ELECTRIC POWER STEERING APPARATUS

Abstract

An electric power steering apparatus including a torque sensor to detect a steering torque and a motor control unit to control a motor that applies an assist torque to a steering system of a vehicle, including: a function to switch a control system of the motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle of a steering in accordance with a predetermined switching trigger. The fade processing time from the torque control system to the position/speed control system and the fade processing time from the position/speed control system to the torque control system are individually set.

Claims

1-14. (canceled)

15. An electric power steering apparatus including a torque sensor to detect a steering torque and a motor control unit to control a motor that applies an assist torque to a steering system of a vehicle, comprising: a function to switch a control system of said motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle of a steering in accordance with a predetermined switching trigger, wherein, when said automatic steering command is turned ON, a fade processing is started and a post-gradual change steering-angle command value in a position/speed control is gradually changed from an actual steering angle to a steering angle command value, and wherein, a level of said assist torque in a torque control is gradually changed from 100% to 0% and then said position/speed control system is operated.

16. The electric power steering apparatus according to claim 15, wherein said predetermined switching trigger is ON/OFF of an automatic steering command.

17. The electric power steering apparatus according to claim 15, wherein said predetermined switching trigger is ON/OFF of a switching command given by an internal judgment of said steering torque.

18. The electric power steering apparatus according to claim 15, wherein said predetermined switching trigger is performed by an automatic steering execution judging section.

19. The electric power steering apparatus according to claim 15, further comprising an external disturbance observer to compensate inertia and friction of a handle.

20. The electric power steering apparatus according to claim 15, wherein said post-gradual change steering-angle command value in said position/speed control is gradually changed by an exponential curve, and said level of the assist torque is gradually changed linearly.

21. The electric power steering apparatus according to claim 15, wherein a fade characteristic of said fade processing can be freely tuned.

22. The electric power steering apparatus according to claim 15, wherein a fade processing time 1 from said torque control system to said position/speed control system and a fade processing time 2 from said position/speed control system to said torque control system are different.

23. The electric power steering apparatus according to claim 22, wherein said fade processing time 2 is shorter than said fade processing time 1.

24. The electric power steering apparatus according to claim 18, wherein said automatic steering execution judging section comprises: a calculating section to calculate an angular speed and an angular acceleration by inputting a steering angle command value; a map judging section to judge each of said steering angle command value, said angular speed and said angular acceleration with a judging map corresponding to a vehicle speed; and a diagnosing section to diagnose based on a judgement result from said map judging section.

25. The electric power steering apparatus according to claim 19, wherein said external disturbance observer estimates an external-disturbance estimation torque from a difference between an output of a steering inverse model of the steering system and an output of an LPF to limit a band.

26. The electric power steering apparatus according to claim 25, wherein values of inertia and friction of said steering system are greater than or equal to values of inertia and friction of said steering inverse model, respectively.

27. An electric power steering apparatus including a torque sensor to detect a steering torque and a motor control unit to control a motor that applies an assist torque to a steering system of a vehicle, comprising: a function to switch a control system of said motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle of a steering in accordance with a predetermined switching trigger, wherein, when said automatic steering command is turned OFF, a fade processing is started and a post-gradual change steering-angle command value in a position/speed control is gradually changed from a steering angle command value to an actual steering angle, and wherein, a level of the assist torque in a torque control is gradually changed from 0% to 100% and then said torque control system is operated.

28. The electric power steering apparatus according to claim 27, wherein said predetermined switching trigger is ON/OFF of an automatic steering command.

29. The electric power steering apparatus according to claim 27, wherein said predetermined switching trigger is ON/OFF of a switching command given by an internal judgment of said steering torque.

30. The electric power steering apparatus according to claim 27, wherein said predetermined switching trigger is performed by an automatic steering execution judging section.

31. The electric power steering apparatus according to claim 27, further comprising an external disturbance observer to compensate inertia and friction of a handle.

