Patent ID: 12195051

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the invention is described below on the basis of the drawings.FIG.1is a block diagram of a configuration of a vehicle driving mode switching control device1according to the present embodiment. The driving mode switching control device1of the present embodiment is also one embodiment that embodies a vehicle driving mode switching control method according to the present invention.

The driving mode switching control device1of the present embodiment comprises a sensor11, a host vehicle position detection device12, a map database13, in-vehicle equipment14, a navigation device15, a presentation device16, an input device17, a drive control device18, and a control device19, as shown inFIG.1. These devices are connected by, for example, a controller area network (CAN) or another onboard LAN, and are capable of exchanging information with each other.

The sensor11detects a travel state of the host vehicle. Possible examples of the sensor11include, inter alia, a forward camera that captures images of the area forward of the host vehicle, a rearward camera that that captures images of the area rearward of the host vehicle, a forward radar that detects obstacles forward of the host vehicle, a rearward radar that detects obstacles rearward of the host vehicle, a side radar that detects obstacles present on the left and right sides of the host vehicle, a vehicle speed sensor that detects a vehicle speed of the host vehicle, a touch sensor (capacitive sensor) that detects whether or not the driver is holding the steering wheel, and an interior camera that captures images of the driver. One of the plurality of abovementioned sensors may be used as the sensor11, or a combination of two or more sensors may be used. A detection result from the sensor11is outputted to the control device19at predetermined time intervals.

The host vehicle position detection device12comprises a GPS unit, a gyro sensor, a vehicle speed sensor, etc. The host vehicle position detection device12detects radio waves transmitted from a plurality of satellite communications using the GPS unit, and periodically acquires position information for a target vehicle (the host vehicle). In addition, the host vehicle position detection device12detects a current position of the target vehicle on the basis of the acquired position information for the threshold value, angle change information acquired from the gyro sensor, and the vehicle speed acquired from the vehicle speed sensor. The position information for the target vehicle detected by the host vehicle position detection device12is outputted to the control device19at predetermined time intervals.

The map database13is a memory that stores three-dimensional high-precision map information including information on the positions of various facilities and specific locations, and that can be accessed from the control device19. The three-dimensional high-precision map information is map information in which information on curved roads, the sizes of curves thereof (e.g., curvature or radius of curvature), and detailed and high-precision positional information, such as that of road junctions, branching points, toll plazas, and locations where the number of lanes is reduced, is associated with map information as three-dimensional information.

The in-vehicle equipment14is a variety of equipment installed in the vehicle, and is actuated through driver operation. Examples of such in-vehicle equipment include a steering wheel, an accelerator pedal, a brake pedal, direction indicators, wipers, lights, a horn, and other specific switches. When the in-vehicle equipment14is operated by the driver, related operation information is outputted to the control device19.

The navigation device15acquires current position information for the host vehicle from the host vehicle position detection device12, superimposes the position of the host vehicle over map information for guidance, and displays the result on a display or the like. In addition, a function of the navigation device15is, when the driver inputs a destination, to calculate a route to the destination and guide the driver along the set route. Using this navigation function, the navigation device15displays a route to the destination on the map of the display and notifies the driver of recommended travel actions on the route by voice or the like.

The presentation device16includes various displays such as the display provided to the navigation device15, a display built into a rearview mirror, a display built into a meter part, and a head-up display projected onto the windshield. In addition, the presentation device16includes devices other than displays, such as a speaker of an audio device and a seat device having a vibrating body embedded therein. The presentation device16informs the driver of various presentation information under the control of the control device19.

The input device17is a device such as, for example, a button switch that allows manual input by the driver, a touch panel placed on a display screen, or a microphone that allows voice input by the driver. In the present embodiment, the driver can operate the input device17to input settings information for presentation information presented by the presentation device16.FIG.2is a front view of part of the input device17of the present embodiment, showing an example of a group of button switches placed in a location such as a spoke of the steering wheel.

The input device17shown is a button switch used to set autonomous travel control functions (an autonomous speed control function and an autonomous steering control function) of the control device19to ON, OFF, etc. The input device17of the present embodiment comprises a main switch171, a resume acceleration switch172, a set coast switch173, a cancel switch174, a vehicle-to-vehicle adjustment switch175, and a lane change assist switch176.

The main switch171is a switch that turns ON and OFF a power source of a system that realizes the autonomous speed control function and the autonomous steering control function of the control device19. The resume acceleration switch172is a switch for, inter alia, restarting the autonomous speed control function after the autonomous speed control function was stopped (OFF) to a pre-OFF set speed raising the set speed, and causing the host vehicle to set off again under control of the control device19after the host vehicle has stopped following a preceding vehicle. The set coast switch173is a switch that, inter alia, starts the autonomous speed control function at a traveling speed and lowers the set speed. The cancel switch174is a switch that turns OFF the autonomous speed control function. The vehicle-to-vehicle adjustment switch175is a switch for setting a vehicle-to-vehicle distance to the preceding vehicle, e.g., a switch that selects one from a plurality of setting levels including short distance, medium distance, and long distance. The lane change assist switch176is a switch for indicating (approving) a start of a lane change when the control device19confirms the start of a lane change with the driver. After the start of the lane change has been approved, the approval of the lane change proposal by the control device19can be canceled by pressing the lane change assist switch176for longer than a predetermined time.

In addition to the group of button switches shown inFIG.2, a direction-indicating lever of a direction indicator or a switch of other in-vehicle equipment14can be used as the input device17. Another possible configuration is, for example, when the control device19proposes whether or not to perform a lane change under autonomous control, the driver inputs approval or permission to change lanes by turning on the switch of a direction indicator. Another possible configuration is, when the control device19proposes whether or not to perform a lane change under autonomous control and the driver operates a direction-indicating lever, the lane change performed is not the proposed lane change, but a lane change toward the direction in which the direction-indicating lever was operated. Settings information input via the input device17is outputted to the control device19.

The drive control device18controls host vehicle travel. For example, when the host vehicle travels steadily at the set speed under the autonomous speed control function, the drive control device18controls actuation of a drive mechanism (including actuation of an internal combustion engine in an engine automotive vehicle, actuation of a travel motor in an electric automotive vehicle, and torque distribution between the internal combustion engine and the travel motor in a hybrid automotive vehicle) and brake actuation in order to maintain acceleration, deceleration, and travel speed so that the host vehicle reaches the set speed. In addition, when the host vehicle is following the preceding vehicle under the autonomous speed control function, the drive control device18controls the actuation of the drive mechanism and brake actuation for realizing an acceleration speed and travel speed so that the vehicle-to-vehicle distance between the host vehicle and the preceding vehicle remains constant.

Under the autonomous steering control function, the drive control device18executes steering control for the host vehicle by controlling actuation of a steering actuator in addition to controlling the actuation of the drive mechanism and the brake as described above. For example, when executing lane-keeping control under the autonomous steering control function, the drive control device18detects lane markers in a host vehicle lane in which the host vehicle is traveling, and controls a width-direction travel position of the host vehicle so that the host vehicle travels in a predetermined position in the host vehicle lane. In addition, when executing lane change assist under a lane change assist function (described hereinafter), the drive control device18controls the width-direction travel position of the host vehicle so that the host vehicle changes lanes. Furthermore, when executing right/left turning assist under the autonomous steering control function, the drive control device18performs travel control for turning right or left at an intersection or the like. The drive control device18controls host vehicle travel according to an indication from the control device19(described hereinafter). In addition, other known methods can also be used as the method by which the drive control device18controls travel.

The control device19comprises, inter alia, a read only memory (ROM) storing programs for controlling host vehicle travel, a central processing unit (CPU) that executes the programs stored in the ROM, and a random access memory (RAM) that functions as an accessible storage device. Other components that can be used as actuation circuits, instead of or in addition to the central processing unit (CPU), include, inter alia, a micro processing unit (MPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), and a field programmable gate array (FPGA).

By using the CPU to execute the programs stored in the ROM, the control device19realizes a travel information acquisition function of acquiring information pertaining to a travel state of the host vehicle, a travel scenario determination function of determining a travel scenario of the host vehicle, and an autonomous travel control function of autonomously controlling the travel speed and/or steering of the host vehicle. The functions of the control device19shall be described below.

The travel information acquisition function of the control device19is a function for the control device19to acquire travel information pertaining to the travel state of the host vehicle. For example, the control device19acquires, as travel information, image information for the host vehicle exterior imaged by the forward camera, rearward camera, and side cameras of the sensor11. In addition, the control device19acquires, as travel information, detection results from the forward radar, rearward radar, and side radars. Furthermore, the control device19also acquires, as travel information, host vehicle speed information detected by the vehicle speed sensor of the sensor11and image information for the driver's face imaged by the interior camera.

Furthermore, the control device19acquires current position information for the host vehicle as travel information from the host vehicle position detection device12. In addition, the control device19acquires the set destination and a route to the destination as travel information from the navigation device15. Furthermore, the control device19acquires information on curved roads, the sizes of the curves thereof (e.g., curvature or radius of curvature), and position information such as that of junctions, branching points, toll plazas, and locations where the number of lanes is reduced, as travel information from the map database13. Additionally, the control device19acquires information on operation of the in-vehicle equipment14by the driver as travel information from the in-vehicle equipment14. What has been described above is the travel information acquisition function realized by the control device19.

The travel scenario determination function of the control device19is a function of referring to a table stored in the ROM of the control device19to determine a travel scenario in which the host vehicle is traveling. In the table stored in the ROM of the control device19, for example, travel scenarios suitable for changing lanes or overtaking and conditions for determining such scenarios are stored for each travel scenario. The control device19refers to the table stored in the ROM to determine whether or not the travel scenario of the host vehicle is, for example, a travel scenario suitable for changing lanes or overtaking.

Four conditions, namely, “preceding vehicle ahead,” “preceding vehicle speed less than host vehicle set speed,” “preceding vehicle to be reached within a predetermined time,” and “lane-changing direction is not a lane-change-prohibiting condition,” are set as determination conditions for “scenario of catching up to the preceding vehicle.” In this case, the control device19assesses whether or not the host vehicle meets the above conditions on the basis of factors such as, for example, a detection result from the forward camera or forward radar included in the sensor11, the host vehicle speed detected by the vehicle speed sensor, and position information for the host vehicle from the host vehicle position detection device12. When the above conditions are met, the control device19determines that the host vehicle is in a “scenario of catching up to the preceding vehicle.” What has been described above is the travel scenario determination function realized by the control device19.

The autonomous travel control function of the control device19is a function for the control device19to autonomously control host vehicle travel without depending on the driver's operation. The autonomous travel control functions of the control device19include the autonomous speed control function by which the travel speed of the host vehicle is autonomously controlled, and the autonomous steering control function by which the steering of the host vehicle is autonomously controlled. The autonomous speed control function and the autonomous steering control function of the present embodiment shall be described below.

The autonomous speed control function is a function by which, when a preceding vehicle is detected, the vehicle speed set by the driver is designated as an upper limit and the host vehicle travels following the preceding vehicle while vehicle-to-vehicle control is performed so as to maintain a vehicle-to-vehicle distance that corresponds to the vehicle speed, and when no preceding vehicle is detected, the host vehicle travels steadily at the vehicle speed set by the driver. The former is referred to as vehicle-to-vehicle control and the latter is referred to as steady-speed control. The autonomous speed control function may include a function by which a speed limit of the road being traveled on is detected by the sensor11from a road sign or the speed limit is acquired from the map information of the map database13and the speed limit is automatically used as the set vehicle speed.

To activate the autonomous speed control function, the driver first inputs a desired travel speed by operating the resume acceleration switch172or the set coast switch173of the input device17shown inFIG.2. For example, if the set coast switch173is pressed while the host vehicle is traveling at 70 km/h, the current travel speed will be set at that level, but if the speed desired by the driver is 80 km/h, the set speed may be raised by pressing the resume acceleration switch172multiple times. The symbol “+” provided to the resume acceleration switch172is to indicate that the switch will increase the set value. Conversely, if the speed desired by the driver is 60 km/h, the set speed may be lowered by pressing the set coast switch173multiple times. The symbol “−” provided to the set coast switch173is to indicate that the switch will reduce the set value. In addition, for the vehicle-to-vehicle distance desired by the driver, the vehicle-to-vehicle adjustment switch175of the input device17shown inFIG.2can be operated to select one from the multiple setting levels including, for example, short distance, medium distance, and long distance.

Steady-speed control, in which the host vehicle travels steadily at the speed set by the driver, is executed when the forward radar or the like of the sensor11has detected that there is no preceding vehicle forward in the host vehicle lane. In steady-speed control, actuation of drive mechanisms such as the engine and brake are controlled by the drive control device18while vehicle speed data provided by the vehicle speed sensor is fed back, so that the set travel speed is maintained.

Vehicle-to-vehicle control, in which the host vehicle travels following a preceding vehicle while vehicle-to-vehicle control is performed, is executed when the presence of a preceding vehicle forward in the host vehicle lane is detected by, inter alia, forward radar of the sensor11. In vehicle-to-vehicle control, actuation of drive mechanisms such as the engine and brake are controlled by the drive control device18while vehicle-to-vehicle distance data detected by the forward radar is fed back, so that the set vehicle-to-vehicle distance is maintained with the set travel speed as an upper limit. When the preceding vehicle stops while the host vehicle is traveling under vehicle-to-vehicle control, the host vehicle also stops following the preceding vehicle. If the preceding vehicle sets off within, for example, 30 seconds of the host vehicle stopping, the host vehicle also sets off and following travel under vehicle-to-vehicle control is started again. When the host vehicle has been stopped for more than 30 seconds, the host vehicle does not automatically set off even if the preceding vehicle sets off, and following travel under vehicle-to-vehicle control is started again if the resume acceleration switch172is pressed or the acceleration pedal is pressed after the preceding vehicle has set off.

The autonomous steering control function is a function for executing steering control for the host vehicle by controlling the actuation of the steering actuator. The autonomous steering control function of the present embodiment includes, inter alia: (1) a lane-keeping function (vehicle-to-vehicle width direction maintenance function) of controlling steering and assisting the driver's steering wheel operation so that the host vehicle travels, for example, near the center of the lane; (2) a lane change assist function of controlling steering when the driver operates a blinker lever, and assisting steering wheel operation necessary for a lane change; (3) an overtaking assist function of controlling steering and assisting an overtaking operation when a vehicle slower than the set vehicle speed is detected ahead, a confirmation that the driver will perform an overtaking operation is made via the display, and the driver operates the approval switch; and (4) a route travel assist function of controlling steering and assisting a lane change when the driver has set a destination in the navigation device or the like, the host vehicle reaches a lane change point needed to travel along a route, a confirmation that the driver will perform a lane change is made via the display, and the driver operates the approval switch.

The lane change assist function of the autonomous steering control function shall now be described.FIG.3is a plan view of an example of lane change control (the lane change assist function) executed by the control device19of the present embodiment. As shown inFIG.3, when the driver operates a blinker lever of a host vehicle V1, the control device19causes a direction indicator to illuminate and starts a lane change operation (a series of autonomous lane change processes; hereinafter also referred to as “LCP”) when preset lane change start conditions are met. The control device19determines whether the lane change start conditions are satisfied on the basis of various pieces of travel information acquired by the sensor11. There are no particular limitations as to the lane change start conditions; one possible example is that all of the following conditions (1) to (8) be satisfied: (1) the vehicle is in a lane-keeping mode of a hands-on mode, (2) the vehicle is in a hands-on determination mode, (3) the vehicle is traveling at a speed of 60 km/h or higher, (4) there is a lane in a lane change direction, (5) there is enough space to allow a lane change in the lane to which the vehicle will change lanes, (6) the type of lane marker is such that a lane change is allowed, (7) the radius of curvature of the road is 250 m or more, and (8) 1 second has not yet passed since the driver has operated a direction indication lever. When the control device19assesses that the lane change start conditions are satisfied by the lane change assist function even 21 without an indication from the driver, the control device19may suggest a lane change to the driver by notifying the driver via the presentation device16.

Of particular note is that the term “lane-keeping mode of a hands-on mode” refers to a state in which the autonomous speed control function and the lane-keeping function of the autonomous steering control function are being executed, and holding of the steering wheel by the driver is detected. The term “during hands-on determination” refers to a state in which the driver continues to hold the steering wheel.

When the lane change start conditions are met, the control device19starts a lane change operation LCP. The lane change operation LCP of the present embodiment, as shown inFIG.3, includes sideways movement of the host vehicle V1to an adjacent lane L2, and a lane change maneuver (hereinafter also referred to as “LCM) of actually moving to the adjacent lane L2. While executing the lane change operation LCP, the control device19presents information indicating that a lane change is being performed under autonomous control to the driver via the presentation device16, and calls attention to the surroundings. When the lane change maneuver LCM is completed, the control device19extinguishes the direction indicator and starts an action such as executing the function of keeping the host vehicle in the adjacent lane L2. A lane change operation LCP refers to a period from when the direction indicator has been illuminated by operation of the blinker lever to when the direction indicator has been extinguished, and a lane change maneuver LCM refers to a period from when the host vehicle V1begins to cross a boundary line between a host vehicle lane L1and the adjacent lane L2until the crossing is finished.

Of particular note is that a plurality of standards are set for the driving assist mode realized by the autonomous travel control function of the present embodiment. The term “driving assist mode” means a form or style of assistance in driving operation assist. In the present embodiment, the degree of assistance is referred to as the assist level. The assist levels of the driving assist mode determine the extent to which the control device19is involved in controlling the travel actions of the vehicle; in other words, the extent to which driver-performed manual operation is involved. The control device19realizes driving operation assistance determined by each assist level when autonomously controlling host vehicle travel by combining autonomous control of the travel speed using the autonomous speed control function and autonomous control of steering operations using the autonomous steering control function.

The assist levels of the present embodiment can be set on the basis of, for example, driving automation levels defined in SAE J3016: SEP2016, Taxonomy and Definitions for Terms Related to Driving Automation Systems for On-Road Motor Vehicle published by the Society of Automotive Engineers (SAE) of America. For example, assist level0defined by SAE is where the driver executes all driving tasks necessary for travel actions. Similarly, the assist level1is where the control device19continuously executes either autonomous speed control or autonomous steering control (but not both at the same time) in a specific limited area, and the driver executes either the travel speed of the host vehicle or steering of the host vehicle by steering (but not both at the same time). Similarly, the assist level2is where the control device19continuously executes autonomous speed control and autonomous steering control in a specific limited area, and the driver executes either the travel speed of the host vehicle or steering of the host vehicle by steering (but not both at the same time). Similarly, the assist level3is where the control device19continuously executes all driving tasks in a limited area. Similarly, the assist level4is where the control device19executes all driving tasks and the response to cases where continuing control is difficult is to continuously execute the tasks in a limited area. Similarly, the assist level5is a standard at which the control device19continuously and indefinitely executes all driving tasks and responds to cases where continuing control is difficult.

There are no particular limitations as to the assist level1set in the present embodiment; this assist level corresponds to the control device19controlling the travel speed of the host vehicle by autonomous speed control. Similarly, the assist level2corresponds to the control device19controlling steering of the host vehicle by autonomous steering control in addition to autonomous speed control. Hands-on mode and hands-off mode are included in the assist level2. The term “hands-on mode” refers to a state in which autonomous steering control is not actuated as long as the driver is not holding the steering wheel, and the term “hands-off mode” refers to a state in which autonomous steering control actuates even if the driver takes their hands off the steering wheel. In addition, there are no particular limitations as to the assist level2set in the present embodiment; in this assist level, autonomous speed control and autonomous steering control for eyes-on mode are executed.

There are no particular limitations as to the assist level3set in the present embodiment; this assist level corresponds to the control device19executing autonomous speed control and autonomous steering control for eyes-on mode in addition to hands-off mode in the assist level2. The term “eyes-on mode” refers to a state in which autonomous speed control and autonomous steering control do not activate when it is detected that the driver is monitoring the surroundings (particularly forward). In eyes-on mode, the driver is imaged by the interior camera and the driver line of sight and facial orientation are monitored. If the driver is not in a situation suited to monitoring of the surroundings, such as when the driver's line of sight is not forward or the driver's face is not oriented to the front, a forward caution warning is activated. The term “eyes-off mode” refers to a state in which the surroundings are monitored and autonomous speed control and autonomous steering control are activated by the control device19under certain conditions, even if it is not detected that the driver is monitoring the surroundings.

In the assist level2of the eyes-on mode, driving operations are controlled by the control device19, but the driver monitors the surroundings and has the responsibility of driving. By contrast, in the assist level3of the eyes-off mode, the control device19also monitors the surroundings in addition to controlling driving operations, and the responsibility of driving is temporarily transferred to the control device19.

FIG.4is a block diagram of an outline of state transitions of the functions established in the control device19. The term “system” shown in this diagram means an autonomous travel control system realized by the control device19. When the main switch171inFIG.2is set to ON from the system OFF state shown in the diagram, the system enters a standby state. From this standby state, by setting the set-coast switch173or the resume acceleration switch172shown inFIG.2to ON, autonomous speed control in the driving assist mode (the assist level1) is activated. As a result, the above-described constant speed control or vehicle-to-vehicle control is started, and the driver can cause the host vehicle to travel simply by operating the steering wheel without depressing the accelerator or brake. The system OFF state and standby state are equivalent to a manual driving mode in which the driver performs driving operations, and the system ON state is equivalent to a driving assist mode in which the driving operations by the driver are assisted by the autonomous travel control system realized by the control device19.

When transitioning from the manual driving mode to the driving assist mode, the control device19controls the switching of the assist level in the driving assist mode. Assist level switching control is executed when the conditions for establishing each assist level are satisfied. There are no particular limitations as to the conditions for establishing switching control; these conditions include: road conditions and geographical conditions such as whether the host vehicle is traveling on a road exclusively for automotive vehicles, a road that is structurally separated from oncoming lanes, or a road for which there is a high-precision map, whether there are toll gates, exits, merges, intersections, or points where the number of lanes is reduced within a specified range ahead, whether lane markers on both sides of the host vehicle are detected, and whether the host vehicle is traveling near the center of the lane; as well as environmental conditions such as whether the host vehicle is traveling at or below the speed limit, whether the wipers are operating at a high speed (HI), whether the driver is holding the steering wheel, whether the acceleration pedal is being depressed, whether the driver has operated the brake, and whether the driver could be detected by a driver monitor camera; and other conditions.

For example, if the conditions for autonomous steering control are satisfied while the autonomous speed control (the assist level1) shown inFIG.4is being executed, the system shifts to autonomous steering control with hands-on mode (the assist level2β). If the conditions for the hands-off mode are satisfied while autonomous steering control with hands-on mode (the assist level2β) is being executed, the system shifts to autonomous steering control with hands-off mode (the assist level2α). By contrast, if, for example, the conditions for the hands-off mode are not met while autonomous steering control with hands-off mode (the assist level2α) is being executed, hands-off mode is canceled and the system shifts to autonomous steering control with hands-on mode (the assist level2β). In addition, if the conditions for autonomous steering control are not met while autonomous steering control with hands-on mode (the assist level2β) is being executed, autonomous steering control is canceled and the system shifts to autonomous speed control (the assist level1). When the conditions for autonomous speed control are no longer met while autonomous speed control (the assist level1) is being executed, the system transitions from the driving assist mode to the manual driving mode and enters a standby state.

The transition from the assist level1to the assist level2, the transition from the assist level2to the assist level1, and the transition from the driving assist mode to the manual driving mode are autonomously switched and controlled by the control device19when conditions for satisfying switching control are met. However, in the transition from the assist level2to the assist level3, as described above, the driving responsibility is temporarily transferred from the driver to the control device19. Therefore, when the conditions for the hands-off mode and eyes-off mode are satisfied while hands-off mode and eyes-on mode (the assist level2α) are being executed, the system immediately enters the standby state without transitioning to the assist level3. When, for example, the driver presses an activation switch for the assist level3in the standby state, it is preferable that the system shifts to hands-off mode and eyes-off mode (the assist level3). The pressing of the activation switch is not a limitation on the transition to the assist level3; driver operation may be omitted, as necessary.

The system turns OFF when the main switch171is set to OFF in any of the following states: hands-off mode and eyes-off mode, autonomous steering control with hands-off mode, autonomous steering control with hands-on mode, autonomous speed control, and the standby state.

The control device19of the present embodiment autonomously controls the switching of the manual driving mode and the driving assist mode, or the assist level in the driving assist mode, when the satisfying conditions are met as described above. However, when operation of the steering wheel, the acceleration pedal, the brake pedal, etc., by the driver is detected while the driving assist mode is active, the control device19transfers driving responsibility including control of driving operations to the driver, and controls switching (overrides) from the driving assist mode to the manual driving mode. There are cases where overrides are performed intentionally on the basis of the driver's intention, but there are also cases where overrides are requested on the basis of a vehicle assessment, such as when an abnormality is detected in the autonomous travel control system.

The prior art citations given in the background-art citations indicate that in cases where switching is controlled from a first driving assist mode of hands-on mode or from a second driving assist mode of the hands-off mode to the manual driving mode, there is determined to be an override when both driver grip on a steering wheel and the steering torque equal to or greater than a preset threshold value are detected, and the system causes a transition from the first driving assist mode or the second driving assist mode to the manual driving mode. However, since there is determined to be an override due to the same conditions in both the first driving assist mode and the second driving assist mode, problems are encountered, such as that the transition to the manual driving mode is not performed smoothly, and conversely, an erroneous detection is made. Therefore, override determination is preferably performed in accordance with the travel assist level.

In view of the above circumstances, in the vehicle driving mode switching control device1according to the present embodiment, in cases where switching from the driving assist mode to the manual driving mode is controlled, an input value from the driver with respect to the steering wheel of the vehicle is detected, and when the input value from the driver is equal to or greater than a threshold value, control over switching from the driving assist mode to the manual driving mode is allowed (an override). In such instances, the threshold value for the driving assist mode in which the assist level is relatively high is set higher than the threshold value for the driving assist mode in which the assist level is relatively low. An embodiment of override control using the control device19is described below usingFIGS.5A to8C.

FIG.5Ais a diagram for illustrating a relationship between state transitions of the control device19and threshold values. In the present embodiment, the assist level1, the assist level2, and the assist level3are set in the driving assist mode, and furthermore, the assist level2β of hands-on mode and the assist level2α of the hands-off mode are set for the assist level2.FIG.5Ashows the assist level becoming progressively higher from the left toward the right.

In cases of an override from the driving assist mode to the manual driving mode, the control device19detects input values from the driver for the steering wheel, the acceleration pedal, the brake pedal, etc., and determines whether or not to activate an override. Upon determining that an override is to be actuated, an override will be activated without being intended by the driver if the detected input value does not depend on the driver's intention, e.g., if there is an erroneous detection due to a mishap such as contact with clothing. In order to prevent such a situation, a threshold value Th is set at which it can be assessed that the driver has operated the steering wheel, accelerator pedal, brake pedal, etc., with the intention of taking over driving. When an input value exceeding the threshold value Th is detected, the control device19activates an override. In addition, the driving load on the driver during an override to the manual driving mode increases commensurately with a rise in the assist level of the driving assist mode. Therefore, in order to more accurately assess the driver's intention to take over, the threshold value Th is set higher commensurately with respect to an increase in the assist level.

In the example shown in Figure SA, the assist level2α and the assist level3are both for the hands-off mode, but in the assist level2α of the eyes-on mode, the driver can monitor the surroundings and immediately take over driving operations. By contrast, in the assist level3of the eyes-off mode, since the driving responsibility has been temporarily transferred to the control device19, the driver is not necessarily able to immediately take over driving operation. Therefore, a threshold value Th3for cases of an override from the assist level3to the manual driving mode is set higher than a threshold value Th2α for cases of an override from the assist level2α to the manual driving mode (TL2α<TL3).

By imposing a high input load on the threshold value Th3of the assist level3, it is possible to minimize erroneous detection and more accurately assess the driver's intention to take over. Conversely, at the threshold value Th2α of the assist level2α, since the driver is able to immediately take over driving operations, the driver can smoothly take over if the input load is lower than the threshold value Th3of the assist level3. Thus, a threshold value Th is set for each assist level, and the threshold value for the driving assist mode in which the assist level is relatively high is set higher than the threshold value for the driving assist mode in which the assist level is relatively low, thereby making it possible to perform an override determination corresponding to the travel assist level.

As described above, there are also cases in which an override switching from the driving assist mode to the manual driving mode is intentionally carried out on the basis of the driver's intention, but there are also cases in which an override is requested on the basis of a vehicle assessment at times such as when a fault is detected in the system of the host vehicle. In cases in which an override is activated on the basis of a vehicle assessment, it is preferable that the driver be notified that control over switching from the driving assist mode to the manual driving mode will be executed.

There are no particular limitations as the form of the notification given to the driver; before an abnormality is detected in the system of the host vehicle and an override to the manual driving mode is executed, a warning message such as “please operate the steering wheel” requesting the driver to grip the steering wheel is displayed on the presentation device16, such as, for example, a display provided on the instrument panel of the host vehicle, as shown in the lower right ofFIG.5B. After an override to the manual driving mode has been executed, a guidance message such as “switched to manual driving mode” is displayed, as shown in the lower left ofFIG.5B. In addition to these displays, actions such as outputting voice guidance and emitting a warning sound may be executed. Such actions can reduce driver anxiety when an override is activated on the basis of a vehicle assessment. These notifications to the driver are not an essential feature in the present invention, and may be omitted, as necessary.

Input values from the driver used in override determination can be detected from the circumstances in which the driver operates onboard devices such as the steering wheel, accelerator pedal, and brake pedal. In the present embodiment, an input value to the steering wheel by the driver is used for override determinations, but a configuration may also be adopted in which input values for the acceleration pedal, the brake pedal, a system activation switch, etc., are detected and an override is determined from these input values for a plurality of devices.

FIG.6is a front view and cross-sectional view of a steering wheel2according to the present embodiment. As shown in the front view ofFIG.6, a sheet-form sensor22such as a pressure-sensitive sensor is provided inside the steering wheel2of the present embodiment, and is disposed along a circumferential direction of a rim21(dashed-line arrows) in order to identify that the driver is in contact with, gripping, or otherwise handling the steering wheel. The sensor22is divided into a right sensor22R located on the right side from the center of the steering wheel, and a left sensor22L located on the left side from the center of the steering wheel. The right sensor22R detects input values to the right, above, and below from the center of the steering wheel, and similarly, the left sensor22L detects input values to the left, above, and below from the center of the steering wheel. The sensor22is also divided into a front surface sensor22S located on a front side on which the steering wheel2faces the driver, and a back surface sensor22B located on a back side facing the windshield, as shown in the cross-sectional view ofFIG.6. The front surface sensor22S detects values of input on the front side of the steering wheel, and similarly, the back surface sensor22B detects values of input on the back side of the steering wheel. In the present embodiment, the sensor22is arranged as being divided into four parts: left, right, front, and back, but this configuration is not provided by way of limitation on the arrangement of the sensor22.

When an input value to the steering wheel by the driver is detected using the sensor22installed inside the steering wheel2, the control device19identifies whether the driver is in a state of gripping or contacting the steering wheel2. The contacting state involves merely touching the steering wheel2, while the gripping state is a state of consciously gripping the steering wheel2; therefore, the driver input load is higher in the gripping state than in the contacting state. On the basis of the identified state, the control device19determines whether or not the input value from the driver is equal to or greater than a threshold value Th. For example, in a case of executing an override from the assist level2α to the manual driving mode, the input value is determined to be equal to or greater than the threshold value Th2α when it is identified that “one hand of the driver is in a contacting state,” in order for the driver to smoothly take over with a low input load. By contrast, in cases of an override from the assist level3to the manual driving mode, the driver's intention to take over must be reliably confirmed; therefore, an input load higher than the threshold value Th2α at which “one hand of the driver is in a contacting state” is imposed, and whether or not the input value is equal to or greater than the threshold value Th3is determined. The method of identifying the gripping state and the contacting state shall be described hereinafter.

For example, if “at least one hand of the driver is in a gripping state,” the control device19determines that the input value is equal to or greater than the threshold value Th3. When the driver is identified to be in a gripping state with any region above, below, left, or right on the steering wheel2as shown inFIG.7A, at least one hand of the driver can be detected as being in a gripping state. If at least one hand is in a gripping state, it can be assessed that the driver is intentionally touching the steering wheel2, and control can therefore be appropriately given to the driver even in the case of an override from the assist level3to the manual driving mode.

The control device19may determine that the input value is equal to or greater than the threshold value Th3if “both hands of the driver are in a contacting state.” When the driver is identified to be in a contacting state with two of regions above, below, left, or right on the steering wheel2as shown inFIG.7B, both hands of the driver can be detected as being in a contacting state. If both hands of the driver are in a contacting state, override can be activated with the position of the steering wheel2being in a stable state. In addition, since the control device identifies whether or not the driver is in a contacting state in two areas, even if a contacting state is detected due to an input value that does not depend on the driver's intention, such as, for example, when the driver's knee is in contact with the lower area of the steering wheel2, the input load will not be determined to be equal to or greater than the threshold value Th3unless a contacting state is detected in areas other than the lower area. Therefore, it is possible to minimize determination of an input value equal to or greater than the threshold value Th3due to erroneous detection of an input value that does not depend on the driver's intention. In the present embodiment, since the front surface sensor22S and the back surface sensor22B are installed inside the steering wheel2, contacting states can be detected from both the front and back surfaces of the steering wheel2, as shown in the lower left drawing ofFIG.7B.

The control device19may determine that the input value is equal to or greater than the threshold value Th3if “one hand of the driver is in a gripping state and the other hand is in a contacting state.” When the driver is identified to be in a gripping state with any one of the regions above, below, left, or right on the steering wheel2and identified to be in a contacting state with another area as shown inFIG.7C, the one hand of the driver can be detected to be in a gripping state and the other hand can be detected to be in a contacting state. Even if the input value identified with a contacting state is that does not depend on the driver's intention, such as in the case of, for example, contact from clothing, if the one hand is in a gripping state, it is assessed that the driver is touching the steering wheel2with the intention of taking over driving, and override can be appropriately activated. In the present embodiment, since the front surface sensor22S and the back surface sensor22B are installed inside the steering wheel2, an input value can be detected from the back surface of the steering wheel2as well, as shown in the lower left drawing ofFIG.7C.

An area of contact between the driver and the steering wheel2can be used to identify whether the driver is in a gripping state or a state of contacting the steering wheel2. For example, a gripping state is identified when the area of contact between the driver's fingers and an outer circumferential surface of the steering wheel, including the front surface sensor22S and the back surface sensor22B, is detected to be equal to or greater than a predetermined value. By contrast, a contacting state is identified when the area of contact with either the front surface sensor22S or the back surface sensor22B is detected to be equal to or greater than the predetermined value. No particular limitations are given with respect to the predetermined value; this value is a certain area suitable for detection as an input value from the driver, such as, for example, an area equivalent to a width of a first finger (thumb), or an area equivalent to a combined width of a second finger (index finger) and a third finger (middle finger). In addition, to minimize erroneous detections, different values may be used as the predetermined values for the front surface sensor22S and the back surface sensor22B, such as, for example, using an area equivalent to the width of the first finger for the predetermined value of the front surface sensor22S, and an area equivalent to the combined width of the second finger and the first finger for the predetermined value of the back surface sensor22B.

FIG.8Ais a drawing of an example in which the driver is identified to be in a state of gripping the steering wheel2. In the left drawing ofFIG.8A, an area of contact of the driver's first finger DF1is detected by the front surface sensor22S and an area of contact of the second finger DF2is detected by the back surface sensor22B; therefore, the control device19identifies the driver to be in a gripping state. Similarly, in the right drawing ofFIG.8A, area of contacts of the driver's first finger DF1and second finger DF2are detected by the front surface sensor22S and an area of contact of the second finger DF2is detected by the back surface sensor22B; therefore, a gripping state is identified.

FIG.8Bis a drawing of an example in which the driver is identified to be in a state of gripping the steering wheel2. In the left drawing ofFIG.8B, an area of contact of the driver's first finger DF1is detected by the front surface sensor22S and an area of contact is not detected by the back surface sensor22B; therefore, the control device19identifies the driver to be in a contacting state. Similarly, in the right drawing ofFIG.8B, an area of contact is not detected by the front surface sensor22S and an area of contact of the driver's second finger DF2is detected by the back surface sensor22B; therefore, a contacting state is identified. On the other hand, when, for example, there is no contact with the front surface sensor22S and an edge of the driver's clothing is in contact with the back surface sensor22B, a contacting state is not identified if the area of contact of the clothing is not equal to or greater than a predetermined value. In this case, a gripping state is also not identified because an area of contact is not detected by the front surface sensor22S. Thus, area of contacts are detected by the front surface sensor22S and the back surface sensor22B of the steering wheel2and whether there is a gripping state or a contacting state is identified on the basis of the area of contacts detected by these sensors22; therefore, accuracy of identification with respect to the input value from the driver can be improved.

A pressure at which the driver grips the steering wheel2may be used to identify whether the driver is in a gripping state or a state of contacting the steering wheel2. In the event of an override from the assist level3to the manual driving mode, the driver's intention to take over driving must be accurately confirmed; therefore, for example, when a gripping pressure that is less than a predetermined value is detected, a contacting state is identified, and when a strong gripping pressure that is equal to or greater than the predetermined value is detected, a gripping state is identified. No particular limitations are given with respect to the predetermined value, but this value is the gripping pressure when the driver grips the steering wheel2in at least a normal travel state.

The left drawing ofFIG.8Cshows an example in which the driver is identified to be in a state of contacting the steering wheel2, and the right drawing shows an example in which the driver is identified to be in a gripping state. In the left drawing ofFIG.8C, a gripping pressure P1from the driver's hand DH is detected by the front surface sensor22S and the back surface sensor22B of the steering wheel2. Since the gripping pressure P1is less than a predetermined value P, the control device19identifies the driver to be in a contacting state. By contrast, in the right drawing ofFIG.8C, a gripping pressure P2from the driver's hand DH is detected by the front surface sensor22S and the back surface sensor22B of the steering wheel2. Since the gripping pressure P2is greater than a predetermined value P, the control device19identifies the driver to be in a gripping state. When a gripping pressure stronger than the normal travel state is detected and the driver is identified to be in a gripping state, it can be assessed that the driver is displaying an intention to take over driving. Thus, by identifying whether the driver is in a gripping state or a contacting state on the basis of the gripping pressure on the steering wheel2, it is possible to confirm the driver's intention to take over and to perform an override.

Next, an override control process of the present embodiment shall be described with reference toFIG.9.FIG.9is a flowchart of an example of an override control process executed by the driving mode switching control device1of the present embodiment. The override control process described below is executed at predetermined time intervals by the driving mode switching control device1. Described below is a case in which the driving assist mode in hands-off mode and eyes-off mode (the assist level3) is executed by the autonomous travel control function of the control device19. The threshold value Th3at which an override is determined is set at an input load higher than the threshold value Th2α at which “the driver is in a contacting state with one hand.”

First, when an abnormality in the autonomous travel control system is detected in step S1, the control device19causes the instrument panel display or the like to display a notification requesting that the driver grip the steering wheel2in step S2.

When an input value from the driver with respect to the steering wheel2is detected by the sensors22installed inside the steering wheel2in step S3, in the next step S4, the control device19identifies whether or not the driver is in a state of gripping the steering wheel2. When the driver is identified to be in a state of gripping the steering wheel2, the process advances to step S5. By contrast, when the driver is identified to not be in a state of gripping the steering wheel2, the process advances to step S6.

When the driver is identified to not be in a state of gripping the steering wheel2as a result of step S4, the control device19identifies whether or not the driver is in a state of contacting the steering wheel2in step S6. When the driver is identified to be in a state of contacting the steering wheel2, the process advances to step S7. By contrast, when the driver is identified to be in a state of contacting the steering wheel2, the input value from the driver is equal to or greater than the threshold value Th3; therefore, the process returns to step S3and the process from this step onward is repeated.

When the driver is identified to be in a state of contacting the steering wheel2as a result of step S6, the control device19identifies whether or not the driver is in a state of contacting the steering wheel2using both hands in step S7. When the driver is identified to be in a contacting state using both hands, the process advances to step S5. By contrast, when the driver is identified to not be in a contacting state using both hands, the input value from the driver is not equal to or greater than the threshold value Th3; therefore, the process returns to step S3and the process from this step onward is repeated.

When the driver is identified to be in a state of gripping the steering wheel2as a result of step S4and also when the driver is identified to be in a state of contacting the steering wheel2using both hands as a result of step S7, the control device19determines that the input value from the driver is equal to or greater than the threshold value Th3and the process advances to step S5. A gripping state may be determined in step S4when the input value is equal to or greater than the threshold value Th3if the driver is in a gripping state using at least one hand.

In the next step S5, the control device19performs an override from the driving assist mode at the assist level3to the manual driving mode.

As described above, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, the threshold value of a driving assist mode in which the assist level is relatively high is set higher than the threshold value of a driving assist mode in which the assist level is relatively low in a vehicle driving mode switching control method in which a switch is made from the driving assist mode, in which a driving operation performed by a driver is assisted by autonomous travel control having a plurality of assist levels, to the manual driving mode, in which the driver performs the driving operation. An input value from the driver with respect to the steering wheel2of the host vehicle V1is detected, and when the input value from the driver is equal to or greater than a threshold value, a switch is made from the driving assist mode to the manual driving mode. It is thereby possible to perform an override determination corresponding to the travel assist level.

In addition, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, a request for the driver to grip the steering wheel2is outputted when a switch is made from the driving assist mode to the manual driving mode, and it is therefore possible to reduce driver anxiety when an override is activated on the basis of a vehicle assessment.

In addition, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, when the driver is identified to be in a state of gripping the steering wheel2in at least one of the regions above, below, left, or right from the center on the outer circumferential surface of the steering wheel2in the driving assist mode in which the assist level is relatively high, the input value from the driver is determined to be equal to or greater than a threshold value Th. It is thereby possible to appropriately allow the driver to take over even in an override from the driving assist mode in which the assist level is relatively high to the manual driving mode.

According to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, when the driver is identified to be in a state of contacting the steering wheel2in two of the regions above, below, left, or right on the outer circumferential surface of the steering wheel2in the driving assist mode in which the assist level is relatively high, the input value from the driver is determined to be equal to or greater than a threshold value Th. It is thereby possible to activate an override in a state in which the position of the steering wheel2is stable. It is also possible to minimize the incidence at which it is determined that the input value is equal to or greater than the threshold value Th due to erroneous detection of an input value that does not depend on the driver's intention.

In addition, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, the input value from the driver is determined to be equal to or greater than a threshold value Th when the driver is identified to be in a state of gripping the steering wheel2in one of the regions above, below, left, or right on the outer circumferential surface of the steering wheel2in the driving assist mode in which the assist level is relatively high, and the driver is identified to be in a state of contacting the steering wheel2in another one of the regions above, below, left, or right. It is thereby possible to assess that the driver is intentionally touching the steering wheel2and to appropriately activate an override.

In addition, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, the identification of whether the driver is in a gripping state or a state of contacting the steering wheel2is that there is a gripping state when the area of contact between the driver and the outer circumferential surface of the steering wheel2, including the front surface facing the driver and the back surface facing the windshield of the vehicle, is equal to or greater than a predetermined value, and that there is a contacting state when the area of contact on either the front surface or the back surface is equal to or greater than a predetermined value. It is thereby possible to improve accuracy of identification with respect to the input value from the driver.

In addition, according to the driving mode switching control method and the vehicle driving mode switching control device1of the present embodiment, the identification of whether the driver is in a gripping state or a state of contacting the steering wheel2is that a gripping state is identified when the gripping pressure exerted by the driver on the steering wheel2is equal to or greater than a predetermined value, and a contacting state is identified when the gripping pressure is less than the predetermined value; therefore, it is possible to confirm the driver's intention to take over and to perform an override determination.

The embodiment described above is described in order to facilitate understanding of the present invention, and is not described in order to limit the present invention. Therefore, the elements disclosed in the above embodiment is intended to include all design changes and equivalents that fall within the technical scope of the present invention.