JPH0958509A - Rear wheel steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict rotation around a shaft of a rear wheel steering shaft generated according to rotation of a nut member without requiring a restricting means. SOLUTION: The axial canter line O2 of a screw part 11 formed in a part of a rear wheel steering shaft 1 and a nut member 3 screw-fitted to the screw part 11, is made eccentric by a prescribed dimension (d) from the original axial center line O1 of the rear wheel steering shaft 1. Therefore, circumferential directional component force F2 generated on a screw surface of the screw part 11 by rotation of the nut member 3, generates the rotation moment around the axial center line O2 , and does not generate torque around the axial center line O1 , and the restriction of rotation of the rear wheel steering shaft 1 is obviated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to four-wheel steering (4W
S) The present invention relates to a rear wheel steering device configured to steer rear wheels in the same phase or in an opposite phase according to steering of front wheels in a vehicle.

[0002]

2. Description of the Related Art A four-wheel steering vehicle having a structure in which the rear wheels are steered in the same phase or in the opposite phase with the front wheels, which are the original steered wheels, is stable in changing lanes at high speeds. It is widely used as a device that can be carried out for a long time and can contribute to the improvement of the running performance of the vehicle, such as improving the small turning performance at low speed running.

In a four-wheel steering vehicle, both ends of a shaft body (rear wheel steering shaft) extending in the left-right direction of the vehicle body are connected to the left and right rear wheels, and the rear-wheel steering shaft is moved in the axial direction. A rear wheel steering device for steering the rear wheels is provided. The movement of the rear wheel steering shaft for this steering has been conventionally realized by various mechanisms. One of them is to form a threaded portion on the outer periphery of the rear wheel steering shaft for an appropriate length. A rear wheel steering device configured to move a rear wheel steering shaft by applying a rotational force to a nut member screwed to the threaded portion is disclosed in
It is disclosed in Japanese Patent Publication No. 6-156306.

When steering the rear wheels, the steering state of the front wheels,
Since it is required to switch the steering direction according to the traveling state of the vehicle such as traveling speed, and to increase or decrease the steering amount, operation control is required.
As an actuator for rotating the nut member, an electric motor that can easily respond to the above-mentioned operation control is used.

FIG. 3 is a front cross-sectional view of the rear wheel steering system. The rear wheel steering shaft 1 is supported in a cylindrical housing 2 so as to be slidable in the axial direction, and the housing 2 of the housing 2 is supported. Both ends of the rear wheel steering shaft 1 projecting to both sides have separate tie rods.
It is connected to the left and right rear wheels (not shown) via 10, 10, and the sliding of the rear wheel steering shaft 1 in the housing 2 is transmitted to the left and right rear wheels via the tie rods 10, 10 and these are steered. It is designed to work.

The vicinity of one end of the rear wheel steering shaft 1 has a larger diameter than the other part over a predetermined length, and a male screw is engraved on the outer periphery thereof to form a screw portion 11. And the threaded portion
A nut member 3 supported on both sides by a pair of ball bearings 20, 20 fitted on the inner surface of the housing 2 is screwed onto the outer side of the housing 11. A worm wheel 30 is fitted on the outer side of the nut member 3, and a worm wheel (not shown) fixed to the output end of the motor M mounted on the outer side of the housing 2 meshes with the worm wheel 30 inside the housing 2. I am allowed.

Then, the rotational force of the motor M is applied to the nut member 3 through the worm and the worm wheel 30 at the output end, and the rear wheel steering is performed by the screw advance of the screw portion 11 accompanying the rotation of the nut member 3. The shaft 1 slides in the axial direction to steer the rear wheels. The motor M is driven in both forward and reverse directions according to the traveling state of the vehicle such as the steering state of the front wheels and the traveling speed. By this drive, the rear wheels are steered by an appropriate amount in the same or opposite phase to the front wheels.

[0008]

In the rear wheel steering system configured as described above, it is necessary to restrain the rotation of the rear wheel steering shaft 1 around the axis due to the rotation of the nut member 3. This restraint must be realized while allowing the movement in the axial direction, and when a general restraint means such as a key or spline is adopted, there is a problem that strict error management of the fitting portion is required, Even if this error management is performed well, there is a disadvantage that the sliding portion is worn with repeated movement of the rear wheel steering shaft 1 in both the forward and reverse directions, and a good restrained state cannot be maintained.

In the rear wheel steering system shown in FIG. 3, the flat portion 1a provided in the middle portion of the rear wheel steering shaft 1 for a proper length is used to constitute the restraining means 4 for performing the above-mentioned restraining action. There is. The restraint means 4 is proposed by the applicant of the present application and disclosed in Japanese Patent Application Laid-Open No. 6-199247. The restraint means 4 penetrates the peripheral wall of the housing 2 supporting the rear wheel steering shaft 1 substantially orthogonal to the axial direction. The through hole 4a is provided, the rotation stopping member 4b is slidably inserted into the through hole 4a, and the flat portion 1a is gripped by the tip of the rotation stopping member 4b, while at the open end of the through hole 4a. A pressing spring 4d is interposed between the screw member 4c and the rotation stopping member 4b to be screwed together, and the spring force of the pressing spring 4d is adjusted by rotating the screw member 4c. By appropriately adjusting the gripping pressure of the flat portion 1a, good restraint is always performed.

As described above, the rear wheel steering system shown in FIG.
Rotational force applied to the nut member 3 is converted into movement of the rear wheel steering shaft 1 in the axial direction by the screw portion 11 screwed onto the nut member 3 to steer the rear wheel, and an electric motor is used as an actuator therefor. Since the motor M can be used, it is an excellent device that enables proper rear wheel steering under various traveling conditions. However, as described above, it is possible to reliably prevent the rear wheel steering shaft 1 from rotating. There is a drawback that the structure of the restraint means 4 is complicated, and it takes a lot of time and labor to process each part of the restraint means 4 and to adjust the spring force during assembly.

The present invention has been made in view of the above circumstances, and the rotation of the rear wheel steering shaft about the axis, which is caused by the rotation of the nut member, can be reliably restrained without the need for restraint means. An object of the present invention is to provide a rear wheel steering device having a simple structure.

[0012]

SUMMARY OF THE INVENTION A rear wheel steering system according to the present invention has a nut formed on a rear wheel steering shaft that moves in the axial direction to steer the rear wheel, and is screwed into the threaded portion. In a rear wheel steering device that applies a rotational force to a member to perform the movement,
A shaft center line of the screw portion and the nut member is deviated from a shaft center line of the rear wheel steering shaft.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a front sectional view of a rear wheel steering system according to the present invention, and FIG. 2 is an enlarged sectional view of a main part thereof.

The rear wheel steering system according to the present invention is, like the conventional rear wheel steering system shown in FIG. 3, arranged inside the cylindrical housing 2 extending in the left-right direction of the vehicle body in the axial direction. A rear wheel steering shaft 1 slidably supported is provided, and both ends of the rear wheel steering shaft 1 projecting on both sides of the housing 2 are connected to left and right rear wheels (not shown) via separate tie rods 10, 10. The sliding of the rear wheel steering shaft 1 in the housing 2 is transmitted to the left and right rear wheels through the tie rods 10 and 10 so that they are steered.

A large-diameter portion 21 having a larger diameter than the other portion is formed in the vicinity of one end of the housing 2 over a predetermined length range, and an opening of the large-diameter portion 21 is formed. The end is closed by a cover plate 22 that is screwed into a threaded portion on the inner periphery of the end plate. The rear wheel steering shaft 1 is supported by a bearing bush 23 fitted to the inner periphery of the cover plate 22 and a bearing bush 24 fitted to the opening on the other end side of the housing 2 in the axial direction. It is designed to allow sliding and rotation around the axis.

Inside the large-diameter portion 21, a cylindrical nut member 3 having an internal thread on a part or all of its inner circumference is rotatably supported by a pair of ball bearings 20, 20. A worm wheel 30 is integrally fitted on the outer side of 3. A motor M is attached to the outside of the large-diameter portion 21 approximately at the center in the axial direction, and a worm (not shown) fixed to the output end of the motor M is attached to the worm wheel 30 inside the large-diameter portion 21. The rotational force generated by the motor M, which is engaged, is transmitted to the nut member 3 via the worm and the worm wheel 30 at the output end, and the nut member 3
However, it is designed to rotate around its axis.

Ball bearings 20, which support both sides of the nut member 3,
Reference numeral 20 denotes angular contact ball bearings as shown in FIG. 2, which are screwed into the cover plate 22 to press the respective outer rings against the front end surface of the cover plate 22 and the shoulder surface at the end of the large diameter portion 21, Further, one inner ring is directly pressed against the stepped surface provided on the outer periphery of the nut member 3 on the one hand, and the other inner ring is indirectly pressed via the worm wheel 30 on the other side, and they are assembled under a predetermined preload, The above-mentioned rotation of the nut member 3 is designed to be firmly supported in both radial and thrust directions.

On the other hand, in the rear wheel steering shaft 1 supported inside the housing 2, a portion located inside the large-diameter portion 21 has a larger diameter than the other portions over a predetermined length. A threaded portion 11 is formed by engraving a male screw on the outer periphery.
Reference numeral 11 is screwed into a female screw on the inner surface of the nut member 3. The screw formed on the outer circumference of the threaded portion 11 and the inner circumference of the nut member 3 has excellent pitch accuracy and is used as a lead screw for feeding a machine tool, or between a male screw and a female screw. It is desirable to use a ball screw that has balls interposed therein and can obtain excellent transmission efficiency, but is not limited thereto.

[0019] The characteristic of the rear wheel steering apparatus according to the present invention, as shown in FIGS. 1 and 2, the axial center line O ₂ of the threaded portion 11 and the axial center line O ₁ of the rear wheel steering shaft 2 They are not the same, but they are offset by a predetermined dimension d. This deviation is due to the width of the step between the threaded portion 11 and the portions on both sides of this,
It is clear that they are different at the top and bottom of FIG.

On the other hand, the nut member 3 screwed into the screw portion 11 is also adapted to rotate on the axis O ₂ .
This means that the ball bearing that supports both sides of the nut member 3
It is apparent that the width of the step between the fitting hole formed to fit 20 and 20 and the inner peripheral surface of the large-diameter portion 21 therebetween is different in the upper and lower parts of FIG.

Thus, in the rear wheel steering system according to the present invention constructed as described above, the motor M is driven in both forward and reverse directions according to the running state of the vehicle such as the steering state of the front wheels and the running speed. As a result, the rotational force of the motor M is applied to the nut member 3 via the worm and the worm wheel 30 at the output end, and the rear wheel steering shaft 1 is driven by the screwing of the screw portion 11 as the nut member 3 rotates. The rear wheels, which slide in the longitudinal direction and are connected to both sides of the rear wheel steering shaft 1 via the tie rods 10, 10, are steered by an appropriate amount in the same phase or in the opposite phase as the front wheels.

At this time, in the screw portion 11, as shown in FIG. 2, the rotational force F of the nut member 3 acts along the inclination of the screw surface formed on the outer peripheral surface, and the axial length of the rear wheel steering shaft 1 is increased. The sliding in the direction is caused by the action of the axial force component F ₁ of the rotational force F. At this time, a circumferential component force F _{2 of the} rotational force F is also generated on the screw surface of the outer periphery of the screw portion 11, and a rotational moment due to the action of the component force F ₂ is applied to the screw portion 11, The moment cannot be the rotational moment of the axis O ₁ of the rear wheel steering shaft 1 which is biased with respect to the axis O ₂ of the screw portion 11, and the nut member 3 is attached to the rear wheel steering shaft 1. The rotational force associated with the rotation of is not applied.

Therefore, the rear wheel steering shaft 1 does not need a restraining means against the rotation around the axis O ₁ , and the bearing bushes 23 and 24 on both sides of the housing 2 can support the rear steering shaft 1 as described above. The circumferential component F ₂ generated as described above is applied as a radial load to the ball bearings 20, 20 supporting the nut member 3.

[0024] Incidentally, the axial center line O ₁ of the rear wheel steering shaft 1, bias amount between the axis line O ₂ of the threaded portion 11 and the nut member 3 d
Is large enough not to be affected by a processing error, and has a large diameter portion of the housing 2 for supporting the nut member 3 inside thereof.
It may be as small as 21 without excessively increasing the diameter, and it is suitable to set it to about several mm.

In the above embodiment, the electric motor M is used as an actuator that applies a rotational force to the nut member 3. However, another rotary actuator such as a hydraulic motor or a reciprocating actuator is used. It is also possible to adopt a configuration in which a rotational force is applied to the nut member 3 by a combination of a link mechanism and a link mechanism, and further by mechanical connection with the steering device for the front wheels.

[0026]

As described above in detail, in the rear wheel steering system according to the present invention, the axial center line of the screw portion formed on the rear wheel steering shaft and the nut member screwed to the screw portion is the shaft of the rear wheel steering shaft. The rotational force applied to the rear wheel steering shaft due to the rotation of the nut member is the rotational moment about the axial center line of the screw part and the nut member, and the axial center line is deviated from this axial center line. No rotational force acts on the rear-wheel steering shaft having, and the restraint means for restraining the rotation of the rear-wheel steering shaft becomes unnecessary,
The present invention has excellent effects such that the movement of the rear wheel steering shaft in the axial direction along with the rotation of the nut member and the steering of the rear wheels according to this movement can be reliably realized with a simple configuration. .

[Brief description of drawings]

FIG. 1 is a front sectional view of a rear wheel steering system according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of a rear wheel steering system according to the present invention.

FIG. 3 is a front sectional view of a conventional rear wheel steering system.

[Explanation of symbols]

1 Rear wheel steering shaft 2 Housing 3 Nut member 11 Screw part 20 Ball bearing 21 Large diameter part 30 Worm wheel M Motor O ₁ shaft core O ₂ shaft core

Claims (1)

[Claims] 1. A rear wheel that moves in the axial direction and steers the rear wheel, has a screw portion formed on a rear wheel steering shaft, and applies a rotational force to a nut member screwed to the screw portion to perform the movement. In the steering system, the axial center lines of the screw portion and the nut member are deviated from the axial center line of the rear wheel steering shaft.