JP2003081119A - Motor-driven power steering device for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always provide a desired assist characteristic and desired behavior and improve steering feel in a motor-driven power steering device for an automobile in which wheel-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 includes a predetermined friction component in a detection value of the wheel-steering torque u.

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.

Further, not only the desired steering feeling cannot be obtained, but also the behavior (yaw rate) of the vehicle generated with respect to the steering force varies due to, for example, variations in the magnitude of inertia and variations in the friction. In some cases, a desired yaw rate does not occur in the vehicle with respect to the steering force. Therefore, there is a disadvantage that the driver may have to adjust the steering force so as to obtain a desired yaw rate.

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.

Further, the second control amount is not set according to the deviation between the target wheel steering angle change rate and the actual wheel steering angle change rate, but the target yaw rate is calculated based on the detected value of the torque sensor. At the same time, it is conceivable to set the second control amount according to the deviation between the target yaw rate and the yaw rate actually occurring in the vehicle.

By doing so, the second control based on the deviation between the target wheel steering angle change rate and the actual wheel steering angle change rate even when the desired wheel steering angle change rate cannot be obtained by the first control amount alone. Even if it becomes possible to generate a desired wheel steering angle change rate depending on the amount, or even if the desired yaw rate does not occur only with the first control amount, the deviation between the target yaw rate and the yaw rate actually occurring in the vehicle It is conceivable that a desired yaw rate can be generated by the second control amount based on.

However, if the electric motor is controlled by the second control amount based on the deviation between the target value and the actual value, the steering feeling may be impaired.

That is, in an ordinary automobile, as shown in FIG.
As shown in, steering wheel torque u and steering wheel angle θ
The characteristic between _H and _H becomes hysteresis. This hysteresis characteristic is caused by the friction of the steering system or the like, but if the electric motor is controlled by the second control amount, the influence of the friction is reduced or completely eliminated. 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. Thus, the characteristic between the steering torque u and the steering angle θ _H is
As a result of having characteristics different from those of a normal automobile, the steering feeling is impaired.

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

[0012]

To achieve the above object, the present invention includes a predetermined friction component in a detection value of a torque sensor for calculating a target wheel steering angle change rate or a target yaw rate. I did it.

Specifically, the invention according to claim 1 is directed 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.

Then, a torque sensor 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 sets the detection value of the torque sensor to a predetermined value. It is a specific matter that the target wheel steering angle change rate is calculated after including the friction component.

According to the first aspect of the present 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 unit calculates the target wheel steering angle change rate from the detected value of the torque sensor and subtracts the actual wheel steering angle change rate from the target wheel steering angle change rate. 2 Determine the controlled variable. 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.

If the desired wheel steering angle change rate is not achieved due to friction or inertia even if the electric motor is controlled by the first control amount, the target wheel calculated based on the steering wheel steering torque detected by the torque sensor. There is a deviation between the steering angle change rate and 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.

However, if the second control amount is set based on the target wheel steering angle change rate that is unrelated to the magnitude of friction, as described above, the control by the second control amount is performed. The hysteresis characteristic between the steering torque and the steering angle will be lost.

Therefore, in the second control section, a predetermined friction component is included in the detection value of the torque sensor relating to the calculation of the target wheel steering angle change rate. That is, a friction component (friction torque) opposite to the direction of the steering angular velocity is added to the detected value of the torque sensor. In this way, by calculating the target wheel steering angle change rate based on the detected value of the torque sensor including the predetermined friction component, the first wheel steering angle change rate based on the deviation between the target wheel steering angle change rate and the actual wheel steering angle change rate is calculated. Even if the electric motor is controlled by the two control amounts, the control is suppressed by the friction component. As a result, a predetermined hysteresis characteristic is provided between the steering wheel steering torque and the steering wheel steering angle. In this way, it becomes possible to leave the hysteresis characteristic of the steering torque and the steering angle of the steering wheel while always changing the steering rate of the steering wheel to the desired change rate.

Further, by adjusting the magnitude of the friction component included in the detection value of the torque sensor, it is possible to adjust the width of hysteresis between the steering torque of the steering wheel and the steering angle of the steering wheel. For this reason, it is possible not only to eliminate variations in assist characteristics among products, but also to make steering force characteristics (steering feeling) always as designed.

A second aspect of the present invention is directed to an electric power steering device for an automobile, wherein a torque sensor provided between a steering wheel and a wheel for detecting steering wheel steering torque and a detection value of the torque sensor are eliminated. A first control unit that determines a first control amount of the electric motor, and a target yaw rate is calculated based on a detection value of the torque sensor, and the yaw rate actually generated in the vehicle is subtracted from the target yaw rate. By the second of the above electric motor
A motor for controlling the electric motor with a second control unit that determines a control amount, and a motor control amount that is the sum of the first control amount by the first control unit and the second control amount by the second control unit. And a control unit.

Then, it is a specific matter that the second control unit is configured to calculate the target yaw rate after including a predetermined friction component in the detected value of the torque sensor.

That is, in the second aspect of the invention, the second
The control unit is configured to calculate the target yaw rate from the detected value of the torque sensor, and subtract the yaw rate actually occurring in the vehicle from the target yaw rate to determine the second control amount. Here, the target yaw rate may be calculated, for example, by a map (gain) for the steering torque of the steering wheel, which is set in advance based on the vehicle specifications such as the wheel base and the vehicle speed.

Then, the motor control unit controls the electric motor with the control amount obtained by adding the first control amount and the second control amount, so that the electric motor is controlled with the first control amount. Even when the desired vehicle behavior (yaw rate) is not obtained, the electric motor is controlled by the second control amount determined by the deviation between the target yaw rate and the actual yaw rate, so that the desired yaw rate is generated in the vehicle. In this way, the desired yaw rate is always generated in the vehicle in response to the steering wheel operation (steering wheel steering torque) by the driver.

In the second control section, since the predetermined friction component is included in the detected value of the torque sensor for calculating the target yaw rate, as described above, the behavior of the vehicle with respect to steering of the steering wheel is always maintained. It is possible to leave the hysteresis characteristic between the steering torque and the steering angle of the steering wheel while making the desired behavior. In this way, the steering feeling is improved.

In these electric power steering devices for automobiles, the friction component may be reduced as the vehicle speed increases, as described in claim 3, for example.

By doing so, when traveling at high speed,
The restoring force of the handle is enhanced, and the return feeling of the handle is improved.

Further, as described in claim 4, the friction component may be increased as the wheel steering angle is increased.

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.

[0033]

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 or the target yaw rate are used. Since the electric motor is controlled by the control amount, the desired assist characteristic or vehicle behavior can be always obtained for steering the steering wheel regardless of the size of friction or inertia. It can be lost.

At the same time, when the target wheel steering angle change rate or the target yaw rate is calculated, a predetermined friction component is included in the detection value of the torque sensor, so that the steering wheel steering torque-steering wheel steering angle characteristic becomes a hysteresis. It is possible to improve the steering feeling.

[0035]

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 in FIG. 1) is provided in the steering gear box 21, and the intermediate shaft 1 is provided in the pinion.
The lower ends of 3 are connected. 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 that applies a force to the pinion side via a reduction gear (not shown in FIG. 1) and a torque sensor 41 (not shown in FIG. 1) (see FIGS. 2, 3 and 8 to 10).
And the torque sensor 41 is disposed 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 the controllers 5 (hereinafter, for the controllers according to the first to third embodiments, 5a to 5c, respectively).
This controller 5 is connected to the controller 5
The electric motor 22 is controlled by.

Next, the structure 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 wheel 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 unit 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 detection 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.

As shown in FIG. 4, the friction gain K _F sets the positive or negative of the friction torque u _F according to the direction of the motor rotation speed ω, and the motor rotation speed ω (that is, steering wheel steering). When the speed) is positive, the friction torque is + u _F, and when the motor rotation speed ω (that is, the steering wheel steering speed) is negative, the friction torque is -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 K _F 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 rudder angular velocity feedback control section 54 then subtracts the friction torque u _F from the steering wheel torque u 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.

That is, the predetermined vehicle speed V _M (40 to 50 km)
/ H) or less, the higher the vehicle speed is, the higher the _Kb is set, and when the vehicle speed is higher than the predetermined vehicle speed V _M , the higher the vehicle speed is, the lower the _Kb is set. As a result, the target motor rotation speed calculated by the transfer function G _v (s) is small when the vehicle is stopped and traveling at low speed, is large when traveling at medium speed, and becomes smaller as the vehicle speed increases when traveling at high speed. Is set. By doing so, the target motor rotation speed has the same characteristic as the steering force characteristic with respect to the vehicle speed in an ordinary vehicle (vehicle without a power steering device).

That is, in a normal vehicle, the steering wheel is heavy due to the tire's stationary steering torque when the vehicle is stopped or traveling at low speed (that is, the wheel steering angle change rate is small with respect to the steering torque), but the steering wheel is operated at medium speed. Has a characteristic that the handle becomes heavier again because the restoring force of the handle increases at high speed. Here, if the characteristic of the target motor rotation speed with respect to the vehicle speed is different from the vehicle speed-steering force characteristic of a normal automobile, the driver will feel a sense of discomfort.

Further, in particular, when the vehicle is traveling at a high speed, the first control amount (control amount by the assist control section 51) is suppressed by the assist control gain K _a for the purpose of improving straight running stability. Control unit 54
Control amount) is relatively large with respect to the first control amount, and as a result, the vehicle responds too quickly to steering.

Therefore, the vehicle speed is reduced by the correction gain K _b .
By matching the characteristic of the target motor rotation speed with the vehicle speed-steering force characteristic of a normal automobile, it is possible to prevent the driver from feeling uncomfortable and improve the steering feeling, and to appropriately set the vehicle responsiveness. it can.

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).

[0057] 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 road surface μ is smaller, 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, with K _o as 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.

Further, 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 section 51, the damping control section 52 and the steering angular velocity feedback control section 54, the motor control section 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, a desired motor rotation speed (target motor rotation speed) cannot be obtained 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
If the control amount (second control amount) is set based on the target motor rotation speed that is unrelated to the magnitude of friction, the hysteresis characteristic between the steering wheel steering torque u and the steering wheel angle θ _H is lost. However, the steering angular velocity feedback control unit 54 calculates the target motor rotational speed after including the predetermined friction torque u _F in the detected value u of the torque sensor 41. Accordingly, even if the electric motor 22 is controlled by the second control amount, the control is suppressed by the friction torque u _F.
As a result, the steering wheel torque u and the steering wheel angle θ _H
Between them and, a predetermined hysteresis characteristic remains as shown in FIG. In this way, the steering feeling can be improved.

By adjusting the magnitude of the friction torque u _F , the width of hysteresis in the relationship between the steering torque u of the steering wheel and the steering angle θ _H of the steering wheel can be adjusted. For this reason, it is possible not only to eliminate variations in assist characteristics among products, but also to make steering force characteristics (steering feeling) always as designed.

The magnitude of the friction torque u _F may be changed according to the vehicle speed or the wheel steering angle. For example, the friction torque u _F may be reduced as the vehicle speed increases. By doing so, the feeling of returning the steering wheel 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.

<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 rudder 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, similar to 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 velocity 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 unit 54 is adapted to calculate the target motor rotation speed from the control amount of the electric motor 22, that is, the control amounts of the assist control unit 51 and the damping control unit 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 rudder angular velocity feedback control section 54
Then, since the target motor rotation speed is calculated after including the predetermined friction torque u _F in the detected value u of the torque sensor 41, the steering wheel torque u and the steering wheel angle θ _H are shown in FIG. As shown, the predetermined hysteresis characteristic remains, and the steering feeling can be improved as in the first embodiment.

<Third Embodiment> FIG. 9 shows the configuration of a controller 5c according to a third embodiment of the present invention, which is an assist control unit 51, a yaw rate feedback control unit 55, and a motor control unit. And 53.

That is, the electric power steering system for an automobile according to the third embodiment, as shown in FIG. 10, calculates the target yaw rate from the detected value of the torque sensor 41 and detects the yaw rate sensor 44 from the target yaw rate. The yaw rate ψ actually occurring in the vehicle
It is configured to determine the second controlled variable by subtracting _s . In the figure, the vehicle is shown as a two-wheel model, where 23 is a reduction gear, 24 is a rack and pinion mechanism, 33 is a rear wheel, Lf is the distance from the front wheel to the center of gravity of the vehicle, and Lr is the rear wheel. The respective distances to the center of gravity of the vehicle are shown.

Next, the configuration of the controller 5c will be described with reference to FIG. This controller 5
In c, since the configuration of the assist control unit 51 is the same as that of the first embodiment, the description thereof will be omitted.

The yaw rate feedback controller 55
Calculates the target yaw rate from the detected value of the torque sensor 41, and based on this target yaw rate, the yaw rate sensor 4
4 is a second control unit that determines the second control amount by subtracting the yaw rate actually generated in the vehicle detected by the transfer function G ₁ for compensating for the phase delay of the detected value ξ of the torque sensor 41. have (s). This transfer function G ₁ (s)
As shown in FIG. 10, the steering wheel inertia I _h , the damping coefficient C _{b of} the torque sensor (torsion bar) 41, and the spring constant K _b of the torsion bar 41 are set by the equation (4).

G ₁ (s) = {ω _h ² (I _h s ² + C _b s + K _b )} / {K _b (s ² +2 η _h ω _h + ω _h ² )} (4) where s is Laplace The operators η _h and ω _h are adjustment parameters.

Then, the output of the above transfer function (G ₁ (s) ·
ξ) is used to calculate the steering wheel steering torque u actually applied to the steering wheel by the driver.

Further, the yaw rate feedback control section 55 has a friction gain K _F for setting a friction component (friction torque u _F ) included in the steering torque u of the steering wheel (see FIG. 4).

The yaw rate feedback controller 55
Has a target gain K _y for calculating a target yaw rate from a value (u−u _F ) obtained by subtracting the friction torque u _F from the steering wheel torque u, and this target gain K _y is
It is preset based on the vehicle specifications such as the wheelbase and the vehicle speed. That is, the control by the yaw rate feedback control unit 55 is targeted for a region where the vehicle response to the steering torque is linear (linear region of vehicle response). This target gain K _y
The details of will be described later.

Further, the yaw rate feedback control section 55 calculates the yaw rate sensor 4 based on the target yaw rate.
4 subtracts the actual yaw rate ψ _s detected by 4 (K _y (G
₁ (s) · ξ−u _F ) −ψ _s ), and this deviation is multiplied by the control gain C (s) to determine the control amount (second control amount). The control gain C (s) is set by the equation (5).

C (s) = ΣB _m s ^m / ΣA _n s ⁿ (5) Note that m = 0, 1, 2, ..., M, n = 0, 1, 2 ,.
Is.

This C (s) may be, for example, a transfer function of the PID control theory for making the deviation between the target yaw rate and the actual yaw rate zero, and in the case of PID control, A (s)
₀ = 0, A ₁ = 1, B ₀ = integral gain, B ₁ = proportional gain,
B ₂ = differential gain. Also, the above C (s) is P
A transfer function using a control theory other than the ID control may be used.

Here, the sensitivity adjustment of the control amount of the yaw rate feedback control unit 55 (adjustment of the target gain K _y or the control gain C (s)) is preferably performed as follows.

When the vehicle speed V is equal to or lower than the predetermined vehicle speed, the target gain K _y is preferably set to 0. This is due to the following reasons. That is, although the target yaw rate is calculated from the detected value of the torque sensor 41 by steering the steering wheel 11, the yaw rate is unlikely to occur (or does not occur) in the vehicle during low-speed turning, for example. Therefore, even if the electric motor 22 is controlled so as to reach the target yaw rate during low-speed turning, the target yaw rate is not achieved. Therefore, when the vehicle speed is equal to or lower than the predetermined vehicle speed, it is preferable that the target gain K _y is set to 0 and the yaw rate feedback control unit 55 does not perform the control. Accordingly, when the vehicle speed is equal to or lower than the predetermined vehicle speed, the assist control unit 51
Is controlled only by.

[0090] On the other hand, when the vehicle speed is higher than a predetermined vehicle speed, 0 the assist gain K _a of the assist control unit 51,
It is preferable that only the control by the yaw rate feedback control unit 55 is performed. This is because control interference may occur between the assist control unit 51 and the yaw rate feedback control unit 55.

The control gain C (s) should be increased as the vehicle speed V increases. This is to improve straight running stability during high-speed traveling. That is, when a disturbance is input to the vehicle due to, for example, side wind or irregular road surface, the yaw rate is generated in the vehicle even though the driver is not steering the steering wheel, that is, the steering torque is 0. become. However, the control of the yaw rate feedback control unit 55 is a control for maintaining the straight traveling state if the steering torque of the steering wheel is 0, that is, the target yaw rate is 0. Therefore, the control gain C (s) increases as the vehicle speed V increases. By increasing, the straight running stability at high speeds will improve. The control gain C (s) may be adjusted by changing A _n and B _m (see equation (5)).

