JPS63181822A - Oil-pressure circuit for oil-pressure shovel - Google Patents

Abstract

PURPOSE:To raise the workability of an oil-pressure shovel performing exact operations without reducing the working and traveling speeds by providing a pilot switching valve for connecting tanks between a relief valve for working attachment and a regulator for pump. CONSTITUTION:Pilot switching valves 44L and 44R for tank connection are provided between the downstream sides of relief valves 21L and 21R for working attachment and regulators 9 and 7 for the second and first pumps. The pilot pressure receivers 45L and 45R of the valves 44L and 44R are led to the pilot pressure receiver 17 of a straightforward traveling valve 16. Before the oil- pressure shovel climbs sloped ground or escapes from sludge ground, overmuch load is applied to other actuator, e.g., oil-pressure cylinder 5 if the actuator is worked. Thereby, the reduction of the working and traveling speeds of the cylinder 5 is avoided without reducing the discharge amount of pump even when the valve 21L is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a hydraulic circuit for a hydraulic excavator with excellent workability.

Conventional technology Figure 3 is a hydraulic circuit diagram of the prior art.
L and IR are left and right travel motors, 2 is a swing motor, 3, 4.
5 are hydraulic cylinders for work attachments, 6 is a first pump, 7 is a regulator for adjusting the tilting angle of the first pump 6, 8 is a second pump, 9 is a regulator for the second pump 8, 10 is a pilot pump, 11L , 11R is a left and right travel valve, 12 is a swing valve, 13, 14, and 15 are cylinder valves, respectively, 16 is a straight travel valve, 17 is a pilot pressure receiving part of the straight travel valve 16, 18 is an on-off valve, 19 is a shuttle valve,
20 is a traveling relief valve, 21L.

21R is a relief valve for work attachment, 22L, 2
2R is a left and right foot relief valve, 23t, 23R is a left and right throttle part, 24 is a remote control valve for switching the swing valve 12, 25
is a remote control valve for switching cylinder valve 15, 26, 27.2
8 are shuttle valves 29 and 30 are check valves, respectively.

Next, a prior art hydraulic circuit will be described with reference to FIG. The various hydraulic actuators installed in the hydraulic excavator are divided into two groups A and B, and the left and right travel valves 11L and 11R are respectively provided in the front row of each group, and all other actuator switching valves are connected in parallel. Group A, B
actuators are operated via each switching valve. The actuators 2, 3, 4.5 other than the left and right travel motors L, IR are actuated via the switching valves 1.2.13, 14.15, respectively, by the remote control valve operation. In FIG. 3, as an example, a remote control valve 24 for switching the swing valve 12 and a remote control valve 2 for switching the cylinder valve 15 are shown.
9 showing only 5? In addition, both the first pump 6 and the second pump are variable displacement hydraulic pumps, but the foot relief valves 22L and 22R
Negative control pressure from the upstream oil passages 31L and 31R is applied to the regulators 9 and 7, respectively, to enable tilting angle adjustment. In addition, the relief setting pressure of the travel relief valve 20 is set higher than that of the work attachment relief valves 21L and 21R, so the various actuators 2 and 3
Even when the relief valves 21L and 21R on the 4.5 side do not provide relief due to load, the travel relief valve 20 does not provide relief.On the other hand, the center bypass oil passage 32L that passes through the travel valve 11L, the swing valve 12, and the cylinder valve 15 A low-pressure foot relief valve 22t and a throttle portion 23t are connected in parallel to the outlet side of the pump, and an upstream oil passage 31t thereof is communicated with the regulator 9 of the second pump 8 via an oil passage 33L. Similarly, a low-pressure foot relief valve 22R and a throttle portion 23R are connected in parallel to the outlet side of the center bypass oil passage 32, which passes through the travel valve 11R and the cylinder valve 13.14, and the upstream oil passage 31R is It is communicated with the regulator of the first pump 6 via a passage 33a. Therefore, the negative control pressures led to the outlet oil passages 33L and 33R of the center bypass oil passages 32t and 32a are controlled by the regulators 9 and 33R, respectively.
7 and the second pump 8. In the negative control system of this hydraulic circuit that adjusts the tilting angle of the first pump 6, when the negative control pressure is increased, the pump discharge oil amount decreases according to the command pressure, and conversely, when the negative control pressure is decreased, the pump discharge oil amount is The amount increases. Further, in the remote control system of this hydraulic circuit, various actuators can be operated by operating remote control valves provided in each switching valve other than the left and right travel valves 11t and 11R. In addition, in this hydraulic circuit, the second pump 8 discharge side oil passage 34 and the first pump 6 discharge side oil passage 35, 3
A straight travel valve 16 is provided on the downstream side of the valve 6, and an oil passage 37° 38 that communicates the left travel motor IL with the left travel valve jl+-.
An on-off valve 18 is provided in parallel with the left travel motor IL, and the on-off valve 18 is operated by a remote control valve 24 when the left travel motor IL is stopped.
．． The pilot oil passage 39 from 25 is shut off, and the pilot oil passage 39 is opened when the main traveling motor IL is operated. Therefore, when only the left and right travel valves 11L and 11R are operated and the other actuator remote control valves are not operated, the pilot pressure oil from the pilot pump 10 is not sent to the oil passage 39, so the straight travel valve 16 is not operated. position, and the left and right traveling motors IL and 1λ are connected to the second. Delivery pressure oil is supplied separately from the first pumps 8.6. However, if you operate both the left and right travel valves IIL and IIR and simultaneously operate the remote control valve 25 among the remote control valves for work attachments, the pilot pump 1
The pilot pressure oil from 0 is an oil path 40, a remote control valve 25,
Shuttle valve 27, oil passage 41, shuttle valve 28, oil passage 39
, the opening oil passage position of the on-off valve 18, and the pilot pressure acting on the pressure receiving part 17 via the oil passage 42. Therefore, the straight travel valve 16 is switched from the A position to the Open position, the hydraulic pressure discharged from the first pump 6 is supplied in parallel to the left and right travel motors ILIIR, and the pressure oil discharged from the second pump 8 is supplied to the swivel valve 12. Oil is sent to the cylinder valve 13°14.15 side. In addition, since a throttle part 43 is provided between the parallel open oil passages of the straight travel valve 16 at the opening position, when the straight travel valve 16 is not switched to the opening position, the discharge side oil passage 36 of the first pump 6 and Second pump 8
It communicates with the discharge side oil passage 34 via the constriction part 43.

