Hydraulic system for construction machine
View Patent ↗The present disclosure relates to a hydraulic system for a construction machine, and more particularly, to a hydraulic system for a construction machine including a plurality of actuators, in which each of the actuators includes a pump/motor, is operated under a control of a corresponding pump/motor, and stores working oil in an accumulator or receives the working oil supplemented from the accumulator in accordance with a difference between a flow rate entering the actuator and a flow rate discharged from the actuator.
1. A hydraulic system for a construction machine, comprising:
a pump/motor configured to serve as both a hydraulic pump driven by an engine and discharging working oil and a motor generating rotational force by the working oil;
an actuator operated by receiving hydraulic pressure from the pump/motor and provided with first and second ports through which the hydraulic pressure flows in and out;
first and second hydraulic pressure lines configured to connect the pump/motor and the actuator;
an accumulator configured to store or discharge the working oil through the first and second hydraulic pressure lines and first and second bypass lines;
first and second check valve units provided on the first and second bypass lines respectively and configured to allow the working oil to move only to the first and second hydraulic pressure lines; and
a control valve unit, of which both pressure receiving portions are connected with the first and second hydraulic pressure lines, and switched so that a hydraulic pressure line having lower pressure between the first and second hydraulic pressure lines communicates with the accumulator,
wherein third and fourth bypass lines connecting the first and second hydraulic pressure lines and the accumulator are installed between the first and second hydraulic pressure lines and the accumulator, and
the hydraulic system further comprises relief valve units, which open and close the third and fourth bypass lines so that the hydraulic pressure is supplied to the accumulator when hydraulic pressure of the first and second hydraulic pressure lines is higher than set pressure, on the third and fourth bypass lines,
wherein the control valve unit comprises:
a valve block, in which a first valve flow path is formed so that a first valve port communicates with a second valve port, a second valve flow path is formed so that a third valve port communicates with a fourth valve port, a third valve flow path communicating with the accumulator is formed, a spool hole communicating with the first, second, and third valve flow paths is formed, and a check valve hole communicating with the first, second, and third valve flow paths is formed; and
a spool disposed in the spool hole, and configured to make lower hydraulic pressure between the first pressure of the first valve flow path and the second pressure of the second valve flow path communicate with the third valve flow path,
wherein first and second chambers are formed at both sides of the spool, and
a common groove is formed in an outer peripheral area of a center of the spool so that the first valve flow path communicates with the third valve flow path or the second valve flow path communicates with the third valve flow path, a first spool hydraulic pressure line is formed so that the first valve flow path communicates with the first chamber, a second spool hydraulic pressure line is formed so that the second valve flow path communicates with the second chamber, and first and second spool orifice hydraulic pressure lines are formed in the first and second spool hydraulic pressure lines, respectively, so that the first pressure and the second pressure compete with each other at both ends of the spool, and the spool moves to a lower pressure side,
wherein first and second orifice units are formed in the first and second spool orifice hydraulic pressure lines, respectively,
first and second orifice holes are formed in the first and second orifice units, respectively, and
response speed of the spool is determined by the first and second orifice holes, and
wherein the first and second orifice units are replaced with other orifice units having different sizes of internal diameters of the first and second orifice holes, so that the response speed of the spool is adjusted.
2. The hydraulic system of claim 1 , wherein the control valve unit comprises an internal flow path comprising a second position connecting the second hydraulic pressure line and the accumulator, a third position connecting the first hydraulic pressure line and the accumulator, and a first position blocking hydraulic pressure from flowing to any one side, and has a spool structure, in which a first pressure and a second pressure of the first and second hydraulic pressure lines are applied to both pressure receiving portions.
3. The hydraulic system of claim 2 , wherein when the first pressure and the second pressure are within a predetermined range, the spool of the control valve unit is maintained at the first position.
4. The hydraulic system of claim 1 , wherein when the first pressure is higher than the second pressure, the control valve unit is configured to be switched so that the second pressure line is connected with the accumulator, and the first pressure is applied to the actuator,
when the first pressure is lower than the second pressure, the control valve unit is configured to be switched so that the first pressure line is connected with the accumulator, and the second pressure is applied to the actuator, and
when the first pressure is the same as the second pressure, the control valve unit is configured to be switched so that the first and second pressure lines are blocked from the accumulator.
5. The hydraulic system of claim 1 , further comprising:
a first check valve unit provided in the first valve flow path and the check valve hole and opened when the first pressure is lower than a third pressure of the third valve flow path; and
a second check valve unit provided in the second valve flow path and the check valve hole and opened when the second pressure is lower than the third pressure.
6. The hydraulic system for a construction machine, comprising:
a pump/motor configured to serve as both a pump and a motor;
an actuator provided with a first port at a head side of a cylinder and a second port at a rod side of the cylinder;
an accumulator configured to store working oil;
a first hydraulic pressure line, through which the pump/motor and the first port are connected, and in which a first pressure is formed;
a second hydraulic pressure line, through which the pump/motor and the second port are connected, and in which a second pressure is formed;
first and second check valve units provided in first and second bypass lines connected with the first and second hydraulic pressure lines and the accumulator and configured to allow the working oil to move only to the first and second hydraulic pressure lines, respectively;
a plurality of relief valve units provided in third and fourth bypass lines connected with the first and second hydraulic pressure lines and the accumulator, and configured to maintain the first and second pressures to be the same as or lower than set pressure; and
a control valve unit, in which the first pressure and the second pressure are applied to both sides of a spool, configured to be switched so that higher pressure is blocked from the accumulator and lower pressure is connected with the accumulator when the higher pressure is formed in any one of the first and second pressures,
wherein the control valve unit comprises:
a valve block, in which a first valve flow path is formed so that a first valve port communicates with a second valve port, a second valve flow path is formed so that a third valve port communicates with a fourth valve port, a third valve flow path communicating with the accumulator is formed, a spool hole communicating with the first, second, and third valve flow paths is formed, and a check valve hole communicating with the first, second, and third valve flow paths is formed; and
a spool disposed in the spool hole, and configured to make lower hydraulic pressure between the first pressure of the first valve flow path and the second pressure of the second valve flow path communicate with the third valve flow path,
wherein first and second chambers are formed at both sides of the spool, and
a common groove is formed in an outer peripheral area of a center of the spool so that the first valve flow path communicates with the third valve flow path or the second valve flow path communicates with the third valve flow path, a first spool hydraulic pressure line is formed so that the first valve flow path communicates with the first chamber, a second spool hydraulic pressure line is formed so that the second valve flow path communicates with the second chamber, and first and second spool orifice hydraulic pressure lines are formed in the first and second spool hydraulic pressure lines, respectively, so that the first pressure and the second pressure compete with each other at both ends of the spool, and the spool moves to a lower pressure side,
wherein first and second orifice units are formed in the first and second spool orifice hydraulic pressure lines, respectively,
first and second orifice holes are formed in the first and second orifice units, respectively, and
response speed of the spool is determined by the first and second orifice holes, and
wherein the first and second orifice units are replaced with other orifice units having different sizes of internal diameters of the first and second orifice holes, so that the response speed of the spool is adjusted.
7. The hydraulic system of claim 6 , wherein the control valve unit comprises an internal flow path comprising a second position connecting the second hydraulic pressure line and the accumulator, a third position connecting the first hydraulic pressure line and the accumulator, and a first position blocking hydraulic pressure from flowing to any one side, and has a spool structure, in which a first pressure and a second pressure of the first and second hydraulic pressure lines are applied to both pressure receiving portions.
8. The hydraulic system of claim 7 , wherein when the first pressure and the second pressure are within a predetermined range, the spool of the control valve unit is maintained at the first position.
9. The hydraulic system of claim 6 , further comprising:
a first check valve unit provided in the first valve flow path and the check valve hole and opened when the first pressure is lower than a third pressure of the third valve flow path; and
a second check valve unit provided in the second valve flow path and the check valve hole and opened when the second pressure is lower than the third pressure.