If the vehicle speed V becomes higher (beyond a predetermined vehicle speed), it is better to lower the target gain K _y as the vehicle speed becomes higher. This is because the behavior of the vehicle with respect to steering of the steering wheel at the time of high speed traveling is made dull. That is, in the medium speed range, it is preferable that the vehicle behavior (yaw rate behavior) reacts more sensitively to the steering wheel steering, for example, because the turning performance is improved. If the behavior reacts sensitively, the behavior may become unstable, and the driver may feel uncomfortable. Therefore, when the vehicle speed V is further increased, that is, when the vehicle is traveling at high speed, it is preferable to lower the target gain K _y to make the vehicle behavior dull with respect to steering.

Therefore, according to the above items (1) to (4), the yaw rate feedback control unit 55 does not perform control in the low speed range, while the yaw rate feedback control unit 55 actively performs control in the medium speed range (M). . Then, in the high speed range (H), the control by the yaw rate feedback control unit 55 is suppressed as compared with the middle speed range.

The target gain K _y should be lowered as the road surface μ decreases. This is because when the road surface μ is low, the tire reaction force is small, and therefore the yaw rate is generated in the vehicle even though the torque sensor 41 does not detect the value (or the detected value is small). For this reason, the target yaw rate and the actual yaw rate ψ _s do not match each other. Therefore, it is preferable to lower the target gain K _y as the road surface μ is lower to reduce the influence of the target yaw rate.

The smaller the wheel steering angle, the better the target gain K _y . This is to further improve straight running stability.

The target gain K increases as the wheel steering angular velocity increases.
_It is better to raise _y . This is because when the wheel steering angular velocity is large, the inertia becomes large and the vehicle behavior tends to be delayed with respect to the steering of the steering wheel 11. Therefore, it is preferable to give a large motor thrust to the electric motor 22.

Although the target gain K _y is adjusted for the above items 1 and 2, the control gain C (s) may be adjusted. On the contrary, in the above description, the control gain C (s) is adjusted, but the target gain K _y may be adjusted.

The yaw rate feedback controller 55
Also, in a predetermined virtual model, the electric motor 2
2 and the transfer function G ₄ (s) for calculating the motor rotation speed with respect to the sum of the torque transmitted from the steering wheel 11 to the wheels 32 via the torque sensor 41, and the predetermined value A transfer function G ₅ (s) for calculating a correction amount for correcting the control amount of the yaw rate feedback control unit 55 from the deviation between the motor rotation speed (steering angular velocity) in the virtual model and the actual motor rotation speed ω have.

The transfer function G ₄ (s) is set by the equation (6).

G ₄ (s) = ΣP _k s ^k / ΣQ _l s ^l (6) Note that k = 0, 1, 2, ..., K, l = 0, 1, 2 ,.
Is. Further, P _k and Q _l may be changed according to the vehicle speed, or may be changed stepwise according to the vehicle speed. At this time,
P _k and Q _l may be finely changed as the vehicle speed is lower (P _k and Q _l may be changed more frequently as the vehicle speed is changed).

On the other hand, the transfer function G ₅ (s) is set by the equation (7).

G ₅ (s) = ω _j K _w / (s + ω _j ) (7) where ω _j and K _w are adjustment parameters.

Damping is applied to the electric motor 22 by these transfer functions G ₄ (s) and G ₅ (s) to improve the stability.

When the assist control section 51 and the yaw rate feedback control section 55 determine the respective control amounts in this manner, the motor control section 53 causes the assist control section 51 and the yaw rate feedback control section 5 to operate.
The control amount of 5 is added to determine the motor control amount for controlling the electric motor 22.

Here, the motor control section 53 has a correction means 56. This correction means 56 is
The motor control amount is corrected so that the torque transmitted through the torque sensor 41 between the vehicle 1 and the wheel 32 is canceled.

The correction means 56 has a first gain K ₁ set according to the vehicle speed V, a second gain K ₂ set according to the steering wheel steering angle θ _H and steering wheel angular velocity θ _H ′, and torque. From the detection value of the sensor 41, the steering wheel 11 and the wheel 3
2 and a transfer function G ₃ (s) for calculating a torque component transmitted via the torque sensor 41.

[0107] The first gain K _1, as shown in FIG. 11, when the vehicle speed is the first vehicle speed V ₁ or less is 0, when higher than the first vehicle speed V _1, in response to an increase in the vehicle speed V When the vehicle speed is increased and is equal to or higher than the second vehicle speed V ₂ , it is set to be constant regardless of the vehicle speed. As a result, the motor control amount is not corrected when the vehicle is stopped or traveling at low speed. In addition, the first vehicle speed V ₁ and the second
The first gain K ₁ may be set to be discontinuous at the first vehicle speed V ₁ without continuously changing the first gain K ₁ with respect to the vehicle speed V ₂ .

On the other hand, the second gain K₂Is shown in Figure 12.
Sea urchin steering angle θ_HIs the first steering angle θ ₁When:
Rudder angle θ_HIs a constant value regardless of the first steering angle θ₁Than
Is also large, the steering angle θ_HDecrease with the increase of
In addition, the second steering angle θ₂Will be 0 if it is greater than
Is set. As a result, the steering wheel steering angle θ
_HBut the second steering angle θ₂Motor control amount when
Is not corrected. The first steering angle θ₁And the second steering angle θ₂When
Between the second gain K₂Without changing continuously
However, the first steering angle θ₁So that there is a discontinuity in
In K₂May be set.

[0109] Also, the second steering angle theta ₂ is 'set according to the steering angular velocity theta _H' steering speed theta _H greater the increases, a point (the drawing is the second steering angle theta ₂ is set smaller See the chain line).

The transfer function G ₃ (s) is set by the equation (8).

G ₃ (s) = ω _i (C _b s + K _b ) / {K _b (s + η _i ω _i )} (8) Here, ω _i and η _i are adjustment parameters.

Thus, the first gain K ₁ , the second gain K ₂ ,
And the transfer function G ₃ (s)
The torque transmitted via the torque sensor 41 is calculated, and the calculated torque is subtracted from the motor control amount.

Thus, in this embodiment, the target target yaw rate is calculated from the value of the torque sensor 41,
By controlling the electric motor 22 so as to attain this target yaw rate, the control amount (K _a ·
Even if the desired yaw rate is not generated by controlling the electric motor 22 with ξ), the target yaw rate (desired yaw rate) is generated in the vehicle by the control of the yaw rate feedback control unit 55.

Since the electric motor 22 is controlled so that the target yaw rate is obtained in this way, even if the magnitude of friction or inertia is different, the steering wheel steering torque (steering wheel steering torque) of the driver The desired yaw rate will always occur in the vehicle. As a result, steering feeling is improved and discomfort is reduced,
It is possible to reduce driver fatigue.

Further, the yaw rate feedback control unit 5
In 5, the target yaw rate is calculated after including the predetermined friction torque u _F in the steering wheel torque u, so that a predetermined hysteresis characteristic remains between the steering wheel torque u and the steering wheel angle θ _H. Becomes the first above
Similar to the embodiment, the steering feeling can be improved.

The motor control unit 53 estimates the torque (estimated torque) transmitted between the steering wheel 11 and the wheels 32 via the torque sensor 41, and subtracts the estimated torque from the motor control amount. It has a correction means 56. Therefore, by correcting the motor control amount by the correction unit 56, the torque actually transmitted from the steering wheel 11 to the wheels 32 and the estimated torque are canceled out, and in terms of control, the steering wheel is moved from the steering wheel 11 to the wheels 32. No torque is transmitted to 32. In this way, when the vehicle is subjected to a disturbance, the yaw rate feedback control unit 55 performs the control, and at the same time, the steering wheel steering torque by the driver is transmitted to the wheels 32, thereby avoiding the interference between the two. be able to.

Further, the correction means 56 is configured to switch prohibition / execution of correction of the motor control amount by changing the first gain K ₁ according to the vehicle speed. By doing so, the correction of the motor control amount is prohibited when the control by the yaw rate feedback control unit 55 is not performed, such as when the vehicle is stopped or running at low speed, and unnecessary correction of the motor control amount is avoided, while the yaw rate feedback control is performed. When the control sensitivity of the control unit 55 is high, the control interference can be avoided by correcting the motor control amount.

Further, the correction means 56 is configured to switch prohibition / execution of correction of the motor control amount by changing the second gain K ₂ according to the steering wheel steering angle θ _H. By doing so, in the linear region of the vehicle response where the steering wheel steering angle is small, control interference can be avoided by correcting the motor control amount, while in the nonlinear region of the vehicle response where the steering wheel steering angle is large, By prohibiting the correction of the motor control amount, torque is transmitted from the wheels 32 to the steering wheel 11, and the state of the wheels or the like can be accurately transmitted to the driver as a steering reaction force.

Incidentally, a vehicle stability control device (DSC: Dynamic Stability Control) for controlling the attitude in the yawing direction such as drift-out and spin, and an anti-lock brake system (ABS: Antilock Brake) for suppressing wheel lock. When the vehicle is equipped with a behavior control device such as System, it is preferable to reduce the control sensitivity of the yaw rate feedback control unit 55 when these behavior control devices operate.

In other words, if the yaw rate feedback control unit 55 based on the deviation between the target yaw rate and the actual yaw rate is operated while the behavior control device for controlling the attitude of the vehicle in the yawing direction is operating, the control is performed. Since the vehicle behavior (yaw rate) changes, control interference may occur, and the performance of control by the behavior control device (behavior control effect) may deteriorate. Further, the yaw rate feedback control unit 55 is set so as to perform control in the state where the tire is gripped, and has the purpose of controlling in the linear region of the vehicle response as described above. On the other hand, the behavior control device operates when the tire is slipping or when the vehicle response is in a non-linear region. Even if the yaw rate feedback control unit 55 is controlled when such a behavior control device operates, the control is not effective, and only the performance of the control by the behavior control device is deteriorated.

Therefore, when the behavior control device is under control, the yaw rate feedback control unit 55
Suppress control in. Specifically, according to the flow of FIG. 13, first, in step S1, it is determined whether or not the behavior control device is operating, and if it is not operating, step S1 is performed.
In step 2, the normal control of the yaw rate feedback controller 55 is performed. On the other hand, when the behavior control device is operating,
In step S3, the sensitivity of the yaw rate feedback controller 55 is reduced. In step S3, the control of the yaw rate feedback controller 55 may be prohibited.

<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.

FIG. 9 is a block diagram corresponding to FIG. 2 showing a configuration of a controller according to a third embodiment.

FIG. 10 is a block diagram showing a configuration of an electric power steering device according to a third embodiment.

FIG. 11 is a diagram showing the characteristic of the first gain in the correction means.

FIG. 12 is a diagram showing a characteristic of a second gain in the correction means.

FIG. 13 is a control flowchart of a yaw rate feedback control unit when the behavior control device is provided.

[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) 55 Yaw Rate Feedback Control Unit (Second Control Unit)
Control unit)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 131: 00 B62D 131: 00 137: 00 137: 00 F term (reference) 3D032 CC08 CC12 DA10 DA15 DA24 DA50 DA63 DA82 DB02 DB03 DB05 DC01 DC02 DC03 DC21 DC34 EA01 EB11 EB12 EB16 EC22 FF01 GG01 3D033 CA13 CA16 CA20 CA21

Claims (4)

[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 for controlling the electric motor with a control amount obtained by adding a second control amount by the second control unit, the second control unit having a predetermined flexion on the detection value of the torque sensor. On including emissions components, automotive electric power steering apparatus characterized by being configured to calculate the target wheel steering angle change rate. 2. 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, the torque sensor being provided between a steering wheel and a wheel for detecting steering wheel steering torque. And a first control unit that determines the first control amount of the electric motor so that the detection value of the torque sensor becomes zero, a target yaw rate is calculated based on the detection value of the torque sensor, and the target yaw rate is actually calculated. A second control unit that determines the second control amount of the electric motor by subtracting the yaw rate generated in the vehicle, a first control amount by the first control unit, and a second control amount by the second control unit. And a motor control unit that controls the electric motor with a motor control amount that is the sum of the two control amounts, and the second control unit determines the detected value of the torque sensor. Of on, including friction component, an electric power steering system of a vehicle, characterized in that it is configured to calculate the target yaw rate. 3. The electric power steering device for a vehicle according to claim 1, wherein the second control unit is configured to reduce the friction component as the vehicle speed increases. 4. The electric power steering apparatus for an automobile according to claim 1, wherein the second control unit is configured to increase the friction component as the wheel steering angle increases. .