CN117141461A - Active front wheel steering and direct yaw moment cooperative control method based on vehicle road state - Google Patents
Active front wheel steering and direct yaw moment cooperative control method based on vehicle road state Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
- B60W30/02—Control of vehicle driving stability
- B60W30/045—Improving turning performance
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
- B60W30/08—Active safety systems predicting or avoiding probable or impending collision or attempting to minimise its consequences
- B60W30/09—Taking automatic action to avoid collision, e.g. braking and steering
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
- G06F17/11—Complex mathematical operations for solving equations, e.g. nonlinear equations, general mathematical optimization problems
- G06F17/13—Differential equations
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
- G06F17/15—Correlation function computation including computation of convolution operations
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
- B60W2050/0001—Details of the control system
- B60W2050/0019—Control system elements or transfer functions
- B60W2050/0028—Mathematical models, e.g. for simulation
- B60W2050/0031—Mathematical model of the vehicle
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
- B60W2050/0001—Details of the control system
- B60W2050/0019—Control system elements or transfer functions
- B60W2050/0028—Mathematical models, e.g. for simulation
- B60W2050/0037—Mathematical models of vehicle sub-units
Abstract
The application discloses a cooperative control method of active front wheel steering and direct yaw moment based on a vehicle road state, which utilizes the monitored vehicle state and road surface adhesion condition to calculate the limit value of tire force in real time; according to the requirements of vehicle collision avoidance track tracking and stability control, an NMPC controller is designed to solve optimal values of longitudinal force and lateral force of a tire, and the coordination control of emergency steering collision avoidance safety and stability is realized through front wheel active steering and four-wheel braking force control. The application has the advantage of improving the comprehensive performance of the intelligent driving vehicle.
Description
Technical Field
The application relates to the technical field of intelligent driving, in particular to a method for cooperatively controlling active front wheel steering and direct yaw moment based on a vehicle road state.
Background
With the rapid development of intelligent driving automobiles, traffic safety technology is becoming more and more important. In the emergency steering collision avoidance process of the intelligent driving vehicle, a path planning module plans a driving track capable of realizing collision avoidance according to state information of the self vehicle and the obstacle vehicle, a track tracking controller calculates steering wheel rotation angle, accelerator opening and braking force, and a bottom layer controller controls an actuator to act to implement emergency collision avoidance. At present, the emergency automatic collision avoidance function mainly comprises two forms of emergency steering collision avoidance and emergency braking collision avoidance. The emergency steering collision avoidance control is good or bad, is greatly influenced by the state of the vehicle and the condition of the road surface, and particularly aims at the situation that the self-vehicle is unstable, side-turned or collision avoidance failure collides with the front vehicle when the control is not good for the passenger car and the commercial vehicle with large sprung mass and high mass center position. It is therefore highly necessary to combine stability control during an emergency steering collision avoidance process, including yaw stability and roll stability. The common stability control methods at present are active front wheel steering and direct yaw moment control methods. The active front wheel steering control realizes the control of the tire cornering force by adjusting the tire cornering angle, so that the vehicle generates additional yaw moment, thereby achieving the purpose of stabilizing the vehicle body. The direct yaw moment control is to control the longitudinal force of the tyre by adjusting the brakes of four wheels, so that the additional yaw moment generated by the vehicle is achieved, and the aim of stabilizing the vehicle body is fulfilled. However, when the vehicle is in an extreme condition, such as a wet road or an adhesion coefficient abrupt road, the vehicle stability control requirement cannot be met by the single active front wheel steering control and the direct yaw moment control, so that the cooperative control of the two methods is very necessary. Since the tire is a complex nonlinear element, its lateral and longitudinal forces are coupled to each other, and its magnitude is limited by road adhesion coefficient and vertical load. In summary, the key to achieving the cooperative control of the active front wheel steering and the direct yaw moment is to study the distribution of the tire longitudinal force and the lateral force, wherein the vehicle and the road condition need to be fully considered to achieve the accurate control of the tire force of the vehicle.
