JPS628870A - Four wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent a car from being rolled even if the car is transversally accelerated when the car is running while a steering angle ratio between a front and a rear wheel is in an antiphase by configurating a device in such a way that, when the car is running at a low speed while the steering angle ratio between the front and rear wheels is in the antiphase, the rolling stiffness of the car is increased by means of a stiffness changing means. CONSTITUTION:A variable damping force controller 36 is actuated based on a signal from a controller 25 is such a way that a rolling stiffness changing means is switched in response to a change of a steering angle ratio K affected by its inphase or antiphase. The rolling stiffness changing means is composed of an air spring type suspension, and the suspension 38 consists of a shock absorber 39, a coil spring 40, and an air spring chamber 41. And the shock absorber 39 is equiped with a step motor 42, in which a damping force is switched into two steps: a large and a small step. The actuation of the step motor 42 is controlled by a signal from the variable damping force controller 36 allowing the stiffness of the shock absorber to be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels.

(Prior Art) Conventionally, as a four-wheel steering system for this type of vehicle, a front wheel steering mechanism that steers the front wheels and a front wheel steering mechanism that steers the rear wheels have been used, for example, as disclosed in Japanese Patent Laid-Open No. 55-91457. It is equipped with a rear wheel steering mechanism that changes the steering angle of the rear wheels according to the steering angle of the front wheels and the vehicle speed, and at low speeds, the front and rear wheels are in opposite phases.
Furthermore, it is known that the wheels are in the same phase at high speeds to prevent wheels from slipping and improve running stability, as well as to improve maneuverability at low speeds.

(Problem to be solved by the invention) However, when the steering ratios of the front and rear wheels are in opposite phases,
The rotation performance is improved and the tight turning ability when turning is improved, but
When a large acceleration is applied in the width direction of the vehicle, such as when turning, the vehicle tends to roll, causing discomfort to the driver.

In particular, since the vehicle rolls following its motion, unstable roll vibrations tend to occur when turning or the like, and there is a problem in that the anti-phase nature of the vehicle results in poor roll feel when driving.

The present invention has been made in view of the above points, and its purpose is to increase the roll rigidity of a vehicle when the steering ratios of the front and rear wheels are in opposite phases. The purpose of this is to improve the roll feeling when driving in reverse phase and improve ride comfort.

In order to achieve the above object, the solution of the present invention includes a front wheel steering mechanism that steers the front wheels in response to steering wheel steering, and a front wheel steering mechanism that steers the front wheels in response to steering of the steering wheel, and a front wheel steering mechanism that steers the rear wheels with a predetermined front and rear wheel steering ratio characteristic in response to the steering of the front wheels. and a rear wheel steering mechanism for steering the vehicle; in addition to this, a variable means for varying the roll stiffness of the vehicle is provided; furthermore, when the front and rear wheel steering ratios are in opposite phases, the variable means controls the roll stiffness of the vehicle; The structure includes a control means for controlling the variable means to increase the rigidity.

(Function) With the above configuration, when the steering ratios of the front and rear wheels are in opposite phases, the roll stiffness of the vehicle is increased by the variable means, so that even if acceleration is applied in the width direction of the vehicle, the vehicle This will prevent a large roll.

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

FIG. 1 shows the overall configuration of a four-wheel steering system for a vehicle according to a first embodiment of the present invention, where 1 indicates left and right front wheels 2L.

2R, the front wheel steering mechanism 1 includes a steering handle 3, a rack and pinion mechanism 4 that converts rotational motion of the steering handle 3 into linear motion, and the rack and pinion. The operation of mechanism 4 is controlled by the front wheel 2.
It consists of left and right tie rods 5.5 and knuckle arms 6.6 that transmit information to L and 2R and steer them left and right.

Reference numeral 7 denotes a rear wheel steering mechanism that steers the left and right rear wheels 8L, 8R, and both ends of the cough rear wheel steering mechanism 7 steer the left and right rear wheels 8L, 8.
Tie rod 9.9 and knuckle arm 10.10 on R
Rear wheel operating rod 1 extending in the vehicle width direction and connected via
1. The rear wheel operating rod 11 is fitted with a hook 12.
is formed, and the pinion 13 meshing with the rack 12 is rotated by the pulse motor 14 via a pair of bevel gears 15, 16 and the pinion shaft 17, thereby corresponding to the direction and amount of rotation of the pulse motor 14. rear wheel 8
The L and 8R are configured to be steered left and right.

Further, a power cylinder 18 is connected to the rear wheel operating rod 11, using the rod 11 as an operating rod.

The power cylinder 18 has a left-turning hydraulic chamber 18b and a right-turning hydraulic chamber 18c partitioned in the vehicle width direction by a piston 18a fixed to the rear wheel operating rod 11, and the eight hydraulic chambers 18b, 18c are Hydraulic passage 1 each
9a.

