A lateral stability control method and system for a vehicle during braking on split-mu surfaces

Abstract

The present invention proposes a method and system for controlling the lateral stability of a vehicle when braking on a split road, belonging to the technical field of vehicle lateral stability control. d The maximum braking intensity z that the vehicle can produce on low-adhesion roads th , when z d ≤z th By designing the controller, the braking force at the high attachment point is suppressed, and the difference between the braking force at the high attachment point and the braking force at the low attachment point is reduced or even eliminated; when z d >z th When braking on an oncoming road, the controller is designed to maintain the low-adhesion braking force at its peak value, regulate the high-adhesion braking force, and simultaneously control the rear wheel angle to generate an additional yaw moment to compensate for the desired yaw moment of the vehicle. This invention also proposes a comprehensive risk index for oncoming road stability to comprehensively evaluate the stability of the vehicle when braking on an oncoming road. Active four-wheel steering intervenes when the vehicle exceeds the steady-state boundary. This invention effectively improves the vehicle's lateral stability when braking on an oncoming road.

Description

Technical Field

[0001] The present invention belongs to the technical field of vehicle lateral stability control, is based on a distributed drive electric vehicle, and specifically relates to a method and system for controlling the lateral stability of a vehicle when braking on an oncoming road. Background Art

[0002] A split road refers to a road with a significant difference in the road adhesion coefficient between the left and right wheels. This condition is common in icy and snowy areas, where snow has been cleared to the roadside. When a vehicle approaches the roadside, one wheel is on the icy road while the other is on dry pavement. When braking on this surface, the different road adhesion coefficients result in different braking forces on the left and right wheels. The resulting yaw torque can cause the vehicle to pull sideways during braking. This phenomenon not only affects the vehicle's handling stability but can also pose serious safety hazards.

[0003] It is crucial to improve the lateral stability of a vehicle when braking on an oncoming road. Most existing technologies currently ensure the lateral stability of a vehicle when braking on an oncoming road through active steering or direct yaw moment control, but they are not very targeted at oncoming roads. Summary of the Invention

[0004] The present invention addresses the deficiencies in the prior art and provides a method and system for controlling the lateral stability of a vehicle when braking on an oncoming road.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for controlling the lateral stability of a vehicle when braking on an oncoming road, comprising:

[0007] Collect vehicle data, calculate the average angular deceleration difference Δα on both sides based on the vehicle data, and fuse the average angular deceleration difference Δα on both sides and the steady-state area of ​​the ω-β phase plane into a comprehensive risk index M for split road stability, where ω is the vehicle's yaw rate and β is the sideslip angle of the center of mass; set the comprehensive risk index threshold M th , when M≤M th When M>M th When M≤M th And the duration exceeds the set threshold t th ;

[0008] The control strategy is to judge the stability through the ω-β phase plane. When |ω+B1β|≤B2, the maximum braking intensity z that the vehicle can produce on the low-adhesion road is compared. th and the expected braking intensity z d , if z d ≤z th, execute controller 1 to regulate the braking force at high and low attachment points; if z d >z th , execute controller 2 to keep the braking force at the low attachment point at the peak value, only regulate the braking force at the high attachment point, and control the rear wheel angle at the same time; when |ω+B1β|>B2, execute controller 3 to make the active four-wheel steering intervene.

[0009] Optionally, the vehicle data includes vehicle yaw rate, longitudinal speed, lateral speed, angular velocity corresponding to each wheel, steering wheel angle and brake pedal travel.

[0010] Optionally, the calculation of the average angular deceleration difference Δα on both sides based on the vehicle data is specifically as follows:

[0011] According to the left front wheel angular velocity ω 11 , right front wheel angular velocity ω 12 , left rear wheel angular velocity ω 21 and the right rear wheel angular velocity ω 22 , calculate the angular deceleration of each wheel by time difference, and get the angular deceleration of the left front wheel α 11 , right front wheel angular deceleration α 12 , left rear wheel angular deceleration α 21 and the right rear wheel angular deceleration α 22 ;

[0012] Calculate the average angular deceleration α on the left side L and the right average angular deceleration α R for:

[0013]

[0014] Then the average angular deceleration difference Δα on both sides is:

[0015] Δα=α L -α R .

[0016] Optionally, the comprehensive risk index M of the split road stability is:

[0017]

[0018] Among them, α th is the threshold of the absolute value of the difference between the average angular deceleration on both sides, B=|ω+B1β| is the stability evaluation index of the ω-β phase plane, and B th is the threshold of B, λ1 and λ2 are weight coefficients, and λ1+λ2=1.

[0019] Optionally, the maximum braking intensity z that the vehicle can produce on a low-adhesion road surface is th =μ1, μ1 is the road adhesion coefficient at low attachment point.

[0020] Optionally, the desired braking intensity z d Obtained by:

[0021] Based on fuzzy control, the braking intention is recognized, and the brake pedal stroke and brake pedal operation speed are used as the input of the braking intention recognition, and the expected braking intensity z is used as the input of the braking intention recognition. d As the output of braking intention recognition.

[0022] Optionally, the controller 1 adopts a hierarchical design; the input of the upper controller is the vehicle yaw angular velocity ω and the reference yaw angular velocity ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β r The output is the additional yaw moment M Z , the additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution;

[0023] The lower controller takes tire utilization as the optimization target, and the objective function J is:

[0024]

[0025] Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively;

[0026] The following constraints are met when distributing the braking force:

[0027]

[0028] Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can generate, μ1 is the road adhesion coefficient at low attachment, m is the sprung mass of the vehicle, and g is the acceleration due to gravity;

[0029] The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

[0030] Optionally, the second controller adopts a hierarchical design; the input of the upper controller is the vehicle yaw angular velocity ω and the reference yaw angular velocity ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β rThe output is the additional yaw moment M Z and rear wheel turning angle δ r ; Set the rear wheel angle δ r Send it to the steering system, and the rear wheel steering motor makes the wheel reach the corresponding turning angle, thereby generating the corresponding additional yaw moment; the additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution;

[0031] The lower controller takes tire utilization as the optimization target, and the objective function J is:

[0032]

[0033] Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively;

[0034] The following constraints are met when distributing the braking force:

[0035]

[0036] Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can produce, is the peak adhesion coefficient, μ2 is the road adhesion coefficient at high adhesion, m is the sprung mass of the vehicle, g is the acceleration of gravity, the left side is a low adhesion road, and the right side is a high adhesion road;

[0037] The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

[0038] Optionally, the controller 3 adopts a hierarchical design; the input of the upper controller is the vehicle yaw angular velocity ω and the reference yaw angular velocity ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β r The output is the front wheel steering angle δ f , rear wheel turning angle δ r and additional yaw moment M Z ; Set the front wheel angle δ f and rear wheel turning angle δ r Send it to the steering system, and the steering motor makes the wheels reach the corresponding turning angle, thereby generating the corresponding additional yaw moment; the additional yaw moment M ZSent to the lower-level controller as the target for braking force distribution;

[0039] The lower controller takes tire utilization as the optimization target, and the objective function J is:

[0040]

[0041] Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively;

[0042] The following constraints are met when distributing the braking force:

[0043]

[0044] Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can generate, μ1 is the road adhesion coefficient at low adhesion, μ2 is the road adhesion coefficient at high adhesion, m is the sprung mass of the vehicle, g is the acceleration of gravity, the left side is a low adhesion road, and the right side is a high adhesion road;

[0045] The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

[0046] In a second aspect, the present invention provides a lateral stability control system for a vehicle when braking on an oncoming road, comprising: a vehicle data acquisition unit, a vehicle stability monitoring unit, and an oncoming road braking lateral stability control unit;

[0047] The vehicle data acquisition unit collects vehicle data; the vehicle stability monitoring unit calculates the average angular deceleration difference Δα on both sides based on the vehicle data, and fuses the average angular deceleration difference Δα on both sides and the steady-state area of ​​the ω-β phase plane into a comprehensive risk index M for the stability of the split road, where ω is the vehicle yaw angular velocity and β is the sideslip angle of the center of mass; and sets a comprehensive risk index threshold M th , when M≤M th When M>M th When the lateral stability control unit starts the control strategy for braking on open roads, it will continue until M≤M th And the duration exceeds the set threshold t th ;

[0048] The control strategy of the braking lateral stability control unit on the split road is to judge the stability through the ω-β phase plane. When |ω+B1β|≤B2, the maximum braking intensity z that the vehicle can produce on the low-adhesion road is compared. th and the expected braking intensity z d , if z d ≤z th , execute controller 1, and adjust the braking force at high and low attachment points; if z d >z th , execute controller 2 to keep the braking force at the low attachment point at the peak value, only regulate the braking force at the high attachment point, and control the rear wheel angle at the same time; when |ω+B1β|>B2, execute controller 3 to make the active four-wheel steering intervene.

[0049] The beneficial effects of the present invention are as follows: the control strategy of the present invention is designed for split-road surfaces and is more suitable for braking on split-road surfaces, effectively resolving the problem of existing technologies being less targeted for split-road surfaces. By comparing the desired braking intensity with the maximum braking intensity that the vehicle can generate on low-adhesion surfaces, the present invention, through the design of the controller, suppresses the braking force at the high-adhesion area, reducing or even eliminating the difference between the braking force at the low-adhesion area and the braking force at the low-adhesion area. When the desired braking intensity exceeds the maximum braking intensity that the vehicle can generate on low-adhesion surfaces, the controller is designed to maintain the braking force at the low-adhesion area at its peak value, regulating only the braking force at the high-adhesion area, thereby minimizing the yaw moment generated by braking on split-road surfaces. Simultaneously, the rear wheel angle is controlled to generate an additional yaw moment to compensate for the desired yaw moment of the vehicle. The present invention also proposes a comprehensive split-road stability risk index, which comprehensively evaluates the stability of a vehicle when braking on split-road surfaces by measuring the difference in average angular deceleration on both sides of the vehicle and the steady-state region of the ω-β phase plane. When it is detected that the vehicle has exceeded the stable boundary, the active four-wheel steering intervenes to further ensure the stability of the vehicle. In summary, the present invention effectively improves the lateral stability of the vehicle when braking on the open road, ensuring the braking safety of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The diagram shows the structure of a lateral stability control system for a vehicle when braking on an oncoming road.

[0051] Figure 2 The present invention is a flow chart of a method for controlling the lateral stability of a vehicle when braking on an oncoming road. DETAILED DESCRIPTION

[0052] The present invention will now be described in further detail with reference to the accompanying drawings.

[0053] Example 1

[0054] This embodiment proposes a lateral stability control system for a vehicle when braking on an oncoming road. Figure 1 As shown, the system includes a vehicle data acquisition unit, a vehicle stability monitoring unit, a road surface recognition unit, a braking intention recognition unit, a split road braking lateral stability control unit and a vehicle execution unit.

[0055] The vehicle data acquisition unit collects the required data, such as vehicle yaw rate, longitudinal speed, lateral speed, angular velocity of each wheel, steering wheel angle, brake pedal travel, etc., and sends the collected data to the corresponding data processing unit for calculation and processing.

[0056] The vehicle stability monitoring unit calculates the average angular deceleration difference Δα on both sides and fuses the average angular deceleration difference Δα on both sides with the steady-state area of ​​the ω-β phase plane to form a comprehensive risk index M for the stability of the split road, where ω is the vehicle's yaw rate and β is the center of mass sideslip angle. th is the comprehensive risk index threshold, when M is greater than M th The control strategy will be enabled.

[0057] The road surface recognition unit processes the data collected by the data collection unit to obtain the road surface adhesion coefficient μ1 at the low adhesion area and the road surface adhesion coefficient μ2 at the high adhesion area.

[0058] Calculate the maximum braking intensity z that the vehicle can produce on this low-adhesion road surface th The maximum braking intensity z that the vehicle can produce on low-adhesion roads th =μ1.

[0059] The braking intention recognition unit recognizes the braking intention based on fuzzy control, takes the brake pedal stroke and brake pedal operation speed as inputs, and takes the expected braking intensity z as inputs. d As the output of the braking intention recognition module.

[0060] The braking lateral stability control unit on open roads activates the control strategy, which is then executed by the vehicle's actuating unit.

[0061] Example 2

[0062] Based on the lateral stability control system proposed in the first embodiment, this embodiment proposes a lateral stability control method for a vehicle when braking on an oncoming road, such as Figure 2 As shown, the specific steps include:

[0063] Step 1: The vehicle data acquisition unit acquires the data required by the method and sends the acquired data to the corresponding data processing unit for calculation and processing.

[0064] Step 2: The vehicle stability monitoring unit calculates the average angular deceleration difference Δα on both sides, and fuses the average angular deceleration difference on both sides and the steady-state area of ​​the ω-β phase plane into the comprehensive risk index M of the split road stability. Set M th is the comprehensive risk index threshold, when M is greater than M th , the following control strategies will be enabled.

[0065] Step 3: The road surface recognition unit processes the data collected by the data acquisition unit to obtain the road surface adhesion coefficient μ1 at the low attachment point and the road surface adhesion coefficient μ2 at the high attachment point.

[0066] Step 4: Calculate the maximum braking intensity z that the vehicle can produce on low-adhesion roads th , z th =μ1.

[0067] Step 5: Based on fuzzy control, the braking intention is identified. The brake pedal stroke and brake pedal operation speed are used as the input of the braking intention identification unit. The expected braking intensity z d As the output of the braking intention recognition module.

[0068] Step 6.1: When z d ≤z th This indicates that the desired braking intensity can be achieved without fully utilizing the high-adhesion road surface for braking. Through the design of the controller, the braking forces at the high-adhesion and low-adhesion areas are regulated, and neither exceeds the adhesion limit of the low-adhesion area. By suppressing the braking force at the high-adhesion area, the difference between the braking force at the high-adhesion area and the low-adhesion area is reduced or even eliminated, thereby minimizing the yaw moment generated by braking on the opposite road surface.

[0069] Step 6.2: When z d >z th When , it means that high-adhesion road surface is needed for braking to achieve the desired braking intensity. By designing the controller, the braking force at the low-adhesion area is kept at the peak value, and only the braking force at the high-adhesion area is regulated, which can minimize the yaw moment generated when braking on the split road surface. At the same time, the rear wheel turning angle δ r Control is performed to generate an additional yaw moment to compensate for the desired yaw moment of the vehicle.

[0070] Step 7: The vehicle stability monitoring unit determines stability using the ω-β phase plane. The stability region of the ω-β phase plane is delineated using the double-line method. The stability region formula is expressed as |ω+B1β|≤B2, where coefficients B1 and B2 are boundary parameters. When |ω+B1β|≤B2, only the control strategy described in Step 6.1 or Step 6.2 is used. If the value of |ω+B1β| exceeds B2, active four-wheel steering is also activated to ensure vehicle stability.

[0071] Step 8: When the vehicle stability monitoring unit calculates the comprehensive risk index M≤M th And the duration exceeds t th , exit the above control strategy.

[0072] Further, step 2 is explained:

[0073] Obtain the left front wheel angular velocity ω from the vehicle data acquisition module 11 , right front wheel angular velocity ω 12 , left rear wheel angular velocity ω 21 , right rear wheel angular velocity ω 22 By calculating the angular deceleration α of each wheel through time difference, the angular deceleration α of the left front wheel can be obtained. 11 , right front wheel angular deceleration α 12 , left rear wheel angular deceleration α 21 , right rear wheel angular deceleration α 22 .

[0074] Calculate the average angular deceleration α on the left side L and the right average angular deceleration α R :

[0075]

[0076] Let Δα be the difference in average angular deceleration on both sides:

[0077] Δα=α L -α R

[0078] Comprehensive risk index M of road stability:

[0079]

[0080] Among them, α th is the threshold of the absolute value of the difference between the average angular deceleration on both sides, B=|ω+B1β| is the stability evaluation index of the ω-β phase plane, and B th is its threshold, λ1 and λ2 are their weight coefficients, and λ1+λ2=1.

[0081] Set the comprehensive risk index threshold M th When M>1, the lateral stability control unit for braking on open roads starts to work.

[0082] Further, step 5 is described in detail:

[0083] Braking intention recognition uses triangular functions to fuzzify input variables. The fuzzy subsets for brake pedal travel are (L, M, H), brake pedal speed are (L, M, H), and braking intensity are (L, M, H). The defuzzification process uses a weighted average method to calculate the exact braking intensity. The specific fuzzy rules are shown in the table below.

[0084] Table 1 Fuzzy rules

[0085]

[0086] Further, step 6.1 is described in detail:

[0087] This controller is designed in a hierarchical manner. The upper-layer controller inputs the deviation of the vehicle's yaw rate and sideslip angle from the reference yaw rate and sideslip angle, and outputs an additional yaw moment. The lower-layer controller distributes the braking torque based on the required longitudinal braking force and required yaw moment.

[0088] Upper controller

[0089] Establish a two-degree-of-freedom model of the vehicle:

[0090]

[0091] Where m is the sprung mass of the vehicle; a is the distance from the front axle to the center of mass; b is the distance from the rear axle to the center of mass; v x is the longitudinal velocity of the car, v y is the lateral speed of the car; k1 and k2 are the front and rear wheel cornering stiffnesses respectively; δ f represents the front wheel turning angle; ω is the vehicle's yaw rate, β is the center of mass side slip angle, I z Represents the vehicle's moment of inertia around the Z axis, M Z To correct the yaw moment.

[0092] Selecting the state variables as the sideslip angle β and the yaw rate ω, the state space equation is as follows:

[0093]

[0094] State variable x = [βω] Τ , output y = [βω] Τ , control quantity u=M Z , δ f The front wheel angle is a known quantity and can be used as a system disturbance, which can be expressed as the following state equation:

[0095]

[0096] in,

[0097]

[0098] Discretize the above continuous system, and the sampling time t s , the discretized state space expression is:

[0099]

[0100] Where k represents the time and τ represents the integral variable.

[0101] In order to reduce or eliminate the static error, an integral term is introduced and the state space equation is rewritten into the following incremental form:

[0102]

[0103] Among them, Δx(k)=x(k)-x(k-1), Δu(k)=u(k)-u(k-1), ΔΨ(k)=Ψ(k)-Ψ(k-1).

[0104] Set the prediction time domain to P and the control time domain to m MPC , and the control time domain does not exceed the prediction time domain, outside the control time domain Δu(k+i)=0(i≥m MPC ), assuming that the external input interference remains unchanged in the prediction time domain P, that is, ΔΨ(k+i)=0(i=1,2,…,P-1), then the P-step prediction output vector and m can be defined MPC The step control input vector is as follows:

[0105] Y P (k+1|k)=[y(k+1|k) y(k+2|k)…y(k+P|k)] T

[0106] ΔU(k+1|k)=[Δu(k+1) Δu(k+2)…Δu(k+m MPC -1)] T

[0107] Where y(k+i|k) is the output of the system at time k+i predicted at time k, and Δu(k+i) is the change in system control at time k+i.

[0108] According to the incremental state space equation, the P-step prediction output Y can be derived P The expression for (k+1|k):

[0109] Y P (k+1|k)=S x Δx(k)+Ν y y(k)+S u ΔU(k)+S Ψ ΔΨ(k)

[0110] in,

[0111]

[0112]

[0113] Where I is the unit vector, S x ,Ν y ,S u ,S Ψ Y P The coefficient matrix of (k+1|k).

[0114] Define the reference sequence as follows:

[0115] R(k+1)=[r(k+1) r(k+2)…r(k+P)] T

[0116] Where r(k+i) represents the reference value at time k+i, r(k+i)=[β r ω r ] Τ , β r is the reference center of mass sideslip angle, ω r is the reference yaw rate.

[0117] During steady-state driving, the vehicle's center of mass lateral slip angular velocity is Yaw angular acceleration Substituting into the above state space equation we get:

[0118]

[0119] in, is the stability coefficient, β d is the ideal center of mass sideslip angle, ω d is the ideal yaw rate.

[0120] The reference center of mass slip angle is set to 0 to ensure the stability of the vehicle at high speed. Considering that the road adhesion condition will impose certain constraints on the yaw rate, the reference center of mass slip angle and reference yaw rate used for optimization can be expressed as:

[0121]

[0122] Where μ is the road adhesion coefficient and g is the acceleration due to gravity.

[0123] In order to achieve the ideal control effect, the actual yaw rate and sideslip angle should be made to coincide with the corresponding ideal values ​​as quickly as possible, while taking into account the control range of the vehicle's yaw moment. The objective function is selected as follows:

[0124]

[0125] Among them, Γ y,i is the weight matrix of the output error predicted in the i-th step, Γ u,i is the weight matrix of the control increment predicted at step i, Γ y,i ,Γ u,i are all diagonal matrices.

[0126] Set the constraints as follows:

[0127]

[0128] Among them, the subscripts max and min correspond to the maximum and minimum values ​​respectively.

[0129] Rewrite the objective function into matrix form:

[0130] J(x(k),ΔU(k),m MPC ,P)=||Γ y (Y P (k+1|k)-R(k+1))|| 2 +||Γ u ΔU(k)|| 2

[0131] Among them, Γ y =diag(Γ y,1 ,Γ y,2 ,…,Γ y,P ), Γ u =diag(Γ u,1 ,Γ u,2 ,…,Γ u,P ).

[0132] The optimal control sequence ΔU can be obtained * (k) is:

[0133]

[0134] E P (k+1|k)=R(k+1)-S x Δx(k)-Ν y y(k)-S Ψ ΔΨ(k)

[0135] Take ΔU * The first item in the (k) sequence gives the current control input, i.e. u(k) = u(k-1) + Δu(k), which is the current required yaw moment value M. Z The additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution.

[0136] Lower-level controller

[0137] Tire utilization can characterize the stability margin of the tire and can be selected as the optimization target. Since the lateral force of the tire is uncontrollable, only the longitudinal force of the tire is considered, and the objective function is:

[0138]

[0139] Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheel (subscript i=1, 2 represents front and rear, subscript j=1, 2 represents left and right, 11 represents the left front wheel, 12 represents the right front wheel, 21 represents the left rear wheel, and 22 represents the right rear wheel).

[0140] The following constraints must be met when distributing the braking force:

[0141]

[0142] Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can generate, and μ1 is the road adhesion coefficient at low attachment points.

[0143] By combining the objective function and the constraints, the braking force required for each wheel can be obtained, and the brakes can be controlled to generate the target braking force, thereby ensuring the stable driving of the vehicle.

[0144] Further, step 6.2 is described in detail:

[0145] This controller is designed in a hierarchical manner. The upper-layer controller inputs the difference between the vehicle's yaw rate and sideslip angle and the reference yaw rate and sideslip angle, and outputs the additional yaw moment and rear wheel angle. The lower-layer controller distributes the braking torque based on the required longitudinal braking force and required yaw moment.

[0146] Upper controller

[0147] A two-degree-of-freedom model of the vehicle is established, and the state variables are selected as the sideslip angle β and the yaw rate ω. The state space equation is as follows:

[0148]

[0149] Among them, δ r Indicates the rear wheel turning angle.

[0150] State variable x = [β ω] Τ, output y = [β ω] Τ , control quantity u=[δ r M Z ] Τ , δ f The front wheel angle is a known quantity and can be used as a system disturbance, which can be written as the following state equation:

[0151]

[0152] in,

[0153]

[0154] The above state space equation is discretized and rewritten into incremental form, and the optimal control sequence ΔU is obtained through model predictive control. * (k) The detailed steps are given above, and only a brief description is given below.

[0155] Set the constraints as follows:

[0156]

[0157] Among them, the subscripts max and min correspond to the maximum and minimum values ​​respectively.

[0158] Take the optimal control sequence ΔU * The first term of (k) can be used to obtain the output of the upper controller, the rear wheel angle δ r and additional yaw moment M Z δ r Send it to the steering system, and the rear wheel steering motor makes the wheel reach the corresponding angle, thereby generating the corresponding additional yaw moment. Z Sent to the lower-level controller as the target for braking force distribution.

[0159] Lower-level controller

[0160] Tire utilization can characterize the stability margin of the tire and can be selected as the optimization target. Since the lateral force of the tire is uncontrollable, only the longitudinal force of the tire is considered, and the objective function is:

[0161]

[0162] The following constraints must be met when distributing the braking force:

[0163]

[0164] Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T maxis the maximum braking torque that the brake can produce, is the peak adhesion coefficient, and μ2 is the road adhesion coefficient at the high adhesion point (assuming the left side is a low adhesion road and the right side is a high adhesion road).

[0165] The maximum braking force that can be generated by the ground is maintained at the maximum value at the low attachment point. d When the brakes are turned in the opposite direction, the difference in braking force between the left and right sides can be minimized, which means that the yaw moment generated by braking on the opposite road can be minimized. The remaining additional yaw moment is compensated by the yaw moment generated by the rear wheel angle.

[0166] By combining the objective function and the constraints, the braking force required for each wheel can be obtained, and the brake can be controlled to generate the target braking force, thereby generating the target additional yaw moment.

[0167] Further, step 7 is described in detail:

[0168] When the value of |ω+B1β| rises to exceed B2, direct yaw moment control and active four-wheel steering are used to ensure vehicle stability.

[0169] Upper controller

[0170] A two-degree-of-freedom model of the vehicle is established, and the state variables are selected as the sideslip angle β and the yaw rate ω. The state space equation is as follows:

[0171]

[0172] State variable x = [β ω] Τ , output y = [β ω] Τ , control quantity u=[δ f δ r M Z ] Τ , then the state equation:

[0173]

[0174] in,

[0175]

[0176] The above state space equation is discretized and rewritten into incremental form, and the optimal control sequence ΔU is obtained through model predictive control. * (k) The detailed steps are given above, and only a brief description is given below.

[0177] Set the constraints as follows:

[0178]

[0179] Among them, the subscripts max and min correspond to the maximum and minimum values ​​respectively.

[0180] Take the optimal control sequence ΔU * The first term of (k) can be used to obtain the output of the upper controller, namely the front wheel angle δ f , rear wheel turning angle δ r and additional yaw moment M Z δ f ,δ r It is sent to the steering system controller, which uses the steering motor to make the wheels reach the corresponding turning angle, thereby generating the corresponding additional yaw moment. Z Sent to the lower-level controller as the target for braking force distribution.

[0181] Lower-level controller

[0182] Tire utilization can characterize the stability margin of the tire and can be selected as the optimization target. Since the lateral force of the tire is uncontrollable, only the longitudinal force of the tire is considered, and the objective function is:

[0183]

[0184] The following constraints must be met when distributing the braking force:

[0185]

[0186] Among them, μ1 is the road adhesion coefficient of low adhesion, and μ2 is the road adhesion coefficient of high adhesion. It is assumed that the left side is a low adhesion road and the right side is a high adhesion road.

[0187] By combining the objective function and the constraints, the braking force required for each wheel can be obtained, and the brake can be controlled to generate the target braking force, thereby generating the target additional yaw moment.

[0188] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the lateral stability of a vehicle when braking on a split road, characterized in that: include: Collect vehicle data, calculate the average angular deceleration difference Δα on both sides based on the vehicle data, and fuse the average angular deceleration difference Δα on both sides with the steady-state area of ​​the ω-β phase plane to form a comprehensive risk index M for split road stability, where ω is the vehicle's yaw rate and β is the sideslip angle at the center of mass. Set the comprehensive risk index threshold M th , when M≤M th When M>M th When M≤M th And the duration exceeds the set threshold t th ; The average angular deceleration difference Δα on both sides is calculated based on the vehicle data, specifically: According to the left front wheel angular velocity ω 11 , right front wheel angular velocity ω 12 , left rear wheel angular velocity ω 21 and the right rear wheel angular velocity ω 22 , calculate the angular deceleration of each wheel by time difference, and get the angular deceleration of the left front wheel α 11 , right front wheel angular deceleration α 12 , left rear wheel angular deceleration α 21 and the right rear wheel angular deceleration α 22 ; Calculate the average angular deceleration α on the left side L and the right average angular deceleration α R for: Then the average angular deceleration difference Δα on both sides is: Dα=α L -a R ; The comprehensive risk index M of the split road stability is: Among them, α th is the threshold of the absolute value of the difference between the average angular deceleration on both sides, B=|ω+B1β| is the stability evaluation index of the ω-β phase plane, and B th is the threshold of B, λ1 and λ2 are weight coefficients, and λ1+λ2=1; The control strategy is to judge the stability through the ω-β phase plane. When |ω+B1β|≤B2, the maximum braking intensity z that the vehicle can produce on the low-adhesion road is compared. th and the expected braking intensity z d , if z d ≤z th , execute controller 1 to regulate the braking force at high and low attachment points; if z d >z th , execute controller 2 to keep the braking force at the low attachment point at the peak value, only regulate the braking force at the high attachment point, and control the rear wheel angle at the same time; when |ω+B1β|>B2, execute controller 3 to make the active four-wheel steering intervene; among them, coefficients B1 and B2 are boundary parameters.

2. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The vehicle data includes vehicle yaw rate, sideslip angle of center of mass, longitudinal speed, lateral speed, angular velocity corresponding to each wheel, steering wheel angle and brake pedal travel.

3. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The maximum braking intensity z that the vehicle can produce on low-adhesion roads th =μ1, μ1 is the road adhesion coefficient at low attachment point.

4. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The expected braking intensity z d Obtained by: Based on fuzzy control, the braking intention is recognized, and the brake pedal stroke and brake pedal operation speed are used as the input of the braking intention recognition, and the expected braking intensity z is used as the input of the braking intention recognition. d As the output of braking intention recognition.

5. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The controller adopts a hierarchical design; the input of the upper controller is the vehicle yaw rate ω and the reference yaw rate ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β r The output is the additional yaw moment M Z , the additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution; The lower controller takes tire utilization as the optimization target, and the objective function J is: Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively; The following constraints are met when distributing the braking force: Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can generate, μ1 is the road adhesion coefficient at low attachment, m is the sprung mass of the vehicle, and g is the acceleration due to gravity; The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

6. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The controller 2 adopts a hierarchical design; the input of the upper controller is the vehicle yaw rate ω and the reference yaw rate ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β r The output is the additional yaw moment M Z and rear wheel turning angle δ r ; Set the rear wheel angle δ r Send it to the steering system, and the rear wheel steering motor makes the wheel reach the corresponding turning angle, thereby generating the corresponding additional yaw moment; the additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution; The lower controller takes tire utilization as the optimization target, and the objective function J is: Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively; The following constraints are met when distributing the braking force: Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can produce, is the peak adhesion coefficient, μ2 is the road adhesion coefficient at high adhesion, m is the sprung mass of the vehicle, g is the acceleration of gravity, the left side is a low adhesion road, and the right side is a high adhesion road; The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

7. The method for controlling lateral stability of a vehicle during braking on an on-road surface according to claim 1, wherein: The controller 3 adopts a hierarchical design; the input of the upper controller is the vehicle yaw rate ω and the reference yaw rate ω r Deviation of the center of mass sideslip angle β and the reference center of mass sideslip angle β r The output is the front wheel steering angle δ f , rear wheel turning angle δ r and additional yaw moment M Z ; Set the front wheel angle δ f and rear wheel turning angle δ r Send it to the steering system, and the steering motor makes the wheels reach the corresponding turning angle, thereby generating the corresponding additional yaw moment; the additional yaw moment M Z Sent to the lower-level controller as the target for braking force distribution; The lower controller takes tire utilization as the optimization target, and the objective function J is: Among them, μ ij is the road adhesion coefficient corresponding to the wheel, F xij is the longitudinal force acting on the wheel, F zij is the vertical force acting on the wheels, and subscripts 11, 12, 21, and 22 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively; The following constraints are met when distributing the braking force: Among them, F x is the total longitudinal force of the vehicle, D is the wheel track, R W is the effective radius of the wheel, T max is the maximum braking torque that the brake can generate, μ1 is the road adhesion coefficient at low adhesion, μ2 is the road adhesion coefficient at high adhesion, m is the sprung mass of the vehicle, g is the acceleration of gravity, the left side is a low adhesion road, and the right side is a high adhesion road; The lower-level controller combines the objective function and constraints to calculate the braking force required for each wheel, controls the brake to generate the target braking force, and thus generates the target additional yaw moment.

8. A lateral stability control system for a vehicle when braking on a split road, characterized in that: include: Vehicle data acquisition unit, vehicle stability monitoring unit and split road braking lateral stability control unit; The vehicle data collection unit collects vehicle data; The vehicle stability monitoring unit calculates the average angular deceleration difference Δα on both sides based on the vehicle data, and fuses the average angular deceleration difference Δα on both sides with the steady-state area of ​​the ω-β phase plane to form a comprehensive risk index M for split road stability, where ω is the vehicle's yaw rate and β is the center of mass sideslip angle; Set the comprehensive risk index threshold M th , when M≤M th When M>M th When the lateral stability control unit starts the control strategy for braking on open roads, it will continue until M≤M th And the duration exceeds the set threshold t th ; The average angular deceleration difference Δα on both sides is calculated based on the vehicle data, specifically: According to the left front wheel angular velocity ω 11 , right front wheel angular velocity ω 12 , left rear wheel angular velocity ω 21 and the right rear wheel angular velocity ω 22 , calculate the angular deceleration of each wheel by time difference, and get the angular deceleration of the left front wheel α 11 , right front wheel angular deceleration α 12 , left rear wheel angular deceleration α 21 and the right rear wheel angular deceleration α 22 ; Calculate the average angular deceleration α on the left side L and the right average angular deceleration α R for: Then the average angular deceleration difference Δα on both sides is: Dα=α L -a R ; The comprehensive risk index M of the split road stability is: Among them, α th is the threshold of the absolute value of the difference between the average angular deceleration on both sides, B=|ω+B1β| is the stability evaluation index of the ω-β phase plane, and B th is the threshold of B, λ1 and λ2 are weight coefficients, and λ1+λ2=1; the control strategy activated by the split road braking lateral stability control unit is: stability is judged by the ω-β phase plane, when |ω+B1β|≤B2, the maximum braking intensity z that the vehicle can produce on the low-adhesion road is compared th and the expected braking intensity z d , if z d ≤z th , execute controller 1 to regulate the braking force at high and low attachment points; if z d >z th , execute controller 2 to keep the braking force at the low attachment point at the peak value, only regulate the braking force at the high attachment point, and control the rear wheel angle at the same time; when |ω+B1β|>B2, execute controller 3 to make the active four-wheel steering intervene; among them, coefficients B1 and B2 are boundary parameters.

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