Semitrailer lateral stability adaptive control method based on online identification of loading conditions

Abstract

The application relates to a semi-trailer transverse stability self-adaptive control method based on online identification of loading conditions, belongs to the field of intelligent commercial vehicle active safety control and vehicle transverse dynamics control, and comprises the following steps: acquiring vehicle dynamics parameters; calculating stability error; online identifying loading conditions; calculating additional yaw moment; and executing brake force distribution control; the application realizes online identification of semi-trailer loading and mass center height, and adaptively adjusts fuzzy PID control parameters according to the identification results, optimizes differential brake moment distribution, effectively suppresses the yaw instability, folding and side-slip risk of the semi-trailer under different loading conditions, and improves the transverse stability and control robustness of the vehicle under complex conditions.

Description

Technical Field

[0001] This invention belongs to the field of active safety control and lateral dynamics control of intelligent commercial vehicles, specifically relating to an adaptive control method for lateral stability of semi-trailers based on online identification of loading conditions. Background Technology

[0002] When semi-trailers are traveling at high speeds or performing emergency maneuvers such as double lane changes or slalom maneuvers, they are prone to dangerous phenomena such as excessive yaw rate, rapid increase in articulation angle, and even folding instability. Simultaneously, due to frequent changes in the cargo loading status of the trailer, the trailer's load and center of gravity height fluctuate significantly. Under different loading conditions, the total vehicle mass, yaw moment of inertia, and roll moment all change significantly, resulting in significant alterations to the vehicle's lateral dynamic characteristics.

[0003] Currently, lateral stability control for heavy vehicles often employs differential braking control strategies based on electronic stability programs, correcting vehicle attitude by applying yaw moment. However, existing control methods are typically designed based on fixed vehicle parameter models, assuming that vehicle mass and center of gravity height remain constant. For semi-trailers, the actual load range varies greatly during operation, and the center of gravity height changes significantly with the way cargo is stacked.

[0004] Therefore, existing technologies urgently need a new technical solution to address the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a semi-trailer lateral stability adaptive control method based on online identification of loading conditions. This method solves the problem that existing semi-trailer stability control methods do not fully consider the influence of load changes and center of gravity shift on lateral dynamic characteristics, resulting in inconsistent control effects under different loading conditions and easy folding or sideslip instability. At the same time, it solves the technical defects of traditional PID controllers, such as fixed parameters, difficulty in adapting to load changes, unreasonable braking torque distribution, and response lag.

[0006] To solve the above-mentioned technical problems, the present invention provides a semi-trailer lateral stability adaptive control method based on online identification of loading conditions, comprising the following steps, which are performed sequentially:

[0007] Step 1: Collect vehicle operating state variables using a high-precision inertial measurement unit (IMU), establish a coupled dynamic model of the tractor and trailer, and obtain vehicle dynamic parameters;

[0008] Step 2: Calculate the stability error using the ideal yaw rate reference model and the relationship between the additional yaw moment and braking moment generated by differential braking;

[0009] Step 3: Using the combined feature vector samples of trailer load and centroid height under simulation conditions, the K-medoids clustering algorithm is used to obtain cluster centers and construct a loading status database. Based on the real-time collected vehicle operation feature vectors, the Euclidean distance between the vehicle and each cluster center is calculated, and fuzzy rules are constructed based on the distance to identify loading conditions online.

[0010] Step 4: Calculate the additional yaw moment based on the control law of the fuzzy PID controller;

[0011] Step 5: Braking force distribution execution control.

[0012] The vehicle operating state variables mentioned in step one include the yaw rate r1 of the tractor, the yaw rate r2 of the trailer, the sideslip angle β1 of the tractor's center of gravity, the sideslip angle β2 of the trailer's center of gravity, the articulation angle θ, and the lateral acceleration a. y This constitutes the loading state feature vector X = [r1,r2,β1,β2,θ,a] y ].

