Patent Publication Number: US-2018029473-A1

Title: Motor vehicle

Description:
This application claims priority to Japanese Patent Application No. 2016-149389 filed 29 Jul. 2016, the contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a motor vehicle and more specifically relates to a motor vehicle configured to include a three-phase motor, an inverter, a battery, a step-up/down converter, a capacitor and a relay. 
     BACKGROUND 
     A proposed configuration of a motor vehicle includes a three-phase motor configured to output power to an axle; an inverter configured to drive the three-phase motor by switching of a plurality of switching elements; a battery configured to transmit electric power to and from the inverter via a power line; a capacitor mounted to the power line; and a relay provided on a battery side of the capacitor in the power line (as shown in, for example, JP 2013-55822A). This motor vehicle is configured to turn off the relay in response to detection of a collision of the motor vehicle. When the three-phase motor is rotated, this motor vehicle is configured to perform three-phase ON control that controls the inverter to turn on all switching elements of an upper armor all switching elements of a lower arm among the plurality of switching elements. When the three-phase motor stops rotation, on the other hand, this motor vehicle is configured to perform discharge control that controls the inverter such as not to output a torque from the three-phase motor and cause an electric charge of the capacitor to be consumed by the motor. 
     SUMMARY 
     In the motor vehicle described above, when a rotating shaft of the three-phase motor is uncoupled from the axle by the effect of a collision of the vehicle, rotation of the three-phase motor is likely to continue irrespective of a stop of the vehicle. The three-phase ON control of the inverter is performed during rotation of the three-phase motor. This configuration fails to discharge the capacitor and thereby fails to decrease the voltage of the capacitor. This may extend a time period from detection of a collision of the vehicle to the time when the voltage of the capacitor becomes equal to or lower than a predetermined voltage (i.e., the time when discharge of the capacitor is terminated) to a relatively long time. 
     The motor vehicle of the disclosure thus mainly aims to suppress a time period from detection of a collision of the vehicle to the time when a voltage of a capacitor becomes equal to or lower than a predetermined voltage (i.e., the time when discharge of the capacitor is terminated) from being extended to a relatively long time. 
     In order to achieve the above object, the motor vehicle of the disclosure is implemented by aspects described below. 
     According to one aspect of the present disclosure, there is provided a motor vehicle including: a three-phase motor configured to output power to an axle; an inverter configured to drive the three-phase motor by switching of a plurality of switching elements; a battery; a step-up/down converter configured to transmit electric power accompanied with a change in voltage between a low voltage-side power line which the battery is connected with and a high voltage-side power line which the inverter is connected with; a capacitor mounted to the high voltage-side power line; a relay provided in the low voltage-side power line; and a control device configured to control the inverter, the step-up/down converter and the relay, wherein in response to detection of a collision of the motor vehicle, the control device is configured to turn off the relay and to perform three-phase ON control that controls the inverter such as to turn on all switching elements of an upper arm or all switching elements of a lower arm among the plurality of switching elements and converter discharge control that controls the step-up/down converter such as to cause an electric charge of the capacitor to be consumed by the step-up/down converter. 
     In response to detection of a collision of the motor vehicle, the motor vehicle of this aspect is configured to turn off the relay and to perform the three-phase ON control that controls the inverter such as to turn on all the switching elements of the upper arm or all the switching elements of the lower arm among the plurality of switching elements and the converter discharge control that controls the step-up/down converter such as to cause the electric charge of the capacitor to be consumed by the step-up/down converter. This configuration enables the capacitor to be discharged even during rotation of the three-phase motor after the relay is turned off in response to detection of a collision of the vehicle. This configuration accordingly suppresses a time period from detection of a collision of the vehicle to the time when the voltage of the capacitor becomes equal to or lower than a predetermined voltage (i.e., the time when discharge of the capacitor is terminated) from being extended to a relatively long time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle according to one embodiment of the present disclosure; 
         FIG. 2  is a configuration diagram illustrating the schematic configuration of an electrical driving system including motors MG 1  and MG 2 ; 
         FIG. 3  is a flowchart showing one example of a collision detection control routine according to the embodiment; 
         FIG. 4  is a diagram illustrating one example of the operations in response to detection of a collision of the vehicle; 
         FIG. 5  is a flowchart showing another example of the collision detection control routine according to a modification; 
         FIG. 6  is a flowchart showing another example of the collision detection control routine according to another modification; 
         FIG. 7  is a diagram illustrating one example of the operations in response to detection of a collision of the vehicle according to the modification; 
         FIG. 8  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle according to a modification; 
         FIG. 9  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle according to another modification; 
         FIG. 10  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle according to another modification; 
         FIG. 11  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle according to another modification; and 
         FIG. 12  is a configuration diagram illustrating the schematic configuration of an electric vehicle according to another modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes some aspects of the present disclosure with reference to embodiments. 
