Patent Publication Number: US-11654792-B2

Title: Motor vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Application No. 2020-194410, filed Nov. 24, 2020. The disclosure of the above application is incorporating herein by reference. 
     FIELD 
     The present disclosure relates to a motor vehicle with a motor performing power driving and regeneration and, more particularly, to a power storage device that supplies energy to the motor in driving mode and restore energy from motor in regeneration mode. 
     BACKGROUND 
     A motor vehicle described in Japanese Unexamined Patent Application Publication No. 2018-166367 is an example of a motor vehicle with a motor configured to perform power driving and regeneration. A power storage device supplies energy to the motor. The motor vehicle can obtain a thrust by a drive force of the motor, and recover the energy into the power storage device by adjusting a braking torque of a driving wheel. According to this motor vehicle, the energy recovered during braking can be stored in the power storage device (battery) and used as drive energy during the power driving. 
     In the related art described above, a voltage of the power storage device is set to a lower limit value of a DC voltage of an inverter or a value lower than the lower limit value. Further, adjustment is made in accordance with setting of the DC voltage of the inverter by stepping up an output voltage of the power storage device. Therefore, in a case of using a power storage device whose output voltage is higher than the lower limit value of the DC voltage of the inverter, the output voltage of the power storage device cannot be stepped down. This causes a range where an actual inverter DC voltage cannot be adjusted to the set value of the DC voltage of the inverter. Thus, in a case where the lower limit value of the DC voltage of the inverter is changed to a voltage lower than the voltage of the power storage device due to a change in motor specifications or the like. Thus, a storage battery designed exclusively for voltage needs to be used. Accordingly, this causes a problem in that a standard-voltage power storage device cannot be used. 
     Adjustment may be made in accordance with the set value of the DC voltage of the inverter by stepping down the output voltage of the power storage device. In this case, however, the output voltage of the power storage device cannot be stepped up. This causes a range where the actual inverter DC voltage cannot be adjusted to the set value of the DC voltage of the inverter. Similarly to the related art described above, the storage battery designed exclusively for voltage needs to be used. Accordingly, this causes a problem in that the standard-voltage storage battery cannot be used. 
     SUMMARY 
     According to a first aspect of the disclosure, a motor vehicle includes a motor to perform power driving and regeneration. An inverter converts a direct current into an alternating current. A first power storage device has a large-capacity characteristic. A second power storage device has a high-power characteristic. A power converter has a voltage step down function during the power driving and a voltage step up function during the regeneration. The power converter, with the voltage step down function during the power driving, is in a circuit connected to the first power storage device and the second power storage device connected in series between a reactor of the power converter and the inverter. During the power driving of the motor, an output voltage of the first power storage device is stepped down to supply energy from the first power storage device and the second power storage device to the inverter. 
     According to a second aspect of the disclosure, during the regeneration in the motor, the resultant output voltage combination of the inverter and the second power storage device may be stepped up to recover the energy into the first power storage device and the second power storage device. 
     According to a third aspect of the disclosure, the motor vehicle may further include a first switch forming a circuit connecting the power converter and the inverter without intervention of the second power storage device. A second switch forms a circuit connecting the power converter and the inverter via the second power storage device. Determination may be made about a power storage status of the second power storage device based on a voltage of the second power storage device. When the power storage status of the second power storage device is equal to or lower than a predetermined lower limit value during the power driving of the motor, the first switch may be turned ON and the second switch may be turned OFF to supply the energy from the first power storage device to the inverter while stepping down the output voltage of the first power storage device. 
     According to a fourth aspect of the disclosure, the motor vehicle may further include a first switch forming a circuit connecting the power converter and the inverter without intervention of the second power storage device. A second switch forms a circuit connecting the power converter and the inverter via the second power storage device. Determination may be made about a power storage status of the second power storage device based on a voltage of the second power storage device. When the power storage status of the second power storage device is equal to or higher than a predetermined upper limit value during the regeneration in the motor, the first switch may be turned ON and the second switch may be turned OFF to store regenerated energy in the first power storage device while stepping up a DC voltage of the inverter. 
     According to a fifth aspect of the disclosure, during current control of the inverter, a DC voltage of the inverter may be controlled based on a rotation speed of the motor. When the rotation speed of the motor is equal to or lower than a predetermined rotation speed, the DC voltage of the inverter may be controlled to decrease as the rotation speed of the motor decreases. 
     According to a sixth aspect of the disclosure, when a rotation speed of the motor is equal to or lower than a predetermined rotation speed during current control of the inverter, a DC voltage of the inverter may be controlled based on a peak value of a motor line-to-line voltage. 
     According to a seventh aspect of the disclosure, the first power storage device may be a large-capacity lithium ion battery or a large-capacity nickel-metal hydride battery. The second power storage device may be a high-power lithium ion battery, a high-power nickel-metal hydride battery, a lithium ion capacitor, or an electric double layer capacitor. 
