Patent Publication Number: US-2023145836-A1

Title: Vehicle driving assist apparatus, vehicle driving assist method, vehicle driving assist program, and vehicle comprising vehicle driving assist apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese patent application No. JP 2021-182973 filed on Nov. 10, 2021, the content of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Field 
     The invention relates to a vehicle driving assist apparatus, a vehicle driving assist method, a vehicle driving assist program, and a vehicle comprising the vehicle driving assist apparatus 
     Description of the Related Art 
     There is known a vehicle driving assist apparatus which decelerates an own vehicle by causing the own vehicle to coast by a moving assist control or an autonomous driving control or an automatic driving control which autonomously accelerates and decelerates the own vehicle so as to maintain a moving speed of the own vehicle in a predetermined speed range (for example, see JP 2017-193334 A). 
     There is also known a technique to (i) determine that an accelerator override state is produced due to an accelerator pedal being operated while the moving assist control is executed, (ii) temporarily stop the moving assist control, and (iii) accelerate the own vehicle, depending on an operation amount of the accelerator pedal. Thereby, the own vehicle stops coasting and is accelerated. Thus, a power output efficiency of a driving apparatus of the own vehicle (i.e., an energy efficiency at which the driving apparatus outputs power) is reduced. If the moving assist control continues to be executed even when the accelerator override state is produced, a reduction of the power output efficiency of the driving apparatus of the own vehicle can be avoided. However, a request of the driver to accelerate the own vehicle is not met. 
     SUMMARY 
     An object of the invention is to provide a vehicle driving assist apparatus which meets the request of the driver to accelerate the own vehicle, limiting the reduction of the power output efficiency of the driving apparatus of the own vehicle when the accelerator override state is produced while the moving assist control is executed. 
     According to the invention, a vehicle driving assist apparatus comprises an electronic control unit configured to execute an ordinary moving assist control and an economy moving assist control. The ordinary moving assist control is a control to autonomously accelerate and decelerate an own vehicle so as to maintain a moving speed of the own vehicle at a set speed, or maintain a distance between the own vehicle and a preceding vehicle which moves ahead of the own vehicle at a set distance. The economy moving assist control is a control to autonomously accelerate and decelerate the own vehicle so as to maintain the moving speed of the own vehicle within a predetermined speed range, or maintain the distance between the own vehicle and the preceding vehicle within a predetermined forward distance range. 
     While the economy moving assist control is executed, the electronic control unit is configured to execute (i) a coasting control to decelerate the own vehicle by causing the own vehicle to coast and (ii) an optimum acceleration control to accelerate the own vehicle by controlling operations of a driving apparatus of the own vehicle at a power output efficiency of the driving apparatus equal to or greater than a predetermined efficiency. 
     While the ordinary moving assist control is executed, the electronic control unit is configured to stop the ordinary moving assist control and execute an ordinary moving control to accelerate the own vehicle, based on an accelerator pedal operation amount when an accelerator override state is produced due to an operation of an accelerator pedal of the own vehicle. 
     In addition, the electronic control unit is configured to accelerate the own vehicle by the optimum acceleration control when an acceleration request condition that the accelerator override state is produced, is satisfied while the economy moving assist control is executed. 
     With the vehicle driving assist apparatus according to the invention, the own vehicle is accelerated by controlling the operations of the driving apparatus so as to maintain the power output efficiency of the driving apparatus at the efficiency equal to or greater than the predetermined efficiency when the accelerator override state is produced while the economy moving assist control is executed. Thus, the request of the driver to accelerate the own vehicle can be met. In addition, the power output efficiency of the driving apparatus can be maintained at the efficiency equal to or greater than the predetermined efficiency and thus, the reduction of the power output efficiency of the driving apparatus of the own vehicle can be limited. 
     According to an aspect of the invention, the acceleration request condition may include a condition that the moving speed of the own vehicle is within the predetermined speed range. 
     If the own vehicle is accelerated when the economy moving assist control is executed, and the moving speed of the own vehicle is not within the predetermined speed range, the moving speed of the own vehicle cannot be maintained within a limited speed range. With the vehicle driving assist apparatus according to this aspect of the invention, the acceleration request condition includes the condition that the moving speed of the own vehicle is within the predetermined speed range while the economy moving assist control is executed. Thus, the moving speed of the own vehicle can be maintained within the limited speed range. 
     According to another aspect of the invention, the acceleration request condition may include a condition that the distance between the own vehicle and the preceding vehicle is within the predetermined forward distance range. 
     If the own vehicle is accelerated when the economy moving assist control is executed, and the distance between the own vehicle and the preceding vehicle is not within the predetermined forward distance range, the distance between the own vehicle and the preceding vehicle cannot be maintained within a limited distance range. With the vehicle driving assist apparatus according to this aspect of the invention, the acceleration request condition includes the condition that the distance between the own vehicle and the preceding vehicle is within the predetermined forward distance range. Thus, the distance between the own vehicle and the preceding vehicle can be maintained within the limited distance range. 
     According to further another aspect of the invention, the electronic control unit may be configured to maintain a distance between the own vehicle and a following vehicle which moves behind the own vehicle within a predetermined rearward distance range by the economy moving assist control. In this aspect, the acceleration request condition may include a condition that the distance between the own vehicle and the following vehicle is within the predetermined rearward distance range. 
     When there is the following vehicle, and the economy moving assist control is executed, the distance between the own vehicle and the following vehicle is desirably maintained within a limited distance range. With the vehicle driving assist apparatus according to this aspect of the invention, the acceleration request condition includes the condition that the distance between the own vehicle and the following vehicle is within the predetermined rearward distance range when the economy moving assist control is executed. Thus, the distance between the own vehicle and the following vehicle can be maintained within the limited distance range. 
     According to further another aspect of the invention, two power sources having different power output properties may be installed on the own vehicle. In this aspect, the electronic control unit may be configured to stop operating at least one of the power sources when the coasting control is executed. In this aspect, the acceleration request condition may include a condition that the unoperated power source will be operated when the own vehicle is accelerated by the ordinary moving control, based on the accelerator pedal operation amount. 
     If the own vehicle is accelerated by changing the coasting control to the optimum acceleration control when the unoperated power source will be operated to accelerate the own vehicle by the ordinary moving control in response to the accelerator pedal being operated while the coasting control is executed, the own vehicle is accelerated by the optimum acceleration control, not by the ordinary moving control. Thus, the power output efficiency is increased. With the vehicle driving assist apparatus according to this aspect of the invention, the acceleration request condition includes the condition that the unoperated power source will be operated when the own vehicle is accelerated by the ordinary moving control, based on the accelerator pedal operation amount. Thus, the power output efficiency can be maintained at the great efficiency. 
     According to the invention, a vehicle driving assist method comprises a step of executing an ordinary moving assist control to autonomously accelerate and decelerate an own vehicle so as to maintain a moving speed of the own vehicle at a set speed, or maintain a distance between the own vehicle and a preceding vehicle which moves ahead of the own vehicle at a set distance. The vehicle driving assist method comprises a step of executing an economy moving assist control to autonomously accelerate and decelerate the own vehicle so as to maintain the moving speed of the own vehicle within a predetermined speed range, or maintain the distance between the own vehicle and the preceding vehicle within a predetermined forward distance range. The vehicle driving assist method comprises a step of, while the economy moving assist control is executed, executing a coasting control to decelerate the own vehicle by causing the own vehicle to coast and an optimum acceleration control to accelerate the own vehicle by controlling operations of a driving apparatus of the own vehicle at a power output efficiency of the driving apparatus equal to or greater than a predetermined efficiency. The vehicle driving assist method comprises a step of, while the ordinary moving assist control is executed, stopping the ordinary moving assist control and executing an ordinary moving control to accelerate the own vehicle, based on an accelerator pedal operation amount when an accelerator override state is produced due to an operation of an accelerator pedal of the own vehicle. The vehicle driving assist method comprises a step of accelerating the own vehicle by the optimum acceleration control when an acceleration request condition that the accelerator override state is produced, is satisfied while the economy moving assist control is executed. 
     With the vehicle driving assist method of the invention, for the reasons described above, the request of the driver to accelerate the own vehicle can be met, and the reduction of the power output efficiency of the driving apparatus of the own vehicle can be limited. 
     According to the invention, a vehicle driving assist program is configured to execute an ordinary moving assist control to autonomously accelerate and decelerate an own vehicle so as to maintain a moving speed of the own vehicle at a set speed, or maintain a distance between the own vehicle and a preceding vehicle which moves ahead of the own vehicle at a set distance. The vehicle driving assist program is configured to execute an economy moving assist control to autonomously accelerate and decelerate the own vehicle so as to maintain the moving speed of the own vehicle within a predetermined speed range, or maintain the distance between the own vehicle and the preceding vehicle within a predetermined forward distance range. The vehicle driving assist program is configured to, while the economy moving assist control is executed, execute a coasting control to decelerate the own vehicle by causing the own vehicle to coast and an optimum acceleration control to accelerate the own vehicle by controlling operations of a driving apparatus of the own vehicle at a power output efficiency of the driving apparatus equal to or greater than a predetermined efficiency. The vehicle driving assist program is configured to, while the ordinary moving assist control is executed, stop the ordinary moving assist control and execute an ordinary moving control to accelerate the own vehicle, based on an accelerator pedal operation amount when an accelerator override state is produced due to an operation of an accelerator pedal of the own vehicle. The vehicle driving assist program is configured to accelerate the own vehicle by the optimum acceleration control when an acceleration request condition that the accelerator override state is produced, is satisfied while the economy moving assist control is executed. 
