CN114889446A - An off-road vehicle two-direction torque vector distribution method, device and storage medium - Google Patents

Abstract

The invention discloses a two-direction torque vector distribution method, equipment and storage medium for off-road vehicles. The method includes a longitudinal motion control method and a lateral stability control method. The invention discloses a method, device and storage medium for distributing torque vector in two directions of off-road vehicles. Taking maneuverability, passability, stability and steering flexibility as optimization goals, a wheel hub computer and drive layer reconstruction optimization vector control are developed. device. The longitudinal control method proposed by the invention can effectively improve the driving stability and passability of off-road vehicles under extreme undulating terrain; the lateral control method solves the common problems of sliding mode controllers on the premise of improving steering flexibility and yaw stability. For the chattering problem, the global optimization of the yaw motion error tracking is realized through the adaptive adjustment of the approach rate.

Description

An off-road vehicle two-direction torque vector distribution method, device and storage medium

technical field

The invention relates to the field of in-wheel motor vehicle driving, in particular to a method, device and storage medium for distributing torque vector in two directions of off-road vehicles.

Background technique

In recent years, thanks to the gradual maturity of integration technology, electronic devices such as microcontrollers have developed by leaps and bounds. Applying it to the development of electric drive system can significantly improve the control precision and dynamic performance of the vehicle. Equipped with a robust algorithm in the microcontroller, and combined with high integration, short transmission chain, low mechanical loss, fast torque response, strong power and many other advantages, the in-wheel motor vehicle has a good development prospect.

Off-road vehicles are increasingly favored by consumers because of their strong power and high passability. However, the driving environment of off-road vehicles is complex, and it needs to have the ability to pass on various grades of roads, muddy roads, sandy grass and other harsh roads, which greatly challenges the mobility and stability of off-road vehicles driven by in-wheel motors.

SUMMARY OF THE INVENTION

In view of this, embodiments of the present invention provide a method, device, and storage medium for distributing torque vectors in two directions of an off-road vehicle.

A first aspect of the present invention provides a two-directional torque vector distribution method for off-road vehicles, including a longitudinal motion control method and a lateral stability control method;

The longitudinal motion control method specifically includes:

Establish a tire mechanics model, and obtain the driving torque transfer equation of the vehicle according to the tire mechanics model;

Calculate the real-time wheel end output torque of the vehicle, and adjust the wheel adhesion utilization rate of the vehicle through the torque vector pre-distribution;

A synovial controller is designed to track the slip rate error of the wheel through the driving torque command output by the synovial controller, so as to improve the longitudinal motion control effect;

The lateral stability control method specifically includes:

Design the vehicle feedforward control method to obtain the feedforward yaw moment;

Design the vehicle feedback control method to get the feedback yaw moment;

According to the feedforward yaw moment and the feedback yaw moment, the vehicle's wheel adhesion utilization is adjusted through the redistribution of the torque vector.

Further, the tire mechanics model is established, and the driving torque transmission equation of the vehicle is obtained according to the tire mechanics model, which specifically includes:

Establish a tire mechanics model, and obtain the ground contact length, longitudinal force, sliding friction and wheel output torque of the vehicle tire from the tire model;

The grounding length is expressed by the following formula:

The longitudinal force is expressed by the following formula:

Sliding friction is expressed by the following formula:

The wheel output torque is expressed by the following formula:

In the formula: z is the average elastic deformation of the tire, v _r is the relative velocity between the tire and the contact surface, ε is the dynamic change of the road adhesion condition, σ ₀ , σ ₁ , and σ ₂ are the normalized set of tire contact surfaces, respectively Total stiffness, lumped damping and viscous relative damping, m is vehicle mass, v _x is actual longitudinal vehicle speed, F _z is vehicle vertical load, g(v _r ) is sliding friction, μ _c is normalized Coulomb friction coefficient , μ _s is the static friction coefficient, v _s is the Stribeck relative velocity describing the low-speed slip stage, Tw is the wheel output torque, J is the wheel rotational inertia, _w is the wheel angular velocity, σ _w is the viscous rotational friction coefficient, and r _w is The effective rolling radius of the wheel;

According to the tire mechanics model combined with the four-wheel slip change rate of the vehicle, the driving torque transmission equation is obtained;

为四轮滑转率变化率，L为拉氏变换。where f _i is the fitting function of the adhesion coefficient; μ _i is the tire adhesion coefficient; λ _i is the tire slip rate; a _x is the longitudinal acceleration of the vehicle; w _i is the tire angular velocity; r _w is the effective rolling radius of the wheel; F _xi is the longitudinal force of the tire; F _zi is the vertical load; J _i is the moment of inertia of the wheel; i _m is the transmission ratio of the reducer,

is the change rate of the four-wheel slip rate, and L is the Laplace transform.

