Steering assist device

Abstract

To enable enhancing steering feeling imparted during an override without impairing the steering assist feature.SOLUTION: A steering assist device is configured to execute: a control torque calculating process that calculates a steering control torque corresponding to a steering wheel angle determined in accordance with a traveling condition; a determining process that determines whether an override, which is a driver's steering action during steering assist, has occurred; a torque limit calculating process that, upon determining that the override has occurred, calculates a limit value for the steering control torque on the basis of the traveling condition; and a torque instruction process that, upon determining that the override has occurred, limits the control torque calculated in the control torque calculating process, with the limit value calculated in the torque limit calculating process, and gives the limited steering control torque as an instruction to a vehicle's steering mechanism.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a steering assist device that controls a vehicle so that it travels within a lane. [Background technology]

[0002] The following Patent Document 1 discloses a technology related to a steering assist device that applies a steering torque to a steering mechanism of a vehicle to assist steering. It describes that when it is determined that the driver has operated the steering wheel, the limit value of the rate of change of the steering torque for steering control is set smaller than when it is determined that the driver has not operated the steering wheel, thereby suppressing the output of the steering torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-89692 Summary of the Invention [Problem to be solved by the invention]

[0004] The steering operation performed by the driver when the vehicle is using steering assistance to keep the vehicle in the center of the lane, or so-called lane keep control operation, is called override. When override is in effect, the driver feels that the steering is heavier than normal steering. To improve the steering feel, it is possible to suppress the steering control torque of the lane keep control operation when override is in effect.

[0005] However, if the steering feel during override is made too light, an override may be determined that the driver did not intend, for example, when entering or during a curve, and lane centering may not be properly performed.For example, when the lane is curving left and steering assist is instructing steering torque to the left, if the driver is holding the steering wheel firmly, the torque sensor output may erroneously determine that the driver is steering to the right.

[0006] Therefore, the present invention proposes a technique for changing the steering feel during an override depending on the driving situation while steering assistance is being performed. [Means for solving the problem]

[0007] One embodiment of the present invention is a steering assist device that performs steering control to keep a vehicle traveling within a lane, and includes one or more processors and one or more storage media on which a program executed by the one or more processors is stored, the program including one or more instructions that cause the one or more processors to execute: a control torque calculation process that calculates a steering control torque according to a steering wheel angle determined according to a traveling situation; a determination process that determines an override, which is a steering operation by the driver during steering assist; a torque limit calculation process that calculates a limit value of the steering control torque based on the traveling situation if the determination process determines an override; and a torque instruction process that limits the control torque calculated by the control torque calculation process with the limit value calculated by the torque limit calculation process and instructs a steering mechanism if the determination process determines an override. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the lane centering function and the override steering feel depending on the driving conditions. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an explanatory diagram of a vehicle equipped with a steering assist device according to an embodiment; [Figure 2] 1 is an explanatory diagram of a configuration example of a steering assist device according to an embodiment; [Figure 3] FIG. 2 is an explanatory diagram of lane centering using steering assistance according to an embodiment. [Figure 4] 10A and 10B are explanatory diagrams of torque control according to a lateral position in the embodiment. [Figure 5] 10A and 10B are explanatory diagrams of torque limit settings according to the lateral position in the embodiment. [Figure 6] 10 is a flowchart of a processing example of a determination / calculation unit according to an embodiment. [Figure 7] 10 is a flowchart of a processing example of an EPS control unit according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Device configuration> Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an outline of the configuration of a vehicle 100 equipped with a steering assist device 1 according to an embodiment, and FIG. 2 is an explanatory diagram of an example of the configuration including the steering assist device 1 and related components.

[0011] Vehicle 100 is configured as, for example, a four-wheeled automobile and has at least one of an engine and a traction motor as a drive source for the wheels. In other words, vehicle 100 can be configured as an EV (Electric Vehicle) vehicle that has only the traction motor out of the engine and traction motor as a drive source for the wheels, an HEV (Hybrid Electric Vehicle) vehicle that has both an engine and a traction motor, or an engine vehicle that has only the engine.

