JPH02162161A - Four-wheels steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve both running stability and steering property by controlling the steering of rear wheels with such characteristics that the same phase steering region of rear wheels with respect to front wheels is increased and the opposite phase steering region is decreased as the car speed is increased. CONSTITUTION:A control device 10 controls the steering angle of rear wheels 2 via a solenoid 20, a rear wheels steering direction selector valve 22, and a hydraulic actuator 23 in response to the steering angle of front wheels 1 detected by a steering angle sensor 4. Rear wheels 2 are steered in the same phase as front wheels 1 in the region with a small front wheels steering angle, and rear wheels 2 are steered in the opposite phase to front wheels 1 in the region with a large front wheels steering angle. In this case, the steering of rear wheels 2 is controlled with such rear wheel steering angle characteristics against the front wheels steering angle that the same phase steering region of rear wheels with respect to front wheels 1 is increased and the opposite phase steering region is decreased as the car speed detected by a car speed sensor 12 is increased. Both running stability and steering property can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for steering both the front wheels and the rear wheels of a four-wheel vehicle such as an automobile, that is, a four-wheel steering system that steers the rear wheels as well as the front wheels by steering the front wheels, which are steering wheels. It is related to the device.

Conventionally, steering devices in four-wheeled vehicles steer only the front wheels, and although the rear wheels may toe in or out to some extent depending on the driving situation, regardless of the steering of the front wheels, they do not actively steer the rear wheels. is not. However, recently, a four-wheel steering device has been proposed in which both the front wheels and the rear wheels are steered, and research on this type of device is being carried out (for example, in Japanese Patent Application Laid-Open No. 55-91458).

The four-wheel steering system enables convenient maneuvering that was previously impossible, as well as driving with improved steering performance, depending on the various driving conditions of the vehicle. For example, when maneuvering a vehicle at extremely low speeds such as parallel parking or parking in a garage, it is possible to significantly change the direction of the vehicle by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase). This makes it possible or easy to park in tight spaces, which was previously impossible or extremely difficult. Further, in a U-turn, the minimum turning radius can be made small, which is advantageous. Furthermore, by steering the rear wheels in a phase opposite to that of the front wheels, the difference between the inner wheels can be minimized or eliminated, which is advantageous when turning a narrow corner. In addition, when steering a vehicle at extremely low speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase), it is possible to move the entire vehicle in parallel, making it easier to park and park. It is often convenient when parking in the garage.

On the other hand, when changing lanes while driving at medium to high speeds,
By performing four-wheel steering in the same phase, lateral force is applied to the front and rear wheels at the same time, making it possible to change lanes smoothly without phase lag. At this time, yawing is suppressed, so you can change lanes at high speed without fear. can be done. Furthermore, when cornering, the direction of the vehicle can be effectively changed by steering the rear wheels in opposite phases.

Furthermore, when driving straight ahead, if the rear wheels are steered in a direction that counteracts the effect of external disturbances such as crosswinds, stable driving can be maintained against external disturbances, and stable high speeds can be maintained. It is also possible to obtain straightness.

Additionally, even if you accelerate or decelerate while keeping the steering angle of the front wheels constant during a turn, the steering angle of the rear wheels will change in accordance with the acceleration or deceleration, so that you will not deviate from your course and make a stable turn. It can also be done.

In other words, in conventional vehicles, the steering characteristics are adjusted to slightly understeer in order to maintain straight-line stability, and when accelerating during a turn, there is a tendency for the vehicle to deviate outward from the course. By doing so, the deviation can be corrected and stable turning can be realized.

In terms of comfort, it is possible to obtain a smaller minimum turning radius with the same wheelbase, so the wheelbase can be increased, and in addition to this, the actual steering angle of the front wheels can be reduced. It has many advantages, including the ability to experiment with new designs.

As described above, four-wheel steering has many practical advantages and is extremely useful.

Regarding this four-wheel steering, various specific configurations have been proposed so far to effectively steer the rear wheels. For example, one that steers the four wheels in opposite phases at low speeds and the same phase at high speeds (Japanese Patent Laid-Open No. 55-91457), and one that steers the four wheels in the same phase when the front wheel steering angle is small and in opposite phases when it is large ( (Japanese Patent Application Laid-Open No. 56-5270) The rear wheels are steered in proportion to the steering angle of the front wheels only when the steering angle of the front wheels is below a predetermined range, and regardless of the steering angle of the front wheels when the steering angle is above the predetermined range. A device with a constant steering angle of the rear wheels (Japanese Patent Application Laid-Open No. 56-16
No. 3969) etc. are known.

These four-wheel steering devices often require a large change in the direction of the vehicle when the vehicle speed is low or the front wheel steering angle is large, and a slight lateral change when the vehicle speed is high or the front wheel steering angle is small. The system always steers the rear wheels in the desired direction based on the empirical rule that there are many cases where a vehicle wants to move.

However, in actual driving of a vehicle, sufficient maneuverability and driving stability cannot be obtained simply by considering the vehicle speed and the front wheel steering angle independently.

For example, when turning with a constant front wheel steering angle,
Even if the rear wheels are steered with a desirable steering ratio corresponding to this steering angle, acceleration or deceleration during a turn may cause the vehicle to deviate from or inward from the course.

This is because centrifugal force (lateral force) changes as the vehicle speed changes, but in order to avoid going off course, the front and rear wheels must be adjusted according to the change in vehicle speed. It is necessary to change the steering ratio.

Therefore, the rear wheel steering angle relative to the front wheel steering angle (steering ratio)
is desirably changed depending on the vehicle speed. In addition, at medium-high speeds, the higher the vehicle speed, the larger the steering ratio in the same phase, increasing the lateral acceleration (G) to enable smooth lane changes, improving maneuverability and improving high-speed It is desirable to reduce the steering ratio and reduce the lateral acceleration as the vehicle speed decreases from low to medium speed.

Furthermore, as disclosed in JP-A No. 58-5270, when the front wheel steering angle is in a small range, the phase is the same, and in a large range, the phase is opposite. The yaw (ψ
) characteristic becomes excessive, which can easily cause the car to spin, which is dangerous.In the low-to-medium speed range, when the front wheels are steered at a small angle, they are in the same phase, resulting in poor turning performance.

The object of the present invention is to provide a four-wheel steering system that improves both running stability and maneuverability in response to the above-mentioned demands.

The four-wheel steering device according to the present invention steers the rear wheels according to the steering of the front wheels, and when steering the rear wheels, the ratio of the rear wheel steering angle to the front wheel steering angle is adjusted according to an increase in vehicle speed. In a four-wheel steering system for a vehicle that steers the vehicle so that the steering angle increases, when the front wheel steering angle is small, the rear wheels are steered in the same phase as the front wheels, and when the front wheel steering angle is large, the rear wheels are steered in the opposite phase to the front wheels. In addition, as the vehicle speed increases, the in-phase steering area of the rear wheels relative to the front wheels increases and the anti-phase steering area decreases. It is characterized by having a control means for controlling steering.

According to the four-wheel steering system of the present invention, in a region where the front wheel steering angle is small where running stability is required, the rear wheels are steered in the same phase as the front wheels in the same phase region, and the lateral acceleration (G) is Since the vehicle is in the G region (region with large G characteristics) in which G is more likely to occur, driving stability can be sufficiently improved. In addition, in the region where the front wheel steering angle is large where maneuverability is required, the rear wheels are steered in the opposite phase to the front wheels, and the yaw region (region with large yaw (ψ) characteristics where yawing is likely to occur) ), the maneuverability can be sufficiently improved.

Furthermore, as the vehicle speed increases, the in-phase region increases and the anti-phase region decreases. In other words, the phase change point described below is changed to the side where the front wheel steering angle is larger. As a result, the front wheel steering angle becomes wider (even in the G range), which can improve running stability, and the yaw range increases as the speed decreases.
Therefore, the yaw region is achieved with a small front wheel turning angle, and maneuverability can be improved.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In the embodiment described below, the present invention is applied particularly to rear wheel steering in a low and medium speed range.

FIGS. 1 and 2 respectively show examples of the characteristics of the rear wheel turning angle θR with respect to the front wheel turning angle θF in the four-wheel steering system of the present invention.

In the example shown in Fig. 1, when the vehicle speed is high (e.g. 801 V/H or higher), the rear wheel turning angle θR increases as the front wheel turning angle θF increases until it reaches the slope change part, and after that it remains constant. Or it gradually decreases but remains within the same phase region. When the vehicle speed is low (for example, about 10km/H to 30km/H) or medium speed (for example, about 301V/H to 80km/H), the rear wheel turning angle θR changes as the front wheel turning angle θF increases. ,
increasing until reaching slope change parts pt, p2 and P3;
After that, it decreases and finally becomes negative. That is, the phase change point CI.

