JPH0522631B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a four-wheel steering device for a vehicle, and more specifically, a hydrostatic four-wheel steering device that steers the rear wheels following the steering of the front wheels. This invention relates to a wheel steering device.

(Prior Art) Conventionally, by steering the rear wheels in accordance with the steering of the front wheels of a vehicle, for example, in a high vehicle speed range with a small steering angle, the front and rear wheels are brought into phase, improving driving stability. It is 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 phases, to improve the turning ability. Also,
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, as shown in Japanese Patent Application Laid-open No. 55-15301, conventional four-wheel steering systems for such vehicles connect the front wheels and rear wheels using a link mechanism such as a relay rod, A link-type version is available in which the wheels are steered simultaneously.

However, in this type of vehicle, the link mechanism for connecting the front wheels and the rear wheels is placed in the longitudinal direction on the underside of the vehicle floor, so there are many layout restrictions, and there are also many restrictions in the tunnel section of the vehicle floor. becomes large and causes a decline in livability, etc. Moreover, since the connection structure is based on a link mechanism, the degree of freedom in the steering ratio between the front wheels and the rear wheels is small, and a large steering force is not generated on the rear wheels.
Moreover, the efficiency of stroke and force was poor, and the operability was poor.

Furthermore, in the case of the link mechanism described above, the steering ratio between the front wheel steering angle and the rear wheel steering angle is usually fixed, and it is not possible 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. Although it is possible to make the steering ratio variable by providing a control mechanism etc. in the link mechanism described above, this would make the mechanism and structure of the device extremely complex and large-scale, resulting in poor operational stability. It lacks performance and reliability, and is also disadvantageous in terms of cost.

(Object of the Invention) The present invention provides a vehicle capable of obtaining a steering ratio according to the driving condition of the vehicle by making the steering ratio between the front wheel steering angle and the rear wheel steering angle variable with a simple structure. The object of the present invention is to provide a four-wheel steering device.

(Structure of the Invention) A four-wheel steering device for a vehicle according to the present invention includes a front cylinder whose volume changes in conjunction with a front wheel steering system;
A vehicle that is equipped with a rear cylinder that steers the rear wheels, and the front cylinder and rear cylinder are configured as a static pressure hydraulic piping by communicating in a fluid-tight manner, so that the rear wheels are steered by following the steering of the front wheels. This is a four-wheel steering system that absorbs the increase in hydraulic pressure caused by the restriction in the hydrostatic hydraulic piping so that the steering ratio between the front and rear wheels can be varied according to the steering speed of the front wheel steering system. The present invention is characterized in that it is provided with a variable steering ratio mechanism comprising a hydraulic pressure absorbing means.

(Effects of the Invention) In the four-wheel steering system for a vehicle of the present invention having the above configuration, the four-wheel steering system of the static pressure type 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. By adopting a steering system, it is only necessary to place hydraulic piping in the front-rear direction under the floor of the vehicle body, which significantly increases the degree of freedom in layout compared to a link-type system, and does not impair comfort, etc. 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. It is possible to generate a large steering force, and the efficiency of stroke and force is high, as well as high precision. Furthermore, since it is a static pressure type, it is more reliable than a dynamic pressure type, and it also has less energy loss, making it a four-wheel steering system with excellent performance such as operability, reliability, and accuracy. can be provided.

Furthermore, in the present invention, since a variable steering ratio mechanism is provided that varies the steering ratio according to the steering speed of the front wheel steering system, more desirable steering performance can be obtained depending on the driving state of the vehicle.

(Embodiment) Hereinafter, a four-wheel steering system for a vehicle according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an overall schematic configuration diagram of a four-wheel steering system for a vehicle according to a first embodiment of the present invention.
In the figure, reference numeral 1 indicates a front wheel steering system that steers the left and right front wheels 2L, 2R. This front wheel steering system 1 is
A steering wheel 3 to be steered, a pinion 4a and a rack 4b that convert the steering force of the steering wheel 3 into reciprocating movement in the vehicle width direction, that is, the left and right directions, and transmit the same, and a base end is connected to each end of the rack 4b. left and right tie rods 5L, 5R
and knuckle arms 6L, 6R, one end of which is connected to the tip of each tie rod 5L, 5R, and the other end connected to the left and right front wheels 2L, 2R, respectively.
The 2R is designed to be steered 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 that is fixed to the vehicle body and extends in the vehicle width direction, a piston 7b that is provided integrally with the rack 4b, and that is slidably fitted into the cylinder case 7a. The piston 7b moves in the vehicle width direction (horizontal direction) in conjunction with the rack 4b of the front wheel steering system 1, thereby opening the left chamber 7c and the right chamber 7d. The right ventricle 7b is configured to change in volume.

