CN113460055B - Online Vehicle Driving Control Area Division and Area Boundary Estimation Method - Google Patents

Abstract

An online vehicle running control area division and area boundary estimation method belongs to the technical field of vehicle safety. The invention aims to obtain an online vehicle running control area division and area boundary estimation method related to a centroid side deviation angle and a yaw rate control area on line according to the behavior of a driver and the information of the running road condition and by considering the lateral-longitudinal-vertical dynamic characteristics of a vehicle. The method comprises the following steps: setting software combined simulation and building a vehicle model; and dividing a vehicle running control area and estimating a boundary. The control area is divided into a stable area, an unstable area and a critical stable area serving as a transition area, different control requirements are given to different areas, and the application potential of the control area in stability control can be better developed.

Description

Online Vehicle Driving Control Area Division and Area Boundary Estimation Method

technical field

The invention belongs to the technical field of vehicle safety.

Background technique

During the driving process of the vehicle, the vehicle state will change in real time according to road conditions and driver behavior. For vehicle stability, the vehicle state that intuitively reflects the handling and stability can be described as a control area, and can be divided according to the stability boundary conditions. Stable area, unstable area, etc., so as to be applied in vehicle stability control. The yaw rate and the side slip angle of the center of mass are important states that reflect the yaw and lateral motion of the vehicle. Usually, the control area about them can be used to describe the vehicle handling performance and lateral stability. The research on regional boundary estimation has the following problems:

1. Most of the existing vehicle driving control areas use the phase plane composed of the centroid sideslip angle and the centroid sideslip angular velocity, and divide the stable area according to its changing characteristics. For moving vehicles, especially in extreme working conditions However, such off-line regions cannot provide reliable vehicle safety assessments in real time.

2. By dividing the control area, the boundary conditions of each area can be obtained according to the dynamic characteristics of the vehicle. However, most of the existing control area division methods only consider the lateral motion of the vehicle, and do not consider the dynamics in other directions. The coupling of dynamics between directions makes the estimation of region boundaries and region divisions inaccurate.

3. In terms of the application of the control area, most of the existing methods only roughly divide the control area into a stable area and an unstable area, and only consider the same control performance to be achieved in different areas, which limits the control area. Application potential in vehicle stability control.

SUMMARY OF THE INVENTION

The purpose of the present invention is to obtain the online vehicle driving control area division and area boundary of the center of mass slip angle and yaw rate control area online, considering the vehicle's transverse-vertical-vertical dynamic characteristics according to the driver's behavior and driving road condition information. estimation method.

The steps of the present invention are:

S1. Software co-simulation setting and vehicle model building;

S2, vehicle driving control area division and boundary estimation

(1) Stable Region Boundary Estimation

①Establishment of vehicle dynamics model

②Tire model

③ Local linearization of nonlinear models

(2) Division of control area

①Transition zone formation and regional division

The area about β and γ will be updated in real time with the driver's steering, driving/braking behavior, and road condition information and change accordingly. The area formed by the boundary under the lowest vehicle speed in the current interval is defined as the stable area under the vehicle speed interval. R1; and the boundary under the condition of the highest vehicle speed in the current interval, the area outside the boundary is the unstable area R3 under the current vehicle speed interval, and the inner area formed by this boundary will overlap with the stable area R1 just obtained, and will not overlap The regional part is defined as the critical stable region R2, which is the transition region between the stable region and the unstable region; in the region where the current vehicle state (β, γ) is located, the control demand for vehicle stability in each region changes, and the control demand for each region changes. as follows:

The introduction of the control requirements of each area is as follows: In the stable area R1, the maneuverability and lateral stability of the vehicle can be guaranteed at this time, so in this area, the longitudinal anti-skid performance of the tire can be considered to prevent the tire from slipping and locking, and the energy can be considered. Consumption; when the vehicle state enters the critical stable region R2, the vehicle state should be guaranteed to return to the stable region as much as possible, so the control requirements for handling stability and lateral stability are increased, and as the vehicle state gradually moves away from R1 in R2 , the center of gravity of tire longitudinal anti-skid and energy consumption should also gradually shift to the handling stability and lateral stability of the vehicle; while in the unstable region R3, the primary control requirement is to ensure handling and lateral stability. sex to ensure driving safety;

②Regional location judgment

For the division of the control area, it is necessary to judge the location of the area to which the current vehicle state (β, γ) belongs in real time, so as to determine the control requirements that the current vehicle state needs to meet. If the current vehicle state (β, γ) is known, and the Knowing that there is a one-to-one correspondence between β _mat and γ _mat on the fitted boundaries, each boundary can be written as the function β _mat (γ _mat ) of the center of mass slip angle on the yaw rate, so the function β _mat (γ _mat ) to obtain the β value of each boundary a _in , b _in , a _out , b _out , c, d under the current γ, then the coordinates of the γ value on each boundary can be obtained as (β _ain , γ), ( β _bin ,γ),(β _aout ,γ),(β _bout ,γ),(β _c ,γ),(β _d ,γ), and compare their abscissa values with the β values fed back by the vehicle respectively , that is, the area where the current vehicle state (β, γ) is located is determined by the following relationship:

If the current center-of-mass slip angle and yaw rate (β, γ) of the vehicle are known, the control area that the vehicle currently belongs to can be determined according to relation (12).

The beneficial effects of the present invention are:

1. The present invention uses a control area composed of yaw rate and center of mass slip angle, which can better describe the maneuverability and stability of the vehicle, and the boundaries of each area can change in real time with driver behavior and road information. Most traditional control methods using off-line phase plane regions can provide a more reliable assessment of vehicle safety;

2. Most area estimation methods only consider the lateral motion dynamics of the vehicle, while ignoring other directions and the coupling characteristics between them. The present invention is based on the lateral-vertical-vertical dynamic characteristics of the vehicle The influence of the load can make the area estimation more accurate for easy application;

3. The present invention divides the control area into a stable area, an unstable area and a critical stable area as a transition area, and assigns different control requirements to different areas, which can better develop the application potential of the control area in stability control .

Description of drawings

Fig. 1 is the flow chart of the present invention;

2 is a schematic diagram of a vehicle dynamics model of the present invention;

Fig. 3 is the relationship between lateral force and slip angle of different road adhesion coefficients of the present invention;

4 is a schematic diagram of the boundary of the control area of the present invention. At this time, the vehicle travels on a straight road with a road adhesion coefficient of 0.35 at V _x =60km/h, wherein the solid line is the controllable condition boundary, the dotted line is the stable condition boundary, and the ordinate is The yaw rate, the unit is rad/s, the abscissa is the center of mass slip angle, the unit is rad;

5 is a schematic diagram of the control area boundary and area division of the present invention. At this time, the vehicle is driving on a straight road with a road adhesion coefficient of 0.35, and the vehicle speed is in the range of 60-65km/h. The solid line is the controllable condition boundary, and the double-dashed line is The inner boundary of the stability condition obtained when the speed is 60km/h, the dotted line is the outer boundary of the stability condition obtained when the speed is 65km/h, the area formed by the inner boundary and the controllable boundary is the stable area R1, and the area formed by the inner and outer boundaries is Critical stable region R2, other parts are regarded as unstable region R3;

Fig. 6 is the present invention when the vehicle speed is in the 60-65km/h interval, the steering wheel angle is 45 degrees, the road surface has no slope, and the adhesion coefficient is 0.35 when the control area division and its boundary conditions;

Fig. 7 is the control area division and its boundary conditions when the vehicle speed is in the range of 75-80km/h, there is no steering behavior, the road surface has no slope, and the adhesion coefficient is 0.35;

Fig. 8 is the control area division and its boundary conditions when the vehicle speed is in the range of 60-65km/h, there is no steering behavior, the road has no slope, and the adhesion coefficient is 0.8 according to the present invention;

9 is the control area division and its boundary conditions when the vehicle speed is in the range of 60-65km/h, there is no steering behavior, the composite road gradient is 6%, and the adhesion coefficient is 0.35.

Detailed ways

The flow chart of the control area division and boundary estimation method according to the present invention is shown in Figure 1, wherein the road environment information and vehicle measurement state are collected from the vehicle dynamics simulation software CarSim, and the vehicle yaw and lateral motion dynamics are established. The model uses the nonlinear tire model to describe the tire lateral force, and locally linearizes the nonlinear vehicle dynamics model through Taylor expansion and local linearization. Based on the relationship between the tire force and the slip angle in the tire model, the stability Conditional yaw angular velocity and centroid slip angle, fit them to form the regional boundary; then combine the boundaries of each speed interval, the region can be divided into stable region, critical stable region and unstable region, the boundaries of each region can be based on Driver behavior and road condition information are estimated online, and each area corresponds to different vehicle stability control requirements. In the present invention, the vehicle model and simulation conditions are constructed in CarSim, and the others are constructed in MATLAB/Simulink.

The objective of the present invention is to realize the division of the control area and the real-time estimation of the boundary of each divided area during the running of the vehicle.

The present invention provides a set of devices based on the above operating principles and operating procedures. The construction and operation process is as follows:

1. Software co-simulation setting and vehicle model building

The simulation models of the controller and the controlled object of the control system are built by the software MATLAB/Simulink and CarSim respectively. The software versions are MATLAB R2016a and CarSim 2016.1 respectively, and the simulation step size is 0.001s. To realize the co-simulation of MATLAB/Simulink and CarSim, first set the working path of CarSim to the specified Simulink Model, then add the set vehicle model and road information to Simulink in CarSim, and run Simulink to achieve both co-simulation and communication. If the model structure or parameter settings in CarSim are modified, it needs to be resent.

As a high-fidelity vehicle dynamics software, CarSim is used to simulate the real controlled object. The vehicle model used in the present invention is constructed based on Dongfeng A60, and its parameters are shown in Table 1.

Table 1 Vehicle model parameter table

2. Vehicle driving control area division and boundary estimation

As mentioned above, the present invention obtains the boundary of each control area online about the yaw rate and the center of mass slip angle according to the driver's behavior and road condition information based on the vehicle's lateral-vertical-vertical dynamic characteristics. Firstly, the nonlinear vehicle dynamics model and tire model are established, and they are locally linearized to screen out reasonable yaw rate and centroid slip angle that satisfy the system stability. As a stable area, the handling stability and lateral stability of the vehicle can be effectively guaranteed in this area, and the anti-skid performance of the vehicle needs to be considered. Then, the stable area boundaries obtained in each vehicle speed interval are synthesized to form a stable area. The transition area between the unstable area and the unstable area is called the critical stable area. In this area, it is necessary to ensure the vehicle's maneuverability and longitudinal and lateral stability, and try to make the vehicle return to the stable area. The handling stability of the vehicle in this area should be the primary performance to be guaranteed.

The present invention is introduced as follows about the specific method of control area division and boundary estimation:

1) Stable Region Boundary Estimation

①Establishment of vehicle dynamics model

First, a dynamic model is established considering the yaw and lateral motion of the vehicle. The schematic diagram is shown in Figure 2. The model is described as follows:

Among them, β is the vehicle center of mass slip angle, γ is the vehicle yaw rate, δ _f is the front wheel angle, F _y is the tire lateral force, the subscript i∈{f,r},j∈{l,r} The combination ij∈{fl,fr,rl,rr} represents the front left, front right, rear left and rear right wheels, respectively.

②Tire model

In order to describe the tire lateral force more accurately, the present invention adopts the Fiala tire model, which uses the tire slip angle as an internal variable, which can better reflect the saturated nonlinear characteristics of the tire force, and its calculation can be described as follows:

Among them, μ is the road adhesion coefficient, F _z is the vertical load, C _i is the rated cornering stiffness of the tire front or rear wheel; α is the tire side slip angle, which is calculated as follows:

其计算考虑车辆在转弯时、斜坡上的载荷重新分配，其中a_x,a_y分别代表纵、侧向加速度，

为侧倾角，η_h,η_c分别代表侧、纵向道路坡度，具体计算如下：Tire vertical load

Its calculation considers the load redistribution of the vehicle when turning and on the slope, where a _x , a _y represent the longitudinal and lateral accelerations, respectively,

is the roll angle, η _h , η _c represent the lateral and longitudinal road slopes respectively, and the specific calculation is as follows:

为合成道路坡度，h_φ是侧倾力臂，

是侧倾角，

为前后悬架侧倾角刚度， k_l＝-k_r＝-1，这样计算可以更准确地考虑轮胎垂向载荷在复杂路面上的分配情况。in,

is the synthetic road gradient, h _φ is the roll arm,

is the roll angle,

For the roll angle stiffness of the front and rear suspensions, k _l =-k _r =-1, so that the calculation can more accurately consider the distribution of tire vertical loads on complex road surfaces.

The relationship between the lateral force of different road adhesion coefficients and the slip angle is shown in Fig. 3. The partial derivative of the tire lateral force with respect to the slip angle can be regarded as the transient cornering stiffness of the tire at the current slip angle.

③ Local linearization of nonlinear models

The vehicle dynamics model (1) is locally linearized by Taylor expansion, described as the following form with respect to linearization points and increments:

β_o、γ_o和δ_fo分别表示各值的线性化点，

Δβ、Δγ、Δδ_f分别表示各值的增量，公式(5)中增量部分可描述为如下形式：in,

β _o , γ _o and δ _fo represent the linearization points of each value, respectively,

Δβ, Δγ, Δδ _f represent the increments of each value, respectively, and the increment part in formula (5) can be described as follows:

in,

即根据轮胎模型(2)中侧向力对侧偏角的偏导可得到轮胎侧偏刚度C_α。In the process of obtaining the partial derivative, only the lateral force is regarded as a function of the sideslip angle, so

That is, the tire cornering stiffness C _α can be obtained according to the deflection of the lateral force to the slip angle in the tire model (2).

According to formula (3), the partial derivatives of α to β and γ can be obtained as follows:

Then according to formulas (1) and (7).

After finishing, you can get:

的特征值，可得到系统的稳定性条件为

即系统的稳定条件和可控条件为：By solving the matrix

The eigenvalues of , the stability condition of the system can be obtained as

That is, the stable and controllable conditions of the system are:

C _αfl +C _αfr ≠0, (10)

According to the boundary conditions (9) and (10), the tire cornering stiffness is obtained from the relationship between the tire force and the side slip angle in the tire model (2), and the qualified C _αfl and C _αfr are screened out, and the corresponding side slip angle is obtained. α _fl and α _fr are then converted to qualifying centroid slip and yaw velocities by changing as follows:

Plot all eligible points (β _mat , γ _mat ) and fit these points as the boundaries of the control region. Taking the vehicle driving on a straight road with a road adhesion coefficient of 0.35 and a speed of 60km/h as an example, the control area boundary at this time is drawn as shown in Figure 4, where the dotted line is the stable condition boundary, which also represents the oversteer boundary; the solid line For the controllable condition boundary, it also represents the understeer boundary.

2) Control area division

①Transition area formation and area division The areas about β and γ obtained from the above boundaries will be updated in real time with the driver's steering, driving/braking behavior, and road condition information and change accordingly. Through analysis and verification, it can be seen that this area will expand with the increase of vehicle speed, translate with the steering of the vehicle, decrease with the decrease of the road adhesion coefficient, and is less affected by the change of slope. In order to improve the real-time performance of the control area boundary obtained online, we divide the vehicle speed into 50-55km/h, 55-60km/h, 60-65km/h, 65-70km/h, 70-75km/h, 75-80km/h h several intervals, and synthesizing the stable condition boundaries obtained at each vehicle speed in the current interval, then the area formed by the boundary at the lowest vehicle speed in the current interval can be obtained, which is defined as the stable area R1 under the vehicle speed interval; and the current The boundary under the condition of the highest vehicle speed in the interval, the area outside the boundary is the unstable area R3 under the current vehicle speed interval, and the inner area formed by this boundary will overlap with the stable area R1 just obtained, and the non-overlapping area is defined as The critical stable region R2 is the transition region between the stable region and the unstable region.

In order to define and explain each area more intuitively, take the vehicle driving on a straight road with a road friction coefficient of 0.35 and the vehicle speed within 60-65km/h as an example, draw the control area of the vehicle speed interval as shown in Figure 5, a _in and _bin is the stable condition boundary obtained when V _x = 60km/h, called the inner boundary; a _out and b _out are the stable condition boundary obtained when V _x = 65km/h, called the outer boundary; c and d are Controllable conditional boundary; and define the area formed by the inner boundary and the controllable boundary as the stable area R1, the area formed by the inner and outer boundaries is the critical stable area R2, and the other parts are regarded as the unstable area R3.

As mentioned above, for each region, different control requirements need to be considered. If the region where the current vehicle state (β, γ) is located is known, the changes in the control requirements for vehicle stability in each region are shown in the table below.

Table 2 Changes in Control Demands by Regions

Combined with Table 2, the introduction of the control requirements of each area is as follows: In the stable area R1, the maneuverability and lateral stability of the vehicle can be guaranteed at this time, so the longitudinal anti-skid performance of the tire can be considered in this area to prevent the tire from slipping and locking. And consider the energy consumption; when the vehicle state enters the critical stability region R2, it should be ensured that the vehicle state can return to the stable region as much as possible, so the control requirements for handling stability and lateral stability are increased, and as the vehicle state is in R2 Gradually away from R1, the center of gravity of tire longitudinal anti-skid and energy consumption should also gradually shift to the handling stability and lateral stability of the vehicle; while in the unstable region R3, the primary control requirement is to ensure handling and stability. Lateral stability to ensure driving safety. The switching of the above control requirements in different regions can be realized by the objective function and its weight value in the controller design, as well as the change and adjustment of the constraints.

②Regional location judgment

在当前γ下的β值，即可得到各边界上对于该γ值的坐标分别为 (β_ain,γ),(β_bin,γ),(β_aout,γ),(β_bout,γ),(β_c,γ),(β_d,γ)，将它们的横坐标值分别与车辆反馈回的β值进行比较，即可通过下列关系判断当前车辆状态(β,γ)所处区域：Based on the above-mentioned division of the control area, it is necessary to determine the location of the area to which the current vehicle state (β, γ) belongs in real time, so as to determine the control requirements that the current vehicle state needs to meet. If the current vehicle state (β, γ) is known, and β _mat and γ _mat are known to be in one-to-one correspondence on each boundary, then each boundary can be written as a function of the center of mass slip angle on the yaw rate β _mat (γ _mat ), so each boundary a _in , b _in , can be obtained through the function β _mat (γ _mat ),

At the β value under the current γ, the coordinates of the γ value on each boundary can be obtained as (β _ain ,γ),(β _bin ,γ),(β _aout ,γ),(β _bout ,γ), (β _c , γ), (β _d , γ), by comparing their abscissa values with the β value fed back by the vehicle, the current vehicle state (β, γ) can be judged by the following relationship:

To sum up, if the current center-of-mass slip angle and yaw rate (β, γ) of the vehicle are known, the control area that the vehicle currently belongs to can be determined according to the relationship (12). In addition, for different road information and driver behaviors, some driving situations are listed in Table 3. In these situations, the division of control areas and the boundaries of each area are shown in Figures 6-9. It can be seen that the method proposed by the present invention can realize real-time It changes according to changes in road information and driver behavior, and provides a reliable safety evaluation for vehicle stability control.

Table 3 Area division and boundary under different road information and driver behavior

Claims (1)

1. An on-line vehicle driving control area dividing and area boundary estimating method comprises the following steps:

s1, setting software joint simulation and building a vehicle model;

s2, vehicle driving control area division and boundary estimation

(1) Steady region boundary estimation

Firstly, establishing a vehicle dynamic model

② tire model

Part linearization of non-linear model

The method is characterized in that:

(2) control region partitioning

Forming transition region and dividing region

The area of the vehicle mass center side deviation angle beta and the vehicle yaw velocity gamma can be updated in real time along with the steering, driving/braking behaviors of a driver and road condition information and correspondingly changed, and the area formed by the boundary at the lowest vehicle speed in the current interval is defined as a stable area R1 in the vehicle speed interval; and a boundary under the condition of the highest vehicle speed in the current interval, wherein the region outside the boundary is an unstable region R3 in the current vehicle speed interval, an inner region formed by the boundary is overlapped with the stable region R1 which is just obtained, and the non-overlapped region part is defined as a critical stable region R2 which is used as a transition region of the stable region and the unstable region; the current vehicle state (β, γ) is in a region, and the control demand for the vehicle stability changes in each region as follows:

the control requirements for each zone are introduced as follows: in the stable region R1, where the maneuverability and lateral stability of the vehicle can be ensured, the tire longitudinal anti-skid performance can be considered, the tire is prevented from locking up, and the energy consumption can be considered; when the vehicle state enters the critical stability region R2, it should be ensured as much as possible that the vehicle state can return to the stable region, so that the control demand regarding the steering stability and the lateral stability is increased, and as the vehicle state is gradually away from R1 in R2, the demand gravity center for the tire longitudinal slip prevention and the energy consumption should be gradually shifted to the steering stability and the lateral stability of the vehicle; in the unstable region R3, the primary control requirement is to ensure maneuverability and lateral stability to ensure driving safety;

region position judgment

For the division of the control area, the area position to which the current vehicle state (β, γ) belongs needs to be judged in real time so as to judge the control requirement that the current vehicle state needs to meet, if the current vehicle state (β, γ) is known, and the fitted β on each boundary is known_matAnd gamma_matAre all in one-to-one correspondence, then each boundary can be written as a function β of the centroid yaw angle with respect to the yaw rate_mat(γ_mat) Therefore, can pass through the function β_mat(γ_mat) Obtain each boundary a_in,b_in,a_out,b_outC, d is the beta value under the current gamma, namely the coordinate of the gamma value on each boundary is (beta)_ain,γ),(β_bin,γ),(β_aout,γ),(β_bout,γ),(β_c,γ),(β_dγ), comparing their abscissa values with β values fed back by the vehicle, i.e. determining the area in which the current vehicle state (β, γ) is located by the following relationship:

if the current centroid slip angle and yaw rate (beta, gamma) of the vehicle are known, the control area to which the vehicle currently belongs can be determined according to the relation (12).

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