Patent ID: 12246755

DESCRIPTION OF EMBODIMENTS

A vehicle controller, a method for vehicle control executed by the vehicle controller, and a computer program for vehicle control will now be described with reference to the attached drawings. In the case where driving control of a vehicle will be transferred to a driver for some reason, the vehicle controller executes deceleration control to decelerate the vehicle at a constant deceleration, at predetermined timing. If the vehicle controller transferred driving control to the driver and stopped deceleration control after a certain period from notification of a transition demand (TD), the vehicle might accelerate in some cases, for example, because of creeping, depending on the speed of the vehicle; and it would be difficult to decelerate by engine braking, which may result in compromising the safety of the vehicle.

Thus the vehicle controller continues deceleration control of the vehicle, even after a predetermined period from notification timing of a transition demand in the case where the speed of the vehicle decreases to a predetermined speed threshold or less within the predetermined period and where the driver's operation to take over driving (hereafter “takeover operation”) is not detected. In the case where the speed of the vehicle does not fall below the predetermined speed threshold, the vehicle controller transfers driving control of the vehicle to the driver at the end of the predetermined period from the notification timing of the transition demand even when the driver's takeover operation is not detected.

FIG.1schematically illustrates the configuration of a vehicle control system equipped with a vehicle controller.FIG.2illustrates the hardware configuration of an electronic control unit, which is an embodiment of the vehicle controller. In the present embodiment, the vehicle control system1, which is mounted on a host vehicle10and controls the vehicle10, includes a GPS receiver2, a camera3, a storage device4, a user interface5, and an electronic control unit (ECU)11, which is an example of the vehicle controller. The ECU11is communicably connected to the GPS receiver2, the camera3, the storage device4, and the user interface5via an in-vehicle network conforming to a standard such as a controller area network. The ECU11is further connected to a steering device6including a steering wheel, a touch sensor7provided on the steering wheel for detecting the driver's touch on the steering wheel, an accelerator device8including an accelerator pedal, and a brake device9including a brake pedal. The ECU11is further connected to a vehicle speed sensor (not illustrated) that measures the speed of the vehicle10. The vehicle control system1may further include a distance sensor (not illustrated), such as LiDAR or radar, which measures the distances from the vehicle10to objects around the vehicle10, and may further include another vehicle-mounted device, such as a wireless communication terminal (not illustrated) for wireless communication with another device or a navigation device (not illustrated) for searching for a planned travel route to a destination.

The GPS receiver2receives GPS signals from GPS satellites at predetermined intervals, and determines the position of the vehicle10, based on the received GPS signals. The GPS receiver2outputs positioning information indicating the result of determination of the position of the vehicle10based on the GPS signals to the ECU11via the in-vehicle network at predetermined intervals. The vehicle control system1may include a receiver conforming to another satellite positioning system, instead of the GPS receiver2.

The camera3, which is an example of a vehicle exterior sensor, includes a two-dimensional detector constructed from an array of optoelectronic transducers, such as CCD or C-MOS, having sensitivity to visible light and a focusing optical system that forms an image of a target region of capturing on the two-dimensional detector. The camera3is mounted, for example, in the interior of the vehicle10so as to be oriented, for example, to the front of the vehicle10. The camera3takes a picture of a region in front of the vehicle10every predetermined capturing period (e.g., 1/30 to 1/10 seconds), and generates images representing the region. Each image obtained by the camera3is an example of an exterior sensor signal representing the surroundings of the vehicle. The images obtained by the camera3may be color or grayscale images. The vehicle10may include multiple cameras taking pictures in different orientations or having different focal lengths. For example, the vehicle10may include a camera oriented to the rear of the vehicle.

Whenever an image is generated, the camera3outputs the generated image to the ECU11via the in-vehicle network.

The storage device4, which is an example of a storage unit, includes, for example, a hard disk drive or a nonvolatile semiconductor memory. The storage device4stores a high-precision map used in autonomous driving control of the vehicle. The high-precision map includes, for example, information indicating road markings, such as lane-dividing lines or stop lines, and signposts for each road included in a predetermined region represented in the map. The high-precision map is an example of map information.

The storage device4may further include a processor for executing, for example, a process to update the high-precision map and a process related to a request from the ECU11to read out the high-precision map. For example, whenever the vehicle10moves a predetermined distance, the storage device4may transmit a request to obtain a high-precision map, together with the current position of the vehicle10, to a map server via the wireless communication terminal (not illustrated). The storage device4may receive a high-precision map of a predetermined region around the current position of the vehicle10from the map server via the wireless communication terminal. When a request from the ECU11to read out the high-precision map is received, the storage device4cuts out that portion of the high-precision map stored therein which includes the current position of the vehicle10and which represents a region smaller than the predetermined region, and outputs the cut portion to the ECU11via the in-vehicle network.

The user interface5, which is an example of the notification device or a notification unit, includes, for example, a display, such as a liquid crystal display, or a touch screen display. The user interface5is mounted in the interior of the vehicle10, e.g., near an instrument panel, so as to face the driver. The user interface5displays predetermined information or predetermined notification, such as a transition demand, received from the ECU11via the in-vehicle network, in the form of an icon or text, to inform the driver of the information or notification. The user interface5may include one or more light sources provided on the instrument panel, a speaker mounted in the vehicle interior, or a vibrator provided in the steering wheel or the driver's seat. In this case, the user interface5outputs the predetermined information or notification received from the ECU11via the in-vehicle network, in the form of a voice signal, to inform the driver of the information or notification. Alternatively, the user interface5may vibrate the vibrator according to a signal received from the ECU11via the in-vehicle network to inform the driver of the predetermined information or notification with the vibration. Alternatively, the user interface5may turn on or blink the light sources according to a signal received from the ECU11via the in-vehicle network to inform the driver of the predetermined information or notification.

The ECU11executes autonomous driving control of the vehicle10when autonomous driving mode is applied to the vehicle10, for example, by the driver's operation of the user interface5. While the vehicle10is under autonomous driving control, the ECU11determines whether autonomous driving control of the vehicle10can continue; and when it is determined that autonomous driving control cannot continue, the ECU11executes a process for transferring control of the vehicle10from the ECU11to the driver. When control of the vehicle10is transferred to the driver, i.e., when manual driving mode is applied to the vehicle10, the ECU11may further execute a function of assisting the driver in driving the vehicle10, such as assistance in lane keeping or in collision avoidance.

As illustrated inFIG.2, the ECU11includes a communication interface21, a memory22, and a processor23. The communication interface21, the memory22, and the processor23may be configured as separate circuits or a single integrated circuit.

The communication interface21includes an interface circuit for connecting the ECU11to the in-vehicle network. Whenever positioning information is received from the GPS receiver2, the communication interface21passes the positioning information to the processor23. Whenever an image is received from the camera3, the communication interface21passes the received image to the processor23. In addition, the communication interface21passes the high-precision map read from the storage device4to the processor23. The communication interface21outputs a signal indicating predetermined information or notification and received from the processor23to the user interface5via the in-vehicle network.

In addition, the communication interface21is connected to the steering device6, the touch sensor7, the accelerator device8, and the brake device9. When a steering torque detection signal indicating torque applied to the steering wheel is received from the steering device6, the communication interface21passes the steering torque detection signal to the processor23. When a detection signal indicating that the driver has held the steering wheel is received from the touch sensor7, the communication interface21passes the detection signal to the processor23. Further, when an accelerator operation signal indicating the amount of pressing-down of the accelerator pedal is received from the accelerator device8, the communication interface21passes the accelerator operation signal to the processor23. Further, when a brake operation signal indicating the amount of pressing-down of the brake pedal is received from the brake device9, the communication interface21passes the brake operation signal to the processor23.

The memory22, which is another example of a storage unit, includes, for example, volatile and nonvolatile semiconductor memories, and stores various algorithms and various types of data used in a vehicle control process executed by the processor23of the ECU11. For example, the memory22stores a speed threshold; messages to be notified to the driver when a transition demand is made; and parameters of the camera3such as the mounted position, the orientation, and the focal length. The memory22further stores various parameters for defining a classifier for object detection, a high-precision map read from the storage device4, and a planned travel route generated by the navigation device. In addition, the memory22temporarily stores information received by the ECU11during the vehicle control process and various types of data generated during the vehicle control process. Examples of the information received by the ECU11during the vehicle control process include images of the surroundings of the vehicle10, positioning information, a detection signal on hold of the steering wheel, a steering torque detection signal, an accelerator operation signal, and a brake operation signal.

The processor23includes one or more central processing units (CPUs) and a peripheral circuit thereof. The processor23may further include another operating circuit, such as a logic-arithmetic unit, an arithmetic unit, or a graphics processing unit. The processor23executes the vehicle control process on the vehicle10.

FIG.3is a functional block diagram of the processor23, related to the vehicle control process. The processor23includes a determination unit31, a notification processing unit32, and a control unit33. These units included in the processor23are functional modules, for example, implemented by a computer program executed by the processor23, or may be dedicated operating circuits provided in the processor23.

The determination unit31determines whether to transfer driving control of the vehicle10to the driver, while the vehicle10is under autonomous driving control. For example, the determination unit31determines to transfer control of the vehicle10to the driver, in the case where the vehicle10will not be able to continue autonomous driving before the vehicle10travels through a predetermined length of section from the current position of the vehicle10indicated by the latest positioning information. More specifically, in the case where the vehicle10will go outside the area represented by the high-precision map before the vehicle10travels through a predetermined length of section from the current position along a planned travel route or along a road being traveled, the vehicle10will not be able to continue autonomous driving. Thus the determination unit31determines to transfer control of the vehicle10to the driver. For example, in the case where the high-precision map represents information on expressways but does not represent information on ordinary roads, an interchange of an expressway is a point where the vehicle goes outside the high-precision map.

The determination unit31may determine whether the vehicle10can continue autonomous driving, depending on the situation around the vehicle10. When it is determined that the vehicle10cannot continue autonomous driving, the determination unit31may determine that control of the vehicle10will be transferred to the driver. For example, when another vehicle cuts in front of the vehicle10on a host vehicle lane on which the vehicle10is traveling, the determination unit31may determine that the vehicle10cannot continue autonomous driving, and that control of the vehicle10will be transferred to the driver. In addition, in some cases, traffic information received via the wireless communication terminal (not illustrated) indicates the presence of road construction, traffic restrictions, or traffic congestion in a predetermined length of section from the current position of the vehicle10along a road being traveled by the vehicle10or along a planned travel route. In such cases, the determination unit31may determine that control of the vehicle10will be transferred to the driver. Alternatively, when a signal indicating a breakdown is received by the ECU11from the camera3or the distance sensor (not illustrated), the determination unit31determines that the ECU11cannot continue autonomous driving control of the vehicle10, and that control of the vehicle10will be transferred to the driver.

When control is transferred because of another vehicle cutting into the host vehicle lane, for example, the determination unit31inputs an image representing the surroundings of the vehicle10generated by the camera3into a classifier to detect a region representing the vehicle that has cut in and regions representing lane-dividing lines in the image. As such a classifier, the determination unit31can use, for example, a deep neural network (DNN) having architecture of a convolutional neural network (CNN) type, such as Single Shot MultiBox Detector (SSD) or Faster R-CNN. Alternatively, as such a classifier, the determination unit31may use a DNN having architecture of a self-attention network (SAN) type, such as a Vision transformer. Alternatively, as such a classifier, the determination unit31may use a DNN for semantic segmentation that identifies, for each pixel, the type of object represented in the pixel, such as a fully convolutional network or U-net. Alternatively, the determination unit31may use a classifier based on another machine learning technique, such as an AdaBoost classifier. Such a classifier is trained in advance with a large number of training images representing vehicles or lane-dividing lines in accordance with a predetermined training technique, such as backpropagation, so as to detect a vehicle and lane-dividing lines from an image.

On each of the left and right sides of the vertical center line of the image, the determination unit31determines the lane-dividing line closest to the center line of the detected lane-dividing lines as a lane-dividing line demarcating the host vehicle lane. The determination unit31then determines a region sandwiched between the left and right lane-dividing lines demarcating the host vehicle lane in the image as a region corresponding to the host vehicle lane. Further, of the one or more detected vehicles, the determination unit31determines a vehicle on the region corresponding to the host vehicle lane as a leading vehicle ahead of the vehicle10on the host vehicle lane. The determination unit31executes the above-described process on each of time-series images obtained from the camera3, and thereby detects a vehicle and lane-dividing lines from each image and identifies a leading vehicle traveling on the host vehicle lane, based on the result of detection. In addition, the determination unit31applies a tracking technique, such as KLT tracker, to a region representing the leading vehicle in the latest image and regions representing a vehicle in past images to track the leading vehicle in reverse chronological order. When the result of tracking suggests that the leading vehicle detected in the latest image lay on a lane different from the host vehicle lane in a preceding predetermined period, the determination unit31determines that the leading vehicle has cut in front of the vehicle10.

When it is determined that control of the vehicle10will be transferred to the driver, the determination unit31notifies the notification processing unit32and the control unit33of the result of determination. The determination unit31further notifies the control unit33of a signal indicating the event causing the determination that control of the vehicle10will be transferred to the driver.

When being notified by the determination unit31that control of the vehicle10will be transferred to the driver, the notification processing unit32notifies the driver of a transition demand via the user interface5. To this end, the notification processing unit32causes a message or an icon representing a transition demand to appear on the display included in the user interface5, or turns on or blinks the light source corresponding to the demand. Alternatively, the notification processing unit32outputs a voice signal representing the demand to the speaker included in the user interface5. Alternatively, the notification processing unit32vibrates the vibrator included in the user interface5in a mode of vibration (period or intensity of vibration) depending on the demand. In the case where the user interface5includes two or more of the above-described devices, the notification processing unit32may notify the driver of a transition demand with all or some of the two or more devices.

The notification processing unit32notifies the control unit33of notification timing at which the transition demand is notified to the driver via the user interface5.

The control unit33executes autonomous driving control of the vehicle10while autonomous driving mode is applied to the vehicle10. The control unit33continues autonomous driving control until predetermined timing after the notification timing of the transition demand or until detection of the driver's takeover operation. At the predetermined timing, the control unit33starts deceleration control to decelerate the vehicle10at a predetermined deceleration as a mode of autonomous driving control. In addition, the control unit33measures the time elapsed since the notification timing. In the case where the speed of the vehicle10decreases to a predetermined speed threshold or less and where the driver's takeover operation is not detected, the control unit33continues deceleration control of the vehicle10, even after a predetermined period. In the case where the speed of the vehicle10does not fall below the predetermined speed threshold and where the driver's takeover operation is not detected within the predetermined period of the notification timing, the control unit33transfers control of the vehicle10to the driver, regardless of whether deceleration control is executed.

The control unit33compares a measurement value of the speed of the vehicle10received by the ECU11from the vehicle speed sensor (not illustrated) with the speed threshold to determine whether the speed of the vehicle10has fallen below the speed threshold.

The predetermined timing at which deceleration control starts is, for example, the timing at which the speed of the vehicle10decreases to the predetermined speed threshold or less after the notification timing. Alternatively, the predetermined timing may be the notification timing of the transition demand or timing after a predetermined waiting period from the notification timing. The predetermined waiting period is set shorter than the predetermined period, e.g., at one to two seconds. The predetermined period may be, for example, three to five seconds. The predetermined speed threshold is set, for example, at the upper limit of the speed range in which the vehicle10may accelerate because of creeping, e.g., at 10 km/h to 20 km/h.

During autonomous driving control of the vehicle10, the control unit33controls components of the vehicle10so that the vehicle10travels at a predetermined speed. The predetermined speed may be a speed set by the driver via the user interface5or the regulation speed of a road being traveled by the vehicle10, which is identified by referring to the high-precision map and the current position of the vehicle10indicated by the latest positioning information. When a leading vehicle is traveling on the host vehicle lane, the control unit33may control the speed of the vehicle10so that the vehicle10keeps a certain distance from the leading vehicle. The distance between the leading vehicle and the vehicle10is estimated on the basis of a region representing the leading vehicle in an image generated by the camera3. More specifically, the bottom position of the region representing the leading vehicle in an image is assumed to correspond to the position at which the leading vehicle is in contact with the road surface. In addition, the bottom position of the region in the image corresponds to the direction viewed from the camera3to the position at which the leading vehicle is in contact with the road surface. Thus the control unit33can estimate the distance between the vehicle10and the leading vehicle, based on the direction from the camera3corresponding to the bottom position of the region representing the leading vehicle in the image and the height of the mounted position of the camera3. In the case where the vehicle10is equipped with a distance sensor, such as LiDAR, the control unit33may use the distance to an object ahead of the vehicle10measured by the distance sensor as the distance between the vehicle10and the leading vehicle.

The control unit33sets the degree of accelerator opening or the amount of braking so that the speed of the vehicle10equals the speed determined as described above. The control unit33then determines the amount of fuel injection according to the set degree of accelerator opening, and outputs a control signal depending on the amount of fuel injection to a fuel injector of an engine of the vehicle10. Alternatively, the control unit33determines the electric power to be supplied to a motor according to the set degree of accelerator opening, and controls a driving circuit of the motor so that the determined electric power is supplied to the motor. The control unit33further outputs a control signal depending on the set amount of braking to the brake device9.

When deceleration control is started, the control unit33sets the degree of accelerator opening or the amount of braking so that the deceleration of the vehicle10equals a predetermined deceleration (e.g., 0.7 m/s2) during the deceleration control. The control unit33then determines the amount of fuel injection according to the set degree of accelerator opening, and outputs a control signal, depending on the amount of fuel injection to the fuel injector of the engine of the vehicle10. Alternatively, the control unit33determines the electric power to be supplied to the motor according to the set degree of accelerator opening, and controls the driving circuit of the motor so that the determined electric power is supplied to the motor. The control unit33further outputs a control signal depending on the set amount of braking to the brake device9.

When the speed of the vehicle10is reduced to zero while deceleration control continues, the control unit33may set the accelerator opening at zero or the amount of braking greater than a predetermined value so as to keep the vehicle10stopped.

The control unit33detects the driver's takeover operation, based on at least one of operation of the steering wheel, hold of the steering wheel, operation of the accelerator, and operation of the brake by the driver. After detection of the driver's takeover operation, the control unit33transfers driving control of the vehicle10to the driver. Thereafter, driving of the vehicle10is controlled according to the driver's driving operation.

For example, until after the predetermined period from the notification timing, the control unit33determines that the driver has performed takeover operation, in one of the following cases (a) to (c).(a) When torque applied to the steering wheel indicated by a steering torque detection signal received from the steering device6is not less than a predetermined torque value. In other words, when it is detected that the driver has operated the steering wheel.(b) When the ECU11receives a detection signal indicating that the driver has held the steering wheel from the touch sensor7and the amount of pressing-down of the accelerator indicated by an accelerator operation signal received from the accelerator device8is not less than a predetermined amount. In other words, when it is detected that the driver has held the steering wheel and operated the accelerator device8.(c) When the ECU11receives a detection signal indicating that the driver has held the steering wheel from the touch sensor7and the amount of pressing-down of the brake pedal is not less than a predetermined amount indicated by a brake operation signal received from the brake device9. In other words, when it is detected that the driver has held the steering wheel and operated the brake device9.

After the predetermined period from the notification timing, the control unit33may determine that the driver has performed takeover operation, on condition that the driver has operated the accelerator device8or the brake device9, even if the driver is not holding the steering wheel. In other words, reception of a detection signal indicating that the driver has held the steering wheel by the ECU11from the touch sensor7may be omitted from criteria (b) and (c) above. This relaxation of the requirements for takeover of driving after the predetermined period from the notification timing enables the control unit33to prevent unintended acceleration of the vehicle10after transfer of control to the driver and to improve the driver's convenience.

After the vehicle10is stopped, the control unit33may determine that the driver has performed takeover operation, when it is detected that the driver has operated the accelerator or the brake or moved a shift lever to a parking position. Alternatively, after the vehicle10is stopped, the control unit33may determine that the driver has performed takeover operation, when an electric parking brake is turned on.

FIG.4Aschematically illustrates duration of autonomous driving control for the case where the speed of the vehicle10is not less than a predetermined speed threshold until after a predetermined period from notification timing.FIG.4Bschematically illustrates duration of autonomous driving control including deceleration control for the case where the speed of the vehicle10falls below a predetermined speed threshold within a predetermined period of notification timing. The abscissas and the ordinates ofFIGS.4A and4Brepresent elapsed time and the speed of the vehicle10, respectively. A graph401inFIG.4Arepresents time-varying changes in the speed of the vehicle10. Similarly, a graph402inFIG.4Brepresents time-varying changes in the speed of the vehicle10.

As illustrated inFIG.4A, the speed of the vehicle10is kept constant until time t1. At time t1, a transition demand is notified to the driver. In other words, time t1 is notification timing. After the notification timing t1, autonomous driving control of the vehicle10continues; and the speed of the vehicle10varies with the passage of time, for example, because of a leading vehicle, but is greater than a speed threshold Thy until after a predetermined period P from the notification timing t1. In addition, the driver's takeover operation is not detected until after the predetermined period P from the notification timing t1. Hence, in this example, control is transferred to the driver at time t2, which is the end of the predetermined period P from the notification timing t1; and after time t2, the speed of the vehicle10is based on the driver's driving operation. In this example, the speed of the vehicle10is not reduced substantially at the time of transfer of control to the driver, and thus is reduced by engine braking even after time t2, unless the driver performs driving operation.

In the example illustrated inFIG.4B, the speed of the vehicle10is also kept constant until time t1. At time t1, a transition demand is notified to the driver. In this example, at time t2 after the notification timing t1, the speed of the vehicle10falls below a speed threshold Thy; and after time t2, deceleration control is executed. The speed of the vehicle10then decreases with the passage of time. In this case, unless the driver's takeover operation is detected, the deceleration control continues even after time t3, which is the end of a predetermined period P from the notification timing t1. After the speed of the vehicle10is reduced to zero, the vehicle10is kept stopped.

FIG.5is an operation flowchart of the vehicle control process executed by the processor23. The processor23executes the vehicle control process in accordance with the operation flowchart described below.

The determination unit31of the processor23determines whether to transfer driving control of the vehicle10to the driver (step S101). When it is determined that driving control of the vehicle10will be transferred to the driver, the notification processing unit32of the processor23notifies the driver of a transition demand via the user interface5(step S102).

After the notification timing at which the driver is notified of a transition demand, the control unit33of the processor23determines whether the driver's takeover operation is detected (step S103). When the driver's takeover operation is detected (Yes in step S103), the control unit33stops autonomous driving control of the vehicle10(step S104). Thereafter, the vehicle10is controlled according to the driver's driving operation; and the ECU11terminates the vehicle control process.

When the driver's takeover operation is not detected (No in step S103), the control unit33determines whether the speed of the vehicle10is greater than a predetermined speed threshold Thy (step S105). When the speed of the vehicle10is greater than the predetermined speed threshold Thy (Yes in step S105), the control unit33determines whether a predetermined period has elapsed since the notification timing (step S106). When the predetermined period has elapsed since the notification timing (Yes in step S106), the control unit33stops autonomous driving control of the vehicle10(step S104). Thereafter, the vehicle10is controlled according to the driver's driving operation; and the ECU11terminates the vehicle control process.

When the predetermined period has not elapsed since the notification timing (No in step S106), the control unit33continues autonomous driving control of the vehicle10with the driver notified of the transition demand (step S107). The control unit33then repeats processing of step S103and the subsequent steps.

In step S105, when the speed of the vehicle10is not greater than the predetermined speed threshold Thy (No in step S105), the control unit33continues deceleration control of the vehicle10with the driver notified of the transition demand (step S108). The control unit33then repeats processing of step S103and the subsequent steps.

As has been described above, the vehicle controller notifies a driver of a transition demand when it is determined that autonomous driving control of a vehicle will not be able to continue for a certain reason. In the case where the vehicle maintains a speed not less than a predetermined speed threshold until after a predetermined period from the notification timing of the transition demand, the vehicle controller transfers driving control to the driver at the end of the predetermined period, even when the driver's takeover operation is not detected. In this way, the vehicle controller can reliably transfer control of the vehicle to the driver when it is not expected that the vehicle will accelerate despite the driver's intention after transfer of control to the driver. At predetermined timing after the notification timing of the transition demand, the vehicle controller executes deceleration control. The vehicle controller continues the deceleration control of the vehicle even after the predetermined period from the notification timing in the case where the speed of the vehicle decreases to the predetermined speed threshold or less within the predetermined period and where the driver's takeover operation is not detected. This enables the vehicle controller to prevent unintended acceleration of the vehicle caused by creeping, which enables raising the level of safety at takeover of driving control of the vehicle from the vehicle controller to the driver.

According to a modified example, the control unit33may change the criteria for determining that the driver has performed takeover operation, depending on the speed of the vehicle. For example, in the case where the speed of the vehicle10is not greater than a predetermined speed threshold, the control unit33may determine that the driver has performed takeover operation, only when the driver has operated the accelerator or the brake. More specifically, in the case where the speed of the vehicle10is not greater than a predetermined speed threshold, the control unit33determines that the driver has performed takeover operation, only when criterion (b) or (c) above is satisfied. In this modified example also, reception of a detection signal indicating that the driver has held the steering wheel by the ECU11from the touch sensor7may be omitted from criteria (b) and (c) above, after the predetermined period from the notification timing. Thus, when the speed of the vehicle10is not greater than a predetermined speed threshold, the control unit33continues deceleration control unless the driver's operation of the accelerator or the brake is detected.

In the case where the speed of the vehicle10is greater than the predetermined speed threshold, the control unit33determines that the driver has performed takeover operation, when any of criteria (a) to (c) above is satisfied, i.e., when predetermined operation including hold of the steering wheel is performed. Alternatively, in the case where the speed of the vehicle10is greater than the predetermined speed threshold, the control unit33may determine that the driver has performed takeover operation, only when it is detected that the driver has operated or held the steering wheel. In other words, detection of the driver's operation of the accelerator device8may be omitted from criterion (b) above. Further, detection of the driver's operation of the brake device9may be omitted from criterion (c) above.

FIG.6is an operation flowchart of the vehicle control process according to this modified example. The determination unit31of the processor23determines whether to transfer driving control of the vehicle10to the driver (step S201). When it is determined that driving control of the vehicle10will be transferred to the driver, the notification processing unit32of the processor23notifies the driver of a transition demand via the user interface5(step S202). The control unit33of the processor23then determines whether the speed of the vehicle10is greater than a predetermined speed threshold Thy (step S203).

When the speed of the vehicle10is greater than the predetermined speed threshold Thy (Yes in step S203), the control unit33determines whether one of criteria (a) to (c) above is satisfied (step S204). When one of criteria (a) to (c) above is satisfied, i.e., when the driver's takeover operation is detected (Yes in step S204), the control unit33stops autonomous driving control of the vehicle10(step S205). Thereafter, the vehicle10is controlled according to the driver's driving operation; and the ECU11terminates the vehicle control process.

When none of criteria (a) to (c) above is satisfied, i.e., when the driver's takeover operation is not detected (No in step S204), the control unit33continues autonomous driving control of the vehicle10(step S206). In this case, the driver is kept notified of the transition demand. The control unit33then repeats the processing of step S203and the subsequent steps.

When the speed of the vehicle10is not greater than the predetermined speed threshold Thy in step S203(No in step S203), the control unit33starts deceleration control (step S207). The control unit33then determines whether criterion (b) or (c) above is satisfied (step S208). As described above, detection that the driver has held the steering wheel may be omitted from criteria (b) and (c). When criterion (b) or (c) above is satisfied, i.e., when the driver's takeover operation including operation of the accelerator or the brake is detected (Yes in step S208), the control unit33stops autonomous driving control (step S205). Thereafter, the vehicle10is controlled according to the driver's driving operation; and the ECU11terminates the vehicle control process.

When neither of criteria (b) and (c) above is satisfied, i.e., when neither accelerator operation nor brake operation is detected (No in step S208), the control unit33continues deceleration control of the vehicle10(step S209). In this case, the driver is kept notified of the transition demand. The control unit33then repeats the processing of step S203and the subsequent steps.

In this modified example also, the control unit33may transfer driving control to the driver in the case where the driver's takeover operation is not detected even after a predetermined period from the notification timing when deceleration control is not applied.

According to this modified example, at a low vehicle speed, the vehicle controller uses the driver's operation of the accelerator or the brake is a condition for takeover of driving, which prevents unintended acceleration of the vehicle when the driver takes over driving operation. At a high vehicle speed, the vehicle controller allows takeover of driving without operation of the accelerator or the brake, which prevents the driver's convenience from being compromised.

In the embodiment or modified example, the control unit33may set the speed threshold dynamically, depending on the environment around the vehicle10. For example, the control unit33may adjust the speed threshold, depending on the gradient of a road being traveled by the vehicle10. In this case, the control unit33may set the speed threshold for the case where the vehicle10is traveling on an uphill road less than the speed threshold for the case where the vehicle10is traveling on a flat road. This is because travel of the vehicle10on an uphill road lowers the possibility that the vehicle10accelerates after the stop of autonomous driving control. Conversely, the control unit33may set the speed threshold for the case where the vehicle10is traveling on a downhill road greater than the speed threshold for the case where the vehicle10is traveling on a flat road. This is because travel of the vehicle10on a downhill road raises the possibility that the vehicle10accelerates after the stop of autonomous driving control. The control unit33determines the gradient of the road being traveled by the vehicle10by referring to the current position of the vehicle10indicated by the latest positioning information and the high-precision map. According to this modified example, the control unit33can adjust the speed threshold at an appropriate value.

In the embodiment or modified examples, the control unit33may determine whether acceleration of the vehicle10after transfer of driving control to the driver causes a danger of a collision between the vehicle10and another object. To this end, the control unit33determines the presence or absence of the danger, depending on the situation around the vehicle10or the cause of determination that driving control of the vehicle10will be transferred to the driver. When acceleration of the vehicle10may cause a danger of a collision between the vehicle10and another object, the control unit33executes a process similar to that in the embodiment. More specifically, the control unit33continues deceleration control in the case where the speed of the vehicle10decreases to a predetermined speed threshold or less and where the driver's takeover operation is not detected even after a predetermined period from notification timing of a transition demand. For example, when the cause of determination of transfer of control to the driver is that another vehicle has cut in front of the vehicle10, the control unit33determines that acceleration of the vehicle10may cause a danger of a collision between the vehicle10and another object, and executes a process similar to that in the embodiment. In addition, the control unit33may determine whether the vehicle10is traveling through a curve at notification timing of a transition demand, by referring to the position of the vehicle10indicated by positioning information at the notification timing and the high-precision map. When the vehicle10is traveling through a curve at the notification timing, the control unit33executes a process similar to that in the embodiment.

In some cases, it is expected that there will not be an immediate danger of a collision between the vehicle10and another object after transfer of control to the driver, as in the case where the cause of a transition demand is that the vehicle10goes outside the region covered by the high-precision map. In such cases, the control unit33may stop autonomous driving control or deceleration control of the vehicle10and transfer control to the driver after the predetermined period from the notification timing regardless of the speed of the vehicle10. When the vehicle10under autonomous driving control is required to accelerate at notification timing at which a transition demand is notified to the driver, the control unit33may omit deceleration control itself.

In addition, when the driver does not perform driving operation despite transfer of control after the predetermined period from the notification timing, the control unit33may determine whether there is a danger of a collision between the vehicle10and a leading vehicle, based on the distance between the vehicle10and the leading vehicle as well as the speed and acceleration of the vehicle10relative to the leading vehicle. When there is such a danger, the control unit33may continue deceleration control in the case where the speed of the vehicle10decreases to a predetermined speed threshold or less and where the driver's takeover operation is not detected even after the predetermined period from the notification timing, as in the embodiment. Conversely, when there is not such a danger, the control unit33may transfer control to the driver at the end of the predetermined period from the notification timing regardless of the speed of the vehicle10. The control unit33executes a process similar to that executed by the determination unit31to detect a leading vehicle from each of time-series images generated by the camera3and to track the detected leading vehicle, thereby determining time-varying changes in the distance between the vehicle10and the leading vehicle. The control unit33then applies a prediction filter, such as a Kalman filter, to the time-varying changes in the distance between the vehicles to predict time-varying changes in the distance between the vehicles, the relative speed, and the relative acceleration after the predetermined period from the notification timing. When the vehicle10is predicted to approach the leading vehicle within a predetermined dangerous distance, based on the result of prediction, the control unit33determines that there is a danger of a collision between the vehicle10and the leading vehicle.

Alternatively, in some cases, continuing deceleration control even after the predetermined period from the notification timing, as in the embodiment, causes a danger of a collision between the vehicle10and a following vehicle traveling behind the vehicle10on the host vehicle lane. In such cases, the control unit33may omit deceleration control regardless of the speed of the vehicle10. The control unit33may then transfer control to the driver at the end of the predetermined period from the notification timing. In this case, the control unit33executes a process similar to that executed by the determination unit31to detect a following vehicle from each of time-series images generated by a camera3provided to take pictures of an area behind the vehicle10. The control unit33then tracks the detected following vehicle to determine time-varying changes in the distance between the vehicle10and the following vehicle. The control unit33applies a prediction filter, such as a Kalman filter, to the time-varying changes in the distance between the vehicles to predict time-varying changes in the distance between the vehicles, the relative speed, and the relative acceleration after the predetermined period from the notification timing. When the vehicle10is predicted to approach the following vehicle within a predetermined dangerous distance, based on the result of prediction, the control unit33determines that there is a danger of a collision between the vehicle10and the following vehicle.

Alternatively, the control unit33may switch control, depending on a deceleration for the case where the vehicle10travels by inertia after the predetermined period from the notification timing. In this case, the control unit33refers to a reference table representing the relationship between the speed and deceleration of the vehicle10to determine the deceleration corresponding to the speed of the vehicle10at the notification timing. Such a reference table may be prestored in the memory22. In the case where the vehicle10is driven by a motor, the reference table may represent not only the relationship between the speed and deceleration of the vehicle10but also the relationship between the remaining battery power and deceleration of the vehicle10. The control unit33refers to the reference table to determine the deceleration corresponding to the speed and remaining battery power of the vehicle10at the notification timing. When the deceleration is less than a predetermined deceleration threshold, the control unit33may continue deceleration control in the case where the speed of the vehicle10decreases to a predetermined speed threshold or less and where the driver's takeover operation is not detected even after the predetermined period from the notification timing, as in the embodiment. Conversely, when the deceleration is not less than the predetermined deceleration threshold, the control unit33may omit deceleration control, regardless of the speed of the vehicle10.

According to this modified example, the control unit33switches whether to continue deceleration control, depending on the cause of determination that driving control of the vehicle10will be transferred to the driver or the situation around the vehicle10, when the driver's takeover operation is not detected. This enables the control unit33to ensure safety of the vehicle10and to make the timing of takeover of driving control to the driver more appropriate.

In addition, when autonomous driving control continues even after the predetermined period from the notification timing, as in the above-described modified example, the control unit33may intensify the notification of the transition demand to the driver after the predetermined period from the notification timing. For example, the control unit33increases the luminance of a message or an icon of the transition demand displayed on the user interface5, and changes the color of the message or the icon to a more conspicuous color to intensify the notification of the transition demand. Alternatively, the control unit33may turn up the volume of a voice of the transition demand outputted from the speaker included in the user interface5or intensify vibration of the vibrator included in the user interface5to intensify the notification of the transition demand. In addition, when the driver's takeover operation is not detected even after a certain period since the notification of the transition demand is intensified, the control unit33may activate an emergency driver assist. More specifically, as activation of the emergency driver assist, the control unit33may honk a horn, turn on hazard lights, or connect to Helpnet via the wireless communication terminal to make notification of emergency.

As described above, those skilled in the art may make various modifications according to embodiments within the scope of the present disclosure.