A distributed electric drive semi-trailer vehicle train lateral stability control method

Abstract

The present invention belongs to the technical field of electric semi-trailer vehicle train control, and specifically relates to a distributed electric drive semi-trailer vehicle train lateral stability control method, the control method comprising the following steps: 1) establishing a vehicle dynamics model; 2) designing the upper lateral stability controller of the tractor and trailer based on the sliding mode control (SMC) algorithm and considering the influence of the articulation angle on the lateral stability of the trailer; 3) making stability judgment on the upper controller; 4) using the equal proportion distribution method on the lower layer to distribute the wheel torque. Compared with the existing distributed electric drive semi-trailer vehicle train lateral stability control method based on PID control, the present invention can reduce the yaw angular velocity, the sideslip angle of the center of mass and the articulation angle of the tractor and trailer, and effectively improve the stability and safety of the semi-trailer vehicle train when it is running at high speed.

Description

Technical Field

[0001] The invention belongs to the technical field of electric semi-trailer vehicle train control, and in particular relates to a distributed electric drive semi-trailer vehicle train lateral stability control method. Background Art

[0002] Distributed electric drive technology is to install the drive motor inside or near the wheel, directly transmit the torque to the wheel, and each wheel is independently controllable, with the advantages of compact structure, high energy efficiency, and fast response. Semi-trailer trains are vehicle combinations consisting of tractors and trailers connected by articulated devices. They have high transportation efficiency and are the main body of high-speed cargo transportation. However, due to the long body, high center of mass, and coupling relationship between the tractor and trailer of semi-trailer trains, lateral instability such as folding, tail swinging, and lateral shimmy are prone to occur when driving on high-speed, low-adhesion roads, which seriously affects driving safety. Combining distributed electric drive technology with semi-trailer trains provides a new direction for improving the lateral stability control of semi-trailer trains.

[0003] The present invention proposes a lateral stability control method for a distributed electric drive semi-trailer vehicle train considering the influence of the articulation angle, applies the distributed electric drive technology to the semi-trailer vehicle train, and designs a direct yaw moment hierarchical control system. The upper layer adopts sliding mode control to calculate the additional yaw moment required by the tractor and the trailer. The tractor obtains the additional yaw moment required by the tractor by tracking the ideal center of mass sideslip angle and yaw angular velocity by the vehicle state. The trailer considers the influence of the articulation angle on the lateral stability of the trailer, and obtains the additional yaw moment required by the trailer by tracking the ideal yaw angular velocity and articulation angle by the vehicle state; the lower layer is torque distribution control, which adopts an equal proportion distribution method. The present invention can effectively improve the stability and safety of the semi-trailer vehicle train when it is traveling at high speed. Summary of the invention

[0004] In order to solve the problems that semi-trailer trains are prone to lateral instability when traveling on high-speed and low-adhesion roads, such as folding, tail swinging and lateral swinging, the present invention proposes a distributed electric drive semi-trailer train lateral stability control method considering the influence of the articulation angle, which can achieve precise control of the lateral stability of the semi-trailer train and improve the stability and safety of the semi-trailer train when traveling.

[0005] A distributed electric drive semi-trailer vehicle train lateral stability control method, the specific steps are as follows:

[0006] S1. Establish vehicle dynamics model;

[0007] S2. Based on the SMC control algorithm and considering the influence of the articulation angle on the lateral stability of the trailer, design the lateral stability controller of the tractor and trailer upper layer;

[0008] The upper layer adopts sliding mode control to calculate the additional yaw moment required by the tractor and trailer. The tractor obtains the additional yaw moment required by the tractor by tracking the ideal sideslip angle and yaw rate of the center of mass from the vehicle state. The trailer considers the influence of the articulation angle on the lateral stability of the trailer and obtains the additional yaw moment required by the trailer by tracking the ideal yaw rate and articulation angle from the vehicle state.

[0009] S3, using Lyapunov method to determine the stability of the upper controller;

[0010] S4. Under the framework of the hierarchical control system for the lateral stability of a distributed electric drive semi-trailer vehicle train, a lower-level torque distribution controller is designed based on the proportional distribution method.

