ELECTRIC POWER STEERING APPARATUS

Abstract

[Problem]

An object of the present invention is to provide an electric power steering apparatus that enables suppression of a high-frequency vibration and enhancement of followability of a motor angular velocity to a motor velocity command by using a velocity control section (for example, PI-control, PID-control) and adding a motor current compensation value to a motor current command value on the basis of a steering state signal, even when a gain of the velocity control section is made large.

[Means for Solving the Problem]

A steering angle control section comprises a position control section that outputs a motor velocity command value based on a first steering state signal and a target steering angle, a velocity control section that outputs a second motor current command value based on the motor velocity command value and a second steering state signal, a stabilization compensating section that outputs a third motor current command value based on a third steering state signal, and a first adding section that inputs the second motor current command value and the third motor current command value, and outputs a first addition value, and outputs a first motor current command value based on the first addition value.

Claims

1-15. (canceled)

16. An electric power steering apparatus that has an automatic steering mode of controlling a motor depending on a target steering angle given by a vehicle when said vehicle autonomously travels by using a steering section for steering a steering system of said vehicle, comprising: a steering angle control section that calculates a first motor current command value based on said target steering angle, a first steering state signal, a second steering state signal and a third steering state signal; wherein said steering angle control section comprises a position control section that outputs a motor velocity command value based on said first steering state signal and said target steering angle, a velocity control section that outputs a second motor current command value based on said motor velocity command value and said second steering state signal, a stabilization compensating section that cuts off a frequency component in about 150 Hz or less from said third steering state signal, and outputs a third motor current command value for suppressing a high-frequency vibration that occurs when a gain of said velocity control section is made large, and a first adding section that inputs said second motor current command value and said third motor current command value, and outputs a first addition value, and outputs said first motor current command value based on said first addition value.

17. The electric power steering apparatus according to claim 16, wherein said first steering state signal is an actual steering angle, said second steering state signal is a motor angular velocity of said motor, and said third steering state signal is said motor angular velocity.

18. The electric power steering apparatus according to claim 16, wherein said first steering state signal is a steering wheel angle, said second steering state signal is a motor angular velocity of said motor, and said third steering state signal is a twist torque signal.

19. The electric power steering apparatus according to claim 16, wherein said first steering state signal is an actual steering angle, said second steering state signal is a motor angular velocity of said motor, and said third steering state signal is a column angle.

20. The electric power steering apparatus according to claim 17, wherein said position control section multiplies a deviation between said first steering state signal and said target steering angle by a deviation gain, and outputs said motor velocity command value.

21. The electric power steering apparatus according to claim 18, wherein said position control section multiplies a deviation between said first steering state signal and said target steering angle by a deviation gain, and outputs said motor velocity command value.

22. The electric power steering apparatus according to claim 19, wherein said position control section multiplies a deviation between said first steering state signal and said target steering angle by a deviation gain, and outputs said motor velocity command value.

23. The electric power steering apparatus according to claim 16, wherein said velocity control section subtracts a proportional gain value obtained by multiplying said second steering state signal by a proportional gain from an integral gain value obtained by integrating and multiplying a steering angular velocity deviation between said motor velocity command value and said second steering state signal by an integral gain, and outputs said second motor current command value.

24. The electric power steering apparatus according to claim 16, wherein an output limiter that limits an upper limit value and a lower limit value is provided at a final stage of said steering angle control section, and said output limiter outputs said first motor current command value.

25. The electric power steering apparatus according to claim 16, wherein said steering angle control section further comprises a motor velocity command feedforward filter section that performs feedforward processing based on said target steering angle, and outputs a feedforward motor angular velocity command value, and a second adding section that adds an output from said position control section and said feedforward motor angular velocity command value, and outputs said motor velocity command value to said velocity control section.

26. The electric power steering apparatus according to claim 16, wherein said steering angle control section further comprises a rate limiter that gradually changes an output value with respect to said target steering angle at a predetermined period so as to match said output value with said target steering angle.

27. The electric power steering apparatus according to claim 16, wherein said steering angle control section further comprises a steering wheel vibration eliminating section that outputs a signal obtained by cutting off a frequency component near a predetermined center frequency in said target steering angle, to said position control section.

28. The electric power steering apparatus according to claim 25, wherein said steering angle control section further comprises a steering wheel vibration eliminating section that outputs a signal obtained by cutting off a frequency component near a predetermined center frequency in said target steering angle, to said position control section.

29. The electric power steering apparatus according to claim 16, wherein said steering angle control section further comprises a steering wheel damping section that outputs a fourth motor current command value in a predetermined second cutoff frequency or more based on a twist torque signal, and inputs said fourth motor current command value into said first adding section.

30. The electric power steering apparatus according to claim 25, wherein said steering angle control section further comprises a steering wheel damping section that outputs a fourth motor current command value in a predetermined second cutoff frequency or more based on a twist torque signal, and inputs said fourth motor current command value into said first adding section.

31. The electric power steering apparatus according to claim 27, wherein said steering angle control section further comprises a steering wheel damping section that outputs a fourth motor current command value in a predetermined second cutoff frequency or more based on a twist torque signal, and inputs said fourth motor current command value into said first adding section.

32. The electric power steering apparatus according to claim 28, wherein said steering angle control section further comprises a steering wheel damping section that outputs a fourth motor current command value in a predetermined second cutoff frequency or more based on a twist torque signal, and inputs said fourth motor current command value into said first adding section.

33. The electric power steering apparatus according to claim 27, wherein said predetermined center frequency is a frequency of a vibration caused by springiness of a torsion bar and an inertia moment of a steering wheel in said automatic steering mode.

34. The electric power steering apparatus according to claim 29, wherein said predetermined second cutoff frequency is a frequency of a vibration caused by springiness of a torsion bar and an inertia moment of a steering wheel in said automatic steering mode.

