Hydraulic pump control device for construction machine

A hydraulic pump control device for use in a construction machine provided with a travelling motor, a working actuator other than the travelling motor, and a variable displacement hydraulic pump as a hydraulic source for the travelling motor and for the working actuator, the hydraulic pump control device comprising:

• a pump regulator which changes a pump flow rate at which hydraulic fluid is discharged from the hydraulic pump;
• a pump pressure detector which detects a pump pressure at which the hydraulic fluid is discharged from the hydraulic pump;
• a travelling operation detector which detects a travelling operation performed to drive the travelling motor;
• a working operation detector which detects a working operation performed to drive the working actuator;
• and
• a controller which instructs the pump flow rate depending on the pump pressure to the pump regulator, wherein
• the controller stores a first P-Q characteristic and a second P-Q characteristic as a horsepower characteristic which is a horsepower characteristic of the pump flow rate with respect to the pump pressure, and
• the controller determines the pump flow rate based on the first P-Q characteristic to instruct the determined pump flow rate to the pump regulator in the case where the travelling operation detector detects the travelling operation, while the controller determines the pump flow rate based on the second P-Q characteristic to instruct the determined pump flow rate to the pump regulator in the case where the working operation detector detects the working operation, the second P-Q characteristic being equal to the first P-Q characteristic in a low-pressure region while being a characteristic which being a characteristic giving a low horsepower relatively to the first P-Q characteristic so as to increase a horsepower difference between the first P-Q characteristic and the second P-Q characteristic as the pump pressure increases, in an intermediate-pressure region and in a high-pressure region.