Vehicle travel assistance method and vehicle travel assistance device

Abstract

Provided is a vehicle travel assistance method in which if there is an obstacle in front of a vehicle, a braking force is generated to avoid a collision between the vehicle and the obstacle. In the method: it is determined whether the vehicle is in a manual driving state or an automatic driving state (S2); the manner of changing the braking force is changed according to whether the vehicle is in the manual driving state or in the automatic driving state (S5); and a braking device is controlled so that the braking force changes more rapidly if the vehicle is in the automatic driving state as compared to when the vehicle is in the manual driving state (S6).

Description

Vehicle driving support method and vehicle driving support device

[0001] The present invention relates to a vehicle driving support method and a vehicle driving support device.

[0002] The following Patent Document 1 describes a vehicle control system that generates a first target trajectory for autonomous driving and a second target trajectory for driving assistance control that controls at least one of steering, acceleration, and deceleration for the purpose of improving the safety of vehicle driving, and then arbitrates between these target trajectories to determine a final target trajectory.

[0003] Japanese Patent Application Laid-Open No. 2021-62777

[0004] When driving assistance control is activated to avoid a collision with an obstacle ahead by controlling the braking of the vehicle, the deceleration caused by the activation of the driving assistance control may cause discomfort to the occupants. The present invention aims to reduce the discomfort caused to the occupants by the deceleration caused by the activation of driving assistance control to avoid a collision with an obstacle ahead by controlling the braking of the vehicle.

[0005] According to one aspect of the present invention, there is provided a vehicle travel assistance method for generating a braking force to avoid a collision between the vehicle and an obstacle when the obstacle is present in front of the vehicle. The vehicle travel assistance method determines whether the vehicle is in a manual driving state or an automatic driving state, changes a manner in which the braking force is changed depending on whether the vehicle is in the manual driving state or the automatic driving state, and controls a braking device so that the braking force changes more rapidly when the vehicle is in the automatic driving state compared to when the vehicle is in the manual driving state.

[0006] According to the present invention, it is possible to reduce the discomfort felt by occupants due to deceleration caused by operation of driving assistance control that controls the braking of the vehicle to avoid a collision with an obstacle ahead. The objects and advantages of the present invention are realized and achieved by using the elements and combinations thereof set forth in the claims. It should be understood that both the foregoing general description and the following detailed description are merely exemplary and explanatory and are not intended to limit the invention as defined by the claims.

[0007] 1 is a schematic configuration diagram of an example of a vehicle driving assistance device according to an embodiment; FIG. 2 is a block diagram of an example of the functional configuration of a controller; FIG. 3 is a diagram showing a comparative example, a first example, and a second example of the characteristics of a target deceleration set according to the degree of proximity to an obstacle; and FIG. 4 is a flowchart of an example of a vehicle driving assistance method according to an embodiment.

[0008] (Configuration) FIG. 1 is a schematic diagram of an example of a vehicle driving assistance device according to an embodiment. The host vehicle 1 includes a vehicle driving assistance device 10. The vehicle driving assistance device 10 executes driving assistance control to assist the host vehicle 1 in driving according to the driving environment around the host vehicle 1. The driving assistance control by the vehicle driving assistance device 10 may include automatic control that generates a braking force to avoid a collision between the host vehicle 1 and an obstacle when an obstacle is present ahead of the host vehicle 1. The driving assistance control may be, for example, automatic emergency braking (AEB). The vehicle driving assistance device 10 also has an automatic driving function that automatically controls at least one of the steering, acceleration, and deceleration of the host vehicle 1 to drive the host vehicle 1. In the following description, a state in which the host vehicle is driving while the automatic driving function of the vehicle driving assistance device 10 controls at least one of the steering, acceleration, and deceleration of the host vehicle 1 is sometimes referred to as an "automatic driving state." In addition, a state in which the occupant is manually driving the vehicle 1 without relying on the automatic driving function of the vehicle driving assistance device 10 may be referred to as a "manual driving state."

[0009] The autonomous driving level, which is the degree of automation of the driving of the host vehicle 1 by the autonomous driving function, may be, for example, any of the following autonomous driving levels: first, second, third, fourth, and fifth. The autonomous driving level of the vehicle driving assistance device 10 may be switchable to any of a plurality of levels among the first to fifth autonomous driving levels (i.e., the autonomous driving level may be changeable). The first autonomous driving level automatically controls the acceleration and deceleration of the host vehicle 1 when an occupant is seated in the driver's seat and can operate the accelerator and brake at any time (i.e., override driving using the accelerator or brake is performed). The second autonomous driving level automatically controls the steering of the host vehicle 1 when an occupant is seated in the driver's seat and can operate the steering wheel at any time (i.e., override driving using the steering wheel is performed).

