DRIVING SUPPORT CONTROL DEVICE AND DRIVING SUPPORT CONTROL

METHOD

FIELD OF THE INVENTION [0001] The invention relates to a driving support control device and a driving support control method. More particularly, the invention relates to a driving support control device and a driving support control method in which a driving support control of supporting the driving of a host vehicle is performed on the basis of a risk of collision between the host vehicle and a detected obstacle.

BACKGROUND OF THE INVENTION

[0002] Driving support control devices that support the driving of a host vehicle in accordance with the state of run of the host vehicle and the situation in the traveling direction of the host vehicle have been proposed. Examples of the driving support control devices include a device as shown in, for example, Japanese Patent Application Publication No. JP-A-10-29464, in which the possibility of collision between the host vehicle and a detected obstacle is determined from the traveling direction of the host vehicle and the distance to the detected obstacle, and warning is performed with regard to the obstacle if there is a possibility of collision between the obstacle and the host vehicle. [0003] Such a driving support control device includes an obstacle detection device that detects an obstacle present in the traveling direction of the host vehicle. The obstacle detection device includes an object detection device that detects an object present forward of the host vehicle, and an obstacle determination device. This object detection device detects the position of an object forward of the host vehicle, that is, the relative positions of the object and the host vehicle, through the use of, for example, a millimeter wave radar. Besides, among the objects present forward of the host vehicle which are detected by the object detection device, the obstacle determination device determines an object present in the traveling direction of the host vehicle as being an obstacle. Therefore, the obstacle detection device is able to detect an obstacle present in

the traveling direction of the host vehicle.

[0004] In the above-described obstacle detection device, it is difficult to continue to detect an obstacle having been detected as being present in the traveling direction of the host vehicle, in every control cycle of the driving support control device. That is, the driving support control device can fail to detect a previously detected obstacle in a control cycle, that is, can sometimes lose track of an obstacle depending on control cycles.

[0005] Furthermore, in conjunction with the driving support control device, when the host vehicle is running on a curved road, the traveling direction of the host vehicle is a direction along the curved road. Specifically, when the host vehicle is running on a ' curved road, the traveling direction of the host vehicle is based on an estimated radius of the curve that is calculated from the rotational velocity of the host vehicle detected via a yaw rate sensor. Therefore, among the objects detected via the object detection device, the obstacle determination device determines the object present in the traveling direction of the host vehicle based on the estimated radius of the curve, as being an obstacle.

[0006] It is to be noted herein that when the host vehicle is running on a linear road, the driver sometimes performs a small amount of steering operation in order to correct the traveling direction of the host vehicle. Since the rotational velocity of the host vehicle changes due to such a small amount of steering operation performed by the driver, the estimated radius of the curve also changes due to the driver's small amount of steering operation. That is, even when the host vehicle is running on a linear road, it can happen that the rotational velocity of the host vehicle changes and an object having been detected as being an obstacle ceases being detected as an obstacle.

[0007] Thus, in conjunction with the above-described driving support control device, it can happen that after determining that there is a possibility of collision with an obstacle, the device determines that there is not a possibility of collision between the obstacle and the vehicle while in reality there is such a possibility of collision. Therefore, in the driving support control device, the warning may be interrupted, and the warning may be repeated with regard to the same obstacle. That is, in the driving support control device,

the driving support control with respect to the same obstacle can sometimes be interrupted or discontinued halfway.

DISCLOSURE OF THE INVENTION [0008] It is an object of the invention to provide a driving support control device and a driving support control method in which even if after an obstacle is detected the detection of the same obstacle becomes impossible, interruption of the driving support control can be restrained.

[0009] A first aspect of the invention relates to a driving support control device. The driving support control device includes obstacle detection means for detecting a position of an obstacle present in a traveling direction of a host vehicle; driving support control means for performing a driving support control of supporting driving of the host vehicle; collision risk calculation means for calculating a risk of collision between the host vehicle and the obstacle detected; and driving support control determination means for determining whether the driving support control is needed or not needed based on the risk of collision calculated. If it is determined that the control is not needed based on the calculated risk of collision after it is determined that the control is needed based on the calculated risk of collision, the driving support control determination means holds a state where the control is needed for a predetermined hold period. [0010] In the driving support control device, the driving support control may include a warning control of warning a driver of the host vehicle.

[0011] In the driving support control device, the driving support control may include an intervention braking control of applying an intervention braking force to the host vehicle. [0012] In the driving support control device, the risk of collision may be a value based on a relative vehicle time distance between the host vehicle and the obstacle detected.

[0013] In the driving support control device, the risk of collision may be higher as the relative vehicle time distance is shorter.

[0014] According to the driving support control device, in the case where the obstacle detection means detects an obstacle and it is determined that the control is needed on the basis of the collision risk calculated by the collision risk calculation means, for example, the relative vehicle time distance between the host vehicle and the detected obstacle, and where the detection of the same obstacle by the obstacle detection means ceases and therefore it is determined that the control is not needed on the basis of the collision risk calculated by the collision risk calculation means, the state where the control is needed is held or maintained for a predetermined hold period by the driving support control means. That is, even if the detection of an obstacle by the obstacle detection means is followed by the cessation of the detection of the same obstacle by the obstacle detection means, the driving support control means keeps performing the driving support control, for example, the warning control or the intervention braking control, for the predetermined hold period following the time of the cessation of the detection of the same obstacle by the obstacle detection means. Therefore, even if after an obstacle is detected the detection of the same obstacle becomes impossible, it is possible to substantially prevent an event in which the driving support control is interrupted halfway, or the driving support control is performed again after an interruption. Therefore, the discomfort or the like of the driver can be restrained.

[0015] Furthermore, in the driving support control device, the predetermined hold period may be different in accordance with kind of the driving support control.

[0016] Still further, the driving support control device may further include hold period calculation means for calculating the predetermined hold period, and the hold period calculation means may calculate the predetermined hold period in accordance with the calculated risk of collision. [0017] Further, in the driving support control device, the hold period calculation means may calculate the predetermined hold period to be shorter as the calculated collision risk is higher.

[0018] According to the driving support control device, the predetermined hold period is varied in accordance with the calculated collision risk or the kind of the driving

support control. For example, the predetermined hold period is calculated to be shorter the higher the collision risk calculated by the hold period calculation means. Besides, in the driving support control that is started when the calculated collision risk is relatively high, the predetermined hold period is made longer than in the driving support control that is started when the calculated collision risk is relatively low. That is, since the predetermined hold period is varied in accordance with the calculated collision risk or the kind of the driving support control, the period until the driving support control having been maintained or performed is stopped can be shortened in accordance with the calculated collision risk or the kind of the driving support control in the case where an obstacle detected by the obstacle detection means ceases being an obstacle, for example, in the case where an obstacle having been detected disappears from the traveling direction of the host vehicle. Therefore, the timing of stopping the driving support control can be brought close to the timing at which the obstacle detected by the obstacle detection means ceases being an obstacle. [0019] In the driving support control device, the driving support control means may cause a within-period braking force applied to the host vehicle in the predetermined hold period to be less than the intervention braking force.

[0020] Furthermore, in the driving support control device, the driving support control means may cause the within-period braking force to be less than the intervention braking force with elapse of time during the predetermined hold period.

[0021] According to the driving support control device, when the driving support control is the intervention braking control, the driving support control means causes the within-period braking force applied to the host vehicle in the predetermined hold period to be not equal to the intervention braking force but be a braking force that is less than the intervention braking force, or causes the within-period braking force to be less than the intervention braking force with the elapse of time during the predetermined hold period. Therefore, the driving support control means can bring the state of run of the host vehicle close to the state where the intervention braking control is ceased, within a predetermined hold period. Therefore, even though the intervention braking control is stopped after the

elapse of a predetermined hold period, the state of run of the host vehicle can be brought close to the state where the intervention braking control is ceased, within the predetermined hold period. Therefore, in comparison with the case where the intervention braking force has been applied to the host vehicle and suddenly ceases being applied to the host vehicle, the state of run of the host vehicle can be more quickly returned to the state where the intervention braking control is ceased. Hence, the discomfort of the driver can be restrained.

[0022] A second aspect of the invention relates to a driving support control method in which a driving support control of supporting the driving of a host vehicle is performed. The driving support control method includes: detecting a position of an obstacle present in a traveling direction of the host vehicle; calculating a risk of collision between the host vehicle and the obstacle detected; determining whether the driving support control is needed or not needed based on the risk of collision calculated; and holding a state where the control is needed for a predetermined hold period if after it is determined that the control is needed based on the calculated risk of collision, it is determined that the control is not needed based on the calculated risk of collision.

[0023] In the driving support control device and the driving support control method in accordance with the first aspect and the second aspect of the invention, the driving support control continues to be performed for the predetermined hold period following the time of the cessation of the detection of the same obstacle by the obstacle detection means. Therefore, even if after an obstacle is detected the detection of the same obstacle becomes impossible, it is possible to substantially prevent an event in which the driving support control is interrupted halfway.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a diagram showing an example of a constitution of a driving support control device in accordance with the invention;

FIG. 2 is an operation flowchart of a warning braking control performed by a driving support control device in accordance with Embodiment 1; FIG. 3 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force;

FIG. 4 is an operation flowchart of an intervention braking control performed by the driving support control device in accordance with Embodiment 1;

FIG. 5 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force;

FIGS. 6 A and 6B are operation flowchart of an intervention braking control performed by a driving support control device in accordance with Embodiment 2;

FIG. 7 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force; FIG. 8 is an operation flowchart of an intervention braking control performed by a driving support control device in accordance with Embodiment 3;

FIG. 9 is a diagram showing a relationship between the TTC and the predetermined hold period T;

FIG. 10 is a diagram showing a relationship between the predetermined hold period T and the hold counter number Nm;

FIG. 11 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force;

FIGS. 12A and 12B are operation flowchart of an intervention braking control performed by a driving support control device in accordance with Embodiment 4; and FIG. 13 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0025] The invention will be described hereinafter in detail with reference to the

accompanying drawings. It is to be noted that the embodiments described below do not limit the invention. Besides, the component elements of the embodiments include elements that can easily be conceived by those in the art, and elements substantially the same as elements that can easily be conceived by those in the art. The embodiments below will be described in conjunction with the case where a driving support control device performs a control of mitigating the impact upon the contact or collision between the host vehicle and an obstacle, that is, a pre-crash safety (PCS) control, as a driving support control. Incidentally, the driving support control device may also be able to perform an automatic driving control of automatically controlling the driving of a host vehicle in accordance with the road configuration in the traveling direction of the host vehicle, the presence/absence of a preceding vehicle, etc., that is, an adaptive cruise control (ACC) control. Besides, the embodiments below will be described in conjunction with the case where the driving support control device performs a warning braking control that is one of the warning controls of warning a driver of the host vehicle, and an intervention braking control, as driving support controls. In addition, the warning control and the driving support control are not limited to those mentioned above. For example, the warning control may be an on/off control of a warning lamp, a warning-sound production control, a seatbelt winding-up control, etc. Besides, the driving support control may be an assist braking control of giving an assist braking force that adds to the braking force applied to the host vehicle by the driver, an airbag activation control, a seatbelt winding-up control, a control of the amount of damping of a suspension shock absorber, etc.

