JP2003081117A - Motor-driven power steering device for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain vehicle behavior for steering operation of a driver at a desired behavior in a motor-driven power steering device for an automobile in which steering operation is assisted by controlling an electric motor 22. SOLUTION: There are provided an assist control part 51 for multiplying a detection value ξ with a gain Ka to produce a controlled variable, a yaw rate feedback control part 52 for determining a controlled variable based on a deviation between a target yaw rate calculated from steering wheel torque u and an actual yaw rate ψS, and a motor control part 53 for controlling an electric motor 22 according to a controlled variable which is a sum of the controlled variables. The motor control part 53 comprises a correction means 54 for correcting the motor controlled variable to compensate torque transmitted from a steering wheel 11 to a wheel 32.

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 device, for example, the size of inertia varies, and 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. The vehicle behavior (yaw rate) generated with respect to the steering force may vary due to the unevenness, and a desired yaw rate with respect to the steering force may not be generated in the vehicle. Therefore, the driver may have to adjust the steering force so as to obtain a desired yaw rate, which causes deterioration of the steering feeling of the driver and a feeling of strangeness, which in turn causes fatigue of the driver. is there.

Therefore, for example, in addition to setting the first control amount (assist control amount) based on the detected value of the torque sensor, the target yaw rate is calculated based on the detected value of the torque sensor, and the target yaw rate and the vehicle are calculated. A second control amount of the electric motor is set according to a deviation from an actually generated yaw rate, and the electric motor is controlled by a motor control amount obtained by adding the first control amount and the second control amount. Can be considered. By doing so, even when the desired yaw rate is not generated by the control with only the first control amount, the second yaw rate based on the deviation between the target yaw rate and the actual yaw rate is obtained.
It is considered that the desired yaw rate is always generated by controlling the electric motor by the control amount.

However, when the electric motor is controlled by the second control amount based on the deviation between the target yaw rate and the actual yaw rate, steering by the driver and control by the second control amount are performed especially when the vehicle is disturbed. May interfere with each other.

That is, according to the control by the second control amount based on the deviation between the target yaw rate calculated from the steering wheel steering torque and the actual yaw rate, the steering wheel steering torque added by the driver is not transmitted to the wheels. Also, because the electric motor is controlled according to the steering torque of the steering wheel,
The wheel steering angle is changed to generate the desired yaw rate in the vehicle.

[0008] Considering now that a disturbance is input to the wheels and a yaw rate occurs in the vehicle due to, for example, an illegal road surface, the wheels and the steering wheel are connected to each other via a torque sensor (torsion bar). The disturbance input to the wheels is transmitted to the steering wheel via the torque sensor.

At this time, if the driver does not steer the steering wheel against the disturbance, the steering wheel steering torque is not generated and the target yaw rate becomes 0 (zero), which causes the second yaw rate to occur in the vehicle. The wheel steering angle is changed to cancel the yaw rate.

However, since the disturbance input to the wheels is transmitted to the driver as a steering reaction force, the driver normally carries out steering of the steering wheel in response to the disturbance. The steering wheel steering torque due to this is transmitted to the wheels via the torque sensor, so that the wheel steering angle is changed. Thus
Since the steering wheel steering by the driver is performed at the same time as the control by the second control amount with respect to the disturbance, the steering wheel steering and the control by the second control amount interfere with each other. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to avoid control interference in an electric power steering apparatus for an automobile which assists steering by steering an electric motor. At the same time, the behavior of the vehicle with respect to the steering of the driver by the driver is always made to be a desired behavior.

[0012]

In order to achieve the above object, the present invention provides a motor control for controlling an electric motor so that the torque transmitted between a steering wheel and a wheel via a torque sensor is canceled. The amount was corrected.

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. And a second yaw rate for determining the second controlled variable of the electric motor by calculating a target yaw rate based on the detection value of the torque sensor and subtracting the yaw rate actually generated in the vehicle from the target yaw rate. A controller and a first controller by the first controller.
A motor control unit for controlling the electric motor with a motor control amount obtained by adding a control amount and a second control amount by the second control unit is provided, and the motor control unit is provided between the steering wheel and the wheel. It is a specific matter to have a correction unit that corrects the motor control amount so that the torque transmitted through the torque sensor is canceled.

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 yaw rate from the detected value of the torque sensor and determines the second control amount by subtracting the yaw rate actually generated in the vehicle from the target yaw rate. . 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.

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

Thus, when the desired vehicle behavior (yaw rate) is not achieved even if the electric motor is controlled by the first control amount, the deviation between the target yaw rate calculated based on the detected value of the torque sensor and the actual yaw rate. Has occurred. Therefore, a desired yaw rate is generated in the vehicle by controlling the electric motor with the second control amount determined by this deviation. In this way, even if the size of the inertia and the size of the friction of the components that make up the electric power steering device vary, the driver operates the steering wheel (steering wheel steering torque).
On the other hand, the desired yaw rate always occurs in the vehicle.

The motor control section has a correction means for correcting the motor control amount so that the torque transmitted between the steering wheel and the wheel via the torque sensor is canceled. To correct the motor control amount, for example, the torque transmitted from the steering wheel to the wheels (estimated torque) is estimated based on the steering torque of the steering wheel, and the estimated torque may be subtracted from the motor control amount.
By doing so, the torque actually transmitted from the steering wheel to the wheels and the estimated torque subtracted from the motor control amount are offset, and in terms of control, the torque is not transmitted from the steering wheel to the wheels, that is, the torque is canceled. become. As a result, it is possible to prevent the steering of the steering wheel by the driver from interfering with the control in the second control unit, and as a result, the accuracy of control by the second control unit can be improved.

In this electric power steering apparatus for an automobile, the first control unit is configured to change the sensitivity of the first control amount according to the vehicle speed from the viewpoint of steering force characteristics and vehicle stability. preferable. Specifically, during low speed traveling (including when the vehicle is stopped), the sensitivity of the first control amount is increased to increase the auxiliary steering force by the electric motor, while during high speed traveling, the sensitivity of the first control amount is decreased. It is preferable to reduce the auxiliary steering force by the electric motor.

Thus, when the sensitivity of the first control amount is lowered as the vehicle speed becomes higher, it is preferable to correct the motor control amount when the sensitivity of the first control amount is low as described in claim 2.

That is, when the sensitivity of the first controlled variable is low, the sensitivity of the second controlled variable is relatively high. For this reason,
The problem of interference between the steering of the steering wheel by the driver and the control by the second control amount becomes remarkable. Therefore, it is preferable to correct the motor control amount in order to avoid the interference between the steering of the steering wheel by the driver and the control interference caused by the second control amount.

Further, as described in claim 3, the correction means comprises:
It is preferable that the correction of the motor control amount is prohibited when the vehicle speed is equal to or lower than the predetermined vehicle speed.

When the vehicle speed is equal to or lower than the predetermined vehicle speed, that is, when the vehicle is stopped or running at a low speed, the yaw rate does not occur or is unlikely to occur in the vehicle. Therefore, when the vehicle is stopped or traveling at a low speed, it is preferable that the control by the first control amount is not performed by the control by the second control amount based on the deviation between the target yaw rate and the actual yaw rate.

As described above, when the control by the second control amount is not performed, the problem of interference with the control by the second control amount does not occur, and when the vehicle is stopped or running at low speed, the influence of disturbance that causes such interference problem. There is no. On the contrary,
If the motor control amount is corrected by the correction means when the control by the second control amount is not performed, the control for canceling the torque transmitted between the steering wheel and the wheel via the torque sensor is performed. The steering torque of the steering wheel by the driver is not transmitted to the wheels, and the steering cannot be turned off.

Therefore, when the vehicle speed is equal to or lower than the predetermined vehicle speed, it is preferable to prohibit the correction of the motor control amount by the correction means.

Further, it is preferable that the second control section is constructed so as to change the sensitivity of the second controlled variable according to a predetermined condition, for example, according to the vehicle speed, etc. As described, the correction means is set so that the second control amount is 0.
In this case, it is preferable to prohibit the correction of the motor control amount.

This is because, as described above, when the second control amount is 0, the problem of interference with the control by the second control amount does not occur.

In addition, as described in claim 5, it is preferable that the correction means is configured to correct the motor control amount when the steering angle of the steering wheel is less than or equal to a predetermined steering angle.

That is, the control of the electric motor is performed by the second control amount based on the deviation between the target yaw rate and the actual yaw rate, which prevents the behavior of the vehicle from varying due to the magnitude of the friction varying from component to component. This is because. The problem of variation in vehicle behavior due to friction is remarkable when the vehicle response (yaw rate) to the steering wheel is linear, and in the non-linear region where the steering wheel steering angle is larger than the predetermined steering angle. , It doesn't really matter. Therefore, as described above, if the target yaw rate related to the second control amount is calculated using a map (gain) for the steering torque that is set in advance, the control becomes simpler, and in the linear region of the vehicle response, depending on the second control amount. The control works effectively, and the desired yaw rate can always be generated even if the magnitude of the friction varies.

Then, in the linear region of the vehicle response when the steering angle of the steering wheel is equal to or smaller than the predetermined steering angle, the steering amount of the driver is controlled and the control of the second control unit is controlled by correcting the motor control amount. Interference can be avoided, and as a result, the accuracy of control by the second controller can be improved.

When the motor control amount is corrected, not only the torque transmitted from the steering wheel to the wheels is canceled but also the torque transmitted from the wheels to the steering wheel is canceled. Therefore, in the non-linear region of the vehicle response where the control by the second control amount is not effective, the correction of the motor control amount is prohibited and the torque is transmitted from the wheel to the steering wheel so that the state of the wheel or the like is used as a steering reaction force. It is preferable to tell.

Further, as described in claim 6, the correction means is
It is preferable that the predetermined steering angle (threshold value relating to the correction of the motor control amount) be reduced as the steering angle speed of the steering wheel increases.

That is, the higher the steering angle speed of the steering wheel, the narrower the linear region of the vehicle response. Therefore, by reducing the predetermined steering angle, which is the threshold value related to the correction of the motor control amount, the execution / prohibition of the correction of the motor control amount can be appropriately switched according to the linear region of the vehicle response. .

[0036]

As described above, according to the electric power steering apparatus for an automobile of the present invention, the electric motor is driven by the first control amount based on the detected value of the torque sensor and the second control amount based on the target yaw rate. Is controlled, it is possible to always obtain a desired vehicle behavior with respect to steering of the steering wheel regardless of the magnitude of friction or inertia, and it is possible to eliminate a performance difference between products, for example.

At the same time, the motor control amount is corrected so that the torque transmitted between the steering wheel and the wheel through the torque sensor is canceled, so that the steering wheel steering by the driver and the second control amount are performed. It is possible to avoid interference with the control of the electric motor.

[0038]

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

1 and 3 show the construction of an electric power steering system for a vehicle, in which 11 is a steering wheel and 1 is a steering wheel.
Reference numeral 2 denotes a steering shaft which is connected to the steering wheel 11 and transmits the rotational force (steering force) of the steering wheel 11.
3 is the steering shaft 12 through a universal joint
Intermediate shaft 21 connected to
Steering gear box provided at the lower end of 3, 31
Is a tie rod arranged on both sides of the steering gear box 21, and 32 is a tire (front wheel) to which the tie rod 31 is connected.

A rack and pinion mechanism 24 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 the reduction gear 23 and a torque sensor 41 are provided, and the torque sensor 41 is arranged between the intermediate shaft 13 and the reduction gear 23. . 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, and the controller 5 controls the electric motor 22.

FIG. 3 shows a vehicle in a two-wheel model, where 33 is the rear wheel, Lf is the distance from the front wheel to the center of gravity of the vehicle, and Lr is the distance from the rear wheel to the center of gravity of the vehicle. Shows.

FIG. 2 shows the configuration of the controller 5, which includes the torque sensor 4
1. The detection values of the yaw rate sensor 42 for detecting the yaw rate generated in the vehicle and the motor rotation speed sensor 43 for detecting the rotation speed of the electric motor are input. still,
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 5 includes 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 target yaw rate based on the detected value of the torque sensor 41. And a yaw rate feedback control unit 52 as a second control unit that determines the second control amount by subtracting the yaw rate actually generated in the vehicle detected by the yaw rate sensor 43 from the target yaw rate, The control amount of the electric motor 22 is determined by adding the control amounts in the respective control units of the assist control unit 51 and the yaw rate feedback control unit 52, and the motor control unit 53 that controls the electric motor 22 with this control amount is used. I have it.

The assist control section 51 is configured to determine the first control amount (K _a · ξ) by multiplying the detected value ξ of the torque sensor 41 by the assist control gain K _a .

[0047] The assist control gain K _a is the vehicle speed V, the
It is a variable that is determined by the detected value ξ of the torque sensor and the differential value of this detected value ξ, and is a non-negative (positive or 0) variable that does not increase with respect to the vehicle speed V (when the vehicle speed is high (H), However, it is smaller than when the vehicle speed is low (L)
It is regarded as a variable.

The yaw rate feedback controller 52
Has a transfer function G ₁ (s) that compensates for the phase delay of the detected value ξ of the torque sensor 41. This transfer function G ₁ (s) is
As shown in FIG. 3, 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 (1).

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 )} (1) where s is Laplace The operators η _h and ω _h are adjustment parameters.

Then, the output of the 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.

The yaw rate feedback control section 52 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. As described above, the reason why the friction torque u _F is included in the steering wheel torque u is that the characteristic between the steering wheel torque u and the steering wheel angle θ _H becomes a hysteresis in a normal automobile, as shown in FIG. This is because

That is, this hysteresis characteristic is caused by the friction of the steering system or the like, but the control of the yaw rate feedback control unit 52 reduces or eliminates the influence of the friction. 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 of a preset magnitude is subtracted from the steering wheel torque u related to the calculation of the target yaw rate (the steering wheel torque u is opposite to the steering speed direction). By adding the friction torque u _F to the direction), 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 yaw rate feedback controller 52
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.
_y is set in advance based on the vehicle specifications such as the wheel base and the vehicle speed. That is, the control by the yaw rate feedback control unit 52 is targeted at a region where the vehicle response to the steering torque is linear (linear region of vehicle response). The details of the target gain K _y will be described later.

Further, the yaw rate feedback control unit 52 calculates the yaw rate sensor 4 based on the target yaw rate.
3 is subtracted from the actual yaw rate ψ _s detected (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 (2).

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

This C (s) may be, for example, a transfer function of 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 52 (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 controller 52 is not controlled. Accordingly, when the vehicle speed is equal to or lower than the predetermined vehicle speed, the assist control unit 51
Is controlled only by.

[0062] 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 to perform only the control by the yaw rate feedback control unit 52. This is because control interference may occur between the assist control unit 51 and the yaw rate feedback control unit 52.

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, if the steering torque of the steering wheel is 0, that is, if the target yaw rate is 0, the control of the yaw rate feedback control unit 52 is to maintain the straight traveling state. Therefore, the higher the vehicle speed V, the control gain C (s). 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 formula (2)).

When the vehicle speed V becomes higher (more than the 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 52 does not control in the low speed range, while the yaw rate feedback control unit 52 positively controls in the medium speed range (M). . Then, in the high speed range (H), the control by the yaw rate feedback control unit 52 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 52
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 52 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 (3).

[0072] _{G 4 (s) = ΣP k} s k / ΣQ l s l ... (3) In addition, k = 0,1,2, ..., K , l = 0,1,2, ..., L
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 (4).

G ₅ (s) = ω _j K _w / (s + ω _j ) (4) 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 52 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 2 is added to determine the motor control amount for controlling the electric motor 22.

Here, the motor control section 53 has a correction means 54, and the correction means 54 has a handle 1
The motor control amount is corrected so that the torque transmitted between the wheel 1 and the wheel 32 via the torque sensor 41 is canceled.

The correction means 54 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 steering 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.

As shown in FIG. 7, the first gain K ₁ is 0 when the vehicle speed is equal to or lower than the first vehicle speed V ₁ , and when the vehicle speed is higher than the first vehicle speed V ₁ , the first gain K ₁ increases in accordance with the increase of 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, as shown in FIG. 8, when the steering angle θ _H of the steering wheel is less than or equal to the first steering angle θ ₁ , the second gain K ₂ is a constant value regardless of the steering angle θ _H. When the steering angle θ ₁ is larger than the steering angle θ ₁ , the steering angle θ _H is decreased according to the increase, and when it is larger than the second steering angle θ ₂ , the steering angle θ _H is set to 0. As a result, the steering wheel steering angle θ _H becomes the second
When it is larger than the steering angle θ ₂ , the motor control amount is not corrected. It should be noted that, even if the second gain K ₂ is not continuously changed between the first steering angle θ ₁ and the second steering angle θ ₂ , the second steering angle θ ₁ is set to be discontinuous at the first steering angle θ ₁ . The gain K ₂ may be set.

[0081] 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 (5).

G ₃ (s) = ω _i (C _b s + K _b ) / {K _b (s + η _i ω _i )} (5) 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)
And a torque component transmitted via the torque sensor 41 are calculated, and correction is performed by subtracting the calculated torque component from the motor control amount.

As described above, in the present embodiment, the target target yaw rate is calculated from the value of the torque sensor 41, and the electric motor 22 is controlled so as to reach this target yaw rate, whereby the assist control section 51 is controlled. Controlled variable (K _a
The target yaw rate (desired yaw rate) is generated in the vehicle by the control of the yaw rate feedback control unit 52 even if the desired yaw rate is not generated by controlling the electric motor 22 with ξ).

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

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 54. By correcting the motor control amount by the correction unit 54, 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 11 moves to the wheels 32. The torque will not be transmitted. In this way, it is possible to prevent the steering of the steering wheel by the driver from interfering with the control by the yaw rate feedback control unit 52, especially when the vehicle is subjected to disturbance.

In the correction means 54, the first
When the vehicle speed is equal to or lower than V _1, the first gain K _{1 is set} to 0, and when the vehicle speed is higher than the first vehicle speed V ₁ , the first gain K ₁ is set to the first gain according to the vehicle speed.
By increasing the gain K ₁ , it is configured to switch prohibition / execution of correction of the motor control amount. By doing so, it is possible to avoid control interference while avoiding unnecessary correction of the motor control amount.

That is, when the vehicle is stopped or traveling at a low speed when the vehicle speed is lower than the first vehicle speed V ₁ , no yaw rate is generated in the vehicle.
Or because it is hard to occur, in the controller 5,
The target gain K _y is set to 0, and the yaw rate feedback control unit 52 does not control the target gain K _{y so} that the target gain K _y is relatively increased when the vehicle runs at medium speed or high speed. on the other hand,
Assist control gain K _a, as shown by a chain line in FIG. 7, while the increase at standstill or low speed, at the time of medium speed or high speed running so that decrease.

Here, when the control by the yaw rate feedback control unit 52 is not performed, the problem of interference with the control by the yaw rate feedback control unit 52 does not occur, and the influence itself of the disturbance on the vehicle is originally caused when the vehicle is stopped or running at a low speed. Absent. Conversely, if the motor control amount is corrected by the correction unit 54 when the yaw rate feedback control unit 52 is not performing the control, the control for canceling the torque transmitted via the torque sensor 41 is performed. The steering torque of the steering wheel by the driver is not transmitted to the wheels, and the steering cannot be turned off.

Therefore, when the vehicle speed is equal to or lower than the first vehicle speed V ₁ , in other words, the yaw rate feedback control unit 52
When the control sensitivity of is 0, the above inconvenience is avoided by prohibiting the correction of the motor control amount. On the other hand, when the vehicle speed is higher than the first vehicle speed V ₁ , in other words, the control sensitivity of the assist control unit 51 is low, and conversely, when the control sensitivity of the yaw rate feedback control unit 52 is high, the motor control amount is corrected. Control interference is avoided.

Further, the correction means 54 is configured to switch prohibition / execution of correction of the motor control amount using the second steering angle θ ₂ as a threshold value. By doing so, while avoiding control interference, in a non-linear region of the vehicle response where the control by the yaw rate feedback control unit 52 is not effectively performed, the state of the wheels or the like can be accurately transmitted to the driver as a steering reaction force. .

That is, as described above, the yaw rate feedback control unit 52 is configured to control the vehicle response in the linear region. Therefore, in the linear region of the vehicle response where the steering wheel steering angle θ _H is equal to or less than the second steering angle θ ₂ , the control interference can be avoided by correcting the motor control amount, while the second control amount is used. Non-linear region of vehicle response where control is not effective (steering wheel steering angle θ _H is the second
When the steering angle is larger than the steering angle θ ₂ , torque is transmitted from the wheels to the steering wheel by prohibiting the correction of the motor control amount, so that the state of the wheels can be accurately transmitted to the driver as a steering reaction force. it can.

Further, the second steering angle θ ₂ which is a threshold for prohibiting / executing the correction of the motor control amount in the correcting means 54 is made smaller as the steering wheel angular velocity θ _H ′ becomes higher, so that a linear region of the vehicle response is obtained. In response to the narrowing of the motor control amount, the correction of the motor control amount is prohibited / executed, and in the linear region of the vehicle response, the desired yaw rate is generated by the control by the yaw rate feedback control unit 52 while avoiding the control interference. On the other hand, in the nonlinear region of vehicle response,
The state of the wheels and the like can be accurately transmitted to the driver as a steering reaction force.

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 52 when these behavior control devices operate.

That is, if the yaw rate feedback control section 52 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 52 is set to perform control in a state where the tire is gripped, and has the purpose of controlling the vehicle response in the linear region 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 52 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 52
Suppress control in. Specifically, according to the flow of FIG. 9, first, in step S1, it is determined whether or not the behavior control device is operating, and when it is not operating, step S2 is performed.
Then, the normal control of the yaw rate feedback control unit 52 is performed. On the other hand, when the behavior control device is operating, the sensitivity of the yaw rate feedback control unit 52 is reduced in step S3. In step S3, the control of the yaw rate feedback controller 52 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 electric motor 22 is configured to apply force to the pinion side, but it may be configured to apply force to the rack side.

[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.

FIG. 3 is a block diagram showing a configuration of an electric power steering device.

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 first gain in the correction means.

FIG. 8 is a diagram showing a characteristic of a second gain in the correction means.

FIG. 9 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) 52 Yaw Rate Feedback Control Unit (Second Control Unit)
Control unit) 53 motor control unit 54 correction means

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3D032 CC08 CC14 DA15 DA33 DC07                       EB11 EC22                 3D033 CA03 CA16

Claims (6)

[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. 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. As the torque transmitted through the torque sensor is canceled, the electric power steering apparatus for an automobile, characterized in that a correcting means for correcting the motor control amount. 2. The first control unit according to claim 1, wherein the first control unit lowers the sensitivity of the first control amount as the vehicle speed increases, and the correction unit reduces the sensitivity of the first control amount when the vehicle speed is low. An electric power steering apparatus for an automobile, which is configured to correct a motor control amount. 3. The electric power steering apparatus for a vehicle according to claim 2, wherein the correction means is configured to prohibit the correction of the motor control amount when the vehicle speed is equal to or lower than a predetermined vehicle speed. 4. The second control unit according to claim 1, wherein the second control unit is configured to change the sensitivity of the second control amount according to a predetermined condition, and the correction unit is configured to change the sensitivity of the second control amount. An electric power steering apparatus for an automobile, characterized in that the correction of the motor control amount is prohibited when 0. 5. The electric power steering apparatus for an automobile according to claim 1, wherein the correction means is configured to correct the motor control amount when the steering angle of the steering wheel is equal to or smaller than a predetermined steering angle. 6. The electric power steering apparatus for an automobile according to claim 5, wherein the correction means is configured to decrease the predetermined steering angle as the steering wheel angular velocity increases.