehicle's driving, the controller will continuously detect and judge the vehicle's status.

[0224] If the vehicle is detected to have the possibility of rolling instability:

[0225] (1) If only the roll instability occurs, only the roll stability control is performed to control the braking of the wheel on one side;

[0226] (2) If only yaw instability occurs, only yaw stability control is performed to control the braking of the wheel on one side;

[0227] (3) In the event of a roll stability problem, continue to apply unilateral wheel braking to the vehicle. If the vehicle oversteers, continue to apply unilateral braking;

[0228] (4) In the case of a roll stability problem, unilateral wheel braking is still performed. However, if the vehicle is understeering and in a yaw instability state, |RI| is detected at this time. When |RI| exceeds the threshold of 0.8, unilateral wheel braking is continued to be applied to the vehicle, otherwise bilateral wheel braking is performed; if the degree of understeering decreases, bilateral wheel braking is performed; if the degree increases, the braking pressure of the inner front wheel is increased to implement yaw stability control. Then continue to check if there is a roll tendency, and reduce the braking pressure of the inner front wheel.

[0229] Step 5) The braking torque distribution module mainly performs the selection of active steering control and active braking control based on the yaw torque calculated by the stability control module and in combination with the current motion state, and further distributes the braking wheels of the active braking control.

[0230] Step 5.1) Braking torque distribution under yaw stability control. When performing vehicle stability control, braking force is preferably applied to the outer front wheel or the inner rear wheel, using two braking methods: single-side braking and double-side braking.

[0231] Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive.

[0232] When the vehicle turns left, that is, the front wheel angle is greater than or equal to 0, and the yaw velocity direction is counterclockwise, and the yaw velocity is greater than 0, if the actual yaw velocity is less than the ideal value, understeer occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw velocity is less than the ideal value, oversteer occurs, and the right front wheel and right rear wheel are braked at this time.

[0233] When the vehicle turns right, that is, the front wheel angle is less than 0, and the yaw velocity direction is clockwise, and the yaw velocity is less than 0, if the actual yaw velocity is less than the ideal value, oversteering occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw velocity is less than the ideal value, understeering occurs, and the right front wheel and right rear wheel are braked at this time.

[0234] Step 5.2) Design a braking torque distribution strategy under roll stability control, and perform unilateral and bilateral wheel braking based on the additional yaw torque calculated by the roll stability controller.

[0235] Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive.

[0236] When the vehicle turns left, the vehicle will tend to tilt to the right. If single-side braking is selected, the right front wheel and right rear wheel will be braked. If double-side braking is selected, the right front wheel, left rear wheel and right rear wheel will be braked. When the vehicle turns right, the vehicle will tend to tilt to the left. If single-side braking is selected, the left front wheel and left rear wheel will be braked. If double-side braking is selected, the left front wheel, left rear wheel and right rear wheel will be braked.

[0237] When the brake pressure is applied to a single wheel, the Z-axis yaw moment changes as follows: Picture 5 As shown in the figure, when the braking force is applied to the rear inner wheel or the front inner wheel in the early stage, a positive yaw moment will be triggered, in which the effect of the rear inner wheel is greater than that of the front inner wheel. When the braking pressure continues to increase, the front inner wheel begins to show a reverse yaw moment.

