JPS6131082Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a hydraulic circuit for turning of a construction machine such as a hydraulic shovel, and more particularly to a hydraulic circuit for turning equipped with a low pressure selection valve.

FIG. 1 is a circuit diagram showing an example of a conventional swing hydraulic circuit for construction machinery. In the figure, 1 is a hydraulic pump, 2 is a swing motor that is operated by the pressure oil of this hydraulic pump 1 and drives an object with large inertia such as a rotating body, and 3 is an inlet side flow that leads pressure oil to the swing motor 2, for example. A passage 4 is an outlet side flow passage that guides oil discharged from the swing motor 2. Reference numerals 5 and 6 are cross relief valves interposed between the flow paths 3 and 4, respectively, which are operated by absolute pressure. 7 is a low pressure selection valve which is interposed between the flow path 3 and the flow path 4 in the same manner as the relief valve 5.6, and is appropriately switched depending on the pressure of the pressure oil flowing through the flow path 3 or the flow path 4. Channel 3
A portion of the hydraulic oil on the low-pressure side of the flow path 4 is caused to flow out into the tank 8. This low pressure selection valve 7 is provided to prevent abnormal pressure from occurring in the flow path 3 or 4 due to thermal expansion of the hydraulic oil that occurs when the swing motor 2 is braked. Note that this low pressure selection valve 7 is configured to close the outflow of hydraulic oil at the neutral position. 9 is a directional control valve that controls the operation of a predetermined actuator; 10 is a swing motor 2;
These directional control valves 9 and 10 are connected via a parallel circuit 11. 12 is a center bypass circuit, 13 is a check valve, and 14 is a main relief valve. The set pressure of the main relief valve 14 is set higher than the set pressure of the cross relief valves 5 and 6.

However, the conventional hydraulic circuit configured as described above has the following problems. Now, suppose that the directional control valve 9 is operated in order to operate a predetermined actuator, and the load on the directional control valve 9 is large, so that the main relief valve 14 is operated and main relief pressure is generated in the parallel circuit 11. Let us consider a case where the user attempts to operate the directional control valve 10 in order to stop the swing motor 2 that was operating until then. At this time, main relief pressure is generated in the parallel circuit 11, so
Main relief pressure is trapped in the flow paths 3 and 4. In this case, since the cross relief valves 5 and 6 operate with absolute pressure, they are always open, making it impossible to maintain brake pressure. If the low pressure selection valve 7 operates at this time, brake pressure can be obtained, but
If the main relief pressure is trapped between the flow paths 3 and 4 as currently assumed, both the cross relief valves 5 and 6 will be in the open state as described above, and the flow paths 3 and 4 will be in an electrically conductive state. Therefore, the flow path 3,
4 is very small, and as a result, the low pressure selection valve 7 may not operate. If this low pressure selection valve 7 does not operate, a situation arises in which the swing motor 2 does not stop.

The present invention was developed in view of the problems in the prior art, and its purpose is to reduce the main relief pressure in the inlet and outlet channels through a low pressure selection valve when main relief pressure is generated in the inlet and outlet channels. An object of the present invention is to provide a hydraulic circuit for turning a construction machine that can drain hydraulic oil from an outlet side flow path.

Hereinafter, the hydraulic circuit of the present invention will be explained based on the drawings. FIG. 2 is a circuit diagram showing a first embodiment of a hydraulic circuit for swinging a construction machine according to the present invention, and FIG. 3 is a circuit diagram showing a main part of a second embodiment of the present invention. In these FIGS. 2 and 3, the same members as those shown in FIG. 1 are designated by the same reference numerals. In the embodiment shown in FIG. 2, the inlet side flow path 3 and the outlet side flow path 4
Similarly to the conventional low pressure selection valve 7 shown in FIG. 1, the low pressure selection valve 15 interposed between the It has a function of draining a part of the hydraulic oil on the low pressure side of the passage 3 and the passage 4, and the neutral position part is connected to the inlet side passage 3 and the outlet side passage 4.
It is designed to allow for the outflow of hydraulic oil. 1
6 is a shuttle valve connected to this low pressure selection valve 15;
17 is a relief valve interposed between the shuttle valve 16 and the tank 8. Note that the set pressure of the relief valve 17 is set to be higher than the operating pressure of the low pressure selection valve 15. The reason for this is that if oil leaks from the relief valve 17 before the low pressure selection valve 15 is switched, brake pressure cannot be generated when a slight load is applied to the swing motor 2. The rest of the configuration is similar to the conventional circuit shown in FIG.

In the hydraulic circuit of the present invention configured in this manner, the directional control valve 9 is operated to operate a predetermined actuator as described above, and the main relief pressure is applied to the swing system, that is, the flow paths 3 and 4. Flow path 3 and flow path 4 that form equal pressure even if
The neutral position portion of the low pressure selection valve 15, the shuttle valve 16,
It can flow out into the tank 8 via the relief valve 17.

The second embodiment shown in FIG.
The basic structure including the first embodiment is the same as that of the first embodiment shown in FIG. 2, but the difference is that two relief valves 18 and 19 are used instead of the shuttle valve 16 and relief valve 17 in the first embodiment. This is what we have set up. The set pressures of these relief valves 18 and 19 are as follows:
The pressure is set higher than the operating pressure of the low pressure selection valve 15. The hydraulic circuit configured in this manner also provides the same effects as the first embodiment.

As described above, in the swing hydraulic circuit for construction machinery of the present invention, the neutral position portion of the low pressure selection valve is formed so that the hydraulic oil in the inlet side flow path and the outlet side flow path can flow out, and the low pressure A relief valve is provided next to the selection valve, and the set pressure of this relief valve is set higher than the operating pressure of the low pressure selection valve, so the main flow path is connected to the inlet side flow path and the outlet side flow path of the swing motor. Even when relief pressure is present, the hydraulic fluid in the inlet and outlet channels can be drained out through the low pressure selection valve, and therefore the swing motor can be operated while other actuators are operating. Even when the rotary motor is stopped, the main relief pressure is not trapped in the inlet-side flow path and the outlet-side flow path, and unlike the conventional art, this swing motor can be stopped reliably.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional hydraulic circuit for swinging a construction machine, FIG. 2 is a circuit diagram showing a first embodiment of the hydraulic circuit for swinging a construction machine of the present invention, and FIG.
The figure is a main circuit diagram showing a second embodiment of the present invention. 2...Swivel motor, 3...Inlet side flow path, 4...
Outlet side flow path, 15...Low pressure selection valve, 16...Shuttle valve, 17, 18, 19...Relief valve.

Claims (1)

[Scope of utility model registration request] It is interposed between a swing motor that drives the swing body and an inlet side flow path and an outlet side flow path of this swing motor, and supplies a part of the hydraulic oil on the low pressure side of the inlet side flow path and the outlet side flow path. In a turning hydraulic circuit for a construction machine equipped with a low-pressure selection valve for flowing out, a neutral position portion of the low-pressure selection valve is formed to allow hydraulic oil in an inlet side flow path and an outlet side flow path to flow out, A hydraulic circuit for turning a construction machine, characterized in that a relief valve is provided in series with the low pressure selection valve, and the set pressure of the relief valve is set to be higher than the operating pressure of the low pressure selection valve.