METHOD FOR CONTROLLING ELECTRIC POWER STEERING APPARATUS, ELECTRIC POWER STEERING APPARATUS AND VEHICLE EQUIPPED WITH THE SAME

Abstract

A method for controlling an electric power steering apparatus, the electric power steering apparatus and a vehicle equipped with the same. The method includes detecting an upper-side angle of a torsion bar; detecting a lower-side angle; setting an angle target value of an opposite side by using one of the upper-side angle or the lower-side angle; detecting an actual angle of the opposite side; and performing an angle follow-up feedback control based on a deviation between the angle target value and the actual angle.

Claims

1.-13. (canceled)

14. A method for controlling an electric power steering apparatus, comprising the steps of: detecting an upper-side angle of a torsion bar by a first angle sensor provided at a handle side of a column shaft of said electric power steering apparatus for said torsion bar; detecting a lower-side angle of said torsion bar by a second angle sensor provided at steered-wheels side of said column shaft of said electric power steering apparatus for said torsion bar; setting an angle target value of an opposite side by using one of said upper-side angle or said lower-side angle; detecting an actual angle of said opposite side; performing an angle follow-up feedback control based on a deviation between said angle target value and said actual angle, wherein an angle which sets said angle target value and a detected actual angle are said lower-side angle of said torsion bar; calculating a road-surface reaction force and a road-surface information based on said upper-side angle of said torsion bar, a motor current and a vehicle information; and calculating said angle target value based on said road-surface reaction force and said road-surface information.

15. An electric power steering apparatus that assist-controls a steering system by driving a motor based on a current command value, comprising: a first angle sensor to detect an upper-side angle of a torsion bar, which is provided at a handle side of a column shaft of said electric power steering apparatus for said torsion bar; a second angle sensor to detect a lower-side angle of said torsion bar, which is provided at steered-wheels side of said column shaft of said electric power steering apparatus for said torsion bar; a target angle calculating section to set an angle target value by using one of said upper-side angle of said torsion bar, or said lower-side angle of said torsion bar, a motor current and a vehicle information; and an angle follow-up control section to perform an angle follow-up control based on a deviation between said angle target value and an actual angle; wherein said current command value is calculated is calculated by means of said target angle calculating section and said angle follow-up control section, and wherein said target angle calculating section comprises a road-surface reaction force/road-surface information calculating section to calculate a road-surface reaction force and a road-surface information, and an angle target calculating section to calculate said angle target value based on said road-surface reaction force and said road-surface information.

16. The electric power steering apparatus according to claim 15, wherein said road-surface reaction force/road-surface information calculating section comprises a reference model to calculate a road-surface reaction force of said reference model based on said upper-side angle of said first angle sensor and a vehicle speed, and a reaction force correction road-surface information calculating section to calculate said road-surface reaction force and said road-surface information based on said road-surface reaction force of said reference model and said motor current.

17. The electric power steering apparatus according to claim 15, wherein said angle target calculating section comprises an ideal steering-force calculating section to calculate an ideal steering torque based on said road-surface reaction force and said road-surface information, and an angle target value calculating section to calculate said angle target value based on said upper-side angle of said first angle sensor and said ideal steering torque.

18. The electric power steering apparatus according to claim 16, wherein said angle target calculating section comprises an ideal steering-force calculating section to calculate an ideal steering torque based on said road-surface reaction force and said road-surface information, and an angle target value calculating section to calculate said angle target value based on said upper-side angle of said first angle sensor and said ideal steering torque.

19. The electric power steering apparatus according to claim 15, wherein resolutions of said first and second angle sensors are respectively 0.02° or less.

20. The electric power steering apparatus according to claim 16, wherein resolutions of said first and second angle sensors are respectively 0.02° or less.

21. The electric power steering apparatus according to claim 17, wherein resolutions of said first and second angle sensors are respectively 0.02° or less.

22. The electric power steering apparatus according to claim 18, wherein resolutions of said first and second angle sensors are respectively 0.02° or less.

23. An electric power steering apparatus that assist-controls a steering system with engagement of a worm and a worm wheel by driving a motor based on a current command value, comprising: a first angle sensor to detect an upper-side angle of a torsion bar, which is provided at a handle side of a column shaft of said electric power steering apparatus for said torsion bar; a second angle sensor to detect a lower-side angle of said torsion bar, which is provided at steered-wheels side of said column shaft of said electric power steering apparatus for said torsion bar; a target angle calculating section to set an angle target value by using one of said upper-side angle of said torsion bar or said lower-side angle of said torsion bar, a motor current and a vehicle information; and an angle follow-up control section to perform an angle follow-up control based on a deviation between said angle target value and an actual angle; wherein said current command value is calculated by means of said target angle calculating section and said angle follow-up control section, wherein a road-surface reaction force and a road-surface information are calculated based on said upper-side angle of said torsion bar, a motor current and a vehicle information, wherein said angle target value is calculated based on said road-surface reaction force and said road-surface information, and wherein an engagement gap of said worm and said worm wheel is zero or minus.