     With the vehicle driving assist program of the invention, for the reasons described above, the request of the driver to accelerate the own vehicle can be met, and the reduction of the power output efficiency of the driving apparatus of the own vehicle can be limited. 
     According to the invention, a vehicle comprises the vehicle driving assist apparatus of the invention. Further, a vehicle comprises a vehicle driving assist apparatus executing the vehicle driving assist method of the invention. Furthermore, a vehicle comprises a vehicle driving assist apparatus executing the vehicle driving assist program of the invention. 
     Elements of the invention are not limited to elements of embodiments and modified examples of the invention described with reference to the drawings. The other objects, features and accompanied advantages of the invention can be easily understood from the embodiments and the modified examples of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view which shows a vehicle driving assist apparatus according to an embodiment of the invention and a vehicle or an own vehicle installed with the vehicle driving assist apparatus. 
         FIG.  2    is a view which shows a forward inter-vehicle distance and a rearward inter-vehicle distance. 
         FIG.  3    is a view which shows a power output efficiency of an internal combustion engine, a power output efficiency of an electric motor, and a requested driving torque. 
         FIG.  4    is a view which shows a flowchart of a routine executed by the vehicle driving assist apparatus according to the embodiment of the invention. 
         FIG.  5    is a view which shows a flowchart of a routine executed by the vehicle driving assist apparatus according to the embodiment of the invention. 
         FIG.  6    is a view which shows a flowchart of a routine executed by the vehicle driving assist apparatus according to the embodiment of the invention. 
         FIG.  7    is a view which shows a flowchart of a routine executed by the vehicle driving assist apparatus according to the embodiment of the invention. 
         FIG.  8    is a view which shows a flowchart of a routine executed by the vehicle driving assist apparatus according to the embodiment of the invention. 
         FIG.  9 A  is a view which shows a scene that the forward inter-vehicle distance is greater than a forward middle distance determination value. 
         FIG.  9 B  is a view which shows a scene that the forward inter-vehicle distance is equal to or smaller than the forward middle distance determination value. 
         FIG.  10 A  is a view which shows a scene that the forward inter-vehicle distance is greater than a forward short distance determination value. 
         FIG.  10 B  is a view which shows a scene that the forward inter-vehicle distance is equal to or smaller than the forward short distance determination value. 
         FIG.  11 A  is a view which shows a scene that the rearward inter-vehicle distance is greater than a rearward short distance determination value. 
         FIG.  11 B  is a view which shows a scene that the rearward inter-vehicle distance is equal to or smaller than the rearward short distance determination value. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Below, a vehicle driving assist apparatus according to an embodiment of the invention will be described with reference to the drawings.  FIG.  1    shows the vehicle driving assist apparatus  10  according to the embodiment of the invention. The vehicle driving assist apparatus  10  is installed on an own vehicle  100 . 
     &lt;ECU&gt; 
     The vehicle driving assist apparatus  10  includes an ECU  90  as a control device. ECU stands for electronic control unit. The ECU  90  includes a microcomputer as a main component. The microcomputer includes a CPU, a ROM, a RAM, a non-volatile memory, and an interface. The CPU is configured or programmed to realize various functions by executing instructions, programs, or routines stored in the ROM. In particular, the ROM stores a vehicle driving assist program which executes a driving assist control described later in detail. The CPU is configured or programmed to execute the driving assist control by executing the vehicle driving assist program. 
     In particular, the ECU  90  has stored a program executing a moving assist control described later in detail in the ROM. In this regard, the ECU  90  may be configured or programmed to acquire and store such a program via a receiving device wirelessly from a device outside of the own vehicle  100 . Alternatively, the ECU  90  may be configured or programmed to update the stored program via the receiving device wirelessly by the device outside of the own vehicle  100 . 
     &lt;Vehicle Moving Apparatus&gt; 
     The own vehicle  100  is installed with a vehicle moving apparatus  20 . The vehicle moving apparatus  20  is an apparatus which drives, brakes, and steers the own vehicle  100 . In this embodiment, the vehicle moving apparatus  20  includes a driving apparatus  21 , a braking apparatus  22 , and a steering apparatus  23 . 
     &lt;Driving Apparatus&gt; 
     The driving apparatus  21  is an apparatus which outputs a driving force or a driving torque to be applied to the own vehicle  100  to move the own vehicle  100 . In this embodiment, the driving apparatus  21  includes two power sources, i.e., a first power source  211  and a second power source  212  which have different power output properties. The first power source  211  may be an internal combustion engine, and the second power source  212  may be at least one electric motor. The first power source  211  and the second power source  212  are electrically connected to the ECU  90 . The ECU  90  controls the driving force or the driving torque output from the first power source  211  and the second power source  212  by controlling operations of the first power source  211  and the second power source  212 . 
     &lt;Braking Apparatus&gt; 
     The braking apparatus  22  is an apparatus which outputs a braking force or a braking torque to be applied to the own vehicle  100  so as to brake the own vehicle  100 . The braking apparatus  22  may be a hydraulic brake apparatus. The braking apparatus  22  is electrically connected to the ECU  90 . The ECU  90  controls the braking force or the braking torque output from the braking apparatus  22  by controlling operations of the braking apparatus  22 . 
     &lt;Steering Apparatus&gt; 
     The steering apparatus  23  is an apparatus which outputs a steering force or a steering torque to be applied to the own vehicle  100  to steer the own vehicle  100 . The steering apparatus  23  may be a power steering apparatus. The steering apparatus  23  is electrically connected to the ECU  90 . The ECU  90  controls the steering force or the steering torque output from the steering apparatus  23  by controlling operations of the steering apparatus  23 . 
     &lt;Sensors, Etc.&gt; 
     Further, the own vehicle  100  is installed with an accelerator pedal  41 , an accelerator pedal operation amount sensor  42 , a brake pedal  43 , a brake pedal operation amount sensor  44 , a steering wheel  45 , a steering angle sensor  46 , a steering torque sensor  47 , a vehicle moving speed detection device  48 , a moving assist operation device  51 , an economy moving operation device  52 , and a surrounding information detection apparatus  60 . 
     &lt;Accelerator Pedal Operation Amount Sensor&gt; 
     The accelerator pedal operation amount sensor  42  is a sensor which detects an operation amount of the accelerator pedal  41 . The accelerator pedal operation amount sensor  42  is electrically connected to the ECU  90 . The accelerator pedal operation amount sensor  42  sends information on the detected operation amount to the ECU  90 . The ECU  90  acquires the operation amount of the accelerator pedal  41  as an accelerator pedal operation amount AP, based on the information sent from the accelerator pedal operation amount sensor  42 . 
     The ECU  90  calculates and acquires the driving torque to be output from the driving apparatus  21  as a driver requested driving torque DTQ_D_RQ, based on the accelerator pedal operation amount AP and a moving speed of the own vehicle  100 , i.e., an own vehicle moving speed when the ECU  90  does not execute the moving assist control described later in detail. The ECU  90  controls the operations of the driving apparatus  21  so as to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ. On the other hand, when the ECU  90  executes the moving assist control, the ECU  90  determines the driving torque necessary to move the own vehicle  100  by the moving assist control as desired as a system requested driving torque DTQ_S_RQ. Then, the ECU  90  controls the operations of the driving apparatus  21  so as to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ. 
     &lt;Brake Pedal Operation Amount Sensor&gt; 
     The brake pedal operation amount sensor  44  is a sensor which detects an operation amount of the brake pedal  43 . The brake pedal operation amount sensor  44  is electrically connected to the ECU  90 . The brake pedal operation amount sensor  44  sends information on the detected operation amount to the ECU  90 . The ECU  90  acquires the operation amount of the brake pedal  43  as a brake pedal operation amount BP, based on the information sent from the brake pedal operation amount sensor  44 . 
     The ECU  90  calculates and acquires the braking torque to be applied to the own vehicle  100  by the braking apparatus  22  as a driver requested braking torque BTO_D_RQ, based on the brake pedal operation amount BP when the ECU  90  does not execute the moving assist control described later in detail. The ECU  90  controls the operations of the braking apparatus  22  so as to apply the braking torque corresponding to the driver requested braking torque BTO_D_RQ to the own vehicle  100 . On the other hand, when the ECU  90  controls the moving assist control, the ECU  90  determines the braking torque necessary to move the own vehicle  100  by the moving assist control as desired as a system requested braking torque BTO_S_RQ. Then, the ECU  90  controls the operations of the braking apparatus  22  so as to apply the braking torque corresponding to the system requested braking torque BTO_S_RQ to the own vehicle  100 . 
     &lt;Steering Angle Sensor&gt; 
     The steering angle sensor  46  is a sensor which detects a rotation angle of the steering wheel  45  with respect to its neutral position. The steering angle sensor  46  is electrically connected to the ECU  90 . The steering angle sensor  46  sends information on the detected rotation angle of the steering wheel  45  to the ECU  90 . The ECU  90  acquires the rotation angle of the steering wheel  45  as a steering angle θ, based on the information sent from the steering angle sensor  46 . 
     &lt;Steering Torque Sensor&gt; 
     The steering torque sensor  47  is a sensor which detects a torque which an own vehicle driver (i.e., a driver of the own vehicle  100 ) inputs to a steering shaft via the steering wheel  45 . The steering torque sensor  47  is electrically connected to the ECU  90 . The steering torque sensor  47  sends information on the detected torque to the ECU  90 . The ECU  90  acquires the torque which the own vehicle driver inputs to the steering shaft via the steering wheel  45  as a driver input steering torque, based on the information sent from the steering torque sensor  47 . 
     The ECU  90  acquires a requested steering force or a requested steering torque, based on the steering angle θ, the driver input steering torque, and the own vehicle moving speed (i.e., the moving speed of the own vehicle  100 ). Then, the ECU  90  controls the operations of the steering apparatus  23  so as to output the steering torque corresponding to the requested steering torque. 
     &lt;Vehicle Moving Speed Detection Device&gt; 
     The vehicle moving speed detection device  48  is a device which detects the moving speed of the own vehicle  100 . The vehicle moving speed detection device  48  may include vehicle wheel rotation speed sensors. The vehicle moving speed detection device  48  is electrically connected to the ECU  90 . The vehicle moving speed detection device  48  sends information on the detected moving speed of the own vehicle  100  to the ECU  90 . The ECU  90  acquires the moving speed of the own vehicle  100  as the own vehicle moving speed VO, based on the information sent from the vehicle moving speed detection device  48 . 
     &lt;Moving Assist Operation Device&gt; 
     The moving assist operation device  51  is a device which is operated by the driver of the own vehicle  100 . The moving assist operation device  51  may include switches and buttons. The switches and the buttons may be provided on the steering wheel  45  or a lever mounted on a steering column of the own vehicle  100 . 
     In this embodiment, the moving assist operation device  51  includes a moving assist selection switch, a vehicle moving speed setting switch, a vehicle moving speed increase button, a vehicle moving speed decrease button, and an inter-vehicle distance set button. The moving assist operation device  51  is electrically connected to the ECU  90 . 
     When the moving assist control is not executed, and the moving assist selection switch is operated, a signal is sent from the moving assist operation device  51  to the ECU  90 . The ECU  90  determines that an execution of the moving assist control is requested in response to receiving the signal in question. On the other hand, when the moving assist control is executed, and the moving assist selection switch is operated by the driver, a signal is sent from the moving assist operation device  51  to the ECU  90 . The ECU  90  determines that the execution of the moving assist control is not requested in response to receiving the signal in question. That is, the ECU  90  determines that the execution of the moving assist control is requested to be terminated. 
     Further, when the moving assist control is executed, and the vehicle moving speed setting switch is operated, a signal is sent from the moving assist operation device  51  to the ECU  90 . The ECU  90  sets the current own vehicle moving speed VO as a set vehicle moving speed V_SET for the moving assist control in response to receiving the signal in question. 
     Further, when the moving assist control is executed, and the vehicle moving speed increase button is operated, a signal is sent from the moving assist operation device  51  to the ECU  90 . The ECU  90  increases the set vehicle moving speed V_SET in response to receiving the signal in question. On the other hand, when the moving assist control is executed, and the vehicle moving speed decrease button is operated, a signal is sent from the moving assist operation device  51  to the ECU  90 . The ECU  90  decreases the set vehicle moving speed V_SET in response to receiving the signal in question. 
     Further, when the moving assist control is executed, and the inter-vehicle distance setting button is operated, a signal is sent from the moving assist operation device  51  to the ECU  90 . The signal in question is a requested inter-vehicle distance signal which represents a requested forward inter-vehicle distance DF_RQ. The requested forward inter-vehicle distance DF_RQ is a distance which the driver requests by operating the inter-vehicle distance setting button as a forward inter-vehicle distance DF for a following moving control of the moving assist control. The forward inter-vehicle distance DF is a distance between the own vehicle  100  and a preceding vehicle  200 F. 
     As shown in  FIG.  2   , the forward inter-vehicle distance DF is a distance between the own vehicle  100  and the preceding vehicle  200 F and is acquired, based on surrounding detection information IS described later in detail. In this embodiment, the preceding vehicle  200 F is a vehicle which moves in front of the own vehicle  100  in an own vehicle moving lane LN (i.e., a traffic lane in which the own vehicle  100  moves) and has the forward inter-vehicle distance DF equal to or smaller than a predetermined distance (i.e., a preceding vehicle determination distance DF_TH). The own vehicle moving lane LN is recognized, based on information on a left lane marking LML at the left side of the own vehicle  100  and a right lane marking LMR at the right side of the own vehicle  100 . The lane markings LML and LMR are acquired, based on the surrounding detection information IS. Further, in this embodiment, the requested forward inter-vehicle distance DF_RQ which the driver can select by operating the inter-vehicle distance setting button, is one of three different distances, i.e., a long distance, a middle distance, and a short distance. 
     In this embodiment, when the ECU  90  receives the requested inter-vehicle distance signal, the ECU  90  sets a set forward inter-vehicle distance DF_SET, based on the current own vehicle moving speed VO and the requested forward inter-vehicle distance DF_RQ. In this regard, the ECU  90  may set the requested forward inter-vehicle distance DF_RQ as the set forward inter-vehicle distance DF_SET, independently of the current own vehicle moving speed VO. 
     In particular, the ECU  90  sets the set forward inter-vehicle distance DF_SET to the forward inter-vehicle distance DF which leads to a predicted reaching time TTC equal to a predetermined time (i.e., a predetermined predicted reaching time TTC_REF). The predicted reaching time TTC is acquired by dividing the forward inter-vehicle distance DF by the current own vehicle moving speed VO. That is, the ECU  90  sets the set forward inter-vehicle distance DF_SET to the forward inter-vehicle distance DF which satisfies a relationship between the current own vehicle moving speed VO, the predetermined predicted reaching time TTC_REF, and the forward inter-vehicle distance DF represented by a formula (1) below. 
         TTC _ REF=DF/VO   (1)
 
     The predetermined predicted reaching time TTC_REF is a long time TTC_L when the requested forward inter-vehicle distance DF_RQ is the long distance. The predetermined predicted reaching time TTC_REF is a middle time TTC_L when the requested forward inter-vehicle distance DF_RQ is the middle distance. The predetermined predicted reaching time TTC_REF is a short time TTC_L when the requested forward inter-vehicle distance DF_RQ is the short distance. It should be noted that the preceding vehicle determination distance DF_TH is set to be greater than the set forward inter-vehicle distance DF_SET. 
     &lt;Economy Moving Operation Device&gt; 
     The economy moving operation device  52  is a device which is operated by the driver of the own vehicle  100 . The economy moving operation device  52  may be a switch or a button. The switch or the button may be provided on the steering wheel  45  of the own vehicle  100 . Alternatively, the switch or the button may be provided on the lever mounted on the steering column of the own vehicle  100 . 
     The economy moving operation device  52  is turned into an ON state when the economy moving operation device  52  is operated while the economy moving operation device  52  is in an OFF state. When the economy moving operation device  52  is turned into the ON state, the economy moving operation device  52  sends a signal to the ECU  90 . When the ECU  90  receives the signal in question, the ECU  90  determines that an execution of an enlarged moving assist control or an economy moving assist control is requested. When the ECU  90  determines that the execution of the enlarged moving assist control is requested, the ECU  90  determines that an economy moving execution condition becomes satisfied. 
     On the other hand, the economy moving operation device  52  is turned into the OFF state when the economy moving operation device  52  is operated while the economy moving operation device  52  is in the ON state. When the economy moving operation device  52  is turned into the OFF state, the economy moving operation device  52  sends a signal to the ECU  90 . When the ECU  90  receives the signal in question, the ECU  90  determines that the execution of the enlarged moving assist control is not requested. When the ECU  90  determines that the execution of the enlarged moving assist control is not requested, the ECU  90  determines that the economy moving execution condition becomes unsatisfied. 
     &lt;Surrounding Information Detection Apparatus&gt; 
     The surrounding information detection apparatus  60  is an apparatus which detects information on a situation around the own vehicle  100 . In this embodiment, the surrounding information detection apparatus  60  includes radio wave sensors  61  and image sensors  62 . 
     &lt;Radio Wave Sensors&gt; 
     Each radio wave sensor  61  is a sensor which detects information on objects around the own vehicle  100  by using radio waves. The radio wave sensor  61  may be a radar sensor such as a millimeter wave sensor, or a sonic wave such as an ultrasonic wave sensor such as a clearance sonar, or a laser radar such as a LiDAR. The radio wave sensors  61  are electrically connected to the ECU  90 . The radio wave sensor  61  transmits radio waves and receives reflected waves (i.e., the radio waves reflected by the objects). The radio wave sensor  61  sends information on the transmitted radio waves and the received waves (i.e., the received reflected waves) to the ECU  90 . In other words, the radio wave sensor  61  detects the objects around the own vehicle  100  and sends information on the detected objects to the ECU  90 . The ECU  90  can acquire surrounding detection information IS (i.e., information on the objects around the own vehicle  100 ), based on the information including radio wave information or radio wave data sent from the radio wave sensors  61 . The objects detected by the radio wave sensors  61  may be vehicles, walls, bicycles, and persons. 
     &lt;Image Sensors&gt; 
     Each image sensor  62  is a sensor which takes images of a view around the own vehicle  100 . The image sensor  62  may be a camera. The image sensors  62  are electrically connected to the ECU  90 . The image sensor  62  takes the images of the view around the own vehicle  100  and sends information on the taken images to the ECU  90 . The ECU  90  can acquire the surrounding detection information IS (i.e., the information on the situation around the own vehicle  100 ), based on the information including image information or image data sent from the image sensors  62 . 
