Driving assistance device for vehicle

Abstract

The driving support ECU executes a collision avoidance support operation for avoiding a collision between the host vehicle and the target when a collision determination condition established when the host vehicle is predicted to collide with the target is established. The driving assistance ECU recognizes a speed limit applied to a lane in which the host vehicle is traveling, and when a current speed limit, which is a newly recognized speed limit at a current time point, drops from a past speed limit recognized immediately before the current time point, the current speed limit is lower than when the current speed limit does not drop from the past speed limit. A collision determination condition is changed to a condition that is easily satisfied so that a collision avoidance assistance operation is executed at an early timing.

Description

Technical Field

[0001] The present invention relates to a driving assistance device for a vehicle that performs driving assistance control for reducing the possibility of a collision between the host vehicle and a target object. Background Art

[0002] Conventional devices obtain image data by using an on-board camera to capture the scene in front of the vehicle, and recognize road signs based on the image data. Conventional devices also extract speed limits (maximum speeds) from the recognized road signs and notify the occupants of the vehicle of the speed limit (see Japanese Patent Application Laid-Open No. 2017-62696). Summary of the invention

[0003] However, conventional devices only report the speed limit, so sometimes the driver of the host vehicle does not immediately notice that the speed limit has changed. For example, when the speed limit has dropped significantly, if the vehicle ahead of the host vehicle decelerates significantly in response to the drop in the speed limit, the timing of applying the brakes will be delayed if the driver of the host vehicle does not notice the drop in the speed limit. As a result, the host vehicle may approach the vehicle ahead. Conventional devices have not been able to effectively utilize the information on the identified speed limit in such situations.

[0004] The present invention has been made to solve the above-mentioned problems. That is, one object of the present invention is to provide a driving assistance device for a vehicle that can more effectively utilize information on a recognized speed limit.

[0005] One embodiment of the driving assistance device of a vehicle of the present invention comprises a controller (10, 50, 70) configured to execute a collision avoidance assistance action (S450, S470) for avoiding a collision between the vehicle and a target object when a collision determination condition that is established when it is predicted that the vehicle will collide with the target object is met (S440, S460).

[0006] The controller is composed of:

[0007] identifying a speed limit that applies to a lane in which the host vehicle is traveling,

[0008] When a newly recognized speed limit (S210) at the current time point, i.e., the current speed limit has decreased from a past speed limit recognized immediately before the current time point (S250: Yes), the collision determination condition is changed to a condition that is easily satisfied (S290) in such a manner that the collision avoidance assistance action is performed at an earlier timing, compared to when the current speed limit has not decreased from the past speed limit (S250: No).

[0009] In the case where the newly identified speed limit (current speed limit) at the current time point has dropped from the previously identified speed limit (past speed limit), the possibility of the preceding vehicle suddenly decelerating is high. Therefore, in such a case, the above scheme changes the collision determination condition to a condition that is easily satisfied in such a way that the collision avoidance auxiliary action is performed at an earlier timing. More specifically, the collision determination condition is a condition that is satisfied when the collision index value indicating the possibility of the vehicle colliding with the target object reaches a threshold. In this case, the collision determination condition can be changed to a condition that is more easily satisfied by changing the threshold or correcting the collision index value. For example, in the case where the collision determination condition is a condition that is satisfied when the time required until the vehicle collides with the target object, i.e., the "collision required time as a collision index value", becomes below the collision determination time threshold, the collision determination condition is changed to a condition that is easily satisfied by increasing the collision determination time threshold or correcting the collision required time to be smaller.

[0010] As a result, even if the driver of the host vehicle fails to notice the speed limit reduction and delays the response to the sudden deceleration of the preceding vehicle, the collision determination condition is satisfied early and the collision avoidance assistance operation is performed early. Therefore, the host vehicle can be prevented from getting extremely close to the preceding vehicle.

[0011] In the above description, in order to help understand the present invention, the names and / or figure marks used in the embodiments described later are added in parentheses to the components of the invention corresponding to the embodiments described later. However, the components of the present invention are not limited to the embodiments specified by the names and / or figure marks. The present invention also relates to a driving assistance method for a vehicle and a program thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like numerals represent like elements, and in which:

[0013] Figure 1 is a schematic structural diagram of a driving assistance device for a vehicle according to an embodiment of the present invention;

[0014] Figure 2 yes Figure 1 The routine executed by the CPU of the driving assistance ECU shown;

[0015] Figure 3 yes Figure 1 The routine executed by the CPU of the driving assistance ECU shown;

[0016] Figure 4 yes Figure 1 The routine executed by the CPU of the driving assistance ECU shown;

[0017] Figure 5A It is shown in Figure 1 FIG. 1 is a diagram of a menu screen displayed by the setting input device shown;

[0018] Figure 5B It is shown in Figure 1 FIG. 1 is a diagram of a collision avoidance assistance timing selection screen displayed by the setting input device shown;

[0019] Figure 5C It is shown in Figure 1 FIG. 1 is a diagram of a modified collision avoidance assistance timing selection screen displayed by the setting input device shown;

[0020] Figure 5D It is shown in Figure 1 FIG. 1 is a diagram of a speed limit decrease amount threshold selection screen displayed by a setting input device shown;

[0021] Figure 5E It is shown in Figure 1 FIG. 1 is a diagram of a screen for selecting the auxiliary timing correction period length displayed by the setting input device shown;

[0022] Figure 6 yes Figure 1 The routine executed by the CPU of the driving assistance ECU shown. DETAILED DESCRIPTION

[0023] A "driving assistance device DS for a vehicle (hereinafter referred to as "device DS")" according to an embodiment of the present invention includes Figure 1 The components shown are applied to (mounted on) this vehicle HV. This vehicle HV may be any of a vehicle powered by an internal combustion engine, a vehicle powered by an electric motor (i.e., a battery electric vehicle), a hybrid electric vehicle, and the like.

[0024] In this specification, "ECU" is an electronic control unit (control unit) including a microcomputer including a CPU (processor), ROM, RAM, a nonvolatile memory capable of writing data, an interface, etc. ECU is also called a controller or a computer. Figure 1 The plurality of ECUs shown are connected to each other via CAN (Controller Area Network) so as to be able to exchange information with each other. Some or all of the plurality of ECUs may be integrated into one ECU.

[0025] Use of driving assistance ECU10 Figure 1The driving assistance control also called "collision avoidance assistance control or collision damage reduction control" is executed by using the components described in the control system to reduce the possibility of collision between the host vehicle and the target object (obstacle).

[0026] The camera device 20 includes a camera (camera) 21 and an image ECU 22. The camera 21 captures the scene in front of the host vehicle HV and obtains image data every time a predetermined time passes. The image ECU 22 generates "camera information including the image data itself, camera target information, and lane information" based on the image data from the camera 21 and sends it to the driving assistance ECU 10.

[0027] The driving assistance ECU 10 extracts the "road sign indicating the speed limit (maximum speed)" contained in the image data based on the image data obtained by the camera device 20. The driving assistance ECU 10 recognizes (obtains) the numerical value shown by the road sign as the speed limit (maximum speed) set / applied to the "lane in which the vehicle HV is traveling at the current time point (hereinafter also referred to as "this lane")". The recognition (obtaining) of the vehicle speed limit may also be performed by the image ECU 22.

[0028] The radar device 30 is a well-known device that uses radio waves in the millimeter wave band to obtain information about a target object in front of the vehicle HV, and includes a radar 31 and a radar ECU 32. The radar 31 transmits millimeter waves to a predetermined detection range every time a predetermined time passes, and receives the millimeter waves reflected by the target object. The radar 31 transmits information about the transmitted and received millimeter waves to the radar ECU 32. The radar ECU 32 obtains radar information based on the information from the radar 31 and transmits the radar information to the driving assistance ECU 10. The radar information includes the distance to the target object, the direction of the target object, and the relative speed of the target object.

