Patent Publication Number: US-10766416-B2

Title: Alarm system for vehicle

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an alarm system for a vehicle. In particular, it relates to an alarm system for a vehicle that raises an alarm in response to an object approaching the vehicle. 
     Description of the Related Art 
     Systems that raise an alarm in response to an object approaching have been proposed. For example, Japanese Patent Laid-Open No. 2012-160103 discloses a system that determines the possibility of an object located at the side of a vehicle colliding with the vehicle based on the distance between the object and the vehicle or the relative velocity of the object with respect to the vehicle. When the system determines that the object can collide with the vehicle, the system raises an alarm to the driver of the vehicle. Japanese Patent Laid-Open No. 2012-160103 also discloses that an alarm is raised when a vehicle is to turn left or right at an intersection or the like. 
     Consider a case where a vehicle running in a predetermined lane turns left or right at an intersection to enter a lane intersecting with the predetermined lane. In the following description, when the vehicle enters the intersection, of a plurality of lanes intersecting with the lane in which the vehicle is running, a lane closer to the vehicle will be referred to as a “first lane”, and an opposing lane to the first lane that is further from the vehicle will be referred to as a “second lane”. For example, in a situation where the traffic laws prescribe that vehicles run in the left lane, such as in Japan, the lane which the vehicle having turned left at the intersection enters corresponds to the “first lane”, and the lane which the vehicle having turned right at the intersection enters corresponds to the “second lane”. 
     With a two-lane, two-way road (that is, a road provided with no median strip or the like), for example, the lateral distance between vehicles in the opposing lanes may decrease even though the vehicles are running safely. In particular, when a vehicle turns left or right at an intersection to enter the first lane, the vehicle temporarily comes closer to another vehicle in the second lane. Such an approach is inevitable because of the structure of the intersection and does not necessarily lead to collision of the vehicle with the other vehicle with high possibility. In addition, since the driver tends to direct their attention in the direction of traveling of the vehicle, the driver is highly likely to recognize the other vehicle in the second lane. Even in such a situation, the system described in Japanese Patent Laid-Open No. 2012-160103 can raise an alarm based on the approach of the other vehicle and irritate the driver. 
     When the vehicle turns right or left at the intersection to enter the second lane, the driver tends to direct more of their attention in the direction of traveling of the vehicle and less attention in the opposite direction. In such a case, an alarm concerning another vehicle approaching from the opposite direction needs to be raised with high reliability. 
     As can be seen, when the vehicle is to turn left or right at the intersection, an alarm needs to be appropriately raised according to the state of running of the vehicle. 
     The present invention has been devised to solve the problems described above, and an object of the present invention is to provide an alarm system for a vehicle that can appropriately raise an alarm to a driver of a vehicle that is entering an intersection. 
     SUMMARY OF THE INVENTION 
     To solve the problems described above, the present invention provides an alarm system for a vehicle, comprising: an alarm line setting part that sets an alarm line that extends forward from the vehicle; an object detection part that detects an object on a side of the vehicle; a collision determination part that determines whether or not the object crosses the alarm line within a predetermined time; an alarm unit control part that activates an alarm unit when the collision determination part determines that the object crosses the alarm line within the predetermined time; and a left/right-turn determination part that determines that the vehicle is to turn left or right at an intersection, wherein, provided that, when the vehicle enters the intersection, of a plurality of lanes at the intersection that intersect with a lane in which the vehicle is running, a lane closer to the vehicle is defined as a first lane, and an opposing lane to the first lane that is further from the vehicle is defined as a second lane; the alarm line setting part sets a length of the alarm line at a first length when the vehicle is running in a straight line; the alarm line setting part and sets the length of the alarm line at a length different from the first length when the vehicle is to turn left or right at the intersection to enter the first lane or the second lane. 
     With this arrangement, when the object will cross the alarm line within the predetermined time, it can be determined that the object can collide with the vehicle, and an alarm can be raised. The alarm line setting part sets the length of the alarm line at different lengths between when the vehicle is running in a straight line and when the vehicle is turn left or right at the intersection to enter the first lane or the second lane. In this way, the alarm line can be set according to the state of running of the vehicle, and the determination of collision can be made based on the alarm line. As a result, alarms that are raised even though the possibility of an object colliding with the vehicle is low can be reduced, or an alarm can be raised to alert the driver to an object that is approaching from the direction to which the driver tends to pay less attention. 
     According to the present invention, preferably, the alarm line setting part sets the length of the alarm line at a second length shorter than the first length when the vehicle is to turn left or right at the intersection to enter the first lane. 
     With this arrangement, when the vehicle is to turn left or right at the intersection to enter the first lane, the alarm line is set to be shorter than when the vehicle is running in a straight line. As a result, even when the vehicle temporarily comes closer to an object in the second lane when the vehicle is entering the first lane, a useless alarm based on the approach can be suppressed. 
     According to the present invention, preferably, the alarm line setting part sets, as the alarm line, a right alarm line for an object on a right side and a left alarm line that is set for an object on a left side independently from the right alarm line; the alarm line setting part sets the length of the right alarm line at the second length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part sets the length of the left alarm line at the second length when the vehicle is to turn left at the intersection to enter the first lane. 
     With this arrangement, the possibility of an object on the right side of the vehicle colliding with the vehicle and the possibility of an object on the left side of the vehicle colliding with the vehicle can be independently determined based on the right alarm line and the left alarm line, respectively. As a result, the precision of the determination can be improved. 
