Straight traveling hydraulic circuit

#This application is based on and claims priority from Korean Patent Application No. 10-2006-82262, filed on Aug. 29, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

#1. Field of the Invention

#The present invention relates to a straight traveling hydraulic circuit which can prevent a declination of equipment when traveling devices and working devices are simultaneously driven.

#The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a circuit diagram of a conventional straight traveling hydraulic circuit;

#FIG. 2 is a circuit diagram of a straight traveling hydraulic circuit according to an embodiment of the present invention;

#Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and thus the present invention is not limited thereto.

#As shown in FIGS. 2 to 7, the straight traveling hydraulic circuit according to an embodiment of the present invention includes first and second variable hydraulic pumps 15 and 18; a left traveling motor 2 and a first working device such as an arm (not illustrated) and so on, connected to the first hydraulic pump 15; a plurality of switching valves 12 and 26 installed in a flow path 1 of the first hydraulic pump 15, and shifted to control hydraulic fluid fed to the left traveling motor 2 and the first working device, respectively, in response to pilot signal pressures a1 and b1 being applied thereto; a right traveling motor 3 and a second working device such as a boom and so on, connected to the second hydraulic pump 18; a plurality of switching valves 11 and 28 installed in a flow path 9 of the second hydraulic pump 18, and shifted to control the hydraulic fluid fed to the right traveling motor 3 and the second working device, respectively, in response to pilot signal pressures a2 and b2 being applied thereto; a straight traveling valve 4 installed in the flow path 9 of the second hydraulic pump 18, and shifted to supply the hydraulic fluid fed from the first hydraulic pump 15 to the left traveling motor 2 and the right traveling motor 3 and to supply the hydraulic fluid fed from the second hydraulic pump 18 to the first working device and the second working device, respectively, in response to a pilot signal pressure a3 being applied thereto; and a control valve 31 installed in a branch flow path 7-1, which is branched from the flow path 9 of the second hydraulic pump 18 and connects an inlet part with an outlet part of the straight traveling valve, and shifted, when a combined operation in which the traveling and working devices are simultaneously driven is performed, to intercept a supply of the hydraulic fluid from the second hydraulic pump 18 to the left traveling motor 2 and the right traveling motor 3 via the straight traveling valve 4.

#In an embodiment of the present invention, the control valve 31 includes a main valve 31a composed of a poppet 47 having a flow path connected to a flow path on an inlet side of the traveling switching valve 11 and opening/closing the branch flow path, a piston 38 pressing the poppet 47 to block the branch flow path 7-1 when a signal pressure is applied from an outside, and an elastic member 46 (e.g., compression coil spring) elastically supported between the poppet 47 and the piston 38 and elastically biasing the pilot poppet 47, which has been pressed to block the branch flow path 7-1, to its initial state; and an auxiliary valve 31b composed of a spool 42 shifted to supply the hydraulic fluid on the inlet side of the straight traveling valve 4 to the piston 38 as a signal pressure, in response to a pilot signal pressure a4 being supplied thereto, and a valve spring 33 elastically biasing the spool 42, which has intercepted the supply of the hydraulic fluid on the inlet side of the straight traveling valve 4 to the piston 38 as the signal pressure, to its initial state.