32. The electric power steering apparatus according to claim 27, wherein said post-gradual change steering-angle command value in said position/speed control is gradually changed by an exponential curve, and said level of the assist torque is gradually changed linearly.

33. The electric power steering apparatus according to claim 27, wherein a fade characteristic of said fade processing can be freely tuned.

34. The electric power steering apparatus according to claim 27, wherein a fade processing time 1 from said torque control system to said position/speed control system and a fade processing time 2 from said position/speed control system to said torque control system are different.

35. The electric power steering apparatus according to claim 34, wherein said fade processing time 2 is shorter than said fade processing time 1.

36. The electric power steering apparatus according to claim 30, wherein said automatic steering execution judging section comprises: a calculating section to calculate an angular speed and an angular acceleration by inputting a steering angle command value; a map judging section to judge each of said steering angle command value, said angular speed and said angular acceleration with a judging map corresponding to a vehicle speed; and a diagnosing section to diagnose based on a judgement result from said map judging section.

37. The electric power steering apparatus according to claim 31, wherein said external disturbance observer estimates an external-disturbance estimation torque from a difference between an output of a steering inverse model of the steering system and an output of an LPF to limit a band.

38. The electric power steering apparatus according to claim 37, wherein values of inertia and friction of said steering system are greater than or equal to values of inertia and friction of said steering inverse model, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the accompanying drawings:

[0027] FIG. 1 is a configuration diagram illustrating an overview of an electric power steering apparatus (column system);

[0028] FIG. 2 is a block diagram illustrating an exemplary configuration of a control system of the electric power steering apparatus;

[0029] FIG. 3 is a block diagram illustrating an exemplary configuration of a control system of the electric power steering apparatus having a parking assist mode (automatic steering) function;

[0030] FIG. 4 is a characteristic diagram illustrating operation system of a conventional electric power steering apparatus;

[0031] FIG. 5 is a configuration diagram illustrating an overview of an electric power steering apparatus (single pinion system);

[0032] FIG. 6 is a configuration diagram illustrating an overview of an electric power steering apparatus (dual pinion system);

[0033] FIG. 7 is a configuration diagram illustrating an overview of an electric power steering apparatus (dual pinion system (exemplary variation));

[0034] FIG. 8 is a configuration diagram illustrating an overview of an electric power steering apparatus (coaxial rack system);

[0035] FIG. 9 is a configuration diagram illustrating an overview of an electric power steering apparatus (rack offset system);

[0036] FIG. 10 is a block diagram illustrating an exemplary configuration of the present invention;

[0037] FIG. 11 is a block diagram illustrating an exemplary configuration of an automatic steering execution judging section;

[0038] FIGS. 12A to 12C are characteristic diagrams illustrating exemplary judging maps (steering angle command value, angular speed and angular acceleration);

[0039] FIG. 13 is a diagram illustrating relationship between an example of mounting sensors and an actual steering angle used in the present invention;

[0040] FIG. 14 is a flowchart illustrating exemplary operations of the present invention;

[0041] FIG. 15 is a flowchart illustrating a part of exemplary operations of the automatic steering judging section;

[0042] FIG. 16 is a timing chart illustrating exemplary operations of the present invention;

[0043] FIGS. 17A and 17B are characteristic diagrams for explaining effects (fade processing) of the present invention;

[0044] FIGS. 18A and 18B are characteristic diagrams for explaining effects (fade processing) of the present invention;

[0045] FIG. 19 is a timing chart illustrating exemplary operations of another embodiment of the present invention;

[0046] FIG. 20 is a block diagram illustrating an exemplary configuration of an external disturbance observer; and

[0047] FIGS. 21A and 21B are characteristic diagrams illustrating exemplary effects of providing the external disturbance observer.

MODE FOR CARRYING OUT THE INVENTION

[0048] In a conventional torque gradual-change control in the electric power steering apparatus, there are problems such as that control is not smoothly switched upon switching between a torque control and a position/speed control and that unintentional self-steer occurs. In the present invention, therefore, a processing that smoothly switches the control without self-steer is implemented by gradually changing a control torque of a torque control and a command value of a position/speed control.

[0049] The present invention includes a function to switch control systems of a motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle upon steering in accordance with a predetermined switching trigger (e.g. an automatic steering command) and implements smooth a fade processing without self-steer.

[0050] Further, in the present invention as compared to a fade processing time (e.g. 500 to 1000 [ms]) to perform a fade processing from the torque control of the normal steering to the position control of the automatic steering, a fade processing time (e.g. 20 to 100 [ms]) from the position control to the torque control is set shorter. Accordingly, the control is switched over relatively slowly so that a driver does not feel uncomfortable upon the fade processing from the torque control to the position/speed control and the control can be switched over in a short time and intention of the driver can be promptly conveyed for avoiding danger upon the fade processing from the position/speed control to the torque control.

[0051] Furthermore, the present invention provides an external disturbance observer to compensate inertia or friction of the handle and therefore this allows a driver to easily intervene in the automatic steering by steering.

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0053] The present invention may be applied to, other than the column system shown in FIG. 1, a single pinion system a schematic configuration of which is shown in FIG. 5, a dual pinion system an overview of which is shown in FIG. 6, a dual pinion system (exemplary variation) a schematic configuration of which is shown in FIG. 7, a rack coaxial system an overview of which is shown in FIG. 8, and a rack offset system an overview of which is shown in FIG. 9. The below descriptions will be given on the column system.

[0054] FIG. 10 is a diagram illustrating an exemplary configuration of the present invention, and the steering torque Ts is inputted into a torque control section 102 and an automatic steering execution judging section 120. A steering assist torque command value Tc from the torque control section 102 is inputted into a torque gradual-changing section 103. A steering angle command value θtc from a CAN or the like is inputted into the automatic steering execution judging section 120, the steering angle command value θt after calculation processing at the automatic steering execution judging section 120 is inputted into a steering-angle command value gradual-changing section 100, and a post-gradual change steering-angle command value θm from the steering-angle command value gradual-changing section 100 is inputted into a position/speed control section 101 together with an actual steering angle θr. A steering-assist torque command value Tg after the torque gradual-change and a position/speed control torque command value Tp from the position/speed control section 101 are inputted into an adding section 104 and the addition result from the adding section 104 is outputted as a motor torque command value. The motor torque command value is inputted into a current control system 130, and a motor 131 is driven and controlled through the current control system 130.

[0055] The automatic steering execution judging section 120 outputs ON/OFF of the automatic steering command being a judgment (diagnosis) result. The “ON/OFF” of the automatic steering command is inputted into the torque gradual-changing section 103 and the steering-angle command value gradual-changing section 100.

[0056] The automatic steering execution judging section 120 has a configuration as illustrated in FIG. 11, the steering angle command value θtc is inputted into a calculating section 121, and the calculating section 121 calculates an angular speed ωtc and an angular acceleration αtc based on the steering angle command value θtc. The angular speed ωtc and the angular acceleration αtc are inputted into a map judging section 122 to judge using a judging map. The map judging section 122 is also inputted with the steering angle command value θtc and a vehicle speed Vs. The map judging section 122 includes a judging map #1 for a steering angle command value θtc having a characteristic A1 or B1 as shown in FIG. 12A, a judging map #2 for an angular speed ωtc having a characteristic A2 or B2 as shown in FIG. 12B, and a judging map #3 for an angular acceleration αtc having a characteristic A3 or B3 as shown in FIG. 12C.

[0057] The characteristic of the judging map #1 with respect to the steering angle command value θtc is at a constant value θtc.sub.0 until a vehicle speed Vs.sub.1 of a low speed and decreases as the characteristic A1 or B1 in a range more than or equal to the vehicle speed Vs.sub.1. The characteristic of the judging map #2 with respect to the angular speed ωtc is at a constant value ωc.sub.0 until a vehicle speed Vs.sub.2 of a low speed and decreases as the characteristic A2 or B2 in a range more than or equal to the vehicle speed Vs.sub.2. Further, the characteristic of the judging map #3 with respect to the angular acceleration αtc is at a constant value αc.sub.0 until a vehicle speed Vs.sub.3 of a low speed and decreases as the characteristic A3 or B3 in a range more than or equal to the vehicle speed Vs.sub.3. Any of the characteristics of the judging maps #1 to #3 can be tuned, and the characteristic may linearly decrease.

[0058] The map judging section 122 judges whether the steering angle command value θtc exceeds the range of characteristic values of the judging map #1, whether the angular speed ωtc exceeds the range of characteristic values of the judging map #2, and further whether the angular acceleration αtc exceeds the range of characteristic values of the judging map #3. A judgment result MD is inputted into a diagnosing section 123. The diagnosing section 123 outputs “ON/OFF” of the automatic steering command based on a diagnosis result by time or times (number) and “ON/OFF” of the automatic steering command is also inputted into an output section 124. The output section 124 outputs the steering angle command value θt only when the automatic steering command is “ON”.

[0059] Although the steering angle command value θt is inputted into the steering-angle command value gradual-changing section 100 together with the actual steering angle θr, the actual steering angle θr is calculated in the following manner in the present invention.

[0060] In a mechanism including a torsion bar 23, for example a sensor as illustrated in FIG. 13 is mounted to a column shaft 2 (2A (input side) and 2B (output side)) and thereby the steering angle is detected. That is, the input shaft 2A on a handle 1 side of the column shaft 2 is mounted with a Hall IC sensor 21 as an angle sensor and a 20° rotor sensor 22 for a torque sensor input-side rotor. The Hall IC sensor 21 outputs an AS_IS angle θh with 296° period. The 20° rotor sensor 22 mounted on the handle 1 side with respective to the torsion bar 23 outputs a column input-side angle θs with 20° period and the column input-side angle θs is inputted into a steering angle calculating section 132. The output shaft 2B on the column shaft 2 is mounted with a 40° rotor sensor 24 for a torque sensor output-side rotor. The 40° rotor sensor 24 outputs a column output-side angle Go and the column output-side angle Go is inputted into the steering angle calculating section 132. The column input-side angle θs and the column output-side angle signal Go are both calculated into an absolute angle by the steering angle calculating section 132. The steering angle calculating section 132 then outputs a steering angle θr on the column input-side and a steering angle θr1 on the column output-side of an absolute value.

[0061] Although the present invention descriptions are given assuming that the steering angle θr on the column input-side is the actual steering angle, the steering angle θr1 on the column output-side may be used as the actual steering angle.

[0062] Exemplary operations in such a configuration will be described with reference to flowcharts in FIG. 14 and FIG. 15 and a timing chart in FIG. 16.

[0063] When the automatic steering command is not “ON” (Step S1), the normal steering with the assist torque level of 100%, that is, the torque control is performed (Step S15). Then, when the automatic steering execution judging section 120 turns “ON” the automatic steering command at a time point t2 (Step S1), a fade processing of the EPS is started from the time point t2 (Step S2). At this time, “ON/OFF” of the automatic steering command is outputted from the automatic steering execution judging section 120, and the steering angle command value gradual-changing section 100 gradually changes the post-gradual change steering-angle command value θm of the position/speed control from the actual steering angle θr to the steering angle command value θt (Step S3). In the torque control of the normal control, the torque gradual-changing section 103 gradually changes the torque level from 100% to 0% (Step S4), thereafter the above operations are repeated until the fade processing ends (Step S5).

[0064] As well, the command value gradual-change of the position/speed control and the level gradual-change of the torque control in a fade section (a gradual-change time) may be in any order.

[0065] At and after a time point t3 when the fade processing ends, the torque control is switched to the automatic steering (the position/speed control) and then the automatic steering is continued (Step S6).

