JPH0679902B2 - 4-wheel steering system for vehicles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a four-wheel steering system for a vehicle in which not only front wheels but also rear wheels are steered.

(Prior Art and its Problems) In some vehicles, as is known as so-called four-wheel steering,
There is one in which the rear wheels are steered together with the front wheels.

In this four-wheel steering, it is common to change the ratio of the front wheel steering angle to the rear wheel steering angle, that is, the rear wheel steering ratio, for example, according to the vehicle speed (see JP-A-60-85067). Further, there is also proposed a method in which a plurality of control characteristics of the rear wheel turning ratio are set so that they can be selectively switched according to information from various sensors or a driver's preference (Japanese Patent Laid-Open No. Sho 60). −
See 135369 publication).

In this type of four-wheel steering system, even if the front wheel steering angles are the same, the rear wheel steering ratio is changed and the rear wheels are steered as the vehicle speed changes or the characteristics are switched. It will be.

By the way, the control characteristic of the rear wheel steering ratio is determined based on the demand of the vehicle in the steady traveling state, and therefore, safety measures are required in the transition period when the rear wheel steering ratio changes.

On the other hand, as seen in the above-mentioned Japanese Patent Laid-Open No. 60-85067, when there is a change in the vehicle speed or a characteristic change that requires a change in the rear wheel steering ratio, the change in the rear wheel steering ratio is slowed down. It is suggested to do with.

According to this proposal, information that directly prompts a change in the rear wheel turning ratio, that is, in response to a change in vehicle speed and a characteristic change,
The change in the behavior of the vehicle due to the change in the rear wheel steering ratio is suppressed.

However, when looking at the effect of changes in the rear wheel steering ratio on vehicle behavior changes, changes in vehicle behavior become a problem because changes in information that force changes in the rear wheel steering ratio, namely vehicle speed and characteristics. The element is not limited to switching.

For example, when the vehicle is in a sharp turning state, the change in the rear wheel steering ratio has a large effect on the change in vehicle behavior.

Therefore, it is an object of the present invention to provide a four-wheel steering system for a vehicle that suppresses a change in the behavior of the vehicle due to a change in the rear wheel steering ratio in relation to the degree of turning of the vehicle.

(Means and Actions for Solving Problems) That is, the present invention, when looking at the relationship between the degree of turning of the vehicle and the behavior change of the vehicle due to the rear wheels being steered,
When the turning radius is small, that is, when the vehicle is in a sharp turning state, even if the rear wheels are slightly steered, it has a great influence on the behavior change of the vehicle. Focusing on the fact that the vehicle is in a sensitive driving state, the speed of change of the rear wheel steering ratio is regulated according to the degree of turning of the vehicle.

Specifically, the four wheels of the vehicle in which the rear wheel steering ratio is variable
As shown in FIG. 1, on the premise of a wheel steering device, a turning degree detecting means for detecting a turning degree of a vehicle, a limiting means for limiting a changing speed of the rear wheel turning ratio, and a turning degree detecting means are provided. When the turning radius is small, a regulation amount adjusting means for increasing the regulation amount by the regulating means when the turning radius is small is provided.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

In FIG. 2, 1R is the right front wheel, 1L is the left front wheel, 2R is the right rear wheel, 2L is the left front wheel, the left and right front wheels 1R, 1L are linked by the front wheel steering mechanism A, and the left and right rear wheels 2R , 2L are linked by a rear wheel steering mechanism B.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R and 3L and tie rods 4R and 4L, and a relay rod 5 that connects the pair of left and right tie rods 4R and 4L.
It consists of and. A steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C is of a rack and pinion type in the embodiment. That is, while the rack 6 is formed on the relay rod 5, the pinion 7 that meshes with the rack 6 is connected to the shaft 8
Is connected to the handle 9 via. As a result, when the handle 9 is turned to the right, the relay rod 5 is displaced to the left in FIG. 2 and the knuckle arms 3R, 3L are moved.
Around the rotation center 3R ', 3L'
The steering wheel is steered in the clockwise direction in the figure by an amount corresponding to the operation displacement amount, that is, the steering wheel steering angle. Similarly, when the steering wheel 9 is turned to the left, the left and right front wheels 1
R and 1L will be steered to the left.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also has a pair of left and right knuckle arms 10R and 10L and a tie rod 11 respectively.
R and 11L, and a relay rod 12 that connects the tie rods 11R and 11L to each other. In the embodiment, the rear wheel steering mechanism B includes a hydraulic power steering mechanism D.

Explaining this power steering mechanism D, a cylinder device 13 is attached to the relay rod 12, and the cylinder 13a is fixed to the vehicle body, while the inside of the cylinder 13a is fixed to two.
The piston 13d defined in the chambers 13b and 13c is the relay rod 12
Is integrated into. Two chambers 13b, 13 in this cylinder 13a
c is control valve 16 via line 14 or 15
It is connected to the. Further, pipes 18 and 19 extending from the reservoir tank 17 are connected to the control valve 16, and an oil pump 20 driven by an engine (not shown) is connected to the pipe 18 serving as an oil supply pipe. The control valve 16 is of a so-called booster valve type (spool type) in which the control rod 21 is of a sliding type, and the input portion 21a of the control rod 21 has a steering ratio changing device E described later.
Control rod 21
The output part 21b of the is integrated with the relay rod 12 of the rear wheel steering mechanism B.

In such a power steering mechanism D, as is known, when the control rod 21 is displaced leftward in FIG. 2, the relay rod 12 is displaced leftward in FIG. 2, whereby the knuckle. The arms 10R, 10L rotate clockwise around the centers of rotation 10R ', 10L', and the rear wheels 2R, 2L are steered to the right. Then, during this steering, oil is supplied into the chamber 13b of the cylinder device 13 in accordance with the amount of displacement of the control rod 21 to assist in driving the relay rod 12 (power boosting action). Similarly,
When the control rod 21 is displaced to the right in FIG. 2, the rear wheels 2R, 2L are acted upon by the boosting action of the cylinder device 13 (the oil is supplied to the chamber 13b) according to the displacement amount.
Will be steered to the left.

The front wheel steering mechanism A also has a power steering mechanism F, like the rear wheel steering mechanism B. The power steering mechanism F includes a cylinder device 65 attached to the relay rod 5 of the front wheel steering mechanism A, and the cylinder 65a thereof is fixed to the vehicle body, while the inside of the cylinder 65a is fixed to two.
The piston 65d defined in the chambers 65b and 65c is the relay rod 5
Is integrated into. Two chambers 65b, 65 in this cylinder 65a
c is a steering mechanism C via a pipe 66 or 67.
It is connected to a rotary type control valve 68 provided on the shaft 8. The control valve 68 is connected to a pipe 70 extending from the flow dividing valve 69 connected on the discharge side of the oil pump 20 and a pipe 71 branched from the pipe 19.

Such a power steering mechanism F boosts the operating force of the handlebar 9 (power boosting by supplying oil to the chamber 65b or 65c of the cylinder device 65) and transmits it to the relay rod 5. Since the operation of the power steering mechanism F itself is basically the same as that of the power steering mechanism D, detailed description thereof will be omitted.

The steering mechanism C and the rear wheel steering mechanism B are linked via a front wheel steering mechanism A and a steering ratio changing device E.
From this steering ratio changing device E, an input rod 22 extends forward, and a pinion 23 attached to the front end portion thereof meshes with a rack 24 formed on the relay rod 5 of the front wheel steering mechanism A. The output rod of the steering ratio changing device E is also used by the input portion 21a of the control rod 21 of the control valve 16 as described above.

An example of the turning ratio changing device E will be described with reference to FIG. In the steering ratio changing device E, the control rod is
The input portion 21a of 21 is held slidably in the vehicle width direction with respect to the vehicle body, and its axis of movement is shown as l ₁ .
The turning ratio changing device E also has a swing arm 31, and the swing arm 31 has its base end pivotally attached to the holder 32 by a pin 33 so as to be swingable. There is. In this holder 32, the rotation axis 32a is the movement axis of the input section 21a.
It is rotatably held on the vehicle body about an orthogonal line l ₂ orthogonal to l ₁ . Then, the pin 33 is connected to both lines l ₁ and l ₂
It is located at the intersection of and and extends in the direction orthogonal to the orthogonal line l ₂ . Therefore, the swing arm 31 is
It is possible to swing about the center of the pin 32, but by rotating the holder 32, the inclination angle formed by the pin 33 and the moving axis l ₁ , that is, the moving axis of the swinging orbital surface about the pin 33 is formed.
The tilt angle with respect to the plane (reference plane) orthogonal to l ₁ is variable.

