JPH0657536B2 - Front and rear wheel steering vehicle rear wheel steering control device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering control device for a front and rear wheel steering vehicle, and more particularly, to a rear wheel steering angle rear wheel steering angle control method for controlling a ratio of a rear wheel steering angle to a front wheel steering angle (steering ratio) according to a vehicle speed. The present invention relates to improvement of a steering control device.

[Prior art]

Conventionally, a rear wheel steering control device for a front and rear wheel steering vehicle is disclosed in, for example, JP-A-55-91457 and JP-A-57-7077.
As disclosed in Japanese Patent No. 4 publication, when a vehicle travels at a speed lower than a predetermined vehicle speed value with a predetermined vehicle speed value as a boundary, the steering ratio of the rear wheel steering angle is opposite to the front wheel steering angle. Set to the value,
Further, it has been proposed that when the vehicle is traveling at a speed higher than a predetermined vehicle speed value, the steering ratio is set to a value such that the rear wheel steering angle is in phase with the front wheel steering angle. According to this rear wheel steering control device, it is possible to reduce the turning radius of the vehicle when traveling at low speed, and it is possible to improve the small turning performance of the vehicle. In addition, when the vehicle travels at medium and high speeds, the turning radius of the vehicle can be increased and the vehicle can be quickly and easily engaged.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional device, the rear wheels are set to the reverse-phase side steering ratio in which the rear wheels are out of phase with the front wheels at low speed, so that the driving vehicle uses a power slide or the like for turning,
There is a problem that the reverse steering wheel operation (counter steering) performed when controlling the vehicle attitude cannot be easily performed. That is, as shown in FIG. 2 (A), when the vehicle body yaw rate φd is generated and the vehicle is about to be in the winding state (spin), the front wheel 1A is steered in the direction opposite to the yaw rate rotation direction. As a result, the slip angle θf of the tire of the front wheel 1A becomes smaller, which makes it easier for the tire to grip, so that the spin of the vehicle can be stopped.
When the reverse steering wheel is operated, as shown in FIG. 2 (A), when the rear wheels 2A are reverse-phase steered in the opposite direction to the front wheels 1A, the tire slip angle θr of the rear wheels 2A increases. The increase in the slip angle θr of the tire of the rear wheel 2A makes it difficult for the vehicle to stop spinning. Therefore, there is a problem that it becomes difficult to control the vehicle attitude. The arrow 3A in FIG. 2 indicates the tire traveling direction.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a rear-wheel steering control device for a front-rear wheel steering vehicle that can easily perform a reverse steering wheel operation during vehicle slip. .

[Means for solving problems]

The present invention sets the steering ratio of the rear wheels to the front wheels to the reverse phase side at low speed,
In the rear-wheel steering control device for a front-rear wheel steering vehicle that is controlled to the in-phase side at high speed, as shown in FIG.
A vehicle speed detecting means 1 for detecting a vehicle speed, a steering ratio determining means 2 for determining the steering ratio according to the detected vehicle speed, and a reverse steering wheel operation detecting means 3 for detecting a reverse steering wheel operation of a driver.
And a steering ratio changing means 4 for changing the determined steering ratio to zero or the in-phase side when the reverse steering wheel operation detecting means 3 detects the reverse steering wheel operation by the driver, and a control corresponding to the determined steering ratio. By providing the output means 5 for outputting a signal and the rear wheel steering mechanism B for steering the rear wheels by setting the rear wheel steering angle based on the determined steering ratio in response to the control signal, Has been achieved. Further, in the embodiment of the present invention, the reverse steering wheel operation detecting means has a vehicle body slip angle obtained from a vehicle lateral speed and a vehicle speed, and the positive and negative signs of the steering angle are opposite to each other, and the vehicle body slip angle and the front wheel are opposite. When the sum of the absolute values of the steering angle and the steering angle is equal to or greater than a predetermined value, it is configured to detect that the steering wheel is operated in reverse. In another embodiment of the present invention, when detecting the vehicle lateral speed, the vehicle lateral speed is detected from the lateral speeds of the vehicle front portion and the vehicle rear portion. Further, in another embodiment of the present invention, the reverse handle operation detecting means is configured such that the positive and negative signs of the vehicle body yaw rate and the front wheel steering angle are opposite to each other, and the absolute values of the yaw angle and the front wheel steering angle based on these vehicle body yaw rates are set. When the sum of the above is greater than or equal to a predetermined value, it is configured to be detected as a reverse steering wheel operation. According to another embodiment of the present invention, the reverse handle operation detecting means has a vehicle body slip angle obtained from a vehicle lateral speed and a vehicle speed, and the positive and negative signs of the front wheel steering angle are opposite to each other, and the vehicle body slip angle. And the absolute value of the front wheel steering angle is equal to or greater than a predetermined value, and the positive and negative signs of the vehicle body yaw rate and the front wheel steering angle are opposite, and the absolute value of the yaw angle and the front wheel steering angle based on these vehicle body yaw rates When the sum of the above is greater than or equal to a predetermined value, it is configured to be detected as a reverse steering wheel operation.

[Action]

In the present invention, in the rear wheel steering control device for a front and rear wheel steering vehicle, which controls the steering ratio of the rear wheels to the front wheels to the low-speed side inversion side and the high-speed side in-phase side, the reverse steering wheel operation of the driver is detected. However, when this reverse steering wheel operation is detected, the steering ratio of the rear wheels is changed to zero or the in-phase side. Therefore, when the steering ratio of the rear wheels is set to zero at the time of operating the reverse steering wheel, the reverse steering wheel operation can be performed similarly to the conventional front two-wheel steering vehicle without impairing the turning performance during normal traveling. Therefore, it becomes possible to easily control the posture of the vehicle by using a power slide or the like for turning. Further, by changing the steering ratio of the rear wheels to the in-phase side when the reverse steering wheel is operated, as shown in FIG. 2 (B), the slip of the tires of the rear wheels 2A is maintained without impairing the turning performance during normal running. The angle θr can be made smaller than that of the conventional front two-wheel steering vehicle. As a result, the gripping force of the tires of the rear wheels 2A can be recovered much faster than that of the front two-wheel steering vehicle, the spin of the vehicle is stopped, and the power slide or the like is used to turn the vehicle. The posture can be easily controlled. Further, when detecting the vehicle lateral speed, if the vehicle lateral speed is detected from the lateral speeds of the vehicle front portion and the vehicle rear portion, the vehicle lateral speed can be accurately obtained. Further, the reverse steering wheel operation detecting means has the positive and negative signs of the front wheel steering angle and the vehicle body slip angle obtained from the vehicle lateral speed and the vehicle speed, and the sum of the absolute values of the vehicle body slip angle and the front wheel steering angle. When is configured to detect a reverse steering wheel operation when is equal to or greater than a predetermined value, the reverse steering wheel operation can be accurately detected. The reverse handle operation detection means reverses when the positive and negative signs of the vehicle body yaw rate and the front wheel steering angle are opposite and the sum of the absolute values of the yaw angle based on the vehicle body yaw rate and the front wheel steering angle is a predetermined value or more. If the steering wheel operation is detected, the reverse steering wheel operation can be easily and easily detected. Further, the reverse steering wheel operation detecting means has the positive and negative signs of the front wheel steering angle and the vehicle body slip angle obtained from the vehicle lateral speed and the vehicle speed, and the absolute values of these vehicle body slip angle and front wheel steering angle are opposite. When the sum is equal to or greater than a predetermined value, or when the positive and negative signs of the vehicle body yaw rate and the front wheel steering angle are opposite, and the sum of the absolute values of the yaw angle and the front wheel steering angle based on these vehicle body yaw rates is the predetermined value or more. In the case where the reverse steering wheel operation is detected, the reverse steering wheel operation can be detected with higher accuracy.

【Example】

Hereinafter, an embodiment of a rear wheel steering control device according to the present invention will be described in detail with reference to the drawings. FIG. 3 shows a front wheel steering mechanism A, a rear wheel steering mechanism B, and an electric control device C for the rear wheel steering mechanism B of a vehicle to which the present invention is applied. The front wheel steering mechanism A includes a pinion and rack mechanism 11,
The mechanism 11 includes a pair of left and right relay rods 12a and 12b connected to the rack portion. The pinion and rack mechanism 11 is connected to a steering handle 14 via a steering shaft 13 at its pinion portion, and converts the rotational movement of the steering handle 14 into the reciprocating movement of the relay rods 12a, 12b. The left and right relay rods 12a, 1
The left and right relay rods 12a and 12b are connected to the left and right front wheels 16a and 16b via left and right tie rods and left and right knuckle arms 15a and 15b (not shown).
The left and right front wheels 16a, 16b are steered by b. The rear wheel steering device B includes a hydraulic pump 20 driven by an engine, and oil discharged from the hydraulic pump 20 is supplied to the servo valve 2.
1 and a hydraulic cylinder 23 for steering both rear wheels 22a and 22b. The hydraulic pump 20 is connected at its inflow port to the reservoir 24 via the conduit P _1, and at its discharge port to the servo valve 21 via the conduit P ₂ . The servo valve 21 has the hydraulic cylinder 2 in its neutral position.
3, the conduit P ₃ connected to the right chamber 23b of the hydraulic cylinder 23 is closed, and the conduit P ₄ connected to the left chamber 23a of the hydraulic cylinder 23 is closed. Also, when the servo valve 21 is switched to the first position,
Conduit P ₂ is connected to conduit P ₃ and conduit P ₄ is connected to conduit P ₅
It is connected to the reservoir 24 via. Also, when switched to the second position, connect conduit P ₂ to conduit P ₄ ,
And the conduit P ₃ is connected to the reservoir 24 via the conduit P ₅ . The switching operation of the servo valve 21 is effected by the operation of the torque motor 21a provided in the servo valve 21, and the operation of the torque motor 21a is effected by the control signal given from the electric control device C. Be done. The hydraulic cylinder 23 has a piston 25 housed inside.
And a pair of left and right piston rods 26a and 26b are connected to each other. The left piston rod 26a is connected to the rear wheel 22a via a tie rod 27a and a knuckle arm 28a.
Are linked to. Also, the piston rod 26b on the right side
Is connected to the rear wheel 22b via a tie rod 27b and a knuckle arm 28b. The electric control unit C is attached to a vehicle speed sensor 30 for picking up the rotation of a vehicle speed detecting gear 16c provided on the right front wheel and generating a pick up signal having a frequency corresponding to the vehicle speed, and a central portion in the front width direction of the vehicle. , A front lateral speed sensor 31 for detecting the lateral lateral accuracy of the vehicle, a rear lateral speed sensor 32 for detecting the lateral lateral accuracy of the vehicle, and a rear lateral speed sensor 32 for detecting the lateral lateral accuracy of the vehicle. A yaw rate sensor 33 which is composed of a gyrometer and detects the yaw rate of the vehicle, and a front wheel steering angle of the front wheels 16a and 16b attached to the steering shaft 13 is detected to generate an analog signal indicating a voltage value corresponding to the front wheel steering angle. The front wheel steering angle sensor 34 and the actual steering angle that is the target rear wheel steering angle are measured to perform steering angle feedback control to the target steering angle. The wheel steering angle sensor 35, a micro computer 38 that outputs target steering control signals for the rear wheels by executing a program described below based on the signals provided from the sensors 30 to 34, and the micro computer 38. A comparator 4 that outputs a difference signal between a control signal and an actual steering angle signal from the rear wheel steering angle sensor 35.
0 and a servo amplifier 41 that amplifies an output signal from the comparator 40 and drives the servo valve 21. The microcomputer 38 constitutes the steering ratio determining means 2, the reverse steering wheel operation detecting means, and the steering ratio changing means 4 shown in FIG. 1, and the program corresponding to the flow chart shown in FIG. A read-only memory (ROM) 38a for storing parameters for calculating the steering ratio pattern (see FIG. 6), a central processing unit (CPU) 38b for executing this program, and variables and flags necessary for this program are stored. A writable memory (RAM) 38c for temporarily storing the vehicle speed sensor 3
0 through a waveform shaper (not shown),
The lateral speed sensors 31, 32, the yaw rate sensor 38, the front wheel steering angle sensor 34, and the rear wheel steering angle sensor 35 are connected to each other via an analog-digital converter (A / D converter) or the like (not shown), and to the comparator 40. Input / output interface circuit (I / O) 38d connected via a digital-analog converter (D / A converter) (not shown), and these ROMs
38a, CPU 38b, RAM 38c, and I / O 38d are connected in common to each other by a bus 38e. The operation of the vehicle rear wheel steering control device configured as described above will be described with reference to the flow chart of FIG. When an ignition switch (not shown) is closed to start the vehicle, the CPU 38b causes the step 100
At step 102, the front lateral speed VLf is read by the front lateral speed sensor 31 at the front of the vehicle. Next, in step 104, the rear lateral speed sensor 32 detects the rear lateral speed VLr.
Read in. Next, in step 106, the front lateral speed VLf obtained in step 102 and the step 104
Based on the rear lateral speed VLr obtained in
After multiplying f and VLr by the gravity center lateral velocity coefficients Cf and Cr respectively, the gravity center lateral velocity VLa which is the lateral velocity at the vehicle center of gravity position is calculated. That is, the lateral velocity of center of gravity VLa is calculated from the relationship of the following equation. VLa = Cf.VLf + Cr.VLr (1) Next, in step 108, the vehicle speed V is read by the vehicle speed sensor 30. Next, in step 110, the lateral velocity of center of gravity VLa obtained in step 106 and the step 1
Based on the vehicle speed V detected at 08, the vehicle body slip angle θs is calculated from the following equation. θs = tan (VLa / V) (2) Next, the process proceeds to step 112 where the front wheel steering angle θf is read from the front wheel steering angle sensor 34. Note that the vehicle body slip angle θs calculated in the preceding step 110, the front wheel steering angle θf detected in the preceding step 112,
The vehicle body yaw rate φd, which will be described later, will be handled and described as positive when rotating counterclockwise with respect to the vehicle longitudinal centerline and negative when rotating clockwise as shown in FIG. Next, the routine proceeds to step 114, where it is judged if the vehicle body slip angle θs obtained at the preceding step 110 is larger than zero. If it is determined to be positive in step 114, that is, if the sign of the vehicle body slip angle θs is determined to be positive, the process proceeds to step 116. In step 116, it is judged whether or not the front wheel steering angle θf obtained in the preceding step 112 is smaller than zero. If it is determined to be positive in step 116, that is, if the sign of the front wheel steering angle θf is determined to be negative, the process proceeds to step 118. In step 118, the sum of the absolute values of the vehicle body slip angle θs and the front wheel steering angle θf is calculated as the reverse steering wheel determination value θh. That is, the vehicle body slip angle θ with a positive sign
The reverse steering wheel determination value θh is calculated by subtracting the negative front wheel steering angle θf from s. Next, in step 120, it is determined whether or not the reverse steering wheel determination value θh obtained in the previous step 118 is larger than the limit value θhc for determining that the steering wheel is in reverse steering wheel operation. In this step 120, if it is determined to be positive, that is, if the reverse handle determination value θh is larger than the limit value θhc, it is determined that the reverse handle is in the operating state, and the process proceeds to step 122. In step 122, the target steering ratio Rc is calculated from the vehicle speed V detected in the preceding step 108 based on the map data of the second steering ratio pattern suitable for the reverse steering wheel operation shown by the broken line A in FIG. Next, in step 124, the time .DELTA.t for allowing the set steering ratio Rn to have the time constant .tau. Is reset. Next, in step 126, in order to smoothly switch the target steering ratio Rc obtained in the previous step 122, a time constant τ between the previous set steering ratio R _n-1 and the target steering ratio Rc is set. The calculation for responding to is performed according to the following equation. _{Rn = R n-1 + (} R c + R n-1) (1-e -Δt / τ) ...
(3) Next, in step 128, the rear wheel steering angle θr is calculated by multiplying the set steering ratio Rn obtained in the front step 126 and the front wheel steering angle θf. Next, in step 130, the control signal corresponding to the rear wheel steering angle θr calculated in the preceding step 128 is sent to the comparator 4.
The output is output to 0 and the rear wheels are steered via the servo amplifier 41. Then, the process returns to the above step 102. If the result of the determination at step 114 is negative,
That is, when it is determined that the sign of the vehicle body slip angle θs is negative, the process proceeds to step 140. At step 140, it is stabilized whether the front wheel steering angle θf is greater than zero. If it is determined to be positive in step 140, that is, if the sign of the front wheel steering angle θf is determined to be positive, the process proceeds to step 142. In step 142, the sum of the absolute values of the front wheel steering angle θf and the vehicle body slip angle θs is calculated as the reverse steering wheel determination value θh. next,
Go to step 120 above. On the other hand, if the above-mentioned steps 116, 120 and 140 are determined to be no, the process proceeds to step 150. In step 150, the yaw rate sensor 33 reads the vehicle body yaw rate φd. Next, step 152
Then, it is determined whether or not the vehicle body yaw rate φd detected in the above-mentioned step 150 is larger than zero. If it is determined to be positive in step 152, that is, if the sign of the vehicle body yaw rate φd is determined to be positive, the process proceeds to step 154. At step 154, it is judged if the front wheel steering angle θf is smaller than zero. If it is determined to be positive in step 154, that is, if the sign of the front wheel steering angle θf is negative, the process proceeds to step 156. In step 156, the sum of the value obtained by multiplying the vehicle body yaw rate φd by the coefficient Cφ and the absolute value of the front wheel steering angle θf is calculated as the reverse steering wheel determination value θhφ. That is, the value φd obtained by multiplying the vehicle body yaw rate φd having a positive sign by the coefficient Cφ.
The reverse steering wheel determination value θh φ is calculated by subtracting the negative front wheel steering angle θf from Cφ. That is, the reverse handle determination value θh φ is calculated from the relationship of the following equation. θh φ = Cφ · φd −θf (4) Next, in step 158, is the reverse steering wheel determination value θh φ obtained in the preceding step 156 greater than the limit value θhc for determining that the steering wheel is in the reverse steering wheel operating state? It is determined whether or not. When it is determined to be positive in this step 158, that is, when the reverse handle determination value θh φ is larger than the limit value θhc, it is determined that the operation is the reverse steering wheel operation, and the process proceeds to the above step 122. If the result of the determination at step 152 is negative,
That is, if it is determined that the sign of the vehicle body yaw rate φd is negative or zero, the process proceeds to step 160. In step 160, it is determined whether the front wheel steering angle θf is greater than zero. When it is determined to be positive in step 160, that is, when the sign of the front wheel steering angle θf is determined to be positive, the process proceeds to step 162. In step 162, the sum of the absolute values of the value obtained by multiplying the vehicle body yaw rate φd by the coefficient Cφ and the front wheel steering angle θf is calculated as the reverse steering wheel determination value θhφ. That is, the reverse handle determination value θh φ is calculated by the relationship of the following equation. θh φ = θf −Cφ · φd (5) Next, the process proceeds to the above step 158. On the other hand, if the above-mentioned steps 154, 158 and 160 are determined to be no, that is, if it is determined that the steering wheel is not the reverse steering wheel operation, the process proceeds to step 170.
At 70, based on the data map of the first steering ratio pattern suitable for normal traveling shown by the solid line B in FIG.
The target steering ratio Rc is calculated from the vehicle speed V detected in step 108. Next, the process proceeds to the above step 124. As can be understood from the above description of the operation, according to the present embodiment, the lateral speeds VLf and VLr of the front and rear parts are detected from the lateral speed sensors 31 and 32 of the front and rear parts, and the lateral speed at the position of the center of gravity of the vehicle is detected based on these. VLa is calculated and the lateral velocity V of this center of gravity is calculated.
The vehicle body slip angle θs is calculated based on La and the vehicle speed V,
Based on the vehicle body slip angle θs and the front wheel steering angle θf, the reverse steering wheel operation of the driver is determined, and at the time of the reverse steering wheel operation, based on the second steering angle ratio pattern (see the broken line A) shown in FIG. The target steering ratio Rc is calculated. Therefore, when the reverse steering wheel is operated, the rear wheels are set to the in-phase side steering ratio R ₁ . As a result, the second
As shown in FIG. (B), the rear wheels 2A are steered in-phase and the tire slip angle θr is reduced, so that the vehicle spin can be easily stopped and the vehicle attitude can be easily controlled. You can Further, the yaw rate φd of the vehicle body is detected, the reverse steering wheel operation is detected based on the vehicle body yaw rate φd and the front wheel steering angle θf, and the rear wheels are steered to the same phase side when the reverse steering wheel is operated. . Therefore, the slip angle θr of the rear wheel tires is reduced as described above, so that the spin of the vehicle can be easily stopped. FIG. 7 is a diagram showing the relationship among the front wheel steering angle θf, the vehicle body slip angle θs, and the set steering ratio Rn on the same time axis when the reverse steering wheel operation is performed. As is apparent from FIG. 8, the front wheel steering angle θf and the vehicle body slip angle θs have different signs, and the sum of the absolute values of the front wheel steering angle θf and the vehicle body slip angle θs is larger than the limit value θhc. In this case, it is determined that the reverse steering operation is performed, and the set steering ratio Rn is switched from the reverse phase to the same phase with a certain time constant τ. When the reverse steering wheel operation is not performed, the rear wheels are steered by the first steering ratio pattern shown by the solid line B in FIG. Therefore, the small turning performance of the vehicle can be improved. Further, in this embodiment, by setting the time constant τ when changing the set steering ratio Rn, the steering ratio can be changed smoothly and the rear wheels can be smoothly steered. In the above embodiment, the reverse steering wheel operation is performed by changing the vehicle body slip angle θs, the front wheel steering angle θf, and the vehicle body yaw rate φ.
The detection accuracy is improved by detecting d and the front wheel steering angle θf respectively. However, the present invention is not limited to this. The detection may be performed by a combination of any one of the angle θf, the vehicle body yaw rate φd, and the front wheel steering angle θf. Further, in the above embodiment, when detecting the vehicle lateral speed,
The vehicle lateral speed is calculated from the lateral speeds of the vehicle front portion and the vehicle rear portion to improve the detection accuracy of the vehicle lateral speed. However, the present invention is not limited to this, and the vehicle lateral speed The detection may be performed based on the position of the center of gravity of the vehicle. Further, in the above-mentioned embodiment, the rear wheel steering ratio is set to the in-phase side when the reverse steering wheel operation is detected, but the present invention is not limited to this, and as shown in FIG. The rear wheels may be steering-controlled based on the third steering ratio pattern indicated by the one-dot chain line C. That is, the third suitable for operating the reverse handle shown by the one-dot chain line C in FIG.
When the rear wheels are steered according to the steering ratio pattern, the target steering ratio Rc is set to zero as in the front two-wheel steering vehicle.

【The invention's effect】

As described above, according to the present invention, there is an excellent effect that the reverse steering wheel operation can be easily performed during the vehicle slip.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a rear wheel steering control device for a front and rear wheel steering vehicle according to the present invention, and FIG. 2 is a front and rear wheel steering angle and yaw rate for explaining the principle of the present invention. FIG. 3 is a partial block diagram showing a front wheel steering mechanism, a rear wheel steering mechanism and an electric control device in an embodiment of a rear wheel steering control device for a front and rear wheel steering vehicle according to the present invention. FIG. 4 is a plan view including a conduit diagram, FIG. 4 is a flow chart showing the operation of the microcomputer in the embodiment, and FIG.
FIG. 6 is a plan view showing the signs of the physical quantities used in the control of this embodiment, FIG. 6 is a diagram showing the relationship of the target steering ratio with respect to the vehicle speed in the embodiment, and FIG. FIG. 5 is a diagram showing the relationship between the front wheel steering angle, the vehicle body slip angle, and the steering ratio on the same time axis. A ... Front wheel steering mechanism, B ... Rear wheel steering mechanism, C ... Electric control device, 11 ... Pinion and rack mechanism, 16a, 16b ... Front wheel, 21 ... Servo valve, 22a, 22b ... Rear wheel , 23 ... hydraulic cylinder, 30 ... vehicle speed sensor, 31, 32 ... lateral speed sensor, 33 ... yaw rate sensor, 34 ... front wheel steering angle sensor, 35 ... rear wheel steering angle sensor, 38 ... micro computer , 40 …… Comparator, 41 …… Servo amplifier.

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Claims (5)

[Claims] 1. A rear wheel steering control device for a front and rear wheel steering vehicle, wherein a steering ratio of a rear wheel to a front wheel is controlled to a reverse phase side at a low speed and a common phase side at a high speed, and a vehicle speed detecting means for detecting a vehicle speed, A steering ratio determining means for determining the steering ratio according to the detected vehicle speed, a reverse steering wheel operation detecting means for detecting a reverse steering wheel operation of the driver, and a reverse steering wheel operation of the driver are detected by the reverse steering wheel operation detecting means. In this case, the steering ratio changing means for changing the determined steering ratio to zero or the in-phase side, the output means for outputting a control signal corresponding to the determined steering ratio, and the rear wheel steering angle in response to the control signal. A rear wheel steering control device, comprising: a rear wheel steering mechanism, which is set based on the determined steering ratio, and which steers the rear wheels. 2. The reverse steering wheel operation detecting means has a vehicle body slip angle obtained from a vehicle lateral speed and a vehicle speed, and the positive and negative signs of the front wheel steering angle are opposite to each other, and the vehicle body slip angle and the front wheel steering angle are opposite to each other. The rear wheel steering control device according to claim 1, configured to detect that a reverse steering wheel operation is performed when the sum of absolute values is equal to or greater than a predetermined value. 3. The front and rear wheel steering vehicle rear wheel steering according to claim 2, wherein the vehicle lateral speed is detected from the lateral speeds of the vehicle front part and the vehicle rear part when the vehicle lateral speed is detected. Control device. 4. The reverse steering wheel operation detecting means has positive and negative signs of a vehicle body yaw rate and a front wheel steering angle, and a sum of absolute values of the yaw angle and the front wheel steering angle based on the vehicle body yaw rate is a predetermined value or more. The rear wheel steering control device according to claim 1, wherein the rear wheel steering control device is configured to detect that the steering wheel is operated in the opposite direction. 5. The reverse steering wheel operation detecting means has a vehicle body slip angle obtained from a vehicle lateral speed and a vehicle speed, and the positive and negative signs of the front wheel steering angle are opposite to each other, and the vehicle body slip angle and the front wheel steering angle are opposite to each other. When the sum of absolute values is greater than or equal to a predetermined value, the signs of the vehicle body yaw rate and the front wheel steering angle are opposite, and the sum of the absolute values of the yaw angle and the front wheel steering angle based on these vehicle body yaw rates is the predetermined value or more. The rear wheel steering control device according to claim 1, wherein the rear wheel steering control device is configured to detect that the steering wheel is operated in the opposite direction.