[0011] Furthermore, the specific process of step S1 is as follows:

[0012] S1.1. Establish the state space equation of the linear three-degree-of-freedom reference model:

[0013]

[0014] The state vector X = [β1 ω1 β2 ω2],

[0015] Input vector u = [δ f ],

[0016] Coefficient Matrix

[0017]

[0018]

[0019] Among them: a 11 =(c+a1)k1+(c-b1)k2;

[0020]

[0021] a 21 =k1+k2;

[0022]

[0023] a 23 =k3;

[0024] a 33 =(a2+b2)k3;

[0025]

[0026] Where: m1 and m2 are the total mass of the tractor and trailer, kg;

[0027] a1 and a2 are the distances from the center of mass of the tractor and trailer to the front axle, m;

[0028] b1 and b2 are the distances from the center of mass of the tractor and trailer to the rear axle, m;

[0029] ω1 and ω2 are the yaw angular velocities of the tractor and trailer, rad / s;

[0030] β1 and β2 are the sideslip angles of the tractor and trailer respectively, rad;

[0031] I z1 ,I z2 are the rotational inertia of the tractor and trailer, kg·m 2 ;

[0032] k1 and k2 are the lateral stiffness of the front and rear wheels of the tractor, N / rad;

[0033] k3 is the lateral stiffness of the rear wheels of the trailer, N / rad;

[0034] θ is the articulation angle, rad;

[0035] c is the distance from the center of mass of the tractor to the articulation point, m;

[0036] δ f is the front wheel turning angle of the tractor, rad.

[0037] S1.2. Establish a distributed electric drive motor model:

[0038]

[0039] Where: T m is the driving or braking torque actually output by the hub motor, N·m;

[0040] is the driving or braking torque expected by the wheel hub motor, N·m;

[0041] ξ is the physical characteristic constant of the motor.

[0042] Furthermore, the specific process of step S2 is as follows:

[0043] S2.1. Determination of ideal value of reference model

[0044] The state quantity of the three-degree-of-freedom linear reference model is taken as the ideal value of the model

[0045] The ideal value of the sideslip angle of the tractor's center of mass is:

[0046]

[0047] The ideal value of the yaw rate of the tractor is:

[0048]

[0049] The ideal value of the trailer's yaw rate is:

[0050]

[0051] The value of the articulation angle of the semi-trailer train is constrained by the yaw angular velocity of the tractor and trailer. The ideal value of the articulation angle is:

[0052]

[0053] S2.2. Upper controller design

[0054] S2.2.1. Design of sliding mode controller for tractor

[0055] Taking the deviation between the actual value and the ideal value of the yaw rate and the sideslip angle as the control target, the sliding surface s1 is designed as:

[0056]

[0057] Derivative of s1

[0058]

[0059] Wherein, c1 and c2 are system control parameters, and c1>0, c2>0.

[0060] The controller approach rate selects the exponential approach rate:

[0061] In the formula, ε1 and k1 are control coefficients, and ε1>0, k1>0.

[0062] make Then, combining formulas (4)-(6), we can get the ideal deviation as:

[0063]

[0064] Therefore, the additional yaw moment of the tractor is:

[0065]

[0066] In order to further weaken the chattering, the saturation function sat(s / Δ) is used to replace the sign function sgn(s). The saturation function is defined as:

[0067]

[0068] Therefore, the final additional yaw moment of the tractor is:

[0069]

[0070] Where: c1, c2 are system control parameters, and c1>0, c2>0; ε1, k1 are control coefficients, and ε1>0, k1>0; Δ is the thickness of the sliding mode boundary layer, and Δ>0;

[0071] S2.2.2. Design of sliding mode controller for trailer

[0072] Taking the deviation between the actual value and the ideal value of the yaw angular velocity and the articulation angle as the control target, the sliding surface s2 is designed as:

[0073]

[0074] Derivative of s2

[0075]

[0076] Wherein, c3 and c4 are system control parameters, and c3>0, c4>0.

[0077] The controller approach rate selects the exponential approach rate:

[0078] In the formula, ε2 and k2 are control coefficients, and ε2>0, k2>0.

[0079] make Combining equations (11)-(13), we can get the ideal deviation as:

[0080]

[0081] Therefore, the additional yaw moment of the trailer is:

[0082]

[0083] In order to further weaken the chattering, the saturation function is used Substituting the sign function sgn(s), the trailer saturation function is defined the same as the tractor:

[0084] Therefore, the final additional yaw moment of the trailer is:

[0085]

[0086] In the formula: c3 and c4 are system control parameters, and c3>0, c4>0; ε2 and k2 are control coefficients, and ε2>0, k2>0.

[0087] Furthermore, the specific process of step S3 is as follows:

[0088] The Lyapunov method is used to determine the stability of the tractor and trailer control system. The Lyapunov function is:

[0089]

[0090] Taking the first-order derivative of formula L, we get:

[0091]

[0092] For traction vehicle control systems there are:

[0093]

[0094] Since the parameters c1>0, c2>0, ε1>0, k1>0, Δ1>0 are selected, Therefore, the tractor control system is stable;

[0095] Similarly, the trailer control system has:

[0096]

[0097] Since the parameters c3>0, c4>0, ε2>0, k2>0, Δ2>0 are selected, So the trailer control system is stable.

[0098] Furthermore, the specific process of step S4 is as follows:

[0099] Ignoring the rolling resistance of the tire, the dynamic equation of the wheel is:

[0100] T i =F xi R (22)

[0101] The torque output constraint of a single wheel hub motor can be expressed as: dmax ≤T i ≤T dmax

[0102] The longitudinal force of the tire is affected by the road adhesion coefficient μ and the tire vertical load F zi The constraints are:

[0103] -μF zi R≤T i ≤μF zi R (23)

[0104] The torque is distributed in equal proportion, that is, the absolute value of the additional torque on the coaxial wheels is the same:

[0105]

[0106]

[0107] Where: T is the wheel torque, T1,2 is the torque of the left and right wheels on the rear axle of the tractor, T 3,4 Indicates the torque of the left and right wheels on the rear axle of the trailer, T dmax is the peak torque of the hub motor, N·m; F xi is the wheel longitudinal force, F zi is the tire vertical load, N; R is the wheel rolling radius, m; μ is the road adhesion coefficient; D1 and D2 represent the rear axle wheelbase of the tractor and the rear axle wheelbase of the trailer, m;

[0108] The driving or braking of the wheel needs to be determined based on the sign of the steering wheel angle and the yaw rate deviation. For example, if turning left is positive, when the steering wheel angle is greater than zero, if the actual yaw rate is less than the ideal yaw rate, it indicates that the vehicle is understeering, then the left wheel is braked and the right wheel is driven.

[0109] The beneficial technical effects of the present invention are:

[0110] The present invention considers the influence of the articulation angle on the semi-trailer train, combines the distributed electric drive technology, builds a distributed electric drive semi-trailer train model, and designs a direct yaw moment control strategy to improve the stability of the vehicle when it is running at high speed. First, a three-degree-of-freedom linear reference model is established to provide the ideal value of the vehicle state quantity. The controller is designed using a hierarchical control concept. The upper layer is the additional yaw moment control. Based on the sliding mode control, the deviation between the ideal value and the actual value of the state quantity of the tractor and trailer is controlled respectively, and the additional yaw moment of the tractor and trailer is obtained respectively; the lower layer is the torque distribution controller, which adopts the proportional distribution method. According to the total driving torque, the additional yaw moment requirements of the tractor and trailer and other constraints, the driving or braking torque of each hub motor is obtained. Compared with PID control, the designed sliding mode control strategy reduces the yaw angular velocity, the sideslip angle of the center of mass and the articulation angle of the tractor and trailer, and effectively improves the stability and safety of the semi-trailer train when it is running at high speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Figure 1 It is a three-degree-of-freedom linear reference model;