CN2020100961714 proposes a vehicle yaw stability predictive control method and system. The system considers the safety constraint of the centroid side deflection angle and the yaw rate and the additional yaw moment driving constraint, designs an NMPC controller, realizes the additional yaw moment control by adjusting the driving moment of the hub motor, and can improve the transverse stability of the vehicle. However, this patent suffers from the disadvantage that, first, roll stability of the vehicle is not considered, and for vehicles with a high centroid position or a large sprung mass, rollover easily occurs during an emergency steering, which requires real-time monitoring of the roll state of the vehicle and application of stability control when necessary; secondly, in the patent, an NMPC controller is utilized to calculate the optimal additional yaw moment, the tire load rate is minimized, the moment output capacity of a driver is taken as constraint to carry out four-wheel moment distribution, the actual road surface condition is not considered, and when the road surface adhesion coefficient is low or suddenly changed, the adhesion between the tire and the road surface is reduced, so that the expected value cannot be reached; finally, the patent implements yaw stability control, i.e., direct yaw moment control, by controlling the four-wheel torque only, and when extreme conditions such as low adhesion road surface, high-speed steering braking, etc. are encountered, the single direct yaw moment control may not meet the requirements, at which time it is necessary to combine the active front wheel steering control technique to further improve vehicle stability.
CN2022105647474 proposes a fuzzy-sliding mode composite control system of a four-wheel drive AFS/DYC integrated control system, which can realize stability control of a vehicle by applying an active front wheel corner and a yaw moment, and improve lateral stability under a limit condition. However, the disadvantage is that the final additional yaw moment and the front wheel rotation angle are obtained by the fuzzy control in the patent, and then four-wheel torque distribution is performed according to the dynamic load mode, wherein the torque distribution does not consider the adhesion between each tire and the road (the maximum adhesion is proportional to the load and the road adhesion coefficient), and if the adhesion is low or the road adhesion coefficient is abrupt, the maximum adhesion between the tire and the road can not reach the distribution value, so that the road and the load distribution situation need to be considered when calculating the additional yaw moment. Furthermore, the patent does not consider roll stability of the vehicle.
CN2022110210848 proposes a method for controlling the coordination of the active front steering system and the direct yaw moment control system based on driving state recognition, the method classifies driving states by using a hidden markov model, determines specific driving states by using an extension theory, determines weight coefficients of the active front steering control system and the direct yaw moment control system based on the current driving states, performs weighted distribution on outputs of the two chassis subsystems, and realizes coordination control of the two chassis subsystems. The patent does not consider roll stability of the vehicle and does not consider coupling analysis of lateral and longitudinal forces in the coordinated control system, namely: the resultant force of the lateral force and the longitudinal force of the tire needs to meet the rule of attaching ellipses, and the maximum value of the resultant force is the product of the vertical load and the road surface attachment coefficient. When the vehicle turns, the change of the tire slip angle is caused along with the change of the front wheel corner, so that the tire lateral force is changed, and finally the longitudinal force limit value of the tire is influenced. Therefore, the coupling characteristics of the transverse and longitudinal forces should be considered in the optimization problem considering the nonlinear constraint of the tire, and the decoupling analysis should be performed.
CN2022111885520 proposes a distributed driving electric vehicle stability control method based on the extension evolution game, which coordinates and controls the active front wheel steering system and the direct yaw moment system, and realizes the distributed driving electric vehicle stability control by optimally distributing the lateral force and the longitudinal force of the tire. The patent does not consider the roll stability of the vehicle and does not consider the influence of the tire side angle on its longitudinal force, i.e., the coupling mechanism of the lateral and longitudinal forces, when calculating the maximum tire output longitudinal force, which would result in a calculated maximum tire output longitudinal force that is greater than the actual value, especially during cornering.
The above is where the present application needs to be improved.
Disclosure of Invention
The application aims to provide a cooperative control method for active front wheel steering and direct yaw moment based on a vehicle road state, and the comprehensive performance of an intelligent driving vehicle is improved.
