Rotation angle detection device, electric power steering device and method of controlling electric power steering device
The power control unit sets a drive interval for driving the sensor by providing power intermittently to the sensor to a first time interval when no change is detected in the sine-wave signal and the cosine-wave signal, sets to the second time interval that is shorter than the first time interval when a change in only one of the sine-wave signal and the cosine-wave signal is detected, and sets to the third time interval that is shorter than the second time interval when a change in one of the sine-wave signal and the cosine-wave signal is detected and then a change in the other is detected.
1. A rotation angle detection device of a motor comprising:
a sensor configured to output a sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a directly measured amount of rotation of a motor rotation shaft of a motor;
a sensor power supply unit configured to supply power to the sensor;
a power control unit configured to control the sensor power supply unit to supply power to the sensor continually when a power switch is on and supply power to the sensor intermittently when the power switch is off;
a sensor signal detection unit configured to detect a change in the sine-wave signal and a change in the cosine-wave signal; wherein
the power control unit sets a drive interval for driving the sensor by providing power intermittently to the sensor to a first time interval when no change is detected in the sine-wave signal and the cosine-wave signal, sets to a second time interval that is shorter than the first time interval when a change in only one of the sine-wave signal and the cosine-wave signal is detected, and sets to a third time interval that is shorter than the second time interval when a change in one of the sine-wave signal and the cosine-wave signal is detected and then a change in the other is detected.
2. The rotation angle detection device according to claim 1 , wherein the power control unit expands by steps the drive interval to the first time interval when a change in neither of the sine-wave signal and the cosine-wave signal is detected even when power is intermittently supplied for a predetermined plurality of times to the sensor while the drive interval is set to be shorter than the first time interval.
3. The rotation angle detection device according to claim 1 , wherein the power control unit increases a duty ratio of a period during which power is supplied to the sensor by shortening the drive interval.
4. The rotation angle detection device according to claim 3 , wherein the duty ratio is 10% when the drive interval is the third time interval.
5. The rotation angle detection device according to claim 4 , wherein the duty ratio when the drive interval is the first time interval is one-third of the duty ratio when the drive interval is the third time interval.
6. The rotation angle detection device according to claim 1 , wherein the power control unit lowers a voltage of power supplied to the sensor when the power switch is off than when the power switch is on.
7. The rotation angle detection device according to claim 6 , wherein a voltage of power supplied to the sensor when the power switch is off is 3.3 V, and a voltage of power supplied to the sensor when the power switch is on is 5V.
8. A rotation angle detection device according to claim 1 , comprising:
a first sensor configured to output a first sensor signal in accordance with a rotation of the motor rotation shaft;
an angular position calculation unit configured to calculate an angular position information that indicates an angular position of the motor rotation shaft based on the first sensor signal;
a rotation number detection unit configured to detect a rotation number of the motor rotation shaft based on the sensor signal output from a second sensor that is the sensor and output rotation number information indicating the rotation number; a rotation angle calculation unit configured to calculate rotation angle information indicating a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information; and
a power supply unit configured to supply power to the first sensor, the angular position calculation unit, the rotation number detection unit, and the rotation angle calculation unit; wherein
the power control unit controls the power supply unit to supply power to the first sensor, the angular position calculation unit, and the rotation angle calculation unit when the power switch is on and to stop supplying power to the first sensor, the angular position calculation unit, and the rotation angle calculation unit when the power switch is off.
9. An electric power steering device comprising;
a torque sensor configured to detect steering torque that is applied to a steering shaft based on a torsion angle between an input shaft and an output shaft connected via a torsion bar mounted on a steering shaft of a vehicle;
a motor configured to provide steering assistance force to a steering mechanism of the vehicle;
the rotation angle detection device according to claim 1 configured to calculate rotation angle information of a motor rotation shaft of the motor;
a motor control unit configured to drive and control the motor based on the steering torque; and
a steering angle calculation unit configured to calculate a steering angle of the input shaft based on the torsion angle, a reduction ratio of a reduction gear, and the rotation angle information.
10. A control method of an electric power steering device according to claim 9 , wherein the steering assistance force provided by the motor is controlled based on the steering angle calculated by the steering angle calculation unit.