Patent ID: 12208692

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 inFIGS.1to4, the motor vehicle includes a motor1, an inverter2, mechanical brakes (3a,3b), a first power storage device4, a second power storage device5, an accelerator operator6, a mechanical brake operator7, a regenerative brake operator8, a power converter10, an ECU11, a start switch12, and a monitor13(auxiliary device).

The motor1is an electromagnetic motor that obtains a drive force by an energy supply. As illustrated inFIGS.2and3, the motor1is electrically connectable to the second power storage device5, the power converter10, and the first power storage device4, via the inverter2. The motor1performs power driving and regeneration. The inverter2(DC-AC inverter) converts a direct current into an alternating current. In this embodiment, the inverter2converts a direct current of the first power storage device4or the second power storage device5into an alternating current. The inverter2supplies the alternating current to the motor1.

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 brake3aperforming braking by releasing kinetic energy of a driving wheel Ta. A driven wheel mechanical brake3bperforms braking by releasing kinetic energy of a driven wheel Tb. The driving wheel mechanical brake3aand the driven wheel mechanical brake3bare connected to the mechanical brake operator7, via a brake actuator9.

The mechanical brake operator7controls the mechanical brake (driven wheel mechanical brake3b) 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 operator7, a mechanical brake controller18(seeFIG.4) may operate the brake actuator9to actuate the driven wheel mechanical brake3b.

The accelerator operator6controls the motor1to 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 inFIG.4, based on an operation amount of the accelerator operator6, an inverter controller16may estimate a torque request and operate the motor1to obtain a desired drive force. The inverter controller16is one controller provided in the ECU11.

The power storage devices are configured to supply energy to the motor1. In this embodiment, the power storage devices are the first power storage device4and the second power storage device5. The first power storage device4is a storage battery with a large-capacity characteristic. As illustrated inFIG.29, examples of the first power storage device4include a large-capacity lithium ion battery and a large-capacity nickel-metal hydride battery. The second power storage device5is a storage battery with a high-power characteristic. As illustrated inFIG.29, examples of the second power storage device5include 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 operator8controls the motor1to adjust a braking torque of the driving wheel Ta and recover the energy into the power storage devices, first power storage device4and second power storage device5. 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 operator8, the motor1performs regeneration to obtain a desired braking force. Through the regeneration in the motor1, the energy can be recovered into the first power storage device4and the second power storage device5.

The power converter10has a voltage step down function during the power driving of the motor1, during energy supply to the motor1. Also, it has a voltage step up function during the regeneration of the motor1, during energy recovery from the motor1. As illustrated inFIGS.2and3, the power converter10is connected between the first power storage device4and the second power storage device5in an electric circuit. More specifically, as illustrated inFIG.2, the power converter10includes two semiconductor switching elements (MOSFETs)10aand10band a reactor10c(coil). The semiconductor switching elements10aand10binclude switches S1and S2and their body diodes, respectively.

In the power converter10, according to this embodiment, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to high-speed switching (duty control). This steps down the voltage during the power driving of the motor1(when a current flows rightward inFIG.3) because the reactor10cis located on a downstream side of the semiconductor switching elements10aand10b. The voltage is stepped up during the regeneration in the motor1(when the current flows leftward inFIG.3) because the reactor10cis located on an upstream side of the semiconductor switching elements10aand10b.

More specifically, this embodiment provides, as illustrated inFIGS.2and3, a circuit where the power converter10, with the voltage step down function during the power driving, is connected to the first power storage device4. The second power storage device5is connected in series between the reactor10cof the power converter10and the inverter2. During the power driving of the motor1, the power converter10steps down an output voltage (Vdc) of the first power storage device4to supply energy from the first power storage device4and the second power storage device5to the inverter2. During the regeneration of the motor1, the power converter10steps up the resultant output voltage (Vinv-Vc) of the combination between the inverter2and second power storage device5to recover the energy into the first power storage device4and the second power storage device5.

As illustrated inFIG.2, this embodiment provides a first switch S3connecting the power converter10and the inverter2without intervention of the second power storage device5. A second switch S4connects the power converter10and the inverter2, via the second power storage device5. The circuit of this embodiment includes a switch Sa to be turned ON when the power converter10is OFF. Stabilization capacitors Ca and Cb are connected to the circuit. The first switch S3and the second switch S4, according to this embodiment, are formed in semiconductor switching elements (MOSFETs)14and15(including their body diodes similarly to the semiconductor switching elements10aand10b), respectively.

The ECU11controls the motor1in response to input driver's requests. As illustrated inFIG.4, the ECU11includes the inverter controller16, a circuit controller17, and the mechanical brake controller18, and is connected to the inverter2, the power converter10, the first power storage device4, the second power storage device5, and the brake actuator9. The ECU11is configured to detect voltages of the first power storage device4and the second power storage device5. The ECU11makes determination on power storage statuses of the first power storage device4and the second power storage device5based on the voltages.FIG.27illustrates the power storage status of the first power storage device4.FIG.28illustrates the power storage status of the second power storage device5.

When the power storage status of the second power storage device5is equal to or lower than a predetermined lower limit value (seeFIG.28), during the power driving of the motor1, the first switch S3is turned ON and the second switch S4is turned OFF to supply energy from the first power storage device4to the inverter2while stepping down the output voltage (Vdc) of the first power storage device4. When the power storage status of the second power storage device5is equal to or higher than a predetermined upper limit value (seeFIG.28), during the regeneration in the motor1, the first switch S3is turned ON and the second switch S4is turned OFF to store regeneration energy in the first power storage device4while stepping up a DC voltage (Vinv) of the inverter2.

The start switch12is an operation switch that allows the vehicle to travel. By operating the accelerator operator6after the start switch12is operated, the motor1may be actuated for traveling. The monitor13is an auxiliary device such as a liquid crystal monitor attached to the vehicle. For example, the monitor13may display conditions of the vehicle (speed, power storage status, or whether malfunction has occurred) or a map of a navigation system.

As illustrated inFIG.4, this embodiment provides a detector19, a sensor detecting a rotation speed of the motor1. When the rotation speed of the motor1, detected by the detector19, is equal to or higher than a predetermined value, a predetermined braking torque, based on an operation amount of the regenerative brake operator8, 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 motor1is a rated torque of the motor1.

When the rotation speed of the motor1, detected by the detector19, is lower than the predetermined value, a braking torque is generated by the mechanical brake (driving wheel mechanical brake3a) based on the operation amount of the regenerative brake operator8. When the charge level of the first power storage device4is equal to or higher than a predetermined value, a braking torque is generated by the mechanical brake (driving wheel mechanical brake3a) based on the operation amount of the regenerative brake operator8.

According to the embodiment,FIG.5illustrates changes in parameters in a case where the accelerator operator6and the regenerative brake operator8are operated after the start switch12is turned ON in the motor vehicle. In particular, a capacitor current (Ic) and a capacitor charge level (SOC2) are a current and a charge level of the second power storage device5of this embodiment, and a battery current (Idc) and a battery charge level (SOC1) are a current and a charge level of the first power storage device4of this embodiment. In a table inFIG.5, “function circuit control number” (FCCNO) corresponds to “FCCNO” inFIGS.4,18, and19.

Next, control on the motor vehicle (main control), according to this embodiment, is described with reference to a flowchart ofFIG.6.

In S1, determination is first made as to whether the start switch12is ON. When determination is made that the start switch12is ON, determination is made in S2as to whether a charge status (Soc1) of the first power storage device4is higher than a predetermined lower limit value (seeFIG.27). When determination is made that the charge status (Soc1) is higher than the predetermined lower limit value, a request process (S3), motor control (S4), and mechanical brake control (S5) are performed sequentially.

