Vehicle Steering System

Abstract

This vehicle steering system comprises a steering control amount computation unit (10) that computes a steering control amount for bringing the vehicle closer to a target travel line, a lateral acceleration rate detection unit (2) that detects the lateral acceleration rate of the vehicle, a steering control amount limit value computation unit (12) that computes a steering control amount limit value such that the lateral acceleration rate is limited to a lateral acceleration rate limit value on the basis of the lateral acceleration rate, a limit determination unit (11) that determines whether the steering control amount limit is valid or invalid on the basis of the lateral acceleration rate, and a steering control amount limit unit (13) that limits the steering control amount when the limit determination unit (11) determines the limit to be valid on the basis of the steering control amount limit value.

Description

Vehicle Steering System

[0001] The present application relates to a vehicle steering system, and more particularly to a vehicle steering system that assists steering operations so that a vehicle travels along a target travel line.

[0002] 2. Description of the Related Art Conventionally, there are known techniques for performing steering assistance or automatic steering of steered wheels so that a vehicle travels along a desired target travel line.

[0003] For example, there is a first technology, as disclosed in Patent Document 1, which uses a camera mounted on the front of the vehicle to recognize white lines on the road and controls the steering so that the vehicle stays in the center of the lane (hereinafter referred to as a lane keeping system).A second technology, as disclosed in Patent Document 2, uses satellite information to determine the vehicle's position, a target point set in advance by the driver, map data, etc., to calculate a target trajectory and controls the steering so that the vehicle follows the target trajectory.

[0004] JP 2015-13545 A JP 2005-67484 A

[0005] In the conventional vehicle steering systems described in Patent Documents 1 and 2, because steering assistance is provided to follow a target driving line based on camera or satellite information, the vehicle steering system may perform abrupt steering depending on the target driving line, increasing the lateral acceleration of the vehicle and causing anxiety or discomfort to the driver. In particular, if, for example, the camera or satellite information is misrecognized and the vehicle is steered in a direction not intended by the vehicle steering system or the driver, the anxiety and discomfort caused to the driver can be significant.

[0006] The present application has been made to solve the above-mentioned problems, and aims to provide a vehicle steering system that reduces the burden on the driver caused by the driver's anxiety and discomfort.

[0007] The vehicle steering system disclosed in the present application includes a steering control amount calculation unit that calculates a steering control amount to bring the vehicle closer to a target driving line, a lateral acceleration detection unit that detects the lateral acceleration of the vehicle, a steering control amount limit value calculation unit that calculates a steering control amount limit value that limits the lateral acceleration to a lateral acceleration limit value based on the lateral acceleration, a limit determination unit that determines whether the steering control amount limit is valid or invalid based on at least the lateral acceleration, and a steering control amount limit unit that limits the steering control amount when the limit determination unit determines that the limit is valid based on the steering control amount limit value.

[0008] According to the vehicle steering system disclosed in the present application, a steering control amount limit value is calculated that limits the lateral acceleration of the vehicle to a lateral acceleration limit value, and the steering control amount is limited based on the steering control amount limit value.Therefore, the lateral angular velocity of the vehicle generated by the system can be uniformly limited regardless of the driving environment, such as vehicle variations or cant of the road, thereby reducing the burden on the driver caused by the driver's anxiety and discomfort.

[0009] FIG. 1 is a functional block diagram showing a vehicle steering system according to embodiment 1. FIG. 2 is a diagram showing a hardware configuration of a vehicle steering device in the vehicle steering system according to embodiment 1. FIG. 3 is a flowchart explaining the operation of a steering control amount limit value calculation unit in the vehicle steering system according to embodiment 1. FIG. 4 is a functional block diagram showing a vehicle steering system according to embodiment 2. FIG. 5 is a flowchart explaining the operation of a steering control amount limit value calculation unit in the vehicle steering system according to embodiment 2. FIG. 6 is a functional block diagram showing a vehicle steering system that is a modified example of embodiment 1. FIG. 7 is a functional block diagram showing a vehicle steering system that is a modified example of embodiment 2.

[0010] Embodiment 1. A vehicle steering system disclosed in the present application will be described below with reference to the drawings according to an embodiment. FIG. 1 is a functional block diagram showing the configuration of the vehicle steering system of this embodiment 1. As shown in FIG. 1, the vehicle steering system includes a vehicle steering device 1 (hereinafter sometimes referred to as "steering device 1"), a lateral acceleration detection unit 2, a roadway recognition unit 3, and a steering actuator 4. In the following description, a vehicle equipped with the steering device 1 will be referred to as the "host vehicle."

[0011] The steering device 1 includes a steering control amount calculation unit 10, a restriction determination unit 11, a steering control amount limit value calculation unit 12, and a steering control amount limit unit 13. The lateral acceleration detected by the lateral acceleration detection unit 2 is input to the restriction determination unit 11 and the steering control amount limit value calculation unit 12, and the roadway information detected by the roadway recognition unit 3 is input to the steering control amount calculation unit 10, which outputs the steering control amount. Here, the steering device 1 may be provided with a control function of a general electric power steering device.

[0012] The lateral acceleration detection unit 2 is, for example, a lateral G sensor, which detects the lateral acceleration of the vehicle and outputs it to the steering device 1. Note that the lateral acceleration detection unit 2 may detect the yaw rate and vehicle speed of the vehicle and output the values ​​of the yaw rate and vehicle speed as the lateral acceleration, and the detection method is not important.

[0013] The travel path recognition unit 3 is, for example, a camera that captures an image ahead of the vehicle, and recognizes lane boundaries, such as outer road lines, road boundary lines, and road center lines, of the travel path ahead based on the captured image. Then, it recognizes the travel lane in which the vehicle is traveling from the positions of the lane boundary lines in the host vehicle coordinate system, and outputs this as travel path information to the steering device 1. The host vehicle coordinate system is a coordinate system centered on a base point on the host vehicle.

[0014] Steering actuator 4 generates steering power (driving torque) which is a target torque corresponding to the steering control amount input from steering device 1, and steers the steered wheels of the vehicle. Steering actuator 4 can be, for example, an electric motor for electric power steering or a hydraulic motor, and the type of motor is not particularly limited, and a DC motor or an AC motor can be used.

[0015] Next, we will explain the internal configuration of the steering device 1. The steering control amount calculation unit 10 sets a target driving line within the driving path, which serves as a target for causing the vehicle to travel following the driving path, based on driving path information in the host vehicle coordinate system, and outputs a steering control amount for causing the host vehicle to follow the target driving line.

[0016] Here, the target driving line is set, for example, at a position a predetermined distance (e.g., 1 / 2 the width of the road) from the right lane boundary line in the host vehicle's coordinate system, i.e., at the center of the driving lane. Note that the predetermined distance may be changed as appropriate depending on the driver's preference, the surrounding environment, etc. Furthermore, the method of calculating the steering control amount by the steering control amount calculation unit 10 is well known in the art of providing steering assistance or automatic steering of the steered wheels so that the vehicle travels along a desired target driving line. For example, the target torque for driving a steering actuator disclosed in Japanese Patent No. 6012824 may be used as the steering control amount, and any means for doing so is acceptable.

[0017] The restriction determination unit 11 determines whether or not the steering control amount is restricted by comparing the lateral acceleration of the host vehicle with a preset arbitrary lateral acceleration limit value, and outputs the result as a restriction determination flag to the steering control amount limit value calculation unit 12. The restriction determination flag is set to "restricted" when at least the lateral acceleration of the host vehicle is equal to or greater than the lateral acceleration limit value, and is set to "unrestricted" when at least the lateral acceleration of the host vehicle is smaller than the lateral acceleration limit value.

[0018] Here, the lateral acceleration limit value used to determine whether or not a limit is present is the same as the lateral acceleration limit value used to calculate the steering control amount limit value in the steering control amount limit value calculation unit 12, which will be described later. However, different values ​​may be set for each. Furthermore, the lateral acceleration limit values ​​used to determine whether or not a limit is present may be set to different values, and hysteresis may be provided. Furthermore, rather than making the determination based solely on the lateral acceleration of the host vehicle, the determination may be based on the magnitude relationship between the steering control amount limit value and the steering control amount in the steering control amount limit value calculation unit 12. In this case, for example, the limit determination unit may determine the limit determination flag as follows: (a) If the lateral acceleration of the host vehicle is equal to or greater than the lateral acceleration limit value and the steering control amount limit value is greater than the steering control amount, the limit determination flag outputs a limit. (b) If the steering control amount limit value is smaller than the steering control amount, the limit determination flag outputs an no limit. (c) In other cases, the limit determination flag maintains the previous output value. By making the above-described judgment, even if the lateral acceleration of the vehicle becomes equal to or less than the lateral acceleration limit value, the steering control amount limit value decreases, and the output continues to indicate that there is a limit until it matches the value of the steering control amount. This makes it possible to suppress fluctuations in the steering control amount corresponding to the difference between the steering control amount limit value and the steering control amount when switching from limited to unlimited, thereby contributing to reducing the burden on the driver caused by feelings of anxiety and discomfort.

[0019] The steering control amount limit value calculation unit 12 calculates a steering control amount limit value based on the input lateral acceleration, steering control amount, and limit judgment flag so that the lateral acceleration generated in the vehicle is equal to or less than a predetermined arbitrary lateral acceleration limit value, and outputs the calculated value to the steering control amount limit unit 13.

[0020] The steering control amount limiting section 13 limits the steering control amount based on the input steering control amount and steering control amount limit value so that the steering control amount is equal to or less than the steering control amount limit value, and outputs the limit value to the steering actuator 4 .

[0021] 2 shows a hardware configuration in the case where each block (steering control amount calculation unit 10, limit determination unit 11, steering control amount limit value calculation unit 12, and steering control amount limit unit 13) of the steering device 1 shown in FIG. 1 is configured using a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). In this case, the function of each block of the steering device 1 is realized by a combination of software, etc. (software, firmware, or software and firmware). The software, etc. is written as a program and stored in memory 103 (storage device).

[0022] An interface (I / F) 101 controls input and output of signals to and from external devices such as the roadway recognition unit 3. Note that Fig. 2 only shows a configuration in which the steering actuator 4 is connected via the I / F 101. The CPU 102 executes various processes in accordance with programs stored in the memory 103, thereby realizing the functions of each block of the steering device 1. The I / F 101, CPU 102, and memory 103 are connected to one another via a bus.

[0023] 3 is a flowchart illustrating the operation of the steering control amount limit value calculation unit 12. First, in step S101, the steering control amount limit value calculation unit 12 reads the lateral acceleration output by the lateral acceleration detection unit 2, the steering control amount output by the steering control amount calculation unit 10, and the limit determination flag output by the limit determination unit 11.

[0024] Next, in step S102, a conditional branch determination is made based on the restriction determination flag, and if the restriction determination flag indicates that there is a restriction, the process proceeds to step S103, and otherwise to step S104.

[0025] In step S103, a conditional branch judgment is further performed based on the control judgment flag. If the restriction judgment flag changes from no restriction to restricted, that is, if the lateral acceleration of the vehicle reaches the lateral acceleration restriction value from a value smaller than an arbitrary lateral acceleration restriction value, the process proceeds to step S105; otherwise, the process proceeds to step S106.

[0026] In steps S104 to S106, the steering control amount limit value corresponding to each limit determination flag is calculated.

[0027] In step S104, since the restriction determination flag indicates no restriction, that is, the lateral acceleration of the host vehicle is smaller than the lateral acceleration restriction value and there is no need to restrict the steering control amount, the steering control amount restriction value is cleared to a value that will not restrict the steering control amount in the steering control amount restriction unit 13, for example, a value that is larger than the steering control amount that the vehicle steering system can take. Note that any value may be set as long as it will not restrict the steering control amount in the steering control amount restriction unit 13.

[0028] In step S105, when the restriction determination flag changes from no restriction to restricted, i.e., when the lateral acceleration of the host vehicle reaches the lateral acceleration restriction from a value smaller than the arbitrary lateral acceleration restriction, the steering control amount restriction is set to a steering control amount so as not to further increase the lateral acceleration of the host vehicle. In other words, the steering control amount restriction is set to a steering control amount such that the lateral acceleration of the host vehicle becomes equivalent to the lateral acceleration restriction.

[0029] In step S106, the restriction determination flag indicates that a restriction is present, indicating that the restriction on the lateral acceleration of the host vehicle should continue, so the steering control amount restriction value is maintained at the previous value, i.e., the value set at the time of step S105. Steps S105 and S106 maintain the steering control amount at the time when the lateral acceleration of the host vehicle reached the lateral acceleration restriction value, thereby making it possible to prevent the lateral acceleration of the host vehicle from increasing any further.

[0030] As described above, a steering control amount limit value that limits the lateral acceleration of the vehicle to the lateral acceleration limit value is calculated, and the steering control amount is limited based on the steering control amount limit value. Therefore, the lateral angular velocity of the vehicle generated by the system can be uniformly limited without depending on the driving environment such as vehicle variations or cant of the road. Therefore, the burden on the driver caused by the driver's anxiety and discomfort can be reduced without depending on the driving environment such as vehicle variations or cant of the road.

[0031] In addition, since the steering control amount of the vehicle steering system is limited, it is easy to make the steering control amount behave continuously before and after the limit, and the lateral acceleration does not become discontinuous, which contributes to reducing the burden on the driver caused by the driver's anxiety and discomfort.

[0032] Embodiment 2. In Embodiment 1, the lateral acceleration of the host vehicle is limited to be equal to or less than an arbitrary lateral acceleration limit value by holding the steering control amount at the time when the lateral acceleration of the host vehicle reaches the lateral acceleration limit value in the steering control amount limit value calculation unit 12. In contrast, in Embodiment 2, a vehicle steering system will be described that uses a vehicle steering device 1a equipped with a steering control amount limit value calculation unit 12a that calculates the steering control amount limit value in accordance with the deviation between the lateral acceleration limit value and the lateral acceleration of the host vehicle.

[0033] FIG. 4 is a functional block diagram showing the configuration of a vehicle steering system according to the second embodiment, and components that are given the same reference numerals as those in the first embodiment are the same or equivalent components.

[0034] The steering control amount limit value calculation unit 12a in the vehicle steering device 1a is equipped with a deviation calculator 120, an integrator 121, and a gain multiplier 122, and the lateral acceleration detected by the lateral acceleration detection unit 2 is input to the deviation calculator 120, the limit judgment flag calculated by the limit judgment unit 11, and the steering control amount calculated by the steering control amount calculation unit 10 are input to the integrator 121, and a steering control amount limit value is calculated so that the lateral acceleration generated in the vehicle is equal to or less than a lateral acceleration limit value that is set arbitrarily, and is output to the steering control amount limit unit 13.

[0035] Next, the internal configuration of the steering control amount limit value calculation unit 12a will be described. The deviation calculator 15 calculates the deviation between an arbitrary lateral acceleration limit value and the absolute value of the lateral acceleration based on the lateral acceleration, and outputs the deviation to the integrator 121 as a lateral acceleration deviation.

[0036] The integrator 121 calculates and outputs an integrated value of lateral acceleration corresponding to the restriction determination flag based on the restriction determination flag, the steering control amount, and the lateral acceleration deviation.

[0037] The gain multiplier 122 multiplies the lateral acceleration integral value by a preset arbitrary gain and outputs the result as the steering control amount limit value. Here, the gain to be multiplied may be a value that can be changed depending on the vehicle speed of the host vehicle. In this case, for example, the gain may be acquired by referring to a map corresponding to the detected vehicle speed of the host vehicle. Note that the integrator 121 and the gain multiplier 122 function as a deviation amplifier 123 that amplifies the output of the deviation calculator 120.

[0038] 5 is a flowchart illustrating the operation of the steering control amount limit value calculation unit 12a. First, in step S201, the steering control amount limit value calculation unit 12a reads the lateral acceleration output by the lateral acceleration detection unit 2, the steering control amount output by the steering control amount calculation unit, and the limit determination flag output by the limit determination unit 11.

[0039] Next, in step S202, the deviation calculator 15 executes a calculation to calculate the deviation between the lateral acceleration limit value and the absolute value of the lateral acceleration as the lateral acceleration deviation, as shown in the following equation (1): dGy = Gy_limit - |Gy| (1) where, dGy: lateral acceleration deviation, Gy_limit: lateral acceleration limit value, and Gy: lateral acceleration

