JPH02200574A - Rear wheel suspension device for rear wheel steering vehicle - Google Patents

Abstract

PURPOSE:To aim at the compaction of a rear wheel steering gear by connecting a shock absorber to a wheel support in such a way that the reaction axis has a three- dimensional point of intersection with the virtual king pin axis of a rear wheel. CONSTITUTION:The reaction axis l1 of a shock absorber 84 is connected to a wheel support 32R (or 32L) in such a way as to have a three-dimensional point of intersection with the virtual king pin axis l2 of a rear wheel 3R (or 3L) in the initial state of a vehicle. Accordingly, at the bumping and rebounding time of the rear wheel 3R, the reaction force of the shock absorber 84 (the damping force of a damper 91 and the spring reaction of a coil spring) acts upon the support 32R in such a way as to intersect the virtual king pin axis l2 as the steering rotation center axis of the rear wheel. This reaction force thus prevents the rear wheel 3R from being steered integrally with the support 32R and thereby prevents the rear wheel steering from adverse effect caused by a rear wheel steering gear 4. Accordingly, the neutral position energizing force (spring force) just enough to overcome the lateral force at the time of cornering is sufficient for a centering spring in a neutral position reset means 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel suspension system for suspending the rear wheels on a vehicle body in a rear wheel steered vehicle in which the rear wheels can be steered.

(Prior art) Conventionally, as a rear wheel steering vehicle, for example,
As disclosed in Japanese Patent No. 1881, in addition to a front wheel steering device that steers the front wheels, when the front wheels are steered by this front wheel steering device, the rear wheels are steered at a predetermined steering ratio with respect to the steering of the front wheels. Vehicles equipped with wheel steering devices are known.

In such rear-wheel steering vehicles, various types of rear wheel suspension systems are used to suspend the rear wheels on the vehicle body, and the above-mentioned publication (Japanese Unexamined Patent Publication No. 62-6188)
In the case of No. 1), a double wishbone type one is used.

This double wishbone type rear wheel suspension system includes a wheel support that rotatably supports the rear wheel, and a wheel support that extends in the vehicle width direction between the wheel support and the vehicle body.
It includes a pair of upper and lower suspension arms (that is, an upper arm and a lower arm) that connect and support the upper and lower parts of the wheel support to the vehicle body, and a shock absorber that dampens the vertical movement of the rear wheel. In the case of a double wishbone type rear wheel steering device, the virtual kingpin axis, which serves as the steering rotation center axis of the rear wheels, connects the connection point between the upper part of the wheel support and the upper arm and the connection point between the lower part of the wheel support and the lower arm. It is a straight line.

(Problem to be Solved by the Invention) However, in the double lash bone type rear wheel suspension system, when connecting the wheel side end (lower end) of the shock absorber to either the suspension arm (usually the lower arm) or the wheel support, There are the following problems.

In other words, when the wheel side end of the shock absorber is connected to the suspension arm, the reaction force from the shock absorber acts on the suspension arm as a concentrated lateral force when the rear wheel bumps or rebounds, so this suspension arm This requires the use of large-sized devices, which poses problems such as increased weight and difficulty in layout. Also,
Since the lever ratio is small and the expansion and contraction stroke of the shock absorber during rear wheel bump/rebound is relatively short, it is necessary to increase the spring constant or damping coefficient of the damper in order to secure the desired damping force. Sometimes the ride becomes uncomfortable.

On the other hand, when the wheel side end of the shock absorber is connected to the wheel support, the rear wheel is steered around the virtual kingpin axis by the reaction force of the shock absorber when the rear wheel bumps or rebounds.

In order to prevent this steering, in conventional rear wheel steering devices, the holding force (spring force) of the centering spring that holds the rear wheels in a straight-ahead state with zero steering angle is set to a large value, but in this case, There is a problem in that the steering force for steering the rear wheels must be greater than the holding force of the centering spring, resulting in a considerable increase in the size of the entire rear wheel steering device. In addition, in the case of a rear wheel steering device in which the rear wheels are steered in response to the steering of the steering wheel (see Japanese Patent Application Laid-open No. 62-61881 cited above), the reaction force of the shock absorbing device also affects the steering of the steering wheel. This results in poor steering feel.

The present invention has been made in view of the above, and its purpose is to steer the rear wheels depending on the reaction force of the shock absorber when connecting the wheel side end of the shock absorber to the wheel support. By configuring the structure so that no moment is generated, the spring force of the centering spring can be reduced (
The object of the present invention is to downsize the rear wheel steering device.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention includes a rear wheel steering device that steers the rear wheels in conjunction with the steering of the front wheels, and the rear wheels have a shock absorbing device. The assumption is that the vehicle is a rear-wheel steered vehicle that is suspended on the vehicle body by a double Witschborn suspension system. The shock absorber is connected to the wheel support so that its reaction axis has a three-dimensional intersection with the virtual kingpin axis of the rear wheel.

(Function) With the above configuration, in the present invention, the reaction force of the rear wheel bump/rebound shock absorber acts on the wheel support so as to intersect with the virtual kingpin axis as the rear wheel steering rotation center axis. The rear wheels are not steered together with the wheel support due to this reaction force, and it is possible to prevent the rear wheel steering by the rear wheel steering device from being adversely affected.

(Example) Embodiments of the present invention will be described below based on the drawings.

Figure 4 shows the overall configuration of a rear-wheel steering vehicle, and this vehicle has the following features:
A steering device 2 is provided for a front wheel I that steers left and right front wheels IL and IR, and a rear wheel steering device 4 that steers left and right rear wheels 3L and 3R. The front wheel steering device 2 extends in the vehicle width direction, and has tie rods IIL, IIR and a knuckle arm 12L at both ends.

A rack 13 connected to the left and right front wheels IL and IR via 12R, and a binion 1 that meshes with the rack 13 at one end.
4, and a steering shaft 16 having a steering handle 15 at the other end, and is configured to displace the rack 13 in the vehicle width direction by operating the steering handle 15 to steer the front wheels LL and IR. ing.

Further, as shown in FIG. 5, the rear wheel steering device t4 includes a rear wheel steering rod 21, a neutral position return means 22, a servo motor 23, a brake 24, and a control unit 25.
It is equipped with

The rear wheel steering rod 21 extends in the vehicle width direction, and its both ends connect to the left and right rear wheels 3L, 3R via tie rods 31L, 31R and wheel sabots 32L, 32R, respectively.
The rear wheels 3L and 3R are steered by displacing this rear wheel steering rod 21 in the vehicle width direction.

The neutral position return means 22 is attached to the rear wheel steering rod 21, and as shown in detail in a cross section in FIG.
1, a pair of spring receivers 43a and 43b are loosely fitted into the casing 42,
Both spring receivers 43a.

A centering spring 44 is disposed between the springs 43b and 43b.

The rear wheel steering rod 21 extends through the casing 42, and the rear wheel steering rod 21 has a pair of flanges 21.
a, 21. b are formed at predetermined intervals, and the flange 2
1a and 21b are configured to stop the spring receivers 43a and 43b, and the centering spring 43 keeps the rear wheel steering rod 21 in the neutral position (that is, the rear wheel 1
8L.

1.8R is the position where the steering angle is zero and the steering wheel is in a straight-ahead state). The centering spring 44 has a spring force sufficient to overcome lateral force (cornering force) during cornering.

The servo motor 23 is a step motor, and as shown in FIG. 5, its output shaft 23a is connected to a gear train 51a.
It is connected to the rear wheel steering rod 21 via a speed reduction mechanism 51 consisting of a ball screw 51b and a ball screw 51b. It is configured to be displaced from a neutral position against forces. The output shaft 23a of the servo motor 23 and the gear train 5 of the reduction mechanism 51
1a, there is a rear wheel steering rod 21 and a servo motor 2.
A clutch 52 for releasing the connection with 3 is provided,
The rear wheel steering rod 21, which has been displaced from the neutral position by the operation of the clutch 52, can be returned to the neutral position by the biasing force of the neutral position return means 22 when a predetermined abnormality occurs.

The brake 24 is an electromagnetic brake, and is attached to the output shaft 23a of the servo motor 23.
It is possible to apply braking to the rotation of the wheel a, and to lock the output shaft 23a (and thus the rear wheel steering rod 21) by the operation of the brake 24 to maintain the rear wheel steering rod 21 in a predetermined displacement state ( In other words, it is now possible to hold the rudder.

Further, the control unit 25 controls the operation of the servo motor 23, brake 24, and clutch 52 to control the steering of the rear wheels 3L and 3R.
The rear wheel steering control by this control unit 25 is as follows:
Although I will not explain the details using diagrams, basically this is done in response to vehicle speed, and when driving at low speeds, the rear wheel 3L,
The 3R is steered in the opposite phase to the front wheels IL and IR to improve turning ability, and the rear wheels 3L and 3R are the front wheels when driving at high speeds.

It is designed to increase driving stability by steering in the same phase as the IR.

In order to perform such rear wheel steering control, the control unit 25 includes a steering wheel angle sensor 61 that detects the steering angle, a vehicle speed sensor 62 that detects the vehicle speed,
The signals from the rotary encoder 63 that detects the rotational position of the servo motor 23 are respectively input, and the control unit 25 calculates a target rear wheel steering angle based on the steering wheel steering angle and the vehicle speed, and performs the necessary rear wheel steering. A control signal corresponding to the amount is output to the servo motor 23. The rotary encoder 63 constantly monitors whether or not the servo motor 23 is operating properly, that is, the rear wheels 3L and 3R are steered under feedback control.

Furthermore, in rear wheel steering control, the control system has a dual configuration for fail-safe purposes.

That is, the front wheel steering angle sensor 64 is connected to the steering wheel steering angle sensor 61, the second vehicle speed sensor 65 is connected to the vehicle speed sensor 62, and the member from the clutch 52 to the rear wheel steering rod 21 side is connected to the rotary encoder 63. Rear wheel steering angle sensors 66 are respectively added to detect the mechanical displacement of the rear wheels, and the rear wheels are steered only when both corresponding sensors in these three sets of sensors 64 to 66 detect the same value. It is like that. Therefore, in the three sets of sensors 64 to 66, if the vehicle speed detected by the first vehicle speed sensor 62 and the vehicle speed detected by the second vehicle speed sensor 65 are different, an abnormality (failure) has occurred, and the control unit 25, the rear wheel 3
It is designed to hold L and 3R at neutral positions.

Further, in order to detect various abnormalities, ON-OFF signals from a neutral clutch switch 71, an inhibitor switch 72, a brake switch 73, and an engine switch 74 are input to the control unit 12, and the alternator terminal 75 A signal indicating the presence or absence of power generation is input from the . Here, in a vehicle equipped with a manual transmission, the neutral switch 71 outputs an OFF signal when the shift position of the manual transmission is neutral or when the clutch pedal is depressed, and outputs an ON signal otherwise. ing.

In a vehicle equipped with an automatic transmission, the inhibitor switch 72 outputs an ON signal when the range is in neutral (N) or parking (P), and outputs an OFF signal when the range is in the driving range. There is. The brake switch 73 outputs an ON signal when the brake pedal is depressed, and the engine switch 7
3 outputs an ON signal when the engine is in operation.

Next, a rear wheel suspension system for suspending the rear wheels 3L and 3R on the vehicle body will be described using, as an example, a suspension system for the right rear wheel 3R shown in FIGS. 1 to 3. Figure 1 is a perspective view of the rear wheel 3R seen from the inside rear of the vehicle body, and Figures 2 and 3 are a side view and a front view, respectively, showing the arrangement of members and parts of the rear wheel suspension system. be.

This rear wheel suspension device is of a double lash bone type, and in addition to a wheel support 32R that rotatably supports the rear wheel 3R, an upper arm 81, a lower arm 82, and a tree ring arm 83 as a pair of upper and lower suspension arms. and a buffer device 84.

The upper arm 81 and the lower arm 82 are both made of rod members extending in the vehicle width direction.The outer end of the upper arm 81 is rotatably connected to the upper part of the wheel sabot 1-32R via a ball joint 85, and the inner end is supported by the vehicle body 41 so as to be able to swing up and down. Further, the outer end of the lower arm 82 is rotatably connected to the lower part of the wheel support 32R via a ball joint 86, and the inner end is supported by the vehicle body 41 so as to be vertically swingable.

The trailing arm 83 extends in the longitudinal direction of the vehicle body,
A tenth end member 87 whose front end is connected to the vehicle body and whose rear end is connected to the lower arm 82, and a twentieth end member 88 whose one end is connected to the tenth end member 87 and the other end is connected to the upper arm 81. It is designed to transmit longitudinal force (for example, braking force, etc.) acting on the rear wheel 3R to the vehicle body and support it.

Furthermore, the above-mentioned shock absorber r! ! , 84 consists of a damper 91 whose one end (upper end) is connected to the vehicle body 41 and the other end (lower end) is connected to the wheel support 32R, and a coil spring 92 disposed on the upper outer periphery of the damper 91.
This damps the vertical motion a (bump rebound motion) of the rear wheel 41. The damper 91 and the coil spring 92 are coaxially provided so as to have a common reaction axis (center axis) 91, and therefore the reaction axis of the shock absorber 84 also serves as this axis 9+.

Here, from the tie rod 31R of the rear wheel steering device 4 to the rear wheel 3
When the steering force is transmitted to the R side, the rear wheel 3R is integrated with the wheel support 32R at the connection point (ball joint 85) between the wheel support 32R and the upper arm 81.
Then, the vehicle is steered around a virtual kingpin axis 92, which is a straight line passing through the connection point (ball joint 86) between the wheel support 32R and the lower arm 82.

As a feature of the present invention, the lower end of the damper 91 of the shock absorbing device 84 is located at the lower end of the damper 91 of the shock absorbing device 84. T! ! Reaction force shaft threat 1 of impact device 84
is connected to the wheel support 32R so as to have a three-dimensional intersection point P with the virtual kingpin axis ρ2 of the rear wheel 3R in the initial state of the vehicle.

Furthermore, having an intersection point P three-dimensionally means that the intersection point P
The height position is the front view (Fig. 3) and side view (Fig. 2).
It means that both are the same.

Therefore, in the above embodiment, the reaction force 1 of the shock absorber 84 is applied to the rear wheel 3R (or 3L) in the initial state of the vehicle.
) is connected to the wheel support 32R (or 32L) so as to have a three-dimensional intersection point P with the virtual king pin 92 of the rear wheel 3R. force and the spring reaction force of the coil spring 92) is the virtual kingpin axis 9 as the steering rotation center axis of the rear wheel with respect to the wheel support 32R.
2, the rear wheel 3R is not steered together with the wheel support 32R due to this reaction force, and it is possible to prevent an adverse effect on rear wheel steering by the rear wheel steering device. . Therefore, the neutral position biasing force of the centering spring 44 in the neutral position return means 22 (
The spring force is sufficient to simply overcome the lateral force (cornering force) during cornering, and the steering force for steering the rear wheels 3L and 3R against this spring force can also be reduced. The rear wheel steering device 4 can be made smaller.

It should be noted that the present invention is not limited to the above embodiments, but includes various other modifications.

For example, in the case of the above embodiment, the rear wheel steering device 4 is not mechanically connected to the front wheel steering device 2, but both steering devices 2.4 are connected by a transmission mechanism made of a rod member or the like extending in the longitudinal direction of the vehicle body. The present invention can also be applied to a type in which the rear wheels are kept steered in response to the steering of the steering handle 15 of the front wheel steering device 2. In this case, the reaction force of the shock absorber does not affect the steering wheel (and also has the effect that the steering feeling can be improved).

Further, in the above embodiment, the damper 91 of the shock absorber 84 and the coil spring 92 share a common reaction axis (center axis) 91.
We have described the case where the
The present invention provides a reaction shaft of a damper 91 and a coil spring 9.
It can also be applied when the second reaction force axis is not coaxial. In this case, the spring reaction force of the coil spring 92 during bump rebound of the rear wheels 3L, 3R is normally larger than the damping force of the damper 91, so the reaction force axis of the coil spring 92 is connected to the virtual king pin of the rear wheels 3L, 3R. Providing the shock absorber so as to intersect with the axis can reduce the influence of the reaction force of the shock absorber on the rear wheel steering device.

(Effects of the Invention) As described above, according to the rear wheel suspension system of a rear wheel steered vehicle according to the present invention, the reaction force of the shock absorber at the time of bump/rebound of the rear wheel is applied to the virtual kingpin axis of the rear wheel against the wheel support. Since this reaction force can be prevented from steering the rear wheels, both the spring force of the centering spring and the steering force can be set small to make the rear wheel steering system smaller and lighter. In addition, in the rear wheel steering device that is sensitive to the steering angle of the steering wheel, the reaction force of the shock absorber does not affect the steering wheel steering, and the steering feeling can be improved.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a perspective view of a rear wheel suspension system, FIG. 2 is a side view showing the arrangement of members and parts of the rear wheel suspension system, and FIG. 3 is a side view of the rear wheel suspension system. 4 is a front view, FIG. 4 is an overall configuration diagram of a rear wheel steering vehicle, FIG. 5 is a configuration diagram of a rear wheel steering device of the same vehicle, and FIG. 6 is a sectional view of a neutral position return means. 3L, 3R...Rear wheel, 4...Rear wheel steering device, 32L, 32R...Wheel support, 84...Buffer device, 91...Damper 92...Coil spring, 91... Reaction force axis, 92...Virtual king pin axis, P...Intersection point. Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) A rear wheel steering vehicle is provided with a rear wheel steering device that steers the rear wheels in conjunction with the steering of the front wheels, and the rear wheels are suspended on the vehicle body by a double wishbone type suspension device having a shock absorber. A rear wheel suspension system for a rear wheel steered vehicle, wherein the shock absorber is connected to a wheel support such that its reaction axis has a three-dimensional intersection with a virtual kingpin axis of the rear wheel.