19b, communicates with a control valve 20 that controls the oil supply direction and oil pressure to the power cylinder 18,
A hydraulic pump 23 is connected to the control valve 20 via an oil supply passage 21 and an oil return passage 22.
The hydraulic pump 23 is rotationally driven by a motor 24. The control valve 20 detects the rotational direction of the pinion shaft 17 and communicates the oil supply passage 21 with the left rotation hydraulic chamber 18b when the rear wheels 8L and 8R are steered to the left (counterclockwise in the figure). In addition, the right diversion hydraulic chamber 18c is connected to the oil return path 2.
On the other hand, when the rear wheel 81.8R is steered to the right (clockwise in the figure), the communication state is opposite to the above,
At the same time, the hydraulic pressure of hydraulic pump 2 a hk etc. is applied to pinion shaft 1.
The pressure is reduced to the pressure corresponding to the rotary saw 7, and the bevel gears 15, 16 and the pinion shaft 17 are reduced by the pulse motor 14.
When the rear wheel operating rod 11 is moved in the axial direction (vehicle width direction) via the pinion 13 and the rack 12, pressure oil is supplied to the power cylinder 18 to assist the movement of the rear wheel operating rod 11. There is.

The operation of the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 is controlled by a control signal output from a controller 25 that is a control section of the rear wheel steering mechanism 7. The controller 25 receives a steering angle signal from a steering angle sensor 26 that detects the front wheel steering angle from the steering amount of the steering wheel 3 in the front wheel steering mechanism 1, and a vehicle speed signal from a vehicle speed sensor 27 that detects the vehicle speed. They are each input, and the battery power source 29 is connected.

As shown in FIG. 2, the controller 25 receives the steering angle signal from the steering angle sensor 26 and the vehicle speed signal from the vehicle speed sensor 27, and steers the front wheels based on the steering ratio characteristic stored in the characteristic storage section 30. a target steering angle calculating section 31 that calculates a target turning angle of the rear wheels corresponding to the angle and vehicle speed; and a pulse outputting a pulse signal corresponding to the target turning angle calculated by the target turning angle calculating section 31. A generator 32 and a pulse motor 14 receiving a pulse signal from the pulse generator 32.
and a driver 33 that converts into a drive pulse signal that drives the drive motor 24 of the hydraulic pump 23, and the ratio of the rear wheel steering angle to the front wheel steering angle (steering ratio)
is variable according to a predetermined steering ratio characteristic, and the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 are set so that the rear wheel steering angle becomes the target steering angle. #J steering ratio variable means 34 is configured.

Here, the steering ratio characteristic A stored in the characteristic storage section 30 is
As shown in Figure 3, there is an anti-phase region (negative region) in which the rear wheels are steered in the opposite phase to the front wheels depending on the vehicle speed, and a negative region in which the rear wheels are steered in the same phase as the front wheels. The steering ratio k of the front and rear wheels changes over the same phase region (positive region), and as the vehicle speed increases from low to high speed, the steering ratio k changes.
The steering ratio k changes from a large value to approach zero in the opposite phase in the negative direction, and in the medium speed range, the steering ratio k changes to the same phase in the positive direction, and in the high speed range, the steering ratio k increases with the same phase. is set to .

When the steering ratio k of the front and rear wheels is varied by the steering ratio variable means 34 according to the steering ratio characteristic A, the difference between the same phase region and the opposite phase region of the steering ratio is determined. The change is determined by a phase determination section 35 provided in the controller 25 based on the output signal from the target steering angle calculation section 31 of the steering ratio variable means 34, and an output signal is output from the phase determination section 35 as a detection signal. is output to a variable damping force controller 36 as a control means for controlling a roll stiffness variable means 37 that varies the roll stiffness of the vehicle.

The variable damping force controller 36 has the same phase and
It operates to change the roll stiffness variable means 37 in response to a change in the opposite phase, and as shown in FIG. 4, when the steering ratio k is in the opposite phase, the variable means 37 is operated to increase the roll stiffness of the vehicle. When the steering ratio k is in the same phase, the variable means 37 is switched and operated so as to reduce the roll stiffness of the vehicle.

Specifically, the variable means 37 is constituted by an air spring type suspension 38 that changes the suspension characteristics for suspending the vehicle body, as shown in FIG. The shock absorber 39 includes a shock absorber 39, a coil spring 40 disposed around the shock absorber 39, and an air spring chamber 41.

Step motor 4 for switching the damping force into two levels, large and small.
2 is provided. The air spring chamber 41 is connected to an accumulator 44 via a vibrator 43, and a solenoid valve 4 is provided in the middle of the vibrator 43 to communicate or cut off communication between the air spring chamber 41 and the accumulator 44.
5 are arranged. The solenoid valve 45 and the step motor 42 are connected to a variable damping force controller 36, and the variable damping force controller 25 controls the opening and closing of the solenoid valve 45 to increase or decrease the amount of air in the air spring chamber 41. The suspension characteristic of the suspension 38 is switched between a soft state and a hard state by driving and controlling the step motor 42 to switch and control the damping force of the shock absorber 39.

Here, the specific structure of the shock absorber 39 will be explained in detail with reference to FIGS. 6 and 7. The stain absorber 39 consists of an upper case 47 attached to the vehicle body via an elastic body 46, and an upper case 47. The lower case 48 is provided to be movable up and down relative to the lower case 47 and is attached to a wheel via a bracket 49. The lower end of the upper case 47 and the upper end of the lower case 48 are connected via a rolling diaphragm 50, and a seal member 5 is provided inside both cases 47 and 48.
An air spring chamber 41 that is partitioned off by 1 and sealed within an upper case 47 is configured. The air spring chamber 41 is connected to the accumulator 44 via the vibrator 43 and the electromagnetic valve 45 as described above, and the upper case 47 and the lower case 48 each have a spring support member 52.5.
3 is fixedly installed, and the coil spring 40 is attached thereto.

The lower case 48 is composed of an outer cylinder 54 and an inner cylinder 55, and a piston rod 56 hanging from the upper case 47 is inserted into the inner cylinder 55 so as to be slidable in the vertical direction. The interior of the inner cylinder 55 is partitioned into an upper oil chamber 58 and a lower oil chamber 59 by a main valve 57 provided at the lower end.

Further, a bottom valve 60 is provided at the lower end of the inner cylinder 55, and a space between the inner cylinder 55 and the outer cylinder 54 is configured as a reservoir chamber 61.

Furthermore, as shown in enlarged detail in FIG. 7, the main valve 57 has an elongated check valve 62 that allows the working fluid to pass only in the direction from the upper oil chamber 58 to the lower oil chamber 59 side. It has a side orifice 63 and a contraction side orifice 65 which is provided to allow the working fluid to pass only in the direction from the lower oil chamber 59 to the upper oil chamber 58 by means of a check valve 64 . The main valve 57 also includes a sleeve 66 whose interior passes through the upper oil chamber 58 through a through hole 66a and which communicates directly with the lower oil chamber 59, and a sleeve 66 that is rotatably fitted into the sleeve 66. It also has an orifice valve 68 consisting of a valve body 67 having a through hole 67a that can communicate with the through hole 66a of the orifice valve 66.
The valve body 67 of No. 8 is drivingly connected to the step motor 42 via a control rod 69 inserted into the piston rod 56, and as shown in the figure, the valve body 67 is
When the through hole 66a in the valve body 67 and the through hole 67a in the valve body 67 match, the upper oil chamber 58 and the lower oil chamber 59 are communicated with each other. Therefore, according to the operation of the step motor 42, the upper oil chamber 58, the lower oil chamber 59, and the main valve 57 create a hard state in which the two chambers 58, 59 are communicated only through the orifice 63 or 65 and have a large damping force. In addition to these, a variable damping force type shock absorber 39 is configured which can be switched to a soft state with a small damping force communicated by an orifice valve 68.

Next, to explain the operation and effect of the first embodiment, in the controller 25 of the wheel-contact steering mechanism 7, the steering ratio characteristic A stored in the characteristic storage section 30 is changed from the opposite phase region according to the vehicle speed. The front wheel steering angle changes over the same phase region, and the target steering angle is calculated by the target steering angle calculation unit 31 of the steering ratio variable means 34 based on the steering ratio characteristic. The steering ratio of the rear wheel steering angle is variably controlled according to the above-mentioned steering ratio characteristic A, and the rear wheels 8L and 8R are steered in the opposite phase to the front wheels 2L and 2R at low speeds, and the front wheels 2L and 2R are steered at high speeds.
, 2R are steered in the same phase.

In this case, the change in the steering ratio between the in-phase region and the anti-phase region is determined by the phase discriminator 35 in the controller 25, and the phase discriminator 35 outputs an output signal as a detection signal to the vehicle. The damping force variable controller 36 controls the variable means 37 that varies the roll stiffness. Then, the variable means 37 is activated by the variable damping force controller 36 which receives the output signal from the phase discriminator 35, and the switching between high and low roll stiffness of the vehicle is performed in the same phase as the steering ratio.
This is done in response to changes in the opposite phase, and when the steering ratio k changes to the opposite phase, it is switched to increase the roll stiffness of the vehicle, and when the steering ratio k changes to the same phase, it reduces the roll stiffness of the vehicle. It can be switched to

That is, when the steering ratio k changes to the opposite phase, the same signal is sent from the variable damping force controller 36 to the solenoid valve 45 to supply air to the air spring chamber 41, and at the same time, a drive signal is sent to the step motor 42. , suspension 3
8, the suspension characteristics are in a hard state. As a result, the roll stiffness of the vehicle increases as shown in Figure 4, so even when a large acceleration in the vehicle width direction is applied to the vehicle during a turn, the vehicle does not roll significantly. will no longer follow that movement and roll, so
It is possible to improve the roll feeling.

On the other hand, when the steering ratio k changes to the same phase, the suspension characteristic of the suspension 38 remains soft and the roll stiffness of the vehicle decreases as shown in FIG. Since the vehicle does not make a large turn, no large acceleration is applied to the vehicle in the vehicle width direction, and a good roll feeling can be obtained.

In the above embodiment, the shock absorber 39 of the suspension 38 is used as the variable means 37, but even if the spring constant of the stabilizer, spring, etc. is made variable, the first
It goes without saying that the same actions and effects as in the embodiment can be achieved.

Furthermore, FIG. 8 shows the overall configuration of a four-wheel steering system for a vehicle according to a second embodiment of the present invention, and the rear wheel steering mechanism 7' in this four-wheel steering system is similar to that of the four-wheel steering system of the first embodiment. Instead of electrically steering the rear wheels 8L and 8R by the operation of the pulse motor 14 as in the rear wheel steering mechanism 7 shown in FIG. It was designed to turn the steering wheel.

That is, the rear wheel steering mechanism 7' includes a steering ratio changing device 70 made of gears or the like, and the rear end of a transmission rod 71 extending in the longitudinal direction of the vehicle body is connected to the steering ratio changing device 70.
A binion 73 is provided at the front end of the transmission rod 71 and meshes with a rack 72 formed on the rack shaft 4a of the rack and binion mechanism 4 of the front wheel steering i-structure 1. Also,
A sliding member 74 extends from the steering ratio changing device 70, and a recess 75 formed on the surrounding member 74
A binion 76 provided at the front end of a binion shaft 17 connected to the rear wheel operating rod 11 via a rack 12 and a binion 13 meshes with it. Thus, the steering force of the front wheel steering mechanism 1 is transmitted from the rack shaft 4a of the rack & pinion mechanism 4 to the steering ratio changing device 70 via the transmission rod 71,
After the steering ratio is changed in accordance with the control of the controller 25 in the steering ratio changing device 70, the steering force is applied to the sliding member 74.
The rear wheels 8L and 8R are configured to be steered left and right by being transmitted to the rear wheel operating rod 11 via the pinion shaft 17. The configuration of the four-wheel steering device is the same as that of the four-wheel steering device of the first embodiment, and the same members are given the same reference numerals and their explanations will be omitted.

The controller 25 itself that controls the steering ratio changing device 70 is the same as in the first embodiment, and
Of course, similar actions and effects can be achieved thereby.

(Effects of the Invention) As described above, according to the four-wheel steering system for a vehicle according to the present invention, when the vehicle speed is low and the front and rear wheel steering ratios are in opposite phases,
Since the vehicle roll rigidity is increased by the variable means, the vehicle does not roll significantly even when the vehicle receives acceleration in the vehicle width direction due to turning, etc. while driving in reverse phase, and also prevents roll that occurs due to following the movement of the vehicle. As a result, the roll feeling during driving due to the opposite phase is improved, and the ride comfort is improved.

[Brief explanation of the drawing]

1 to 7 show the first embodiment, FIG. 1 is an overall configuration diagram of a four-wheel steering system for a vehicle, FIG. 2 is a block configuration diagram of a controller, and FIG. 3 is a controller for steering based on vehicle speed. A diagram showing the steering ratio characteristics in the case of ratio control, FIG. 4 is a diagram showing the roll stiffness characteristics depending on the vehicle speed of the dampable controller, FIGS. 5 to 7 show the variable means, and FIG. 5 is an overall outline. FIG. 6 is an enlarged cross-sectional view of the main parts of each suspension, and FIG. 7 is an enlarged cross-sectional view of the main parts of the shock absorber. Moreover, FIG. 8 is a diagram corresponding to FIG. 1 showing the second embodiment. 1... Front wheel steering mechanism, 7, 7'... Rear wheel steering mechanism,
25... Controller, 36... Damping force variable control Figure 3 Figure 4 missing

Claims (1)

[Claims] (1) A front wheel steering mechanism that steers the front wheels in response to steering wheel steering, a rear wheel steering mechanism that steers the rear wheels with predetermined front and rear wheel steering ratio characteristics in response to the steering of the front wheels, and vehicle roll. 4. A vehicle characterized in that it comprises a variable means for varying the stiffness, and a control means for controlling the variable means to increase the roll stiffness of the vehicle when the front and rear wheel steering ratios are in opposite phases.
Wheel steering device.