[0112] Figure 2 It is a block diagram of the yaw stability control structure of a distributed electric drive semi-trailer train;

[0113] Figure 3 This is a schematic diagram of the simulation results of the yaw angular velocity of the tractor;

[0114] Figure 4 This is a schematic diagram of the simulation results of the trailer's yaw angular velocity;

[0115] Figure 5 It is a schematic diagram of the simulation results of the hinge angle;

[0116] Figure 6 This is a schematic diagram of the simulation results of the sideslip angle of the tractor's center of mass;

[0117] Figure 7 This is a schematic diagram of the simulation results of the sideslip angle of the trailer's center of mass;

[0118] Figure 8 It is the phase diagram of “center of mass sideslip angle-center of mass sideslip angle change rate” of the tractor;

[0119] Fig. 9 This is the phase diagram of "center of mass sideslip angle-center of mass sideslip angle change rate" of the trailer. DETAILED DESCRIPTION

[0120] In conjunction with the accompanying drawings, a method for controlling the lateral stability of a distributed electric drive semi-trailer vehicle train taking into account the influence of the articulation angle is further described below.

[0121] A distributed electric drive semi-trailer vehicle train lateral stability control method specifically comprises the following steps:

[0122] S1. Establish vehicle dynamics model

[0123] S1.1, the state space equation of the linear three-degree-of-freedom reference model is:

[0124]

[0125] Where the state vector X = [β1 ω1 β2 ω2];

[0126] Input vector u = [δ f ];

[0127] Coefficient Matrix

[0128]

[0129]

[0130] Among them: a 11 =(c+a1)k1+(c-b1)k2;

[0131]

[0132] a 21 =k1+k2;

[0133]

[0134]

[0135] a 33 =(a2+b2)k3;

[0136]

[0137] Where: m1 and m2 are the total mass of the tractor and trailer, kg;

[0138] a1 and a2 are the distances from the center of mass of the tractor and trailer to the front axle, m;

[0139] b1 and b2 are the distances from the center of mass of the tractor and trailer to the rear axle, m;

[0140] ω1 and ω2 are the yaw angular velocities of the tractor and trailer, rad / s;

[0141] β1 and β2 are the sideslip angles of the tractor and trailer respectively, rad;

[0142] I z1 ,I z2 are the rotational inertia of the tractor and trailer, kg·m 2 ;

[0143] k1 and k2 are the lateral stiffness of the front and rear wheels of the tractor, N / rad;

[0144] k3 is the lateral stiffness of the rear wheels of the trailer, N / rad;

[0145] θ is the articulation angle, rad;

[0146] c is the distance from the center of mass of the tractor to the articulation point, m;

[0147] δ f is the front wheel turning angle of the tractor, rad.

[0148] S1.2, the distributed electric drive motor model is:

[0149]

[0150] Where: T m is the driving or braking torque actually output by the hub motor, N·m;

[0151] is the driving or braking torque expected by the wheel hub motor, N·m;

[0152] ξ is the physical characteristic constant of the motor.

[0153] S2. Based on S1, design a yaw stability controller:

[0154] S2.1. Determination of ideal value of reference model

[0155] The state quantity of the three-degree-of-freedom linear reference model is taken as the ideal value of the model

[0156] The ideal value of the sideslip angle of the tractor's center of mass is:

[0157]

[0158] The ideal value of the yaw rate of the tractor is:

[0159]

[0160] The ideal value of the trailer's yaw rate is:

[0161]

[0162] The value of the articulation angle of the semi-trailer train is constrained by the yaw angular velocity of the tractor and trailer. The ideal value of the articulation angle is:

[0163]

[0164] S2.2. Upper controller design

[0165] S2.2.1. Design of sliding mode controller for tractor

[0166] Taking the deviation between the actual value and the ideal value of the yaw rate and the sideslip angle as the control target, the sliding surface s1 is designed as:

[0167]

[0168] Derivative of s1

[0169]

[0170] Wherein, c1 and c2 are system control parameters, and c1>0, c2>0.