       FIG. 1  is a configuration diagram illustrating the schematic configuration of a hybrid vehicle  20  according to one embodiment of the present disclosure.  FIG. 2  is a configuration diagram illustrating the schematic configuration of an electrical driving system including motors MG 1  and MG 2 . As shown in  FIG. 1 , the hybrid vehicle  20  of the embodiment includes an engine  22 , a planetary gear  30 , motors MG 1  and MG 2 , inverters  41  and  42 , a battery  50 , a step-up/down converter  55 , a system main relay  56 , a transmission  60  and a hybrid electronic control unit (hereinafter referred to as “HVECU”)  70 . 
     The engine  22  is configured as an internal combustion engine to output power using, for example, gasoline or light oil as a fuel. This engine  22  is operated and controlled by an engine electronic control unit (hereinafter referred to as “engine ECU”)  24 . 
     The engine ECU  24  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. The engine ECU  24  receives signals input from various sensors required for operation control of the engine  22  via the input port, for example, a crank angle θcr from a crank position sensor  23  configured to detect the rotational position of a crankshaft  26  of the engine  22 . The engine ECU  24  outputs various control signals for the operation control of the engine  22  via the output port. The engine ECU  24  is connected with the HVECU  70  via the respective communication ports. The engine ECU  24  calculates a rotation speed Ne of the engine  22 , based on the crank angle θcr input from the crank position sensor  23 . 
     The planetary gear  30  is configured as a single pinion-type planetary gear mechanism. The planetary gear  30  includes a sun gear that is connected with a rotor of the motor MG 1 . The planetary gear  30  also includes a ring gear that is connected with an input shaft  61  of the transmission and with a rotor of the motor MG 2 . The planetary gear  30  further includes a carrier that is connected with the crankshaft  26  of the engine  22  via a damper  28 . 
     The motor MG 1  is configured as a synchronous motor generator having a rotor with permanent magnets embedded therein and a stator with three-phase coils wound thereon. As illustrated, this rotor is connected with the sun gear of the planetary gear  30 . Like the motor MG 1 , the motor MG 2  is configured as a synchronous motor generator having a rotor with permanent magnets embedded therein and a stator with three-phase coils wound thereon. This rotor is connected with the ring gear of the planetary gear  30  and with the input shaft  61  of the transmission  60 . 
     As shown in  FIG. 2 , the inverter  41  is connected with high voltage-side power lines  54   a . This inverter  41  is configured to include six transistors T 11  to T 16  and six diodes D 11  to D 16  that are connected in parallel to and in a reverse direction to the transistors T 11  to T 16 . The transistors T 11  to T 16  are arranged in pairs, such that two transistors in each pair respectively serve as a source and a sink relative to a positive electrode line and a negative electrode line of the high voltage-side power lines  54   a . The respective phases of the three-phase coils (U phase, V phase and W phase) of the motor MG 1  are connected with connection points of the respective pairs of the transistors T 11  to T 16 . Accordingly, when a voltage is applied to the inverter  41 , a motor electronic control unit (hereinafter referred to as “motor ECU”)  40  serves to regulate the rates of ON times of the respective pairs of the transistors T 11  to T 16 , such as to provide a rotating magnetic field in the three-phase coils and thereby rotate and drive the motor MG 1 . Like the inverter  41 , the inverter  42  is also connected with the high voltage-side power lines  54   a  and is configured to include six transistors T 21  to T 26  and six diodes D 21  to D 26 . When a voltage is applied to the inverter  42 , the motor ECU  40  serves to regulate the rates of ON times of the respective pairs of the transistors T 21  to T 26 , such as to provide a rotating magnetic field in the three-phase coils and thereby rotate and drive the motor MG 2 . In the description below, the transistors T 11  to T 13  of the inverter  41  and the transistors T 21  to T 23  of the inverter  42  may be called “upper arm”, and the transistors T 14  to T 16  of the inverter  41  and the transistors T 24  to T 26  of the inverter  42  may be called “lower arm”. 
     The step-up/down converter  55  is connected with the high voltage-side power lines  54   a  with which the inverters  41  and  42  are connected and with low voltage-side power lines  54   b  with which the battery  50  is connected. This step-up/down converter  55  is configured to include two transistors T 31  and T 32 , two diodes D 31  and D 32  connected in parallel to and in a reverse direction to the transistors T 31  and T 32 , and a reactor L. The transistor T 31  is connected with the positive electrode line of the high voltage-side power lines  54   a . The transistor T 32  is connected with the transistor  31  and with negative electrode lines of the high voltage-side power lines  54   a  and of the low voltage-side power lines  54   b . The reactor L is connected with a connection point between the transistors T 31  and T 32  and with a positive electrode line of the low voltage-side power lines  54   b . The motor ECU  40  serves to regulate the rates of ON times of the transistors T 31  and T 32 , such that the step-up/down converter  55  steps up an electric power of the low voltage-side power lines  54   b  and supplies the stepped-up electric power to the high voltage-side power lines  54   a , while stepping down an electric power of the high voltage-side power lines  54   a  and supplying the stepped-down electric power to the low voltage-side power lines  54   b . The transistor T 31  of the step-up/down converter  55  may be called “upper arm”, and the transistor T 32  of the step-up/down converter  55  may be called “lower arm”. A smoothing capacitor  57  is mounted to the positive electrode line and the negative electrode line of the high voltage-side power lines  54   a . A smoothing capacitor  58  is mounted to the positive electrode line and the negative electrode line of the low voltage-side power lines  54   b.    
