A wheel-hub motor driven automobile yaw stability control system and control method

Abstract

The application discloses a kind of wheel hub motor driven automobile yaw stability control system and control method, the system includes information perception module, state estimation module, state monitoring module, control module and lower execution module;Information perception module obtains vehicle actual state information and is transmitted to state estimation module, state estimation module calculates the ideal yaw angular velocity of vehicle and mass center side angle, and estimates vehicle mass center side angle and mass center side angle change rate;State monitoring module monitors and judges the yaw state where current vehicle is located, and according to different yaw state, the corresponding steering control, torque control and integrated control module are started;Steering and torque control module uses non-singular fast terminal sliding mode control method, realizes active front wheel steering and direct yaw torque control, integrated control module uses sliding mode control method based on linear matrix inequality, realizes the integrated control of both;The application can improve the robustness of control strategy to parameter uncertainty and external interference.

Description

Technical Field

[0001] This invention relates to the field of vehicle dynamics control technology, and mainly to a wheel hub motor driven vehicle yaw stability control system and control method. Background Technology

[0002] Globally, energy shortages and environmental pollution are becoming increasingly severe, leading the automotive industry to focus on energy conservation and environmental protection. Electric vehicles have become a new favorite, with in-wheel motor-driven electric vehicles attracting particular attention. However, the large number of vehicles, congested roads, and increasingly high driving speeds easily lead to traffic accidents, making vehicle safety and stability even more crucial.

[0003] Because the driving torque of each wheel in a four-wheel independently driven electric vehicle is independently controllable, theoretically, the output torque of each wheel can be directly controlled according to different operating conditions, optimizing the distribution of front and rear driving braking force. This can prevent the vehicle from slipping due to excessive torque and provide sufficient driving force as needed. At the same time, the independent drive of four-wheel hub motors in electric vehicles makes it easy to control external yaw moments, effectively controlling the vehicle's lateral movement without interfering with driver operation. Furthermore, the fast response speed and accurate torque output control significantly improve the speed and precision of vehicle stability control.

[0004] Currently, the development of four-wheel hub motor driven electric vehicles is still in its early stages. The control methods used are mostly traditional PID control and logic threshold control. However, due to the complexity of vehicle driving conditions and the uncertainty of vehicle parameters, the effects of these control methods often fail to meet expectations. Therefore, it is necessary to improve the robustness of the control strategy to parameter changes and external disturbances. Summary of the Invention

[0005] Purpose of the invention: To address the problems existing in the background technology mentioned above, the present invention provides a vehicle yaw stability control system and control method driven by a hub motor. It designs a control system and control method that integrates information perception, state estimation, state monitoring, and the actual control scheme provided by the control module, and drives the lower-level execution module to complete specific actions.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0007] A wheel hub motor driven vehicle yaw stability control system includes an information sensing module, a state estimation module, a state monitoring module, a control module, and a lower-level execution module.

[0008] The information sensing module includes a yaw rate sensor, a lateral acceleration sensor, a vehicle speed sensor, and a steering wheel angle sensor installed on the vehicle. The information sensing module obtains real-time vehicle status information, including yaw rate, lateral acceleration, vehicle speed, and steering wheel angle, by receiving sensor information.

[0009] The state estimation module receives real-time vehicle state information, calculates the current ideal yaw rate and sideslip angle of the vehicle, and estimates the actual sideslip angle and the rate of change of the sideslip angle.

[0010] The condition monitoring module uses the estimated actual sideslip angle of the vehicle's center of gravity and the rate of change of the sideslip angle to monitor the current yaw state of the vehicle.

[0011] The control module includes a steering control module, an integrated control module, and a torque control module; the steering control module performs active front wheel steering control; the torque control module performs direct yaw torque control; and the integrated control module integrates the control of active front wheel steering and direct yaw torque.

[0012] The lower-level execution module controls the steering motor and hub motor to achieve stability control based on the control law generated by the control module.

[0013] A control method employing the above-mentioned vehicle yaw stability control system includes the following steps:

[0014] Step S1: The information perception module acquires the actual state information of the vehicle and transmits it to the state estimation module;

[0015] Step S2: The state estimation module calculates the ideal yaw rate and sideslip angle of the vehicle based on the state information transmitted by each sensor in the information perception module, and estimates the sideslip angle and the rate of change of the sideslip angle.

