Hydraulic shovel

A hydraulic shovel comprising:

• a base;
• a boom mounted on the base so as to be raised and lowered;
• an arm rotatably coupled to a distal end of the boom;
• a bucket rotatably coupled to a distal end of the arm;
• a boom hydraulic actuator that is operated so as to raise and lower the boom by receiving supply of hydraulic oil;
• an arm hydraulic actuator that is operated so as to rotate the arm relatively to the boom by receiving supply of hydraulic oil;
• a bucket hydraulic actuator that is operated so as to rotate the bucket relatively to the arm by receiving supply of hydraulic oil;
• a first pump that is formed of a hydraulic pump discharging a hydraulic oil, the first pump connected to only the boom hydraulic actuator and the bucket hydraulic actuator in parallel among a group consisting of the boom hydraulic actuator, the arm hydraulic actuator and the bucket hydraulic actuator;
• a second pump that is formed of a hydraulic pump discharging a hydraulic oil, the second pump connected to only the arm hydraulic actuator and the boom hydraulic actuator in parallel among the group consisting of the boom hydraulic actuator, the arm hydraulic actuator and the bucket hydraulic actuator;
• a third pump that is formed of a hydraulic pump discharging a hydraulic oil, the third pump connected only to the arm hydraulic actuator among the group consisting of the boom hydraulic actuator, the arm hydraulic actuator and the bucket hydraulic actuator;
• a boom operation member to which an operation for moving the boom hydraulic actuator is applied;
• an arm operation member to which an operation for moving the arm hydraulic actuator is applied;
• a bucket operation member to which an operation for moving the bucket hydraulic actuator is applied;
• a boom control valve including a first pilot port and interposed between the first pump and the boom hydraulic actuator and configured to be opened in response to the operation applied to the boom operation member when a pilot pressure exceeding a boom start pilot pressure corresponding to a boom start operation amount which has been set in advance with respect to the operation of the boom operation member is input to the first pilot port to control the supply of the hydraulic oil from the first pump to the boom hydraulic actuator;
• an arm control valve including a second pilot port and interposed between the second pump and the arm hydraulic actuator and configured to be opened in response to the operation applied to the arm operation member when a pilot pressure exceeding an arm start pilot pressure corresponding to an arm start operation amount which has been set in advance with respect to the operation of the arm operation member is input to the second pilot port to control the supply of the hydraulic oil from the second pump to the arm hydraulic actuator;
• a bucket control valve interposed between the first pump and the bucket hydraulic actuator and configured to be opened in response to the operation applied to the bucket operation member to control the supply of the hydraulic oil from the first pump to the bucket hydraulic actuator;
• a boom merging valve interposed between the second pump and the boom hydraulic actuator and configured to be opened only when an amount of the operation applied to the boom operation member exceeds a preset boom-speed-increase-start operation amount larger than the boom start operation amount to permit the hydraulic oil discharged by the second pump to be merged into the hydraulic oil supplied from the first pump to the boom hydraulic actuator;
• and
• an arm merging valve interposed between the third pump and the arm hydraulic actuator and configured to be opened only when an amount of the operation applied to the arm operation member exceeds a preset arm-speed-increase-start operation amount larger than the arm start operation amount to permit the hydraulic oil discharged by the third pump to be merged into the hydraulic oil supplied from the second pump to the arm hydraulic actuator.