Vehicle multi-system coordinated torque control method for complex working conditions

Abstract

This invention discloses a multi-system coordinated torque control method for vehicles under complex operating conditions, belonging to the field of vehicle stability control technology. Specifically, it includes the following steps: 1) acquiring real-time state information of the vehicle during driving through vehicle sensors; 2) analyzing the vehicle's stability boundary and ideal trajectory by combining various data; 3) designing an integrated multi-system coordinated controller, using ideal operating condition data as system input, and calculating the lateral and longitudinal forces and yaw moment required for the vehicle to operate under ideal conditions; 4) further allocating the above dynamic parameters and distributing them to specific lower-level systems to achieve final control. This invention proposes a multi-system coordinated control scheme based on AFS, DYC, and SFS from a holistic perspective. The controller adopts a hierarchical management framework, combining model predictive control and optimization control methods. It overcomes the shortcomings of single-system control and can significantly improve the stability of vehicle motion under complex operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of vehicle stability control technology, and is a method for coordinated torque control of multiple vehicle systems under complex operating conditions. Background Technology

[0002] With increasing environmental pollution and energy crises, energy-efficient and environmentally friendly electric vehicles are attracting more and more attention. Four-wheel independent drive electric vehicles (4WIDEV) abandon traditional drive systems, allowing independent control of the torque of each motor to achieve independent four-wheel drive. This fully leverages the potential of 4WIDEV and represents one of the main trends in future electric vehicle development. Furthermore, 4WIDEV can be combined with active safety systems to improve overall vehicle performance and help drivers maintain control, especially under adverse driving conditions such as high-speed obstacle avoidance and road surfaces with varying friction coefficients. The primary goal of vehicle control is to maintain the vehicle's ideal state, and the selection of this ideal state directly determines vehicle performance. However, with the increase in controllable actuators, the distribution of ideal control is no longer unique, posing challenges to vehicle stability control.

[0003] In recent decades, road traffic accidents have been frequent, making vehicle safety and stability a hot research topic. In emergency situations, it is difficult for drivers to maintain vehicle stability. For example, under extreme driving conditions, tire slippage can cause novice drivers to panic and make improper operations, leading to accidents. Therefore, many active control systems, such as Active Front Steering (AFS), Direct Yaw Moment Control (DYC), and Active Suspension (ASS), have been developed and applied to assist drivers in controlling vehicle stability. However, with the increase in active control systems, potential conflicts between these systems reduce vehicle stability. For example, the active control of DYC, ASS, and AFS all alter tire forces, making the coordination of these subsystems one of the challenges in vehicle stability control.

[0004] Most studies only consider the two-dimensional stability region of vehicle yaw rate and sideslip angle, without considering the improvement in vehicle stability by the ideal roll angle. Furthermore, current research rarely considers vehicle stability control under varying road conditions. To address these issues, it is necessary to study the three-dimensional stability region composed of "lateral velocity-yaw rate-roll angle" to obtain the ideal roll angle under different operating conditions. This will allow for better vehicle stability by controlling the vehicle to travel along the ideal trajectory on different road surfaces. Summary of the Invention

[0005] In view of the above-mentioned problems in the prior art, the purpose of this invention is to propose a multi-system coordinated torque control method for vehicles under complex working conditions, which can be applied to vehicle control to solve the problem of vehicle driving stability on different road surfaces.

[0006] This invention provides a coordinated torque control method for multiple vehicle systems under complex operating conditions, comprising the following steps:

[0007] S1: Real-time acquisition of the vehicle's longitudinal and lateral velocities v l and v s Roll angle φ, yaw rate k, and front wheel steering angle δ.

[0008] S2: Based on the analysis of the ideal motion state of the vehicle and the corresponding vehicle dynamics calculation of the data collected in real time in step 1, and taking into account the roll angle, yaw rate and lateral velocity, a three-dimensional stable region is established based on the three variables of roll angle, yaw rate and lateral velocity.

[0009] S3: Design an integrated multi-system coordination controller, using the ideal vehicle state obtained from the analysis in S2 as the input of the multi-system coordination controller, and calculate the total torque of the vehicle running under the ideal state.

