Hydraulic drive device

A hydraulic driving system, comprising:

• a pump that is rotationally driven by a power source to discharge oil and has a capacity which is changeable;
• an actuator that is activated by a supply of the oil discharged from the pump;
• and
• a controller that controls the capacity of the pump in accordance with a manipulation content for the actuator, wherein
• the controller changes, on the basis of a rotational speed of the pump, an upper limit value of a magnitude of a pump capacity change amount being a change amount of the capacity of the pump per unit time
• wherein the controller executes:
• setting the upper limit value to a first upper limit value when a rotational speed of the pump is a first rotational speed;
• and
• setting the upper limit value to a second upper limit value which is smaller than the first upper limit value when the rotational speed of the pump is a second rotational speed which is higher than the first rotational speed,
• wherein the controller sets the upper limit value in such a manner that the upper limit value decreases as the rotational speed of the pump increases,
• wherein the controller sets the upper limit value so that a change amount in a discharge flow rate of the pump per unit time is fixed when the rotational speed of the pump falls within a predetermined range, and
• wherein the controller:
• determines a reference upper limit value being the upper limit value at a reference rotational speed as a reference of the pump rotational speed,
• calculates a rotational speed ratio being a ratio between the reference rotational speed and a use rotational speed which is a present pump rotational speed, and
• calculates the upper limit value at the use rotational speed on the basis of the reference upper limit value and the rotational speed ratio.