JP2003127884A - Vehicular steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicular steering apparatus with a steering actuator having higher responsiveness for achieving both improved turning performance and straight moving performance of a vehicle. SOLUTION: The movement of the steering actuator 2 is transmitted to wheels 4 in such a manner as to produce a change in steering angle. The steering actuator 2 can be controlled by a control system in such a manner that the ratio of the control input of an operating member 1 to the steering amount of each of the wheels 4 is changed. The control system stores predetermined straight moving keeping conditions corresponding to the operation of the operating member 1 for keeping the vehicle in a straight moving condition and determines whether the straight moving keeping conditions are satisfied or not. A control command value for the steering actuator 2 with the straight moving keeping conditions being satisfied is such that an additional control command value computed corresponding to the target steering angle thereof is added to a control command value with the conditions being not satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system capable of changing a steering angle and a ratio between an operation amount of an operation member and a turning amount of a wheel by controlling a steering actuator. Regarding

[0002]

2. Description of the Related Art An operating member, a steering actuator,
A mechanism that transmits the movement of the steering actuator to the wheels so as to change the steering angle, and a control system that can control the steering actuator so that the ratio between the operation amount of the operation member and the steering amount of the wheels changes. There has been proposed a vehicle steering system including: Such steering devices include those that mechanically connect the operating member to the wheels and those that do not.
When mechanically connecting an operating member to a wheel, steering that transmits the rotation of the input shaft according to the operation of the steering wheel to the output shaft via the planetary gear mechanism, and drives the ring gear that constitutes the planetary gear mechanism during the transmission. The ratio between the operation amount and the steering amount is changed by controlling the actuator for use. Further, when the operation member is not mechanically connected to the wheel, when the movement of the steering actuator is transmitted to the wheel so that the steering angle changes, the steering actuator is controlled to control the operation amount and the steering amount. The ratio of has been changed.

In the vehicle steering system as described above,
It is desired to improve the turning performance of the vehicle by increasing the response of the steering actuator to the operation of the operation member. On the other hand, in automobiles, it is desired to improve the straightness by stabilizing the behavior of the vehicle when traveling straight ahead. Therefore, in the conventional vehicle steering system, the turning performance is improved by increasing the ratio of the turning amount of the wheels to the operation amount of the operating member at a low vehicle speed,
At high vehicle speeds, the driving stability is improved by reducing the speed.

[0004]

In the case of an automobile, it is desired that the vehicle behavior is stable even when traveling straight at a low vehicle speed. However, since the ratio of the turning amount of the wheel to the operation amount of the operating member is changed only in accordance with the vehicle speed as in the conventional case, there is a contradictory need for improvement in straightness at low vehicle speed and improvement in turning performance. And it was difficult to make them compatible. For example, it is conceivable to provide a mechanism for returning the wheels to the straight-ahead position by applying a pressurizing force for canceling the change in the steering angle from the midpoint of the rudder angle to improve the straight traveling property. Since the responsiveness is lowered, the turning performance cannot be improved. Further, if such a pressurizing mechanism is provided, the manufacturing cost increases. Therefore, it is conceivable to combine the technique of improving the straightness of the vehicle by controlling the brake device so as to cancel the change in the vehicle behavior with the steering device. However, there is a problem that the configuration becomes complicated. It is an object of the present invention to provide a vehicle steering system that can solve the above problems.

[0005]

SUMMARY OF THE INVENTION A vehicle steering system according to the present invention comprises an operating member, a steering actuator, a mechanism for transmitting the movement of the steering actuator to a wheel so as to change the steering angle, and its operation. A control system capable of controlling the steering actuator so that the ratio between the operation amount of the member and the turning amount of the wheel changes is provided, and the control system determines the target steering angle of the vehicle according to at least the operation amount of the operation member. Means to calculate
A means for calculating a control command value of the steering actuator according to the target steering angle, a means for storing a predetermined straight-ahead maintaining condition according to the operation of the operation member for maintaining the straight-ahead state of the vehicle, and It has means for determining whether or not the straight traveling maintenance condition is satisfied, and the control command value when the straight traveling maintenance condition is satisfied is calculated according to the target steering angle to the control command value when the straight traveling maintenance condition is not satisfied. The additional control command value is added. According to the configuration of the present invention, when the straight traveling maintaining condition is satisfied by operating the operation member for maintaining the straight traveling state of the vehicle,
Since the additional control command value calculated according to the target steering angle is added to the control command value when not satisfied, it is possible to increase the steering angle change in the operation direction for maintaining the straight traveling state. . As a result, the straightness of the vehicle can be improved without deteriorating the response of the steering actuator.

The straight-ahead maintaining condition is satisfied when the magnitude of the target rudder angle from the midpoint of the rudder angle is less than or equal to a set value and the magnitude of the change speed of the target rudder angle is less than or equal to the set value. Preferably, it is defined as follows. When attempting to maintain the straight traveling state, the amount of operation of the operating member by the driver from the straight traveling position decreases, and the operating speed of the operating member also decreases. According to this configuration, the target steering angle corresponding to the operation speed of the operating member is equal to or smaller than the set value of the target steering angle from the steering angle midpoint according to the operation amount of the operating member from the straight-ahead position. The straight-ahead maintenance condition is satisfied when the magnitude of the change speed of the angle is equal to or smaller than the set value. Therefore, by satisfying the straight-ahead maintenance condition, it is possible to reflect the driver's intention to move the vehicle straight.

The additional control command value is preferably proportional to the deviation of the target steering angle from the midpoint of the steering angle. Alternatively,
The additional control command value is preferably proportional to the time integral value of the deviation of the target steering angle from the steering angle midpoint. As a result, the straightness of the vehicle can be improved by the feedforward control of the steering actuator when the straight-ahead maintenance condition is satisfied.

The additional control command value is preferably proportional to the deviation of the target steering angle from the actual steering angle. Alternatively, the additional control command value is preferably proportional to the time integral value of the deviation of the target steering angle from the actual steering angle. As a result, the straightness of the vehicle can be improved by the feedback control of the steering actuator when the straight-ahead maintenance condition is satisfied.

The control command value is preferably a value to which an offset value for canceling the dead zone of the steering actuator is added. As a result, the control amount of the steering actuator can be reliably increased and the straightness of the vehicle can be improved.

It is preferable that the straight traveling maintenance condition is not satisfied when the vehicle speed is less than a set value. At low vehicle speeds, the amount of control of the steering actuator with respect to the operation of the operating member does not greatly affect straightness, so if the vehicle speed is less than the set value, the straight ahead maintaining condition is not satisfied, and the control amount is reduced. The load on the steering actuator can be reduced without unnecessarily increasing.

[0011]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the present invention will be described with reference to FIGS. The vehicle steering system shown in FIG.
The operation member 1 imitating a steering wheel, the steering actuator 2 driven in response to the rotational operation of the operation member 1, and the movement of the steering actuator 2 are transferred to the front left and right wheels 4 by the operation member 1. The steering gear 3 is provided as a mechanism for transmitting the steering angle change to the front left and right wheels 4 without being mechanically coupled.

The steering actuator 2 can be composed of an electric motor such as a known brushless motor. The steering gear 3 is composed of a motion conversion mechanism such as a ball screw mechanism that converts the rotational motion of the output shaft of the steering actuator 2 into the linear motion of the steering rod 7. The movement of the steering rod 7 is transmitted to the wheel 4 via the tie rod 8 and the knuckle arm 9, and the toe angle of the wheel 4 changes. The steering gear 3 may be a known one,
The structure is not limited as long as the movement of the steering actuator 2 can be transmitted to the front left and right wheels 4 so that the steering angle changes. The wheel alignment is set so that the front left and right wheels 4 can be returned to the straight-ahead position by the self-aligning torque when the steering actuator 2 is not driven.

The operating member 1 is connected to a rotary shaft 10 which is rotatably supported by the vehicle body. An elastic member 30 is provided that imparts elastic force in the direction of returning the operating member 1 to the straight-ahead steering position. This elastic member 3
Zero can be configured by, for example, a spring that imparts elasticity to the rotary shaft 10.

An angle sensor 11 for detecting the rotation angle δh of the operating member 1 from the straight-ahead position is provided as the operation amount of the operating member 1. A steering angle sensor 13 is provided as means for detecting the steering angle δ of the vehicle, and in the present embodiment, the steering angle sensor 13 is configured by a potentiometer that detects the operation amount of the steering rod 7 corresponding to the steering angle δ. The steering angle δ becomes a behavior index value that is an index of the actual vehicle behavior caused by the turning of the wheels 4. Speed sensor 1 for detecting vehicle speed V
4 are provided. The angle sensor 11, the rudder angle sensor 13, and the speed sensor 14 are connected to a control device 20 including a computer. The control device 20 controls the steering actuator 2 via a drive circuit 22.

FIG. 2 is a block diagram showing a control system constituted by the control device 20, and Ck is an adjusting portion of the target steering angle δ ^{* with} respect to the rotation angle δh of the operating member 1. The gain of the adjusting unit Ck is set to Kδ (V), and the control device 20 stores δ ^* = Kδ (V) · δ stored in advance.
The relationship between h and the rotation angle δ detected by the angle sensor 11.
The target steering angle δ ^* is calculated from h and. In the present embodiment, the target steering angle δ ^* is the rotation angle δ that is the operation amount of the operation member 1.
It is a target behavior index value corresponding to h. That gain K
δ (V) is a function of the vehicle speed V, and decreases as the vehicle speed V increases as shown in FIG. 3, for example, and the relationship between the gain Kδ (V) and the vehicle speed V is stored in the control device 20. It

The control device 20 calculates a control command value for the steering actuator 2 according to the target steering angle δ ^* . That is, C _FF is an adjusting unit of the feedforward compensation value ia ^* with respect to the target steering angle δ ^* , and constitutes a feedforward compensation element in the control system. _{Assuming that} the transfer function in the adjusting unit C _FF is Ga, the control device 20
The feedforward compensation value ia ^* is calculated from the relationship of ia ^* = Ga · δ ^* stored in advance and the calculated target steering angle δ ^{* .}
Is calculated. The adjusting unit C _FF is, for example, proportional integral (PI).
The transfer function Ga in this case is a control element, and Ga is a gain, Ta is a time constant, and s is a Laplace operator.
Ka · [1 + 1 / (Ta · s)], and the controller 20
Memorized in. The gain Ka and the time constant Ta are appropriately set so that optimum control can be performed.

C _FB is an adjusting unit of the feedback compensation value ib ^{* with} respect to the deviation (δ ^* -δ) between the target steering angle δ ^* and the steering angle δ detected by the steering angle sensor 13, and the feedback compensation in the control system. Configure elements. This adjusting part C
_{Assuming that} the transfer function in _FB is Gb, the control device 20 controls the steering angle detected by the steering angle sensor 13 and the target steering angle δ ^* calculated with the relationship of ib ^* = Gb · (δ ^* −δ) stored in advance. The feedback compensation value ib ^* is calculated from δ. The adjusting unit C _FB is, for example, a proportional-integral (PI) control element, and the transfer function Gb in this case is obtained by using Kb as a gain, T
Letting b be the time constant and s be the Laplace operator, Gb = Kb.
[1 + 1 / (Tb · s)], which is stored in the control device 20. The gain Kb and the time constant Tb are set appropriately so that optimum control can be performed.

The control device 20 stores a straight-ahead maintaining condition predetermined according to the operation of the operating member 1 for maintaining the straight-ahead state of the vehicle. In the present embodiment, the stored straight traveling maintenance condition is that the vehicle speed V is a set value α (for example, 15 k).
m / h) or more, and the magnitude of the target rudder angle δ ^* from the midpoint of the rudder angle is less than or equal to a set value β (for example, 1 degree),
Moreover, the magnitude of the change speed of the target rudder angle δ ^* is set to ε.
It is set to be satisfied when the amount of change in the target steering angle in one control cycle is equal to or less than the change speed of 0.2 degrees. That is, the straight traveling maintenance condition is not satisfied when the vehicle speed is less than the set value. The control system configured by the control device 20 includes a determination unit 35 that determines whether or not the straight traveling maintenance condition is satisfied.

When the straight-ahead maintenance condition is satisfied, it must not be satisfied.
Operation direction for a constant operation amount of the operation member 1 than when
The controller 20 controls the steering angle so that the change in the steering angle is increased.
The rudder actuator 2 is controlled. In this embodiment,
The above control system uses the target steering angle δ^* Deviation from the midpoint of the steering angle (δ^* 
−0) additional control command value E2^* With the adjustment unit Ce
To do. This adjusting unit Ce is a proportional control element, and the gain is
As K1, the control device 20 is predetermined and stored.
E2^* = K1 · δ^* And the calculated target steering angle δ^* When
To additional control command value E2^* Is calculated. That gain K1
Is set as appropriate so that optimum control can be performed.
Is the minimum unit gain, and this gain K1 is the control device.
Stored in 20. As a result, the additional control command value E2^* 
Is the target steering angle δ^* Is proportional to the deviation from the steering angle midpoint of
Has been done. When the straight running maintenance conditions are not satisfied, the above fee
Deforward compensation value ia^* And feedback compensation value ib
^* Sum of E1^* Is the target drive of the steering actuator 2.
Current Im^* Is set as the control command value corresponding to. Straight ahead maintenance article
Control command value E1 when conditions are satisfied or not satisfied^* To
Via a switch 36 that is closed by a signal from the determination unit 35
Additional control command value E2 ^* Is added and the sum (E1^* +
E2^* ) Is the target drive current Im of the steering actuator 2
^* Is set as the control command value corresponding to. The second control command
Value E2^* Is the first control command value E1^* Is the size of
Made smaller, usually E2^* / E1^*Is 1 /
It may be set to be about 5 to 1/10.

The drive circuit 22 drives the steering actuator 2 by, for example, a PWM wave in accordance with the control command value corresponding to the target drive current Im ^* so that the deviation between the target steering angle δ ^* and the steering angle δ is eliminated. Steering actuator 2
Are controlled by the controller 20. Also, the gain K
Since δ (V) is a function of the vehicle speed V, the steering actuator is arranged so that the ratio of the rotation angle δh, which is the operation amount of the operating member 1, and the turning amount of the wheels 4 changes according to the vehicle speed V. 2 can be controlled.

The control procedure of the steering actuator 2 by the control device 20 will be described with reference to the flowchart of FIG. First, the value detected by each sensor is read (step S1). Next, the gain Kδ (V) corresponding to the detected vehicle speed V
Is calculated (step S2), and the calculated gain Kδ (V)
The target steering angle δ ^* is calculated from the detected rotation angle δh of the operating member 1 (step S3), and the feedforward compensation value ia ^* for the obtained target steering angle δ ^* is calculated using the transfer function Ga (step S4). ), And a feedback compensation value ib ^* for the deviation between the calculated target steering angle δ ^* and the detected steering angle δ is calculated using the transfer function Gb (step S
5) Find the sum E1 ^* of the feedforward compensation value ia ^* and the feedback compensation value ib ^* (step S
6). Next, if the detected vehicle speed V is not less than the set value α,
And, whether the size of the target steering angle [delta] ^* of the steering angle midpoint is equal to or less than the set value beta, and the size of the target steering angle [delta] ^* rate of change is less than the set value ε It is determined whether or not the straight-ahead maintenance condition is satisfied (step S
7). If the straight traveling maintaining condition is not satisfied in step S7, E1 ^* obtained in step S6 is set as the target drive current Im ^* corresponding to the control command value (step S8).
If the straight traveling maintenance condition is satisfied in step S7,
From the target steering angle δ ^* and the gain K1, the additional control command value E2 ^*
Is calculated (step S9), and the additional control command value E2 ^*
Is added to E1 ^* obtained in step S6 (E1 ^* +
E2 ^* ) is set as the target drive current Im ^* corresponding to the control command value (step S10). The steering actuator 2 is driven according to the target drive current Im ^* (step S1).
1). Next, it is determined whether or not the control is ended (step S12), and if not ended, the process returns to step S1. The determination of the end can be made, for example, by whether or not the key switch for starting the vehicle is turned on.

According to the first embodiment described above, when the straight traveling maintaining condition is satisfied by operating the operating member 1 for maintaining the straight traveling state of the vehicle, the control command when the straight traveling maintaining condition is not satisfied is given. since ^* values E1 ^* to be calculated in accordance with the target steering angle [delta] ^* were added control command value E2 is added, it is possible to increase the steering angle changes to the operation direction for maintaining the straight traveling state. As a result, the straightness of the vehicle can be improved without deteriorating the response of the steering actuator 2. Since the target steering angle δ ^* is calculated not only according to the operation amount of the operating member 1 but also according to the vehicle speed, it is necessary to cope with the operation amount of the driver who intends to make the vehicle go straight according to the vehicle speed. You can Further, the target steering angle δ ^* corresponding to the operation amount of the operating member 1 from the straight-ahead position is smaller than the set value β from the midpoint of the steering angle, and the target corresponding to the operating speed of the operating member 1. When the magnitude of the change speed of the steering angle δ ^* is equal to or less than the set value ε, the straight-ahead maintenance condition is satisfied, so that it is possible to reflect the driver's intention to move the vehicle straight. Since the additional control command value E2 ^* is proportional to the deviation of the target steering angle δ ^* from the midpoint of the steering angle, the straightforwardness of the vehicle should be improved by the feedforward control of the steering actuator 2 when the straight traveling maintenance condition is satisfied. You can Further, at a low vehicle speed, since the magnitude of the control amount of the steering actuator 2 with respect to the operation of the operation member 1 does not greatly affect the straight traveling property, the straight traveling maintaining condition is not satisfied when the vehicle speed V is less than the set value α. As a result, the control amount does not unnecessarily increase and the load on the steering actuator 2 can be reduced.

FIG. 5 shows a first modification of the present invention. The same parts as those in the first embodiment are designated by the same reference numerals, and only different points will be described. This modified example has an integrator 37 connected in series to the output side of the adjusting unit Ce, and the output of the integrator 37 is the additional control command value E3 ^* . That is, the additional control command value E3 ^* is proportional to the time integral value of the deviation of the target steering angle δ ^{* from} the steering angle midpoint. Others are the same as those in the first embodiment.

FIG. 6 shows a second modification of the present invention, which is the same as the first embodiment described above, and the same portions are denoted by the same reference numerals and only different points will be described. In the present modification, an offset unit 38 that outputs an offset value Eost ^* corresponding to the dead zone width of the steering actuator 2 with respect to the input of the target steering angle δ ^*.
And its offset value Eost ^* is added to the sum E1 ^* of the feedforward compensation value ia ^* and the feedback compensation value ib ^* . That is, the control command value is the offset value Eo that cancels the dead zone of the steering actuator 2.
It is a value obtained by adding st ^* . Others are the same as those in the first embodiment. As a result, even if the steering actuator 2 has a dead zone due to friction of the operating portion of the steering device, loss torque of the steering actuator 2, or the like, the control amount of the steering actuator 2 is reliably increased to improve the straightness of the vehicle. can do.

FIG. 7 shows a third modification of the present invention. The same parts as those in the first embodiment are designated by the same reference numerals, and only the differences will be described. In the first embodiment, the additional control command value E2 ^*
Is the value according to the deviation of the target rudder angle δ ^* from the midpoint of the rudder angle, but the additional control command value in this modification is a value according to the deviation of the target rudder angle δ ^{* from} the actual rudder angle δ. ing. That is, the feedback compensation value ib ^* in this modified example is a value obtained in the same manner as in the first embodiment when the straight traveling maintenance condition is not satisfied, but is set to a value when the straight traveling maintenance condition is not satisfied. A value obtained by adding an additional control command value according to the deviation of the steering angle δ ^{* from} the actual steering angle δ. The feedforward compensation value ia ^* and the feedback compensation value ib
The sum of ^* and the target drive current Im of the steering actuator 2 is
^The control command value corresponding to ^* . The additional control command value may be proportional to the deviation of the target steering angle δ ^{* from} the actual steering angle δ, or may be proportional to the time integral value of the deviation.
The control command value is the offset value Eo that cancels the dead zone of the steering actuator 2 as in the second modification.
It may be a value obtained by adding st ^* . As a result, the straightness of the vehicle can be improved by the feedback control of the steering actuator 2 when the straight-ahead maintaining condition is satisfied.

A second embodiment of the present invention will be described with reference to FIGS. In the above embodiment, the operation member 1 and the wheels 4
The present invention is applied to a steering device that employs a steer-by-wire system in which and are not mechanically coupled, but in the second embodiment, a steering wheel H that is an operating member is mechanically coupled to wheels (not shown). Steering device 1
The present invention is applied to No. 01.

The rotation of the input shaft 102 in response to the operation of the steering wheel H is transmitted to the output shaft 111 by the rotation transmission mechanism 130, and the rotation of the output shaft 111 changes the steering angle to the wheels. (Not shown). As the steering gear, known gears such as a rack and pinion type steering gear and a ball screw type steering gear can be used. By driving the constituent elements of the rotation transmission mechanism 130 by a motor (steering actuator) 139, the movement of the motor 139 is transmitted to the wheels so that the steering angle changes. The input shaft 102 and the output shaft 111 are arranged coaxially with each other with a gap therebetween, and are supported by the housing 110 via bearings 107, 108, 112 and 113. The rotation transmission mechanism 1
In the present embodiment, 30 is a planetary gear mechanism, and the planetary gear 133 meshes with the sun gear 131 and the ring gear 132.
Are held by the carrier 134. The sun gear 131
Are connected to the end of the input shaft 102 so as to rotate together. The carrier 134 is the output shaft 1
11 is connected to rotate together. The ring gear 132 is used for the holder 13 surrounding the input shaft 102.
It is being fixed to 6 through the bolt 362. The holder 136 is supported via a bearing 109 by a tubular member 135 fixed to the housing 110 so as to surround the input shaft 102. A worm wheel 137 is fitted on the outer periphery of the holder 136 so as to rotate together. A worm 138 that meshes with the worm wheel 137 is supported by the housing 110. The worm 138 is driven by a motor 139 attached to the housing 110.

The motor 139 is controlled by a control system composed of a control device 140 mounted on the vehicle. When the movement of the motor 139 is transmitted to the wheels so as to change the steering angle, the input shaft 102 is controlled according to the variable by controlling the variable according to the variable representing the traveling state of the vehicle.
To the output shaft 111, that is, the ratio of the operation amount of the steering wheel H and the turning amount of the wheels can be changed. In the present embodiment, the variable representing the traveling state is the vehicle speed. For example, the motor 1
By controlling the rotation speed of the ring gear 132 to a higher speed under the control of 39 and causing the planetary gear mechanism 130 to function as a reduction gear mechanism, the turning performance of the vehicle at low speed and the running stability at high speed can be improved. .

As shown in FIG. 9, a vehicle speed sensor 141 for detecting a vehicle speed V is connected to the control device 140 as a sensor for detecting a variable representing a running state. Further, in the control device 140, a rotation angle sensor 142 for detecting the rotation angle θi of the input shaft 102 as a sensor for detecting the operation amount of the steering wheel H, and a sensor for detecting the turning amount of the wheel corresponding to the steering angle. A steering angle sensor 143 that detects the rotation angle θo of the output shaft 111 is connected.

FIG. 10 is a block diagram showing a control system constituted by the control device 140. Ti is the steering torque of the steering wheel H, and i ^* is the target drive current corresponding to the control command value of the motor 139. . Control device 140
Is the target steering angle θo of the output shaft 111 based on the rotation angle θi of the input shaft 102 corresponding to the operation amount of the steering wheel H and the vehicle speed V corresponding to the variable representing the traveling state.
^Ask for ^* . In this embodiment, the output shaft 111
The target rudder angle θo ^* of corresponds to the target rudder angle corresponding to the operation amount of the steering wheel H. That is, the control device 140
Is the input shaft 1 detected by the rotation angle sensor 142.
The target steering angle θo ^* of the output shaft 111 with respect to the rotation angle θi of 02 is adjusted by the adjustment unit C1. Its input shaft 10
Output shaft target rudder angle θo ^* for rotation angle θi of 2
The adjusting portion C1 of the output shaft 11 is a proportional control element.
The target steering angle of 1 is obtained by θo ^* = K (V) · θi. Here, K (V) is a proportional gain and is a function of the vehicle speed V. This proportional gain K (V) is assumed to decrease as the vehicle speed V increases, and the control device 140
Memorized in. The target steering angle θo ^* of the output shaft 111 is calculated based on the stored proportional gain K (V), the detected rotation angle θi of the input shaft 102, and the detected vehicle speed V. The control command value of the motor 139 is calculated by the control device 140 according to the target steering angle θo ^* .

That is, Cα in the control system is an adjusting unit of the feedforward compensation value iα ^* with respect to the target steering angle θo ^* of the output shaft 111, and constitutes a feedforward compensation element in the control system. This adjusting part C
With the transfer function at α being Gα, the control device 140
Predetermined and stored iα ^* = Gα · ^{θo *} target steering angle .theta.o ^* and the feed-forward compensation value i which is calculated with the relationship
Calculate α ^* . The adjusting part Cα is, for example, proportional integral (P
I) It is a control element, and the transfer function Gα in this case is Kα
Where G is the gain, Tα is the time constant, and s is the Laplace operator.
α = Kα · [1 + 1 / (Tα · s)], which is stored in the control device 140. The gain Kα and the time constant Tα are appropriately set so that optimum control can be performed.

In the control system, Cβ is an output system.
Target rudder angle θo of chaft 111^* And the detected rotation angle θo
Difference (θo^* -Θo) feedback compensation value iβ
^* Is the adjusting part of the feedback control in the control system.
Configure elements. The transfer function in this adjusting part Cβ is G
As β, the control device 140 stores iβ stored in advance.
^* = Gβ · (θo^* -Θo) and calculated deviation (θ
o^* −θo) and feedback compensation value iβ^* Calculate
To do. The controller Cβ requires, for example, proportional integral (PI) control.
The transfer function Gβ in this case is K, and Kβ is a gain,
Gβ = Kβ · with Tβ as a time constant and s as a Laplace operator
[1 + 1 / (Tβ · s)] and written in the control device 140.
Remembered The gain Kβ and the time constant Tβ are optimal for control.
It is set appropriately so that it can be performed.

The control device 140 stores a straight-ahead maintenance condition predetermined according to the operation of the steering wheel H for maintaining the straight-ahead state of the vehicle. The straight traveling maintenance condition is that the vehicle speed V is equal to or higher than a set value α, the size of the target steering angle θo ^* from the midpoint of the steering angle is equal to or smaller than the set value β, and the target steering angle θo ^{* is} maintained ^. It is set to be satisfied when the magnitude of the changing speed of is less than or equal to the set value ε. That is, the straight traveling maintenance condition is not satisfied when the vehicle speed is less than the set value. The control system configured by the control device 140 has a determination unit 35 'that determines whether or not the straight traveling maintenance condition is satisfied.

The motor 139 is controlled by the control device 140 so that the steering angle change in the operating direction with respect to the constant operation amount of the steering wheel H is increased when the straight running maintaining condition is satisfied than when it is not satisfied. That is, the control system controls the deviation of the target steering angle θo ^* from the midpoint of the steering angle (θo ^* −
0), which has an adjusting portion Ce ′ for the additional control command value Eb ^* . The adjusting unit Ce ′ is a proportional control element, and its proportional gain is, for example, a minimum unit gain as in the first embodiment, and an additional control command value proportional to the deviation of the target steering angle θo ^{* from} the steering angle midpoint. Calculate Eb ^* . When not satisfying the straight maintaining condition, the sum of the feed-forward compensation value i.alpha ^* and the feedback compensation value i.beta ^* Ea ^* is, the motor 13
The control command value corresponds to the target drive current i ^* of 9.
When the straight running maintenance condition is satisfied, the additional control command value Eb ^* is added to the control command value Ea ^* when not satisfied, through the switch 36 'that is closed by a signal from the determination unit 35', and the sum (Ea ^* + Eb ⁾ is added. ^* ) Is the control command value corresponding to the target drive current i ^* of the motor 139. The magnitude of the second control command value Eb ^* is made smaller than the magnitude of the first control command value Ea ^* , and normally the magnitude of Eb ^* / Ea ^* is 1.
It may be set to be about / 5 to 1/10.

In accordance with the control command value corresponding to the target drive current i ^* , the control device 140 causes the motor 139 to drive, for example, PW.
By driving with the M wave, the motor 139 is controlled by the control device 140 so as to eliminate the deviation between the target steering angle θo ^* and the detected rotation angle θo. Since the gain K (V) is a function of the vehicle speed V, the motor 139 can be controlled so that the ratio between the operation amount of the steering wheel H and the turning amount of the wheels changes.

A control procedure by the control device 140 will be described with reference to the flowchart of FIG. First, the detection value of each sensor is read (step S101). Next, the proportional gain K (V) corresponding to the detected vehicle speed V is obtained (step S102). From the obtained proportional gain K (V) and the detected rotation angle θi of the input shaft 102, the output shaft 1
The target steering angle θo ^* of 11 is calculated (step S10).
3). The determined feedforward compensation value i.alpha ^* with respect to the target steering angle .theta.o ^* calculated using a transfer function G.alpha (step S104), and also, the feedback compensation for the deviation between the determined target steering angle .theta.o ^* and the detected rotation angle .theta.o The value iβ ^* is calculated using the transfer function Gβ (step S10
5) Find the sum Ea ^* of the feedforward compensation value iα ^* and the feedback compensation value iβ ^* (step S
106). Next, the detected vehicle speed V is equal to or greater than the set value α, the size of the target steering angle θo ^* from the midpoint of the steering angle is equal to or smaller than the set value β, and the target steering angle θo ^*. It is determined whether or not the straight-ahead maintenance condition is satisfied depending on whether or not the magnitude of the change speed of is less than or equal to the set value ε (step S107). If the straight traveling maintenance condition is not satisfied in step S107, Ea obtained in step S106
^{Let * be} the target drive current i ^* corresponding to the control command value (step S108). If satisfied the straight maintaining condition in step S107, it calculates the additional control command value Eb ^* in proportion to the target steering angle .theta.o ^* (step S109), Ea of the additional control command value Eb ^* calculated in step S106
^The value (Ea ^* + Eb ^* ) added to ^* is set as the target drive current i ^* corresponding to the control command value (step S110). The motor 139 is driven according to the target drive current i ^* (step S111). Next, it is determined whether or not the control is ended (step S112), and if not ended, the process returns to step S101.

