Electric power steering device and control method of electric power steering device

1. An electric power steering device, comprising:

a motor, which includes a stator including at least two independent coil winding groups, and is configured to rotate a steering mechanism of a vehicle;

a drive control circuit, which is configured to drive the at least two independent coil winding groups of the motor independently of each other; and

a controller, which is configured to calculate a control amount through feedback control to output the control amount, to thereby cause the drive control circuit to drive the at least two independent coil winding groups, wherein:

the at least two independent coil winding groups are controlled independently or in cooperation;

the controller includes a failure detector, which is configured to detect a failure of the motor or the drive control circuit; and

the controller is configured to:

output, when occurrence of a failure in one group out of the at least two independent coil winding groups is detected by the failure detector, a control amount so that control is continued solely by another normal group;

resume, when recovery of the one group from the failure is detected by the failure detector during a period in which the control is continued solely by the another group, cooperative control by the one group and the another group; and

set, when starting the cooperative control, target current values of the one group and the another group to values different from a final target current value common to the at least two independent coil winding groups so that a sum of an actual current of the one group, which has recovered from the failure, and an actual current of the another group falls within an acceptable change amount based on an actual current value or a target current value of the another group at a time of the recovery from the failure, to thereby output respective control amounts for the cooperative control.

2. The electric power steering device according to claim 1 , wherein the controller is configured to, at the time of the recovery from the failure:

set the target current value of the another group to a value equal to or larger than half of the actual current value or the target current value of the another group at the time of the recovery from the failure;

set the target current value of the one group to a value equal to or smaller than half of the final target current value; and

change the target current value of the one group and the target current value of the another group toward the final target current value as time elapses.

3. The electric power steering device according to claim 1 , wherein the controller is configured to, at the time of the recovery from the failure:

set the target current value of the another group to a value equal to or smaller than half of the actual current value or the target current value of the another group at the time of the recovery from the failure;

set the target current value of the one group to a value equal to or larger than half of the final target current value; and

change the target current value of the one group and the target current value of the another group toward the final target current value as time elapses.

4. The electric power steering device according to claim 1 , wherein the controller is configured to change the target current values or output the control amounts so that the one group, which has recovered from the failure, follows the target current value earlier than the another group when the controller carries out the cooperative control toward the final target current value after the recovery from the failure.

5. The electric power steering device according to claim 2 , wherein the controller is configured to change the target current value of the one group so that the target current value gradually increases to the final target current value, and change the target current value of the another group so that the target current value gradually decreases to the final target current value when the actual current value of the another group at the time of the recovery from the failure is equal to or larger than a half value of the final target current value, to thereby carry out the cooperative control.

6. A method of controlling an electric power steering device,

the electric power steering device including:

a motor, which includes a stator including at least two independent coil winding groups, and is configured to rotate a steering mechanism of a vehicle;

a drive control circuit, which is configured to drive the at least two independent coil winding groups of the motor independently of each other; and

a controller, which is configured to calculate a control amount through feedback control to output the control amount, to thereby cause the drive control circuit to drive the at least two independent coil winding groups,

the at least two independent coil winding groups being controlled independently or in cooperation,

the method, which is carried out by the controller, comprising:

a failure detection step of detecting a failure of the motor or the drive control circuit;

a sole control step of outputting, when occurrence of a failure in one group out of the at least two independent coil winding groups is detected in the failure detection step, a control amount so that control is continued solely by another normal group;

a control change step of resuming, when the one group recovers from the failure during a period in which the control is continued solely by the another group, cooperative control by the one group and the another group;

a first cooperative control step of setting, when starting the cooperative control, target current values of the one group and the another group to values different from a final target current value common to the at least two independent coil winding groups so that a sum of an actual current of the one group, which has recovered from the failure, and an actual current of the another group falls within an acceptable change amount based on an actual current value or a target current value of the another group at a time of the recovery from the failure, to thereby output respective control amounts for the cooperative control; and

a second cooperative control step of changing, after the cooperative control is started, the target current value of the one group and the target current value of the another group toward the final target current value as time elapses.

7. The electric power steering device according to claim 3 , wherein the controller is configured to change the target current value of the one group so that the target current value gradually increases to the final target current value, and change the target current value of the another group so that the target current value gradually decreases to the final target current value when the actual current value of the another group at the time of the recovery from the failure is equal to or larger than a half value of the final target current value, to thereby carry out the cooperative control.

8. The electric power steering device according to claim 4 , wherein the controller is configured to change the target current value of the one group so that the target current value gradually increases to the final target current value, and change the target current value of the another group so that the target current value gradually decreases to the final target current value when the actual current value of the another group at the time of the recovery from the failure is equal to or larger than a half value of the final target current value, to thereby carry out the cooperative control.