JPH01295928A - Oil-hydraulic circuit for civil engineering and construction machinery - Google Patents

Abstract

PURPOSE:To completely prevent leakage, by releasing check valves before start of operation of actuators when there is any possibility of producing abnormal high pressure at the actuators that are equipped with pilot check valves. CONSTITUTION:An oil-hydraulic circuit is composed of oil-hydraulic pumps 31a and 31b, a plurality of actuators, a plurality of direction shift valves 33-37, a necessary number of pilot check valves 12 and 13 and others. When the shift valves 33-37, connected to the actuators equipped with the check valves 12 and 13, are operated, the check valves 12 and 13 are released before start of operation of the actuators, and the valves are deprived of their checking function thereby. When other shift valves 33-37 that are liable to make the actuators equipped with the check valves 12 and 13 produce abnormal high pressure are operated, a similar effect is applied to the check valves.

Description

[Detailed description of the invention] [Hydraulic actuator for holding the load of civil engineering and construction machinery in industrial applications (
This invention relates to a hydraulic circuit that prevents natural descent (leakage from the spool land) when the complex switching valve of a power shovel (boom, arm, etc.) is in neutral.

[Prior Art] FIG. 6 shows a simplified hydraulic circuit for civil engineering and construction machinery in the prior art, and will be explained using this diagram.

In the figure, pressure oil discharged from hydraulic pumps 31a, 31b is supplied to composite control valves 32a, 32b, and respective switching valves 33, 34, 35a, 35b.

36. and 37 respectively have arm cylinders 38. Turning morph 39. Left running motor 40a, right running motor 40
b. Boom cylinder 41. A packet cylinder 42 is connected, and each actuator is operated by operating each switching valve. 43a and 43b are main relief valves that prevent abnormally high pressure in the hydraulic pump.

44a.

44b, 45a, 45b, 46a, 46b are overload relief valves for actuator protection, and 47a, 47b, 48a.

Make-up valves 48b, 49a, and 49b are provided at necessary locations to prevent cavitation, and are arranged in an orderly manner within the composite control valves 32a and 32b.

[Problem to be solved by the invention] In recent years, hydraulic circuits for civil engineering and construction machinery have become higher in pressure, and therefore the load pressure that holds each actuator when the switching valve is in the neutral state has also increased.6 However, the structure of the known switching valve is As shown in the cross-sectional view in Figure 4, the part that prevents the amount of leakage is the land between the valve body and the spool, but in order for the spool to move, a gap between the valve body and the valve body is required, and this gap There were limits to preventing leaks. An easy solution to this problem is to provide a pilot check valve between the actuator and the switching valve, but in this case, the location of the overload relief valve becomes a problem. In other words, by installing a pilot check valve, it is necessary to move the overload relief valve between the actuator and the pilot check valve. However, in the structure of a well-known switching valve, as shown in Figure 4, overload relief valves are arranged in an orderly manner within the valve body, and all switching valves of the complex control valve are located where leak prevention is required. Since the pilot check valve is not attached to the valve, if the pilot check valve is installed inside the valve body, unnecessary parts will become longer and longer.On the other hand, if the pilot check valve is installed outside the valve body only in the necessary places, it will become longer. In this case, in addition to the pilot check valve, an overload relief valve and another tank passage must be installed externally, which increases costs.

Furthermore, since the overload relief valve is installed between the pilot check valve and the actuator, in a strict sense, it is not possible to prevent leakage from the overload relief valve itself. Although the pilot check valve is installed between the actuator and the switching valve, the overload relief valve and the tank passage can be placed in the conventional valve body, and are therefore used in switching valves where leakage must be prevented. To provide a hydraulic circuit for civil engineering and construction machinery in which a pilot check valve designed to be installed outside the valve body is installed only at certain points, and there is no need to worry about leakage from an overload relief valve. purpose.

[Means for Solving the Problem] A hydraulic pump, a plurality of actuators driven by pressure oil from the hydraulic pump, and a plurality of directions for controlling the direction and flow rate of the pressure oil supplied from the hydraulic pump to the actuator. A hydraulic circuit for civil engineering and construction machinery comprising a switching valve and pilot check valves provided at any location and number for the purpose of preventing the actuator from falling naturally, connected to an actuator provided with a pilot check valve. The pilot check valve is activated when the directional control valve is operated (because it is necessary to allow oil to flow from the cylinder to the tank), or when the directional control valve connected to the actuator equipped with the pilot check valve at any location is in the neutral position. When operating a directional control valve at any other point connected to an actuator that can generate abnormally high pressure in the actuator installed, each pilot must The hydraulic circuit is designed to release the check valve and eliminate the check function.

