JP3074582B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus for a vehicle, and more particularly to a rear wheel steering control by adding or subtracting a signal calculation value obtained from each detection signal of a vehicle speed, a front wheel steering angle, a front wheel steering angle change rate and a yaw rate. The present invention relates to a vehicle steering apparatus configured to determine a target value for use.

[0002]

2. Description of the Related Art Conventionally, a steering apparatus for a vehicle configured to steer a rear wheel in accordance with steering of a front wheel has been known in which a rear wheel is steered in accordance with a front wheel steering angle or in accordance with the front wheel steering angle and a vehicle speed. It is known that the steering is performed.
As disclosed in Japanese Patent Application Publication No. 108079, by turning the rear wheels in consideration of the change rate of the front wheel steering angle and the yaw rate as other vehicle state variables, the turning property and the directional stability when the vehicle is running can be improved. Some are also known to be improved.

The above-mentioned steering apparatus is configured to determine a rear wheel turning control target value by adding or subtracting a signal operation value obtained from each detection signal of a vehicle speed, a front wheel steering angle, a front wheel steering angle change rate, and a yaw rate. However, it is desirable to limit the signal operation value to a value within a predetermined allowable range from the viewpoint of ensuring safety and the like.

[0004]

However, even if the signal operation value obtained from each of the detection signals is limited to a value within a predetermined allowable range as described above, an unexpected value will be obtained if these values are added or subtracted. It is possible that

On the other hand, there is no particular limitation on the above-mentioned signal operation values, and the signal operation values are set to values within a predetermined allowable range with respect to a rear wheel turning control target value which is an addition / subtraction value. However, in such a case, the tuning sensitivity to each signal operation value becomes insufficient, and it becomes impossible to perform fine-grained rear wheel steering control.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a vehicle steering system capable of performing fine-grained rear wheel steering control while ensuring safety and the like. It is the purpose.

[0007]

SUMMARY OF THE INVENTION A steering apparatus for a vehicle according to the present invention limits both a signal operation value from each detection signal and a rear wheel turning control target value which is an addition / subtraction value thereof. Thus, the above object is achieved.

That is, as described in claim 1, a signal calculation value obtained by limiting each of the detection signals of the vehicle speed, the front wheel steering angle, the change rate of the front wheel steering angle and the yaw rate to a value within a predetermined range. And a target value determining means for determining a target value for rear wheel steering control by adding or subtracting the target value.When the target value determined by the target value determining means exceeds a predetermined allowable range set in accordance with the vehicle speed, Target value correcting means for correcting the target value to a value within the allowable range.

The "rear wheel turning control target value" is not particularly limited as long as it is a target value used for the rear wheel turning control. For example, the rear wheel turning angle, the turning ratio (ie, the front wheel turning The ratio of the rear wheel steering angle to the angle can be adopted.

[0010]

As described above, when the rear wheel turning control target value determined by adding or subtracting the signal operation values exceeds the allowable range, the target value is set to a value within the allowable range. Since the correction is made, even if an unexpected value is obtained by the addition / subtraction, it can be regarded as an abnormal value and a restriction can be added.

Further, in this case, if an attempt is made to limit only by correcting the target value for rear wheel steering control, an excessive limit is imposed on any of the above-mentioned signal calculation values. However, in the present invention, each of the signal calculation values is obtained from each of the detection signals so as to be limited to a value within a predetermined range. In addition to the correction, the restriction on each signal calculation value is also performed, whereby the correction amount can be set smaller than the case where the restriction is added only by correction to the rear wheel steering control target value, Therefore, sufficient tuning sensitivity for each signal operation value can be ensured.

Therefore, according to the present invention, it is possible to perform fine-grained rear wheel steering control while ensuring safety and the like.

In view of the fact that each of the signal calculation values tends to be large in the middle vehicle speed region, it is preferable to set the permissible range to be the narrowest in the middle vehicle speed region.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing one embodiment of a vehicle steering system according to the present invention.

As shown in the figure, a vehicle steering system 10 according to the present embodiment includes a front wheel steering mechanism 14 for steering a front wheel 12,
The front wheel steering mechanism 14 is mechanically connected to the front wheel steering mechanism 14 via a transmission shaft 16, and the rear wheel 18 is interlocked with the front wheel steering by the front wheel steering mechanism 14 and the front wheel steering angle input from the front wheel steering mechanism 14. A rear wheel steering mechanism 20 that steers to a predetermined target rear wheel steering angle TGθ _R (this will be described later) according to θ _F , and a front wheel steering angle θ provided in the rear wheel steering mechanism 20. includes a steering-angle-ratio adjusting mechanism 22 for setting and changing the steering angle ratio theta _S, expressed as a ratio of rear wheel steering angle theta _R for _F, and a control unit 24 for controlling the steering-angle-ratio adjusting mechanism 22 In the control unit 24,
The vehicle speed V from the vehicle speed sensor 26, the yaw rate ψ 'from the yaw rate sensor 28, the steering ratio θ _S from the steering ratio sensor 30, and the front wheel steering angle θ _F from the front wheel steering angle sensor 32 (provided on the steering shaft). A signal is input.

The control unit 24 is obtained from respective detection signals of the vehicle speed V, the yaw rate ψ ', the front wheel steering angle θ _F , and the front wheel steering angle change rate θ' _F2 obtained by differentiating the front wheel steering angle θ _F. by adding or subtracting a signal calculated value determines a target steering angle ratio TGθ _S (rear wheel steering control target value) for the steering ratio variable mechanism 22, further the target steering angle ratio TGshita _S
But when it exceeds a predetermined allowable range set in accordance with the vehicle speed is adapted to correct this target steering ratio TGshita _S to a value within the allowable range. Then, using the corrected target steering ratio TGθ _S1 , the target rear wheel steering angle TGθ _R is calculated by the following equation: TGθ _R = θ _F · TGθ _S1 .

[0018] The target steering ratio TGshita _S, the following formula _{TGθ S = -G 1 · f 1} (V) · θ S · ST + G 2 · K
₂ (θ _F2 ) · J ₂ (| θ ' _F2 |) · f ₂ (V) · θ
_{S ・ YAW} -G ₃・ K ₃ (θ _F2 ) ・ f ₃ (V) ・ θ _{S ・ STD} + G ₄
・ Set at f ₄ (V).

In the above equation, the first term on the right side is a steering angle correction term,
The second term is a yaw rate correction term, the third term is a steering angle change rate correction term, and the fourth term is a vehicle speed sensitive term that is a base when performing rear wheel turning control according to the vehicle speed. By thus setting the target steering ratio TGshita _S, a vehicle speed sensitive rear wheel steering control as a basis, when turning the front wheels from the straight running condition, and the rear wheel on the turning initial front orientation Control to increase the turning performance by turning to the opposite phase side where the direction is opposite, and then to steer the rear wheel to the same phase side where the direction of the front wheel becomes the same as the front wheel due to the yaw rate generation (phase control) (Inversion control).

In the above equation, G ₁ , G ₂ , G ₃ , and G ₄ are constants, and other variables are a vehicle speed V, a yaw rate ψ ', and a front wheel steering angle θ _F as shown in FIG. Based on this, it is calculated as follows.

First, the variables f ₁ (V), f
₂ (V), f ₃ (V), and f ₄ (V) are vehicle speed-sensitive gains, and are obtained from the vehicle speed V based on maps m10, m5, m13,
Each of them is calculated by m1. Among the above maps, the maps m10, m5, and m13 are variables f ₁
(V), f ₂ (V), and f ₃ (V) are characteristics that are 0 in a low vehicle speed region, a value proportional to a steering angle in a medium vehicle speed region, and a constant value in a high vehicle speed region. The remaining map m1 changes the variable f ₄ (V) from a negative value to a positive value in a low vehicle speed region, from a negative value to a positive value as the vehicle speed increases in a medium vehicle speed region, and to a positive positive value in a high vehicle speed region. It is a characteristic to be a value.

Next, the variable θ _{S · ST} of the first term on the right side is a steering angle correction value, and the front wheel steering angle θ _F is added with an offset by using a map m8 to obtain θ _{F1, which} is then obtained by a map m11. Hysteresis is added to θ _F1 to obtain θ _F2 , and the absolute value thereof is calculated from | θ _F2 | using a map m9. Adding an offset in map m8 is
This is to prevent unnecessary control from being performed by providing a dead zone in the small steering angle area.
The reason why the hysteresis is added at 1 is to prevent hunting from occurring in the control. The map m9 indicates that the variable θ _{S · ST} is 0 in the small steering angle region, a value proportional to the steering angle in the middle steering angle region, a constant value in the large steering angle region, and abnormal when the steering angle region is larger. Is set to be 0 when the occurrence of the error occurs.

Next, the variable theta _{S · YAW} of the second term is a yaw rate correction value, after the ₁ '[psi by adding an offset by map m2' yaw rate [psi, map m3
The ψ from 'hysteresis was ψ added to _{1' 2,} and calculates the map m4 by. The reason for adding the offset and the hysteresis is the same as in the case of the variable θ _{S · ST} . The map m4 has a characteristic that the variable θ _{S · YAW} is a value proportional to ψ ′ ₂ in the small yaw rate area, a constant value in the middle yaw rate area, and 0 in the large yaw rate area when an abnormality occurs.

The variable K ₂ (θ _F2 ) of the second term on the right side is
Steering angle sensitive gain, θ _F2 obtained in map m11
From the map m6. The map m6 has a characteristic that the variable K ₂ (θ _F2 ) is a value that is substantially proportional to θ _F2 in the small front wheel steering angle region, and a value that decreases as the front wheel steering angle increases.

Further, the variable J ₂ (| θ ′ of the second term on the right side
_F2 |) is a steering angle change rate sensitive gain, and is a map m1
The absolute value was obtained by differentiating θ _F2 obtained in Step 1 | θ ' _F2 |
From the map m7. The map m7 is obtained by converting the variable J ₂ (| θ ′ _F2 |) into | θ ′ _F2 |
Is small, that is, a small value in the small front wheel steering angle change rate area, a large value in the middle front wheel steering angle change rate area, and a smaller value in the large front wheel steering angle change rate area than the small front wheel steering angle change rate area. Has become.

Next, the variable θ _{S · STD} of the third term on the right side is a steering angle change rate correction value, and is calculated from a value θ ′ _F2 obtained by differentiating θ _F2 obtained in the map m11 by using a map m12. It has become. The map m12 expresses the variable θ _{S · STD} by:
In the small front wheel rudder angle change rate region, the value is proportional to θ ' _F2 , in the middle front wheel rudder angle change rate region, a constant value, and in the large front wheel rudder angle change rate region, it is set to 0 when an abnormality occurs.

The variable K ₃ (θ _F2 ) of the third term on the right side is
Steering angle sensitive gain, θ _F2 obtained in map m11
From the map m14. The map m14 has a characteristic that the variable K ₃ (θ _F2 ) is set to a value that is substantially proportional to θ _F2 in the small front wheel steering angle region, and a value that decreases as the front wheel steering angle increases.

The target turning ratio TGθ _S is determined by adding and subtracting a signal operation value obtained by multiplying the above constants and variables for each term on the right side of the above equation. taking, the target steering angle ratio TGshita _S becomes an abnormal value, the map m15, the target steering ratio TGshita _S is,
When exceeding the set allowable range in accordance with the vehicle speed V (the portion indicated by hatching in the map m15), the curve representing the target turning ratio TGshita _S by the broken line in the upper or lower limit (map m15 within the allowable range ). The solid line curve in the map m15 is the variable f ₄ (v) shown in the map m1.

The allowable range is set so as to be narrowest in the middle vehicle speed range. This is because there is a high possibility that the value of the correction term (the first to third terms) on the right side of the above equation becomes large in the middle vehicle speed region.

As described above in detail, in this embodiment, the vehicle speed V, the yaw rate ψ ′, the front wheel steering angle θ _F , and the front wheel steering angle change rate θ ′ obtained by differentiating the front wheel steering angle θ _F.
As when the target steering angle ratio TGshita _S determined by adding or subtracting a signal calculation value obtained from _F2 each detected signal exceeds the allowable range to correct this the upper or lower limit within the allowable range Therefore, even if an unexpected value is obtained by the above addition / subtraction, it can be regarded as an abnormal value and a restriction can be added.

Further, in this case, the target turning ratio TGθ is simply obtained.
If an attempt is made to limit only by modifying _S, an excessive limit will be added to any of the above-described signal operation values. In the present embodiment, however, the maps m4, m9, and m12 have As shown in the figure, since each of the signal calculation values is obtained from each of the detection signals so as to be limited to a value within a predetermined range, the target turning ratio TGθ
Limits for signal calculation value in addition to the modifications to the _S also be a result of performed, thereby, in comparison with the case of adding the limited only by the modification to the target steering angle ratio TGshita _S can be set smaller the correction amount Therefore, the tuning sensitivity for each signal operation value can be sufficiently ensured. Therefore, according to the present embodiment, it is possible to perform fine-grained rear wheel steering control while ensuring safety and the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a vehicle steering system according to the present invention.

FIG. 2 is a control block diagram showing the operation of the embodiment.

[Explanation of symbols]

Reference Signs List 10 steering device 14 front wheel turning mechanism 20 rear wheel turning mechanism 22 variable turning ratio mechanism 24 control unit (target value determining means, target value correcting means) 26 vehicle speed sensor 28 yaw rate sensor 30 turning ratio sensor 32 front wheel steering angle sensor

Continuation of the front page (56) References JP-A-4-138968 (JP, A) JP-A-3-248967 (JP, A) JP-A-2-220974 (JP, A) JP-A-4-108079 (JP) JP-A-4-85178 (JP, A) JP-A-4-183678 (JP, A) JP-A-3-74265 (JP, A) JP-A-4-43166 (JP, A)

Claims (2)

(57) [Claims] 1. A method for controlling rear wheel turning by adding or subtracting a signal operation value obtained by limiting each of detection signals of a vehicle speed, a front wheel steering angle, a change rate of a front wheel steering angle and a yaw rate to a value within a predetermined range. A target value determining means for determining a target value, when the target value determined by the target value determining means exceeds a predetermined allowable range set according to the vehicle speed, the target value is set to a value within the allowable range. And a target value correcting means for correcting the vehicle steering speed. 2. The vehicle steering system according to claim 1, wherein the allowable range is set to be narrowest in a middle vehicle speed region.