JPH0637174B2 - Four-wheel steering system - Google Patents

Description

The present invention relates to an improvement of a four-wheel steering system.

[Conventional technology]

In recent years, various proposals for four-wheel steering have been made in order to improve steering stability during high-speed traveling of a four-wheel vehicle and improve small turning performance during low-speed traveling.

For example, as an example, in the proposal as shown in FIG. 6, the front wheel T _f side of the four-wheeled vehicle has the power steering mechanism 1 and the rear wheel Tr side has the steering mechanism 2. In addition, in the steering mechanism 2, the pressure oil supplied to the power cylinder 2a connected to the axle A _r of the rear wheel _Tr is switched according to a signal from the controller 2b. The electromagnetic directional control valve 2c is used. The controller 2b is supposed to receive a detection signal from the operation of the rack 1a and the pinion 1b by operating the steering wheel in the power steering mechanism 1 together with other detection signals such as vehicle speed.

Therefore, in the case of the above-mentioned conventional proposal, the supply direction of the pressure oil to the power cylinder 2a is switched by the output signal from the controller 2b to which the signal is input in accordance with the steering of the front wheel _Tf , and the rear wheel _Tf . _{The r} will be steered in the desired direction.

[Problems to be solved by the invention]

However, in the case of the above-mentioned conventional proposal, since the switching of the direction of the pressure oil supplied to the power cylinder 2a is solely based on the output signal from the controller 2b, the case of the above-mentioned conventional proposal apparatus is as follows. Steering of the rear wheel _Tr requires the installation of various sensors and the maintenance of a controller that processes and outputs the input signals from these various sensors, increasing the number of parts and increasing the equipment. As a result, the overall complexity is increased, and as a result of the increase in the number of parts and the overall complexity of the device, there are disadvantages that the cost is increased and the durability is easily deteriorated.

Therefore, in view of the above-mentioned circumstances, the present invention newly provides a four-wheel steering device that reduces the number of sensors installed, simplifies maintenance of a controller, and is inexpensive and capable of improving durability. To aim.

[Means for solving problems]

In order to solve the above-mentioned problems, the configuration of the present invention is a four-wheel steering system including a front-wheel-side power steering mechanism and a rear-wheel-side steering mechanism, in which the rear-wheel-side steering mechanism is , A power cylinder connected to the rear wheel axle, a pressure oil supply source that enables pressure oil to be supplied to the power cylinder via an electromagnetic flow control valve, and a hydraulic pressure generated in the power cylinder in the power steering mechanism on the front wheel side. And a hydraulic pilot control valve for controlling the pressure oil supplied from the pressure oil supply source to the power cylinders on the rear wheel side while directly switching as the pilot pressure, and the rear wheel side for the power steering mechanism on the front wheel side. And a solenoid direction switching valve for selectively switching the steering direction of the steering mechanism between the same phase and the opposite phase.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiments.

FIG. 1 is a diagram schematically showing an embodiment of the present invention, which is a vehicle equipped with a four-wheel steering device (hereinafter referred to as a four-wheel vehicle).
The front wheel Tf side has a power steering mechanism 10 that enables steering of the front wheel Tf, and the rear wheel _Tr side has a steering mechanism 20 that enables steering of the rear wheel T _r. I will do it.

The power steering mechanism 10 on the front wheel T _f side supplies a power cylinder 12 mounted on a rack 11 connected to an axle A _f of the front wheel T _f , and pressure oil into the power cylinder 12 via a switching valve 13. A pinion 1 that has a pump 14 that operates and that meshes with the rack 11 by operating the handle 15.
When the steering wheel 6 is rotated, the switching valve 13 is switched to a predetermined direction according to the steering direction of the steering wheel 15, and the pressure oil is selectively supplied to the left and right of the power cylinder 12 so that the front wheel T _f is desired. It is formed so that it can be switched in the direction.

Rear wheel T _r side of the steering mechanism 20 includes a power cylinder 21 connected to the axle A _r of the rear wheels T _r, the pressurized oil source 22, variable supply of pressure oil to the power cylinder 21, Electromagnetic directional control valve 2 which can switch the flow direction of pressure oil from the pressure oil supply source 22 and supply it to the power cylinder 21.
3, and is discharged from the pressure oil supply source 22 into an oil passage 24 that allows the pressure oil from the pressure oil supply source 22 to be supplied to the power cylinder 21. The electromagnetic flow control valve 25 for controlling the amount of pressure oil and the power cylinder 1 in the power steering mechanism 10 on the front wheel Tf side.
A hydraulic pressure that controls the flow of the pressure oil that has passed through the electromagnetic flow control valve 25 in conjunction with the pressure oil that is generated in the power cylinder 12 on the front wheel Tf side, while directly switching the pressure oil that is generated in 2 as the pilot pressure. And a controller 27 for inputting signals to the electromagnetic directional control valve 23 and the electromagnetic flow control valve 25.

The power cylinder 21 has a first chamber 21a and a second chamber 21b which are internally partitioned from each other, and each chamber 21a, 21b.
Reaction force springs 21'a, 21'b are provided inside so as to face each other. When no hydraulic pressure is applied to the power cylinder 21, the springs 21'a, 21'a,
The power cylinder 21 is formed by 21'b so as to keep the balance state, that is, the rear wheel Tr in a straight traveling state.

The pressure oil supply source 22 is formed so as to suck up the oil from the reservoir tank 22a and discharge the oil to the power cylinder 21 side, and in this embodiment, it is separate from the pump 14 of the power steering mechanism 10. However, instead of this, the pump 14 may also function as the pressure oil supply source 22 in the steering mechanism 20.

The electromagnetic directional control valve 23 is formed as shown in FIG. That is, the housing 30 is provided with passages 31 and 32 communicating with the front side hydraulic pilot control valve 26, and is provided with passages 33 and 34 communicating with the rear side power cylinder 21. The passage 31
Are communicated with a passage 31 a branched in the housing 30.

The passages 31, 31a, 32, 33, 34 are the housing 3
An oil chamber 30a is formed in a portion where the oil merges in the 0. The spool 35 is slidably accommodated in the oil chamber 30a. The spool 35 has one end, that is, the second
At the right end in the figure, the spring 36 is urged to the other end side, that is, the solenoid 23a side. When the spool 35 is pressed to the solenoid 23a side by the urging force of the spring 36, the land portions 35a and 35b Passages 31, 32
And the land portion 35c closes the passage 31a to allow the passage 31 and the passage 33 and the passage 32 and the passage 34 to communicate with each other, and the spool 35 is springed by the excitation of the solenoid 23a. 36, the land portion 35a closes the passage 31 and the land portions 35b and 35c allow the passage 32 and the passage 33 and the passage 31a and the passage 34 to communicate with each other. Has been done.

The electromagnetic flow control valve 25 has a solenoid 25a and is formed to have a conventionally well-known structure. The electromagnetic flow control valve 25 exhibits a flow rate characteristic as shown in FIG. 3 depending on the strength of the exciting force applied to the solenoid 25a. Is set. That is, when the vehicle speed is in the extremely low speed range (0 to V ₁ ) near the stop time, the solenoid is not excited and the flow rate Q is substantially zero, but in the low speed range (V _{1 to} V ₂ ), Once at a speed V ₁ , the solenoid is excited to a relatively large extent and the flow rate Q rapidly rises to Q ₁ , and as the speed approaches V ₂ , the solenoid is gradually magnetized so that the flow rate Q becomes zero. Become. Then, when the vehicle speed is in the medium speed range (V _{2 to} V ₃ ), the solenoid is excited again to gradually increase its exciting force and gradually increase the flow rate Q (0 to Q ₃ ). Further, when the vehicle speed is in the high speed range (V ₃ or more), the solenoid is greatly excited and its flow rate Q
Is formed to have a maximum Q ₃ . That is, it is formed so that the steering amount control of the rear wheels _Tr can be performed according to the traveling speed of the vehicle. The electromagnetic flow control valve 2
It is needless to say that the excitation, demagnetization, and its strength of 5 are performed by the controller 27.

The hydraulic pilot control valve 26 is formed as shown in FIG. That is, the housing 40 has a passage 41 communicating with the electromagnetic flow control valve 25 on the front side and a passage 42 communicating with the reservoir tank 22a, and a passage communicating with the electromagnetic directional control valve 23 on the rear side. Four
3 and 44 are provided. The passage 42 is
It communicates with a passage 42 a branched in the housing 40. A hydraulic pressure 40a is formed at a portion where the passages 41, 42, 42a, 43, 44 meet in the housing 40, and a spool 45 is slidably accommodated in the oil chamber 40a. .

The spool 45 is formed so that springs 46 and 47 are in contact with both ends thereof to balance the spool,
When balanced by the springs 46 and 47, the central land portion 45a opens the passage 41 evenly, and the inflow is made under the condition that an even hydraulic pressure acts in the passages 43 and 44. The pressure oil is formed so as to flow out to the reservoir tank 22a through the passages 42 and 42a.