[0010] The integrated multi-system coordination controller adopts a hierarchical structure. The upper-level controller, based on real-time vehicle status feedback and the ideal trajectory obtained from S2, uses the traditional MPC method to obtain the lateral force F. s Longitudinal force F l And yaw and roll moment T y and T r .

[0011] The lower-level controller will control the front and rear tires according to F s ,F l ,T y ,T r The optimal force distribution problem is transformed into a multi-objective constraint optimization problem for solution, and finally the magnitudes of the longitudinal force of the front and rear tires and the lateral force of the front tire are obtained. The results are then transmitted to each actuator.

[0012] The advantages of this invention are as follows: This invention provides a multi-system coordinated torque control method for vehicles under complex operating conditions. From a holistic perspective, it proposes a method for determining the three-dimensional stable region of "roll angle-yaw rate-lateral velocity," and a multi-system coordinated control scheme based on AFS, DYC, and SFS. The controller adopts a hierarchical management framework, combining model predictive control and optimization control methods. This overcomes the shortcomings of single-system control and significantly improves the stability of vehicle motion under complex operating conditions. Attached Figure Description

[0013] Figure 1 This is a flowchart of the vehicle multi-system coordinated torque control method of the present invention;

[0014] Figure 2 This is a schematic diagram of a vehicle model;

[0015] Figure 3 This is a schematic diagram of the friction ellipse and its corresponding inscribed octagon. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings.

[0017] This invention provides a coordinated torque control method for multiple vehicle systems under complex operating conditions, such as... Figure 1 As shown, it includes the following steps:

[0018] S1: Real-time acquisition of the vehicle's longitudinal and lateral velocities v l and v s Important real-time data such as roll angle φ, yaw rate k, and front wheel steering angle δ.

[0019] Currently, most vehicles are equipped with various sensors, selectively acquiring relevant data as needed. Based on this, this invention first considers the complex operating conditions of vehicles: skidding, rollover, or oversteer. From a vehicle dynamics perspective, skidding refers to a lateral acceleration exceeding the maximum acceleration provided by the ground; rollover refers to an imbalance of forces on both sides of the vehicle in the vertical direction, causing it to overturn; and oversteer refers to a lateral angular velocity exceeding a limit value. To address the instability issue, the longitudinal and lateral velocities v of the vehicle are selected for acquisition. l and v s Important real-time data such as roll angle φ, yaw rate k, and front wheel steering angle δ are used to determine the vehicle's operating status.

[0020] S2: Based on the real-time data collected in step 1, the following analysis focuses on the ideal motion state of the vehicle and the corresponding vehicle dynamics calculations. Taking into account roll angle, yaw rate, and lateral velocity, a three-dimensional coordinate system is established to determine the stable region. Because the analysis involves three variables, a three-dimensional coordinate system is chosen for this analysis and calculation. The specific method is as follows:

[0021] S2.1: Determine the basic stable region based on the stable range of each variable. The basic stable region consists of multiple discrete points and is defined as the stable region point.

[0022] S2.2: Select the point in the stable domain where the limit roll angle is located under different lateral velocities and yaw rates, and define it as the limit stable point of the roll angle;

[0023] S2.3: Among the extreme stability points of the roll angle, take the stability point corresponding to the extreme lateral velocity to establish the inner extreme stability point;

[0024] S2.4: Select 8 extreme stable points at the inner limit points to form an inner and outer hexahedral stable region, and select this stable region as the final three-dimensional stable region.

[0025] S2.5: The stable range of the roll angle needs to be further analyzed based on the current operating conditions. By controlling the vehicle at a suitable roll angle, rollover problems can be prevented.

[0026] Therefore, based on the three-dimensional stable region described in step S2.4 Combined with vehicle technical manual Select appropriate yaw rate and lateral velocity profiles under the current operating conditions. ， Furthermore, the influence of the friction coefficient of the road surface on which the vehicle operates should be taken into account. For example, the more obvious the vehicle tilting tendency is at potholes and bumps, the larger the ideal roll angle range is under this working condition.

[0027] S3: Design an integrated multi-system coordination controller, using the ideal vehicle state obtained from the analysis in S2 as the input of the multi-system coordination controller, and calculate the total torque of the vehicle running under the ideal state.