     Furthermore, when the vehicle is to turn right at the intersection to enter the first lane (provided that the traffic laws prescribe that vehicles run in the right lane, such as in the U.S.), the alarm line setting part sets the length of the right alarm line at the second length. Furthermore, when the vehicle is to turn left at the intersection to enter the first lane (provided that the traffic laws prescribe that vehicles run in the left lane, such as in Japan), the alarm line setting part sets the length of the left alarm line at the second length. In this way, even when the vehicle temporarily comes closer to an object in the second lane when the vehicle is entering the first lane, a useless alarm based on the approach can be suppressed. 
     That is, with this arrangement, both improvement of the precision of the determination and suppression of a useless alarm can be achieved. 
     According to the present invention, preferably, the alarm line setting part sets the length of the left alarm line at the first length or a third length longer than the first length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part sets the length of the right alarm line at the first length or the third length when the vehicle is to turn left at the intersection to enter the first lane. 
     With this arrangement, the precision of determination of collision of an object on the side opposite to the direction in which the vehicle is to travel can be improved. That is, with this arrangement, when the vehicle is entering the first lane, an alarm concerning an object that is apt to escape attention of the driver can be raised with reliability while suppressing a useless alarm based on the vehicle coming closer to an object in the second lane. 
     According to the present invention, preferably, the alarm line setting part sets the length of the alarm line at a fourth length longer than the first length when the vehicle is to turn left or right at the intersection to enter the second lane. 
     With this arrangement, the precision of the determination of collision of an object on the side opposite to the direction in which the vehicle is to travel can be improved. That is, with this arrangement, when the vehicle is entering the second lane, an alarm concerning an object that is apt to escape attention of the driver can be raised with reliability. 
     According to the present invention, preferably, the left/right-turn determination part determines that the vehicle is to turn left or right at the intersection based on at least one of a turn signal switch and a steering angle. 
     With this arrangement, it can be simply determined that the vehicle is to turn left or right at an intersection. 
     The present invention can provide an alarm system for a vehicle that can appropriately raise an alarm to a driver of a vehicle that is entering an intersection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an alarm system for a vehicle according to a first embodiment of the present invention; 
         FIG. 2  is a diagram for illustrating determination of collision performed by the alarm system for a vehicle shown in  FIG. 1 ; 
         FIG. 3  is a diagram for illustrating determination of collision at an intersection; 
         FIG. 4  is a diagram for illustrating determination of collision at the intersection; 
         FIG. 5  is a diagram for illustrating determination of collision at the intersection; 
         FIG. 6  is a flowchart showing a process performed by an ECU shown in  FIG. 1 ; 
         FIG. 7  is a flowchart showing a process performed by the ECU shown in  FIG. 1 ; 
         FIG. 8  is a diagram for illustrating determination of collision performed by an alarm system for a vehicle according to a second embodiment; and 
         FIG. 9  is a diagram for illustrating determination of collision at the intersection. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components are denoted by like reference numerals throughout the drawings, and redundant descriptions thereof will be omitted. 
     First Embodiment 
     First, with reference to  FIG. 1 , a configuration of an alarm system  1  for a vehicle (referred to simply as an alarm system  1 , hereinafter) according to a first embodiment will be described.  FIG. 1  is a block diagram showing the alarm system  1 . 
     The alarm system  1  is mounted on a vehicle and raises an alarm to the driver of the vehicle to alert the driver. In this specification, the vehicle on which the alarm system  1  is mounted will be referred to as a “vehicle  2 ”. The alarm system for a vehicle according to the present invention can be applied not only to a four-wheeled vehicle but also to a two-wheeled vehicle. 
     In this specification, the direction in which the vehicle  2  runs forward is defined as “forward”, and the direction in which the vehicle  2  runs backward is defined as “backward”. The left side of the vehicle running forward is defined as “left”, and the right side of the vehicle running forward is defined as “right”. 
     The alarm system  1  includes a side radar  31 , an external camera  32 , a navigation device  33 , a turn signal switch  34 , and a steering sensor  35 . The alarm system  1  further includes a speaker  41 , a display  42 , a turn signal  43 , and an electronic control unit (ECU)  5 . 
     The side radar  31  is used to detect the presence of an object outside of the vehicle  2 , the velocity of the object, and the distance between the object and an alarm line, which will be described later. Detectable objects include a vehicle, a structure fixed on a road, and a pedestrian, for example. The vehicle is not limited to a four-wheeled vehicle but may be any running body, such as a two-wheeled vehicle or a bicycle. As described later, the detections described above performed by the side radar  31  are targeted to an object in a detection region set at a side of the vehicle  2 . The side radar  31  is a millimeter wave radar (which has an operating frequency of 76 GHz to 77 GHz), for example, and has antennas directed to the left and right of the vehicle  2 . Each antenna may be a single antenna used for both transmission and reception or a set of a transmitting antenna element and a receiving antenna element. The side radar  31  transmits a measuring wave from the antennas to the sides of the vehicle  2  and receives a reflection wave from an object. The side radar  31  transmits a signal corresponding to the received reflection wave to the ECU  5 . 
     The external camera  32  takes an image of a range including the detection region of the side radar  31  and obtains image information. The external camera  32  is an image sensor, for example, and is installed on a rear view mirror (not shown) or the like of the vehicle  2 . The external camera  32  transmits a signal corresponding to the obtained image information. 
