CN112668093A - Optimal distribution control method for all-wheel longitudinal force of distributed driving automobile - Google Patents
Optimal distribution control method for all-wheel longitudinal force of distributed driving automobile Download PDFInfo
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Abstract
The invention discloses a distributed driving automobile all-wheel longitudinal force optimal distribution control method, which comprises the following steps of: s1: establishing a motion stability control system based on optimal distribution of all-wheel longitudinal force; s2: setting a motion controller and a motion distributor; s3: longitudinal force distribution is carried out on the distributed drive automobile. According to the invention, the vehicle key parameter state observer is established according to the characteristic that the distributed electric vehicle has a plurality of information sources, so that the accurate online estimation of key parameters is completed, and the real-time performance and the accuracy of the calculation of the target yaw moment are improved. Meanwhile, the influence of the front wheel corner is considered in the process of calculating the target yaw moment, and the accuracy of the calculation model is improved. The vehicle longitudinal force distribution method considers the coupling relation between the tire load rate and the tire slip rate, realizes the optimal distribution of the vehicle motion stability and the dynamic property, and further improves the performance of a vehicle motion control system.
Description
Technical Field
The invention belongs to the technical field of optimization control, and particularly relates to an optimal distribution control method for all-wheel longitudinal force of a distributed drive automobile.
Background
The distributed driving electric automobile has the advantages that the driving force distribution of each wheel is flexible, various longitudinal force distribution methods can be realized, the research on the distribution algorithm can effectively improve the motion safety and the operation stability of the whole automobile, and the distributed driving electric automobile has strong engineering practical significance. Some key parameters of the vehicle, such as tire cornering angle, tire lateral force, tire cornering stiffness, and road adhesion coefficient, cannot be measured with sensors. Online estimation of these parameters plays an important role in the design of active safety systems for vehicles.
Some prior arts propose to establish a vehicle state parameter observer by using an extended kalman filter algorithm (EKF) based on a conventional vehicle structure, and to distribute a longitudinal force according to a tire load rate, thereby improving the stability of vehicle motion. And the control of the driving skid resistance of the vehicle is finished by limiting the adhesion coefficient of the tire and the ground and the slip ratio of the tire while distributing the longitudinal force, so that the dynamic property of the vehicle is improved. However, these techniques often only consider a single index, and cannot reasonably optimize distribution control globally.
Disclosure of Invention
The invention aims to solve the problem of optimal distribution of distributed drive automobiles, and provides an optimal distribution control method for all-wheel longitudinal force of a distributed drive automobile.
The technical scheme of the invention is as follows: the optimal distribution control method for the longitudinal force of all wheels of the distributed driving automobile comprises the following steps:
s1: establishing a motion stability control system based on optimal distribution of all-wheel longitudinal force;
s2: respectively arranging a motion controller and a motion distributor according to the motion stability control system;
s3: and the motion controller and the motion distributor are utilized to distribute longitudinal force to the distributed drive automobile.
The invention has the beneficial effects that: according to the invention, the vehicle key parameter state observer is established according to the characteristic that the distributed electric vehicle has a plurality of information sources, so that the accurate online estimation of key parameters is completed, and the real-time performance and the accuracy of the calculation of the target yaw moment are improved. Meanwhile, the influence of the front wheel corner is considered in the process of calculating the target yaw moment, and the accuracy of the calculation model is improved. The vehicle longitudinal force distribution method considers the coupling relation between the tire load rate and the tire slip rate, realizes the optimal distribution of the vehicle motion stability and the dynamic property, and further improves the performance of a vehicle motion control system. Meanwhile, the vehicle state observer comprises an extended Kalman filter and a Dugoff tire inverse model, so that real-time and accurate online estimation of key state parameters of the vehicle can be realized, the accuracy of calculation of the target yaw moment is improved, and the capability of the vehicle for realizing driving intention is improved. The longitudinal force distribution of the vehicle simultaneously considers the tire load rate and the tire slip rate, and provides a comprehensive distribution mode. The method has the advantages that reasonable weight coefficient distribution is carried out on vehicle stability control and dynamic control according to the stable state of the vehicle, driving anti-skid control is carried out while road adhesion allowance is reserved, slipping and locking of tires are reduced, coupling control of the load rate and the slip rate of the tires of the vehicle is achieved through optimal distribution of the longitudinal force of all wheels, and the control performance of a vehicle motion system is further improved.
Further, step S1 includes the following sub-steps:
s11: determining variables required by a motion stability control system;
s12: according to the required variables in the motion stability control system, a vehicle dynamics equation is established;
s13: and setting a vehicle state parameter observer according to a vehicle dynamics equation to complete the establishment of the motion stability control system.
Further, in step S11, the vehicle body coordinate system R ═ { G, x, y, z }, where G denotes the center of mass of the vehicle and x denotes the center of mass of the vehicleThe positive direction is from the origin of the body coordinate system to the right front of the vehicle, the positive direction is from the origin of the body coordinate system to the left front of the vehicle side represented by the y axis, and the positive direction is from the origin o of the body coordinate system to the x axis and the y axis of the body coordinate system; the desired variable being a speed variable
The expression of the method in an inertial coordinate system is [ u, v, r]TWherein, in the step (A),
representing a speed variation of the vehicle in the x-axis direction, wherein
Representing the speed variation of the vehicle in the direction of the y-axis,
the speed variable of the vehicle around a z-axis is represented, u represents an abscissa of the speed variable in an inertial coordinate system, v represents an ordinate of the speed variable in the inertial coordinate system, and r represents a vertical coordinate of the speed variable in the inertial coordinate system;
in the step S12, the vehicle dynamics equation includes a vehicle longitudinal motion equation
Equation of lateral motion of vehicle
And equations of yaw motion of the vehicle
The expressions are respectively:
where δ represents the angle of rotation of the front wheels of the vehicle, B represents the track of the left and right wheels of the vehicle, and lfRepresenting the distance from the front axle of the vehicle to the centre of mass,/rRepresenting the distance from the rear axle of the vehicle to the centre of mass,/zRepresenting the moment of inertia of the vehicle about the z-axis, M representing the mass of the vehicle as a whole, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FyflRepresenting the lateral force of the front left wheel of a vehicle tyre, FyfrRepresenting the lateral force of the front right wheel of a vehicle tyre, FyrlRepresenting the lateral force of the rear left wheel of a vehicle tyre, FyrrRepresenting the lateral force of the rear right wheel of the vehicle tyre,
which is indicative of the longitudinal acceleration of the vehicle,
which represents the lateral acceleration of the vehicle,
which represents the yaw acceleration of the vehicle.
Further, in step S13, the vehicle state parameter observer includes an electric wheel basic parameter observer, a tire cornering power observer, and a road surface adhesion coefficient observer.
The beneficial effects of the further scheme are as follows: in the invention, the vehicle state parameter observer can realize the on-line estimation of the longitudinal force, the lateral force, the cornering stiffness, the longitudinal-slip stiffness and the road adhesion coefficient of the vehicle wheels, and improve the accuracy and the real-time performance of the distribution calculation of the target yaw moment and the longitudinal force of the wheels.
Further, the electric wheel basic parameter observer is used for calculating the wheel speed, the wheel slip rate, the longitudinal slip rigidity and the vertical load of each wheel of the vehicle, and the calculation formulas are respectively as follows:
λfl＝1-ωflR/utfl
λfr＝1-ωfrR/utfr
λrl＝1-ωrlR/utrl
λrr＝1-ωrrR/utrr
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
therein, utflIndicating the wheel speed, ut, of the front left wheel of the vehiclefrIndicating the wheel speed, ut, of the front right wheel of the vehiclerlIndicating the wheel speed, ut, of the rear left wheel of the vehiclerrIndicating the wheel speed, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrRepresenting the longitudinal sliding stiffness of the rear right wheel of the vehicle, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresents the vertical load of the right and rear wheels of the vehicle, u represents the abscissa of the vehicle velocity vector in the inertial frame, v represents the ordinate of the vehicle velocity vector in the inertial frame, r represents the ordinate of the vehicle velocity vector in the inertial frame, B represents the track width of the right and left wheels of the vehicle, l represents the vertical load of the right and left rear wheels of the vehicle, andfrepresenting the distance, omega, from the front axle of the vehicle to the centre of massflRepresenting the angular velocity, omega, of the front left wheel of the vehiclefrRepresenting angular velocity, omega, of the front right wheel of the vehiclerlRepresenting the angular velocity, omega, of the rear left wheel of the vehiclerrRepresenting the angular velocity of the rear right wheel of the vehicle, R representing the load radius of the electric wheel, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre,/rRepresenting the distance from the rear axle of the vehicle to the center of mass, M representing the mass of the vehicle, hcogIndicating vehicleThe height of the center of mass of the vehicle; g represents the gravitational acceleration; a isxRepresenting the longitudinal acceleration of the vehicle; a isyIndicating the lateral acceleration of the vehicle.
The beneficial effects of the further scheme are as follows: in the invention, the electric wheel basic parameter observer estimates basic parameters of the vehicle, such as longitudinal force of a tire, wheel speed of each wheel, slip rate of each wheel, longitudinal slip stiffness and vertical load of each wheel, according to linear velocity and angular velocity information of the vehicle.
Further, the tire cornering stiffness observer comprises the longitudinal and slip stiffness of the vehicle tire, and the calculation formulas are respectively as follows:
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
wherein, CxflRepresenting the longitudinal sliding stiffness, C, of the left front wheel of a vehicle tyrexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of a vehicle tyrexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of a vehicle tyrexrrRepresenting the longitudinal sliding stiffness, F, of the rear left wheel of a vehicle tyrexflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force, λ, of the right and rear wheels of a vehicle tyreflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle.
The beneficial effects of the further scheme are as follows: in the present invention, the cornering stiffness of the tire is affected by many factors such as the adhesion coefficient of the road surface and the vertical load of the tire during actual movement of the vehicle. In the invention, the cornering stiffness of the tire is a key vehicle parameter for calculating the target yaw moment, so that the real-time and accuracy of the calculated value of the target yaw moment can be improved by carrying out real-time online estimation on the dynamic parameter of the cornering stiffness of the tire.
Further, in step S13, a road adhesion coefficient observer is calculated according to the electric wheel basic parameter observer and the tire deflection stiffness observer, the road adhesion coefficient observer includes the adhesion coefficients of the tire and the road, and the calculation formulas are respectively:
wherein, muflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresenting the vertical load of the rear right wheel of the vehicle, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrLongitudinal slide steel for rear right wheel of vehicleDegree, lambdaflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle, f(L)Representing a value factor.
The beneficial effects of the further scheme are as follows: in the invention, a Dugoff tire model is selected, the tire model has a simple form and fewer required parameters, has better precision in the range of the tire slip ratio lower than 0.4, and meets most of the running conditions of the vehicle.
Further, in step S2, the setting of the motion controller includes the following sub-steps:
a21: setting state equations for motion controllers
Control target beta of centroid slip angle betadThe expressions are respectively:
βd＝0
wherein A represents an actual vehicle state variable coefficient matrix, x represents an actual vehicle state matrix, E represents a known constant matrix, u represents an actual vehicle longitudinal velocity matrix, M represents an actual vehicle yaw moment matrix,
M＝Mz，
lzrepresenting the moment of inertia of the vehicle about the z-axis;
r represents the vertical coordinate of the vehicle velocity vector in the inertial coordinate system, beta represents the centroid slip angle, u represents the center of mass1Representing the actual vehicle first longitudinal speed, u2Representing the actual vehicle second longitudinal speed, MzRepresenting the actual vehicle yaw moment, a11Indicating a first actual vehicle stateCoefficient of variation, a12Representing a second actual vehicle state variable coefficient, a21Representing a third actual vehicle state variable coefficient, a22Representing a fourth actual vehicle state variable coefficient;
a22: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadObtaining a control target r of the yaw rate rdThe calculation formula is as follows:
a23: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadAnd a control target r of the yaw rate rdCalculating a feed-forward moment MffThe calculation formula is as follows:
a24: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadControl target r of yaw rate rdAnd a feed forward moment MffAnd obtaining a response model of the expected vehicle, wherein the expression is as follows:
wherein x isdIndicating the target vehicle state, AdCoefficient matrix, u, representing the state variables of the target vehicledWhich is indicative of the target longitudinal speed of the vehicle,
a25: setting an optimal target function according to a response model of the expected vehicle, and calculating the optimal feedback moment M of the motion stability control system by linear quadratic calculation according to the optimal target functionfbThe calculation formula is as follows:
Mfb＝(-R-1ETP)Te
wherein E represents the feedback control error of the vehicle, R represents the feedback yaw velocity, P represents the unique positive definite symmetric solution matrix of the equation, and E represents the known constant value matrix;
a26: according to a feed-forward moment MffAnd an optimum feedback moment MfbCalculating a target yaw moment M of a motion stability control systemzdAnd completing the setting of the motion controller, wherein the calculation formula is as follows:
Mzd＝Mff+Mfb。
the beneficial effects of the further scheme are as follows: in the invention, a motion controller utilizes a Linear Quadratic Regulator (LQR) to control and calculate a vehicle target direct yaw moment (consisting of a feed-forward moment and a feedback moment) according to the current driver input (a steering command and an accelerator opening degree) of a vehicle and the real-time motion state (the vehicle speed, the mass center sideslip angle and the yaw angular velocity) of the vehicle. In the vehicle steering dynamics, the steering stability of the vehicle can be improved by adopting a method of zero mass center slip angle, and the riding comfort of a driver and passengers is improved. In the process of feeding back the torque MfbIn the calculation, an excessive feedback quantity is not introduced while the error e is reduced, so that the feedback moment needs to be restrained, and an optimal objective function needs to be designed.
Further, in step S2, the setting of the motion distributor includes the following sub-steps:
b21: according to the motion stability control system, setting an objective function min of longitudinal force optimized distributionuJ1And an optimization objective function min driving antiskid controluJ2The expressions are respectively:
minuJ2＝[(Fxflλfl)2+(Fxfrλfr)2+(Fxrlλrl)2+(Fxrrλrr)2]/(Fxdλmax)2
wherein, muflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresenting the vertical load, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio, λ, of the rear right wheel of the vehiclemaxRepresenting the maximum slip ratio, F, of the vehicle tyrexdRepresenting the longitudinal force demand of the whole vehicle;
b22: objective function min for optimal distribution of longitudinal forcesu J1And an optimization objective function min driving antiskid controluJ2Normalization processing is carried out to obtain the optimal distribution objective function minuJ, completing the setting of the motion distributor, wherein the expression is as follows:
minuJ＝kminuJ1+(1-k)minuJ2
where k represents a weight coefficient.
The beneficial effects of the further scheme are as follows: in the present invention, the target longitudinal force requirement in the motion distributor is designed as an open loop, relying on the driver to perform closed loop control by itself. The design of the comprehensive longitudinal force optimization distribution algorithm fully considers the stability distribution based on the principle of minimum tire load rate and the driving anti-skid distribution based on the maintenance of smaller wheel slip rate so as to keep the mass center slip angle upper limit value beta of the vehicle motion stability0The weight coefficient between the two distribution laws is adjusted to achieve the coupling between vehicle stability and drive slip prevention. The slip rate of the tires is an important parameter for measuring the longitudinal adhesion level of the vehicle, the smaller slip rate of each tire is kept through reasonable longitudinal force distribution of the wheels, the safety and the dynamic property of the vehicle are improved, when the slip rate of one wheel is larger, the driving torque of the wheel is reduced, and the slipping or locking of the vehicle is avoided. Therefore, an optimized objective function for driving anti-skid control is designed and normalized, and the normalization is convenient to perform with J1And establishing comprehensive evaluation.
Drawings
FIG. 1 is a flow chart of a distributed drive vehicle all-wheel longitudinal force optimal distribution control method;
FIG. 2 is a block diagram of a motion stability control system;
fig. 3 is a block diagram of a motion stabilization control system.
Detailed Description
The embodiments of the present invention will be further described with reference to the accompanying drawings.
As shown in fig. 1, the invention provides a distributed drive vehicle all-wheel longitudinal force optimal distribution control method, which comprises the following steps:
s1: establishing a motion stability control system based on optimal distribution of all-wheel longitudinal force;
s2: respectively arranging a motion controller and a motion distributor according to the motion stability control system;
s3: and the motion controller and the motion distributor are utilized to distribute longitudinal force to the distributed drive automobile.
In the embodiment of the present invention, as shown in fig. 1, step S1 includes the following sub-steps:
s11: determining variables required by a motion stability control system;
s12: according to the required variables in the motion stability control system, a vehicle dynamics equation is established;
s13: and setting a vehicle state parameter observer according to a vehicle dynamics equation to complete the establishment of the motion stability control system.
In the embodiment of the present invention, as shown in fig. 2, in step S11, the vehicle body coordinate system R is { G, x, y, z }, where G denotes a center of mass of the vehicle, x denotes that a positive direction is defined as a direction passing through an origin of the vehicle body coordinate system toward a front side of the vehicle, y denotes that a positive direction is defined as a direction passing through the origin of the vehicle body coordinate system toward a left front side of the vehicle, and z denotes that a positive direction is defined as a direction passing through an origin o of the vehicle body coordinate system and perpendicular to x and y axes of the vehicle body coordinate system; the desired variable being a speed variable
The expression of the method in an inertial coordinate system is [ u, v, r]TWherein, in the step (A),
representing a speed variation of the vehicle in the x-axis direction, wherein
Representing the speed variation of the vehicle in the direction of the y-axis,
the speed variable of the vehicle around a z-axis is represented, u represents an abscissa of the speed variable in an inertial coordinate system, v represents an ordinate of the speed variable in the inertial coordinate system, and r represents a vertical coordinate of the speed variable in the inertial coordinate system;
in step S12, the vehicle dynamics equations include vehicle longitudinal motion equations
Equation of lateral motion of vehicle
And equations of yaw motion of the vehicle
The expressions are respectively:
where δ represents the angle of rotation of the front wheels of the vehicle, B represents the track of the left and right wheels of the vehicle, and lfRepresenting the distance from the front axle of the vehicle to the centre of mass,/rRepresenting the distance from the rear axle of the vehicle to the centre of mass,/zRepresenting the moment of inertia of the vehicle about the z-axis, M representing the mass of the vehicle as a whole, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FyflRepresenting the lateral force of the front left wheel of a vehicle tyre, FyfrRepresenting the lateral force of the front right wheel of a vehicle tyre, FyrlRepresenting the lateral force of the rear left wheel of a vehicle tyre, FyrrRepresenting the lateral force of the rear right wheel of the vehicle tyre,
which is indicative of the longitudinal acceleration of the vehicle,
which represents the lateral acceleration of the vehicle,
which represents the yaw acceleration of the vehicle.
In the embodiment of the invention, as shown in fig. 3, in step S13, the vehicle state parameter observer includes an electric wheel basic parameter observer, a tire cornering power observer, and a road surface adhesion coefficient observer.
In the invention, the electric wheel basic parameter observer comprises the resultant moment applied to the electric front left wheel
Resultant moment of electric front and right wheels
Resultant moment of electric rear left wheel
And resultant moment received by electric rear right wheel
The calculation formulas are respectively as follows:
wherein, JwRepresenting the moment of inertia of rotation of the motorized wheel,
indicating the angular velocity of the motorized front left wheel,
representing the angular velocity of the motorized front right wheel,
indicating the angular velocity of the motorized rear left wheel,
indicating the angular velocity, T, of the electrically-driven rear right wheelflRepresenting the driving torque, T, of the electrically-driven front left wheelfrRepresenting the driving torque, T, of the electrically-driven front and right wheelsrlRepresenting the driving torque, T, of the electrically-driven left wheelrrRepresenting the driving torque of the right and rear electrically-driven wheels, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of the vehicle tyre, R representing the load radius of the electric wheel, TbRepresenting the braking torque of the electric wheel.
The vehicle state parameter observer can realize the on-line estimation of the longitudinal force, the lateral force, the cornering stiffness, the longitudinal-slip stiffness and the road adhesion coefficient of the vehicle wheels, and improves the accuracy and the real-time performance of the distribution calculation of the target yaw moment and the longitudinal force of the wheels.
In the embodiment of the present invention, as shown in fig. 1, the electric wheel basic parameter observer is used for calculating the wheel speed, the wheel slip rate, the wheel longitudinal slip stiffness and the wheel vertical load of each wheel of the vehicle, and the calculation formulas are respectively:
λfl＝1-ωflR/utfl
λfr＝1-ωfrR/utfr
λrl＝1-ωrlR/utrl
λrr＝1-ωrrR/utrr
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
therein, utflIndicating the wheel speed, ut, of the front left wheel of the vehiclefrIndicating the wheel speed, ut, of the front right wheel of the vehiclerlIndicating the wheel speed, ut, of the rear left wheel of the vehiclerrIndicating the wheel speed, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrIndicating vehicleSlip ratio of rear right wheel, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrRepresenting the longitudinal sliding stiffness of the rear right wheel of the vehicle, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresents the vertical load of the right and rear wheels of the vehicle, u represents the abscissa of the vehicle velocity vector in the inertial frame, v represents the ordinate of the vehicle velocity vector in the inertial frame, r represents the ordinate of the vehicle velocity vector in the inertial frame, B represents the track width of the right and left wheels of the vehicle, l represents the vertical load of the right and left rear wheels of the vehicle, andfrepresenting the distance, omega, from the front axle of the vehicle to the centre of massflRepresenting the angular velocity, omega, of the front left wheel of the vehiclefrRepresenting angular velocity, omega, of the front right wheel of the vehiclerlRepresenting the angular velocity, omega, of the rear left wheel of the vehiclerrRepresenting the angular velocity of the rear right wheel of the vehicle, R representing the load radius of the electric wheel, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre,/rRepresenting the distance from the rear axle of the vehicle to the center of mass, M representing the mass of the vehicle, hcogRepresenting the height of the center of mass of the vehicle; g represents the gravitational acceleration; a isxRepresenting the longitudinal acceleration of the vehicle; a isyIndicating the lateral acceleration of the vehicle.
