Patent ID: 7380489

Claim:
A hydraulic circuit for an option device of heavy construction equipment, comprising: a variable displacement hydraulic pump; an option device connected to the hydraulic pump; a first spool, installed in a flow path between the hydraulic pump and the option device, for being shifted in response to a pilot signal pressure applied from an outside to control a flow rate applied from the hydraulic pump to the option device; a poppet, operatively installed in a flow path between the hydraulic pump and the first spool, for supplying hydraulic fluid from the hydraulic pump to the option device when the first spool is shifted, and a piston resiliently urged in a back pressure chamber of the poppet; a second spool for being shifted by a pressure difference between pressures of the hydraulic fluid before and after the hydraulic fluid passes through the first spool, and controlling the flow rate applied from the hydraulic pump to the back pressure chamber of the poppet via a through-path communicating with the back pressure chamber when the second spool is shifted; a first orifice, formed on the piston, for controlling the hydraulic fluid discharged from the hydraulic pump and supplied to the back pressure chamber of the poppet when the second spool is shifted; a second orifice, installed in a flow path between the second spool and the back pressure chamber of the piston, for controlling the hydraulic fluid supplied from the hydraulic pump to the back pressure chamber of the piston when the second spool is shifted; and a third orifice, having an inlet that communicates with a flow path between the first spool and the poppet and an outlet installed in a path that communicates with the second spool, for controlling the hydraulic fluid that is discharged from the hydraulic pump and shifts the second spool, wherein if the hydraulic fluid is supplied from the hydraulic pump to the option device, a pressure loss produced between signal pressures that shift the second spool is maintained constant by a repeated shifting of the second spool to control the hydraulic fluid to be constantly supplied to the option device.