JPH09273504A - Swing system hydraulic circuit for construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cavitation in a swing motor from occurring when rotation of the swing motor is to be stopped in a construction machine provided with a negative control circuit. SOLUTION: Outlet pressure of a shuttle valve 23 is detected by a pressure switch 24 as a device for detecting operation of a remote control valve 4. A charge oil path 27 is branched from a negative control signal oil path 8 and an electromagnetic switch valve 28 is mounted in the course of the charge oil path 27 and connected to driving oil paths 10, 11 of a swing motor 2. When operation of the remote control valve 4 is stopped and the pressure switch 24 is switched from ON to OFF, a signal is provided to a solenoid 31 from a controller 26 and the electromagnetic switch valve 28 is switched for a certain time to exert high signal pressure of the negative control signal oil path d and increase suction amount of the swing motor 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a swing hydraulic circuit for a construction machine, and more particularly to a negative control circuit for saving energy when the directional control valve is in a neutral position.

[0002]

2. Description of the Related Art Conventionally, in a hydraulic circuit of a construction machine, a negative control circuit for minimizing energy consumption by minimizing a discharge amount of a hydraulic pump when a directional control valve is in a neutral position to reduce idle loss. It has been known.

FIG. 3 shows a swing hydraulic circuit of a hydraulic excavator as an example of a negative control circuit. A directional control valve 3 is provided between a variable displacement hydraulic pump 1 and a swing motor 2.
Is provided, and the directional control valve 3 is provided by the remote control valve 4.
Are switching operations. The directional control valve 3 is in the neutral position 3
When it is at c, the discharge oil of the hydraulic pump 1 passes through the negative control throttle 6 provided in the center bypass oil passage 5 and communicates with the tank 7. However, the negative control throttle 6 generates a negative control pressure.

This negative control pressure is led to the regulator 9 via a negative control signal oil passage 8 provided by branching from the center bypass oil passage 5. That is, when the directional control valve 3 is in the neutral position 3c, the negative control pressure is high, the tilt angle is reduced by the action of the regulator 9, and the discharge amount of the hydraulic pump 1 is reduced to save energy. There is.

Here, for example, the remote control valve 4
When the directional control valve 3 is switched to the position of 3a by the operation of, the discharge oil of the hydraulic pump 1 is supplied from the one drive oil passage 10 to the swing motor 2 and the vehicle body starts to swing. Then, if the directional control valve 3 is returned to the neutral position 3c to stop the turning of the machine body, immediately after that, the swing motor 2 tries to continue to rotate due to the large inertia of the machine body.

Therefore, the pressure in the drive oil passage 11 on the discharge side of the two drive oil passages 10 and 11 in the closed state increases, and the oil in the drive oil passage 11 is released from the relief valve 12 and the check valve 13. And flows into the drive oil passage 10 side on the suction side. As a result, the rotation of the turning motor 2 is gradually stopped while absorbing the inertia of the machine body.

[0007]

In the construction machine having the conventional negative control circuit, when the directional control valve 3 is returned to the neutral position 3c while the machine body is turning, as described above. The oil in the drive oil passage 11 on the discharge side flows into the drive oil passage 10 on the suction side, and the rotation of the swing motor 2 is stopped while absorbing the inertia of the machine body.

Since the directional control valve 3 is in the neutral position 3c, the negative control pressure is increased and the discharge amount of the hydraulic pump 1 is controlled so as to decrease.
The flow rate passing through the return oil passage 14 decreases and the pressure in the return oil passage 14 decreases. Therefore, the pressure of the make-up port 15 that connects the drive oil passage 10 on the suction side and the drive oil passage 11 on the discharge side of the swing motor 2 becomes low, and the oil supplied to the swing motor 2 becomes insufficient, resulting in cavitation. appear.

In order to prevent this cavitation, check valves 16 and 17 are installed in the return oil passage 14 to increase the pressure. However, the pressure is increased too much in consideration of the pressure resistance of the oil cooler 18. I can't.

Therefore, in a construction machine equipped with a negative control circuit, there is a technical problem to be solved in order to prevent cavitation from occurring in the swing motor when the rotation of the swing motor is stopped. Therefore, the present invention aims to solve this problem.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been proposed in order to achieve the above object, and a variable displacement hydraulic pump and a swing motor are connected by a drive oil passage, and the drive oil is connected. A directional control valve is installed in the path to enable switching operation by a remote control valve, a center bypass oil path is provided in the neutral position of the directional control valve, and a negative control throttle is installed downstream of the directional control valve. A negative control signal oil passage is branched from the upstream side of the control throttle, and a device for detecting the operation of the remote control valve by turning it on and off is provided in the swing hydraulic circuit connected to the regulator of the hydraulic pump. The charge oil passage is branched from the control signal oil passage, and an electromagnetic opening / closing valve is provided in the middle of the charge oil passage to connect to the drive oil passage. When the detection device is switched from ON to OFF to stop the operation of the over preparative control valve,
A swing system hydraulic circuit for a construction machine is provided in which a solenoid control valve is switched for a certain period of time so that the signal pressure of a negative control signal oil passage acts on the drive oil passage.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a swing hydraulic circuit of a hydraulic excavator. For convenience of explanation, the same components as those of the conventional one are designated by the same reference numerals, and the description thereof will be omitted.

As a device for detecting the turning operation of the remote control valve 4, the oil passages 21 and 22 are branched from the pilot oil passages 19 and 20 of the remote control valve 4 to connect the shuttle valve 23, and the outlet of the shuttle valve 23. A pressure switch 24 is provided in the oil passage. The pressure switch 24 is turned on by detecting the pilot pressure generated in the pilot oil passages 19 and 20, and turned off when the pilot pressure is exhausted. The pressure switch 24 is connected to a controller 26 by a cable 25.

On the other hand, the charge oil passage 27 is branched from the negative control signal oil passage 8 connected to the regulator 9 of the hydraulic pump 1, and an electromagnetic opening / closing valve 28 is provided in the middle of the charge oil passage 27 so that the swing motor 2 of the swing motor 2 can operate. Drive oil passage 1
Connect to 0 and 11. Note that check valves 29 and 30 are provided in order to prevent backflow from the drive oil passages 10 and 11 to the charge oil passage 27.

The solenoid 31 of the solenoid valve 28 is connected to the controller 26 by a cable 32. Further, the electromagnetic opening / closing valve 28 is connected to a position 28a that cuts off the charge oil passage 27 and communicates with the tank 7, and connects the charge oil passage 27 to the signal pressure of the negative control signal oil passage 8 to drive the oil passages 10, Two positions, that is, a position 28b leading to 11 and a position 28b are provided, and the spool is formed so as to switch from the position 28a to the position 28b when the solenoid 31 is excited.

When the remote control valve 4 is operated, for example, to the right in the figure, the pilot oil is discharged to the pilot oil passage 19 and the directional control valve 3 is switched to the position 3a, so that the oil discharged from the hydraulic pump 1 is discharged. It is supplied to the turning motor 2 via one of the drive oil passages 10. The pressure oil that rotates the swing motor 2 reaches the return oil passage 14 via the other drive oil passage 11, passes through the oil cooler 18, and returns to the tank 7.

The operation of the turning hydraulic circuit at this time is shown in FIG.
The explanation will be given with reference to the graph of. Pilot pressure is generated by the start of operation of the remote control valve 4, the direction control valve 3 is switched, and the oil discharged from the hydraulic pump 1 is led to the drive oil passage 10. At this time, since the pressure oil does not pass through the negative control throttle 6, the negative control pressure becomes low, and this negative control pressure is led to the regulator 9 via the negative control signal oil passage 8, and the action of the regulator 9 causes the hydraulic pump 1 to operate. The discharge amount increases.

Thus, high-pressure oil is supplied to the swing motor 2, and the rotation of the swing motor 2 causes the machine body to swing. Moreover, since the discharge amount of the hydraulic pump 1 is large, the makeup port pressure also becomes high.

As described above, when the remote control valve 4 is operated, a part of the pilot oil is in the oil passage 21.
Or via 22, the high pressure is selected by the shuttle valve 23,
When this pilot pressure is detected, the pressure switch 24 is turned on. The ON signal of the pressure switch 24 is input to the controller 26 via the cable 25, and the controller 26 determines that the machine is currently in a turning state.

In this state, no signal is output from the controller 26 to the cable 32, and the solenoid 31 is not excited. Therefore, the electromagnetic opening / closing valve 28 is at the position 28a shown in the figure, and the charge oil passage 27 is cut off to communicate with the tank 7. are doing.

Next, when the operation of the remote control valve 4 is completed, the pilot pressure is exhausted, the directional control valve 3 is switched to the neutral position 3c, and the drive oil passages 10, 11 are driven.
Is cut off and the oil discharged from the hydraulic pump 1 is no longer supplied to the swing motor 2, but the swing motor 2 tries to continue to rotate due to the inertia of the machine body, and the pressure oil in the drive oil passage 11 on the discharge side becomes high pressure. It flows into the drive oil passage 10 on the suction side from the makeup port 15.

At this time, the oil discharged from the hydraulic pump 1 passes through the center bypass oil passage 5 and the negative control throttle 6
Since the negative control pressure becomes high, the negative control pressure is led to the regulator 9, and the discharge amount of the hydraulic pump 1 is reduced by the action of the regulator 9. Further, the return oil passage 14 has a low pressure, and the pressure of the makeup port 15 decreases.

Here, since the pilot pressure of the remote control valve 4 disappears, the pressure switch 24 is turned off. When the pressure switch 24 is switched from on to off, a signal is output from the controller 26 to the cable 32, the solenoid 31 is excited for a certain period of time, and the electromagnetic opening / closing valve 28 is switched to the position of 28b. During that time, the charge oil passage 27 is connected, and the high signal pressure of the negative control signal oil passage 8 is led to the drive oil passages 10 and 11.

The signal pressure from the charge oil passage 27 acts as a make-up assist pressure, and the amount of oil flowing into the suction-side drive oil passage 10 increases, so that cavitation occurs in the turning motor 2. Without inertia, the rotation of the turning motor 2 stops.

After a lapse of a certain period of time, the signal from the controller 26 to the solenoid 31 disappears and the electromagnetic opening / closing valve 28 returns to the original position 28a. Therefore, the charge oil passage 27 communicates with the tank 7 to reduce the makeup assist pressure, and the negative control is performed again to control the energy saving.

The present invention can be variously modified without departing from the spirit of the present invention, and it goes without saying that the present invention extends to the modified ones.

[0027]

As described above, according to the present invention, in the construction machine having the negative control circuit, when the operation of the remote control valve is stopped, the high pressure is applied to the drive oil passage of the swing motor for a certain time. Applying signal pressure. Therefore, during that time, the amount of oil sucked into the swing motor increases, and cavitation due to insufficient suction can be prevented.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a hydraulic circuit diagram of a swing system of a hydraulic excavator.

FIG. 2 is a graph showing changes in the state of each device from the start to the end of operation of the remote control valve.

FIG. 3 is a hydraulic circuit diagram of a swing system of a conventional hydraulic excavator.

[Explanation of symbols]

 1 hydraulic pump 2 swing motor 3 directional control valve 4 remote control valve 5 center bypass oil passage 6 negative control throttle 8 negative control signal oil passage 9 regulator 10, 11 drive oil passage 24 pressure switch 26 controller 27 charge oil passage 28 electromagnetic opening / closing Valve 27 solenoid

Claims (1)

[Claims] 1. A variable displacement hydraulic pump and a swing motor are connected by a drive oil passage, and a direction control valve is provided in the drive oil passage so that switching can be performed by a remote control valve. A center bypass oil passage is provided at the neutral position of the control valve, and a negative control throttle is provided downstream of the directional control valve. In the swirl system hydraulic circuit, a device for detecting the operation of the remote control valve by turning on / off is provided, the charge oil passage is branched from the negative control signal oil passage, and the electromagnetic opening / closing is performed in the middle of the charge oil passage. A valve is provided to connect to the drive oil passage, and the operation of the remote control valve is stopped to switch the detection device from on to off. When it crosses, the electromagnetic on-off valve is switched for a certain period of time so that the signal pressure of the negative control signal oil passage acts on the drive oil passage.