JPS5847831A - Oil-pressure circuit for oil-pressure shovel - Google Patents

Abstract

PURPOSE:To effectively utilize the energy of return oil from a boom cylinder by using a system in which a switch valve is switched to a return port during the lowering action of the boom when the pressure of an oil-pressure pump is low and direction switch valves other than the for boom are directly connected. CONSTITUTION:A boom direction switch valve 12, a bucket direction switch valve 13, and a right side running direction switch valve 14 are connected in parallel to an oil-pressure pump, and the center bypass ports C2 and C3 of direction switch valves 13 and 14 other than that 12 for boom are connected to a center bypass 41 downstream of the direction switch valve 12 for boom. The boom switch valve 12 is provided with a return port r1 through which return oil from the boom cylinder is flowed out during the lowering action of boom. When the pressure of the discharges side pipeline 15 of the oil-pressure pump is lower than a set pressure, the switch valve 37 is switched and the direction switch valves 13 and 14 other than that for boom are connected in series to the return port r1. When the pressure of the pipeline 15 is higher than the set pressure, the valves are connected to a tank.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modified JILK hydraulic circuit for a hydraulic excavator in which a plurality of directional control valves are connected in parallel to a hydraulic pump.

FIG. 1 shows an example of a hydraulic circuit of a conventional hydraulic excavator.

Two hydraulic pumps 2.3 are driven by the prime mover IK, and the discharge side of each hydraulic pump 2.3 is connected to a directional valve group 4.
．． 5 common pump ports 6°7 and 0.
Common tank port 8.9 of directional valve group 4°5 is filter 10! After that, Tank IIKm! Continued. In the directional valve group 4KTh, a first boom directional valve 12, a packet directional valve 13, and a right travel directional valve 14 are connected in parallel to the hydraulic pump 2 by a pump circuit 15. In the directional valve group 5, a swing directional valve 16, a second boom directional valve 1
7. Directional switching valve 18 for arm and directional switching valve 1 for left travel
9 is connected in parallel to the hydraulic pump 3 by the pump circuit 20
Continued. The work ports of each directional control valve 12-14.118-20 are output circuits M3, B, ~M? , Bt +
Thereafter, there is a boom cylinder 21, a packet cylinder 22, a right travel motor 23, a swing motor 24, an arm cylinder 25,
They are respectively connected to the left travel motor 26. 27 is a boom, 28 is an arm, 29 is a packet, 30.31 is a relief valve, 32.33 is a makeup valve, 34.35 is a four-
It is a check valve. The boom directional switching valves 12 and 17 are connected by a link 36, and when the operating lever is operated, the boom directional switching valve 12 is switched first, and then the boom directional switching valve 17 is switched. When returning to the neutral position, return in the reverse order.

In FIG. 1, the boom directional control valve 12 is switched to the right switching position, the boom 27 is moved in the lowering direction, and at the same time, the packet directional switching valve 13 is switched to the left switching position (bucket). 29t- When you try to move it in the reeling direction, the boom cylinder 21 has a force acting in the direction of pushing the rod due to the weight of the boom 27, so the boom cylinder 2
1C) The amount of oil flowing out from the bottom side oil chamber to the tank 11 becomes larger than the amount of oil discharged from the hydraulic pump 2, and the pump circuit ls
The pressure becomes negative pressure. Therefore, packet 29 cannot be moved.

An object of the present invention is to solve the above-mentioned problems, and to solve the above-mentioned problems, when the boom is lowered, nine other seven
By allowing the pressure oil pipe to flow into the directional switching valve for the cutter evaporator, it is possible to provide a hydraulic circuit for a hydraulic pump that can utilize the potential energy pipe due to the dead weight of the boom.

In order to achieve this objective, the present invention provides a return port through which the return oil from the boom cylinder flows out during the boom circumferential switching valve kS team lowering operation, and when the pump circuit pressure of the hydraulic pump is lower than the set pressure. The present invention is characterized in that another actuator directional switching valve is connected in series to the return port, and a switching valve 1 is provided to connect the return port to a tank pipe when the pressure exceeds a set pressure.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 2 shows an embodiment of the invention. Components similar to those in FIG. 1 are designated by the same reference numerals. The first boom directional switching valve 12 has a boom cylinder 21 in the switching position during lowering operation (right).
A turn port R is provided through which the return oil flows out. The return port r1 is closed at the neutral position and during boom raising operation.

The return boat r1 is connected to the tank circuit 3 by the switching valve 37.
8 and bypass line 39.

The packet directional control valve 1 is downstream from the boom directional control valve 12 via the bypass line 39IIi and the check valve 40.
3 is connected to the center bypass 41 upstream from the center bypass 41 . When the pressure of the switching valve 37Fi and the pump circuit 15 is lower than the set pressure, the return port y and the 17 bypass line 39 connect the packet directional switching valve 13't in series. Connecting in series means that when the packet directional control valve 13 is in the neutral position, the center bypass port C8! - Connect return port rIK, and pump boat P in left and right reswitching position
st center bypass passport cat-return port)
It means to connect to rl. When the pressure of the pump circuit 15 is higher than the set pressure, the switching valve 37 is connected to the return valve (return valve) through the rlK tank circuit 38 pipe.

Packet directional switching valve 13 and right travel directional switching valve 14
In the left/right reswitching position, the pump port (p2+Ps) and the center bypass port (p2+Ps) are configured to communicate with the center bypass port)el and el. In addition, a second boom directional control valve 17Fi
, pump port in switching position during boom lowering operation (right))
Ps closes, center bypass port C1 opens □,
A tank port t is configured to open through the throttle 42.

At the same time as switching the boom directional switching valve 12 to the switching position for boom lowering operation, the packet directional switching valve 13 or the right travel directional switching valve 14t - either left or right switching position K
fJ! If the oil is rapidly discharged from the bottom side oil chamber of the boom cylinder 21 due to the weight of the boom 27, the pressure in the pump circuit 15 will become lower than the set pressure.
The switching valve 37 is connected to the return port r1t bypass line 39
Connect to. As a result, the return oil from the boom cylinder 21 flows out to the return boat r1 and passes through the bypass line 39vt to the packet directional control valve 1 which is in combined operation.
3 or the center bypass port c1 of the right travel direction switching valve 14. , and pump port) Pew Pg is supplied. Therefore, the packet cylinder 22 or the right travel motor 23 can operate. That is, a pressure that is the sum of the pressure of the hydraulic pump 2 and the self-weight holding pressure generated in the bottom side oil chamber of the boom cylinder 21 is applied to the packet cylinder 22 or the right travel motor 23. Therefore, the load pressure of the 1-packet cylinder 22 and the right travel motor 23 is the switching valve 3.
If the pressure is less than the sum of the set pressure of No. 7 and the self-weight holding pressure of the boom cylinder 21, the packet cylinder 22
Alternatively, the right travel motor 23 becomes operable. Therefore, the set pressure of the switching valve 370 is determined according to the maximum load pressure of the packet cylinder 22 or the right travel motor 23.

The boom directional control valve 17, which is later switched to the switching position for the boom lowering operation in a side operation, is located at its pump port (Pg).
is closed, pressure oil from the hydraulic pump 3 is not supplied to the boom cylinder 21.

Only the return from the boom cylinder 21 and the oil are in the tank boat 1 with the boom directional control valve 17. from tank 1]. Note that the throttle #) 42 is the ninth one that allows more flow from the boom cylinder 21 to the directional switching valve 12 for the oil company boom.

During the boom lowering operation, the hydraulic pump 30 pressure oil is not supplied to the directional switching valve 17 for one poom, so the hydraulic pump 3 is supplied to the other swing directional switching valves 16, arm directional switching valve 18, and left running directional switching valve 19. Pressure oil is supplied to enable combined operation of the boom 27, arm 28, etc.

In the illustrated embodiment, the boom directional switching valve 12, the packet directional switching valve 13, and the right travel directional switching valve 14 are connected in parallel, but the ones connected in parallel to the boom directional switching valve 12 are other actuators. A directional control valve may also be used.

In addition, it is sufficient if at least one other actuator directional control valve is connected in parallel.As explained above, according to the present invention, the return oil from the boom cylinder flows out during the boom lowering operation. The pump circuit pressure of the hydraulic pump is the set pressure in Bow F)
Since the directional control valve for other actuators is connected in series using the directional control valve, the return oil discharged from the boom cylinder due to the weight of the boom can flow into the directional control valve for the other actuator. This allows effective use of potential energy due to the boom's own weight.

[Brief explanation of drawings]

1wJ is a circuit diagram showing an example of a hydraulic circuit of a conventional hydraulic pump, and FIG. 2 is a hydraulic circuit diagram showing an embodiment of the present invention. 2... Hydraulic pump, 12... Directional switching valve for boom, 13... Directional switching valve for packet,
14... Directional switching valve for right travel, 15...
・Pump circuit, 21... Boom cylinder, 22
......Packet cylinder, 23...Right travel motor, 37...Switching valve, 39...
Bypass line, rl...Return port. 1

Claims (1)

[Claims] 1. Connect the boom directional valve and at least one other actuator directional valve in parallel to the hydraulic pump by Km.
Next, connect the center bypass port of the other actuator directional control valve to the center bypass on the downstream side of the boom directional control valve, and lower the boom directional control valve by one poum in the hydraulic circuit of the hydraulic excavator. A return port is provided through which oil flows out from the boom cylinder during operation, and when the pump circuit pressure of the hydraulic pump is lower than the set pressure, the return port (K) is connected in series with a directional control valve for another actuator. A hydraulic circuit for a hydraulic excavator, characterized in that a switching valve is provided to connect a tank to a front return port when the pressure exceeds a set pressure.