Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Patent
1993-05-19
1996-01-09
Ryznic, John E.
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
60452, F16D 3102
Patent
active
054818753
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an apparatus for changing and controlling the volume of hydraulic oil in a hydraulic excavator which is used for crushing a block of rock or a building and so forth with the use of a hydraulic breaker or a crusher as an attachment, instead of a bucket which is usually incorporated as a working unit, and in particular to an apparatus for changing and controlling the volume of hydraulic oil in a hydraulic excavator, adapted to set a low power mode in which a hydraulic pump is subjected to load sensing control so as to set an optimum hydraulic volume, and in which an engine for driving the hydraulic pump is driven under low fuel consumption during a breaker work or the like that requires a smaller volume of hydraulic oil as compared with a usual excavating work.
BACKGROUND OF THE INVENTION
It is sometimes necessary to attach a hydraulic breaker as an attachment, instead of a bucket which is usually incorporated as a working unit, to a hydraulic excavator in order to crush a building, a block of rock or the like. In this breaker work, a smaller volume of hydraulic oil, which is approximately one-half of that in the excavating work, is sufficient. Accordingly, the rotational speed of the engine is controlled to N1, N2 or N3 (rev/min) at a predetermined torque T0 by decreasing the volume of fuel injection along engine torque curves shown in FIG. 7, in order to aim at reducing fuel consumption of the engine, thereby controlling the hydraulic oil volume necessary for the breaker work while setting the volume of the hydraulic oil to V (cc/rev), so as to obtain a hydraulic volume of V*N1, V*N2 or V*N3 (cc/min). It is noted that the suction torque T of the hydraulic pump is exhibited by T=kP.times.V where K is a proportional constant, and P is a load pressure of the hydraulic pump, and accordingly, if the volume V (cc/rev) of the hydraulic oil is set to be constant, the load pressure P0 of the hydraulic pump using the torque T0 shown in FIG. 7 as the above-mentioned suction torque is proportional to the above-mentioned suction torque T0. Further, as shown in FIG. 8, a merging change-over circuit for two hydraulic pumps is provided, in which one of two service valves is changed over so as to change the flow rates of first and second pumps in order to control the volumes of hydraulic oil required respectively for an excavation work and a breaker work. That is, referring to FIG. 8, a variable displacement hydraulic pump (which will be simply denoted "main pump") 51, has connected in parallel thereto five control valves for driving actuators for turning, boom Hi, service, arm Lo and leftward running, and a main pump 52 has connected in parallel thereto five selector valves for driving actuators for rightward running, bucket, boom Lo, arm Hi and service. Further, pipe lines 54, 55 connected to outlet ports of a service valve 53 are connected respectively to hydraulic circuits extending from a left side service valve 56 to an actuator 57 for a breaker or the like, and are merged together. A pedal 58 for manipulating an attachment such as the breaker or the like abuts against a pilot pressure control valve 39 (which will be denoted "PPC valve"), using a control pump 40 as a hydraulic pressure source. One of two pilot circuits 41, 42 extending from the PPC valve 39, is connected to a left pilot cylinder belonging to the service valve 56, and the other one of them is connected to a right pilot cylinder of the service valve 56. Further, the pilot circuits 41, 42 are provided respectively with branch circuits 43, 44 which are connected to left and right pilot cylinders belonging to the service valve 53, by way of solenoid type pilot circuit selector valves 45, 46. Solenoids of these pilot circuit selector valves 45, 46 are connected to a change-over switch 50. During normal excavation work or the like, if the actuator 57 requires a flow rate corresponding to two pumps, the change-over switch 50 is manipulated to the turn-on side so that the solenoids of the pilot circu
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Haraoka Yoshinao
Takamura Fujitoshi
Kabushiki Kaisha Komatsu Seisakusho
Ryznic John E.
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