Control method and controller for vehicle steering system

Abstract

A control method for a vehicle steering system and a controller are disclosed. The method comprises the following steps: acquiring a first steering wheel angle and a first yaw velocity of a target vehicle during operation; determining a theoretical system response value based on a system transfer function of the target vehicle and the first steering wheel angle, and fusing the first yaw velocity and the theoretical system response value into a second yaw velocity; determining an error value based on the target yaw velocity and the second yaw velocity, and inputting the error value into a position closed-loop PID controller to obtain a rotation angle increment; whether a steering wheel motor of the target vehicle supports a speed closed-loop PID controller or not is judged, if not, the rotation angle increment is output to the steering wheel motor, if yes, the rotation angle increment is output to the speed closed-loop PID controller, a rotation speed instruction is obtained, and the rotation speed instruction is output to the steering wheel motor. In addition, parameters in the closed-loop PID controller can be automatically calibrated. The debugging efficiency and the performance of the vehicle steering system can be improved through the method.

Description

Technical Field

[0001] The present application relates to the technical field of vehicle steering control, and in particular to a control method and a controller for a vehicle steering system. Background Art

[0002] Due to the large mass of the vehicle, its moment of inertia is also large, which makes it difficult to achieve accurate control and positioning when the vehicle performs steering and return operations. In addition, due to the large differences in the physical quantities controlled by different vehicle steering systems, it is difficult to directly apply the control method applied to one steering system to another steering system.

[0003] Therefore, there is an urgent need for an efficient control method for a vehicle steering system to improve the control capability of the vehicle steering system. Summary of the invention

[0004] In view of this, the present application discloses a control method and a controller for a vehicle steering system to improve the control capability of the vehicle steering system.

[0005] In the first aspect, the present application discloses a control method for a vehicle steering system, including: obtaining a first steering wheel angle of a target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle; determining a theoretical system response value based on a system transfer function and the first steering wheel angle of the target vehicle, inputting the first yaw angular velocity and the theoretical system response value into a fusion device to obtain a second yaw angular velocity; determining an error value based on the target yaw angular velocity and the second yaw angular velocity, and inputting the error value into a position closed-loop PID controller to obtain an angle increment; judging whether the steering wheel motor of the target vehicle supports a speed closed-loop PID controller, and if not, outputting the angle increment to the steering wheel motor, and if supported, outputting the angle increment to the speed closed-loop PID controller to obtain a speed command, and outputting the speed command to the steering wheel motor.

[0006] Optionally, the steering wheel motor receives an angle increment or a speed command and generates a compensation response value based on a system transfer function; the method also includes: inputting the compensation response value, the first yaw angular velocity and the theoretical system response value into a fusion device to obtain a second yaw angular velocity.

[0007] Optionally, the fuser is a Kalman filter, an extended Kalman filter or an unscented Kalman filter.

[0008] Optionally, obtaining a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle includes: installing an encoder on a steering wheel motor; and recording data of the encoder when the target vehicle is running to obtain the first steering wheel angle.

[0009] Optionally, obtaining a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle includes: installing an inertial sensor on the target vehicle; recording data from the inertial sensor when the target vehicle is running to obtain the first yaw angular velocity; or installing an antenna for a global navigation satellite system on the target vehicle; receiving satellite signals through the antenna when the target vehicle is running, and processing the satellite signals into the first yaw angular velocity.

[0010] Optionally, the control method for a vehicle steering system further includes: constructing a system transfer function of a target vehicle; the system transfer function includes a proportional link and a time-delay link, and the proportional coefficient of the proportional link is determined by a first proportional constant and a second proportional constant; wherein the first proportional constant is the quotient of a front wheel turning angle of the target vehicle and a first steering wheel turning angle, and the second proportional constant is the quotient of a vehicle speed of the target vehicle and a wheelbase of a front and rear axle of the target vehicle.

[0011] Optionally, the control method for a vehicle steering system further includes: calibrating parameters in a position closed-loop PID controller and a speed closed-loop PID controller, the parameters including a proportional gain parameter and a differential gain parameter.

