Drive device and drive method for brushless motor

1. A drive device for a brushless motor comprising:

a control unit that switches two phases according to a pulse induced voltage induced in a non-energized phase, the two phases being selected from three phases of the brushless motor and to be applied with a pulse voltage according to a pulse width modulation signal;

a detecting unit that detects whether an abnormality occurs or not in control executed by the control unit; and

a selecting unit that selects between continuation and stop of the control executed by the control unit according to the pulse induced voltage at an angle of switching the two phases to be applied with the pulse voltage, when the abnormality occurs in the control executed by the control unit,

wherein the control unit detects a timing of switching the two phases to be applied with the pulse voltage by comparing the pulse induced voltage induced in the non-energized phase with a threshold,

wherein the selecting unit changes the threshold when the control executed by the control unit is to be continued, and

wherein the selecting unit changes the threshold to a voltage closer to a voltage of a neutral point.

2. The drive device for the brushless motor according to claim 1 , wherein

the selecting unit continues the control executed by the control unit when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage satisfies a predetermined condition, and stops the control executed by the control unit when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage does not satisfy the predetermined condition.

3. The drive device for the brushless motor according to claim 1 , wherein

the selecting unit continues the control executed by the control unit when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage falls within a predetermined range corresponding to each of the angles of the switching, and stops the control executed by the control unit when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage does not fall within the predetermined range.

4. The drive device for the brushless motor according to claim 1 , wherein

the detecting unit detects occurrence of the abnormality in the control executed by the control unit when the pulse induced voltage does not reach the threshold.

5. The drive device for the brushless motor according to claim 1 , wherein

the selecting unit restricts a motor current to be lower than that flowing before occurrence of the abnormality when the control executed by the control unit is to be continued.

6. The drive device for the brushless motor according to claim 1 , wherein

when the abnormality occurs in the control executed by the control unit, the selecting unit successively drives the brushless motor to the angles of switching the two phases to be applied with the pulse voltage, and measures the pulse induced voltage of the non-energized phase at each angle of switching.

7. The drive device for the brushless motor according to claim 6 , wherein

the selecting unit sets a duty cycle used in a case of measuring the pulse induced voltage at the angle of switching to be lower than a duty cycle used in a case of driving the brushless motor toward the angle of switching.

8. The drive device for the brushless motor according to claim 1 , wherein

the selecting unit selects between continuation and stop of the control executed by the control unit based on whether the pulse induced voltage at each of the angles of switching the two phases to be applied with the pulse voltage is lower than the voltage at the neutral point or not.

9. A drive device for a brushless motor comprising:

control means that switches two phases according to a pulse induced voltage induced in a non-energized phase, the two phases being selected from three phases of the brushless motor and to be applied with a pulse voltage according to a pulse width modulation signal;

detecting means that detects whether an abnormality occurs or not in control executed by the control means; and

selecting means that selects between continuation and stop of the control executed by the control means according to the pulse induced voltage at an angle of the switching of the two phases to be applied with the pulse voltage, when the abnormality occurs in the control executed by the control means,

wherein the control means detects a timing of switching the two phases to be applied with the pulse voltage by comparing the pulse induced voltage induced in the non-energized phase with a threshold,

wherein the selecting means changes the threshold when the control executed by the control means is to be continued, and

wherein the selecting means changes the threshold to a voltage closer to a voltage of a neutral point.

10. A drive method for a brushless motor comprising the steps of:

switching two phases according to a pulse induced voltage induced in a non-energized phase, the two phases being selected from three phases of the brushless motor and to be applied with a pulse voltage according to a pulse width modulation signal;

detecting whether an abnormality occurs or not in switching control of the two phases to be applied with the pulse voltage;

measuring the pulse induced voltage at an angle of switching the two phases to be applied with the pulse voltage, when the abnormality occurs in the switching control; and

selecting between continuation and stop of the control of the brushless motor according to the measured pulse induced voltage,

wherein the step of switching the two phases to be applied with the pulse voltage comprises the step of detecting a timing of switching the two phases to be applied with the pulse voltage by comparing the pulse induced voltage induced in the non-energized phase with a threshold,

wherein the step of selecting between the continuation and the stop of the control of the brushless motor comprises the step of changing the threshold when the control of the brushless motor is to be continued, and

wherein the step of changing the threshold comprises the step of changing the threshold to a voltage closer to a voltage of a neutral point.

11. The drive method for the brushless motor according to claim 10 , wherein the step of selecting between the continuation and the stop of the control of the brushless motor comprises the steps of:

continuing the control of the brushless motor when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage satisfies a predetermined condition; and

stopping the control of the brushless motor when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage does not satisfy the predetermined condition.

12. The drive method for the brushless motor according to claim 10 , wherein the step of selecting between the continuation and the stop of the control of the brushless motor comprises the steps of:

continuing the control of the brushless motor when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage falls within a predetermined range corresponding to each of the angles of the switching; and

stopping the control of the brushless motor when the pulse induced voltage at the angle of switching the two phases to be applied with the pulse voltage does not fall within the predetermined range.

13. The drive method for the brushless motor according to claim 10 , wherein

the step of detecting whether the abnormality occurs or not in the switching control comprises the step of:

detecting occurrence of the abnormality in the switching control when the pulse induced voltage does not reach the threshold.

14. The drive method for the brushless motor according to claim 10 , wherein the step of selecting between the continuation and the stop of the control of the brushless motor comprises the step of:

restricting a motor current to be lower than that flowing before occurrence of the abnormality when the control of the brushless motor is to be continued.

15. The drive method for the brushless motor according to claim 10 , wherein the step of measuring the pulse induced voltage comprises the step of:

setting a duty cycle used in a case of measuring the pulse induced voltage at the angle of switching to be lower than a duty cycle used in a case of driving the brushless motor toward the angle of switching.

16. The drive method for the brushless motor according to claim 10 , wherein the step of selecting between the continuation and stop of the control of the brushless motor comprises the steps of:

comparing the pulse induced voltage at each of the angles of switching the two phases to be applied with the pulse voltage with the neutral point; and

selecting between the continuation and the stop of the control of the brushless motor based on a result of the comparison.