阅读说明：本技术 自主驾驶模式中的转向控制装置和方法 (Steering control apparatus and method in autonomous driving mode ) 是由 金泰弘 于 2021-04-16 设计创作，主要内容包括：本申请公开了一种自主驾驶模式中的转向控制器装置和方法,该装置可包括：命令转向角加速度检测器,所述命令转向角加速度检测器被配置为使用从自主驾驶系统输入的命令转向角加速度来检测命令转向角加速度；自主驾驶确定器,所述自主驾驶确定器被配置为使用转向轴的柱转矩、车辆的车辆速度和所述命令转向角加速度中的一者或多者来确定是否取消所述自主驾驶模式；以及转向角控制器,所述转向角控制器被配置为基于来自所述命令转向角加速度检测器的输出,通过根据所述命令转向角和当前转向角之间的转向角误差调整增益来控制转向角。(The application discloses a steering controller device and a method in an autonomous driving mode, the device can comprise: a command steering angular acceleration detector configured to detect a command steering angular acceleration using a command steering angular acceleration input from an autonomous driving system; an autonomous driving determiner configured to determine whether to cancel the autonomous driving mode using one or more of a column torque of a steering shaft, a vehicle speed of a vehicle, and the commanded steering angle acceleration; and a steering angle controller configured to control a steering angle by adjusting a gain according to a steering angle error between the command steering angle and a current steering angle based on an output from the command steering angle acceleration detector.)

1. A steering control apparatus in an autonomous driving mode, comprising:

a command steering angular acceleration detector configured to detect a command steering angular acceleration using a command steering angle input from the autonomous driving system;

an autonomous driving determiner configured to determine whether to cancel the autonomous driving mode using one or more of a column torque of a steering shaft, a vehicle speed of a vehicle, the commanded steering angle acceleration; and

a steering angle controller configured to control a steering angle by adjusting a gain according to a steering angle error between the command steering angle and a current steering angle based on an output from the command steering angle acceleration detector.

2. The steering control device according to claim 1, wherein the command steering angular acceleration detector includes:

a first differentiator configured to detect a command steering angular velocity by differentiating the command steering angle;

a second differentiator configured to detect the command steering angular acceleration by differentiating the command steering angular velocity; and

a noise filter configured to filter noise of the commanded steering angular acceleration output from the second differentiator.

3. The steering control apparatus according to claim 1, wherein the autonomous driving determiner includes:

a pseudo vibration filtering unit configured to filter a preset frequency component corresponding to vibration similar to a resonance point of a motor-driven steering device among frequency components of the column torque; and

an autonomous driving mode determination unit configured to determine whether to maintain the autonomous driving mode according to whether the column torque filtered by the pseudo vibration filtering unit satisfies a condition for determining that a driver has intervened in steering.

4. The steering control device according to claim 3, wherein the autonomous driving mode determination unit determines whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration when the column torque is kept at a preset value or more for a preset time or more.

5. The steering control device according to claim 3, wherein the autonomous driving mode determination unit determines whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration.

6. The steering control device according to claim 5, wherein the autonomous driving mode determination unit compares a value obtained by multiplying a load of a vehicle load pattern curve based on the vehicle speed by the command steering angle acceleration with a preset autonomous driving cancellation prohibition threshold value, and cancels the autonomous driving mode according to a comparison result.

7. The steering control device according to claim 6, wherein the autonomous driving mode determination unit cancels the autonomous driving mode when a value obtained by multiplying the load of the vehicle load pattern curve based on the vehicle speed by the commanded steering angle acceleration is equal to or smaller than the autonomous driving cancellation prohibition threshold.

8. The steering control device according to claim 1, wherein the steering angle controller includes:

a variable high-pass filter configured to remove a noise component of the steering angle error between the command steering angle and the current steering angle by adjusting a cutoff frequency according to an output from the command steering angle acceleration detector;

a gain adjustment unit configured to adjust a gain of the variable high-pass filter using one or more of the vehicle speed and the commanded steering angle acceleration; and

a steering angle control unit configured to correct the steering angle error between the command steering angle and the current steering angle by controlling the steering angle according to the gain adjusted by the gain adjustment unit.

9. The steering control device according to claim 8, wherein the variable high-pass filter adjusts the cutoff frequency by adjusting a differential time of a transfer function of the command steering angular velocity from the command steering angular acceleration detector.

10. The steering control device according to claim 8, wherein the gain adjustment unit adjusts the gain by multiplying a load curve gain based on the vehicle speed, the commanded steering angular acceleration, and a preset ratio.

11. A steering control method in an autonomous driving mode, comprising:

detecting a commanded steering angular acceleration using a commanded steering angular acceleration input from an autonomous driving system;

determining whether to cancel the autonomous driving mode using one or more of a column torque of a steering shaft, a vehicle speed of a vehicle, the commanded steering angle acceleration; and

the steering angle is controlled by adjusting a gain according to a steering angle error between the command steering angle and the current steering angle based on an output from the command steering angle acceleration detector.

12. The steering control method according to claim 11, wherein detecting the commanded steering angular acceleration includes: the method includes detecting a command steering angular velocity by first differentiating the command steering angle, detecting the command steering angular acceleration by second differentiating the command steering angular velocity, and then filtering noise of the command steering angular acceleration.

13. The steering control method according to claim 11, wherein determining whether to cancel the autonomous driving mode includes:

filtering a preset frequency component corresponding to vibration similar to a resonance point of a motor-driven steering apparatus among frequency components of the column torque; and

determining whether to maintain the autonomous driving mode based on whether the column torque satisfies a condition that determines that a driver has intervened in steering.

14. The steering control method of claim 13, wherein determining whether to maintain the autonomous driving mode comprises: determining whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration when the column torque remains at a preset value or greater for a preset time or longer.

15. The steering control method of claim 13, wherein determining whether to maintain the autonomous driving mode comprises: determining whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration.

16. The steering control method of claim 15, wherein determining whether to maintain the autonomous driving mode comprises: comparing a value obtained by multiplying a load of a vehicle load pattern curve based on the vehicle speed by the command steering angle acceleration with a preset autonomous driving cancellation prohibition threshold value, and canceling the autonomous driving pattern according to the comparison result.

17. The steering control method of claim 16, wherein determining whether to maintain the autonomous driving mode comprises: canceling the autonomous driving mode when a value obtained by multiplying the load of the vehicle load pattern curve based on the vehicle speed by the commanded steering angle acceleration is equal to or smaller than the autonomous driving cancellation prohibition threshold.

18. The steering control method according to claim 11, wherein controlling the steering angle includes:

removing a noise component of the steering angle error between the command steering angle and the current steering angle by adjusting a cutoff frequency of a variable high-pass filter according to an output from the command steering angle acceleration detector;

adjusting a gain of the variable high-pass filter using one or more of the vehicle speed and the commanded steering angle acceleration; and

correcting the steering angle error between the commanded steering angle and the current steering angle by controlling the steering angle according to the gain.

19. The steering control method according to claim 18, wherein removing the noise component of the steering angle error between the command steering angle and the current steering angle includes: the cutoff frequency is adjusted by adjusting a differential time of a transfer function of the command steering angular velocity from the command steering angular acceleration detector.

20. The steering control method of claim 18, wherein adjusting the gain of the variable high-pass filter comprises: adjusting the gain by multiplying by a load curve gain based on the vehicle speed, the commanded steering angle acceleration, and a preset ratio.

Technical Field

Exemplary embodiments of the present disclosure relate to a steering control apparatus and method in an autonomous driving mode, and more particularly, to a steering control apparatus and method in an autonomous driving mode that may improve steering performance without canceling the autonomous driving mode in a case where abrupt steering is required during the autonomous driving mode.

Background

Generally, when there is a risk of a collision or other accident suddenly occurring during an autonomous driving process, a vehicle needs to avoid an obstacle by reducing a vehicle speed or performing steering control.

Generally, it is effective to reduce the vehicle speed to avoid the risk. However, in an emergency situation, a sudden turn may be required. When the autonomous driving mode is suddenly cancelled or abnormally operated, a driver may present a danger. Therefore, it is necessary to continuously maintain the autonomous driving mode. Further, since fast steering is additionally and instantaneously performed, responsiveness needs to be maximized during the time when steering is performed.

The related art of the present disclosure is disclosed in korean patent application laid-open No. 10-2019-0098783, which is published on 23.8.2019 and entitled "Apparatus for Controlling handles of Vehicles".

In the related art, autonomous vehicles have been designed to determine that autonomous driving is not normal when sudden steering is performed during autonomous driving, and cancel the autonomous driving mode.

