JPH06107206A - Steering device for vehicle - Google Patents

Abstract

PURPOSE:To increase steering ability and turning performance by setting a yaw rate gain used for steering control as a function of front wheel steering angle speed and also setting the function to a characteristic that the yaw rate gain increases as the steering angle speed increases and decreases as it increases further. CONSTITUTION:A rear wheel steering device 10 is provided with a rear wheel steering mechanism 18 which steers rear wheels 16 so that they have a specified target steering angle according to a front wheel steering angle in co-operation with the front wheel steering. The rear wheel steering mechanism 18 is provided with a steering ratio variable mechanism 20 to control a steering ratio which is a ratio of front wheel steering angle to rear wheel steering angle, and controlled according to the steering ratio obtained in a control unit 22 according to outputs from a yaw rate sensor 25, vehicle speed sensor 24, front wheel steering angle sensor 26, and a steering ratio sensor 28. In this case, functions with characteristics to increase a yaw rate gain as the steering angle speed of front wheels is increased and decrease as it is increased further are stored, and steering control is made according to the yaw rate gain corresponding to the steering angle speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus for a vehicle, which controls steering of front wheels or rear wheels using a yaw rate as a parameter, and more particularly to improvement of steering stability when a limit turning operation is performed. .

[0002]

2. Description of the Related Art A steering apparatus for a vehicle, for example, a rear wheel steering apparatus steers rear wheels so that a predetermined rear wheel steering angle corresponding to a front wheel steering angle is obtained, as disclosed in, for example, Japanese Patent Laid-Open No. 3-193558. However, the rear wheel steering is conventionally performed by proportional control according to a predetermined steering ratio set according to the vehicle speed, the yaw rate, and the like. This is a so-called vehicle speed sensitive type or yaw rate feedback control type rear wheel steering device.

That is, generally, in a yaw rate feedback control type rear wheel steering system, in order to secure the directional stability of the vehicle, the steering ratio is controlled to be positive, that is, the same phase in the medium and high speed regions of the vehicle speed. However, since this control is based on proportional control as described above, the rear wheels are steered to the same phase side at the same time when the steering wheel is started, and sufficient turning performance is obtained. There was a problem that there was not. In order to solve this problem, for example, JP-A-57-44568 and JP-A-2-249765 propose a phase inversion type rear wheel steering device. This makes it possible to detect the yaw rate of the vehicle, steer the rear wheels to the opposite phase side to the front wheels immediately after the start of steering of the front wheels, and then to the same phase side as the yaw rate occurs. This is so-called "phase inversion control by yaw rate feedback", and it is possible to achieve both turning performance and directional stability.

Particularly, in the above-mentioned Japanese Patent Laid-Open No. 3-193558, as shown in FIG. 1, the control gain is increased as the absolute value of the steering speed θ'of the steering wheel increases. That is, in the region where the steering angular velocity is low, it is ensured that the rear wheels are steered to the opposite phase side in order to obtain the turning ability when steered from the straight traveling state. In the setting of the control gain of the yaw rate feedback having the characteristic shown in FIG. 1, when the steering wheel operation is performed earlier, the control gain is increased so that the steering ratio is increased in the in-phase direction. Will be done. By this correction, control is performed in which importance is attached to traveling stability rather than turning ability.

[0005]

However, depending on the driving conditions of the vehicle, the steering wheel operation may be panicked in some cases. That is, it is a limit steering operation for avoiding danger. When such a limit steering operation is performed, the rear wheels are steered in the in-phase direction: A force exceeding the road grip of the front tires is applied to the tires. : This will cause the driver to feel uncomfortable because the turning ability will be lost.

The above problem is not limited to the rear wheel steering control (so-called four-wheel steering control). It also occurs in vehicles in which yaw rate feedback control is added to normal front wheel steering control. In such a vehicle, when a sudden steering wheel operation is performed, yaw rate feedback control is performed with respect to the front wheel turning angle in a direction that suppresses turning, but when a limit steering wheel operation is performed. This is because it is considered that the above problems (1) and (2) occur in the same manner.

Therefore, the present invention has been made in order to improve the above-mentioned drawbacks of the prior art, and its purpose is to secure the turning ability at the start of turning, and to run when the steering is performed faster. The present invention proposes a vehicle steering system that can ensure control in a more stable direction and can also ensure turning performance and turning performance when steering is marginal.

[0008]

[Means for Solving the Problems] and

The vehicle steering system according to the present invention for achieving the above object is a vehicle steering system for controlling steering of front wheels or rear wheels using a yaw rate as a parameter, and detecting means for detecting a steering angular velocity of front wheels. The yaw rate gain is preset and stored as a function of the steering angular velocity of the front wheels, and the steering control means performs steering control according to the yaw rate gain corresponding to the steering angular velocity detected by the detection means. Has a characteristic that the yaw rate gain increases as the steering angular velocity increases, and decreases when the steering angular velocity further increases.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the steering system of the present invention is applied to a so-called "four-wheel steering system" of a vehicle and a rear-wheel steering system for performing so-called "yaw rate feedback control" will be described in detail with reference to the accompanying drawings. I will describe. In this embodiment, the steering ratio θ _S is the steering angle θ of the front wheels with respect to the steering angle θ _R of the rear wheels.
It is defined by the ratio of _F (= θ _R / θ _F ). <System Configuration> FIG. 2 shows the configuration of the four-wheel steering system of the embodiment.

As shown in the figure, the rear wheel steering system 10 is mechanically connected to a front wheel steering mechanism 14 for steering the front wheels 12 via a transmission shaft 52. A rear wheel steering mechanism 18 that interlocks with the rear wheel steering mechanism 18 to steer the rear wheel 16 to a predetermined target rear wheel steering angle TGθ _R corresponding to the front wheel steering angle θ _S input from the front wheel steering mechanism 14. A steering ratio variable mechanism 20 provided in the wheel steering mechanism 18 for setting and changing a steering ratio θ _S represented as a ratio of a rear wheel steering angle θ _R to a front wheel steering angle θ _F , and this steering ratio. And a control unit 22 for controlling the variable mechanism 20. The control unit 22 includes a vehicle speed sensor 24 to a vehicle speed V, a front wheel steering angle sensor 26 (provided on the steering shaft) to a front wheel steering angle θ _F , a steering ratio sensor 28 to a steering ratio θ _S , and a yaw rate sensor 25. Each signal of the yaw rate ψ from is input.

The control of the turning ratio variable mechanism 20 by the control unit 22 is performed in the medium vehicle speed or high vehicle speed range.
When the front wheels 12 are steered from a steering angle of zero, the so-called "phase inversion" is performed so that the steering ratio θ _S becomes negative immediately after the start of the front wheel steering and thereafter the steering ratio θ _S becomes positive. Control "is performed. FIG. 3 is a perspective view showing the rear wheel steering mechanism 18, and FIG.
First, the steering ratio variable mechanism 20 in the rear wheel steering mechanism 18 is shown in detail in the VV direction in FIG.

As shown in FIG. 3, 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, a bevel gear 42, a swing shaft member 44,
It comprises a pendulum arm 46 and a connecting rod 48, and these respective members are housed in a case 50 as shown in FIG.

The output rod 40 is supported by the case 50 slidably 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 supported by the case 50 about an axis L ₁ coaxial with the axis L ₃ of the output rod 40. 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 from the front wheel steering mechanism 14 to the rear wheel steering mechanism 18 via the transmission shaft 52.

The oscillating shaft member 44 has an axis L _{2 which} can be located at a position coaxial with the axis L ₃ of the output rod 40 (position shown in the drawing).
And is fixed to the swing gear 54. The rocking gear 54 meshes with a worm 58 that is rotated by the drive of a servo 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 , thereby rocking. The shaft member 44 can also be rotated at the same time. That is, as will be apparent from the detailed description later, the servomotor 56 can variably set the steering 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 is connected to the output rod 40, the bevel gear 42 and the pendulum arm 46. The connection to the output rod 40 is made by screwing one end of a 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. The pendulum arm 46 is formed by inserting the other end of the connecting rod 48 into the insertion hole 42a formed in the bevel gear 42 at the distance γ.
The pendulum arm 46 is inserted through the insertion hole 60a of the ball joint member 60 provided at the end of the connecting rod 48 so as to be rotatable in all directions.
Therefore, the connecting rod 48 is fixed to the output rod 40, but is connected to the bevel gear 42 by the axis L _5.
Is slidable in the direction (i.e. the axis L ₃ direction), the axis L ₃ in the state of the axis L ₄ direction (for pendulum arm 46
Can be slid in a direction orthogonal to. The axis line L ₄ of the pendulum arm 46 is changed to the axis line L ₂ by the rotation of the swing shaft member 44.
And the pendulum arm 46 slides in this inclined direction. In this case as well, the pendulum arm 46 includes a sliding component in the orthogonal direction of the axis L ₃ and the rotation of the ball joint member 60. Since the change in the angle of inclination between the axis L ₄ and the axis L ₅ is absorbed by the action, 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, Relative movement in that direction is possible.

As described above, since the pendulum arm 46 and the connecting rod 48 in the steering ratio variable 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
It is a circular locus or an elliptical locus on the outer peripheral surface of a cylinder having a radius γ centered at.

FIG. 5 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, the axis L ₄ of the pendulum arm 46 is perpendicular to the axis L ₃ ). FIG. 9 is a diagram showing the state of displacement of the output rod 40 when tilted by θ. As is clear from the figure, even if the pendulum arm 46 swings in either the left or right direction, if the swing amounts are equal, the displacement of the connection point between the pendulum arm 46 and the connecting rod 48 is respectively in the direction of the axis L _3. S and output rod 4
Since 0 and the connecting rod 48 are fixedly connected, the displacement of the output rod 4 is also S in the direction of the axis L ₃ .

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. However, the displacement amount S itself has the same steering amount of the steering wheel and the same rotation amount of the bevel gear 42 accordingly. However, it changes depending on the magnitude of θ. Therefore, the steering ratio θ _S is equal to the servo motor 5
6 can be set and changed by setting and changing the magnitude of the inclination θ of the swing shaft 46 by the operation control of 6.
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. Thus, the steering wheel can be steered or the rear wheels can be steered in the same phase or in the opposite phase with respect to the front wheels.

The turning ratio θ _S set and changed by the turning ratio variable mechanism 20 is determined by the turning ratio sensor 28 attached to the turning shaft member 44 as shown in FIG. The inclination θ of 44 is detected. Next, portions of the rear wheel steering mechanism 18 other than the steering ratio variable 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.

The rear wheel steering rod 34 is the chamber rod 4
It extends in the vehicle width direction parallel to the axis line L _{3 of} 0 and is displaced in that direction to steer the rear wheels connected to the left and right ends via tie rods and knuckle arms (not shown). It is performed by the hydraulic pressure of the power cylinder 38. Further, the rear wheel steering rod 34 is provided with a centering spring 70. 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 of the rear wheel steering system 10 is damaged or malfunctions, which causes the above hydraulic pressure. When the system is opened to the drain and the hydraulic pressure in the hydraulic power cylinder 38 is lost, 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 the straight traveling state. However, it is configured to achieve so-called fail-safe.

The hydraulic power cylinder 38 is for displacing the rear wheel steering rod 34 in the vehicle width direction by an oil compression force, and the piston 72 is directly fixed to the rear wheel steering rod 34. Left and right oil chambers 68,6
Sealing members 74 and 76 forming 6 are arranged.
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 transmission 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 D are respectively connected to the output rod 40, the rear wheel steering rod 34 and the spool 64.
With respect to the axial direction, is movably and rotatably engaged in the other direction, and the engaging end C is rotatably and immovably engaged by the ball joint. ing.

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 transmitting mechanism 36, whereby both ends of the rear wheel steering rod 34 are displaced. Although the rear wheel (not shown) connected to the section is steered, the operating principle of the steering amount transmission is not directly related to the present invention, and this is disclosed in JP-A-1-273772. Since it has been described in detail, its detailed description is omitted.

As described in detail above, the rear wheel steering system 10 according to this 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. <Control> Next, the control of the present embodiment will be described.

FIGS. 6, 7 and 8 are for rear wheel steering control.
Function blocks performed in the control unit 22
FIG. The main entry into the control system shown in the figure
The force signal is based on the vehicle speed V detected by the vehicle speed sensor 24 and the yaw.
Yaw rate signal ψ detected by the rate sensor 25
And the steering angle θ of the front wheel_FIs. Turn on these signals
Control unit 22 outputs the target steering ratio signal._SL
Is output. However, θ _SLIs the target turning ratio θ_SOf FIG.
Limit correction is performed by the limiter, so
The main calculation of the control unit 22 is θ_SCan be calculated
And.

The control logic shown in FIGS. 6, 7 and 8 will now be described below. That is, θ _S = G ₄ · f ₄ (v) (1) −G ₁ · f ₁ (v) · θ _FSC (2) + G ₂ · K ₂ (θ _H ) · J ₂ (| θ ′ _H │) ・ f ₂ (v) ・ θ _FYW … (3) −G ₃・ K ₃ (θ _F ) ・ f ₃ (v) ・ θ _FVC … (4) Normally, the sensor has unique offset characteristics and hysteresis characteristics. Have. Therefore, in FIG. 6, FIG. 7, and FIG. 8, the yaw rate signal ψ and the steering wheel steering angle signal θ _F are offset-processed in FIG. 6B, respectively, and hysteresis-processed in FIG. Offset processing is performed in (h), and hysteresis processing is performed in (l). Therefore, for convenience, in the above equation, the signals ψ and θ _F subjected to the offset process and the hysteresis process are represented again as ψ and θ _F.

In the above equation, the first term is the basic term.
The second term is a steering angle correction term, the third term is a yaw rate correction term, and the fourth term is a steering angular velocity correction term. A characteristic of the present invention when applied to rear wheel steering control is that, as shown in FIG. 6 (g), the control gain J ₂ with the steering angular velocity θ ′ _F as a variable with respect to the yaw rate is effective. Is.

In the above equation, the yaw rate compensation equation (3) is added.
Steering angular velocity response gain J in positive term ₂Always takes a positive value
Is set so that it increases in the in-phase direction.
It is effective as a correction of. This J₂Rudder angular velocity
Absolute value of degree | θ '_FThe characteristics for | are shown in FIG. In Figure 9
As shown, the control gain J₂Is | θ '_F| Is from 0 to | θ '
_F0Maintains "1" until |, and | θ '_F0｜ 〜 ｜ θ '_F1Of
Interval increases, | θ '_F1｜ 〜 ｜ θ '_F2A value of 1 or more between |
Hold, ｜ θ '_F2｜ 〜 ｜ θ '_F3It decreases during |, and | θ '_F3
｜ For the above, it has the property of holding a value less than 1.
To do.

J ₂ between | θ ' _F | and 0 to | θ' _F0 |
Keeps "1", the yaw rate feedback control due to the fluctuation of the steering angular velocity is disabled. As a result, the phase inversion control in the opposite phase direction according to the equation (1) at the initial stage of turning is effective. Between | θ ' _F | and | θ' _F0 | ~ | θ ' _F1 |, that is, when the steering wheel is turned relatively quickly, the yaw rate feedback control is effective in the in-phase direction because J ₂ increases. Increases stability.

Further, by maintaining a value of 1 or more in a region where the steering wheel is sharply turned, that is, between | θ ' _F1 | and | θ' _F2 |, abrupt correction control in the opposite phase direction is performed. Suppress. In addition, the area where the handle is sharply turned,
That is, J ₂ is decreased between | θ ′ _F2 | and | θ ′ _F3 | to improve the turning ability to assist the danger avoiding operation. However, | θ _'F | is | θ' _F3 | since stem turning performance becomes excessive is further corrected in the opposite phase side in a region that exceeds the, maintains the value less than 1. <Modification> The present invention can be variously modified without departing from the spirit thereof.

For example, in the above embodiment, the control gain J ₂
Although the characteristic of (1) is stepwise, it may be a smooth characteristic as shown in FIG. Further, although the present invention is applied to the rear wheel steering in the above-described embodiment, the present invention is also applicable to a vehicle in which the yaw rate feedback control is applied to the front wheel steering. This is because the yaw rate feedback control makes a correction in a direction that suppresses the turning of the vehicle when the yaw rate is generated. This is because when an operation is performed, it is preferable to suppress the control for correcting the steering ratio in the in-phase direction.

[0034]

As described above, according to the present invention, in the vehicle steering system for controlling the steering of the front wheels or the rear wheels using the yaw rate as a parameter, the detection means for detecting the steering angular velocity of the front wheels and the yaw rate gain are set as the front wheels. Steering control means for presetting and storing as a function of the steering angular velocity, and performing steering control according to a yaw rate gain corresponding to the steering angular velocity detected by the detecting means,
The function is characterized in that the yaw rate gain increases as the steering angular velocity increases, and decreases when the steering angular velocity further increases.

Therefore, since the yaw rate feedback control is performed according to the function having such a characteristic, the turning performance at the start of steering is ensured, and the traveling is further stabilized in the case where steering is performed faster. It is possible to secure control, and also to ensure turning performance and turning performance when steering is marginal.

[Brief description of drawings]

FIG. 1 is a graph illustrating a conventional problem.

FIG. 2 is a diagram illustrating the overall configuration of a four-wheel steering system that is a preferred embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a main part of the rear wheel steering system of the embodiment shown in FIG.

FIG. 4 is a diagram illustrating a configuration of a main part of a turning ratio variable mechanism of the embodiment shown in FIG.

FIG. 5 is a diagram for explaining the operating principle of the turning ratio variable mechanism of FIG.

FIG. 6 is a functional block diagram showing the control logic of the embodiment.

FIG. 7 is a functional block diagram showing the control logic of the embodiment.

FIG. 8 is a functional block diagram showing the control logic of the embodiment.

FIG. 9 is a graph showing the characteristics of the control gain J ₂ .

FIG. 10 is a graph showing the deformation characteristic of the control gain J ₂ .

[Explanation of symbols]

 18 rear wheel steering mechanism, 20 steering ratio variable mechanism, 22 control unit, 25 yaw rate sensor 24 vehicle speed sensor 31 hydraulic pressure release circuit, 56 step motor, 83 open / close valve, 70 brake switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number in the agency FI Technical display location B62D 137: 00 (72) Inventor Shigefumi Kumabe 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation Within

Claims (3)

[Claims] 1. A steering device for a vehicle, which performs steering control of front wheels or rear wheels using a yaw rate as a parameter, wherein detection means for detecting a steering angular velocity of a front wheel and yaw rate gain are preset as a function of a steering angular velocity of a front wheel. A yaw rate gain that is stored and that performs a steering control according to a yaw rate gain corresponding to a steering angular velocity detected by the detection means, wherein the function increases the yaw rate gain as the steering angular velocity increases. However, the vehicle steering device has a characteristic that the steering angular velocity decreases as the steering angular velocity further increases. 2. The vehicle steering system according to claim 1, wherein the function has a steering wheel angular velocity correction term, and the steering wheel angular velocity correction term corrects the steering angular velocity up to a predetermined first speed value. Has a predetermined first gain value such that the steering angular speed increases from the first speed value to the second speed value, and the steering angular speed increases from the second speed value to the third speed value. Up to a constant gain value and the steering angular velocity is the third
The vehicle steering apparatus is characterized in that a predetermined second gain value is maintained from the speed value of 4 to the fourth speed value. 3. The vehicle steering system according to claim 1, wherein the function has a variable of an absolute value of a steering wheel angular velocity.