JPH05131945A - Rear wheel steering contol device for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To prevent deterioration of a running stability of a vehicle in a slalom run in a vehicle of which rear wheels are steered and controlled according to a lateral acceleration. CONSTITUTION:A front wheel steering angle sensor 51, a car speed sensor 52, a yaw rate sensor 53, and a lateral acceleration sensor 54 detect a front wheel steering angle deltaf, a car speed V, a yaw rate gamma, and a lateral acceleration Gy respectively. In steering front wheels, a microcomputer 57 controls a rear wheel steering mechanmsm B to steer the rear wheels at a desired rear wheel steering angle deltar*=K1 (V)deltaf+ K2(V)gamma+K3Gy. However, when a steering direction and a direction of the lateral acceleration Gy do not coincide with each other, the computer 57 steers the rear wheels at a desired rear wheel steering angle deltar*=K1(V)deltaf+K2(V)gamma. When the front wheel steering direction and the lateral acceleration direction do not coincide with each other by effects of rolling of a car body on the lateral acceleration Gy because of a slalom run, steering control to the rear wheels by the lateral acceleration is prohibited for preventing steering control to the rear wheels in an inverse direction.

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 control device for a four-wheel steering vehicle, which steers and controls rear wheels according to lateral acceleration of a vehicle body.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Unexamined Patent Publication No. 0-161258, the lateral acceleration of the vehicle body is detected by the lateral acceleration detecting means provided in the vehicle body, and the rear wheel is moved in the direction of action of the lateral acceleration, that is, the rear wheel in accordance with the detected lateral acceleration. Steering is done in-phase with the front wheels to improve the running stability of the vehicle.

[0003]

However, in the above-mentioned conventional apparatus, when the front wheels are alternately steered to the left or right due to slalom traveling or the like, when the steering of the front wheels is turned back, the influence of the roll of the vehicle body immediately before remains. Therefore, the lateral acceleration in the opposite direction to the lateral acceleration generated by steering the front wheels may be detected by the lateral acceleration detecting means. Therefore, there is a problem that the rear wheels are steered in an opposite phase with respect to the front wheels, which are opposite to the original control direction, and the running stability of the vehicle deteriorates. The present invention has been made to solve the above problem, and an object of the present invention is to provide a four-wheel steering vehicle that does not deteriorate the traveling stability of the vehicle even when the front wheels are alternately steered left and right due to slalom traveling. To provide a rear wheel steering control device.

[0004]

In order to achieve the above object, a structural feature of the present invention is a control device for electrically controlling a rear wheel steering mechanism for steering a rear wheel, which is a lateral control unit for a vehicle body. Rear-wheel steering control device for a four-wheel steering vehicle including lateral acceleration detection means for detecting acceleration, and steering control means for steering the rear wheels by controlling the rear-wheel steering mechanism according to the detected lateral acceleration. In the above, when the front wheel steering detection means for detecting the steering direction of the front wheels does not match the detected lateral acceleration direction with the detected steering direction of the front wheels, steering control of the rear wheels by the steering control means is prohibited. There is a prohibition means.

[0005]

In the present invention constructed as described above, the steering direction of the front wheels is detected by the front wheel steering detecting means, and the detected steering direction and the lateral acceleration of the vehicle body detected by the lateral acceleration detecting means. If the directions do not match, the steering control means prohibits the steering control of the rear wheels according to the detected lateral acceleration by the steering control means. As a result, if the lateral acceleration in the opposite direction to the lateral acceleration generated by the steering of the front wheels is detected by the lateral acceleration detecting means due to slalom traveling or the like, the rear wheels are steered in the opposite direction. Since the situation can be avoided and the deterioration of the traveling stability due to the steering of the rear wheels can be prevented, the traveling stability of the vehicle during slalom traveling becomes better than that of the conventional device.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before explaining specific embodiments of the present invention, theoretical support that steering control of rear wheels according to lateral acceleration of a vehicle body improves running stability of the vehicle and use for this steering control The basic theory regarding the control will be described in order to confirm the value of the proportional coefficient.

A. Basic Theory FIG. 4 shows a two-wheel model of a vehicle, and various variables and constants in the figure are as follows. V: Vehicular movement direction speed u: Vehicle traveling direction speed (u = Vcosβ = about V) v: Vehicle side slip velocity (v = Vsinβ = about Vβ) β: Vehicle side slip angle δf: Front wheel steering angle δr: Rear wheel steering angle a : Front wheel-center of gravity distance b: rear wheel-center of gravity distance L: wheel base (L = a + b) where M: vehicle weight I: vehicle yaw moment of inertia Cf: front wheel equivalent cornering power (for two wheels) Cr: rear Assuming the wheel equivalent cornering power (for two wheels), the equation of motion of the vehicle is expressed by the following mathematical expressions 1 and 2.

[0008]

[Equation 1]

[0009]

[Equation 2]

On the other hand, assuming that the rear wheels are steered according to the front wheel steering angle δf, the yaw rate γ and the lateral acceleration Gy, the rear wheel steering angle δr as a result of this control is expressed by the following expression 3.

[0011]

## EQU3 ## δr = K ₁ δf + K ₂ γ + K ₃ Gy Note that K ₁ , K ₂ and K ₃ in the above equation ₂ are coefficients. Further, the lateral acceleration Gy can be expressed by the following equation 4 by coordinate conversion of the rotating coordinate system.

[0012]

[Mathematical formula-see original document] Gy = dv / dt + u [gamma] Here, by substituting the above equation 4 into the above equation 3 and substituting the above equation 3 into the above equations 1 and 2, and rearranging, the system equation can be expressed as the following equation 5. ..

[0013]

## EQU00005 ## dX / dt = AX + B.delta.f However, X, A and B in the above equation 5 are defined as in the following equations 6-12.

[0014]

[Equation 6]

[0015]

[Equation 7]

[0016]

[Equation 8]

[0017]

[Equation 9]

[0018]

[Equation 10]

[0019]

[Equation 11]

[0020]

[Equation 12]

Here, when the characteristic equation is obtained by Laplace transforming the above equation 5, the following equation 13 is obtained.

[0022]

[Expression 13] | SI-A | = S ² + 2ξωS + ω ² = 0 However, 2ξω and ω ² in the above Expression 13 are the following Expressions 14 and 1
It can be represented by 5.

[0023]

[Equation 14]

[0024]

[Equation 15]

Note that these 2ξω and ω ² are indices representing the yawing damping coefficient and the yawing resonance frequency, respectively.

Consider a two-wheel steering vehicle in which the rear wheels are not steered.
Set. Each coefficient K mentioned above₁, K₂, K ₃Are both "0"
Therefore, the above 2ξω, ω in this case² 2 ξω₀, Ω₀ ²
Then, these 2ξ₀ω₀, Ω₀ ²Is the following number 16,17
Can be expressed as

[0027]

[Equation 16]

[0028]

[Equation 17]

Further, in the case of steering the rear wheels, the above 2ξ
ω, ω ² and the above 2ξ ₀ ω ₀ , ω ₀ ² when the rear wheels are not steered
And each difference Δ1 = 2ξω-2ξ ₀ ω ₀ , Δ2
= Ω ² −ω ₀ ² can be expressed as in the following Equations 18 and 19.

[0030]

[Equation 18]

[0031]

[Formula 19]

Note that (aCf-bC in the above equations 18 and 19)
r) is a term representing the steering characteristic of the vehicle, which is negative in the case of an ordinary vehicle. Therefore, the coefficient K ₃ is 0 <K ₃ <M /
If the relationship of Cr is satisfied, the relationships of Δ1> 0 and Δ2> 0 are always established, and the relationships of 2ξω> 2ξ ₀ ω ₀ and ω ² > ω ₀ ² are established. As a result, the coefficient K ₃ in the above relationship is set to the lateral acceleration Gy.
If the rear wheels are steered according to the term K ₃ Gy multiplied by, the yaw damping coefficient 2ξω of the vehicle and the yawing resonance frequency ω ² are both larger than when the rear wheels are not steered, so the running stability of the vehicle is improved. Can be understood to be good.

On the other hand, the lateral acceleration sensor is usually mounted on the vehicle body, and the output of the sensor includes a component due to the roll of the vehicle body. Therefore, when the vehicle runs in slalom, the steering wheel is turned back. The last roll component of the vehicle body remains, and the lateral acceleration in the direction opposite to the lateral acceleration Gy generated by steering the front wheels is detected. Therefore, if the lateral acceleration Gy detected by the lateral acceleration sensor is used as it is for the steering control of the rear wheels, the running stability of the vehicle may be deteriorated. Therefore, the detected lateral acceleration G
If the rear wheel steering control is performed using the coefficient K ₃ having the above relationship only when the lateral acceleration Gy detected by the lateral acceleration sensor and the steering direction of the front wheels match without using y as it is. As described above, the running stability of the vehicle is improved.

B. Specific Example Next, a specific example of the present invention will be described with reference to the drawings. FIG. 1 schematically shows an entire four-wheel steering vehicle according to the example. This four-wheel steering vehicle has left and right front wheels FW
1, a front wheel steering mechanism A for steering FW2, and left and right rear wheels RW
1, a rear wheel steering mechanism B that steers the RW2, and an electric control device C that electrically controls the rear wheel steering mechanism B.

The front wheel steering mechanism A has a steering handle 11. The steering handle 11 is fixed to the upper end of a steering shaft 12, and the lower end of the coaxial shaft 12 meshes with a rack bar 14 via a pinion 13. Left and right tie rods 15a and 15b and left and right knuckle arms 16 are provided at both ends of the rack bar 14.
The left and right front wheels FW1 and FW2 are steerably connected via a and 16b, and the bar 14 is provided with the left and right front wheels FW1 and FW2 in accordance with axial displacement due to rotation of the steering wheel 11.
Steer. A control valve 17 made up of a four-way valve is assembled in the middle of the steering shaft 12, and the valve 17 is provided with a hydraulic pump 18 according to the steering torque acting on the steering shaft 12.
The hydraulic oil is supplied to the oil chamber of the power cylinder 22 from one side through the flow dividing valve 21, and the hydraulic oil in the other oil chamber of the cylinder 22 is discharged to the reservoir 23. The power cylinder 22 assists the steering of the left and right front wheels FW1 and FW2 by driving the rack bar 14 in the axial direction according to the supply and discharge of the hydraulic oil.

The rear wheel steering mechanism B has a relay rod 31 for axially displacing the left and right rear wheels RW1 and RW2, similarly to the rack bar 14 described above. Similar to the case of the front wheel steering mechanism A, the left and right tie rods 32a, 32b and the left and right knuckle arms 33a, 3 are provided on both ends of the relay rod 31, respectively.
The left and right rear wheels RW1, RW2 are steerably connected via 3b. The relay rod 31 is axially displaceably supported by a housing 34 supported by the vehicle body, and a power cylinder 35 is formed in the housing 34. The power cylinder 35 drives the relay rod 31 in the axial direction according to the supply and discharge of hydraulic oil.
Is divided into left and right oil chambers 35b and 35c by a piston 35a fixed to the relay rod 31. A spring 36 for neutral biasing is attached to the side of the power cylinder 35 on the outer periphery of the relay rod 31 with a preload applied.

A spool valve 37, which constitutes a hydraulic pressure copying mechanism together with the power cylinder 35, is incorporated in the housing 34. The spool valve 37 is a valve sleeve 37a fixed in the housing 34.
And a valve spool 37b installed in the sleeve 37a so as to be liquid-tight and slidable in the axial direction. The hydraulic oil supplied via the hydraulic cylinder is supplied to the right oil chamber 35c of the power cylinder 35, and the hydraulic oil in the left oil chamber 35b of the cylinder 35 is discharged to the reservoir 23. Further, when the valve spool 37b is displaced leftward in the drawing, the spool valve 37 transfers the hydraulic oil from the hydraulic pump 18 via the flow dividing valve 21 to the power cylinder 3.
5 to the left oil chamber 35b of the cylinder 35
The hydraulic oil in the right oil chamber 35c is discharged to the reservoir 23.

A through hole 37c is provided at the right end of the valve spool 37b, and the lever 4 is inserted in the through hole 37c.
1 is penetrated. A spherical nodular ridge is provided in the middle of the lever 41, and the lever 41 is slidably and slidably engaged with the inner peripheral surface of the through hole 37c at the outer peripheral surface of the nodal ridge. .. The lower end of the lever 41 is fitted in an annular groove 31 a provided on the outer circumference of the relay rod 31 so as to be rotatable and slidable in the vertical direction, and the upper end of the lever 41 is eccentric to the rotary plate 42. Is rotatably connected to the fixed pin 43. The rotating plate 42 is meshed with the worm 44 on the outer periphery thereof, and the worm 44 is connected to the rotating shaft of the step motor 45 and is connected to the motor 4
It rotates together with 5. In this case, when the step motor 45 rotates in the positive (or negative) direction, the pin 43 is displaced rightward (or leftward).

The electric control unit C includes a front wheel steering angle sensor 5
1, a vehicle speed sensor 52, a yaw rate sensor 53, a lateral acceleration sensor 54, and a rear wheel steering angle sensor 55. The front wheel steering angle sensor 51 detects the front wheel steering angle δf by measuring the rotation angle of the steering shaft 12, and outputs a detection signal indicating the same steering angle δf. The vehicle speed sensor 52 is a transmission 56.
The vehicle speed V is detected by measuring the rotation speed of the output shaft of, and a detection signal indicating the vehicle speed V is output. The yaw rate sensor 53 is mounted on the vehicle body and detects a rotational angular velocity around the vertical axis of the vehicle body, that is, a yaw rate γ, and outputs a detection signal representing the yaw rate γ. Lateral acceleration sensor 54
Is attached to the vehicle body, detects the lateral acceleration Gy of the vehicle body, and outputs a detection signal representing the lateral acceleration Gy. The rear wheel steering angle sensor 55 detects the rear wheel steering angle δr by measuring the rotation angle of the rotation shaft of the step motor 45,
The detection signal indicating the rear wheel steering angle δr is output. The front wheel steering angle δf, the yaw rate γ, the lateral acceleration Gy, and the rear wheel steering angle δr are positive in the right direction and negative in the left direction.

Each of these sensors 51 to 55 is connected to a microcomputer 57, and the computer 57.
Consists of ROM, CPU, RAM, timer and I / O (input / output interface). A program corresponding to the flowchart of FIG. 2 is stored in the ROM of the microcomputer 57, and as shown in FIGS. 3A and 3B, a coefficient K ₁ (V), which changes according to the vehicle speed V, K
₂ (V) is stored in the form of a table. The microcomputer 57 is connected to the step motor 45 and outputs a rotation control signal by executing the program to control the rotation of the motor 45.

Next, the operation of the embodiment configured as described above will be described. When the ignition switch (not shown) is closed, the microcomputer 57 starts executing the program in step 100 of FIG.
After setting the flag FLG to "0" at 01, step 1
A circulation process consisting of 02 to 114 is executed. In this circulation process, at step 102, the sensors 51 to 55 are
The detection signals representing the front wheel steering angle δf, the vehicle speed V, the yaw rate γ, the lateral acceleration Gy, and the rear wheel steering angle δr are read from, and RO is calculated based on the vehicle speed V in step 103.
The tables in M are referenced to determine the coefficients K ₁ (V) and K ₂ (V).

Next, at step 104, the absolute value | δf | of the front wheel steering angle δf read in is a predetermined value T
It is determined whether or not f0 or more, and in step 105, the front wheel steering speed dδf / d is calculated by differentiating the front wheel steering angle δf.
In addition to calculating t, the calculated front wheel steering speed dδf / d
It is determined whether or not the absolute value | dδf / dt | of t is greater than or equal to a predetermined value and Df0. In step 106, the product δfGy of the front wheel steering angle δf and the read lateral acceleration Gy is calculated. At the same time, it is determined whether the calculated product δfGy is positive. In this case, if it is determined to be "NO" in any of the steps 104 to 106, the program proceeds to step 107.

In step 107, it is determined whether the flag FLG is "1". In this case, the flag FLG is
Since FLG is set to "0" as described above, it is determined to be "NO" in the same step 107, and step 108 is executed.
In the following equation 2 based on the read front wheel steering angle δf, yaw rate γ and the determined coefficients K ₁ (V) and K ₂ (V)
By executing the calculation of 0, the target rear wheel steering angle δr * is calculated.

[0044]

## EQU20 ## δr * = K ₁ (V) δf + K ₂ (V) γ After calculating the target rear wheel steering angle δr *, in step 109, the target rear wheel steering angle δr * is processed by the process of step 102. The steering amount δr * −δr to be steered by the left and right rear wheels RW1 and RW2 is calculated by subtracting the read current rear wheel steering angle δr, and this steering amount δr * −δr
The rotation control signal corresponding to is output to the step motor 45.

As a result, the step motor 45 rotates corresponding to the steering amount δr * -δr, so that the same rotation is transmitted to the lever 41 via the worm 44, the rotary plate 42 and the pin 43, and the lever 41 moves. The valve spool 37b is swung left and right with the lower end as a fulcrum to displace the valve spool 37b left and right by an amount corresponding to the steering amount δr * −δr. In this case, if the valve spool 37b is displaced rightward (or leftward), hydraulic oil is supplied from the hydraulic pump 18 to the right oil chamber 35c (or left oil chamber 35b) of the power cylinder 35 via the flow dividing valve 21. And the cylinder 3
The hydraulic oil in the left oil chamber 35b (or the right oil chamber 35c) of No. 5 is discharged to the reservoir 23, the relay rod 31 is displaced leftward (or rightward), and the left and right rear wheels RW1, RW2 are moved rightward (or rightward). Steer to the left). On the other hand, when the relay rod 31 is displaced leftward (or rightward), the lower end of the lever 41 is displaced leftward (or rightward) about the upper end of the lever 41, and the valve spool 37b is leftward (or rightward). Displace to the right). Then, when the valve spool 37b returns to the reference position, that is, when the relative displacement between the valve spool 37b and the valve sleeve 37a disappears, the supply and discharge of the hydraulic oil is stopped, and the displacement of the relay rod 31 to the left is also stopped. Since the vehicle is stopped, the left and right rear wheels RW1 and RW2 are the rear wheel steering amount δr * − from the past state.
The steering angle δ is steered to the right by an amount corresponding to δr.
r becomes equal to the target rear wheel steering angle δr *.

After the processing of step 109, the program is returned to step 102, and the circulation processing of steps 102 to 109 is repeatedly executed, so that the left and right rear wheels RW1, RW.
2 is controlled to the target rear wheel steering angle δr *. in this case,
The target rear wheel steering angle δr * is defined by the above equation 20, and the coefficient K ₁ of the front wheel steering angle δf is a negative value at medium speed, as shown in FIG. The initial turning property at the time of turning of the vehicle running at high speed is improved. Further, as shown in FIG. 3 (B), the coefficient K _{2 of the} yaw rate γ is a positive value at medium and high speeds, so that the yaw rate of the vehicle during medium and high speed traveling is suppressed, and the running stability of the vehicle is good. Become.

On the other hand, while the vehicle is traveling, the left and right front wheels FW1, FW
When 2 is steered to the left or right to some extent at a certain speed, the absolute value | δf | of the front wheel steering angle δf and the absolute value | dδf / dt | of the front wheel steering speed dδf / dt increase, and in steps 104 and 105, Both are determined to be “YES” and the program proceeds to step 106. In this case, the lateral acceleration Gy detected by the lateral acceleration sensor 54 is not affected by the roll of the vehicle body and the left and right front wheels FW are
If the steering directions of 1 and FW2 and the direction of the lateral acceleration Gy are coincident with each other, "YES" in step 106, that is, the product δfGy of the front wheel steering angle δf and the lateral acceleration Gy is determined to be positive, and step 110 is executed. The flag FLG is set to "1" and the count value of the timer in the microcomputer 57 is cleared to "0" at step 111. Next, at step 112, the following numbers based on the read front wheel steering angle δf, yaw rate γ, lateral acceleration Gy, the determined coefficients K ₁ (V), K ₂ (V) and the predetermined coefficient K _3. By executing the calculation of 21, a target rear wheel steering angle δr * different from the above is calculated.

[0048]

## EQU21 ## δr * = K ₁ (V) δf + K ₂ (V) γ + K ₃ Gy If the vehicle weight is M and the rear wheel equivalent cornering power (for two wheels) is Cr, the coefficient K ₃ is 0 <K
₃ <M / Cr.

After the calculation of the target rear wheel steering angle δr *, the left and right rear wheels RW1 and RW are processed by the processing of step 109 described above.
2 is steered to the target rear wheel steering angle δr *. Step 109
After the above processing, the program is returned to step 102 again, the absolute value | δf | of the front wheel steering angle δf is equal to or greater than the predetermined value Tf0, and the absolute value | dδf / dt | of the front wheel steering speed dδf / dt |
Is a predetermined value Df0 or more and the product δfGy of the front wheel steering angle δf and the lateral acceleration Gy is positive, steps 102 to 1
The circulation process consisting of 06, 110 to 112, 109 is continuously executed, and the left and right rear wheels RW1 and RW2 are steered to the target rear wheel steering angle δr * expressed by the equation 21. on the other hand,
If any one of the above three conditions is not satisfied during this circulation processing, it is determined to be "NO" in any of steps 104 to 106, and the program proceeds to step 107.

In this case, the flag FLG is set in step 11 above.
Since it is set to "1" by the processing of 0, it is determined "YES" in step 107, and it is determined in step 113 whether or not the cleared timer is counting up. The count-up time is 0.
It is set to about 5 seconds. If the timer is not counted up, it is determined to be "NO" in step 113, so steps 102, 103, 104 (10
5, 106), 107, 113, 112, 109 continues to be executed, and the left and right rear wheels RW1, RW2
Is steered to the target rear wheel steering angle δr * expressed by the above equation (21). Then, when the timer counts up, it is determined to be "YES" in step 113, the flag FLG is set to "0" in step 114, and step 1
By the processing of 08 and 109, the left and right rear wheels RW1 and RW2 are calculated again without taking the lateral acceleration Gy into consideration,
The target rear wheel steering angle δr * represented by 0 is steered.

Thus, in this embodiment, the left and right front wheels F
In a state where the steering directions of W1 and FW2 and the direction of the lateral acceleration Gy are the same and the lateral acceleration Gy detected by the lateral acceleration sensor 54 is not affected by the roll of the vehicle body,
When the left and right front wheels FW1 and FW2 are steered to some extent quickly and largely, the left and right rear wheels RW1 and RW2 have
The target rear wheel steering angle δr * in consideration of the lateral acceleration Gy is steered for at least a predetermined time (about 0.5 seconds). As a result, as described in the basic theory, both the yawing damping coefficient 2ξω and the yawing resonance frequency ω ² become large, and the running stability during steering of the vehicle becomes good.

On the other hand, while the vehicle is traveling, the left and right front wheels FW1, FW
If the product δfGy of the front wheel steering angle δf and the lateral acceleration Gy is not positive even if 2 is steered to a certain extent quickly and largely, it is determined to be “NO” in step 106 and the program proceeds to steps 107 and 108. .. As a result, in this case, the left and right rear wheels RW1 and RW2 are steered to the target rear wheel steering angle δr * of the equation 20 calculated without considering the lateral acceleration Gy. As a result, since the vehicle is running in slalom, the lateral acceleration Gy detected by the lateral acceleration sensor 54 is influenced by the roll of the vehicle body,
If the steering directions of the left and right front wheels FW1 and FW2 and the direction of the lateral acceleration Gy do not match, the control by the wrong lateral acceleration Gy can be avoided, and the running stability of the vehicle deteriorates due to the control by the lateral acceleration Gy. There is nothing to do.

In the above embodiment, the above equation 21
Although a constant is used as the coefficient K ₃ of the lateral acceleration Gy, the vehicle speed V is set as the coefficient K ₃ as shown in FIG.
The value K ₃ (V) that is “0” when is small and increases as the vehicle speed V becomes larger than a predetermined value may be used. Also in this case, K ₃ (V) is a value larger than “0” and smaller than M / Cr. As a result, the left and right rear wheels RW1 and RW2 are controlled according to the lateral acceleration Gy only during medium- and high-speed traveling, and the traveling stability of the vehicle during the same traveling is emphasized. In the above embodiment, the front wheels are steered and the product of the front wheel steering angle δf and the lateral acceleration Gy δfGy.
Is positive, the left and right rear wheels RW1, R based on the above equation 20
From the steering control of W2, the rear wheels RW1,
When the control is switched to the steering control of the RW2 and the timer counts up in this state, the steering control of the left and right rear wheels RW1 and RW2 based on the above formula 21 to the steering control of the rear wheels RW1 and RW2 based on the above formula 20. I was able to switch to. However, in this case, the target rear wheel steering angle δr * may suddenly change and the left and right rear wheels RW1 and RW2 may be steered steeply at this switching time, which may deteriorate the running stability of the vehicle for a moment. To prevent the deterioration of sex,
By gradually changing the target rear wheel steering angle Δr * at the time of this switching, it is possible to avoid the momentary deterioration of the running stability. In this case, the target rear wheel steering angle δr *
The processing (low-pass filter function processing) for alleviating the change of 1 may be added to the above program.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a four-wheel steering vehicle showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a program executed by the microcomputer of FIG.

3A to 3C are graphs of change characteristics of coefficients K ₁ (V) to K ₃ (V).

FIG. 4 is a schematic diagram showing a two-wheel model of a vehicle.

[Explanation of symbols]

A ... Front wheel steering mechanism, B ... Rear wheel steering mechanism, C ... Electric control device, FW1, FW2 ... Front wheels, RW1, RW2 ... Rear wheels, 3
5 ... Power cylinder, 37 ... Spool valve, 45 ... Step motor, 51 ... Front wheel steering angle sensor, 52 ... Vehicle speed sensor, 53 ... Yaw rate sensor, 54 ... Lateral acceleration sensor, 55 ... Rear wheel steering angle sensor, 57 ... Microcomputer ..

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

Claims (1)

[Claims] 1. A control device for electrically controlling a rear wheel steering mechanism for steering a rear wheel, comprising: lateral acceleration detecting means for detecting a lateral acceleration of a vehicle body; and the rear acceleration according to the detected lateral acceleration. A rear wheel steering control device for a four-wheel steering vehicle, comprising: a steering control means for controlling a wheel steering mechanism to steer the rear wheels; a front wheel steering detection means for detecting a steering direction of a front wheel; and the detected lateral acceleration. And a detected steering direction of the front wheels do not coincide with each other, a rear wheel steering control device for a four-wheel steering vehicle is provided, which prohibits the steering control of the rear wheels by the steering control means. ..