     The navigation device  33  provides predetermined information to a passenger of the vehicle  2 . The navigation device  33  stores map information or obtains map information by communicating with a server outside the vehicle  2 . The map information includes information about roads, intersections, traffic lights, buildings or the like. The navigation device  33  has a sensor that detects the location of the vehicle  2 , such as a global positioning system (GPS) sensor or a self-contained navigation sensor. The navigation device  33  determines the location of the vehicle  2  on a map, audibly or visually provides information about the location, and transmits a signal corresponding to the information to the ECU  5 . 
     The turn signal switch  34  accepts a selective operation on a turn signal lever (not shown) by the driver (that is, an operation of selecting at least one of turn signals  43  (see  FIG. 2 ) provided on left and right side parts of the vehicle  2 ). The turn signal switch  34  transmits a signal corresponding to turn on/off of the turn signal  43 . 
     The steering sensor  35  detects a steering direction and a steering angle of a steering wheel of the vehicle  2 . The steering sensor  35  has an encoder, for example, and counts slits that rotate with the steering wheel. The steering sensor  35  transmits a signal corresponding to the detected steering direction and steering angle to the ECU  5 . 
     The speaker  41  and the display  42  are examples of alarm devices of an alarm unit according to the present invention. The speaker  41  operates based on a received control signal and raises an alarm by outputting an alarm or other sound. The display  42  is a liquid crystal panel, for example. The display  42  operates based on a received control signal and raises an alarm by displaying a picture, text or the like. 
     The turn signals  43  are directional indicators provided on left and right side parts of the vehicle  2  (see  FIG. 2 ). The turn signal  43  operates based on a received control signal and blinks to inform that the vehicle  2  will turn. 
     The ECU  5  is a controller that controls equipment by transmitting and receiving signals. The ECU  5  may be partially or wholly formed by an analog circuit or formed as a digital processor. The ECU  5  includes an alarm line setting part  51 , an object detection part  52 , a collision determination part  53 , an alarm unit control part  54 , a turn signal control part  55 , and a left/right-turn determination part  56 . 
       FIG. 1  shows functions of the ECU  5  in the form of blocks. However, the analog circuit or the software module incorporated in the digital processor of the ECU  5  is not necessarily divided as shown in  FIG. 1 . That is, the functional blocks shown in  FIG. 1  may be further divided, or some of the functional blocks may be integrated into a single functional block. Those skilled in the art can modify the internal configuration of the ECU  5  as appropriate, as far as the processes described later can be performed. 
     The alarm line setting part  51  sets an alarm line. The alarm line is a virtual line set in the vicinity of the vehicle  2 , which is used for determination of collision by the collision determination part  53 . The alarm line will be described in more detail later. 
     The object detection part  52  detects the direction of movement of an object outside the vehicle  2 , the distance of the object from an alarm line, and the relative velocity of the object with respect to the alarm line. Specifically, the object detection part  52  performs a predetermined calculation based on a signal received from the side radar  31  and performs the detections based on the calculation result. 
     The collision determination part  53  performs determination of collision. In determination of collision, it is determined whether or not an object outside the vehicle  2  will cross the alarm line within a predetermined time. The determination of collision will be described in more detail later. 
     The alarm unit control part  54  transmits a control signal to the speaker  41  or the display  42  based on the result of the determination of collision by the collision determination part  53 . Specifically, the alarm unit control part  54  transmits a control signal to activate the speaker  41  or the display  42  when the collision determination part  53  determines that the object can collide with the vehicle  2 . 
     The turn signal control part  55  transmits a control signal to the turn signal(s) based on the signal received from the turn signal switch  34 . Specifically, based on the signal received from the turn signal switch  34 , the turn signal control part  55  transmits a control signal to at least one of the turn signals  43  provided on the left and right side parts of the vehicle  2  to activate the turn signal(s)  43 . 
     The left/right-turn determination part  56  determines whether or not the vehicle  2  is to turn left or right at an intersection. Specifically, the left/right-turn determination part  56  determines whether or not the vehicle  2  is located in the vicinity of an intersection based on signals received from the external camera  32  or the navigation device  33 . The left/right-turn determination part  56  further determines whether or not the vehicle  2  is to turn left or right based on signals received from the turn signal switch  34  or the steering sensor  35 . The “intersection” is not limited to a crossroad but may be a T junction, a roundabout intersection or the like. 
     Next, with reference to  FIG. 2 , the determination of collision performed by the alarm system  1  will be described.  FIG. 2  is a diagram for illustrating the determination of collision performed by the alarm system  1 . 
     When the vehicle  2  is stopped or running at a relatively low velocity (10 km/h or less, for example), the alarm line setting part  51  (see  FIG. 1 ) of the ECU  5  sets a right alarm line  61  and a left alarm line  62 , as shown in  FIG. 2 . The right alarm line  61  and the left alarm line  62  are invisible virtual lines. The right alarm line  61  is set at a predetermined distance (1 m or less, for example) in the right direction from the right edge of the vehicle  2 , and the left alarm line  62  is set at a predetermined distance (1 m or less, for example) in the left direction from the left edge of the vehicle  2 . That is, the distance between the right alarm line  61  and the left alarm line  62  is greater than the width of the vehicle  2 . 
