CN109733382B - Automobile rollover prevention method based on model predictive control - Google Patents

Abstract

The invention discloses an automobile rollover prevention method based on model predictive control, which comprises the steps of firstly measuring the front wheel corner, the speed, the yaw angular velocity and the transverse position of an automobile; then calculating the transverse load transfer rate of the vehicle; and then comparing the transverse load transfer rate with a preset transverse load transfer rate threshold value, comparing the difference value between the transverse position and a preset reference transverse position with a preset maximum difference threshold value, adjusting the front wheel rotation angle of the vehicle according to the comparison result of the transverse load transfer rate and the preset reference transverse position, and controlling the braking force of the four wheels. The invention considers the different influences of the sprung mass and the unsprung mass on the rollover of the vehicle body, and has more accurate effect on the rollover prevention control effect.

Description

A Model Predictive Control-Based Vehicle Rollover Prevention Method

technical field

The invention relates to the technical field of vehicle active safety, in particular to a vehicle rollover prevention method based on model predictive control.

Background technique

With the development of the economy, the number of cars around the world continues to grow, the roads become congested, and the danger of car travel increases. Therefore, while people pay attention to the comfort and economy of the car, they also turn their attention to safety. Among all automobile safety accidents, there is a type of accident with a low incidence rate, but the probability of death and injury is quite high. According to the National Highway Traffic Safety Administration (NHTSA) investigation report, in 2014, the number of deaths caused by rollover accidents accounted for one-third of all traffic deaths in that year, and the number of deaths due to rollover accidents was 7,659. more than other models.

At present, the anti-roll control methods mainly used in the field of anti-rollover include active steering, differential braking, active/semi-active suspension, and LTR based on roll angle and roll angular velocity are commonly used in rollover evaluation indicators. Rollover evaluation method. Among them, the anti-rollover control performed by active steering mainly reduces the rollover index by intervening in the reverse additional angle of the steering motor. Differential braking can generate an additional yaw moment and reduce the vehicle speed to reduce the risk of rollover. Active/ The semi-active suspension mainly adjusts the damping by changing the hydraulic hole of the suspension damper to enhance the anti-rollover ability of the vehicle.

However, most of the above-mentioned control methods only pay attention to the body posture when preventing rollover, and achieve the anti-rollover effect by controlling the body, and then ignore the control effect produced by it, which may cause the vehicle to deviate from the original path or drive into other Lanes in turn create secondary collisions, or other hazards, contrary to driver intent and control intent, so there is room for improvement.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a vehicle rollover prevention and tracking system based on model predictive control and its control, aiming at the defects involved in the background technology.

The present invention adopts the following technical solutions for solving the above-mentioned technical problems:

A method for preventing vehicle rollover based on model predictive control, comprising the following steps:

Step 1), measure the front wheel angle δ _f of the vehicle, the vehicle speed v _r , the yaw rate β _r , and the lateral position y;

Step 2), calculate the lateral load transfer rate LTR of the vehicle:

Step 3), compare the lateral load transfer rate LTR with the preset lateral load transfer rate threshold LTR _des , compare the difference between the lateral position Y and the preset reference lateral position Y _des with n, and n is the preset Maximum difference threshold:

When |(YY _des )|<η and LTR<LTR _des , the body state is not adjusted;

When |(YY _des )|>η and LTR<LTR _des , control the two front wheels of the car to steer;

When |(YY _des )|<η and LTR>LTR _des , control the four wheels of the car to brake,

When |(YY _des )|>η and LTR>LTR _des , the two front wheels of the car are controlled to steer, and the four wheels of the car are controlled to brake at the same time.

