Steering control method and steering control device

Abstract

In this steering control method for controlling steering force generated by actuators that steer the steered wheels of a vehicle, a state in which the rack gear of a steering mechanism that steers the steered wheels is in proximity of the stroke end is detected (S2), and if the rack gear is in proximity of the stroke end and the actuator drive current is at least a prescribed value (Ipre), the actuator drive current is restricted to a first upper limit that is less than the prescribed value (Ipre) (S3), and if the rack gear is not in proximity of the stroke end and the actuator drive current is at least the prescribed value (Ipre), the actuator drive current is restricted to a second upper limit that is less than the first upper limit (S4).

Description

Steering control method and steering control device

[0001] The present invention relates to a steering control method and a steering control device.

[0002] The following Patent Document 1 describes a technology in which, during parking assistance control using automatic steering, if the motor cannot rotate to the target steering angle even when a first upper limit current is passed through the motor, the upper limit current of the motor is switched to a second upper limit current that is smaller than the first upper limit current and enables steering to be maintained.

[0003] JP 2014-136430 A

[0004] When a state in which the steered wheels of a vehicle cannot be steered to a target steering angle even when the actuator that steers the steered wheels is driven continues, it is necessary to suppress the drive current to prevent abnormal overheating of the actuator. On the other hand, if the drive current is suppressed when rack end contact occurs, which is a state in which the rack shaft of the steering mechanism reaches the end of its stroke, there is a risk that the steering angle will not be maintained at the maximum allowable steering angle. An object of the present invention is to maintain the steering angle at the maximum allowable steering angle when rack end contact occurs by steering the steered wheels using the actuator, and to suppress overheating of the actuator due to a state in which the steered wheels cannot be steered to the target steering angle even when the actuator is driven continues.

[0005] According to one aspect of the present invention, there is provided a steering control method for controlling a steering force generated in an actuator that steers steered wheels of a vehicle. The steering control method detects a state in which a rack shaft of a steering mechanism that steers the steered wheels is near a stroke end, and when the rack shaft is near the stroke end and a drive current of the actuator is equal to or greater than a predetermined value, limits the drive current of the actuator to a first upper limit value that is less than the predetermined value, and when the rack shaft is not near the stroke end and the drive current of the actuator is equal to or greater than the predetermined value, limits the drive current of the actuator to a second upper limit value that is less than the first upper limit value.

[0006] According to the present invention, when rack end contact occurs by steering the steered wheels with an actuator, the steering angle can be maintained at the maximum allowable steering angle, and overheating of the actuator due to a state in which the steered wheels cannot be steered to the target steering angle even when the actuator is driven can be suppressed. The objects and advantages of the present invention are realized and achieved by using the elements and combinations thereof recited in the claims. It should be understood that both the foregoing general description and the following detailed description are merely exemplary and explanatory and do not limit the invention as defined by the claims.

[0007] FIG. 1 is a diagram illustrating an example of a schematic configuration of a driving assistance device according to an embodiment. FIG. 2 is a block diagram illustrating an example of the functional configuration of the controller of FIG. 1. FIG. 3 is a flowchart of a steering control method according to a first embodiment. FIG. 4(a) is a schematic diagram illustrating a change in drive current when a state in which the steered wheels cannot be steered to a target steering angle and steering becomes impossible does not occur, FIG. 4(b) is a schematic diagram illustrating a change in drive current when rack end hit occurs, and FIG. 4(c) is a schematic diagram illustrating a change in drive current when steering becomes impossible before rack end hit occurs. FIG. 4(a) and FIG. 4(b) are schematic diagrams illustrating parking assistance control in a first assistance mode. FIG. 4(c) is a schematic diagram illustrating parking assistance control in a second assistance mode. FIG. 5 is a flowchart of a steering control method according to a third embodiment.

[0008] (First embodiment) (Configuration) FIG. 1 is a diagram showing an example of a schematic configuration of a driving assistance device according to an embodiment. The host vehicle 1 is equipped with a driving assistance device 10 having a parking assistance function and a driving assistance function. The driving assistance device 10 is an example of a "steering control device" as defined in the claims. The parking assistance function is a function that assists the host vehicle 1 in traveling along a target parking path from the current position of the host vehicle 1 to a target parking position. For example, the driving assistance device 10 may perform automatic driving, which controls the host vehicle 1 to travel along the target parking path of the host vehicle 1 to the target parking position. Automatic driving that controls the host vehicle 1 to travel along the target parking path of the host vehicle 1 means control that automatically performs all or part of the traveling of the host vehicle 1 along the target parking path by controlling at least the steering angle of the host vehicle 1, among the steering angle, driving force, and braking force.