35. The electric power steering apparatus according to claim 16, wherein said stabilization compensating section includes a primary filter or a quadratic filter that performs filtering processing to said third steering state signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the accompanying drawings:

[0015] FIG. 1 is a configuration diagram illustrating a general outline of an electric power steering apparatus;

[0016] FIG. 2 is a diagram showing an example of mounting sensors and relation between a column angle and a steering wheel angle;

[0017] FIG. 3 is a mechanism diagram showing relation among a torsion bar, the steering wheel angle and the column angle;

[0018] FIG. 4 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a first embodiment of the present invention;

[0019] FIG. 5 is a block diagram showing a configuration example of a steering angle control section in the first embodiment of the present invention;

[0020] FIG. 6 is a block diagram showing an example of a rate limiter in the first embodiment of the present invention;

[0021] FIG. 7 is a block diagram showing a configuration example of a changed part setting section in the first embodiment of the present invention;

[0022] FIG. 8 is a diagram showing time variations (0 to 2 seconds) of a motor angular velocity (shown by a thin line) and a motor current command value (shown by a thick line) outputted from the steering angle control section in the case of not providing a stabilization compensating section, in the first embodiment of the present invention;

[0023] FIG. 9 is a diagram showing time variations (0 to 2 seconds) of the motor angular velocity (shown by a thin line) and the motor current command value (shown by a thick line) outputted from the steering angle control section in the case of providing the stabilization compensating section, in the first embodiment of the present invention;

[0024] FIG. 10 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a first modified example of the first embodiment of the present invention;

[0025] FIG. 11 is a block diagram showing a configuration example of a steering angle control section in the first modified example of the first embodiment of the present invention;

[0026] FIG. 12 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a second modified example of the first embodiment of the present invention;

[0027] FIG. 13 is a block diagram showing a configuration example of a steering angle control section in the second modified example of the first embodiment of the present invention;

[0028] FIG. 14 is a block diagram showing a configuration example of a steering angle control section in a second embodiment of the present invention;

[0029] FIG. 15 is a characteristic diagram showing frequency characteristics of a gain and a phase of a steering wheel vibration eliminating section in the second embodiment of the present invention (a characteristic diagram of a notch filter centered at 12.5 [Hz]);

[0030] FIG. 16 is a whole block diagram from a target steering angle ref to an actual steering angle h in the second embodiment of the present invention;

[0031] FIG. 17 is a diagram showing transfer functions from the target steering angle to a torsion bar torque, wherein (A) shows a frequency characteristic of a gain in a conventional example, (B) shows a frequency characteristic of a gain of a transfer function in the first embodiment of the present invention, (C) shows a frequency characteristic of a phase in the conventional example, and (D) shows a frequency characteristic of a phase of the transfer function in the first embodiment of the present invention;

[0032] FIG. 18 is a diagram showing time responses of the torsion bar torque, wherein waveform (A) shows a time response of the torsion bar torque without the steering wheel vibration eliminating section, and waveform (B) shows a time response of the torsion bar torque with the steering wheel vibration eliminating section;

[0033] FIG. 19 is a diagram showing time responses of the actual steering angle, wherein waveform (A) shows a time response of the actual steering angle following the target steering angle without the steering wheel vibration eliminating section, waveform (B) shows a time response of the actual steering angle following the target steering angle with the steering wheel vibration eliminating section, and waveform (C) shows a time response of the target steering angle;

[0034] FIG. 20 is a block diagram showing a configuration example of a steering angle control section in a third modified example of the second embodiment of the present invention;

[0035] FIG. 21 is a block diagram showing a configuration example of a steering angle control section in a fourth modified example of the second embodiment of the present invention;

[0036] FIG. 22 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a third embodiment of the present invention;

[0037] FIG. 23 is a block diagram showing a configuration example of a steering angle control section in the third embodiment of the present invention;

[0038] FIG. 24A is a diagram showing a frequency characteristic of a gain in a steering wheel damping section, and FIG. 24B is a diagram showing a frequency characteristic of a phase in the steering wheel damping section;

[0039] FIG. 25 is a whole block diagram from the target steering angle ref to the actual steering angle h in the third embodiment of the present invention;

[0040] FIG. 26 is a whole block diagram obtained by an equivalent transformation of the whole block diagram from the target steering angle ref to the actual steering angle h in the third embodiment of the present invention;

[0041] FIG. 27 is a whole block diagram obtained by an equivalent transformation of the whole block diagram from the target steering angle ref to the actual steering angle h in the third embodiment of the present invention;

[0042] FIG. 28 is a diagram showing time responses of the actual steering angle, wherein waveform (A) shows a time response of the target steering angle, waveform (B) shows a time response of the actual steering angle h in the case of inputting the target steering angle, and waveform (C) shows a time response of the actual steering angle h with both the steering wheel damping section and the steering wheel vibration eliminating section;

[0043] FIG. 29 is a diagram showing time responses of the actual steering angle, wherein waveform (A) (shown by a thin line) shows a time response of the actual steering angle h to the target steering angle without compensation by the steering wheel damping section, the steering wheel vibration eliminating section or the like, waveform (B) (shown by a dotted line) shows a time response of the actual steering angle h to the target steering angle with only the steering wheel vibration eliminating section, and waveform (C) (shown by a thick line) shows a time response of the actual steering angle h to the target steering angle with both the steering wheel damping section and the steering wheel vibration eliminating section;

[0044] FIG. 30 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a fifth modified example of the third embodiment of the present invention;

[0045] FIG. 31 is a block diagram showing a configuration example of a steering angle control section in the fifth modified example of the third embodiment of the present invention;

[0046] FIG. 32 is a block diagram showing a configuration example of a control system of an electric power steering apparatus in a sixth modified example of the third embodiment of the present invention;

[0047] FIG. 33 is a block diagram showing a configuration example of a steering angle control section in the sixth modified example of the third embodiment of the present invention;

[0048] FIG. 34 is a block diagram showing a configuration example of a steering angle control section in a fourth embodiment of the present invention;

[0049] FIG. 35 is a diagram showing time responses of the target steering angle and the actual steering angle, wherein waveform (A) shows a time response of the target steering angle, waveform (B) shows a time response of the actual steering angle without a motor velocity command FF filter, and waveform (C) shows a time response of the actual steering angle with the motor velocity command FF filter;

[0050] FIG. 36 is a block diagram showing a configuration example of a steering angle control section in a seventh modified example of the fourth embodiment of the present invention; and

[0051] FIG. 37 is a block diagram showing a configuration example of a steering angle control section in an eighth modified example of the fourth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

[0052] The present invention is an electric power steering apparatus (EPS) that has an assist mode of controlling a motor which provides a steering system of a vehicle with an assist torque when a driver steers the steering system and an automatic steering mode of controlling the motor depending on a target steering angle given by the vehicle when the vehicle autonomously travels, and is the electric power steering apparatus that enables suppression of a high-frequency vibration and enhancement of followability of the motor angular velocity to the motor velocity command by using a velocity control section (performing, for example, PI-control, P-control, PID-control, or proportional preceding type PI control) and comprising a stabilization compensating section for adding a motor current compensation value to a motor current command value on the basis of a motor angular velocity, a torsion bar torque or a column angle, even when a gain of the velocity control section is made large. Further, the present invention enables suppression of a vibration originating in a response characteristic, and enables elimination of a vibration (a vibration originating in a spring inertia system) caused by springiness of a torsion bar and an inertia moment of a steering wheel in an automatic steering mode by using a rate limiter and a filter.

[0053] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings in detail.

[0054] First, an electric power steering apparatus of a first embodiment of the present invention uses two operation mode, that is, an assist mode and an automatic steering mode. They are the assist mode of controlling a motor which provides a steering system of a vehicle with an assist torque when a driver steers the steering system and the automatic steering mode of controlling the motor depending on a target steering angle given by the vehicle when the vehicle autonomously travels.

[0055] FIG. 4 shows a configuration example of the first embodiment of the present invention. A rotation sensor 151 such as a resolver for detecting a motor rotational angle s is connected to a motor 150, and the motor 150 is driven and controlled through a vehicle-side-ECU 130 and an EPS-side-ECU 140.

[0056] The vehicle-side-ECU 130 comprises a switching command section 131 which outputs a switching command SW to switch to the automatic steering mode or the assist mode on the basis of a button, a switch or the like indicating an intention of a driver, and a target steering angle generating section 132 which generates a target steering angle ref on the basis of a signal from a camera (an image), a distance sensor or the like. An actual steering angle h which is detected by a steering angle sensor 152 providing for a column shaft, is inputted into a steering angle control section 201 in the EPS-side-ECU 140 through the vehicle-side-ECU 130.

[0057] The switching command section 131 outputs the switching command SW on the basis of a signal for discerning that the automatic steering mode is entered, for example, a signal of a button or a switch which is provided for a dashboard or in the vicinity of a steering wheel and indicates the intention of the driver, or a signal of a vehicle state determined in accordance with such as a parking mode set in a shift, and the switching command SW is inputted into a switching section 142 in the EPS-side-ECU 140. The target steering angle generating section 132 generates the target steering angle ref on the basis of the signal from the camera (the image), the distance sensor or the like by a known method, and the generated target steering angle ref is inputted into the steering angle control section 201.

[0058] The EPS-side-ECU 140 comprises a torque control section 141 which outputs a motor current command value Itref calculated on the basis of a steering torque Th and a motor angular velocity c, the steering angle control section 201 which calculates and outputs a motor current command value Imref for steering angle automatic control on the basis of the target steering angle ref, the actual steering angle h and the motor angular velocity c, the switching section 142 which switches between the motor current command values Itref and Imref by the switching command SW, a motor driving section 143 which drives and controls the motor 150 on the basis of the motor current command value (Itref or Imref) outputted from the switching section 142, and a motor angular velocity calculating section 144 which calculates the motor angular velocity c on the basis of the motor rotational angle s outputted from the rotation sensor 151. The switching section 142 switches between the assist mode by the torque control section 141 and the automatic steering mode by the steering angle control section 201 on the basis of the switching command SW outputted from the switching command section 131 in the vehicle-side-ECU 130. The switching section 142 outputs the motor current command value Itref in the assist mode, and outputs the motor current command value Imref in the automatic steering mode. The motor driving section 143 comprises a PI current control section, a PWM-control section, an inverter or the like (not shown).

[0059] The steering angle control section 201 is configured as shown in FIG. 5, and is a position control system including a velocity control loop system as a minor loop. A rate limiter 211 for rate limit processing is provided to perform smoothing when the target steering angle ref changes rapidly, that is, to smoothly change the target steering angle ref within a predetermined time change rate. A target steering angle ta which is obtained by the rate limit processing to the target steering angle ref at the rate limiter 211, is addition-inputted into a subtracting section 213A.

[0060] The actual steering angle h is subtraction-inputted into the subtracting section 213A. An angle deviation b between the actual steering angle h and the smoothed target steering angle ta is multiplied by a gain Kpp at a position control section (Kpp) 214, and the multiplied result is addition-inputted into a subtracting section 213B as a motor velocity command value ref. The motor angular velocity c outputted from the motor angular velocity calculating section 144 is subtraction-inputted into the subtracting section 213B. A velocity deviation Df calculated at the subtracting section 213B is addition-inputted into a subtracting section 213C through an integrating section (having a gain Kiv) 215a. The motor angular velocity c is multiplied by a gain Kpv at a proportional section 215b, and the multiplied result is subtraction-inputted into the subtracting section 213C.

[0061] An output of the subtracting section 213C is inputted into an adding section 213D, and an output obtained by filtering processing to the motor angular velocity c by a stabilization compensating section 220 is inputted into the adding section 213D.

[0062] A limiter 217 limits an input to a set upper limit value and a set lower limit value. The limiter 217 outputs a value obtained by limiting the added result of the adding section 213D to the switching section 142 as the motor current command value Imref. The position control section 214 and a velocity control section 215 constitutes a current command value calculating section.

[0063] The first embodiment of the present invention is characterized by providing the steering angle control section 201 in the EPS-side-ECU 140 with the rate limiter 211 for the target steering angle and the stabilization compensating section 220 that contributes to stabilization of the system and suppresses a high-frequency vibration when a gain of the velocity control section is made large. This enables enhancement of followability of the motor angular velocity c to the motor velocity command value. Providing the rate limiter 211 achieves an effect of relaxing response of the actual steering angle when the target steering angle changes rapidly, enables a vehicle to be accurately moved corresponding to the target steering angle ref regardless of a vehicle speed, and enables improvement of safety to a driver.

[0064] Here, the rate limiter 211 will be described. When the target steering angle t (=ref) changes rapidly, the rate limiter 211 smooths the target steering angle t, and outputs the smoothed result. For example, the rate limiter 211 is configured as shown in FIG. 6. That is, the target steering angle t is addition-inputted into a subtracting section 211-1, and a changed part t2 is set at a changed part setting section 211-2 on the basis of a difference t1 obtained by subtracting a past value of an output of the rate limiter 211 from the target steering angle t. The changed part setting section 211-2 performs the setting on the basis of the difference t1 between the past value from a retaining section (Z.sup.1) 211-4 and the target steering angle t. A result of adding the changed part t2 and the past value at an adding section 211-3, is outputted as a new target steering angle t3 (=ta). The changed part setting section 211-2 does not make the changed part t2 exceed a set upper limit and a set lower limit. The difference t1 between the target steering angle t and the past value is calculated at every calculation period T, when the difference t1 is out of range between the upper limit and the low limit, the output t3 is changed stepwise or gradually as shown in FIG. 7 by repeatedly adding the upper limit or the lower limit to the past value, and finally the output t3 is matched with the target steering angle t. When the difference t1 between the target steering angle t and the past value is within the range between the upper limit and the low limit set at the changed part setting section 211-2, the changed part t2 equal to the difference t1 is outputted, is added to the past value, and as a result, the output t3 coincides with the target steering angle t. As these results, even when the target steering angle t changes rapidly, the rate limiter 211 can smoothly change the rapidly changing target steering angle t, prevents a rapid change of a current, and performs a function of reducing anxious feeling of a driver in automatic driving

[0065] Next, with respect to the first embodiment of the present invention, an effect of the stabilization compensating section will be described by using time changes of the motor current command values in the case of providing the stabilization compensating section and in the case of not providing it. The time changes of the motor angular velocity and the motor current command value outputted from the steering angle control section in the case of not providing the stabilization compensating section are shown in FIG. 8. The time changes of the motor angular velocity and the motor current command value outputted from the steering angle control section in the case of providing the stabilization compensating section are shown in FIG. 9. A range of the horizontal axes of FIG. 8 and FIG. 9 is a time range from 0 to 2 seconds. The motor angular velocity [deg/s] and the motor current command value [deg/s] are converted into rotational angular velocities on a column shaft. A state where the motor angular velocity changes is represented by a thin line, and a state where the motor current command value changes is represented by a thick line. From FIG. 8 and FIG. 9, it is confirmed that providing the stabilization compensating section 220 contributes to stabilization of the system, and enables suppression of an oscillation and a vibration in a high frequency region. That is, it is shown that a gain of the velocity control section 215 can be enlarged in a state of suppressing the oscillation and the vibration in the high frequency region. The stabilization compensating section 220 performs the filtering processing to the motor angular velocity. For example, the stabilization compensating section 220 can set a primary filter having a cutoff frequency f.sub.c1 as shown by the following expression 1.

[00001]$\begin{array}{cc}{G}_{s.Math.t.Math.a.Math.b.Math.l.Math.e}=K_{s.Math.t.Math.a}.Math.\frac{\frac{1}{2.Math..Math.f_{c.Math.1}}.Math.s}{\frac{1}{2.Math..Math.f_{c.Math.1}}.Math.s+1}.Math..Math.\left(f_{c.Math.1}=.Math.150.Math.\left[\mathrm{Hz}\right]\right)& \left[\mathrm{Expression}.Math..Math.1\right]\end{array}$

[0066] FIG. 10 shows a configuration example of a first modified example of the first embodiment of the present invention. The rotation sensor 151 such as a resolver for detecting the motor rotational angle s is connected to the motor 150, and the motor 150 is driven and controlled through the vehicle-side-ECU 130 and the EPS-side-ECU 240.

[0067] A steering angle control section 202 is configured as shown in FIG. 11, and is a position control system including a velocity control loop system as a minor loop.

[0068] The first modified example is different from the first embodiment in that a steering wheel angle hd is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs a torsion bar torque Tt.

[0069] Other configurations and effects are the same as those of those of the first embodiment.

[0070] FIG. 12 shows a configuration example of a second modified example of the first embodiment of the present invention. The rotation sensor 151 such as a resolver for detecting the motor rotational angle s is connected to the motor 150, and the motor 150 is driven and controlled through the vehicle-side-ECU 130 and the EPS-side-ECU 340.

[0071] A steering angle control section 203 is configured as shown in FIG. 13, and is a position control system including a velocity control loop system as a minor loop.

[0072] The second modified example is different from the first embodiment in that the actual steering angle h is subtraction-inputted into the subtracting section 213A, the velocity control section 215 inputs the actual steering angle h, and the stabilization compensating section 220 inputs a column angle c.

[0073] Other configurations and effects are the same as those of those of the first embodiment.

[0074] Next, a second embodiment will be described around difference from the first embodiment with reference to the accompanying drawings. For convenience of explanation, the same configurations as those of the first embodiment are designated with the same numerals or with numerals adding X at the end, and the explanation is omitted.

[0075] The difference between the first embodiment and the second embodiment is that a steering wheel vibration eliminating section 212 is provided for a steering angle control section 201X.

[0076] FIG. 14 is a block diagram showing a configuration example of the steering angle control section according to the second embodiment of the present invention. The steering wheel vibration eliminating section 212 eliminates a vibration (a vibration originating in a spring inertia system) caused by the springiness of the torsion bar and the inertia moment of the steering wheel in the automatic steering mode.

[0077] The steering wheel vibration eliminating section 212 cuts off a component in a predetermined frequency or less of the vibration caused by the springiness of the torsion bar and the inertia moment of the steering wheel in the automatic steering mode, and a signal obtained by the cutoff is addition-inputted into the subtracting section 213A. Since the actual steering angle h is subtraction-inputted into the subtracting section 213A, the steering angle control section 201X includes a configuration where a difference between the output of the steering wheel vibration eliminating section 212 and the actual steering angle h is inputted into the position control section 214. This enables enhancement of the followability of the motor angular velocity to the motor velocity command. Further, since the spring inertia system of the steering wheel is considered, the vibration component originating in the spring inertia system is eliminated, the vibration of the steering wheel is suppressed, and it is possible to suppress the steering wheel vibration during operation.

[0078] Here, a frequency characteristic of the steering wheel vibration eliminating section 212 will be described. It is known that a steering wheel vibration frequency of the vibration caused by the springiness of the torsion bar and the inertia moment of the steering wheel is about 12.5 [Hz]. Since the steering wheel vibration eliminating section 212 decreases a gain in the vicinity of the steering wheel vibration frequency, that is, in 12.55.0 [Hz], a quadratic filter is suitable for the purpose. A quadratic filter used in the second embodiment can be expressed, for example, by the following expression 2 being an expression of a transfer function of a notch filter.

