Steering apparatus for vehicle

Abstract

A steering apparatus for a vehicle, which can reduce the steering load and allows accurate steering angle control, is provided. In the steering apparatus for a vehicle, an estimation unit estimates a mechanical impedance upon a driver's steering manipulation. A control unit controls the steering reaction force of a steering wheel based on the estimated mechanical impedance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the arrangement of a steering apparatus according to the first embodiment;

FIG. 2 is a block diagram showing the arrangement of a control unit according to the first embodiment;

FIG. 3 is a flowchart showing steering reaction force control processing according to the first embodiment;

FIGS. 4A to 4C show examples of the data structure of a human impedance calculation LUT according to the first embodiment;

FIG. 5 is a flowchart showing an example of the steering reaction force change processing according to the first embodiment;

FIG. 6 is a schematic diagram showing the arrangement of the steering apparatus according to a modification of the first embodiment;

FIG. 7 is a schematic diagram showing the arrangement of a steering apparatus according to the second embodiment;

FIG. 8 is a flowchart showing the steering reaction force control processing according to the second embodiment;

FIG. 9 is a flowchart showing a practical example of the processing for calculating a human impedance including a disturbance impedance according to the second embodiment;

FIGS. 10A to 10C are graphs showing examples of a measurement signal, steering angle sensor output, and steering torque sensor output according to the second embodiment;

FIG. 11 is a flowchart showing an example of the calculation sequence of a rigidity coefficient, viscosity coefficient, and inertia coefficient according to the second embodiment;

FIG. 12 is a view for explaining the calculation sequence of the rigidity coefficient, viscosity coefficient, and inertia coefficient according to the second embodiment;

FIGS. 13A to 13C are graphs for explaining the calculation sequence of the rigidity coefficient, viscosity coefficient, and inertia coefficient according to the second embodiment;

FIG. 14 is a flowchart showing a practical example of the processing for calculating disturbance impedance according to the second embodiment;

FIG. 15 is a flowchart showing a practical example of the processing for calculating human impedance free from the influence of any disturbance according to the second embodiment;

FIGS. 16A to 16C are graphs showing examples of a measurement signal, steering angle sensor, and steering torque sensor according to the fourth embodiment;

FIGS. 17A1 to 17C2 are graphs showing examples of a measurement signal, steering angle sensor, and steering torque sensor according to the fifth embodiment;

FIG. 18 is a graph showing an example of an envelope of the frequency spectrum of a steering angle sensor output signal according to the fifth embodiment;

FIGS. 19A to 19C are graphs showing examples of a measurement signal, steering angle sensor, and steering torque sensor according to the sixth embodiment;

FIG. 20 is a flowchart showing a practical example of the processing for calculating human impedance including disturbance impedance according to the seventh embodiment;

FIG. 21 is a flowchart showing a practical example of the processing for calculating human impedance including disturbance impedance according to the eighth embodiment;

FIGS. 22A and 22B are views for different steering behaviors depending on drivers;

FIG. 23 is a flowchart showing a practical example of the processing for calculating human impedance including a disturbance impedance according to the ninth embodiment; and

FIGS. 24A to 24F are graphs for explaining the processing for calculating human impedance including a disturbance impedance according to the ninth embodiment.

Claims

1. A steering apparatus for a vehicle, comprising: an estimation unit configured to estimate a mechanical impedance on a driver's steering manipulation; anda control unit configured to control a steering reaction force of a steering wheel based on the estimated mechanical impedance.

2. The apparatus according to claim 1, further comprising: a motor configured to turn the steering wheel; anda generation unit configured to generate a drive signal as a measurement signal required to drive said motor so as to forcibly turn the steering wheel a predetermined amount,wherein said estimation unit estimates the mechanical impedance of the driver based on an amount of steering manipulation which is applied in response to the turn of the steering wheel by driving said motor according to the measurement signal.

3. The apparatus according to claim 2, further comprising: a torque sensor configured to detect a rotational torque on the steering wheel; anda steering angle sensor configured to detect a steering angle of the steering wheel,wherein said estimation unit estimates the mechanical impedance based on outputs from said torque sensor and said steering angle sensor.

