Hydraulic circuit for construction machinery having floating function and method for controlling floating function

A method for controlling a floating function for a construction machine including at least two hydraulic pumps, a hydraulic cylinder driven by hydraulic fluids supplied from the hydraulic pumps, a boom driving control valve installed in a flow path between any one of the hydraulic pumps and the hydraulic cylinder, a boom confluence control valve installed in a flow path between another of the hydraulic pumps and the hydraulic cylinder, a manipulation lever (RCV), a first pressure sensor configured to measure a pressure of the hydraulic fluid on a large chamber of the hydraulic cylinder, a second pressure sensor configured to measure a boom-down pilot pressure that is applied to an end of the boom driving control valve, and a control valve installed in a flow path between the manipulation lever and the boom driving control valve, and installed in another flow path between the manipulation lever the boom confluence control valve, the method comprising:

• a step of determining whether a boom floating function switch is operated to be turned on;
• a step of, if the boom floating function switch is operated to be turned on, shifting the control valve to an on state in response to the application of an electrical signal to the control valve to cause the boom confluence control valve to be shifted to a floating state through application of the boom-down pilot pressure to the boom confluence control valve;
• a step of measuring the hydraulic fluid pressure of the large chamber of the hydraulic cylinder through the first pressure sensor, and measuring the boom-down pilot pressure that is applied to the end of the boom driving control valve through the second pressure sensor;
• and
• a step of shifting the control valve to an off state if the boom-down pilot pressure is higher than or equal to a predetermined pressure based on a detection signal of the second pressure sensor, and the hydraulic fluid pressure of the large chamber of the hydraulic cylinder is lower than or equal to another predetermined pressure based on a detection signal of the first pressure sensor.

A hydraulic circuit for a construction machine having a floating function, comprising:

• at least two hydraulic pumps;
• a hydraulic cylinder driven by hydraulic fluids supplied from the hydraulic pumps;
• a boom driving control valve installed in a flow path between any one of the hydraulic pumps and the hydraulic cylinder and configured to be shifted to control a start, a stop, and a direction change of the hydraulic cylinder;
• a boom confluence control valve installed in a flow path between another of the hydraulic pumps and the hydraulic cylinder and configured to be shifted to allow the hydraulic fluids discharged from the hydraulic pumps to join together so as to be supplied to a large chamber of the hydraulic cylinder or to allow hydraulic fluids of the large chamber and a small chamber of the hydraulic cylinder to join together so as to be supplied to a hydraulic tank;
• a manipulation lever (RCV) configured to output a manipulation signal corresponding to a manipulation amount;
• a first pressure sensor configured to measure a pressure of the hydraulic fluid on the large chamber of the hydraulic cylinder;
• a second pressure sensor configured to measure a boom-down pilot pressure that is applied to an end of the boom driving control valve;
• a first electronic proportional control valve installed in a flow path between the manipulation lever and the boom confluence control valve and configured to shift the boom confluence control valve to a floating mode by generating the boom-down pilot pressure in proportion to an electrical signal applied thereto and applying the generated boom-down pilot pressure to the boom confluence control valve;
• a second electronic proportional control valve installed in a flow path between the manipulation lever and the boom driving control valve and configured to supply the hydraulic fluid of the one of the hydraulic pumps to the small chamber of the hydraulic cylinder by generating the boom-down pilot pressure in proportion to the electrical signal applied thereto and applying the generated boom-down pilot pressure to the boom driving control valve;
• and
• a controller configured to receive an input of the pressure values detected by the first and second pressure sensors, calculate the electrical signal corresponding to the pressure value detected by the second pressure sensor, and apply the calculated electrical signal to the first and second electronic proportional control valves.

A method for controlling a floating function for a construction machine including at least two hydraulic pumps, a hydraulic cylinder driven by hydraulic fluids supplied from the hydraulic pumps, a boom driving control valve installed in a flow path between any one of the hydraulic pumps and the hydraulic cylinder, a boom confluence control valve installed in a flow path between another of the hydraulic pumps and the hydraulic cylinder, a manipulation lever (RCV), a first pressure sensor configured to measure a pressure of the hydraulic fluid on a large chamber of the hydraulic cylinder, a second pressure sensor configured to measure a boom-down pilot pressure that is applied to the boom driving control valve, a first electronic proportional control valve installed in a flow path between the manipulation lever and the boom confluence control valve, and a second electronic proportional control valve installed in a flow path between the manipulation lever and the boom driving control valve, the method comprising:

• a step of determining whether a boom floating function switch is operated to be turned on;
• a step of measuring the hydraulic fluid pressure of the large chamber of the hydraulic cylinder through the first pressure sensor, and measuring the boom-down pilot pressure that is applied to the boom driving control valve through the second pressure sensor;
• a step of supplying the hydraulic fluid of the one of the hydraulic pumps to a small chamber of the hydraulic cylinder by applying the boom-down pilot pressure, which is generated in proportion to an electrical signal corresponding to a pressure detection value of the second pressure sensor, to the boom driving control valve if the boom-down pilot pressure is higher than or equal to another predetermined pressure based on a detection signal of the second pressure sensor, and the hydraulic fluid pressure of the large chamber of the hydraulic cylinder is lower than or equal to a predetermined pressure based on a detection signal of the first pressure sensor;
• and
• a step of shifting the boom confluence control valve to a floating mode by applying the boom-down pilot pressure, which is generated in proportion to the electrical signal corresponding to the pressure detection value of the second pressure sensor, to the boom confluence control valve if the boom-down pilot pressure is lower than the predetermined pressure based on the detection signal of the second pressure sensor, and the hydraulic fluid pressure of the large chamber of the hydraulic cylinder is higher than the other predetermined pressure based on the detection signal of the first pressure sensor.