[0016] Step S3: The status monitoring module monitors and determines the current yaw state of the vehicle and classifies the yaw state into three types: stable, critically stable, and unstable, based on the vehicle's center of gravity sideslip angle phase plane diagram.

[0017] Step S4: Activate the corresponding control module according to the current yaw state of the vehicle: When the vehicle is in a stable state, activate the steering control module to generate the front wheel angle correction value; when the vehicle is in a critical stable state, activate the integrated control module to generate the front wheel angle correction value and the additional yaw moment value; when the vehicle is in an unstable state, activate the torque control module to generate the additional yaw moment value.

[0018] Step S5: When the vehicle is in a critically stable or unstable state, the additional yaw moment value is converted and distributed through the torque control and integrated control module to generate the target longitudinal moment.

[0019] Step S6: The lower-level execution module receives the control law generated by the control module and controls the steering motor and hub motor to achieve stability control.

[0020] Furthermore, the specific method for calculating the ideal yaw rate and sideslip angle of the vehicle in step S2 includes:

[0021] First, a two-degree-of-freedom model of the vehicle is established as follows:

[0022]

[0023] in B2=-ak1 / I z β is the centroid sideslip angle. The yaw rate is angular velocity. Let u be the vehicle's heading angle, k1 and k2 be the lateral stiffness of the front and rear wheels respectively, a and b be the distances from the vehicle's center of gravity to the front and rear axles respectively, m be the vehicle's mass, and I be the vehicle's lateral speed. z Let δ be the moment of inertia of the yaw rotation. f The front wheel steering angle is ΔM, and the additional yaw moment is ΔM.

[0024] The ideal yaw rate and sideslip angle of the vehicle, determined from the above two-degree-of-freedom vehicle model, are as follows:

[0025]

[0026]

[0027] Where, ω d β d Let μ be the vehicle's ideal yaw rate and sideslip angle, μ be the road adhesion coefficient, and g be the acceleration due to gravity. β m =arctan(0.2μg), As the stability factor, L = a + b.

[0028] Furthermore, the criteria for distinguishing the current yaw state of the vehicle in step S3 are as follows:

[0029]

[0030] Further, in step S4, when the vehicle is in a stable state, the steering control module is activated to generate a front wheel steering angle correction value; specifically, the steering control module uses the yaw rate as the control target, causing... A non-singular fast terminal sliding mode control method is used to construct the following sliding mode surface:

[0031]

[0032] in

[0033] The front wheel steering angle control law is designed as follows:

[0034]

[0035] Among them, the control law parameters λ1, λ2, γ1, γ2, K1, and K2 are determined by experimental testing based on the specific vehicle parameters of the application and must satisfy λ1>0, λ2>0, 1<γ2<2, γ1>γ2, K1>0, and K2>0.

[0036] When the vehicle is in an unstable state, the torque control module is activated to generate an additional yaw moment value; specifically, the torque control module uses the sideslip angle of the center of gravity as the control target, causing... A non-singular fast terminal sliding mode control method is used to construct the following sliding mode surface:

[0037]

[0038] The additional yaw moment control law is designed as follows:

[0039]

[0040] Among them, the control law parameters λ3, λ4, γ3, γ4, K3, and K4 are determined by experimental testing based on the specific vehicle parameters for the application and must satisfy λ3>0, λ4>0, 1<γ4<2, γ3>γ4, K3>0, and K4>0.

[0041] When the vehicle is in a critical stable state, the integrated control module is activated, which simultaneously generates the front wheel steering angle correction value and the additional yaw moment value; specifically, the integrated control module uses the yaw rate and the center of gravity sideslip angle as the control objects.

[0042] Let the state variable x = [β, ω] T Ideal state variable x d =[β d ,ω d ] T Control input u = [δ f ,△M] T Based on the two-degree-of-freedom model of the vehicle, the state-space equations of the controlled object are established as follows:

[0043]

[0044] Where d represents unknown interference in the system.

[0045] Using the sliding mode control method, the following sliding mode surface is constructed:

[0046] z = xxd

[0047] Design integrated control law:

[0048]

[0049] Where ||η||>||d||, and F is the state feedback gain, obtained by solving the following matrix inequality:

[0050] A T P+M T +PA+M<0

[0051] Where F = (PB) -1 M and P are diagonal matrices and P > 0.

[0052] Beneficial effects:

[0053] The in-wheel motor driven vehicle yaw stability control system and method provided by this invention fully utilize the unique advantages of in-wheel motor driven vehicles, effectively achieving vehicle stability control. This invention selects the optimal control object based on the dynamic characteristics of the vehicle under different stability states. Addressing the issues of vehicle model parameter uncertainty and external disturbances, it proposes a non-singular fast terminal sliding mode stability control method and a sliding mode control method based on linear matrix inequalities. This achieves integrated control of direct yaw moment and active front wheel steering, improving the robustness of the control strategy to parameter uncertainties and external disturbances. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the vehicle yaw stability control system driven by a hub motor provided by the present invention.

[0055] Figure 2 This is a schematic flowchart of the yaw stability control method for a wheel hub motor driven vehicle in an embodiment of the present invention. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0057] The vehicle yaw stability control system based on hub motor drive provided by this invention is as follows: Figure 1 As shown, it includes an information perception module, a state estimation module, a state monitoring module, a control module, and a lower-level execution module.

[0058] The information perception module includes a yaw rate sensor, a lateral acceleration sensor, a vehicle speed sensor, and a steering wheel angle sensor installed on the vehicle. By receiving information from these sensors, the information perception module acquires real-time vehicle status information, including yaw rate, lateral acceleration, vehicle speed, and steering wheel angle.

[0059] The state estimation module receives real-time vehicle state information, calculates the current ideal yaw rate and sideslip angle of the vehicle, and estimates the actual sideslip angle and the rate of change of the sideslip angle.

[0060] The condition monitoring module uses the estimated actual sideslip angle of the vehicle's center of gravity and the rate of change of the sideslip angle to monitor the current yaw state of the vehicle.

[0061] The control module includes a steering control module, an integrated control module, and a torque control module. The steering control module performs active front wheel steering (AFS). The torque control module performs direct yaw moment control (DYC). The integrated control module integrates the control of active front wheel steering and direct yaw moment.

[0062] The lower-level execution module uses the control law generated by the control module to control the steering motor and hub motor to achieve stability control.

[0063] The various modules transmit information via a CAN bus, and the specific control method is as follows: Figure 2 As shown:

[0064] Step S1: The information perception module acquires the vehicle's actual state information through various sensors installed on the vehicle body and transmits it to the state estimation module. The vehicle's actual state information includes the current yaw rate ω and lateral acceleration a. y Vehicle speed u and steering wheel angle δ.

[0065] Step S2: The state estimation module calculates the vehicle's ideal yaw rate and sideslip angle based on the state information transmitted by each sensor in the information perception module. First, a two-degree-of-freedom model of the vehicle needs to be established as follows:

[0066]

[0067] in B2=-ak1 / I z β is the centroid sideslip angle. The yaw rate is angular velocity. Let u be the vehicle's heading angle, k1 and k2 be the lateral stiffness of the front and rear wheels respectively, a and b be the distances from the vehicle's center of gravity to the front and rear axles respectively, m be the vehicle's mass, and I be the vehicle's lateral speed. z Let δ be the moment of inertia of the yaw rotation. f The front wheel steering angle is ΔM, and the additional yaw moment is ΔM.

[0068] The ideal yaw rate and sideslip angle of the vehicle are determined from the two-degree-of-freedom model of the vehicle as follows:

[0069]

[0070]

[0071] Where, ω d β d Let μ be the vehicle's ideal yaw rate and sideslip angle, μ be the road adhesion coefficient, and g be the acceleration due to gravity. β m =arctan(0.2μg), As the stability factor, L = a + b.

[0072] After calculating the ideal yaw rate and sideslip angle of the vehicle, the state estimation module further estimates the actual sideslip angle and the rate of change of the sideslip angle. Many methods for estimating the vehicle's sideslip angle have been studied and are not innovative in this invention. This embodiment uses the Kalman filter estimation method, and the algorithm is as follows:

[0073]

[0074] Among them, the state estimate Observed value y = [a y ,ω] T A is the state matrix, Q is the process noise covariance matrix, R is the observation noise covariance matrix, P is the estimation error covariance matrix (which needs to be iteratively updated), and H is the observation matrix.

[0075] Step S3: The state monitoring module monitors and determines the current yaw state of the vehicle. Based on the estimated vehicle sideslip angle in step S2, it uses the sideslip angle phase plane diagram to classify the vehicle yaw state into three types: stable, critically stable, and unstable. The specific expressions are as follows:

[0076]

[0077] Step S4: Activate the corresponding control module based on the vehicle's current yaw state. This includes the following three scenarios:

[0078] (1) When the vehicle is in a stable state, the steering control module is activated to generate the front wheel steering angle correction value.

[0079] At this point, the yaw rate is taken as the control target, and... A non-singular fast terminal sliding mode control method is used to construct the following sliding mode surface:

[0080]

[0081] The sign function exponential form in the sliding surface formula represents the product of the corresponding exponent power of the absolute value of the variable and the sign of the variable, i.e. The exponential form of the symbolic function mentioned below all represent this meaning;

[0082] The front wheel steering angle control law is designed as follows:

[0083]

[0084] Among them, the control law parameters λ1, λ2, γ1, γ2, K1, and K2 are determined by experimental testing based on the specific vehicle parameters of the application and must satisfy λ1>0, λ2>0, 1<γ2<2, γ1>γ2, K1>0, and K2>0.

[0085] By designing Lyapunov functions Differentiating it and substituting it into the front wheel steering angle control law, we get:

[0086]

[0087] The effectiveness of the front wheel steering angle control law can be proven.

[0088] (2) When the vehicle is in a critical stable state, the integrated control module is activated, and the front wheel steering angle correction value and the additional yaw moment value are generated at the same time.

[0089] At this point, the yaw rate and the sideslip angle are considered as the controlled objects, and the state variable is set to x = [β, ω]. T Ideal state variable x d =[β d ,ω d ] T Control input u = [δ f ,△M] T The state-space equations of the controlled object are established based on the two-degree-of-freedom model of the vehicle:

[0090]

[0091] Where d represents unknown interference in the system.

[0092] Using the sliding mode control method, the following sliding mode surface is constructed:

[0093] z = xx d

[0094] Design integrated control law:

[0095]

[0096] Where ||η||>||d||, and F is the state feedback gain, which can be obtained by solving the following matrix inequality:

[0097] A T P+M T +PA+M<0

[0098] Where F = (PB) -1 M and P are diagonal matrices and P > 0.

[0099] Design the Lyapunov function V = z T Taking the derivative of Pz and substituting it into the integrated control law, we get:

[0100]

[0101] That is, to prove that the closed-loop system consisting of the state-space equation of the controlled object and the integrated control law is asymptotically stable.

[0102] (3) When the vehicle is in an unstable state, the torque control module is activated to generate an additional yaw torque value.

[0103] At this point, the sideslip angle of the center of mass is taken as the control target, and... A non-singular fast terminal sliding mode control method is used to construct the following sliding mode surface:

[0104]

[0105] The additional yaw moment control law is designed as follows:

[0106]

[0107] Among them, the control law parameters λ3, λ4, γ3, γ4, K3, and K4 are determined by experimental testing based on the specific vehicle parameters for the application and must satisfy λ3>0, λ4>0, 1<γ4<2, γ3>γ4, K3>0, and K4>0.

[0108] Step S5: When the vehicle is in a critically stable or unstable state, the additional yaw moment value is converted and distributed through the torque control and integrated control module to generate the target longitudinal moment. If the vehicle is in a stable state, this step is skipped.

[0109] There are many studies on methods for distributing additional yaw moment, but these are not the core innovation of this invention. This embodiment uses an average distribution method for illustration. The target longitudinal moment of each wheel after distribution is as follows:

[0110]

[0111] Among them, T d d is the driving torque, r is the wheel radius, and d is the vehicle width.

[0112] Step S6: The lower-level execution module receives the control law generated by the control module and controls the steering motor and hub motor to achieve stability control.

[0113] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method of a yaw stability control system of an in-wheel motor-driven automobile, characterized by, The information perception module, the state estimation module, the state monitoring module, the control module and the lower layer execution module are included. The information perception module includes a yaw rate sensor, a lateral acceleration sensor, a vehicle speed sensor and a steering wheel angle sensor installed on the vehicle; the information perception module acquires real-time state information of the vehicle by receiving sensor information, including the yaw rate, the lateral acceleration, the vehicle speed and the steering wheel angle. The state estimation module receives the real-time state information of the vehicle, calculates the ideal yaw rate and the mass center side slip angle of the vehicle, and estimates the actual mass center side slip angle and the mass center side slip angle change rate of the vehicle. The state monitoring module monitors the yaw state of the current vehicle by using the estimated actual mass center side slip angle and the mass center side slip angle change rate of the vehicle. The control module includes a steering control module, an integrated control module and a torque control module; the steering control module performs active front wheel steering control; the torque control module performs direct yaw torque control; and the integrated control module performs integrated control on the active front wheel steering and the direct yaw torque. The lower layer execution module controls the steering motor and the in-wheel motor to realize stability control based on the control law generated by the control module. The method comprises the following steps: Step S1: The information perception module acquires the actual state information of the vehicle and transmits it to the state estimation module. Step S2: The state estimation module calculates the ideal yaw rate and the mass center side slip angle of the vehicle based on the state information transmitted by the sensors in the information perception module, and estimates the mass center side slip angle and the mass center side slip angle change rate of the vehicle. Step S3: The state monitoring module monitors and judges the yaw state of the current vehicle, and divides the yaw state into stable, critical stable and unstable according to the mass center side slip angle phase plane. Step S4: According to the current yaw state of the vehicle, the corresponding control module is started: when the vehicle is in a stable state, the steering control module is started to generate a front wheel angle correction value; when the vehicle is in a critical stable state, the integrated control module is started to generate a front wheel angle correction value and an additional yaw torque value; when the vehicle is in an unstable state, the torque control module is started to generate an additional yaw torque value. Step S5: When the vehicle is in a critical stable or unstable state, the additional yaw torque value is converted and distributed through the torque control and integrated control modules to generate a target longitudinal force. Step S6: The lower layer execution module receives the control law generated by the control module to control the steering motor and the in-wheel motor to realize stability control. The specific method for calculating the ideal yaw rate and the mass center side slip angle of the vehicle in step S2 comprises: First, a two-degree-of-freedom vehicle model is established as follows: wherein B2 = -ak1 / I z β is the centroid side slip angle, is the yaw rate, is the vehicle heading angle, u is the longitudinal vehicle speed, k1, k2 are the side slip stiffness of the front wheel and the rear wheel respectively, a, b are the distance from the centroid of the vehicle to the front axle and the rear axle respectively, m is the mass of the vehicle, I z is the yaw moment of inertia, δ f is the front wheel steering angle, ΔM is the additional yaw moment; In the step S4, when the vehicle is in a stable state, a steering control module is started to generate a front wheel steering angle correction value; specifically, the steering control module takes the yaw rate as a control target, and makes A non-singular fast terminal sliding mode control method is adopted to construct a sliding mode surface as follows: wherein The front wheel angle control law is designed as follows: Wherein, λ1, λ2, γ1, γ2, K1, K2 are control law parameters, which are determined by test according to the vehicle parameters of specific application, and need to satisfy λ1>0, λ2>0, 1<γ2<2, γ1>γ2, K1>0, K2>0; When the vehicle is in the unstable state, the torque control module is started to generate an additional yaw torque value; specifically, the torque control module takes the center of mass side slip angle as the control target, and makes A non-singular fast terminal sliding mode control method is adopted to construct the following sliding mode surface: The additional yaw torque control law is designed as follows: Wherein, control law parameters λ3, λ4, γ3, γ4, K3, K4 are determined by test according to vehicle parameters of specific application and need to satisfy λ3>0, λ4>0, 1<γ4<2, γ3>γ4, K3>0, K4>0; When the vehicle is in critical stable state, the integrated control module is started, and the front wheel angle correction value and the additional yaw moment value are generated; specifically, the integrated control module takes the yaw rate and the center side slip angle as the control object; Let state variable x = [β, ω] T , ideal state variable x d = [β d , ω d ] T , control input u = [δ f , ΔM] T , state space equation of the controlled object is established according to the two-degree-of-freedom model of the vehicle: where d is the unknown disturbance of the system, The following sliding mode surface is constructed by using the sliding mode control method: z = x - x d The integrated control law is designed as follows: Wherein, ||η||>||d||, F is the state feedback gain, and the following matrix inequality is solved: A T P+M T +PA+M<0 where F = (PB) -1 M, P are diagonal matrices and P > 0.

2. The control method of a vehicle yaw stability control system driven by an in-wheel motor according to claim 1, characterized by, The specific method for calculating the ideal yaw rate and the center side slip angle in the step S2 further includes: The ideal yaw rate and the center side slip angle of the vehicle are determined by the two-degree-of-freedom model of the vehicle as follows: where ω d , β d are the ideal yaw rate and the vehicle's mass side slip angle, respectively, μ is the road adhesion coefficient, and g is the gravitational acceleration, β m = arctan(0.2μg), is the stability factor, and L = a + b.

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