Next, request characteristics of the motor vehicle according to this embodiment are described with reference toFIGS.7to10.

The characteristics illustrated inFIG.7show the relationship between a vehicle speed and both of the drive torque and the braking torque of the driving wheel Ta. The characteristics illustrated inFIG.8show the relationship between a motor torque of the driving wheel Ta and a rotation speed (ω) of the motor1. Particularly in a case of high-speed traveling,FIG.7illustrates relationships where the drive torque gradually decreases and the braking torque is constant relative to the vehicle speed. InFIG.8, a positive side (upper half) from the vertical axis shows a drive torque based on an operation amount of the accelerator operator6. A negative side (lower half) from the vertical axis shows a braking torque based on an operation amount of the regenerative brake operator8. InFIG.8, reference symbol Tm1represents the rated torque of the motor1.

The characteristics illustrated inFIG.9show the relationship between the vehicle speed and a braking torque of the driven wheel Tb. The characteristics illustrated inFIG.10show the relationship between a braking torque of the driven wheel Tb (mechanical braking torque (Tbmf)) and the rotation speed (ω) of the motor1. SinceFIGS.9and10illustrate the characteristics of the driven wheel Tb, only a negative side (lower half) from the vertical axis shows the characteristics (braking torques).

Next, control on the motor vehicle (request process control), according to this embodiment, is described with reference to a flowchart ofFIG.11.

In S1, 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 S2as to whether the accelerator operator6is operated (whether an accelerator operation amount Ap is larger than 0). When determination is made that the accelerator operator6is operated larger than 0, the process proceeds to S5for motor driving mode. A motor torque (Tm), based on the operation amount of the accelerator operator6, is calculated with reference to Table 1 illustrated inFIG.12.

After the calculation in S5, the process proceeds to S9(driving wheel mechanical break). A mechanical braking torque (Tbmr), based on an operation amount of the regenerative brake operator8, is calculated with reference to Table 5 illustrated inFIG.16. Then, the process proceeds to S13(driven wheel mechanical break). A mechanical braking torque (Tbmf), based on an operation amount of the mechanical brake operator7, is calculated with reference to Table 6 illustrated inFIG.17. The mechanical braking torque (Tbmr) calculated in S9is the braking torque of the driving wheel Ta. The mechanical braking torque (Tbmf) calculated in S13is the braking torque of the driven wheel Tb.

When determination is made in S2that the accelerator operator is not operated, determination is made in S3as to whether the regeneration in the motor1is possible. In S3, determination is made that the regeneration in the motor1is possible when the power storage status (Soc1) of the first power storage device4is equal to or lower than a predetermined upper limit value (seeFIG.27) and the rotation speed of the motor is equal to or higher than ω1(seeFIG.8). When determination is made that the regeneration in the motor1is possible, determination is made in S4as to whether the power storage status (Soc2) of the second power storage device5is higher than the predetermined upper limit value (seeFIG.28).

When determination is made in S4that the power storage status (Soc2) of the second power storage device5is higher than the predetermined upper limit value (seeFIG.28), the process proceeds to S6(power regeneration to only first storage device). A motor torque (Tm), based on the operation amount of the regenerative brake operator8, is calculated with reference to Table 2, illustrated inFIG.13. In the calculation of the motor torque (Tm), with reference to Table 2, when the rotation speed of the motor1is equal to or lower than a predetermined rotation speed (ω2), illustrated inFIG.8, a correction is made such that Tm=Tm(ω−ω1)/(ω2−ω1). After the calculation in S6, the process proceeds to S10. A mechanical braking torque of driving wheel (Tbmr), based on the operation amount of the regenerative brake operator8, is calculated with reference to Table 4, illustrated inFIG.15. Then, S13is sequentially performed as described above.

