JPH06286639A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the durability of a centering mechanism by installing a centering mechanism equipped with a coil-shaped centering spring at the middle part of an input shaft, interposing each elliptical deformation preventing member at both the edges of the spring, and supporting the preventing member so as to be deformed by tension according to the revolution direction of the input shaft. CONSTITUTION:At the middle part of a rear steering shaft 27, a centering mechanism 30 having a coil spring 76 accommodated into a centering mechanism accommodation part 3c is arranged. One edge of the coil spring 76 is supported in an accommodation part 3c so as to be pulling-elastic-deformed by the revolution in the direction of arrow C of the rear steering shaft 27 by a supporting arm 78a. The other edge is supported by a supporting arm 79a so as to be by tensile elasticity by the revolution in the direction of arrow CC similarly. Further, in the vicinity of each edge of a spring 76, contact arms 79b and 78b for preventing the elliptical deformation of the spring 76 are arranged in contact with the inner peripheral surface of the spring 76.

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 vehicle, and more particularly to a rear wheel steering system for a four-wheel steering vehicle.

[0002]

2. Description of the Related Art A four-wheel steering vehicle is equipped with a front-wheel steering device and a rear-wheel steering device to steer the front and rear wheels in an interlocking manner to improve turning stability during high-speed running and low-speed running. The radius of gyration is reduced. The rear wheel steering system includes an input shaft that extends from the front wheel steering system and that rotates in conjunction with steering of the front wheels, a steering shaft that can steer the rear wheels by displacing in the vehicle width direction, and a steering that rotates the input shaft. There is a mechanism provided with a mechanism for converting the displacement of the shaft in the axial direction and a centering mechanism provided in the middle of the input shaft for positioning the input shaft at a neutral position and maintaining the straight traveling state of the rear wheels. 62-181960).

The centering mechanism comprises a coil spring arranged around the input shaft. The coil spring is elastically deformed when the input shaft rotates with respect to the housing, and thus exerts a spring force that returns the input shaft to the neutral position.

[0004]

By the way, when the input shaft rotates, the end portion of the coil spring is pulled and elastically deformed. Therefore, the coil spring is
It may be deformed into a substantially elliptical shape when viewed in the axial direction, and the portion protruding outward in the radial direction may slide on the housing.
Therefore, there is a problem that the centering spring and the housing are worn and the durability of the centering mechanism is deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a rear wheel steering system for a vehicle which can improve the durability of the centering mechanism.

[0006]

To achieve the above object, according to the present invention, an input shaft extending from a front wheel steering device of a vehicle and rotating in association with steering of the front wheels, and extending in a vehicle width direction,
A rear wheel steering system comprising: a steering shaft that moves in the vehicle width direction to steer the rear wheels; and a unit that converts the rotation of the input shaft into a displacement in the axial direction of the steering shaft, wherein a centering mechanism is provided in the middle of the input shaft. This centering mechanism supports a housing, a coil-shaped centering spring housed in the housing and arranged around the input shaft, and one end of the centering spring, and the input shaft rotates in one direction with respect to the housing. The first support part that pulls and elastically deforms one end of the spring and the other end of the centering spring that pulls and elastically deforms the other end of the spring when the input shaft rotates in the other direction with respect to the housing. A second supporting portion that extends from the first and second supporting portions, and the centering spring extends near the respective ends of the centering spring. Contact with the inner peripheral surface, in which the centering spring is configured by including the first and second contact portions to prevent the deformation in an elliptical shape.

[0007]

When the front wheel is steered to rotate the input shaft, the first or second support portion of the centering mechanism pulls one end or the other end of the centering spring to elastically deform it. At this time, each contact portion prevents the centering spring from deforming into a substantially elliptical shape when viewed in the axial direction. Therefore, the centering spring does not slide on the housing.

[0008]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a rear wheel steering system according to the present invention. The rear wheel steering system 1 includes a housing 3 and
A steering shaft 5 penetrating the housing 3 in the vehicle width direction, a small steering angle steering means 6, a large steering angle steering means 7, a coupling mechanism 8 and an electronic control unit 9 (FIG. 2) which are housed in the housing 3. Has been done.

The housing 3 is mounted on the rear portion of the vehicle body and extends in the vehicle width direction. The housing 3 has a cam accommodating portion 3b located on one side of the cylindrical portion 3a and a centering mechanism accommodating portion located in front of the cam accommodating portion 3b. The cylindrical portion 3c includes a portion 3c and a rear cover 4 that closes the cam housing portion 3b from the rear of the vehicle.
The cam housing 3b and the centering mechanism housing 3c are integrally formed.