Claims

1. A heavy vehicle yaw and roll integrated stability control method, characterized in that: The following steps are involved: (1) Establishing a two-degree-of-freedom vehicle model including yaw motion and a three-degree-of-freedom vehicle model including yaw and roll motion; (2) Calculating the ideal state information of yaw motion and determining yaw stability based on the two-degree-of-freedom vehicle model of step (1); calculating the ideal state information of roll motion and determining roll stability based on the three-degree-of-freedom vehicle model of step (1); (3) Based on the yaw stability determination and roll stability determination in step (2), a yaw-roll stability control logic is established; in order to improve the operating efficiency of the stability control system, a logical analysis is performed on the stability of the intelligent vehicle under different operating conditions, and the stability operating conditions that may be encountered in the actual operation of the intelligent vehicle are divided into the following three types: (301) Yaw instability condition: When the vehicle's yaw rate or center of mass slip angle reaches the instability judgment threshold, and the real-time roll angle and roll rate are still within the stability threshold range, yaw stability control is adopted; (302) Roll instability condition: When the vehicle's yaw rate and center of mass slip angle are within the stability threshold range, but the real-time roll angle and roll rate exceed the stability threshold range, roll stability control is required; (303) Yaw-roll instability condition: When the vehicle's center of mass slip angle and yaw angular velocity reach the instability determination threshold, and the real-time roll angle and roll angular velocity exceed the stability threshold range, it is necessary to comprehensively consider the yaw stability and roll stability, and then perform corresponding stability integrated control; according to the obtained yaw stability determination target and roll stability determination threshold, perform corresponding stability control respectively, compare the actual vehicle operation state with the ideal state information in real time, perform real-time instability determination of the vehicle according to the stability determination condition, and further perform corresponding stability control until the stability condition is within the stability threshold range; (4) Establishing a controller: According to the yaw-roll stability control logic of step (3), a yaw stability controller, a roll stability controller, and a yaw-roll stability integrated controller are established respectively; (5) Using the controller established in step (4) to distribute braking torque to control the vehicle.

2. The heavy vehicle yaw and roll integrated stability control method according to claim 1, characterized in that: The yaw stability determination is performed by the yaw angular velocity and the sideslip angle of the center of mass of the vehicle, wherein the ideal state information is obtained based on a two-degree-of-freedom vehicle model; The yaw rate threshold condition is: in, is the current ideal yaw rate of the vehicle, is the actual yaw rate of the vehicle at present, is the calibration constant after experimental testing; The center of mass sideslip angle threshold condition is: Among them, C β2 , is the calibration constant, β is the sideslip angle of the center of mass, is the sideslip angular acceleration of the center of mass; The yaw stability needs to be determined by comprehensively considering the yaw angular velocity and the sideslip angle of the center of mass, that is, the deviation between the real-time feedback values ​​of the two variables and their respective ideal values ​​is comprehensively considered to detect whether the vehicle is in a yaw instability state; if both deviations are within the threshold range, the vehicle is determined to be in a stable driving condition; otherwise, the vehicle is in an unstable condition; when the vehicle meets the above two threshold conditions at the same time, the vehicle is considered to be stable, otherwise the vehicle is determined to be yaw unstable.

3. The heavy vehicle yaw and roll integrated stability control method according to claim 1, characterized in that: The roll stability is determined by the real-time roll angle and roll angular velocity of the vehicle, and the real-time roll factor RI is calculated according to the feedback values ​​of the real-time roll angle and roll angular velocity: in, is the vehicle roll angle, is the roll angular velocity; C RI1 , C RI2 is a parameter related to the vehicle, specifically expressed as: Among them, h u is the height of the center of mass of the unsprung mass, h R is the height of the roll center, h is the total height of the vehicle, m u is the unsprung mass, m s is the sprung mass, m is the total mass of the vehicle, h is the height of the center of mass of the vehicle, t f is the wheelbase, K φ is the roll stiffness coefficient, C φ is the roll damping coefficient, g is the acceleration of gravity; The roll stability is determined by the absolute value of the roll factor RI |RI|.

4. The heavy vehicle yaw and roll integrated stability control method according to claim 1, characterized in that: The roll stability determination comprises the following steps: setting the lower limit of the absolute value |RI| of the roll factor RI to | RI |、The upper limit value is Based on the roll factor, the roll condition is controlled as follows: (401)If |RI|<| RI |, at this time, the risk of vehicle rollover is considered small and anti-roll control is not required; (402) If At this time, the risk of vehicle rollover is relatively high, and anti-roll control is required to prevent the vehicle from rolling over; (403) In this case, one side of the wheel has left the ground and rollover has occurred; in order to ensure the stability of the vehicle, a full braking strategy is adopted.