[0013] The semi-trailer consists of a three-axle tractor and a three-axle trailer connected by a saddle hinge, and has yaw degree of freedom and hinge angle degree of freedom. The coupled dynamic model of the tractor and trailer includes lateral, yaw, and roll motion equations:

[0014] Lateral force balance equation of the tractor:

[0015] ,

[0016] In the formula: The total mass of the tractor unit; This refers to the sprung mass of the tractor unit. The lateral velocity of the tractor's center of gravity; The longitudinal velocity of the tractor's center of gravity; The yaw rate of the tractor unit; The side tilt angle of the tractor unit; This is the distance from the center of the sprung mass of the tractor to the roll axis; This represents the total lateral force on the front axle tires of the tractor unit. This represents the equivalent total lateral force of the tires on the rear axle of the tractor. This refers to the lateral interaction force between the tractor and trailer at the fifth wheel. The turning angle of the front wheels of the tractor;

[0017] The yaw moment balance equation for the tractor unit:

[0018] ,

[0019] In the formula: Let yaw moment of inertia be the moment of inertia of the tractor unit about its center of mass. The product of inertia of the tractor's yaw and tilt; This is the distance from the front axle of the tractor to its center of gravity. This is the equivalent distance from the rear axle of the tractor to the center of mass. This is the longitudinal distance from the fifth wheel to the center of gravity of the tractor unit;

[0020] The tractor's roll moment balance equation:

[0021] ,

[0022] In the formula: The moment of inertia of the tractor unit during lateral tilt; For tractor roll damping; For the tractor roll stiffness; The roll stiffness at the fifth wheel; This refers to the trailer's body roll angle; denoted as ρ, and ρ is the vertical distance from the fifth wheel to the tilt axis of the tractor; g is the acceleration due to gravity.

[0023] Trailer lateral force balance equation:

[0024] ,

[0025] In the formula: The total mass of the trailer; This refers to the sprung mass of the trailer; The lateral velocity of the trailer's center of gravity; The longitudinal velocity of the trailer's center of gravity; This refers to the trailer's yaw rate. This refers to the trailer's body roll angle; This is the distance from the center of the trailer's sprung mass to the roll axis; The equivalent total lateral force of the trailer axle to the tires; This refers to the longitudinal interaction force at the fifth stage; The articulation angle between the tractor and the trailer;

[0026] Trailer yaw moment balance equation:

[0027] ,

[0028] In the formula: Let the moment of inertia of the trailer about its center of mass be the yaw motion. The product of inertia of the trailer's yaw and tilt; This is the longitudinal distance from the trailer axle to the trailer's center of gravity. This is the longitudinal distance from the fifth wheel to the trailer's center of gravity;

[0029] Trailer roll moment balance equation:

[0030] ,

[0031] In the formula: This refers to the moment of inertia of the trailer during tilting. For trailer roll damping; For trailer roll stiffness; This is the vertical distance from the fifth wheel to the trailer's tilt axis;

[0032] Kinematic constraints between the tractor and trailer:

[0033] .

[0034] The ideal yaw rate reference model mentioned in step two is:

[0035] ,

[0036] In the formula: L is the wheelbase, K is the steering characteristic coefficient, g is the gravitational acceleration, and δ is the front wheel steering angle;

[0037] Define the yaw rate error of the tractor Its rate of change ec1, trailer yaw rate error and its rate of change ec2;

[0038] The relationship between the additional yaw moment generated by the differential braking and the braking torque is as follows:

[0039] ,

[0040] In the formula: t is the track width, and R is the effective radius of the wheel. These are the braking torques of the right and left wheels, respectively.

[0041] The specific method for identifying loading conditions in step three is as follows: Offline, different combinations of trailer load m2 and center of gravity height h2 are set. Feature vectors X under each condition are collected through simulation. The K-medoids clustering algorithm is used to classify the samples, obtaining k cluster centers. Each center corresponds to a set of known loading parameters ( This forms a loading status database;

[0042] During vehicle operation, the current feature vector is collected in real time. Calculate its Euclidean distance to each cluster center:

[0043] ,

[0044] In the formula: The yaw rate of the tractor at the current moment; Let be the yaw rate of the tractor at the i-th cluster center; This represents the yaw rate of the trailer at the current moment. Let yaw rate be the angular velocity of the trailer at the i-th cluster center; The sideslip angle of the tractor's center of gravity at the current moment; The sideslip angle of the tractor's centroid at the i-th cluster center; The sideslip angle of the trailer's center of gravity at the current moment; The trailer centroid sideslip angle at the i-th cluster center; The current articulation angle between the tractor and the trailer; The hinge angle of the i-th cluster center; The lateral acceleration at the current moment; Let be the lateral acceleration of the i-th cluster center;

[0045] Fuzzy rules are constructed based on distance, and the current trailer load is estimated through fuzzy inference. and center of mass height This enables online identification of loading conditions.

[0046] The method for calculating the additional yaw moment described in step four is as follows: a fuzzy PID controller is used, with the yaw angular velocity error e and its rate of change ec as inputs, and the additional yaw moment ΔM is output; the discretized form of the PID control law is as follows:

[0047] ,

[0048] In the formula: These are the proportional coefficient, integral time constant, and derivative time constant, respectively.

[0049] The braking force distribution execution control method described in step five is as follows: based on the additional yaw moment ΔM output by the fuzzy PID controller... z The braking wheels are determined by combining the steering direction and vehicle condition; the wheel selection rule is as follows:

[0050] ,

[0051] In the formula: Let be the lateral distance of the wheel relative to the center of mass; the relationship between the braking force of a single wheel and the additional yaw moment is:

[0052] ,

[0053] The braking torque of the target wheel is calculated according to the formula and output to the electronic braking system.

[0054] The beneficial effects of this invention are as follows: This invention is based on an online identification method for the lateral stability adaptive control of semi-trailers under loading conditions. It realizes the online identification of the trailer load and center of gravity height, and adaptively adjusts the fuzzy PID control parameters according to the identification results to optimize the differential braking torque distribution. This effectively suppresses the risks of yaw instability, folding and sideslip of semi-trailers under different loading conditions, and improves the lateral stability and control robustness of the vehicle under complex conditions. Attached Figure Description

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0056] Figure 1 This is a schematic diagram of the process of the adaptive control method for lateral stability of semi-trailers based on online identification of loading conditions according to the present invention.

[0057] Figure 2 This is a schematic diagram of the fuzzy PID controller structure of the semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to the present invention. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] An adaptive control method for lateral stability of a semi-trailer based on online identification of loading conditions includes the following steps:

[0060] Step 1: Vehicle Status Data Collection;

[0061] High-precision inertial measurement units (IMUs) are deployed on both the tractor and trailer to collect vehicle operating state variables. These variables include the tractor's yaw rate r1, the trailer's yaw rate r2, the tractor's sideslip angle β1, the trailer's sideslip angle β2, the articulation angle θ, and the lateral acceleration a. y This constitutes the loading state feature vector X = [r1,r2,β1,β2,θ,a] y The vehicle consists of a three-axle tractor and a three-axle trailer connected by a saddle hinge, possessing yaw and hinge angle degrees of freedom. A coupled dynamic model of the tractor and trailer is established, including equations for lateral, yaw, and roll motions.

[0062] The motion of the tractor is described by three equations: lateral force balance, yaw moment balance, and roll moment balance.

[0063] Lateral force equilibrium equation:

[0064] According to Newton's second law, the lateral inertial force of the tractor is balanced by the lateral force of the tires and the lateral force at the articulation point, while the lateral tilting motion of the sprung mass generates an additional inertial force.

[0065]

[0066] in:

[0067] The total mass of the tractor unit;

[0068] This refers to the sprung mass of the tractor unit.

[0069] The lateral velocity of the tractor's center of gravity;

[0070] The longitudinal velocity of the tractor's center of gravity;

[0071] The yaw rate of the tractor unit;

[0072] The side tilt angle of the tractor unit;

[0073] This is the distance from the center of the sprung mass of the tractor to the roll axis;

[0074] This represents the total lateral force on the front axle tires of the tractor unit.

[0075] This represents the equivalent total lateral force of the tires on the rear axle of the tractor.

[0076] This refers to the lateral interaction force between the tractor and trailer at the fifth wheel.

[0077] This refers to the turning angle of the front wheels of the tractor.

[0078] Equation for yaw moment balance:

[0079] The yaw moment around the center of gravity of the tractor is generated by the lateral force of the tires and the lateral force at the hinge point, while the inertial product caused by the lateral tilting motion cannot be ignored.