     According to the present disclosure, the motor vehicle includes the power converter with the voltage step down function during the power driving and the voltage step up function during the regeneration. The power converter, with the voltage step down function during the power driving, is in a circuit connected to the first power storage device and the second power storage device connected in series between the reactor of the power converter and the inverter. During the power driving of the motor, the output voltage of the first power storage device is stepped down to supply the energy from the first power storage device and the second power storage device to the inverter. In combination with the increase in the voltage of the second power storage device, the inverter DC voltage can be stepped up and down relative to the output voltage of the first power storage device. Therefore, adjustment can be made in accordance with a set voltage range of the inverter by stepping up and down the output voltage of the first power storage device. Thus, even if the set value of the DC voltage of the inverter is changed, a standard-voltage storage battery can be used and an increase in manufacturing costs can be prevented. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a schematic diagram of a motor vehicle. 
         FIG.  2    is a circuit diagram of a power conversion device of the motor vehicle. 
         FIG.  3    is a conceptual diagram of the power conversion device of the motor vehicle. 
         FIG.  4    is a schematic diagram of control relationships in the motor vehicle. 
         FIG.  5    is a time chart of power control in the motor vehicle. 
         FIG.  6    is a flowchart of the overall power control in the motor vehicle. 
         FIG.  7    is a graph of request characteristics of the motor vehicle (vehicle requests on a driving wheel). 
         FIG.  8    is a graph of request characteristics of the motor vehicle (motor requests on the driving wheel). 
         FIG.  9    is a graph of request characteristics of the motor vehicle (vehicle requests on a driven wheel). 
         FIG.  10    is a graph of request characteristics of the motor vehicle (brake requests on the driven wheel). 
         FIG.  11    is a flowchart of request process control in the power control in the motor vehicle. 
         FIG.  12    is a graph of a driver&#39;s request table of the motor vehicle (Table 1). 
         FIG.  13    is a graph of a driver&#39;s request table of the motor vehicle (Table 2). 
         FIG.  14    is a graph of a driver&#39;s request table of the motor vehicle (Table 3). 
         FIG.  15    is a graph of a driver&#39;s request table of the motor vehicle (Table 4). 
         FIG.  16    is a graph of a driver&#39;s request table of the motor vehicle (Table 5). 
         FIG.  17    is a graph of a driver&#39;s request table of the motor vehicle (Table 6). 
         FIG.  18    is a flowchart of motor control in the power control in the motor vehicle. 
         FIG.  19    is a table of power conversion circuit control in the motor vehicle. 
         FIG.  20    is a graph of a voltage request table of the motor vehicle (Table A in a case of PWM). 
         FIG.  21    is a graph of a voltage request table of the motor vehicle (Table B in the case of PWM). 
         FIG.  22    is a graph of a voltage request table of the motor vehicle (Table C in the case of PWM). 
         FIG.  23    is a graph of a voltage request table of the motor vehicle (Table A in a case depending on a peak value of a motor line-to-line voltage). 
         FIG.  24    is a graph of a voltage request table of the motor vehicle (Table B in the case depending on the peak value of the motor line-to-line voltage). 
         FIG.  25    is a graph of a voltage request table of the motor vehicle (Table C in the case depending on the peak value of the motor line-to-line voltage). 
         FIG.  26    is a time chart of an example of an operation depending on a peak value of a motor line-to-line voltage in a motor vehicle according to another embodiment. 
         FIG.  27    is a graph of a power storage status of a first power storage device of the motor vehicle. 
         FIG.  28    is a graph of a power storage status of a second power storage device of the motor vehicle. 
         FIG.  29    is a table of combinations of power storage devices of the motor vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described below in detail with reference to the drawings. 
     A motor vehicle according to each of the embodiments is a saddled vehicle, such as a motorcycle, traveling by using a drive force of a motor. As illustrated in  FIGS.  1  to  4   , the motor vehicle mainly includes a motor  1 , an inverter  2 , mechanical brakes ( 3   a ,  3   b ), a first power storage device  4 , a second power storage device  5 , an accelerator operator  6 , a mechanical brake operator  7 , a regenerative brake operator  8 , a power converter  10 , an ECU  11 , a start switch  12 , and a monitor  13 . 
     The motor  1  is an electromagnetic motor for obtaining a drive force by energy supply. As illustrated in  FIGS.  2  and  3   , the motor  1  is electrically connectable to the second power storage device  5 , the power converter  10 , and the first power storage device  4 , via the inverter  2 . The motor performs power driving and regeneration. The inverter  2  (DC-AC inverter) converts a direct current into an alternating current. In this embodiment, the inverter  2  converts a direct current of the first power storage device  4  or the second power storage device  5  into an alternating current, and supplies the alternating current to the motor  1 . 
