Four-wheel independent steering dynamic control method and system

Abstract

A four-wheel independent steering dynamic control method and system belong to the field of automobile chassis control, including obtaining vehicle running state parameters and tire state parameters of each wheel; determining the working area of each wheel tire based on the tire magic formula, the working area at least includes linear area, nonlinear transition area and saturation area; the product of tire side slip angle absolute value and road adhesion coefficient and vertical load is taken as an input variable, input to a preset fuzzy controller to obtain a steering switching weight coefficient; based on the steering switching weight coefficient, the control parameters of the steady-state steering mode and the control parameters of the oblique steering mode are weighted and fused to obtain target steering control parameters; based on the target steering control parameters, the four-wheel independent steering actuator is controlled to steer. The present application can switch steering mode in real time according to tire side slip state, ensure that the tire is always in the linear area, realize smooth dynamic switching of steering mode, avoid the wheel reaching the side slip limit, and improve the driving stability and safety of the vehicle.

Description

Technical Field

[0001] This application relates to the field of automotive chassis control, specifically to a four-wheel independent steering dynamic control method and system. Background Technology

[0002] The steering system of a car is a crucial component of the chassis, directly determining the vehicle's safety, stability, and driving comfort during steering. With the modernization of the automotive industry and the development of electronic technology, vehicle steering systems have evolved from traditional mechanical transmission steering systems (including hydraulic power steering and electro-hydraulic power steering) to electric power steering (EPS) and steer-by-wire (SBW) systems. In particular, four-wheel independent drive and independent steering electric vehicles based on in-wheel motors employ in-wheel motor corner module steering systems, where the steering motor drives the wheel assembly to achieve steering. Due to the physical decoupling of the steering structures between the coaxial wheels, the wheel turning angle is no longer limited by the traditional universal joint angle, enabling larger wheel turning angles. This allows for various flexible steering modes such as stationary turning, crabbing, and lateral translation, significantly improving the vehicle's maneuverability and passability in complex road environments.

[0003] In terms of control strategies for four-wheel independent steering vehicles, existing technologies typically utilize the coordination of front and rear wheel steering angles to achieve different steering modes. For example, at low speeds, the front and rear wheel steering angles are controlled in opposite directions (counter-phase steering) to reduce the turning radius and improve parking agility; at high speeds, the front and rear wheel steering angles are controlled in the same direction (co-phase steering) to suppress the center of gravity sideslip angle and improve vehicle handling stability. Furthermore, some solutions attempt to reduce the vehicle's yaw moment by having the front and rear wheels move in the same direction, allowing the vehicle to quickly corner within a limited space through an approximate "translation" motion.

[0004] However, existing four-wheel independent steering control methods still have the following major drawbacks in practical applications: (1) Rigid steering mode switching strategy: Traditional four-wheel steering systems usually switch steering modes based on preset vehicle speed thresholds (such as switching from opposite phase to same phase). This switching method based on a fixed threshold lacks a smooth transition mechanism. Under complex dynamic conditions, a single steering mode cannot simultaneously meet the requirements of stability and maneuverability. If the switching timing is inappropriate, it may cause sudden changes in vehicle posture, affecting driving comfort and safety.

[0005] (2) Neglecting tire nonlinear characteristics and extreme states: Existing control strategies are mostly based on linear two-degree-of-freedom vehicle models, assuming that tire lateral force and lateral angle are always linearly related. However, under extreme conditions (such as high-speed sharp turns and low-adhesion road surfaces), the tire lateral angle is very likely to exceed the linear region and enter the nonlinear saturation region, resulting in a decrease in tire lateral force or even loss of grip. Existing technologies lack monitoring and intervention of the tire's real-time lateral state, making it difficult to avoid the phenomenon of a wheel reaching its lateral limit during steering.

[0006] (3) Insufficient environmental adaptability: Existing solutions rarely consider the impact of dynamic changes in road surface adhesion coefficient (μ) and wheel vertical load (Fz) on steering control. Under different vertical loads and different road surface adhesion coefficients, the tire's side slip characteristics vary greatly, making it difficult to establish a clear standard for switching steering modes. Fixed control parameters cannot guarantee that the tire always operates within the linear range, and cannot fully utilize the redundant degrees of freedom of the four-wheel independent steering system to optimize the tire side slip angle distribution.

