Crowell & Moring LLP
Safety device for hydraulic working machine
There are provided: control valves 22-24 that control flow of pressure oil from the hydraulic source 21 to the hydraulic actuators 15-17; electric lever devices 51-53 that output electrical operation signals v51-v53 in correspondence to lever operation; electromagnetic proportional valves 25-30 through which control pressures for controlling the control valves 22-24 are output; a pressure calculating unit 50 that calculates control pressures P25-P30 in correspondence to the operation signals V51-v53; a control unit 50 that controls the electromagnetic proportional valves 25-30 so that control pressures to be output from the electromagnetic proportional valves 25-30 become the control pressures P25-P30 that have been calculated; a high-pressure selection circuit 41-44 that selects a higher pressure between control pressures that have been output from the electromagnetic proportional valves 25-30; pressure detectors 45 and 46 that detect a control pressure selected by the high-pressure selection circuit 41-44; an abnormality determination unit 50 that determines an abnormality in the electromagnetic proportional valves 25-30 based upon the control pressure detected by the pressure detectors 45 and 46 and the control pressure calculated by the pressure calculating unit; and an inhibiting device 47 and 48 that prohibits control of the control valves 22-24 when it is determined that an abnormality has occurred in the electromagnetic proportional valves 25-30. 
Hitachi Construction Machinery Co., Ltd.
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F15B F15B F15B E02F F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B F15B E02F
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Kazuhiro Katsuaki Yuuki Yuuji Hidetoshi
Ichimura Kodaka Gotou Nagashima Satake