JPH0764265B2 - 4-wheel steering system for vehicles - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for a vehicle, and more particularly to a system for controlling a rear wheel steering ratio based on a predetermined rear wheel steering characteristic. .

(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 control the rear wheel steering ratio, that is, the ratio between the front wheel steering angle and the rear wheel steering angle based on a predetermined steering characteristic. In this regard, there has been proposed a device which can be selectively changed according to information from various sensors or a driver's preference (see JP-A-60-135369).

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 characteristics are switched. For this reason, it is necessary to take measures against changes in the behavior of the vehicle during the transition period of the characteristic switching. In addition, it is necessary to consider the safety measures against the erroneous operation and erroneous operation of the characteristic switching means for instructing the change of the steering characteristic, such as various sensors or the manual switch.

On the other hand, it has been proposed to provide a delay means as seen in Japanese Patent Laid-Open No. 60-135369. According to this proposal, the turning ratio is changed slowly, and a sudden behavior change of the vehicle is prevented.

(Problems to be Solved by the Invention) However, as described above, when changing the steering characteristics,
In any case, since the behavior of the vehicle is changed, it is desirable to change the characteristics when the behavior change does not affect the driving safety.

In particular, even if the characteristics are changed slowly on a so-called low μ road where the road surface condition such as a snowy road is slippery, the behavior change of the vehicle is greatly affected.

Therefore, an object of the present invention is to provide a four-wheel steering system for a vehicle, which controls the change of the steering characteristics in relation to the road surface condition.

(Means and Actions for Solving Problems) The present invention has a great effect on the behavior change of the vehicle even if the rear wheels are slightly steered on a low μ road, that is, on a snowy road. Focusing on the fact that the vehicle is in a driving state that is sensitive to changes in the wheel turning ratio, on low μ roads, even if a characteristic switching signal is output from the characteristic switching means, the characteristic change is regulated and the vehicle behavior change This is to allow the change of the characteristic only under the condition that the influence is not so much.

That is, the specific configuration of the present invention is based on a four-wheel steering system for a vehicle, which has a plurality of turning characteristics, and the turning ratio characteristics can be changed by receiving a signal from the characteristic switching means. As shown in FIG. 1, in a four-wheel steering system for a vehicle, which has a plurality of steering characteristics and the steering characteristics can be changed by receiving a signal from the characteristic switching means, μ of the traveling road surface is detected. To detect whether the road surface μ is high μ or low μ, and a signal from the μ determining means. When the μ of the traveling road surface is low μ, the characteristic change restricting means for restricting the change of the steering characteristic by the characteristic switching means based on a predetermined condition 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 nuck arms 3R and 3L are centered around their rotation centers 3R 'and 3L'. The steering wheel 9 is steered clockwise by an amount corresponding to the operation displacement amount of the steering wheel 9, that is, the steering wheel steering angle. Similarly, when the steering wheel 9 is turned to the left, the left and right front wheels 1R,
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 the power steering mechanism D as described above, as is known, when the control rod 21 is displaced leftward in FIG. 2, the relay rod 12 is displaced leftward in FIG. 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, at the time of steering, oil is supplied into the chamber 13b of the cylinder device 13 in accordance with the displacement amount 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
It is possible to swing about 33, but by rotating the holder 32, the inclination angle formed by this pin 33 and the moving axis l ₁ , that is, the moving axis of the swinging orbital surface about the pin 33. 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 material 34
Is connected to the tip of the swing arm 31 via a ball joint 35, and is also input via a ball joint 36.
It is linked to 21a.

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 located on the moving axis l _1, and the connecting rod 34 is connected to the eccentric portion of the rotating plate 37 by the ball joint. It penetrates slidably through 38. 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 angle of the swing track surface of the swing arm 31 is the reference plane δ. α, ball joint 35 pin
When the eccentric distance from 33 is γ, the displacement X of the ball joint 3 in the direction of the moving axis l ₁ becomes X = r tan α · sin θ, which is a function having 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,
If the value of this inclination angle α is changed, the value of X will change even if the steering wheel steering angle θF is the same. Then, the change of the inclination angle α is expressed as a change of the rear wheel steering ratio R. That is, the stepping motor 44
The rotation angle (stepping numerical value) and the steering ratio R are uniquely associated with each other.

As shown in FIG. 4, the steering ratio R is variable with the vehicle speed (V) as a parameter, and the steering characteristics are as follows.
Here, the first turning characteristic (hereinafter referred to as No. 1 characteristic),
The second steering characteristic (hereinafter referred to as the No. 2 characteristic), which is an offset of this No. 1 characteristic to the low speed side, is set, and the No. 1 characteristic and the No. 2 characteristic can be switched appropriately by manual operation. It is supposed to be done. Therefore, even if both the vehicle speed V and the steering wheel steering angle θF are constant, the rear wheels are steered as shown in FIG. 5 as the characteristics are changed.

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 the neutral position can be set against the external force received from the rear wheel 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 is provided with a vehicle speed signal from a vehicle speed sensor 52 for detecting a vehicle speed V and steering characteristics.
A characteristic switching signal from a manual selector switch 53 for switching between No. 1 characteristic and No. 2 characteristic, a front wheel steering angle signal from a steering angle detecting means 54 for detecting a front wheel steering angle θF, directly from the road surface or raindrops, slip Road surface μ that detects μ of the traveling road surface indirectly from the amount or by the switching signal of the manual switch
The road surface μ signal is input from the detecting means 55, and is output from the control unit 51 to the stepping motor 44 and the opening / closing valve 47.

The control contents of the control unit 51 will be described in brief. It is determined whether the road surface condition is a high μ road such as a dry pavement road or a low μ road such as a snow road, and it is a high μ road. Sometimes the steering characteristic (No.1 characteristic, No.2 characteristic) is allowed to be changed according to the characteristic change signal from the manual changeover switch 53, while the predetermined condition is satisfied when the road is low μ. Under the condition, the change of the steering characteristic is allowed. And, as the predetermined condition,
In this embodiment, when the front wheel steering angle θF is small (θF <θF
Therefore, the change of the steering characteristic on the low μ road is allowed only when the steering wheel is hardly turned. That is, when the front wheel steering angle θF is small, even if the rear wheel steering ratio R changes, the rear wheel steering angle θR
This is due to the fact that there is little effect on the steering stability and there is almost no effect on steering stability.

The above contents will be concretely described based on 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 determined based on the vehicle speed signal (V) from the vehicle speed sensor 52. That is, of the No. 1 characteristic and No. 2 characteristic stored in advance in the memory 72,
The target turning ratio (R) is determined based on the characteristics that have been selected and determined, and the obtained target turning ratio (R) is input to the motor drive signal generation circuit 73, where the target turning ratio (R) and It is converted into the target stepping number CP of the motor 44 required to operate.
Then, a pulse signal corresponding to the target stepping number CP is output from the motor drive signal generation circuit 73, and this pulse signal passes through the driver circuit 74.
Entered in. As a result, the stepping motor 44 has a target stepping number CP at a speed corresponding to the input speed of the pulse signal.
The target steering ratio (R) is changed to the target steering ratio (R).

The change of the steering characteristic (No. 1 characteristic → No. 2 characteristic) is made based on the characteristic change signal from the manual changeover switch 53, that is, the H or L signal. A data latch circuit 75 is provided between the steering ratio calculation circuit 71 and the steering ratio calculation circuit 71. An AND circuit 77 is provided between the clock input terminal of the data latch circuit 75 and the oscillator 76 that outputs the clock signal, and when a predetermined condition is satisfied (one input terminal of the AND circuit 77 When the H signal is input), the clock signal output from the oscillator 76 is input to the data latch circuit 75. As a result, the data latch circuit 75
The signal output from the steering ratio calculation circuit 71 to the steering ratio calculation circuit 71 is converted into a signal corresponding to the characteristic switching signal from the manual switch 52, and the steering characteristic is changed.

A signal from the road surface μ detection means 55 is input to one input terminal of the AND circuit 77, and a comparison circuit 78 and an OR circuit 79 are provided between the two 77 and 55. That is, the μ signal from the road surface μ detection means 55 is first input to the comparison circuit 78 and compared with the comparison value μo in the comparison circuit 78, and when the high μ road (μ> μo) is satisfied, "H"
When the signal is output and the low μ road (μ <μo), the “L” signal is output.

Therefore, when the road is high μ, the OR circuit 79
Then, the "H" signal is output from the AND circuit 77 to the AND circuit 77, and the above-described condition for changing the steering characteristic is generated. Therefore, it is possible to change the steering characteristic according to the characteristic switching signal from the manual switch.

The output signal from the comparison circuit 78 is also input to the second AND circuit 81 via the inverter 80, and the output signal from the second AND circuit 81 is input to one input terminal of the OR circuit 79. It has become so. And the second
The front wheel steering angle signal θF from the front wheel steering angle detection means 54 is input to one input terminal of the AND circuit 81 via the second comparison circuit 82. That is, the second comparison circuit 82 compares with the comparison value θFo,
When the front wheel steering angle θF is larger than the comparison value θFo (θF> θF
o), that is, when the steering wheel is largely turned, the “L” signal is output, and when the front wheel steering angle θF is smaller than the comparison value θFo (θF <θFo), that is, when the steering wheel is hardly turned, “H” is output. The signal is output.

Therefore, when low μ is detected by the road surface μ detecting means 55, that is, when the first comparing circuit 78 determines that the road is a low μ (μ <μo), the first comparing circuit 78 is used. "L" signal output from the inverter
The signal is converted into an “H” signal by 80 and input to the second AND circuit 81, while the second AND circuit 81 also outputs an “H” signal when the front wheel steering angle θF is small (θF <θFo). Is input, the second AND circuit 81 outputs an “H” signal to the OR circuit 79, and the above-described condition for changing the steering characteristic is generated.

On the other hand, when the front wheel steering angle θF detected by the front wheel steering angle detecting means 54 is larger than the comparison value θF (θF> θFo), the “L” signal is sent from the second comparison circuit 82 to the second AND circuit 81. Since it is output, the second AND circuit 81 and the OR circuit 79
Outputs an "L" signal, which prohibits changing the steering characteristic.

Therefore, on the high μ road (μ> μo), the characteristics are immediately changed in response to the switching signal of the manual changeover switch, while on the low μ road (μ <μo), when the all-wheel steering angle θF is small (θF < The steering characteristic will be changed under the condition that it is θFo). Such braking contents are divided into regions and shown in FIG. In the figure, the shaded area is an area where the characteristic change is allowed.

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 characteristic change permission condition on the low μ road may be a condition that the vehicle speed is low, that is, a low speed, or that the change amount of the rear wheel steering ratio due to the characteristic change is in a small region. It may be one that does. Further, the steering characteristics include those shown in FIGS. 8 to 10.

(Effects of the Invention) As is apparent from the above description, according to the present invention, during low-μ road traveling, which is a driving state sensitive to changes in the steering characteristics, steering based on a predetermined condition is performed. Since the change of the characteristics is regulated, the steering stability on the low μ road can be improved.

[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 due to characteristic changes, FIG. 6 is a block diagram in control of the embodiment, FIG. 7 is a region diagram allowing characteristic changes, 8 to 10 are diagrams showing modified examples of the turning ratio characteristic. 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: Vehicle speed sensor 53: Steering angle detection means 71 : Steering ratio calculation circuit 75: Data latch circuit

Claims (1)

[Claims] 1. A four-wheel steering system for a vehicle, comprising a plurality of steering characteristics, the steering characteristics being changeable in response to a signal from a characteristic switching means. Road surface μ detection for detecting μ of a traveling road surface. Means for receiving the signal from the road surface μ detection means and for determining whether μ of the traveling road surface is high μ or low μ, and a signal from the μ determination means for receiving a signal from the road surface μ A four-wheel steering system for a vehicle, comprising: characteristic change restricting means for restricting the change of the steering characteristic by the characteristic changing means based on a predetermined condition when μ is low.