JP2000186704A - Return oil circuit for hydraulic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of surge pressure and protect a circuit element by halving a return oil conduit between the tank port of a control valve and a tank into an upstream part and a downstream part, and providing a back pressure valve on the downstream part. SOLUTION: A return oil conduit 12 and a bypass line 13 are provided between the tank port 11a of a control valve 11 and a tank T by use of mutually independent pipes. The return oil conduit 12 is provided with an oil cooler 14 and a check valve with spring 14 as a back pressure valve opened at a fixed pressure, and the bypass line 13 is provided with a check valve with spring 16 as a bypass valve opened at a pressure higher than the check valve with spring 15. Both the check valves 15, 16 are directly connected to the tank T, or provided on the downstream part when the whole piping length part of the return oil and bypass lines 12, 13 is halved to the upstream and the downstream.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a return oil circuit of a hydraulic circuit in a hydraulic working machine such as a hydraulic shovel and a hydraulic crane.

[0002]

2. Description of the Related Art In a hydraulic circuit of a work machine, a back pressure valve for applying a constant back pressure to a return oil circuit to prevent cavitation may be provided.

A prior art related to this return oil circuit with a back pressure valve will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a control valve for controlling the operation of a hydraulic actuator such as a hydraulic motor (not shown).
a return oil pipeline 2 is provided between the oil tank 2 and the tank T, and a check valve with a spring as a back pressure valve that opens the return oil pipeline 2 at a constant pressure and allows oil to flow as shown by the solid arrow A in FIG. (Hereinafter referred to as a boost check valve) 3 is provided.

In the circuit shown in the figure, an oil cooler 4 for cooling return oil is provided in the return oil line 2 as a circuit configuration frequently used in work machines, and a bypass line is provided in parallel with the oil cooler 4. 5 are provided.

The bypass line 5 is provided with a spring check valve (hereinafter referred to as a bypass check valve) 6 serving as a bypass valve that opens at a higher pressure than the boost check valve 3. Is operated, the bypass check valve 6 is opened and the return oil is bypassed as shown by the dashed arrow B in FIG. 2 to protect the oil cooler 4.

[0007]

However, according to the conventional circuit configuration, the disadvantage of providing the boost check valve 3 is that a surge pressure is generated downstream of the check valve when the check valve 3 is opened and closed. Had occurred.

That is, if the check valve 3 is closed while the boost check valve 3 is open and return oil is flowing,
On the downstream side of the check valve 3, the oil in the pipeline tends to flow in the downstream direction by inertia, so that a liquid column separation phenomenon occurs in which a cavity is generated near the downstream side of the check valve.

Immediately after this, a surge pressure is generated in the downstream portion of the check valve due to collapse of the cavity.

[0010] This phenomenon also occurs when the bypass check valve 6 is opened and closed.

Here, the surge pressure is determined by the check valve 3,
It becomes larger as the inertia of the oil in the pipeline downstream of 6 becomes larger.

In this case, in the conventional circuit, the two check valves 3 and 6 are provided by using the coupling at the pipe branch point 7 near the control valve 1 as shown in the figure, and from the viewpoint of providing the two check valves 3 and 6, Since the position of 6 is near the most upstream side of the return oil circuit, the length of each downstream pipe is long and the inertia of the oil is large, the surge pressure becomes high.

[0013] Therefore, the surge pressure easily causes oil leakage from the coupling on the downstream side of the pipeline, generation of abnormal noise of the check valves 3 and 6, early setting, and damage of the oil cooler 4.

Accordingly, the present invention provides a return oil circuit of a hydraulic circuit capable of protecting circuit elements by suppressing generation of surge pressure.

[0015]

According to a first aspect of the present invention, a return oil pipe is provided between a tank and a tank port of a control valve for controlling the operation of a hydraulic actuator,
In a return oil circuit of a hydraulic circuit provided with a back pressure valve that opens at a constant pressure in the return oil line, the back pressure valve is a downstream portion when the return oil line is divided into an upstream portion and a downstream portion. It is provided in.

According to a second aspect of the present invention, in the first aspect, the back pressure valve is provided directly connected to the tank.

According to a third aspect of the present invention, in the configuration of the first or second aspect, an oil cooler is provided upstream of the back pressure valve in the return oil line.