This is because a situation in which abrupt steering is performed does not generally occur during autonomous driving. If a sudden turn is performed, a dangerous situation may occur when the driver significantly rolls. However, depending on the situation, in the case where the vehicle should urgently avoid an obstacle according to the situation, it may be necessary to perform abrupt steering.

Disclosure of Invention

Various embodiments relate to a steering control apparatus and method in an autonomous driving mode, which may improve steering performance in a case where abrupt steering is required during the autonomous driving mode while not canceling the autonomous driving mode.

In one embodiment, a steering control apparatus in an autonomous driving mode may include: a command steering angular acceleration detector configured to detect a command steering angular acceleration using a command steering angle input from the autonomous driving system; an autonomous driving determiner configured to determine whether to cancel the autonomous driving mode using one or more of a column torque of a steering shaft, a vehicle speed of the vehicle, and a commanded steering angle acceleration; and a steering angle controller configured to control the steering angle by adjusting the gain according to a steering angle error between the command steering angle and the current steering angle based on an output from the command steering angle acceleration detector.

The command steering angular acceleration detector may include: a first differentiator (differentiator) configured to detect a command steering angular velocity by differentiating the command steering angle; a second differentiator configured to detect a command steering angle acceleration by differentiating the command steering angle velocity; and a noise filter configured to filter noise of the commanded steering angular acceleration output from the second differentiator.

The autonomous driving determiner may include: a pseudo vibration filtering unit configured to filter a preset frequency component corresponding to vibration similar to a resonance point of the motor-driven steering device among frequency components of the column torque; and an autonomous driving mode determination unit configured to determine whether to maintain the autonomous driving mode according to whether the column torque filtered by the pseudo vibration filtering unit satisfies such a condition that it is determined that the driver has intervened in the steering.

When the column torque remains at the preset value or more for the preset time or more, the autonomous driving mode determination unit may determine whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration.

The autonomous driving mode determination unit may determine whether to maintain the autonomous driving mode based on one or more of a vehicle speed and a commanded steering angle acceleration.

The autonomous driving mode determining unit may compare a value obtained by multiplying a load of a vehicle load pattern curve based on a vehicle speed by a command steering angular acceleration with a preset autonomous driving cancellation prohibition threshold value, and cancel the autonomous driving mode according to a comparison result.

The autonomous driving mode determining unit may cancel the autonomous driving mode when a value obtained by multiplying a load of a vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration is equal to or less than an autonomous driving cancellation prohibition threshold.

The steering angle controller may include: a variable high-pass filter configured to remove a noise component of a steering angle error between a command steering angle and a current steering angle by adjusting a cutoff frequency according to an output from the command steering angle acceleration detector; a gain adjustment unit configured to adjust a gain of the variable high-pass filter using one or more of a vehicle speed and a commanded steering angle acceleration; and a steering angle control unit configured to correct a steering angle error between the command steering angle and the current steering angle by controlling the steering angle according to the gain adjusted by the gain adjustment unit.

The variable high-pass filter may adjust the cutoff frequency by adjusting a differential time of a transfer function of the command steering angular velocity from the command steering angular acceleration detector.

The gain adjustment unit may adjust the gain by multiplying a load curve gain based on the vehicle speed, the commanded steering angle acceleration, and a preset ratio.

The steering control apparatus may further include a vibration sensor configured to detect vibration based on the number of times the sign of the steering angular velocity changes, and return the cutoff frequency or the gain to an initial value according to the vibration.

In one embodiment, a steering control method in an autonomous driving mode may include: detecting a commanded steering angle acceleration using a commanded steering angle acceleration input from an autonomous driving system; determining whether to cancel the autonomous driving mode using one or more of a column torque of a steering shaft, a vehicle speed of the vehicle, and a commanded steering angle acceleration; and controlling the steering angle by adjusting the gain according to a steering angle error between the commanded steering angle and the current steering angle based on an output from the commanded steering angle acceleration detector.

The detection of the commanded steering angular acceleration may include: the command steering angular velocity is detected by first differentiating the command steering angle, the command steering angular acceleration is detected by second differentiating the command steering angular velocity, and then noise of the command steering angular acceleration is filtered.

Determining whether to cancel the autonomous driving mode may include: filtering a preset frequency component corresponding to vibration similar to a resonance point of the motor-driven steering apparatus among frequency components of the column torque; and determining whether to maintain the autonomous driving mode based on whether the column torque satisfies such a condition that it is determined that the driver has intervened in the steering.

Determining whether to maintain the autonomous driving mode may include: when the column torque remains at a preset value or more for a preset time or more, it is determined whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration.

Determining whether to maintain the autonomous driving mode may include: determining whether to maintain the autonomous driving mode based on one or more of the vehicle speed and the commanded steering angle acceleration.

Determining whether to maintain the autonomous driving mode may include: the autonomous driving cancellation control method includes comparing a value obtained by multiplying a load of a vehicle load pattern curve based on a vehicle speed by a command steering angular acceleration with a preset autonomous driving cancellation prohibition threshold, and canceling the autonomous driving pattern according to a comparison result.

Determining whether to maintain the autonomous driving mode may include: the autonomous driving mode is cancelled when a value obtained by multiplying a load of a vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration is equal to or smaller than an autonomous driving cancellation prohibition threshold value.

Controlling the steering angle may include: removing a noise component of a steering angle error between the command steering angle and the current steering angle by adjusting a cutoff frequency of the variable high-pass filter according to an output from the command steering angle acceleration detector; adjusting a gain of the variable high-pass filter using one or more of vehicle speed and commanded steering angle acceleration; and correcting a steering angle error between the commanded steering angle and the current steering angle by controlling the steering angle according to the gain.

Removing the noise component of the steering angle error between the commanded steering angle and the current steering angle may include: the cutoff frequency is adjusted by adjusting the differential time of the transfer function of the command steering angular velocity from the command steering angular acceleration detector.

Adjusting the gain of the variable high-pass filter may include: the gain is adjusted by multiplying by a load curve gain based on the vehicle speed, the commanded steering angular acceleration, and a preset ratio.

The steering control method may further include: detecting vibration based on the number of times the sign of the steering angular velocity changes, and returning the cutoff frequency or gain to the initial value in accordance with the vibration.

The steering control apparatus and method in the autonomous driving mode according to the embodiment of the present invention can improve steering performance in the case where abrupt steering is required in the autonomous driving mode, while not canceling the autonomous driving mode, and allow the vehicle to urgently avoid a dangerous moment.

Drawings

Fig. 1 is a block configuration diagram showing a steering control apparatus in an autonomous driving mode according to an embodiment of the present disclosure.

Fig. 2 is a diagram illustrating a shape change of a high pass filter according to an embodiment of the present disclosure.

Fig. 3 is a diagram showing an example of changing the sign of the steering angular velocity according to the embodiment of the present disclosure.

Fig. 4 is a flowchart illustrating a steering control method in an autonomous driving mode according to an embodiment of the present disclosure.

Detailed Description

Some example embodiments may be illustrated in the figures as functional blocks, units and/or modules, as is conventional in the corresponding art. Those of ordinary skill in the art will appreciate that the blocks, units and/or modules are physically implemented by electronic (or optical) circuits such as logic circuits, discrete components, processors, hard-wired circuits, memory elements, wired connections, and the like. When the blocks, units, and/or modules are implemented by a processor or similar hardware, they may be programmed and controlled using software (e.g., code) to perform the various functions discussed herein. Alternatively, each block, unit and/or module may be implemented by dedicated hardware for performing certain functions, or as a combination of dedicated hardware for performing certain functions and a processor (e.g., one or more programmed processors and associated circuits) for performing other functions. Each block, unit and/or module of some example embodiments may be physically separated into two or more interactive and discrete blocks, units and/or modules without departing from the scope of the present inventive concept. In addition, the blocks, units and/or modules of some example embodiments may be physically combined into more complex blocks, units and/or modules without departing from the scope of the present inventive concept.

Hereinafter, a steering control apparatus and method in an autonomous driving mode will be described with reference to the accompanying drawings by way of various exemplary embodiments. It should be noted that the drawings are not to precise scale and that the thickness of lines or the size of components may be exaggerated for convenience and clarity of description only. Further, terms used herein are defined by considering functions of the present invention, and may be changed according to custom or intention of a user or an operator. Therefore, the definition of terms should be made in accordance with the general disclosure herein.

For example, the embodiments described in this specification can be implemented by a method or process, an apparatus, a software program, a data stream, or a signal. Although a feature may be discussed in only a single context (e.g., only in one method), the feature discussed may be implemented in another type (e.g., an apparatus or program). The apparatus may be implemented in suitable hardware, software or firmware. The method may be implemented in a device such as a processor, which refers generally to a processing device including, for example, a computer, microprocessor, integrated circuit, or programmable logic device. Processors also include communication devices such as computers, cellular telephones, PDAs (personal digital assistants), and other devices that facilitate the communication of information between end users.

Fig. 1 is a block configuration diagram showing a steering control device in an autonomous driving mode according to an embodiment of the present disclosure, fig. 2 is a diagram showing a shape change of a high-pass filter according to an embodiment of the present disclosure, and fig. 3 is a diagram showing an example of changing a sign of a steering angular velocity according to an embodiment of the present disclosure.

Referring to fig. 1, a steering control apparatus in an autonomous driving mode according to an embodiment of the present disclosure includes: sensing module 10, autonomous driving determiner 20, autonomous driving system 30, commanded steering angle acceleration detector 40, steering angle controller 60, vibration sensor 70.

The sensing module 10 senses information required for autonomous driving and steering control. The sensing module 10 may include: a column torque sensing unit 11 for sensing a column torque of a steering shaft, a vehicle speed sensing unit 12 for sensing a vehicle speed of the vehicle, a steering angle sensing unit 13 for sensing a steering angle of a steering wheel, a steering angle speed detecting unit 14 for detecting a steering angle speed of the steering wheel, a surrounding environment sensing unit 15 for sensing surrounding environment information required for operation of the autonomous driving system 30.

The steering angular velocity detection unit 14 may directly detect the steering angular velocity from the steering wheel, or detect the steering angular velocity by differentiating the steering angle sensed by the steering angle sensing unit 13.

Examples of the surrounding environment sensing unit 15 may include a laser radar, a radar, an ultrasonic sensor, an image sensor, and the like. The surrounding environment information may include road information, obstacle information, weather information, and the like. The surrounding environment information is not limited to the above-described embodiment.

In the autonomous driving mode, the autonomous driving system 30 outputs a command steering angle for autonomous driving control of the vehicle based on the surrounding environment information input from the surrounding environment sensing unit 15.

Since the configuration of the autonomous driving system 30 that performs autonomous driving control based on the surrounding environment information can be easily performed by those skilled in the art, a detailed description thereof will be omitted herein.

The command steering angular acceleration detector 40 detects a command steering angular acceleration using a command steering angular velocity input from the autonomous driving system 30.

The command steering angular acceleration detector 40 includes a first differentiator 41, a second differentiator 42, and a noise filter 43.

The first differentiator 41 detects the command steering angular velocity by once differentiating the command steering angle input from the autonomous driving system 30.

The second differentiator 42 detects the command steering angle acceleration by twice differentiating the command steering angle velocity detected by the first differentiator 41.

The noise filter 43 filters the noise of the commanded steering angular acceleration output from the second differentiator 42.

The autonomous driving determiner 20 uses one or more of the column torque of the steering shaft, the speed of the vehicle, and the commanded steering angle acceleration to determine whether to cancel the autonomous driving mode.

The autonomous driving determiner 20 includes a pseudo vibration filter unit 21 and an autonomous driving mode determining unit 22.

The pseudo vibration filtering unit 21 filters a preset frequency component corresponding to vibration similar to a resonance point of the motor-driven steering apparatus among frequency components of the column torque. As the pseudo vibration filter unit 21, a band elimination filter may be employed.

Typically, vibrations similar to the resonance point of the torsion bar of a motor driven steering arrangement may be sensed in case of an unintentional steering intervention. Therefore, the pseudo vibration filter unit 21 may filter a frequency component corresponding to vibration similar to a resonance point of a torsion bar of the motor-driven steering apparatus, so that the column torque corresponding to the frequency component is removed when the autonomous driving is cancelled. Thus, the autonomous driving mode is not cancelled in case of an unintended steering intervention.

The autonomous driving mode determining unit 22 determines whether to maintain the autonomous driving mode according to whether the column torque filtered by the pseudo vibration filtering unit 21 satisfies a condition that can determine that the driver has intervened in the steering.

That is, when the column torque filtered by the pseudo vibration filtering unit 21 is maintained at the preset value or more for the preset time or more, the autonomous driving mode determining unit 22 multiplies the load of the vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration, compares the multiplication result with the preset autonomous driving cancellation prohibition threshold value, and cancels the autonomous driving mode according to the comparison result.

In this case, the autonomous driving mode determination unit 22 cancels the autonomous driving mode when a value obtained by multiplying the load of the vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration is equal to or smaller than the autonomous driving cancellation prohibition threshold value.

More specifically, the autonomous driving mode determining unit 22 may determine that the driver is intervening in steering when the column torque filtered by the pseudo vibration filtering unit 21 is maintained at a preset value or more for a preset time or more. However, even when the autonomous driving system 30 changes the commanded steering angle rapidly while the driver does not intervene in steering, the column torque may be maintained at the preset value or more for the preset time or more. In this case, although the driver does not actually intervene in the steering, the autonomous driving mode may be cancelled to cause a large accident.

To prevent such cancellation, the autonomous driving mode determination unit 22 determines not to cancel the autonomous driving mode by the vehicle speed and the commanded steering angle acceleration even if the column torque is kept at the preset value or more for the preset time or more.

Generally, depending on the geometry of the vehicle, the load of the vehicle is maximum when the vehicle is stopped, and is minimized when the vehicle speed is about 5 kph. As the traveling speed of the vehicle gradually increases, the self-aligning force gradually increases.

In addition to these features, the column torque increases as the commanded steering angular acceleration becomes higher. Therefore, although the column torque is maintained at the preset value or more for the preset time or more, the autonomous driving mode determination unit 22 does not cancel the autonomous driving mode.

That is, the autonomous driving mode determining unit 22 multiplies the load of the vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration, and cancels the autonomous driving mode only when the multiplication result is equal to or smaller than the autonomous driving cancellation prohibition threshold value.

Thus, the autonomous driving mode may be continuously maintained despite the autonomous driving system 30 performing sudden steering to avoid the obstacle. Therefore, even if the driver does not intervene in the steering, the vehicle can safely avoid an obstacle or the like.

Based on the output from the command steering angle acceleration detector 40, the steering angle controller 60 controls the steering angle by adjusting the gain according to the position control error between the command steering angle and the current steering angle.

The steering angle controller 60 includes a variable high-pass filter 61, a gain adjustment unit 62, and a steering angle control unit 63.

The variable high-pass filter 61 removes a noise component of a position control error between the command steering angle and the current steering angle by adjusting the cutoff frequency according to the output from the command steering angle acceleration detector 40. In this case, the variable high-pass filter 61 adjusts the cutoff frequency by adjusting the differential time of the transfer function of the command steering angular velocity input from the command steering angular acceleration detector 40.

In general, in order to temporarily avoid an obstacle or the like, it is necessary to temporarily increase the steering angle control performance.

When the steering angle control performance is excessively high in the general autonomous driving mode, control stability is deteriorated due to external noise, the surrounding environment, and the like, and vibration or the like may occur. In this case, the steering angle control performance may be considerably deteriorated. Therefore, it is very important to improve the steering angle control performance as much as possible when necessary.

For such an operation, it is effective to use a PI-P or PID-PI controller combination instead of using a position controller based on a commonly used P-PI controller combination. However, when the D controller is applied, vibration may occur due to noise of a command steering angle, external environment, or noise. Typically, a D-controller may be added to improve responsiveness to position changes. However, in this case, since vibration may be caused and amplified by disturbance or noise introduced from the external environment, the steering angle control performance may be considerably deteriorated.

In order to prevent deterioration of the steering angle control performance, a low-pass filter or a hysteresis compensator is generally applied to the front stage of the D controller. However, in this case, when it is necessary to change the structure depending on the steering situation, the structure becomes complicated, and the number of parameters or factors to be changed increases. That is, in order to ensure the steering angle control performance, the P controller of the P-PI controller combination may be designed as a PI or PID controller to use a PI-PI or PID-PI controller combination. However, there is a need for a more efficient method that can maximize steering angle control performance depending on the steering situation and significantly improve responsiveness while having the ability to resist noise or interference.

Typically, when a low-pass filter or a lag compensator is applied to a D controller in a PID controller, the transfer function can be expressed as g(s) -Kp (1+1/Ti × s + Td × s/(1+ s × Td)).

Here, g(s) denotes a transfer function, Kp denotes a proportional gain, Ti denotes an integration time, Td denotes a differentiation time, and s is a complex number.

When the PID control gains are separated to rearrange the equations or the gains Kp are separated according to the I or D controller, the equations can be expressed as g(s) ═ Kp + Ki/Ti × s + Kd × s/(1+ Td × s). At this time, for the D controller, the equations may be rearranged to (1/Td)/((1/Td) + s)) × Td × Kp × s.

Here, Ki denotes an integral gain, and Kd denotes a differential gain.

Furthermore, (1/Td)/((1/Td) + s)) and s are similar to the shape of the primary high pass filter. In order to improve the steering angle control performance without applying the D controller, the variable high-pass filter 61 and the gain adjustment unit 62 may be applied. In this case, noise resistance and steering angle control performance can be significantly improved.

In particular, the gain and cut-off frequency of the variable high-pass filter 61 are very important. Typically, the cut-off frequency of the high-pass filter may be set by applying a Motor control bandwidth of a Motor Driven Steering device (e.g., MDPS (Motor Driven Power Steering)). However, in order not to affect the resonance point of the torsion bar of the MDPS, it is very important to set the cut-off frequency of the high-pass filter to about 12Hz in the case of the C-MDPS or about 9Hz in the case of the R-MDPS. For reference, the largest factor affecting MDPS stability is the torsion bar. This is because the torsion bar has the lowest stiffness and is the point where resonance is most likely to occur because of the lowest stiffness.

Generally, Td may define the control period and frequency of the D controller in the PID controller. In (1/Td)/((1/Td) + s)) × Td × Kp × s) of the transfer function, (1/Td)/((1/Td) + s)) is equal to the shape of the high-pass filter and can be set to a desired frequency by 1/Td. That is, the transfer filter of a general high-pass filter can be expressed as s/(s + w). Here, w is 2 π f, where f denotes the cutoff frequency. In the above transfer function, 1/Td directly becomes w. Therefore, the variable high-pass filter 61 can adjust the cutoff frequency by changing Td so as to set the desired frequency.

The gain adjustment unit 62 adjusts the gain by multiplying the load curve gain based on the vehicle speed, the commanded steering angle acceleration, and the preset ratio.

The gain adjustment unit 62 changes the differential gain Kd to control the gain. As above, the gain adjustment unit 62 may change the gain response characteristic of the steering angle control unit 63 by increasing Kd as the steering angle acceleration in the transfer function becomes higher, and decreasing Kd as the steering angle acceleration becomes lower.

Important factors determining the gain are the vehicle speed and the commanded steering angle acceleration. In order to determine the load of the vehicle and the load applied to the MDP, it is necessary to consider the vehicle speed and the command steering angle acceleration.

Therefore, the gain adjustment unit 62 finally sets the gain by multiplying by the load curve gain based on the vehicle speed, the commanded steering angle acceleration, and the ratio for maintaining the appropriate parameters. The ratio may be set to various values in consideration of various sudden steering environments under actual autonomous driving conditions. Therefore, as shown in fig. 2, the shape of the variable high-pass filter 61 is changed.

The steering angle control unit 63 corrects a steering angle error between the command steering angle and the current steering angle by controlling the steering angle according to the gain adjusted by the gain adjustment unit 62.

That is, the steering angle control unit 63 compares the command steering angle input from the autonomous driving system 30 with the current steering angle input from the steering angle sensing unit 13, and inputs the steering angle error to the variable high-pass filter 61.

Further, the steering angle control unit 63 improves the response characteristic of the steering angle and minimizes an error between the commanded steering angle and the current steering angle according to the gain input from the gain adjustment unit 62.

The vibration sensor 70 returns the cutoff frequency or gain to the initial value according to the change in the number of times the sign changes based on the steering angular velocity.

In general, when abrupt steering is performed during autonomous driving, vibration or the like may be generated by factors such as an external environment. In this case, it is necessary to sense the vibration to prevent an excessive gain increase or a cut-off frequency change.

For this operation, the vibration sensor 70 monitors in real time the number of times the sign of the steering angular velocity changes during the vibration setting time. For example, as shown in fig. 3, when the sign of the steering angular velocity changes three times in total within the counter time of one second, it can be determined that noise of 1 hz occurs.

Typically, vibration occurs most frequently at the resonant frequency of the torsion bar, since the stiffness of the torsion bar is the lowest in MDPS. The vibration typically ranges from 8Hz to 12 Hz. For example, it can be assumed that vibration of 8Hz occurs when the sign of the steering angular velocity changes 17 times per second. This may be based on the assumption that the G gain is excessively increased or the cutoff frequency of the variable high-pass filter 61 is excessively decreased. Therefore, the vibration sensor 70 senses vibration based on the number of times the sign of the steering angular velocity changes, and returns the cutoff frequency or gain to the initial value when the sensed vibration is equal to or greater than the preset vibration.

The initial value is the G gain or cutoff frequency in the general autonomous driving mode.

By this operation, the cancellation of the autonomous driving can be prohibited in the case of sudden steering, and the performance of the steering angle control unit 63 can be maximized by the variable high-pass filter 61, so that the autonomous vehicle can avoid the obstacle in an emergency.

Further, the variable high-pass filter 61 that changes can be recovered according to the general autonomous driving situation. When vibration occurs in the case of abrupt steering, the vibration may be sensed to optimize the variable high-pass filter 61, which makes it possible to prevent side effects caused by abrupt steering.

Hereinafter, a steering control method in the autonomous driving mode according to an embodiment of the present disclosure will be described with reference to fig. 4.

Fig. 4 is a flowchart illustrating a steering control method in an autonomous driving mode according to an embodiment of the present disclosure.

Referring to fig. 4, in the autonomous driving mode, the autonomous driving system 30 outputs a command steering angle for autonomous driving control of the vehicle based on the surrounding environment information input from the surrounding environment sensing unit in step S10.

Then, in step S20, the first differentiator 41 detects the command steering angular velocity by differentiating the command steering angle once, the second differentiator 42 detects the command steering angular acceleration by differentiating the command steering angular velocity twice, and the noise filter 43 detects the command steering angular acceleration by filtering the noise of the command steering angular acceleration.

In step S30, the pseudo vibration filter unit 21 filters a preset frequency component corresponding to vibration similar to the resonance point of the motor-driven steering device, from among the frequency components of the column torque.

Then, in step S40, the autonomous driving mode determining unit 22 determines whether the column torque filtered by the pseudo vibration filtering unit 21 is maintained at a preset value or more for a preset time or more.

When the determination result of step S40 indicates that the column torque remains at the preset value or more for the preset time or more, the autonomous driving mode determining unit 22 multiplies the load of the vehicle load pattern curve based on the vehicle speed by the command steering angular acceleration in step S50, and determines whether the multiplication result is equal to or less than a preset autonomous driving cancellation prohibition threshold in step S60.

When the determination result of step S60 indicates that the multiplication result is equal to or smaller than the autonomous driving cancellation prohibition threshold, in step S70, the autonomous driving mode determination unit 22 cancels the autonomous driving mode.

On the other hand, when the determination result of step S60 indicates that the multiplication result exceeds the autonomous driving cancellation prohibition threshold, the autonomous driving mode determination unit 22 continues to maintain the autonomous driving mode.

The steering angle control unit 63 compares the command steering angle input from the autonomous driving system 30 with the current steering angle input from the steering angle sensing unit 13, and inputs the steering angle error to the variable high-pass filter 61.

In this case, in step S80, the variable high-pass filter 61 adjusts the cutoff frequency according to the output from the command steering angle acceleration detector 40, and removes the noise component of the position control error between the command steering angle and the current steering angle according to the adjusted cutoff frequency.

In step S90, the gain adjustment unit 62 adjusts the gain by multiplying by a load curve gain based on the vehicle speed, the commanded steering angle acceleration, and a preset ratio.

Therefore, in step S100, the steering angle control unit 63 corrects the steering angle error between the command steering angle and the current steering angle by controlling the steering angle according to the gain adjusted by the gain adjustment unit 62.

During this process, the vibration sensor 70 senses the vibration of the steering angle by monitoring the number of times the sign of the steering angle speed is changed during the vibration setting time in real time in step S110, and determines whether the sensed vibration is equal to or greater than a preset vibration in step S120.

When the determination result of step S120 indicates that the vibration is equal to or greater than the preset vibration, the vibration sensor 70 returns the cutoff frequency or gain to the initial value in step S130.

Therefore, the steering control apparatus and method in the autonomous driving mode according to the embodiment of the present invention can improve the steering performance in the case where abrupt steering is required in the autonomous driving mode, while not canceling the autonomous driving mode, and allow the vehicle to urgently avoid a dangerous moment.

Although the exemplary embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims. Therefore, the true technical scope of the present disclosure should be defined by the appended claims.