As a further optimization scheme of the vehicle rollover prevention method based on model predictive control of the present invention, the detailed steps of the step 2) are as follows:

Step 2.1), according to a _y =v _r β _r , calculate the lateral acceleration a _y of the vehicle

Step 2.2), analyze the force in the y direction to obtain the roll angle acceleration

为侧倾角加速度；k₁、k₂分别为车辆前后轮侧偏刚度；a、b分别为车辆质心到前后轴的距离；β为质心侧偏角；β_r为横摆角速度；where m is the total mass of the vehicle; m _s is the sprung mass; e is the distance from the sprung mass to the roll center;

is the roll angle acceleration; k ₁ and k ₂ are the cornering stiffnesses of the front and rear wheels of the vehicle respectively; a and b are the distances from the center of mass of the vehicle to the front and rear axles respectively; β is the side slip angle of the center of mass; β _r is the yaw rate;

Step 2.3), do moment balance in the x direction:

为车身为侧倾角，

为侧倾刚度，

为侧倾阻尼，

为车身侧倾角速度；In the formula, I _xs is the moment of inertia of the car sprung mass around the x-axis of the vehicle coordinate system; m _s is the sprung mass; g is the acceleration of gravity,

is the body roll angle,

is the roll stiffness,

is the roll damping,

is the body roll angular velocity;

Step 2.4), do the moment balance in the z direction to obtain the yaw angular acceleration

为横摆角加速度；Among them, I _z is the moment of inertia of the vehicle mass around the z-axis of the vehicle coordinate system;

is the yaw angular acceleration;

Step 2.5), establish a three-degree-of-freedom vehicle model, and obtain the roll angle and roll angle speed of the vehicle in the current state according to the vehicle speed and turning angle;

Step 2.5), according to the force analysis of the tire pressure on the road surface during the rollover process of the car:

In the formula, F _R and F _L are the sum of the longitudinal reaction forces of the right wheel and the left wheel respectively, T is the wheel base, m _d is the unsprung mass, and h _d is the distance from the center of mass of the unsprung mass to the ground. ;

且F_R+F_L＝mg，则：step 2.6), due to the lateral load transfer rate

And F _R + F _L =mg, then:

As a further optimization scheme of the vehicle rollover prevention method based on the model predictive control of the present invention, the specific steps of controlling the two front wheels of the vehicle to perform steering in the step 3) are as follows:

Step 3.1.1), the electronic control unit calculates the corresponding additional front wheel rotation angle δ _f according to Y and the reference lateral position Y _des using the model predictive control method:

Step 3.1.2), establish the nonlinear model of the active front wheel steering controller:

为纵向加速度；

为横向车速；c₁，c₂分别为前后轮纵向刚度；s₁，s₂分别为前后轮滑移率；

为横向加速度；

为纵向车速；

惯性坐标系横向速度；

为惯性坐标系纵向速度；r为横摆角；where:

is the longitudinal acceleration;

is the lateral vehicle speed; c ₁ , c ₂ are the longitudinal stiffness of the front and rear wheels respectively; s ₁ , s ₂ are the slip rates of the front and rear wheels respectively;

is the lateral acceleration;

is the longitudinal speed;

Inertial coordinate system lateral velocity;

is the longitudinal velocity of the inertial coordinate system; r is the yaw angle;

将其离散化：Step 3.1.3), get the state equation

Discretize it:

u＝δ_f，A、B均为系数；in

u=δ _f , A and B are coefficients;

Step 3.1.4), the design objective function is as follows, and the additional front wheel rotation angle is calculated:

Satisfy front wheel rotation angle constraints: δ _f,min ≤δ _f ≤δ _f,max

In the formula, Y(t) is the lateral position of the actual output of the system at time t; Y _c (t) is the lateral position of the reference at time t; N _p is the prediction time domain; N _c is the control time domain; u(t) is t is the control variable output by the active front wheel steering controller at all times; δ _f is the front wheel angle, Q and R are the weight matrices of the first and second terms of the objective function, p is the weight coefficient, and ε is the relaxation factor; δ _{f, min} is the minimum front wheel rotation angle, δf _{, max} is the maximum front wheel rotation angle;

Step 3.1.5), the controller controls the two front wheels of the car to steer according to the calculated additional front wheel angle;

As a further optimization scheme of the vehicle rollover prevention method based on the model predictive control of the present invention, the specific steps of controlling the four wheels of the vehicle to brake in the step 3) are as follows:

Step 3.2.1), the electronic control unit uses the active brake controller to calculate the longitudinal forces F _xfl , F _xfr , F _xrl of the front left, front right, rear left and rear right tires according to the LTR and the reference lateral load transfer rate LTR _des , F _xrr , the nonlinear model of the active braking controller is:

In the formula, F _yfl , F _yfr , F _yrl , and F _yrr are the lateral forces of the front left, front right, rear left and rear right tires, respectively;

将其离散化：Step 3.2.2), get the state equation

Discretize it:

U＝[F_xfl，F_xfr，F_xrl，F_xrr]^TC、D均为系数；in

U=[F _xfl , F _xfr , F _xrl , F _xrr ] ^T C and D are coefficients;

Step 3.2.3), the design objective function is as follows, and the braking force of the four tires is calculated:

Satisfy the four tire braking force constraints: U _min ≤U≤U _max

为松弛因子；U_min为最小轮胎力，U_max为最大轮胎力；In the formula, Y ₁ (t) is the LTR actually output by the system at time t; Y _1c (t) is the LTR _des referenced at time t; _{Ph is the prediction time domain; C h is} the control time domain; U(t) is t is the control variable output by the active braking controller at all times; S and W are the weight matrices of the first and second terms of the objective function respectively, i is the weight coefficient,

is the relaxation factor; U _min is the minimum tire force, and U _max is the maximum tire force;

Step 3.2.4), the controller brakes the four wheels according to the calculated braking force of the four tires.

Compared with the prior art, the present invention adopts the above technical scheme, and has the following technical effects:

The invention provides an anti-rollover method based on model prediction control. Most of the existing anti-rollover systems adopt active steering or differential braking, and rarely consider other influences caused by the control effect during the working process of the controller. , for example: moving into another lane, deviating from the driver's intent. This will lead to greater danger. By using active steering and active braking and their switching control modes, the patent of the present invention can switch the mode according to the driving state, so as to realize the perfect integration of anti-rollover and tracking path;

Compared with the previous LTR acquisition method, the rollover evaluation index proposed in the present invention is more accurate, considering the different effects of sprung mass and unsprung mass on the rollover of the vehicle body, and has a more accurate effect on the control effect of rollover prevention .

Description of drawings

Fig. 1 is the structure diagram of the patent system of the present invention;

Fig. 2 is the schematic flow chart of the present invention;

Figure 3 is a flow chart of the steering of the two front wheels.

Detailed ways

Below in conjunction with accompanying drawing, the technical scheme of the present invention is described in further detail:

The present invention may be embodied in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, components are exaggerated for clarity.

The structure of the present invention is shown in FIG. 1 , including interconnected sensors, electronic control units and actuators; the electronic control units include a state determination unit, a state identification unit and an actuator control unit. Both the state determination unit and the state identification unit are connected to the sensor, the state evaluation unit is connected to the state identification unit through the trigger unit, and the state identification unit is connected to the state identification unit through the actuator control unit (model predictive control). the actuator; the information of the actuator unit is fed back to the electronic control unit. The executive mechanism is an active front wheel steering mechanism and an active braking mechanism.

As shown in Figure 2, the present invention discloses a method for preventing vehicle rollover based on model predictive control, comprising the following steps:

Step 1), measure the front wheel angle δ _f of the vehicle, the vehicle speed v _r , the yaw rate β _r , and the lateral position y;

Step 2), calculate the lateral load transfer rate LTR of the vehicle:

Step 2.1), according to a _y =v _r β _r , calculate the lateral acceleration a _y of the vehicle

Step 2.2), analyze the force in the y direction to obtain the roll angle acceleration

为侧倾角加速度；k₁、k₂分别为车辆前后轮侧偏刚度；a、b分别为车辆质心到前后轴的距离；β为质心侧偏角；β_r为横摆角速度；where m is the total mass of the vehicle; ms is the sprung mass; e is the distance from the sprung mass to the roll center;

is the roll angle acceleration; k ₁ and k ₂ are the cornering stiffnesses of the front and rear wheels of the vehicle respectively; a and b are the distances from the center of mass of the vehicle to the front and rear axles respectively; β is the side slip angle of the center of mass; β _r is the yaw rate;