[00002]$\begin{array}{cc}{G}_{n.Math.o.Math.t.Math.c.Math.h}=\frac{{}_d^2}{{}_n^2}.Math.\frac{s^2+2.Math.{}_n.Math.{}_n.Math.s+{}_n^2}{s^2+2.Math.{}_d.Math.{}_d.Math.s+{}_d^2}& \left[\mathrm{Expression}.Math..Math.2\right]\end{array}$

In the case that respective parameters of the expression 2 are set as center frequencies n=d=212.5 [rad/s], a damping constant =0.2, and a damping constant =0.6, a Bode diagram is shown in FIG. 15. It is found out that a gain in a range where the center frequency is about 12.5 [Hz] is decreased in the frequency characteristic of the steering wheel vibration eliminating section 212. The center frequency is set on the basis of the steering wheel vibration frequency of the vibration caused by the springiness of the torsion bar and the inertia moment of the steering wheel, and, for example, may be set within 12.55.0 [Hz]. Further, n and d may not be coincide, and may be set from 27.5 to 217.5 [rad/s].

[0079] Next, a model which is generated by unifying a system from a column to a tire as an integrated inertia (column inertia) system by using a transfer function, will be shown. In order to model the column inertia system, the following physical quantities are used.

[0080] Jc: column inertia [kg.Math.m.sup.2]

[0081] Dc: column damping coefficient [N.Math.m/(rad/s)]

[0082] Jh: steering wheel inertia [kg.Math.m.sup.2]

[0083] Dh: steering wheel damping coefficient [N.Math.m/(rad/s)]

[0084] Ks: torsion bar spring constant [N.Math.m/rad]

[0085] Ds: torsion bar damping coefficient [N.Math.m/(rad/s)]

[0086] Kt: motor torque constant [N.Math.m/A]

A motor torque is converted into a torque on a column shaft (considering an amount by reduction gears). Since it is assumed that an actual motor current is equal to a motor current command value Iref, current control is omitted. Further, since the stabilization compensating section influences a high frequency region, it is omitted.

[0087] ref: target steering angle [rad]

[0088] h: actual steering angle [rad]

[0089] c: column angle [rad]

[0090] c: column angular velocity [rad/s]

The column angular velocity c is obtained by converting a motor rotational velocity obtained by difference calculation of a motor rotational angle into a value on the column shaft in an ECU. Practically, filtering processing to the column angular velocity c by a low-pass filer (LPF) is performed in order to eliminate a noise in a high frequency region (not shown).

[0091] Tt: torsion bar torque [N.Math.m]

[0092] Iref: motor current command value [A]

[0093] ref: motor velocity command value [rad/s]

[0094] By using the above physical quantities, a whole block diagram from the target steering angle ref to the actual steering angle h can be shown as a configuration in FIG. 16. The model will be described on the basis of this configuration.

[0095] The model is a position control system including a velocity control loop system as a minor loop. The target steering angle ref is inputted into a rate limiter 311 that performs smoothing when the target steering angle ref changes rapidly, that is, makes the target steering angle ref changed smoothly within a predetermined time change rate. The target steering angle ta going through a steering wheel vibration eliminating section 312 that eliminates a vibration (a vibration originating in a spring inertia system) caused by the springiness of the torsion bar and the inertia moment of the steering wheel in the automatic steering mode, is addition-inputted into a subtracting section 313a.

[0096] The actual steering angle h is subtraction-inputted into the subtracting section 313a. The angle deviation b between the smoothed target steering angle ta and the actual steering angle h is multiplied by a gain Kpp at a position control section (Kpp) 314, and the multiplied result is addition-inputted into a subtracting section 313b as the motor velocity command value ref. The velocity deviation Df that is calculated at the subtracting section 313b by subtraction-inputting the motor angular velocity c outputted from a differentiating section 319, is addition-inputted into a subtracting section 313c through an integrating section (having the gain Kiv) 315a. At the same time, the motor angular velocity c is multiplied by a gain Kpv at a proportional section 315b, and the multiplied result is subtraction-inputted into the subtracting section 313c. In the whole block diagram, the subtracted result of the subtracting section 313c is outputted to a motor torque converting section 316 as the motor current command value Iref, the motor torque converting section 316 converts the motor current command value Iref into a motor torque Tm, and outputs the motor torque Tm to an adding section 313e. An addition torque Ts that is generated by inputting the torsion bar torque Tt generated by a torsion bar section 317 and the motor torque Tm into the adding section 313e, is inputted into a column inertia section 318a, and an output from the column inertia section 318a is inputted into an integrating section 318b. An output of the integrating section 318b is inputted into the differentiating section 319 and a subtracting section 313d as the column angle c. The differentiating section 319 converts the inputted column angle c into the motor angular velocity c, and outputs the motor angular velocity c to the proportional section (Kpv) 315b and the subtracting section 313b. The motor current command value Iref and the motor torque Tm are generated on the basis of the motor angular velocity c. The torsion bar torque Tt generated by the torsion bar section 317 is outputted to a delay section 320a, an output of the delay section 320a is inputted into a steering wheel inertia section 320b, an output of steering wheel inertia section 320b is inputted into an integrating section 320c, and the actual steering angle h is generated as the result calculated at the integrating section 320c. The actual steering angle h generated by the integrating section 320c is subtraction-inputted into the subtracting section 313a, and is used to generate the motor velocity command value ref. The column angle c outputted from the integrating section 318b is subtraction-inputted into the subtracting section 313d, and the actual steering angle h is addition-inputted into the subtracting section 313d. Thus, at the torsion bar section 317 in the whole block diagram, the torsion bar torque Tt is generated on the basis of a difference between the column angle c and the actual steering angle h.

[0097] Therefore, a transfer function Get from the target steering angle ta to the torsion bar torque Tt in the whole block diagram as shown in FIG. 16, becomes the following. In the case that the target steering angle is ta [rad] and the torsion bar torque is Tt [N.Math.m], the transfer function G.sub.t is expressed as the expression 3.

[00003]$\begin{array}{cc}{G}_{.Math.t}=\frac{T_t}{{}_{t.Math.a}}=G_{.Math..Math.i}.Math.G_{\mathrm{it}}& \left[\mathrm{Expression}.Math..Math.3\right]\end{array}$

G.sub.i and G.sub.it in the expression 3 are expressed as the expression 4 and the expression 5 respectively.

[00004]$\begin{array}{cc}{G}_{.Math..Math.i}=\frac{I_{\mathrm{ref}}}{{}_{\mathrm{ta}}}=\frac{K_{\mathrm{pp}}.Math.G_{.Math..Math.i}}{K_{\mathrm{pp}}.Math.G_{.Math..Math.i}.Math.G_{\mathrm{ih}}+1}& \left[\mathrm{Expression}.Math..Math.4\right]\\ G_{\mathrm{it}}=\frac{T_t}{I_{\mathrm{ref}}}=G_{\mathrm{ic}}.Math.G_{\mathrm{ct}}& \left[\mathrm{Expression}.Math..Math.5\right]\end{array}$

G.sub.i and G.sub.ib in the expression 4 are expressed as the expression 6 and the expression 7 respectively.

[00005]$\begin{array}{cc}{G}_{.Math.i}=\frac{I_{\mathrm{ref}}}{{}_{\mathrm{ref}}}=\frac{\frac{K_{\mathrm{iv}}}{s}}{\left(K_{\mathrm{pv}}.Math.s+K_{\mathrm{iv}}\right).Math.G_{\mathrm{ic}}+1}& \left[\mathrm{Expression}.Math..Math.6\right]\\ G_{\mathrm{ih}}=-\frac{G_{\mathrm{it}}}{J_h.Math.s^2+D_h.Math.s}& \left[\mathrm{Expression}.Math..Math.7\right]\end{array}$

G.sub.ic in the expression 5 is expressed as the expression 8.

[00006]$\begin{array}{cc}{G}_{i.Math.c}=\frac{{}_c}{I_{r.Math.e.Math.f}}=\frac{K_t}{J_c.Math.s^2+D_c.Math.s-G_{c.Math.t}}& \left[\mathrm{Expression}.Math..Math.8\right]\end{array}$

G.sub.ct in the expression 5 and the expression 8 is expressed as the expression 9.

[00007]$\begin{array}{cc}{G}_{c.Math.t}=\frac{T_t}{{}_c}=\frac{\left(D_s.Math.s+K_s\right).Math.\left(J_h.Math.s^2+D_h.Math.s\right)}{J_h.Math.s^2+\left(D_h+D_s\right).Math.s+K_s}& \left[\mathrm{Expression}.Math..Math.9\right]\end{array}$

[0098] Here, on the basis of the above description and the model configured as the block diagram shown in FIG. 16, frequency characteristics of a transfer function from the target steering angle to the torsion bar torque in the case of providing the steering angle control section 201X with the steering wheel vibration eliminating section 212 and in the case of not providing, are simulated. The result of the comparison is shown in FIG. 17.

[0099] In FIG. 17, a frequency characteristic of a gain in the case of not providing the steering angle control section 201X with the steering wheel vibration eliminating section 212 is shown by the dotted line (A), a frequency characteristic of a phase in that case is shown by the dotted line (C), a frequency characteristic of a gain in the case of providing the steering angle control section 201X with the steering wheel vibration eliminating section 212 is shown by the solid line (B), and a frequency characteristic of a phase in that case is shown by the solid line (D). Comparing these, in the case of providing the steering angle control section 201X with the steering wheel vibration eliminating section 212, the gain is decreased around about 12.5 [Hz]. That is, it is found out that the steering wheel vibration caused by the springiness of the torsion bar and the inertia moment of the steering wheel is eliminated. Further, the torsion bar torque in the case of a response of the steering angle in FIG. 19 as described below, is shown in FIG. 18. Astringency of the vibration is improved.

[0100] In order to describe an effect of the present invention, time responses of the torsion bar torque with the steering wheel vibration eliminating section 212 and without it are shown in FIG. 18. As shown in FIG. 18, it is found out that the time response with the steering wheel vibration eliminating section 212 has a peak but the vibration is more suppressed.

[0101] Time responses of the actual steering angle h in the case of inputting the target steering angle ref to the steering angle control section 201X, are shown in FIG. 19. Waveform (A) shows a time response of the actual steering angle following the target steering angle without the steering wheel vibration eliminating section. Waveform (B) shows a time response of the actual steering angle following the target steering angle with the steering wheel vibration eliminating section. The leftmost graph in FIG. 19, that is, waveform (C) shows a time response of the target steering angle. (A) and (B) in FIG. 18 and (A) and (B) in FIG. 19 are time sequence data in the same simulation result.

[0102] The time response of the actual steering angle h following the target steering angle with the steering wheel vibration eliminating section 212 and the time response of the actual steering angle h following the target steering angle without the steering wheel vibration eliminating section 212 are almost the same, almost overlap each other, and this shows that the steering wheel vibration eliminating section 212 does not influence the time response of the actual steering angle h.

[0103] FIG. 20 is a block diagram showing a configuration example of a steering angle control section 202X in a third modified example of the second embodiment of the present invention. The steering wheel vibration eliminating section 212 eliminates the vibration (the vibration originating in the spring inertia system) caused by the springiness of the torsion bar and the inertia moment of the steering wheel in the automatic steering mode.

[0104] The third modified example is different from the second embodiment in that the steering wheel angle hd is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs the torsion bar torque Tt.

[0105] Other configurations and effects are the same as those of the second embodiment.

[0106] FIG. 21 is a block diagram showing a configuration example of a steering angle control section 203X in a fourth modified example of the second embodiment of the present invention. The steering wheel vibration eliminating section 212 eliminates the vibration (the vibration originating in the spring inertia system) caused by the springiness of the torsion bar and the inertia moment of the steering wheel in the automatic steering mode.

[0107] The fourth modified example is different from the second embodiment in that the actual steering angle h is subtraction-inputted into the subtracting section 213A, the velocity control section 215 inputs the motor angular velocity c, and the stabilization compensating section 220 inputs the column angle c.

[0108] Other configurations and effects are the same as those of the second embodiment.

[0109] Next, a third embodiment will be described around difference from the second embodiment with reference to the accompanying drawings. For convenience of explanation, the same configurations as those of the first embodiment and the second embodiment are designated with the same numerals or with numerals adding Y at the end, and the explanation is omitted.

[0110] The difference between the second embodiment and the third embodiment is that a steering wheel damping section 216 is provided for a steering angle control section 201Y. The steering wheel damping section 216 enables more suppression of the steering wheel vibration.

[0111] FIG. 22 is a block diagram showing a configuration example of a control system of an electric power steering apparatus according to the third embodiment of the present invention. FIG. 22 will be described by focusing on difference from the second embodiment. An EPS-side-ECU 140A comprises the torque control section 141 which outputs the motor current command value Itref calculated on the basis of the steering torque Th and the motor angular velocity c, and the steering angle control section 201Y which calculates and outputs the motor current command value Imref for the steering angle automatic control on the basis of the target steering angle ref, the actual steering angle h, the motor angular velocity c, and moreover the torsion bar torque Tt. That is, the EPS-side-ECU 140A is configured to add a configuration that the torsion bar torque Tt is inputted into the steering angle control section 201Y to the configuration shown in the above-mentioned FIG. 4. Moreover, a signal of the torsion bar torque Tt is also called a twist torque signal.

[0112] FIG. 23 is a block diagram showing a configuration example of the steering angle control section 201Y in the third embodiment of the present invention. The steering wheel damping section 216 is provided for the steering angle control section 201Y to suppress the steering wheel vibration during operation. In the steering angle control section 201Y, the output from the subtracting section 213C is inputted into the adding section 213D, and the output obtained by the filtering processing to the motor angular velocity c by the stabilization compensating section 220 is inputted into the adding section 213D. An output of the adding section 213D is inputted into an adding section 213E. The steering wheel damping section 216 performs signal processing to cut off a predetermined frequency or less of the torsion bar torque Tt. An output of the steering wheel damping section 216 is inputted into the adding section 213E. The steering angle control section 201Y is configured so that an output from the adding section 213E is inputted into the limiter 217 at the final stage. That is, the steering angle control section 201Y is configured to add a configuration of adding a signal outputted from the adding section 213D and the output of the steering wheel damping section 216 at the adding section 213E, and outputting the added result to the limiter 217, to the configuration shown in FIG. 14. This enables the cutoff of the predetermined frequency or less of the torsion bar torque Tt and the suppression of the steering wheel vibration during operation.

[0113] With respect to a frequency characteristic of the steering wheel damping section, FIG. 24A is a characteristic diagram showing a frequency characteristic of a gain, and FIG. 24B is a characteristic diagram showing a frequency characteristic of a phase. As shown in the characteristic diagrams of FIGS. 24A and 24B, the steering wheel damping section 216 is a phase advance filter, whose cutoff frequency is 12.5 [Hz], attenuates components of its frequency or less, and performs phase advance (primary) compensation. A cutoff frequency of the phase advance filter is set on the basis of the steering wheel vibration frequency of the vibration caused by the springiness of the torsion bar and the inertia moment of the steering wheel, and may be set, for example, within 12.55.0 [Hz]. Not only the phase advance filter but a filter that can reduce a resonance gain characteristic in the vicinity of 12.5 [Hz], may be used.

[0114] Also in the third embodiment, as with the second embodiment, a whole block diagram from the target steering angle ref to the actual steering angle h can be shown as a configuration in FIG. 25. The model will be described on the basis of this configuration.

[0115] FIG. 25 will be described by focusing on difference from the second embodiment. In this case, the model comprises a proportional section 321 where the torsion bar torque Tt is multiplied by a gain Ct, and the multiplied result is addition-inputted into the subtracting section 313c, in addition to the above configuration (shown in FIG. 16).

[0116] By an equivalent transformation of the whole block diagram from the target steering angle ref to the actual steering angle h as shown in FIG. 25, a block diagram as shown in FIG. 26 is obtained. By a further equivalent transformation, a block diagram as shown in FIG. 27 is obtained. Here, the rate limiter, the limiter and the steering wheel vibration eliminating section are omitted.

[0117] In the case that the target steering angle is ta [rad] and the torsion bar torque is Tt [N.Math.m], as with the above first embodiment, the transfer function Get from the target steering angle ta to the torsion bar torque Tt in the whole block diagram as shown in FIG. 27 is expressed as the expression 3, and G.sub.i and G.sub.it in the expression 3 are expressed as the expression 4 and the expression 5 respectively.

[0118] In the third embodiment, G.sub.ih and G.sub.i in the expression 4 are expressed as the expression 10 and the expression 11 respectively.

[00008]$\begin{array}{cc}{G}_{\mathrm{ih}}=-\frac{G_{\mathrm{it}}}{J_h.Math.s^2+D_h.Math.s}& \left[\mathrm{Expression}.Math..Math.10\right]\\ G_{.Math..Math.i}=\frac{I_{\mathrm{ref}}}{{}_{\mathrm{ref}}}=\frac{\frac{K_{\mathrm{iv}}}{s}.Math.G_t^{}}{\left(K_{\mathrm{pv}}.Math.s+K_{\mathrm{iv}}\right).Math.G_t^{}.Math.G_{\mathrm{ic}}+1}& \left[\mathrm{Expression}.Math..Math.11\right]\end{array}$

G.sub.t in the expression 11 is expressed as the expression 12.

[00009]$\begin{array}{cc}{G}_t^{}=\frac{1}{1-C_t.Math.G_{i.Math.t}}& \left[\mathrm{Expression}.Math..Math.12\right]\end{array}$

[0119] G.sub.ct and G.sub.ic in the expression 5 are expressed as the expression 13 and the expression 14 respectively.

[00010]$\begin{array}{cc}{G}_{c.Math.t}=\frac{T_t}{{}_c}=-\frac{\left(D_s.Math.s+K_s\right).Math.\left(J_h.Math.s^2+D_h.Math.s\right)}{J_h.Math.s^2+\left(D_h+D_s\right).Math.s+K_s}& \left[\mathrm{Expression}.Math..Math.13\right]\\ G_{i.Math.c}=\frac{{}_c}{I_{r.Math.e.Math.f}}=\frac{K_t}{J_c.Math.s^2+D_c.Math.s-G_{\mathrm{ct}}}& \left[\mathrm{Expression}.Math..Math.14\right]\end{array}$

[0120] Here, an effect of the third embodiment of the present invention will be described by using FIG. 28. Waveform (A) in FIG. 28 shows a time response of the target steering angle. Waveform (B) shows a time response of the actual steering angle h to the target steering angle with only the steering wheel vibration eliminating section. Waveform (C) shows a time response of the actual steering angle h to the target steering angle with both the steering wheel damping section and the steering wheel vibration eliminating section. A simulation result of a time response of the torsion bar torque is shown in FIG. 29. According to the simulation result shown in FIG. 29, the steering angle control section using the steering wheel damping section and the steering wheel vibration eliminating section has an effect of suppressing the steering wheel vibration during operation. Further, the astringency of the vibration is improved.

[0121] FIG. 30 is a block diagram showing a configuration example of a control system of an electric power steering apparatus according to a fifth modified example of the third embodiment of the present invention.

[0122] FIG. 31 is a block diagram showing a configuration example of a steering angle control section 202Y in the fifth modified example of the third embodiment of the present invention.

[0123] The fifth modified example is different from the third embodiment in that the steering wheel angle hd is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs the torsion bar torque Tt.

[0124] Other configurations and effects are the same as those of the third embodiment.

[0125] FIG. 32 is a block diagram showing a configuration example of a control system of an electric power steering apparatus according to a sixth modified example of the third embodiment of the present invention.

[0126] FIG. 33 is a block diagram showing a configuration example of a steering angle control section 203Y in the sixth modified example of the third embodiment of the present invention.

[0127] The sixth modified example is different from the third embodiment in that the actual steering angle h is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs the column angle c.

[0128] Other configurations and effects are the same as those of the third embodiment.

[0129] Next, a fourth embodiment will be described around difference from the third embodiment with reference to the accompanying drawings.

[0130] The difference between the third embodiment and the fourth embodiment is that a motor velocity command FF filter 218 is provided for a steering angle control section 201Z. For convenience of explanation, the same configurations as those of the first embodiment to the third embodiment are designated with the same numerals or with numerals adding Z at the end, and the explanation is omitted.

[0131] FIG. 34 is a block diagram showing a configuration example of the steering angle control section 201Z in the fourth embodiment of the present invention.

[0132] FIG. 34 will be described by focusing on difference from the third embodiment. In the steering angle control section 201Z, the output of the rate limiter 211 is inputted into the motor velocity command FF filter 218. The steering angle control section 201Z is configured so that the motor velocity command FF filter 218 performs feedforward (FF) processing to the output of the rate limiter 211 and the result is inputted into an adding section 213F as a feedforward motor angular velocity command value. The motor velocity command FF filter 218 is provided in order to improve responsiveness of steering angle control by extending a control band of the actual steering angle corresponding to the target steering angle to a high-frequency side.

[0133] In the case of providing the steering angle control section 201Z with the motor velocity command FF filter 218, a result of a simulation is shown in FIG. 35. In FIG. 35, waveform (A) shows a time response of the target steering angle, waveform (B) shows a time response of the actual steering angle without the motor velocity command FF filter, and waveform (C) shows a time response of the actual steering angle with the motor velocity command FF filter. As shown in FIG. 35, it is found out that followability of the steering angle control with the motor velocity command FF filter is more improved than that without it. The motor velocity command FF filter enables the extension of the control band of the actual steering angle corresponding to the target steering angle after the rate limit processing to a high-frequency side. Further, followability of the actual steering angle to the target steering angle is enhanced, responsiveness of vehicle motion control is also improved, so that the motor velocity command FF filter is effective in a rapid lane change.

[0134] FIG. 36 is a block diagram showing a configuration example of a steering angle control section 202Z in a seventh modified example of the fourth embodiment of the present invention.

[0135] The seventh modified example is different from the fourth embodiment in that the steering wheel angle hd is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs the torsion bar torque Tt.

[0136] Other configurations and effects are the same as those of the fourth embodiment.

[0137] FIG. 37 is a block diagram showing a configuration example of a steering angle control section 203Z in an eighth modified example of the fourth embodiment of the present invention.

[0138] The eighth modified example is different from the fourth embodiment in that the actual steering angle h is subtraction-inputted into the subtracting section 213A, and the stabilization compensating section 220 inputs the column angle c.

[0139] Other configurations and effects are the same as those of the fourth embodiment.

[0140] All of the above embodiments of the present invention are only what shows an example of incorporating the present invention (for example, sensor information such as the target steering angle, the actual steering angle, the torsion bar torque, the motor angular velocity or the like, control quantity, etc.) in the case of implementing the present invention, and technical scope of the present invention should not be interpreted attributivelyby these. That is, the present invention can be implemented in various forms without departing from its technical idea or its main feature. Further, functions performed by the above embodiments may be fittingly implemented by combining them as much as possible. Various stages are included in the above embodiment, and various inventions can be extractedby fittingly combining disclosed plural elements. Therefore, if several elements are deleted from all elements shown in the embodiment but the effect can be obtained, the configuration where these elements are deleted can be extracted as an invention. For example, the configuration where the rate limiter, the limiter or the like is deleted can be extracted as an invention. Moreover, all of the graphs and so on shown in the embodiments of the present invention show a result of a numerical analysis by a simulation.

[0141] In each embodiment of the present invention, the actual steering angle, the motor angular velocity and the torsion bar torque (the twist torque) are collectively referred to as a steering state signal. All of them are signals or data relating to an operation of a steering wheel or a state of a motor in an electric power steering apparatus.

EXPLANATION OF REFERENCE NUMERALS

[0142] 2 column shaft (steering wheel shaft) [0143] 2A input shaft [0144] 2B output shaft [0145] 20 motor [0146] 23 torsion bar [0147] 100 control unit [0148] 130 vehicle-side-ECU [0149] 131 switching command section [0150] 132 target steering angle generating section [0151] 140, 140A EPS-side-ECU [0152] 240, 240A EPS-side-ECU [0153] 340, 340A EPS-side-ECU [0154] 141 torque control section [0155] 142 switching section [0156] 143 motor driving section [0157] 150 motor [0158] 151 rotation sensor [0159] 152 steering angle sensor [0160] 201, 201X, 201Y, 201Z steering angle control section [0161] 202, 202X, 202Y, 202Z steering angle control section [0162] 203, 203X, 203Y, 203Z steering angle control section [0163] 211 rate limiter [0164] 212 steering wheel vibration eliminating section [0165] 213A, 213B, 213C subtracting section [0166] 213D, 213E, 213F adding section [0167] 214 position control section [0168] 215 velocity control section [0169] 215a integrating section (gain Kiv) [0170] 215b proportional section (Kpv) [0171] 216 steering wheel damping section [0172] 217 limiter [0173] 218 motor velocity command FF filter [0174] 220 stabilization compensating section [0175] 311 rate limiter [0176] 312 steering wheel vibration eliminating section [0177] 313a, 313b, 313c, 313d subtracting section [0178] 313e adding section [0179] 314 proportional section (Kpp) [0180] 315a integrating section (gain Kiv) [0181] 315b proportional section (Kpv) [0182] 316 motor torque converting section (Kt) [0183] 317 torsion bar section [0184] 318a column inertia section [0185] 318b integrating section (l/s) [0186] 319 differentiating section (s) [0187] 320a delay section [0188] 320b steering wheel inertia section [0189] 320c integrating section