Driving assistance device

Abstract

PURPOSE: To provide a driving support device capable of suppressing control (deceleration control) of an own vehicle against expectation (prediction) of a driver of the own vehicle in a specific scene.SOLUTION: The processor is configured to determine that the preceding vehicle is stopped before the traffic light, the traffic light color of the traffic light is "green", another vehicle is not stopped immediately in front of the preceding vehicle, and the direction indicator of the preceding vehicle is turned off; And a process of controlling the predetermined device such that the own vehicle travels at a constant speed when the distance between the own vehicle and the preceding vehicle exceeds a threshold value at a time point when the preceding vehicle is detected, or a process of controlling the predetermined device of the own vehicle such that the speed of the own vehicle decreases in a second mode slower than the first mode.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a driving assistance device that controls the drive device and / or braking device of a vehicle when another vehicle (preceding vehicle) is located immediately in front of the vehicle so that the inter-vehicle distance between the vehicle and the preceding vehicle matches a target value. [Background technology]

[0002] A driving assistance device has been proposed that controls the drive device and / or braking device of the host vehicle so that the inter-vehicle distance between the host vehicle and a preceding vehicle matches a target value (see, for example, Patent Document 1 below). This driving assistance device (hereinafter referred to as the "conventional device") controls the drive device and / or braking device (hereinafter referred to as the "drive device, etc.") of the host vehicle so that, when the preceding vehicle is stopped (stationary), the host vehicle decelerates and stops behind the preceding vehicle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-264571 Summary of the Invention

[0004] When a leading vehicle is stopped, a conventional device determines a target deceleration value (target value of the speed reduction rate) of the host vehicle based on the inter-vehicle distance (current value) between the host vehicle and the leading vehicle and the host vehicle's speed (current value). The conventional device then controls a drive unit, etc., so that the host vehicle's deceleration (current value) matches the determined target value. Consider a scenario in which the leading vehicle is stopped in front of a traffic light and the light color of the traffic light is "green" (immediately after it has turned "green"). In this scenario, a driver of the host vehicle approaching the leading vehicle from behind the leading vehicle is likely to predict that the leading vehicle will soon start moving. In this case, the driver is likely to predict that the host vehicle can be safely driven without excessively approaching the leading vehicle, even if the host vehicle is not decelerated too much. In this case, the driver is likely to expect the driving assistance device to control the host vehicle so that the host vehicle decelerates relatively gradually.

[0005] In contrast, conventional devices determine a target value for the deceleration of the host vehicle based on the distance between the host vehicle and the preceding vehicle and the relative speed (the speed of the host vehicle in the scene) regardless of the color of the traffic light. Therefore, in a scene where it is predicted that the preceding vehicle will soon start moving, there is a risk that the deceleration of the host vehicle will become large contrary to the expectations (predictions) of the driver of the host vehicle.

[0006] An object of the present invention is to provide a driving assistance device that can suppress control (deceleration control) of the vehicle that goes against the expectations (predictions) of the driver of the vehicle in a particular scene.

[0007] In order to achieve the above object, the driving assistance device (1) of the present invention comprises: a vehicle sensor (20) that acquires information (sp0) about a host vehicle (V0) and information (spr, D) about targets (V1, V2, S) located ahead of the host vehicle; a processor (10) capable of executing a speed adjustment process (ACC) for controlling predetermined devices (30, 40) of the host vehicle so that an inter-vehicle distance (D) between the host vehicle and a preceding vehicle, which is another vehicle positioned immediately before the host vehicle, coincides with a predetermined target value (Dt), the processor being configured to start, as the speed adjustment process, a first process for controlling the predetermined devices so that the host vehicle decelerates in a predetermined first manner when a stopped preceding vehicle is detected; Equipped with. The processor: (A) The preceding vehicle is stopped in front of a traffic light, (B) The light color of the traffic light is "green" and (C) There is no other vehicle stopped immediately in front of the preceding vehicle, (D) The turn signal lights of the preceding vehicle are off, and (E) When the distance between the vehicle and the preceding vehicle at the time when the preceding vehicle is detected exceeds a threshold value, A second process is started as an alternative process to the first process, which is a process of controlling the specified device so that the vehicle proceeds at a constant speed, or a process of controlling the specified device so that the speed of the vehicle decreases in a second manner that is slower than the first manner.

[0008] As described above, in a specific scenario where a preceding vehicle stopped ahead of the host vehicle is predicted to start moving soon, the driver of the host vehicle is likely to predict that the host vehicle can proceed safely without significantly slowing down the host vehicle. When a condition for determining that the preceding vehicle is likely to start moving soon is met, the processor of the driving assistance device according to the present invention executes a process of causing the host vehicle to travel at a constant speed or a process of gradually decelerating the host vehicle. According to the present invention, in a specific scenario, it is possible to suppress control of the host vehicle (sudden deceleration) that goes against the expectations (predictions) of the driver of the host vehicle.

[0009] In one aspect of the present invention, there is provided a driving assistance device, The processor assigns a larger value to the threshold value as the speed of the host vehicle increases.

[0010] If the processor detects a leading vehicle and the host vehicle is quite close to the leading vehicle at the time of detection, and if the second process is started from that time, the risk of contact between the host vehicle and the leading vehicle is high. In particular, if the second process is started from the time the processor detects a leading vehicle while the host vehicle is traveling at a relatively high speed, the risk of contact between the host vehicle and the leading vehicle is high. When the host vehicle is traveling at a relatively high speed, the processor of the driving assistance device according to this aspect can start the second process only if the distance between the host vehicle and the leading vehicle is relatively large. Therefore, the driving assistance device according to this aspect can reduce the risk of contact between the host vehicle and the leading vehicle.

[0011] , In a driving assistance device according to another aspect of the present invention, The processor ends the second process when a predetermined time (Tx) has elapsed since the start of the second process.

[0012] There may be cases where the preceding vehicle continues to be stopped after the processor starts the second process. If the processor continues to execute the second process under such circumstances, there is a risk that the host vehicle will come too close to the preceding vehicle. In the assistance device according to this aspect, the time during which the processor can continue the second process is limited. In other words, the processor ends the second process when a predetermined time has elapsed since starting the second process. If the preceding vehicle has not yet started moving at this point, the processor can start the first process from this point. This reduces the risk of contact between the host vehicle and the preceding vehicle.

[0013] In a driving assistance device according to another aspect of the present invention, The processor terminates the second process when it detects that another vehicle has entered between the leading vehicle and the host vehicle while the second process is being executed.

[0014] According to this, when another vehicle enters between the host vehicle and the preceding vehicle, the processor terminates the second process and controls the host vehicle so that the inter-vehicle distance between the host vehicle and the preceding vehicle coincides with the target value, thereby reducing the risk of contact between the host vehicle and the preceding vehicle.

[0015] In a driving assistance device according to another aspect of the present invention, The processor: The first process is to operate a friction brake to decelerate the vehicle; The second process is configured to execute a process of decelerating the vehicle by activating engine braking or regenerative braking.

[0016] According to the driving assistance device of this aspect, the ride comfort of the host vehicle is better during the period in which the second process is being executed than the ride comfort of the host vehicle during the period in which the first process is being executed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram of a driving assistance device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing a change in speed of the host vehicle (first aspect) in a specific first scene. [Figure 3] FIG. 3 is a graph showing a change in speed of the host vehicle (second aspect) in a specific second scene. [Figure 4] FIG. 4 is a flowchart of a program executed by the CPU to realize the function of maintaining a safe distance between vehicles. DETAILED DESCRIPTION OF THE INVENTION

[0018] (Outline) As shown in Fig. 1, a driving assistance device 1 according to one embodiment of the present invention is applied to a vehicle V0 (hereinafter referred to as "host vehicle") equipped with an automatic driving function. When the automatic driving function is disabled, the driving assistance device 1 has a function of controlling the host vehicle (drive device 30 and / or braking device 40) so that the inter-vehicle distance D between the host vehicle and another vehicle V1 (hereinafter referred to as "preceding vehicle") located immediately in front of the host vehicle matches a predetermined target value Dt. Note that this control may be executed as one of the automatic driving functions.

[0019] (Specific Configuration) As shown in FIG. 1, the driving assistance device 1 includes an ECU 10, an on-vehicle sensor 20, a drive device 30, and a braking device 40.

[0020] The ECU 10 includes a microcomputer equipped with a CPU 10a, a ROM 10b, a RAM 10c, a timer 10d, etc. The ECU 10 is connected to other ECUs provided in the vehicle via a CAN (Controller Area Network).

[0021] The on-board sensor 20 includes a forward sensor that acquires information about a leading vehicle. Specifically, the on-board sensor 20 includes a millimeter wave radar 21 as a forward sensor, and a forward camera 22.

[0022] The millimeter-wave radar 21 includes a transmitter / receiver and a signal processor (not shown). The transmitter / receiver emits millimeter-wave band radio waves (hereinafter referred to as "millimeter waves") ahead of the vehicle and receives millimeter waves (reflected waves) reflected by a three-dimensional object (a preceding vehicle) located within the emission range. The millimeter waves emitted from the transmitter / receiver pass under the floor of the preceding vehicle and are reflected by a three-dimensional object (another vehicle V2) located ahead of the preceding vehicle. The transmitter / receiver receives the reflected waves. The signal processor calculates the distance between the vehicle and the three-dimensional object (e.g., the preceding vehicle and another vehicle located ahead of it), the speed (relative speed) of the vehicle with respect to the three-dimensional object, and the like, based on the time from when the transmitter / receiver emits the millimeter waves to when it receives the reflected waves, the phase difference between the transmitted millimeter waves and the received reflected waves, the attenuation level of the reflected waves, and the like. The signal processor provides these calculation results to the ECU 10.

[0023] The forward camera 22 includes an imaging device and an image analysis device. The imaging device incorporates a lens and an imaging element such as a charge coupled device (CCD) or a CMOS image sensor (CIS). The imaging device is located above the front windshield and faces forward. The imaging device captures images of the front view of the vehicle at a predetermined frame rate to acquire image data. The imaging device transmits the image data to the image analysis device. The image analysis device analyzes the acquired image data and acquires information about objects located in front of the vehicle from the images. For example, the image analysis device identifies (recognizes) the type of object located in front of the vehicle (e.g., a preceding vehicle, lane markings, traffic light color, and the operating status of the turn signal lights of the preceding vehicle (right turn signal light flashing / left turn signal light flashing / both turn signal lights flashing / both turn signal lights off)), and provides the identification results to the ECU 10.

[0024] Additionally, the on-board sensor 20 includes a vehicle sensor that acquires information about the behavior (speed and acceleration) of the vehicle itself. Specifically, the on-board sensor 20 includes a speed sensor 23 and an acceleration sensor 24 as vehicle sensors.

[0025] The speed sensor 23 detects the rotation speed (wheel speed) of each wheel, and calculates the speed sp0 (measured value) of the host vehicle based on the wheel speed. The speed sensor 23 provides the calculation result to the ECU 10.

[0026] The acceleration sensor 24 detects the acceleration of the host vehicle in the longitudinal direction (the rate of change α of the speed sp0). The acceleration sensor 24 provides the ECU 10 with the detection result.

[0027] The drive unit 30 applies driving force to the drive wheels. The drive unit 30 includes an engine ECU, an internal combustion engine, a transmission, a driving force transmission mechanism that transmits the driving force to the wheels, and the like. The engine ECU acquires information (target value) that indicates a target driving force from another ECU (e.g., ECU 10). The engine ECU drives the throttle valve of the internal combustion engine to make the driving force applied to the drive wheels match the target value. The output (driving force) of the internal combustion engine is transmitted to the drive wheels via the transmission and the driving force transmission mechanism.

[0028] If the vehicle to which the driving assistance device 1 is applied is a hybrid vehicle (HEV), the engine ECU can adjust the output (driving force) of either or both of the "internal combustion engine and electric motor" as the vehicle drive source. Also, if the vehicle to which the driving assistance device 1 is applied is an electric vehicle (BEV), an electric motor ECU is used instead of the engine ECU to adjust the output (driving force) of the "electric motor" as the vehicle drive source.

[0029] The braking device 40 is a friction brake device that applies braking force (friction force) to the wheels (brake discs). The braking device 40 includes a brake ECU, a brake caliper, etc. The brake caliper includes an actuator that presses brake pads against the brake discs. The brake ECU acquires information (target value) that indicates a target braking force from another ECU. The brake ECU drives the actuator of the brake caliper to make the braking force applied to the wheels (brake discs) match the target value.

[0030] (Operation) When an ACC switch (not shown) mounted on the host vehicle is in the on state, the ECU 10 determines whether or not there is a preceding vehicle, and controls the drive unit 30 and / or braking unit 40 (drive unit, etc.) of the host vehicle based on the determination result, as will be described below. This control is generally called adaptive cruise control (ACC). ACC includes constant speed control and following distance maintenance control.

[0031] [Constant-Speed ​​Cruise Control] The ECU 10 determines whether or not there is a preceding vehicle based on information acquired from the forward sensors (millimeter-wave radar 21 and forward camera 22). If there is no preceding vehicle, the ECU 10 executes constant-speed cruise control. Specifically, the ECU 10 controls the drive system and the like so that the speed sp0 of the host vehicle coincides with a predetermined target value spt (for example, a value set by the driver or a speed value that minimizes fuel consumption). Even if there is a preceding vehicle, if its speed sp1 is greater than the target value spt, the ECU 10 executes constant-speed cruise control.

[0032] [Inter-vehicle distance maintenance control] When it is determined that a preceding vehicle is present, the ECU 10 executes inter-vehicle distance maintenance control. Specifically, the ECU 10 acquires the distance between the host vehicle and the preceding vehicle (inter-vehicle distance D), the relative speed spr, and the speed sp0 of the host vehicle from the on-board sensor 20. The ECU 10 also acquires the speed sp1 of the preceding vehicle. The ECU 10 then calculates (determines) a target value Dt of the inter-vehicle distance D based on the speed sp1. Note that the target value Dta when the speed sp1 is relatively small is smaller than the target value Dtb when the speed sp1 is relatively large. A database DB1 (table) that indicates the relationship between the speed sp1 and the target value Dt is stored in the ROM 10b. The ECU 10 acquires the target value Dt by referring to the database DB1.

[0033] The ECU 10 controls the drive devices of the host vehicle so that the inter-vehicle distance D (actual measured value) coincides with the target value Dt and the speed sp0 coincides with the speed sp1. The ECU 10 also controls the drive devices so that the rate of change α of the host vehicle's speed sp0 becomes "0" when the speed sp0 coincides with the speed sp1.

[0034] More specifically, the ECU 10 refers to the database DB2 stored in advance in the ROM 10b to determine the target value αt of the change rate α (increase rate or decrease rate) of the speed sp0 of the host vehicle. Then, the ECU 10 controls the drive device or the like so that the change rate α matches the target value αt. Here, the database DB2 defines the relationship between "the difference ΔD between the inter-vehicle distance D (measured value) and the target value Dt, and the relative speed spr (the speed sp0 and the speed sp1)" and the "target value αt". When the target value αt is greater than "0", the host vehicle is accelerated, and when the target value αt is less than "0", the host vehicle is decelerated.

[0035] For example, the database DB2 is designed as follows. When the inter-vehicle distance D is excessive (ΔD>0) and the relative speed spr is excessive (sp0>sp1), a negative value with a large absolute value is assigned to the target value αt so that the speed sp0 approaches the speed sp1 relatively rapidly. Also, for example, when the inter-vehicle distance D is excessive (ΔD>0) and the relative speed spr is too small (sp0<sp1), a positive value with a large absolute value is assigned to the target value αt so that the speed sp0 once exceeds the speed sp1. Also, for example, when the inter-vehicle distance D is slightly greater than the target value Dt (D≒Dt) and the relative speed spr is slightly greater than "0", a negative value with a small absolute value is assigned to the target value αt so that the decrease rate of the speed sp0 becomes relatively small. Also, for example, when the inter-vehicle distance D is slightly greater than the target value Dt (D≒Dt) and the relative speed spr is slightly less than "0", a positive value with a small absolute value is assigned to the target value αt so that the increase rate of the speed sp0 becomes relatively small.

[0036] Also, for example, when the inter-vehicle distance D is too small (ΔD < 0) and the relative speed spr is too large (sp0 > sp1), a negative value with a large absolute value is assigned to the target value αt so that the speed sp0 once falls below the speed sp1. Also, for example, when the inter-vehicle distance D is too small (ΔD < 0) and the relative speed spr is too small (sp0 < sp1), a positive value with a large absolute value is assigned to the target value αt so that the speed sp0 approaches the speed sp1 relatively rapidly. Also, for example, when the inter-vehicle distance D is slightly smaller than the target value Dt (D ≒ Dt) and the relative speed spr is slightly larger than "0", a negative value with a small absolute value is assigned to the target value αt so that the deceleration rate of the speed sp0 becomes relatively small. Also, for example, when the inter-vehicle distance D is slightly smaller than the target value Dt (D ≒ Dt) and the relative speed spr is slightly smaller than "0", a positive value with a small absolute value is assigned to the target value αt so that the acceleration rate of the speed sp0 becomes relatively small.

[0037] Next, the mode of change of the inter-vehicle distance D and the speed sp0 when the inter-vehicle distance holding control is executed when the preceding vehicle is stopped (stationary) will be described.

[0038] Figure 2 shows a scene where the preceding vehicle (other vehicle V1) has stopped for some reason. In this scene, the host vehicle (vehicle V0) is approaching the preceding vehicle from behind the preceding vehicle. When the ECU10 determines that the preceding vehicle exists in front of the host vehicle based on the information acquired from the in-vehicle sensor 20 at time t0, the ECU10 acquires the speed sp1 of the preceding vehicle based on this information. Next, the ECU10 determines the target value Dt (target value of the inter-vehicle distance D) corresponding to the speed sp1. In this example, since the speed sp1 is "0", the target value Dt is relatively small. Also, in this example, at time t0 when the ECU10 detects the preceding vehicle, the inter-vehicle distance D is larger than the target value Dt. Also, as described above, since the target value Dt is determined according to the speed sp1 of the preceding vehicle, the target value Dt does not change during the period in which the preceding vehicle continues to be stopped.

[0039] In this example, at time t0 when the ECU 10 detects the preceding vehicle, the speed sp0 of the host vehicle is relatively high. Therefore, the ECU 10 controls the drive system and other devices so that the rate of decrease of the speed sp0 becomes relatively large. Thereafter, as the inter-vehicle distance D decreases, the ECU 10 gradually decreases the rate of decrease of the speed sp0 toward "0." Then, when the inter-vehicle distance D matches the target value Dt (ΔD=0) and the speed sp0 becomes "0" (=sp1), the rate of decrease of the speed sp0 becomes "0." In the following description, the manner in which the speed sp0 of the host vehicle changes (the speed change curve C1 shown in FIG. 2) when the inter-vehicle distance maintenance control is executed when the preceding vehicle is stopped is referred to as the "first manner." Furthermore, the process in which the ECU 10 controls the drive system and other devices so as to achieve this speed change is referred to as the "first process."

[0040] 2, if the preceding vehicle starts moving before the inter-vehicle distance D decreases and coincides with the target value Dt, the ECU 10 sequentially updates the target value Dt based on the speed sp1 of the preceding vehicle from that point on. Every time the ECU 10 updates the target value Dt, it references the database DB2 to obtain the target value αt of the rate of change α. Then, the ECU 10 controls the drive device and the like so that the rate of change α (current value) coincides with the target value αt (normal processing).

[0041] As shown in FIG. 3, a scenario is assumed in which ECU 10 detects a preceding vehicle stopped in front of traffic light S, and at time t0, the light color of traffic light S is "green." In this scenario, the driver of the host vehicle is likely to predict that the preceding vehicle will soon start moving. In this case, the driver is likely to predict that the host vehicle can travel safely without significantly decelerating the host vehicle and without approaching the preceding vehicle excessively. In this case, the driver is likely to expect that the drive unit and the like will be controlled so that the host vehicle decelerates in a second manner (speed change curve C2 in FIG. 3) that is gentler than the first manner.

[0042] Therefore, as will be described below, when ECU 10 detects a preceding vehicle stopped ahead of the host vehicle, it determines whether the situation is such that the host vehicle can proceed safely without significantly slowing down the host vehicle (whether condition X is met). If condition X is met, ECU 10 executes a second process that controls the drive device and the like so that the host vehicle is decelerated in a second manner that is gentler than the first manner.

[0043] Here, even if the light color of traffic light S is "green," it may take some time for the leading vehicle stopped in front of the traffic light S to start moving. For example, if another vehicle V2 is stopped just before the leading vehicle, it is likely that the leading vehicle will stop until the other vehicle V2 starts moving and the distance between the other vehicle V2 and the leading vehicle becomes somewhat large. Also, for example, even if there is no other vehicle V2 in front of the leading vehicle, when the leading vehicle turns left or right (when the left or right turn signal light is flashing), it may wait until a pedestrian or another vehicle traveling in the oncoming lane has passed.

[0044] Furthermore, there are cases where the host vehicle is quite close to the preceding vehicle at time t0 when the ECU 10 detects the preceding vehicle. For example, if the road curves sharply just before traffic light S, there is a high possibility that the inter-vehicle distance D will be quite small when the host vehicle detects the stopped preceding vehicle. In this case, if the host vehicle is gradually decelerated from time t0 when the ECU 10 detects the preceding vehicle, there is a high risk of contact between the host vehicle and the preceding vehicle. In particular, if the host vehicle is gradually decelerated under conditions where the speed sp0 of the host vehicle at time t0 is relatively high, there is a high risk of contact between the host vehicle and the preceding vehicle.

[0045] Therefore, the ECU 10 determines that the condition X is satisfied when the following conditions A to E are satisfied at the time t0 when the preceding vehicle is detected. Condition A: The preceding vehicle is stopped just before traffic light S. Condition B: The light color of traffic light S is green. Condition C: The preceding vehicle is stopped alone. Condition D: The turn signal lights of the vehicle ahead are off. Condition E: The inter-vehicle distance D exceeds the threshold value Dth. The ECU 10 determines that the preceding vehicle is stopped (stationary) when the speed sp1 of the preceding vehicle is equal to or less than a small threshold sp1th. The ECU 10 also determines a value to be assigned to the threshold Dth according to the speed sp0 of the host vehicle at time t0. Specifically, the ECU 10 assigns a larger value to the threshold Dth as the speed sp0 at time t0 increases.

[0046] If condition X is satisfied, ECU 10 starts a second process. That is, ECU 10 controls the drive devices and the like so that the host vehicle decelerates according to a second pattern (speed change curve C2) that is gentler than the first pattern (speed change curve C1). Specifically, ECU 10 assumes that the preceding vehicle continues to be stopped, and sequentially refers to database DB2 to acquire the target value αt. Each time it acquires the target value αt, ECU 10 corrects the target value αt as follows. That is, ECU 10 multiplies the target value αt acquired from database DB2 by a predetermined coefficient k (for example, k = "0.5"), and acquires the resulting value as the corrected target value αt. Then, ECU 10 controls the drive devices and the like so that the rate of change α (current value) of the speed sp0 matches the corrected target value αt.

[0047] In the first process, the ECU 10 preferably activates the braking device 40 (friction brake). In contrast, in the second process, the ECU 10 preferably activates the engine brake (or regenerative brake).

[0048] The ECU 10 executes the second process until time t1 when the time Δt elapsed since the start of the second process (t0) reaches a predetermined threshold value Tx. Here, the threshold value Tx is preset as a standard time (e.g., 3 seconds) required for the preceding vehicle to start moving and for the speed sp1 of the preceding vehicle to increase to a certain level after the light color of the traffic light S changes from "red" to "green." Even if the preceding vehicle starts moving during this period, the ECU 10 continues the second process. As described above, one of the conditions for the ECU 10 to execute the second process is the condition E that "the inter-vehicle distance D between the host vehicle and the preceding vehicle is sufficiently large." Therefore, a situation in which the host vehicle approaches the preceding vehicle excessively during execution of the second process does not occur. From time t1, the ECU 10 sequentially updates the target value Dt based on the speed sp1 of the preceding vehicle and controls the drive device, etc., so that the inter-vehicle distance D matches the updated target value Dt and the speed sp0 of the host vehicle matches the speed sp1 at that time. In the example shown in Fig. 3, the host vehicle is accelerated from time t1, but depending on the behavior of the preceding vehicle, the host vehicle may be controlled to continue decelerating (first process) or to proceed at a constant speed. Also, if another vehicle enters between the preceding vehicle and the host vehicle while the ECU 10 is executing the second process, the ECU 10 ends the second process at that point. Then, the ECU 10 recognizes the other vehicle and the host vehicle as new preceding vehicles and executes ACC.

[0049] Next, with reference to FIG. 4, a program PR1 executed by the CPU 10a (hereinafter simply referred to as "CPU") to realize the inter-vehicle distance maintaining function of the driving assistance device 1 will be described.

[0050] The CPU executes the program PR1 at time t0 when it detects a preceding vehicle while the ACC switch is in the on state.

[0051] (Program PR1) The CPU starts execution of the program PR1 from step 100 and proceeds to step 101.

[0052] In step 101, the CPU determines whether the speed sp1 is equal to or less than a threshold value sp1th (whether the preceding vehicle is stopped). If the CPU determines that the preceding vehicle is stopped (101: Yes), the CPU proceeds to step 102. On the other hand, if the CPU does not determine that the preceding vehicle is stopped (101: No), the CPU proceeds to step 112, which will be described later.

[0053] In step 102, the CPU determines whether the light color of traffic light S is "green." If the CPU determines that the light color of traffic light S is "green" (102: Yes), the CPU proceeds to step 103. On the other hand, if the CPU does not determine that the light color of traffic light S is "green" (102: No), the CPU proceeds to step 112.

[0054] In step 103, the CPU determines whether the preceding vehicle is stopped alone. If the CPU determines that the preceding vehicle is stopped alone (103: Yes), the CPU proceeds to step 104. On the other hand, if the CPU does not determine that the preceding vehicle is stopped alone (103: No), the CPU proceeds to step 112.

[0055] In step 104, the CPU determines whether the turn signal lights of the preceding vehicle are off. If the CPU determines that the turn signal lights of the preceding vehicle are off (104: Yes), the CPU proceeds to step 105. On the other hand, if the CPU does not determine that the turn signal lights of the preceding vehicle are off (104: No), the CPU proceeds to step 112.

[0056] In step 105, the CPU determines whether the inter-vehicle distance D exceeds the threshold value Dth. If the CPU determines that the inter-vehicle distance D exceeds the threshold value Dth (105: Yes), the CPU proceeds to step 106. On the other hand, if the CPU does not determine that the inter-vehicle distance D exceeds the threshold value Dth (105: No), the CPU proceeds to step 112.

[0057] The CPU starts measuring the time Δt with the timer 10d in step 106. Then, the CPU proceeds to step 107.

[0058] In step 107, the CPU refers to the database DB2 to acquire (update) the target value αt corresponding to the difference ΔD and the relative speed spr. Next, the CPU proceeds to step .

[0059] The CPU corrects the target value αt in step 108. That is, the CPU multiplies the target value αt obtained in step 107 by the coefficient k to obtain the corrected target value αt. Next, the CPU proceeds to step 109.

[0060] In step 109, the CPU controls the drive device and the like so that the rate of change α of the host vehicle speed sp0 matches the target value αt (corrected value).

[0061] In step 110, the CPU determines whether or not another vehicle has entered between the host vehicle and the preceding vehicle. If the CPU determines that another vehicle has entered between the host vehicle and the preceding vehicle (110: Yes), the CPU proceeds to step 114, which will be described later. On the other hand, if the CPU does not determine that another vehicle has entered between the host vehicle and the other vehicle (110: No), the CPU proceeds to step 111.

[0062] In step 111, the CPU determines whether the time Δt exceeds the threshold value Tx. If the CPU determines that the time Δt exceeds the threshold value Tx (111: Yes), the CPU proceeds to step 112. On the other hand, if the CPU does not determine that the time Δt exceeds the threshold value Tx (110: No), the CPU returns to step 107.

[0063] The CPU executes normal processing in step 112. That is, the CPU refers to the database DB2 to acquire the target value αt, and controls the drive device, etc. so that the rate of change α matches the target value αt. Next, the CPU proceeds to step 113.

[0064] In step 113, the CPU determines whether a predetermined termination condition is met. The termination condition is met, for example, when it becomes impossible to detect a preceding vehicle, or when the speed sp1 of the preceding vehicle exceeds the target value spt. If the CPU determines that the termination condition is met (113: Yes), the CPU proceeds to step 114. On the other hand, if the CPU does not determine that the termination condition is met (113: No), the CPU returns to step 111.

[0065] In step 114, the CPU ends the execution of the program PR1.

[0066] (Effect) As described above, in a specific scenario in which a preceding vehicle stopped ahead of the host vehicle is predicted to start moving soon, the driver of the host vehicle is likely to predict that the host vehicle can proceed safely without significantly decelerating the host vehicle. When condition X for determining that the preceding vehicle is likely to start moving soon is satisfied, ECU 10 controls the drive device, etc., so that the host vehicle decelerates in a second manner that is gentler than the first manner. This makes it possible to suppress control of the host vehicle (sudden deceleration) that goes against the expectations (predictions) of the driver of the host vehicle in a specific scenario.

[0067] (Modification) In the inter-vehicle distance maintenance control, the rate of change α of the speed sp0 in the process in which the inter-vehicle distance D approaches the target value Dt may be constant. Also, in the second processing, the rate of change α of the speed sp0 may be "0." That is, in the second processing, the ECU 10 may cause the host vehicle to travel at a constant speed sp0. [Explanation of symbols]

[0068] 1... driving assistance device, 10... ECU, 20... on-vehicle sensor, 30... drive device, 40... braking device

Claims

1. a vehicle sensor for acquiring information about the host vehicle and information about a target located in front of the host vehicle; a processor capable of executing a speed adjustment process to control a predetermined device of the host vehicle so that an inter-vehicle distance between the host vehicle and a preceding vehicle, which is another vehicle located immediately before the host vehicle, matches a predetermined target value, the processor being configured to start, as the speed adjustment process, a first process to control the predetermined device so that the host vehicle decelerates in a predetermined first manner when a stopped preceding vehicle is detected; A driving assistance device comprising: The processor: The preceding vehicle is stopped in front of a traffic light, The traffic light is green, There are no other vehicles stopped immediately in front of the preceding vehicle, The turn signal lights of the preceding vehicle are off, and When the distance between the host vehicle and the preceding vehicle at the time when the preceding vehicle is detected exceeds a threshold value, a second process as an alternative process to the first process, initiating a process of controlling the predetermined device so that the host vehicle travels at a constant speed, or a process of controlling the predetermined device so that the speed of the host vehicle decreases in a second manner that is more gradual than the first manner; A driving assistance device configured as follows.

2. The driving assistance device according to claim 1, The driving assistance device is configured such that the processor assigns a larger value to the threshold value as the speed of the host vehicle increases.

3. The driving assistance device according to claim 2, The driving assistance device is configured such that the processor terminates the second process when a predetermined time has elapsed since the start of the second process.

4. The driving assistance device according to claim 3, The driving assistance device is configured such that, when the processor detects that another vehicle has entered between the preceding vehicle and the subject vehicle while the second processing is being executed, the processor terminates the second processing.

5. 5. The driving assistance device according to claim 1, The processor: The first process is to operate a friction brake to decelerate the vehicle; A driving assistance device configured to execute, as the second process, a process of decelerating the host vehicle by activating engine braking or regenerative braking.

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