JPH06107203A - Steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent a step motor from stepping out in a steering device of a vehicle in which rear wheels are steered by the open control of the step motor through a hydraulic selector valve. CONSTITUTION:A control unit monitors a shift position and a throttle valve opening (S1 and S2) and, when the shift position is located at neutral position and a throttle valve is closed, the maximum drive speed of a step motor is set at 1/2.N pps that is half the maximum drive speed N pps (S6) in the normal condition (S3, S4, and S5). Even if a gear shift lever is set at neutral position and a steering wheel is turned sharply during the high-speed running, the amount of pressure oil to be supplied to a hydraulic selector valve is not reduced so remarkably as compared with a step motor drive speed demanded from the control unit. Thus the stepping-out of the step motor can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system, and more particularly to a vehicle steering system configured to steer wheels via hydraulic valves by open control of a step motor.

[0002]

2. Description of the Related Art In a steering device configured to steer rear wheels in response to front wheel steering, conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-274663, a step motor is opened. It is known that a rear wheel is steered by a hydraulic valve via control.
By adopting such an open control type four-wheel steering device, phase reversal control is performed (that is, the rear wheels are steered to the opposite phase side in which the direction is opposite to the front wheels at the initial stage of turning to improve the turning ability. At the same time, it becomes easy to carry out control for steering the rear wheels to the same phase side where the direction of the front wheels is the same as that of the front wheels with the generation of the yaw rate to achieve directional stability.

[0003]

However, when the wheels are steered through the hydraulic valve by the open control of the step motor, in order to smoothly perform the steered control, the step from the drive control means is performed. It is necessary to supply the hydraulic valve with a hydraulic pressure of a flow rate corresponding to the required motor drive speed. That is, if the hydraulic pressure flow rate supplied to the hydraulic valve becomes extremely small compared to the step motor drive request speed from the drive control means, the hydraulic valve operation corresponding to this will not be performed even if the step motor is driven. Drive energy is consumed simply because it elastically deforms the return spring of the hydraulic valve, which eventually leads to stepping out of the step motor, making it impossible to perform appropriate steering control. Will end up.

The present invention has been made in view of such circumstances, and even if the wheels are steered via the hydraulic valve by the open control of the step motor, the step motor is not operated. An object of the present invention is to provide a steering device for a vehicle that can prevent the occurrence of a key.

[0005]

SUMMARY OF THE INVENTION A vehicle steering system according to the present invention is capable of traveling at a high speed in a situation where a hydraulic pressure flow rate supplied to a hydraulic valve is extremely small compared to a step motor drive request speed from a drive control means. Sometimes it is possible to turn the steering wheel suddenly while coasting with the shift lever in the neutral position, but under such high-speed coasting, it is not necessary to steer the wheels rapidly. In view of this, the above object is achieved by setting an upper limit value to the step motor drive speed when the supplied hydraulic pressure flow rate becomes a predetermined value or less.

That is, as described in claim 1, the hydraulic valve for steering the wheels, the step motor for operating the hydraulic valve, and the step motor are driven by open control according to the traveling state of the vehicle. In a vehicle steering system including drive control means, when the hydraulic flow rate supplied to the hydraulic valve is equal to or less than a predetermined value,
A maximum drive speed regulation means for regulating the maximum drive speed of the step motor to a predetermined value or less is provided.

As a means for detecting that the "hydraulic flow rate supplied to the hydraulic valve has fallen below a predetermined value", as described in claim 2, the engine speed has fallen below a predetermined value. It may be detected, or as described in claim 3, it may be detected that the shift position is in the neutral position and the throttle valve is closed.

[0008]

As described above, the maximum drive speed of the step motor is regulated to a predetermined value or less when the hydraulic flow rate supplied to the hydraulic valve becomes a predetermined value or less. As compared with the step motor drive request speed from the drive control means, the amount of hydraulic pressure supplied to the hydraulic valve does not become extremely small, and therefore step out of the step motor can be prevented. .

When the maximum drive speed of the step motor is regulated in this way, the responsiveness of wheel steering may be sacrificed. However, the step motor drive request speed from the drive control means may be reduced. Compared with this, the situation in which the hydraulic flow rate supplied to the hydraulic valve becomes extremely small compared to the above, specifically, when the vehicle is coasting with the shift lever in the neutral position during high-speed traveling, the sudden steering wheel is turned off. In such a case, the necessity of steering the wheels suddenly is low originally, and therefore, the above regulation does not cause actual damage.

Therefore, according to the present invention, even when the wheels are steered via the hydraulic valve by the open control of the step motor, it is possible to prevent the step motor from being out of step. Therefore, appropriate steering control can be performed.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle steering system according to the present invention.

As shown in the figure, a vehicle steering system 10 according to this embodiment includes a front wheel steering mechanism 14 for steering front wheels 12.
The front wheel steering mechanism 14 is mechanically connected to the front wheel steering mechanism 14 via a transmission shaft 52. The front wheel steering angle is input to the rear wheels 16 from the front wheel steering mechanism 14 by interlocking with the front wheel steering by the front wheel steering mechanism 14. A rear wheel steering mechanism 18 that steers to a predetermined target rear wheel steering angle TGθ _R (which will be described later) according to θ _F , and a front wheel steering angle θ provided in the rear wheel steering mechanism 18. _A steering ratio variable mechanism 20 for setting and changing a steering ratio θ _S represented as a ratio of a rear wheel steering angle θ _{R to F,} and a control unit 22 for controlling the steering ratio variable mechanism 20 are provided. Then, in the control unit 22,
Signals of the vehicle speed V from the vehicle speed sensor 24, the yaw rate ψ ′ from the yaw rate sensor 26, and the front wheel steering angle θ _F from the front wheel steering angle sensor 28 (provided on the steering shaft) are input.

The control of the turning ratio variable mechanism 20 by the control unit 22 is such that when the front wheels 12 are steered from a steering angle of zero in the medium vehicle speed or high vehicle speed range, the steering ratio is set immediately after the start of the front wheel steering. negatively theta _S, then it is carried out as positively to said transfer steering ratio theta _S, a so-called phase inversion control.

[0015] The control unit 22 is obtained from vehicle speed V, the yaw rate ψ each detected signal _F 'and front wheel steering angle theta _F, further front wheel steering angle change rate theta obtained by differentiating the front wheel steering angle theta _F' Target turning ratio TG which is a control target value for the turning ratio variable mechanism 20 by adding and subtracting the signal calculation value
It is designed to determine θ _S. Then, using this target turning ratio TGθ _S , the target rear wheel steering angle TGθ _R is calculated by the following equation: TGθ _R = θ _F · TGθ _S.

The target turning ratio TGθ _S is expressed by the following equation: TGθ _S = -k ₁ · θ _F + k ₂ · ψ′-k ₃ · θ ′ _F +
k ₄ · f (V) (k ₁ , k ₂ , k ₃ , k ₄ are constants).

In the above equation, the first term on the right side is the steering angle correction term, the second term is the yaw rate correction term, the third term is the steering angle change rate correction term, and the fourth term is according to the vehicle speed. It is a vehicle speed response term which is a base for performing rear wheel steering control. By setting the target steering ratio TGθ _S in this way, the rear wheels are steered to the opposite phase side in which the direction is opposite to the front wheels in the initial stage of turning based on the vehicle speed-sensitive rear wheel steering control. Phase inversion control is performed to improve directional stability by steering the rear wheels to the same phase side where the direction is the same as that of the front wheels when the yaw rate is generated.

In this embodiment, the rear wheels 16 are steered by hydraulic power. The hydraulic pressure supply source is the pump 2 in FIG.
It is 9. The pump 29 is configured to send the oil accumulated in the oil tank 19 to the rear wheel steering mechanism 18 via the hydraulic pressure release circuit 31 through the pipe 90. The release circuit 31 is a circuit for releasing the hydraulic pressure in the rear wheel steering mechanism 18 so that the rear wheels are forcibly brought to the neutral position when a failure occurs. Reference numeral 91 in the figure denotes a return pipe from the rear wheel steering mechanism 18.

FIG. 2 is a perspective view showing the rear wheel steering mechanism 18, and FIG. 3 is a steering ratio variable mechanism 2 in the rear wheel steering mechanism 18.
FIG. 3 is a diagram showing 0 in detail in a cross section taken along line III-III of FIG. 2.

As shown in FIG. 2, the rear wheel steering mechanism 18 is
The steering ratio variable mechanism 20, the hydraulic switching valve 32, the rear wheel steering rod 34, the displacement transmission mechanism 36, and the hydraulic power cylinder 38 are provided.

The turning ratio variable mechanism 20 includes an output rod 40.
3, a bevel gear 42, a swing shaft member 44, a pendulum arm 46, and a connecting rod 48. These members are housed in a case 50 as shown in FIG.

The output rod 40 is slidably supported by the case 50 in the direction of the axis L ₃ thereof, and is stroke-displaced in the direction of the axis L _{3 to} move the rear wheel steering rod 34 through the displacement transmission mechanism 36. By displacing it in the axial direction (vehicle width direction), the rear wheels connected to both ends of the rear wheel steering rod 34 are steered.

The bevel gear 42 is rotatably mounted on the case 50 about an axis L ₁ coaxial with the axis L ₃ of the output rod 40.
Supported by. The pinion 52a at the rear end of the transmission shaft 52 that meshes with the bevel gear 42 rotates about the axis L _{1 as} the pinion 52a rotates by steering the handle 30. That is, the front wheel steering angle θ
_F is input to the rear wheel steering mechanism 18 from the front wheel steering mechanism 14 via the transmission shaft 52.

The oscillating shaft member 44 can take a position (position shown in the drawing) coaxial with the axis L ₃ of the output rod 40.
₂ and is fixed to the swing gear 54. The swing gear 54 meshes with a worm 58 that is rotated by the drive of a step motor 56 controlled by the control unit 22, and rotates about an axis perpendicular to the plane of the drawing that intersects with the axis L ₂ and thereby swings. The shaft member 44 can also be rotated at the same time. That is, as will be apparent from the detailed description later, the step motor 56 is capable of variably setting the turning ratio according to its rotation angle position.

The pendulum arm 46, be coupled to swingably rocking shaft member 44 about the axis L ₂ of the pivot shaft member 44, the axis L ₄ of該振Ko arm 46, the pivot shaft member 44
The connecting position to the swing shaft member 44 is determined so as to pass through the intersection of the rotation axis line and the axis line L ₂ of the swing shaft member 44.

The connecting rod 48 has an axis L ₅ parallel to the axis L ₃ of the output rod 40, and the output rod 4
0, bevel gear 42 and pendulum arm 46. The connection to the output rod 40 is made by hingedly attaching one end of the connecting rod 48 to a lever 40a fixed to the end of the output rod 40, and the connection to the bevel gear 42 is made from the axis L ₁ of the bevel gear 42. It is made by inserting the other end of the connecting rod 48 into the insertion hole 42a formed in the bevel gear 42 at the point of the distance r, and the pendulum arm 46 is connected to the end of the connecting rod 48 so as to be rotatable in all directions. This is done by inserting the pendulum arm 46 into the insertion hole 60a of the ball joint member 60 provided. Therefore, although the connecting rod 48 is fixed to the output rod 40, the bevel gear 42
Is slidable in the direction of the axis L ₅ (that is, the direction of the axis L ₃ ), and is slidable in the direction of the axis L ₄ (the direction orthogonal to the axis L ₃ in the illustrated state) with respect to the pendulum arm 46. Is. The axis L ₄ of the pendulum arm 46 is tilted with respect to the direction orthogonal to the axis L ₃ by the rotation of the swing shaft member 44,
The pendulum arm 46 slides in this inclined direction, but in this case as well, the sliding component in the direction orthogonal to the axis L ₃ is included, and due to the rotating action of the ball joint member 60, the axes L ₄ and L _{4. Since the} change in the narrow angle with ₅ is absorbed, the component of the force transmitted from the pendulum arm 46 to the connecting rod 48 in the direction orthogonal to the axis L ₃ is absorbed at the connecting point, and relative movement in that direction is possible. Become.

As described above, since the pendulum arm 46 and the connecting rod 48 in the steering ratio varying mechanism 20 are connected to each other so as to move relative to each other in the direction orthogonal to the axis L ₃ , the pendulum arm 46. The locus of the connecting point between the pendulum arm 46 and the connecting rod 48 when the wrench rotates is the axis L ₃
Is a circular locus or an elliptical locus on the outer peripheral surface of a cylinder having a radius r centered at.

FIG. 4 shows that when the axis L ₂ of the swing shaft member 8 is inclined by θ with respect to the axis L ₃ of the output rod 40 (that is,
FIG. 9 is a diagram showing a state of displacement of the output rod 40 when the axis L ₄ of the pendulum arm 46 is inclined by θ with respect to the direction orthogonal to the axis L ₃ . As is clear from the figure, the pendulum arm 46
If the swing amounts are equal, the displacement of the connection point between the pendulum arm 46 and the connecting rod 48 is S in the direction of the axis L ₃ and the output rod 40 and the connecting rod 48 are oscillated. each also displacement of the output rod 40 from being fixedly connected to the shaft line L ₃ direction becomes S is.

As mentioned above, the output rod 40 shown in FIG.
If the swing amount of the pendulum arm 46 is equal, the left and right displacement amounts are equal to each other at S, but the displacement amount S itself has the same handle operation amount, and the bevel gear 42 accordingly has the same rotation amount. However, it changes depending on the magnitude of θ. Therefore, the turning ratio θ _S can be set and changed by setting and changing the magnitude of the inclination θ of the swing shaft 46 by the drive control of the step motor 56. Further, the rocking shaft member 44 can be tilted not only in the counterclockwise direction as described above but also in the clockwise direction. At this time, the moving direction of the output rod 40 with respect to the rotation of the bevel gear 42 is opposite to the above case. Become. Accordingly, the steering wheel can be steered or the rear wheels 16 can be steered in the same phase or in the opposite phase with respect to the front wheels 12.

Next, parts of the rear wheel steering mechanism 18 other than the steering ratio varying mechanism 20 will be described.

First, the hydraulic pressure switching valve 32 includes a valve housing 62 and the housing 6 inside the housing 62.
2 includes a spool 64 accommodated so as to be displaceable in a direction of an axis L ₆ parallel to the axis L ₃ of the output rod 40. The spool 52 is displaced by the output rod 40 and the rear wheel steering rod 34 via the displacement transmission mechanism 36. The displacement of the spool 64 controls the supply of the hydraulic pressure to the hydraulic power cylinder 38, that is, when the spool 64 is displaced rightward from the neutral position with respect to the valve housing 62, the hydraulic pressure is supplied to the right oil chamber 66 of the hydraulic power cylinder 38. When displaced to the left, the oil chamber is supplied to the left oil chamber 68 of the hydraulic power cylinder 38.

After the rear wheel steering rod 34 extends in the vehicle width direction parallel to the axis L ₃ of the output rod 40 and is displaced in that direction, it is connected to the left and right ends via tie rods and knuckle arms (not shown). To steer the wheels,
The displacement is performed by the hydraulic pressure of the hydraulic power cylinder 38. Further, the rear wheel steering rod 34 is provided with a centering spring 70. If the hydraulic system of the hydraulic switching valve 32 or the hydraulic power cylinder 38 is damaged or malfunctions and the hydraulic pressure in the hydraulic power cylinder 38 is lost, or if the mechanical system of the rear wheel steering system 10 is damaged or malfunctions, the above hydraulic pressure is generated. When the hydraulic pressure in the hydraulic power cylinder 38 is lost by releasing the system to the drain, the centering spring 70 positions the rear wheel steering rod 34 to the neutral position, that is, to the position where the rear wheel is not steered and is in a straight traveling state. However, it is configured to achieve so-called fail-safe.

The hydraulic power cylinder 38 displaces the rear wheel steering rod 34 in the vehicle width direction by an oil compression force. A piston 72 is fixedly mounted directly on the rear wheel steering rod 34. Left and right oil chambers 68, 6
Sealing members 74 and 76 forming 6 are provided.
The seal members 74 and 76 are fixed to the housing 78 of the hydraulic power cylinder 38 and can slide on the rear wheel steering rod 34.

The displacement transmitting mechanism 36 includes the output rod 34.
The spool 64 and the rear wheel steering rod 34 are engaged with each other, and the spool 64 is displaced in a predetermined direction by the displacement of the output rod 40, and the rear wheel steering rod is generated by the displacement of the spool 64. Three
The displacement of 4 causes the spool 64 to be actuated in a direction in which it is displaced in the opposite direction.

That is, the displacement transmission mechanism 36 is composed of a cross lever composed of a vertical lever and a horizontal lever,
One end A of the vertical lever is the output rod 40, the other end B is the rear wheel steering rod 34, one end of the horizontal lever is fixed to the case of the rear wheel steering device 10, and the other end D is the spool 64.
Is engaged with. The engaging ends A, B and C are respectively connected to the output rod 40, the small rear wheel steering rod 34 and the spool 6.
4 is engaged so as to be immovable in the axial direction and movably and rotatably in the other directions.
Are engaged by a ball joint in a rotatable and immovable manner.

The stroke displacement of the output rod 40 in the direction of the axis L ₃ causes the rear wheel steering rod 34 to be axially displaced through the displacement transmission mechanism 36, whereby both ends of the rear wheel steering rod 34 are displaced. A rear wheel (not shown) connected to the steering wheel is steered, but the operating principle of the steering amount transmission is not directly related to the present invention, and this is described in JP-A-1-273772. Since it has already been described, detailed description thereof will be omitted.

As described above in detail, the rear wheel steering system 10 according to the present embodiment has a variable steering ratio mechanism 20 provided in a rear wheel steering mechanism 18 mechanically connected to the front wheel steering mechanism 14.
Since the phase reversal control is performed by controlling the above, when the front wheels 12 have a steering angle of zero, the rear wheels 14 can be mechanically reliably held at a steering angle of zero.

Next, the hydraulic circuit for the rear wheel steering mechanism 18 will be described with reference to FIG.

As described above, in this steering apparatus, the rear wheels are steered by the hydraulic force. Then, when the hydraulic system of the hydraulic switching valve 32 or the hydraulic power cylinder 38 is damaged or malfunctions and the hydraulic pressure in the hydraulic power cylinder 38 is lost, or the mechanical system or the electrical system of the rear wheel steering system 10 is damaged or malfunctions. Accordingly, the centering spring 70 positions the rear wheel steering rod 34 at the neutral position when the hydraulic system is released to the drain to eliminate the hydraulic pressure in the hydraulic power cylinder 38 accordingly. In FIG. 1, the hydraulic pressure release circuit 31 interposed between the pump 29 and the steering mechanism 18 is a circuit for releasing the hydraulic pressure in the steering device 18 to operate the spring 70.

Next, the operation of this embodiment will be described.

As shown in FIG. 2, the steering apparatus according to the present embodiment is configured to steer the rear wheels 16 via the hydraulic pressure switching valve 32 by the open control of the step motor 56 by the control unit 22. However, in order to perform this steering control smoothly, the hydraulic pressure of the flow rate corresponding to the step motor drive required speed from the control unit 22 is supplied from the oil tank 19 to the hydraulic pressure switching valve 32 by the pump 29. There is. this is,
When the flow rate of the hydraulic pressure supplied to the hydraulic pressure switching valve 32 from the control unit 22 is extremely small compared to the speed required for driving the step motor, even if the step motor 56 is driven, the operation of the hydraulic pressure switching valve 32 corresponding to this and the hydraulic power is accordingly reduced. Since the cylinder 38 is not actuated, the drive energy of the step motor 56 is consumed simply for deforming the return spring of the hydraulic pressure switching valve 32, and the step motor 56 eventually loses its synchronization. This is because it becomes impossible to perform appropriate steering control.

When the steering wheel is turned suddenly while the shift lever is in the neutral position during high-speed traveling and the vehicle is coasting, the hydraulic switching valve is compared with the step motor drive required speed from the control unit 22. The hydraulic pressure flow rate supplied to 32 will be extremely reduced.

For this reason, in the present embodiment, the control unit 22 performs maximum drive speed regulation control for regulating the maximum drive speed of the step motor 56 to a predetermined value or less.

That is, as shown in the flowchart of FIG. 5, the control unit 22 monitors the shift position and the throttle valve opening (step S
1, S2), the shift position is in the neutral position, and the throttle valve is closed, the maximum drive speed of the step motor 56 is ½ · Npps, which is half the maximum drive speed Npps in normal operation (step S6).
Is set to (steps S3, S4, S
5). The maximum driving speed Npps is set also in the normal state in order to prevent the step motor 56 from overshooting.

As described above, according to this embodiment, when the shift position is in the neutral position and the throttle valve is closed, the drive speed of the step motor 56 is restricted to the maximum drive speed or less. Therefore, even if the steering wheel is turned suddenly while the shift lever is in the neutral position during high-speed traveling and the vehicle is coasting, the hydraulic pressure is switched in comparison with the step motor drive required speed from the control unit 22. The supply hydraulic pressure flow rate to the valve 32 does not become extremely low.

Therefore, according to this embodiment, even when the rear wheel 16 is steered via the hydraulic pressure switching valve 32 by the open control of the step motor 56,
It is possible to prevent step-out from occurring in the step motor 56, and it is possible to perform appropriate rear wheel steering control.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle steering system according to the invention.

FIG. 2 is a perspective view showing a configuration of a main part of the above embodiment.

FIG. 3 is a sectional view taken along line III-III of FIG.

FIG. 4 is a diagram for explaining the operating principle of the turning ratio variable mechanism of the above embodiment.

FIG. 5 is a flowchart showing the operation of the above embodiment.

[Explanation of symbols]

10 Steering device 14 Front wheel steering mechanism 18 Rear wheel steering mechanism 20 Steering ratio variable mechanism 22 Control unit (drive control means, maximum drive speed regulation means) 24 Vehicle speed sensor 26 Yaw rate sensor 28 Front wheel steering angle sensor 32 Hydraulic switching valve (hydraulic pressure) Valve) 56 step motor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 125: 00 137: 00

Claims (3)

[Claims] 1. A vehicle including a hydraulic valve for steering wheels, a step motor for operating the hydraulic valve, and drive control means for driving the step motor by open control according to a running state of the vehicle. The steering device of claim 1, further comprising maximum drive speed regulation means for regulating the maximum drive speed of the step motor to a predetermined value or less when the hydraulic flow rate supplied to the hydraulic valve becomes a predetermined value or less. The vehicle steering system. 2. A detection means for detecting that the hydraulic flow rate supplied to the hydraulic valve is below a predetermined value by detecting that the engine speed is below a predetermined value. The steering apparatus for a vehicle according to claim 1. 3. A detection means for detecting that the hydraulic flow rate supplied to the hydraulic valve is below a predetermined value by detecting that the shift position is in the neutral position and the throttle valve is closed. The steering apparatus for a vehicle according to claim 1, wherein: