POWER STEERING SYSTEM

Abstract

In a power steering system, the steering state of wheels is detected based on the steering speed to judge as to whether the steering state is in turning of the steering wheel or holding of steering speed is the steering wheels. At the time of the steering operation state, the control is executed so that a difference between a torque command value to an electric motor and the actual torque thereof will become smaller. Also, at the time of the holding operation state, the control is executed so that a difference between the revolution speed of the electric motor and a revolution-speed command value thereto will become smaller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an entire diagram of a power steering system in a first embodiment according to the present invention;

FIG. 2 is a graph for illustrating pump load characteristics in the first embodiment according to the present invention;

FIG. 3 is a block diagram for illustrating a flow of motor control at the time of wheels' steering-operation/holding-operation according to the present invention;

FIG. 4 is a diagram for illustrating a judgment method at the time of the wheels' steering-operation/holding-operation according to the present invention;

FIG. 5 is a diagram for illustrating setting of a judgment flag at the time of the wheels' steering-operation/holding-operation according to the present invention;

FIG. 6 is a flowchart diagram for illustrating creation flow of a motor command value inside a power steering control unit according to the present invention;

FIG. 7 is a diagram for illustrating a motor driver and an electric motor according to the present invention with a block-line diagram;

FIG. 8 is a diagram for illustrating an example of creation map of a torque command value according to the present invention;

FIG. 9 is a diagram for illustrating an example of creation map of a revolution-speed command value according to the present invention;

FIG. 10 is a graph for illustrating an example of a temperature compensation gain K1 in the first embodiment according to the present invention;

FIG. 11 is a block diagram for illustrating a flow of the motor control at the time of wheels' steering-operation/holding-operation in another embodiment according to the present invention;

FIG. 12 is a block diagram for illustrating a flow of the motor control at the time of wheels' steering-operation/holding-operation in another embodiment according to the present invention;

FIG. 13 is an entire diagram of the power steering system in another embodiment according to the present invention;

FIG. 14 is an entire diagram of the power steering system in another embodiment according to the present invention; and

FIG. 15 is a block diagram for illustrating a flow of the motor control at the time of wheels' steering-operation/holding-operation in another embodiment according to the present invention.

Claims

1. A power steering system, comprising: an electric motor for adding a steering assist force to wheels based on driving state of a vehicle, andsteering-speed detection means for detecting or estimating steering speed of said wheels, whereinthere is provided motor control means for executing a torque control over said electric motor if said steering speed is higher than a predetermined value, and for executing a control over said electric motor based on revolution speed of said electric motor if said steering speed is lower than said predetermined value.

2. The power steering system according to claim 1, further comprising: a steering wheel whose steering operation is performed by a driver, anda steering shaft connected to said steering wheel, and whereinsaid steering-speed detection means detects revolution speed of said steering shaft.

3. The power steering system according to claim 2, wherein said steering-speed detection means includes a steering-angle sensor provided on said steering shaft, and a calculation circuit for calculating change ratio of a steering angle detected by said steering-angle sensor.

4. The power steering system according to claim 1, further comprising: a rack bar connected to said wheels, and whereinsaid steering-speed detection means detects axis-direction displacement speed of said rack bar.

5. The power steering system according to claim 4, wherein said steering-speed detection means includes a position sensor for detecting axis-direction position of said rack bar, and a calculation circuit for calculating change ratio of said axis-direction position of said rack bar detected by said position sensor.

6. The power steering system according to claim 1, further comprising: revolution-speed difference detection means for detecting or estimating a revolution-speed difference between said right and left wheels, and whereinsaid steering-speed detection means calculates said steering speed based on said revolution-speed difference detected by said revolution-speed difference detection means.

7. The power steering system according to claim 6, wherein said revolution-speed difference detection means includes a revolution-speed sensor for detecting revolution speeds of said right and left wheels, and a calculation circuit for calculating said revolution-speed difference between said right and left wheels.

8. The power steering system according to claim 1, further comprising: a yaw-rate sensor for detecting yaw rate of said vehicle, and whereinsaid steering-speed detection means estimates said steering speed based on said yaw rate.

9. The power steering system according to claim 1, further comprising: a transverse-acceleration sensor for detecting transverse acceleration of said vehicle, and whereinsaid steering-speed detection means estimates said steering speed based on said transverse acceleration.

10. The power steering system according to claim 1, further comprising: a vehicle-speed sensor for detecting driving speed of said vehicle, and whereinsaid motor control means executes said torque control over said electric motor regardless of said steering speed, if said driving speed of said vehicle detected by said vehicle-speed sensor is higher than a predetermined value.

11. The power steering system according to claim 1, wherein said predetermined value has a hysteresis, value of said hysteresis being corrected after a state where said steering speed is higher has changed to a state where said steering speed is lower and after said state where said steering speed is lower has changed to said state where said steering speed is higher.

12. A power steering system, comprising: an electric motor for adding a steering assist force to wheels based on driving state of a vehicle, andmotor-speed detection means for detecting or estimating revolution speed of said electric motor, whereinthere is provided motor control means for executing a torque control over said electric motor if said revolution speed of said electric motor is higher than a predetermined value, and for executing a control over said electric motor based on said revolution speed of said electric motor if said revolution speed of said electric motor is lower than said predetermined value.

13. The power steering system according to claim 12, wherein said electric motor is a brushless motor having a revolution-position sensor for detecting revolution position of a rotor,said motor-speed detection means estimating said revolution speed of said electric motor based on a sensor output detected by said revolution-position sensor.

14. The power steering system according to claim 12, wherein said electric motor is a brush-attached motor,said motor-speed detection means estimating said revolution speed of said electric motor based on actual current value and actual voltage value of said electric motor.

15. The power steering system according to claim 12, further comprising: a vehicle-speed sensor for detecting driving speed of said vehicle, and whereinsaid motor control means executes said torque control over said electric motor regardless of said revolution speed of said electric motor, if said driving speed of said vehicle detected by said vehicle-speed sensor is higher than a predetermined value.

16. The power steering system according to claim 12, wherein said predetermined value has a hysteresis, value of said hysteresis being corrected after a state where a steering speed is higher has changed to a state where said steering speed is lower and after said state where said steering speed is lower has changed to said state where said steering speed is higher.

17. The power steering system according to Claim 12, further comprising: a vehicle-speed sensor for detecting driving speed of said vehicle, and whereinsaid predetermined value is corrected based on said driving speed of said vehicle detected by said vehicle-speed sensor.

18. A power steering system, comprising: a hydraulic power cylinder for assisting a steering force of a steering mechanism connected to wheels, and having a first hydraulic chamber and a second hydraulic chamber,a first pathway connected to said first hydraulic chamber,a second pathway connected to said second hydraulic chamber,a reversible pump having a pair of outlet openings continuously connected to said first pathway and said second pathway, said reversible pump selectively supplying an outlet pressure to said pair of outlet openings,an electric motor for revolving said reversible pump in a forward/reverse direction,steering-load detection means for detecting or estimating steering load of a steering wheel for executing a steering control over said wheels,steering-speed detection means for detecting or estimating steering speed of said wheels, andmotor control means for outputting, based on said steering load, a driving signal to said electric motor so as to causing said electric motor to generate a desirable hydraulic pressure,said motor control means also executing a torque control over said electric motor if said steering speed is higher than a predetermined value, and executing a control over said electric motor based on revolution speed of said electric motor if said steering speed is lower than said predetermined value.

19. The power steering system according to claim 18, further comprising: an oil-temperature sensor for detecting or estimating oil temperature of a hydraulic oil inside said system,a revolution-speed sensor for detecting said revolution speed of said electric motor or revolution speed of said reversible pump, anda hydraulic-pressure sensor for detecting or estimating said hydraulic pressure inside said hydraulic power cylinder, and whereinsaid steering-speed detection means estimates said steering speed of said wheels based on said oil temperature, said revolution speed, and said hydraulic pressure.

