Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1992-10-29
1994-05-03
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
91517, 91459, F16D 3102
Patent
active
053076311
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a hydraulic control apparatus for a hydraulic construction machine for which a load sensing control and an input torque limiting control can be performed.
BACKGROUND ART
A wheel type hydraulic shovel, for example, as shown in FIG. 10 has been known as a hydraulic construction machine equipped with the above type of hydraulic control apparatus. In the figure, a reference numeral 4 represents a hydraulic motor for vehicle travelling, and rear wheels 103 are driven through a transmission 101 and a propeller shaft 102 by the rotation of the hydraulic motor 4 to allow a vehicle to travel. A boom 104 serving as a part of a front attachment is upwardly and downwardly moved through a lengthening and shortening operation of a boom cylinder 21. In this specification, a digging work and the like using the front attachment while the vehicle does not travel is referred to merely as "work", and these works are distinguished from a term "travel".
As one of the hydraulic construction machines as described above has been proposed a machine in which a load sensing control and an input torque limiting control are selectively carried out (for example, as disclosed in Japanese Laid-open Patent Application No. 2-118203). These control systems will be described hereunder with reference to FIG. 11.
FIG. 11 shows a hydraulic circuit for the travel and the work of the hydraulic shovel as described above, and a reference numeral 1 represents a variable displacement hydraulic pump which is driven by a diesel engine 27. The rotational speed of the engine 27 is controlled through rotational member of a governor lever 27b of a governor 27a which is driven, in accordance with an manipulation amount of a fuel lever (not shown) or an operation amount of an acceleration pedal 6a for the travel (hereinafter referred to as a travelling pedal), by a pulse motor 28. A variable displacement hydraulic pump 1 discharges an oil whose flow amount corresponds to the engine rotational speed and the displacement thereof. The discharged oil is communicated through a travel-control valve 2 to the hydraulic motor 4, and further communicated through a work-control valve 20 to a boom-driving hydraulic cylinder 21.
The load sensing control is characterized in that the displacement (hereinafter also referred to as "tilt angle") of the variable displacement hydraulic pump 1 is so controlled that the difference pressure between front and rear stages of the travel-control valve 2 or the work-control valve 20, that is, the difference pressure between a pressure (pump pressure) at an inlet port of the control valve 2, 20 and a pressure (load sensing pressure) at an outlet port thereof is fixed to a constant value to thereby keeping the pump pressure to a value higher than the load sensing pressure by a predetermined target value. The load sensing pressure is a pressure selected by a shuttle valve 29 and higher one of load pressures of the hydraulic motor 4 and the hydraulic cylinder 21.
The system for carrying out the load sensing control as shown in FIG. 11 is equipped with a load sensing regulator 11 whose switching operation is carried out in accordance with the difference pressure between the pump pressure and the load sensing pressure. When the difference pressure between the pump pressure and the load sensing pressure exceeds a pressure which is set by a spring 11a, the load sensing regulator 11 is switched to a position b in accordance with the pressure. At the position b, the pump pressure is communicated to a servo cylinder 12, and the displacement of the hydraulic pump 1 is reduced through a lengthening operation of the servo cylinder 12, so that the delivery flow rate of the pump is reduced. Conversely, when the difference pressure is dropped down to a value lower than the predetermined pressure, the load sensing regulator 11 is switched to a position a, and the servo cylinder 12 is intercommunicated to a tank. Consequently, the displacement as described above is increased, and thus the pump delivery flow ra
REFERENCES:
patent: 4655689 (1987-04-01), Westveer et al.
patent: 4672811 (1987-06-01), Yoshida et al.
patent: 4704866 (1987-11-01), Myers
patent: 4759183 (1988-07-01), Kreth et al.
patent: 4967557 (1990-11-01), Izumi et al.
patent: 5074194 (1991-12-01), Hirata et al.
patent: 5182908 (1993-02-01), Devier et al.
Ichimura Kazuhiro
Kihara Mitsuo
Nakamura Shigetaka
Onoue Hiroshi
Tamura Seiji
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
LandOfFree
Hydraulic control apparatus for hydraulic construction machine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic control apparatus for hydraulic construction machine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic control apparatus for hydraulic construction machine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2107043