[0066] Thereafter, when the automatic steering command is turned “ON” (a time point t4), or when a driver steers the handle during the automatic steering such that the steering torque Ts exceeds a certain threshold and the automatic steering command is turned “OFF” (the time point t4), the automatic steering is completed (Step S10) and the fade processing is started (Step S11). Also in this case, “OFF” of the automatic steering command is outputted from the automatic steering execution judging section 120. In this way, the steering-angle command value gradual-changing section 100 gradually changes the post-gradual change steering-angle command value θm of the position/speed control from the steering angle command value θt to the actual steering angle θr (Step S12) and the torque gradual-changing section 103 gradually changes the torque level from 0% to 100% (Step S13). This fade processing is continued until a time point t5 (Step S14). At and after the time point t5 when the fade processing ends, the automatic steering is switched to the torque control of the normal steering (Step S15).

[0067] Note that, a fading characteristic of the steering angle command value in the position/speed control is represented by an exponential curve while the torque gradual-change in the torque control is represented by a linear line in FIG. 16, however, these may be freely tuned according to handling feeling. Further, a term between the time point t3 and the time point t4 in FIG. 16 is an automatic steering section with a deviation “0”.

[0068] Exemplary operations of the automatic steering execution judging section 120 is as shown in the flowchart of FIG. 15. The calculating section 121 in the automatic steering execution judging section 120 is inputted with the steering angle command value θtc from the CAN or the like (Step S20) and calculates the angular speed ωtc and the angular acceleration αtc based on the steering angle command value θtc (Step S21). The angular speed ωtc and the angular acceleration αtc are inputted into the map judging section 122, and the vehicle speed Vs is also inputted into the map judging section 122 (Step S22). The map judging section 122 first judges whether the steering angle command value θtc corresponding to the vehicle speed Vs is within the range of the characteristic values of the judging map #1 shown in FIG. 12A, that is, whether the steering angle command value θtc is below the characteristic line in FIG. 12A (Step S23). If the steering angle command value θtc is within the range of the characteristic values of the judging map #1, next whether the angular speed ωtc corresponding to the vehicle speed Vs is within the range of the characteristic values of the judging map #2 shown in FIG. 12B, that is, whether the angular speed ωtc is below the characteristic line in FIG. 12B is then judged (Step S24). If the angular speed ωtc is within the range of the characteristic values of the judging map #2, whether the angular acceleration αtc corresponding to the vehicle speed Vs is within the range of the characteristic values of the judging map #3 shown in FIG. 12C, that is, whether the angular speed ωtc is below the characteristic line in FIG. 12C is then judged (Step S25). If all of the judging targets are within the range of the respective characteristic values, the automatic steering execution judging section 120 turns “ON” the automatic steering command (Step S31) and outputs the steering angle command value θtc as the steering angle command value θt for inputting to the steering-angle command value gradual-changing section 100 (Step S32).

[0069] Further, when the steering angle command value θtc corresponding to the vehicle speed Vs is not within the range of the characteristic values of the judging map #1 shown in FIG. 12A at the above Step S23, or the angular speed ωtc corresponding to the vehicle speed Vs is not within the range of the characteristic values of the judging map #2 shown in FIG. 12B at the above Step S24, or the angular acceleration αtc corresponding to the vehicle speed Vs is not within the range of the characteristic values of the judging map #3 shown in FIG. 12C at the above Step S25, the diagnosing section 123 compares the number of times when the range is exceeded to a predetermined threshold number of times or compares the length of a time period when the range is exceeded to a predetermined threshold period of time (Step S30). Then, when they do not exceed the thresholds, the operation skips to the above Step S31, where the automatic steering command is turned “ON”. When the number of times or the length of the time period exceeds the thresholds, the automatic steering command is turned “OFF” (Step S33), and the steering angle command value θt is blocked and is not outputted (Step S34).

[0070] As well, the order of the aforementioned Steps S23 to S25 may be changed as appropriate.

[0071] When the automatic steering command is turned “ON” as shown in FIGS. 17A and 17B (a time point t10), the fade processing is started. The post-gradual change steering-angle command value θm is gradually changed from the actual steering angle θr to the steering angle command value θt. The actual steering angle θr is position/speed-controlled in such a manner as to follow the post-gradual change steering-angle command value θm. Consequently, it is possible to automatically and smoothly change the torque command value of the position/speed control, thereby providing the soft handling feeling to the driver.

[0072] As well, FIG. 17B shows that a deviation in position is represented as torque.

[0073] On the other hand, even when the excessive variations in the steering torque occur after a time point t21 upon the fade processing of the switching from the automatic steering to the torque control (a time point t20) as shown in FIGS. 18A and 18B, the excessive variations in the steering torque is automatically compensated by the position/speed control since the post-gradual change steering-angle command value θm is gradually changed from the steering angle command value θt to the actual steering angle θr. This prevents the driver from losing control of the handle. That is, as shown in FIG. 18A, in the present invention, since the actual steering angle θr is position/speed-controlled in such a manner as to follow the post-gradual change steering-angle command value θm, an occurrence of a peak is delayed and the position/speed control torque command value Tp is generated according to a difference between the post-gradual change steering-angle command value θm and the actual steering angle θr, and then smoothly converges. In the conventional control, however, since the gradual-change starts from a peak of the torque as shown in a broken line in FIG. 18A, the convergence is not smooth. Moreover, a position θr where torque (acceleration) is integrated twice has a trace as in the broken line shown in FIG. 18A and the handle thus moves more.

[0074] Furthermore, in another embodiment of the present invention, as compared to the fade processing time (e.g. 1000 [ms]) to perform the fade processing from the torque control of the normal steering to the position/speed control of the automatic steering, the fade processing time (e.g. 100 [ms]) from the position/speed control to the torque control is set shorter as shown in FIG. 19. As a result of this, the control is switched over relatively slowly so that the driver does not feel uncomfortable upon the fade processing from the torque control to the position/speed control, and the control can be switched over in a short period of time and intention of the driver can be promptly conveyed for avoiding danger upon the fade processing from the position/speed control to the torque control.

[0075] In the present invention as further shown in FIG. 20, an external disturbance observer 150 to compensate inertia or friction of the handle is provided in the position/speed control section 101 so that a handle manual-input of the driver is not prevented. Further, the external disturbance observer 150 also functions as a torque sensor that detects the handle manual-input at a high speed by estimating a torque input by the driver based on the motor current.

[0076] The position/speed control section 101 in FIG. 10 comprises a position/speed feedback controller 170 and the external disturbance observer 150 illustrated in FIG. 20. That is, an input of the position/speed control section 101 is the post-gradual change steering-angle command value θm and an output therefrom is the position/speed control torque command value Tp, and state feedback variables are the steering angle θr and the steering angular speed ωr. The position/speed feedback controller 170 comprises a subtracting section 171 to obtain a steering angle deviation between the post-gradual change steering-angle command value θm and the steering angle θr, a position controller 172 to position-control the steering angle deviation, a subtracting section 173 to obtain a speed deviation between the angular speed from the position controller 172 and the steering angular speed ωr, and a speed controller 174 to speed-control the speed deviation. An output from the speed controller 174 is adding-inputted into a subtracting section 154 in the external disturbance observer 150. Further, the external disturbance observer 150 comprises a steering inverse model 151 of a controlled object that is represented by a transfer function “(J.sub.2.Math.s+B.sub.2)/(τ.Math.s+1)”, a low pass filter (LPF) 152 of a transfer function “1/(τ.Math.s+1)” that is inputted with the position/speed control torque command value Tp and limits a band thereof, a subtracting section 153 to obtain an external-disturbance estimation torque Td*, and a subtracting section 154 to output the position/speed control torque command value Tp by subtraction.

[0077] A steering system 160 subjected to the controlled object comprises an adding section 161 to add an unknown external disturbance torque Td to the position/speed control torque command value Tp, a steering system 162 represented by a transfer function “1/(J.sub.1.Math.s+B.sub.1)”, and an integral section 163 to integrate (1/s) the angular speed ωr from the steering system 162 and to output the steering angle θr. The steering angular speed ωr is fed back to the position/speed feedback controller 170 and is also inputted into the integral section 163. The steering angle θr is fed back to the position/speed feedback controller 170.

[0078] The symbol “J.sub.1” in the transfer function represents the inertia in the steering system 162, “B.sub.1” represents the friction in the steering system 162, “J.sub.2” represents the inertia in the steering inverse model 151, “B.sub.2” represents the friction in the steering inverse model 151, and “τ” represents a predetermined time constant. These have relationships represented by the following equations 1 and 2.

J.sub.1≧J.sub.2  (Equation 1)

B.sub.1≧B.sub.2  (Equation 2)

[0079] The external disturbance observer 150 estimates the unknown external disturbance torque Td base on a difference between outputs of the steering inverse model 151 and the LPF 152 and obtains the external-disturbance estimation torque Td* as an estimation value. The external-disturbance estimation torque Td* is subtracting-inputted into the subtracting section 154, and it is possible to realize a robust position/speed control by subtracting the external-disturbance estimation torque Td* from an output of the speed controller 174. However, the robust position/speed control results in contradiction that the handle cannot be stopped even with intervention by the driver. In order to improve this point, the inertia J.sub.2 and the friction B.sub.2 smaller than or equal to the inertia J.sub.1 and the friction B.sub.1, respectively, which the steering system 162 actually has, are inputted as the steering inverse model 151. As a result of this, the inertia and the friction of the handle that the driver feels becomes seemingly smaller. This allows the driver to easily intervene in the automatic steering by steering.

[0080] Moreover, by monitoring the external-disturbance estimation torque Td* in the external disturbance observer 150, it is possible to detect the steering torque of the driver instead of the torque sensor. Especially, when the torque sensor uses digital signals, detection of steering intervention by the driver may be delayed due to influence of communication delay or other reasons. Similarly to the torque sensor, when the external-disturbance estimation torque Td* exceeds a threshold value for a predetermined period of time, the steering intervention may be determined to be performed and the fade processing may be performed.

[0081] FIGS. 21A and 21B are diagrams illustrating characteristics of the angle and the torque, respectively, in the fade processing from the position/speed control to the torque control when the external disturbance observer 150 is provided. The driver turns the handle in an opposite direction to a direction of the steering angle command value θt in the automatic operation and releases the handle when the automatic steering is turned “OFF” (the fade processing is started). In FIGS. 21A and 21B, the characteristics of the external disturbance observer 150 in a case where the inertia and the friction satisfy “J.sub.1>J.sub.2” and “B.sub.1>B.sub.2” and a case where “J.sub.1=J.sub.2” and “B.sub.1=B.sub.2” are satisfied are illustrated. FIG. 21A is a diagram illustrating exemplary variations in the actual steering angle θr when the external disturbance observer 150 is provided. FIG. 21B is a diagram illustrating exemplary variations in the steering torque Ts and the position/speed control torque command value Tp when the external disturbance observer 150 is provided.

[0082] Providing the external disturbance observer 150 allows for providing a smoother operation feeling, thereby enabling switching control at a high speed. Smaller inertia and friction facilitate the steering intervention.

EXPLANATION OF REFERENCE NUMERALS

[0083] 1 handle (steering wheel) [0084] 2 column shaft (steering shaft, handle shaft) [0085] 10 torque sensor [0086] 12 vehicle speed sensor [0087] 20, 131 motor [0088] 30 control unit (ECU) [0089] 40 CAN [0090] 41 Non-CAN [0091] 50 automatic steering command unit [0092] 51, 101 position/speed control section [0093] 52, 120 automatic steering execution judging section [0094] 53 torque control section [0095] 54 torque command value gradual-change switching section [0096] 100 steering-angel command value gradual-changing section [0097] 102 torque control section [0098] 103 torque gradual-changing section [0099] 121 calculating section [0100] 122 map judging section [0101] 123 diagnosing section [0102] 130 current control system [0103] 150 external disturbance observer