JPS63305080A - Rear steering gear for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To aim at the miniaturization of a steering gear as a whole by setting up an electric motor for a rear steering ratio variable mechanism, contolling each steering ratio of rear wheels according to each steering action of front wheels, on the same axis with that of a variable mechanism body. CONSTITUTION:In a body 3 of a rear steering ratio variable mechanism 1, its boss part 3a is supported by bearings 21a, 21b free of rotation to a bracket 2, while a motor 6 is fixed to the side of the bracket 2 so as be situated on the same axis Z-Z at the tip side of the boss part 3a. And, the motor output shaft 6a is connected to a first transmission shaft 22 constituting a rotation transmission system 20 via a reduction gear part 23 utilizing a planetary gear mechanism or the like. The motor 6 is designed so as to be controlled for current-energization from a battery 27 by a signal out of a signal controller 26 via a power controller 26b so as to become the frequency conformed to driving condactions of a vehicle and also to be controlled for driving.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a rear wheel steering device for a four-wheel steered vehicle, which allows the front wheels and the rear wheels to be steered in conjunction with the front wheels by a steering operation.

[Conventional technology]

In recent years, four-wheel vehicles have been developed that can improve turning ability at low speeds and improve running stability at medium and high speeds by steering the rear wheels in accordance with the steering IT (steering amount) of the front wheels. Steering vehicles are attracting attention.

For example, when driving at low speeds, the front wheels are steered with a large steering angle, but if the front and rear wheels are steered in opposite phases (reverse direction steering), the turning radius of the vehicle will be minimized and the turning (small turning) performance will be improved. will improve. On the other hand, when driving at high speeds, steering is often performed with a small steering angle, but in this case, it is possible to have the front and rear wheels steered in the same phase (same direction steering) or to set the rear wheels' steering angle to zero. This is preferable in terms of improving the running stability of east vehicles.

As such rear wheel steering devices for four-wheel steering vehicles, various configurations have been proposed in the past. By skillfully combining the above levers and adjusting and controlling the mutual relationship of these levers with an electric motor, a variable rear wheel steering ratio mechanism is created that controls the steering operation of the front wheels by steering operation, that is, the steering ratio of the rear wheels relative to the steering angle. 2. Description of the Related Art A device is known in which a steering force transmission rod system is provided in the middle of a steering force transmission rod system that mechanically transmits the steering operation of the front wheels to the rear wheels by movement in the longitudinal direction of the vehicle body.

According to such a conventional configuration, the electric motor is
By simply controlling the drive with a controller that inputs vehicle speed signals, etc., the rear wheels can be steered by steering the front wheels by freely adjusting the required steering ratio to be in the same phase or in opposite phases. Moreover, it had advantages such as superior structure and operational reliability.

[Problem that the invention seeks to solve]

However, although a certain degree of effectiveness can be expected with the conventional device that has been used in the past, it has had several problems both in terms of its structure and functionality. That is, in the conventional device described above, the main body is rotatably supported on the vehicle body side about a substantially vertical axis (Z axis), and the
an arm portion extending laterally (Y-axis) and connected to a transmission rod from the front wheel side; an electric motor provided on the main body so as to be orthogonal to the main body axis and facing in the longitudinal direction (X-axis) of the vehicle body;
A lever is fixed at a position intersecting the Z wheel of the motor shaft and whose tip is connected to a transmission rod to the rear wheels, and the rear wheel steering system controls the steering ratio of the rear wheels in accordance with the steering operation of the front wheels. It constitutes a variable steering ratio mechanism, and controls the rear wheel steering ratio by changing the lateral position of the connecting point of the rear wheel side transmission rod to the lever with respect to the Z axis by rotating the lever by the electric motor. It was said to be a composition.

According to such a conventional structure, the lever connected to the rear wheel side is fixed on the motor output shaft at the intersection of the X-axis and the Z-axis, and the lever is fixed on the motor output shaft at the intersection of the X-axis and the Z-axis. In order to rotate the lever, it is necessary to pivot the main body toward the vehicle body at both ends on the Z-axis, avoiding the rotation range of the lever. However, due to the limitations on the rear wheel steering ratio, some groups were unable to achieve a large rear wheel steering ratio. This is because the length of this lever is one of the factors that determines the rear wheel steering ratio due to the lever ratio with the length of the arm mentioned above, and by increasing the length of this lever and rotating it, it is possible to steer from the Z axis. It is easy to understand that the rear wheel steering ratio can be increased to the extent that the distance between the two wheels can be secured.

In addition, in order to increase the rear wheel steering ratio, if the length of this lever is increased, it is necessary to increase the distance between the shaft supports at both ends of the main body so that they do not interfere with the lever, and the entire device is There was also the problem that it became largely unified in the axial direction.

For this reason, -): As a result of various research and development conducted by the present inventors regarding the variable rear wheel steering ratio mechanism described above, it is possible to adopt a configuration as shown in FIG. It has been found that by increasing the length of the lever, the rear wheel steering ratio can be increased, and the entire device can be made smaller.

To explain this simply, the variable rear wheel steering ratio mechanism, which is indicated by the reference numeral 1 as a whole, has a U-shaped bracket 2 on the vehicle body side (not shown).
A rotating body 3, which is a rotating shaft member rotatably supported on an axis Z-Z-hi in the vertical direction of the vehicle body through An arm 4 whose tip 4a is connected to a front wheel side rod 5a for transmitting steering force via a pole electric ind, etc. passes through the intersection 0 between the rotating body 3 and the arm 4 and extends along the body axis Z-Z. An electric motor 6 such as a stepping motor, which has an output @6a extending perpendicularly on the axis x-x in the longitudinal direction of the vehicle body and is integrally provided on the side of the rotating body 3, and the rotating body 3. A tip 7a that is rotatably supported on the side and extends laterally of the main body 3.
It is composed of a rear wheel side rod 5b for transmitting steering force and a lever 7 connected via a pole joint or the like.

Note that 8a, 8b; 9 are the brackets 2 of the rotating main body 3.
This is a bearing provided at the shaft support of the motor output shaft 6a within the rotating body 3.

In this example, the lever 7 is connected to the motor output shaft 6.
a at a position spaced apart from the intersection O with the main body axis Z-Z, and the connection point between the tip 7a and the rear wheel side rod 5b is located on the main body axis Z when the rear wheels are not steered (when two wheels are steered). - The lever tip 7a is formed by being displaced by a curved part or the like so that it is located on the extension line of Lever 7 and movable body 3 connected to the wheel side
By selecting the length of the lever 7 appropriately, the lever ratio can be increased compared to the conventional device, and the rear wheel steering ratio can be increased, and the distance between the shaft supports at both ends of the movable body 3 can be increased. This allows the space to be narrowed and the overall size to be reduced.

However, in such a device configuration, the motor 6 attached to the rotating body 3 so as to protrude from the side makes a large turn in response to the turning and steering operations of the front wheels. This adversely affects the rotational movement of the rotating body 3, which not only poses a problem in obtaining an appropriate steering operation for the rear wheels, but also increases the size of the entire device due to the need to secure the turning space. In order to protect the rotational movement of the motor 6 from the outside, it is necessary to attach a cover or the like, which tends to complicate the structure of the cover, and it is also troublesome to handle the connection cords etc. for connecting the motor 6 to the outside. There are various problems in putting it into practical use, and further improvements are required after taking these problems into consideration.

[Means for solving problems]

In order to meet such demands, the rear wheel steering vtt of a four-wheel steering vehicle according to the present invention has a variable rear wheel steering ratio mechanism that controls the steering ratio of the rear wheels according to the steering operation of the front wheels. A rotating body that is rotatably supported by a shaft, an arm that extends laterally from this body and whose tip is connected to a front wheel rod for transmitting steering force, and a rotating body that passes through the intersection of these bodies and the arm. a lever that is rotatably supported on an axis perpendicular to the axis of the main body and whose tip extending to the side of the main body is connected to a rear wheel side rod for transmitting steering force; an electric motor for rotational displacement, and the electric motor is arranged coaxially with the axis of the main body at one end side of the main body, the motor main body is fixed to the vehicle body side, and the motor output shaft is connected to the main body. It is connected to the lever side via a rotation transmission system provided inside.

[Effect]

According to the present invention, the rotary body is rotatably supported on an axis substantially perpendicular to the rotary body by an electric motor disposed coaxially with the rotary body that is swung and rotated by the arm in accordance with the steering operation of the front wheels. This is achieved by controlling the rotation of the lever as appropriate depending on various driving conditions such as vehicle speed and steering angle, as well as the rear wheel turning angle, and displacing the position of the connection point with the rear wheel rod in the left-right direction from the axis of the main body. The connection point of the lever with the rear wheel rod rotates with the rotation of the rotating body, and the steering amount controlled to the required rear wheel steering ratio is transmitted to the rear wheels via the rear wheel rod. This enables appropriate and reliable steering control of the rear wheels.

〔Example〕

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

Figures 1 to 5 show an embodiment of the rear wheel steering device for a four-wheel steering vehicle according to the present invention, and in these figures, the same or corresponding parts as in Figure 8 described above are designated by the same numbers. A detailed explanation will be omitted.

First, the general structure of the entire steering system of a four-wheel steering vehicle will be briefly described using FIG.

are a pair of left and right front wheels (only one is shown), and 11 is a steering wheel *m on the front wheel side for steering these front wheels 10 according to the steering operation of the steering handle 12, and in this embodiment, it is an integral type. The case of the hydraulic power steering 11tR is illustrated. Incidentally, the middle wheels 11a and 11b have a pitman arm and a drag link whose steering bodies are also pulled out, and are configured to be able to transmit steering force to the steering link system 13 side that supports the front wheels 10. Further, in the figure, 11c and lid are an oil pump and an oil tank that serve as a pressure oil supply tank in the power steering device.

14.14 is a pair of left and right rear wheels (only one is shown)
These rear wheels 14 are also rotatably supported by a steering link system 15 having the same configuration as the front wheels 10 described above, and together with this steering link system 15, the rear wheels are steered. A variable rear wheel steering ratio machine mt that constitutes the C station 16 and a linkage type power steering device 2 that generates a steering assist force
! 17, the front wheels 10 are steered in the same phase or in opposite phase with a required steering wheel depending on the amount of steering of the front wheels 10.

The steering link mechanism 1 for these front wheels 10 and rear wheels 14
Between 3.15 and 15, a part of the steering force transmission system to the front wheel lO side (
In this embodiment, a front wheel rod 5a and a rear wheel rod 5b are provided as a steering force transmission rod system 5 extending from the front wheel drive link 1lb) in the longitudinal direction of the vehicle body. The structure is such that steering force is transmitted from the front wheels to the rear wheels by the movement of the wheels. In addition, 18FL.

18b is the linkage type hydraulic power steering for the longitudinal movement of the rear wheel side rod 5b. c, a transmission lever and a transmission rod for transmitting data to 117.

Further, the linkage type power steering device 17 described above has a known configuration, one end of which is fixed to the vehicle body (not shown), and the other end is connected to the steering link mechanism 15 on the rear wheel side. From the rear wheel side rod 5b side to the transmission rod 18b
The steering assist force generated by the power cylinder is transmitted to the rear wheels 14 in accordance with the rear wheel steering ratio transmitted through the rear wheels 14, etc. In addition, 17a and 17b in the figure are an oil pump and an oil tank provided on the vehicle body side and serving as a pressure oil supply source.

In the rear wheel steering device lO of a four-wheel steering vehicle having such a configuration, the steering rod system 5 is provided in the middle of the transmission rod system 5 that transmits the steering operation of the front wheels 10 by the steering operation to the rear wheels 14 side by movement in the longitudinal direction of the vehicle body. As is clear from FIGS. 1 to 5, the rear wheel steering ratio variable mechanism 1 that controls the steering ratio of the rear wheels 14 with respect to the angle in consideration of vehicle speed, etc. is provided with an L-shaped bracket 2 on the vehicle body side (not shown). Axis Z in the downward direction of the vehicle body through
- A rotating body 3 which is a rotating shaft member rotatably supported on Z, and a front wheel whose tip 4a extends sideways (in the Y direction) integrally from this body 3 and which transmits steering force. The arm 4 is connected to the side rod 5a via the ball joint 14, and can be rotated on an axis x-x-hi that passes through the intersection O between the rotating body 3 and the arm 4 and is orthogonal to the axis Z-Z of the body. A lever 7 which is supported and whose tip 7a extends laterally to the main body 3 is connected to a rear wheel side load 7b for transmitting steering force;
and an electric motor 6 for rotationally displacing the motor on the axis x-xh. Here, this rear wheel steering ratio variable mechanism 1
As is clear from FIG. 5, the electric motor 6 described later
is often installed on the vehicle body with the direction facing upward, but in FIG. 1, etc., the top and bottom are shown reversed.

Now, according to the present invention, the above-mentioned rear wheel steering ratio variable mechanism l
In this case, the electric motor 6 is arranged coaxially with the main body axis Z-Z at one end side of the main body 3, and the motor main body 6b including the stator is fixed to the vehicle body side (bracket 2 side), and the motor output shaft 6a is connected to the lever 7 via a rotation transmission system 20 provided inside the main body 3. Furthermore, in this embodiment, the lever 7 is provided at a position spaced apart from the intersection O of the axis X-x-E perpendicular to the main body axis Z-Z, and the lever tip 7a is connected to the rear wheel side rod 5b. The structure is such that the point is located on the extension line 1 of the main body axis Z-Z when the rear wheels 14 are not steered.

In other words, according to the present invention, the electric motor 6, which was rotating together with the rotating body 3 which is oscillated and rotated by the arm 4 in response to the steering operation of the front wheels 10, is rotated coaxially with the main body 2 (2-2).
By arranging it in a fixed manner with respect to the bladder 2, which is the identification side, no turning space is required for the motor 6, and the entire device can be made smaller compared to the conventional structure.
There is no negative effect due to inertia, etc., and since the motor 6 is located on the same axis Z-Z as the main body 3 and does not rotate, the structure is simple and easy to assemble.
It has the advantage that it is only necessary to provide the following items (see figure) as necessary. In particular, in such a device with a fixed motor, there is no problem such as twisting of the external connection cord 6c pulled out from the motor 6, which is a great advantage.
Reference numeral 0 designates a connecting cylindrical body which has a reduction gear portion described later installed therein, and the motor 6 is screwed into one end flange 30a, and the other end flange 30b is screwed one screw into the bracket I2. Fixed.

Here, the problem with adopting such a configuration is that the main body 3 rotates when the front wheel steering operation is transmitted to the arm 4, and the main body 3 and the motor output shaft 6a rotate.
A positional shift occurs in the rotational direction between the two, which causes a problem when rotating and displacing the lever 7 supported on the main body 3 side. However, such a positional shift in the rotational direction can be easily resolved by detecting the positional relationship between the main body 3 and the lever 7 and controlling the drive of the motor 6 using a value calculated based on the detected positional relationship.

Furthermore, according to the present invention, the lever 7, which is rotated together with the main body 3 and the motor 6 described above, is controlled to rotate as appropriate by the motor 6 according to various driving conditions such as vehicle speed and steering angle, rear wheel turning angle, etc. However, by displacing the position of the connection point with the rear wheel side rod 5b in the left-right direction from the main body axis Z-2,
The connection point (7a) of this lever 7 with the rear wheel side rod 5b rotates with the rotation of the rotating body 3, and the steering amount controlled to the required rear wheel steering ratio is applied to the rear wheel. There is also the advantage that the signal is transmitted to the rear wheel 14 side via the wheel side rod 5b, allowing appropriate and reliable steering control of the rear wheels.

According to such a configuration, the function of the variable rear wheel steering ratio mechanism 1 can be appropriately and sufficiently ensured, while problems such as interference between the lever 7 connected to the rear wheel side and the movable body 3 can be avoided. No consideration is required and the length of the lever 7 can be selected as appropriate, making it possible to increase the lever ratio compared to conventional devices and increase the rear wheel steering ratio.
It also becomes possible to downsize the entire device, including the

Here, to briefly explain the operation of the variable rear wheel steering ratio mechanism l having the above-described configuration, first, as shown in FIG. Z-
When the vehicle is in the
Regardless of the steering operation on the O side, the rear wheels 14 are maintained in an unsteered state. This is easily understood because even if the rotating body 3 is rotated by the arm 4 due to the steering operation of the front wheel 10, the lever tip 7a only rotates on the axis Z-Z.

In addition, when the electric motor 6 is driven according to various driving conditions such as vehicle speed and steering angle, and the rear wheel turning angle, and the lever tip 7a is turned in the left-right direction, the front wheel 1O side is turned by the steering operation. Due to the movement of the rotating body 3, the lever tip 7a is aligned with the axis Z.
- Rotates around this axis Z-Z in accordance with the displacement from above Z, and as a result, the rear wheel side rod 5b moves in the longitudinal direction of the vehicle body and turns the rear wheel 14 with an appropriate steering ratio. It is something that can be steered. In this case, the rear wheels are steered in the same or opposite phase to the front wheels depending on the direction in which the lever 7 is tilted, and the steering characteristics can be freely selected by controlling the motor 6 as necessary. It is.

Further, in this embodiment, details of the rear wheel steering ratio variable mechanism 1 described above are as follows. That is, the main body 3 is
As is clear from FIG. 1, etc., the boss portion 3a of the bracket 2 is rotatably supported by bearings 21a and 21b, and is located on the same axis Z-Z at the tip side of the boss portion 3a of the bracket 2. The motor 6 is fixed to the bracket 2 in this manner, and the motor output shaft 6a is connected to the first transmission shaft 22 constituting the rotation transmission system 20 through a reduction gear unit 23 using a planetary gear mechanism or the like. are connected via. Note that this reduction gear part 23 is not necessarily required, and in some cases, the motor output shaft 6a
Of course, it is also possible to connect directly to the first transmission shaft 22.

Further, the first transmission shaft 22 extending inside the boss portion a along the axis Z-Z is arranged inside the main body 3 along the axis Z-Z.
A second transmission shaft 24 is rotatably supported in the direction of the axis x-x perpendicular to the axis XX, and is connected to the lever 7 by transmission gears 25a and 25b such as bevel gears so that rotation can be transmitted. The proximal end of the lever 7 is fixed, so that the lever 7 can be swung in response to the rotation of the motor 6. It goes without saying that the first and second transmission shafts 22, 24, etc. described above are supported by bearings or the like so that they can rotate freely within the main body 3.

Further, the above-mentioned motor 6 is energized by the battery 27 via the power controller 26b in response to a signal from the signal controller 26a so that the rotation speed is determined based on various running conditions of the vehicle, such as vehicle speed and steering angle. The system is configured such that the drive is controlled by the driver and the vehicle is stopped by feeding back the rear wheel steering ratio. Here, 28a in FIG. 5 is a vehicle speed sensor.

28b is a steering angle sensor provided on the steering shaft, and 29 is a steering angle sensor provided on the main body 3 side of the rear wheel steering ratio variable mechanism so as to face the base end of the lever 7 on the axis x-x. This is a rear wheel steering ratio detection sensor provided. According to such a rear wheel steering ratio detection sensor 29, its installation is extremely easy, and
It is possible to detect the rear wheel steering ratio with high precision, which has great advantages. Moreover, the input signal to the controller 26a described above is not limited to the vehicle speed and steering angle described above,
For example, lateral G applied to the vehicle body may be used.

Furthermore, according to the variable rear wheel steering ratio mechanism l described above, as is clear from FIG. Even if the motor 6 is driven and the lever 7 is rotated due to a change in the motor 6, there is no effect on the rear wheels and the rear wheels 14 can be maintained in a straight traveling state.

By the way, according to the rear wheel steering device 16 including the rear wheel steering ratio variable mechanism lt- configured as described above, the rear wheel 1
A stopper is required to mechanically lock the amount of steering on the 4th side within a predetermined range.
As is clear from FIG. 6, a second
It is preferable to provide a stopper member 31 having a V-groove 31a for sandwiching the lever 7 provided on the transmission shaft 24U from both sides. According to such a configuration, the transmission of external force from the rear wheel 14 side to the lever 7 described above is smaller than that to the steering link mechanism 15 etc. on the rear wheel side, so that the force acting on the stopper member 31 is reduced. This has the advantage that the stopper structure can be reduced to ms compared to the conventional one.

Further, in the rear wheel steering device 116 having the above-described configuration, a fail-safe mechanism is required that locks the rear wheel steering operation at a neutral position and performs two-wheel steering of only the front wheels in the event of a failure in the electrical system or the like. However, as a fail-safe measure, for example, as shown in FIG. A pair of springs 32 interposed between
It is preferable to use a and 32b. In a fail-safe mechanism using such a spring,
Like the stopper described above, it has the advantage of being able to maintain the rear wheel steering system in a neutral state with a small force, and can be even more effective when used in combination with the stopper member 31 described above.

Note that the present invention is not limited to the structure of the embodiment described above, but
Rear wheel steering equipment, including the rear wheel side steering link mechanism 13.15! ! 116 The shape, structure, etc. of each part may be modified or changed as appropriate, and various modifications may be considered. Although the case where the cover 19 for protecting the electric motor 6 is fixedly provided on the bracket 2 side is shown, the present invention is not limited to this, and when the protection is not necessary due to the location of the motor 6 etc., It is possible to simply provide a boot on the motor body to protect only the cord etc. pulled out from the motor 6.Also, various rotation transmission systems using bevel gears etc. that transmit the rotation from the motor 6 to the lever 7 can be used. Possible variations are as follows.

Furthermore, in the above-described embodiment, in order to obtain rear wheel steering force in the rear wheel steering device 16, the power steering device 17 is used as a steering assist means similarly to the front wheel IO side, For example, it can be effective in preventing negative effects on steering operation, which can be a problem when large vehicles are heavy and require large steering resistance when turning the rear wheels. Alternatively, a manual steering mechanism may be used.

〔Effect of the invention〕

As explained above, according to the rear wheel steering device for a four-wheel steering vehicle according to the present invention, in the variable rear wheel steering ratio mechanism that controls the steering ratio of the rear wheels according to the steering operation of the front wheels, The electric motor is rotated toward the vehicle body to swing and displace the lever on the rear wheel side, which is tiltable with respect to the rotating body rotated by the arm of the main body. The motor is fixed on the vehicle body side on the same axis as the dynamic axis, and the motor output shaft is connected to the lever side via the rotation transmission system provided within the main body, so the structure is simple and inexpensive. First, while the function as a variable rear wheel steering ratio mechanism can be properly and sufficiently secured, there is no need for a space for the motor to operate, the overall size can be reduced, and it is easy to assemble. Eliminates the adverse effects of inertia caused by motor turning, and enables appropriate and reliable rear wheel steering ratio control.
Furthermore, problems such as kinking, which had been a problem in the past, in the pull-out portion of the external connection cord drawn out from the motor are eliminated, and there are various excellent effects such as excellent reliability of each part.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a variable rear wheel steering ratio mechanism showing an embodiment of the rear wheel steering device for a four-wheel steered vehicle according to the present invention, FIG. 2 is a side view thereof, and FIG. 3 is the same as that shown in FIG. FIG. 4 is a plan view of FIG. 1, FIG. 5 is a schematic perspective view showing the overall steering system configuration of a four-wheel steering vehicle, FIG. 6 and FIG. FIG. 8 is a schematic side view showing an embodiment of the present invention, and FIG. 8 is a schematic perspective view of a conventional variable rear wheel steering ratio mechanism. l... Rear wheel steering ratio variable mechanism, 2... Bracket, 3... Rotating body, 4... φ arm, 5a, 5b
...Front and rear wheel side ports constituting the steering force transmission rod system, 6...Electric motor, 6a...Output shaft, 6b...Motor body, 6c... ...External connection cord, 7...Lever, lO...Front tll...
...Front wheel side steering device, 12... Steering handle, 13... Front wheel side steering link mechanism, 14...
・Rear wheel, 15... Rear wheel side steering link mechanism, 16.
... Rear wheel steering device, 17... Hydraulic power steering device on the rear wheel side, 18a, 18b... Transmission lever and transmission rod, 19... Protective cover, 20...・Rotation transmission system, 22.24...first and second transmission shafts, 25a, 25b...transmission gears such as bevel gears, 2
6a, 26b---controller, 28a-
...Vehicle speed sensor, 28b...Steering angle sensor, 29
... Rear wheel steering ratio detection sensor, 30 ... Connection cylinder. Patent applicant: Mekashakkiki Co., Ltd. Agent: Masatsuna Yamakawa (and 2 others) Figure 6 Figure 7

Claims (2)

[Claims] (1) A rotating body that is pivotably supported on the vehicle body side, an arm that extends laterally from this body and whose tip is connected to a front wheel rod for transmitting steering force, and these bodies and the arm. a lever that is rotatably supported on an axis that passes through an intersection with the main body axis and that is orthogonal to the main body axis, and whose tip that extends to the side of the main body is connected to a rear wheel side rod for transmitting steering force; A variable rear wheel steering ratio mechanism includes an electric motor that rotationally displaces the lever on the axis, the electric motor is disposed coaxially with the axis of the main body at one end side of the main body, and the motor main body is A rear wheel steering device for a four-wheel steered vehicle, characterized in that the device is fixed to a vehicle body side, and a motor output shaft is connected to the lever side via a rotation transmission system provided in the main body. (2) The lever is rotatably provided at a position spaced apart from the intersection on the axis perpendicular to the axis of the rotating body, and
The four-wheel vehicle according to claim 1, wherein the connection point between the tip of the lever and the rear wheel rod is located on an extension of the main body axis when the rear wheels are not steered. Rear wheel steering device for steered vehicles.