Patent Publication Number: US-2021188295-A1

Title: Vehicle control system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority from Japanese Patent Application No. 2019-228548 filed on Dec. 18, 2019. The entire disclosures of the above application are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a vehicle control system for controlling a traveling state of a vehicle. 
     BACKGROUND 
     In a conventional data collection device, vehicle traveling state data are collected and stored in an external memory slowly, that is, at a low frequency of a long period. When a collision accident occurs, for example, the vehicle traveling state data are collected and stored in the external memory quickly, that is, at a high frequency of a short period. As a result, the storage capacity of the external memory is saved, and the life of the external memory is extended by reducing the number of writings of data to the external memory. 
     The data collection device switches the sampling frequency for sampling the vehicle traveling state data as accident signals, which include an operation signal of an airbag or an acceleration signal output from an impact detection device installed in a vehicle, to the high frequency, when the accident signal is detected. In this way, the data collection device switches the sampling period in response to an actual occurrence of an accident. 
     SUMMARY 
     According to the present disclosure, a vehicle control system for controlling a traveling state of a vehicle comprises a storage buffer unit, a sampling period change unit and a storage control unit. The storage buffer unit is configured to sample and store, at a predetermined sampling period, control instruction data of a control target device which varies the travelling state of the vehicle. The sampling period change unit configured to change the sampling period for selecting the control instruction data stored in the storage buffer unit in accordance with a driving state of the vehicle. The storage control unit is configured to select and store in a non-volatile memory, at the sampling period set by the sampling period change unit, the control instruction data stored in the storage buffer unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram showing an overall configuration of a vehicle control system according to a first embodiment; 
         FIG. 2  is an illustration showing an example of a sampling period table of a steering instruction value; 
         FIG. 3  is an illustration showing an example of a sampling period table of a vehicle speed instruction value; 
         FIG. 4  is a flowchart showing processing executed in a VCIB when an autonomous driving mode is started; 
         FIG. 5  is a flowchart showing details of the sampling processing in step S 130  of the flowchart of  FIG. 4 ; 
         FIG. 6  is an illustration showing a table used in selection processing of selecting data to be stored in an eMMC in step S 210  of the flowchart of  FIG. 5 ; 
         FIG. 7  is a flowchart showing details of selection processing of selecting data to be stored in the eMMC  29  in step S 210  of the flowchart of  FIG. 5 ; 
         FIG. 8  is a timing chart showing one example of changes in a sampling period for selecting a vehicle speed instruction value to be stored in the eMMC from among vehicle speed instruction values stored in a temporary storage buffer when the vehicle speed instruction value is a target data of the sampling processing; 
         FIG. 9  is a configuration diagram showing an overall configuration of a vehicle control system according to a second embodiment; and 
         FIG. 10  is a flowchart showing an example of a sampling period table update processing in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     First Embodiment 
     Hereinafter, a vehicle control system according to a first embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the present embodiment, a vehicle control system is exemplified to execute control for autonomously driving an own vehicle as control of a traveling state of the vehicle. This autonomous driving may be executed, for example, in a limited area such as an expressway only or in any other roads including general roads. 
     As shown in  FIG. 1 , a vehicle control system  1  includes an autonomous drive ECU (electronic control unit)  10 . The autonomous drive ECU  10  includes a control instruction calculation unit  11 , which calculates control instruction values (control instruction data) for autonomously driving a vehicle based on detection data detected by various sensors  12 ,  33 ,  39  and  43 . 
     The sensor  12  may be at least one of a camera, a radar, a sonar and a LIDAR (light detection and ranging). The sensor  12  outputs detection data indicating a distance and a direction to other vehicles, artificial structures, objects such as humans and animals existing in a peripheral area around an own vehicle. Further, in case a camera is used as the sensor  12 , the sensor  12  also outputs detection data indicating traffic display such as lane markings and traffic signs of a road on which the vehicle travels. The sensor  12  performs detection at a predetermined period, and outputs the detection data that is a detection result to the control instruction calculation unit  11  of the autonomous drive ECU  10 . For example, in case a camera is used as the sensor  12 , the camera repeatedly captures a detection area (front, rear, sides, etc.) around the vehicle at a predetermined period. The sensor  12  identifies an object or a traffic display in the captured image and outputs detection data indicating an identification result to the control instruction calculation unit  11  of the autonomous drive ECU  10 . 
     It is to be noted that  FIG. 1  shows an example in which the sensor  12  directly outputs the detection data to the control instruction calculation unit  11 . However, the sensor  12  may be configured to output the detection data to the autonomous drive ECU  10  via a VCIB (vehicle control interface box)  20  described later. As a result, the detection data detected by the sensor  12  may also be stored in an eMMC (embedded multi media card)  29 , which is a non-volatile memory. 
     Other sensors  33 ,  39  and  43  detect driving states of the own vehicle and output respective detection data to the autonomous drive ECU  10 . The detection data of the detected driving states are, for example, a travel speed of the own vehicle, longitudinal acceleration in the front-back direction, lateral acceleration in the left-right direction, steering angle of a steering wheel, yaw angular velocity, engine rotation speed, engine water temperature, and brake fluid pressure. 
     Although  FIG. 1  illustrates one sensor  12  that outputs detection data to the autonomous drive ECU  10 , and one sensor  33 ,  39  and  43  that outputs detection data to each ECU  30 ,  35  and  40 , the detection data may be input from a plurality of sensors to each of the ECUs  10 ,  30 ,  35  and  40 . 
     Furthermore, the autonomous drive ECU  10  acquires road information (road type, road width, road shape, etc.) regarding the road, on which the own vehicle travels, from an external data center  50  or a navigation device (not shown). The road width and the road shape may be calculated based on a result of identifying lane markings detected by the camera. Detection data detected by the other sensors  33 ,  39  and  43 , road information from the data center  50  and the like are provided to the autonomous drive ECU  10  via the VCIB  20 . 
     The control instruction calculation unit  11  calculates and outputs to each ECU  30 ,  35  and  40  control instruction data for controlling the driving state of the own vehicle based on input various detection data (including road information) so that the own vehicle travels in correspondence to a planned travel route. For example, the control instruction calculation unit  11  calculates and outputs a steering instruction value indicating a target steering angle as the control instruction data to an EPS (electric power steering) ECU  30  described later at a predetermined period (for example, 10 ms) so that the own vehicle travels within the lane of the road on the planned travel route based on the detected lane markings. Alternatively, in case that the road on which the own vehicle travels has multiple lanes and an obstacle such as a stopped vehicle on the traffic lane on which the own vehicle travels, the control instruction calculation unit  11  calculates and outputs to the EPSECU  31  the steering instruction value indicating the target steering angle at a predetermined period so that the own vehicle changes the present travel lane to the adjacent lane to avoid the obstacle and returns to the original lane. 
     In addition, the control instruction calculation unit  11  calculates and outputs to a drive power ECU  35  described later a vehicle speed instruction value indicating a target travel speed of the vehicle as the control instruction data based on a legal speed limit of a travel road, a road shape, a distance and a relative speed relative to the other vehicle traveling ahead, and the like at a predetermined period (for example, 25 ms). Furthermore, when stopping of another vehicle traveling ahead of the own vehicle, the presence of an obstacle, a stop line, a red traffic light, or the like is detected in front of the own vehicle, the control instruction calculation unit  11  calculates and outputs to a brake power ECU  40  a deceleration instruction value indicating a target deceleration, which reduces the vehicle speed to zero before reaching a stop position of the own vehicle, as the control instruction data at a predetermined period. In addition, when it is necessary to reduce the travel speed of the own vehicle, for example, when an engine braking is not sufficient and a brake  42  needs to be activated, the control instruction value calculation unit  11  calculates and outputs to the brake power ECU  40  a deceleration instruction value at a predetermined period. 
     The EPS ECU  30  has an EPS control unit  31 . The EPS control unit  31  controls driving of an electric motor of an electric power steering (EPS)  32  so that an actual steering angle of the vehicle matches a given steering instruction value. Further, the EPS control unit  31  outputs the detection data detected by the sensor  33  to the control instruction calculation unit  11  at a predetermined period. The drive power ECU  35  has a drive power control unit  36 . The drive power control unit  36  controls an engine torque generated by an engine  37  and a gear shift stage of a transmission (TM)  38  so that an actual travel speed of the own vehicle matches a given vehicle speed instruction value. Further, the drive power control unit  36  outputs the detection data detected by the sensor  39  to the control instruction calculation unit  11  at a predetermined period. The brake power ECU  40  has a brake power control unit  41 . The brake power control unit  41  controls the brake power to be provided by the brake  42  so that an actual deceleration of the own vehicle matches a given deceleration instruction value. Further, the brake power control unit  41  outputs the detection data detected by the sensor  43  to the control instruction calculation unit  11  at a predetermined period. The periods at which the EPS control unit  31 , the drive power control unit  36  and the brake power control unit  41  output the detection data may be the same or different. 
     The VCIB  20  is provided between the autonomous drive ECU  10 , and a group of the EPS ECU  30 , drive power ECU  35  and brake power ECU  40 . The VCIB samples the control instruction data and the detection data at respective sampling periods and stores such data in a temporary storage buffer  26 , by routing the control instruction data output from the control instruction calculation unit  11  of the autonomous drive ECU  10  to the control units  31 ,  36  and  41  of the respective ECUs  30 ,  35  and  40  and the detection data of the sensors  33 ,  39  and  43  output from the respective control units  31 ,  36  and  41  to the control instruction calculation unit  11 . It should be noted that, for at least the control instruction data, the sampling period for storing data in the temporary storage buffer  26  is preferably equal to the shortest sampling period (highest sampling frequency) in a sampling period data table described later. 
     Further, the VCIB  20  selects and saves in the eMMC  29  the data stored in the temporary storage buffer  26  at a sampling period set according to the driving state of the vehicle. Hereinafter, the VCIB  20  will be described in detail. 
     As shown in  FIG. 1 , the VCIB  20  includes a first microcomputer (MCU 1 )  21 , a second microcomputer (MCU 2 ), and an SoC (system on a chip)  25 . The first microcomputer  21  is provided between the control instruction calculation unit  11  and the EPS control unit  31  and the drive power control unit  36 . The second microcomputer  23  is provided between the control instruction calculation unit  11  and the brake power control unit  41  and a communication unit  46  of a DCM (data communication module)  45  described later. The SoC  25  includes the temporary storage buffer  26 , a period change unit  27 , a data storage control unit  28  and the eMMC  29  that is a non-volatile memory. 
     The first microcomputer  21  has a data communication unit  22 . The data communication unit  22  receives from the control instruction calculation unit  11  the steering instruction value and the vehicle speed instruction value, which are the control instruction data output at respective predetermined periods. The data communication unit  22  outputs the received steering instruction value to the EPS control unit  31  and outputs the vehicle speed instruction value to the drive power control unit  36 , thereby routing the control instruction data. Further, the data communication unit  22  outputs the steering instruction value and the vehicle speed instruction value received at predetermined periods to the temporary storage buffer  26 . As a result, the temporary storage buffer  26  stores the steering instruction value and the vehicle speed instruction value output from the control instruction calculation unit  11  at the respective predetermined periods. 
     In addition, the data communication unit  22  receives the detection data detected by the sensor  33  and output from the EPS control unit  31  at the predetermined period, and the detection data detected by the sensor  39  and output from the drive power control unit  36  at a predetermined period. Then, the data communication unit  22  routes the detection data by outputting the received detection data to the control instruction calculation unit  11 . Further, the data communication unit  22  outputs each detection data received at each period to the temporary storage buffer  26 . As a result, the temporary storage buffer  26  stores each data detected by each sensor  33 ,  39  and provided to the control instruction calculation unit  11  at the predetermined period. 
     Similarly to the first microcomputer  21 , the second microcomputer  23  also has a data communication unit  24 . The data communication unit  24  receives from the control instruction calculation unit  11  the deceleration instruction value which is the control instruction data output at a predetermined period. The data communication unit  24  routes the control instruction data by outputting the received deceleration instruction value to the brake power control unit  41 . Further, the data communication unit  24  outputs the deceleration instruction value received at a predetermined period to the temporary storage buffer  26 . As a result, the temporary storage buffer  26  stores the deceleration instruction value output from the control instruction calculation unit  11  at the predetermined period. 
     In addition, the data communication unit  24  receives the detection data detected by the sensor  43  and output from the brake power control unit  41  at a predetermined period. The data communication unit  24  routes the detection data by outputting the received detection data to the control instruction calculation unit  11 . Further, the data communication unit  24  outputs the detection data received at a predetermined period to the temporary storage buffer  26 . Accordingly, the temporary storage buffer  26  stores the detection data detected by the sensor  43  and provided to the control instruction calculation unit  11  at the predetermined period. 
     Further, the data communication unit  24  of the second microcomputer  23  receives data (for example, road information or traffic information) transmitted from the data center  50  and received by the communication unit  46  of the DCM  45 , and outputs such data to the control instruction calculation unit  11 . Further, the data communication unit  24  receives data (for example, travel destination of the own vehicle and planned travel route, etc.) output from the control instruction calculation unit  11  toward the data center  50  provided externally away from the vehicle, and outputs such data to the communication unit  46  of the DCM  45 . The communication unit  46  transmits the received data to the data center  50 . In this way, the data communication unit  24  also routes the data exchanged between the control instruction calculation unit  11  and the data center  50 . The data communication unit  24  may output the data communicated between the control instruction calculation unit  11  and the data center  50  to the temporary storage buffer  26  and store the data therein. 
     In the above example, the VCIB  20  has two microcomputers  21  and  23 , and these two microcomputers  21  and  23  share the data, which are routed and output to the temporary storage buffer  26 . However, the VCIB  20  may have only a single microcomputer and that single computer may perform routing and outputting of all the data for storing in the temporary storage buffer  26 . Alternatively, the VCIB  20  may have three or more microcomputers, and the data shared by each microcomputer may be subdivided more. 
     The period change unit  27  receives detection data (including road information) indicating the driving state of the vehicle from the data communication units  22  and  24 . The period change unit  27  has a sampling period table in which the driving state of the vehicle and the sampling period are linked with each other. The period change unit  27  refers to the sampling period table and sets the sampling period corresponding to the driving state of the vehicle as the sampling period for selecting the data to be stored in the eMMC  29  from the data stored in the temporary storage buffer  26 . 
     Examples of the sampling period tables will be described with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  shows an example of a sampling period table of the steering instruction values, and  FIG. 3  shows an example of a sampling period table of the vehicle speed instruction values. 
     According to the example of the sampling period table shown in  FIG. 2 , the steering instruction value sampling period is set to 10 ms as a short sampling period in case that the driving state of the own vehicle is traveling on a road having a radius of curvature of 150 m or less, a magnitude of a yaw angular velocity is 7 deg/s or more in absolute value, a magnitude of a lateral acceleration is 0.25 G or more in absolute value and a width of a road on which a vehicle travels is 5 m or less, that is, when the own vehicle is quickly turning on a road with a relatively narrow width and a small radius of curvature. This driving state corresponds to a driving state having a high possibility of an accident. On the other hand, when the driving state of the own vehicle is any other state, the sampling period of the steering instruction value is set to 100 ms as a long the sampling period. 
     Further, according to the example of the sampling period table shown in  FIG. 3 , the sampling period of the vehicle speed instruction value is set to 25 ms, in case that the driving state of the own vehicle is such that a distance to a preceding vehicle traveling in front of the own vehicle is less than 40 m and a magnitude of a longitudinal acceleration is 0.1 G or more. In addition, the sampling period of the vehicle speed instruction value is set to 25 ms, in case that the driving state of the own vehicle is such that the travel speed of the own vehicle is higher than 40 km/h, the absolute value of the steering angle of the own vehicle is larger than 20 deg, and the absolute value of the relative speed with respect to the preceding vehicle is less than 2 km/h. On the other hand, in case that the driving state of the own vehicle is any other state, the sampling period of the vehicle speed instruction value is set to 100 ms. 
     In this way, when the vehicle driving state becomes highly likely that the vehicle will possibly be involved in an accident because of the control in the vehicle control system (that is, control of the EPS  32 , the engine  37 , the transmission  38 , the brake  42 , etc.) based on the control instruction data output from the control instruction calculation unit  11 , the sampling period is changed to a short period, which is shorter than that of the normal sampling period of the driving state in which the vehicle is not likely to be involved in an accident. It is to be noted that the driving states for which the sampling period is set to be short as shown in  FIG. 2  and  FIG. 3  are merely exemplary, and other driving states may be adopted as the driving state of the own vehicle corresponding to the short sampling period. 
     The data storage control unit  28  samples the data stored in the temporary storage buffer  26  and stores the sampled data in the eMMC  29  in accordance with the sampling period set by the period change unit  27 . That is, according to the present embodiment, the sampling period for selecting the data to be stored in the eMMC  29  (non-volatile memory) from the data stored in the temporary storage buffer  26  is not changed in response to the actual occurrence of an accident. It is rather changed to the shorter sampling period at the earlier time when the possibility of accident increases because of the control by the vehicle control system  1 . Therefore, while maintaining the life of the eMMC  29  by reducing the number of times of writing data thereto, data that are used when the control that may cause an accident is performed by the vehicle control system  1  are surely stored in the eMMC  29 . 
     In the above example, the period change unit  27  individually has the sampling period table in which the driving state of the vehicle and the sampling period are linked with each other for each of the plurality of types of control instruction data. Further, the period change unit  27  sets the short sampling period only for the control instruction data in which the driving state of the vehicle is in the driving state linked with the short sampling period. 
     However, when the driving state of the vehicle changes to a driving state which is linked to the short sampling period in regard to at least one of a plurality of types of control instruction data, the period change unit  27  may set the short sampling period for the control instruction data (including detection data) other than the control instruction data of the same driving state. As a result, since the eMMC  29  stores various data sampled at the short sampling period at any occurrence of accident, it is possible to analyze the cause of the accident in detail. 
     Further, the period change unit  27  may set the short sampling period of the plurality of types of data individually as the sampling period table in place of setting the short sampling period commonly for the plurality of types of control instruction data. 
     Regarding the detection data stored in the temporary storage buffer  26 , the sampling data table linking the driving state of the vehicle with the sampling period for setting the sampling period of selecting the detection data to be stored in the eMMC  29  may be provided individually for each detection data or commonly for all the detection data in the same manner as the control instruction data. Alternatively, the data storage control unit  28  may select the detection data that is the basis for generating the control instruction data from the temporary storage buffer  26  at the same sampling period and store the selected data in the eMMC  26 . 
     The VCIB  20  is configured to execute various processing including selecting each data of the control instruction data and the detection data stored in the temporary storage buffer  26  at the sampling period corresponding to the driving state of the vehicle and storing the selected data in the eMMC  29 . These processing will be described with reference to flowcharts shown in  FIG. 4 ,  FIG. 5  and  FIG. 7 , a table shown in  FIG. 6  and a timing chart shown in of  FIG. 8 . The following processing may be executed by at least one microcomputer of the VCIB  20 . 
       FIG. 4  is a flowchart showing processing executed in the VCIB  20  when the autonomous driving mode is started. In a first step S 100  of  FIG. 4 , the data communication units  22  and  24  of the first and second microcomputers  21  and  23  of the VCIB  20  receive each data at the period predetermined in correspondence to each data. Then, in step S 110 , the data communication units  22  and  24  output the received data to the temporary storage buffer  26 . Thus, each data is stored in the temporary storage buffer  26 . 
     In step S 120 , it is checked whether a predetermined time has elapsed after the previous processing of storing data in the eMMC  29 . When it is determined that the predetermined time has elapsed in this checking, sampling processing is executed to sample each data stored in the temporary storage buffer  26  in order to select the data to be stored in the eMMC  29  from each data stored in the temporary storage buffer  26  in step S 130  and store the sampled data in the eMMC  29 . On the other hand, when it is determined that the predetermined time has not elapsed yet, step S 140  is executed by skipping the sampling process of step S 130 . That is, in the present embodiment, the sampling process of step S 130  is performed at the timing when the data for the predetermined time is accumulated in the temporary storage buffer  26 . In step S 140 , it is checked whether the autonomous driving mode has ended. When it is determined that the autonomous driving mode has ended, the processing shown in the flowchart of  FIG. 4  is finished. On the other hand, when it is determined that the autonomous driving mode has not ended, the above processing is repeated from step S 100 . 
     Details of the sampling process in step S 130  are shown in the flowchart of  FIG. 5 . On the other hand, when the driving state of the own vehicle is any other state, the sampling period of the steering instruction value is set to 100 ms Hereinafter, the sampling process of each data stored in the temporary storage buffer  26  will be described with reference to the flowchart of  FIG. 5 . In first step S 200  of  FIG. 5 , target data to be sampled is selected from a plurality of types of data. 
     In following step S 210 , with respect to the data selected as the sampling target, the data to be stored in the eMMC  29  is selected from the plurality of data stored in the temporary storage buffer  26  in accordance with the sampling period set by the period change unit  27 . The process of selecting the data to be stored in the eMMC  29  will be described later in detail. 
     In step S 220 , it is checked whether all types of data are selected as the target data of the sampling process, and the selection process of the data to be stored in the eMMC  29  is completed for all types of data. When it is determined in step S 220  that the selection process of the data to be stored in the eMMC  29  has not been completed for all types of data, the above processing is repeated from step S 200  to select other data, which has not been processed yet as the target data. On the other hand, when it is determined that the selection process of the data to be stored in the eMMC  29  has been completed for all types of data, the processing illustrated in the flowchart of  FIG. 5  is finished. After step S 220 , step S 140  of the flowchart of  FIG. 4  is executed. 
     Hereinafter, an example of the data selection processing in step S 210  of  FIG. 5  will be described in detail with reference to the table of  FIG. 6  and the flowchart of  FIG. 7 . 
     In  FIG. 6 , B(i).t indicates a time when each data communication unit  22 ,  24  has received data B(i), and B(i).v indicates a value of the data B(i). As shown in the table of  FIG. 6 , the temporary storage buffer  26  stores the time B(i).t when the data B(i) is received and the value of the data B(i) in the linked manner with each other. Further, in  FIG. 6 , B(i).samp is a sampling period, which is set by referring to a sampling period table and variable with the driving state of the own vehicle at the time when each data B(i) is received. This sampling period B(i).samp may be set by the period change unit  27  when each data is stored in the temporary storage buffer  26 , and may be stored in the temporary storage buffer  26  together with the data reception time and the data value. Alternatively, it may be set by the period change unit  27  when selecting the data to be stored in the eMMC  29  from the data stored in the temporary storage buffer  26 . 
     In first step S 300  of the flowchart of  FIG. 7 , a variable “s” indicating the data having been stored in the eMMC  29  is set to 0. At this time, the first data B(0) which corresponds to the variable s=0 may be selected as the target data for storage in the eMMC  29  and then stored in the eMMC  29 . In following step S 310 , a variable “i” indicating whether it is a target data to be checked for storage is set to 1. 
     Then, in step S 320 , it is checked whether a time difference between the reception time B(i).t of the check target data B(i) and the reception time B(s).t of the data B(s) stored in the eMMC  29  is equal to or larger than the sampling period B(i).samp, which is set according to the driving state of the own vehicle at the time of receiving the check target data B(i). When the time difference B(i).t−B(s).t is equal to or larger than the sampling period B(i).samp, the reception time B(i).t of the check target data B(i) is later than the reception time B(s).t of the data B(s) stored in the eMMC  29  at the previous time by the sampling period B(i).samp or larger. In this case, the check target data B(i) is selected as the storage target data and stored in the eMMC  29  in step S 340 . On the other hand, when it is determined in step S 320  that the time difference B(i).t−B(s).t is smaller than the sampling period B(i).samp, step S 330  is executed. 
     In step S 330 , it is checked whether an absolute value of a difference between the data value B(i).v of the check target data B(i) and a data value B(i−1).v of the immediately preceding data B(i−1) is larger than a predetermined abnormality determination threshold value. The abnormality determination threshold value is set to a value capable of checking a magnitude that does not normally occur as a change in data. When it is determined in this check process that the absolute value of the difference between the two data |B(i).v−B(i−1).v| is larger than the abnormality determination threshold value, the check target data B(i) is selected as the storage target data and stored in the eMMC  29  in step S 340 . That is, in the present embodiment, when the difference between the two data stored presently and preciously in the temporary storage buffer  26  is larger than the predetermined abnormality determination threshold value continuously in time, the check target data B(i) is selected as the storage target data and stored in the eMMC  29  regardless of the sampling period set by the period changing unit  27 . This can prevent the abnormal data from being excluded from the data to be stored in the eMMC  29 . On the other hand, when it is determined in step S 330  that the absolute value | B(i).v−B(i−1).v| of the difference between the two data is equal to or smaller than the abnormality determination threshold value, step S 360  is executed. 
     In step S 350 , since the data B(i) has been stored in the eMMC  29  in step S 340 , the variable “s” indicating the data stored in the eMMC  29  is rewritten to s=i. In step S 360 , the variable “i” is incremented so that the check target data is updated. In next step S 370 , it is checked whether the variable “i” indicating the check target data has become larger than the number “n” of data stored in the temporary storage buffer  26  within a fixed time. When it is determined in this check process that the variable “i” is larger than the data number “n,” the storage data selection processing shown in the flowchart of  FIG. 7  is finished and the processing of the flowchart shown in  FIG. 5  is executed. On the other hand, when it is determined in step S 370  that the variable “i” is equal to or smaller than the number of data “n,”, the process returns to step S 320 . 
       FIG. 8  is a timing chart of one example showing changes of the sampling period, which is for selecting the vehicle speed instruction value to be stored in the eMMC  20  from the vehicle speed instruction value stored in the temporary storage buffer  26 , in correspondence to the driving state of the own vehicle, when the vehicle speed instruction value becomes the target data of the sampling processing in step S 200  in the flowchart of  FIG. 5 . 
     In the timing chart of  FIG. 8 , until elapsed time on the horizontal axis reaches approximately 300 ms, the driving state of the own vehicle is such that the first distance between the own vehicle and the preceding vehicle in the sampling period table of  FIG. 3  is shorter than 40 m as shown in (a) and the longitudinal acceleration of the own vehicle is larger than 0.1 G as shown in (b). This driving state corresponds to the first state, which is set as a state having higher possibility of an accident in the sampling period table of  FIG. 3 . Therefore, as shown in (f), the sampling period is set to 25 ms as a short sampling period until the elapsed time on the horizontal axis reaches about 300 ms. As a result, the sampling timing of the vehicle speed instruction value arrives every time 25 ms elapses until the elapsed time reaches approximately 300 ms, and the vehicle speed instruction value corresponding to this sampling timing is selected and stored in the eMMC  29 . 
     When the distance to the preceding vehicle exceeds 40 m immediately before the elapsed time reaches 300 ms as shown in (a) of  FIG. 8 , the driving state of the own vehicle does not correspond to the driving state in the sampling period table of  FIG. 3 . Therefore, as shown in (f), the sampling period of the vehicle speed instruction value is changed to 100 ms set as a long sampling period. 
     After that, when the elapsed time reaches about 400 ms, the driving state of the own vehicle is such that the speed of the own vehicle is higher than 40 km/h as shown in (c), the steering angle is larger than 20 deg as shown in (d) and the relative speed with respect to the preceding vehicle is within 2 km/h as shown in (e). This driving state corresponds to the second driving state, which is set as a state having higher possibility of an accident in the sampling period table of  FIG. 3 . Therefore, as shown in (f), the sampling period of the vehicle speed instruction value is returned to 25 ms again immediately after the elapsed time exceeds 400 ms. 
     Second Embodiment 
     Next, a vehicle control system according to the second embodiment of the present disclosure will be described.  FIG. 9  is an overall configuration diagram of a vehicle control system  2  of the present embodiment. 
     As shown in  FIG. 9 , the vehicle control system  2  has a locator ECU  47  added to the vehicle control system  1  according to the first embodiment. Other configurations are the same as the first embodiment. 
     The locator ECU  47  includes a present position calculation unit  48  and a GPS receiver  49 . The GPS receiver  49  receives signals transmitted from a plurality of GPS satellites. The present position calculation unit  48  calculates a present position of the own vehicle based on the signals from the plurality of GPS satellites received by the GPS receiver  49 . Then, the present position of the own vehicle calculated by the present position calculation unit  48  is transmitted to a data center  50  via the communication unit  46  of the DCM  45 . 
     The data center  50  identifies an area (region or road type) in which the vehicle is traveling based on the present position transmitted from the vehicle. The data center  50  has a sampling period table which is adapted to characteristics of each area. The data center  50  selects the sampling period table corresponding to the specified area and transmits it as update data to the vehicle. 
     For example, in case there is an area where an accident rate of a vehicle traveling at the vehicle speed higher than a specified value is high, the sampling period table is set to have stricter restrictions on the conditions related to the vehicle speed. In case there is an area where an accident rate on a curved road is high, the sampling period table is set to have stricter restrictions on the yaw angular speed and the lateral acceleration, which indicate a sharp turn. As a result, it becomes possible to use a sampling period table which reflects a statistical accident rate. In case an expressway is specified as a traveling area of a vehicle, for example, a sampling period table may be set so that an inter-vehicle distance from the preceding vehicle and the vehicle speed of the own vehicle are adapted to the traveling on the expressway. 
     It is also possible to configure the period change unit  27  to have the sampling period tables for various areas in advance, and select a sampling period table which corresponds to a new area when the traveling area of the own vehicle changes to the new area. 
       FIG. 10  is a flowchart showing an example of sampling period table update processing in the present embodiment. In first step S 400 , the present position of the own vehicle is calculated based on the signals received by the GPS receiver  49  from the plurality of GPS satellites. In next step S 410 , the calculated present position of the own vehicle is transmitted to the data center  50  via the communication unit  46  of the DCM  45 . 
     In step S 420 , it is checked whether update data of the sampling period table has been received from the data center  50 . When it is determined that the update data of the sampling period table has been received, step S 430  is executed. In step S 430 , the sampling period table is updated with the received update data. Then, in step S 440 , It is checked whether the vehicle has finished traveling. When it is determined in this check process that the vehicle has finished traveling, the processing shown in the flowchart of  FIG. 10  is terminated. On the other hand, when it is determined that the own vehicle has not finished traveling yet, the above processing is executed from S 400  again. 
     In the vehicle control system  2  according to the present embodiment, the sampling period of data such as control instruction data is set by referring to the sampling period table regardless of the type of data. Therefore, the sampling period of each data can be flexibly changed by changing the sampling period table. 
     The vehicle control system according to the present disclosure described above is not limited to the above embodiments and may be variously modified within the spirit and scope of the disclosure. 
     For example, in the first and second embodiments, the vehicle control systems  1  and  2  are assumed to have configurations for driving the vehicle autonomously. However, the vehicle control system is not necessarily limited to a system that performs autonomous driving, and may be, for example, a system that performs cruise control in which the vehicle is controlled simply to travel at a constant speed or to follow the preceding vehicle.