     The ECU  90  acquires a forward inter-vehicle distance DF and a preceding vehicle moving speed VF, based on the surrounding detection information IS. The forward inter-vehicle distance DF is a distance between the preceding vehicle  200 F and the own vehicle  100 . The preceding vehicle moving speed VF is the moving speed of the preceding vehicle  200 F. Further, the ECU  90  acquires a rearward inter-vehicle distance DR and a following vehicle moving speed VR, based on the surrounding detection information IS. The rearward inter-vehicle distance DR is a distance between a following vehicle  200 R and the own vehicle  100 . The following vehicle moving speed VR is the moving speed of the following vehicle  200 R. 
     As shown in  FIG.  2   , the rearward inter-vehicle distance DR is a distance between the own vehicle  100  and the following vehicle  200 R. In this embodiment, the following vehicle  200 R is a vehicle which moves behind the own vehicle  100  in the own vehicle moving lane LN and has the rearward inter-vehicle distance DR equal to or smaller than a following vehicle determination distance DR_TH. 
     &lt;Summary of Operations of Vehicle Driving Assist Apparatus&gt; 
     Next, a summary of operations of the vehicle driving assist apparatus  10  will be described. The vehicle driving assist apparatus  10  is configured to execute the moving assist control. The moving assist control is a control which causes the own vehicle  100  to move by autonomously accelerating and decelerating the own vehicle  100  even when the driver does not operate the accelerator pedal  41  and the brake pedal  43 . 
     As described above, in this embodiment, the driving apparatus  21  includes the first power source  211  and the second power source  212 . The first power source  211  and the second power source  212  have the different power output properties. The power output property corresponds to an energy efficiency of outputting power. In this embodiment, the first power source  211  and the second power source  212  have the power output properties shown in  FIG.  3   . In particular, as shown by a line DTQ_ENG, a power output efficiency E 1  of the first power source  211  takes the greatest value when the driving torque which the first power source  211  outputs, is a value DTQ_A. Further, as shown by a line DTQ_MT, a power output efficiency E 2  of the second power source  212  takes the greatest value when the driving torque which the second power source  212  outputs, is a value DTQ_B smaller than the value DTQ_A. 
     It should be noted that when the first power source  211  and the second power source  212  are the internal combustion engine and the electric motor, respectively, the power output efficiency E 1  of the first power source  211  relates to a so-called fuel consumption, and the power output efficiency E 2  of the second power source  212  relates to a so-called electric power consumption. 
     As described above, a power output efficiency E of the driving apparatus  21  has a property that the power output efficiency E takes peak values when the driving torque which the driving apparatus  21  outputs, is particular values (i.e., optimum driving torques DTQ_OPT). In this embodiment, the power output efficiency E has two peak values. Thus, if the own vehicle  100  is accelerated by controlling the operations of the driving apparatus  21  to output the driving torque corresponding to the optimum driving torque DTQ_OPT, the power output efficiency E of the driving apparatus  21  is increased. 
     Accordingly, as far as an economy moving forbiddance condition does not become satisfied, the vehicle driving assist apparatus  10  executes the economy moving assist control when (i) the moving assist execution condition is satisfied, and (ii) the economy moving execution condition is satisfied. The economy moving forbiddance condition is a condition that an acceleration and a deceleration of the own vehicle  100  to keep the power output efficiency E of the driving apparatus  21  great, are not permitted. As described later in detail, in general, the economy moving assist control is an optimum acceleration control to autonomously accelerate and decelerate the own vehicle  100  so as to (i) maintain the own vehicle moving speed VO within a predetermined speed range (i.e., a predetermined vehicle moving speed range RNG_E), or (ii) maintain the forward inter-vehicle distance DF within a predetermined forward distance range, or (iii) the rearward inter-vehicle distance DR within a predetermined rearward distance range. The economy moving assist control includes a coasting control to decelerate the own vehicle  100  and an optimum acceleration control to accelerate the own vehicle  100 . 
     The coasting control is a control to cause the own vehicle  100  to coast by causing the driving apparatus  21  to output the driving force not to accelerate nor decelerate the own vehicle  100 . In this embodiment, the coasting control is a control to cause the own vehicle  100  to coast by (i) stopping the operations of the first power source  211  such as the internal combustion engine and (ii) causing the second power source  212  to output the driving torque so as to keep the power output efficiency E 2  of the second power source  212  such as the electric motor at the greatest efficiency. Thereby, the own vehicle  100  is decelerated mainly by a moving resistance of the own vehicle  100 . 
     On the other hand, the optimum acceleration control is a control to (i) calculate an optimum acceleration G_OPT as a system requested acceleration G_S_RQ, (ii) calculate the driving torque realizing the system requested acceleration G_S_RQ as the system requested driving torque DTQ_S_RQ, and (iii) control the operations of the driving apparatus  21  to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ to accelerate the own vehicle  100 . The optimum acceleration G_OPT is an acceleration of the own vehicle  100  which maintains the power output efficiency E of the driving apparatus  21  at the maximum efficiency at the current own vehicle moving speed VO. 
     It should be noted that the optimum acceleration control may be a control to (i) calculate as the system requested acceleration G_S_RQ, the acceleration of the own vehicle  100  which maintains the power output efficiency E of the driving apparatus  21  at a value slightly greater or smaller than the maximum efficiency at the current own vehicle moving speed VO, (ii) calculate the driving torque realizing the system requested acceleration G_S_RQ as the system requested driving torque DTQ_S_RQ, and (iii) control the operations of the driving apparatus  21  to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ to accelerate the own vehicle  100 . That is, the optimum acceleration control may be a control to control the operations of the driving apparatus  21  at the optimum power output efficiency including the maximum power output efficiency and the power output efficiency slightly smaller than the maximum power output efficiency. That is, the optimum acceleration control is a control to control the operations of the driving apparatus  21  to accelerate the own vehicle  100  so as to maintain the power output efficiency of the driving apparatus  21  at an efficiency equal to or greater than a predetermined efficiency. 
     Below, the controls executed by the vehicle driving assist apparatus  10  will be described in detail. 
     &lt;Ordinary Moving Control&gt; 
     When the moving assist execution condition is not satisfied, the vehicle driving assist apparatus  10  executes an ordinary moving control. The ordinary moving control is a control to (i) calculate the driver requested driving torque DTQ_D_RQ to be output from the driving apparatus  21 , based on the accelerator pedal operation amount AP and the own vehicle moving speed VO and (ii) control the operations of the driving apparatus  21  to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ, and (i) calculate the driver requested braking torque BTQ_D_RQ to be applied to the own vehicle  100  by the braking apparatus  22 , based on the brake pedal operation amount BP and (ii) control the operations of the braking apparatus  22  to output the braking torque corresponding to the driver requested braking torque BTQ_D_RQ. 
     It should be noted that when the vehicle driving assist apparatus  10  executes the ordinary moving control, and the driver requested driving torque DTQ_D_RQ is greater than an operation switching threshold DTQ_SW greater than zero, the vehicle driving assist apparatus  10  causes the driving apparatus  21  to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ by causing the first power source  211  and the second power source  212  to output the driving torque. On the other hand, when the vehicle driving assist apparatus  10  executes the ordinary moving control, and the driver requested driving torque DTQ_D_RQ is equal to or smaller than the operation switching threshold DTQ_SW, the vehicle driving assist apparatus  10  causes the driving apparatus  21  to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ by stopping the operations of the first power source  211  and causing the second power source  212  to output the driving torque. 
     &lt;Ordinary Moving Assist Control&gt; 
     On the other hand, when the moving assist execution condition is satisfied, the vehicle driving assist apparatus  10  determines whether the economy moving execution condition is satisfied. When the economy moving execution condition is not satisfied, the vehicle driving assist apparatus  10  execute an ordinary moving assist control as the moving assist control. 
     In this embodiment, the vehicle driving assist apparatus  10  determines that the moving assist execution condition is satisfied when the vehicle driving assist apparatus  10  determines that the execution of the moving assist control is requested, and the accelerator pedal  41  and the brake pedal  43  are not operated. In this regard, the vehicle driving assist apparatus  10  may be configured to determine that the moving assist execution condition is satisfied, independently of whether the accelerator pedal  41  or the brake pedal  43  is operated when the moving assist operation device  51  is operated, and the execution of the moving assist control is requested. 
     Further, the vehicle driving assist apparatus  10  determines that the moving assist execution condition becomes unsatisfied, that is, a moving assist control termination condition for terminating the moving assist control becomes satisfied when the moving assist operation device  51  is operated while the moving assist control is executed, and a termination of the moving assist control is requested. Further, the vehicle driving assist apparatus  10  determines that the moving assist control termination condition becomes satisfied when the brake pedal  43  is operated while the moving assist control is executed, that is, the brake pedal operation amount BP becomes greater than zero. When the moving assist control termination condition becomes satisfied, the vehicle driving assist apparatus  10  terminates the moving assist control and starts the ordinary moving control. 
     When there is the preceding vehicle  200 F, the vehicle driving assist apparatus  10  executes an ordinary following moving control as the ordinary moving assist control. As described above, the vehicle driving assist apparatus  10  determines that there is the preceding vehicle  200 F when there is a vehicle moving ahead of the own vehicle  100  in the own vehicle moving lane LN and having the forward inter-vehicle distance DF equal to or smaller the preceding vehicle determination distance DF_TH. On the other hand, when there is not the preceding vehicle  200 F, the vehicle driving assist apparatus  10  executes an ordinary constant speed moving control as the ordinary moving assist control. 
