Safety device for hydraulic working machine

1. A safety device for hydraulic working machine, comprising:

a hydraulic source;

at least first and second hydraulic actuators that are driven by pressure oil from the hydraulic source;

first and second control valves that control flow of pressure oil from the hydraulic source to the first and second hydraulic actuators;

first and second electric lever devices that output first and second electrical operation signals, which are drive instructions for the first hydraulic actuator and second hydraulic actuator respectively, in correspondence to lever operation;

first and second electromagnetic proportional valves through which control pressures for controlling the first control valve are output;

third and fourth electromagnetic proportional valves through which control pressures for controlling the second control valve are output;

a pressure calculating unit that calculates first and second control pressures in correspondence to a first operation signal that is output from the first electric lever device, and calculates third and fourth control pressures in correspondence to a second operation signal that is output from the second electric lever device;

a control unit that controls the first and second electromagnetic proportional valves so that control pressures to be output from the first and second electromagnetic proportional valves become the first and second control pressures that have been calculated by the pressure calculating unit, and controls the third and fourth electromagnetic proportional valves so that control pressures to be output from the third and fourth electromagnetic proportional valves become the third and fourth control pressures that have been calculated by the pressure calculating unit;

a high-pressure selection circuit that selects a maximum control pressure from among control pressures that have been output from the first to fourth electromagnetic proportional valves;

a pressure detector that detects a control pressure selected by the high-pressure selection circuit;

an abnormality determination unit that determines an abnormality in the first to fourth electromagnetic proportional valves based upon the control pressure detected by the pressure detector and the first to fourth control pressures calculated by the pressure calculating unit; and

an inhibiting device that prohibits the first to fourth electromagnetic proportional valves from controlling the first and second control valves when the abnormality determination unit determines that an abnormality has occurred in the first to fourth electromagnetic proportional valves, wherein:

said control unit determines whether the first operation signal output from the first electric lever device and the second operation signal output from the second electric lever device are abnormal, and

when said control unit determines that the first operation signal output from the first electric lever device or the second operation signal output from the second electric lever device is abnormal, the pressure calculating unit calculates the first and second control pressures or the third and fourth control pressures to be smaller than the first and second control pressures or the third and fourth control pressures calculated when the first operation signal or the second operation signal is normal.

2. A safety device for hydraulic working machine according to claim 1 , wherein:

said control unit determines whether the first operation signal output from the first electric lever device and the second operation signal output from the second electric lever device fall in a normal range, in a first error range ranging beyond the normal range by a predetermined value, or in a second error range ranging further beyond the first error range;

when said control unit determines that the first operation signal output from the first electric lever device or the second operation signal output from the second electric lever device falls in the first error range, the pressure calculating unit calculates the first and second control pressures or the third and fourth control pressures to be smaller than those calculated when the first operation signal or the second operation signal falls in the normal range; and

when said control unit determines that the first operation signal output from the first electric lever device or the second operation signal output from the second electric lever device falls in the second error range, the control unit stops outputting a control signal of the first and second control pressures corresponding to the first operation signal or a control signal of the third and fourth control pressures corresponding to the second operation signal.

3. A safety device for hydraulic working machine, comprising:

a hydraulic source;

at least first, second, and third hydraulic actuators that are driven by pressure oil from the hydraulic source;

first, second, and third control valves that control flow of pressure oil from the hydraulic source to the first, second, and third hydraulic actuators, respectively; first, second, and third electric lever devices that output first, second and third electrical operation signals, which are drive instructions for the first, second, and third hydraulic actuators respectively, in correspondence to lever operation;

first and second electromagnetic proportional valves through which control pressures for controlling the first control valve are output;

third and fourth electromagnetic proportional valves through which control pressures for controlling the second control valve are output;

fifth and sixth electromagnetic proportional valves through which control pressures for controlling the third control valve are output;

a pressure calculating unit that calculates first and second control pressures in correspondence to a first operation signal that is output from the first electric lever device, third and fourth control pressures in correspondence to a second operation signal that is output from the second electric lever device, and fifth and sixth control pressures in correspondence to a third operation signal that is output from the third electric lever device;

a control unit that controls the first to sixth electromagnetic proportional valves so that control pressures to be output from the first to sixth electromagnetic proportional valves respectively become the first to sixth control pressures that have been calculated by the pressure calculating unit;

a first high-pressure selection circuit that selects a maximum control pressure from among control pressures that have been output from the first to fourth electromagnetic proportional valves;

a second high-pressure selection circuit that selects a higher pressure between control pressures that have been output from the fifth and sixth electromagnetic proportional valves;

a first pressure detector that detects the control pressure selected by the first high-pressure selection circuit;

a second pressure detector that detects the control pressure selected by the second high-pressure selection circuit;

an abnormality determination unit that determines an abnormality in the first to fourth electromagnetic proportional valves based upon the control pressure detected by the first pressure detector and the first to fourth control pressures calculated by the pressure calculating unit, and determines an abnormality in the fifth and sixth electromagnetic proportional valves based upon the control pressure detected by the second pressure detector and the fifth and sixth control pressures calculated by the pressure calculating unit; and

an inhibiting device that prohibits the first to fourth electromagnetic proportional valves from controlling the first and second control valves when the abnormality determination unit determines that an abnormality has occurred in the first to fourth electromagnetic proportional valves, and prohibits the fifth and sixth electromagnetic proportional valves from controlling the third control valve when the abnormality determination unit determines that an abnormality has occurred in the fifth and sixth electromagnetic proportional valves, wherein:

said control unit determines whether the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device, and the third operation signal output from the third electric lever device are abnormal, and

when said control unit determines that the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device or the third operation signal output from the third electric lever device is abnormal, the pressure calculating unit calculates the first and second control pressures, the third and fourth control pressures or the fifth and sixth control pressures to be smaller than the first and second control pressures, the third and fourth control pressures or the fifth and sixth control pressures calculated when the first operation signal, the second operation signal or the third operation signal is normal.

4. A safety device for hydraulic working machine according to claim 3 , wherein:

the first and second hydraulic actuators are actuators for performing one operation, whereas the third hydraulic actuator is an actuator for performing another operation.

5. A safety device for hydraulic working machine according to claim 4 , wherein:

the hydraulic working machine includes an undercarriage, a revolving superstructure, a work front that is rotatably supported by the revolving superstructure, and a working attachment that is removably attached to the work front; and

the first and second hydraulic actuators are driving actuators for the working attachment.

6. A safety device for hydraulic working machine according to claim 3 , wherein:

said control unit determines whether the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device and the third operation signal output from the third electric lever device fall in a normal range, in a first error range ranging beyond the normal range by a predetermined value, or in a second error range ranging further beyond the first error range;

when said control unit determines that the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device or the third operation signal output from the third electric lever device falls in the first error range, the pressure calculating unit calculates the first and second control pressures, the third and fourth control pressures or the fifth and sixth control pressures to be smaller than those calculated when the first operation signal, the second operation signal or the third operation signal falls in the normal range; and

when said control unit determines that the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device or the third operation signal output from the third electric lever device falls in the second error range, the control unit stops outputting a control signal of the first and second control pressures corresponding to the first operation signal, a control signal of the third and fourth control pressures corresponding to the second operation signal or a control signal of the fifth and sixth control pressures corresponding to the third operation signal.