[0040] Next, in steps S203 to S206, calculations are performed in the integrator 121. First, in step S203, a conditional branch determination is performed based on the restriction determination flag. If the restriction determination flag indicates that there is a restriction, i.e., if the lateral acceleration of the host vehicle is equal to or greater than the lateral acceleration limit value, the process proceeds to step S204; otherwise, the process proceeds to step S205. In step S204, the lateral acceleration integral value is calculated using lateral acceleration integral value calculation (A) according to the following equation (2): I_Gy = I_Gy previous value + dGy × dT (2) where, I_Gy: lateral acceleration integral value dT: integral calculation period Gy_limit: lateral acceleration limit value Gy: lateral acceleration

[0041] In step S205, the lateral acceleration integral is calculated by lateral acceleration integral calculation (B) using the following equation (3). That is, by setting the lateral acceleration integral to a value such that the steering control amount limit value is equivalent to the steering control amount, the steering control amount limiter 13 does not limit the steering control amount when the control determination flag is set to "no limit." Also, when the control determination flag changes from "no limit" to "limited" and steering control amount limiting begins, the steering control amount limit value becomes discontinuous with respect to the steering control amount, preventing discontinuity in the steering control amount. I_Gy = Q_ctr / KI (3) where, I_Gy: lateral acceleration integral Q_ctr: steering control amount KI: gain

[0042] Next, in step S206, the gain multiplier 122 performs calculation according to the following equation (4), multiplying the lateral acceleration integral value by a preset arbitrary gain to calculate the steering control amount limit value: Q_limit=KI×I_Gy (4) where Q_limit: steering control amount limit value

[0043] As described above, when the lateral acceleration of the vehicle is greater than the lateral acceleration limit value, the steering control amount limit value is adjusted based on the deviation between the lateral acceleration limit value and the lateral acceleration. Therefore, compared to the case in which the steering control amount limit value is maintained in embodiment 1, the lateral acceleration of the vehicle can be more accurately limited even in response to changes in the driving environment such as vehicle variations or cant of the road. Therefore, it is possible to improve the effect of reducing the burden on the driver caused by the driver's anxiety and discomfort, regardless of the driving environment such as vehicle variations or cant of the road.

[0044] In the second embodiment, the steering control amount limit value calculation unit 12a is configured to calculate the steering control amount limit value based only on the integral element of the lateral acceleration deviation, which is the deviation between the lateral acceleration limit value and the absolute value of the lateral acceleration, but a configuration may also be adopted in which a proportional element and a differential element of the lateral acceleration deviation are added. For example, adding a proportional element can improve the follow-up to the lateral acceleration limit value. When a proportional element is added, the reset process of the lateral acceleration integral value in equation (3) in step S205 can be replaced with the following equation (5), and the gain multiplication process in equation (4) in step S206 can be replaced with the following equation (6): I_Gy = Q_ctr / KI - KP × dGy (5) where, KP: proportional element gain Q_limit = KI × I_Gy + KP × dGy (6)

[0045] In the first and second embodiments, a camera is used as the roadway recognition unit 3, and the roadway ahead is recognized by the camera, but the roadway may be recognized by means other than a camera, and the same effect as that of the vehicle steering device shown in the present embodiment can be obtained. For example, the roadway ahead of the vehicle may be recognized based on the vehicle's own position and map information received from a satellite with which communication is possible, or the roadway ahead may be recognized based on the trajectory of a vehicle traveling ahead acquired by a radar, a camera, or the like, and the means for doing so is not important.

[0046] <Modification of the embodiment> Furthermore, the steering control amount is, for example, a target torque (driving torque) for driving the steering actuator 4, but it may also be a target steering angle for steering the vehicle so that the vehicle travels following a target travel line.

[0047] 6 shows a functional block diagram illustrating the configuration of the vehicle steering system according to the first embodiment of the present invention, in which the steering control amount and steering control amount limit value in steering control amount limit value calculation unit 12 and steering control amount limit unit 13 are the target steering angle and target steering angle limit value, respectively. In this case, the system includes steering angle detection unit 5 and steering angle control unit 14, and steering angle detection unit 5 detects the steering angle of the vehicle and outputs it to steering angle control unit 14. Based on the steering control amount input from steering control amount limit unit 13, i.e., the target steering angle and the steering angle input from steering angle detection unit 5, steering angle control unit 14 calculates a target torque (driving torque) such that the steering angle of the vehicle follows the target steering angle, and outputs it to steering actuator 4.

[0048] Here, the calculation of the target torque (driving torque) in the steering angle control unit 14 may be performed by a known control method based on a proportional element, an integral element, etc. of the deviation between the target steering angle and the steering angle, and the calculation means is not limited. With this configuration, the steering control amount limit value calculation unit 12 holds the steering angle, which is the steering control amount, at the time when the lateral acceleration of the host vehicle reaches the lateral acceleration limit value, thereby preventing the lateral acceleration of the host vehicle from increasing further, i.e., it becomes possible to limit the lateral acceleration of the host vehicle to the lateral acceleration limit value, as in the first embodiment.

[0049] In this case, a functional block diagram showing the configuration of the vehicle steering system related to this embodiment 2 would be, for example, as shown in Figure 7, and would include a steering angle detection unit 5 and a steering angle control unit 14, similar to Figure 6.

[0050] With this configuration, when the lateral acceleration of the vehicle is greater than the lateral acceleration limit value, the steering control amount limit value calculation unit 12a adjusts the steering angle, which is the steering control amount, based on the deviation between the lateral acceleration limit value and the lateral acceleration, thereby preventing the lateral acceleration of the vehicle from increasing further, as in embodiment 2, i.e., it becomes possible to accurately limit the lateral acceleration of the vehicle using the lateral acceleration limit value.

[0051] Although various exemplary embodiments and examples are described in this application, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0052] REFERENCE SIGNS LIST 1 Steering device, 2 Lateral acceleration detection unit, 3 Travel path recognition unit, 4 Steering actuator, 5 Steering angle detection unit, 10 Steering control amount calculation unit, 11 Limit determination unit, 12 Steering control amount limit value calculation unit, 13 Steering control amount limit unit, 14 Steering angle control unit

Claims

1. A vehicle steering system that assists steering operations so that a vehicle follows a target driving line, comprising: a steering control amount calculation unit that calculates a steering control amount to bring the vehicle closer to the target driving line; a lateral acceleration detection unit that detects the lateral acceleration of the vehicle; a steering control amount limit value calculation unit that calculates a steering control amount limit value that limits the lateral acceleration to a lateral acceleration limit value based on the lateral acceleration; a limit determination unit that determines whether the steering control amount limit is valid or invalid based on at least the lateral acceleration; and a steering control amount limit unit that limits the steering control amount when the limit determination unit determines that the limit is valid based on the steering control amount limit value.

2. A vehicle steering system according to claim 1, wherein the restriction determining unit determines whether the steering control amount restriction is valid or invalid based on at least the lateral acceleration and the steering control amount restriction value.

3. A vehicle steering system according to claim 1, wherein the steering control amount limit value calculation unit sets the steering control amount at the time when the lateral acceleration reaches the lateral acceleration limit value as the steering control amount limit value.

4. A vehicle steering system as claimed in any one of claims 1 to 3, characterized in that the steering control amount limit value calculation unit comprises a deviation calculator that calculates the deviation between the lateral acceleration limit value and the lateral acceleration, and a deviation amplifier that amplifies the output of the deviation calculator, and calculates the steering control amount limit value based on the output of the deviation amplifier.

5. A vehicle steering system according to claim 4, wherein said deviation amplifier includes at least an integrator for integrating the output of said deviation calculator.

6. A vehicle steering system as described in claim 5, characterized in that the deviation amplifier sets the integral element of the integrator to a value such that the steering control amount limit value coincides with the steering control amount when the limit determination unit determines that the limit is invalid.

7. A vehicle steering system as described in any one of claims 1 to 6, characterized in that it comprises a steering actuator that steers the steered wheels of the vehicle, the steering control amount is the drive torque of the steering actuator, the steering control amount limit value calculated by the steering control amount limit value calculation unit is a drive torque limit value, and the steering control amount limit unit limits the drive torque of the steering actuator to the drive torque limit value.

8. A vehicle steering system as described in any one of claims 1 to 6, characterized in that it comprises a steering angle detection unit that detects the steering angle of the steered wheels of the vehicle, a steering actuator that steers the steered wheels of the vehicle, and a steering angle control unit that drives the steering actuator so that the steering angle follows the target steering angle, the steering control amount being a target steering angle of the vehicle, the steering control amount limit value calculated by the steering control amount limit value calculation unit being a target steering angle limit value, and the steering control amount limit unit limits the target steering angle to the target steering angle limit value.

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