In addition, in response to abnormally high pressure caused by a sudden stop of the actuator, etc., the hydraulic circuit is configured such that the check function is activated at a later time (the overload activation time is several seconds) so that the hydraulic circuit can operate the hydraulic circuit.

[Work] This will be explained using the civil engineering/construction machine shown in Fig. 5.

In the figure, 38, 41, and 42 are arm cylinders, boom cylinders, and packet cylinders that are the same as the numbers in FIG. 6, and actuate the actuators of the arm 51, the boom 52, and the packet 53.

Currently, the biggest problem is the amount of leakage from the boom and arm, and this will be discussed below.

(This application is not particularly limited.) The amount of leakage becomes a problem when the arm, boom, and packet switching valves are all in neutral and holding loads in the air. When one actuator is actuated, there is no problem in terms of appearance or use.

Furthermore, the overload relief valve operates when a large force is applied from the outside when the actuator is at rest (when the switching valve is in neutral), and in most cases, the external force is
caused by another actuator on the machine itself, or when the actuator itself suddenly stops working (
This is probably due to the impact load when the switching valve suddenly returns to the neutral state.

In Fig. 5, in the state shown, when the packet is on the ground and the arm switching valve is stopped in a neutral state, when the switching valve is operated in the direction of lowering the boom (the boom cylinder 41 is retracted), the vehicle body tries to float up, and its own weight exerts an external force in the direction in which the arm cylinder 38 extends.

At this time, the arm switching valve is in a neutral state, so when its holding pressure becomes higher than the overload relief valve setting pressure due to an external force due to its own weight, the overload relief valve on the arm cylinder rod side is activated. In this way, by operating the boom, the overload relief valve for the arm is activated at this time.

Therefore, the present invention uses the above-mentioned means to delay the activation time of the check function against abnormally high pressure caused by external force generated by another actuator of the machine itself and shock load when the actuator itself suddenly stops. (Load operation time is several seconds) The hydraulic circuit is equipped with pilot check valves at arbitrary locations and numbers to enable overload operation, and also prevents leakage at required locations when the switching valve is in neutral. A pilot check valve configured to operate in this manner eliminates the need to change the position of the overload relief valve.

[Embodiment] Fig. 1 shows a hydraulic circuit according to an embodiment of the present invention, and except for the parts related to the pilot check valves 12 and 13 and the release signal in the circuit, the configuration is the same as that of Fig. 6 for the prior art. These components are designated by the same reference numerals, and repeated explanation will be omitted.

In this hydraulic circuit, pilot check valves 12 and 13 are provided on the rod side of the arm cylinder 38 and on the bottom side of the boom cylinder 41, respectively, and 14 and 13 are connected to the pilot check valve opening/closing signal lines, respectively.
5 slow return valves are provided, and are configured to open quickly and close with a time delay. In addition, a pilot pump 16 is provided for the pilot check valve opening/closing signal pressure, and the pressure oil from the pilot pump 16 is supplied to the arm, boom, and packet switching valves 3 through a throttle 21, respectively.
3.36.37 interlocking selector valve 17.18.
Pass through 19 and return to tank 5°. Further, the pressure oil from the pilot pump 16 is kept at a constant pressure (usually 30 to 4 kgf/cm'') by the relief valve 20, and is led to the pilot check valve via the Px communication path downstream of the throttle 4o. Each selector valve 17, 18, 19 linked to each switching valve is set to O at an early point in the middle of its stroke.
The timing is set at the time before the passage leading from the cylinder boat of each switching valve to the tank is opened. Here, when the switching valves for the arm, boom, and packet are in the neutral state, the selector valves 17, 18, and 19 that are linked to each other are open, so the pressure oil from the pilot pump is unloaded, and the pressure is low, so Px The positive pressure is low and each pilot check valve is closed to completely prevent leakage. Sixth arm switching valve 33
When is operated, the selector valve 17 is interlocked and closes the pressure oil from the pilot pump, so the positive pressure of Px increases and each pilot check valve opens. Since this timing is before the passage from the cylinder boat of the switching valve to the tank opens, there is no resistance to oil flow from the rod side of the arm cylinder 38 to the tank.At this time, the pilot check valve 13 on the boom cylinder side also opens. Although it would open, it would not be a big problem like the above, and it would no longer be possible to prevent the boom overload relief valve from operating due to arm operation.

When the packet switching valve 37 is operated, the packet cylinder 42 is not provided with a pilot check valve, but the arm and boom pilot check valves 12 and 13 are activated by the selector valve 19 to operate the above-mentioned overload relief valve. It is designed to open. (In practice, the pilot pressure selector valve is also provided in the swing switching valve 6) Furthermore, as described above, the slow return valves 14 and 15 open quickly and cause a time delay when closing.

The pilot check valve shown in Figure 2 is a common one.
This will be explained below.

When releasing, the Px positive pressure increases (relief setting pressure 30~
40 kg f/cm2), piston 22
, and push up the pilot poppet valve 23.

If the piston area is set to approximately 10 times the pilot poppet seat diameter (approximately 3 times the diameter), the cylinder load pressure will be 3.
00 to 400 kg f/cm" (maximum operating circuit pressure). When the pilot poppet valve 23 is released, the pressure in the main poppet spring chamber 24 decreases and the main poppet 25 opens. The oil discharged from the poppet is the cylinder boat 2 of the switching valve.
6 side (at this time, the passage from the cylinder boat of the switching valve to the tank is blocked), so there is no instantaneous lowering of the cylinder.However, the orifice 27 provided in the main poppet has a response delay in the free flow direction. Also, when the pilot poppet 23 is opened, the spring chamber 2
4 It is necessary to set the setting carefully so that the pressure at 4 falls.6 Furthermore, when oil flows from the cylinder boat 45 of the switching valve to the cylinder, the pressure of the cylinder boat 45 acts on the spring chamber 24 of the main check valve. A check valve 28 is provided in the passage to the pilot poppet to prevent the check valve from becoming stuck open.

FIG. 3 shows another embodiment of the pilot check valve shown in FIG. 2, in which a pressure switch 29 and a timer 30 are used to open and close the pilot check valve early and to close it late. This is an example.

[Effects of the Invention] As explained above, the hydraulic circuit for civil engineering and construction machinery of the present invention can completely prevent leaks due to actuator load pressure, and the overload relief valve can be installed at the conventional control valve position. This allows pilot check valves to be easily installed only in the necessary locations.

[Brief explanation of the drawing]

FIG. 1 is a simplified diagram of the hydraulic circuit for civil engineering and construction machinery of the present invention.
Fig. 2 is a basic structural diagram of a pilot check valve used in the hydraulic circuit of the present invention, Fig. 3 is another embodiment of the pilot check valve shown in Fig. 2, and Fig. 4 is a diagram of a pilot check valve arranged in a composite control valve. A cross-sectional view of the switching valve, Figure 5 is a side view of the civil engineering/construction machine,
Figure 6 is a simplified diagram of a conventional hydraulic circuit for civil engineering and construction machinery. 12.13...Pilot check valve, 14°15.
...Slow return valve, 16...Pilot pump 17
．． 18.19... Selector valve, 22... Piston, 23... Pilot poppet valve, 24... Spring chamber, 25... Main poppet, 27... Orifice, 28... Check valve, 29...Pressure switch, 30...-Timer, 31a, 31b=-Hydraulic pump, 32a, 32b-Combined switching valve, 33.34° 35a,
35b, 36.37-switching valve, 38...Arm cylinder, 41...Boom cylinder, 42...Packet cylinder, 44a, 44b. 45a, 45b, 46a, 46b - 1 barload relief valve, 47a, 47b, 48a, 48b. 49a, 49b...Make-up valve, 51...Arm 52...Boom, 53...Packet.

Claims (2)

[Claims] (1) A hydraulic pump, a plurality of actuators driven by pressure oil from the hydraulic pump, a plurality of directional switching valves that control the direction and flow rate of the pressure oil supplied from the hydraulic pump to the actuator, and the actuator. In a hydraulic circuit for civil engineering and construction machinery consisting of a pilot check valve at any location and number provided for the purpose of preventing natural descent of the , when operating any other directional control valve connected to the actuator that can generate abnormally high pressure in the actuator provided with the pilot check valve by operating when the directional control valve is neutral, each of the directional control valves is operated. A hydraulic circuit for civil engineering and construction machinery, characterized in that each of the pilot check valves can be released before an actuator connected to the valve starts operating. (2) The hydraulic circuit for civil engineering and construction machinery according to claim 1, wherein the pilot check valve is configured to open and close quickly when opening and late when closing.