Electronically controlled power steering system for vehicle and method and system for motor control

• US 20040267421A1
• Filed: 04/28/2003
• Published: 12/30/2004
• Est. Priority Date: 04/30/2002
• Status: Active Grant

• Current Assignee: Electronic Motion Systems Holdings Limited, Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG), Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Inventors: Yamazaki, Yoshiyuki, Jounokuchi, Hideki, Eskritt, James B., Kuehner, Joel E.
• Granted Patent: US 6,995,679 B2
• Time in Patent Office: Days
• US Class Current: 701/41
• CPC Class Codes: B62D 5/065 characterised by specially adapted means for varying pressurised fluid supply based on need, e.g. on-demand, variable assist
• CPC Class Codes: Y10S 388/933 Radiant energy responsive device

Abstract

A power steering device capable of obtaining a high rotary speed in the medium low torque range of an electric motor without incurring a drastic increase in manufacturing cost. The power steering device generates an auxiliary steering power by oil pressure that is generated by a pump which is driven by an electric power motor. The electric motor is a triple-phase brushless motor, with its angle of rotation being detected by the Hall sensors. The field coils are provided with the electric current from a drive circuit which is driven by a drive signal from the motor drive control part. The motor drive control part controls the electric motor by PWM control in the low medium speed rotation range and controls the electric motor by phase advance angle control, with PWM duty at 100 percent, in the medium high speed range.

Claims

1. A steering device for generating auxiliary steering power by means of an oil pressure generated by a pump that is driven by an electric motor, the electric motor having a conduction angle during which electrical power is provided to at least one motor phase, the steering device comprising:

a rotary angle detector that detects the rotary angle of the rotor of said electric motor,

a steering angular speed sensor for detecting a steering angular speed of a steering operating member,

a drive target value setting device that sets a drive target value of said electric motor based on an output of the steering angular speed sensor,

a drive signal generator that generates a drive signal for driving said electric motor on the basis of the drive target value which is set by the drive target value setting device, and

an angle setting device that sets a phase advance angle of said drive signal with respect to the rotary angle that is detected by said rotary angle detector in relation to the drive target value which is set by said drive target value setting device, thereby varying the conduction angle.

2. The power steering device of claim 1, wherein the phase advance angle setting device sets a preset phase advance angle irrespective of said drive target value at a time when the drive signal to said electric motor is in an unsaturated state and sets the phase advance angle on the basis of the drive target value that is set by said drive target value setting device at a time when the drive signal to said electric power motor has been saturated.

3. The power steering device of claim 2, wherein the preset phase advance angle when the drive signal is unsaturated is a fixed angle that may be zero degrees.

4. The power steering device of claim 2, wherein the conduction angle has a base conduction angle of 120 degrees and the phase advance angle when the drive signal is saturated is a phase advance angle greater than zero degrees and less than or equal to 60 degrees.

5. The power steering device of claim 2, wherein the unsaturated state comprises a state of pulse width modulation of less than 100% duty cycle.

6. The power steering device of claim 4, wherein in a region defined by the phase advance angle, the drive signal to the electric motor is saturated and control of the electric motor is obtained by varying the amount of the phase advance angle.

7. The power steering device of claim 1, further wherein the drive target value setting device is responsive to vehicle speed.

8. The power steering device of claim 1 wherein the electric motor is a brushless 3 phase motor.

9. A method for generating auxiliary steering power by means of an oil pressure generated by a pump that is driven by an electric motor, the electric motor having a conduction angle during which electrical power is provided to at least one motor phase, the method comprising:

detecting the rotary angle of the rotor of said electric motor,

detecting a steering angular speed of a steering operating member,

setting a drive target value of said electric motor based on the steering angular speed,

generating a drive signal for driving said electric motor on the basis of the drive target value, and

setting a phase advance angle of said drive signal with respect to the rotary angle in relation to the drive target value, thereby varying the conduction angle.

10. The method of claim 9, further comprising setting a preset phase advance angle irrespective of said drive target value at a time when the drive signal to said electric motor is in an unsaturated state and setting the phase advance angle on the basis of the drive target value at a time when the drive signal to said electric power motor has been saturated.

11. The method of claim 10, wherein the preset phase advance angle when the drive signal is unsaturated is a fixed angle that may be zero degrees.

12. The method of claim 10, wherein the conduction angle has a base conduction angle of 120 degrees and the phase advance angle when the drive signal is saturated is a phase advance angle greater than zero degrees and less than or equal to 60 degrees.

13. The method of claim 10, wherein the unsaturated state comprises a state of pulse width modulation of less than 100% duty cycle.

14. The method of claim 12, wherein in a region defined by the phase advance angle, the drive signal to the electric motor is saturated and control of the electric motor is obtained by varying the amount of the phase advance angle.