In the invention, the electric wheel basic parameter observer estimates basic parameters of the vehicle, such as longitudinal force of a tire, wheel speed of each wheel, slip rate of each wheel, longitudinal slip stiffness and vertical load of each wheel, according to linear velocity and angular velocity information of the vehicle.
In an embodiment of the present invention, as shown in fig. 1, the tire cornering stiffness observer includes a longitudinal-to-slip stiffness of a vehicle tire, and the calculation formulas thereof are respectively:
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
wherein, CxflRepresenting the longitudinal sliding stiffness, C, of the left front wheel of a vehicle tyrexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of a vehicle tyrexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of a vehicle tyrexrrRepresenting the longitudinal sliding stiffness, F, of the rear left wheel of a vehicle tyrexflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force, λ, of the right and rear wheels of a vehicle tyreflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle.
In the present invention, the cornering stiffness of the tire is affected by many factors such as the adhesion coefficient of the road surface and the vertical load of the tire during actual movement of the vehicle. In the invention, the cornering stiffness of the tire is a key vehicle parameter for calculating the target yaw moment, so that the real-time and accuracy of the calculated value of the target yaw moment can be improved by carrying out real-time online estimation on the dynamic parameter of the cornering stiffness of the tire.
Calculating the centroid slip angle of the vehicle according to the vehicle dynamics equation
Yaw rate of vehicle
And the absolute speed of the vehicle
The calculation formulas are respectively as follows:
selecting the measurement variables of the tire cornering stiffness observer, which are respectively the sum F of the lateral forces of the front wheel tire of the vehicleyfAnd the sum of the side forces F of the rear wheel tire of the vehicleyrThe calculation formulas are respectively as follows:
Fyf＝Fyfl+Fyfr
Fyr＝Fyrl+Fyrr
when selecting the measurement variable X, since FyflAnd FyfrThere is no corresponding decoupling relation, only the sum (F) of the side forces of the front wheel tireyfl+Fyfr) Is considerable, FyrlAnd FyrrSimilarly, the lateral force of each tire can be distributed according to the vertical force of the tire.
According to the vehicle's centroid slip angle
Yaw rate of vehicle
Absolute speed of vehicle
Vehicle front wheel tire side force sum FyfAnd the sum of the side forces F of the rear wheel tire of the vehicleyrDetermining a state variable X of the tire cornering stiffness observer, wherein the expression is as follows:
in the embodiment of the present invention, as shown in fig. 1, in step S13, a road adhesion coefficient observer is calculated based on an electric wheel basic parameter observer and a tire deflection stiffness observer, the road adhesion coefficient observer includes adhesion coefficients of tires and a road surface, and the calculation formulas are respectively:
wherein, muflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresenting the vertical load of the rear right wheel of the vehicle, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrExpressing the longitudinal-sliding stiffness, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle, f(L)Representing a value factor.
In the invention, a Dugoff tire model is selected, the tire model has a simple form and fewer required parameters, has better precision in the range of the tire slip ratio lower than 0.4, and meets most of the running conditions of the vehicle.
In the embodiment of the present invention, as shown in fig. 1, the setting of the motion controller in step S2 includes the following sub-steps:
a21: setting state equations for motion controllers
Control target beta of centroid slip angle betadThe expressions are respectively:
βd＝0
wherein A represents an actual vehicle state variable coefficient matrix, x represents an actual vehicle state matrix, E represents a known constant matrix, u represents an actual vehicle longitudinal velocity matrix, M represents an actual vehicle yaw moment matrix,
M＝Mz，
lzrepresenting the moment of inertia of the vehicle about the z-axis;
r represents the vertical coordinate of the vehicle velocity vector in the inertial coordinate system, beta represents the centroid slip angle, u represents the center of mass1Representing the actual vehicle first longitudinal speed, u2Representing the actual vehicle second longitudinal speed, MzRepresenting the actual vehicle yaw moment, a11Representing a first actual vehicle state variable coefficient, a12Representing a second actual vehicle state variable coefficient, a21Representing a third actual vehicle state variable coefficient, a22Representing a fourth actual vehicle state variableA coefficient;
a22: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadObtaining a control target r of the yaw rate rdThe calculation formula is as follows:
a23: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadAnd a control target r of the yaw rate rdCalculating a feed-forward moment MffThe calculation formula is as follows:
a24: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadControl target r of yaw rate rdAnd a feed forward moment MffAnd obtaining a response model of the expected vehicle, wherein the expression is as follows:
wherein x isdIndicating the target vehicle state, AdCoefficient matrix, u, representing the state variables of the target vehicledWhich is indicative of the target longitudinal speed of the vehicle,
a25: according to the desired vehicle soundSetting an optimal target function according to the model, and calculating the optimal feedback moment M of the motion stability control system by linear quadratic calculation according to the optimal target functionfbThe calculation formula is as follows:
Mfb＝(-R-1ETP)Te
wherein E represents the feedback control error of the vehicle, R represents the feedback yaw velocity, P represents the unique positive definite symmetric solution matrix of the equation, and E represents the known constant value matrix;
a26: according to a feed-forward moment MffAnd an optimum feedback moment MfbCalculating a target yaw moment M of a motion stability control systemzdAnd completing the setting of the motion controller, wherein the calculation formula is as follows:
Mzd＝Mff+Mfb。
in the invention, a motion controller utilizes a Linear Quadratic Regulator (LQR) to control and calculate a vehicle target direct yaw moment (consisting of a feed-forward moment and a feedback moment) according to the current driver input (a steering command and an accelerator opening degree) of a vehicle and the real-time motion state (the vehicle speed, the mass center sideslip angle and the yaw angular velocity) of the vehicle. In the vehicle steering dynamics, the steering stability of the vehicle can be improved by adopting a method of zero mass center slip angle, and the riding comfort of a driver and passengers is improved. In the process of feeding back the torque MfbIn the calculation, an excessive feedback quantity is not introduced while the error e is reduced, so that the feedback moment needs to be restrained, and an optimal objective function needs to be designed.