[0171] The controller approach rate selects the exponential approach rate:

[0172] In the formula, ε1 and k1 are control coefficients, and ε1>0, k1>0.

[0173] make Then, combining formulas (4)-(6), we can get the ideal deviation as:

[0174]

[0175] Therefore, the additional yaw moment of the tractor is:

[0176]

[0177] In order to further weaken the chattering, the saturation function sat(s / Δ) is used to replace the sign function sgn(s). The saturation function is defined as:

[0178]

[0179] Therefore, the final additional yaw moment of the tractor is:

[0180]

[0181] Where: c1, c2 are system control parameters, and c1>0, c2>0; ε1, k1 are control coefficients, and ε1>0, k1>0; Δ is the thickness of the sliding mode boundary layer, and Δ>0;

[0182] S2.2.2. Design of sliding mode controller for trailer

[0183] Taking the deviation between the actual value and the ideal value of the yaw angular velocity and the articulation angle as the control target, the sliding surface s2 is designed as:

[0184]

[0185] Derivative of s2

[0186]

[0187] Wherein, c3 and c4 are system control parameters, and c3>0, c4>0.

[0188] The controller approach rate selects the exponential approach rate:

[0189] In the formula, ε2 and k2 are control coefficients, and ε2>0, k2>0.

[0190] make Combining equations (11)-(13), we can get the ideal deviation as:

[0191]

[0192] Therefore, the additional yaw moment of the trailer is:

[0193]

[0194] In order to further weaken the buffeting, the saturation function sat(s / Δ) is used to replace the sign function sgn(s). The definition of the trailer saturation function is the same as that of the tractor:

[0195] Therefore, the final additional yaw moment of the trailer is:

[0196]

[0197] In the formula: c3 and c4 are system control parameters, and c3>0, c4>0; ε2 and k2 are control coefficients, and ε2>0, k2>0.

[0198] S3. The specific process of using Lyapunov method to determine the stability of the upper controller is:

[0199] The Lyapunov method is used to determine the stability of the tractor and trailer control system. The Lyapunov function is:

[0200]

[0201] Taking the first-order derivative of formula L, we get:

[0202]

[0203] For traction vehicle control systems there are:

[0204]

[0205] Since the parameters c1>0, c2>0, ε1>0, k1>0, Δ1>0 are selected, Therefore, the tractor control system is stable;

[0206] Similarly, the trailer control system has:

[0207]

[0208] Since the parameters c3>0, c4>0, ε2>0, k2>0, Δ2>0 are selected, So the trailer control system is stable.

[0209] S4. Under the framework of the hierarchical control system for the lateral stability of the distributed electric drive semi-trailer vehicle train, based on the proportional distribution method, the specific process of designing the lower-layer torque distribution controller is as follows:

[0210] Ignoring the rolling resistance of the tire, the dynamic equation of the wheel is:

[0211] T i =F xi R (22)

[0212] The torque output constraint of a single wheel hub motor can be expressed as: dmax ≤T i ≤T dmax

[0213] The longitudinal force of the tire is affected by the road adhesion coefficient μ and the tire vertical load F zi The constraints are:

[0214] -μF zi R≤T i ≤μF zi R (23)

[0215] The torque is distributed in equal proportion, that is, the absolute value of the additional torque on the coaxial wheels is the same:

[0216]

[0217]

[0218] Where: T is the wheel torque, T 1,2 is the torque of the left and right wheels on the rear axle of the tractor, T 3,4 Indicates the torque of the left and right wheels on the rear axle of the trailer, T dmax is the peak torque of the hub motor, N·m; F xi is the wheel longitudinal force, F zi is the tire vertical load, N; R is the wheel rolling radius, m; μ is the road adhesion coefficient; D1 and D2 represent the rear axle wheelbase of the tractor and the rear axle wheelbase of the trailer, m;

[0219] The driving or braking of the wheel needs to be determined based on the sign of the steering wheel angle and the yaw rate deviation. For example, if turning left is positive, when the steering wheel angle is greater than zero, if the actual yaw rate is less than the ideal yaw rate, it indicates that the vehicle is understeering, then the left wheel is braked and the right wheel is driven.

