Electric drive vehicle

1. An electric drive vehicle comprising:

an induction motor for braking or driving wheels;

a power converter for driving the induction motor;

a motor controller for controlling the power converter to control the induction motor;

mechanical brakes for braking the wheels;

an acceleration pedal for the vehicle; and

a shift lever for determining a traveling direction of the vehicle;

wherein the power converter outputs a voltage corresponding to a current command from the motor controller, and while the shift lever is at a forward (F) position and the accelerator pedal is not depressed, the motor controller gives a constant current command and a frequency command to make the frequency of electric power for driving the induction motor zero to the power converter so that the power converter outputs a DC voltage based on the current and frequency commands wherein constant current flows through the stator of the induction motor to make the induction motor generate torque for stopping the vehicle and maintain the vehicle in a halt state, and

wherein under conditions in which the shift lever is at a forward position, the accelerator pedal is not depressed and the mechanical brakes are released, the motor controller generates a command signal including a current command and a zero frequency command and the command signal is supplied to the power converter and, based on the command signal, the power converter controls the induction motor, so that the stator current of the induction motor is maintained in a constant DC current value and an output torque of the induction motor varies depending on a slip frequency of the induction motor.

2. The electric drive vehicle according to claim 1 , wherein the mechanical brakes are not operating while the vehicle is maintained in the halt state by the torque generated by the induction motor.

3. The electric drive vehicle according to claim 1 , wherein when the vehicle starts, the motor controller, through the power converter, applies a voltage to the induction motor and adjusts magnitude of said voltage to supply the stator of said induction motor with a predetermined magnitude of a current so that a frequency of the voltage applied to the stator of the induction motor is raised at a predetermined rate.

4. The electric drive vehicle according to claim 1 , wherein when the vehicle in roll stops, the motor controller, through the power converter, applies a voltage to the induction motor and adjusts magnitude of said voltage to supply the stator of said induction motor with a predetermined magnitude of a current so that a frequency of the voltage applied to the stator of the induction motor is lowered at a predetermined rate.

5. The electric drive vehicle according to claim 1 , wherein the motor controller is equipped with a current controller, and a current command supplied to the current controller changes with an opening degree of the accelerator pedal so that as the opening degree of said accelerator pedal is increased the current command is increased.

6. An electric drive vehicle comprising:

an induction motor for braking or driving wheels;

a power converter for driving the induction motor;

a motor controller for controlling the power converter to control the induction motor;

mechanical brakes for braking the wheels;

an accelerator pedal for the vehicle; and

a shift lever for determining a traveling direction of the vehicle,

wherein the power converter outputs a voltage corresponding to a current command from the motor controller, and while the shift lever is at forward (F) position and the accelerator pedal is not depressed the motor controller gives a frequency command to make the frequency of electric power for driving the induction motor zero to the power converter so that the power converter outputs a DC voltage based on the current and frequency commands wherein constant current flows through the stator of the induction motor to make the induction motor generate torque for stopping the vehicle and maintain the vehicle in a halt state;

wherein under conditions in which the shift lever is at a forward position, the accelerator pedal is not depressed and the mechanical brakes are released, the motor controller generates a command signal including a current command and a zero frequency command and the command signal is supplied to the power converter and, based on the command signal, the power converter controls the induction motor, so that the stator current of the induction motor is maintained in a constant DC current value and an output torque of the induction motor varies depending on a slip frequency of the induction motor, and

wherein when the vehicle starts from a state in which the vehicle is in halt on a sloped road while the mechanical brakes are operating, said shift lever is set at a position for driving the vehicle forward or backward, said motor controller starts output of a voltage to said induction motor, and upon depression of the acceleration pedal, following the release of the mechanical brakes, a frequency of the voltage is raised from zero to start the vehicle.

7. The electric drive vehicle according to claim 1 , further comprising a current command portion that outputs a current command to apply a constant current value to the stator of said induction motor.

