Patent Publication Number: US-11662724-B2

Title: Vehicle control system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 16/897,723, filed Jun. 10, 2020, which is a divisional application of U.S. patent application Ser. No. 15/795,680, filed Oct. 27, 2017, which claims the benefit of priority to Japanese Patent Application No. 2016-212163 filed on Oct. 28, 2016 with the Japanese Patent Office, the entire contents of all which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     Embodiments of the present disclosure relate to the art of a control system of an autonomous vehicle. 
     Discussion of the Related Art 
     JP-A-2014-106854 describes an automatic driving vehicle control apparatus for operating vehicles autonomously without a driver. The control apparatus taught by JP-A-2014-106854 includes a detection means that acquires a running state of the vehicle, a circumferential state of the vehicle, and a state of the driver. When the condition for automatic operation is satisfied, the control apparatus operates the vehicle autonomously by controlling actuators for controlling output power, braking force, steering angle, etc. 
     According to the teachings of JP-A-2014-106854, the running state detection means includes a GPS unit, a vehicle speed sensor, an acceleration sensor, and a steering angle sensor. The circumferential state detection means includes a RADAR an on-board camera, an inter-vehicle communication system. The driver state detection means includes a biometric sensor for detecting a cardiac beat, and a camera for detecting an expression and a pupil of the passenger. 
     In the conventional automobiles, a power transmission between an engine and drive wheels may be interrupted by releasing a power transmission clutch to save fuel. 
     In the conventional autonomous vehicle, however, a battery may not be charged during coasting while the engine is stopped. In this situation, electricity is continuously consumed to actuate the actuators such as the steering actuator, and consequently a state of charge level of the battery may drop excessively. In addition, during coasting of the vehicle, a mechanical oil pump may not be driven by the engine to apply the power transmission clutch. For this reason, it is necessary to driven an electric oil pump to apply the power transmission clutch and hence the charge level of the battery may further drop. In this situation, the vehicle may not be operated autonomously. 
     SUMMARY 
     Aspects of embodiments of the present disclosure have been conceived noting the foregoing technical problems, and it is therefore an object of the present disclosure is to provide a vehicle control system configured to maintain a state of charge level of the battery during autonomous operation of the vehicle. 
     The control system according to at least one of the embodiments of the present disclosure may comprise: an engine that generates a drive force by burning fuel; a generator that generates electricity by the drive force generated by the engine or a force delivered from drive wheels to the engine; a battery that is charged by the electricity delivered from the generator; a clutch that selectively interrupts power transmission between the engine and the drive wheels; a state of charge detector that detects a state of charge level of the battery; a brake system that applies braking torque to wheels; a steering system that turns the wheels; and a controller that controls the engine and the clutch. The vehicle may be operated autonomously without requiring a driver by controlling at least the engine, the clutch, the generator, the battery, the brake system and the steering system. In addition, the vehicle is allowed to coast by manipulating the clutch. Specifically, the controller is configured to: determine execution of autonomous operation of the vehicle, satisfaction of a predetermined condition to allow the vehicle to coast, and the state of charge level of the battery; select a first coasting mode in which the engine is stopped and the clutch is disengaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, and that the state of charge level of the battery is higher than a threshold level; and select a second coasting mode in which the engine is activated and the clutch is disengaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, and that the state of charge level of the battery is lower than the threshold level. 
     In a non-limiting embodiment, the control system may further comprise a road grade detector that estimates a grade of a road on which the vehicle travels. In addition, the controller may be further configured to: determine the grade of the road on which the vehicle travels; and select a third coasting mode in which the engine is stopped and the clutch is engaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than the threshold level, and that a downhill grade of the road is steeper than a threshold grade. 
     In a non-limiting embodiment, the control system may further comprise: a fuel level detector that detects a fuel level in a fuel tank; and a passenger sensor that detects an existence of a passenger in the vehicle. In addition, the controller may be further configured to: determine the fuel level in the fuel tank, and the existence of the passenger in the vehicle; and terminate the autonomous operation of the vehicle in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than the threshold level, that the fuel level is lower than a threshold fuel level, and that the vehicle carries the passenger. 
     In a non-limiting embodiment, the control system may further comprise: a fuel level detector that detects a fuel level in a fuel tank; and a passenger sensor that detects an existence of a passenger in the vehicle. In addition, the controller may be further configured to: determine the fuel level in the fuel tank, and the existence of the passenger in the vehicle; and set a destination of the vehicle to at least one of a gas station and a charging station in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than the threshold level, that the fuel level is lower than a threshold fuel level, and that the vehicle is operated without carrying a passenger. 
     In a non-limiting embodiment, the control system according to another embodiment of the present disclosure may comprise: an engine that generates a drive force by burning fuel; a motor having a generating function; a battery that is charged by electricity delivered from the motor; a state of charge detector that detects a state of charge level of the battery; a first clutch that selectively interrupts power transmission between the engine and the motor; a second clutch that selectively interrupts power transmission between the motor and the drive wheels; a road grade detector that estimates a grade of a road on which the vehicle travels; a brake system that applies braking torque to wheels; a steering system that turns the wheels; and a controller that controls the engine, the first clutch and the second clutch. The vehicle may be operated autonomously without requiring a driver by controlling at least the engine, the battery, the motor, the first clutch, the second clutch, the brake system and the steering system. In addition, the vehicle is allowed to coast by manipulating the first clutch and the second clutch. Specifically, the controller is configured to: determine execution of autonomous operation of the vehicle, satisfaction of a predetermined condition to allow the vehicle to coast, the state of charge level of the battery, and the grade of the road on which the vehicle travels; select a fourth coasting mode in which the engine is stopped and the first clutch and the second clutch are engaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than a first threshold level, and that a downhill grade of the road is steeper than a first threshold grade; select a fifth coasting mode in which the engine is stopped and the first clutch and the second clutch are disengaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is higher than the first threshold level, and that the downhill grade of the road is milder than the first threshold grade; and select a sixth coasting mode in which the engine is stopped, the first clutch is disengaged, and the second clutch is engaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is higher than the first threshold level but lower than a second threshold level, and that the downhill grade of the road is milder than the first threshold grade. 
     In a non-limiting embodiment, the control system may further comprise a fuel level detector that detects a fuel level in a fuel tank. In addition, the controller may be further configured to: determine the fuel level in a fuel tank; select a seventh coasting mode in which the engine is activated, the first clutch is disengaged, and the second clutch is engaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the downhill grade of the road is milder than the first threshold grade but steeper than a second threshold grade, and that the that the fuel level is higher than a threshold fuel level; and select an eighth coasting mode in which the engine is activated, the first clutch is engaged and the second clutch is disengaged, in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the downhill grade of the road is milder than the second threshold grade, and that the that the fuel level is higher than the threshold fuel level. 
     In a non-limiting embodiment, the control system may further comprise a generator that is rotated by an output power of the engine to generate electricity. In addition, the battery may include a first battery that is charged with the electricity generated by the generator and that supplies electricity to an auxiliary activated by low-voltage, and a second battery that is charged with the electricity generated by the motor and that supplies electricity to an auxiliary activated by high-voltage. 
     In a non-limiting embodiment, the control system may further comprise a passenger sensor that detects an existence of a passenger in the vehicle. In addition, the controller may be further configured to: determine the existence of the passenger in the vehicle; and terminate the autonomous operation of the vehicle in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than the first threshold level, that the downhill grade of the road is milder than the first threshold grade, that the fuel level is lower than the threshold fuel level, and that the vehicle carries the passenger. 
     In a non-limiting embodiment, the control system may further comprise a passenger sensor that detects an existence of a passenger in the vehicle. In addition, the controller may be further configured to: determine the existence of the passenger in the vehicle; and set a destination of the vehicle to at least one of a gas station and a charging station in a case that the predetermined condition is satisfied during autonomous operation of the vehicle, that the state of charge level of the battery is lower than the first threshold level, that the downhill grade of the road is milder than the first threshold grade, that the fuel level is lower than the threshold fuel level, and that the vehicle is operated without carrying a passenger. 
     Thus, according to the embodiments of the present disclosure, the coasting mode may be selected from a plurality of modes to prevent a reduction of the state of charge level of the battery. Specifically, if the state of charge level is lower than the threshold level, the second coasting mode in which the clutch is disengaged and the engine is activated is selected to allow the vehicle to coast while charging the battery. According to the embodiments of the present disclosure, therefore, the autonomous operation of the vehicle will not be terminated undesirably due to reduction of the state of charge level of the battery. 
     The third coasting mode is selected when the state of charge level of the battery is lower than the threshold level, and the downhill grade of the road is steeper than a threshold grade. In the third coasting mode, the engine is inactivated but rotated by torque delivered from the wheels so that the generator is rotated by a rotation of the engine to charge the battery. In addition, in the third coasting mode, an engine braking force may be established to reduce a vehicle speed. 
     When the state of charge level of the battery is lower than the threshold level and the fuel level is lower than the threshold fuel level during autonomous operation while carrying the passenger, the autonomous operation is terminated to allow the passenger to operate the vehicle manually. In this case, the vehicle is allowed to go to the gas station or the charging station before running out of the fuel. 
     The control system is further configured to take the vehicle to the gas station or the charging station before running out of the fuel even if the vehicle is operated autonomously without carrying the passenger. 
     The fourth coasting mode in which the engine is stopped and the first clutch and the second clutch are engaged is selected when the state of charge level of the battery is lower than the first threshold level, and the downhill grade of the road is steeper than a first threshold grade. In the fourth coasting mode, therefore, the battery may be charged while establishing an engine braking force. 
     The seventh coasting mode and the eighth coasting mode are selected when the fuel level of the battery is sufficiently high. In the seventh coasting mode and the eighth coasting mode, therefore, the vehicle may be powered by the engine while charging the battery. 
     In addition, since two batteries are arranged in the vehicle, the coasting mode may be selected depending on the state of charge levels of those batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and advantages of exemplary embodiments of the present invention will become better understood with reference to the following description and accompanying drawings, which should not limit the invention in any way. 
         FIG.  1    is a schematic illustration showing a first example of a vehicle to which the control system according to the present disclosure is applied; 
         FIG.  2    is a flowchart showing a control example for selecting a coasting mode in the vehicle according to the first example; 
         FIG.  3    is a table showing conditions for determining the coasting mode according to the first example; 
         FIG.  4    is a schematic illustration showing a second example of a vehicle to which the control system according to the present disclosure is applied; 
         FIG.  5    is a flowchart showing a control example for selecting the coasting mode in the vehicle according to the second example; 
         FIG.  6    is a table showing conditions for determining the coasting mode in the vehicle according to the second example; 
         FIG.  7    is a schematic illustration showing a third example of a vehicle to which the control system according to the present disclosure is applied; and 
         FIG.  8    is a table showing conditions for determining the coasting mode in the vehicle according to the third example. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Preferred embodiments of the present application will now be explained with reference to the accompanying drawings. 
     Referring now to  FIG.  1   , there is schematically shown a first example of a vehicle  10 . An operating mode of the vehicle  10  may be selected from a manual mode in which the vehicle  10  is operated by a driver, and an autonomous mode in which the vehicle  10  is operated autonomously even if the vehicle  10  does not carry any passenger. For example, the operating mode is shifted from the autonomous mode to the manual mode when the driver operates a steering wheel, an accelerator pedal, or a brake pedal intentionally. In addition, the vehicle  10  may be operated completely autonomously without stay in a specific formation of vehicles. 
     According to the first example, the vehicle  10  is provided with an engine  11  as a prime mover for generating driving force. Output power of the engine  11  is delivered to a pair of rear wheels (i.e., drive wheels)  14  and  15  through an automatic transmission (as will be simply called the “transmission” hereinafter)  12  and a differential gear unit  13 . In order to selectively transmit power between the engine  11  and the drive wheels  14  and  15 , a clutch  17  is disposed between the engine  11  and the transmission  12 . 
     The engine  11  comprises a plurality of cylinders individually having a combustion chamber and a piston held in the cylinder while being allowed to reciprocate within the cylinder (neither of which are shown). A reciprocating motion of each of the pistons is translated into a rotary motion through a connecting rod to rotate an output shaft  11   a  through a crankshaft (not shown) of the engine  11 . 
     According to the embodiments of the present disclosure, not only a diesel engine but also a gasoline engine may be used as the engine  11 . In the engine  11 , number of the cylinders, arrangements of the cylinders and valves etc. may be altered according to need. Alternatively, the output power of the engine  11  may also be applied to front wheels (not shown) instead of the rear wheels  14  and  15 . 
     The clutch  17  is interposed between the output shaft  11   a  of the engine  11  and an input shaft  12   a  of the transmission  12  to selectively transmit power between the output shaft  11   a  and the input shaft  12   a . Optionally, a damper device and a torque converter may be arranged between the clutch  17  and the transmission  12 . 
     In order to control the engine  11 , an engine controller  23  is electrically connected to the engine  11 . The engine controller  23  comprises a throttle valve controller  20  and an injection controller  21 . Specifically, the throttle valve controller  20  is configured to control an opening degree of a throttle valve in accordance with a position of an accelerator pedal thereby controlling an air intake. The injection controller  21  is configured to control fuel injection, and further configured to execute a fuel cut-off control for stopping fuel supply to the engine  11  upon satisfaction of a predetermined condition. Here, the fuel  1  cut-off control may be executed to stop fuel supply only to some of the cylinder(s). 
     An electronic control unit (to be abbreviated as the “ECU” hereinafter)  25  as a main controller is electrically connected to the engine controller  23  and a battery controller  28 . 
     The battery controller  28  is electrically connected to an alternator  26  as a generator through a first switch  40 . The alternator  26  is rotated by a part of the power generated by the engine  11  to convert mechanical energy of the engine  11  to electrical energy in the form of three-phase alternating current. The alternating current thus generated is rectified into a direct current by a rectifier circuit including a diode to be delivered to a battery  27  through the first switch  40 . To this end, the alternator  26  comprises a voltage controller  29  such as a voltage regulator for regulating an output voltage according to need. 
     The first switch  40  comprises a switch that is turned off when the battery  27  is almost fully charged, and a switch operated in conjunction with an operation of a starting switch  41  such as an ignition switch. In the first switch  40 , those switches are connected in series. An auxiliary  30  such as an electrical load is connected to the voltage controller  29  of the alternator  26  through a change-over switch and the starting switch  41 . According to the embodiments, the auxiliary  30  includes an ignition plug, an air compressor, an actuator of door window, lighting devices, an electric oil pump  34 , a steering actuator  36 , and on-board sensors such as a RADAR (i.e., a radio detection and ranging), a LIDAR (i.e., a laser imaging detection and ranging), an on-board camera and so on. 
