Hydraulic system of excavator, excavator, and method for controlling excavator

A hydraulic system of an excavator, the hydraulic system comprising:

• a first hydraulic pump;
• a second hydraulic pump;
• a boom cylinder that moves a boom of working equipment;
• an arm cylinder that moves an arm of the working equipment;
• a bucket cylinder that moves a bucket of the working equipment;
• a first boom operation valve that controls passing of hydraulic oil from the first hydraulic pump to the boom cylinder;
• a first arm operation valve that controls passing of hydraulic oil from the first hydraulic pump to the arm cylinder;
• a first bucket operation valve that controls passing of hydraulic oil from the first hydraulic pump to the bucket cylinder;
• a second boom operation valve that controls passing of hydraulic oil from the second hydraulic pump to the boom cylinder;
• a second arm operation valve that controls passing of hydraulic oil from the second hydraulic pump to the arm cylinder;
• a second bucket operation valve that controls passing of hydraulic oil from the second hydraulic pump to the bucket cylinder;
• an arm check valve that prevents backflow of hydraulic oil from the arm cylinder to the second hydraulic pump via the second arm operation valve;
• a bucket check valve that prevents backflow of hydraulic oil from the bucket cylinder to the second hydraulic pump via the second bucket operation valve;
• an operation device operated to actuate at least one of the boom cylinder, the arm cylinder, and the bucket cylinder;
• a work state determination unit that determines a work state of the working equipment based on an operation state of the operation device, a boom bottom pressure indicating a pressure of a bottom chamber of the boom cylinder, an arm bottom pressure indicating a pressure of a bottom chamber of the arm cylinder, and a bucket bottom pressure indicating a pressure of a bottom chamber of the bucket cylinder;
• and
• a valve control unit that controls at least one of the first boom operation valve, the first arm operation valve, the first bucket operation valve, the second boom operation valve, the second arm operation valve, and the second bucket operation valve based on the work state of the working equipment determined by the work state determination unit, wherein
• the work state determination unit determines that the work state of the working equipment is a normal state when an arm excavation operation amount of the operation device is equal to or larger than a first threshold, or a bucket excavation operation amount of the operation device is equal to or larger than a second threshold, and the boom bottom pressure is higher than a higher value of the arm bottom pressure and the bucket bottom pressure, and determines that the work state of the working equipment is a heavy excavation state when a higher value of the arm bottom pressure and the bucket bottom pressure is higher than the boom bottom pressure, and
• when it is determined that the work state of the working equipment is the heavy excavation state,
• the valve control unit controls the first boom operation valve, the first arm operation valve, the first bucket operation valve, the second boom operation valve, the second arm operation valve, and the second bucket operation valve such that passing of hydraulic oil from the first hydraulic pump to the boom cylinder is restricted, hydraulic oil is supplied from the second hydraulic pump to the boom cylinder, hydraulic oil is supplied from both the first hydraulic pump and the second hydraulic pump to the arm cylinder, and hydraulic oil is supplied from one or both of the first hydraulic pump and the second hydraulic pump to the bucket cylinder.