According to the second embodiment, the same effect as the first embodiment can be obtained. As in the first modification, the additional control command value of the second embodiment may be proportional to the time integral value of the deviation of the target steering angle θo ^{* from} the steering angle midpoint, or the second modification. As with the example, the motor 139
The offset value for canceling the dead zone of may be added to the control command value, or the additional control command value may be a value corresponding to the deviation of the target steering angle θo ^{* from} the actual detected rotation angle θo as in the third modification. .

The present invention is not limited to the above embodiment. For example, the configuration of the control system is not limited to the above embodiments.

[0039]

According to the present invention, the responsiveness of the steering actuator is increased to improve the turning performance of the vehicle.
It is possible to provide a vehicle steering system that can improve the straightness of the vehicle at the same time.

[Brief description of drawings]

FIG. 1 is a structural explanatory diagram of a vehicle steering system according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a control system in the vehicle steering system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a proportional gain Kδ (V) and a vehicle speed V in the control system according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a control procedure of the vehicle steering system according to the first embodiment of the present invention.

FIG. 5 is a block diagram of a control system in a vehicle steering system according to a first modified example of the first embodiment of the present invention.

FIG. 6 is a block diagram of a control system in a vehicle steering system of a second modified example of the first embodiment of the present invention.

FIG. 7 is a block diagram of a control system in a vehicle steering system according to a third modified example of the first embodiment of the present invention.

FIG. 8 is a vertical sectional view of a vehicle steering system according to a second embodiment of the present invention.

FIG. 9 is an explanatory diagram of a control configuration of a vehicle steering system according to a second embodiment of the present invention.

FIG. 10 is a block diagram of a control system in a vehicle steering system according to a second embodiment of the present invention.

FIG. 11 is a flowchart showing a control procedure of the vehicle steering system according to the second embodiment of the present invention.

[Explanation of symbols]

1 Operation member 2 Steering actuator 3 steering gear Four wheels 20 Control device 35, 35 'judging unit 139 motor 140 control device H steering wheel

Claims (8)

[Claims] Claim: What is claimed is: 1. An operating member, a steering actuator, a mechanism for transmitting the movement of the steering actuator to a wheel so as to change a steering angle, and a ratio of an operating amount of the operating member and a steering amount of the wheel. Is provided with a control system capable of controlling the steering actuator, and the control system calculates a target steering angle of the vehicle according to at least the operation amount of the operating member, and the target steering angle according to the target steering angle. A means for calculating a control command value of the steering actuator, a means for storing a straight-ahead maintaining condition predetermined according to the operation of the operating member for maintaining the straight-ahead state of the vehicle, and whether or not the straight-ahead maintaining condition is satisfied. The control command value when the straight traveling maintenance condition is satisfied is added to the control command value when not satisfied, and the additional control command value calculated according to the target steering angle is added. Is the value The vehicle steering system, characterized in that there. 2. The straight running maintaining condition is that the magnitude of the target rudder angle from the midpoint of the rudder angle is less than or equal to a set value, and the magnitude of the change speed of the target rudder angle is less than or equal to the set value. The vehicle steering system according to claim 1, wherein the steering system is defined to be satisfied from time to time. 3. The vehicle steering system according to claim 1, wherein the additional control command value is proportional to the deviation of the target steering angle from the steering angle midpoint. 4. The vehicle steering system according to claim 1, wherein the additional control command value is proportional to a time integral value of a deviation of the target steering angle from the steering angle midpoint. 5. The vehicle steering system according to claim 1, wherein the additional control command value is proportional to the deviation of the target steering angle from the actual steering angle. 6. The additional control command value is proportional to the time integral value of the deviation of the target steering angle from the actual steering angle.
Alternatively, the vehicle steering system according to the second aspect. 7. The vehicle steering system according to claim 1, wherein the control command value is a value obtained by adding an offset value for canceling a dead zone of the steering actuator. 8. The steering apparatus for a vehicle according to claim 1, wherein the straight traveling maintaining condition is not satisfied when the vehicle speed is less than a set value.