When determination is made in S4that the power storage status (Soc2) of the second power storage device5is not higher than the predetermined upper limit value (seeFIG.28), the process proceeds to S7. A motor torque (Tm), based on the operation amount of the regenerative brake operator8, is calculated with reference to Table 3, illustrated inFIG.14. In the calculation of the motor torque (Tm), with reference to Table 3, when the rotation speed of the motor1is equal to or lower than the predetermined rotation speed (ω2) illustrated inFIG.8, a correction is made such that Tm=Tm(ω−ω1)/(ω2−ω1), similarly to Table 2. After the calculation in S7, the mechanical braking torque (Tbmr) is set to 0 in S11, and then S13is performed as described above.

When determination is made in S1that the malfunction signal is generated or when determination is made in S3that the regeneration is not possible, the process proceeds to S8. The motor torque (Tm) is set to 0. Then, the process proceeds to S12. A mechanical braking torque (Tbmr), based on the operation amount of the regenerative brake operator8, is calculated with reference to Table 5 illustrated inFIG.16. Thus, when determination is made that the regenerative system has malfunctioned or the regeneration is not possible, the braking torque can be generated by the mechanical brake (driving wheel mechanical brake3a) based on the operation amount of the regenerative brake operator8. After the calculation in S12, S13is performed as described above.

Next, control on the motor vehicle (motor control) according to this embodiment is described with reference to a flowchart ofFIG.18.

In S1, 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 S2as to whether the accelerator operator6is operated (whether the accelerator operation amount Ap is larger than 0). When determination is made that the accelerator operator6is operated, determination is made in S3as to whether the power storage status (Soc2) of the second power storage device5is higher than the predetermined lower limit value (seeFIG.28).

When determination is made in S3that the power storage status (Soc2) of the second power storage device5is not higher than the predetermined lower limit value (seeFIG.28), determination is made in S6as to whether the rotation speed (ω) of the motor1is lower than ω3(seeFIGS.20and23). When determination is made that the rotation speed (ω) of the motor1is not lower than ω3(high-speed rotation), the process proceeds to S7, and function circuit control (FCC) is set to 1. When determination is made in S6that the rotation speed (ω) of the motor1is lower than ω3(low-speed rotation), the process proceeds to S8, and FCC is set to 2.

When determination is made in S3that the power storage status (Soc2) of the second power storage device5is higher than the predetermined lower limit value (seeFIG.28), the process proceeds to S9, and FCC is set to 3. When determination is made in S2that the accelerator operator6is not operated, determination is made in S4as to whether the regeneration in the motor1is possible. In S4, determination is made that the regeneration in the motor1is possible when the power storage status (Soc1) of the first power storage device4is equal to or lower than the predetermined upper limit value (seeFIG.27) and the rotation speed of the motor is equal to or higher than ω1(seeFIG.8).

When determination is made in S4that the regeneration in the motor1is possible, determination is made in S5as to whether the power storage status (Soc2) of the second power storage device5is higher than the predetermined upper limit value (seeFIG.28). When determination is made that the power storage status (Soc2) of the second power storage device5is higher than the predetermined upper limit value, the process proceeds to S10, and FCC is set to 4. When determination is made that the power storage status (Soc2) of the second power storage device5is not higher than the predetermined upper limit value, the process proceeds to S11, and FCC is set to 5. When determination is made in S1that the malfunction signal is generated or when determination is made in S4that the regeneration in the motor1is not possible, the process proceeds to S12, 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 S13as 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 S14, and the FCCNO determined in any one of S7to S12is maintained. When determination is made that the mode is changed, the process proceeds to S15, and (FCCNO) is set to 7. Then, control associated with the FCCNO is performed in S16. In S17, the mode determined in the current process FCC is stored as FCCO. In S18, inverter control is performed.

The control in S16is performed with reference to a control table ofFIG.19. The following are details of the control in the control table.

When FCCNO=1, the switches S1and S2of the semiconductor switching elements10aand10bare turned OFF (the power converter10is turned OFF), the first switch S3and the second switch S4are turned OFF, and the switch Sa is turned ON. In the control table, “capacitor series connection” means a state where “the second power storage device5is connected in series between the reactor10cof the power converter10and the inverter2”.

When FCCNO=2, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to duty control during the power driving. Thus, the power converter10steps down the output voltage of the first power storage device4. Further, the first switch S3is turned ON, the second switch S4is turned OFF, and the switch Sa is turned OFF. When FCCNO=2, current control of the inverter2is performed with reference to Table A illustrated inFIG.20.

According to Table A, when the current control of the inverter2is performed under PWM control, the DC voltage of the inverter2is controllable based on the rotation speed (ω) of the motor1as illustrated inFIG.20. When the rotation speed of the motor1is equal to or lower than the predetermined rotation speed (ω3), the DC voltage of the inverter2is controlled to decrease as the rotation speed of the motor1decreases. Also in Tables B and C described later, it is assumed that the current control of the inverter2is performed under the PWM control.

When FCCNO=3, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to duty control during the power driving. Thus, the power converter10steps down the output voltage of the first power storage device4. Further, the first switch S3is turned OFF, the second switch S4is turned ON, and the switch Sa is turned OFF. When FCCNO=3, the current control of the inverter2is performed with reference to Table A illustrated inFIG.20similarly to the case where FCCNO=2.

When FCCNO=4, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to duty control during the regeneration so that the power converter10steps up the inverter DC voltage. Further, the first switch S3is turned ON, the second switch S4is turned OFF, and the switch Sa is turned OFF. When FCCNO=4, the current control of the inverter2is performed with reference to Table B illustrated inFIG.21.

When FCCNO=5, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to duty control during the regeneration. Thus, the power converter10steps up the resultant output voltage of the inverter2and the second power storage device5. Further, the first switch S3is turned OFF, the second switch S4is turned ON, and the switch Sa is turned OFF. When FCCNO=5, the current control of the inverter2is performed with reference to Table C illustrated inFIG.22.

When FCCNO=6, the switches S1and S2of the semiconductor switching elements10aand10bare turned OFF (the power converter10is turned OFF). The first switch S3, the second switch S4, and the switch Sa are turned OFF. When FCCNO=7, the switches S1and S2of the semiconductor switching elements10aand10bare subjected to duty control. The first switch S3, the second switch S4, 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 inverter2is performed under the pulse width modulation (PWM) control. Instead, the current control of the inverter2may 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. The control depending on the peak value of the motor line-to-line voltage is control for changing the DC voltage of the inverter depending on the peak value of the motor line-to-line voltage as illustrated inFIGS.23to26.

In the case where the current control of the inverter2is performed under the control depending on the peak value of the motor line-to-line voltage, in Table A illustrated inFIG.23, the DC voltage of the inverter2is controlled based on the peak value of the motor line-to-line voltage when the rotation speed of the motor1is equal to or lower than the predetermined rotation speed (ω3). In Table B, control is performed as illustrated inFIG.24. In Table C, control is performed as illustrated inFIG.25.FIG.26is a time chart illustrating an example of a switching operation of the inverter circuit and behavior of the motor line-to-line voltage. A fundamental wave is illustrated of the motor line-to-line voltage in a case where the current is controlled with reference to any one of the tables inFIGS.23to25. 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 (Vinv) 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 motor1is equal to or higher than the predetermined value, the predetermined braking torque, based on the operation amount of the regenerative brake operator8, 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 motor1.

That is, the predetermined braking torque is generated only by the regenerative braking based on the operation amount of the regenerative brake operator8. 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 brake3a) 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 motor1is the rated torque of the motor1. Therefore, a sufficient braking torque intended by the driver can be obtained and the regenerated energy can be increased at the predetermined rotation speed or higher. Further, the power converter10, with the voltage step down function during the power driving and the voltage step up function during the regeneration, is provided and the energy is recovered via the power converter10during 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 motor1is lower than the predetermined value, the braking torque is generated by the mechanical brake (driving wheel mechanical brake3a) based on the operation amount of the regenerative brake operator8. In an extremely low-speed rotation range of the motor1, 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 device4, a large-capacity characteristic, and the second power storage device5, 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 device4and the second power storage device5is connected in series between the reactor10cof the power converter10and the inverter2. During the regeneration in the motor1, the energy is recovered into the first power storage device4and the second power storage device5by 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 device4during the regeneration in the motor1.

When the charge level of the first power storage device4is equal to or higher than the predetermined value, the braking torque is generated by the mechanical brake (driving wheel mechanical brake3a) based on the operation amount of the regenerative brake operator8. Determination is made that no more charging can be made when the charge level of the first power storage device4is 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 that are the regenerative brake operator8and the mechanical brake operator7are 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 device4is stepped down to supply the energy from the first power storage device4and the second power storage device5to the inverter2. The series combination of the converter10output voltage and the voltage of the second storage device5enable step up of the voltage at the inverter2DC terminals. The adjustment can be made in accordance with the setting of the DC voltage of the inverter2by stepping up and down the resultant output voltage of the first power storage device4and the second power storage device5. Therefore, even if the set value of the DC voltage of the inverter2is changed, a standard-voltage storage battery can be used and an increase in manufacturing costs can be prevented.

Particularly in this embodiment, the switches S1and S2of the semiconductor switching elements10aand10bof the power converter10are subjected to duty control during the power driving to optimally step up and down the inverter DC voltage of the motor1relative to the voltage of the first power storage device4combined with the second power storage device5. Further, the supplied power driving energy is shared by the first power storage device4and the second power storage device5. Therefore, the current of the first power storage device4is smaller than that in a case where the same amount of power driving energy is supplied only by the first power storage device4. Thus, even if the power driving energy is large, the current of the first power storage device4can be kept small and the life of the first power storage device4can be prolonged.

The first switch S3and the second switch S4are provided and determination can be made about the power storage status of the second power storage device5based on the voltage level of the second power storage device5. When the power storage status of the second power storage device5is equal to or lower than the predetermined lower limit value during the power driving of the motor1, the first switch S3is turned ON and the second switch S4is turned OFF. This supplies energy from only the first power storage device4to the inverter2while stepping down the output voltage of the first power storage device4. Thus, even if the charge in the second power storage device5is empty, the power driving of the motor1can be continued by using the energy of the first power storage device4, thereby allowing the vehicle to travel.

The first switch S3and the second switch S4are provided and determination can be made about the power storage status of the second power storage device5based on the voltage of the second power storage device5. When the power storage status of the second power storage device5is equal to or higher than the predetermined upper limit value during the regeneration in the motor1, the first switch S3is turned ON and the second switch S4is turned OFF. This stores regenerative energy in the first power storage device4while stepping up the DC voltage of the inverter2. Thus, even if the charge in the second power storage device5is full, the regeneration in the motor1can be continued by storing the regenerative energy in the first power storage device4.

During the current control of the inverter2, the DC voltage of the inverter2is controllable based on the rotation speed of the motor1. When the rotation speed of the motor1is equal to or lower than the predetermined rotation speed, the DC voltage of the inverter2is controlled to decrease as the rotation speed of the motor1decreases. Therefore, the DC voltage of the inverter2can 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 motor1is equal to or lower than the predetermined rotation speed during the current control of the inverter2, the DC voltage of the inverter2is 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). Thus, 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 those embodiments. For example, the first power storage device4may be a power storage device in another form with a larger-capacity characteristic than the second power storage device5. Alternatively, the second power storage device5may be a power storage device in another form with a higher-power characteristic than the first power storage device4. The semiconductor switching element may be an IGBT in place of the MOSFET. The present disclosure may be applied to a vehicle without the monitor13, or to a three-wheel or four-wheel vehicle such as a buggy.

The present disclosure is also applicable to a motor vehicle having a different appearance or having 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.