Vehicle travel assistance method and vehicle travel assistance device

Abstract

In this vehicle travel assistance method, when there is an obstacle in front of a vehicle, a braking force for avoiding a collision between the vehicle and the obstacle is generated. The method includes: determining whether the vehicle is in a manual driving state or an automated driving state (S2); modifying, on the basis of whether the vehicle is in the manual driving state or the automated driving state, the way the braking force is changed, according to the degree of approach between the vehicle and the obstacle (S5); and controlling a braking device so that, in the manual driving state compared to the automated driving state, a change in braking force occurs after the vehicle has approached closer to the obstacle (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, and changes a way of changing the braking force according to the degree of proximity between the vehicle and the obstacle 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 is changed after the vehicle gets closer to the obstacle in the manual driving state than in the automatic 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) that is greater than the third deceleration D3. For example, the driving support unit 31 sets the target deceleration so that the host vehicle 1 decelerates at the first deceleration D1 (e.g., 1.0 G) that is 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). Details of the control by the driving support unit 31 will be described 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, a description will be given of the control of the driving support unit 31. When the TTC between the vehicle 1 and the obstacle becomes shorter (i.e., the degree of proximity becomes higher) and the driving support unit 31 sets a relatively strong target deceleration, the arbitration unit 32 switches the arbitrated deceleration to the target deceleration of the driving support unit 31. There is a risk that the resulting change in deceleration will cause discomfort to the occupants.

[0026] For example, when the host vehicle 1 is traveling at a relatively high level of automated driving, the occupants may not be concentrating on driving. Therefore, if the deceleration rate changes suddenly, the occupants may feel burdened or frightened, which may cause discomfort. Such sudden changes in deceleration rate can be mitigated by starting deceleration early (i.e., starting deceleration at a point away from obstacles). However, when the host vehicle 1 is traveling manually or at a relatively low level of automated driving, the occupants are aware of obstacles ahead and operate the accelerator and brakes themselves. Therefore, if deceleration starts early, the occupants may feel that the brakes have been applied unintentionally, which may cause discomfort.

[0027] For this reason, the driving assistance unit 31 changes the way in which the target deceleration is changed 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 autonomous driving state. The driving assistance unit 31 changes the target deceleration after the host vehicle 1 approaches the obstacle more closely when the host vehicle 1 is in a manual driving state than when the host vehicle 1 is in an autonomous driving state. The driving assistance unit 31 changes the target deceleration after the host vehicle 1 approaches the obstacle more closely when the autonomous driving level is lower than when the autonomous driving level is higher. This makes it possible to reduce the discomfort felt by the occupants by starting deceleration early before the host vehicle 1 approaches the obstacle when the host vehicle 1 is driving manually or at a relatively low autonomous driving level.

[0028] Furthermore, the driving assistance unit 31 sets the target deceleration so that the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the vehicle is in a manual driving state than when the vehicle is in an automatic driving state. For example, the driving assistance unit 31 sets the target deceleration so that the slope of the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the driving assistance unit 31 is in a manual driving state than when the vehicle is in an automatic driving state. The driving assistance unit 31 sets the target deceleration so that the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the driving assistance unit 31 is in a lower automatic driving level than when the driving assistance unit 31 is in a higher automatic driving level. For example, the driving assistance unit 31 sets the target deceleration so that the slope of the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the driving assistance unit 31 is in a lower automatic driving level than when the driving assistance unit 31 is in a higher automatic driving level. This makes it possible to reduce the discomfort felt by the occupants due to a sudden change in deceleration and a large jerk when the host vehicle 1 is traveling at a relatively high automatic driving level.

[0029] 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).

[0030] 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.

[0031] 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.

[0032] 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 calculated by the proximity degree calculation unit 31b (TTC in this embodiment). For example, the braking force calculation unit 31c changes the target deceleration after the host vehicle approaches the obstacle more closely in a manual driving state than in an autonomous driving state. The braking force calculation unit 31c changes the target deceleration after the host vehicle approaches the obstacle more closely when the autonomous driving level is lower than when it is higher.

[0033] Furthermore, the target deceleration is set so that the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the vehicle is in a manual driving state than when the vehicle is in an automatic driving state. For example, the target deceleration is set so that the slope of the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the vehicle is in a manual driving state than when the vehicle is in an automatic driving state. The braking force calculation unit 31c sets the target deceleration so that the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the automatic driving level is lower than when it is higher. For example, the target deceleration is set so that the slope of the change in the target deceleration with respect to the change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the automatic driving level is lower than when it is higher.

[0034] 3B shows an example of a target deceleration characteristic set by the braking force calculation unit 31c according to the TTC (time to collision) to an obstacle, and FIG. 3A shows a comparative example of a deceleration characteristic according to the TTC. In the comparative example characteristic (C0) shown in FIG. 3A, in the FCW section where the TTC is longer than the first threshold T1, the deceleration is reduced to a relatively weak third deceleration D3 (e.g., 0.3 G) or less. For example, while the TTC decreases to the second threshold T2, which is longer than the first threshold T1, the deceleration may be gradually increased to the third deceleration D3 as the TTC shortens. In the section where the TTC is equal to or less than the second threshold T2 but greater than the first threshold T1, the deceleration may be at the third deceleration D3. In the main braking section (emergency braking section) where the TTC is equal to or less than the first threshold T1, the deceleration is at a relatively strong first deceleration D1 (e.g., 1.0 G). In this way, if the deceleration rate is switched when the TTC becomes equal to or less than the first threshold value T1, the occupants may feel burdened or scared, and may experience discomfort.

[0035] In Figure 3(b), characteristic C1 represents the target deceleration characteristic in a manual driving state or the first automatic driving level, characteristics C2 and C3 represent the target deceleration characteristic in the second and third automatic driving levels, respectively, and characteristic C4 represents the target deceleration characteristic in the fourth and fifth automatic driving levels. Characteristics C2 to C4 include a preparatory braking section for reducing jerk caused by an increase in the target deceleration from the third deceleration D3 to the first deceleration D1, which is set in a range where the TTC is longer than the first threshold T1 and shorter than the second threshold T2. In the preparatory braking section, the target deceleration is set so that it gradually increases as the TTC becomes shorter (i.e., characteristics C2 to C4 are set so that the target deceleration is larger when the TTC is short compared to when the TTC is long), thereby reducing jerk caused by the increase in target deceleration.

[0036] Furthermore, in the manual driving state (characteristic C1), the target deceleration increases stepwise from the third deceleration D3 to the first deceleration D1 when the TTC reaches the first threshold T1, whereas in the autonomous driving state (characteristics C2 to C4), the target deceleration gradually increases in the preparatory braking section. That is, the slope of the change in the target deceleration with respect to the change in the TTC is smaller in the autonomous driving state than in the manual driving state. This reduces the discomfort felt by the occupants in the autonomous driving state, which would otherwise occur if the occupants were not concentrating on driving and the deceleration were suddenly increased, resulting in a large jerk. Furthermore, the slope of the change (increase) in the target deceleration with respect to the change (decrease) in the preparatory braking section is smaller when the autonomous driving level is higher than when the autonomous driving level is lower. This reduces the discomfort felt by the occupants in the autonomous driving state, which would otherwise occur if the occupants were not concentrating on driving and the deceleration were suddenly increased, resulting in a large jerk.

[0037] Furthermore, in the case of the autonomous driving state (characteristics C2 to C4), the target deceleration starts increasing from the third deceleration D3 to the first deceleration D1 when the TTC is longer than the first threshold T1, whereas in the case of the manual driving state (characteristic C1), the target deceleration starts increasing when the TTC reaches the first threshold T1. That is, in the case of the manual driving state, the target braking force is increased after the host vehicle 1 approaches an obstacle closer than in the case of the autonomous driving state. As a result, when the host vehicle 1 is being driven manually, deceleration starts earlier before the host vehicle approaches an obstacle, thereby reducing the discomfort felt by the occupants. Furthermore, when the autonomous driving level is lower than when it is higher, the TTC at which the target deceleration starts increasing from the third deceleration D3 to the first deceleration D1 is shorter than when it is higher. That is, the target braking force is increased after the host vehicle 1 approaches an obstacle closer. As a result, when the host vehicle 1 is being driven at a relatively low autonomous driving level, deceleration starts earlier before the host vehicle approaches an obstacle, thereby reducing the discomfort felt by the occupants.

[0038] In the characteristics C2 to C4 illustrated in FIG. 3( b), the target deceleration is set so that the slope of the change (increase) in the target deceleration becomes steeper as the TTC becomes shorter (the degree of proximity increases) in the preparatory braking zone. However, the example illustrated in FIG. 3( b) is not intended to limit the target deceleration set by the braking force calculation unit 31c to such characteristics. For example, the braking force calculation unit 31c may set the target deceleration so that it increases linearly with the decrease in the TTC in the preparatory braking zone. FIG. 3( c) is a diagram showing another example of the target deceleration characteristic set by the braking force calculation unit 31c according to the degree of proximity (TTC) to an obstacle. In FIG. 3( c), characteristic C11 represents the target deceleration characteristic in a manual driving state or the first autonomous driving level, characteristics C12 and C13 represent the target deceleration characteristics in the second and third autonomous driving levels, respectively, and characteristic C14 represents the target deceleration characteristic in the fourth and fifth autonomous driving levels.

[0039] Note that even when the host vehicle 1 is in an autonomous driving state, if a degradation of the autonomous driving function of the host vehicle 1 occurs, the braking force calculation unit 31c may generate a braking force in the driving assistance control that generates a braking force to avoid a collision between the host vehicle 1 and an obstacle, in the same manner as in a manual driving state. For example, the controller 17 may determine that a degradation of the autonomous driving function is likely to occur if the environment around the host vehicle 1 (e.g., weather, etc.) is outside the operational design domain (ODD) of the autonomous driving function of the vehicle driving assistance device 10 or if a system failure occurs in the vehicle driving assistance device 10.

[0040] 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.

[0041] 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.

[0042] (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, and changes how the braking force is changed according to the degree of proximity between the host vehicle 1 and the obstacle 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 is changed after the host vehicle 1 approaches the obstacle more closely in the manual driving state than in the automatic driving state. This reduces the discomfort felt by the occupants in the manual driving state by starting deceleration earlier before approaching the obstacle.

[0043] (2) The controller 17 may control the braking device so that the change in braking force in response to a change in the degree of proximity between the host vehicle 1 and an obstacle is greater when the vehicle is in a manual driving state than when the vehicle is in an autonomous driving state. This can reduce the discomfort felt by the occupants when a large jerk occurs due to a sudden change in deceleration caused by the operation of the driving assistance control when the vehicle is in an autonomous driving state. (3) The controller 17 may control the braking device so that the braking force changes only after the host vehicle 1 approaches an obstacle when the host vehicle 1 has a high level of autonomous driving required by the autonomous driving level compared to when the occupants' involvement in the driving of the host vehicle 1 is low. This can reduce the discomfort felt by the occupants when deceleration begins earlier before the host vehicle approaches an obstacle at a relatively low autonomous driving level.

[0044] (4) The controller 17 may control the braking device so that the change in braking force in response to a change in the degree of proximity between the vehicle 1 and an obstacle is greater when the autonomous driving level of the vehicle 1 requires greater occupant involvement in the driving of the vehicle 1 compared to when it is low. This reduces the discomfort experienced by the occupant when a large jerk occurs due to a sudden change in deceleration caused by the operation of the cruise assist control at a relatively high autonomous driving level. (5) The autonomous driving level may be set to any of the following: first, second, third, fourth, and fifth autonomous driving levels. The degree of occupant involvement in the driving of 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.

[0045] (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.

[0046] (7) The controller 17 may generate a larger braking force when the degree of proximity at which generation of a braking force to avoid a collision between the host vehicle 1 and an obstacle is initiated is high compared to when the degree of proximity is low. This generates a larger braking force as the degree of proximity increases, thereby reducing the occupant's fear of the risk of a collision. (8) When there is a risk of degradation of the autonomous driving function of the host vehicle 1, the controller 17 may generate a braking force to avoid a collision between the host vehicle 1 and an obstacle in the same manner as when the host vehicle 1 is in a manual driving state, even when the host vehicle 1 is in an autonomous driving state. This ensures braking performance when there is a risk of degradation of the autonomous driving function of the host vehicle 1.

[0047] 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.

[0048] 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 vehicle is in front of the vehicle, the method comprising: determining whether the vehicle is in a manual driving state or an automatic driving state; changing a way in which the braking force is changed according to the degree of proximity between the vehicle and the obstacle 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 is changed only after the vehicle gets closer to the obstacle when the vehicle is in the manual driving state compared to when the vehicle is in the automatic driving state.

2. The vehicle driving assistance method described in claim 1, characterized in that the braking device is controlled so that the change in braking force in response to a change in the degree of proximity between the vehicle and the obstacle is greater when the vehicle is in the manual driving state than when the vehicle is in the automatic driving state.

3. A vehicle driving assistance method as described in claim 1 or 2, characterized in that when the level of autonomous driving of the vehicle requires that the involvement of occupants in the driving of the vehicle is high compared to when it is low, the braking device is controlled so that the braking force changes after the vehicle approaches the obstacle more closely.

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 change in braking force in response to a change in the degree of proximity between the vehicle and the obstacle becomes larger when the level of autonomous driving of the vehicle requires greater involvement of the occupants in the driving of the vehicle compared to when it is low.

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 method according to any one of claims 1 to 10, characterized in that a greater braking force is generated when the degree of proximity at which generation of the braking force to avoid collision between the vehicle and the obstacle is initiated is high compared to when the degree of proximity is low.

12. A vehicle driving assistance method as described in any one of claims 1 to 11, characterized in that when there is a risk of a deterioration in the automatic driving function of the vehicle, even when the vehicle is in the automatic driving state, a braking force to avoid a collision between the vehicle and the obstacle is generated in the same way as when the vehicle is in the manual driving state.

13. A vehicle driving assistance device that generates a braking force to avoid a collision between the 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, and changes the way in which the braking force is changed according to the degree of proximity between the vehicle and the obstacle 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 is changed only after the vehicle gets closer to the obstacle when in the manual driving state compared to when in the automatic driving state.

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