Patent Publication Number: US-2020282983-A1

Title: Brake assistance apparatus, control apparatus, and brake assistance method for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application No. PCT/JP2018/039481, filed Oct. 24, 2018, which claims priority to Japanese Patent Application No. 2017-225511, filed Nov. 24, 2017. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a brake assistance apparatus, a control apparatus, and a brake assistance method for a vehicle. 
     Related Art 
     A technology for avoiding collision with an obstacle that is present in the periphery of a vehicle based on detection results from a camera and a radar is known. In this technology, for example, when there is a likelihood of an own vehicle colliding with an obstacle ahead, the own vehicle is controlled to be braked. 
     SUMMARY 
     An aspect of the present disclosure provides a brake assistance apparatus for a vehicle. The brake assistance apparatus includes: a detecting unit that detects an object in a periphery of an own vehicle; a brake assisting unit that assists in braking of the own vehicle; and a control unit that controls the brake assisting unit. When determined that there is a likelihood of the own vehicle colliding with a first object that is present in a travelling direction of the own vehicle based on detection results from the detecting unit, the control unit determines an avoidance area, that is an area in which there is no second object in the periphery of the first object that is present in the travelling direction of the own vehicle, is available for avoiding the collision by steering of the own vehicle. When no avoidance area is present, the control unit increases a brake assistance level of the own vehicle using the brake assisting unit to be higher than when the avoidance area is present, and causes the brake assisting unit to perform brake assistance. Increasing the brake assistance level includes at least one of: advancing a timing for starting brake assistance of the own vehicle; and increasing the strength of brake assistance of the own vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram of a vehicle that includes a brake assistance apparatus according to a first embodiment; 
         FIG. 2  is a diagram of the brake assistance apparatus; 
         FIG. 3  is a flowchart of a brake assistance method; 
         FIG. 4  is a diagram for explaining an overlap ratio and an avoidance area; 
         FIG. 5  is a map of relationship between the overlap ratio and a brake assistance level according to the first embodiment; 
         FIG. 6  is a map of relationship between the overlap ratio and the brake assistance level according to a second embodiment; 
         FIG. 7  is a map of relationship between the overlap ratio and the brake assistance level according to a third embodiment; 
         FIG. 8  is a diagram of an example in which the other object is an oncoming vehicle; 
         FIG. 9  is a diagram of an example in which the other object is a vehicle that approaches the own vehicle from behind and to the side of the own vehicle; and 
         FIG. 10  is a diagram of a vehicle that includes a brake assistance apparatus according to a sixth embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A technology for avoiding collision with an obstacle that is present in the periphery of a vehicle based on detection results from a camera and a radar is known. JP-A-2017-56795 describes that, in a case in which there is a likelihood of an own vehicle colliding with an obstacle ahead, control to brake the own vehicle is performed when an overlap ratio between the own vehicle and the obstacle ahead is equal to or greater than a predetermined value that is based on a vehicle speed of the own vehicle, and control to brake the own vehicle is not performed when the overlap ratio is less than the predetermined value that is based on the vehicle speed of the own vehicle. 
     In the technology described in JP-A-2017-56795, whether the vehicle is braked is determined based on the overlap ratio. Therefore, for example, in a state in which another obstacle, such as a guardrail, is present in the periphery of the obstacle ahead and avoidance through steering avoidance is difficult, control to brake the own vehicle may not be performed when the overlap ratio is low. 
     An exemplary embodiment of the present disclosure provides a brake assistance apparatus for a vehicle. The brake assistance apparatus includes: a detecting unit that detects an object in a periphery of an own vehicle; a brake assisting unit that assists in braking of the own vehicle; a control unit that controls the brake assisting unit. In response to determining that there is a likelihood of the own vehicle colliding with a first object that is present in a travelling direction of the own vehicle based on detection results from the detecting unit, the control unit determines there is an avoidance area, that is an area in which there is no second object in the periphery of the first object that is present in the travelling direction of the own vehicle, is available for avoiding the collision by steering of the own vehicle. When no avoidance area is present, the control unit increases a brake assistance level of the own vehicle using the brake assisting unit to be higher than when the avoidance area is present, and causes the brake assisting unit to perform brake assistance. Increasing the brake assistance level includes at least one of: advancing a timing for starting brake assistance of the own vehicle; and increasing the strength of brake assistance of the own vehicle. 
     According to this exemplary embodiment, when the likelihood of a collision between the own vehicle and the first object that is present in the travelling direction of the own vehicle is present and the avoidance area is not present in the periphery of the first object, at least one of: brake assistance being started earlier and the strength of brake assistance being increased compared to that when the avoidance area is present is performed. Therefore, the likelihood of a collision between the own vehicle and the first object that is present in the travelling direction of the own vehicle can be reduced. In addition, the likelihood of a collision with the second object in the periphery of the first object can be reduced. 
     First Embodiment 
     As shown in  FIG. 1 , a brake assistance apparatus  10  according to a first embodiment is used to be mounted in a vehicle  500 . The brake assistance apparatus  10  includes a control unit  100 , a millimeter-wave radar  21 , a monocular camera  22 , a vehicle speed sensor  24 , a yaw rate sensor  25 , a brake assistance actuator  30 , and a brake apparatus  502 . The vehicle  500  includes a wheel  501 , a brake line  503 , a steering wheel  504 , a front windshield  510 , and a front bumper  520 . 
     As a detecting unit that detects an object in the periphery of an own vehicle, the vehicle  500  may be provided with at least the millimeter-wave radar  21 . The vehicle  500  may be provided with at least one of the monocular camera  22  and a laser radar (LIDAR), together with the millimeter-wave radar  21 . Alternatively, a stereo camera may be provided instead of the millimeter-wave radar  21 . The stereo camera may be provided together with the millimeter-wave radar  21 . According to the present embodiment, the millimeter-wave radar  21  and the monocular camera  22  are provided as the detecting unit. 
     The brake apparatus  502  is provided in each wheel  501 . Each brake apparatus  502  actualizes braking of the wheel  501  by brake fluid pressure that is supplied through the brake line  503  based on a brake pedal operation by a driver. The brake line  503  includes a brake piston that generate the brake fluid pressure based on the brake pedal operation and a brake fluid line. According to the present embodiment, the brake assistance actuator  30  is provided in the brake line  503 . Fluid pressure control can be performed independent of the brake pedal operation, and brake assistance is thereby actualized. Here, a configuration in which, instead of the brake fluid line, a control signal line is used as the brake line  503  and an electric actuator that is provided in each brake apparatus  502  is operated may be used. The brake assistance actuator  30  and the brake apparatus  502  are also collectively referred to as a “brake assisting unit”. 
     The steering wheel  504  is connected to the wheels  501  on a front side by a steering rod and a steering mechanism. 
     As shown in  FIG. 2 , the control unit  100  includes a central processing unit (CPU)  110 , a memory  120 , and an input/output interface  140 . The control unit  100  includes a single CPU  110  or more. The CPU  110 , the memory  120 , and the input/output interface  140  are connected by a bus such as to be capable of two-way communication. For example, the memory  120  includes a read-only memory (ROM) and a random access memory (RAM). The millimeter-wave radar  21 , the monocular camera  22 , the vehicle speed sensor  24 , the yaw rate sensor  25 , and the brake assistance actuator  30  are each connected to the input/output interface  140  by a control signal line. Detection information of each sensor is inputted from the millimeter-wave radar  21 , the monocular camera  22 , the vehicle speed sensor  24 , the yaw rate sensor  25 . A control signal that designates a brake assistance level is outputted to the brake assistance actuator  30 . The brake assistance level is a degree of intervention through brake assistance by the brake apparatus  502 . 
     The CPU  110  functions as an attribute information acquiring unit  111 , a collision determining unit  112 , an avoidance area determining unit  113 , and an assistance level determining unit  114  and performs brake assistance by expanding and running a program that is stored in the memory  120 . Details of processes by the attribute information acquiring unit  111 , the collision determining unit  112 , the avoidance area determining unit  113 , and the assistance level determining unit  114  will be described hereafter. Of the control unit  100 , an apparatus that provides the functions of the avoidance area determining unit  113  and the assistance level determining unit  114  is also simply referred to as a “control apparatus”. 