However, the spring 4 that balances the spool 45
The chamber in which 6, 47 are housed is the pilot hydraulic chamber 46.
a, 47a, and the pilot hydraulic chambers 46a, 47
In a, the power steering mechanism 1 on the front wheel T _f side described above.
Since the hydraulic pressure in the power cylinder 12 (see FIG. 1) at 0 can directly act as the pilot pressure, one of the pilot hydraulic chambers,
For example, the pilot pressure acts on the pilot hydraulic chamber 46a on the left side in FIG. The spool 45 slides to the right in the figure, and the central land 45a is located in the passage 4
1 and 44 are closed and the passages 41 and 43 are opened to a large extent, and the land portion 45b greatly opens the passage 42 and at the same time the land portion 45c closes the passage 42a.
The passage 41 communicates only with the passage 43 and the passage 42 communicates with the passage 44.

On the other hand, when the spool 45 slides to the left in FIG. 4 due to the action of pilot pressure, conversely, the central land portion 45a closes the communication between the passages 41 and 43 and the passage 41, 43. 44 communication is wide open, and the land part
45b closes the passage 42 and at the same time the land portion 45c closes the passage 42a.
The passage 41 is communicated with the passage 44, and the passage 42 is communicated with the passage 43 through the passage 42a.

That is, since the hydraulic pilot control valve 26 is to steer the front wheels _Tf , when hydraulic pressure is applied to any one chamber in the power cylinder 12 of the power steering mechanism 10, the hydraulic pilot control valve 26 uses the hydraulic pressure as pilot pressure. The spool 45 is slid so that the pressure oil from the pressure oil supply source 22 is supplied into the power cylinder 21 of the steering mechanism 20, so that when the front wheel T _f is steered, the rear wheel T _r is simultaneously moved. It is formed so that desired steering can be performed.

The controller 27 outputs a predetermined signal to the solenoid 23a of the electromagnetic directional control valve 23 and the solenoid 25a of the electromagnetic flow control valve 25 according to an input signal from the outside. Corner signal b,
Signals such as the output signal c of the power steering mechanism 10 and the engine speed signal d are input.

The operation of the four-wheel steering system according to the present invention formed as described above will be briefly described.

First, when the four-wheeled vehicle is traveling at a low speed and trying to turn to the left in FIG. 1, the power cylinder 1 in the power steering mechanism 10 on the front wheel T _f side.
The inside of one chamber 12a in 2 becomes the high pressure side, and the hydraulic pressure in the one chamber 12a acts on one pilot hydraulic chamber 46a of the hydraulic pilot control valve 26 in the steering mechanism 20 on the rear wheel _Tr side.

When the pilot pressure chamber 46a is acted upon by the pilot pressure, the internal spool 45 slides to the right in FIG. 4, and the pressure oil from the pressure oil supply source 22 is electromagnetically transferred through the passages 41 and 43. It will flow toward the direction switching valve 23.

Then, the pressure oil through the passage 43 of the hydraulic pilot control valve 26 flows into the passage 31 of the electromagnetic directional control valve 23. At this time, the four-wheeled vehicle is running at low speed,
The rear wheels T _r are preferably steered to the right opposite to the direction of the front wheels T _f . Therefore, the solenoid 23 a in the electromagnetic directional control valve 23 is not excited by the controller 27 and the inside of the passage 31 is The circulating pressure oil flows through the passage 33 and is discharged toward the power cylinder 21.

The pressure oil via the passage 33 flows into the one chamber 21a in the power cylinder 21, and the rear wheel T _r is steered to the right as opposed to the front wheel T _f as desired.

It should be noted that when the four-wheeled vehicle is running at an extremely low speed or is stopped, the electromagnetic flow control valve 25 does not receive an excitation signal by the controller 27, that is, the flow rate is controlled to be substantially zero, and as a result, Wheel T _r is not steered in either direction and keeps a neutral state.

Next, when the four-wheeled vehicle is going to turn to the left at the medium speed or the high speed in the same manner as described above, the hydraulic pilot control valve 26 causes the one chamber 12 of the power cylinder 12 on the front wheel T _f side.
Due to the hydraulic pressure from inside a, the pressure oil supply source 2
The pressure oil from 2 flows into the passage 31 of the electromagnetic directional control valve 23. Here, in steering when the traveling speed of the vehicle is medium or high, it is preferable that the rear wheel T _r is steered in the same direction as the front wheel T _f (leftward in this description). Therefore, for the electromagnetic directional control valve 23, the solenoid 23a
Is input with an excitation signal from the controller 27, and the excitation causes the spool 35 to slide to the right in FIG.
The pressure oil flowing into the passage 31 flows into the oil chamber 30a via the branch passage 31a, and the pressure oil is supplied to the other chamber 21b of the power cylinder 21 via the passage 34, The rear wheels T _r are steered in the same direction as the front wheels T _f as desired.

The above table is shown in the table on the next page.
In the table, the electromagnetic directional control valve 23 is excited when the vehicle speed is extremely low, but at the time of the excitation, the flow rate by the front electromagnetic flow rate control valve 25 is almost zero, so the rear wheel _Tr. The other chamber in the power cylinder 21
It does not cause a change enough to steer the rear wheel _Tr in 21b. Although not shown in the table, when the vehicle travels straight ahead, the hydraulic pilot control valve 2
Of course, 6 does not have the effect of pilot pressure, and accordingly, the rear wheels _Tr are not steered and the neutral state is maintained with respect to the front wheels. Further, even when the steering wheel 15 is turned at an arbitrary angle and the turning state is maintained as in the case where the vehicle travels on a curved line having a large radius, the power cylinder 12 on the front wheel T _f side is not provided. Since the internal pressure is maintained, the pilot pressure is always transmitted in the hydraulic pilot control valve 26, and the desired hydraulic pressure is continuously applied in the power cylinder 21 on the rear wheel _Tr side.
A situation where only the rear wheel T _r returns to the neutral state is not brought about.

FIG. 5 shows another embodiment according to the present invention. The basic structure is the same as that of the embodiment shown in FIG. 1, but in the installation position of the electromagnetic directional control valve 23. Only different.

That is, in the present embodiment, the electromagnetic directional control valve 23 is
Is disposed in a pilot oil passage 28 to a hydraulic pilot control valve 26 for controlling the flow rate by using the internal pressure of the power cylinder 12 in the power steering mechanism 10 on the front wheel T _f side as the pilot pressure.

Therefore, in this embodiment, the electromagnetic directional control valve 23 is
Since it suffices to switch the direction of a small amount of pressure oil in the pilot passage 28, when the pressure oil for operating the power cylinder 21 in the above-mentioned embodiment is arranged in the oil passage 24 which allows the circulation of the pressure oil. Rather than that, there is an advantage that the structure can be made smaller.

In this embodiment, the electromagnetic directional control valve 23 may be a simple on / off valve instead of this.

〔The invention's effect〕

As described above, according to the present invention, the internal pressure generated in the power cylinder in the power steering mechanism on the front wheel side during steering of the front wheels is directly used as the pilot pressure, and the desired amount is set in the power cylinder in the steering mechanism on the rear wheel side. Pressure oil can be supplied in accordance with the steering direction of the front wheels, which makes it possible to increase or decrease the steering amount of the rear wheels without using the controller and without affecting the responsiveness of the steering of the front wheels. There is an advantage that it is possible to follow the increase / decrease in the steering amount. Then, it suffices to control only the oil amount that determines the steering direction and the steering amount of the rear wheels with respect to the front wheels, based on the command from the controller according to the traveling speed of the vehicle. The number of sensors for steering control can be greatly reduced, and the maintenance of the controller can be simplified, so that the desired device can be inexpensive and the durability can be improved. It will be possible.

[Brief description of drawings]

FIG. 1 is a schematic overall view showing a four-wheel steering system according to an embodiment of the present invention, FIG. 2 is a sectional view showing a partially cutaway electromagnetic directional control valve, and FIG. 3 is a vehicle with an electromagnetic flow control valve. FIG. 4 is a cross-sectional view showing a hydraulic pilot control valve, FIG. 5 is a schematic overall view showing a four-wheel steering system according to another embodiment of the present invention, and FIG. 6 is a conventional view. FIG. 2 is a schematic overall view showing the four-wheel steering device. 10 ... Power steering mechanism, 12 ... Power cylinder, 20 ... Steering mechanism, 21 ... Power cylinder, 2
2 ... Pressure oil supply source, 23 ... Electromagnetic directional control valve, 24 ...
Oil passage, 25 ... electromagnetic flow control valve, 26 ... hydraulic pilot control valve, 27 ... controller, 28 ... pilot oil passage, A _f , A _r ... axle, T _f ... front wheel, T _r ... Rear wheel.

Claims (1)

[Claims] 1. A four-wheel steering system comprising a front-wheel-side power steering mechanism and a rear-wheel-side steering mechanism, wherein the rear-wheel-side steering mechanism includes a power cylinder connected to a rear-wheel axle. While directly switching the pressure oil supply source that allows the pressure oil to be supplied to the power cylinder via the electromagnetic flow control valve and the hydraulic pressure generated in the power cylinder in the power steering mechanism on the front wheel side as the pilot pressure, , A hydraulic pilot control valve for controlling the pressure oil supplied from the pressure oil supply source to the power cylinders on the rear wheel side, and the steering direction of the steering mechanism on the rear wheel side with respect to the power steering mechanism on the front wheel side. A four-wheel steering system comprising: an electromagnetic direction switching valve that selectively switches between a phase and a reverse phase.