     The motor ECU  40  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. As shown in  FIG. 1 , the motor ECU  40  receives signals input from various sensors required for drive control of the motors MG 1  and MG 2  and the step-up/down converter  55  via the input port. The signals input into the motor ECU  40  include, for example, rotational positions θm 1  and θm 2  from rotational position detection sensors  43  and configured to detect the rotational positions of the respective rotors of the motors MG 1  and MG 2 . The input signals also include a voltage VH of the capacitor  57  (i.e., voltage of the high voltage-side power lines  54   a ) from a voltage sensor  57   a  mounted between terminals of the capacitor  57  and a voltage VL of the capacitor  58  (i.e., voltage of the low voltage-side power lines  54   b ) from a voltage sensor  58   a  mounted between terminals of the capacitor  58 . The motor ECU  40  outputs, for example, switching control signals to the transistors T 11  to T 16  of the inverter  41  and the transistors T 21  to T 26  of the inverter  42  and switching control signals to the transistors T 31  and T 32  of the step-up/down converter  55  via the output port. The motor ECU  40  is connected with the HVECU  70  via the respective communication ports. The motor ECU  40  calculates rotation speeds Nm 1  and Nm 2  of the respective motors MG 1  and MG 2 , based on the rotational positions θm 1  and θm 2  of the respective rotors of the motors MG 1  and MG 2  input from the rotational position detection sensors  43  and  44 . 
     The battery  50  may be configured by, for example, a lithium ion rechargeable battery or a nickel metal hydride battery and is connected with the low voltage-side power lines  54   b . This battery  50  is under management of a battery electronic control unit (hereinafter referred to as “battery ECU”)  52 . 
     The battery ECU  52  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. The battery ECU  52  receives signals input from various sensors required for management of the battery  50  via the input port. The signals input into the battery ECU  52  include, for example, a battery voltage Vb from a voltage sensor placed between terminals of the battery  50 , a battery current Ib from a current sensor mounted to an output terminal of the battery  50 , and a battery temperature Tb from a temperature sensor mounted to the battery  50 . The battery ECU  52  is connected with the HVECU  70  via the respective communication ports. The battery ECU  52  calculates a state of charge SOC of the battery  50 , based on an integrated value of the battery current Ib from the current sensor. The state of charge SOC denotes a ratio of the capacity of electric power dischargeable from the battery  50  to the overall capacity of the battery  50 . 
     The system main relay  56  is provided on a battery  50 -side of the capacitor  58  in the low voltage-side power lines  54   b . The HVECU  70  controls on and off this system main relay  56 , such that the system main relay  56  connects and disconnects the battery  50  with and from a step-up/down converter  55 -side in the low voltage-side power lines  54   b.    
     The transmission  60  is configured as a four-speed transmission to include an input shaft  61  that is connected with the ring gear of the planetary gear  30  and with the rotor of the motor MG 2 , an output shaft serving as a driveshaft  36  that is coupled with drive wheels  39   a  and  39   b  via an axle  39   s  and a differential gear  38 , a plurality of planetary gears, and a plurality of hydraulically-driven frictional engagement elements (clutches and brakes). This transmission  60  is controlled by the HVECU  70 , such as to change gear among first to fourth forward gear positions, neutral position and first back gear position. 
     The HVECU  70  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. The HVECU  70  receives signals input from various sensors via the input port. The signals input into the HVECU  70  include, for example, an ignition signal from an ignition switch  80  and a shift position SP from a shift position sensor  82  configured to detect an operating position of a shift lever  81 . The input signals also include an accelerator position Acc from an accelerator pedal position sensor  84  configured to detect a depression amount of an accelerator pedal  83 , a brake pedal position BP from a brake pedal position sensor  86  configured to detect a depression amount of a brake pedal  85 , and a vehicle speed V from a vehicle speed sensor  88 . The input signals further include a vehicle body acceleration α from acceleration sensors  89  provided, for example, on a center and on both sides in a vehicle front side. The HVECU  70  is connected with the engine ECU  24 , the motor ECU  40  and the battery ECU  52  via the respective communication ports as described above. 
     The hybrid vehicle  20  of the embodiment having the configuration described above may be driven in a hybrid drive (HV drive) mode or in an electric drive (EV) drive mode. The HV drive mode is a drive mode with operation of the engine  22 , and the EV drive mode is a drive mode without operation of the engine  22 . 
     The following describes operations of the hybrid vehicle  20  of the embodiment having the above configuration and more specifically series of operations in response to detection of a collision of the vehicle.  FIG. 3  is a flowchart showing one example of a collision detection control routine performed by the HVECU  70  according to the embodiment. This routine is triggered by detection of a collision of the vehicle. According to this embodiment, a collision of the vehicle is detected when the vehicle speed acceleration α detected by the acceleration sensors  89  exceeds a reference value αref for collision detection. When a collision of the vehicle is detected during operation of the engine  22 , the operation of the engine  22  is to be stopped. 
     When the collision detection control routine is triggered, the HVECU  70  first turns off the system main relay  56  and sends an operation stop command of the step/up/down converter  55  to the motor ECU  40  (step S 100 ). When receiving this operation stop command, the motor ECU  40  stops the operation of the step-up/down converter  55 . 
     The HVECU  70  subsequently starts three-phase ON control of the inverters  41  and  42  and sends a control start command for discharge control of the step-up/down converter  55  (hereinafter referred to as “converter discharge control”) to the motor ECU  40  (step S 110 ). When receiving this control start command, the motor ECU  40  starts the converter discharge control. 
     The three-phase ON control of the inverter  41  denotes a control process of either turning on all the transistors T 11  to T 13  (upper arm) among the transistors T 11  to T 16  of the inverter  41  while turning off all the transistors T 14  to T 16  (lower arm) or turning off all the transistors T 11  to T 13  (upper arm) while turning on all the transistors T 14  to T 16  (lower arm). The three-phase ON control of the inverter  42  is performed similarly to the three-phase ON control of the inverter  41 . Performing the three-phase ON control of the inverters  41  and  42  in the state that the motors MG 1  and MG 2  are rotated generates torques (drag torques) in a direction of reducing the absolute values of the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  and thereby stops the rotations of the motors MG 1  and MG 2 . 
     The converter discharge control denotes a control process of controlling the step-up/down converter  55 , such as to cause electric charges of the capacitor  57  and the capacitor  58  to be consumed by the step-up/down converter  55 . According to this embodiment, the converter discharge control sets a duty D of the transistors T 31  and T 32  to a predetermined value D 1  (for example, 50%) and performs switching control of the transistors T 31  and T 32  of the step-up/down converter  55 . The duty D herein denotes a ratio of the ON time of the transistor T 32  (lower arm) to the sum of the ON time of the transistor T 31  (upper arm) and the ON time of the transistor T 32  (lower arm). When the converter discharge control is performed to turn off the transistor T 31  and turn on the transistor T 32 , the electric charges of the capacitor  58  are consumed as a loss of the reactor L and the transistor T 32 . When the converter discharge control is performed to turn on the transistor T 31  and turn off the transistor T 32 , on the other hand, the electric charges of the capacitor  57  are consumed as a loss of the transistor T 31  and the reactor L. The converter discharge control enables the capacitor  57  and the capacitor  58  to be discharged in this manner, such as to decrease the voltage of the high voltage-side power lines  54   a  and the voltage of the low voltage-side power lines  54   b.    
     After starting the three-phase ON control of the inverters  41  and  42  and the converter discharge control, the HVECU  70  receives the inputs of the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  and the voltage VH of the capacitor  57  (step S 120 ). The rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are calculated based on the rotational positions θm 1  and θm 2  of the respective rotors of the motors MG 1  and MG 2  from the rotational position detection sensors  43  and  44  and are input from the motor ECU  40  by communication. The voltage VH of the capacitor  57  is detected by the voltage sensor  57   a  and is input from the motor ECU  40  by communication. 
     The HVECU  70  subsequently determines whether both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to value 0 (step S 130 ) and compares the voltage VH of the capacitor  57  with a reference value VHref (step S 140 ). The reference value VHref is used to determine whether discharge of the capacitor  57  (and the capacitor  58 ) is to be terminated and may be, for example, 50 V, 60V or 70 V. 
     When it is determined at step S 130  that at least one of the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  is not equal to the value 0 or when it is determined at step S 140  that the voltage VH of the capacitor  57  is higher than the reference value VHref, the HVECU  70  goes back to step S 120 . 
     When it is determined at step S 130  that both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0 and it is determined at step S 140  that the voltage VH of the capacitor  57  is equal to or lower than the reference value VHref, on the other hand, the HVECU  70  terminates the three-phase ON control of the inverters  41  and  42  and sends a control stop command for the converter discharge control to the motor ECU  40  (step S 150 ) and terminates this routine. When receiving this control stop command, the motor ECU  40  terminates the converter discharge control. 
     In the event of a collision of the vehicle, the rotation of the motor MG 2  is generally stopped, accompanied with stop of the vehicle (i.e., stop of the rotation of the drive wheels  39   a  and  39   b ). The effect of the collision is, however, likely to uncouple the driveshaft  36  (i.e., the rotating shaft of the motor MG 2 ) from the axle  39   s  or to change gear of the transmission  60  to the neutral position. This may result in continuing the rotation of the motor MG 2 , in spite of the stop of the vehicle. In the event of a collision of the vehicle, the motor MG 1  is rotated in many cases. Accordingly the control procedure of this embodiment turns off the system main relay  56  in response to detection of the collision of the vehicle and subsequently performs the three-phase ON control of the inverters  41  and  42 , such as not to supply an electric power caused by generation of a back electromotive force accompanied with the rotation of the motors MG 1  and MG 2 , to the capacitor  57 . The procedure of this embodiment performs the converter discharge control, in addition to the three-phase ON control of the inverters  41  and  42 . This enables the capacitor  57  and the capacitor  58  to be discharged even during the rotation of the motors MG 1  and MG 2 , such as to decrease the voltage VH of the capacitor  57  and the voltage VL of the capacitor  58 . This configuration accordingly suppresses the time period from detection of a collision of the vehicle to the time when the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref (i.e., when discharge of the capacitor  57  (and the capacitor  58 ) is terminated) from being extended to a relatively long time. 
     The control procedure of the embodiment continues the three-phase ON control of the inverters  41  and  42  and the converter discharge control until both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  become equal to the value 0 and the voltage VH of the capacitor  57  becomes equal to or lower than the reference value Vhref. The three-phase ON control and the converter discharge control are performed until both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  become equal to the value 0, i.e., until generation of a back electromotive force is stopped accompanied with the rotation of the motors MG 1  and MG 2 . This configuration accordingly suppresses the electric power caused by generation of the back electromotive force accompanied with the rotation of the motors MG 1  and MG 2  from being supplied to the capacitor  57  and thereby suppresses the voltage VH of the capacitor  57  from becoming higher than the reference value VHref, after termination of the three-phase ON control and the converter discharge control. 
       FIG. 4  is a diagram illustrating one example of the operations in response to detection of a collision of the vehicle. In the diagram, solid lines indicate the operations of the embodiment and broken lines indicate the operations of a comparative example, with regard to the control of the inverters  41  and  42 , the control of the step-up/down converter  55  and a change in the voltage VH of the capacitor  57 . The comparative example controls the step-up/down converter  55  and the inverters  41  and  42  as described below. The comparative example stops the operation of the step-up/down converter  55 , whether both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0 or not. When at least one of the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  is not equal to the value 0, the comparative example performs the three-phase ON control of the inverters  41  and  42 . When both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0, on the other hand, the comparative example performs inverter discharge control that controls the inverters  41  and  42  such as to output no torques from the motors MG 1  and MG 2  and such as to cause the electric charges of the capacitor  57  and the capacitor  58  to be consumed by the motors MG 1  and MG 2 . The discharge control of the inverters  41  and  42  is generally performed by controlling the inverters  41  and  42  such as to cause d-axis current to flow in the motors MG 1  and MG 2 . In this state, when the voltage VH of the capacitor  57  becomes lower relative to the voltage VL of the capacitor  58 , the electric charges of the capacitor  58  are supplied from the capacitor  58  to the motors MG 1  and MG 2  via the low voltage-side power lines  54   b , the diode D 31  of the step-up/down converter  55 , the high voltage-side power lines  54   a  and the inverters  41  and  42  and are consumed by the motors MG 1  and MG 2 . 
     Both the embodiment and the comparative example turn off the system main relay  56 , in response to detection of a collision of the vehicle at a time t 11 . The comparative example starts the three-phase ON control of the inverters  41  and  42  at a time t 12  and changes over the control of the inverters  41  and  42  from the three-phase ON control to the inverter discharge control when the rotation speed Nm 2  of the motor MG 2  (and the rotation speed Nm 1  of the motor MG 1 ) become equal to the value 0 at a time t 13 . When the voltage VH of the capacitor  57  subsequently becomes equal to or lower than the reference value VHref at a time t 14 , the comparative example terminates the inverter discharge control. As described above, when the rotation speed Nm 2  of the motor MG 2  is not equal to the value 0, the comparative example fails to discharge the capacitor  57  and thereby fails to decrease the voltage VH of the capacitor  57 . This may extend the time period from detection of a collision of the vehicle to the time when the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref to a relatively long time. The embodiment, on the other hand, starts the three-phase ON control of the inverters  41  and  42  and the converter discharge control at the time t 12  and terminates the three-phase ON control of the inverters  41  and  42  and the converter discharge control when the rotation speed Nm 2  of the motor MG 2  (and the rotation speed Nm 1  of the motor MG 1 ) become equal to the value 0 and the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref at the time t 13  that is prior to the time t 14 . As described above, when the rotation speed Nm 2  of the motor MG 2  is not equal to the value 0, the embodiment enables the capacitor  57  to be discharged such as to decrease the voltage VH of the capacitor  57 . Compared with the comparative example, this configuration of the embodiment accordingly shortens the time period from detection of a collision of the vehicle to the time when the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref (i.e., when discharge of the capacitor  57  (and the capacitor  58 ) is terminated). 
     The hybrid vehicle  20  of the embodiment described above turns off the system main relay  56  and performs the three-phase ON control of the inverters  41  and  42  and the converter discharge control, in response to detection of a collision of the vehicle. This configuration enables the capacitor  57  to be discharged even during rotation of the motors MG 1  an MG 2  after the system main relay  56  is turned off in response to detection of a collision of the vehicle. This configuration accordingly suppresses the time period from detection of a collision of the vehicle to the time when the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref (i.e., when discharge of the capacitor  57  (and the capacitor  58 ) is terminated) from being extended to a relatively long time. 
     The hybrid vehicle  20  of the embodiment performs the collision detection control routine of  FIG. 3 , in response to detection of a collision of the vehicle. According to a modification, in response to detection of a collision of the vehicle, a collision detection control routine of  FIG. 5  may be performed, in place of the collision detection control routine of  FIG. 3 . The collision detection control routine of  FIG. 5  is similar to the collision detection control routine of  FIG. 3 , except addition of steps S 200  to S 250  to the collision detection control routine of  FIG. 3 . The like steps are expressed by the like step numbers, and their detailed description is omitted. 
     In the collision detection control routine of  FIG. 5 , after turning off the system main relay  56  and stopping the operation of the step-up/down converter  55  at step S 100 , the HVECU  70  receives the inputs of the rotation speed Nm 1  and Nm 2  of the motors MG 1  and MG 2  (step S 200 ) and determines whether both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to value 0 (step S 210 ). When it is determined that at least one of the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  is not equal to the value 0, the HVECU  70  performs the processing of steps S 110  to S 150  described above and terminates this routine. 
     When it is determined at step S 210  that both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0, on the other hand, the HVECU  70  starts the inverter discharge control and sends a control start command for the converter discharge control to the motor ECU  40  (step S 220 ). When receiving this control start command, the motor ECU  40  starts the converter discharge control. 
     The HVECU  70  subsequently receives the input of the voltage VH of the capacitor  57  (step S 230 ) and compares the input voltage VH of the capacitor  57  with the reference value VHref (step S 240 ). When the voltage VH of the capacitor  57  is higher than the reference value VHref, the HVECU  70  returns to step S 230 . When the voltage VH of the capacitor  57  is equal to or lower than the reference value VHref, on the other hand, the HVECU  70  terminates the inverter discharge control and sends a control stop command for the converter discharge control to the motor ECU  40  (step S 250 ) and terminates this routine. When receiving the control stop command, the motor ECU  40  terminates the converter discharge control. 
     As described above, this modification performs both the inverter discharge control and the converter discharge control when both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0 immediately after the system main relay  56  is turned off in response to detection of a collision of the vehicle. The configuration of this modification accordingly shortens the time period elapsed until the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref, compared with the configuration that performs only one of the inverter discharge control and the converter discharge control. 
     The hybrid vehicle  20  performs the collision detection control routine of  FIG. 3  according to the embodiment and performs the collision detection control routine of  FIG. 5  according to the above modification. According to another modification, in response to detection of a collision of the vehicle, a collision detection control routine of  FIG. 6  may be performed, in place of the collision detection control routine of  FIG. 3  or  FIG. 5 . The collision detection control routine of  FIG. 6  is similar to the collision detection control routine of  FIG. 5 , except addition of step S 300  to the collision detection control routine of  FIG. 5 . The like steps are expressed by the like step numbers, and their detailed description is omitted. 
     In the collision detection control routine of  FIG. 6 , after starting the three-phase ON control of the inverters  41  and  42  and the converter discharge control (step S 110 ), when it is determined that both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are equal to the value 0 (step S 130 ), the HVECU  70  subsequently compares the voltage VH of the capacitor  57  with the reference value VHref (step S 140 ). When the voltage VH of the capacitor  57  is equal to or lower than the reference value VHref, the HVECU  70  performs the processing of step S 150  and terminates this routine. 
     When the voltage VH of the capacitor  57  is higher than the reference value VHref at step S 140 , on the other hand, the HVECU  70  terminates the three-phase ON control of the inverters  41  and  42  and starts the inverter discharge control (step S 300 ). This configuration accordingly performs both the inverter discharge control and the converter discharge control. The HVECU  70  subsequently performs the processing of steps S 230  to S 250  and terminates this routine. 
     As described above, this modification performs both the inverter discharge control and the converter discharge control when both the rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  become equal to the value 0 but the voltage VH of the capacitor  57  is higher than the reference value VHref during the three-phase ON control of the inverters  41  and  42  and the converter discharge control performed after the system main relay  56  is turned off in response to detection of a collision of the vehicle. The configuration of this modification accordingly shortens the time period elapsed until the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref, compared with the configuration that performs the three-phase ON control of the inverters  41  and  42  and the converter discharge control like the embodiment and the configuration that performs the inverter discharge control and stops the operation of the step-up/down converter  55  when both the rotation speeds Nm 1  and M 2  of the motors MG 1  and MG 2  are equal to the value 0 and the voltage VH of the capacitor  57  is higher than the reference value VHref. 
       FIG. 7  is a diagram illustrating one example of the operations in response to detection of a collision of the vehicle. In the diagram, solid lines indicate the operations of this modification (in which the collision detection control routine of  FIG. 6  is performed) and one-dot chain lines indicates the operations of the embodiment described above (in which the collision detection control routine of  FIG. 3  is performed), with regard to the control of the inverters  41  and  42 , the control of the step-up/down converter  55  and a change in the voltage VH of the capacitor  57 . Both the embodiment and the modification turn off the system main relay  56  in response to detection of a collision of the vehicle at a time t 21  and start the three-phase ON control of the inverters  41  and  42  and the converter discharge control at a time t 22 . When the rotation speed Nm 2  of the motor MG 2  (and the rotation speed Nm 1  of the motor MG 1 ) are equal to the value 0 and the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref at a time t 25 , the embodiment terminates the three-phase ON control of the inverters  41  and  42  and the converter discharge control. The modification, on the other hand, changes over the control of the inverters  41  and  42  from the three-phase ON control to the converter discharge control when the rotation speed Nm 2  of the motor MG 2  becomes equal to the value 0 at a time t 23  before the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref. This configuration enables the electric charges of the capacitor  57  and the capacitor  58  to be consumed by the motors MG 1  and MG 2  and the step-up/down converter  55  and thereby further accelerates discharging the capacitor  57  and the capacitor  58 . When the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref at a time t 24  prior to the time t 25 , the modification terminates the inverter discharge control and the converter discharge control. The configuration of this modification further shortens the time period from detection of a collision of the vehicle to the time when the voltage VH of the capacitor  57  becomes equal to or lower than the reference value VHref, compared with the configuration of the embodiment. 
     The hybrid vehicle  20  of the embodiment employs the four-speed transmission for the transmission  60 . Another type of transmission, for example, a three-speed transmission, a five-speed transmission, a six-speed transmission, an eight-speed transmission or a ten-speed transmission may also be employed for the transmission  60 . 
     The hybrid vehicle  20  of the embodiment is configured to include the engine ECU  24 , the motor ECU  40  and the HVECU  70 . According to a modification, the engine ECU  24 , the motor ECU  40  and the HVECU  70  may be configured by a single electronic control unit. 
     The hybrid vehicle  20  of the embodiment is configured such that the ring gear of the planetary gear  30  and the motor MG 2  are connected via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b  and that the sun gear and the carrier of the planetary gear  30  are respectively connected with the motor MG 1  and the engine  22 . As shown in  FIG. 8 , however, a hybrid vehicle  120  of a modification may be configured to further include a motor MG 3  that is coupled with wheels  39   c  and  39   d  different from the drive wheels  39   a  and  39   b , in addition to the configuration of the hybrid vehicle  20 . 
     The hybrid vehicle  20  of the embodiment is configured such that the transmission  60  is placed between the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b , and the ring gear of the planetary gear  30  and the motor MG 2 . As shown in  FIG. 9 , however, a hybrid vehicle  220  of a modification may be configured to exclude a transmission and directly connect the drive shaft  36  with the ring gear of the planetary gear  30  and with the motor MG 2 . Another modification may be configured to include a motor that is coupled with wheels  39   c  and  39   d  different from the drive wheels  39   a  and  39   b , in addition to the configuration of the hybrid vehicle  220 . 
     The hybrid vehicle  20  of the embodiment is configured such that the ring gear of the planetary gear  30  and the motor MG 2  are connected via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b  and that the sun gear and the carrier of the planetary gear  30  are respectively connected with the motor MG 1  and the engine  22 . As shown in  FIG. 10 , however, a hybrid vehicle  320  of a modification may be configured to connect a motor MG via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b  and to connect the engine  22  with a rotating shaft of the motor MG via a clutch  329 . Another modification may be configured to include a motor that is coupled with wheels  39   c  and  39   d  different from the drive wheels  39   a  and  39   b , in addition to the configuration of the hybrid vehicle  320 . 
     The hybrid vehicle  20  of the embodiment is configured such that the ring gear of the planetary gear  30  and the motor MG 2  are connected via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b  and that the sun gear and the carrier of the planetary gear  30  are respectively connected with the motor MG 1  and the engine  22 . As shown in  FIG. 11 , however, the present disclosure may also be implemented by a hybrid vehicle  420  of a modification that is configured as a series hybrid vehicle to connect a motor MG 2  for driving via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b  and to connect a motor MG 1  for power generation with an output shaft of the engine  22 . Another modification may be configured to exclude a transmission from the configuration of the hybrid vehicle  420  and to directly connect the driveshaft  36  with the motor MG 2 . Another modification may be configured to include a motor that is coupled with wheels  39   c  and  39   d  different from the drive wheels  39   a  and  39   b , in addition to the configuration of the hybrid vehicle  420  or in addition to the configuration of excluding the transmission from the configuration of the hybrid vehicle  420 . 
     The embodiment describes the hybrid vehicle  20  configured to include the engine  22  and the motors MG 1  and MG 2 . As shown in  FIG. 12 , however, the present disclosure may also be implemented by an electric vehicle  520  of a modification that is configured to connect a motor MG for driving via the transmission  60  with the driveshaft  36  that is coupled with the drive wheels  39   a  and  39   b . Another modification may be configured to exclude a transmission from the configuration of the electric vehicle  520  and to directly connect the driveshaft  36  with the motor MG. Another modification may be configured to include a motor that is coupled with wheels  39   c  and  39   d  different from the drive wheels  39   a  and  39   b , in addition to the configuration of the electric vehicle  520  or in addition to the configuration of excluding the transmission from the configuration of the electric vehicle  520 . 
     In the motor vehicle of the disclosure described above, when a rotation speed of the three-phase motor is equal to value 0 and a voltage of the capacitor becomes equal to or lower than a predetermined voltage after start of the three-phase ON control and the converter discharge control, the control device may be configured to terminate the three-phase ON control and the converter discharge control. The motor vehicle of this aspect suppresses an electric power caused by generation of a back electromotive force accompanied with the rotation of the three-phase motor from being supplied to the capacitor after termination of the three-phase ON control and the converter discharge control. This configuration accordingly suppresses the voltage of the capacitor from becoming higher than the predetermined voltage. 
     In the motor vehicle of the disclosure described above, when a rotation speed of the three-phase motor becomes equal to value 0 and a voltage of the capacitor is higher than a predetermined voltage after start of the three-phase ON control and the converter discharge control, the control device may be configured to terminate the three-phase ON control and to perform the converter discharge control and inverter discharge control that controls the inverter such as not to output a torque from the three-phase motor and such as to cause an electric charge of the capacitor to be consumed by the three-phase motor, and when the voltage of the capacitor becomes equal to or lower than the predetermined voltage, the control device may be configured to terminate the converter discharge control and the inverter discharge control. The motor vehicle of this aspect performs the converter discharge control and the inverter discharge control when the rotation speed of the three-phase motor becomes equal to the value 0 and the voltage of the capacitor is higher than the predetermined voltage after the relay is turned off in response to detection of a collision of the vehicle. This configuration accordingly further suppresses the time period from detection of a collision of the vehicle to the time when the voltage of the capacitor becomes equal to or lower than the predetermined voltage from being extended to a relatively long time. 
     The following describes the correspondence relationship between the primary elements of the above embodiment and the primary elements of the disclosure described in Summary. The motors MG 1  and MG 2  of the embodiment correspond to the “three-phase motor” of the disclosure. The inverters  41  and  42  correspond to the “inverter”. The battery  50  corresponds to the “battery”. The step-up/down converter  55  corresponds to the “step-up/down converter”. The capacitor  57  corresponds to the “capacitor”. The system main relay  56  corresponds to the “relay”. The HVECU  70  and the motor ECU  40  correspond to the “control device”. 
     The correspondence relationship between the primary components of the embodiment and the primary components of the present disclosure, regarding which the problem is described in Summary, should not be considered to limit the components of the present disclosure, regarding which the problem is described in Summary, since the embodiment is only illustrative to specifically describes the aspects of the present disclosure, regarding which the problem is described in Summary. In other words, the present disclosure, regarding which the problem is described in Summary, should be interpreted on the basis of the description in the Summary, and the embodiment is only a specific example of the present disclosure, regarding which the problem is described in Summary. 
     The aspect of the present disclosure is described above with reference to the embodiment. The present disclosure is, however, not limited to the above embodiment but various modifications and variations may be made to the embodiment without departing from the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The above aspects of the present disclosure are applicable to, for example, the manufacturing industry of motor vehicles.