JPH04342664A - Vehicle rear wheel steering device and neutral adjustment device therefor - Google Patents

Abstract

PURPOSE:To reduce the rattling and deadband of a mechanical system by providing a valve spool energization means at a hydraulic selector valve constituting a displacement transmission means for linking two of mechanical and hydraulic systems to each other in a device for controlling a rear wheel steering shaft with the two systems. CONSTITUTION:In a vehicle rear wheel steering device, a mechanical system for causing the displacement of a rear wheel steering shaft is connected to a hydraulic system for hydraulic assistance in the displacement via, for example, a displacement transmission means comprising a parts assembly. Namely, the cross lever 14a of the parts assembly is linked to a hydraulic selector valve 15 for controlling a power steering means. In this case, a valve spool 42 as linked to the engagement end D of the cross lever 14a is so provided in the housing 41 of the valve 15 as to be axially displaceable. Also, between a plug 71 to close one end of the valve housing 41 and one end of the valve spool 42, there is provided a coil spring 72 for normally energizing the spool 42 to the other end.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering system that controls a rear wheel steering shaft for steering the rear wheels using two systems, a mechanical system and a hydraulic system, and a neutral adjustment method thereof.

0002

[Prior Art] Conventionally, as a rear wheel steering device for a vehicle,
For example, as described in JP-A-1-273772, a mechanical system that displaces a rear wheel steering shaft that steers the rear wheels includes an input shaft that inputs the amount of steering angle of the front wheels, and an input shaft that inputs the amount of steering angle of the front wheels. An output rod member that strokes in the direction of a receiving shaft, and a yoke assembly that is linked to and swingably supported by the output rod member, and that controls the stroke amount of the output rod member due to the rotation of the input shaft depending on the swing angle of the output rod member. and a displacement transmitting means linked to the output rod member, the rear wheel steering shaft, and the vehicle body,
a power steering means configured to transmit the stroke amount of the output rod member to the rear wheel steering shaft, and a hydraulic system that assists the displacement of the rear wheel steering shaft hydraulically assists the displacement of the rear wheel steering shaft; It is known to include a hydraulic switching valve for controlling the power steering means, and the hydraulic switching valve is linked to the displacement transmitting means so that the mechanical system and the hydraulic system are connected.

In such a rear wheel steering device, in the mechanical system, the stroke amount of the output rod member and hence the displacement amount of the rear wheel steering shaft is determined by the rotation angle of the input shaft and the swing angle of the yoke assembly, and in the hydraulic system, , the rear wheel steering shaft is hydraulically assisted by the power steering means so that it is displaced by an amount corresponding to the displacement amount. Therefore, in order to accurately control the rear wheel steering axis, that is, the rear wheel steering axis, it is necessary to use the neutral (neutral) It is necessary to connect both systems so that the neutral state (zero phase) of the hydraulic system that hydraulically assists the displacement of the rear wheel steering shaft coincides with the neutral state (zero phase).

By the way, when connecting both systems, the mechanical system (input shaft and yoke assembly) must be neutrally adjusted, and then the displacement transmitting means must be connected to the mechanical system (input shaft and yoke assembly).
In other words, the support part on the vehicle body side of the displacement transmitting means is connected to the output rod member and the rear wheel steering shaft, and the support part on the vehicle body side of the displacement transmitting means is connected to the output rod member and the rear wheel steering shaft, and then the hydraulic switching valve is assembled and the neutral position of both systems is the same when hydraulic pressure is applied. By determining the above, it is possible to eliminate deviations in the neutral of the hydraulic switching valve itself due to machining errors, etc., and to absorb deviations between the neutral of the mechanical system and the neutral of the hydraulic system. In other words, when measuring the stroke of the rear wheel steering shaft (output shaft) with respect to the displacement of the support part with hydraulic pressure applied, there is a dead zone in which the output shaft does not displace with respect to the displacement of the support part, and this dead zone By fixing the support portion at a position corresponding to the neutral position, it is possible to absorb the deviation between the neutral of the mechanical system and the neutral of the hydraulic system.

The above-mentioned dead zone is basically caused by the spring force of the centering spring attached to the rear wheel steering shaft, and when the front wheels are steered with the rear wheels in a neutral state, the hydraulic pressure acting on the rear wheel steering shaft increases. Until the steering force exceeds the spring force of the centering spring, the hydraulic pressure switching valve is operated as the front wheels are steered, and even if the hydraulic pressure increases, the rear wheels are maintained at the neutral position. By providing the above-mentioned centering spring, when the hydraulic pressure in the hydraulic switching valve or the power steering means disappears, or when the mechanical system of the rear wheel steering device is damaged or malfunctions, the above-mentioned hydraulic system is drained and released. When the hydraulic pressure in the cylinder disappears, the rear wheel steering shaft can be positioned at a neutral position, that is, a position where the rear wheels are not steered and are traveling straight. In other words, in the event of a system failure, the rear wheels are
It operates in the same way as an S car, and can be provided with a so-called fail-safe function.

[0006]

[Problem to be Solved by the Invention] However, in the neutral adjustment in which the mechanical system and the hydraulic system are connected while adjusting each neutral so that the neutrals match, it is difficult to adjust the rear wheel steering shaft (output shaft) in response to the displacement of the support part. ), due to the spring characteristics of the centering spring of the rear wheel steering shaft and the disc springs provided on both sides of the spring,
In addition, due to the presence of mechanical play such as the clearance of the fitting parts and the backlash of gears, which are inevitably included in the above mechanical system, hysteresis appears in the above stroke characteristics, resulting in the above dead zone. width and the dead band becomes substantially larger.

That is, as shown in FIG. 13, if there is no hysteresis, the stroke of the output shaft changes along the same polygonal line (see the dashed-dotted polygonal line in FIG. 13) regardless of the direction of displacement of the support part. , Eo appears, but when the above hysteresis occurs, the dead band also increases in width according to the deviation between the outbound and return paths (see the solid line in FIG. 13), and the dead zone increases. The band is essentially E
It is expanded to h. If this dead zone is large, it becomes more difficult to accurately identify the neutral position and perform highly accurate neutral adjustment when performing neutral adjustment between the mechanical system and the hydraulic system, and This has the drawback of being disadvantageous in terms of improving the responsiveness of the rear wheels during wheel steering.

Among the dead zones mentioned above, those caused by play in the mechanical system can be reduced by eliminating play in the assembled state between parts linked in series. This state can be achieved by applying a force that presses one of the linked parts to the other.

[0009] By the way, the hydraulic switching valve of the rear wheel steering system normally has a mechanism that, when a failure occurs in the mechanical system, returns the hydraulic system to the neutral state, thereby moving the rear wheels to the neutral position by the action of the centering spring. A fail-safe mechanism is provided to restore the That is, as shown in FIG. 14, the hydraulic switching valve 105 is housed in the housing 106 so as to be displaceable in the axial direction while being connected to one end of the displacement transmitting means 104a, and the power steering means ( A valve spool 107 is provided to control the supply of hydraulic pressure to the valve spool 10 (not shown).
A coil spring 11 is inserted between the end face of the plug 108 fastened and fixed to the tip of the plug 7 and the stepped portion 106a of the housing 106.
0 (spool centering spring) is installed. The spool centering spring 110 is attached to the housing 10
6 step portion 106a and the shoulder portion 107 of the valve spool 107
The dimensions are set so that the free length is set in a flush state with a, and the hydraulic switching valve 105 is at the neutral position at this time, and the power steering means is also set to be maintained in the neutral state.

Therefore, for example, if a mechanical system failure occurs with the valve spool 107 moved to the right in FIG. 14 and the input side of the displacement transmitting means 104a becomes free, the valve spool 107 will A leftward biasing force is applied from the spool centering spring 110, and as a result, the valve spool 107 is returned to the neutral position.
The power steering means is adapted to be returned to a neutral state. Even if a failure occurs with the valve spool 107 moving in the opposite direction, the valve spool 1
07 is automatically returned to the neutral position. When this fail-safe mechanism works, each linking part is maintained in a free state where no force acts on each other.

However, in order to reduce the above-mentioned dead zone, if a force is constantly applied between each part of the mechanical system to press one against the other, and the parts are assembled without any play, the above-mentioned A biasing force in one direction always acts on the valve spool as well. Therefore, when a failure occurs in the mechanical system, the valve spool is moved in the direction in which the biasing force is applied, and cannot automatically return to the neutral position. In other words, there was a problem in that the failsafe mechanism could no longer function.

The present invention has been made in view of the above-mentioned problems, and in the above vehicle rear wheel steering system, the dead zone is reduced by minimizing the influence of backlash in the mechanical system. An object of the present invention is to provide a vehicle rear wheel steering device and its neutral adjustment method that can ensure a fail-safe function in the event of a mechanical system failure.

[0013]

[Means for Solving the Problems] Therefore, the first invention of the present application is such that a mechanical system for displacing a rear wheel steering shaft for steering rear wheels includes an input shaft for inputting a steering angle amount of the front wheels, and an input shaft for inputting a steering angle amount of the front wheels. An output rod member that receives input from the shaft and strokes in the axial direction, and is linked to and swingably supported by the output rod member, and controls the stroke amount of the output rod member due to the rotation of the input shaft depending on the swing angle. a yoke assembly configured to transmit the stroke amount of the output rod member to the rear wheel steering shaft by a displacement transmitting means linked to the output rod member, the rear wheel steering shaft, and the vehicle body; The hydraulic system for assisting the displacement of the rear wheel steering shaft includes a power steering means for hydraulically assisting the displacement of the rear wheel steering shaft, and a hydraulic switching valve for controlling the power steering means, the hydraulic switching valve for controlling the displacement of the rear wheel steering shaft. In a vehicle rear wheel steering system in which the mechanical system and the hydraulic system are connected to each other by being linked to a transmission means, the hydraulic switching valve has an axially displaced valve within a valve housing while being linked to the displacement transmission means. A valve spool is provided that is retractably housed and controls the supply of hydraulic pressure to the power steering means in accordance with the displacement of the valve spool, as well as biasing means that biases the valve spool in one direction within the valve housing. It was made to look like this.

A second invention of the present application is that in the first invention, a fuse mechanism is provided in the displacement transmission path of the mechanical system from the input shaft to the output rod member, and when the fuse mechanism is activated, The control means for controlling the supply and discharge of hydraulic pressure to the hydraulic system is held on the hydraulic discharge side.

Furthermore, the third invention of the present application is based on the first invention, by comparing the parameter related to the front wheel steering angle and the parameter related to the actual rear wheel steering angle,
Detects failures in the displacement transmission path from the front wheels to the rear wheels,
When a failure is detected, the control means for controlling the supply and discharge of hydraulic pressure to the hydraulic system is held on the hydraulic discharge side.

Furthermore, the fourth invention of the present application is such that the mechanical system for displacing the rear wheel steering shaft for steering the rear wheels includes an input shaft for inputting the amount of steering angle of the front wheels, and an input shaft for receiving input from the input shaft. The yoke assembly includes an output rod member that strokes in the axial direction, and a yoke assembly that is linked to and swingably supported by the output rod member, and that controls the stroke amount of the output rod member due to the rotation of the input shaft depending on the swing angle of the yoke assembly. , the stroke amount of the output rod member is transmitted to the rear wheel steering shaft by a displacement transmitting means linked to the output rod member, the rear wheel steering shaft, and the vehicle body; The hydraulic system for assisting the displacement includes a power steering means for hydraulically assisting the displacement of the rear wheel steering shaft, and a hydraulic switching valve for controlling the power steering means, and the hydraulic switching valve is linked to the displacement transmitting means. In the neutral adjustment method for a vehicle rear wheel steering system in which the mechanical system and the hydraulic system are connected, hydraulic pressure is applied when adjusting the neutral position of a support member that supports one end of the displacement transmission means with respect to the vehicle body. in a state of
The oil pressure supplied to the hydraulic system is monitored while the support member is displaced, and the point at which the oil pressure shows the lowest value is set as the neutral position of the support member.

[0017]

According to the first aspect of the present invention, the hydraulic switching valve is provided with a biasing means for biasing the valve spool in one direction within the valve housing, so that the displacement transmitting means has the following features: A force pushing in one direction from the valve spool eliminates play between the two. At the same time, the pressing force caused by the above-mentioned urging force acts on the connecting portions between the output rod member, the rear wheel steering shaft, and the vehicle body, so that an assembled state with no looseness can be obtained in these connecting portions as well. Furthermore, as a result of the pressing force acting in one direction on the gears or fitting parts of the mechanical system through these linking parts, backlash in the mechanical system due to gear backlash or clearance of the fitting part is also reduced. be done. That is, when the rear wheel steering device is assembled, play in the mechanical system can be minimized, and the dead zone can be reduced. As a result, neutral adjustment between the mechanical system and the hydraulic system can be easily and accurately performed, and the responsiveness of the rear wheels when steering the front wheels can be improved.

According to a second invention of the present application, in the first invention, a fuse mechanism is provided in the displacement transmission path of the mechanical system from the input shaft to the output rod member,
When the fuse mechanism is activated, the control means for controlling the supply and discharge of hydraulic pressure to the hydraulic system is held on the hydraulic discharge side, so if an abnormality occurs in the transmission of displacement of the mechanical system, the control means is held on the hydraulic discharge side. No hydraulic pressure is applied to the rear wheels, and the rear wheels are held in a neutral position. That is, even when a biasing means for biasing the valve spool in one direction is provided, a fail-safe function can be provided, and while maintaining the effect of the first invention,
The safety of the rear wheel steering device can be ensured.

Furthermore, according to the third invention of the present application, in the first invention, by comparing the parameter related to the front wheel steering angle and the parameter related to the actual rear wheel steering angle, When a failure is detected in the displacement transmission path that leads to If an abnormality occurs in the transmission, no hydraulic pressure is applied to the rear wheels, and the rear wheels are held in a neutral position. That is, even when a biasing means for biasing the valve spool in one direction is provided, a fail-safe function can be provided. Moreover, in this case, it is also possible to detect displacement and damage in the intermediate coupling system from the front wheel steering system to the rear wheel steering device, and while maintaining the effect of the first invention, the rear wheel steering device and the front wheel side It is possible to further improve the safety of the displacement transmission system from the rear wheel side to the rear wheel side.

Furthermore, according to the fourth invention of the present application, in the neutral adjustment method of the vehicle rear wheel steering system, when adjusting the neutral position of the support member, the support member is adjusted with hydraulic pressure applied. The neutral position is the point where the hydraulic pressure supplied to the hydraulic system shows the lowest value when displaced.
It is possible to relatively easily and accurately adjust the mechanical system and the hydraulic system so that there is no deviation between their respective neutrals. In particular, even in a type equipped with a biasing means for biasing the valve spool in one direction, the neutral adjustment can be easily and accurately performed by simply monitoring the oil pressure.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. A vehicle rear wheel steering system 1, which is a premise of the present invention, has a steering ratio variable means 11, a power steering means 12, and a rear wheel steering shaft 1, as schematically shown in FIG.
3, a displacement transmitting means 14, and a hydraulic switching valve 15 as a hydraulic assist means. (not shown) and is configured to change the steering ratio according to the vehicle speed.

The rear wheel steering shaft 13 extends in the vehicle width direction, and both ends thereof are connected to a pair of left and right rear wheels via a pair of left and right tie rods and a knuckle arm. The rear wheels are steered by stroke displacement in the width direction. The stroke displacement of the rear wheel steering shaft 13 in the vehicle width direction is performed by the steering ratio variable means 11 and the power steering means 12. The steering ratio variable means 11 changes the steering ratio when steering the rear wheels, and has an output rod member 16 that is stroke-displaced in the vehicle width direction according to the amount of steering angle of the front wheels.

As will be described later, the ratio of the displacement amount of the output rod member 16 to the steering angle amount of the front wheels (corresponding to the steering ratio) depends on the swing angle of the yoke assembly 18 that is swing-driven by the stepping motor 17. It is configured so that it changes depending on the situation. The amount of rotation of the stepping motor 17 is appropriately controlled based on a vehicle speed signal output from a vehicle speed sensor (not shown), and the actual amount of rotation of the stepping motor 17 is detected by a steering ratio sensor (not shown). and is feedback-controlled by the detection signal. Power steering means that controls switching of the hydraulic switching valve 15 according to the stroke displacement amount of the output rod member 16 in the steering ratio variable means 11, and generates a steering force using hydraulic pressure by the hydraulic switching valve 15. 12, and the rear wheel steering is hydraulically assisted according to the displacement of the rear wheel steering shaft 13.

In addition to the output rod member 16, stepping motor 17 and yoke assembly 18 (swing shaft member 22, pendulum arm 23, swing gear 31), the steering ratio variable means 11 includes a bevel gear 21 and a connecting rod. 24
These members 16, 17, 18, 21
, 24 are housed in a casing 25, as shown in detail in FIGS. 2 to 6. The output rod member 16 of the variable steering ratio means 11 is supported by the casing 25 so as to be slidable in the axial direction, and by making a stroke displacement in the axial direction, the output rod member 16 of the variable steering ratio means 11 is moved by the displacement transmitting means 1 as described later.
4, the rear wheel steering shaft 13 is displaced in its axial direction (vehicle width direction), thereby steering the rear wheels linked to both ends of the rear wheel steering shaft 13.

The bevel gear 21 is connected to the output rod member 1.
It is supported by the output rod member 16 via a cylindrical support member 52, on the side of the output rod member 16 from the lever 28 of No. 6, so as to be rotatable along with the output rod member 16 and about an axis coaxial with the output rod member 16. . A pinion 27 at the rear end of the input shaft 26, which meshes with the bevel gear 21 and inputs the amount of steering angle of the front wheels, rotates around the axis as the steering wheel rotates.

The swing shaft member 22 is connected to the output rod member 1.
It has an axis line that can take a position coaxial with oscillating gear 3.
It is fixed at 1. This swing gear 31 meshes with a worm 32 that rotates by the driving of the stepping motor 17, and rotates around the axis of a swing shaft 31a (see FIG. 4) that is perpendicular to the plane of the paper and intersects the axis l1 of the swing shaft member 22. This causes the swing shaft member 22 to rotate at the same time. Note that the shaft 32a of the worm 32 is connected to the motor shaft 17 of the stepping motor 17 via the coupling 54.
a (see Figure 6).

The pendulum arm 23 is connected to the swing shaft member 22 so as to be swingable about the axis l1 of the swing shaft member 22, and the axis l2 of the pendulum arm 23 is
The connection position to the swing shaft member 22 is determined so as to pass through the intersection of the rotation axis of No. 2 and the axis l1 of the swing shaft member 22.

Similar to the rear wheel steering shaft 13, the connecting rod 24 has an axis parallel to the axis l3 of the output rod member 16, and the connecting rod 24 has an axis parallel to the axis l3 of the output rod member 16.
and a pendulum arm 23 to link the output rod member 16 and the yoke assembly 18. The connection to the output rod member 16 is made by splitting and coupling the intermediate portion of the connecting rod 24 to a lever 28 fixed to the end of the output rod member 16, and the connection to the bevel gear 21 is made by
The connection to the pendulum arm 23 is achieved by inserting one end of the connecting rod 24 through an insertion hole formed in the extension 52a of the support member 52 to which the bevel gear 21 is attached. This is accomplished by inserting the pendulum arm 23 through an insertion hole of a ball joint member 33 that is provided so as to be rotatable in the direction.

Therefore, the connecting rod 24 is fixed to the output rod member 16, but the bevel gear 2
1 in the direction of the axis l4, and is slidable relative to the pendulum arm 23 in the direction of the axis l2. Note that the axis l2 of the pendulum arm 23 is tilted with respect to the direction orthogonal to the axis l3 due to the rotation of the swing shaft member 22, and the pendulum arm 23 slides in this tilted direction. Since the included angle change between the axis l2 and the axis l4 is absorbed, the component of the force transmitted from the pendulum arm 23 to the connecting rod 24 in the direction perpendicular to the axis l3 of the output rod member 16 is absorbed at the connecting point, Relative movement in the orthogonal direction is possible.

[0030] In this way, the pendulum arm 23 (yoke assembly 18) and the connecting rod 24 in the variable steering ratio means 11 are connected so that they can be moved relative to each other in the direction perpendicular to the axis l3. Therefore, when the pendulum arm 23 rotates, the pendulum arm 23 and the connecting rod 2
The locus of 4 and the connection point is a circular locus or an elliptical locus on the outer circumferential surface of a cylinder having a predetermined radius and centered on the axis l3. As described above, by connecting the pendulum arm 23 and the connecting rod 24 so that they can move relative to each other in the direction perpendicular to the axis l3 of the output rod member 16, the connecting rod 24
The angle between the axis l4 of the output rod member 16 and the axis l3 of the output rod member 16 can be made constant, and thereby it is possible to prevent a left-right deviation from occurring in the displacement of the output rod member 16.

The output rod member 16 has one end connected to the connecting rod 24 via the lever 28, and the other end of the output rod 36 connected to the cylindrical rod guide 35, which is movable in the direction of the axis l3. The ends of the rod guide 35 and the output rod 36 are supported by the casing 25. The rod guide 35 includes a first cylindrical member 35b having an engaging portion 35a that engages with the engaging end A of the displacement transmitting means 14, and a second cylindrical member 35c screwed onto the first cylindrical member 35b. A spring 37 is interposed between the output rod 36 and the output rod 36. Therefore, the connecting rod 24
When a displacement in the direction of the axis l3 is transmitted to the output rod 36 by
From there, the displacement is transmitted to the engagement end A of the displacement transmission means 14 engaged with the engagement portion 35a. However, the displacement transmission means 14
If the movement of the engaging end A of the output rod 36 is restricted, and therefore a load greater than the spring force of the spring 37 acts on the rod guide 35 when the output rod 36 is displaced, the displacement of the output rod 36 will be caused by the force of the spring 37. It is absorbed by contraction and is not transmitted to the rod guide 35.

The hydraulic switching valve 15 is housed within a valve housing 41 and is movable in the direction of an axis 15 parallel to the axis 13 of the output rod member 16 with respect to the valve housing 41. It consists of a valve spool 42. The valve spool 42 is connected to the output rod member 1 via a displacement transmission means 14, which will be described in detail below.
6 and the rear wheel steering shaft 13. The supply of hydraulic pressure to the power steering means 12 is controlled by this displacement of the valve spool 42. Note that this rear wheel steering shaft 13 is provided with a centering spring 45.
If the hydraulic pressure in the hydraulic switching valve 15 or the power steering means 12 disappears, or if the mechanical system of the rear wheel steering device 1 is damaged or malfunctions, the hydraulic system is drained and the hydraulic pressure in the cylinder of the power steering means 12 is reduced. When the rear wheels disappear, the centering spring 45 positions the rear wheel steering shaft 13 at a neutral position, that is, a position where the rear wheels are not steered and are traveling straight, so as to provide a so-called fail-safe.

The cylinder of the power steering means 12 displaces the rear wheel steering shaft 13 in the vehicle width direction by hydraulic pressure, and the piston 46 directly displaces the rear wheel steering shaft 13.
There are left and right oil chambers 44 on the left and right sides of this piston 46.
, 43 are formed. In addition to the output rod member 16 (rod guide 35), the displacement transmission means 14 engages with the valve spool 42, the rear wheel steering shaft 13, and the vehicle body (support support 38), and is caused by the displacement of the output rod member 16. The valve spool 42 is operated in a direction to displace the valve spool 42 in a predetermined direction, and the valve spool 42
The valve spool 42 is operated in a direction opposite to the above direction by the displacement of the rear wheel steering shaft 13 caused by the displacement of the rear wheel steering shaft 13.

Specifically, the displacement transmitting means 14 has a cross lever 14a consisting of a vertical lever and a horizontal lever, and the engaging end A, which is one end of the vertical lever, is connected to the rod guide 35 of the output rod member 16. The other end of the engagement end B is connected to the rear wheel steering shaft 13, and the engagement end C that is one end of the horizontal lever is connected to the rear wheel steering shaft 13.
is fixed to the vehicle body, and the other end, the engagement end D, is engaged with the valve spool 42, respectively. Note that the cross lever 1 of the housing 25
A sealing member 56 is attached to the portion through which 4a is inserted. Further, the bolt insertion hole 38 of the support support 38 is
h is formed in the shape of an elongated hole, and the support 38 can be fastened and fixed to the vehicle body while being slid and adjusted within the range of the elongated hole 38h. The engaging ends A, B, and D are immovable in the axial direction with respect to the rod guide 35 of the output rod member 16, the rear wheel steering shaft 13, and the valve spool 42, but are movable in other directions. They are rotatably engaged, and the engagement ends C are engaged in a rotatable but non-movable manner by a ball joint (not shown).

Therefore, the output rod member 1 is moved from the state where both the valve spool 42 and the rear wheel steering shaft 13 are in the neutral position.
6 is displaced to the right, the engagement end A of the cross lever 14a is displaced to the right together with the output rod member 16,
Since tire reaction force and reaction force from the centering spring 45 are acting on the rear wheel steering shaft 13 when the engagement end A is displaced,
This engaging end B is axially immovable, and the engaging end C
Since the cross lever 14a is fixedly attached to the support support 38 (vehicle body) and is immovable, the cross lever 14a is tilted about the straight line connecting the engaging end B and the engaging end C, that is, the cross lever 1
4a is operated in a direction to displace the valve spool 42 in a predetermined direction, that is, rightward, and the engaging end D displaces the valve spool 42 in the rightward direction. When the valve spool 42 is displaced rightward from the neutral position in this way, the oil pressure in the right oil chamber 43 increases, the oil pressure in the left oil chamber 44 decreases, and the power steering means 12 is connected to the rear wheel steering shaft 13.
This generates hydraulic pressure that pushes the to the left. The hydraulic pressure that pushes the rear wheel steering shaft 13 leftward increases in accordance with the increase in the rightward displacement of the valve spool 42, resulting in a balance position. When the valve spool 42 is displaced to the right by a predetermined amount from the neutral position to the balance position, the hydraulic pressure of the power steering means 12 generated thereby causes an external force (centering spring force or tire (reaction force, etc.).

When the valve spool 42 is further displaced to the right from this state, the hydraulic pressure generated in the power steering means 12 is applied to the rear wheel steering shaft 1.
3, and the rear wheel steering shaft 13 is displaced to the left by the hydraulic force. and,
When the rear wheel steering shaft 13 is displaced to the left, the engagement end B of the cross lever 14a is displaced to the left together with the rear wheel steering shaft 13, and at this time, the output rod member 16 receives the steering wheel steering force and the like. Since the tire reaction force of the front wheel is acting, the engaging end A is immovable, and the engaging end C is also immovable, so this cross lever 14a is connected to the engaging end A and the engaging end. The rear wheel steering shaft 13 is tilted about the straight line connecting the rear wheel steering shaft 13, and when the rear wheel steering shaft 13 returns to the balance position, the displacement of the rear wheel steering shaft 13 stops.

From this state, when the output rod member 16 is further displaced to the right and the valve spool 42 is displaced to the right, the rear wheel steering shaft 13 is displaced to the left in the same manner as described above.
It stops when the valve spool 42 returns to the balance position, and by repeating this operation, the output rod member 1
The rear wheel steering shaft 13 is displaced by an amount corresponding to the displacement amount of 6,
The rear wheels are steered according to the amount of displacement. In addition, when the output rod member 16 is displaced to the left, the movements of the cross lever 14a, the valve spool 42, and the rear wheel steering shaft 13 are simply reversed from the above case.
Since the operating principle is the same, the explanation will be omitted.

The steering ratio changing control by the steering ratio variable means 11 can be performed based on various factors, and various changing control patterns can be considered. In this embodiment, based on the vehicle speed, the rear wheels are steered in the opposite phase to the steering wheel and front wheels in low speed ranges to improve turning performance, and in high speed ranges, they are steered in the same phase to improve running stability. Controlled to improve performance. Note that in this case, the bundle steering and the front wheel steering are always in the same phase.

In this embodiment, the hydraulic switching valve 15 is provided with a biasing means for biasing the valve spool 42 in a predetermined direction so as to minimize play between components of the mechanical system. It is being That is, as shown in FIG. 9, the valve spool 42 is connected to the hydraulic switching valve 15.
Inside the valve housing 41, the cross lever 14a
The valve spool 42 is disposed between one end of the valve spool 42 and a plug 71 which is displaceably displaceable in the axial direction while being connected to the valve housing 41 (engaging end D) and closes one end of the valve housing 41. A coil spring 72 that always biases the other end (right side in FIG. 9) is compressed.

Therefore, a biasing force from the valve spool 42 in the above direction is always applied to the engagement end D of the cross lever 14a, and as a result, the valve spool 42 is pressed toward the cross lever 14a, and as a result, the gap between the two 42 and 14a is The looseness will disappear. At the same time, the output rod member 16 and the rear wheel steering shaft 13
The pressing force caused by the above-mentioned urging force also acts on the connecting parts A, B, and C with the vehicle body side 38 (support support), and the assembled state with no looseness can be achieved in these connecting parts A, B, and C as well. It will be done. Furthermore, as a result of the pressing force acting in one direction on the gears or fitting parts of the mechanical system through these linking parts A, B, and C, mechanical damage caused by backlash of the gears or clearance of the fitting part may occur. System looseness is also reduced.

That is, when the rear wheel steering device 1 is assembled, the play in the mechanical system can be minimized, and the dead zone can be reduced. As a result, neutral adjustment between the mechanical system and the hydraulic system can be easily and accurately performed, and the responsiveness of the rear wheels when steering the front wheels can be improved.

Furthermore, in this embodiment, the hydraulic switching valve 15
In order to prevent the fail-safe function from being impaired in the event of a failure as a result of providing the coil spring 72 in the input shaft 26, a fuse mechanism is provided in the input shaft 26, and when the fuse mechanism is activated, the hydraulic pressure in the hydraulic system is dissipated. I have to. The above fuse mechanism will be explained below. As shown in FIG. 10, the input shaft 26 includes a shaft main body 81 having a pinion 27 formed at its tip, which is rotatably supported by a cylindrical case 82 via bearings 83 and 84. A flange 85 is attached to the side of 82.
A rotation angle sensor 86 is attached via

00
43. In the middle of the shaft body 81, a notch portion 80 having a substantially U-shaped cross section, for example, is formed in an annular shape as a fuse mechanism of the rear wheel steering device 1. The portion of the shaft body 81 where the notch portion 80 is provided is the rear wheel steering device 1.
The shape and dimensions of the notch portion 80 are set so as to constitute the weakest cross section in the mechanical system. In other words, when the mechanical system is damaged and breaks, it is set so that the breakage occurs preferentially at the notch portion 80 (fuse mechanism). The rotation angle sensor 86 is attached at a position corresponding to the shaft portion 81a between the notch portion 80 and the pinion 27, and outputs a change in the rotation angle of the shaft portion 81a as a change in voltage value.

Although not specifically shown, a steering angle sensor is also provided in the front wheel steering system of the vehicle, and depending on the amount of deviation between the output of the steering angle sensor and the output of the rotation angle sensor 86, System damage is detected electrically. That is, when damage occurs to the mechanical system, the fuse mechanism is activated (in other words, the input shaft body 81 is cut at the notch 80), and the shaft body 81 is separated into front and rear parts at the notch 80, so that the front wheels are steered. Even if the shaft portion 8 between the notch portion 80 and the pinion 27
Rotation due to front wheel steering is not transmitted to 1a, and there is a difference in output between the rotation angle sensor 86 and the front wheel steering angle sensor (not shown), making it possible to detect damage to the mechanical system. Furthermore, by providing sensors at the above two locations, damage to the intermediate shaft connecting the front wheel steering system and the rear wheel steering system 1,
Alternatively, it is also possible to detect deviations in this intermediate connection system.

Then, if the mechanical system of the rear wheel steering device 1 is damaged or the intermediate connection system is damaged, the output of the rotation angle sensor 86 and the front wheel side steering angle sensor (not shown) decreases by a predetermined amount. If the above deviation occurs, a signal is output to an electromagnetic solenoid valve (not shown) that controls the supply and discharge of hydraulic pressure to the hydraulic system, and the solenoid valve (not shown) is switched to the hydraulic discharge side, and the power steering The hydraulic pressure in the cylinder of means 12 is dissipated. Due to this loss of hydraulic pressure,
The rear wheel steering shaft 13 is returned to the neutral position by the spring force of the centering spring 45, making it possible to steer the vehicle as a normal 2WS vehicle. That is, the valve spool 42
Even when a biasing means (coil spring 72) is provided for biasing in one direction, a fail-safe function can be provided and safety can be ensured. Furthermore, in this case, it is possible to detect not only the rear wheel steering device 1 but also the displacement and damage of the intermediate connection system from the front wheel steering system to the rear wheel steering device 1.
It is possible to further improve the safety of the rear wheel steering device 1 and the displacement transmission system from the front wheel side to the rear wheel side.

Next, in the rear wheel steering system 1, we will explain how to adjust the neutrality between the mechanical system and the hydraulic system, which affect the accuracy of the controlled steering amount of the rear wheels. Explain how to connect. still,
This is done after neutrally adjusting the mechanical system (input shaft 26 and yoke assembly 18), and then adjusting the cross lever 14.
A is connected to the mechanical system (that is, to the output rod member 16 and the rear wheel steering shaft 13), the support 38 is temporarily assembled, and the hydraulic switching valve 15 is installed to apply hydraulic pressure.

By performing the adjustment in this state, it is possible to eliminate the deviation of the neutral position of the hydraulic switching valve 15 itself due to errors in machining the valve 15, and also to adjust the neutral position of the mechanical system and the neutral position of the hydraulic system. can absorb deviations. That is, when the support support 38 is displaced in the above state, there is a dead zone in which the rear wheel steering shaft 13 (output shaft) does not displace with respect to the displacement of the support support 38, and the position corresponding to this dead zone is called the neutral position. By fixing the support support 38 as the above, it is possible to absorb the deviation between the neutral state of the mechanical system and the neutral state of the hydraulic system.

In this embodiment, the mechanical system and the hydraulic system are connected via the cross lever 14a, and with hydraulic pressure applied, the hydraulic pressure supplied to the hydraulic system is monitored while displacing the support 38. The neutral position of the support 38 is determined by determining the point at which the oil pressure exhibits the lowest value. An example of a specific measurement system is shown in FIGS. 7 and 8. A locking member 62 that locks (temporarily assembles) the support support 38 is displaceably provided via a ball screw means 63, and a threaded rod 63a of the ball screw means 63 is connected to a stepping motor via a coupling 64. 65, and when the stepping motor 65 is driven, the rotation of the threaded rod 63a causes the locking member 62 to move in the axial direction of the threaded rod 63a. The amount of rotation of the stepping motor 65 is measured by a rotary encoder 66, and the amount of displacement of the locking member 62 is detected by a non-contact distance sensor 67. and encoder 65 are both connected to a controller (not shown) whose main part is a microcomputer. On the other hand, although not specifically shown, the hydraulic system of the rear wheel steering device 1,
For example, on the oil pressure supply side of the oil pressure switching valve 15, a pressure measuring means (pressure gauge) for measuring the oil pressure supplied to the hydraulic system is provided.

When determining the neutral position of the support support 38 using the measurement system configured as described above, first, the pump device (not shown) of the hydraulic system is driven to apply hydraulic pressure.
In this state, the stepping motor 65 is driven. Then, while measuring the displacement of the locking member 62 as the motor 65 is driven, the supply pressure of the hydraulic system is monitored by the pressure measuring means. At this time, the above supply oil pressure is
Displacement of the locking member 62 (that is, displacement of the support support 38)
For example, it changes as shown in the graph of FIG. 11,
The lowest value is shown at a certain displacement position So of the support support 38.

That is, at this displacement position So, the supply pressure to the hydraulic system becomes minimum, and the hydraulic system is maintained in a neutral state. Therefore, at this displacement position So, the support support 3
By pressing 8 against the vehicle body side seat surface and fastening it,
The supporting support 38 can be fixed in a neutral position;
The mechanical system and hydraulic system of the rear wheel steering device 1 can be connected so that there is no deviation between their neutral positions.

The rear wheel steering system 1 according to the present embodiment has the valve spool 42 of the hydraulic switching valve 15 biased in one direction by a coil spring 72 (see FIG. 9), and a spool centering spring inside the hydraulic switching valve 105. 110 (Figure 14
A test was conducted to compare the amount of dead zone with a conventional rear wheel steering system equipped with a conventional rear wheel steering system. The test was conducted by creating samples of three types of hydraulic switching valves for the embodiment of the present invention and six types for the conventional example, and for the rear wheel steering system in which these samples were assembled, neutral adjustment was performed between the mechanical system and the hydraulic system. After performing this, measure the rotation angle (deg.) of the input shaft, which indicates the dead zone amount, and also measure the displacement of the valve spool when a predetermined hydraulic pressure (for example, 15 kg/cm2) is applied to the hydraulic system. went. The setting conditions for the hydraulic system in this test are shown below.・Hydraulic pump relief pressure: 80kg/cm2
・Oil supply flow rate: 4 liters/min ・Oil temperature:
45℃

The test results are as shown in the graph of FIG. 12, and are related to the embodiment of the present invention (see the circle mark on the graph).
In this case, compared to the conventional example (see the x mark in the graph), the amount of dead zone is reduced to about 4 [deg. ] can be reduced,
The effects of the present invention were confirmed.

As described above, according to this embodiment, the rear wheel steering device 1 is assembled by biasing the valve spool 42 of the hydraulic switching valve 15 in one direction within the valve housing 41. In some cases, it is possible to minimize the backlash in the mechanical system and reduce the dead zone. As a result, neutral adjustment between the mechanical system and the hydraulic system can be easily and accurately performed, and
The responsiveness of the rear wheels during front wheel steering can be improved. Furthermore, in this case, a fail-safe function can be provided, and the safety of the rear wheel steering device and further the intermediate connection system from the front wheel side to the rear wheel side can be further improved. Furthermore, in this case, accurate neutral adjustment can be performed by a relatively simple operation of simply monitoring the oil pressure supplied to the hydraulic system.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a vehicle rear wheel steering device according to an embodiment of the present invention.

FIG. 2 is a sectional view of the steering ratio variable means according to the above embodiment.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

4 is a sectional view taken along the line IV-IV in FIG. 2. FIG.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 2.

6 is a sectional view taken along the line VI-VI in FIG. 2. FIG.

FIG. 7 is a schematic diagram showing the relationship between the support and the rear wheel steering device according to the above embodiment.

8 is a sectional view taken along line SS in FIG. 7. FIG.

FIG. 9 is a longitudinal sectional view of the hydraulic switching valve according to the above embodiment.

FIG. 10 is an explanatory longitudinal cross-sectional view of the input shaft according to the above embodiment.

FIG. 11 is a graph showing the relationship between the displacement of the support and the oil pressure according to the above embodiment.

FIG. 12 is a graph showing the amount of dead zone in the rear wheel steering device.

FIG. 13 is a graph showing a dead zone when there is hysteresis.

FIG. 14 is a vertical cross-sectional view of a hydraulic switching valve according to a conventional example.

[Explanation of symbols]

1... Rear wheel steering device 13... Rear wheel steering shaft (output shaft) 12... Power steering means 14... Lever assembly (displacement transmission means) 14a...
Cross lever 15...Hydraulic switching valve 16...Output rod member 18...Yoke assembly 26...Input shaft 38...Support support 41...Valve housing 42...Valve spool 72...Coil spring (biasing means) 80... ...Notch part (fuse mechanism) 86...Rotation angle sensor

Claims (4)

[Claims] Claim 1: A mechanical system for displacing a rear wheel steering shaft that steers the rear wheels includes an input shaft that inputs a steering angle amount of the front wheels, and an output rod member that receives input from the input shaft and strokes in the axial direction. , a yoke assembly that is linked to and swingably supported by the output rod member and controls the stroke amount of the output rod member due to the rotation of the input shaft according to the swing angle of the yoke assembly; The stroke amount of the output rod member is configured to be transmitted to the rear wheel steering shaft by a displacement transmitting means linked to the shaft and the vehicle body side, while a hydraulic system that assists the displacement of the rear wheel steering shaft is configured to transmit the stroke amount of the output rod member to the rear wheel steering shaft. A power steering means for hydraulically assisting the displacement of the wheel steering shaft, and a hydraulic switching valve for controlling the power steering means, the hydraulic switching valve being linked to the displacement transmitting means, so that the mechanical system and the hydraulic system are connected to each other. In the rear wheel steering system of the vehicle to be connected, the hydraulic switching valve is housed in the valve housing so as to be displaceable in the axial direction while being linked to the displacement transmission means, and the hydraulic switching valve is displaceable in the axial direction in accordance with the displacement. A vehicle rear wheel steering system, comprising: a valve spool for controlling the supply of hydraulic pressure; and a biasing means for biasing the valve spool in one direction within the valve housing. 2. A fuse mechanism is provided in a displacement transmission path of the mechanical system from the input shaft to the output rod member, and when the fuse mechanism is activated, a control means for controlling supply and discharge of hydraulic pressure to the hydraulic system is provided. The vehicle rear wheel steering device according to claim 1, wherein the vehicle rear wheel steering device is held on the hydraulic discharge side. 3. By comparing the parameters related to the front wheel steering angle and the parameters related to the actual rear wheel steering angle, a failure in the displacement transmission path from the front wheel side to the rear wheel side is detected, and when the failure is detected, the above-mentioned hydraulic pressure 2. The vehicle rear wheel steering system according to claim 1, wherein the control means for controlling the supply and discharge of hydraulic pressure to the system is held on the hydraulic pressure discharge side. 4. A mechanical system for displacing a rear wheel steering shaft that steers the rear wheels includes an input shaft that inputs a steering angle amount of the front wheels, and an output rod member that receives input from the input shaft and strokes in the axial direction. , a yoke assembly that is linked to and swingably supported by the output rod member and controls the stroke amount of the output rod member due to the rotation of the input shaft according to the swing angle of the yoke assembly; The stroke amount of the output rod member is configured to be transmitted to the rear wheel steering shaft by a displacement transmitting means linked to the shaft and the vehicle body side, while a hydraulic system that assists the displacement of the rear wheel steering shaft is configured to transmit the stroke amount of the output rod member to the rear wheel steering shaft. A power steering means for hydraulically assisting the displacement of the wheel steering shaft, and a hydraulic switching valve for controlling the power steering means, the hydraulic switching valve being linked to the displacement transmitting means, so that the mechanical system and the hydraulic system are connected to each other. In a neutral adjustment method for a connected vehicle rear wheel steering device, when adjusting the neutral position of a support member that supports one end of the displacement transmitting means relative to the vehicle body,
A rear wheel of a vehicle characterized in that the hydraulic pressure supplied to the hydraulic system is monitored while displacing the supporting member in a state where hydraulic pressure is applied, and the point at which the hydraulic pressure shows the lowest value is set as the neutral position of the supporting member. How to adjust the steering gear to neutral.