JP2002037109A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the feeling in steering by correcting the compensation in static friction according to a steering torque. SOLUTION: This electric power steering device generating a steering auxiliary power by driving a motor based on a steering torque signal outputted from a torque sensor detecting the steering torque and reducing the steering force of a driver is provided with a means finding a static friction estimation value estimating the static friction of a steering system, and a means compensating the static friction based on the static friction estimation value. The static friction compensation means is provided with a correcting means correcting the static friction compensation value according to the steering torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for assisting a steering force by the power of a motor.

[0002]

2. Description of the Related Art FIG.
FIG. 349 is a control block diagram of a conventional electric power steering apparatus, wherein 1 is a motor connected to a later-described steering system via a later-described decelerator to generate a steering assist force, and 2 is a steering torque signal. The static friction calculating means 3 for calculating the estimated value Tf of the static friction of the steering system from Vt calculates the back electromotive force of the motor 1 from the motor detected current Im and the motor applied voltage Vm to calculate the estimated value ω of the motor angular velocity. The motor angular velocity calculating means 4 differentiates the motor angular velocity estimated value ω obtained by the motor angular velocity calculating means 3 and calculates an estimated value dω / dt of the motor angular acceleration. The motor angular acceleration calculating means 4 is based on the steering torque signal Vt. A steering force assisting current calculating means 6 for calculating a current Is for assisting the steering force of the driver, 6 is a steering system static friction based on the static friction estimated value Tf. Static friction compensating current calculation means for calculating the current If to compensate, 7 current compensates for the Coulomb friction of the steering system based on the motor angular velocity estimate omega I
c is a Coulomb friction compensation current calculating means for calculating c, 8 is a viscous friction compensation current detecting means for calculating a current Id for compensating viscous friction of the steering system based on the estimated motor angular velocity ω, and 9 is an estimated motor angular acceleration dω / dt. Means 10 for calculating a current Ij for compensating the moment of inertia of the steering system based on
s, static friction compensation current If, and Coulomb friction compensation current Ic
This is a current control means for controlling the current of the motor 1 so that a motor target current Isum obtained by adding the motor compensation current Id and the inertia compensation current Ij matches the motor detection current Im.

FIG. 12 is an overall configuration diagram of an electric power steering apparatus, in which reference numeral 11 denotes a steering wheel,
2 is a steering shaft, 13 is a vehicle speed sensor that measures the vehicle speed of the vehicle and outputs a vehicle speed signal Vs, 14 is a torque sensor that measures the driver's steering torque and outputs a steering torque signal Vt, and 15 is the output of the motor 1 A speed reducer for transmitting torque to the steering shaft 12;
Reference numeral 17 denotes a controller that drives the motor 1 based on a signal input from the torque sensor 14 or the like. Reference numeral 17 denotes a battery serving as a power supply of the controller 16.

Next, the operation of the above-described conventional electric power steering apparatus will be described. Generally, the controller 16 controls the electric power steering apparatus.

The controller 16 fetches external signals such as a vehicle speed signal Vs and a steering torque signal Vt, estimates a static friction estimated value Tf of the steering system, an estimated motor angular velocity ω,
Internal signals such as the motor angular acceleration estimated value dω / dt are calculated, and then current values based on these signals are calculated by the calculation means for each current. That is, the steering force auxiliary current calculating means 5 calculates the steering force auxiliary current Is based on the steering torque signal Vt and the vehicle speed signal Vs, and the static friction compensation current calculating means 6 calculates the estimated static friction value Tf of the steering system and the vehicle speed signal Vs.
s, the Coulomb friction compensation current calculation means 7 and the viscous friction compensation current calculation means 8 calculate the Coulomb friction compensation current Ic and the viscous friction compensation current Id based on the estimated motor angular velocity ω and the vehicle speed signal Vs. The inertia compensation current calculator 9 calculates the inertia compensation current Ij based on the estimated motor angular acceleration dω / dt and the vehicle speed signal Vs.
Next, all of the current values calculated as described above are added as shown in Expression 1 to obtain a motor target current Isum used for controlling the motor current.

[0006]

(Equation 1)

Then, an assist torque is generated by controlling the current of the motor 1 by the current control means 10 so that the motor target current Isum matches the motor detection current Im.

Here, the compensation of the static friction will be described in detail. The static friction calculating means 2 estimates the static friction of the steering system by applying, for example, a high-pass filter as shown in FIG. 13 to the steering torque signal Vt. Here, the time constant of the high-pass filter may be substantially the same as the mechanical time constant or acceleration constant of the motor. FIG. 14 shows the obtained static friction estimated value Tf.

The static friction compensation current calculating means 6 calculates the current value for compensating for the static friction of the steering system by performing the calculation of equation (2).

[0010]

(Equation 2)

In the equation 2, the first term on the right side is a linear term for calculating a current proportional to the estimated static friction value Tf, and the second term on the right side is the motor 1 and the speed reducer 15 in the output direction of the estimated static friction value Tf.
Is a nonlinear term that outputs a current corresponding to the friction torque of If the current of the motor 1 and the output torque of the motor at the steering shaft are linear, the first term on the right-hand side becomes the static friction compensation current, but in reality, nonlinear components such as friction of the motor 1 and the speed reducer 15 are generated. Therefore, the value obtained by adding the second term on the right side becomes the static friction compensation current If.

FIG. 1 shows the details of the static friction compensation current calculating means 6.
It is shown in FIG. The first term on the right side computes a term proportional to the estimated static friction value Tf, and the second term on the right side computes a term for compensating for non-linearity such as friction of the motor 1 and the speed reducer 15 by a linear term computing means 21. This is performed by the term calculation means 22. The motor torque constant Kt, the motor reduction ratio n, the friction torque TL between the motor and the reducer, and the friction torque compensation dead zone DZ are determined as parameters unique to the electric power steering device.

Further, since the static friction compensation is for compensating the friction when the steering starts to be turned from the stationary state, a coefficient Kf for multiplying the estimated static friction compensation value Tf and a motor angular velocity estimation are obtained as shown in FIG. Window function 2 for value ω
3, the coefficient Kf may be changed by the window function 23. If the estimated value of the static friction compensation in this case is Tf1, it is expressed by Expression 3.

[0014]

(Equation 3)

Here, by setting the characteristic of the window function 23 so that the coefficient Kf decreases as the estimated motor angular velocity ω increases as shown in FIG. 17, the static friction can be obtained only when the estimated angular velocity ω of the motor is small. The compensation current If is output.

As described above, by adding the motor current to the static friction compensation current If, the static friction of the steering system can be compensated, and the feeling of being stuck when the steering starts to be turned from the stationary state can be eliminated. Further, the window function 23 for the estimated motor angular velocity ω enables the static friction compensation to be performed only when the estimated motor angular velocity ω is small.

[0017]

The behavior of the vehicle during traveling has a characteristic that the steering returns to neutral due to the self-aligning torque. For this reason, even in the case of performing steering for moving the steering from the stationary state in the same manner, the steering force when turning from near neutral is larger than that when returning from the turning state to near neutral. Therefore, the driver feels a sense of being caught in the vicinity of the neutral position more than in the case of returning from the cut state to the vicinity of the neutral position.

However, according to the conventional technique, the estimated value of the static friction is the same regardless of whether the amount of change in the steering torque signal is the same when the vehicle is turned from near the neutral position or when the vehicle is returned to the vicinity of the neutral position. In some cases, the driver feels a stuck feeling when cutting from near the neutral position, and when returning from the cutting state to near neutral, the steering becomes too light in some cases.

In general, as the vehicle speed increases, the self-aligning torque increases, and the steering angle decreases.
As the vehicle speed increases, it is necessary to increase the static friction compensation current and increase the sensitivity to changes in the steering torque signal. However, when the gains of the linear term and the non-linear term in the static friction current calculation are increased, control noise may be generated and static friction may become excessive in a low vehicle speed range.

The present invention has been made to solve the above problems, and has as its object to improve the steering feeling by compensating for the static friction in accordance with the steering torque.

Further, by changing the frequency characteristic of the calculation of the estimated value of the static friction according to the vehicle speed, it is possible to set the characteristic of the static friction compensation control with respect to the change in the behavior of the vehicle due to the vehicle speed. The purpose is to improve the steering feeling.

[0022]

SUMMARY OF THE INVENTION An electric power steering apparatus according to the present invention generates a steering assist force by driving a motor based on a steering torque signal output from a torque sensor for detecting a steering torque. An electric power steering apparatus for reducing a steering force of a driver, comprising: means for obtaining a static friction estimated value obtained by estimating static friction of a steering system; and means for compensating for static friction based on the static friction estimated value. Friction compensation means,
There is provided a correcting means for correcting the static friction compensation value in accordance with the steering torque signal.

The correction means corrects the static friction compensation value in accordance with the steering state determined by the direction of the steering torque and the direction of the motor angular velocity.

The correction means determines a turning state when the direction of the steering torque and the direction of the motor angular velocity match, and determines a return state when the direction of the steering torque and the direction of the motor angular velocity do not match, and determines the return state. In this case, the correction is made so that the static friction compensation value is smaller than that in the case where it is determined that the vehicle is in the cut state.

The correction means corrects the static friction compensation value according to a function of the steering torque.

The correction means corrects the static friction compensation value by a first correction corresponding to a steering state obtained from a direction of the steering torque and a direction of the motor angular velocity, and a second correction corresponding to a function of the steering torque. Is what you do.

Further, in an electric power steering apparatus for generating a steering assist force by driving a motor based on a steering torque signal output from a torque sensor for detecting a steering torque to reduce a driver's steering force,
Means for obtaining a static friction estimated value obtained by estimating the static friction of the steering system; and means for compensating the static friction based on the static friction estimated value. The static friction compensating means includes a filter used for calculating the static friction estimated value. Is changed in accordance with the vehicle speed.

Still further, the static friction estimating means reduces the cutoff frequency of a filter used for calculating an estimated static friction value as the vehicle speed increases.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a control block diagram of an electric power steering apparatus according to the present invention. The basic configuration is the same as that of a controller 16 of a conventional electric power steering apparatus. Is omitted. The overall configuration of the electric power steering device is the same as that of the conventional electric power steering device shown in FIG. 12, and a detailed description thereof will be omitted.

In FIG. 1, reference numeral 18 denotes a steering state determining means for determining a steering state signal Smode from the motor angular velocity ω and the steering torque signal Vt, and 6 denotes a static friction compensation value based on the estimated static friction value Tf and the steering state signal Smode. As static friction compensation current calculating means for calculating a current If for compensating for static friction of the steering system.

Next, the operation will be described. The control of the electric power steering device is performed by the controller 16. First, external signals such as a vehicle speed signal Vs and a steering torque signal Vt are fetched, and internal signals such as a steering system static friction estimated value Tf, a motor angular velocity estimated value ω, a motor angular acceleration estimated value dω / dt, and a steering state signal Smode. Is calculated.

Next, a current value based on these signals is calculated by the calculation means for each current. That is, the steering force auxiliary current calculation means 5, the Coulomb friction compensation current calculation means 7, the viscous friction compensation current calculation means 8, and the inertia compensation current calculation means 9 are respectively provided with the steering force auxiliary current Is as in the conventional electric power steering apparatus. , A Coulomb friction compensation current Ic, a viscous friction compensation current Id, and an inertia compensation current Ij.

The static friction compensation current calculation means 6 calculates a static friction current If based on the estimated static friction value Tf of the steering system, the steering state signal Smode, and the vehicle speed signal Vs.
The current values thus calculated are added in the same manner as in the conventional electric power steering apparatus, and become the motor target current Isum used for controlling the motor current.
0, the motor target current Isum and the motor detection current I
An assist torque is generated by controlling the current of the motor 1 so that m coincides with each other.

Here, the compensation of the static friction will be described in detail. In the first embodiment, a steering state determination unit 18 is added to a conventional electric power steering apparatus. As shown in FIG. 2, the steering state determination unit 18 cuts the first quadrant and the fourth quadrant in FIG. 2 when the steering torque signal Vt and the motor angular velocity estimated value ω are in the same direction, It is determined that the second and fourth quadrants of FIG. 2 are to be returned, and according to the determination result, the steering state signal Smode is set to 0 at the time of turning and 1 at the time of returning.
Output as

The static friction compensating current calculating means 6 is shown in FIG.
As shown in FIG. 1, as in the conventional electric power steering apparatus, the linear term calculating means 21 and the nonlinear term calculating means 22
And a coefficient switching means 24 for switching the coefficient Kf1 according to the value of the steering state signal Smode. After obtaining the static friction compensation current If0 in the same manner as in the conventional electric power steering apparatus, the static friction compensation current If is multiplied by the coefficient Kf1. Is calculated. The calculation of the static friction compensation current calculation means 6 is as follows.
Equation 4 can be expressed.

[0036]

(Equation 4)

Here, for example, if the characteristics of the coefficient switching means 24 are set as shown in Table 1, the static friction compensation current I at the time of return is set.
f is 0.7 times the value at the time of cutting.

[0038]

[Table 1]

In general, as a characteristic of a vehicle at the time of traveling, there is a self-aligning torque as shown in FIG.
It occurs in the direction to reduce the sideslip angle. The steering force increases when turning from neutral due to the influence of the self-aligning torque, but the steering force decreases when returning from the cut state to neutral. On the other hand, according to the first embodiment, by setting the coefficient Kf1 of the static friction compensation current at the time of return as described above to be smaller than that at the time of cutting, the static friction compensation current at the time of returning from the cut state to neutral is set. It is possible to prevent If to be small and the assist torque from becoming excessive. Thereby, the steering feeling can be improved.

The steering force assisting current calculating means 5, Coulomb friction compensating current calculating means 7, viscous friction compensating current calculating means 8 and inertia compensating current calculating means 9 in FIG. 1 may be replaced by any alternative means. . Further, if unnecessary due to the characteristics of the vehicle, it may be omitted.

Further, although the motor angular velocity calculating means 3 is obtained from the back electromotive force of the motor, it may be replaced by any other means such as a rotation sensor.

The steering state determining means 18 in FIG.
The characteristic of is that the steering torque signal Vt and the estimated motor angular velocity ω
Of the steering torque signal Vt or the estimated motor angular velocity ω, a dead zone or hysteresis may be provided, or the characteristic may be determined by a non-linear characteristic.

Embodiment 2 In the first embodiment, the static friction compensation current I is determined according to the determination of the turning and return of the steering.
By changing the coefficient Kf1 for calculating f, the assist torque was prevented from becoming excessive when returning from the cut state to the neutral state. However, as shown in FIG. The coefficient Kf2 for calculating the compensation current If may be changed.

The static friction compensation current calculating means 6 calculates the static friction compensation current If0 in the same manner as in the prior art, and then calculates the window function 2
The static friction compensation current If is calculated by multiplying by a coefficient Kf2 set by S5. Static friction compensation current I
f can be represented by Equation 5.

[0045]

(Equation 5)

Here, the characteristic of the window function 25 is set such that the coefficient Kf2 decreases as the steering torque signal Vt increases as shown in FIG. 6, so that the static friction compensation current If is reduced when the steering torque signal Vt is small. Only output. Since the steering torque signal Vt increases as the steering is turned, the static friction compensation current I when returning from the turned state to neutral as in the first embodiment.
f becomes small, and the steering feeling can be improved.

Embodiment 3 In the first embodiment, the coefficient Kf1 for calculating the static friction compensation current If is calculated based on the steering state signal Smode. In the second embodiment, the static friction compensation current I is calculated based on the window function 25 for the steering torque signal Vt.
Although the coefficient Kf2 of f is changed, these may be combined as shown in FIG.

[0048]

(Equation 6)

As shown in Expression 6, for If0 obtained in the same manner as in the conventional static friction compensation calculation, a coefficient Kf1 switched by the steering state signal Smode and a coefficient set by the window function 25 for the steering torque signal Vt. Kf
By multiplying by 2, the steering feeling can be improved as in the first and second embodiments.

Embodiment 4 In the first, second, and third embodiments, the steering torque signal Vt
Is applied to If0, which is the calculation result of the static friction compensation current, but may be arbitrarily set for each term of the calculation of the static friction compensation current, that is, the linear term or the nonlinear term. good.

In FIG. 8, the coefficient switched by the steering state signal Smode is Kf1, and the coefficients set by the window function 25 and the window function 26 for the steering torque signal Vt are Kf2 and Kf3, respectively. Kf1 is multiplied by Kf2, the output of the non-linear term calculating means 22 is multiplied by Kf2, and the sum of the terms is multiplied by Kf3. The static friction compensation current If in this case is expressed by Expression 7. Thus, the steering feeling can be improved as in the above-described first, second, and third embodiments.

[0052]

(Equation 7)

Embodiment 5 In the above-described first, second, third and fourth embodiments, the frequency characteristics of the high-pass filter in the static friction calculating means 9 have a constant value. It may be changed accordingly.

As shown in FIG. 9, when the cutoff frequency fc of the high-pass filter of the static friction calculation means 9 is reduced,
Since the gain in the low frequency range is increased, the estimated value T of the static friction is calculated.
The output of f increases. In general, the self-aligning torque of a vehicle increases as the vehicle speed increases. Therefore, if the cutoff frequency fc is reduced as the vehicle speed signal Vs increases as shown in FIG. 10, the increase in the self-aligning torque with respect to the vehicle speed can be compensated for by increasing the static friction compensation current If. Feeling can be improved.

Although the cutoff frequency is reduced in FIG. 9, the same effect may be obtained by changing the order of the filter.

[0056]

As described above, the electric power steering apparatus according to the present invention generates the steering assist force by driving the motor based on the steering torque signal output from the torque sensor for detecting the steering torque. An electric power steering apparatus for reducing a driver's steering force, comprising: means for obtaining a static friction estimated value obtained by estimating static friction of a steering system; and means for compensating for static friction based on the static friction estimated value. The static friction compensating means has a correcting means for correcting the static friction compensation value according to the steering torque signal, and can improve the steering feeling.

The correction means corrects the static friction compensation value in accordance with the steering state determined by the direction of the steering torque and the direction of the motor angular velocity, and can improve the steering feeling regardless of the steering state. .

The correcting means determines a turning state when the direction of the steering torque and the direction of the motor angular velocity match, and determines a return state when the direction of the steering torque and the direction of the motor angular velocity do not match, and determines the return state. In this case, the static friction compensation value is corrected so as to be smaller than when it is determined that the vehicle is in the cut state. Can be prevented from becoming excessive, and the steering feeling can be further improved.

The correcting means corrects the static friction compensation value according to the function of the steering torque, and can improve the steering feeling.

Further, the correction means corrects the static friction compensation value by a first correction according to the steering state obtained from the direction of the steering torque and the direction of the motor angular velocity, and a second correction according to the function of the steering torque. This makes it possible to make fine corrections according to the steering state and the steering torque, so that the steering feeling can be further improved.

Furthermore, in an electric power steering apparatus for generating a steering assist force by driving a motor based on a steering torque signal output from a torque sensor for detecting a steering torque to reduce a driver's steering force,
Means for obtaining a static friction estimated value obtained by estimating the static friction of the steering system; and means for compensating the static friction based on the static friction estimated value. The static friction compensating means includes a filter used for calculating the static friction estimated value. Is changed according to the vehicle speed, the steering feeling in the entire vehicle speed range can be improved.

Further, the static friction estimating means reduces the cutoff frequency of the filter used for calculating the estimated static friction value as the vehicle speed increases, and in particular, reduces the self-aligning torque which increases as the vehicle speed increases. Compensation can be made, and the steering feeling can be further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a controller according to a first embodiment.

FIG. 2 is a diagram illustrating characteristics of a steering state determination unit according to the first embodiment.

FIG. 3 is a block diagram showing static friction compensation current calculation means according to the first embodiment;

FIG. 4 is a diagram showing characteristics of a general self-aligning torque.

FIG. 5 is a block diagram showing static friction compensation current calculation means according to the second embodiment.

FIG. 6 is a diagram illustrating characteristics of a window function with respect to a steering torque signal according to the second embodiment.

FIG. 7 is a block diagram showing static friction compensation current calculation means according to the third embodiment.

FIG. 8 is a block diagram showing static friction compensation current calculation means according to the fourth embodiment.

FIG. 9 is a diagram illustrating frequency characteristics of a high-pass filter according to the fifth embodiment.

FIG. 10 is a diagram illustrating a cutoff frequency of a high-pass filter with respect to a vehicle speed in the fifth embodiment.

FIG. 11 is a block diagram showing a conventional electric power steering device.

FIG. 12 is an overall configuration diagram of a conventional electric power steering device.

FIG. 13 is a diagram showing frequency characteristics of a high-pass filter in a conventional electric power steering device.

FIG. 14 is a timing chart showing an example of an estimated value of static friction.

FIG. 15 is a block diagram showing static friction compensation current calculation means in a conventional electric power steering device.

FIG. 16 is a block diagram showing static friction compensation current calculation means using a window function in a conventional electric power steering device.

FIG. 17 is a diagram showing characteristics of a window function with respect to a motor electric angular velocity estimated value of a conventional electric power steering apparatus.

[Explanation of symbols]

 Reference Signs List 1 motor 2 static friction calculating means 3 motor angular velocity calculating means 4 motor angular acceleration calculating means 5 steering force auxiliary current calculating means 6 static friction compensating current calculating means 7 Coulomb friction compensating current calculating means 8 viscous friction compensating current calculating means 9 inertia compensating current Calculation means 10 Current control means 11 Steering wheel 12 Steering shaft 13 Vehicle speed sensor 14 Torque sensor 15 Reducer 16 Controller 17 Battery 18 Steering state determination means 21 Linear term calculation means of static friction compensation current calculation means 22 Static friction compensation current calculation means Nonlinear term calculating means 23 Window function for motor angular velocity estimated value 24 Coefficient switching means based on steering state signal 25 Window function for steering torque signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Matsumoto, Inventor 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Shigeki Otagaki 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 Inside Ryo Denki Co., Ltd. (72) Inventor Tetsuya Matsumoto 1-4-1, Chuo, Wako, Saitama Pref. Inside Honda R & D Co., Ltd. (72) Takahiko Adachi 1-4-1, Chuo, Wako, Saitama Pref. Inside the Honda R & D Center (72) Inventor Taku Natsume 1-4-1 Chuo, Wako-shi, Saitama F-term in the Honda R & D Co., Ltd. (reference) 3D032 CC08 DA15 DA23 DA64 DA65 DA66 DB11 DC11 DD02 DD07 DE02 EB11 EC23 GG01 3D033 CA13 CA16 CA20 CA21

Claims (7)

[Claims] 1. An electric power steering apparatus that generates a steering assist force by driving a motor based on a steering torque signal output from a torque sensor that detects a steering torque to reduce a driver's steering force. Means for obtaining a static friction estimated value obtained by estimating the static friction of the steering system; and means for compensating for the static friction based on the static friction estimated value. The static friction compensating means includes a static friction compensation value corresponding to the steering torque. An electric power steering apparatus, comprising: a correction unit that corrects a power steering. 2. The electric power steering apparatus according to claim 1, wherein the correction means corrects the static friction compensation value according to a steering state determined by a steering torque direction and a motor angular velocity direction. 3. The correction means determines a turning state when the direction of the steering torque and the direction of the motor angular velocity match, and determines a return state when the direction of the steering torque and the direction of the motor angular velocity do not match, and determines the return state. 3. The electric power steering apparatus according to claim 2, wherein the correction is performed such that the static friction compensation value is smaller in a case than in a case where it is determined that the vehicle is in a cutting state. 4. The electric power steering apparatus according to claim 1, wherein the correction means corrects the static friction compensation value according to a function of the steering torque. 5. The correction means corrects a static friction compensation value by a first correction according to a steering state obtained from a direction of a steering torque and a direction of a motor angular velocity, and a second correction according to a function of a steering torque. The electric power steering apparatus according to claim 1, wherein 6. An electric power steering apparatus that generates a steering assist force by driving a motor based on a steering torque signal output from a torque sensor that detects a steering torque to reduce a driver's steering force. Means for obtaining a static friction estimated value obtained by estimating the static friction of the steering system; and means for compensating the static friction based on the static friction estimated value. The static friction compensating means includes a filter used for calculating the static friction estimated value. An electric power steering apparatus characterized in that the frequency characteristic of the electric power steering is changed according to the vehicle speed. 7. The electric power steering apparatus according to claim 6, wherein the static friction estimating means lowers a cutoff frequency of a filter used for calculating an estimated static friction value as the vehicle speed increases.