DRIVER ASSISTANCE DEVICE FOR VEHICLES

Abstract

A driver assistance ECU executes a collision avoidance assistance operation to avoid a collision between a host vehicle and an object when a collision determination condition, which is satisfied when the host vehicle is predicted to collide with the object, is met. The driver assistance ECU detects a speed limit applied to a lane in which the host vehicle is currently traveling, and, if a current speed limit newly detected at a current time is lower than a past speed limit detected up to immediately before the current time, changes the collision determination condition to a condition that is easily satisfied so that the collision avoidance assistance operation is performed at an earlier time than when the current speed limit is not lower than the past speed limit.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe invention relates to a driver assistance device for a vehicle that performs driver assistance control for reducing a possibility of collision between a host vehicle and an object.2. Description of Related ArtA related-art device acquires image data by capturing an image of a scene in front of a host vehicle with an on-board camera and recognizing a road sign in the image data. Further, the related-art apparatus extracts a speed limit (maximum speed) from the recognized road sign and notifies this speed limit to an occupant of the host vehicle (see Japanese Unexamined Patent Application JP 2017-62 696 A).SUMMARY OF THE INVENTIONHowever, the related art apparatus makes only notification of the speed limit, and therefore, there is a case that a driver of the host vehicle does not immediately notice that the speed limit has been changed. For example, when the speed limit largely decreases and a preceding vehicle largely decelerates according to the decrease of the speed limit, when the driver of the host vehicle does not notice the decrease of the speed limit, a time point at which the driver applies a brake is decelerated. This results in the possibility that the host vehicle approaches the vehicle traveling ahead. The related-art apparatus cannot effectively use the information on the recognized speed limit in such a situation.The present invention has been made to solve such a problem. In other words, one of the objects of the present invention is to provide a driver assistance device for a vehicle, the driver assistance device being capable of more effectively utilizing the information regarding the recognized speed limit.An aspect of a driver assistance apparatus for a vehicle of the present invention includes a controller (10, 50, 70) configured to perform a collision avoidance assistance process (S450, S470) when a collision determination condition is satisfied (S440, S460), wherein the collision avoidance assistance process is a process for avoiding a collision between a host vehicle and an object, and the collision determination condition is a condition satisfied when it is predicted that the host vehicle will collide with the object.The controller is configured to recognize a speed limit applicable to a traveling lane in which the host vehicle is traveling, and when a current speed limit is lower than a past speed limit (S 250: YES), to change the collision determination condition to a condition that is slightly satisfied (S 290), to perform the collision avoidance assist process at a timing earlier than when the current speed limit is not lower than the past speed limit (S 250: NO), wherein the current speed limit is a speed limit newly recognized at a current timing (S 210), and wherein the past speed limit is a speed limit recognized until immediately before the current timing.When the speed limit (current speed limit) newly detected at the present time is lower than the speed limit (past speed limit) detected so far, it is highly likely that a preceding vehicle is rapidly decelerating. Thus, in such a case, in the above aspect, the collision determination condition is changed to a condition that is easily satisfied in order for the collision avoidance assist process to be performed at an earlier time. More specifically, the collision determination condition is a condition that is satisfied when a collision index value indicating a possibility of a collision between the host vehicle and the object has reached a threshold value. In this case, the collision determination condition may be changed to a more readily satisfied condition by changing the threshold value or correcting the collision index value. For example, when the collision determination condition is a condition that is satisfied when a "time-to-collision as a collision index value" that becomes a remaining time until the host vehicle collides with the object becomes equal to or less than a collision determination time threshold, the collision determination condition is changed to a condition that is more easily satisfied by increasing the collision determination time threshold or making a correction to decrease the time-to-collision.As a result, even if a driver of the host vehicle overlooks the decrease in the speed limit and responds too late to rapid deceleration of the preceding vehicle, the collision determination condition is satisfied early and the collision avoidance assist process is executed early. This can prevent the host vehicle from extremely approaching the preceding vehicle.In the above description, names and / or reference numerals used in the embodiment are attached in brackets to components of the invention corresponding to the embodiment to be described later in order to facilitate understanding of the invention. However, the respective constituent elements of the invention are not limited to those indicated by the terms and / or the reference numerals. The present invention relates to a driver assistance method for a vehicle and to a program of the driver assistance method.BRIEF DESCRIPTION OF THE FIGURESFeatures, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1 is a schematic configuration diagram of a driver assistance device for a vehicle according to an embodiment of the present invention; FIG. 2 shows a routine illustrated in FIG. 1 to be executed by a CPU of a driver assistance ECU; FIG. 3 shows a routine to be executed by the CPU of the driver assistance ECU shown in FIG. 1 ; FIG. 4 shows a routine to be executed by the CPU of the driver assistance ECU shown in FIG. 1 ; FIG. 5A is a view showing a menu screen displayed on a setting input device illustrated in FIG. 1 ; FIG. 5B is a view showing a collision avoidance assistance timing selection window displayed on the setting input device illustrated in FIG. 1 ; FIG. 5C is a view showing the corrected collision avoidance assistance timing selection window displayed on the setting input device in FIG. 1 ; FIG. 5D is a view showing a speed limit decrease threshold selection window displayed on the setting input device illustrated in FIG. 1 ; FIG. 5E is a view showing an assist timing correction period length selection window illustrated in the setting input device in FIG. 1 ; and FIG. 6 shows a routine to be executed by the CPU of the driver assistance ECU shown in FIG. 1.DETAILED DESCRIPTION OF THE EMBODIMENTSA "driver assistance device DS" for a vehicle (hereinafter referred to as "device DS")" according to an embodiment of the present invention includes the components illustrated in FIG. 1 and is applied to a host vehicle HV. The host vehicle HV may be a vehicle having an engine as a power source, a vehicle having an electric motor as a power source (i.e., a battery electric vehicle), a hybrid electric vehicle, and the like.In the present specification, an "ECU" is an electronic control unit (controller) including a microcomputer including a CPU (processor), a ROM, a RAM, a nonvolatile memory, an interface, and the like. The control device is also referred to as a controller or computer. A plurality of the controllers illustrated in FIG. 1 are connected so as to be able to exchange information with each other via a controller area network (CAN). Some or all of the plurality of controllers may be integrated into one controller.The driver assistance ECU 10 executes a driver assistance control, also referred to as "collision avoidance assistance control", for reducing a possibility of collision between a host vehicle and an object (obstacle) using the components illustrated in FIG. 1.A camera device 20 includes a camera 21 and an image ECU 22. The camera 21 captures an image of a scene in front of the host vehicle HV whenever a predetermined period has elapsed to acquire image data. The image ECU 22 generates "camera information including the image data itself, camera object information, and lane information" based on the image data from the camera 21, and transmits the camera information to the driver assistance ECU 10.The driver assistance ECU 10 extracts a "road sign indicating a maximum speed" included in the image data on the basis of the image data captured by the camera device 20. The driver assistance ECU 10 recognizes (detects) a numerical value displayed in the road sign as a speed limit (maximum speed) set / valid for a "lane (hereinafter also referred to as "own lane") on which the host vehicle HV is traveling at a current time.". The recognition (detection) of the speed limit can be carried out by the image control device 22.The radar device 30, which is a known device that acquires information regarding an object located in front of the host vehicle HV using a radio wave in a millimeter wave band, includes a radar 31 and a radar ECU 32. The radar 31 transmits a millimeter wave within a predetermined detection range every time a predetermined period of time has elapsed, and receives a millimeter wave reflected from the object. The radar 31 transmits information on the transmitted and received millimeter wave to the radar ECU 32 and back. The radar ECU 32 acquires radar information based on the information of the radar 31 and transmits the radar information to the driver assistance ECU 10. The radar information includes a distance to the object, a direction of the object, a relative speed of the object, and the like.A powertrain ECU 40 controls a driving device (not illustrated) including a power source of the host vehicle HV by driving a powertrain actuator 41 to thereby generate driving force.A brake ECU 50 controls a brake device (not illustrated) of the host vehicle HV by driving a brake actuator 51 to thereby apply a braking force to the host vehicle HV. When the brake ECU 50 receives a command from the driver assistance ECU 10, the brake ECU 50 performs automatic braking that automatically applies a braking force to the host vehicle HV by driving the brake actuator 51.A steering ECU 60 controls a steering device (not illustrated) of the host vehicle HV by driving a steering motor 61 to thereby change a steering angle of the host vehicle HV. When the steering ECU 60 receives a command from the driver assistance ECU 10, the steering ECU 60 automatically changes the steering angle of the host vehicle HV (i.e., performs automatic steering) by driving the steering motor 61.A notification ECU (alarm ECU) 70 is connected to a display device 71 disposed at a position where the display device 71 can be viewed from a seat of a driver, and an alarm sound generator 72 that generates an alarm sound and controls the display device 71 and the alarm sound generator 72 according to a command (command signal) from the driver assistance ECU 10. In the display device 71, an area 71 ain which a speed limit (maximum speed) is displayed and an alarm display area 71 bin which an alarm sign making a notification of a collision risk is displayed are provided. The notification ECU 70 displays a speed limit included in the instruction of the driver assistance ECU 10 in the area 71 a, and displays an alarm mark according to the instruction of the driver assistance ECU 10 in the alarm display area 71 b.A navigation control device 80 is connected to a GPS receiver 81, a map database 82 in which map information is stored, and a display touch panel 83 that displays a touch button and constitutes an on-board navigation system with the GPS receiver 81, the map database 82, and the display touch panel 83. The navigation ECU 80 detects a current position of the host vehicle HV based on a GPS signal received from the GPS receiver 81. The navigation ECU 80 may determine the speed limit set / valid for the own lane at the current time based on the detected current position of the host vehicle HV and the map information stored in the map database 82.A communication ECU 90 may perform wireless communication with external devices (such as a road machine and an information management center) of the host vehicle HV and obtain "various kinds of information including information regarding the speed limit" from the external devices.The driver assistance ECU 10 receives inputs of detection values (output values) of the following "sensors and switches":an accelerator pedal operation amount sensor 91 that detects an accelerator pedal operation amount AP of the host vehicle HVa brake pedal operation amount sensor 92 that detects a brake pedal operation amount BP of the host vehicle HVa vehicle speed sensor 93 that detects a speed (i.e., host vehicle speed) of the host vehicle HVA setting input device 94 includes a display touch panel provided at a location where the display touch panel can be operated by the driver, the display touch panel displaying a touch button. By the driver operating the setting input device 94, a "collision determination time threshold TTCth, a collision avoidance assist control execution start timing correction time dTTth, a magnitude of a speed limit decrease threshold VLTth for the shift control, a length of a control shift period (change time threshold) Tth, and the like" which will be described later may be changed.Overview of OperationThe device DS detects (recognizes) a speed limit VLT of a lane in which the host vehicle HV is traveling from image data. When the speed limit VLT largely decreases, the device DS increases the collision determination time threshold TTCth for starting a collision avoidance assist operation (here, automatic braking) by an amount corresponding to the timing correction time dTTth during a period (correction period) until a period corresponding to the change time threshold Tth has elapsed since the speed limit VLT largely decreases. In other words, the device DS changes the collision determination condition for the start of the collision avoidance assist process (automatic braking) to a condition that is more easily satisfied during the correction period.Specific OperationA CPU 10 a(hereinafter, simply referred to as "CPU") of the driver assistance ECU 10 executes routines displayed in the flowcharts of FIGS. 2 to 4 and 6 each time a predetermined period (calculation period) dt has elapsed. Note that hereinafter, "step" is expressed as "S".Collision Determination Time Threshold Correction (Correction of Execution Start Timing of Collision Avoidance Assist Operation)At a predetermined time, the CPU starts the processing of S 200 in FIG. 2, the process proceeds to S 210, and the CPU determines whether the speed limit set for the own lane is newly detected (recognized from the image) based on the image data transmitted from the camera device 20. Note that the CPU may determine the speed limit set for the own lane from the current position of the host vehicle HV and the map information via the navigation controller 80.When the speed limit is newly detected, the process proceeds from S 210 to S 220, and the CPU stores the speed limit newly detected in S 210 in a RAM 10 c(hereinafter referred to as "RAM") as the current speed limit VLTnow. In this case, the CPU changes the speed limit displayed in the area 71 aof the display device 71 to the current speed limit VLTnow.Then, the process proceeds to S 230, and the CPU reads out the speed limit decrease threshold VLTth from a nonvolatile memory 10 d(hereinafter, referred to as "nonvolatile memory"). Then, the process proceeds to S 240 and the CPU reads a reference threshold value TTCthStd from the nonvolatile memory.Then, the process proceeds to S 250, and the CPU determines whether a speed limit reduction amount dV 1 is larger than the speed limit decrease threshold VLTth read out from the nonvolatile memory. The speed limit reduction amount dV 1 is a value obtained by subtracting the current speed limit VLTnow from a speed limit detected until the present in the past (past speed limit) VLTold. In other words, the CPU determines whether the speed limit decreases by an amount larger than the speed limit decrease threshold VLTth in S 230.When the speed limit reduction amount dV 1 is less than or equal to the speed limit decrease threshold VLTth (i.e., when the speed limit does not decrease by an amount greater than the speed limit decrease threshold VLTth), the process of the CPU proceeds from S 250 to S 260. In S 260, the CPU sets the reference threshold value TTCthStd read out from the nonvolatile memory to the collision determination time threshold value TTCth, and stores the threshold value in the RAM. Note that S 260 may be omitted. The "reference threshold value TTCthStd" read out from the nonvolatile memory is set to the collision determination time threshold value TTCth upon starting of the host vehicle HV. Then, the process proceeds to S 270 and the CPU sets the current speed limit VLTnow to the past speed limit VLTold. In other words, the CPU stores the current speed limit VLTnow stored in the RAM in S 220 as the past speed limit VLTold in the RAM. Then, the process proceeds to S 295, and the CPU ends the current routine once.In contrast, when the speed limit reduction amount dV 1 is larger than the speed limit decrease threshold VLTth (i.e., when the speed limit decreases by an amount larger than the speed limit decrease threshold VLTth), when the process of the CPU proceeds to S 250, the process of the CPU proceeds from S 250 to S 280. The CPU reads out the timing correction time dTTth from the nonvolatile memory in S 280. Then, the process proceeds to S 290, and the CPU sets a "value obtained by adding the timing correction time dTTth to the reference threshold value TTCthStd" to the collision determination time threshold value TTCth, and stores the threshold value in the RAM. The "value obtained by adding the timing correction time dTTth to the reference threshold value TTCthStd" is also referred to as a corrected collision determination time threshold value. Then, the process of the CPU proceeds to S 270 and proceeds to S 209.Compensating End of Collision Determination Time ThresholdAt a predetermined timing, the CPU starts the processing from S 300 in FIG. 3, and the process proceeds to S 310. In S 310, 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 dTTth to the reference threshold TTCthStd") (whether the collision determination time threshold TTCth is in a corrected state).When the collision determination time threshold TTCth is the corrected determination time threshold (= TTCthStd+dTTth), the process proceeds from S 310 to S 320, and the CPU reads out the change time threshold Tth from the nonvolatile memory.Then, the process proceeds to S 330 and the CPU determines whether a duration since the collision determination time threshold TTCth has been changed to the corrected determination time threshold (= TTCthStd+dTTth) is equal to or greater than the change time threshold Tth. In other words, the CPU determines whether the change time threshold Tth has elapsed from a time point at which the speed limit has decreased by an amount larger than the speed limit decrease threshold VLTth in S 330.When the change time threshold Tth has elapsed from the time point when the collision determination time threshold TTCth was changed to the corrected determination time threshold (= TTCthStd+dTTth), the process proceeds from S 330 to S 340, and the CPU sets the reference threshold TTCthStd to the collision determination time threshold TTCth. In other words, the CPU resets the collision determination time threshold value TTCth to a value before the timing correction time dTTth is added (before change). Then, the process proceeds to S395 and the CPU once ends the current routine.Note that when the collision determination time threshold TTCth is not the corrected determination time threshold (= TTCthStd+dTTth) (i.e., when the collision determination time threshold TTCth is uncorrected), when the process of the CPU proceeds to S 310, the process of the CPU directly proceeds from S 310 to S 195.Further, when the change time threshold Tth has not elapsed from the time point when the collision determination time threshold TTCth has been changed to the corrected determination time threshold (= TTCthStd+dTTth), when the process of the CPU proceeds to S 330, the process of the CPU directly proceeds from S 330 to S 195. By the above-described method, the collision determination time threshold TTCth is maintained at the corrected determination time threshold (= TTCthStd+dTTth) until the change time threshold Tth has elapsed from the time point when the speed limit has decreased by an amount larger than the speed limit decrease threshold VLTth.Collision Avoidance Assist ControlAt a predetermined time, the CPU starts the processing of S 400 in FIG. 4, the method proceeds to S 410, and the CPU determines whether an object (obstacle) exists in an area in which the host vehicle HV is to travel within a specified period of time based on the camera information and the radar information. When there is no object (obstacle) in the area where the host vehicle HV is to travel within the specified period of time, the process directly proceeds from S 410 to S 495, and the CPU ends the current routine once.On the other hand, when an object (obstacle) exists in the area in which the host vehicle HV is to travel within the set period of time, the process proceeds from S 410 to S 420, and the CPU calculates a time-to-collision TTC by dividing a distance between the obstacle and the host vehicle HV by a relative speed of the obstacle. In other words, the CPU calculates, as the time-to-collision TTC, a remaining time until the host vehicle collides with the obstacle. Then, the process proceeds to S 430 and the CPU reads out the collision determination time threshold TTCth from the RAM.Then, the process proceeds to S 440, and the CPU determines whether the time-to-collision TTC is less than or equal to a "value obtained by adding an alarm difference time DTW to the collision determination time threshold TTCth". In other words, the CPU determines whether a first collision determination condition (alarm generation condition) that is satisfied when it is predicted that the host vehicle will collide with the object is satisfied in S 440. When the time-to-collision TTC is less than or equal to "the value obtained by adding the alarm difference time DTW to the collision determination time threshold TTCth", the process of the CPU proceeds from S 440 to S 450. In S 450, the CPU displays an alarm mark in the alarm display area 71 bof the display device 71, and causes the alarm sound generator 72 to generate alarm sound by transmitting a command signal to the notification ECU 70. The display of the alarm sound is one of the collision avoidance assistance operations for avoiding a collision between the host vehicle and the object. After that, the process of the CPU proceeds to S 460.On the other hand, when the time-to-collision TTC is longer than the "value obtained by adding the alarm difference time DTW to the collision determination time threshold TTCth", the process of the CPU directly proceeds from S 440 to S 460.The CPU determines whether the time-to-collision TTC is equal to or less than the collision determination time threshold TTCth in S 460. In other words, the CPU determines whether a second collision determination condition (automatic brake execution condition) that is satisfied when it is predicted that the host vehicle will collide with the object is satisfied in S 460. When the time-to-collision TTC is less than or equal to the collision determination time threshold TTCth, the process of the CPU proceeds from S 460 to S 470. In S 470, the CPU performs the automatic braking of the host vehicle HV so that the host vehicle HV stops in front of the obstacle by sending a command signal to the brake ECU 50. The execution of the automatic braking is one of the collision avoidance assist operations for avoiding a collision between the host vehicle and the object. Then, the process proceeds to S 495, and the CPU once ends the current routine. On the other hand, when the time-to-collision TTC is longer than the collision determination time threshold TTCth, the process directly proceeds from S 460 to S 495, and the CPU ends the current routine once.setting the thresholdIncidentally, the setting input device 94 includes a display touch panel that displays a touch button and displays a menu screen 500 illustrated in FIG. 5A at normal times.When the driver touches a display button 501 to change "collision avoidance assistance timing", the setting input device 94 displays a collision avoidance assistance timing selection window 510 illustrated in FIG. 5B. The driver touches a display button of one of "early 511, normal 512 and late 513" from the selection window 510. In this way, the reference threshold TTCthStd for determining the collision avoidance assist timing may be changed by the routine indicated in FIG. 6, which will be described later. Note that in a default state (initial state), "normal 512" is automatically selected, and a default value TStdN is set to the reference threshold value TTCthStd and stored in the nonvolatile memory of the driver assistance ECU 100.When the driver touches a display button 502 on the menu screen 500 to change the "corrected collision avoidance assistance timing", the setting input device 94 displays a corrected collision avoidance assistance timing selection window 520 illustrated in FIG. 5C. The driver touches a display button of one of the options "early 521, normal 522 and late 523" from the selection window 520. In this way, the timing correction time dTTth for determining the corrected collision avoidance assist timing may be changed by the routine indicated in FIG. 6, which will be described later. Note that in a default state (initial state), the "normal 522" is automatically selected, and a "value of 2 / 3 times a correction margin TS" is set to the timing correction time dTTth and stored in the nonvolatile memory of the driver assistance ECU 100. The correction margin TS is a value also referred to as a "difference value TS" which will be described later.When the driver touches a display button 503 on the menu screen 500 to change a "speed limit decrease threshold", the setting input device 94 displays a speed limit decrease threshold selection window 530 illustrated in FIG. 5D. The driver can change the speed limit decrease threshold VLTth by the routine shown in FIG. 6 described later by touching a display button of one of the options "large 531, normal 532, and small 533" from the selection window 530. Note that in a default state (initial state), the "normal 532" is automatically selected, and a default value VLTthNis set to the speed limit decrease threshold value VLTthand stored in the nonvolatile memory of the driver assistance ECU 100.When the driver touches a display button 504 on the menu screen 500 to change a "length of collision avoidance assistance timing correction period", the setting input device 94 displays an assistance timing correction period length selection window 540 illustrated in FIG. 5E. The driver can change the change time threshold Tth by the routine shown in FIG. 6, which will be described later, by touching a display button of one of the options "long 541, normal 542, and short 543" from the selection window 540. Note that in a default state (initial state), "normal 542" is automatically selected, and a default value TthN is set to the change time threshold value Tth and stored in the nonvolatile memory of the driver assistance ECU 100.At a predetermined timing, the CPU starts the processing of S 600 in FIG. 6, and the process proceeds to S 605. In S 605, the CPU determines which of "early 511, normal 512 and late 513" is selected as a display button on the collision avoidance assist timing selection window 510 illustrated in FIG. 5B.When "early 511" is selected, the CPU performs the processing described below in S 610. When "normal 512" is selected, the CPU performs the processing described below in S 615. When "late 513" is selected, the CPU performs the processing described below in S 620. After the CPU performs one of the processings, the process proceeds to S625.S 610: The CPU sets a value (first value) TStdL corresponding to a relatively long time to the reference threshold value TTCthStd, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 615: The CPU sets a default value TSthN corresponding to an average time to the reference threshold value TTCthStd, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 620: The CPU sets a value (second value) TStdS corresponding to a relatively short time to the reference threshold value TTCthStd, and stores the value in the nonvolatile memory of the driver assistance ECU 100.Note that the respective values are set so as to satisfy the following inequality.When the process proceeds to S625, the CPU stores a value (TStdL - TTCthStd) obtained by subtracting the "reference threshold value TTCthStd" set in one of S 610 to S 620 from the "relatively long time corresponding value TStdL" in the nonvolatile memory of the driver assistance ECU 100 as the correction margin TS. After that, the process of the CPU proceeds to S630.The CPU determines which of "early 521, normal 522, and late 523" is selected as a display button on the corrected collision avoidance assistance timing selection window 520 illustrated in FIG. 5C in S 630.When "early 521" is selected, the CPU performs the processing described below in S 333. When "normal 522" is selected, the CPU performs the processing described below in S 640. When "late 523" is selected, the CPU performs the processing described below in S 645. After the CPU performs one of the processings, the process proceeds to S650.S 365: The CPU sets the correction margin TS to the timing correction time dTTth corresponding to a relatively long time, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 640: The CPU sets a "value 2 / 3 times the correction margin TS", i.e., a value corresponding to a mean time at the timing correction time dTTth, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 645: The CPU sets a "value that is 1 / 3 times the correction margin TS", i.e., a value that corresponds to a relatively short time at the timing correction time dTTth, and stores the value in the nonvolatile memory of the driver assistance ECU 100.Note that the correction margin TS is a positive value, and thus an inequality "TS>(2 / 3)-TS>(1 / 3)-TS" is naturally satisfied for the respective values.Due to the timing correction time dTTth thus set, the corrected determination time threshold (= TTCthStd+dTTth) changes in a range from "value TStdL corresponding to the relatively long time" to "reference threshold TTCthStd (exactly, TTCthStd+(1 / 3)-TS)" set in one of S 610 to S 620". Thus, a start timing of the collision avoidance assist process is set to the earliest timing between a start timing of the collision avoidance assist process desired by the driver in the normal driving operation and a start timing of the collision avoidance assist process that is permitted in a system during a period (correction period) until the change time threshold Tth has elapsed since the speed limit value has decreased by an amount larger than the speed limit decrease threshold VLTth. Thereby, in the correction period during which the collision avoidance assist process is started at a timing earlier than the start timing of the collision avoidance assist process desired by the driver in normal travel, a situation in which the collision avoidance assist process is started at a timing earlier than required is avoided.The CPU determines which of "large 531, normal 532, and small 533" is selected as the display button on the speed limit decrease threshold selection window 530 illustrated in FIG. 5D in S 650.When "large 531" is selected, the CPU performs the processing described below in S655. When "normal 532" is selected, the CPU performs the processing described below in S 606. When "small 533" is selected, the CPU performs the processing described below in S 665. After the CPU performs one of the processings, the process proceeds to S670.S655: The CPU sets a relatively large value VLTthL to the speed limit decrease threshold value VLTth and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 606: The CPU sets an average value VLTthN to the speed limit decrease threshold value VLTth and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 665: The CPU sets a relatively small value VLTthS to the speed limit decrease threshold VLTth and stores the value in the nonvolatile memory of the driver assistance ECU 100.Note that the respective values are set so as to satisfy the following inequality.The CPU determines which of "long 541, normal 542, and short 543" is selected as a display key on the assist timing correction period length selection window 540 illustrated in FIG. 5E in S 670.When "long 541" is selected, the CPU performs the processing described below in S 675. When "normal 542" is selected, the CPU performs the processing described below in S 680. When "short 543" is selected, the CPU performs the processing described below in S 685. After the CPU performs one of the processings, the process proceeds to S695, and the CPU once ends the current routine.S 675: The CPU sets a value TthL corresponding to a relatively long time to the change time threshold value Tth, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 680: The CPU sets a value TthN corresponding to a middle-length time to the change time threshold value Tth, and stores the value in the nonvolatile memory of the driver assistance ECU 100.S 685: The CPU sets a value Tths corresponding to a relatively short time to the change time threshold value Tth, and stores the value in the nonvolatile memory of the driver assistance ECU 100.Note that the respective values are set so as to satisfy the following inequality.As described above, the device DS changes the collision determination time threshold TTCth to the corrected determination time threshold (= TTCthStd+dTTth) when the current speed limit is lower than the past speed limit by an amount larger than the speed limit decrease threshold VLTth. Thereby, the collision determination condition for the collision avoidance assist process is changed to a condition that is more easily satisfied. Even if the driver of the host vehicle overlooks the decrease in the speed limit and responds too late to the rapid deceleration of the preceding vehicle, the collision determination condition is satisfied early and the collision avoidance assist process is executed early. This can prevent the host vehicle from extremely approaching the preceding vehicle.Note that the present invention is not limited to the above-described embodiment and modifications, and various modifications may be used within the scope of the present invention. For example, the CPU may recognize the current speed limit by receiving the speed limit from the roadside machine via the communication controller 90 in S 210. Further, the present invention can be applied to a host vehicle in a state in which a driving mode transitions from autonomous driving to driving by the driver in an autonomous driving vehicle. While the number of types of values to be changed by operation of the setting input device 94 is three, N types (N is an integer greater than or equal to 2) of values may be changed. Further, the CPU determines whether the current speed limit is higher than the past speed limit when "No" is determined in S 330. The process of the CPU may proceed to S 340 when the current speed limit is higher than the past speed limit, and may proceed to S 195 when the current speed limit is not higher than the past speed limit.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2017-62 696 A

[0002]

Claims

A driver assistance apparatus for a vehicle, the driver assistance apparatus comprising a controller configured to perform a collision avoidance assistance process when a collision determination condition is satisfied, wherein the collision avoidance assistance process is a process for avoiding a collision between a host vehicle and an object, and wherein the collision determination condition is a condition satisfied when it is predicted that the host vehicle will collide with the object, wherein the controller is configured to: - recognize a speed limit applicable to a lane in which the host vehicle is traveling; and when a current speed limit is lower than a past speed limit, changing the collision determination condition to a condition that is easily satisfied so that the collision avoidance assist process is performed at a time earlier than when the current speed limit is not lower than the past speed limit, wherein the current speed limit is a speed limit newly detected at a current time, and wherein the past speed limit is a speed limit detected until immediately before the current time.The driver assistance device according to claim 1, further comprising a setting input device operated by an occupant of the host vehicle, wherein: the controller is configured to, when the current speed limit is lower than the past speed limit by a speed limit decrease threshold or more, change the collision determination condition to the condition that is easily satisfied; and the controller is further configured to change the speed limit decrease threshold based on an input to the setting input device.The driver assistance device according to claim 1, further comprising a setting input device operated by an occupant of the host vehicle, wherein: the controller is configured to, when an elapsed time from a time point at which the collision determination condition has been changed to the condition that is easily satisfied reaches a change time threshold, reset the collision determination condition to the condition before change; and the controller is further configured to change the change time threshold based on an input to the setting input device.The driver assistance device according to claim 1, further comprising a setting input device operated by an occupant of the host vehicle, wherein the controller is further configured to simply change the condition that is easily satisfied based on an input to the setting input device.The driver assistance apparatus according to claim 1, further comprising a setting input device operated by an occupant of the host vehicle, wherein: the controller is configured to: calculate a time-to-collision that is a remaining time until the host vehicle collides with the object, and determine that the collision determination condition is satisfied when the time-to-collision becomes equal to or less than a collision determination time threshold; the controller is further configured to: change, based on an input to the setting input device, the collision determination time threshold as a reference threshold between a first value and a second value that is smaller than the first value, the collision determination time threshold being a threshold used to determine whether the collision determination condition is satisfied when the collision determination condition is not changed, change the collision determination condition to the condition that is easily satisfied by changing the collision determination time threshold to a value obtained by adding a timing correction time to the reference threshold, and change the timing correction time based on the input to the setting input device; and set the timing correction time to a value smaller than or equal to a difference value obtained by subtracting the reference threshold from the first value.

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