JPS58193906A - Hydraulic circuit for construction machine - Google Patents

Abstract

PURPOSE:To prevent a cavitation from being occured by a method wherein a hydraulic oil discharged from an actuater is flowed to a supplying part when the potential energy of the actuater is released and the low discharged volume of a hydraulic pump is applied. CONSTITUTION:Change-over valves 28 and 29 are connected between the pipes 23 and 24 connected to an actuater 4 and the change-over valves are connected to the cylinder coupled to the iron plate of a hydraulic pump, and a direction change-over valve 26 to be changed over by the change-over valve 10 when the potential energy of the actuater is released. The direction change-over valve 26 is connected to the pilot ports of change-over valves 28 and 29 and an auxiliary pump 18. Thereby, when the change-over valve 10 is changed over to such a position as the actuater releases the potential energy, the change-over valves 28 and 29 are changed over, the hydraulic oil discharged from the actuater is flowed into the supplying part, the discharged volume of a hydraulic pump 7 is decreased, so that it is possible to prevent the cavitation from being occured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit used in various working machines,
In particular, the present invention relates to a hydraulic circuit for a working machine suitable for an actuator that stores potential energy or inertial energy while driving the actuator.

#! 1lil is a product equipped with such an actuator! ! 1 is a system diagram of a conventional hydraulic circuit of a hydraulic excavator as an example of a machine.

In the figure, l is the boom of the hydraulic excavator, 2 is the same arm,
3G1 is also a packet, and these constitute the front mechanism of the hydraulic cylinder. 4 is a boom cylinder that raises and raises the boom 1; 5 is an arm cylinder that swings the arm 2; and 6 is a packet cylinder that rotates the foot 3. 7 ft each of these cylinders, hydraulic motor,
Capacity Jll for driving other actuators
The numeral 9α is an operating lever for the hydraulic pump 9. ^ indicates an actuator connected to the control valve 9, and is representative of one of the actuators other than the boom cylinder 4. lO is a control valve 10α that controls the driving direction and driving speed of boom cylinder 4.
This is the operating lever for the W-rubulp 10. Figure 11 shows only the combination of two actuators and control pulp, and the others are omitted.01
1 is an oil tank, and 12 is a relief valve.

A servo valve 13 controls the amount of tilting of the swash plate 8 of the variable displacement hydraulic body 7'7, and is operated according to the discharge pressure of the variable displacement hydraulic pump 7. 13α is a spring, and 13b is a sleeve of the servo valve 13. 14 is a cylinder controlled by the servo valve 13, and 16 is a piston. 16
is a link connecting the piston 15 and the swash plate 8, and when pressure oil is supplied to the rod side of the cylinder 14, the piston 15,
The link 16 moves upward, and accordingly, the swash plate 8 changes its tilt angle so that the discharge amount of the variable displacement fj and hydraulic pump 7 decreases. When pressure oil is supplied to the bottom side of the cylinder 14, the piston 15, link 16, and swash plate 8 are operated to increase the discharge amount of the variable volume III hydraulic cylinder 17. 17 is the sleeve 13b of the piston 15 and the servo valve 13
The link connects the sleeve 13b to follow the movement of the piston 15 to shift the sleeve 13b so that the servo valve 13 is in the neutral position. 18 is connected to the cylinder 1 via the servo valve 13.
This is an auxiliary bong 7 that supplies pressurized oil to 4.

19.20.21.22 is a pipe connecting the Loe variable displacement hydraulic bongua and each Funtrol valve 9.10; 23.
Reference numeral 24 denotes a pipeline connecting the lubricant 10 and the rod side and bottom side of the boom cylinder 4; 25 denotes a pipeline for transmitting the pressure of the discharge mw passage 19 of the variable capacity violet-type gripping bongua to the servo valve 13; It is.

Next, the operation of such a conventional hydraulic circuit will be explained.

For example, in order to raise the boom 1, the operator ``'' 1
When the control pulp 10 is switched from the neutral position 11N to the left position by 08, the pressure oil discharged from the variable displacement violet type hydraulic pump 7 is supplied to the bottom of the boom cylinder 4 through the pipe 19.21°24. and raise boom 1. At this time, the pressure in the pipe line 19 is transmitted to the servo valve 13 through the pipe line 25, and the servo valve 13 is switched from the neutral position IIN to the upper position υ against the spring 13g. Pressure oil is supplied to the rod side of the cylinder 14, and the 1 piston 15 is driven upward, link 1
6 to change the tilt angle of the swash plate 8 to reduce the discharge amount of the variable volume acoustic hydraulic pump 7. - 10,000, the movement of the piston 15 is transmitted to the sleeve 13b of the servo valve 13 via the link 17, and the servo valve 13 follows so that it is in the neutral position 1iIIN. When the pressure in the pipe line 19 decreases, the servo valve 13 is switched to the lower position @D by the spring 135, and the piston 15 of the cylinder 14 is actuated as a head to increase the discharge amount of the variable capacity m hydraulic cylinder 17. In this way,
The output can be utilized extremely efficiently within a range that does not exceed the horsepower of the prime mover connected to the variable displacement hydraulic pump 7.

In such a hydraulic circuit, consider a case where the operating lever 10α is switched from the neutral position N to the right position R in order to lower the boom 1 that has risen. In this case, positional energy is accumulated on the bottom side of the boom cylinder 4 due to the raised boom 1, and since the boom 1 is in a state of descending under its own weight, IFj18 is stored on the rod side of the boom cylinder 4.
A large amount of pressure oil flows through 19, 21.2323, and a large pressure loss occurs in the control pulp 1 (NC) through which this pressure oil passes.

Furthermore, in order to gradually lower the boom 1, the control pulp 10 is set at an intermediate position between the neutral position @N and the right position R, and the passage from the bottom side of the boom cylinder 4 to the oil tank 11 is narrowed. The pressure oil from the hydraulic pump 7 is also throttled at the hunt roll valve 10, and part of this pressure oil is returned to the rod side of the boom cylinder 4, and the other part is returned to the oil tank 15. As a result, the pressure loss in the control pulp 10 increases significantly.

In order to avoid such a pressure loss, when the poop 1 is lowered, the discharge amount of the variable capacity reservoir hydraulic bongua should be set to the minimum to reduce the flow rate of the pressure oil flowing through the control pulp 10til, but the variable hydraulic pump If the discharge amount of 7 is set to the minimum, the amount of oil on the rod side of the poom cylinder 4 will be insufficient when the control pulp 10 is completely set to the right position B.
For this reason, a situation occurs in which cavitation occurs.

An object of the present invention is to reduce the pressure loss of the control pulp by reducing the discharge amount of the hydraulic pump when the actuator operates to release its position power. To provide a hydraulic circuit rtf1 for a working machine which can prevent the occurrence of cavitation due to insufficient supply of pressure oil.

To achieve this objective, the present invention detects when the Funtrol pulp is operated to actuate the actuator in the direction of its potential energy release, and directs the discharge pressure oil from the actuator to the supply side of the actuator. It is characterized in that the amount of discharge from the hydraulic bong 1 is reduced.

Hereinafter, the present invention will be explained based on an embodiment shown in Fig. 2.

112&! ! The same parts as those in FIG. Reference numeral 26 designates a direction switching valve which is connected to the auxiliary bonder 18 and which detects the direction of movement of the pool 1 in conjunction with the movement of the funnel pulp 10. 27
27a is a rod connected to the control pulp 10, 27b is a rod connected to the directional valve 26, and 27C is the tip of the rod 27α. The tip of the rod 27b is connected to the tip of the rod 27a and the space 2.
It is engaged within 7C. In the connecting portion 27, the rod 276 moves the rod 27b and switches the directional control valve 26 from the left position to the right position only when the control seal pulp 10 is switched from the neutral position @N to the right position i1R. For any other operation of the Control Seal pulp 10, the directional valve 26 is held in the left-hand position. 28
One boat is in pipe 23 and the other boat is in pipe 24.
This is a directional valve with a built-in check valve connected to the 28g
28b is a spring that normally holds the directional control valve 28 with a built-in check valve in the upper position υ, and 28b is the flow of pressure oil from the pipe 1824 to the pipe line 23 when the directional control valve 28 with a built-in check valve is switched to the lower position. This is a check valve that allows flow in the opposite direction.

29 is a directional switching valve provided between the servo valve 13 and the cylinder 14, and 29g is a spring that holds the directional switching valve 9 (normally in the upper position MD).

When the directional control valve 29 is in the lower position, the servo valve 1
3 and the cylinder 14 are in the *i state, and when they are in the J:@ position, the auxiliary pump 18 and the rod side of the cylinder 14, and the bottom side of the cylinder 14 and the oil tank 11 are in a [conducting state].

30 is a pipe connecting the auxiliary pump 18 and the directional control valve 26; 31 is a pipe that transmits the hydraulic pressure of the auxiliary bonder 18 to the directional control valve 28 with a built-in check valve when the directional control valve 26 is in the right position hole; Similarly, when the directional control valve 26 is in the right position WR, a conduit 33 transmits the hydraulic pressure of the auxiliary pump 18 to the directional control valve 29, and a conduit 33 connects the auxiliary bonder 18 and the directional control valve 29.

Next, the operation of the hydraulic pressure 1g circuit of this embodiment shown in FIG. #I2 will be explained.

When raising pool 1, control pulp I pump 1
0 is in the left position, the directional control valve 26 is in the left position I.
IL, the pressure oil of the auxiliary pump 18 is cut off,
The directional control valve 28 with built-in check valve is located in the upper part IfU, and
The directional control valve 29 is in the lower position. Therefore, the pipe line 23 and the line 24 are in a blocked state, and the servo valve 13 and the cylinder 14 are in a conductive state. Since the oil field circuit in such a state is the same as the hydraulic circuit shown in FIG. 1, the operation when raising the pool 1 is the same as that of the hydraulic circuit shown in FIG.

When lowering the poom 1, the hunt roll pulp lO is switched to the right position lIR by the lever 1 (ML. With this operation, the connection ff127 is also pulled to the left in the figure, and the directional control valve 26 is moved from the left position to the right position lIR. Therefore, the hydraulic pressure of the auxiliary pump 18 is passed through the pipe M30 and the directional control valve 26, one of which passes through the pipe 31 to the directional control valve 28 with a built-in Chetsuta valve, and the other goes through the pipe 32 to the directional control valve 28. For this reason, the directional control valve 28 with a built-in check valve is switched to the lower position, and the directional control valve 29 is switched to the upper position U. By switching the directional control valve 29, the servo valve 13 and the cylinder 14 are The pressure oil of the auxiliary pump 18 is supplied to the rod side of the cylinder 14 via the pipe line 33 and the upper position U of the directional control valve 29.Thereby,
The piston 15 is pushed up, the swash plate 8 is driven, and the discharge amount of the variable displacement hydraulic pump 7 is reduced. That is, in this case, since the operation of the servo valve 13 is irrelevant, the variable volume fI
The discharge amount of the kWl hydraulic pump 7 is forcibly reduced regardless of the pressure in the pipe line 19. Since the discharge amount of variable displacement ij & hydraulic pump 7 becomes smaller, Ii! to the rod side of boom cylinder 4 in 1 control pulp 10! The pressure loss in the passage is also reduced.

- force, the boom 1 descends from its own weight (position energy) V, and from the bottom side of the boom cylinder 4 there is a pipe p 24,
:) > ) Pressure oil is discharged to the oil tank 11 via the roll pulp 10. At this time, the pressure oil in the pipe line 24 flows into the pipe line 23 through the check valve 28b. therefore,
Variable displacement hydraulic pump 7 (rl Even if the discharge amount is reduced, the oil amount does not decrease, and therefore cavitation on the boom cylinder 40 Rondo side can also be prevented. Furthermore, it is equipped with a directional switch with a built-in check valve. The amount of oil that would have flowed from the bottom side of the boom cylinder 4 to the oil tank 11 via the control pulp 10 when the valve 28 was not provided is transferred to the boom cylinder 40 via the check valve 28b.
The boom cylinder 4 inside the control valve 10 is reduced by the amount flowing into the rod side (if the volume ratio between the rod side and the bottom side of the boom cylinder 4 is 1:2, 1 reaches approximately 1/2). The pressure loss in the passage from the bottom side to the oil tank 11 is also reduced.

Note that the check valve 2 in the directional control valve 28 with a built-in check valve
8b supplies pressure oil to the rod side of the boom cylinder 4;
Boom 1f: This is provided to avoid a short circuit between the bottom side of the boom cylinder 4 and the rod side when trying to forcefully lower the object, rather than using the own weight of the boom 1, as when pushing an object with the Bakut 3. It is.

In this example, a directional switching valve with a built-in check valve is provided between the rod side and bottom side of the boom cylinder, and a directional switching valve is provided between the servo valve and the cylinder for driving the swash plate, and these are separately operated when the boom is lowered. Since the switching is performed by transmitting hydraulic pressure through the directional switching valve, the discharge amount of the hydraulic cylinder 1 can be reduced without causing cavitation, thereby reducing the pressure loss in the control valve.

In addition, in the following explanation, hydraulic excavators, etc. are used as working machines.
Further, although a boom cylinder is illustrated as an example of an actuator of a hydraulic circuit, the present invention is not limited to a hydraulic excavator and its boom cylinder, and can be applied to any actuator that releases potential energy while being driven.

As described above, in the present invention, the pressure oil discharged from the actuator when the actuator releases potential energy is made to flow into the supply side of the actuator, and the discharge amount of the hydraulic pump is made small, thereby preventing cavitation from occurring. Therefore, the discharge amount of the hydraulic pump can be reduced without any problems, and therefore the pressure loss of the control valve can be minimized.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional oil l1lE circuit of a hydraulic excavator, and Fig. 2 is a hydraulic silopel 8 according to an embodiment of the present invention.
... Swash plate, 10 ... Control pulp vine 1
4...Cylinder, 15...Piston,
16... Rondo, 18... Auxiliary pump, 26.29... Directional switching valve, 28...
・Directional switching valve with built-in check valve.

Claims (1)

[Claims] A hydraulic circuit comprising a variable capacity hydraulic bong, an actuator that drives a member having potential energy, and a control valve that connects the variable capacity hydraulic bong and the actuator and controls driving of the actuator. detecting means for detecting that the actuator is driven in a direction in which potential energy is released; and a signal from the detecting means to supply discharge pressure oil from the actuator to the supply side of the actuator as the actuator releases potential energy. 1. A hydraulic circuit for a working machine, comprising means for reducing the discharge amount of the variable capacity hydraulic bong 1.