Patent Publication Number: US-2023148012-A1

Title: Driving support device, driving support method, and driving support program

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving support device which is mounted on a vehicle to control a speed of the vehicle, a driving support method, and a driving support program. 
     2. Description of the Related Art 
     Hitherto, there has been known a driving support device which is mounted on a vehicle to control a speed of the vehicle (own vehicle) (hereinafter referred to as “related-art device”) (see, for example, Japanese Patent No. 6552064). Specifically, the related-art device includes a speed control device which controls, for example, an engine and brakes such that the speed of the own vehicle matches a predetermined first speed when there is no other vehicle (preceding vehicle) in front of the own vehicle. Further, the related-art device includes an image pickup device (camera) which photographs the foreground of the own vehicle and outputs obtained image data, and an image analysis device which analyzes the image data and determines (recognizes) a signal color of a traffic light in front of the own vehicle. The speed control device controls the speed of the own vehicle in accordance with the analysis result obtained by the image analysis device when the own vehicle passes through the traffic light. 
     When a traffic light enters the angle of view (field of view) of the image pickup device, the image analysis device attempts to determine the signal color of the traffic light. When the signal color of the traffic light is not determinable by the image analysis device at that time, the speed control device decelerates the own vehicle. The magnitude (absolute value) of the acceleration (negative value) at that time is relatively small. When the own vehicle approaches the traffic light and the image analysis device can determine the signal color of the traffic light, the speed control device controls the speed of the own vehicle in accordance with the determination result. Specifically, when the signal color of the traffic light is “yellow” or “red,” the own vehicle is further decelerated and stopped before the traffic light. Meanwhile, when the signal color of the traffic light is “green,” the speed control device causes the own vehicle to travel at a constant speed to pass through the traffic light. 
     There is assumed a case in which the own vehicle passes through a first traffic light, which is the nearest traffic light positioned in front of the own vehicle, and then a second traffic light, which is the traffic light next in front from the first traffic light. In this case, in the related-art device, when the signal color of the first traffic light is not determinable by the image analysis device at the time at which the first traffic light enters the angle of view of the image pickup device, the speed control device decelerates the own vehicle. Then, when the image analysis device determines that “the signal color of the first traffic light is ‘green’,” the speed control device causes the own vehicle to travel at a constant speed to pass through the first traffic light. When the second traffic light is not within the angle of view of the image pickup device at the time at which the own vehicle passes through the first traffic light, the speed control device accelerates the own vehicle. When the own vehicle advances, the second traffic light enters the angle of view of the image pickup device, and the signal color of the second traffic light is not determinable by the image analysis device at that time, the speed control device decelerates the own vehicle again. In this case, when the distance between the first traffic light and the second traffic light is relatively short, acceleration and deceleration of the own vehicle are repeated within a relatively short period of time, and hence there is a fear in that the occupants of the vehicle may feel uncomfortable. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a driving support device capable of reducing discomfort of occupants of a vehicle. 
     In order to solve the above-mentioned problem, according to at least one embodiment of the present invention, there is provided a driving support device ( 1 ) which is mounted on an own vehicle (V). The driving support device includes: a speed control device ( 10 ) configured to control a drive device ( 20 ) and a braking device ( 30 ) of the own vehicle such that a speed of the own vehicle matches a predetermined first target value (Vd) when another vehicle is not present in front of the own vehicle; a signal color recognition device ( 53 ) configured to recognize a signal color of a traffic light (S 1 , S 2 ) present in a predetermined area extending in front from the own vehicle; and a position detection device ( 55 ) configured to detect a position of the own vehicle and a position of the traffic light. The signal color of the traffic light is recognizable by the signal color recognition device when a distance to the traffic light positioned in front of the own vehicle is equal to or shorter than a first predetermined value (Lr). The speed control device is configured to: control the drive device and the braking device of the own vehicle before a first point (Pr 1 ) such that a speed of the own vehicle at a time at which the own vehicle reaches the first point is equal to or lower than a second target value (V 1 ) which is a lower speed than the predetermined first target value, the first point being a point at which a distance to a first traffic light (S 1 ), which is the nearest traffic light positioned in front of the own vehicle, is the first predetermined value; and control the drive device and the braking device such that, when the signal color recognition device recognizes a signal color of the first traffic light, the signal color is green, and a distance (DS) between the first traffic light (S 1 ) and a second traffic light (S 2 ) next in front from the first traffic light is equal to or shorter than a predetermined threshold value (DSth), the own vehicle travels at a constant speed equal to or lower than the second target value until the signal color recognition device recognizes a signal color of the second traffic light. 
     When the signal color of the first traffic light is “green” and the distance between the first traffic light and the second traffic light is relatively short (equal to or shorter than a predetermined value), the speed control device of the driving support device according to the at least one embodiment of the present invention causes the own vehicle to travel at a constant speed (suppresses acceleration) until the signal color recognition device recognizes the signal color of the second traffic light. Therefore, it is possible to suppress the repetition of acceleration and deceleration when the interval between the first traffic light and the second traffic light is relatively short. As a result, according to the at least one embodiment of the present invention, the discomfort of the occupants of the vehicle can be reduced. 