As shown in FIGS. 2 and 3, the rear cover 4 is composed of an annular wall 4a, and an outer peripheral wall 4b and an inner peripheral wall 4c extending from the outer peripheral edge and the inner peripheral edge of the annular wall 4a toward the front of the vehicle. It is integrally formed of a material having excellent heat dissipation, such as aluminum. The space inside the rear cover 4 is defined by an annular seal plate 11.
Therefore, the space inside the rear cover 4 is oil-tightly separated from the space inside the cam housing 3b. A hole 4d is formed at a predetermined position on the annular wall 4a.

The housing 3 is fixed to, for example, a suspension mounting subframe (not shown). The steering shaft 5 extends in the vehicle width direction in the housing 3, is supported by bearings (not shown) at a plurality of positions, and is movable in the vehicle width direction with respect to the housing 3. Both ends of the steering shaft 5 are connected to knuckle arms (both not shown) via tie rods. Therefore, when the steering shaft 5 moves in the vehicle width direction, the knuckle arm rotates and a steering angle is given to the rear wheel (not shown).

The small steering angle steering means 6 is a steering means utilizing hydraulic pressure, and is composed of a hydraulic cylinder 13 and a steering angle control valve 14 as shown in FIG. Hydraulic cylinder 13
Is formed by partitioning the inside of the housing 3 with a pair of partition walls 15 and 16. The partition walls 15 and 16 are arranged near both ends of the cylindrical portion 3a. Each of the partition walls 15 and 16 is formed in an annular shape, and the steering shaft 5 slidably penetrates through a central hole. The partition walls 15 and 16 and the housing 3 and the steering shaft 5 are oil-tightly sealed.

The piston 17 is arranged between the partitions 15 and 16 and divides the inside of the cylindrical portion 3a into hydraulic chambers 18 and 19. As shown in detail in FIG. 4, the piston 17 is composed of an annular piston body 17a and an extending portion 17b extending from the inner peripheral edge of one side surface of the piston body 17a in a cylindrical shape along the axial direction. Is molded into. The piston body 17a is fitted and fixed in a predetermined position of the steering shaft 5. Therefore, the piston 17 and the steering shaft 5 move integrally.

The cylindrical portion 3 facing each hydraulic chamber 18, 19
Ports 21 and 22 are formed at predetermined positions of a (FIG. 1). The steering angle control valve 14 is, for example, an electromagnetic switching valve having four ports and is fixed at a predetermined position of the cylindrical portion 3a of the housing 3, and thus these are unitized. The first port of the steering angle control valve 14 is connected to a hydraulic pump (not shown), and the second port is connected to a reserve tank (not shown). Further, the third port of the steering angle control valve 14 is connected to one port 21 of the hydraulic cylinder 13, and the fourth port is connected to the other port 22 of the hydraulic cylinder 13 via an oil passage 23. Further, the solenoid of the steering angle control valve 14 is electrically connected to the electronic control unit 9, so that the steering angle control valve 14 is operated by the electronic control unit 9 to switch.

The electronic control unit 9 has a microcomputer and is constructed on an annular substrate. As shown in FIG. 2, the electronic control unit 9 is arranged in the space defined by the seal plate 11 in the rear cover 4 and is screwed and fixed to the rear cover 4. A connector 25 is attached to the electronic control unit 9 at a position facing the hole 4d. The connector 25 extends to the outside of the rear cover 4, and various sensors are electrically connected to its input side. The various sensors include, for example, a steering angle sensor 45, a steering wheel angle sensor (not shown), a vehicle speed sensor, a front power steering pressure sensor, an oil temperature sensor, an oil amount sensor, a lateral G sensor, and the like. The connector 25 is screwed and fixed to the rear cover 4 to prevent damage to the board when the connector 25 is connected.

The electronic control unit 9 operates the rudder angle control valve 14 based on detection signals from various sensors according to a control program stored in advance, and the hydraulic cylinder 1
3 is operated to reciprocate the steering shaft 5 to give the rear wheel a steering angle suitable for the running state of the vehicle. The large steering angle steering means 7 is
A so-called steering means that mechanically imparts an opposite phase to the rear wheels,
It is composed of a rear steering shaft 27, an inner cam mechanism, a sleeve 29, a centering mechanism 30, and the like.

As shown in FIG. 1, the sleeve 29 is fitted onto the steering shaft 5 and is relatively movable in the axial direction. One end of this sleeve 29 is located near the left end of the cylindrical portion 3a of the housing 3, while the other end is located on the piston 17 side.
It is located in the vicinity. The rear steering shaft 27 shown in FIG. 2 extends from a front wheel steering device (both not shown) that steers the front wheels, and rotates according to the steering angle when the steering wheel in the driver's seat is operated. The rear steering shaft 27 extends to the rear part of the vehicle via an appropriate number of joints, and the rear end thereof is arranged in the cam accommodating portion 3b of the housing 3 and is rotatably supported by a plurality of bearings. . A drive gear 31 is fixed to the rear end of the shaft 27.