In order to solve the technical problems, the application provides a cooperative control method for active front wheel steering and direct yaw moment based on a vehicle road state, which utilizes the monitored vehicle state and road surface adhesion condition to calculate the limit value of tire force in real time; according to the requirements of vehicle collision avoidance track tracking and stability control, an NMPC controller is designed to solve optimal values of longitudinal force and lateral force of a tire, and the coordination control of emergency steering collision avoidance safety and stability is realized through front wheel active steering and four-wheel braking force control, and the specific steps are as follows:
step S1: establishing a linear eight-degree-of-freedom vehicle dynamics model and a tire force calculation model considering road surface adhesion and load transfer, wherein the eight-degree-of-freedom vehicle dynamics model comprises longitudinal direction, transverse direction, yaw, roll and four-wheel rotation;
the eight-degree-of-freedom whole vehicle dynamics model is shown in formulas (1) - (4):
wherein: m is the mass of the whole vehicle, v x 、v y 、Longitudinal speed, lateral speed, longitudinal acceleration and lateral acceleration, respectively, delta of the vehicle f 、β、/>φ、/>Respectively front wheel rotation angle, centroid side deflection angle, yaw rate acceleration, side dip angle velocity and side dip angle acceleration, F l_fl 、F l_fr 、F l_rl 、F l_rr Longitudinal forces of front left, front right, rear left, rear right tires, F c_fl 、F c_fr 、F c_rl 、F c_rr Lateral forces of front left, front right, rear left, rear right tires, respectively, l f 、l r The distances from the center of mass to the front and rear axes are respectively B w For the track, h 1 Distance from the centroid to the roll axis; i x 、I z The moment of inertia of the vehicle around the x axis and the z axis respectively; />Is a course angle;
step S2: designing a path tracking and stability coordination controller based on a nonlinear model predictive control algorithm to obtain longitudinal force and lateral force of the tire; determining a sign of a difference between the desired yaw rate and the actual yaw rate, and a sign of a front wheel rotation angle value to determine whether to apply a braking force to the rear left wheel or the rear right wheel; further judging whether the yaw moment generated by the braking force applied by the wheels is larger than the expected yaw moment or not so as to determine whether the right front wheel braking or the left front wheel braking is respectively increased or not; if the accessory yaw moment generated by the braking force is still smaller than the expected value, the steering angle of the additional front wheels and the additional yaw moment value are required to be optimized again until the requirements are met, and then control signals are output to a braking system and a steering system;
the NMPC controller receives the expected track information from the track planning module, the vehicle state information of the inertia measuring unit, the road surface adhesion coefficient estimated by the observer, the mass center position, the roll axis position, the tire slip angle and other information, and solves the expected front wheel corner required by tracking an expected path and the expected additional yaw moment and the four-wheel braking force required by maintaining the stability of the vehicle by combining the eight-degree-of-freedom vehicle dynamics model.
The desired track signal of the track planning module comprises a desired speed, a course angle and track point coordinates.
The tire lateral and longitudinal forces are calculated as follows:
step S21: calculating the lateral force and the longitudinal force of the tire by using a magic tire formula, wherein the formula (5) is as follows:
M＝Dsin[Carctan{Bχ-E(Bχ-arctanBχ)}] (5)；
when χ is the longitudinal slip rate and the tire slip angle respectively, M is the tire longitudinal force and the tire lateral force respectively, wherein a B, C, D, E coefficient calculation formula is shown as (6), b 0 ,b 1 ,b 2 ,b 3 ,b 4 ,b 5 ,b 6 ,b 7 ,b 8 For fitting coefficients, from tire test data:
step S22: calculating the tire slip angle according to the formula (7), and carrying out the formula (5) to obtain the lateral force of the tire:
wherein: alpha fl 、α fr 、α rl 、α rr The side angles of the front left, front right, rear left and rear right tires are respectively;
step S23: calculating the longitudinal slip rate of the tire according to the formula (8), and carrying out the formula (5) to obtain the longitudinal force of the tire:
wherein: s is S ij 、ω ij R is divided into the longitudinal slip rate of four tires, the rotating speed of four wheels and the rolling radius of the wheels;
step S24: the sum of the tire lateral force and the longitudinal force cannot exceed the peak adhesion force as shown in formula (9); peak adhesion is the product of the vertical load of the tire and the adhesion coefficient as shown in equation (10); equation (11) is a calculation equation of the vertical load of each tire;
F l +F c ≤F ij_max (9)；
F ij_max ＝F z_ij μ ij (10)；
wherein: f (F) z_fl 、F z_fr 、F z_rl 、F z_rr Vertical loads of front left, front right, rear left and rear right tires respectively; h is a 2 Is the height of the mass center, F l 、F c Is the longitudinal and lateral force of the tyre; mu (mu) ij The adhesion coefficients of the four wheels and the road surface are respectively a x ，a y Longitudinal and lateral acceleration of the vehicle respectively;
the values of the longitudinal force and the lateral force of the tire taking the road adhesion coefficient and the load transfer into consideration are calculated in real time from the formulas (5) - (11).
The monitored vehicle state refers to the motion state of the front vehicle, including speed, acceleration and relative distance, and the motion state of the own vehicle, including speed, acceleration, longitude and latitude coordinates, yaw angle and roll attitude.
The application has the advantages that:
1) According to the application, the eight-degree-of-freedom vehicle dynamics model of the vehicle is established, the vehicle states such as yaw and roll of the vehicle and the conditions of a road surface are fully considered, the coupling mechanism of the longitudinal force and the lateral force of the tire is analyzed and researched, and the full utilization of the tire force is realized by utilizing the cooperative control method of the steering of the active front wheels and the direct yaw moment, so that the comprehensive performance of the intelligent driving vehicle is improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:
FIG. 1 is a planar seven-degree-of-freedom dynamics model of a vehicle in accordance with an embodiment of the present application;
FIG. 2 is a vehicle roll dynamics model of an embodiment of the present application;
FIG. 3 is a flow chart of a control method according to an embodiment of the present application;
FIG. 4 is a flow chart of the distribution of longitudinal and lateral forces of a tire according to an embodiment of the present application.
Detailed Description
Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
The application provides a front wheel steering and direct yaw moment cooperative control method based on a vehicle road state, as shown in fig. 3, wherein the method for monitoring the motion state of a front vehicle by utilizing a millimeter wave radar in the running process of the vehicle comprises the following steps: speed, acceleration and relative distance, while utilizing inertial measurement unit to monitor the motion state of bicycle, include: speed, acceleration, longitude and latitude coordinates, yaw angle, and roll attitude information. When emergency steering collision avoidance is needed in emergency, firstly outputting a desired track by a track planning module, wherein the desired track comprises a desired speed, a course angle and track point coordinates; the NMPC controller receives expected track information from the track planning module, self-vehicle state information of the inertia measuring unit, road surface adhesion coefficient, mass center position, roll axis position and tire side deflection angle information estimated by the state observer, solves expected front wheel rotation angles required by tracking an expected path and expected additional yaw moment and four-wheel braking force required by maintaining vehicle stability by combining an eight-degree-of-freedom whole vehicle dynamics model, and sends control signals to the actuator to optimize yaw stability, roll stability and collision avoidance safety performance of the vehicle; wherein: and calculating an objective function min J (k) in the NMPC module through calibrating a Q, R matrix, so as to realize the optimal comprehensive consideration of the whole vehicle performance. The method comprises the following specific steps:
step S1: establishing a linear eight-degree-of-freedom vehicle dynamics model and a tire force calculation model considering road surface adhesion and load transfer, wherein the eight-degree-of-freedom vehicle dynamics model comprises longitudinal direction, transverse direction, yaw, roll and four-wheel rotation;
step S11: establishing an eight-degree-of-freedom whole vehicle dynamics model, wherein the eight-degree-of-freedom whole vehicle dynamics model comprises a vehicle plane seven-degree-of-freedom dynamics model shown in fig. 1 and a vehicle roll dynamics model shown in fig. 2, and the eight-degree-of-freedom whole vehicle dynamics model is shown in formulas (1) - (4):
wherein m is the mass of the whole vehicle, v x 、v y 、Longitudinal speed, lateral speed, longitudinal acceleration and lateral acceleration, respectively, delta of the vehicle f 、β、/>φ、/>Respectively front wheel rotation angle, centroid side deflection angle, yaw rate acceleration, side dip angle velocity and side dip angle acceleration, F l_fl 、F l_fr 、F l_rl 、F l_rr Longitudinal forces of front left, front right, rear left, rear right tires, F c_fl 、F c_fr 、F c_rl 、F c_rr Lateral forces of front left, front right, rear left, rear right tires, respectively, l f 、l r The distances from the center of mass to the front and rear axes are respectively B w For the track, h 1 Distance from the centroid to the roll axis; i x 、I z The moment of inertia of the vehicle around the x axis and the z axis respectively; />Is the heading angle.