[0010] The third autonomous driving level allows the vehicle 1 to automatically drive when an occupant is sitting in the driver's seat, looking ahead, and not gripping the steering wheel. The fourth autonomous driving level allows the vehicle 1 to automatically drive when an occupant is sitting in the driver's seat, not looking ahead, and not gripping the steering wheel. The fifth autonomous driving level allows the vehicle 1 to automatically drive when an occupant is sitting in the driver's seat, not looking ahead, and not gripping the steering wheel.

[0011] The first autonomous driving level requires greater involvement from the occupant in driving the vehicle 1 than the second autonomous driving level, which requires greater involvement than the third autonomous driving level, which requires greater involvement than the fourth autonomous driving level, which requires greater involvement than the fifth autonomous driving level. In other words, the less involvement the occupant requires in driving the vehicle 1 (the higher the degree of automation of the driving of the vehicle 1), the higher the autonomous driving level. Furthermore, for example, levels 1 to 5 defined by the Society of Automotive Engineers (SAE) may be used as the autonomous driving levels of the vehicle driving assistance device 10. In the following description, the above-mentioned first to fifth autonomous driving levels are used as examples of the autonomous driving levels of the vehicle driving assistance device 10.

[0012] The vehicle driving assistance device 10 includes an object sensor 11, a vehicle sensor 12, a positioning device 13, a map database (map DB) 14, a navigation device 15, an actuator 16, and a controller 17. The object sensor 11 detects objects within a predetermined distance range from the host vehicle 1. The object sensor 11 detects the surrounding environment of the host vehicle 1, such as the relative position between the host vehicle 1 and an object present around the host vehicle 1, the distance between the host vehicle 1 and the object, and the direction in which the object is present. The object sensor 11 may include, for example, a camera that captures the surrounding environment of the host vehicle 1. The object sensor 11 may also include a ranging device such as a laser range finder, radar, LiDAR (Light Detection and Ranging), or sonar. The object sensor 11 outputs surrounding environment information, which is information on the detected surrounding environment of the host vehicle 1, to the controller 17.

[0013] The vehicle sensors 12 are mounted on the host vehicle 1, detect various pieces of information obtained from the host vehicle 1 (hereinafter sometimes referred to as "host vehicle information"), and output the information to the controller 17. The vehicle sensors 12 include, for example, a vehicle speed sensor that detects the vehicle speed of the host vehicle 1, a wheel speed sensor that detects the rotational speed of the tires of the host vehicle 1, a three-axis acceleration sensor that detects the acceleration and deceleration in three axial directions of the host vehicle 1, a steering angle sensor that detects the steering angle of the steering wheel, a turning angle sensor that detects the turning angle of the steered wheels, a gyro sensor that detects the angular velocity of the host vehicle 1, a yaw rate sensor that detects the yaw rate, an accelerator sensor that detects the accelerator opening of the host vehicle, and a brake sensor that detects the amount of brake operation by the driver.

[0014] The positioning device 13 includes a Global Navigation System (GNSS) receiver and receives radio waves from multiple navigation satellites to measure the current position of the vehicle 1. The GNSS receiver may be, for example, a Global Positioning System (GPS) receiver. The positioning device 13 may be, for example, an inertial navigation system. The map database 14 stores road map data. The map database 14 may store map data for navigation (hereinafter, sometimes referred to as "navigation map data") as the road map data. The navigation map data includes information on a road-by-road basis.

[0015] The map database 14 may store high-precision map data as road map data. The high-precision map data is map data suitable as map information for automated driving, and includes lane-level information that is more detailed than road-level information. The navigation device 15 recognizes the current position of the vehicle using the positioning device 13 and obtains navigation map data for the current position from the map database 14. The navigation device 15 sets a target driving route to a destination input by the occupant and provides route guidance to the occupant along the target driving route. The navigation device 15 also outputs information about the set target driving route to the controller 17. When the controller 17 causes the vehicle 1 to autonomously drive to a destination using the automated driving function, the controller 17 automatically drives the vehicle 1 so that the vehicle 1 travels along the target driving route set by the navigation device 15.

[0016] The actuator 16 operates the steering device, accelerator opening, and braking device of the host vehicle 1 in response to control signals from the controller 17 to generate vehicle behavior of the host vehicle 1. The actuator 16 includes a steering actuator, an accelerator opening actuator, and a brake control actuator. The steering actuator controls the steering direction and steering amount of the steering device of the host vehicle 1. The accelerator opening actuator controls the accelerator opening of the host vehicle 1. The brake control actuator controls the braking operation of the braking device of the host vehicle.

[0017] The controller 17 is an electronic control unit that performs driving assistance control of the host vehicle 1. The controller 17 includes a processor 17a and peripheral components such as a storage device 17b. The processor 17a may be, for example, a CPU or an MPU. The storage device 17b may include a semiconductor storage device, a magnetic storage device, an optical storage device, or the like. The storage device 17b may include memories such as ROM and RAM used as main storage devices, as well as registers and cache memories. The functions of the controller 17 described below are realized, for example, by the processor 17a executing computer programs stored in the storage device 17b. The controller 17 may be formed by dedicated hardware for executing the information processing described below. For example, the controller 17 may include functional logic circuits set in a general-purpose semiconductor integrated circuit. For example, the controller 17 may include a PLD such as an FPGA.

[0018] 2 is a block diagram showing an example of the functional configuration of the controller 17. The controller 17 includes an obstacle information acquisition unit 20, an automatic driving control unit 21, a steering control unit 22, a drive control unit 23, and a braking control unit 24.

[0019] The obstacle information acquisition unit 20 acquires obstacle information regarding an obstacle present ahead of the host vehicle 1 based on the surrounding environment information output from the object sensor 11. For example, the obstacle information may include position information of the obstacle (e.g., the distance and direction to the obstacle relative to the host vehicle 1). The autonomous driving control unit 21 performs autonomous driving control to drive the host vehicle 1 by automatically controlling at least one of the steering, acceleration, and deceleration of the host vehicle 1. The autonomous driving level of the autonomous driving control by the autonomous driving control unit 21 may be any one of the above-mentioned first to fifth autonomous driving levels. Furthermore, the autonomous driving level of the autonomous driving control unit 21 may be switchable and set to any one of these multiple autonomous driving levels (i.e., the autonomous driving level may be changeable). Furthermore, when an obstacle is present ahead of the host vehicle 1, the autonomous driving control unit 21 performs driving assistance control to generate braking force to avoid a collision between the host vehicle 1 and the obstacle.

[0020] The autonomous driving control unit 21 includes a driving control unit 30, a driving assistance unit 31, and an arbitration unit 32. When an autonomous driving activation switch that switches between an autonomous driving state and a manual driving state is on and autonomous driving control is being executed, the driving control unit 30 controls at least one of steering, acceleration, and deceleration of the host vehicle 1. For example, when the autonomous driving activation switch is on and the autonomous driving level is a first autonomous driving level, the driving control unit 30 sets a target vehicle speed of the host vehicle 1 so that the vehicle speed of the host vehicle 1 becomes the speed limit or a predetermined speed. Alternatively, the driving control unit 30 sets the target vehicle speed so that the inter-vehicle distance between the host vehicle 1 and a preceding vehicle is maintained at a constant distance. Furthermore, for example, when the autonomous driving activation switch is on and the autonomous driving level is a second autonomous driving level, the driving control unit 30 controls the steering of the host vehicle 1 so that the lateral position of the host vehicle 1 is maintained within the lane.

[0021] Furthermore, for example, when the autonomous driving start switch is on and the autonomous driving level is one of the third to fifth autonomous driving levels, the driving control unit 30 calculates a target driving trajectory for the host vehicle 1 based on the current position of the host vehicle 1, the target driving route set by the navigation device 15, road map data in the map database 14, surrounding environment information output from the object sensor 11, and host vehicle information output from the vehicle sensor 12. For example, the driving control unit 30 generates a route space map representing the route around the host vehicle 1 and the presence or absence of objects, and a risk map that quantifies the risk of the driving environment, and generates a target driving trajectory and a target vehicle speed profile for the host vehicle 1 based on the motion characteristics of the host vehicle 1, the vehicle state information, the route space map, and the risk map. The steering control unit 22 controls the steering actuator of the actuator 16 so that the host vehicle 1 drives along the target driving trajectory generated by the driving control unit 30.

[0022] Furthermore, when the degree of proximity between the host vehicle 1 and an obstacle present ahead of the host vehicle 1 is higher than a threshold, the controller 17 executes forward collision warning (FCW) control to warn the occupants of a risk of collision with the obstacle ahead. For example, the time-to-collision (TTC) may be used as the degree of proximity between the host vehicle 1 and the obstacle. The shorter the TTC, the higher the degree of proximity, and the longer the TTC, the lower the degree of proximity. In the following description, the TTC is used as an example of the degree of proximity between the host vehicle 1 and the obstacle, but other indicators may also be used as the degree of proximity. In the FCW control, when the autonomous driving activation switch is on and the TTC becomes equal to or lower than a threshold, the cruise control unit 30 generates a target vehicle speed profile to decelerate the host vehicle 1 at a deceleration up to a relatively weak third deceleration D3 (e.g., 0.3 G). In addition, the driving control unit 30 may generate a target vehicle speed profile so that the vehicle decelerates at a deceleration rate up to the third deceleration rate D3 when the TTC falls below the threshold value, not only when the automatic driving switch is on but also when the vehicle 1 is being driven manually.

[0023] When an obstacle is present ahead of the host vehicle 1, the driving support unit 31 executes driving support control to generate a braking force to avoid a collision between the host vehicle 1 and the obstacle. The deceleration generated in the driving support control may be a second deceleration D2 (e.g., 0.5 G) or a first deceleration D1 (e.g., 1.0 G) greater than the third deceleration D3. For example, the driving support unit 31 sets a target deceleration such that the host vehicle 1 decelerates at a first deceleration D1 (e.g., 1.0 G) greater than the third deceleration D3 when the TTC becomes equal to or less than the first threshold T1 (i.e., sets the target deceleration to the first deceleration D1). Furthermore, before generating the strong first deceleration D1 (i.e., before the TTC decreases to the first threshold T1), the driving support unit 31 decelerates at a second deceleration D2 greater than the third deceleration D3 but weaker than the first deceleration D1 (i.e., sets the target deceleration to the second deceleration D2), thereby performing pre-braking to notify the occupant that strong deceleration will occur in the driving support control. The control by the driving support unit 31 will be described in detail later.

[0024] The arbitration unit 32 arbitrates between the target vehicle speed profile generated by the cruise control unit 30 and the target deceleration set by the cruise support unit 31 to determine an arbitrated deceleration or an arbitrated acceleration. For example, if the target deceleration set by the cruise support unit 31 is stronger than the deceleration caused by the target vehicle speed profile generated by the cruise control unit 30, the arbitration unit 32 determines the target deceleration set by the cruise support unit 31 as the arbitrated deceleration. In other cases, the arbitration unit 32 determines the deceleration or acceleration caused by the target vehicle speed profile generated by the cruise control unit 30 as the arbitrated deceleration or the arbitrated acceleration. The drive control unit 23 and the braking control unit 24 control the brake control actuator of the actuator 16 so that the deceleration caused by the host vehicle 1 approaches the arbitrated deceleration. Furthermore, the arbitration unit 32 controls the accelerator opening actuator of the actuator 16 so that the acceleration caused by the host vehicle 1 approaches the arbitrated acceleration.

[0025] Next, the control of the driving support unit 31 will be described. When the TTC between the host vehicle 1 and the obstacle becomes shorter (i.e., the degree of proximity increases) and the driving support unit 31 sets a target deceleration stronger than the third deceleration D3, the arbitration unit 32 switches the arbitrated deceleration to the target deceleration of the driving support unit 31. If the driving support unit 31 gradually increases the target deceleration at this time, if the occupant is not concentrating on driving during automated driving, the occupant may not notice the increase in deceleration and may be late in realizing that an emergency braking due to driving support control is occurring. As a result, the occupant may be surprised and feel uncomfortable by the strong deceleration D1 that occurs afterwards.

[0026] For this reason, the driving assistance unit 31 changes the way in which the target deceleration is set according to the degree of proximity between the host vehicle 1 and an obstacle, depending on whether the host vehicle 1 is in a manual driving state or an automatic driving state. When the host vehicle 1 is in an automatic driving state, the driving assistance unit 31 sets the target deceleration so that the braking force changes more rapidly compared to when the host vehicle 1 is in a manual driving state. For example, the target deceleration may be set so that the deceleration in the pre-braking described above changes more rapidly. This reduces the discomfort felt by the occupants when they are not concentrating on driving during automatic driving, as they may be late in noticing that emergency braking due to driving assistance control is occurring, and the subsequent strong deceleration.

[0027] Furthermore, the driving assistance unit 31 may set the target deceleration so that the braking force changes more rapidly when the driving automation level is higher than when it is lower. For example, the target deceleration may be set so that the deceleration during the preliminary braking described above changes more rapidly. This reduces the discomfort felt by the occupants when the host vehicle 1 is driving at a high driving automation level and the strong deceleration that occurs afterwards, as it delays the occupants' realization that emergency braking due to driving assistance control will occur.

[0028] The driving assistance unit 31 includes an autonomous driving operation state determination unit 31a, a proximity degree calculation unit 31b, and a braking force calculation unit 31c. The autonomous driving operation state determination unit 31a determines the autonomous driving operation state of the host vehicle 1. For example, the autonomous driving operation state determination unit 31a may determine that the host vehicle 1 is in a manual driving state when the autonomous driving start switch is off, and that the host vehicle 1 is in an autonomous driving state when the autonomous driving start switch is on. Furthermore, for example, the autonomous driving operation state determination unit 31a may determine that the current autonomous driving level is a first autonomous driving level when the autonomous driving start switch is on, an occupant is seated in the driver's seat, and the acceleration and deceleration of the host vehicle 1 are automatically controlled in a state in which the occupant can operate the accelerator and brake at any time (i.e., override driving using the accelerator or brake is being performed).

[0029] The autonomous driving operation state determination unit 31a may determine that the current autonomous driving level is the second autonomous driving level when the autonomous driving start switch is on, an occupant is sitting in the driver's seat, and the steering of the host vehicle 1 is being automatically controlled in a state where the occupant can operate the steering wheel at any time (i.e., override driving using the steering wheel is being performed).The autonomous driving operation state determination unit 31a may determine that the current autonomous driving level is the third autonomous driving level when the autonomous driving start switch is on, an occupant is sitting in the driver's seat, the occupant is looking ahead, and the host vehicle 1 is traveling in a state where the occupant is not gripping the steering wheel.

[0030] The autonomous driving operation state determination unit 31a may determine that the current autonomous driving level is level 4 when the autonomous driving start switch is on, an occupant is sitting in the driver's seat, the occupant is not looking ahead, and the occupant is not gripping the steering wheel while the host vehicle 1 is traveling. The autonomous driving operation state determination unit 31a may determine that the current autonomous driving level is level 5 when the autonomous driving start switch is on, and the occupant is not sitting in the driver's seat while the host vehicle 1 is traveling. Whether the occupant is overriding the vehicle by using the accelerator, brake, or steering wheel may be determined, for example, based on the output of sensors provided on the accelerator, brake, or steering wheel. Whether the occupant is stopping the vehicle ahead may be determined, for example, based on video footage from a camera monitoring the occupant. Whether the occupant is gripping the steering wheel may be determined, for example, based on the output of a touch sensor provided on the steering wheel. Whether the occupant is sitting in the driver's seat may be determined, for example, based on whether a seat belt is fastened.

[0031] The proximity degree calculation unit 31b calculates the degree of proximity between the host vehicle 1 and an obstacle present in front of the host vehicle 1. In this embodiment, the TTC between the host vehicle 1 and the obstacle is calculated as the degree of proximity. The braking force calculation unit 31c calculates a target deceleration (i.e., calculates the braking force to be generated by the braking device) according to the autonomous driving operation state determined by the autonomous driving operation state determination unit 31a and the degree of proximity (TTC in this embodiment) calculated by the proximity degree calculation unit 31b. For example, the braking force calculation unit 31c sets the target deceleration so that the host vehicle 1 decelerates at a first deceleration D1 (e.g., 1.0 G) when the TTC becomes equal to or less than a first threshold T1 (i.e., sets the target deceleration to the first deceleration D1).

[0032] Furthermore, in a preparatory braking section where the TTC is longer than the first threshold T1 and is equal to or smaller than a second threshold T2 that is longer than the first threshold T2, the braking force calculation unit 31c sets a target deceleration for preparatory braking to notify the occupant that strong deceleration will occur due to activation of the driving assistance control. In the preparatory braking section, a deceleration weaker than the first deceleration D1 and stronger than the third deceleration D3 is set, thereby notifying the occupant of the activation of the driving assistance control. The braking force calculation unit 31c changes the target deceleration so that the braking force changes more rapidly (i.e., so that the target deceleration changes more rapidly) in the preparatory braking section when the vehicle is in an autonomous driving state compared to when the vehicle is in a manual driving state. The braking force calculation unit 31c changes the target deceleration so that the braking force changes more rapidly (i.e., so that the target deceleration changes more rapidly) in the preparatory braking section when the autonomous driving level is higher compared to when the autonomous driving level is lower.

[0033] 3B is a diagram showing an example of a target deceleration characteristic set by the braking force calculation unit 31c according to the degree of proximity (TTC) to an obstacle, and FIG. 3A is a diagram showing a comparative example of a deceleration characteristic according to the degree of proximity (TTC). The characteristic C0m shown in FIG. 3A shows a comparative example of a characteristic in a manual driving state, and the characteristic C0a shows a comparative example of a characteristic in an automatic driving state. In the manual driving state (characteristic C0m), the host vehicle 1 is not decelerated in the FCW section where the TTC is longer than the second threshold T2, and pre-braking is initiated when the TTC decreases to the second threshold T2. In contrast, in the automatic driving state (characteristic C0a), the deceleration is gradually increased up to a third deceleration D3 as the TTC becomes shorter in the FCW section while the TTC decreases to the second threshold T2, and pre-braking is initiated when the TTC decreases to the second threshold T2.

[0034] In the preliminary braking section where the TTC is longer than the first threshold T1 and less than the second threshold T2, the deceleration is gradually increased from the third deceleration D3 to the second deceleration D2 as the TTC decreases, and then maintained at the second deceleration D2 until the TTC decreases to the first threshold T1, in both the manual driving state (characteristic C0m) and the automatic driving state (characteristic C0a). In the main braking section (emergency braking section) where the TTC is less than the first threshold T1, the host vehicle 1 is decelerated at the first deceleration D1 in both the manual driving state (characteristic C0m) and the automatic driving state (characteristic C0a). In the comparative example of FIG. 3( a), in the manual driving state (characteristic C0m), preliminary braking begins from a state where no deceleration has occurred (i.e., a state where the deceleration is 0), so the occupant can easily notice the change in deceleration. On the other hand, in the case of the automatic driving state (characteristic C0a), preparatory braking starts when the third deceleration D3 is occurring in the FCW section, so the occupant may not easily notice the change in deceleration. As a result, there is a risk that the occupant will be late in noticing that an emergency braking situation is occurring, and the large deceleration that occurs in the subsequent main braking section (emergency braking section) will cause discomfort.

[0035] In FIG. 3B, characteristic C1 represents the target deceleration characteristic in a manual driving state or at the first or second autonomous driving level. Characteristic C2 represents the target deceleration characteristic in a third autonomous driving level. Characteristic C3 represents the target deceleration characteristic in a fourth or fifth autonomous driving level. The target deceleration when the TTC reaches the second threshold T2 (i.e., when pre-braking begins) changes more rapidly in an autonomous driving state (characteristics C2 and C3) than in a manual driving state (characteristic C1). This makes it easier for occupants to notice changes in deceleration even when they are not concentrating on driving during autonomous driving. Furthermore, the target deceleration when the TTC reaches the second threshold T2 (i.e., when pre-braking begins) changes more rapidly when the autonomous driving level is higher than when it is lower. This makes it easier for occupants to notice changes in deceleration even when they are not concentrating on driving when the host vehicle 1 is traveling at a high autonomous driving level.

[0036] 3C is a diagram showing another example of the characteristics of the target deceleration set by the braking force calculation unit 31c according to the degree of proximity (TTC) to an obstacle. In FIG. 3C, characteristic C11 indicates the characteristic of the target deceleration in the manual driving state or the first or second autonomous driving level, characteristic C12 indicates the characteristic of the target deceleration in the third autonomous driving level, and characteristic C13 indicates the characteristic of the target deceleration in the fourth and fifth autonomous driving levels. The braking force calculation unit 31c may set the second TTC thresholds T22 and T22 for initiating preparatory braking in the automatic driving state (characteristics C12 and C13) longer than the second TTC threshold T21 for initiating preparatory braking in the manual driving state (characteristic C11) (i.e., the threshold for the degree of proximity between the host vehicle 1 and an obstacle for initiating preparatory braking may be set lower). This allows the occupant to be aware of the need for emergency braking in the actual braking section (emergency braking section) in the automatic driving state more quickly than in the manual driving state.

[0037] The braking force calculation unit 31c may set the TTC threshold for initiating preparatory braking longer when the driving automation level is higher than when it is lower. For example, the second TTC threshold T22 for initiating preparatory braking for the third driving automation level (characteristic C12) may be set longer than the second TTC threshold T21 for initiating preparatory braking for the first driving automation level or the second driving automation level (characteristic C11). Furthermore, the second TTC threshold T23 for initiating preparatory braking for the fourth driving automation level or the fifth driving automation level (characteristic C13) may be set longer than the second TTC threshold T22 for initiating preparatory braking for the third driving automation level (characteristic C12). This allows the occupant to be made aware of the need to perform emergency braking in the main braking section (emergency braking section) earlier when the driving automation level is higher.

[0038] 4 is a flowchart of an example of a vehicle driving assistance method according to an embodiment. In step S1, the controller 17 acquires surrounding environment information output from the object sensor 11 and host vehicle information output from the vehicle sensor 12. The obstacle information acquisition unit 20 acquires obstacle information relating to an obstacle present ahead of the host vehicle 1 based on the surrounding environment information output from the object sensor 11. In step S2, the autonomous driving operation status determination unit 31a determines whether the host vehicle 1 is in an autonomous driving state. If the host vehicle 1 is not in an autonomous driving state (step S2: N), the process proceeds to step S4. If the host vehicle 1 is in an autonomous driving state (step S2: Y), the process proceeds to step S3. In step S3, the autonomous driving operation status determination unit 31a determines the autonomous driving operation status (e.g., the autonomous driving level) of the host vehicle 1.

[0039] In step S4, the proximity calculation unit 31b calculates the TTC between the obstacle and the host vehicle 1. The braking force calculation unit 31c determines whether the TTC is less than the threshold value. If the TTC is not less than the threshold value (step S4: N), the process ends. In this case, the braking force or driving force of the host vehicle 1 is controlled so as to generate the deceleration or acceleration set by the automatic driving control or FCW control by the driving control unit 30. If the TTC is less than the threshold value (step S4: Y), the process proceeds to step S5. In step S5, the braking force calculation unit 31c sets a braking force (target deceleration) according to the automatic driving operation state and the TTC of the host vehicle 1. The braking force calculation unit 31c sets the braking force according to whether the automatic driving operation state is automatic driving state or manual driving state, or according to the automatic driving level. In step S6, the brake control unit 24 controls the brake control actuator to decelerate with the braking force set in step S5. The process then ends.

[0040] (Effects of the Embodiment) (1) When an obstacle is present ahead of the host vehicle 1, the vehicle driving assistance device 10 generates a braking force to avoid a collision between the host vehicle 1 and the obstacle. The controller 17 determines whether the host vehicle 1 is in a manual driving state or an automatic driving state, changes the way in which the braking force is changed depending on whether the host vehicle 1 is in a manual driving state or an automatic driving state, and controls the braking device so that the braking force changes more rapidly when the host vehicle 1 is in an automatic driving state compared to when the host vehicle 1 is in a manual driving state. This reduces the discomfort felt by the occupants when they are not concentrating on driving during automatic driving and are late in noticing that an emergency braking due to driving assistance control will occur, and then a strong deceleration occurs.

[0041] (2) In a manual driving state, the controller 17 may control the braking device so that the braking force changes after the vehicle approaches an obstacle closer than in an automatic driving state. This allows the occupant to be made aware that emergency braking will be performed in the actual braking section (emergency braking section) earlier in the automatic driving state than in a manual driving state. (3) When the occupant's involvement in the driving of the host vehicle 1, as required by the autonomous driving level of the host vehicle 1, is lower than when it is higher, the controller 17 may control the braking device so that the braking force changes more rapidly. This reduces the discomfort felt by the occupant when the occupant is late in noticing that emergency braking due to cruise assist control will occur when the host vehicle 1 is traveling at a high autonomous driving level and then experiences strong deceleration.

[0042] (4) The controller 17 may control the braking device so that braking force changes only after the vehicle approaches an obstacle when the autonomous driving level of the vehicle 1 requires greater occupant involvement in driving the vehicle 1 compared to when the level is lower. This allows the occupant to be made aware of the need to perform emergency braking in the actual braking section (emergency braking section) sooner when the autonomous driving level is higher. (5) The autonomous driving level may be set to any of the following levels: first, second, third, fourth, and fifth autonomous driving levels. Occupant involvement in driving the vehicle increases in the order of first, second, third, fourth, and fifth autonomous driving levels. This allows braking force to be generated according to the autonomous driving level.

[0043] (6) The controller 17 may determine that the autonomous driving level is the first autonomous driving level when the autonomous driving start switch is on, an occupant is in the driver's seat, and the vehicle is traveling with acceleration and deceleration automatically controlled. The controller 17 may determine that the autonomous driving level is the second autonomous driving level when the autonomous driving start switch is on, an occupant is in the driver's seat, and the vehicle is traveling with steering automatically controlled. The controller 17 may determine that the autonomous driving level is the third autonomous driving level when the autonomous driving start switch is on, an occupant is in the driver's seat, is looking ahead, and the vehicle is traveling with the occupant not holding the steering wheel. The controller 17 may determine that the autonomous driving level is the fourth autonomous driving level when the autonomous driving start switch is on, an occupant is in the driver's seat, is not looking ahead, and the vehicle is traveling with the occupant not holding the steering wheel. When the autonomous driving start switch is on and the vehicle is traveling with no occupant in the driver's seat, the controller 17 may determine that the autonomous driving level is the fifth autonomous driving level, thereby enabling braking force to be generated according to the autonomous driving level.