[0080]

[0081] in:

[0082] Let yaw moment of inertia be the moment of inertia of the tractor unit about its center of mass.

[0083] The product of inertia of the tractor's yaw and tilt;

[0084] This is the distance from the front axle of the tractor to its center of gravity.

[0085] This is the distance (equivalent) from the rear axle of the tractor to the center of mass;

[0086] This is the longitudinal distance from the fifth wheel to the center of gravity of the tractor.

[0087] Rolling moment equilibrium equation:

[0088] The torque about the roll axis is caused by the combined action of spring force, damping force, hinge force, gravity, and inertial force.

[0089]

[0090] in:

[0091] The moment of inertia of the tractor unit during lateral tilt;

[0092] For tractor roll damping;

[0093] For the tractor roll stiffness;

[0094] The roll stiffness at the fifth wheel;

[0095] This refers to the trailer's body roll angle;

[0096] This is the vertical distance from the fifth wheel to the tilt axis of the tractor.

[0097] g is the acceleration due to gravity.

[0098] Trailers also exhibit dynamic behavior in three directions: lateral, yaw, and tilt.

[0099] Lateral force equilibrium equation:

[0100]

[0101] in:

[0102] The total mass of the trailer;

[0103] This refers to the sprung mass of the trailer;

[0104] The lateral velocity of the trailer's center of gravity;

[0105] The longitudinal velocity of the trailer's center of gravity;

[0106] This refers to the trailer's yaw rate.

[0107] This refers to the trailer's body roll angle;

[0108] This is the distance from the center of the trailer's sprung mass to the roll axis;

[0109] This represents the total lateral force on the trailer axle (equivalent) tires;

[0110] This refers to the longitudinal interaction force at the fifth stage;

[0111] It is the articulation angle between the tractor and the trailer.

[0112] Equation for yaw moment balance:

[0113]

[0114] in:

[0115] Let the moment of inertia of the trailer about its center of mass be the yaw motion.

[0116] The product of inertia of the trailer's yaw and tilt;

[0117] This is the longitudinal distance from the trailer axle (equivalent) to the trailer's center of gravity;

[0118] This is the longitudinal distance from the fifth wheel to the trailer's center of gravity.

[0119] Rolling moment equilibrium equation:

[0120]

[0121] in:

[0122] This refers to the moment of inertia of the trailer during tilting.

[0123] For trailer roll damping;

[0124] For trailer roll stiffness;

[0125] This is the vertical distance from the fifth wheel to the trailer's tilt axis.

[0126] Through the fifth wheel connection, the speeds of the tractor and trailer are constrained. According to rigid body kinematics, the speed of the trailer's center of gravity can be derived from the speed of the tractor's center of gravity and the geometric relationship of the articulation point.

[0127]

[0128] Under the assumption of small hinge angle Trailer center of gravity sideslip angle

[0129] It can be approximated as:

[0130]

[0131] The tire lateral force is modeled using a linear lateral deflection model:

[0132]

[0133] The front wheel slip angle Rear wheel slip angle .

[0134] Step 2: Stability Error Calculation

[0135] Six-axle semi-trailers are typical multi-rigid-body articulated coupled systems. Their lateral stability is affected not only by the lateral forces of the tires but also by the trailer's inertia and the torque transmitted by the articulated structure. Compared to a single-vehicle model, a semi-trailer has an additional trailer degree of freedom, increasing the system order and making the coupling relationships more complex. Therefore, it is more prone to serpentine swaying or folding instability under high-speed or emergency conditions. To reveal its dynamic nature, it is necessary to establish separate lateral dynamic models for the tractor and trailer, and conduct coupling analysis through the dynamic relationship of the articulation angle.

[0136] For the tractor unit, its lateral motion satisfies the lateral force balance relationship:

[0137]

[0138] In the formula, m1 is the mass of the tractor, u1 is the longitudinal velocity at the center of gravity of the tractor, v1 is the lateral velocity at the center of gravity, and r1 is the yaw rate. This represents lateral acceleration. The terms u1 and r1 are velocity coupling terms generated by the vehicle's rotational motion, reflecting the coupling characteristics of longitudinal and lateral motion in curvilinear motion. and These represent the lateral forces generated by the tires on the front and rear axles, respectively. This equation illustrates that the lateral inertial forces of the vehicle must be balanced by the lateral forces generated by the tires; therefore, the tire's lateral deflection capability directly determines the vehicle's lateral stability.

[0139] The yaw motion of the tractor unit satisfies the torque balance relationship:

[0140]

[0141] in: Let be the yaw moment of inertia of the tractor unit about its center of mass. Let denot be the yaw acceleration, and a1 and b1 be the distances from the center of mass to the front and rear axles, respectively. The lateral force on the front axle generates a torque in front of the center of mass, while the lateral force on the rear axle generates a counter-torque behind the center of mass. Together, they determine the vehicle's yaw response. This is the coupling torque transmitted from the trailer to the tractor unit through the articulation mechanism. This is a key factor that distinguishes the dynamics of semi-trailer trains from those of ordinary single-unit trains. When the trailer exhibits hysteretic yaw, it applies additional disturbance torque to the tractor unit through the articulation mechanism, thereby exacerbating the system's instability.

[0142] For a trailer, its lateral force balance equation is:

[0143]

[0144] In the formula: m2 is the trailer mass, u2 and v2 are the longitudinal and lateral velocities at the trailer's center of gravity, respectively, and r2 is the trailer's yaw rate. This represents the total lateral force generated by the trailer axle assembly. This represents the lateral force transmitted at the articulation point. This equation shows that the lateral movement of the trailer is controlled by both the lateral forces of its own tires and the constraints imposed by the tractor.

[0145] The yaw dynamics equation for the trailer is:

[0146]

[0147] in: Let b1 be the yaw moment of inertia of the trailer about its center of mass, and b2 be the distance from the trailer's center of mass to the center of the axle assembly. Since trailers typically have a large mass and moment of inertia, their yaw response lags significantly behind that of the tractor unit. This lag is a major physical cause of the folding instability of semi-trailer trains.

[0148] The coupling relationship between the tractor and the trailer is described by the articulation angle φ, and its dynamic relationship is as follows:

[0149]

[0150] When the yaw rates of the tractor and trailer are inconsistent, the articulation angle will change. If the tractor yaws too quickly and the trailer responds too slowly, the articulation angle will increase rapidly, potentially triggering folding instability.

[0151] Tire lateral forces are typically approximated using a linear lateral slip model:

[0152]

[0153] in: Tire lateral stiffness represents the lateral force capacity generated per unit slip angle. This refers to the tire slip angle. The front wheel slip angle is:

[0154]

[0155] The rear wheel slip angle is:

[0156]

[0157] Where: δ is the front wheel steering angle, β is the vehicle's sideslip angle, a and b are the distances from the center of gravity to the front and rear axles, respectively, u is the longitudinal velocity, and r is the yaw rate. These relationships reveal the coupling between steering input, vehicle attitude, and velocity.

[0158] In yaw stabilization control, an additional yaw moment can be generated by differential braking of the left and right wheels, and its expression is as follows:

[0159]

[0160] Where: t is the wheel track. and These are the longitudinal braking forces for the right and left wheels, respectively. The longitudinal force and braking torque satisfy the following relationship:

[0161]

[0162] in: Let R be the braking torque of the wheel, and R be the effective radius of the wheel. Therefore, the additional yaw moment can be further expressed as:

[0163]

[0164] This relationship clearly shows that as long as the braking torques of the left and right wheels are not equal, an additional yaw moment will be generated at the vehicle's center of gravity, thereby adjusting the yaw rate.

[0165] To determine the control target, the ideal yaw rate is usually defined as:

[0166]

[0167] Where: L is the wheelbase, K is the steering characteristic coefficient, and g is the acceleration due to gravity. The control error is defined as:

[0168]

[0169] The fuzzy PID controller outputs an additional yaw moment ΔM based on the error e and its rate of change. z Then, the braking torque is converted into braking torque for each wheel through the braking torque distribution module, thereby achieving active lateral stability control of the six-axle semi-trailer.