4. The apparatus according to claim 3, wherein the measurement signal is a pulse signal.

5. The apparatus according to claim 4, wherein the amplitude of the pulse signal is gradually increased.

6. The apparatus according to claim 4, wherein the pulse width is not more than 0.4 sec, and a steering angle change at that time is not more than 5° or a steering angle torque is not less than 1.5N nor more than 3N.

7. The apparatus according to claim 6, wherein the pulse width is about 0.2 sec, and the steering angle change at that time is about 2° or the steering torque is about 2N.

8. The apparatus according to claim 3, wherein the measurement signal is a signal corresponding to three-band frequencies which respectively correspond to an inertia term, a viscosity term, and a rigidity term that represent characteristics of the mechanical impedance.

9. The apparatus according to claim 8, wherein said estimation unit applies an estimation method using a spectrum of an output signal from said torque sensor.

10. The apparatus according to claim 3, wherein the measurement signal is a signal which simulates a road surface reaction force.

11. The apparatus according to claim 4, further comprising: a travel state detection unit configured to detect a travel state of the vehicle; anda correction unit configured to correct the pulse signal in accordance with the travel state of the vehicle detected by said travel state detection unit.

12. The apparatus according to claim 11, wherein the travel state includes a road surface μ, a turn state, and a vehicle velocity.

13. The apparatus according to claim 4, further comprising: a driver's state detection unit configured to detect a driver's state; anda correction unit configured to correct the pulse signal in accordance with the driver's state detected by said driver's state detection unit.

14. The apparatus according to claim 13, wherein the driver's state includes a state indicating whether the driver holds the steering wheel with a single hand or both hands, a tension level of the driver, and a seating posture.

15. The apparatus according to claim 14, wherein the driver's state further includes gripping positions and a gripping strength of the steering wheel.

16. The apparatus according to claim 4, further comprising: a physical construction estimation unit configured to estimate a driver's physical construction; anda correction unit configured to correct the pulse signal in accordance with the driver's physical construction estimated by said physical construction estimation unit.

17. The apparatus according to claim 2, further comprising: a determination unit configured to determine whether or not the mechanical impedance can be stably estimated; andan estimation inhibition unit configured to, when said determination unit determines that the mechanical impedance cannot be stably estimated, inhibit said estimation unit from estimating the mechanical impedance.

18. The apparatus according to claim 17, wherein said determination unit determines based on at least one of a tension level of the driver and a road surface μ whether or not the mechanical impedance can be stably estimated.

19. The apparatus according to claim 2, wherein said generation unit generates the measurement signal at one of the timings of an engine start-up timing, of during a steady turn, and of after an elapse of a predetermined period of time of continuous travel.

20. The apparatus according to claim 19, wherein said generation unit does not generate the measurement signal when the driver is not gripping the steering wheel at the engine start-up timing.

21. The apparatus according to claim 2, wherein when the vehicle is a vehicle which uses an electric motor as a drive source in addition to an engine, said generation unit generates the measurement signal at one of timings of a start-up timing of the electric motor, and of during a steady turn and after an elapse of a predetermined period of time of continuous travel.

22. The apparatus according to claim 1, further comprising: a detection unit configured to detect the amount of steering manipulation of the steering wheel which is done at a predetermined timing,wherein said estimation unit estimates the mechanical impedance of the driver based on the manipulation amount detected by said detection unit.

23. The apparatus according to claim 22, further comprising: a torque sensor configured to detect a rotational torque on the steering wheel; anda steering angle sensor configured to detect a steering angle of the steering wheel,wherein said estimation unit estimates the mechanical impedance based on outputs from said torque sensor and said steering angle sensor.

24. The apparatus according to claim 22, further comprising: a road surface drop detection unit configured to detect a road surface drop,wherein the predetermined timing falls within a predetermined period after said road surface drop detection unit detects the road surface drop.

25. The apparatus according to claim 23, wherein the predetermined timing is a timing when an output from said torque sensor changes to be larger than a predetermined value within a predetermined period of time or when an output from said steering angle sensor changes to be larger than a predetermined value within a predetermined period of time.

26. The apparatus according to claim 22, wherein said detection unit superposes a characteristic signal required to measure the mechanical impedance on steering characteristics, and detects the amount of steering manipulation in response to the turn of the steering wheel based on the steering characteristics superposed with the characteristic signal.

27. The apparatus according to claim 1, further comprising: a storage unit configured to store a lookup table which describes a relationship between physical constructions of drivers and mechanical impedances of the drivers associated with steering manipulations; anda detection unit configured to detect a physical construction of the driver,wherein said estimation unit estimates the mechanical impedance corresponding to the physical construction detected by said detection unit using the lookup table stored in said storage unit.

28. The apparatus according to claim 27, wherein said detection unit detects the physical construction based on one of a telescopic position, a steer position, and a seat slide position.

29. The apparatus according to claim 27, wherein said detection unit includes a unit configured to read information of a physical construction of a driver from a detachable storage medium in which the information is stored.

30. The apparatus according to claim 27, wherein said detection unit detects the physical construction based on an image of the driver detected by an image sensor arranged to face the driver.

31. The apparatus according to claim 27, wherein the lookup table includes an inertia coefficient, a viscosity coefficient, and a rigidity coefficient as characteristic parameters of the mechanical impedance for each physical construction of a driver, and said estimation unit includes a unit configured to calculate a steering torque to be applied by the driver using the inertia coefficient, the viscosity coefficient, and the rigidity coefficient corresponding to the physical construction detected by said detection unit.

32. The apparatus according to claim 1, wherein said estimation unit estimates the mechanical impedance of the driver based on one of the amount of steering manipulation, which appears as a reaction of the driver when the steering wheel is forcibly turned by a predetermined amount, and the amount of steering manipulation, which is made at a predetermined timing, said apparatus further comprises a disturbance removal unit configured to remove a disturbance, which is included in the mechanical impedance estimated by said estimation unit and is received from the vehicle, andsaid control unit controls the steering reaction force of the steering wheel based on the mechanical impedance from which the disturbance is removed by said disturbance removal unit.

33. The apparatus according to claim 32, wherein said disturbance removal unit includes: a disturbance measurement signal generation unit configured to generate a disturbance measurement signal required to drive said motor so as to forcibly turn the steering wheel while the driver does not grip the steering wheel;a disturbance estimation unit configured to estimate the disturbance based on a steering behavior while the driver does not grip the steering wheel upon turning of the steering wheel driven by said motor in accordance with the disturbance measurement signal; anda subtraction unit configured to subtract the disturbance estimated by said disturbance estimation unit from the mechanical impedance estimated by said estimation unit.

34. The apparatus according to claim 32, wherein an operation of said disturbance removal unit is inhibited when the vehicle is not at a stop or when the driver does not grip the steering wheel.

35. The apparatus according to claim 32, wherein an impedance of the disturbance is set to be a pre-stored predetermined value when a high-speed straight travel is in progress or when a steady turn within a constant angle range is in progress.

36. The apparatus according to claim 33, wherein said subtraction unit subtracts an average value of a plurality of disturbances estimated by said disturbance estimation unit from the mechanical impedance estimated by said estimation unit.

37. The apparatus according to claim 33, wherein said subtraction unit excludes the disturbance from an object to be subtracted when a value indicating the disturbance estimated by said disturbance estimation unit falls outside a predetermined range.

38. The apparatus according to claim 1, wherein said estimation unit estimates the mechanical impedance of the driver based on one of the amount of steering manipulation, which appears as a reaction of the driver when the steering wheel is forcibly turned by a predetermined amount, and the amount of steering manipulation, which is made at a predetermined timing, and said apparatus further comprising:a setting unit configured to set a steering reaction force of the steering wheel based on the mechanical impedance estimated by said estimation unit; anda change unit configured to change the steering reaction force set by said setting unit based on a drive state of the vehicle.

39. The apparatus according to claim 38, wherein said change unit increases the amount of change in steering reaction force at the beginning of travel, and decreases the amount of change during travel.

40. The apparatus according to claim 38, further comprising: an unit configured to check if a driver is the same driver as in a previous processing,wherein said change unit decreases the amount of change in the steering reaction force when the driver is the same driver as in the previous processing.

41. The apparatus according to claim 38, wherein said change unit gradually changes the steering reaction force during travel.

42. The apparatus according to claim 38, wherein said change unit changes the steering reaction force during straight travel.