[0220] Simulation verification and analysis

[0221] In order to verify the correctness and effectiveness of the designed control strategy, the control strategy built in MATLAB / Simulink is co-simulated with the vehicle model of the vehicle dynamics software TruckSim. There is no electric vehicle model in the TruckSim software, so the original transmission system in TruckSim needs to be modified, and a motor model is built in MATLAB / Simulink. The input torque of the motor model in MATLAB / Simulink is directly applied to the drive wheels through the input and output interface of the TruckSim software. In this embodiment, the parameters of the TruckSim software vehicle model are shown in Table 1.

[0222] Table 1 Vehicle model parameters

[0223] parameter Numeric parameter Numeric <![CDATA[m1]]> 6050kg <![CDATA[m2]]> 16930kg <![CDATA[a1]]> 1.4781m <![CDATA[a2]]> 4.6943m <![CDATA[b1]]> 2.4219m <![CDATA[b2]]> 3.8057m <![CDATA[I z1 ]]> <![CDATA[20830.8kg·m 2 ]]> <![CDATA[I z2 ]]> <![CDATA[120937.8kg·m 2 ]]> <![CDATA[k1]]> -438670N / rad <![CDATA[k2]]> -671820N / rad <![CDATA[k3]]> -761250N / rad c 1.5219m

[0224] In this embodiment, the simulation condition refers to the international standard ISO 3888-1-2018 for double lane change test, setting the constant vehicle speed to 80km / h and the road adhesion coefficient to 0.4. By comparing the stability under no control, sliding mode control, and PID control, the simulation results are as follows: Figures 3 to 9 The peak values ​​of each parameter curve are shown in Table 2.

[0225] Table 2 Peak values ​​of various parameter curves

[0226] <![CDATA[ω1(deg / s)]]> <![CDATA[ω2(deg / s)]]> <![CDATA[β1(deg)]]> <![CDATA[β2(deg)]]> θ(deg) Sliding Mode Control 11.17 10.95 -2.061 -1.882 -4.413 PID Control 11.46 11.29 -2.307 -2.218 -4.546 No Control 12.93 11.86 -2.794 -2.589 -5.076

[0227] like Figures 3 to 7 As shown in the figure, both sliding mode control and PID control effectively improve the yaw rate, sideslip angle and articulation angle characteristics of the tractor and trailer, and effectively limit the change of state quantity. Sliding mode control shows better control effect, making the state quantity yaw rate closer to the ideal value. Figure 8 , Fig. 9 As shown in the figure, the phase diagram of "center of mass slip angle-center of mass slip angle change rate" of the tractor and trailer converges and has a small range of change, indicating that the vehicle state is stable. As can be seen from the figure, the phase diagram of "center of mass slip angle-center of mass slip angle change rate" of the tractor and trailer can converge, and the phase diagram range of the sliding mode control is the smallest, which effectively limits the change of the vehicle's center of mass slip angle and has a better stability control effect.

[0228] It can be seen from Table 2 that the yaw angular velocity of the tractor under sliding mode control is 2.53% lower than that of PID control at the peak value, and is 13.61% lower than that of the uncontrolled state; the yaw angular velocity of the trailer is 3.01% lower than that of PID control at the peak value, and is 7.67% lower than that of the uncontrolled state; the sideslip angle of the tractor's center of mass is 10.66% lower than that of PID control at the peak value, and is 26.23% lower than that of the uncontrolled state; the sideslip angle of the trailer's center of mass is 15.14% lower than that of PID control at the peak value, and is 27.30% lower than that of the uncontrolled state; the articulation angle is 2.92% lower than that of PID control at the peak value, and is 13.06% lower than that of the uncontrolled state.

[0229] The present invention studies the lateral stability control problem of a semi-trailer vehicle train when traveling at high speed, applies distributed electric drive technology to the semi-trailer vehicle train, and designs a direct yaw moment hierarchical control system. The upper layer adopts sliding mode control to calculate the additional yaw moment required by the tractor and trailer. The tractor obtains the additional yaw moment required by the tractor by tracking the ideal center of mass sideslip angle and yaw angular velocity from the vehicle state. The trailer considers the influence of the articulation angle on the lateral stability of the trailer, and obtains the additional yaw moment required by the trailer by tracking the ideal yaw angular velocity and articulation angle from the vehicle state; the lower layer is torque distribution control, which adopts an equal-proportional distribution method.

[0230] The control strategy built in MATLAB / Simulink and the vehicle model of the vehicle dynamics software TruckSim were co-simulated to verify the correctness and effectiveness of the control strategy under high-speed, low-adhesion road double lane change conditions. The simulation results show that the designed sliding mode control strategy reduces the yaw rate, center of mass sideslip angle and articulation angle of the tractor and trailer compared to PID control, and effectively improves the stability and safety of the semi-trailer train when driving at high speed. Combining distributed electric drive technology with semi-trailer trains provides a new direction for improving the lateral stability control of semi-trailer trains.

[0231] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A distributed electric drive semi-trailer vehicle train lateral stability control method, characterized in that: The specific steps are as follows: S1. Establish vehicle dynamics model; S2. Based on the SMC control algorithm and considering the influence of the articulation angle on the lateral stability of the trailer, design the lateral stability controller of the tractor and trailer upper layer; The upper layer adopts sliding mode control to calculate the additional yaw moment required by the tractor and trailer. The tractor obtains the additional yaw moment required by the tractor by tracking the ideal sideslip angle and yaw rate of the center of mass from the vehicle state. The trailer considers the influence of the articulation angle on the lateral stability of the trailer and obtains the additional yaw moment required by the trailer by tracking the ideal yaw rate and articulation angle from the vehicle state. S3, using Lyapunov method to determine the stability of the upper controller; S4. Under the framework of the hierarchical control system for the lateral stability of a distributed electric drive semi-trailer vehicle train, a lower-level torque distribution controller is designed based on the proportional distribution method.

2. The method for controlling lateral stability of a distributed electric drive semi-trailer vehicle train according to claim 1 is characterized in that: The specific process of step S1 is as follows: S1.

1. Establish the state space equation of the linear three-degree-of-freedom reference model: The state vector X = [β1 ω1 β2 ω2], Input vector u = [δ f ], Coefficient Matrix Among them: a 11 =(c+a1)k1+(c-b1)k2; a 21 =k1+k2; <h2 style=";text-align:left;direction:ltr">a<h2 style=";text-align:left;direction:ltr"> 23 <h2 style=";text-align:left;direction:ltr"> =k3;<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">a<h2 style=";text-align:left;direction:ltr"> 33 <h2 style=";text-align:left;direction:ltr"> (a2+b2)k3 Where: m1 and m2 are the total mass of the tractor and trailer, kg; a1 and a2 are the distances from the center of mass of the tractor and trailer to the front axle, m; b1 and b2 are the distances from the center of mass of the tractor and trailer to the rear axle, m; ω1 and ω2 are the yaw angular velocities of the tractor and trailer, rad / s; β1 and β2 are the sideslip angles of the tractor and trailer respectively, rad; I z1 ,I z2 are the rotational inertia of the tractor and trailer, kg·m 2 ; k1 and k2 are the lateral stiffness of the front and rear wheels of the tractor, N / rad; k3 is the lateral stiffness of the rear wheels of the trailer, N / rad; θ is the articulation angle, rad; c is the distance from the center of mass of the tractor to the articulation point, m; δ f is the front wheel turning angle of the tractor, rad; S1.

2. Establish a distributed electric drive motor model: Where: T m is the driving or braking torque actually output by the hub motor, N·m; is the driving or braking torque expected by the wheel hub motor, N·m; ξ is the physical characteristic constant of the motor.

3. The method for controlling lateral stability of a distributed electric drive semi-trailer vehicle train according to claim 1 is characterized in that: The specific process of step S2 is: S2.