[0009] The driving assistance function refers to control that automatically performs all or part of the driving of the host vehicle 1 by controlling at least the steering angle among the steering angle, driving force, and braking force of the host vehicle 1. For example, the driving assistance function may include a lane keeping assistance function that assists the host vehicle 1 in driving within a driving lane. Furthermore, for example, the driving assistance function by the driving assistance device 10 may be an autonomous driving function that autonomously drives the host vehicle 1 along a target driving route to a set destination. In the following description, the controls by the driving assistance device 10 to realize the parking assistance function, driving assistance function, lane keeping assistance function, and autonomous driving function may be referred to as "parking assistance control," "driving assistance control," "lane keeping assistance control," and "autonomous driving control," respectively.

[0010] The driving assistance device 10 includes a positioning device 11, a map database (map DB) 12, an external sensor 15, a vehicle sensor 16, a controller 19, a steering actuator 21 a, an accelerator actuator 21 b, and a brake actuator 21 c. The positioning device 11 measures the current position of the vehicle 1. The positioning device 11 includes, for example, a Global Navigation System (GNSS) receiver. Map data is stored in the map database 12. The map data stored in the map database 12 may be, for example, map data for navigation or high-precision map data suitable for use as a map for autonomous driving.

[0011] The external sensor 15 detects objects within a predetermined distance range from the host vehicle 1. The external sensor 15 detects the surrounding environment of the host vehicle 1, such as the relative position of the host vehicle 1 and objects present around the host vehicle 1, the distance between the host vehicle 1 and the objects, and the direction in which the objects are present. The external sensor 15 may include, for example, a camera that captures images of the surrounding environment of the host vehicle 1. The external sensor 15 may include a distance measuring device such as a laser range finder, radar, LiDAR (Light Detection and Ranging), or sonar. The vehicle sensor 16 detects various information (vehicle information) about the host vehicle 1. For example, the vehicle sensor 16 may include a vehicle speed sensor that detects the traveling speed of the vehicle 1, an acceleration sensor that detects the acceleration (including deceleration) in three axes of the vehicle 1, a steering angle sensor that detects the steering angle of the steered wheels and steering wheel of the vehicle 1, a torque sensor that detects the steering torque applied to the steering wheel, a current sensor that detects the drive current of each of the steering actuator 21a, accelerator actuator 21b, and brake actuator 21c, and a temperature sensor that detects the temperature of each of the steering actuator 21a, accelerator actuator 21b, brake actuator 21c, and controller 19.

[0012] The steering actuator 21a controls the steering direction and steering amount of the steering mechanism of the vehicle 1 in response to a control signal from the controller 19. For example, if the steering mechanism of the vehicle 1 includes a steer-by-wire system in which the steering wheel and steered wheels are mechanically separated, the steering actuator 21a may be a steering motor that generates a steering force to steer the steered wheels. Alternatively, if the steering mechanism is an electric power steering system that applies a steering assist force to assist the driver in steering the steering wheel, the steering actuator 21a may be a steering assist motor that generates a steering assist force. The steering mechanism may include a backup clutch that mechanically connects or disconnects the steering wheel and the steered wheels. The electric power steering system and the steer-by-wire system may be switched between by engaging or disengaging the backup clutch. The accelerator actuator 21b controls the accelerator opening of a drive unit, such as an engine or a drive motor, in response to a control signal from the controller 19. The brake actuator 21c activates a braking device in response to a control signal from the controller 19.

[0013] The controller 19 is an electronic control unit that performs parking assistance control and driving assistance control of the host vehicle 1. The controller 19 includes a processor 19a and peripheral components such as a storage device 19b. The processor 19a may be, for example, a CPU or an MPU. The storage device 19b may include a semiconductor storage device, a magnetic storage device, an optical storage device, or the like. The functions of the controller 19 described below are realized, for example, by the processor 19a executing a computer program stored in the storage device 19b. For example, in parking assistance control, the controller 19 may detect a target parking position near the host vehicle 1 and control the steering actuator 21a, accelerator actuator 21b, and brake actuator 21c so that the host vehicle 1 travels from its current position to the target parking position. For example, in lane keeping assistance control, the controller 19 may recognize lane markings of the driving lane in which the host vehicle 1 is traveling based on a detection signal from the external sensor 15 and control the steering actuator 21a so that the host vehicle 1 travels along the driving lane (e.g., so that the host vehicle 1 travels at a predetermined lateral position within the driving lane). Further, for example, in autonomous driving control, the controller 19 may control the steering actuator 21a, accelerator actuator 21b, and brake actuator 21c so that the vehicle 1 travels along a target travel route to a set destination.

[0014] When the controller 19 automatically steers the steered wheels, the driving of the steering actuator 21a may result in the wheels not being able to be steered to the target steering angle, resulting in a continuous steering stop. For example, if the steering angle of the steered wheels does not increase because the steered wheels are abutting an obstacle or the like, the driving of the steering actuator 21a may result in the wheels not being able to be steered to the target steering angle, resulting in a continuous steering stop. Furthermore, if rack end contact occurs, in which the rack shaft of the steering mechanism reaches the end of its stroke, the wheels may not be able to be steered to the target steering angle, resulting in a continuous steering stop. When the driver manually steers the wheels, the steering actuator 21a may continue to output a steering assist force for the same reason, even though the steering of the steered wheels has stopped. If the driving of the steering actuator 21a continues while the steering of the steered wheels has stopped, a large drive current continues to flow due to the increase in output torque of the steering actuator 21a, resulting in abnormal overheating of the steering actuator 21a. Therefore, in such cases, it is necessary to limit the drive current. On the other hand, in certain situations, the steering angle of the steered wheels of the host vehicle 1 may be maintained at the maximum allowable steering angle. For example, when parking the host vehicle 1, the steering angle of the steered wheels may be maintained at the maximum allowable steering angle. When attempting to steer the steered wheels to the maximum allowable steering angle, rack end contact may occur due to an alignment error or a neutral position error in the steering mechanism, and the steered wheels may not be steered to the target steering angle, resulting in a state in which steering is stopped. For this reason, if rack end contact occurs in certain situations, limiting the drive current of the steering actuator 21a may make it impossible to maintain the steering angle of the steered wheels at the maximum allowable steering angle. In the case of manual steering, the steering assist force may be reduced, causing the driver to feel uncomfortable.

[0015] Therefore, the controller 19 detects whether a state in which the rack shaft is near the stroke end has occurred. The state in which the rack shaft is near the stroke end may be, for example, whether rack end contact has occurred. When the rack shaft is near the stroke end and the drive current of the steering actuator 21a is equal to or greater than a predetermined value Ipre, the upper limit of the drive current of the steering actuator 21a is set to a first upper limit value IL1 that is less than the predetermined value Ipre. For example, the first upper limit value IL1 may be set to a minimum value of the drive current that can maintain the steering angle of the steered wheels so that it does not decrease from the maximum allowable steering angle. On the other hand, when the rack shaft is not near the stroke end and the drive current of the steering actuator 21a is equal to or greater than the predetermined value Ipre, the upper limit of the drive current of the steering actuator 21a is set to a second upper limit value IL2 that is less than the first upper limit value IL1. For example, the second upper limit value may be set to zero. Alternatively, the second upper limit value may be set to a value greater than zero and less than the first upper limit value IL1 so as not to cause discomfort to the driver, or may be set to the maximum drive current value that does not cause abnormal overheating. 2 is a block diagram of an example of a functional configuration for controlling the steering force generated by the steering actuator 21a using the controller 19. The controller 19 includes a target steering angle setting unit 30, a current command value setting unit 31, a rack end contact detection unit 32, a current limiting unit 33, and a drive unit 34. The target steering angle setting unit 30 sets a target steering angle θt, which is a target value for the steering angle of the steered wheels or steering wheel, in parking assist control or driving assist control. For example, in autonomous driving control, the target steering angle θt may be set to cause the host vehicle 1 to travel along a target driving trajectory set based on the surrounding environment of the host vehicle 1 and the driving state of the host vehicle 1. Furthermore, for example, in lane keeping assist control, the target steering angle θt may be set to cause the host vehicle 1 to travel along a target driving trajectory that passes through a predetermined lateral position based on lane markings (lane markers) detected ahead of the host vehicle 1. Further, for example, in parking assist control, a target steering angle θt may be set to make the vehicle 1 travel along a target parking path from the current position of the vehicle 1 to the target parking position.