[0170] Step 3: Identify loading conditions online

[0171] The offline collected sample data was classified using the K-medoids clustering algorithm with a fixed number of classes k. During the clustering process, Euclidean distance was used as the similarity measure, and sample points were selected as center points to minimize the sum of distances from samples within a class to the center point. Finally, k loading state cluster centers were obtained. Each cluster center Corresponding to a set of known loading parameters After clustering is completed, a loading status database is formed, realizing the mapping relationship between feature vectors and loading parameters.

[0172] During vehicle operation, the current feature vector is collected in real time. The Euclidean distance between each cluster center and the cluster center is calculated, and fuzzy rules are constructed accordingly.

[0173]

[0174] Based on the statistical and fitting results of offline simulation data, fuzzy rules are constructed and embedded into the control system. Using the front wheel speed and front wheel steering angle as inputs, steady-state values ​​are obtained according to the model constructed in step one. The trailer mass and center of gravity position are estimated using the fuzzy estimation module.

[0175] Step 4: Calculate the additional yaw moment

[0176] A PID controller consists of a proportional unit (P), an integral unit (D), and a derivative unit (D). PID control is based on proportional control; integral control can eliminate steady-state error but may increase overshoot; derivative control can accelerate the response speed of large inertia systems and reduce the tendency for overshoot.

[0177] The PID control law is:

[0178]

[0179] It can be written in the form of a transfer function as follows:

[0180]

[0181] In the formula, KP is the proportionality coefficient; TI is the integral time constant; and TD is the differential time constant. Since computer-processed data is discrete, the formula is discretized:

[0182]

[0183] In the above formula, K is the sampled signal; u(kT) is the controller output value at the k-th sampling time; e(kT) is the distance deviation value at the k-th sampling time; and e(kT-T) is the distance deviation value at the (k-1)-th sampling time. The PID algorithm control principle is simple and easy to implement, and it has strong adaptability and robustness.

[0184] Fuzzy PID control overcomes the limitation of traditional PID controllers, which cannot adjust parameters in real time, by utilizing fuzzy logic and certain fuzzy rules to optimize PID parameters in real time. Fuzzy PID control includes fuzzification, determination of fuzzy rules, and defuzzification. By determining the deviation *e* and the change *ec* between the current and previous deviations, fuzzy inference is performed according to given fuzzy rules. Finally, the fuzzy parameters are defuzzified, and the PID control parameters are output.

[0185] In this fuzzy PID controller, the deviation el between the actual yaw rate of the tractor and the reference yaw rate, and its rate of change ec1, are used as inputs, and the output parameter is the additional yaw moment ΔM1 of the tractor. In the semi-trailer fuzzy PID controller, the deviation el between the actual yaw rate of the semi-trailer and the reference yaw rate, and its rate of change ec2, are used as inputs, and the output parameter is the additional yaw moment ΔM2 of the tractor. Both share a single fuzzy PID control structure. The fuzzy PID control structure module constructed in Simulink is shown in the figure.

[0186] In the design of the fuzzy PID controller, the input quantities e and ec are fuzzified, and their universes of discourse are set to [-15, 15] and [-80, 80], respectively. The fuzzy universes of discourse for the output quantities kp, ki, and kd are all set to [0, 1]. The fuzzy linguistic variables used in the system include: NB (negative large), NM (negative medium), NS (negative small), ZO (zero), PS (positive small), PM (positive medium), and PB (positive large). For e, ec, kp, ki, and kd, their membership functions partially adopt a Gaussian distribution and partially adopt a triangular membership function.

[0187] Step 5: Construct a differential braking torque distribution system

[0188] During control, the target braking wheel is determined primarily based on the front wheel steering angle, steering angle change rate, yaw rate deviation between the tractor and semi-trailer, and vehicle steering characteristics. In the vehicle coordinate system, each parameter has directionality; this paper defines leftward steering as positive and leftward yaw moment as positive.

[0189] The core objective of differential braking lateral stability control is to generate an additional yaw moment by applying braking force to one side of the wheel, so that the actual yaw rate tracks the desired yaw rate given by the linear reference model.

[0190] The yaw rate error is defined as:

[0191]

[0192] γ* is the reference yaw rate, γ is the actual yaw rate, and ΔMz is the required additional yaw torque.

[0193] Considering only the longitudinal force generated by braking At that time, the yaw moment of the vehicle about its center of mass is:

[0194]

[0195] The longitudinal braking force of the i-th wheel, The lateral distance of the i-th wheel relative to the center of mass.

[0196] Assume the steering angle δ > 0 (vehicle turning left):

[0197] right wheel > 0

[0198] left wheel < 0

[0199] During braking < 0, therefore:

[0200]

[0201] Its symbol is Decide.

[0202] Therefore, the wheel selection rule can be expressed as:

[0203]

[0204] Let the wheelbase be t and the effective radius of the wheel be R. The yaw moment generated by a single wheel is:

[0205]

[0206] The braking force is:

[0207]

[0208] The braking torque at the wheel end is:

[0209]

[0210] In summary:

[0211]

[0212] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0213] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A semi-trailer lateral stability adaptive control method based on online identification of loading conditions, characterized in that: Includes the following steps, And the following steps are performed in sequence: Step 1: Collect vehicle operating state variables using a high-precision inertial measurement unit (IMU), establish a coupled dynamic model of the tractor and trailer, and obtain vehicle dynamic parameters; Step 2: Calculate the stability error using the ideal yaw rate reference model and the relationship between the additional yaw moment and braking moment generated by differential braking; Step 3: Using the combined feature vector samples of trailer load and centroid height under simulation conditions, the K-medoids clustering algorithm is used to obtain cluster centers and construct a loading status database. Based on the real-time collected vehicle operation feature vectors, the Euclidean distance between the vehicle and each cluster center is calculated, and fuzzy rules are constructed based on the distance to identify loading conditions online. Step 4: Calculate the additional yaw moment based on the control law of the fuzzy PID controller; Step 5: Braking force distribution execution control; The vehicle operating state variables mentioned in step one include the yaw rate r1 of the tractor, the yaw rate r2 of the trailer, the sideslip angle β1 of the tractor's center of gravity, the sideslip angle β2 of the trailer's center of gravity, the articulation angle θ, and the lateral acceleration a. y This constitutes the loading state feature vector X = [r1,r2,β1,β2,θ,a] y ].

2. The semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to claim 1, characterized in that: The semi-trailer consists of a three-axle tractor and a three-axle trailer connected by a saddle hinge, and has yaw degree of freedom and hinge angle degree of freedom. The coupled dynamic model of the tractor and trailer includes lateral, yaw, and roll motion equations: Lateral force balance equation of the tractor: ， In the formula: The total mass of the tractor unit; This refers to the sprung mass of the tractor unit. The lateral acceleration of the tractor's center of gravity; The longitudinal velocity of the tractor's center of gravity; The yaw rate of the tractor unit; This refers to the roll acceleration; This is the distance from the center of the sprung mass of the tractor to the roll axis; This represents the total lateral force on the front axle tires of the tractor unit. This represents the equivalent total lateral force of the tires on the rear axle of the tractor. This refers to the lateral interaction force between the tractor and trailer at the fifth wheel. The turning angle of the front wheels of the tractor; The yaw moment balance equation for the tractor unit: ， In the formula: Let yaw moment of inertia be the moment of inertia of the tractor unit about its center of mass. This is the yaw acceleration; The product of inertia of the tractor's yaw and tilt; This is the distance from the front axle of the tractor to its center of gravity. This is the equivalent distance from the rear axle of the tractor to the center of mass. This is the longitudinal distance from the fifth wheel to the center of gravity of the tractor unit; The tractor's roll moment balance equation: In the formula: The moment of inertia of the tractor unit during lateral tilt; For tractor roll damping; For the tractor roll stiffness; The roll stiffness at the fifth wheel; The lateral tilt rate of the tractor unit; The side tilt angle of the tractor unit; This refers to the trailer's body roll angle; denoted as ρ, and ρ is the vertical distance from the fifth wheel to the tilt axis of the tractor; g is the acceleration due to gravity. Trailer lateral force balance equation: ， In the formula: The total mass of the trailer; For trailer sprung mass; The lateral acceleration of the trailer's center of gravity; The trailer body roll angle acceleration; The longitudinal velocity of the trailer's center of gravity; This refers to the trailer's yaw rate. This refers to the trailer's body roll angle; This is the distance from the center of the trailer's sprung mass to the roll axis; The equivalent total lateral force of the trailer axle to the tires; This refers to the longitudinal interaction force at the fifth stage; The articulation angle between the tractor and the trailer; Trailer yaw moment balance equation: ， In the formula: Let the moment of inertia of the trailer about its center of mass be the yaw motion. This refers to the yaw acceleration of the trailer. The product of inertia of the trailer's yaw and tilt; This is the longitudinal distance from the trailer axle to the trailer's center of gravity. This is the longitudinal distance from the fifth wheel to the trailer's center of gravity; Trailer roll moment balance equation: In the formula: This refers to the moment of inertia of the trailer during tilting. For trailer roll damping; For trailer roll stiffness; This is the vertical distance from the fifth wheel to the trailer's tilt axis; Dual speed for trailer body roll angle; Kinematic constraints between the tractor and trailer: In the formula, The lateral velocity of the tractor's center of gravity; The lateral velocity of the trailer's center of gravity.

3. The semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to claim 2, characterized in that: The ideal yaw rate reference model mentioned in step two is: ， In the formula: L is the wheelbase, K is the steering characteristic coefficient, g is the acceleration due to gravity, and δ is the front wheel steering angle. Ideal yaw rate; Define the yaw rate error of the tractor Its rate of change ec1, trailer yaw rate error and its rate of change ec2; The relationship between the additional yaw moment generated by the differential braking and the braking torque is as follows: ， In the formula: To add yaw moment, t is the track width, and R is the effective radius of the wheel. These are the braking torques of the right and left wheels, respectively.

4. The semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to claim 3, characterized in that: The specific method for online identification of loading conditions in step three is as follows: Offline, different combinations of trailer load m2 and center of gravity height h2 are set. Feature vectors X under each working condition are collected through simulation. The K-medoids clustering algorithm is used to classify the samples, obtaining k cluster centers. Each center corresponds to a set of known loading parameters ( This forms a loading status database; During vehicle operation, the current feature vector is collected in real time. Calculate its Euclidean distance to each cluster center: ， In the formula: This represents the yaw rate of the tractor unit at the current moment. Let be the yaw rate of the tractor at the i-th cluster center; The yaw rate of the trailer at the current moment; Let yaw rate be the angular velocity of the trailer at the i-th cluster center; The sideslip angle of the tractor's center of gravity at the current moment; The sideslip angle of the tractor's centroid at the i-th cluster center; The sideslip angle of the trailer's center of gravity at the current moment; The trailer centroid sideslip angle at the i-th cluster center; The current articulation angle between the tractor and the trailer; The hinge angle of the i-th cluster center; The lateral acceleration at the current moment; Let be the lateral acceleration of the i-th cluster center; Fuzzy rules are constructed based on distance, and the current trailer load is estimated through fuzzy inference. and center of mass height This enables online identification of loading conditions.

5. The semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to claim 4, characterized in that: The method for calculating the additional yaw moment described in step four is as follows: a fuzzy PID controller is used, with the yaw angular velocity error e and its rate of change ec as inputs, and the additional yaw moment ΔM is output; the discretized form of the PID control law is as follows: ， In the formula: Here, denoted as proportional coefficient, integral time constant, and derivative time constant, respectively; K is the sampled signal; u(kT) is the controller output value at the k-th sampling time; e(kT) is the distance deviation value at the k-th sampling time; e(kT-T) is the distance deviation value at the (k-1)-th sampling time; T is the sampling period; and e(jT) is the deviation value at the j-th sampling time.

6. The semi-trailer lateral stability adaptive control method based on online identification of loading conditions according to claim 5, characterized in that: The braking force distribution execution control method described in step five is as follows: based on the additional yaw moment ΔM output by the fuzzy PID controller... z The braking wheels are determined by combining the steering direction and vehicle condition; the wheel selection rule is as follows: ， In the formula: This is the lateral distance of the wheel relative to the center of mass; Let be the braking torque of the i-th wheel; The relationship between the braking force of a single wheel and the additional yaw moment is as follows: ， In the formula: The longitudinal braking force for one side of the wheel; The braking torque for one wheel; The braking torque of the target wheel is calculated according to the formula and output to the electronic braking system.

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