[0012] Optionally, calibrating parameters in the position closed-loop PID controller and the speed closed-loop PID controller includes: initializing a second steering wheel angle, the second steering wheel angle being the maximum angle of the initial steering wheel of the target vehicle; based on the second steering wheel angle, controlling the target vehicle to rotate during operation, and recording a third yaw angular velocity that matches the second steering wheel angle; judging whether the third yaw angular velocity is within a preset range, and if not, correcting the second steering wheel angle using the target yaw angular velocity and the maximum value in the preset range until the third yaw angular velocity is within the preset range, and if so, obtaining the corresponding maximum angle, minimum angle, maximum yaw angular velocity and minimum yaw angular velocity using the second steering wheel angle, and determining parameters in the position closed-loop PID controller and the speed closed-loop PID controller.

[0013] Optionally, the differential gain parameter is in a multiple relationship with the proportional gain parameter.

[0014] In a second aspect, the present application further discloses a controller, which is used for a target vehicle and executes the control method for a vehicle steering system disclosed in the first aspect above.

[0015] In summary, the control method and controller for a vehicle steering system disclosed in the present application have at least the following beneficial effects:

[0016] 1. This solution takes the yaw rate as the target value, so that it can be widely adapted to different steering forms;

[0017] 2. Improve the control effect of the nonlinear steering system through variable gain + cascade PID control method, and realize the conversion control from steering wheel angle to motor speed;

[0018] 3. The present invention uses the values ​​of the inertial sensor and the encoder, taking advantage of the characteristics of the inertial sensor's instantaneous absolute value being accurate and the encoder's relative value being accurate, stable and free of response delay, taking the advantages and making up for the disadvantages, and using the fused value as feedback to improve the control accuracy and stability;

[0019] 4. For the parameters needed in the control system, this solution has designed a set of automatic calibration acquisition methods to enable it to adapt to a wide range of vehicle models more quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following is a brief introduction to the drawings used in describing the embodiments of the present application.

[0021] Figure 1 An example diagram of a control method for a vehicle steering system provided by an embodiment of the present application is shown.

[0022] Figure 2 An example diagram of another control method for a vehicle steering system provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the specific implementation methods of the present application will be described below with reference to the accompanying drawings. The accompanying drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other accompanying drawings and other implementation methods can be obtained based on these drawings without creative work. Adjustments and improvements made without departing from the concept of the present application are all within the scope of protection of the present application.

[0024] In order to simplify the drawings, only the parts related to the corresponding embodiments are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, only part of the components with the same structure or function in some figures are schematically drawn, and there may be more or fewer components with the same structure or function in reality.

[0025] In this application, unless otherwise clearly specified and limited, ordinal numbers, such as "first", "second", etc., are only used to distinguish and describe associated objects, and cannot be understood as indicating or implying the relative importance or order between associated objects; in addition, they do not represent the number of associated objects. "Multiple" includes two or more, and other quantifiers are similar. " / " is used to describe the relationship between associated objects, which indicates the "or" relationship between associated objects. "And / or" is used to describe the relationship between associated objects, which includes any combination relationship between associated objects, such as "a and / or b" includes: "alone a", "alone b", or "a and b". "One or more" or "at least one" in multiple objects refers to any object or any combination of multiple objects, such as "one or more of a1, a2, a3" or "at least one of a1, a2, a3" includes: "alone a1", "alone a2", "alone a3", "a1 and a2", "a1 and a3", "a2 and a3", or "a1, a2 and a3".

[0026] For heavy or large-load mobile machinery (such as vehicles with large mass), its rotational inertia is large, so it is difficult to effectively improve the response speed of heavy mobile machinery during steering and return process. In addition, because there are a large number of nonlinear links in the mechanical transmission process, the system response time lag is large. Combining the above factors, it is difficult to perform precise steering control.

[0027] In different vehicle steering systems, the physical quantities controlled vary greatly. For example, the steering wheel movement of an Ackerman steering vehicle drives the front wheels to rotate, while the front and rear wheels of a four-wheel steering vehicle rotate simultaneously. Articulated vehicles achieve direction changes by rotating the hinge point, and differential vehicles steer by changing the differential speed of the left and right wheels. These different forms of vehicles have significantly different motion models.

[0028] In the current common solutions, steering control is usually achieved by controlling the movement of actuators such as the front wheel angle of the vehicle. This method cannot be universal when the vehicle type changes. Even if the same steering type is used, the control parameters may not be universal when applied to different vehicles, resulting in the need to re-debug the control algorithm each time, making it difficult to quickly reuse.