[0026] FIG. 1 is a diagram showing an example of the construction of a driving support control device in accordance with the invention. As shown in FIG. 1, an driving support control device 1-1 in accordance with Embodiment 1 is mounted in a host vehicle (not shown), and includes a control device 2, a forward millimeter wave radar 3, a brake device 4, a yaw rate sensor 5, a G-sensor 6, a vehicle speed sensor 7, and a brake sensor 8.

[0027] The control device 2 controls the entire vehicle driving support device. The

control device 2 includes an obstacle detection portion 21, a collision risk calculation portion 22, a driving support control determination portion 23, a hold counter 24, a control counter 25, a driving support control portion 26, and a hold counter setting portion 27. [0028] The obstacle detection portion 21 can be regarded as a portion of obstacle detection means. The obstacle detection portion 21 detects, among objects detected by the forward millimeter wave radar 3, an object present in the traveling direction of the host vehicle, that is, an object that is present in the same traffic lane that the host vehicle is traveling in (e.g., a preceding vehicle traveling in the same traffic lane as the host vehicle, a fallen object on the same traffic lane), as an obstacle.

[0029] The collision risk calculation portion 22 can be regarded as collision risk calculation means. The collision risk calculation portion 22 calculates the risk of the collision between the host vehicle and an obstacle detected by the obstacle detection portion 21. In Embodiment 1, the collision risk calculation portion 22 uses, as a collision risk, a relative vehicle time distance between the host vehicle and the obstacle detected by the obstacle detection portion 21 (hereinafter, referred to as "TTC"). It is to be noted herein that the collision risk becomes higher the shorter the TTC (time to collision) is, and becomes lower the longer the TTC is. In addition, the collision risk calculation portion 22 calculates the TTC to be infinite if the obstacle detection portion 21 does not detect an obstacle. That is, if the obstacle detection portion 21 does not detect position data of an obstacle, the collision risk becomes the lowest. Besides, the TTC is "0", when a detected obstacle and the host vehicle collide with each other.

[0030] The driving support control determination portion 23 can be regarded as driving support control determination means. The driving support control determination portion 23 determines whether the driving support control by the driving support control portion 26 is needed or not needed on the basis of the collision risk calculated by the collision risk calculation portion 22. That is, the driving support control determination portion 23 determines whether the driving support control is needed or not needed on the basis of the calculated TTC. The driving support control determination portion 23

includes a request determination portion 23a and a control determination portion 23b.

[0031] The request determination portion 23a can be regarded as a portion of the driving support control determination means. The request determination portion 23a determines the presence/absence of a request for the driving support control performed by the driving support control portion 26, on the basis of the collision risk calculated by the collision risk calculation portion 22. That is, the request determination portion 23a determines the presence/absence of a request for the driving support control on the basis of the calculated TTC. The request determination portion 23a determines that there is a request for the driving support control if the calculated TTC is less than or equal to a predetermined value (TTCl for the warning braking control, and TTC2 for the intervention braking control). If the calculated TTC is greater than the predetermined value, the request determination portion 23a determines that there is not a request for the driving support control. In addition, if determining that there is a request for the driving support control, the request determination portion 23a turns a request flag on, and if determining that there is not a request for the driving support control, the request determination portion 23a turns request flag off.

. [0032] The control determination portion 23b can be regarded as a portion of the driving support control determination means. The control determination portion 23b determines whether the driving support control by the driving support control portion 26 is needed or not needed, on the basis of the presence/absence of a request for the driving support control determined by the request determination portion 23a. Basically, the control determination portion 23b determines that the driving support control is needed if the request determination portion 23a determines that there is a request for the driving support control. On the other hand, if the request determination portion 23a determines that there is not a request for the driving support control, or if the control counter described below reaches or exceeds a predetermined control counter number (NcI for the warning braking control, and Nc2 for the intervention braking control), the control determination portion 23b determines that the driving support control is not needed. In addition, if determining that the driving support control is needed, the control

determination portion 23b turns a control flag on, and if determining that the driving support control is not needed, the control determination portion 23b turns control flag off.

[0033] The hold counter 24 measures the period of time following the determination made by the driving support control determination portion 23 that the driving support control is not needed. That is, the hold counter 24 measures the period of time following the determination made by the control determination portion 23b that the driving support control is not needed. In addition, the hold counter 24 decrements the count from a hold counter number Nm that has been set on the basis of a predetermined hold period T by the hold counter setting portion 27 described below. [0034] The control counter 25 measures the period of time following the performance of the driving support control by the driving support control portion 26.

[0035] The driving support control portion 26 can be regarded as driving support control means. The driving support control portion 26 performs the driving support control of supporting the driving of the host vehicle. The driving support control portion 26 performs the warning braking control of applying a warning braking force to the host vehicle, that is, a warning control of warning the driver of the host vehicle, and the intervention braking control of applying an intervention braking force to the host vehicle. The driving support control portion 26 is able to output to the brake device 4 brake control signals that cause the brake device 4 to generate the warning braking force Fl or the intervention braking force F2. Incidentally, the intervention braking force F2 is a braking force that brings about the greatest deceleration of the host vehicle, for example, a maximum braking force. Besides, the warning braking force Fl is such a level of braking force that the driver of the host vehicle can perceive that the host vehicle has decelerated, and is a braking force that is smaller than the intervention braking force. [0036] The hold counter setting portion 27 sets the hold counter number Nm of the hold counter 24. In this embodiment, the hold counter setting portion 27 sets a predetermined counter number NmI pre-stored in a storage portion (not shown) into the hold counter 24 as a hold counter number Nm when the warning braking control is to be performed by the driving support control portion 26. When the intervention braking

control is to be performed by the driving support control portion 26, on the other hand, the hold counter setting portion 27 sets a predetermined counter number Nm2 pre-stored in the storage portion into the hold counter 24 as a hold counter number Nm. The predetermined counter number NmI is a number calculated on the basis of a predetermined hold period Tl during which the warning braking control is continued in the case where the warning braking control is performed by the driving support control portion 26. The predetermined counter number Nm2 is a number calculated on the basis of a predetermined hold period T2 during which the intervention braking control is continued in the case where the intervention braking control is performed by the driving support control portion 26. The predetermined counter number Nm2 is set shorter than the predetermined counter number NmI. That is, the predetermined hold period T2 for the intervention braking control is set shorter than the predetermined hold period Tl for the warning braking control. Thus, the predetermined hold period T varies depending on the kind of driving support control. [0037] Various data is input to the above-described control device 2. For example, the data input thereto include position data of an object detected by the forward millimeter wave radar 3, the rotational velocity of the host vehicle detected by the yaw rate sensor 5, the acceleration of the host vehicle detected by the G-sensor 6, the vehicle speed of the host vehicle detected by the vehicle speed sensor 7, the intention to brake of a driver (not shown) driving the host vehicle which is detected by the brake sensor 8, etc. On the other hand, the control device 2 in Embodiment 1 outputs a brake control signal that actuates brakes 43 of the brake device 4 on the basis of the aforementioned various input data, a map stored in the storage portion (not shown), etc.

[0038] The control device 2 includes an input/output port (I/O), a processing portion, and the storage portion although they are not shown in the drawings. The input/output port (not shown) is connected to the aforementioned various sensors and the aforementioned various devices, and inputs the data from the various sensors into the control device 2, and outputs control signals from the control device 2 to the various devices. The processing portion (not shown) includes a RAM (Random Access

Memory), a CPU (Central Processing Unit), etc. The processing portion executes programs based on a driving support control method of the driving support control device 1-1 in accordance with the invention by, for example, loading the programs to the RAM, whereby the driving support control method is realized. The storage portion (not shown) includes a ROM (Read Only Memory), or the RAM, or a combination thereof. In Embodiment 1, the driving support control method of the driving support control device 1-1 in accordance with the invention is realized by the control device 2. However, this is not restrictive; for example, the driving support control method may also be realized by a control device that is formed separately from the control device 2. [0039] The forward millimeter wave radar 3 can be regarded as a portion of the obstacle detection means. The forward millimeter wave radar 3 may also be regarded as object detection means. The forward millimeter wave radar 3 is mounted, for example, in a central portion of a front face portion of the host vehicle. The forward millimeter wave radar 3 detects an object that exists forward of the host vehicle. The position data of the object detected by the forward millimeter wave radar 3 is input to the control device 2. The forward millimeter wave radar 3 is, for example, a narrow angle/wide angle switch type millimeter wave radar in which a long-distance narrow-angle DBF system is combined with a short-distance wide-angle mono-pulse system. Incidentally, the forward millimeter wave radar 3 is a radar that detects the position of an object through the use of millimeter waves. The forward millimeter wave radar 3 emits millimeter waves, specifically in this embodiment, emits millimeter waves from the front face of the host vehicle to a predetermined forward range that includes the traveling direction of the host vehicle, and receives millimeter waves reflected from an object present forward of the host vehicle. Then, by measuring the time from the emission till the reception, the forward millimeter wave radar 3 calculates the distance from the forward millimeter wave radar to the object, that is, the distance from the host vehicle to the object present forward of the host vehicle. Besides, the forward millimeter wave radar 3 is also able to calculate the relative speed with respect to the object by utilizing the Doppler effect. Furthermore, the forward millimeter wave radar 3 detects the

direction of the millimeter waves reflected and received most strongly of the entire millimeter waves received, and calculates, from that direction, the angle between the forward direction of the host vehicle and the direction of the object. Therefore, if the position of an object is detected by the forward millimeter wave radar 3, the distance to the object, the relative speed thereto and the angle thereto are input as position data of the detected object. Incidentally, when the forward millimeter wave radar 3 receives millimeter waves reflected from an object, it means that the position of the object is detected. Thus, every time the forward millimeter wave radar 3 receives millimeter waves reflected from an object, it means that the position of one object is obtained. Although the forward millimeter wave radar 3 in this embodiment is constructed so as to emit millimeter waves, and receive millimeter waves, and calculate the distance, the relative velocity and the angle to an object, this construction is not restrictive. For example, the forward millimeter wave radar 3 may perform only the emission and reception of millimeter waves, and outputs a detection value based on the received millimeter waves to the control device 2, and the control device 2 may calculate the distance, the relative speed and the angle to the object.

[0040] The brake device 4 applies braking force to the host vehicle so as to decelerate the host vehicle or keep a stopped state of the host vehicle. The brake device 4 includes a brake control device 41, a brake actuator 42, the brakes 43, a brake pedal 44 that is provided with a master cylinder (not shown). The brake control device 41 controls the operation of the controls system, for example, the operation of the brake actuator 42 connected to the brake control device 41. Besides, the brake control device 41 operates the brake actuator 42 on the basis of the amount of depression of the brake pedal 44 caused by the driver which is detected by the brake sensor 8, and the state of run of the host vehicle. The brake control device 41 is also able to operate the brake actuator 42 in accordance with a brake control signal that is output by the control device 2. The brake actuator 42 controls the supply of oil to the hydraulically actuated brakes 43. The brakes 43 apply braking force to the host vehicle on the basis of the oil pressure that is controlled by the brake actuator 42. The brakes 43 are disposed so as to make

pairs with wheels (not shown) of the host vehicle. The brakes 43 are hydraulic brakes that are hydraulically actuated brakes, for example, disc brakes, drum brakes, etc. The brake pedal 44 directly controls the operation of the brake actuator 42 via the master cylinder so as to apply braking force to the host vehicle on the basis of the driver's intention to decelerate the vehicle.

[0041] When the driver depresses the brake pedal 44, the brake device 4 directly operates the brake actuator 42 via the master cylinder so as to give oil pressure to the brakes 43. Thus, braking force is applied to the host vehicle by the driver, accomplishing the deceleration of the host vehicle by the driver. Besides, the brake device 4 also provides assistance for the deceleration of the host vehicle caused by the driver. That is, when the driver depresses the brake pedal 44, the brake control device 41 operates the brake actuator 42 on the basis of the amount of depression of the brake pedal 44 caused by the driver, so as to apply to the brakes 43 such an oil pressure that a braking force greater than the braking force applied to the host vehicle by the driver is produced. Furthermore, even when the driver is not depressing the brake pedal 44, the brake device 4 is able to apply braking force to the host vehicle and thus decelerate the host vehicle by the brake control device 41 operating the brake actuator 42 so as to apply oil pressure to the brakes 43 in accordance with the brake control signal from the control device 2. [0042] The yaw rate sensor 5 detects the rotational velocity of the host vehicle. The rotational velocity detected by the yaw rate sensor 5 is output to the control device 2. The rotational velocity of the host vehicle is used, for example, in the case where, of the objects detected by the forward millimeter wave radar 3, an object present in the traveling direction of the host vehicle is detected as an obstacle by the obstacle detection portion 21.

[0043] The G-sensor 6 detects the acceleration of the host vehicle. The acceleration detected by the G-sensor 6 is input to the control device 2. The acceleration of the host vehicle is used, for example, when the driving support control is performed by the driving support control portion 26.

[0044] Te vehicle speed sensor 7 detects the vehicle speed of the host vehicle. The vehicle speed detected by the vehicle speed sensor 7 is input to the control device 2. The vehicle speed of the host vehicle is used, for example, when the TTC is calculated by the collision risk calculation portion 22. [0045] The brake sensor 8 detects the depression amount when the brake pedal 44 is depressed by the driver. Besides, the brake sensor 8 also detects whether or not the driver has an intention of braking. The depression amount of the brake pedal 44 detected by the brake sensor 8 is input to the control device 2.

[0046] Next, a driving support control method using the driving support control device 1-1 in accordance with Embodiment 1 will be described. FIG. 2 is an operation flowchart of a warning braking control performed by the driving support control device in accordance with Embodiment 1. FIG. 3 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force. FIG. 4 is an operation flowchart of the intervention braking control of the driving support control device in accordance with Embodiment 1. FIG. 5 is a diagram showing relationships of TTC with the request flag, the hold counter, the control flag, the control counter and the braking force.

[0047] In the driving support control method performed by the driving support control device 1-1 in accordance with Embodiment 1, a warning braking control method will be first described. The driving support control of the driving support control device 1-1 is performed in every control cycle of the driving support control device 1-1. As shown in FIG. 2, the obstacle detection portion 21 of the control device 2 detects an obstacle (step STlOl). In this step, in the case where the forward millimeter wave radar 3 detects objects forward of the host vehicle, the obstacle detection portion 21 detects an obstacle present in the traveling direction of the host vehicle if, of the objects detected by the forward millimeter wave radar 3, an object is present in the traveling direction of the host vehicle based on an estimated radius of the curve that is calculated on the basis of the rotational velocity of the host vehicle that is detected by the yaw rate sensor 5 and that is input to the control device 2.

[0048] Subsequently, the collision risk calculation portion 22 of the control device 2 calculates a TTC (step ST102). The collision risk calculation portion 22 calculates the

TTC at least on the basis of the position data of the obstacle detected by the obstacle detection portion 21, and the vehicle speed of the host vehicle detected by the vehicle speed sensor 7 and input to the control device 2.

[0049] Subsequently, the request determination portion 23a of the driving support control determination portion 23 of the control device 2 determines whether or not the calculated TTC is less than or equal to a predetermined value TTCl (step ST103). In this step, the request determination portion 23a determines whether or not the calculated TTC has reached the TTCl that is the timing at which the warning braking control is performed by the driving support control portion 26.

[0050] If it is determined that the calculated TTC is less than or equal to the predetermined value TTCl, the request determination portion 23a turns the request flag on (step ST104). In this step, the request determination portion 23a switches the request flag from the off-state to the on-state when the calculated TTC reaches the predetermined value TTCl (see Al in FIG. 3).

[0051] Subsequently, following the request determination portion 23a turning the request flag on, the control determination portion 23b of the driving support control determination portion 23 turns the control flag on (step ST105). In this step, the control determination portion 23b switches the control flag from the off-state to the on-state upon the turning-on of the request flag (see Cl in FIG. 3). That is, the driving support control determination portion 23 determines that the warning braking control by the driving support control portion 26 is needed.

[0052] Subsequently, upon the turning-on of the control flag, the hold counter setting portion 27 of the control device 2 sets a hold counter number Nm in the hold counter 24 (step ST106). In this step, the hold counter setting portion 27 sets a predetermined counter number NmI that is pre-stored in a storage portion (not shown) and that is used when the warning braking control is performed by the driving support control portion 26, as the hold counter number Nm in the hold counter 24 (see Bl in FIG. 3).

[0053] Subsequently, the control counter 25 of the control device 2 performs counting (step ST107). In this step, the control counter 25 starts counting (see Dl in

FIG. 3) when the control determination portion 23b determines that the control flag is on.

[0054] Subsequently, the driving support control portion 26 of the control device 2 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to a predetermined control counter number NcI (step ST108).

Incidentally, the predetermined control counter number NcI is a control counter number

Nc based on a predetermined control period that begins at the start of the warning braking control by the driving support control portion 26 following the turning-on of the control flag and that ends when the warning braking control stops. Therefore, the driving support control portion 26 determines whether or not the predetermined control period following the turning-on of the control flag has elapsed.

[0055] Subsequently, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number NcI, the driving support control portion 26 starts the warning braking control (step ST109). Specifically, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number NcI, the driving support control portion

, 26 outputs to the brake device 4 the brake control signal that causes the brake device 4 to generate a warning braking force Fl. Then, in accordance with the brake control signal, the brake control device 41 of the brake device 4 operates the brake actuator 42 so as to supply an oil pressure that causes the brakes 43 to apply the warning braking force to the host vehicle. Therefore, the warning braking force Fl is generated by the brake device 4, and is applied to the host vehicle (see El in FIG. 3). Incidentally, if the control flag remains in the on-state, the driving support control portion 26 keeps performing the warning braking control, that is, continues the control, until it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number NcI. That is, the driving support control portion 26 keeps applying the warning braking force Fl to the host vehicle via the brake device 4 until it is determined that the control counter number Nc of the control counter 25 is

greater than or equal to the predetermined control counter number NcI.

[0056] When the control counter number Nc of the control counter 25 is determined as being greater than or equal to the predetermined control counter number NcI, the driving support control portion 26 stops the warning braking control (step STIlO). Specifically, when it is determined that the predetermined control period for performing the warning braking control has elapsed after the control counter 25 has kept counting with the control flag remaining in the on-state, the driving support control portion 26 stops the warning braking control (see D2 in FIG. 3). Therefore, the generation of the warning braking force Fl by the brake device 4 stops, so that the warning braking force Fl discontinues to be applied to the host vehicle (see E2 in FIG. 3). Incidentally, when the warning braking control is stopped in step STIlO, the driving support control device 1-1 then ends the current control cycle, and proceeds to the next control cycle. In the case where the warning braking control is stopped in step STIlO and the process proceeds to the next control cycle, the control counter number Nc of the control counter 25 is not cleared, so that it is determined again in step ST108 that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number NcI. Therefore, in the case where the same obstacle existing in the traveling direction of the host vehicle is continually detected in step STlOl and it is determined in step ST103 that the TTC calculated on the basis of the same obstacle is less than or equal to the TTCl, the warning braking control is not performed again by the driving support control portion 26. That is, if the same obstacle can be detected in control cycles, the driving support control portion 26 does not perform the warning braking control twice with respect to the obstacle.

[0057] In some cases, during the warning braking control by the driving support control portion 26, or after the warning braking control is stopped, it happens that it becomes impossible to detect a object present forward of the host vehicle by the forward millimeter wave radar 3, or that the traveling direction of the host vehicle changes so that an object detected as an obstacle in the previous control cycle is not currently detected as an obstacle. In such a case, the obstacle detection portion 21 does not detect an obstacle

present in the traveling direction of the host vehicle in step STlOl, and the collision risk calculation portion 22 calculates the TTC to be infinite in step ST102.

[0058] Therefore, it is determined in step ST103 that the calculated TTC is greater than the predetermined value TTCl, and then the request determination portion 23a turns the request flag off (step STlIl). The request determination portion 23a switches the request flag from the on-state to the off-state (see A2 in FIG. 3) if an obstacle present in the traveling direction of the host vehicle is not detected.

[0059] Subsequently, the hold counter 24 determines whether or not the control flag is on (step ST112) as shown in FIG. 2. During the warning braking control by the driving support control portion 26, or after the warning braking control is stopped, it is determined in step ST112 that the control flag is on, since the control flag has been switched from the off-state to the on-state by the control determination portion 23b due to the processing of step ST105. On the other hand, if the warning braking control by the driving support control portion 26 has not been started, it is determined that the control flag is off. Incidentally, when the control flag is determined as being off in step ST112, the driving support control device 1-1 then ends the current control cycle, and proceeds to the next control cycle.

[0060] If it is determined that the control flag is on, the hold counter 24 decrements the hold counter (step ST113). Specifically, the hold counter 24 starts decrementing from a hold counter number Nm (=Nml) set by the hold counter setting portion 27 (see B2 in FIG. 3).

[0061] Subsequently, the hold counter 24 determines whether or not the decremented hold counter number Nm is greater than zero (step ST114). That is, the hold counter 24 determines whether or not the decremented hold counter number Nm has reached 0. Specifically, the hold counter 24 determines whether or not the predetermined hold period Tl when the warning braking control is performed by the driving support control portion 26 has elapsed.

[0062] If the decremented hold counter number Nm is determined as being greater than 0, the control counter 25 performs counting (step ST107). Specifically, if it is

determined that the hold counter number Nm decremented by the hold counter 24 is greater than 0, the control counter 25 continues counting (see D3 in FIG. 3).

[0063] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number NcI (step ST108). In this step, if the warning braking control is being performed by the driving support control portion 26, it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number NcI. On the other hand, if the warning braking control by the driving support control portion 26 has been stopped, it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number NcI.

[0064] If it is determined in step ST108 that the control counter number Nc of the control counter 25 is less than the predetermined control counter number NcI, the driving support control portion 26 continues the warning braking control (step ST109). While the warning braking control is being performed, the driving support control portion 26 continues the warning braking control as long as the decremented hold counter number Nm is greater than 0 even if the detection of the obstacle becomes impossible. That is, during the warning braking control, the driving support control portion 26 continues the warning braking control unless the predetermined hold period Tl has elapsed. [0065] On the other hand, if it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number NcI, the driving support control portion 26 stops the warning braking control (step STIlO). In this step, in the case where the warning braking control has been stopped, the driving support control portion 26 maintains the stop of the warning braking control if the decremented hold counter number Nm is greater than 0 even though the detection of an obstacle becomes impossible. That is, after the warning braking control has been stopped, the driving support control portion 26 maintains the stop of the warning braking control unless the predetermined hold period Tl has elapsed, as shown in FIG. 3.

[0066] In some cases, during the warning braking control performed by the driving support control portion 26, or after the warning braking control has been stopped, it happens that the obstacle that once ceased being detected is detected again. In such a case, the obstacle detection portion 21 detects the obstacle present in the traveling direction of the host vehicle in step STlOl, and it is determined in step ST103 that the TTC calculated on the basis of the same obstacle is less than or equal to the TTCl. Subsequently in step ST104, the request flag is switched from the off-state to the on-state (see A3 in FIG. 3). Then in step ST106, the hold counter setting portion 27 sets the predetermined hold counter number NmI again as a hold counter number Nm in the hold counter 24 having been subjected to decrementing (see B3 in FIG. 3).

[0067] On the other hand, in the case where during the warning braking control by the driving support control portion 26, or after the warning braking control is stopped, the detection of an obstacle ceases and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the predetermined hold period Tl elapses. In this case, the obstacle detection portion 21 does not detect an obstacle present in the traveling direction of the host vehicle in step STlOl, and it is determined in step ST103 that the TTC calculated to be infinite exceeds the predetermined value TTCl. Subsequently in step STlIl, the request flag is switched from the on-state to the off-state (see A4 in FIG. 3). Then in step ST114, it is determined that the decremented hold counter number Nm is greater than 0 (see B4 in FIG. 3). However, as the driving support control device 1-1 repeatedly performs the control cycle, the predetermined hold period Tl elapses, so that it is determined that the decremented hold counter number Nm is 0 (see B5 in FIG. 3), and then the control determination portion 23b turns the control flag off (step ST115). In this step, the control determination portion 23b switches the control flag from the on-state to the off-state (see C4 in FIG. 3) when the predetermined hold period Tl elapses. That is, the driving support control determination portion 23 determines that the warning braking control by the driving support control portion 26 is not needed.

[0068] Subsequently, the driving support control portion 26 stops the warning braking control (step ST116). In this step, the driving support control portion 26 stops

the warning braking control if the control flag is switched from the on-state to the off-state by the control determination portion 23b.

[0069] Subsequently, the control counter 25 clears the counter number (step ST117). Specifically, if the control flag is switched from the on-state to the off-state by the control determination portion 23b, the control counter 25 sets the control counter number Nc to 0 (see D5 in FIG. 3). In addition, after setting the control counter number Nc of the control counter 25 to 0 in step ST117, the driving support control device 1-1 ends the current control cycle, and proceeds to the next control cycle.

[0070] In the related-art driving support control device, if the detection of an obstacle ceases during the warning braking control or after the warning braking control is stopped, the request determination portion 23a switches the request flag from the on-state to the off-state in step STlIl, so that the control flag is switched from the on-state to the off-state (C2 in FIG. 3). By this operation, the control counter 25 in the related-art driving support control device clears the counter number (D3 in FIG. 3). Therefore, for example, in the case where the obstacle that once ceased being detected is detected again after the warning braking control by the driving support control portion 26 is stopped, the request flag is switched again from the off-state to the on-state in step ST104 (A3 in FIG. 3), and in step ST105, the control flag is switched from the off -state to the on-state (C3 in FIG. 3). In step ST107, the control counter 25 whose control counter number Nc was cleared in step ST117 performs counting again (D4 in FIG. 3). Then in step ST109, the warning braking control is started again (E2 in FIG. 3).

[0071] However, the driving support control device 1-1 according to Embodiment 1 performs the warning braking control as follows. That is, when the obstacle detection portion 21 detects an obstacle, the control determination portion 23b of the driving support control determination portion 23 determines whether the control is needed on the basis of the TTC, that is, the collision risk calculated with respect to the detected obstacle by the collision risk calculation portion 22 (i.e., on the basis of the fact that TTC is less than or equal to the predetermined value TTCl). If after it is determined that the control is needed, the detection of the same obstacle by the obstacle detection portion 21 ceases

and therefore the control determination portion 23b of the driving support control determination portion 23 determines that the control is not needed on the basis of the TTC, that is, the collision risk calculated by the collision risk calculation portion 22 (i.e., the TTC (infinity) is greater than the predetermined value TTCl), the state in which the control is needed is maintained by the driving support control portion 26 for the predetermined hold period Tl. That is, even if the detection of an obstacle by the obstacle detection portion 21 is followed by the cessation of the detection of the same obstacle by the obstacle detection portion 21, the driving support control portion 26 continues performing the warning braking control, that is, a warning control, for the predetermined hold period Tl following the time of the cessation of the detection of the same obstacle by the obstacle detection portion 21. Therefore, even if after an obstacle is detected the same obstacle becomes unable to be detected, it is possible to substantially prevent an event in which the warning braking control is interrupted halfway, or the warning braking control is performed again after an interruption. Therefore, the discomfort or the like of the driver can be restrained.

[0072] Next, in the driving support control method performed by the driving support control device 1-1 in accordance with Embodiment 1, an intervention braking control method will be described. Incidentally, the driving support control by the driving support control device 1-1 is performed in every control cycle of the driving support control device 1-1. Besides, the intervention braking control method by the driving support control device 1-1 in accordance with Embodiment 1 is substantially the same in basic operation as the above-described warning braking control method, and therefore will be described in a simplified manner.

[0073] As shown in FIG. 4, the obstacle detection portion 21 of the control device 2 detects an obstacle (step ST201).

[0074] Subsequently, the collision risk calculation portion 22 of the control device 2 calculates a TTC (step ST202).

[0075] Subsequently, the request determination portion 23a of the driving support control determination portion 23 of the control device 2 determines whether or not the

calculated TTC is less than or equal to a predetermined value TTC2 (step ST203). In this step, the request determination portion 23a determines whether or not the calculated TTC has reached the TTC2 that is the timing at which the intervention braking control is performed by the driving support control portion 26. [0076] If it is determined that the calculated TTC is less than or equal to the predetermined value TTC2, the request determination portion 23a turns the request flag on (step ST204). In this step, the request determination portion 23a switches the request flag from the off-state to the on-state when the calculated TTC reaches the predetermined value TTC2 (see A5 in FIG. 5). [0077] Subsequently, following the request determination portion 23a turning the request flag on, the control determination portion 23b of the driving support control determination portion 23 turns the control flag on (step ST205). In this step, the control determination portion 23b switches the control flag from the off-state to the on-state upon the turning-on of the request flag (see C5 in FIG. 5). That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is needed.

[0078] Subsequently, upon the turning-on of the control flag, the hold counter setting portion 27 of the control device 2 sets a hold counter number Nm in the hold counter 24 (step ST206). In this step, the hold counter setting portion 27 sets a predetermined counter number Nm2 that is pre-stored in a storage portion (not shown) and that is used when the intervention braking control is performed by the driving support control portion 26, as the hold counter number Nm in the hold counter 24 (see B6 in FIG. 5).

[0079] Subsequently, the control counter 25 of the control device 2 performs counting (step ST207). In this step, the control counter 25 starts counting (see D6 in FIG. 5) when the control determination portion 23b determines that the control flag is on.

[0080] Subsequently, the driving support control portion 26 of the control device 2 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to a predetermined control counter number Nc2 (step ST208).

Incidentally, the predetermined control counter number Nc2 is a control counter number

Nc based on a predetermined control period from the start of the intervention braking control by the driving support control portion 26 following the turning-on of the control flag until the intervention braking control stops.

[0081] Subsequently, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 starts the intervention braking control (step ST209).

Specifically, if it is determined that the control counter number Nc of the control counter

25 is less than the predetermined control counter number Nc2, the driving support control portion 26 causes the brake device 4 to generate an intervention braking force F2, so that the intervention braking force F2 is applied to the host vehicle (see E4 in FIG. 5). Incidentally, if the control flag remains in the on-state, the driving support control portion

26 keeps performing the intervention braking control, that is, continues the control, until it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2. [0082] When the control counter number Nc of the control counter 25 is determined as being greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST210).

[0083] It is to be noted herein that in some cases, during the intervention braking control performed by the driving support control portion 26, it happens that an object that was detected as an obstacle in the previous control cycle is not currently detected as an obstacle. In such a case, it is determined in step ST203 that the calculated TTC is greater than the predetermined value TTC2, and then the request determination portion 23a turns the request flag off (step ST211). The request determination portion 23a switches the request flag from the on-state to the off-state (see A6 in FIG. 5) if an obstacle present in the traveling direction of the host vehicle is not detected.

[0084] Subsequently, the hold counter 24 determines whether or not the control flag is on (step ST212). During the intervention braking control by the driving support control portion 26, it is determined that the control flag is on, since the control flag has been switched from the off -state to the on-state by the control determination portion 23b

due to the processing of step ST205.

[0085] If it is determined that the control flag is on, the hold counter 24 decrements the hold counter (step ST213). Specifically, the hold counter 24 starts decrementing from a hold counter number Nm (=Nm2) set by the hold counter setting portion 27 (see B7 in FIG. 5).

[0086] Subsequently, the hold counter 24 determines whether or not the decremented hold counter number Nm is greater than zero (step ST214). Specifically, the hold counter 24 determines whether or not the predetermined hold period T2 used when the intervention braking control is performed by the driving support control portion 26 has elapsed.

[0087] If the decremented hold counter number Nm is determined as being greater than 0, the control counter 25 performs counting (step ST207). Specifically, if it is determined that the hold counter number Nm decremented by the hold counter 24 is greater than 0, the control counter 25 continues counting (see D5 in FIG. 5). [0088] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2 (step ST208).

[0089] If it is determined that the control counter number Nc of the control counter

25 is less than the predetermined control counter number Nc2, the driving support control portion 26 continues the intervention braking control (step ST209). That is, during the intervention braking control, the driving support control portion 26 continues the intervention braking control unless the predetermined hold period T2 has elapsed.

[0090] On the other hand, if it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST210).

[0091] Specifically, in the case where during the intervention braking control by the driving support control portion 26, an obstacle that once ceased being detected is detected again, it is then determined in step ST203 that the TTC calculated on the basis of the

same obstacle is less than or equal to the TTC2. Subsequently in step ST204, the request flag is switched from the off-state to the on-state (see A7 in FIG. 5). Then in step ST206, the hold counter setting portion 27 sets the predetermined hold counter number Nm2 again as a hold counter number Nm in the hold counter 24 having been subjected to decrementing (see B8 in FIG. 5).

[0092] On the other hand, in the case where during the intervention braking control by the driving support control portion 26, an obstacle ceases being detected and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the predetermined hold period T2 elapses. Therefore, in step ST211, the request flag is switched from the on-state to the off-state (see A8 in FIG. 5). Then in step ST214, it is determined that the decremented hold counter number Nm is greater than 0 (see B9 in FIG. 5). However, as the driving support control device 1-1 repeatedly performs the control cycle, the predetermined hold period T2 elapses, so that it is determined that the decremented hold counter number Nm is 0 (see BlO in FIG. 5), and then the control determination portion 23b turns the control flag off (step ST215). In this step, the control determination portion 23b switches the control flag from the on-state to the off-state (see C8 in FIG. 5) when the predetermined hold period T2 elapses. That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is not needed. [0093] Subsequently, the driving support control portion 26 stops the intervention braking control (step ST216).

[0094] Subsequently, the control counter 25 clears the counter number (step ST217). Specifically, if the control flag is switched from the on-state to the off-state by the control determination portion 23b, the control counter 25 sets the control counter number Nc to 0 (see D9 in FIG. 5).

[0095] In the related-art driving support control device, if the detection of an obstacle ceases during the intervention braking control, the request determination portion 23a switches the request flag from the on-state to the off-state in step ST211, so that the control flag is switched from the on-state to the off-state (C6 in FIG. 5) and thus the

intervention braking control by the driving support control portion 26 is stopped (E5 in FIG. 5). Thus, in the related-art driving support control device, the control counter 25 clears the counter number (D7 in FIG. 5). Hence, for example, in the case where the obstacle that once ceased being detected is detected again during the intervention braking control by the driving support control portion 26, the request flag is switched again from the off-state to the on-state in step ST204 (A7 in FIG. 5), and in step ST205, the control flag is switched from the off-state to the on-state (C7 in FIG. 5). In step ST207, the control counter 25 whose control counter number Nc was cleared in step ST217 performs counting again (D8 in FIG. 5). Then in step ST209, the intervention braking control is started again (E6 in FIG. 5).

[0096] However, the driving support control device 1-1 according to Embodiment 1 performs the intervention braking control as follows. That is, when the obstacle detection portion 21 detects an obstacle, the control determination portion 23b of the driving support control determination portion 23 determines whether the control is needed on the basis of the TTC, that is, the collision risk calculated with respect to the detected obstacle by the collision risk calculation portion 22 (i.e., on the basis of the fact that TTC is less than or equal to the predetermined value TTC2). If after it is determined that the control is needed, the detection of the same obstacle by the obstacle detection portion 21 ceases and therefore the control determination portion 23b of the driving support control determination portion 23 determines that the control is not needed on the basis of the TTC (i.e., the TTC (infinite) is greater than the predetermined value TTC2), that is, the collision risk calculated by the collision risk calculation portion 22, the state in which the control is needed is maintained by the driving support control portion 26 for the predetermined hold period T2. That is, even if the detection of an obstacle by the obstacle detection portion 21 is followed by the cessation of the detection of the same obstacle by the obstacle detection portion 21, the driving support control portion 26 keeps performing the intervention braking control for the predetermined hold period T2 following the time of the cessation of the detection of the same obstacle by the obstacle detection portion 21. Therefore, even if after an obstacle is detected the

detection of the same obstacle becomes impossible, it is possible to substantially prevent an event in which the intervention braking control is interrupted halfway, or the intervention braking control is performed again after an interruption. Therefore, the discomfort or the like of the driver can be restrained. [0097] In the driving support control device 1-1 in accordance with Embodiment 1, the predetermined hold period T varies depending on the kind of the driving support control that the driving support control portion 26 performs, that is, in accordance with whether the driving support control is the warning braking control or the intervention braking control. In this embodiment, with regard to the predetermined hold period T that is the period of time until the driving support control is stopped if an obstacle detected by the obstacle detection portion 21 ceases being an obstacle, for example, if an obstacle having been detected disappears from the traveling direction of the host vehicle, the predetermined hold period T2 used in the case of the intervention braking control is shorter than the predetermined hold period Tl used in the case of the warning braking control. Therefore, the timing of stopping the driving support control by the driving support control portion 26 can be brought closer to the timing at which the obstacle detected by the obstacle detection portion 21 ceases being an obstacle in the case where the intervention braking control is performed than in the case where the warning braking control is performed. Therefore, when the intervention braking control is performed, the detection of an obstacle by the obstacle detection portion 21 ceases earlier than when the warning braking control is performed. That is, in reality, the intervention braking control can be stopped soon after a state where there exists no obstacle in the traveling direction of the host vehicle is obtained.

[0098] Next, a driving support control device 1-2 in accordance with Embodiment 2 will be described. The driving support control device 1-2 in accordance with Embodiment 2 is different from the driving support control device 1-1 in accordance with Embodiment 1 in that a within-period braking force applied to the host vehicle in the predetermined hold period T2 during the intervention braking control is made less than the intervention braking force, more specifically in Embodiment 2, is made less than the

intervention braking force with the elapse of time within the predetermined hold period T2. The driving support control device 1-2 in accordance with Embodiment 2 is substantially the same in basic construction as the driving support control device 1-1 in accordance with Embodiment 1, and will not be described again. Furthermore, the basic operation of the driving support control device 1-2 in accordance with Embodiment 2 is substantially the same as the basic operation of the driving support control device 1-1 in accordance with Embodiment 1, and will be described in a simplified fashion. The warning braking control method performed by the driving support control device 1-2 in accordance with Embodiment 2 is substantially the same as the warning braking control method performed by the driving support control device 1-1 of Embodiment 1, and will not be described. Only the intervention braking control method in accordance with Embodiment 2 will be described.

[0099] FIGS. 6A and 6B are operation flowchart of an intervention braking control performed by the driving support control device in accordance with Embodiment 2. FIG. 7 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force.

[0100] As shown in FIGS. 6A and 6B, the obstacle detection portion 21 of the control device 2 first detects an obstacle (step ST301). Subsequently, the collision risk calculation portion 22 calculates a TTC (step ST302). Subsequently, the request determination portion 23a of the driving support control determination portion 23 determines whether or not the calculated TTC is less than or equal to a predetermined value TTC2 (step ST303). If it is determined that the calculated TTC is less than or equal to the predetermined value TTC2, the request determination portion 23a turns the request flag on (step ST304). In this step, the request determination portion 23a switches the request flag from the off-state to the on-state when the calculated TTC reaches the predetermined value TTCl (see A9 in FIG. 7).

[0101] Subsequently, following the request determination portion 23a turning the request flag on, the control determination portion 23b of the driving support control determination portion 23 turns the control flag on (step ST305). In this step, the control

determination portion 23b switches the control flag from the off-state to the on-state upon the turning-on of the request flag (see C9 in FIG. 7). That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is needed. [0102] Subsequently, upon the turning-on of the control flag, the hold counter setting portion 27 sets a hold counter number Nm in the hold counter 24 (step ST306). In this step, the hold counter setting portion 27 sets a predetermined counter number Nm2 that is pre-stored in a storage portion (not shown) and that is used when the intervention braking control is performed by the driving support control portion 26, as the hold counter number Nm in the hold counter 24 (see BIl in FIG. 7).

[0103] Subsequently, the control counter 25 performs counting (step ST307). In this step, the control counter 25 starts counting (see DlO in FIG. 7) when the control determination portion 23b determines that the control flag is on.

[0104] Subsequently, the driving support control portion 26 of the control device 2 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to a predetermined control counter number Nc2 (step ST308). Subsequently, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 starts the intervention braking control (step ST309). Specifically, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 causes the brake device 4 to generate an intervention braking force F2, so that the intervention braking force F2 is applied to the host vehicle (see E8 in FIG. 7).

[0105] When the control counter number Nc of the control counter 25 is determined as being greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST310).

[0106] If during the intervention braking control performed by the driving support control portion 26, an object detected as an obstacle in the previous control cycle ceases being detected as an obstacle, it is determined in step ST303 that the calculated TTC is

greater than the predetermined value TTC2, and then the request determination portion 23a turns the request flag off (step ST311). The request determination portion 23a switches the request flag from the on-state to the off-state (see AlO in FIG. 7) if an obstacle present in the traveling direction of the host vehicle is not detected. [0107] Subsequently, the hold counter 24 determines whether or not the control flag is on (step ST312). If it is determined that the control flag is on, the hold counter 24 decrements the hold counter (step ST313). Specifically, the hold counter 24 starts decrementing from a hold counter number Nm (=Nm2) set by the hold counter setting portion 27 (see B12 in FIG. 7). [0108] Subsequently, the hold counter 24 determines whether or not the decremented hold counter number Nm is greater than zero (step ST314). Specifically, the hold counter 24 determines whether or not the predetermined hold period T2 used when the intervention braking control is performed by the driving support control portion 26 has elapsed. [0109] If the decremented hold counter number Nm is determined as being greater than 0, the control counter 25 performs counting (step ST318). Specifically, if it is determined that the hold counter number Nm decremented by the hold counter 24 is greater than 0, the control counter 25 continues counting (see DIl in FIG. 7).

[0110] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2 (step ST319).

[0111] If it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 continues the intervention braking control (step ST320). That is, during the intervention braking control, the driving support control portion 26 continues the intervention braking control unless the predetermined hold period T2 has elapsed.

[0112] During the predetermined hold period T2 during which the driving support control portion 26 continues the intervention braking control as mentioned above, the within-period braking force that the brake device 4 is caused to generate during the

period T2 is not the ordinary intervention braking force F2, but is made less than the intervention braking force F2. Therefore, the braking force applied to the host vehicle during this period is smaller than the intervention braking force F2. Besides, in every control cycle, if it is determined in step ST314 that the decremented hold counter number Nm is greater than 0, the driving support control device 1-2 causes the within-period braking force to be even less than the intervention braking force F2 (see the range of E9 to ElO in FIG. 7). That is, the braking force applied to the host vehicle is made smaller than the intervention braking force with the elapse of time during the predetermined hold period T2. Therefore, the driving support control portion 26 can bring the state of run of the host vehicle close to a state where the intervention braking control is ceased, within the predetermined hold period T2.

[0113] On the other hand, if it is determined in step S308 that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST310).

[0114] Specifically, in the case where during the intervention braking control by the driving support control portion 26, an obstacle that once ceased being detected is detected again, it is then determined in step ST303 that the TTC calculated on the basis of the same obstacle is less than or equal to the TTC2. Subsequently in step ST304, the request flag is switched from the off-state to the on-state (see All in FIG. 7). Then in step ST306, the hold counter setting portion 27 sets the predetermined hold counter number Nm2 again as a hold counter number Nm in the hold counter 24 having been subjected to decrementing (see B13 in FIG. 7).

[0115] On the other hand, in the case where during the intervention braking control by the driving support control portion 26, an obstacle ceases being detected and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the predetermined hold period T2 elapses. Therefore, in step ST311, the request flag is switched from the on-state to the off-state (see A12 in FIG. 7). Then in step ST314, it is determined that the decremented hold counter number Nm is greater than 0 (see B14 in FIG. 7).

However, as the driving support control device 1-2 repeatedly performs the control cycle, the predetermined hold period T2 elapses, so that it is determined that the decremented hold counter number Nm is 0 (see B15 in FIG. 7), and then the control determination portion 23b turns the control flag off (step ST315). In this step, the control determination portion 23b switches the control flag from the on-state to the off-state (see ClO in FIG. 7) when the predetermined hold period T2 elapses. That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is not needed.

[0116] Subsequently, the driving support control portion 26 stops the intervention braking control (step ST316). Subsequently, the control counter 25 clears the counter number (step ST317). Specifically, if the control flag is switched from the on-state to the off-state by the control, determination portion 23b, the control counter 25 sets the control counter number Nc to 0 (see D 12 in FIG. 7).

[0117] As described above, when the driving support control device 1-2 in accordance with Embodiment 2 performs the intervention braking control, the device 1-2 is able to substantially prevent an event in which the intervention braking control is interrupted halfway or the intervention braking control is performed again after an interruption, even if after an obstacle is detected the same obstacle becomes unable to be detected, as in the driving support control device 1-1 in accordance with Embodiment 1. Therefore, the discomfort or the like of the driver can be restrained. Besides, the predetermined hold period T is varied depending on the kind of the driving support control performed by the driving support control portion 26, that is, in accordance with whether the driving support control is the warning braking control or the intervention braking control. When the intervention braking control is performed, the detection of an obstacle by the obstacle detection portion 21 ceases earlier than when the warning braking control is performed. The intervention braking control can be stopped quickly if a state where there indeed exists no obstacle in the traveling direction of the host vehicle is obtained.

[0118] Furthermore, when the driving support control device 1-2 in accordance with

Embodiment 2 performs the intervention braking control, the driving support control portion 26 brings the state of run of the host vehicle close to a state where the intervention braking control is ceased, within the predetermined hold period T2. Therefore, even though the intervention braking control is stopped after the predetermined hold period T2 elapses (see B16 in FIG. 7), the state of run of the host vehicle can be brought closer to the state where the intervention braking control is ceased, within the predetermined hold period T2 (see ElO in FIG. 7). Therefore, in this case, the return of the state of run of the host vehicle to the state where the intervention braking control is ceased can be achieved earlier (by the amount of Xl in FIG. 7) than in the case (see Ell in FIG. 7) where the intervention braking force F2 having been applied to the host vehicle suddenly ceases being applied to the host vehicle after the elapse of the predetermined hold period T2. Thus, the discomfort of the driver can be restrained.

[0119] Next, a driving support control device 1-3 in accordance with Embodiment 3 will be described. The driving support control device 1-3 in accordance with Embodiment 3 is different from the driving support control device 1-1 in accordance with Embodiment 1 in that the predetermined hold period T is made shorter, in accordance with the calculated collision risk, that is, in Embodiment 3, as the calculated collision risk is higher, that is, as the TTC is shorter. The driving support control device 1-3 in accordance with Embodiment 3 is substantially the same in basic construction as the driving support control device 1-1 in accordance with Embodiment 1, and will not be described again. In this construction, the hold counter setting portion 27 calculates the predetermined hold period T in accordance with the calculated collision risk. In Embodiment 3, the hold counter setting portion 27 calculates the predetermined hold period T in accordance with the calculated TTC, and sets a hold counter number Nm in the hold counter 24 on the basis of the calculated predetermined hold period T. Furthermore, the basic operation of the driving support control device 1-3 in accordance with Embodiment 3 is substantially the same as the basic operation of the driving support control device 1-1 in accordance with Embodiment 1, and will be described in a simplified fashion. The warning braking control method performed by the driving

support control device 1-3 in accordance with Embodiment 3 is substantially the same as the warning braking control method performed by the driving support control device 1-1 of Embodiment 1, and will not be described. Only the intervention braking control method in accordance with Embodiment 3 will be described. [0120] FIG. 8 is an operation flowchart of an intervention braking control performed by the driving support control device in accordance with Embodiment 3. FIG. 9 is a diagram showing a relationship between the TTC and the predetermined hold period T. FIG. 10 is a diagram showing a relationship between the predetermined hold period T and the hold counter number Nm. FIG. 11 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force.

[0121] As shown in FIG. 8, the obstacle detection portion 21 of the control device 2 first detects an obstacle (step ST401). Subsequently, the collision risk calculation portion 22 calculates a TTC (step ST402). Subsequently, the request determination portion 23a of the driving support control determination portion 23 determines whether or not the calculated TTC is less than or equal to a predetermined value TTC2 (step ST403). If it is determined that the calculated TTC is less than or equal to the predetermined value TTC2, the request determination portion 23a turns the request flag on (step ST404). In this step, the request determination portion 23a switches the request flag from the off-state to the on-state when the calculated TTC reaches the predetermined value TTC2 (seeA13 in FIG. 11).

[0122] Subsequently, following the request determination portion 23a turning the request flag on, the control determination portion 23b of the driving support control determination portion 23 turns the control flag on (step ST405). In this step, the control determination portion 23b switches the control flag from the off-state to the on-state upon the turning-on of the request flag (see CIl in FIG. 11). That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is needed.

[0123] Upon the turning-on of the control flag, the hold counter setting portion 27

calculates a predetermined hold period T on the basis of the calculated TTC (step ST417). Specifically, the hold counter setting portion 27 calculates the predetermined hold period T on the basis of the collision risk, that is, the TTC, in order to set the hold counter number Nm in the hold counter 24. The predetermined hold period T calculated on the basis of the TTC is set so as to become shorter the higher the collision risk, that is, the shorter the TTC, as shown in FIG. 9. That is, the hold counter setting portion 27 calculates the predetermined hold period T to be shorter as the TTC approaches 0.

[0124] Subsequently, the hold counter setting portion 27 sets the hold counter number Nm in the hold counter 24 on the basis of the calculated predetermined hold period T (step ST418). Specifically, the hold counter setting portion 27 calculates the hold counter number Nm on the basis of predetermined hold period T that is calculated on the basis of the collision risk, that is, the TTC, and sets the calculated hold counter number Nm in the hold counter 24. The hold counter number Nm calculated on the basis of the predetermined hold period T is set so as to become greater as the predetermined hold period T is longer, as shown in FIG. 10. Therefore, the hold counter setting portion 27, firstly in step ST417, sets the hold counter number Nm3 calculated on the basis of the predetermined hold period T3 calculated on the basis of the TTC2, as the hold counter number Nm in the hold counter 24 (see B16 in FIG. 11).

[0125] Subsequently, the control counter 25 performs counting (step ST406). In this step, the control counter 25 starts counting (see D14 in FIG. 11) when the control determination portion 23b determines that the control flag is on.

[0126] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to a predetermined control counter number Nc2 (step ST407). Subsequently, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 starts the intervention braking control (step ST408). Specifically, if it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 causes the brake

device 4 to generate an intervention braking force F2, so that the intervention braking force F2 is applied to the host vehicle (see E13 in FIG. 11).

[0127] If the control flag remains in the on-state, the driving support control portion. 26 keeps performing the intervention braking control, that is, continues the control (step ST408), until it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2. Therefore, during the intervention braking control performed by the driving support control portion 26, the TTC is calculated in step ST402 in every control cycle, and in step ST417, the predetermined hold period T is calculated on the basis of the TTC calculated in every control cycle, and in step ST418, the hold counter number Nm is set in the hold counter 24 on the basis of the predetermined hold period T calculated in every control cycle.

[0128] When the control counter number Nc of the control counter 25 is determined as being greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST409). [0129] If during the intervention braking control performed by the driving support control portion 26, an object detected as an obstacle in the previous control cycle ceases being detected as an obstacle a plurality of times, it is determined in step ST403 that the calculated TTC is greater than the predetermined value TTC2 every time the object is left undetected. Then, the request determination portion 23a turns the request flag off (step ST410). That is, if an obstacle present in the traveling direction of the host vehicle is not detected, the request determination portion 23a switches the request flag from the on-state to the off-state (see A14 and A16 in FIG. 11) every time the object is left undetected.

[0130] Subsequently, the hold counter 24 determines whether or not the control flag is on (step ST411).

[0131] If it is determined that the control flag is on, the hold counter 24 decrements the hold counter (step ST412). At this time, the hold counter number Nm set in the hold counter 24 is a hold counter number Nm4 or Nm5 calculated in the previous control cycle on the basis of the calculated predetermined hold period T4 or T5. Therefore, every

time the object is left undetected, the hold counter 24 starts decrementing the hold counter number Nm (=Nm4, Nm5) set by the hold counter setting portion 27 (see B 17, B19 in FIG. 11).

[0132] Subsequently, the hold counter 24 determines whether or not the decremented hold counter number Nm is greater than 0 (step ST413). Specifically, the hold counter

24 determines whether or not the predetermined hold period T4, T5 used when the intervention braking control is performed by the driving support control portion 26 has elapsed.

[0133] If the decremented hold counter number Nm is determined as being greater than 0, the control counter 25 performs counting (step ST406). Specifically, if it is determined that the hold counter number Nm decremented by the hold counter 24 is greater than 0, the control counter 25 continues counting (see D15, D16 in FIG. 11).

[0134] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2 (step ST407).

[0135] If it is determined that the control counter number Nc of the control counter

25 is less than the predetermined control counter number Nc2, the driving support control portion 26 continues the intervention braking control (step ST408). That is, during the intervention braking control, the driving support control portion 26 continues the intervention braking control unless the predetermined hold period T4 or T5 set at every cessation of the detection of the obstacle has elapsed (see B21, B22 in FIG. 11).

[0136] On the other hand, when it is determined in step S407 that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST409).

[0137] Specifically, in the case where during the intervention braking control by the driving support control portion 26, an obstacle that once ceased being detected is detected again, it is then determined in step ST403 that the TTC calculated on the basis of the same obstacle is less than or equal to the TTC2. Subsequently in step ST404, the

request flag is switched from the off-state to the on-state (see A15, A17 in FIG. 11). Then in step ST417, the predetermined hold period T is calculated on the basis of the calculated TTC, and in step ST418, the hold counter number Nm is set in the hold counter 24 again on the basis of the calculated predetermined hold period T (see B 18, B20 in FIG. 11).

[0138] On the other hand, in the case where during the intervention braking control by the driving support control portion 26, an obstacle ceases being detected and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the predetermined hold period T5 elapses. Therefore, in step ST410, the request flag is switched from the on-state to the off-state (see A16 in FIG. 11). Then in step ST413, it is determined that the decremented hold counter number Nm is greater than 0 (see B20 in FIG. 11). However, as the driving support control device 1-3 repeatedly performs the control cycle, the predetermined hold period T5 elapses, so that it is determined that the decremented hold counter number Nm is 0 (see B22 in FIG. 11), and then the control determination portion 23b turns the control flag off (step ST414). In this step, the control determination portion 23b switches the control flag from the on-state to the off-state (see C12 in FIG. 11) when the predetermined hold period T5 elapses. That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is not needed. [0139] Subsequently, the driving support control portion 26 stops the intervention braking control (see E18 in FIG. 11) (step ST415). Subsequently, the control counter 25 clears the counter number (step ST416). Specifically, if the control flag is switched from the on-state to the off-state by the control determination portion 23b, the control counter 25 sets the control counter number Nc to 0 (see D17 in FIG. 11). [0140] As described above, when the driving support control device 1-3 in accordance with Embodiment 3 performs the intervention braking control, the device 1-3 is able to substantially prevent an event in which the intervention braking control is interrupted halfway or the intervention braking control is performed again after an interruption, even if after an obstacle is detected the detection of the same obstacle

becomes impossible, as in the driving support control device 1-1 in accordance with Embodiment 1. Therefore, the discomfort or the like of the driver can be restrained. Besides, the predetermined hold period T is varied depending on the kind of the driving support control performed by the driving support control portion 26, that is, in accordance with whether the driving support control is the warning braking control or the intervention braking control. When the intervention braking control is performed, the detection of an obstacle by the obstacle detection portion 21 ceases earlier than when the warning braking control is performed. The intervention braking control can be stopped quickly if a state where there indeed exists no obstacle in the traveling direction of the host vehicle is obtained.

[0141] Furthermore, when the driving support control device 1-3 in accordance with Embodiment 3 performs the intervention braking control, the device 1-3 calculates the predetermined hold period T in accordance with the calculated collision risk. If an obstacle detected by the obstacle detection portion 21 ceases being an obstacle, for example, if an obstacle having been detected disappears from the traveling direction of the host vehicle, the predetermined hold period T that is the period of time until the intervention braking control is stopped is made shorter the higher the calculated collision risk, that is, the shorter the TTC. Therefore, the timing (E15, E17 in FIG. 11) of stopping the intervention braking control by the driving support control portion 26 can be brought closer to the timing (E14, E16 in FIG. 11) at which the obstacle detected by the obstacle detection portion 21 ceases being an obstacle, as the TTC is shorter. Hence, in the case where, during the intervention braking control, the detection of an obstacle by the obstacle detection portion 21 ceases and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the intervention braking control can be stopped earlier (X2>X3 in FIG. 11) the higher the collision risk.

[0142] Next, a driving support control device 1-4 in accordance with Embodiment 4 will be described. Differences between the driving support control device 1-4 in accordance with Embodiment 4 and the driving support control device 1-3 in accordance with Embodiment 3 will be described. In Embodiment 3, the within-period braking

force applied to the host vehicle in the predetermined hold period T2 during the intervention braking control is made less than the intervention braking force. In Embodiment 4, on the other hand, the within-period braking force is decreased with the elapse of time during the predetermined hold period T2. The basis construction of the driving support control device 1-4 in accordance with Embodiment 4 is as shown in FIG. 1, and is substantially the same as that of the driving support control device 1-3 in accordance with Embodiment 3, and will not be described again. In Embodiment 4, the hold counter setting portion 27 calculates the predetermined hold period T in accordance with the calculated collision risk, that is, in accordance with the calculated TTC, and sets a hold counter number Nm in the hold counter 24 on the basis of the calculated predetermined hold period T, as in Embodiment 2. Furthermore, the basic operation of the driving support control device 1-4 in accordance with Embodiment 4 is substantially the same as the basic operation of the driving support control device 1-3 in accordance with Embodiment 3, and will be described in a simplified fashion. The warning braking control method performed by the driving support control device 1-4 in accordance with Embodiment 4 is substantially the same as the warning braking control method performed by the driving support control device 1-1 of Embodiment 1, and will not be described. Only the intervention braking control method in accordance with Embodiment 4 will be described. [0143] FIGS. 12A and 12B are operation flowchart of an intervention braking control of a driving support control device in accordance with Embodiment 4. FIG. 13 is a diagram showing relationships of the TTC with the request flag, the hold counter, the control flag, the control counter and the braking force.

[0144] As shown in FIGS. 12A and 12B, the obstacle detection portion 21 of the control device 2 first detects an obstacle (step ST501). Subsequently, the collision risk calculation portion 22 calculates a TTC (step ST502). Subsequently, the request determination portion 23a of the driving support control determination portion 23 determines whether or not the calculated TTC is less than or equal to a predetermined value TTC2 (step ST503). If it is determined that the calculated TTC is less than or

equal to the predetermined value TTC2, the request determination portion 23a turns the request flag on (step ST504). In this step, the request determination portion 23a switches the request flag from the off-state to the on-state when the calculated TTC reaches the predetermined value TTCl (see A19 in FIG. 13). [0145] Subsequently, following the request determination portion 23a turning the request flag on, the control determination portion 23b of the driving support control determination portion 23 turns the control flag on (step ST505). In this step, the control determination portion 23b switches the control flag from the off-state to the on-state upon the turning-on of the request flag (see C13 in FIG. 13). That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is needed.

[0146] Upon the turning-on of the control flag, the hold counter setting portion 27 calculates a predetermined hold period T on the basis of the calculated TTC (step ST521). Specifically, the hold counter setting portion 27 calculates the predetermined hold period T on the basis of the collision risk, that is, the TTC, in order to set the hold counter number Nm in the hold counter 24. That hold counter setting portion 27 calculates the predetermined hold period T to be shorter as the TTC approaches 0 (see FIG. 9).

[0147] Subsequently, the hold counter setting portion 27 sets the hold counter number Nm in the hold counter 24 on the basis of the calculated predetermined hold period T (step ST522). Specifically, the hold counter setting portion 27 calculates the hold counter number Nm on the basis of predetermined hold period T that is calculated on the basis of the collision risk, that is, the TTC, and sets the calculated hold counter number Nm in the hold counter 24. The hold counter setting portion 27 sets the hold counter number Nm larger the longer the predetermined hold period T is. Therefore, the hold counter setting portion 27, firstly in step ST522, sets the hold counter number Nm3 calculated on the basis of the predetermined hold period T3 calculated on the basis of the TTC2, as the hold counter number Nm in the hold counter 24 (see B23 in FIG. 13).

[0148] Subsequently, the control counter 25 performs counting (step ST507). In this step, the control counter 25 starts counting (see D18 in FIG. 13) when the control

determination portion 23b determines that the control flag is on.

[0149] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to a predetermined control counter number Nc2 (step ST508). Subsequently, when it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 starts the intervention braking control (step ST509). Specifically, when it is determined that the control counter number Nc of the control counter 25 is less than the predetermined control counter number Nc2, the driving support control portion 26 causes the brake device 4 to generate an intervention braking force F2, so that the intervention braking force F2 is applied to the host vehicle (see E19 in FIG. 13).

[0150] If the control flag remains in the on-state, the driving support control portion 26 keeps performing the intervention braking control, that is, continues the control (step ST509), until it is determined that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2. Therefore, during the intervention braking control performed by the driving support control portion 26, the TTC is calculated in step ST502 in every control cycle, and in step ST521, the predetermined hold period T is calculated on the basis of the TTC calculated in every control cycle, and in step ST522, the hold counter number Nm is set in the hold counter 24 on the basis of the predetermined hold period T calculated in every control cycle.

[0151] When the control counter number Nc of the control counter 25 is determined as being greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST510). [0152] If during the intervention braking control performed by the driving support control portion 26, an object detected as an obstacle in the previous control cycle ceases being detected as an obstacle a plurality of times, it is determined in step ST503 that the calculated TTC is greater than the predetermined value TTC2 every time the object is left undetected. Then, the request determination portion 23a turns the request flag off (step ST511). That is, if an obstacle present in the traveling direction of the host vehicle is

not detected, the request determination portion 23a switches the request flag from the on-state to the off-state (see A20 and A22 in FIG. 13) every time the object is left undetected.

[0153] Subsequently, the hold counter 24 determines whether or not the control flag is on (step ST512).

[0154] If it is determined that the control flag is on, the hold counter 24 decrements the hold counter (step ST513). At this time, the hold counter number Nm set in the hold counter 24 is a hold counter number Nm4 or Nm5 calculated in the previous control cycle on the basis of the calculated predetermined hold period T4 or T5. Therefore, every time the object is left undetected, the hold counter 24 starts decrementing the hold counter number Nm (=Nm4, Nm5) set by the hold counter setting portion 27 (see B24, B26 in FIG. 13).

[0155] Subsequently, the hold counter 24 determines whether or not the decremented hold counter number Nm is greater than 0 (step ST514). Specifically, the hold counter 24 determines whether or not the predetermined hold period T4, T5 used when the intervention braking control is performed by the driving support control portion 26 has elapsed.

[0156] If the decremented hold counter number Nm is determined as being greater than 0, the control counter 25 performs counting (step ST518). Specifically, if it is determined that the hold counter number Nm decremented by the hold counter 24 is greater than 0, the control counter 25 continues counting (see D19, D20 in FIG. 13).

[0157] Subsequently, the driving support control portion 26 determines whether or not the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2 (step ST519). [0158] If it is determined that the control counter number Nc of the control counter

25 is less than the predetermined control counter number Nc2, the driving support control portion 26 continues the intervention braking control (step ST520). That is, during the intervention braking control, the driving support control portion 26 continues the intervention braking control unless the predetermined hold period T4 or T5 has elapsed

(see B24, B28 in FIG. 13).

[0159] During the predetermined hold period T2 during which the driving support control portion 26 continues the intervention braking control as mentioned above, the within-period braking force that the brake device 4 is caused to generate during the period T4, T5 is not the ordinary intervention braking force F2, but is made less than the intervention braking force F2. Therefore, the braking force applied to the host vehicle during this period is smaller than the intervention braking force F2. Besides, in every control cycle, if it is determined in step ST514 that the decremented hold counter number Nm is greater than 0, the driving support control device 1-4 causes the within-period braking force to be even less than the intervention braking force F2 (see the range of E20 to E21, and the range of E23 to E24 in FIG. 13). That is, the braking force applied to the host vehicle is made smaller than the intervention braking force with the elapse of time during the predetermined hold period T4, T5. Therefore, the driving support control portion 26 can bring the state of run of the host vehicle close to a state where the intervention braking control is ceased, within the predetermined hold period T.

[0160] On the other hand, when it is determined in step S508 that the control counter number Nc of the control counter 25 is greater than or equal to the predetermined control counter number Nc2, the driving support control portion 26 stops the intervention braking control (step ST510). [0161] Specifically, in the case where during the intervention braking control by the driving support control portion 26, an obstacle that once ceased being detected is detected again, it is then determined in step ST503 that the TTC calculated on the basis of the same obstacle is less than or equal to the TTC2. Subsequently in step ST504, the request flag is switched from the off-state to the on-state (see A21, A23 in FIG. 13). Then in step ST521, the predetermined hold period T is calculated on the basis of the calculated TTC, and in step ST522, the hold counter number Nm is set in the hold counter 24 again on the basis of the calculated predetermined hold period T (see B25, B27 in FIG. 13).

[0162] On the other hand, in the case where during the intervention braking control

by the driving support control portion 26, an obstacle ceases being detected and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the predetermined hold period T5 elapses. Therefore, in step ST511, the request flag is switched from the on-state to the off-state (see A22 in FIG. 13). Then in step ST514, it is determined that the decremented hold counter number Nm is greater than 0 (see B27 in FIG. 13). However, as the driving support control device 1-4 repeatedly performs the control cycle, the predetermined hold period T5 elapses, so that it is determined that the decremented hold counter number Nm is 0 (see B28 in FIG. 13), and then the control determination portion 23b turns the control flag off (step ST515). In this step, the control determination portion 23b switches the control flag from the on-state to the off-state (see C14 in FIG. 13) when the predetermined hold period T5 elapses. That is, the driving support control determination portion 23 determines that the intervention braking control by the driving support control portion 26 is not needed.

[0163] Subsequently, the driving support control portion 26 stops the intervention braking control (see E26 in FIG. 13) (step ST516). Subsequently, the control counter 25 clears the counter number (step ST517). Specifically, if the control flag is switched from the on-state to the off-state by the control determination portion 23b, the control counter 25 sets the control counter number Nc to 0 (see D21 in FIG. 13).

[0164] As described above, when the driving support control device 1-4 in accordance with Embodiment 4 performs the intervention braking control, the device 1-4 is able to substantially prevent an event in which the intervention braking control is interrupted halfway or the intervention braking control is performed again after an interruption, even if after an obstacle is detected the detection of the same obstacle becomes impossible, as in the driving support control device 1-1 in accordance with Embodiment 1. Therefore, the discomfort or the like of the driver can be restrained. Besides, the predetermined hold period T is varied depending on the kind of the driving support control performed by the driving support control portion 26, that is, in accordance with whether the driving support control is the warning braking control or the intervention braking control. During the intervention braking control, the control can be

stopped earlier than during the warning braking control, in the case where the detection of an obstacle by the obstacle detection portion 21 ceases and, indeed, there exists no obstacle in the traveling direction of the host vehicle.

[0165] Furthermore, when the driving support control device 1-4 in accordance with Embodiment 4 performs the intervention braking control, the device 1-4 calculates the predetermined hold period T in accordance with the calculated collision risk. If an obstacle detected by the obstacle detection portion 21 ceases being an obstacle, for example, if an obstacle having been detected disappears from the traveling direction of the host vehicle, the predetermined hold period T that is the period of time until the intervention braking control is stopped is made shorter the higher the calculated collision risk, that is, the shorter the TTC. Therefore, the timing (E20, E23 in FIG. 13) of stopping the intervention braking control by the driving support control portion 26 can be brought closer to the timing (E22, E25 in FIG. 13) at which the obstacle detected by the obstacle detection portion 21 ceases being an obstacle, as the TTC is shorter. Furthermore, the driving support control portion 26 brings the state of run of the host vehicle close to a state where the intervention braking control is ceased, within the predetermined hold period T (e.g., T4, T5). Therefore, even though the intervention braking control is stopped after the predetermined hold period T2 elapses (see B24, B29 in FIG. 13), the state of run of the host vehicle can be brought closer to the state where the intervention braking control is ceased, within the predetermined hold period T2 (see E22, E25 in FIG. 13). Hence, in the case where, during the intervention braking control, the detection of an obstacle by the obstacle detection portion 21 ceases and, indeed, there exists no obstacle in the traveling direction of the host vehicle, the intervention braking control can be stopped earlier the higher the collision risk is. Furthermore, the return of the state of run of the host vehicle to the state where the intervention braking control is ceased can be achieved earlier (by the amount of X4 or the amount of X5 in FIG. 13) than in the case (see E22, E25 in FIG. 13) where the intervention braking force F2 having been applied to the host vehicle suddenly ceases being applied to the host vehicle after the elapse of the predetermined hold period T. Thus, the discomfort of the driver can be

restrained.

[0166] Although in Embodiment 2 and Embodiment 4, the within-period braking force is made less than the intervention braking force as time elapses during the predetermined hold period T, the invention is not limited to this construction. For example, the within-period braking force may be set at a constant braking force that is less than the intervention braking force. Furthermore, the within-period braking force may also be the current braking force. With this construction, in the case where the start of the intervention braking control by the driving support control portion 26 is immediately followed by the detection of an obstacle and then the detection of the same obstacle becomes impossible and, therefore, the braking force applied to the host vehicle has not reached the intervention braking force, what is performed is that the current braking force that is smaller than the intervention braking force is applied to the vehicle as a within-period braking force during the predetermined hold period T.

[0167] As described above, the driving support control device and the driving support control method in accordance with the invention are useful in the driving support control performed on the basis of the risk of collision between the host vehicle and a detected obstacle, and are particularly suitable to restrain interruption of the driving support control even if after an obstacle is detected the detection of the same obstacle becomes impossible. [0168] While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.