[0007] (4) Weak dynamic coordination and control capability: During the steering mode switching process, there is a lack of dynamic weight allocation mechanism based on tire state feedback. The coordinated control of the front and rear wheel steering angles often relies on open-loop calibration or simple closed-loop feedback, making it difficult to adjust the steering strategy in time when the tires are about to enter the nonlinear region, resulting in insufficient vehicle stability margin and the risk of loss of control and fishtailing.

[0008] Therefore, there is an urgent need to develop a dynamic control method for four-wheel independent steering that can fully utilize the high redundancy of the actuators in four-wheel independent steering vehicles, effectively address the problem of nonlinear tire changes under complex working conditions, and prevent the wheels from reaching the lateral deviation limit during steering, thereby improving the driving stability and safety of the vehicle under complex working conditions. Summary of the Invention

[0009] This application provides a dynamic control method and system for four-wheel independent steering, which can solve the technical problems existing in the prior art, such as stiff switching of steering modes in four-wheel independent steering vehicles, neglecting tire nonlinear characteristics leading to easy wheel reaching the side slip limit, and insufficient adaptability under different road surface adhesion coefficients and vertical loads, thus affecting vehicle driving stability.

[0010] In a first aspect, embodiments of this application provide a four-wheel independent steering dynamic control method, the method comprising: Obtain vehicle driving status parameters and tire status parameters of each wheel; Based on the tire state parameters, the working area of ​​each wheel tire is determined, and the working area includes at least a linear region, a nonlinear transition region, and a saturation region; The absolute value of the tire slip angle and the product of the road adhesion coefficient and the vertical load are used as input variables and input to the preset fuzzy controller to obtain the steering switching weight coefficient. Based on the steering switching weight coefficient, the control parameters of the steady-state steering mode and the control parameters of the slant steering mode are weighted and fused to obtain the target steering control parameters. Based on the target steering control parameters, the four-wheel independent steering actuators are controlled to steer.

[0011] In conjunction with the first aspect, in one implementation, determining the working area of ​​each wheel tire based on the tire state parameters includes: The relationship curve between tire lateral force and lateral angle was fitted based on the tire magic formula; Based on the aforementioned relationship curve, determine the slip angle threshold when the tire enters the nonlinear region and the slip angle threshold when the tire loses grip. The working area is divided based on the comparison between the current tire slip angle and the slip angle threshold.

[0012] In conjunction with the first aspect, in one embodiment, the expression for the tire magic formula is: ; in, It is the lateral force. Side slip angle, For stiffness factor, For shape factor, As the peak factor, For curvature factor, This is the vertical offset.

[0013] In conjunction with the first aspect, in one embodiment, determining the sideslip angle threshold for the tire entering the nonlinear region includes: Calculate the tire lateral stiffness to obtain the fitted value of the lateral force in the linear region; When the relative deviation between the actual lateral force and the fitted value of the lateral force in the linear region reaches a preset nonlinearity determination threshold, the corresponding minimum lateral angle is determined as the lateral angle threshold for the tire to enter the nonlinear region.

[0014] In conjunction with the first aspect, in one embodiment, determining the sideslip angle threshold when the tire loses traction includes: Obtain the maximum lateral force that the tire can provide; When the current lateral force is less than or equal to the product of the maximum lateral force and the preset grip loss coefficient, the corresponding lateral angle is determined as the lateral angle threshold when the tire loses grip.

[0015] In conjunction with the first aspect, in one implementation, the input variables of the fuzzy controller include: The absolute value of tire slip angle has a fuzzy subset including the linear region, the nonlinear transition region, and the saturation region. The product of the road surface adhesion coefficient and the vertical load has a fuzzy subset including small load and large load; The output variable of the fuzzy controller is the steering switching weight coefficient, and its fuzzy subset includes steady-state steering mode, transitional steering mode and diagonal steering mode.

