JP2003137119A - Electric power steering device for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constantly provide desired behavior in behavior of a vehicle to operation of a steering wheel 1 of a driver in regard to an electric power steering device of an automobile assisting steering of the steering wheel 1 by control of an electric motor 11. SOLUTION: The electric power steering device for the automobile is provided with an assist control part 21 providing a controlled variable by multiplying a detected value ξ of a torque sensor 12 by a gain Ka, a lateral acceleration feedback control part 22 calculating a target lateral acceleration from a steering wheel steering torque u and determining a controlled variable on the basis of a deviation between the target lateral acceleration and an actual lateral acceleration G, and a motor control part 23 controlling the electric motor 11 by a controlled variable provided by adding each controlled variable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field relating to an electric power steering apparatus in which steering of a vehicle steering wheel is assisted by controlling an electric motor.
In the present invention, an automobile is also called a "vehicle".

[0002]

2. Description of the Related Art Conventionally, as a power steering device for an automobile, a device for assisting steering by an electric motor or hydraulic pressure is known. In this device, steering torque for steering and steering speed for steering (differentiation of steering angle for steering) are known. The control amount of the electric motor or the hydraulic pressure amount is adjusted according to the value) to realize a predetermined assist characteristic. Also,
There are also known ones that change the assist characteristics according to, for example, the vehicle speed, and ones that change according to the lateral acceleration and the yaw rate in addition to the vehicle speed (for example, see Japanese Patent Laid-Open No. 8-72734).

[0003]

In a conventional electric power steering apparatus using an electric motor, a torque sensor (which is usually provided between a steering wheel and a wheel (steering wheel) and detects steering torque of a steering wheel ( A torsion bar is provided, and the control value of the electric motor is determined by multiplying the detected value by a predetermined gain (assist control gain). Then, the value of the assist control gain is adjusted so as to obtain a desired assist characteristic based on a test conducted on a predetermined automobile.

However, in this electric power steering apparatus, for example, the lateral acceleration and the sideslip angle as the behavior of the vehicle generated with respect to the steering force vary for each product, and the desired lateral acceleration and sideslip angle with respect to the steering force vary. May not occur in the vehicle. In this case, the driver needs to adjust the steering force so that the desired lateral acceleration or sideslip angle is obtained.

The variations in the lateral acceleration and the sideslip angle are, for example, variations in the amount of inertia, or the magnitude of friction in an electric motor or a reduction gear mechanism provided between the electric motor and the steering shaft. The cause is that there are variations. For example, variations in the magnitude of friction are mainly due to manufacturing errors of parts, etc., and when the friction is larger than usual, the control amount obtained by multiplying the detected value of the torque sensor by a predetermined gain. Even if the electric motor is controlled by, the motor thrust is consumed by the friction, and the driver must increase the steering force without the auxiliary steering force by the electric motor being insufficient.

The case where the desired lateral acceleration or sideslip angle does not occur when the driver steers the steering wheel is not limited to the case where the inertia or the variation in the magnitude of the friction is caused, and for example, when traveling straight ahead ( When the steering force of the driver is 0), lateral acceleration or sideslip angle may occur in the vehicle due to disturbance to the vehicle such as side wind or irregular road surface. Also in this case, the driver needs to adjust the steering of the steering wheel to obtain the desired vehicle behavior.

As described above, since the desired lateral acceleration or sideslip angle is not generated for steering the steering wheel, the steering feeling of the driver is deteriorated or the user feels uncomfortable, and the driver is tired. there were.

The present invention has been made in view of the above circumstances, and an object thereof is to cope with a steering wheel of a driver in an electric power steering apparatus for an automobile, which assists the steering wheel by controlling the electric motor as described above. The object is to always make the vehicle behave as desired.

[0009]

In order to achieve the above object, in the present invention, feedback control based on the detected value of the torque sensor is added to the assist control in the conventional electric power steering apparatus. .

Specifically, the invention of claim 1 is directed to an electric power steering apparatus for an automobile, which assists steering by steering an electric motor.

A torque sensor provided between the steering wheel and the wheel for detecting the steering torque of the steering wheel, and a first control unit for determining the first control amount of the electric motor so that the detection value of the torque sensor becomes zero. And a second lateral acceleration that determines the second controlled variable of the electric motor by calculating the target lateral acceleration from the detected value of the torque sensor and subtracting the lateral acceleration actually occurring in the vehicle from the target lateral acceleration. And a motor control unit that controls the electric motor based on a control amount obtained by adding a first control amount by the first control unit and a second control amount by the second control unit. Characterize.

Further, according to the invention of claim 2, as an electric power steering device for an automobile, which assists the steering of the steering wheel by controlling the electric motor, a torque sensor provided between the steering wheel and the wheel for detecting steering torque of the steering wheel. And a first control unit that determines a first control amount of the electric motor so that the detection value of the torque sensor is eliminated, and a target sideslip angle is calculated from the detection value of the torque sensor, and from the target sideslip angle, A second control unit that determines the second control amount of the electric motor by subtracting the estimated sideslip angle estimated by calculation, a first control amount by the first control unit, and a second control unit by the second control unit. And a motor control unit that controls the electric motor based on the control amount obtained by adding the two control amounts.

According to the configurations of these inventions, as the steering wheel is steered, the torque sensor provided between the steering wheel and the wheel detects the steering torque of the steering wheel, and the detected value of the torque sensor is detected by the first controller. The first control amount is determined so that it disappears, that is, the detected value of the torque sensor is multiplied by a predetermined gain. This corresponds to the conventional assist control.

On the other hand, in the second control section, the target lateral acceleration or the target side slip angle is calculated from the detected value of the torque sensor, and the lateral acceleration actually generated in the vehicle or the target side slip angle is calculated from the target lateral acceleration. The second control amount is determined by subtracting the estimated sideslip angle estimated by calculation from Here, the target lateral acceleration and the target sideslip angle may be calculated 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 control unit controls the electric motor with a control amount obtained by adding the first control amount and the second control amount. Here, even if the electric motor is controlled by the first control amount, desired vehicle behavior (lateral acceleration or sideslip angle)
If not, it means that the deviation between the target lateral acceleration calculated based on the detection value of the torque sensor and the actual lateral acceleration or the deviation between the target sideslip angle and the estimated sideslip angle occurs. Therefore, the desired lateral acceleration or sideslip angle is generated in the vehicle by controlling the electric motor with the second control amount determined by this deviation.

As described above, by controlling the electric motor so that the target lateral acceleration or the target sideslip angle is obtained, even if the magnitude of the inertia or the friction of the components constituting the electric power steering device varies. , Driver's steering wheel operation (steering wheel steering torque)
In contrast, the desired lateral acceleration or sideslip angle will always occur in the vehicle. As a result, it is possible to improve the steering feeling and reduce the discomfort.

Further, for example, when the vehicle is in a straight traveling state, the steering wheel steering torque is 0 because the driver is not steering the steering wheel. Therefore, if lateral acceleration or sideslip angle occurs in the vehicle due to side wind or irregular road surface, the second
The control unit of (1) controls the target lateral acceleration or the target sideslip angle to be zero, that is, the control to maintain the straight traveling state, so that the straight traveling stability against the disturbance such as the lateral wind or the road surface irregularity can be improved. This eliminates the need for the driver to adjust the steering of the steering wheel and reduces the fatigue of the driver.

In the electric power steering system for an automobile according to the first or second aspect of the present invention, more preferable control is realized by adjusting the sensitivity of the second controlled variable. Specifically, as in the third aspect of the present invention, it is preferable that the second control unit be configured to increase the sensitivity of the second controlled variable as the vehicle speed increases. That is, in the region where the vehicle speed is high,
Since the driver turns the steering angle little by little and quickly, the driver is concerned about being caught by friction, so it is preferable to increase the sensitivity of the second control amount. On the other hand, in the low vehicle speed range, the driver turns the steering angle largely and slowly so that he / she does not have to worry about being caught by friction, etc., and at low speeds, a large thrust force is required and energy consumption becomes large. It is not preferable to raise it.

Further, as in the invention of claim 4, it is preferable that the second control portion lowers the sensitivity of the second controlled variable as the road surface friction coefficient becomes lower. That is, when the road surface friction coefficient is low, stability is desired, but when the sensitivity of the second control amount is high, the behavior of the vehicle becomes faster, which causes a feeling of strangeness. Further, when the road surface friction coefficient is low, the force that can be generated by the wheel is also small, and therefore the vehicle cannot follow even if the sensitivity of the second control amount is increased, and in some cases the control oscillates.

Further, as in the fifth aspect of the present invention, it is preferable that the second control section increases the sensitivity of the second controlled variable as the vehicle weight becomes heavier. That is, when the vehicle weight becomes heavy,
Although the movement of the vehicle becomes slow, this can be solved by increasing the sensitivity of the second control amount.

In addition, as in the sixth aspect of the invention, it is preferable that the second control section increases the sensitivity of the second controlled variable as the wheel steering angle becomes smaller. That is, the area where the wheel steering angle is small is an area where the steering wheel is steered in small increments in order to maintain the straightness of the vehicle, and catching or the like can be prevented by increasing the sensitivity of the second control amount in this area. is necessary. In addition, in the region where the steering angle is large, no significant problem occurs, and the non-linear region of the wheel becomes involved, which causes a difference from the model. From this point of view, it is uncomfortable to reduce the sensitivity of the second control amount. Can be reduced.

Further, as in the seventh aspect of the present invention, it is preferable that the second control section is configured to increase the sensitivity of the second controlled variable as the wheel steering angular velocity increases. That is, since the followability and the feeling of being caught become more prominent as the steering angular velocity increases, it is preferable to increase the sensitivity of the second control amount.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIGS. 1 and 3 show the configuration of an electric power steering apparatus A for an automobile according to Embodiment 1 of the present invention, in which 1 is a steering wheel (steering wheel) and 2 is the steering wheel. A steering shaft that is connected to 1 and transmits the rotational force (steering force) of the steering wheel 1, 3
Is an intermediate shaft connected to the steering shaft 2 via a universal joint, 4 is a steering gear box provided at the lower end of the intermediate shaft 3, 5 is tie rods arranged on both sides of the steering gear box 4, 6 Is a front wheel (tire) as a steering wheel to which the tie rods 5 are connected.

FIG. 3 shows the vehicle as a left and right two-wheel model, where 7 is the rear wheel, Lf is the distance from the front wheel 6 to the center of gravity P of the vehicle, and Lr is the rear wheel from the vehicle 7. It is the distance to the center of gravity P.

In the steering gear box 4,
A rack and pinion mechanism 8 (see FIG. 3) including a rack and a pinion (not shown) meshed with the rack is provided, and the lower end of the intermediate shaft 3 is connected to the pinion, while the rack Both ends are connected to the front wheels 6 via the tie rods 5.

The steering gear box 4 is provided with an electric motor 11 for applying a force to the pinion side via a reduction gear mechanism 10 and a torque sensor 12 as a torsion bar. It is arranged between the shaft 3 and the reduction gear mechanism 10. As a result, the torque sensor 12 has the handle 1
It is provided between the front wheel 6 and the front wheel 6 to detect the steering torque of the steering wheel.

The torque sensor 12 and the electric motor 11
Are connected to the controller 15, and the controller 15 controls the electric motor 11.
As shown in FIG. 2, the controller 15 includes the torque sensor 12, the lateral acceleration sensor 16 for detecting the lateral acceleration G generated in the vehicle, and the motor rotation speed sensor 17 for detecting the rotation speed of the electric motor 11. The detection value is input. The motor rotation speed sensor 1
7 may be one that directly detects the rotational speed ω of the electric motor 11, or one that is estimated from the voltage applied to the electric motor 11 or the like.

The lateral acceleration sensor 16 is arranged at the center of gravity P of the vehicle or in front of it.
That is, if the lateral acceleration sensor 16 is arranged behind the center of gravity P of the vehicle, the lateral acceleration G detected by the lateral acceleration sensor 16 in the oversteer state of the vehicle is the lateral acceleration at the center of gravity P. Is reduced by
The electric power steering device A attempts to compensate for this by performing extra assist control in the direction in which the steering angle of the front wheels 6 is further cut, the handle 1 becomes lighter, and oversteer is excessively increased, causing a problem. On the other hand, by disposing the lateral acceleration sensor 16 at the position of the center of gravity P or in front of it, it is possible to prevent the oversteer from being increased due to a reduction in the feel of the steering wheel 1 during oversteer, and to perform the understeer correction. .

As shown in FIG. 2, the controller 15 includes an assist control section 21 as a first control section that determines a first control amount so that the detection value of the torque sensor 12 is eliminated, and the torque sensor 12 described above. The second lateral control amount is determined by calculating the target lateral acceleration from the detected value of the above and subtracting the lateral acceleration actually detected in the vehicle by the lateral acceleration sensor 16 from the target lateral acceleration. The electric motor 1 is obtained by adding the respective control amounts of the lateral acceleration feedback control unit 22 as a control unit and the assist control unit 21 and the lateral acceleration feedback control unit 22.
The control amount of 1 is determined, and with this control amount, the electric motor 1
1 and a motor control unit 23 for controlling 1.

The assist control unit 21 is configured to determine the first control amount (K _a · ξ) by multiplying the detected value ξ of the torque sensor 12 by the assist control gain K _a . The assist control gain K _a is the vehicle speed V, the a variable non-negative as determined by the detection value ξ and the differential value of the detected value ξ of the torque sensor 12 (positive or 0), and the non-increasing with respect to the vehicle speed V ( (When the vehicle speed is high (H), it is smaller than when the vehicle speed is low (L))
It is regarded as a variable.

The lateral acceleration feedback control unit 22
Has a transfer function G ₁ (s) that compensates for the phase delay of the detected value ξ of the torque sensor 12. 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 12 (torsion bar), and the spring constant K _b of the torsion bar are set by the following 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 above transfer function (G ₁ (s) ·
ξ) is used to calculate the steering wheel steering torque u actually applied to the steering wheel 1 by the driver.

Further, the lateral acceleration feedback control unit 22
Has a friction gain K _F for setting a friction component (friction torque u _F ) included in the steering torque u. 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, although this hysteresis characteristic is caused by the friction of the steering system or the like, the influence of the friction is reduced or completely eliminated by the control of the lateral acceleration feedback control unit 22, and the influence of the friction is completely eliminated. As indicated by the alternate long and short dash line, the hysteresis characteristic between the steering torque u and the steering angle θ _H may be lost. 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 relating to the calculation of the target lateral acceleration (the steering wheel torque u is the steering speed direction. By applying the friction torque u _F in the opposite 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
Depending on the direction of the motor rotation speed ω, as shown in FIG.
Friction torque u_FTo set the sign of
The motor rotation speed ω (that is, steering wheel steering speed)
Is positive, the friction torque is + u_FAnd the motor
If the rotation speed ω (that is, the steering wheel steering speed) is negative,
The reduction torque is -u_FAnd The motor rotation speed
Friction torque u at the point where ω is ω = 0 (zero)
_FDiscontinuity in driving may cause the driver to feel uncomfortable
Because of this, for example, as shown in FIG.
The friction torque u near the point ω = 0 point_FIs continuously
Set the friction gain to connect
Yes. In other words, in the vicinity of the motor rotation speed ω = 0 point, the friction
Torque u _FThe absolute value of may be decreased.

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 V increases. By doing so, the restoring force of the steering wheel 1 is increased and the sense of return of the steering wheel 1 can be improved during high-speed traveling. Further, the friction torque u _F may be reduced as the wheel steering angle (the steering angle of the front wheels 6) 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 lateral acceleration feedback controller 22
Is the steering torque u to the friction torque
u_FValue (u-u_F) Based on the target lateral acceleration
Target gain K_yAnd this target gain K_yIs Hui
Preset based on vehicle specifications such as vehicle base and vehicle speed V
It has been done. That is, this lateral acceleration
The control by the feedback control unit 22 is performed by the steering wheel steering torque.
The region where the vehicle response to
Area). This target gain K _yDetails of
Details will be described later.

Further, the lateral acceleration feedback control section 22 subtracts the actual lateral acceleration G detected by the lateral acceleration sensor 16 from the target lateral acceleration, and this deviation (K _y
(G ₁ (s) · ξ−u _F ) −G) 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 a transfer function of PID control theory for making the deviation between the target lateral acceleration and the actual lateral acceleration G zero, and in the case of PID control, A ₀
= 0, A ₁ = 1 and 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.

Sensitivity adjustment of the control amount of the lateral acceleration feedback control unit 22 (target gain K _y or control gain C (s)
It is recommended to adjust the following).

When the vehicle speed V is equal to or lower than the predetermined vehicle speed, the target gain K _y is preferably set to K _y = 0. This is due to the following reasons. That is, although the target lateral acceleration is calculated from the detected value of the torque sensor 12 by steering the steering wheel 1, the lateral acceleration does not easily occur (or does not occur) in the vehicle during low-speed turning, for example. For this reason, even if the electric motor 11 is controlled so that the target lateral acceleration is achieved during low-speed turning, the target lateral acceleration is not achieved. Therefore, when the vehicle speed V 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 lateral acceleration feedback control unit 22 does not perform the control. This allows
When the vehicle speed V is equal to or lower than the predetermined vehicle speed, only the control by the assist control unit 21 is performed.

On the other hand, when the vehicle speed V is equal to or higher than a predetermined vehicle speed, the assist gain K _a of the assist control portion 21 as the K _a = 0, it is preferable to perform only the control by the lateral acceleration feedback controller 22. This is because control interference may occur between the assist control unit 21 and the lateral acceleration feedback control unit 22.

It is preferable to increase the control gain C (s) as the vehicle speed V is higher. 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 road surface irregularity, the vehicle is not laterally accelerated even if the steering wheel 1 is not steered by the driver. Will occur. However, the lateral acceleration feedback control unit 2
When the steering torque of the steering wheel is 0, that is, the target lateral acceleration is 0, the control of 2 is a control for maintaining the straight traveling state. Therefore, the higher the vehicle speed V is, the higher the control gain C (s) is, so The straight running stability when driving is improved. The control gain C (s) may be adjusted by changing A _n and B _m (see formula (2)).

If the vehicle speed V further increases and becomes equal to or higher than the predetermined vehicle speed, it is better to lower the target gain K _y as the vehicle speed V increases. This is the steering wheel 1 when driving at high speed.
This is because the vehicle behavior with respect to the steering of is slowed down. That is, in the medium speed range, it is preferable that the vehicle behavior (lateral acceleration behavior) reacts more sensitively to the steering of the steering wheel 1 because, for example, the turning performance is improved, but in the high speed range, steering of the steering wheel 1 is preferable. On the other hand, if the lateral acceleration 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 slow down the vehicle behavior with respect to steering of the steering wheel 1.

Therefore, according to the above items (1) to (4), the lateral acceleration feedback control unit 22 does not control in the low speed region of the vehicle speed V, while the lateral acceleration feedback control unit 22 actively controls in the medium speed region (M). Is done in a regular manner. Then, in the high speed range (H), the control by the lateral acceleration feedback control unit 22 is suppressed as compared with the middle speed range.

The target gain K _y is preferably lowered as the road surface μ (road surface friction coefficient) is lower. This is because when the road surface μ is low, the tire reaction force is small, and therefore the torque sensor 12 does not detect a value or the detected value is small,
Lateral acceleration is generated in the vehicle. For this reason, since the target lateral acceleration and the actual lateral acceleration G do not match, it is preferable to lower the target gain K _y as the road surface μ is lower to reduce the influence of the target lateral acceleration.

The smaller the steering angle of the front wheels 6 (wheel steering angle), the better the target gain K _y . This is to further improve straight running stability.

Steering angular velocity of front wheels 6 (wheel steering angular velocity)
It is better to increase the target gain K _y as is larger. 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 1. Therefore, it is preferable to give a large motor thrust to the electric motor 11.

The target gain K _y should be increased as the vehicle weight increases. That is, even if the behavior of the vehicle with respect to the steering of the steering wheel 1 is delayed, such as the case where the load is increased and the vehicle weight is increased, the target gain K is obtained.
Raising _y is preferable because a large motor thrust can be applied to the electric motor 11.

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 lateral acceleration feedback control section 22 also uses the electric motor 11 in a predetermined virtual model.
And a transfer function G ₄ (s) for calculating the motor rotation speed with respect to the sum of the output of the motor and the torque transmitted from the steering wheel 1 to the front wheels 6 via the torque sensor 12, A transfer function G ₅ (s) for calculating a correction amount for correcting the control amount of the lateral acceleration feedback control unit 22 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).

[0056] _{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 V or may be changed stepwise according to the vehicle speed V. 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 V 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 11 by these transfer functions G ₄ (s) and G ₅ (s) to improve the stability.

When the control amounts are determined by the assist control unit 21 and the lateral acceleration feedback control unit 22 in this way, the control amounts of the assist control unit 21 and the lateral acceleration feedback control unit 22 are determined by the motor control unit 23. Is added to determine the motor control amount for controlling the electric motor 11.

Then, the motor control section 23 includes the correction section 2
4, the correction unit 24 corrects the motor control amount so that the torque transmitted between the steering wheel 1 and the front wheel 6 via the torque sensor 12 is canceled. .

The correction section 24 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. A transfer function G ₃ (s) for calculating a torque component transmitted between the steering wheel 1 and the front wheels 6 via the torque sensor 12 from a detection value of the sensor 12 is provided.

As shown in FIG. 7, the first gain K ₁ is 0 when the vehicle speed V is equal to or lower than the first vehicle speed V ₁ , and when the vehicle speed V 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. If the second vehicle speed V ₂ or more increases, the vehicle speed V increases.
It is set to be constant regardless of. 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 .

[0064] On the other hand, the second gain K _2, as shown in FIG. 8, when the steering angle theta _H is first steering angle theta ₁ below is a constant value regardless of the steering angle theta _H, said first When it is larger than 1 rudder angle θ ₁ , it decreases as the rudder angle θH increases,
Further, it is set to 0 when it is larger than the second steering angle θ ₂ . Accordingly, when the steering angle θ _H is larger than the second 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.

[0065] Also, the second steering angle theta ₂ is 'set according to the steering angular velocity theta _H' steering speed theta _H second steering angle theta ₂ is set smaller the higher (see the one-dot chain lines in FIG. ).

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 torque component transmitted between the steering wheel 1 and the front wheel 6 via the torque sensor 12 is calculated by the first gain K ₁ , the second gain K ₂ and the transfer function G ₃ (s), Correction is performed by subtracting this from the motor control amount.

Therefore, in the above embodiment, the target lateral acceleration that is the target is calculated from the value of the torque sensor 12, and the electric motor 11 is controlled so as to obtain this target lateral acceleration. Therefore, the control amount (K
_{Even if the} desired lateral acceleration is not generated by controlling the electric motor 11 with a.ξ), the target lateral acceleration (desired lateral acceleration) is generated in the vehicle by the control of the lateral acceleration feedback control unit 22.

By controlling the electric motor 11 so as to achieve the target lateral acceleration in this way, the steering of the steering wheel 1 (steering wheel steering torque) of the driver can be performed even if the magnitude of friction or inertia is different. On the contrary, the desired lateral acceleration is always generated in the vehicle. As a result, steering feeling is improved and discomfort is reduced,
It is possible to reduce driver fatigue.

Further, even in the case where the behavior of the vehicle with respect to steering of the steering wheel 1 is delayed, for example, when the load is increased and the vehicle weight is heavy, the target lateral acceleration and the actual lateral acceleration are Since the electric motor 11 is controlled on the basis of the deviation of the steering wheel 1, regardless of the vehicle weight, the steering wheel 1
The desired lateral acceleration is always generated in the vehicle in response to the steering. That is, the same steering feeling is always obtained.

Further, for example, when the vehicle is in a straight traveling state and lateral acceleration occurs in the vehicle due to lateral wind or irregular road surface, the lateral acceleration feedback control unit 22 controls the target lateral acceleration to 0, that is, the straight traveling. Control to maintain the state. Therefore, it is possible to improve the straight running stability against the disturbance such as the side wind and the irregular road surface.

Then, the motor control unit 23 estimates the torque (estimated torque) transmitted between the steering wheel 1 and the front wheels 6 via the torque sensor 12, and subtracts the estimated torque from the motor control amount. The correction unit 24 is provided. The correction of the motor control amount by the correction unit 24 cancels the torque actually transmitted from the steering wheel 1 to the front wheels 6 and the estimated torque.
In terms of control, the torque is not transmitted from the steering wheel 1 to the front wheels 6. In this way, it is possible to prevent the steering of the steering wheel 1 by the driver from interfering with the control in the lateral acceleration feedback control unit 22, especially when the vehicle is subjected to disturbance.

In the correction section 24, the first gain K _{1 is set} to 0 and the first gain K ₁ is set to the first vehicle speed V ₁ or less.
When the vehicle speed V is higher than the vehicle speed V _1, the first gain K ₁ is increased according to the vehicle speed V 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 not higher than the first vehicle speed V ₁ , lateral acceleration does not occur or is unlikely to occur in the vehicle.
The target gain K _y is set to 0 and the lateral acceleration feedback control unit 22 does not perform control, and the target gain K _y is relatively increased when traveling at medium speed or high speed. On the other hand, the 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, the lateral acceleration feedback control unit 2
When the control by No. 2 is not performed, the problem of interference with the control of the lateral acceleration feedback control unit 22 does not occur, and the vehicle itself is not affected by the disturbance itself when the vehicle is stopped or at low speed. Conversely, if the lateral acceleration feedback control unit 22 does not perform the control, and the correction unit 24 corrects the motor control amount, the control for canceling the torque transmitted via the torque sensor 12 is performed. Therefore, the steering wheel steering torque by the driver is not transmitted to the front wheels 6 and the steering cannot be turned off.

Therefore, when the vehicle speed V is less than or equal to the first vehicle speed V ₁ , in other words, the lateral acceleration feedback control unit 22
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, vehicle speed V
Is higher than the first vehicle speed V ₁ , in other words, the control sensitivity of the assist control unit 21 is low, and conversely, when the control sensitivity of the lateral acceleration feedback control unit 22 is high, the control interference is corrected by correcting the motor control amount. Is avoided.

Further, in the correction section 24, the second
The steering angle θ ₂ is used as a threshold to switch prohibition / execution of correction of the motor control amount. By doing this,
In the non-linear region of the vehicle response in which the control by the lateral acceleration feedback control unit 22 is not effectively performed while avoiding the control interference, the state of the front wheels 6 and the like can be accurately transmitted to the driver as a steering reaction force.

That is, as described above, the lateral acceleration feedback control section 22 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. In the non-linear region of the vehicle response where the control is not effective (when the steering angle θ _H is larger than the second steering angle θ ₂ ), the correction of the motor control amount is prohibited to transmit the torque from the front wheels 6 to the steering wheel 1. Thus, the state of the front wheels 6 and the like can be accurately transmitted to the driver as a steering reaction force.

Further, the second steering angle θ ₂ which is a threshold value for prohibiting / executing the correction of the motor control amount in the correction unit 24 is made smaller as the steering wheel angular velocity θ _H ′ becomes higher, so that the linear region of the vehicle response is reduced. Corresponding to the narrowing, the prohibition / execution of the correction of the motor control amount is switched, and in the linear region of the vehicle response, the lateral acceleration feedback control unit 22 controls the desired lateral acceleration while avoiding the control interference. On the other hand, in the non-linear region of the vehicle response, the state of the front wheels 6 and the like can be accurately transmitted to the driver as a steering reaction force.

(Second Embodiment) FIG. 9 shows a second embodiment (the same parts as those in FIGS. 1 to 8 are designated by the same reference numerals and detailed description thereof will be omitted).
In the lateral acceleration feedback control section 22 as a control section of the electric motor 11, the second lateral control amount of the electric motor 11 is determined by subtracting the actual lateral acceleration G from the target lateral acceleration calculated based on the detection value of the torque sensor 12. On the other hand, the second control amount of the electric motor 11 is determined by subtracting the estimated sideslip angle β from the target sideslip angle calculated based on the detection value of the torque sensor 12.

That is, the torque sensor 1 similar to that of the first embodiment is included in the controller 15 of the second embodiment.
2, lateral acceleration sensor 16 and motor rotation speed sensor 17
In addition, each detection value of the yaw rate sensor 18 for detecting the yaw rate generated in the vehicle is input.

Further, the controller 15 includes an assist control unit 21 as a first control unit that determines the first control amount so that the detection value of the torque sensor 12 is eliminated, and a target skid angle from the detection value of the torque sensor 12. And a sideslip angle feedback controller 27 as a second controller that determines the second control amount by subtracting the estimated sideslip angle β estimated by the sideslip angle estimator 28 from the target sideslip angle. A control amount of the electric motor 11 is determined by adding the control amounts of the assist control unit 21 and the sideslip angle feedback control unit 27, and a motor control unit 23 that controls the electric motor 11 with this control amount is provided. There is.

The side slip angle estimator 28 uses the lateral acceleration G actually detected by the lateral acceleration sensor 16 in the vehicle and the yaw rate ψ actually detected in the vehicle detected by the yaw rate sensor 18. The sideslip angle β is estimated by calculation, and the estimated sideslip angle β is calculated by the equation (6).

Β = ∫ {(G + r · ψ ″) / V + ψ ′} dt (6) Here, r is the distance from the center of gravity P of the vehicle to the position of the lateral acceleration sensor 16 on the front side thereof. When the acceleration sensor 16 is at the position P of the center of gravity of the vehicle, r = 0, and therefore the equation (6) is β = ∫ {(G / V) + ψ ′} dt.

The sideslip angle feedback control unit 27
Has a target gain K _y for computing a target slip angle based on the steering torque u from the value obtained by subtracting the friction torque u _F (u-u _F), the target gain K _y is the wheelbase or the like It is set in advance based on vehicle specifications, vehicle speed V, and the like.

Further, the sideslip angle feedback control unit 27 calculates the sideslip angle estimation unit 2 from the target sideslip angle.
The estimated sideslip angle β calculated in 8 is subtracted, and this deviation (K _y (G ₁ (s) · ξ−u _F ) −β) is multiplied by the control gain C (s) to obtain the control amount (second The control amount) is determined. The control gain C (s) is calculated by the equation (2)
Is set by.

This C (s) may be, for example, a transfer function of the PID control theory for making the deviation between the target sideslip angle and the actual estimated sideslip angle β zero, and the transfer using a control theory other than the PID control. It may be a function.

Since the other structure is the same as that of the first embodiment, the detailed description thereof will be omitted.

Therefore, in the case of this embodiment, the target target sideslip angle is calculated from the value of the torque sensor 12,
The electric motor 11 is controlled so that this target sideslip angle is achieved. Therefore, even if a desired sideslip angle is not generated by controlling the electric motor 11 with the control amount of the assist controller 21, the sideslip angle feedback controller 27 controls the target sideslip angle (desired sideslip angle). Corners occur on the vehicle. By controlling the electric motor 11 so that the target sideslip angle is obtained as described above, even if the magnitudes of friction and inertia are different,
With respect to the steering of the steering wheel 1 by the driver (steering wheel steering torque), a desired side slip angle is always generated in the vehicle.
Therefore, the same effect as that of the first embodiment can be obtained.

[0091]

As described above, according to the electric power steering apparatus for an automobile of the invention of claim 1 or 2,
Since the electric motor is controlled by the second control amount based on the target lateral acceleration or the target side slip angle, it is possible to always obtain a desired vehicle behavior with respect to the steering wheel regardless of the magnitude of friction or inertia. The difference in performance between products can be eliminated, and even if a disturbance is input to the vehicle, the second control unit performs control to maintain the straight traveling state, thereby improving straight traveling stability. Therefore, it is possible to prevent the driver's steering feeling from being deteriorated and discomfort.

In addition, according to the inventions of claims 3 to 7, by further adjusting the sensitivity of the second control amount according to the vehicle speed, the road surface friction coefficient, the vehicle weight, the wheel steering angle and the wheel steering angular speed, A preferred electric power steering device is constructed.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an electric power steering device according to a first 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 a correction unit.

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

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

[Explanation of symbols]

A electric power steering device 1 handle 6 front wheels (wheels) 11 electric motor 12 Torque sensor 15 Controller 16 Lateral acceleration sensor 17 Motor rotation speed sensor 18 Yaw rate sensor 21 Assist control unit (first control unit) 22 Lateral acceleration feedback control unit (second control unit) 23 Motor control unit 27 Side slip angle feedback control unit (second control unit) 28 Side slip angle estimation unit P center of gravity position V vehicle speed ξ Torque sensor detection value u steering wheel steering torque G lateral acceleration β sideslip angle

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 137: 00 B62D 137: 00 F term (reference) 3D032 CC02 CC08 DA02 DA10 DA23 DA29 DA39 DD06 EB17 EB21 EC21

Claims (7)

[Claims] 1. An electric power steering apparatus for a vehicle, which assists steering of a steering wheel by controlling an electric motor, comprising: a torque sensor 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 sensor is eliminated, and a target lateral acceleration is calculated from the detection value of the torque sensor,
A second control unit that determines the second control amount of the electric motor by subtracting the lateral acceleration actually generated in the vehicle from the target lateral acceleration; and a first control amount by the first control unit. An electric power steering apparatus for an automobile, comprising: a motor control unit that controls the electric motor based on a control amount obtained by adding a second control amount by a second control unit. 2. An electric power steering apparatus for a vehicle, which assists steering of a steering wheel by controlling an electric motor, the torque sensor being provided between a steering wheel and a wheel for detecting steering torque of the steering wheel. A first control unit that determines a first control amount of the electric motor so that the detection value of the sensor is eliminated; and a target sideslip angle is calculated from the detection value of the torque sensor,
A second control unit for determining a second control amount of the electric motor by subtracting an estimated skid angle estimated by calculation from the target skid angle; a first control amount and a first control amount by the first control unit; An electric power steering apparatus for a vehicle, comprising: a motor control unit that controls the electric motor based on a control amount obtained by adding a second control amount by the second control unit. 3. The electric power steering apparatus for a vehicle according to claim 1 or 2, wherein the second controller is configured to increase the sensitivity of the second controlled variable as the vehicle speed increases. Electric power steering device. 4. The electric power steering apparatus for an automobile according to claim 1 or 2, wherein the second control unit is configured to lower the sensitivity of the second control amount as the road surface friction coefficient is lower. Electric power steering system for automobiles. 5. The electric power steering apparatus for an automobile according to claim 1 or 2, wherein the second controller is configured to increase the sensitivity of the second controlled variable as the vehicle weight becomes heavier. Electric power steering system for automobiles. 6. The electric power steering apparatus for an automobile according to claim 1 or 2, wherein the second control unit is configured to increase the sensitivity of the second control amount as the wheel steering angle becomes smaller. Electric power steering system for automobiles. 7. The electric power steering apparatus for an automobile according to claim 1 or 2, wherein the second control unit is configured to increase the sensitivity of the second controlled variable as the wheel steering angular velocity increases. Electric power steering system for automobiles.