Patent ID: 8113233

Claim:
A hydraulic circuit of an option device for an excavator, comprising: a variable hydraulic pump; an option device connected to the hydraulic pump; a first spool installed in a first flow path between the hydraulic pump and the option device and shifted to control hydraulic fluid being supplied from the hydraulic pump to the option device in response to a first pilot signal pressure applied to the first spool; a poppet installed to open/close the first flow path between the hydraulic pump and the first spool and controlling hydraulic fluid fed from the hydraulic pump to the option device when the first spool is shifted, and a piston elastically supported in a back pressure chamber of the poppet; a second spool shiftable to control hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the poppet via a through flow path connected to the back pressure chamber of the poppet, in response to a difference between a pressure of an inlet part of the first spool and a sum of a pressure of an outlet part of the first spool and an elastic force of a valve spring; an option spool installed in a second flow path between the first spool and the option device and being shiftable to control hydraulic fluid fed to the option device via the first spool in response to second and third pilot signal pressures; a first orifice formed in the piston and controlling the hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the poppet when the second spool is shifted; a second orifice formed in the through flow path between the second spool and the back pressure chamber of the piston and controlling the hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the piston when the second spool is shifted; and a third orifice installed in a flow path having an inlet part connected to a flow path between the first spool and the poppet and an outlet part connected to the second spool, and controlling the hydraulic fluid fed from the hydraulic pump to shift the second spool; and a control means for controlling hydraulic fluid passing through an orifice of the poppet when the second spool is shifted and the piston is acted on by the hydraulic fluid fed from the hydraulic pump, through the shifting of the second spool such that during an initial control period of the option device, the flow rate of the hydraulic fluid fed from the back chamber of the poppet to the option device is prevented from being increased over a predetermined flow rate set by the control means, the control means including a shim placed on an inlet part of the orifice of the poppet and defining a hole formed in the center thereof to be connected to the orifice of the poppet, and an orifice check valve defining an orifice in the center thereof, installed inside the poppet, the flow rate of the hydraulic fluid passing through the orifice of the poppet and from the back chamber to the option device being reduced by the shim and the orifice check valve in the poppet.