[0016] The current command value setting unit 31 sets a current command value Ic, which is a target value of the drive current of the steering actuator 21a. For example, when parking assist control or driving assist control is being executed, the current command value Ic may be set based on the deviation between the actual steering angle θa of the steered wheels or the steering wheel detected by the steering angle sensor of the vehicle sensor 16 and the target steering angle θt. Furthermore, during manual steering, the current command value Ic may be set based on the steering torque applied to the steering wheel detected by the torque sensor of the vehicle sensor 16. The rack end hit detection unit 32 determines whether a state in which the rack shaft is near the stroke end has occurred. For example, the rack end hit detection unit 32 may determine whether rack end hit has occurred by assuming that the rack shaft is near the stroke end. For example, the rack end hit detection unit 32 may detect the stroke amount of the rack shaft using a stroke sensor, and determine that the rack shaft is near the stroke end when the stroke amount is equal to or greater than a first predetermined value and equal to or less than a second predetermined value. For example, the rack shaft may be detected as being near the stroke end when the drive current of the steering actuator 21a is equal to or greater than a third predetermined value and equal to or less than a fourth predetermined value. Alternatively, as exemplified in a second embodiment described later, it may be determined whether the rack shaft is near the stroke end based on the steering angular velocity of the steered wheels or the steering wheel and the drive current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16. The current limiting unit 33 limits the upper limit of the current command value Ic when the drive current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16 is equal to or greater than a predetermined value Ipre.

[0017] Specifically, when the rack end contact detection unit 32 determines that the rack shaft is near the stroke end and the drive current of the steering actuator 21a is equal to or greater than the predetermined value Ipre, the upper limit of the current command value Ic is set to a first upper limit value IL1 that is less than the predetermined value Ipre. On the other hand, when the rack end contact detection unit 32 does not determine that the rack shaft is near the stroke end and the drive current of the steering actuator 21a is equal to or greater than the predetermined value Ipre, the upper limit of the current command value Ic is set to a second upper limit value IL2 that is less than the first upper limit value IL1. Furthermore, the current limiting unit 33 limits the upper limit of the current command value Ic when the temperature of the steering actuator 21a or the controller 19 detected by the temperature sensor of the vehicle sensor 16 exceeds a predetermined temperature threshold. The drive unit 34 drives the steering actuator 21a in accordance with the current command value Ic whose upper limit has been limited by the current limiting unit 33. For example, the drive voltage applied to the steering actuator 21a is controlled so as to reduce the deviation between the current command value Ic, the upper limit of which is limited by the current limiting unit 33, and the drive current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16.

[0018] (Operation) Figure 3 is a flowchart of the steering control method of the first embodiment. In step S1, the current limiting unit 33 determines whether the drive current of the steering actuator 21a is equal to or greater than a predetermined value Ipre. If the drive current is not equal to or greater than the predetermined value Ipre (step S1: N), the steering actuator 21a is driven based on the current command value Ic set by the current command value setting unit 31. Note that the upper limit of the current command value Ic may be limited if the temperature of the steering actuator 21a or the controller 19 detected by the temperature sensor of the vehicle sensor 16 exceeds a predetermined temperature threshold. If the drive current is equal to or greater than the predetermined value Ipre (step S1: Y), the process proceeds to step S2. In step S2, the rack end contact detection unit 32 determines whether a state has occurred in which the rack shaft is near the stroke end.

[0019] If the rack shaft is near the stroke end (step S2: Y), the process proceeds to step S3. If the rack shaft is not near the stroke end (step S2: N), the process proceeds to step S4. In step S3, the current limiting unit 33 limits the drive current of the steering actuator 21a to a first upper limit value IL1 that is less than a predetermined value Ipre. In step S4, the current limiting unit 33 limits the drive current of the steering actuator 21a to a second upper limit value IL2 that is less than the first upper limit value IL1.

[0020] Second Embodiment The controller 19 of the second embodiment determines whether a state in which the rack shaft is near the stroke end has occurred based on the steering angular velocity of the steered wheels or steering wheel and the drive current of the steering actuator 21 a detected by the current sensor of the vehicle sensor 16. For example, it determines whether rack end hit has occurred. See FIG. 2 . The rack end hit detection unit 32 determines that a state in which the rack shaft is near the stroke end has occurred (for example, determines whether a state in which the rack shaft is near the stroke end has occurred) when the steering angular velocity of the steered wheels or steering wheel is equal to or less than the angular velocity threshold and the drive current of the steering actuator 21 a is within a threshold range R set to be less than a predetermined value Ipre. If the steering angular velocity of the steered wheels or steering wheel is not equal to or less than the angular velocity threshold or the drive current of the steering actuator 21 a is not within a threshold range R set to be less than the predetermined value Ipre, it does not determine that a state in which the rack shaft is near the stroke end has occurred (for example, does not determine whether a state in which the rack shaft is near the stroke end has occurred).

[0021] For example, the rack-end hit detection unit 32 may calculate the steering angular velocity by time-differentiating the steering angle detected by the steering angle sensor of the vehicle sensor 16. Furthermore, for example, the threshold range R may be set based on the drive current Ix that flows through the steering actuator 21a when the steered wheels are steered to the maximum allowable steering angle without rack-end hit occurring. For example, the threshold range R may be set to a range between a lower limit (Ix-α) and an upper limit (Ix+α), with a predetermined margin α. In the following description, the drive current Ix may be referred to as the "rack-end drive current Ix." The operation of the controller 19 of the second embodiment will be described with reference to FIGS. 4(a) to 4(c). FIG. 4(a) is a schematic diagram illustrating changes in the drive current of the steering actuator 21a when the steered wheels cannot be steered to the target steering angle and a state in which they become unsteerable does not occur. When steering is initiated at time t1, the steering angle of the steered wheels increases in accordance with an increase in the target steering angle, and the drive current increases as the steering angle increases. In the example of FIG. 4A , the steered wheels can be controlled to follow the target steering angle, so no sudden increase in drive current occurs. Therefore, the drive current is maintained below the threshold range R, and the current limiting unit 33 does not limit the drive current. After that, when the steered wheels are steered to the maximum allowable steering angle without rack-end contact occurring, the drive current reaches the rack-end drive current Ix at time t2 and stops increasing. The steered wheels are then maintained at the maximum allowable steering angle until time t3. During this time, the steered wheels can be controlled to follow the target steering angle without rack-end contact occurring, so the current limiting unit 33 does not limit the drive current. As a result, the drive current is maintained at the rack-end drive current Ix. When the steering angle begins to decrease from time t3, the drive current decreases, and when steering control ends at time t4, the drive current returns to zero.

[0022] FIG. 4B is a schematic diagram showing changes in drive current when rack end hit occurs. When steering is initiated at time t11, the steering angle of the steered wheels increases in accordance with the increase in the target steering angle, and the drive current increases as the steering angle increases. When the steering angle of the steered wheels approaches the maximum allowable steering angle sufficiently, the value of the drive current enters the threshold range R. When rack end hit occurs at time t12, steering of the steered wheels stops, and the steering angular velocity falls below the angular velocity threshold. Therefore, because the steering angular velocity is below the angular velocity threshold and the drive current is within the threshold range R, the rack end hit detection unit 32 determines that rack end hit has occurred. In other words, it determines that the rack shaft is near the stroke end. When rack end hit occurs, the steered wheels cannot be steered to the target steering angle for a certain period of time, and the drive current of the steering actuator 21a rapidly increases to a predetermined value Ipre. Therefore, at time t13, the current limiting unit 33 sets the upper limit of the drive current to a first upper limit value IL1. As a result, the drive current is limited to the first upper limit value IL1. When the steering angle starts to decrease from time t14, the drive current decreases, and when the steering control ends at time t15, the drive current returns to zero.

[0023] FIG. 4C is a schematic diagram showing changes in drive current when steering becomes impossible before rack end contact occurs. When steering is initiated at time t21, the steering angle of the steered wheels increases in accordance with the increase in the target steering angle, and the drive current increases as the steering angle increases. In FIG. 4C, we assume that steering stops at time t22 due to the steered wheels hitting an obstacle or other obstacle before the steering angle of the steered wheels approaches the maximum allowable steering angle. Therefore, the drive current of the steering actuator 21a rapidly increases to the predetermined value Ipre before the drive current value falls within the threshold range R. Therefore, the rack end contact detection unit 32 does not detect a state in which the drive current is within the threshold range R and therefore does not detect the occurrence of rack end contact. In other words, it does not determine that the rack shaft is near the stroke end. Therefore, at time t23, the current limiting unit 33 sets the upper limit of the drive current to the second upper limit IL2. This limits the drive current to the second upper limit IL2. Thereafter, the drive current is maintained at 0 until the steering control is ended at time t24.

[0024] (Third Embodiment) The controller 19 of the third embodiment executes parking assist control to assist in parking at a pre-registered target parking position. Alternatively or in addition to this, the controller 19 may execute parking assist control to assist in parking at a target parking position that is not pre-registered. In the following description, the control mode of the parking assist control to assist in parking at a pre-registered target parking position may be referred to as a "first assist mode," and the control mode of the parking assist control to assist in parking at a target parking position that is not pre-registered may be referred to as a "second assist mode."

[0025] 5(a) and 5(b) are schematic diagrams illustrating parking assist control in the first assist mode. When using parking assist control in the first assist mode, a target parking position 41 where the host vehicle 1 should be parked is registered in advance in the driving assist device 10. Specifically, targets present around the target parking position 41 are extracted and stored (registered) in advance in the storage device 19b. In the following description, the targets around the target parking position 41 stored in the storage device 19b are referred to as "learned targets." In FIG. 5(a), circles schematically represent learned targets. When registering the target parking position 41 in the driving assist device 10, for example, the user performs an operation to instruct registration of the target parking position 41 (hereinafter, this may be referred to as a "registration operation").

[0026] For example, when the host vehicle 1 is positioned near the target parking position 41 (e.g., when the user manually parks the host vehicle 1 at the target parking position 41), the controller 19 detects targets around the host vehicle 1 using the external sensor 15 and stores the targets as learned targets. For example, targets may be detected from a surrounding image obtained by capturing an image of the surroundings of the host vehicle 1 with a camera. For example, targets may be detected as edge points or points (feature points) with characteristic shapes, such as edges or corners of targets such as road markings, road boundaries, and obstacles, in the captured image obtained by the camera, where the brightness of adjacent pixels changes by a predetermined amount or more. The controller 19 stores learned target data related to the learned targets in the storage device 19b. For example, the learned target data may include data representing the feature amounts of the learned targets (hereinafter referred to as "feature amount data") and data on the relative positional relationship between the target parking position 41 and the learned targets (hereinafter referred to as "relative position data"). The relative position data may be stored, for example, as the relative position of the learned target with respect to the target parking position 41. For example, the controller 19 can acquire the position of the learned target detected when the host vehicle 1 is parked at the target parking position 41 as the relative position of the learned target with respect to the target parking position 41. The coordinates of the learned target and the target parking position 41 in a coordinate system with a fixed point as the reference point (hereinafter referred to as the "map coordinate system") may be stored.

[0027] FIG. 5B is an explanatory diagram of an example of processing when parking assistance is performed. For example, the controller 19 may start parking assistance control of the host vehicle 1 when a user performs an operation to instruct activation of parking assistance control of the host vehicle 1. Alternatively, the controller 19 may automatically start parking assistance control when the host vehicle 1 approaches a registered target parking position 41. When parking assistance control starts, the controller 19 extracts targets around the host vehicle 1 using the external sensor 15. In the following description, targets around the host vehicle 1 extracted when parking assistance is performed are referred to as "surrounding targets." In FIG. 5B, triangular plots represent surrounding targets. The controller 19 detects the target parking position 41 by matching the learned targets with the surrounding targets and associating identical feature points. The controller 19 calculates the relative position of the host vehicle 1 with respect to the target parking position 41 based on the relative positional relationship between the surrounding targets detected when parking assistance is performed and the host vehicle 1, and the relative positional relationship between the learned targets associated with the surrounding targets and the target parking position 41.

[0028] For example, the controller 19 calculates the position of the target parking position 41 on a coordinate system (hereinafter referred to as the "vehicle coordinate system") based on the current position of the host vehicle 1. Note that if the coordinates of the learned targets and the target parking position 41 on the map coordinate system are stored in the storage device 19b, the coordinates of the target parking position 41 on the map coordinate system may be converted to coordinates on the vehicle coordinate system based on the positions of the surrounding targets detected when parking assistance is performed and the positions of the learned targets in the map coordinate system. The host vehicle 1's own position on the map coordinate system may be calculated based on the positions of the surrounding targets detected when parking assistance is performed and the positions of the learned targets in the map coordinate system, and the relative position of the host vehicle 1 with respect to the target parking position 41 may be calculated from the difference between the coordinates of the host vehicle 1 and the coordinates of the target parking position 41 in the map coordinate system. The controller 19 calculates a target parking path 44 from the current position 43 of the host vehicle 1 to the target parking position 41. The controller 19 performs parking assistance control of the host vehicle 1 based on the calculated target parking path 44.

[0029] 6 is a schematic diagram illustrating parking assist control in the second assist mode. When the user performs an activation operation to instruct activation of parking assist control, the controller 19 starts parking assistance for the host vehicle 1. When parking assist control in the second assist mode is started, the controller 19 detects available parking spaces around the host vehicle 1 as target parking positions 41a to 41d based on the detection results of the external sensor 15 detecting white lines 45 around the host vehicle 1 and objects around the host vehicle 1. Hereinafter, the target parking positions 41a to 41d may be collectively referred to as "target parking positions 41."

[0030] For example, the controller 19 may detect an available parking space around the host vehicle 1 as the target parking position 41 based on the detection result of parking frame lines 45 that indicate the parking space. Alternatively, for example, the controller 19 may detect parked vehicles as objects around the host vehicle 1 and detect the space between the parked vehicles as the target parking position 41. The controller 19 calculates a target parking path 44 from the current position 43 of the host vehicle 1 to the target parking position 41. The controller 19 performs parking assist control of the host vehicle 1 based on the calculated target parking path 44.