Step S2: calculating the lateral force and the longitudinal force of the tire;
as shown in fig. 4, in the MIMO-NMPC controller, an expected additional yaw moment is calculated by the stability control module, and then the expected front wheel steering angle output by the trajectory planning control module is combined, and then the maximum longitudinal force and lateral force that can be achieved by the four tires in the current vehicle state are calculated by using the magic tire formula according to the road adhesion coefficient, the tire vertical load, the tire slip angle and the slip rate parameter output by the state observer, and finally the difference between the expected yaw rate and the actual yaw rate is determined, namelyAnd the sign of the front wheel steering angle value to determine the application of braking force on the rear left or right wheel: further, whether the right front wheel brake or the left front wheel brake is respectively increased or not is determined by judging whether the yaw moment generated by the braking force applied by the wheels is larger than the expected yaw moment; if the accessory yaw moment generated by the braking force is still less than the desired value, additional pre-optimization is requiredThe steering angle of the wheels and the additional yaw moment value are output to a braking system and a steering system until the requirements are met, so that the high-efficiency and safe control of the vehicle is realized; the method comprises the following specific steps:
step S21: tire lateral force and longitudinal force calculations:
calculating the lateral force and the longitudinal force of the tire by using a magic tire formula, as shown in a formula (5):
M＝Dsin[Carctan{Bχ-E(Bχ-arctanBχ)}] (5)；
when χ is the longitudinal slip rate and the tire slip angle respectively, M is the tire longitudinal force and the tire lateral force respectively, wherein a B, C, D, E coefficient calculation formula is shown as (6), b 0 ,b 1 ,b 2 ,b 3 ,b 4 ,b 5 ,b 6 ,b 7 ,b 8 For fitting coefficients, from tire test data:
step S22: calculating the tire slip angle according to the formula (7), and carrying out the formula (5) to obtain the lateral force of the tire:
wherein: alpha fl 、α fr 、α rl 、α rr The side angles of the front left, front right, rear left and rear right tires are respectively;
step S23: calculating the longitudinal slip rate of the tire according to the formula (8), and carrying out the formula (5) to obtain the longitudinal force of the tire:
wherein: s is S ij 、ω ij R is divided into the longitudinal slip rate of four tires, the rotating speed of four wheels and the rolling radius of the wheels;
step S3: because the interaction force between the tire and the ground is required to meet the adhesion ellipse characteristic, the sum of the lateral force and the longitudinal force of the tire cannot exceed the peak adhesion force, as shown in a formula (9), the peak adhesion force is the product of the vertical load of the tire and the adhesion coefficient, as shown in a formula (10), and a formula (11) is a calculation formula of the vertical load of each tire;
F l +F c ≤F ij_max (9)；
F ij_max ＝F z_ij μ ij (10)；
wherein: f (F) z_fl 、F z_fr 、F z_rl 、F z_rr Vertical loads of front left, front right, rear left and rear right tires respectively; h is a 2 Is the height of the mass center, F l 、F c Is the longitudinal and lateral force of the tyre; mu (mu) ij The adhesion coefficients of the four wheels and the road surface are respectively a x ，a y Longitudinal and lateral acceleration of the vehicle respectively;
in summary, calculating the longitudinal force and lateral force values of the tire taking the road adhesion coefficient and load transfer into consideration in real time according to formulas (5) - (11);
step S4: track tracking and stability control optimization problems are established and solved;
equations (1) - (11) as described above describe a nonlinear dynamics model of the vehicle, expressed by differential equations shown in equation (12):
wherein: state quantityInput vector Δu= [ F fl ,F fr ,F rl ,F rr ,Δδ f ] T Wherein F fl 、F fr 、F rl 、F rr And delta f The four-wheel braking force and the additional front wheel steering angle are respectively;
the motion of the vehicle in the geodetic coordinate system X-Y is described as:
an objective function is designed for the stability control problem in the vehicle movement process under complex and severe working conditions, as shown in a formula (14):
wherein: q, R is a weight coefficient matrix, epsilon is a relaxation factor, np is a prediction time domain, nc is a control time domain, and ρ is a weight coefficient; the first reaction control system has stable tracking capacity to reference track including yaw stability, roll stability and track tracking precision, and its reference value is set asThe second term is a constraint on the control volume change and adds a relaxation factor term to avoid situations where no solution is available during execution.
The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, and various modifications and variations may be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (6)
1. A cooperative control method for active front wheel steering and direct yaw moment based on a vehicle road state is characterized by comprising the following steps of: calculating a limit value of tire force in real time based on the monitored vehicle state and the road surface adhesion condition; according to the vehicle collision avoidance track tracking and stability control requirements, the NMPC controller solves optimal tire longitudinal force and lateral force values, and the coordination control of emergency steering collision avoidance safety and stability is realized through front wheel active steering and four-wheel braking force control.