1. Determination of ideal value of reference model The state quantity of the three-degree-of-freedom linear reference model is taken as the ideal value of the model The ideal value of the sideslip angle of the tractor's center of mass is: The ideal value of the yaw rate of the tractor is: The ideal value of the trailer's yaw rate is: The value of the articulation angle of the semi-trailer train is constrained by the yaw angular velocity of the tractor and trailer. The ideal value of the articulation angle is: S2.

2. Upper controller design S2.2.

1. Design of sliding mode controller for tractor Taking the deviation between the actual value and the ideal value of the yaw rate and the sideslip angle as the control target, the sliding surface s1 is designed as: Derivative of s1 In the formula, c1 and c2 are system control parameters, and c1>0, c2>0; The controller approach rate selects the exponential approach rate: In the formula, ε1 and k1 are control coefficients, and ε1>0, k1>0; make Then, combining formulas (4)-(6), we can get the ideal deviation as: Therefore, the additional yaw moment of the tractor is: In order to further weaken the chattering, the saturation function sat(s / Δ) is used to replace the sign function sgn(s). The saturation function is defined as: Therefore, the final additional yaw moment of the tractor is: Where: c1, c2 are system control parameters, and c1>0, c2>0; ε1, k1 are control coefficients, and ε1>0, k1>0; Δ is the thickness of the sliding mode boundary layer, and Δ>0; S2.2.

2. Design of sliding mode controller for trailer Taking the deviation between the actual value and the ideal value of the yaw angular velocity and the articulation angle as the control target, the sliding surface s2 is designed as: Derivative of s2 In the formula, c3 and c4 are system control parameters, and c3>0, c4>0; The controller approach rate selects the exponential approach rate: In the formula, ε2 and k2 are control coefficients, and ε2>0, k2>0; make Combining equations (11)-(13), we can get the ideal deviation as: Therefore, the additional yaw moment of the trailer is: In order to further weaken the buffeting, the saturation function sat(s / Δ) is used to replace the sign function sgn(s). The definition of the trailer saturation function is the same as that of the tractor: Therefore, the final additional yaw moment of the trailer is: In the formula: c3 and c4 are system control parameters, and c3>0, c4>0; ε2 and k2 are control coefficients, and ε2>0, k2>0.

4. The method for controlling lateral stability of a distributed electric drive semi-trailer vehicle train according to claim 1, characterized in that: The specific process of step S3 is: The Lyapunov method is used to determine the stability of the tractor and trailer control system. The Lyapunov function is: Taking the first-order derivative of formula L, we get: For traction vehicle control systems there are: Since the parameters c1>0, c2>0, ε1>0, k1>0, Δ1>0 are selected, Therefore, the tractor control system is stable; Similarly, the trailer control system has: Since the parameters c3>0, c4>0, ε2>0, k2>0, Δ2>0 are selected, So the trailer control system is stable.

5. The method for controlling lateral stability of a distributed electric drive semi-trailer vehicle train according to claim 1, characterized in that: The specific process of step S4 is as follows: Ignoring the rolling resistance of the tire, the dynamic equation of the wheel is: T i =F xi R (22) The torque output constraint of a single wheel hub motor can be expressed as: dmax ≤T i ≤T dmax The longitudinal force of the tire is affected by the road adhesion coefficient μ and the tire vertical load F zi The constraints are: -μF zi R≤T i ≤μF zi R (23) The torque is distributed in equal proportion, that is, the absolute value of the additional torque on the coaxial wheels is the same: Where: T is the wheel torque, T 1,2 is the torque of the left and right wheels on the rear axle of the tractor, T 3,4 Indicates the torque of the left and right wheels on the rear axle of the trailer, T dmax is the peak torque of the hub motor, N·m; F xi is the wheel longitudinal force, F zi is the tire vertical load, N; R is the wheel rolling radius, m; μ is the road adhesion coefficient; D1 and D2 represent the rear axle wheelbase of the tractor and the trailer, m respectively.

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