[0031] See FIG. 2 . In the third embodiment, the current limiting unit 33 sets the first upper limit value IL1, which limits the current command value Ic, to different values ​​depending on whether the controller 19 is performing parking assist control or whether the driver is manually steering the steering wheel. For example, the current limiting unit 33 may set the first upper limit value IL1 to a relatively large value IL1a when the controller 19 is performing parking assist control and to a relatively small value IL1b (i.e., a value smaller than IL1a) when the driver is manually steering the steering wheel. This is because when the driver manually steers the steering wheel, the steering force of the driver is applied to the steering mechanism, so that the steering force of the steering actuator 21a can be small. This allows the drive current of the steering actuator 21a to be further reduced when rack end contact occurs, thereby suppressing heat generation. Note that when the steering mechanism of the host vehicle 1 is a steer-by-wire system or when the backup clutch is disengaged, the steering force of the driver is not applied to the steering mechanism. For this reason, when the driver performs manual steering in an electric power steering system or when the driver performs manual steering with the backup clutch engaged, the first upper limit value IL1 may be set to a relatively small value IL1b, and when the driver performs manual steering in a steer-by-wire system or when the driver performs manual steering with the backup clutch disengaged, the first upper limit value IL1 may be set to a relatively large value IL1a, as in the case where parking assist control is being performed.

[0032] 7 is a flowchart of the steering control method of the third embodiment. In step S10, the current limiting unit 33 determines whether parking assist control is being performed. If parking assist control is being performed (step S10: Y), the process proceeds to step S11. If the driver is manually steering (step S10: N), the process proceeds to step S12. In step S11, the current limiting unit 33 sets the first upper limit value IL1 to a relatively large value IL1a. Thereafter, the process proceeds to step S13. In step S12, the current limiting unit 33 sets the first upper limit value IL1 to a relatively small value IL1b. Thereafter, the process proceeds to step S13.

[0033] In step S13, the current command value setting unit 31 sets a current command value Ic, which is a target value of the drive current of the steering actuator 21a. In step S14, the current limiting unit 33 determines whether the drive current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16 is equal to or greater than a predetermined value Ipre. If the drive current is not equal to or greater than the predetermined value Ipre (step S14: N), the process proceeds to step S15. If the drive current is equal to or greater than the predetermined value Ipre (step S14: Y), the process proceeds to step S16. In step S15, the drive unit 34 drives the steering actuator 21a based on the current command value Ic set by the current command value setting unit 31. Note that the upper limit of the current command value Ic may be limited if the temperature of the steering actuator 21a or the controller 19 detected by the temperature sensor of the vehicle sensor 16 exceeds a predetermined temperature threshold.

[0034] In step S16, the rack end contact detection unit 32 determines whether a state in which the rack shaft is near the stroke end has occurred. If the rack shaft is near the stroke end (step S16: Y), the process proceeds to step S17. If the rack shaft is not near the stroke end (step S16: N), the process proceeds to step S18. In step S17, the current limiting unit 33 limits the current command value Ic to a first upper limit value IL1. The drive unit 34 drives the steering actuator 21a based on the current command value Ic limited by the first upper limit value IL1. In step S18, the current limiting unit 33 limits the current command value Ic to a second upper limit value IL2. The drive unit 34 drives the steering actuator 21a based on the current command value Ic limited by the second upper limit value IL2.

[0035] (Effects of the Embodiment) (1) The controller 19 controls the steering force generated in the actuator 21 a that steers the steered wheels of the vehicle 1. The controller 19 detects a state in which a rack shaft of a steering mechanism that steers the steered wheels is near a stroke end, and when the rack shaft is near the stroke end and the drive current of the actuator 21 a is equal to or greater than a predetermined value Ipre, the controller 19 limits the drive current of the actuator 21 a to a first upper limit value that is less than the predetermined value Ipre. When the rack shaft is not near the stroke end and the drive current of the actuator 21 a is equal to or greater than the predetermined value Ipre, the controller 19 limits the drive current of the actuator 21 a to a second upper limit value that is less than the first upper limit. This makes it possible to maintain the steering angle at the maximum allowable steering angle when rack end contact occurs and to prevent the actuator from overheating, which would occur if the steered wheels could not be steered to the target steering angle even when the actuator is driven.

[0036] (2) For example, the second upper limit may be zero. This prevents overheating of the actuator 21a when the steered wheels become unable to be steered before reaching the maximum allowable steering angle. (3) The first upper limit may be a current value that maintains the current steering angle. This prevents overheating of the actuator 21a when rack-end contact occurs while maintaining the steering angle at the maximum allowable steering angle. (4) The controller 19 may determine that the rack shaft is near the stroke end when the steering angular velocity of the steered wheels or the steering wheel is equal to or less than the angular velocity threshold and the drive current of the actuator 21a is within a threshold range set below a predetermined value Ipre. This allows for accurate determination of whether rack-end contact has occurred even if there is an alignment error or a neutral position error in the steering mechanism. (5) The first upper limit during manual steering may be set to a smaller value than the first upper limit during automatic parking control, which controls the host vehicle 1 to travel to a target parking position. This reduces the drive current of the actuator 21a when rack end contact occurs during manual steering compared to when automatic parking control is being executed, thereby preventing overheating of the actuator 21a.

[0037] (6) The controller 19 may detect targets existing around the target parking position in advance, register data representing the relative positional relationship between the detected targets and the target parking position in the storage device as learned target data, and when driving the vehicle 1 to the target parking position after registering the learned target data in the storage device, detect the positions of surrounding targets, which are targets existing around the vehicle 1, calculate the relative positional relationship between the target parking position and the current position of the vehicle 1 based on the learned target data and the positions of the surrounding targets, generate a target parking path from the current position of the vehicle 1 to the target parking position based on the calculated relative positional relationship, and control the vehicle 1 to drive along the target parking path to the target parking position. This allows the user to use parking assist control that assists the user in parking the vehicle 1 at the pre-registered target parking position.

[0038] All examples and conditional terms described herein are intended for educational purposes to aid the reader in understanding the present invention and the concepts provided by the inventor for the advancement of technology, and should be construed without limitation to the specifically described examples and conditions above, and the configuration of examples herein for illustrating the advantages and disadvantages of the present invention. Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the present invention.

[0039] 1...Own vehicle, 10...Driving assistance device, 11...Positioning device, 12...Map database, 15...External sensor, 16...Vehicle sensor, 19...Controller, 19a...Processor, 19b...Storage device, 21a...Steering actuator, 21b...Accelerator actuator, 21c...Brake actuator, 30...Target steering angle setting unit, 31...Current command value setting unit, 32...Rack end contact detection unit, 33...Current limiting unit, 34...Drive unit

Claims

1. A steering control method for controlling a steering force generated in an actuator that steers steered wheels of a vehicle, comprising: Detecting a state in which a rack shaft of a steering mechanism that steers the steered wheels is near a stroke end, when the rack shaft is near a stroke end and the drive current of the actuator is equal to or greater than a predetermined value, the drive current of the actuator is limited to a first upper limit value that is less than the predetermined value; The first upper limit value during manual steering is set to a value smaller than the first upper limit value in the case of automatic parking control that controls the vehicle so that the vehicle travels to a target parking position. A steering control method comprising:

2. 2. The steering control method according to claim 1, wherein, when the rack shaft is not near a stroke end and the drive current of the actuator is equal to or greater than a predetermined value, the drive current of the actuator is limited to a second upper limit value that is less than the first upper limit value.

3. 3. The steering control method according to claim 1, wherein the first upper limit value is a current value that allows the current steering angle to be maintained.

4. 4. The steering control method according to claim 1, wherein the rack shaft is determined to be near a stroke end when the steering angular velocity of the steered wheels or the steering wheel is equal to or less than an angular velocity threshold value and the drive current of the actuator is within a threshold range set to be less than the predetermined value.

5. (delete)

6. Detecting targets present around the target parking position in advance, and registering data representing a relative positional relationship between the detected targets and the target parking position in a storage device as learned target data; When the vehicle is driven to the target parking position after the learned target data is registered in the storage device, positions of surrounding targets that are targets present around the vehicle are detected; Calculating a relative positional relationship between the target parking position and the current position of the vehicle based on the learned target object data and the positions of the surrounding targets; generating a target parking path from the current position of the vehicle to the target parking position based on the calculated relative position relationship; controlling the vehicle to travel along the target parking path to the target parking position; 2. The steering control method according to claim 1.

7. an actuator for steering the steered wheels of the vehicle; a controller that detects a state in which a rack shaft of a steering mechanism that steers the steered wheels is near a stroke end, and when the rack shaft is near the stroke end and a drive current of the actuator is equal to or greater than a predetermined value, limits the drive current of the actuator to a first upper limit value that is less than the predetermined value, and sets the first upper limit value during manual steering to a value smaller than the first upper limit value during automatic parking control that controls the vehicle to travel to a target parking position; A steering control device comprising: