JPH0774006B2 - Steering angle ratio controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention smoothly turns to the left when a vehicle starts from a parking state in which the vehicle is tilted with respect to a side wall, such as a garage, without the side surface of the vehicle contacting the side wall. Or you can turn right,
The present invention relates to a steering angle ratio control device for a four-wheel steering vehicle.

[Prior Art] In a four-wheel steering vehicle, if the rear wheels are steered in the opposite phase to the front wheels,
The turning radius is reduced, and the turning performance is improved. However, compared to conventional front-wheel steering vehicles, the range of motion in the rear corners of the vehicle is wider, and if there are obstacles such as side walls on the side of the track (hereinafter referred to as side walls), the rear corners of the vehicle at the time of turning are changed. May come into contact with the side wall.

In order to solve the above-mentioned problem, in a four-wheel steering vehicle disclosed in Japanese Patent Laid-Open No. 61-27767, when the steering wheel is greatly turned, the rear wheel steering angle is gradually changed to a target steering angle every predetermined traveling distance. Approach the corner. However, in the above-described four-wheel steering vehicle, the yaw angle (the inclination angle of the front-rear axis of the vehicle with respect to the side wall) also changes stepwise in accordance with the rear-wheel steering angle, so that the movement of the vehicle becomes very unnatural and driving Person feels uncomfortable.

In the rear wheel steering control device disclosed in JP-A-62-120275, as shown in FIG. 8, when the vehicle starts, the turning center of the vehicle 44 is previously determined from the front wheel steering angle θF and the rear wheel steering angle θR. Q is calculated, the distance between the turning center Q and the rear corner R of the vehicle 44, that is, the turning radius Ro is calculated, and the overhang amount s1 of the rear corner R accompanying the turning of the vehicle is calculated.
The steering angle ratio is controlled so that the overhang amount s1 does not become larger than the gap so between the side surface of the vehicle 44 and the side wall 80.

However, in the above-mentioned rear wheel steering control device, the vehicle 44 is mounted on the side wall.
There is no problem if the vehicle is parked in parallel with 80, but if the vehicle 44 is parked at an angle with respect to the side wall 80, the following from the mounting positions before and after the distance sensor that detects the gap so with respect to the side surface of the vehicle 44: Such problems arise. That is, when the vehicle 44 is parked at an angle with respect to the side wall 80a indicated by the chain line,
Although the rear corner R of the vehicle 44 does not come into contact with the side wall 80a even when the vehicle is out of the garage or turned to the left at the illustrated front wheel steering angle θF and rear wheel steering angle θR, a distance sensor is provided at the rear corner R. In the case of, the overhang amount s1 becomes larger than the clearance so, and the rear wheel steering control device determines that the turning is impossible. Therefore, the distance sensor
If it is provided at the point B in the center of 44, the overhang amount s1 is
Therefore, the rear wheel steering control device determines that turning is possible. However, even when the vehicle 44 is tilted with respect to the side wall 80b indicated by the chain line and the rear corner R of the vehicle 44 contacts the side wall 80b, the rear wheel steering control device determines that the vehicle can turn.

[Problems to be Solved by the Invention] In view of the above problems, an object of the present invention is that regardless of the parking posture of the vehicle, when the vehicle starts to turn and the vehicle speed is equal to or lower than a predetermined value, the steering angle ratio is equal to the front and rear wheels of the vehicle. It is an object of the present invention to provide a steering angle ratio control device in which the side surface of a vehicle is controlled to a value that does not contact any of the left and right side walls in relation to the distance between the support portion and the side wall.

[Means for Solving the Problem] In order to achieve the above object, the configuration of the present invention is such that the rear wheel is steered in a phase opposite to that of the front wheel when the vehicle speed is a predetermined value or less and the ratio of the rear wheel steering angle to the front wheel steering angle is set to In a four-wheel steering vehicle including a steering angle ratio control mechanism for controlling, a front and rear wheel steering angle sensor and a pair of front and rear distance sensors that detect a distance to a side wall are provided on front and rear wheel support portions of the vehicle. The inclination angle of the vehicle front-rear direction axis with respect to the side wall is obtained from the distance between the front and rear wheel support portions of the vehicle and the side wall detected by the pair of distance sensors, and the vehicle front wheel steering angle and rear wheel steering angle detected by the front and rear wheel steering angle sensor The turning center is obtained, the turning radius of the rear corner of the vehicle is obtained from the turning center of the vehicle, the distance between the turning center and the side wall of the vehicle is obtained from the turning radius and the distance between the rear wheel support of the vehicle and the side wall, and the previous steering angle is calculated. The maximum turning radius is larger than the distance between the turning center and the side wall. Each of the maximum rear wheel steering angles that does not occur is controlled, and the steering angle ratio is controlled so that the rear wheel steering angle does not exceed the maximum rear wheel steering angle.

[Operation] In the present invention, when the vehicle is started, the front and rear wheel steering angles and the respective distances between the side wall and the front and rear wheel supporting portions of the vehicle are detected, and the yaw of the vehicle with respect to the side wall is detected from the respective distances between the side wall and the front and rear wheel supporting portions of the vehicle. Angle (the inclination angle of the vehicle's front-rear axis with respect to the side wall), the maximum rear wheel steering angle is determined from the yaw angle and distance so that the front wheel steering angle is maximum and the vehicle does not contact the side wall, and the rear wheel steering angle is the maximum rear wheel steering angle. The steering angle ratio is controlled so that the angle is not exceeded.

In practice, the rear wheel steering angle opposite in phase to the front wheels is negative (-) for the convenience of calculation, and thus the minimum rear wheel steering angle is the maximum rear wheel steering angle. The steering angle ratio kL is obtained from the current absolute value of the front wheel steering angle θF and the minimum rear wheel steering angle θRmin.

On the other hand, the steering angle ratio k corresponding to the vehicle speed during normal traveling is obtained. The steering angle ratio kL is compared with the steering angle ratio k corresponding to the vehicle speed, and when the steering angle ratio k corresponding to the vehicle speed is larger than the steering angle ratio kL,
The steering angle ratio kL is set as the target steering angle ratio kt, and the steering angle ratio k corresponding to the vehicle speed is set.
Is smaller than the steering angle ratio kL, the steering angle ratio k corresponding to the vehicle speed is set as the target steering angle ratio kt. As a result, the steering angle ratio continuously changes with the steering of the driver without the rear corners of the vehicle coming into contact with the side wall, and smooth turning travel is realized.

After starting, when the vehicle speed V is higher than a predetermined value V2 or when the steering angle ratio k corresponding to the vehicle speed becomes larger than the steering angle ratio kL, the steering angle ratio k corresponding to the vehicle speed is set as a target steering angle ratio kt. To do.

[Embodiment of the Invention] As shown in FIG. 1, a knuckle arm 3 for supporting each of the left and right front wheels 2 is rotatably supported on a vehicle by a support shaft 3a and interlockingly connected by a tie rod 4. The arm of the right knuckle arm 3 is connected to the front wheel steering mechanism 7 via a drag link 10. When the steering shaft 6 is rotated by the handle 5 in the front wheel steering mechanism 7, the output shaft 7a is rotated, the drop arm 8 coupled to the output shaft 7a is swung, and the drag link 10 is moved back and forth. A rod 12 is connected to a pin 9 connected to an intermediate portion of the drop arm 8, and a rear end of the rod 12 is connected to an input link 14 of the steering angle ratio control mechanism A by a pin 13.

The input link 14 is connected to the end of the control lever 30 by a pin 15. A control lever 30 rotatably supported on the vehicle by a support shaft 23 is connected to an output link 27 by a connecting pin 28. Output link 27 is a rod 3 that moves back and forth by pin 27a.
Concatenated with 1. The rod 31 is connected to one valve element of the servo control valve 32 of the rear wheel steering mechanism 34.

The rear wheel steering mechanism 34 integrally includes a servo control valve 32 and an actuator. The actuator has a piston 35 fitted in a cylinder 33, and an outer end of a rod connected to the piston 35 is supported by the vehicle. The other valve element of the servo control valve 32 is integral with the cylinder 33 and connects the rod 36.

A rod 36 is attached to one end of a lever 37 supported by a spindle 38 on the vehicle.
, And the rod 39 that moves back and forth is connected to the other end. The rear end of the rod 39 is a knuckle arm that supports the rear wheel 40.
Connected with 41 arms. The left and right knuckle arms 41 are interlockingly connected by a tie rod 42.

The control lever 30 of the steering angle ratio control mechanism A is provided with an arcuate groove 29 centered on the pin 27a, and the connecting pin 28 is slidably engaged with the groove 29. In order to slide the connecting pin 28, an arc-shaped partial gear 22 is integrally formed at an end of the output link 27, and the gear 17 meshing with the partial gear 22 is a steering angle ratio control motor.
Driven by 18. Therefore, the worm shaft 21 of the steering angle ratio control motor 18 is meshed with the gear 16 coaxially connected to the gear 17. The steering angle ratio control motor 18 and the gear 17 are integrally supported by a frame, and the frame is slid by an actuator 19 along a guide groove 20 of the vehicle. The actuator 19 is formed by fitting a piston to a cylinder, and the piston is connected to the frame of the steering angle ratio control motor 18 by a rod. Normally, the force of a spring releases the front (the engagement between the gear 17 and the partial gear 22). Direction).

The support shaft 23 of the control lever 30 has a groove continuous with the groove 29. When the lever 24 connected to the support shaft 23 is rotated by the actuator 25 to a position where it hits the stopper 26a, the groove of the support shaft 23 is cut off from the groove 29 of the control lever 30. The actuator 25 has a piston fitted to a cylinder, and the piston and the lever 24 are connected by a rod. Normally, the lever 24 is pressed against the stopper 26 by the spring force of the actuator 25, and the groove of the support shaft 23 and the groove 29 of the control lever 30 are brought into a continuous state.

Now, when the steering wheel 5 is turned to the right, the drag link 10 of the front wheel steering mechanism 7 moves forward, and the knuckle arm 3 is pivoted.
The front wheel 2 is deflected rightward by rotating clockwise around 3a. At the same time, the rod 12 also moves forward and the control lever
30 rotates counterclockwise about the spindle 23. The output link 27 pulls the rod 31 forward and the servo control valve 32
By the action of, the pressure oil is supplied to the chamber on the front side of the actuator. The cylinder 33 moves forward, the rod 39 moves backward via the lever 37, the knuckle arm 41 rotates counterclockwise about the support shaft 41a, and the rear wheel 40 moves leftward (in the opposite phase to the front wheel). Biased. Therefore, the turning radius of the vehicle is reduced, and the small turning ability at low speed traveling is improved.

When the gear 17 is rotated by the steering angle ratio control motor 18 in relation to the vehicle speed and the output link 27 is rotated counterclockwise around the pin 27a, the connecting pin 28 moves to the left side of the support shaft 23. At this time, the rear wheels 40 are deflected in the same phase as the front wheels 2 (see FIG. 3), and the steering stability when changing lanes at high speed is improved.

According to the present invention, when the vehicle starts or when the vehicle turns around a narrow road, the rear corner R of the vehicle is pushed out of the road and comes into contact with the side wall 80 by the rear wheel steering in a phase opposite to that of the front wheel 2. In order to prevent, the steering angle ratio k is limited to the limit steering angle ratio kL (negative value). In other words, from the front and rear wheel steering angles θF, θR to the turning radius
While calculating Ro, the initial yaw angles ψL, ψR (the inclination angle of the vehicle front-rear axis with respect to the left and right side walls 80) are calculated from the distances sF, sR between the front and rear wheel supports and the side walls 80 and the turning center Q of the vehicle. Is calculated, and the turning radius Ro of the vehicle is determined by the turning center Q and the side wall.
Limit rudder angle ratio to a value that does not exceed 80
Control kL. In this case, the limit rudder ratios kLL and kLR for the left-turn and the right-turn of the vehicle are calculated, and the larger value is used as the limit rudder angle ratio. The turning center is obtained from the front wheel steering angle θF, the rear wheel steering angle θR, and the yaw angle ψ. The turning radius Ro is the distance between the rear corner R of the vehicle and the turning center Q.

Assuming that the front wheel steering angle is θF and the steering angle ratio is k, the rear wheel steering angle θR is θR = k · θF. Now, consider a right turn of the vehicle. In FIG. 2, the center O of the rear wheel 40 (the spindle 41a of the rear wheel 40 is at the center of the rear wheel 40) is the origin, and the center P of the front wheel 2 (the front wheel 2 is perpendicular to the traveling direction of the front wheel 2). An intersection of a straight line H passing through the support shaft 3a of the vehicle and the straight line J passing through the center O perpendicular to the traveling direction of the rear wheel 40 may be regarded as the turning center Q of the vehicle.

The yaw angle of the vehicle with respect to the side wall 80 is ψ (here, the yaw angle with respect to the left side wall), the wheel base (the center P of the front wheel 2 and the rear wheel 40).
If the distance between the centers O of the vehicle is W, the yaw angle ψ of the vehicle is obtained from Wsinψ = sR−sF sinψ = (sR−sF) / W, and the slope a of the straight line H and the slope b of the straight line J are: = Tan (θF + ψ) b = tan (θR + ψ).

The equation of the straight line H is Y = aX + c (1) Here, the coordinate P (x, y) of the center P of the front wheel 2 is x = −Wsinψ (2) y = Wcosψ (3) (2), (3) Substituting equation (1) into equation (1), Wcosψ = a (-Wsinψ) + cc = W (cosψ + a sinψ) ∴Y = aX + W (cosψ + a sinψ) (4) The equation of straight line J is Y = bX (5) The coordinates Q (xo, yo) of the turning center Q of the vehicle are (4), (5)
From the formula, y = ax + W (cosψ + a sinψ) y = bx As shown in FIGS. 2 and 3, the coordinates of the left rear corner R of the vehicle are as follows: R (x, y) is x = e sin (ψ + α) (8) y = e cos (ψ + α) (9) Here, e: distance between the center O of the rear wheel 40 and the rear corner R: α: center O of the rear wheel 40 with respect to the longitudinal axis G of the vehicle
And the turning radius Ro of the angle vehicle line T connecting the rear corners R, the distance QR of turning center Q and the rear corner portions R
And is expressed by the following equation from the equations (6) and (7) and the equations (8) and (9).

Ro ² = [xo-e sin (ψ + α)] ² + [yo-e cos (ψ +
α)] ^{2 The} condition that the rear corner R of the vehicle does not contact the side wall 80 is Ro <xo + s, where xo: the distance O between the center O of the rear wheel 40 and the turning center Q in the direction perpendicular to the side wall 80 s: rear Distance between the center O of the wheel 40 and the side wall 80 The same can be obtained when the vehicle turns left.

From the above, the steering angle ratio kL at the time of starting is obtained from the equation k = f (ψ, s). Here, since θFmax, α, e are values peculiar to the vehicle, the yaw angle ψ and the minimum rear wheel steering angle θRmin can be obtained by detecting the front and rear wheel steering angle θ and the distance s between the side wall and the front and rear wheel support portion of the vehicle. The steering angle ratio kL is obtained. As a result, even if the vehicle is started with the front wheel steering angle θF maximized, the rear corners of the vehicle do not come into contact with the side walls. In addition, even if the vehicle leans too close to the side wall and tries to make a right turn or a left turn while traveling, a contact accident can be prevented.

As shown in FIG. 5, according to the present invention, two pairs of front and rear distance sensors 62a and 62b, which are arranged adjacent to the front and rear wheel supporting portions of the vehicle and detect a distance by reflected waves of ultrasonic waves, and a front and rear wheel steering angle sensor 5 are provided.
Based on the signals of 9,60, the electronic control unit 51 controls the minimum rear wheel steering angle θ so that the rear corners of the vehicle do not contact the left and right side walls 80.
Rmin is calculated and the steering angle ratio kL is controlled so that the actual rear wheel steering angle does not exceed the minimum rear wheel steering angle θRmin.

On the other hand, in normal traveling, the steering angle ratio k is controlled according to the vehicle speed V (see FIG. 4). For example, based on a signal from a vehicle speed sensor 55 arranged facing the output shaft of the transmission, an electronic control unit
The steering angle ratio k corresponding to the vehicle speed is obtained by the steering angle ratio setting means 51, and the steering angle ratio control motor 18 is driven by the steering angle ratio control means with the steering angle ratio k corresponding to the vehicle speed as the target steering angle ratio kt. Then, when the actual steering angle ratio ks detected by the steering angle ratio sensor 56 arranged so as to face the partial gear 22 matches the target steering angle ratio kt, the steering angle ratio control motor 18 is stopped.

FIG. 6 is a flow chart of a program for performing the above-mentioned control by the electronic control unit 51 including a microcomputer. This program starts at p11 and is initialized at p12, and at p13 the target steering angle ratio kt is set to a predetermined value kmin (a sufficiently small constant value that does not touch the side wall) for the time being. The start mode flag is turned on at p14. The vehicle speed V is read by the vehicle speed sensor 55 at p15. At p16, the front and rear wheel steering angles sensors 59 and 60 read the front wheel steering angles θF and θR. In p17, it is determined whether or not the absolute value of the vehicle speed V is smaller than a value V2 (for example, 5 km / h) that requires attention to contact with the side wall. If the vehicle speed V is higher than the value V2, the start mode flag is turned off at p18 and the process proceeds to p28.

When the absolute value of the vehicle speed V is smaller than V2 in p17, it is determined in p19 whether the vehicle speed V is smaller than the low level value V1 (for example, 2 km / h). If the vehicle speed V is greater than the value V1, p2
When the vehicle speed V is smaller than the value V1 in step 3, the distance sensors 62a and 62b read the distances sF and sR between the front and rear wheel support portions of the vehicle and the left and right sidewalls at p20.

At p21, the left and right yaw angles ψL and ψR are obtained from the distances sF and sR between the front and rear wheel support portions of the vehicle and the left and right side walls. yaw angle ψL, ψ at p22
The minimum rear wheel steering angles θRLmin and θRRmin are obtained from R and the distances sF and sR between the left and right side walls and the front and rear wheel support portions of the vehicle. In p23, it is determined whether or not the front wheel steering angle θF is 0 (whether or not the vehicle is in a straight traveling state). If the front wheel steering angle θF is 0, proceed to p34 and the front wheel steering angle θF is 0.
If not, it is determined in p24 whether the front wheel steering angle θF is greater than 0 (whether the steering wheel is turned to the right). When the steering wheel is turned left, the minimum rear wheel steering angle θRRmin is set to the minimum rear wheel steering angle θR at p25, and the process proceeds to p27. When the steering wheel is turned to the right at p24, the minimum rear wheel steering angle θRLmin is set to the minimum rear wheel steering angle θRmin at p26. The steering angle ratio kL (minimum rear wheel steering angle θRmin divided by front wheel steering angle θF) is calculated in p27.

In p28, the steering angle ratio k corresponding to the vehicle speed is obtained from the steering angle ratio setting means (the control map stored in the RAM of the microcomputer). In p29, it is determined whether or not the start mode flag is ON. If the start mode flag is not ON, the start mode flag is turned OFF at p30, the steering angle ratio k corresponding to the vehicle speed is set as the target rear wheel steering angle ratio kt at p31, and the process proceeds to p34.

When the start mode flag is ON in p29, it is determined in p32 whether the steering angle ratio k corresponding to the vehicle speed is smaller than the steering angle ratio kL. When the steering angle ratio k corresponding to the vehicle speed is greater than the steering angle ratio kL in p32, the process proceeds to p30. When the steering angle ratio k corresponding to the vehicle speed is smaller than the steering angle ratio kL in p32, the steering angle ratio kL is set as the target steering angle ratio kt in p33, and the rear wheel steering angle is calculated in p34 based on the interrupt program shown in FIG. The ratio control motor 18 is driven.

The interrupt program shown in FIG. 7 starts at p41, and at p42 the steering angle ratio control motor 18 is set so that the steering angle ratio becomes the target steering angle ratio kt.
To drive. The actual steering angle ratio ks is detected with p43 and the actual steering angle ratio is detected with p44.
It is determined whether ks is equal to the target steering angle ratio ks. Actual steering angle ratio
If ks is not equal to the target steering angle ratio kt, return to p42. When the actual steering angle ratio ks is equal to the target steering angle ratio kt, the steering angle ratio control motor 18 is stopped at p45, and the program returns to the program shown in FIG. 6 at p46. The above program returns from p34 to p15 every predetermined time and is repeatedly executed.

[Advantages of the Invention] As described above, the present invention includes the steering angle ratio control mechanism that steers the rear wheels in the opposite phase to the front wheels when the vehicle speed is equal to or lower than the predetermined value and controls the ratio of the rear wheel steering angle to the front wheel steering angle. In a four-wheel steering vehicle, a pair of front and rear distance sensors that detect the distance to the side wall and a front and rear wheel steering angle sensor are disposed on the front and rear wheel support portions of the vehicle, and the vehicle is detected by the pair of front and rear distance sensors. The tilt angle of the longitudinal axis of the vehicle with respect to the side wall is calculated from the distances between the front and rear wheel supports and the side wall, and the turning center of the vehicle is calculated from the front wheel steering angle and the rear wheel steering angle detected by the front and rear wheel steering angle sensors. The turning radius of the rear corner of the vehicle is calculated from the turning radius and the distance between the turning center and the side wall of the vehicle is calculated from the turning radius and the distance between the rear wheel support of the vehicle and the side wall. The turning radius at the maximum front wheel steering angle is the turning center. And the maximum rear wheel steering angle that does not become larger than the side wall distance. Since the steering angle ratio is controlled so that the rear wheel steering angle does not exceed the maximum rear wheel steering angle, the following effects are obtained.

When a vehicle departs from a garage or changes direction on a narrow road, the vehicle starts from a parking position that is inclined with respect to the side wall, and at the same time, the distance between the side wall and the front and rear wheel supports of the vehicle, the yaw angle of the vehicle with respect to the side wall, and the front and rear wheel rudder. From the angle, the maximum rear wheel steering angle at which the rear corner of the vehicle does not come into contact with the side wall is obtained, and the steering angle ratio is controlled corresponding to the front wheel steering angle with the maximum rear wheel steering angle as a reference.
Therefore, the rear wheel steering angle is continuously controlled so that the rear corners of the vehicle do not come into contact with the side walls when the vehicle speed is lower than the predetermined value, so smooth steering can be obtained without any discomfort for the driver. To be

The rear wheel steering angle is controlled in relation to the front wheel steering angle so that the rear corner of the vehicle does not contact the side wall, so even if the driver turns the steering wheel to the maximum with the same feeling as a normal front wheel steering vehicle. It is possible to prevent the side surface of the vehicle from coming into contact with the side wall.

Since the steering angle ratio is automatically determined regardless of the steering direction of the steering wheel, driving is easy and safe against contact accidents.

[Brief description of drawings]

FIG. 1 is a plan view showing a schematic configuration of a four-wheel steering vehicle equipped with a steering angle ratio control device according to the present invention, and FIGS. 2 and 3 are plan views illustrating the relationship between front and rear wheel steering angles and turning radii, FIG. 4 is a characteristic diagram of the steering angle ratio setting means, FIG. 5 is a block diagram showing the steering angle ratio control device, FIGS. 6 and 7 are flow charts of a program for controlling the steering angle ratio control device, and FIG. It is a top view explaining the operation of the conventional steering angle ratio control device. A: Steering angle ratio control mechanism, R: Rear corner, 2: Front wheel, 6: Steering shaft, 1
7: Gear, 18: Steering angle ratio control motor, 19, 25: Actuator, 22: Partial gear, 23: Support shaft, 27: Output link, 28: Connecting pin, 30: Control lever, 34: Rear wheel steering mechanism , 40: rear wheels, 51: electronic control unit, 55: vehicle speed sensor, 56: steering angle ratio sensor, 59: front wheel steering angle sensor, 60: rear wheel steering angle sensor, 62: yaw angle detection means, 62a, 62b: Distance sensor, 80: Side wall

Claims (1)

[Claims] 1. A four-wheel steering vehicle equipped with a steering angle ratio control mechanism for steering a rear wheel in a phase opposite to that of a front wheel at a vehicle speed equal to or lower than a predetermined value and controlling a ratio of a rear wheel steering angle to a front wheel steering angle. A pair of front and rear distance sensors that detect the distance to the side wall and a front and rear wheel steering angle sensor are arranged on the front and rear wheel support portions of the vehicle, and the front and rear wheel support portions and the side walls of the vehicle detected by the pair of front and rear distance sensors. The tilt angle of the longitudinal axis of the vehicle with respect to the side wall is calculated from the distance,
The turning center of the vehicle is obtained from the front wheel steering angle and the rear wheel steering angle detected by the front and rear wheel steering angle sensors, and the turning radius of the rear corner of the vehicle is obtained from the turning center of the vehicle. The distance between the turning center of the vehicle and the side wall is calculated from the distance between the side wall and
The maximum rear wheel steering angle is calculated so that the turning radius at the maximum front wheel steering angle does not become larger than the distance between the center of turning and the side wall, and the steering angle ratio is set so that the rear wheel steering angle does not exceed the maximum rear wheel steering angle. A steering angle ratio control device for controlling a steering angle ratio.