JP3147891B2 - 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 a vehicle configured to steer a rear wheel in accordance with steering of a front wheel.

(Prior Art) Conventionally, a four-wheel steering vehicle (4W) configured to steer rear wheels according to steering of front wheels by a steering handle.
S vehicle) is put into practical use, but in this 4WS vehicle, as disclosed in Japanese Patent Application Laid-Open No. 61-9937, for example, when the steering angle of the steering wheel is large, the left and right rear wheels are out of phase with the front wheels. When the steering angle of the steering wheel is small, the left and right rear wheels are steered in the same phase as the front wheels to improve running stability.

By the way, in a general front two-wheel steering vehicle (2WS vehicle), in order to give a rear wheel a side slip angle and generate a cornering force when turning at medium to high speeds,
You need to slide that much. In other words, the turning of the 2WS vehicle is instantaneous traveling direction (tangential direction of the turning locus circle)
In contrast, the vehicle body is turned inward, and the vehicle slip angle is on the plus side. On the other hand, in a 4WS vehicle, the rear wheels are steered in phase with the front wheels to give a slip angle independently of the vehicle body, thereby reducing the vehicle's sideslip angle, and A turn that matches the direction can be performed. In other words, in a 4WS vehicle, the steering angle (side slip angle) is positively given to the rear wheels, so that the side slip angle of the vehicle body can be suppressed to a small value. Cornering that occurs
Since the force acts in a direction to attenuate the yawing, there is an advantage that running stability is improved.

In the rear wheel steering system disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-9937, when the steering angle of the steering wheel is within a predetermined angle (for example, about 240 °), the rear wheels rotate in the same phase as the front wheels are steered. The so-called "proportional control" of steering is performed, so the moment the vehicle tries to change direction at the beginning of a turn, the cornering force also rises on the rear wheels, acting in the direction that hinders yawing. For this reason, the vehicle body moves in a parallel movement, and the vehicle body slip angle becomes negative. That is, the response to front wheel steering decreases, and the turning performance deteriorates.In this case, the driver tries to correct by turning the steering wheel larger, so that the slip angle of the front wheels increases sharply and the tire The grip force may approach the saturation region.

As means for eliminating the yaw delay by this proportional control, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-164447, after turning the front wheels, wait until sufficient yawing has occurred. Although "delay control" in which the rear wheels are steered has been proposed, this delay control has a more improved turning performance than the above-described proportional control, but has a disadvantage in that the control is complicated.

On the other hand, in a 4WS vehicle, as disclosed in, for example, Japanese Patent Application Laid-Open No. 58-214463, a technique for reducing rear wheel steering force by optimizing wheel alignment of rear wheels is known.

(Object of the Invention) The present invention relates to a vehicle equipped with a rear wheel steering device capable of turning the left and right rear wheels in the same phase with respect to the front wheel in accordance with the steering of the front wheel, and mounting the damper of the rear wheel suspension device on the wheel support. An object of the present invention is to provide a rear wheel suspension device of a 4WS vehicle in which the turning property at the initial stage of turning is improved by devising the position and the mounting angle.

(Constitution of the Invention) The present invention relates to a rear wheel suspension device for a vehicle including a rear wheel steering device capable of turning the left and right rear wheels in phase with respect to the front wheels at a predetermined vehicle speed or more in accordance with steering of the front wheels. An elastic bush is provided at the vehicle-body-side pivot of the wheel suspension device, and the reaction force due to the damping force of the shock-absorbing damper is towed out around the kingpin axis with respect to the rear outside wheel that is steered to the toe-in state during turning. The lower end of the damper is pivotally connected to a wheel support so as to act as a moment.

(Effects of the Invention) According to the present invention, the following effects can be obtained.

(1) The tamper generates a reaction force proportional to the speed of the force applied thereto. Therefore, in the configuration of the present invention, a toe-out moment is generated around the kingpin axis of the turning outer wheel at the moment when the vehicle body rolls at the beginning of turning and the damper on the turning outer wheel contracts. The elastic bush interposed between the arm of the suspension device and the vehicle body is mainly deformed by this toe-out moment, and the kingpin axis of the turning outer wheel that is to be steered in the toe-in direction moves to move the turning outer wheel in the toe-out direction. Try to turn.

On the other hand, the turning inner wheel tends to be steered in the toe-out direction, but the reaction force of the damper outside the turning inner wheel undergoing extension tends to direct the turning inner wheel in the toe-in direction.

Therefore, in the initial stage of turning at a predetermined vehicle speed or more, the in-phase turning amount in the proportional control decreases, and the same effect as if the above-described delay control was performed can be easily obtained without using electronic control. Responsiveness can be improved.

(2) Further, since the damper generates a reaction force proportional to the speed of the force applied thereto, no reaction force is generated from the damper if the initial transient state is passed and a steady state is reached at the time of turning. The steering angle amount in the control is not reduced, and the stability can be improved by the in-phase turning at the time of turning.

(3) According to the present invention, it is also possible to improve running stability during straight running. In other words, if one of the rear wheels, for example, the right rear wheel, rides on a protrusion on the road while traveling straight, the vehicle tries to change its direction to the right, but due to the reaction force of the right rear wheel side damper that is contracted. Since the right rear wheel is directed in the toe-out direction, a force for moving the vehicle to the left works, and a force for changing the direction to the right can be canceled.

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

FIG. 3 is a diagram schematically showing an overall configuration of a four-wheel steering device for a vehicle applied to the embodiment of the present invention, and includes left and right front wheels 1L and 1R.
The front wheel steering device A for turning the steering wheel 2 includes a steering wheel 2, a rack and pinion mechanism 3 that converts a rotational motion of the steering wheel 2 into a linear reciprocating motion,
It comprises a front wheel steering rod 4 provided with this mechanism 3 and left and right knuckle arms 6L, 6R connected to left and right ends of the rod 4 via tie rods 5L, 5R, respectively.
In order to further assist the movement of the rod 4, a power cylinder 8 having a piston 7 and a control valve 9 for switching an oil passage by operating the steering wheel 2
And a power steering device including an oil pump 10.

On the other hand, a rear wheel steering device B for steering the left and right rear wheels 11L and 11R includes a rear wheel steering rod 12 and right and left knuckles connected to left and right ends of the rod 12 via tie rods 13L and 13R, respectively. With arms 14L and 14R, a rear wheel steering rod
The rear wheels 11L and 11R are steered by the movement of 12 in the left-right direction. Also, a power steering device for assisting the movement of the rod 12 is integrally attached to the rear wheel steering rod 12, so that the rod
12 penetrates through the power cylinder 15, and the piston 16 of the power cylinder 15 is fixed to the rod 12. further,
A centering spring 19 for biasing the rear wheel steering rod 12 to a middle position is attached to the rear wheel steering rod 12 for fail-safe use.

FIG. 4 shows the rear wheel steering apparatus B which shows the steering ratio θ _R / θ _F (θ _R is the rear wheel steering angle and θ _F is the front wheel steering angle) of the rear wheels 11L and 11R with respect to the front wheels 1L and 1R. As shown, a variable steering ratio mechanism C that changes according to the vehicle speed is provided. Reference numeral 17 denotes an input shaft of the mechanism C, and reference numeral 18 denotes a control rod as its output shaft. The linear motion of the front wheel steering rod 4 according to the operation of the steering wheel 2 is controlled by a second rack and pinion provided on the rod 4. The rotational motion is converted by the mechanism 20, and the rotational motion is converted into the universal joints 21 and 22 and the connecting rod 23.
Through the input shaft 17 of the variable steering ratio mechanism C. On the other hand, the control rod 18 as an output shaft is provided so as to move in parallel with the rear wheel steering rod 12. The variable steering ratio mechanism C is connected with a stepping motor 25 for changing the steering ratio θ _R / θ _F.
The rotation direction is controlled by a control circuit (CPU) 27 to which an output signal corresponding to the vehicle speed detected by the vehicle speed sensors 26, 26 (the two are provided for improving safety) is given. And the amount of rotation is controlled according to the vehicle speed.

Reference numeral 28 denotes a turning ratio sensor provided in the turning ratio variable mechanism C.
The output of the sensor 28 is given to the control circuit 27, and the stepping motor 25 is feedback-controlled. The configuration and operation of the variable steering ratio mechanism C are described in detail, for example, in Japanese Patent Application Laid-Open No. Sho 59-48054 filed by the present applicant, and further description is omitted here.
The control valve 18, which is the output shaft of the variable steering ratio mechanism C, activates the spool valve type control valve 30 of the rear wheel power steering device, and as is apparent from FIG. 4, the vehicle speed ranges from 0 to 35 km / h. Then, the turning angle θ of the rear wheel
_R is the front wheel turning angle theta _F antiphase, in the vicinity of 35km / h neutral 2WS state, in 35km / h or more is controlled to be in phase.

Control valve 30 for rear wheel power steering system
Is supplied with oil from an oil pump 31, a solenoid valve 32 is interposed in the middle of the oil passage. In the event that an abnormality occurs in the control system, the solenoid valve 32 is actuated by a signal from the control circuit 27 to stop the supply of pressure oil to the control valve 30. The hydraulic pressure in 15 disappears, and the rear wheel steering rod 12 returns to the neutral position by the spring force of the centering spring 19. Therefore, when an abnormality occurs in the control system, the rear wheels 11L and 11R are not steered, and are immediately returned to the neutral position even when steered.

In addition, in addition to the above configuration, an oil passage from the oil pump 31 to the control valve 30 and a control valve 30
A bypass passage may be provided between the oil passage returning to the oil tank and the solenoid valve 32 provided in the bypass passage.

FIG. 1 is a perspective view showing a first embodiment of a rear wheel suspension device to which the present invention is applied in a vehicle provided with the above-described rear wheel steering device B. FIG. 1 shows a suspension system for the right rear wheel 11R,
A wheel support (hub carrier) 40 integrally provided with a knuckle arm 14R protruding toward the rear of the vehicle body and connected to the tie rod 13R via a ball joint 50,
One I-type upper arm 41 and one I-type lower arm
42 is supported by ball joints 43 and 44, respectively, to form a double wishbone type. The upper arm 41 and the lower arm 42 are supported on the vehicle body via elastic bushes 51 and 52, respectively. in this case,
The kingpin axis KP connecting the centers of the two ball joints 43 and 44 is substantially vertical when viewed from the inside of the vehicle body and the caster rail is substantially zero as shown in FIG. 2 (a). As shown in FIG. 2 (b), when viewed from the rear side of the vehicle body, it has an inclination angle of a predetermined angle α so as to expand outwardly of the vehicle body as it goes downward. And wheel support
The lower end of a cylindrical damper 45 for cushioning is pivotally attached to the rear of the kingpin shaft KP at 40, and the kingpin shaft
On the front side of the KP, the guide shaft 47 of the coil spring 46
Is pivotally mounted at its lower end. The axes of the damper 45 and the spring guide shaft 47 are substantially perpendicular. Further, the rear ends of the trailing links 48 and 49 are connected to the upper arm 41 and the lower arm 42, respectively. The front end of the trailing tank 49 is supported by the vehicle body via an elastic bush 53.

With the above configuration, when this 4WS vehicle is running at a speed in the same phase region of 35 km / h or more, the front wheels 1L and 1R are steered to the left by operating the steering wheel 2, and the vehicle body moves to the left. Suppose that you are going to turn. In this case, the right rear wheel 11R on the outside of the turn tries to be steered to a toe-in state, but in the initial stage of the turn, the right side of the vehicle body sinks with the turning of the front wheels 1L and 1R, and the compressive force is applied to the damper 45. Since it works instantaneously, the transient reaction force of the damper 45 at this time acts on the wheel support 40 downward.

In the first embodiment of the present invention, as described above, the kingpin axis KP has a predetermined inclination angle α such that the kingpin axis KP expands outward from the vehicle body as it goes downward, and the lower end of the damper 45 has the kingpin axis KP. Of the damper 45, a toe-out moment is generated around the kingpin axis KP, and the elastic bushing is
51 to 53 are deformed to move the kingpin axis KP forward, and temporarily restrain the right rear wheel 11R, which is to be steered to the toe-in state, toward the toe-out direction in the neutral state.
This restraining force is transmitted not only to the left rear wheel 11L via the rear wheel steering rod 12, but also to the left rear wheel 11L which is extended in the direction to extend the left rear wheel 11L to be steered in the toe-out direction. Since the reaction force of the damper on the 11L side tends to turn the left rear wheel 11L in the toe-in direction, it is as if "delay control" described above
Is performed, and the turning performance at the beginning of turning can be improved.

On the other hand, the reaction force of the coil spring 46, in which the lower end of the guide shaft 47 is pivotally supported by the wheel support 40 in front of the kingpin shaft KP, constantly generates a toe-in moment around the kingpin shaft KP. , 11R is urged in the toe-in direction, improving running stability.

In the above-described first embodiment of the present invention, a twin damper mechanism using the spring guide shaft 47 in front of the kingpin shaft KP as a damper is conceivable. In that case, the damping coefficient of this damper may be smaller than the damping coefficient of the damper 45 behind the kingpin axis KP. In addition, the rear damper 45
Alternatively, a coil spring may be attached. In that case,
The spring constant of this coil spring may be set smaller than the spring constant of the front coil spring 46.

Next, FIGS. 5 (a) and 5 (b) are explanatory views showing a second embodiment of the present invention in correspondence with FIGS. 2 (a) and 2 (b).
In the case of the present embodiment, as shown in FIG. 5A, contrary to the first embodiment, the damper 45 is located on the front side of the kingpin axis KP, and the coil spring 46 is located on the rear side of the kingpin axis KP. . As shown in FIG. 5B, the characteristic feature is that the axes of the damper 45 and the coil spring guide shaft 47 are inclined with respect to the kingpin shaft KP.

Also in the configuration of the second embodiment of the present invention, the toe-out moment is generated around the kingpin axis KP of the rear wheel 11R on the outside of the turn by the reaction force of the damper 45 at the initial stage of the turn, so that the turning property is improved. It is clear that the toe-in moment is constantly generated around the kingpin axis KP by the reaction force of 46, and the running stability is enhanced.

As is apparent from the above description of the embodiment, in the present invention, the kingpin axis KP and the axis of the damper 45 are positively shifted so that they do not have an intersection or are not parallel to each other. This is characterized in that the reaction force of the damper 45 acts on the wheel support 40.

Incidentally, in the configuration described in the above-mentioned Japanese Patent Application Laid-Open No. 58-214463, the kingpin axis and the damper axis have an intersection at the vertex of the strut. In such a configuration, the reaction force of the damper does not affect the wheel support, and since the axis of the coil spring also has an intersection with the kingpin axis, the reaction force of the coil spring does not affect the wheel support. .

The above-described embodiment is a case where the present invention is applied to a double wishbone type rear wheel suspension. However, a strut type rear wheel suspension in which the damper shaft and the kingpin shaft do not have an intersection or are not parallel to each other. It can also be applied to devices. In addition, the present invention is not applied to a double wishbone type suspension device having a structure in which the lower end of the damper is attached to the lower arm instead of the wheel support.

Further, in the present invention, it is sufficient that the reaction force of the damper generates a toe-out moment around the kingpin axis at least in the normal operation range, and there is no need to consider different behaviors other than the normal operation range.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention, FIG.
(B) is an explanatory diagram thereof, FIG. 3 is a system diagram of a steering system, FIG. 4 is a graph showing a relationship between a vehicle speed and a turning ratio, and FIGS. 5 (a) and (b) are second embodiments of the present invention. It is explanatory drawing of an example. 12 ... rear wheel steering rod 15 ... power cylinder 17 ... input shaft, 18 ... control rod 19 ... centering spring 25 ... stepping motor 26 ... vehicle speed sensor 27 ... control circuit 28 ... steering ratio Sensor 30 Control valve 40 Wheel support 45 Damper 46 Coil spring 47 Coil spring guide shaft 51, 52, 53 Elastic bush

Continuation of the front page (56) References JP-A-63-287612 (JP, A) JP-A-1-3111906 (JP, A) JP-A-61-263809 (JP, A) JP-A-60-193771 (JP) JP-A-62-80173 (JP, A) JP-A-62-110506 (JP, A) JP-A-62-175208 (JP, A) JP-B-61-44690 (JP, B2) (58) Field surveyed (Int.Cl. ⁷ , DB name) B60G 3/18-3/28 B62D 7/14

Claims (1)

(57) [Claims] 1. A rear wheel suspension system for a vehicle equipped with a rear wheel steering device capable of steering the left and right rear wheels in the same phase with respect to the front wheels at a predetermined vehicle speed or more according to the steering of the front wheels. An elastic bush is provided on the vehicle body-side pivot, and the reaction force due to the damping force of the shock absorbing damper acts as a toe-out moment around the kingpin axis against the rear wheel that is turned to the toe-in state during turning. like,
A rear wheel suspension device for a rear-wheel steering vehicle, wherein a lower end of the damper is pivotally attached to a wheel support.