Abstract: An engine control system includes pressure sensors (73, 74), position sensors (75, 76), pressure sensors (77, 78), a target revolution speed modification value computing unit (90), and a modification value adder (70r). A target revolution speed NR2 for use in control is computed based on changes of status variables such that the target revolution speed NR2 increases from the target revolution speed NR1 applied from an input unit (71), and then moderately returns to the target revolution speed NR1. In accordance with the computed target revolution speed NR2, a target fuel injection amount FN1 is computed and a fuel injection amount is controlled. As a result, a drop of an engine revolution speed attributable to an abrupt increase of an engine load can be suppressed without sacrificing the work efficiency, and lowering of durability caused by an excessive increase of the engine revolution speed can be prevented.

Abstract: A machine body controller 70A includes a modification control unit 70Ab for computing a torque modification value based on detected signals from environment sensors 75 to 83, and modifies a maximum absorption torque of a hydraulic pump controlled by a basic control unit 70Aa. An engine controller 70B includes a modification control unit 70Bb for computing an injection modification value based on detected the signals from the environment sensors 75 to 83, and modifies a fuel injection state of a fuel injection device 14 controlled by a basic control unit 70Ba. The controllers 70A, 70B further include computation element altering units 171, 181. A communication controller 70C downloads alteration data obtained from an external terminal 150 to the computation element altering units 171, 181, whereby corresponding computation elements contained in the modification control units 70Ab, 70Bb are altered.

Abstract: A current load rate of an engine 10 is computed and a maximum absorption torque of at least one hydraulic pump 1, 2 is controlled so that the load rate is held at a target value. Engine stalling can be prevented by decreasing the maximum absorption torque of the hydraulic pump under a high-load condition. When an engine output lowers due to environmental changes, the use of poor fuel or other reasons, the maximum absorption torque of the hydraulic pump can be decreased without a lowering of the engine revolution speed. Further, the present invention is adaptable for any kinds of factors causing a lowering of the engine output, such as those factors that cannot be predicted in advance or are difficult to detect by sensors. In addition, because of no necessity of sensors, such as environment sensors, the manufacturing cost can be reduced.

Abstract: A machine body controller 70A includes a modification control unit 70Ab for computing a torque modification value based on detected signals from environment sensors 75 to 83, and modifies a maximum absorption torque of a hydraulic pump controlled by a basic control unit 70Aa. An engine controller 70B includes a modification control unit 70Bb for computing an injection modification value based on detected the signals from the environment sensors 75 to 83, and modifies a fuel injection state of a fuel injection device 14 controlled by a basic control unit 70Ba. The controllers 70A, 70B further include computation element altering units 171, 181. A communication controller 70C downloads alteration data obtained from an external terminal 150 to the computation element altering units 171, 181, whereby corresponding computation elements contained in the modification control units 70Ab, 70Bb are altered.

Abstract: In the arm-crowding or track operation, a calculating portion (700d2 or 700d4) calculates a modification gain (KAC or KTR) depending on an operation pilot pressure and a calculating portion (700g) calculates a decrease modification (DND) based on the KAC or KTR, while a calculating portion (700m or 700p) calculates a modification gain (KACH or KTRH) depending on an operation pilot pressure and calculating portions (700q-700s) calculate an increase modification (DNH) based on the KACH or KTRH. A reference target engine revolution speed NR0 is modified using the DND and DNH. In other operations than the arm-crowding and track operations, NR0 is modified using only the decrease modification (DND) calculated from the modification gain just depending on the operation pilot pressure. In the operation where an engine revolution speed is desired to become higher as an actuator load increases, the engine revolution speed can be controlled in accordance with change of the actuator load as well.

Abstract: A reference pump-delivery-rate calculating portion calculates a reference delivery rate of a hydraulic pump by referring to a table stored in a memory based on a control pilot pressure for the hydraulic pump. A target pump-delivery-rate calculating portion divides the reference delivery rate by a ratio of a maximum revolution speed to a target engine revolution speed, thereby calculating a target delivery rate. A target pump tilting calculating portion divides the target delivery rate by an actual engine revolution speed and a constant, thereby calculating a target tilting. A solenoid output current calculating portion calculates a drive current to provide the target tilting and outputs the drive current to a solenoid control valve. The pump delivery rate is thereby controlled with good response following input change of an operation instructing device.