Steering control method and steering control device

Abstract

In a steering control method for controlling a steering force generated in an actuator for steering a steered wheel of a vehicle, a state in which a rack shaft of a steering mechanism for steering the steered wheel is in the vicinity of a stroke end is detected (S2), and when the rack shaft is in the vicinity of the stroke end and a drive current of the actuator is equal to or greater than a predetermined value (Ipre), the steering force generated in the actuator is controlled. When the rack shaft is in the vicinity of the stroke end and the drive current of the actuator is greater than or equal to a predetermined value (Ipre), the drive current of the actuator is limited at a first upper limit value (S3) that is lower than the predetermined value (Ipre) (S4), and when the rack shaft is not in the vicinity of the stroke end and the drive current of the actuator is greater than or equal to the predetermined value (Ipre), the drive current of the actuator is limited at a second upper limit value that is lower than the first upper limit value (S4).

Description

Technical Field

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

[0002] Patent document 1 below describes a technology that, when performing parking assist control through automatic steering, switches the upper limit current of the motor to a second upper limit current that is smaller than the first upper limit current and capable of maintaining steering when the motor cannot rotate to a target steering angle even if a first upper limit current flows through the motor.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-136430 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] If the steering wheel of a vehicle continues to be unable to be steered to the target steering angle even after the actuator is driven, the drive current must be suppressed to prevent abnormal overheating of the actuator. On the other hand, if the drive current is suppressed when the steering mechanism's rack shaft reaches the end of its stroke, i.e., when rack end contact occurs, the steering angle may not be maintained at the maximum allowable steering angle.

[0008] The present invention aims to maintain the steering angle at the maximum allowable steering angle when rack end contact occurs due to steering the steering wheel by an actuator, and to suppress overheating of the actuator caused by a state in which the steering wheel cannot be steered to the target steering angle even when the actuator is driven.

[0009] Technical solutions to solve problems

[0010] According to one aspect of the present invention, a steering control method for controlling a steering force generated by an actuator for steering a vehicle's steering wheel is provided. In the steering control method, a state is detected in which a rack shaft of a steering mechanism for steering the steering wheel is near a stroke end. When the rack shaft is near a stroke end and the actuator drive current is at or above a specified value, the actuator drive current is limited to a first upper limit value lower than the specified value. When the rack shaft is not near a stroke end and the actuator drive current is at or above the specified value, the actuator drive current is limited to a second upper limit value lower than the first upper limit value.

[0011] Effects of the Invention

[0012] According to the present invention, when the rack end touches due to steering the steering wheel by the actuator, the steering angle is maintained at the maximum allowable steering angle, and overheating of the actuator caused by the state in which the steering wheel cannot be steered to the target steering angle even when the actuator is driven can be suppressed.

[0013] The objects and advantages of the present invention are embodied and achieved by the elements and combinations thereof shown in the claims. Both the above general description and the following detailed description are merely illustrative and explanatory, and should not be understood to limit the present invention as the claims do. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing a schematic configuration example of a driving assistance device according to an embodiment.

[0015] Figure 2 yes Figure 1 A block diagram showing an example of the functional configuration of a controller.

[0016] Figure 3 This is a flowchart of the steering control method according to the first embodiment.

[0017] Figure 4 (a) is a schematic diagram showing changes in the driving current when the steering wheel cannot be steered to the target steering angle and the steering is not disabled. Figure 4 (b) is a schematic diagram showing the change in drive current when rack end contact occurs. Figure 4 (c) is a schematic diagram showing the change in drive current when steering becomes impossible before the rack end contacts the vehicle.

[0018] Figure 5 (a) and (b) are schematic diagrams for explaining parking assist control in the first assist mode.

[0019] Figure 6 This is a schematic diagram for explaining parking assist control in the second assist mode.

[0020] Figure 7 This is a flowchart of the steering control method according to the third embodiment. DETAILED DESCRIPTION

[0021] (First embodiment)

[0022] (constitute)

[0023] Figure 1 1 is a diagram showing a schematic configuration example of a driving assistance device according to an embodiment. A vehicle 1 includes 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" described in the claims.

[0024] The parking assistance function assists the vehicle 1 in traveling along a target parking path from its current position to its target parking location. For example, the driving assistance device 10 may also perform automated driving, controlling the vehicle 1 to travel along its target parking path to its target parking location. This automated driving control involves controlling the vehicle 1 to travel along its target parking path to its target parking location, and includes controlling at least the steering angle, driving force, and braking force of the vehicle 1 to automatically execute all or part of the vehicle 1's travel along the target parking path.

[0025] A driving assistance function refers to a function that automatically controls at least the steering angle, among the driving force, and braking force, of the host vehicle 1, to automatically implement all or part of the driving of the host vehicle 1. For example, a driving assistance function may include a lane keeping assistance function that assists the host vehicle 1 in staying within its lane. Alternatively, for example, a driving assistance function implemented by the driving assistance device 10 may include an autonomous driving function that enables the host vehicle 1 to autonomously drive along a target driving route to a set destination.

[0026] It should be noted that in the following description, the controls performed by the driving assistance device 10 for realizing the parking assistance function, driving assistance function, lane keeping assistance function and autonomous driving function are sometimes respectively expressed as "parking assistance control", "driving assistance control", "lane keeping assistance control" and "autonomous driving control".

[0027] The driving support 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 .

[0028] The positioning device 11 measures the current position of the vehicle 1. The positioning device 11 includes, for example, a Global Navigation Satellite 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, high-precision map data, preferably used for navigation or automated driving.

[0029] The external sensors 15 detect objects within a specified distance range from the vehicle 1. They detect the surrounding environment of the vehicle 1, including the relative position of objects around the vehicle 1, the distance between the vehicle 1 and the objects, and the direction of the objects. For example, the external sensors 15 may include a camera that captures images of the surrounding environment of the vehicle 1. Alternatively, the external sensors 15 may include a laser rangefinder, radar, LiDAR (Light Detection and Ranging), sonar, or other ranging devices.

[0030] The vehicle sensors 16 detect various types of information (vehicle information) about the host vehicle 1. For example, the vehicle sensors 16 may include a vehicle speed sensor for detecting the traveling speed of the host vehicle 1, an acceleration sensor for detecting acceleration (including deceleration) in three axial directions of the host vehicle 1, a steering angle sensor for detecting the steering angle of the steering wheel or steering wheel of the host vehicle 1, a torque sensor for detecting the steering torque applied to the steering wheel, a current sensor for detecting the driving current of each of the steering actuator 21a, the accelerator actuator 21b, and the brake actuator 21c, and a temperature sensor for detecting the temperature of each of the steering actuator 21a, the accelerator actuator 21b, and the brake actuator 21c or the controller 19.

[0031] The steering actuator 21a controls the steering direction and steering amount of the steering mechanism of the vehicle 1 based on the control signal of the controller 19. For example, in the case where the steering mechanism of the vehicle 1 has a steer-by-wire system in which the steering wheel and the steering wheel are mechanically separated, the steering actuator 21a can be a steering motor that generates a steering force for steering the steering wheel. In addition, for example, in the case where the steering mechanism is an electric power steering system that provides a steering assist force to assist the driver in steering the steering wheel, the steering actuator 21a can be a steering assist motor that generates the steering assist force. It should be noted that the steering mechanism can also have a backup clutch that mechanically connects or disconnects the steering wheel and the steering wheel. The electric power steering system and the steer-by-wire system can also be switched by connecting and releasing the backup clutch.

[0032] The acceleration actuator 21b controls the accelerator opening of a driving device such as an engine or a driving motor according to a control signal from the controller 19. The brake actuator 21c operates a brake device according to a control signal from the controller 19.

[0033] The controller 19 is an electronic control unit that performs parking assistance and driving assistance control for the vehicle 1. The controller 19 includes peripheral components such as a processor 19a and a storage device 19b. The processor 19a may be, for example, a CPU or an MPU. The storage device 19b may include a semiconductor memory device, a magnetic storage device, an optical storage device, or the like. The functions of the controller 19 described below are implemented, for example, by the processor 19a executing a computer program stored in the storage device 19b.

[0034] For example, in parking assist control, the controller 19 can detect a target parking position near the host vehicle 1 and control the steering actuator 21a, accelerator actuator 21b, and brake actuator 21c to move the host vehicle 1 from its current position to the target parking position. Furthermore, in lane keeping assist control, the controller 19 can identify the lane dividing line of the driving lane, i.e., the lane in which the host vehicle 1 is traveling, based on detection signals from the external sensors 15 and control the steering actuator 21a to ensure that the host vehicle 1 travels along the driving lane (e.g., the host vehicle 1 travels at a predetermined lateral position within the driving lane). Furthermore, in autonomous driving control, the controller 19 can control the steering actuator 21a, accelerator actuator 21b, and brake actuator 21c to ensure that the host vehicle 1 travels along the target driving path to a set destination.

[0035] When the controller 19 automatically steers the steering wheel, there are cases where the steering actuator 21a cannot be driven to steer the steering wheel to the target steering angle, and the steering state may continue to be stopped. For example, if the steering wheel contacts an obstacle, etc., and the steering angle does not increase, there are cases where the steering actuator 21a cannot be driven to steer the steering wheel to the target steering angle, and the steering state may continue to be stopped. In addition, if the rack shaft of the steering mechanism reaches the end of its stroke and the rack shaft hits the rack end, there are cases where the steering wheel cannot be steered to the target steering angle, and the steering state may continue to be stopped. When the driver manually steers, there are cases where the steering actuator 21a continues to output steering assist force even when the steering wheel is stopped, for similar reasons.

[0036] If the steering actuator 21a continues to be driven while the steering wheel is stopped, a large drive current will continue to flow as the output torque of the steering actuator 21a increases, causing abnormal overheating of the steering actuator 21a. Therefore, in such a case, the drive current needs to be limited.

[0037] On the other hand, in certain scenarios, the steering angle of the steering wheel of the vehicle 1 may be maintained at the maximum allowable steering angle. For example, when parking the vehicle 1, the steering angle of the steering wheel may be maintained at the maximum allowable steering angle. If the steering wheel is to be steered to the maximum allowable steering angle, there may be a situation where the rack end touches due to an alignment error or a neutral position error of the steering mechanism, and the steering wheel cannot be steered to the target steering angle, and the steering stop state continues. Therefore, in certain scenarios, if the driving current of the steering actuator 21a is limited when the rack end touches, the steering angle of the steering wheel cannot be maintained at the maximum allowable steering angle. In the case of manual steering, the steering assist force may be reduced, causing discomfort to the driver.

[0038] Therefore, the controller 19 detects whether the rack shaft is near its stroke end. For example, rack end contact can be detected as a condition indicating the rack shaft is near its stroke end. When the rack shaft is near its stroke end and the driving current of the steering actuator 21a is above a predetermined value Ipre, the upper limit of the driving current of the steering actuator 21a is set to a first upper limit IL1, which is lower than the predetermined value Ipre. For example, the first upper limit IL1 can be set to the minimum driving current value that maintains the steering wheel steering angle from decreasing from the maximum allowable steering angle.

[0039] On the other hand, when the rack shaft is not near the stroke end and the driving current of the steering actuator 21a is greater than or equal to the predetermined value Ipre, the upper limit of the driving current of the steering actuator 21a is set to a second upper limit IL2 that is lower than the first upper limit IL1. For example, the second upper limit can be set to zero. Alternatively, the second upper limit can be set to a value greater than zero and lower than the first upper limit IL1, which does not cause discomfort to the driver, or to a maximum driving current value that does not cause abnormal overheating.

[0040] Figure 2 This is a block diagram showing an example of a functional configuration for controlling the steering force generated by the steering actuator 21a by 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 driving unit 34.

[0041] The target steering angle setting unit 30 sets the target steering angle θt, which is the target value of the steering wheel or steering angle, during parking assist control or driving assist control. For example, during autonomous driving control, the target steering angle θt can be set based on the surrounding environment of the host vehicle 1 and the driving state of the host vehicle 1 to ensure that the host vehicle 1 follows a set target driving trajectory. Alternatively, during lane keeping assist control, the target steering angle θt can be set based on the lane dividing line (lane marking) detected ahead of the host vehicle 1 to ensure that the host vehicle 1 follows a target driving trajectory that passes through a predetermined lateral position. Furthermore, during parking assist control, the target steering angle θt can be set to ensure that the host vehicle 1 follows a target parking path from the current position of the host vehicle 1 to the target parking position.

[0042] The current command value setting unit 31 sets the current command value Ic, which is the target value of the drive current for the steering actuator 21a. For example, when executing parking assist control or driving assist control, the current command value Ic can be set based on the deviation between the actual steering angle θa of the steering wheel or 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 can be set based on the steering torque applied to the steering wheel detected by the torque sensor of the vehicle sensor 16.

[0043] The rack end contact detection unit 32 determines whether the rack shaft is in the vicinity of the stroke end. For example, the rack end contact detection unit 32 may determine whether the rack end contact occurs as the state in which the rack shaft is in the vicinity of the stroke end.

[0044] For example, the rack end contact detection unit 32 may detect the stroke of the rack shaft using a stroke sensor and detect that the rack shaft is near its stroke end when the stroke is greater than a first predetermined value and less than a second predetermined value. Alternatively, for example, the rack shaft may be detected as being near its stroke end when the drive current of the steering actuator 21a is greater than a third predetermined value and less than a fourth predetermined value. Alternatively, as illustrated in the second embodiment described below, whether the rack shaft is near its stroke end may be determined based on the steering angular velocity of the steering wheel and the drive current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16.

[0045] The current limiting unit 33 limits the upper limit of the current command value Ic when the drive current of the steering actuator 21 a detected by the current sensor of the vehicle sensor 16 is equal to or greater than a predetermined value Ipre.

[0046] 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 greater than or equal to the predetermined value Ipre, the upper limit of the current command value Ic is set to a first upper limit value IL1 that is lower 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 greater than or equal to the predetermined value Ipre, the upper limit of the current command value Ic is set to a second upper limit value IL2 that is lower than the first upper limit value IL1.

[0047] Furthermore, the current limiting unit 33 limits the upper limit of the current command value Ic when the temperature of the steering actuator 21 a or the controller 19 detected by the temperature sensor of the vehicle sensor 16 exceeds a predetermined temperature threshold.

[0048] The driving unit 34 drives the steering actuator 21a according to the current command value Ic whose upper limit is limited by the current limiting unit 33. For example, the driving voltage applied to the steering actuator 21a is controlled so as to reduce the difference between the current command value Ic whose upper limit is limited by the current limiting unit 33 and the driving current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16.

[0049] (action)

[0050] Figure 3 This is a flowchart of the steering control method according to the first embodiment. In step S1, the current limiting unit 33 determines whether the driving current of the steering actuator 21a is greater than or equal to the predetermined value Ipre. If the driving current is not greater than or equal to 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. It should be noted that the upper limit of the current command value Ic may also 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.

[0051] 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 the rack shaft is near the stroke end.

[0052] 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 .

[0053] In step S3 , the current limiting unit 33 limits the drive current of the steering actuator 21 a to a first upper limit value IL1 that is lower than the predetermined value Ipre.

[0054] In step S4 , the current limiting unit 33 limits the drive current of the steering actuator 21 a to a second upper limit value IL2 that is lower than the first upper limit value IL1 .

[0055] (Second embodiment)

[0056] The controller 19 of the second embodiment determines whether the rack shaft is near the stroke end based on the steering angular velocity of the steering wheel and the driving current of the steering actuator 21a detected by the current sensor of the vehicle sensor 16. For example, it determines whether the rack end touches.

[0057] Reference Figure 2When the steering angular velocity of the steering wheel or steering wheel is less than the angular velocity threshold and the driving current of the steering actuator 21a is within the threshold range R set to be less than the prescribed value Ipre, the rack end contact detection unit 32 determines that the rack shaft is in a state near the stroke end (for example, determines whether the rack shaft is in a state near the stroke end). When the steering angular velocity of the steering wheel or steering wheel is not less than the angular velocity threshold or the driving current of the steering actuator 21a is not within the threshold range R set to be less than the prescribed value Ipre, it is not determined that the rack shaft is in a state near the stroke end (for example, it is not determined whether the rack shaft is in a state near the stroke end).

[0058] For example, the rack end contact detection unit 32 may calculate the steering angular velocity by differentiating the steering angle detected by the steering angle sensor of the vehicle sensor 16 with respect to time.

[0059] Alternatively, for example, the threshold range R can be set based on the drive current Ix flowing through the steering actuator 21a when the steering wheel is steered to the maximum permissible steering angle without rack end contact. For example, a predetermined margin can be set as α, and the range between a lower limit (Ix - α) and an upper limit (Ix + α) can be set as the threshold range R. In the following description, the drive current Ix may be referred to as "rack end drive current Ix."

[0060] Reference Figure 4 (a)~ Figure 4 (c) The operation of the controller 19 according to the second embodiment will be described. Figure 4 (a) is a schematic diagram showing changes in the driving current of the steering actuator 21 a when the steering wheel cannot be steered to the target steering angle and a steering disabled state has not occurred.

[0061] If steering is started at time t1, the steering angle of the steering wheel increases as the target steering angle increases, and the drive current increases as the steering angle increases. Figure 4In example (a), because the steering wheel can be controlled to follow the target steering angle, a sudden increase in the drive current does not occur. Therefore, the drive current remains below the threshold range R, and the current limiter 33 does not limit the drive current. Subsequently, if the steering wheel is steered to the maximum allowable steering angle without rack-end contact, the drive current reaches the rack-end drive current Ix at time t2 and stops increasing. The steering wheel is then maintained at the maximum allowable steering angle until time t3. During this period, because the steering wheel can be controlled to follow the target steering angle without rack-end contact, the current limiter 33 does not limit the drive current. As a result, the drive current remains at the rack-end drive current Ix. If the steering angle is reduced from time t3, the drive current decreases, and when steering control ends at time t4, the drive current returns to zero.

[0062] Figure 4 (b) is a schematic diagram illustrating the change in drive current when rack end contact occurs. If steering begins at time t11, the steering wheel steering angle increases as the target steering angle increases, and the drive current increases as the steering angle increases. If the steering wheel steering angle is sufficiently close to the maximum allowable steering angle, the drive current value enters the threshold range R. If rack end contact occurs at time t12, steering of the steering wheel 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 contact detection unit 32 determines that rack end contact has occurred. In other words, it determines that the rack shaft is near the end of its stroke.

[0063] If rack end contact occurs, the steering wheel cannot be steered to the target steering angle, causing the drive current of the steering actuator 21a to surge to a predetermined value Ipre. Therefore, at time t13, the current limiter 33 sets the upper limit of the drive current to the first upper limit IL1. As a result, the drive current is limited to the first upper limit IL1. If the steering angle is reduced from time t14 onward, the drive current decreases. When steering control is terminated at time t15, the drive current returns to zero.

[0064] Figure 4 (c) is a schematic diagram showing the change in drive current when steering becomes impossible before the rack end contacts the target. If steering is started at time t21, the steering angle of the steering wheel increases as the target steering angle increases, and the drive current increases as the steering angle increases. Figure 4In (c), it is assumed that steering is stopped at time t22 due to, for example, contact between the steering wheel and an obstacle, before the steering wheel's steering angle approaches sufficiently near the maximum allowable steering angle. Therefore, the driving current of the steering actuator 21a surges to the specified value Ipre before the driving current value enters the threshold range R. Consequently, the rack end contact detection unit 32 does not detect the occurrence of rack end contact because it does not detect that the driving current is within the threshold range R. In other words, it does not determine that the rack shaft is near the stroke end.

[0065] Therefore, at time t23, the current limiting unit 33 sets the upper limit of the drive current to the second upper limit IL2. As a result, the drive current is limited to the second upper limit IL2. Thereafter, the drive current is maintained at zero until the steering control is terminated at time t24.

[0066] (Third embodiment)

[0067] The controller 19 of the third embodiment executes parking assist control to assist the vehicle with parking at a pre-registered target parking position. Alternatively or in addition thereto, the controller 19 may also execute parking assist control to assist the vehicle with 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 the vehicle with parking at the 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 the vehicle with parking at a target parking position that is not pre-registered may be referred to as a "second assist mode."

[0068] Figure 5 (a) and Figure 5 (b) is a schematic diagram illustrating the parking assist control of the first assist mode. When utilizing the parking assist control of the first assist mode, the target parking position 41 at which the vehicle 1 is to be parked is pre-registered in the driving assist device 10. Specifically, target objects existing around the target parking position 41 are extracted and pre-stored (registered) in the storage device 19b. In the following description, the target objects around the target parking position 41 stored in the storage device 19b are referred to as "learned target objects." Figure 5 In (a), a circle schematically represents a learning completion target object. When registering the target parking position 41 in the driving assistance device 10 , for example, the user performs an operation to instruct registration of the target parking position 41 (hereinafter sometimes referred to as “registration operation”).

[0069] For example, when the vehicle 1 is near the target parking location 41 (e.g., when the user manually parks the vehicle 1 at the target parking location 41), the controller 19 uses the external sensor 15 to detect objects around the vehicle 1 and stores them as learned objects. For example, objects can be detected from an image of the surrounding area of ​​the vehicle 1 captured by a camera. For example, edges or corners of objects such as road markings, road boundaries, and obstacles in the captured image captured by the camera, where the brightness of adjacent pixels changes by more than a specified amount, or points with characteristic shapes (feature points) can be detected as objects.

[0070] Controller 19 stores learned target data related to the learned target object in storage device 19b. For example, the learned target data may include data representing characteristic quantities of the learned target object (hereinafter referred to as "characteristic quantity data") and data regarding the relative positional relationship between target parking position 41 and the learned target object (hereinafter referred to as "relative position data").

[0071] For example, the relative position of the learned target object relative to target parking position 41 may be stored as relative position data. For example, controller 19 may obtain the position of the learned target object detected when vehicle 1 is parked at target parking position 41 as the relative position of the learned target object relative to target parking position 41. Alternatively, the coordinates of the learned target object and target parking position 41 in a coordinate system (hereinafter referred to as the "map coordinate system") based on a fixed location may be stored.

[0072] Figure 5 (b) is an illustrative diagram of an example of processing during parking assistance. For example, controller 19 may initiate parking assistance control for host vehicle 1 upon a user operation instructing the activation of parking assistance control for host vehicle 1. Alternatively, controller 19 may automatically initiate parking assistance control when host vehicle 1 approaches registered target parking position 41.

[0073] When the parking assist control is started, the controller 19 uses the external sensor 15 to extract objects around the host vehicle 1. In the following description, the objects around the host vehicle 1 extracted when the parking assist is performed are referred to as "surrounding objects". Figure 5 In (b), the triangles represent surrounding objects. Controller 19 detects target parking position 41 by matching the learned objects with the surrounding objects, associating common feature points. The relative position of vehicle 1 relative to target parking position 41 is calculated based on the relative positional relationship between the surrounding objects detected during parking assistance and the host vehicle 1, and the relative positional relationship between the learned objects associated with the surrounding objects and target parking position 41.

[0074] For example, controller 19 calculates the position of target parking position 41 in a coordinate system based on the current position of host vehicle 1 (hereinafter referred to as the "vehicle coordinate system"). Note that if the map coordinate system coordinates of learned objects and target parking position 41 are stored in storage device 19b, the coordinates of target parking position 41 in the map coordinate system can be converted to coordinates in the vehicle coordinate system based on the positions of surrounding objects detected during parking assistance and the positions of the learned objects in the map coordinate system. Alternatively, the position of host vehicle 1 in the map coordinate system can be determined based on the positions of surrounding objects detected during parking assistance and the positions of the learned objects in the map coordinate system. The relative position of host vehicle 1 with respect to target parking position 41 can be calculated based on the difference between the coordinates of host vehicle 1 in the map coordinate system and the coordinates of target parking position 41. Controller 19 calculates a target parking path 44 from current position 43 of host vehicle 1 to target parking position 41. Controller 19 implements parking assistance control for host vehicle 1 based on calculated target parking path 44.

[0075] Figure 6 This schematic diagram illustrates parking assist control in the second assist mode. When the user initiates a start operation to activate parking assist control, controller 19 initiates parking assistance for vehicle 1. When parking assist control in the second assist mode is initiated, controller 19 detects target parking positions 41a to 41d, based on the detection results of white lines 45 or objects around vehicle 1 by external sensors 15. Target parking positions 41a to 41d will sometimes be collectively referred to as "target parking positions 41."

[0076] For example, the controller 19 may detect a parking space around the host vehicle 1 as a target parking position 41 based on the detection result of the parking frame line 45 representing the parking space. Alternatively, for example, the controller 19 may detect a parked vehicle as an object around the host vehicle 1 and 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 implements parking assistance control for the host vehicle 1 based on the calculated target parking path 44.

[0077] Reference Figure 2The current limiting unit 33 of the third embodiment sets the first upper limit IL1 of the limiting current command value Ic to different values ​​depending on whether the controller 19 implements parking assist control or the driver manually steers the steering wheel. For example, the current limiting unit 33 can set the first upper limit IL1 to a larger value IL1a when the controller 19 implements parking assist control, and set the first upper limit IL1 to a smaller value IL1b (i.e., a value smaller than IL1a) when the driver manually steers the steering wheel. The reason for this is that when the driver manually steers the steering wheel, the steering force generated by the steering actuator 21a only needs to be small because the steering force generated by the driver is applied to the steering mechanism. As a result, the drive current of the steering actuator 21a when rack end contact occurs can be further reduced, thereby suppressing heat generation.

[0078] It should be noted that when the steering mechanism of the vehicle 1 is a steer-by-wire system or when the backup clutch is released, the steering force applied by the driver is not applied to the steering mechanism. Therefore, when the driver is manually steering using the electric power steering system or when the driver is manually steering with the backup clutch engaged, the first upper limit IL1 may be set to a smaller value IL1b. When the driver is manually steering using the steer-by-wire system or when the driver is manually steering with the backup clutch released, the first upper limit IL1 may be set to a larger value IL1a, similar to when parking assist control is being implemented.

[0079] Figure 7 This is a flowchart of the steering control method according to the third embodiment. In step S10, the current limiting unit 33 determines whether parking assist control is being implemented. If parking assist control is being implemented (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 IL1 to a larger value IL1a. The process then proceeds to step S13. In step S12, the current limiting unit 33 sets the first upper limit IL1 to a smaller value IL1b. The process then proceeds to step S13.

[0080] In step S13, the current command value setting unit 31 sets the target value of the driving current for the steering actuator 21a, namely the current command value Ic. In step S14, the current limiting unit 33 determines whether the driving current of the steering actuator 21a, as detected by the current sensor of the vehicle sensor 16, is greater than or equal to the specified value Ipre. If the driving current is not greater than or equal to the specified value Ipre (step S14: N), the process proceeds to step S15. If the driving current is greater than or equal to the specified value Ipre (step S14: Y), the process proceeds to step S16. In step S15, the driving unit 34 drives the steering actuator 21a based on the current command value Ic set by the current command value setting unit 31. It should be noted that the upper limit of the current command value Ic may also be limited if the temperature of the steering actuator 21a or the controller 19, as detected by the temperature sensor of the vehicle sensor 16, exceeds a specified temperature threshold.

[0081] In step S16, the rack end contact detection unit 32 determines whether the rack shaft is near the stroke end. 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 the first upper limit value IL1. The drive unit 34 drives the steering actuator 21a based on the current command value Ic limited to the first upper limit value IL1. In step S18, the current limiting unit 33 limits the current command value Ic to the second upper limit value IL2. The drive unit 34 drives the steering actuator 21a based on the current command value Ic limited to the second upper limit value IL2.

[0082] (Effects of Implementation Methods)

[0083] (1) The controller 19 controls the steering force generated by the actuator 21a for steering the steering wheel of the vehicle 1. The controller 19 detects whether the rack shaft of the steering mechanism for steering the steering wheel is near the end of its stroke. When the rack shaft is near the end of its stroke and the drive current of the actuator 21a is greater than or equal to a predetermined value Ipre, the controller 19 limits the drive current of the actuator 21a to a first upper limit value lower than the predetermined value Ipre. When the rack shaft is not near the end of its stroke and the drive current of the actuator 21a is greater than or equal to the predetermined value Ipre, the controller 19 limits the drive current of the actuator 21a to a second upper limit value lower than the first upper limit value. This maintains the steering angle at the maximum allowable steering angle even when rack end contact occurs, and prevents overheating of the actuator caused by a persistent state in which the steering wheel cannot be steered to the target steering angle even when the actuator is driven.

[0084] (2) For example, the second upper limit value may be 0. This can suppress overheating of the actuator 21 a when the steered wheel cannot be steered before being steered to the maximum permissible steering angle.

[0085] (3) The first upper limit may be a current value that can maintain the current steering angle. This maintains the steering angle at the maximum allowable steering angle when the rack end contacts the steering wheel, and prevents overheating of the actuator 21a.

[0086] (4) The controller 19 can determine that the rack shaft is near the stroke end when the steering angular velocity of the steering wheel or steering wheel is below 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 highly accurate determination of rack end contact even when there is an alignment error or neutral position error in the steering mechanism.

[0087] (5) The first upper limit value during manual steering may be set to a value smaller than the first upper limit value during automatic parking control for controlling the vehicle 1 to move to the target parking position. This allows the drive current of the actuator 21a to be lowered when rack end contact occurs during manual steering than when automatic parking control is executed, thereby suppressing overheating of the actuator 21a.

[0088] (6) The controller 19 may pre-detect targets existing around the target parking position, register data indicating the relative positional relationship between the detected targets and the target parking position in a storage device as learned target object data, and when the host vehicle 1 is driven to the target parking position after the learned target object data is registered in the storage device, detect the positions of targets existing around the host vehicle 1, i.e., surrounding targets, and calculate the relative positional relationship between the target parking position and the current position of the host vehicle 1 based on the learned target object data and the positions of the surrounding targets. Based on the calculated relative positional relationship, a target parking path is generated from the current position of the host vehicle 1 to the target parking position, and the host vehicle 1 is controlled to drive along the target parking path to the target parking position. Thus, the user can utilize parking assistance control that assists the host vehicle 1 in parking toward the pre-registered target parking position.

[0089] All examples and conditional terms described herein are intended for teaching purposes to help the reader understand the present invention and the concepts given by the inventors for the advancement of technology, and should be interpreted as not being limited to the specifically described examples and conditions, as well as the examples in this specification related to the illustration of the advantages and disadvantages of the present invention. The embodiments of the present invention are described in detail, but it should be understood that various changes, substitutions, and modifications can be made thereto without departing from the spirit and scope of the present invention.

[0090] Description of Reference Numerals

[0091] 1: This vehicle

[0092] 10: Driving assistance devices

[0093] 11: Positioning device

[0094] 12: Map Database

[0095] 15: External sensors

[0096] 16: Vehicle Sensor

[0097] 19: Controller

[0098] 19a: Processor

[0099] 19b: Storage device

[0100] 21a: Steering actuator

[0101] 21b: Acceleration actuator

[0102] 21c: Brake actuator

[0103] 30: Target steering angle setting unit

[0104] 31: Current command value setting unit

[0105] 32: Rack end contact detection unit

[0106] 33: Current limiting unit

[0107] 34: Drive unit

Claims

1. A steering control method for controlling a steering force generated in an actuator for steering a steering wheel of a vehicle, wherein: detecting that the rack shaft of the steering mechanism for steering the steering wheel 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 lower than the predetermined value. 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 lower than the first upper limit value.

2. The steering control method according to claim 1, characterized in that: The second upper limit value is zero.

3. The steering control method according to claim 1 or 2, characterized in that: The first upper limit is a current value capable of maintaining the current steering angle.

4. The steering control method according to any one of claims 1 to 3, characterized in that: When the steering angular velocity of the steering wheel or the steering wheel is equal to or less than an angular velocity threshold and the drive current of the actuator is within a threshold range set to be lower than the predetermined value, it is determined that the rack shaft is near a stroke end.

5. The steering control method according to any one of claims 1 to 4, characterized in that: The first upper limit value during manual steering is set to a value smaller than the first upper limit value during automatic parking control for controlling the vehicle so that the vehicle travels to a target parking position.

6. The steering control method according to claim 5, characterized in that: detecting an object existing around the target parking position in advance, and registering data indicating a relative positional relationship between the detected object and the target parking position as learned object data in a storage device; After the learned target object data is registered in the storage device, when the vehicle is driven to the target parking position, the positions of targets existing around the vehicle, namely, surrounding targets, are detected. Calculating the 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; The vehicle is controlled to travel along the target parking path to the target parking position.

7. A steering control device, characterized in that: have: an actuator that steers the vehicle's steering wheels; and A controller that detects when a rack shaft of a steering mechanism for steering the steering wheel is near a stroke end, and when the rack shaft is near the stroke end and the drive current of the actuator is greater than or equal to a specified value, limits the drive current of the actuator to a first upper limit value that is lower than the specified value; and when the rack shaft is not near the stroke end and the drive current of the actuator is greater than or equal to the specified value, limits the drive current of the actuator to a second upper limit value that is lower than the first upper limit value.

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