[0028] The integrated multi-system write coordination controller adopts a hierarchical structure, wherein the design method of the upper-level controller is as follows:

[0029] Because MPC has the characteristics of roll optimization and feedback correction, it can compensate for uncertainties caused by disturbances in a timely manner. Therefore, the upper-level controller uses the traditional MPC method to process and obtain the lateral force F based on the vehicle's real-time state feedback and the ideal state trajectory (roll angle, yaw rate, and lateral velocity) obtained from S2. s Longitudinal force F l And yaw and roll moment T y and T r ;

[0030] In order to obtain F s ,F l ,T y ,T r To obtain the optimal controllable tire force, the present invention transforms the optimal controllable tire force allocation problem into a multi-objective constraint optimization problem based on the control characteristics of the front and rear tires, and finally obtains the magnitude of the longitudinal force of the front and rear tires and the lateral force of the front tire.

[0031] The design method for the lower-level controller is as follows:

[0032] a. Based on the control characteristics of the front and rear tires, the optimal force distribution problem is transformed into a multi-objective constrained optimization problem;

[0033] b. Optimal controllable tire force f * The acquisition is achieved through target tracking, with the desired force F. td The objective function J is the ideal state input from the upper-level controller and is obtained by the MPC method. Therefore, the objective function J is expressed as follows:

[0034]

[0035] Where Q1 and Q2 are the target tracking weight and tire force amplitude, respectively. When the tire force f0 at the previous moment is 0, f T Q2f represents the amplitude of the tracking tire force. When f0 is not zero, (f-f0) T Q2(f-f0) represents the increment of the ultimate tire force. (Power coefficient) satisfy:

[0036]

[0037]

[0038] Among them, l f ,l r ,w f ,w r These represent the distances from the front / rear wheel axles to the vehicle center, and the half-widths of the front / rear vehicle body, respectively. Figure 2 As shown; in addition, the tire force distribution F t It also satisfies the following equations:

[0039]

[0040] Among them, F sRL This indicates the lateral force acting on the left rear tire. Its naming convention is as follows: the first letter s / l indicates lateral or longitudinal force, the second letter F / R indicates front or rear, and the third letter L / R indicates left or right. Therefore, F... sRR This indicates the lateral force acting on the right rear tire.

[0041] c. The optimization process is also subject to some constraints in tire dynamics. Since the front and rear tires have different structures, and the front wheels have steering capabilities, constraints on both lateral and longitudinal forces, as well as torque constraints, must be considered. The rear wheels do not have steering capabilities, so torque constraints are not required. Tire forces are considered under friction ellipse constraints, and to speed up calculations, the ellipse is represented as an inscribed octagon, such as... Figure 3 As shown, the specific constraints are expressed as follows:

[0042] stCF lj -DF sj ≤K

[0043] L lbj ≤F lj ≤U lbj

[0044] L lbn ≤F ln ≤U lbn

[0045] Lsbj ≤F sj ≤U sbj

[0046]

[0047] Where j = FL, FR, n = RL, RR; u lpj and u spj These are the coefficients of friction corresponding to the peak longitudinal and lateral forces of each tire; K s F is the reciprocal of the coefficient of the difference between the transverse and longitudinal forces. zi The vertical load on the tire; the coefficient matrix C,D,K is:

[0048] C = [c1 c2 c3 c4 c5 c6 c7 c8] T

[0049]

[0050] D = [d1 d2 d3 d4 d5 d6 d7 d8] T

[0051]

[0052] K = [k1 k2 k3 k4 k5 k6 k7 k8] T

[0053]

[0054] Among them, u peak Let be the peak friction coefficient of the road. The final optimization problem is formulated as follows:

[0055]

[0056] stCF lj -DF sj ≤K

[0057] L lbj ≤F lj ≤U lbj

[0058] L lbn ≤F ln ≤U lbn

[0059] L sbj ≤F sj ≤U sbj

[0060] Considering the coupling effect between lateral and longitudinal dynamics and the interaction between actuators, the lower-level controller mainly performs a finer optimal tire force distribution on the total vehicle torque output by the upper-level controller in step S3, which is the final QP optimization problem mentioned above. Finally, the result is transmitted to each actuator to achieve more precise tracking control.

[0061] The actuators in this invention mainly include an active suspension system (ASS), an active forward steering system (AFS), and a direct yaw moment control system (DYC). Furthermore, a fast-end sliding mode control method is used to ensure that the torque control of each wheel follows the required slip ratio, thereby achieving precise tracking of the tire's longitudinal force.

Claims

1. A method for coordinated torque control of multiple vehicle systems under complex operating conditions, characterized in that: Includes the following steps: S1: Real-time acquisition of the vehicle's longitudinal and lateral speeds and Roll angle Yaw rate and front wheel steering angle ; S2: Based on the analysis of the ideal motion state of the vehicle and the corresponding vehicle dynamics calculation of the data collected in real time in step 1, and taking into account the roll angle, yaw rate and lateral velocity, a three-dimensional stable region is established based on the three variables of roll angle, yaw rate and lateral velocity. The method for establishing a stable region is as follows: A. Determine the basic stable region based on the stable range of each variable. The basic stable region consists of multiple discrete points and is defined as the stable region point. B. Select the point in the stability domain where the roll angle is at the limit under different lateral velocities and yaw rates, and define it as the limit stability point of the roll angle. C. Among the extreme stability points of the roll angle, take the stability point corresponding to the extreme lateral velocity to establish the inner extreme stability point; D. Select 8 extreme stable points at the inner limit points to form an inner and outer hexahedral stable region, and select this stable region as the final three-dimensional stable region. S3: Design an integrated multi-system coordination controller, using the ideal vehicle state obtained from the analysis in S2 as the input of the multi-system coordination controller, and calculate the total torque of the vehicle running under the ideal state; The integrated multi-system coordination controller adopts a hierarchical structure. The upper-level controller, based on the vehicle's real-time state feedback and the ideal trajectory obtained from S2, uses the traditional MPC method to process and obtain the lateral force. Longitudinal force as well as yaw and roll moments and ; The lower-level controller will control the front and rear tire characteristics. The optimal force distribution problem is transformed into a multi-objective constraint optimization problem for solution, and finally the magnitudes of the longitudinal force of the front and rear tires and the lateral force of the front tire are obtained. The results are then transmitted to each actuator.

2. The vehicle multi-system coordinated torque control method for complex operating conditions as described in claim 1, characterized in that: When establishing a stable region, the stable range of the roll angle is determined by selecting a suitable yaw rate and lateral velocity profile under the current operating conditions based on the established three-dimensional stable region, and taking into account the influence of the friction coefficient of the road surface on which the vehicle is running. The more obvious the vehicle tilting trend, the larger the ideal roll angle range under the current operating conditions.

3. The vehicle multi-system coordinated torque control method for complex operating conditions as described in claim 1, characterized in that: The optimal force in the lower-level controller is obtained through target tracking, and the desired force is... The objective function is the ideal state input to the upper-level controller, processed by the MPC method, and therefore the optimization objective function is... The statement is as follows: in, and These represent the target tracking weights and tire force amplitude, respectively, and the tire force at the current moment. When the value is 0, Indicates the amplitude of the tracking tire force; when When it is not 0, Indicates the increment of the ultimate tire force; power coefficient satisfy: in, These represent the distances from the front / rear wheel axles to the vehicle center, and half the width of the front / rear vehicle body, respectively; additionally, tire force distribution... It also satisfies the following equations: in, This indicates the lateral force experienced by the left rear tire. Its naming convention is as follows: the first letter... Indicates lateral or longitudinal force, the second letter Indicates before or after, the third letter Indicates left or right, therefore This indicates the lateral force acting on the right rear tire; The forces acting on the tire are considered under the constraint of a frictional ellipse, which is equivalent to an inscribed octagon. The specific constraint is expressed as follows: in, , ; and These are the coefficients of friction corresponding to the peak longitudinal and lateral forces of each tire, respectively. It is the reciprocal of the coefficient of the difference between the transverse and longitudinal forces; For the vertical load on the tire; coefficient matrix for: in, Let be the peak friction coefficient of the road; the final optimization problem is formulated as: 。 4. The vehicle multi-system coordinated torque control method for complex operating conditions as described in claim 1, characterized in that: The actuators include an active suspension system, an active forward steering system, and a direct yaw torque control system; wherein, a fast-end sliding mode control method is also used to ensure that the torque control of each wheel follows the required slip ratio.

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