     The right alarm line  61  and the left alarm line  62  extend in the forward direction of the vehicle  2  from a base line BL as a base end. The base line BL is a virtual line set rearward from the front edge of the vehicle  2  by a predetermined distance (2 m, for example). The right alarm line  61  and the left alarm line  62  extend straight substantially in parallel with each other in the longitudinal direction of the vehicle  2 . 
     The object detection part  52  (see  FIG. 1 ) of the ECU  5  sets a detection region A 11  at the right side of the right alarm line  61 , and a detection region A 21  at the left side of the left alarm line  62 . The detection region A 11  is defined by the right alarm line  61 , a line at a predetermined distance in the right direction from the right alarm line  61 , and lines extending from the right alarm line  61  at approximately 135° with respect to the right alarm line  61 . The detection region A 21  is defined by the left alarm line  62 , a line at a predetermined distance in the left direction from the left alarm line  62 , and lines extending from the left alarm line  62  at approximately 135° with respect to the left alarm line  62 . The object detection part  52  detects an object in the detection regions A 11  and A 21  based on the signal received from the side radar  31 . 
     In the following, the determination of collision of another vehicle  91  in the detection region A 11  approaching the vehicle  2  will be described. When a virtual line L 91  extending in the direction of movement of the other vehicle  91  intersects with the right alarm line  61 , the collision determination part  53  (see  FIG. 1 ) of the ECU  5  calculates a time to collision (TTC) for the other vehicle  91  with respect to the right alarm line  61  based on information detected by the object detection part  52 . In general, the TTC is expressed by the following formula f1, provided that the distance between relevant objects is defined as L 0 , and the relative velocity between the objects is defined as V 0 . The relative velocity V 0  of the object is positive when the object is approaching the alarm line. The formula f1 is derived from the equation of motion on the condition that the object is moving at a constant velocity. 
     
       
         
           
             
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                   TTC 
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     The collision determination part  53  determines whether or not the other vehicle  91  will cross the right alarm line  61  within a predetermined time based on the calculated TTC. Specifically, when the TTC is equal to or less than a preset threshold (2 seconds, for example), the collision determination part  53  determines that the other vehicle  91  will cross the right alarm line  61  within a predetermined time (2 seconds, for example). Then, the other vehicle  91  can collide with the vehicle  2 . 
     As described above, the alarm system  1  determines whether the object at the right side of the vehicle  2  can collide with the vehicle  2  or not with respect to the right alarm line  61 . Similarly, the alarm system  1  determines whether the object at the left side of the vehicle  2  can collide with the vehicle  2  or not with respect to the left alarm line  62 . 
     When the vehicle  2  is stopped or is running in a straight line, the alarm line setting part  51  sets the length of the right alarm line  61  and the left alarm line  62  at L1 (7 m, for example). L1 is an example of a first length according to the present invention. The alarm line setting part  51  can also set the length of the right alarm line  61  and the left alarm line  62  at a different length than L1. Specifically, the alarm line setting part  51  may set the length of the right alarm line  61  and the left alarm line  62  at L2 (5 m, for example), which is shorter than L1, or L3 (9 m, for example), which is longer than L1 (that is, L2&lt;L1&lt;L3). L2 is an example of a second length according to the present invention, and L3 is an example of a third length and a fourth length according to the present invention. 
     Such a change in length of the right alarm line  61  and the left alarm line  62  has an effect on the determination of collision. As an example, the determination of collision in a case where other vehicles  92  and  93  in the detection region A 21  are approaching the left alarm line  62  will be described. When the length of the left alarm line  62  is set at L3, both virtual lines L 92  and L 93  extending in the direction of traveling of the other vehicles  92  and  93  intersect with the left alarm line  62 . Therefore, the collision determination part  53  performs the determination of collision of the other vehicles  92  and  93 . 
     However, when the length of the left alarm line  62  is set at L1 or L2, the virtual line L 93  extending in the direction of traveling of the other vehicle  93  does not intersect with the left alarm line  62 . Therefore, the collision determination part  53  does not perform the determination of collision of the other vehicle  93  and performs only the determination of collision of the other vehicle  92 . That is, the alarm unit control part  54  (see  FIG. 1 ) of the ECU  5  does not activate the speaker  41  or the display  42  (see  FIG. 1 ) in response to the other vehicle  93  approaching. 
     The alarm system  1  configured described above is particularly advantageous in a situation where there is a blind spot for the driver of the vehicle  2 . An example of the situation where there is a blind spot for the driver is a situation where there is a wall near the lane in which the vehicle is running or a situation where there is another vehicle parked around the vehicle  2 . That is, when an object in the blind spot is approaching the vehicle  2  and can collide with the vehicle  2 , at least one of the speaker  41  and the display  42  raises an alarm to alert the driver to the object so that the driver can operate the vehicle to avoid collision. 
     Next, with reference to  FIGS. 3 to 5 , determination of collision at an intersection will be described.  FIGS. 3 to 5  are diagrams for illustrating determination of collision at an intersection  83 .  FIGS. 3 to 5  show situations where the traffic laws prescribe that vehicles run in the left lane, such as in Japan. 
     At the intersection  83 , a lane  80  intersects with lanes  81  and  82 . In the following description, the lane closer to the vehicle  2  when the vehicle  2  enters the intersection  83  will be referred to as a “first lane  81 ”, and the opposing lane to the first lane  81  that is further from the vehicle  2  will be referred to as a “second lane  82 ”. 
     As shown in  FIG. 3 , when the vehicle  2  running in a straight line in the lane  80  approaches the intersection  83  and decelerates (to 10 km/h or less), the alarm system  1  sets the right alarm line  61  and the left alarm line  62 . At this point, the length of the right alarm line  61  and the left alarm line  62  is set at L1 (see  FIG. 2 ). 
     Now, consider a comparative example in which a vehicle  2   a  is to turn left at the intersection  83 . When the vehicle  2   a  turns left to enter the first lane  81 , the vehicle  2   a  may temporarily come closer to another vehicle  94  in the second lane  82 . In such a case, when the length of the left alarm line  62  is still set at L1, the virtual line in the direction of traveling of the other vehicle  94  may intersect with the left alarm line  62 . 
     When the virtual line intersects with the left alarm line  62 , the alarm system  1  calculates the TTC for the other vehicle  94 . When the TTC is equal to or less than a threshold, the alarm system  1  determines that the other vehicle  94  can cross the left alarm line  62  within a predetermined time. That is, the alarm system  1  determines that the other vehicle  94  can collide with the vehicle  2   a  and raises an alarm to the driver of the vehicle  2   a.    
     However, such an approach of the other vehicle  94  to the vehicle  2   a  is inevitable because of the structure of the intersection  83  and does not necessarily lead to collision of the other vehicle  94  with the vehicle  2   a  with high possibility. In addition, since the driver tends to direct their attention in the direction of traveling of the vehicle  2   a , the driver is highly likely to recognize the other vehicle  94  in the second lane  82 . When the alarm system  1  raises an alarm concerning the other vehicle  94  in such a case, the alarm can irritate the driver. On the other hand, when the vehicle  2   a  is to turn left to enter the first lane  81 , another vehicle  95  or the like approaching from the right is apt to escape attention of the driver. 
     In view of this, when the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81 , the alarm system  1  according to the first embodiment sets the length of the right alarm line  61  and the left alarm line  62  as shown in  FIG. 4 . 
     First, the alarm system  1  sets the length of the left alarm line  62  at L2 (see  FIG. 2 ). That is, the alarm system  1  reduces the length of the left alarm line  62  compared with when the vehicle  2  is running in a straight line. As a result, even when the vehicle  2  temporarily comes closer to the other vehicle  94  in the second lane  82  when the vehicle  2  enters the first lane  81 , the vertical line in the direction of traveling of the other vehicle  94  is less likely to intersect with the left alarm line  62 . As a result, the alarm system  1  is less likely to determine that the other vehicle  94  crosses the left alarm line  62  and thus can reduce useless alarms based on the approach of the vehicle  94 . 
     In addition, the alarm system  1  sets the length of the right alarm line  61  at L3 (see  FIG. 2 ). That is, the alarm system  1  increases the length of the right alarm line  61  compared with when the vehicle  2  is running in a straight line. As a result, when the vehicle  2  enters the first lane  81 , the virtual line in the direction of traveling of the other vehicle  95  is more likely to intersect with the right alarm line  61 . As a result, the precision of the determination of collision with the other vehicle  95  approaching from the right, which is apt to escape attention of the driver, can be improved. 
     When the vehicle  2  is to turn right at the intersection  83  to enter the second lane  82 , the alarm system  1  sets the length of the left alarm line  62  at L3 (see  FIG. 2 ), as shown in  FIG. 5 . That is, the alarm system  1  increases the length of the left alarm line  62  compared with when the vehicle  2  is running in a straight line. As a result, when the vehicle  2  enters the second lane  82 , the virtual line in the direction of traveling of the other vehicle  94  is more likely to intersect with the left alarm line  62 . As a result, the precision of the determination of collision with the other vehicle  94  approaching from the left, which is apt to escape attention of the driver, can be improved. 
     Next, with reference to  FIGS. 6 and 7 , processes performed by the ECU  5  (see  FIG. 1 ) will be described.  FIGS. 6 and 7  are flowcharts showing processes performed by the ECU  5 . The processes are repeatedly performed at a predetermined period. In the following description, for ease of explanation, any processing that is performed by a functional block of the ECU  5  in a strict sense will be described as being performed by the ECU  5 . 
     First, in Step S 10  shown in  FIG. 6 , the ECU  5  determines whether or not the velocity v of the vehicle  2  falls within a range from 0 km/h to 10 km/h inclusive. The ECU  5  determines the velocity v of the vehicle  2  based on the signal received from the speed sensor (not shown). When it is determined that the velocity v falls within the range (YES in Step S 10 ), the ECU  5  proceeds to Step S 11 . 
     In Step S 11 , the ECU  5  sets the alarm lines. With reference to  FIG. 7 , a process of the ECU  5  setting the alarm lines will be described. 
     In Step S 30  shown in  FIG. 7 , the ECU  5  determines whether or not the vehicle  2  is located in the vicinity of an intersection. The ECU  5  performs the determination based on the signal received from the external camera  32  or the navigation device  33  (see  FIG. 1 ). When it is determined that the vehicle  2  is located in the vicinity of an intersection (YES in Step S 30 ), the ECU  5  proceeds to Step S 31 . 
     In Step S 31 , the ECU  5  determines whether or not the turn signal switch  34  (see  FIG. 1 ) is in an ON state. That is, the ECU  5  determines whether or not any turn signal  43  is operating. When it is determined that the turn signal switch  34  is in the ON state (when YES in Step S 31 ), the ECU  5  proceeds to Step S 32 . 
     In Step S 32 , the ECU  5  determines whether or not the steering angle of the steering wheel of the vehicle  2  is equal to or greater than 90°. The ECU  5  determines the steering angle of the steering wheel based on the signal received from the steering sensor  35  (see  FIG. 1 ). When it is determined that the steering angle is equal to or greater than 90° (when YES in Step S 32 ), the ECU  5  proceeds to Step S 33 . 
     In Step S 33 , the ECU  5  determines whether or not the steering wheel of the vehicle  2  is being turned to the left. That is, the ECU  5  determines whether or not the vehicle  2  is to change the direction of traveling to the left. The ECU  5  determines the steering direction of the steering wheel based on the signal received from the steering sensor  35 . When the steering angle of the steering wheel is equal to or greater than 90° (YES in Step S 32 ), and the steering direction of the same is left (YES in Step S 33 ), the vehicle  2  is considered to be turning left. When it is determined that the steering wheel is being turned to the left (when YES in Step S 33 ), the ECU  5  proceeds to Step S 34 . 
     In Step S 34 , the ECU  5  sets the length of the right alarm line  61  at L3 (see  FIGS. 2 and 4 ). In Step S 35  following Step S 34 , the ECU  5  sets the length of the left alarm line  62  at L2 (see  FIGS. 2 and 4 ). Alternatively, in Step S 34 , the ECU  5  may set the length of the right alarm line  61  at L1. 
     On the other hand, when it is determined in Step S 33  that the steering wheel of the vehicle  2  is not being turned to the left (when NO in Step S 33 , or in other words, when the steering wheel is being turned to the right), the ECU  5  proceeds to Step S 36 . When the steering angle of the steering wheel is equal to or greater than 90° (YES in Step S 32 ), and the steering direction of the same is right (NO in Step S 33 ), the vehicle  2  is considered to be turning right. 
     In Step S 36 , the ECU  5  sets the length of the right alarm line  61  at L1 (see  FIGS. 2 and 5 ). In Step S 37  following Step S 36 , the ECU  5  sets the length of the left alarm line  62  at L3 (see  FIGS. 2 and 5 ). 
     When it is determined in Step S 30  that the vehicle  2  is not located in the vicinity of an intersection (NO in Step S 30 ), when it is determined in Step S 31  that the turn signal switch  34  is not in the ON state (NO in Step S 31 ), or when it is determined in Step S 32  that the steering angle of the steering wheel of the vehicle  2  is not equal to or greater than 90° (NO in Step S 32 ), the ECU  5  proceeds to Step S 38 . 
     In Step S 38 , the ECU  5  sets the length of the right alarm line  61  at L1. In Step S 39  following Step S 38 , the ECU  5  sets the length of the left alarm line  62  at L1. 
     Referring to  FIG. 6  again, the process performed by the ECU  5  will be described. After completing setting of the right alarm line  61  and the left alarm line  62  in Step S 11 , the ECU  5  proceeds to Step S 12 . 
     In Step S 12 , the ECU  5  determines whether or not, in the detection region A 11  or the detection region A 21  (see  FIG. 2 ), there is an object (referred to simply as a “crossing object”, hereinafter) whose virtual line extending in the direction of traveling thereof intersects with the right alarm line  61  or the left alarm line  62 . The ECU  5  performs the determination based on the signal received from the side radar  31  (see  FIG. 1 ). When it is determined that there is a crossing object (YES in Step S 12 ), the ECU  5  proceeds to Step S 13 . 
     In Step S 13 , the ECU  5  calculates the TTC for the crossing object. The ECU  5  calculates the distance between the crossing object and the right alarm line  61  or the left alarm line  62  and the velocity of the crossing object with respect to the alarm line (that is, the relative velocity) based on the signal received from the side radar  31 . Furthermore, the ECU  5  calculates the TTC according to the formula f1 described above. When a plurality of crossing objects are detected, the ECU  5  calculates the TTC for each crossing object. After completing calculation of the TTC, the ECU  5  proceeds to Step S 14 . 
     In Step S 14 , the ECU  5  determines whether or not the TTC calculated in Step S 13  is equal to or less than 2 seconds. When it is determined that the TTC is equal to or less than 2 seconds (YES in Step S 14 ), the ECU  5  proceeds to Step S 15 . 
     In Step S 15 , the ECU  5  determines whether or not the TTC calculated in Step S 13  is more than 1 second. When the TTC is more than 1 second, the necessity for alarm is relatively low. When it is determined that the TTC is more than 1 second (YES in Step S 15 ), the ECU  5  proceeds to Step S 16 . 
     In Step S 16 , the ECU  5  activates the display  42  (see  FIG. 1 ). Specifically, the ECU  5  transmits a control signal to the display  42 , and in response to the control signal, the display  42  provides an indication that an object outside the vehicle  2  can collide with the vehicle  2 . After making the display  42  display the alarm, the ECU  5  ends the process. That is, when the TTC is equal to or less than 2 seconds (YES in Step S 14 ) and more than 1 second (YES in Step S 15 ), the necessity for alarm is relatively low, so that the ECU  5  does not activate the speaker  41  (see  FIG. 1 ) but activates the display  42  to raise an alarm to the driver of the vehicle  2 . 
     On the other hand, when the TTC is equal to or less than 1 second, the necessity for alarm is relatively high. When it is determined in Step S 15  that the TTC calculated in Step S 13  is not more than 1 second (NO in Step S 15 ), the ECU  5  proceeds to Step S 17 . 
     In Step S 17 , the ECU  5  determines whether or not the velocity v of the vehicle  2  is 0 km/h. In other words, the ECU  5  determines whether or not the vehicle  2  is stopped. When the vehicle  2  is stopped, the necessity for alarm is relatively low compared with when the vehicle  2  is running. Therefore, when it is determined that the velocity v of the vehicle  2  is 0 km/h (YES in Step S 17 ), the ECU  5  proceeds to Step S 16 . As described above, in Step S 16 , the ECU  5  makes the display  42  display an alarm and ends the process. That is, when the TTC is equal to or less than 1 second (NO in Step S 15 ), and the vehicle  2  is stopped (YES in Step S 17 ), the ECU  5  does not activate the speaker  41  but activates the display  42  to raise an alarm to the driver of the vehicle  2 . 
     On the other hand, when it is determined in Step S 17  that the velocity v of the vehicle  2  is not 0 km/h (NO in Step S 17 ), or in other words, when the vehicle  2  is not stopped, the ECU  5  proceeds to Step S 18 . 
     When the vehicle  2  is not stopped, the necessity for alarm is higher than when the vehicle  2  is stopped. In Step S 18 , the ECU  5  activates the display  42  to display an alarm and activates the speaker  41  to raise an alarm by producing an alarm or other sound in Step S 19 . That is, when the TTC is equal to or less than 1 second (NO in Step S 15 ), and the vehicle  2  is not stopped (NO in Step S 17 ), the ECU  5  activates the display  42  and the speaker  41  to raise more alarms to the driver of the vehicle  2 . 
     When it is determined in Step S 10  that the velocity v of the vehicle  2  does not fall within the predetermined range (NO in Step S 10 ), when it is determined in Step S 12  that there is no crossing object (NO in Step S 12 ), or when it is determined in Step S 14  that the TTC is not equal to or less than 2 seconds (NO in Step S 14 ), the ECU  5  activates neither the display  42  nor the speaker  41  and ends the process. 
     [Effects and Advantages] 
     According to the first embodiment, when an object will cross any alarm line within a predetermined time, it can be determined that the object can collide with the vehicle  2 , and an alarm can be raised. The alarm line setting part  51  sets the length of the alarm lines at different lengths between when the vehicle  2  is running in a straight line and when the vehicle  2  is turn left or right at the intersection  83  to enter the first lane  81  or the second lane  82 . In this way, the alarm lines can be set according to the state of running of the vehicle  2 , and the determination of collision can be made based on the alarm lines. As a result, alarms that are raised even though the possibility of an object colliding with the vehicle  2  is low can be reduced, or an alarm can be raised to alert the driver to an object that is approaching from the direction to which the driver tends to pay less attention. 
     When the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81 , the alarm line setting part  51  sets the alarm lines at L2, which is shorter than L1. 
     With this arrangement, when the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81 , the left alarm line  62  is set to be shorter than when the vehicle  2  is running in a straight line. As a result, even when the vehicle  2  temporarily comes closer to an object in the second lane  82  when the vehicle  2  is entering the first lane  81 , a useless alarm based on the approach can be suppressed. 
     The alarm line setting part  51  sets the right alarm line  61 , which is set for an object on the right side of the vehicle  2 , and the left alarm line  62 , which is set for an object on the left side of the vehicle  2  independently from the right alarm line  61 . When the vehicle  2  is to turn right at the intersection to enter the second lane  82 , the alarm line setting part  51  sets the length of the right alarm line  61  at L2. When the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81 , the alarm line setting part  51  sets the length of the left alarm line  62  at L2. 
     With this arrangement, the possibility of an object on the right side of the vehicle  2  colliding with the vehicle  2  and the possibility of an object on the left side of the vehicle  2  colliding with the vehicle  2  can be independently determined based on the right alarm line  61  and the left alarm line  62 , respectively. As a result, the precision of the determination can be improved. 
     Furthermore, when the vehicle  2  is to turn right at the intersection  83  to enter the first lane  81  (provided that the traffic laws prescribe that vehicles run in the right lane, such as in the U.S.), the alarm line setting part  51  sets the length of the right alarm line  61  at L2. Furthermore, when the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81  (provided that the traffic laws prescribe that vehicles run in the left lane, such as in Japan), the alarm line setting part  51  sets the length of the left alarm line  62  at L2. In this way, even when the vehicle  2  temporarily comes closer to an object in the second lane  82  when the vehicle  2  is entering the first lane  81 , a useless alarm based on the approach can be suppressed. 
     In short, with this arrangement, both improvement of the precision of the determination and suppression of a useless alarm can be achieved. 
     When the vehicle  2  turns right at the intersection  83  to enter the first lane  81 , the alarm line setting part  51  sets the length of the left alarm line  62  at L1 or L3. When the vehicle  2  turns left at the intersection  83  to enter the first lane  81 , the alarm line setting part  51  sets the length of the right alarm line  61  at L1 or L3. 
     With this arrangement, the precision of determination of collision of an object on the side opposite to the direction in which the vehicle  2  is to travel can be improved. That is, with this arrangement, when the vehicle  2  is entering the first lane  81 , an alarm concerning an object that is apt to escape attention of the driver can be raised with reliability while suppressing a useless alarm based on the vehicle  2  coming closer to an object in the second lane  82 . 
