An angle smooth response and fast intervention angle control method

Abstract

This invention relates to the field of steering system technology, specifically to an angle control method with smooth angle response and rapid intervention. The method includes an angular velocity feedforward PID algorithm. This algorithm calculates the angle difference by subtracting the requested angle from the actual angle. The angle difference is then processed by the PID algorithm to obtain the target motor torque. This target motor torque is then converted into the actual executed motor torque through gradient output, controlling the steering wheel rotation. The key feature is that the smooth angle response includes low-frequency compensation and high-frequency compensation strategies. Compared to existing technologies, this method provides an angle control method with smooth angle response and rapid intervention. It uses an angular velocity feedforward PID algorithm to calculate the motor torque and introduces low-frequency and high-frequency compensation strategies, as well as a rapid intervention strategy, to control the steering wheel to smoothly and quickly achieve the target angle.

Description

Technical Field

[0001] This invention relates to the field of steering system technology, specifically to an angle control method that provides smooth angle response and rapid intervention. Background Technology

[0002] Currently, autonomous driving technology is widely used in the automotive field. Lateral control in autonomous driving is primarily based on steering, and the steering end often uses an electric power steering system as a platform to design an angle control system, completing steering by responding to angle requests from the autonomous driving system. From a stability perspective, the autonomous driving system does not want angle control functions to be easily disrupted by external interference. Vehicle systems typically require that angle control functions only disengage when both the driver's hand torque and duration reach a set threshold. Furthermore, the electric power steering system is required to not respond to driver input when the hand torque is low, so that human intervention does not easily affect the vehicle's path planning. However, when the autonomous driving system cannot handle complex or sudden situations, there are risks such as the inability to turn the steering wheel quickly when the driver takes over, and uneven disengagement of the angle control function. These issues can easily cause driving panic and prevent timely obstacle avoidance when autonomous driving planning malfunctions.

[0003] Traditional angle control systems use a feedforward PID algorithm based on angular velocity to calculate motor torque. Part of the calculation involves subtracting the requested angle from the actual angle to obtain the angle difference, which is then processed by the PID algorithm to arrive at the target motor torque. Another part involves subtracting the actual angular velocity from 0 and multiplying by a corresponding coefficient to obtain a portion of the motor torque. The sum of these two calculations constitutes the basic torque for angle control. When stationary or moving at low speeds, significant resistance exists due to the large resistance between the tires and the ground, as well as the large self-centering torque caused by the vehicle's structural components and longitudinal forces. When the vehicle requests a low-frequency, small angle, the motor torque calculated by the PID algorithm is initially low, causing the motor to be unable to overcome the resistance, resulting in the steering wheel not turning or turning very slowly. However, because the angle difference persists, the integral term accumulates, eventually increasing the motor torque and causing the steering wheel to turn rapidly. When the target angle is reached, this process repeats, leading to a problem of the steering wheel initially moving slowly and then accelerating, resulting in a sluggish steering wheel. However, when the vehicle requests a high frequency and large angle, the initial angle difference is large, the calculated motor torque is large, and the actual angular velocity is large. This results in a fast steering wheel rotation speed and large acceleration at the start. However, when the target angle is about to be reached, the calculated target torque begins to decrease. The increase in steering angle also increases the steering system's return force and mechanical friction, causing a short-term decrease in steering wheel rotation speed and acceleration. This repeated cycle causes the steering wheel to become stuck, going from fast to slow.

[0004] The above reasons can easily cause uneven steering wheel operation, affecting the driving experience. Based on this, this paper proposes an angle smoothness response and driver quick intervention angle control system to solve the above problems and improve the driving experience. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an angle control method with smooth angle response and rapid intervention. It uses an angular velocity feedforward PID algorithm to calculate motor torque and introduces low-frequency and high-frequency compensation strategies, as well as a rapid intervention strategy, to control the steering wheel to smoothly and quickly achieve the target angle.