In an embodiment of the present invention, as shown in fig. 1, the step S2 of setting the motion distributor includes the following sub-steps:
b21: according to the motion stability control system, setting an objective function min of longitudinal force optimized distributionuJ1And an optimization objective function min driving antiskid controluJ2The expressions are respectively:
minuJ2＝[(Fxflλfl)2+(Fxfrλfr)2+(Fxrlλrl)2+(Fxrrλrr)2]/(Fxdλmax)2
wherein, muflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresenting the vertical load, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio, λ, of the rear right wheel of the vehiclemaxRepresenting the maximum slip ratio, F, of the vehicle tyrexdRepresenting the longitudinal force demand of the whole vehicle;
b22: objective function min for optimal distribution of longitudinal forcesuJ1And an optimization objective function min driving antiskid controluJ2Normalization processing is carried out to obtain the optimal distribution objective function minuJ, completing the setting of the motion distributor, wherein the expression is as follows:
minuJ＝kminuJ1+(1-k)minuJ2
where k represents a weight coefficient.
In the present invention, the target longitudinal force requirement in the motion distributor is designed as an open loop, relying on the driver to perform closed loop control by itself. The design of the comprehensive longitudinal force optimization distribution algorithm fully considers the design based on the tire loadStability distribution based on minimum load rate and driving anti-skid distribution based on maintaining smaller wheel slip rate to keep stable vehicle motion0The weight coefficient between the two distribution laws is adjusted to achieve the coupling between vehicle stability and drive slip prevention. The slip rate of the tires is an important parameter for measuring the longitudinal adhesion level of the vehicle, the smaller slip rate of each tire is kept through reasonable longitudinal force distribution of the wheels, the safety and the dynamic property of the vehicle are improved, when the slip rate of one wheel is larger, the driving torque of the wheel is reduced, and the slipping or locking of the vehicle is avoided. Therefore, an optimized objective function for driving anti-skid control is designed and normalized, and the normalization is convenient to perform with J1And establishing comprehensive evaluation.
The working principle and the process of the invention are as follows: the method comprises the step of establishing a motion stability control system based on optimal distribution of all-wheel longitudinal force for a 4WD distributed drive electric automobile. The vehicle state observer is established by utilizing the characteristic of more information sources of the distributed driving vehicle according to the Kalman filtering algorithm and the Dugoff tire inverse model, and the accuracy of expected direct yaw moment calculation is improved. In the process of establishing the optimal distribution strategy of the longitudinal force of the whole wheel, the load rate and the slip rate of the tire are considered at the same time, and the comprehensive control of the stability and the dynamic property of the vehicle is realized.
The invention has the beneficial effects that: according to the invention, the vehicle key parameter state observer is established according to the characteristic that the distributed electric vehicle has a plurality of information sources, so that the accurate online estimation of key parameters is completed, and the real-time performance and the accuracy of the calculation of the target yaw moment are improved. Meanwhile, the influence of the front wheel corner is considered in the process of calculating the target yaw moment, and the accuracy of the calculation model is improved. The vehicle longitudinal force distribution method considers the coupling relation between the tire load rate and the tire slip rate, realizes the optimal distribution of the vehicle motion stability and the dynamic property, and further improves the performance of a vehicle motion control system. Meanwhile, the vehicle state observer comprises an extended Kalman filter and a Dugoff tire inverse model, so that real-time and accurate online estimation of key state parameters of the vehicle can be realized, the accuracy of calculation of the target yaw moment is improved, and the capability of the vehicle for realizing driving intention is improved. The longitudinal force distribution of the vehicle simultaneously considers the tire load rate and the tire slip rate, and provides a comprehensive distribution mode. The method has the advantages that reasonable weight coefficient distribution is carried out on vehicle stability control and dynamic control according to the stable state of the vehicle, driving anti-skid control is carried out while road adhesion allowance is reserved, slipping and locking of tires are reduced, coupling control of the load rate and the slip rate of the tires of the vehicle is achieved through optimal distribution of the longitudinal force of all wheels, and the control performance of a vehicle motion system is further improved.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (9)
1. The optimal distribution control method for the longitudinal force of all wheels of the distributed driving automobile is characterized by comprising the following steps of:
s1: establishing a motion stability control system based on optimal distribution of all-wheel longitudinal force;
s2: respectively arranging a motion controller and a motion distributor according to the motion stability control system;
s3: and the motion controller and the motion distributor are utilized to distribute longitudinal force to the distributed drive automobile.
2. The method for controlling the optimal distribution of the longitudinal force of all wheels of the distributed drive automobile according to claim 1, wherein the step S1 comprises the following sub-steps:
s11: determining variables required by a motion stability control system;
s12: according to the required variables in the motion stability control system, a vehicle dynamics equation is established;
s13: and setting a vehicle state parameter observer according to a vehicle dynamics equation to complete the establishment of the motion stability control system.
3. The method for optimally distributing and controlling the longitudinal force of all wheels of the distributed drive automobile according to claim 2, wherein in the step S11, the body coordinate system R is { G, x, y, z }, wherein G represents the center of mass of the vehicle, x-axis represents the positive direction from the origin of the body coordinate system to the right front of the vehicle, y-axis represents the positive direction from the origin of the body coordinate system to the left front of the vehicle side, and z-axis represents the positive direction from the origin o of the body coordinate system to the x-axis and the y-axis perpendicular to the body coordinate system; the desired variable being a speed variable
The expression of the method in an inertial coordinate system is [ u, v, r]TWherein, in the step (A),
representing a speed variation of the vehicle in the x-axis direction, wherein
Representing the speed variation of the vehicle in the direction of the y-axis,
the speed variable of the vehicle around a z-axis is represented, u represents an abscissa of the speed variable in an inertial coordinate system, v represents an ordinate of the speed variable in the inertial coordinate system, and r represents a vertical coordinate of the speed variable in the inertial coordinate system;
in the step S12, the vehicle dynamics equation includes a vehicle longitudinal motion equation
Equation of lateral motion of vehicle
And equations of yaw motion of the vehicle
The expressions are respectively:
where δ represents the angle of rotation of the front wheels of the vehicle, B represents the track of the left and right wheels of the vehicle, and lfRepresenting the distance from the front axle of the vehicle to the centre of mass,/rRepresenting the distance from the rear axle of the vehicle to the centre of mass,/zRepresenting the moment of inertia of the vehicle about the z-axis, M representing the mass of the vehicle as a whole, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FyflRepresenting the lateral force of the front left wheel of a vehicle tyre, FyfrRepresenting the lateral force of the front right wheel of a vehicle tyre, FyrlRepresenting the lateral force of the rear left wheel of a vehicle tyre, FyrrRepresenting the lateral force of the rear right wheel of the vehicle tyre,
which is indicative of the longitudinal acceleration of the vehicle,
which represents the lateral acceleration of the vehicle,
which represents the yaw acceleration of the vehicle.
4. The method for optimally controlling distribution of all-wheel longitudinal force of a distributed-drive automobile according to claim 2, wherein in step S13, the vehicle state parameter observer includes an electric-wheel basic parameter observer, a tire cornering stiffness observer, and a road surface adhesion coefficient observer.
5. The method for optimally distributing and controlling the longitudinal force of all wheels of the distributed-type driven automobile according to claim 4, wherein the electric wheel basic parameter observer is used for calculating the wheel speed, the wheel slip rate, the wheel longitudinal slip stiffness and the wheel vertical load of each wheel of the automobile, and the calculation formulas are respectively as follows:
λfl＝1-ωflR/utfl
λfr＝1-ωfrR/utfr
λrl＝1-ωrlR/utrl
λrr＝1-ωrrR/utrr
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
therein, utflIndicating the wheel speed, ut, of the front left wheel of the vehiclefrIndicating the wheel speed, ut, of the front right wheel of the vehiclerlIndicating the wheel speed, ut, of the rear left wheel of the vehiclerrIndicating the wheel speed, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrRepresenting the longitudinal sliding stiffness of the rear right wheel of the vehicle, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresents the vertical load of the right and rear wheels of the vehicle, u represents the abscissa of the vehicle velocity vector in the inertial frame, v represents the ordinate of the vehicle velocity vector in the inertial frame, r represents the ordinate of the vehicle velocity vector in the inertial frame, B represents the track width of the right and left wheels of the vehicle, l represents the vertical load of the right and left rear wheels of the vehicle, andfrepresenting the distance, omega, from the front axle of the vehicle to the centre of massflRepresenting the angular velocity, omega, of the front left wheel of the vehiclefrRepresenting angular velocity, omega, of the front right wheel of the vehiclerlRepresenting the angular velocity, omega, of the rear left wheel of the vehiclerrRepresenting the angular velocity of the rear right wheel of the vehicle, R representing the load radius of the electric wheel, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre,/rRepresenting the distance from the rear axle of the vehicle to the center of mass, M representing the mass of the vehicle, hcogRepresenting the height of the center of mass of the vehicle; g represents the gravitational acceleration; a isxRepresenting the longitudinal acceleration of the vehicle; a isyIndicating the lateral acceleration of the vehicle.
6. The method for optimally distributing and controlling the longitudinal force of all wheels of the distributed-drive automobile according to claim 4, wherein the tire cornering stiffness observer comprises the longitudinal-slip stiffness of the vehicle tire, and the calculation formulas are respectively as follows:
Cxfl＝Fxfl/λfl
Cxfr＝Fxfr/λfr
Cxrl＝Fxrl/λrl
Cxrr＝Fxrr/λrr
wherein, CxflRepresenting the longitudinal sliding stiffness, C, of the left front wheel of a vehicle tyrexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of a vehicle tyrexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of a vehicle tyrexrrRepresenting the longitudinal sliding stiffness, F, of the rear left wheel of a vehicle tyrexflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force, λ, of the right and rear wheels of a vehicle tyreflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle.
7. The method for optimally controlling distribution of all-wheel longitudinal force of a distributed-drive automobile according to claim 6, wherein in step S13, a road adhesion coefficient observer is calculated according to the electric-wheel basic parameter observer and the tire deflection stiffness observer, wherein the road adhesion coefficient observer comprises the tire-road adhesion coefficients, and the calculation formulas are as follows:
wherein, muflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrVertical indicating rear right wheel of vehicleLoad, CxflRepresenting the longitudinal sliding stiffness, C, of the front left wheel of the vehiclexfrRepresenting the longitudinal sliding stiffness, C, of the front right wheel of the vehiclexrlRepresenting the longitudinal sliding stiffness, C, of the rear left wheel of the vehiclexrrExpressing the longitudinal-sliding stiffness, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio of the rear right wheel of the vehicle, f(L)Representing a value factor.
8. The method for controlling the optimal distribution of the longitudinal force of all wheels of the distributed drive automobile according to claim 7, wherein the step S2, the setting of the motion controller comprises the following sub-steps:
a21: setting state equations for motion controllers
Control target beta of centroid slip angle betadThe expressions are respectively:
βd＝0
wherein A represents an actual vehicle state variable coefficient matrix, x represents an actual vehicle state matrix, E represents a known constant matrix, u represents an actual vehicle longitudinal velocity matrix, M represents an actual vehicle yaw moment matrix,
M＝Mz，
lzrepresenting the moment of inertia of the vehicle about the z-axis;
r represents the vertical coordinate of the vehicle velocity vector in the inertial coordinate system, beta represents the centroid slip angle, u represents the center of mass1Representing the actual vehicle first longitudinal speed, u2Representing the actual vehicle second longitudinal speed, MzRepresenting the actual vehicle yaw moment, a11Representing a first actual vehicle state variable coefficient, a12Representing a second actual vehicle state variable coefficient, a21Representing a third actual vehicle state variable coefficient, a22Representing a fourth actual vehicle state variable coefficient;
a22: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadObtaining a control target r of the yaw rate rdThe calculation formula is as follows:
a23: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadAnd a control target r of the yaw rate rdCalculating a feed-forward moment MffThe calculation formula is as follows:
a24: according to the equation of state of the motion controller
Control target beta of centroid slip angle betadControl target r of yaw rate rdAnd a feed forward moment MffAnd obtaining a response model of the expected vehicle, wherein the expression is as follows:
wherein x isdIndicating the target vehicle state, AdCoefficient matrix, u, representing the state variables of the target vehicledWhich is indicative of the target longitudinal speed of the vehicle,
a25: setting an optimal target function according to a response model of the expected vehicle, and calculating the optimal feedback moment M of the motion stability control system by linear quadratic calculation according to the optimal target functionfbThe calculation formula is as follows:
Mfb＝(-R-1ETP)Te
wherein E represents the feedback control error of the vehicle, R represents the feedback yaw velocity, P represents the unique positive definite symmetric solution matrix of the equation, and E represents the known constant value matrix;
a26: according to a feed-forward moment MffAnd an optimum feedback moment MfbCalculating a target yaw moment M of a motion stability control systemzdAnd completing the setting of the motion controller, wherein the calculation formula is as follows:
Mzd＝Mff+Mfb。
9. the method for controlling the optimal distribution of the longitudinal force of all wheels of the distributed drive automobile according to claim 1, wherein the step S2 of setting the motion distributor comprises the following sub-steps:
b21: according to the motion stability control system, setting an objective function min of longitudinal force optimized distributionuJ1And an optimization objective function min driving antiskid controluJ2The expressions are respectively:
minuJ1＝[(Fxflλfl)2+(Fxfrλfr)2+(Fxrlλrl)2+(Fxrrλrr)2]/(Fxdλmax)2
wherein, FxdTarget longitudinal force requirement, mu, of the entire vehicleflRepresents the coefficient of adhesion, μ, of the vehicle tire to the front left wheel of the road surfacefrRepresents the coefficient of adhesion, μ, of the vehicle tire to the right and front wheels of the road surfacerlDenotes the coefficient of adhesion, μ, of the vehicle tire to the left rear wheel of the road surfacerrRepresenting the coefficient of adhesion of the vehicle tyre to the right and rear wheels of the road surface, FxflRepresenting the longitudinal force of the front left wheel of a vehicle tyre, FxfrRepresenting the longitudinal force of the front right wheel of a vehicle tyre, FxrlRepresenting the longitudinal force of the rear left wheel of a vehicle tyre, FxrrRepresenting the longitudinal force of the rear right wheel of a vehicle tyre, FzflRepresenting the vertical load of the front left wheel of the vehicle, FzfrRepresenting the vertical load of the front right wheel of the vehicle, FzrlRepresenting the vertical load of the rear left wheel of the vehicle, FzrrRepresenting the vertical load, λ, of the rear right wheel of the vehicleflRepresenting the slip ratio, λ, of the front left wheel of the vehiclefrRepresenting the slip ratio, λ, of the front right wheel of the vehiclerlRepresenting the slip ratio, λ, of the rear left wheel of the vehiclerrRepresenting the slip ratio, λ, of the rear right wheel of the vehiclemaxRepresenting the maximum slip ratio, F, of the vehicle tyrexdRepresenting the longitudinal force demand of the whole vehicle;
b22: objective function min for optimal distribution of longitudinal forcesuJ1And an optimization objective function min driving antiskid controluJ2Normalization processing is carried out to obtain the optimal distribution objective function minuJ, completing the setting of the motion distributor, wherein the expression is as follows:
minuJ＝kminuJ1+(1-k)minuJ2
where k represents a weight coefficient.
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| CN113341997A (en) * | 2021-06-28 | 2021-09-03 | 湖南大学无锡智能控制研究院 | Transverse control method and system based on multi-state parameter collaborative estimation |
| CN113341997B (en) * | 2021-06-28 | 2022-04-05 | 湖南大学无锡智能控制研究院 | Transverse control method and system based on multi-state parameter collaborative estimation |
| CN114475575A (en) * | 2022-04-15 | 2022-05-13 | 北京理工大学 | Automobile control system and method and automobile |
| CN115384322A (en) * | 2022-10-28 | 2022-11-25 | 无锡金阳电机有限公司 | Dual-motor coupling complementary driving power assisting method and system |
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