阅读说明：本技术 驾驶辅助方法及驾驶辅助装置 (Driving assistance method and driving assistance device ) 是由 伊东敦 中村昌平 于 2020-03-30 设计创作，主要内容包括：在提高了驾驶辅助等级的车道保持行驶场景中,在需要唤起驾驶员的注意的状况时,通过降低驾驶辅助等级,督促基于适当的驾驶辅助的行驶。具备模式切换控制器(47),该模式切换控制器(47)具有车速/车间控制功能和车道保持功能作为辅助驾驶员的驾驶操作的驾驶辅助功能,切换辅助本车辆在行驶中维持在车道内的车道保持辅助模式。在选择了允许驾驶员手离开方向盘(23)的“手离开模式(M1)”作为车道保持辅助模式的车道保持行驶中,判定本车辆的实际车速(VR)超过本车辆正在行驶的道路的限制速度(VL(n))的行驶条件是否成立。当判定为实际车速(VR)超过限制速度(VL(n))的行驶条件成立时,从“手离开模式(M1)”向以驾驶员将手放在方向盘(23)上为条件的“手持模式(M2)”切换。(In a lane keeping driving scene in which the driving assistance level is increased, when a driver needs to be alerted, the driving assistance level is decreased, thereby prompting driving by appropriate driving assistance. The vehicle control system is provided with a mode switching controller (47), wherein the mode switching controller (47) has a vehicle speed/vehicle distance control function and a lane keeping function as a driving assistance function for assisting the driving operation of a driver, and switches a lane keeping assistance mode for assisting the vehicle to maintain in a lane during driving. In lane-keeping running in which a 'hand-off mode (M1)' for allowing a driver to leave the steering wheel (23) is selected as a lane-keeping assist mode, it is determined whether or not a running condition is satisfied in which the actual vehicle speed (VR) of the host vehicle exceeds a limit speed (VL (n)) of a road on which the host vehicle is running. When it is determined that a running condition that the actual vehicle speed (VR) exceeds the limit speed (VL (n)) is satisfied, the vehicle switches from the "hands-off mode (M1)" to the "hand-held mode (M2)" that requires the driver to place a hand on the steering wheel (23).)

1. A driving assistance method based on a mode switching controller having a vehicle speed/vehicle-to-vehicle control function and a lane keeping function as a driving assistance function for assisting a driving operation of a driver and switching a lane keeping assistance mode for assisting a host vehicle to be maintained in a lane while the host vehicle is traveling,

the vehicle speed/vehicle-to-vehicle control function has a function of rewriting a set vehicle speed used for vehicle speed control to a speed limit when the speed limit of a road on which the vehicle is traveling is detected,

as the lane keeping assist mode, it is determined whether or not a running condition that an actual vehicle speed of the host vehicle exceeds a limit speed of a road on which the host vehicle is running is satisfied in lane keeping running in which a hand-off mode that allows the driver to take off the hand from the steering wheel is selected,

if it is determined that the running condition that the actual vehicle speed exceeds the limit speed is satisfied, the mode is switched from the hands-off mode to a hold-in mode that is conditioned on the driver placing a hand on a steering wheel.

2. The driving assistance method according to claim 1,

determining whether or not a set vehicle speed changing operation for making the set vehicle speed higher than the limit speed is performed by a driver during the lane keeping running in which the hand-off mode is selected,

if it is determined that the driver has performed an operation to increase the set vehicle speed and it is determined that the actual vehicle speed has increased to or above a vehicle speed determination value obtained by adding an error to the vehicle speed limit, the mode is switched from the hand-off mode to the hand-held mode.

3. The drive assist method according to claim 1 or 2,

determining whether or not the driver has performed an accelerator depression operation during the lane keeping running in which the hand-off mode is selected,

if it is determined that the driver has performed an accelerator depression operation, the driver is requested to hold the steering wheel,

when it is confirmed that the driver holds the steering wheel, the mode is switched from the hands-off mode to the hand-held mode.

4. The drive assist method according to claim 3,

when the driver performs an accelerator depression operation while the lane keeping running mode in which the hand-off mode is selected, the acceleration of the vehicle is kept until the hand-held mode is switched,

after switching to the handheld mode, acceleration of the host vehicle corresponding to an accelerator depression operation by the driver is started.

5. The drive assist method according to any one of claims 1 to 4,

determining whether or not a newly detected speed limit is lower than a previous speed limit during the lane keeping running in which the hand-off mode is selected,

determining whether the actual vehicle speed exceeds the limit speed after a set time has elapsed after determining that the newly detected limit speed has decreased,

if it is determined that the actual vehicle speed exceeds the limit speed, switching from the hand-off mode to the hand-held mode.

6. The drive assist method according to any one of claims 1 to 5,

determining a switching condition from the handheld mode to the hand-off mode in a case where the handheld mode is selected,

and if the switching condition is satisfied, switching from the handheld mode to the hand leaving mode.

7. A driving assistance device having a mode switching controller that has a vehicle speed/vehicle-to-vehicle control function and a lane keeping function, functions as a driving assistance function for assisting a driving operation of a driver, and switches a lane keeping assistance mode for assisting a host vehicle to stay in a lane while the host vehicle is traveling,

the vehicle speed/vehicle-to-vehicle control function has a function of rewriting a set vehicle speed used for control to a speed limit when the speed limit of a road on which the vehicle is traveling is detected,

the mode switching controller includes:

a travel condition determination unit that determines whether or not a travel condition in which an actual vehicle speed of the host vehicle exceeds a limit speed of a road on which the host vehicle is traveling is satisfied during lane-keeping travel in which a hand-off mode that allows a driver to remove a hand from a steering wheel is selected as the lane-keeping assist mode;

and a mode switching unit that switches from the hands-off mode to a hold mode that is conditioned by a driver placing a hand on a steering wheel, when it is determined that a running condition in which the actual vehicle speed exceeds the limit speed is satisfied.

Technical Field

The present invention relates to a driving assistance method and a driving assistance apparatus.

Background

Conventionally, in a driving assistance device mounted in a vehicle capable of executing follow-up running control for automatically running a host vehicle following a preceding vehicle, a limited speed acquisition unit acquires a limited speed of a road on which the host vehicle is running. The notification speed determination section determines a notification speed based on the limit speed. The notification unit notifies when the traveling speed of the host vehicle is equal to or higher than the notification speed. There is known a device in which a notification speed determination unit lowers a notification speed during execution of follow-up running control compared to non-execution of follow-up running control (for example, see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2000-20898

The conventional device notifies the driver when the traveling speed of the host vehicle becomes a notification speed based on the speed limit. However, in the driving assistance control for assisting the driving operation of the driver, there are problems as follows: with the advancement of the driving assistance for increasing the level of assistance in the driving operation by the driver, there is a possibility that the driving by the appropriate driving assistance cannot be prompted only by a simple notification.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object of the present invention is to promote driving by appropriate driving assistance by lowering a driving assistance level when it is determined that a driving condition is required to call the attention of a driver in a lane-keeping driving scene in which the driving assistance level is raised.

In order to achieve the above object, the present disclosure is a driving assistance method based on a mode switching controller that has a vehicle speed/vehicle-to-vehicle control function and a lane keeping function as a driving assistance function that assists a driving operation of a driver, and switches a lane keeping assist mode that assists the host vehicle in traveling while remaining in a lane. As the lane keeping assist mode, in lane keeping running in which a hand-off mode (hand-off mode) that allows the driver to take off the hand from the steering wheel is selected, it is determined whether or not a running condition is established in which the actual vehicle speed of the host vehicle exceeds the limit speed of the road on which the host vehicle is running. If it is determined that the running condition that the actual vehicle speed exceeds the limit speed is satisfied, the mode is switched from the hands-off mode to the hand-held mode on the condition that the driver places the hands on the steering wheel.

Effects of the invention

In the lane keeping driving scene in which the driving assistance level is increased, the driving assistance level is lowered when it is determined that the driving condition is a driving condition that requires the attention of the driver, and thus the driving by the appropriate driving assistance can be promoted.

Drawings

Fig. 1 is an overall system diagram showing a high-level driving assistance system to which the driving assistance method and the driving assistance device of embodiment 1 are applied.

Fig. 2 is a view showing a vehicle interior structure when a front window is viewed from a driver's seat position of the driving assist vehicle.

Fig. 3 is an enlarged view showing an operation switch of the driver provided on the steering wheel of the driving assist vehicle.

Fig. 4 is a control block diagram showing the configuration of a mode switching controller included in the ADAS control unit.

Fig. 5 is a flowchart showing a flow of the lane keeping assist mode switching control process executed by the mode switching controller provided in the ADAS control unit.

Fig. 6 is a diagram showing an example of the running condition of the host vehicle in which the hands-off mode is selected and an example of the hands-off mode display.

Fig. 7 is a diagram showing an example of the running condition of the vehicle selected in the handheld mode and an example of the display of the handheld mode.

Fig. 8 is a time chart showing characteristics when the lane keeping assist mode is switched to the handheld mode based on a change in the set vehicle speed operated by the driver.

Fig. 9 is a timing chart showing characteristics when the lane keeping assist mode is switched to the hold mode based on the accelerator depression operation by the driver.

Fig. 10 is a sequence diagram showing characteristics when the lane keeping assist mode is switched to the handheld mode based on a change in the speed limit of the road on which the host vehicle travels.

Detailed Description

Hereinafter, a mode for implementing the driving assistance method and the driving assistance device of the present disclosure will be described based on embodiment 1 shown in the drawings.

Example 1

The driving Assistance method and the driving Assistance apparatus according to embodiment 1 are applied to a driving Assistance vehicle equipped with an Advanced driving Assistance system ADAS ("short for Advanced Driver Assistance Systems") for assisting a Driver in driving operations. Hereinafter, the configuration of embodiment 1 will be described as being divided into "overall system configuration", "control block configuration of mode switching controller", and "lane keeping assist mode switching control processing configuration".

(Overall System Structure)

Fig. 1 shows an advanced driving assistance system to which the driving assistance method and the driving assistance device of embodiment 1 are applied. Fig. 2 shows a vehicle interior structure when a front window is viewed from a driver's seat position of the driving assist vehicle. Fig. 3 shows a driver's operation switch provided on a steering wheel of the driving assist vehicle. The overall system configuration will be described below with reference to fig. 1 to 3.

The advanced driving assistance system ADAS is a system having a vehicle speed/vehicle-to-vehicle control function and a lane keeping function. As shown in fig. 1, the present invention includes: the vehicle-mounted sensor 1, the map data storage unit 2, the external data communicator 3, the ADAS control unit 4, the actuator 5, the HMI device 6, the navigation system 7, the operation switch 8, and the control information sensor group 9. In addition, "HMI" is a "human-machine interface: short for Human Machine Interface ".

The in-vehicle sensor 1 includes: a camera 11, radar 12, GPS13 and an onboard data communicator 14. The sensor information acquired by the in-vehicle sensor 1 is output to the ADAS control unit 4.

The camera 11 is a vehicle periphery recognition sensor that realizes a function of acquiring periphery information of the own vehicle, such as the own lane, an adjacent lane, a vehicle around the own vehicle, and a pedestrian around the own vehicle, from image data. The camera 11 is configured by combining a front recognition camera, a rear recognition camera, a right recognition camera, a left recognition camera, and the like, and has a panoramic monitoring function. The camera 11 detects an object on the road on which the vehicle is traveling, a lane, an object outside the road on which the vehicle is traveling (a road structure, a preceding vehicle, a following vehicle, an oncoming vehicle, a surrounding vehicle, a pedestrian, a bicycle, a two-wheeled vehicle), a road on which the vehicle is traveling (a white road line, a road boundary, a stop line, a crosswalk), a road sign (speed limit), and the like.

The radar 12 is a ranging sensor that realizes a function of detecting the presence of an object around the own vehicle and a function of detecting a distance to the object around the own vehicle. Here, "radar 12" is a generic term including radar using radio waves, laser radar using light, and sonar using ultrasonic waves. The radar 12 can detect the position of an object on the road on which the host vehicle is traveling, an object outside the road on which the host vehicle is traveling (a road structure, a preceding vehicle, a following vehicle, an oncoming vehicle, a surrounding vehicle, a pedestrian, a bicycle, a two-wheel vehicle), and the like, and can detect the distance to each object.

The GPS13 is a vehicle position sensor that has a GNSS antenna 13a and detects the position (latitude, longitude) of the vehicle while it is parked or traveling by satellite communication. In addition, "GNSS" is "Global Navigation Satellite System: abbreviation of Global navigation satellite System, "GPS" is "Global Positioning System: global positioning system ("gps") is short.

The in-vehicle data communicator 14 is an external data sensor that acquires information that cannot be acquired by the in-vehicle sensor 1 or the map data from the outside by performing wireless communication with the external data communicator 3 via the transmitting and receiving antennas 3a, 14 a. Here, for example, in the case where the "external data communicator 3" is a data communicator mounted on another vehicle traveling around the host vehicle, it is possible to perform inter-vehicle communication between the host vehicle and the other vehicle and to request acquisition of information necessary for the host vehicle among various information held by the other vehicle. In addition, for example, in the case where the "external data communicator 3" is a data communicator provided in an infrastructure, it is possible to perform infrastructure communication between the host vehicle and the infrastructure and to acquire information necessary for the host vehicle by requesting it. For example, when there is insufficient information or information changed from the map data in the map data stored in the map data storage unit 2, the insufficient/changed information can be supplemented. In addition, traffic information such as traffic jam information and travel restriction information on the travel route of the vehicle can be acquired.

The map data storage unit 2 is constituted by an in-vehicle memory storing so-called electronic map data corresponding to latitude and longitude and map information. The map data stored in the map data storage unit 2 is high-precision map data having an accuracy with which the lane level can be recognized basically, except for regions not having high-precision map data. When the ADAS control unit 4 recognizes the position of the vehicle detected by the GPS13, high-precision map data of a predetermined range centered on the position of the vehicle is transmitted to the ADAS control unit 4 and the navigation system 7.

Here, the "high-accuracy map data" has road information corresponding to each of the sites, and the road information is defined by links between the nodes and the connection nodes. The road information includes information for determining a road according to a position/area of the road, a road type of each road, a lane width of each road, and shape information of the road. The road information stores the position of the intersection, the direction of entry of the intersection, the type of the intersection, and information relating to the intersection in association with each other for each piece of identification information of each road link. The road information is stored in association with a road type, a lane width, a road shape, a straight-ahead possibility, a priority relationship of travel, an overtaking possibility (an adjacent lane is allowed or not), a speed limit, a sign, and other information related to the road, in accordance with identification information of each road link.

The ADAS control unit 4 is a unit for integrated driving assistance control, and includes, as a controller for sharing a vehicle speed/vehicle-to-vehicle control function: an accelerator/brake assist controller 41, a travel drive source controller 42, and a brake controller 43. The controller that shares the lane keeping function includes a steering wheel assist controller 44 and a steering controller 45. Further, in the case of the advanced driving assistance system ADAS, the HMI controller 46 is provided as a controller that shares a function of acquiring communication between the driver and the system. In the case of the advanced driving assistance system ADAS, the driver has a mode switching controller 47, and the mode switching controller 47 controls the lane keeping assistance mode to be switched in accordance with a "hand-off mode M1" in which the driving assistance level is increased to the driver's hand-off steering wheel.

The accelerator/brake assist controller 41 performs the following control that assists the accelerator operation and the brake operation of the driver.

(a) When a preceding vehicle is detected, the vehicle-to-vehicle control is performed so as to maintain the vehicle-to-vehicle distance corresponding to the vehicle speed, with the vehicle speed set by the driver as the upper limit.

(b) When the preceding vehicle is not detected, the vehicle travels at a set vehicle speed at a constant speed.

(c) When the preceding vehicle stops, the own vehicle also stops after the preceding vehicle.

(d) When the preceding vehicle starts, the return/acceleration switch 82 (see fig. 3) is pressed or the accelerator pedal is depressed to release the stopped state, and the follow-up running is started again.

(e) When the vehicle is stopped by the vehicle speed/vehicle-to-vehicle control function, the electric parking brake is actuated by a command to the electric parking brake actuator 53 when the system release operation is performed.

The accelerator/brake assist controller 41 performs the following control in addition to the vehicle speed/vehicle-to-vehicle control of the above-described (a) to (e), which are generally referred to as "cruise control".

(f) When the host vehicle is traveling by the vehicle speed/vehicle-to-vehicle control function, a change (up-down) of the set vehicle speed based on a switch operation by the driver is permitted.

(g) When a new speed limit is detected by the speed limit indicator detection function, the speed limit auxiliary display is turned on, and "the set vehicle speed has been changed" is displayed on the display, and the detected speed limit is reflected to the set vehicle speed. However, after the set vehicle speed is set to a speed higher than the limit speed by the switch operation of the driver, the limit speed is not reflected to the set vehicle speed (speed limit assist) when the limit speed does not exceed the set vehicle speed even if the limit speed is increased.

(h) When the vehicle is traveling by the vehicle speed/vehicle-to-vehicle control function and temporary acceleration is desired, acceleration is permitted when the accelerator pedal is depressed. When the accelerator pedal is operated to accelerate, the brake control, the approach warning, and the curve warning are not performed. When the accelerator pedal is released, the vehicle speed/vehicle shop control up to now (before) is resumed.

(i) When the host vehicle is traveling by the vehicle speed/inter-vehicle distance control function and the host vehicle is temporarily decelerated, the deceleration is permitted by depressing the brake pedal. When the vehicle is to be set again at the set vehicle speed before deceleration, the return/acceleration switch 82 (see fig. 3) is pressed.

(j) When traveling on a curve, vehicle speed control is performed based on map information so that the vehicle can travel at a vehicle speed corresponding to the size of the curve ahead.

When the target vehicle speed is generated by the accelerator/brake assist controller 41, the travel drive source controller 42 calculates a drive command value so that the actual vehicle speed of the host vehicle becomes the target vehicle speed, and performs vertical control output to the drive actuator 51.

When the target braking deceleration is generated by the accelerator/brake assist controller 41, the brake controller 43 calculates a brake command value so that the actual braking deceleration of the host vehicle becomes the target braking deceleration, and performs vertical control to be output to the brake actuator 52.

The steering wheel support controller 44 performs steering control (lateral control) so that the host vehicle travels in the center of the lane based on the detection of the lane marks on both sides of the lane by the front recognition camera, and performs a lane keeping function for supporting the steering operation of the driver.

When a target steering angle for causing the host vehicle to travel in the center portion of the lane is generated by the steering wheel assist controller 44, the steering controller 45 calculates a steering angle command value so that the actual steering angle of the host vehicle becomes the target steering angle, and executes lateral control output to the steering angle actuator 54.

The HMI controller 46 generates display instructions to the head-up display 61 and the meter display 62 so that the action state or the change in the action state of the vehicle speed/vehicle-to-vehicle control function and the lane keeping function can be visually recognized. For example, when displaying the "hand-off mode" and the "hand-held mode", color display, icon display, and message display are flexibly performed for each mode, and display is performed so that the driver can understand the operation state at a glance. When it is necessary to notify the driver of an audible notification, a sound signal is generated to the speaker 63, and when it is necessary to notify the driver of an audible alarm, an operation/stop command of the alarm 64 is generated.

Here, as shown in fig. 2, a head-up display 61 of the HMI device 6 is set at a lower position of the front window 21, and a system state and the like are displayed on the windshield by a lamp. The meter display 62 is set in a meter display portion of the instrument panel 22, and displays a system operation state, a state of a surrounding vehicle, and the like. The speaker 63 and the alarm 64 are set at predetermined positions inside the panel of the instrument panel 22.

The mode switching controller 47 determines whether or not a running condition in which the actual vehicle speed of the host vehicle exceeds the speed limit of the road on which the host vehicle is running is satisfied during the lane-keeping running in which the hand-off mode is selected. When it is determined that the running condition that the actual vehicle speed exceeds the speed limit is satisfied, control is performed to switch from the hands-off mode to the hands-on mode.

Here, the "hand-off mode" refers to a lane keeping assist mode that allows the driver to take the hand off the steering wheel 23. The "hold mode" refers to a lane keeping assist mode conditioned on the driver placing his hand on the steering wheel 23. That is, the "hand-off mode" and the "hand-held mode" are modes different only in a point of allowing the driver to take off the hand from the steering wheel 23 or requiring the hand to be placed on the steering wheel 23, and are not modes of changing the driving assistance control itself. Therefore, when the "hands-off mode" is selected, the driver can travel in the automatic driving state without participating in the driving operation at all. When the "hold mode" in which the driving assistance level is lowered from the "hold mode" is selected, the vehicle travels in a state ready to shift to the steering operation without the driver directly participating in the steering operation.

The navigation system 7 is a system that combines the map data stored in the map data storage unit 2 and the GPS13 using satellite communication, sets a destination, generates a travel route from the current position of the host vehicle to the destination, and guides the host vehicle to the destination by making a road. Then, when the travel route is generated, the road map screen is displayed on the navigation display 71 together with the own vehicle icon along with the travel route. As shown in fig. 2, the navigation display 71 is disposed at the center upper position of the instrument panel 22, and has a function of setting a destination by a touch operation of the driver or the like.

As shown in fig. 2, the operation switch 8 is set at a position of a steering wheel hub connecting a steering wheel and a steering shaft in the steering wheel 23 where a driver can operate with fingers while holding the steering wheel. The operation switch 8 includes: a main switch 81, a recovery/acceleration switch 82, a set/coast switch 83, a cancel switch 84, a vehicle room adjustment switch 85, and a lane change assist switch 86. The main switch 81 is a power on/off switch of the system. The recovery/acceleration switch 82 has: a function of restarting the operation at a set vehicle speed before the release after the release of the operation, a function of increasing the set vehicle speed, and a function of stopping and restarting following the preceding vehicle. The set/slide switch 83 has: a function of starting operation at a vehicle speed during traveling, and a function of reducing a set vehicle speed. The cancel switch 84 is a switch for canceling the operation. The shop regulation switch 85 is a switch for switching the set shop. The lane change assist switch 86 is a switch for instructing the start of a lane change when the system confirms the start of the lane change to the driver.

Here, when the main switch 81 is pressed, the vehicle is accelerated or decelerated to a desired vehicle speed, and when the set/coast switch 83 is pressed, the speed limit of the road on which the vehicle is traveling becomes the set vehicle speed, and the driving assistance control operation of the ADAS control unit 4 is started. When the speed limit of the road on which the vehicle is traveling is not detected or when the speed limit assist is turned off, the speed at which the set/coast switch 83 is pressed becomes the set vehicle speed, and the operation of the driving assist control by the ADAS control unit 4 is started.

When the operation of the driving assistance control by the ADAS control unit 4 is canceled, any one of the operations of pressing the cancel switch 84, pressing the main switch 81, and depressing the brake pedal (except when the vehicle is stopped by the vehicle speed/vehicle-to-vehicle control function) is performed.

The control information sensor group 9 acquires information required when the driving assistance control of the ADAS control unit 4 is executed. As shown in fig. 2, the control information sensor group 9 includes: a driver monitor camera 91, a touch sensor 92, a seating sensor 94, and a seatbelt buckle switch 95. As shown in fig. 1, the present invention further includes: torque sensor 93, vehicle speed sensor 96, and accelerator opening sensor 97.

The driver monitor camera 91 sets a camera lens toward the driver, and monitors the forward gaze (face orientation, eye opening/closing) of the driver. The touch sensor 92 (electrostatic capacitance sensor) is set in the steering wheel 23 on which the driver places his hand, and detects that the driver places his hand on the steering wheel 23. The torque sensor 93 is provided in a steering force transmission portion of the steering mechanism, and detects that the driver applies a steering torque and operates the steering wheel. A seating sensor 94 (weight sensor) is provided on the seat cushion 24 of the driver seat to detect that the driver is seated. The belt lock switch 95 detects that the belt is locked. The vehicle speed sensor 96 detects an actual vehicle speed of the host vehicle. When the driver performs an accelerator operation, the accelerator opening sensor 97 detects an accelerator operation amount.

(control Block Structure of mode switching controller)

Hereinafter, the configuration of the control block of the mode switching controller 47 will be described based on fig. 4 showing the mode switching controller 47 included in the ADAS control unit 4.

As shown in fig. 4, the mode switching controller 47 includes "hands-off mode M1" and "hands-on mode M2" as the lane keeping assist modes, and includes a driving condition determination unit 471 and a mode switching unit 472. A switching condition determining unit 473 and a mode switching unit 474 are also provided.

The travel condition determination unit 471 determines whether or not a travel condition is satisfied in which the actual vehicle speed of the host vehicle exceeds the speed limit of the road on which the host vehicle is traveling during the lane-keeping travel in which the "hands-off mode M1" is selected.

When it is determined that the running condition that the actual vehicle speed exceeds the speed limit is satisfied, the mode switching unit 472 switches the lane keeping assist mode from the "hand-off mode M1" to the "hand-held mode M2".

When the "hand mode M2" is selected, the switching condition determination unit 473 determines whether or not the switching condition from the "hand mode M2" to the "hand leaving mode M1" is satisfied. Here, the switching condition from the "hand-held mode M2" to the "hands-off mode M1" is given by a plurality of conditions such as "traveling at a vehicle speed equal to or less than a speed limit", "the driver holds the steering wheel 23", and "no accelerator pedal depression".

When the switching condition from the "handheld mode M2" to the "hands-off mode M1" is satisfied, the mode switching unit 474 switches the lane keeping assist mode from the "handheld mode M2" to the "hands-off mode M1". Here, if all of the plurality of switching conditions are simultaneously satisfied, the switching conditions are satisfied.

The vehicle speed/vehicle-to-vehicle control function in the accelerator/brake assist controller 41 includes a function of allowing the vehicle speed/vehicle-to-vehicle control to be changed by the driver's operation. As shown in fig. 4, the travel condition determination unit 471 has a set vehicle speed change determination unit 471a, and the mode switching unit 472 has a first mode switching unit 472a, in accordance with the set vehicle speed changing function.

The set vehicle speed change determination unit 471a determines whether the driver has performed an operation to increase the set vehicle speed above the speed limit during lane-keeping running in which the "hands-off mode M1" is selected.

If it is determined that the driver has performed an operation to increase the set vehicle speed and the actual vehicle speed is equal to or greater than the vehicle speed determination value (vehicle speed limit + α), the first mode switching unit 472a switches from the "hands-off mode M1" to the "hand-held mode M2".

The vehicle speed/vehicle speed control function in the accelerator/brake assist controller 41 includes a function of allowing the driver to accelerate by an accelerator depression operation. As shown in fig. 4, the travel condition determination unit 471 has an accelerator operation determination unit 471b, and the mode switching unit 472 has a second mode switching unit 472 b.

The accelerator operation determination unit 471b determines whether the driver has performed an accelerator depression operation while the lane keeping driving mode in which the "hand leaving mode M1" is selected. When it is determined that the driver has performed the accelerator depression operation, the driver is requested to hold the steering wheel. Even if it is determined that the driver has performed the accelerator depression operation, the acceleration of the host vehicle corresponding to the accelerator depression operation is not performed and is maintained.

When it is confirmed that the driver has gripped the steering wheel 23, the second mode switching portion 472b is switched from the "hands-off mode M1" to the "hand-held mode M2". In addition, the acceleration of the own vehicle corresponding to the accelerator depression operation by the driver is started after switching to the "handheld mode M2".

The vehicle speed/vehicle-to-vehicle control function of the accelerator/brake assist controller 41 includes a function of, when a speed limit of a road on which the vehicle is traveling is detected, rewriting a set vehicle speed used for vehicle speed/vehicle-to-vehicle control to the detected speed limit. As shown in fig. 4, the driving condition determining unit 471 has a speed limit determining unit 471c, and the mode switching unit 472 has a third mode switching unit 472c, as a function of rewriting the set vehicle speed.

The speed limit determination unit 471c determines whether the newly detected speed limit is lower than the previous speed limit during the lane-keeping running in which the "hand-off mode M1" is selected.

After determining that the set time has elapsed since the speed limit was decreased, the third mode switching unit 472c determines whether the actual vehicle speed exceeds the speed limit. When it is determined that the actual vehicle speed exceeds the speed limit, the mode is switched from the "hands-off mode M1" to the "hands-on mode M2".

(Lane keeping assist mode switching control processing configuration)

The configuration of the lane keeping assist mode switching control process at each step will be described below with reference to fig. 5 showing the flow of the lane keeping assist mode switching control process executed by the mode switching controller 47 provided in the ADAS control unit 4. The process is started by turning on the main switch 81, and is ended by canceling the operation of the driving assistance control.

In step S1, after pressing of the main switch 81 is started, it is determined whether or not the set/coast switch 83 is pressed. If yes (setting/coasting SW is pressed), the process proceeds to step S2, and if no (setting/coasting SW is not pressed), the determination of step S1 is repeated.

In step S2, after determining in step S1 that the set/coast SW is pressed, or determining in step S4 or S19 or S21 as no, it is next determined whether the speed limit of the road on which the vehicle is traveling is not detected, or whether the speed limit assist is turned off. If "yes" (speed limit or the like is not detected), the routine proceeds to step S3, and if "no" (speed limit or the like is detected), the routine proceeds to step S5.

That is, when the speed limit of the road on which the vehicle is traveling is detected and the speed limit assist is turned on, the speed limit is set to the set vehicle speed by the speed limit assist, and the operation of the driving assist control by the ADAS control unit 4 that selects the "hand-held mode M2" is started. On the other hand, when the speed limit of the road on which the vehicle is traveling is not detected or when the speed limit assist is turned off, the speed at which the set/coast switch 83 is pressed becomes the set vehicle speed. Then, the action of the driving assistance control by the ADAS control unit 4 that selects the "hand-held mode M2" is started.

In step S3, after it is determined in step S2 that the speed limit or the like is not detected, the "hold mode M2" is selected as the lane keeping assist mode, and the process proceeds to step S4.

In step S4, after "the handheld mode M2" is selected in step S3, or "no" is determined in step S6, or steps S7, S12, S18, and S24, it is next determined whether or not an operation cancellation condition of the driving assistance control by the ADAS control unit 4 is satisfied. If "yes" (the cancellation condition is satisfied), the routine proceeds to end, and if "no" (the cancellation condition is not satisfied), the routine returns to step S2.

Here, when any of the cancellation conditions (a) pressing the cancel switch 84, (b) pressing the main switch 81, and (c) depressing the brake pedal (except when the vehicle is stopped by the vehicle speed/vehicle-to-vehicle control function) is detected, it is determined that the conditions are satisfied.

In step S5, after it is determined in step S2 that the speed limit or the like is detected, it is next determined whether or not "handheld mode M2" is selected. If "yes" (selection of "hand-held mode M2"), the routine proceeds to step S6, and if "no" (selection of "hand-off mode M1"), the routine proceeds to step S8.

In step S6, after it is determined in step S5 that "handheld mode M2" is selected, it is next determined whether or not a hand-off condition for switching from "handheld mode M2" to "hand-off mode M1" is satisfied. If "yes" (the hand leaving condition is satisfied), the routine proceeds to step S7, and if "no" (the hand leaving condition is not satisfied), the routine proceeds to step S4.

In step S7, after it is determined in step S6 that the hand-off condition is satisfied, the mode is switched from "handheld mode M2" to "hand-off mode M1", and the process proceeds to step S4.

In step S8, after it is determined in step S5 that "hands-off mode M1" is selected, it is next determined whether or not the set vehicle speed is higher than the detected speed limit. If "yes" (set vehicle speed > speed limit), the routine proceeds to step S9, and if "no" (set vehicle speed ≦ speed limit), the routine proceeds to step S14.

In step S9, after it is determined in step S8 that the vehicle speed is set to > the speed limit, it is next determined whether or not the driver has performed an operation to increase the set vehicle speed. If "yes" (operation to raise the set vehicle speed is present), the routine proceeds to step S10, and if "no" (operation to not raise the set vehicle speed) the routine proceeds to step S12.

In step S10, after it is determined in step S9 that the set vehicle speed has been increased, it is next determined whether or not the actual vehicle speed has increased to or above a vehicle speed determination value obtained by adding the error amount α to the vehicle speed limit. If "yes" (actual vehicle speed ≧ vehicle speed determination value), the routine proceeds to step S11, and if "no" (actual vehicle speed < vehicle speed determination value), the routine proceeds to step S4. When the set vehicle speed is increased, the set vehicle speed is increased by a predetermined vehicle speed (for example, 5km/h) when the driver operates the push switch once.

In step S11, after it is determined in step S10 that the actual vehicle speed is equal to or greater than the vehicle speed determination value or that the vehicle speed difference is greater than the vehicle speed threshold in step S13, the mode is switched from "hands-off mode M1" to "hands-on mode M2", and the process proceeds to step S4.

In step S12, after it is determined in step S9 that the set vehicle speed has not been increased, it is next determined whether or not the speed limit of the road on which the vehicle is traveling is newly detected and whether or not a predetermined time has elapsed after the newly detected speed limit has decreased. If "yes" (the set time has elapsed after the vehicle speed reduction is limited), the routine proceeds to step S21, and if "no" (the set time has not elapsed after the vehicle speed reduction is limited), the determination of step S20 is repeated. Here, the "set time" is determined based on a time required from the start of rewriting of the set vehicle speed to the time when the actual vehicle speed converges on the rewritten set vehicle speed when the set vehicle speed is rewritten with a decrease in the limited speed during the limited speed assist.

In step S13, after it is determined in step S12 that the set time has elapsed since the vehicle speed was limited and decreased, it is next determined whether or not the vehicle speed difference obtained by subtracting the limited speed from the actual vehicle speed exceeds a vehicle speed threshold value indicating vehicle speed convergence. The routine proceeds to step S11 if yes (vehicle speed difference > vehicle speed threshold), and proceeds to step S4 if no (vehicle speed difference ≦ vehicle speed threshold).

In step S14, after it is determined in step S8 that the vehicle speed is set to be equal to or less than the speed limit, it is next determined whether or not an accelerator depression operation is performed by the driver. If yes (accelerator depression operation), the process proceeds to step S15, and if no (no accelerator depression operation), the process proceeds to step S4.

In step S15, after it is determined in step S14 that there is an accelerator depression operation, it is next determined whether or not the driver has separated his or her hand from the steering wheel 23. If "yes" (hands are off the steering wheel 23), the routine proceeds to step S16, and if "no" (hands are on the steering wheel 23), the routine proceeds to step S20.

In step S16, after it is determined in step S15 that the hand is separated from the steering wheel 23, the driver is notified by display, broadcast, or the like to place the hand on the steering wheel 23, and the process proceeds to step S16.

In step S17, after the notification to the driver in step S16, it is next determined whether the driver has put his or her hand on the steering wheel 23. If "yes" (hands are on the steering wheel 23), the process proceeds to step S18, and if "no" (hands are off the steering wheel 23), the process proceeds to step S4.

In step S18, after it is determined in step S15 that a hand is placed on the steering wheel 23 or in step S17 that a hand is placed on the steering wheel 23, the control device switches from the "hand leaving mode M1" to the "hand held mode M2" and proceeds to step S19.

In step S19, after switching to "handheld mode M2" in S18, acceleration corresponding to the accelerator depression operation by the driver is started, and the process proceeds to step S4. That is, even if the accelerator-on operation by the driver is detected in step S14, the actual acceleration of the own vehicle is maintained until the switch to the "handheld mode M2" is made.

Next, a description is given of a background art and a solution to the problem. The operation of embodiment 1 will be described as "lane keeping assist mode switching control processing operation" and "mode switching control operation for each traveling condition exceeding the speed limit".

A known driving assist vehicle has a vehicle speed/vehicle speed control function and a lane keeping function as a driving assist function for assisting a driving operation of a driver, and performs lane keeping running while maintaining a single lane on condition that the driver puts his hands on a steering wheel.

This driving assistance vehicle is conditioned on the driver placing his or her hands on the steering wheel, but is required to be able to perform driving assistance without being conditioned on the driver placing his or her hands on the steering wheel, with a further increase in the driving assistance level.

However, in order to increase the level of the driving assistance and to establish the driving assistance that does not require the driver to place his or her hands on the steering wheel, it is necessary to provide a function of releasing the driving assistance that places his or her hands on the steering wheel to the driver when there is a possibility that the driving situation of the lane keeping function cannot be ensured. This is based on the premise that the driver always places his hand on the steering wheel, and the driver can always release the request that the conventional driving assistance system for driving assistance does not have.

In contrast, in the technique described in patent document 1, information is transmitted from the system to the driver only by a display or broadcast notification. Therefore, there are problems as follows: when the driving assistance level is increased and the vehicle is developed for a driving assistance vehicle that does not require hands to be placed on the steering wheel, there is a possibility that the driver cannot be prompted to perform appropriate action if information is transmitted from the system to the driver only by notification.

The present inventors have focused on the point that, in order to receive and reflect transmission information from a system, a driver needs to be alerted not only to a simple notification but also to the driver's attention.

In view of the above, in the driving assistance method of the present disclosure, it is determined whether or not a running condition in which the actual vehicle speed of the host vehicle exceeds the limit speed of the road on which the host vehicle is running is satisfied in the lane-keeping running in which the "hands-off mode M1" allowing the driver to leave the hands from the steering wheel 23 is selected. When it is determined that the running condition that the actual vehicle speed exceeds the speed limit is established, the vehicle switches from the "hands-off mode M1" to the "hand-held mode M2" on condition that the driver places his hands on the steering wheel 23.

For example, in the lane keeping running mode in which the "hand-off mode M1" is selected, if the driver increases the set vehicle speed, or the driver performs an accelerator depression operation, or the speed limit of the road on which the vehicle is running decreases, the actual vehicle speed may exceed the speed limit. In this case, if only a visual or audible notification is given, the driver may leave his or her hands away from the steering wheel 23, and the driver may not be sufficiently alerted, which may delay the instantaneous steering wheel operation. In particular, when the speed limit has changed, the driver may leave the steering wheel 23 with a higher probability than when the driver is operating the vehicle.

On the other hand, when it is determined that the running condition that the actual vehicle speed exceeds the speed limit is satisfied, the mode is switched from the "hands-off mode M1" to the "hand-held mode M2" on the condition that the driver places his or her hands on the steering wheel 23. That is, in a driving scene in which the actual vehicle speed exceeds the limit speed, when the driver moves his hand away from the steering wheel 23, the "hand-held mode M2" is switched to place the driver's hand on the steering wheel 23. Therefore, by switching the mode in which the driver is alerted to the sense of touch, the driver can be reliably prompted to be alerted when the actual vehicle speed exceeds the speed limit. Further, the instantaneous steering wheel operation can be dealt with by placing the driver's hand on the steering wheel 23.

Therefore, in the driving scene in the "hands-off mode M1" in which the driving assistance level is raised, when it is determined that the driving condition in which the attention of the driver needs to be called, the driving assistance level is lowered to the "handheld mode M2" in which the hands of the driver are placed on the steering wheel 23. In other words, by taking the switching to the "handy mode M2" in which the driving assistance level is lowered as a backup measure, the driving assistance system in which the "hands-off mode M1" in which the driving assistance level is raised can be selected can be established. Further, by allowing selection of the "hands-off mode M1" that enables hands-off running similar to automatic driving, running based on appropriate driving assistance with an improved driving assistance level can be prompted.

Here, when the mode is switched from the "hand-off mode M1" to the "hand-held mode M2", the visual or audible notification can be provided by the display change or broadcast performed by the head-up display 61 and the instrument display 62. The following description is made with reference to fig. 6 and 7.

First, the head-up display 61 and the instrument display 62 have: a steering wheel icon display unit, a vehicle speed limit display unit, a set vehicle speed display unit, a message display unit, a lane/own vehicle display unit, and the like. When the "hand leave mode M1" is selected, as shown in fig. 6, the steering wheel icon display unit displays only the icon of the steering wheel, for example, in blue.

On the other hand, when the "hand-held mode M2" is selected, the steering wheel icon display unit is displayed, for example, in green, and the icons of the steering wheel and the hands are displayed, as shown in fig. 7. Then, "please hold the steering wheel" is displayed on the message display unit and broadcast.

Therefore, when switching from the "hand-off mode M1" to the "hand-held mode M2", the driver can be notified that the lane keeping assist mode has been switched by changing the display of the head-up display 61 and the instrument display 62. In addition, it is possible to confirm that the driver has placed his or her hand on the steering wheel 23 by a sensor signal from at least one of the touch sensor 92 and the torque sensor 93.

(Lane keeping assist mode switching control processing action)

The following describes the operation of the lane keeping assist mode switching control process executed by the mode switching controller 47, based on the flowchart shown in fig. 5. In the following description, the actual vehicle speed is referred to as VR, the limit speeds are referred to as VL (n) and VL (n +1), the set vehicle speeds are referred to as VS (n) and VS (n +1), the vehicle speed difference is referred to as Δ V, and the vehicle speed threshold is referred to as Vth.

First, when the main switch 81 is pressed, the speed is increased or decreased to reach a desired set speed. Then, when the set/coast switch 83 is pressed, if the speed limit vl (n) of the road on which the vehicle is traveling is not detected or the speed limit assist is off, the process proceeds to step S1 → S2 → S3 → S4. In step S3, the "handheld mode M2" is selected as the lane keeping assist mode. If the operation cancellation condition of the driving assistance control is not satisfied in step S4, the process returns to step S2. That is, when speed limit vl (n) of the road on which the vehicle is traveling is not detected or when speed limit assist is turned off, the speed at which set/coast switch 83 is pressed becomes set vehicle speed vs (n). Then, the operation of the driving assistance control by the ADAS control unit 4 based on the selection of the "handheld mode M2" is started. After the start of the operation of the driving assistance control, if the state of the speed limit vl (n) is not detected or the speed limit assistance is continuously turned off, the selection of the "hold mode M2" is maintained.

On the other hand, when the set/coast switch 83 is pressed after the main switch 81 is pressed, if the speed limit vl (n) of the road on which the vehicle is traveling is detected and the speed limit assist is turned on, the process proceeds to step S1 → S2 → S5 → S6. In step S5, it is determined whether or not the "handheld mode M2" is selected, and in step S6, it is determined whether or not a switching condition from the "handheld mode M2" to the "hands-off mode M1" is satisfied. That is, when the speed limit vl (n) of the road on which the vehicle is traveling is detected and the speed limit assist is turned on, the speed limit vl (n) is set to the set vehicle speed vs (n) by the speed limit assist, and the operation of the driving assist control by the ADAS control means 4 in which the "hand mode M2" is selected is started. Further, when the switching condition from the "handheld mode M2" to the "hands-off mode M1" is established, the process proceeds from step S6 to step S7 → S4, and in step S7, the mode is switched from the "handheld mode M2" to the "hands-off mode M1".

When the set vehicle speed vs (n) is higher than the detected limit speed vl (n) due to the driver' S operation to raise the set vehicle speed vs (n) during traveling in which the "hands-off mode M1" is selected, the routine proceeds to step S2 → S5 → S8 → S9 → S10. In step S9, it is determined whether or not the driver has performed an operation to raise the set vehicle speed vs (n). In step S10, it is determined whether or not the actual vehicle speed VR has increased to or above a vehicle speed determination value (vehicle speed limit + α).

When it is determined in step S10 that the actual vehicle speed VR has increased to or above the vehicle speed determination value, the flow proceeds from step S10 to step S11 → S4. In step S11, the mode is switched from "hand-off mode M1" to "hand-held mode M2".

During traveling in which the "hands-off mode M1" is selected, the set vehicle speed vs (n) is equal to or lower than the detected limit speed vl (n), but when the driver performs an accelerator depression operation, the routine proceeds to step S2 → S5 → S8 → S14 → S15. In step S14, it is determined whether or not there is an accelerator depression operation by the driver. In step S15, it is determined whether the driver has separated his or her hands from the steering wheel 23.

If it is determined in step S15 that the driver has left his or her hand from the steering wheel 23, the flow proceeds from step S15 to step S16 → S17, and in step S16, the driver is notified by display, broadcast, or the like to place his or her hand on the steering wheel 23. In step S17, it is determined whether the driver has placed his or her hand on the steering wheel 23. If it is determined in step S17 that the driver has placed his or her hand on the steering wheel 23, the flow proceeds from step S17 to step S18, and in step S18, the mode is switched from "hands-off mode M1" to "handheld mode M2". On the other hand, when it is determined in step S15 that the driver has placed his or her hand on the steering wheel 23, the flow proceeds from step S15 to step S18, and in step S18, the mode is switched from "hand-off mode M1" to "hand-held mode M2".

If the switching is made to the "handheld mode M2" in step S18, the flow proceeds from step S18 to step S19 → S4. In step S19, acceleration corresponding to the accelerator depression operation by the driver is started. That is, even if the accelerator depression operation by the driver is detected in step S14, the acceleration is maintained until the switch to the "handheld mode M2" is made, and after the switch to the "handheld mode M2", the acceleration is started.

When the set vehicle speed vs (n) is higher than the detected speed limit VL (n) and the newly detected speed limit VL (n +1) is lower than the current speed limit VL (n) and the set time T has elapsed during traveling in which the "hands-off mode M1" is selected, the routine proceeds to step S2 → S5 → S8 → S9 → S12 → S13.

When it is determined in step S12 that the set time T has elapsed after the decrease in the speed limit VL (n +1) is detected, the flow proceeds from step S12 to step S13, and in step S13, it is determined whether or not a vehicle speed difference Δ V obtained by subtracting the speed limit VL (n +1) from the actual vehicle speed VR exceeds a vehicle speed threshold Vth indicating vehicle speed convergence. If it is determined in step S13 that the vehicle speed difference Δ V is equal to or less than the vehicle speed threshold Vth, the routine proceeds from step S13 to step S4.

On the other hand, when it is determined in step S13 that the vehicle speed difference Δ V > the vehicle speed threshold Vth, the flow proceeds from step S13 to step S11, and in step S11, the mode is switched from the "hands-off mode M1" to the "hand-held mode M2". In step S4, when the operation cancellation condition of the driving assistance control is satisfied, the routine proceeds to end, and the operation of the driving assistance control is cancelled.

As described above, in the lane keeping assist mode switching control process of switching between the "hand leaving mode M1" and the "hand mode M2", the following control processes (a) to (e) are executed.

(a) When the speed limit vl (n) of the road on which the vehicle is traveling is not detected or when the speed limit assist is turned off, selection of the "hands-off mode M1" is prohibited and only the "hand-held mode M2" is selected.

(b) During the lane keeping running in which the "hand-held mode M2" is selected, it is determined whether or not the hand-off condition is satisfied, and when the hand-off condition is satisfied, the mode is switched to the "hand-off mode M1".

(c) In the lane keeping running mode in which the "hand-off mode M1" is selected, when the set vehicle speed vs (n) is higher than the detected limit speed vl (n) due to the driver's operation to raise the set vehicle speed vs (n), the vehicle switches to the "hand-held mode M2" on the condition that the actual vehicle speed VR is equal to or higher than the vehicle speed determination value (limit speed + α).

(d) In the lane keeping running mode in which the "hand-off mode M1" is selected, the set vehicle speed vs (n) is equal to or lower than the detected limit speed vl (n), but when the accelerator depression operation by the driver is performed, the vehicle switches to the "hand-held mode M2" on the condition that the driver places the hand on the steering wheel 23. In addition, after switching to the "hand-held mode M2", acceleration by an accelerator depression operation is started.

(e) In the lane keeping running mode in which the "hand-off mode M1" is selected, when the set vehicle speed vs (n) is higher than the detected speed limit VL (n) because the new lowered speed limit VL (n +1) is detected, the vehicle speed difference Δ V after the set time T has elapsed from the detection exceeds the vehicle speed threshold Vth, and the mode is switched to the "hand-held mode M2".

(mode switching control action for running condition each exceeding limit speed)

The control process (c) of the control processes (a) to (e) is a mode switching control based on an operation to raise the set vehicle speed VS. The following describes the operation of switching control of the lane keeping assist mode based on a change in the set vehicle speed VS operated by the driver, based on the time chart shown in fig. 8.

In lane-keeping running in which the "hands-off mode M1" is selected and the speed limit vl (n) is set as the set vehicle speed vs (n), the driver performs the set vehicle speed changing operation of setting the set vehicle speed vs (n) higher than the speed limit vl (n) 2 times at time t1 and time t 2. In this case, the increase in actual vehicle speed VR is started at time t3 by the operation to increase set vehicle speed vs (n). Then, at time t4, when the actual vehicle speed VR increases to or above the vehicle speed determination value (the speed limit vl (n) + α), the mode is switched from the "hands-off mode M1" to the "hands-on mode M2".

As described above, when the set vehicle speed change operation is performed such that the set vehicle speed vs (n) becomes higher than the limit speed VL during the lane keeping running in which the "hand-off mode M1" is selected, it is a condition for switching to the "hand-held mode M2" that the actual vehicle speed VR increases to the vehicle speed determination value or more.

The control process (d) of the control processes of (a) to (e) is mode switching control based on an accelerator depression operation. Hereinafter, a switching control operation of the lane keeping assist mode based on the accelerator depression operation by the driver will be described based on the time chart shown in fig. 9.

During lane keeping running with the "hands-off mode M1" selected and the speed limit VL set as the set vehicle speed vs (n), the driver performs an accelerator depression operation at time t 1. In this case, at time t1 when the driver performs the accelerator depression operation, the driver is requested to hold the steering wheel 23. Then, when it is confirmed at time t2 that the driver has gripped the steering wheel 23, the mode is switched from the "hands-off mode M1" to the "handheld mode M2".

In this way, when the driver performs an accelerator depression operation during lane keeping running with the "hand-off mode M1" selected, the driver grips the steering wheel 23, and the condition for switching to the "hand-held mode M2" is satisfied. Then, after switching to the "handheld mode M2" at time t2, acceleration of the host vehicle corresponding to the accelerator depression operation by the driver is started, and the actual vehicle speed VR corresponding to the accelerator depression amount is reached at time t 3. That is, the acceleration start of the host vehicle is conditioned on the driver holding the steering wheel 23 and preparing for the steering wheel operation.

The control process (e) among the control processes (a) to (e) is a mode switching control caused by a decrease in the limit speed vl (n). Next, a switching control operation of the lane keeping assist mode based on a change in the speed limit vl (n) of the road on which the host vehicle travels will be described based on the time chart shown in fig. 10.

During lane keeping running with the "hands-off mode M1" selected and the speed limit VL (n) set as the vehicle speed vs (n), the speed limit VL (n +1) newly detected at time t1 is lower than the previous speed limit VL (n). In this case, at time T2 when it is determined that the set time T has elapsed after the newly detected speed limit VL (n +1) has decreased, it is determined whether or not the actual vehicle speed VR exceeds the speed limit VL (n + 1). Then, when it is determined that the actual vehicle speed VR exceeds the limit speed VL (n +1) (Δ V > Vth), the mode is switched from the "hands-off mode M1" to the "hand-held mode M2".

As described above, when the newly detected speed limit VL (n +1) is lower than the previous speed limit VL (n) during the lane keeping running in which the "hand-off mode M1" is selected, the condition for switching to the "hand-held mode M2" is satisfied in which the actual vehicle speed VR does not converge on the speed limit VL (n +1) even if the vehicle waits for the set time T. When the limit speed assist is normally performed, as shown by the broken line characteristic in fig. 10, the limit speed VL (n +1) newly detected at time T1 becomes the set vehicle speed VS (n +1), and the actual vehicle speed VR converges on the limit speed VL (n +1) at time T2 when the set time T has elapsed.

As described above, the driving assistance method and the driving assistance apparatus according to embodiment 1 can exhibit the following effects.

(1) A driving assistance method is a driving assistance method based on a mode switching controller 47, the mode switching controller 47 having a vehicle speed/vehicle-to-vehicle control function and a lane keeping function as driving assistance functions for assisting a driver's driving operation, and switching a lane keeping assistance mode for assisting the host vehicle to maintain the host vehicle in a lane while the host vehicle is traveling, wherein the vehicle speed/vehicle-to-vehicle control function has a function of rewriting a set vehicle speed used for vehicle speed control to a limit speed when the limit speed of a road on which the host vehicle is traveling is detected; as the lane keeping assist mode, during lane keeping running in which the "hands-off mode M1" that allows the driver to leave the hands from the steering wheel 23 is selected, it is determined whether or not a running condition in which the actual vehicle speed VR of the host vehicle exceeds the limit speed vl (n) of the road on which the host vehicle is running is satisfied, and when it is determined that the running condition in which the actual vehicle speed VR exceeds the limit speed vl (n) is satisfied, the "hands-off mode M1" is switched to the "hands-on mode M2" (fig. 4) that is conditioned on the driver placing the hands on the steering wheel 23.

Therefore, in the lane keeping running scene in which the driving assistance level is raised, by lowering the driving assistance level when a situation in which the driver's attention needs to be called, it is possible to provide a driving assistance method that prompts running with appropriate driving assistance.

(2) During the lane-keeping running in which the "hand-off mode M1" is selected, it is determined whether or not a set vehicle speed changing operation is performed by the driver to increase the set vehicle speed vs (n) above the limit speed vl (n), and if it is determined that the driver performs an operation to increase the set vehicle speed vs (n) and the actual vehicle speed VR has increased to or above the vehicle speed determination value obtained by adding the error amount α to the limit speed vl (n), the mode is switched from the "hand-off mode M1" to the "hand-held mode M2" (S9 → S10 → S11 in fig. 5).

Therefore, when the "hands-off mode M1" is selected, if the driver performs a set vehicle speed changing operation to make the set vehicle speed vs (n) higher than the limit speed vl (n), the vehicle speed can be switched to the "hands-on mode M2" on the condition that the actual vehicle speed VR is increased to or above the vehicle speed determination value. Further, during the lane keeping running in which the "hands-off mode M1" is selected, it is possible to have a function of allowing the set vehicle speed vs (n) used for the vehicle speed/vehicle speed control to be changed by the driver's operation.

(3) During the lane keeping driving in which the "hand-off mode M1" is selected, it is determined whether the driver has performed an accelerator depression operation, and when it is determined that the driver has performed the accelerator depression operation, the driver is requested to hold the steering wheel 23, and when it is confirmed that the driver has held the steering wheel 23, the mode is switched from the "hand-off mode M1" to the "hand-held mode M2" (S14 to S18 in fig. 5).

Therefore, when the "hand-off mode M1" is selected, the driver can switch to the "hand-held mode M2" on the condition that the driver grips the steering wheel 23 when the driver performs an accelerator depression operation. Further, the lane keeping running mode in which the "hand leaving mode M1" is selected can have a function of allowing the driver to accelerate by an accelerator depression operation.

(4) When the driver performs the accelerator depression operation while traveling with the "hands-off mode M1" selected, the acceleration of the host vehicle is maintained until the switching is made to the "handheld mode M2", and after the switching is made to the "handheld mode M2", the acceleration of the host vehicle corresponding to the accelerator depression operation of the driver is started (S18 → S19 in fig. 5).

Therefore, when the driver performs an accelerator depression operation while the lane keeping running mode in which the "hand leaving mode M1" is selected, the vehicle can start accelerating after the vehicle has shifted to a state in which the driver can perform a steering operation.

(5) During the lane-keeping running in which the "hand-off mode M1" is selected, it is determined whether or not the newly detected speed limit VL (n +1) is lower than the previous speed limit VL (n), and after the set time T has elapsed since the newly detected speed limit VL (n +1) was determined to be lower, it is determined whether or not the actual vehicle speed VR has exceeded the speed limit VL (n +1), and when it is determined that the actual vehicle speed VR has exceeded the speed limit VL (n +1), the mode is switched from the "hand-off mode M1" to the "hand-held mode M2" (S12 → S13 → S11 in fig. 5).

Therefore, when the "hand-off mode M1" is selected, if the newly detected speed limit VL (n +1) is lower than the previous speed limit VL (n), the vehicle speed can be switched to the "hand-held mode M2" on the condition that the vehicle speed does not converge even after waiting for the set time T. Further, when the speed limit VL (n +1) of the road on which the host vehicle is traveling is newly detected during the lane keeping travel in which the "hand-off mode M1" is selected, the vehicle speed/vehicle-to-vehicle control system can have a function of rewriting the set vehicle speed VS (n +1) used for vehicle speed/vehicle-to-vehicle control to the speed limit VL (n + 1).

(6) When the "handheld mode M2" is selected, a switching condition (hands-off condition) from the "handheld mode M2" to the "hands-off mode M1" is determined. When the switching condition (hands-off condition) is established, switching is made from the "handheld mode M2" to the "hands-off mode M1" (S5 → S6 → S7 in fig. 5).

Therefore, when the "hand-held mode M2" is selected, the route to return to the "hand-off mode M1" is opened, whereby the travel section in which the "hand-off mode M1" is selected during lane-keeping travel can be ensured to be long.

(7) A driving assistance device is provided with a mode switching controller (47), wherein the mode switching controller (47) has a vehicle speed/vehicle-to-vehicle control function and a lane keeping function as a driving assistance function for assisting a driver's driving operation, and switches a lane keeping assistance mode for assisting a host vehicle to maintain a lane while the host vehicle is traveling, and wherein the mode switching controller (47) has a function for rewriting a set vehicle speed used for vehicle speed control to a speed limit when the speed limit of a road on which the host vehicle is traveling is detected, as the vehicle speed/vehicle-to-vehicle control function, and has: a travel condition determination unit 471 that determines whether or not a travel condition in which the actual vehicle speed VR of the host vehicle exceeds the limit speed vl (n) of the road on which the host vehicle is traveling is satisfied during lane-keeping travel in which a "hand-off mode M1" is selected as a lane-keeping assist mode that allows the driver to leave the hand from the steering wheel 23; and a mode switching unit 472 for switching from the "hands-off mode M1" to the "hand-held mode M2" (fig. 4) on condition that the driver places his or her hands on the steering wheel 23 when it is determined that the running condition that the actual vehicle speed VR exceeds the limit speed vl (n) is satisfied.

Therefore, in the lane keeping running scene in which the driving assistance level is increased, by decreasing the driving assistance level when the driver needs to be alerted in a situation, it is possible to provide the driving assistance device that prompts the driver to run with appropriate driving assistance.

The driving assistance method and the driving assistance device according to the present disclosure have been described above based on embodiment 1. However, the specific configuration is not limited to this embodiment 1, and changes, additions, and the like in design are allowed without departing from the spirit of the invention according to each claim of the scope of the claims.

In embodiment 1, an example in which the travel condition determination unit 471 is composed of a set vehicle speed change determination unit 471a, an accelerator operation determination unit 471b, and a speed limit determination unit 471c is illustrated. However, the travel condition determination unit is not limited to the above determination units as long as it is a determination unit that determines whether or not a travel condition in which the actual vehicle speed of the host vehicle exceeds the speed limit of the road on which the host vehicle travels is satisfied during travel in which the "hands-off mode M1" is selected.

In embodiment 1, an example is shown in which the driving assistance method and the driving assistance apparatus of the present disclosure are applied to a driving assistance vehicle equipped with an advanced driving assistance system ADAS that assists the driving operation of the driver. However, the driving assistance method and the driving assistance apparatus of the present disclosure may also be applied to an automated driving vehicle that performs operation assistance control of a driving/braking/steering angle according to a target travel locus when an automated driving mode is selected and travels in Automated Driving (AD).