     The millimeter-wave radar  21  is a sensor that emits millimeter waves and receives reflected waves that are reflected by an object, thereby detecting a position and a distance of the object. The millimeter-wave radar  21  includes a transmitter and a receiver. According to the present embodiment, the millimeter-wave radar  21  is arranged in a center of the front bumper  502 . However, a plurality of millimeter-wave radars  21  may be provided on an overall surface of the front bumper  520 . Alternatively, the millimeter-wave radars  21  may be arranged on both side surfaces of the front bumper  520 . For example, detection signals outputted from the millimeter-wave radar  21  may be signals that are composed of a series of points that indicate representative positions of an object, obtained by reception waves being processed in a processing circuit provided in the millimeter-wave radars  21 . Alternatively, the detection signals may be signals that indicate unprocessed reception waves. When the unprocessed reception waves are used as the detection signals, the CPU  110  performs signal processing to identify the position and distance of the object. Here, a LIDAR may be used instead of the millimeter-wave radar. 
     The monocular camera  22  is an imaging apparatus that includes a single image sensor, such as a charge coupled device (CCD). The monocular camera  22  is a sensor that outputs, as image data that is a detection result, outer appearance information on an object by receiving visible light. The image data outputted from the monocular camera  22  is configured by a plurality of frame images that are continuous in time series. Each frame image is expressed by pixel data. According to the present embodiment, the monocular camera  22  is arranged in an upper center portion of the front windshield  510 . The pixel data outputted from the monocular camera  22  is monochromic pixel data or color pixel data. 
     The wheel speed sensor  24  is a sensor that detects a rotational speed of the wheel  501 . The wheel speed sensor  24  is provided in each wheel  501 . A detection signal outputted from the wheel speed sensor  24  is a voltage value that is proportional to a wheel speed or a pulse wave that indicates an interval based on the wheel speed. Information such as vehicle speed and traveling distance of the vehicle can be acquired based on the detection signal from the wheel speed sensor  24 . 
     The yaw rate sensor  23  is a sensor that detects a rotation angle speed of the vehicle  500 . For example, the yaw rate sensor  23  is arranged in a center portion of the vehicle  500 . A detection signal outputted from the yaw rate sensor  23  is a voltage value that is proportional to a rotation direction and an angular speed. 
     The brake assistance actuator  30  is an actuator for performing braking by the brake apparatus  502  regardless of the brake pedal operation by the driver. According to the present embodiment, the brake assistance actuator  30  is provided on the brake line  503 . The brake assistance actuator  30  increases and decreases the brake fluid pressure on the brake line  503  based on a control signal from the control apparatus  100 . For example, the brake assistance actuator  30  is composed of a module that includes an electric motor and a brake hydraulic piston that is driven by the electric motor. Alternatively, a brake control actuator that is already provided as an anti-skidding apparatus or an anti-lock brake system may be used. 
     A brake assistance process that is performed by the brake assistance apparatus  10  according to the first embodiment will be described with reference to  FIG. 3  and  FIG. 4 . Brake assistance is repeatedly performed by the CPU  110  from when a start switch of the vehicle  500  is turned until the start switch is turned off, or while a brake assistance switch that is provided in the vehicle  500  is set to on. 
     The attribute information acquiring unit  111  acquires attributes of an object in the periphery of an own vehicle B 0  ( FIG. 4 ) using the detection results that are inputted from the detecting unit, such as the millimeter-wave radar  21  and the monocular camera  22  (step S 10  in  FIG. 3 ). According to the present embodiment, as the attributes, for example, a distance from the own vehicle B 0  to the object, a relative speed of the object relative to the own vehicle B 0 , an orientation of the object, a degree of overlap between the own vehicle B 0  and the object, and a collision margin time (time-to-collision [TTC]) until the own vehicle B 0  collides with the object are calculated and acquired, based on the detection results inputted from the millimeter-wave radar  21 . In addition, for example, the attribute information acquiring unit  111  calculates and acquires a relative position of the object relative to the own vehicle B 0 , and the shape and size of the object, using the image data from the monocular camera  22 . 
     Here, the degree of overlap is the degree of overlap of the object in the vehicle width direction of the own vehicle. Here, the degree of overlap is the degree of overlap of the object in a vehicle width direction of the own vehicle B 0 . According to the present embodiment, the degree of overlap is an overlap ratio OL of the own vehicle B 0  and the object. The degree of overlap may be an amount of overlap with the object in the vehicle width direction of the own vehicle B 0 . The collision margin time TTC is an amount of time until the own vehicle B 0  and the object collide under an assumption that the relative speed between the own vehicle B 0  and the object is fixed. The attribute information acquiring unit  111  performs the above-described acquisition of the attributes at all times while the present routine is being performed. 
     Next, the collision determining unit  112  determines whether the object is present in a travelling direction of the own vehicle B 0  using the attributes acquired by the attribute information acquiring unit  111  (step S 20  in  FIG. 3 ) When determined that the object is not present in the travelling direction of the own vehicle B 0  (NO at step S 20  in  FIG. 3 ), the CPU  110  ends the present routine. 
     When determined that the object is present in the travelling direction of the own vehicle B 0  (YES at step S 20  in  FIG. 30 ), the collision determining unit  112  determines whether a likelihood of the own vehicle B 0  colliding with the object that that is present in the travelling direction of the own vehicle B 0  is present using the attributes acquired by the attribute information acquiring unit  111  (step S 30  in  FIG. 3 ). 
     At step S 30 , when the overlap ratio OL is greater than 0 and the collision margin time TTC is equal to or less than a first threshold that is based on the relative speed stored in the memory  120 , the collision determining unit  112  determines that the likelihood of a collision between the own vehicle B 0  and an object B 1  (corresponding to a first object) is present (YES at step S 30  in  FIG. 3 ). When the likelihood of a collision is not present (NO at step S 30  in  FIG. 3 ), the CPU  110  ends the present routine. The first threshold is a value that enables a collision with the object B 1  to be avoided by braking of the own vehicle B 0  when the driver operates the brake pedal of the own vehicle B 0  when the collision margin time TTC is at the first threshold. 
     The vehicle  500  includes a warning apparatus that gives notification of the likelihood of a collision through sound, light, or vibrations. For example, before step S 30 , the CPU  110  may output a signal through the input/output interface  140  at a timing at which the collision margin time TTC reaches a second threshold that is longer than the above-described first threshold, and perform notification by the notification apparatus. Here, in an example shown in  FIG. 4 , the object B 1  is a leading vehicle of the own vehicle B 0 . However, the object B 1  is not limited to a four-wheeled vehicle and may be another moving object, such as a two-wheeled vehicle or a person, or may be a stationary object, such as a solid structure. 
     When the collision determining unit  112  determines that the likelihood of a collision is present, the avoidance area determining unit  113  determines there is an avoidance area in the periphery of the object B 1  (step S 40  in  FIG. 3 ). The avoidance area is an area in which there is no other object in the periphery of the object B 1  that is present in the travelling direction of the own vehicle B 0 , and is an area is available for avoiding a collision with the object B 1  by steering of the own vehicle B 0 . The other object is an object that differs from the object B 1 . According to the present embodiment, the other object B 2  (corresponding to a second object) is a stationary object such as a broken-down vehicle or a guardrail. 
     According to the present embodiment, for example, the avoidance area determining unit  113  calculates a lateral movement amount of the own vehicle B 0  that is required to avoid a collision between the own vehicle B 0  and the object B 1  by multiplying the vehicle width of the own vehicle B 0  by the overlap ratio OL. The avoidance area determining unit  113  then estimates a traveling trajectory area that is an area through which the own vehicle B 0  travels under an assumption that the own vehicle B 0  is traveling at a current vehicle speed and steering based on the lateral movement amount is performed in the own vehicle B 0 . 
     The avoidance area determining unit  113  determines whether there is a pixel area that indicates the other object is present in the estimated traveling trajectory area, using the detection results from the millimeter-wave radar  21  and the monocular camera  22 . The avoidance area determining unit  113  determines that no avoidance area is present when there is no pixel area indicating the other object in the estimated traveling trajectory area, and determines that the avoidance area is present when there is a pixel area indicating the other object in the estimated traveling trajectory area. 
     An area S 1  on a left side of the object B 1  in  FIG. 4  is the estimated traveling trajectory area, and the other object B 2  is present in the area S 1 . An area S 2  on a right side of the object B 1  shown in  FIG. 4  is an area to which the own vehicle B 0  cannot move by the collision margin time TTC. In the example shown in  FIG. 4 , the avoidance area determining unit  113  determines that the avoidance area is not present. 
     After determination of the avoidance area, the assistance level determining unit  114  determines the brake assistance level of the own vehicle B 0  by the brake assistance unit based on the presence/absence of the avoidance area (step S 50  in  FIG. 3 ). When the avoidance area is not present, the assistance level determining unit  114  determines a higher brake assistance level compared to that when the avoidance area is present. According to the present embodiment, the brake assistance level prescribes a timing for starting brake assistance. Increasing the brake assistance level means advancing the timing for starting brake assistance of the own vehicle B 0  by the brake assisting unit. 
     According to the present embodiment, the memory  120  stores therein a map MP 1  and a map MP 2 , shown in  FIG. 5 . The map MP 1  indicates the timing for starting brake assistance when the avoidance area is present. The map MP 2  indicates the timing for starting brake assistance when the avoidance area is not present. The assistance level determining unit  114  references the map MP 1  when the avoidance area is present and references the map MP 2  when the avoidance area is not present, and determines the timing for starting brake assistance corresponding to the overlap ratio OL. 
     In the map MP 1 , the overlap ratio OL and the timing for starting brake assistance are set such that, when the overlap ratio OL is less than a predetermined value (hereafter, threshold OLth), the timing for starting brake assistance is later compared to that when the overlap ratio OL is equal to or greater than the threshold OLth, or brake assistance is not performed. Specifically, in the map MP 1  for when the avoidance area is present, the relationship between the overlap ratio OL and the timing for starting brake assistance is set such that brake assistance is started at a timing at which the collision margin time reaches TTC 1  when the overlap ratio OL is equal to or greater than the threshold OLth. The timing for starting brake assistance becomes later as the overlap ratio OL becomes less than the threshold OLth. Brake assistance is not performed when the overlap ratio OL is equal to or less than a value OL 1  that is less than the threshold OLth. For example, the threshold OLth is 40%. For example, the timing TTC 1  for brake assistance start at the threshold OLth is a timing at which the collision margin time TTC is 1.4 seconds. For example, the value OL 1  is 30% or 25%. 
     Here, the relationship between the overlap ratio OL and the timing for starting brake assistance is set as described above because, when the overlap ratio OL is small, collision avoidance through operation of the steering wheel  504  is easier compared to that in the case of a full lap, for example. In addition, for example, when the own vehicle B 0  is attempting to avoid and overtake the object B 1 , the own vehicle B 0  may intentionally approach the object B 1 . When brake assistance is actively performed in such cases, the brake apparatus  502  of the own vehicle B 0  may operate regardless of the intentions of the driver when the own vehicle B 0  is attempting to overtake the object B 1 . As a result, a likelihood of overtaking not being achieved and a likelihood of the driver of the own vehicle B 0  experiencing discomfort are present. The foregoing is to reduce such likelihoods. 
     In the map M 2  for when the avoidance area is not present, the relationship between the overlap ratio OL and the timing for starting brake assistance is set such that brake assistance is started at the timing at which the collision margin time becomes TTC 1  when the overlap ratio OL is equal to or greater than a value OL 2 . The timing for starting brake assistance becomes later as the overlap ratio OL becomes less than the value OL 2 . Brake assistance is not performed when the overlap ratio OL reaches 0. The value OL 2  at which the timing for starting brake assistance starts to become later in the map MP 2  is less than the value OLth at which the timing for starting brake assistance starts to become later in the map MP 1 . For example, the value OL 2  is a value such as 5%, 10%, or 15%. 
     Next, the assistance level determining unit  114  outputs a signal to the brake assistance actuator  30  such that brake assistance is performed at the determined timing for starting brake assistance, and causes the brake apparatus  502  to perform brake assistance (step S 60  in  FIG. 3 ). 
     According to the first embodiment, the timing at which brake assistance is started when the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  is present, the avoidance area is not present in the periphery of the object B 1 , and the degree of overlap OL is less than the predetermined value OLth becomes earlier compared to the timing at which brake assistance is started when the avoidance area is present. Therefore, the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  can be reduced. In addition, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Furthermore, according to the first embodiment, even when the overlap ratio OL is relatively small, brake assistance is performed when the avoidance area is not present. Therefore, the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  can be reduced. Moreover, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Second Embodiment 
     The brake assistance apparatus  10  according to a second embodiment will be described with reference to  FIG. 6 , mainly focusing on differences with the first embodiment. According to the second embodiment, the brake assistance level prescribes strength of brake assistance. According to the second embodiment, increase in the brake assistance level means increase in the strength of brake assistance of the own vehicle B 0  by the brake assisting unit. In other words, a braking force that is generated by the brake assistance unit is increased. 
     According to the present embodiment, the memory  120  stores therein a map MP 3  and a map MP 4 , shown in  FIG. 6 . The map MP 3  indicates a magnitude of the braking force when the avoidance area is present. The map MP 4  indicates the magnitude of the braking force when the avoidance area is not present. The assistance level determining unit  114  references the map MP 3  when the avoidance area is present and references the map MP 4  when the avoidance area is not present, and determines the magnitude of the braking force. According to the present embodiment, the maps MP 3  and MP 4  show the relationships between the overlap ratio OL and the magnitude of the braking force when the collision margin time TTC is the above-described first threshold. However, the maps MP 3  and MP 4  may show the relationships when the collision margin time TTC is the above-described second threshold. 
     As shown in  FIG. 6 , in the map MP 3  for when the avoidance area is present, the relationship between the overlap ratio OL and the braking force is set such that, when the overlap ratio OL is less than the threshold OLth, the braking force is smaller compared to that when the overlap ratio OL is equal to or greater than the threshold OLth, or brake assistance is not performed. Specifically, in the map MP 3 , the relationship between the overlap ratio and the magnitude of the braking force is set such that brake assistance is performed at a magnitude of braking force F 1  when the overlap ratio OL is equal to or greater than the threshold OLth. The braking force decreases as the overlap ratio OL becomes less than the threshold OLth. The braking force becomes zero when the overlap ratio OL is equal to or less than the value OL 1  that is less than the threshold OLth. 
     For example, the magnitude of braking force F 1  when the overlap ratio OL is equal to or greater than the threshold OLth is 3G. Here, 1G is acceleration that is of a same magnitude as gravitational acceleration. The relationship between the overlap ratio OL and the magnitude of the braking force is set as described above so that, in a manner similar to the timing for starting brake assistance being set based on the overlap ratio OL according to the first embodiment, a likelihood of overtaking not being achieved and a likelihood of the driver of the own vehicle B 0  experiencing discomfort as a result of the brake apparatus  502  of the own vehicle B 0  operating regardless of the intentions of the driver are reduced. 
     In the map MP 4  for when the avoidance area is not present, the relationship between the overlap ratio OL and the braking force is set such that brake assistance is performed at the magnitude of braking force F 1  when the overlap ratio OL is equal to or greater than the value OL 2 . The braking force decreases as the overlap ratio OL becomes less than the value OL 2 . Brake assistance is not performed when the overlap ratio OL reaches 0. The value OL 2  at which the braking force starts to decrease in the map MP 4  is less than the threshold OLth at which the braking force starts to decrease in the map MP 3 . 
     According to the second embodiment, the braking force when the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  is present, the avoidance area is not present in the periphery of the object B 1 , and the degree of overlap OL is less than the predetermined threshold OLth is greater than the braking force when the avoidance area is present. Therefore, the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  can be reduced. In addition, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Furthermore, in a manner similar to that according to the first embodiment, even when the overlap ratio OL is relatively small, brake assistance is performed when the avoidance area is not present. Therefore, the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  can be reduced. Moreover, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Third Embodiment 
     The brake assistance apparatus  10  according to a third embodiment will be described with reference to  FIG. 7 , mainly focusing on differences with the first embodiment and the second embodiment. According to the third embodiment, the brake assistance level prescribes the timing for starting brake assistance and the magnitude of the braking force. According to the third embodiment, an increase in the brake assistance level means advancing of the timing for starting brake assistance of the own vehicle B 0  by the brake assisting unit and increase in the braking force. 
     According to the present embodiment, the memory  120  stores therein a map MP 5  and a map MP 6 , shown in  FIG. 7 . The map MP 5  shows the timing for starting brake assistance when the avoidance area is present. The map MP 6  shows the timing for starting brake assistance and the magnitude of the braking force when the avoidance area is not present. The assistance level determining unit  114  references the map MP 5  when the avoidance area is present and references the map MP 6  when the avoidance area is not present, and determines the magnitude of the braking force. 
     In the map MP 5  for when the avoidance area is present, the relationship between the overlap ratio OL and the timing for starting brake assistance is set such that, when the overlap ratio OL is less than the threshold OLth, the timing for starting brake assistance is later compared to that when the overlap ratio OL is equal to or greater than the threshold OLth. For example, the first braking force F 1  at the timing TTC 1  for brake assistance start is 3 G. 
     In the map MP 6  for when the avoidance area is not present, the relationship between the timing at which brake assistance is started at the first braking force F 1  and the overlap ratio OL is similar to the relationship described using the map MP 2  described according to the first embodiment. According to the present embodiment, when the avoidance area is not present, brake assistance is further performed at the second braking force F 2  that is less than the first braking force F 2  at a timing that is earlier than the timing at which brake assistance is started at the first braking force F 1 . 
     According to the third embodiment, when the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  is present and the avoidance area is not present in the periphery of the object B 1 , first, brake assistance is performed at the relatively small second braking force F 2  and then brake assistance is subsequently performed at the first braking force F 1  that is greater than the second braking force F 2 . As a result, brake assistance can be performed in multiple stages. The likelihood of a collision between the own vehicle B 0  and the object B 1  can be further reduced. In addition, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Furthermore, according to the third embodiment, even when the overlap ratio OL is relatively small, brake assistance is performed when the avoidance area is not present. Therefore, in a manner similar to that according to the first embodiment and the second embodiment, the likelihood of a collision between the own vehicle B 0  and the object B 1  that is present in the travelling direction of the own vehicle B 0  can be reduced. Moreover, when the other object B 2  is present in the periphery of the object B 1 , the likelihood of a collision between the own vehicle B 0  and the other object B 2  can be reduced. 
     Fourth Embodiment 
     According to the various embodiments described above, the avoidance area determining unit  113  may determine that the avoidance area is not present when, in a case in which the above-described other object is a moving body and the vehicle  500  moves, by steering, to an area in the periphery of the object B 1  that is present in the travelling direction of the vehicle  500 , the other object is predicted to be positioned in the area to which the vehicle  500  moves. 
     In an example shown in  FIG. 8 , the other object (corresponding to a second object) is an oncoming vehicle B 3  that is traveling such as to oppose the travelling direction of the own vehicle B 0 . The attribute information acquiring unit  111  calculates and acquires a distance to the oncoming vehicle B 3 , a relative speed of the oncoming vehicle B 3  relative to the own vehicle B 0 , an orientation of the oncoming vehicle B 3 , the overlap ratio OL of the own vehicle B 0  and the oncoming vehicle B 3 , and the like, using the millimeter-wave radar  21  and the image data from the monocular camera  22 . 
     The avoidance area determining unit  113  determines whether the oncoming vehicle B 3  is present in the traveling trajectory area by the collision margin time TTC of collision with the object B 1 . In the example shown in  FIG. 8 , the oncoming vehicle B 3  is present in an area S 4  by the collision margin time TTC of collision with the object B 1 . An area S 3  on the left side of the object B 1  is an area to which the own vehicle B 0  cannot move by the collision margin time TTC of collision with the object B 1 . In the example shown in  FIG. 8 , the avoidance area determining unit  113  determines that the avoidance area is not present. 
     According to the fourth embodiment, the avoidance area is determined to not be present when the other object is predicted to move to the area to which the own vehicle B 0  is moved. The brake assistance level is determined to be a higher brake assistance level than that when the avoidance area is present. Therefore, the likelihood of collisions between the own vehicle B 0  and the object B 1 , and between the own vehicle B 0  and the other object can be reduced. In addition, the likelihood of collisions between the own vehicle B 0  and the object B 1 , and between the own vehicle B 0  and the oncoming vehicle B 3  that is the other object can be reduced. 
     Fifth Embodiment 
     According to the above-described embodiments, the detecting unit is the millimeter-wave radar  21  and the monocular camera  22  that are provided in the front of the vehicle  500 . However, the vehicle  500  may further include a millimeter-wave radar and a monocular camera in the rear of the vehicle  500  as the detecting unit. The CPU  110  may detect a vehicle that approaches the own vehicle B 0  from behind and to the side of the own vehicle B 0 , based on detection results from the rear millimeter-wave radar and monocular camera. 
     As shown in  FIG. 9 , when the other object (corresponding to a second object) is a vehicle B 4  that approaches the own vehicle B 0  from behind and to the side of the own vehicle B 0 , and when the own vehicle B 0  moves, by steering, to an area S 6  in the periphery of the object B 1 , the avoidance area determining unit  113  may determine that the avoidance area is not present when the vehicle B 4  is predicted to be positioned in the area S 6  to which the own vehicle B 0  moves. 
     The attribute information acquiring unit  111  calculates and acquires a distance to the vehicle B 4 , a relative speed of the vehicle B 4  relative to the own vehicle B 0 , an orientation of the vehicle B 4 , and the overlap ratio OL of the own vehicle B 0  and the vehicle B 4 , using the image data from the millimeter-wave radar and the monocular camera provided in the rear of the vehicle  500 . In an example in  FIG. 9 , the vehicle B 4  is present in the area S 6  by the collision margin time TTC of collision with the object B 1 . An area S 5  on the left side of the object B 1  is an area to which the own vehicle B 0  cannot move by the collision margin time TTC of collision with the object B 1 . In the example shown in  FIG. 9 , the avoidance area determining unit  113  determines that the avoidance area is not present. 
     According to the fifth embodiment, the likelihood of a collision between the own vehicle B 0  and the vehicle B 4  that is approaching the own vehicle B 0  from behind and to the side can be reduced. 
     Sixth Embodiment 
     In a vehicle  500   a  that includes a brake assistance apparatus  10   a  according to a sixth embodiment shown in  FIG. 10 , the steering wheel  504  is connected to the wheels  501  on the front side by a steering apparatus  42  that includes a steering rod and a steering mechanism. For example, in the steering apparatus  42 , a steering assistance apparatus  31  that is capable of driving the steering apparatus  42  by an actuator, such as an electric motor, is arranged. The steering assistance apparatus  31  is capable of controlling the steering apparatus  42  independent of the operation of the steering wheel  504 . Steering assistance is performed by control by a control unit  100   a . When the avoidance area is present, the control unit  100   a  may output a control signal to the steering apparatus  42  and cause the steering apparatus to perform steering assistance to the avoidance area. As a result of an embodiment such as this, the likelihood of a collision between the own vehicle B 0  and the object can be reduced. 
     Other Embodiments 
     According to the above-described embodiments, the assistance level determining unit  114  determines the timing for starting brake assistance or the magnitude of the braking force by referencing the maps that are stored in the memory. However, instead of the foregoing, an expression that expresses the relationship between the timing for starting brake assistance or the magnitude of the braking force, and the overlap ratio OL may be stored in the memory. The assistance level determining unit  114  may determine the timing for starting brake assistance or the magnitude of the braking force based on the overlap ratio OL. 
     The present disclosure can also be actualized according to various embodiments other than the brake assistance apparatus. For example, the present disclosure can be actualized according to embodiments such as a brake assistance method, a computer program for actualizing the method, a storage medium that stores therein the computer program, or a vehicle in which a collision estimation apparatus is mounted. In addition, according to the above-described embodiments, some or all of the functions and processes actualized by software may be actualized by hardware. Furthermore, some or all of the functions and processes actualized by hardware may be actualized by software. For example, as hardware, various circuits, such as integrated circuits, discrete circuits, and circuit modules combining integrated circuits and discrete circuits, may be used. 
     The present disclosure is not limited to the above-described embodiments. The present disclosure can be actualized through various configurations without departing from the spirit of the disclosure. For example, technical features according to the embodiments that correspond to technical features according to aspects described in the summary of the invention can be replaced and combined as appropriate to solve some or all of the above-described issued or to achieve some or all of the above-described effects. Furthermore, the technical features may be omitted as appropriate unless described as a requisite in the present specification.