Collision prevention system

Abstract

To provide a collision prevention system capable of minimizing a fear that an own vehicle may collide with a preceding vehicle even in a situation where a distance between the own vehicle and preceding vehicle rapidly diminishes.SOLUTION: A collision prevention system includes a driving assist ECU that, when determining based on information acquired by a target information acquisition unit, which acquires information on a target around an own vehicle, that an obstacle exists ahead of the own vehicle (S30), determines a fear that the own vehicle may collide with the obstacle (S80 and S100), and that, when determining that there is the fear, implements countermeasure control for minimizing the fear (S90 and S110). When determining that the obstacle is a preceding vehicle which tentatively halts and the preceding vehicle has set off, the driving assist ECU implements at least one of changing a requirement for determining a fear or enhancing an effect of countermeasure control so that it can be more readily determined that there is the fear (S70).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a collision prevention device that reduces the risk of a host vehicle colliding with an obstacle. [Background technology]

[0002] One type of collision prevention device for vehicles such as automobiles is known to have the following features: when an obstacle is detected in front of the vehicle, the device determines whether the vehicle is at risk of colliding with the obstacle, and if it determines that there is such a risk, the device executes countermeasure control such as automatic deceleration to reduce the risk.

[0003] For example, Patent Document 1 listed below describes a collision prevention device that detects a preceding vehicle ahead of the vehicle based on images captured by an on-board camera, determines the possibility of a collision between the vehicle and the preceding vehicle, and displays the determination result on a display to inform the driver.

[0004] With the collision prevention device, even if there is an obstacle in front of the vehicle and there is a risk of the vehicle colliding with the obstacle, countermeasures such as automatic deceleration and warning of the possibility of a collision are carried out, thereby reducing the risk of the vehicle colliding with the obstacle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 11-039597 Summary of the Invention

[0006] [Problem to be solved by the invention] For example, when the vehicle is following a preceding vehicle, the traffic light turns red and the preceding vehicle and the vehicle stop temporarily in front of the traffic light, and when the traffic light turns green and the preceding vehicle starts moving, the vehicle also starts moving. However, if the preceding vehicle suddenly decelerates or stops immediately after starting due to traffic congestion in front of the preceding vehicle, the distance between the vehicle and the preceding vehicle suddenly decreases, and the risk of the vehicle colliding with the preceding vehicle increases.

[0007] Conventional collision prevention devices such as the collision prevention device described in Patent Document 1 above do not take into account situations in which the distance between the vehicle and the preceding vehicle suddenly decreases, making it difficult to reduce the risk of the vehicle colliding with the preceding vehicle in such situations.

[0008] The present invention provides an improved collision prevention device that is more likely than conventional devices to reduce the risk of a vehicle colliding with a preceding vehicle even in situations where the distance between the vehicle and the preceding vehicle suddenly decreases. [Means for solving the problems and effects of the invention]

[0009] According to the present invention, there is provided a collision prevention device (100) including a target information acquisition device (17) that acquires information on targets around a host vehicle (102), and a control unit (driving assistance ECU 10) configured to, when it is determined that there is an obstacle ahead of the host vehicle based on the information acquired by the target information acquisition device (S20), determine a risk of the host vehicle colliding with the obstacle (S80, S100), and, when it is determined that there is such a risk, execute countermeasure control to reduce the risk (S90, S110).

[0010] When the control unit (driving assistance ECU10) determines that the obstacle is a preceding vehicle (112) that is temporarily stopping (S230) and that the preceding vehicle has started moving (S250), the control unit (driving assistance ECU10) is configured to execute at least one of changing the conditions for determining the above-mentioned risk so that it is easier to determine that there is such a risk and increasing the effectiveness of countermeasure control (S70).

[0011] According to the above configuration, when it is determined that the obstacle is a preceding vehicle that has stopped temporarily and that the preceding vehicle has started moving, at least one of the following is performed: the conditions for determining the above-mentioned risk are changed so that it is easier to determine that there is such a risk, and the effectiveness of the countermeasure control is increased.

[0012] When the conditions for determining the risk are changed, it becomes easier to determine that there is a risk, so countermeasure control is started early. Thus, the risk of the vehicle colliding with the preceding vehicle can be effectively reduced compared to when the conditions for determining the risk are not changed. Furthermore, when the effect of the countermeasure control is increased, the countermeasure control is effectively executed, so the risk of the vehicle colliding with the preceding vehicle can be effectively reduced compared to when the effect of the countermeasure control is not increased. [Mode of the invention]

[0013] In one aspect of the present invention, the control unit (driving assistance ECU 10) is configured to calculate (S40) the distance (Lr) between the host vehicle and the preceding vehicle (112) based on information acquired by the target information acquisition device (17), and determine (S80, S100) that there is the above-mentioned risk when the distance is equal to or less than a reference distance (Lrc1, Lrc2). Furthermore, when it is determined that the preceding vehicle has started moving (S250), the control unit is configured to change the conditions for determining the above-mentioned risk by increasing the reference distance (S70).

[0014] According to the above aspect, when it is determined that the preceding vehicle has started moving, the reference distance is increased, and it becomes easier to determine that the distance between the vehicle itself and the preceding vehicle is less than or equal to the reference distance, so that the conditions for determining the risk of a collision can be changed so that it becomes easier to determine that there is a risk of a collision.

[0015] In another aspect of the present invention, the countermeasure control includes automatic deceleration (S110) that automatically decelerates the host vehicle, and when the control unit (driving assistance ECU10) determines that the preceding vehicle has started moving (S250), it is configured to increase the deceleration rate of the automatic deceleration (S70) to enhance the effectiveness of the countermeasure control.

[0016] According to the above aspect, when it is determined that the preceding vehicle has started moving, the deceleration rate of the automatic deceleration is increased, and the deceleration of the host vehicle is effectively executed, thereby enhancing the effectiveness of the countermeasure control for reducing the risk of the collision.

[0017] In another aspect of the present invention, the control unit (driving assistance ECU 10) is configured to terminate (S300) the execution of at least one of the above operations when the elapsed time from the time when it was determined that the above-mentioned risk exists is equal to or greater than a reference time (Tc).

[0018] According to the above aspect, the execution of at least one of the above processes is terminated when the elapsed time from the time when it is determined that there is a risk is equal to or greater than a reference time, thereby reducing the risk of the execution of at least one of the above processes continuing excessively.

[0019] Furthermore, in another aspect of the present invention, the control unit (driving assistance ECU 10) is configured to terminate the execution of at least one of the above (S300) when the mileage of the vehicle from the time when it was determined that there was a risk is equal to or greater than a reference mileage (Lc).

[0020] According to the above aspect, when the distance traveled by the vehicle from the time when it is determined that there is a risk is equal to or greater than a reference distance, the execution of at least one of the above processes is terminated, thereby reducing the risk of the execution of at least one of the above processes continuing excessively.

[0021] In the above description, other objects, other features and attendant advantages of the present invention will be easily understood from the following description of the embodiments of the present invention which will be described with reference to the drawings. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic configuration diagram showing a collision prevention device according to an embodiment. [Diagram 2] 5 is a flowchart corresponding to a collision prevention control program in the embodiment. [Diagram 3] 5 is a flowchart corresponding to a flag control program in the embodiment. [Figure 4] FIG. 1 is a diagram showing a situation where the traffic light at a crossroads is red, a preceding vehicle is stopped, and the vehicle is stopped behind the preceding vehicle. [Diagram 5]FIG. 1 is a diagram showing a situation in which the traffic light at a crossroads has turned green, the preceding vehicle has started moving, and the vehicle is stopped. [Figure 6] FIG. 13 is a diagram showing a situation in which a preceding vehicle starts moving, and the vehicle starts moving immediately thereafter, but the preceding vehicle suddenly decelerates or stops immediately after starting due to congestion of vehicles ahead of the preceding vehicle, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A collision prevention device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] As shown in Fig. 1, a collision prevention device 100 according to an embodiment of the present invention is applied to a vehicle 102 and includes a driving assistance ECU 10. The vehicle 102 is an autonomous vehicle, and includes a drive ECU 20, a braking ECU 30, and a meter ECU 50. The ECU stands for an electronic control unit having a microcomputer as a main component. The vehicle 102 is referred to as the host vehicle 102 as necessary.

[0025] The microcomputer of each ECU includes a CPU, ROM, RAM, a readable / writable non-volatile memory (N / M), and an interface (I / F). The CPU realizes various functions by executing instructions (programs, routines) stored in the ROM. Furthermore, these ECUs are connected to each other via a Controller Area Network (CAN) 104 so that they can exchange data (communicate). Therefore, the detection values ​​of sensors (including switches) connected to a specific ECU are also sent to other ECUs.

[0026] The driving assistance ECU 10 is a central control device that performs driving control for driving assistance such as collision prevention control, adaptive cruise control, lane keeping control, etc. In the embodiment, the driving assistance ECU 10 cooperates with other ECUs to perform collision prevention control for the vehicle 102, as will be described in detail later. Note that adaptive cruise control is abbreviated as ACC.

[0027] The driving assistance ECU 10 is connected to a camera sensor 12, a radar sensor 14, a sonar device 16, and a setting operation device 18. The camera sensor 12 and the radar sensor 14 each include a plurality of camera devices and a plurality of radar devices, and the sonar device 16 includes a plurality of sonars. The camera sensor 12, the radar sensor 14, and the sonar device 16 function as a target information acquisition device 17 that acquires target information around the vehicle 102.

[0028] Although not shown in the figure, each camera device of the camera sensor 12 includes a camera unit that captures images of the surroundings of the vehicle 102, and a recognition unit that analyzes image data captured by the camera unit to recognize targets such as white lines on the road and other vehicles. The recognition unit supplies information about the recognized targets to the driving assistance ECU 10 at predetermined time intervals.

[0029] Each radar device of the radar sensor 14 includes a radar transmission / reception unit and a signal processing unit (not shown). The radar transmission / reception unit emits millimeter-wave radio waves (hereinafter referred to as "millimeter waves") and receives millimeter waves (i.e., reflected waves) reflected by a three-dimensional object (e.g., another vehicle, a bicycle, etc.) present within the emission range. The signal processing unit supplies information indicating the distance between the vehicle and the three-dimensional object, the relative speed between the vehicle and the three-dimensional object, the relative position (direction) of the three-dimensional object with respect to the vehicle, etc. to the driving assistance ECU 10 at predetermined time intervals based on the phase difference between the transmitted millimeter waves and the received reflected waves, the attenuation level of the reflected waves, and the time from transmitting the millimeter waves to receiving the reflected waves. Note that a LiDAR (Light Detection And Ranging) may be used instead of or in addition to the radar sensor 14.

[0030] The sonar device 16 includes multiple sonars, which are provided at multiple positions on the outer periphery of the vehicle 102, for example, at the left front end, right front end, left rear end, and right rear end. Each sonar is configured to transmit ultrasonic waves in a direction away from the vehicle 102, receive ultrasonic waves transmitted by its own sonar and reflected by an object, i.e., direct waves, and receive ultrasonic waves transmitted by other sonars and reflected by an object, i.e., indirect waves. Each sonar is also configured to output a signal indicating the peak value of the received voltage corresponding to the received ultrasonic waves, and therefore a signal indicating the peak value of the received ultrasonic waves, to a control device of the sonar device 16.

[0031] The control device of the sonar device 16 determines that the corresponding sonar is receiving ultrasonic waves when the wave height value is equal to or greater than a reference value. The control device of the sonar device 16 also estimates the distance between the object that reflected the direct wave and the indirect wave and the vehicle 102 and the direction of the object relative to the vehicle based on the flight times of the direct wave and the indirect wave.

[0032] The setting operation device 16 is provided at a position operable by the driver, like a steering wheel (not shown in Fig. 1), and is adapted to be operated by the driver. Although not shown in Fig. 1, the setting operation device 16 includes a driving assistance switch. As will be described in detail later, when the driving assistance switch is on, the driving assistance ECU 10 executes collision prevention control.

[0033] The drive ECU 20 is connected to a drive device 22 that accelerates the vehicle 102 by applying a drive force to drive wheels 24. The drive ECU 20 normally controls the drive device 22 so that the drive force generated by the drive device 22 changes according to the driving operation by the driver, and when a command signal is received from the driving assistance ECU 10, the drive ECU 20 controls the drive device 22 based on the command signal.

[0034] A braking device 32 that applies a braking force to wheels 34 to decelerate the vehicle 102 is connected to the braking ECU 30. The braking ECU 30 normally controls the braking device so that the braking force generated by the braking device 32 changes according to the braking operation by the driver, and when it receives a command signal from the driving assistance ECU 10, it controls the braking device 32 based on the command signal to perform automatic braking.

[0035] Thus, the brake ECU 30 and the brake device 32 cooperate with each other to function as an automatic braking device 36. When braking force is applied to the wheels by collision prevention control or the like, brake lights (not shown in FIG 1) are turned on.

[0036] A touch panel type display 52 that displays the status of control by the driving assistance ECU 10 and an alarm device 54 that issues an alarm are connected to the meter ECU 50. The display 52 may be, for example, a multi-information display that displays meters and various information, or may be a display of a navigation device 80 described later. As described later, when the display 52 receives a signal from the driving assistance ECU 10, it displays the status of collision prevention control.

[0037] The warning device 54 is activated when it is determined that the vehicle 102 is at risk of colliding with an obstacle, and issues a warning as one of the collision prevention controls, that is, issues a warning that the vehicle 102 is at risk of colliding with an obstacle. The warning device 54 may be any of a warning device that issues a visual warning such as a warning lamp, a warning device that issues an auditory warning such as a warning buzzer, and a warning that issues a physical warning such as seat vibration, or any combination thereof.

[0038] The driving operation sensor 60 and the vehicle condition sensor 70 are also connected to the CAN 104. Information detected by the driving operation sensor 60 and the vehicle condition sensor 70 (called sensor information) is transmitted to the CAN 104. The sensor information transmitted to the CAN 104 can be used appropriately in each ECU. Note that the sensor information may be information of a sensor connected to a specific ECU and transmitted to the CAN 104 from the specific ECU.

[0039] The driving operation sensor 60 includes a driving operation amount sensor that detects the amount of operation of the accelerator pedal, a braking operation amount sensor that detects the master cylinder pressure or the depression force on the brake pedal, a brake switch that detects whether the brake pedal is operated, a steering angle sensor that detects the steering angle, a steering torque sensor that detects the steering torque, etc.

[0040] The vehicle condition sensor 70 includes a vehicle speed sensor that detects the vehicle speed V of the vehicle 102, a longitudinal acceleration sensor that detects the longitudinal acceleration of the vehicle, a lateral acceleration sensor that detects the lateral acceleration of the vehicle, and a yaw rate sensor that detects the yaw rate of the vehicle.

[0041] Furthermore, a navigation device 80 is also connected to the CAN 104. The navigation device 80 includes a GPS receiver that detects the position of the vehicle 102, a storage device that stores map information and road information, and a communication device that acquires the latest information on the map information and road information from an external device. In particular, the road information may include information on locations where the vehicle may temporarily stop, such as intersections, T-junctions, and pedestrian crossings. Note that the navigation device 80 does not necessarily have to be provided.

[0042] In this embodiment, the ROM of the driving assistance ECU 10 stores a collision prevention control program corresponding to the flowchart shown in Fig. 2. Also, in this embodiment, the ROM of the driving assistance ECU 10 stores a flag control program corresponding to the flowchart shown in Fig. 3. <Collision prevention control (Fig. 2)>

[0043] Next, the collision prevention control in the embodiment will be described with reference to the flowchart shown in Fig. 2. The collision prevention control according to the flowchart shown in Fig. 2 is repeatedly executed at predetermined time intervals by the CPU of the driving assistance ECU 10 in a situation where the driving assistance switch is on.

[0044] First, in step S10, the CPU determines whether or not the vehicle speed V of the vehicle 102 is equal to or lower than a reference value Vc (positive constant) for low vehicle speed determination. If a positive determination is made, the control proceeds to step S30, and if a negative determination is made, that is, if the vehicle is traveling at a medium to high speed, the control proceeds to step S20.

[0045] In step S20, the CPU executes pre-crash safety control (hereinafter referred to as PCS control) in a manner known in the art. In PCS control, it is determined whether the host vehicle will collide with the preceding vehicle based on the distance between the host vehicle and the preceding vehicle and the relative speed of the host vehicle to the preceding vehicle, which are detected by, for example, the camera sensor 12 or the radar sensor 14. If it is determined that there is a risk of collision, an alarm is issued by the alarm device 54, and the host vehicle is decelerated by automatic braking by the automatic braking device 36, thereby preventing the collision.

[0046] In step S30, the CPU determines whether or not there is an obstacle ahead of the vehicle 102 based on information about a target ahead of the vehicle 102 acquired by the sonar device 16 or the radar sensor 14 of the target information acquisition device 17. If a negative determination is made, this control is temporarily terminated, and if a positive determination is made, this control proceeds to step S40.

[0047] In step S40, the CPU calculates the distance Lr from the vehicle 102 to the obstacle and the relative speed Vr of the vehicle 102 with respect to the obstacle, based on information about the target ahead of the vehicle 102 acquired by the sonar device 16 or the radar sensor 14.

[0048] In step S50, the CPU calculates the target stopping distance Lst so that it increases as the ratio Lr / Vr of the distance Lr to the relative speed Vr decreases. The target stopping distance Lst is a target value of the stopping distance Ls, with the distance Lr between the vehicle 102 and an obstacle when the vehicle 102 stops due to automatic deceleration being the stopping distance Ls. The CPU also calculates a target deceleration Gbt of the vehicle 102 for bringing the stopping distance Ls into the target stopping distance Lst, based on the current distance Lr, the target stopping distance Lst, and the current vehicle speed V. The target deceleration Gbt is calculated so that it increases as the relative speed Vr increases and increases as the difference Lr-Lst between the distance Lr and the target stopping distance Lst decreases.

[0049] In step S60, the CPU determines whether or not a flag Fa controlled according to a routine shown in Fig. 3 described later is 1, that is, whether or not it has been determined that the preceding vehicle that had been temporarily stopped has started moving. If a negative determination is made, the control proceeds to step S80, and if a positive determination is made, the control proceeds to step S70.

[0050] In step S70, the CPU increases the target deceleration Gbt by increasing the target stopping distance Lst. The CPU also increases the first and second reference distances Lrc1 and Lrc2 used in the determinations in steps S80 and S100, which will be described later. The first reference distance Lrc1 is greater than the second reference distance Lrc2. Therefore, the conditions for determining the risk of collision of the host vehicle with an obstacle in steps S80 and S100 are changed so that it is more likely to be determined that there is a risk of collision of the host vehicle with an obstacle.

[0051] The increasing correction may be performed by multiplying the target deceleration Gbt by a correction coefficient greater than 1, or by adding a corresponding correction amount (positive constant). The target deceleration Gbt may be increased without increasing the target stopping distance Lst. Furthermore, a command signal may be output to the meter ECU 50 to operate the display 52, thereby notifying the user that a warning will be issued and automatic deceleration will be started early.

[0052] In step S80, the CPU determines whether or not the distance Lr from the vehicle 102 to the obstacle is equal to or shorter than a first reference distance Lrc1, that is, whether or not there is a risk that the vehicle 102 will collide with the obstacle. If a negative determination is made, this control is temporarily terminated, and if a positive determination is made, this control proceeds to step S90.

[0053] In step S90, the CPU outputs a command signal to the meter ECU 50 to activate the alarm device 54, thereby issuing an alarm that the vehicle 102 may collide with an obstacle. The CPU also outputs a command signal to the meter ECU 50 to activate the display 52, thereby notifying that the vehicle 102 may collide with an obstacle.

[0054] In step S100, the CPU determines whether or not the distance Lr from the vehicle 102 to the obstacle is equal to or shorter than a second reference distance Lrc2. If a negative determination is made, this control is temporarily terminated, and if a positive determination is made, this control proceeds to step S110.

[0055] In step S110, the CPU outputs a command signal to the drive ECU 20 and the brake ECU 30 to reduce the driving force of the drive device 22, and activates the automatic braking device 36 to apply a braking force to the vehicle 102, thereby performing automatic deceleration so that the vehicle deceleration becomes the target deceleration Gbt.

[0056] As can be seen from the above description, in the embodiment, the countermeasure controls for reducing the risk of the vehicle colliding with an obstacle are the issuance of an alarm by the activation of the alarm device 54, the reduction of the driving force of the drive device 22, and the automatic deceleration by the application of a braking force by the automatic braking device 36. However, any of the countermeasure controls may be omitted. <Flag control (Fig. 3)>

[0057] Next, the flag control in the embodiment will be described with reference to the flowchart shown in Fig. 3. The flag control according to the flowchart shown in Fig. 3 is repeatedly executed at predetermined time intervals by the CPU of the driving assistance ECU 10 when the driving assistance switch is on. Note that the flags Fa and Fb are reset to 0 when the flag control starts.

[0058] First, in step S210, the CPU determines whether or not the flag Fa is 1, that is, whether or not it has been determined that the preceding vehicle that was temporarily stopped has started transmitting. If a positive determination is made, the control proceeds to step S280, and if a negative determination is made, the control proceeds to step S220.

[0059] In step S220, the CPU determines whether or not the flag Fb is 1, that is, whether or not it has already been determined in step S230 described below that there is a preceding vehicle that is temporarily stopped ahead of the host vehicle. If a positive determination is made, the control proceeds to step S250, and if a negative determination is made, the control proceeds to step S230.

[0060] In step S230, the CPU determines whether or not the vehicle speed V of the host vehicle is equal to or less than the vehicle speed reference value Vs and there is a preceding vehicle that is temporarily stopped ahead of the host vehicle, based on information acquired by the target information acquisition device 17, etc. If a negative determination is made, this control is temporarily terminated, whereas if a positive determination is made, the flag Fb is set to 1 in step S240, and then this control proceeds to step S250.

[0061] The vehicle speed reference value Vs is a reference value for determining whether the vehicle is at an extremely low speed, and is a positive constant smaller than the reference value Vc for determining a low vehicle speed used in the determination in step S10. The determination in step S230 may be a determination as to whether the host vehicle is temporarily stopped and whether there is a preceding vehicle that is temporarily stopped ahead of the host vehicle.

[0062] In step S250, the CPU determines whether the preceding vehicle that was temporarily stopped has started moving. If a negative determination is made, the control ends, and if a positive determination is made, the control proceeds to step S260.

[0063] In step S260, the CPU variably sets a reference time Tc and a reference mileage Lvc to be used in the determinations of steps S280 and S290, respectively, described below, depending on at least one of the type of road and the degree of vehicle congestion ahead of the position where the host vehicle and the preceding vehicle were temporarily stopped.

[0064] When the road ahead is a crossroads or a T-junction, the reference time Tc and the reference travel distance Lvc may be set to be larger as the width and number of lanes of the road intersecting the road on which the vehicle is traveling are larger. When the road ahead is a road with a pedestrian crossing or a stop line, the reference time Tc and the reference travel distance Lvc may be set to be smaller than when the road ahead is a crossroads or a T-junction. Furthermore, the reference time Tc and the reference travel distance Lvc may be set to be larger as the degree of vehicle congestion ahead of the vehicle increases.

[0065] In step S270, the CPU sets a flag Fa to 1 and resets a flag Fb to 0.

[0066] In step S280, the CPU determines whether the time that has elapsed since it was determined in step S80 that the vehicle 102 is at risk of colliding with an obstacle is equal to or longer than the reference time Tc. If a positive determination is made, the control proceeds to step S300, and if a negative determination is made, the control proceeds to step S290. The elapsed time may be the time that has elapsed since it was determined in step S100 that the vehicle 102 is at risk of colliding with an obstacle.

[0067] In step S290, the CPU determines whether the distance traveled by the vehicle from the time when it was determined in step S80 that the vehicle 102 may collide with an obstacle is equal to or greater than the reference distance traveled Lvc. If a negative determination is made, the control ends temporarily, whereas if a positive determination is made, in step S300, the flag Fa is reset to 0, and then the control ends temporarily. The distance traveled may be the distance traveled from the time when it was determined in step S100 that the vehicle 102 may collide with an obstacle. <Operation and Effects of the Embodiment> <When the vehicle ahead and your vehicle are stopped (Fig. 4)>

[0068] For example, Fig. 4 shows a situation where the traffic light 112 at the intersection 110 is red, the preceding vehicle 114 is stopped, and the host vehicle 102 is stopped behind the preceding vehicle. In the situation shown in Fig. 4, negative determinations are made in steps S210 and S220, and a positive determination is made in step S230, so that the flag Fb is set to 1 in step S240. Since a negative determination is made in step S250, steps S260 and S270 are not executed.

[0069] Therefore, since the flag Fa remains at 0, a negative determination is made in step S60, and step S70 is not executed. Therefore, the first and second reference distances Lrc1 and Lrc2 are not increased, and the target deceleration Gbt is not increased. The determinations in steps S80 and S100 are performed while the first and second reference distances Lrc1 and Lrc2 are maintained at their standard values. <When the preceding vehicle starts moving (Fig. 5)>

[0070] Fig. 5 shows a situation in which the traffic light 112 at the crossroads 110 turns green, the preceding vehicle 114 starts moving, and the host vehicle 102 is stopped. In the situation shown in Fig. 5, similarly to the situation shown in Fig. 4, negative determinations are made in steps S210 and S220, and a positive determination is made in step S230, so that the flag Fb is set to 1 in step S240. Furthermore, a positive determination is made in step S250, a reference time Tc and a reference travel distance Lvc are set in step S260 according to the type of road ahead, and the flag Fa is set to 1 and the flag Fb is reset to 0 in step S270.

[0071] Therefore, a positive determination is made in step S60, and step S70 is executed, whereby the first and second reference distances Lrc1 and Lrc2 are corrected to increase. That is, the conditions for determining the risk in steps S80 and S100 are changed so that it becomes easier to determine that there is a risk of the host vehicle colliding with an obstacle. As a result, the determinations in steps S80 and S100 are made using the first and second reference distances Lrc1 and Lrc2 that have been corrected to increase, and thus a positive determination is made earlier than when the first and second reference distances are standard values. <When the preceding vehicle suddenly decelerates or stops immediately after starting (Fig. 6)>

[0072] 6 shows a situation in which a leading vehicle 114 starts moving, and then the host vehicle 102 starts moving, but the leading vehicle suddenly decelerates or stops immediately after starting due to traffic congestion ahead of the leading vehicle 114. In a situation such as that shown in FIG 6, the distance between the host vehicle 102 and the leading vehicle 114 suddenly decreases, increasing the risk of the host vehicle colliding with the leading vehicle.

[0073] However, according to the embodiment, as described above, the determinations in steps S80 and S100 become positive earlier than when the first and second reference distances are standard values, and therefore the issuance of a warning in step S90 and the automatic deceleration in step S110 are started earlier. Therefore, compared to the conventional case in which the first and second reference distances Lrc1 and Lrc2 are not increased, the risk of the host vehicle colliding with the preceding vehicle can be effectively reduced.

[0074] Furthermore, according to the embodiment, not only the first and second reference distances Lrc1 and Lrc2 are increased, but also the target deceleration Gbt is increased, so that the host vehicle can be decelerated at a high deceleration. Therefore, compared to the conventional case in which the target deceleration Gbt is not increased, the risk of the host vehicle colliding with the preceding vehicle can be effectively reduced.

[0075] According to the embodiment, when the time elapsed since it was determined that the vehicle 102 may collide with an obstacle is equal to or longer than the reference time Tc (S280), the execution of the countermeasure control (S80 and S100) for reducing the risk of the vehicle colliding with the preceding vehicle as an obstacle is terminated (S300). Thus, the risk of the countermeasure control being executed for an excessively long time can be reduced.

[0076] According to the embodiment, when the travel distance of the vehicle from the time when it is determined that the vehicle 102 is likely to collide with an obstacle is equal to or greater than the reference travel distance Lvc (S290), the execution of the countermeasure control for reducing the risk of the vehicle colliding with the preceding vehicle as an obstacle is terminated (S300). This also reduces the risk of the countermeasure control being executed for an excessively long time.

[0077] Furthermore, according to the embodiment, in step S260, the reference time Tc and the reference mileage Lvc are variably set according to at least one of the type of road ahead of the position where the vehicle and the preceding vehicle were stopped and the degree of vehicle congestion. Therefore, compared to the case where the reference time Tc and the reference mileage Lvc are constant, it is possible to reduce the risk that the countermeasure control is executed for an excessively long time and the risk that the time for which the countermeasure control is executed is insufficient. Note that step S260 may be omitted. That is, the reference time Tc and the reference mileage Lvc may be constant.

[0078] Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to the above-described embodiments, and it will be apparent to those skilled in the art that various other embodiments are possible within the scope of the present invention.

[0079] For example, in the above embodiment, the target deceleration Gbt and the first and second reference distances Lrc1 and Lrc2 are increased in step S70. However, only the target deceleration Gbt or only the first and second reference distances Lrc1 and Lrc2 may be increased.

[0080] In the above embodiment, in step S280, it is determined whether the elapsed time is equal to or greater than the reference time Tc, and in step S290, it is determined whether the vehicle's travel distance is equal to or greater than the reference travel distance Lvc. However, step S280 or S290 may be omitted. In that case, setting of the reference time Tc or the reference travel distance Lvc corresponding to the omitted determination (step S260) is omitted.

[0081] In the above embodiment, even if the flag Fa is 1, the effect of the alarm, which is one of the countermeasure controls, is not increased. However, when the flag Fa is 1, the appealing effect of the alarm may be increased. For example, when the alarm is issued by an intermittent buzzer sound, the intermittent buzzer sound may be changed to a continuous sound.

[0082] Furthermore, in the above-described embodiment, the countermeasure control is to issue an alarm and to control the automatic deceleration of the vehicle. However, the countermeasure control may be to issue an alarm or to control the automatic deceleration of the vehicle, and in that case, the effect of the countermeasure control may be set higher than when the countermeasure control is to issue an alarm and to control the automatic deceleration of the vehicle. [Explanation of symbols]

[0083] 10... driving assistance ECU, 12... camera sensor, 14... radar sensor, 16... sonar device, 17... target detection device, 22... drive device, 32... braking device, 36... automatic braking device, 100... collision prevention device, 102... vehicle, 114... preceding vehicle

Claims

1. A collision prevention device including a target information acquisition device that acquires information on targets around a vehicle, and a control unit that is configured to determine, when it is determined based on the information acquired by the target information acquisition device that there is an obstacle ahead of the vehicle, whether the vehicle is likely to collide with the obstacle, and, when it is determined that there is such a risk, to execute a countermeasure control to reduce such a risk, A collision prevention device configured, when the control unit determines that the obstacle is a preceding vehicle that has stopped temporarily and that the preceding vehicle has started moving, to at least one of change the conditions for determining the risk so that the risk is more likely to be determined and increase the effectiveness of the countermeasure control.

2. 2. A collision prevention device according to claim 1, wherein the control unit is configured to calculate a distance between the subject vehicle and the preceding vehicle based on information acquired by the target information acquisition device, and to determine that there is a risk when the distance is equal to or shorter than a reference distance, and further, when it is determined that the preceding vehicle has started moving, the control unit is configured to change the conditions for determining that there is a risk by increasing the reference distance.

3. 2. The collision prevention device according to claim 1, wherein the countermeasure control includes automatic deceleration for automatically decelerating the host vehicle, and the control unit is configured to increase the deceleration of the automatic deceleration when it determines that the preceding vehicle has started moving, thereby enhancing the effect of the countermeasure control.

4. 2. The collision prevention device according to claim 1, wherein the control unit is configured to terminate the execution of at least one of the processes when an elapsed time from a time when it is determined that there is a risk is equal to or greater than a reference time.

5. 2. The collision prevention device according to claim 1, wherein the control unit is configured to terminate the execution of at least one of the processes when a distance traveled by the host vehicle from a time when the risk is determined to exist is equal to or greater than a reference distance.

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