24. The electric power steering apparatus according to claim 23, wherein said worm is rigidly fixed in directions other than a rotational direction of a rotational shaft.

25. The electric power steering apparatus according to claim 23, wherein a support bearing of said worm is deep groove ball bearings and four-point-contact ball bearings.

26. The electric power steering apparatus according to claim 24, wherein a support bearing of said worm is deep groove ball bearings and four-point-contact ball bearings.

27. The electric power steering apparatus according to claim 23, wherein a support bearing of said worm comprises two deep groove ball bearings, and a play of said deep groove ball bearings is zero or minus by preload in an axial direction using a rigid body at a time of assembling.

28. The electric power steering apparatus according to claim 24, wherein a support bearing of said worm comprises two deep groove ball bearings, and a play of said deep groove ball bearings is zero or minus by preload in an axial direction using a rigid body at a time of assembling.

29. A vehicle equipped with said electric power steering apparatus according to claim 15.

30. A vehicle equipped with said electric power steering apparatus according to claim 23.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the accompanying drawings:

[0026] FIG. 1 is a schematic structural diagram of a conventional electric power steering apparatus;

[0027] FIG. 2 is a block diagram showing an example of a control structure of a control unit (ECU) of the electric power steering apparatus;

[0028] FIG. 3 is a block diagram of an exemplary structure according to the embodiment of the present invention;

[0029] FIG. 4 is a structural diagram showing an example of EPS-steering system and sensors according to the embodiment of the present invention;

[0030] FIG. 5 is a block diagram showing an example structure of road-surface reaction force and road-surface information calculating section;

[0031] FIG. 6 is a block diagram showing an example structure of an angle target calculating section;

[0032] FIG. 7 is a cross-sectional view showing an example of a bearing structure of a reduction mechanism; and

[0033] FIG. 8 is a cross-sectional view showing an example of a bearing structure of a reduction mechanism.

MODE FOR CARRYING OUT THE INVENTION

[0034] In the present invention, an assist-control of an electric power steering apparatus is separated into a target angle calculating section which is affected to a feeling of a driver and an angle follow-up control section which is affected to a responsibility, a stability and an external disturbance suppression. An item on the feeling is performed by the target angle calculating section, and the responsibility, the stability and the external disturbance suppression are performed by the angle follow-up control section. In this connection, there is no necessity to provide individual compensating section such as a friction compensation, an inertia compensation or the like, the compensation for the secular variation of the mechanical portion is performed by the feedback control of the angle follow-up control, and it is possible to always maintain the feeling of the target angle calculated in the target angle calculating section. Further, it is possible to easily realize an improvement of an on-center feeling, and influences of another function due to a functional addition or the like and a stability become clear.

[0035] Further, in the present invention, an engagement gap (backlash) of a worm and a worm wheel is set to zero or minus in a hardware structure of a reduction mechanism, and the degree of freedom other than a rotational direction does not almost exist by fixing the worm rigidly. Therefore, a teeth rattling sound does not occur, it is possible to raise rigidity from a motor output angle to a lower-side angle of a torsion bar and to realize a hardware mechanism to readily control. In this connection, the hardware mechanism can contribute to an improvement in performance of the angle follow-up control, and an improvement in the feeling is desired.

[0036] Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings.

[0037] FIG. 3 is a block diagram showing an embodiment of the present invention, and a control section to perform an assist-control is separated into a target angle calculating section 110 and an angle follow-up control section 120. An item on a feeling is performed by the target angle calculating section 110, and a control of a responsibility, a stability and an external disturbance suppression is performed by the angle follow-up control section 120. The target angle calculating section 110 comprises a road-surface reaction force/road-surface information calculating section 111 and an angle target calculating section 112. The road-surface reaction force/road-surface information calculating section 111 calculates a road-surface reaction force Fr and a road-surface information (a friction coefficient) μ based on a handle angle θ.sub.1 detected by an upper-side angle sensor, a motor current Im detected by a current detector and a vehicle speed Vs serving as a vehicle information. The angle target calculating section 112 calculates an angle target value θ.sub.2ref based on the road-surface reaction force Fr and the road-surface information (the friction coefficient) μ. In a case of setting a torque (a torsion bar torque) to feel for hands, the angle target value θ.sub.2ref is calculated by using the handle angle θ.sub.1 and a spring constant Kt of a torsion bar. The angle follow-up control section 120 is an actual angle feedback control to control based on a deviation between the angle target value θ.sub.2ref obtained at a subtracting section 101 and an actual angle θ.sub.2 detected by an EPS-steering system/vehicle system 100, and a motor current command value Iref obtained in the angle follow-up control section 120 is inputted into an adding section 102. External disturbance 103 is also inputted into the adding section 102, and the addition result is inputted into the EPS-steering system/vehicle system 100 and then the electric power steering apparatus performs the assist-control.

[0038] FIG. 4 is a structural diagram of the EPS-steering system and a mounting example of various sensors according to the embodiment of the present invention, and the road-surface reaction force Fr and the road-surface information μ act to the steered wheels 8L and 8R. The upper-side angle sensor (angle θ.sub.1) is provided to a handle side of a column shaft 2 having a torsion bar 2A, and a lower-side angle senor (angle θ.sub.2) is provided to the steered wheels side of the column shaft 2. Any resolution of the upper-side and lower angle sensors is 0.02° or less, and the motor current Im of the motor 20 is detected by the current detector.

[0039] FIG. 5 is a block diagram showing the structure of the road-surface reaction force/road-surface information calculating section 111, and a road-surface reaction force Fra of a reference model (a standard road-surface) 111-1 is calculated by using the angle θ.sub.1 (≈ the handle angle) of the upper-side angle sensor of the torsion bar 2A and the vehicle speed V.sub.s. At this time, a reference motor current is also calculated. Then, by comparing the reference motor current with the actual motor current Im, a reaction force correction road-surface information calculating section 111-2 corrects the road-surface reaction force Fra and calculates the road-surface information (the friction coefficient) μ. As stated-above, the road-surface reaction force Fr and the road-surface information (the friction coefficient) μ can be calculated with a few number of information.

[0040] Further, by inputting a yaw rate V, a lateral acceleration (G-force) G, a sideslip angle or the like as the vehicle information into the reaction force correction road-surface information calculating section 111-2, the more precise road-surface reaction force Fr may be calculated. Furthermore, the road-surface reaction force Fr may directly be measured by using a tire sensor and a rack-axial force measuring sensor. By calculating the road-surface reaction force accurately, the road-surface information is appropriately transmitted to the driver.

[0041] In addition, FIG. 6 is a block diagram showing a structure of the angle target calculating section 112, and the angle target calculating section 112 comprises an ideal steering-force calculating section 112-1 and an angle target value calculating section 112-2. The ideal steering-force calculating section 112-1 calculates an ideal steering torque Tref, which should be transmitted to the driver, based on the road-surface reaction force Fr and the road-surface information μ. The ideal steering torque Tref is inputted into the angle target value calculating section 112-2, and the angle target value θ.sub.2ref is calculated in the angle target value calculating section 112-2 based on the information of the angle θ.sub.1 of the upper-side angle sensor.

[0042] As stated-above, in comparison to the conventional torque control, according to the present invention, the target angle calculating section 110 to perform an item which influences on the feeling and the angle follow-up control section 120 to perform items which influence on the responsibility, the stability or the like are separated. Consequently, by setting a band of the angle follow-up control section 120 to a required value (the responsibility, the external disturbance suppression or the like), the friction compensation and the inertia compensation which are individually set in the conventional apparatus, are not required. Further, since the secular variation or the like in mechanical portion is compensated by the feedback control of the angle follow-up control, the feeling calculated (designed) in the target angle calculating section 110 is always realized.

[0043] As a result, an improvement in the on-center feeling which is a technical problem up to this time and is difficult to be tuned, is easily realized. Since the target angle calculating section 110 and the angle follow-up control section 120 are separated, the influence on another function due to the functional addition and the stability becomes clear.

[0044] In addition, the electric power steering apparatus of the present invention does not decide the assist force from the detected torque as prior arts, and calculates the assist torque based on the road-surface information. Accordingly, the driver appropriately feels the road-surface reaction force Fr and the road-surface information μ.

[0045] In the torque target value control such as disclosed in Patent Document 1, the torque target value is set by using the handle angle sensor and the torque sensor. However, since the resolution of the handle angle sensor is normally about 0.1°, this resolution is too rough to generate the target value. Because the feeling does not change when the handle angle is within 0.1°, the driver feels uncomfortable. On the contrary, in the present invention, since the resolutions of two angle sensors provided by inclosing the torsion bar 2A are respectively 0.02° or less, it is possible to set more accurately the target value and to realize the control without uncomfortable. Further, because the apparatus of the present invention does not control the torque target value and performs the angle target value control, it is capable of performing as it is the position control, without newly providing the position control section, against the position command from the superior (vehicle) in the automatic operation which is marked as the future technology. Furthermore, since the target value is the lower-side angle of the torsion bar, it is possible to control with a value (in a state that the influence on the torsion of the torsion bar is excluded) near a cutting angle of the vehicle's tire.

[0046] Although the column EPS is described in the above embodiment according to the present invention, it is possible to apply to a pinion EPS, a dual pinion EPS and a ball-screw pinion EPS.

[0047] On the other hand, in the engagement of the worm and the worm wheel which constitute the conventional reduction mechanism, there are problems that the teeth rattling sound occurs if the gap (backlash) exists, and the friction torque increases and then the feeling near the handle neutral position is deteriorated when the gap is too small. Accordingly, it is necessary to control the parts precisely and assemble them accurately.

[0048] For the above problem, in the present invention, the engagement gap (backlash) of the worm and the worm wheel is set to zero or minus as the hardware structure of the reduction mechanism, and the degree of freedom other than a rotational direction does not almost exist by fixing the worm rigidly with the bearings. That is, a play of the worm support bearings does not almost exist and the degree of freedom other than the rotational direction of the worm is nearly zero.

[0049] By taking the above structure, it is possible to raise the rigidity from a motor output angle to the lower-side angle senor θ.sub.2 of the torsion bar and to realize the readily control hardware. Therefore, it is possible to contribute to the performance improvement of the angle follow-up control, and an improvement of the feeling is desired. Further, since the engagement gap of the worm and the worm wheel is set to zero or minus, the teeth rattling sound does not occur. Although there is no fear on the occurrence of the teeth rattling sound, the large friction is badly affected to the feeling. However, because the hardware constitutes the structure of the above separated control, the friction is compensated by the angle follow-up control and the improvement of the feeling is realized.

[0050] FIGS. 7 and 8 show examples of the bearing structure of the reduction mechanism. FIG. 7 illustrates “a deep groove ball bearing+a four-point contact ball bearing”, and FIG. 8 does “a deep groove ball bearing+a deep groove ball bearing+a preload in the axial direction”. In the bearing structure of FIG. 7, a load in the axial direction is supported by the four-point contact ball bearing 303 and an axial gap does not almost exist. Further, in the bearing structure of FIG. 8, the load in the axial direction is supported by the two ball bearings 304 and 305, and the bearings are fixed to the reduction mechanism in size such that the axial gap does not exist by means of the preload pressure. The preload pressure is performed by using a rigid body such as a retaining ring and a nut.

[0051] For the both examples, the worm 301 is rigidly fixed to the output shaft 20A of the motor 20 and the rubber damper does not exist in the axial direction. The worm 301 does not move in the axial direction and the degree of the freedom is only the rotational direction. Therefore, the rigidities in the axial and radial directions are high. Further, the worm wheel 302 is engaged with the worm 301, and the engagement gap is set to zero or minus.

[0052] As stated-above, since the worm 301 is rigidly fixed (the degree of the freedom is only the rotational direction) and the engagement gap (backlash) between the worm 301 and the worm wheel 302 does not exist, the mechanical rigidity from the output shaft 20A of the motor 20 to the lower-side angle senor of the torsion bar becomes high. Accordingly, the performance (the responsibility, the stability and so on) of the angle follow-up control is improved and the feeling is also improved. If the rubber damper and the spring preload pressure exist in the axial and radial directions, the rigidity from the motor output decreases due to the rubber and the responsibility is deteriorated. Then, the control design is restricted to this mechanical rigidity. It is concerned that the feel is deteriorated because of increases in the friction and the inertia according to the present structure. Since the overall control section is compensated by the improvement of the responsibility of the angle follow-up control, a more comfortable feeling is realized.

EXPLANATION OF REFERENCE NUMERALS

[0053] 1 handle [0054] 2 column shaft (steering shaft, handle shaft) [0055] 3 reduction mechanism [0056] 10 torque sensor [0057] 12 vehicle speed sensor [0058] 14 steering angle sensor [0059] 20 motor [0060] 30 control unit (ECU) [0061] 100 EPS-steering system/vehicle system [0062] 110 target angle calculating section [0063] 111 road-surface reaction force/road-surface information calculating section [0064] 111-1 reference model (standard road-surface) [0065] 111-2 reaction force correction road-surface information calculating section [0066] 112 angle target calculating section [0067] 112-1 ideal steering-force calculating section [0068] 112-2 angle target value calculating section [0069] 120 angle follow-up control section