JP2003081118A - Motor-driven power steering device for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always provide a desired assist characteristic and improve steering feel in a motor-driven power steering device for an automobile in which steering is assisted by controlling an electric motor 22. SOLUTION: There are provided an assist control part 51 for multiplying wheel-steering torque u with a gain Ka to produce a controlled variable, a steering angular velocity feedback control part 54 for determining a controlled variable based on a deviation between a target motor rotational speed calculated from wheel-steering torque u and an actual motor rotational speed ω, and a motor control part 53 for controlling an electric motor 22 according to a controlled variable which is a sum/subtraction of the controlled variables. The steering angular velocity feedback control part 54 corrects the target motor rotational speed smaller for a higher vehicle speed.

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 an automobile, which has an electric motor and assists steering of a steering wheel by controlling the electric motor.

[0002]

2. Description of the Related Art Conventionally, there has been known a power steering device for assisting steering by an electric motor or hydraulic pressure. In this power steering device, steering torque or steering speed (differential value of steering angle) is used. The control amount or hydraulic pressure of the electric motor is adjusted to achieve a predetermined assist characteristic. In addition, the above assist characteristics are
For example, one that is changed according to the vehicle speed, and one that is changed according to the lateral acceleration and the yaw rate in addition to the vehicle speed (for example, see JP-A-8-72734) are known.

[0003]

By the way, in a conventional electric power steering apparatus, that is, a power steering apparatus using an electric motor, a torque sensor is usually provided between a steering wheel and a wheel to detect steering wheel steering torque. The control value of the electric motor is determined by multiplying the detected value of the (torsion bar) by a predetermined gain (assist control gain). The value of the assist control gain is adjusted so as to obtain a desired assist characteristic by performing a test on a predetermined automobile.

However, in this electric power steering apparatus, for example, the size of inertia varies, or the size of friction in the electric motor or a reduction gear provided between the electric motor and the steering shaft varies depending on the component. There is a problem in that the assist characteristics may vary from product to product due to variations in the product, and the desired steering feel may not be obtained.

Therefore, for example, in addition to setting the first control amount (assist control amount) based on the detection value of the torque sensor, the target wheel steering angle change rate is calculated based on the detection value of the torque sensor, and the target The second control amount of the electric motor is set according to the deviation between the wheel steering angle change rate and the actual wheel steering angle change rate, and the motor control amount is obtained by adding the first control amount and the second control amount. It is conceivable to control the electric motor. By doing so, even when the desired wheel steering angle change rate cannot be obtained by the control of only the first control amount, the second control based on the deviation between the target wheel steering angle change rate and the actual wheel steering angle change rate. By controlling the electric motor by the amount,
A desired wheel steering angle change rate can be obtained. As a result, it is considered possible to eliminate the inconvenience that the assist characteristics vary from product to product.

However, if the electric motor is controlled by the second control amount based on the deviation between the target wheel steering angle change rate and the actual wheel steering angle change rate, steering wheel steering may be uncomfortable.

That is, in a normal automobile without a power steering device, the steering wheel is heavy due to tire stationary torque when the vehicle is stopped or traveling at a low speed (that is, the change rate of the wheel steering angle with respect to the steering torque is small). The handle has a characteristic that the handle becomes lighter during high-speed running, and the restoring force of the handle increases during high-speed running, so that the handle becomes heavy again. Therefore, the second
Even in the control by the control amount, unless the steering force characteristic with respect to the vehicle speed is taken into consideration, the steering force characteristic is different from that of a normal vehicle, which may cause the driver to feel uncomfortable.

In particular, the gain of the first control amount (assist control amount) based on the detection value of the torque sensor is set low for the purpose of improving straight running stability during high speed traveling. For this reason, during high-speed traveling, the control by the second control amount becomes relatively large with respect to the first control amount, and there is a fear that the response of the vehicle to the steering wheel becomes too fast.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a desired assist characteristic in an electric power steering apparatus for a vehicle which assists steering by steering an electric motor. It is intended to improve the steering feeling while always obtaining it.

[0010]

In order to achieve the above object, the present invention corrects the target wheel steering angle change rate so as to have a predetermined characteristic with respect to the vehicle speed.

Specifically, the invention according to claim 1 is directed to an electric power steering apparatus for an automobile having an electric motor and assisting steering of a steering wheel by controlling the electric motor.

A torque sensor is provided between the steering wheel and the wheel for detecting the steering torque of the steering wheel, and a first control for determining the first control amount of the electric motor so that the detection value of the torque sensor becomes zero. Section, calculates the target wheel steering angle change rate based on the detection value of the torque sensor,
A second control unit that determines a second control amount of the electric motor by subtracting an actual wheel steering angle change rate from the target wheel steering angle change rate; and a first control amount by the first control unit. A motor control unit for controlling the electric motor with a control amount obtained by adding a second control amount by the second control unit is provided, and the second control unit controls the target wheel steering as the vehicle speed increases. It is a specific matter to configure the correction so as to reduce the angular change rate.

In the case of the first aspect of the invention, when the steering wheel is steered, the torque sensor provided between the steering wheel and the wheel detects the steering torque of the steering wheel.

The first control unit determines the first control amount so that the detection value of the torque sensor becomes zero, that is, the detection value of the torque sensor is multiplied by a predetermined gain. This corresponds to the conventional assist control.

On the other hand, the second control section calculates the target wheel steering angle change rate based on the detected value of the torque sensor, and subtracts the actual wheel steering angle change rate from the target wheel steering angle change rate. The second controlled variable is determined by. Here, the target wheel steering angle change rate may be calculated based on, for example, a vehicle model that models the system from the torque sensor to the wheels (tires). Examples of the vehicle model include an electric motor and a knuckle. The model may take into consideration the inertia of the arm, the spring component of the tire, and the damping component of the tire.

The control means controls the electric motor with a control amount obtained by adding the first control amount and the second control amount.

Here, even if the electric motor is controlled by the first control amount, when the desired wheel steering angle change rate is not obtained due to friction or inertia, the target wheel steering angle change rate calculated based on the steering wheel steering torque is set. There is a deviation from the actual wheel steering angle change rate. For this reason, the electric motor is controlled by the second control amount determined by the deviation, so that the insufficient motor thrust to reach the target wheel steering angle change rate (desired wheel steering angle change rate). It is generated in the electric motor, and the wheel steering angle change rate is set to a desired wheel steering angle change rate.

Since the second control amount is set on the basis of the target wheel steering angle change rate irrelevant to the variation in the magnitude of friction or inertia, even if the magnitude of friction or inertia is different. A desired wheel steering angle change rate is always obtained for steering the steering wheel. Therefore,
For example, there is no variation in assist characteristics between products.

The second control unit is adapted to make a correction such that the target wheel steering angle change rate becomes smaller as the vehicle speed becomes higher. By doing so, the characteristic of the target wheel steering angle change rate is such that the vehicle speed in a normal vehicle is such that the wheel steering angle change rate becomes smaller than the steering wheel steering torque during high speed traveling.
It has the same characteristics as the steering force characteristics, and the steering wheel becomes moderately heavy when traveling at high speeds. Further, if the target wheel steering angle change rate is made small, the control by the second control amount is also suppressed, so that the second control amount may become relatively larger than the first control amount during high speed traveling. Avoided. As a result, the vehicle responsiveness is set appropriately. In this way, it is possible to prevent the driver from feeling uncomfortable.

The target wheel steering angle change rate in the second control section may be calculated based on the first control amount set in the first control section from the detected value of the torque sensor.
By doing so, for example, when the second control unit calculates the target wheel steering angle change rate from the detection value of the torque sensor, as in the case where the first control unit determines the first control amount,
In the second control unit, a target is set based on the first control amount by the first control unit, in which the target wheel steering angle change rate must be calculated in consideration of the gain to be multiplied by the detection value of the torque sensor. When the wheel steering angle change rate is calculated, this first
Since the gain is considered in the control amount, the second
It is not necessary for the control unit to newly perform the calculation considering the gain. This simplifies the arithmetic processing in the second controller, and eliminates the need for the second controller to store the gain. Thus, even when the target wheel steering angle change rate is set on the basis of the detected value of the torque sensor and the first control amount in the first control unit, the higher the vehicle speed, the smaller the target wheel steering angle change rate is corrected. By doing so, the characteristic of the target wheel steering angle change rate becomes the same characteristic as the vehicle speed-steering force characteristic of a normal vehicle during high-speed traveling, and the second
It is possible to prevent the control amount from becoming relatively large with respect to the first control amount, and as a result, the vehicle responsiveness is appropriately set, and the driver's discomfort can be prevented.

In this electric power steering apparatus for an automobile, it is preferable to make a correction to reduce the target wheel steering angle change rate when the vehicle speed is equal to or lower than a predetermined speed.

Thus, the characteristic of the target wheel steering angle change rate is such that the vehicle speed in a normal vehicle is such that the wheel steering angle change rate becomes smaller than the steering wheel steering torque during low speed running.
It has the same characteristic as the steering force characteristic. In this way, it is possible to prevent the driver from feeling uncomfortable.

Further, as set forth in claim 3, correction is made so that the target wheel steering angle change rate is increased as the vehicle speed becomes higher when the vehicle speed is lower than the predetermined vehicle speed, and the target speed becomes higher when the vehicle speed is higher than the predetermined vehicle speed. It is preferable to make a correction to reduce the wheel steering angle change rate.

By doing so, the wheel steering angle change rate with respect to the steering wheel steering torque is small when the vehicle is stopped or traveling at low speed, the wheel steering angle change rate with respect to the steering wheel steering torque is large at medium speed traveling, and the steering wheel steering torque is against the steering wheel steering torque during high speed traveling. The rate of change in the wheel steering angle becomes smaller again,
The target wheel steering angle change rate has a mountain-shaped characteristic with respect to the vehicle speed. Since this mountain-shaped characteristic is the same as the vehicle speed-steering force characteristic in a normal vehicle, it is possible to prevent the driver from feeling uncomfortable.

[0025]

As described above, according to the electric power steering system for an automobile of the present invention, the first control amount based on the detected value of the torque sensor and the second control amount based on the target wheel steering angle change rate are provided. Therefore, since the electric motor is controlled, it is possible to always obtain a desired assist characteristic regardless of the magnitude of friction or inertia, and to eliminate a performance difference between products, for example.

At the same time, by correcting the target wheel steering angle change rate according to the vehicle speed, the characteristic of the target wheel steering angle change rate becomes the same as the vehicle speed-steering force characteristic in a normal vehicle, and as a result, The steering feeling can be improved.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows an electric power steering apparatus for an automobile, in which 11 is a steering wheel,
12 is connected to the handle 11 and
Steering shaft that transmits the rotational force (steering force) of
13 is this steering shaft 1 via a universal joint
2, an intermediate shaft 21 connected to 2, a steering gear box 21 provided at the lower end of the intermediate shaft 13, 3
Reference numeral 1 is a tie rod arranged on both sides of the steering gear box 21, and 32 is a tire (wheel) to which the tie rod 31 is connected.

A rack and pinion mechanism (not shown) is provided in the steering gear box 21, and the lower end of the intermediate shaft 13 is connected to the pinion. On the other hand, both ends of the rack are connected to the tire 32 via tie rods 31.

The steering gear box 21 includes:
An electric motor 22 for applying a force to the pinion side via a reduction gear (not shown) and a torque sensor 41 (see FIGS. 2, 3 and 8) not shown in FIG. 1 are provided. The torque sensor 41 is arranged between the intermediate shaft 13 and the reduction gear. As a result, the torque sensor 41 is provided between the steering wheel 11 and the tire 32 to detect steering wheel steering torque.

The torque sensor 41 and the electric motor 22
Are respectively connected to the controller 5 (hereinafter, 5a for the controller according to the first embodiment and 5b for the controller according to the second embodiment described later), and the controller 5 controls the electric motor 22. Controlled.

Next, the configuration of the controller 5a will be described with reference to FIG. This controller 5
In a, a torque sensor 41 for detecting the steering torque u of the steering wheel, a vehicle speed sensor 42 for detecting the vehicle speed V, and the electric motor 2 are shown.
The detection value of each sensor of the motor rotation speed sensor 43 that detects the rotation speed ω of 2 is input. The vehicle speed sensor 4
2 may be, for example, a wheel speed sensor provided on each wheel. Further, the motor rotation speed sensor 43 may directly detect the rotation speed ω of the electric motor 22, or may be estimated from the voltage applied to the electric motor 22 or the like.

The controller 5a is provided with an assist control unit 51 as a first control unit that determines the first control amount so that the detected value of the torque sensor 41 disappears, and a brake control amount applied to the electric motor 22. The second control is performed by calculating the target wheel steering angle change rate (target wheel steering angular velocity) from the determined damping control unit 52 and the detection value of the torque sensor 41, and subtracting the actual wheel steering angular velocity from the target wheel steering angular velocity. The electric motor by adding and subtracting the control amounts in the steering angular velocity feedback control unit 54 as a second control unit that determines the amount and the control units of the assist control unit 51, the damping control unit 52, and the steering angular velocity feedback control unit 54. The motor control unit 53 that determines the control amount of the electric motor 22 and controls the electric motor 22 with this control amount.
It has and.

Here, the wheels 32 and the electric motor 22 are
Since they are connected to each other via the rack and pinion mechanism, the motor rotation speed ω is proportional to the wheel steering angular speed. Therefore, in the present embodiment, the motor rotation speed sensor 43 detects the motor rotation speed ω and substitutes it for the actual wheel steering angular speed. At the same time, instead of calculating the target wheel steering angle change rate, the target motor rotation speed is calculated. However, the present invention is not limited to this, and the target wheel steering angular velocity may be calculated while directly detecting the wheel steering angular velocity.

The assist control section 51 is configured to determine the first control amount (K _a · u) by multiplying the steering torque u of the steering wheel, which is the detected value of the torque sensor 41, by the assist control gain K _a. Has been done. The assist control gain K _a is a variable determined by the differential value of the vehicle speed V, the steering torque u and the steering torque u, nonnegative (positive or 0) is a variable and non-increasing with respect to the vehicle speed V ( The variable when the vehicle speed is high (H) is smaller than the variable when the vehicle speed is low (L). The assist control gain K _a is adjusted to a predetermined assist characteristic.

Further, the damping control section 52 is configured to determine the control amount (K _d · ω) by multiplying the motor rotation speed ω by the damping control gain K _d . This damping control gain K _d is the vehicle speed V,
It is a non-negative variable determined by the steering torque u of the steering wheel and the number of rotations of the motor, and is adjusted so as to obtain a predetermined damping characteristic, that is, a predetermined convergence.

The rudder angular velocity feedback control section 54
Is a transfer function G described later._vSteering of steering wheel which is the input of (s)
Friction component included in torque u (friction
Luk u _F) Friction gain K for setting_FHave
is doing. In this way, the steering torque u
Schontork u_FIncludes a normal car odor
As shown in FIG. 6, the steering torque u of the steering wheel and the steering torque u
Dollar rudder angle θ_HBecause the characteristic between and becomes hysteresis
is there.

That is, although this hysteresis characteristic is caused by the friction of the steering system or the like, the influence of the friction is reduced or completely eliminated by the control by the steering angular velocity feedback control section 54. For this reason, there is a possibility that the hysteresis characteristic between the steering torque u and the steering angle θ _H may be lost, as indicated by the alternate long and short dash line in FIG. As described above, the characteristic between the steering wheel torque u and the steering wheel angle θ _H becomes different from that of an ordinary vehicle, and as a result, the steering feeling is impaired.

Therefore, for the purpose of improving the steering feeling, the friction torque u _F having a preset magnitude is subtracted from the steering torque u of the steering wheel for calculating the target motor rotation speed (the steering wheel torque u is equal to the steering speed direction). Applies a friction torque u _F in the opposite direction) so that a predetermined hysteresis characteristic remains between the steering wheel torque u and the steering wheel angle θ _H.

Specifically, the above friction gain K _F
As shown in FIG. 4, the positive / negative of the friction torque u _F is set according to the direction of the motor rotation speed ω, and when the motor rotation speed ω (that is, the steering wheel steering speed) is positive, The friction torque is + u _F ,
When the motor rotation speed ω (that is, the steering wheel steering speed) is negative, the friction torque is set to −u _F. Since the friction torque u _F becomes discontinuous at the 0 (zero) point of the motor rotation speed ω, the driver may feel uncomfortable. For example, as shown in FIG. The friction gain may be set so that the friction torque u _F is continuously connected near the point. That is, the absolute value of the friction torque u _F may be reduced near the zero point of the motor rotation speed ω.

The width of the hysteresis can be adjusted by adjusting the magnitude of the friction torque u _F. As a result, the steering force characteristic (steering feeling) can always be made as designed. The friction torque u _F may be reduced as the vehicle speed increases. By doing so, the restoring force of the handle 11 is increased and the sense of return of the handle 11 can be improved during high-speed traveling. Further, the friction torque u _F may be reduced as the wheel steering angle increases. By doing so, the stability of the vehicle is improved in the region where the wheel steering angle is large, and the responsiveness of the vehicle is improved in the region where the wheel steering angle is small.

The steering angular velocity feedback control section 54 then subtracts the friction torque u _F from the steering torque u of the steering wheel in the torque sensor 41 (u−u _F ).
Has a transfer function G _v (s) that outputs the target motor rotation speed as an input, and based on the steering torque u of the steering wheel, the target motor rotation speed (G _v (s) · (u−u _F ))
Is configured to calculate.

Here, the transfer function G _v (s) is determined from a vehicle model in which the torque sensor 41 to the wheels (tires) 32 are modeled, as shown in FIG. That is, in this vehicle model, the reaction force of the tire 32 is represented by a spring, and modeling is performed assuming that one end of this spring is fixed. And this tire 32
In consideration of the spring component K _t and the damping component C _t of the steering wheel and the inertia I _m around the pinion shaft of the electric motor 22 and the knuckle arm in the system from the torque sensor 41 to the tire 32, the steering wheel steering torque u is input. The transfer function G _v (s) that outputs the target motor rotation speed is set by the equation (1).

G _v (s) = K _b × (K _a +1) s / {I _m s ² + (C _t + K _d ) s + K _t } ... (1) Here, s is a Laplace operator.

Further, K _b is a correction gain, which has a characteristic of having a mountain shape with respect to the vehicle speed as shown in FIG. 7.

That is, the predetermined vehicle speed V _M (for example, 40 to 5)
When the vehicle speed is 0 km / h or less, the higher the vehicle speed is, the higher the above K _b is set, and the predetermined vehicle speed V _{M is set.}
When the vehicle speed is higher than the above, the higher the vehicle speed, the smaller _Kb is set. As a result, the transfer function G
_The target motor rotation speed calculated by _v (s) is small when the vehicle is stopped and traveling at low speed, and large when traveling at medium speed.
It is set so that it decreases as the vehicle speed increases at high speeds.

Then, the rudder angular velocity feedback control section 54, the target motor rotational speed and the actual motor rotational speed ω detected by the motor rotational speed sensor 43.
And the deviation (G _v (s) · (u−u _F ) −ω) is calculated, and the deviation is multiplied by the gain G _o (s) to determine the control amount (second control amount). It is configured.

Here, when the gain G _o (s) is set to a constant K _o , it is preferable to adjust the following requirements (1) to (3).

[0049] That is, the K _o as variables of the vehicle speed, it is preferable to increase as the vehicle speed V is high. This is at low speed
This is because the influence of friction and the like is small and the vehicle model in which the tire 32 is represented by a spring does not match the actual vehicle.

Further, it is preferable that K _{o be} a variable of the road surface μ and that the smaller the road surface μ, the smaller. This is also because the reaction force against the torsion of the tire becomes small on the low μ road, and the vehicle model in which the tire 32 is represented by a spring does not match the reality. The road surface μ may be detected, for example, based on the wheel speed, or by any other known method.

Further, it is preferable that K _o be a variable of the vehicle weight and that the heavier the vehicle weight, the larger. This is because the tire 32 becomes difficult to move when the vehicle weight is heavy, and it is preferable to increase the motor thrust of the electric motor 22 accordingly. The vehicle weight may be detected by providing a road sensor or may be estimated based on the engine load.

In addition, let K _{o be} a variable of the wheel steering angle,
The smaller the wheel steering angle, the better it should be. By doing so, the convergence is further improved and the straight running stability is improved.

Furthermore, it is preferable that K _{o be} a variable of the wheel steering angular velocity and that it be increased as the wheel steering angular velocity increases. This is because when the wheel steering angular velocity is large, the inertia becomes large and the wheel steering angular velocity tends to be delayed with respect to the steering of the steering wheel. Therefore, it is preferable to give a large motor thrust to the electric motor 22.

The gain G _o (s) may be a high-pass filter instead of the case where K _o is a variable of the wheel steering angular velocity and is increased as the wheel steering angular velocity increases.
That is, even if G _o (s) = K _o ω _n s / (s + ω _n ) ... (2), the sensitivity of the control amount of the steering angular velocity feedback control unit 54 increases when the wheel steering angular velocity is large. Note that ω _n
Is an adjustment parameter and may be appropriately adjusted.

In this way, if each control amount is determined in the assist control unit 51, the damping control unit 52, and the steering angular velocity feedback control unit 54, the motor control unit 5
3, the control amounts of the assist control unit 51 and the steering angular velocity feedback control unit 54 are added, and the control amount of the damping control unit 52 is subtracted, so that the electric motor 22
The control amount is determined and the electric motor 22 is controlled.

As a result, in the first embodiment, the target motor rotation speed (wheel steering angle change rate) is calculated from the value of the torque sensor 41, and the electric motor 22 is controlled to reach this target motor rotation speed. It

Therefore, when the electric motor 22 is controlled by the control amount (K _a · u) by the assist control unit 51, the desired motor rotation speed (target motor rotation speed) cannot be achieved due to friction or inertia. Even if the electric motor 22
Is controlled. For this reason, the insufficient motor thrust to reach the target motor rotation speed is caused by the electric motor 22.
Occurs in. At this time, the target motor rotation speed is set irrespective of variations in the size of the friction of the actual components that make up the electric power steering device and variations in the size of the inertia. , The desired motor rotation speed is always obtained. Therefore, a desired assist characteristic can always be obtained.

Further, the steering angular velocity feedback control section 54
The correction gain K _b is used to correct the target motor rotation speed as the vehicle speed increases.
By doing so, the characteristic of the target motor rotation speed becomes the same characteristic as the vehicle speed-steering force characteristic in a normal vehicle in which the rate of change in the wheel steering angle becomes smaller with respect to the steering wheel steering torque during high-speed traveling. It is possible to prevent discomfort.

Further, during high speed running, the control by the assist control section 51 (control by the first control amount) is suppressed by the assist control gain K _a , but the target motor rotation speed is reduced by the correction gain K _b . Therefore, the control by the steering angle feedback control unit 54 (control by the second control amount) is also suppressed. As a result, it is possible to prevent the second control amount from becoming relatively large with respect to the first control amount during high-speed traveling, and as a result, it is possible to appropriately set the vehicle responsiveness.

In addition, the steering angular velocity feedback control unit 5
The correction gain K _b is used to make a correction to increase the target motor rotation speed during medium speed running, and to make a correction to reduce the target motor rotation speed during low speed running. As a result, the characteristics of the target motor rotation speed during low-speed and medium-speed traveling are made to match the vehicle speed-steering force characteristics of a normal vehicle, and the driver's discomfort is prevented and the steering feeling is improved. You can

<Second Embodiment> FIG. 8 shows the configuration of a controller 5b according to a second embodiment of the present invention, in which the configuration of the steering angular velocity feedback control section 54 is different from that of the first embodiment. . In addition, in the controller 5b according to the second embodiment, the configurations of the assist control unit 51 and the damping control unit 52 are the same as those of the first embodiment, and therefore the description thereof will be omitted.

The rudder angular velocity feedback control section 54
Has a transfer function G _v (s), and this transfer function G _v (s)
Is configured to calculate the target motor rotation speed. The input of this transfer function G _v (s) is the torque sensor 4
In addition to the steering wheel torque u (including the friction torque u _F ) detected by 1, the steering wheel torque u is added to the control amount of the electric motor 22 which is the output of the motor control unit 53. Is configured.

The transfer function G _v (s) is determined by the vehicle model shown in FIG. 3 and is set by the equation (3).

G _v (s) = K _b s / {I _m s ² + (C _t + K _d ) s + K _t } (3) Here, K _b is a correction gain, which is described in the first embodiment. Similarly to the above, it is configured to have a mountain-shaped characteristic with respect to the vehicle speed (see FIG. 7). Incidentally, as can be seen from equation (3), the steering angular speed feedback control section 54 in the second embodiment does not include the assist control gain K _a.

This steering angular velocity feedback control unit 54
Calculates the deviation between the target motor rotation speed calculated by the transfer function G _v (s) and the actual motor rotation speed ω detected by the motor rotation speed sensor 43, and the gain G _o is calculated for this deviation. Multiply by (s) and control amount (second control amount)
To decide. Then, in the motor control unit 53, the control amounts of the assist control unit 51 and the steering angular velocity feedback control unit 54 are added, and the damping control unit 52 is added.
The control amount of the electric motor 22 is determined by subtracting the control amount of
The electric motor 22 is controlled. still,
Also in the electric power steering system according to the second embodiment, it is preferable to appropriately adjust the gain G _o (s) as described above.

In the second embodiment, as in the first embodiment, since the feedback control of the motor rotation speed ω is performed, the target motor rotation speed is obtained by the control amount of the steering angular speed feedback control section 54. Insufficient motor thrust is generated in the electric motor 22. As a result, the desired assist characteristic can always be obtained.

The steering angular velocity feedback control section 54 calculates the target motor rotation speed from the control amount of the electric motor 22, that is, the control amounts of the assist control section 51 and damping control section 52. here,
Since the assist control gain K _a is already taken into consideration in the control amount by the assist control unit 51, the transfer function G _v (s)
It is not necessary to incorporate the assist control gain K _a (see equation (3)). Accordingly, it does not require differential values or the like of the steering torque u required for the determination of the assist control gain K _a. Therefore, the configuration of the steering angular velocity feedback control unit 54 is simplified, and the calculation processing is also simplified. Further, it is not necessary to store the assist control gain K _{a and the} like, and the memory capacity is saved.

Further, the steering angular velocity feedback control unit 54
However, since the correction gain K _b is configured to correct the target motor rotation speed according to the vehicle speed, the characteristic of the target motor rotation speed with respect to the vehicle speed is the same as the vehicle speed-steering force characteristic in a normal vehicle. Therefore, it is possible to prevent the driver from feeling uncomfortable.

<Other Embodiments> The present invention is not limited to the above-described embodiments, but includes various other embodiments. That is, in the above embodiment, the thrust of the electric motor 22 is configured to be applied to the pinion side, but it may be configured to be applied to the rack side. In this case, the vehicle model may be changed appropriately.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a controller according to the first embodiment.

FIG. 3 is a diagram showing a vehicle model.

FIG. 4 is a diagram showing an example of a friction gain.

5 is a diagram showing an example of a friction gain different from FIG.

FIG. 6 is a diagram showing a relationship between a steering wheel steering torque and a steering wheel steering angle.

FIG. 7 is a diagram showing a characteristic of a correction gain.

FIG. 8 is a diagram corresponding to FIG. 2 showing a configuration of a controller according to a second embodiment.

[Explanation of symbols]

11 Handle 22 Electric Motor 32 Wheel 41 Torque Sensor 51 Assist Control Unit (First Control Unit) 53 Motor Control Unit 54 Steering Angular Speed Feedback Control Unit (Second Control Unit)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 137: 00 B62D 137: 00 F term (reference) 3D032 CC08 CC12 DA03 DA09 DA15 DA24 DA50 DA63 DA82 DB02 DB03 DB05 DC21 DC29 DC34 DD02 DD06 DD07 DD08 DD17 EA01 EB04 EB11 EC22 GG01 3D033 CA11 CA13 CA16 CA18 CA19 CA20 CA21

Claims (3)

[Claims] 1. An electric power steering apparatus for an automobile, comprising an electric motor, for assisting steering of a steering wheel by controlling the electric motor, the torque sensor being provided between a steering wheel and a wheel for detecting steering wheel steering torque. A first control unit that determines a first control amount of the electric motor so that the detection value of the torque sensor becomes zero; and a target wheel steering angle change rate is calculated based on the detection value of the torque sensor. A second control unit that determines a second control amount of the electric motor by subtracting an actual wheel steering angle change rate from a target wheel steering angle change rate; and a first control amount and a first control amount by the first control unit. And a motor control unit that controls the electric motor with a control amount obtained by adding the second control amount by the second control unit. The second control unit has a target vehicle wheel steering angle change rate as the vehicle speed increases. Small An electric power steering system of a vehicle, characterized by being configured to the Kusuru correction. 2. The electric power of an automobile according to claim 1, wherein the second control unit is configured to make a correction to reduce a target wheel steering angle change rate when the vehicle speed is equal to or lower than a predetermined vehicle speed. Steering device. 3. The vehicle control system according to claim 1, wherein the second control unit corrects the target wheel steering angle change rate to be larger as the vehicle speed is lower than a predetermined vehicle speed and is higher than the predetermined vehicle speed. An electric power steering apparatus for an automobile, characterized in that the higher the higher, the smaller the target wheel steering angle change rate is corrected.