The phase changes from the same phase to the opposite phase at C2 and C3.

Low and medium vehicle speeds Vl, V2 and V3 (V l>V2
>V3), the relationship between the front wheel turning angle θF and the rear wheel turning angle θR is that for the same front wheel turning angle, the higher the vehicle speed, the larger the rear wheel turning angle θR becomes. P2 and P3
changes to the side where the front wheel steering angle θF is large and the rear wheel steering angle θR is large as the vehicle speed increases, and the phase change point C1
, C2 and C3 change to the side where the front wheel steering angle θF is larger (to the right in the figure) as the vehicle speed increases. When the vehicle speed is very low (for example, about 0 to 10 km/h), the rear wheel turning angle θR is zero until the front wheel turning angle θF becomes large to a certain extent, and when it becomes more than that, it becomes negative, that is, in reverse phase.

In this embodiment, a case has been described in which the gradient changing portions Pl, P2, and P3 change to the side where the front wheel steering angle θF is large and the rear wheel steering angle θR is large as the vehicle speed increases. The gradient changing portions Pi, P2, and P3 may change to the side where the front wheel steering angle θF is small and the rear wheel steering angle is large as the vehicle speed increases, and this embodiment is shown in FIG. .

In the example shown in Figure 2, the front wheel steering angle θ at high speed and extremely low speed is
The characteristics of the rear wheel turning angle θ with respect to F are the same as in the example shown in FIG. 1, and a description thereof will be omitted here. In the case of low and medium speeds, the rear wheel turning angle θR increases as the front wheel turning angle θF increases until it reaches the slope change portions P1, P2, and P3, as in the example of FIG. 1, and then decreases. At a certain point, it becomes negative and enters the antiphase region.

At this time, the phase change points C1, C2, and C3 move to the side where the front wheel steering angle θF is larger as the vehicle speed increases, and the slope change portions PL, P2, and P3 move to the side where the front wheel steering angle θF is larger as the vehicle speed increases. changes to the smaller side and the larger side of the rear wheel steering angle.

In addition, the rate of increase in the rear wheel turning angle θR relative to the increase in the front wheel turning angle θF in the range up to reaching the slope change part in the high speed range is not only for changing lanes but also for turning gentle curves even at high speeds. Yes, and if not only G characteristics but also some yaw (ψ) characteristics are required, the maximum value is 0.6.
It is best to keep the angle of inclination to about 31 degrees.

Next, with reference to FIGS. 3 and 4, a specific configuration of a four-wheel steering system that achieves the characteristics as in the above embodiment will be explained.

FIG. 3 shows an example using hydraulic pressure, and FIG. 4 shows an example using links.

In the configuration shown in FIG. 3, the front wheels 1.1 and the rear wheels 2.2 are mechanically separated, and the steering wheel 3 has a steering angle θ□
The output 4a of the front wheel steering angle sensor 4 that detects the front wheel steering angle is inputted to a controller 10 which is a control means of the rear wheel steering device, and the rear wheels 2.2 are steered by this input signal. As is well known, the front wheel steering device moves a rack 6 in the width direction of the vehicle (indicated by arrow A) using a pinion 5 fixed to a steering shaft 3A to which a steering wheel 3 is fixed. The knuckle arms 8 of the left and right front wheels 1.1 are connected to the left and right front wheels 1.1 via tie rods 7.7 that are continuous at both ends.
, 8 around their axes 8a, 8a to rotate the front wheels l,
1 to the left and right. That is,
When the steering wheel 3 in the figure is rotated in the direction of the arrow, the steering shaft 3A is rotated in the direction of the arrow.
The pinion 5 is also rotated in the L direction, and the rack 6 is moved in the L direction. As a result, the knuckle arms 8, 8 of the left and right front wheels 1.1 rotate in the L direction via the link 7.7,
Rotate the front wheel 1.1 in the L direction around the axis 8a, Jla of the knuckle arm 8.8, and steer it to the left. At this time, the front wheel steering angle sensor 4 outputs as an output signal 4a that the steering wheel 3 has rotated by an angle θ8 in the L direction, and inputs this to the front wheel steering angle manual power 10A of the controller 1o of the rear wheel steering device. .

The controller 10 is powered by a power source 11,
In addition to the front wheel steering angle input 10A, a vehicle speed input 10B connected to the vehicle speed sensor 12 and a feedback input 10C connected to the rear wheel steering angle sensor 13 are provided to further control the steering direction of the rear wheels. It includes a steering direction output 10D connected to the solenoid 20 and a hydraulic pump motor output 10E connected to the motor 21A of the hydraulic main pump 21 that controls the steering angle θR of the rear wheels.

The hydraulic main pump 21 includes a pump 21B that discharges oil (hydraulic oil), and this pump 21B is connected to a hydraulic actuator 23 via a steering direction switching valve 22, and between this valve 22 and the pump 21B. An orifice path 24B is provided which short-circuits the oil outward path 24A and the oil return path 24C, and includes an orifice 24b in the middle, and an oil reservoir 25 is arranged in the middle of the oil outward path 24C.

The steering direction switching valve 22 has two inlets connected to an oil outgoing path 24A and an oil return path 24C, and two inlets communicating therewith.
The valve part consisting of two outlets is
Three stop valves 22C (7) are provided in parallel and can be switched freely, and by operating the solenoid 20, these three valve parts 22A, 22B.

22C is the above oil outgoing path 24A1 return path 2
It is designed to be connected to 4C. The two outlets of this valve 22 are connected to the right oil passage 23R and the left oil passage 23L of the hydraulic actuator 23, respectively.
These right oil passage 23R and left oil passage 23L
The outgoing path 24A and the return path 24 are connected via this valve 22.
It is connected to C.

The hydraulic actuator 23 has right and left oil passages 23R.
, 23L causes the rod 26, which is the output shaft thereof, to move in the width direction of the vehicle (indicated by arrow B), and the knuckle arms 2B, 2g of the rear wheels 2.2 are moved through the tie rods 27.27. It rotates around the shafts 28a, 28a, thereby steering the rear wheels 2, 2 left and right.

In the illustrated example, the front wheels 1.1 are steered to the left,
When steering the rear wheel 2.2 in the same phase as the front wheel 1, the steering direction switching valve 22 is set to the positive 22A position, and the oil is diverted from the forward path 24A to the long path 2 through the orifice path 24B.
4C and returns to pump 21B via reservoir 25.

As a result, the front of the orifice 24b, that is, the outward path 24
The pressure on the A side increases, and the pressure on the rear side of the orifice 24b, that is, on the far path 24C side, decreases, causing the positive 2 side of the valve 22 to decrease.
Through the portion 2A, the pressure in the right oil passage 23H becomes higher than the pressure in the left oil passage 23L, and the operating rod 26 of the hydraulic actuator 23 is driven leftward. The amount of drive at this time is determined by the amount of current input to the main pump motor 21A. As a result, the rear wheels 2, 2
is steered to the left via the tie rod 27°27,
The rear wheels 2, 2 are steered in the same phase as the front wheels L.

The front wheels 1.1 are steered to the right, and the rear wheels 2, 2 are turned to the front wheels 1.

When steering in the same phase as l, the steering direction switching valve 2
2 to the reverse 22B position, and open the right oil passage 23R.
The pressure relationship between the left oil passage 23L and the left oil passage 23L is reversed to that described above, and the actuating rod 26 is driven rightward.

In addition, when steering the rear wheels 2.2 in the opposite phase to the front wheels 1.1, the steering direction and the steering direction switching valve 22 are
The correspondence of 2A1 inverse 22B is opposite to the case of same phase as above,
In other words, when steering the front wheels 1.1 to the left, reverse 22
B, when steering the front wheel 1.1 to the right, use the positive 22A.
Set to .

When the steering angle θR of the rear wheels 2, 2 is set to zero, the valve 22
Connect the stop 22C part of the pump 2 to the aisle passage.
1C and the hydraulic actuator 23, the pressure difference between the left and right oil passages 23L and 23R of the hydraulic actuator 23 is eliminated, and the actuating rod 26 is set at a neutral position. At this time, in order to ensure that the actuating rod 26 is set at the neutral position, it is desirable to apply a set load to the actuating rod 26 so that it is mechanically biased to the neutral position.

The steering direction of the front wheels 1.1 is determined by the output 4 of the front wheel steering angle sensor 4.
a to the controller 10, and the rear wheels 2.a.
2 to be in the same phase or in opposite phase with respect to the front wheels 1.1 is determined by the controller 10 according to the vehicle speed detected by the vehicle speed sensor 12 and according to a preset vehicle speed correspondence pattern.

The controller 10 receives an input θ from the front wheel steering angle sensor 4.
H (which is proportional to the steering angle θF of the front wheels 1.1) and the input V from the vehicle speed sensor 12 in FIGS.
A control signal is output according to the characteristics shown in the figure, and the rear wheels 2.2 are steered.

According to the four-wheel steering device using the hydraulic actuator as described above, the rear wheels can be smoothly steered without applying a special load to the steering wheel for four-wheel steering, which is advantageous in practice.

However, hydraulic systems require heavy and costly components such as motors, pumps, hydraulic actuators, and control valves, which increase the weight of the vehicle and
It is not suitable for relatively small vehicles because it complicates manufacturing assembly and causes high costs. Therefore, a four-wheel steering system using a simple link mechanism may be advantageous in practice.

An example of this type of link type mechanism will be explained below with reference to FIG. In the configuration of FIG. 4, the same members as those in the configuration of FIG. 3 are denoted by the same reference numerals, and the explanation thereof will be omitted.

In the link type configuration shown in FIG. 4, a slot 6A for sliding engagement is provided in a part of the rack 6 that is moved in the width direction of the vehicle by the steering wheel 3, and the rear wheels 2.2 are steered from this slot 6A. A link mechanism connects the rod 41 up to the sliding engagement slot 41A,
The rear wheels 2.2 are steered in a desired direction by a desired magnitude of the steered angle θR in accordance with the steered angle θF of the front wheels 1.1.

This link mechanism includes a first L-shaped bar 31 that has one end 31A that is slidably engaged with a sliding engagement slot 6A on the front wheel side and is pivotally supported on a fixed shaft 31a. A connecting lever 32 has one end 32A rotatably connected to the other end 31B of the lever 31, and a swinging lever 33 has one end 33A connected to the other end 32B of the connecting lever 32, and the other end 33B is pivotally supported on a fixed shaft 33a. , the one end 3 of this swing lever 33
A control lever 34 whose one end 34A is rotatably connected to a connecting shaft between the intermediate lever 3A and the other end 32B of the intermediate lever 32.
The sleeve 35 and the screw rod 37 are slidably engaged in the vicinity of the free end of the control lever 34 and are pivotally supported with a rotation shaft 35A on a feed sleeve 36 screwed onto the screw rod 37. a motor 38 for rotating the control lever 34, and a connecting lever 39 whose one end 39A is pivotally supported by a shaft support 34A provided at an intermediate position of the control lever 34.
, and the other end 39B of this connecting lever 39 has one end 40A.
The second L-shaped lever 40 has its other end 40B slidingly engaged with the sliding engagement slot 41A on the rear wheel side.

The motor 38 is connected to a controller 50 and driven by the output of the controller 50.

This controller 50 is supplied with electric power from the electric power unit 1FE51, and the output of the vehicle speed sensor 52 is inputted thereto. Also, in the vicinity of the screw rod 37, this screw rod 3
The position of the feed sleeve 36 screwed into the motor 38
A potentiometer 53 that feeds back to the input of the feed sleeve 36 is arranged to control the position of the feed sleeve 36.

According to the four-wheel steering device equipped with the link mechanism as described above, when the steering wheel 3 is rotated to the left (in the direction of the arrow), the pinion 5, the rack 6, the tie rod 7.7, the knuckle arms 8, 8, and the front wheel 1 .1 all rotate or move in the direction of the arrow, and the front wheels l.

At the same time, the first L-shaped lever 31 is rotated in the L direction around the fixed shaft 31a, and the intermediate lever 3
2 around the fixed shaft 33a.
The control lever 34 is rotated in the L direction around the sleeve 35, and the connecting lever 39 is moved in the L direction, and at the same time, the second L-shaped lever 40 is rotated in the L direction. The steering rod 4 of the rear wheels 2, 2
1 in the L direction, thereby steering the rear wheels 2.2 to the left in the same phase.

When the motor 38 is driven by the controller 50 and the feed sleeve 36 moves downward (to the left of the vehicle) in the figure, and the feed sleeve 36 reaches the position of one end 39A of the connecting lever 39, the control lever 34 Since the connecting lever 39 does not move back and forth (in the left-right direction in the figure) even if it swings around the rotation axis 35A of the rear wheel 2.2, the rear wheel 2.2 is not steered.

When the sleeve 35 is moved further downward by the drive of the motor 38 and exceeds the position of one end 39A of the connection lever 39, the swing of the control lever 34 in the same direction as above (L direction) causes the connection lever 39 to move. Move it forward in the opposite way to the above. This is because the control lever 34 swings around the pivot shaft 35A of the sleeve 35. Therefore, in this case the third L-shaped lever 40
rotates in the direction of arrow R, the steering rods 41 of the rear wheels 2, 2 move in the direction of arrow R, the rear wheels 2, 2 are steered to the right, and four-wheel steering with opposite phase is performed. It turns out.

In this way, the output of the controller 50 causes the motor 38 to
The receiver moves the sleeve 35 through the feed sleeve 36, thereby changing the position of the axis of swing of the control lever 34 and, as a result, changing the direction of movement of the coupling lever 39. The steering direction of the wheels 2, 2 can be changed. Furthermore, the receiver is sleeve 3
By controlling the magnitude of the distance of movement of the rear wheels 1. It becomes possible to arbitrarily control the direction and magnitude of the steering of the rear wheels 2.2 in response to the steering of the rear wheels 2.1.

Since the output from the vehicle speed sensor 52 is input to the controller 50, the steering of the rear wheels 2.2 is performed according to the magnitude of the steering angle θF of the front wheels 1.1 via the above link. It is possible to control the magnitude (including the direction) of the angle θ depending on the characteristics of the steering ratio described in each of the above embodiments.

In this way, even with the link type configuration shown in FIG.
It is possible to realize the rear wheel turning angle characteristics with respect to the front wheel turning angle as in the above-described embodiments. In particular, this link type mechanism is lighter in weight and has a simpler structure than the hydraulic type.
It is easy to assemble and can be manufactured at low cost, making it suitable for small vehicles.

As explained above, the four-wheel steering system of the present invention is controlled so that when the front wheel steering angle is small, the front wheels are in the same phase, and when it is large, the front wheels are in opposite phases, thereby improving driving stability (large G characteristic) and maneuverability. (
In addition, as the vehicle speed increases, the in-phase region increases and the anti-phase region decreases, so the G region increases as the vehicle speed increases. Therefore, even if the front wheel steering angle is large, it will be in the G region, which can further improve driving stability, and the yaw region will increase as the speed becomes lower. It is possible to greatly improve maneuverability.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of a characteristic curve showing the relationship between the front wheel turning angle and the rear wheel turning angle in the four-wheel steering system of the present invention, FIG. 2 is a graph showing the other side of the same characteristic curve, and FIG.
The figure is a schematic diagram showing an example of the four-wheel steering device of the present invention that uses hydraulic pressure, and FIG. 4 is a schematic diagram showing an example of the four-wheel steering device of the present invention that uses a link mechanism. l...Front wheel 2...Rear wheel 3.
... Steering wheel 4 ... Steering angle sensor 5 ...
・Pinion B...Large 7.27・
・・Tie rod 8, 28・・Knuckle arm to
, 50... Controller 12. 52... Vehicle speed sensor 20... Solenoid 21... Main pump 22... Rear wheel steering direction switching valve 23... Hydraulic actuator 25... Reservoir 26... Rear wheel steering rod 31...first L-shaped arm 32...intermediate lever 33...swing lever 34...control lever 3
4A...Shaft support 35...Sleeve 35A...Rotating shaft 36...Feed sleeve 37...Screw rod 38...Drive motor 39...Connection lever 40...No. 2 L-shaped lever 41... Rear wheel steering rod R Fig.

Claims (1)

[Claims] A vehicle that steers rear wheels in response to steering of the front wheels, and in steering the rear wheels such that the ratio of the rear wheel steering angle to the front wheel steering angle increases as the vehicle speed increases. In a four-wheel steering system, the rear wheels are steered in the same phase as the front wheels in a region where the front wheel steering angle is small, and the rear wheels are steered in the opposite phase to the front wheels in a region where the front wheel steering angle is large, and the vehicle speed is increased. control means for controlling the steering of the rear wheels according to rear wheel steering angle characteristics with respect to the front wheel steering angle such that an in-phase steering area of the rear wheels with respect to the front wheels increases and an anti-phase steering area of the rear wheels decreases according to the A four-wheel steering device for a vehicle characterized by: