Patent ID: 8583332

Claim:
A prime mover revolution speed control system for a hydraulic construction machine, the prime mover revolution speed control system comprising: a prime mover; at least one variable-displacement hydraulic pump that is driven by the prime mover; a plurality of hydraulic actuators that are driven by hydraulic fluid of the hydraulic pump; a plurality of control valves that control the flow rate and flow direction of the hydraulic fluid delivered from the hydraulic pump to the hydraulic actuators; operating command means, that is provided for each of the hydraulic actuators, for issuing operating commands for the hydraulic actuators in accordance with the amount of operation in each operation direction by driving the control valves on an individual basis; operating command detection means for detecting the operating commands of the operating command means; pump pressure detection means for detecting the pressure of the hydraulic pump; standard target revolution speed setup means for setting a standard target revolution speed for the prime mover; target revolution speed correction means for acquiring a target revolution speed for the prime mover by adding a predetermined correction value to the standard target revolution speed in accordance with an operating state invoked by the operating command means; and excavation state identification means for judging, in accordance with the operation direction, the operation amount, and the pump pressure, whether an excavation state prevails; wherein the excavation state identification means comprises, with reference to the operation direction, the operation amount, and the pump pressure, first judgment conditions used when a result of a last judgment does not indicate that an excavation state prevails, and second judgment conditions, different from the first judgment conditions, used when the result of the last judgment indicates that the excavation state prevails, and the excavation state identification means is configured to judge whether or not the excavation state prevails in the last judgment, and to conclude that the excavation state prevails by using the first judgment conditions when the excavation state does not prevail in the last judgment and to conclude that the excavation state prevails by using the second judgment conditions when the excavation state prevails in the last judgment; and wherein, when the excavation state identification means concludes that an excavation state prevails, the target revolution speed correction means adds the predetermined correction value to the standard target revolution speed.