Abstract: A civil machine having a flow-rate controller which applies a preset signal instead of a normal flow-rate signal to a variable type hydraulic pump when delivery pressure of the hydraulic pump exceeds a preset pressure value. The normal flow-rate signal corresponds to the position of an operating lever. The preset signal has a value of minimum flow rate to hold a working tool in a certain posture. With this control system, pressure loss and temperature rise in hydraulic operating oil as well as fuel consumption of the machine can be reduced and cycle time of the work can be improved.

Abstract: A semi-automatic hydraulic excavator capable of automatically controlling arm and bucket angles when bringing the bucket back to the original excavation posture after completion of dumping excavated soil. For this purpose, arm and bucket angle detectors are provided therein and the automatic control is performed by negatively feeding back values detected by these detectors to minimize deviations between these values and preset values produced from arm and bucket angle setters corresponding to the arm and bucket angles in the original excavation posture. The automatic control mode is selected by a signal from an automatic control command signal producing circuit. With this system, the bucket is swiftly brought back to the original excavation posture from the dumping posture without requiring much operator's skill and efforts.

Abstract: The control device for an earthwork machine according to the invention is designed for reducing the manufacturing cost of the earthwork machine by eliminating some of the calculating circuitry and the control circuitry. According to the control device, one of the cylinders necessary for carrying out straight excavation is directly manually controlled without using calculating circuitry, and the operations of the cylinders are respectively detected by detecting circuitry. The other two cylinders are also controlled by the arithmetic unit provided in the control device for performing calculation necessary to move the sharp edge of the bucket along a straight line of predetermined inclination in accordance with detected pivoted angles of the boom, arm and bucket.