KR20230147473A - Apparatus and method for controlling electronic power steering system - Google Patents

Abstract

The present invention predicts the command steering angle based on an LPF (Low Pass Filter) that filters the command steering angle output from the autonomous driving system and control information output from the autonomous driving system, and compares the predicted command steering angle with the current steering angle of the vehicle. and a controller that controls the cutoff frequency of the LPF based on a result of comparing the predicted command steering angle and the current steering angle of the vehicle to vary the control response of the electric steering system.

Description

Control device and method for electric steering system {APPARATUS AND METHOD FOR CONTROLLING ELECTRONIC POWER STEERING SYSTEM}

The present invention relates to a control device and method for an electric steering system, and more particularly, to a control device and method for an electric steering system provided in an autonomous vehicle.

A vehicle's power steering is a power-based steering device that helps the driver operate the steering wheel. This type of power steering was mainly used using hydraulic pressure, but recently, the use of the motor driven power steering (MDPS) system, which uses the power of a motor, has been increasing. Compared to existing hydraulic power steering systems, the MDPS system has the advantage of being lighter in weight, taking up less space, and requiring no oil changes.

The MDPS system determines the vehicle's driving conditions through a torque sensor that measures the driver's steering torque input to the steering wheel, a steering angle sensor that measures the steering angle or steering angle speed of the steering wheel, and a vehicle speed sensor that measures the vehicle speed. As the steering wheel is steered, auxiliary torque is provided through the electric motor based on the steering torque applied to the steering shaft.

Meanwhile, the autonomous vehicle controls the operation of the MDPS system applied to the autonomous vehicle by recognizing the road environment on which it is driving through the autonomous driving module in autonomous driving mode and determining the command steering angle and command torque required for the operation of the MDPS system.

However, in the case of the MDPS system applied to an autonomous vehicle, even if the difference between the command steering angle and the current steering angle is slight, it responds sensitively to the command steering angle calculated through the autonomous driving module, so when driving straight or turning at a certain angle, the vehicle may slightly There is a problem that driving stability and ride comfort deteriorate as the vehicle continues to shake left and right.

The background technology of the present invention is disclosed in Korean Patent Publication No. 10-2021-0007112 (2021.01.20.) ‘Electric steering device for vehicle and control method thereof’.

The present invention was created to solve the above-mentioned problems, and the object according to one aspect of the present invention is a control device for an electric steering system that can adaptively vary the control response of an electric steering system provided in an autonomous vehicle. and method are provided.

A control device for an electric steering system according to an aspect of the present invention includes a low pass filter (LPF) that filters the command steering angle output from the autonomous driving system; and predicting a command steering angle based on control information output from the autonomous driving system, comparing the predicted command steering angle with the current steering angle of the vehicle, and varying the control responsiveness of the electric steering system based on the comparison result. and a controller that controls the cutoff frequency of the LPF.

In the present invention, the control information is characterized in that it includes information about the distance and direction between the target path and the vehicle, information about the lateral acceleration of the vehicle, and information about the turning radius of the vehicle.

In the present invention, the controller predicts the command steering angle using the following equation.

[formula]

here, is the command steering angle, is the difference between the tangential direction of the reference point located on the target path and the vehicle's heading direction, e(t) is the distance between the front wheel axis of the vehicle and the reference point located on the target path, a(t) is the target lateral acceleration of the vehicle, and k is is the tracking gain, and r is the turning radius of the vehicle.

In the present invention, the controller reduces the cutoff frequency of the LPF as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.

In the present invention, the controller controls the gain of at least one of a position controller, a speed controller, and a current controller provided in the electric steering system based on the comparison result to vary the control response of the electric steering system. It is characterized by

In the present invention, the controller reduces the gain as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.

A control method of an electric steering system according to an aspect of the present invention includes the steps of a controller predicting a command steering angle based on control information output from an autonomous driving system; Comparing, by the controller, the predicted command steering angle and the current steering angle of the vehicle; and controlling, by the controller, a cutoff frequency of a low pass filter (LPF) that filters the command steering angle output from the autonomous driving system based on the comparison result so as to vary the control response of the electric steering system. It is characterized by including.

In the present invention, the control information is characterized in that it includes information about the distance and direction between the target path and the vehicle, information about the lateral acceleration of the vehicle, and information about the turning radius of the vehicle.

In the prediction step of the present invention, the controller predicts the command steering angle using the following equation.

[formula]

here, is the command steering angle, is the difference between the tangential direction of the reference point located on the target path and the vehicle's heading direction, e(t) is the distance between the front wheel axis of the vehicle and the reference point located on the target path, a(t) is the target lateral acceleration of the vehicle, and k is is the tracking gain, and r is the turning radius of the vehicle.

In the present invention, in the controlling step, the controller reduces the cutoff frequency of the LPF as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.

In the present invention, the controller controls the gain of at least one of a position controller, a speed controller, and a current controller provided in the electric steering system based on the comparison result to vary the control response of the electric steering system. It is characterized in that it further includes a step;

In the step of controlling the gain in the present invention, the controller reduces the gain as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.

According to one aspect of the present invention, driving stability and riding comfort of an autonomous vehicle can be improved by adaptively varying the control response of an electric steering system provided in an autonomous vehicle depending on the situation.

1 is a configuration diagram for explaining a control device of an electric steering system according to an embodiment of the present invention.
Figure 2 is an exemplary diagram for explaining a control device of an electric steering system according to an embodiment of the present invention.
Figure 3 is a flowchart for explaining a control method of an electric steering system according to an embodiment of the present invention.

Hereinafter, a control device and method for an electric steering system according to an embodiment of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of lines or sizes of components shown in the drawing may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are terms defined in consideration of functions in the present invention, and may vary depending on the intention or custom of the driver or operator. Therefore, definitions of these terms should be made based on the content throughout this specification.

FIG. 1 is a configuration diagram for explaining a control device for an electric steering system according to an embodiment of the present invention, and FIG. 2 is an exemplary diagram for explaining a control device for an electric steering system according to an embodiment of the present invention.

Referring to Figure 1, the control device of the electric steering system according to an embodiment of the present invention includes an autonomous driving system 100, an electric steering system 200, a low pass filter (LPF) 300, and a controller 400. It can be included.

The autonomous driving system 100 may include a first autonomous driving module and a second autonomous driving module. The first autonomous driving module 110 provides commands based on radar signals measured through a radar installed in the vehicle, video signals measured through a camera installed in the vehicle, and driving information (such as speed information and steering information) of the vehicle. Control information for calculating the steering angle can be calculated. The second autonomous driving module 120 may calculate the command steering angle based on control information output from the first autonomous driving module 110. The second autonomous driving module 120 can calculate the command steering angle using various well-known methods.

The electric steering system 200 may include a position controller 210, a speed controller 220, a current controller 230, and a steering motor 240. The position controller 210 may generate a command speed based on the command steering angle output from the autonomous driving system 100 and the current steering angle. The speed controller 220 may generate a command current value based on the command speed output from the position controller 210 and the current speed. The current controller 230 may calculate an output current based on the command current value and the current current value output from the speed controller 220 and output it to the steering motor 240. The position controller 210, speed controller 220, and current controller 230 may be PID controllers (Proportional Integral Differential Controllers).

The LPF 300 is provided between the autonomous driving system 100 and the electric steering system 200 and can filter the command steering angle output from the autonomous driving system 100. The LPF 300 may be a variable LPF whose cut-off frequency is variable under the control of the controller 400, which will be described later.

The controller 400 predicts the command steering angle based on the control information output from the autonomous driving system 100, compares the predicted command steering angle with the current steering angle of the vehicle, and determines the result of comparing the predicted command steering angle with the current steering angle. Based on this, the control responsiveness of the electric steering system 200 can be varied.

In general, when an autonomous vehicle is driving straight or turning at a certain angle, it is desirable to keep the command steering angle constant, but the autonomous driving system 100 sets the target regardless of whether the vehicle is driving straight or turning at a certain angle. A new command steering angle for following the path is continuously generated and output to the electric steering system 200, and the electric steering system 200 continuously controls the steering angle of the vehicle according to the command steering angle output from the autonomous driving system 100. Therefore, when driving straight or turning at a certain angle, the vehicle continues to slightly shake left and right, causing a problem that reduces driving stability and ride comfort.

The present invention was created to solve the above-described problem. It predicts the command steering angle output from an autonomous vehicle, compares the predicted command steering angle with the current steering angle of the vehicle, and then determines the difference between the predicted command steering angle and the current steering angle. When it is relatively large, the control responsiveness of the electric steering system 200 is increased to ensure that the steering control of the vehicle is performed quickly, and when the difference between the predicted command steering angle and the current steering angle is relatively small, the electric steering system 200 By reducing the control responsiveness of the vehicle, it is possible to improve driving stability and ride comfort by stabilizing vehicle shaking caused by fine steering adjustments.

According to one embodiment, the control information may include information about the distance and direction between the target path and the vehicle, information about the lateral acceleration of the vehicle, and information about the turning radius of the vehicle. More specifically, control information is information about the difference between the tangential direction of the reference point located on the target path (the point closest to the vehicle among the points located on the target path) and the heading direction of the vehicle, and between the front wheel axle of the vehicle and the reference point located on the target path. It may include information about the distance, information about the target lateral acceleration of the vehicle, and information about the turning radius of the vehicle.

According to one embodiment, the controller 400 can predict the command steering angle using Equation 1 below (i.e., Stanley method).

here, is the command steering angle, is the difference between the tangential direction of the reference point located on the target path (the closest point to the vehicle among the points located on the target path) and the vehicle's heading direction, e(t) is the distance between the front wheel axis of the vehicle and the reference point located on the target path, v (t) may be the vehicle's speed, a(t) may be the vehicle's target lateral acceleration, k may be the tracking gain, and r may be the vehicle's turning radius. Figure 2 shows the geometry for Equation 1 above.

According to one embodiment, the controller 400 may vary the control responsiveness of the electric steering system 200 by controlling the cut off frequency of the LPF 300. That is, the controller 400 can vary the control responsiveness of the electric steering system 200 by controlling the frequency of the command steering angle input to the electric steering system 200 through the LPF 300.

According to one embodiment, the controller 400 may decrease the cutoff frequency of the LPF 300 as the difference between the predicted command steering angle and the current steering angle becomes smaller. That is, the controller 400 reduces the period of the command steering angle input to the autonomous driving system 100 by reducing the cutoff frequency of the LPF 300 as the difference between the predicted command steering angle and the current steering angle becomes smaller, thereby reducing the period of the command steering angle input to the electric steering system 200. ) and increases the cycle of the command steering angle input to the electric steering system 200 by increasing the cutoff frequency of the LPF (300) as the difference between the predicted command steering angle and the current steering angle becomes larger, thereby increasing the period of the command steering angle input to the electric steering system (200). 200) can increase the control responsiveness.

Cut-off frequency (Hz) One 2 3 4 Error amount (deg) 0~0.5 0.5~10 10~20 20~40

For example, as shown in Table 1 above, the controller 400 sets the cutoff frequency of the LPF 300 to 1 Hz when the difference (i.e., error amount) between the predicted command steering angle and the current steering angle is 0.5 deg or less. And, if the difference (i.e., error amount) between the predicted command steering angle and the current steering angle is greater than 0.5deg and less than 10deg, the cutoff frequency of the LPF (300) is set to 2Hz, and the difference (i.e., error amount) between the predicted command steering angle and the current steering angle is set to 2Hz. If the difference (i.e., error amount) between the predicted command steering angle and the current steering angle is more than 20deg and less than or equal to 40deg, the cutoff frequency of the LPF (300) is set to 3Hz. It can be set to 4Hz.

According to one embodiment, the controller 400 controls the gain of at least one of the position controller 210, the speed controller 220, and the current controller 230 provided in the electric steering system 200 to provide electric steering. The control responsiveness of the system 200 can be varied.

According to one embodiment, the controller 400 may reduce the gain of at least one of the position controller 210, speed controller 220, and current controller 230 as the difference between the predicted command steering angle and the current steering angle becomes smaller. . That is, the controller 400 reduces the gain of at least one of the position controller 210, speed controller 220, and current controller 230 as the difference between the predicted command steering angle and the current steering angle becomes smaller, thereby improving the electric steering system 200. It is possible to react insensitively to the command steering angle output from the autonomous driving system 100.

As described above, the present invention can improve driving stability and ride comfort of an autonomous vehicle by adaptively varying the control response of the electric steering system provided in the autonomous vehicle depending on the situation.

Figure 3 is a flowchart for explaining a control method of an electric steering system according to an embodiment of the present invention.

Hereinafter, with reference to FIG. 3, we will look at a control method of an electric steering system according to an embodiment of the present invention.

First, the controller 400 can predict the command steering angle based on control information output from the autonomous driving system 100 (S301).

Subsequently, the controller 400 may compare the predicted command steering angle with the current steering angle of the vehicle (S303). That is, the controller 400 can calculate an error amount that is the difference between the predicted command steering angle and the current steering angle.

Subsequently, the controller 400 may vary the control responsiveness of the electric steering system 200 based on the result of comparing the predicted command steering angle and the current steering angle (S305). The controller 400 can vary the control responsiveness of the electric steering system 200 by controlling the cutoff frequency of the LPF 300. The controller 400 may decrease the cutoff frequency of the LPF 300 as the difference (i.e., error amount) between the predicted command steering angle and the current steering angle becomes smaller.

As described above, the control device and method for an electric steering system according to an aspect of the present invention improves the driving stability and stability of the autonomous vehicle by adaptively varying the control response of the electric steering system provided in the autonomous vehicle according to the situation. It can improve riding comfort.

Implementations described herein may be implemented, for example, as a method or process, device, software program, data stream, or signal. Although discussed only in the context of a single form of implementation (eg, only as a method), implementations of the features discussed may also be implemented in other forms (eg, devices or programs). The device may be implemented with appropriate hardware, software, firmware, etc. The method may be implemented in a device such as a controller, which generally refers to a processing device including, for example, a computer, microcontroller, integrated circuit, or programmable logic device. Controllers also include communication devices such as computers, cell phones, personal digital assistants (“PDAs”) and other devices that facilitate communication of information between end-drivers.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely illustrative, and those skilled in the art will recognize that various modifications and other equivalent embodiments can be made therefrom. You will understand. Therefore, the true technical protection scope of the present invention should be determined by the scope of the patent claims below.

100: autonomous driving system 110: first autonomous driving module
120: second autonomous driving module 200: electric steering system
220: position controller 230: speed controller
240: current controller 250: steering motor
300: LPF 400: Controller

Claims (12)

LPF (Low Pass Filter), which filters the command steering angle output from the autonomous driving system; and
Predict a command steering angle based on control information output from the autonomous driving system, compare the predicted command steering angle with the current steering angle of the vehicle, and vary the control responsiveness of the electric steering system based on the comparison result. A controller that controls the cutoff frequency of the LPF;
A control device for an electric steering system comprising a.
According to clause 1,
The control information includes information on the distance and direction between the target path and the vehicle, information on the lateral acceleration of the vehicle, and information on the turning radius of the vehicle.
According to clause 1,
The controller is a control device for an electric steering system, characterized in that it predicts the command steering angle using the following equation.
[formula]

(here, is the command steering angle, is the difference between the tangential direction of the reference point located on the target path and the vehicle's heading direction, e(t) is the distance between the front wheel axis of the vehicle and the reference point located on the target path, a(t) is the target lateral acceleration of the vehicle, and k is is the tracking gain, and r is the turning radius of the vehicle.)
According to clause 1,
The controller is a control device for an electric steering system, wherein the cutoff frequency of the LPF decreases as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.
According to clause 1,
The controller controls the gain of at least one of a position controller, a speed controller, and a current controller provided in the electric steering system based on the comparison result to vary the control response of the electric steering system. Control device for an electric steering system.
According to clause 5,
The controller is a control device for an electric steering system, wherein the gain is reduced as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.
Predicting, by the controller, a command steering angle based on control information output from the autonomous driving system;
Comparing, by the controller, the predicted command steering angle and the current steering angle of the vehicle; and
Controlling, by the controller, a cutoff frequency of a low pass filter (LPF) that filters the command steering angle output from the autonomous driving system based on the comparison result to vary the control response of the electric steering system;
A control method for an electric steering system comprising a.
According to clause 7,
The control information includes information on the distance and direction between the target path and the vehicle, information on the lateral acceleration of the vehicle, and information on the turning radius of the vehicle.
According to clause 7,
In the predicting step, the controller:
A control method for an electric steering system, characterized in that predicting the command steering angle using the following equation.
[formula]

(here, is the command steering angle, is the difference between the tangential direction of the reference point located on the target path and the vehicle's heading direction, e(t) is the distance between the front wheel axis of the vehicle and the reference point located on the target path, a(t) is the target lateral acceleration of the vehicle, and k is is the tracking gain, and r is the turning radius of the vehicle.)
According to clause 7,
In the controlling step, the controller:
A control method for an electric steering system, characterized in that the cutoff frequency of the LPF is reduced as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.
According to clause 7,
controlling, by the controller, a gain of at least one of a position controller, a speed controller, and a current controller provided in the electric steering system based on the comparison result to vary the control response of the electric steering system;
A control method for an electric steering system further comprising:
According to clause 11,
In the step of controlling the gain, the controller:
A control method for an electric steering system, characterized in that the gain is reduced as the difference between the predicted command steering angle and the current steering angle of the vehicle becomes smaller.

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