[0016] In conjunction with the first aspect, in one implementation, the fuzzy rules of the fuzzy controller include: When the absolute value of the tire slip angle is in the linear region and the product of the road adhesion coefficient and the vertical load is large, the steering switching weight coefficient corresponds to the steady-state steering mode. When the absolute value of the tire slip angle is in the saturation zone and the product of the road adhesion coefficient and the vertical load is small, the steering switching weight coefficient corresponds to the oblique steering mode. In other cases, the steering switching weight coefficient corresponds to the transition steering mode.

[0017] In conjunction with the first aspect, in one implementation, the weighted fusion of the control parameters for the steady-state steering mode and the control parameters for the swerving steering mode includes: The target control parameters are calculated using the following formula: ; in, For target control parameters, For the weighting coefficient of the steering switch, These are the control parameters for steady-state steering mode. These are the control parameters for the diagonal steering mode.

[0018] In conjunction with the first aspect, in one implementation, the control parameters include a feedforward proportional coefficient and a feedback proportional coefficient. The control parameters for the steady-state steering mode are determined based on the condition that the vehicle's center of gravity sideslip angle is zero. The control parameters for the yaw steering mode are determined based on the condition that the vehicle's yaw rate is zero.

[0019] Secondly, embodiments of this application provide a four-wheel independent steering dynamic control system, the system comprising: The parameter acquisition module is used to acquire vehicle driving status parameters and tire status parameters of each wheel; The area determination module is used to determine the working area of ​​each wheel tire based on the tire state parameters; The weight calculation module is used to input the absolute value of the tire slip angle and the product of the road adhesion coefficient and the vertical load as input variables to the preset fuzzy controller to obtain the steering switching weight coefficient. The parameter fusion module is used to perform weighted fusion of the control parameters of the steady-state steering mode and the control parameters of the slant steering mode based on the steering switching weight coefficient to obtain the target steering control parameters. The steering control module is used to control the four-wheel independent steering actuators to steer based on the target steering control parameters.

[0020] The beneficial effects of the technical solutions provided in this application include: The working area is determined based on tire state parameters, and a fuzzy controller is used to determine the absolute value of the tire slip angle. and the product of road surface adhesion coefficient and vertical load This invention calculates the steering switching weight coefficient λ and weights and fuses the control parameters of steady-state steering mode and oblique steering mode, solving the technical problems in related technologies such as rigid steering mode switching strategies, neglect of tire nonlinear characteristics leading to easy wheel reaching of the sideslip limit, and insufficient adaptability under different road surface adhesion coefficients and vertical loads. This application enables smooth dynamic switching of steering modes, avoiding abrupt changes in vehicle attitude during the switching process; simultaneously, it ensures that the tires remain within the linear region, preventing the wheels from reaching the sideslip limit, thereby increasing the tire stability margin and significantly improving the vehicle's driving stability and safety under complex conditions. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating an embodiment of the four-wheel independent steering dynamic control method of this application; Figure 2 This is a schematic diagram illustrating the relationship between tire lateral force and slip angle in this application; Figure 3 This is a schematic diagram of the two-degree-of-freedom vehicle dynamics model of this application; Figure 4 This is a functional module diagram of an embodiment of the four-wheel independent steering dynamic control system of this application. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0024] Firstly, embodiments of this application provide a four-wheel independent steering dynamic control method, such as... Figure 2 As shown, the main steps include: Step S1: Obtain vehicle driving status parameters and tire status parameters of each wheel.

[0025] Step S2: Based on tire state parameters, determine the working area of ​​each wheel tire. The working area includes at least the linear region, the nonlinear transition region, and the saturation region.

[0026] Step S3: Calculate the absolute value of the tire slip angle. and road surface adhesion coefficient With vertical load product As an input variable, it is input to a preset fuzzy controller to obtain the steering switching weight coefficient λ.

[0027] Step S4: Based on the steering switching weight coefficient The control parameters of the steady-state steering mode and the slant steering mode are weighted and fused to obtain the target steering control parameters.

[0028] Step S5: Based on the target steering control parameters, calculate the target rear wheel steering angle and control the four-wheel independent steering actuators to steer.

[0029] In this embodiment, the working area is determined based on tire state parameters, and a fuzzy controller is used to determine the absolute value of the tire slip angle. and the product of road surface adhesion coefficient and vertical load This invention calculates the steering switching weight coefficient λ and weights and fuses the control parameters of steady-state steering mode and oblique steering mode, solving the technical problems in related technologies such as rigid steering mode switching strategies, neglect of tire nonlinear characteristics leading to easy wheel reaching of the sideslip limit, and insufficient adaptability under different road surface adhesion coefficients and vertical loads. This application enables smooth dynamic switching of steering modes, avoiding abrupt changes in vehicle attitude during the switching process; simultaneously, it ensures that the tires remain within the linear region, preventing the wheels from reaching the sideslip limit, thereby increasing the tire stability margin and significantly improving the vehicle's driving stability and safety under complex conditions.

[0030] Reference Figure 2 In a preferred embodiment, in step S2, the present invention estimates the tire slip angle entering the nonlinear region based on the tire magic formula. Determine the wheel's linear zone, transition zone, and saturation zone, as well as the slip angle when the tire loses traction. .

[0031] Among them, the magic formula for tire lateral force The fitting expression is: (1); In the formula: α: Side slip angle; B: Stiffness factor, which determines the initial slope of the curve; C: Shape factor, which determines the S-shaped characteristics of the curve; D: Peak factor, corresponding to the maximum value of the lateral force. ; E: Curvature factor, which determines the slope of the descending segment after the peak of the curve; Vertical offset, which is generally negligible.

[0032] Furthermore, the linear region of tire lateral slip characteristics is characterized by: lateral force Side slip angle Approximately proportional, corresponding to the initial straight line segment of the magic formula curve.

[0033] The slope of the linear region of the magic formula represents the tire's lateral stiffness. (2); The fitted value of the lateral force in the linear region is: (3); When the actual lateral force with linear fit value When the relative deviation reaches a threshold for nonlinear determination, it is determined that the threshold has been reached. The corresponding minimum sideslip angle is the sideslip angle for entering the nonlinear region. : (4); For ordinary passenger car tires, the sideslip angle entering the nonlinear region is between 2° and 4°. A deviation threshold for nonlinearity determination is typically defined. The percentage is 5% to 10%, depending on the tire type, tire pressure, and vertical load.

[0034] Furthermore, the limiting sideslip angle It is the tire that can provide the maximum lateral force. The sideslip angle at this time: (5); When the sideslip angle is greater than the limit sideslip angle, local slippage occurs in the contact patch between the tire and the ground, and the sideslip force continues to decrease as the sideslip angle increases.

[0035] When the lateral force meets the following conditions, the tire is deemed to have lost effective grip: (6); Typically, k is taken as 0.8 to 0.9. Substitute into the magic formula: (7); The calculated slip angle is the slip angle when the tire loses traction. The maximum slip angle of ordinary passenger tires is usually between 6° and 12°.

[0036] refer to Figure 3 In a preferred embodiment, the present invention employs a feedforward and feedback four-wheel steering control method, using the vehicle's yaw rate feedback to compensate for the rear wheel steering angle.

[0037] First, by equating the external forces and torques acting on the vehicle to the vehicle's center of mass, we obtain the net external force along the y-direction and the net external torque about the z-axis for a two-degree-of-freedom four-wheel independent steering vehicle as follows: (8); In the formula: / These are the lateral stiffness of the front and rear tires, respectively. / These are the steering angles of the front and rear wheels, respectively. The yaw rate is angular velocity (rad / s). m represents the total vehicle mass (kg); Let Z be the moment of inertia of the vehicle about the Z-axis (kg·m²). / The distance (m) from the front / rear axle to the center of mass; / Longitudinal / lateral vehicle speed (m / s).

[0038] The front and rear wheel steering angle control expressions are: (9); in: This is the feedforward proportional coefficient, which is the ratio of the front and rear wheel steering angles; This is the feedback proportional coefficient, which is the feedback adjustment gain of the vehicle's real-time motion state.

[0039] Secondly, in steady-state steering control, the sideslip angle of the vehicle's center of gravity during steady-state steering is... A value of 0 indicates that the vehicle's direction of travel is consistent with its heading. At this point, the sideslip angle is: (10).

[0040] Will and Substituting the force and moment equations of the four-wheel independent steering reference model, and after Laplace transform and rearranging, setting the response of the center of gravity sideslip angle to the front wheel steering angle to 0, the control parameters under steady-state steering are obtained: (11).