According to a fourth aspect of the present invention, in the configuration of the third aspect, a bypass line is provided in parallel with the oil cooler, and a bypass valve that opens at a pressure higher than a set pressure of the back pressure valve is provided in the bypass line. It is a thing.

According to a fifth aspect of the present invention, in the configuration of the fourth aspect, the bypass valve divides a pipe connecting the control valve and the tank via the bypass valve into an upstream portion and a downstream portion. It is provided in.

According to a sixth aspect of the present invention, in the configuration of the fourth or fifth aspect, the return oil line and the bypass line are provided between the control valve and the tank by independent pipes.

According to a seventh aspect of the present invention, in any one of the fourth to sixth aspects, the bypass valve is provided directly connected to the tank.

According to the above configuration, since the back pressure valve is provided on the downstream side of the return oil pipeline, the inertia of the oil downstream of the valve is reduced, and the generation of surge pressure when opening and closing the back pressure valve is suppressed accordingly. . Further, the range of the pipeline affected by the surge pressure is reduced.

In particular, according to the structure of claim 2, since the back pressure valve is directly connected to the tank, the inertia of the oil downstream thereof becomes almost zero, and no surge pressure itself occurs.

The surge pressure generation suppressing action is as follows:
The structure of claim 3 works in a return oil circuit with an oil cooler, and the structures of claims 4 to 7 work in the most common return oil circuit having an oil cooler and a bypass line with a bypass valve, and therefore have high practical value. .

In this case, since the bypass valve is also provided on the downstream side according to the configuration of claim 5, generation of surge pressure due to opening and closing of the bypass valve is suppressed.

According to the sixth aspect of the present invention, since the return oil pipe and the bypass line are provided between the control valve and the tank by independent pipes, the back pressure valve and the bypass valve are located as close to the tank as possible. (Position on the downstream side).

In particular, since the bypass valve is provided directly connected to the tank, generation of surge pressure can be minimized.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

First Embodiment (Refer to FIGS. 1 and 2) A return oil pipe 12 and a bypass line 13 are provided between the tank port 11a of the control valve 11 and the tank T by independent pipes.

An oil cooler 14 for cooling the return oil and a check valve with a spring as a back pressure valve that opens at a constant pressure downstream of the oil cooler 14 are provided in the return oil line 12 (hereinafter, description of the prior art). (Referred to as a boost check valve) 15.

On the other hand, a check valve with a spring (also called a bypass check valve) 16 as a bypass valve that opens at a pressure higher than the boost check valve 15 (pressure near the pressure resistance of the oil cooler 14) is provided in the bypass line 13.
Is provided.

This boost and bypass double check valve 1
5, 16 are directly connected (directly attached) to the tank T, respectively.
In other words, a downstream portion where the entire length of the return oil and bypass lines 12, 13 is divided into an upstream side and a downstream side, which is also provided at the most downstream position.

FIG. 2 shows a state in which the two check valves 15 and 16 are directly attached to the tank T. In the figure, reference numeral 17 denotes an oil filter on the return oil side, and both check valves 15 and 16 are provided on the inlet side of the oil filter 17. 18
Denotes an oil filter on the oil suction side.

According to this circuit configuration, both check valves 1
5 and 16 are directly attached to the tank T, and the inertia of the oil downstream of the tank T is almost zero, so that the surge pressure itself due to the opening and closing of the check valves 15 and 16 does not occur.

For this reason, it is possible to prevent the occurrence of troubles due to surge pressure such as breakage of the oil cooler 14 and oil leakage from the coupling.

Second Embodiment (See FIG. 3) Only differences from the first embodiment will be described.

Due to problems at the actual machine level, such as the convenience of piping and piping space, both check valves 1 are used as in the first embodiment.
In some cases, 5 and 16 cannot be directly attached to tank T.
The embodiment deals with this case.

That is, in the second embodiment, the check valves 15 and 16 are not directly attached to the tank T, but are provided at positions downstream from the return oil pipe line 12 and the bypass line 13 and away from the tank T. I have.

Even in such a case, both check valves 15, 1
Compared with the conventional case where 6 is provided on the upstream side, the inertia of the oil on the downstream side is reduced and the generation of surge pressure when the check valve is opened / closed is suppressed accordingly, so that a corresponding effect is obtained.

In this case, the return oil pipe 12 and the bypass line 13 may be provided as independent pipes as in the first embodiment, or may be joined at the check valve outlet side as shown. .

As the back pressure valve and the bypass valve, the check valves with springs 15 and 1 described in the above embodiment are used.
Instead of 6, a pilot check valve or a relief valve may be used.

The present invention can also be applied to a return oil circuit without the oil cooler 14 and a return oil circuit without the oil cooler 14 and the bypass line 13 with the bypass valve.

[0043]

As described above, according to the present invention, since the back pressure valve is provided on the downstream side of the return oil pipeline, the inertia of the oil downstream of the valve is reduced, and the surge when opening and closing the back pressure valve is accordingly reduced. The generation of pressure is suppressed. Further, the range of the pipeline affected by the surge pressure is reduced.

In particular, according to the second aspect of the present invention, since the back pressure valve is directly connected to the tank, the inertia of the oil downstream thereof becomes substantially zero, and no surge pressure itself occurs.

Therefore, the circuit element can be protected from surge pressure. The function of suppressing the generation of surge pressure can be achieved in the return oil circuit with an oil cooler in the invention of claim 3 and in the invention of claims 4 to 7. The invention has a high practical value because it works in the most common return oil circuit including an oil cooler and a bypass line with a bypass valve.

In this case, according to the invention of claim 5, since the bypass valve is also provided on the downstream side, generation of surge pressure due to opening and closing of the bypass valve is suppressed.

According to the sixth aspect of the present invention, since the return oil pipe and the bypass line are provided between the control valve and the tank by independent pipes, the back pressure valve and the bypass valve are located as close to the tank as possible (the most (Position on the downstream side).

In particular, according to the invention of claim 7, since the bypass valve is provided directly connected to the tank, generation of surge pressure can be suppressed to a minimum.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a return oil circuit according to a first embodiment of the present invention.

FIG. 2 is a front view showing a state in which a check valve is directly attached to a tank in the embodiment.

FIG. 3 is a circuit diagram of a return oil circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional return oil circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Control valve 11a Tank port of control valve 12 Return oil line 13 Bypass line 14 Oil cooler 15 Check valve with spring as back pressure valve (boost check valve) 16 Check valve with spring as bypass valve (bypass check valve)

Continued on the front page (72) Inventor Keishin Okamura 3-12-4 Gion, Asaminami-ku, Hiroshima City Inside Aburaya Heavy Industries, Ltd. (72) Inventor Shigeaki Saito 3-12-4, Gion, Asaminami-ku, Hiroshima City In-house F term (reference) 2D003 AA01 BA07 BB03 CA09 DB02 3F204 AA01 AA09 BA02 BA05 CA05 CA07 FA07 FB20 GA01 3F333 AA02 AA08 AB13 FA08 FH08 3H089 AA01 BB08 BB11 BB26 BB30 CC08 DB03 DB33 DB46 DB49 DB08 DC01 DC02

Claims (7)

[Claims] 1. A hydraulic circuit comprising: a return oil pipe provided between a tank port of a control valve for controlling operation of a hydraulic actuator and a tank; and a back pressure valve provided at a constant pressure in the return oil pipe. A return oil circuit for a hydraulic circuit, wherein the back pressure valve is provided in a downstream portion when the return oil pipeline is divided into an upstream portion and a downstream portion. 2. The return oil circuit according to claim 1, wherein the back pressure valve is provided directly connected to the tank. 3. The return oil circuit of a hydraulic circuit according to claim 1, wherein an oil cooler is provided upstream of the back pressure valve in the return oil line. 4. The return oil circuit of a hydraulic circuit according to claim 3, wherein a bypass line is provided in parallel with the oil cooler, and a bypass valve that opens at a pressure higher than a set pressure of the back pressure valve is provided in the bypass line. A return oil circuit of a hydraulic circuit, characterized in that the return oil circuit is provided. 5. A bypass valve is provided in a downstream portion when a pipe connecting the control valve and the tank via the bypass valve is divided into an upstream portion and a downstream portion. Return oil circuit of the described hydraulic circuit. 6. The return oil circuit according to claim 4, wherein the return oil line and the bypass line are provided between the control valve and the tank by independent pipes. 7. The return oil circuit of a hydraulic circuit according to claim 4, wherein the bypass valve is provided directly connected to the tank.