Rotation angle detection device, electric power steering device and method of controlling electric power steering device

1. A rotation angle detection device comprising:

a first sensor that is supplied with power when a power switch is on and outputs a first sensor signal in accordance with a rotation of a motor rotation shaft of a motor, and to which power supply is stopped when the power switch is off;

an angular position calculation unit that is supplied with power when the power switch is on and calculates angular position information representing an angular position of the motor rotation shaft based on the first sensor signal, and to which power supply is stopped when the power switch is off;

a second sensor that outputs a second sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a rotation of the motor rotation shaft;

a power management unit that supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than a voltage of the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal; and

a rotation angle calculation unit that is supplied with power when the power switch is on and calculates rotation angle information representing a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information, and to which power supply is stopped when the power switch is off,

wherein the power management unit includes:

a power supply unit that generates the first power and the second power;

a comparator; and

a counter that detects a rotation number of the motor rotation shaft by counting an output of the comparator, wherein

the comparator compares the second sensor signal and a reference voltage of a first voltage based on the voltage of the first power when the power switch is on,

when the power switch is turned off from on, the reference voltage to be compared to the second sensor signal by the comparator is switched from the first voltage to a second voltage based on the voltage of the second power, and

the second voltage is lower than the first voltage.

2. The rotation angle detection device according to claim 1 , wherein the power supply unit supplies the first power to the counter when the power switch is on, generates third power that is continuous power having a same voltage as the second power and supplies to the counter when the power switch is off.

3. The rotation angle detection device according to claim 2 , wherein:

the power management unit includes a regulator that generates fourth power that is continuous power having a first regulator voltage from an external power source when the power switch is on and generates fifth power that is continuous power having a second regulator voltage lower than the first regulator voltage from the external power source when the power switch is off.

4. The rotation angle detection device according to claim 1 , wherein the comparator and the power supply unit are arranged in a single integrated circuit chip.

5. The rotation angle detection device according to claim 1 , wherein a time width of one intermittent output of the second power is less than or equal to 220 μsec. when the power switch is off.

6. The rotation angle detection device according to claim 5 , wherein a time width of one intermittent output of the second power is set in accordance with a time constant of the second sensor signal when the second power is intermittently supplied.

7. 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;

a rotation angle detection device comprising:

a first sensor that is supplied with power when a power switch is on and outputs a first sensor signal in accordance with a rotation of a motor rotation shaft of the motor, and to which power supply is stopped when the power switch is off;

an angular position calculation unit that is supplied with power when the power switch is on and calculates angular position information representing an angular position of the motor rotation shaft based on the first sensor signal, and to which power supply is stopped when the power switch is off;

a second sensor that outputs a second sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a rotation of the motor rotation shaft;

a power management unit that supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than a voltage of the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal; and

a rotation angle calculation unit that is supplied with power when the power switch is on and calculates rotation angle information representing a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information, and to which power supply is stopped when the power switch is off,

wherein the power management unit of the rotation angle detection device includes:

a power supply unit that generates the first power and the second power;

a comparator; and

a counter that detects a rotation number of the motor rotation shaft by counting an output of the comparator, wherein,

the comparator compares the second sensor signal and a reference voltage of a first voltage based on the voltage of the first power when the power switch is on,

when the power switch is turned off from on, the reference voltage to be compared to the second sensor signal by the comparator is switched from the first voltage to a second voltage based on the voltage of the second power, and

with respect to rotation angle detection device, the second voltage is lower than the first voltage,

wherein the rotation angle detection device is configured to calculate rotation angle information of the 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.

8. A control method of an electric power steering device, the 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; and

a rotation angle detection device comprising:

a first sensor that is supplied with power when a power switch is on and outputs a first sensor signal in accordance with a rotation of a motor rotation shaft of a motor, and to which power supply is stopped when the power switch is off;

an angular position calculation unit that is supplied with power when the power switch is on and calculates angular position information representing an angular position of the motor rotation shaft based on the first sensor signal, and to which power supply is stopped when the power switch is off;

a second sensor that outputs a second sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a rotation of the motor rotation shaft;

a power management unit that supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than a voltage of the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal; and

a rotation angle calculation unit that is supplied with power when the power switch is on and calculates rotation angle information representing a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information, and to which power supply is stopped when the power switch is off,

wherein the power management unit includes:

a power supply unit that generates the first power and the second power;

a comparator; and

a counter that detects a rotation number of the motor rotation shaft by counting an output of the comparator, wherein

the comparator compares the second sensor signal and a reference voltage of a first voltage based on the voltage of the first power when the power switch is on,

when the power switch is turned off from on, the reference voltage to be compared to the second sensor signal by the comparator is switched from the first voltage to a second voltage based on the voltage of the second power, and

the second voltage is lower than the first voltage; and

wherein the rotation angle detection device is configured to calculate rotation angle information of a motor rotation shaft of the motor;

the electric power steering device further comprising:

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, the control method comprising:

controlling the steering assistance force applied by the motor based on the steering angle calculated by the steering angle calculation unit.

9. The electric power steering device according to claim 7 , further comprising a vehicle speed sensor configured to detect a speed of the vehicle, wherein

the motor control unit is further configured to drive and control the motor based on the vehicle speed.