The internal cam mechanism includes a rotor 33 and an internal cam 3.
4, a roller 37, a shaft rotation preventing mechanism, and the like, and is arranged in the cam accommodating portion 3b. The rotor 33 has a disc shape, and a flange 33a extending forward of the vehicle is integrally formed on the front side surface and a hub 33b is integrally formed on the rear side surface (FIG. 2). The rotor 33 is rotatably supported by a rotor shaft 39 extending in the vehicle front-rear direction. The rotor shaft 39 is press-fitted into the hole 33c at the center of the rotor 33, so that they rotate together. The front end portion of the rotor shaft 39 is connected to the housing 3 via a needle bearing 41, and the rear end portion is connected to the inner peripheral wall 4c of the rear cover 4 via a ball bearing 42.
Each of them is rotatably supported. The rear end of the rotor shaft 39 is fastened to the ball bearing 42 with a bolt 43.
The displacement of 9 in the axial direction is prevented.

On the rear end surface of the rotor shaft 39,
The hole is bored, and the detection portion of the steering angle sensor 45 is inserted. The rudder angle sensor 45 is screwed and fixed to the rear cover 4, and the detecting portion is engaged with a concave portion of the inner peripheral surface of the center hole of the rotor shaft 39. Therefore, the steering angle sensor 45 can detect the rotational position of the rotor shaft 39.

A driven gear 47 and an inner cam 34 are attached to the rotor 33. These rotors 33,
The driven gear 47 and the inscribed cam 34 are positioned with high precision by pins and are fixed by screws with a plurality of bolts 48. The driven gear 47 superposed on the rear side surface of the rotor 33 has a ring shape, is fitted into the hub 33b, and is arranged concentrically with the rotor shaft 39. The gear provided on the outer periphery of the driven gear 47 meshes with the drive gear 31, and therefore, when the drive gear 31 rotates, the driven gear 47 and the rotor 33 rotate at a rotational speed reduced at a predetermined ratio. Therefore, when the steering wheel is operated and the steering angle reaches the maximum values θ3 and θ4 in both left and right directions, the driven gear 47 and the rotor 33 rotate 90 degrees in both left and right directions (FIGS. 5B and 5C). )).

The inner cam 34 has a ring shape, is fitted on the inner surface of the flange 33a, and is superposed on the front side surface of the rotor 33. The inner circumference of the inscribed cam 34 has a bilaterally symmetrical cam surface. As shown in FIG. 5, the contour of the cam surface is composed of a pair of inoperative portions 51, convex portions 52, and concave portions 54. More specifically, each inactive portion 51 abuts on a pair of rollers 37 described later in the state of the inner cam 34 in the straight traveling state of the vehicle (the state shown in FIG. 5A), and one point in the figure It coincides with a virtual reference circle D indicated by a chain line.
The convex portion 52 is located below each inactive portion 51 in the drawing (a) and projects into the virtual reference circle D. The recesses 54 are located above the inactive portions 51 in FIG. 5A and are recessed outside the virtual reference circle D. The respective non-actuating portions 51, the convex portions 52 and the concave portions 54 are smoothly and continuously formed to form the contour of the cam surface. On this cam surface, the inscribed cam 34 has the rotor 33
It is finished as a single item before being assembled to.

Each roller 37 is a cam follower that rolls along the cam surface. Each roller 37 is attached to the sleeve 29 via a roller shaft 58 and a bracket 62. The rollers 37 are arranged side by side in the vehicle width direction and abut on the cam surface at mutually opposite positions with respect to the center of the inscribed cam 34. Therefore, when the inner cam 34 rotates, the rollers 37 roll without separating from the cam surface and are displaced in the vehicle width direction along the contour shape of the cam surface. With the displacement of each roller 37, the sleeve 29 is attached to the housing 3
Move against.

Each roller shaft 58 is composed of a large diameter portion and a small diameter portion, which are integrally molded. The small diameter portion is attached to the support portion 62a of the bracket 62. Further, the large diameter portion is located in the area near the inner side of the inscribed cam 34, and therefore, the roller 37 which supports the roller 37 so as to be rotatable relative to each other.
Are brought into rolling contact with the cam surface. The small diameter portion and the large diameter portion of the roller shaft 58 are eccentric to each other by a small distance (for example, about 1 mm). Therefore, when the roller shaft 58 is assembled to the bracket 62, by rotating the roller shaft 58 with respect to the bracket 62, the distance between the cam surface and the roller 37 can be changed, which may cause a manufacturing error of each member. It is possible to absorb the gap between the cam surface and the roller 37 which is caused by this.

