Patent ID: 9657461
Date: 2017-05-23
CPC Classifications: E02F,F15B

Claim:
1. A hydraulic circuit for a construction machine including a center bypass passage, into which a pressurized oil discharged from a hydraulic pump is supplied, the hydraulic circuit comprising: a directional control valve group including a plurality of directional control valves arranged in tandem with the center bypass passage; and a bleed-off valve arranged in the center bypass passage on a downstream side of the directional control valve group, wherein each directional control valve includes a first internal passage for causing the pressurized oil supplied to the directional control valve to flow out to the center bypass passage and a second internal passage for supplying the pressurized oil to a cylinder port, wherein a parallel passage is formed by the center bypass passage and the first internal passage by causing, by the first internal passage, the pressurized oil discharged from the hydraulic pump to flow out to the center bypass passage on the downstream side of the directional control valve, wherein the second internal passage supplies the pressurized oil along at least one flow path among a flow path from the center bypass passage through a spool opening to the cylinder port and a flow path from the center bypass passage through a bypass passage to the cylinder port, wherein a bypass switching valve is arranged in the bypass passage, and wherein the bypass switching valve controls a flow rate of the pressurized oil supplied to the cylinder port through the bypass passage by changing an opening area of the bypass switching valve.