Patent Publication Number: US-11643113-B2

Title: Target identification device and driving assistance device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2019-090364 filed May 13, 2019, the description of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a target identification device and a driving assistance device. 
     Related Art 
     A target identification device has been known in which a type of a moving object is identified by using information detected by a sensor such as a radar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG.  1    is a schematic diagram showing a configuration of an automatic driving system; 
         FIG.  2    is a flow chart showing a driving assistance process; 
         FIG.  3    is an explanatory diagram showing an example in which a likelihood is obtain from trajectory information; and 
         FIG.  4    is a schematic diagram showing a configuration of an autonomous driving system according to a second embodiment. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENT 
     As disclosed in, for example, JP-A-2018-59884, a type of a moving object is identified by using a speed of the moving object measured by a radar and an amount of change in the speed. However, the target identification device is not limited thereto. 
     It is desired to have a technique for more reliably identifying types of moving objects. 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, in which like reference numerals refer to like or similar elements regardless of reference numerals and duplicated description thereof will be omitted. 
     A. First Embodiment 
     As shown in  FIG.  1   , a vehicle  10  includes an autonomous driving control system  100 . In the present embodiment, the autonomous driving control system  100  includes a driving assistance device  200  including a target identification device  110  and a driving assistance unit  210 , a surrounding sensor  122 , a driving force control Electronic Control Unit (ECU)  220 , a braking force control ECU  230 , and a steering control ECU  240 . The driving assistance device  200 , the driving force control ECU  220 , the braking force control ECU  230 , and the steering control ECU  240  are connected to each other via an in-vehicle network  250 . 
     The surrounding sensor  122  detects a situation in the surroundings of the vehicle  10 . Examples of the surrounding sensor  122  include surrounding sensors using a reflected wave such as a laser radar, a millimeter wave radar, and an ultrasonic sensor. In the present embodiment, the surrounding sensor  122  is a millimeter wave radar. 
     The target identification device  110  includes an acquisition unit  111 , a calculation unit  112 , a target identification unit  113 , and a storage unit  114 . The target identification device  110  is composed of a microcomputer composed of a central processing unit (CPU), a RAM, and a ROM. The microcomputer executes a preinstalled program to implement functions of the components of the target identification device  110 . However, some or all of the functions of the components may be implemented by a hardware circuit. 
     The acquisition unit  111  acquires trajectory information including information on a movement trajectory of a moving object in the surroundings of the vehicle  10  detected by the surrounding sensor  122 . The “trajectory information” is information including positions of a moving object chronologically obtained. The acquisition unit  111  may acquire part or all of the information through inter-vehicle communication with another vehicle. 
     The calculation unit  112  calculates a likelihood for each type of moving object from the trajectory information by using a plurality of models predefined for each type of moving object. The “likelihood” is a value indicating a probability of an estimated value for each model, and a higher likelihood indicates a higher probability. In the present embodiment, the estimated value is, for example, future trajectory information, and is specifically a movement trajectory including a future estimated position of the moving object. Details of the calculation of the likelihood will be described later. 
     The target identification unit  113  identifies the type of the moving object according to the likelihood calculated by the calculation unit  112 . 
     The storage unit  114  stores the models used by the calculation unit  112 . The storage unit  114  does not need to be included in the target identification device  110 . Instead of being stored in the storage unit  114 , the models may be stored in a storage unit of the vehicle  10  or the like. The models are, for example, a motion model for the case where a pedestrian moves straight, a motion model for the case where a pedestrian turns, a motion model for the case where a vehicle moves straight, a motion model for the case where a vehicle turns, and the like. The models can be generated from the previously obtained observation data by using a neural network as machine learning. The models may be generated by performing a simulation or an experiment in advance. 
     The driving assistance unit  210  is composed of a microcomputer composed of a central processing unit (CPU), a RAM, and a ROM. The microcomputer executes a preinstalled program to implement a driving assistance function. For example, according to the future movement trajectory of the moving object estimated by the calculation unit  112  and the target type obtained by the target identification unit  113 , the driving assistance unit  210  controls the driving force control ECU  220 , the braking force control ECU  230 , and the steering control ECU  240  to perform driving assistance. 
     The driving force control ECU  220  is an electronic control unit that controls an actuator, such as an engine, that generates a driving force of the vehicle. In the case of manual driving by a driver, the driving force control ECU  220  controls a power source, which is an engine or an electric motor, according to an amount of operation of an accelerator pedal. On the other hand, in the case of autonomous driving, the driving force control ECU  220  controls the power source according to a required driving force calculated by the driving assistance unit  210 . 
     The braking force control ECU  230  is an electronic control unit that controls a brake actuator that generates a braking force of the vehicle. In the case of manual driving by the driver, the braking force control ECU  230  controls the brake actuator according to an amount of operation of a brake pedal. On the other hand, in the case of autonomous driving, the braking force control ECU  230  controls the brake actuator according to a required braking force calculated by the driving assistance unit  210 . 
     The steering control ECU  240  is an electronic control unit that controls a motor that generates a steering torque of the vehicle. In the case of manual driving by the driver, the steering control ECU  240  controls the motor according to operation of a steering wheel to generate an assist torque for the steering operation. Thus, the driver can operate the steering with a small amount of power to steer the vehicle. On the other hand, in the case of autonomous driving, the steering control ECU  240  controls the motor according to a required steering angle calculated by the driving assistance unit  210  to steer the vehicle. 
     A driving assistance process shown in  FIG.  2    is a series of process steps in which the target identification device  110  identifies a type of a moving object in the surroundings of the vehicle  10  and the driving assistance unit  210  performs driving assistance according to the result of the identification. This process is repeatedly performed by the driving assistance device  200  when, while the vehicle  10  is traveling, the target identification device  110  detects a moving object from information detected by the surrounding sensor  122 . 
     First, at step S 100 , the acquisition unit  111  acquires trajectory information. More specifically, the acquisition unit  111  acquires trajectory information indicating a chronological movement trajectory of a moving object by using information detected by the surrounding sensor  122 . The acquisition unit  111  may acquire trajectory information for each moving object by identifying an individual moving object using a known clustering technique in which a group of data detected by the surrounding sensor  122  are classified for each moving object. 
     Next, at step S 110 , the calculation unit  112  calculates a likelihood by using the trajectory information acquired at step S 100  and the plurality of models recorded in the storage unit  114 . The likelihood can be obtained, together with estimation of a movement trajectory of the moving object, for example, by using an Interacting Multiple Model (IMM) method which is a known state estimation method. More specifically, as shown in  FIG.  3   , by using the plurality of models that have been predefined for each type of moving object and recorded in the storage unit  114 , the calculation unit  112  estimates a future state of the moving object for each type of moving object from the trajectory information acquired at step S 100 , and calculates a likelihood of the estimated movement trajectory. In the present embodiment, the “state of the moving object” is, for example, information such as a speed, a position, a size, and the like of the moving object. In order to calculate the likelihood, for example, a likelihood L can be obtained by the following formula (1). 
     
       
         
           
             
               
                 
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     In formula (1), S represents a covariance of observation residual, the Z-tilde symbol represents an observation residual between an observed value which is a value of the trajectory information and an estimated value which is a value of the trajectory information estimated for each model, specifically, a value indicating the state of the moving object, and exp represents an exponential function. 
     Subsequently, at step S 120 , the target identification unit  113  identifies the type of the moving object by using the likelihood calculated at step S 110 . For example, the target identification unit  113  can identify, as the type of the moving object, a target indicated by the model having the highest likelihood. When the likelihoods of all the models are a predetermined threshold or less, the target identification unit  113  may determine that none of the targets indicated by the models corresponds to the type of the moving object. 
     Finally, at step S 130 , the driving assistance unit  210  performs driving assistance according to the future movement trajectory of the moving object estimated at step S 110  and the type of the moving object identified at step S 120 . For example, the driving assistance unit  210  can perform control so that when a moving object in front of the vehicle  10  is a two-wheeled vehicle and turns left, the vehicle  10  travels on a right side of a lane. Furthermore, the driving assistance unit  210  can perform control so that when a moving object that is located in front of the vehicle  10  and is moving in the same direction as a direction of movement of the vehicle  10  is an automobile, the vehicle  10  travels following the automobile, and perform control so that when such a moving object is a bicycle, the vehicle  10  passes the bicycle. 
     According to the driving assistance device  200  of the present embodiment described above, the target identification unit  113  of the target identification device  110  can identify the type of the moving object according to the likelihood for each type of the moving object calculated from the trajectory information by the calculation unit  112 . The type of the moving object can be identified by using only the trajectory information acquired from the surrounding sensor  122 , thereby identifying the type of the moving object without using a camera. Furthermore, the driving assistance unit  210  can perform driving assistance according to the movement trajectory and the type of the moving object estimated by the target identification device  110 , thereby achieving more appropriate driving assistance. 
     In a case where the acquisition unit  111  acquires trajectory information without performing clustering of a moving object, even when a plurality of moving objects are overlapped with each other, the type of the moving object can be accurately identified. For example, when the moving object is a crowd of pedestrians, if the crowd of pedestrians is considered as a single moving object and subjected to clustering, and one of the pedestrians moves in a direction opposite to a direction in which the other pedestrians move, it is difficult to identify the moving object as a pedestrian. However, when no clustering is performed, the acquisition unit  111  can acquire trajectory information including information on a movement trajectory of each of the pedestrians, thereby preventing each trajectory information from becoming noise and allowing accurate calculation of the likelihood. 
     B. Second Embodiment 
     A configuration of an autonomous driving control system  100 A according to a second embodiment shown in  FIG.  4    differs from that of the autonomous driving control system of the first embodiment in that the autonomous driving control system  100 A includes a camera  124 , and the rest of the configuration is the same as that of the first embodiment. The camera  124  captures an image of the surroundings of the vehicle  10  to acquire the image. Examples of the camera  124  include a stereo camera and a monocular camera. 
     The acquisition unit  111  can acquire the image of the surroundings of the vehicle  10  captured by the camera  124 . In the present embodiment, in addition to the likelihood, the target identification unit  113  uses the image of the surroundings of the vehicle  10  captured by the camera  124  to identify the type of the moving object. For example, when the target identification unit  113  cannot determine from the image of the surroundings of the vehicle  10  whether the moving object is a pedestrian or a bicycle, the target identification unit  113  can compare the likelihood of the model for the pedestrian with the likelihood of the model for the bicycle, and identify, as the type of the moving object, the model having a higher likelihood. 
     According to the driving assistance device  200  of the present embodiment described above, the target identification unit  113  of the target identification device  110  identifies the type of the moving object by using the image of the surroundings of the vehicle  10  captured by the camera  124  in addition to the likelihood for each type of the moving object calculated from the trajectory information by the calculation unit  112 , thereby achieving more accurate identification of the type of the moving object. 
     Modifications 
     The present disclosure is not limited to the above embodiments, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, in order to solve the above problem or to achieve some or all of the above effects, replacement or combination may be performed as appropriate in the technical features in the embodiments corresponding to the technical features in each embodiment described in Summary of the Disclosure. Unless the technical features are described as essential in the present specification, the technical features can be deleted as appropriate.