JPH0774005B2 - Steering angle ratio controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention smoothly turns 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. The side surface of the vehicle is controlled in relation to the distance between the supporting portion and the side wall so that the side surface of the vehicle does not come into contact with any of the left and right side walls. It is to provide a steering angle ratio control device.

[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 equipped with a steering angle ratio control mechanism for controlling, two pairs of front and rear distance sensors for detecting the distance to the left and right side walls and front and rear wheel steering angle sensors are arranged on front and rear wheel support portions of the vehicle, The tilt angle of the longitudinal axis of the vehicle with respect to the left and right side walls is obtained from the distance between the front and rear wheel support portions of the vehicle and the left and right side walls detected by the front and rear wheel steering angle sensors and the rear wheel steering angle detected by the front and rear wheel steering angle sensors. The turning center of the vehicle is obtained from the wheel steering angle, the turning radius of the rear corner of the vehicle is obtained from the turning center of the vehicle, and the turning center of the vehicle is determined from the turning radius and the distance between the rear wheel support of the vehicle and the left and right side walls. Find the distance between the left and right side walls, and turn the handle right and left The maximum rear wheel steering angle is determined so that the maximum turning radius does not exceed the distance between the turning center and the left and right sidewalls, and the steering wheel is steered so as not to exceed the smaller maximum rear wheel steering angle. It controls the angular ratio.

[Operation] In the present invention, when the vehicle starts, the front and rear wheel steering angles and the respective distances between the left and right sidewalls and the front and rear wheel supporting portions of the vehicle are detected, and the vehicle from the respective distances of the front and rear wheel supporting portions of the vehicle to the left and right sidewalls is detected. Each yaw angle (the inclination of the longitudinal axis of the vehicle with respect to the left and right side walls) is calculated, and the maximum rear wheel when turning to the left and turning left so that the front wheel steering angle is maximum and the vehicle does not touch the side wall from the yaw angle and distance. The steering angle ratios are controlled so as not to exceed the smaller one of the maximum rear wheel steering angles, that is, the maximum rear wheel steering angle of which the rear corners of the vehicle have a small protrusion amount. 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.

Actually, for convenience of calculation, if the front wheel steering angle when turning right is +, the rear wheel steering angle is −, the front wheel steering angle when left turning is −, and the rear wheel steering angle is −, the maximum is when turning left. It becomes the rear wheel steering angle (positive value).
The minimum rear wheel steering angles θRLmin and θRRmin at the time of left turning and right turning are calculated from the equation θRmin = f (ψ, s). The sign of the minimum rear wheel steering angle θRLmin when turning right is reversed, and the sign of the minimum rear wheel steering angle θRLmin when turning left and the minimum rear wheel steering angle θRRmin when turning right are unified to be positive (+). The smaller one is the minimum rear wheel steering angle θRmin
And Current absolute value of front wheel steering angle θF and minimum rear wheel steering angle θ
Determine the steering angle ratio kL from Rmin. On the other hand, the steering angle ratio k corresponding to the vehicle speed during normal traveling is calculated. The steering angle ratio kL is compared with the steering angle ratio k corresponding to the vehicle speed. If 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 vehicle speed When the steering angle ratio k corresponding to 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.

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 this, the steering angle ratio k is limited to the minimum steering angle ratio kL (negative value). In other words, from the front and rear wheel steering angles θF, θR to the turning radius
While obtaining Ro, the initial yaw angles ψL, ψR (the inclination angle of the front-rear axis of the vehicle 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 turning center Q of the side walls 80 and 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 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). Since θFmax, α, e is a value peculiar to the vehicle, the minimum rear wheel steering angle θRmin can be obtained by detecting the front and rear wheel steering angles θF, θF and the distance s between the side wall and the front and rear wheel support portions of the vehicle.
The steering angle ratio kL is obtained. Thus, even if the vehicle is started with the front wheel steering angle θF maximized, the rear corners of the vehicle do not contact the left and right 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.
RLmin and θRRmin are obtained, and the steering angle ratio kL is controlled so as not to exceed the minimum rear wheel steering angle θRmin, whichever has the smaller absolute value.

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 means 18 drives the steering angle ratio control motor 18 with the steering angle ratio k as the target steering angle ratio kt. And the partial gear 22
The steering angle ratio control motor 18 is stopped when the actual steering angle ratio ks detected by the steering angle ratio sensor 56 arranged opposite to the target steering angle ratio kt matches the target steering angle ratio kt.

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, is initialized at p12, and sets the target steering angle ratio kt to a predetermined value kmin for the time being at p13. 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 θF and θR are read by the front and rear wheel steering angle sensors 59 and 60. In p17, the absolute value of the vehicle speed V is a value V2 (for example, 5k
m / h) It is determined whether or not it is too small. When the vehicle speed V is higher than the value V2, the start mode flag is turned off at p18 and p2 is set.
Go to 5.

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, the distance sensor 62b reads the distances sF and sR between the front and rear wheel support portions of the vehicle and the left and right side walls at p20. At p21, the left and right yaw angles ψR and ψL are obtained from the distances sF and sR.

At p22, the yaw angles ψR and ψL and the distances sF and sR between the front and rear wheel supports of the vehicle and the left and right sidewalls are used to determine the minimum rear wheel rudder θRLmi for each turning direction.
Find n and θRRmin. Minimum rear wheel steering angle θRR when turning right with p23
Reverse the sign of min. Minimum rear wheel steering angle θ when turning left at p24
It is determined whether RLmin is larger than the minimum rear wheel steering angle θRRmin when turning right. When the absolute value of the minimum rear wheel steering angle θRLmin is larger than the absolute value of the minimum rear wheel steering angle θRRmin, the minimum rear wheel steering angle θRRmin is set as the rear wheel steering angle θRmin at p25, and the process proceeds to p27.

At p24, the absolute value of the minimum rear wheel steering angle θRLmin is the minimum rear wheel steering angle θRR.
If it is smaller than the absolute value of min, the minimum rear wheel steering angle θ
Let RLmin be the rear wheel steering angle θRmin. The front wheel steering angle θF is 0 at p27
It is determined whether or not, that is, whether or not the vehicle is in a straight traveling state. When the front wheel steering angle θF is 0, the process proceeds to p35. When the front wheel steering angle θF is not 0, the steering angle ratio kL (rear wheel steering angle θRmin is set to the front wheel steering angle θ
Divide by the absolute value of F).

In p29, the steering angle ratio k corresponding to the vehicle speed V is obtained from the steering angle ratio setting means (control map stored in the RAM of the microcomputer). At p30, 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 p31 and the steering angle ratio k corresponding to the vehicle speed V is set at p32.
Set the target steering angle ratio to kt and proceed to p35.

When the start mode flag is ON at p30, it is determined at p33 whether the steering angle ratio k corresponding to the vehicle speed V is smaller than the steering angle ratio kL. When the steering angle ratio k is larger than the steering angle ratio kL in p33, the process proceeds to p31. When the steering angle ratio k corresponding to the vehicle speed is smaller than the steering angle ratio kL in p33, the steering angle ratio kL is set as the target steering angle ratio kt in p34, and p35
Then, the steering angle ratio control motor 18 is driven based on the interrupt program shown in FIG.

The interruption program shown in FIG. 7 starts at p41 and drives the steering angle ratio control motor 18 so that the steering angle ratio becomes the target steering angle ratio kt at p42. The actual steering angle ratio ks is detected with p43, and the actual steering angle ratio ks is detected with p44.
Is equal to the target steering angle ratio kt. Actual steering angle ratio ks
If 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 is repeatedly executed every predetermined time.

[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, two pairs of front and rear distance sensors that detect the distances to the left and right sidewalls and front and rear wheel steering angle sensors are provided on the front and rear wheel support portions of the vehicle, and the front and rear wheel pair angle sensors detect the distance. The tilt angle of the vehicle front-rear direction axis with respect to the left and right side walls is calculated from the distance between the front and rear wheel support parts of the vehicle and the left and right side walls, and the turning center of the vehicle is determined from the front wheel steering angle and the rear wheel steering angle detected by the front and rear wheel steering angle sensors. Then, the turning radius of the rear corner of the vehicle is obtained from the turning center of the vehicle, and the distance between the turning center of the vehicle and the left and right sidewalls is obtained from the turning radius and the distance between the rear wheel support of the vehicle and the left and right sidewalls. The turning radius when the front wheel steering angle is maximum when turning right and turning left The maximum rear wheel steering angle is determined so that it does not become larger than the distance between the center of rotation and the left and right side walls, and the steering angle ratio is controlled so that it does not exceed the smaller maximum rear wheel steering angle. Produce the effect of.

When the vehicle is started or when the vehicle turns around on a narrow road, the yaw angle with respect to the left and right sidewalls and the left and right rear angles of the vehicle can be determined from the distance between the front and rear wheel supports and the left and right sidewalls and the front and rear wheel steering angles when the vehicle starts. The turning radius of the corner and the distance between the turning center of the vehicle and the left and right sidewalls are calculated, and the maximum turning radius for each turning direction is such that the turning radius at the maximum front wheel steering angle is smaller than the distance between the turning center and the left and right sidewalls. The rear wheel rudder angle is calculated respectively, and the rudder angle ratio is controlled so as not to exceed each smaller maximum rear wheel rudder (maximum rear wheel rudder angle with the smaller amount of protrusion of the rear angle corner of the vehicle). When the vehicle starts from a parking state in which the vehicle is inclined with respect to the side wall, the side surface of the vehicle does not contact any of the left and right side walls, and particularly in the case of crank traveling, there is no discomfort in steering to the left and to the right.

Since the steering angle ratio is continuously controlled, the rear wheel steering angle also changes continuously, and the driver does not feel uncomfortable.The rear wheel steering angle is limited to a predetermined value or less, so Even if the steering wheel is turned to the maximum with the same feeling as in a front-wheel steering vehicle, the side surface of the vehicle can be prevented from coming into contact with the side wall.

[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. The front and rear wheel support portions of the vehicle are provided with two pairs of front and rear distance sensors that detect the distance to the left and right side walls and front and rear wheel steering angle sensors. The inclination angle of the longitudinal axis of the vehicle with respect to the left and right side walls is obtained from each distance of the side walls of the vehicle, 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 vehicle turning center is calculated from the vehicle turning center. The turning radius of the rear corners of the vehicle is calculated, and the distance between the turning center of the vehicle and the left and right side walls is calculated from the turning radius and the distance between the rear wheel support of the vehicle and the left and right side walls. The turning radius at the maximum front wheel steering angle is the distance between the turning center and the left and right side walls Each rear wheel steering angle maximum that also does not increase demanded steering angle ratio control system and controls the steering ratio so as not to exceed the maximum rear-wheel steering angle of the smaller one Ri.