[0029] Therefore, one of the concepts of the present application is to control the yaw rate so that it can be widely applied to different steering forms. Commonly used sensors in existing steering control systems include encoders and inertial sensors (IMUs). The encoder can obtain the steering wheel angle, while the IMU can obtain the motion state of the vehicle body. However, the encoder readings may offset (error accumulation) over time, and the IMU may introduce greater noise due to vehicle jitter. By fusing feedback data from multiple sensors, the robustness of the system is improved.

[0030] In addition, the debugging of existing control parameters usually relies on manual experience, and the manual debugging process is complicated and time-consuming. To this end, this application designs a set of explainable automatic calibration processes that can automatically debug and calibrate the required parameters to achieve faster and more convenient promotion and application.

[0031] The following is a description with reference to the accompanying drawings.

[0032] Figure 1 An example diagram of a control method for a vehicle steering system provided by an embodiment of the present application is shown. Figure 1 , a control method for a vehicle steering system includes:

[0033] S100, obtaining a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle;

[0034] S200, determining a theoretical system response value based on a system transfer function of the target vehicle and a first steering wheel angle, inputting the first yaw angular velocity and the theoretical system response value into a fusion device to obtain a second yaw angular velocity;

[0035] S300, determining an error value based on the target yaw angular velocity and the second yaw angular velocity, and inputting the error value into a position closed-loop PID controller to obtain a rotation angle increment;

[0036] S400, determining whether the steering wheel motor of the target vehicle supports a speed closed-loop PID controller. If not, outputting the angle increment to the steering wheel motor. If supported, outputting the angle increment to the speed closed-loop PID controller to obtain a speed command, and outputting the speed command to the steering wheel motor.

[0037] The above method can be applied to the scenario of autonomous driving, such as autonomous driving of mobile machinery, to achieve walking control of the mobile machinery.

[0038] The yaw rate describes the rotation speed of the vehicle around its vertical axis, reflecting the overall steering dynamic behavior of the vehicle when turning or changing lanes. This quantity is closely related to the vehicle's motion state, and has nothing to do with the specific steering mechanism (such as front wheels, rear wheels, differentials or hinge points). Whether the vehicle changes direction by turning the front wheels, four-wheel steering, differential control or articulated steering, it will eventually manifest as a change in yaw rate. By controlling the yaw rate, the steering behavior of the vehicle can be uniformly controlled without relying on the specific physical structure of the actuator. When controlling the entire vehicle, the vehicle body can be regarded as a rigid body. Since the vehicle does not have independent lateral motion, the vehicle motion can be decomposed into longitudinal motion and yaw motion. The current common control algorithm is to control the yaw motion by controlling indirect quantities such as the front wheel angle of the vehicle. This method directly controls the yaw amount, that is, controls the yaw rate of the vehicle. Regardless of whether the vehicle is Ackerman steering, rear-wheel steering, differential steering or multi-axle vehicle, its body motion can be abstracted into longitudinal motion and yaw motion. In this way, the control method of the present application can adapt to different steering forms.

[0039] In vehicles, some motors do not support position loop (i.e. position closed-loop PID controller) control, but only support speed loop (i.e. speed closed-loop PID controller). The control method of the present application can enable the motor to support both speed loop and position loop control. Position loop control and speed loop control are essentially two nested control loops: the goal of the position loop is to control the position of the motor (such as the steering wheel angle), that is, the motor rotates to a certain target angle; and the goal of the speed loop is to control the speed of the motor so that the motor rotates at a specified speed. The output of the position loop can be a target speed, which tells the motor at what speed to rotate in order to reach a predetermined angle. Therefore, the speed loop can actually be used to assist the position loop to control how the motor reaches the target position at an appropriate speed.

[0040] For motors that do not support position loops (only support speed control), position control can be indirectly achieved by adjusting the speed loop: although the motor cannot be directly controlled to rotate to a specific position, the motor rotation amplitude can be controlled by continuously adjusting the motor speed. For example, the system can control the motor speed through the speed loop according to the difference between the current position and the target position, so that the motor gradually approaches the target position. When approaching the target position, the speed is gradually reduced so that the motor can stop smoothly at the target position. The core control target of this solution is the yaw rate, which can be achieved by adjusting the motor speed. Therefore, whether it is a motor that supports the position loop or only supports the speed loop, as long as the motor speed can be controlled, the vehicle's yaw rate can be controlled by adjusting the speed. For motors that do not support the position loop, the solution can calculate the difference between the target position and the current position, and convert this difference into a target speed and input it into the speed loop. The motor adjusts the steering wheel according to the target speed to achieve the effect of the target position.

