Active steering control method and apparatus for stability of drive-by-wire vehicle

Abstract

The invention discloses an active steering control method for the stability of a drive-by-wire vehicle, and the method comprises the steps: 1, obtaining the current state information of the vehicle, and enabling the state information to comprise the vehicle speed and a front wheel steering angle; 2, current state information of the vehicle is substituted into the ideal two-degree-of-freedom vehicle model, and the expected yaw velocity and the expected side slip angle are obtained; step 3, establishing a vehicle state observer, and estimating the actual side slip angle and yaw velocity of the vehicle by using Kalman filtering according to the vehicle speed, the yaw velocity and the front wheel rotation angle; and step 4, inputting the expected yaw velocity, the expected side slip angle and the error between the estimated actual side slip angle and the estimated yaw velocity into an improved sliding mode controller, calculating and outputting a compensation control rotation angle, and finally controlling the steering of the vehicle through the compensated front wheel rotation angle so as to minimize the tracking error.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile steering control, and in particular to an active steering control method and device for the stability of a wire-controlled vehicle. Background Art

[0002] As a crucial component of the automotive chassis system and a key element in the human-vehicle interface, the steering system plays a crucial role in a vehicle's handling stability, comfort, and safety. With the advent of the era of electrification, connectivity, intelligence, and shared mobility, automotive by-wire chassis technology has entered a period of rapid development, placing higher demands on active control and active safety technologies for automotive steering systems. As a key component of automotive by-wire chassis systems, the steer-by-wire system eliminates the mechanical connection between the steering wheel and the steering actuator, achieving mechanical decoupling between the two. The by-wire drive-by-wire nature of the steering actuator enables variable-angle transmission ratio control and active front-wheel steering, thereby improving vehicle handling stability. However, since the steer-by-wire system eliminates the mechanical connection and the steering wheel is driven by the steering actuator motor, the current technical challenge is how to effectively design the steering actuator motor's angle tracking control algorithm to ensure that the steering actuator motor accurately tracks the desired angle. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides an active steering control method for the stability of a controlled-by-wire vehicle, comprising:

[0004] Step 1: Obtain vehicle current status information, including vehicle speed and front wheel angle;

[0005] Step 2: Use the current state information of the vehicle to bring in the ideal two-degree-of-freedom vehicle model to obtain the desired yaw rate and sideslip angle;

[0006] Step 3: Establish a vehicle state observer and use Kalman filtering to estimate the vehicle's actual sideslip angle and yaw rate based on vehicle speed, yaw rate, and front wheel angle.

[0007] In step 4, the error between the desired yaw rate and sideslip angle and the estimated actual sideslip angle and yaw rate is input into the improved sliding film controller, and the output compensation control angle is calculated. Finally, the vehicle steering is controlled by the compensated front wheel angle to minimize the tracking error.

[0008] Preferably, in step 2, the desired yaw rate and sideslip angle are limited according to the tire and road adhesion coefficients.

[0009] Preferably, in step 3, the Kalman filter estimates the actual sideslip angle and yaw rate of the vehicle based on a feedback control method.

[0010] Preferably, in step 4, an improved sliding film controller is designed by designing a sliding surface and selecting a reaching law.

[0011] Preferably, the sliding surface is designed according to a desired yaw rate and sideslip angle of the center of mass, and an ideal two-degree-of-freedom vehicle model.

[0012] Preferably, the reaching law is an exponential reaching law.

[0013] The present invention also provides an active steering control device, including an upper steering road sensing system, a vehicle signal processing system and a lower steering execution system, wherein the lower steering execution system includes an active steering control functional module, and the active steering control functional module controls the vehicle steering according to the aforementioned active steering control method.

[0014] Preferably, the lower steering execution system also includes an AFS active steering intervention judgment function module, a TLC torque limit coordination module, an RCO redundancy coordination module, a FOC motor control module, a TAS angle acquisition and processing module and a fault processing module, and other wire control angle related function modules.

[0015] The present invention has the following technical effects:

[0016] By designing a sliding mode control law to track the desired yaw rate and sideslip angle, the vehicle's handling stability is improved.

[0017] Actively controls the front wheel angle based on feedback from the vehicle's operating status, thereby changing the tire's lateral force to generate compensatory yaw torque and ensure the vehicle's yaw stability.

[0018] By monitoring the vehicle's operating conditions and the driver's operating intentions, the front wheel steering operation is performed in real time to control the vehicle's motion state, thereby improving the vehicle's stability and trajectory tracking performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0020] Figure 1 and Figure 2 Schematic diagram of the structure of the active steering control device of Example 1;

[0021] Figure 3 This is a driving state diagram of the active front wheel steering system of Example 2;

[0022] Figure 4 This is a schematic diagram of the active steering control method of Example 2;

[0023] Figure 5 This is a schematic diagram of the Kalman filter principle of Example 2;

[0024] Figure 6 and Figure 7 Schematic diagram of the Kalman filter estimated values and ideal values of the center of mass sideslip angle and yaw angular velocity in Example 2;

[0025] Figure 8 Schematic diagram of the front wheel active steering compensation angle in Example 2. DETAILED DESCRIPTION

[0026] The following describes the implementation manner of the present invention through specific specific embodiments. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through different specific implementation manners, and the various details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without deviating from the overall design concept of the invention. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in a variety of different forms and should not be interpreted as being limited to the specific embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art.

[0027] Example 1

[0028] like Figure 1 and Figure 2 As shown, this embodiment provides an active steering control device, including an upper steering road sensing system, a vehicle signal processing system and a lower steering execution system.

[0029] The upper steering road sense system mainly includes a steering wheel 2, a TAS torque and angle sensor 3 (4+2, 2 refers to two angles, which are provided to ECUs A and B for TAS angle calculation respectively), an upper steering column assembly 5, an upper steering road sense motor and a dual-redundant ECU 4 (including two ECUs A and B. The two sides A and B exchange internal data through UART and IPC. The two sides A and B can interact with the vehicle line through the same CAN1 line).

[0030] The lower steering execution module mainly includes the lower steering execution motor 10, a dual redundant ECU6 (Electrical Control Unit, electronic control unit, including two ECUs A and B. The A and B sides exchange internal data through UART and IPC. The A and B sides can interact with the vehicle line through the same CAN line), a motor position sensor 10, and a TAS angle sensor 9.

[0031] The upper steering road sense system and the lower steering execution system communicate and interact through private CAN (the upper steering ECU A side communicates with the lower steering ECU A side, and the upper steering ECU B side communicates with the lower steering ECU B side), and both the upper and lower systems (AB sides of the ECU) communicate and interact with the entire vehicle through the CAN1 bus.

[0032] The steering wheel 2 is used for driving by the driver, and the input end of the steering column assembly 5 is connected to the steering wheel 2; the TAS torque sensor 3 of the upper steering road sense module detects the driver's operating torque and angle, and the road sense ECU4 is used to collect and process data signals (hand torque and steering wheel angle), and transmits them to the lower steering actuator ECU6 through the private CAN, which is used for judgment conditions in the static angle initialization process.

[0033] The lower steering power motor 10 is installed on the steering gear and provides an execution torque to the rack through the reduction mechanism. The torque of the steering execution motor acts on the rack assembly and the pull rod assembly 8 through the turbine assembly to achieve steering assistance; the TAS angle sensor 9 is used to detect the angle value of the steering shaft to determine the absolute value of the lower steering angle; it is used to calculate the lower steering angle.

[0034] like Figure 2 As shown in the figure, the upper steering road sense system includes a steering wheel TAS angle signal acquisition and processing module and a wire-controlled angle ratio module. It is mainly used to provide a steering wheel ratio request angle for downward steering and transmit it to the lower steering execution system through the private CAN. It is an important part of the lower steering active steering control.

[0035] The vehicle signal processing system includes a vehicle speed acquisition module, which is mainly used to calculate the vehicle speed signal and transmit it to the lower steering execution system through the CAN line.

[0036] The lower steering actuation system primarily includes the active steering control module, the active steering intervention determination module, the torque limiting coordination module, the redundant control module, the field-of-control (FOC) motor control module, the angle acquisition and processing module (TAS) and fault handling module, as well as other control-by-wire angle control modules. The lower steering system consists of two master-slave (AB) sides, each with identical functions. During normal operation, the MCUs on both sides each drive the three-phase outputs of the six-phase motor. The system uses a set of rules to determine the dominant and subordinate positions of the MCUs on each side. The MCU in the subordinate position will output commanded torque in accordance with the dominant MCU. If a component on one side fails, an internal signal can be used to detect a valid signal from the component on the other side. In this case, the invalid signal on the local side is replaced by a valid signal on the remote side, allowing the system to maintain normal operation.

[0037] Active Steering Control Functional Module: The front-wheel active steering system utilizes a multi-objective sliding-mode active front-wheel steering controller designed based on vehicle driving conditions. This controller uses a sliding-mode control law to track the desired yaw rate and sideslip angle, providing a corrected front-wheel steering angle. This provides the driver with improved maneuverability and enhances vehicle stability. The specific active steering control method is described in detail in Example 2.

[0038] TLC output torque limit module: limits the motor's requested torque to meet functional safety requirements and prevent the output torque from exceeding the motor's load capacity;

[0039] RCO Redundancy Coordination Module: The lower steering system ECU is designed with redundancy for functional safety. The RCO module is mainly used to calculate the status and roles of the local A and remote B sides, and arbitrate the output torque of both sides.

[0040] FOC motor control module: converts the currently calculated torque into a current signal used by the motor, controlling the motor to operate normally according to the designed route;

[0041] TAS angle acquisition module: used to provide the absolute values of the left and right extreme learnable angles and the median angle value, and participate in the real-time calculation of the steering angle;

[0042] Fault handling module: When an unexpected fault occurs during learning, the fault handling module stores the fault and executes relevant safety measures;

[0043] Example 2

[0044] This embodiment describes in detail the active steering control method for the stability of a controlled-by-wire vehicle according to the present invention.

[0045] like Figure 3 As shown in the figure, understeer and oversteer can cause the car to fail to follow the intended trajectory, posing a threat to the safety of occupants. Active steering vehicle control involves determining the desired control objective, such as trajectory tracking or lane keeping. The controller uses a sliding membrane control algorithm to determine the ideal front wheel angle based on current vehicle speed and state feedback variables such as the lateral displacement of the vehicle's center of mass and yaw angle, to track the desired trajectory or achieve lane keeping control. The vehicle's EPS inner-loop control, based on the ideal front wheel angle determined by the outer-loop control, uses SMC control to ensure that the EPS's AFS actuator outputs an appropriate angle, quickly reducing the deviation between the actual and ideal front wheel angles.

[0046] like Figure 4 As shown, the active steering control method for the stability of a controlled-by-wire vehicle provided in this embodiment includes:

[0047] Step 1: Get the current status information of the vehicle, including the vehicle speed vx , front wheel turning angle δ sw ;

[0048] Step 2: Use the vehicle's current state information to bring in the ideal two-degree-of-freedom vehicle model to obtain the desired yaw rate γ d and the center of mass sideslip angle β d ;

[0049] Step 3: Establish a vehicle state observer based on the vehicle speed v x , yaw angular velocity γ d and the front wheel steering angle δ sw , use Kalman filter to estimate the actual center of mass sideslip angle γ and yaw rate β of the vehicle;

[0050] Step 4: Input the error between the desired yaw rate and center of mass sideslip angle and the estimated actual center of mass sideslip angle and yaw rate into the improved sliding film controller to calculate the output compensation control angle Δδ fw , and finally the compensated front wheel angle δ zf , control the vehicle steering to minimize the tracking error.

[0051] Based on the linear two-degree-of-freedom vehicle model and considering the restrictions of road adhesion conditions during vehicle driving, the correction values of the ideal center of mass sideslip angle and yaw rate are calculated. The linear two-degree-of-freedom motion differential equation during vehicle steering is:

[0052]

[0053] Where β represents the sideslip angle of the center of mass, γ represents the yaw rate, and v x represents the longitudinal speed of the vehicle, and δ represents the steering wheel angle δ sw The front wheel turning angle is calculated based on the preset transmission ratio. a represents the distance from the center of mass to the front axle, b represents the distance from the center of mass to the rear axle, k1 represents the cornering stiffness of the front axle tire, k2 represents the cornering stiffness of the rear axle tire, m represents the vehicle mass, and I z represents the vehicle's z-axis moment of inertia;

[0054]

[0055] According to the tire and road adhesion coefficients, the upper limits of yaw rate and center of mass sideslip angle are:

[0056]

[0057] β max =arctan(0.02μg)

[0058] Where μ is the road adhesion coefficient and g is the acceleration of gravity. The reference values of the controller's horizontal angular velocity γ and center of mass sideslip angle β are obtained as follows:

[0059]

[0060] After sorting out, the differential equation of motion of a two-degree-of-freedom vehicle is obtained:

[0061]

[0062] The vehicle dynamics model is expressed using the discrete differential state space equation:

[0063]

[0064] Assume that the linear discrete system equation and the measurement equation are

[0065]

[0066] Where x k is the actual value of the state vector, u k is the control vector, z k is the actual value of the measurement vector; They are the state transfer matrix, control input gain matrix, and measurement transfer matrix, respectively. k and v k are the noise vectors of the system and the measurement respectively, assuming that they are uncorrelated white noises and satisfy the normal distribution

[0067]

[0068] Where, is the system noise covariance, is the measurement noise covariance.

[0069] Defining the prior estimation error and the posterior error e k and their respective error covariances P k They are

[0070]

[0071] Where, and are the prior and posterior estimates of the transition state, respectively.

[0072] Measuring the residual (z k and The difference between the two) contains information about the true value of the system, based on the measurement residual Make corrections and you can get

[0073]

[0074] Where K k is the Kalman filter gain.

[0075] If e k With z k Orthogonal, then is x k Further optimal linear prediction estimation, so use e k With z k The orthogonality condition, The Kalman filter gain can be obtained as

[0076] The Kalman filter estimates the system based on the feedback control method: first, the filter estimates the system state at a certain moment, and then uses the noisy measurement value for feedback control. Therefore, the Kalman filter equation can be divided into a time update equation and a measurement update equation. The former calculates the prior estimate of the next moment based on the current state and the error covariance estimate, and the latter corrects the prior estimate based on the measurement value to obtain the posterior estimate. Figure 5 The figure shows the Kalman filter KF recursive cycle process. When the estimation at time k-1 is completed, the estimation at time k begins, and the posterior estimate obtained is and P k-1 As the initial value of the k-time estimate, calculate and Then based on z k Correct the prior estimate and get and P k , and cycle in sequence to form a recursive process.

[0077] After discretizing the vehicle's linear two-degree-of-freedom state equation according to the above formula, it can be used as the input of the Kalman filter algorithm to obtain an estimate of the state value. Figure 6 and Figure 7 Shown is a schematic diagram of the Kalman filter estimated and ideal values of the center of mass sideslip angle and yaw rate.

[0078] After eliminating the nonlinearity of the vehicle, the sliding mode controller for the vehicle's active front wheel steering can be designed by designing the sliding surface and selecting the reaching law. The sliding surface S is designed based on the desired value of the controlled object (ideal yaw rate and sideslip angle) and the state equation (two-degree-of-freedom vehicle dynamics model) to ensure that the system state reaches the desired sliding surface. Constructing the reaching law To ensure that the system can move to the sliding surface according to the desired dynamic characteristics.

[0079] After determining the expected value of the controlled object, the error of the controlled quantity can be expressed as follows:

[0080]

[0081] Based on this, the synovial surface is designed as shown below.

[0082]

[0083] Where p = e β +λe r ,ξ is an adjustable weight coefficient, which is a positive value.

[0084] Derivative of the sliding surface As shown below

[0085]

[0086] Where: λ is an adjustable coefficient, which is a positive value.

[0087] In addition to designing the sliding surface, the selection of a reaching law is also crucial for improving the dynamic characteristics of sliding mode control and eliminating chattering caused by its switching characteristics. The reaching law describes the system's movement from its initial state to the sliding surface. In this paper, an exponential reaching law is chosen, as shown below.

[0088]

[0089] Where: ε, k are positive constant coefficients.

[0090] To reduce chattering, the sign function Sgn(s) is replaced by a saturation function, that is,

[0091]

[0092] Where, Is a constant greater than 0. Saturation function As shown, it is equivalent to establishing a thickness of When S is outside the boundary layer, the system is made to approach the sliding film surface through conventional sliding film control. After the system enters the boundary layer, the saturation function is used for linear feedback control, which can effectively weaken the chattering. The sliding film controller finally outputs the compensation angle, such as Figure 8 shown.

[0093] The present invention has been described in detail above by way of specific embodiments and examples, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may make many variations and improvements, which should also be considered within the scope of protection of the present invention.

Claims

1. An active steering control method for the stability of a controlled-by-wire vehicle, characterized in that: include: Step 1: Obtain vehicle current status information, including vehicle speed and front wheel angle; Step 2: Use the current state information of the vehicle to bring in the ideal two-degree-of-freedom vehicle model to obtain the desired yaw rate and sideslip angle; Step 3: Establish a vehicle state observer and use Kalman filtering to estimate the vehicle's actual sideslip angle and yaw rate based on vehicle speed, yaw rate, and front wheel angle. In step 4, the error between the desired yaw rate and sideslip angle and the estimated actual sideslip angle and yaw rate is input into the improved sliding film controller, and the output compensation control angle is calculated. Finally, the vehicle steering is controlled by the compensated front wheel angle to minimize the tracking error.

2. The active steering control method for the stability of a controlled-by-wire vehicle according to claim 1, characterized in that: In step 2, the desired yaw rate and sideslip angle are limited according to the tire and road adhesion coefficients.

3. The active steering control method for vehicle stability according to claim 1, characterized in that: In step 3, the Kalman filter estimates the actual sideslip angle and yaw rate of the vehicle based on a feedback control method.

4. The active steering control method for stabilization of a controlled-by-wire vehicle according to claim 1, wherein: In step 4, an improved sliding film controller is designed by designing a sliding surface and selecting a reaching law.

5. The active steering control method for stabilization of a controlled-by-wire vehicle according to claim 4, characterized in that: The sliding surface is designed according to the desired yaw rate and sideslip angle, as well as an ideal two-degree-of-freedom vehicle model.

6. The active steering control method for the stability of a controlled-by-wire vehicle according to claim 4, characterized in that: The reaching law is an exponential reaching law.

7. An active steering control device, comprising an upper steering road sensing system, a vehicle signal processing system and a lower steering execution system, characterized in that: The lower steering execution system includes an active steering control function module, the active steering control function module The active steering control method according to claim 1 controls vehicle steering.

8. The active steering control device according to claim 8, characterized in that: The lower steering execution system also includes an AFS active steering intervention judgment function module, a TLC torque limit coordination module, an RCO redundancy coordination module, a FOC motor control module, a TAS angle acquisition and processing module and a fault processing module, and other wire control angle related function modules.

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