The bracket 62 is fixed to the outer peripheral surface of the sleeve 29 and is arranged in front of the inscribed cam mechanism. As shown in detail in FIG. 6, the bracket 62 is composed of a tubular portion 62b to which the sleeve 29 is fitted, and a pair of support portions 62a hanging from both ends of the tubular portion 62b, which are integrally formed. ing. The tubular portion 62b is fixed to the sleeve 29 so as not to be relatively rotatable. A shaft insertion hole 62 extending in the vehicle front-rear direction is formed in each of the support portions 62a.
The small diameter portion of the roller shaft 58 is inserted into each shaft insertion hole 62c and is fixed by the nut 57.

The shaft rotation preventing mechanism comprises a guide plate 56 fixed to the housing 3, a roller 59 attached to each roller shaft 58, and the like, and prevents the steering shaft 5 and the sleeve 29 from rotating. is there. The guide plate 56 is disposed in front of the rotor 33 and is screwed and fixed to the housing 3 with a plurality of bolts 60 (FIGS. 2 and 3). The guide plate 56 includes a bracket 62
A pair of notches 56a are formed so as to face the respective support portions 62a. Each notch 56a extends in the vehicle width direction, and the width in the vertical direction is set to be substantially the same as the diameter of the roller 59.

On the other hand, each roller 59 is connected to the guide plate 5
It is disposed in the notch 56a of No. 6 and is displaceable in the vehicle width direction with respect to the guide plate 56, but is not displaceable in the vertical direction. Further, each roller 59 is rotatably attached to a position of the roller shaft 58 in front of the roller 37 as a cam follower. Therefore, when each roller 37 of the inscribed cam mechanism rolls along the cam surface,
While the movement of the roller shaft 58 is limited only in the vehicle width direction, the roller shaft 58 does not tilt even when a force for tilting the roller shaft 58 acts, and the rotation of the steering shaft 5 can be prevented. .

The head portion 60a and the shaft portion 60b of each bolt 60 are eccentric to each other.
Therefore, when the guide plate 56 is assembled to the housing 3, the rotation of each bolt 60 can be prevented, and each bolt 60 can be fixed by the nut 64 (FIG. 2) without locking the head portion 60a with a jig or the like. Can be fixed.

The connecting mechanism 8, as shown in detail in FIG.
A spring 66 interposed between the sleeve 29 and the extending portion 17b of the piston 17, a pair of spring seats 67 and 68 for holding the spring 66 from both ends and limiting the elastic deformation amount thereof, and a cylinder surrounding these. Body 69
Etc. This cylinder 69 is the piston 1
The spring seat 67 on the large steering angle steering means 7 side (left side in the drawing) is locked at the tip portion while being fixed to the extending portion 17b of the steering wheel 7.

The spring seats 67 and 68 are loosely fitted around the sleeve 29 and are relatively movable in the axial direction.
Each spring seat 67, 68 is arranged between a pair of locking pieces 71, 72 fixed to the sleeve 29. The respective locking pieces 71, 72 are fixed at a predetermined distance, so that the respective spring seats 67, 68 can move in the axial direction within the range of the distance L1.

The spring 66 is used for each spring seat 6
A predetermined preset force is applied between 7 and 68 to be contracted to have a predetermined spring force. Therefore, the sleeve 29
It is also possible to transmit the reciprocating motion of the piston 17 to the piston 17 without elastically deforming it, and it is also possible to elastically deform and absorb the movement of the piston 17 with respect to the sleeve 29. That is, when the hydraulic cylinder 13 is not operating, the sleeve 29 is moved to the right in the vehicle width direction by the inner cam mechanism under the condition that the road surface resistance is small, and the left spring seat is moved through the left locking piece 71. When 67 is moved in the same direction, the spring 66 does not elastically deform and moves the right side spring seat 68 by the same distance as the moving distance of the left side spring seat 67. Therefore, the piston 17
The extending portion 17b of the steering wheel 5 moves to the right by the same distance, and the steering shaft 5 steers the rear wheels to the left. Similarly, when the sleeve 29 is moved leftward in the vehicle width direction and the right locking piece 72 moves the right side spring seat 68 in the same direction, the spring 66 does not elastically deform and the left side spring seat 67 does. To move the piston 1 through the cylindrical body 69.
The extension 17b of 7 is pulled to the left. Therefore, the piston 17 moves to the left, and the steering shaft 5 steers the rear wheels to the right.

