JP2871239B2 - Rear wheel steering angle control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering angle control device for providing an in-phase rear wheel auxiliary steering angle in a small steering wheel angle region and an opposite-phase rear wheel auxiliary steering angle in a large steering wheel angle region.

[0002]

2. Description of the Related Art Conventionally, as this kind of rear wheel steering angle control device, for example, one disclosed in Japanese Patent Application Laid-Open No. 61-18572 is known.

[0003] In the conventional source described above, the steering wheel angle is detected,
When the steering wheel angle is smaller than a predetermined value, the rear wheel is steered to the same phase as the front wheel, and when the steering wheel angle is larger than the predetermined value, the rear wheel is steered to the opposite phase to the front wheel, so that the steering wheel angle is reduced. There is disclosed a rear wheel steering angle control technique for achieving both stability in a small middle and high speed range and turning performance in a low speed range with a large steering wheel angle.

[0004]

However, in the above-mentioned conventional rear wheel steering angle control device, since the steering wheel angle for changing from the same phase to the opposite phase is set to a constant value, the following enumeration is required. There's a problem.

(1) If the rear wheel steering angle is set to return to the opposite phase in the region where the steering wheel angle is small, at the time of low-speed small radius turning,
Because the lateral force of the rear wheel is reduced by the reverse phase steering while the lateral force of the front wheel is still being generated, the yaw moment suddenly increases, and a feeling of rotating on the spot appears.

(2) On the other hand, when the rear wheel steering angle is set to return to the opposite phase in the region where the steering wheel angle is large, the vehicle body slip angle becomes large as shown in FIG. As a result, the slip angle of the front wheel increases at a small steering wheel angle, and the lateral force is saturated.
At this time, since the rear wheels are steered in the same phase, the yaw moment decreases even if the rear wheel auxiliary steering angle is increased, increasing the understeer, thereby deteriorating the turning performance. As shown in FIG. 10, the lateral force characteristics with respect to the slip angle of the tire show that the cornering power CP and the maximum cornering force CF are higher when the road becomes a low μ road compared to a high μ road.
It shows the characteristic that max decreases.

The present invention has been made in view of the above-mentioned problem, and provides an in-phase rear wheel auxiliary steering angle in a small steering wheel angle region and an opposite-phase rear wheel auxiliary steering angle in a large steering wheel angle region. A first object of the rear wheel steering angle control device is to achieve optimum turning performance irrespective of a road surface friction coefficient and a turning situation.

In addition to the above-mentioned first problem, a second problem is to secure the steering effect with good response in a limit region where the lateral force of the front wheels is saturated.

In addition to the above-mentioned second problem, a third problem is to achieve both the stability of lane change in the grip region of the front wheel and the effectiveness of the rudder in the limit region where the lateral force of the front wheel is saturated. I do.

In addition to the above-mentioned third problem, in the grip region of the front wheel, stability such as lane change is further improved, and in the limit region where the lateral force of the front wheel is saturated, response of the rudder is ensured without delay. This is the fourth problem.

[0011]

According to a first aspect of the present invention, there is provided a rear wheel steering angle control device for changing the auxiliary steering angle of a rear wheel from the same phase to the opposite phase with respect to a steering wheel angle. A phase change handle angle setting means for changing the phase change handle angle by parameters of the vehicle speed and the lateral acceleration is provided.

That is, as shown in the claim correspondence diagram of FIG. 1, a rear wheel auxiliary steering angle providing means a for providing an auxiliary steering angle to a rear wheel.
A steering wheel angle detecting means b for detecting a steering wheel angle, a vehicle speed detecting means c for detecting a vehicle speed, a lateral acceleration detecting means d for detecting a lateral acceleration, and an auxiliary steering angle of a rear wheel with respect to the steering wheel angle. A phase change handle angle setting means e for setting the phase change handle angle to be changed to the opposite phase to a smaller angle as the vehicle speed increases, and to a larger angle as the lateral acceleration increases, and the handle angle becomes larger than the phase change handle angle. In small areas, the rear wheels are given the same steering angle as the front wheels,
In a region where the steering wheel angle is larger than the phase change steering wheel angle, rear wheel steering angle control means f for providing an auxiliary steering angle in a phase opposite to that of the front wheel to the rear wheel.
And characterized in that:

In order to solve the second problem, the rear wheel steering angle control device according to the second aspect of the present invention, as shown in the claim correspondence diagram of FIG.
A rear wheel auxiliary steering angle calculating means g for obtaining a rear wheel auxiliary steering angle in accordance with a predetermined control law; and, when the steering wheel angle is smaller than the phase changing steering wheel angle, the steering wheel angle is directly used as a calculation steering wheel angle, and the steering wheel angle is changed to the phase changing steering wheel angle. In the above case, the steering wheel angle setting means h for calculating the steering wheel angle, the steering wheel angular velocity, and the steering wheel angular acceleration as the sum of the steering wheel angle, and the rear wheel return for returning the rear wheel in the opposite phase direction based on the steering wheel angle for calculation. A rear wheel return steering angle calculating means i for calculating a steering angle is provided, and the rear wheel steering angle control means f provides an actual rear wheel auxiliary steering angle by a value obtained by subtracting the rear wheel return steering angle from the rear wheel auxiliary steering angle. Means.

In order to solve the third problem, the rear wheel steering angle control device according to the third aspect of the present invention, as shown in FIG.
The rear wheel return steering angle calculating means i is used to calculate the steering wheel angle.
The larger the larger, the larger the increase ratio of the rear wheel return steering angle
Characteristic, the characterized in that the means for obtaining a wheel tempering steering angle after the reverse phase direction to increase with respect to computational steering wheel angle.

In order to solve the fourth problem, in the rear wheel steering angle control device according to the fourth aspect, as shown in the claim correspondence diagram of FIG.
When the steering wheel angle is smaller than the phase changing steering wheel angle, the time constant is set to be smaller as the steering wheel angle increases, and when the steering wheel angle is equal to or larger than the phase changing steering wheel angle, the time constant setting means j is provided to set the time constant to zero. Angle calculation means i
The larger the steering wheel angle for calculation, the more the temporary rear wheel
By increasing the ratio increases characteristic corners, that it has a means for obtaining a steering angle tempering also the rear wheels by multiplying the first-order lag filter according to the time constant of the steering angle tempering also provisionally rear wheel to increase in relative calculation wheel angle Features.

[0016]

The operation of the first aspect of the present invention will be described.

During turning or the like, the phase change handle angle setting means e changes the phase change handle angle for changing the auxiliary steering angle of the rear wheel from the same phase to the opposite phase with respect to the handle angle, and the vehicle speed from the vehicle speed detection means c. The angle is set to be smaller as the size is increased, and is set to be larger as the lateral acceleration from the lateral acceleration detecting means d is increased. In the rear wheel steering angle control means f, an auxiliary steering angle having the same phase as that of the front wheel is given to the rear wheel in a region where the steering wheel angle is smaller than the phase changing steering wheel angle, and to the rear wheel in a region where the steering wheel angle is larger than the phase changing steering wheel angle. Control for providing an auxiliary steering angle in a phase opposite to that of the front wheels is performed.

Here, the lateral force of the front wheels generated during turning or the like is more likely to be saturated as the vehicle speed increases, such as during high-speed turning, and the lateral force of the front wheels is increased as when turning on a low μ road. The smaller the lateral acceleration, the more likely it is to saturate. In contrast,
By setting the phase change handle angle according to the vehicle speed and the lateral acceleration as described above, the set phase change handle angle substantially coincides with the point at which the lateral force of the front wheels is saturated.

Therefore, as in the case where the phase change steering wheel angle is set smaller than the angle at which the lateral force of the front wheel is saturated, the turning performance of strong oversteer is obtained, or the phase is larger than the angle at which the lateral force of the front wheel is saturated. Unlike the case where the change steering wheel angle is set, the turning performance does not become strong understeer, and the optimum turning performance can be obtained according to the road surface friction coefficient and the turning condition.

The operation of the present invention will be described.

At the time of turning or the like, the rear wheel assist steering angle calculating means g calculates the rear wheel assist steering angle according to a predetermined control law. On the other hand, in the calculation handle angle setting means h, when the handle angle is less than the phase change handle angle, the handle angle is directly used as the calculation handle angle, and when the handle angle is equal to or greater than the phase change handle angle, the handle angle, the handle angular velocity and The sum of the steering wheel angular acceleration and the calculated steering wheel angle is calculated, and the rear wheel returning steering angle calculating means i calculates the rear wheel returning steering angle for returning the rear wheel in the opposite phase direction based on the calculation steering wheel angle. Then, in the rear wheel steering angle control means f, control is performed to give an actual rear wheel auxiliary steering angle by a value obtained by subtracting the rear wheel return steering angle from the rear wheel auxiliary steering angle.

Therefore, if the steering wheel angle is equal to or larger than the phase change steering wheel angle and the steering wheel is further turned, the steering wheel angle for calculation is set to a larger angle than the actual steering wheel angle in accordance with the operating speed or the operating acceleration. Therefore, in the limit region where the lateral force of the front wheels is saturated, the rear wheels are steered in the opposite phase at a higher speed and with higher response than when the steering wheel angle is used as it is, and the decrease in the lateral forces at the front wheels is reduced at the rear wheels. The steering is covered by the high-response reversed-phase steering, and the effectiveness of the steering by the turning direction yaw moment is secured.

The operation of the invention according to claim 3 will be described.

At the time of turning or the like, the rear wheel return steering angle calculating means i
In the above, the rear wheel return steering angle in the opposite phase direction that increases progressively with respect to the calculation steering wheel angle is calculated.

When turning, etc., the rear wheel return steering angle calculating means i
, The larger the steering wheel angle for calculation, the
And the increase ratio becomes large characteristic of the steering angle, wheel tempering steering angle after the reverse phase direction to increase with respect to computational steering wheel angle is to be calculated.

The operation of the invention will be described.

At the time of turning or the like, the time constant setting means j sets a smaller time constant as the steering wheel angle increases when the steering wheel angle is smaller than the phase changing steering wheel angle. Zeroed. Then, in the rear wheel return steering angle calculating means i, the total
As the steering wheel angle increases, the temporary rear wheel return steering angle increases.
The characteristics a large percentage increases, so that the steering angle tempering also the rear wheels by multiplying the first-order lag filter according to the time constant to increase <br/> pressure to the steering angle tempering also provisionally rear wheel relative to the steering wheel angle is obtained.

Therefore, in the grip region of the front wheel, the first-order delay is effective, so that the stability such as lane change is improved.
In the limit region where the lateral force of the front wheels is saturated, the rudder effectiveness is secured without delay.

[0029]

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 four-wheel steering vehicle to which the rear wheel steering angle control device according to the embodiment of the present invention is applied.

In FIG. 2, reference numeral 1 denotes a front wheel, and 2 denotes a rear wheel. By transmitting a steering input to a steering wheel 3 to a front wheel 1 via a steering gear 4, normal main steering can be performed. At the same time, the case of the steering gear 4 is stroked by the actuator 5 to enable auxiliary steering up to a maximum of α degrees with respect to the main steering angle. The rear wheel 2 is capable of assisting the steering up to a maximum of β degrees by the stroke of the actuator 6 (corresponding to a rear wheel assist steering angle applying means). In this embodiment, it is assumed that α degrees> β degrees. The front / rear auxiliary steering system includes, in addition to the actuators 5 and 6, an oil pump 7, a flow dividing valve 12, and steering angle control valves 14 and 15, and the oil pump 7 sucks oil in the reservoir 8 to The oil is discharged to the circuit 9 and the oil on the main circuit 9 is separated by the flow dividing valve 12 into the front wheel assist steering circuit
0 and the rear wheel assist steering circuit 11. Dividing valve 12
Is constructed by elastically supporting a shuttle spool 12a at a neutral position by springs 12b and 12c.
Pressure chambers 12d and 12e are defined at both ends of a. These pressure chambers 12d and 12e communicate with the main circuit 9 through orifices 12f and 12g having different diameters formed in the spool 12a, and also connect the horizontal holes 12h and 12i and the output ports 12j and 12k similarly formed in the spool 12a. The auxiliary steering circuits 11 and 10 communicate with each other. These horizontal holes 12h and 12i increase or decrease the degree of communication with the output ports 12j and 12k in accordance with the stroke of the spool 12a responding to the pressure in the pressure chambers 12d and 12e, respectively, and perform the following branching function.

[0033] That is, the required flow rate Q _f of the circuit 10, represented by the product of the piston pressure receiving area A and the piston traveling speed v of the front wheel auxiliary steering actuator _{5 (Q f = A · v} ),
For example, assuming that the stroke of the actuator 5 is δ and the front wheel steering frequency is f, (v = 2π · f · δ), so that Q _f = A · 2π · f · δ). Circuit 11
Motomari required flow Q _r be the same, when the discharge amount of the pump 7 to the Q _O and _{(Q O = Q f + Q} r), the distribution ratio to obtain the required required flow rate Q _f, the Q _r, orifice 12 g, 12f
The diameter (Q _f / Q _O), obtained by setting corresponding to the (Q _r / Q _O). Each of the steering angle control valves 14 and 15 is constituted by a pressure control valve, which is interposed between the auxiliary steering circuits 10 and 11 and the common drain circuit 13 and the actuators 5 and 6. One of the steering angle control valves 14 is a solenoid 1
When the switches 4a and 14b are turned off (non-energized), they are in the neutral position shown in the figure, and the entire amount of oil from the circuit 10 is returned to the drain circuit 13, and both chambers 5a and 5b of the actuator 5 are kept in a non-pressure state. At this time, the actuator 5 is set to the neutral position by the built-in springs 5c and 5d, and keeps the steering gear 4 at a position where the front wheels 1 are not assisted. The steering angle control valve 14 pressurizes the chamber 5a when the solenoid 14a is turned on (when energized), drains the chamber 5b to extend the actuator 5, and causes the steering gear 4 to move rightward in the vehicle width direction, thereby turning the front wheel 1 To the left steering direction. Further, the steering angle control valve 1
4 indicates that when the solenoid 14b is on, the chamber 5b is pressurized and the chamber 5
a, the actuator 5 is contracted to move the steering gear 4 to the left in the vehicle width direction.
To the right steering direction. Since the other steering angle control valve 15 and the actuator 6 have the same function as the one side steering angle control valve 14 and the actuator 5,
Corresponding parts are denoted by the same reference numerals with the same suffixes a to d, and detailed description thereof is omitted.

The controller 16 controls the steering angle control valve 1
4, 15 solenoids 14a, 14b, 15a, 15
b on / off control.
Are a steering angle sensor 17 (corresponding to a steering wheel angle detecting means) for detecting a steering wheel angle θ of the steering wheel 3, a vehicle speed sensor 18 (corresponding to a vehicle speed detecting means) for detecting a vehicle speed V, A stroke sensor 19 for detecting a stroke, and a lateral acceleration sensor 2 for detecting a lateral acceleration Yg
A signal from 0 (corresponding to a lateral acceleration detecting means) is input, and a control law described later is executed to perform auxiliary steering angle control.

The basic control law is a front / rear wheel auxiliary steering angle control law which combines the phase inversion control of the rear wheel 2 and the turning angle control of the front wheel 1. The phase inversion control of the rear wheel 2
This is a control in which the yaw rate rises by momentarily reverse-phase steering, and then reverses to the same phase side to suppress the increase in the yaw rate and stabilize the vehicle body. This is effective in low and medium speed ranges. In addition, the steering angle control of the front wheel 1 is increased by turning the front wheel 1 to provide an auxiliary steering angle in response to an increase in the steering wheel angle, and by flattening the frequency characteristics of the yaw rate and the lateral acceleration, the vehicle body slip angle is reduced to zero, thereby stabilizing the vehicle body. This is a control that balances responsiveness and responsiveness at a high level.

The operation will be described.

FIGS. 3 and 4 are flowcharts showing the flow of the rear wheel assist steering angle control operation performed by the controller 16, and each step will be described below (corresponding to rear wheel steering angle control means).

In step 101, the steering wheel angle θ, the vehicle speed V, and the lateral acceleration Yg are input.

In step 102, the steering wheel angular velocity θ ′ and the steering wheel angular acceleration θ ″ are calculated based on the steering wheel angle θ by the following equation.

Θ ′ = (d / dt) · θθ ″ = (d / dt) · θ ′ In step 103, the phase inversion control parameters k, τ, and τ ′ are calculated according to the vehicle speed V by the following equations. Is calculated.

K = f ₁ (V) τ = f ₂ (V) τ ′ = f ₃ (V) In step 104, the rear wheel auxiliary steering angle δ in the phase inversion control
_rs is calculated by the following equation (corresponding to rear wheel assist steering angle calculating means).

Δ _rs = k · θ + τ · θ ′ + τ ′ · θ ”This rear wheel auxiliary steering angle δ _rs has the same phase on the high vehicle speed side because the parameters k, τ and τ ′ are values corresponding to the vehicle speed. It is obtained as an opposite phase value on the low vehicle speed side.

In step 105, the phase change handle angle θ ₀ is calculated by the following equation (corresponding to the phase change handle angle setting means).

Θ ₀ = f ₄ (V, Yg) = γ · Yg · {A ₀ + (A ₁ / V ² )} A ₀ , A ₁ ; constant determined by vehicle specifications γ; characteristic change parameter step 106 Then, it is determined whether the handle angle θ is equal to or larger than the phase change handle angle θ ₀ .

When θ <θ ₀ , step 10
7 and the steering wheel angle θ _X for calculating the rear wheel return steering angle is θ
_X = θ is set.

If θ ≧ θ ₀ , step 108
To advances, the rear wheels tempering steering angle calculation wheel angle theta _X is calculated by the following equation (step 106 to step 108 corresponds to the calculation wheel angle setting means).

Θ _X = θ + k ₁ · θ ′ + k ₂ · θ ”where θ ₀ ≦ θ _X ≦ k _3. | Θ−θ ₀ | In step 109, the first-order lag filter for the temporary rear wheel return steering angle is used. the time constant T is calculated by the following equation based on the rear wheel tempering steering angle and calculation wheel angle theta _X phase change wheel angle theta ₀ (corresponding to the time constant setting means).

T = f ₅ · (θ ₀ , θ _X ) In step 110, the temporary rear wheel return steering angle δ _rc ′ before being subjected to the first-order lag filter is calculated by the following equation. The rear wheel return rudder angle calculation means described).

Δ _rc ′ = f ₆ · (θ _X , θ ₀ ) In step 111, a first-order lag filter is applied to the temporary rear wheel return steering angle δ _rc ′, and the rear wheel return steering angle δ _rc is _calculated by the following equation. This is calculated (corresponding to a rear wheel return steering angle calculating means according to claim 4).

Δ _rc = {1 / (1 + Ts)} · δ _rc 's; Laplace operator In step 112, it is determined whether the rear wheel assist steering angle δ _rs by the phase inversion control is in phase or out of phase.

If the rear wheel auxiliary steering angle δ _rs is in the opposite phase, the _routine proceeds to step 113, where the rear wheel auxiliary steering angle δ _rs is directly used as the rear wheel auxiliary steering angle control value δ _r (= δ _rs ), The control command is output so as to make use of the movement of the lane change or the like as it is only by the phase inversion control.

On the other hand, if the rear wheel auxiliary steering angle δ _rs is in phase, the _routine proceeds to step 114, where a value obtained by subtracting the rear wheel returning steering angle δ _rc from the rear wheel auxiliary steering angle δ _rs is used as the rear wheel auxiliary steering angle control. Value δ
_r (= δ _rs −δ _rc ), and outputs a control command in consideration of this control in order to improve the turning performance (see FIG. 5).

Next, the turning action by changing the phase change handle angle θ _{0 and} the turning action by the rear wheel return steering angle δ _rc will be described.

[0054] (b) a phase change wheel angle theta ₀ swirling action rear wheel 2 due to the change of the phase change wheel angle theta ₀ is the steering wheel angle is steered in the opposite phase are that the lateral force of the front wheel 1 is saturated The vehicle speed V and the lateral acceleration Yg are estimated and calculated in the above step 105 so that they substantially coincide with each other.

As shown in FIG. 5, when the vehicle speed V increases, the phase change steering wheel angle θ ₀ is reduced so as to cancel the understeer corresponding to the stability factor.

On the other hand, with respect to the lateral acceleration Yg, when traveling on a low μ road, the characteristic of the tire lateral force CF with respect to the tire slip angle SA decreases as shown in FIG. 10, and the cornering power CP and the maximum lateral force CFmax are reduced. As the lateral force of the front wheel 1 saturates at an early stage, the lateral acceleration Y decreases as shown in FIG.
As g is smaller, the phase change handle angle θ ₀ decreases, and as the lateral acceleration Yg increases, the phase change handle angle θ ₀ increases.

As described above, the phase change handle angle θ ₀ at which the lateral force of the front wheel 1 is determined to be saturated is calculated by the virtual lateral acceleration Yg ^* calculated from the handle angle θ and the lateral acceleration sensor 20.
From the actual lateral acceleration Yg.

That is, the virtual lateral acceleration Yg ^* is equal to the actual lateral acceleration Yg ^.
g, the vehicle is already understeer, and the lateral force of the front wheels 1 is saturated, so that the rear wheels 2 are moved to reduce the understeer of the vehicles and make the vehicle move in the yaw direction. It is necessary to reduce the lateral force, that is, return the steering angle of the rear wheel 2 to the opposite phase.

For this purpose, the phase change handle angle θ ₀ may be obtained by the following equation.

Yg ^* = A / {k _S + (1 / V ² )} (1) γ = Yg ^* / Yg (2) where A is a constant determined by the wheel base and the steering gear ratio k _S is the stability The factor γ is a parameter of the characteristic change. Assuming that the handle angle θ in the above equation (1) is the phase change handle angle θ ₀ , θ ₀ = (1 / A) · {k _S + (1 / V ² )} · Yg ^* . (1) ′ From the above equations (1) ′ and (2), θ ₀ = (1 / A) · {k _S + (1 / V ² )} · γ · Yg (3) Comparing the described θ ₀ = γ · Yg · {A ₀ + (A ₁ / V ² )} with the expression (3), it corresponds to k _S / A = A ₀ , 1 / A = A ₁ .

Accordingly, during turning, the lateral force of the front wheels 1 is saturated by the vehicle speed V and the lateral acceleration Yg by changing the phase-changed steering wheel angle θ _{0 at} which the reverse phase steering of the rear wheels 2 is started with respect to the steering wheel angle θ. Since the rear wheels 2 are steered in the opposite phase at the same time, optimum turning performance can be achieved regardless of the road surface friction coefficient and turning conditions.

For example, during a low-speed small-radius turn in which the saturation of the lateral force of the front wheel 1 appears slowly, the phase change handle angle θ ₀ is set to a large angle, the rear wheel in-phase turning range becomes long, and the small phase change handle angle is set. Unlike in the case of the fixed phase inversion control, strong oversteer such as rotating on the spot does not occur, and optimum turning performance can be obtained.

On a low μ road or a high-speed large-radius turn in which the lateral force of the front wheel 1 is saturated early, the phase change steering wheel angle θ ₀ is set to be small. The rear wheels 2
The yaw moment in the turning direction is given to the vehicle by the reverse phase turning of the vehicle, and the optimum turning performance is obtained without the strong understeer as in the case of the phase inversion control fixed to the large phase change steering wheel angle .

(B) Turning action by rear wheel return steering angle δ _rc First, when θ <θ _{0 in} step 106, step 1
At 07, the handle angle θ is directly used as the calculation handle angle θ _{X. When} θ ≧ θ ₀ , the calculation handle angle θ as shown in FIG.
_X

[0065] This is, in the phase change the steering wheel angle θ ₀ or more of the steering wheel angle θ, because tire slip angle of the front wheels 1 is large, the lateral force of the front wheel 1 is saturated, the front wheels of the phase change the steering wheel angle θ ₀ or less In order to generate a force equivalent to the speed of change of the yaw moment when the lateral force 1 is increasing only on the rear wheel 2, the lateral force of the rear wheel 2 must be changed faster and larger. . The upper limit of k ₃ · | θ-θ ₀ | is set for the calculation steering wheel angle θ _X , as shown in FIG. 8, during steering of the steering wheel from θ <θ ₀ to θ ≧ θ _0. This is to prevent a sudden change at the time of becoming.

Therefore, when θ ≧ θ ₀ , if the steering wheel turning operation is being performed, the steering wheel angle θ _X for calculation becomes larger than the actual steering wheel angle θ according to the operating speed or the operating acceleration.
Is set, in the limit region where the lateral force of the front wheel 1 is saturated, the rear wheel 2 is steered in the opposite phase at a higher speed and with a higher response than when the steering wheel angle is used as it is, and the lateral force at the front wheel 1 is changed. The decrease is covered by the high-response reverse-phase steering at the rear wheels 2, and the rudder effect by the turning direction yaw moment is secured.

[0067] In step 110, as shown in FIG. 6, also provisional rear wheel as calculated for steering wheel angle theta _X increases
Due to the characteristic that the increasing ratio of the steering angle δ _rc ′ increases, 1
Temporary rear wheel return steering angle δ _rc 'before applying to next delay filter
There is calculated as a value that increases with respect to calculation wheel angle theta _X.

Therefore, in the grip region of the front wheel 1 in which the steering wheel angle θ is smaller than the phase change steering wheel angle θ ₀ , the rear wheel return steering angle δ _rc is small, and the stability by the in-phase control of the rear wheel 2 is obtained. In the limit region where the lateral force of the front wheel 1 larger than the phase change handle angle θ ₀ is saturated, the rear wheel 2 is returned by the rear wheel return steering angle δ _{rc in the} opposite phase as the calculation handle angle θ _X is larger. Thus, the effect of the rudder can be obtained by increasing the yaw moment in the turning direction. That is, the stability at the time of lane change and the like, and the effectiveness of the rudder at the turning limit are compatible.

Further, in step 109, as shown in FIG. 7, when the steering wheel angle θ is smaller than the phase changing steering wheel angle θ _{0, the} time constant T becomes smaller as the calculating steering wheel angle θ _X increases, and the steering wheel angle θ becomes smaller. Phase change handle angle θ
When it is ₀ or more, the time constant T is set to zero. In step 11, the temporary higher computational steering wheel angle theta _X increases
Due to the characteristic that the increase ratio of the rear wheel return steering angle δ _rc ′ increases.
Ri, so that the rear wheels by multiplying the first-order lag filter according to the time constant T in calculation steering wheel angle θ steering angle tempering also provisionally rear wheel to increase in relative _X [delta] _rc 'tempering steering angle [delta] _rc is obtained.

Therefore, in the grip region of the front wheel 1, the first-order lag is effective, the in-phase amount increases, and the stability of lane change and the like is improved. In the limit region where the lateral force of the front wheel 1 is saturated, the vehicle responds without delay. The effectiveness of the rudder is secured.

The effect will be described.

(1) In a rear wheel steering angle control device for providing an in-phase rear wheel auxiliary steering angle in the steering wheel angle region and providing an opposite-phase rear wheel auxiliary steering angle in the large steering wheel angle region, Since a means for changing the phase change handle angle θ ₀ for changing the auxiliary steering angle from the same phase to the opposite phase with the vehicle speed V and the lateral acceleration Yg is provided, the optimum steering angle θ ₀ is optimal regardless of the road surface friction coefficient and the turning condition. Turning performance can be achieved.

(2) When the steering wheel angle θ is equal to or larger than the phase change steering wheel angle θ ₀ , the steering wheel angle θ _X for calculating the rear wheel returning steering angle δ _rc is determined by the steering wheel angular velocity θ ′ and the steering wheel angular acceleration θ ″.
Is provided, the steering effect can be ensured with good response in the limit region where the lateral force of the front wheel 1 is saturated.

(3) The calculation handle angle θ _X increases.
As the rear wheel return steering angle δ _rc increases,
More rear wheels of relative calculation wheel angle theta _X in the opposite phase direction increases tempering for providing a means for obtaining a steering angle [delta] _rc, the front wheels 1
Stability such as lane change in the grip area and front wheel 1
In the limit region where the lateral force is saturated.

(4) The calculation handle angle θ _X increases.
As the temporary rear wheel return steering angle δ _rc ′ increases,
The gender, provisional rear wheel to increase in relative calculation steering wheel angle [delta] _rc to tempering steering angle [delta] _rc ', back rear wheels over the first-order lag filter according to the time constant T is given by phase change wheel angle theta ₀ or less Since the means for obtaining the steering angle δ _rc is provided, the stability such as lane change is further improved in the grip region of the front wheel 1, and the steering effect responds without delay in the limit region where the lateral force of the front wheel 1 is saturated. Can be secured.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and even if there are changes and additions without departing from the gist of the invention, the invention is included in the invention. It is.

For example, in the embodiment, an example of application to a vehicle in which an auxiliary steering angle is provided to both the front and rear wheels has been described. However, the invention can also be applied to a vehicle in which an auxiliary steering angle is provided only to the rear wheels.

In the embodiment, the example of the rear wheel phase inversion control is described as a basic control law, but the present invention can be applied to a method of giving an auxiliary steering angle to the rear wheel by another control law such as a rear wheel first order lag control.

[0079]

As described above, according to the first aspect of the present invention, an in-phase rear wheel auxiliary steering angle is provided in the steering wheel angle region, and an anti-phase rear wheel auxiliary steering angle is provided in the large steering wheel angle region. In a rear wheel steering angle control device to be provided, a phase change handle angle setting means for changing a phase change handle angle for changing a rear wheel auxiliary steering angle from the same phase to an opposite phase with respect to a handle angle by parameters of a vehicle speed and a lateral acceleration. Is provided, an effect that optimum turning performance can be achieved irrespective of the road surface friction coefficient and the turning condition.

According to the second aspect of the present invention, the steering wheel angle for calculating the rear wheel return steering angle when the steering wheel angle is equal to or larger than the phase change steering wheel angle is set in consideration of the steering wheel angular velocity and the steering wheel angular acceleration. Is provided, an effect is obtained that the steering effect can be secured with good response in the limit region where the lateral force of the front wheels is saturated.

According to the third aspect of the present invention, calculation
The larger the steering wheel angle, the larger the rear wheel return steering angle
The characteristics becomes large, rear wheels of relative calculation wheel angle in the opposite phase direction increasing <br/> pressurized tempering for providing a means for obtaining a steering angle, the stability of the lane change or the like in the front wheel grip region And the effect of the rudder in the limit region where the lateral force of the front wheels is saturated can be obtained.

According to the fourth aspect of the present invention, calculation
Increase ratio of temporary rear wheel return steering angle as steering wheel angle increases
The characteristic rate increases, with respect to calculation wheel angle
The steering angle tempering also provisionally rear wheel to increase, because of providing the means for obtaining a steering angle tempering also the rear wheels by multiplying the first-order lag filter by a time constant given by the following phase changes the steering angle, more lane change in front wheel grip region And the like, and the effect that the steering effect can be secured without delay in the limit region where the lateral force of the front wheels is saturated can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim showing a rear wheel steering angle control device of the present invention.

FIG. 2 is an overall system diagram showing a four-wheel steering vehicle to which the rear wheel steering angle control device according to the embodiment is applied;

FIG. 3 is a diagram showing a first half of a flowchart showing a flow of a rear wheel steering angle control operation by a controller.

FIG. 4 is a diagram showing a latter half of a flowchart showing a flow of a rear wheel steering angle control operation by the controller.

FIG. 5 is a characteristic diagram of an actual rear wheel assist steering angle with respect to a calculation steering wheel angle.

FIG. 6 is a characteristic diagram of a temporary rear wheel returning steering angle with respect to a calculation steering wheel angle.

FIG. 7 is a time constant characteristic diagram with respect to a calculation handle angle.

FIG. 8 is a time chart showing a relationship between a steering wheel angle and a steering wheel angle for calculation.

FIG. 9A is a diagram showing the occurrence of a vehicle body slip angle when turning on a high μ road, and FIG. 9A is a diagram showing the occurrence of a vehicle body slip angle when turning on a low μ road.

FIG. 10 is a lateral force characteristic diagram with respect to a tire slip angle when a road surface μ is used as a parameter.

[Explanation of symbols]

 a rear wheel assist steering angle applying means b handle angle detecting means c vehicle speed detecting means d lateral acceleration detecting means e phase changing handle angle setting means f rear wheel steering angle control means g rear wheel assist steering angle calculating means h steering wheel setting for calculation Means i Rear wheel return steering angle calculating means j Time constant setting means

Claims (4)

(57) [Claims] 1. A rear wheel assist steering angle providing means for providing an auxiliary steering angle to a rear wheel, a steering wheel angle detecting means for detecting a steering wheel angle, a vehicle speed detecting means for detecting a vehicle speed, and a lateral acceleration detecting for detecting a lateral acceleration. Means for changing the steering angle of the rear wheels from the same phase to the opposite phase with respect to the steering wheel angle. The phase changing steering wheel angle is set to a smaller angle as the vehicle speed increases, and to a larger angle as the lateral acceleration increases. A phase change handle angle setting means, wherein in the region where the handle angle is smaller than the phase change handle angle, an auxiliary steering angle in phase with the front wheel is given to the rear wheel, and in the region where the handle angle is larger than the phase change handle angle, the rear wheel is in opposite phase with the front wheel. And a rear wheel steering angle control means for providing an auxiliary steering angle of: 2. The rear wheel steering angle control device according to claim 1, wherein a rear wheel auxiliary steering angle calculating means for obtaining a rear wheel auxiliary steering angle according to a predetermined control law, wherein the steering wheel angle is smaller than the phase change steering wheel angle. A steering wheel angle setting means for calculating the steering wheel angle as it is, and when the steering wheel angle is greater than or equal to the phase change steering wheel angle, a steering wheel angle for calculating the sum of the steering wheel angle, the steering wheel angular velocity, and the steering wheel angular acceleration; A rear wheel return steering angle calculating means for calculating a rear wheel return steering angle for returning the rear wheel in the reverse phase direction based on the steering wheel angle, wherein the rear wheel steering angle control means controls the rear wheel return from the rear wheel auxiliary steering angle. A rear wheel steering angle control device characterized in that it is means for giving an actual rear wheel auxiliary steering angle by a value obtained by subtracting the angle. 3. The rear wheel steering angle control device according to claim 2, wherein the rear wheel return steering angle calculation means includes a steering wheel for calculation having a large steering wheel angle.
The larger the steering angle, the greater the increase in the rear wheel return steering angle
Sex, the wheel steering angle control system being characterized in that the means for obtaining a wheel tempering steering angle after the reverse phase direction to increase with respect to computational steering wheel angle. 4. The rear wheel steering angle control device according to claim 3, wherein when the steering wheel angle is smaller than the phase changing steering wheel angle, the time constant becomes smaller as the steering wheel angle increases, and when the steering wheel angle is larger than the phase changing steering wheel angle. A time constant setting means for setting a constant to zero, wherein the rear wheel return steering angle calculating means has a large steering wheel angle for calculation.
The larger the ratio, the larger the increase ratio of the temporary rear wheel return steering angle
The characteristics, wheel steering angle after being characterized in that the means for obtaining a steering angle tempering also the rear wheels by multiplying the first-order lag filter according to the time constant tempering of the steering angle even temporary rear wheel to increase in relative calculation wheel angle Control device.