[0041] During extreme cornering with high lateral acceleration, a larger lateral force is obtained by aligning the front and rear wheels, thereby minimizing the vehicle's yaw rate and reducing the vehicle's rotational speed around itself.

[0042] Setting the steady-state yaw rate to 0, at which point the vehicle stops rotating around itself and begins to corner. Setting the coefficient of the 's' term and the constant term in the numerator of the yaw rate response to the front wheel steering angle to 0, we obtain: .

[0043] At this moment, the steady-state centroid sideslip angle of the diagonally moving vehicle is... .make To ensure that the front and rear wheel angles are consistent, that is This reduces tire wear during diagonal driving.

[0044] Therefore, the control parameters for diagonal steering are: .

[0045] In a preferred embodiment, in step S3, a steering mode switching fuzzy controller is designed based on the absolute value of the tire slip angle. and road surface adhesion coefficient With vertical load product Weighting coefficients to control steering switching .

[0046] The input variables of the fuzzy controller include: absolute value of tire slip angle Its fuzzy subsets include the linear region (LA), the nonlinear transition region (NA), and the saturation region (SA), with units of degrees (°) and a universe of discourse of [0,12].

[0047] The product of road surface adhesion coefficient and vertical load Its fuzzy subsets include small load (SF) and large load (BF), unit: kN, universe of discourse: [1,5].

[0048] The output variable of the fuzzy controller is the steering switching weight coefficient. Its fuzzy subset includes steady-state turning mode (S), transitional turning mode (M), and slant turning mode (L), with a universe of discourse of [0,1].

[0049] Both input and output variables use triangular or Gaussian membership functions.

[0050] The fuzzy rules are established as shown in the table below: Table 1. Fuzzy Rule Relationship Table

[0051] The specific logic of the fuzzy rules is as follows: If μF_z is a small load (SF) and |α| is in the linear region (LA), then λ takes the value of transition steering mode (M); If μF_z is a small load (SF) and |α| is in the nonlinear transition region (NA), then λ takes the value of transition steering mode (M); If μF_z is a small load (SF) and |α| is in the saturation region (SA), then λ takes the value of the slant steering mode (L); If μF_z represents a large load (BF) and |α| is in the linear region (LA), then λ takes the value of steady-state steering mode (S). If μF_z is a large load (BF) and |α| is in the nonlinear transition region (NA), then λ takes the value of transition steering mode (M); If μF_z is a large load (BF) and |α| is in the saturation region (SA), then λ takes the value of transition steering mode (M).

[0052] By adopting the above technical solution, the precise input variables are converted into fuzzy linguistic values, the universe of discourse and membership function are set, a fuzzy rule base is established, and the fuzzy set of the output variable is calculated using inference methods. Finally, the centroid method or the average maximum membership method is used to defuzzify the fuzzy set, and the fuzzy set of the output variable λ is transformed to obtain the precise value of the output variable.

[0053] In a preferred embodiment, in step S4, the rear wheel steering control parameters under steady-state steering are set to... and Let the rear wheel steering control parameters be as follows when driving at an angle: and If the two steering control parameters are combined using a linear combination method, then: (12).

[0054] The logic of the dynamic switching control method for steering modes is as follows: When the tire slip angle is in the linear region, controllable lateral force can be generated, primarily using steady-state steering mode. (approaching 0) When the tire slip angle is not in the linear region, and steady-state steering alone cannot achieve the required lateral force, the rear wheel steering angle gradually increases. The control objective is to ensure that the vehicle's yaw rate and lateral acceleration do not change abruptly, thus achieving smooth steering. This is a transitional process from steady-state steering mode to oblique steering mode. (between 0 and 1) When the tire slip angle is in the saturation range, and the vehicle's steering transition process still cannot meet the required lateral force, it switches to oblique steering mode. This mode distributes the lateral force among the four wheels to reduce the tire slip angle of each wheel, thereby improving the vehicle's stability and safety. Approaching 1).

[0055] Ultimately, the controller will calculate the... and Substitute into the front and rear wheel steering angle control expressions Obtain the target rear wheel angle And send it to the steering motor for execution.