     In the driving support device according to one aspect of the present invention, the speed control device is configured to decelerate the own vehicle at a predetermined acceleration from a predetermined point before the first point such that the speed of the own vehicle at the time at which the own vehicle reaches the first point matches the second target value. 
     In the driving support device according to the one aspect of the present invention, the speed control device is configured to calculate a distance (L 0 ) for which the own vehicle travels until a vehicle speed matches the second target value (V 1 ) when the own vehicle decelerates from a current vehicle speed (V 0 ) at the predetermined acceleration (a 1 ), and to determine a point positioned before the first point by the calculated distance as the predetermined point (Psd). 
     Further, in those cases, the predetermined acceleration may have a magnitude of 0.1 G (G: gravitational acceleration) or less. 
     In the above-mentioned related-art device, when it is recognized that a traffic light has entered the angle of view (frame) of the image pickup device, and the image analysis device starts determination of the signal color of the traffic light but the signal color is not determinable, the speed control device gradually decelerates the vehicle. Then, when the signal color of the traffic light is determinable by the image analysis device, the speed control device accelerates the vehicle, decelerates the vehicle, or causes the vehicle to travel at a constant speed in accordance with the signal color. Accordingly, for example, in a case in which the road has a large curve before the traffic light, when the traffic light enters the angle of view of the image pickup device after the distance between the vehicle and the traffic light becomes relatively short, the speed control device decelerates the vehicle at a relatively large acceleration in order to stop the vehicle. 
     In contrast, with the speed control device of the driving support device according to the aspects of the present invention, the vehicle is gently decelerated even before the own vehicle reaches the first point, regardless of the recognition result of the signal color recognition device. Therefore, even when the signal color can be recognized by the signal color recognition device at the time at which the distance between the own vehicle and the traffic light has become relatively short, the speed of the own vehicle is relatively low at that time. As a result, even when the signal color of the traffic light is “yellow” or “red” at that time, the speed control device can decelerate the own vehicle at a relatively small acceleration (acceleration which does not cause discomfort to the occupants) to stop the own vehicle before the traffic light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of a driving support device according to at least one embodiment of the present invention. 
         FIG.  2    is a plan view for illustrating an outline of constant speed traveling control. 
         FIG.  3    is a graph for showing how a vehicle decelerates from a deceleration start point. 
         FIG.  4    is a graph for showing a relationship between a vehicle speed (initial speed V 0 ) and the deceleration start point. 
         FIG.  5    is a graph for showing a change in a vehicle speed Vs when a signal color of a traffic light S 1  is “yellow” or “red” at a recognizable point Pr 1 . 
         FIG.  6    is a graph for showing a change in the vehicle speed Vs when the signal color of the traffic light S 1  is “green” at the recognizable point Pr 1  and a distance between the traffic light S 1  and a traffic light S 2  is relatively long. 
         FIG.  7    is a graph for showing a change in the vehicle speed Vs when the signal color of the traffic light S 1  is “green” at the recognizable point Pr 1  and the distance between the traffic light S 1  and the traffic light S 2  is relatively short. 
         FIG.  8    is a graph for showing a change in the vehicle speed Vs when the signal color of the traffic light S 1  is not determinable at the recognizable point Pr 1 , the signal color successfully determined thereafter is “green,” and the distance between the traffic light S 1  and the traffic light S 2  is relatively long. 
         FIG.  9    is a graph for showing a change in the vehicle speed Vs when the signal color of the traffic light S 1  is not determinable at the recognizable point Pr 1 , the signal color successfully determined thereafter is “green,” and the distance between the traffic light S 1  and the traffic light S 2  is relatively short. 
         FIG.  10 A  is a graph for showing a change in the vehicle speed Vs when a vehicle V reaches the recognizable point Pr 1  without the vehicle speed Vs exceeding a target value V 1 , the signal color of the traffic light S 1  is “green,” and the distance between the traffic lights is relatively long. 
         FIG.  10 B  is a graph for showing a change in the vehicle speed Vs when the vehicle V reaches the recognizable point Pr 1  without the vehicle speed Vs exceeding the target value V 1  and the signal color of the traffic light S 1  is “yellow” or “red.” 
         FIG.  10 C  is a graph for showing a change in the vehicle speed Vs when the vehicle V reaches the recognizable point Pr 1  without the vehicle speed Vs exceeding the target value V 1 , the signal color of the traffic light S 1  is “green,” and the distance between the traffic lights is relatively short. 
         FIG.  11    is a flow chart for illustrating a constant speed traveling program. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     (Outline of Configuration) 
     As illustrated in  FIG.  1   , a driving support device  1  according to at least one embodiment of the present invention is mounted on a vehicle V. As described in detail later, the driving support device  1  controls an engine, brakes, and the like of the vehicle V such that the vehicle V travels at a constant speed or follows a preceding vehicle based on information acquired from sensors mounted on the vehicle V. The control is hereinafter referred to as “cruise control.” The vehicle on which the driving support device  1  is mounted may be referred to as “own vehicle” in order to distinguish the vehicle from other vehicles. 
     (Specific Configuration) 
     As illustrated in  FIG.  1   , the driving support device  1  includes a driving support ECU  10 , a drive device  20 , a braking device  30 , a shift switching device  40 , ambient sensors  50 , and an operation switch  60 . 
     The driving support ECU  10  includes a microcomputer including, for example, a CPU  10   a , a RAM  10   b , and a ROM  10   c . As used herein, “ECU” means an electronic control unit, and the ECU includes a microcomputer including, for example, a CPU, a RAM, and a ROM. The CPU implements various functions by executing instructions stored in the ROM. 
     The driving support ECU  10  is connected to other ECUs (engine ECU  21 , brake ECU  31 , and SBW ECU  41  described later) via a controller area network (CAN) in a manner that enables information to be transmitted and received to and from each other. 
     The drive device  20  generates a driving force, and applies the driving force to drive wheels out of wheels (left front wheel, right front wheel, left rear wheel, and right rear wheel). The drive device  20  includes, for example, an engine ECU  21 , an engine actuator  22 , an internal combustion engine  23 , a transmission  24 , and a driving force transmission mechanism (not shown) which transmits a driving force to the wheels. The engine ECU  21  is connected to the engine actuator  22 . The engine actuator  22  includes a throttle valve actuator which changes an opening degree of a throttle valve of the internal combustion engine  23 . The engine ECU  21  can change a torque generated by the internal combustion engine  23  by driving the engine actuator  22 . The torque generated by the internal combustion engine  23  is transmitted to the drive wheels via the transmission  24  and the driving force transmission mechanism (for example, a drive shaft). As described above, the engine ECU  21  controls the driving force of the vehicle V by controlling the engine actuator  22 . 
     When the vehicle V to which the driving support device  1  is applied is a hybrid electric vehicle (HEV) or a battery electric vehicle (BEV), the engine ECU  21  can control the driving force of the vehicle generated by any one or both of “an internal combustion engine and an electric motor” serving as a vehicle drive source. 
     The braking device  30  applies a braking force to the wheels. The braking device  30  includes a brake ECU  31 , a hydraulic circuit  32 , and a brake caliper  33 . The hydraulic circuit  32  includes, for example, a reservoir, an oil pump, various valve devices, and a hydraulic sensor (which are not shown). The brake caliper  33  is a hydraulic actuator including a cylinder and a piston. When oil is supplied to the cylinder, the piston is pushed out of the cylinder. A brake pad is arranged at the tip of the piston, and the brake pad is pressed against a brake disc. The hydraulic circuit  32  adjusts the hydraulic pressure in the cylinder of the brake caliper  33  in response to a command from the brake ECU  31 . As a result, the braking force of the wheel (brake disc) generated by the brake caliper  33  is controlled. 
     The shift switching device  40  switches a shift position of the transmission  24 . The shift switching device  40  includes, for example, the shift-by-wire (SBW) ECU  41 , an SBW actuator  42 , and a shift switching mechanism  43 . The SBW ECU  41  is connected to the SBW actuator  42 . The SBW actuator  42  controls the shift switching mechanism  43  in response to a shift switching command from the SBW ECU  41  to switch the shift position of the transmission  24 . 
     The ambient sensors  50  are configured to acquire vehicle peripheral information including information on three-dimensional objects present around the vehicle V and information on separation lines of a road surface around the vehicle V. The three-dimensional objects are, for example, moving objects, such as an automobile (another vehicle), a pedestrian, or a bicycle, and fixed objects, such as a guardrail or a traffic light. 
     The ambient sensors  50  include a radar sensor  51 , an ultrasonic sensor  52 , a camera  53 , a vehicle speed sensor  54 , and a navigation system  55 . 
     The radar sensor  51  includes a radar transmitting/receiving unit and a signal processing unit (which are not shown). The radar transmitting/receiving unit radiates radio waves in the millimeter wave band (hereinafter referred to as “millimeter waves”) into an area around the vehicle, and receives the millimeter waves reflected by a three-dimensional object present within a radiation range (that is, reflected waves). The signal processing unit acquires information representing, for example, a distance between the vehicle V and the three-dimensional object, a relative speed between the vehicle V and the three-dimensional object, and a relative position (direction) of the three-dimensional object with respect to the vehicle V based on, for example, a phase difference between the transmitted millimeter waves and the received reflected waves, an attenuation level of the reflected waves, and a period of time from the transmission of the millimeter waves to the reception of the reflected waves, and outputs the acquired information to the driving support ECU  10 . 
     The ultrasonic sensor  52  transmits ultrasonic waves in pulses into a predetermined range around the vehicle, and receives the reflected waves reflected by the three-dimensional object. The ultrasonic sensor  52  can detect, for example, a “reflection point, which is a point on the three-dimensional object from which the transmitted ultrasonic waves are reflected,” and a “distance between the ultrasonic sensor and the three-dimensional object” based on the period of time from the transmission of the ultrasonic waves to the reception of the reflected waves. 
     The camera  53  includes an image pickup device  531  and an image analysis device  532 . The image pickup device  531  is, for example, a digital camera having a built-in image pickup element being a charge-coupled device (CCD) or a CMOS image sensor (CIS). The image pickup device  531  is arranged on an upper part of a front windshield glass. The image pickup device  531  outputs image data obtained by photographing the foreground of the vehicle at a predetermined frame rate to the image analysis device  532 . The image analysis device  532  analyzes the acquired image data, and acquires information on a target object positioned in front of the vehicle V from the image. The image analysis device  532  acquires (recognizes), for example, a signal color of a traffic light positioned in front of the vehicle V in a traveling direction thereof. In order for the image analysis device  532  to accurately determine whether or not an aggregate of pixels exhibiting a red circle in the image data is light emitted from a signal portion of the traffic light, it is required that the vehicle V be somewhat close to the traffic light. For example, when the vehicle V approaches the traffic light and a distance Lvs to the traffic light becomes “120 m,” it becomes possible for the image analysis device  532  to accurately determine the signal color of the traffic light. In the following description, the maximum value of the distance Lvs (distance between the vehicle V and the traffic light) at which the image analysis device  532  can accurately determine the signal color of the traffic light is referred to as “recognizable distance Lr.” Further, a point positioned before the traffic light by the recognizable distance Lr is referred to as “recognizable point Pr.” The recognizable distance Lr depends on the specifications of the image pickup device  531 . The recognizable distance Lr is experimentally calculated in the development stage of the vehicle V, and results of the experiment are stored in the ROM of the driving support ECU  10 . 
     The vehicle speed sensor  54  includes a wheel speed sensor which generates one pulse signal (wheel pulse signal) each time the wheel of the own vehicle rotates by a predetermined angle. The vehicle speed sensor  54  measures the number of pulses of the wheel pulse signal transmitted from the wheel speed sensor in unit time, calculates a rotation speed (wheel speed) of each wheel based on the measured number of pulses, and calculates a vehicle speed Vs (actual vehicle speed) of the own vehicle based on the wheel speed of each wheel. The vehicle speed sensor  54  transmits data representing the vehicle speed Vs to the driving support ECU  10 . 
     The navigation system  55  receives GPS signals from a plurality of satellites, and detects a current position PV (latitude and longitude) of the vehicle V based on the plurality of received GPS signals. Further, the navigation system  55  stores map data representing a map. The map data includes road information representing roads and traffic light position information indicating installation positions of traffic lights. The navigation system  55  transmits vehicle position data representing the detected current position PV to the driving support ECU  10 . Moreover, the navigation system  55  has a function of calculating a distance between two points (distance along the road). For example, the navigation system  55  calculates the distance Lvs from the current position of the vehicle V to the traffic light (nearest traffic light) that the vehicle V is to pass first when traveling straight along the road on which the vehicle V is currently traveling, and transmits data on the distance to the driving support ECU  10 . 
     The operation switch  60  is an operation element (for example, a push button type switch operation element) which is operated when a driver requests the start or end of cruise control. When the driver operates the operation switch  60  (when the driver presses the button) during a period in which cruise control is not being executed, the operation switch  60  transmits a cruise control start signal indicating that “the driver requests the start of cruise control (cruise control start request)” to the driving support ECU  10 . Meanwhile, when the driver operates the operation switch  60  during a period in which cruise control is being executed, the operation switch  60  transmits a cruise control end signal indicating that “the driver requests the end of cruise control (cruise control end request)” to the driving support ECU  10 . 
     Further, the operation switch  60  includes an operation element for designating a target value Dd of an inter-vehicle distance in cruise control and a target value Vd of the vehicle speed during constant speed traveling, which are described later. 
     (Cruise Control) 
     &lt;Following Control&gt; 
     When the driving support ECU  10  receives the cruise control start signal from the operation switch  60 , the driving support ECU  10  executes cruise control (ACC). That is, the driving support ECU  10  determines, based on the information acquired from the ambient sensors  50 , whether or not there is another vehicle (preceding vehicle) to be followed. When it is determined that a preceding vehicle to be followed is present, the driving support ECU  10  detects an inter-vehicle distance between the preceding vehicle and the vehicle V (own vehicle) based on the information acquired from the ambient sensors  50 . Next, the driving support ECU  10  controls the drive device  20 , the braking device  30 , and the shift switching device  40  (hereinafter referred to as “drive device and the like”) such that the inter-vehicle distance (actual measurement value) detected in the manner described above matches the target value Dd set in advance. However, when the signal color of the traffic light acquired from the camera  53  is “yellow” or “red,” the driving support ECU  10  decelerates the vehicle V and stops the vehicle V before the traffic light even when the preceding vehicle does not start deceleration. 
     &lt;Constant Speed Traveling Control&gt; 
     Meanwhile, when it is determined that a preceding vehicle to be followed is not present, the driving support ECU  10  accelerates or decelerates the vehicle V at a predetermined acceleration a 0  such that the vehicle speed Vs matches the target value Vd set in advance. Further, the driving support ECU  10  accelerates the vehicle V, decelerates the vehicle V, or causes the vehicle V to travel at a constant speed in accordance with the signal color of the traffic light. That is, when the signal color of the traffic light acquired from the camera  53  during travel of the vehicle V is “green,” the driving support ECU  10  causes the vehicle V to travel as it is (accelerates the vehicle V or causes the vehicle V to travel at a constant speed) to pass through the traffic light. Meanwhile, when the signal color of the traffic light acquired from the camera  53  is “yellow” or “red,” the driving support ECU  10  decelerates the vehicle V and stops the vehicle V before the traffic light. When the signal color of the traffic light becomes “green,” the driving support ECU  10  accelerates the vehicle V and causes the vehicle V to pass through the traffic light. As used herein, “traveling at a constant speed (constant speed traveling)” means that the vehicle V travels at a constant speed. 
     Next, the constant speed traveling control is specifically described with reference to  FIG.  2   . When the driving support ECU  10  starts the constant speed traveling control, the driving support ECU  10  acquires from the navigation system  55  a point PS 1  at which the nearest traffic light S 1  positioned in front of the vehicle V is installed and a recognizable point Pr 1  corresponding to the traffic light S 1 . Further, the driving support ECU  10  repeatedly acquires the current position PV of the vehicle V from the navigation system  55  at predetermined time intervals. Moreover, the driving support ECU  10  repeatedly acquires the vehicle speed Vs from the vehicle speed sensor  54  at predetermined time intervals. 
     The driving support ECU  10  controls the drive device and the like from before the recognizable point Pr 1  such that the vehicle speed Vs is equal to or lower than a predetermined target value V 1  at the time at which the vehicle V reaches the recognizable point Pr 1 . The target value V 1  is defined in advance as a speed at which the vehicle V can be stopped before the traffic light S 1  by decelerating the vehicle V from the recognizable point Pr 1  at an acceleration a 2  which does not cause discomfort to the driver. 
     Specifically, as shown in  FIG.  3   , when the vehicle speed Vs before the recognizable point Pr 1  is faster than the target value V 1 , the driving support ECU  10  decelerates the vehicle V at an acceleration a 1  smaller than the acceleration a 2  when the vehicle V arrives at a predetermined point (deceleration start point Psd 1  described later). The magnitude (absolute value) of the acceleration a 1  is a predetermined value A 1 . The predetermined value A 1  is, for example, “0.1 G” (G: gravitational acceleration). The predetermined value A 1  may be a value smaller than “0.1 G.” 
     As described above, the absolute value of the acceleration a 1  at the time of decelerating the vehicle V is set to be relatively small. Accordingly, as shown in  FIG.  4   , when the vehicle speed Vs before the recognizable point Pr 1  (hereinafter also referred to as “initial speed V 0 ”) is a relatively high speed (Vda of  FIG.  4   ), the driving support ECU  10  is required to start deceleration from a point at which the vehicle V is relatively far from the recognizable point Pr 1  (Psd 1   a  of  FIG.  4   ). Meanwhile, when the initial speed V 0  is slightly higher than the target value V 1  (Vdb of  FIG.  4   ), the driving support ECU  10  may start deceleration from a point relatively close to the recognizable point Pr 1  (Psd 1   b  of  FIG.  4   ). The driving support ECU  10  calculates the point at which deceleration is to start before the traffic light S 1  (deceleration start point Psd 1 ) as follows. 
     First, the driving support ECU  10  calculates, when the vehicle speed is decelerated from a current vehicle speed Vs to the acceleration a 1 , a distance L 0  (see  FIG.  2   ) for which the vehicle V travels until the vehicle speed Vs matches the target value V 1 . Then, the driving support ECU  10  determines a point positioned before the recognizable point Pr 1  by the distance L 0  as the deceleration start point Psd 1  corresponding to the current vehicle speed Vs. For example, in a situation in which the vehicle V is accelerated (or decelerated) in order to make the vehicle speed Vs match the target value Vd, the vehicle speed Vs (initial speed V 0 ) is gradually increased (or decreased). Thus, the driving support ECU  10  repeatedly calculates (updates) the deceleration start point Psd 1  at predetermined time intervals. 
     When the vehicle V reaches the deceleration start point Psd 1  (when the current position PV matches the deceleration start point Psd 1 ), the driving support ECU  10  decelerates the vehicle V at the acceleration a 1 . 
     When the vehicle V reaches the recognizable point Pr 1 , the driving support ECU  10  acquires the signal color of the traffic light S 1  from the camera  53 . When the acquired signal color is “yellow” or “red,” as shown in  FIG.  5   , the driving support ECU  10  decelerates the vehicle V at the acceleration a 2 , and stops the vehicle V before the traffic light S 1  (point PS 1 ). As described above, the magnitude (absolute value) of the acceleration a 2  is a predetermined value A 2  larger than the predetermined value A 1 . The driving support ECU  10  acquires the signal color of the traffic light S 1  from the camera  53  at the predetermined time intervals. When the acquired signal color becomes “green,” the driving support ECU  10  accelerates the vehicle V at the acceleration a 0  to cause the vehicle V to pass through the traffic light S 1 , and starts the calculation of the deceleration start point Psd 2  corresponding to the traffic light S 2 . The upper limit value of the vehicle speed Vs at that time is the target value Vd. Further, the magnitude (absolute value) of the acceleration a 0  is a predetermined value A 0  larger than the predetermined value A 1 . 
     Meanwhile, when the signal color acquired at the recognizable point Pr 1  is “green,” the driving support ECU  10  acquires, from the navigation system  55 , a distance DS (see  FIG.  2   ) between the traffic light S 1  and the traffic light S 2  next in front from the traffic light S 1 . 
     &lt;When Distance DS is Relatively Long&gt; 
     When the distance DS is longer than a threshold value DSth, as shown in  FIG.  6   , the driving support ECU  10  accelerates the vehicle V at the acceleration a 0  to cause the vehicle V to pass through the traffic light S 1 , and starts the calculation of a deceleration start point Psd 2 . The upper limit value of the vehicle speed Vs at that time is the target value Vd. 
     &lt;When Distance DS is Relatively Short&gt; 
     When the distance DS is equal to or shorter than the threshold value DSth, as shown in  FIG.  7   , the driving support ECU  10  stops the acceleration/deceleration of the vehicle V, and causes the vehicle V to travel at a constant speed to pass through the traffic light S 1 . That is, the vehicle speed Vs at the time at which the vehicles V passes through the traffic light S 1  is the vehicle speed Vs at the time at which the vehicle V reaches the recognizable point Pr 1  (that is, the target value V 1 ). In this case, when the signal color of the traffic light S 2  next in front from the traffic light S 1  is “yellow” or “red,” the speed is reduced to a speed at which the vehicle V can be safely stopped. Therefore, the driving support ECU  10  is not required to calculate the deceleration start point Psd 2  before the traffic light S 2 . As a result, when the vehicle V passes through the traffic light S 1 , the driving support ECU  10  attempts to acquire the determination result of the signal color of the traffic light S 2  from the camera  53  at predetermined time intervals. Then, when the driving support ECU  10  has successfully acquired the signal color of the traffic light S 2 , the driving support ECU  10  executes the same control as the control executed when the vehicle V passes through the traffic light S 1  in accordance with the acquired signal color. 
     Incidentally, there may be a case in which, for example, the road on which the vehicle V is traveling has a large curve immediately before the traffic light S 1 , and the signal color of the traffic light S 1  is not determinable by the camera  53  at the time at which the vehicle V reaches the recognizable point Pr 1 . In such a case, the driving support ECU  10  tentatively determines that the signal color of the traffic light S 1  is “red,” and decelerates the vehicle V at the acceleration a 2  from the recognizable point Pr 1 . When the vehicle V advances further, the camera  53  can determine the signal color of the traffic light S 1 , and the determined signal color is “yellow” or “red,” the driving support ECU  10  further decelerates the vehicle V at the acceleration a 2 , and stops the vehicle V before the traffic light S 1 . Meanwhile, as shown in  FIG.  8   , when the camera  53  can determine the signal color of the traffic light S 1  and the determined signal color is “green,” the driving support ECU  10  acquires the distance DS. When the distance DS is longer than the threshold value DSth, the driving support ECU  10  accelerates the vehicle Vat the acceleration a 0  to cause the vehicle V to pass through the traffic light S 1 , and starts the calculation of the deceleration start point Psd 2 . Meanwhile, when the distance DS is equal to or shorter than the threshold value DSth, as shown in  FIG.  9   , the driving support ECU  10  stops the deceleration of the vehicle V, and causes the vehicle V to travel at a constant speed to pass through the traffic light S 1 . That is, the vehicle speed Vs at the time at which the vehicles V passes through the traffic light S 1  is lower than the target value V 1 , which is the speed at the time at which the vehicle V reaches the recognizable point Pr 1 . 
     Further, as shown in  FIG.  10 A  to  FIG.  10 C , there may be a case in which the vehicle speed Vs is constantly lower than the target value V 1  before the vehicle V reaches the recognizable point Pr 1  (for example, when the target value Vd is equal to or higher than the target value V 1 , but the vehicle V is accelerated from a state in which the vehicle speed Vs is lower than the target value V 1  and reaches the recognizable point Pr 1  before the target value V 1  is reached). In such a case, under the state in which the vehicle speed Vs is equal to or lower than the target value V 1 , the driving support ECU  10  matches the deceleration start point Psd 1  with the recognizable point Pr 1  (initializes the deceleration start point Psd 1 ). As a result, deceleration control is not executed until the vehicle V reaches the recognizable point Pr 1 . In this case, the vehicle speed Vs at the time at which the vehicle V reaches the recognizable point Pr 1  is lower than the target value V 1 , but the subsequent control mode is the same as the control mode executed when the vehicle speed Vs is the target value V 1 . That is, the driving support ECU  10  accelerates/decelerates the vehicle V in accordance with the signal color of the traffic light S 1  and the distance DS (see  FIG.  10 A ,  FIG.  10 B , or  FIG.  10 C ). 
     There may be a case in which the vehicle V is quite close to the traffic light S 1  when the cruise control start command is received. For example, in the following cases, there is a high likelihood that it is difficult for the driving support ECU  10  to safely control the vehicle V.
         When the current position PV is between the recognizable point Pr 1  and the point PS 1     When the current position PV is before the recognizable point Pr 1 , but the vehicle speed Vs is a relatively high speed and even when the vehicle is decelerated at the acceleration a 1  from the current time, the vehicle speed Vs may not match the target value V 1  at the recognizable point Pr 1 .       

     In such cases, the driving support ECU  10  notifies the driver that cruise control is not executable, and does not execute the cruise control. 
     Next, with reference to  FIG.  11   , operation (constant speed traveling program implementing the above-mentioned constant speed traveling control) of the CPU of the driving support ECU  10  (hereinafter simply referred to as “CPU”) is specifically described. When there is no preceding vehicle to be followed during a period in which cruise control is being executed, the CPU starts constant speed traveling processing from Step  100 . Next, in Step  101 , the CPU initializes a flag F to “1” indicating that “acceleration/deceleration is permitted.” Then, the CPU advances the process to Step  102 . 
     When the process advances to Step  102 , the CPU acquires, from the navigation system  55 , the recognizable point Pr (Pr 1 , Pr 2 ) corresponding to the nearest traffic light S (S 1 , S 2 ) positioned in front of the vehicle V. Then, the CPU advances the process to Step  103 . 
     When the process advances to Step  103 , the CPU determines whether or not the value of the flag F is “1”. That is, the CPU determines whether acceleration/deceleration is permitted. When the value of the flag F is “1” (“Yes” in Step  103 ), the CPU advances the process to Step  104 . 
     When the process advances to Step  104 , the CPU controls the drive device and the like such that the vehicle speed Vs matches the target value Vd. Then, the CPU advances the process to Step  105 . 
     When the process advances to Step  105 , the CPU determines whether or not the vehicle speed Vs exceeds the target value V 1 . When the vehicle speed Vs exceeds the target value V 1  (“Yes” in Step  105 ), the CPU advances the process to Step  106 . 
     When the process advances to Step  106 , the CPU calculates the deceleration start point Psd (Psd 1 , Psd 2 ). Then, the CPU advances the process to Step  107 . 
     When the process advances to Step  107 , the CPU determines whether or not the vehicle V has reached the deceleration start point Psd (Psd 1 , Psd 2 ). That is, the CPU determines whether or not the current position PV matches the deceleration start point Psd. When the vehicle V has reached the deceleration start point Psd (“Yes” in Step  107 ), the CPU advances the process to Step  108 . 
     In Step  107 , when the vehicle V has not yet reached the deceleration start point Psd (“No” in Step  107 ), the CPU returns the process to Step  103 . 
     When the process advances to Step  108 , the CPU decelerates the vehicle V at the acceleration a 1 . Then, the CPU advances the process to Step  109 . 
     When the process advances to Step  109 , the CPU determines whether or not the vehicle V has reached the recognizable point Pr. That is, the CPU determines whether or not the current position PV matches the recognizable point Pr. When the vehicle V has reached the recognizable point Pr (“Yes” in Step  109 ), the CPU advances the process to Step  110 . Meanwhile, when the vehicle V has not reached the recognizable point Pr (“No” in Step  109 ), the CPU returns the process to Step  108 . 
     When the process advances to Step  110 , the CPU attempts to acquire the signal color of the traffic light S from the camera  53 . Next, in Step  111 , the CPU determines whether or not the signal color has successfully been acquired. When the signal color has successfully been acquired (“Yes” in Step  111 ), the CPU advances the process to Step  115 . Meanwhile, when the signal color has not successfully been acquired (for example, when the signal color is not determinable by the camera  53  due to road being curved (“No” in Step  111 ), the CPU advances the process to Step  112 . 
     When the process advances to Step  112 , the CPU determines whether or not the value of the flag F is “1”. That is, the CPU determines whether acceleration/deceleration is permitted. When the value of the flag F is “1” (“Yes” in Step  112 ), in Step  113 , the CPU decelerates the vehicle V at the acceleration a 2 , and then returns the process to Step  110 . Meanwhile, when the value of the flag F is “0” (“No” in Step  112 ), in Step  114 , the CPU causes the vehicle V to travel at a constant speed, and returns the process to Step  110 . 
     When the process advances to Step  115 , the CPU determines whether or not the acquired signal color is “green.” When the signal color is “green” (“Yes” in Step  115 ), the CPU advances the process to Step  116 . 
     When the process advances to Step  116 , the CPU determines whether or not the distance DS between the nearest traffic light S and the traffic light S next in front from the nearest traffic light S is equal to or shorter than the threshold value DSth. When the distance DS is equal to or shorter than the threshold value DSth (“Yes” in Step  116 ), the CPU advances the process to Step  117 . 
     When the process advances to Step  117 , the CPU sets the value of the flag F to “0” indicating that “acceleration and deceleration are prohibited and constant speed traveling is permitted.” Next, in Step  118 , the CPU causes the vehicle V to travel at a constant speed. Then, the CPU advances the process to Step  119 . 
     When the process advances to Step  119 , the CPU determines whether or not the vehicle V has reached the nearest traffic light S. That is, the CPU determines whether or not the current position PV has reached the point PS. When the vehicle V has reached the nearest traffic light S (“Yes” in Step  119 ), the CPU returns the process to Step  102 . Meanwhile, when the vehicle V has not yet reached the nearest traffic light S (“No” in Step  119 ), the CPU returns the process to Step  118 . That is, the CPU causes the vehicle V to travel at a constant speed and waits until the vehicle V reaches the nearest traffic light. 
     In Step  115 , when the signal color is “yellow” or “red,” the CPU advances the process to Step  120 . When the process advances to Step  120 , the CPU decelerates the vehicle V, and stops the vehicle V before the nearest traffic light S. Then, the CPU waits until the signal color of the traffic light S becomes “green.” That is, in Step  121 , the CPU acquires the signal color of the nearest traffic light S and determines whether or not the signal color is “green.” When the signal color is “green” (“Yes” in Step  121 ), the CPU advances the process to Step  122 . Meanwhile, when the signal color is “yellow” or “red,” the CPU returns the process to Step  121 . 
     When the process advances to Step  122 , the CPU sets the value of the flag F to “1”. Then, the CPU advances the process to Step  123 . 
     When the process advances to Step  123 , the CPU accelerates the vehicle V at the acceleration a 0 . Then, the CPU advances the process to Step  124 . 
     When the process advances to Step  124 , the CPU determines whether or not the vehicle V has reached the nearest traffic light S. That is, the CPU determines whether or not the current position PV has reached the point PS. When the vehicle V has reached the nearest traffic light S (“Yes” in Step  124 ), the CPU returns the process to Step  102 . Meanwhile, when the vehicle V has not yet reached the nearest traffic light S (“No” in Step  124 ), the CPU returns the process to Step  123 . That is, the CPU accelerates the vehicle V and waits until the vehicle V reaches the nearest traffic light S. 
     Further, in Step  116 , when the distance DS exceeds the threshold value DSth, the CPU advances the process to Step  122 . 
     In Step  103 , when the value of the flag F is other than “1” (“No” in Step  103 ), the CPU advances the process to Step  110 . 
     For example, in the example shown in  FIG.  7   , the distance DS is equal to or shorter than the threshold value DSth, and hence, when the vehicle V reaches the recognizable point Pr 1  (“Yes” in Step  109 ), the CPU executes Step  110 , Step  115 , Step  116  to Step  119 , and Step  102  to then execute Step  103 . In this case, the value of the flag F is set to “0” in Step  117 , and hence the CPU advances the process from Step  103  to Step  110 . 
     Further, in Step  105 , when the vehicle speed Vs is equal to or lower than the target value V 1 , in Step  125 , the CPU initializes the deceleration start point Psd. That is, the CPU matches the deceleration start point Psd with the recognizable point Pr. Then, the CPU advances the process to Step  107 . 
     For example, in the example shown in  FIG.  10 A  to  FIG.  10 C , the vehicle speed Vs is lower than the target value V 1  before the recognizable point Pr 1 . Therefore, in this case, the CPU advances the process from Step  105  to Step  125  and to Step  107  in the stated order. 
     (Effects) 
     When the signal color of the traffic light S 1  is “green” and the distance DS is relatively short (DS&lt;DSth), the driving support ECU  10  of the driving support device  1  according to the at least one embodiment causes the own vehicle V to travel at a constant speed (suppresses acceleration) until the camera  53  recognizes the signal color of the second traffic light S 2  next in front from the first traffic light S 1 . Therefore, it is possible to suppress the repetition of acceleration and deceleration when the interval between the adjacent traffic lights is relatively short. As a result, according to the at least one embodiment, the discomfort of the occupants of the vehicle V can be reduced. 
     Further, in the above-mentioned related-art device, when the camera has recognized that a traffic light has entered the angle of view (frame) thereof, and the related-art device starts determination of the signal color of the traffic light but the signal color is not determinable, the driving support ECU gradually decelerates the vehicle. Then, when the signal color of the traffic light is determinable by the camera, the driving support ECU accelerates the vehicle, decelerates the vehicle, or causes the vehicle to travel at a constant speed in accordance with the signal color. Accordingly, for example, in a case in which the road has a large curve before the traffic light, when the traffic light enters the angle of view of the camera after the distance between the vehicle and the traffic light becomes relatively short, the driving support ECU decelerates the vehicle at a relatively large acceleration in order to stop the vehicle. 
     In contrast, the driving support ECU  10  according to the at least one embodiment decelerates the vehicle V from the deceleration start point Psd 1  before the recognizable point Pr 1  of the vehicle V. That is, the driving support ECU  10  gently decelerates the vehicle V at the acceleration a 1  from the deceleration start point Psd 1  regardless of whether or not the traffic light S 1  is within the angle of view of the camera  53 . Therefore, even when the signal color of the traffic light S 1  is determinable at the time at which the distance between the own vehicle V and the traffic light S 1  has become relatively short, the vehicle speed Vs is relatively low at that time. As a result, even when the signal color of the traffic light S 1  is “yellow” or “red” at that time, the driving support ECU can decelerate the vehicle V at a relatively small acceleration a 2  (acceleration which does not cause discomfort to the occupants), and can stop the vehicle V before the traffic light S 1 . 
     The present invention is not limited to the at least one embodiment described above, and various modification examples can be adopted within the scope of the present invention as described below. 
     Modification Example 
     In the example shown in  FIG.  9    and  FIG.  10 C , the driving support ECU  10  causes the vehicle V to travel at a constant speed lower than the target value V 1  to pass through the traffic light S 1 . However, instead of this, the driving support ECU  10  may accelerate the vehicle V at an acceleration a 0  (or an acceleration smaller than acceleration a 0 ) from the time at which the signal color of the traffic light S 1  is determined to be “green” to match the vehicle speed Vs with the target value V 1 , and then cause the vehicle V to travel at a constant speed until the camera  53  determines the signal color of the traffic light S 2 . 
     The vehicle V may be an autonomous vehicle.