Further, when the sleeve 29 is displaced as described above under the condition that the resistance of the road surface is large, the spring 66 is used.
Is elastically deformed and the spring seats 67 and 68 contact each other, and the displacement of the sleeve 29 is transmitted to the steering shaft 5. On the other hand, when the sleeve 29 is not moving and the hydraulic cylinder 13 operates to move the piston 17 to the right in the vehicle width direction, the extending portion 17b pulls the left spring seat 67 via the cylindrical body 69. Therefore, the spring 66 begins to contract, and accordingly, the piston 17 starts moving, but this movement is not transmitted to the right side spring seat 68. When the amount of elastic deformation of the spring 66 reaches the distance L1, the spring seats 67 and 68 come into contact with each other. At this time, the sleeve 29 is attached to each roller 37.
Cannot be moved to rotate the inner cam 34, and therefore, the sleeve 29 cannot be moved unless the driver performs a steering operation. For this reason,
After the spring seats 67 and 68 have come into contact with each other,
The piston 17 cannot move, and the left maximum steering angle β1 by the small steering angle steering means 6 is determined.

Similarly, when the hydraulic cylinder 13 operates to move the piston 17 to the left in the vehicle width direction, the piston 17 also moves within the range of the distance L1 and the small steering angle steering means 6 is operated.
The right-side maximum steering angle β2 by is determined. As shown in FIGS. 7 and 8, the centering mechanism 30 includes a centering spring 76, a pair of sleeves 78 and 79, a pair of eccentric plates 81 and 82, and a pair of adjusting bolts 84 and 8.
5 and the like, which are housed in the centering mechanism housing 3c of the housing 3 and arranged around the rear end of the rear steering shaft 27.

The pair of eccentric plates 81, 82 are arranged at a predetermined interval, and the rear steering shaft 27
It is fitted so that it cannot rotate relative to it. Each eccentric plate 81, 82 has a disc shape, and is eccentric to the opposite sides in the radial direction of the rear steering shaft 27. The eccentric plates 81, 82 are provided with pressing pieces 87, 8
8 is attached. Each pressing piece 87, 88 is arranged at a portion where the radial dimension of the eccentric plates 81, 82 is maximized, and the pressing portions 87a, 88a are projected from the surfaces of the eccentric plates facing each other. An elastic member is fixed to one side surface of the pressing portion 87a on the first eccentric plate 81 side and the other side surface of the pressing portion 88a on the second eccentric plate 82 side.

The pair of sleeves 78 and 79 are arranged between the eccentric plates 81 and 82 while being in contact with them, and are fitted into the rear steering shaft 27 via bearings (not shown). Therefore, the sleeves 78 and 79 are provided with the rear steering shaft 27 and the eccentric plates 81 and 8 respectively.
It is relatively rotatable with respect to 2. A spacer 93 is provided between the sleeves 78 and 79,
Axial displacement is blocked.

Each of the sleeves 78 and 79 has a support arm 78.
a, 79a and contact arms 78b, 79b. These arms 78a, 79a, 78b, 79b
Extend radially. The support arm 78a of the first sleeve 78 faces one side surface of the pressing portion 87a on the side of the first eccentric plate 81, and the support arm 79a of the second sleeve 79 faces the pressing portion 88a on the side of the second eccentric plate 82. Are arranged so as to face the other side surface. Therefore, when the rear steering shaft 27 rotates in the direction of arrow C, the support arm 78a of the first sleeve 78 is
The pressing portion 87a on the side of the eccentric plate 81 rotates in the same direction while being pressed by the pressing portion 87a on the side of the second eccentric plate 82.
Is separated from the support arm 79a of the second sleeve 79. Conversely, when the rear steering shaft 27 rotates in the direction of arrow CC, the support arm 79a of the second sleeve 79 is pushed by the pressing portion 88a on the second eccentric plate 82 side and rotates in the same direction. The pressing portion 87a on the side of the first eccentric plate 81 has a support arm 78 of the first sleeve 78.
Separate from a.

An anchor pin 95 is erected on each of the support arms 78a and 79a of the sleeves 78 and 79. Each anchor pin 95 extends in a direction facing each other. Abutment arm 78 of each sleeve 78, 79
b and 79b are provided at positions shifted by approximately 90 degrees on the pressing portions 87a and 88a sides of the support arms 78a and 79a. The tip surfaces of the contact arms 78b and 79b are in contact with the inner peripheral surface of the centering spring 76, and prevent the centering spring 76 from being pulled inward in the radial direction when deformed.

The adjusting bolts 84 and 85 are attached to the housing 3 side. First adjusting bolt 8
4 extends from the other of the support arms 78a of the first sleeve 78 in the direction of arrow C.
8a is in contact with the other side surface. Therefore, the first adjusting bolt 84 restricts the rotation of the first sleeve 78 in the arrow CC direction. The second adjusting bolt 85 extends from one of the support arms 79a of the second sleeve 79 along the direction of the arrow CC and abuts one side surface of the support arm 79a. Therefore, the second adjusting bolt 85
The rotation of the second sleeve 79 in the arrow C direction is restricted. Elastic members are fixed to the tips of the adjusting bolts 84 and 85, respectively.