[0041] In the above method, firstly, the first steering wheel angle of the target vehicle when it is running and the first yaw angular velocity matching the first steering wheel angle are obtained. In some embodiments of the present application, an encoder can be installed on the steering wheel motor, and the data of the encoder can be recorded when the target vehicle is running to obtain the first steering wheel angle. Exemplarily, the encoder can be compensated for the median position. As time goes by, the encoder reading may produce a zero offset (i.e., the initial zero point drifts) or a cumulative error, causing it to be unable to accurately reflect the actual angle of the steering wheel. This error may be caused by temperature changes, mechanical wear, installation errors or external interference. Median compensation is a correction technique used to eliminate the effects caused by encoder zero drift or cumulative errors. Its basic principle is to determine how much its actual "median position" (i.e., the theoretical zero point) is offset by recording and analyzing the behavior of the encoder over a period of time, and then compensate and correct its measured value to restore the true angle of the steering wheel. In terms of its implementation process, the system first records the motion data of the steering wheel over a period of time, and determines the offset of the encoder reading through some mathematical methods (such as filtering or averaging). This offset is called the mid-point offset, which represents the deviation of the encoder's measured zero point from the true zero point. After that, the system corrects each encoder reading to compensate for this mid-point offset, making each measured angle closer to the true angle of the steering wheel.

[0042] In some embodiments of the present application, an inertial sensor may be installed on the target vehicle, and the data of the inertial sensor may be recorded when the target vehicle is running to obtain a first yaw velocity; or, an antenna for a global navigation satellite system may be installed on the target vehicle, and satellite signals may be received through the antenna when the target vehicle is running, and the satellite signals may be processed into a first yaw velocity. In other words, the first yaw velocity of the target vehicle when it is running may be obtained through an inertial sensor or an antenna for a global navigation satellite system (GNSS). Moreover, there is a corresponding relationship between the first yaw velocity and the first steering wheel angle, that is, when the steering wheel angle of the target vehicle is the above first steering wheel angle, the yaw velocity that can be obtained by the IMU or the antenna for GNSS is the above first yaw velocity. If the first yaw velocity is obtained through an antenna for GNSS, the first yaw velocity may be obtained through calculation based on the heading data obtained by the antenna.

[0043] In some embodiments of the present application, the control method for a vehicle steering system also includes: constructing a system transfer function of a target vehicle; the system transfer function includes a proportional link and a time-delay link, and the proportional coefficient of the proportional link is determined by a first proportional constant and a second proportional constant; wherein the first proportional constant is the quotient of the front wheel angle of the target vehicle and the first steering wheel angle, and the second proportional constant is the quotient of the vehicle speed of the target vehicle and the wheelbase of the front and rear axles of the target vehicle.

[0044] When the target vehicle keeps moving forward (i.e. the target vehicle is running), the steering wheel movement will cause the vehicle to yaw. There is a mapping relationship between the steering wheel angle θ and the yaw rate ω: ω = f(θ); where θ is the steering wheel angle and ω is the yaw rate. Taking the Ackerman model as an example, the steering wheel angle θ and the front wheel angle δ are proportional links: δ = k 1 θ, k 1 is the first proportional constant, that is, the first proportional constant is the quotient of the front wheel angle of the target vehicle and the first steering wheel angle. The relationship between the front wheel angle δ and the yaw rate ω based on the kinematic model is as follows: Where V is the vehicle speed and L is the wheelbase of the front and rear axles of the target vehicle. When the target vehicle moves at a constant speed, these two terms can be regarded as constants. When the front wheel turning angle of the target vehicle is small, tanδ is approximately equal to δ, so it can be regarded as a proportional function. The second proportional constant k 2 =V / L, that is, the second proportional constant is the quotient of the target vehicle's speed and the target vehicle's front and rear axle distance. 2 δ,ω=k 3 θ, where k 3 is the proportional coefficient of the proportional link, and k 3 =k 1 *k2 . It is proved that the yaw angular velocity ω and the steering wheel angle θ are proportional under limited conditions.

[0045] Due to the delay of the steering transmission system and the delay of the rotational inertia response, the steering system can be regarded as a combination of a proportional link and a time-delay link. The system transfer function can be written as: Where τ is the time constant of the link. In some embodiments of the present application, if the steering system is not linear, a piecewise function can be used to linearize it in stages, and the calculation formula is as follows: That is to say, the nonlinear system is adjusted to a linear state in each segment through a segmented approach.

[0046] For the target vehicle, the yaw rate is controlled, and the feedback is naturally the yaw rate. The inertial sensor can obtain the current yaw rate of the vehicle body (the antenna used for GNSS can obtain the yaw rate of the target vehicle by calculating the obtained heading). The value obtained by the inertial sensor is regarded as the system response plus the sensor observation noise, and the encoder reading of the steering wheel motor is the system input plus the encoder reading zero bias. For example, the real steering wheel angle can be read out by encoder mid-position compensation. According to the angle value, the system response can be calculated according to the aforementioned transfer function. Since the response is obtained by theoretical calculation through the steering wheel angle, the sensor observation noise and system response delay of the direct observation system output are avoided. By calculating the amount of action of the steering wheel encoder in the previous τ time, the value obtained by the transfer function calculation can be used as compensation for the delay in the direct observation of the vehicle body yaw response. In addition, the vehicle body yaw rate directly measured by the inertial sensor is used as the system response measurement value. Use them together in the Kalman filter for observation, and the value obtained is a relatively accurate feedback value of the vehicle body. This value is named the second yaw rate ω N .

[0047] The above embodiments combine the values ​​of the inertial sensor and the motor encoder, taking advantage of the characteristics of the inertial sensor's instantaneous absolute value being accurate (but with large noise and including vehicle response delay) and the encoder's relative value being accurate and stable and not including response delay (but with zero offset), taking advantage of their strengths and making up for their weaknesses, and using the fused value as feedback to improve control accuracy and stability.

[0048] In the present application, an error value is determined based on the target yaw rate and the second yaw rate, and the error value is input into the position closed-loop PID controller to obtain the angle increment; then, it is determined whether the steering wheel motor of the target vehicle supports the speed closed-loop PID controller. If not, the angle increment is output to the steering wheel motor; if supported, the angle increment is output to the speed closed-loop PID controller to obtain a speed command, and the speed command is output to the steering wheel motor. In some embodiments of the present application, the steering wheel motor receives the angle increment or the speed command, and generates a compensation response value based on the system transfer function; the control method further includes: inputting the compensation response value, the first yaw rate and the theoretical system response value into the fusion device to obtain the second yaw rate. In some embodiments of the present application, the fusion device is a Kalman filter, an extended Kalman filter or an unscented Kalman filter.

[0049] The target yaw rate issued by the upper control can be called ω T At this time, the error between the target yaw rate and the second yaw rate is: e ω =ω T -ω N , the target action increment (position loop increment pid) at this time is: Among them, k p , k i and k d The proportional, integral and differential coefficients of the position closed-loop PID controller. For the speed loop control, the speed loop is controlled by connecting a first-level PID in series: Among them, k ′ p , k i ′ and k ′ d are the proportional, integral and differential coefficients of the speed closed-loop PID controller.

[0050] In some embodiments of the present application, for the nonlinear problem of the steering system (mainly the virtual position of the steering wheel caused by the steering clearance, which is called the dead zone in control). ′ ,θ ′ ], the dead zone can be overcome by changing the position loop gain. The calculation formula is as follows: in, is the gain set for the dead zone, and k p dz >k p Similarly, the nonlinearity in the non-dead zone can be applied to the idea of ​​the above piecewise function (refer to the above embodiment), and a piecewise variable gain PID control is set.

[0051] In the above embodiments, the control effect of the nonlinear steering system is improved by the variable gain + cascade PID control method, and the conversion control from the steering wheel angle to the motor speed is realized at the same time.

[0052] Figure 2 Another example diagram of a control method for a vehicle steering system provided by an embodiment of the present application is shown. Figure 2 In some embodiments of the present application, the control method for a vehicle steering system further includes:

[0053] S500, calibrating parameters in the position closed-loop PID controller and the speed closed-loop PID controller, the parameters including proportional gain parameters and differential gain parameters.

[0054] For example, please continue to refer to Figure 2 , the calibration methods include:

[0055] S510, initializing a second steering wheel angle, where the second steering wheel angle is a maximum angle of an initial steering wheel of the target vehicle;

[0056] S520, based on the second steering wheel angle, controlling the target vehicle to rotate during operation, and recording a third yaw angular velocity that matches the second steering wheel angle;

[0057] S530, determining whether the third yaw angular velocity is within a preset interval, if not, using the target yaw angular velocity and the maximum value in the preset interval to correct the second steering wheel angle until the third yaw angular velocity is within the preset interval, if so, using the second steering wheel angle to obtain the corresponding maximum angle, minimum angle, maximum yaw angular velocity and minimum yaw angular velocity, and determining the parameters in the position closed-loop PID controller and the speed closed-loop PID controller. In some embodiments of the present application, the differential gain parameter is in a multiple relationship with the proportional gain parameter.

[0058] Automatic calibration of parameters includes calibration of position loop control parameters and calibration of speed loop control parameters. First, the calibration program flow can be used to obtain the motor position loop control parameters. The calibration process can be referred to as follows. In the initial state, the target vehicle starts at a stable constant speed. The yaw angular velocity of the target vehicle is directly or indirectly obtained through an inertial sensor or an antenna for GNSS. By adjusting the steering wheel position, the yaw angular velocity slowly converges to zero, so that the steering wheel returns to the center and the target vehicle is driving in a straight line. Then set the steering wheel to swing in the form of a periodic function, such as a sine function: Among them, A 0is a constant, that is, the second steering wheel angle, which is the maximum angle of the initial steering wheel of the target vehicle, t is the time to start the movement, l is an arbitrary positive number, and f is the control frequency; thereby completing the initialization of the second steering wheel angle. In this process, the action of the steering wheel causes the vehicle to swing left and right. At this time, the vehicle yaw rate under the timing is recorded synchronously, that is, based on the second steering wheel angle, the target vehicle is controlled to rotate during operation, and the third yaw rate matching the second steering wheel angle is recorded. Then, it is determined whether the maximum value of the vehicle yaw rate (that is, the third yaw rate above) in the previous stage is within the preset interval, and the preset interval can be, for example, [1,3]° / s. If not, the second steering wheel angle is corrected using the target yaw rate and the maximum value in the preset interval. The calculation formula is as follows: Among them, A ′ 0 This is the corrected second steering wheel angle. Then repeat the above recording and judging operations until the third yaw angular velocity is within the preset range. If the third yaw angular velocity is within the preset range, the target vehicle can stop moving and proceed to the next step of calculation, that is, using the second steering wheel angle to obtain the corresponding maximum angle, minimum angle, maximum yaw angular velocity and minimum yaw angular velocity, and determine the parameters in the position closed-loop PID controller and the speed closed-loop PID controller. The calculation formula is as follows. If there is no gap in the vehicle steering system, the transmission coefficient can be regarded as a constant: Otherwise, k should be calculated piecewise: Then, according to the k calculated in the above formula, the control parameters can be calculated through the time series data: Where q represents the number of cycles expected to converge to the current error. d With k p The differential gain parameter and the proportional gain parameter are related in multiples: k d =w·k p For example, w is 0.2, and k d =0.2k p At this time, k j Take the yaw offset of the full calibration cycle: At this point, the position loop control parameter calibration function is completed.

[0059] After the position loop is calibrated, the speed loop control parameters can be calibrated, that is, the unit conversion of the motor input dimension obtains the speed control parameters. The command issued by the position loop is degrees per second (° / s). For example, taking the speed command received by the motor as rpm (that is, how many revolutions per minute), assuming that the motor control frequency is T and the expected period is n, the following calculation formula can be obtained: In some implementations, assuming that the motor control frequency is 20 Hz, and the motor is expected to complete the target motion within 2 cycles, the following calculation formula is used: Thus, the automatic calibration of the speed loop parameters is completed.

[0060] Since the control parameters of different types of vehicles, or even vehicles of the same type with different specifications, may not be universal in the prior art, and it is difficult to use the experience-based tuning method, which is not conducive to the promotion of the method. In the above embodiment, the automatic calibration method of the design parameters can effectively improve the debugging efficiency.

[0061] Based on similar technical concepts, the present application also discloses a controller for a target vehicle, and executes the control method for a vehicle steering system disclosed in the first aspect above. Exemplarily, the controller can be, for example, an electronic control unit (ECU). The ECU is the core of the entire control system, which is responsible for executing the PID control algorithm (position loop and speed loop) and calculating the required motor control parameters, such as kp and kd, based on the feedback signals provided by sensors (such as IMU, GNSS). In addition, the ECU receives sensor data such as vehicle speed, yaw rate, steering wheel angle, etc., and performs real-time calculations and adjustments to ensure that the vehicle can turn according to the set path or target under different steering conditions.

[0062] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments. In addition, the above embodiments can be freely combined as needed.

Claims

1. A control method for a vehicle steering system, characterized in that: include: Acquire a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle; Determine a theoretical system response value based on the system transfer function of the target vehicle and the first steering wheel angle, input the first yaw rate and the theoretical system response value into a fusion device, and obtain a second yaw rate; Determine an error value based on the target yaw angular velocity and the second yaw angular velocity, and input the error value into a position closed-loop PID controller to obtain a rotation angle increment; Determine whether the steering wheel motor of the target vehicle supports a speed closed-loop PID controller. If not, output the angle increment to the steering wheel motor. If supported, output the angle increment to the speed closed-loop PID controller to obtain a speed command, and output the speed command to the steering wheel motor.

2. The control method for a vehicle steering system according to claim 1, characterized in that: The steering wheel motor receives the rotation angle increment or the rotation speed command and generates a compensation response value based on the system transfer function; the method further includes: The compensation response value, the first yaw angular velocity, and the theoretical system response value are input into the fusion device to obtain the second yaw angular velocity.

3. The control method for a vehicle steering system according to claim 1 or 2, characterized in that: The fuser is a Kalman filter, an extended Kalman filter or an unscented Kalman filter.

4. The control method for a vehicle steering system according to claim 1, characterized in that: The step of obtaining a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle includes: Installing an encoder on the steering wheel motor; The data of the encoder is recorded when the target vehicle is running to obtain the first steering wheel angle.

5. The control method for a vehicle steering system according to claim 1 or 4, characterized in that: The step of obtaining a first steering wheel angle of the target vehicle when it is running and a first yaw angular velocity matching the first steering wheel angle includes: installing an inertial sensor on the target vehicle; Recording data of the inertial sensor when the target vehicle is running to obtain the first yaw angular velocity; or, installing an antenna for a global navigation satellite system on the target vehicle; The target vehicle receives a satellite signal through the antenna when the target vehicle is running, and processes the satellite signal into the first yaw angular velocity.

6. The control method for a vehicle steering system according to claim 1, characterized in that: Also includes: Constructing a system transfer function of the target vehicle; The system transfer function includes a proportional link and a time-delay link, and the proportional coefficient of the proportional link is determined by a first proportional constant and a second proportional constant; The first proportional constant is the quotient of the front wheel angle of the target vehicle and the first steering wheel angle, and the second proportional constant is the quotient of the vehicle speed of the target vehicle and the wheelbase of the front and rear axles of the target vehicle.

7. The control method for a vehicle steering system according to claim 1, characterized in that: Also includes: Calibrate parameters in the position closed-loop PID controller and the speed closed-loop PID controller, wherein the parameters include proportional gain parameters and differential gain parameters.

8. The control method for a vehicle steering system according to claim 7, characterized in that: The calibrating of the parameters in the position closed-loop PID controller and the speed closed-loop PID controller comprises: Initializing a second steering wheel angle, where the second steering wheel angle is a maximum angle of an initial steering wheel of the target vehicle; Based on the second steering wheel angle, controlling the target vehicle to rotate during operation, and recording a third yaw angular velocity matching the second steering wheel angle; Determine whether the third yaw angular velocity is within a preset interval; if not, correct the second steering wheel angle by using the target yaw angular velocity and the maximum value in the preset interval until the third yaw angular velocity is within the preset interval; if so, obtain the corresponding maximum angle, minimum angle, maximum yaw angular velocity and minimum yaw angular velocity by using the second steering wheel angle, and determine parameters in the position closed-loop PID controller and the speed closed-loop PID controller.

9. The control method for a vehicle steering system according to claim 7 or 8, characterized in that: The differential gain parameter is in a multiple relationship with the proportional gain parameter.

10. A controller, characterized in that: Used in a target vehicle, and executing a control method for a vehicle steering system as claimed in any one of claims 1 to 9.

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