Electric power steering device

Patent metadata

Field	Value
Publication number	US-10196085-B2
Application number	US-201515541081-A
Country	US
Kind code	B2
Filing date	Feb 26, 2015
Priority date	Feb 26, 2015
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

In an electric power steering device assisted by a brushless motor, an induced voltage from a brushless motor is detected when a main power supply is off. The motor is determined to be in a high rpm state when the induced voltage is in a first transient state from a voltage≤a high rpm detection threshold Th1 to a voltage≥Th1, thereby setting an intermittent excitation cycle of a revolution angle sensor connected to the motor to a short cycle. The motor is determined to be in a low rpm state when the induced voltage becomes a voltage≥a high rpm detection threshold Th2 after a wait period corresponding to an electrical angle between peaks or valleys of an output voltage has elapsed in a second transient state from a voltage≥Th1 to a voltage≤Th2, thereby setting the cycle to a long cycle.

First claim

What is claimed is:

1. An electric power steering device to be assisted by a brushless motor, the electric power steering device comprising a cycle switching part configured to:
detect an induced voltage from the brushless motor, which is revolved by an external force, via a rectification circuit when a main power supply is off;
compare the induced voltage with a high rpm detection threshold and a low rpm detection threshold;
determine that the induced voltage is in a first transient state when the induced voltage transitions from a voltage equal to or less than the high rpm detection threshold to a voltage equal to or greater than the high rpm detection threshold;
determine that the induced voltage is in a second transient state when the induced voltage transitions from a voltage equal to or greater than the high rpm detection threshold to a voltage equal to less than the high rpm detection threshold;
determine that the induced voltage is in a third transient state when the induced voltage transitions from the first transient state to a voltage equal to or less than the low rpm detection threshold;
determine that the brushless motor is in a high rpm state when the induced voltage is in the first transient state, thereby setting an intermittent excitation cycle of a revolution angle sensor connected to the brushless motor to a predetermined short cycle; and
determine that the brushless motor is in a low rpm state when the induced voltage enters into the third transient state after a wait period corresponding to an electrical angle between peaks of an output voltage of the rectification circuit has elapsed in the second transient state, thereby setting the intermittent excitation cycle to a predetermined long cycle.

2. The electric power steering device according to claim 1 , wherein:
the brushless motor comprises a rotor composed of k pairs of permanent magnets, where a P pole and an N pole of a permanent magnet form one pair, and field coil groups each comprising h coils installed so as to be shifted by a predetermined angle from one another and having electric terminals with h phases;
the cycle switching part is configured to turn on/off a switch in accordance with a trigger from a timer configured to count a clock to measure a period, thereby causing a current to flow through the revolution angle sensor at an intermittent cycle based on a time interval of the timer;
the output voltage of the rectification circuit comprises a half-wave rectified voltage for h induced voltages corresponding to the h phases; and
the wait period comprises a time corresponding to a revolution angle of angle_a (deg)=360 (deg)÷h (phase), which is acquired from twait_a (sec)=360 (deg)÷h÷k÷(360 (deg)×60 (sec)×r_m (rpm)), where r_m (rpm) is an rpm of a revolution shaft of the brushless motor.

3. The electric power steering device according to claim 1 , wherein:
the brushless motor comprises a rotor composed of k pairs of permanent magnets, where a P pole and an N pole of a permanent magnet form one pair, and field coil groups each comprising h coils installed so as to be shifted by a predetermined angle from one another and having electric terminals with h phases;
the cycle switching part is configured to turn on/off a switch in accordance with a trigger from a timer configured to count a clock to measure a period, thereby causing a current to flow through the revolution angle sensor at an intermittent cycle based on a time interval of the timer;
the output voltage of the rectification circuit comprises a full-wave rectified voltage for h induced voltages corresponding to the h phases; and
the wait period comprises a time corresponding to a revolution angle of angle_a (deg)=360 (deg)÷h (phase)÷2, which is acquired from twait_a (sec)=360 (deg)÷h÷2÷k÷(360 (deg)×60 (sec)×r_m (rpm)), where r_m (rpm) is an rpm of a revolution shaft of the brushless motor.

4. The electric power steering device according to claim 1 , wherein:
the high rpm detection threshold is set to a value substantially equal to a peak at a minimum predicted high rpm of the brushless motor; and
the low rpm detection threshold is set to a value substantially equal to a value that is a forward voltage of a rectification element used for the rectification circuit, and is more than a maximum predicted value of a valley of the forward voltage.

5. The electric power steering device according to claim 2 , wherein the cycle switching part is configured to hold a revolution angle of the brushless motor in a previous intermittent cycle under a state in which the first transition state is held, cumulatively add a revolution angle movement amount, which is a difference between the revolution angle held in the previous intermittent cycle and a revolution angle in a current intermittent cycle, for each intermittent excitation cycle, and set as the wait period a time when the revolution angle movement amount represented by the cumulative addition after the first transition state reaches angle_a (deg)=360 (deg)÷h (phase).

6. The electric power steering device according to claim 3 , wherein the cycle switching part is configured to hold a revolution angle of the brushless motor in a previous intermittent cycle under a state in which the first transition state is continuously held, cumulatively add a revolution angle movement amount, which is a difference between the revolution angle held in the previous intermittent cycle and a revolution angle in a current intermittent cycle, for each intermittent excitation cycle, and set as the wait period a time when a revolution angle movement amount represented by the cumulative addition after the second transition state reaches angle_b (deg)=360 (deg)÷h (phase)÷2.

7. The electric power steering device according to claim 5 , wherein the revolution angular velocity detection part is configured to detect, in place of a motor rpm based on a voltage signal from an induced voltage detection part, a motor rpm from an angle position difference between an output of a revolution angle position detection part that has received an output signal of the revolution angle sensor and an output of the previous cycle angle position holding part.

8. The electric power steering device according to claim 5 , wherein the revolution angular velocity detection part is configured to detect, in addition to a motor rpm based on a voltage signal from an induced voltage detection part, a motor rpm from an angle position difference between an output of a revolution angle position detection part that has received an output signal of the revolution angle sensor and an output of the previous cycle angle position holding part.

9. The electric power steering device according to claim 2 , wherein:
the high rpm detection threshold is set to a value substantially equal to a peak at a minimum predicted high rpm of the brushless motor; and
the low rpm detection threshold is set to a value substantially equal to a value that is a forward voltage of a rectification element used for the rectification circuit, and is more than a maximum predicted value of a valley of the forward voltage.

10. The electric power steering device according to claim 3 , wherein:
the high rpm detection threshold is set to a value substantially equal to a peak at a minimum predicted high rpm of the brushless motor; and
the low rpm detection threshold is set to a value substantially equal to a value that is a forward voltage of a rectification element used for the rectification circuit, and is more than a maximum predicted value of a valley of the forward voltage.

11. The electric power steering device according to claim 6 , wherein the revolution angular velocity detection part is confi

Assignees

• Mitsubishi Electric Corp

Inventors

• Iida Hajime
• Gokan Hiroshi
• Ogawa Kenji

Classifications

• H02P23/0086

  specially adapted for high speeds, e.g. above nominal speed · CPC title

• B62D5/046 Primary

  Controlling the motor · CPC title

• H02P6/182

  using back-emf in windings · CPC title

• H02K11/215

  Magnetic effect devices, e.g. Hall-effect or magneto-resistive elements · CPC title

• H02P6/17

  and for generating speed information · CPC title