Abstract: Fault diagnosis of hydraulic pumps is made automatically during an actual operation of a working machine, particularly when there is a problem with horsepower limiting control of the hydraulic pumps. A controller 50 performs horsepower limiting control for a plurality of variable displacement hydraulic pumps 1 to 6. The controller 50 measures a pump delivery pressure and pump delivery rate of each hydraulic pump when the pump delivery rate reaches a maximum during operation of the hydraulic drive system based on their detected values, collects the measured values as fault diagnostic data, and then compares a calculated target pump delivery rate with the collected pump delivery rate to decide if there is a fault of the hydraulic pump.

Abstract: In a pump fault diagnostic apparatus for a hydraulic drive system, it is possible to make a fault diagnosis of hydraulic pumps automatically during an actual operation of a working machine and to detect a fault when there is a problem with horsepower limiting control of the hydraulic pumps as well. A controller 50 performs horsepower limiting control for a plurality of variable displacement hydraulic pumps 1 to 6.