[0012] As shown in FIG. 1, a steering assist device 1 provided in a vehicle 100 includes a driving assist control unit 13 and an EPS (Electric Power Steering) control unit 20. The driving assist control unit 13 performs assistance control relating to various functions other than steering assist, such as a collision avoidance function, a collision damage mitigation function, a navigation function, and a communication function, but in this example, a determination and calculation unit 14, which is a part of the function of the driving assist control unit 13, cooperates with the EPS control unit 20 to realize the functions of the steering assist device 1. The determination and calculation unit 14 is shown as a software function that performs determination processing and calculation processing related to EPS control.

[0013] Note that the steering assistance device 1 configured by the driving assistance control unit 13 (judgment / calculation unit 14) and the EPS control unit 20, each having a processor, working together is just one example, and a device unit with a single processor can also perform processing equivalent to the processing described below.

[0014] FIG. 2 shows the driving assistance control unit 13 and the EPS control unit 20 that function as the steering assistance device 1, and their peripheral configuration. The driving assistance control unit 13 is provided in the imaging unit 10, for example.

[0015] The imaging unit 10 includes imaging sections 11L and 11R, an image processing section 12, and a driving assistance control section 13, which are installed in the vehicle 100 so as to be able to capture images in the traveling direction (forward). A vehicle speed sensor 16, a motion sensor 17, and an actual steering angle sensor 18 are connected to the imaging unit 10, and the image processing unit 12 and the driving assistance control unit 13 provided within the imaging unit 10 can input detection signals from these sensors.

[0016] The vehicle speed sensor 16 is a sensor that detects the speed of the vehicle 100 . The motion sensor 17 comprehensively refers to sensors that detect the motion of the vehicle 100, such as a yaw rate (angular velocity) sensor, an acceleration sensor, a sensor capable of measuring turning angular velocity and acceleration, and the like.

[0017] The actual steering angle sensor 18 detects the actual turning angle of the steered wheels (for example, the angle between the steered wheels and the longitudinal axis of the vehicle 100) as the actual steering angle. The steering torque sensor 19 detects, for example, the input torque to the steering shaft, thereby detecting the steering force (steering input torque) input by the driver via the steering wheel.

[0018] The imaging sections 11L and 11R of the imaging unit 10 are arranged at a predetermined distance in the vehicle width direction, for example, near the top of the windshield of the vehicle 100, so as to enable distance measurement by the so-called stereo method. The optical axes of the imaging sections 11L and 11R are parallel, and the focal lengths are the same. In addition, the frame periods are synchronized, and the frame rates are also the same.

[0019] The electrical signals (captured image signals) obtained by the imaging elements of the imaging units 11L and 11R are converted from analog to digital (A / D) to digital image signals (captured image data) that represent luminance values ​​at a predetermined gradation on a pixel-by-pixel basis. The captured image data may be, for example, color image data.

[0020] The image processing unit 12 is configured with a microcomputer equipped with, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory) as a work area, and the CPU executes various processes in accordance with programs stored in the ROM.

[0021] The image processing unit 12 stores in an internal memory each frame of image data as captured image data obtained by the imaging units 11L and 11R when capturing an image of the area ahead of the vehicle 100. Then, based on the two frames of captured image data, the image processing unit 12 executes various processes for recognizing the environment outside the vehicle, specifically, for recognizing objects present ahead of the vehicle 100. For example, the image processing unit 12 recognizes restriction lines (e.g., white lines, orange lines, etc.) formed on the road, leading vehicles, pedestrians, obstacles, and various three-dimensional objects such as guardrails, curbs, and side walls present along the road. Here, the restriction lines refer to lines that separate the lane that a vehicle is traveling in. The image processing unit 12 recognizes the lane that the vehicle 100 is traveling in (the lane that the vehicle is traveling in) based on the information of the recognized restriction lines.

[0022] The image recognition result information obtained by the image processing unit 12, such as the position, speed, and acceleration information of the three-dimensional object and the lane information of the vehicle, is used for various driving assistance controls. In order to recognize the surroundings of the vehicle, a distance measurement sensor capable of grasping the situation around the vehicle, such as a RADAR or LIDAR, may be provided in addition to or instead of the imaging units 11L and 11R.

[0023] The driving assistance control unit 13 performs control for various driving assistance based on the image recognition result information by the image processing unit 12. 1, in this embodiment, as a configuration related to EPS control, particularly lane keeping control, the driving assistance control unit 13 is provided with a determination and calculation unit 14 that has the function of making determinations and calculations related to lane keeping control. The determination and calculation unit 14 performs processes such as determining whether to override when the EPS control unit 20 performs lane keeping control, and setting the torque limit value for steering control according to the driving situation.

[0024] The EPS control unit 20 is configured with, for example, a microcomputer, and controls the EPS motor in the steering mechanism 30 based on a steering command value (steering wheel angle HA) from the driving assistance control unit 13 (determination and calculation unit 14) and a torque sensor value Ts that is a detected value by the steering torque sensor 19. Specifically, the EPS control unit 20 calculates a steering control torque corresponding to the steering wheel angle HA for the steering mechanism 30 to keep the vehicle centered in the lane, and outputs the calculated torque to the steering mechanism 30 as a command torque Td. In the steering mechanism 30, the EPS motor is driven based on a current value corresponding to the command torque Td, and steering is performed.

[0025] As a normal power steering operation, the EPS control unit 20 calculates a steering command current value so as to obtain a steering assist torque corresponding to the torque sensor value Ts, which is the steering input torque by the driver obtained from the detection signal of the steering torque sensor 19. Then, the EPS motor of the steering mechanism 30 is driven based on the command current value. This realizes power steering control that assists the steering by the driver.

[0026] The driver is allowed to steer even during lane keeping control, but when steering is performed as an override during lane keeping control, the EPS control unit 20 adds up the steering command current value based on the command torque Td corresponding to the steering wheel angle HA from the judgment / calculation unit 14 and the steering command current value for power steering control calculated as described above, and drives the EPS motor based on the added current value.

[0027] The torque sensor value Ts is also supplied to the determination and calculation unit 14 for determining whether or not an override has occurred. Furthermore, for control during an override, the determination / calculation unit 14 transmits an override control flag FG and a limit value LM of the control torque to the EPS control unit 20.

[0028] <Steering torque control> The steering torque control during lane keeping control in this embodiment will be described. 3 shows a schematic diagram of lane keeping control, which is performed when there is no override, and automatic steering control is performed by generating a command torque Td corresponding to the steering wheel angle HA determined based on the recognition of the white lines 101 by the imaging unit 10 so that the vehicle 100 stays centered in the lane.

[0029] When an override is detected, the limit value LM for the command torque Td for lane keeping control is changed according to the driving situation. 4 shows a schematic diagram illustrating that the limit value LM of the command torque Td is varied depending on the lateral position of the vehicle 100, which is one of the driving conditions. The lateral position refers to the lateral position of the vehicle 100 within the lane. Vehicles 100A, 100B, and 100C are shown in different lateral positions.

[0030] The vehicle 100A is shown in a case where its lateral position is approximately in the center of the lane. In this case, the limit value LM for the command torque Td is set low, so that the command torque Td by the lane keeping control is kept low. Therefore, the driver feels that steering to the left or right is relatively light. For example, the torque is set weak enough that the driver can feel the lane keeping control operating.

[0031] Vehicle 100C shows a case where the lateral position is almost at the edge of the lane. In this case, the limit value LM for the command torque Td is set high. Therefore, the command torque Td becomes strong according to the steering wheel angle HA. It can be said that the steering torque to the right toward the center of the lane becomes large. For the driver, when steering left intentionally, the steering feels heavy, but even if an override determination is made that is not intended by the driver, the vehicle will be steered toward the center of the lane.

[0032] Vehicle 100B shows a case where the lateral position is intermediate between vehicle 100A and vehicle 100B. In this case, limit value LM for command torque Td is set to a medium level. Therefore, command torque Td becomes a medium torque according to steering wheel angle HA.

[0033] Fig. 5 shows an example of the travelling situation (lateral position) of the vehicle 100 and the change in the limit value LM and the command torque Td. The upper part of Fig. 5 shows the state where the lateral position of the vehicle 100 is different, and the lower part shows the change in the command torque Td and the limit value LM, with the torque value on the vertical axis. The horizontal axis is the time axis.

[0034] Assume that up until time t1, the vehicle 100 is at the edge of the lane and very close to the white line 101. In this case, the limit value LM is set to a high value of LM1. As a result, the command torque Td corresponding to the steering wheel angle HA is output with the limit value LM1 as the upper limit. If necessary, a strong command torque Td is output to the steering mechanism 30 to return the vehicle to the center of the lane.

[0035] The limit value LM is changed as the vehicle 100 approaches the center of the lane. For example, between times t2 and t3, the lateral position is approximately in the center, so the limit value LM = LM3, and the upper limit of the command torque Td is kept to the lowest. Between time points t3 and t4, the lateral position is closer to the edge than the center, so the limit value LM is set to LM2, and the upper limit of the command torque Td is set to a medium level.

[0036] In this way, by changing the limit value LM according to the driving conditions when an override determination is made during lane keeping control, the driver feels a lighter steering feel when there is no risk of lane departure. On the other hand, when the possibility of lane departure increases due to a torque decrease, the command torque Td is no longer limited to a small value.

[0037] Examples of processing performed by the determination and calculation unit 14 of the driving assistance control unit 13 and the EPS control unit 20 for such control are shown in Figures 6 and 7. The determination and calculation unit 14 and the EPS control unit 20 repeatedly perform the processing shown in Figures 6 and 7, respectively, during lane keeping control.

[0038] 6, the determination / calculation unit 14 acquires information relating to the traveling and state of the vehicle 100. Specifically, this information includes image recognition result information such as information on the lane the vehicle is traveling in by the image processing unit 12, and detection information from the vehicle speed sensor 16, the motion sensor 17, and the actual steering angle sensor 18.

[0039] In step S102, the determination and calculation unit 14 determines the driving situation based on the information acquired in step S101, and calculates the steering wheel angle HA for keeping the vehicle centered in the lane accordingly. The determination and calculation unit 14 then notifies the EPS control unit 20 of the calculated steering wheel angle HA.

[0040] In step S103, the judgment / calculation unit 14 calculates a limit value LM of the steering control torque (command torque Td) for lane keeping based on the driving conditions determined from the information acquired in step S101, such as the lateral position, curvature, yaw angle, and transverse gradient. For example, the determination / calculation unit 14 sets the limit values ​​LM1, LM2, LM3, etc. in Fig. 5 by referring to the lateral position obtained from image recognition result information such as information on the lane the vehicle is traveling in by the image processing unit 12. Note that if one of the white lines 101 can no longer be recognized from the image, the white line information before it could no longer be recognized can be retained, and the lateral position can be determined from the result, and the limit value LM can be calculated, etc.

[0041] In step S104, the determination / calculation unit 14 determines whether or not an override has occurred based on the torque sensor value Ts. If the determination / calculation unit 14 determines that an override exists, the process proceeds to step S105, where it transmits to the EPS control unit 20 the override control flag FG, whose value has been set to "1," and the limit value LM calculated in step S103.

[0042] If it is determined that there is no override, the determination and calculation unit 14 proceeds to step S106 and transmits the override control flag FG, the value of which has been set to "0", to the EPS control unit 20.

[0043] Meanwhile, in step S201 of FIG. 7, the EPS control unit 20 calculates a steering control torque that follows the steering wheel angle HA notified in the process of step S102 of the determination / calculation unit 14. Then, in step S202, the EPS control unit 20 branches the processing depending on the override control flag FG transmitted from the determination / calculation unit 14 in step S105 or step S106.

[0044] If the override control flag FG is "1", the EPS control unit 20 proceeds to step S203, where it limits the steering control torque calculated in step S201 with the limit value LM and outputs the limit value as the command torque Td to the steering mechanism 30. As a result, the command torque Td is limited in accordance with the driving conditions, as described in FIG.

[0045] If the override control flag FG is "0", the EPS control unit 20 proceeds to step S204, and outputs the steering control torque calculated in step S201 to the steering mechanism 30 as the command torque Td.

[0046] When there is no override as in step S204, the calculated steering control torque is output as the command torque Td as is, and the command torque Td is not limited according to the driving conditions as described in FIG. 5. However, a limit is provided to prevent a situation in which an extremely high command torque Td is output due to a calculation error or the like, making it impossible for the driver to steer.

