JPH03572A - Hydraulic pressure control mechanism for four-wheel steering vehicle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic pressure control mechanism for steering the rear wheels of a four-wheel steering vehicle that uses hydraulic pressure to steer the rear wheels.

[Conventional technology]

An example of the structure of a conventional four-wheel steering vehicle is disclosed in "Nirasan Service Bulletin No. 619" published by Nissan Motor Co., Ltd. in March 1989, for example.

That is, each of the front wheels can be steered by a known mechanism via a steering gear using a steering wheel, and this steering wheel is also linked to a control valve for the rear wheels. This control valve is connected on one side to a hydraulic pump, and on the other side to the left and right pressure chambers of the power cylinder for steering the rear wheels via two fluid paths, and the hydraulic pump supplies water to the left and right pressure chambers. The hydraulic pressure is controlled.

The power cylinder for rear wheel steering is divided in the middle into left and right pressure chambers by a piston, and this piston has piston rods extending toward both ends of the power cylinder, forming a double-rond type cylinder. The end of this piston rod is connected to a knuckle arm, and by rotating this, the rear wheels are steered. Further, this piston is pressed from both sides by coil springs contained in both pressure chambers, and is biased toward the steering neutral position when no hydraulic pressure is applied to both pressure chambers.

Therefore, according to this hydraulic pressure control mechanism, when the control valve is activated and hydraulic pressure is applied to one of the left and right pressure chambers, the piston separating the two moves to either the left or right, steering the rear wheels, and steering the rear wheels to either the left or right. If no pressure is applied, this piston will remain in the neutral position and the rear wheels will continue to move straight. Furthermore, since the control valve is linked to the front wheels, the left and right rear wheels steered by this hydraulic pressure are linked to the movement of the front wheels.

[Problem to be solved by the invention]

However, in such conventional hydraulic pressure control mechanisms, the control valve and the power cylinder for steering the rear wheels are directly connected by a liquid path, and in the neutral steering position, no hydraulic pressure is applied to both pressure chambers of the power cylinder. Both piston ronds are mainly supported by the coil spring.

Therefore, if a kick pack force is input due to unevenness of the road surface while the vehicle is traveling straight, the toe angle will fluctuate.
There was a problem in that it was difficult to improve the straight-line performance of the vehicle.

Therefore, the present invention has been made in consideration of the above-mentioned problems, and its purpose is to increase the toe rigidity of the rear wheels of a four-wheel steering vehicle when moving straight, thereby improving straight-line running performance. .

[Means for Solving the Problems] The present invention connects the hydraulic pump side and the left and right pressure chambers of a power cylinder for rear wheel steering by two liquid passages, and injects liquid from the pump side into both liquid passages. By configuring a hydraulic pressure control mechanism for a four-wheel steering vehicle in which on-off valves that open with pressure and do not operate with hydraulic pressure from the power cylinder side are provided, and both on-off valves are connected by an interlocking mechanism that synchronizes their opening and closing, The above issues have been resolved.

[Function] When the control valve operates in accordance with the steering angle and the hydraulic pressure from the hydraulic pump is supplied to either the left or right liquid path, the on-off valve provided in this liquid path opens and the hydraulic pressure is applied to one side of the power cylinder. pressure chamber.

When the opening/closing valve opens, the other opening/closing valve is also opened by the interlocking mechanism, and the other pressure chamber is also communicated with the control valve, and this pressure chamber is communicated with the hydraulic pump, so that the piston is connected to the liquid in both pressure chambers. It steers the left and right rear wheels in response to changes in pressure balance.

Further, while the vehicle is moving straight, the control valve maintains a neutral position and does not supply hydraulic pressure to the power cylinder side, so both on-off valves are in a closed state. Therefore,
When a kickback force is input to the rear wheel due to irregularities in the road surface, this is converted into a force to move the piston, and further converted into hydraulic pressure in the pressure chamber to increase the internal pressure, but the hydraulic pressure from the power cylinder side is applied. However, since the on-off valve does not open, this liquid pressure is confined within the pressure chamber. For this reason, the toe rigidity of the rear wheels increases.

Furthermore, even if the hydraulic pump's drive belt breaks while the rear wheels are turning and the hydraulic pressure on the hydraulic pump side decreases, the on-off valve will still contain the hydraulic pressure in the pressure chamber. The rear wheels were unstable, and the vehicle did not return to a straight-line state, resulting in two problems with vehicle behavior.
, prevent change.

〔Example〕

A configuration diagram of the hydraulic pressure control mechanism of the present invention is shown in FIG.

As shown in the figure, a driving force is applied to the hydraulic pump 3 from an engine (not shown) via a drive belt, and the pump 3 is supplied with a sublimation pump via an output side liquid path 4a and both return liquid paths 4b. It is connected to a rear wheel control valve 5 that is linked to the wheel 6. The steering wheel 6 has a known structure for steering the front wheels IR and IL via a steering gear 7.

The control valve 5 is connected to the left and right pressure chambers 9R19L of the power cylinder 9 for steering the rear wheels through liquid passages 8R and 8L, respectively. These left and right pressure chambers 9R and 9L are the piston 1
0, and is biased from both sides by coil springs 12 arranged in both pressure chambers 9R and 9L, and is adjusted to be located at the center of the power cylinder 9 when no hydraulic pressure is applied to the pressure chambers 9R and 9L. has been done. Also,
Piston rods IIR and IIL are connected to the piston 10 so as to extend on both sides of the power cylinder 9, making the power cylinder 9 a double-rond type cylinder. The tips of these piston rods 11R and IIL are connected to the rear wheel 2.
It is connected to knuckle arms 15R and 15L of R and 2L, and has a structure that allows these rear wheels 2R and 2L to be steered.

Note that the output side liquid path 4a from the hydraulic pump 3 and the return side flow path 4b are connected in the middle, and the electromagnetic variable throttle valve 1 is connected between them.
3, which is opened and closed by a control device 14 that operates in response to a vehicle speed signal, and when the speed is below a predetermined speed, it opens and the rear wheel steering mechanism does not operate.

A cut-off valve 20 is interposed in the middle of the two liquid paths 8R and 8L at a position close to the power cylinder 9. This cutoff valve 20 is shown in FIG.

As shown in the figure, this cut-off valve 20 has a main body 2.
0a has two pairs of entrances and exits 21R, 21L, 22R,
22L, and the ports 21R and 21L are liquid paths 8R and 8.
L is connected to the hydraulic pump 3 side respectively, and the ports 22R, 2
2L is connected to the power cylinder 9 side of the liquid paths 8R and 8L, respectively.

The ports 21R, 21L and the ports 22R, 22L communicate with each other via a hollow portion 23 within the cut-off valve body 20a. Openings 26R and 26L that open into the hollow portion 23 continuously from the ports 21R and 21L have a larger diameter than openings 27R and 27L that open into the hollow portion 23 and continue from the ports 22R and 22L.

A spool 24 is inserted into the hollow portion 23, thereby partitioning the hollow portion 23 into a right chamber 23R and a left chamber 23L. The spool 24 has a small diameter part 25 formed in the center in the longitudinal direction, and the parts on both sides form on-off valves 24R, 24L, and the spool 24 has a small diameter part 25 formed in the center in the longitudinal direction.
The coil springs 28R' and 28L compressed to the neutral position.

The on-off valves 24R, 24L close the openings 27R, 27L in the neutral position, and the openings 26R, 26L close the left chamber 24L and the right chamber 23R on the end side of the spool 24.
By opening each of the valves 24R and 2, the small-diameter portion 25 is opened by the hydraulic pressure from the hydraulic pump 3 side, but not by the hydraulic pressure from the power cylinder 9 side.
It forms an interlocking mechanism that synchronizes the 4L.

An adjustment screw is screwed into the right end of the hollow portion 23, and by turning the adjustment screw to move it forward or backward, the positioning of the spool 24 can be finely adjusted.

Next, the operation of this embodiment will be explained below.

First, if the vehicle is traveling straight, control valve 5
does not operate, the hydraulic pressure of the hydraulic pump 3 circulates through the liquid passages 4a and 4b, and no hydraulic pressure is supplied to the liquid passage 8R or the liquid passage 8L. Therefore, the left and right pressure chambers 9 of the power cylinder 9 for rear wheel steering
Since no hydraulic pressure is supplied to R and 9L, the piston 10 maintains the neutral position by the biasing of the coil springs 12 on both sides, and the rear wheels 2R and 2L keep moving straight.

In this state, when a kickback force is input from the rear wheels 2R, 2L due to unevenness of the road surface, this becomes a moving force of the piston 10, and this piston 10 presses one of the pressure chambers 9R, 9L, causing the internal pressure to increase. Although the pressure is increased, the on-off valves 24R and 24L of the cut-off valve 20 do not open even if hydraulic pressure is applied from the power cylinder 9 side, so the hydraulic pressure is confined in the right pressure chamber 9R or the left pressure chamber 9L. Therefore, the toe rigidity of the rear wheels is increased, the rear wheels 2R and '2L do not change toe, and the straight-line performance of the vehicle is not adversely affected.

Next, when the control valve 5 is operated in conjunction with the steering of the front wheels IR and LL, the hydraulic pressure from the hydraulic pump 3 is applied to either the liquid path 8R or the liquid path 8L, and the cut-off valve 20 is opened.

The operating state of the cutoff valve 20 at this time will be explained based on FIG. 3. First, when hydraulic pressure is supplied from the hydraulic pump 3 side to the liquid path 8R, this hydraulic pressure flows from the port 21R and flows into the right ventricle 23R via the opening 26R. As a result, the hydraulic pressure in the right chamber 23R increases, side pressure is applied to the spool 24, and the on-off valve 24R moves toward the left chamber 23L against the bias of the coil spring 28L. Then, the opening 27R, which was previously blocked by the on-off valve 24R, communicates with the right chamber 23R, and the hydraulic pump 3 side and the power cylinder 9 side of the fluid path 8R are connected.

On the other hand, the left opening/closing valve 24L synchronizes opening and closing with the right opening/closing valve 24R by the small-diameter portion 25, so it similarly moves toward the left ventricle 23L. Then, the opening 27L is unblocked, and the opening 27L is opened through the space between the opening/closing valves 24R and 24L.
6L and the opening 27L communicate with each other, so the liquid path 8L on the left
Also, the hydraulic pump 3 side and the power cylinder 9 side are connected.

Note that the above description has been made for the case where hydraulic pressure is applied to the right liquid passage 8R, but when hydraulic pressure is applied to the left liquid passage 8L, both on-off valves 24R, 24L are moved toward the right ventricle 23R by the same action as above. to open both liquid passages 8R and 8L.

When the cutoff valve 20 is opened in this way, the hydraulic pressure in either the left or right pressure chambers 9L, 9R of the rear wheel steering power cylinder 9 increases and expands, and the piston 10 is moved. Then, the piston rods IIR and IIL fixed to the piston 10 are moved, and the knuckle arms 15R and 15L connected to these ends are rotated to steer the rear wheels 2R and 2L.

Note that when one of the left and right pressure chambers 9R, 9L expands, the other contracts and the hydraulic pressure increases, but this pressure passes through the cut-off valve 20 and is output to the control valve side, so the piston It responds smoothly to changes in the hydraulic pressure balance of chambers 9R and 9L.

In addition, while the rear wheels are being steered as described above, the hydraulic pressure on the hydraulic pump 3 side may suddenly decrease due to the drive belt of the hydraulic pump 3 breaking or the liquid passages 8R and 8L being damaged. In this case, both open/close valves 24R, 24L of the cut-off valve 20 return to the neutral position by the action of the coil springs 28R, 28L, and the openings 27R, 27 on the power cylinder 9 side
Block L.

Since the hydraulic pressure on the power cylinder 9 side cannot pass through this cut-off valve 20 and is confined to the power cylinder 9 side, the rear wheels 2R and 2L do not suddenly return to the straight-ahead state, and the behavior of the vehicle changes. Never.

Note that this hydraulic pressure gradually leaks to the hydraulic pump 3 side through the cut-off valve 20 and is gently reduced in pressure, and after a predetermined period of time, the power cylinder 9 returns to the straight-moving state.

As described above, according to this embodiment, by simply placing a cut-off valve with a simple structure in which a spool is connected in the middle of the fluid path, the toe rigidity of the rear wheel when traveling straight is increased and excellent straight-line performance is achieved. It is possible to create a four-wheel steering vehicle, and furthermore, it is possible to prevent sudden changes in vehicle behavior due to pressure reduction, such as in the case of hydraulic pumps.

Note that in this embodiment, the opening 2 of the cut-off valve 20
6R and 26L were enlarged to communicate with the hollow part 23 on the end side of the spool 24, but as shown in FIG.
A branch passage 30 is formed inside the cut-off valve body 2°a.
It is also possible to provide a structure in which R and 30L are provided and these are communicated with the right ventricle 23R and left ventricle 23L of the hollow portion 23.

Further, in this embodiment, a spool valve mechanism was used as an on-off valve that controls the passage direction of hydraulic pressure, but the on-off valve of the present invention is not limited to this structure, and may be used with a known directional control valve mechanism such as a poppet valve. Of course, it is possible to use .

〔Effect of the invention〕

As explained above, according to the hydraulic pressure control mechanism for a four-wheel steered vehicle of the present invention, the toe rigidity of the rear wheels is increased when the vehicle is running straight, thereby providing a four-wheel steered vehicle with excellent straight-line running performance. I can do it.

In addition, when the four-wheel steering mechanism is in operation, even if the hydraulic pressure on the hydraulic pump side suddenly decreases due to a failure of the hydraulic pump, the hydraulic pressure in the pressure chamber of the rear wheel steering brush fork can be contained. The rear wheels do not suddenly return to the straight-ahead state, which prevents sudden changes in the vehicle's behavior.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a hydraulic pressure control mechanism for a four-wheel steering vehicle according to the present invention, FIG. 2 is a partially cutaway plan view of a cut-off valve, and FIG. 3 is an explanatory diagram showing the operating state of the cuff-off valve.
FIG. 4 is an explanatory diagram showing another embodiment of the cut-off valve.

Claims (1)

[Claims] (1) The hydraulic pump side and the left and right pressure chambers of the power cylinder for rear wheel steering are each connected by two liquid passages, and both liquid passages are opened by the hydraulic pressure from the pump side, and the liquid from the power cylinder side is opened. A hydraulic pressure control mechanism for a four-wheel steering vehicle, characterized in that an on-off valve that cannot be opened by pressure is provided, and the two on-off valves are connected by an interlocking mechanism that synchronizes their opening and closing.