[0029] The powertrain ECU 40 controls a driving device including a power source of the host vehicle HV (not shown) by driving a powertrain actuator 41 to generate a driving force.

[0030] The brake ECU50 controls the brake device of the host vehicle HV (not shown) by driving the brake actuator 51 to apply braking force to the host vehicle HV. Upon receiving an instruction from the driving support ECU10, the brake ECU50 drives the brake actuator 51 to perform automatic braking to automatically apply braking force to the host vehicle HV.

[0031] The steering ECU 60 controls the steering device of the host vehicle HV (not shown) by driving the steering motor 61 to change the steering angle of the host vehicle HV. Upon receiving an instruction from the driving assistance ECU 10, the steering ECU 60 automatically changes the steering angle of the host vehicle HV by driving the steering motor 61 (i.e., performs automatic steering).

[0032] The notification ECU (alarm ECU) 70 is connected to a display 71 disposed at a position that can be visually confirmed from the driver's seat, and an alarm sound generating device 72 that generates an alarm sound (alarm sound), and controls them according to the instruction (instruction signal) from the driving assistance ECU 10. The display 71 is provided with an area 71a that displays a speed limit (maximum speed) and an alarm display area 71b that displays an alarm mark that notifies of the risk of collision. The notification ECU 70 displays the speed limit included in the instruction from the driving assistance ECU 10 in the area 71a, and displays the alarm mark in the alarm display area 71b according to the instruction from the driving assistance ECU 10.

[0033] The navigation ECU 80 is connected to a GPS receiver 81, a map database 82 storing map information, and a display touch panel 83 displaying touch buttons, and together they constitute a car navigation system. The navigation ECU 80 obtains the current position of the host vehicle HV based on the GPS signal received by the GPS receiver 81. The navigation ECU 80 can obtain the speed limit set / applied to the host lane at the current time point based on the obtained current position of the host vehicle HV and the map information stored in the map database 82.

[0034] The communication ECU 90 can wirelessly communicate with a device external to the host vehicle HV (for example, a roadside device, an information management center, etc.), and acquire "various information including information on speed limits" from the external device.

[0035] The driving support ECU 10 inputs detection values ​​(output values) of the following “sensors and switches”.

[0036] An accelerator pedal operation amount sensor 91 that detects the accelerator pedal operation amount AP of the host vehicle HV.

[0037] A brake pedal operation amount sensor 92 that detects the brake pedal operation amount BP of the host vehicle HV.

[0038] A vehicle speed sensor 93 that detects the speed of the host vehicle HV (ie, the host vehicle speed).

[0039] The setting input device 94 is provided at a position operable by the driver and has a display touch panel displaying touch buttons. By the driver operating the setting input device 94, the "collision determination time threshold TTCth, the execution start timing correction time dTTCth of the collision avoidance auxiliary control, the size of the speed limit reduction amount threshold VLTth for control switching, and the length of the control switching period (change time threshold) Tth, etc." described later can be changed.

[0040] Summary of work

[0041] The device DS obtains (recognizes) the speed limit (maximum speed) VLT of the lane where the host vehicle HV is traveling based on the image data. When the speed limit VLT drops significantly, the device DS increases the collision determination time threshold TTCth for starting the collision avoidance assistance action (here, automatic braking) by the time correction time dTTCth from the time point to the time point when the time corresponding to the change time threshold Tth has passed (correction period). That is, the device DS changes the collision determination condition for starting the collision avoidance assistance action (automatic braking) to a condition that is easier to be satisfied during the correction period.

[0042] Specific work

[0043] The CPU 10a (hereinafter referred to as "CPU") of the driving assistance ECU 10 executes the following operation every time a predetermined time (operation cycle) dt has passed. Figure 2 to Figure 4 as well as Figure 6 In the following, "step" is referred to as "S".

[0044] Correction of the collision judgment time threshold (correction of the execution start timing of the collision avoidance assist action)

[0045] When the predetermined timing is reached, the CPU Figure 2 The process starts from S200 and proceeds to S210 to determine whether the speed limit set for the own lane is newly acquired (recognized from the image) based on the image data sent from the camera device 20. In addition, the CPU can also acquire the speed limit set for the own lane based on the current position of the own vehicle HV and map information via the navigation ECU 80.

[0046] When a new speed limit is obtained, the CPU proceeds from S210 to S220, and stores the new speed limit obtained in S210 as the current speed limit VLTnow in RAM 10c (hereinafter referred to as "RAM"). At this time, the CPU changes the speed limit displayed in area 71a of display 71 to the current speed limit VLTnow.

[0047] Next, the CPU proceeds to S230 and reads the speed limit reduction amount threshold value VLTth from the nonvolatile memory 10d (hereinafter referred to as "nonvolatile memory"). Next, the CPU proceeds to S240 and reads the reference threshold value TTCthStd from the nonvolatile memory.

[0048] Next, the CPU proceeds to S250 to determine whether the speed limit decrease amount dV1 is greater than the speed limit decrease amount threshold value VLTth read from the nonvolatile memory. The speed limit decrease amount dV1 is a value obtained by subtracting the current speed limit VLTnow from the past speed limit (past speed limit) VLTold recognized until now. That is, the CPU determines in S230 whether the speed limit has decreased significantly more than the speed limit decrease amount threshold value VLTth.

[0049] When the speed limit decrease amount dV1 is less than the speed limit decrease amount threshold value VLTth (i.e., the speed limit has not decreased significantly more than the speed limit decrease amount threshold value VLTth), the CPU enters S260 from S250. In S260, the CPU sets the collision determination time threshold value TTCth to the reference threshold value TTCthStd read from the non-volatile memory and saves it to the RAM. In addition, S260 can also be omitted. The collision determination time threshold value TTCth is set to the "reference threshold value TTCthStd read from the non-volatile memory" at the start of the vehicle HV. Next, the CPU enters S270 and sets the past speed limit VLTold to the current speed limit VLTnow. That is, the CPU saves the current speed limit VLTnow saved to the RAM in S220 as the past speed limit VLTold to the RAM. After that, the CPU enters S295 and ends this routine once.

[0050] In contrast, when the speed limit decrease amount dV1 is greater than the speed limit decrease amount threshold value VLTth when the CPU enters S250 (i.e., when the speed limit has decreased significantly compared to the speed limit decrease amount threshold value VLTth), the CPU enters S280 from S250. In S280, the CPU reads the timing correction time dTTCth from the non-volatile memory. Next, the CPU enters S290, sets the collision determination time threshold value TTCth to "the value obtained by adding the timing correction time dTTCth to the reference threshold value TTCthStd" and saves it to the RAM. "The value obtained by adding the timing correction time dTTCth to the reference threshold value TTCthStd" is also referred to as the corrected collision determination time threshold value. Thereafter, the CPU enters S270 and enters S295.

[0051] Correction of collision judgment time threshold has been completed

[0052] When the predetermined timing is reached, the CPU Figure 3The process starts from S300 and enters S310. In S310, the CPU determines whether the collision determination time threshold TTCth stored in the RAM is equal to the corrected determination time threshold (i.e., "the value obtained by adding the timing correction time dTTCth to the reference threshold TTCthStd") (whether it is in a state where the collision determination time threshold TTCth is corrected).

[0053] When the collision determination time threshold value TTCth is the corrected determination time threshold value (=TTCthStd+dTTCth), the CPU proceeds from S310 to S320 to read the changed time threshold value Tth from the nonvolatile memory.

[0054] Next, the CPU proceeds to S330 to determine whether the duration from when the collision determination time threshold TTCth was changed to the corrected determination time threshold (=TTCthStd+dTTCth) is greater than the change time threshold Tth. That is, the CPU determines in S330 whether the change time threshold Tth has passed since the time point when the speed limit has dropped significantly from the speed limit reduction threshold VLTth.

[0055] When the change time threshold Tth has passed since the time point when the collision determination time threshold TTCth is changed to the corrected determination time threshold (=TTCthStd+dTTCth), the CPU enters S340 from S330 and sets the collision determination time threshold TTCth to the reference threshold TTCthStd. That is, the CPU restores the collision determination time threshold TTCth to the value before the change (before the change) by adding the timing correction time dTTCth. Thereafter, the CPU enters S395 and ends this routine once.

[0056] When the collision determination time threshold TTCth is not the corrected determination time threshold (=TTCthStd+dTTCth) when the CPU proceeds to S310 (ie, when the collision determination time threshold TTCth is not corrected), the CPU proceeds directly from S310 to S395.

[0057] Furthermore, when the CPU enters S330, if the time point at which the collision determination time threshold value TTCth is changed to the modified determination time threshold value (=TTCthStd+dTTCth) has not passed the modified time threshold value Tth, the CPU directly enters S395 from S330. As described above, during the period from the time point at which the speed limit drops significantly below the speed limit reduction amount threshold value VLTth to the time point at which the modified time threshold value Tth is passed, the collision determination time threshold value TTCth is maintained as the modified determination time threshold value (=TTCthStd+dTTCth).

[0058] Collision Avoidance Assist Control

[0059] When the predetermined timing is reached, the CPU Figure 4 The process starts from S400 and enters S410, and determines whether there is a target object (obstacle) in the area where the vehicle HV is to travel within a certain period of time based on the camera information and radar information. If there is no target object (obstacle) in the area where the vehicle HV is to travel within a certain period of time, the CPU directly enters S495 from S410 and ends this routine once.

[0060] In contrast, when there is a target object (obstacle) in the area where the host vehicle HV is to travel within a certain period of time, the CPU enters S420 from S410 and calculates the time required for collision TTC by dividing the distance between the obstacle and the host vehicle HV by the relative speed of the obstacle. That is, the CPU calculates the time required until the host vehicle collides with the obstacle as the time required for collision TTC. Then, the CPU enters S430 and reads the collision determination time threshold TTCth from the RAM.

[0061] Next, the CPU enters S440 to determine whether the time required for collision TTC is less than "the value obtained by adding the alarm time difference DTW to the collision determination time threshold TTCth". That is, the CPU determines in S440 whether the first collision determination condition (alarm generation condition) that is established when it is predicted that the vehicle will collide with the target object is established. When the time required for collision TTC is less than "the value obtained by adding the alarm time difference DTW to the collision determination time threshold TTCth", the CPU enters S450 from S440. In S450, the CPU displays an alarm mark in the alarm display area 71b of the display 71 and generates an alarm sound by sending an instruction signal to the notification ECU 70. The display of the alarm mark and / or the generation of the alarm sound is one of the collision avoidance auxiliary actions for avoiding the collision of the vehicle with the target object. After that, the CPU enters S460.

[0062] On the other hand, when the time required for collision TTC is longer than “the value obtained by adding the warning time difference DTW to the collision determination time threshold TTCth”, the CPU proceeds directly from S440 to S460.

[0063] In S460, the CPU determines whether the time required for collision TTC is less than the collision determination time threshold TTCth. That is, in S460, the CPU determines whether the second collision determination condition (automatic braking execution condition) that is established when it is predicted that the vehicle will collide with the target object is established. When the time required for collision TTC is less than the collision determination time threshold TTCth, the CPU enters S470 from S460. In S470, the CPU performs automatic braking (automatically applies braking force to the vehicle HV) in a manner that stops the vehicle HV in front of the obstacle by sending an instruction signal to the brake ECU50. The execution of this automatic braking is one of the collision avoidance auxiliary actions for avoiding the collision between the vehicle and the target object. Afterwards, the CPU enters S495 and ends this routine once. On the other hand, when the time required for collision TTC is longer than the collision determination time threshold TTCth, the CPU directly enters S495 from S460 and ends this routine once.

[0064] Threshold setting

[0065] The setting input device 94 includes a display touch panel that displays touch buttons. Figure 5A Menu screen 500 is shown.

[0066] If the driver touches the display button 501 to change the "collision avoidance assistance timing", the setting input device 94 displays Figure 5B The collision avoidance assistance timing selection screen 510 is shown. The driver touches any one of the display buttons "early 511, normal 512 and late 513" from the selection screen 510. Figure 6 In the routine shown, the reference threshold value TTCthStd for determining the collision avoidance assistance timing is changed. In the default state (initial state), “Normal 512” is automatically selected, and the reference threshold value TTCthStd is set to the standard value TStdN and stored in the nonvolatile memory of the driving assistance ECU 100.

[0067] If the driver touches the display button 502 on the menu screen 500 to change the "corrected collision avoidance assistance timing", the setting input device 94 displays Figure 5C The driver touches one of the display buttons of "early 521, normal 522 and late 523" from the selection screen 520. Figure 6The routine shown in the figure changes the timing correction time dTTCth of the corrected collision avoidance assistance timing. In addition, in the default state (initial state), "Normal 522" is automatically selected, and the timing correction time dTTCth is set to "a value of 2 / 3 times the correction margin TS" and stored in the non-volatile memory of the driving assistance ECU 100. The correction margin TS is also called the "difference TS", and its details will be described later.

[0068] If the driver touches the display button 503 on the menu screen 500 to change the "speed limit decrease amount threshold value", the setting input device 94 displays Figure 5D The speed limit decrease threshold selection screen 530 is shown. The driver can select the speed limit decrease threshold value by touching any one of the display buttons "slightly larger 531, normal 532, and slightly smaller 533" from the selection screen 530. Figure 6 In the default state (initial state), “Normal 532” is automatically selected, and the speed limit reduction amount threshold value VLTth is set to a standard value VLTthN and stored in the nonvolatile memory of the driving assistance ECU 100 .

[0069] If the driver touches the display button 504 on the menu screen 500 to change the length of the collision avoidance assistance timing correction period, the setting input device 94 displays Figure 5E The auxiliary timing correction period length selection screen 540 is shown. The driver can select the auxiliary timing correction period length by touching any one of the display buttons of "slightly longer 541, normal 542 and slightly shorter 543" from the selection screen 540. Figure 6 The change time threshold Tth is changed by the routine shown in the figure. In the default state (initial state), “Normal 542” is automatically selected, and the change time threshold Tth is set to the standard value TthN and stored in the nonvolatile memory of the driving assistance ECU 100.

[0070] When the predetermined timing is reached, the CPU Figure 6 The CPU starts processing from S600 and enters S605. In S605, the CPU determines whether Figure 5B The collision avoidance assistance timing selection screen 510 shown is displayed as to which of the buttons selected is “early 511, normal 512, and late 513”.

[0071] When "early 511" is selected, the CPU performs the processing of S610 described below. When "normal 512" is selected, the CPU proceeds to the processing of S615 described below. When "later 513" is selected, the CPU performs the processing of S620 described below. After performing any of these processes, the CPU proceeds to S625.

[0072] S610 : The CPU sets the reference threshold value TTCthStd to a value (first value) TStdL corresponding to a relatively longer time, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0073] S615 : The CPU sets the reference threshold value TTCthStd to a standard value TStdN corresponding to a medium period of time, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0074] S620 : The CPU sets the reference threshold value TTCthStd to a value (second value) TStdS corresponding to a relatively shorter time, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0075] In addition, the above-mentioned values ​​are set so that the following inequality is satisfied.

[0076] TStdL>TStdN>TStdS

[0077] When the CPU proceeds to S625, it subtracts "the reference threshold value TTCthStd set in any of S610 to S620" from "the value TStdL corresponding to a relatively long time" and stores the value (TStdL-TTCthStd) as the correction margin TS in the nonvolatile memory of the driving support ECU 100. Thereafter, the CPU proceeds to S630.

[0078] The CPU determines in S630 that the Figure 5C The corrected collision avoidance assistance timing selection screen 520 shown is displayed as to which of the buttons selected is “early 521, normal 522, and late 523”.

[0079] When "early 521" is selected, the CPU performs the processing of S635 described below. When "normal 522" is selected, the CPU performs the processing of S640 described below. When "later 523" is selected, the CPU performs the processing of S645 described below. After performing any of these processes, the CPU proceeds to S650.

[0080] S635 : The CPU sets the timer correction time dTTCth to a correction margin TS corresponding to a relatively longer time, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0081] S640 : The CPU sets the timer correction time dTTCth to a value corresponding to a medium time, that is, “a value 2 / 3 times the correction margin TS”, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0082] S645 : The CPU sets the timer correction time dTTCth to a value corresponding to a relatively shorter time, that is, “a value 1 / 3 times the correction margin TS”, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0083] Note that the correction margin TS is a positive value, and therefore, the inequality “TS>(2 / 3)·TS>(1 / 3)·TS” naturally holds true for the above-mentioned values.

[0084] Since the timing correction time dTTCth is set in this way, the corrected judgment time threshold (=TTCthStd+dTTCth) changes from "a value TStdL corresponding to a relatively slightly longer time" to "the reference threshold TTCthStd set in any one of S610 to S620 (to be precise, TTCthStd+(1 / 3)·TS)". Therefore, in the period from the time point when the speed limit drops significantly below the speed limit decrease amount threshold VLTth to the time point when the change time threshold Tth is passed (correction period), the start timing of the collision avoidance assistance action is set to the earliest timing between the start timing of the collision avoidance assistance action desired by the driver during normal driving and the start timing of the collision avoidance assistance action allowed by the system. Therefore, in the correction period, the collision avoidance assistance action is started at a timing earlier than the start timing of the collision avoidance assistance action desired by the driver during normal driving, but the situation in which the collision avoidance assistance action is started at an unnecessarily early timing can be avoided.

[0085] The CPU passes the S650 Figure 5D The speed limit decrease amount threshold value selection screen 530 shown is which of the display buttons selected is "slightly larger 531, normal 532, and slightly smaller 533".

[0086] When "slightly larger 531" is selected, the CPU performs the processing of S655 described below. When "normal 532" is selected, the CPU performs the processing of S660 described below. When "slightly smaller 533" is selected, the CPU performs the processing of S665 described below. After performing any of these processes, the CPU proceeds to S670.

[0087] S655 : The CPU sets the speed limit reduction amount threshold value VLTth to a relatively larger value VLTthL, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0088] S660 : The CPU sets the speed limit reduction amount threshold value VLTth to a medium value VLTthN, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0089] S665 : The CPU sets the speed limit reduction amount threshold value VLTth to a relatively small value VLTthS, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0090] In addition, the above-mentioned values ​​are set so that the following inequality is satisfied.

[0091] VLTthL>VLTthN>VLTthS

[0092] The CPU passes the S670 judgment. Figure 5E The auxiliary timing correction period length selection screen 540 shown is displayed to indicate which of the buttons selected is “slightly longer 541, normal 542, and slightly shorter 543”.

[0093] When "slightly longer 541" is selected, the CPU performs the processing of S675 described below. When "normal 542" is selected, the CPU performs the processing of S680 described below. When "slightly shorter 543" is selected, the CPU performs the processing of S685 described below. After performing any of these processes, the CPU enters S695 and ends this routine once.

[0094] S675 : The CPU sets the change time threshold value Tth to a value TthL corresponding to a relatively longer time, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0095] S680 : The CPU sets the change time threshold value Tth to a value TthN corresponding to a time of medium length, and stores the value in the nonvolatile memory of the driving assistance ECU 100 .

[0096] S685 : The CPU sets the change time threshold value Tth to a value TthS corresponding to a relatively shorter time, and stores it in the nonvolatile memory of the driving assistance ECU 100 .

[0097] In addition, the above-mentioned values ​​are set so that the following inequality is satisfied.

