Abstract:
A collision avoidance apparatus capable of executing an appropriate vehicle control in order to avoid a collision between an own vehicle and a movable object is provided. A collision avoidance apparatus for avoiding a collision between an own vehicle and a movable object includes: a laterally-existing movable object detector for detecting for a movable object that approaches from a direction lateral to the own vehicle; a side collision determination section for determining whether or not a risk that the own vehicle and the movable object collide with each other is high, when the laterally-existing movable object detector has detected the movable object that approaches from the direction lateral to the own vehicle; a passage and avoidance determination section for determining, when the risk that the own vehicle and the movable object collide with each other is determined to be high, whether or not a possibility that a collision between the own vehicle and the movable object can be avoided by the own vehicle passing in front of the movable object, is high; and an accelerated state/decelerated state controller for controlling the own vehicle to be in one of an accelerated state and a decelerated state, according to a determination result of the passage and avoidance determination section.

Description:
TECHNICAL FIELD 
     The present invention relates to collision avoidance apparatuses for use in vehicles, and more particularly to collision avoidance apparatuses for avoiding side collision between vehicles. 
     BACKGROUND ART 
     Apparatuses and systems for predicting collision between vehicles, and controlling the vehicles so as to avoid the collision have been developed to date. 
     An example of the collision avoidance apparatus as described above is disclosed in Patent Literature 1. A vehicle travelling support apparatus disclosed in Patent Literature 1 firstly obtains information on travelling of another vehicle, such as a position of the other vehicle approaching an own vehicle, by communication between the vehicles. Subsequently, the vehicle travelling support apparatus determines whether or not the own vehicle collides with the other vehicle, based on a travelling state of the own vehicle, and the information on the travelling of the other vehicle. When the collision between the own vehicle and the other vehicle is predicted, the vehicle travelling support apparatus controls the travelling state of the own vehicle so as to alleviate impact of the collision. Specifically, the vehicle travelling support apparatus executes a vehicle control by, for example, decreasing a speed of the own vehicle according to a steered state of the other vehicle. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Laid-Open Patent Publication No. 2007-022263 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, the vehicle travelling support apparatus disclosed in Patent Literature 1 has the following problems. Namely, an optimal vehicle control for avoiding the collision between the own vehicle and the other vehicle may not be able to be executed. 
     Once the vehicle travelling support apparatus described above starts to execute the vehicle control for avoiding the collision by, for example, decreasing a speed of the own vehicle, the contents of the control are not changed. On the other hand, the travelling states of the own vehicle and the other vehicle change from moment to moment, and therefore the vehicle control being executed is not always an optimal vehicle control for avoiding the collision. 
     For example, a case is assumed in which a possibility that the other vehicle collides with the own vehicle at the front-lateral side portion of the own vehicle is determined to be high in a state where a distance between the own vehicle and the other vehicle is relatively great, and a control for decreasing a speed of the own vehicle is executed. Even if such a control is executed, the other vehicle may approach the rear-lateral side portion of the own vehicle in practice during the passage of time. In such a case, by another vehicle control being executed instead of continuing the control for decreasing the speed of the own vehicle, a collision between the own vehicle and the other vehicle may be avoided with enhanced certainty. 
     Thus, in conventional arts, an optimal vehicle control for avoiding a collision between the own vehicle and another vehicle may not be able to be executed. 
     The present invention is made in order to solve the aforementioned problems, and an object of the present invention is to make available a collision avoidance apparatus that enables an appropriate vehicle control for avoiding a collision between an own vehicle and a movable object to be executed. 
     Solution to the Problems 
     In order to solve the aforementioned problems, the present invention has the following features. Specifically, a first aspect of the present invention is directed to a collision avoidance apparatus for avoiding a collision between an own vehicle and a movable object, and the collision avoidance apparatus includes: a laterally-existing movable object detector for detecting for a movable object that approaches from a direction lateral to the own vehicle; a side collision determination section for determining whether or not a risk that the own vehicle and the movable object collide with each other is high, when the laterally-existing movable object detector has detected the movable object that approaches from the direction lateral to the own vehicle; a passage and avoidance determination section for determining, when the risk that the own vehicle and the movable object collide with each other is determined to be high, whether or not a possibility that the own vehicle passes in front of the movable object and a collision between the own vehicle and the movable object can be avoided, is high; and an accelerated state/decelerated state controller for controlling the own vehicle to be in one of an accelerated state and a decelerated state, according to a determination result of the passage and avoidance determination section. 
     In a second aspect based on the first aspect, an automatic deceleration section for automatically decelerating the own vehicle when the risk that the own vehicle and the movable object collide with each other is determined to be high, and a deceleration detector for detecting a deceleration of the own vehicle when the own vehicle is decelerating, are further provided, and the accelerated state/decelerated state controller controls the automatic deceleration section to reduce a deceleration so as to be less than a deceleration having been most recently detected, when the passage and avoidance determination section determines the possibility that a collision between the own vehicle and the movable object can be avoided, is high. 
     In a third aspect based on the second aspect, a travelling information detector for detecting information on travelling of each of the own vehicle and the movable object, and a target deceleration calculator for calculating a target deceleration of the own vehicle, which is required to avoid a collision between the own vehicle and the movable object, based on the information, on travelling of each of the own vehicle and the movable object, which has been most recently obtained, are further provided, and the accelerated state/decelerated state controller controls the automatic deceleration section such that the deceleration becomes less than or equal to the target deceleration. 
     In a fourth aspect based on the third aspect, the travelling information detector includes: an own vehicle speed detector for detecting a travelling speed Vh (km/h) of the own vehicle, and a movable object information detector for detecting: a speed component Vw (km/h) of a speed at which the movable object travels, in a direction orthogonal to a travelling direction of the own vehicle; a distance H (km) in the travelling direction of the own vehicle from a lateral side end, of the movable object, which is directed in a same direction as the travelling direction of the own vehicle, to a rear end of the own vehicle; and a distance W (km) in the direction orthogonal to the travelling direction of the own vehicle from a lateral side end, of the own vehicle, which is opposed to a direction from which the movable object approaches, to a front end of the movable object, and when the target deceleration is represented as GT (km/h/s), the target deceleration calculator calculates, as a target deceleration GT, a value satisfying equation (A) indicated below:
 
 GT= 2 ×Vh×Vw/W− 2× Vw^ 2 ×H/W^ 2  (A).
 
     In a fifth aspect, the automatic deceleration section automatically decelerates the own vehicle by automatically generating a braking force for the own vehicle, and the accelerated state/decelerated state controller enhances the braking force generated by the automatic deceleration section to reduce a deceleration of the own vehicle when the passage and avoidance determination section determines that a possibility that a collision between the own vehicle and the movable object can be avoided, is high. 
     In a sixth aspect based on one of the first aspect and the second aspect, a driving force controller for controlling a driving force for the own vehicle is further provided, and the accelerated state/decelerated state controller causes the driving force controller to enhance a driving force for the own vehicle to accelerate the own vehicle when the passage and avoidance determination section determines that a possibility that a collision between the own vehicle and the movable object can be avoided, is high. 
     In a seventh aspect based on the first aspect, the passage and avoidance determination section determines whether or not a risk that the movable object collides with the own vehicle in a rear lateral end portion of the own vehicle is high, and the passage and avoidance determination section determines, when determining that the risk that the movable object collides with the own vehicle in the rear lateral end portion of the own vehicle is high, that a possibility that the collision between the own vehicle and the movable object can be avoided by the own vehicle passing in front of the movable object, is high. 
     In an eighth aspect based on the seventh aspect, the laterally-existing movable object detector includes: a front-lateral side radar device for detecting for an object that exists front-lateral to the own vehicle; and a rear-lateral side radar device for detecting for an object that exists rear-lateral to the own vehicle, and the side collision determination section determines whether or not a risk that the own vehicle and the movable object collide with each other is high, based on an object detection result obtained by the front-lateral side radar device and the rear-lateral side radar device. 
     In a ninth aspect based on the first aspect, the passage and avoidance determination section includes: a rear-lateral side radar detection determination section for determining whether or not the movable object has been detected by a rear-lateral side radar device; a time determination section for calculating a predicted time that is to elapse before the movable object collides with the own vehicle, and determining whether or not the predicted time indicates a value less than or equal to a predetermined threshold value; a predicted position determination section for calculating a predicted position of the own vehicle and a predicted position of the movable object which are to be obtained when the predicted time has elapsed, and determining whether or not the predicted position of the movable object is within a range defined relative to the predicted position of the own vehicle; and an overall determination section for determining that a risk that the movable object collides with the own vehicle in a rear lateral end portion of the own vehicle, is high, when it is determined that the rear-lateral side radar device has detected the movable object, it is determined that the predicted time indicates a value less than or equal to the predetermined threshold value, and it is determined that the predicted position of the movable object is within the range defined relative to the predicted position of the own vehicle. 
     Advantageous Effects of the Invention 
     According to the first aspect, an appropriate vehicle control for avoiding a collision between the own vehicle and a movable object can be executed. Specifically, whether or not a possibility that a collision can be avoided by allowing the own vehicle to pass in front of the movable object approaching from a direction lateral to the own vehicle, is high is repeatedly determined. Therefore, a content of control of the own vehicle can be changed in real time according to the determination result. Thus, a collision between the own vehicle and another vehicle in passing can be avoided with enhanced certainty. 
     According to the second aspect, even after a speed of the own vehicle is reduced in order to avoid a collision between the own vehicle and the movable object, the deceleration of the own vehicle can be controlled according to a predicted position at which the collision with the own vehicle occurs. 
     According to the third aspect, an accelerated state or a decelerated state of the own vehicle can be changed according to the target deceleration required for avoiding a collision with the movable object. Therefore, the collision between the own vehicle and the movable object can be avoided with enhanced certainty. Further, the target deceleration can be accurately calculated with the use of the most recently obtained information on travelling of each of the own vehicle the movable object. 
     According to the fourth aspect, the target deceleration can be calculated by using a parameter which can be relatively easily detected, and by using a simple calculation process. Therefore, the target deceleration can be quickly calculated in a reduced amount of process steps, to appropriately control the traveling of the own vehicle. 
     According to the fifth aspect, a braking force for the own vehicle is controlled, thereby controlling a speed and a deceleration of the own vehicle with ease and certainty. 
     According to the sixth aspect, in a case where the own vehicle attempts to avoid a collision by passing in front of the movable object, even if a speed of the own vehicle is insufficient, the own vehicle can be accelerated to avoid the collision. 
     According to the seventh aspect, whether or not a collision can be avoided by the own vehicle passing in front of the movable object can be determined in a simple process. 
     According to the eighth aspect, a movable object in a wide range around the own vehicle can be detected, with the use of a plurality of radar devices, with ease and accuracy. 
     According to the ninth aspect, whether or not a risk that the movable object collides with the own vehicle in the rear lateral portion of the own vehicle is high, i.e., whether or not a collision can be avoided by the own vehicle passing in front of the movable object, can be determined in a simple process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a structure of a collision avoidance apparatus  1  according to a first embodiment. 
         FIG. 2  is a diagram of a mounted state illustrating positions at which a front-lateral side radar  11  and a rear-lateral side radar  12  are mounted to an own vehicle  100 . 
         FIG. 3  is a flow chart showing a process performed by a collision determination ECU  20  according to the first embodiment. 
         FIG. 4  is a plan view illustrating a positional relationship between the own vehicle  100  and another vehicle  200 , which is obtained at time t 1 . 
         FIG. 5  is a plan view illustrating a positional relationship between the own vehicle  100  and the other vehicle  200 , which is obtained at time t 2 . 
         FIG. 6  is a plan view illustrating a positional relationship between the own vehicle  100  and the other vehicle  200 , which is obtained at time t 3 . 
         FIG. 7  is a block diagram illustrating a structure of the collision avoidance apparatus  1  according to a second embodiment. 
         FIG. 8  is a flow chart showing a process performed by the collision determination ECU  20  according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (First Embodiment) 
     Hereinafter, a collision avoidance apparatus  1  according to a first embodiment of the present invention will be described. Firstly, a structure of the collision avoidance apparatus  1  will be described with reference to  FIG. 1 .  FIG. 1  is a block diagram illustrating the structure of the collision avoidance apparatus  1  according to the first embodiment of the present invention. The collision avoidance apparatus  1  includes a front-lateral side radar  11 , a rear-lateral side radar  12 , a speed sensor  13 , a deceleration sensor  14 , a collision determination ECU  20 , and a brake device  30 . Hereinafter, an exemplary case in which the collision avoidance apparatus  1  is mounted to an own vehicle  100  will be described. 
     The front-lateral side radar  11  is a radar device for detecting for an object that exists front-lateral to the own vehicle  100 , or approaches from a direction front-lateral to the own vehicle  100 . For example, the front-lateral side radar  11  is mounted to the front right side portion of the own vehicle  100  as shown in  FIG. 2 .  FIG. 2  is a diagram of a mounted state illustrating positions at which the front-lateral side radar  11  and the rear-lateral side radar  12  are mounted to the own vehicle  100 . In  FIG. 2 , a region FA represents a region within which an object detectable by the front-lateral side radar  11  exists. When the front-lateral side radar  11  has detected a movable object in the region FA that is front-lateral to the own vehicle  100 , the front-lateral side radar  11  detects information on travelling of the movable object relative to the own vehicle  100 . Specifically, the front-lateral side radar  11  detects a relative speed V (km/h) of the movable object relative to the own vehicle  100 , and a distance D (km) from the movable object to the own vehicle  100 , as the information on the travelling of the movable object. The front-lateral side radar  11  transmits, to the collision determination ECU  20 , data representing the relative speed V and the distance D. As a method used by the front-lateral side radar  11  for detecting the relative speed V and the distance D, any conventionally known method may be used. 
     The rear-lateral side radar  12  is a radar device for detecting for an object that exists rear-lateral to the own vehicle  100 , or approaches from a direction rear-lateral to the own vehicle  100 . For example, the rear-lateral side radar  12  is mounted to the rear right side portion of the own vehicle  100  as shown in  FIG. 2 . In  FIG. 2 , a region RA represents a region within which an object detectable by the rear-lateral side radar  12  exists. When the rear-lateral side radar  12  has detected a movable object in the region RA that is rear-lateral to the own vehicle  100 , the rear-lateral side radar  12  detects information on travelling state of the movable object. Specifically, the rear-lateral side radar  12  detects a relative speed V, a distance D, an orthogonal speed component Vw (km/h), an own vehicle travelling direction distance H (km), and an own vehicle lateral distance W (km). A coordinate system in which an axis line representing a travelling direction of the own vehicle  100  is defined as a Y axis, and an axis line orthogonal to the Y axis on the horizontal plane is defined as an X axis, is assumed (see  FIG. 5 ). The orthogonal speed component Vw represents a speed component, in the X-direction, of a traveling speed of the movable object. The own vehicle travelling direction distance H (km) represents a Y-axis component distance, from a lateral side end, of the movable object, which is directed in the same direction as the travelling direction of the own vehicle  100 , to the rear end of the own vehicle  100 . The own vehicle lateral distance W represents a distance in the X-axis direction, from the lateral side end, of the own vehicle  100 , which is opposed to the direction from which the movable object approaches, to the front end of the movable object. The rear-lateral side radar  12  detects the relative speed V, the distance D, the orthogonal speed component Vw, the own vehicle travelling direction distance H, and the own vehicle lateral distance W, and transmits data representing each of them, to the collision determination ECU  20 . As a method used by the rear-lateral side radar  12  for detecting the orthogonal speed component Vw, the own vehicle travelling direction distance H, and the own vehicle lateral distance W, any conventionally known method may be used. 
     As shown in  FIG. 2 , since the collision avoidance apparatus  1  according to the first embodiment includes a plurality of radar devices such as the front-lateral side radar  11  and the rear-lateral side radar  12 , the movable object that approaches from a direction lateral to the own vehicle  100  can be detected in a wide range. The number of the radar devices included in the collision avoidance apparatus  1  is not limited to the number described above, and the number of the radar devices included therein may be greater than or equal to three. Further, in a case where a single radar can perform detection with a sufficient resolution, and in a sufficient range, the single radar device may double as both the front-lateral side radar  11  and the rear-lateral side radar  12 . 
     The speed sensor  13  is a sensor device for detecting a travelling speed Vh (km/h) of the own vehicle  100 . The speed sensor  13  transmits, to the collision determination ECU  20 , data representing the travelling speed Vh of the own vehicle  100 , which has been detected. As a method used by the speed sensor  13  for detecting the travelling speed Vh, any conventionally known method may be used. 
     The deceleration sensor  14  is a sensor device for detecting a deceleration G (km/h/s) of the own vehicle  100 . The deceleration sensor  14  transmits, to the collision determination ECU  20 , data representing the deceleration G of the own vehicle  100 , which has been detected. As a method used by the deceleration sensor  14  for detecting the deceleration G; any conventionally known method may be used. 
     The collision determination ECU  20  is typically a control device that includes an information processing apparatus such as a CPU (Central Processing Unit), a storage device such as a memory, and an interface circuit. The collision determination ECU  20  controls the brake device  30  based on data obtained from the front-lateral side radar  11 , the rear-lateral side radar  12 , and the speed sensor  13 , to control an accelerated state or a decelerated state of the own vehicle  100 . The process performed by the collision determination ECU  20  will be described below in detail. 
     The brake device  30  is a braking device for generating a braking force for the own vehicle  100 . The brake device  30  generates a braking force for the own vehicle  100  according to an instruction from the collision determination ECU  20 . 
     Next, a process performed by the collision determination ECU  20  will be described with reference to  FIG. 3 .  FIG. 3  is a flow chart showing an exemplary process performed by the collision determination ECU  20  according to the first embodiment. When, for example, an IG power source of the own vehicle  100  is set to be on, the collision determination ECU  20  performs the process shown in  FIG. 3 . 
     The collision determination ECU  20  firstly determines whether or not a movable object approaching from a lateral direction has been detected (step S 1 ). Specifically, the collision determination ECU  20  determines whether or not information on travelling of a movable object has been received from the front-lateral side radar  11  or the rear-lateral side radar  12 . When the collision determination ECU  20  has received the information on travelling of a movable object, the collision determination ECU  20  determines that a movable object approaching from the lateral direction has been detected (Yes in step S 1 ), and determines whether or not a risk that the movable object and the own vehicle  100  collide with each other is high (step S 2 ). On the other hand, when the collision determination ECU  20  receives no information on travelling of a movable object, the collision determination ECU  20  determines that a movable object approaching from the lateral direction has not been detected (No in step Si), and advances the process to step S 7 . 
     In step S 2 , the collision determination ECU  20  firstly calculates a time which is to elapse before collision between the movable object and the own vehicle  100 , as a predicted collision time TTC, according to the following equation (1).
 
TTC=D/V  (1)
 
Subsequently, the collision determination ECU  20  determines whether or not the predicted collision time TTC indicates a value that is less than or equal to a predetermined threshold value Thc. The threshold value Thc is a constant that is previously stored in the storage device of the collision determination ECU  20 . When the predicted collision time TTC indicates a value that is less than or equal to the threshold value Thc, the collision determination ECU  20  determines that a risk that the movable object and the own vehicle  100  collide with each other is high (Yes in step S 2 ), and starts automatic braking (step S 3 ). On the other hand, when the predicted collision time TTC indicates a value that is greater than the threshold value Thc, the collision determination ECU  20  determines that a risk that the movable object and the own vehicle  100  collide with each other is low (No in step S 2 ), and advances the process to step S 7 .
 
     The process step described above is an exemplary process step of step S 2 . The collision determination ECU  20  may determine whether or not a risk that the movable object and the own vehicle  100  collide with each other is high, by using a conventionally known method. 
     In step S 3 , the collision determination ECU  20  transmits, to the brake device  30 , an instruction signal for automatically generating a braking force for the own vehicle  100 , regardless of an operation performed by a driver of the own vehicle  100 . Hereinafter, the automatic operation performed by the brake device  30  according to the process of the collision determination ECU  20  is referred to as automatic braking. When the automatic braking has been already started, the collision determination ECU  20  transmits, to the brake device  30 , an instruction signal for instructing the automatic braking to be continued. After the own vehicle  100  has started the braking, the collision determination ECU  20  determines whether or not a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100 , is high (step S 4 ). 
     In the process steps of step S 1  to step S 3 , when a risk that the movable object and the own vehicle  100  collide with each other is high, the automatic braking is started. Namely, a control for decreasing the travelling speed of the own vehicle  100  is executed. 
     In step S 4 , the collision determination ECU  20  determines whether or not, for example, a first to a third conditions described below are all satisfied. When all of the first to the third conditions are satisfied, a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100 , is determined to be high. 
     The first condition is that a movable object has been detected by the rear-lateral side radar  12 . 
     The second condition is that the own vehicle travelling direction distance H indicates a value that is less than or equal to a predetermined threshold value THh, and the own vehicle lateral distance W indicates a value that is less than or equal to a predetermined threshold value THw. 
     The third condition is that a predicted travelling direction distance H 2  indicates a value that is less than or equal to a predetermined threshold value THh 2 , and a predicted lateral distance W 2  indicates a value that is less than or equal to a predetermined threshold value THw 2 . The predicted travelling direction distance H 2  represents a predicted value of the own vehicle travelling direction distance H to be obtained when the collision time TTC becomes zero. The predicted lateral distance W 2  represents a predicted value of the own vehicle lateral distance W to be obtained when the collision time TTC becomes zero. Specifically, the collision determination ECU  20  firstly predicts a positional relationship between the own vehicle  100  and the movable object, which is to be obtained when the collision time TTC elapses after the current time, based on the information on the movable object, which has been previously received from the front-lateral side radar  11  and the rear-lateral side radar  12 , and performs mapping. The own vehicle travelling direction distance H and the own vehicle lateral distance W obtained based on the predicted positional relationship are calculated as the predicted travelling direction distance H 2  and the predicted lateral distance W 2 , respectively. A technique used by the collision determination ECU  20  for predicting the positional relationship between the own vehicle  100  and the movable object, to be obtained when a predetermined time elapses, is a conventionally known technique, and a detailed description thereof is not given. 
     In the process step of step S 4 , the collision determination ECU  20  is allowed to determine whether or not a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100  is high, in a simple process. Namely, the collision determination ECU  20  is allowed to easily determine whether or not a possibility that the own vehicle  100  can avoid the collision by passing in front of the movable object, is high. The process step described above is an exemplary process step of step S 4 , and the collision determination ECU  20  may perform the determination by using any manner, other than the process step described above, by which whether or not a possibility that the own vehicle  100  can avoid the collision by passing in front of the movable object is high can be determined. For example, when any one of the first to the third conditions is satisfied, the collision determination ECU  20  may determine that a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100  is high. Further, the collision determination ECU  20  may determine whether or not a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100  is high, by using any conventionally known technique. 
     When the collision determination ECU  20  determines that a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100  is low (No in step S 4 ), the process is advanced to step S 9 . 
     On the other hand, when the collision determination ECU  20  determines that a risk that the own vehicle  100  and the movable object collide with each other in the rear portion of the own vehicle  100  is high (Yes in step S 4 ), a target deceleration GT is calculated (step S 5 ). The target deceleration GT is a deceleration of the own vehicle  100  which is to be required to avoid the collision with the movable object. Specifically, the collision determination ECU  20  calculates the target deceleration GT according to the following equation (2).
 
 GT= 2 ×Vh×Vw/W− 2× Vw^ 2× H/W^ 2   (2)
 
     In equation (2), a sign “^” represents an exponentiation operator. 
     The collision determination ECU  20  calculates the target deceleration GT, and lessens the automatic braking according to the target deceleration GT (step S 6 ). Specifically, the collision determination ECU  20  controls a braking force by the brake device  30  such that the deceleration G of the own vehicle  100  becomes less than or equal to the target deceleration GT. When the collision determination ECU  20  has performed the process step of step S 6 , the process is advanced to step S 9 . 
     In the process steps of step S 4  to step S 6 , when a possibility that the movable object collides with the own vehicle  100  in the rear lateral side portion of the own vehicle  100  is high, the braking force of the automatic braking is reduced such that the deceleration of the own vehicle  100  becomes less than or equal to the target deceleration GT. Namely, when a possibility that a collision can be avoided by the own vehicle  100  passing in front of the movable object is high, the accelerated state or the decelerated state of the own vehicle  100  is controlled such that the deceleration of the own vehicle  100  becomes less than or equal to the target deceleration GT. Therefore, a collision between the own vehicle  100  and the movable object can be avoided with enhanced certainty. Further, in the process step of step S 5 , the target deceleration GT can be calculated in a simple calculation process. 
     The calculation method for calculating the target deceleration GT as described above is an exemplary one. The collision determination ECU  20  may calculate the target deceleration GT by using any conventionally known method. Further, the collision determination ECU  20  may previously store the target deceleration GT as a constant in the storage device, and control the braking force of the automatic braking based on the constant. When a constant is used as the target deceleration GT, a process step of calculating the target deceleration GT can be omitted, so that the control for the decelerated state of the own vehicle  100  can be executed in a relatively short time period. Further, the collision determination ECU  20  may execute any vehicle control, other than the above-described control, which enables the deceleration G of the own vehicle  100  to be decreased. 
     On the other hand, in step S 7 , the collision determination ECU  20  determines whether or not the automatic baking is being executed. When the collision determination ECU  20  determines that the automatic braking is being executed (Yes in step S 7 ), the automatic braking is stopped (step S 8 ). Specifically, the collision determination ECU  20  transmits, to the brake device  30 , an instruction signal for stopping the automatic braking. On the other hand, when the collision determination ECU  20  determines that the automatic braking is not being executed (No in step S 7 ), the process step of step S 8  is skipped, and the process is advanced to step S 9 . 
     In the process steps of step S 1 , step S 2 , step S 7 , and step S 8 , when no movable object is detected by the front-lateral side radar  11  or the rear-lateral side radar  12 , or when a risk that the movable object and the own vehicle  100  collide with each other is low, the automatic braking is stopped. Further, in a state where the automatic braking has not been executed, the state is maintained. 
     In step S 9 , the collision determination ECU  20  determines whether or not the IG power source of the own vehicle  100  is set to be off When the collision determination ECU  20  determines that the IG power source is not set to be off, the process is returned to step S 1 . On the other hand, when the collision determination ECU  20  determines that the IG power source is set to be off, the process of the flow chart shown in  FIG. 3  is ended. By the process step of step S 9  being performed, while the IG power source of the own vehicle  100  is on, the process steps described above are repeatedly performed. 
     Next, a state in which the collision avoidance apparatus  1  enables the own vehicle  100  to avoid a collision with the movable object will be described with reference to  FIG. 4  to  FIG. 6 . Hereinafter, an exemplary case in which the other vehicle  200  is detected as the movable object approaching the own vehicle  100  will be described.  FIG. 4  is a plan view illustrating a positional relationship between the own vehicle  100  and the other vehicle  200 , which is obtained at time t 1 .  FIG. 5  is a plan view illustrating a positional relationship between the own vehicle  100  and the other vehicle  200 , which is obtained at time t 2  at which a predetermined time period has elapsed since time t 1 .  FIG. 6  is a plan view illustrating a positional relationship between the own vehicle  100  and the other vehicle  200 , which is obtained at time t 3  at which a predetermined time period has elapsed since time t 2 . 
     As shown in  FIG. 4 , at time t 1 , the other vehicle  200  is travelling on a road orthogonal to a road on which the own vehicle  100  is travelling. Namely, the other vehicle  200  approaches the right lateral side portion of the own vehicle  100  at an intersection. When the front-lateral side radar  11  detects the other vehicle  200 , the collision determination ECU  20  determines whether or not a risk that the other vehicle  200  and the own vehicle  100  collide with each other is high, in the process steps of step Si and step S 2  described above. When the collision determination ECU  20  determines that a risk that the other vehicle  200  and the own vehicle  100  collide with each other is high, the automatic braking is started, to decelerate the own vehicle  100 . Such an automatic braking is performed in order to avoid a collision between the own vehicle  100  and the other vehicle  200  by the own vehicle  100  reducing its speed or stopping short of the other vehicle  200 , and the other vehicle  200  passing in front of the own vehicle  100 . 
     On the other hand, even when the own vehicle  100  reduces its speed, it may be difficult for the other vehicle  200  to pass in front of the own vehicle  100 , depending on a state in which the other vehicle  200  is travelling. For example, as shown in  FIG. 5 , in a case where, at the time  2  at which the predetermined time period has elapsed since time t 1 , the own vehicle  100  has been travelling on a route on which the other vehicle  200  travels, even if the own vehicle  100  is decelerated, it is difficult for the other vehicle  200  to pass in front of the own vehicle  100 . In such a case, the collision determination ECU  20  reduces the braking force of the automatic braking in the process steps of step S 6  to step S 8  described above. 
     When the braking force of the automatic braking is reduced, the deceleration of the own vehicle  100  is reduced. Namely, the own vehicle  100  continues to travel without reducing its speed or stopping. Therefore, as shown in  FIG. 6 , at time t 3  at which the predetermined time period has elapsed since time t 2 , the own vehicle  100  passes in front of the other vehicle  200 . Thereafter, the other vehicle  200  passes behind the own vehicle  100 . Namely, a collision between the own vehicle  100  and the other vehicle  200  can be avoided. 
     As described above, the collision avoidance apparatus  1  according to the first embodiment of the present invention can execute an appropriate vehicle control for avoiding a collision between the own vehicle  100  and a movable object. Namely, the collision avoidance apparatus  1  can avoid a collision between the own vehicle  100  and a movable object more assuredly as compared to in conventional arts. 
     (Second Embodiment) 
     In the first embodiment, an exemplary case is described in which the collision determination ECU  20  controls the brake device  30  to reduce the braking force of the automatic braking, thereby controlling the accelerated state or decelerated state of the own vehicle  100 . However, the collision determination ECU  20  may control a driving device of the own vehicle  100 , to accelerate the own vehicle  100 . Hereinafter, a collision avoidance apparatus  2  according to a second embodiment will be described. 
       FIG. 7  is a block diagram illustrating a structure of the collision avoidance apparatus  2  according to the second embodiment. As shown in  FIG. 7 , the collision avoidance apparatus  2  includes the front-lateral side radar  11 , the rear-lateral side radar  12 , the speed sensor  13 , the deceleration sensor  14 , the collision determination ECU  20 , the brake device  30 , and an engine control device  31 . The same components as described for the first embodiment are denoted by the same corresponding reference numerals, and a detailed description thereof is not given. 
     The engine control device  31  is a device for controlling the number of times an engine of the own vehicle  100  rotates, to control a driving force for the own vehicle  100 . The engine control device  31  is typically an electronically controlled engine throttle. The engine control device  31  is electrically connected to the collision determination ECU  20 . The engine control device  31  controls a driving force for the own vehicle  100  according to an instruction signal received from the collision determination ECU  20 . 
     Next, a process performed by the collision determination ECU  20  according to the second embodiment will be described with reference to  FIG. 8 .  FIG. 8  is a flow chart showing a process performed by the collision determination ECU  20  according to the second embodiment. In the flow chart shown in  FIG. 8 , the same process steps as described with reference to the flow chart of  FIG. 3  for the first embodiment are denoted by the same corresponding numbers, and a detailed description thereof is not given. 
     In the flow chart shown in  FIG. 8 , the collision determination ECU  20  firstly performs process steps of step Si to step S 4  described above. The collision determination ECU  20  performs process steps of step S 5 - 2  and step S 6 - 2  described below, instead of the process steps of step S 5  and step S 6 . 
     Specifically, when the collision determination ECU  20  determines in step S 4  that a risk that the own vehicle  100  collides with the movable object in the rear portion f the own vehicle  100  is high (Yes in step S 4 ), the automatic braking is stopped (step S 5 - 2 ). More specifically, the collision determination ECU  20  transmits, to the brake device  30 , an instruction signal for stopping the automatic braking. When the collision determination ECU  20  has completed the process step of step S 5 - 2 , an acceleration control is executed (step S 6 - 2 ). Specifically, the collision determination ECU  20  outputs, to the engine control device  31 , an instruction signal for increasing the driving force. When the collision determination ECU  20  has completed the process step of step S 6 - 2 , the process is advanced to step S 9 . 
     In the process steps of step S 5 - 2  and step S 6 - 2 , when a risk that the own vehicle  100  collides with the movable object in the rear portion of the own vehicle  100  is high, the accelerated state or decelerated state of the own vehicle  100  is controlled so as to accelerate the own vehicle  100 . Therefore, in a case where the own vehicle  100  attempts to avoid a collision by passing in front of the movable object, even if a speed of the own vehicle is insufficient, the collision between the own vehicle  100  and the movable object can be avoided with enhanced certainty. 
     As described above, the collision avoidance apparatus  2  according to the second embodiment of the present invention can execute an appropriate vehicle control for avoiding a collision between the own vehicle  100  and a movable object, similarly to the collision avoidance apparatus  1  according to the first embodiment. 
     The collision determination ECU  20  according to the second embodiment may perform the process steps of step S 5 - 2  and step S 6 - 2  after the process step of step S 5  described above has been performed. Specifically, when the collision determination ECU  20  determines in step S 4  that a risk that the own vehicle  100  collides with the movable object in the rear portion of the own vehicle  100  is high (Yes in step S 4 ), the target deceleration GT is calculated in the process step of step S 5 . When the collision determination ECU  20  has completed the process step of step S 5 , the automatic braking is stopped in the process step of step S 5 - 2 . The collision determination ECU  20  accelerates the own vehicle  100  in the process step of step S 6 - 2  such that the deceleration G becomes less than or equal to the target deceleration GT. 
     In the second embodiment, an exemplary case in which the driving device of the own vehicle  100  is an engine is described. However, the driving device of the own vehicle  100  may be an electric motor. In such a structure, the collision determination ECU  20  outputs, to a control device for controlling the electric motor, an instruction signal for controlling a driving force by the electric motor. 
     In each of the embodiments described above, an exemplary case in which the front-lateral side radar  11  and the rear-lateral side radar  12  are mounted to the own vehicle  100  on the right side of the own vehicle  100  is described. However, the front-lateral side radar  11  and the rear-lateral side radar  12  may be mounted to the own vehicle  100  on the left side of the own vehicle  100 . Further, the front-lateral side radar  11  and the rear-lateral side radar  12  may be mounted on each of the right and left sides thereof. 
     Industrial Applicability 
     The collision avoidance apparatus according to the present invention is useful as, for example, a collision avoidance apparatus that enables execution of an appropriate vehicle control for avoiding collision between vehicles. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
           1 ,  2  collision avoidance apparatus 
           11  front-lateral side radar 
           12  rear-lateral side radar 
           13  speed sensor 
           14  deceleration sensor 
           20  collision determination ECU  20   
           30  brake device 
           31  engine control device 
           100  own vehicle 
           200  another vehicle