[0056] In summary, this invention fully utilizes the characteristics of large steering angles, high degrees of freedom, and highly redundant actuators of four-wheel independent steering vehicles. It adopts a feedforward and feedback four-wheel steering control method, with the steering of the front and rear wheels cooperating to maintain the steering posture consistent with the vehicle's direction of travel. This generates the required lateral force while preventing the vehicle from losing control and "fishtailing." At the same time, by reducing the yaw moment of the vehicle by having the front and rear wheels move in the same direction, the yaw angle of the vehicle rotating around itself is reduced. The sideslip angles of all four wheels are within a small range, ensuring tire stability margin. Especially in corners, the vehicle can quickly corner in a limited space by using an almost "translational" method, ensuring the lateral stability of the vehicle.

[0057] In the dynamic switching of steering modes in a four-wheel independent steering vehicle, the steering mode is determined based on the tire lateral slip state to ensure that the tires remain within the linear range. Since tire lateral slip characteristics vary significantly under different vertical loads and road surface adhesion coefficients, it is difficult to establish a clear standard for switching steering modes. This invention employs fuzzy control to switch steering modes in real time based on the lateral slip state of the four tires. Dynamic switching between steady-state steering and oblique steering modes keeps the tires within the linear range, increasing tire stability margin and improving vehicle stability and safety. The fuzzy control system has strong adaptability, can quickly respond to dynamic changes, shorten adjustment time, and improve system efficiency.

[0058] Secondly, embodiments of this application provide a four-wheel independent steering dynamic control system, applied to a hub motor corner module electric vehicle with four-wheel independent drive and independent steering. For example... Figure 4 As shown, the system includes: Sensor module 1 is used to collect vehicle driving status parameters and tire status parameters of each wheel. Specifically, it includes wheel speed sensors, steering angle sensors, and inertial measurement units (IMUs) to acquire longitudinal vehicle speed. Front wheel steering angle yaw rate Tire slip angle Data such as...

[0059] The controller (ECU) 2 is used to execute the four-wheel independent steering dynamic control method provided in this application. The controller internally stores a tire magic formula model, a vehicle dynamics model, and a fuzzy control rule base.

[0060] Actuator 3 includes four hub motor angle modules, each wheel equipped with an independent steering motor to receive the target rear wheel steering angle command from the controller. And perform a steering maneuver.

[0061] The controller 2 integrates a parameter acquisition module, a region determination module, a weight calculation module, a parameter fusion module, and a steering control module, which are used to execute corresponding data processing and control command generation tasks respectively.

[0062] The beneficial effects of the technical solutions provided in this application include: The working area is determined based on tire state parameters, and a fuzzy controller is used to determine the absolute value of the tire slip angle. and the product of road surface adhesion coefficient and vertical load This invention calculates the steering switching weight coefficient λ and weights and fuses the control parameters of steady-state steering mode and oblique steering mode, solving the technical problems in related technologies such as rigid steering mode switching strategies, neglect of tire nonlinear characteristics leading to easy wheel reaching of the sideslip limit, and insufficient adaptability under different road surface adhesion coefficients and vertical loads. This application enables smooth dynamic switching of steering modes, avoiding abrupt changes in vehicle attitude during the switching process; simultaneously, it ensures that the tires remain within the linear region, preventing the wheels from reaching the sideslip limit, thereby increasing the tire stability margin and significantly improving the vehicle's driving stability and safety under complex conditions.

[0063] The functions of each module in the above-mentioned four-wheel independent steering dynamic control system correspond to the steps in the above-mentioned four-wheel independent steering dynamic control method embodiment, and their functions and implementation processes will not be described in detail here.

[0064] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0065] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0066] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0067] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0068] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0069] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0070] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A dynamic control method for four-wheel independent steering, characterized in that, The method includes: Obtain vehicle driving status parameters and tire status parameters of each wheel; Based on the tire state parameters, the working area of ​​each wheel tire is determined, and the working area includes at least a linear region, a nonlinear transition region, and a saturation region; The absolute value of the tire slip angle and the product of the road adhesion coefficient and the vertical load are used as input variables and input to the preset fuzzy controller to obtain the steering switching weight coefficient. Based on the steering switching weight coefficient, the control parameters of the steady-state steering mode and the control parameters of the slant steering mode are weighted and fused to obtain the target steering control parameters. Based on the target steering control parameters, the four-wheel independent steering actuators are controlled to steer.