The tip portion of the swing arm 31 and the input portion 21a are connected by a connecting rod 34. That is, the connecting member 34 is
It is connected to the tip end of the swing arm 31 via a ball joint 35, and the input unit 21a via a ball joint 36.
Are linked to.

By the connecting rod 34 as described above, the distance between the ball joints 35 and 36 at each end of the swing arm 31 is always kept constant. Therefore, if the ball joint 35 is displaced in the left-right direction in FIG. 3, the input portion 21a is displaced in the left-right direction in FIG. 3 according to this displacement.

The swing of the swing arm 31 about the pin 33 is performed according to the operation displacement of the steering mechanism C, that is, the steering angle of the steering wheel. Therefore, in the embodiment, the connecting rod 34 is moved from the bevel gear to the connecting rod 34. The rotating plate 37 is connected. The rotating plate 37 is rotatably held by the vehicle body so that its rotating shaft 37a is on the moving axis l, and with respect to the eccentric portion of the rotating plate 37, the connecting rod 34 is connected to the ball joint 38. It is slidably penetrated through. A bevel gear 39 connected to the input rod 22 is meshed with the rotating plate 37 formed of a bevel gear.

With such a rotating plate 37, the swing arm 31 is swung about the pin 33 by an amount corresponding to the steering angle of the steering wheel, but the axis of the pin 33 and the moving axis l ₁ are inclined. As a result, the ball joint 35 is displaced in the left-right direction in FIG. 3, that is, in the direction of the moving axis l _{1 in accordance} with the swing around the pin 33, and this displacement is transmitted through the connecting rod 34 to the input portion. 21a
And the input portion 21a is displaced.
The displacement of the ball joint 35 in the left-right direction in FIG. 3 is such that even if the swing angle of the swing arm 31 about the pin 33 is the same, the inclination angle of the pin 33, that is, the rotation angle of the holder 32. Is changed (change in steering ratio).

In order to change the inclination angle, a sector gear 40 as a worm wheel is attached to the rotation shaft 32a of the holder 32, and a worm gear meshing with the sector gear 40 is attached.
41 is rotatably driven by a stepping motor 44 as a tilt angle changing means via a pair of bevel gears 42 and 43.

Here, the swing angle about the pin 33 of the swing arm 31 and the tilt angle of the swing arm 31 (the tilt angle of the pin 33) described above.
Will be described for the influence on the displacement of the ball joint 35 (input portion 21a) in the direction of the moving axis l ₁ . Now, the swing angle of the swing arm 31 about the pin 33 is θ, the reference plane orthogonal to the moving axis l ₁ is δ, and the swing orbit surface of the swing arm 31 is the tilt angle formed with the reference plane δ. α, ball joint 35 pin
If the eccentric distance from 33 is r, the displacement X of the ball joint 3 in the direction of the moving axis l ₁ is X = r tan α ・ sin θ
Is a function with α and θ as parameters.
Therefore, if the inclination angle α is fixed to a certain value, X
Becomes a function of θ, that is, the steering angle θF of the steering wheel, and the steering angle θF of the steering wheel can be changed by changing the value of the inclination angle α.
Even if they are the same, the value of X will change.
Then, the change of the inclination angle α is expressed as a change of the rear wheel steering ratio R. That is, the rotation angle (stepping numerical value) of the stepping motor 44 and the turning ratio R uniquely correspond to each other.

As shown in FIG. 4, the turning ratio R is variable with the vehicle speed (V) as a parameter, and the turning ratio characteristic is as follows.
Here, the steering ratio on the opposite phase side is given in the low speed operation state, and the steering ratio on the same phase side is given in the high speed operation state.As the vehicle speed increases, the steering ratio changes in the same phase direction. It is supposed to do. Therefore, the steering angle θF
Even if is constant, the rear wheel steering ratio (R) changes in the same phase direction in the acceleration state as shown in FIG. 5, and the rear wheel steering ratio (R) in the deceleration state as the vehicle speed changes. Changes in the opposite phase direction.

Here, a pair of return springs 13e and 13f are attached to the rear wheel power steering mechanism D in order to forcibly bring the rear wheels 2R and 2L into a neutral position, that is, a straight traveling state. The springs 13e and 13f bias the rear wheel relay rod 12 from the left and right opposite directions with equal forces. Further, both oil chambers 13 of the power steering mechanism D are
b and 13c are connected via a communication passage 46, and an electromagnetic on-off valve 47 is connected to the communication passage 46. As a result, when the on-off valve 47 is closed, the oil chamber 13b or 1
Supplying hydraulic pressure to 3c causes rear wheels 2R and 2L to spring 13.
When the steering is turned against e or 13f and the on-off valve 47 is opened to make both oil chambers 13b and 13c at the same pressure, the rear wheels 2R and 2C are forced to the neutral position by the action of the springs 13e and 13f. To be done.
Of course, the urging force of the springs 13e and 13f is set to such a magnitude that it can take a neutral position against the external force received from the rear wheels 2R or 2L during turning.

Further, the swinging stroke ends of the sector gear 40 driven by the stepping motor 44 are restricted by the in-phase side stopper 48 and the anti-phase side stopper 49 (see FIG. 3).

In FIG. 2, reference numeral 51 denotes a control unit composed of, for example, a microcomputer. The control unit 51 receives signals from a control degree detecting means 52 for detecting a degree of turning of the vehicle and a vehicle speed sensor 53 for detecting a vehicle speed V. It is input and is also output from the control unit 51 to the stepping motor 44 and the opening / closing valve 47. Then, the turning degree detecting means
As 52, in the present embodiment, a right rotation speed sensor 52a for detecting the rotation speed of the right wheel, a left rotation speed sensor 52b for detecting the rotation speed of the left wheel, a right rotation speed sensor 52a and a left rotation speed sensor.
52b and a rotation difference calculation circuit 76 for calculating the rotation difference between the left and right wheels, and detects the turning radius from the rotation difference between the left and right wheels.

Now, the control content of the control unit 51 will be described with reference to the functional block diagram shown in FIG.

In the figure, reference numeral 71 is a steering ratio calculation circuit 71.
Then, the corresponding target turning ratio (R) is calculated based on the vehicle speed signal (V) from the vehicle speed sensor 53. Of course, the target turning ratio (R) corresponding to the vehicle speed (V) may be determined from the turning ratio data (see FIG. 5) stored in advance in the memory. The obtained target turning ratio (R) is input to the motor drive signal generation circuit 72 and converted into the target stepping number CP of the motor 44 required to obtain the target turning ratio (R). The generation circuit 72 outputs a pulse signal corresponding to the target stepping CP. This pulse signal is input to the stepping motor 44 via a delay circuit 73 and a driver circuit 74 described later. As a result, the stepping motor 44 is driven to the target stepping number CP at a speed corresponding to the input speed of the pulse signal, and the rear wheel steering ratio is changed to the target steering ratio (R).

In the delay circuit 73, the pulse signal output to the driver circuit 74 is delayed by a predetermined time (T). This delay time T is set in the delay time setting circuit 75 to a value according to the turning radius of the vehicle. That is, the turning radius signal from the rotational speed calculating circuit 76 is input to the delay time setting circuit 75, and based on the turning radius signal, as shown in FIG. 7, the delay time T increases as the turning radius increases. Is set to a smaller value, in other words, as the turning radius becomes smaller, the delay time T is set to a larger value, and the delay time setting circuit 75
Based on the delay time T set in step 3, the delay process in the delay circuit 73 is performed.

From this, as shown in FIG. 8, the smaller the turning radius is, that is, the steeper the turning state, the more the stepping motor 44 is moved.
The drive speed of the vehicle is greatly regulated, and the changing speed of the rear wheel steering ratio is suppressed. As a result, the sharper the turn,
Since the rear wheels are slowly steered, abrupt behavior change of the vehicle is suppressed.

FIGS. 9 and 12 to 14 show a second embodiment of the present invention. The same elements as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. Only the characteristic part will be described.

The present embodiment shows an application example in which a plurality of control characteristics of the rear wheel steering ratio are set, and a change in the rear wheel steering ratio due to characteristic switching. Fig. 12 shows multiple characteristics set according to the road surface condition, and Fig. 13 shows normal steering of only the front wheels, that is, the characteristic that the rear wheels are always neutral, according to the driver's preference. The figure exemplifies a case where a large steering ratio on the same phase side is given at a low speed for the convenience of parking. These characteristics are switched by, for example, detection means such as a μ sensor or a manual selection switch.

For this reason, the control unit 51, as shown in FIG.
The signal from the characteristic switching means 80 is input, and the signal from the characteristic switching means 80 is input to the target turning ratio calculation circuit 71 and the timer circuit 81.

In the target turning ratio calculation circuit 71, the turning ratio characteristic map stored in advance in the memory 82 is changed according to the signal from the characteristic switching means 80, and the vehicle speed V is dealt with based on the corresponding characteristic map. A change to the target turning ratio R is made. On the other hand, the timer 81 receives a signal from the characteristic switching means 80, and outputs a delay signal toward the delay circuit 73 for a predetermined time after inputting this signal, In the delay circuit 73, when the delay signal from the timer circuit 81 is received, the delay processing described in the first embodiment is performed. The delay processing performed here is the same as that of the first embodiment described above, and thus the description thereof is omitted. Of course, when there is no switching of the characteristics, that is, the processing involving the change of the turning ratio within the same turning ratio characteristic is the same as that of the first embodiment.

Therefore, in the present embodiment, in addition to the control of the first embodiment, when there is a characteristic change, the change in the steering ratio due to this is carried out slowly for a fixed time after the characteristic change. Then, the regulation of the turning ratio changing speed is carried out according to the turning degree of the vehicle. For this reason, even if the characteristics are switched during a sharp turn, the steered ratio changes slowly, so that a sudden behavior change of the vehicle can be suppressed. From this, it is significant as a safety measure against the case where the characteristic is erroneously switched during turning.

Although the embodiment of the present invention has been described above, when the control unit 51 is configured by a computer, it may be either a digital type or an analog type. Further, the delay time T set by the delay time setting circuit 75 may be set stepwise as shown in FIG. The control characteristics in this case are as shown in FIG.

(Effect of the Invention) As is clear from the above description, according to the present finding, the change rate of the rear wheel steering ratio is suppressed by the turning degree of the vehicle, so that the behavior change of the vehicle accompanying the change of the rear wheel steering ratio is suppressed. Can be suppressed in relation to the degree of turning of the vehicle. In particular, it is possible to ensure the stability of the vehicle during a sharp turn.

[Brief description of drawings]

1 is an overall configuration diagram of the present invention, FIG. 2 is an overall plan view showing an embodiment of the present invention, FIG. 3 is a skeleton diagram for explaining a rear wheel steering mechanism portion, and FIG. 4 is a rear wheel steering ratio. FIG. 5 is a characteristic diagram showing an example of control, FIG. 5 is a diagram showing changes in the rear wheel steering angle with respect to the front wheel steering angle, FIG. 6 is a block diagram in the rear wheel changing speed control of the first embodiment, and FIG. 7 is a delay time. FIG. 8 is a diagram showing an example of setting, FIG. 8 is a control characteristic diagram of the first embodiment, FIG. 9 is a block diagram in rear wheel turning ratio changing speed control of the second embodiment, and FIG. 10 is a modification of delay time setting. FIG. 11, FIG. 11 is a characteristic diagram showing a mode change of the control content in the turning ratio changing speed control, and FIGS. 12 to 14 are characteristics showing an example of characteristics when a plurality of turning ratio characteristics are set. It is a figure. A: Front wheel steering mechanism B: Rear wheel steering mechanism R: Rear wheel steering ratio changing device 1R, 1L: Front wheels 2R, 2L: Rear wheel 44: Stepping motor 51: Control unit 52: Turning degree detection means 53: Vehicle speed sensor 71 : Turning ratio calculation circuit 73: Delay circuit 74: Driver circuit 75: Delay time setting circuit

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

Claims (1)

[Claims] 1. A four-wheel steering system for a vehicle that enables a rear wheel steering ratio, a turning degree detecting means for detecting a turning degree of the vehicle, and a regulating means for regulating a changing speed of the rear wheel turning ratio. And a regulation amount adjustment means for receiving a signal from the turning degree detection means and increasing the regulation amount by the regulation means when the turning radius is small as compared to when the turning radius is large. Wheel steering device.