     When the vehicle  2  is to turn left or right at the intersection  83  to enter the second lane  82 , the alarm line setting part  51  sets the length of one of the alarm lines at L3, which is shorter than L1. 
     With this arrangement, the precision of the determination of collision of an object on the side opposite to the direction in which the vehicle  2  is to travel can be improved. That is, with this arrangement, when the vehicle  2  is entering the second lane  82 , an alarm concerning an object that is apt to escape attention of the driver can be raised with reliability. 
     The left/right-turn determination part  56  determines that the vehicle  2  is turn left or right at the intersection  83  based on at least one of the turn signal switch  34  and the steering angle. 
     With this arrangement, it can be simply determined that the vehicle  2  is to turn left or right at an intersection. 
     Second Embodiment 
     Next, with reference to  FIGS. 8 and 9 , an alarm system  10  for a vehicle (referred to simply as an “alarm system  10 ”, hereinafter.) according to a second embodiment will be described.  FIG. 8  is a diagram for illustrating determination of collision by an alarm system  10 , and  FIG. 9  is a diagram for illustrating determination of collision at an intersection. 
     As with the alarm system  1  according to the first embodiment, the alarm system  10  according to the second embodiment is a system that raises an alarm to the driver of the vehicle to alert the driver. The alarm system  10  differs from the alarm system  1  according to the first embodiment in setting of the alarm lines and determination of collision. Of the components of the alarm system  10  and the controls performed by the alarm system  10 , descriptions of those that are the same as those in the first embodiment will be omitted as appropriate. 
     As shown in  FIG. 8 , the alarm system  10  only sets a central alarm line  63 . The central alarm line  63  substantially is set along the longitudinal center line of the vehicle  2 . The central alarm line  63  extends straight in the longitudinal direction of the vehicle  2  from the base line BL. 
     When the vehicle  2  is stopped or running in a straight line, the alarm system  10  sets the length of the central alarm line  63  at L1 (7 m, for example). L1 is an example of the first length according to the present invention. The alarm system  10  can also set the length of the central alarm line  63  at a length different from L1. Specifically, as shown in  FIG. 8 , the alarm system  10  may set the length of the central alarm line  63  at L2 (5 m, for example), which is shorter than L1, or L3 (9 m, for example), which is longer than L1 (that is, L2&lt;L1&lt;L3). L2 is an example of the second length according to the present invention, and L3 is an example of the fourth length according to the present invention. 
     The alarm system  10  sets a detection region A 12  on the right side of the central alarm line  63  and a detection region A 22  on the left side of the central alarm line  63 . The alarm system  10  detects an object in the detection region A 12  or the detection region A 22 . When a virtual line L 96 , L 97  or L 98  of another vehicle  96 ,  97  or  98  intersects with the central alarm line  63 , the object detection part  52  obtains information about the vehicle  96 ,  97  or  98 . 
     As with the alarm system  1  according to the first embodiment, the alarm system  10  calculates the TTC for the other vehicle  96 ,  97  or  98 . Furthermore, based on the calculated TTC, the alarm system  10  determines whether or not the other vehicle  96 ,  97  or  98  will cross the central alarm line  63  within a predetermined time. Specifically, when the TTC is equal to or less than a predetermined threshold (2 seconds, for example), the alarm system  10  determines that the vehicle  96 ,  97  or  98  will cross the central alarm line  63  within the predetermined time (2 seconds, for example). In that case, the other vehicle  96 ,  97  or  98  can collide with the vehicle  2 . 
     As shown in  FIG. 9 , when the vehicle  2  is to turn left at the intersection  83  to enter the first lane  81 , the alarm system  10  changes the length of the central alarm line  63 . That is, the alarm system  10  reduces the length of the central alarm line  63  compared with when the vehicle  2  crosses the intersection  83 , and sets the length at L2 (see  FIG. 8 ). As a result, even when the vehicle  2  temporarily comes closer to the other vehicle  94  in the second lane  82  when the vehicle  2  is entering the first lane  81 , the virtual line in the direction of traveling of the other vehicle  94  is less likely to intersect with the central alarm line  63 . As a result, the alarm system  10  is less likely to determine that the other vehicle  94  will cross the central alarm line  63 , so that a useless alarm based on such an approach can be suppressed. 
     When the vehicle  2  is to turn right at the intersection  83  to enter the second lane  82  (not shown), the alarm system  10  sets the length of the central alarm line  63  at L3 (see  FIG. 8 ). That is, the alarm system  10  increases the length of the central alarm line  63  compared with when the vehicle  2  crosses the intersection  83 . As a result, when the vehicle  2  is entering the second lane  82 , the virtual line in the direction of traveling of the other vehicle  94  is more easily intersect with the central alarm line  63 . As a result, the precision of the determination of collision of the other vehicle  94  that is approaching from the left and is apt to escape attention of the driver can be improved. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  10  alarm system for vehicle (alarm system) 
           2  vehicle 
           41  speaker (alarm device) 
           42  display (alarm device) 
           51  alarm line setting part 
           52  object detection part 
           53  collision determination part 
           54  alarm unit control part 
           56  left/right-turn determination part 
           61  right alarm line (alarm line) 
           62  left alarm line (alarm line) 
           63  central alarm line (alarm line) 
           81  first lane 
           82  second lane 
           83  intersection