2. The four-wheel independent steering dynamic control method according to claim 1, characterized in that, The step of determining the working area of ​​each wheel tire based on the tire state parameters includes: The relationship curve between tire lateral force and lateral angle was fitted based on the tire magic formula; Based on the aforementioned relationship curve, determine the slip angle threshold when the tire enters the nonlinear region and the slip angle threshold when the tire loses grip. The working area is divided based on the comparison between the current tire slip angle and the slip angle threshold.

3. The four-wheel independent steering dynamic control method according to claim 2, characterized in that, The expression for the tire magic formula is: ； in, It is the lateral force. Side slip angle, For stiffness factor, For shape factor, As the peak factor, For curvature factor, This is the vertical offset.

4. The four-wheel independent steering dynamic control method according to claim 2, characterized in that, The determination of the skid angle threshold for the tire entering the nonlinear region includes: Calculate the tire lateral stiffness to obtain the fitted value of the lateral force in the linear region; When the relative deviation between the actual lateral force and the fitted value of the lateral force in the linear region reaches a preset nonlinearity determination threshold, the corresponding minimum lateral angle is determined as the lateral angle threshold for the tire to enter the nonlinear region.

5. The four-wheel independent steering dynamic control method according to claim 2, characterized in that, The threshold for determining the slip angle when a tire loses traction includes: Obtain the maximum lateral force that the tire can provide; When the current lateral force is less than or equal to the product of the maximum lateral force and the preset grip loss coefficient, the corresponding lateral angle is determined as the lateral angle threshold when the tire loses grip.

6. The four-wheel independent steering dynamic control method according to claim 1, characterized in that, The input variables of the fuzzy controller include: The absolute value of tire slip angle has a fuzzy subset including the linear region, the nonlinear transition region, and the saturation region. The product of the road surface adhesion coefficient and the vertical load has a fuzzy subset including small load and large load; The output variable of the fuzzy controller is the steering switching weight coefficient, and its fuzzy subset includes steady-state steering mode, transitional steering mode and diagonal steering mode.

7. The four-wheel independent steering dynamic control method according to claim 6, characterized in that, The fuzzy rules of the fuzzy controller include: When the absolute value of the tire slip angle is in the linear region and the product of the road adhesion coefficient and the vertical load is large, the steering switching weight coefficient corresponds to the steady-state steering mode. When the absolute value of the tire slip angle is in the saturation zone and the product of the road adhesion coefficient and the vertical load is small, the steering switching weight coefficient corresponds to the oblique steering mode. In other cases, the steering switching weight coefficient corresponds to the transition steering mode.

8. The four-wheel independent steering dynamic control method according to claim 1, characterized in that, The weighted fusion of control parameters for steady-state steering mode and oblique steering mode includes: The target control parameters are calculated using the following formula: ； in, For target control parameters, For the weighting coefficient of the steering switch, These are the control parameters for steady-state steering mode. These are the control parameters for the diagonal steering mode.

9. The four-wheel independent steering dynamic control method according to claim 8, characterized in that, The control parameters include the feedforward proportional coefficient and the feedback proportional coefficient; The control parameters for the steady-state steering mode are determined based on the condition that the vehicle's center of gravity sideslip angle is zero. The control parameters for the yaw steering mode are determined based on the condition that the vehicle's yaw rate is zero.

10. A four-wheel independent steering dynamic control system, characterized in that, The system includes: The parameter acquisition module is used to acquire vehicle driving status parameters and tire status parameters of each wheel; The area determination module is used to determine the working area of ​​each wheel tire based on the tire state parameters; The weight calculation module is used to input the absolute value of the tire slip angle and the product of the road adhesion coefficient and the vertical load as input variables to the preset fuzzy controller to obtain the steering switching weight coefficient. The parameter fusion module is used to perform weighted fusion of the control parameters of the steady-state steering mode and the control parameters of the slant steering mode based on the steering switching weight coefficient to obtain the target steering control parameters. The steering control module is used to control the four-wheel independent steering actuators to steer based on the target steering control parameters.

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