Abstract: A hydraulic system of an excavator includes a work state determination unit and a valve control unit. When it is determined that a work state of working equipment is a heavy excavation state, the valve control unit controls a first boom operation valve, a first arm operation valve, a first bucket operation valve, a second boom operation valve, a second arm operation valve, and a second bucket operation valve such that passing of hydraulic oil from a first hydraulic pump to a boom cylinder is restricted, hydraulic oil is supplied from a second hydraulic pump to a boom cylinder, hydraulic oil is supplied from both the first hydraulic pump and the second hydraulic pump to an arm cylinder, and hydraulic oil is supplied from one or both of the first hydraulic pump and the second hydraulic pump to a bucket cylinder.

Abstract: A hydraulic system includes: an arm hydraulic cylinder; a first hydraulic pump and a second hydraulic pump; an arm first direction switching valve; an arm second direction switching valve; and a controller that controls an operation of the arm second direction switching valve when the arm hydraulic cylinder is extended and operated. Further, the arm first direction switching valve incorporates an arm regeneration passage capable of supplying oil when the arm hydraulic cylinder is extended and operated, and the controller monitors a pressure state of the arm hydraulic cylinder, and when determining that oil flow through the arm regeneration passage is possible, the controller blocks oil flow between the arm hydraulic cylinder and the arm second direction switching valve, and otherwise, the controller operates the arm second direction switching valve so that oil can be supplied from the second hydraulic pump to the bottom chamber.

Abstract: A hydraulic system includes: an arm hydraulic cylinder; a first hydraulic pump and a second hydraulic pump; an arm first direction switching valve; an arm second direction switching valve; and a controller that controls an operation of the arm second direction switching valve when the arm hydraulic cylinder is extended and operated. Further, the arm first direction switching valve incorporates an arm regeneration passage capable of supplying oil when the arm hydraulic cylinder is extended and operated, and the controller monitors a pressure state of the arm hydraulic cylinder, and when determining that oil flow through the arm regeneration passage is possible, the controller blocks oil flow between the arm hydraulic cylinder and the arm second direction switching valve, and otherwise, the controller operates the arm second direction switching valve so that oil can be supplied from the second hydraulic pump to the bottom chamber.

Abstract: A hydraulic circuit includes: a direction switching valve, which is in a state where a bottom oil path is connected to a first tank oil path and where a bypass oil path is connected to a second tank oil path when a pump oil path is connected to a rod oil path and when the rod oil path is connected to the bypass oil path when the pump oil path is connected to the bottom oil path, and a pilot operation control valve which allows flows of oil in both directions between the direction switching valve and the bottom oil path when the pump oil path is connected to the rod oil path and allows only a flow of oil from the direction switching valve to the bottom oil path when the pump oil path is connected to the bottom oil path by the direction switching valve.

Abstract: A hydraulic circuit includes: a direction switching valve, which is in a state where a bottom oil path is connected to a first tank oil path and where a bypass oil path is connected to a second tank oil path when a pump oil path is connected to a rod oil path and when the rod oil path is connected to the bypass oil path when the pump oil path is connected to the bottom oil path, and a pilot operation control valve which allows flows of oil in both directions between the direction switching valve and the bottom oil path when the pump oil path is connected to the rod oil path and allows only a flow of oil from the direction switching valve to the bottom oil path when the pump oil path is connected to the bottom oil path by the direction switching valve.

Abstract: A hydraulic valve includes: two spools arranged in a valve main body individually movable in an axial direction and in parallel with each other, end parts thereof being housed in a common pressure chamber, and having respective guide shaft parts on the end parts thereof; a return spring provided between each of the spools and the valve main body, so that a flow of oil is controlled by a movement of the two spools with respect to the valve main body against a spring force of each of the return springs in a case where a pilot pressure is supplied to the pressure chamber; and a coupling member that is arranged in bridged between the guide shaft parts of the two spools and that is pressed in a direction of becoming closer to the spools by the return springs.