Slewing-type hydraulic work machine

A slewing-type hydraulic work machine comprising:

• a lower travelling body;
• an upper slewing body mounted on the lower travelling body so as to be capable of being slewed;
• a work device mounted on the upper slewing body, the work device including a boom connected to the upper slewing body so as to be capable of being raised and lowered;
• a slewing motor formed of a variable displacement type hydraulic motor and operated by hydraulic oil supplied to the slewing motor to slew the upper slewing body in response to the supply of the hydraulic oil;
• a boom actuator that is operated by hydraulic oil supplied to the boom actuator to raise and lower the boom;
• an oil pressure supply device including at least one hydraulic pump that discharges hydraulic oil to be supplied to the variable displacement type hydraulic motor and the boom actuator, the at least one hydraulic pump including a distribution pump that is connectable to both the slewing motor and the boom actuator to distribute the hydraulic oil to the slewing motor and the boom actuator;
• a slewing control device configured to control a direction and a flow rate of the hydraulic oil supplied from the oil pressure supply device to the slewing motor in accordance with a slewing command operation that is applied to the slewing control device for slewing the upper slewing body;
• a boom control device configured to control a flow rate of the hydraulic oil supplied from the oil pressure supply device to the boom actuator in accordance with a boom raising command operation that is applied to the boom control device for actuating the boom in a rising direction;
• a boom raising working pressure detection unit that detects boom raising working pressure corresponding to pressure of the hydraulic oil supplied from the oil pressure supply device to the boom actuator to drive the boom in a rising direction;
• and
• a capacity control device configured to control a slewing motor capacity that is a capacity of the slewing motor based on the boom raising working pressure detected by the boom raising working pressure detection unit during a performance of a slewing and boom-raising operation in which the slewing command operation is applied to the slewing control device and the boom raising command operation is applied to the boom control device, simultaneously, wherein:
• the capacity control device includes a distribution factor correspondence value detection unit that detects an actual slewing distribution factor correspondence value that is a value that increases and decreases correspondingly to a slewing energy distribution factor that is a ratio of energy actually distributed to the slewing motor to energy of the hydraulic oil discharged from the oil pressure supply device during the performance of the slewing and boom-raising operation, a boundary value setting unit that sets a boundary value for the actual slewing distribution factor correspondence value, the boundary value setting unit configured to change the boundary value according to the boom raising working pressure to limit the slewing energy distribution factor more strictly with increase in the boom raising working pressure;
• and a motor capacity operation unit configured to render the slewing motor capacity higher than a preset limit capacity within a slewing priority allowable period after the slewing motor starts until the actual slewing distribution factor correspondence value reaches the boundary value during the performance of the slewing and boom-raising operation and configured to limit the slewing motor capacity to the limit capacity or less after the actual slewing distribution factor correspondence value reaches the boundary value.