[0006] To achieve the above objectives, an angle control method with smooth angle response and rapid intervention is designed, including an angular velocity feedforward PID algorithm. The angular velocity feedforward PID algorithm calculates the angle difference by subtracting the requested angle from the actual angle. This angle difference is then processed by the PID algorithm to obtain the target motor torque. The target motor torque is then converted into the actual executed motor torque through gradient output to control the steering wheel rotation. The method is characterized by: the smooth angle response including low-frequency compensation strategies and high-frequency compensation strategies.

[0007] The low-frequency compensation strategy is as follows:

[0008] S11, the vehicle speed range is set to 0-5 km / h;

[0009] S12, calculate the angle difference between the requested angle and the actual angle, and then calculate the angle following coefficient σ1 based on the angle difference; S13, calculate the viscosity compensation coefficient σ2 based on the angular velocity;

[0010] S14, Calculate the initial torque value of low-frequency compensation LowFreqMotTorq based on the vehicle speed table;

[0011] S15, calculate the low-frequency compensation torque LowMotTorq and output it to the motor in gradient;

[0012] The high-frequency compensation strategy is as follows:

[0013] S21, Calculate the maximum limit of the virtual hand torque based on the vehicle speed table;

[0014] S22, Calculate the virtual hand force gain coefficient with respect to angular velocity by looking up a table based on the angular velocity.

[0015] S23, Calculate the virtual hand force gain coefficient based on vehicle speed by referring to a table.

[0016] S24, read the actual hand torque value TBT measured at the electric power steering system end;

[0017] The rapid intervention strategy is as follows:

[0018] S31, calculate the rate of change of the true hand torque value TBT at adjacent n time points;

[0019] S32, determine if the angular velocity is less than the boundary;

[0020] S33, calculate whether the cumulative value of the true hand torque TBT within time n is greater than the boundary;

[0021] S34. When the conditions of steps S32 and S33 are met, calculate the quick intervention hand torque value QuickGetTBT, and after gradient processing, complete the steering operation in the basic power assist module.

[0022] The formula for calculating the target motor torque in the aforementioned angular velocity feedforward PID algorithm is as follows:

[0023] Where TarMotTorq is the target motor torque, TarAng is the requested angle, CurAng is the actual steering wheel angle, CurAngSpd is the actual steering wheel angular velocity, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, and Kv is the coefficient for angular velocity to participate in torque calculation.

[0024] The formula for the low-frequency compensation torque is LowMotTorq=LowFreqMotTorq*σ1*σ2; where LowMotTorq is the low-frequency compensation torque, LowFreqMotTorq is the initial torque value for low-frequency compensation, σ1 is the angle following coefficient, and σ2 is the viscous compensation coefficient.

[0025] The formula for calculating the virtual hand torque value is as follows: Where HighMotTorq represents high-frequency compensated torque, and TBT represents the actual hand torque value. The virtual hand force gain coefficient varies with angular velocity. This is the virtual hand force gain coefficient that varies with vehicle speed.

[0026] During the high-frequency compensation process, the actual hand torque value TBT is less than 1 Nm.

[0027] To ensure that the high-frequency compensation strategy does not conflict with the low-frequency compensation strategy, the virtual hand force gain coefficient with angular velocity involved in the high-frequency compensation strategy is... The calibration is smaller when the angular velocity is small, and the virtual hand force gain coefficient with vehicle speed is involved. The calibration is smaller at low speeds; because the actual hand torque value TBT is relatively small during low-frequency motion, the final target motor torque for angle tracking is... Where TarMotTorq is the target motor torque, TarAng is the requested angle, CurAng is the actual steering wheel angle, CurAngSpd is the actual steering wheel angular velocity, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, Kv is the coefficient for angular velocity in torque calculation, LowMotTorq is the low-frequency compensation torque, and HighMotTorq is the high-frequency compensation torque.

[0028] The formula for calculating the quick-intervention hand torque value is QuickGetTBT=(abs(TBT)-δ)*ω*Sign(TBT); where QuickGetTBT is the quick-intervention hand torque value, abs(TBT) is the absolute value of the hand force, δ is the set TBT value, ω is the coefficient obtained by looking up the table according to the vehicle speed, and Sign(TBT) is the actual hand force direction.

[0029] In step S34, a portion of the compensated virtual hand force value GetOutTBT is first calculated and given to the basic power steering module, and then the driver continues to control the steering wheel. The specific process is as follows:

[0030] (1) Calculate the virtual hand force value VirtualTBT based on the vehicle speed table;

[0031] (2) Calculate the virtual compensation coefficient μ of the hand force by looking up the table based on the TBT value, and multiply the two to get GteOutTBT, i.e. GetOutTBT=VirtualTBT*μ;

[0032] (3) GteOutTBT decreases to 0 after a certain gradient. During the gradient descent of GteOutTBT, the base assist is increasing.

[0033] Compared with the prior art, this invention provides an angle control method with smooth angle response and rapid intervention. It uses an angular velocity feedforward PID algorithm to calculate motor torque and introduces low-frequency and high-frequency compensation strategies, as well as a rapid intervention strategy, which can control the steering wheel to achieve the target angle smoothly and quickly. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention.

[0035] Figure 2 Flowchart for rapid intervention and handling strategies.

[0036] Figure 3 This is a graph showing the actual vehicle performance during rapid intervention.

[0037] Figure 4 This is a graph showing the overall vehicle's angular response performance. Detailed Implementation

[0038] The present invention will now be further described with reference to the accompanying drawings.

[0039] like Figure 1 As shown, the control method of the present invention includes an angular velocity feedforward PID algorithm. The angular velocity feedforward PID algorithm obtains the angle difference by subtracting the requested angle from the actual angle. The angle difference is used to obtain the target motor torque through the PID algorithm. The target motor torque is converted into the actual motor torque by the gradient output to control the steering wheel rotation.

[0040] In the control process, it is expected that the steering wheel will reach a target angle. Once the target angle is reached, the actual angular velocity is 0. Therefore, the actual angular velocity is introduced into the torque calculation. The parameters involved in the PID algorithm and the angular velocity feedforward part are calculated based on the vehicle speed. Furthermore, the P, I, and D terms all have motor torque limits at different vehicle speeds to prevent the risk of vehicle instability caused by excessive motor torque saturation and rapid steering wheel rotation at high speeds.

[0041] The formula for calculating the target motor torque in angle control is as follows:

[0042] Where TarMotTorq is the target motor torque, TarAng is the requested angle, CurAng is the actual steering wheel angle, CurAngSpd is the actual steering wheel angular velocity, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, and Kv is the coefficient for angular velocity to participate in torque calculation.

[0043] The existing electric power steering system calculates the assist torque based on vehicle speed, hand torque value (TBT), etc., which is called the basic assist mode. The basic assist mode controls the motor to achieve the steering requirements.

[0044] The angle control function involved in this invention can decouple the basic power assist mode from the angle control mode. When the angle control function is activated, if the magnitude of the hand torque and the short-term integral of the hand torque do not meet the requirements, the steering will not be changed in response to the hand torque value, thereby reducing the impact of the driver on the automatic driving system.

[0045] The angle smoothness response processing strategy involved in this invention consists of two parts: a low-frequency compensation strategy and a high-frequency compensation strategy. The purpose of the low-frequency compensation strategy is to overcome the resistance caused by tire-ground friction, vehicle kingpin structure and longitudinal force return torque, and mechanical friction, so as to accelerate the response of the electric power steering system to the target angle requested by the vehicle. Specifically, it is implemented as follows: 1) Set the vehicle speed range Vspd: 0~5Km / h to ensure that the low-frequency compensation torque is output only within the vehicle speed range, and the vehicle speed range can be calibrated; 2) Calculate the difference between the requested angle and the actual angle, and calculate the coefficient σ1 based on the angle difference; 3) Calculate the coefficient σ2 based on the angular velocity; 4) Calculate the initial low-frequency compensation torque value LowFreqMotTorq based on the vehicle speed (the table is for vehicle speed on the X-axis and motor torque on the Y-axis); 5) Calculate the low-frequency compensation torque and output it to the motor in a gradient.

[0046] The formula for calculating low-frequency compensation torque is LowMotTorq=LowFreqMotTorq*σ1*σ2.

[0047] The high-frequency compensation strategy aims to provide initial reaction force to address the issue of high angular velocity and speed during steering wheel start-up when responding to large-angle requests. Because the angular velocity is high for a period during the response to a large-angle request, it also drags the TAS sensor in the opposite direction, resulting in a large actual hand torque value (TBT). Therefore, in high-frequency compensation, the actual hand torque value (TBT) and angular velocity can be incorporated into the compensation logic. Specifically, this is implemented as follows: 1) Calculate the maximum virtual hand torque value using a lookup table based on vehicle speed; 2) Calculate the gain coefficient using a lookup table based on angular velocity (where the X-axis represents angular velocity and the Y-axis represents the gain coefficient). 3) Calculate the gain coefficient using the on-board speed table. 4) Read the actual hand torque value TBT measured at the electric power steering system end; 5) To prevent the driver from accidentally triggering the steering wheel, the actual hand torque value TBT during high-frequency compensation should be less than 1 Nm.

[0048] During the initial operation phase when the angle control system receives high-frequency angle requests, the actual hand torque value TBT is relatively large. However, the hand torque value collected by the sensor during the autonomous driving start-up phase is in the opposite direction to the value collected by the driver operating the steering wheel. By calculating the virtual hand torque value HighMotTorq, and then passing the virtual hand torque through a limit, it is transmitted to the basic power assist module to replace the actual hand torque value TBT to look up the table for virtual power assist. This improves the steering wheel sticking problem caused by excessive torque and sudden acceleration changes during the high-frequency angle request phase.

[0049] The formula for calculating the virtual hand torque value is as follows:

[0050] To ensure that high-frequency logic and low-frequency logic do not conflict, the gain coefficient involved in the high-frequency logic section... The calibration is smaller when the angular velocity is small, and the gain coefficient involved is smaller. The calibration is small at low speeds, and the TBT is relatively small at low frequency motion. According to the calculation formula of the target motor torque in angle control, the influence of the high frequency logic on the low frequency logic is greatly reduced.

[0051] The formula for calculating the target motor torque required for the final angle to follow is as follows:

[0052] like Figure 2 As shown, the quick intervention component calculates a virtual hand torque value (QuickGetTBT) based on the hand force and vehicle speed, and provides it to the basic power steering module to obtain assistance, helping the driver change direction in angle control mode. Specifically, it implements the following: 1) Calculates the rate of change of the actual hand torque value (TBT) over adjacent n time steps; 2) Determines whether the angular velocity is less than the boundary to prevent the actual hand torque value (TBT) from being too large due to excessive angular velocity during response angle, thus reducing the probability of false triggering; 3) Calculates whether the cumulative value of the actual hand torque value (TBT) within n time steps is greater than the boundary to prevent accidental triggering due to accidental hand contact with the steering wheel. When all conditions are met, the quick intervention hand torque is calculated, processed by gradient, and then provided to the basic power steering module to complete the steering operation.

[0053] The formula for calculating the quick-intervention hand torque value is QuickGetTBT=(abs(TBT)-δ)*ω*Sign(TBT). Where abs(TBT) is the absolute value of the hand force, δ is the set TBT value, ω is a coefficient obtained from a speed-based lookup table, and Sign(TBT) is the actual direction of the hand force. In traditional steering, the TAS sensor can collect a value, which is the hand force, abbreviated as TBT. abs(TBT) is simply the absolute value of TBT, i.e., the absolute value of the hand force.