Problems to be Solved by the Invention In the hydraulic circuit of the prior art described above, when the work attachment relief valves 21t and 21R are relieved, the relieved hydraulic oil is transferred to the upstream oil passages 31L and 31R of the foot relief valves 22L and 22H. It has a negative contrast cut-off function that reduces the discharge flow rate of the second pump 8 or the first pump when the relief set pressure is reached. In other words, since the hydraulic oil that is relieved and returned to the return circuit causes energy loss, the pump discharge capacity is minimized from the viewpoint of energy conservation. Therefore, if the relief valves 21L and 21R for the work attachment do not relieve when the hydraulic excavator is operating only the work attachment or when traveling and operating the work attachment at the same time, the above negative control force... to-off function will not work. Since this does not work, a sufficient amount of oil discharged by four pumps can be supplied to various actuators without causing any problems.

However, hydraulic excavators sometimes run up steep slopes or escape from muddy areas. At the same time, when one of the work attachments is operated and the work attachment relief valves 21L and 21R are relieved by the load applied to the work attachment, this becomes a negative contact cutoff command and acts on the regulator 9 of the second pump 8. This will reduce the amount of oil discharged from the second pump 8. As a result, the operating speed of the work attachment is reduced, making it difficult to climb slopes or escape from muddy areas, and work efficiency is reduced. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a hydraulic circuit that can supply a sufficient amount of pump discharge oil when traveling and operating a work attachment at the same time.

Means for Solving the Problem The means of the present invention taken to solve the above problem are as follows: (a) Divide the various actuators into two groups A and B, and group 1. Driven by a second pump, left and right travel valves were provided in the front row of each group, and these and other actuator switching valves were respectively connected in parallel. And the first.
The straight valve installed on the discharge side of the second pump is installed in the first position where both the left and right traveling valves are in the neutral position or only the left and right traveling valves are in the simultaneous operation position.
In this case, the oil passage from the first pump is shut off, and the oil passage from the second pump is opened. In case, the oil passages from the first and second pumps can be switched to the parallel open oil passage position, and
The pressure oil supply side oil passage of the switching valve for the work attachment inside and the first. In an oil path circuit in which a work attachment relief valve is interposed between each regulator for the second pump, the opening is located downstream of the work attachment relief valve and the first. A pilot switching valve for tank communication is provided between each regulator for the second pump, and the pilot pressure receiving part of the pilot switching valve and the pilot pressure receiving part of the straight travel valve are configured to communicate with each other. .

Operation A. In the second case where the left/right travel valve and any other actuator switching valve are in an operating position other than the neutral position,
The pilot switching valves connected downstream of the work attachment relief valves of groups A and B are both switched to the tank communication oil path position.

1. When the relief valve for the work attachment relieves, the relieved hydraulic oil returns to the oil tank. The regulator of the second pump no longer works.

C. As mentioned above, when the left and right travel motors and any other actuator are operated simultaneously, even if the relief valve for the work attachment relieves, the relieved hydraulic fluid will not issue the negative contact cutoff command, so the first 1.
The amount of oil discharged from the second pump does not decrease.

2. For this reason, when the hydraulic excavator operates the work attachment while climbing a slope with a large inclination angle or escaping from a muddy area, the relief valve for the work attachment releases due to the load applied to the work attachment. Even when this occurs, the amount of oil discharged from the first and second pumps does not decrease and the work can be continued.

Example Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram of the present invention.
L and IR are left and right travel motors, 2 is a swing motor, 3, 4.
5 are hydraulic cylinders for work attachments, 6 is a first pump, 7 is a regulator for adjusting the tilting angle of the first pump 6, 8 is a second pump, 9 is a regulator for the second pump 8, 10 is a pilot pump, 11t ,,llR are left and right travel valves, 12 is a swing valve, 13, 14.15 are cylinder valves, respectively, 16 is a straight travel valve, 17 is a pilot pressure receiving part of the straight travel valve 16, 18 is an on-off valve, and 19 is a shuttle valve. , 20 is a travel relief valve, 21t21a is a work attachment relief valve, 22t, 22R is a left and right foot relief valve, 24°25 is a remote control valve, 44t, 4
4R is the left and right pilot switching valves, 45L and 45R are pilot pressure receiving parts of the pilot switching valves 44L and 44R, respectively, and 46 is an oil tank. Therefore, the configuration of the hydraulic circuit of the present invention differs from the conventional hydraulic circuit in that
Relief valve 21L for work attachment shown in the figure.

21R downstream and 2nd. Tank communication pilot switching valves 44L, 44a are provided between the first pump regulators 9, 7, respectively, and pilot pressure receiving portions 45t, 45t, 44a of the pilot switching valves 44L, 44R are provided.
Pilot pressure receiving part 17 of straight forward valve 16 traveling on 5R together
The point is that it is configured so that it is connected to the

Next, the operating function of the hydraulic circuit of the present invention will be described with reference to FIG. A case will be described in which one of the other actuators (for example, the hydraulic cylinder 5) is operated while the hydraulic excavator is running. Simultaneously operate the left traveling valve 11L to the C position and the right traveling valve 11R to the 2nd position, and then turn the remote control valve 25
When the is switched to the E position, a part of the hydraulic pressure for operating the left traveling motor IL acts on the pilot pressure receiving part 48 of the on-off valve 18 via the oil passages 38 and 47, and the on-off valve 18 is switched to the open oil passage position. Further, the pilot pressure oil from the pilot pump 10 passes through the oil passage 49, the remote control valve 25, and the pilot oil passage 50, and switches the cylinder valve 15 to the position. At the same time, the pilot pressure oil from the pilot pump 10 is transmitted to the remote control valve 25, the shuttle valve 27, the oil passage 41, and the shuttle valve 2.
8, oil passage 39, open oil passage position of on-off valve 18, oil passage 51,
52, it acts on the pilot pressure receiving portion 17 of the straight travel valve 16, and switches the straight travel valve 16 from the A position to the Open position. At the same time, the pilot pressure oil is transferred to the oil passage 5.
It branches at 1 and passes through oil passages 53, 54 and 55,
Pilot pressure receiving part 4 of pilot switching valve 44L44R
5t, 45R, and the pilot switching valve 44L.
, switch 44R to the tank communication oil path position. Therefore, the pressure oil discharged from the first pump 6 is delivered to the discharge side oil passage 35, one branched from the oil passage 36, the oil passage 56 at the mouth position of the straight traveling valve 16, and the oil passage 56 at the opening position of the left traveling valve 11L to the left traveling motor. IL
, and the other side branches off from the discharge side oil passage 35 and becomes oil passage 5.
7. The right travel motor IR is reached through the two positions of the right travel valve 11R, and the left and right travel motors 11 and IR are rotated at the same time. The discharge pressure oil of the second bomb 8 is supplied to the discharge side oil passage 34,
The opening position of the straight travel valve 16, the oil passage 58, the check valve 29,
The hydraulic cylinder 5 is operated through the oil passages 59 and 60 and the position of the cylinder valve 15. In that case, when an excessive load is applied to the hydraulic cylinder 5 and the work attachment relief valve 21L is relieved, the work attachment relief valve 21L is released from the upstream oil passage 59 of the cylinder valve 15.
The relieved hydraulic oil returns to the oil tank 46 via the tank communication oil path position of the pilot switching valve 44t and the oil path 61. Therefore, in this hydraulic circuit, when the work attachment is operated while the hydraulic excavator is running, even if the load on the work attachment is large and the relief valve for the work attachment releases, the relieved hydraulic oil returns to the oil tank. . Therefore, the relieved hydraulic oil does not act on the regulator, so the negative contrast cutoff function does not work in this case. The amount of oil discharged from the second pump does not decrease.

Effects of the Invention As mentioned above, the hydraulic circuit of the present invention provides separate first and second actuators for both the left and right travel motors and other actuators when the left and right travel motors and other actuators are operated simultaneously. The straight travel valve is switchably provided so as to supply pressure oil from the second pump, and the pressure oil supply side oil passages of the switching valves for work attachments in groups A and B are connected to the oil passages for the first and second pumps. Between the regulator and
In a hydraulic circuit provided with work attachment relief valves whose pressures are set lower than the relief setting pressure of the travel relief valve, the first and second work attachment relief valves are provided on the downstream side of the work attachment relief valve and the first relief valve. A pilot switching valve for tank communication is provided between each regulator for the second pump, and the pilot pressure receiving part of the pilot switching valve is communicated with the pilot pressure receiving part of the straight travel valve.

In conventional hydraulic circuits, when the left and right travel motors and other actuators are operated simultaneously, for example, when a hydraulic excavator operates one of the work attachments while it is running, the relief valve for the work attachment is activated due to the load on that work attachment. When it is relieved, it becomes a negative contrast cutoff command, which acts on the regulator of the second pump and reduces the amount of oil discharged from the second pump.

For this reason, for example, when a hydraulic excavator climbs a slope or escapes from muddy ground, if the work attachment is used to relieve the relief valve for the work attachment, the amount of pump discharged oil will decrease. The operating speed and travel speed were reduced, making the above operations difficult.

However, in the present invention, when the hydraulic excavator climbs up a slope or escapes from muddy ground, the pump discharge amount does not decrease even if the work attachment is used to relieve the work attachment relief valve.

The work attachment can operate reliably and improve work efficiency without reducing the operating speed and traveling speed of the work attachment.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are hydraulic circuit diagrams of the present invention, and FIG. 3 is a hydraulic circuit diagram of the prior art. 1 L, 1 a --------One left and right travel motor 3.4.5-□Hydraulic cylinder 6 -11□First pump 7.9-=----Regulator 8 -One Second pump 16------straight travel valve 18--1 open/close valve 21t, 21 R-1--1 work attachment relief valve 22L, 22R--foot relief valve 44L, 44R--pilot switching valve and above

Claims (1)

[Claims] The various hydraulic actuators installed in the hydraulic excavator are divided into two groups A and B, and left and right travel valves are provided in the front row of each group, and all other actuator switching valves are arranged in parallel, and groups A, A foot relief valve and a throttle part are connected in parallel to the outlet sides of the center bypass oil passages passing through the switching valves in B, and the upstream sides thereof are connected to the regulators of the first and second pumps, respectively, and the downstream sides thereof are connected in parallel. A straight travel valve is provided in the oil passages communicating with the oil tank and on the discharge side of the first and second pumps, and an on-off valve is provided in parallel with the left travel motor in the oil passage communicating with the left travel motor and the left travel valve. When the left and right travel motors are stopped, the pilot oil passage from the remote control valve is shut off, and when the left and right travel motors are activated, the pilot oil passage is opened, and the pilot pressure for the remote control from the pilot pump is transferred to the straight travel valve. When the left and right travel valves are both neutral or only the left and right travel valves are in the simultaneous operation position, the oil passage from the first pump is shut off and the second pump is operated.
Open the oil passage from the pump, and in the second case where the left/right travel valve and any other actuator switching valve are in an operating position other than the neutral position, open the oil passage from the first and second pumps in parallel. In addition, relief valves for work attachments are interposed between the pressure oil supply side oil passages of the switching valves for work attachments in groups A and B and each regulator for the first and second pumps. In the hydraulic circuit, a pilot switching valve for tank communication is provided between the downstream side of the work attachment relief valve and each regulator for the first and second pumps, and a pilot pressure receiving part of the pilot switching valve and a pilot pressure receiving part of the pilot switching valve are provided. A hydraulic circuit for a hydraulic excavator, characterized in that the hydraulic circuit is configured to communicate with a pilot pressure receiving section of the straight travel valve.