5. The heavy vehicle yaw and roll integrated stability control method according to claim 3, characterized in that: The lower limit value| RI |=0.7, upper limit 6. The heavy vehicle yaw and roll integrated stability control method according to claim 2, characterized in that: The step (4) of establishing a yaw stability controller comprises the following steps: Step 7.1) Establishing yaw stability control logic, and performing active steering and active braking control based on yaw instability; During the yaw stability control process, the active steering system achieves stability control by superimposing additional steering angles, and the active braking system achieves stability control by adjusting the braking forces of the four tires to form a yaw moment; when the vehicle is working in the nonlinear area under extreme working conditions, the vehicle's center of mass side slip angle phase plane exceeds a certain threshold Active braking alone cannot completely solve the yaw instability problem. The integrated control of active braking and active steering is adopted to improve the instability of the vehicle through active steering intervention. In the process of active braking and active steering integration, in order to avoid interference between the two systems and obtain better stability control effect, the intervention logic of the active braking system and the active steering system is designed. If the judgment condition of the yaw angular velocity determines the instability state, that is, The vehicle is considered to have reached a yaw instability state; if the judgment condition based on the sideslip angle of the center of mass is within the threshold range, that is, The stability control system mainly takes active braking system control; if the judgment condition based on the sideslip angle of the center of mass exceeds the threshold range, that is, Then the integrated control of active braking-active steering is performed; Step 7.2) The sliding mode variable structure control method is used to design the yaw stability controller. According to the yaw instability state of the vehicle, the yaw stability controller is divided into an active braking system yaw torque controller and an active braking-active steering integrated stability controller; Step 7.2.1) In order to simultaneously solve the stability control problem based on yaw rate and sideslip angle, the yaw moment controller of the active braking system is designed based on the two-degree-of-freedom vehicle model and the sliding mode variable structure control method; First, the front wheel steering angle and yaw moment are used as input, and the yaw rate and center of mass sideslip angle are used as state variables to establish a two-degree-of-freedom vehicle model in the following form: Among them, C f , C r are the front and rear wheel cornering stiffness, l f , l r are the distances from the front and rear axles to the center of mass, v x is the longitudinal speed of the vehicle, m is the mass of the vehicle, I zz is the yaw moment of inertia of the vehicle mass, δ f is the front wheel turning angle, ΔM z is the additional yaw moment. At the same time, the vehicle yaw dynamics equation can be expressed as: Among them, F yfl 、F yrl 、F yfr 、F yrr The lateral forces provided by the left front wheel, left rear wheel, right front wheel and right rear wheel respectively, t f is the wheelbase; The difference between the actual yaw rate and sideslip angle of the center of mass and the ideal yaw rate and sideslip angle of the center of mass is used as the control basis, and the deviation combination is made as small as possible through the control of the yaw torque controller of the active braking system; the sliding surface is defined as follows: Among them, β d is the ideal center of mass sideslip angle, λ is a constant coefficient; Taking the derivative of the sliding surface, we get: Will Substitute into the sliding surface derivative Win: make The target additional yaw moment can be obtained as follows: To ensure ΔM z In the presence of disturbances and parameter uncertainties, the sliding mode conditions can still be met. The exponential reaching law sliding mode control is adopted. The expression of the control rate of the yaw torque controller of the active braking system can be specifically expressed as: △M zev =△M z -k1s-k2sgn(s); Where k1 and k2 are control gains, and k1, k2>0, sgn(s) is the sign function; Step 7.2.2) Design an active braking-active steering integrated stability controller; The front wheel steering angle and yaw moment are used as system inputs, the yaw rate and the sideslip angle of the center of mass are used as state variables, and a two-degree-of-freedom vehicle model is established and rewritten into the state space form as follows: Among them, A and B are coefficient matrices, x and u are state variables and input variables respectively, and the expressions are, In order to enable the vehicle to better track the ideal yaw rate and sideslip angle, the tracking error is expressed as: Among them, x d , x is the ideal and actual state variables - yaw rate and center of mass sideslip angle, e1 is the center of mass sideslip angle deviation, e2 is the yaw rate deviation; The sliding surface is taken as follows: Among them, c1, c2>0, and both are constants; Taking the derivative of the sliding surface, we get: Among them, c is the coefficient matrix, the expression is: Take the exponential reaching law as: in ε a ,ε b ,k a ,k b >0, and are all constants; The expression for the control rate of the active braking-active steering integrated stability controller is:

7. The heavy vehicle yaw and roll integrated stability control method according to claim 2, characterized in that: The step (4) establishes a roll stability controller according to the yaw-roll stability control logic, comprising the following steps: The sliding mode variable structure control method is used to design the roll stability controller and calculate the additional yaw moment required to reduce the vehicle roll factor RI. According to the expression of yaw motion in step 1), the additional yaw moment is introduced to obtain: Among them, I xz is the pitch moment of inertia of the vehicle mass; For the analysis of vehicle roll stability, when the vehicle rolls stably, |RI| should be less than 0.

7. When the system detects |RI|≥0.7, it starts anti-roll control to make the vehicle roll factor |RI| lower than or close to the roll threshold value |RI|. The sliding surface function is designed as: s=RI-RI; By taking the derivative of the sliding surface function and combining it with the vehicle three-degree-of-freedom model established in step 1), we can obtain: in, Among them, K φ is the roll angle stiffness, C φ is the roll damping coefficient, l e is the distance from the center of mass of the vehicle's sprung mass to the roll center, I xzs is the pitching moment of inertia of the sprung mass, I xx is the rolling moment of inertia of the vehicle mass In order to eliminate the chattering phenomenon of the sliding mode variable structure control system, the sliding mode approach rate is selected as: In the formula, k1>0, k2>0, k1 is increased as much as possible, and k2 is reduced as much as possible. By reasonably selecting parameters k1 and k2, the state point can be quickly brought close to the sliding surface, and the vibration frequency of the sliding mode can also be effectively reduced; Substituting the sliding mode reaching law expression into the above formula, the additional yaw moment expression of the roll stability controller is obtained as follows:

8. The heavy vehicle yaw and roll integrated stability control method according to claim 1, characterized in that: The step (4) designs a yaw-roll integrated stability controller according to the yaw-roll stability integrated control controller, and includes the following steps: When the vehicle status detection finds that yaw and roll instability exist at the same time, roll stability control is performed first; during the execution of roll stability control, it is necessary to determine whether understeer exists. If understeer does not exist, roll stability control will continue; if understeer exists, it is necessary to determine whether there is a risk of roll; if there is no risk of roll, the wheel brake pressure will be set to the target pressure value calculated by the roll stability control; conversely, when there is a risk of roll, roll stability control will continue; the specific controlled wheels are mainly determined by the wheel brake distribution calculation by the brake force distribution module; after the risk of roll is eliminated, the yaw stability control function is performed; at this time, the wheel brake pressure will be set to the target pressure calculated by the yaw stability control, and the controlled wheels are still determined by the brake force distribution module; The implementation of roll stability control is determined by the current roll stability state of the vehicle; the degree of roll is determined mainly by whether the roll factor value exceeds the danger threshold. The danger threshold is set. RI | r =0.8; the roll stability control is specifically implemented as follows: if the vehicle state is small roll, that is, when the roll factor is 0.7≤|RI|≤0.8, the engine torque reduction is executed; if the vehicle state is large roll, that is, when the roll factor is |RI|>0.8, the engine torque reduction is executed and active braking is coordinated; The yaw stability control and roll stability control calculate the additional yaw moment and anti-roll braking moment for their own separate control, and then complete the control through the integrated control logic; if the vehicle is in both yaw instability and roll instability at the same time, the roll stability control should be prioritized, followed by the yaw stability control; The contradictory logic of yaw-roll integrated stability control can be specifically described as: (1) The goals of yaw stability control and roll stability control are to keep the vehicle in proper understeer, ensuring that the vehicle can make stable and accurate steering responses under various complex road conditions and driving conditions, thereby improving the driving safety of the vehicle; (2) Roll stability control may cause the vehicle to understeer more severely. Further roll stability control will increase the vehicle's understeer tendency and increase the risk of yaw instability. On the contrary, if yaw stability control works, reducing the vehicle's understeer tendency will increase the risk of roll. Therefore, these two control objectives are contradictory in this case. Excessive lateral acceleration may cause serious vehicle roll. Reducing vehicle speed and yaw rate is a conventional method to limit lateral acceleration. However, excessive reduction of yaw rate may cause understeer, which in turn causes the wheels to lose ground adhesion, resulting in reduced steering performance of the vehicle and possible triggering of yaw stability control. Therefore, reducing vehicle speed can better resolve the conflict between these two problems. In roll stability control, the specific braking torque distribution strategy can be adopted in different ways. In terms of preventing vehicle roll, the roll stability of the vehicle can be improved by reducing the yaw rate. The specific control logic of braking torque distribution in this study is as follows: When the vehicle is unstable due to yaw or roll, anti-roll control is given priority; during the vehicle's driving, the controller will continuously detect and judge the vehicle's status; If the possibility of the vehicle rolling instability is detected, control is performed in the following situations: (1) If only the roll instability occurs, only the roll stability control is performed to control the braking of the wheel on one side; (2) If only yaw instability occurs, only yaw stability control is performed to control the braking of one side of the wheel; (3) In the event of a roll stability problem, continue to apply unilateral wheel braking to the vehicle. If the vehicle oversteers, continue to apply unilateral braking; (4) In the event of a roll stability problem, single-side wheel braking is still performed. However, if the vehicle is understeering and in a yaw instability state, |RI| is detected at this time. When |RI| exceeds the threshold value of 0.8, single-side wheel braking is continued to be applied to the vehicle, otherwise double-side wheel braking is performed. If the degree of understeering decreases, double-side wheel braking is performed. If the degree increases, the braking pressure of the inner front wheel is increased to implement yaw stability control. Then, the inspection continues. If there is a roll tendency, the braking pressure of the inner front wheel is reduced.

