JPH0464912B2 - - Google Patents

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 following the steering of the front wheels, and particularly relates to a hydrostatic four-wheel steering system. Regarding.

(Conventional technology) Conventionally, by steering the rear wheels in accordance with the steering of the front wheels of a vehicle, driving stability has been improved by, for example, keeping the front wheels and rear wheels in phase at high vehicle speeds with small steering angles. It is also known that in a low vehicle speed range with a large steering angle, the steering ratio of the rear wheels to the front wheels is made as small as possible, preferably in opposite phase, to improve the turning ability. It is also known that when parking the vehicle in a garage, parallel parking, pulling alongside, etc., it is preferable to have the front wheels and rear wheels in the same phase because these driving operations become easier.

Therefore, conventionally, as a four-wheel steering system for such a vehicle, the front and rear wheels are connected using a link mechanism such as a relay rod, as shown in Japanese Patent Application Laid-open No. 55-15301. A link-type type that allows simultaneous steering has been proposed.

(Problems to be Solved by the Invention) However, in this device, the link mechanism for connecting the front wheels and the rear wheels is arranged in the longitudinal direction on the lower surface of the vehicle body floor, so there are many restrictions on the layout. In addition, the tunnel portion of the vehicle body floor becomes large, resulting in a decrease in comfort. Moreover,
Because the connection structure uses a link mechanism, the degree of freedom in the steering ratio between the front and rear wheels is small, a large steering force is not generated on the rear wheels, and the stroke and force efficiency are poor, resulting in poor operability. It was inferior.

Furthermore, in the case of the link mechanism as described above, the steering ratio between the front wheel steering angle and the rear wheel steering angle is uniquely determined, and it is difficult to change the steering ratio depending on the driving condition of the vehicle. For example, by changing the steering ratio when the steering angle of the steered wheels, that is, when the front wheel steering angle is small and large, it is possible to improve running stability in the small steering angle region and small turning ability in the large steering angle region. It was impossible to meet demands such as achieving a balance between work and work. still,
Although it is possible to make the steering ratio variable by providing a control mechanism etc. in the link mechanism described above, the mechanism and structure would be extremely complicated and large-scale, resulting in problems with operational stability and reliability. It is also disadvantageous in terms of cost.

In view of this, an object of the present invention is to steer the rear wheels by following the steering of the front wheels using a static pressure type hydraulic mechanism instead of the above-mentioned link type, so that the comfort etc. are not impaired. In addition to a large degree of freedom in layout, there is also a large degree of freedom in the steering ratio of the front and rear wheels, and a large steering force is generated for the rear wheels, with high efficiency in stroke and force, excellent operability, and even greater reliability. To provide a high-performance four-wheel steering device with low energy loss.

Furthermore, an object of the present invention is to make the steering ratio between the front wheel steering angle and the rear wheel steering angle variable with a simple structure using the above-mentioned hydrostatic hydraulic mechanism, thereby adjusting the steering angle according to the running condition of the vehicle. To easily obtain variety in steering ratio characteristics such as steering ratio.

(Means for Solving the Problems and Their Effects) In order to achieve the above object, the solving means of the present invention includes a front cylinder whose volume changes in conjunction with a front wheel steering system that steers the front wheels, and a front cylinder that steers the rear wheels. A rear cylinder is provided, and the front cylinder and the rear cylinder are connected in a liquid-tight manner, so that the volume of the front cylinder changes as the front wheels are steered,
This change in volume is transmitted to the rear cylinder via the static pressure circuit, so that the rear wheels are steered following the steering of the front wheels. Furthermore, the static pressure circuit between the front cylinder and the rear cylinder is provided with a volume variable means for increasing or decreasing the volume of the static pressure circuit, and the volume variable means is configured to control the ratio of the front wheel turning angle to the rear wheel turning angle (steering angle). By configuring it as a variable steering ratio mechanism that changes the ratio (ratio), the steering ratio can be made variable by changing the volume change rate of the rear cylinder due to the front cylinder.

(Effects of the Invention) Therefore, according to the present invention, a hydrostatic four-wheel steering system is provided that steers the rear wheels by transmitting the volume change of the front cylinder, which changes volume in conjunction with the front wheel steering system, to the rear cylinder. As a result, it is only necessary to arrange hydraulic piping in the longitudinal direction of the lower surface of the vehicle body floor, so the degree of freedom in layout is significantly increased compared to the link type, and the comfort etc. are not impaired. Moreover, the steering ratio of the front and rear wheels can be easily changed by changing the cylinder diameter ratio, and the degree of freedom in the steering ratio is large. A large steering force can be generated, and the stroke and force efficiency are high, resulting in high precision. Furthermore, since it is a static pressure type, it is more reliable than a dynamic pressure type, and also has less energy loss, and provides a four-wheel steering device that has excellent performance such as operability, reliability, and accuracy. I can do it.

Furthermore, the present invention makes the steering ratio variable by changing the volume change rate of the rear cylinder due to the front cylinder, so that even with a simple structure, the steering ratio characteristics such as the steering ratio according to the running condition of the vehicle can be adjusted. It is possible to easily obtain a variety of the four-wheel steering system, and it is possible to provide a four-wheel steering system suitable for practical use at low cost and easily.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

In FIG. 1, 1 is a front wheel steering system that steers left and right front wheels 2L and 2R. The front wheel steering system 1 is
The steering wheel 3 to be steered and the steering wheel 3
A pinion 4a and a rack 4b which convert the steering force into movement in the vehicle width direction (left and right direction) and transmit the same, right and left tie rods 5, 5 whose base ends are connected to each end of the rack 4b, and one end of which is connected to each end of the rack 4b. At the tips of the tie rods 5, 5, there are knuckle arms 6, 6 whose other ends are connected to the left and right front wheels 2L, 2R, respectively.
5 in the vehicle width direction to move the left and right front wheels 2L and 2R.
It is configured to steer left and right.

A front cylinder 7 is provided on the rack 4b of the front wheel steering system 1. The front cylinder 7 includes a cylinder case 7a fixed to the vehicle body,
A piston 7b is provided integrally with the rack 4b and is slidably fitted into the cylinder case 7a.
and a left chamber 7c partitioned by the piston 7b.
and a right chamber 7d, and when the piston 7b moves in the vehicle width direction (horizontal direction) in conjunction with the rack 4b of the front wheel steering system 1, the left chamber 7c and the right chamber 7d
is configured so that its volume changes.

On the other hand, reference numerals 8 and 8 are wheel support members that rotatably support the left and right rear wheels 9L and 9R, and two lateral rings 10, front and rear, extending in the vehicle width direction are provided at the front and rear ends of each wheel support member 8. , 11 are connected to each other. Left and right front lateral links 1
0 and 10 are connected between their inner ends by a link-like connecting member 12, while the inner ends of each rear lateral link 11 are supported by the vehicle body via a bush 13 (or ball joint). As the front lateral link 10 moves in the vehicle width direction (horizontal direction), the left and right rear wheels 9 rotate around the connection portion of the rear lateral link 11 with the wheel support member 8 as a fulcrum.
It supports L and 9R so that they can be steered.

Furthermore, the connecting member 12 includes a rear cylinder 1.
4 is provided. The rear cylinder 14 includes a cylinder case 14a fixed to the vehicle body, and a piston 14b integrally provided with the connecting member 12 and slidably fitted into the cylinder case 14a.
and the left ventricle 1 divided by the piston 14b.
4c and a right ventricle 14d,
Return springs 14e are fitted symmetrically in the left and right chambers 14c and 14d, one end of each return spring 14e abuts each end surface of the cylinder case 14a, and the other end is fitted with a pressing plate 14f.
are attached, and each pressing plate 14f is connected to the connecting member 12.
It can be engaged with an annular engagement piece 14g provided integrally with the cylinder case 14a, and is regulated by a stopper piece 14h provided integrally with the cylinder case 14a. Therefore, the connecting member 12, that is, the piston 14
b is pressed and held in the neutral position with a set load _p1 by the left and right return springs 14e, 14e, and the connecting member 12 is moved in the left-right direction in accordance with the left-right movement of the piston 14b, thereby forming the left and right front lateral links 10. , 10 to steer the left and right rear wheels 9L, 9R.

The left and right chambers 7 of the front cylinder 7
c, 7d and the left and right chambers 14c, 1 of the rear cylinder 14
4d is fluid-tightly communicated with the oil passages 15, 15 through two oil passages 15, 15, and a switching valve 16 having two positions, a forward position and a reverse position, is interposed between the two oil passages 15, 15. The switching valve 16
When the front cylinder 7 and the rear cylinder 14 are in the order position, the left chambers 7c and 14c of the front cylinder 7 and the rear cylinder 14 and the right chamber 7
d and 14d are communicated with each other, while when the switching valve 16 is in the reverse position, the left chamber 7c of the front cylinder 7
and the right chamber 14d of the rear cylinder 14, the right chamber 7d of the front cylinder 7, and the left chamber 14 of the rear cylinder 14.
c, thereby causing the left and right chambers 7c, 7 of the front cylinder 7 to communicate with each other when the front wheels 2L, 2R are steered.
The change in volume of d is calculated from the left and right chambers 14 of the rear cylinder 14.
c, 14d to steer the rear wheels 9L, 9R following the steering of the front wheels 2L, 2R.

Furthermore, the switching valve 1 of the oil passages 15, 15
A pair of accumulators 17, 17 are disposed downstream of 6. Each of the accumulators 17 includes a casing 17c having a constant volume, and has an inlet 17a communicating with one oil passage 15 via an inflow passage 18 and an outlet 17b communicating with the other oil passage 15 via an outlet passage 19; The above inlet port 17a
It is equipped with a valve body 17d that opens and closes, and a return spring 17e that presses the valve body 17d in the valve closing direction with a set load _p2 . When the set load _p2 of the return spring 17e becomes larger, the valve body 17d
The oil passage 1 opens against the biasing force of 7e.
No. 5 oil flows from the inlet 17a to the casing 17c.
As a result, the volume of the static pressure circuit between the front cylinder 7 and the rear cylinder 14 increases.
The volume change rate of the rear cylinder 14 decreases due to the change in volume, and the ratio of the front wheel steering angle θ _F to the rear wheel steering angle θ _R (steering ratio θ _R /θ _F ) decreases. Means 20 are constructed. In addition, the return spring 17e of the above-mentioned accumulator 17
The set load _p2 of the return spring 14e of the rear cylinder 14 is larger than the set load _p1 of the return spring 14e of the rear cylinder 14 ( _p2 >
_p1 ) is set. Further, an orifice 21 is interposed in the middle of the inflow path 18.

In FIG. 1, 22 is a reserve tank, and the reserve tank 22 is communicated with the left chamber 7c and the right chamber 7d of the front cylinder 7 via supply passages 23, 23 to supply oil. ing. In addition, 24, 24 are left and right rear wheels 9L, 9
This is a trailing link that supports the R wheel support members 8, 8 in a vertically swingable manner.

Next, to explain the operation of the above embodiment,
When the switching valve 16 is in the normal position, the steering wheel 3 of the front wheel steering system 1 is operated to control the left and right front wheels 2L, 2R.
For example, when steering the front wheel to the right, as the rack 4b of the front wheel steering 1 moves to the left, the piston 7b of the front cylinder 7 also moves to the left, and as a result, the left chamber 7c of the front cylinder 7 The volume changes and its oil pressure increases. This increase in oil pressure is transmitted to the rear cylinder 1 through the oil passage 15.
When the pressure becomes larger than the set load _p1 of the return spring 14e in the right chamber 14d of the rear cylinder 14, the piston 14b moves to the right against the biasing force of the return spring 14e. The volume of the left ventricle 14c increases. As a result, the connecting member 12 also moves to the right, and the left and right front lateral links 1
The left and right rear wheels 9L, 9R are steered rightward at a constant steering ratio through the steering wheels 0 and 10.

Furthermore, when the steering wheel 3 is steered to the right and the front wheel steering angle θ _F becomes a predetermined value or more, and the hydraulic pressure in the left chamber 7c of the front cylinder 7 reaches the set load p ₂ of the return spring 17e of the accumulator 17, Oil flows from the oil passage 15 to the inflow passage 18
It begins to flow into the accumulator 17 through the. As a result, the front cylinder 7
The volume of the static pressure circuit between the front cylinder 7 and the rear cylinder 14 increases, and the rate of change in volume of the rear cylinder 14 due to the front cylinder 7 decreases.
Ratio between front wheel steering angle θ _F and rear wheel steering angle θ _R (steering ratio θ _R /
θ _F ) decreases, and the rear wheels 9L and 9R are steered to the right even with this decreased steering ratio. Therefore, the rear wheels 9L, 9R are steered in the same phase as the front wheels 2L, 2R with a steering ratio characteristic having a bending point as shown by the solid line in FIG. The degree of decrease in the steering ratio can be adjusted by changing the ratio between the spring constant of the return spring 14e of the rear cylinder 14 and the spring constant of the return spring 17e of the accumulator 17. Also,
Similarly, when the front wheels 2L, 2R are steered to the left, the rear wheels 9L, 9R follow the steering of the front wheels 2L, 2R and are in the same phase to the left with the steering ratio characteristics as shown in FIG. Be steered.

On the other hand, when the switching valve 16 is switched to the reverse position, the left chamber 7c of the front cylinder 7 and the right chamber 14d of the rear cylinder 14 communicate with each other.
c is in communication with the front cylinder 7, and the change in volume of the front cylinder 7 is transferred to the rear cylinder 1 via the oil passages 15, 15.
4 as a volume change in the direction opposite to the above, the rear wheels 9L, 9R are steered in opposite phases with the same characteristics as above, following the steering of the front wheels 2L, 2R.

Therefore, when the switching valve 16 is in the normal position,
In a small steering angle region such as a high vehicle speed region, the front wheels 2L, 2R and the rear wheels 9L, 9R are steered in the same phase with a constant steering ratio, so it is possible to improve running stability, while also In large steering angle ranges such as vehicle speed ranges, the above-mentioned steering ratio is reduced and in-phase steering is performed, suppressing an increase in the rear wheel turning angle θ _R with respect to the front wheel turning angle θ _F , thereby improving small turning performance. Therefore, it is possible to obtain a steering ratio according to the running condition of the vehicle, and it is possible to provide a variety of steering ratio characteristics.
If the switching valve 16 is positioned in the opposite position in a low vehicle speed range, the front wheels 2L, 2R and the rear wheels 9L, 9R can be steered in opposite phases, thereby further improving the turning ability. In addition, when parking the vehicle in a garage, parallel parking, or pulling to the side, the switching valve 16 is positioned in the forward position and the same phase steering is performed, thereby simplifying the driving operation.

In this way, the steering of the rear wheels 9L, 9R that follows the steering of the front wheels 2L, 2R is carried out by the so-called static pressure type, in which the change in the volume of the front cylinder 7 is transmitted fluid-tightly to the rear cylinder 14 via the static pressure circuit. Because it relies on a four-wheel steering system, it is only necessary to pipe the oil passages 15, 15 in the front-rear direction under the car body floor, which increases the degree of freedom in layout compared to the conventional link type, and allows for a larger tunnel section of the car body floor. without impairing livability, etc.

Moreover, front cylinder 7 and rear cylinder 1
By changing the cylinder diameter ratio between front wheel 2 and 4,
Since the steering ratio between L and 2R and the rear wheels 9L and 9R can be easily changed, the degree of freedom in the steering ratio is greater than that of the link type, and by adjusting the cylinder diameter ratio, A large steering force can be generated for the rear wheels 9L and 9R, and operability can be improved. Furthermore, since the transmission is based on volume changes, the efficiency of the stroke and force during transmission is higher than that of the link type, and accuracy can be improved.

In addition, since it is a static pressure type, it has the advantage of less pressure loss and vibration than a dynamic pressure type, reliable operation and high reliability, and less energy loss.

Furthermore, a volume variable means 20 as a variable steering ratio mechanism that varies the steering ratio characteristic by changing the characteristic having a bending point as shown in FIG. Since only one pair of accumulators 17, 17 is required, the structure is extremely simple, and the structure is excellent in operational stability and reliability, and can be implemented at low cost and easily. Moreover, in the above embodiment, since the steering ratio characteristic is decreased in the large steering angle region, the influence of road resistance can be reduced as much as possible, and the steering of the rear wheels 9L and 9R can be stabilized. This is advantageous because it allows for Furthermore, an orifice 21 is provided in the inflow path 18 to the above-mentioned accumulator 17.
By providing this, sudden changes in oil pressure caused by sudden external forces such as road surface irritation can be avoided.
By buffering the rear wheels from road surface irritation, etc.
It also has the advantage of suppressing fluctuations in L and 9R.

In addition, at the time of oil failure, the volume change of the front cylinder 7 is not transmitted to the rear cylinder 14, but in the rear cylinder 14, the piston 14
b is pressed and held at the neutral position by the return springs 14e and 14e, and the rear wheels 9L and 9R are held at zero phase.
Wheel steering is guaranteed and preferred from a safety standpoint. Also, by maintaining the neutral position by the return springs 14e, 14e, the rear wheels 9L, 9 in the central dead zone are
Fluctuations in R can be suppressed, and straight-line driving performance can be improved.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, with FIG. 1 being a schematic diagram of the overall configuration, and FIG. 2 being a diagram showing steering ratio characteristics. 1...Front wheel steering system, 2L, 2R...Front wheels, 7...
...Front cylinder, 9L, 9R...Rear wheel, 14
...Rear cylinder, 15...Oil passage, 17...
...accumulator, 20...capacity variable means.

Claims (1)

[Claims] 1 Equipped with a front cylinder whose volume changes in conjunction with the front wheel steering system and a rear cylinder that steers the rear wheels, the front cylinder and rear cylinder are fluid-tightly connected, and the rear cylinders follow the front wheel steering system A four-wheel steering device of a static pressure type vehicle, which is provided with a static pressure circuit between the front cylinder and the rear cylinder, and includes a volume variable means for increasing and decreasing the volume of the static pressure circuit. A four-wheel steering system for a vehicle, characterized in that the volume variable means is configured as a variable steering ratio mechanism that changes a ratio between a front wheel steering angle and a rear wheel steering angle.