15. The method of claim 9, further wherein the drive target value is responsive to vehicle speed.

16. A method for controlling an electric motor, the motor having at least one sensor output for determining a switching instant for a switch of a switching converter controlling a conduction angle determining a conduction time during a revolution of the motor, the method comprising:

receiving the sensor output;

advancing a switching-on time of a switch of the switching inverter connecting a d-c bus voltage to a motor phase drive input by a phase angle prior to the next sensor output determining the switching instant; and

controlling the speed of the motor by changing the amount of the phase angle.

17. The method of claim 16, further comprising increasing the conduction angle by the amount of said phase angle.

18. The method of claim 16, wherein the phase angle comprises a fixed phase angle amount and a variable phase angle amount controllable by a controller to control the speed of the motor.

19. The method of claim 18, wherein the variable phase angle increases the conduction angle and the fixed phase angle shifts the conduction time temporally.

20. The method of claim 16, further comprising pulse width modulating the switch during the conduction angle.

21. The method of claim 18, wherein two alternately conducting switches arranged in a half bridge are provided and further comprising advancing a switching-on time of each switch by the phase angle.

22. The method of claim 21, wherein the motor is a three phase motor and three half bridges are provided, each comprising two alternately conducting switches, one comprising a high side switch and the other a low side switch and further comprising advancing a switching-on time of each switch by the phase angle.

23. The method of claim 22, wherein the conduction angle varies between 120°

and 180°

, and the variable phase angle varies between 0° and

60°

.

24. The method of claim 23, wherein the fixed phase angle advance equals approximately 15°

.

25. The method of claim 18, wherein the fixed phase angle is provided so that a turn-off instant for the switch is aligned with a transition of the sensor output independently of the amount of conduction angle.

26. The method of claim 16, further comprising pulse width modulating during the conduction angle at a duty cycle of 100%.

27. The method of claim 16, further comprising selecting between the two following options a) and b) to control the motor speed:

a) varying the phase angle and 100% duty cycle pulse width modulation during the conduction angle; and

b) zero phase angle and varying the duty cycle by pulse width modulation during the conduction angle.

28. The method of claim 27, further comprising selecting option b) if a desired speed can be reached at a 120°

conduction angle and less than 100% duty cycle.

29. The method of claim 27, further comprising selecting option b) if a current drawn by the motor exceeds a predetermined limit with 120°

conduction angle and 100% duty cycle.

30. The method of claim 27, further comprising selecting option a) if a desired motor speed cannot be reached with 120°

conduction angle and 100% duty cycle and the current drawn by the motor is below a predetermined limit.

31. A motor speed control regulator comprising:

a switching inverter selectively switching a dc bus voltage for powering the motor;

a controller for controlling a switching operation of the inverter, an on-time of each switch of the inverter determining the conduction angle, the controller having at least one input from at least one sensor providing a sensor signal related to a rotational position of the rotor of the motor;

the controller changing the phase angle at which each switch of the inverter switches on in response to the sensor signal such that each switch switches on at a phase angle in advance of the sensor signal, the amount of the phase angle advance controlling the motor speed.

32. The motor speed control regulator of claim 31, further wherein the controller includes a pulse width modulator for modulating the inverter output during the conduction angle.

33. The motor speed control regulator of claim 32, further wherein the controller is operable to perform speed control of the motor by selecting between the following two options a) and b):

a) varying the phase angle and 100% duty cycle pulse width modulation during the conduction angle; and

b) zero phase angle and varying the duty cycle of pulse width modulation during the conduction angle.

34. The motor speed control regulator of claim 33, wherein the controller is operable to select option b) if a desired speed can be reached at a 120°

conduction angle and less than 100% duty cycle.

35. The motor speed control regulator of claim 33, wherein the controller is operable to select option b) if a current drawn by the motor exceeds a predetermined limit with 120°

conduction angle and 100% duty cycle.

36. The motor speed control regulator of claim 33, wherein the controller is operable to select option a) if a desired motor speed cannot be reached with 120°

conduction angle and 100% duty cycle and the current drawn by the motor is below a predetermined limit.

37. The motor speed control regulator of claim 31, wherein the phase angle increases the conduction angle by the amount of the phase angle.

38. The motor speed control regulator of claim 31, wherein the phase angle comprises a fixed phase angle amount and a variable phase angle amount controllable to control the speed of the motor.

39. The motor speed control regulator of claim 38, wherein the variable phase angle increases the conduction angle and the fixed phase angle shifts the on-time temporally.

40. The motor speed control regulator of claim 31, wherein the motor is a three phase motor and the converter inverter comprises three half bridges, each comprising two alternately conducting switches, one comprising a high side switch and the other a low side switch.

41. The motor speed control regulator of claim 40, wherein the motor is a brushless three phase DC motor.

42. The motor speed control regulator of claim 31, wherein the conduction angle varies between 120°

and 180° and

the variable phase angle varies between 0° and

60°

.

43. The motor speed control regulator of claim 38, wherein the fixed phase angle is provided so that a turn-off instant for each switch is aligned with a transition of the sensor output independently of the amount of conduction angle.