8. An electric vehicle comprising:

an induction motor for braking or driving wheels;

a power converter for driving the induction motor;

a controller for controlling the power converter in accordance with a current command value and a frequency command value; and

mechanical brakes for braking the wheels,

wherein before the mechanical brakes are shifted into a release state and during a period from when a shift lever is shifted into a driving state to when an acceleration required by an accelerator occurs, the controller sets the current command value to a predetermined value and the frequency command value to zero value to apply a DC voltage to the induction motor wherein constant current flows through the stator so that the induction motor generates a torque, which is reflective of slip frequency generated between the stator and rotor of the induction motor, for halting a vehicle,

wherein under conditions in which the shift lever is at a forward position, the accelerator pedal is not depressed and the mechanical brakes are released, the motor controller generates a command signal including a current command and a zero frequency command and the command signal is supplied to the power converter and, based on the command signal, the power converter controls the induction motor, so that the stator current of the induction motor is maintained in a constant DC current value and an output torque of the induction motor varies depending on a slip frequency of the induction motor, and

wherein after the acceleration required by the accelerator occurs, the controller increases the current command value and gradually the frequency of the frequency command value with time to apply an AC voltage to the stator of the induction motor so that the induction motor generates a torque for accelerating the vehicle.

9. Method of operating an electric vehicle including an induction motor for braking or driving wheels, a power converter for driving the induction motor, a motor controller for controlling the power converter to control the induction motor, mechanical brakes for braking the wheels, an accelerator pedal for the vehicle, and a shift lever for determining a traveling direction of the vehicle, the method comprising:

enabling the power converter to output a voltage corresponding to a current command from the motor controller, and while the shift lever is at a forward (F) position and the accelerator pedal is not depressed, the motor controller gives a constant current command and a frequency command to make the frequency of electric power for driving the induction motor zero to the power converter so that the power converter outputs a DC voltage based on the current and frequency commands wherein constant current flows through the stator of the induction motor to make the induction motor generate torque for stopping the vehicle and maintain the vehicle in a halt state, and

wherein under conditions in which the shift lever is at a forward position, the accelerator pedal is not depressed and the mechanical brakes are released, the motor controller generates a command signal including a current command and a zero frequency command and the command signal is supplied to the power converter and, based on the command signal, the converter controls the induction motor, so that the stator current of the induction motor is maintained in a constant DC current value and an output torque of the induction motor varies depending on a slip frequency of the induction motor.

10. The method of operating an electric vehicle according to claim 9 , wherein the mechanical brakes are not operating while the vehicle is maintained in the halt state by the torque generated by the induction motor.

11. The method of operating an electric vehicle according to claim 9 , wherein when the vehicle starts, the motor controller, through the power converter, applies a voltage to the induction motor and adjusts magnitude of said voltage to supply the stator of said induction motor with a predetermined magnitude of a current so that a frequency of the voltage applied to the stator of the induction motor is raised at a predetermined rate.

12. The method of operating an electric vehicle according to claim 9 , wherein when the vehicle in roll stops, the motor controller, through the power converter, applies a voltage to the induction motor and adjusts magnitude of said voltage to supply the stator of said induction motor with a predetermined magnitude of a current so that a frequency of the voltage applied to the stator of the induction motor is lowered at a predetermined rate.

13. The method of operating an electric vehicle according to claim 9 , wherein the motor controller is equipped with a current controller, and a current command supplied to the current controller changes with an opening degree of the accelerator pedal so that as the opening degree of said accelerator pedal is increased the current command is increased.

14. Method of operating an electric vehicle including an induction motor for braking or driving wheels, a power converter for driving the induction motor, a controller for controlling the power converter in accordance with a current command value and a frequency command value, and mechanical brakes for braking the wheels, the method comprising:

before the mechanical brakes are shifted into a release state and during a period from when a shift lever is shifted into a driving state to when an acceleration required by an accelerator occurs, the controller sets the current command value to a predetermined value and the frequency command value to zero value to apply a DC voltage to the induction motor wherein constant current flows through the stator so that the induction motor generates a torque, which is reflective of slip frequency generated between the stator and rotor of the induction motor, for halting a vehicle,

under conditions in which the shift lever is at a forward position, the accelerator pedal is not depressed and the mechanical brakes are released, the motor controller generates a command signal including a current command and a zero frequency command and the command signal is supplied to the power converter and, based on the command signal, the power converter controls the induction motor, so that the stator current of the induction motor is maintained in a constant DC current value and an output torque of the induction motor varies depending on a slip frequency of the induction motor, and

after the acceleration required by the accelerator occurs, the controller increases the current command value and gradually the frequency of the frequency command value with time to apply an AC voltage to the stator of the induction motor so that the induction motor generates a torque for accelerating the vehicle.