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A hydraulic drive system including at least one hydraulic actuator, two variable displacement hydraulic pumps each connected to the hydraulic actuator to form a closed circuit therewith and connected in parallel with each other, two prime movers each driving one of the hydraulic pumps, and direction

A hydraulic drive system including at least one hydraulic actuator, two variable displacement hydraulic pumps each connected to the hydraulic actuator to form a closed circuit therewith and connected in parallel with each other, two prime movers each driving one of the hydraulic pumps, and directional control valves each arranged between the hydraulic actuators and one of the hydraulic pumps. The directional control valves are each operative to shut, when one of the prime movers associated therewith is shut down, the hydraulic pump connected to the shutdown prime mover off the other hydraulic pump and the hydraulic actuator, to thereby prevent the hydraulic pump from being rotated by the pressure fluid delivered by the other hydraulic pump.

대표청구항 ▼

1. A hydraulic drive system including at least one hydraulic actuator, a plurality of variable displacemtnt hydraulic pumps, each of said hydraulic pumps being connected to said hydraulic actuator in a manner so as to form a closed hydraulic circuit therewith and said hydraulic pumps being connected

1. A hydraulic drive system including at least one hydraulic actuator, a plurality of variable displacemtnt hydraulic pumps, each of said hydraulic pumps being connected to said hydraulic actuator in a manner so as to form a closed hydraulic circuit therewith and said hydraulic pumps being connected in parallel with each other, and a plurality of prime movers each connected to one of said plurality of hydraulic pumps to drive the same, characterized by: valve means associated with each one of said hydraulic pumps to fluidly and selectively shut off the hydraulic pump associated therewith from said hydraulic actuator and from the other hydraulic pump, said valve means being respectively disposed between said hydraulic actuator and the associated hydraulic pump; and control means associated with each one of said prime movers to control said valve means in accordance with an operating condition of the prime mover in such a manner that when the prime mover is not in a normal operating condition, the hydraulic pump connected to the prime mover not normally operating is fluidly shut off from said hydraulic actuator and the other hydraulic pump. 2. A hydraulic drive system as claimed in claim 1, wherein each of said valve means comprise a two-position directional control valve formed with two input ports communicating with one of the hydraulic pumps and two outputs communicating with the actuator, said two-position directional control valve being movable between a first position in which the two input ports are brought into communication with each other and the two output ports are shut off from each other and a second position in which the two input ports and the two output ports are connected to each other. 3. A hydraulic drive system as claimed in claim 2, wherein said two-position directional control valve comprises a pilot-operated valve normally disposed in the first position, and wherein said control means each comprise a hydraulic pilot pump driven by the prime mover, and conduit means to cause a pressure fluid delivered by said pilot pump to act on the directional control valve in a manner to shift same to the second position. 4. A hydraulic drive system as claimed in claim 2, wherein said two-position directional control valve comprises a solenoid-operated valve normally disposed in the first position, including a solenoid energized when the prime mover is in normal operating condition. 5. A hydraulic drive system as claimed in claim 4, wherein said control means each comprise means for sensing the number of revolutions of the prime mover, means for determining whether the sensed number of revolutions is greater or smaller than a predetermined set value, and means for energizing the solenoid of the directional control valve when the sensed number of revolutions is greater than the set value. 6. A hydraulic drive system as claimed in claim 1, wherein said control means for said valve means each comprise additional means operative to control said valve means in response to the flow rate of pressure fluid delivered by the hydraulic pump, to thereby fluidly shut off the hydraulic pump from said hydraulic actuator and the other hydraulic pump when the flow rate of pressure fluid delivered by the hydraulic pump is essentially zero. 7. A hydraulic drive system as claimed in claim 6, wherein said valve means each comprise a two-position directional control valve formed with two input ports communicating with one of the hydraulic pumps and two output ports communicating with the actuator, said two-position directional control valve being movable between a first position in which the two input ports are brought into communication with each other and the two output ports are shut off each other and a second position in which the two input ports and the two output ports are connected to each other. 8. A hydraulic drive system including at least one hydraulic actuator, a plurality of variable displacement hydraulic pumps, each of said hydraulic pumps being connected to said hydraulic actuator in a manner to form a closed hydraulic circuit therewith and said hydraulic pumps being connected in parallel with each other, and a plurality of prime movers each connected to one of said plurality of hydraulic pumps to drive the same, characterized by: valve means each associated with one of said hydraulic pumps to fluidly and selectively shut off the hydraulic pump associated therewith from said hydraulic actuator and the other hydraulic pump, said valve means each comprise a two position directional control valve formed with two input ports communicating with one of the hydraulic pumps and two output ports communicating with the actuator, said two position directional control valve being movable between a first position in which the two input ports are brought into communication with each other end the two output ports are shut off from each other and a second position in which the two input ports and the two output ports are connected to each other, wherein said directional control valve comprises a pilot-operated valve normally disposed in the first position; and control means each associated with one of said prime movers to control said valve means in accordance with an operating condition of the prime mover in such a manner that when the prime mover is not in a normal operating condition, the hydraulic pump connected to the prime mover not normally operating is fluidly shut off from said hydraulic actuator and the other hydraulic pump, said control means for said valve means each comprise additional means operative to control said valve means in response to the flow rate of pressure fluid delivered by the hydraulic pump, to thereby fluidly shut off the hydraulic pump from said hydraulic actuator and the other hydraulic pump when the flow rate of pressure fluid delivered by the hydraulic pump is essentially zero, and wherein said control means each comprise a hydraulic pilot pump driven by said prime mover, a shuttle valve communicating with opposite two pressure chambers of a control cylinder which is provided to drive displacement volume adjusting means for the hydraulic pump, first conduit means supplying an output of said shuttle valve to the pilot operated directional control valve as pilot pressure, the pilot operated two-position change-over valve mounted in said first conduit means and movable between a first position in which the directional control valve has a pilot pressure released therefrom and a second position in which said shuttle valve is brought into communication with the directional control valve, and a second conduit means for supplying pressure fluid delivered by said pilot pump to said change-over valve as a pilot pressure. 9. A hydraulic drive system as claimed in claim 6, further comprising a bypass passage connecting together two main lines connected to two ports of each said hydraulic pump, and an additional shut-off valve for opening and blocking said bypass passage, said additional shut-off valve being operatively connected to said valve means. 10. A hydraulic drive system as claimed in claim 7, wherein said directional control valve is a solenoid-operated valve normally disposed in the first position, and wherein said control means each comprise means for sensing the number of revolutions of the prime mover, first means for sensing whether the sensed number of revolutions is greater or smaller than a predetermined set value, second means for determining whether or not the flow rate of pressure fluid delivered by the hydraulic pump and the command value given thereto are both essentially zero, and means responsive to said first means and said second means to energize said solenoid-operated value when the sensed number of revolutions is greater than the predetermined set value and the flow rate of pressure fluid delivered by the hydraulic pump and the command value given thereto are not essentially zero.