9. The heavy vehicle yaw and roll integrated stability control method according to claim 1, characterized in that: The step (5) controls the vehicle by distributing the braking torque, selecting active steering control and active braking control according to the yaw torque calculated by the stability control module in step (4) and in combination with the current motion state, and further distributing the braking wheels of the active braking control, including the following steps: (1) Braking torque distribution under pendulum stability control: When performing vehicle stability control, braking force is applied to the outer front wheel or the inner rear wheel first, using single-side braking or double-side braking. Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive; When the vehicle turns left, that is, the front wheel angle is greater than or equal to 0, and the yaw velocity direction is counterclockwise, and the yaw velocity is greater than 0, if the actual yaw velocity is less than the ideal value, understeering occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw velocity is less than the ideal value, oversteering occurs, and the right front wheel and right rear wheel are braked at this time; When the vehicle turns right, that is, the front wheel angle is less than 0, and the yaw rate direction is clockwise, and the yaw rate is less than 0, if the actual yaw rate is less than the ideal value, oversteering occurs, and the left rear wheel and left front wheel are braked at this time; if the actual yaw rate is less than the ideal value, understeering occurs, and the right front wheel and right rear wheel are braked at this time; (2) Design a braking torque distribution strategy under roll stability control to perform unilateral and bilateral wheel braking based on the additional yaw torque calculated by the roll stability controller; Assume that the wheel turns left, let δ f ≥0, at this time, the yaw angular velocity is positive. When the vehicle turns left, the vehicle will tend to tilt to the right. If single-side braking is selected, the right front wheel and right rear wheel will be braked. If double-side braking is selected, the right front wheel, left rear wheel and right rear wheel will be braked. When the vehicle turns right, the vehicle will tend to tilt to the left. If single-side braking is selected, the left front wheel and left rear wheel will be braked. If double-side braking is selected, the left front wheel, left rear wheel and right rear wheel will be braked.

10. A control system for a heavy vehicle yaw and roll integrated stability control method according to any one of claims 1 to 9, characterized in that: It includes a stability target calculation module, a stability determination module, an integrated stability control module, and a braking torque distribution module; The stability target calculation module includes a vehicle speed sensor, a navigation positioning sensor, an inertial navigation sensor, and a rotation angle sensor; The vehicle speed sensor is installed on the vehicle tire to obtain the longitudinal speed of the vehicle and transmit the collected information to the required module; the navigation positioning sensor is installed at the geometric center of the top of the vehicle to obtain the real-time position and heading angle of the vehicle, and the inertial navigation sensor is installed at the center position on the longitudinal axis of the agricultural machinery chassis to obtain the lateral acceleration and yaw angular velocity of the vehicle; the angle sensor is installed on the main shaft pin of the vehicle steering wheel to measure the steering angle; the pressure sensor is installed on the brake oil pipeline to measure the brake pressure; the control system combines the vehicle's operating status to establish a three-degree-of-freedom model including yaw and roll motion, calculates the yaw and roll stability control targets, and distributes the braking torque according to the control targets.

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