Steering device

1. A steering device comprising:

a turning mechanism arranged to turn steered wheels;

an electric motor which includes a motor rotor and a stator coil, and which is arranged to provide a steering force to the steered wheels;

a command current signal producing section configured to produce a first command current signal to control and drive the electric motor;

a feedback control section configured to produce a second command current signal based on the first command current signal and a second sensed current signal;

a PWM duty ratio signal producing section configured to produce a duty ratio signal which is a signal of a duty ratio, based on the second command current signal;

a drive circuit which includes an inverter, and which is configured to control and drive the inverter based on the duty ratio signal, and to control electric power supplied to the stator coil;

a current sensor configured to sense a current value of a current flowing in the stator coil, and to output the sensed current value as a first sensed current signal;

a motor rotation speed signal receiving section configured to receive a motor rotation speed signal which is a signal of a rotation speed of the electric motor;

a second sensed current signal producing section configured to produce the second sensed current signal based on the first sensed current signal and an offset correction value; and

an offset correction value storing section configured to store the offset correction value including a first offset correction value and a second offset correction value,

the first offset value being a current value for correcting the first sensed current signal so that a value of a vibration of the electric motor is equal to or smaller than a first predetermined value when the motor rotation speed signal is a first rotation speed, or when a modulation rate of the PWM duty ratio signal producing section is a first modulation rate, and

the second offset value being a current value for correcting the first sensed current signal so that the value of the vibration of the electric motor is equal to or smaller than a second predetermined value when the motor rotation speed signal is a second rotation speed, or when the modulation rate of the PWM duty ratio signal producing section is a second modulation rate,

wherein the drive circuit includes a bridge circuit the current sensor is configured to sense a direct current bus bar current flowing in a direct current bus bar, and to output as the first sensed current signal; and the direct current bus bar is a wire between the bridge circuit and a power source arranged to supply electric power to the bridge circuit, or a wire between the bridge circuit and a ground,

wherein the steering device include a phase current presuming section; the electric motor is a three phase brushless motor; the stator coil includes a u phase, a v phase, and a w phase;

the PWM duty ratio signal producing section is configured to produce a u phase duty ratio signal, a v phase duty ratio signal, and a w phase duty ratio signal which are, respectively, the duty signals for the u phase, the v phase, and the w phase; and

the phase current presuming section is configured

to presume the current values flowing in the u phase, the v phase, and the w phase, based on a first direct current bus bar current which is the direct current bus bar current sensed by the current sensor when the duty ratio signal of a maximum phase in which an energization time period is longest in the u phase duty ratio signal, the v phase duty ratio signal, and the w phase duty ratio signal is an ON state, when the duty signal of a minimum phase in which the energization time period is shortest in the u phase duty ratio signal, the v phase duty ratio signal, and the w phase duty ratio signal is an OFF state, and when the duty signal of an intermediate phase in which the energization time period is shorter than the energization time period of the maximum phase, and longer than the energization time period of the minimum phase is the OFF state, and

to presume the current values flowing in the u phase, the v phase, and the w phase, based on a second direct current bus bar current which is the direct current bus bar current sensed by the current sensor when the duty ratio signal of the maximum phase is the ON state, when the duty ratio signal of the intermediate phase is the ON state, and when the duty ratio signal of the minimum phase is the OFF state.

2. The steering device as claimed in claim 1 , wherein when a difference between an ON timing of the duty ratio signal of the maximum phase and the ON timing of the duty ratio signal of the intermediate phase becomes smaller than a first predetermined value, a pulse shift control section is configured to correct the phase of the ON timing of the duty ratio signal of the maximum phase or the ON timing of the duty ratio signal of the intermediate phase so that the difference between the ON timing of the duty ratio signal of the maximum phase and the ON timing of the duty ratio signal of the intermediate phase becomes equal to or greater than a second predetermined value greater than the first predetermined value; and

when a difference between the ON timing of the duty ratio signal of the intermediate phase and the ON timing of the duty ratio signal of the minimum phase becomes smaller than the first predetermined value, the pulse shift control section is configured to correct the phase of the ON timing of the duty ratio signal of the intermediate phase or the phase of the ON timing of the duty ratio signal of the minimum phase so that the difference between the ON timing of the duty ratio signal of the intermediate phase and the ON timing of the duty ratio signal of the minimum phase becomes equal to or greater than the second predetermined value.

3. The steering device as claimed in claim 2 , wherein the first offset correction value is a current value for correcting the first sensed current signal so that the value of the vibration of the electric motor is equal to or smaller than the first predetermined value when the motor rotation speed signal is the first rotation speed during the pulse shift control; and

the second offset correction value is a current value for correcting the first sensed current signal so that the value of the vibration of the electric motor is equal to or smaller than the second predetermined value when the motor rotation speed signal is the second rotation speed during the pulse shift control.

4. The steering device as claimed in claim 1 , wherein the offset correction value storing section includes a data interpolation section;

the data interpolation section is configured to determine, by an interpolation, a value between the first offset correction value and the second offset correction value when the motor rotation speed signal is between the first rotation speed and the second rotation speed, and to output the determined value as an offset correction value interpolation value; and

the second sensed current signal producing section is configured to produce the second sensed current signal based on the first sensed current signal, and the offset correction value interpolation value which is the offset correction value.

5. The steering device as claimed in claim 4 , wherein the data interpolation section is configured to determine, by a linear interpolation, a value between the first offset correction value and the second offset correction value when the motor rotation speed signal is between the first rotation speed and the second rotation speed, and to output the determined value as the offset correction value interpolation value.

6. The steering device as claimed in claim 4 , wherein the offset correction value storing section includes a map; and the first offset correction value and the second offset correction value are map data stored in the map.

7. The steering device as claimed in claim 1 , wherein the first offset correction value is a current value for correcting the first sensed current signal when the motor rotation speed signal is the first rotation speed, and a rotation direction of the motor rotator is both in a normal direction and in a reverse direction; and

the second offset correction value is a current value for correcting the first sensed current signal when the motor rotation speed signal is the second rotation speed, and the rotation direction of the motor rotator is both in the normal direction and in the reverse direction.

8. The steering device as claimed in claim 1 , wherein the first offset correction value is a current value for correcting the first sensed current signal so that the value of the vibration of the electric motor is equal to or smaller than the first predetermined value when the motor rotation speed signal is the first rotation speed; and

the second offset correction value is a current value for correcting the first sensed current signal so that the value of the vibration of the electric motor is equal to or smaller than the second predetermined value when the motor rotation speed signal is the second rotation speed.

9. The steering device as claimed in claim 8 , wherein the offset correction value storing section includes an offset correction value adjusting section; and the offset correction value adjusting section is configured to vary and adjust the offset correction value in accordance with a variation of an environment temperature.

10. The steering device as claimed in claim 1 , wherein the PWM duty ratio signal producing section is configured to vary and adjust a carrier frequency when the motor rotation speed signal is equal to or greater than a third rotation speed.

11. The steering device as claimed in claim 10 , wherein the second sensed current signal producing section is configured to produce the second sensed current signal without using the offset correction value when the motor rotation speed signal is equal to or greater than a fourth rotation speed which is higher than the first rotation speed, the second rotation speed, and the third rotation speed.