Hydraulic driving apparatus for working machine

A hydraulic driving apparatus for a working machine, comprising:

• an engine;
• at least one variable displacement hydraulic pump driven by the engine to discharge a hydraulic fluid;
• a hydraulic actuator supplied with the hydraulic fluid discharged by the hydraulic pump to be thereby actuated;
• an engine operation member to which an operation for specifying a target rotation speed for the engine is applied;
• an actuator-operation member to which an operation for specifying a speed of actuation of the hydraulic actuator is applied;
• a pump-load-pressure detector that detects a load pressure on the at least one hydraulic pump;
• an engine-operation detector that detects an amount of the operation applied to the engine operation member;
• an actuator-operation detector that detects an amount of operation applied to the actuator operation member;
• and
• a controller that outputs a command for a pump displacement volume of the at least one hydraulic pump and a command for a rotation speed of the engine, based on the pump load pressure detected by the pump-load pressure detector and the amounts of respective operations detected by the engine-operation detector and the actuator-operation detector, wherein:
• the controller includes:
• a temporary-target-engine-rotation-speed calculation section that calculates a temporary target engine rotation speed corresponding to the amount of operation applied to the engine operation member;
• a temporary-target-pump-displacement-volume calculation section that calculates a first-control target pump displacement volume corresponding to the amount of the operation applied to the actuator operation member and a second-control target pump displacement volume corresponding to the pump load pressure and selects a smaller one of the first-control target pump displacement volume and the second-control target pump displacement volume as a temporary target pump displacement volume for the at least one hydraulic pump;
• and a command section that calculates a final target engine rotation speed and a final target pump displacement volume based on the temporary target engine rotation speed and the temporary target pump displacement volume and outputs commands for the engine rotation speed and for the pump displacement volume based on the final target engine rotation speed and the final target pump displacement volume;
• in the case where the temporary target pump displacement volume is larger than a maximum pump displacement volume of the at least one hydraulic pump, the command section performs setting the final target engine rotation speed to the temporary target engine rotation speed and setting the final target pump displacement volume to the maximum pump displacement volume;
• and
• in the case where the temporary target pump displacement volume is equal to or smaller than the maximum pump displacement volume of the at least one hydraulic pump, the command section performs:
• calculating a target pump discharge amount for an amount of hydraulic fluid discharged by the at least one hydraulic pump based on the temporary target engine rotation speed and the temporary target pump displacement volume:
• setting the final target pump displacement volume to a volume which is larger than the temporary target pump displacement volume and which is equal to or smaller than the maximum pump displacement volume;
• and setting the final target engine rotation speed to a specific engine rotation speed lower than the temporary target engine rotation speed, the specific engine rotation speed allowing a pump discharge amount equivalent to the target pump discharge amount to be obtained with the final target engine rotation speed and the final target pump displacement volume.