Step 2.3), do moment balance in the x direction:

为车身为侧倾角，

为侧倾刚度，

为侧倾阻尼，

为车身侧倾角速度；In the formula, I _xs is the moment of inertia of the car sprung mass around the x-axis of the vehicle coordinate system; m _s is the sprung mass; g is the acceleration of gravity,

is the body roll angle,

is the roll stiffness,

is the roll damping,

is the body roll angular velocity;

Step 2.4), do the moment balance in the z direction to obtain the yaw angular acceleration

为横摆角加速度；Among them, I _z is the moment of inertia of the vehicle mass around the z-axis of the vehicle coordinate system;

is the yaw angular acceleration;

Step 2.5), establish a three-degree-of-freedom vehicle model, and obtain the roll angle and roll angle speed of the vehicle in the current state according to the vehicle speed and turning angle;

Step 2.5), according to the force analysis of the tire pressure on the road surface during the rollover process of the car:

In the formula, F _R and F _L are the sum of the longitudinal reaction forces of the right wheel and the left wheel respectively, T is the wheel base, m _d is the unsprung mass, and h _d is the distance from the center of mass of the unsprung mass to the ground. ;

且F_R+F_L＝mg，则：step 2.6), due to the lateral load transfer rate

And F _R + F _L =mg, then:

Step 3), compare the lateral load transfer rate LTR with the preset lateral load transfer rate threshold LTR _des , compare the difference between the lateral position Y and the preset reference lateral position Y _des with n, and n is the preset Maximum difference threshold:

When |(YY _des )|<η and LTR<LTR _des , the body state is not adjusted;

When |(YY _des )|>η and LTR<LTR _des , control the two front wheels of the car to steer;

When |(YY _des )|<η and LTR>LTR _des , control the four wheels of the car to brake,

When |(YY _des )|>η and LTR>LTR _des , control the two front wheels of the car to steer, and control the four wheels of the car to brake at the same time;

Among them, as shown in Figure 3, the specific steps for controlling the steering of the two front wheels of the car are as follows:

Step 3.1.1), the electronic control unit calculates the corresponding additional front wheel rotation angle δ _f according to Y and the reference lateral position Y _des using the model predictive control method:

Step 3.1.2), establish the nonlinear model of the active front wheel steering controller:

为纵向加速度；

为横向车速；c₁，c₂分别为前后轮纵向刚度；s₁，s₂分别为前后轮滑移率；

为横向加速度；

为纵向车速；

惯性坐标系横向速度；

为惯性坐标系纵向速度；r为横摆角；where:

is the longitudinal acceleration;

is the lateral vehicle speed; c ₁ , c ₂ are the longitudinal stiffness of the front and rear wheels respectively; s ₁ , s ₂ are the slip rates of the front and rear wheels respectively;

is the lateral acceleration;

is the longitudinal speed;

Inertial coordinate system lateral velocity;

is the longitudinal velocity of the inertial coordinate system; r is the yaw angle;

将其离散化：Step 3.1.3), get the state equation

Discretize it:

u＝δ_f，A、B均为系数；in

u=δ _f , A and B are coefficients;

Step 3.1.4), the design objective function is as follows, and the additional front wheel rotation angle is calculated:

Satisfy front wheel rotation angle constraints: δ _f,min ≤δ _f ≤δ _f,max

In the formula, Y(t) is the lateral position of the actual output of the system at time t; Y _c (t) is the lateral position of the reference at time t; N _p is the prediction time domain; N _c is the control time domain; u(t) is t is the control variable output by the active front wheel steering controller at all times; δ _f is the front wheel angle, Q and R are the weight matrices of the first and second terms of the objective function respectively, the function is to make the system achieve the expected effect as soon as possible, p is the weight coefficient, ε is the relaxation factor, the purpose is to prevent no optimal solution in the solution process; δ _f,min is the minimum front wheel rotation angle, and δ _fmax is the maximum front wheel rotation angle;

Step 3.1.5), the controller controls the two front wheels of the car to steer according to the calculated additional front wheel angle;

The specific steps to control the four wheels of the car to brake are as follows:

Step 3.2.1), the electronic control unit uses the active brake controller to calculate the longitudinal forces F _xfl , F _xfr , F _xrl of the front left, front right, rear left and rear right tires according to the LTR and the reference lateral load transfer rate LTR _des , F _xrr , the nonlinear model of the active braking controller is:

In the formula, F _yfl , F _yfr , F _yrl , and F _yrr are the lateral forces of the front left, front right, rear left and rear right tires, respectively;

将其离散化：Step 3.2.2), get the state equation

Discretize it:

U＝[F_xfl,F_xfr,F_xrl,F_xrr]^T，C、D均为系数；in

U=[F _xfl , F _xfr , F _xrl , F _xrr ] ^T , C and D are coefficients;

Step 3.2.3), the design objective function is as follows, and the braking force of the four tires is calculated:

Satisfy the four tire braking force constraints: U _min ≤U≤U _max

为松弛因子，目的是防止出现求解过程中没有最优解；U_min为最小轮胎力，U_max为最大轮胎力；In the formula, Y ₁ (t) is the LTR actually output by the system at time t; Y _1c (t) is the LTR _des referenced at time t; _{Ph is the prediction time domain; C h is} the control time domain; U(t) is t The control variables output by the active braking controller at all times; S and W are the weight matrices of the first and second terms of the objective function, respectively, the function is to make the system achieve the expected effect as soon as possible, i is the weight coefficient,

is the relaxation factor, the purpose is to prevent that there is no optimal solution in the solution process; U _min is the minimum tire force, and U _max is the maximum tire force;

Step 3.2.4), the controller brakes the four wheels according to the calculated braking force of the four tires.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as herein, are not to be taken in an idealized or overly formal sense. explain.

The specific embodiments described above further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. A model predictive control-based automobile rollover prevention method is characterized by comprising the following steps:

step 1.1), measuring the front wheel corner delta of the vehicle_fVehicle speed v_rYaw rate β_rA lateral position y;

step 1.2), calculating the lateral load transfer rate LTR of the vehicle:

step 1.3), the transverse load transfer rate LTR and a preset transverse load transfer rate threshold value LTR are compared_desComparing the horizontal position Y with a preset reference horizontal position Y_desComparing the difference value of η with η, wherein η is a preset maximum difference threshold:

when (Y-Y)_des) < η and LTR < LTR_desWhen the vehicle body state is not adjusted;

when (Y-Y)_des) | is greater than η and LTR < LTR_desWhen the automobile is driven, two front wheels of the automobile are controlled to steer;

when (Y-Y)_des) < η and LTR > LTR_desWhen the four wheels of the automobile are controlled to carry outThe brake is carried out by the brake device,

when (Y-Y)_des) I > η and LTR > LTR_desWhen the automobile is in use, two front wheels of the automobile are controlled to steer, and four wheels of the automobile are controlled to brake;

step 1.4), the step 1.3) LTR is obtained by the following formula, and the detailed steps are as follows:

step 1.4.1), according to a_y＝v_rβ_rCalculating the lateral acceleration a of the vehicle_y；

Step 1.4.2), force analysis is carried out on the y direction to obtain the roll angle acceleration

In the formula, m is the total mass of the automobile; m is_sIs the sprung mass; e is the distance from the sprung mass to the centre of roll;

is the roll angular acceleration; k is a radical of₁、k₂The yaw stiffness of the front wheel and the rear wheel of the vehicle respectively, the distance from the center of mass of the vehicle to the front axle and the rear axle respectively, the yaw angle of the center of mass β, β_rThe yaw angular velocity;

step 1.4.3), performing moment balance on the x direction:

in the formula I_xsThe moment of inertia of the sprung mass of the automobile around the x axis of the vehicle coordinate system; m is_sIs the sprung mass; g is the acceleration of gravity and the acceleration of gravity,

the vehicle body is in a side inclination angle,

in order to be the roll rigidity,

in order to damp the roll,

is the vehicle body roll angle velocity;

step 1.4.4), carrying out moment balance on the z direction to obtain the yaw angular acceleration

Wherein, I_zThe moment of inertia of the whole vehicle mass around the z axis of a vehicle coordinate system;

yaw angular acceleration;

step 1.4.5), establishing a three-degree-of-freedom vehicle model, and obtaining the roll angle and the roll angle speed of the vehicle in the current state according to the vehicle speed and the rotation angle;

step 1.4.6), carrying out stress analysis according to the pressure of tires on the road surface in the rollover process of the automobile:

in the formula, F_R、F_LThe longitudinal counter-force sum of the right wheel and the left wheel, T is the wheel track, m_dUnsprung mass, h_dThe distance from the center of mass of the unsprung mass to the ground, and h is the height from the center of mass to the ground;

step 1.4.7) due to lateral load transfer rate

And F_R+F_LWhen the weight is mg:

2. the model predictive control-based automobile rollover prevention method according to claim 1, wherein the specific steps of controlling two front wheels of the automobile to steer in the step 1.3) are as follows:

step 2.1), the electronic control unit determines the reference transverse position Y from Y_desCalculating corresponding additional front wheel corner delta by using model prediction control method_f：

Step 2.2), establishing a nonlinear model of the active front wheel steering controller:

in the formula:

is the longitudinal acceleration;

is the transverse vehicle speed; c. C₁，c₂Longitudinal stiffness of the front and rear wheels, respectively; s₁，s₂Respectively the slip rates of the front wheel and the rear wheel;

is the lateral acceleration;

is the longitudinal vehicle speed;

inertial coordinate system lateral velocity;

is the longitudinal velocity of the inertial coordinate system; r is a yaw angle;

step 2.3), obtaining an equation of state

Discretizing the method:

wherein

u＝δ_fA, B are coefficients, X is the longitudinal position of the inertial frame, and Y is the transverse position of the inertial frame;

step 2.4), designing an objective function as follows, and calculating an additional front wheel corner:

the front wheel steering angle constraint is satisfied: delta_f,min≤δ_f≤δ_f,max

Wherein Y (t) is the lateral position actually output by the system at time t; y is_c(t) is the lateral position referenced at time t; n is a radical of_pIs the prediction time domain; n is a radical of_cIs the control time domain; u (t) is a control variable output by the active front wheel steering controller at the time t; delta_fQ, R are weight matrixes of a first term and a second term of an objective function respectively for front wheel turning angles, p is a weight coefficient, and epsilon is a relaxation factor; delta_f,minAt the smallest front wheel angle, delta_f，maxIs the maximum front wheel turning angle;

and 2.5), controlling two front wheels of the automobile to steer by the controller according to the calculated additional front wheel steering angle.

3. The model predictive control-based vehicle rollover prevention method according to claim 1, wherein the specific steps of controlling four wheels of the vehicle to brake in the step 1.3) are as follows:

step 3.1), the electronic control unit transfers the rate LTR according to the LTR and the reference transverse load_desThe longitudinal force F of the front left tire, the front right tire, the rear left tire and the rear right tire is calculated by adopting an active braking controller_xfl、F_xfr、F_xrl、F_xrrThe nonlinear model of the active braking controller is:

in the formula, F_yfl、F_yfr、F_yrl、F_yrrThe lateral forces of the front left tire, the front right tire, the rear left tire and the rear right tire are respectively;

step 3.2), obtaining an equation of state

Discretizing the method:

wherein

U＝[F_xfl,F_xfr,F_xrl,F_xrr]^TC, D are coefficients;

step 3.3), designing an objective function as follows, and calculating the braking force of four tires:

four tire braking force constraints are satisfied: u shape_min≤U≤U_max

In the formula, Y₁(t) LTR actually output by the system at time t; y is_1c(t) LTR referenced at time t_des；P_hIs the prediction time domain; c_hIs the control time domain; u (t) isthe control variable output by the active brake controller at the moment t; s, W are weight matrices for the first and second terms of the objective function, respectively, i is a weight coefficient,

is a relaxation factor; u shape_minFor minimum tire force, U_maxMaximum tire force;

and 3.4), the controller brakes the four wheels according to the calculated braking forces of the four tires.

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