Motor drive control device, electric power steering device, and vehicle

A motor drive control device comprising:

• an annular or disk-shaped magnet placed on a motor rotating shaft of an electric motor to be rotatable in synchronism with the motor rotating shaft and includes at least two different magnetic poles arranged alternately in a circumferential direction;
• at least two systems of rotation information detection function units each including a rotation position information detection unit configured to detect a magnetic flux of the magnet which changes depending on a rotation position of the motor rotating shaft as rotation position information, a motor rotation angle calculation unit configured to calculate a motor rotation angle based on the rotation position information detected by the rotation position information detection unit, a rotation position information diagnosis unit configured to diagnose an abnormality of the rotation position information detected by the rotation position information detection unit, and a rotation change amount measurement unit configured to measure an amount of change in the rotation position of the electric motor;
• and
• a motor drive control unit configured to control driving of the electric motor based on the motor rotation angle output from the at least two systems of the rotation information detection function units,
• wherein the rotation position information detection unit includes a plurality of sensor elements configured to detect magnetic signals out of phase with each other as the rotation position information,
• the electric motor is configured to apply a steering assist force to a steering shaft of a vehicle equipped with the motor drive control device,
• the motor drive control device is configured to supply power from a battery of the vehicle to the at least two systems of the rotation information detection function units even while an ignition switch is OFF,
• the rotation change amount measurement unit is configured to continuously measure the amount of change in the rotation position even while the ignition switch is OFF,
• the rotation change amount measurement unit includes a change amount measurement unit configured to measure an amount of change in the rotation position of the electric motor based on the rotation position information detected by the rotation position information detection unit, a change amount storage unit configured to store the amount of change measured by the change amount measurement unit, and a measurement abnormality diagnosis unit configured to diagnose an abnormality of the change amount measurement unit and the change amount storage unit,
• the motor drive control unit is configured to, when the rotation position information diagnosis unit diagnoses at least one of the at least two systems of the rotation information detection function units as abnormal, control driving of the electric motor based on the motor rotation angle output from another of the rotation information detection function units that is normal,
• the motor drive control unit is configured to calculate a steering angle that is a rotation angle of the steering shaft based on the amount of change in the rotation position measured by the rotation change amount measurement unit when the ignition switch changes from OFF to ON, and calculate the steering angle based on the motor rotation angle while the ignition switch is subsequently kept ON, and control driving of the electric motor based on the calculated steering angle, and
• the motor drive control unit is configured to, when the measurement abnormality diagnosis unit diagnoses at least one of the at least two systems of the rotation information detection function units as abnormal, calculate the steering angle based on the amount of change output from another of the rotation information detection function units that is normal.