JPH02279463A - Rear-wheel steering gear for vehicle - Google Patents

Abstract

PURPOSE:To aim at the equalization of driving force required for rear-wheel steering in both directions by varying the winding direction of a coil spring in space between a pair of shock absorbers, in a device which installs the paired shock absorbers comprising a buffer coil spring, between a pair of rear-wheel support members and a car body. CONSTITUTION:A rear-wheel steering gear 2 is provided with a pair of rear- wheel support members 6 (5L, 6R) supporting symmetrical rear wheels 4 (4L, 4R) and a rear-wheel steering mechanism 8 being connected to these rear-wheel support members and steering respective rear wheels 4. In addition, it is provided with a neutral energizing means 12 energizing this rear-wheel steering mechanism 8 to a position serving as a criterion for the steering at all times, and a pair of shock absorbers 18L, 18R installed between the rear-wheel support members 6 and a car body 10, comprising buffer coil springs 14 (14L, 14R). In this case, these coil springs 14L, 14R are formed so as to cause the winding direction to become the reverse direction with each other. With this constitution, a sense of load acting on the rear-wheel steering mechanism 8 is reversed right and left, and thereby both loads are made so as to be offset.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle, and particularly to a shock absorbing device thereof.

(Prior Art) In a four-wheel steering vehicle configured to steer not only the front wheels but also the rear wheels, for example, Japanese Patent Laid-Open No. 59-8
As disclosed in Japanese Patent No. 1273, a rear wheel steering device for rear wheel steering is provided. This rear wheel steering device is
Generally, a rear wheel steering mechanism is provided that is connected to each rear wheel support member, and each rear wheel is steered by the operation of this rear wheel steering mechanism. The rear wheel steering mechanism is operated by mechanical or electric drive means, but in any case, in order to equalize the driving force required for steering between rightward steering and leftward steering, the rear wheel steering mechanism is operated by mechanical or electric driving means. The above operations are performed based on the orientation of the rear wheels.

Further, the rear wheel steering device moves the rear wheel steering mechanism to a reference position for its operation (i.e., a neutral position) in order to provide a fail-safe in the event that an abnormality occurs in the rear wheel steering by the rear wheel steering mechanism. In many cases, a neutral biasing means is provided that constantly biases the vehicle toward the target.

In a rear wheel steering device equipped with such a neutral biasing means, it is necessary to steer the rear wheels against the biasing force of the neutral biasing means, but it is necessary to minimize the maximum driving force required for this steering. In order to suppress the force, the biasing force of the neutral biasing means is normally set equally in both left and right directions.

(Problems to be Solved by the Invention) However, when a vehicle equipped with a rear wheel steering device configured in this manner was actually driven, a phenomenon occurred in which the left and right sides were uneven in turning performance.

That is, the neutral biasing means uses its biasing force to shift the rear wheel steering mechanism to the neutral position in response to a lateral force that acts on the vehicle when the vehicle is turned in a state where the rear wheels are not steered by the rear wheel steering mechanism. The limit lateral force that can be maintained clearly showed different values when turning to the right and turning to the left.

After conducting various studies on this result and pursuing the cause, we found that the above phenomenon was caused by the deformation of the shock absorbing coil spring of the shock absorber installed between the rear wheel support member and the vehicle body. found. That is, the coil spring is deformed (generally compressively deformed) due to a sprung load, and along with this deformation, the coil spring tends to undergo torsional deformation. However, since both ends of the coil spring are generally fixed to the sprung upper portion and the unsprung lower portion of the shock absorber, the above-mentioned torsional deformation is hindered and torque is generated between the sprung portion and the unsprung portion. In this case, since the sprung upper portion of the shock absorber is fixed to the vehicle body, the above torque is transmitted from the unsprung portion to the rear wheel support member, and serves as a moment that rotates the rear wheel support member around the kingpin axis. It will work. However, the above-mentioned coil spring is conventionally
Since both the left and right shock absorbers use the same winding direction, the above moment acts on the left and right rear wheel support members in the same direction, causing them to ffi'! The biasing force acting as a reaction force from the neutral biasing means to the rear wheel steering mechanism is an amount that opposes the moment. Then, based on the state in which this biasing force is acting, the lateral force during turning is applied manually to the neutral biasing means, so there is a difference in the limit lateral force when turning to the right and when turning to the left. It is.

If there is a difference between the left and right limit lateral forces as described above, it is necessary to increase the biasing force of the neutral biasing means in order to raise the smaller limit lateral force to a predetermined setting value. Since it is necessary to perform rear wheel steering with a driving force that overcomes this biasing force, this results in disadvantages such as an increase in the size of the actuator and a violation of energy saving requirements.

Furthermore, in a rear wheel steering system that does not have a neutral biasing means, the rear wheels are steered based on the state in which the rear wheels are tilted to either the left or right due to the moment caused by the coil spring. The driving force required for steering is different for rightward steering and leftward steering, and furthermore, the actuator must be operated even when traveling straight, and the above-mentioned disadvantages occur in this case as well.

The present invention has been made in view of the above circumstances, and provides a rear wheel steering device for a vehicle that can equalize the driving force required for rear wheel steering between rightward steering and leftward steering.
1.

(Means for Solving the Problems) The rear wheel steering device for a vehicle according to the present invention is designed in view of the fact that it has been clarified that the above-mentioned left-right difference that has conventionally occurred is caused by a shock absorbing coil spring. By making the winding directions of the coil springs different between the left and right shock absorbers, the moments about the king pin axis acting from each shock absorber on the rear wheel support member are offset, thereby achieving the above objective. This is how it was done.

That is, a pair of rear wheel support members that support left and right rear wheels, a rear wheel steering mechanism that is connected to each of these rear wheel support members and that steers each of the rear wheels, and a buffer coil spring are provided, respectively. In a rear wheel steering system for a vehicle including a pair of shock absorbers installed between each rear wheel support member and a vehicle body, the winding directions of the coil springs are different between the pair of shock absorbers. It is characterized by the fact that

(Function) As shown in configuration 1, the winding directions of the coil springs are different between the pair of shock absorbers, so as the coil springs deform due to the main spring load, the rear wheel support is removed from the shock absorbers. The directions of the torques acting on the members are opposite to each other between the two shock absorbers, and the moments acting on the rear wheel support member around its king pin axis are also opposite. Therefore, the direction of the load acting on the rear wheel steering mechanism connected to each rear wheel support member is reversed, and both loads cancel each other out.

(Effects of the Invention) Therefore, according to the present invention, the driving force required for rear wheel steering by the rear wheel steering mechanism can be equalized between rightward steering and leftward steering. As a result, the actuator that generates the driving force can be made smaller and save energy.

In addition, in a rear wheel steering device equipped with a neutral biasing means,
Since the required biasing force of the neutral biasing means can be reduced, from this point of view as well, the actuator that generates the driving force can be made smaller and save energy.

(Examples) Examples of the present invention will be described in detail below with reference to the accompanying drawings.

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

The rear wheel steering device 2 constitutes a part of a four-wheel steering device that also steers the rear wheels in accordance with front wheel steering, and includes a pair of rear wheel support members that support left and right rear wheels 4L and 4R. 6L, 6R
, a rear wheel steering mechanism 8 connected to each of these rear wheel support members 6L, 6R and for steering each rear wheel 4L, 4R, a control unit 10 for controlling the operation of this rear wheel steering mechanism 8, and a control unit 10 for controlling the operation of this rear wheel steering mechanism 8; A neutral biasing means 12 provided in conjunction with the steering mechanism 8 and constantly biasing the rear wheel steering mechanism 8 to a position (neutral position) serving as the 2FA of the steering, and buffer coil springs 14L and 14R, respectively. , each rear wheel support member 6L
, 6R and a pair of shock absorbers 18L and 18R installed between the vehicle body 1G.

The rear wheel steering mechanism 8 includes a rear wheel steering rod 20 and a servo motor 22 that displaces the rear wheel steering rod 20 from a neutral position in the axial direction (vehicle width direction) against the urging force of the neutral urging means 12. , a brake 24 and a clutch 26 provided on the output shaft 22 a of the servo motor 22 , and a speed reduction mechanism 28 that transmits the driving force of the servo motor 22 to the rear wheel steering rod 20 .

The rear wheel steering rod 20 extends in the vehicle width direction, and its both ends are connected to the knuckle arms 32L, 32 of the left and right rear wheel support members 6L, 6R via the left and right tie rods 30L, 30R.
By displacing the rear wheel steering rod 20 in the vehicle width direction, the rear wheel supporting members 6L, 6R are rotated around the king pin axes 34L, 34R, and the rear wheels 4L,
It is designed to steer 4R.

The servo motor 22 is a step motor, and the servo motor 22 is a step motor.
As shown in the figure, the output shaft 22a is connected to the rear wheel steering rod 20 via a speed reduction mechanism 28 consisting of a gear train 28a and a ball screw 28b, and as shown in FIG. actuated by a control signal;
The rear wheel steering rod 20 is displaced from the neutral position against the biasing force of the neutral biasing means 12. The output shaft 22a of the servo motor 22 is provided with a brake 24 that applies braking to the rotation of the output shaft 22a, and the operation of the brake 24 locks the output shaft 22a (and thus the rear wheel steering rod 20). The rear wheel steering rod 20 can be maintained at a predetermined displacement state.

The operation of this brake 24 is controlled by the control unit IO.
controlled by

The clutch 2G is provided between the output shaft 22a of the servo motor 22 and the gear train 28a, and releases the connection between the rear wheel steering rod 20 and the servo motor 22 when a predetermined abnormality occurs.
Thereby, the rear wheel steering rod 20 displaced from the neutral position is returned to the neutral position by the urging force of the neutral urging means 12. The operation of this clutch 2B is controlled by the control unit IO.

The neutral biasing means 12 is attached to the rear wheel steering rod 20,
As shown in detail in FIG. 3, it has a casing 36 fixed to the vehicle body 16, and a pair of spring receivers 38A and 38B are loosely fitted into this cage 36. A compression spring 40 is disposed between the spring receivers 38A and 38B. The rear wheel steering rod 20 extends through the casing 3G, and the rear wheel steering rod 20 is formed with a pair of flanges 20a and 20b spaced apart from each other.
0a and 20b form the spring receiver 38A.

38B, and the rear wheel steering rod 2
0 is a predetermined neutral position that is always maintained by the compression spring 40 (i.e., a position where the rear wheels 4L and 4R are in a straight-ahead state with a steering angle of zero)
is being energized towards. The compression spring 40 is provided with a spring force sufficient to overcome the lateral force during turning.

The shock absorbers 18L and IIIR are strut portions of a MacPherson strut type suspension device 42R (the right shock absorber is not shown), as shown in the right shock absorber 111R in FIG. 4 (the same applies to the left shock absorber 18L). It consists of

As already mentioned, the shock absorber 18R is equipped with the shock absorbing coil spring +4R, but in addition to this, the shock absorber 18R is also equipped with a damper 44R. The coil spring 14R is held between the upper and lower sides by an upper spring receiver 46R and a lower spring receiver 41iR, and the upper spring receiver 48R is supported by the piston rod 44a of the damper 44R.
The lower spring receiver 48R is fixed to the upper end of the damper 44R by bolt engagement, while the lower spring receiver 48R is fixed to the cylinder 44bR of the damper 44R. The buffer position 118R is bolted to the vehicle body 1B via a mount 50R at the upper end of the piston rod 44aH, and bolted to the knuckle 54R via a mounting bracket 52R fixed to the cylinder 44bR. It is fixed by.

This knuckle 54R constitutes a part of a rear wheel support member 6R, and the rear wheel support member 6R includes an axle 58R that rotatably supports the knuckle 54R and the rear wheel 4R.
It consists of At the lower end of the knuckle 54R, the tip of the lower arm 60R, which is swingably supported by a subframe 58 fixed to the vehicle body 16, is connected to a ball joint 62.
They are connected via R.

In addition, in FIG. 1, the knuckle arm 32R connected to the tie rod 30R is integrally formed with the knuckle 54R.

As shown in Fig. 1, left and right shock absorbers 18L, 18R
The coil springs 14L and 14R provided in the coil springs 14L and 14R have different winding directions. That is, coil springs wound in opposite directions are used.

The reason why the winding directions of the coil springs 14L and 14H are reversed in this way is as follows.

That is, the coil springs 14L and 14R are as follows:
The spring loads acting on the loose 'tk1 devices 111L and tgR compressively deform the coil springs 14L and 14R in the direction of the arrow shown in the figure, but along with this deformation, the coil springs 14L and 14R tend to undergo torsional deformation. However, the coil spring 14
Both ends of L and 14R are the coil springs 14L.

Upper spring receiver 46L to prevent 14R from rotating accidentally
, 46R and the lower spring receivers 48L, 48R, the torsional deformation is prevented and torque is generated between the sprung mass and the unsprung mass.

This torque is generated by the left and right coil springs 14L, 14
Since the winding directions of R are opposite to each other, the directions are opposite to each other as shown by arrow B in the figure. In this case, since the upper spring receivers 46L, 46R are fixed to the vehicle body 16, the torque is transmitted from the lower spring receivers 48L, 48R to the rear wheel support members 6L, 6R1, and the rear wheel support members 6L, 6R1: This acts as a moment in the direction C shown in the figure that rotates 6R around the king pin axes 34L and 34R. However, since this moment also acts in opposite left and right directions, the axial forces applied to the rear wheel steering rod 20 via the tie rods 30L and 30R due to this moment are in opposite directions, as shown by the arrows in the figure. Since both sizes are equal to each other, they cancel each other out, and the rear wheel steering rod 20 ends up not being displaced at all in its axial direction.

The kingpin axis 34R refers to a straight line connecting the center of the mount 50R and the center of the pole joint 82R in FIG. 4 (the same applies to the kingpin axis 34L).

As shown in FIG. 1, the control unit 10 includes the servo motor 22, the brake 24, and the clutch 2B.
As already mentioned, this control unit IO controls the operation of the rear wheel steering device 2, which is a part of a four-wheel steering device, as shown in the figure. Therefore, this is done to achieve the required four-wheel steering function.

In addition to the rear wheel steering device 2, the four-wheel steering device includes a front wheel steering mechanism 70 and various sensors that send various information to the control unit 10 for appropriate rear wheel steering control according to driving conditions. It has become.

The front wheel steering mechanism 70 extends in the vehicle width direction, and has left and right tie rods 72L, 72R and a knuckle arm 7 at both ends.
A rack 78 is connected to the left and right front wheels 7[, 78R via 4L and 74R, and a steering shaft 84 is provided with a pinion 80 that meshes with the rank 78 at one end and a steering wheel 82 at the other end. By operating the steering wheel 82, the rack 78 is displaced in the vehicle width direction, and the front wheel 713L is
, and is designed to steer the 7GR.

The rear wheel steering control by the control unit 10 is performed in response to vehicle speed, and an example of changing the steering ratio (rear wheel steering angle/front wheel steering angle) according to the vehicle speed is as shown in FIG. There are cases. When the control characteristics shown in FIG. 6 are applied, the rear wheel steering angle relative to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, and this situation is shown in FIG.

In order to perform such rear wheel steering control, as shown in FIG. 1, the control unit IO includes a steering wheel steering angle sensor 86, a vehicle speed sensor 88, and the servo motor 22.
The control unit 10 calculates a target rear wheel steering angle based on the steering wheel steering angle (theoretically equal to the front wheel steering angle) and the vehicle speed. A control signal corresponding to the required amount of rear wheel steering is output to the servo motor 22. Then, the rear wheels 4L and 4R are steered while constantly monitoring whether or not the servo motor 22 is operating properly using a row encoder 64, that is, under feedback control.

An example of rear wheel steering control in the control unit 10 will be described with reference to the flowchart in FIG. 7. Note that in the following explanation, P indicates a step.

Control starts when the ignition key switch is turned on. First, the brake 24 is released at Pl, the clutch 26 is disengaged at P2, and then the sensor G4.
'8G, the signal from 8g is read.

After P3, in P4, it is determined whether a failure has occurred in a part of the rear wheel steering device (1 to 8), for example, whether a failure has occurred that prevents the drive control of the motor 22 from being performed normally. If the determination in P4 is No, the target steering angle θR is determined by comparing the vehicle speed and steering angle with the steering ratio characteristics shown in FIG. 5 (FIG. 6). At P6, the above θR is output (feedback control).

When the determination in P4 is YES, the clutch 2G is disengaged at Pl. As a result, the rear wheels 4L and 4R are brought to the neutral position by the neutral biasing means 13. After this, P8
After the brake 24 is engaged in step P9, the power to the motor 22 is interrupted and analyzed.

Then, at PIO, after confirming that a predetermined time has elapsed, clutch 2G is connected at pH. The above PIO
This process is performed by disengaging the clutch 26 at Pl.
This is to wait for L and 4R to reliably return to the neutral position/return, and the reason why the clutch 26 is connected at pH is to maintain the neutral position using the brake 24 as well.

As described in detail above, according to this embodiment, the coil spring 14 is connected between the left and right shock absorbers 1.8L and 18R.
Since the winding directions of L and 14R are reversed, the loads acting on the rear wheel steering rod 20 of the rear wheel steering mechanism 8 connected to each rear wheel support member are offset. The driving force required for rear wheel steering by the rear wheel steering mechanism 8 can be made equal between rightward steering and leftward steering.

Since there is no left-right difference in the limit lateral force with which the neutral biasing means 12 can hold the rear wheel steering rod 20 in the neutral position during cornering, etc., it is possible to set the spring force of the neutral biasing means 12 small. As a result, the servo motor 22
It is possible to reduce the size and save energy.

In this embodiment, a case where the shock absorber is provided in a MacPherson strut suspension device has been described, but similar effects can be obtained when the shock absorber is provided in a double wishbone suspension device, etc. I can do it.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a vehicle rear wheel steering device according to the present invention, FIG. 2 is a configuration diagram showing a rear wheel steering mechanism of the above embodiment, and FIG. 3 is a neutral diagram of the above embodiment. A detailed cross-sectional view showing the biasing means, FIG. 4 is a view showing the rear suspension device equipped with the shock absorbing device of the above embodiment as seen from the rear, and FIGS. 5 and 6 constitute the rear wheel steering device according to the above embodiment. FIG. 7 is a characteristic diagram showing the action of the four-wheel steering device which is a part of the elements. FIG. 7 is a flowchart showing an example of control by the control unit of the above embodiment. 2... Rear wheel steering device 4L, 4R... Rear wheel 6L
, 6R... Rear wheel support member 8... Rear wheel steering mechanism 12... Neutral biasing means 1
4L, 14R...Buffer coil spring 1B...
Vehicle body 18L, 18R... shock absorber 2
0... Rear wheel steering rod Figure 2 Figure 3 Figure \-=,,/ Figure

Claims (1)

[Scope of Claims] A pair of rear wheel support members that support left and right rear wheels, a rear wheel steering mechanism that is connected to each of these rear wheel support members and that steers each of the rear wheels, and a buffer coil spring. A rear wheel steering system for a vehicle comprising a pair of shock absorbers installed between each of the rear wheel support members and the vehicle body, wherein the winding direction of the coil spring is set in the pair of shock absorbers. A rear wheel steering device for a vehicle characterized by being different from one another.