CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/KR2018/010094 filed on Aug. 30, 2018, the disclosure and content of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a hydraulic circuit for construction equipment, and more specifically, to a hydraulic circuit for construction equipment capable of increasing energy efficiency by regenerating or recovering return-oil when a boom is lowered.

BACKGROUND ART

Generally, construction equipment generates power using hydraulic pressure.

A working unit of the construction equipment excavates soil or rock or allows the excavated soil or rock to be loaded.

A hydraulic pump is provided to use hydraulic pressure and supplies hydraulic oil to an actuator, which drives the working unit, by pumping oil stored in an oil tank.

In this case, an engine has to be operated in order to operate the hydraulic pump, and fuel has to be consumed in order to operate the engine.

FIG. 1schematically illustrates a hydraulic circuit of construction equipment according to a conventional art, and as shown inFIG. 1, a main pump2is operated using power generated by an engine1to generate hydraulic pressure. Hydraulic pressure of the main pump2is supplied to a main control valve3and is selectively supplied to a large chamber4aor a small chamber4bof a boom cylinder4by a hydraulic control of the main control valve3.

The hydraulic pressure of the main pump2is supplied to the main control valve3and is selectively supplied to a large chamber4aor a small chamber4bof a boom cylinder4by a hydraulic control of the main control valve3.

In this case, as one method of reducing fuel consumption of construction equipment, when a spool control is performed on the main control valve3so that the large chamber4aand the small chamber4bcommunicate with each other when a boom is lowered, the hydraulic oil discharged from the large chamber4ais supplied to the small chamber4bthrough the main control valve3, and thus an energy regeneration function is performed.

In order to decrease fuel consumption of the construction equipment and increase fuel efficiency of construction equipment, an energy generation technology is used.

Further, construction equipment may require a boom floating function.

The boom floating function refers to a function that allows an attachment to be moved vertically along a curved surface of ground due to a weight of a boom even when an operator lowers the boom.

That is, even when an arm moves forward and backward and a boom moves downward, the attachment moves along the curved surface without damaging the curved surface of the ground due to the boom floating function.

Therefore, when the operator changes a mode to a floating mode according to the type of works, the work may stop in a state in which working oil is not supplied from the hydraulic pump, and when in a general excavation mode, the floating mode is canceled, the working oil is supplied from the hydraulic pump, and the work starts. When the work stops in the floating mode, the working oil of the hydraulic pump is not used, and thus efficiency and productivity of work can be increased.

Therefore,FIG. 2schematically illustrates a configuration in which a float valve is added to a hydraulic circuit of construction equipment according to a conventional art, as shown inFIG. 2. In the case of the construction equipment that requires the above-described floating function, a float valve5is disposed between a main control valve3and a boom cylinder4.

In this case, when a float valve5is controlled to be opened, a state in which a large chamber4aand a small chamber4bof the boom cylinder4directly communicate with each other is maintained, and thus a floating mode is performed.

However, it is necessary for the float valve to be installed in the construction equipment that additionally requires the floating function, and a passage for supplying and controlling hydraulic oil is additionally installed in the float valve, and thus a configuration of the construction equipment becomes complicated, and the volume of the construction equipment is increased.

DISCLOSURE OF INVENTION

Technical Problem

The present invention is directed to providing a hydraulic circuit of construction equipment capable of increasing energy efficiency by regenerating and recovering return-oil when a boom of the construction equipment is lowered and simplifying a configuration thereof.

Solution to Problem

One aspect of the present invention provides a hydraulic circuit of construction equipment including a boom cylinder for controlling up and down operation of a boom, which includes a valve unit having a first control valve configured to control a large chamber of the boom cylinder to selectively communicate with a small chamber of the boom cylinder, a second control valve configured to control the large chamber to selectively communicate with an oil tank, a third control valve configured to control the large chamber to selectively communicate with an accumulator, and a fourth control valve configured to control a part of hydraulic oil flowing to the accumulator to selectively flow to an assist motor.

The hydraulic circuit may further include a first oil line configured to connect the large chamber with the first control valve.

The hydraulic circuit may further include a second oil line configured to connect the first control valve with the small chamber of the boom cylinder.

The hydraulic circuit may further include a third oil line configured to connect the second control valve with an oil tank.

The hydraulic circuit may further include a fourth oil line configured to connect the accumulator with the third control valve.

The hydraulic circuit may further include a fifth oil line configured to connect the fourth control valve with the assist motor.

The hydraulic circuit may further include a float valve disposed between the first oil line and the second oil line to be connected with the first oil line and the second oil line in parallel.

Each of the first to third control valves may be a poppet valve.

Each of the first to third control valves may be a spool valve.

The hydraulic circuit may further include a holding valve disposed in the valve unit and connected with the large chamber of the boom cylinder at an upper stream of a path through which the first to third control valves are connected.

The hydraulic circuit may further include a main control valve interposed between the first oil line and the second oil line.

The hydraulic circuit may further include a main pump for supplying hydraulic oil to the main control valve.

The main pump may be connected with a power take-off (PTO) to receive power.

The assist motor may be connected with the PTO so that power received from the accumulator may be supplied to the PTO.

Advantageous Effects of Invention

According to an embodiment of the present invention, return-oil generated when a boom of construction equipment is lowered is recovered or regenerated, and thus energy efficiency can be increased.

Further, when the construction equipment requires a floating function, a float valve is disposed in a valve unit, and thus a configuration of the construction equipment can be simplified.

It should be understood that effects of the present invention are not limited to the aforementioned effects, and include all of the effects deducible from the detailed description of the present invention or the configuration of the invention described in the claims.

