JPH09132160A - Rear wheel steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the drive shaft of an actuator from generating unexpected bending moment even if relative positional errors are generated among a plurality of fitting positions, in a rear wheel steering device fitted to a vehicle body at a plurality of positions spaced in the lateral direction of a vehicle. SOLUTION: Right and left tie rods 132 are connected to each other by a connecting body of a first relay rod 154, a second relay rod 156, and the drive shaft 60 of an actuator 50 through ball joint 170, 180. A relay rod housing 160 supporting the first relay rod 154 movably in the axial direction is fitted to the side rail 38 of a subframe 30, meanwhile, the actuator housing 52 of the actuator 50 is fitted to the front cross member 32 of the subframe 30, and if a relative positional error is generated between these fitted positions, the error is absorbed by the ball joints 170, 180.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a four-wheel vehicle, and more particularly to an improvement of a mechanical section of the rear wheel steering system.

[0002]

2. Description of the Related Art Generally, a four-wheeled vehicle has left and right front wheels as steering wheels, and a steering angle is changed according to a driver's intention.
Further, it has already been performed that the left and right rear wheels can be steered to actively control the behavior of the vehicle.

A device for steering the rear wheels generally includes left and right wheel supports, left and right steering rods, and actuators, as described in Japanese Patent Application Laid-Open No. 2-99463. Is composed of. The left and right wheel supports are attached to the vehicle body such that the left and right rear wheels are rotatable and rotatable about substantially vertical straight lines. Further, the left and right wheel supports are provided with left and right steering arms for giving steering angles to the left and right rear wheels, respectively. Each of the left and right steering rods is connected to one end of each steering arm so as to be bendable by each first joint. The actuator consists of (a) an actuator housing mounted on the vehicle body, and (b)
A drive shaft that is supported by the actuator housing so as to be movable in the axial direction and has both ends protruding from the actuator housing, and each end of the drive shaft can be bent by the second joint to the other end of each steering rod. It is configured to include a connected component and (c) a drive source that drives the drive shaft in the axial direction. The drive source is, for example, an electric motor or a hydraulic control device.

[0004]

The portion of the rear wheel steering system that connects the left and right steering rods to each other, that is, the actuator, is attached to the vehicle body at a plurality of locations separated in the axial direction thereof. At this time, when a plurality of mounting positions can be provided in the same constituent member of the vehicle body, the relative positional accuracy between the mounting positions can be relatively easily improved. However, when it is necessary to provide a plurality of mounting positions across a plurality of different constituent members of the vehicle body, it is relatively difficult to improve the relative positional accuracy between the mounting positions. In any case, the longer the distance between the plurality of mounting positions is, the more difficult it is to improve the relative positional accuracy between the mounting positions.

On the other hand, as described in the above publication, in the conventional rear wheel steering system, the left and right steering rods are connected to each other by one drive shaft, and the drive shaft is bent. Is not allowed. Therefore, in the conventional rear wheel steering system, when a relative position error occurs between a plurality of mounting positions, mounting distortion occurs on the drive shaft and an unexpected bending moment is constantly applied to the drive shaft. As a result, the driving resistance of the actuator increases and the durability of the actuator decreases.

Therefore, in both the first and second inventions according to claims 1 and 2, the left and right steering rods are connected to each other by a plurality of bendable shaft members to absorb a relative position error between a plurality of mounting positions. By making it possible, it was made as a subject to solve the above-mentioned problem.

[0007]

[Solution Means, Actions and Effects of the First Invention]
In order to solve the problem, the left and right wheel supports, the left and right steering rods, the actuator housing,
In a rear wheel steering system including a drive shaft and an actuator including a drive source, a connection between at least one of both ends of the drive shaft and the steering rod is axially movable to a relay rod housing attached to the vehicle body. The other end of the first relay rod is supported and has both ends projecting from the relay rod housing, and the steering rod is bendably connected to the one end by the second joint, and the drive shaft is attached to the one end. Is connected to the other end of the second relay rod that is bendably connected by the third joint by a relay rod connecting body that is bendably connected by the fourth joint.

Therefore, in the rear wheel steering system according to the present invention, the portions of the rear wheel steering system that connect the left and right steering rods are attached to the vehicle body at two locations, the actuator housing and the relay rod housing. The steering rods are connected to each other not by one non-flexible shaft member but by a connecting body of the drive shaft and the relay rod connecting body, that is, a plurality of bendable shaft members. As a result, for example, because the mounting position of the actuator housing and the mounting position of the relay rod housing are not provided in the same component member of the vehicle body, and the distance between the mounting positions is long, the mounting positions between the mounting positions are different. Even if a relative position error occurs, the error is absorbed by the bending of the plurality of shaft members.

As a result, according to the present invention, even if a relative position error occurs between a plurality of mounting positions of the rear wheel steering device, an unexpected bending moment does not always act on the drive shaft, and the actuator of the actuator does not move. The drive resistance does not increase and the durability of the actuator is improved.

The present invention will be supplementarily described below. [1] As a mode of "connecting at least one of both ends of the drive shaft to the steering rod by a relay rod connecting body", for example, as shown in FIG.
In the rear wheel steering system in which the actuator 308 having the actuator housing 306 attached to the vehicle body 304 is located between 00 and 302, one end portion 312 of the drive shaft 310 is connected to one steering rod 302 by the second joint 313. The other end 314 is a first rod supported by a relay rod housing 316 attached to the vehicle body 304.
The relay rod connecting body of the relay rod 318 and the second relay rod 320 may be connected to the other steering rod 300. In the relay rod connection body, the first relay rod 318 is connected to the steering rod 300 by the second joint 313, and the second relay rod 320 is connected.
The other end of the drive shaft 310 is connected to the other end 314 of the drive shaft 310 by the third joint 322, and the other end of the second relay rod 320 is connected to the first relay rod 318 by the fourth joint 324. [2] As a mode of "connecting at least one of both ends of the drive shaft to the steering rod by a relay rod connecting body", as shown in FIG. 11, one end portion 312 of the drive shaft 310 is also changed to that shown in FIG. In the same manner as the other end portion 314 in, the steering is performed via the second relay rod coupling body of the third relay rod 342 and the fourth relay rod 344 supported by the second relay rod housing 340 attached to the vehicle body 304. A mode in which it is connected to the rod 302 can also be adopted. [3] The present invention can be applied not only to the case where the actuator housing and the relay rod housing are attached to a plurality of different constituent members of the vehicle body, but also to the case where they are attached to the same constituent member.

[0011]

[Solution Means, Actions and Effects of the Second Invention]
The rear wheel steering system according to claim 1, wherein at least one of a bending angle between the first relay rod and the second relay rod and a bending angle between the second relay rod and the drive shaft is within a certain range. It is characterized in that it is provided with a bending angle limiting means for limiting.

For example, as shown in FIG. 10, before the actuator housing 306 and the relay rod housing 316 are attached to the vehicle body 304, the drive shaft 310 and the first
When the relay rod 318 and the second relay rod 320 are connected to each other and the connected body is attached to the vehicle body 304,
It is desirable that the connecting body does not bend more than necessary in order to improve the mountability.

Prior to mounting on the vehicle body 304, the first relay rod 318 and the second relay rod 320 are coupled to each other, and the coupling body and the actuator housing 306.
When and are attached to the vehicle body 304 separately,
The fact that the second relay rod 320 does not bend more than necessary with respect to the first relay rod 318 attached to the vehicle body 304 facilitates the subsequent connection work between the second relay rod 320 and the drive shaft 310. Desirable for.

Further, prior to mounting on the vehicle body 304,
The actuator 308 and the second relay rod 320 are coupled to each other, and the coupling body and the relay rod housing 316.
(When the first relay rod 318 is supported) and the vehicle body 304 are separately attached to the vehicle body 304,
The second relay rod 320 does not bend more than necessary with respect to the drive shaft 310 attached to the second relay rod 320 and the first relay rod 318.
It is desirable to facilitate connection work with.

Based on such knowledge, in the rear wheel steering system according to the second aspect of the present invention, the bending angle restricting means causes the bending angle between the first relay rod and the second relay rod, the second relay rod and the drive shaft to change. And at least one of the bending angles is limited to a certain range.

Therefore, according to the present invention, while the plurality of shaft members connecting the left and right steering rods can be bent, it is possible to improve the mountability of the rear wheel steering device to the vehicle body.

The present invention will be supplementarily described below. [1] The “bending angle limiting means” is, for example, a first bending rod for limiting the bending angle between the first relay rod and the second relay rod.
It is possible to adopt a mode in which a member whose relative displacement with respect to the relay rod is prevented is engaged with the second relay rod, and bending of the first relay rod and the second relay rod is mechanically limited.
For example, the member may extend from the first relay rod or may extend from the relay rod housing. [2] In addition, the "bending angle limiting means" includes the first relay to limit both the bending angle between the first relay rod and the second relay rod and the bending angle between the second relay rod and the drive shaft. In a state where the rod, the second relay rod, and the drive shaft are connected to each other, a member whose relative displacement with respect to the first relay rod is prevented is engaged with the actuator housing to limit a bending angle between the first relay rod and the actuator. However, it is also possible to limit both the bending angle between the first relay rod and the second relay rod and the bending angle between the second relay rod and the drive shaft. The member can also extend from the first relay rod or extend from the relay rod housing, for example. [3] Further, the "bending angle limiting means" may be, for example, a mode in which the bending angle is always limited, or a mode in which the bending angle is limited only when a certain condition is satisfied. Here, in the case of “when a certain condition is satisfied”, for example,
It is possible to select a case where the work of connecting the second relay rod and the drive shaft is performed, and it is possible to prevent the "bending angle limiting means" from operating after the end of the connecting work.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Some preferred embodiments of the present invention will be listed below in the same expression form as the claims. (1) The rear wheel steering system according to claim 1 or 2, wherein at least one of the drive shaft, the first relay rod, and the second relay rod is adjustable in axial length. A rear wheel steering device characterized in that When the rear wheel steering device is mounted on the vehicle body at a plurality of positions separated in the vehicle left-right direction, if there are mounting position errors at these plural positions, the errors are absorbed by the relay rod connecting body. It is possible that the steering angles of the wheels do not match each other. Therefore, in this embodiment, after the rear wheel steering device is mounted on the vehicle body, the length of the drive shaft or the relay rod can be adjusted according to the actual mounting position error, so that the steering angles of the left and right rear wheels can be simplified. Allows you to match. (2) A vehicle in which the rear wheel steering system according to claim 1 or 2 is mounted, and the driving torque of the engine is distributed to the left and right rear wheels by a differential device to drive the left and right rear wheels, wherein the actuator is In the space between the underbody of the vehicle and the differential device, it is mounted in a portion located in front of the vehicle from a vertical plane that passes through the rear end of the differential device and extends in the vehicle left-right direction. vehicle. As described in the above publication, in the conventional rear wheel steering system,
The actuator is mounted on the rear side of the differential device in the vehicle. On the other hand, in a vehicle, a muffler to which exhaust gas from the engine is generally guided is also arranged on the rear side of the differential device.
Therefore, the actuator is arranged at a position close to the muffler, the muffler becomes a heat source of the actuator, and there is a problem that sufficient heat countermeasures must be taken for the actuator. On the other hand, in the vehicle according to the present embodiment, in the space between the underbody of the vehicle and the differential gear, the actuator passes through the rear end of the differential gear and extends from the vertical plane extending in the vehicle left-right direction to the vehicle. It will be installed in the front part. Since the actuator is mounted so as to be located in front of the vehicle from the conventional mounting position, therefore, according to the present embodiment, the actuator is mounted away from the muffler generally arranged on the rear side of the differential device in the vehicle. It becomes possible. As a result, according to the present embodiment, since the actuator is mounted on the vehicle away from the heat source, the actuator is less likely to be affected by heat, and it is possible to omit some of the heat countermeasures that were necessary until now. The effect that the device cost can be reduced and the device size can be reduced easily can be obtained. Hereinafter, this embodiment will be supplementarily described. [1] "Underbody" is a general term for floors such as passenger rooms and luggage compartments. [2] Further, the "underbody" can have a structure with a frame or a structure without a frame. In the case of a structure with a frame, for example, there are an integral type in which a front wheel portion and a rear wheel portion are integrated, and a partial type independent from each other. An example of a partial frame is a subframe. (3) The vehicle according to claims 1 and 2 and the rear wheel steering system according to the embodiment (1) or the embodiment (2), wherein the actuator is
The drive source includes a motor having a rotary shaft, a drive shaft linearly displaced in the axial direction, and a motion conversion mechanism for converting rotation of the rotary shaft into linear motion of the drive shaft, and the rotary shaft and the drive shaft. And the motion converting mechanism are coaxial type having a common axis, and the actuator is mounted in a posture in which the common axis is parallel to the vehicle left-right direction. In this embodiment, the actuator is
The rotation shaft of the motor, the drive shaft, and the motion conversion mechanism are coaxial type having a common axis. Therefore, according to the present embodiment, as compared with a case where the actuator is designed such that the rotary shaft and the drive shaft are arranged in parallel to each other in the diametrical direction, the diametrical dimension of the actuator as a whole is reduced. Can be shortened easily.
Further, in this embodiment, the coaxial actuator is mounted on the vehicle in such a posture that the common axis is parallel to the vehicle left-right direction. Therefore, according to the present embodiment, the actuator can be mounted in a portion of the space extending in the vehicle left-right direction between the underbody and the differential device, where the vehicle front-rear dimension is relatively short. By the way, in a vehicle, the differential device is generally arranged in a space below an underbody of the vehicle, in a portion facing a center floor (see the embodiment) on the front side and a rear floor (see the embodiment) on the rear side. . In addition, a rear tire floor is generally provided with a spare tire pan (see the embodiment) that is locally recessed below the vehicle in order to form a spare tire house that houses the spare tire. Under such circumstances, conventionally, as described in the above publication, the actuator has a rear side of the differential device, that is, a space between the rear end of the differential device and the spare tire pan (hereinafter referred to as a rear space). Was said to have been installed. However, in order to mount the actuator in the rear space of the differential, it is necessary to widen the rear space, but if it is attempted to widen the space between the front part of the differential and the center floor (hereinafter , The front side space) becomes narrower, while in order to widen the front side space, the position of the center floor has to be shifted to the front of the vehicle, but if this is done, the cabin space of the vehicle will be sacrificed. is there. That is, when the actuator is arranged in the rear space of the differential device, there is a problem in that the mounting of the actuator in the vehicle and the securing of the passenger compartment cannot be sufficiently achieved at the same time. On the other hand, according to the present embodiment, it is easy to shorten the dimension of the actuator mounted in the vehicle in the vehicle front-rear direction, and therefore, the actuator is mounted above or in front of the differential between the underbody and the differential. Even if the actuator is mounted in the front space where it is located, the passenger space of the vehicle is not so much sacrificed. Further, the actuator can be mounted even in a vehicle where it has not been possible to mount the actuator to secure a cabin space in the past, and the range of vehicle models that can be mounted is expanded. Hereinafter, this embodiment will be supplementarily described. [1] The “coaxial actuator” may have a structure in which at least the motor rotation shaft and the drive shaft are arranged on the same straight line at different axial positions. [2] Further, the structure may be such that they are arranged on the same straight line at the same axial position. (4) In the vehicle according to embodiment (2) or (3), the actuator is sandwiched by a pair of vertical surfaces extending in the vehicle left-right direction passing through the front end and the rear end of the differential device, respectively. Vehicle mounted on the part. (5) The vehicle according to any one of the embodiments (2) to (4), wherein the differential device and the rear suspension device are attached to a subframe that is a component different from the underbody, and the rear suspension device is interposed via the subframe. In the so-called subframe system, which is attached to the underbody, the actuator is attached to a front crossmember located on the front side of the differential gear in a state of being attached to the vehicle among a pair of crossmembers that are constituent elements of the subframe. Vehicle. (6) In the vehicle of embodiment (5), the actuator is of the coaxial type, and if the actuator is removed from the subframe, the actuator is removed without removing the differential device and the subframe from the vehicle. A vehicle that can be taken out to the outside of the vehicle by pulling out the vehicle in the left-right direction through the space between the underbody and the subframe. (7) The vehicle according to any one of the embodiments (2) to (6), wherein the actuator is mounted at a position offset in the vehicle left-right direction with respect to the differential device.
That is, the actuator is mounted on the vehicle so as to overlap the differential in the vehicle front-rear direction, and if mounted in this way, it extends in the vehicle left-right direction between the underbody and the differential, and The actuator can be mounted on the vehicle by more effectively utilizing the space having a relatively short dimension in the vehicle front-rear direction. (8) Claims 1 and 2, the rear wheel steering system of the embodiment (1), the actuator in the vehicle of the embodiments (2) to (7), wherein: (a) a hollow cylindrical actuator housing;
(b) a drive shaft coaxially arranged in the actuator housing and linearly displaced in the axial direction, and (c) a motor coaxially arranged in the actuator housing and having a hollow rotating shaft, The drive shaft is inserted coaxially with the hollow hole of the rotary shaft,
(d) An actuator, which is disposed in the actuator housing and includes a motion conversion mechanism that converts the rotation of the rotary shaft into the linear motion of the drive shaft. (9) The actuator of embodiment (8), further comprising:
An actuator including a speed reducer, which is provided between the motor and the motion conversion mechanism and reduces the rotation of the motor and transmits the rotation to the motion conversion mechanism. (10) The actuator according to the embodiment (8) or (9), wherein the motor is a brushless motor or a brushed motor in which a hollow stator and a rotor are coaxially arranged. An actuator in which the drive shafts are coaxially penetrated through and. The stator and the rotor can be arranged on the same straight line at the same straight line position or on the same straight line at different straight line positions. (11) The actuator according to any one of the embodiments (8) to (10), wherein the motion conversion mechanism is (i) a male screw coaxially coupled to the drive shaft, and (ii) rotatable in the actuator housing. And a nut that is supported immovably in the axial direction, the male screw is screwed directly or indirectly via a ball, and the rotary shaft of the motor is directly or indirectly via the speed reducer, An actuator including a nut that is coaxially coupled. (12) The actuator according to (9) to (11), wherein the reduction gear has a sun gear arranged in the center, three or more planetary gears meshing with the sun gear are arranged on the outside thereof, and the planetary gears are arranged by a carrier. , Each of which is capable of rotating and is relatively displaceable relative to each other, and the planetary gears are configured to include at least one planetary speed reducer that meshes with a non-rotatable internal gear, and the sun gear has a rotation shaft of the motor. An actuator that is coaxially coupled, and the motion conversion mechanism is coaxially coupled to a carrier. (13) The actuator according to the embodiment (12), wherein the speed reducer includes two planetary speed reducers and two planetary speed reducers arranged in series along the drive shaft, the sun gear being one of the two planetary speed reducers. An actuator in which the rotation of the carrier of the input speed reducer into which the rotation of the rotary shaft is input is input to the sun gear of the output speed reducer in which the rotation of the carrier is input into the motion conversion mechanism. (14) The rear wheel steering system according to claim 2, embodiments (1) to (13), wherein the bending angle limiting means extends from the relay rod housing in parallel to the axial direction of the relay rod housing. A rear wheel steering system comprising a rigid cover that covers the relay rod from the outside with a radial gap. In the present embodiment, the second relay rod is covered with a rigid cover extending from the relay rod housing from the outside with a radial gap. This allows the second relay rod to bend with respect to the first relay rod while the radial clearance is present, and after the second relay rod disappears, the second relay rod mechanically engages with the rigid cover and bends further. Is prevented. Therefore, the bending angle between the first relay rod and the second relay rod is limited within a certain range. The "rigid body cover" may be formed integrally with the relay rod housing or may be formed separately. (15) The rear wheel steering system according to claim 2, embodiment (1) to (13), wherein the bending angle limiting means extends from (a) the relay rod housing in parallel to an axial direction thereof. A rigid cover that covers at least the second relay rod from the outside of the second relay rod and the actuator housing with a radial gap, and (b) is provided between the rigid cover and the actuator housing, and bends both. A rear wheel steering device including an elastic body that allows the above-mentioned bending angle but limits the bending angle within a certain range. In this embodiment, the bending angle between the relay rod housing and the actuator housing is limited to a certain range by the rigid body cover and the elastic body extending from the relay rod housing, and as a result, the bending between the first relay rod and the second relay rod is limited. Both the angle and the bending angle of the second relay rod and the drive shaft are limited to a certain range. Further, in this embodiment, since the bending of the relay rod housing and the actuator housing is allowed within a certain range, a relative position error occurs between the vehicle body mounting position of the relay rod housing and the vehicle body mounting position of the actuator housing. However, the error is absorbed. Hereinafter, this embodiment will be supplementarily described. [1] The “rigid body cover” can be configured integrally with the relay rod housing or can be configured separately. [2] The “elastic body” is arranged so as to fill the axial gap between the rigid body cover and the actuator housing when the rigid body cover extends to the second relay rod but not to the actuator housing. To be done. [3] Further, the "elastic body" is arranged so as to fill the radial gap between the rigid body cover and the actuator housing when the rigid body cover also extends to the actuator housing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, more specific embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a side view showing a state in which a differential device for left and right rear wheels is mounted on a rear wheel drive type four-wheeled vehicle (hereinafter referred to as a vehicle) equipped with a rear wheel steering device, and FIG. 2 is a plan view. It is a figure.

In FIG. 1, reference numeral 10 indicates a differential device. In the differential device 10, the drive torque of the engine is input via the transmission and the propeller shaft, and the input drive torque is input to the left and right rear wheels 12 (see FIG. 2).
To drive the rear left and right wheels 12,
The left and right rear wheels 12 are allowed to rotate in the presence of a difference in rotational speed between them. The differential device 10 is the underbody 1 of the vehicle.
3 is attached.

The underbody 13 is constructed to include a front floor (not shown), a center floor 16 and a rear floor 18. The front floor is a portion that constitutes the floor of the passenger compartment that extends in the vehicle front-rear direction. The center floor 16 is a portion that curves and extends along the wheel house arch 20 of the left and right rear wheels 12 from the rear end of the front floor toward the rear of the vehicle. The rear floor 18 is a portion extending from the rear end of the center floor 16 toward the rear of the vehicle, and a part of the rear floor 18 is recessed downward in the vehicle to form a spare tire house 21. A space is formed between the center floor 16 and the spare tire pan 22 on the outside of the vehicle, and the differential device 10 is arranged in the space.

The differential 10 is not directly attached to the underbody 13 but is attached via the sub-frame 30. FIG. 3 is a plan view showing only the subframe 30. As is apparent from the drawing, the subframe 30 is joined to each other by welding in a state where a pair of cross members 32 and 34 extending parallel to each other and a pair of side rails 36 and 38 extending parallel to each other intersect each other. It is composed by.

The subframe 30 is on the underbody 13,
As shown in FIGS. 1 and 2, the cross member 32 is mounted on the front side of the vehicle, and the cross member 34 is mounted on the rear side of the vehicle. That is, the cross member 32
Can be called a front cross member, and the cross member 34 can be called a rear cross member. Subframe 30 is underbody 13, mount cushion 40
Mounted in an elastically supported state by means of the differential 1
0 is the subframe 30 and the mount cushions 42, 4
4 is attached in an elastically supported state. It should be noted that the sub-frame 30 is equipped with a rear suspension device (not shown) at a portion located on the right side of the vehicle and a portion located on the left side of the sub-frame 30 when the vehicle is mounted.

The rear wheel steering system comprises an actuator 50, the details of which are shown in cross section in FIG.

The actuator 50 has an actuator housing 52 having a hollow cylindrical shape. The actuator housing 52 is configured by closing both ends of a thin-walled cylindrical main body portion 54 (for example, made of pipe) having the same diameter and extending straight, by a pair of closing members 56, 58. A drive shaft 60 is coaxially passed through the actuator housing 52. Drive shaft 60
Is positioned by the respective closing members 56 and 58 so as to be coaxial with the actuator housing 52 and supported slidably in the axial direction. Also, the drive shaft 60
Is spline-fitted with the closing member 56 to prevent rotation with respect to the actuator housing 52.

A brushless motor 64 (hereinafter, simply referred to as a motor) is arranged in the actuator housing 52. The motor 64 is a rotor 6 having a cylindrical shape.
6 and the stator 68 are coaxially arranged and arranged so that their diametrical directions coincide with each other. Rotor 66
4 has four or substantially four permanent magnets mounted in a state in which the polarities of the permanent magnets alternate in the circumferential direction between the N pole and the S pole.
It is considered to be extreme. The stator 68 corresponds to the rotor 66, and is of a three-pole type in which the amateur coil 70 is mounted in a state in which the polarity alternates between the N pole and the S pole in the circumferential direction. The stator 68 is arranged outside the rotor 66 with a suitable magnetic gap. On the other hand, the drive shaft 60 is coaxially inserted into the hollow hole of the rotor 66. The rotor 66 is arranged on the outer peripheral surface of the drive shaft 60 with an appropriate gap, and both ends thereof are arranged in the actuator housing 52.
It is rotatably supported by a pair of bearing mechanisms 74 mounted on the shaft so as not to move in the axial direction. Therefore, when the amateur coil 70 of the stator 68 is excited, the rotor 66 is rotated accordingly.

In addition, according to the present invention, for example, the brushless motor 64 may be replaced by a brushed motor, the rotor 66 may be made of permanent magnets of a number less than four, or the number of rotors of more than four may be used. It can also be carried out by using a permanent magnet.

The rotation of the motor 64 is converted into a linear motion by a screw mechanism 78 as a motion converting mechanism, and the drive shaft 60 is rotated.
Is transmitted to A screw 80 on a part of the outer peripheral surface of the drive shaft 60
Is formed, and a nut 82 screwed to the male screw 80 is rotatably and immovably supported by the actuator housing 52. Those male screw 80 and nut 82
The screw mechanism 78 is configured by screwing with. In this embodiment, both the male screw 80 and the nut 82 are trapezoidal screws.

In the present embodiment, the rotation of the motor 64 is not directly transmitted to the screw mechanism 78, but is transmitted via the reduction gear 90 in order to boost the rotational force of the motor 64.

The speed reducer 90 has a structure in which two planetary speed reducers 92 and 94 are connected in series. As is well known, the planetary type speed reducers 92, 94 are arranged between (a) one sun gear 100, (b) one ring gear 102, and (c) the sun gear 100 and the ring gear 102. Multiple planetary gears 1
04, and (d) a carrier 106 that rotatably supports each planetary gear 104 while keeping their relative positional relationship constant.

The two ring gears 102 are fixed to the actuator housing 52. 2 sun gears 10
Both 0s are hollow, and the drive shaft 60 is coaxially passed through them. As a result, the two planetary reduction gears 92 and 94 are arranged side by side in the axial direction of the drive shaft 60. . Those planetary type speed reducers 92, 9
Among the four, those closer to the rotor 66 are referred to as the input side speed reducer 92, and those closer to the screw mechanism 78 are referred to as the output side speed reducer 94. In the input side speed reducer 92, the sun gear 100
Is rotatably connected to the rotor 66 integrally therewith, while in the output-side speed reducer 94, the sun gear 100 is rotatably connected integrally to the carrier 106 of the input-side speed reducer 92. The carrier 106 of the speed reducer 94 is rotatably fixed to the nut 82 integrally therewith.

Therefore, when the rotor 66 is rotated, the sun gear 10 in the input-side speed reducer 92 is correspondingly rotated.
0 and the planetary gear 104 are rotated, and the rotation speed of the sun gear 100 is reduced, so that the carrier 10 is rotated.
6 is rotated. Further, along with the rotation, the sun gear 100 and the planetary gear 104 are rotated in the output reduction gear 94, the rotation speed of the sun gear 100 is reduced, and the carrier 106 is rotated.
Furthermore, the nut 82 is rotated in accordance with the rotation, and the rotation is converted into a linear motion by the screw mechanism 78, and the drive shaft 60 is moved in a direction parallel to its axis.

The actuator 50 further includes a rotational position sensor 110 for detecting the rotational position of the rotor 66,
Axial position sensor 1 for detecting the axial position of the drive shaft 60
12 and 12 are provided respectively.

The rotational position sensor 110 is of a magnetic type (an example of a non-contact type) in the present embodiment, and is a rotor 66.
It is composed of a combination of a permanent magnet 116 that rotates together with the three fixed-position magnetic detection elements 118. The magnetic detection element 118 is arranged in proximity to the permanent magnet 116 and outputs a pulse signal that changes in response to detecting passage of the permanent magnet 116, thereby detecting the rotational position (relative position) of the rotor 66. To be done. Magnetic detection element 118
One example is a Hall element. The rotational position sensor 110 is
It is used to make the amount of change in the rotation angle of the motor 64 equal to the command value during the rear wheel steering angle control.

On the other hand, the axial position sensor 112 is
In the present embodiment, the potentiometer type (contact type)
It has been. The axial position sensor 112 includes the drive shaft 60.
And a linearly displaced slider and a fixed position electric resistor are combined. The electric resistor is provided so as to be in constant contact with the slider, the electric resistance value changes according to the position of the slider, and an electric signal corresponding to the change is output, whereby the axial position of the drive shaft 60 ( Absolute position) is detected. The axial position sensor 112 is used to initialize the rotational position of the motor 64 (return to the origin) prior to the rear wheel steering angle control.

As shown in FIG. 1, the coaxial actuator 50 constructed as described above passes through the rear end of the differential gear 10 in the space between the center floor 16 and the differential gear 10. It is mounted in a portion located in front of the vehicle with respect to a vertical surface extending in the vehicle left-right direction. Specifically, the actuator 50 is attached to the sub-frame 30 with the drive shaft 60 extending in a direction parallel to the vehicle left-right direction. The subframe 30 is separable from the underfloor 16 which is a part of the vehicle body, but is substantially a part of the vehicle body.

Further, as shown in FIG. 2 which is a plan view, the actuator 50 is mounted on the vehicle while being offset in the vehicle left-right direction with respect to the differential device 10. The actuator 50 is mounted so as to overlap the differential device 10 in the vehicle front-rear direction. As a result, it is almost unnecessary to widen the vehicle front-rear direction gap between the differential position 10 and the center floor 16 in order to secure the mounting space for the actuator 50. There is almost no need to shift to the end, and in the end, the guest room space is not so much sacrificed.

The actuator 50, as shown in FIG.
Both ends of the drive shaft 60 are projected from the actuator housing 52, and each end is connected to a tie rod (an example of a steering rod) 132 via a ball joint (an example of a second joint) 130. Only one end is shown in the drawing. Each tie rod 132 is arranged coaxially with the drive shaft 60 in the vehicle. On the other hand, each rear wheel 12 has a sub-frame 30.
It is rotatably attached to a carrier (an example of a wheel support) sandwiched between an upper arm and a lower arm of the rear suspension device attached to the vehicle (an example of a wheel support) and rotatable about a substantially vertical straight line. Knuckle arm (one example of steering arm) from the left and right carriers 1
34 extends. Each tie rod 132 is connected to the tip end portion of each knuckle arm 134 via a ball joint (an example of a first joint) 136.

Each tie rod 132 is a knuckle arm 1
A ball joint 136 having an external thread to be screwed to the tip end portion of 34 is provided. This ball joint 136
Has a ball slidably fitted in a socket, and the ball has an external thread formed on the tip of the knuckle arm 134 to be screwed into the thread. A shaft portion 138 extends from the socket and is screwed with a shaft portion 139 extending from the ball of the ball joint 130 inside the vehicle body, whereby the tie rod 132 is assembled.

The relationship between the tie rod 132, the ball joints 130 and 136, the actuator 50, and the relationship between the actuator 50 and the vehicle body is shown in FIG. 7 in a plan view.

As shown in the figure, a bracket 140 is attached to the front cross member 32 of the sub-frame 30. On the other hand, two bosses 144 are formed in the actuator housing 52. The actuator housing 52 is attached to the bracket 140 at its boss 144 by two bolts 146 at two positions separated in the vehicle left-right direction.

The right end of the drive shaft 60 is connected to the right tie rod 132 by a ball joint 130. In the figure, reference numeral 148 indicates a rubber boot capable of elastic bending and expansion / contraction in order to prevent water, dust and the like from entering the connecting portion. Ball joint 130
Is the ball 15 formed at the end of the right tie rod 132.
0 is slidably fitted into a socket 152 formed at the right end of the drive shaft 60.

On the other hand, the left end of the drive shaft 60 has the first
It is connected to the left tie rod 132 by a relay rod connecting body of the relay rod 154 and the second relay rod 156.
The bracket 158 is attached to the left side rail 38 of the sub-frame 30.
8. Steel relay rod housing 160 has bolts 162
Are mounted parallel to the vehicle left-right direction. The first relay rod 154 is supported by the relay rod housing 160 so as to be movable in the axial direction. Both ends of the first relay rod 154 are relay rod housings 160.
And sockets 164 are formed at both ends thereof. The left socket 164 is slidably fitted to a ball 166 formed at the end of the left tie rod 132 to form a ball joint (an example of a second joint) 130, while the right socket 164 is a second relay. A ball joint (an example of a fourth joint) 170 is slidably fitted to a ball 168 formed at the end of the rod 156. Accordingly, the first relay rod 154 is bendably connected to both the left tie rod 132 and the second relay rod 156. In the figure, reference numerals 172 and 174 also indicate boots.

The first of the both ends of the second relay rod 156
A ball 176 is formed at a portion opposite to the connecting portion with the relay rod 154, and is slidably fitted into a socket 178 formed at the left end portion of the drive shaft 60. Thereby, a ball joint (an example of a third joint) 180 is configured. In the figure, reference numeral 182 also indicates boots.

The length of the second relay rod 156 is adjustable. The second relay rod 156 is configured such that shaft portions respectively extending from balls 168 and 176 formed at both ends thereof are screwed by a turnbuckle 184 (an example of a nut). Turnbuckle 184
The rotation of the ball in one direction shortens the distance between the pair of balls 168 and 176, and the rotation in the opposite direction lengthens it, whereby the length of the second relay rod 156 is adjusted. In the figure, reference numeral 186 indicates a lock nut for preventing loosening.

The right end portion of the second relay rod 156 is the drive shaft 6
It is connected to the left end of 0. The connection is made by the socket 178 of the ball joint 180 of the second relay rod 156.
It is performed by screwing a male screw extending from the screw into the male screw formed on the left end portion of the drive shaft 60.

Here, the rear wheel steering device is installed in the subframe 30.
The work process of attaching to the will be described. The rear wheel steering device is attached to the subframe 30 which is not attached to the underbody 16, and the subframe 30 is attached to the underbody 16 together with the rear wheel steering device after the attachment.

Before the rear wheel steering device is attached to the subframe 30, the left and right carriers, the left tie rod 132, the first relay rod 154, and the second relay rod 156 are used.
The actuator 50 and the right tie rod 132 are disassembled into a connecting body connected to each other.

At the time of attachment to the subframe 30, first, the left and right carriers are attached to the subframe 30 by the rear suspension device. Next, the connected body is attached to the sub-frame 30. Specifically, the actuator housing 52 is attached to the bracket 140, and the relay rod housing 160 is attached to the bracket 158. Next, the tips of the left and right tie rods 132 are screwed onto the tips of the knuckle arms 134 extending from the carriers.

After the mounting of the rear wheel steering device to the sub-frame 30 is completed, the turn buckle 184 is appropriately rotated to adjust the steering angle of the left and right rear wheels, that is, the toe-in adjustment, for example.

As is apparent from the above description, in this embodiment, the left and right tie rods 132 are the first relay rod 154 and the second relay rod 156 by the ball joints 170 and 180, and the drive shaft 60 of the actuator 50.
Are connected to each other by a connecting body. The first relay rod 154 is attached to the side rail 38 of the sub-frame 30 in the relay rod housing 160 that supports it so that it can move in the axial direction, while the actuator 50
Is attached to the front cross member 32 of the sub-frame 30 in its actuator housing 52, and if a relative positional error occurs between the mounting positions, the error is absorbed by the ball joints 170 and 180.

Therefore, according to the present embodiment, the bracket 1 attached to each of the plurality of welded members.
Even if the rear wheel steering device is mounted across 40 and 158, even if a relative position error occurs between the brackets 140 and 158, the error is absorbed by the ball joints 170 and 180. The bending moment does not act on the drive shaft 60 due to the relative position error between the plurality of brackets 140 and 158, and the durability and reliability of the actuator 50 are improved.

Further, in this embodiment, since the length of the second relay rod 156 can be adjusted and the adjusting portion is exposed, the adjustment work can be facilitated. can get.

Further, in the present embodiment, the longitudinal dimension of the actuator 50 becomes short when the rear wheel steering device is disassembled into the smallest unit that can be disassembled, and the same is achieved only by replacing parts such as the relay rod with other parts. The actuator 50 can be mounted on different types of vehicles or can be mounted on the same type of vehicle at different positions, so that the versatility of the actuator 50 can be improved.

Further, according to the present embodiment, the actuator 50 is arranged on the front side of the differential device 10 and apart from the muffler of the engine, so that the number of parts necessary for heat countermeasures, cost, etc. can be reduced. The effect that it becomes easy is also obtained.

According to the present embodiment, the actuator 50 does not directly face the road surface but faces the differential device 10 with the differential device 10 interposed therebetween. Further, it is possible to prevent pebbles, mud, water, and the like from which the tire bounces from directly colliding with or adhering to the actuator 50, thereby improving the reliability of the actuator 50.

Further, according to the present embodiment, the actuator 50 is made coaxial so that the actuator 50 is miniaturized in the diametrical direction, and is a space between the underbody 13 and the differential gear 10 and above the differential gear 10. Since it can be arranged in a relatively narrow space that is a dead space in the past, the cabin space may be sacrificed as compared to the conventional example in which the differential device 10 is arranged on the rear side. The effect that the room space is hardly sacrificed is also obtained.

Furthermore, according to this embodiment, when the actuator 50 is removed from the vehicle, the sub-frame 3
It is not essential to remove 0 from the underbody 13 or the tie rod 132 from the actuator 50, and the effect of facilitating maintenance / inspection work of the actuator 50 is also obtained. Hereinafter, a specific description will be given.

That is, when the actuator 50 is removed from the vehicle, first the body (particularly the body on the rear side) is removed.
Is brought up to bring the rear suspension device into a full rebound state, whereby a space extending in the vehicle front-rear direction is created between the rear suspension device and the wheel house arch 20. Further, the tires of the left and right rear wheels 12 are removed from the rear wheel axle. In this state, first, the tie rod 132 is removed from the knuckle arm 134, and then the actuator 50 and the relay rod housing 1
60 is removed from the subframe 30. Further, the actuator 50 extends in the vehicle left-right direction between the side rails 36, 38 of the sub-frame 30 and the side member of the underbody 13 in the vehicle front-rear direction, and between the rear suspension device and the wheel house arch 20. The actuator 50 is taken out to the outside of the vehicle by pulling out through the space extending in the front-rear direction in order. At this time, the actuator 50 is integrally removed without releasing the connection with the left and right tie rods 132.

As described above, according to this embodiment, the actuator 50 can be removed from the vehicle while the sub-frame 30 is still attached to the underbody 13 and the tie rod 132 is still connected to the actuator 50. The effect of facilitating the maintenance and inspection work of 50 is also obtained.

The mechanical structure of the rear wheel steering system has been described above in detail, but the electrical structure will be described in detail below.
As shown in FIG. 5, the rear wheel steering system includes a controller 200
It has. The controller 200 includes a CPU 202,
Computer 2 including ROM 204 and RAM 206
08 is the main component.

On its input side, a vehicle speed sensor 210, a steering angle sensor 212, a yaw rate sensor 214, the rotational position sensor 110 and an axial position sensor 112.
And are connected respectively. The vehicle speed sensor 210 detects a vehicle speed V that is the traveling speed of the vehicle. Steering angle sensor 21
Reference numeral 2 detects a steering angle θ which is a rotation angle of a steering wheel operated by a driver. Yaw rate sensor 2
14 detects the actual yaw rate γ of the vehicle. On the other hand, the actuator 50 is provided on the output side of the controller 200.
Motor 64 is connected. In the motor 64, the CPU 202 uses the RAM 2 based on input signals from various sensors.
It is controlled by executing various control programs stored in advance in the ROM 204 while using 06.

The main one of the control programs
The rear wheel steering angle control routine is shown in the flowchart in FIG.
Have been. The contents of this routine will be described below. Book roux
In Chin, first, step S1 (hereinafter, simply S1
Expressed by Same for the other steps) Smell
Based on the signals from various sensors,
Information is obtained. That is, the vehicle speed V, the actual front wheel steering angle δ_f,
Actual yaw rate γ and actual rear wheel steering angle δ_rIs acquired
is there. Note that the actual front wheel steering angle δ_fTo the steering angle sensor 212
Based on the steering angle θ detected by the
Angle δ _rIs based on the signal from the rotational position sensor 110
It is determined.

Next, in S2, the yaw rate expected to occur in the vehicle is determined as the target yaw rate γ ^* based on the vehicle speed V and the actual front wheel steering angle δ _f , assuming that the vehicle is in a steady circular turning state. To be done. In the present embodiment, the relationship between the vehicle speed V, the front wheel steering angle δ _f, and the yaw rate γ is stored in the ROM 204 in advance in the form of a functional expression, a table, etc., and the target yaw rate γ of this time is stored according to the relationship.
^* Is determined.

Then, in S3, the yaw rate deviation Δγ is calculated by subtracting the actual yaw rate γ from the target yaw rate γ ^* , and subsequently, in S4, the rear wheel steering angle change command value Δ is calculated based on the yaw rate deviation Δγ.
δ _r is determined. In the present embodiment, the relationship between the yaw rate deviation Δγ and the rear wheel steering angle change command value Δδ _r is stored in advance in the ROM 204 in the form of a functional expression, a table, etc. Value Δδ
_r is determined. Then, in S5, the drive signal necessary for realizing the rear wheel steering angle change command value Δδ _r of this time is output to the motor 64. As described above, one execution of this routine is completed, and the execution of this routine is started again after the elapse of a predetermined time.

Next, another embodiment will be described with reference to FIG. Note that this embodiment has many parts in common with the embodiment shown in FIG. 7, and only the parts of the first relay rod and the second relay rod differ, so only that part will be described in detail, and other parts will be described. The same reference numerals are used to omit detailed description.

A bracket 220 is attached to the left side rail 38 of the subframe 30, and a relay rod housing 222 is attached to the bracket 220 with bolts 224. First relay rod 2
26 is supported by the relay rod housing 222 so as to be movable in the axial direction. The first relay rod 226 is axially movably supported by both ends of the first relay rod 226 by an annular support member 228 provided on the inner peripheral surface of the relay rod housing 222.

The relay rod housing 222 extends axially parallel to the right from the position of the first relay rod 226, and extends to the second relay rod 230 connected to the first relay rod 226. . A portion of the relay rod housing 222 that covers the second relay rod 230 from the outside also has a bolt 234 on the bracket 232 attached to the front cross member 32 of the subframe 30.
The relay rod housing 222, which is attached to the subframe 30 and is long in the axial direction, is firmly fixed to the subframe 30.

The relay rod housing 222 covers the second relay rod 230 from the outside with a radial gap larger than the radial gap with the first relay rod 226.
This is because the bending of the second relay rod 230 with respect to the first relay rod 226 is allowed within a certain range.

The relay rod housing 222 does not extend to a position where it covers the actuator housing 52 from the outside, and an axial gap is left between the relay rod housing 222 and the actuator housing 52. A tool access space is secured when the right end of the second relay rod 230 is screwed into the left end of the drive shaft 60. After the screwing, the tool access space is provided with the actuator housing 5 and the right end portion of the relay rod housing 222.
The rubber boot 23 that is mounted across the left end of
It is cut off from the outside air by 5. Therefore, after screwing, the gap between the relay rod housing 222 and the actuator housing 52 is filled with the boot 235,
Water and dust are prevented from entering the connecting parts. Further, the boot 235 allows the actuator housing 52 to be
The bending angle between the second relay rod 230 and the second relay rod 230 is limited to a certain range.

That is, in this embodiment, the portion of the relay rod housing 222 that covers the second relay rod 230 from the outside constitutes an example of a "rigid body cover", and the boot 235 constitutes an example of an "elastic body". The rigid body cover and the boot 235 constitute an example of the "bending angle limiting means" in the invention of claim 2.

The second relay rod 230 has a pair of ball joints 236. Each ball joint 23
6, the ball 238 is slidably fitted in the socket 240. The shaft portion 242 extends leftward from the left ball 238 and is screwed to the right end portion of the first relay rod 226. A shaft portion 244 extends rightward from the right ball 238 and is screwed to the left end portion of the drive shaft 60. The shaft portions 246, 2 are arranged so as to face each other from the respective sockets 240.
48 extend respectively, and the shaft portions 246, 248 are screwed to the nut 250 common to them,
The pair of ball joints 236 are connected to each other.

The second relay rod is adjusted by adjusting the screwing length of the screwing portion between the shaft portion 246 and the drive shaft 60 and the screwing length of the screwing portion between the shaft portion 248 and the first relay rod 226. The length of 230 can be adjusted. In the figure, reference numerals 252 and 254 denote lock nuts for preventing loosening of the screwed portions.

In the present embodiment, the length of the relay rod housing 222 does not reach the position of the actuator housing 52, but the present invention is, for example, as shown in FIG.
As shown in FIG. 7, the relay rod housing 222 may have a length extending to the position of the actuator housing 52, and the elastic body 260 made of rubber may be arranged so as to fill the annular gap existing between them in the radial direction. Is.

In the embodiment shown in FIG. 9, when the relay rod housing 222 is not mounted on the first relay rod 226, the connection between the first relay rod 226 and the second relay rod 230 and the connection between the second relay rod 230 and the second relay rod 230 are performed. The connection with the actuator 50 is performed, and then the relay rod housing 222 is attached to the first relay rod 226, the second relay rod 230, and the actuator 50.
Therefore, unlike in the embodiment shown in FIG.
It is not necessary to provide a tool access space between the relay rod housing 222 and the actuator housing 52.

In the embodiment shown in FIG. 9, the bending angle between the first relay rod 226 and the actuator 50 is limited to a certain range by the relay rod housing 222 and the elastic body 260. Therefore, according to the present embodiment,
Left and right tie rods 132, first relay rod 226, and second
When the connecting body in which the relay rod 230 and the actuator 50 are connected to each other is attached to the sub-frame 30, the connecting body is prevented from being bent more than necessary, and the attachability is improved.

Further, in the present embodiment, the radial gap between the relay rod housing 222 and the actuator housing 52 is filled with the elastic body 260, and water, dust and the like enter the interior of the relay rod housing 222 through the gap. And the elastic body 260 is prevented.
The elastic deformation of the first relay rod 226 and the actuator 50 allows the bending of the first relay rod 226 within a certain range. Therefore, according to the present embodiment, the relay rod housing 222
Even if a relative position error occurs between the mounting position of 1 and the mounting position of the actuator housing 52, the error is absorbed by the elastic body 260, and the drive shaft 60 is not subjected to an unexpected bending moment.

Although some embodiments of the present invention have been described in detail above with reference to the drawings, various modifications other than these will be made based on the knowledge of those skilled in the art without departing from the scope of the claims. The present invention can be implemented in an improved form.

[Brief description of the drawings]

FIG. 1 is a side view for explaining a relationship between an actuator and a vehicle body in a vehicle equipped with a rear wheel steering system that is an embodiment of the present invention.

FIG. 2 is a plan view for explaining a relationship between an actuator and a vehicle body.

FIG. 3 is a plan view showing a subframe taken out in FIGS. 1 and 2;

FIG. 4 is a front sectional view showing the actuator shown in FIGS. 1 and 2 in an enlarged manner.

FIG. 5 is a block diagram conceptually showing the electrical structure of the rear wheel steering system.

FIG. 6 is a flowchart showing main control programs stored in a ROM shown in FIG.

FIG. 7 is a plan view showing a mechanical configuration of the rear wheel steering device.

FIG. 8 is a plan view showing a mechanical configuration of a rear wheel steering system that is another embodiment of the present invention.

FIG. 9 is a plan view showing a mechanical configuration of a rear wheel steering system that is still another embodiment of the present invention.

FIG. 10 is a front view for conceptually explaining one embodiment of the present invention.

FIG. 11 is a front view for conceptually explaining another embodiment of the present invention.

[Explanation of symbols]

 30 Sub-frame 32 Front cross member 50 Actuator 52 Actuator housing 60 Drive shaft 130 Ball joint 132 Tie rod 154, 226 First relay rod 156, 230 Second relay rod 160, 222 Relay rod housing 170, 180 Ball joint 235 Boot 260 Elastic body

Claims (2)

[Claims] Claim: What is claimed is: 1. A left and right wheel support for mounting left and right rear wheels on a vehicle body so as to be rotatable and rotatable about a substantially vertical straight line. A steering arm, a left and right steering rod to which each of the steering arms is bendably connected by one of the first joints at one end, (a) an actuator housing attached to the vehicle body, and (b) an actuator housing A drive shaft which is movably supported in the axial direction and has both ends projecting from the actuator housing, each end of which is flexibly connected to the other end of each steering rod by each second joint. And (c) an actuator including a drive source that drives the drive shaft in the axial direction, a rear wheel steering system comprising: A connection between one of the steering rods and the steering rod is supported by a relay rod housing attached to the vehicle body so as to be movable in the axial direction, both ends thereof project from the relay rod housing, and one end of the steering rod has the second steering rod. The other end of the first relay rod flexibly connected by a joint and the second end of the drive shaft flexibly connected by a third joint at one end.
A rear wheel steering system characterized in that the relay rod is connected to the other end of the relay rod by a fourth joint so as to be bendable. 2. The rear wheel steering system according to claim 1, further comprising at least a bending angle between the first connecting rod and the second relay rod and a bending angle between the second relay rod and the drive shaft. A rear wheel steering system including a bending angle limiting means for limiting one of them to a certain range.