2. The vehicle road state-based active front wheel steering and direct yaw moment cooperative control method according to claim 1, characterized in that: the monitored vehicle state refers to the motion state of the front vehicle, including speed, acceleration and relative distance, and the motion state of the own vehicle, including speed, acceleration, longitude and latitude coordinates, yaw angle and roll attitude.
3. The vehicle road state-based active front wheel steering and direct yaw moment cooperative control method according to claim 1, characterized in that: the method comprises the following steps of:
step S1: establishing a linear eight-degree-of-freedom vehicle dynamics model and a tire force calculation model considering road surface adhesion and load transfer, wherein the eight-degree-of-freedom vehicle dynamics model comprises longitudinal direction, transverse direction, yaw, roll and four-wheel rotation;
step S2: designing a path tracking and stability coordination controller based on a nonlinear model predictive control algorithm to obtain longitudinal force and lateral force of the tire; determining a sign of a difference between the desired yaw rate and the actual yaw rate, and a sign of a front wheel rotation angle value to determine whether to apply a braking force to the rear left wheel or the rear right wheel; further judging whether the yaw moment generated by the braking force applied by the wheels is larger than the expected yaw moment or not so as to determine whether the right front wheel braking or the left front wheel braking is respectively increased or not; if the accessory yaw moment generated by the braking force is still smaller than the expected value, the steering angle of the additional front wheels and the additional yaw moment value need to be optimized again until the requirements are met and then control signals are output to a braking system and a steering system.
4. The active front wheel steering and direct yaw moment cooperative control method based on the road state of claim 3, wherein: and S2, the NMPC controller receives expected track information from the track planning module, vehicle state information of the inertia measuring unit, road adhesion coefficient estimated by the observer, mass center position, roll axis position, tire slip angle and other information, and solves expected front wheel rotation angles required by tracking an expected path and expected additional yaw moment and four-wheel braking force required by maintaining vehicle stability by combining an eight-degree-of-freedom whole vehicle dynamics model.
5. The vehicle road state-based active front wheel steering and direct yaw moment cooperative control method according to claim 4, wherein: the desired track signal of the track planning module comprises a desired speed, a course angle and track point coordinates.
6. The active front wheel steering and direct yaw moment cooperative control method based on the road state of claim 3, wherein: the tire lateral and longitudinal forces are calculated as follows:
step S21: calculating the lateral force and the longitudinal force of the tire by using a magic tire formula, wherein the formula (5) is as follows:
M＝Dsin[Carctan{Bχ-E(Bχ-arctanBχ)}] (5)；
when χ is the longitudinal slip rate and the tire slip angle respectively, M is the tire longitudinal force and the tire lateral force respectively, wherein a B, C, D, E coefficient calculation formula is shown as (6), b 0 ,b 1 ,b 2 ,b 3 ,b 4 ,b 5 ,b 6 ,b 7 ,b 8 For fitting coefficients, from tire test data:
step S22: calculating the tire slip angle according to the formula (7), and carrying out the formula (5) to obtain the lateral force of the tire:
wherein: alpha fl 、α fr 、α rl 、α rr The side angles of the front left, front right, rear left and rear right tires are respectively;
step S23: calculating the longitudinal slip rate of the tire according to the formula (8), and carrying out the formula (5) to obtain the longitudinal force of the tire:
wherein: s is S ij 、ω ij R is divided into the longitudinal slip rate of four tires, the rotating speed of four wheels and the rolling radius of the wheels;
step S24: the sum of the tire lateral force and the longitudinal force cannot exceed the peak adhesion force as shown in formula (9); peak adhesion is the product of the vertical load of the tire and the adhesion coefficient as shown in equation (10); equation (11) is a calculation equation of the vertical load of each tire;
F l +F c ≤F ij_max (9)；
F ij_max ＝F z_ij μ ij (10)；
wherein: f (F) z_fl 、F z_fr 、F z_rl 、F z_rr Vertical loads of front left, front right, rear left and rear right tires respectively; h is a 2 Is the height of the mass center, F l 、F c Is the longitudinal and lateral force of the tyre; mu (mu) ij The adhesion coefficients of the four wheels and the road surface are respectively a x ，a y Longitudinal and lateral acceleration of the vehicle respectively;
the values of the longitudinal force and the lateral force of the tire taking the road adhesion coefficient and the load transfer into consideration are calculated in real time from the formulas (5) - (11).
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