     The battery  27  includes a secondary battery and a lead battery, and charged with the electricity generated by the alternator  26 . The electricity stored in the battery  27  is supplied to the auxiliary  30 . 
     The battery controller  28  comprises a state of charge detector (to be abbreviated as the “SOC detector” hereinafter)  37  that detects a state of charge level (to be abbreviated as the “SOC level” hereinafter) of the battery  27  based on a charge current value and a discharge current value detected by a current sensor  38 . 
     In order to regenerate electric energy by the alternator  26 , the ECU  25  observes the SOC level of the battery  27 . Specifically, during operation of the engine  11 , the ECU  25  stops generation of the alternator  26  to reduce a load on the engine  11  thereby saving the fuel, and supplies electricity to the auxiliary  30  from the battery  27 . By contrast, during execution of the fuel cut-off control while the vehicle  10  is decelerating or coasting, the engine  11  is rotated by a torque from the drive wheels  14  and  15 . In this situation, the ECU  25  allows the alternator  26  to generate electricity to charge the battery  27  by driving the alternator  26  a rotation of the engine  11 . Thus, the ECU  25  selectively allows the alternator  26  to regenerate power depending on a running condition of the vehicle  10 . 
     The battery controller  28  transmits information about the SOC level of the battery  27  detected by the SOC detector  37  to the ECU  25  so that the ECU determines the SOC level of the battery  27 . In order to prevent the battery  27  from being fully charged, when the battery  27  is almost fully charged, the ECU  25  turns off the first switch  40  to stop power supply to the battery  27 . Thus, the ECU  25  and the battery controller  28  serve as the controller of the embodiments of the present disclosure. 
     The engine  11  is provided with a starter motor  32  for cranking the crankshaft to start the engine  11 . When the starting switch  41  is turned on, the ECU  25  sends a command signal to start the engine  11  to a second switch  42 . The second switch  42  is turned on upon reception of the command signal from the ECU  25 , and consequently the starter motor  32  is activated by the electricity supplied from the battery  27 . 
     As described, the auxiliary  30  includes the electric oil pump (referred to as “EOP” in  FIG.  1   )  34  that is activated by the electricity supplied from the battery  27 . A hydraulic control system  24  comprises a mechanical oil pump (referred to as “MOP” in  FIG.  1   )  43  driven by the crankshaft of the engine  11 , and an oil passage (not shown) connected to the electric oil pump  34  and the mechanical oil pump  43 . For example, the electric oil pump  34  and the mechanical oil pump  43  are driven to deliver pressurized oil to the hydraulic control system  24  so as to maintain a pressure level of operating oil to a predetermined level. Specifically, cooling oil, lubrication oil, operating oil are supplied to the engine  11 , the clutch  17 , the transmission  12  and so on from the hydraulic control system  24 . 
     In a case of using a geared transmission as the transmission  12 , a gear stage of the transmission  12  may be selected from a plurality of stages by manipulating clutches and brakes to change a speed ratio. In order to shift the gear stage of the transmission  12 , the hydraulic control system switches the oil passage in such a manner as to shift the gear stage to the target stage commanded by the ECU  25 . Instead, a belt-driven continuously variable transmission may also be used as the transmission  12 . 
     The clutch  17  serving as an input clutch of the transmission  12  is a frictional engagement device that is hydraulically engaged and disengaged by the hydraulic control system  24 . According to the embodiments of the present disclosure, the ECU  25  is configured to select a coasting mode of the vehicle  10  depending on the situation. 
     The coasting mode may be selected from a first coasting mode, a second coasting mode and a third coasting mode. Specifically, in the first coasting mode, the clutch  17  is disengaged to disconnect the engine  11  from the drive wheels  14  and  15 , and the engine  11  is stopped (i.e., free-run mode). In turn, in the second coasting mode, the clutch  17  is also disengaged to disconnect the engine  11  from the drive wheels  14  and  15 , and the fuel is supplied to at least some of the cylinders of the engine  11  (i.e., neutral coasting mode). By contrast, in the third coasting mode, the clutch  17  is engaged to connect the engine  11  to the drive wheels  14  and  15 , and fuel supply to the engine  11  is stopped (i.e., fuel-cut coasting mode). 
     The ECU  25  is a microcomputer comprising a CPU (i.e., Central Processing Unit), a ROM (i.e., Read Only Memory) a RAM (i.e., Random Access Memory), an input interface and an output interface. Specifically, the ECU  25  controls the battery controller  28  and the engine controller  23  utilizing data stored temporarily in the RAM and programs installed in the ROM. To this end, to the ECU  25 , information about depression of the brake pedal is transmitted from a brake sensor  45 , and information about depression of the accelerator pedal is transmitted from an accelerator sensor  46 . The ECU  25  comprises a fuel level detector  50 , and information about fuel level in a fuel tank is transmitted to the fuel level detector  50  from a fuel sensor  47  such as a fuel level gauge. 
     An engine speed sensor  48  is attached to the crankshaft of the engine  11  to send information about engine speed to the ECU  25 . Likewise, a vehicle speed sensor  49  is attached to the output shaft of the transmission  12  to send information about vehicle speed to the ECU  25 . 
     The ECU  25  is further configured to obtain a required power of the engine  11  based on a position of the accelerator pedal, and to shift the gear stage of the transmission  12  based on the obtained engine power and a current vehicle speed with reference to a shift map. In a case that the vehicle  10  is operated autonomously, a required engine power is calculated while taking account of a speed limit of a road, a road grade, a distance from a car ahead, a steering angle etc. 
     In order to control a steering system  58 , a drive system  60  and a brake system  59  during autonomous propulsion of the vehicle  10  the ECU  25  further comprises a position recognizer  51 , an external condition recognizer  52 , a running condition recognizer  53 , a travel plan creator  54 , a passenger detector  55 , an auxiliary controller  56  a travel controller  57 , a coasting condition determiner  62 . 
     The drive system  60  comprises a throttle actuator  64  that actuates a throttle valve in accordance with a command from the ECU  25 , and an accelerator sensor  46  that detects a position of the accelerator pedal. The detected position of the accelerator pedal is sent to the ECU  25 . During autonomous propulsion, the throttle actuator  64  is controlled based on a required power calculated by the ECU  25 . The throttle actuator  64  and the accelerator sensor  46  are also activated by the electricity supplied from the battery  27 . 
     The brake system  59  comprises a brake actuator  61  that actuates a brake device to apply braking force (or braking torque) to the wheels in accordance with a command from the ECU  25 , and a brake sensor  45  that detects a depression of the brake pedal. The detected depression of the brake pedal is also sent to the ECU  25 . During autonomous propulsion, the brake actuator  61  is controlled based on a required braking force calculated by the ECU  25 . The brake actuator  61  and the brake sensor  45  are also activated by the electricity supplied from the battery  27 . 
     The steering system  58  comprises the steering actuator  36  and a torque sensor  63 . The steering system  58  is also controlled by the ECU  25  to turn e.g., a pair of front wheels by the steering actuator  36 , and the steering system  58  includes an electric power steering system and an SBW (i.e., a steer by wire) system. In the steering system  58 , a plurality of the steering actuator  36  may be used to turn the wheels. The torque sensor  63  detects a torque applied to a steering wheel by the driver, and the detected torque is also sent to the ECU  25 . During autonomous propulsion, the steering actuator  36  is controlled based on a required steering angle calculated by the ECU  25 . The steering actuator  36  and the torque sensor  63  are also activated by the electricity supplied from the battery  27 . 
     In order to operate the vehicle  10  autonomously, the ECU  25  is connected to an internal sensor  65 , an external sensor  66 , a GPS (i.e., a Global Positioning System) receiver  67 , a map database  68 , a navigation system  69  and a passenger sensor  70 . The internal sensor  65  includes different kinds of sensors for detecting conditions and behaviors of the vehicle  10 , the engine  11 , and the transmission  12 . Specifically, the internal sensor  65  includes a longitudinal acceleration sensor for detecting a longitudinal acceleration of the vehicle  10 , a lateral acceleration sensor for detecting a lateral acceleration of the vehicle  10 , a yaw rate sensor for detecting a yaw rate of the vehicle  10 , a shift sensor for detecting a position of a shift lever (or a shift switch) and so on. The aforementioned torque sensor  63 , the accelerator sensor  46 , the brake sensor  45 , the vehicle speed sensor  49  may serve as the internal sensor  65 . The longitudinal acceleration sensor, the lateral acceleration sensor, the yaw rate sensor, the shift sensor are also activated by the electricity supplied from the battery  27 . 
     In  FIG.  1   , the above-mentioned longitudinal acceleration sensor etc. are simply referred to as “Internal Sensor”  65 . 
     The ECU  25  carries out a calculation based on incident data from the above-mentioned sensors as well as data and formulas installed in advance, and transmits calculation results in the form of command signals to the engine controller  23 , the steering system  58 , the brake system  59 , the drive system  60 , the hydraulic control system  24  and so on. 
     The external sensor  66  for detecting an external condition includes at least one of the aforementioned on-board camera, the RADAR, the LIDAR. The external sensor  66  is also activated by the electricity supplied from the battery  27 . 
     Specifically, the on-board camera is arranged inside of a windshield and transmits recorded information about the external condition to the ECU  25 . To this end, not only a monocular camera but also a stereo camera having a plurality of lenses and image sensors to achieve a binocular vision may be used as the on-board camera. If the stereo camera is used as the on-board camera, the ECU  25  is allowed to obtain three-dimensional information of the recorded object. 
     The RADAR is adapted to detect obstacles utilizing radio waves such as millimetric-waves and microwaves, and to transmit detected information to the ECU  25 . Specifically, the RADAR detects an obstacle such as other vehicles and so on by emitting radio waves and analyzing the radio waves reflected from the obstacle. 
     The LIDAR is adapted to detect obstacles utilizing laser light and to transmit detected information to the ECU  25 . Specifically, the LIDAR detects an obstacle such as other vehicles and so on by emitting laser light and analyzing the laser light reflected from the obstacle. 
     The GPS receiver  67  is adapted to obtain positional information such as latitude and longitude of the vehicle  10  based on incident signals from GPS satellites, and to transmit the positional information to the ECU  25 . As the map database  68 , map information stored in external online information processing systems may be available. Alternatively, the map database  68  may also be stored in a storage device of the ECU  25 . The navigation system  69  is configured to determine a travelling route of the vehicle  10  based on the positional information obtained by the GPS receiver  67  and the map database  68 . 
     The position recognizer  51  is configured to recognize a current position of the vehicle  10  on a map based on positional information received by the GPS receiver  67  and the map database  68 . The current position of the vehicle  10  may also be obtained from the positional information used in the navigation system  69 . Optionally, the vehicle  10  may also be adapted to communicate with external sensors and signposts arranged along the road to obtain the current position of the vehicle  10 . 
     The external condition recognizer  52  is configured to recognize external condition of the vehicle  10  such as a location of a traffic lane, a road width, a road configuration, a road grade, an existence of obstacles around the vehicle  10  and so on, based on the recorded information of the on-board camera, or detection data of the RADAR or the LIDAR. Optionally, weather information, a friction coefficient of road surface etc. may be obtained according to need. 
     The running condition recognizer  53  is configured to recognize running condition of the vehicle  10  such as a vehicle speed, a longitudinal acceleration, a lateral acceleration, a yaw rate and so on based on detection result of the internal sensors  65 . 
     The travel plan creator  54  is configured to create a travel locus of the vehicle  10  based on a target course determined by the navigation system  69 , a position of the vehicle  10  recognized by the position recognizer  51 , and an external condition recognized by the external condition recognizer  52 . That is, the travel plan creator  54  creates a travel locus of the vehicle  10  within the target course in such a manner that the vehicle  10  is allowed to travel safely and properly while complying with the traffic rules. 
     In addition, the travel plan creator  54  is further configured to create a travel plan in line with the travel locus and the target course created based on the external conditions recognized by the external condition recognizer  52  and the map database  68 . 
     Specifically, the travel plan is created based on prospective data after few seconds from the present moment to determine a future condition of the vehicle  10  such as a driving force or the like required in future. Optionally, the travel plan may also be created based on prospective data after several ten seconds depending on the external conditions and the running conditions. Thus, the travel plan creator  54  creates a future plan to change a vehicle speed, acceleration, steering torque etc. during travelling along the target course in the form of e.g., a map. 
     Alternatively, the travel plan creator  54  may also create a pattern to change the vehicle speed, acceleration, steering torque etc. between predetermined points on the travel locus. Specifically, such patterns may be determined by setting target values of those parameters at each point on the travel locus taking account of a required time to reach the point at the current speed. 
     The travel controller  57  is configured to operate the vehicle  10  autonomously in line with the travel plan created by the travel plan creator  54 . To this end, specifically, the travel controller  57  transmits command signals to the engine controller  23 , the drive system  60 , the brake system  59  and the steering system  58  to manipulate the throttle actuator  64 , the brake actuator  61 , the steering actuator  36  and so on in accordance with the travel plan. In addition, the travel controller  57  is further configured to switch a control mode from a normal control mode to a coast control mode upon satisfaction of a predetermined condition. 
     The passenger sensor  70  comprises a weight sensor that is arranged e.g., in a seat base to detect the existence of the passenger, a passenger condition sensor such as a biometric sensor for detecting e.g., a cardiac beat of the passenger, and a camera for detecting a facial expression and a condition of pupil of the passenger. Such information detected by the passenger sensor  70  is sent to the ECU  25 . 
     The auxiliary controller  56  is configured to operate the auxiliaries  30  through an auxiliary system  72 . The auxiliaries  30  further include the starter motor  32 , the throttle actuator  64 , the brake actuator  61 , the passenger sensor  70 , a wiper, a direction indicator and so on. 
     The coasting condition determiner  62  is configured to determine a satisfaction of the condition to execute a coast control. The condition to execute a coast control includes a first condition and a second condition. Specifically, the first condition is satisfied given that a vehicle speed is higher than a predetermined value, that the brake actuator  61  is inactive, that the drive force is not required (i.e., the accelerator pedal is not depressed), that a distance from a car running ahead is greater than a predetermined value, and that a steering angle is smaller than a predetermined value. The second condition includes the SOC level of the battery  27  and a road grade. 
     The coasting condition determiner  62  determines that the SOC level of the battery  27  is “low” if the SOC level falls between zero and a threshold SOC level, and that the SOC level of the battery  27  is “high” if the SOC level falls between the threshold SOC level and the full level. 
     In order to detect a road grade, the coasting condition determiner  62  is provided with a road grade detector  75 . Specifically, the coasting condition determiner  62  estimates a road grade based on a drive force or a position of the accelerator pedal and longitudinal acceleration, or based on road information contained in the map data of the navigation system. For example, when the vehicle  10  travels on a downhill slope, the road grade detector  75  determines that a downhill grade is “steep” if a downhill grade is steeper than a threshold grade, and that a downhill grade is “mild” or a road is “flat” if a down grade is milder than the threshold grade. 
     Upon satisfaction of the condition to execute the coast control, the travel controller  57  selects a coasting mode from a first coasting mode, a second coasting mode and a third coasting mode depending on the satisfied condition. 
     Turning to  FIG.  2   , there is shown a routine to select the coasting mode according to the first example. 
     At step S 1 , it is determined whether or not the vehicle  10  is being operated autonomously. If the vehicle  10  is currently not operated autonomously so that the answer of step S 1  is NO, the routine returns. By contrast, the vehicle  10  is being operated autonomously so that the answer of step S 1  is YES, the routine progresses to step S 2  to determine whether or not the first condition is satisfied. If the first condition is not satisfied so that the answer of step S 2  is NO, the routine returns. By contrast, if the first condition is satisfied so that the answer of step S 2  is YES, the routine progresses to step S 3  to determine whether or not the SOC level of the battery  27  falls above the threshold SOC level. If the SOC level of the battery  27  falls above the threshold SOC level, that is, the SOC level of the battery  27  is “high” so that the answer of step S 3  is YES, the routine progresses to step S 4  to determine whether or not the vehicle  10  is travelling on a downhill slope steeper than the threshold grade. If the downhill grade is steeper than the threshold grade, that is, if the vehicle  10  is travelling on a steep downhill so that the answer of step S 4  is YES, the routine returns. By contrast, if the downhill grade is milder than the threshold grade, that is, if the vehicle  10  is travelling on a mild downhill or a flat road so that the answer of step S 4  is NO, the routine progresses to step S 5  to select the first coasting mode. 
     Then, at step S 6 , it is determined whether or not the first condition is no longer satisfied. If the first condition is no longer satisfied so that the answer of step S 6  is YES, the routine progresses to step S 7  to terminate the coasting control in the first coasting mode, and then returns. By contrast, if the first condition is still satisfied so that the answer of step S 6  is NO, the routine also returns. 
     If the SOC level of the battery  27  falls below the threshold SOC level, that is, the SOC level of the battery  27  is “low” so that the answer of step S 3  is NO, the routine progresses to step S 8  to determine whether or not the vehicle  10  is travelling on a downhill slope steeper than the threshold grade. If the downhill grade is steeper than the threshold grade, that is, if the vehicle  10  is travelling on a steep downhill so that the answer of step S 9  is YES, the routine progresses to step S 9  to select the third coasting mode. Then, the routine progresses to step S 6 . 
     By contrast, if the downhill grade is milder than the threshold grade, that is, if the vehicle  10  is travelling on a mild downhill or a flat road so that the answer of step S 4  is NO, the routine progresses to steep S 10  to determine whether or not a fuel level is higher than a predetermined threshold fuel level. If the fuel level is higher than the threshold fuel level so that the answer of step S 10  is YES, the routine progresses to step S 11  to select the second coasting mode. Then, the routine also progresses to step S 6 . 
     By contrast, if the fuel level is lower than the threshold fuel level so that the answer of step S 10  is NO, the routine progresses to steep S 12  to determine whether or not the vehicle  10  is propelling without carrying a passenger. If the vehicle  10  is propelling without carrying a passenger so that the answer of step S 12  is YES, the routine progresses to steep S 13  to change a destination of the navigation system to a closest gas station or charging station from a present location of the vehicle  10 . Alternatively, a gas station possible to get there earliest in terms of time may also be selected as the destination. Then, the routine returns. 
     By contrast, if the vehicle  10  is propelling while carrying a passenger so that the answer of step S 12  is NO, the routine progresses to steep S 14  to terminate autonomous operation or coasting of the vehicle  10 . Then, the routine returns. At step S 14 , optionally, it is possible to notify the driver or passenger of termination of the autonomous operation by an audio means or an indication means. 
     In the routine shown in  FIG.  2   , an order of executing determinations of SOC level and road gradient may be altered. In addition, the determination of rode gradient may be omitted. 
     In addition, an activation of the engine  11  and an engagement of the clutch  17  may be patterned depending on a selected coasting mode, and the engine  11  and the clutch  17  may be controlled separately to allow the vehicle  10  to coast in the selected coasting mode. 
     Further, the determination of satisfaction of the first condition may also be executed immediately prior to step S 5 , S 9  or S 11 . 
     Details of the first coasting mode to the third coasting mode are shown in  FIG.  3   . In  FIG.  3   , the electric oil pump  34  is referred to as “EOP”, and the mechanical oil pump  43  is referred to as “MOP”. 
     As shown in  FIG.  3   , during autonomous operation of the vehicle  10 , the first coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is high, and the vehicle  10  travels on a mild downhill or on a flat road. 
     In the first coasting mode, the engine  11  is stopped, and hence the operating oil is delivered to the hydraulic control system  24  by driving the electric oil pump  34 . In addition, generation of the alternator  26  is stopped. Thus, in the first coasting mode, the auxiliary  30  such as the electric oil pump  34  is operated by the battery  27  without generating electric power by the alternator  26 . In the first coasting mode, therefore, an electric consumption of the battery  27  is increased in comparison with the second coasting mode and the third coasting mode. 
     In the first coasting mode, however, the engine  11  is stopped while disengaging the clutch  17 . For this reason, fuel consumption may be reduced to improve mileage. In addition, since the SOC level is high, the internal sensor  65  and the external sensor  66  can be activated by the battery  27  to continue the autonomous operation of the vehicle  10 . 
     During autonomous operation of the vehicle  10 , the second coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is low, the vehicle  10  travels on a mild downhill or on a flat road, and the fuel level is high. 
     In the second coasting mode, the engine  11  is activated but the clutch  17  is disengaged. In this case, since the fuel level is high, the mechanical oil pump  43  is driven by the engine  11  to deliver the operating oil to the hydraulic control system  24 . In the second coasting mode, therefore, fuel consumption may be increased in comparison with the first coasting mode and the third coasting mode. However, since the alternator  26  is activated, the battery  27  may be charged with the electricity generated by the alternator  26 . In addition, since the electric oil pump  34  is stopped, electric consumption may be reduced. For this reason, the internal sensor  65  and the external sensor  66  may be activated by the battery  27  to continue the autonomous operation of the vehicle  10 . In the second coasting mode, optionally, some of the cylinders of the engine  11  may be inactivated. 
     During autonomous operation of the vehicle  10 , the third coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is high, the vehicle  10  travels down a steep downhill. 
     In the third coasting mode, the engine  11  is stopped (i.e., inactivated) and the clutch  17  is engaged so that fuel consumption is reduced. In the third coasting mode, since the vehicle  10  is travelling down the steep downhill while engaging the clutch  17 , the alternator  26  may be driven by a rotation of the engine  11  to charge the battery  27 . In the third coasting mode, therefore, the internal sensor  65  and the external sensor  66  may be activated by the battery  27  to continue the autonomous operation of the vehicle  10 , and the mechanical oil pump  43  may be driven by the engine  11  to deliver the operating oil to the hydraulic control system  24 . In addition, an engine braking force may be established by thus rotating the engine  11  passively to reduce a vehicle speed. 
     The third coasting mode may be omitted, and the coasting mode may be selected only from the first coasting mode and the second coasting mode. In addition, the coasting mode may be selected based only on the SOC level of the battery  27 . Further, in the third coasting mode, the cylinders of the engine  11  may be halted to reduce the engine braking force. 
     Second Example 
     Turning to  FIG.  4   , there is shown the second example of the vehicle to which the control system according to the present disclosure is applied. As illustrated in  FIG.  4   , the vehicle  77  comprises the engine  11 , a first clutch  78 , a second clutch  79  and a motor-generator (as will be simply called the “motor” hereinafter)  80  arranged coaxially with the engine  11 . The vehicle  77  may be powered only by the motor  80  while disconnecting the engine  11  completely from the powertrain. In addition, when the vehicle is powered by the engine  11 , an output power of the motor  80  may be added to an output power of the engine  11  to start or accelerate the vehicle  77 . 
     As shown in  FIG.  4   , the first clutch  78  is interposed between the output shaft  11   a  of the engine  11  and an input shaft  80   a  of the motor  80  to selectively transmit power therebetween. On the other hand, the second clutch  79  is interposed between an output shaft  80   b  of the motor  80  and the input shaft  12   a  of the transmission  12  to selectively transmit power therebetween. Both of the first clutch  78  and the second clutch  79  are actuated hydraulically the operating oil delivered from the hydraulic control system  24 . 
     For example, a permanent magnet synchronous motor may be used as the motor  80 . Specifically, the motor  80  comprises a rotor in which permanent magnets are arranged on an outer circumferential face, and a stator in which a three-phase coil is wound (neither of which are shown). When the motor  80  is energized by the electricity supplied from the battery  27 , the motor  80  generates a kinetic power, and when the motor  80  is rotated by a power delivered from the drive wheels  14  and  15 , the motor  80  generates an electric power. The electric power generated by the motor  80  is delivered to the battery  27  through an inverter  82 . A regenerative torque resulting from power regeneration of the motor  80  may be utilized as an engine braking force. In addition, the motor  80  may also be used to crank the engine  11 . 
     When operating the motor  80  as a motor, the inverter  82  is controlled by a motor controller  83  in such a manner as to convert direct current supplied from the battery  27  to alternate current, and to supply alternate current to the motor  80  to generate torque. By contrast, when operating the motor  80  as a generator, the inverter  82  is controlled by a motor controller  83  in such a manner as to convert alternate current generated by the motor  80  to direct current, and to charge the battery  27  with direct current. Thus, the inverter  82  serves as a rectifier and a voltage regulator. 
     As described, the coasting condition determiner  62  is configured to determine a satisfaction of the condition to execute the coast control. As also described, the first condition is satisfied given that a vehicle speed is higher than a predetermined value, that the brake actuator  61  is inactive, that the drive force is not required (i.e., the accelerator pedal is not depressed), that a distance from a car running ahead is greater than the predetermined value, and that a steering angle is smaller than the predetermined value. The second condition includes the SOC level of the battery  27  and a road grade. 
     According to the second example, the coasting condition determiner  62  determines that the SOC level of the battery  27  is “low” if the SOC level falls between zero and a first threshold SOC level, that the SOC level of the battery  27  is “medium” if the SOC level falls between the first threshold SOC level and a second SOC level, and that the SOC level of the battery  27  is “high” if the SOC level falls above the second threshold SOC level. 
     According to the second example, the road grade detector  75  determines that a downhill grade is “steep” if a downhill grade is steeper than a first threshold grade, that a downhill grade is “mild” if a down grade is milder than the first threshold grade but steeper than a second threshold grade, and that a road is “flat” if a down grade is milder than the second threshold grade. 
     As described, the travel controller  57  selects the coasting mode from a plurality of coasting modes depending on a running condition. 
     Turning to  FIG.  5   , there is shown a routine to select the coasting mode according to the second example. 
     At step S 15 , it is determined whether or not the vehicle  77  is being operated autonomously. If the vehicle  77  is currently not operated autonomously so that the answer of step S 15  is NO, the routine returns. By contrast, the vehicle  77  is being operated autonomously so that the answer of step S 15  is YES, the routine progresses to step S 16  to determine whether or not the first condition is satisfied. If the first condition is not satisfied so that the answer of step S 16  is NO, the routine returns. By contrast, if the first condition is satisfied so that the answer of step S 16  is YES, the routine progresses to step S 17  to determine whether or not the SOC level of the battery  27  falls above the first threshold SOC level. If the SOC level of the battery  27  falls below the first threshold SOC level, that is, the SOC level of the battery  27  is “low” so that the answer of step S 17  is NO, the routine progresses to step S 18  to determine whether or not the vehicle  77  is travelling on a downhill slope steeper than the first threshold grade. If the downhill grade is steeper than the first threshold grade, that is, if the vehicle  77  is travelling on a steep downhill so that the answer of step S 18  is YES, the routine progresses to step S 19  to select a fourth coasting mode. 
     Then, at step S 20 , it is determined whether or not the first condition is no longer satisfied. If the first condition is no longer satisfied so that the answer of step S 20  is YES, the routine progresses to step S 21  to terminate the coasting control in the first coasting mode, and then returns. By contrast, if the first condition is still satisfied so that the answer of step S 21  is NO, the routine also returns. 
     If the SOC level of the battery  27  falls above the first threshold SOC level, that is, the SOC level of the battery  27  is “high” or “medium” so that the answer of step S 17  is YES, the routine progresses to step S 22  to determine whether or not the SOC level of the battery  27  falls above the second threshold SOC level. If the SOC level of the battery  27  falls above the second threshold SOC level, that is, the SOC level of the battery  27  is “high” so that the answer of step S 22  is YES, the routine progresses to step  23  to determine whether or not the vehicle  77  is travelling on a downhill slope steeper than the first threshold grade. If the downhill grade is milder than the first threshold grade, that is, if the vehicle  77  is travelling on a mild downhill or a flat road so that the answer of step S 23  is NO, the routine progresses to step S 24  to select a fifth coasting mode. Then, the routine also progresses to step S 20 . By contrast, if the downhill grade is steeper than the first threshold grade, that is, if the vehicle  77  is travelling on a steep downhill so that the answer of step S 23  is YES, the routine returns. In this case, alternatively, the fourth coasting control may also be selected, or a current coasting mode may also be maintained. 
     If the SOC level of the battery  27  falls below the second threshold SOC level, that is, the SOC level of the battery  27  is “medium” so that the answer of step S 22  is NO, the routine progresses to step  25  to determine whether or not determine whether or not the vehicle  77  is travelling on a downhill slope steeper than the first threshold grade. If the downhill grade is milder than the first threshold grade, that is, if the vehicle  77  is travelling on a mild downhill or a flat road so that the answer of step S 25  is NO, the routine progresses to step S 26  to determine whether or not the vehicle  77  is travelling on a downhill slope steeper than the second threshold grade. If the downhill grade is steeper than the second threshold grade, that is, if the vehicle  77  is travelling down a mild downhill so that the answer of step S 26  is YES, the routine progresses to step S 27  to select a sixth coasting mode. Then, the routine also progresses to step S 20 . 
     By contrast, if the downhill grade is steeper than the first threshold grade, that is, if the vehicle  77  is travelling on a steep downhill so that the answer of step S 25  is YES, the routine returns. In this case, alternatively, the fourth coasting control may also be selected or a current coasting mode may also be maintained. Likewise, if the downhill grade is milder than the second threshold grade, that is, if the vehicle  77  is travelling on a flat road so that the answer of step S 26  is NO, the routine also returns. In this case, alternatively, the fifth or eighth coasting control may also be selected, or a current coasting mode may also be maintained. 
     If the downhill grade is milder than the first threshold grade, that is, if the vehicle  77  is travelling on a mild downhill or a flat road so that the answer of step S 18  is NO, the routine progresses to step S 28  to determine whether or not the fuel level is higher than a predetermined threshold fuel level. If the fuel level is higher than the threshold fuel level so that the answer of step S 28  is YES, the routine progresses to step S 29  to determine whether or not the vehicle  77  is travelling on a downhill slope steeper than the second threshold grade. If the downhill grade is milder than the second threshold grade, that is, if the vehicle  77  is travelling on a flat road so that the answer of step S 29  is NO, the routine progresses to step S 30  to select the eighth coasting mode. Then, the routine also progresses to step S 20 . 
     By contrast, if the downhill grade is steeper than the second threshold grade, that is, if the vehicle  77  is travelling down a mild downhill so that the answer of step S 29  is YES, the routine progresses to step S 31  to select a seventh coasting mode. Then, the routine also progresses to step S 20 . 
     If the fuel level is lower than the threshold fuel level so that the answer of step S 28  is NO, the routine progresses to steep S 32  to determine whether or not the vehicle  77  is propelling without carrying a passenger. If the vehicle  77  is propelling without carrying a passenger so that the answer of step S 32  is YES, the routine progresses to steep S 33  to change a destination of the navigation system to a closest gas station or charging station from a present location of the vehicle  77 . Alternatively, a gas station possible to get there earliest in terms of time may also be selected as the destination. Then, the routine returns. 
     By contrast, if the vehicle  77  is propelling while carrying a passenger so that the answer of step S 32  is NO, the routine progresses to steep S 34  to terminate autonomous operation or coasting of the vehicle  77 . Then, the routine returns. 
     In the routine shown in  FIG.  5   , an order of executing determinations of the SOC level and the road gradient may also be altered. In addition, the autonomous operation of the vehicle  77  may also be terminated without taking account of the road gradient. In addition, an activation of the engine  11 , and an engagement of each of the first clutch  78  and the second clutch  79  may be patterned depending on a selected coasting mode, and the engine  11  and the clutches  78  and  79  may be controlled separately to allow the vehicle  77  to coast in the selected coasting mode. 
     Further, the determination of satisfaction of the first condition may also be executed immediately prior to step S 19 , S 24 , S 27 , S 31  or S 30 . In addition, the sixth to eight coasting modes may be omitted. In this case, the coasting control is selected from the fourth coasting mode and the fifth coasting mode. 
     Details of the fourth coasting mode to the eighth coasting mode are shown in  FIG.  6   . In  FIG.  6   , the electric oil pump  34  is referred to as “EOP”, and the mechanical oil pump  43  is referred to as “MOP”. 
     As shown in  FIG.  6   , during autonomous operation of the vehicle  77 , the fourth coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is low, and the vehicle  77  travels on a steep downhill. In the fourth coasting mode, the engine  11  is stopped (i.e., inactivated) and both of the first clutch  78  and the second clutch  79  are engaged so that the engine  11  and the motor  80  are rotated by torque delivered from the drive wheels  14  and  15 . 
     In the fourth coasting mode, since the engine  11  is stopped, fuel consumption is reduced in comparison with the seventh coasting mode and the eighth coasting mode. Moreover, since the vehicle  77  is travelling down the steep downhill while engaging the first clutch  78  and the second clutch  79 , the motor  80  may be operated as a generator to charge the battery  27 , and the mechanical oil pump  43  may be driven by the engine  11  to deliver the operating oil to the hydraulic control system  24 . That is, in the fourth coasting mode, it is not necessary to operate the electric oil pump  34 . In the fourth coasting mode, therefore, electric consumption may be reduced in comparison with the fifth coasting mode and the sixth coasting mode. In addition, strongest engine braking force may be established by thus rotating the engine  11  passively to reduce vehicle speed. 
     During autonomous operation of the vehicle  77 , the fifth coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is high, and the vehicle  77  travels on a mild downhill or on a flat road. In the fifth coasting mode, both of the first clutch  78  and the second clutch  79  are disengaged to disconnect the engine  11  and the motor  80  from the drive wheels  14  and  15 , and the engine  11  is stopped. 
     In the fifth coasting mode, therefore, the motor  80  may not be operated as a generator. In addition, the electric oil pump  34  is activated to deliver the operating oil to the hydraulic control system  24 . That is, in the fifth coasting mode, the auxiliary  30  such as the electric oil pump  34  is operated by the battery  27  without charging the battery  27 . For this reason, an electric consumption of the battery  27  may be increased in comparison with the fourth, the seventh and the eighth coasting modes. 
     During autonomous operation of the vehicle  77 , the sixth coasting mode is selected given that the first condition is satisfied, that the SOC level of the battery  27  is medium, and that the vehicle  77  travels on a mild downhill. In the sixth coasting mode, the engine  11  is stopped and disconnected from the drive wheels  14  and  15  by disengaging the first clutch  78  while engaging the second clutch  79 . 
     In the sixth coasting mode, since the engine  11  is stopped, fuel consumption is reduced in comparison with the seventh coasting mode and the eighth coasting mode. However, although the motor  80  is operated as a generator to charge the battery  27 , the electricity of the battery  27  is consumed to operate the auxiliary  30  such as the electric oil pump  34 . In the sixth coasting mode, therefore, an electric consumption of the battery  27  may be increased in comparison with the fourth, the sixth the seventh and the eighth coasting modes. In the sixth coasting mode, the engine braking force may also be established by the regenerative torque of the motor  80 , and such engine braking force is stronger than that established in the fifth coasting mode. 
     During autonomous operation of the vehicle  77 , the seventh coasting mode is selected given that the first condition is satisfied, that the fuel level is high, that the SOC level of the battery  27  is low, and that the vehicle  77  travels on a mild downhill. In the seventh coasting mode, the engine  11  is operated but disconnected from the drive wheels  14  and  15  by disengaging the first clutch  78  while engaging the second clutch  79 . In the seventh coasting mode, optionally, some of the cylinders of the engine  11  may be inactivated. 
     In the seventh coasting mode, since the fuel level is high, the mechanical oil pump  43  may be driven by the engine  11  to deliver the operating oil to the hydraulic control system  24 . In the seventh coasting mode, therefore, fuel consumption may be increased in comparison with the fourth to sixth coasting modes. However, since the electric oil pump  34  is allowed to be stopped, electric consumption may be reduced. In addition, since the second clutch  79  is in engagement, the motor  80  may be rotated by the torque delivered from the drive wheels  14  and  15  to serve as a generator so as to charge the battery  27 . For this reason, electric consumption of the battery  27  may be reduced in comparison with the fifth coasting mode. In addition, the engine braking force may also be established by the regenerative torque of the motor  80 . 
     During autonomous operation of the vehicle  77 , the eighth coasting mode is selected given that the first condition is satisfied, that the fuel level is high, that the SOC level of the battery  27  is low, and the vehicle  77  travels on a flat road. In the eighth coasting mode, the engine  11  is operated but the engine  11  and the motor  80  are disconnected from the drive wheels  14  and  15  by engaging the first clutch  78  while disengaging the second clutch  79 . In the eighth coasting mode, optionally, some of the cylinders of the engine  11  may be inactivated. 
     In the eighth coasting mode, since the fuel level is high, the mechanical oil pump  43  may also be driven by the engine  11  to deliver the operating oil to the hydraulic control system  24 . In the eighth coasting mode, therefore, the electric oil pump  34  may also be stopped. In addition, the motor  80  may be rotated by the engine  11  to charge the battery  27 . For this reason, electric consumption of the battery  27  may be reduced in comparison with the fifth and the sixth coasting modes. In the eighth coasting mode, however, the second clutch  79  is in disengagement and hence the engine braking force generated by the regenerative torque of the motor  80  may not be applied to the drive wheels  14  and  15 . That is, fuel consumption may be reduced. 
     Third Example 
     Turning to  FIG.  7   , there is shown the third example of the vehicle to which the control system according to the present disclosure is applied. As illustrated in  FIG.  7   , in the vehicle  90  according to the third example, the alternator  26  used in the first example is arranged in the vehicle  77  according to the second example. The vehicle  90  further comprises: a first battery  91  as a low-voltage battery that is charged with electricity generated by the alternator  26 , and that supplies electricity to the auxiliaries  30  activated by low-voltage such as the internal sensor  65  and the external sensor  66 ; and a second battery  92  as a high-voltage battery that is charged with electricity generated by the motor  80 , and that supplies electricity to the auxiliaries  30  activated by high voltage such as the steering actuator  36 . According to the third example, the SOC detector  37  of the battery controller  28  is adapted to detect an SOC level of each of the first battery  91  and the second battery  92 . 
     As described, the travel controller  57  selects the coasting mode from a plurality of coasting modes depending on a running condition including an SOC level of each of the first battery  91  and the second battery  92 . 
     Details of a ninth coasting mode to a thirteenth coasting mode are shown in  FIG.  8   . The ninth coasting mode is selected upon satisfaction of the same condition as the fourth coasting mode, and details of the ninth coasting mode is substantially identical to those of the fourth coasting mode. In the ninth coasting mode, specifically, the engine  11  is stopped (i.e., inactivated) and both of the first clutch  78  and the second clutch  79  are engaged. 
     In the ninth coasting mode, the first battery  91  and the second battery  92  may be charged by both of the alternator  26  and the motor  80 . For this reason, reduction in the SOC levels of the first battery  91  and the second battery  92  may be prevented in comparison with a tenth coasting mode and an eleventh coasting mode. In addition, strong engine braking force may be established by regenerative torque of the motor  80  and pumping loss of the engine  11  itself to reduce vehicle speed when travelling down the steep downhill. 
     In the tenth coasting mode, both of the first clutch  78  and the second clutch  79  are disengaged to disconnect the engine  11  and the motor  80  from the drive wheels  14  and  15 , and the engine  11  is stopped. During autonomous operation of the vehicle  90 , the tenth coasting mode is selected given that the first condition is satisfied, that the SOC levels of the first battery  91  and the second battery  92  are high, and the vehicle  90  travels on a mild downhill or on a flat road. Thus, the tenth coasting mode is selected upon satisfaction of the same conditions as the fifth coasting mode. 
     In the eleventh coasting mode, the engine  11  is stopped and disconnected from the drive wheels  14  and  15  by disengaging the first clutch  78  while engaging the second clutch  79 . As the sixth coasting mode of the second example, the eleventh coasting mode is selected during autonomous operation of the vehicle  90  given that the first condition is satisfied, that the SOC levels of the first battery  91  and the second battery  92  are medium, and that the vehicle  90  travels on a mild downhill. 
     In the eleventh coasting mode, the second battery  92  may be charged while operating the low-voltage auxiliary  30  such as the electric oil pump  34  by supplying electricity from the first battery  91 . In the eleventh coasting mode, engine braking force stronger than that established in the tenth coasting mode may be established by regenerative torque of the motor  80 . 
     In the twelfth coasting mode, the engine  11  is operated but disconnected from the drive wheels  14  and  15  by disengaging the first clutch  78  while engaging the second clutch  79 . As the seventh coasting mode of the second example, the twelfth coasting mode is selected during autonomous operation of the vehicle  90  given that the first condition is satisfied, the SOC levels of the first battery  91  and the second battery  92  are low, and that the vehicle  90  travels on a mild downhill. 
     In the twelfth coasting mode, the first battery  91  and the second battery  92  may also be charged by both of the alternator  26  and the motor  80 . For this reason, reduction in the SOC levels of the first battery  91  and the second battery  92  may be prevented in comparison with the tenth coasting mode and the eleventh coasting mode. In addition, engine braking force stronger than that established in the tenth coasting mode may be established by regenerative torque of the motor  80 . 
     In the thirteenth coasting mode, the engine  11  is operated the first clutch  78  is engaged, and the second clutch  79  is disengaged. As the eighth coasting mode, during autonomous operation of the vehicle  90 , the thirteenth coasting mode is selected given that the first condition is satisfied, the SOC levels of the first battery  91  and the second battery  92  are low, and that the vehicle  90  travels on a flat road. 
     In the thirteenth coasting mode, electric consumption of any of the first battery  91  and the second battery  92  may be reduced in comparison with the tenth coasting mode and the eleventh coasting mode. In addition, since the second clutch  79  is disengaged, the engine braking force generated by regenerative torque of the motor  80  is not applied to the drive wheels  14  and  15 . For this reason, the vehicle  90  is allowed to coast while saving the fuel. 
     Although the above exemplary embodiments of the present application have been described, it will be understood by those skilled in the art that the present application should not be limited to the described exemplary embodiments, and various changes and modifications can be made within the spirit and scope of the present application. 
     For example, in the vehicle  10  according to the first example, a motor-generator may also be arranged in addition to the engine  11  while omitting the alternator  26 . In this case, output power of the engine  11  is distributed to the output shaft and the motor-generator so that the motor-generator is allowed to be rotated passively by the output power of the engine  11  to generate electric power. An output torque of the motor-generator may also be added to an output torque of the engine  11 . 
     In addition, a second motor as a motor-generator may also be arranged in the vehicle  77  according to the second example. In this case, output power of the engine  11  is distributed to the output shaft and the second motor through an additional power split device so that the second motor is allowed to be rotated passively by the output power of the engine  11  to generate electric power. In this case, as the third example, the first clutch  78  may be interposed between the output shaft and the second motor, and the second clutch  79  may be interposed between the second motor and the transmission  12 .