When the adjusting bolts 84 and 85 are rotated, the adjusting bolts 84 and 85 are displaced in the axial direction, and the protrusion amount with respect to the housing 3 can be changed. Therefore, the position of each support arm 78a, 79a can be adjusted at the position of the rear steering shaft 27 in the rotation direction (hereinafter referred to as the straight-ahead position) when the vehicle is in the straight-ahead state, and the preload of the centering spring 76 is set to a desired value. Can be set.

A centering spring (hereinafter simply referred to as a spring) 76 is arranged between the support arms 78a and 79a of the sleeves 78 and 79. One end of the spring 76 has an anchor pin 95 on the first sleeve 78 side.
The other end is locked to the anchor pin 95 on the second sleeve 79 side. The spring 76 has a predetermined preload at the straight-ahead position of the rear steering shaft 27, and supports the support arm 78 of the first sleeve 78.
a in the direction of arrow CC to push the first adjusting bolt 84
The support arm 79 of the second sleeve 79.
A is pressed in the direction of arrow C and pressed against the second adjustment bolt 85.

When the rear steering shaft 27 rotates in the direction of arrow C, the spring 76 has the first sleeve 7 pressed against the first eccentric plate 81.
8 is elastically deformed by the support arm 78a, while the rear steering shaft 27 is rotated in the direction of arrow CC, the second sleeve 7 pressed by the second eccentric plate 82 is pressed.
It is elastically deformed by the support arm 79a of No. 9.

The operation of the rear wheel steering system 1 will be described below. First, the large steering angle steering means 7 will be described. Figure 5
Shows the positional relationship between the inner cam 34 of the large steering angle steering means 7 and each roller 37. In FIG. 5A, the steering wheel is not operated, and the inner cam 34 (that is, the inner cam in the straight-ahead position) and the roller 37 in the straight traveling state of the vehicle.
Shows the positional relationship with. In this state, each roller 3
7 is in contact with the non-actuating portion 51 of the cam surface. And
Since the non-actuated portion 51 coincides with the virtual reference circle D, the displacement distance of each roller 37 in the vehicle width direction becomes 0, the sleeve 29 does not move, and the steering shaft 5 does not steer the rear wheels. .

From this state, when the driver operates the steering wheel to the right, the inner cam 34 rotates in the direction of arrow C. As a result, each roller 37 rolls along the cam surface, but within a range in which the steering wheel operation angle is small, each roller 37 rolls over the non-actuated portion 51. Therefore, the displacement distance of each roller 37 in the vehicle width direction is a value. It is held at 0.

Then, when the steering wheel operation angle, that is, the steering angle reaches the angle θ1,
The roller 37 on the left side in the middle reaches the convex portion 52 on the cam surface, and the roller 37 on the right side reaches the concave portion 54, and the rollers 37 start to be displaced rightward in the vehicle width direction. As a result, the sleeve 29 and the steering shaft 5 start moving to the right in the vehicle width direction, and therefore the rear wheels are steered to the left.

When the steering wheel is further operated to the right and the steering angle reaches the maximum angle θ3, the inscribed cam 34 rotates to the position shown in FIG. 5 (b), and each roller 37 becomes Cam surface convex portion 52 and concave portion 54
Reach the top (center part) of each. Therefore, the moving distance of the sleeve 29 and the steering shaft 5 reaches the maximum distance, and the steering angle to the left of the rear wheel by the large steering angle steering means 7 reaches the maximum steering angle α1.

On the other hand, if the steering wheel is operated to the left from the state shown in FIG.
(C) Rotate in the direction of the middle arrow CC. Therefore, each roller 3
No. 7 rolls along the cam surface, but in the range where the steering angle is small, each roller 37 rolls on the inactive portion 51, and the displacement distance of each roller 37 to the left in the vehicle width direction is maintained at the value 0.

When the steering angle reaches the angle .theta.2, the roller 37 on the left side in FIG.
The rollers 37 on the right side reach the protrusions 52 on the cam surface,
Therefore, each roller 37 starts to move to the left side in the vehicle width direction, the sleeve 29 and the steering shaft 5 start to move to the left side in the vehicle width direction,
The rear wheels are steered to the right. Then, when the steering wheel is further operated to the left and the steering angle reaches the maximum angle θ4, the inscribed cam 34 rotates to the position shown in FIG. 5C, and each roller 37 is recessed in the cam surface. 54 and the apex (center portion) of the convex portion 52 are respectively reached. Therefore, the moving distance of the sleeve 29 and the steering shaft 5 reaches the maximum distance, and the steering angle to the right of the rear wheel by the large steering angle steering means 7 reaches the maximum steering angle α2.

Next, the small steering angle steering means 6 will be described. The small steering angle steering means 6 is operated by the electronic control unit 9. The electronic control unit 9 repeatedly executes a predetermined program and operates the steering angle control valve 14 based on signals from various sensors. While the vehicle is traveling straight, the electronic control unit 9 operates the steering angle control valve 14 to move the hydraulic cylinder 1
The hydraulic chambers 18 and 19 of No. 3 communicate with each other, and in this state, the piston 17 is held at the neutral position by the neutral biasing force of the spring 66. Therefore, even when an external force in the vehicle width direction is applied to the rear wheels, the rear wheels are maintained in the straight traveling state by applying the predetermined preset force to the springs 66.

From this state, when the electronic control unit 9 switches the position of the steering angle control valve 14 and operates the hydraulic cylinder 13 to move the piston 17 to the right, the steering shaft 5 moves within the range of the distance L1. Therefore, the rear wheel is angled to the left by β
It is steered in the range of 1. Similarly, when the electronic control unit 9 switches the position of the steering angle control valve 14 and actuates the hydraulic cylinder 13 to move the piston 17 to the left, the steering shaft 5 moves within the range of the distance L1 and therefore the rear wheel. Is steered to the right within the range of the angle β2.

The maximum steering angles β1, β2 of the rear wheels by the small steering angle steering means 6 are significantly smaller than the maximum steering angles α1, α2 of the rear wheels by the large steering angle steering means 7. FIG. 9 is a steering characteristic diagram of the rear wheel steering system 1. The steering angles of the rear wheels are set within the shaded area in the drawing by the steering mechanisms 6 and 7 steering the rear wheels. That is, the operation amount of the steering wheel is small, and the steering angle angles θ1 to θ2
Within the range, only the small steering angle steering means 6 steers the rear wheels. Normally, when the vehicle is traveling at high speed, the driver does not largely operate the steering wheel, and the steering angle changes within the above range. Therefore, when the vehicle is traveling at a high speed, the large steering angle steering means 7 does not give a large steering angle to the rear wheels, and when the electronic control unit 9 recognizes the necessity, the small steering angle steering means 6 operates the small steering angle. Are given to the rear wheels to improve the turning performance when changing lanes.

Further, when the steering wheel is largely operated and the steering angle is out of the above range,
When the large steering angle steering means 7 steers the rear wheels and the electronic control unit 9 recognizes the necessity, the small steering angle steering means 6 is used.
Also steer the rear wheels. Therefore, at the time of so-called U-turn of the vehicle, the rear wheels are largely steered to the opposite phase side, the minimum turning radius of the wheels is reduced, and the operability of the vehicle is improved.

On the other hand, the centering mechanism 30 positions the rear steering shaft 27 at the straight traveling position. That is, when the steering operation is not performed, the spring 76 causes the support arms 78a and 79a of the first and second sleeves 78 and 79 to move to the first and second adjustment bolts 8 respectively.
4,85 and thus each of these first arms 78
The a and 79a position the eccentric plates 81 and 82, that is, the rear steering shaft, in the straight-ahead position via the first and second pressing pieces 87 and 88.

From this state, when the steering is operated and the rear steering shaft rotates from its straight-ahead position in the direction of arrow C in FIGS. 7 and 8, the first eccentric plate 81.
The pressing piece 87 presses the support arm 78a of the first sleeve 78. At this time, the support arm 7 of the second sleeve 79
9a contacts the second adjusting bolt 85 and is restricted from rotating in the direction of arrow C. Therefore, the spring 76 elastically deforms, and its spring force increases in the upward direction in FIG. As a result, the spring force of the spring 76 is increased by the first sleeve 7
The supporting arm 78a of No. 8 is pressed in the direction of the arrow CC, and acts so as to return the first eccentric plate 81, that is, the rear steering shaft 27 to its straight-ahead position.

Similarly, when the rear steering shaft 27 rotates from the straight-ahead position in the direction of the arrow CC in the drawing, the pressing piece 88 of the second eccentric plate 82 presses the support arm 79a of the second sleeve 79. First sleeve 7
Since the support arm 78a of No. 8 contacts the first adjustment bolt 84 and is restricted from rotating in the direction of arrow CC, the spring 76 elastically deforms in the direction opposite to the above-mentioned case, and the spring force thereof is as shown in FIG. Increases in the downward direction. Therefore, the spring force of the spring 76 causes the support arm 79 of the second sleeve 79 to move.
It presses a in the direction of arrow C and acts in a direction to return the second eccentric plate 82, that is, the rear steering shaft 27 to its straight-ahead position.

By the way, when the spring 76 is elastically deformed, the respective sleeves 78, 79 are brought into contact with the contact arms 78b, 79.
Assuming that b does not have this spring 76
Deformed into an elliptical shape when viewed in the axial direction, and is retracted radially inward at a portion offset by about 90 degrees from the portion where the support arms 78a and 79a are locked, and the support arm 78a is locked. The part on the opposite side of the part (about 18
At a position offset by 0 °), it protrudes outward in the radial direction, and therefore, the protruding portion slides on the centering mechanism accommodating portion 3c of the housing 3.

In the centering mechanism 30 of the rear wheel steering system 1 according to the present invention, the contact arms 78b, 79b of the sleeves 78, 79 are fixed to the support arms 78a, 79a of the spring 76. It abuts the inner peripheral surface at a position offset by about 90 degrees and prevents the spring 76 from retracting radially inward. Therefore, the deformation of the elliptical shape of the spring 76 is prevented, and the sliding of the spring 76 and the housing 3 can be prevented.

[0056]

As described above, according to the vehicle rear wheel steering system of the present invention, the centering mechanism provided in the middle of the input shaft is housed in the housing and arranged around the input shaft. Supported coiled centering spring and one end of the centering spring,
When the input shaft rotates in one direction with respect to the housing, the first support portion that pulls and elastically deforms one end of the spring and the other end of the centering spring are supported, and the input shaft rotates in the other direction with respect to the housing. A second support portion that pulls and elastically deforms the other end of the spring,
First and second contact portions that extend from the first and second support portions and contact the inner peripheral surface of the centering spring at positions near the ends of the centering spring to prevent the centering spring from deforming into an elliptical shape. And is configured. Therefore, there is an excellent effect that the centering spring can be prevented from sliding on the housing and the durability of the centering mechanism can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a rear wheel steering system for a vehicle to which the present invention is applied.

FIG. 2 is a sectional view of the rear wheel steering system taken along the line II-II in FIG.

3 is a view of the rear cover of FIG. 1 as viewed from the rear of the vehicle.

4 is a cross-sectional view of the connecting mechanism of FIG.

5 shows a schematic configuration of the inscribed cam mechanism of FIG. 1, (a)
Is a diagram showing the positional relationship between the cam surface and each roller in a straight-ahead position, (b) is a diagram showing the positional relationship between the cam surface and each roller when steered to the same phase side, and (c) is an opposite phase side FIG. 6 is a diagram showing a positional relationship between the cam surface and each roller in a state in which the roller is steered to the right.

FIG. 6 is a view showing a shaft rotation preventing mechanism of an inner cam mechanism.

7 is a cross-sectional view showing the centering mechanism of FIG.

8 is a cross-sectional view of the centering mechanism taken along the line VIII-VIII in FIG.

9 is a steering characteristic diagram of the rear wheel steering system of FIG. 1. FIG.

FIG. 10 is a graph showing an increase / decrease in spring force of a spring with respect to a rotation angle of the input shaft using a rear steering shaft as an input shaft.

[Explanation of symbols]

 1 Rear Wheel Steering Device 3 Housing 3c Centering Mechanism Housing 3c 5 Steering Axis 6 Small Steering Angle Steering Means 7 Large Steering Angle Steering Means 8 Connection Mechanism 9 Electronic Control Unit 13 Hydraulic Cylinder 14 Steering Angle Control Valve 27 Rear Steering Shaft 29 Sleeve 30 Centering mechanism 34 Inner cam 37 Roller 76 Spring 78, 79 Sleeve 78a, 79a Support arm 78b, 78b Contact arm 81, 82 Eccentric plate

Claims (1)

[Claims] 1. An input shaft that extends from a front wheel steering device of a vehicle and that rotates in conjunction with steering of the front wheels; a steering shaft that extends in the vehicle width direction and moves in the vehicle width direction to steer the rear wheels; And a means for converting the rotation of the shaft into a displacement in the axial direction of the steering shaft, wherein a centering mechanism is provided in the middle of the input shaft, and the centering mechanism is housed in the housing and Supports a coiled centering spring arranged around the axis and one end of the centering spring,
When the input shaft rotates in one direction with respect to the housing, the first support portion that pulls and elastically deforms one end of the spring and the other end of the centering spring are supported, and the input shaft rotates in the other direction with respect to the housing. A second support portion that pulls and elastically deforms the other end of the spring,
First and second contact portions that extend from the first and second support portions and contact the inner peripheral surface of the centering spring at positions near the ends of the centering spring to prevent the centering spring from deforming into an elliptical shape. A rear-wheel steering device for a vehicle, comprising: