JP2001080538A - Steering device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply realize the steering stability compatible with initial turnability by controlling the steering angle so as to be an opposite phase at the initial time of the steering and so as to be the same phase at the intermediate time of the turning and so as to be neutral in the steady turning condition. SOLUTION: Rise of a yaw rate is delayed in relation to rise of the steering angle speed of a steering wheel 9 at the initial time of turning. An absolute value of a dδh/dt is larger than an absolute value of dγ/dt. Since a rear wheel target steering angle has a negative value, rear wheels 7R, 7L are steered to the opposite phase in relation to front wheels 8R, 8L. At the intermediate time of turning, an absolute value of the steering angle of the steering wheel 9 is smaller than an absolute value of the yaw angle acceleration. The rear wheel target steering angle δr becomes a positive value, and the rear wheels 7R, 7L are steered to the same phase in relation to the front wheels 8R, 8L. In steady turning condition, both of the steering angle δh and the yaw rate γdo not change. Both of the steering angle speed dδh/dt and the yaw angle acceleration dγ/dt become zero, and the rear wheel target steering angle δr becomes zero.

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, and more particularly to a vehicle steering system having a steering mechanism applicable to a four-wheel steering vehicle.

[0002]

2. Description of the Related Art In the case of a two-wheel steering vehicle (hereinafter abbreviated as 2WS vehicle) in which only the front wheels are steered by a steering wheel, the only way to provide the sideslip angle to the rear wheels when turning is to add the vehicle body sideslip angle. In order to obtain a vehicle body side slip angle, the vehicle body must start to rotate around the vertical center of gravity axis by the action of the yawing moment. This not only hinders obtaining a high turning response, but also adversely affects the convergence of the yawing motion, that is, the convergence of the behavior. Therefore, a four-wheel steering vehicle (hereinafter abbreviated as 4WS vehicle) has been developed in which the front and rear wheels are both steered to positively control the rear wheel sideslip angle, and many commercial 4WS vehicles have already been seen.

In such a 4WS vehicle, a steering angle, a vehicle speed, and a generated yaw rate are detected, and a first rear wheel steering angle target value is set based on the steering angle, the steering angular speed, the steering angular acceleration, and the vehicle speed. A target yaw rate based on vehicle specifications is calculated from the target value, the actual steering angle, and the actual vehicle speed, and a second rear wheel steering angle target value is set based on the deviation between the target value and the actual yaw rate value. Japanese Patent Application Laid-Open No. 5-185945 discloses a configuration in which the rear wheel steering angle is optimally controlled in consideration of the feedforward control and the feedback control based on the target value.

[0004]

However, according to the technique proposed in the above publication, it is necessary to set an appropriate rear wheel steering angle with respect to the amount of exercise in advance and to calculate a final rear wheel steering angle target value. Is complicated, and the control algorithm tends to be complicated. In addition, there is a problem that the load on the actuator is increased due to excessive adjustment to the target characteristic.

[0005] The present invention has been devised to remedy such disadvantages of the prior art, and its main objects are as follows.
An object of the present invention is to provide a vehicular steering device configured to be able to achieve both higher turning performance at the initial turn and stability during a turn with relatively simple control.

[0006]

In order to achieve the above object, according to the present invention, a front wheel steering mechanism 10 for changing a steering angle of front wheels 8R and 8L in accordance with a rotation angle of a steering wheel 9; Rear wheel 7R ・ 7 according to running condition
Actuating the steering angle of L (motor 2 in the embodiment)
The rear-wheel steering mechanism for a vehicle having the rear-wheel steering mechanism 1 and the rear-wheel steering mechanism 1 is changed in the following manner. The control is performed so that the rear wheel steering angles become the same phase and become neutral in a steady circular turning state.

According to this, the yaw rate rises early by turning the rear wheels in the opposite phase at the beginning of turning, so that the turning performance is enhanced. During the turning, so-called spin in which the rear part of the vehicle body is swung by setting the rear wheels to the same phase. The tendency is suppressed, and the characteristic equivalent to that of the 2WS vehicle can be obtained by making the rear wheel neutral in steady circular turning.

Specifically, the vehicle body side slip angular velocity is detected,
The actuator is controlled to reduce the absolute value of the vehicle body side slip angular velocity, the actuator is controlled based on a comparison value between the rotational angular velocity of the steering wheel and the yaw angular acceleration, and the steering angular velocity of the steering wheel is The actuator may be controlled based on a comparison value with the steering angular acceleration.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a vehicle steering system according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a 4WS vehicle to which the present invention is applied. The rear wheel steering mechanism 1 of this vehicle has an electric motor 2 and a steering shaft 3 arranged coaxially. The rotational torque of the electric motor 2 generated by the drive current from the control unit 4 is converted into a rear wheel steering force consisting of the axial force of the steering shaft 3 in the left and right direction via a rotational force / axial force conversion mechanism such as a ball screw mechanism. Is done.

Both ends of the steering shaft 3 are connected to a steering link member 5R.
The rear wheel 7R is connected to the rear knuckle arms 6R and 6L through the rear wheels 7R and 7L.
To the steering angle.

For the front wheels 8R and 8L, the rotational force applied to the steering wheel 9 is converted into the axial force of the rack shaft of the front wheel steering mechanism 10, and a steering angle corresponding to the rotation angle of the steering wheel 9 is given to the front wheels 8R and 8L. Can be

The control unit 4 of the rear wheel steering mechanism 1
As shown in FIG. 2, a side slip angular velocity calculator 11 that calculates a vehicle body slip angular velocity at an arbitrary point ahead of a rear axle on the vehicle body, and a vehicle body slip angular velocity value given from the skid angular velocity calculator 11. The rear wheel target steering angle calculation unit 12 determines the steering angle of the rear wheels 7R and 7L, and the steering angle is given to the rear wheels 7R and 7L based on the steering angle value obtained by the rear wheel target steering angle calculation unit 12. Rear wheel steering angle control unit 1 that controls wheel steering mechanism 1
3 is provided. Also, the control unit 4
Vehicle speed value V detected by vehicle speed sensor 14, lateral acceleration sensor 1
5 detects the lateral acceleration value αy and the yaw rate sensor 1
The yaw rate value γ detected by the counter 6 is output.

When the vehicle speed value V, the lateral acceleration value αy, and the yaw rate value γ are obtained, the vehicle body side slip angular velocity βx at a point separated by a distance x from the front axle can be obtained from the following equation.

Βx = γ + [(dγ / dt) · (x−a)
/ V]-(αy · 1 / V)

Here, a is the distance from the center of the front axle to the center of gravity.

Note that the vehicle body side slip angular velocity βx is not limited to the above equation, and may be estimated using, for example, other state quantities (Japanese Patent Application No. Hei.
0-235415), or may be obtained from a measured value of a measuring instrument.

The feedback gain calculating section 18 calculates the side slip angular velocity calculating section 1 based on the output V of the vehicle speed sensor 14.
The feedback gain k for the vehicle body side slip angular velocity βx obtained in step 1 is determined. This feedback gain k is
For example, as shown in FIG. 3, the value is directly proportional to the vehicle speed V.

The rear wheel target steering angle δr is sent to the rear wheel target steering angle calculating section 12 from the vehicle body side slip angular velocity βx output from the side slip angular velocity calculating section 11 and the feedback gain k output from the feedback gain calculating section 18. It is determined by the following built-in equation.

Δr = kβx

Further, the rear wheel target steering angle δr is determined by the output δr0 of the rear wheel steering angle sensor 19 provided in the rear wheel steering mechanism 1.
The actual steering angle Δδr is determined by comparing the (rear wheel actual steering angle) with the rear wheel steering angle comparison unit 20.

Δδr = δr−δr0

The actually required steering angle Δδr is converted by the rear wheel steering angle control unit 13 into a drive current for the electric motor 2 of the rear wheel steering mechanism 1, and the electric motor 2 is driven to thereby convert the rear wheels 7 R
7L is steered.

As shown in FIG. 4, in the case of a 2WS vehicle, in a high-speed turn, even if the front wheels are steered, the vehicle body tries to maintain a straight running state by the inertial force at the beginning of the turn. There is a tendency for the vehicle sideslip angle to be outward with respect to the tangent. In a steady circular turn, the cornering forces of the front and rear wheels and the centrifugal force are balanced, but the yaw moment is applied to the vehicle body, so that there is a tendency for the vehicle body to have a side slip angle inward with respect to the tangent of the turning circle.

According to the present invention, when the outward (negative) vehicle body side slip angular velocity βx rises at the beginning of a turn, the rear wheels 7R and 7L naturally reverse the front wheels 8R and 8L in order to suppress the change in the vehicle body side slip angle. Yaw rate γ
Is easy to stand up and the turning property is enhanced.

If the vehicle continues to turn with anti-phase steering, the rear wheels 7
Since the tire sideslip angle of R · 7L becomes small, the inward (positive direction) body sideslip angle tends to increase in order to obtain a cornering force that balances the centrifugal force.
Since the rear wheel steering angle δr is controlled so as to suppress the change in the vehicle body side slip angle, the rear wheels 7R and 7L are steered to increase the tire side slip angle, that is, the front wheels 8R and 8L naturally.
And the behavior of the vehicle body is stabilized.

Then, in a steady circular turning where the vehicle body slip angle does not change, that is, the vehicle body skid angular velocity βx becomes zero,
Naturally, the rear wheel steering force does not act, so that the characteristics equivalent to those of the 2WS vehicle come to be exhibited.

As shown in FIG. 5, the response of the vehicle body skidding angular velocity βx when the steering wheel is turned sharply by 90 degrees from the straight running state at 120 km / h converges to zero after swinging only in the forward direction on the rear axle. On the other hand, as the vehicle goes forward from the rear axle, the vehicle tends to swing in the negative direction once. That is, the vehicle body skidding angular velocity β used when calculating the rear wheel steering angle βr
It can be said that, as the detection position of x is set further forward, the gain of the anti-phase steering angle of the rear wheels 7R and 7L in the initial stage of turning increases.

4W in which the rear wheel steering angle δr is controlled based on the vehicle body skidding angular velocity βx on the front axle while traveling at 120 km / h.
FIG. 6 shows a comparison diagram of the characteristics of the S vehicle and the 2WS vehicle. The left side of the figure represents the yaw rate response, the right side represents the lateral acceleration response, and the frequency response of the gain, the frequency response of the phase, and the step response when the steering wheel 9 is rapidly rotated 90 degrees from the top.

Regarding the yaw rate response to the frequency (steering speed), the peak gain is suppressed as compared with the 2WS vehicle, the phase lag in the high frequency range is reduced, and the responsiveness and stability are both improved. You can see that. Moreover, since the rise of the yaw rate γ with respect to the steering of the steering wheel 9 is sharp and no overshoot occurs, it can be seen that the convergence of the behavior is higher than that of the 2WS vehicle.

Regarding the lateral acceleration response to the frequency,
It can be seen that both the gain increase and the phase advance at high frequency are eliminated as compared with the 2WS vehicle, and the stability is improved. In addition, it can be seen that the response of the steering wheel 9 to steering is also smooth.

From these results, it can be seen that the present invention makes it possible to achieve both high turning performance and high stability without changing the steady circular turning characteristics.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the steering angular velocity (the rotation angle δ of the steering wheel 9)
h) and yaw angular acceleration (differential value of yaw rate γ)
The rear wheel target steering angle δr is determined based on the above. Therefore, the control unit 4 includes the first
As compared with the embodiment, the output of the steering angle sensor 21 for detecting the rotation angle δh of the steering wheel 9 is input (see FIG. 7). Since other configurations are the same as those described above, the same reference numerals as in FIG. 1 are assigned and the description thereof is omitted.

In the control unit 4 of this embodiment, as shown in FIG. 8, the steering angular velocity dδh / dt obtained by differentiating the steering angle δh output from the steering angle sensor 21 with the steering angular velocity calculating section 22 is obtained. , Yaw rate sensor 16
The yaw rate γ output from the yaw rate
The yaw angular acceleration dγ / dt obtained by differentiating the vehicle speed and the vehicle speed V output from the vehicle speed sensor 14 are calculated by the feedback gain calculation unit 1.
8, two feedback gains k1 and k obtained by inputting
2 is output to the rear wheel target steering angle calculation unit 12.

Here, the two feedback gains k1 and k2 obtained by the feedback gain calculator 18 are, for example, as shown in FIG. 9, a value (k1) that gradually decreases as the vehicle speed V increases and a value (k2) that gradually increases. Have been. The first feedback gain k1 is set to be high in a low speed range to improve responsiveness to steering (turning performance), and is reduced in a high speed range to avoid an excessive response. The second feedback gain k2 is set low in a low-speed range to avoid deterioration in turning performance, and is increased in a high-speed range to stabilize the behavior.

The rear wheel target steering angle calculation section 12 determines a rear wheel target steering angle δr based on the following equation.

Δr = −k1 (dδh / dt) + k2 (dγ / dt)

On the other hand, in the rear wheel steering angle comparison section 20, this rear wheel target steering angle δr is compared with the output δr0 (rear wheel actual steering angle) of the rear wheel steering angle sensor 19 attached to the rear wheel turning mechanism 1. The required turning amount Δδr corresponding to the deviation is obtained.

Δδr = δr−δr0

The required steering amount Δδr is converted into a drive current for the electric motor 2 of the rear wheel steering mechanism 1 by the rear wheel steering angle control unit 13, and the rear wheels 7 R and 7 are driven by driving the electric motor 2.
L is steered.

By the way, in the initial stage of turning, the steering wheel 9
Of the yaw rate γ (change of the yaw angular velocity) is delayed with respect to the rise of the steering angular velocity (change of the steering angle δh), that is, k1 with respect to the absolute value of k2 (dγ / dt).
The absolute value of (dδh / dt) increases. Therefore, since the rear wheel target steering angle δr has a negative value, the rear wheels 7R and 7L are turned in the opposite phase to the front wheels 8R and 8L.

In the middle of turning, the absolute value of the steering angular velocity (k1 (dδh / dt)) of the steering wheel 9 becomes smaller than the absolute value of the yaw angular acceleration (k2 (dγ / dt)). Therefore, since the rear wheel target steering angle δr has a positive value, the rear wheels 7R and 7L are steered in the same phase as the front wheels 8R and 8L.

In a steady circular turn, both the steering angle δh and the yaw rate γ do not change, that is, the steering angular velocity dδh /
dt and yaw angular acceleration dγ / dt are both zero. Therefore, the rear wheel target steering angle δr is also zero, and is 2WS.

FIG. 10 shows the response characteristics when the steering wheel is turned sharply by 90 degrees from a straight running state at 120 km / h. The change in the steering angle δh, the change in the actual rear wheel steering angle δr0, and the change in the yaw rate γ are shown in order from the top. according to this,
In the initial stage of steering, the rear wheels 7R and 7L are turned in the opposite phase to the front wheels 8R and 8L, and the responsiveness of the yaw rate γ is improved as compared with 2WS, and thereafter, the rear wheels 7R and 7L and the front wheels 8R and 8L Overshoot of yaw rate γ is reduced by phase steering,
It can be seen that the behavior converges smoothly.

From these results, it can be seen that the present invention makes it possible to achieve both high turning performance and high stability without changing the steady circular turning characteristics.

Next, a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the rear wheel target steering angle δr is determined based on the angular velocity and angular acceleration of the steering wheel 9. Basic configuration requirements corresponding to this are described in the second section above.
Since the third embodiment is the same as the first embodiment, the description thereof is omitted.

First, based on the steering angle δh output from the steering angle sensor 21, the steering angular velocity calculator 23 calculates the steering angle δh
Differential value dδh / dt (steering angular speed), second order differential value dδh ² / dt of the steering angle acceleration calculator 24 is the steering angle δh
² (steering angular acceleration) is output. However, when calculating each value, a low-pass filter having a sufficiently small cutoff frequency is used. Then, the rear wheel target steering angle calculation unit 12 outputs the feedback gain k
1, k2 and the target steering angle δ of the rear wheels based on the following equation:
Determine r.

Δr = k1 · (dδh / dt) −k2 ·
(Dδh ² / dt ² )

Here, the two feedback gains k1 and k2 obtained by the feedback gain calculator 18 are both values that gradually decrease as the vehicle speed V increases, as shown in FIG. These are intended to improve responsiveness (turning performance) to steering. The gain is increased in a low speed range, and the gain is reduced in a high speed range to avoid excessive response.

In the rear wheel steering angle comparing section 20, this rear wheel steering angle δr is compared with the output δr0 of the rear wheel steering angle sensor 19 attached to the rear wheel steering mechanism 1, and the required steering amount Δδr
Is required.

Δδr = δr−δr0

The required turning amount Δδr is converted into a drive voltage for the electric motor 2 of the rear wheel steering mechanism 1 by the rear wheel steering angle control unit 13 and the electric motor 2 is driven, so that the rear wheels 7R and 7R are driven.
L is steered.

According to this control, at the beginning of turning, the steering angle
Change rate of steering angular velocity compared to change rate (dδh / dt)
(Dδh^Two/ Dt^Two) Increases, the rear wheel steering angle δr is negative.
, And the rear wheels 7R and 7L have opposite phases to the front wheels 8R and 8L.
Is steered. And in the middle of turning, the rate of change of the steering angle
(Dδh / dt), the rate of change of the steering angular velocity (dδh
^Two/ Dt^Two) Becomes smaller, so that δr becomes a positive value and the rear wheel
The wheels 7R and 7L are steered in the same phase as the front wheels 8R and 8L. So
In a steady circular turn, both the steering angle and the steering angular velocity change.
The rear wheel steering angle δr is also zero because there is no
You.

FIG. 13 shows a response characteristic when the steering wheel is turned sharply by 90 degrees from a straight running state at 120 km / h. From the top, the change in the steering angle δh, the change in the rear wheel steering angle δr0,
The change in the yaw rate γ is shown. According to this, in the initial stage of steering, the rear wheels 7R and 7L are turned in the opposite phase to the front wheels 8R and 8L, and the responsiveness of the yaw rate γ is improved as compared with 2WS.
It can be seen that the overshoot of the yaw rate γ is reduced by the in-phase steering of the rear wheels 7R and 7L and the front wheels 8R and 8L thereafter, and the vehicle body behavior smoothly converges. Since the primary low-pass filter is applied to the steering angle command values Δδr of the rear wheels 7R and 7L, the change of the steering angles of the rear wheels 7R and 7L is gradual.

From these results, it can be seen that, similarly to the above-described two embodiments, the turning performance and the stability can be achieved at a high level without changing the steady circular turning characteristics.

[0056]

As described above, according to the present invention, by turning the rear wheel in the opposite phase to the front wheel at the beginning of turning, the yaw rate rises early and the turning property is enhanced, and during the turning, the rear wheel is the same as the front wheel. By turning to the phase, the so-called spin tendency in which the rear portion of the vehicle body is swung is suppressed, and in the steady circular turning, the rear wheel is neutralized, so that the steering angle control of the rear wheel is not performed. The load is reduced. Moreover, according to the present invention, it is not necessary to preset an appropriate rear wheel steering angle for the amount of exercise, so that it is not necessary to correct or change the target characteristic value according to uncertain factors such as road surface conditions and occupants. Therefore, the control algorithm can be simplified.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a vehicle to which the present invention is applied.

FIG. 2 is a block diagram relating to control of the present invention.

FIG. 3 is a relationship diagram between a feedback gain and a vehicle speed.

FIG. 4 is a conceptual diagram illustrating vehicle behavior during turning of a 2WS vehicle.

FIG. 5 is a response characteristic diagram of the vehicle body skidding angular velocity at the beginning of a turn.

FIG. 6 is a comparative dynamic characteristic diagram of a vehicle to which the present invention is applied and a 2WS vehicle.

FIG. 7 is a schematic configuration diagram of a vehicle according to a second embodiment of the present invention.

FIG. 8 is a block diagram relating to control according to a second embodiment of the present invention.

FIG. 9 is a relationship diagram between a feedback gain and a vehicle speed according to a third embodiment of the present invention.

FIG. 10 is a comparative kinetic characteristic diagram of a vehicle according to a third embodiment of the present invention and a 2WS vehicle.

FIG. 11 is a block diagram related to control according to a third embodiment of the present invention.

FIG. 12 is a relationship diagram between a feedback gain and a vehicle speed according to a third embodiment of the present invention.

FIG. 13 is a comparative kinetic characteristic diagram of a vehicle according to a third embodiment of the present invention and a 2WS vehicle.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 rear wheel steering mechanism 2 electric motor (actuator) 7R / 7L rear wheel 8R / 8L front wheel 9 steering wheel 10 front wheel steering mechanism 11 sideslip angular velocity calculation unit 12 rear wheel target steering angle calculation unit 13 rear wheel steering angle control unit 16 yaw rate sensor 20 Rear wheel steering angle comparison unit 21 Steering angle sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) B62D 137: 00 (72) Inventor Koji Shibata 1-4-1, Chuo, Wako-shi, Saitama F-term (Reference) 3D032 CC02 CC12 CC16 CC48 DA03 DA06 DA09 DA13 DA23 DA29 DA33 DA34 DA39 DB02 DB03 DB12 DC03 DC12 DC29 DD02 DD06 DD17 DE02 EA06 EB01 EB04 EB08 EB11 EC23 GG01 3D034 CA02 CC09 CC12 CD04 CD06 CD07

Claims (4)

[Claims] 1. A vehicle steering system comprising: a front wheel steering mechanism that changes a front wheel steering angle according to a rotation angle of a steering wheel; and a rear wheel steering mechanism that changes a rear wheel steering angle by an actuator according to a running state of the vehicle. The device, wherein the rear wheel steering mechanism, the rear wheel steering angle at the time of turning, the initial phase of the steering is in the opposite phase with respect to the front wheel steering angle, and then in phase with the front wheel steering angle, in a steady state A steering apparatus for a vehicle, wherein the actuator is operated so as to be neutral. 2. The vehicle according to claim 1, further comprising a vehicle body slip angular velocity output means for detecting or estimating a vehicle body skid angular velocity, and a control means for controlling an actuator to reduce an absolute value of the vehicle body skid angular velocity. Vehicle steering system. 3. A means for detecting a rotation angle of a steering wheel, a means for detecting a yaw rate, and a rate of change of the output per unit time (steering angular velocity and yaw angular acceleration).
2. The vehicle steering apparatus according to claim 1, further comprising control means for controlling the actuator based on a comparison value of: 4. A means for detecting a rotation angle of a steering wheel, and comparing a rate of change of the output per unit time (steering angular velocity) with a rate of change of the rate of change per unit time (steering angular acceleration). The vehicle steering apparatus according to claim 1, further comprising control means for controlling the actuator based on a value.