Abstract: An oil hydraulic circuit having a pilot operated control valve, for performing control of pressure oil supply to a hydraulic actuator and a pilot valve gear for outputting a pilot pressure to the control valve, that improves operationality when a fine operation is performed. The pilot valve gear has a first pressure controller that outputs a pilot pressure corresponding to the degree of operation of an operating lever and a second pressure controller that reduces the pilot pressure outputted from the first pressure controller based on a signal from an operating speed changeover switch and outputs the reduced pilot pressure to the control valve.

Abstract: In an oil hydraulic circuit comprising a pilot operated type control valve for performing control of pressure oil supply to a hydraulic actuator and a pilot valve gear for outputting a pilot pressure to this control valve, in order to improve operationality in a case where a fine operation is performed, the pilot valve gear (8) comprises a first pressure controller (9) for outputting a pilot pressure corresponding to the degree of operation with an operating lever (12) and a second pressure controller (10) for reducing the pilot pressure outputted from this first pressure control means based on a signal from an operating speed changeover switch 16 and outputting the reduced pilot pressure to the control valve 5.

Abstract: A hydraulic pilot circuit having a pilot pump which discharges pilot oil, and a plurality of pilot valves which control a plurality of hydraulic directional control valves by supplying the pilot oil with control, wherein heating of hydraulic oil due to retaining pilot pressure oil is reduced, and controllability is not damaged even if the plurality of pilot valves are operated at the same time, because sufficient pilot oil is supplied to the pilot valves. A variable displacement pump is adopted as the pilot pump. An operation detecting means detects operating condition of the hydraulic pilot valves, a controller computes the necessary discharge of the pilot pump for operating the hydraulic directional control valves from the operating condition, and the pilot pump discharges only the necessary oil flow.

Abstract: A method for controlling a hydraulic pump driven by an engine, including measuring a temperature of at least one of the engine and a hydraulic fluid, comparing the measured temperature with a first predetermined temperature to judge as to whether the measured temperature is higher than the first predetermined temperature or not, comparing the measured temperature with a second predetermined temperature to calculate a difference between the measured temperature and the second predetermined temperature, and decreasing an output flow rate of the hydraulic pump by a degree according to the difference between the measured temperature and the second predetermined temperature, when the measured temperature is judged to be higher than the first predetermined temperature.

Abstract: A method for controlling a hydraulic pump included by an apparatus, comprises the steps of: measuring a circumferential atmospheric temperature of the apparatus, comparing the measured circumferential atmospheric temperature with a first temperature to judge as to whether the measured circumferential atmospheric temperature is higher than the first temperature or not, and decreasing an output of the hydraulic pump when the measured circumferential atmospheric temperature is judged to be higher than the first temperature.

Abstract: An excavator includes an upper structure swingably supported by a lower structure. A worker position sensor consists of a plurality of radio frequency transceivers provided in the excavator and a radio frequency transceiver carried by each of the excavation workers working within the working range of the excavator. A signal processing unit determines whether the relative distance between each worker and the excavator is either of short distance, slightly long distance or long distance and identifies the position of each worker for each of the predetermined identifying areas. A determining signal from the signal processing unit is supplied to a control unit. The control unit is connected to a drive unit which includes electro-hydraulic proportional valves for energizing actuators for positioning, swing, and traveling of the excavator. This control unit is also connected to a machine sensor which includes a swing angle sensor, a traveling level sensor, and a swing operation lever sensor.