JPH0624305Y2 - Vehicle four-wheel steering system - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention connects a front wheel steering mechanism and a rear wheel steering mechanism with a rotary shaft, and transfers the front wheel steering amount from the front wheel steering mechanism to the rear wheel steering mechanism by a rotary shaft. The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in conjunction with the front wheels by transmitting via the vehicle.

(Prior Art) Conventionally, an apparatus of this type has been disclosed in, for example, JP-A-60-64073.
As disclosed in Japanese Patent Laid-Open No. 60-64074 and Japanese Patent Laid-Open No. 60-64074, the rotary shaft is divided into first and second rotary shafts at the front and rear, and a first joint portion formed on the first rotary shaft side. Small rudder angle steering of the front wheels by connecting the first and second rotary shafts to each other via a power transmission mechanism having a clearance between the first and second rotary shafts formed on the side of the second rotary shaft so that the rotational force can be transmitted. Sometimes I try not to steer the rear wheels. As a result, when the rear wheels are steered in phase with the steering of the front wheels (when the vehicle is traveling at high speed), the rear wheels are kept in the neutral state at the initial steering of the front wheels (during small steering angle steering). When the turning performance of the vehicle is improved and the rear wheels are steered in reverse phase in conjunction with the steering of the front wheels (when the vehicle is running at low speed), the front wheels should be installed to avoid ruts, pebbles and other obstacles on the road. Even if the vehicle is steered frequently within the small steering angle range, the rear wheels are kept in the neutral state, so that the running stability of the vehicle is improved.

(Problems to be solved by the invention) However, in the above-mentioned conventional device, when the steering angle of the front wheels is within the range of the small steering angle, the clearance between the first rotary shaft and the second rotary shaft is provided. Therefore, the influence from the road surface to the rear wheels is not transmitted to the steering wheel, and the driver cannot obtain the road feeling regarding the rear wheels. For example, even if there is a reverse input from the road surface to the rear wheels and the rear wheels are slightly steered, the driver cannot grasp the situation. As a result, there is a problem that it is difficult to drive the vehicle.

The present invention has been devised in view of such a problem, and an object thereof is to maintain the turning stability during in-phase steering of the rear wheels and the traveling stability during reverse-phase steering due to the above clearance,
It is an object of the present invention to provide a four-wheel steering system for a vehicle, which is capable of obtaining the road feeling of the rear wheels even when steering the front wheels at a small steering angle.

(Means for Solving the Problems) In order to achieve the above object, the structural features of the present invention are as follows.
A front wheel steering mechanism that steers the front wheels according to the turning of the steering wheel, and a front end that is connected to the front wheel steering mechanism and extends rearward to rotate around an axis in response to the steering of the front wheels to rotate the rotation backward. And a neutral urging device connected to the rear end of the rotary shaft for steering the rear wheel according to the rotation of the rotary shaft and for urging the steering of the rear wheel to the neutral position. In a four-wheel steering system for a vehicle including a rear wheel steering mechanism, the rotary shaft is divided into first and second rotary shafts in the front and rear, and a first joint portion and the second joint formed on the first rotary shaft side. The first and second rotary shafts are coupled to each other via a power transmission mechanism having a clearance between the first and second rotary shafts, the first and second rotary shafts being formed so as to transmit the rotational force. To Some that were connected by Shonba.

In the present invention configured as described above, if the steering angle of the front wheels is small and the rotation of the first rotary shaft is within the amount corresponding to the clearance, the rotational force of the first rotary shaft is equal to the clearance. Therefore, it is not transmitted to the second rotating shaft via the power transmission mechanism, but is transmitted via the torsion bar. However, since the rear wheels are urged to the neutral position by the neutral urging mechanism in the rear wheel steering mechanism, the rotational force transmitted to the second rotary shaft via the torsion bar is the initial load in the neutral urging mechanism. While it is smaller, the torsion bar is only twisted in proportion to the rotation of the first rotary shaft, and the rear wheel is kept in the neutral state. And
If the rotational force transmitted to the second rotary shaft via the torsion bar becomes larger than the initial load in the neutral biasing mechanism, or if the torsion angle of the torsion bar becomes larger than the amount corresponding to the clearance, the torsion bar is moved. The rotational force transmitted to the second rotary shaft via the first rotary shaft overcomes the initial load, and the rear wheel steering mechanism is driven by the rotary force transmitted via the first rotary shaft, the torsion bar and the second rotary shaft, or the power is transmitted. First in transmission mechanism
The rear wheel steering mechanism is driven by the rotational force transmitted through the first and second rotating shafts by the joining of the first and second joints, and the rear wheels are steered in conjunction with the rotation of the first rotating shaft, that is, the front wheels. Become so.

Further, even when the steering angle of the front wheels is small and the rear wheels are not steered, the front wheel steering mechanism and the rear wheel steering mechanism are mechanically connected via the first and second rotating shafts and the torsion bar. The force reversely input to the rear wheels from the road surface is also transmitted to the steering wheel. For example, when there is a reverse input from the road surface to the rear wheels and the rear wheels are slightly steered, the steering state of the rear wheels is transmitted to the driver via the steering wheel.

[Effects of the Invention] As can be understood from the above description of the operation, by providing a clearance in the power transmission mechanism, the rear wheel is driven by the action of the neutral biasing mechanism in the rear wheel steering mechanism within the small steering angle range of the front wheel. Since the neutral state is maintained, the turning characteristics of the rear wheels during in-phase steering and the traveling stability during reverse-phase steering are not impaired, as in the above-described conventional device. Even under such a situation, the situation of the road surface of the rear wheels is transmitted to the driver via the steering wheel, so that the driver can drive the vehicle while always feeling the road feeling of the rear wheels. It becomes easy to exercise.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. Third
The figure schematically shows the entire vehicle according to the present invention. The vehicle has a front wheel steering mechanism A for steering left and right front wheels FW1 and FW2.
And a steering force transmission shaft B which is connected to the front wheel steering mechanism A at the front end and extends rearward, and a rear wheel steering mechanism which is connected to the rear end of the shaft B and steers the left and right rear wheels RW1 and RW2. It has C and.

The front wheel steering mechanism A has a rack bar 11. The rack bar 11 has a steering handle 13 at the upper end in the gear box 12.
Is connected to the lower end of the steering shaft 14 connected to
3 is displaced in the axial direction in accordance with the rotation of the steering wheel 3, and the left and right front wheels FW1 and FW2 are steerably connected at both ends thereof via the left and right tie rods 15a and 15b and the left and right knuckle arms 16a and 16b so as to be displaced in the axial direction. According to the same front wheel F
It is designed to steer W1 and FW2.

The steering force transmission shaft B includes a pinion shaft 21, an intermediate shaft 22, a first rotating shaft 23, and a second rotating shaft 24. The pinion shaft 21 meshes with the rack bar 11 in the gear box 12,
It is designed to rotate around the axis according to the axial displacement of the. The intermediate shaft 22 is connected to the rear end of the pinion shaft 21 by a universal joint 25 at the front end, and is connected to the front end of the first rotary shaft 23 at the rear end by a universal joint 26 to rotate the pinion shaft 21. First
It is transmitted to the rotary shaft 23.

As shown in FIGS. 1 and 2, the rear end of the first rotary shaft 23 is inserted through the bush 27 on the inner circumference of the front end of the second rotary shaft 24 formed in a cylinder.
The bush 27 is press-fitted onto the outer periphery of the rear end portion of the first rotary shaft 23 and is slidable with respect to the inner peripheral surface of the second rotary shaft 24. It regulates movements other than rotation around the axis. The first rotary shaft 23 has a shaft 23 at an intermediate portion thereof.
Cylindrical projections 23a and 23b are provided at symmetrical positions on the outer periphery of the cylindrical projections 23a and 23b. The projections 23a and 23b are cylindrical through holes provided at the symmetrical position at the large diameter portion 24a at the front end of the second rotary shaft 24. It is inserted in 24b and 24c. Protrusion 23
A predetermined clearance is provided between the outer peripheral surface of each of the a and 23b and the inner peripheral surface of each of the through holes 24b and 24c, and the projections 23a and 23b and the through holes 24b and 24c have a clearance and the first and A capacity transmission mechanism that connects the second rotating shaft so as to transmit the rotational force is configured.
In addition, the first rotary shaft 23 and the second rotary shaft 24
Is coaxially provided in both shafts 23 and 24 and is fixed to the first rotary shaft 23 by a pin 28a at the front end and the second rotary shaft 24 by a pin 28b at the rear end.
Are connected by a torsion bar 29 fixed to.

Then, the relationship between the torque T applied to the first and second rotary shafts 23 and 24 and the rotation angle θ of the rotary shafts 23 and 24 by the action of the power transmission mechanism having such clearance and the torsion bar 29 is the eighth. It is defined by the characteristic graph shown in the figure. That is, while the rotation of the second rotary shaft 24 (or the first rotary shaft 23) is restricted, the torque T is applied to the first rotary shaft 23 (or the second rotary shaft 24) to give the same shaft 23 (or the same shaft 23). 24) is rotated, the first rotary shaft 23
The rotation θ of (or the second rotation shaft 24), that is, the relative rotation angle θ between the first and second rotation shafts 23 and 24 increases in proportion to the torque T while the torsion bar 29 is twisted in the range where the torque T is small. To do. In this case, if the spring constant of the torsion bar 29 is k ₁ , the torque T
And the relative rotation angle θ is T = k ₁ · θ. But,
When the torque T increases and the relative rotation angle θ reaches a predetermined value θ ₁ corresponding to the clearance, the outer peripheral surfaces of the protrusions 23a and 23b are joined to the inner peripheries of the through holes 24b and 24c, so that the torque T becomes large. Becomes a predetermined value T ₁ (= k ₁ ·
Even if θ ₁ ) or more, the relative rotation angle θ is maintained at the predetermined value θ ₁ .

The rear wheel steering mechanism C includes, as shown in FIGS. 3 to 7, an input shaft 32 connected to the rear end of the second rotary shaft 24 via a universal joint 31, and left and right tie rods 33a at both ends.
33b and left and right knuckle arms 34a and 34b, the left and right rear wheels RW1 and RW2 are operatively connected to each other, and an operating rod 35 and a motor 36 that rotationally drives the rod 35 are provided, and the left and right front wheels FW1 and FW2 are steered. Input shaft 11
Rotation of the left and right rear wheels RW1 and RW2 by converting the rotation of the left and right wheels into axial displacement of the actuating rod 35.
The left and right front wheels FW1 and FW1 are driven by the rotation of the operating rod 35 accompanying the rotation of the motor 36 while steering in conjunction with W2.
The ratio of the steering angles of the left and right rear wheels RW1 and RW2 to W2 (hereinafter simply referred to as the steering angle ratio) is controlled from the reverse phase to the same phase.

As shown in FIG. 6, the input shaft 32 is rotatably supported by a housing 38 via a bearing 37, and a pinion 41 is integrally provided on the coaxial 32 at the rear end thereof. The pinion 41 meshes with the sector gear 43 formed on the upper portion of the rotating member 42. This rotating member 42
Is an annular first support body 44 through which the operating rod 35 passes.
Are integrally formed with the member 42, and the rotating member 42
The first support body 44 is rotatably supported by the housing 38 via bearings 45 and 46.

As shown in FIGS. 4 and 6, a pinion 47 is formed in the lower portion of the rotating member 42, and the pinion 47 is formed on the upper surface of a rack bar 48 that extends horizontally in the housing 38 and is accommodated therein. The rack teeth 48a mesh with each other.
The rack bar 48 is formed into a cylindrical shape, and the outer peripheral surface on the lower side thereof is formed into two flat surfaces forming a predetermined angle.
It is supported by a support mechanism SM on a plane and is urged to a neutral position by a neutral urging mechanism CM.

The support mechanism SM includes a bolt 51, a pair of rack guides 52,
53 and the disc spring 54 are the main constituent members. The bolt 51 is fixed to the housing 38 so as to extend below the rack bar 48 in a direction orthogonal to the bar 48. The rack guides 52 and 53 are formed in a conical shape, and are rotatably and axially displaceably assembled on the outer circumference of the foot portion of the bolt 51. Abut on 2 planes and the same bar 4
Functions as a rolling bearing of 8. The disc spring 54 is provided with a bolt 51 between the rack guide 52 and the housing 38.
The bolts 51 are mounted on the outer periphery of the rack bar 52 and are urged to the right in FIG. 6 to urge the rack bar 48 upward in FIGS. 4 and 6. is doing.

As shown in FIG. 4, the neutral urging mechanism CM has a shaft 5
5, the pair of retainers 56 and 57, and the spring 58 are the main constituent members. The shaft 55 is screwed to one end of the rack bar 48, and the shaft 55 and the rack bar 48 are integrally displaced in the axial direction. The retainer 56 has an inner cylinder 56a and an outer cylinder 56b that are integrally formed, and the inner cylinder 56a slides on the outer circumference of the shaft 55 and the outer cylinder 56b slides in the cylindrical portion 38a of the housing 38. As described above, the stopper 61 fixed to the shaft 55 restricts outward displacement with respect to the shaft 55, and the end face of the plug 62 fixed to the cylindrical portion 38a of the housing 38 prevents the cylindrical portion 38a from moving. The displacement in the outward direction with respect to is restricted. The retainer 57 is slidably mounted on the outer periphery of the shaft 55, and its displacement in the outer peripheral direction with respect to the shaft 55 is restricted by a stopper 63 fixed to the shaft 55, and the inner end surface 38a1 of the cylindrical portion 38a of the housing 38 is regulated. Thus, the displacement in the outer direction with respect to the cylindrical portion 38a is restricted. The spring 58 is assembled on the outer periphery of the shaft 55 so that both ends thereof are supported by the retainers 56 and 57, respectively, in a state where an initial load is applied.

By the action of the neutral biasing mechanism CM, the relationship between the torque T applied to the input shaft 32 and the rotation angle θ of the coaxial shaft 32 is defined by the characteristic graph shown in FIG.
That is, if the initial load of the spring 58 is F ₀ ,
Even if a small torque T is applied to the input shaft 32, the torque T is a predetermined value T corresponding to the initial load F ₀ of the spring 58.
_The input shaft 32 does not rotate until it reaches ₂ , and when the torque T exceeds the predetermined value T ₂ , the rotation angle θ increases in proportion to the torque T according to the spring constant of the spring 58. In such a case, as shown in FIG. 6, the distance from the pinion 47 to the rotation center axis of the rotating member 42 is r ₁ , the distance from the rotation center axis to the sector gear 43 is r ₂ , and the radius of the input shaft 32 is Is r ₃ , the predetermined value T ₂ is r ₁
It is expressed as r ₃ · F ₀ / r ₂ .

On the other hand, as shown in FIG. 5 and FIG.
An annular second support body 66 is assembled on the inner circumference of the support body via bearings 64 and 65. The support body 66 rotates integrally with the first support body 44 as the first support body 44 rotates. The first support 44 is rotatable in the circumferential direction. A slide 67, which constitutes a ball joint with the second support 66, is attached to the second support 66. The slide 67 has a spherical outer periphery, and has a hole 67a at the center thereof. The slide 67 is provided integrally with the operating rod 35 in the hole 67a and extends in a direction orthogonal to the axis of the rod 35. A tip portion of the extended pin 68 is slidably and movably fitted in the axial direction (extending direction of the pin 68). As a result, the tip portion of the pin 68 is rotatably supported by the first support body 44 in the circumferential direction (around the axis of the operation rod 35), and the displacement of the support position according to the rotation of the first support body 44. As a result, the actuating rod 35 is pressed in the axial direction. 5 and 6 show a state in which the pin 68 is at the reference position.

As shown in FIG. 5, the operating rod 35 is axially slidably and rotatably supported by the housing 38 via a bush 71 on the left side thereof, and has an outer spline on the right side thereof. In the portion 35a, the spline portion 35a
7 having an inner spline portion 72a slidably fitted to
It is supported by the housing 38 so as to be slidable in the axial direction and rotatable about the axis through bearings 73 and 74 interposed between the wheel 72 and the wheel 72 and the housing 38.

The operating rod 35 and the wheel 72 are connected to the motor 36.
The worm 75 is meshed with the wheel 72 as shown in FIGS. 5 and 7. The worm 75 is supported at both ends of a worm shaft 75a integrally formed with the worm 75 via bearings 76 and 77 in the housing 38 so as not to be axially displaceable but rotatable about the axis. A rotating shaft 36a of a motor 36 formed to have a two-face width is fitted on the upper end of the worm shaft 75a, and the shaft 75a is driven to rotate by the motor 36. The motor 36 is fixed to the housing 38 and is drive-controlled by an electric control device (not shown).

An auxiliary gear 78 is press-fitted and fixed to the outer peripheral side of the wheel 72. The auxiliary gear 78 is provided for detecting the rotation angle (corresponding to the steering angle ratio) of the wheel 72 and the operating rod 35. The gear 78 is, as shown in FIG. 4, a steering angle ratio sensor unit. It meshes with a gear 82 for driving a potentiometer 81 incorporated in the SS. The steering angle ratio sensor unit SS is connected to the above-described electric control device, and the control device cooperates with the steering angle ratio sensor unit SS to change the rotational position of the rotation shaft 36a of the motor 36 to a target steering angle ratio (for example, depending on the vehicle speed). Feedback control to the position corresponding to the change.

Next, the operation of the embodiment configured as described above will be described.
When the steering wheel 13 is rotated, the rack bar 11 is displaced in the axial direction and the left and right front wheels FW1 and FW2 are steered according to the rotation of the steering wheel 13. On the other hand, the rack bar 11
The displacement of the pinion shaft 21 causes the pinion shaft 21 to rotate about its axis, and the rotation is transmitted to the first rotating shaft 23 via the intermediate shaft 22 to rotate the shaft 23. At the same time, the shaft 23 rotates the second rotating shaft 24. I try to rotate it. However, the protrusion 23 of the first rotary shaft 23
a, 23b and through holes 24b, 2 of the second rotary shaft 24
4c is provided with a clearance at the joint between the shafts 23 and 24 and the torsion bar 2 is provided between the shafts 23 and 24.
9 and the second rotary shaft 24 is biased to the neutral position by the neutral biasing mechanism CM via the input shaft 32, the rotary member 42 and the rack bar 48.
While the rotation angle of the rotary shaft 23 is small, the torsion bar 29 is only twisted and the second rotary shaft 24 does not rotate. Therefore, in such a state, the rear wheel steering mechanism C is not driven, and the left and right rear wheels RW1 and RW2 are kept in a neutral state.

On the other hand, when the steering wheel 13 is further rotated from this state and the left and right front wheels FW1 and FW2 start to be steered to a large steering angle, the second rotary shaft 24 and the input shaft 32 in the rear wheel steering mechanism C start to rotate, and The rear wheels RW1 and RW2 start to be steered in conjunction with the steering of the left and right front wheels FW1 and FW2.

In such a case, the spring constant of the torsion bar 29, the protrusions 23a and 23b and the through holes 24b, so that the predetermined values T ₁ and T ₂ (see FIGS. 8 and 9) have a relationship of T ₁ ≦ T ₂ .
If the clearance to 24c and the spring constant of the spring 58 are set, the torsion bar 29 and the second
Before the torque T transmitted to the input shaft 32 via the rotary shaft 24 reaches a predetermined value T ₂ , the torsion angle of the torsion bar 29 increases and reaches a predetermined value θ ₁ , so that the outer peripheral surfaces of the protrusions 23a and 23b Is joined to the inner peripheral surfaces of the through holes 24b and 24c. After the joining, when the torque T is applied to the first rotary shaft 23 as the steering handle 13 rotates, the relative rotation angle θ between the first and second rotary shafts 23 and 24 becomes as shown in FIG. In addition, the torsion bar 29 does not twist any more. This allows
Rotational force is transmitted from the first rotary shaft 23 to the second rotary shaft 24 through the joints of the protrusions 23a, 23b and the through holes 24b, 24c, and the first and second rotary shafts 2
3, 24 integrally rotate according to the characteristics of the spring 58. This rotation is transmitted to the input shaft 32, and the rotation member 42
To rotate. In this state, the rack bar 48
While being supported by the support mechanism SM, the spring 48
It is displaced in the axial direction against the urging force of.

On the other hand, the first support 44 also rotates with the rotation of the rotating member 42, and the rotation of the first support 44 causes the second support 6 to rotate.
6 also rotates integrally with the first support body 44. In such cases,
When the pin 68 is at the position shown in FIG. 6, the second support 66 only rotates about the axis of the pin 68, so that the pin 68 is not rotated.
Is not pressed in the left-right direction in FIG. 5, and the operating rod 13 is kept at the reference position. In such a case, the left and right rear wheels RW1 and RW2 are not steered.

Further, based on the target steering angle ratio determined by the electric control device and the steering angle ratio (rotational positions of the working rod 35 and the wheel 72) detected by the steering angle ratio sensor unit SS,
When the motor 36 is drive-controlled and the rotation shaft 36a of the motor 36 is rotated, the rotational force is transmitted to the operating rod 35 via the worm 75 and the wheel 72, and the rod 35 rotates about its axis. With the rotation of the operating rod 35, the pin 68 also moves the second support 66 and the slider 67.
At the same time, it rotates around the axis of the rod 35. By this rotation, when the pin 68 is set to the upper or lower rotation position from the reference position as shown by the phantom line in FIGS. 5 and 6, the pin 68 steers the left and right front wheels FW1 and FW2. In accordance with the rotation of the first and second supports 44, 66 associated with the movement, the operating rod 13 is displaced in the same direction by being pushed in the left and right direction in FIG. 5 via the slider 67. As a result, the left and right rear wheels RW1 and RW2 are steered leftward or rightward according to the displacement of the operating rod 35.

In this case, if the pin 68 is in the upper position in FIG. 5,
The actuation rod 35 is displaced rightward (or leftward) with respect to the clockwise (or counterclockwise) rotation of the first and second supports 44, 66. Further, if the pin 55 is at the lower position in FIG. 5, the actuating rod 35, conversely to the above, moves clockwise (or counterclockwise) of the first and second supports 44 and 66.
Is displaced leftward (or rightward) with respect to the rotation of. The displacement amount of the actuating rod 35 is determined by the left and right front wheels FW1,
The pin 68 is proportional to the amount of rotation of the first and second supports 44, 66 due to the steering of the FW2, and from the central axis of the rod 35.
Since it is proportional to the vertical distance to the support position of the tip end of the second support body 66, the left and right rear wheels RW1 and RW2 are steered in conjunction with the steering of the left and right front wheels FW1 and FW2, and
The steering angle ratio is changed and controlled from the reverse phase to the same phase according to the rotation of the operating rod 35 and the pin 68, that is, the rotation of the motor 36.

As a result, the vehicle speed of the vehicle is detected by the vehicle speed sensor, the left and right rear wheels RW1 and RW2 are in opposite phase to the left and right front wheels FW1 and FW2 when the vehicle is running at low speed, and the left and right rear wheels RW1 are running when the vehicle is running at high speed. , RW2 is left and right front wheel FW
If the rotation of the motor 36 is drive-controlled according to the detected vehicle speed so as to be in phase with 1, 1 and FW2, as shown in FIG. 10, the front wheel steering angle θ _f becomes a predetermined small steering angle θ _f0 . When the steering angle θ _r is within the range, the rear wheel steering angle θ _r is maintained at zero, and when the front wheel steering angle θ _f exceeds the range of the steering angle θ _f0 , the rear wheel steering angle θ _r is set to the set steering angle ratio during low speed traveling. The steering angle θ _f increases in a reverse phase in proportion to the front-wheel steering angle θ _f with a negative inclination according to, and the rear-wheel steering angle θ _r has a positive inclination according to the set steering-angle ratio when the vehicle is traveling at high speed. It increases in the in-phase direction in proportion to _r .

Thus, as long as the steering handle 13 is rotated within a small range and the left and right front wheels FW1, FW2 are steered within the small steering angle range, the left and right rear wheels RW1, RW2 are maintained in the neutral state and the left and right front wheels FW1, Since the FW2 is not steered in the opposite phase or in the same phase, the front wheels are often steered within the small rudder angle range to avoid obstacles on the road such as ruts and pebbles when the vehicle runs at low speed. In addition, the running stability of the vehicle is improved and the left and right front wheels FW1, FW are
When the steering wheel 2 is steered, the turning performance of the vehicle at the beginning of steering becomes good. Further, when the steering handlebar 13 is largely rotated and the left and right front wheels FW1 and FW2 are steered to a large steering angle, the left and right rear wheels RW1 and RW2 are steered in reverse phase with respect to the left and right front wheels FW1 and FW2 during low speed traveling. Therefore, the small turning performance of the running vehicle is improved, and the left and right rear wheels RW1 and RW2 become the left and right front wheels FW during high speed running.
Since the steering wheel is steered in phase with respect to 1 and FW2, the running stability of the running vehicle is improved.

Further, even when the left and right rear wheels RW1 and RW2 are not steered, since the first and second rotating shafts 23 and 24 are connected by the torsion bar 29, the front wheel steering mechanism A and the rear wheel steering mechanism C are connected. And are mechanically connected via the steering force transmission shaft B. As a result, the force reversely input from the road surface to the left and right rear wheels RW1 and RW2 is also transmitted to the steering handle 13, and, for example, from the road surface to the left and right rear wheels R2.
When there is a reverse input to W1 and RW2 and the rear wheels RW1 and RW2 are slightly steered, the steering is transmitted to the steering wheel 13, so that the driver feels the road feeling regarding the left and right rear wheels RW1 and RW2. However, the vehicle can be driven, and the vehicle can be easily driven.

Further, the predetermined value _T 1, _{T 2} (FIG. 8 and FIG. 9 see) is _T 1> torsion bar 2 so that the relation of _{T 2}
9 spring constant, protrusions 23a, 23b and through holes 24b, 2
4c and the spring constant of the spring 58 are set, the torsion bar 29 and the second rotary shaft before the outer peripheral surfaces of the protrusions 23a and 23b are joined to the inner peripheral surfaces of the through holes 24b and 24c. Since the torque T transmitted to the input shaft 32 via 24 becomes larger than the predetermined value T ₂ , the torque T is applied to the spring 5 in the neutral biasing mechanism CM.
8 overcoming the initial load and the input shaft 32 is spring 5
It begins to rotate against the biasing force of 8. In such a case, in the initial stage, the torsion bar 29 is further twisted, so that the rotation amount of the second rotary shaft 24 with respect to the rotation of the first rotary shaft 23 is small, and as shown in FIG. 11, with respect to the front wheel steering angle θ _f . The change in the rear wheel steering angle θ _r is small.

When the first rotating shaft 23 is further rotated while the left and right front wheels FW1 and FW2 are being steered, the torsion of the torsion bar 29 is increased and the outer peripheral surfaces of the protrusions 23a and 23b are the inner peripheral surfaces of the through holes 24b and 24c. Will come to join. After this, since the second rotary shaft 24 rotates integrally with the first rotary shaft 23 as in the case described above, as shown in FIG. 1, the change of the rear wheel steering angle θ _r with respect to the front wheel steering angle θ _f . Is larger than the initial case.

Thus, even in such a case, when the front wheel steering angle θ _f is within the range of the predetermined small steering angle θ _f0 , the rear wheel steering angle θ _r is maintained at zero and the front wheel steering angle θ _f is the steering angle θ _f. When the range of θ _f0 is exceeded, the rear wheel steering angle θ _r increases in proportion to the front wheel steering angle θ _r , so that the same effect as the above case is achieved. Further, in such a case, since the rear wheel steering angle θ _r is bent and changed at the steering angle θ _f1 larger than the steering angle θ _f0 , the steering of the left and right rear wheels RW1 and RW2 becomes smooth, and It also has the effect of improving the running stability of the vehicle.

[Brief description of drawings]

1 is a partially cutaway enlarged view of a rotary shaft portion (inside a B1 frame in FIG. 3) of a four-wheel steering system according to an embodiment of the present invention, FIG.
1 is a sectional view taken along the line II-II in FIG. 1, FIG. 3 is an overall schematic view of a vehicle equipped with a four-wheel steering system showing an embodiment of the present invention, and FIG. 4 is FIG. FIG. 5 is a partially cutaway front view of the rear wheel steering mechanism as seen from the front of the vehicle, FIG. 5 is a vertical sectional front view of the rear wheel steering mechanism, and FIG. 6 is a sectional view taken along line VI-VI of FIG. ,
FIG. 7 is a sectional view taken along the line VII-VII of FIG.
The figure shows the torque-rotation angle characteristic graph of the rotating shaft of FIG. 1, and FIG. 9 shows the torque of the input shaft of the rear wheel steering mechanism of FIG.
The rotation angle characteristic graphs and FIGS. 10 and 11 are steering characteristic graphs for the rear wheels with respect to the front wheels. Explanation of symbols A ... front wheel steering mechanism, B ... steering force transmission shaft, C ...
… Rear wheel steering mechanism, FW1, FW2 …… Front wheels, RW1, R
W2 ... rear wheel, SM ... support mechanism, CM ... neutral biasing mechanism, SS ... steering angle ratio sensor unit, 11 ... rack bar, 13 ... steering handle, 23 ... first rotary shaft, 23a , 23b ... Protrusion, 24 ... Second rotating shaft, 24b, 24c ... Through hole, 32 ... Input shaft, 35
...... Actuating rod, 36 ...... Motor, 38 ...... Housing, 42 ...... Rotating member, 44 ...... First support, 48 ......
Rack bar, 55 ... Shaft, 56, 57 ... Retainer, 58 ... Spring, 66 ... Second support, 68 ...
… Pins, 72… Wheels, 75… Worms.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 61-18570 (JP, A) JP-A 60-64074 (JP, A) Actually open 61-50080 (JP, U) Actual-open Sho 62- 176078 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. A front wheel steering mechanism for steering front wheels in response to turning of a steering wheel, and a front end connected to the front wheel steering mechanism and extending rearward for rotation about an axis in response to steering of the front wheels. And a rotation shaft for transmitting the rotation to the rear, and a neutral attachment connected to a rear end of the rotation shaft to steer the rear wheels according to the rotation of the rotation shaft and to bias the steering of the rear wheels to a neutral position. In a four-wheel steering system for a vehicle including a rear wheel steering mechanism having a built-in biasing device, the rotary shaft is divided into first and second rotary shafts in front and rear, and a first joint is formed on the first rotary shaft side. The first and second rotary shafts via a power transmission mechanism having a clearance between the first rotary shaft and the second joint formed on the second rotary shaft side, and
A four-wheel steering system for a vehicle, wherein the first and second rotating shafts are connected by a torsion bar.