Patent Publication Number: US-2023150489-A1

Title: Braking control device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Application No. PCT/JP2018/040803, filed Nov. 2, 2018, which claims priority to Japanese Patent Application No. 2017-215149, filed Nov. 8, 2017. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to braking control. 
     2. Related Art 
     There is a technique for avoiding the risk of a rear-end collision in which, when an idling stop is executed and the parking brake is activated while a vehicle is stopped in an intersection, the parking brake is released and the vehicle is moved when it is determined that there is a risk of rear-end collision. 
     SUMMARY 
     An aspect of the technique according to the present disclosure is a braking control device, including: an operating unit that operates automatic emergency braking in response to detecting that an obstacle presents in a traveling direction of a vehicle; a determining unit that, in a case where the vehicle is stopped in an intersection by the automatic emergency braking, determines whether it is safer for the vehicle to continue being stopped, or safer for the vehicle to start moving; and a safety ensuring unit that, in a case where the determining unit determines that it is safer for the vehicle to start moving, releases the stopped state which was caused by the automatic emergency braking. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG.  1    is a block diagram of a vehicle; 
         FIG.  2    is a flowchart illustrating a braking process; 
         FIG.  3    is a flowchart illustrating a determination process; 
         FIG.  4    is a diagram illustrating a state in which a vehicle is stopped inside an intersection; 
         FIG.  5    is a graph illustrating a braking force by primary braking, secondary braking, and stop maintenance braking; 
         FIG.  6    is a graph illustrating a braking force by primary braking; and 
         FIG.  7    is a flowchart illustrating a safety ensuring process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     JP2008-121583A (Japanese Unexamined Patent Application Publication No. 2008- 121583) discloses a technique for avoiding the risk of a rear-end collision in which, when an idling stop is executed and the parking brake is activated while a vehicle is stopped in an intersection, the parking brake is released and the vehicle is moved when it is determined that there is a risk of rear-end collision. 
     In the case of the background art described above, safety when the vehicle has stopped due to automatic emergency braking is not considered. In view of the above, it is an object of the present disclosure to improve safety while a vehicle is stopped in an intersection by automatic emergency braking. 
     An aspect of the technique according to the present disclosure is a braking control device, including: an operating unit that operates automatic emergency braking in response to detecting that an obstacle presents in a traveling direction of a vehicle; a determining unit that, in a case where the vehicle is stopped in an intersection by the automatic emergency braking, determines whether it is safer for the vehicle to continue being stopped, or safer for the vehicle to start moving; and a safety ensuring unit that, in a case where the determining unit determines that it is safer for the vehicle to start moving, releases the stopped state which was caused by the automatic emergency braking. According to this embodiment, safety while a vehicle is stopped in an intersection by automatic emergency braking is improved. 
     The above and other objectives, features and advantages of the present disclosure will be made more clear by the following detailed description, given referring to the appended drawings. 
     Embodiments of the present disclosure are described below with reference to the drawings. 
     As illustrated in  FIG.  1   , a vehicle  30  includes a sensor group  11 , a control device  20 , a braking device  40 , an internal combustion engine  42 , and a hazard lamp  45 . The vehicle  30  is a self-driving car of level 1 or higher. More specifically, the vehicle  30  has at least a function of automatically performing braking. 
     The sensor group  11  includes a millimeter-wave radar  12 , an image sensor  14 , a vehicle speed sensor  16 , and a yaw rate sensor  18 . The millimeter-wave radar  12  emits a frequency-modulated radar wave in the millimeter wave band and measures the reflected wave. The millimeter-wave radar  12  emits a millimeter wave toward a range that can include a target existing in front of the vehicle  30 . The target is, for example, another vehicle, a pedestrian, a bicycle, or the like. The front of the vehicle  30  includes right front and left front in addition to the front. 
     The image sensor  14  captures an image of the front of the vehicle  30 . The imaging range of the image sensor  14  is a range that can include a target existing in front of the vehicle  30 . The vehicle speed sensor  16  inputs the vehicle speed of the vehicle  30  to the control device  20 . 
     A current location acquiring device  21  acquires the latitude and longitude indicating the current location of the vehicle  30  (hereinafter, simply referred to as the current location) and inputs the acquired latitude and longitude to a map information output device  23 . The current location acquiring device  21  acquires the current location using a signal from a GPS satellite or the like. 
     The map information output device  23  inputs the map information at the inputted current location to the control device  20 . When the current location is near an intersection, the map information to be inputted includes information about the intersection. The information about the intersection includes information on how the roads intersect, the presence or absence of a traffic signal, and the like. 
     The intersection in the present embodiment means an area where two or more roads intersect, and means an area where a vehicle may travel across an oncoming lane. Therefore, the intersection in the present embodiment is not limited to a crossroad, but also includes a T-junction and the like. 
     The internal combustion engine  42  is for example a gasoline engine. The control device  20  controls the rotation speed of the internal combustion engine  42 . In a case where the vehicle speed is zero and a specified condition such as the remaining capacity of the battery or the like is satisfied, the control device  20  executes an idling stop. 
     The braking device  40  includes a service brake and a parking brake. The service brake is operated when a driver steps on a brake pedal. The parking brake is activated by a driver manually pulling up a brake lever. The service brake and the parking brake may be automatically operated by the control device  20  in some cases. 
     The control device  20  includes a plurality of ECUs. The control device  20  controls the components of the vehicle  30  described above. 
     The control device  20  repeatedly executes a braking process illustrated in  FIG.  2    while the automatic braking function is set to ON. 
     The control device  20  first performs a determination process as S 100 . After the determination process is started, as illustrated in  FIG.  3   , the control device  20  determines whether at least a part of the vehicle  30  is located within the intersection as S 110 . In the example illustrated in  FIG.  4   , the area J corresponds to the intersection. In S 110  and in S 120  next, information outputted from the current location acquiring device  21  and the map information output device  23  is used. 
     In a case where YES is determined in S 110 , the control device  20  proceeds to S 120  and determines whether the current location is on an oncoming lane. Here, the oncoming lane means an area where an oncoming vehicle traveling straight ahead travels. Since S 120  is based on the determination of YES in S 110 , in the example illustrated in  FIG.  4   , in a case where at least a part of the vehicle  30  is located in the area J 1 , YES is determined in S 120 .  FIG.  4    illustrates a case where a part of the vehicle  30  is located in the area J 1 . 
     In a case where YES is determined in S 120 , the control device  20  proceeds to S 130  and determines whether an oncoming vehicle is prohibited from traveling straight ahead. More specifically, it is determined whether the right arrow of an arrow traffic signal to be followed by the host vehicle is lit up green. In Japan, when the right arrow of an arrow traffic signal to be followed by the host vehicle is lit up green, the signal to be followed by the oncoming vehicle is operated so as to prohibit travel straight ahead.  FIG.  4    illustrates a state in which the right arrow is lit up green on the arrow traffic signal S to be followed by the host vehicle. 
     In a case where NO is determined in S 130 , the control device  20  proceeds to S 140  and sets the flag to ON. The flag being ON indicates that, when a vehicle is stopped inside an intersection when automatic emergency braking is activated, it is safer for the vehicle to start moving than to continue being stopped. Automatic emergency braking is also referred to as collision avoidance braking. 
     The term “safe” as used here means the level of probability of collision with an oncoming vehicle that is traveling straight ahead. Stopping in the present embodiment means a state where the vehicle speed is zero. In a situation where YES is determined in S 110  and S 120  and NO is determined in S 130 , there is a high probability that a collision will occur if the vehicle  30  continues to be stopped and the oncoming vehicle traveling straight ahead does not avoid the collision. 
     When NO is determined in any of S 110  and S 120 , or when YES is determined in S 130 , the control device  20  proceeds to S 150  and sets the flag to OFF. In other words, in these cases, when the vehicle is stopped in a case where automatic emergency braking is operated, it is safer to continue being stopped than for the vehicle to start moving. 
     When the flag is set, the control device  20  proceeds to S 160 , which determines whether the situation is such that automatic emergency braking should be operated. The control device  20  executes S 160  based on input from the millimeter-wave radar  12  and the image sensor  14 . In a case where NO is determined in S 160 , the control device  20  returns to S 110 . In a case where YES is determined in S 160 , the control device  20  terminates the determination process and proceeds to S 210 . 
     After proceeding to S 210 , the control device  20  executes primary braking. Primary braking is braking with a braking force G 1  illustrated in  FIG.  5    and  FIG.  6    as an upper limit. Here, the braking force is a parameter having a correlation with the deceleration (m/s 2 ) when the vehicle  30  is traveling. However, in the present embodiment, the braking force may be controlled even in a case where the vehicle speed of the vehicle  30  is zero. In this case, the braking force is a parameter not related to the deceleration. 
     The control device  20  proceeds to S 220  while executing primary braking, and determines whether the flag is set to ON. In a case where the flag is set to OFF, the control device  20  proceeds to S 230  and determines whether secondary braking is necessary. Secondary braking is braking with the braking force G 2  illustrated in  FIG.  5    as the upper limit of the braking force. The braking force G 2  is larger than the braking force G 1 . 
     In a case where the risk of a collision with an obstacle ahead is avoided by primary braking before the vehicle speed becomes zero, the control device  20  determines that secondary braking is unnecessary. In this case, the control device  20  proceeds to S 250  at the timing when the vehicle speed becomes zero. 
     On the other hand, when it is determined that secondary braking is necessary, the control device  20  executes secondary braking. The control device  20  proceeds to S 250  at the timing when the vehicle speed becomes zero. In  FIG.  5   , the timing at which the vehicle speed becomes zero is indicated as being time t1. 
     After proceeding to S 250 , the control device  20  changes the braking force to the braking force Gh, and maintains the braking force Gh for a specified time T 1 . The operation of maintaining the braking force at the braking force Gh is also called a stop maintenance braking. In the present embodiment A, the parking brake is used for stop maintenance braking. While stop maintenance braking is continued, the vehicle  30  does not start to move even when stepping on the accelerator pedal. After S 250  terminates, the control device  20  repeats the braking process from S 100 . 
     On the other hand, in a case where the flag is ON, the control device  20  proceeds to S 300  and executes a safety ensuring process. 
     As illustrated in  FIG.  7   , after the safety ensuring process is started, the control device  20  prohibits secondary braking as S 305 . Continuing, the control device  20  causes the hazard lamp  45  to flash as S 310 . This reduces the risk of a rear-end collision by a following vehicle. 
     Next, the control device  20  proceeds to S 320  and prohibits an idling stop. Subsequently, the control device  20  proceeds to S 325  and determines whether the vehicle has stopped. In the present embodiment, in a case where automatic emergency braking is operated while the flag is ON, braking by primary braking is executed until the vehicle stops. S 325  is repeatedly executed until the vehicle stops. 
     After it is determined that the vehicle has stopped, the control device  20  proceeds to S 330  and determines whether it is safe for the vehicle to start moving. The term “safe” as used herein means that there is no longer a risk of colliding with an obstacle that has caused automatic emergency braking to operate even when the vehicle starts to move. In a case where there is a risk of colliding with an obstacle when the vehicle starts to move, S 330  is repeatedly executed. While S 330  is being repeated, stop maintenance braking is continued. 
     When it is determined that it is safe for the vehicle to start moving, the control device  20  proceeds to S 340  and releases stop maintenance braking. Idling stop is prohibited, so the vehicle  30  will start moving when the accelerator pedal is depressed. 
       FIG.  6    illustrates an example in which, at the time the vehicle is stopped at time t2, it is determined that it is safe even when the vehicle starts moving. Therefore, stop maintenance braking is not performed. In this case, S 340  is substantially not performed. 
     The control device  20  then proceeds to S 350  and prohibits automatic emergency braking. The control device  20  then proceeds to S 360  and turns OFF the hazard lamp  45 . The control device  20  then proceeds to S 370 , which determines whether the vehicle has exited the intersection. The control device  20  repeats S 370  until it is determined that the vehicle has exited the intersection. 
     When it is determined that the vehicle has exited the intersection, the control device  20  terminates the safety ensuring process. After that, the control device  20  proceeds to S 410  and releases the prohibition of automatic emergency braking. Continuing, the control device  20  proceeds to S 420  and releases the prohibition of the idling stop. After S 420 , the control device  20  repeats the braking process from S 100 . 
     According to the embodiment described above, the safety when the vehicle stops within an intersection due to automatic emergency braking is improved. In a situation where the vehicle is stopped in an intersection and on the oncoming lane, and a signal allows an oncoming vehicle to pass through the intersection by going straight ahead, there is a risk that the vehicle will collide with the oncoming vehicle if the vehicle continues to be stopped. In such a situation, it is more likely that quickly passing through the intersection will be safer. In the present embodiment, in order to realize such an operation, stop maintenance braking is terminated in the shortest possible time in the above situation. 
     In the situation described above, by prohibiting secondary braking, the risk of being hit by a following vehicle is reduced, and this prevents the stopped position of the vehicle from deviating from the original route due to the occurrence of skidding which was caused by secondary braking, making it possible to turn right smoothly. 
     The correspondence between the embodiments and the claims will be described. The control device  20  corresponds to a braking control device, S 100  and S 220  correspond to a determining unit, S 210  and S 240  correspond to an operating unit, and S 300  corresponds to a safety ensuring unit. 
     The present disclosure is not limited to the embodiments, examples, and modifications of the present description, and may be implemented by various configurations without departing from the gist of the present disclosure. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary of the invention section are for solving some or all of the problems described above, or in order to achieve some or all of the effects described above, replacement and combination may be made as appropriate. Technical features that are not described as essential in this description may be deleted as appropriate. For example, the following example is given. 
     The embodiments describe left-hand traffic as an example; however, the embodiments may also be applied to right-hand traffic. In the case of right-hand traffic, replacement may be performed as appropriate. For example, a right turn is replaced with a left turn, and a right arrow is replaced with a left arrow. 
     In the embodiments described above, some or all of the functions and processes realized by software may be realized by hardware. Moreover, some or all of the functions and processes realized by hardware may be realized by software. As the hardware, for example, various circuits such as integrated circuits, discrete circuits, or a circuit module or the like combining those circuits may be used.