[0098] TthL>TthN>TthS

[0099] As described above, when the current speed limit is significantly reduced from the previous speed limit by the speed limit reduction threshold VLTth, the device DS changes the collision determination time threshold TTCth to the corrected determination time threshold (=TTCthStd+dTTCth). Thus, the collision determination condition of the collision avoidance auxiliary action is changed to a condition that is easier to be satisfied. Even if the driver of the host vehicle misses the speed limit reduction and delays the response to the sudden deceleration of the preceding vehicle, the collision determination condition will be satisfied as early as possible, thereby executing the collision avoidance auxiliary action as early as possible. Thus, it is possible to avoid the host vehicle from being extremely close to the preceding vehicle.

[0100] In addition, the present invention is not limited to the above-mentioned embodiments and modifications, and various modifications can be adopted within the scope of the present invention. For example, the CPU can also identify the current speed limit by receiving the speed limit from the roadside machine via the communication ECU 90 in S210. Moreover, the present invention can be applied to the vehicle in which the driving mode has been transferred from the automatic driving to the driver's driving in the automatic driving vehicle. The types of values ​​changed by setting the operation of the input device 94 are 3, but can also be N (N is an integer greater than 2). Moreover, when the CPU determines "No" in S330, it determines whether the current speed limit is greater than the past speed limit. The CPU can also enter S340 when the current speed limit is greater than the past speed limit, and enter S395 when the current speed limit is not greater than the past speed limit.

Claims

1. A driving assistance device for a vehicle, The driving assistance device includes a controller configured to execute a collision avoidance assistance operation for avoiding a collision between the host vehicle and the target object when a collision determination condition that is established when it is predicted that the host vehicle will collide with the target object is established. The controller is composed of: identifying a speed limit that applies to a lane in which the host vehicle is traveling, When a speed limit newly identified at a current time point, i.e., a current speed limit, has decreased from a speed limit identified immediately before the current time point, i.e., a past speed limit, the collision determination condition is changed to a condition that is easily satisfied in such a manner that the collision avoidance assistance action is performed at an earlier timing than when the current speed limit has not decreased from the past speed limit.

2. The driving assistance device for a vehicle according to claim 1, The driving assistance device includes a setting input device operated by a passenger of the host vehicle. The controller is configured to change the collision determination condition to the condition that is likely to be satisfied when the current speed limit is reduced by a speed limit reduction amount threshold or more from the past speed limit, The controller is further configured to be capable of changing the speed limit decrease amount threshold value based on an input to the setting input device.

3. The driving assistance device for a vehicle according to claim 1, The driving assistance device includes a setting input device operated by a passenger of the host vehicle. The controller is configured to restore the collision determination condition to the condition before the change when the elapsed time from the time point when the collision determination condition is changed to the condition that is easily satisfied reaches a change time threshold, The controller is further configured to be capable of changing the change time threshold based on an input to the setting input device.

4. The driving assistance device for a vehicle according to claim 1, The driving assistance device includes a setting input device operated by a passenger of the host vehicle. The controller is further configured to be capable of changing the degree to which the easily satisfied condition is easily satisfied based on an input to the setting input device.

5. The driving assistance device for a vehicle according to claim 1, The driving assistance device includes a setting input device operated by a passenger of the host vehicle. The controller is composed of: calculating a collision time required until the host vehicle collides with the target object, When the collision required time becomes equal to or smaller than a collision determination time threshold, it is determined that the collision determination condition is satisfied, The controller is further configured to change the collision determination time threshold used for determining whether the collision determination condition is satisfied when the collision determination condition is not changed to a reference threshold between a first value and a second value smaller than the first value based on an input to the setting input device. The controller is further configured to change the collision determination condition to the condition that is likely to be satisfied by changing the collision determination time threshold to a value obtained by adding a timing correction time to the reference threshold, The controller is further configured to be able to change the timing correction time based on an input to the setting input device, The timing correction time is set so as to be equal to or less than a difference value obtained by subtracting the reference threshold value from the first value.

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