JP3989640B2 - Return circuit of hydraulic circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a return oil circuit of a hydraulic circuit in a hydraulic work machine such as a hydraulic excavator or a hydraulic crane.
[0002]
[Prior art]
In a hydraulic circuit of a work machine, a back pressure valve that applies a constant back pressure to the return oil circuit may be provided to prevent cavitation.
[0003]
The prior art relating to the return oil circuit with the back pressure valve will be explained with reference to FIG. 3.
[0004]
In the figure, reference numeral 1 denotes a control valve that controls the operation of a hydraulic actuator such as a hydraulic motor (not shown). A return oil pipe 2 is provided between a tank port 1a and a tank T of the control valve 1, and this return oil pipe 2, spring-loaded check valve as back pressure valve to flow of oil as shown in Figure 3 solid arrows b open at a predetermined pressure (hereinafter, boost referred check valve) is provided 3.
[0005]
In the circuit shown in the figure, as a circuit configuration frequently used in work machines, an oil cooler 4 for cooling the return oil is provided in the return oil pipeline 2, and a bypass line 5 is provided in parallel with the oil cooler 4. It has been.
[0006]
The bypass line 5 is provided with a spring-loaded check valve (hereinafter referred to as a bypass check valve) 6 as a bypass valve that opens at a pressure higher than that of the boost check valve 3, and a high pressure in the vicinity of the pressure resistance of the oil cooler 4 acts. Occasionally, by bypassing the return oil as shown in FIG. 3 dashed arrows b the bypass check valve 6 is opened, and is configured to protect the oil cooler 4.
[0007]
[Problems to be solved by the invention]
However, according to this conventional circuit configuration, a problem that a surge pressure is generated downstream of the check valve when the check valve 3 is opened and closed occurs as a disadvantage of providing the boost check valve 3.
[0008]
That is, when the boost check valve 3 opens the return oil is the check valve 3 to have a state where the flow close, at the downstream side of the check valve 3 in Rukoto be about to flow in a downstream direction in oil inertia in the conduit A liquid column separation phenomenon in which a cavity is generated in the vicinity of the check valve downstream side occurs.
[0009]
Immediately after this, the cavity collapses, and a surge pressure is generated in the downstream portion of the check valve.
[0010]
This phenomenon also occurs when the bypass check valve 6 is opened or closed.
[0011]
Here, the surge pressure increases as the inertia of the oil in the pipe downstream of the check valves 3 and 6 increases.
[0012]
In this case, in the conventional circuit, the positions of both check valves 3 and 6 are provided from the viewpoint of providing both check valves 3 and 6 using the coupling at the pipe branching point 7 portion close to the control valve 1 as shown in the figure. Is close to the most upstream side of the return oil circuit, and the length of each downstream pipe is long and the inertia of the oil is large, so the surge pressure becomes high.
[0013]
For this reason, oil leakage from the coupling on the downstream side of the pipeline, abnormal noise in the check valves 3 and 6, premature sag, damage to the oil cooler 4, etc. are likely to occur due to surge pressure.
[0014]
Therefore, the present invention provides a return oil circuit of a hydraulic circuit that can suppress the generation of surge pressure and protect circuit elements.
[0015]
[Means for Solving the Problems]
The invention according to claim 1, the oil pipe back between the tank port and the tank control valve for controlling the operation of the hydraulic actuator is provided, the oil cooler on the upstream side of definitive to the return oil pipe, a constant pressure on the downstream side The hydraulic circuit is provided with a back pressure valve that is opened at the same time, a bypass line is provided in parallel with the oil cooler, and a bypass valve that is opened at a pressure higher than the set pressure of the back pressure valve is provided in the bypass line . In the return oil circuit, the back pressure valve and the bypass valve are directly attached to the tank at the most downstream position in a state where the inertia of the oil on the downstream side is almost zero .
[0016]
According to a second aspect of the present invention, in the configuration of the first aspect, the return oil pipe and the bypass line are provided between the control valve and the tank by pipes independent of each other .
[0017]
According to the above configuration, since the back pressure valve and the bypass valve are directly attached to the tank at the most downstream position of the pipeline in a state where the inertia of the oil on the downstream side is almost zero, no surge pressure itself is generated. .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The embodiments of the present invention is described with reference, 2.
[0019]
First embodiment (see FIGS. 1 and 2)
Between the tank port 11a of the control valve 11 and the tank T, a return oil pipe 12 and a bypass line 13 are provided by pipes independent of each other.
[0020]
The return oil pipe 12 includes 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 (hereinafter, in accordance with the description of the prior art). 15 (referred to as a boost check valve).
[0021]
On the other hand, the bypass line 13 is provided with a spring-loaded check valve (also referred to as a bypass check valve) 16 as a bypass valve that opens at a pressure higher than the boost check valve 15 (pressure in the vicinity of the pressure resistance of the oil cooler 14). .
[0022]
Both the boost and bypass check valves 15 and 16 are directly connected (directly attached) to the tank T, that is, when the entire length of the return oil and bypass pipes 12 and 13 is divided into the upstream side and the downstream side. The downstream portion, which is also provided at the most downstream position.
[0023]
FIG. 2 shows a state in which both the 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. Reference numeral 18 denotes an oil filter on the oil suction side.
[0024]
According to this circuit configuration, both the check valves 15 and 16 are directly attached to the tank T, and the inertia of the oil on the downstream side becomes almost zero, so that the surge pressure itself due to the opening and closing of both the check valves 15 and 16 does not occur.
[0025]
For this reason, it is possible to prevent occurrence of trouble due to surge pressure such as breakage of the oil cooler 14 and oil leakage from the coupling .
[0026]
And in time, as the back pressure valve and the bypass valve may be used a pilot-type check valve or a relief valve in place of the spring-loaded check valve 15, 16 mentioned in the above embodiment.
[0027]
【The invention's effect】
As described above, according to the present invention, the back pressure valve and the bypass valve are directly attached to the tank in a state where the inertia of each downstream oil is almost zero at the most downstream position of the pipe. Surge pressure itself does not occur when opening and closing.
[0028]
For this reason, BRIEF DESCRIPTION OF THE DRAWINGS in which it is possible to protect the circuit elements from surge pressure
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 the check valve is directly attached to the tank in the embodiment.
FIG. 3 is a circuit diagram of a conventional return oil circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Control valve 11a Control valve tank port 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)

Claims (2)

Oil line back between the tank port and the tank control valve for controlling the operation of the hydraulic actuator is provided, the oil cooler on the upstream side of definitive to the return oil pipe, the back pressure valve to open at a certain pressure on the downstream side, respectively In the return oil circuit of the hydraulic circuit , a bypass line is provided in parallel with the oil cooler, and a bypass valve that opens at a pressure higher than the set pressure of the back pressure valve is provided in the bypass line. A return oil circuit of a hydraulic circuit, wherein the pressure valve and the bypass valve are directly attached to the tank at the most downstream position in a state where the inertia of the oil on the downstream side is substantially zero . 2. The return oil circuit of the hydraulic circuit according to claim 1, wherein the return oil pipe and the bypass line are provided between the control valve and the tank by independent pipes .

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