20. A power steering system, comprising: a hydraulic power cylinder for assisting a steering force of a steering mechanism connected to wheels and having a first hydraulic chamber and a second hydraulic chamber,a first pathway connected to said first hydraulic chamber,a second pathway connected to said second hydraulic chamber,a reversible pump having a pair of outlet openings continuously connected to said first pathway and said second pathway, said reversible pump selectively supplying an outlet pressure to said pair of outlet openings,an electric motor for revolving said reversible pump in a forward/reverse direction,steering-load detection means for detecting or estimating steering load of a steering wheel for executing a steering control over said wheels,revolution-speed detection means for detecting or estimating revolution speed of said electric motor or said reversible pump, andmotor control means for outputting, based on said steering load, a driving signal to said electric motor so as to causing said electric motor to generate a desirable hydraulic pressure,said motor control means also executing a torque control over said electric motor if said revolution speed is higher than a predetermined value, and executing a control over said electric motor based on said revolution speed of said electric motor if said revolution speed of said electric motor is lower than said predetermined value.

21. The power steering system according to claim 20, wherein said electric motor is a brushless motor having a revolution-position sensor for detecting revolution position of a rotor,said revolution-speed detection means estimating said revolution speed of said electric motor based on a sensor output detected by said revolution-position sensor.

22. The power steering system according to claim 20, wherein said electric motor is a brush-attached motor,said motor-speed detection means estimating said revolution speed of said electric motor based on actual current value and actual voltage value of said electric motor.

23. The power steering system according to claim 20, further comprising: a vehicle-speed sensor for detecting driving speed of said vehicle, and whereinsaid motor control means executes said torque control over said electric motor regardless of said revolution speed of said electric motor, if said driving speed of said vehicle detected by said vehicle-speed sensor is higher than a predetermined value.

24. The power steering system according to claim 20, wherein said predetermined value has a hysteresis, value of said hysteresis being corrected after a state where a steering speed is higher has changed to a state where said steering speed is lower and after said state where said steering speed is lower has changed to said state where said steering speed is higher.

25. The power steering system according to claim 20, further comprising: a vehicle-speed sensor for detecting driving speed of said vehicle, and whereinsaid predetermined value is corrected based on said driving speed of said vehicle detected by said vehicle-speed sensor.

26. The power steering system according to claim 20, further comprising: an oil-temperature sensor for detecting or estimating oil temperature of a hydraulic oil inside said system, and whereinsaid predetermined value is corrected based on said oil temperature.

27. The power steering system according to claim 26, wherein said predetermined value is corrected to a larger value as said oil temperature becomes higher.

28. The power steering system according to claim 20, further comprising: a hydraulic-pressure sensor for detecting or estimating said hydraulic pressure of said hydraulic power cylinder, and whereinsaid predetermined value is corrected based on said hydraulic pressure.

29. The power steering system according to claim 21, further comprising: an oil-temperature sensor for detecting or estimating oil temperature of a hydraulic oil inside said system, and whereinsaid motor control means executes a driving control over said electric motor so that actual current value of said electric motor becomes larger as said oil temperature becomes higher.

30. A power steering system, comprising: an electric motor for adding a steering assist force to wheels based on driving state of a vehicle, whereinthere is provided motor control means for executing a torque control over said electric motor if steering torque, actual steering angle, or vibration of said electric motor is larger than a predetermined value, and for executing a control over said electric motor based on revolution speed of said electric motor if said steering torque, said actual steering angle, or said vibration of said electric motor is smaller than said predetermined value.

31. The power steering system according to claim 30, wherein said vibration of said electric motor is estimated based on a change quantity of said revolution speed of said electric motor.

32. A power steering system, comprising: a hydraulic power cylinder for assisting a steering force of a steering mechanism connected to wheels, and having a first hydraulic chamber and a second hydraulic chamber,a first pathway connected to said first hydraulic chamber,a second pathway connected to said second hydraulic chamber,a reversible pump having a pair of outlet openings continuously connected to said first pathway and said second pathway, said reversible pump selectively supplying an outlet pressure to said pair of outlet openings,an electric motor for revolving said reversible pump in a forward/reverse direction,steering-load detection means for detecting or estimating steering load of a steering wheel for executing a steering control over said wheels,a hydraulic-pressure sensor for detecting a hydraulic pressure inside said system, andmotor control means for outputting, based on said steering load, a driving signal to said electric motor so as to causing said electric motor to generate a desirable hydraulic pressure,said motor control means also executing a torque control over said electric motor if a change quantity of said hydraulic pressure is larger than a predetermined value, and executing a control over said electric motor based on revolution speed of said electric motor if said change quantity of said hydraulic pressure is smaller than said predetermined value.