Patent ID: 8424301

Claim:
A hydraulic flow sharing system for excavating and pipe laying work, comprising: first and second variable displacement hydraulic pumps and a pilot pump coupled to an engine; a left traveling motor and a boom cylinder coupled to the first hydraulic pump; control valves installed in a center bypass path of the first hydraulic pump, and shifted to control the flow direction and flow amount of hydraulic fluid being supplied to the left traveling motor and the boom cylinder; a right traveling motor, a swing motor, and a winch motor coupled to the second hydraulic pump; control valves installed in a center bypass path of the second hydraulic pump, and shifted to control the flow direction and flow amount of hydraulic fluid being supplied to the right traveling motor, the swing motor, and the winch motor; a straight traveling valve installed on an upstream side of the center bypass path of the first hydraulic pump, and shifted, in response to a signal pressure applied from an outside when a work mode for simultaneously driving the boom cylinder, the swing motor, the winch motor, and the left and right traveling motors is selected, to share and supply the hydraulic fluid fed from the first hydraulic pump to the control valve for the boom cylinder and the control valves for the swing motor and the winch motor, and to share and supply the hydraulic fluid fed from the second hydraulic pump to the control valves for the left and right traveling motors, respectively; an unloading valve open, in response to the signal pressure for shifting the straight traveling valve, to prevent the occurrence of overload in the center bypass paths of the first and second hydraulic pumps; a selection valve releasing an unloading function of the corresponding unloading valve when any one of the boom cylinder, the swing motor, the winch motor, and the left and right traveling motors is driven in a shift mode of the straight traveling valve; a first shuttle valve controlling an inclination angle of a swash plate of the second hydraulic pump in accordance with the pressure selected between the pilot signal pressure being applied to the selection valve and the pressure on a downstream side of the center bypass path of the second hydraulic pump; and a second shuttle valve controlling an inclination angle of a swash plate of the first hydraulic pump in accordance with the pressure selected between the pilot signal pressure being applied to the selection valve and the pressure on a downstream side of the center bypass path of the first hydraulic pump.