Control method and control device for motor of electric vehicle, and electric vehicle including control device

1 . A control method for a motor of an electric vehicle, the method comprising:

setting a current-related upper limit value of a current-related value related to a current flowing through a battery of the electric vehicle in accordance with a vehicle state when the electric vehicle is driven by the motor; and

calculating a torque upper limit value of a command torque for commanding the motor to maintain a state where the current-related value is equal to or less than the current-related upper limit value, based on an accelerator operation amount input to the electric vehicle and the current-related upper limit value, wherein

when the accelerator operation amount is maximum, the command torque is calculated such that the current-related value becomes the current-related upper limit value, and

the command torque is controlled to increase with an increase in the accelerator operation amount until the accelerator operation amount reaches the maximum.

2 . The control method according to claim 1 , wherein

the command torque is calculated from following relation,

command torque=command torque before correction×(current-related upper limit value/maximum current-related upper limit value), where

the command torque before correction is a torque based on the accelerator operation amount input by a driver, and

the maximum current-related upper limit value is a maximum value of the current-related upper limit value.

3 . The control method according to claim 1 , wherein

the command torque is calculated based on the accelerator operation amount and a rotation speed of the motor.

4 . The control method according to claim 1 , wherein

the current-related upper limit value is set based on an upper limit current allowed to flow through the battery.

5 . The control method according to claim 1 , wherein

when the battery includes a plurality of batteries electrically connected in parallel,

the current-related upper limit value is set for each of the plurality of batteries, and

the current-related upper limit value is set based on a smallest current-related upper limit value among current-related upper limit values set for each of the plurality of batteries.

6 . The control method according to claim 1 , further comprising:

drive control for driving the motor by bringing the battery into a discharge state where electric power is discharged toward the motor; and

regeneration control for charging the battery by bringing the battery into a charge state where electric power is supplied from the motor during regenerative braking of the electric vehicle, wherein

the current-related upper limit value varies depending on whether the battery is in the discharge state or the charge state.

7 . The control method according to claim 6 , wherein

the regeneration control includes:

charging the battery by bringing the battery into the charge state when the current-related value is equal to or less than the current-related upper limit value during the regenerative braking of the electric vehicle; and

stopping charging the battery when the current-related value exceeds the current-related upper limit value during the regenerative braking of the electric vehicle.

8 . The control method according to claim 1 , wherein

the battery includes a plurality of batteries electrically connected in parallel, the electric vehicle includes:

a switch configured to switch between a parallel connection of the plurality of batteries to connect the parallel connection with the motor and a connection of one of the plurality of batteries with the motor; and

an electric circuit electrically connected to the battery, the motor, and the switch, and

the current-related upper limit value is set based on an upper limit current of a circuit element included in the electric circuit whose connection state is switched by the switch.

9 . The control method according to claim 8 , wherein

the electric circuit includes:

a switching element electrically connected to the battery; and

a diode electrically connected in parallel to the switching element, and

the current-related upper limit value is set to an allowable current of the diode when the switching element is opened.

10 . The control method according to claim 9 , wherein

in a case where the battery is in a chargeable state where a current is allowed to flow from the motor to the battery by the switching element being closed, when a condition for preventing overcharge of the battery is satisfied, the battery is switched to a charge prohibited state where the current is prohibited from flowing from the motor to the battery by the switching element being opened.

11 . An electric vehicle comprising a control device configured to execute the control method according to claim 1 .

12 . The control method according to claim 1 , wherein

a ratio of increasing in accordance with the accelerator operation amount is suppressed until the accelerator operation amount reaches the maximum.

13 . The control method according to claim 1 , wherein

the command torque based on the accelerator operation amount varies depending on different rotation speeds of the motor.

14 . The control method according to claim 1 , wherein

the command torque based on the accelerator operation amount varies between when the electric vehicle starts and when the electric vehicle travels at a constant speed.

15 . The control method according to claim 1 , wherein

the torque upper limit value refers to a torque that corresponds to the current-related upper limit when the accelerator operation amount reaches maximum,

the command torque is controlled such that the torque does not reach the torque upper limit value until the accelerator operation amount reaches the maximum,

the torque is controlled such that the command torque increases as the accelerator operation amount increases,

the command torque at a time when the accelerator operation amount reaches the maximum, is the torque that results from motor operation at the current-related upper limit, and

the torque upper limit value is set in accordance with the current-related upper limit and is independent of the accelerator operation amount.

16 . The control method according to claim 1 , wherein

the command torque is corrected to be equal to or less than the torque upper limit value until the accelerator operation amount reaches the maximum, and

the corrected command torque increasing in accordance with the accelerator operation amount has an increase ration that gradually increases as compared to the command torque before correction.

17 . The control method according to claim 1 , wherein

the electric vehicle includes:

a charging switching element electrically connected to the battery; and

a discharging diode electrically connected in parallel to the charging switching element, the discharging diode being configured to allow a current to flow from the battery to the motor and prevent the current from flowing from the motor to the battery,

the current-related upper limit value is set at an allowable current of the discharging diode in a state where the charging switching element is open.

18 . A control method for a motor of an electric vehicle, the electric vehicle including: the motor; a plurality of batteries electrically connected in parallel; and a switch configured to selectively switch the batteries to be connected to the motor, the method comprising:

setting a current-related upper limit value of a current-related value related to a current flowing through a battery of the electric vehicle in accordance with a vehicle state when the electric vehicle is driven by the motor; and

calculating a torque upper limit value of a command torque for commanding the motor to maintain a state where the current-related value is equal to or less than the current-related upper limit value, based on an accelerator operation amount input to the electric vehicle and the current-related upper limit value, wherein

the current-related upper limit value is switched based on a connection state of the batteries switched by the switch.

19 . A control method for a motor of an electric vehicle, the electric vehicle including: the motor; a battery; a charging switching element electrically connected to the motor and the battery; and a discharging diode electrically connected in parallel to the charging switching element, the discharging diode being configured to allow a current to flow from the battery to the motor and prevent the current from flowing from the motor to the battery, the method comprising:

setting a current-related upper limit value of a current-related value related to a current flowing through a battery of the electric vehicle in accordance with a vehicle state when the electric vehicle is driven by the motor; and

calculating a torque upper limit value of a command torque for commanding the motor to maintain a state where the current-related value is equal to or less than the current-related upper limit value, based on an accelerator operation amount input to the electric vehicle and the current-related upper limit value,

wherein the current-related upper limit value is set at an allowable current of the discharging diode in a state where the charging switching element is open.