Patent ID: 8387289
Filing Date: 2013-03-05
Classification: E02F,F15B,Y10T

Abstract:
1. A hydraulic circuit system for a hydraulic excavator, which includes a hydraulic circuit for an attachment which allows at least a hydraulic breaker and a crusher to be attached as a front attachment for the hydraulic excavator, the hydraulic breaker crushing a rock and the like and the crusher being used for a disassembling operation, the system comprising: a directional control valve that supplies and discharges a hydraulic fluid to and from an attachment connected to the hydraulic circuit for an attachment; a first over-load relief valve unit including a check valve and a variable relief valve, the first over-load relief valve unit provided in the one of lines of the hydraulic circuit for an attachment; a second over-load relief valve unit including a check valve and a variable relief valve, the second over-load relief valve unit provided in the other of the lines of the hydraulic circuit for an attachment; a breaker relief valve and a breaker relief stop valve that are provided between the one of the lines of the hydraulic circuit for an attachment and the other of the lines of the hydraulic circuit for an attachment; a first proportional solenoid valve that is connected to the relief valve included in the first over-load relief valve unit and the breaker relief valve, the first proportional solenoid valve for controlling set pressure of the relief valve included in the first over-load relief valve unit and set pressure of the breaker relief valve; a second proportional solenoid valve that controls set pressure of the relief valve included in the second over-load relief valve unit; and a solenoid valve that opens and closes the breaker relief stop valve.