Patent Publication Number: US-2023154322-A1

Title: Driving assistance apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-185414 filed on Nov. 15, 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a driving assistance apparatus that assists a driving operation of a driver. 
     Description of the Related Art 
     Conventionally, as an apparatus of this type, there is a known apparatus that notifies a start timing of accelerator-off operation to a driver of the vehicle traveling on the road where the traffic light is installed. Such an apparatus is described, for example, in Japanese Unexamined Patent Publication No. 2014-096016 (JP2014-096016A). In the apparatus described in JP2014-096016A, a timing of a deceleration operation is notified to the driver via the display unit so that the vehicle can pass through the intersection where the traffic light is installed in a non-stop manner. 
     In a situation where there is a preceding vehicle traveling in front of the subject vehicle, by providing information in accordance with the situation to the driver, it is possible to suppress a decrease in the traffic smoothing while improving traffic safety without hindering the traffic flow in the vicinity. However, the device described in JP2014-096016A does not propose any information presentation to the driver when the preceding vehicle is present. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is a driving assistance apparatus including: a display part displaying information; a detection part detecting a degree of approach from a subject vehicle to a preceding vehicle traveling ahead of the subject vehicle; and an electronic control unit including a microprocessor and a memory connected to the microprocessor. The microprocessor is configured to perform: acquiring traffic light information including switching information on a traffic light and position information on a position of the subject vehicle with respect to the traffic light, the traffic light informing a driver of stopping or non-stopping at a predetermined position; deriving a recommended driving for the driver, based on the traffic light information and the position information; and controlling the display part so as to notify the driver of information on a recommended vehicle speed included in the recommended driving. The microprocessor is configured to perform the controlling including controlling the display part so as to change and display information on a maximum value of the recommended vehicle speed included in the recommended driving in accordance with the degree of approach detected by the detection part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, and advantages of the present invention will become clearer from the following description of embodiments in relation to the attached drawings, in which: 
         FIG.  1 A  is a diagram showing an example of a travel scene of a vehicle having a driving assistance apparatus according to an embodiment of the present invention; 
         FIG.  1 B  is a diagram showing another example of the travel scene of the vehicle having the driving assistance apparatus according to the embodiment of the present invention; 
         FIG.  2 A  is a diagram showing an example of a display screen by the driving assistance apparatus according to the embodiment of the present invention; 
         FIG.  2 B  is a diagram showing another example of the display screen by the driving assistance apparatus according to the embodiment of the present invention; 
         FIG.  3    is a block-diagram illustrating a configuration of a main part of the driving assistance apparatus according to the embodiment of the present invention; 
         FIG.  4    is a diagram showing an example of the display screen when a preceding vehicle exists; and 
         FIG.  5    is a flowchart illustrating an example of processing executed by a controller in  FIG.  3   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention is explained with reference to  FIGS.  1 A to  5   .  FIGS.  1 A and  1 B  are diagrams showing examples of travel scenes of a subject vehicle having a driving assistance apparatus according to an embodiment of the present invention.  FIGS.  1 A and  1 B  illustrates an example of the vehicle  101  traveling along an arrow “A” on a road on which a traffic light  201  is installed. In particular, in  FIG.  1 A , an example in which a preceding vehicle traveling ahead of the subject vehicle  101  does not exist in a section from the subject vehicle  101  to the traffic light  201  is illustrated, and in  FIG.  1 B , an example in which the preceding vehicle  102  exists in the section is illustrated. 
     The traffic light  201  is configured to sequentially switch between a red light indicating a stop instruction, a green light (a blue light) indicating that traveling is possible, and a yellow light indicating that traveling is possible but safe stop is difficult at a predetermined cycle. The traffic light may be an arrow traffic light which indicates a travelable direction by an arrow, rather than the light color is switched. The traffic light may be sequentially switched between green light and red light. 
     The vehicle  101  receives traffic light information on the traffic light  201  from a communication device (e.g., an optical beacon roadside unit  202 ) such as an optical beacon, a radio beacon installed on the side of the road. The traffic light information includes switching information of the traffic light  201 , for example, switching information such as remaining time until the traffic light  201  switches from green to yellow and from red to green.  FIG.  1 A  and  FIG.  1 B  illustrate the example in which the subject vehicle  101  passes through the intersection where the traffic light  201  is installed without stopping, that is, the example in which the subject vehicle  101  travels without stopping at a stop line  203 . 
     In the situation where the subject vehicle  101  travels toward the intersection where the traffic light  201  is installed in this way, the driving assistance apparatus according to the embodiment of the present invention is configured to provide predetermined information to the driver of the subject vehicle  101  based on the traffic light information received from the optical beacon roadside unit  202 . That is, the driving assistance apparatus has a driving assistance function for notifying the driver of information (information of a target vehicle speed range) of a vehicle speed range in which the subject vehicle  101  can pass without stopping at the intersection, information of a deceleration instruction when the subject vehicle  101  stops at an intersection, and the like. 
     The information on the vehicle speed range and the information on the deceleration instruction are displayed on a display device provided on an instrument panel facing the driver. A display of a navigation unit disposed at the vicinity of the instrument panel can also be used as the display device. The display device may be configured by a head-up display for projecting an image on a panel provided at a windshield or near the windshield. 
       FIG.  2 A  is a diagram showing an example of a display screen  10   a  displayed on the display device (monitor) when the subject vehicle is approaching the traffic light. 
     As shown in  FIG.  2 A , on the display screen  10   a , an image indicating the target vehicle speed range is displayed in the area A 1  of one of the left and right sides (e.g., the right side), and an image indicating whether or not the subject vehicle can pass through the intersection where the traffic light is installed without stopping is displayed in the area A 2  of another of the left and right sides (e.g., the left side).  FIG.  2 A  corresponds to the display screen  10   a  of the vehicle  101  traveling toward the traffic light  201  as shown in  FIG.  1 A , for example. 
     The image of the area A 1  includes a scale image  11  indicating the vehicle speed on a scale along with a numerical value, a target vehicle speed image  12  (hatching) indicating the target vehicle speed range in which the subject vehicle can pass through the intersection where the traffic light ahead of the vehicle is installed without stopping, a bar-shaped subject vehicle speed image  13  indicating the current vehicle speed of the subject vehicle, and a bar-shaped legal speed image  14  indicating the legal speed of the road. The target vehicle speed image  12 , the subject vehicle speed image  13 , and the legal speed image  14  are displayed on the scale image  11  in association with the scale image  11 . The monitor has a color display. The scale image  11 , the target vehicle speed image  12 , the subject vehicle speed image  13 , and the legal speed image  14  are displayed in different colors from each other. The target vehicle speed image  12  is indicated by a belt-shaped image extending from the minimum value V0 to the maximum value V1 of the target vehicle speed. In  FIG.  2 A , the maximum value of the target vehicle speed range coincides with the legal speed. The display of the legal speed image  14  may be omitted. 
     In the area A 2 , a background image  15  schematically showing a road and a traffic light, and a driving behavior image  16  (hatching) indicating that the subject vehicle can travel without stopping at the intersection where the traffic light is installed, are displayed. The driving behavior image  16  is an image showing the driving behavior of the subject vehicle  101  passing through the intersection where the traffic light  201  is installed without the subject vehicle  101  stopping. If the subject vehicle speed is within the target vehicle speed range, the subject vehicle can travel without stopping at the intersection. In response to this situation, in the example of  FIG.  2 A , the driving behavior image  16  is represented by an image of an arrow exceeding the traffic light image on the road image of the background image  15 . Thus, on the display screen  10   a , the subject vehicle speed image  13  indicating the current vehicle speed is displayed in association with the target vehicle speed image  12  indicating the target vehicle speed range, and further, the driving behavior image  16  of the subject vehicle is displayed. Therefore, the driver can easily grasp necessity of acceleration and deceleration of the subject vehicle for smoothly passing through the intersection where the traffic light is installed, and good driving assistance for the driver is possible. 
     If the traffic light switches from green to red before the subject vehicle reaches the traffic light, or if the traffic light is still red when the subject vehicle reaches the traffic light, the subject vehicle needs to stop in front of the traffic light.  FIG.  2 B  is a diagram illustrating an example of the display screen  10   a  in such a case.  FIG.  2 B  corresponds to the display screen  10   a  when the subject vehicle stops at the stop line  203  in front of the traffic light  201  in  FIG.  1   , for example. 
     As shown in  FIG.  2 B , the target vehicle speed image  12 , the subject vehicle speed image  13 , and the legal speed image  14  are displayed in the area A 1 . The target vehicle speed image  12  is an image showing the target vehicle speed range for the traveling vehicle to stop smoothly on the stop line while suppressing the deceleration to a predetermined value or less. The target vehicle speed image  12  may be omitted. In the area A 2 , a deceleration instruction image  17  indicating the deceleration instruction of the vehicle is displayed on the background image  15 . Specifically, the deceleration instruction image  17  including an image  17   a  of the stop line and a band-shaped image  17   b  as shown by hatching toward the image  17   a  is displayed. Thus, when the deceleration of the subject vehicle is required to stop the subject vehicle in front of the traffic light (when the subject vehicle speed is larger than the target vehicle speed), the deceleration instruction image  17  indicating an instruction of the deceleration operation is displayed on the display screen  10   a . Accordingly, the driver can easily recognize necessity of the deceleration operation, and can decelerate the subject vehicle at a good timing. 
     By the way, when the subject vehicle travels by the driver&#39;s operation according to display of the display screen  10   a  in a state where the preceding vehicle  102  exists as illustrated in  FIG.  1 B , the subject vehicle  101  may approach (e.g., rapidly approach) the preceding vehicle  102 . Specifically, in a case where the maximum value V1 of the target vehicle speed defined by the target vehicle speed image  12  is faster than the vehicle speed of the preceding vehicle  102  and the driver referring to information regarding the target vehicle speed range drives to travel at the maximum value V1 of the target vehicle speed in order to pass through the intersection without stopping, the subject vehicle  101  approaches the preceding vehicle  102 . In order to enhance safety in such a case, the present embodiment provides a driving assistance apparatus as follows. 
       FIG.  3    is a block-diagram schematically illustrating a configuration of a main part of the driving assistance apparatus  100  according to the embodiment of the present invention. As shown in  FIG.  3   , the driving assistance apparatus  100  includes a controller  20 , and a communication unit  1 , a positioning sensor  2 , a vehicle speed sensor  3 , distance sensor  4  and a monitor  10  which are communicably connected to the controller  20 , respectively. 
     The communication unit  1  is configured to be capable of wirelessly communicating with the optical beacon roadside unit  202  ( FIGS.  1 A and  1 B ) provided on the road, that is, capable of road-to-vehicle communication. The communication unit  1  receives, from the communication device provided in the optical beacon roadside unit  202 , the traffic light information on the traffic light located in the traveling direction of the subject vehicle, i.e., the traffic light information on the traffic light installed at the intersection where the subject vehicle passes next. The traffic light information includes position information of the traffic light and information on the switching time of the light color of the traffic light. The information on the switching time includes information on the remaining time until the traffic light is switched from green to yellow when the traffic light is currently green, and information on the remaining time until the traffic light is switched to green next when the traffic light is not currently green (for example, red). 
     The positioning sensor  2  receives signal for positioning transmitted from the positioning satellite. Positioning satellites are artificial satellites such as GPS satellites and quasi-zenith satellites. Using positioning information received by the positioning sensor  2 , the current position of the subject vehicle (latitude, longitude, altitude) is measured. The positioning sensor  2  is used to detect the position (distance to the signal, etc.) of the subject vehicle relative to the position of the intersection where the traffic light is installed. Therefore, it is also possible to use a distance detector (radar, LIDAR, etc.) for detecting the distance from the subject vehicle to the object (object in the vicinity of the intersection) in place of the positioning sensor  2 . The vehicle speed sensor  3  detects the vehicle speed of the vehicle. 
     The distance sensor  4  detects an inter-vehicle distance L between the subject vehicle  101  and the preceding vehicle  102  as illustrated in  FIG.  1 B . The distance sensor  4  can be, for example, a LIDAR that measures a distance and direction from an object (preceding vehicle) by emitting a pulsed infrared laser beam and detecting a reflected beam reflected by the object or a radar that detects a distance and direction from the object by emitting an electromagnetic wave and detecting a reflected wave. The LIDAR and the radar can also detect a speed of the object. 
     A controller  20  executes predetermined processing on the basis of signals from a communication unit  1 , a positioning sensor  2 , a vehicle speed sensor  3 , and the distance sensor  4  and outputs a control signal to a monitor  10  including the display screen  10   a . The controller  20  includes an electronic control unit having a microprocessor and a memory connecting the microprocessor. More specifically, the controller  20  includes a computer including a CPU, a ROM, a RAM, and other peripheral circuits such as an I/O interface. The controller  20  includes, as functional components, an information acquisition unit  21 , a driving derivation unit  22 , a vehicle speed detection unit  23 , and a display control unit  24 . A memory of the controller  20  stores road information in advance. The road information includes information regarding a legal speed of each road. 
     The information acquisition unit  21  acquires traffic light information received by the communication unit  1 , information (position information) regarding a current position of the subject vehicle detected by the positioning sensor  2 , information (vehicle speed information) regarding the vehicle speed of the subject vehicle detected by the vehicle speed sensor  3 , and information (inter-vehicle distance information) regarding the inter-vehicle distance from the preceding vehicle detected by the distance sensor  4 . The inter-vehicle distance information also includes the speed of the preceding vehicle. Further, the information acquisition unit  21  specifies a road on which the subject vehicle is traveling according to the position information of the subject vehicle and acquires information (legal speed information) regarding the legal speed corresponding to the road on the basis of the road information stored in advance in the memory. 
     The driving derivation unit  22  derives recommended driving for the driver on the basis of the traffic light information, the position information, the vehicle speed information, and the legal speed information acquired by the information acquisition unit  21 . Specifically, the driving derivation unit calculates a distance between the subject vehicle and the intersection where a traffic light is installed by using the position information and also calculates a vehicle speed range in which the subject vehicle can pass through the intersection without stopping on the basis of the above distance and a remaining time until the traffic light ahead of the subject vehicle changes from green to yellow included in the traffic light information. Then, the driving derivation unit calculates, as the target vehicle speed range, a vehicle speed range equal to or lower than the legal speed within the above vehicle speed range. The target vehicle speed range is included in the recommended driving for the driver. 
     Meanwhile, when determining that the subject vehicle cannot pass through the intersection without stopping at the vehicle speed lower than the legal speed, the driving derivation unit  22  calculates a target vehicle speed range for the subject vehicle to smoothly stop in front of the traffic light, i.e., in front of the stop line at the intersection. Then, in case where the vehicle speed of the subject vehicle included in the vehicle speed information exceeds the target vehicle speed, the driving derivation unit derives a deceleration instruction including the target vehicle speed range as the recommended driving. Alternatively, the driving derivation unit simply derives a deceleration instruction for stopping the subject vehicle in front of the traffic light, without calculating the target vehicle speed range. 
     The vehicle speed detection unit  23  detects the vehicle speed of the preceding vehicle on the basis of the vehicle speed of the subject vehicle detected by the vehicle speed sensor  3  and an amount of change in the inter-vehicle distance L detected by the distance sensor  4 . That is, since the amount of change in the inter-vehicle distance L per unit time corresponds to a relative vehicle speed of the preceding vehicle to the subject vehicle, the vehicle speed of the preceding vehicle is detected (calculated) by adding the relative vehicle speed to the vehicle speed of the subject vehicle. The vehicle speed of the preceding vehicle may be detected by acquiring vehicle speed information from the preceding vehicle via the communication unit  1 . 
     The display control unit  24  controls display of the monitor  10  so as to display the recommended driving derived by the driving derivation unit  22 . For example, when the driving derivation unit  22  determines that the subject vehicle can pass through the intersection without stopping in a state where no preceding vehicle exists as illustrated in  FIG.  1 A , the display control unit controls the monitor  10  such that, as illustrated in  FIG.  2 A , the target vehicle speed image  12 , the subject vehicle speed image  13 , and the legal speed image  14  are displayed in association with the scale image  11  and, in addition, the driving behavior image  16  indicating that the subject vehicle can pass through the intersection without stopping is displayed on the background image  15 . 
     Meanwhile, when the driving derivation unit  22  determines that the subject vehicle cannot pass through the intersection without stopping, the display control unit  24  controls the monitor  10  such that, as illustrated in  FIG.  2 B , the target vehicle speed image  12 , the subject vehicle speed image  13 , and the legal speed image  14  are displayed in association with the scale image  11  and, in addition, the deceleration instruction image  17  indicating the deceleration operation instruction is displayed on the background image  15 . The images in  FIGS.  2 A and  2 B  are display images in a case where there is no possibility of approaching the preceding vehicle in the section to the traffic light  201  or there is no possibility of approaching the preceding vehicle by a predetermined degree or more. 
     In the state where the preceding vehicle exists as illustrated in  FIG.  1 B , the display control unit  24  controls the monitor  10  as follows. First, the display control unit  24  determines whether or not the vehicle speed of the preceding vehicle detected by the vehicle speed detection unit  23  is smaller than the maximum value V1 of the target vehicle speed range derived by the driving derivation unit  22 . When it is determined that the vehicle speed of the preceding vehicle is larger than or equal to the maximum value V1 of the target vehicle speed range, the subject vehicle does not approach the preceding vehicle. In this case, the display control unit controls the monitor  10  such that the image indicating the recommended driving is displayed as in  FIG.  2 A . 
     Meanwhile, when it is determined that the vehicle speed of the preceding vehicle is smaller than the maximum value V1 of the target vehicle speed range, the subject vehicle may approach the preceding vehicle. In this case, the display control unit  24  further determines whether or not the inter-vehicle distance L is equal to or less than a predetermined value La on the basis of the inter-vehicle distance information acquired by the information acquisition unit  21 . The predetermined value La is set according to the vehicle speed, and the predetermined value La increases as the vehicle speed increases. In a case where the inter-vehicle distance L is larger than the predetermined value La, the display control unit controls the monitor  10  such that the images as in  FIG.  2 A  is displayed. When the inter-vehicle distance L is equal to or smaller than the predetermined value La, the display control unit controls the monitor  10  so as to decrease the maximum value V1 of the target vehicle speed indicated by the target vehicle speed image  12 . 
       FIG.  4    illustrates an example thereof and is an example where the subject vehicle can pass through the intersection with a green light. As illustrated in  FIG.  4   , the target vehicle speed image  12  different from that in  FIG.  2 A  is displayed on the display screen  10   a . That is, the maximum value V2 of the target vehicle speed indicated by the target vehicle speed image is smaller than the maximum value V1 in  FIG.  2 A , and the entire length of the target vehicle speed image  12  is shorter than that in  FIG.  2 A . Although in  FIG.  4   , the display of the legal speed image  14  is omitted, the legal speed image  14  may be displayed. 
     The maximum value V2 of the target vehicle speed in  FIG.  4    is set to, for example, the same value as the vehicle speed of the preceding vehicle. This makes it possible to prevent the subject vehicle from approaching the preceding vehicle. The maximum value V2 may be set according to the inter-vehicle distance L between the subject vehicle and the preceding vehicle. For example, the maximum value V2 may be set to a smaller value as the inter-vehicle distance L is shorter. The maximum value V2 may also be set to a smaller value as the vehicle speed of the subject vehicle is faster than the vehicle speed of the preceding vehicle. The maximum value V2 of the target vehicle speed when the preceding vehicle exists is smaller than the maximum value V1 when the preceding vehicle does not exist. Therefore, a driver drives the vehicle such that the vehicle speed falls within the target vehicle speed range, and thus, the subject vehicle can smoothly pass through an intersection, without excessively approaching the preceding vehicle. As a result, it is possible to provide useful information to the driver in a case where the preceding vehicle exists. 
       FIG.  5    is a flowchart showing an example of processing executed by the controller  20  (microprocessor) in  FIG.  3   . The processing shown in the flowchart starts when, for example, a power key switch is turned on and is repeated at predetermined cycles. 
     As illustrated in  FIG.  5   , first, in S 1  (S: processing step), the controller acquires the traffic light information received by the communication unit  1  and also acquires the position information of the subject vehicle based on a signal from the positioning sensor  2 , the vehicle speed information based on a signal from the vehicle speed sensor  3 , and the inter-vehicle distance information based on a signal from the distance sensor  4 . The traffic light information includes information regarding a remaining time (green light remaining time, red light remaining time) until the traffic light is switched from green to yellow or from red to green. In S 1 , the controller further acquires information regarding a legal speed of a road on which the subject vehicle is traveling by referring to the road information stored in advance in the memory. The legal speed information of the road on which the subject vehicle is traveling may also be acquired by recognizing a road sign by using a vehicle-mounted camera. 
     Next, in S 2 , the controller calculates a target vehicle speed range having the legal speed as an upper limit as recommended driving for the driver on the basis of the traffic light information, the position information, and the legal speed information acquired in S 1 . That is, the controller calculates a target vehicle speed range in which the subject vehicle can pass through the intersection where a traffic light is installed without stopping or a target vehicle speed range in a case where the subject vehicle stops in front of the traffic light. In other words, the controller calculates the minimum value V0 and the maximum value V1 of the target vehicle speed. 
     Next, in S 3 , the controller determines whether or not a preceding vehicle exists within a predetermined distance on the basis of the signal from the distance sensor  4 . The controller may determine whether or not the preceding vehicle exists on the basis of an image from a camera mounted on the subject vehicle to capture surroundings of the subject vehicle. The predetermined distance is, for example, a distance from a current location to the traffic light. When it is determined in S 3  that no preceding vehicle exists, the processing proceeds to S 4 . 
     In S 4 , the controller outputs a control signal to the monitor  10  such that an image of the recommended driving including the target vehicle speed range calculated in S 2  is displayed. For example, as illustrated in  FIGS.  2 A and  2 B , the controller outputs a control signal to the monitor  10  such that the target vehicle speed image  12  including the minimum value V0 and the maximum value V1, the subject vehicle speed image  13 , and the legal speed image  14  are displayed in association with the scale image  11  in an area A 1  and, in addition, the driving behavior image  16  or the deceleration instruction image  17  is displayed on the background image  15 . 
     Meanwhile, when it is determined in S 3  that the preceding vehicle exists, the processing proceeds to S 5 , and the controller detects a vehicle speed Vf of the preceding vehicle on the basis of the vehicle speed information and the inter-vehicle distance information acquired in S 1 . 
     Next, in S 6 , the controller calculates a speed difference by subtracting the maximum value V1 of the target vehicle speed range calculated in S 2  from the vehicle speed Vf detected in S 5 , and determines whether or not the speed difference is equal to or larger than a predetermined value (predetermined difference) Va. This determination is a determination as to whether or not the subject vehicle traveling according to the recommended driving may approach the preceding vehicle, the predetermined value is set to 0, for example. When it is determined in S 6  that the speed difference is equal to or larger than the predetermined value Va, the processing proceeds to S 7 . If not, the processing proceeds to S 4 . 
     In S 7 , the controller sets the predetermined value La according to the vehicle speed by using the vehicle speed information acquired in S 1  and determines whether or not the inter-vehicle distance L is equal to or smaller than the predetermined value La by using the inter-vehicle distance information. When it is determined in S 7  that the inter-vehicle distance L is equal to or smaller than the predetermined value La, the processing proceeds to S 8 . If not, the processing proceeds to S 4 . 
     In S 8 , the controller calculates a maximum value V2 for displaying which is different from the maximum value V1 of the target vehicle speed included in the recommended driving calculated in S 2 , based on the inter-vehicle distance information acquired in S 1 . That is, the controller calculates a new maximum value V2 smaller than V1. For example, the controller calculates the vehicle speed Vf of the preceding vehicle detected in S 5  as the maximum value V2. The controller may calculate the maximum value V2 of the target vehicle speed in accordance with the inter-vehicle distance L or in accordance with the speed difference between the subject vehicle and the preceding vehicle so that the subject vehicle does not approach the preceding too much. 
     Next, in S 9 , the controller outputs a control signal to the monitor  10  such that an image of the recommended driving including the maximum value V2 of the target vehicle speed calculated in S 8  is displayed. For example, the controller controls the monitor  10  so that the image illustrated in  FIG.  4    is displayed. 
     The operation of the driving assistance apparatus  100  according to the present embodiment is summarized as follows. For example, the image of the recommended driving in  FIG.  2 A  is displayed on the monitor  10  in a state where the subject vehicle  101  is approaching the intersection where the traffic light  201  is installed and no preceding vehicle exists ahead of the subject vehicle  101  as illustrated in  FIG.  1 A . Specifically, the driving behavior image  16  indicating that the subject vehicle  101  can pass through the intersection where the traffic light  201  is installed without stopping is displayed together with the target vehicle speed image  12  indicating the target vehicle speed range for the subject vehicle to pass through the intersection without stopping, that is, the target vehicle speed image  12  indicating a range from the minimum value V0 to the maximum value V1 of the target vehicle speed (S 4 ). Therefore, the driver can easily recognize the target vehicle speed for passing through the intersection without stopping and thus can perform a smooth traveling operation of the subject vehicle  101 . 
     On the other hand, as illustrated in  FIG.  1 B , when the preceding vehicle  102  exists ahead of the subject vehicle  101  by a distance L, an image is displayed on the monitor  10  in accordance with a difference between the maximum value V1 of the target vehicle speed indicated by the target vehicle speed image  12  and the vehicle speed Vf of the preceding vehicle  102  and the inter-vehicle distance L between the subject vehicle  101  and the preceding vehicle  102 . That is, when a speed difference (a difference in speed) obtained by subtracting the maximum value V1 of the target vehicle speed from the vehicle speed Vf of the preceding vehicle  102  is equal to or larger than the predetermined value Va (e.g. when the vehicle speed Vf is equal to or larger than the maximum value V1), the image indicating the recommended driving similar to that when the preceding vehicle  102  does not exist is displayed (S 6 →S 4 ). Even in a case where the speed difference is smaller than the predetermined value Va, if the inter-vehicle distance L is larger than the predetermined value La, there is no possibility that the subject vehicle  101  rapidly approaches the preceding vehicle  102 , and, also in this case, the image indicating the recommended driving similar to that when the preceding vehicle  102  does not exist is displayed (S 7 →S 4 ). 
     Meanwhile, in a case where the speed difference obtained by subtracting the maximum value V1 of the target vehicle speed from the vehicle speed Vf of the preceding vehicle  102  is smaller than the predetermined value Va and the inter-vehicle distance L is equal to or smaller than the predetermined value La, for example, the image of the recommended driving including the target vehicle speed image  12  illustrated in  FIG.  4    is displayed on the monitor  10  (S 9 ). In this case, the maximum value V2 of the target vehicle speed is displayed to be more limited than the maximum value V1 in  FIG.  2 A  (V2&lt;V1). Therefore, even in a case where the preceding vehicle  102  exists, the subject vehicle  101  does not excessively approach the preceding vehicle  102  and can pass through the intersection without stopping if the driver drives the vehicle such that the vehicle speed of the subject vehicle falls within the target vehicle speed range. This enhances traveling safety when passing assist display for the intersection is performed. 
     According to the present embodiment, the following operations and effects are achievable. 
     (1) A driving assistance apparatus  100  according to the present embodiment includes: an information acquisition unit  21  that acquires traffic light information including switching information of a traffic light and position information indicating a position of a subject vehicle  101  with respect to the traffic light; a driving derivation unit  22  that derives recommended driving for a driver on the basis of the traffic light information and the position information acquired by the information acquisition unit  21 ; a monitor  10  that displays information; a display control unit  24  that controls the monitor  10  so as to notify the driver of information regarding the recommended driving derived by the driving derivation unit  22 ; and a detection part that detects a degree of approach between the subject vehicle  101  and a preceding vehicle  102  that travels ahead of the subject vehicle, for example, a distance sensor  4  that measures an inter-vehicle distance L between the subject vehicle  101  and the preceding vehicle  102  ( FIG.  3   ). The display control unit  24  controls the monitor  10  such that information regarding a maximum value V1 of a recommended vehicle speed derived by the driving derivation unit  22  is displayed while being changed according to the degree of approach (e.g. the inter-vehicle distance L) between the subject vehicle  101  and the preceding vehicle  102  detected by the detection part ( FIG.  5   ). 
     More specifically, the display control unit  24  controls the monitor  10  such that, when the degree of approach (e.g. the inter-vehicle distance L) between the subject vehicle  101  and the preceding vehicle  102  detected by the distance sensor  4  or the like is equal to or larger than the predetermined value La, the recommended driving information including the information regarding the maximum value V1 of the recommended vehicle speed included in the recommended driving derived by the driving derivation unit  22  is displayed, and, when the inter-vehicle distance L is smaller than the predetermined value La, the recommended driving information including the information regarding the maximum value V2 smaller than the maximum value V1 is displayed. With this configuration, it is possible to notify the driver of the target vehicle speed range in which the subject vehicle  101  does not rapidly approach the preceding vehicle  102  and can pass through the intersection without stopping. As a result, the subject vehicle can smoothly pass through the intersection while improving safety. 
     (2) A vehicle speed detection unit  23  detects a vehicle speed Vf of the preceding vehicle  102  that affects the degree of approach by using signal from a vehicle speed sensor  3  and a distance sensor  4 . The display control unit  24  controls the monitor  10  such that, when a speed difference obtained by subtracting the maximum value V1 from the vehicle speed Vf of the preceding vehicle  102  detected by the vehicle speed detection unit  23  is equal to or larger than a predetermined value Va, the recommended driving information including the information regarding the maximum value V1 is displayed ( FIG.  2 A ), and, when the speed difference is smaller than the predetermined value Va, the recommended driving information including the information regarding the maximum value V2 smaller than the maximum value V1 is displayed ( FIG.  4   ). By changing display of the maximum value of the target vehicle speed according to the speed difference from the preceding vehicle  102  as described above, it is possible to notify the driver of an optimum target vehicle speed that prevents the subject vehicle  101  from approaching the preceding vehicle  102 . 
     (3) The display control unit  24  controls the monitor  10  such that a range of the target vehicle speed is displayed by a belt-shaped target vehicle speed image  12  having a length corresponding to a range from a minimum value V0 to the maximum values V1 and V2 of the target vehicle speed ( FIGS.  2 A and  4   ). Therefore, the driver can easily recognize the target vehicle speed range on the basis of the length of the image. 
     The above embodiment can be modified to various forms. Several modifications will be described below. In the above embodiment, the information acquisition unit  21  acquires the traffic light information including the switching information of the traffic light transmitted from the optical beacon roadside unit  202 . However, after the current position of the subject vehicle is specified by the positioning sensor  2 , the information acquisition unit may acquire the traffic light information transmitted from the server device that manages the switching of the traffic light corresponding to the current position of the subject vehicle. Although in the above embodiment, the position of the subject vehicle is detected by the positioning sensor  2 , the position of the subject vehicle with respect to the traffic light may be detected by using a radar, a LIDAR, or a camera. 
     In the above embodiment, the driving derivation unit  22  derives the recommended driving for the driver based on the traffic light information and the position information of the subject vehicle acquired by the information acquisition unit  21 . Specifically, the range of the vehicle speed to be satisfied by the subject vehicle (target vehicle speed range) and the instruction to perform the deceleration operation (deceleration instruction) are derived as part of the recommended driving. However, the configuration of a derivation unit is not limited to those described above. In the above embodiment, the information on the recommended driving derived by the driving derivation unit  22  is notified to the driver via the monitor  10  (display part). However, the information may be notified to the driver by an audio output in addition to the display. 
     Although in the above embodiment, the maximum value of the target vehicle speed is changed from V1 (a first maximum value) to V2 (a second maximum value) on the condition that the speed difference obtained by subtracting the maximum value V1 of the target vehicle speed from the vehicle speed Vf of the preceding vehicle is smaller than the predetermined value (predetermined difference) Va and the inter-vehicle distance L is equal to or smaller than predetermined value (predetermined distance) La, the maximum value of the target vehicle speed may be changed from V1 to V2 on the condition that the speed difference obtained by subtracting V1 from the vehicle speed Vf is smaller than the predetermined value Va or the inter-vehicle distance L is equal to or smaller than the predetermined value La. Alternatively, the maximum value of the target vehicle speed may be changed from V1 to V2 in accordance with other parameters representing the degree of approach. That is, as long as controlling the monitor  10  so as to display recommended driving information including information on the maximum value V1 of the recommended vehicle speed included in the recommended driving derived by the driving derivation unit  22  (a derivation unit) when the degree of approach between the subject vehicle and the preceding vehicle is smaller than the predetermined value, and to display recommended driving information including information on other maximum value V2 when the degree of approach is equal to or larger than the predetermined value, a display control unit may be any configuration. The display control unit may control the monitor  10  so as to display recommended driving information including information on the maximum value V1 of the recommended vehicle speed when the vehicle speed Vf of the preceding vehicle  102  is equal to or larger than the maximum value V1 of the target vehicle speed or the vehicle speed Vf is equal to or larger than the vehicle speed of the subject vehicle detected by the vehicle speed sensor  3 , and to display recommended driving information including information on other maximum value V2 when the vehicle speed Vf is smaller than the maximum value V1 of the target vehicle speed or the vehicle speed Vf is smaller than the vehicle speed of the subject vehicle. 
     In the above embodiment, the vehicle speed detection unit  23  (a vehicle speed detection part) detects using the inter-vehicle distance L detected by the distance sensor  4  and the vehicle speed detected by the vehicle speed sensor  3 , and as an example of a degree of approach, and by using the vehicle speed Vf of the preceding vehicle detected by the vehicle speed detection unit  23 , the speed difference between the preceding vehicle and the subject vehicle is detected (calculated). However, the configuration of a detection part detecting a degree of approach between the subject vehicle and the preceding vehicle is not limited to the above configuration. The controller calculates a rate of change of a relative speed by time-differentiating the inter-vehicle distance L between the subject vehicle and the preceding vehicle, and thereby the degree of approach may be detected. 
     In the above embodiment, the range of the recommended vehicle speed is displayed by the belt-shaped target vehicle speed image  12  having a length corresponding to the range from the minimum value V0 of the recommended vehicle speed (target vehicle speed) to the maximum value V1, V2. However, the configuration of a target vehicle speed image is not limited to the above configuration. For example, the minimum value and the maximum value of the recommended vehicle speed may be displayed as numerical values. Only the maximum value of the recommended vehicle speed may be displayed. An image indicating the maximum value V1 and an image indicating the maximum value V2 may be displayed differently so that the driver can recognize that the maximum value of the recommended vehicle speed is limited from V1 to V2 due to the presence of the preceding vehicle. For example, the two may be displayed in different display colors. In the above embodiment, the target vehicle speed image  12 , the subject vehicle speed image  13 , the legal speed image  14 , and the like are displayed on the display screen  10   a , but the display of the subject vehicle speed image  13  and the legal speed image  14  may be omitted. 
     In the above embodiment, the configuration of the driving assistance apparatus  100  is described by referring to the case where the subject vehicle passes through the intersection where the traffic light is installed. However, the traffic light may be installed in not only the intersection but also a pedestrian crossing or the like. In this case also, the driving assistance apparatus of the present invention can be applied. 
     The present invention can also be used as a driving assistance method including 
     detecting a degree of approach from a subject vehicle  101  to a preceding vehicle  102  traveling ahead of the subject vehicle  101 , acquiring traffic light information including switching information on a traffic light  201  and position information on a position of the subject vehicle  101  with respect to the traffic light  201 , the traffic light  201  informing a driver of stopping or non-stopping at a predetermined position, deriving a recommended driving for the driver based on the traffic light information and the position information, and controlling a display part so as to notify the driver of information on a recommended vehicle speed included in the recommended driving. The controlling includes controlling the display part so as to change and display information on a maximum value V1 of the recommended vehicle speed included in the recommended driving in accordance with the degree of approach from the subject vehicle  101  to the preceding vehicle  102 . 
     The above embodiment can be combined as desired with one or more of the above modifications. The modifications can also be combined with one another. 
     According to the present invention, it is possible to perform a driving assist considering safety in a case where a preceding vehicle exists. 
     Above, while the present invention has been described with reference to the preferred embodiments thereof, it will be understood, by those skilled in the art, that various changes and modifications may be made thereto without departing from the scope of the appended claims.