On the other hand, reference numerals 8L and 8R denote wheel support members that extend in the longitudinal direction of the vehicle body and rotatably support the left and right rear wheels 9L and 9R. Two front and rear lateral links 10L, 10R and 11 extending to
L and 11R are each connected. The left and right lateral links 10L and 10R on the front side are connected at their inner ends by a link-shaped connecting member 12. Each rear lateral link 11L, 11R
The inner end is a push or ball joint 13
It is supported by the vehicle body through. With this structure, as the front lateral links 10L, 10R move in the vehicle width direction, that is, in the left-right direction, the left and right rear wheels 9L, 9R can be steered using the connecting portion of the rear lateral link 11 with the wheel support member 8 as a branch. I support it.

The connecting member 12 is provided with a rear cylinder 14 . This rear cylinder 14 is connected to a cylinder case 14a fixed to the vehicle body and a connecting member 12.
The piston 14b is integrally provided in the cylinder case 14a and is slidably fitted in the cylinder case 14a, and a left chamber 14c and a right chamber 14d are partitioned by the piston 14b. Above left and right chambers 14
Return springs 14e are symmetrically installed in the cylinders c and 14d, and one end of the return spring 14e abuts each end face of the cylinder case 14a, and a pressing plate 14f is attached to the other end. Each pressing plate 14f is connected to the connecting member 1
2, and is regulated by the cylinder case 14h. In the following configuration, the connecting member 12, that is, the piston 14b, is pressed and held in the neutral position by the set load _P1 of the left and right return springs 14e, and the connecting member 12 is reciprocated in the left-right direction as the piston 14b moves from side to side. Move the left and right front lateral links 10L, 10
The left and right rear wheels 9L and 9R are steered via R.

Between the front cylinder 7 and the rear cylinder 14, each chamber 7c of the two cylinders 7, 14,
Oil passages 15 and 16 are provided to connect 7d, 14c, and 14d as appropriate. A switching valve 17 is provided between these oil passages 15 and 16 and can take two positions, a forward position and a reverse position. When in the forward position, this switching valve 17 communicates between the left chambers 7c and 14c of the front cylinder 7 and the rear cylinder 14 and between the right chambers 7d and 14d, while when in the reverse position, the left chamber 7c of the front cylinder 7 and the rear cylinder communicate with each other. 14 right ventricle 1
4d, the right chamber 7d of the front cylinder 7 and the left chamber 14c of the rear cylinder 14 are communicated with each other. With this configuration, front wheels 2L, 2R
The left and right chambers 7 of the front cylinder 7 due to the steering of the
The changes in volume of the cylinders c and 7d are transmitted to the left and right chambers 14c and 14d of the rear cylinder 14, and the rear wheels 9L and 9R are steered in the same phase direction with respect to the front wheels at high vehicle speeds, following the steering of the front wheels 2L and 2R. Stability is improved, and steering performance is improved by steering in the opposite phase direction at low vehicle speeds.

The oil passages 15 and 16 are further provided with a throttle 1.
8 and 19, and accumulators 20 and 21 as hydraulic pressure absorbing means provided closer to the front cylinder than these. Above aperture 1
Reference numerals 8 and 19 are for preventing oil discharged from the front cylinder 7 from being suddenly supplied into the rear cylinder 14 when the steering wheel 3 is suddenly turned or rotated. The multors 20 and 21 are for absorbing the increase in oil pressure caused by the throttles 18 and 19.

That is, the throttles 18 and 19 prevent the rear wheels from rapidly turning in the same phase direction when the steering wheel 3 is suddenly turned at high vehicle speeds, thereby improving steering performance at high vehicle speeds. On the other hand, if the steering wheel 3 is suddenly turned at low vehicle speeds, it prevents the rear wheels from rapidly turning in the opposite phase direction, and prevents steering at low vehicle speeds. This prevents spin from occurring.

Next, a four-wheel steering system according to a second embodiment of the present invention will be described with reference to FIG. 2 and subsequent figures. Note that members and elements of this second embodiment may have the same configuration as those of the first embodiment, namely the front wheel steering system 1, wheel support members 8L, 8R, lateral links 10, 10R, 11L, 11R, and connections. Part 1
2. The rear cylinder 14 and other members and elements are designated by the same reference numerals as in FIG. 1, and their explanations will be omitted.

The lateral links 11L and 11R are connected at their inner ends by a link-shaped connecting member 41, and this connecting member 41 is connected to a rear cylinder 42.
is provided. This rear cylinder 42, that is, the rear rear cylinder 42 is the rear cylinder 1
4, that is, the structure may be the same as that of the front rear cylinder 14, so the same suffix will be given and a detailed explanation of the structure will be omitted. Oil passages 4 are provided in the left chamber 14c and right chamber 14d of the front rear cylinder 14.
3 and 44 are the left chamber 42 of the rear cylinder 42 on the rear side.
Oil passages 45 and 46 are connected to c and 42d, respectively. The throttles 18 and 19 are provided in the oil passages 43 and 44.

A dividing valve 47 is provided between the oil passage 15 connected to the left chamber 7c of the front cylinder 7 and the oil passages 43 and 45, and a flow divider valve 47 is provided between the oil passage 16 connected to the right chamber 7d of the front cylinder 7 and the oil passage 44. A dividing valve 48 is provided between the hydraulic pressure absorbing means and 46, respectively. Divider valve 47 serves to switch said passage 15 between passages 43 and 45, while diverter valve 48 serves to switch said passage 15 between passages 43 and 45.
6 between passages 44 and 46. Since the structures of the above-mentioned flow dividing valves 47 and 48 are the same or symmetrical, only the flow dividing valve 48 will be explained below.
Regarding the flow dividing valve 47, the same suffix as that of the flow dividing valve 48 is attached to the reference numeral, and the explanation thereof will be omitted.

The flow dividing valve 48 has two cylindrical cases 48a and 48b arranged in line. case 48
A passage 16 communicates with approximately the center of the case 48a, a passage 44 communicates with the vicinity of the left end of the case 48a, and a passage 46 communicates with the vicinity of the right end of the case 48a. A ball 48c is fitted inside the case 48a, and the ball 48c divides the inside of the case 48a into a left chamber 48d and a right chamber 48e.
A piston 48f is slidably fitted into the case 48b. A piston rod 48g is provided on the end surface of the piston 48f on the case 48a side, and this piston rod 48g passes through the case 48b and extends into the case 48a. A spring 48h is compressed in the chamber on the side where the piston rod 48g of the piston 48f of the case 48b is installed.
Even with the set load P ₂ due to P 8h, the piston 48f and hence the piston rod 48g are urged in the direction away from the case 48a. (hereinafter referred to as the rightmost position).
This set load _P2 is set larger than the set load _P1 for the purpose explained later. A spring 48i is compressed in the left chamber 48d of the case 48a, and this spring 48i biases the ball 48c in the direction of the piston rod 48g, pressing the ball 48c against the tip of the rod 48g. The length of the piston rod 48g is set such that when the rod 48g is at the rightmost position, the ball 48c can be positioned slightly closer to the case 48b than the passage 16, as shown in the figure. ing. ball 4
8c is adapted to communicate passageway 16 with passageway 44 via left ventricle 48d when positioned in this position.

Moreover, as is clear from FIG. 2, the case 48a
The left ventricle 48d of the case 48 is connected to the case 48 through a passage 48j.
The right chamber 48e of the case 48a communicates with the chamber 48h of the case 48b on the side where the spring 48h is provided via a passage 48k. It communicates with the left ventricle at its approximate center.

Next, the operation of the four-wheel steering system having the above structure will be described with respect to only the right wheel when the left and right front wheels 2L, 2R are steered to the left.

When steering the right front wheel 2R to the left, the steering wheel 3 of the front wheel steering system 1 may be rotated counterclockwise as shown in the figure. When the steering wheel 3 is thus rotated counterclockwise, the pinion 4a is rotated in the same direction, thereby moving the rack 4b to the right.
The right front wheel 2R is steered to the left.

When the front wheels 2R are steered to the left in this way, as the rack 4b of the front wheel steering system 1 moves to the right, the piston 7b of the front cylinder 7 also moves to the right, and as a result, the front cylinder 7
The volume of the right ventricle 7d decreases and its oil pressure increases. This increase in oil pressure is transmitted to the right chamber 14d of the front rear cylinder 14 via the passages 16 and 44. The pressure causes the piston 14b to move to the left against the action of the return spring 14e, increasing the volume of the right chamber 14d. As a result, the connecting member 12 also moves to the left, and the lateral link 10R
The right rear wheel 9R has a constant front wheel steering angle θ _F and a constant rear wheel steering angle θ _R as shown by the solid line A in FIG.
The vehicle is steered to the left at the ratio of the steering angle θ _F /θ _R.

Steering the steering wheel 3 further to the left,
When the front wheel steering angle θ _F exceeds a predetermined value and the hydraulic pressure in the right chamber 7d of the front cylinder 7 exceeds the set load P ₂ of the spring 48h of the diverter valve 48, the action of this hydraulic pressure causes the piston 48 in the case 48b to
f moves to the left against the action of the spring 48h. As the piston 48f moves to the left, the piston rod 48g also moves to the left, thereby moving the ball 48c inside the case 48a to the left, and passing the passage 16 through the chamber 48e to the passage 4.
Connect to 6. As a result, front cylinder 7
The pressure in the right chamber 7d of the rear cylinder 42 on the rear side
, and moves the piston 42b to the left against the action of the spring 42e of the left chamber 42c. When the piston 42b moves to the left in this way, the connecting member 41 and the lateral link 10R also move to the left, thereby steering the rear wheel 9R to the right.

At the same time, the right chamber 7d of the front cylinder 7
The pressure is led to the chamber provided with the spring 48h of the case 48b, that is, the left chamber, through the passage 48k, and this time pushes the piston 48f to the right.
Then, the ball 48c moves to the right position again,
The passage 16 is communicated with the passage 44, thereby steering the rear wheel 9R to the left again. By repeating the above steps, the rear wheels 9R are steered at a reduced steering ratio that is different from the steering ratio indicated by a solid line A as indicated by a broken line B in FIG. Therefore, the rear wheel is 9L,
9R is steered in the same phase as the front wheels 2L and 2R with a steering ratio characteristic having a bending point as shown in FIG.

Similarly, when steering the front wheels 2L, 2R to the right, the rear wheels 9L, 9R are steered to the right.
Following the steering of R, the steering wheel is steered to the right in the same phase with the steering ratio characteristic shown in FIG.

The case where the steering wheel 3 is turned at a normal speed has been described above, but if the steering wheel 3 is then turned suddenly, the portion of the passage 44 on the front cylinder 7 side from the restriction 19 will be affected by the action of the restriction 19. The pressure quickly exceeds the set load _p2 of the spring 48h, which causes the switching of the diversion valve 48 at an early stage. Therefore, if the wheel 3 is suddenly turned, the rear wheels will be steered at a steering ratio as shown by the dashed line C in FIG. The embodiment also provides substantially the same effects as the first embodiment.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of a four-wheel steering system according to a first embodiment of the present invention, FIG. 2 is an overall schematic diagram of a four-wheel steering system according to a second embodiment of the present invention, and FIG. , is a graph showing steering ratio characteristics obtained by the second embodiment. 1...Front wheel steering system, 2L, 2R...Front wheels, 3...
... Steering wheel, 7... Front cylinder, 9L, 9R... Rear wheel, 14... Rear cylinder, 18, 19... Aperture.

Claims (1)

[Claims] 1. A front cylinder whose volume changes in conjunction with a front wheel steering system, and a rear cylinder that steers the rear wheels. A four-wheel steering system for a vehicle in which the rear wheels are steered following the steering of the front wheel, the steering ratio between the front wheels and the rear wheels being variable in accordance with the steering speed of the front wheel steering system. A four-wheel steering system for a vehicle, characterized in that a steering ratio variable mechanism comprising a throttle and a hydraulic pressure absorbing means for absorbing an increase in hydraulic pressure due to the throttle is provided in the hydrostatic hydraulic piping.