JP2728484B2 - Rear wheel suspension system for rear wheel steering vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rear wheel suspension device for suspending a rear wheel on a vehicle body in a rear-wheel steering vehicle capable of steering the rear wheel.

(Prior Art) Conventionally, as a rear-wheel steering vehicle, for example, Japanese Patent Application Laid-Open No. 62-61
As disclosed in JP-A-881, apart from the front wheel steering device for steering the front wheels, when the front wheels are steered by the front wheel steering device, the rear wheels are steered at a predetermined steering ratio with respect to the steering of the front wheels. Those with a wheel steering device are known.

In such rear-wheel-steered vehicles, various types of rear-wheel suspension devices for suspending the rear wheels from the vehicle body are used, as disclosed in the above-mentioned publications (JP-A-62-61881).
No.), the double wishbone type is used. This double wishbone type rear wheel suspension device is provided with a wheel support rotatably supporting a rear wheel, and extending in the wheel direction between the wheel support and the vehicle body. And a pair of upper and lower suspension arms (that is, an upper arm and a lower arm) that are connected and supported to the vehicle, and a shock absorber for attenuating the vertical movement of the rear wheel. In the case of a double wishbone type rear wheel suspension device, the virtual kingpin axis as the steering rotation center axis of the rear wheel is defined by the connection point between the upper wheel support and the upper arm and the connection point between the lower wheel support and the lower arm. It is a straight line that connects.

(Problems to be Solved by the Invention) However, in the above-mentioned double wishbone type rear wheel suspension, even when the wheel end (lower end) of the shock absorber is connected to either the suspension arm (usually the lower arm) or the wheel support. There are the following problems.

That is, when the lower end of the shock absorber is connected to the suspension arm, the reaction force from the shock absorber acts as a one-point concentrated lateral force on the suspension arm when the rear wheel bumps and rebounds. Must be used, and there are problems such as an increase in weight and difficulty in layout. In addition, since the lever ratio is small and the expansion and contraction stroke of the shock absorber at the time of bump / rebound of the rear wheel is relatively short, it is necessary to increase the spring constant or the damping coefficient of the damper to secure a predetermined damping force. In this case, the ride quality is poor.

On the other hand, when the lower 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 and rebounds. In order to prevent this turning, in a conventional rear wheel steering device, a holding force (spring force) of a centering spring for holding the rear wheels in a straight traveling state with a steering angle of zero is set to be large. The steering force for steering the rear wheel must be greater than the holding force of the centering spring, and there is a problem that the entire rear wheel steering device becomes considerably large. Further, in the case of a rear wheel steering device in which the rear wheels are steered in response to the steering of the steering handle (see Japanese Patent Application Laid-Open No. 62-61881 as exemplified above), the reaction force of the shock absorber also affects the steering of the steering wheel. And the steering feeling deteriorates.

The present invention has been made in view of the above, and an object of the present invention is, particularly, in a double wishbone type suspension device, in connecting a lower end of the shock absorber to a wheel support, a reaction force of the shock absorber is used. Depending on the configuration, the moment to steer the rear wheel is not induced, so that the spring force of the centering spring is reduced,
It is to reduce the size of a rear wheel steering device.

(Means for Solving the Problems) In order to achieve the above object, a solution of the present invention includes a rear wheel steering device for steering a rear wheel along with steering of a front wheel, and the rear wheel includes a shock absorber. It is assumed that the vehicle is a rear-wheel-steered vehicle that is suspended on a vehicle body by a double wishbone type suspension device. The shock absorber is swingably connected at the upper end to the vehicle body and the lower end is swingably connected to the wheel support, and is arranged such that the reaction force axis of the shock absorber is parallel to the virtual kingpin axis of the rear wheel. It is configured.

(Operation) According to the present invention, the reaction force of the shock absorber of the double wishbone suspension during the bump / rebound of the rear wheel is reduced by the virtual kingpin axis as the steering rotation center axis of the rear wheel with respect to the wheel support. Acts in parallel with
This reaction force does not cause the rear wheel to be integrally steered with the wheel support, and can prevent adverse effects on rear wheel steering by the rear wheel steering device.

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

FIG. 4 shows the entire configuration of a rear-wheel steering vehicle. This vehicle includes a front-wheel steering device 2 for steering left and right front wheels 1L and 1R, and a rear-wheel steering device 4 for steering left and right rear wheels 3L and 3R. Have. The front wheel steering device 2 extends in the vehicle width direction, and has tie rods 11L, 11R and knuckle arms 12L, 1
A rack 13 connected to the left and right front wheels 1L, 1R via 2R,
A pinion 14 that meshes with the rack 13 is provided at one end,
A steering shaft 16 provided with a steering handle 15 at the other end thereof. The rack 13 is displaced in the vehicle width direction by operating the steering handle 15 so that the front wheels 1L, 1R
Is configured to be steered.

Further, as shown in FIG. 5, the rear wheel steering device 4 includes a rear wheel steering rod 21, a neutral position return means 22, a servomotor 23, a brake 24, and a control unit 25.

The rear wheel steering rod 21 extends in the vehicle width direction, and both ends thereof are connected to left and right rear wheels 3L, 3R via tie rods 31L, 31R and wheel supports 32L, 32R, respectively.
The rear wheels 3L and 3R are steered by displacing the 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 has a casing 42 fixed to a vehicle body 41, as shown in detail in FIG. The spring receivers 43a and 43b are loosely fitted, and
A centering spring 44 is provided between a and 43b. The rear wheel steering rod 21 extends through a casing 42. The rear wheel steering rod 21 has a pair of flanges 21a and 21b formed at a predetermined interval. The flanges 21a and 21b The rear wheel steering rod 21 is constantly biased by the centering spring 43 toward a neutral position (that is, a position where the rear wheels 18L and 18R are in a straight-ahead state where the steering angle is zero). Have been. Centering spring 44
Are provided with a spring force enough to overcome the lateral force (cornering force) during cornering.

The servo motor 23 is a stepping motor, and as shown in FIG. 5, its output shaft 23a is connected to the rear wheel steering rod 21 via a speed reduction mechanism 51 including a gear train 51a and a ball screw 51b. The operation of the servomotor 23 causes the rear wheel steering rod 21 to be displaced from the neutral position against the urging force of the neutral position return means 22 (centering spring 44). Output shaft 23a of the servo motor 23
Between the rear wheel steering rod 2 and the gear train 51a of the speed reduction mechanism 51.
Clutch 5 for releasing connection between 1 and servo motor 23
2, the rear wheel steering rod 21 displaced from the neutral position can be returned to the neutral position by the biasing force of the neutral position return means 22 when a predetermined abnormality occurs by the operation of the clutch 52. I have.

The brake 24 is an electromagnetic brake, which is attached to the output shaft 23a of the servomotor 23, and can apply a brake to the rotation of the output shaft 23a. The rear wheel steering rod 21) is locked so that the rear wheel steering rod 21 can be maintained in a predetermined displacement state (that is, maintained).

Further, the control unit 25 controls the operation of the servo motor 23, the brake 24, and the clutch 52 to perform steering control of the rear wheels 3L and 3R. Although it is not described in detail using, it is basically performed in response to vehicle speed, and when driving at low speed, the rear wheels 3L, 3R are steered in the opposite phase to the front wheels 1L, 1R to increase small turning characteristics, and high speed Rear wheel when driving
The 3L and 3R are steered in the same phase as the front wheels 1L and 1R to enhance running stability.

In order to perform such rear wheel steering control, the control unit 25 includes a signal from a steering wheel steering angle sensor 61 for detecting a steering wheel steering angle, and a vehicle speed sensor 62 for detecting a vehicle speed.
And the signal of the rotary encoder 63 for detecting the rotational position of the servo motor 23 are respectively input.The control unit 25 calculates the target rear wheel steering angle based on the steering angle and the vehicle speed, A control signal corresponding to the wheel steering amount is output to the servo motor 23. Then, while the rotary encoder 63 constantly monitors whether the operation of the servo motor 23 is properly performed, that is, the rear wheels 3L, 3R are steered under feedback control.

Further, in the rear wheel steering control, the control system has a double configuration for fail-safe. That is.
A front wheel steering angle sensor 64 is provided with respect to the steering wheel steering angle sensor 61.
A rear wheel steering angle sensor for detecting a mechanical displacement of a member on the rear wheel steering rod 21 side from the clutch 52 with respect to the rotary encoder 63;
66 are added, and these three sensors 64 to
At 66, the rear wheel is steered only when the corresponding sensor detects the same value. Therefore, when the vehicle speed detected by the first vehicle speed sensor 62 is different from the vehicle speed detected by the second vehicle speed sensor 65 in the three sensors 64 to 66, for example, an abnormality (failure) occurs and the control unit 25 , The rear wheels 3L and 3R are held at the neutral position.

Further, for detection of various abnormalities, ON / OFF signals of 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 L terminal 75 of the alternator. Is a signal indicating the presence or absence of power generation. 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 travel range. I have. The brake switch 73 outputs an ON signal when the brake pedal is depressed, and the engine switch 73 outputs an ON signal when the engine is operating.

Next, a description will be given of a rear wheel suspension device for suspending the rear wheels 3L, 3R to the vehicle body, taking as an example a suspension device for the right rear wheel 3R shown in FIGS. FIG. 1 is a perspective view of the rear wheel 3R as viewed from the inside rear side of the vehicle body, and FIGS. 2 and 3 are a side view and a front view, respectively, showing the arrangement of members and components of the rear wheel suspension device. .

This rear wheel suspension device is of a double wishbone type, and in addition to a wheel support 32R that rotatably supports the rear wheel 3R, an upper arm 81 and a lower arm 82 and a treeing arm 83 as a pair of upper and lower suspension arms. And a shock absorber 84.

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

The treeling arm 83 extends in the front-rear direction of the vehicle body,
A first rod member 87 having a front end connected to the vehicle body and a rear end connected to the lower arm 82;
The other end is composed of a second rod member 88 connected to the upper arm 81, and transmits and supports a longitudinal force (for example, a braking force) acting on the rear wheel 3R to the vehicle body.

Further, the shock absorber 84 has one end (upper end) of the vehicle body 41.
A damper 91 having the other end (lower end) swingably connected to and supported by the wheel support 32R, and a coil spring 92 disposed on the outer periphery of the upper portion of the damper 91;
This attenuates the vertical movement (bump rebound movement) of the rear wheel 41. The above damper 91 and a coil spring 92 is provided coaxially to have a common reaction force axis (center axis) l _1, therefore, this axis also the reaction force axis of the shock absorber 84
l becomes ₁ .

Here, from the tie rod 31R of the rear wheel steering device 4 to the rear wheel 3R
When the steering force is transmitted to the side, the rear wheel 3R is integrated with the wheel support 32R, and the connection point (ball joint 85) between the wheel support 32R and the upper arm 81 and the connection between the wheel support 32R and the lower arm 82. point steers the virtual kingpin axis l ₂ around a straight line passing through the (ball joint 86).

Then, as a feature point of the present invention, the damper 91 the lower end of the shock absorber 84, the shock absorber reaction force axis l ₁ of 84 and a virtual kingpin axis l ₂ of the rear wheel 3R in the initial state of the vehicle three-dimensionally parallel Connected to the wheel support 32R. Note that being three-dimensionally parallel means being parallel in both the front view (FIG. 3) and the side view (FIG. 2).

Therefore, in the above embodiment, the virtual kingpin axis l ₂ of the rear wheel 3R (or 3L) is set in the initial state of the vehicle with the reaction force axis l ₁ of the shock absorber 84 of the double wishbone suspension.
Wheel support 32R so that it is three-dimensionally parallel with
(Or 32L), the rear wheel 3R bumps
During rebound, the reaction force of the shock absorber 84 (damping force and the spring reaction force of the coil spring 92 of the damper 91) acting parallel with the virtual kingpin axis l ₂ as a steering rotation center axis of the rear wheel with respect to the wheel support 32R Therefore, the rear wheel 3R is not integrally steered with the wheel support 32R due to the reaction force, and it is possible to prevent the rear wheel steering device from adversely affecting the rear wheel steering. Therefore, the neutral position return means 22
The biasing force (spring force) of the centering spring 44 at the neutral position only needs to overcome the lateral force (cornering force) during cornering, and the rear wheels 3L, 3R are steered against this spring force. Therefore, the rear-wheel steering device 4 can be reduced in size.

The present invention is not limited to the above embodiment,
Other various modifications are included. 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 the steering devices 2, 4 are connected by a transmission mechanism including a rod member extending in the vehicle longitudinal direction. The present invention can also be applied to a type in which the rear wheels are steered in response to the steering of the steering handle 15 of the front wheel steering device 2.

In the above embodiment has dealt with the case of the damper 91 and the coil spring 92 of the shock absorber 84 is provided coaxially with a common reaction force axis (center axis) l _1, the present invention provides a damper 91 The present invention can also be applied to a case where the reaction force axis is not coaxial with the reaction force axis of the coil spring 92. In this case, the spring reaction force of the coil spring 92 at the time of bump / rebound of the rear wheels 3L and 3R is larger than the damping force of the normal damper 91.
Providing it so as to be parallel to the virtual kingpin axes of the 3L and 3R can reduce the influence on the rear wheel steering device due to the reaction force of the shock absorber.

(Effect of the Invention) As described above, according to the rear wheel suspension device of the rear wheel steering vehicle of the present invention, the reaction force of the shock absorber of the double wishbone type suspension device against the wheel support when the rear wheel bumps and rebounds. Acting in parallel with the virtual kingpin axis of the rear wheel, it is possible to prevent the rear wheel from being steered by this reaction force, so that both the spring force and the steering force of the centering spring are set to be small, and the rear wheel steering device 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 of the steering wheel, and the steering feeling can be improved. .

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a perspective view of a rear wheel suspension device, FIG. 2 is a side view showing the arrangement of members and components of the rear wheel suspension device, and FIG. FIG. 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 vehicle, and FIG. 6 is a cross-sectional view of a neutral position returning unit. 3L, 3R: Rear wheel, 4: Rear wheel steering device, 32L, 32R: Wheel support, 84: Shock absorber, 91: Damper, 92: Coil spring, l _1: Reaction axis, l ₂ …… Virtual kingpin axis.

Claims (1)

(57) [Claims] 1. A rear-wheel steering vehicle comprising a rear wheel steering device for steering a rear wheel in accordance with steering of a front wheel, wherein the rear wheel is suspended from a vehicle body by a double wishbone type suspension device having a shock absorber. The shock absorber is supported so that the upper end thereof is swingably connected to the vehicle body and the lower end thereof is swingably connected to the wheel support, and the reaction force axis of the shock absorber is parallel to the virtual kingpin axis of the rear wheel. A rear-wheel suspension device for a rear-wheel-steered vehicle.