A body stability control method based on a distributed drive electric vehicle

Abstract

The application discloses a body stability control method based on a distributed drive electric vehicle, which comprises the following steps: step one, establishing a phase plane stability formula to determine the intervention proportion of the vehicle lateral stability controller; step two, establishing a single-wheel and double-wheel switching controller, and formulating a single-wheel control rule of single-wheel driving or braking and a double-wheel control rule of diagonal wheel driving or braking; and step three, based on the principle of outputting few control quantities, when being within a set range, single-wheel driving or braking is adopted, and when being beyond the set range, the double-wheel control rule is adopted. The single-wheel or double-wheel driving and braking control is realized through cooperative control, the influence on the driving behavior of the driver is greatly reduced under the premise of ensuring the lateral stability of the vehicle, and the loss of the longitudinal speed of the vehicle is reduced.

Description

Technical Field

[0001] This invention relates to a vehicle stability control method for distributed drive electric vehicles, belonging to the field of automotive technology. Background Technology

[0002] Currently, the methods for controlling the vehicle stability of distributed drive vehicles include: (1) Single-wheel braking adjustment, which selects the wheel to be controlled by judging whether the vehicle is understeer or oversteer. Single-wheel braking has a significant impact on longitudinal vehicle speed, and the braking torque applied to the wheel to correct the yaw moment is often large, which has a significant impact on the driver's driving behavior; (2) Same-side dual-wheel braking adjustment, which judges whether the left or right wheel of the vehicle is braked by the vehicle's steering direction. Same-side dual-wheel braking is prone to vehicle sideslip when the road surface adhesion coefficients on both sides are different, and has a significant impact on the vehicle's longitudinal speed.

[0003] Compared to existing vehicle stability control methods on the market, the technical problem this invention aims to solve is to provide a vehicle stability control method based on distributed drive electric vehicles. By establishing a phase-plane stability formula, the intervention ratio of the vehicle's lateral stability controller is determined, resulting in additional yaw moment and additional front wheel steering angle. This allows the established cooperative control rules to smoothly implement and deactivate the additional yaw moment and additional front wheel steering angle. Furthermore, by establishing a single / dual-wheel control switching controller, four-wheel control rules are formulated for single-wheel drive or braking and diagonal wheel drive or braking. This ensures vehicle lateral stability within a certain range, adhering to a smaller control output and employing single-wheel drive or braking; beyond this range, diagonal dual-wheel control rules are adopted. While maintaining vehicle lateral stability, this significantly reduces the impact on driver behavior, minimizes longitudinal speed loss, and improves vehicle fuel economy. Summary of the Invention

[0004] This invention designs and develops a vehicle stability control method based on distributed drive electric vehicles. Through cooperative control, it realizes drive / braking control of single or dual wheels, which greatly reduces the impact on the driver's driving behavior and reduces the loss of longitudinal speed of the vehicle while ensuring the lateral stability of the vehicle.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for vehicle stability control based on distributed drive electric vehicles, comprising:

[0007] Step 1: Establish the phase plane stability formula and determine the intervention ratio of the vehicle's lateral stability controller;

[0008] Step 2: Establish a single / dual wheel switching controller, and formulate single-wheel control rules for single-wheel drive / braking and dual-wheel control rules for diagonal wheel drive / braking;

[0009] Based on the cooperative control strategy, a single / dual wheel switching controller is established, including:

[0010] Collaborative control strategies include upper and lower layers;

[0011] The upper layer consists of a collaborative controller, while the lower layers consist of an AFS controller and a DYC controller.

[0012] The upper-level controller receives the actual vehicle sideslip angle and actual sideslip velocity, and determines the coordinated control coefficients q for the AFS controller and DYC controller in the lower-level controller based on the established phase plane strategy. afs ,q dyc ;

[0013] The AFS controller calculates the additional front wheel steering angle and combines it with the steering system to obtain the final front wheel steering angle; the DYC controller calculates the additional yaw moment.

[0014] Step 3: Based on the principle of minimizing the control input, when the output value is within the set control threshold range, single-wheel drive or braking is adopted; when it exceeds the set threshold range, dual-wheel control is adopted.

[0015] Preferably, in step one, the established phase plane stability formula is:

[0016]

[0017] In the formula, β is the centroid sideslip angle. denoted as the centroid sideslip angular velocity, μ as the road surface adhesion coefficient, and vx as the vehicle's longitudinal speed.

[0018] Preferably, in step two, the cooperative control coefficients of the AFS controller and the DYC controller satisfy q. afs =1-q dyc .

[0019] Preferably, step three includes:

[0020] When the vehicle's center of gravity sideslip angle does not meet the requirements This indicates that the vehicle is in an unstable state, at which point the AFS controller needs to intervene to restore the vehicle to stability;

[0021] In the formula, P1 is the slope and P2 is the intercept;

[0022] When the AFS controller exceeds the control threshold, the DYC controller is used for supplementary adjustment.

[0023] When the collaborative controller determines that the DYC controller needs to intervene, it establishes a switching control rule at the lower level, using the magnitude of the yaw rate difference as the signal:

[0024]

[0025] In the formula, Δγ represents the actual yaw rate γ and the desired yaw rate γ. d The dynamic difference, σ is a constant, taken as an empirical value of 0.165, e n The decision coefficient for the single / dual wheel switching controller;

[0026] When e n If the value is ≤0, a single-wheel braking control strategy is adopted;

[0027] When e n >0, adopt diagonal dual-wheel control.

[0028] Preferably, it also includes:

[0029] When the vehicle is traveling straight and the front wheel steering angle is 0, no additional adjustments are made to the vehicle's four-wheel drive or braking force. When the DYC controller intervenes, it determines the current magnitudes of δ and Δγ, and then obtains e through the single / dual wheel switching controller. n The magnitude of the torque applied is calculated from the above three parameter values ​​to determine the wheel that needs to be controlled, and then the magnitude of the torque applied is calculated, including:

[0030] When a vehicle turns left, if δ>0 and Δγ>0 are met, the vehicle is oversteering, and e n If the value is greater than 0, then the left rear wheel will be braked, and the braking torque will be -T. rl At this point, a driving torque T is applied to the right front wheel of the vehicle. fr ; when e n If the value is less than 0, a single-wheel braking strategy is adopted, and the right front wheel is selected for braking.

[0031] When a vehicle turns left, if the conditions δ>0 and Δγ<0 are met, the vehicle is understeering, and e n If the value is greater than 0, then the right front wheel will be braked, and the braking torque will be -T. fr At this point, a driving torque T is applied to the left rear wheel of the vehicle. rl ; when e n <0, select to brake the left rear wheel;

[0032] When a vehicle turns right, if the conditions δ < 0 and Δγ > 0 are met, the vehicle is oversteering, and e n If the value is greater than 0, then the right rear wheel will be braked, and the braking torque will be -T. rr At this point, a driving torque T is applied to the left front wheel of the vehicle. rl ; when e n <0, select to brake the left front wheel;

[0033] When a vehicle turns right, if δ < 0 and Δγ < 0, the vehicle is understeering, and e n If the value is greater than 0, then the left front wheel will be braked, and the braking torque will be -T. rl At this point, a driving torque T is applied to the right rear wheel of the vehicle. rr ; when e n <0, select to brake the right rear wheel;

[0034] In the formula, δ is the front wheel steering angle, Δγ is the dynamic difference between the actual yaw rate and the desired yaw rate, and e n The decision coefficient for the single / dual wheel switching controller.

[0035] Preferably, it also includes:

[0036] The formula for distributing the drive / braking torque T of the four wheels is as follows:

[0037] T = T fl +T rl +T fr +T rr ;

[0038] Among them, taking the direction of car travel as the positive direction, T fl T rl T fr T rr These are the drive / braking torques for the front left, rear left, front right, and rear right wheels of the vehicle, respectively.

[0039] The additional yaw moment generated by the torque of the four wheels should meet the vehicle's drive / braking control requirements:

[0040]

[0041] In the formula: d is the wheel track, and the front and rear wheel tracks are set to be equal; R is the wheel rolling radius;

[0042] The formula for calculating the yaw moment generated by the four wheels during distribution is as follows:

[0043]

[0044] Where: M Zfl Yaw moment distributed to the left front wheel; M Zfr Yaw moment distributed to the right front wheel; M Zrl Yaw moment distributed to the left rear wheel; M Zrr Yaw moment distributed to the right rear wheel;

[0045] Based on the vertical load on the front and rear axles, when using diagonal dual-wheel distribution to distribute the direct yaw moment, ΔM is:

[0046]

[0047] When single-wheel braking is used to distribute the direct yaw moment, ΔM is:

[0048] ΔM=M Zfl =M Zfr =M Zrl =M Zrr ;

[0049] In the formula: a and b are the distances from the center of mass to the front and rear axes, respectively.

[0050] Preferably, the upper limits of the desired yaw rate and the centroid deflection angle need to satisfy:

[0051]

[0052] In the formula, v x For the longitudinal speed of the car, γ max β is the upper limit of the yaw rate. max denoted as the upper limit of the centroid sideslip angle, μ as the road surface adhesion coefficient, and g as the gravitational acceleration.

[0053] Preferably, the desired yaw rate and desired sideslip angle of the vehicle are:

[0054]

[0055] In the formula, γd is the desired yaw rate, β d Let sgn() be the expected centroid sideslip angle, δ be the sign function, and δ be the front wheel steering angle.

[0056] The beneficial effects of this invention are as follows:

[0057] This vehicle stability control method based on distributed drive electric vehicles switches between single and dual wheel control, executes four-wheel control rules of single-wheel drive / braking and diagonal wheel drive / braking, reduces the impact on driver behavior, minimizes longitudinal speed loss to ensure vehicle economy, and greatly improves vehicle responsiveness and lateral stability. Attached Figure Description

[0058] Figure 1 This is a block diagram of the collaborative control strategy described in this invention.

[0059] Figure 2 This is a diagram of the synergistic intervention ratio coefficients described in this invention.

[0060] Figure 3 This is the test path diagram for the double line shifting described in this invention.

[0061] Figure 4 This is a graph showing the change in longitudinal velocity loss under low adhesion coefficient as described in this invention.

[0062] Figure 5 This is a yaw rate response curve under low adhesion coefficient as described in this invention.

[0063] Figure 6 This is a lateral acceleration response curve under low adhesion coefficient as described in this invention.

[0064] Figure 7 This is a graph showing the centroid side slip angle response curve under low adhesion coefficient as described in this invention.

[0065] Figure 8 This is a graph showing the change in longitudinal velocity loss under high adhesion coefficient as described in this invention.

[0066] Figure 9 This is a yaw rate response curve under high adhesion coefficient as described in this invention.

[0067] Figure 10 This is a lateral acceleration response curve under high adhesion coefficient as described in this invention.

[0068] Figure 11 This is a graph showing the centroid side slip angle response curve under high adhesion coefficient as described in this invention. Detailed Implementation

[0069] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0070] like Figure 1-11 As shown, this invention provides a vehicle stability control method for distributed drive electric vehicles. Through cooperative control, it achieves single-wheel or dual-wheel drive / braking control, significantly reducing the impact on driver behavior while ensuring vehicle lateral stability. The method includes:

[0071] Step 1: Establish the phase plane stability formula and determine the intervention ratio of the vehicle's lateral stability controller;

[0072] Step 2: Establish a single / dual wheel switching controller, and formulate single-wheel control rules for single-wheel drive or braking and dual-wheel control rules for diagonal wheel drive or braking;

[0073] Step 3: Based on the principle of minimizing the control output, when the output is within the set range, single-wheel drive or braking is adopted; when the output exceeds the set range, dual-wheel control is adopted.

[0074] like Figure 1As shown, to better improve the synergistic effect of the Active Front Wheel Steering (AFS) controller and the Direct Yaw Moment Control (DYC) controller in a distributed drive vehicle, a collaborative control strategy is adopted. In this strategy, the upper-level controller receives the actual vehicle center-of-gravity sideslip angle and the actual sideslip angular velocity. Based on the established phase plane strategy, it determines the coordination control coefficients q for the AFS controller and the DYC controller in the lower-level controller. afs ,q dyc The lower-level controllers include the AFS controller and the DYC controller. The AFS controller calculates the additional front wheel steering angle and combines it with the steering system to obtain the front wheel steering angle. The DYC controller calculates the additional yaw moment and then controls the drive / braking torque of one or more wheels. The cooperative controller executes the work of the AFS controller and the DYC controller according to the real-time driving status of the vehicle. When the cooperative controller fails, it will not affect the normal operation of the AFS controller and the DYC controller, which greatly improves the reliability of the chassis control systems.

[0075] First, based on the reaction to the vehicle's lateral stability Phase plane formula (1):

[0076]

[0077] Equation (1) describes the vehicle stability margin boundary, where β is the sideslip angle of the center of gravity. Let P1 be the sideslip velocity, and P2 be the slope and intercept of the vehicle's longitudinal speed v. x Boundary coefficients related to the road adhesion coefficient μ vary depending on the vehicle's longitudinal speed v. x Different boundary coefficients can be obtained by combining the road surface adhesion coefficient μ, and the results can be obtained by fitting the parameters:

[0078] P1 = 0.82μ 2 +4.6μ+2.7;

[0079]

[0080] Based on the phase plane control strategy and the double straight line method, the phase plane graphs were plotted at vehicle speeds of 60km / h, 90km / h, and 30km / h, with adhesion coefficients of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1, respectively, and the slope of the fitting parameter p1 was determined.

[0081] Table 1 Different v x The values ​​of slope p1 and intercept p2 under μ

[0082]

[0083]

[0084] By performing spline interpolation on the three sets of data in Table 1, the fitting formulas for slope and intercept versus road surface adhesion coefficient are shown in equations (2) and (3):

[0085] Slope:

[0086] P1 = 0.82μ 2 +4.6μ+2.7; (2)

[0087] intercept:

[0088] P3 = 0.037 μ 2 +0.14μ-0.00029; (3)

[0089] The intercept and slope parameters of the double-straight-line method are set for different vehicle speeds on the same road surface with a coefficient of adhesion of 0.9, as shown in Table 2:

[0090] Table 2 Different v x The values ​​of the slope p1 and intercept p2 under the given conditions

[0091] Vehicle speed (km / h) slope intercept 20 -4.762 0.2721 40 -4.254- 0.1854 60 -3.125 0.1415 80 -3.827 0.1368 100 -3.030 0.1313 120 -2.667 0.1184

[0092] The relationship between the intercept and vehicle speed, derived from the fitting in Table 2, is as follows:

[0093] P4 = 3 × 10 -4 v x 2 -0.017v x +0.34; (4)

[0094] By combining the relationship between the intercept and the road adhesion coefficient (3) and the relationship between the intercept and the vehicle speed (4), a more accurate fit is obtained for the relationship with longitudinal vehicle speed v. x The intercept relationship P2 between the road surface adhesion coefficient μ and the required change is finally obtained as the fitting formula for intercept P2:

[0095]

[0096] Therefore, the invention described herein The phase plane formula is established as follows:

[0097]

[0098] According to the phase plane formula, if the vehicle's center of gravity sideslip angle does not satisfy the equation... This indicates that the vehicle is in an unstable state, at which point the AFS controller needs to intervene to restore stability to the vehicle.

[0099] However, the AFS controller has limited adjustment capabilities. To improve the adjustment margin and expand the adjustable range, a DYC controller is used for supplementary adjustment. When the AFS controller exceeds the threshold, it will gradually exit.

[0100] Selecting the S-shaped membership function for the cooperability coefficient q afs Solving for (x) yields equation (6):

[0101]

[0102] In the formula, N1 and N2 are the boundary values ​​of the working judgment area of ​​the cooperative controller, and x is the judgment value obtained from the functional relationship of the judgment vehicle's location area, with a threshold value of N1 = 0.8P2.

[0103] Meanwhile, the cooperative control coefficients of the AFS controller and the DYC controller satisfy q afs =1-q dyc The proportional control settings for the AFS controller and DYC controller are as follows: Figure 2 As shown.

[0104] If the DYC controller needs to intervene after the judgment of the collaborative controller (upper-level controller), a switching controller with the magnitude of the yaw rate difference as the signal is established in the torque distribution layer, as shown in formula (7).

[0105]

[0106] In the formula, Δγ represents the actual yaw rate γ and the desired yaw rate γ. d The dynamic difference, σ is a constant, taken as an empirical value of 0.165, e n The decision coefficient for the single / dual wheel switching controller.

[0107] Based on the characteristic of independently controllable individual wheels in distributed drive electric vehicles, the dynamic difference Δγ between the actual and desired yaw rates, along with the front wheel steering angle δ, is used as inputs to the logic controller to determine understeer and oversteer during vehicle turns. To further enhance handling capabilities and optimize driving behavior, a diagonal dual-wheel control strategy is adopted, as shown in Table 3.

[0108] Table 3 Wheel Control Rules

[0109]

[0110]

[0111] Based on the wheel control rules in Table 3, when the vehicle is traveling straight, i.e., when the front wheel steering angle is 0, no additional adjustments are applied to the vehicle's four-wheel drive or braking force; when the DYC controller intervenes, it determines the current magnitudes of δ and Δγ, and then obtains e through the single / dual wheel switching controller. n The required wheel size is calculated from the above three parameter values, and then the applied torque is calculated.

[0112] When a vehicle turns left, satisfying the conditions δ>0 and γ>0, the vehicle is oversteering, and e n If the value is greater than 0, then the left rear wheel will be braked, and the braking torque will be -T. rl To compensate for longitudinal velocity loss and correct yaw moment, a driving torque T is applied to the right front wheel of the vehicle. fr This allows the vehicle to maintain lateral stability while minimizing longitudinal speed loss; if e n <0, at this time the difference is very small, that is, the yaw moment that needs to be corrected is small, and a single-wheel braking strategy is adopted, selecting to brake the right front wheel to adjust the lateral stability of the vehicle.

[0113] Similarly, when the vehicle turns left, satisfying the conditions δ>0 and Δγ<0, the vehicle is understeering, and the switching controller output value is e. n >0, select to brake the right front wheel, size -T fr Give the vehicle a driving torque T to the left rear wheel rl If e n <0, select to brake the left rear wheel to adjust the vehicle's lateral stability.

[0114] Similarly, when a vehicle turns right, satisfying the conditions δ<0, Δγ>0, the vehicle is oversteering, and e n If the value is greater than 0, then the right rear wheel will be braked, with a value of -T. rr Give the vehicle a driving torque T to the left front wheel rl If e n <0, select to brake the left front wheel to adjust the vehicle's lateral stability.

[0115] Similarly, when a vehicle turns right, satisfying the conditions δ < 0 and Δγ < 0, the vehicle is understeering, and e n If the value is greater than 0, then select to brake the left front wheel, with a value of -T. rl Give the right rear wheel of the vehicle a driving torque T rr If e n <0, select to brake the right rear wheel to adjust the vehicle's lateral stability.

[0116] According to the wheel control rules, the torque distribution of the four wheels of a distributed drive electric vehicle should also meet the overall vehicle drive requirements; since the front wheel steering angle is very small, the simplified formula for the distribution of drive / braking torque T is:

[0117] T = T fl +T rl +T fr +T rr (8)

[0118] In the formula: T fl T rl T fr T rr These are the driving / braking torques for the front left, rear left, front right, and rear right wheels of the vehicle, respectively.

[0119] The additional yaw moment generated by the torque of the four wheels should meet the overall vehicle drive / braking control requirements, namely:

[0120]

[0121] In the formula: d is the wheel track, and it is assumed that the front and rear wheel tracks are equal; R is the wheel rolling radius.

[0122] Based on the principle of elliptical friction in tires:

[0123]

[0124] In the formula: F xi For the longitudinal force of the tire; F yi F is the lateral force of the tire. Zi This refers to the vertical load on the tire.

[0125] Therefore, the following must be satisfied when allocating driving / braking forces:

[0126]

[0127] The formula for calculating the yaw moment generated by the four wheels during distribution is as follows:

[0128]

[0129] Where: M Zfl Yaw moment distributed to the left front wheel; M Zfr Yaw moment distributed to the right front wheel; M Zrl Yaw moment distributed to the left rear wheel; M Zrr Yaw moment distributed to the right rear wheel.

[0130] Based on the vertical load on the front and rear axles, when using diagonal dual-wheel distribution to distribute the direct yaw moment, ΔM is:

[0131]

[0132] When single-wheel braking is used to distribute the direct yaw moment, ΔM is:

[0133] ΔM=MZfl =M Zfr =M Zrl =M Zrr (14)

[0134] In the formula: a and b are the distances from the center of mass to the front and rear axes, respectively.

[0135] The magnitude of the torque distributed to the four wheels is calculated by formula (12), and its sign is determined by the controlled rules in Table 3. Finally, the wheel torque that corrects the yaw moment is output.

[0136] The solution process for the vehicle's yaw rate and sideslip angle is as follows:

[0137] Based on the linear two-degree-of-freedom reference model of the whole vehicle, the state-space equation is obtained as shown in equation (15).

[0138]

[0139] In the formula, The angular velocity of the center of mass deflection. Let v be the yaw acceleration, m be the total mass of the vehicle, and β be the sideslip angle at the center of mass. β = v / v x v is the lateral velocity of the car, v x γ is the longitudinal velocity of the car, γ is the yaw rate, a and b are the distances from the center of mass to the front and rear axles respectively, δ is the front wheel steering angle, and C is the yaw rate. f C r These are the front and rear axle lateral stiffness, I Z M represents the moment of inertia of the entire vehicle about the Z-axis. Z This is the direct yaw moment.

[0140] When a vehicle travels at a constant speed under a step input to the front wheel angle, entering a steady-state response is called constant-velocity circular motion. Substituting into equation (15), the initial yaw rate γ0 and the initial centroid sideslip angle β0 of the vehicle can be obtained by using a linear two-degree-of-freedom model of the whole vehicle:

[0141]

[0142] In the formula, K is the vehicle stability factor, l is the wheelbase, and v x This represents the longitudinal speed of the vehicle.

[0143] Meanwhile, the expected yaw rate is limited by the tire-road adhesion coefficient, and the center-of-gravity sideslip angle takes into account the influence of the road adhesion coefficient; therefore, the upper limits of both must satisfy:

[0144]

[0145] In the formula, v x For the longitudinal speed of the car, γ maxβ is the upper limit of the yaw rate. max denoted as the upper limit of the centroid sideslip angle, μ as the road surface adhesion coefficient, and g as the gravitational acceleration.

[0146] Therefore, according to equations (16) and (18), the desired yaw rate and desired sideslip angle of the car are:

[0147]

[0148] In the formula, γ d For the desired yaw rate, β d Let sgn() be the expected centroid sideslip angle, and let sgn() be the sign function.

[0149] The setup process for the AFS controller and DYC controller is as follows:

[0150] The AFS controller is based on the sliding mode control principle. The difference between the actual yaw rate and the desired yaw rate is selected as the control error e1 of the AFS controller, which is e1 = γ - γ d .

[0151] Define the sliding surface switching function S1 as follows:

[0152]

[0153] In the formula, λ is the convergence rate coefficient, λ>0, and the larger λ is, the faster the convergence rate. Used to limit steady-state error.

[0154] By differentiating the sliding surface switching function S1 in equation (20), we obtain:

[0155]

[0156] In the formula, It is the first reciprocal of the control error e1.

[0157] Combine formula (15), and Substituting into equation (11), the equivalent control input δ is obtained as:

[0158]

[0159] In the formula, Let I be the desired yaw rate, γ be the actual yaw rate of the vehicle, and I be the yaw rate of the vehicle. Z v is the vehicle's moment of inertia. x β is the longitudinal velocity of the vehicle, β is the sideslip angle of the vehicle's center of gravity, and e1 is the control error of the AFS controller.

[0160] The final control law for the AFS controller is determined as follows:

[0161] δafs =δ-k1sgn(S1); (23)

[0162] Where: δ afs The additional front wheel steering angle is given; k1 is the rate of change of speed of the system's state point moving to the switching surface. When k1 is large, the movement speed is faster, and the chattering during control is also greater.

[0163] The DYC controller is established based on the sliding mode principle, selecting the difference between the actual yaw rate and the desired yaw rate, and the difference between the actual center-of-gravity sideslip angle and the desired center-of-gravity sideslip angle, as the control error e of the DYC system, i.e.:

[0164] e=(γ-γ d )+ρ(β-β d ); (twenty four)

[0165] In the formula, ρ is a positive weighting coefficient. When the road surface adhesion coefficient μ is small, stability is improved by increasing ρ.

[0166] Therefore, the relation for ρ is defined as:

[0167]

[0168] The slid surface switching function S of the constructed slid controller is:

[0169]

[0170] In the formula: λ is a positive weighting coefficient.

[0171] Differentiating the above equation, we get:

[0172]

[0173] Combined formula (15), Substituting into equation (27) yields M Z Due to system uncertainties, the equivalent expression for the DYC controller's control law is ultimately determined as follows:

[0174] ΔM=M Z -ksgn(S); (28)

[0175] In the formula, ΔM is the additional yaw moment of the final output of the system; k is the rate of change of velocity of the system state point moving to the switching surface, and M Z To be Substituting the defined sliding surface switching function into the formula for differentiation, we obtain the equivalent control input.

[0176] Therefore, the final formulas for the additional front wheel steering angle and the additional yaw moment are:

[0177] δ afs=δ-k1sgn(S1); (29)

[0178] ΔM=M Z -ksgn(S); (30)

[0179] Therefore, by combining the output coefficients of the two controllers from the cooperative controller, the additional front wheel steering angle δ is finally obtained. afs The formula for the direct yaw moment ΔM is:

[0180] δ afs =q afs ×(δ-k1sgn(S1)); (31)

[0181] ΔM=q dyc ×(M Z -ksgn(S)); (32)

[0182] Equations (31) and (32) respectively obtain the front wheel steering angle and the additional direct yaw moment obtained by the torque distribution layer through the steering system.

[0183] In Carsim 2019 software, set up the dual-track changeover test simulation environment. The dual-track changeover test path is as follows: Figure 3 As shown; in the simulation of the double lane change test, the road adhesion coefficients were selected as 0.45 for a wet and slippery road surface and 0.85 for a good road surface, with an initial speed of 78 km / h. To verify the superiority of the single / dual wheel drive / braking coordinated control used in this invention when it is not coordinated with its independent action, and when it is based on the individual braking coordinated action, the simulation analysis results are compared as shown in the curves. Figures 4 to 11 As shown.

[0184] Curve comparisons show that the control effect based on single / dual-wheel drive / braking coordinated control is significantly improved. In particular, the curve response index when it acts independently without coordination is significantly better than the control effect under single braking coordinated action. Furthermore, the longitudinal speed loss of the vehicle based on single / dual-wheel drive / braking coordinated control is very small, which greatly improves the economy of the vehicle during driving.

[0185] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for vehicle stability control based on distributed drive electric vehicles, characterized in that, include: Step 1: Establish the phase plane stability formula and determine the intervention ratio of the vehicle's lateral stability controller; Step 2: Establish a single / dual wheel switching controller, and formulate single-wheel control rules for single-wheel drive / braking and dual-wheel control rules for diagonal wheel drive / braking; Based on the cooperative control strategy, a single / dual wheel switching controller is established, including: Collaborative control strategies include upper and lower layers; The upper layer consists of a collaborative controller, while the lower layers consist of an AFS controller and a DYC controller. The upper-level controller receives the actual vehicle sideslip angle and actual sideslip velocity, and determines the coordinated control coefficients for the AFS controller and DYC controller in the lower-level controller based on the established phase plane strategy. , ; The AFS controller calculates the additional front wheel steering angle and combines it with the steering system to obtain the final front wheel steering angle; the DYC controller calculates the additional yaw moment. Step 3: Based on the principle of minimizing control input, when the output value is within the set control threshold range, single-wheel drive or braking is applied; when it exceeds the set threshold range, dual-wheel control is applied, including: When the vehicle's center of gravity sideslip angle does not meet the requirements This indicates that the vehicle is in an unstable state, at which point the AFS controller needs to intervene to restore the vehicle to stability; In the formula, The slope The intercept; When the AFS controller exceeds the control threshold, the DYC controller is used for supplementary adjustment. When the collaborative controller determines that the DYC controller needs to intervene, it establishes a switching control rule at the lower level, using the magnitude of the yaw rate difference as the signal: ； In the formula, in the formula: Actual yaw rate With the expected yaw rate The dynamic difference, Let be a constant, and take the empirical value of 0.

165. The decision coefficient for the single / dual wheel switching controller; when At that time, a single-wheel braking control strategy is adopted; when At that time, diagonal dual-wheel control is adopted.

2. The vehicle stability control method for a distributed drive electric vehicle according to claim 1, characterized in that, In step one, the established formula for phase plane stability is: ； In the formula, The sideslip angle is the angle of the centroid. The angular velocity of the center of mass deflection. The road surface adhesion coefficient, This refers to the vehicle's longitudinal speed.

3. The vehicle stability control method for a distributed drive electric vehicle according to claim 2, characterized in that, In step two, the cooperative control coefficients of the AFS controller and the DYC controller satisfy... .

4. The vehicle stability control method for a distributed drive electric vehicle according to claim 3, characterized in that, Also includes: When the vehicle is traveling straight, and the front wheel angle is 0, no additional adjustments are made to the vehicle's four-wheel drive or braking force. When the DYC controller intervenes, it determines the current... and Size, and then obtained through a single / double wheel switching controller. The magnitude of the torque applied is calculated from the above three parameter values ​​to determine the wheel that needs to be controlled, and then the magnitude of the torque applied is calculated, including: When the vehicle turns left, the following conditions are met. Under certain conditions, the vehicle is oversteering, and Then, select to brake the left rear wheel, with a braking torque of - At this point, a driving torque is applied to the right front wheel of the vehicle. ;when A single-wheel braking strategy was adopted, selecting to brake the right front wheel; When the vehicle turns left, the following conditions are met. Under certain conditions, the vehicle is understeering, and Then, select to brake the right front wheel, with a braking torque of - At this point, a driving torque is applied to the left rear wheel of the vehicle. ;when Select to brake the left rear wheel; When the vehicle turns right, it meets the requirements. Under certain conditions, the vehicle is oversteering, and Then, select to brake the right rear wheel, with a braking torque of - At this point, a driving torque is applied to the vehicle's left front wheel. ;when Select to brake the left front wheel; When the vehicle turns right, it meets the requirements. Under certain conditions, the vehicle is understeering, and Then, select to brake the left front wheel, and the braking torque is - At this point, a driving torque is applied to the right rear wheel of the vehicle. ;when Select to brake the right rear wheel; In the formula, For the front wheel steering angle, This represents the dynamic difference between the actual yaw rate and the desired yaw rate. The decision coefficient for the single / dual wheel switching controller.

5. The vehicle stability control method for a distributed drive electric vehicle according to claim 4, characterized in that, Also includes: The formula for distributing the drive / braking torque T of the four wheels is as follows: ； Among them, the direction of car travel is taken as the positive direction. These are the drive / braking torques for the front left, rear left, front right, and rear right wheels of the vehicle, respectively. The additional yaw moment generated by the torque of the four wheels should meet the vehicle's drive / braking control requirements: ； In the formula: d is the wheel track, and the front and rear wheel tracks are set to be equal; R is the wheel rolling radius; The formula for calculating the yaw moment generated by the four wheels during distribution is as follows: ； In the formula, Yaw moment distributed to the left front wheel, Yaw moment distributed to the right front wheel Yaw moment distributed to the left rear wheel Yaw moment distributed to the right rear wheel; Based on the vertical load on the front and rear axles, when using diagonal dual-wheel distribution to distribute the direct yaw moment... for: ； When using single-wheel braking to distribute direct yaw moment for: ； In the formula, , These are the distances from the center of mass to the front and rear axles, respectively. This refers to the wheelbase.

6. The vehicle stability control method for a distributed drive electric vehicle according to claim 5, characterized in that, The upper limits of the desired yaw rate and the center-of-mass sideslip angle need to satisfy: ； In the formula, For the longitudinal speed of the car, This represents the upper limit of the yaw rate. This is the upper limit of the centroid sideslip angle. denoted as the road surface adhesion coefficient, and g is the acceleration due to gravity.

7. The method for vehicle stability control in a distributed drive electric vehicle according to claim 6, characterized in that, The desired yaw rate and desired sideslip angle of the car are: ； In the formula, For the desired yaw rate, Let sgn() be the expected centroid sideslip angle, and let sgn() be the sign function. For the front wheel steering angle, The initial yaw rate of the vehicle. The initial centroid sideslip angle.

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