     The mechanical brakes perform braking by releasing energy, as typified by a disc brake or a drum brake. The mechanical brakes are a driving-wheel mechanical brake  3   a  that performs braking by releasing kinetic energy of a driving wheel Ta. A driven-wheel mechanical brake  3   b  performs braking by releasing kinetic energy of a driven wheel Tb. The driving-wheel mechanical brake  3   a  and the driven-wheel mechanical brake  3   b  are connected to the mechanical brake operator  7  via a brake actuator  9 . 
     The mechanical brake operator  7  controls the mechanical brake (driven-wheel mechanical brake  3   b ) to adjust a braking torque. In this embodiment, an operation lever is attached to the right end of a handle bar. Based on an operation amount of the mechanical brake operator  7 , a mechanical brake controller  18  (see  FIG.  4   ) may operate the brake actuator  9  to actuate the driven-wheel mechanical brake  3   b.    
     The accelerator operator  6  controls the motor  1  to adjust a drive torque of the driving wheel Ta. In this embodiment, an accelerator grip is attached to the right end of the handle bar. As illustrated in  FIG.  4   , based on an operation amount of the accelerator operator  6 , an inverter controller  16  may estimate a torque request and operate the motor  1  to obtain a desired drive force. The inverter controller  16  is one controller provided in the ECU  11 . 
     The power storage devices supply energy to the motor  1 . In this embodiment, the power storage devices are the first power storage device  4  and the second power storage device  5 . The first power storage device  4  is a storage battery with a large-capacity characteristic. As illustrated in  FIG.  29   , examples of the first power storage device  4  include a large-capacity lithium ion battery and a large-capacity nickel-metal hydride battery. The second power storage device  5  is a storage battery with a high-power characteristic. As illustrated in  FIG.  29   , examples of the second power storage device  5  include a high-power lithium ion battery, a high-power nickel-metal hydride battery, a lithium ion capacitor, and an electric double layer capacitor. 
     The regenerative brake operator  8  controls the motor  1  to adjust a braking torque of the driving wheel Ta and recover the energy into the power storage devices, first power storage device  4  and second power storage device  5 . In this embodiment, an operation lever is attached to the left end of the handle bar. Based on an operation amount of the regenerative brake operator  8 , the motor  1  performs regeneration to obtain a desired braking force. Through the regeneration in the motor  1 , the energy can be recovered into the first power storage device  4  and the second power storage device  5 . 
     The power converter  10  has a voltage step down function during the power driving of the motor  1  (during energy supply to the motor  1 ) and a voltage step up function during the regeneration in the motor  1  (during energy recovery from the motor  1 ). As illustrated in  FIGS.  2  and  3   , the power converter  10  is connected between the first power storage device  4  and the second power storage device  5  in an electric circuit. More specifically, as illustrated in  FIG.  2   , the power converter  10  includes two semiconductor switching elements (MOSFETs)  10   a  and  10   b  and a reactor  10   c  (coil). The semiconductor switching elements  10   a  and  10   b  include switches S 1  and S 2  and their body diodes, respectively. 
     In the power converter  10 , according to this embodiment, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to high-speed switching (duty control) to step down the voltage during the power driving of the motor  1 , when a current flows rightward in  FIG.  3   , because the reactor  10   c  is located on a downstream side of the semiconductor switching elements  10   a  and  10   b . The power converter steps up the voltage during the regeneration in the motor  1  (when the current flows leftward in  FIG.  3   ) because the reactor  10   c  is located on an upstream side of the semiconductor switching elements  10   a  and  10   b.    
     More specifically, this embodiment provides, as illustrated in  FIGS.  2  and  3   , a circuit where the power converter  10 , with the voltage step down function during the power driving, is connected to the first power storage device  4 . The second power storage device  5  is connected in series between the reactor  10   c  of the power converter  10  and the inverter  2 . During the power driving of the motor  1 , the power converter  10  steps down an output voltage (Vdc) of the first power storage device  4  to supply energy from the first power storage device  4  and the second power storage device  5  to the inverter  2 . During the regeneration in the motor  1 , the power converter  10  steps up the resultant output voltage (Vinv-Vc) of the combination between the inverter  2  and second power storage device  5  to recover the energy into the first power storage device  4  and the second power storage device  5 . 
     As illustrated in  FIG.  2   , this embodiment provides a first switch S 3  forming a circuit connecting the power converter  10  and the inverter  2  without intervention of the second power storage device  5 . A second switch S 4  forms a circuit connecting the power converter  10  and the inverter  2  via the second power storage device  5 . The circuit of this embodiment includes a switch Sa to be turned ON when the power converter  10  is OFF, and stabilization capacitors Ca and Cb are connected to the circuit. The first switch S 3  and the second switch S 4 , according to this embodiment, are formed in semiconductor switching elements (MOSFETs)  14  and  15  (including their body diodes similarly to the semiconductor switching elements  10   a  and  10   b ), respectively. 
     The ECU  11  controls the motor  1  in response to input driver requests. As illustrated in  FIG.  4   , the ECU  11  includes the inverter controller  16 , a circuit controller  17 , and the mechanical brake controller  18 , and is connected to the inverter  2 , the power converter  10 , the first power storage device  4 , the second power storage device  5 , and the brake actuator  9 . The ECU  11  detects voltages of the first power storage device  4  and the second power storage device  5 . It makes determination on power storage statuses of the first power storage device  4  and the second power storage device  5  based on the voltages.  FIG.  27    illustrates the power storage status of the first power storage device  4 .  FIG.  28    illustrates the power storage status of the second power storage device  5 . 
     When the power storage status of the second power storage device  5  is equal to or lower than a predetermined lower limit value (see  FIG.  28   ), during the power driving of the motor  1 , the first switch S 3  is turned ON and the second switch S 4  is turned OFF to supply energy from the first power storage device  4  to the inverter  2  while stepping down the output voltage (Vdc) of the first power storage device  4 . When the power storage status of the second power storage device  5  is equal to or higher than a predetermined upper limit value (see  FIG.  28   ), during the regeneration in the motor  1 , the first switch S 3  is turned ON and the second switch S 4  is turned OFF to store regenerated energy in the first power storage device  4  while stepping up a DC voltage (Vine) of the inverter  2 . 
     The start switch  12  is an operation switch that enables the vehicle to travel. By operating the accelerator operator  6  after the start switch  12  is operated, the motor  1  may be actuated for traveling. The monitor  13  is an auxiliary device such as a liquid crystal monitor attached to the vehicle. For example, the monitor  13  may display conditions of the vehicle (speed, power storage status, or whether malfunction has occurred) or a map of a navigation system. 
     As illustrated in  FIG.  4   , this embodiment provides a detector  19 , a sensor, detecting a rotation speed of the motor  1 . When the rotation speed of the motor  1 , detected by the detector  19 , is equal to or higher than a predetermined value, a predetermined braking torque, based on an operation amount of the regenerative brake operator  8 , is generated by regenerative braking (particularly in this embodiment, generated only by the regenerative braking). The maximum value of the predetermined braking torque during the regeneration in the motor  1  is a rated torque of the motor  1 . 
     When the rotation speed of the motor  1 , detected by the detector  19 , is lower than the predetermined value, a braking torque is generated by the mechanical brake (driving-wheel mechanical brake  3   a ) based on the operation amount of the regenerative brake operator  8 . When the charge level of the first power storage device  4  is equal to or higher than a predetermined value, a braking torque is generated by the mechanical brake (driving-wheel mechanical brake  3   a ) based on the operation amount of the regenerative brake operator  8 . 
     According to the embodiment,  FIG.  5    illustrates changes in parameters in a case where the accelerator operator  6  and the regenerative brake operator  8  are operated after the start switch  12  is turned ON in the motor vehicle. In particular, a capacitor current (Ic) and a capacitor charge level (SOC 2 ) are a current and a charge level of the second power storage device  5  of this embodiment. A battery current (Idc) and a battery charge level (SOC 1 ) are a current and a charge level of the first power storage device  4  of this embodiment. In a table in  FIG.  5   , “function circuit control number” (FCCNO) corresponds to “FCCNO” in  FIGS.  4 ,  18 , and  19   . 
     Next, control on the motor vehicle (main control), according to this embodiment, is described with reference to a flowchart of  FIG.  6   . 
     In S 1 , determination is first made as to whether the start switch  12  is ON. When determination is made that the start switch  12  is ON, determination is made in S 2  as to whether a charge status (Soc 1 ) of the first power storage device  4  is higher than a predetermined lower limit value (see  FIG.  27   ). When determination is made that the charge status (Soc 1 ) is higher than the predetermined lower limit value, a request process (S 3 ), motor control (S 4 ), and mechanical brake control (S 5 ) are performed sequentially. 
     Next, according to this embodiment, request characteristics of the motor vehicle are described with reference to  FIGS.  7  to  10   . 
     The characteristics illustrated in  FIG.  7    show the relationship between a vehicle speed and both of the drive torque and the braking torque of the driving wheel Ta. The characteristics illustrated in  FIG.  8    show the relationship between a motor torque of the driving wheel Ta and a rotation speed (ω) of the motor  1 . Particularly in a case of high-speed traveling,  FIG.  7    illustrates relationships where the drive torque gradually decreases and the braking torque is constant relative to the vehicle speed. In  FIG.  8   , a positive side, (upper half) from the vertical axis, shows a drive torque based on an operation amount of the accelerator operator  6 . A negative side, (lower half) from the vertical axis, shows a braking torque based on an operation amount of the regenerative brake operator  8 . In  FIG.  8   , reference symbol Tm 1  represents the rated torque of the motor  1 . 
     The characteristics illustrated in  FIG.  9    show the relationship between the vehicle speed and a braking torque of the driven wheel Tb. The characteristics illustrated in  FIG.  10    show the relationship between a braking torque of the driven wheel Tb (mechanical braking torque (Tbmf)) and the rotation speed (ω) of the motor  1 . Since  FIGS.  9  and  10    illustrate the characteristics of the driven wheel Tb, only a negative side, (lower half) from the vertical axis, shows the characteristics (braking torques). 
     Next, according to this embodiment, control on the motor vehicle (request process control) is described with reference to a flowchart of  FIG.  11   . 
     In S 1 , determination is first made as to whether the regenerative system is normal based on whether a malfunction signal is generated. When determination is made that the malfunction signal is not generated, determination is made in S 2  as to whether the accelerator operator  6  is operated (whether an accelerator operation amount Ap is larger than 0). When determination is made that the accelerator operator  6  is operated larger than 0, the process proceeds to S 5  for motor driving mode. A motor torque (Tm), based on the operation amount of the accelerator operator  6 , is calculated with reference to Table 1 illustrated in  FIG.  12   . 
     After the calculation in S 5 , the process proceeds to S 9  (driving wheel mechanical break). A mechanical braking torque (Tbmr), based on an operation amount of the regenerative brake operator  8 , is calculated with reference to Table 5 illustrated in  FIG.  16   . Then, the process proceeds to S 13  (driven wheel mechanical break). A mechanical braking torque (Tbmf), based on an operation amount of the mechanical brake operator  7 , is calculated with reference to Table 6 illustrated in  FIG.  17   . The mechanical braking torque (Tbmr) calculated in S 9  is the braking torque of the driving wheel Ta. The mechanical braking torque (Tbmf) calculated in S 13  is the braking torque of the driven wheel Tb. 
     When determination is made in S 2  that the accelerator operator is not operated, determination is made in S 3  as to whether the regeneration in the motor  1  is possible. In S 3 , determination is made that the regeneration in the motor  1  is possible when the power storage status (Soc 1 ) of the first power storage device  4  is equal to or lower than a predetermined upper limit value (see  FIG.  27   ) and the rotation speed of the motor is equal to or higher than ω1 (see  FIG.  8   ). When determination is made that the regeneration in the motor  1  is possible, determination is made in S 4  as to whether the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined upper limit value (see  FIG.  28   ). 
     When determination is made in S 4  that the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined upper limit value (see  FIG.  28   ), the process proceeds to S 6  (power regeneration to only first storage device. A motor torque (Tm), based on the operation amount of the regenerative brake operator  8 , is calculated with reference to Table 2 illustrated in  FIG.  13   . In the calculation of the motor torque (Tm), with reference to Table 2, when the rotation speed of the motor  1  is equal to or lower than a predetermined rotation speed (ω2) illustrated in  FIG.  8   , a correction is made such that Tm=Tm(ω−ω1)/(ω2−ω1). After the calculation in S 6 , the process proceeds to S 10 . A mechanical braking torque of driving wheel (Tbmr), based on the operation amount of the regenerative brake operator  8 , is calculated with reference to Table 4 illustrated in  FIG.  15   . Then, S 13  is sequentially performed as described above. 
     When determination is made in S 4  that the power storage status (Soc 2 ) of the second power storage device  5  is not higher than the predetermined upper limit value (see  FIG.  28   ), the process proceeds to S 7 . A motor torque (Tm), based on the operation amount of the regenerative brake operator  8 , is calculated with reference to Table 3 illustrated in  FIG.  14   . In the calculation of the motor, torque (Tm) with reference to Table 3, when the rotation speed of the motor  1  is equal to or lower than the predetermined rotation speed (ω2) illustrated in  FIG.  8   , a correction is made such that Tm=Tm(ω−ω1)/(ω2−ω1) similarly to Table 2. After the calculation in S 7 , the mechanical braking torque (Tbmr) is set to 0 in S 11 , and then S 13  is performed as described above. 
     When determination is made in S 1  that the malfunction signal is generated or when determination is made in S 3  that the regeneration is not possible, the process proceeds to S 8 , and the motor torque (Tm) is set to 0. Then, the process proceeds to S 12 , and a mechanical braking torque (Tbmr), based on the operation amount of the regenerative brake operator  8 , is calculated with reference to Table 5 illustrated in  FIG.  16   . Thus, when determination is made that the regenerative system has malfunction or the regeneration is not possible, the braking torque can be generated by the mechanical brake (driving-wheel mechanical brake  3   a ) based on the operation amount of the regenerative brake operator  8 . This occurs after the calculation in S 12 , S 13  is performed as described above. 
     Next, according to this embodiment, control on the motor vehicle (motor control) is described with reference to a flowchart of  FIG.  18   . 
     In S 1 , determination is first made as to whether the regenerative system is normal based on whether the malfunction signal is generated. When determination is made that the malfunction signal is not generated, determination is made in S 2  as to whether the accelerator operator  6  is operated (whether the accelerator operation amount Ap is larger than 0). When determination is made that the accelerator operator  6  is operated, determination is made in S 3  as to whether the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined lower limit value (see  FIG.  28   ). 
     When determination is made in S 3  that the power storage status (Soc 2 ) of the second power storage device  5  is not higher than the predetermined lower limit value (see  FIG.  28   ), determination is made in S 6  as to whether the rotation speed (ω) of the motor  1  is lower than ω3 (see  FIGS.  20  and  23   ). When determination is made that the rotation speed (ω)) of the motor  1  is not lower than ω3 (high-speed rotation), the process proceeds to S 7 , and function circuit control (FCC) is set to 1. When determination is made in S 6  that the rotation speed (ω) of the motor  1  is lower than ω3 (low-speed rotation), the process proceeds to S 8 , and FCC is set to 2. 
     When determination is made in S 3  that the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined lower limit value (see  FIG.  28   ), the process proceeds to S 9 , and FCC is set to 3. When determination is made in S 2  that the accelerator operator  6  is not operated, determination is made in S 4  as to whether the regeneration in the motor  1  is possible. In S 4 , determination is made that the regeneration in the motor  1  is possible when the power storage status (Soc 1 ) of the first power storage device  4  is equal to or lower than the predetermined upper limit value (see  FIG.  27   ) and the rotation speed of the motor is equal to or higher than ω1 (see  FIG.  8   ). 
     When determination is made in S 4  that the regeneration in the motor  1  is possible, determination is made in S 5  as to whether the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined upper limit value (see  FIG.  28   ). When determination is made that the power storage status (Soc 2 ) of the second power storage device  5  is higher than the predetermined upper limit value, the process proceeds to S 10 , and FCC is set to 4. When determination is made that the power storage status (Soc 2 ) of the second power storage device  5  is not higher than the predetermined upper limit value, the process proceeds to S 11 , and FCC is set to 5. When determination is made in S 1  that the malfunction signal is generated or when determination is made in S 4  that the regeneration in the motor  1  is not possible, the process proceeds to S 12 , and FCC is set to 6. 
     After any one of the modes (FCC) from 1 to 6 is determined as described above, determination is made in S 13  as to whether a mode determined in a previous process (FCCO) is changed to the mode determined in the current process (FCC). When determination is made that the mode is not changed, the process proceeds to S 14 , and the FCCNO determined in any one of S 7  to S 12  is maintained. When determination is made that the mode is changed, the process proceeds to S 15 , and (FCCNO) is set to 7. Then, control associated with the FCCNO is performed in S 16 . In S 17 , the mode determined in the current process (FCC) is stored as FCCO. In S 18 , inverter control is performed. 
     The control in S 16  is performed with reference to a control table of  FIG.  19   . The following are details of the control in the control table. 
     When FCCNO=1, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are turned OFF (the power converter  10  is turned OFF), the first switch S 3  and the second switch S 4  are turned OFF, and the switch Sa is turned ON. In the control table, “capacitor series connection” means a state where “the second power storage device  5  is connected in series between the reactor  10   c  of the power converter  10  and the inverter  2 ”. 
     When FCCNO=2, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to duty control during the power driving. Thus, the power converter  10  steps down the output voltage of the first power storage device  4 . Further, the first switch S 3  is turned ON, the second switch S 4  is turned OFF, and the switch Sa is turned OFF. When FCCNO=2, current control of the inverter  2  is performed with reference to Table A illustrated in  FIG.  20   . 
     According to Table A, when the current control of the inverter  2  is performed under PWM control, the DC voltage of the inverter  2  is controllable based on the rotation speed (ω) of the motor  1 , as illustrated in  FIG.  20   . When the rotation speed of the motor  1  is equal to or lower than the predetermined rotation speed (ω3), the DC voltage of the inverter  2  is controlled to decrease as the rotation speed of the motor  1  decreases. Also in Tables B and C described later, it is assumed that the current control of the inverter  2  is performed under the PWM control. 
     When FCCNO=3, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to duty control during the power driving. Thus, the power converter  10  steps down the output voltage of the first power storage device  4 . Further, the first switch S 3  is turned OFF, the second switch S 4  is turned ON, and the switch Sa is turned OFF. When FCCNO=3, the current control of the inverter  2  is performed with reference to Table A illustrated in  FIG.  20    similarly to the case where FCCNO=2. 
     When FCCNO=4, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to duty control during the regeneration. Thus, the power converter  10  steps up the inverter DC voltage. Further, the first switch S 3  is turned ON, the second switch S 4  is turned OFF, and the switch Sa is turned OFF. When FCCNO=4, the current control of the inverter  2  is performed with reference to Table B illustrated in  FIG.  21   . 
     When FCCNO=5, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to duty control during the regeneration. Thus, the power converter  10  steps up the resultant output voltage of the inverter  2  and the second power storage device  5 . Further, the first switch S 3  is turned OFF, the second switch S 4  is turned ON, and the switch Sa is turned OFF. When FCCNO=5, the current control of the inverter  2  is performed with reference to Table C illustrated in  FIG.  22   . 
     When FCCNO=6, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are turned OFF (the power converter  10  is turned OFF), and the first switch S 3 , the second switch S 4 , and the switch Sa are turned OFF. When FCCNO=7, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  are subjected to duty control, and the first switch S 3 , the second switch S 4 , and the switch Sa are turned OFF. 
     In the embodiment described above, Tables A to C are applied on the premise that the current control of the inverter  2  is performed under the pulse width modulation (PWM) control. Instead, the current control of the inverter  2  may depend on a peak value of a motor line-to-line voltage considering Pulse Amplitude Modulation (PAM) technique. That is, the PWM control is control for changing a width of a switching frequency (pulse width) (changing a current flow rate of the inverter) relative to the predetermined inverter DC voltage. However, the control depending on the peak value of the motor line-to-line voltage is controlled for changing the DC voltage of the inverter depending on the peak value of the motor line-to-line voltage as illustrated in  FIGS.  23  to  26   . 
     In the case where the current control of the inverter  2  is performed under the control depending on the peak value of the motor line-to-line voltage, in Table A illustrated in  FIG.  23   , the DC voltage of the inverter  2  is controlled based on the peak value of the motor line-to-line voltage when the rotation speed of the motor  1  is equal to or lower than the predetermined rotation speed (ω3). In Table B, control is performed as illustrated in  FIG.  24   . In Table C, control is performed as illustrated in  FIG.  25   .  FIG.  26    is a time chart illustrating an example of a switching operation of the inverter circuit and behavior of the motor line-to-line voltage and a fundamental wave of the motor line-to-line voltage in a case where the current is controlled with reference to any one of the tables in  FIGS.  23  to  25   . The inverter DC voltage is equal to the peak value of the motor line-to-line voltage. In this time chart, the inverter DC voltage (Vine) agrees with a peak value of the fundamental wave of the motor line-to-line voltage. 
     In the motor vehicle according to the embodiment described above, when the rotation speed of the motor  1  is equal to or higher than the predetermined value, the predetermined braking torque, based on the operation amount of the regenerative brake operator  8 , is generated by the regenerative braking. Thus, a braking torque intended by the driver can be generated by the regenerative braking over a wide rotation range of the motor  1 . 
     That is, the predetermined braking torque is generated only by the regenerative braking based on the operation amount of the regenerative brake operator  8 . Therefore, the braking force intended by the driver can stably be obtained without a sense of discomfort about brake actuation characteristics (response and brake application level) compared with a case where the predetermined braking torque is generated by combining the mechanical brake and the regenerative braking during high-speed rotation of the motor. Since the speed range for the use of the regenerative braking is wide, the energy regeneration efficiency increases and the frequency of use of the mechanical brake (driving-wheel mechanical brake  3   a ) decreases. Thus, a decrease in the durability of the mechanical brake component can be suppressed. 
     The maximum value of the predetermined braking torque during the regeneration in the motor  1  is the rated torque of the motor  1 . Therefore, a sufficient braking torque intended by the driver can be obtained. Thus, the regenerated energy can be increased at the predetermined rotation speed or higher. Further, the power converter is provided with the voltage step down function during the power driving and the voltage step up function during the regeneration. The energy is recovered via the power converter  10  during the regeneration. Therefore, the predetermined braking torque can be generated only by the regenerative braking in a range covering lower-speed rotation compared with a system where the voltage is not stepped up during the regeneration. Thus, the regenerated energy can be increased. 
     When the rotation speed of the motor  1  is lower than the predetermined value, the braking torque is generated by the mechanical brake (driving-wheel mechanical brake  3   a ) based on the operation amount of the regenerative brake operator  8 . In an extremely low-speed rotation range of the motor  1 , it is difficult to perform the regenerative braking until the vehicle is stopped even though step-up control is performed. Therefore, when the vehicle speed is lower than a predetermined value, the braking torque can securely be generated by the mechanical brake instead of the regenerative braking. 
     The power storage devices are the first power storage device  4 , with a large-capacity characteristic, and the second power storage device  5 , with a high-power characteristic. The motor vehicle includes the circuit where the power converter, with voltage step down function during the power driving, is connected to the first power storage device  4  and the second power storage device  5  is connected in series between the reactor  10   c  of the power converter  10  and the inverter  2 . During the regeneration in the motor  1 , the energy is recovered into the first power storage device  4  and the second power storage device  5  by using the circuit. Thus, the rated torque can be generated only by the regenerative braking in a range covering higher-speed rotation compared with a motor rotation speed where the rated torque can be generated only in the first power storage device  4  during the regeneration in the motor  1 . 
     When the charge level of the first power storage device  4  is equal to or higher than the predetermined value, the braking torque is generated by the mechanical brake (driving-wheel mechanical brake  3   a ) based on the operation amount of the regenerative brake operator  8 . Determination is made that no more charging can be made when the charge level of the first power storage device  4  is equal to or higher than the predetermined value. Even though the regenerative braking is difficult, the braking torque can securely be generated by the mechanical brake instead of the regenerative braking. This embodiment is applied to the saddled vehicle. Even though the two brake operators, the regenerative brake operator  8  and the mechanical brake operator  7 , are provided, an increase in costs can be avoided because there is no need to add a new operator separately. 
     During the power driving of the motor, the output voltage of the first power storage device  4  is stepped down to supply the energy from the first power storage device  4  and the second power storage device  5  to the inverter  2 . The series combination of the converter  10  output voltage and the voltage of the second storage device  5  enable step up of the voltage at the inverter  2  DC terminals. The adjustment can be made in accordance with the setting of the DC voltage of the inverter  2  by stepping up and down the resultant output voltage of the first power storage device  4  and the second power storage device  5 . Therefore, even if the set value of the DC voltage of the inverter  2  is changed, a standard-voltage storage battery can be used and an increase in manufacturing costs can be prevented. 
     Particularly in this embodiment, the switches S 1  and S 2  of the semiconductor switching elements  10   a  and  10   b  of the power converter  10  are subjected to duty control during the power driving to optimally step up and down the inverter DC voltage of the motor  1  relative to the voltage of the first power storage device  4  combined with the second power storage device  5 . Further, the supplied power driving energy is shared by the first power storage device  4  and the second power storage device  5 . Therefore, the current of the first power storage device  4  is smaller than in a case where the same amount of power driving energy is supplied only by the first power storage device  4 . Thus, even if the power driving energy is large, the current of the first power storage device  4  can be kept small and the life of the first power storage device  4  can be prolonged. 
     The first switch S 3  and the second switch S 4  are provided and determination can be made about the power storage status of the second power storage device  5  based on the voltage of the second power storage device  5 . When the power storage status of the second power storage device  5  is equal to or lower than the predetermined lower limit value during the power driving of the motor  1 , the first switch S 3  is turned ON and the second switch S 4  is turned OFF to supply energy from only the first power storage device  4  to the inverter  2  while stepping down the output voltage of the first power storage device  4 . Thus, even if the charge in the second power storage device  5  is empty, the power driving of the motor  1  can be continued by using the energy of the first power storage device  4 , thereby allowing the vehicle to travel. 
     The first switch S 3  and the second switch S 4  are provided and determination can be made about the power storage status of the second power storage device  5  based on the voltage of the second power storage device  5 . When the power storage status of the second power storage device  5  is equal to or higher than the predetermined upper limit value during the regeneration in the motor  1 , the first switch S 3  is turned ON and the second switch S 4  is turned OFF to store regenerative energy in the first power storage device  4  while stepping up the DC voltage of the inverter  2 . Thus, even if the charge in the second power storage device  5  is full, the regeneration in the motor  1  can be continued by storing the regenerative energy in the first power storage device  4 . 
     During the current control of the inverter  2 , the DC voltage of the inverter  2  is controllable based on the rotation speed of the motor  1 . When the rotation speed of the motor  1  is equal to or lower than the predetermined rotation speed, the DC voltage of the inverter  2  is controlled to decrease as the rotation speed of the motor  1  decreases. Therefore, the DC voltage of the inverter  2  can be reduced during low-speed rotation, and instantaneous power of the switches can be reduced. Thus, the switching loss can be reduced during the low-speed rotation. 
     When the rotation speed of the motor  1  is equal to or lower than the predetermined rotation speed during the current control of the inverter  2 , the DC voltage of the inverter  2  is controlled based on the peak value of the motor line-to-line voltage. Therefore, a fixed PAM switching pattern for reducing the low-order harmonic component having a switching frequency that is about three times as high as the fundamental waveform frequency can be used as the switching pattern. Thus, the switching frequency can become 1/30 or lower than switching frequency in the PWM control (duty control at a constant inverter DC voltage), and the switching loss can become 1/30 or lower than switching loss in the PWM control. 
     Although the embodiments are described above, the present disclosure is not limited to the embodiments. For example, the first power storage device  4  may be a power storage device in another form having a larger-capacity characteristic than the second power storage device  5 . The second power storage device  5  may be a power storage device in another form having a higher-power characteristic than the first power storage device  4 . The semiconductor switching element may be an IGBT in place of the MOSFET. The present disclosure may be applied to a vehicle without the monitor  13 , or to a three-wheel or four-wheel vehicle such as a buggy. 
     The present disclosure is also applicable to a motor vehicle with a different appearance or with other functions as long as the predetermined braking torque based on the operation amount of the regenerative brake operator is generated by the regenerative braking when the rotation speed of the motor is equal to or higher than the predetermined value. 
     The present disclosure has been described with reference to the preferred embodiment. Obviously, modifications and alternations will occur to those of ordinary skill in the art upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed to include all such alternations and modifications insofar as they come within the scope of the appended claims or their equivalents.