JPH06278631A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To eliminate the high gain feeling and the startling feeling by the yaw rate feedback control in the turning with medium to high transverse acceleration in a four-wheel steering device to provide the auxiliary steering angle by the yaw rate feedback control in steering the front wheels. CONSTITUTION:A four-wheel steering device is provided with a calculating means (h) of the auxiliary steering angle in response to the steering angle to calculate the auxiliary steering angle in response to the steering angle which becomes larger as the turning transverse acceleration becomes larger according to the vehicle speed and the steering angle, and a calculating means (i) of the targeted auxiliary steering angle to calculate the targeted auxiliary steering angle by correcting the yaw rate to be generated by the feedback auxiliary steering angle based on the targeted yaw rate stationary value in the reducing direction by the auxiliary steering angle in response to the steering angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system which gives an auxiliary steering angle by yaw rate feedback control when steering front wheels.

[0002]

2. Description of the Related Art Conventionally, as a four-wheel steering system for giving an auxiliary steering angle to rear wheels by yaw rate feedback control when steering front wheels, for example, a system disclosed in Japanese Patent Laid-Open No. 63-192667 is known.

[0003]

However, in the above-mentioned conventional four-wheel steering system, the unit steering steering wheel is set for each vehicle speed as the target yaw rate steady value corresponding to the vehicle speed and the steering angle for obtaining the target yaw rate. Since it is only set as the yaw rate value per angle, conventionally, as shown by the alternate long and short dash line characteristic in FIG. 10, the yaw rate characteristic with respect to the steering angle is generated along the steady yaw rate target value.

However, as shown by the solid line characteristic in FIG. 10, the target yaw rate characteristic is a characteristic in which the increase in yaw rate is suppressed in the high steering steering angle region, and the conventional characteristic is also obtained when turning at a low lateral acceleration. The target characteristics are almost the same by maintaining linearity in the relationship between the steering angle and the yaw rate, but there is no problem in the medium to high lateral acceleration turning range (large steering angle range). Despite this, conventionally, the yaw rate rises while maintaining the linear characteristics, and due to the deviation of the generated yaw rate, the function of the yaw rate feedback control is insufficient during turning with medium to high lateral acceleration, and a high gain feeling and a feeling of jerkiness are exhibited. I will end up.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a four-wheel steering system which gives an auxiliary steering angle by yaw rate feedback control during steering of the front wheels. This is to eliminate the feeling of high gain and tingling due to yaw rate feedback control during acceleration turning.

[0006]

In order to solve the above-mentioned problems, in the four-wheel steering system of the present invention, the steering angle responsive auxiliary steering angle amount increases as the turning lateral acceleration increases according to the vehicle speed and the steering steering angle. The target steering angle amount is corrected by correcting the yaw rate generated by the steering angle response auxiliary steering angle amount calculating means and the yaw rate generated by the feedback auxiliary steering angle amount based on the target yaw rate steady value. A target auxiliary steering angle amount calculating means for calculating is provided.

That is, as shown in the claim correspondence diagram of FIG. 1, an auxiliary steering angle actuator a capable of giving an auxiliary steering angle to at least one of the front and rear wheels by an external command.
A vehicle speed detecting means b for detecting a vehicle speed, a steering rudder angle detecting means c for detecting a steering rudder angle, a yaw rate detecting means d for detecting a yaw rate, and a target yaw rate steady value corresponding to the vehicle speed and the steering rudder angle. Target yaw rate steady value calculating means e, target yaw rate steady value and target yaw rate calculating means f for calculating a target yaw rate by a predetermined delay time constant, and the actual yaw rate from the yaw rate detecting means d matches the target yaw rate. Feedback assist rudder angle amount calculating means g for calculating the feedback assist rudder angle amount, and rudder angle response assist for calculating the rudder angle response assist rudder angle amount that increases as the turning lateral acceleration increases in accordance with the vehicle speed and the steering rudder angle. The steering angle amount calculation means h and the yaw rate generated by the feedback auxiliary steering angle amount are steered. A target auxiliary rudder angle amount calculation means i for correcting the target auxiliary rudder angle amount by correcting the target auxiliary rudder angle amount, and a control command for obtaining the target auxiliary rudder angle amount to the auxiliary rudder angle actuator a. And an auxiliary steering angle control means j for outputting.

[0008]

When the front wheel is steered, the target yaw rate steady value calculating means e calculates the target yaw rate steady value according to the vehicle speed from the vehicle speed detecting means b and the steering steering angle from the steering steering angle detecting means c. At f, the target yaw rate is calculated from the steady-state target yaw rate and a predetermined delay time constant, and in the feedback assist steering angle amount calculation means g, the feedback assist steering angle amount at which the actual yaw rate from the yaw rate detecting means d matches the target yaw rate. Is calculated.

At the same time, the steering angle responsive auxiliary steering angle amount calculating means h calculates the steering angle responsive auxiliary steering angle amount that increases as the lateral turning acceleration increases in accordance with the vehicle speed and the steering angle.

Then, the target auxiliary rudder angle amount calculating means i calculates the target auxiliary rudder angle amount by correcting the yaw rate generated by the feedback auxiliary rudder angle amount so as to be reduced by the rudder angle response auxiliary rudder angle amount. In the steering angle control means j, a control command for obtaining the target auxiliary steering angle amount is output to the auxiliary steering angle actuator a, and at least one of the front and rear wheels is provided with the auxiliary steering angle.

Therefore, for example, when the auxiliary steering angle is given to the rear wheels, when the steering angle is large and the vehicle is turning at medium to high lateral acceleration, the auxiliary steering angle is given by the feedback auxiliary steering angle amount based on the calculation of the steering angle response auxiliary steering angle amount. The amount of reverse phase generated is reduced by the amount of the steering angle response auxiliary steering angle, and the yaw rate of the vehicle is suppressed. As a result, the yaw rate characteristic in the medium to high lateral acceleration turning region substantially matches the aimed characteristic, and the high gain feeling and the tingling feeling due to the yaw rate feedback control are eliminated.

It should be noted that the expression has the steering angle responsive auxiliary steering angle amount calculating means h for correcting the auxiliary steering angle amount in the medium to high lateral acceleration turning region, but this correction function is incorporated in the target yaw rate steady value calculating means e. , Target yaw rate steady increase in
Equivalent control can be performed as the target yaw rate steady value calculating means that is given by the non-linear characteristic suppressed in the high lateral acceleration turning region.

[0013]

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

The configuration will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system according to the embodiment of the present invention is applied.

In FIG. 2, the steering of the front wheels 1 and 2 is performed by a steering handle 3 and a mechanical link type steering mechanism 4.
Done by. This is composed of, for example, a steering gear, a pitman arm, a relay rod, side rods 5, 6 and knuckle arms 7, 8.

The steering of the rear wheels 9 and 10 is performed by the electric steering device 11 (corresponding to the auxiliary steering angle actuator a). The rear wheels 9 and 10 are connected by a rack shaft 12, side rods 13 and 14, and knuckle arms 15 and 16, and a rack tube 17 in which the rack 12 is inserted has a reduction mechanism 18 and a motor 19 connected thereto.
And a fail-safe solenoid 20. The motor 19 and the fail-safe solenoid 20 are provided with a vehicle speed sensor 21 (corresponding to vehicle speed detecting means b), a front wheel steering angle sensor 22.
The controller 26 inputs signals from (corresponding to the steering rudder angle detecting means c), the rear rudder angle sub sensor 23, the rear rudder angle main sensor 24, the yaw rate sensor 25 (corresponding to the yaw rate detecting means d), and the like.

FIG. 3 is a sectional view showing a specific structure of the electric steering device 11.

In FIG. 3, the rack tube 17 in which the rack 12 is inserted is fixed to the vehicle body via a bracket. The side rods 13 and 14 are connected to both ends of the rack 12 via ball joints 30 and 31, respectively. The reduction mechanism 18 includes a motor pinion 32 connected to a motor shaft of a motor 19, a ring gear 33 meshing with the motor pinion 32, and a rack pinion 35 fixed to the ring gear 33 and meshing with the rack gear 12a. Has been done. Therefore, when the motor shaft of the motor 19 rotates, the rotation is transmitted to the motor pinion 32 → ring gear 33 → rack pinion 35, and the rack shaft 12 moves in the axial direction due to the meshing of the rotating rack pinion 35 and the rack gear 12a. The rear wheels 9 and 10 are steered. This rear wheel 9,10
The steering amount is proportional to the movement amount of the rack shaft 12, that is, the rotation amount of the motor shaft.

The rack and pinion 35 is provided with a rear rudder angle main sensor 24 having a potentiometer structure for detecting the rear wheel rudder angle based on the amount of rotation thereof.

The fail-safe solenoid 20 includes:
The lock pin 20a is provided so as to be movable back and forth, and when the electronic control system or the like fails, the lock pin 20a is fitted into the lock groove 12b formed in the rack shaft 12 so that the rack shaft 12 is moved to the rear wheels 9 and 10. It is fixed at a position that maintains the neutral rudder angle position.

The operation will be described.

[Rear Wheel Steering Angle Control Operation] FIG. 4 is a flow chart showing the flow of the rear wheel steering angle control operation performed by the controller 26. Each step will be described below.

At step 40, the feedback rear wheel steering angle δrF / B obtained by the processing of FIG. 5, the steering angle responsive rear wheel steering angle δrm obtained by the processing of FIG. 6, and the rear steering angle main sensor value δrS are calculated. Is read.

In step 41, the rear wheel steering angle target value δrM is calculated from the feedback rear wheel steering angle δrF / B and the steering angle responsive rear wheel steering angle δrm (corresponding to the target auxiliary steering angle amount calculating means i).

In step 42, the rear wheel steering angle target value δrM obtained in step 41 is converted into a motor rotation target value THi.

In step 43, the rear steering angle main sensor value δrS is converted into the actual motor rotation value THNO.

In step 44, the motor control current IM is calculated from the motor rotation target value THi and the motor rotation actual value THNO.

At step 45, the PW is issued in response to the output command.
The duty ratio of M is controlled, and the motor control current IM is output.

The steps 42 to 45 correspond to the auxiliary steering angle control means j.

[Feedback Rear Wheel Steering Angle Calculation Processing] FIG.
Is a flowchart showing a flow of feedback rear wheel steering angle calculation processing performed by the controller 26.
Each step will be described.

In step 50, the vehicle speed V, the steering angle θ, and the yaw rate detection value ψ'S are read.

In step 51, a target yaw rate steady value ψ'MO as a yaw rate value per unit steering rudder angle is calculated for each vehicle speed from the vehicle speed V and the steering steering angle θ (the target yaw rate steady value calculating means e is calculated. Equivalent).

In step 52, the delay time constant TO is set, for example, according to the changing direction of the steering angle.

In step 53, the target yaw rate ψ'M is calculated from the steady-state target yaw rate ψ'MO and the delay time constant TO by the following formula (corresponding to the target yaw rate calculating means f).

Ψ'M = ψ'MO / (1 + TO · S) S;
In the Laplace operator step 54, the deviation ε between the target yaw rate ψ′M and the yaw rate detection value ψ ′S is calculated.

In step 55, the deviation ε according to the vehicle speed V
The proportional term KP and the differential term KD of are set based on the map.

In step 56, the deviation ε and the proportional term K
Feedback based on P and differential term KD Feedback steering angle δrF
/ B is calculated (feedback assist steering angle amount calculation means g
Equivalent to).

[Steering Angle Response Rear Wheel Steering Angle Calculation Processing] FIG. 5 is a flow chart showing the flow of the steering angle response rear wheel steering angle calculation processing performed by the controller 26. Each step will be described below (steering angle response Corresponding to the auxiliary steering angle amount calculation means h).

In step 60, the yaw rate detection value ψ '
S, vehicle speed V, steering angle θ are read.

In step 61, the yaw rate detection value ψ'S
Then, the lateral acceleration YG is estimated from the vehicle speed V.

In step 62, the estimated lateral acceleration Y
The lateral acceleration gain GO is set by G. For example, in a region where the lateral acceleration YG is larger than a predetermined value, the lateral acceleration gain GO with a constant value is given.

At step 63, the parameters A, B, C, θ1, θ2, θ3 are set based on the vehicle speed V based on the map.

In step 64, the steering angle direction is judged.

In step 65, when it is determined that the steering angle direction is away from neutral, 1 is set.
Next-order delay constants τ1, τ2, τ3 are set to τ1p, τ2p, τ3p.

In step 66, when it is determined that the steering angle direction is close to neutral, the first-order delay constants τ1, τ2, τ3 are set to τ1m, τ2m, τ3m. Note that (τ1p, τ2p, τ3p) <(τ1m, τ2m, τ3
m).

In step 67, the steering angle responsive rear wheel steering angle δrm
Is calculated by the following formula.

(1) When θ <θ1 δrm = 0 (2) When θ1 ≦ θ <θ2 δrm = −1 / N · {(Kr + A) · (θ−θ1)} · 1 / (1+ τ1 ・ S) ・ GO (3) When θ2 ≦ θ <θ3 δrm = −1 / N ・ {(Kr + A) ・ (θ−θ1) + (Kr + B) ・ (θ−θ2)} ・
1 / (1 + τ2 ・ S) ・ GO (4) When θ3 ≦ θ δrm ＝ −1 / N ・ {(Kr + A) ・ (θ−θ1) + (Kr + B) ・ (θ−θ2) +
(Kr + C) * ([theta]-[theta] 3)} * 1 / (1+ [tau] 3 * S) * GO, and the steering angle responsive rear wheel steering angle δrm is shown in the diagram in FIG. 7.

In step 68, it is judged whether the vehicle is traveling counter or not depending on whether the steering angle direction is the same as the estimated lateral acceleration YG direction. During a normal turn, the steering angle direction and the estimated lateral acceleration YG direction appear in opposite directions.

In step 69, when it is determined that the vehicle is traveling counter, the steering angle responsive rear wheel steering angle δrm is δrm = 0.
Is set.

[At Low Lateral Acceleration Turning] At low lateral acceleration turning with a small steering angle, as shown in FIG. 7, the steering angle responsive rear wheel steering angle δrm is set to δrm = 0.

Therefore, the rear wheel steering angle target value δrM calculated in step 41 of FIG.
It becomes equal to rF / B, and this feedback rear wheel steering angle δrF / B
Corresponds to the steady-state target yaw rate value ψ′MO given by the linear characteristic, and as shown in FIG. 9, a yaw rate characteristic that substantially matches the desired linear characteristic can be obtained during low lateral acceleration turning.

[Middle to High Lateral Acceleration Turning] When the steering angle is large When turning to medium to high lateral acceleration, as shown in FIG. 7, the steering angle responsive rear wheel steering angle δrm increases as the steering steering angle increases. It is set to a value of δrm, which has a large negative absolute value.

Therefore, the rear wheel steering angle target value δrM calculated in step 41 of FIG.
It becomes a value obtained by subtracting the steering angle responsive rear wheel steering angle δrm from rF / B, and the antiphase amount given by the feedback rear wheel steering angle δrF / B is reduced by the steering angle responsive rear wheel steering angle δrm, and yaw rate is generated. As shown in FIG. 9, it is possible to obtain the yaw rate characteristic that substantially matches the target non-linear characteristic even when the vehicle is turning at medium to high lateral acceleration, as shown in FIG.

That is, a control equivalent to the control in which the target yaw rate steady value ψ'MO given by the linear characteristic is nonlinearized by the correction by the steering angle responsive rear wheel steering angle δrm is performed.

As a result, the yaw rate characteristic in the medium to high lateral acceleration turning region substantially matches the target characteristic, and the high gain feeling and the tingling feeling due to the yaw rate feedback control are eliminated.

The effect will be described.

(1) In a four-wheel steering system that gives an auxiliary steering angle to the rear wheels 9 and 10 by yaw rate feedback control when steering the front wheels 1 and 2, the vehicle speed V and the steering steering angle θ
The steering angle response rear wheel steering angle δrm increases as the turning lateral acceleration increases, and the yaw rate generated by the feedback rear wheel steering angle δrF / B based on the target yaw rate steady value ψ'MO is calculated. Because the rear wheel steering angle target value δrM is calculated by correcting the rear wheel steering angle δrm to reduce it, and the yaw rate feedback control is performed so that the yaw rate detection value ψ'S matches the rear wheel steering angle target value δrM. , It is possible to eliminate the feeling of high gain and the feeling of jerk due to the yaw rate feedback control at the time of turning with medium to high lateral acceleration.

(2) Steering angle response The first-order delay constants τ1, τ2, τ3 used for calculating the rear-wheel steering angle δrm are set to the first-order delay constant τ1 when the steering angle changes in the direction away from neutral.
Since p, τ2p, and τ3p are smaller than the first-order lag constants τ1m, τ2m, and τ3m when the steering steering angle changes in the direction approaching from neutral, the steering angle-responsive rear wheel steering in yaw rate feedback control during medium to high lateral acceleration turning. The corrected response of the angle δrm is high response on the steering turning side and low response on the steering turning back side, and it is possible to eliminate the uncomfortable feeling of the vehicle behavior given to the driver. In particular, it is prevented that the driver feels that the vehicle response is too sensitive when the steering wheel is turned back.

Although the embodiments have been described above with reference to the drawings, the specific configuration is not limited to the embodiments, and modifications and additions within the scope of the present invention are included in the present invention. Be done.

For example, in the embodiment, the example of the four-wheel steering system using the electric actuator is shown, but the present invention can be applied to the four-wheel steering system using the hydraulic actuator.

In the embodiment, the example in which only the rear wheels are assisted to be steered is shown, but the invention can be applied to a device in which the front and rear wheels are assisted to be steered.

[0063]

As described above, according to the present invention, in a four-wheel steering system that gives an auxiliary steering angle by yaw rate feedback control when steering front wheels, the turning lateral acceleration can be increased depending on the vehicle speed and the steering steering angle. The steering angle response assist steering angle amount calculation means for calculating the steering angle response assist steering angle amount that increases and the yaw rate generated by the feedback assist steering angle amount based on the target yaw rate steady value are reduced by the steering angle response assist steering angle amount. Since the target auxiliary rudder angle amount calculation means for calculating the target auxiliary rudder angle amount by correcting to the direction to be performed is provided, it is possible to eliminate the feeling of high gain and tingling due to the yaw rate feedback control at the time of turning with medium to high lateral acceleration. Is obtained.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a four-wheel steering system according to the present invention.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system of the embodiment is applied.

FIG. 3 is a cross-sectional view of an electric steering device of the embodiment device.

FIG. 4 is a flowchart showing a flow of rear wheel steering angle control operation performed by the controller of the embodiment apparatus.

FIG. 5 is a flowchart showing a flow of feedback rear wheel steering angle calculation processing performed by the controller of the embodiment apparatus.

FIG. 6 is a flowchart showing a flow of steering angle responsive rear wheel steering angle calculation processing performed by the controller of the embodiment apparatus.

FIG. 7 is a steering angle response rear wheel steering angle characteristic diagram with respect to a steering steering angle.

FIG. 8 is a characteristic diagram of a rear wheel steering angle target value with respect to a steering steering angle.

FIG. 9 is a yaw rate characteristic chart with respect to a steering angle in the embodiment apparatus at a certain vehicle speed.

FIG. 10 is a yaw rate characteristic diagram with respect to a steering angle in the conventional device at a certain vehicle speed.

[Explanation of symbols]

 a auxiliary steering angle actuator b vehicle speed detection means c steering steering angle detection means d yaw rate detection means e target yaw rate steady value calculation means f target yaw rate calculation means g feedback auxiliary steering angle amount calculation means h steering angle response auxiliary steering angle amount calculation means i Target auxiliary rudder angle amount calculation means j Auxiliary rudder angle control means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 137: 00

Claims (1)

[Claims] 1. An auxiliary steering angle actuator capable of giving an auxiliary steering angle to at least one of the front and rear wheels according to an external command, a vehicle speed detecting means for detecting a vehicle speed, and a steering steering angle detecting means for detecting a steering steering angle. A yaw rate detecting means for detecting a yaw rate, a target yaw rate steady value calculating means for calculating a target yaw rate steady value according to a vehicle speed and a steering angle, and a target yaw rate according to the target yaw rate steady value and a predetermined delay time constant. Target yaw rate calculation means, feedback auxiliary steering angle amount calculation means for calculating a feedback auxiliary steering angle amount at which the actual yaw rate from the yaw rate detection means matches the target yaw rate, and turning lateral acceleration according to the vehicle speed and the steering steering angle. Steering angle response auxiliary steering angle amount A steering angle responsive auxiliary rudder angle amount calculating means for calculating the target auxiliary rudder angle amount by correcting the yaw rate generated by the feedback auxiliary rudder angle amount in a direction to be reduced by the rudder angle responsive auxiliary rudder angle amount. A four-wheel steering device comprising: an angle amount calculation means; and an auxiliary steering angle control means for outputting a control command for obtaining the target auxiliary steering angle amount to the auxiliary steering angle actuator.