[0044] 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.

[0045] 1...Own vehicle, 10...Vehicle driving assistance device, 11...Object sensor, 12...Vehicle sensor, 13...Positioning device, 14...Map database, 15...Navigation device, 16...Actuator, 17...Controller, 17a...Processor, 17b...Storage device, 20...Obstacle information acquisition unit, 21...Automatic driving control unit, 22...Steering control unit, 23...Drive control unit, 24...Braking control unit, 30...Driving control unit, 31...Driving assistance unit, 31a...Automatic driving operation state determination unit, 31b...Calculation unit, 31c...Braking force calculation unit, 32...Arbitration unit

Claims

1. A vehicle driving assistance method that generates a braking force to avoid a collision between a vehicle and an obstacle when the obstacle is present in front of the vehicle, the vehicle driving assistance method comprising: determining whether the vehicle is in a manual driving state or an automatic driving state; changing a manner in which the braking force is changed depending on whether the vehicle is in the manual driving state or the automatic driving state; and controlling a braking device so that the braking force changes more rapidly when the vehicle is in the automatic driving state compared to when the vehicle is in the manual driving state.

2. The vehicle driving assistance method according to claim 1, characterized in that, in the manual driving state, the braking device is controlled so that the braking force is changed after the vehicle approaches the obstacle closer than in the automatic driving state.

3. A vehicle driving assistance method as described in claim 1 or 2, characterized in that the braking device is controlled so that the braking force changes more rapidly when the occupant's involvement in the driving of the vehicle, as required by the autonomous driving level of the vehicle, is lower than when it is higher.

4. A vehicle driving assistance method as described in any one of claims 1 to 3, characterized in that the braking device is controlled so that the braking force is changed after the vehicle approaches the obstacle more closely when the vehicle's autonomous driving level requires greater occupant involvement in the driving of the vehicle compared to when the occupant involvement is less.

5. A vehicle driving assistance method as described in claim 3 or 4, characterized in that the autonomous driving level can be set to any one of a first autonomous driving level, a second autonomous driving level, a third autonomous driving level, a fourth autonomous driving level and a fifth autonomous driving level, and the involvement of the occupant in driving the vehicle increases in the order of the first autonomous driving level, the second autonomous driving level, the third autonomous driving level, the fourth autonomous driving level and the fifth autonomous driving level.

6. A vehicle driving assistance method as described in claim 5, characterized in that the autonomous driving level is determined to be the first autonomous driving level when the autonomous driving start switch is on, the occupant is seated in the driver's seat, and the vehicle is traveling with acceleration and deceleration automatically controlled.

7. A vehicle driving assistance method as described in claim 5 or 6, characterized in that when the automatic driving start switch is on, the occupant is seated in the driver's seat, and the vehicle is driving with steering automatically controlled, the automatic driving level is determined to be the second automatic driving level.

8. A vehicle driving assistance method as described in any one of claims 5 to 7, characterized in that the autonomous driving level is determined to be the third autonomous driving level when the autonomous driving start switch is on, the occupant is sitting in the driver's seat, the occupant is looking ahead, and the occupant is not holding the steering wheel while driving.

9. A vehicle driving assistance method as described in any one of claims 5 to 8, characterized in that the autonomous driving level is determined to be the fourth autonomous driving level when the autonomous driving start switch is on, the occupant is sitting in the driver's seat, the occupant is not looking ahead, and the occupant is not holding the steering wheel while driving.

10. A vehicle driving assistance method as described in any one of claims 5 to 9, characterized in that when the autonomous driving start switch is on and the vehicle is being driven with no occupant sitting in the driver's seat, the autonomous driving level is determined to be the fifth autonomous driving level.

11. A vehicle driving assistance device that generates a braking force to avoid a collision between a vehicle and an obstacle when the obstacle is present in front of the vehicle, comprising: a braking device that generates a braking force on the vehicle; and a controller that determines whether the vehicle is in a manual driving state or an automatic driving state, changes the way in which the braking force is changed depending on whether the vehicle is in the manual driving state or the automatic driving state, and controls the braking device so that the braking force changes more rapidly when the vehicle is in the automatic driving state compared to when the vehicle is in the manual driving state.

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