[0047] In the above process, the determination / calculation unit 14 determines the limit value LM according to the driving situation in step S103, but the driving situation may include various information other than the lateral position described above. Examples of setting the limit value LM according to the information on the driving situation will be described below.

[0048] As for the lateral position, as described above, the limit value LM is set to the lowest when the vehicle is in the center of the lane, and the limit value LM is set to a higher value as the vehicle approaches the edge of the lane. The driving conditions related to the setting of the limit value LM include the curvature of the lane, the cross gradient, the yaw angle relative to the lane, and the acceleration of the yaw angle relative to the lane, in addition to the lateral position.

[0049] The lane curvature is the curve of the lane, and the greater the curvature, the more disadvantageous the lane keeping control becomes. Therefore, the limit value LM is set to the lowest when the lane is straight, and the greater the curvature, the higher the limit value LM is set.

[0050] The cross slope is the gradient of the road in the lateral direction. When the gradient decreases toward the center of the lane, the limit value LM is lowered, and when the gradient increases toward the center of the lane, the limit value LM is raised.

[0051] The lane yaw angle is the angle of the longitudinal axis of the vehicle relative to the white line 101, and it is desirable for the vehicle to be parallel to the white line 101. Therefore, when the vehicle is parallel to the white line 101, the limit value LM is set to the lowest, and as the parallelism breaks down and the angle between the white line 101 and the longitudinal axis of the vehicle increases, the limit value LM is increased.

[0052] The lane yaw angle acceleration is the acceleration of the change in the angle of the longitudinal axis of the vehicle relative to the white line 101, and the smaller the acceleration, the lower the limit value LM is set, and the greater the acceleration, the higher the limit value LM is set.

[0053] Of these elements of the driving conditions, at least one, such as the lateral position, may be used to set the limit value LM, but it is preferable to calculate the limit value LM using a calculation algorithm that combines a plurality of elements. Furthermore, factors of the driving conditions that can be used to set the limit value LM include various factors that affect steering, such as the vehicle speed, the gradient of the road in the longitudinal direction, and the road surface conditions.

[0054] <Effects of the embodiment> According to the above embodiment, the following effects can be obtained.

[0055] In the steering assist device 1 of the embodiment, one or more processors execute a control torque calculation process (S201) that calculates a steering control torque according to a steering wheel angle HA determined according to the driving conditions, a determination process (S104) that determines an override, a torque limit calculation process (S103) that calculates a limit value LM of the steering control torque based on the driving conditions, and a torque instruction process (S203) that, if an override is determined, limits the calculated control torque with the limit value LM and instructs the steering mechanism 30.

[0056] As a result, during hands-on lane keeping control, the limit value LM when an override is determined is variably set according to the driving conditions, and the strength of the command torque Td is controlled according to the driving conditions. Therefore, it is possible to output a command torque Td with an appropriate control force (which makes it difficult to deviate and makes steering easier) according to the driving conditions. For example, when there are no safety issues, the limit value LM is lowered to weaken the command torque Td, giving the driver a lighter steering feel. On the other hand, when the driving conditions are unfavorable for lane keeping, the limit value LM is raised, making it possible to output a relatively strong command torque Td, thereby strengthening the lane centering function. In other words, it is possible to achieve an enhanced lane centering function and an improved override steering feel according to the driving conditions.

[0057] In the embodiment, an example was given in which the limit value LM was calculated based on the lateral position of the host vehicle within the lane. The lateral position of the host vehicle, i.e., the driving conditions, such as whether the lateral position within the lane is centered or toward the edge, is information that can directly determine whether the conditions are favorable or unfavorable for the lane centering function through steering assistance. Therefore, the closer the lateral position is to the center, the lower the limit value should be to suppress the command torque Td. However, the closer to the edge, the more unfavorable the driving conditions are for maintaining the lane centering, so the limit value LM should be increased and the command torque Td should not be suppressed. This makes it possible to achieve control of the command torque Td that maintains safety and improves the steering feel of the driver's vehicle. For example, it is possible to avoid interfering with the driver's steering near the center of the lane and to return the vehicle 100 to the center of the lane before it deviates from the lane.

[0058] In the embodiment, an example has been given in which the limit value LM is calculated with reference to at least one of the lane curvature, the cross slope, the lane-to-lane yaw angle, and the lane-to-lane yaw angle acceleration. The lane curvature, cross slope, lane-to-lane yaw angle, and lane-to-lane yaw angle acceleration are also information that can be used to determine whether a situation is favorable or unfavorable for the lane centering function using steering assistance. If one or more of these factors determine that the driving conditions make it easy to maintain the lane center, the limit value LM can be lowered and the command torque Td can be suppressed. Conversely, if the driving conditions determine that it is difficult to maintain the lane center, the limit value LM can be increased and the command torque Td can be suppressed. For example, by referring to the lane curvature, when overriding on a curve, increasing the limit value LM compared to when driving on a straight line can be effective in preventing unintended deviation to the outside of the curve.

[0059] In the embodiment, a processing example has been described in which the driving situation is determined from the image captured by the imaging unit 10 and the limit value LM is calculated with reference to the determination result. For example, the lateral position of the vehicle is determined based on the image captured by the imaging unit 10. The lateral position can be accurately determined by using the captured image.

[0060] In the embodiment, as shown in FIGS. 6 and 7, an example has been described in which the determination / calculation unit 14 and the EPS control unit 20 perform processing in cooperation with each other, but it is also possible to have one processor perform the processing of FIGS. 6 and 7 together.

[0061] For example, one processor performs the following processing: Step S101: The driving / vehicle status is acquired. Steps S102 and S201: The steering wheel angle HA is calculated, and the steering control torque according to the steering wheel angle HA is calculated. Step S103: The limit value LM of the steering control torque is calculated. Step S104: Determine whether to override. Step S203: If an override has occurred, the calculated steering control torque is limited by the limit value LM and the command torque Td is output. Step S204: If there is no override, the calculated steering control torque is output as is as the command torque Td.

[0062] 6 and 7 are merely examples, and various modifications of the processing procedures and contents are conceivable. For example, in Fig. 6, the limit value LM is calculated in step S103, and then an override determination is made in step S104, but the limit value LM may be calculated only if an override determination is made. [Explanation of symbols]

[0063] 1 Steering assist device 10. Imaging unit 11L, 11R imaging unit 12 Image processing section 13 Driving assistance control unit 14 Judgment / Calculation Department 16 Vehicle speed sensor 17 Motion Sensor 18 Actual steering angle sensor 19 Steering torque sensor 30 Steering mechanism 100 vehicles 101 White Line Ts Torque sensor value Td Indicated torque HA Steering wheel angle FG override control flag LM Limit Value

Claims

1. A steering assist device that performs steering control to keep a vehicle traveling within a lane, one or more processors; one or more storage media storing a program to be executed by the one or more processors; the program includes one or more instructions; The instructions may be to the one or more processors: a control torque calculation process for calculating a steering control torque according to a steering wheel angle determined according to a driving situation; a determination process for determining an override, which is a steering operation by the driver during steering assistance; a torque limit calculation process for calculating a limit value of the steering control torque based on a driving situation; and when it is determined in the determination process that an override has been performed, a torque instruction process is executed in which the control torque calculated in the control torque calculation process is limited by the limit value calculated in the torque limit calculation process and the limited control torque is instructed to a steering mechanism. Steering assist device.

2. The instructions may be to the one or more processors: In the torque limit calculation process, a limit value is calculated based on the lateral position of the vehicle within the lane as the driving condition. The steering assist device according to claim 1 .

3. The instructions may be to the one or more processors: In the torque limit calculation process, a process is executed in which a limit value is calculated using at least one of a lane curvature, a cross gradient, a lane-to-lane yaw angle, and an acceleration of the lane-to-lane yaw angle as a driving condition. The steering assist device according to claim 1 or 2.

4. The instructions may be to the one or more processors: In the torque limit calculation process, a process is executed in which a driving situation is determined from a captured image and a limit value is calculated by referring to the determination result. The steering assist device according to claim 1 or 2.

Images