Further, the calculation of the real-time wheel end output torque of the vehicle, through the torque vector pre-allocation, adjusts the wheel adhesion utilization rate of the vehicle, specifically including:

Calculate the real-time wheel end output torque by the following formula:

为加速踏板开度变化率；OS_i为稳定性判定标志位；

为

的一阶惯性延时系统；τ_acc为电子踏板、电机峰值电流采样周期，t为采样时间，m为整车质量，g为重力加速度。Where: T _i (k) is the real-time wheel end output torque; T _maxi (k) is the real-time wheel end output maximum output torque; ΔT _i (k) is the drive anti-skid adjustment command;

is the rate of change of the accelerator pedal opening; OS _i is the stability determination flag;

for

τ _acc is the sampling period of the electronic pedal and motor peak current, t is the sampling time, m is the mass of the vehicle, and g is the acceleration of gravity.

Further, the designed synovial controller tracks the slip rate error of the wheel through the driving torque command output by the synovial controller, so as to improve the longitudinal motion control effect, specifically including:

Design the sliding surface and reaching law of the adaptive sliding mode controller:

s(k)=1-DPUR _i (k)

In the formula: s represents the sliding mode surface function; q is the approach rate gain to adjust the convergence speed of λ _i ;

The formula for calculating the design gain q:

Obtain the driving torque command T _i (k):

In the formula, the driving torque command T _i (k) is constrained by the minimum torque of the motor (T _min =0).

Further, the design of the vehicle feedforward control method to obtain the feedforward yaw moment specifically includes:

Calculate the front wheel slip angle of the vehicle according to the steering angle of the front wheel of the vehicle, the side slip angle of the center of mass of the vehicle, the distance from the center of mass of the vehicle to the front axle, the yaw rate of the vehicle and the longitudinal vehicle speed;

Calculate the rear wheel slip angle of the vehicle according to the distance from the center of mass of the vehicle to the rear axle, the yaw rate of the vehicle, the longitudinal vehicle speed and the side slip angle of the center of mass of the vehicle;

Establish the cornering force equation:

F _yi =C _i α _i

Expand to get:

Establish the feedforward yaw moment equation:

In the formula: α _F , α _R are the front and rear wheel side slip angles; δ _F is the front wheel rotation angle; _LF , _LR are the distances from the center of mass of the vehicle to the front and rear axles; β is the side slip angle of the body center of mass; γ is the vehicle transverse Swing angular velocity; C _i is the cornering stiffness of the front and rear wheels, and the subscript i uses FL, FR, RL, and RR to refer to the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; F _yi is the cornering force; m is the vehicle mass, v _x is the longitudinal vehicle speed, v _y is the lateral vehicle speed; I _z is the moment of inertia of the vehicle around the z-axis; M _zFF is the feedforward yaw moment;

近似等于质心侧偏角速度

将侧偏力方程与前馈横摆力矩方程联立化简得到前馈横摆力矩表达式：under steady state

approximately equal to the centroid sideslip angular velocity

Simultaneously simplify the cornering force equation and the feedforward yaw moment equation to obtain the feedforward yaw moment expression:

The feedforward yaw moment expression is positively correlated with the vehicle front wheel rotation angle.

Further, after the feedforward yaw moment is obtained, the method further includes:

Feedforward yaw moment calculation using desired front wheel angle instead of front wheel angle to apply differential steering yaw moment

δ _Fd = δ _F (1+K)

where _δFd is the expected front wheel turning angle of the vehicle, and K is the cornering stability parameter that characterizes the steering characteristics of the vehicle.

Further, the designed vehicle feedback control method to obtain the feedback yaw moment specifically includes:

Compute the maximum value of the centroid sideslip angle:

In the formula, g is the acceleration of gravity; μ is the adhesion coefficient of the road surface;

Design coordination control weights:

In the formula, F _xmax represents the real-time peak value of the longitudinal driving force at the wheel end; m is the mass of the vehicle; ε ₁ and ε ₂ are the constraint coefficients of ξ;

Calculate tracking error:

Where: β _d is the expected center of mass side slip angle, β is the side slip angle of the center of mass, and γ _correct is the additional yaw moment;

p(t) is a bounded uncertain perturbation;

Get the feedback yaw moment:

In the formula, the characteristic parameters k ₁ and k ₂ are both positive numbers, sgn is the sign function, and k ₄ is the control weight factor.

Further, according to the feedforward yaw moment and the feedback yaw moment, the redistribution of the torque vector is used to adjust the wheel adhesion utilization rate of the vehicle, which specifically includes:

Add the feedforward yaw moment and the feedback yaw moment to the executive layer;

Calculate the adjustment amount of the in-wheel motor in each wheel of the vehicle to complete the torque vector distribution.

A second aspect of the present invention discloses an electronic device, including a processor and a memory;

the memory is used to store programs;

The processor executes the program to implement a two-direction torque vector distribution method for off-road vehicles.

A third aspect of the present invention discloses a computer-readable storage medium, the storage medium stores a program, and the program is executed by a processor to implement a two-direction torque vector distribution method for an off-road vehicle.

The invention has the following beneficial effects: the invention discloses a method, device and storage medium for distributing torque vector in two directions of an off-road vehicle. Taking maneuverability, passability, stability and steering flexibility as optimization goals, a hub computer is developed. And the driver layer reconfigures the optimized vector controller. The longitudinal control method proposed by the invention can effectively improve the driving stability and passability of off-road vehicles under extreme undulating terrain; the lateral control method solves the common problems of sliding mode controllers on the premise of improving steering flexibility and yaw stability. For the chattering problem, the global optimization of the yaw motion error tracking is realized through the adaptive adjustment of the approach rate.

Additional aspects and advantages of the present invention will be presented in the description which follows, in part, which will become apparent from the following description, or may be learned by practice of the invention.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the drawings that are used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

1 is a main flow chart of a method for distributing torque vectors in two directions of an off-road vehicle according to the present invention;

FIG. 2 is a schematic diagram of vehicle parameters of a method for distributing torque vectors in two directions of an off-road vehicle according to the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

This embodiment discloses a two-directional torque vector distribution method for off-road vehicles. The main process is shown in Figure 1, including SA. longitudinal motion control method and SB. lateral stability control method;

The longitudinal motion control methods specifically include:

SA-1. Establish a tire mechanics model, and obtain the driving torque transfer equation of the vehicle according to the tire mechanics model;

SA-2. Calculate the real-time wheel end output torque of the vehicle, and adjust the wheel adhesion utilization rate of the vehicle through the torque vector pre-distribution;

SA-3. Design a synovial controller to track the slip rate error of the wheel through the driving torque command output by the synovial controller to improve the longitudinal motion control effect;

The lateral stability control method specifically includes:

SB-1. Design the vehicle feedforward control method to obtain the feedforward yaw moment;

SB-2. Design the vehicle feedback control method to obtain the feedback yaw moment;

SB-3. According to the feedforward yaw moment and the feedback yaw moment, through the moment vector redistribution, adjust the wheel adhesion utilization of the vehicle.

The implementation of each part of the method will be discussed in detail below:

SA-1. Establish a tire mechanics model, and obtain the driving torque transfer equation of the vehicle according to the tire mechanics model:

The LuGre tire mechanics model was built, and the contact length, longitudinal force, sliding friction and wheel output torque of the vehicle tire were obtained from the tire model.

The grounding length is expressed by the following formula:

The longitudinal force is expressed by the following formula:

Sliding friction is expressed by the following formula:

The wheel output torque is expressed by the following formula:

表示轮胎接地长度；z表示轮胎平均弹性变形量；v_r表示轮胎与接触面之间的相对速度；ε表征路面附着条件的动态变化；σ₀、σ₁、σ₂分别为轮胎接触面归一化集总刚度、集总阻尼以及粘性相对阻尼；m为整车质量；v_x为实际纵向车速；F_z为车辆垂向载荷；g(v_r)为滑动摩擦，描述了摩擦力在不同相对速度、滑动条件下的变化；μ_c为归一化库仑摩擦系数；μ_s为静态摩擦系数；v_s为描述低速滑动阶段的Stribeck相对速度；T_w为车轮输出力矩；J为车轮转动惯量；w为车轮角速度；σ_w为黏性转动摩擦系数；r_w为车轮有效滚动半径。where:

Represents the tire contact length; z represents the average elastic deformation of the tire; v _r represents the relative speed between the tire and the contact surface _; ε represents the dynamic change _of the road adhesion condition _; lumped stiffness, lumped damping and viscous relative damping; m is the mass of the vehicle; v _x is the actual longitudinal speed; F _z is the vertical load of the vehicle; g(v _r ) is the sliding friction, which describes the friction force in different relative Changes under speed and sliding conditions; μ _c is the normalized Coulomb friction coefficient; μ _s is the static friction coefficient; v _s is the Stribeck relative _velocity describing the low-speed sliding stage; Tw is the wheel output torque; J is the wheel moment of inertia; w is the wheel angular velocity; σ _w is the viscous rotational friction coefficient; r _w is the effective rolling radius of the wheel.

SA-2. Calculate the real-time wheel-end output torque of the vehicle, and adjust the wheel adhesion utilization rate of the vehicle through the torque vector pre-distribution:

与LuGre轮胎力学模型联立得到驱动时力矩的传递方程：The four-wheel slip rate change rate

Combined with the LuGre tire mechanics model, the torque transfer equation during driving is obtained:

where f _i is the fitting function of the adhesion coefficient; μ _i is the tire adhesion coefficient; λ _i is the tire slip rate; a _x is the longitudinal acceleration of the vehicle; w _i is the tire angular velocity; r _w is the effective rolling radius of the wheel; F _xi is the longitudinal force of the tire; F _zi is the vertical load; J _i is the moment of inertia of the wheel; i _m is the transmission ratio of the reducer;

The above formulas are combined, and the transfer function of the driving torque can be obtained by using the pull transformation:

In order to analyze the performance of the torque control system more intuitively, the transfer function expression can be transformed into a polynomial based on Equation (7) to analyze the system stability, convergence ability, etc. by calculating the zeros and poles of the transfer function:

In the formula: K _di and τ _di are both internal parameters of formula (8), and L represents Laplace transform (Laplace transform).

有负实根，证明力矩传递为稳定系统。According to the analysis of equations (1) and (8), since the slip rate satisfies the condition 1-λ _i >0, τ _di (k) is a dynamic non-negative number, that is, the transfer function

There are negative real roots, which proves that the torque transfer is a stable system.

受CAN通讯时滞与功率逆变器响应时间的影响，此处可将

简化成延时时长为τ_w的一阶惯性系统：In the actual driving process, the driving torque of each in-wheel motor is determined and constrained by multiple discrete variables such as the accelerator pedal opening, the motor peak current, and the driving anti-skid adjustment command ΔT _i . See equation (9), and its update period is related to the electronic pedal The sampling periods τ _acc are equal. Considering the real-time wheel end output torque change

Affected by the time delay of CAN communication and the response time of the power inverter, the

Simplify to a first-order inertial system with delay time _τw :

为加速踏板开度变化率；OS_i为稳定性判定标志位；

为

的一阶惯性延时系统；τ_acc为电子踏板、电机峰值电流采样周期，t为采样时间，m为整车质量，g为重力加速度。Where: T _i (k) is the real-time wheel end output torque; T _maxi (k) is the real-time wheel end output maximum output torque; ΔT _i (k) is the drive anti-skid adjustment command;

is the rate of change of the accelerator pedal opening; OS _i is the stability determination flag;

for

τ _acc is the sampling period of the electronic pedal and motor peak current, t is the sampling time, m is the mass of the vehicle, and g is the acceleration of gravity.

与轮毂电机传递至轮端的驱动力(T_wi(k)/r_W)的比值，并得到其离散化表达式，并基于各轮稳定性标志位设计了式(11)中的误差校正与积分计算的触发机制。Based on equation (10), the in-wheel motor drive power utilization ratio (DPUR _i ) can be expressed as the longitudinal estimated force of each wheel

and the ratio of the driving force (T _wi (k)/r _W ) transmitted by the in-wheel motor to the wheel end, and its discretized expression is obtained, and the error correction and integration in Eq. (11) are designed based on the stability flags of each wheel Calculation trigger mechanism.

Among them: i and j are designed to distinguish the driving power utilization formula at different moments k and k+1.

SA-3. Design a synovial controller to track the slip rate error of the wheel through the driving torque command output by the synovial controller to improve the longitudinal motion control effect:

The sliding surface and reaching law of the adaptive sliding mode controller are designed based on equation (11):

s(k)=1-DPUR _i (k) (13)

In formula (14): s represents the sliding mode surface function; q is the approach rate gain to adjust the convergence speed of λ _i ; at the same time, the gain of the sign function sgn(s(k)) is set as a time-varying variable (|s (k)|/2) to reduce the buffeting of the system around the sliding surface.

In order to satisfy the stable convergence condition and make the sliding mode region exist, the calculation formula of the gain q is designed:

Substitute the discrete approach rate that meets the design requirements into equation (12) to obtain the driving torque command T _i (k) constrained by the minimum torque of the motor (T _min =0):

SB-1. Design the vehicle feedforward control method to obtain the feedforward yaw moment:

期望质心侧偏角与角速度

The purpose of the feedforward link control is to shorten the response time for the vehicle to reach the ideal steady state by applying the feedforward yaw moment M _zFF , and its control objectives include the desired yaw angular acceleration

Desired centroid slip angle and angular velocity

Equation (17) shows that the vehicle yaw and sideslip motions should converge to steady-state motions under the ideal steady state model. Referring to the simplified two-degree-of-freedom vehicle dynamics model shown in Figure 2, the ideal sideways motion of the vehicle in the feedforward link can be obtained. , the tire slip angle and the calculation expressions of the yaw motion:

F _yi =C _i α _i (20)

In the formula: α _F , α _R are the front and rear wheel side slip angles; δ _F is the steering angle of the front wheels; _LF , _LR are the distances from the vehicle center of mass to the front and rear axles; β is the body center of mass side slip angle; γ is the vehicle yaw rate; C _i is the cornering stiffness of the front and rear wheels; F _yi is the cornering force; m is the vehicle mass, v _x is the longitudinal vehicle speed, v _y is the lateral vehicle speed; I _z is the moment of inertia of the vehicle around the z-axis; subscript i can use L and R to refer to the left and right; M _zFF is the feedforward yaw moment.

可近似为

代入式(21)，并与式(22)联立可得横摆和侧滑运动的计算式：Under steady-state conditions, the side-slip angular velocity of the center of mass

can be approximated as

Substitute into Equation (21) and combine with Equation (22) to obtain the calculation formulas of the yaw and sideslip motions:

Substituting the target value in equation (17) into the above equation, the expression for the desired yaw rate γ _d can be obtained:

Then, formulas (24) and (25) are combined to obtain the feedforward yaw moment that is positively related to the front wheel angle _δF :

In addition, considering that the low-speed steering resistance torque is relatively large, and the differential steering based on the in-wheel motor drive system can also play the role of adjusting the steering gain, the present invention introduces the desired front wheel rotation angle _δFd based on the optimization of handling flexibility instead of δ _F calculates the feedforward moment M _ZFF and applies the differential steering yaw moment.

δ _Fd = δ _F (1+K) (27)

In the above formula, K is the cornering stability parameter that characterizes the steering characteristics of the vehicle.

SB-2. Design the vehicle feedback control method to obtain the feedback yaw moment:

The invention adopts discrete control technology to realize feedback tracking of lateral motion. Firstly, the lateral motion state parameters are selected as the yaw rate γ and the center of mass sideslip angle β. The former can be used to adjust the desired steering characteristics, and the latter represents the severity of the vehicle's sideslip motion and lateral stability margin. The state tracking error of feedback control is further designed to realize the coordinated control of yaw motion and lateral stability:

In the formula: g is the acceleration of gravity; μ is the adhesion coefficient of the road surface.

The road surface adhesion condition (μ=Σμ _i /4) is used as a constraint to improve the environmental adaptability of the stability control. Further, based on the phase plane analysis method of β, the coordinated control weight ξ is designed:

In formula (31), F _xmax represents the real-time peak value of the wheel-end longitudinal driving force; m is the vehicle mass; ε ₁ and ε ₂ are the constraint coefficients of ξ.

In order to eliminate the inherent chattering effect of discrete sliding mode control, optimize the control smoothness and improve the convergence speed of the error, the present invention adopts a second-order sliding mode controller (SOSMC) composed of continuous and discontinuous components.

In the formula: the characteristic parameters k ₁ and k ₂ are both positive numbers, and p(t) represents the bounded uncertain disturbance. The additional yaw moment output by the in-wheel motor drive system can be used to correct the vehicle attitude:

的表达式：Substitute equation (33) into the differential equation of tracking error e to get

expression:

in:

均为零，因此包含不确定扰动项的p(t)可简化表示为：because

are all zero, so p(t) including the uncertain disturbance term can be simplified as:

p(t) is a bounded disturbance, so a constant k ₃ can be introduced to represent the extreme value of |P(t)|:

|P(t)|≤P≤k ₃ (37)

在逼近滑模面过程中逐渐收敛，即滑模面宽度(SW)逐渐减小，可有效减小抖振：Unlike the sliding mode controller which vibrates near the sliding mode surface due to the action of the sign function, the gain of the sign function due to the discontinuous part of the approach rate of the second-order sliding mode control

Gradually converge in the process of approaching the sliding mode surface, that is, the sliding mode surface width (SW) gradually decreases, which can effectively reduce the chattering:

It can be seen from equation (38) that the width of the sliding mode surface of SOSMC can converge to zero. However, when driving in a straight line or turning with a large radius, the small ambient noise and sensor measurement noise cause e(t) to oscillate with a high frequency and a narrow amplitude near the zero point, which deteriorates driving comfort. On the other hand, considering the high position of the center of mass of off-road vehicles, the body roll and wheel load transfer are more obvious under medium and high-speed steering conditions, and the risk of inner tire instability will be significantly increased. Significantly increases steering resistance torque. Therefore, this paper introduces a control weight factor k ₄ to dynamically adjust the optimization weights of three control objectives such as driving smoothness, steering flexibility, and lateral stability under different working conditions such as straight or slight steering, low-speed steering, and medium-high-speed steering:

As shown in equation (39), two piecewise functions related to steering wheel angle and longitudinal vehicle speed describe the lateral motion state of the vehicle. Among them, the vehicle speed is divided into three continuous speed domains: low, medium and high. Under the low speed and high speed conditions, the reaching law of SOSMC is relatively fast; on the other hand, under the conditions with high lateral stability margin, k ₄ is set to zero to ensure that the yaw moment will not interfere with the subjective operation intention, and the control approach rate will also speed up with the increase of the steering wheel angle amplitude |δ| _; negative number.

SB-3. According to the feedforward yaw moment and the feedback yaw moment, through the moment vector redistribution, adjust the wheel adhesion utilization of the vehicle:

The feedforward and feedback yaw moment are added and input to the execution layer, and the coordination and optimization of the adhesion utilization rate of each wheel is taken as the control objective, and the adjustment amount ΔT _mi of each in-wheel motor in Eq. , to realize the redistribution of the torque vector and to respond to the direct yaw moment command.

The embodiment of the present invention also discloses a computer program product or computer program, where the computer program product or computer program includes computer instructions, and the computer instructions are stored in a computer-readable storage medium. A processor of the computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions to cause the computer device to perform the method shown in FIG. 1 .

In some alternative implementations, the functions/operations noted in the block diagrams may occur out of the order noted in the operational diagrams. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/operations involved. Furthermore, the embodiments presented and described in the flowcharts of the present invention are provided by way of example in order to provide a more comprehensive understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of the various operations are altered and in which sub-operations described as part of larger operations are performed independently.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, The scope of the invention is defined by the claims and their equivalents.

The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the described embodiments, and those skilled in the art can also make various equivalent deformations or replacements on the premise of not violating the spirit of the present invention, These equivalent modifications or substitutions are all included within the scope defined by the claims of the present application.

Claims (10)

1. A two-direction torque vector distribution method for an off-road vehicle is characterized by comprising a longitudinal motion control method and a transverse stability control method;

the longitudinal motion control method specifically comprises the following steps:

building a tire mechanics model, and obtaining a driving torque transfer equation of the vehicle according to the tire mechanics model;

calculating the real-time wheel end output torque of the vehicle, and adjusting the wheel attachment utilization rate of the vehicle through torque vector pre-distribution;

designing a sliding mode controller, and tracking the slip rate error of the wheel through a driving torque command output by the sliding mode controller so as to improve the control effect of longitudinal motion;

the lateral stability control method specifically comprises the following steps:

designing a vehicle feedforward control method to obtain a feedforward yaw moment;

designing a vehicle feedback control method to obtain a feedback yaw moment;

and adjusting the wheel attachment utilization rate of the vehicle through moment vector redistribution according to the feedforward yaw moment and the feedback yaw moment.

2. A method of distributing a two-directional torque vector for an off-road vehicle as in claim 1, wherein the establishing a tire mechanics model from which to derive a drive torque transfer equation for the vehicle comprises:

building a tire mechanical model, and obtaining the ground contact length, longitudinal force, sliding friction and wheel output torque of the vehicle tire from the tire model;

wherein the grounding length is expressed by the following formula:

the longitudinal force is expressed by the following formula:

the sliding friction is expressed by the following formula:

the wheel output torque is expressed by the following equation:

in the formula: z is the average elastic deformation of the tire, v _r Is the relative speed between the tyre and the contact surface,. epsilon.is the dynamic variation of the road adhesion conditions,. sigma ₀ 、σ ₁ 、σ ₂ Normalized lumped stiffness, lumped damping and viscous relative damping of a tire contact surface respectively, m is the mass of the whole vehicle, v _x For actual longitudinal vehicle speed, F _z For vertical loading of the vehicle, g (v) _r ) For sliding friction, mu _c To normalize the Coulomb coefficient of friction, μ _s Is the static coefficient of friction, v _s To describe the Stribeck relative velocity, T, for the low speed slip phase _w Is the wheel output torque, J is the wheel moment of inertia, w is the wheel angular velocity, σ _w Is a viscous coefficient of rotational friction, r _w Is the effective rolling radius of the wheel;

obtaining a driving torque transfer equation according to a tire mechanics model and the vehicle four-wheel slip change rate;

in the formula: f. of _i Fitting a function to the adhesion coefficient; mu.s _i Is the tire adhesion coefficient; lambda _i Is the tire slip ratio; a is a _x Is the vehicle longitudinal acceleration; w is a _i Is the tire angular velocity; r is _w Is the effective rolling radius of the wheel; f _xi For longitudinal forces of the tyre；F _zi Is a vertical load; j. the design is a square _i Is the rotational inertia of the wheel; i.e. i _m In order to realize the transmission ratio of the speed reducer,

the four wheel slip rate change rate, L is the Laplace transform.

3. The method as claimed in claim 2, wherein the calculating of the real-time wheel-end output torque of the vehicle, the adjusting of the wheel attachment utilization of the vehicle by the pre-distribution of the torque vector, specifically comprises:

calculating the real-time wheel end output torque by the following formula:

in the formula: t is _i (k) Outputting torque for the real-time wheel end; t is _maxi (k) Outputting the maximum output torque for the real-time wheel end; delta T _i (k) Adjusting instructions for driving the antiskid devices;

is the accelerator pedal opening change rate; OS _i Determining a flag bit for stability;

is composed of

The first-order inertial delay system of (1); tau is _acc The method is characterized in that the sampling period of peak current of an electronic pedal and a motor is shown, t is sampling time, m is the mass of the whole vehicle, and g is gravity acceleration.

4. A method as claimed in claim 3, wherein the slip controller is configured to track slip error of the wheels via drive torque commands output from the slip controller to improve longitudinal motion control, and comprises:

designing a sliding surface and an approach law of the adaptive sliding mode controller:

s(k)＝1-DPUR _i (k)

in the formula: s represents a sliding mode surface function; q is the approximate rate gain to adjust lambda _i The convergence rate of (2);

designing a calculation formula of the gain q:

obtaining a driving torque command T _i (k)：

In which the drive torque command T is _i (k) Minimum torque (T) of motor _min 0) constraint.

5. The method for allocating two-directional torque vectors of an off-road vehicle according to claim 1, wherein the method for designing the vehicle feed-forward control to obtain the feed-forward yaw moment specifically comprises:

calculating the side slip angle of the front wheel of the vehicle according to the steering angle of the front wheel of the vehicle, the side slip angle of the mass center of the vehicle body, the distance from the mass center of the vehicle to a front shaft, the yaw velocity of the vehicle and the longitudinal speed of the vehicle;

calculating the side slip angle of the rear wheel of the vehicle according to the distance from the mass center of the vehicle to the rear axle, the yaw angular velocity of the vehicle, the longitudinal speed and the mass center side slip angle of the vehicle body;

establishing a lateral deviation force equation:

F _yi ＝C _i α _i

unfolding to obtain:

establishing a feedforward yaw moment equation:

in the formula: alpha is alpha _F 、α _R Is the side deflection angle of the front wheel and the rear wheel; delta _F Is a front wheel corner; l is _F 、L _R The distance from the center of mass of the vehicle to the front and rear axes; beta is the vehicle body mass center slip angle; gamma is the yaw velocity of the vehicle; c _i For front and rear wheel side deflection rigidity, subscript i respectively refers to a left front wheel, a right front wheel, a left rear wheel and a right rear wheel by using FL, FR, RL and RR; f _yi Is the lateral bias force; m is the total vehicle mass, v _x For longitudinal vehicle speed, v _y Is the transverse vehicle speed; I.C. A _z Rotating inertia around a z-axis for the vehicle; m _zFF A feedforward yaw moment;

under steady state operating conditions

/v _x Approximately equal to centroid slip angular velocity

And (3) simultaneously simplifying a lateral deviation force equation and a feedforward yaw moment equation to obtain a feedforward yaw moment expression:

the feed-forward yaw moment expression is positively correlated with the vehicle front wheel steering angle.

6. An off-road vehicle two-way torque vector allocation method as claimed in claim 5, further comprising, after obtaining a feed forward yaw moment:

feedforward yaw moment calculation using desired front wheel turning angle instead of front wheel turning angle to apply differential steering yaw moment

δ _Fd ＝δ _F (1+K)

In the formula of _Fd The desired front wheel angle for the vehicle, and K is a yaw stability parameter that characterizes the steering characteristics of the vehicle.

7. An off-road vehicle two-way torque vector distribution method as claimed in claim 6, wherein said design vehicle feedback control method, resulting in a feedback yaw moment, specifically comprises:

calculating the maximum value of the centroid slip angle:

wherein g is the acceleration of gravity; mu is the road surface adhesion coefficient;

designing a coordination control weight:

in the formula, F _xmax Representing a real-time wheel end longitudinal drive force peak; m is the mass of the whole vehicle; epsilon ₁ And epsilon ₂ A constraint coefficient of ξ;

calculating a tracking error:

wherein: beta is a _d To obtain a desired centroid slip angle, β is the centroid slip angle, γ _correct An additional yaw moment;

p (t) is a bounded uncertain disturbance;

obtaining a feedback yaw moment:

in the formula, the characteristic parameter k ₁ And k is ₂ Are all positive numbers, sgn is a sign function, k ₄ To control the weighting factors.

8. An off-road vehicle two-way torque vector distribution method as claimed in claim 7, wherein the adjusting of the wheel attachment utilization of the vehicle by torque vector redistribution according to the feed-forward yaw moment and the feedback yaw moment comprises:

adding the feedforward yaw moment and the feedback yaw moment and inputting the sum to an execution layer;

and calculating the adjustment quantity of the hub motor in each wheel of the vehicle to complete the distribution of the torque vector.

9. An electronic device comprising a processor and a memory;

the memory is used for storing programs;

the processor executing the program realizes the method according to any one of claims 1-8.

10. A computer-readable storage medium, characterized in that the storage medium stores a program, which is executed by a processor to implement the method according to any one of claims 1-8.

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