     &lt;Ordinary Following Moving Control&gt; 
     The ordinary following moving control is a control to autonomously accelerate and decelerate the own vehicle  100  so as to maintain the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) at the set forward inter-vehicle distance DF_SET. 
     Thus, while the vehicle driving assist apparatus  10  executes the ordinary following moving control, the vehicle driving assist apparatus  10  accelerates and decelerates the own vehicle  100  so as to maintain the forward inter-vehicle distance DF at the set forward inter-vehicle distance DF_SET. In this embodiment, while the vehicle driving assist apparatus  10  executes the ordinary following moving control, the vehicle driving assist apparatus  10  accelerates and decelerates the own vehicle  100  so as to maintain the predicted reaching time TTC at the predetermined predicted reaching time TTC_REF. 
     In particular, while the vehicle driving assist apparatus  10  executes the ordinary following moving control, the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ necessary to maintain the predicted reaching time TTC at the predetermined predicted reaching time TTC_REF. 
     When the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ, the vehicle driving assist apparatus  10  calculates the driving torque to be output from the driving apparatus  21  as the system requested driving torque DTQ_S_RQ and the braking torque to be applied to the own vehicle  100  by the braking apparatus  22  as the system requested braking torque BTQ_S_RQ to realize the system requested acceleration G_S_RQ. Then, the vehicle driving assist apparatus  10  controls the operations of the driving apparatus  21  to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ and the operations of the braking apparatus  22  to apply the braking torque corresponding to the system requested braking torque BTQ_S_RQ to the own vehicle  100 . 
     Thereby, when the predicted reaching time TTC becomes greater than the predetermined predicted reaching time TTC_REF, the own vehicle  100  is accelerated. On the other hand, when the predicted reaching time TTC becomes smaller than the predetermined predicted reaching time TTC_REF, the own vehicle  100  is decelerated. Thereby, the predicted reaching time TTC is maintained at the predetermined predicted reaching time TTC_REF. 
     It should be noted that when the accelerator pedal  41  is operated, and the driver requested driving torque DTQ_D_RQ becomes greater than the system requested driving torque DTQ_S_RQ while the ordinary following moving control is executed, the vehicle driving assist apparatus  10  determines that an accelerator override state or a driver override state is produced and temporarily stops the ordinary following moving control. Then, the vehicle driving assist apparatus  10  controls the operations of the driving apparatus  21  to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ. That is, the vehicle driving assist apparatus  10  temporarily stops the ordinary following moving control and executes the ordinary moving control. Thereafter, when the accelerator pedal  41  becomes unoperated, and the driver requested driving torque DTQ_D_RQ becomes equal to or smaller than the system requested driving torque DTQ_S_RQ, the vehicle driving assist apparatus  10  restarts the ordinary following moving control. 
     &lt;Ordinary Constant Speed Moving Control&gt; 
     The ordinary constant speed moving control is a control to autonomously accelerate and decelerate the own vehicle  100  so as to maintain the own vehicle moving speed VO at the set vehicle moving speed V_SET. 
     Thus, while the vehicle driving assist apparatus  10  executes the ordinary constant speed moving control, the vehicle driving assist apparatus  10  accelerates and decelerates the own vehicle  100  so as to maintain the own vehicle moving speed VO at the set vehicle moving speed V_SET. 
     In particular, while the vehicle driving assist apparatus  10  executes the ordinary constant speed moving control, the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ necessary to maintain the own vehicle moving speed VO at the set vehicle moving speed V_SET. 
     When the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ, the vehicle driving assist apparatus  10  calculates the driving torque to be output from the driving apparatus  21  as the system requested driving torque DTQ_S_RQ and the braking torque to be applied to the own vehicle  100  by the braking apparatus  22  as the system requested braking torque BTQ_S_RQ to realize the system requested acceleration G_S_RQ. Then, the vehicle driving assist apparatus  10  controls the operations of the driving apparatus  21  to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ and the operations of the braking apparatus  22  to apply the braking torque corresponding to the system requested braking torque BTQ_S_RQ to the own vehicle  100 . 
     Thereby, when the own vehicle moving speed VO becomes smaller than the set vehicle moving speed V_SET, the own vehicle  100  is accelerated. On the other hand, when the own vehicle moving speed VO becomes greater than the set vehicle moving speed V_SET, the own vehicle  100  is decelerated. Thereby, the own vehicle moving speed VO is maintained at the set vehicle moving speed V_SET. 
     As described above, in this embodiment, the vehicle driving assist apparatus  10  accelerates and decelerates the own vehicle  100 , based on the set vehicle moving speed V_SET while the vehicle driving assist apparatus  10  executes the ordinary constant speed moving control. In this regard, the vehicle driving assist apparatus  10  may be configured to set an ordinary vehicle moving speed control range RNG_N used for determining whether to accelerate or decelerate the own vehicle  100 . The ordinary vehicle moving speed control range RNG_N is a range of the vehicle moving speed which includes and depends on the set vehicle moving speed V_SET. In this case, the vehicle driving assist apparatus  10  accelerates the own vehicle  100  to increase the own vehicle moving speed VO when the own vehicle moving speed VO decreases and becomes smaller than an ordinary vehicle moving speed lower limit VL_N (i.e., a lower limit of the ordinary vehicle moving speed control range RNG_N). On the other hand, the vehicle driving assist apparatus  10  decelerates the own vehicle  100  to decrease the own vehicle moving speed VO when the own vehicle moving speed VO increases and becomes greater than an ordinary vehicle moving speed upper limit VU_N (i.e., an upper limit of the ordinary vehicle moving speed control range RNG_N). Thereby, an average VO_AVE of the own vehicle moving speed VO is maintained at around the set vehicle moving speed V_SET. 
     Further, when the accelerator pedal  41  is operated, and the driver requested driving torque DTQ_D_RQ becomes greater than the system requested driving torque DTQ_S_RQ while the ordinary constant speed moving control is executed, the vehicle driving assist apparatus  10  determines that the accelerator override state is produced and temporarily stops the ordinary constant speed moving control. Then, the vehicle driving assist apparatus  10  controls the operations of the driving apparatus  21  to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ. That is, the vehicle driving assist apparatus  10  temporarily stops the ordinary constant speed moving control and executes the ordinary moving control. Thereafter, when the accelerator pedal  41  becomes unoperated, and the driver requested driving torque DTQ_D_RQ becomes equal to or smaller than the system requested driving torque DTQ_S_RQ, the vehicle driving assist apparatus  10  restarts the ordinary constant speed moving control. 
     &lt;Economy Moving Assist Control (Enlarged Moving Assist Control)&gt; 
     As described above, when the moving assist execution condition and the economy moving execution condition are both satisfied, the vehicle driving assist apparatus  10  executes the economy moving assist control. The economy moving assist control will be described with referent to flowcharts shown in  FIG.  4    to  FIG.  8   . The vehicle driving assist apparatus  10  is configured to execute a routine shown in  FIG.  4    with a predetermined calculation cycle. 
     At a predetermined timing, the vehicle driving assist apparatus  10  starts a process from a step  400  of the routine shown in  FIG.  4    and proceeds with the process to a step  405  to determine whether the moving assist execution condition is satisfied. When the moving assist execution condition is not satisfied, the vehicle driving assist apparatus  10  does not execute the moving assist control. Thus, when the vehicle driving assist apparatus  10  determines “No” at the step  405 , the vehicle driving assist apparatus  10  proceeds with the process directly to a step  495  to terminate this routine once. In this case, the vehicle driving assist apparatus  10  executes the ordinary moving control. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “Yes” at the step  405 , the vehicle driving assist apparatus  10  proceeds with the process to a step  410  to determine whether the economy moving execution condition is satisfied. When the vehicle driving assist apparatus  10  determines “No” at the step  410 , the vehicle driving assist apparatus  10  proceeds with the process to a step  425  to set a control mode to an inter-vehicle distance maintaining mode. That is, when the moving assist execution condition is satisfied, but the economy moving execution condition is not satisfied, the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode. 
     When the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode, the vehicle driving assist apparatus  10  executes the ordinary following moving control or the ordinary constant speed moving control, depending on whether there is the preceding vehicle  200 F. 
     Thus, after the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode at the step  425 , the vehicle driving assist apparatus  10  proceeds with the process to a step  430  to calculate the acceleration of the own vehicle  100  necessary to maintain the predicted reaching time TTC at the predetermined predicted reaching time TTC_REF as the system requested acceleration G_S_RQ when there is the preceding vehicle  200 F. On the other hand, when there is not the preceding vehicle  200 F, the vehicle driving assist apparatus  10  calculates the acceleration of the own vehicle  100  necessary to maintain the own vehicle moving speed VO at the set vehicle moving speed V_SET as the system requested acceleration G_S_RQ. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to a step  435  to calculate the driving torque to be output from the driving apparatus  21  as the system requested driving torque DTQ_S_RQ and the braking torque to be applied to the own vehicle  100  by the braking apparatus  22  as BTQ_S_RQ so as to realize the system requested acceleration G_S_RQ calculated at the step  430 . It should be noted that when the system requested driving torque DTQ_S_RQ calculated is greater than zero, the system requested braking torque BTQ_S_RQ calculated is zero. Similarly, when the system requested braking torque BTQ_S_RQ calculated is greater than zero, the system requested driving torque DTQ_S_RQ calculated is zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to a step  440  to determine whether to operate the first power source  211  in order to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ calculated at the step  435  from the driving apparatus  21 . When the system requested driving torque DTQ_S_RQ is greater than the operation switching threshold DTQ_SW, the vehicle driving assist apparatus  10  determines to operate the first power source  211 . On the other hand, when the system requested driving torque DTQ_S_RQ is equal to or smaller than the operation switching threshold DTQ_SW, the vehicle driving assist apparatus  10  determines not to operate the first power source  211 . 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to a step  445  to calculate commanded driving torques DTQ_COM for the first power source  211  and the second power source  212 . When the vehicle driving assist apparatus  10  determines to operate the first power source  211  at the step  440 , and the vehicle driving assist apparatus  10  proceeds with the process to the step  445 , the commanded driving torques DTQ_COM calculated are the driving torques to be output from the first power source  211  and the second power source  212 , respectively so as to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ calculated at the step  435  from the driving apparatus  21 . It should be noted that in this embodiment, the commanded driving torque DTQ_COM calculated at this step for the second power source  212  is zero. 
     On the other hand, when (i) the system requested driving torque DTQ_S_RQ calculated at the step  435  is greater than zero, (ii) the vehicle driving assist apparatus  10  determines not to operate the first power source  211  at the step  440 , and (iii) the vehicle driving assist apparatus  10  proceeds with the process to the step  445 , the commanded driving torque DTQ_COM calculated for the second power source  212  corresponds to the system requested driving torque DTQ_S_RQ calculated at the step  435 . 
     Further, when the system requested braking torque BTQ_S_RQ calculated at the step  435  is greater than zero, and the vehicle driving assist apparatus  10  proceeds with the process to the step  445 , the vehicle driving assist apparatus  10  calculates a commanded braking torque BTQ_COM. The commanded braking torque BTQ_COM calculated corresponds to the system requested braking torque BTQ_S_RQ calculated at the step  435 . It should be noted that in this embodiment, the commanded driving torques DTQ_COM calculated at the step  445  for the first power source  211  and the second power source  212  are zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to a step  450  to control the operations of the first power source  211  and the first power source  211  so as to output the driving torques corresponding to the commanded driving torques DTQ_COM calculated at the step  445  and the operations of the braking apparatus  22  so as to apply the braking torque corresponding to the commanded braking torque BTQ_COM calculated at the step  445  to the own vehicle  100 . Thereby, the ordinary following moving control or the ordinary constant speed moving control is executed. 
     After the vehicle driving assist apparatus  10  executes a process of the step  450 , the vehicle driving assist apparatus  10  proceeds with the process to the step  495  to terminate this routine once. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “Yes” at the step  410 , the vehicle driving assist apparatus  10  proceeds with the process to a step  415  to determine whether the rearward inter-vehicle distance DR is greater than the following vehicle determination value DR_TH. That is, when the moving assist execution condition and the economy moving execution condition are both satisfied, the vehicle driving assist apparatus  10  determines whether there is not the following vehicle  200 R. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  415 , that is, the vehicle driving assist apparatus  10  determines that there is not the following vehicle  200 R, the vehicle driving assist apparatus  10  proceeds with the process to a step  505  of a routine shown in  FIG.  5    to determine whether the forward inter-vehicle distance DF is greater than the following vehicle determination value DR_TH. That is, the vehicle driving assist apparatus  10  determines whether there is not the preceding vehicle  200 F. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  505 , the vehicle driving assist apparatus  10  proceeds with the process to a step  605  of a routine shown in  FIG.  6    to determine whether the own vehicle moving speed VO is greater than the economy vehicle moving speed upper limit VU_E. That is, when there are not the following vehicle  200 R and the preceding vehicle  200 F, the vehicle driving assist apparatus  10  determines whether the own vehicle moving speed VO is greater than the economy vehicle moving speed upper limit VU_E. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  605 , the vehicle driving assist apparatus  10  proceeds with the process to a step  610  to set the control mode to a coasting mode. That is, when there are not the following vehicle  200 R and the preceding vehicle  200 F, and the own vehicle moving speed VO is greater than the economy vehicle moving speed upper limit VU_E, the vehicle driving assist apparatus  10  sets the control mode to the coasting mode. Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  430  of the routine shown in  FIG.  4   . 
     At the step  430 , the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ. At this time, the control mode is set to the coasting mode. Thus, the system requested acceleration G_S_RQ calculated at this time is the acceleration which makes the system requested driving torque DTQ_S_RQ calculated at the next step  435  zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  435  to calculate the system requested driving torque DTQ_S_RQ realizing the system requested acceleration G_S_RQ calculated at the step  430 . As described above, when the control mode is set to the coasting mode, the system requested acceleration G_S_RQ calculated at the step  430  is the acceleration which makes the system requested driving torque DTQ_S_RQ zero. Thus, the system requested driving torque DTQ_S_RQ calculated at the step  435  is zero. It should be noted that the system requested braking torque BTQ_S_RQ calculated at this time is also zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  440  to determine whether to operate the first power source  211  in order to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ calculated at the step  435  from the driving apparatus  21 . At this time, the system requested driving torque DTQ_S_RQ is zero. Thus, the vehicle driving assist apparatus  10  determines not to operate the first power source  211 . 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  445  to calculate the commanded driving torques DTQ_COM, based on the system requested driving torque DTQ_S_RQ. At this time, the system requested driving torque DTQ_S_RQ is zero. Thus, the commanded driving torques DTQ_COM calculated at the step  445  for the first power source  211  and the second power source  212  are zero. It should be noted that the commanded braking torque BTQ_COM calculated at the step  445  is also zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  450  to control the operations of the first power source  211  and the first power source  211  so as to output the driving torques corresponding to the commanded driving torques DTQ_COM calculated at the step  445  and the operations of the braking apparatus  22  so as to apply the braking torque corresponding to the commanded braking torque BTQ_COM calculated at the step  445  to the own vehicle  100 . That is, at this time, the commanded driving torques DTQ_COM and the commanded braking torque BTQ_COM are all zero. Thus, the vehicle driving assist apparatus  10  does not operate the first power source  211  and controls the operations of the second power source  212  at the optimum power output efficiency. Thereby, the coasting control is executed. 
     After the vehicle driving assist apparatus  10  executes the process of the step  450 , the vehicle driving assist apparatus  10  proceeds with the process to the step  495  to terminate this routine once. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  605  of the routine shown in  FIG.  6   , the vehicle driving assist apparatus  10  proceeds with the process to a step  615  to determine whether the own vehicle moving speed VO is smaller than the economy vehicle moving speed lower limit VL_E. That is, when there are not the following vehicle  200 R and the preceding vehicle  200 F, and the own vehicle moving speed VO is equal to or smaller than the economy vehicle moving speed upper limit VU_E, the vehicle driving assist apparatus  10  determines whether the own vehicle moving speed VO is smaller than the economy vehicle moving speed lower limit VL_E. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  615 , the vehicle driving assist apparatus  10  proceeds with the process to a step  620  to set the control mode to an optimum accelerating mode. That is, when there are not the following vehicle  200 R and the preceding vehicle  200 F, and the own vehicle moving speed VO is smaller than the economy vehicle moving speed lower limit VL_E, the vehicle driving assist apparatus  10  sets the control mode to the optimum accelerating mode. Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  430  of the routine shown in  FIG.  4   . 
     At the step  430 , the vehicle driving assist apparatus  10  calculates the system requested acceleration G_S_RQ. At this time, the control mode is set to the optimum accelerating mode. Thus, the system requested acceleration G_S_RQ calculated at this time is the acceleration which leads to the system requested driving torque DTQ_S_RQ calculated at the next step  435  which leads to the optimum power output efficiency of the driving apparatus  21 . 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  435  to calculate the system requested driving torque DTQ_S_RQ realizing the system requested acceleration G_S_RQ calculated at the step  430 . As described above, when the control mode is set to the optimum accelerating mode, the system requested acceleration G_S_RQ calculated at the step  430  leads to the system requested driving torque DTQ_S_RQ which leads to the optimum power output efficiency of the driving apparatus  21 . Thus, the system requested driving torque DTQ_S_RQ calculated at the step  435  is the driving torque which leads to the optimum power output efficiency of the driving apparatus  21 . It should be noted that the system requested braking torque BTQ_S_RQ calculated at this time is zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  440  to determine whether to operate the first power source  211  in order to output the driving torque corresponding to the system requested driving torque DTQ_S_RQ calculated at the step  435  from the driving apparatus  21 . 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  445  to calculate the commanded driving torques DTQ_COM, based on the system requested driving torque DTQ_S_RQ. It should be noted that when the control mode is set to the optimum accelerating mode, the commanded braking torque BTQ_COM calculated at the step  445  is zero. 
     Next, the vehicle driving assist apparatus  10  proceeds with the process to the step  450  to control the operations of the first power source  211  and the first power source  211  so as to output the driving torques corresponding to the commanded driving torques DTQ_COM calculated at the step  445 . It should be noted that the commanded braking torque BTQ_COM calculated at the step  445  is zero and thus, the braking apparatus  22  is not operated. Thereby, the optimum acceleration control is executed. 
     After the vehicle driving assist apparatus  10  executes the process of the step  450 , the vehicle driving assist apparatus  10  proceeds with the process to the step  495  to terminate this routine once. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  615  of the routine shown in  FIG.  6   , the vehicle driving assist apparatus  10  proceeds with the process to a step  625 . That is, when there are not the following vehicle  200 R and the preceding vehicle  200 F, and the own vehicle moving speed VO is between the economy vehicle moving speed upper limit VU_E and the economy vehicle moving speed lower limit VL_E (i.e., within the predetermined vehicle moving speed range RNG_E), the vehicle driving assist apparatus  10  proceeds with the process to the step  625 . In this embodiment the predetermined vehicle moving speed range RNG_E is a range having the economy vehicle moving speed upper limit VU_E greater than the set vehicle moving speed V_SET by a predetermined value and the economy vehicle moving speed lower limit VL_E smaller than the set vehicle moving speed V_SET by a predetermined value. 
     At this time, the own vehicle moving speed VO is within the predetermined vehicle moving speed range RNG_E. Thus, when a moving mode is set to the coasting mode, and the coasting control is executed, the moving mode may be maintained at the coasting mode (i.e., the current moving mode may be unchanged) until the own vehicle moving speed VO becomes smaller than the economy vehicle moving speed lower limit VL_E. On the other hand, when the moving mode is set to the optimum accelerating mode, and the optimum acceleration control is executed, the moving mode may be maintained at the optimum accelerating mode (i.e., the current moving mode may be unchanged) until the own vehicle moving speed VO becomes greater than the economy vehicle moving speed upper limit VU_E. However, in this embodiment, the vehicle driving assist apparatus  10  sets the moving mode as described below. 
     For example, when the moving mode is set to the coasting mode, the coasting control is executed, and the own vehicle  100  coasts. In this case, the moving mode does not change to the optimum accelerating mode until the OV becomes smaller than the economy vehicle moving speed lower limit VL_E. Thus, the driver may feel that the moving speed of the own vehicle  100  is too small and thus, operate the accelerator pedal  41  to accelerate the own vehicle  100 . 
     In this case, the driver requested driving torque DTQ_D_RQ calculated, based on the accelerator pedal operation amount AP may become greater than the system requested driving torque DTQ_S_RQ. In this case, the accelerator override state is determined to be produced, and the operations of the driving apparatus  21  are controlled, based on the driver requested driving torque DTQ_D_RQ. In this case, the first power source  211  may start to be operated. In this case, the first power source  211  may not be always operated at the optimum power output efficiency. Thus, the power output efficiency E of the driving apparatus  21  may be decreased. 
     Accordingly, when the vehicle driving assist apparatus  10  determines “No” at the step  615  and proceeds with the process to the step  625 , the vehicle driving assist apparatus  10  determine whether an acceleration request condition is satisfied. The acceleration request condition is a condition that the accelerator override state is produced, and the first power source  211  will be operated to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ from the driving apparatus  21 . 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  625 , the vehicle driving assist apparatus  10  proceeds with the process to a step  630  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  625  of the routine shown in  FIG.  6   , the vehicle driving assist apparatus  10  proceeds with the process to a step  635  to determine whether the accelerator override state is produced. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  635 , the vehicle driving assist apparatus  10  proceeds with the process to a step  640  to set the control mode to the ordinary moving mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    to execute the ordinary moving control and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the ordinary moving control is executed. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  635 , the vehicle driving assist apparatus  10  proceeds with the process to a step  645  to set the control mode to a mode previously set. That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. 
     As described above, in this embodiment, the acceleration request condition determined at the step  625  is the condition that the accelerator override state is produced, and the first power source  211  will be operated when the driving apparatus  21  is operated, based on the driver requested driving torque DTQ_D_RQ. In this regard, the acceleration request condition may be a condition that the accelerator override state is produced. In this case, when the vehicle driving assist apparatus  10  determines “Yes” at the step  625 , the vehicle driving assist apparatus  10  proceeds with the process to the step  630  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  625 , the vehicle driving assist apparatus  10  proceeds with the process directly to the step  645  to set the control mode to the mode previously set without executing a process of the step  635 . That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. Thereby, the ordinary moving control is not executed. Thus, the power output efficiency is increased. 
     As can be understood from the processes of the steps  605  to  620  of the routine shown in  FIG.  6    and the processes of the steps  430  to  450  of the routine shown in  FIG.  4   , executing these processes leads to executing the economy moving assist control to autonomously accelerate and decelerate the own vehicle  100  so as to maintain the own vehicle moving speed VO (i.e., the moving speed of the own vehicle  100 ) within the predetermined vehicle moving speed range RNG_E (i.e., the predetermined speed range). 
     Thus, the acceleration request condition determined at the step  625  substantially includes a condition that the economy moving assist control is executed, and the moving speed of the own vehicle  100  is within the predetermined speed range. 
     When the vehicle driving assist apparatus  10  determines “No” at the step  505  of the routine shown in  FIG.  5   , the vehicle driving assist apparatus  10  proceeds with the process to a step  510  to determine whether the forward inter-vehicle distance DF is greater than a forward middle distance determination value DF_M which is smaller than the preceding vehicle determination distance DF_TH. That is, when there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, the vehicle driving assist apparatus  10  determines whether the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) is relatively great. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  510 , the vehicle driving assist apparatus  10  proceeds with the process to a step  705  of a routine shown in  FIG.  7    to determine whether the control move is set to the optimum accelerating mode, and a forward vehicle moving speed difference ΔVF is greater than a positive predetermined forward vehicle moving speed difference ΔVF_TH. The forward vehicle moving speed difference ΔVF is a difference of a preceding vehicle moving speed VF (i.e., the moving speed of the preceding vehicle  200 F) with respect to the own vehicle moving speed VO (i.e., ΔVF=VO−VF). That is, when there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, and the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) is relatively great, the own vehicle  100  is accelerated by the optimum acceleration control and thus, the own vehicle moving speed VO is greater than the moving speed of the preceding vehicle  200 F. Thus, the vehicle driving assist apparatus  10  determines whether the own vehicle  100  is approaching the preceding vehicle  200 F. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  705 , the vehicle driving assist apparatus  10  proceeds with the process to a step  710  to set the control mode to the coasting mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the coasting control is executed. Thus, the own vehicle moving speed VO decreases. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  705 , the vehicle driving assist apparatus  10  proceeds with the process to a step  715  to determine whether (i) the control move is set to the coasting mode, (ii) the forward vehicle moving speed difference ΔVF is smaller than the negative predetermined forward vehicle moving speed difference ΔVF_TH, and (iii) the own vehicle moving speed VO is smaller than the economy vehicle moving speed lower limit VL_E. That is, when (i) there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, (ii) the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) is relatively great, and (iii) the preceding vehicle  200 F moves away from the own vehicle  100 , the own vehicle  100  is decelerated by the coasting control and thus, the own vehicle moving speed VO is smaller than the preceding vehicle moving speed VF. Thus, the vehicle driving assist apparatus  10  determines whether the preceding vehicle  200 F moves away from the own vehicle  100 , and the own vehicle moving speed VO is smaller than the predetermined vehicle moving speed range RNG_E. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  715 , the vehicle driving assist apparatus  10  proceeds with the process to a step  720  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. Thus, the own vehicle  100  is accelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  715 , the vehicle driving assist apparatus  10  proceeds with the process to a step  725  to determine whether the acceleration request condition is satisfied. The acceleration request condition is the condition that (i) the accelerator override state is produced, and (ii) the first power source  211  will be operated to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ from the driving apparatus  21 . 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  725 , the vehicle driving assist apparatus  10  proceeds with the process to a step  730  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. Thus, the own vehicle  100  is accelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  725  of the routine shown in  FIG.  7   , the vehicle driving assist apparatus  10  proceeds with the process to a step  735  to determine whether the accelerator override state is produced. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  735 , the vehicle driving assist apparatus  10  proceeds with the process to a step  740  to set the control mode to the ordinary moving mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    to execute the ordinary moving control and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the ordinary moving control is executed. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  735 , the vehicle driving assist apparatus  10  proceeds with the process to a step  745  to set the control mode to the mode previously set. That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. 
     As described above, in this embodiment, the acceleration request condition determined at the step  725  is the condition that (i) the accelerator override state is produced, and (ii) the first power source  211  will be operated when the driving apparatus  21  is operated, based on the driver requested driving torque DTQ_D_RQ. In this regard, the acceleration request condition may be the condition that the accelerator override state is produced. In this case, when the vehicle driving assist apparatus  10  determines “Yes” at the step  725 , the vehicle driving assist apparatus  10  proceeds with the process to the step  730  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  725 , the vehicle driving assist apparatus  10  proceeds with the process directly to the step  745  to set the control mode to the mode previously set without executing a process of the step  735 . That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. Thereby, the ordinary moving control is not executed. Thus, the power output efficiency is increased. 
     As can be understood from (i) the processes of the step  510  of the routine shown in  FIG.  5   , (ii) the processes of the steps  705  to  720  of the routine shown in  FIG.  7   , and (iii) the processes of the steps  430  to  450  of the routine shown in  FIG.  4   , executing these processes leads to executing the economy moving assist control to autonomously accelerate and decelerate the own vehicle  100  so as to maintain the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) within a predetermined forward distance range (i.e., a limited range between the preceding vehicle determination distance DF_TH and the forward middle distance determination value DF_M). 
     Thus, the acceleration request condition determined at the step  625  substantially includes a condition that (i) the economy moving assist control is executed, and (ii) the distance between the own vehicle  100  and the preceding vehicle  200 F is within the predetermined forward distance range. 
     When the vehicle driving assist apparatus  10  determines “No” at the step  510  of the routine shown in  FIG.  5   , the vehicle driving assist apparatus  10  proceeds with the process to a step  515  to determine whether the forward inter-vehicle distance DF is greater than a forward short distance determination value DF_S which is smaller than the forward middle distance determination value DF_M. That is, when (i) there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, and (ii) the distance between the own vehicle  100  and the preceding vehicle  200 F is not relatively great as shown in  FIG.  9 B , the vehicle driving assist apparatus  10  determines whether the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) is not extremely small. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  515 , the vehicle driving assist apparatus  10  proceeds with the process to a step  520  to set the control mode to the coasting mode. That is, when (i) there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, (ii) the forward inter-vehicle distance DF (i.e., the distance between the own vehicle  100  and the preceding vehicle  200 F) is not relatively great, and (iii) the forward inter-vehicle distance DF is not extremely small as shown in  FIG.  10 A , the vehicle driving assist apparatus  10  sets the control mode to the coasting mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the coasting control is executed. Thus, the own vehicle  100  is decelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  515  of the routine shown in  FIG.  5   , the vehicle driving assist apparatus  10  proceeds with the process to a step  525  to set the control mode to the inter-vehicle distance maintaining mode. That is, when (i) there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, and (ii) the distance between the own vehicle  100  and the preceding vehicle  200 F is extremely small, the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the ordinary following moving control is executed. 
     When the vehicle driving assist apparatus  10  determines “No” at the step  415  of the routine shown in  FIG.  4   , the vehicle driving assist apparatus  10  proceeds with the process to a step  420  to determine whether the forward inter-vehicle distance DF is greater than the preceding vehicle determination value DF_TH. That is, when (i) the moving assist execution condition and the economy moving execution condition are both satisfied, and (ii) there is the following vehicle  200 R, the vehicle driving assist apparatus  10  determines whether there is the preceding vehicle  200 F. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  420 , the vehicle driving assist apparatus  10  proceeds with the process to a step  805  of the routine shown in  FIG.  8    to determine whether the rearward inter-vehicle distance DR is greater than a rearward short distance determination value DR_S which is smaller than the following vehicle determination value DR_TH. That is, when there is the following vehicle  200 R, but there is not the preceding vehicle  200 F, the vehicle driving assist apparatus  10  determines whether the following vehicle  200 R is extremely near the own vehicle  100 . 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  805 , the vehicle driving assist apparatus  10  proceeds with the process to a step  810  to determine whether (i) the control mode is set to the coasting mode, (ii) a following vehicle moving speed difference ΔVR is a negative predetermined following vehicle moving speed difference ΔVR_TH, and (iii) the own vehicle moving speed VO is smaller than the economy vehicle moving speed upper limit VU_E. The following vehicle moving speed difference ΔVR is a difference of a following vehicle moving speed VR with respect to the own vehicle moving speed VO (ΔVR=VO−VR). The following vehicle moving speed VR is the moving speed of the following vehicle  200 R. That is, when (i) there is the following vehicle  200 R, but there is not the preceding vehicle  200 F, and (ii) the following vehicle  200 R is not extremely near the own vehicle  100  as shown in  FIG.  11 A , the own vehicle  100  is decelerated by the coasting control, and the own vehicle moving speed VO is smaller than the following vehicle moving speed VR. Thus, the vehicle driving assist apparatus  10  determines whether (i) the following vehicle  200 R is approaching the own vehicle  100 , and (ii) the own vehicle moving speed VO is greater than the predetermined vehicle moving speed range RNG_E. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  810 , the vehicle driving assist apparatus  10  proceeds with the process to a step  815  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. Thus, the own vehicle  100  is accelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  810 , the vehicle driving assist apparatus  10  proceeds with the process to a step  820  to determine whether the acceleration request condition is satisfied. The acceleration request condition is the condition that (i) the accelerator override state is produced, and (ii) the first power source  211  will be operated to output the driving torque corresponding to the driver requested driving torque DTQ_D_RQ from the driving apparatus  21 . 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  820 , the vehicle driving assist apparatus  10  proceeds with the process to a step  825  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. Thus, the own vehicle  100  is accelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  820  of the routine shown in  FIG.  8   , the vehicle driving assist apparatus  10  proceeds with the process to a step  830  to determine whether the accelerator override state is produced. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  830 , the vehicle driving assist apparatus  10  proceeds with the process to a step  835  to set the control mode to the ordinary moving mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    to execute the ordinary moving control and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the ordinary moving control is executed. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  830 , the vehicle driving assist apparatus  10  proceeds with the process to a step  840  to set the control mode to the mode previously set. That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. 
     As described above, in this embodiment, the acceleration request condition determined at the step  820  is the condition that (i) the accelerator override state is produced, and (ii) the first power source  211  will be operated when the driving apparatus  21  is operated, based on the driver requested driving torque DTQ_D_RQ. In this regard, the acceleration request condition may be the condition that the accelerator override state is produced. In this case, when the vehicle driving assist apparatus  10  determines “Yes” at the step  820 , the vehicle driving assist apparatus  10  proceeds with the process to the step  825  to set the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  820 , the vehicle driving assist apparatus  10  proceeds with the process directly to the step  840  to set the control mode to the mode previously set without executing a process of the step  830 . That is, the vehicle driving assist apparatus  10  maintains the current control mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, when the coasting control is executed, the coasting control continues to be executed, and when the optimum acceleration control is executed, the optimum acceleration control continues to be executed. Thereby, the ordinary moving control is not executed. Thus, the power output efficiency is increased. 
     As can be understood from the processes of the processes of the steps  805  to  815  of the routine shown in  FIG.  8   , and the processes of the steps  430  to  450  of the routine shown in  FIG.  4   , executing these processes leads to executing the economy moving assist control to autonomously accelerate and decelerate the own vehicle  100  so as to maintain the rearward inter-vehicle distance DR (i.e., the distance between the own vehicle  100  and the following vehicle  200 R) within a predetermined rearward distance range (i.e., a limited range between the following vehicle determination value DR_TH and the rearward short distance determination value DR_S). 
     Thus, the acceleration request condition determined at the step  820  substantially includes a condition that (i) the economy moving assist control is executed, and (ii) the distance between the own vehicle  100  and the following vehicle  200 R is within the predetermined rearward distance range. 
     When the vehicle driving assist apparatus  10  determines “No” at the step  805  of the routine shown in  FIG.  8   , the vehicle driving assist apparatus  10  proceeds with the process to a step  845  to determine whether the own vehicle moving speed VO is smaller than the economy vehicle moving speed upper limit VU_E. That is, when (i) there is not the following vehicle  200 R, but there is the preceding vehicle  200 F, and (ii) the following vehicle  200 R is extremely near the own vehicle  100  as shown in  FIG.  11 B , the vehicle driving assist apparatus  10  determines whether the own vehicle moving speed VO is smaller than the economy vehicle moving speed upper limit VU_E. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  845 , the vehicle driving assist apparatus  10  proceeds with the process to a step  850  to set the control mode to the optimum accelerating mode. That is, when (i) there is the following vehicle  200 R, but there is not the preceding vehicle  200 F, (ii) the following vehicle  200 R is not extremely near the own vehicle  100 , and (iii) the own vehicle moving speed VO is smaller than the economy vehicle moving speed upper limit VU_E, the vehicle driving assist apparatus  10  sets the control mode to the optimum accelerating mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the optimum acceleration control is executed. Thus, the own vehicle  100  is accelerated. 
     On the other hand, when the vehicle driving assist apparatus  10  determines “No” at the step  845  of the routine shown in  FIG.  8   , the vehicle driving assist apparatus  10  proceeds with the process to a step  855  to set the control mode to the inter-vehicle distance maintaining mode. That is, when (i) there is the following vehicle  200 R, but there is not the preceding vehicle  200 F, (ii) the following vehicle  200 R is not extremely near the own vehicle  100 , and (iii) the own vehicle moving speed VO is greater than the predetermined vehicle moving speed range RNG_E, the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thereby, the ordinary constant speed moving control is executed. 
     When the vehicle driving assist apparatus  10  determines “Yes” at the step  420  of the routine shown in  FIG.  4   , the vehicle driving assist apparatus  10  proceeds with the process to a step  425  to set the control mode to the inter-vehicle distance maintaining mode. That is, when there are the following vehicle  200 R and the preceding vehicle  200 F, the vehicle driving assist apparatus  10  sets the control mode to the inter-vehicle distance maintaining mode. Thereafter, the vehicle driving assist apparatus  10  executes the processes of the steps  430  to  450  of the routine shown in  FIG.  4    and then, proceeds with the process to the step  495  to terminate this routine once. Thus, the ordinary following moving control is executed. 
     &lt;Advantages&gt; 
     With the vehicle driving assist apparatus  10  described above, when the accelerator override state is produced while the economy moving assist control is executed, the ordinary moving control does not start to be executed promptly, but the economy moving assist control continues to be executed. Thereby, the power output efficiency of the driving apparatus  21  for moving the own vehicle  100  can be maintained at the great efficiency. 
     It should be noted that the invention is not limited to the aforementioned embodiments, and various modifications can be employed within the scope of the invention.