[0054] like Figure 3 The image shows the actual vehicle performance curve during rapid intervention. After the rapid intervention indicator is positioned, QuickGetTBT obtains the response value based on the formula for calculating the rapid intervention hand torque. Even if the overall vehicle angle request remains unchanged, it can still change the actual steering wheel angle to help the driver cope with situations that autonomous driving cannot handle.

[0055] In the angle control system, the functional safety requirement is that the angular velocity be less than the safety boundary value. When the rapid intervention logic is activated, the high-frequency compensation section stops working. When the rapid intervention section is working, the angular velocity may not meet the functional safety requirements as the system begins to provide basic power assist, causing the rapid intervention section to stop working. If the angle control function exits at this time, this invention can still calculate a portion of the compensated virtual hand force value GetOutTBT according to the calculation formula of the compensated virtual hand force value and provide it to the basic power assist module to continue supporting the driver's control of the steering wheel. This prevents the rapid intervention section from exiting immediately and causing a sudden increase in hand force, which would lead to a two-stage problem in the hand feel due to the slow increase in power assist. The specific implementation is as follows: 1) Calculate the virtual hand force value VirtualTBT according to the vehicle speed table; 2) Calculate the coefficient μ according to the TBT value table, and multiply the two to obtain GteOutTBT, i.e., GetOutTBT = VirtualTBT * μ; 3) GteOutTBT decreases to 0 after a certain gradient. During the gradient decrease of GteOutTBT, the basic power assist is increasing.

[0056] When the rapid intervention logic is running, it looks up a larger attenuation coefficient α1 from the table based on the torque calculated by the current PID controller, multiplies it by the torque calculated by the PID controller, and transmits it to the motor actuator. This weakens the PID torque's resistance to the driver's hand movements on the steering wheel. When the rapid intervention does not cause the function to exit, the driver's hand movements on the steering wheel will cause a large angle difference. Because the integral term of the PID algorithm does not accumulate, a large torque value will be calculated at this time, causing the steering wheel to rotate rapidly. This poses a significant risk, especially at high speeds, and can also cause the driver to kick back.

[0057] When the invention determines that the rapid intervention condition does not cause the angle control function to exit, the rapid intervention section uses the motor torque calculated by the PID controller to look up a table to calculate the attenuation coefficient α2. This coefficient is then multiplied by the torque calculated by the PID controller to attenuate the calculated torque. The attenuation coefficient α1 is less than the attenuation coefficient α2. When the difference between the requested angle and the actual executed angle is detected to be small, the motor torque attenuation strategy is exited to prevent the steering wheel from quickly returning to the target angle position due to a large angle difference, thereby reducing driving risk and improving the steering wheel kickback issue.

[0058] like Figure 4 As shown, the curve of the vehicle's angle response is as follows. According to the above theory, during the test, the actual response angle of the vehicle's steering wheel and the target angle curve requested by the vehicle are smoothly close to each other, which meets the requirements.

Claims

1. An angle control method with smooth response and rapid intervention, comprising an angular velocity feedforward PID algorithm, wherein the angular velocity feedforward PID algorithm obtains the angle difference by subtracting the requested angle from the actual angle, the angle difference is used by the PID algorithm to obtain the target motor torque, and the target motor torque is converted into the actual executed motor torque through gradient output to control the steering wheel rotation, characterized in that: The aforementioned angle smoothness response includes low-frequency compensation strategies and high-frequency compensation strategies. The low-frequency compensation strategy is as follows: S11, the vehicle speed range is set to 0-5 km / h; S12, calculate the angle difference between the requested angle and the actual angle, and then calculate the angle following coefficient σ1 based on the angle difference; S13, calculate the viscosity compensation coefficient σ2 based on the angular velocity; S14, Calculate the initial torque value of low-frequency compensation LowFreqMotTorq based on the vehicle speed table; S15, calculate the low-frequency compensation torque LowMotTorq and output it to the motor in gradient; The high-frequency compensation strategy is as follows: S21, Calculate the maximum limit of the virtual hand torque based on the vehicle speed table; S22, Calculate the virtual hand force gain coefficient with respect to angular velocity by looking up a table based on the angular velocity. S23, Calculate the virtual hand force gain coefficient based on vehicle speed by referring to a table. S24, read the actual hand torque value TBT measured at the electric power steering system end; The rapid intervention strategy is as follows: S31, calculate the rate of change of the true hand torque value TBT at adjacent n time points; S32, determine if the angular velocity is less than the boundary; S33, calculate whether the cumulative value of the true hand torque TBT within time n is greater than the boundary; S34. When the conditions of steps S32 and S33 are met, calculate the quick intervention hand torque value QuickGetTBT, and after gradient processing, complete the steering operation in the basic power assist module.

2. The angle control method with smooth angle response and rapid intervention according to claim 1, characterized in that: The formula for calculating the target motor torque in the aforementioned angular velocity feedforward PID algorithm is as follows: Where TarMotTorq is the target motor torque, TarAng is the requested angle, CurAng is the actual steering wheel angle, CurAngSpd is the actual steering wheel angular velocity, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, and Kv is the coefficient for angular velocity to participate in torque calculation.

3. The angle control method with smooth angle response and rapid intervention according to claim 1, characterized in that: The formula for the low-frequency compensation torque is LowMotTorq=LowFreqMotTorq*σ1*σ2; where LowMotTorq is the low-frequency compensation torque, LowFreqMotTorq is the initial torque value for low-frequency compensation, σ1 is the angle following coefficient, and σ2 is the viscous compensation coefficient.

4. The angle control method with smooth angle response and rapid intervention according to claim 1, characterized in that: The formula for calculating the virtual hand torque value is as follows: Where HighMotTorq represents high-frequency compensated torque, and TBT represents the actual hand torque value. The virtual hand force gain coefficient varies with angular velocity. This is the virtual hand force gain coefficient that varies with vehicle speed.

5. The angle control method with smooth angle response and rapid intervention according to claim 1 or 4, characterized in that: During the high-frequency compensation process, the actual hand torque value TBT is less than 1 Nm.

6. The angle control method with smooth angle response and rapid intervention according to claim 1 or 4, characterized in that: To ensure that the high-frequency compensation strategy does not conflict with the low-frequency compensation strategy, the virtual hand force gain coefficient with angular velocity involved in the high-frequency compensation strategy is... The calibration is smaller when the angular velocity is small, and the virtual hand force gain coefficient with vehicle speed is involved. The calibration is smaller at low speeds; because the actual hand torque value TBT is relatively small during low-frequency motion, the final target motor torque for angle tracking is... Where TarMotTorq is the target motor torque, TarAng is the requested angle, CurAng is the actual steering wheel angle, CurAngSpd is the actual steering wheel angular velocity, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, Kv is the coefficient for angular velocity in torque calculation, LowMotTorq is the low-frequency compensation torque, and HighMotTorq is the high-frequency compensation torque.

7. The angle control method with smooth angle response and rapid intervention according to claim 1, characterized in that: The formula for calculating the quick-intervention hand torque value is QuickGetTBT=(abs(TBT)-δ)*ω*Sign(TBT); where QuickGetTBT is the quick-intervention hand torque value, abs(TBT) is the absolute value of the hand force, δ is the set TBT value, ω is the coefficient obtained by looking up the table according to the vehicle speed, and Sign(TBT) is the actual hand force direction.

8. The angle control method with smooth angle response and rapid intervention according to claim 1, characterized in that: In step S34, a portion of the compensated virtual hand force value GetOutTBT is first calculated and given to the basic power steering module, and then the driver continues to control the steering wheel. The specific process is as follows: (1) Calculate the virtual hand force value VirtualTBT based on the vehicle speed table; (2) Calculate the virtual compensation coefficient μ of the hand force by looking up the table based on the TBT value, and multiply the two to get GteOutTBT, i.e. GetOutTBT=VirtualTBT*μ; (3) GteOutTBT decreases to 0 after a certain gradient. During the gradient descent of GteOutTBT, the base assist is increasing.

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